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Applied Surface Science (v.252, #4)

Publisher's Note (pp. 871-871).

Interface evolution during electrochemical oxidation-dissolution by Deeder Aurongzeb (pp. 872-877).

We present results from an experimental study on the roughening of Al thin film during electrochemical oxidation reduction. The surface reaction occurred in two stages. Anodic alumina forms during oxidation of aluminum followed by immediate dissolution of alumina. The surface image using AFM showed randomly oriented grains with lateral feature size ∼280nm at early stage (30s) of oxidation-dissolution (OD). As farther dissolution of alumina (90s) progressed, oriented rectangular grains were observed with lateral feature size ∼400nm, indicating a disordered to ordered transition at the surface. The roughness exponent at the earlier stage found to be 0.44±0.02, consistent with nonlinear KPZ equation. However, for the later case, roughness exponent increased to 0.84±0.03, which is close to the value derived in continuum model. The value of dissolution exponent (growth exponent) β found to be 0.47±0.1. These values are slightly different from the theoretical values but they are consistent with the theoretical models within the experimental error. Shadow instability found to be a dominant feature in this experiment and contributed to the discrepancy. Interface instabilities are discussed in terms of local and non-local effects.

Keywords: Electrochemical oxidation reduction; Interface instabilities; KPZ; Shadow instability

Interactions of germanium atoms with silica surfaces by Scott K. Stanley; Shawn S. Coffee; John G. Ekerdt (pp. 878-882).

GeH₄ is thermally cracked over a hot filament depositing 0.7–15ML Ge onto 2–7nm SiO₂/Si(100) at substrate temperatures of 300–970K. Ge bonding changes are analyzed during annealing with X-ray photoelectron spectroscopy. Ge, GeH_x, GeO, and GeO₂ desorption is monitored through temperature programmed desorption in the temperature range 300–1000K. Low temperature desorption features are attributed to GeO and GeH₄. No GeO₂ desorption is observed, but GeO₂ decomposition to Ge through high temperature pathways is seen above 750K. Germanium oxidization results from Ge etching of the oxide substrate. With these results, explanations for the failure of conventional chemical vapor deposition to produce Ge nanocrystals on SiO₂ surfaces are proposed.

Keywords: PACS; 68.43.Vx; 68.47.Jn; 81.15.GhSilicon dioxide; Germanium; Surface reactions; Thermal desorption; Nanocrystals; Germane; Etching

High level compressive residual stresses produced in aluminum alloys by laser shock processing by G. Gomez-Rosas; C. Rubio-Gonzalez; J.L Oca�a; C. Molpeceres; J.A. Porro; W. Chi-Moreno; M. Morales (pp. 883-887).

Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results for metal surface treatments in underwater laser irradiation at 1064nm. A convergent lens is used to deliver 1.2J/cm² in a 8ns laser FWHM pulse produced by 10Hz Q-switched Nd:YAG, two laser spot diameters were used: 0.8 and 1.5mm.Results using pulse densities of 2500pulses/cm² in 6061-T6 aluminum samples and 5000pulses/cm² in 2024 aluminum samples are presented. High level of compressive residual stresses are produced −1600MPa for 6061-T6 Al alloy, and −1400MPa for 2024 Al alloy. It has been shown that surface residual stress level is higher than that achieved by conventional shot peening and with greater depths. This method can be applied to surface treatment of final metal products.

Keywords: PACS; 52.50.Jm; 62.50.+p; 81.65.−b; 81.40.−z; 81.70−qLaser shock processing; Compressive residual stress

Magnetic nanocomposite thin films of BaFe₁₂O₁₉ and TiO₂ prepared by sol–gel method by Jianxun Qiu; Mingyuan Gu (pp. 888-892).

The composite films with different weight ratio of barium ferrite to titanium dioxide are successfully prepared using sol–gel method for the first time. The morphology, crystal structure and magnetic properties of composite films are investigated with atomic force microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that the composite films are uniform with no microcracks. The grain diameters are less than 100nm. With the increase of barium ferrite, the grain diameter decreases. The composite films are composed of M-type hexagonal barium ferrite and rutile titanium dioxide. The composite films possess the excellent magnetic properties. The specific saturation magnetization and coercivity reach 18.3emu/g and 3350Oe, respectively. The application of composite films in magnetic recording and electromagnetic absorption fields is promising.

Keywords: PACS; 75.70.Ak; 61.46.+wNanocomposite films; Barium ferrite; Sol–gel; Microcrack; Magnetic properties

High resolution quantitative SIMS analysis of shallow boron implants in silicon using a bevel and image approach by S. Fearn; D.S. McPhail (pp. 893-904).

Secondary ion mass spectrometry (SIMS) is frequently used as the preferred tool for dopant profiling due to its sensitivity and depth resolution. However, as dopant profiles become shallower most, if not all of the implant profile lies in the pre-equilibrium or transient region of an SIMS depth profile. In this region sputter yield and ionisation rate vary making accurate quantification of the implant profile very difficult. These problems can be reduced through the use of much lower beam energies or oxygen flooding of the sample. However, most SIMS instruments do not have these capabilities. In this paper an alternative technique for producing an accurate depth profile of a shallow implant, using existing SIMS technology is presented.Through the fabrication of bevels with very small slope angles on a shallow boron implanted silicon via a chemical etch, SIMS ion imaging is performed on the exposed surface. Ion image data is then summed, and in conjunction with accurate measurement of the bevel morphology, a shallow boron implant profile produced. The ‘bevel-image’ profile compares very well with a profile obtained using a 1keV oxygen beam. To ensure a good dynamic range on the ‘bevel-image’ profile it is important to clean the bevel with a HF etch, prior to imaging.

Keywords: PACS; 61.72.Tt; 82.80.MsChemical bevelling; SIMS ion imaging; SIMS; Shallow boron implanted silicon; Oxygen loading

The backscattering factor for the Au N₆₇VV Auger transition by A. Jablonski; J. Zemek; P. Jiricek (pp. 905-915).

The Au N₆₇VV Auger transition may take place after direct ionization of the N₆₇ subshells or after ionization of the N₄₅ subshells followed by the Coster–Kronig transitions N₄₅N₆₇V. The subshells N₆₇ and N₄₅ have much different ionization energies, by a factor of four, and this creates a problem in quantification of the N₆₇VV signal. Calculations of the backscattering factor from the analytical expressions require knowledge of a single value of the ionization energy. Furthermore, a single value of the ionization energy is needed in calculations of the ionizations cross section. An attempt is made here to decide which ionization energy should be used in calculations by comparison of the experimental energy and emission angle dependence of the AES signal intensity with this dependence determined from theory using different ionization energies. It has been found that the N₆₇VV signal intensity is strongly dominated by ionizations of the N₅ subshell. Furthermore, the ionization cross section for the N₅ subshell is well described by the Casnati et al. formula.

Keywords: PACS; 11.80La; 34.80.−i; 72.10.−dAuger electron spectroscopy; Theory of electron transport; Backscattering factor

Residual surface stress measurements in YBa₂Cu₃O_x superconductors by Kh.A. Ziq; J. Shirokoff; S.N. Alfaer (pp. 916-920).

XRD and residual surface stress (sin² ψ) measurements were carried out on YBa₂Cu₃O_x superconductors with varying oxygen stoichiometry (6.3< x<7.0). Slopes of the surface strain versus sin² ψ were plotted against oxygen content for certain reflections. Compressional surface stress has been found along the c-axis, while a tensile surface stress has been observed along the ab-plane. Both surface stresses were found to vary slightly with oxygen content. These findings qualitatively agree with a very small hydrostatic pressure effect on T_c for fully oxygenated YBa₂Cu₃O_x ( x=7) compared to oxygen deficient material at the surface.

Keywords: PACS; 61.10.−i; 61.10.YhX-ray diffraction; sin; ²; ψ; analysis; Surface residual stress

Nitridation of iron by the mixing technology with laser and plasma beams by Junyou Liu; Fengjiu Sun; Hanjing Yu (pp. 921-928).

Iron nitride (Fe_xN) is obtained by the mixing technology with laser and plasma beams coaxially on the surface of pure iron in atmosphere. In this technology, laser and plasma provide heat source and nitrogen ion source, respectively, easily to nitriding the sample. The feasibility of the method is analyzed in theory. Small-angle X-ray diffraction measurements reveal formation of iron nitride in the as-treated sample, and scanning tunneling microscope measurements describe the surface profiles of the irradiated area, at different laser energy densities or different scanning velocities.

Keywords: PACS; 81.65.Lp; 61.80.Ba; 62.50.tpIron nitrides; Laser and plasma; Surface modification; Laser nitriding

Influence of air annealing on the structural, morphological, optical and electrical properties of chemically deposited ZnSe thin films by R.B. Kale; C.D. Lokhande (pp. 929-938).

Zinc selenide nanocrystalline thin films are grown onto amorphous glass substrate from an aqueous alkaline medium, using chemical bath deposition (CBD) method. The ZnSe thin films are annealed in air for 4h at various temperatures and characterized by structural, morphological, optical and electrical properties. The as-deposited ZnSe film grew with nanocrystalline cubic phase alongwith some amorphous phase present in it. After annealing metastable nanocrystalline cubic phase was transformed into stable polycrystalline hexagonal phase with partial conversion of ZnSe into ZnO. The optical band gap, E_g, of as-deposited film is 2.85eV and electrical resistivity of the order of 10⁶–10⁷Ωcm. Depending upon annealing temperature, decrease up to 0.15eV and 10²Ωcm were observed in the optical band gap, E_g, and electrical resistivity, respectively.

Keywords: Chemical deposition; ZnSe thin films; Air annealing; Crystallite size effect; Phase transformation

Characterization of Cr/SiO₂ catalysts and ethylene polymerization by XPS by A.B. Gaspar; C.A.C. Perez; L.C. Dieguez (pp. 939-949).

Cr/SiO₂ catalysts with 1 or 3wt.% Cr loadings and different chromium precursors were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A method to determine chromium species in the sample was developed through the decomposition of the Cr 2p XPS spectrum in Cr⁶⁺ and Cr³⁺ standard spectra. The results of the binding energy from the Cr 2p region and of the distribution of chromium species allowed to evaluate the dynamic photo-reduction of the surface chromium species during XPS analysis. Photo-reduction of surface Cr⁶⁺ to Cr³⁺ species was verified for all samples supported in silica, depending on the precursor and chromium content. Bulk CrO₃ and Cr₂O₃ standards did not reveal variation in the binding energy of Cr 2p_3/2, but a physical mixture of CrO₃ with SiO₂ presented photo-reduction. The behavior of this mixture resembled to the catalysts and suggests the participation of the surface hydroxyls of silica in the photo-reduction process. XPS intensity measurements for assessing dispersion of chromium oxide were used to compare the calcined and reduced catalysts to different chromium precursors. Polyethylene chains were detected by in situ XPS, while oligomerization products were not observed.

Keywords: PACS; 61.82.d; 61.80.Cb; 79.60.−i; 81.70.Jb; 82.35.−xChromium; XPS; Species distribution; Polymerization

Inhibiting effects of some oxadiazole derivatives on the corrosion of mild steel in perchloric acid solution by Mounim Lebrini; Fouad Bentiss; Herv� Vezin; Michel Lagren�e (pp. 950-958).

The efficiency of 3,5-bis( n-pyridyl)-1,3,4-oxadiazole ( n-POX, n=1, 2, 3), as corrosion inhibitors for mild steel in 1M perchloric acid (HClO₄) have been determined by weight loss measurements and electrochemical studies. The results show that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles shows that 3-POX was the best inhibitor. Polarisation curves indicate that n-pyridyl substituted-1,3,4-oxadiazoles are mixed type inhibitors in 1M HClO₄. The adsorption of these inhibitors follows a Langmuir isotherm model. The electronic properties of n-POX, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR).

Keywords: Corrosion inhibition; Mild steel; Oxadiazole; Perchloric acid

Model of electroless Ni deposition on SiC_p/Al composites and study of the interfacial interaction of coatings with substrate surface by Libo Li; Maozhong An; Gaohui Wu (pp. 959-965).

Metallization techniques based on electroless plating are used to coat SiC_p/Al composite materials. The directly palladium chloride (PdCl₂) solutions in HCl is used to render the surface of such non-conductive substrates catalytically active towards metal deposition in the electroless plating solution. The microstructures of Ni-coated composites provided by scanning electron microscope (SEM) bring light into the palladium activation and electroless coating process. Also, X-ray photoelectron spectroscopy (XPS) and Line-scan have allowed to monitor the chemical and compositional surface modifications of activated and coated SiC_p/Al composites, as well as to understand the mechanisms of the catalyst (palladium species) chemisorption on the composites surface and the interaction mechanisms of Ni layer with the SiC_p/Al composites. The experimental results show that a nickel-substrate bonding action takes place during plating. Ni atom existing on the surface of the composites can partially obtain electrons from metals Al of the SiC_p/Al composites when the substrate is embedded in the Ni layers, that is, the orbital interaction through the mutual overlap of the electronic orbits does exist in the interfacial regions between the coated Ni atoms and composites substrate instead of the mechanical-interlocked form. On the basis of the evidence, a model of electroless Ni deposition on SiC_p/Al composites is submitted including Pd activation and Ni deposition processes to describe the formation of catalytic centers and the growth of deposited layer. The deposition model reveals that metal-substrate bond plays an important role in the high adhesion strength between the Ni coatings and the composites.

Keywords: Electroless Ni plating; SiC; _p; /Al composites; Interfacial interaction; Deposition model

Influence of poly(aminoquinone) on corrosion inhibition of iron in acid media by C. Jeyaprabha; S. Sathiyanarayanan; K.L.N. Phani; G. Venkatachari (pp. 966-975).

The inhibitor performance of chemically synthesized water soluble poly(aminoquinone) (PAQ) on iron corrosion in 0.5M sulphuric acid was studied in relation to inhibitor concentration using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. On comparing the inhibition performance of PAQ with that of the monomer o-phenylenediamine (OPD), the OPD gave an efficiency of 80% for 1000ppm while it was 90% for 100ppm of PAQ. PAQ was found to be a mixed inhibitor. Besides, PAQ was able to improve the passivation tendency of iron in 0.5M H₂SO₄ markedly.

Keywords: Iron; Corrosion; Sulphuric acid; Inhibition; Polyaminoquinone

A structural analysis of W–Sb mixed oxide catalyst by Y.S. Lim; S.H. Jung; S.-T. Hong; S.M. Jung; J. Kim; J.H. Chae; W.-H. Lee (pp. 976-980).

An investigation on the structure of W–Sb mixed oxide catalyst, W₁₂Sb_xO_y ( x=1, 3, 5), is proposed. The W–Sb mixed oxide powders were prepared by the calcination of aqueous precursors, antimony tartrate and ammoniummetatungstate, and characterized with scanning electron microscope, X-ray diffractometer, and transmission electron microscope. At low content of Sb ( x=1), the W–Sb mixed oxide powder consisted of polyhedral particles, and their crystal structure was triclinic WO₃. At higher content ( x=3, 5), majority of the oxide powders were bar-shaped particles, consisting of triclinic WO₃ and tetragonal WO₃. With electron diffraction pattern and simulation, Sb incorporation into the cuboctahedral sites of perovskite-like WO₃ was proved and its effect on the phase transition from triclinic to tetragonal was discussed.

Keywords: Catalyst; WO; ₃; Transmission electron microscopy; Polymorph

Self-assembled monolayers and chemical derivatization of Ba_0.5Sr_0.5TiO₃ thin films: Applications in phase shifter devices by Angel L. Morales-Cruz; Fred W. Van Keuls; F�lix A. Miranda; Carlos R. Cabrera (pp. 981-995).

Thin films of barium strontium titanate (Ba1−_xSr_x TiO₃ (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9eV, indicative of a possible SO interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780cm⁻¹, which is characteristic of an OSC stretching and reveals the modification of the BSTO thin film by the coupling of the O of the BSTO with the S of the mercapto compound. All the modification using mercapto compounds is through sulfur to the BSTO thin film. MHDA SAM on BSTO thin film was chemically derivatized using APS shown by XPS and FT-IR. The SAMs modified phase shifters showed an improvement in performance with respect to those phase shifters fabricated with standard methods.

Keywords: Self-assembled monolayers; Ba; _0.5; Sr; _0.5; TiO; ₃; Coupled microstrip phase shifters; 3-Aminopropyltrimethoxysilane; 16-Mercaptohexadecanoic acid; 3-Mercaptopropyltrimethoxysilane; 3-Mercaptopropionic acid; X-ray photoelectron spectroscopy

Optical simulation, optimized design and fabrication of (ZrO₂)_x–(Al₂O₃)1−_x composite films with thin inserted TiO₂ layers for ArF-line high transmission attenuated phase shift mask blank applications by Fu-Der Lai (pp. 996-1005).

The tunable optical constants of the stoichiometric (ZrO₂)_x–(Al₂O₃)1−_x composite films with thin inserted TiO₂ layers are simulated as π-phase shifters. The optimized composition range of the superlattices to be used as a high transmission attenuated phase shift mask (HT-APSM) blank is found. The absorption edge shifts to the longer wavelengths when the thickness fraction of the TiO₂ layer increases. The optimized film for ArF-line HT-APSM blank applications must have the lower inspection transmittance for the better inspection and the lower reflectance at the exposure wavelength for a better aerial image as π-phase shifters, and they will be easier to fabricate than a superlattice. In order to find such a film, (ZrO₂)_x–(Al₂O₃)1−_x composite films with various inserted TiO₂ layers are simulated. The optimal deposition processes of such a film are also determined. For example, a (ZrO₂)_0.187–(Al₂O₃)_0.813 composite film with two inserted TiO₂ thin layers is fabricated. The optical properties are as follows: a transmittance of 19.8%, a reflectance of 9.1%, a calculated phase shift of ∼181.5° at the exposure wavelength of 193nm, and a transmittance of 18.9% at the inspection wavelength of 257nm. Such a film should be used as an optimized HT-APSM blank.

Keywords: ArF-line; High transmission attenuated phase shift mask; Reflection–transmittance method

Ion beam etching of high resolution structures in Ta₂O₅ for grating-assisted directional coupler applications by Andreas Perentos; Arnan Mitchell; Anthony Holland (pp. 1006-1012).

An investigation on thin Ta₂O₅ films patterning using argon ion beam etching (IBE) is presented. The etch rates are characterised by varying the angle of incidence of the beam onto the substrate. Ta₂O₅ gratings with a period of 2.2μm (1.1μm linewidth) and 0.25μm thickness are fabricated using an angle of incidence of 0°. The resulting Ta₂O₅ grating cross sectional profiles are analysed using AFM and SEM imaging. A fabrication method is thus demonstrated which could be used to implement wavelength selective gratings in applications such as grating-assisted directional couplers (GADCs).

Keywords: PACS; 77.55.+f; 79.20.R; 81.65.C; 85.40.H; 85.60Tantalum oxide Ta; ₂; O; ₅; Ion beam etching IBE; Grating-assisted directional coupler; High resolution

Adsorption of argon and nitrogen in cylindrical pores of MCM-41 materials: application of density functional theory by E.A. Ustinov; D.D. Do; M. Jaroniec (pp. 1013-1028).

Adsorption of argon and nitrogen at their respective boiling points in cylindrical pores of MCM-41 type silica-like adsorbents is studied by means of a non-local density functional theory (NLDFT), which is modified to deal with amorphous solids. By matching the theoretical results of the pore filling pressure versus pore diameter against the experimental data, we arrive at a conclusion that the adsorption branch (rather than desorption) corresponds to the true thermodynamic equilibrium. If this is accepted, we derive the optimal values for the solid–fluid molecular parameters for the system amorphous silica–Ar and amorphous silica–N₂, and at the same time we could derive reliably the specific surface area of non-porous and mesoporous silica-like adsorbents, without a recourse to the BET method. This method is then logically extended to describe the local adsorption isotherms of argon and nitrogen in silica-like pores, which are then used as the bases (kernel) to determine the pore size distribution. We test this with a number of adsorption isotherms on the MCM-41 samples, and the results are quite realistic and in excellent agreement with the XRD results, justifying the approach adopted in this paper.

Keywords: Density functional theory; Adsorption; Capillary condensation; MCM-41

Change of sheet resistance of high purity alumina ceramics implanted by Cu and Ti ions by Dexing Li; Jizhong Zhang; Miao Yu; Jianchang Kang; Wenzhi Li (pp. 1029-1034).

High purity alumina ceramics (99% Al₂O₃) was implanted by copper ion and titanium ion in a metal vapour vacuum arc (MEVVA) implanter, respectively. The influence of implantation parameters was studied varying ion fluence. The samples were implanted by 68keV Cu ion and 82keV Ti ion with fluences from 1�10¹⁵ to 1�10¹⁸ions/cm², respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), glancing X-ray diffraction (GXRD), scanning Auger microscopy (SAM), and four-probe method. Different morphologies were observed on the surfaces of the as-implanted samples and clearly related to implantation parameters. For both ion implantations, the sheet resistances of the alumina samples implanted with Cu and Ti ion fluences of 1�10¹⁸ions/cm², respectively, reached the corresponding minimum values because of the surface metallization. The experimental results indicate that the high-fluence ion implantation resulted in conductive layer on the surface of the as-implanted high purity alumina ceramics.

Keywords: PACS; 85.40.Ry; 68.00.00; 81.05.Mh99% Al; ₂; O; ₃; Ion implantation; Copper and titanium ions; Sheet resistance

Electrochemical studies of zinc–nickel codeposition in sulphate bath by Mortaga M. Abou-Krisha (pp. 1035-1048).

The electrodeposition of Zn–Ni alloys from a sulphate bath was studied under different conditions. The bath had the composition 0.40M sodium sulphate, 0.01M sulphuric acid, 0.16M boric acid, 0.20M zinc sulphate and 0.20M nickel sulphate. It is found that the plating bath temperature has a great effect on the cyclic voltammograms, galvanostatic measurements during electrodeposition, and consequently linear polarization resistance for corrosion study and the alloy composition. Under the examined conditions, the electrodeposition of the alloys was of anomalous type. X-ray diffraction measurements revealed that the alloys consisted of the δ-phase (Ni₃Zn₂₂) or a mixture of the two phases δ and γ (Ni₅Zn₂₁). The comparison between Ni deposition and Zn–Ni codeposition revealed that the remarkable inhibition of Ni deposition takes place due to the presence of Zn²⁺ in the plating bath. The Ni deposition starts at −0.85V in the bath of Ni deposition only, but the deposition starts at more negative potentials in the codeposition bath although the concentration of Ni²⁺ is the same in the both baths.

Keywords: Zn–Ni alloy; Electroplating; Anomalous codeposition; Plating bath temperature; Electrochemical studies; Sulphate bath

Low-frequency excess noise characterizations of laser-assisted de-bonded GaN films by C.P. Chan; B.H. Leung; W.K. Fong; P.K. Lai; Y.H. Loke; C. Surya; T.M. Yue; H.C. Man; X. Xiu; R. Zhang (pp. 1049-1056).

Systematic characterization of flicker noise was conducted on GaN-based metal–semiconductor–metal (MSM) interdigitated devices. The devices were fabricated on both the regular GaN-on-sapphire (type A) and laser de-bonded films followed by layer transfer of hydride vapor phase epitaxy-grown GaN films to Si substrates (type B). Experimental results indicated no significant degradation in the I– V characteristics for Schottky MSM devices fabricated on type B films compared to those fabricated on type A films. However, substantial increase in the flicker noise level, particularly in the low-temperature regime, is observed among the ohmic MSM devices fabricated on type B films. The experimental data suggest that material degradation occurs at the vicinity of the GaN–sapphire interface, while in regions close to the GaN film surface there is practically no change in the film quality. This is supported by finite element simulation of the temperature of the film during laser irradiation. The results indicate that the temperature dropped from 1400K at the GaN–sapphire interface to about 1000K within 0.5μm away from the interface stipulating that material degradation occurs only within 0.5μm from the GaN–sapphire interface.

Keywords: PACS; 72.70.+m; 73.20.−r; 73.50.TdGaN; Laser-assisted de-bonding; Low-frequency noise

Effects of laser intensity and ambient conditions on the laser-induced plume by Zhaoyan Zhang; George Gogos (pp. 1057-1064).

Laser ablation presents a promising technique for material processing. The quality of products is strongly influenced by the properties of the laser-induced plume. In compressible flow, the ambient conditions can be transmitted upstream. Therefore, the laser ablation process is strongly affected by the ambient conditions. In this paper, the effects of laser intensity, back pressure and temperature on the laser-induced plume were studied using a numerical model, which calculates the density, pressure and temperature of the laser-induced plume at different laser intensity and ambient conditions. The results are in agreement with experimental results available in the literature and can be used for the optimization of the pulsed laser deposition process.

Keywords: Laser intensity; Laser ablation; Pulsed laser deposition

Annealing and amorphous silicon passivation of porous silicon with blue light emission by Yue Zhao; Deren Yang; Dongsheng Li; Minghua Jiang (pp. 1065-1069).

The photoluminescence (PL) of the annealed and amorphous silicon passivated porous silicon with blue emission has been investigated. The N-type and P-type porous silicon fabricated by electrochemical etching was annealed in the temperature range of 700–900°C, and was coated with amorphous silicon formed in a plasma-enhanced chemical vapor deposition (PECVD) process. After annealing, the variation of PL intensity of N-type porous silicon was different from that of P-type porous silicon, depending on their structure. It was also found that during annealing at 900°C, the coated amorphous silicon crystallized into polycrystalline silicon, which passivated the irradiative centers on the surface of porous silicon so as to increase the intensity of the blue emission.

Keywords: Porous silicon; Blue emission; Annealing; Amorphous silicon

Modified polypropylene fabrics and their metal ion sorption role in aqueous solution by A. Ehrhardt; K. Miyazaki; Y. Sato; T. Hori (pp. 1070-1075).

Polypropylene non-woven fabrics were grafted with glycidyl methacrylate by the electron beam irradiation method and the introduced epoxide rings were chemically conversed to hydroxyl and thiol groups. The modified polypropylene fabrics showed sufficient hydrophilicity to adsorb the metal ions from the aqueous solutions. The modified fibers were examined as adsorbents for metal ions dissolved in seawater and its model solutions at various conditions. The amount of ions adsorbed on the fabrics was determined by a sequential plasma spectrometry. The modified polypropylene fabrics adsorbed extremely high amount of Au(III) and Hg(II) ions. The equilibrium adsorption of Au(III) was almost not disturbed, even if Cu(II), Cd(II), Pb(II) and the other ions coexisted in the same aqueous solution. Nowadays, the most widely advantages of this technique are the recovery of metal ions dissolved in water and the treatment of industrial wastewater systems.

Keywords: Electron beam grafting; Modified polypropylene; Thiol group; Metal ion sorption; Wastewater

An XPS study of CrO_x on a thin alumina film and in alumina supported catalysts by J. Sainio; M. Aronniemi; O. Pakarinen; K. Kauraala; S. Airaksinen; O. Krause; J. Lahtinen (pp. 1076-1083).

We have investigated chromium layers evaporated onto a thin alumina film at room temperature. The oxidation and reduction behavior of this model catalyst was compared to atomic layer deposition (ALD) and impregnated alumina supported catalysts using X-ray photoelectron spectroscopy (XPS) with a detailed analysis method utilizing asymmetric peak shapes to represent both metallic and oxidic states. The ALD and impregnated catalysts were measured after calcination in air and after reduction with several gases at 850 K. Both catalysts show Cr³⁺ and Cr⁶⁺ species after calcination and mostly Cr³⁺ after reduction. The chromium layers deposited in vacuum show initially small partial oxidation due to the interaction with the oxygen terminated alumina film. These model catalysts can be oxidized in vacuum to Cr³⁺ species but not to higher oxidation states. The model catalysts were also subjected to calcination and reduction treatments after deposition in vacuum. Under these conditions the model systems exhibit similar oxidation/reduction behavior as the supported catalysts. Photoreduction of Cr⁶⁺ during the measurements was also studied and found to be very slow having a negligible effect on the results.

Keywords: PACS; 82.65.-i; 82.80.PvX-ray photoelectron spectroscopy; Chromium oxide; Catalyst

Investigation on friction and wear behaviors of FeS films on L6 steel surface by Hai-dou Wang; Bin-shi Xu; Jia-jun Liu; Da-ming Zhuang (pp. 1084-1091).

Low temperature ion sulfuration technique was utilized to prepare the solid lubrication iron sulfide (FeS) film on the surface of die-steel AISI L6. The friction and wear behaviors of sulfurized L6 steel were investigated on the ring-on-block tester of MM-200 under dry sliding condition. Atomic force microscopy and scanning electron microscopy were adopted to analyze the morphologies and compositions of surfaces and wear scars of the FeS film. X-ray diffractometer was used to study the film phase structure. Scanning Auger microprobe was employed to detect the elements distribution with depth. The results showed that the tribological properties of sulfurized L6 steel were superior to that of the unsulfurized one.

Keywords: Friction and wear behaviors; FeS film; Nano-structure; Solid lubrication

Factors affecting phase and height contrast of diblock copolymer PS–b-PEO thin films in dynamic force mode atomic force microscopy by H. Wang; A.B. Djurišić; W.K. Chan; M.H. Xie (pp. 1092-1100).

Asymmetric PS–b-PEO block copolymer exhibits well-ordered cylindrical morphology with nanoscale domain sizes due to microphase separation. Since the PS and PEO blocks have large stiffness difference, this polymer system represents an ideal candidate for studies of the phase contrast behavior in atomic force microscopy (AFM). In this paper, PS–b-PEO films are investigated under different scanning conditions using two different atomic force microscopes. It is found that the phase contrast of the film can be well described in terms of energy dissipation, though the exact phase image may also depend on the scanning parameters (e.g., the repulsive versus attractive regimes) as well as the settings of the microscope. Height variation on sample surface does not have significant effect on phase contrast. However, in order to obtain true topography of the polymer film, care has to be taken to avoid damage to the sample by AFM. Under certain conditions, true topography can be obtained during the first scan in spite of the surface-damaging forces are used.

Keywords: PACS; 68.37.Ps; 83.80.UvAtomic force microscopy; Phase contrast; Block copolymers

Optical and electrical characterization of TiO₂ nanotube arrays on titanium substrate by Y.K. Lai; L. Sun; C. Chen; C.G. Nie; J. Zuo; C.J. Lin (pp. 1101-1106).

Novel oriented aligned TiO₂ nanotube (TN) arrays were fabricated by anodizing titanium foil in 0.5% HF electrolyte solution. It is indicated that the sizes of the TNs greatly depended on the applied voltages to some extent. The electrical properties of the TN arrays were characterized by current–voltage ( I– V) measurements. It exhibits a nonlinear, asymmetric I– V characterization, which can be explained that there exists an n-type semiconductor/metal Schottky barrier diode between TN arrays and titanium substrate interface. The absorption edges shift towards shorter wavelengths with the decrease of the anodizing voltages, which is attributed to the quantum size effects. At room temperature, a novel wide PL band consisting of four overlapped peaks was observed in the photoluminescence (PL) measurements of the TN arrays. Such peaks were proposed to be resulted from the direct transition X₁→X₂/X₁, indirect transition Γ₁→X₂/X₁, self-trapped excitons and oxygen vacancies, respectively.

Keywords: TiO; ₂; nanotube arrays; Schottky barrier diode; Photoluminescence; Optical and electrical characterization

Thermally oxidised rutile-TiO₂ coating on stainless steel for tribological properties and corrosion resistance enhancement by D. Siva Rama Krishna; Y. Sun (pp. 1107-1116).

In the present work, a novel process has been developed to improve the tribological and corrosion properties of austenitic stainless steels. Efforts have been made to deposit titanium coatings onto AISI 316L stainless steel by magnetron sputtering, and then to partially convert the titanium coatings to titanium oxide by thermal oxidation. The resultant coating has a layered structure, comprising of rutile-TiO₂ layer at the top, an oxygen and nitrogen dissolved α-Ti layer in the middle and a diffuse-type interface. Such a hybrid coating system showed good adhesion with the substrate, improved corrosion resistance, and significantly enhanced surface hardness and tribological properties of the stainless steel in terms of much reduced friction coefficient and increased wear resistance.

Keywords: Stainless steel; Titanium; Titanium oxide; Coating; Adhesion; Friction and wear; Corrosion

Influence of chromate, molybdate and tungstate on pit formation in chloride medium by J.W.J. Silva; E.N. Codaro; R.Z. Nakazato; L.R.O. Hein (pp. 1117-1122).

It has been characterized and evaluated the 2024-T351 and 7050-T7451 aluminum alloys pitting corrosion in naturally aerated chloride aqueous solutions containing chromate, molybdate and tungstate. It has been carried out electrochemical and non-electrochemical immersion corrosion tests accompanied by surface metallography analysis using an optical microscopy. Chromate for the two alloys and in molybdate for 7050 has corrosion inhibiting effects, whereas tungstate promotes the pitting corrosion for these alloys. Quantitative surface analysis upon the alloys after immersion has indicated that pits are predominantly conical or quasi-conical and irregular. In general, pits have been wider than deep and the widest have been also the deepest. Despite inhibitor presence, when pits have been nucleated, they grow with the same intensity.

Keywords: Aluminum alloys; Aircraft alloys; Pitting corrosion; Image analysis

Thermal stability and surface acidity of mesoporous silica doubly doped by incorporation of sulfate and zirconium ions by P. Salas; L.F. Chen; J.A. Wang; H. Armend�riz; M.L. Guzman; J.A. Montoya; D.R. Acosta (pp. 1123-1131).

A sulfated Si–Zr–MCM-41 solid with highly ordered mesostructure was synthesized through a templated synthesis route where the CTAB surfactant was used as template. During the synthesis procedure, various amounts of (NH₄)₂SO₄ were added into the mixed solution of Zr and Si precursors to in situ sulfate the MCM-41 solids, aiming to enhance the acidity and thermal stability. The resultant materials showed a long-range ordered hexagonal arrangement with high surface area larger than 797m²/g and an average pore size distributed at approximate 2.5–2.8nm. The high-resolution TEM observations confirmed that the order of the mesostructure gained when the molar ratio of SO₄²⁻/(ZrO₂+SiO₂) increased from 0.1 to 0.3 but decreased as it reached 0.5, which is consistent with the results of²⁹Si MAS–NMR and XRD analysis. Compared to Si–MCM-41, the (Q²+Q³)/Q⁴ ratio derived from the NMR spectra of the Zr-doped sample was higher, indicating that zirconium atoms were incorporated into the silica framework. Unexpectedly, in situ sulfation does not enhance the surface Brönsted acidity, most likely due to the sulfur retained within the bulk of the materials; however, it indeed improved the thermal stability of the solid and long-range order of the structure.

Keywords: Mesoporous solid; Zr–MCM-41; In situ sulfation; Thermal stability; Acidity

Shear-induced slippage of the self-assembly of crown ether-centered two-armed copolymers by Jun Fu; Yang Cong; Xiang Yu; Jian Li; Caiyuan Pan; Binyao Li; Yanchun Han (pp. 1132-1138).

Crown ether-centered two-armed polymers, i.e., polystyrene-dibenzo-18-crown-6-polystyrene (PSCS) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCM), were designed to self-assemble in a proposed manner directed by the specific affinity between the polar crown ether rings. When spin coated onto a silicon wafer surface, macroporous films were obtained. In contrast, the proposed assemblies were strongly adsorbed on a highly polar mica surface, looking like porous islands near the spin center. At areas far from the spin center, these islands slipped to form terrace islands under the huge shear by the centrifugal force. The formation of the porous islands and terrace islands provide further evidence to the proposed assembling of the two-armed polymers.

Keywords: Adsorption; Crown ether-centered two-armed polymers; Self-assembly; Slippage; Spin coating

Morphology of the Si–ZnO interface by U. Meier; C. Pettenkofer (pp. 1139-1146).

For Si–ZnO heterostructures, prepared by magnetron sputtering, the interface morphology is studied by XPS and UPS. ZnO films on Si(111) surfaces (H-termination and 7×7) were prepared by magnetron sputtering and metal organic molecular beam epitaxy (MOMBE) and are investigated in well defined deposition steps and the interface properties were studied in situ. All samples were handled in situ under ultra high vacuum (UHV) conditions. Up to five different interface phases were detected depending on ZnO preparation. Beside a SiO_x film induced by the sputter process, ZnO and Zn₂SiO₄ phases are resolved. In addition hydrogen, appearing as ZnOH_x, is found in considerable concentrations in the films.

Keywords: PACS; 73.40Lq; 73.61Ga; 79.60JvPhotoemission; Zincoxide; Heterostructure; Interfaces

Characterization of cubic phase MgZnO/Si(100) interfaces by J. Liang; H.Z. Wu; Y.F. Lao; N.B. Chen; P. Yu; T.N. Xu (pp. 1147-1152).

The microstructural properties of the Mg_xZn1−_xO/Si(100) interface were investigated using transmission electron microscopy (TEM) and chemical states of the heterostructure were studied by high resolution X-ray photoelectron spectroscopy (XPS). By analyzing the valence band spectra of thin Mg_xZn1−_xO/Si(100) heterostructures, the valence band offset between such Mg_0.55Zn_0.45O and Si(100) was obtained to be 2.3eV. Using the cubic ternary thin films as insulators, metal–insulator–semiconductor (MIS) capacitors have been fabricated. Leakage current density lower than 3×10⁻⁷A/cm² is obtained under the electrical field of 600kV/cm by current–voltage ( I– V) measurement. Frenkel-Poole conduction mechanism is the main cause of current leakage under high electrical field.

Keywords: MgZnO thin film; Band offset; MIS structure; Leakage mechanism

Temperature dependent electrical characteristics of Sn/p-Si Schottky diodes by Enise Ayyildiz; Hidayet Cetin; Zs. J. Horv�th (pp. 1153-1158).

Current–voltage and capacitance–voltage characteristics of Sn/p-Si Schottky diodes measured in the temperature range 80–320K are presented and analysed. Anomalous strong temperature dependencies of the ideality factor and apparent barrier height were obtained. There was also a considerable difference between the apparent barrier heights obtained from current–voltage and capacitance–voltage characteristics. These anomalies are explained by the domination of the current by a high level of thermionic-field emission, and by the presence of deep levels near the Sn/Si interface, which yield a reduction of free hole concentration and a significant temperature dependence of the charge stored near the metal–semiconductor (MS) interface. The evaluation of temperature dependence of forward current for thermionic-field emission resulted in the following parameters: characteristic energy E₀₀=9.8meV, Schottky barrier height at zero bias Φ_b0=0.802eV, bias coefficient of barrier height β=0, and effective Richardson constant A*=37.32Acm⁻²K⁻².

Keywords: Thermionic-field emission; Schottky junctions; Current–voltage and capacitance–voltage characteristics

Investigation of the effects of plasma treatments on biodeteriorated ancient paper by L. Laguardia; E. Vassallo; F. Cappitelli; E. Mesto; A. Cremona; C. Sorlini; G. Bonizzoni (pp. 1159-1166).

Deterioration of paper-based materials is mainly due to the degradation of cellulose caused by a lot of factors such as chemical attack due to acidic hydrolysis, oxidative agent, light, air pollution and biological attack and also due to the presence of microorganisms like bacteria and fungi. It is therefore desirable to focus the research activities on restoration and conservation techniques to develop appropriate treatments.¹1CNR Patent, n� Mi2004A000068, 21/01/2004. The aim of this paper is the removal or reduction of the microbial contamination and paper consolidation by means of plasma treatment. For plasma processes, different gas mixtures are utilised, and the different gas mixtures are compared as a function of pressure, power, and treatment time. To demonstrate the efficiency of the sterilisation treatment, two fungi: Aspergillus niger and Penicillium funiculosum, commonly found in libraries and archives were spread on naturally aged paper (19th century). Microorganisms were let to grow by using the organic compounds found in the historical records as a sole source of carbon and energy. The microbial abatement was measured before and after the plasma treatment by using the standard plate count method. Surface chemical and morphological characterisation of paper before and after plasma treatment has been carried out by X-ray photoelectron spectroscopy (XPS) and ATR infrared spectroscopy (ATR FTIR). The tensile strength of the plasma-treated papers was also determined.

Keywords: Plasma treatment; Microbial reduction; Tensile strength; Biodeterioration; Paper-based materials; XPS and ATR FTIR

Structural and spectroscopic analysis of hot filament decomposed ethylene deposited at low temperature on silicon surface by F.-K. Tung; E. Perevedentseva; P.-W. Chou; C.-L. Cheng (pp. 1167-1174).

The deposition of decomposed ethylene on silicon wafer at lower temperature using hot filament chemical vapor deposition (HFCVD) method was applied to compose thin film of carbon and its compounds with silicon and hydrocarbon structures. The films were analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy with elemental microanalysis by energy dispersive X-ray spectrometer. The structure and morphology of the early stage of the film deposition was analyzed. The obtaining of SiC as well as diamond-like structure with this method and catalytic influence of chemical admixtures on the film structure and properties are discussed.

Keywords: PACS; 61.18.−j; 61.43.Er; 68.55.−a; 68.55.JkHot filament chemical vapor deposition; Raman spectroscopy; Silicon carbide

Characterization of bilayer coatings of TiN/ZrN grown using pulsed arc PAPVD by D.F. Arias; Y.C. Arango; A. Devia (pp. 1175-1181).

Nitride coatings have been used to increase hardness and to improve the wear and corrosion resistance of structural materials. Coatings of TiN/ZrN were grown on stainless steel substrates using a physical vapour deposition system assisted by pulsed arc plasma (PAPVD). The coatings have been characterized by X-ray diffraction (XRD) in order to identify the present phases of the films, microstrain level generated, crystallite size and the variation of the lattice parameter. The results showed plane orientations (111) and (200) in both TiN and ZrN films. Morphology surface analysis of the samples were performed using a scanning probe microscope to characterize the grain size and roughness in the mode of the atomic force microscopy (AFM) hence it was observed that the root-mean-squared (rms) roughness for ZrN is smaller than for TiN. Besides elastic and friction properties of the films were characterized qualitatively, and then, they were compared with those of the substrates by using force modulation microscopy (FMM) and lateral force microscopy (LFM) modes. In addition, an elemental analysis of the samples was realized by means of energy dispersive spectroscopy (EDS). Both, XRD and AFM results are given as a function of the number of shots. Chemical states of the TiN and ZrN films were determined by X-ray photoelectron spectroscopy (XPS).

Keywords: TiN/ZrN; Bilayers; Hard coatings; Materials characterization

Well-dispersed gold nanowire suspension for assembly application by Cai-ling Xu; Li Zhang; Hao-li Zhang; Hu-lin Li (pp. 1182-1186).

A method for fabricating well-dispersed nanowire suspension has been demonstrated in the paper. Thin gold nanowires were prepared by template synthesis, and then functionalized with sulphonate group-terminated thiols before suspended in different solvents. The degree of aggregation of the obtained suspension was evaluated with transmission electron microscopy (TEM) and UV–vis spectroscopy. It was found that the degree of aggregation was predominated by the solvents, and the best degree of dispersion was obtained when isopropyl alcohol (IPA) was used as the solvent. The gold nanowires from the suspension can be selectively assembled onto chemically patterned substrates. This well-dispersed nanowire suspension is potentially useful for fabricating novel nanodevices.

Keywords: PACS; 81.15.P; 52.25; 31.70.D; 81.65.CGold nanowires; Chemical pattern; Selective assembly; Electrostatic interactions

Erratum to “STM-induced light emission from the surface of H₂TBP porphyrin/PFP porphyrin/Cu(100)�? [Appl. Surf. Sci. 241 (2005) 28–32] by X.-L. Guo; Z.-C. Dong; A.S. Trifonov; K. Miki; K. Kimura; S. Mashiko (pp. 1187-1188).

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Applied Surface Science (v.252, #4)