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Applied Surface Science (v.253, #3)

Synthesis and characterization of corrosion protective poly(2,5-dimethylaniline) coatings on copper by Vandana Shinde; A.B. Gaikwad; P.P. Patil (pp. 1037-1045).

Poly(2,5-dimethylaniline) coatings were synthesized on copper (Cu) by electrochemical polymerization of 2,5-dimethylaniline in aqueous salicylate solution by using cyclic voltammetry. The characterization of these coatings was carried out by cyclic voltammetry, UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The results of these characterizations indicate that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of 2,5-dimethylaniline to generate strongly adherent and smooth poly(2,5-dimethylaniline) coatings on Cu substrates. The performance of poly(2,5-dimethylaniline) as protective coating against corrosion of Cu in aqueous 3% NaCl was assessed by the potentiodynamic polarization technique. The results of the potentiodynamic polarization demonstrate that the poly(2,5-dimethylaniline) coating has ability to protect the Cu against corrosion. The corrosion potential was about 0.078V versus SCE more positive in aqueous 3% NaCl for the poly(2,5-dimethylaniline) coated Cu than that of uncoated Cu and reduces the corrosion rate of Cu almost by a factor of 31.

Keywords: Corrosion resistant coatings; Conducting polymers; Poly(2,5-dimethylaniline) coatings; Copper; Electrochemical polymerization; Cyclic voltammetry

XPS studies of short pulse laser interaction with copper by P. Stefanov; N. Minkovski; I. Balchev; I. Avramova; N. Sabotinov; Ts. Marinova (pp. 1046-1050).

The effect of laser ablation on copper foil irradiated by a short 30ns laser pulse was investigated by X-ray photoelectron spectroscopy. The laser fluence was varied from 8 to 16.5J/cm² and the velocity of the laser beam from 10 to 100mm/s. This range of laser fluence is characterized by a different intensity of laser ablation. The experiments were done in two kinds of ambient atmosphere: air and argon jet gas.The chemical state and composition of the irradiated copper surface were determined using the modified Auger parameter ( α′) and O/Cu intensity ratio. The ablation atmosphere was found to influence the size and chemical state of the copper particles deposited from the vapor plume. During irradiation in air atmosphere the copper nanoparticles react with oxygen and water vapor from the air and are deposited in the form of a CuO and Cu(OH)₂ thin film. In argon atmosphere the processed copper surface is oxidized after exposure to air.

Keywords: PACS; 79.20.D; 68.35.B; 79.60Laser ablation; Copper; X-ray photoelectron spectroscopy (XPS)

Nanocrystalline Ni–B coating surface strengthening pure copper by Shi Ziyuan; Wang Deqing; Ding Zhimin (pp. 1051-1054).

An electroless deposition technique is used to synthesize nanocrystalline Ni–B coating in strengthening the surface of pure copper. The microstructure and some properties of Ni–B coating are studied. It is practicable to coat a uniform and continuous nanocrystalline Ni–B hardening layer on copper surface by this technique, Ni₂B and Ni₃B are formed in the Ni–B coated layer during heat treatment, and the average grain size of nanocrystalline Ni–B coating is about 42–65nm and properties of the prepared copper alloys are also improved.

Keywords: Electroless deposition; Nanocrystalline Ni–B coating; Pure copper; Amorphous

Characterization of Ohmic contacts on GaN/AlGaN heterostructures by S. Kaciulis; L. Pandolfi; S. Viticoli; M. Peroni; A. Passaseo (pp. 1055-1064).

The surface morphology and electrical resistance of the contacts on semiconductor devices are strongly influenced by metallization scheme and annealing conditions. In this work is presented an investigation of Ohmic contacts formed by metal–semiconductor alloying on epitaxial GaN/AlGaN heterostructures. After the deposition of metallic multi-layers (Ti, Al, Au and Pt), the process of rapid thermal annealing was carried out in nitrogen, argon and forming gas atmosphere.A series of the samples with different sequences of metallic layers and diverse thicknesses was prepared by employing electron beam evaporation and lift-off deposition techniques. The chemical composition of the samples before and after annealing was studied by means of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques combined with low energy Ar⁺ ion sputtering. The sputtering has been carried out in two different modes: by using constant (square) or gradually narrowed sputtered area. The changes in the chemical state of constituent elements and compositional profiles of the contacts after thermal annealing were revealed from the obtained results. Among the technological problems, influencing on the quality of the contact, were found to be the oxidation and nitridation of the contact surface during thermal annealing, as well as the intermediate sub-layers of Al and Ti oxides, formed during the deposition of metallic multi-layered structure.

Keywords: PACS; 61.16.Ms; 81.05.Ba; 81.05.Bx; 81.40.Bf; 82.80.PyOhmic contacts; Annealing; AlGaN; XPS; AES

Illumination dependence of I– V and C– V characterization of Au/InSb/InP(100) Schottky structure by B. Akkal; Z. Benamara; N. Bachir Bouiadjra; S. Tizi; B. Gruzza (pp. 1065-1070).

The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He–Ne laser of 1mW power and 632.8nm wavelength. The current–voltage I( V_G), the capacitance–voltage C( V_G) measurements were plotted and analysed. The saturation current I_s, the serial resistance R_s and the mean ideality factor n are, respectively, equal to 2.03×10⁻⁵A, 85Ω, 1.7 under dark and to 3.97×10⁻⁵A, 67Ω, 1.59 under illumination. The analysis of I( V_G) and C( V_G) characteristics allows us to determine the mean interfacial state density N_ss and the transmission coefficient θ_n equal, respectively, to 4.33×10¹²eV⁻¹cm⁻², 4.08×10⁻³ under dark and 3.79×10¹²eV⁻¹cm⁻² and 5.65×10⁻³ under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C⁻²( V_G) characteristic.

Diffusion behaviour of Nb in yttria-stabilized zirconia single crystals: A SIMS, AFM and X-ray reflectometry investigations by G. Kuri; M. Gupta; R. Schelldorfer; D. Gavillet (pp. 1071-1080).

Using secondary ion mass spectrometry (SIMS) we have investigated the concentration vs. depth profile of Nb, thermally diffused into (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystal substrates. The surface morphology of Nb films and YSZ substrates was analyzed using atomic force microscopy (AFM). The structural disorder and the interface configuration of the samples were investigated by X-ray reflectometry (XRR). Two kinds of substrates were used: as-received (AR) and reduced (R) ones. The R-substrates were obtained by thermal annealing of AR-substrates in air for 2 h at 1250°C. The bulk diffusion coefficientsDT in the temperature range of 780–1000°C, activation energy Q, and the pre-exponential factor,D0, have been obtained for Nb in YSZ. For the AR single crystals, the results can be well represented by the expression:D(cm2s−1)=2.93×101exp�?�−3.91[eV]kBTThe diffusion behaviour of Nb in the R-substrates yields slightly different results. It is concluded that incorporation of Nb into YSZ lattice is governed by the vacancy mechanism.

Keywords: PACS; 68.60.Dv; 68.35.FxYSZ; Nb diffusion; SIMS; XRR; AFM

Thermo-stimulated surface segregation in the ordering alloy Pt₈₀Co₂₀(111): Experiment and modeling by M.A. Vasylyev; V.A. Tinkov; A.G. Blaschuk; J. Luyten; C. Creemers (pp. 1081-1089).

In this paper, a method of Ionization Spectroscopy (IS) is proposed for the non-destructive layer-by-layer analysis of the elemental composition of a solid surface. Using ionization energy loss spectra, a layer-by-layer concentration profile of the Pt₈₀Co₂₀(111) alloy surface is obtained for different annealing temperatures. For the disordered Pt₈₀Co₂₀(111) at room temperature, the first atomic layer consists of pure Pt with damped oscillations in the deeper layers. Heating the sample reduces the oscillations. However, at a temperature of 823K, a sandwich-like structure of the type Pt/Co/Pt was found in the first three atomic layers. For the ordered state the first atomic layer also consists of pure Pt with bulk concentration in other layers. LEED analysis shows a p(2×2) superstructure for the surface of the ordered Pt₈₀Co₂₀(111) alloy. The segregation behavior in this alloy is further studied by Monte Carlo (MC) simulations combined with the Constant Bond Energy (CBE) model. The results of the MC simulations agree well with the experiments at the higher temperatures, both for the surface composition and the concentration depth profile. At lower temperatures, some discrepancies exist between the MC results and the measured concentration profile.

Keywords: PACS; 79.20.H; 64.75; 68.35.B; 05.70.; 07.05.TpLayer-by-layer non-destructive analysis; Ionization Spectroscopy; Surface segregation; Surface structure; (Dis)ordered alloy; Pt; ₈₀; Co; ₂₀; (1; 1; 1); Monte Carlo modeling

IR wavelength-selective laser desorption via OH and CH stretching modes by C. Mihesan; M. Ziskind; B. Chazallon; E. Therssen; P. Desgroux; S. Gurlui; C. Focsa (pp. 1090-1094).

We present new results on wavelength-selective desorption of solid samples using the resonant interaction between the laser beam and the bulk. The experimental set-up is based on the coupling of three techniques: laser desorption in the near-infrared (IR) (2.7–4μm) with a tunable IR optical parametric oscillator (OPO), UV multi-photon ionization, and reflectron time-of-flight mass spectrometry. The resonant character of the laser desorption process has been investigated for an ice/polycyclic aromatic hydrocarbon (PAH) mixture, by excitation of the OH and CH stretching modes. Highly preferential desorption has been evidenced, with exclusive desorption of water and PAH molecules at the OH and CH resonances, respectively. Potential analytical (e.g. selective analysis of complex samples) and technological (e.g. dry laser cleaning, DLC) applications are discussed.

Keywords: PACS; 68.43.Tj; 79.20.La; 82.50.Bc; 82.80.RtSelective desorption; Photon stimulated desorption; Mass spectrometry; OPO; Ice; PAH

Possibilities of C 1s XPS and N( E) C KVV Auger spectroscopy for identification of inherent peculiarities of diamond growth by A.P. Dementjev; K.I. Maslakov (pp. 1095-1100).

The interaction of C-atoms and CH_n-radicals with uncleaned and argon cleaned silicon substrate and with diamond surface after H-treatment have been studied in situ by XPS and Auger spectroscopy. It was found the formation of a new chemical surface state of carbon atoms in the case of carbon atoms and radicals interaction with cleaned silicon. The same chemical state was revealed on the H-treated diamond surface. Graphite-like structure of carbon atoms was observed on the surface of unlearned silicon and H-treated diamond after interaction with carbon atoms and radicals. N( E) C KVV Auger spectrum for the new chemical state of carbon atoms significantly differs from typical spectra for sp²- and sp³-bonded carbon materials. The high energy part of this spectrum was interpreted under the hypothesis of sp³-bonded carbon atoms but with shifted fermi level position.

Keywords: XPS; XAES; Diamond; Nucleation; Growth

A strategy for immunoassay signal amplification using clusters of immunogold nanoparticles by Yan-lei Su (pp. 1101-1106).

The clusters of immunogold nanoparticles were fabricated through cross-linking immunogold nanoparticles with glutaraldehyde. A novel strategy for immunoassay signal amplification using the clusters of immunogold nanoparticles on glass slides based on electroless deposition was described. The immunoassay signal amplification through the clusters of immunogold nanoparticles was about three to four times higher than that through single immunogold nanoparticles. The purple attachments were readily discernible on glass slides by naked eye at a concentration of 0.1pg/mL antigen in PBS solution. The indirect detection of antigen using the clusters of immunogold nanoparticles is an efficient way to improve the detection sensitivity.

Keywords: Immunoassay signal amplification; Clusters of immunogold nanoparticles

Synthesis of styrene–maleic anhydride copolymer esters and their surface enriched properties when blending with polyethylene by Gufeng Chen; Yi Zhang; Xie Zhou; Jiarui Xu (pp. 1107-1110).

Three kinds of comb-like amphiphilic copolymers based on styrene–maleic anhydride copolymer (SMA) backbone and long fatty alcohol grafts were synthesized by esterification of SMA with octanol, tetradecanol and octadecanol, respectively. SMA and the esters were used as surface modifiers to blend with high density polyethylene (HDPE). The surface composition of the binary blends has been determined by Attenuated Total Reflection Fourier Transform infra-red (ATR-FT-IR) spectroscopy. It was found that grafting of alcohols onto SMA can promote the enrichment of the modifiers on the surface of the blending film, and that the enrichment effect enhances when using shorter fatty alcohols. The data of contact angle measurements and surface tension of the blend film show that the addition of SMA esters to HDPE can improve the hydrophilicity of the HDPE surface.

Keywords: Polyethylene; Blend; SMA esters; Macromolecular surface modifier

Influence of negative ion element impurities on laser induced damage threshold of HfO₂ thin film by ShiGang Wu; GuangLei Tian; ZhiLin Xia; JianDa Shao; ZhengXiu Fan (pp. 1111-1115).

Negative ion element impurities breakdown model in HfO₂ thin film was reported in this paper. The content of negative ion elements were detected by glow discharge mass spectrum analysis (GDMS); HfO₂ thin films were deposited by the electron-beam evaporation method. The weak absorption and laser induced damage threshold (LIDT) of HfO₂ thin films were measured to testify the negative ion element impurity breakdown model. It was found that the LIDT would decrease and the absorption would increase with increasing the content of negative ion element. These results indicated that negative ion elements were harmful impurities and would speed up the damage of thin film.

Keywords: PACS; 68.55.Ln; 81.70. −qNegative ion elements; Impurities breakdown model; HfO; ₂; thin film; Weak absorption; LIDT

Formation and Shape Transition of Nanostructures on Si(100) surfaces after MeV Sb Implantation by Soma Dey; Dipak Paramanik; V. Ganesan; Shikha Varma (pp. 1116-1121).

We have studied the formation of nanostructures on Si(100) surfaces after 1.5 MeV Sb implantation. Scanning Probe Microscopy has been utilized to investigate the ion implanted surfaces. We observe the formation of nanostructures after a fluence of1×1013 ions/cm². These surface structures are elliptical in shape with an eccentricity of 0.86 and their major and minor axes having dimensions of about 11.6 nm and 23.0 nm, respectively. The area of the nanostructure is 210 nm²at this fluence. Although the nanostructures remain of elliptical shape, their area increase with increasing fluence. However, after a fluence of5×1014 ions/cm² a transition in shape of nanostructures is observed. Nanostructures become approximately circular with an eccentricity of 0.19 and a diameter of about 30.1 nm. At this fluence we also observe a large increase in the area of the nanostructures to 726 nm². Surface morphology and surface roughness of the ion implanted surfaces has also been discussed.

Keywords: PACS; 61.72.Tt; 68.37.Ps; 68.37.-dImplantation; Atomic force microscope; Surface roughness; Nanostructures; Silicon; Antimony

Effect of focus position on informational properties of acoustic emission generated by laser–material interactions by Evgueni V. Bordatchev; Suwas K. Nikumb (pp. 1122-1129).

To achieve desired accuracy, precision and surface roughness during laser–material removal process, monitoring and control of the process parameters related to laser, optics, workpiece material and its motion are required. Focus position, defined as a gap between the focusing lens and the surface of the sample workpiece, is one of the most critical process parameters, which determines the projection of the intensity of the laser beam on the surface to be ablated and therefore directly affects volume and geometry of the material removed and there by machining quality. In this paper, acoustic emission (AE) generated by laser–material interactions was statistically analyzed with respect to the variations in the focus position. The study involved on-line measurements of the AE signal from the laser–material interaction zone as a function of the focus position and the width of the machined trenches. Several basic statistical parameters, e.g. average amplitude, variance and power spectrum density were analyzed to select distinct informational parameters. Pattern recognition analysis of three informational parameters based on variances within frequency diapasons of 20–180, 180–300, and 300–500kHz was used for reliable classification of the focus position and width of the machined trenches. The results provide important information for future development of on-line monitoring and control systems for laser–material removal process.

Keywords: PACS; 52.38.Mf; 42.62.Cf; 52.35.Tc; 43.35.Kp; 43.60.Cg; 43.60.Lq; 52.35.Dm; 05.45.Tp; 43.20.Fn; 43.60.+dLaser–material interaction; Focus position; Acoustic emission; Statistic analysis; Informational properties; Pattern recognition; On-line monitoring

Characterization of a Co–Se thin film by scanning Auger microscopy and Raman spectroscopy by M. Teo; P.C. Wong; L. Zhu; D. Susac; S.A. Campbell; K.A.R. Mitchell; R.R. Parsons; D. Bizzotto (pp. 1130-1134).

Scanning Auger microscopy and micro-Raman spectroscopy are combined to characterize a Co–Se thin film sample, containing 84at.% Se, which had been modified in localized areas following excitation with an intense focused Ar⁺ laser (514.5nm). The information obtained helps to establish that a previous assignment for a Co–Se sample of Raman features between 168 and 175cm⁻¹ actually refers to an oxygenated Co–Se species, and that Co–Se interactions in a Se-rich environment give rise to Raman structure between 181 and 184cm⁻¹. Comparisons are made for the use of Ar⁺ and HeNe laser sources for Raman measurements in this context; the latter in general gives both better resolution and better signal-to-noise characteristics.

Keywords: PACS; 82.80.Dx; 82.80.GkCobalt; Selenium; Co–Se thin film; Scanning Auger microscopy; Micro-Raman spectroscopy

Surface nano-structural modifications and characteristics in nitrogen ion implanted W as a function of temperature and N⁺ energy by Hadi Savaloni; Farzaneh Modiri (pp. 1135-1142).

The surface modifications of tungsten massive samples (0.5mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16–30keV with a fluence of 1×10¹⁸N⁺cm⁻² were implanted in tungsten samples for 1600s at different temperatures. XRD patterns clearly showed WN₂ (018) (rhombohedral) very close to W (200) line. Crystallite sizes (coherently diffracting domains) obtained from WN₂ (018) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The surface roughness variation with temperature generally showed a decrease with increasing temperature. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in W studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in W at certain temperatures, which are both consistent with XRD results (i.e., IW (20₀₎/ IW (21₁₎) for W (bcc). Hence, showing a correlation between XRD and SIMS results.

Keywords: PACS; 68.55.Ln; 68.49.Sf; 82.80.Ms; 68.37.PsSEM; AFM; XRD; SIMS; Ion implantation; Depth profile

Elaboration of (111)-oriented La-doped PZT thin films on platinized silicon substrates by G. Leclerc; B. Domengès; G. Poullain; R. Bouregba (pp. 1143-1149).

PLZT thin films with different thickness were deposited in situ on platinum coated silicon substrates using a multi-target sputtering system. The purpose was to grow (111)-textured PLZT films on Pt (111). To this aim, the role of some key parameters on both crystalline quality and electrical properties was investigated. An ultra-thin TiO₂ seeding layer was deposited, prior to PLZT, which strongly affected the crystallographic orientation of the films. The relation between temperature deposition and film crystallinity is analysed. TEM observations show the presence of some very small grains of Zr_0.9La_0.1O_1.95 at the film bottom interface. In the range of thickness investigated, the plot of the inverse capacitance as a function of the film thickness split up into two different curves, each with a linear shape, which however allows determination of a single value of interface capacitance. Above a thickness of 400–500nm a saturation of the dielectric properties seems to be reached.

Keywords: PACS; 68.37.-d; 68.55.Jk; 77.84.-s; 81.15.CdPLZT films; Ferroelectric; Multi-target sputtering; Interfaces; Electron microscopy

H uptake kinetics of FeTi films coated with Ni by E.M.B. Heller; A.M. Vredenberg; D.O. Boerma (pp. 1150-1153).

The H₂ storage material FeTi can be fully charged through a Ni coating in the course of hours. A mild activation, either by long H₂ exposure at RT, or annealing in 35mbar H₂ at 150°C, leads to a full uptake in minutes. The enhancement of the uptake rate after activation is caused by a reduction of the Ni-oxide surface. Ni does not limit the hydrogen uptake rate once the surface is clean. However, the Ni surface is sensitive to contamination, as for instance by CO adsorbed from air.

Keywords: PACS; 68.35 Fx; 81.05 Bx; 81.65 Mq; 89.30 xfFeTi; Ni; Hydrides; Hydrogen storage; Kinetics; Thin films; Energy storage

Effect of an in-situ applied electric field on growth of Bi₄Ti₃O₁₂ films by sol–gel by Ai-Dong Li; Jin-Bo Cheng; Hui-Qing Ling; Di Wu; Nai-Ben Ming (pp. 1154-1159).

Bi₄Ti₃O₁₂ (BIT) films were prepared on Pt/TiO₂/SiO₂/Si substrates by the sol–gel method. A low electric field was in-situ applied to BIT films during rapid thermal annealing (RTA). It was first found that a bias electric field has great influence on the structure, orientation, and morphology of BIT films at proper temperatures. Under the electric field of very low V/cm, BIT films show highly c-axis-oriented growth with second phase of bismuth oxide at 600 and 650°C. The possible origin is proposed. On one hand, the electrostatic energy provides an extra driving force and the co-interaction of the electrostatic energy and interface energy promotes the c-axis-oriented growth of the BIT grains. On the other hand, the second phase of bismuth oxide produced during RTA in an electric field also plays an important role in the control of film orientation.

Keywords: PACS; 68.55.-a; 68.55.Jk; 61.10.-iIn-situ applied electric field; Orientation; Ferroelectric films; BIT film

Behaviour of discontinuous gold films on SrTiO₃ substrates under annealing by Imre Beszeda; Tamás Kocsis; Gergely Imreh; Frank Weigl; Hans-Gerd Boyen; Paul Ziemann; Dezső L. Beke (pp. 1160-1164).

Morphological changes of thin, discontinuous gold films on SrTiO₃ substrates, resulting from evaporation in the temperature range of 1143–1278K, have been investigated by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). If the gold covered fraction of the surface is small, the evaporation kinetics can be related to the desorption of adatoms. Measuring the density of the gold beads and the time dependence of the effective thickness of the film as calculated from the diameter of the beads, the following parameters have been determined: the surface diffusion length of the gold adatoms,λs(m)=(2.2−2.0+26.7)×10−3×exp[−(77±26)kJ/mol/RT], the mass transfer surface diffusion coefficient,D′s(m2/s)=(3.25−3.23+433)×1010×exp[−(560±49)kJ/mol/RT] and the evaporation flux,J(m−2s−1)(2.79−2.76+267)×1035×exp[−(426±46)kJ/mol/RT].

Keywords: PACS; 68.08.Bc; 68.37.Hk; 68.37.Ps; 68.43.Jk; 68.43.Mn; 68.47.Jn; 68.55.-aSrTiO; ₃; Gold; Surface diffusion; Discontinuous film; Evaporation

SHI induced silicide formation and surface morphology at Co/Si system by Garima Agarwal; Pratibha Sharma; I.P. Jain (pp. 1165-1169).

Ion beam mixing is a useful technique to produce modifications at the surface and interface of the solid material. In the present work, ion beam induced modifications at Co/Si interface using 120MeV Au-ion irradiation has been studied at ion fluences in the range of 10¹² to 10¹⁴ions/cm² by secondary ion mass spectroscopy (SIMS) technique and calculated mixing efficiency at the interface. Silicide formation has been discussed on the basis of swift heavy ion (SHI) irradiation induced effects. Surface morphology and roughness of irradiated system with fluence 5×10¹³ and 1×10¹⁴ions/cm² is studied by scanning tunneling microscopy (STM). Roughness of the surface shows marks of melting process and confirms the appearance of some pinholes in the reacted Co/Si system. Comparative study was also undertaken on annealed sample at 300°C and then irradiated at a dose 1×10¹⁴ions/cm².

Keywords: Ion beam mixing; Surface; Interface; Silicide; Ion irradiation

Nanosecond pulse laser melting investigation by IR radiometry and reflection-based methods by J. Martan; O. Cibulka; N. Semmar (pp. 1170-1177).

Experimental system for nanosecond laser melting investigation was developed containing three independent noncontact methods: infrared radiometry, time-resolved reflectivity of He–Ne laser and sample surface reflected KrF heating laser pulse. The system was applied to the investigation of laser melting of Cu, Mo, Ni, Si, Sn, Ti, steel ČSN 15330 and stainless steel ČSN 17246 samples. For metallic samples the IR radiometry signal was transformed to temperature. Obtained surface temperature and reflectivity spectra in nanosecond time scale (10–1000ns) for wide range of energy densities (100–5500mJcm⁻²) are presented. Interesting evolutions were found. Melting thresholds and melting durations were determined from the measured curves. The applicability of the methods is evaluated.

Keywords: PACS; 42.62.−b; 06.60.Jn; 78.47.+p; 64.70.Dv; 44.40.+a; 42.55.Lt; 07.57.Kp; 07.07.Df; 07.20.Ka; 07.60.DqNanosecond pulsed laser melting; Melting duration; Melting threshold; Infrared radiometry; Surface temperature measurement; Time-resolved reflectivity; Experimental

Investigation of IrO₂–SnO₂ thin film evolution from aqueous media by Lourdes Vázquez-Gómez; Erzsébet Horváth; János Kristóf; �?kos Rédey; Achille De Battisti (pp. 1178-1184).

The thermal evolution process of IrO₂–SnO₂/Ti mixed oxide thin films of varying noble metal content has been investigated under in situ conditions by thermogravimetry–mass spectrometry, Fourier transform infrared emission spectroscopy and cyclic voltammetry. The gel-like films prepared from aqueous solutions of the precursor salts Sn(OH)₂(CH₃COO)2−_xCl_x and H₂IrCl₆ on titanium metal support were heated in an atmosphere containing 20% O₂ and 80% Ar up to 600°C.The thermal decomposition reactions practically take place in two separate temperature ranges from ambient to about 250°C and between 300 and 600°C. In the low temperature range the liberation of solution components and – to a limited extent – an oxidative cracking reaction of the acetate ligand takes place catalyzed by the noble metal. In the high temperature range the evolution of chlorine as well as the decomposition of surface species formed (carbonyls, carboxylates, carbonates) can be observed. The acetate ligand shows extreme high stability and is decomposed in the 400–550°C range, only.Since the formation and decomposition of the organic surface species can significantly influence the morphology (and thus the electrochemical properties) of the films, the complete understanding of the film evolution process is indispensable to optimize the experimental conditions of electrode preparation.

Keywords: Iridium oxide; Tin oxide; Electrocatalysis; Thin films

Pulsed laser deposition of polyhydroxybutyrate biodegradable polymer thin films using ArF excimer laser by G. Kecskemeti; T. Smausz; N. Kresz; Zs. Tóth; B. Hopp; D. Chrisey; O. Berkesi (pp. 1185-1189).

We demonstrated the pulsed laser deposition (PLD) of high quality films of a biodegradable polymer, the polyhydroxybutyrate (PHB). Thin films of PHB were deposited on KBr substrates and fused silica plates using an ArF ( λ=193nm, FWHM=30ns) excimer laser with fluences between 0.05 and 1.5Jcm⁻². FTIR spectroscopic measurements proved that at the appropriate fluence (0.05, 0.09 and 0.12Jcm⁻²), the films exhibited similar functional groups with no significant laser-produced modifications present. Optical microscopic images showed that the layers were contiguous with embedded micrometer-sized grains. Ellipsometric results determined the wavelength dependence ( λ∼245–1000nm) of the refractive index and absorption coefficient which were new information about the material and were not published in the scientific literature. We believe that our deposited PHB thin films would have more possible applications. For example to our supposal the thin layers would be applicable in laser induced forward transfer (LIFT) of biological materials using them as absorbing thin films.

Keywords: PACS; 81.15.Fg; 82.35.Pq; 87.68.+zAblation; AFM; Ellipsometry; FTIR spectra; PLD; Polyhydroxybutyrate; Surface analysis

Metal–CdZnTe contact and its annealing behaviors by Qiang Li; Wanqi Jie; Li Fu; Xiaoqin Wang; Xinggang Zhang (pp. 1190-1193).

The electrical properties of different metal–CdZnTe contacts by sputtering deposition method are investigated by current–voltage. The results show that Au is the most suitable electrical contact materials, which forms the nearly ideal Ohmic contact with high resistivity p-CdZnTe crystals. Ohmicity coefficient b is the closest to 1 after 10min annealing at 333K, which is analyzed by current–voltage characteristics. XPS analyses show that Au atoms diffuse into CdZnTe during annealing process and Cd and Te atoms diffuse into Au contact. Diffused Au atoms do not form any compound with any element in CdZnTe crystal. PL spectra results of Au deposition on CdZnTe crystals at 10K show that the inter-diffused donors [Au]³⁺ recombine with acceptors [ V_Cd]²⁻ during sputtering process. Meanwhile, the intensity of ( D_complex) peak of with Au contact increases sharply in comparison with un-deposited CdZnTe crystal and donor [Au]³⁺ and[Au3+⋅VCd2−]+can compensate Cd vacancy [ V_Cd]²⁻ wholly.

Keywords: CdZnTe; Annealing; PL spectra

Corrosion-wear monitoring of TiN coated AISI 316 stainless steel by electrochemical noise measurements by Zhenlan Quan; Pei-Qiang Wu; Lin Tang; J.-P. Celis (pp. 1194-1197).

A modified electrochemical noise (EN) technique has been applied to monitor corrosion-wear of TiN coated AISI 316 stainless steel sliding against corundum in 0.5M H₂SO₄. Experimental results show that the EN technique can sensitively detect potential and current variations during a corrosion-wear process. Corrosion-wear mechanisms of TiN coatings depend on their substrate properties. When the substrate is passive, such as AISI 316 stainless steel, the potential and current variations reflect the properties of coatings. Depassivation and repassivation alternately take place on the tribo-activated wear area during the steady-state phase.

Keywords: TiN coatings; Electrochemical noise; Corrosion-wear

Structural and photo-luminescence properties of nanocrystalline silicon films deposited at low temperature by plasma-enhanced chemical vapor deposition by Atif Mossad Ali; Takao Inokuma; Seiichi Hasegawa (pp. 1198-1204).

Nanocrystalline silicon (nc-Si) films were prepared by a plasma-enhanced chemical vapor deposition method at a deposition temperature below 220°C with different dynamic pressures ( P_g), hydrogen flow rates ([H₂]), and RF powers, using SiH₄/H₂/SiF₄ mixtures. We examined the photo-luminescence (PL) spectra and the structural properties. We observed two stronger and weaker PL spectra with a peak energies around E_PL=1.8 and 2.2–2.3eV, respectively, suggesting that the first band was related to nanostructure in the films, and another band was associated with SiO-related bonds. The nc-Si films with rather large PL intensity was obtained for high [H₂] and/or low pressure values, However, effects of [H₂] are likely to be different from those of P_g. The average grain size ( δ) and the crystalline volume fraction ( �?) at first rapidly increase, and then slowly increase, with increasing P_g. Other parameters exhibited opposite behaviors from those of δ or �?. These results were discussed in connection with the changes in the PL properties with varying the deposition conditions.

Keywords: PACS; 81.07.Bc; 68.55.−a; 78.55.Ap; 78.66.Li; 81.15.Gh; 81.10.BkNanocrystalline silicon; Plasma-enhanced chemical vapor deposition (PECVD); Photo-luminescence; Low temperature; Dynamic pressure; Optical and structural properties; Defect properties; H and F addition

Study to improve the quality of a Mexican straight run gasoil over NiMo/γ-Al₂O₃ catalysts by M.A. Domínguez-Crespo; L. Díaz-García; E.M. Arce-Estrada; A.M. Torres-Huerta; M.T. Cortéz-De la Paz (pp. 1205-1214).

Four NiMo catalyst supported on Al₂O₃ with different textural properties have been studied in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) of a Mexican straight run gasoil (SRGO). All reactions were carried out at three different temperatures 613, 633, and 653K. Alumina supports were analysed by pyridine FTIR-TPD and nitrogen physisorption in order to determine their surface acidity and textural properties, respectively. TPR studies of the NiMo catalysts were analysed to correlate their hydrogenating properties. Metallic particles were characterized (after sulfidation) using transmission electron microscopy (TEM). Catalytic activities are discussed in relation to the physicochemical properties of NiMo catalysts. The importance of textural properties on coke deposition has been emphasized. The results of catalytic activity of these materials varied depending on dispersed MoS particles and pore distribution in final catalysts. The optimum pore diameter was found around 80Å for HDS and HDN.

Keywords: Catalysis; Hydrotreating; Heavy gasoil; NiMoS particles

Characteristics of sputtered Ta–B–N thin films as diffusion barriers between copper and silicon by Shun-Tang Lin; Chiapyng Lee (pp. 1215-1221).

Ta–B–N thin films were prepared by rf-magnetron sputtering from a TaB₂ target in N₂/Ar reactive gas mixtures and then used as diffusion barriers between Cu and Si substrates. In order to investigate the performance of Cu/Ta–B–N/Si contact systems, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe measurement, scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and Auger electron spectroscopy (AES) depth profile were used. Results of this study indicate that the barrier characteristics are significantly affected by the nitrogen content. In addition, the failure mechanism for the Cu/Ta–B–N/Si contact systems is also discussed herein.

Keywords: Ta–B–N film; Diffusion barrier; Microstructure properties; Cu metallization

Stress driven phase transformation in ZrO₂ film by B. Benali; M. Herbst Ghysel; I. Gallet; A.M. Huntz; M. Andrieux (pp. 1222-1226).

Zirconia thin layers (250nm) were deposited on stainless steel substrates using organo-metallic injection chemical vapour deposition (MOCVD) process with zirconium beta-diketonate as precursor at low oxygen pressure and 900°C. Low roughness zirconia films were made up of a mixture of tetragonal and monoclinic phases depending on the process conditions. As the zirconia tetragonal phase is known to be stabilized by small grain size and/or internal compressive stresses, tensile and/or compressive external stress fields were applied at room temperature using a bending test device. Then, XRD measurements were used to determine tetragonal/monoclinic phase ratio and also residual stresses in the films before and after the tests. The film surface was observed at the various stages of the experiments by field electron gun–scanning electron microscopy (FEG-SEM).Under these stress fields, phase transformation occurs in the film, from tetragonal structure to a monoclinic one. Some preferential tetragonal planes give rise to monoclinic ones. The external stress field is also likely to redistribute the internal stresses within the films.

Keywords: Zirconia thin films; Tetragonal and monoclinic phases; Phase transformation; Bending test; Mechanical properties

Catalytic growth of TiO₂ nanowires from a TiN thin film by A.-C. Dupuis; L. Jodin; E. Rouvière (pp. 1227-1235).

We report in this work synthesis of TiO₂ nanowires from a TiN thin film overlayed with nickel. The nanowires have been analyzed with EELS, XPS, XRD and HRTEM. It has been shown that the nanowires are single-crystalline and of the rutile structure. The growth mechanism has been studied, allowing to determine in which process conditions synthesis of nanowires occurs and to propose a growth scenario.

Keywords: Nanowires; TiO; ₂; Catalytic growth; Oxydation of TiN

Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production by Hui Tian; Charles E. Reece; Michael J. Kelley; Shancai Wang; Lukasz Plucinski; Kevin E. Smith; Matthew M. Nowell (pp. 1236-1242).

The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (100), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3–1.4 times that resulting from static solution. The standard deviation of the roughness measurements is ±30% and that of the surface composition is ±5%.

Keywords: Niobium RF cavities; Surface analysis; Chemical etching; Accelerator cavities

Si layer transfer to InP substrate using low-temperature wafer bonding by J. Arokiaraj; S. Tripathy; S. Vicknesh; S.J. Chua (pp. 1243-1246).

Using a low-temperature wafer bonding process, InP substrates are bonded to silicon-on-insulator (SOI) substrates at 220°C. A combination of oxygen plasma and chemical treatment results in a direct contact bonding at room temperature. After the bonding process at 220°C for 45min, removal of the Si handle substrate by sacrificial etching of the buried oxide layer in SOI, results in a thin membrane of Si robustly bonded to InP. The thin Si membrane bonded to InP shows uniformly bonded interface under high-resolution electron microscopy. Micro-Raman analysis has also been carried out to study the bonded interface. I– V characteristics of the bonded structures suggest that such bonding and layer transfer processes are suitable for device integration.

Keywords: PACS; 81.05Ea; 81.65−b; 78.55−m; 78.30−jWafer bonding; SOI; InP; Oxygen plasma; Micro-Raman; Thin-film

Laser synthesis of palladium–alumina composite membranes for production of high purity hydrogen from gasification by Binay Singh; Atul C. Sheth; Narendra B. Dahotre (pp. 1247-1254).

This paper describes a special method of laser-based deposition to synthesize palladium–ceramic composite membranes. Thin film Pd was deposited on a ceramic substrate by Nd-YAG laser irradiation of coating precursor PdCl₂ on γ-alumina substrate. The parameters of the laser processing technique were optimized to synthesize metal–ceramic composite membranes. The physical and chemical characteristics of Pd coated γ-alumina membranes were studied and compared with various other alumina membranes referenced in the literature. Hydrogen permeation experiments were performed in a CO+CO₂+CH₄+H₂ environment under typical catalytic steam gasifier exit conditions. The Pd–ceramic composite showed good mechanical and thermal stability and resulted in a hydrogen permeability flux of about 0.061mol/m²s. The activation energy of the Pd membrane was found to be 5.39kJ/mol in a temperature range of 900–1300°F.

Keywords: Palladium membranes; Hydrogen permeation; Ceramic membranes; Laser deposition; Inorganic membranes; Catalytic steam gasification

Use of TiB₂ diffusion barriers for Ni/Au ohmic contacts on p-GaN by Lars Voss; Rohit Khanna; S.J. Pearton; F. Ren; I.I. Kravchenko (pp. 1255-1259).

The use of a TiB₂ diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25–950°C) dependence of ohmic contact characteristics using a Ni/Au/TiB₂/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500°C . A minimum specific contact resistivity of ∼3×10⁻⁴Ωcm⁻² was obtained after annealing over a broad range of temperatures (800–950°C for 60s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB₂ at 800°C. By 900°C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB₂ diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500°C.

Keywords: GaN; Ohmic contacts; Annealing

Effect of Al content on the properties of Cr1−_xAl_xC films prepared by RF reactive magnetron sputtering by Tsow-Chang Fu; Guo-Wei Li (pp. 1260-1264).

Cr1−_xAl_xC films were deposited on high-speed steel by RF reactive magnetron sputtering. In this study, we aimed to identify the effect of the Al content on the properties of Cr1−_xAl_xC films. We found that Cr1−_xAl_xC films exhibited a fine columnar grain microstructure with some special characteristics, such as high hardness of Hv 1426, a low friction coefficient of 0.29, and a large contact angle of 90° for x=0.18. Furthermore, an increase in Al content resulted in a decrease in film hardness and an increase in contact angle. Moreover, on annealing at 923K, the mechanical properties of the films improved and a dense protective film of complex Cr₂O₃ and Al₂O₃ oxides was formed on the surface for better wear resistance, which will ultimately increase the lifetime of the high-speed steel substrate.

Keywords: PACS; 81.15.Cd; 81.15.-z; 62.20.-x; 68.35.MdSputtering; Chromium carbides; Aluminum

Characterization of conductance under finite bias for a self-assembled monolayer coated Au quantized point contact by T. Zheng; H. Jia; R.M. Wallace; B.E. Gnade (pp. 1265-1268).

We have demonstrated that an experimental cross-wire junction set-up can be used to measure the I– V characteristics of a self-assembled monolayer (SAM) stabilized metal quantized point contact. The increased stability due to the presence of the SAM allows the measurement of the I– V characteristics. However, the SAM also provides additional conductance paths in addition to the pure metal point contact. The presence of the SAM may contribute to the non-integral quantum conductance transition and the non-linear I– V characteristics of the quantum contact. Nonetheless, a straight I– V curve is obtained for the Au quantized point contact from 0 to 1V with a conductance of approximately 1 G₀, in contrast to previous work reported in the literature.

Keywords: PACS; 73.23.AdQuantum conductance; I; –; V; behavior; Cross-wire junction

Comparison of CH₄/H₂ and C₂H₆/H₂ inductively coupled plasma etching of ZnO by Wantae Lim; Lars Voss; Rohit Khanna; B.P. Gila; D.P. Norton; S.J. Pearton; F. Ren (pp. 1269-1273).

CH₄/H₂-based discharges are attractive for dry etching of single crystal ZnO because of their non-corrosive nature. We show that substitution of C₂H₆ for CH₄ increases the ZnO etch rate by approximately a factor of 2 both with and without any inert gas additive. The C₂H₆/H₂/Ar mixture provides a strong enhancement over pure Ar sputtering, in sharp contrast to the case of CH₄/H₂/Ar. The threshold ion energy for initiating etching is 42.4eV for C₂H₆/H₂/Ar and 59.8eV for CH₄/H₂/Ar. The etched surface morphologies were smooth, independent of the chemistry and the Zn/O ratio in the near-surface region was unchanged within experimental error after etching with both chemistries. The plasma etching improved the band-edge photoluminescence intensity and suppressed the deep level emission from the bulk ZnO under our conditions, due possibly to removal of surface contamination layer.

Keywords: ZnO; Etching; Surface modification

Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness by D.C. Hurley �?�; M. Kopycinska-Müller; D. Julthongpiput; M.J. Fasolka (pp. 1274-1281).

The effects of surface functionality and relative humidity (RH) on nanomechanical contact stiffness were investigated using atomic force acoustic microscopy (AFAM), a contact scanned-probe microscopy (SPM) technique. Self-assembled monolayers (SAMs) with controlled surface energy were studied systematically in a controlled-humidity chamber. AFAM amplitude images of a micropatterned, graded-surface-energy SAM sample revealed that image contrast depended on both ambient humidity and surface energy. Quantitative AFAM point measurements indicated that the contact stiffness remained roughly constant for the hydrophobic SAM but increased monotonically for the hydrophilic SAM. To correct for this unphysical behavior, a viscoelastic damping term representing capillary forces between the tip and the SAM was added to the data analysis model. The contact stiffness calculated with this revised model remained constant with RH, while the damping term increased strongly with RH for the hydrophilic SAM. The observed behavior is consistent with previous studies of surface energy and RH behavior using AFM pull-off forces. Our results show that surface and environmental conditions can influence accurate measurements of nanomechanical properties with SPM methods such as AFAM.

Keywords: PACS; 62.25.+g; 68.37.Ps; 82.35.GhAtomic force microscopy (AFM); Nanomechanics; Self-assembled monolayer (SAM)

Optimization of the surface texture for silicon carbide sliding in water by Xiaolei Wang; Koshi Adachi; Katsunori Otsuka; Koji Kato (pp. 1282-1286).

Surface texturing has been recognized as an effective means to improve the tribological performances of sliding surfaces. Usually, generation additional hydrodynamic pressure to increase the load carrying capacity is regarded as the most significant effect of surface texture. In the case of silicon carbide sliding against identical material in water, the experimental results indicate that surface texture is also helpful to improve the running-in progress to smooth the contact surfaces, showing another reason to result in low friction. Based on the consideration of enhancing the generation of hydrodynamic pressure and improving running-in progress, a surface texture pattern, which was combined with large (circle, 350μm in diameter) and small (rectangular, 40μm in length) dimples, was designed to maximize the texture effect on the load carrying capacity of SiC surfaces sliding in water. The friction coefficient of such textured surface was evaluated and compared with that of untextured and those only with large or small dimples only. The friction reduction mechanisms of the patterns with different dimples in size are discussed.

Keywords: PACS; 81.40.Pq; 46.55.td; 06.60.Vz; 47.85.DhSurface texturing; SiC; Water lubrication; Running-in

The effect of hydrogen as an additive in reactive ion etching of GaAs for obtaining polished surface by F.N. Dultsev; L.A. Nenasheva (pp. 1287-1290).

The effect of hydrogen on the reactive ion etching (RIE) of GaAs in the CF₂Cl₂ plasma is discussed. The addition of hydrogen into the reaction mixture improves the sharpness of etch borders; the etched surface is smooth for etching depth>1μm, etching rate is time-constant.

Keywords: Reactive ion etching; Gallium arsenide; Hydrogen; Surface roughness

Hydrocarbons imbibition for geometrical characterization of porous media through the effective radius approach by L. Labajos-Broncano; J.A. Antequera-Barroso; M.L. González-Martín; J.M. Bruque (pp. 1291-1298).

Surface energetic characterization of porous solids usually requires the determination of the contact angle. This quantity is deduced by imbibition experiments carried out in such media with high surface tension liquids. Now then, this methodology needs the geometrical characterization of the porous medium by means of the deduction of its effective radius. Normally, this is made by imbibition experiments with n-alkanes, liquids whose surface tension is low enough as to suppose their contact angles with the solid surface are null. However, this last procedure is not free from some criticisms. Among them, the possible influence of the imbibition velocity on the contact angle, the effect of the precursor liquid film ahead the advancing liquid front on the driving force that gives rise to the movement, or the dependence of the effective radius on the length of the hydrocarbon chain of the n-alkanes. In an attempt of going deeply in these questions, imbibition experiments with n-alkanes have been carried out in porous columns of powdered calcium fluoride. These experiments have consisted of the measurement of the increase in the weight of the columns caused by the migration of the liquids through their interstices. The analysis of their results has been carried out by means of a new procedure based on the study of the velocity profile associated to the weight increase. This analysis has permitted us to conclude that, at least in the calcium fluoride columns, the contact angle of the n-alkane is not influenced by the capillary rise velocity, it taking in fact a null value during the process. On the other hand, it has been also proved that the driving force of the movement is caused by the replacement of the solid–vapour interface by the solid–liquid interface that happens during the imbibition, which means that only the Laplace's pressure, and not the precursor liquid film, contributes to the development of the phenomenon. Finally, it has been compared the values of the effective radius associated to each n-alkane, similar values being found independently from the particular liquid employed in the experiments, fact that indicates that the porous solid can be considered as a bunch of cylindrical and parallel capillaries of the same radius.

Keywords: Imbibition; Porous media; Effective radius; Contact angle; Precursor film

The effect of femtosecond laser micromachining on the surface characteristics and subsurface microstructure of amorphous FeCuNbSiB alloy by Wei Jia; Zhinong Peng; Zhijun Wang; Xiaochang Ni; Ching-yue Wang (pp. 1299-1303).

Detailed studies on the effects of femtosecond laser ablation on surface characteristics and subsurface microstructure of amorphous FeCuNbSiB alloy are reported. Three types of ripple structures were observed on the material surface in the gentle ablated (damaged) zone. As observed with X-ray diffraction (XRD), amorphous form is kept in the damaged zone, and there is few crystallization form in ablation zone.

Keywords: PACS; 52.38.Mf; 75.50.KjLaser ablation; Femtosecond laser; Amorphous alloy; Micromachining

The importance of the series resistance in calculating the characteristic parameters of the Schottky contacts by M.E. Aydin; K. Akkiliç; T. Kiliçoğlu (pp. 1304-1309).

Cd/p-Si Schottky barrier diodes (SBDs) with and without the native oxide layer have been fabricated to determine the importance of the fact that the series resistance value is considered in calculating the interface state density distribution (ISDD) from the forward bias current–voltage ( I– V) characteristics of the Cd/p-Si SBDs. The statistical analysis yielded mean values of 0.71±0.02eV and 1.24±0.12 for the BH and ideality factor of the Cd/p-Si SBDs (15 dots) without the native oxide layer (MS), respectively, and mean values of 0.79±0.02eV and 1.36±0.06eV for the Cd/p-Si SBDs (28 dots) with the native oxide layer (metal-insulating layer-semiconductor (MIS)). The interface state density ( Nss) distributions of the devices were calculated taking into account their series resistance values. At the same energy position near the top of the valence band, the interface state density values without taking into account the series resistance value of the devices are almost one order of magnitude larger than Nss obtained taking into account series resistance value.

Keywords: Ideality factor; Interface states distribution; Schottky barrier height; Series resistance

Carbon monoxide oxidation over well-defined Pt/ZrO₂ model catalysts: Bridging the material gap by Attila Wootsch; Claude Descorme; Sophie Rousselet; Daniel Duprez; Claude Templier (pp. 1310-1322).

Four different Pt/ZrO₂/(C/)SiO₂ model catalysts were prepared by electron beam evaporation. The morphology of these samples was examined before and after the catalytic reaction by Rutherford back-scattering (RBS), transmission electron microscopy (TEM) and grazing-incidence small-angle scattering (GISAXS). The catalytic behavior of such model catalysts was compared to a conventional Pt/ZrO₂ catalyst in the CO oxidation reaction using different oxygen excess ( λ=1 and 2). The so-called material gap was observed: model catalysts were active at higher temperature (620–770K) and resulted in higher activation energy values ( E_a=77–93kJmol⁻¹ at λ=1 and 129–141kJmol⁻¹ at λ=2) compared to the powdered Pt/ZrO₂ catalyst (370–470K, E_a=74–76kJmol⁻¹). This material gap is discussed in terms of diffusion limitations, reaction mechanism and apparent compensation effect. Diffusion processes seem to limit the reaction on planar samples in the reactor system that was shown to be appropriate for the evaluation of the catalytic activity of powder samples. Kinetic parameters obeyed the so-called apparent compensation effect, which is discussed in detail. Langmuir–Hinshelwood-type of reaction, between CO_ads and O_ads, was proposed as the rate-determining step in all cases. Pt particles deposited on planar structures can be used for modeling conventional powdered catalysts, even though some limitations must be taken into account.

Keywords: CO oxidation; Platinum; Pt; Model catalysts; Electron beam evaporation; Pt/ZrO; ₂; RBS; GISAX; Compensation effect; Material gap

Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers by R. Das; M.K. Bera; S. Chakraborty; S. Saha; J.F. Woitok; C.K. Maiti (pp. 1323-1329).

Rapid thermal oxidation of high-Ge content (Ge-rich) Si1−_xGe_x ( x=0.85) layers in dry O₂ ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (∼6–8nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO₂+GeO₂) and pile-up of Ge at the oxide/Si1−_xGe_x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance–voltage (C–V) and current–voltage (J–V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.

Keywords: PACS; 81.65.Mq; 73.40.Qv; 68.55.ÀaGe-rich SiGe; Rapid thermal oxidation; Ge segregation; Mixed-oxide

Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles by Gregory L. Fisher; Rollin E. Lakis; Charles C. Davis; Christopher Szakal; John G. Swadener; Christopher J. Wetteland; Nicholas Winograd (pp. 1330-1342).

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5MeV⁴He²⁺ ions from a tandem accelerator to doses between 1×10⁶ and 5×10¹⁰Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20keV C₆₀⁺ source, was employed to probe chemical changes as a function of α dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of α particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing α particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of α dose.The data show that PTFE nominally retains its innate chemical structure and morphology at α doses <10⁹Rad. At α doses ≥10⁹Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At α doses >10¹⁰Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of α particle irradiation and show morphological roughening of the sample with increased α dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of α particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

Keywords: PACS; 61.80.Jh (ion radiation effects); 81.40.Wx (radiation treatment)ToF-SIMS; PTFE; Nanoindentation; Alpha particle; Ionizing radiation

Volatile corrosion inhibitor film formation on carbon steel surface and its inhibition effect on the atmospheric corrosion of carbon steel by Da-quan Zhang; Zhong-xun An; Qing-yi Pan; Li-xin Gao; Guo-ding Zhou (pp. 1343-1348).

A novel volatile corrosion inhibitor (VCI), bis-piperidiniummethyl-urea (BPMU), was developed for temporary protection of carbon steel. Its vapor corrosion inhibition property was evaluated under simulated operational conditions. Electrochemical impedance spectroscopy was applied to study the inhibition effect of BPMU on the corrosion of carbon steel with a thin stimulated atmospheric corrosion water layers. Adsorption of BPMU on carbon steel surfaces was investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The results indicate that BPMU can form a protective film on the metal surface, which protects the metal against further corrosion. The structure of the protective film was suggested as one BPMU molecule chelated with one Fe atom to form a complex with two hexa-rings.

Keywords: Steel; Corrosion; Volatile corrosion inhibitor; Electrochemical impedance spectroscopy (EIS); Atomic force microscopy (AFM)

Scale-dependent nature of the surface fractal dimension for bi- and multi-disperse porous solids by mercury porosimetry by Baoquan Zhang; Wei Liu; Xiufeng Liu (pp. 1349-1355).

The surface fractal dimension was calculated by using a mathematical model and mercury intrusion data for a variety of bi- and multi-disperse porous solids including silica gels, alumina pellets, and building stones. The mathematical model was obtained by modifying the well-established scaling relation published previously [ Ind. Eng. Chem. Res., 34 (1995) 1383–1386]. It was also verified by comparing with the theoretical surface fractal dimensions for regular fractal structures ( Skerpinski tetrahedron and Menger sponge) and the calculated surface fractal dimensions for silica gel and alumina particles via the linear fitting method established previously. The calculation results for various bi- and multi-disperse porous solids have demonstrated that the scale-dependent nature of the surface fractal dimension is ubiquitous. The difference in the surface fractal dimension between pore size intervals usually exists. The estimation of the surface fractal dimension on an average stand may lead to erroneous results.

Keywords: PACS; 05.45.Df; 81.05.RmFractal; Porous media; Mercury porosimetry

Structural and electrical analysis of S⁺ ion bombarded p-InP(100) by Q. Zhao; G.J. Zhai; R.W.M. Kwok (pp. 1356-1364).

The chemical state of sulfur and surface structure on low-energy S⁺ ion-treated p-InP(100) surface have been investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). S⁺ ion energy over the range of 10–100eV was used to study the effect of ion energy on surface damage and the process of sulfur passivation on p-InP(100) by S⁺ ion beam bombardment. It was found that sulfur species formed on the S⁺ ion-treated surface. The S⁺ ions with energy above 50eV were more effective in formation of In–S species, which assisted the InP surface in reconstruction into an ordered (1×1) structure upon annealing. After taking into account physical damage due to the process of ion bombardment, we found that 50eV was the optimal ion energy to form In–S species in the sulfur passivation of p-InP(100). The subsequent annealing process removed donor states that were introduced during the ion bombardment of p-InP(100). Results of theoretical simulations by Transport of Ions in Materials (TRIM) are in accordance with those of experiments.

Keywords: PACS; 41.75.AK; 61.72.Vv; 81.65.Rv; 79.60.-IInP; Ion beam bombardment; Sulfur passivation; XPS; LEED

Characterization of a thin CeO₂–ZrO₂–Y₂O₃ films electrochemical deposited on stainless steel by I. Avramova; D. Stoychev; Ts. Marinova (pp. 1365-1370).

In this paper, we report for the first time formation of a thin CeO₂–ZrO₂–Y₂O₃ films electrodeposited on a stainless steel substrate. The samples have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD and XPS data indicate formation of a solid solution and additional existence of Ce³⁺ states near the surface. After annealing, SEM examination has shown a microstructure formed by dispersed spherical agglomerates having a size between 20 and 60nm.

Keywords: PACS; 68.37.Hk; 81.15.Pq; 82.80.PvCeO; ₂; –ZrO; ₂; –Y; ₂; O; ₃; oxide; Electrodeposition; XPS

2-Mercapto-1-methylimidazole as corrosion inhibitor for copper in hydrochloric acid by L. Larabi; O. Benali; S.M. Mekelleche; Y. Harek (pp. 1371-1378).

The inhibition of corrosion of copper in hydrochloric acid by 2-mercapto-1-methylimidazole was investigated by dc polarization, ac impedance and weight loss techniques. A significant decrease in the corrosion rate of copper was observed in the presence of the investigated compound. The corrosion rate was found to depend on the concentration of the inhibitor. The degree of surface coverage of the adsorbed inhibitor is determined by ac impedance technique, and it was found that the results obey the Langmuir adsorption isotherm. The potentiodynamic polarization data indicated that the inhibitor was of mixed type, but the anodic effect is more pronounced. The slopes of the cathodic and anodic Tafel lines are approximately constant and independent on the inhibitor concentration. This inhibitor lowered the corrosion reaction by blocking the copper surface through physical and chemical adsorption. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitor. Also, some thermodynamic data for the adsorption and dissolution processes are calculated and discussed. The reactivity of the compound under investigation was analyzed through Fukui indices, which are reactivity descriptors derived from density functional theory (DFT), to explain the great efficiency of this compound as corrosion inhibitor comparatively to other imidazole derivatives.

Keywords: Copper; Corrosion inhibition; Hydrochloric acid; 2-Mercapto-1-methylimidazole; Fukui indices

Capacitance dispersion in electrochemical impedance spectroscopy measurements of iodide adsorption on Au(111) by Rodrigo S. Neves; Eveline De Robertis; Artur J. Motheo (pp. 1379-1386).

Electrochemical interfaces that display dispersive characteristics do not present the purely capacitive behaviour predicted by the theory of ideally polarised interfaces. For interfaces involving solid electrodes, capacitance dispersion phenomena in the double layer region are usually attributed to the structural characteristics of the electrode surface as well as to the interfacial region. This paper presents a study of the dispersive characteristics, in the double layer potential region, related to the iodide adsorption on an Au(111) electrode. The study was performed by using electrochemical impedance spectroscopy, and the corresponding spectra fitted with an equivalent circuit containing a constant phase element (CPE). The fitting results are compared with capacitance curves obtained by chronocoulometry, in order to analyse the relationship between the CPE and the interfacial capacitance. It was observed the occurrence of dispersive behaviour in the potential regions associated with phase transition processes in the adsorbed layer and to the potential induced reconstruction phenomena. On the other hand, in the potential regions where such phenomena do not occur, the interface presents almost pure capacitive behaviour. These observations provide evidence of the strong contribution of the solution properties to the capacitance dispersion.

Keywords: PACS; 73.30.+y; 74.25.Nf; 79.60.Dp; 79.60.JvCPE; EIS; Capacitance dispersion; Adsorption; Iodide; Au(1; 1; 1)

Novel luminescent RE/TiO₂ (RE=Eu, Gd) catalysts prepared by in-situation sol–gel approach construction of multi-functional precursors and their photo or photocatalytic oxidation properties by Wei Zhou; Yu-hui Zheng; Guang-hui Wu (pp. 1387-1392).

In this context, a novel synthesis method was used to fabricate rare earth/TiO₂ catalyst for the first time. Lanthanide (Eu, Gd) coordination polymers with picolinic acids were applied as precursors of titania oxide components, in particular, polyethylene glycol and polyacrylamide were added to assemble inorganic–organic hybrid polymeric network through an in-situation sol–gel technique. After sintering treatment of the multi-component precursor under 600°C for 3h, fluorescence excitation and emission spectra show that Eu/TiO₂ crystalline phosphor exhibits strong red luminescence under excitation wavelength at 394 and 464nm. SEM and BET indicate the two hybrids are porous and homogenous. The oxidation experiments from trivalent arsenite As(III) to pentavalent arsenate As(V) by the above two catalysts substantiate that their surfaces have higher affinity to arsenate and can enhance photocatalytic oxidation activity in comparison with pure titania.

Keywords: Rare earth; Emission; Catalyst; Titania

Oxidation and contact resistance of Sn–Ag coated superconducting strands for the Large Hadron Collider (LHC) by C. Scheuerlein; M. Taborelli; M. Cantoni (pp. 1393-1398).

The oxides formed on the Sn–Ag coated Large Hadron Collider (LHC) superconducting cables during a 200°C heat treatment in air are described and the oxide composition is compared with the interstrand contact resistance ( R_C). The analysis of more than 250 interstrand contact areas shows that the higher the average Cu content with respect to the Sn content in the oxide, the higher is R_C. During the 200°C heat treatment, Sn in the coating is transformed into a Cu₃Sn layer, on which an oxide grows that consists essentially of a thin outermost layer of CuO on top of Cu₂O, similar to the oxide structure formed on bare Cu. The underlying Cu₃Sn layer acts as an O diffusion barrier that prevents O diffusion into the Cu bulk during the subsequent cable heat treatment under high pressure. On contact zones where the Cu₃Sn layer is not formed during the 200°C heat treatment mainly Sn oxide grows and R_C is comparatively low.

Keywords: Contact resistance (73.40.Cg); Oxidation (81.65.Mq); Electron spectroscopy (82.80.Pv); Large Hadron Collider (LHC)

Electrodeposition and magnetic properties of Ni nanowire arrays on anodic aluminum oxide/Ti/Si substrate by Cai-Ling Xu; Hua Li; Guang-Yu Zhao; Hu-Lin Li (pp. 1399-1403).

Ni nanowire arrays with different diameters have now been extended to directly fabricate in porous anodic alumina oxide (AAO) templates on Ti/Si substrate by direct current (DC) electrodeposition. An aluminum film is firstly sputter-deposited on a silicon substrate coated with a 300nm Ti film. AAO/Ti/Si substrate is synthesized by a two-step electrochemical anodization of the aluminum film on the Ti/Si substrate and then used as template to grow Ni nanowire arrays with different diameters. The coercivity and the squareness in parallel direction of Ni nanowires with about 10nm diameters are 664Oe and 0.90, respectively. The Ni nanowire arrays fabricated on AAO/Ti/Si substrates should lead to practical applications in ultrahigh-density magnetic storage devices because of the excellent properties.

Keywords: PACS; 75.30.Gw; 75.50.Ss; 75.60.Ej; 82.45.QrNanowire arrays; Electrodeposition; AAO/Ti/Si substrate

Effect of temperature on the sliding wear behavior of laser surface alloyed Ni-base on Al–Mg–Si alloy by Yao-Chih Chuang; Shih-Chin Lee; Hsin-Chih Lin (pp. 1404-1410).

The surface microstructures of 6061 Al–Mg–Si alloy coated with laser surface alloyed (LSA) Ni–Cr–B–Si powder and their sliding wear performance have been investigated. Experimental results show that there are three regions, as grayish region (G.R.), dark region (D.R.) and bright region (B.R.), in the pool. The Al₃Ni and Al₃Ni₂ compounds appear in the G.R. and D.R., respectively. The Al–Ni–Cr amorphous structure can be observed in the B.R. The hardness of the LSA specimens is much higher than the Al-matrix. Compared with the Al-matrix, the LSA specimens have excellent sliding wear performance. They have lower friction coefficient and wear rate. The critical temperature of sliding wear resistance of LSA specimen is higher than that of Al-matrix by about 50°C. The stress relief during thermal treatment will slightly reduce the hardness and the wear resistance of LSA specimens, especially at testing temperature >200°C.

Keywords: Laser surface alloying; High temperature sliding wear; Nickel–chromium–boron–silicon powders

Investigation on the direct laser metallic powder deposition process via temperature measurement by Guijun Bi; Andres Gasser; Konrad Wissenbach; Alexander Drenker; Reinhart Poprawe (pp. 1411-1416).

The direct laser metallic powder deposition process was investigated with the aid of a radiant thermometer by building thin walls. The measured infrared (IR) temperature signal showed good correlation with the deposition process and the quality of the deposited samples. The influence of the powder particle size and the z-increment on the quality of the deposited samples and the IR-temperature signal was examined. It was found that the particle size of the powders shows no significant influence on the measured IR-temperature signal and the deposition process. However, both the deposition process and the measured temperature signal depended strongly on the z-increment. The variation of the melt pool temperature and cooling rate resulted in an inhomogeneous dimension accuracy, microstructure and hardness of the deposited sample. An abnormal deposition process can be recognized by the IR-temperature signal.

Keywords: PACS; 81.15.FgMetallic powder deposition; Laser; Temperature measurement; Radiant thermometer

High-throughput concept for tailoring switchable mirrors by A. Borgschulte; R. Gremaud; S. de Man; R.J. Westerwaal; J.H. Rector; B. Dam; R. Griessen (pp. 1417-1423).

The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg–Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness of the catalytic capping layer. For this, a high-throughput experiment is introduced. The switching kinetics and the reversibility of switchable mirrors are strongly thickness dependent, though the details hinge on the fine structure of the clustered capping layer. Therefore, the kinetics is correlated with the surface structures of Pd on Mg_yNi1−_y as investigated by scanning tunneling microscopy. The results are explained by the so-called strong metal–support interaction (SMSI) state, characterized by a complete encapsulation of the capping layer clusters by oxidized species originating from the support. The SMSI-effect is less important with increasing Pd-layer thickness, and is suppressed by a good wetting of the Pd-clusters on the optically active film. This explains the critical thickness for the catalyzed hydrogen uptake observed in many switchable mirror systems. Moreover, the degradation of the kinetics during cycling is found to depend on the Pd-layer thickness and on the gas environment. Only films, covered with at least 15nm Pd, show small degradation caused by the SMSI-effect. The SMSI-effect is partly reversible: after changing the gas environment from hydrogen to oxygen, the oxide on the Pd-clusters can be partly removed.

Keywords: Hydrogen switchable mirror; Mg–Ni alloy; Pd; Hydrogen uptake kinetics; High-throughput method; Hydrogenography; STM; AES

Microstructure study of direct laser fabricated Ti alloys using powder and wire by Fude Wang; J. Mei; Xinhua Wu (pp. 1424-1430).

A compositionally graded material has been fabricated using direct laser fabrication (DFL). Two types of feedstock were fed simultaneously into the laser focal point, a burn resistant (BurTi) alloy Ti–25V–15Cr–2Al–0.2C powder and a Ti–6Al–4V wire. The local composition of the alloy was changed by altering the ratio of powder to wire by varying the feed rate of the powder whilst maintaining a fixed feed rate of wire-feed. For the range of compositions between about 20% and 100% BurTi only the beta phase was observed and the composition and lattice parameter varied monotonically. The grain size was found to be much finer in these functionally graded samples than in laser fabricated Ti64. Some samples were made using the wire-feed alone, where it was found that the microstructure is different from that found when using powder feed alone. The results are discussed in terms of the power requirements for laser fabrication of powder and wire samples.

Keywords: Direct laser fabrication; Functionally graded materials; Microstructure and phases; Titanium alloys

Cleaning with water decomposed products obtained by laser irradiation by Hirofumi Hidai; Hitoshi Tokura (pp. 1431-1434).

ArF excimer laser irradiation can decompose water, and decomposed products contain highly reactive substrates, such as radicals. We propose cleaning using pure water with the aid of water decomposed products obtained by ArF excimer laser irradiation. In this study, the oxidation potential of decomposed products was estimated in metal etching. Then, cleaning of cutting oil was examined. The focal point of the lens used was set at the water surface. Specimens were aligned parallel to the laser beam, so that only decomposed products affected contaminants. As a result, decomposed products could not etch nickel and copper plates, but only zinc plates. Cutting oil was cleaned after 18000 irradiation pulses. The range of the region cleaned was 5mm around the focal point.

Keywords: PACS; 42.62.−b laser applicationsLaser; Cleaning; Water; Machine oil

XRD, XPS and AFM studies of the unknown phase formed on the surface during electrodeposition of Ni–W alloy by Remigijus Juškėnas; Ignas Valsiūnas; Vidas Pakštas; Algirdas Selskis; Vitalija Jasulaitienė; Violeta Karpavi�?ienė; Vidmantas Kapo�?ius (pp. 1435-1442).

XRD, XRD in situ XPS, electrochemical and AFM studies of an unknown phase formed during electrochemical deposition of Ni–W alloy in a citrate electrolyte were carried out. It has been determined that a thin, highly textured film of nonstoichiometric NiWO₄ was formed during codeposition of nickel and tungsten. The amount of the nickel tungstate was higher on the coating electrodeposited in electrolyte containing amine acid—asparagine. The quantity of the nickel tungstate grew in the electrodeposition period of ∼60min and subsequently kept constant although the thickness of Ni–W alloy continued to increase. The quantity of the nickel tungstate formed increased with the temperature of electrolyte, however it decreased with the pH and current density.

Keywords: PACS; 73.61At; 81.15Pq; 68.55Nq; 61.10NzNickel; Tungsten; Tungstate; Phase composition; XRD

Morphology of femtosecond laser-induced structural changes in KTP crystal by Yuhua Li; Peixiang Lu; Nengli Dai; Hua Long; Ying Wang; Benhai Yu (pp. 1443-1446).

The morphology of structural changes in KTP crystal induced by single femtosecond laser pulse has been investigated by means of CCD camera, scanning electron microscopy (SEM) and atom force microscopy (AFM). The structurally changed region is depressed at energies close to the threshold for producing a structural change and melting ablation morphologies are observed as pulse energy is increased. Furthermore, periodic nanostructures are formed around the edge of the laser-induced spots.

Keywords: Morphology; Femtosecond laser; KTP crystal; SEM

Wet oxidation behaviors of Hi-Nicalon fibers by Shoujun Wu; Laifei Cheng; Litong Zhang; Yongdong Xu; Jun Zhang; Hui Mei (pp. 1447-1450).

Wet oxidation behaviors of Hi-Nicalon fibers were investigated in environment ofPH2O:O2:Ar=14:8:78kPa with a slow gas flow rate of 3.5cms⁻¹ above 1300°C for 1h. Experimental results indicated that oxidized Hi-Nicalon fibers were covered by silica. The weight gains and surface micromorphologies were strongly affected by temperature. Below 1500°C, the surface of the oxidized fibers were rough-hewn and cracked, and there were no changes detected in fiber diameter. After oxidation at 1600°C, the silica locally spalled and the fiber swelled in diameter. The Young–Laplace equation was applied to interpret surface micromorphologies change during wet oxidation of the specimens. The cracks in silica produced by oxidation and the microcrystal growth of the fibers at high temperature were considered for the strength degradation of the fibers.

Keywords: Hi-Nicalon fiber; Wet oxidation; Microstructure; Tensile strength

Structural and electrical properties of fluorine doped tin oxide films prepared by spray-pyrolysis technique by Kodigala Subba Ramaiah; V. Sundara Raja (pp. 1451-1458).

Fluorine doped SnO₂ films have been successfully prepared at optimized substrate temperature of 723K by spray pyrolysis technique. The XRD analysis confirmed that films deposited with F/Sn ratio of 0.05 showed a partial amorphous nature whereas films deposited with F/Sn=0.10 exhibited tetragonal structure (200) as the preferred orientation and polycrystalline structure. The lattice constants were found to be a=0.4750 and c=0.3197nm. The theoretically constructed XRD pattern for SnO₂ was used to compare with experimental pattern, the difference between them is discussed. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of F/Sn ratio. At low temperature, the mobility due to lattice, polar, impurity, grain boundary and neutral scattering was estimated for SnO₂ and the possible scattering mechanisms were assigned to SnO₂:F films using experimentally obtained electrical data. The Mott parameters were determined by applying variable range hopping (VRH) conduction mechanism for SnO₂:F films (F/Sn=0.05) where band conduction mechanism shifted to VRH conduction at below about 250K.

Keywords: FTO; Spray; XRD; Mobility; SEM

Effect of plasma treatment on interface property of BCN/GaN structure by Yoshiaki Shimada; Kentaro Chikamatsu; Chiharu Kimura; Hidemitsu Aoki; Takashi Sugino (pp. 1459-1463).

Interface properties of BCN/GaN metal–insulator–semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage ( C– V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N₂) and hydrogen (H₂) plasma treatment. The interface state density is estimated from C– V characteristics measured at 1MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0×10¹⁰eV⁻¹cm⁻² for the BCN/GaN structure with mixed N₂ and H₂ plasma treatment for 25min. Even after annealing at 430°C for 10min, the interface state density as low as 6.0×10¹⁰eV⁻¹cm⁻² is maintained.

Keywords: BCN; GaN; Passivation; Plasma treatment

Microtrench of oxynitride thin films in a C₂F₆ inductively coupled plasma by Byungwhan Kim; Byung Teak Lee (pp. 1464-1468).

An etching of oxynitride (SiON) films was conducted using an inductively coupled plasma. The experimental ranges for the radio frequency source power, the bias power, the pressure, and the C₂F₆ flow rates were 400–1000W, 30–90W, 6–12mTorr, and 30–60sccm, respectively. The etch characteristics examined include etch rate, profile angle, and microtrench. Particular emphasis was placed on the investigation of microtrench etch mechanisms. For this, both etch rate and profile angle variations were correlated to microtrench variation. In general, microtrench variation was complex depending on process parameters or experimental ranges given a certain parameter. Microtrench variation with the bias power was opposite to the profile angle variation. Little relationship between them was noticed for the source power variation. In contrast, microtrench variation was highly correlated to the profile angle variation for C₂F₆ flow rates. For the pressure variation, microtrench variation was reasonably explained by the distribution of polymer deposition. The empirical relationships identified can be utilized for microtrench control.

Keywords: Plasma etching; Microtrench; SiON film

Kinetics of slow collapse process: Thermodynamic description of rate constants by M. Weis (pp. 1469-1472).

Insoluble monolayer formed at the air/water interface compressed at a surface pressure above the equilibrium spreading pressure is unstable. In presented paper the classical theory for homogeneous nucleation is modified adding the activation energy term. It allows quantitative thermodynamic interpretation of the slow collapse phase transformation. The collapse of stearic acid Langmuir films has been carried out by systematic measurements of the area loss–time isobaric dependencies at various temperatures and isothermal dependencies at various pressures. Activation energies (activation enthalpies) and activation entropies have been evaluated for the nucleation ( E_α=1.32eV) and the growth ( E_β=1.55eV) processes. The experimental data for various pressures are discussed on the basis of the Gibbs energy analysis.

Keywords: PACS; 68.18.Fg; 64.70.Nd; 68.35.RhLangmuir–Blodgett films on liquids—; Structure: measurements and simulations; Structural transitions in nanoscale materials; Phase transitions and critical phenomena

X-PEEM/NEXAFS and AFM of polypyrrole and copper micro-patterns on insulating fluoropolymer substrates by P. Kappen; P.S. Hale; N. Brack; W. Prissanaroon; P.J. Pigram (pp. 1473-1479).

Micro-patterns (80μm and 10μm) of copper and semi-conducting polypyrrole on insulating fluorinated ethylene propylene substrates were characterized using synchrotron-based X-ray Photoemission Electron Microscopy (X-PEEM), Near Edge X-ray Absorption Fine Structure (NEXAFS), and Atomic Force Microscopy (AFM). Electronic states in the polypyrrole are verified using the NEXAFS data, and sample degradation upon irradiation is addressed. X-PEEM images show homogeneous distributions of the corresponding elements in the patterns. They do not exhibit dichroic effects and give information about the growth of copper and polypyrrole (i.e. nucleation of Cu, overgrowth of PPy, formation of PPy granules). AFM results are used to verify the topography of the patterns and support the findings on pattern growth.

Keywords: PACS; 68.37.-d; 61.10.Ht; 73.61.PhPolypyrrole; Micro-patterns; Synchrotron radiation; PEEM; NEXAFS; AFM

AFM investigation on surface evolution of amorphous carbon during ion-beam-assisted deposition by X.D. Zhu; F. Ding; H. Naramoto; K. Narumi (pp. 1480-1483).

Hydrogen-free amorphous carbons (a-C) have been prepared on mirror-polished Si(111) wafers through thermally evaporated C₆₀ with simultaneous bombardments of Ne⁺ ions. The time evolution of film surfaces has been characterized by atomic force microscopy (AFM) at two temperatures of 400 and 700°C, respectively. Based on the topography images and the root-mean-square (rms) roughness analysis, it is found that the a-C surfaces present roughening growth at the initial stage. With increasing growth time, the cooperative nucleation of the islands and pits appears on the surfaces, suggesting three-dimensional growth, and then they continue to evolve to irregular mounds at 400°C, and elongated mounds at 700°C. At the steady growth stage, these surfaces further develop to the structures of bamboo joints and ripples corresponding to these two temperatures, respectively. It is believed that besides ion sputtering effect, the chemical bonding configurations in the amorphous carbon films should be taken into considerations for elucidating the surface evolutions.

Keywords: PACS; 68.37.Ps; 68.55.Jk; 81.05.UwAmorphous carbon; Surface morphology; Ion beam

Reactive sputtering: A method to modify the metallic ratio in the novel silver–copper oxides by J.F. Pierson; D. Wiederkehr; J.-M. Chappé; N. Martin (pp. 1484-1488).

Composite silver–copper targets were sputtered for the first time in various reactive Ar–O₂ mixtures to deposit the novel silver–copper oxides on glass substrates. The effect of two deposition parameters (oxygen flow rate and target composition) on the films structure was investigated. Depending on these two deposition parameters, three types of silver–copper oxides were synthesised using the reactive sputtering process: Ag_xCu2−_xO, Ag_xCu4−_xO₃ and Ag1−_xCu1+_xO₂. Although conventional processes led to the formation of silver–copper oxides with stoichiometric Cu/Ag atomic ratio, it was demonstrated that the reactive sputtering process was suitable to modify this ratio in the deposited films. Finally, the optical and electrical properties of the silver–copper oxides were investigated and compared to that of copper oxides exhibiting similar structures.

Keywords: Sputtering; Silver–copper oxides; Structure; Electrical properties

La1−_xCa_xCoO₃ perovskite-type oxides: Identification of the surface oxygen species by XPS by Nora A. Merino; Bibiana P. Barbero; Pierre Eloy; Luis E. Cadús (pp. 1489-1493).

A detailed study of the La1−_xCa_xCoO₃ perovskites surface by XPS was carried out since this is a potentially useful tool to identify the oxygen species involved in the catalytic reaction and discriminate them. Mainly, the concentration of surface oxygen vacancies ( λ′) can be estimated from the XPS atomic ratio.

Keywords: PACS; 82.65.+r; 81.05.Je; 68.43.−h; 68.47.Gh; 82.80.PvPerovskites; Oxygen species; XPS; Catalytic oxidation; Propane

Study on the microstructure and wear resistance of the composite coatings fabricated on Ti–6Al–4V under different processing conditions by Y.S. Tian; C.Z. Chen; L.B. Chen; L.X. Chen (pp. 1494-1499).

Composite coatings mainly containing titanium carbides and borides were produced by laser surface alloying of Ti–6Al–4V with graphite and boron mixed powders. The test results show that the coatings have higher hardness (1600–1700 HV_0.1) and are more resistant to wear than the as-received sample. Laser scanning speed and the content of alloying elements (weight ratio of graphite to boron) have an effect on both the microstructure and the wear resistance of the coatings. TEM results show that strip titanium carbides and borides grow alternately and thus restrain the formation of coarse needle-like TiB and dendritic TiC crystals produced by laser alloying of titanium alloys with boron and graphite separately.

Keywords: Laser surface alloying; Wear resistance; Titanium carbides and borides

Investigation the effects of the excess Pb content and annealing conditions on the microstructure and ferroelectric properties of PZT (52-48) films prepared by sol–gel method by Chen Zhu; Zeng Yong; Yang Chentao; Yang Bangchao (pp. 1500-1505).

The effects of the PbO volatilization, excess Pb content of PbZr_0.52Ti_0.48 (PZT) precursor, PbTiO₃ (PT) seeding layers and annealing condition on the microstructures, surface morphologies, preferred orientation and ferroelectric properties of PbZr_0.52Ti_0.48 films were systematically investigated. PZT films with a variety of excess Pb (0–20%) were spin-deposited on Si(100) and Pt(111)/Ti/SiO₂/Si(100) substrates by sol–gel technique. The films composition, Pb/Zr/Ti/O atom rate and Pb loss were semiquantitative analyzed by X-ray photoelectron spectrometer (XPS). When the excess Pb of PZT precursor was 10%, the Pb/Zr/Ti/O atomic rate of the fabricated films was very close to the designed rate of 1:0.52:0.48:3. The XRD and AFM investigations confirmed that PT seeding layer promoted the PZT films perovskite phase transformation and grains growth with (110) plane preferred orientation, accordingly lowered perovskite phase crystallization temperature and reduced Pb loss. The PZT films annealed in O₂ flow demonstrated better microstructure and ferroelectric properties comparing with films annealed in air by double remnant polarization increase and 8% coercive field increase. The underlying mechanism was also investigated.

Keywords: PZT; Sol–gel; PbO volatilization; Seeding layer; Perovskite; Ferroelectric property

The effect of fluorine-based plasma treatment on morphology and chemical surface composition of biocompatible silicone elastomer by Dariusz Szmigiel; Krzysztof Domański; Piotr Prokaryn; Piotr Grabiec; Janusz W. Sobczak (pp. 1506-1511).

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been used to investigate the effect of reactive ion etching (RIE) on poly(methylhydrogensiloxane-co-dimethylsiloxane) surface in fluorine-based plasmas. Polysiloxane layers supported on the standard silicon wafers were etched using SF₆+O₂ or CF₄+O₂ plasmas. SEM studies show that the polysiloxane morphology depends on plasma chemical composition strongly. Presence of a columnar layer likely covered with a fluorine rich compound was found on the elastomer surface after the CF₄+O₂ plasma exposure. After the SF₆+O₂ or CF₄+O₂ plasma treatment the polysiloxane surface enriches with fluorine or with fluorine and aluminum, respectively. Different morphologies and surface chemical compositions of the silicone elastomer etched in both plasmas indicate different etching mechanisms.

Keywords: PACS; 52.77.Bn; 68.47.Mn; 79.60Biocompatible polysiloxane; Silicone elastomer; Dry etching; Fluorine-based plasma; XPS

Direct observation of dynamic shape transformation and coalescence in platinum nanosheets on graphite surface at room temperature by time-resolved AFM by Hideya Kawasaki; Go Sakai; Tsuyoshi Kijima (pp. 1512-1516).

The shape transformation of platinum (Pt) nanosheets with a uniform thickness of as thin as 3.5±1nm supported on graphite was investigated by in situ atomic force microscopy (AFM). The AFM observations revealed the shape transformation and the coalescence in preferred directions for the Pt nanosheets at room temperature (25°C), which is much lower than the melting point of bulk metallic platinum (1769°C). The behavior may be attributed to the high surface energy for the edge parts of Pt nanosheets with the small curvature of the nanometer scale.

Keywords: Nanocrystalline materials; Self-assembly; Thin films; Metals; Surfactants

Organic thin films based on a dicyanovinyl-quaterthiophene: Influence of electrode configuration on third-order nonlinear optical properties measured by electroabsorption spectroscopy by Christine Videlot-Ackermann; Takashi Isoshima; Abderrahim Yassar; Tatsuo Wada; Hiroyuki Sasabe; Denis Fichou (pp. 1517-1521).

Electroabsorption (EA) studies at room temperature on organic thin films based on a dicyanovinyl-quaterthiophene 4T-V(CN)₂ are reported. An electric field modulation is applied to the samples for two different electrode geometries, i.e. sandwich and coplanar versus the organic layer. Changes in optical absorption coefficient of 4T-V(CN)₂ based thin films are measured and analyzed to determine the character of the optical transition in the visible range (400–800nm). Depending on the experimental electrode configuration, magnitude of electroabsorption responses are different, possibly due to different distribution of the externally applied electric field. The results indicate a higher resolution of EA response for the sandwich electrode configuration and confirm the charge transfer exciton character of 4T-V(CN)₂ in contrast to the unsubstituted quaterthiophene 4T. Finally, a third-order nonlinear susceptibility χ⁽³⁾ (− ω; ω, 0, 0) of 16×10⁻¹²e.s.u. is obtained.

Keywords: PACS; 72.80.Le; 33.15.−e; 78.66.−w; 42.70.Mp; NqOrganic semiconductors; Quaterthiophene; Molecular structure; Electron-withdrawing peripheral substitution; Thin films; Optical properties; Nonlinear optical properties

Structure and properties of transparent conductive doped ZnO films by pulsed laser deposition by Sang-Moo Park; Tomoaki Ikegami; Kenji Ebihara; Paik-Kyun Shin (pp. 1522-1527).

High quality transparent conductive ZnO thin films were deposited on quartz glass substrates using pulsed laser deposition (PLD). We varied the growth conditions such as the substrate temperature and oxygen pressure. X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and atomic force microscopy (AFM) measurements were done on the samples. All films show n-type conduction, the best transparent conductive oxide (TCO) performance (Al-doped ZnO=1.33×10⁻⁴Ωcm, Ga-doped ZnO=8.12×10⁻⁵Ωcm) was obtained on the ZnO film prepared at pO₂=5mTorr and T_s=300°C.

Keywords: ZnO; XPS; Electric and optical properties; TCO; PLD

Adsorption behaviors of V₂O₅ nanowires on binary mixed self-assembled monolayers by Jae Pil Koo; Yong-Kwan Kim; Jeong Sook Ha (pp. 1528-1533).

The adsorption behaviors of V₂O₅ nanowires on binary mixed self-assembled monolayers (SAMs) were investigated with variation of the mixing ratio of two differently terminated thiolates on Au. Hydroxyl-covered V₂O₅ nanowires showed a preferential adsorption on amine (NH₂)-terminated thiolates over methyl (CH₃)-terminated ones. However, on the binary mixed SAM of NH₂- and CH₃-terminated thiols, the adsorption behavior did not follow a simple expectation based upon the electrostatic interaction. The total number of adsorbed V₂O₅ nanowires increased with the mole fraction of NH₂-terminated thiolates up toχNH2∼0.5, then it decreased with further increase ofχNH2. The height distribution of adsorbed nanowires showed that the relative portion of the agglomerated wires thicker than 3.5nm to individual wires thinner than 3.5nm increased up toχNH2∼0.75 and then it decreased with further increase ofχNH2. The dispersion of molecules with polar-functional groups as well as the molecular ordering of mixed SAMs is attributed to such adsorption behaviors of V₂O₅ nanowires.

Keywords: PACS; 82.65.; +; rBinary mixed self-assembled monolayers; V; ₂; O; ₅; nanowires; Selective adsorption; Atomic force microscope

Graft and characterization of 9-vinylcarbazole conjugated molecule on hydrogen-terminated silicon surface by Heping Yao; Yujing Dai; Jiachun Feng; Wei Wei; Wei Huang (pp. 1534-1539).

Using wet chemical reaction between N-vinylcarbazole and hydrogen-terminated silicon surface, we present a new and simple route to directly bond π-conjugated organic molecule on silicon surface. The Si can be in the form of single crystal Si including heavily doped p-type Si, intrinsic Si, heavily doped n-type Si, on Si(111) and Si(100), and on n-type polycrystalline Si. The covalent bond between 9-vinylcarbazole and silicon surface was confirmed by reflectance FTIR, XPS and contact angle measurement, respectively. A data-encompassing explanation for the mechanism discusses the possible route of the reaction. This simple and low-costly reaction offers an attractive route to attach functional conjugated molecules onto the semiconductor surface which aims to create some unique molecular device in the future.

Keywords: PACS; 81.15.LM; 81.65.CFGraft; Covalent bond; N; -vinylcarbazole; Silicon surface

Synthesis of MgB₂ films by diffusion of magnesium into electrophoretically deposited boron films by R.S. Hyam; K.M. Subhedar; S.H. Pawar (pp. 1540-1543).

The boron films were formed from the optimized stable suspension solution of boron particles using electrophoretic deposition technique. The magnesium film with optimized thickness was deposited onto boron films by vacuum evaporation technique. The heterogeneous structure was given heat treatment in ambient and vacuum atmosphere for diffusion of Mg into the boron films to form MgB₂ phase. XRD studies were carried out on both as deposited and heat treated heterostructure films to investigate their structure and phase. Surface morphological studies of these films were done by SEM.

Keywords: Electrophoretic deposition; Diffusion; Thin films

Field emission from ZnS nanorods synthesized by radio frequency magnetron sputtering technique by P.K. Ghosh; U.N. Maiti; S. Jana; K.K. Chattopadhyay (pp. 1544-1550).

The field emission property of zinc sulphides nanorods synthesized in the thin film form on Si substrates has been studied. It is seen that ZnS nanorod thin films showed good field emission properties with a low-macroscopic turn-on field (2.9–6.3V/μm). ZnS nanorods were synthesized by using radio frequency magnetron sputtering of a polycrystalline prefabricated ZnS target at a relatively higher pressure (10⁻¹mbar) and at a lower substrate temperature (233–273K) without using any catalyst. Transmission electron microscopic image showed the formation of ZnS nanorods with high aspect ratio (>60). The field emission data were analysed using Fowler–Nordhiem theory and the nearly straight-line nature of the F–N plots confirmed cold field emission of electrons. It was also found that the turn-on field decreased with the decrease of nanorod's diameters. The optical properties of the ZnS nanorods were also studied. From the measurements of transmittance of the films deposited on glass substrates, the direct allowed bandgap values have been calculated and they were in the range 3.83–4.03eV. The thickness of the films was ∼600nm.

Keywords: PACS; 79.70+q; 81.05.Cy; 81.07.BcField emission; Zinc sulphide; Nanorods; Magnetron sputtering

Improved performance and stability by an Al/Ni bilayer cathode in organic light-emitting diodes by Shengwei Shi; Dongge Ma (pp. 1551-1554).

Al/Ni bilayer cathode was used to improve the electroluminescent (EL) efficiency and stability in N, N′-bis(1-naphthyl)- N, N′-diphenyl-1,1′ biphenyl 4,4′-dimaine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq₃)-based organic light-emitting diodes. The device with LiF/Al/Ni cathode achieved a maximum power efficiency of 2.8lm/W at current density of 1.2mA/cm², which is 1.4 times the efficiency of device with the state-of-the-art LiF/Al cathode. Importantly, the device stability was significantly enhanced due to the utilization of LiF/Al/Ni cathode. The lifetime at 30% decay in luminance for LiF/Al/Ni cathode was extrapolated to 400h at an initial luminance of 100cd/m², which is 10 times better than the LiF/Al cathode.

Keywords: PACS; 85.60.Jb; 85.60.HaAl/Ni cathode; Organic light emitting diode; Stability

Production of two-dimensional periodical structures by laser interference irradiation on bi-layered metallic thin films by A. Lasagni; C. Holzapfel; F. Mücklich (pp. 1555-1560).

The production of one- and two-dimensional periodical structures produced by Laser Interference Metallurgy (LIMET) on bi-layered metallic films by using nanosecond pulsed laser is reported. The systems investigated are Fe/Al and Cu/Al and represent model systems where the melting point of the upper layer is higher tan the lower one. Aspect ratio, height and width of the structures are discussed as a function of laser fluence, partial energies and arrangement of the laser beams. Cross sectional analysis of the structured samples demonstrates the flux of molten metal parallel to the thermal gradient generated by the laser heating.

Keywords: JEL classification; 61.80.B; 73.30; 68.35.B; 64.70.D; 42.25.H; 68.10.CLaser Interference Metallurgy; Bi-layer; Thin film; Microstructure

Y₂O₃ stabilized ZrO₂ thin films deposited by electron beam evaporation: Structural, morphological characterization and laser induced damage threshold by Shi Gang Wu; Hong Ying Zhang; Guang Lei Tian; Zhi Lin Xia; Jian Da Shao; Zheng Xiu Fan (pp. 1561-1565).

Four kinds of Y₂O₃ stabilized ZrO₂ (YSZ) thin films with different Y₂O₃ content have been prepared on BK7 substrates by electron-beam evaporation method. Structural properties and surface morphology of thin films were investigated by X-ray diffraction (XRD) spectra and scanning probe microscope. Laser induced damage threshold (LIDT) was determined. It was found that crystalline phase and microstructure of YSZ thin films was dependent on Y₂O₃ molar content. YSZ thin films changed from monoclinic phase to high temperature phase (tetragonal and cubic) with the increase of Y₂O₃ content. The LIDT of stabilized thin film is more than that of unstabilized thin films. The reason is that ZrO₂ material undergoes phase transition during the course of e-beam evaporation resulting in more numbers of defects compared to that of YSZ thin films. These defects act as absorptive center and the original breakdown points.

Keywords: PACS; 79.20.Ds; 68.37.Ps; 68.37.Yz; 68.55.JkStructure; Morphology; LIDT; YSZ thin film

Organic modification of TEOS based silica aerogels using hexadecyltrimethoxysilane as a hydrophobic reagent by Nagaraja D. Hegde; A. Venkateswara Rao (pp. 1566-1572).

The experimental results on the synthesis and characterization of tetraethoxysilane (TEOS) based hydrophobic silica aerogels using hexadecyltrimethoxysilane (HDTMS) as a hydrophobic reagent by two step sol–gel process, are described. The molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), acidic water (0.001M, oxalic acid) and basic water (10M, NH₄OH) was kept constant at 1:55:3.25:1.25 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 28.5×10⁻². The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the aerogels was tested by the contact angle measurements. The maximum contact angle of 152° was obtained for M=22.8×10⁻². The aerogels retained the hydrophobicity up to a temperature of 240°C and above this temperature the aerogels became hydrophilic. The aerogels were characterized by the thermal conductivity, density, contact angle measurements, optical transmission and scanning electron micrographs.

Keywords: PACS; 82.33.Ln; 82.70.Uv; 06.30.Bp; 68.37.Hk; 78.30.LyAerogels; Hydrophobicity; Contact angle; Scanning electron microscopy (SEM); Infrared spectroscopy (IR)

Laser-induced site-selective silver seeding on polyimide for electroless copper plating by Dongsheng Chen; Qinghua Lu; Yan Zhao (pp. 1573-1580).

Ag particles were generated on Ag⁺-doped polyimide film by laser direct writing, followed by selective copper deposition using the metallic silver particles as seeds. Laser irradiation caused in situ reduction and agglomeration of silver on the polyimide film. The copper lines were less uniform and compact with higher scanning velocity and the width of the deposited copper line could reach 25μm. Equations of the relationship between scanning velocity and connectivity of the deposited copper patterns have been derived. The process was characterised by AFM, XPS, SEM, and semiconductor characterisation system.

Keywords: PACS; 42.62.−bElectroless plating; Ion exchange; Laser; Lithography; Polyimide; Silver

Silicon etching in Cl₂ environment by R. Knizikevi�?ius (pp. 1581-1583).

The ion-beam-assisted etching of silicon in Cl₂ environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl₂ molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl₂ molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl₂ molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio.

Keywords: PACS; 81.65.Cf; 82.20.NkCl; ₂; Silicon; Ion-beam-assisted etching

Microstructure and wear properties of laser clad Cu_ss/Cr₅Si₃ metal silicide composite coatings by Y.X. Yin; H.M. Wang (pp. 1584-1589).

Wear resistant Cu-based solid solution (Cu_ss) toughened Cr₅Si₃ metal silicide composite coatings were fabricated on austenitic stainless steel AISI321 by laser cladding process. Due to the rapidly solidified microstructural characteristics and the excellent toughening effect of Cu_ss on Cr₅Si₃, the Cu_ss/Cr₅Si₃ coatings have outstanding wear resistance and low coefficient of friction under room temperature dry sliding wear test conditions coupling with hardened 0.45% C steel.

Keywords: PACS; 81.15.Fg; 81.40.PqCoating; Laser cladding; Metal silicide; Wear; Microstructure

X-ray multiple diffraction in the characterization of TiNO and TiO₂ thin films grown on Si(001) by Th. Chiaramonte; E. Abramof; F. Fabreguette; M. Sacilotti; L.P. Cardoso (pp. 1590-1594).

TiO₂ and TiN_xO_y thin films grown by low pressure metal-organic chemical vapor deposition (LP-MOCVD) on top of Si(001) substrate were characterized by X-ray multiple diffraction. X-ray reflectivity analysis of TiO₂[110] and TiNO[100] polycrystalline layers allowed to determine the growth rate (−80Å/min) of TiO₂ and (−40Å/min) of TiNO films. X-ray multiple diffraction through the Renninger scans, i.e., ϕ-scans for (002)Si substrate primary reflection is used as a non-conventional method to obtain the substrate lattice parameter distortion due to the thin film conventional deposition, from where the information on film strain type is obtained.

Keywords: TiO; ₂; TiNO; MOCVD; Thin film; X-ray multiple diffraction; Renninger scan

Enhancing the adhesive bonding strength of NiTi shape memory alloys by laser gas nitriding and selective etching by H.C. Man; N.Q. Zhao (pp. 1595-1600).

Laser gas nitriding process (LGN) was applied on NiTi shape memory alloy to obtain an alloyed surface consisting of TiN dendrites in NiTi matrix. By applying subsequent selective etching process, the matrix material in the alloyed layer can be selectively removed and a three-dimensional network of TiN dendrites is left on the surface protruding from the metal substrate. The 3D dendritic network provides extra surface area and locking mechanism for the adhesion joint. The microstructures of such textured surface were examined. The adhesion jointing characteristics of the surfaces were studied. A 150% increase in the lap-joint strength was achieved in the laser gas nitrided and etched specimen as compared with the sandblasted and etched ones.

Keywords: Laser gas nitriding; NiTi alloy; Shape memory alloy; Adhesive bonding; Textured surface

Effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure by Y.S. Lim; J.W. Park; M.S. Kim; J. Kim (pp. 1601-1605).

Surface area effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure was investigated. For a systematic comparison, graphite and three kinds of carbon black powder were used as source materials for the carbothermal reduction. Depending on the surface area, the carbothermal reduction at 800°C for 30min resulted in Zn-silicate island or ZnO nanorod at the same experimental condition. These structures were characterized with a scanning electron microscopy, a transmission electron microscopy, an energy dispersive spectroscopy and an X-ray photoelectron spectroscopy. The results show that the reducing power of ZnO_(s) source into Zn_(g) vapor is strongly dependent on the surface area of carbon source, and that the fabrication of ZnO nanostructure can be performed more efficiently by using carbon source with large surface area.

Keywords: ZnO; Carbothermal reduction; Nanorod; Transmission electron microscopy; X-ray photoelectron spectroscopy

Study on structure change of carbon nanotubes depending on different reaction gases by Tingzhi Wang; Biben Wang (pp. 1606-1610).

Aligned carbon nanotubes were grown by plasma-enhanced hot filament chemical vapor deposition using different reaction gases and they were investigated by scanning electron microscopy and transmission electron microscopy. It is found that the hollow carbon nanotubes were formed using methane and hydrogen as the reaction gases, but the bamboo-structured carbon nanotubes were grown when ammonia was added into the reaction gases, indicating that the structure of the aligned carbon nanotubes was changed depending on different reaction gases. On setting of diffusion of carbon, the effects of the nitrogenous gas on the structure change of carbon nanotubes are studied.

Keywords: PACS; 52.77.Bn; 81.07.Bc; 81.15.GhStructure of carbon nanotubes; Chemical vapor deposition; Nitrogenous gas

Nano-structured Fe thin film deposition using plasma focus device by R.S. Rawat; T. Zhang; K.S. Thomas Gan; P. Lee; R.V. Ramanujan (pp. 1611-1615).

This paper reports the deposition of nano-structured Fe thin films using 3.3kJ Mather-type plasma focus. The conventional hollow copper anode was replaced by anode fitted with solid Fe top and the deposition was done using different numbers of deposition shots at two different angular positions. Scanning Electron Microscopy shows that the size of nano-phase agglomerate is smaller when the sample is deposited using either lesser number of deposition shots or at higher angular position with respect to anode axis. X-ray Diffraction shows that crystal structure characteristics change with increase in number of deposition shots. Measurements of magnetic properties using Vibrating Sample Magnetometer identify intermediate magnetization and coercivity in Fe thin films deposited at smaller angular position with respect to anode axis. It is concluded that the morphological, structural and magnetic characteristics of Fe thin films deposited using plasma focus device depend not only on the number of focus deposition shots but also on the angular position of the sample.

Keywords: Plasma focus; Fe thin film; Nano-structure

Parametric study on femtosecond laser pulse ablation of Au films by Xiaochang Ni; Ching-yue Wang; Li Yang; Jianping Li; Lu Chai; Wei Jia; Ruobing Zhang; Zhigang Zhang (pp. 1616-1619).

Ablation process of 1kHz rate femtosecond lasers (pulse duration 148fs, wavelength 775nm) with Au films on silica substrates has been systemically studied. The single-pulse threshold can be obtained directly. For the multiple pulses the ablation threshold varies with the number of pulses applied to the surface due to the incubation effect. From the plot of accumulated laser fluence N× ϕ_th( N) and the number of laser pulses N, incubation coefficient of Au film can be obtained ( s=0.765). As the pulse energy is increased, the single pulse ablation rate is increasing following two ablation logarithmic regimes, which can be explained by previous research.

Keywords: PACS; 52.38Mf; 42.70.Hj; 68.55-a; 81.05BXFemtosecond laser; Laser micromachining; Incubation effect; Laser fluency threshold

Positive secondary Ion emission from Si1−_xGe_x bombarded by O₂⁺ by A. Mikami; T. Okazawa; K. Saito; Y. Kido (pp. 1620-1625).

The positive secondary ion yields of B⁺ (dopant), Si⁺ and Ge⁺ were measured for Si1−_xGe_x (0≤ x≤1) sputtered by 5.5keV¹⁶O₂⁺ and¹⁸O₂⁺. It is found that the useful yields of Ge⁺ and B⁺ suddenly drop by one order of magnitude by varying the elemental composition x from 0.9 to 1 (pure Ge). In order to clarify the role of oxygen located near surface regions, we determined the depth profiles of¹⁸O by nuclear resonant reaction analysis (NRA:¹⁸O(p,α)¹⁵N) and medium energy ion scattering (MEIS) spectrometry. Based on the useful yields of B⁺, Si⁺ and Ge⁺ dependent on x together with the elemental depth profiles determined by NRA and MEIS, we propose a probable surface structure formed by 5.5keV O₂⁺ irradiation.

Keywords: PACS; 82.80.Ms; 82.80.YcSIMS; SiGe; Oxygen; Ionization probability; NRA; MEIS

Pump-dependent luminescence in the Ag nanoparticles doped by Erbium by J. Ebothe; K. Ozga; A. Ali Umar; M. Oyama; I.V. Kityk (pp. 1626-1630).

A substantial spectral shift of the UV-laser induced luminescence in the Ag nanoparticles (NP) doped by Er³⁺ ions attached to ITO substrates was observed at T=4.2K. We have established high energy spectral shift of principal luminescent maxima (from wavelength equal to about 1.45 up to 1.15μm) with increasing of the pumping nanosecond nitrogen laser power density up to 1.1GW/cm² operating at λ=337nm. With increasing Erbium content with respect to Ag the spectral shift and spectral line broadening increase. It may be caused by specific features of trapping level occupation kinetics on interfaces NP/ITO substrate. The observed process is fully reversible. The luminescence is observed only during excitation by the 337nm laser pulses and is absent for laser pulses operating at other wavelengths (like excimer laser at 218nm and nitrogen laser at 371nm).

Keywords: Nanoparticles; Optical properties

Nanostructured two-phase nc-TiN/a-(TiB₂, BN) nanocomposite thin films by Y.H. Lu; Y.G. Shen; K.Y. Li (pp. 1631-1638).

Thin films of Ti–B–N with different N contents were deposited on Si(100) at room temperature by reactive unbalanced close-field dc-magnetron sputtering using three Ti targets and one TiB₂ target in an Ar–N₂ gas mixture. The effect of N content on bonding structure, microstructure, phase configuration, surface roughness and mechanical properties have been investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and microindentation measurements. It was found that the N content significantly affected phase segregation and microstructure. The nitrogen-free TiB_0.65 films showed an amorphous compound consisting of Ti and TiB₂ (Ti–TiB₂). After adding about 28at.% N, Ti was preferentially bonded to N to form TiN, accompanying with formation of small amounts of TiB and BN bonds. At this stage they combined TiB₂ to form a two-phase nanocomposite with microstructures comprising of nanocrystalline (nc-) TiN phase in nitrogen-containing amorphous (a-) TiB₂ matrix. Addition of more N promoted formation of BN bonding at cost of TiB₂, which resulted in formation of nanocomposite nc-TiN/a-(TiB₂, BN) thin films. A small grain less than 8nm in size was found at low N content, and the grain size increased with increasing N content. A low microhardness value of about 20GPa was obtained in the amorphous Ti–TiB₂ compound, and a maximum microhardness value of about 50GPa was achieved in nc-TiN/a-TiB₂. A decrease of microhardness took place after formation of BN (i.e. amorphous matrix composed by both TiB₂ and BN) with further increasing N content, and a hardness value of about 35GPa was followed at high N contents. The surface roughness strongly depended on the phase configuration. The higher the mole fraction of nanocrystalline TiN phase, the rougher the surface became.

Keywords: Hardness; Microstructure; Nanocomposite thin films; Surface roughness; Ti–B–N

The influence of different doping elements on microstructure, piezoelectric coefficient and resistivity of sputtered ZnO film by X.B. Wang; C. Song; D.M. Li; K.W. Geng; F. Zeng; F. Pan (pp. 1639-1643).

ZnO film is attractive for high frequency surface acoustic wave device application when it is coupled with diamond. In order to get good performance and reduce insertion loss of the device, it demands the ZnO film possessing high electrical resistivity and piezoelectric coefficient d₃₃. Doping ZnO film with some elements may be a desirable method. In this paper, the ZnO films undoped and doped with Cu, Ni, Co and Fe, respectively (doping concentration is 2.0at.%) are prepared by magnetron sputtering. The effect of different dopants on the microstructure, piezoelectric coefficient d₃₃, and electrical resistivity of the film are investigated. The results indicate that Cu dopant can enhance the c-axis orientation and piezoelectric coefficient d₃₃, the Cu and Ni dopant can increase electrical resistivity of the ZnO film up to 10⁹Ωcm. It is promising to fabricate the ZnO films doped with Cu for SAW device applications.

Keywords: PACS; 68.55.Jk; 68.55.Ln; 73.61.-r; 73.61.Ga; 77.65.Bn; 77.84.BwDoping element; ZnO film; Piezoelectric coefficient; Electrical resistivity

Incorporation of nano zinc oxide for improvement of electroless nickel plating by S.M.A. Shibli; B. Jabeera; R.I. Anupama (pp. 1644-1648).

The advantages of electroless nickel plating (EN) include excellent corrosion resistance, wear resistance, solderability, low porosity and uniform thickness even on complex parts and ability to plate on nonconductors. In the present study nano ZnO particles were synthesized by using an electrochemical technique and incorporated the particles into Ni–P plates. An alkaline bath was selected and used for nano zinc oxide incorporation. The electrochemical and metallurgical properties of the Ni–nano ZnO–P plates were evaluated and compared with that of the un-reinforced Ni–P plates. The incorporation of the nano ZnO particles resulted in improvement of metallurgical and corrosion resistance characteristics of the plates.

Keywords: Zinc oxide; Electroless plating; Nickel plating; Composite nickel coating; Nickel phosphorous coating

Effects of temperature and velocity of droplet ejection process of simulated nanojets onto a moving plate's surface by Te-Hua Fang; Win-Jin Chang; Shih-Lung Lin (pp. 1649-1654).

This paper uses molecular dynamics simulation based on the Lennard–Jones potential to study the effects that temperature and velocity have on, the nanojet droplet ejection process, when the droplet is ejected at an angle onto a moving plate's surface. According to the analysis, it was found that the width of the spreading droplet increased as the temperature and the time were increased. Also found was an energy wave phenomenon. The contact angle of the droplet deposited on the plate decreased as the temperature was increased. Furthermore, the layer phenomena became apparent when the atoms were deposited on a moving plate. Thinner film layers were obtained as the velocity of the moving plate was increased. The contact angle on the left side of the droplet was larger than that on the right side when the plate was moving from right to left.

Keywords: Nanojet; Spreading droplets; Molecular dynamics simulation; Lennard–Jones potential

Large well-aligned nanostructures of β-Ga₂O₃ synthesized by microwave plasma chemical vapor deposition by Feng Zhu; ZhongXue Yang; WeiMin Zhou; YaFei Zhang (pp. 1655-1659).

In this paper, we demonstrate the novel β-Ga₂O₃ nanostructures synthesized by microwave plasma chemical vapor deposition (MPCVD) of Ga droplet in the presence of Au catalysts at 600W. The morphology and structure of the products were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Large well alignment of network-like layered crystal β-Ga₂O₃ structures that consisted of many nanobelts were formed on the Au-coated silicon substrate under the suitable vapor concentration. These novel β-Ga₂O₃ nanostructures are expected to have potential application in functional nanodevices.

Keywords: PACS; 81.05.Hd; 81.07.Bc; 81.10.Bk; 52.50.Sw; 61.30.HnNanostructures; Nanobelts; Nanowires; Microwave plasma; Alignment

Deposition of Fe–Ni nanoparticles on Al₂O₃ for dechlorination of chloroform and trichloroethylene by Shu-Huei Hsieh; Jao-Jia Horng (pp. 1660-1665).

This research proposes an efficient method for depositing Fe–Ni nanoparticles on Al₂O₃ microparticles to decompose containments in ground water, such as chloroform and trichloroethylene. The Fe–Ni nanoparticles can be deposited onto the surface of Al₂O₃ microparticles by electroless plating technique. The reasons why the Fe–Ni nanoparticles would be deposited on the surface of Al₂O₃ microparticles is to avoid the agglomeration of Fe–Ni nanoparticles due to their surface effect and magnetic property.The results show that the sizes of Fe–Ni particles on Al₂O₃ particles are between several and several hundreds of nanometers, the contents of Fe and Ni in Fe–Ni nanoparticles can be adjusted from 8 to 60at.% for Fe and 40 to 92at.% for Ni, the specific surface area of Fe–Ni nanoparticles can reach to 117m²/g, and the reaction mechanism of dechlorination of chloroform of 2mg/L by Fe–Ni/Al₂O₃ particles of 5g/L appears to be pseudo first order with a half life of 0.7h and the half life is 0.25h for the dechlorination of trichloroethylene of 2mg/L.

Keywords: Fe–Ni nanoparticle; Electroless plating; Al; ₂; O; ₃; substrate; Dechlorination; Chloroform; Trichloroethylene

Superior thermal stability of Ta/TaN bi-layer structure for copper metallization by Qi Xie; Xin-Ping Qu; Jing-Jing Tan; Yu-Long Jiang; Mi Zhou; Tao Chen; Guo-Ping Ru (pp. 1666-1672).

Ta/TaN bi-layer structure is currently used in the ultra-large scale integrated circuits (ULSI) interconnect as barrier for copper because of its good adhesion to both SiO₂ and Cu wire. In this work Cu, Ta and TaN layers were prepared by sputtering technology. X-ray diffraction, Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) as well as transmission electron microscopy (TEM) were applied to characterize the thin film thermal stability and microstructure evolution. The results show that the Ta/TaN bi-layer structure has much better diffusion barrier properties than pure Ta or pure TaN film. A mechanism was proposed to explain the better thermal stability of the Ta/TaN bi-layer structure based on the correlation between TaN layer thickness and TaN crystallization kinetics. The microstructure evolution for Ta/TaN bi-layer structure during annealing was described.

Keywords: PACS; 85.40.Ls; 66.30.Ny; 6630.XjCopper interconnect; Diffusion barrier; Thermal stability; Ta/TaN

Influence of substrate temperature on surface structure and electrical resistivity of the evaporated tin sulphide films by M. Devika; N. Koteeswara Reddy; K. Ramesh; V. Ganesan; E.S.R. Gopal; K.T. Ramakrishna Reddy (pp. 1673-1676).

Tin sulphide films have been deposited with an average thickness of 0.5μm at different substrate temperatures. The surface structure and electrical resistivity of the films were investigated at room temperature. The surface profiles were examined for crystallite size and roughness with respect to substrate temperature. The as-deposited films grown at low temperatures exhibited blurred hill shape grains with an average diameter and roughness of 85 and 14.5nm, respectively. However, the films grown at higher temperatures showed nice square shape grains with an average size of 180nm and roughness of 5.12nm. More crystalline tin sulphide films showed a lower electrical resistivity of 29.9Ωcm than other films.

Keywords: PACS; 68.35.–p; 72.20.–I; 73.50.–hTin sulphide thin films; Surface structure; Electrical properties

XPS depth profiling study of n/TCO interfaces for p-i-n amorphous silicon solar cells by Shuran Sheng; Huiying Hao; Hongwei Diao; Xiangbo Zeng; Ying Xu; Xianbo Liao; Theodore L. Monchesky (pp. 1677-1682).

Detailed X-ray photoelectron spectroscopy (XPS) depth profiling measurements were performed across the back n-layer/transparent conducting oxide (n/TCO) interfaces for superstrate p-i-n solar cells to examine differences between amorphous silicon ( a-Si:H) and microcrystalline silicon (μc-Si:H) n-layer materials as well as TCO materials ZnO and ITO in the chemical, microstructural and diffusion properties of the back interfaces. No chemical reduction of TCO was found for all variations of n-layer/TCO interfaces. We found that n- a-Si:H interfaces better with ITO, while n-μc-Si:H, with ZnO. A cross-comparison shows that the n- a-Si:H/ITO interface is superior to the n-μc-Si:H/ZnO interface, as evidenced by the absence of oxygen segregation and less oxidized Si atoms observed near the interface together with much less diffusion of TCO into the n-layer. The results suggest that the n/TCO interface properties are correlated with the characteristics of both the n-layer and the TCO layer. Combined with the results reported on the device performance using similar back n/TCO contacts, we found the overall device performance may depend on both interface and bulk effects related to the back n/TCO contacts.

Keywords: PACS; 82.65.+r; 73.40.Lq; 68.35.−p; 79.60.−I; 78.20.−eAmorphous silicon; Microcrystalline silicon; n/TCO interfaces; XPS

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Applied Surface Science (v.253, #3)

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Applied Surface Science (v.253, #3)