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Applied Surface Science (v.243, #1-4)
Energy analysis for (111) twist grain boundary in noble metals by Jian-Min Zhang; Xiu-Mei Wei; Hong Xin (pp. 1-6).
With modified analytical embedded atom method (MAEAM), the energies of twist grain boundaries (GBs) have been calculated for three noble metals, Cu, Ag and Au with the same FCC structure. The results are similar for all the three metals: (1) the unrelaxed energies keep almost constant with twist angles θ; (2) after expansion perpendicular to the boundary, GB energies drop significantly to less than one-third of their surface energies respectively; (3) in-boundary translation results in periodic energy variation with the period of L Σ/ Σ, but the energy variation is slight.
Keywords: Noble metals; Grain boundary energy; MAEAM; Calculation
Chromophore binding to in vitro engineered bio-mimetic surfaces by Joseph M. Kinsella; Albena Ivanisevic (pp. 7-10).
In the retina, a chromophore isomerizes and the protein to which it binds changes shape. In this proof-of-concept experiment we engineer an artificial surface to mimic the physiochemical environment of the retina and the key reaction of the visual cycle. We immobilized small peptides on silicon and assessed changes in their surface properties upon chromophore binding via ellipsometry, X-ray photoelectron spectroscopy and atomic force microscopy. Our observations suggest that when binding occurs it is accompanied by changes in the properties of the film composed of surface-anchored peptides.
Keywords: Bio-mimetic surfaces; Peptides; X-ray photoelectron spectroscopy
A theoretical study of Cs adsorption at tips of single-wall carbon nanotubes: field emission properties by Xiaofeng Duan; Brahim Akdim; Ruth Pachter (pp. 11-18).
Cs intercalation has demonstrated experimentally a significant reduction of the work function of carbon nanotubes, thus improving field emission properties. In this paper, we report a density functional theory (DFT) study within the generalized gradient approximation (GGA), regarding the effects of Cs on field emission of single-wall carbon nanotubes (SWCNTs). Specifically, a comprehensive examination was carried out to investigate the effects of Cs adsorbed on capped and open-ended C(5,5) armchair SWCNT tips. Our calculations showed a reduction in the ionization potential (IP) upon Cs physisorption, thus improving the emission properties of carbon nanotubes, as reported experimentally. The structure of the adsorbed Cs-cluster, the corresponding adsorption energies, and the IPs, were altered upon the inclusion of a local electric field in the calculations to mimic the emission environment.
Keywords: PACS; 71.15.Mb; 79.70.+qDensity functional theory; Field emission; Single-wall carbon nanotubes; Cs adsorption
Ion bombardment in a normal-gate FED by Yingbin Gao; Xiaobing Zhang; Wei Lei; Min Liu; Yuning Zhang; Daniel den Engelsen (pp. 19-23).
Due to the electron-gas collision ionization in a FED, positively charged ions bombard the cathode. This can destroy the field emitters and cause instabilities. In this study we have selected a normal-gate sub-cell to calculate the ion bombardment (IB). In the cases of uniform emitting and ring emitting, the process of ion bombardment and cathode damage has been investigated.
Keywords: Ion bombardment; CNT cathode; Numerical simulation
Growth and characteristics of ZnO thin film on CaF2 (11–21) substrate by metalorganic vapor phase epitaxy by Yan Ma; Guotong Du; Xu Wang; Wancheng Li; Jingzhi Yin; Dengli Qiu; Bo Song; Xi Zhang; Yuantao Zhang; Dali Liu (pp. 24-29).
Zinc oxide (ZnO) thin film was grown on CaF2 (11–21) substrate by metalorganic vapor phase epitaxy (MOVPE) and the structure, surface morphology and the opto-electrical properties of the film were investigated. It was found that preferential c-axis oriented ZnO film was highly transparent and quite smooth. In photoluminescence (PL) spectrum at 10K, the neutral donor bound exciton (D0X) emission was identified at 3.362eV (I4), the neutral acceptor bound exciton (A0X) emission at 3.346eV (I9). Free A- and B-exciton emissions at 3.374eV and 3.386eV, respectively, as well as the phonon replicas of free A-exciton and D0X were also observed, indicating high optical quality of the ZnO film. Temperature-dependent PL spectra demonstrated that the free exciton emission was dominant at a temperature larger than 215K. Hall measurement showed that the ZnO/CaF2 film exhibited n-type conduction, with the resistivity of 114Ωcm and the Hall mobility of 15.7cm2/Vs.
Keywords: PACS; 81.15.Gh; 78.66.Hf; 68.55.Jk; 73.61.GaZnO thin film; Metalorganic vapor phase epitaxy; CaF; 2; substrate; Properties
Raman scattering characterization of macro- and nanoporous silicon by N. Korsunska; B. Bulakh; B. Jumayev; L. Khomenkova; V. Yukhymchuk; T. Torchynska (pp. 30-35).
The structural properties and Raman scattering spectra of porous silicon layers were investigated. The enhancement of intensity of Raman line from porous silicon in comparison with a substrate without any shift of peak position was observed. It is shown that this effect is due to presence of macropores in investigated samples. The enhancement is explained by multiple absorption of probe light scattered and reflected inside macropores while a coincidence of shape and peak position of Raman lines from porous layer and silicon substrate is due to low thickness of nanoporous layer. The method of investigation of porous layer structure based on the combination of Raman scattering effect with variation of probe light wavelength is proposed.
Keywords: PACS; 78.67.−n; 78.30.−j; 78.55.−mAtomic force microscopy; Raman scattering effect; Nanoporous silicon
Research on optical property of phase transition PcNi/VO2 films by H.T. Yuan; K.C. Feng; X.J. Wang; C.J. He; D.H. Li; Y.X. Nie; K.A. Feng (pp. 36-39).
Highly oriented VO2 thin films were deposited on sapphire substrate and PcNi thin films were spin coated onto VO2 thin films. The microstructure of VO2 thin films were studied with XRD. The phase transition was observed and the change in the optical properties of the PcNi/VO2 multilayer-films were investigated. It was found that the mid-infrared transmittance of the complex films from 1.5 to 5.5μm wavelength was raised with PcNi film coating. The thermochromism of PcNi/VO2 films was not changed compared with VO2 films and the transition temperature was same to that of VO2.
Keywords: PACS; 6890; 7865; 8115C; 7830VO; 2; PcNi; Optical limiting; Thermochromism
Interaction of hydrogen sulfide with Zr0.92Y0.08O2− δ/40% Ni cermet by R.V. Siriwardane; J.A. Poston Jr.; E.P. Fisher (pp. 40-54).
The interaction of hydrogen sulfide with a cermet composed of zirconium oxide and yttrium oxide doped with metallic nickel (Ni) in the stoichiometric form Zr0.92Y0.08O2− δ/40vol% Ni and a pure nickel metal was studied at 500 and 650°C utilizing high temperature X-ray photoelectron spectroscopy and high-temperature scanning electron microscopy. The hydrogen sulfide (H2S) did not appear to interact with the cermet at 500°C with H2S exposures of 6×10−5Torr for 1h, but interaction of H2S with the cermet was observed at 650°C at similar H2S exposures. The amount and the rate of reaction of H2S were significantly lower with the cermet than with the pure nickel metal at 650°C with similar H2S exposures. The dispersion of nickel in the zirconium and yttrium oxide matrix decreased the reaction of H2S with nickel in the cermet.
Keywords: High temperature cermets; Gas separation membranes; Ceramic membranes; Surface characterization of membranes; Interaction of H; 2; S with cermets; Fuel cell electrodes; Cermets
Characterization and conductive coating of phosphors for improved brightness by Chia-Hao Chang; Bi-Shiou Chiou; Kuen-Shian Chen; Jia-Chong Ho (pp. 55-61).
In this study, the phosphors used in CRTs are coated with In2O3 conductive layer derived from the hydrolysis of indium chloride. The conductive coating retards/eliminates charging-up on the phosphor surface during the bombardment of the electrons and improves the cathodoluminescent brightness of the phosphor. However, the non-emissive conductive coating also degrades the cathodoluminescent brightness when it is too thick. The cathodoluminescent brightness increases initially with the amount of coating, reaches a maximum at 10wt.% InCl3, and decreases with further increase of coating. It is found that with a 10wt.% InCl3 coating, the brightness of phosphor increases by 20% at 500V and 1μA.
Keywords: Brightness; InCl; 3; Phosphor
Giant magnetoreistance in evaporated nanometer scale Fe/W and Co/W multilayers by Y. Chushkin; M. Jergel; Š. Luby; E. Majková; M. Ožvold; Y. Kuwasawa; S. Okayasu; E. D’Anna; A. Luches; M. Martino (pp. 62-67).
Giant magnetoresistance (GMR) is often studied in multilayers (MLs) composed of mutually immiscible pairs of metals. Low miscibility is expected also in Fe/W and Co/W couples where the heat of compound formation is Δ H ≈ 0. Therefore, the GMR in these types of MLs was studied in this work. The MLs were UHV e-beam deposited onto Si, number of periods being 5 or 10. The substrate temperature was kept between 70 and 200°C. The layer thicknesses of Fe, Co and W were between 1 and 7nm, resulting in different designs. The samples were analyzed by the X-ray diffraction, X-ray reflectivity and grazing incidence X-ray diffuse scattering. The GMR was measured in the field ≤5T. In RT deposited samples, the GMR ratio was ≤0.6% even at 4.2K. It could be increased by a KrF laser irradiation. A GMR enhancement was achieved by the deposition of Fe/W MLs at 190°C. Here, the GMR ratio was 2% already at RT. At 190°C, a structural coherency and strong lateral and vertical interface roughness correlations in the MLs were found. The increase of the GMR is explained by different factors including also the elimination of magnetic shortcuts due to well-replicated and slowly varying interface profiles.
Keywords: PACS; 61.10; Kw; 68.35 − p; 75.70; PaGiant magnetoresistance; Iron; Cobalt; Tungsten; Interface replication
Plume dynamics of laser-produced aluminum plasma in ambient nitrogen by A.K. Sharma; R.K. Thareja (pp. 68-75).
We report on the plume dynamics of pulsed laser ablated aluminum in ambient nitrogen pressure varying from 0.01 to 70Torr using ICCD images of the expanding plasma plume. At pressures of 0.01 to 1Torr plasma expansion followed shock model whereas at 10 and 70Torr plasma expansion followed drag model. The difference in the values of vapor and shock temperatures calculated at 0.1 and 70Torr has been used to understand the formation of AlN in vapor phase. At pressures ≥1Torr and later times plasma–gas interface showed instability in the leading edge of the expanding plume attributed to Rayleigh–Taylor instability.
Keywords: PACS; 52.50.Jm; 52.35.TcShock wave; Drag model; Rayleigh–Taylor instability
Surface-enhanced Raman scattering (SERS) spectra of sodium benzoate and 4-picoline in Ag colloids prepared by γ-irradiation by Seong-Ho Choi; Hyun Gyu Park (pp. 76-81).
PVP-protected silver colloids were prepared by γ-irradiation and chemical reduction method. Surface-enhanced Raman scattering (SERS) spectra of sodium benzoate and 4-picoline in Ag colloids prepared by γ-irradiation were recorded. The SERS spectra of sodium benzoate were successfully recorded in Ag colloids, whereas the Raman spectra did not appear without Ag colloids. The Raman spectra of 4-picoline were not detected without Ag colloids, while the SERS spectra of 4-picoline were increased by adding Ag colloids. The carboxylate group of sodium benzoate and N donor of 4-picoline were adsorbed on the surface of Ag nanoparticles.
Keywords: Surface-enhanced Raman scattering (SERS) spectra; Ag colloids; γ-Irradiation; Chemical reduction; Sodium benzoate; 4-Picoline
The current fluctuations and accumulated pitting damage of mild steel in NaNO2–NaCl solution by Yuming Tang; Yu Zuo; Hao Zhao (pp. 82-88).
Metastable pitting behavior of mild steel in 0.1M NaNO2+0.05M NaCl solution at constant potentials was studied. The current fluctuations showed the feature of quick rise and relatively slow decay, indicating quick breakdown and slow repassivation of the passive film on the surface. The current fluctuations resulted in observable pits on sample surface. A bigger pit may be composed of several small pits, which suggests that a repassivated metastable pit may still be active site for following metastable pits to nucleate. Repeated local dissolution events around a certain active site caused accumulated corrosion damage. The pit size distribution calculated from the current fluctuations was very close to that observed with SEM, indicating that there is good correlation between current fluctuations and the growth process of metastable pits. Corrosion products may pile up at pit mouth and lead the pit to an occluded state, thus metastable pitting process was replaced by stable pitting. Once the pit mouth was completely blocked up by corrosion products, the pit would stop growing.
Keywords: Metastable pitting; Mild steel; Current fluctuations; Accumulated damage
Formation of silicon on plasma synthesized SiO xN y and reaction mechanism by Ming Zhu; Xuejie Shi; Peng Chen; Weili Liu; Man Wong; Chenglu Lin; Paul K. Chu (pp. 89-95).
The application of silicon-on-insulator (SOI) substrates to high-power integrated circuits is hampered by self-heating effects due to the poor thermal conductivity of the buried SiO2 layer. We propose to replace the buried SiO2 layer in SOI with a plasma synthesized SiO xN y thin film to mitigate the self-heating effects. The SiO xN y films synthesized on silicon by plasma immersion ion implantation (PIII) exhibit outstanding surface topography, and excellent insulating characteristics are maintained up to an annealing temperature of 1100°C. Hence, the polycrystallization in our SiO xN y materials is insignificant during conventional complementary metal oxide silicon (CMOS) processing. Using Si/SiO xN y direct bonding and the hydrogen-induced layer transfer, a silicon-on-SiO xN y structure has been successfully fabricated. Cross-sectional high-resolution transmission electron microscopy (HRTEM) and spreading resistance profiling (SRP) reveal that the bonded interface is abrupt and the top Si layer exhibits nearly perfect single crystalline quality. The reaction mechanism of SiO xN y and Si wafer bonding are also discussed.
Keywords: PACS; 52.77.Dq; 82.30.Rs; 73.40.TySilicon-on-insulator (SOI); Plasma immersion ion implantation (PIII); Wafer bonding
Micro-Raman study of photoexcited plasma in GaAs bevelled structures by R. Srnanek; G. Irmer; J. Geurts; M. Lentze; D. Donoval; B. Sciana; D. Radziewicz; M. Tlaczala; M. Florovic; I. Novotny (pp. 96-105).
The properties of the photoexcited plasma in n-GaAs and its influence on micro-Raman spectra were studied on bevelled structures. The modes of the photoexcited free-carriers plasmon–LO–phonon (PLP) coupling have been detected in the surface depletion layer at room temperature in continuum wave (CW) mode. The strong modifications of the intensities of TO–phonon and LO–phonon modes were observed along the bevel. They were discussed in terms of scattering by PLP coupling. The dependence of the ratio of the intensities of TO–phonons and LO–phonons was linear along the bevel in the region of the surface depletion layer. The first derivative of this dependence is a characteristic value for the corresponding doping concentration. Five Si-doped GaAs layers with different doping levels were analyzed in this way to obtain a calibration function for determining the doping concentration profile in the very thin GaAs layers.
Keywords: PACS; 78.30. Fs; 68.55.Ln; 73. 20 MfMicro-Raman; GaAs; Bevel; Photoexcited plasma; Plasmon–LO–phonon coupling
Activation of binary Zr–V non-evaporable getters: synchrotron radiation photoemission study by V. MatolÃn; V. Dudr; S. FabÃk; V. Cháb; K. MaÅ¡ek; I. MatolÃnová; K.C. Prince; T. Skála; F. Å utara; N. Tsud; K. Veltruská (pp. 106-112).
Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by synchrotron radiation photoelectron spectroscopy using photon excitation energies of 600, 250 and 73eV. Depth resolved results were compared to the results of the SIMS profiling. The measurements confirmed the disappearance of the superficial oxide layer covering the air-exposed Zr–V surfaces via its progressive reduction during the thermal activation. The depth sensitive results showed that the activated getter surface is covered by a residual zirconium sub-oxide.
Keywords: PACS; 81.65.Tx; 81.05.3x; 81.15.Cd; 82.65.Pa; 82.80.Ms; 82.80.PvZirconium; Vanadium; Alloys; Photoelectron spectroscopy; Secondary ion mass spectrometry; Getters
Effects of adhesion layer (Ti or Zr) and Pt deposition temperature on the properties of PZT thin films deposited by RF magnetron sputtering by C.C. Mardare; E. Joanni; A.I. Mardare; J.R.A. Fernandes; C.P.M. de Sá; P.B. Tavares (pp. 113-124).
The effect of different bottom electrode structures (Pt/Ti/SiO2/Si and Pt/Zr/SiO2/Si) and Pt deposition temperatures on the properties of ferroelectric lead zirconate titanate (PZT) thin films deposited by RF magnetron sputtering and crystallized either in the furnace or by RTA was investigated. The orientation of the films was strongly affected by all those parameters in the case of Ti adhesion layer, whereas for Zr only a slight effect could be detected. The best ferroelectric properties were obtained for Pt/Ti bottom electrodes with the Pt deposited at 500°C and for Pt/Zr bottom electrodes with the Pt made at room temperature, in both cases the PZT being crystallized in the furnace. The results are explained in terms of different stress levels and diffusion processes taking place in the bottom electrode structures during their deposition and the crystallization of the PZT thin films.
Keywords: PACS; 77.84.−s; 77.55.+f; 81.15.CdPZT; Zirconium; Titanium; Ferroelectric properties; Sputtering
Conversion of a solid surface from super-hydrophobic to super-hydrophilic by photocatalytic remote oxidation and photocatalytic lithography by Wakana Kubo; Tetsu Tatsuma (pp. 125-128).
A super-hydrophobic surface, of which contact angle was 151°, was obtained by modifying a SiO2 microparticle film-coated glass plate with octadecyltriethoxysilane (ODS). The super-hydrophobic surface was converted to super-hydrophilic by remote oxidation using a TiO2 photocatalyst for 40min, due to oxidative decomposition of the ODS monolayer. The increase in the wettability of the super-hydrophobic surface with water was faster than that of a normal hydrophobic surface. Patterning of the super-hydrophobic surface was also possible by means of photocatalytic lithography based on the remote oxidation using a photomask. It was possible to entrap water in the oxidized regions.
Keywords: Super-hydrophobic; Super-hydrophilic; Photocatalytic lithography; Remote oxidation; TiO; 2; photocatalyst
Wavelength dependence of the single pulse femtosecond laser ablation threshold of indium phosphide in the 400–2050nm range by A. Borowiec; H.F. Tiedje; H.K. Haugen (pp. 129-137).
We present single pulse femtosecond laser ablation threshold measurements of InP obtained by optical, scanning electron, and atomic force microscopy. The experiments were conducted with laser pulses 65–175fs in duration, in the wavelength range from 400 to 2050nm, covering the photon energy region above and below the bandgap of InP. The ablation thresholds determined from depth and volume measurements varied from 87mJ/cm2 at 400nm to 250mJ/cm2 at 2050nm. In addition, crater depths and volumes were measured over a range of laser fluences extending well above the ablation threshold.
Keywords: PACS; 79.20.Ds; 61.80.BaIndium phosphide; Femtosecond laser ablation of semiconductor; Atomic force microscopy
The deepness enhancing of an AFM-tip induced surface nanomodification by D.V. Sheglov; A.V. Latyshev; A.L. Aseev (pp. 138-142).
The novel method of the semiconductor nanostructuring (TINE&MEMO) has been developed on the base of the simultaneous AFM-tip induced local anodic oxidation and mechanical modification of the surface under the applying of advanced electric potentials. The TINE&MEMO-based technology allows obtaining the principle new scale of the depth up to 100 nm for the nanostructure fabrication with a low aspect relation between the width and deepness. The developed nanoscale AFM-lithography has been clearly demonstrated on titanium, gallium arsenide and silicon substrates for creation of electronic nanodevices.
Keywords: PACS; 81.16.Nd; 68.37.PsAFM; Nanostructuring; Local anodic oxidation; Surface nanomodification
Microstructural and interband transition properties in CdTe quantum dots grown on ZnTe buffer layers by using atomic layer epitaxy by Y.S. No; T.W. Kim; H.S. Lee; H.L. Park (pp. 143-147).
The microstructural and the optical properties of CdTe/ZnTe quantum dots (QDs) grown by atomic layer epitaxy (ALE) were investigated by using atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The AFM image showed that uniform CdTe QDs are formed, and the TEM image showed that the CdTe QDs were embedded into the ZnTe buffer layers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the CdTe/ZnTe QDs shifted to lower energy with increasing temperature. The full widths at half maxima of the PL peaks for CdTe/ZnTe QDs grown by ALE remained almost constant regardless of the temperature variation. These present observations can help to improve understanding for the microstructural and the optical the properties of the CdTe/ZnTe QDs grown by using the ALE method.
Keywords: PACS; 68. 55. Bd; 78. 20. -e.CdTe/ZnTe; Quantum dots; Interband transition
Electron beam induced surface modification of amorphous Sb2S3 chalcogenide films by R.K. Debnath; A.G. Fitzgerald (pp. 148-150).
A surface modification (expansion) has been observed in amorphous antimony based chalcogenide (Sb2S3) thin films when a pulsed electron beam is focused onto the surface of the film at accelerating voltages between 15 and 30kV. The dependence of pattern heights and width on parameters such as exposure time, beam current and accelerating voltage have also been studied. The modification of the film surface involves lateral and vertical expanded which is typically in the micrometre and sub-micrometre range. This phenomenon can be explained in terms of electrostatic force.
Keywords: PACS; 61.80.FAmorphous materials; Antimony; Atomic force microscopy
Preparation of carbon nanotubes at the surface of Fe/SBA-15 mesoporous molecular sieve by X.Q. Wang; M. Wang; H.X. Jin; Z.H. Li; P.M. He (pp. 151-157).
Multi-walled carbon nanotubes were produced by the decomposition of the acetylene gas with chemical vapor deposition (CVD) method, in which the Fe/SBA-15 mesoporous molecular sieves were prepared in acid solution with the sol–gel method. TEM, high-resolution transmission electron microscope (HRTEM) and SEM were used to observe the Fe/SBA-15 molecular sieve and the as-prepared carbon nanotubes, respectively. And the purified carbon nanotubes was also characterized by Raman spectrum. It's surprising that carbon nanotubes grow from the surface of the Fe/SBA-15 mesoporous molecular sieve. The open, straight carbon nanotubes prepared in this way are well graphitized, and carbon nanotubes array are found somewhere. Furthermore, the diameter of carbon nanotubes becomes large with increasing the Fe content in SBA-15 mesoporous molecular sieve.
Keywords: Carbon nanotubes; SBA-15 mesoporous molecular sieve; Chemical vapor deposition (CVD); Raman spectrum
Macro and microthermal analysis of plant wax/surfactant interactions: plasticizing effects of two alcohol ethoxylated surfactants on an isolated cuticular wax and leaf model by Mark C. Perkins; Clive J. Roberts; David Briggs; Martyn C. Davies; Adrian Friedmann; Clifford Hart; Gordon Bell (pp. 158-165).
Synperonic A7 and A20 are surfactants commonly used in the agrochemical industry to improve the physicochemical properties of formulations. This paper describes the use of differential scanning calorimetry (DSC) and localised thermal analysis (LTA) to investigate the bulk and surface effects of these surfactants on extracted leaf wax and an intact leaf system. Both DSC and LTA analysis reveal a plasticizing effect in the presence of the A7 surfactant. Further to this, LTA analysis allows us to spatially map micron scale variations in this effect throughout the residue of individual deposits. In contrast to this no plasticizing effect is revealed following the application of the A20 surfactant in either the DSC of LTA analysis. These results are discussed in context with the current theory of surfactant/wax interaction.
Keywords: Scanning thermal microscopy; Surface wetting; Surfactants
Charging effects on electron-stimulated desorption of cations from gadolinia-doped ceria surfaces by Haiyan Chen; Yanfeng Chen; Alex Aleksandrov; Jian Dong; Meilin Liu; Thomas M. Orlando (pp. 166-177).
Electron beam-induced charging and -stimulated desorption have been used to probe the electronic properties of gadolinia-doped ceria (GDC) surfaces. The main cationic desorption products resulting from electron bombardment are H+, H3O+ and O+. The dependence of the H+ and H3O+ ion kinetic energies and yields on the surface potentials have been systematically investigated. Positive potentials increase the cation kinetic energies linearly while negative potentials reduce the cation yields dramatically. The charging of GDC by electron beam bombardment is dependent on the incident electron energy: negative at lower energy and positive at higher energy. Irradiation with 400eV electrons can produce a positive surface potential of several volts while irradiation of the sample with 75eV electrons can produce a negative sample potential of at least −6V. The positive charge caused by high-energy electron irradiation can be neutralized by the negative charge generated by low-energy electrons and vice versa. The probable hole traps are sites close to Gd3+, and the abundant presence of defects at oxygen vacancy-rich grain boundaries can serve as very effective electron traps.
Keywords: PACS; 79.20.Kz; 81.05.JeElectron-stimulated desorption; Surface potentials; Gadolinia-doped ceria; Solid oxide fuel cells
Growth of thick AlGaN by mixed-source hydride vapor phase epitaxy by H.S. Ahn; K.H. Kim; M. Yang; J.Y. Yi; H.J. Lee; C.R. Cho; H.K. Cho; S.W. Kim; T. Narita; Y. Honda; M. Yamaguchi; N. Sawaki (pp. 178-182).
Growth of a thick AlGaN layer on GaN/Al2O3 substrate is performed by mixed-source hydride vapor phase epitaxy (HVPE) method. The AlGaN material is compounded from chemical reaction between a NH3 and an aluminum-gallium chloride formed by HCl which is flown over metallic Ga mixed with Al. The AlGaN epitaxial layer is analyzed by Auger-electron spectroscopy (AES) and X-ray diffraction (XRD) measurement to characterize the AlGaN. Al concentration is estimated to be in the range of 0.5–6%. We suggest that the metallic Ga mixed with Al can be used as a group III source material in the HVPE growth of the AlGaN layer.
Keywords: PACS; 81.05.Ea; 81.10AlGaN; HVPE; GaN; Optical property; XRD; AES
Characterisation of nanosize thin films of electrografted N-vinylcarbazole copolymers (P[NVCz–co-VBSA] and P[NVCz–co-3-MeTh]) onto carbon fibre by A. Sezai Sarac /; Marina Serantoni; Syed A.M. Tofail; John Henry; Vincent Cunnane; James B. McMonagle (pp. 183-198).
N-Vinylcarbazole-containing random copolymers were electrochemically coated (grafted) onto micron-size carbon fibre by constant current electrolysis and the resulting nanosize thin films of polymers and copolymers were characterised using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The efficiency of the electrocopolymerisation process on the carbon fibre surfaces under preparative constant current electrolysis conditions, depending on experimental conditions, was evaluated in order to ascertain the effects of copolymer thickness, dopant and morphology.
Keywords: Nanosize polymer coatings; Random conductive copolymers; Carbon fibre; AFM; XPS; Raman spectroscopy
Formation of Si nanodot arrays on the oxidized Si(1 0 0) surface by A.A. Saranin; A.V. Zotov; V.G. Kotlyar; O.A. Utas; K.V. Ignatovich; T.V. Kasyanova; Y.S. Park; W.J. Park (pp. 199-203).
Self-organized formation of Si nanodot arrays on the oxidized Si(1 0 0) surfaces has been studied using scanning tunneling microscopy. The growth of the oxide layer and subsequent Si deposition have been conducted under ultra-high vacuum conditions. Number density of the grown Si nanodots was in the range from3×1012 to8×1012 cm−2 and their average size varied from 3 to 5 nm. Effect of the SiO2 layer thickness (0.2–2.2 nm), amount of deposited Si (0.5–7.5 ML) and growth temperature (60–450°C) on the Si nanodot number density and size distribution has been determined.
Keywords: Atom–solid interactions; Silicon; Oxygen; Surface structure, morphology, roughness, and topography; Scanning tunneling microscopy (STM)
Microhardness and toughness of the TiN coating prepared by reactive plasma spraying by Wenran Feng; Dianran Yan; Jining He; Guling Zhang; Guangliang Chen; Weichao Gu; Size Yang (pp. 204-213).
The in-situ titanium nitride (TiN) coating with a great thickness was reactive plasma sprayed in a nitrogen-containing environment. The microhardness of the coating was measured, and the indentations were used to determine the fracture toughness of the coating. The toughening mechanism was characterized by analyzing the SEM morphologies of TiN coating's fracture surfaces. Results show that the coating possesses a high hardness and toughness. The average hardness of the coating is 1200 HV100g; and the fracture toughness ( KIC) of it is 4.51MPa·m0.5. The cross-section of the TiN coating shows an obvious phenomenon of indentation size effect (ISE). The toughening mechanisms of the coating are crack deflection and pores, etc.
Keywords: TiN coating; Reactive plasma spraying; Fracture toughness
Laser ablation of cobalt and cobalt oxides in liquids: influence of solvent on composition of prepared nanoparticles by Takeshi Tsuji; Taroh Hamagami; Tetsuya Kawamura; Junichi Yamaki; Masaharu Tsuji (pp. 214-219).
Laser ablation of Co, CoO and Co3O4 was carried out in water and hexane. Nano-sized particles were produced from all materials in both solvents. It was found that atomic compositions of nanoparticles depended on solvent species in which laser ablation was carried out. In water, Co3O4 nanoparticles were produced from all materials. In hexane, Co nanoparticles were produced from Co3O4 and Co, while CoO particles were dominantly produced from CoO.
Keywords: PACS; 81.16.Mk; 82.70.Dd; 87.14.Cc; 81.05.−tLaser; Ablation; Liquid; Colloids; Nanoparticles; Metal; Metal oxides; Cobalt; Cobalt oxides
Surface and electrical-transport studies of Ag/Al bilayer-structures grown by molecular beam epitaxy by A.K. Debnath; Niraj Joshi; K.P. Muthe; J.C. Vyas; D.K. Aswal; S.K. Gupta; J.V. Yakhmi (pp. 220-227).
The Ag/Al bilayer-structures consisting of 10nm Al and 100nm Ag have been grown on (111) Si substrates using molecular beam epitaxy (MBE). The bilayer-structures were annealed in situ under a vacuum of 10−8Torr at different temperatures between 25 and 800°C for a fixed period of 30min and, characterized by in situ X-ray photoelectron spectroscopy (XPS) and ex situ X-ray diffraction (XRD), Atomic force microscopy (AFM) and four-probe dc electrical resistivity measurements. The XPS results revealed that the surface composition of bilayer-structures becomes systematically depleted in Ag and gets enriched in Al and oxygen with increasing annealing temperature. However, at 800°C the Si also appeared at the surface. The room temperature resistivity value exhibited an unusual dependence on annealing temperature, which is understood in terms of Al induced disorder in Ag. In addition, the temperature dependence of resistivity of bilayer-structures annealed at 500 and 800°C showed an anomalous metal-to-insulator transition and could be explained using a thermally activated polaron hopping mechanism.
Keywords: PACS; 81.15.Hi; 68.37.Ps; 61.10.Nz; 79.60.−i; 71.55.JvAg/Al bilayer-structures; Molecular beam epitaxy; XPS; AFM; Metal-to-insulator transition
Electron beam induced chemical modification of amorphous chalcogenide–metal bilayers and its application by R.K. Debnath; N. Nusbar; A.G. Fitzgerald (pp. 228-231).
Metal migration and surface modification have been observed in metal-doped amorphous arsenic and antimony-based chalcogenide systems such as As2Se3 and Sb2S3 under the irradiation of an electron beam. Surface expansion of the order of 5–35% of the film thickness has been observed by applying 5–30kV electron accelerating voltages. This electron beam induced surface modification has been employed to produce submicron and nanometre dimensional patterns which will have applications in single stage processing of X-ray masks fabricated on an X-ray transparent silicon nitride (Si3N4) membrane. Masks with a silver deficient trough-like structure have been obtained at lower accelerating voltages (5–10kV). Silver-rich protruding structures were obtained at higher accelerating voltages (15–30kV). These two types of masks exhibit a different X-ray absorption behaviour by comparison with the regions unexposed to the electron beam.
Keywords: PACS; 61.80.F; 85.40.HAmorphous materials; Atomic force microscopy; X-ray mask
High laser-induced damage threshold HfO2 films prepared by ion-assisted electron beam evaporation by Dawei Zhang; Shuhai Fan; Yuanan Zhao; Weidong Gao; Jianda Shao; Ruiying Fan; Yingjian Wang; Zhengxiu Fan (pp. 232-237).
HfO2 films were deposited by electron beam evaporation with different deposition parameters. The properties such as refractive index, weak absorption, and laser induced damage thresholds (LIDTs) of these films have been investigated. It was found that when pulsed Nd:YAG 1064nm laser is used to investigate LIDT of films: Metallic character is the main factor that influences LIDTs of films obtained from Hf starting material by ion-assisted reaction, and films prepared with higher momentum transfer parameter P have fewer metallic character; The ion-assisted reaction parameters are key points for preparing high LIDT films and if the parameters are chose properly, high LIDT films can be obtained.
Keywords: PACS; 77.55.+f; 81.15.−zHfO; 2; films; Laser-induced damage threshold; Ion-assisted reaction; Weak absorption
Grazing angle infrared microspectroscopy of micropatterned self-assembled monolayers by F. Bensebaa; P. L’Ecuyer; K. Faid; Ch. Py; T.J. Tague; R.S. Jackson (pp. 238-244).
We report for the first time an infrared spectrum of an alkanethiolate coated microsized metal pattern. Sub-femtomole detection limit of octadecanethiolate is demonstrated using grazing angle Fourier Transform Infrared (GA-FTIR) microspectroscopy. The conformational ordering and surface coverage of alkanethiolate self-assembled monolayer on micropatterned gold substrates obtained using two different approaches are analyzed. Conventional solution incubation of pre-patterned gold on a silicon wafer provides infrared features similar to those reported in the literature on macrosized gold substrate. Infrared spectra showed that microcontact printing gives raise to lower density alkanethiolate monolayer.
Keywords: PACS; 87.64.JEFTIR; Microscopy; Microcontact; Alkanethiol; Monolayer
Effect of heat-treatment temperature on the luminescent properties of Lu2O3:Eu film prepared by Pechini sol–gel method by Hai Guo; Min Yin; Ning Dong; Mei Xu; Liren Lou; Weiping Zhang (pp. 245-250).
Lutetium oxide (Lu2O3) films were prepared by a simple Pechini sol–gel method with LuCl3·6H2O as precursor for the first time. Thermogravimetric analysis and differential thermal analysis were used to study the thermal chemistry properties of dried gel. Structural properties of Lu2O3 films heat-treated at different temperature were investigated through X-ray diffraction and Fourier transform infrared spectroscopy. The results show that Lu2O3 starts to crystallize at about 400°C and the crystallite size increases with the increasing annealing temperature. The dopant Eu3+ presents its typical emission in Lu2O3:Eu films. The effect of heat-treatment temperature on the luminescent properties (broadening of emission peak and change of lifetimes of energy level) of the films was also discussed.
Keywords: PACS; 81.20.F; 78.66Sol–gel; Lutetium oxide (Lu; 2; O; 3; ); Luminescent property; Film
Deposition behaviour and morphology of Ni–SiC electro-composites under triangular waveform by F. Hu; K.C. Chan (pp. 251-258).
The deposition behaviour and morphology of Ni–SiC electro-composites were investigated under a triangular waveform. It was found that the grain size of the Ni–SiC composites decreased with increasing average current density, and the hardness of the composites increased with decreasing nickel matrix grain size. An equivalent circuit model based on the results of electrochemical impedance spectroscopy was formulated to simulate the charge transfer process under triangular waveform. Compared with deposits produced under the direct current, the triangular waveform with relaxation time provided a higher instantaneous peak current for charge transfer, which resulted in an improvement in morphology and hardness of the composites. The mathematical model was found to be in agreement with the experimental results.
Keywords: PACS; 81.15.pqElectrodeposition; Ni–SiC; Triangular waveform; Morphology; Equivalent circuit model
Interfacial reactions of electroless nickel thin films on silicon by C.M. Liu; W.L. Liu; S.H. Hsieh; T.K. Tsai; W.J. Chen (pp. 259-264).
Interfacial reactions of electroless nickel thin films on blank silicon annealed at 300–900°C have been studied by both cross-sectional and planview TEM as well as by sheet resistance measurement. Samples were prepared by depositing Ni on (001)Si substrate by electroless plating deposition followed by annealing to form a silicide. An amorphous interlayer was found in interface between electroless nickel thin films and silicon. The amorphous interlayer blocks the reaction between Ni and Si and change the silicide formation sequence. The epitaxial NiSi2 was found on electroless plating nickel thin films on silicon at the temperature as low as 300 and 400°C. The presence of phosphorus in the electroless Ni films and/or amorphous interlayer between electroless Ni films and Si were found to promote the formation of the epitaxial NiSi2 at low temperature. The dominant phase was NiSi in samples annealed at 500–700°C. The results have shown that NiSi film formed by electroless plating process has the same resistance property as the NiSi film formed by vacuum plating process. The electroless plating technique can provide a cheap and easy process for forming nickel silicide, and has potentiality of application for the electronic device industries.
Keywords: Electroless; Epitaxial; Silicide; Ni films
TEM and ellipsometry studies of nanolaminate oxide films prepared using atomic layer deposition by D.R.G. Mitchell; D.J. Attard; K.S. Finnie; G. Triani; C.J. Barbé; C. Depagne; J.R. Bartlett (pp. 265-277).
Nanolaminate oxide layers consisting of TiO2 and Al2O3 have been deposited on silicon using atomic layer deposition (ALD). Characterisation of these films has been achieved by use of a range of modern transmission electron microscopy (TEM)-based techniques, including plasmon loss imaging, energy filtered imaging and scanning TEM (STEM) X-ray line profiling. These have shown that the target thickness of the individual layers in the nanolaminate structures (20nm) has been met with a high degree of accuracy, that the layers are extremely flat and parallel and that the interfaces between the layers are compositionally abrupt. Localised crystallisation within the stacks, and responses to electron beam irradiation point to the presence of a stress gradient within the layers. The performance of ellipsometry in characterising multilayer stacks has been benchmarked against the TEM measurements. Errors in determination of individual layer thicknesses were found to increase with growing stack size, as expected given the increasing number of interfaces incorporated in each model. The most sophisticated model gave maximum deviations of ±4nm from the TEM determined values for the 5- and 10-layer stacks.
Keywords: PACS; 68.37.−d; 68.55.−a; 68.65.ac; 07.60.fsALD; Nanolaminates; TiO; 2; Al; 2; O; 3; Ellipsometry
Microstructure and wear properties of laser clad TiCo/Ti2Co intermetallic coatings on titanium alloy by Y. Xue; H.M. Wang (pp. 278-286).
Wear resistant TiCo/Ti2Co dual-phase intermetallic coatings were fabricated on a titanium alloy by laser cladding. Microstructure of the coatings consists of isolated irregular block-like TiCo primary phase in the Ti2Co matrix. The coatings have high hardness and excellent abrasive and adhesive wear resistance under dry sliding wear test conditions.
Keywords: Laser cladding; Intermetallics; Wear; Titanium alloy; Coating
Radiation and storage-induced ageing of polypyrrole doped with dodecylbenzene sulfonic acid by P. Kappen; N. Brack; P.S. Hale; W. Prissanaroon; E. Welter; P.J. Pigram (pp. 287-295).
The effects of storage and exposure to X-rays on the surface chemistry of electrochemically prepared polypyrrole (PPy) doped with dodecylbenzene sulfonic acid (DBSA) were investigated using X-ray photoelectron spectroscopy (XPS). For irradiation, different photon sources (lab source and synchrotron radiation) and energies (1.4–9keV) were chosen. This covers an energy range of relevance for many X-ray based investigations (e.g. XPS or X-ray absorption spectroscopy) of PPy[DBSA], PPy–metal interfaces, and transition metals embedded into PPy.The DBSA doping level and the concentration ratio of sulfonate species are discussed as a function of storage and irradiation times, and links between both ageing parameters are given. New sulfur species are found to emerge upon repeated soft X-ray irradiation. Severe changes in the polaron/bipolaron structure of PPy[DBSA] during exposure to high energy (several keV) synchrotron radiation are observed, and the results are discussed in the light of photon absorption and photoelectron generation in the polymer surface.
Keywords: PACS; 61.82.P (polymers – radiation effects); 79.60.F (polymers – photoemission and photoelectron spectra); 72.80.L (conducting polymers), 73.61.P. (conducting polymers)Polypyrrole; Ageing; X-rays; Damage; XPS; Synchrotron radiation
Interfacial studies for improving the adhesion of diamond-like carbon films on steel by Chun-Chin Chen; Franklin Chau-Nan Hong (pp. 296-303).
The adhesion of diamond-like carbon (DLC) films on steel is usually very poor. Adhesion of DLC on SKD11 steel was improved for tribological purposes in this study by applying chromium (Cr) metal intermediate layers using magnetron sputtering with substrate bias. DLC films were deposited by inductively coupled plasma (ICP) chemical vapor deposition. However, the adhesion was only at medium level. Intermixing at the Cr–steel interface was further achieved by ion bombardment and found to remarkably improve the adhesion. A reliable process was established to improve the adhesion to top level.
Keywords: PACS; 61.43.Er; 61.46.+w; 62.20.−x; 62.20.Qp; 62.40.+iDiamond-like carbon; Chromium; Intermixing layer; Adhesion
Effects of different laser and plasma treatments on the interface and adherence between evaporated aluminium and polyethylene terephthalate films: X-ray photoemission, and adhesion studies by H. Ardelean; S. Petit; P. Laurens; P. Marcus; F. Arefi-Khonsari (pp. 304-318).
Chemical functionalities, topography and adherence between Al and polyethylene terephthalate (PET) films, modified by laser treatment below the polymer ablation threshold fluence in air and in helium at different wavelengths, fluences, pulse numbers and by low pressure plasma treatment in He 95% with O2 5%, at 0.2W/cm3 were investigated by XPS, AFM, water contact angle and adhesion measurements. XPS results revealed (i) formation of polar-oxygenated functional groups (CO, OCO) by laser treatments in air and (ii) incorporation of ester and ether groups by plasma treatment in He 95% with O2 5%. After deposition of thermally evaporated Al on laser or plasma treated PET films, U-Peel tests indicated that laser treatment in air at 248nm and 20mJ/cm2, and plasma treatment improved Al/PET adhesion. XPS studies revealed the presence of an increasing number of AlOC stable and cohesive interfacial complexes formed by chemical interaction between aluminium and the laser treated in air or plasma treated in He 95% with O2 5% PET films. These interfacial compounds play an important role in the enhancement of the metal/polymer adhesion.
Keywords: Polyethylene terephthalate; Aluminium; Laser treatment; Plasma treatment; Metal/polymer adhesion
Surfactant-controlled synthesis of Pd/Ce0.6Zr0.4O2 catalyst for NO reduction by CO with excess oxygen by L.F. Chen; G. González; J.A. Wang; L.E. Noreña; A. Toledo; S. Castillo; M. Morán-Pineda (pp. 319-328).
For the first time, this work reports a surfactant-controlled synthetic method to obtain a nanophase of mesoporous ceria–zirconia solid solution containing cationic defects in the crystalline structure. The incorporation of a cationic surfactant (myristyltrimethylammonium bromide) into the ceria–zirconia solid network not only controlled the pore diameter distribution but also induced creation of the lattice defect. Ceria–zirconia solid solution showed crystal microstrain and structural distortion that varied with the calcination temperature. Compared to pure ceria, the addition of zirconium to the ceria promoted the bulk oxygen reducibility and enhanced the thermal stability of the solid. Hydrogen could be stored into or released from the PdO/Ce0.6Zr0.4O2 catalyst during the TPR procedure, which is associated to the formation/decomposition of a PdH x phase, due to the hydrogen dissociation catalyzed by metallic Pd. At cool start of reaction, NO reduction by CO with excess oxygen over the Pd/Ce0.6Zr0.4O2 catalyst showed selectivity around 100% to N2. A competition between NO reduction by CO and CO oxidation by O2 was observed: at reaction temperatures below 200°C, NO inhibited CO oxidation activity; however, at reaction temperatures above 200°C, high activity of CO oxidation resulted in an inhibition effect on NO reduction.
Keywords: NO reduction; CO oxidation; Three-way catalyst; Ceria–zirconia; Surfactant-controlled synthesis
Percolation characters of sputtered and vaporized semi-continuous silver island films by Qu-Quan Wang; Jun-Bo Hun; Sha Ding; Gui-Guang Xiong; De-Cheng Tian (pp. 329-334).
A series of discontinuous and semi-continuous silver island films were prepared with sputtering technique and vaporizing method, respectively. The plasmon resonance absorption in visible region, critical percolation infrared transmittance and the fractal dimension of two types of samples were investigated. Only discontinuous vaporized Ag films show resonant plasmon absorption. For sputtered samples, both discontinuous and semi-continuous films show plasmon absorption in visible region. The value of fractal dimension, critical exponent and critical percolation infrared transmittance ( Df, ν, Tc) are measured to be (1.56, 1.26, 60%) for sputtered Ag films and (1.60, 1.14, 15%) for vaporized samples.
Keywords: Sputtering; Thin films; Optical properties
Synchrotron radiation photoemission study of indium oxide surface prepared by spray pyrolysis method by V. Brinzari; G. Korotcenkov; V. Matolin (pp. 335-344).
In2O3 thin films with preferred (400) orientation prepared by the spray pyrolysis method were studied by synchrotron radiation photoemission and ion scattering spectroscopes. O 1s, O 2s, In 4d core level and valence band spectra were monitored at photon energies 660, 245, 150, and 73eV to see their evolution with UHV treatments (heating, sputtering and exposure of oxygen). Reduction of the surface layer to nearly metallic indium was found with thermal treatment at T≥300°C. This surface demonstrates high reactivity to reversible oxidation/reduction processes. This was evidenced by evolution of the O 2s core level peak and of the band gap emission intensity. In spite of such surface reduction it was found that within a probing depth of ≤10Å the material displays spectral features characteristic of stoichiometric In2O3. We tentatively explain such behavior in terms of the In2O3 crystallographic structure and some conclusions relating to gas-sensing properties were made.
Keywords: In; 2; O; 3; Thin film; Synchrotron radiation photoemission spectroscopy; In; 2; O; 3; core level and valence band spectra
Influence of the growth-surface on the incorporation of phosphorus in SiC by E. Rauls; U. Gerstmann; Th. Frauenheim (pp. 345-354).
Phosphorus is a common and desired n-type dopant of SiC, but it turned out that doping by diffusion or during growth is rarely successful. To avoid the efforts and the creation of damage if ion implantation is used instead, these techniques were, though, highly desirable. In this work, we have investigated theoretically the experimental observation that phosphorus obviously hardly diffuses into the material. Not the diffusivity of the dopant but its addiction to occupy a three-fold coordinated surface site are critical, together with the way the surface affects the bulk migration barriers of the dopants. Whereas the most common growth direction for 4H-SiC, the polar silicon terminated (0001) surface, seems to be least appropriate for the incorporation of phosphorus atoms, growth along the nonpolar [112¯0] provides a good possibility to achieve efficient P-doping during growth.
Keywords: SiC; Growth; Phosphorus; Surface; Diffusion
Enhancement of electroplex emission by using multi-layer device structure by Yuan-Min Wang; Feng Teng; Zheng Xu; Yan-Bing Hou; Yong-Sheng Wang; Xu-Rong Xu (pp. 355-359).
Electroplex emission based on poly( N-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been improved dramatically by using a multi-layer device structure indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulphonic acid) (PEDOT:PSS)/PVK/BCP/PVK/BCP/LiF/Al. Electroplex emission at 595nm has been improved about 10 times under low voltage and four times under high voltage compared to the double layer device ITO/PVK/BCP/Al. The maximum brightness of the device also has been improved about eight times. Bright white emission via electroplex formation can be obtained with Commission International d’Eclairage (CIE) coordinates (0.336, 0.320) at 26V with a brightness of 123cd/m2. Based on the analysis of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the materials, we suggest the enhancement is mainly ascribed to the confinement effect of the quantum-well-like multi-layer device structure. Every hole and electron has more possibilities to cross recombination at the PVK/BCP interface.
Keywords: Electroplex; White emission; Multi-layer device structure
Reducibility of Co3+ in perovskite-type LaCoO3 and promotion of copper on the reduction of Co3+ in perovskite-type oxides by Lin Huang; Mahbod Bassir; Serge Kaliaguine (pp. 360-375).
The reducibility of Co3+ in LaCoO3 and the promotion of copper on the reduction of Co3+ in perovskite-type oxides have been studied by temperature programmed reduction (TPR), temperature programmed oxidation (TPO), X-ray diffraction (XRD) and infrared spectroscopy (IR). Quantitative TPR and TPO analyses propose that the reduction of Co3+ in LaCoO3 to Co0 belongs to a one-step process and that every TPR peak represents the reduction of every Co3+ species to Co0 in the crystallite structure. Accordingly, the produced Co0 is assumed to be atomically located in the perovskite lattice provided the perovskite structure is retained after reduction. Quantitative TPR analyses also indicates that copper located in LaCo0.85Cu0.15O3 promotes regularly the reduction of various Co3+ species whereas copper doped on LaCoO3 does irregularly. The action of the latter leads to more efficient reduction of Co3+ to atomically dispersed Co0 over a useful temperature range for catalytic purposes. TPR, XRD and IR studies show that the perovskite structure of LaCo0.85Cu0.15O3 is somewhat less stable than that of LaCoO3 and that the perovskite structural stability of LaCoO3 is not weakened by the doping of copper.
Keywords: LaCoO; 3; LaCo; 0.85; Cu; 0.15; O; 3; Copper; Perovskite; Reduction; Co; 3+; Co; 0
Structural modifications of carbon–carbon composites under high temperature and ion irradiation by T. Paulmier; M. Balat-Pichelin; D. Le Quéau (pp. 376-393).
Carbon–carbon composites are the most interesting materials for the conception of the thermal shield of the solar probe space mission designed to study the solar wind and solar corona. The physico-chemical behavior and the structural modifications of some carbon–carbon composites at high temperature and under proton irradiation have been studied using SEM, XRD and Raman spectroscopy. The characterization of the as-received carbon–carbon composites show that the processing routes and the fiber preform have a strong influence on the microstructure of the composites: the fibrous preform 2.5D, the liquid consolidation and a final heat treatment allows to enhance drastically the graphitization degree of the carbon matrix and the fibers and the size of the crystallites. The high temperatures induce especially a decrease of the open porosity due to an amorphous carbon deposit at the surface of the material. This evolution has been observed mainly for the 2.5D structure. The high temperatures come to an evolution of the microstructure with a better crystallinity, an increase of the size and orientation of the crystallites of the fibers and matrix. The 2D structure presents, however, an increase of the disorder with the temperature.Finally, the hydrogen irradiation has only a very weak influence on the inner and surface degradation of the carbon–carbon composites.
Keywords: PACS; 81.05.Uw; 81.40.Gh; 81.40.WxCarbon–carbon composites; Heat treatment; Ion irradiation; Scanning electronic microscopy; X-ray diffraction; Microstructure; Radiation damage
Influence of thickness on field emission characteristics of AlN thin films by Y.X. Wang; Y.A. Li; W. Feng; W.Q. Li; C.H. Zhao; L.H. Liu; K.C. Feng; Y.N. Zhao (pp. 394-400).
Aluminum nitride (AlN) thin films with various thicknesses (20–150nm) are prepared on substrate Si(100) by radio-frequency (rf) magnetic reactive sputtering in an Ar–N2 gas mixture. The field emission characteristics of the AlN thin films are measured in an ultra-high vacuum system. They depend evidently on the thicknesses. There is an optimum film thickness for the best field emission characteristics of AlN thin films. A turn-on electric field of 10V/μm and the highest emission current density of 284μA/cm2 at an electric field of 35V/μm are obtained for the about 44-nm-thick AlN film. The Fowler–Nordheim plots show that electrons are emitted from AlN to vacuum by tunneling through the potential barrier at the surface of AlN thin films.
Keywords: PACS; 79.70.+q; 68.55.JKAluminum nitride; Thin films; Field emission; Current emission; Turn-on electric field
Annealing and deposition effects of the chemical composition of silicon-rich nitride by K.N. Andersen; W.E. Svendsen; T. Stimpel-Lindner; T. Sulima; H. Baumgärtner (pp. 401-408).
Silicon-rich nitride, deposited by LPCVD, is a low stress amorphous material with a high refractive index. After deposition the silicon-rich nitride thin film is annealed at temperatures above 1100°C to break NH bonds, which have absorption peaks in the wavelength band important for optical telecommunication. However, silicon clustering appears in the thin films when annealing above 1150°C. Clustering is undesirable in waveguide materials because the localized variations of the refractive index associated with the clusters lead to Raleigh scattering, which can cause significant propagation loss in optical waveguides. This means that the annealing temperature must be high enough to break the NH bonds, but no so high as to produce clusters. Therefore, the process window for an annealing step lies between 1100 and 1150°C.The chemical composition of amorphous silicon-rich nitride has been investigated by Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS). The influence of deposition parameters and annealing temperatures on the stoichiometry and the chemical bonds will be discussed. The origin of the clusters has been found to be silicon due to severe silicon out-diffusion from the substrate during annealing at temperatures above 1100°C.
Keywords: Silicon rich nitride; LPCVD; X-ray photoelectron spectroscopy (XPS); Stoichiometry; Si diffusion; Annealing
Nitrogen ion implantation on stainless steel: AFM study of surface modification by B. Chico; L. Martinez; F.J. Pérez (pp. 409-414).
This work presents a study by means of atomic force microscopy (AFM) of the modification of the surface topography of AISI 304 austenitic stainless steel after N-ion implantation, irradiated by 1×1015 N2+/cm2 at 80keV. Prior to the implantation surface modification, the samples were electropolished for the optimum observation of the surface at a small scale to obtain an initial surface with the smaller roughness. The electrolytic bath was composed of a mixture of water/sulphuric acid/orthophosphoric acid in percentages 20, 20 and 60%, respectively. Once the surface was optimized, the samples were implanted and observed by AFM, a new technique whose importance relies on its resolution power, allowing the acquisition of topographic images of the surface with nanometric resolution. Thanks to the high resolution power could be observed that ion implantation increases the surface roughness and promotes the apparition of 3μm wide and 10nm depth craters as well as the apparition of products with singular morphology.
Keywords: PACS; 61.16.C; 68.55.LIon implantation; Electropolishing; AISI 304 SS; AFM; Roughness
Precise etching of fused silica for micro-optical applications by K. Zimmer; R. Böhme (pp. 415-420).
The current challenge of laser processing is the high quality etching of transparent materials for micro-optical applications. Laser ablation of transparent material with UV and ultrashort pulse lasers is characterized by a high etch rate and a considerable surface roughness. The combination of specific laser processing techniques, e.g., scanning contour mask technique and direct writing with a small laser spot, with laser-induced backside wet etching (LIBWE) allows both the direct machining of diffractive as well as refractive topographies into dielectric materials with almost optical quality. The etching of variable depth gratings and free-form surface topographies with a PV-value of less than 500nm, a nanometer depth resolution, and a low roughness of less than 10nmrms is presented and demonstrates the capabilities of this laser processing approach.
Keywords: PACS; 81.65.C; 81.05.J; 79.20.D; 61.80.B; 42.62.C; 42.55.LExcimer laser; Laser etching; Fused silica; Solid–liquid interface
The study of the effect of Ba coverage through the accelerations lifetime of activated BaO/SrO cathodes by A.A. Hashim; A.K. Ray; A.K. Hassan; D.S. Barratt (pp. 421-428).
A novel type of BaO/SrO oxide cathode with 5% addition of Ni powder by weight on a Ni cap containing an activating impurity was studied.The conductivity and the electron activation energy were studied as a function of temperature in the range of 300–1200K after conversion and activation of the cathode at 1200K for 1h. The experimental results yield three values for the activation energy of 1.49, 2.23 and 3.3eV, which are close to BaO band structure parameters with a small shift due to the effect of other oxide components and metallic fraction additions.The experiments furthermore confirm that the current density of the cathode was enhanced at high temperature range with the long operation. The conduction mechanisms observed a metallic conduction at low temperature after operation for several 100h due to improvements in the Ba coverage layer on the grains of oxide layer.Additionally, there appears a qualified conduction stability of the current density J=10–45mAcm−2 at the acceleration temperature range of 1100–1150K under the duty of low voltage. The low voltage duty V=30mV is focused on the conduction electrons faraway from the emission electrons.
Keywords: Oxide cathode; Ba and Sr oxides; Electron emission; Electrical properties
Effect of boron paste thickness on the growth kinetics of Fe2B boride layers during the boriding process by I. Campos; O. Bautista; G. Ramírez; M. Islas; J. De La Parra; L. Zúñiga (pp. 429-436).
Through this work we study the influence of the thickness of boron paste in the growth of Fe2B boride layer during the paste boriding thermochemical treatment applied on AISI 1045 steel. Different thickness of boron paste over the material surface with constant temperature and time show the variability of the diffusion coefficient of boron in Fe2B phase depending, basically, on the boron potential at the external surface of the substrate. The mobility of boron in the formed phase is determined by the balance mass equation that considers the concentration profiles in the corresponding interphases layer–substrate, the thermodynamic equilibrium in the growth of the iron boride layer and the experimental results obtained during the process.
Keywords: Boron potential; Kinetics; Boriding; Diffusion coefficient
Annealing characteristics of the vanadium oxide films prepared by modified ion beam enhanced deposition by Jinhua Li; Ningyi Yuan; Jiansheng Xie (pp. 437-442).
Different annealing conditions were adopted to anneal the vanadium oxide films prepared by modified ion beam enhanced deposition (IBED) method. An X-ray diffraction (XRD) was used to analyze the orientation of the IBED films and the resistance was tested with temperature change to measure the temperature coefficient of resistance (TCR). Experiments indicated that there existed a critical temperature for crystallization of VO2, which changed with the different deposition conditions of the IBED method. It is very difficult to obtain VO2 structure if the annealing temperature was lower than the critical temperature. If the temperature is much higher than the critical temperature or annealing time is too long, the valence of vanadium in VO2 film will easily reduce from four to low value. The TCR of the IBED VO2 polycrystalline films annealed in appropriate condition could reach higher than 4%/K.
Keywords: Vanadium oxide films; Annealing; Ion beam enhanced deposition