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Applied Surface Science (v.242, #3-4)
Monte Carlo simulations of electron transport in solids: applications to electron backscattering from surfaces by A. Jablonski; C.J. Powell (pp. 220-235).
We report results of Monte Carlo simulations to investigate the effects of backscattered electrons in scanning Auger microscopy (SAM) on the radial distributions of emitted Auger electrons. We considered the emission of copper M3VV and L3VV Auger electrons from a thin Cu overlayer on a substrate of silicon or gold for primary electrons with energies of 5 and 10keV that were normally incident on the sample. The Cu layer was assumed to be sufficiently thin that there were no changes in the angular and energy distributions of primary and backscattered electrons passing through the overlayer. We report values of the information radius,raP, from which a selected percentage P of the emitted Auger electron intensity originates. Values ofraP found here range from 119Å (Cu L3M45M45 Auger transition, E0 = 5keV, Au substrate, P = 80) to 6757Å (Cu M3VV Auger transition, E0 = 10keV, Si substrate, P = 95). For the same substrate, primary energy, and chosen value of P, values ofraP are larger for Auger electrons from the Cu M3VV Auger transition than for the Cu L3M45M45 Auger transition. In addition, values ofraP increase with primary energy and are larger for the Si substrate than the Au substrate. The values ofraP are generally much larger than the radius of the primary beam (assumed to be 50Å here) on account of inner-shell ionizations by backscattered electrons. We also report values of the mean escape radius, 〈 r〉, that range from 82.5Å (Cu L3M45M45 Auger transition, E0 = 5keV, Au substrate) to 1169Å (Cu M3VV Auger transition, E0 = 10keV, Si substrate). Knowledge ofraP and 〈 r〉 is important in the analysis of fine features in SAM because appreciable Auger signal can be collected from the nearby region as well as from the feature of interest. Finally, we report Monte Carlo simulations of Auger line scans across the edge of a thin Cu overlayer on a Si or Au substrate. The shapes of the line scans depended only weakly on the Cu Auger transition, although the differences were more pronounced for the Si than the Au substrate. On account of backscattered electrons, the lateral distance corresponding to signal variations of 25% and 75% of the maximum intensity in a line scan varied from 53.6Å (Cu L3M45M45 transition, E0 = 5keV, Si substrate) to 75.1Å (Cu M3VV transition, E0 = 10keV, Au substrate).
Keywords: PACS; 11.80.La; 34.80.−i; 72.10.−dAuger electron spectroscopy; Electron–solid interactions; Monte Carlo simulations; Copper; Gold; Silicon
Structural evolution in films of alloy Zn70Al27Cu3 (ZA27) by Y.H. Zhu; W.B. Lee; Z. Mei; S. To; Y.K. Sze (pp. 236-244).
Films of alloy ZA27 were produced using electron deposition technique. Structural evolution and phase decomposition of the films were studied. It was found that the alloy films were relatively stable because of a strong preferred crystal orientation of the nano-phases. The dependence of nano-phase stability on the Zn content and the preferred crystal orientation is discussed from point of view of Gibbs free energy.
Keywords: Structural evolution; Nano-phase stability; Ageing; Zn–Al alloy films
AFM surface imaging of AISI D2 tool steel machined by the EDM process by Y.H. Guu (pp. 245-250).
The surface morphology, surface roughness and micro-crack of AISI D2 tool steel machined by the electrical discharge machining (EDM) process were analyzed by means of the atomic force microscopy (AFM) technique. Experimental results indicate that the surface texture after EDM is determined by the discharge energy during processing. An excellent machined finish can be obtained by setting the machine parameters at a low pulse energy. The surface roughness and the depth of the micro-cracks were proportional to the power input. Furthermore, the AFM application yielded information about the depth of the micro-cracks is particularly important in the post treatment of AISI D2 tool steel machined by EDM.
Keywords: Atomic force microscopy (AFM); Electrical discharge machining (EDM); Surface morphology; Micro-crack; Surface roughness
Influence of nanoscale topography on the hydrophobicity of fluoro-based polymer thin films by Y.B. Gerbig; A.R. Phani; H. Haefke (pp. 251-255).
In this report, the influence of surface features in the nanoscale range on the hydrophobicity of fluoro-based polymer thin films was studied. For this purpose, poly[4,5 difluoro 2,2-bis (trifluoromethyl)-(1,3 dioxole)-co-tetrafluoroethylene] was deposited by sol-gel spin coating technique on sputtered Cr–N interlayers with different surface structures. The wettability of the fluoro-based polymer thin film on the Cr–N interlayers was determined by dynamic contact angle measurements. It could be proved that structural changes in the nanometer range influences the contact angles and their hysteresis of low-surface energy materials. By applying fluoro-based polymer thin films on a nearly flat Si(100) wafer and a cone-like Cr–N structure with a certain roughness, the advancing contact angle for water on fluoro-based polymer thin film increased from 120° to 148° on the rough Cr–N interlayer.
Keywords: PACS; 81.15.Cd; 81.20.Fw; 81.65.YaHydrophobicity; Surface structure; Fluoro-based polymer thin films
Defect-related photoluminescence of silicon nanoparticles produced by pulsed ion-beam ablation in vacuum by X.P. Zhu; Tomiyuki Yukawa; Makoto Hirai; Tsuneo Suzuki; Hisayuki Suematsu; Weihua Jiang; Kiyoshi Yatsui (pp. 256-260).
Visible light emission has been observed from Si nanoparticles produced using an intense pulsed ion-beam evaporation (IBE) technique in vacuum. The as-prepared Si nanoparticles possess good crystallinity without any post-annealing. Room-temperature photoluminescence (PL) spectra for the Si nanoparticles were registered in blue–green range. The average crystal size (around 20nm) estimated from glancing angle X-ray diffraction (GAXRD) was relatively large, inconsistent with quantum size effect for the light emission. The Si nanoparticles was exposed to O2 gas at elevated temperature and hydrofluoric acid (HF) vapor at room temperature for examining the PL source, where significant deterioration of PL intensity was found subsequently. Combined with analyses of X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), the PL is attributable to oxide defects of the samples.
Keywords: PACS; 61.46.+w; 78.66.−w; 78.55.−m; 81.15.−zSi nanoparticle; Photoluminescence; Pulsed ion-beam evaporation; Ablation plasma
Structure and properties of diamond-like carbon nanocomposite films containing copper nanoparticles by Chun-Chin Chen; Franklin Chau-Nan Hong (pp. 261-269).
Diamond-like carbon (DLC) nanocomposite films, containing copper (Cu) nanocrystallites, were synthesized and studied. Cu bonds very weakly with carbon, and does not form a carbide phase. Therefore, Cu nanoparticles can be easily formed in a DLC matrix by depositing Cu and carbon together. The mechanical properties of DLC films that contain Cu nanoparticles are interesting since the film toughness may be increased by grain–matrix interface sliding. Hard, tough and stress-free DLC/Cu films were prepared by a sputtering Cu target in an argon/acetylene atmosphere while biasing the substrate with a radio frequency power supply. The residual stress of the film, calculated by Stoney's equation, was as low as 0.7GPa. The reduced stress and the increased film toughness increased the critical load from 66N for a conventional DLC film to 80N for the DLC/Cu film, as measured in a scratch test. However, the DLC/Cu films were slightly less hard than the DLC films.
Keywords: PACS; 61.43.Er; 61.46.+w; 62.20.−x; 62.20.Qp; 62.40.+iDiamond-like carbon (DLC); Nanocomposite film; Copper; Nanoparticles; Mechanical properties
Initial adsorption and C-incorporation of organosilanes at Si(001) investigated by temperature-programmed desorption by K. Senthil; M. Suemitsu (pp. 270-275).
Temperature-programmed desorption (TPD) has been used to study the initial adsorption and C-incorporation of organosilanes [monomethylsilane (MMS), dimethylsilane (DMS) and trimethylsilane (TMS)] at Si(001) surfaces. Hydrogen was the only desorbing species observed in the TPD spectra from organosilanes. Organosilane molecules adsorb dissociatively on the Si(001) surfaces at room temperature. TPD spectra from DMS- and TMS-adsorbed Si surfaces present carbon-related hydrogen (H2) desorption peaks from the initial adsorption. The carbon-incorporation ratio was found to be larger in the order of TMS > DMS > MMS, with the sticking probability of molecules being almost identical for the three organosilane molecules.
Keywords: PACS; 68.47.Fg; 68.43.Vx; 68.43.MnSi(0; 0; 1) surface; Organosilanes; Carbon incorporation; Thermal desorption
Synchrotron radiation stimulated etching SiO2 thin films with a contact cobalt mask by Changshun Wang; Tsuneo Urisu (pp. 276-280).
Patterning SiO2 thin film on the Si (100) surface was demonstrated by synchrotron radiation (SR) stimulated etching with a contact cobalt mask. The reaction gas was a mixture of SF6 and O2. The contact cobalt mask was fabricated by sputtering cobalt films on a photolithography resist pattern and lift-off technique. The thickness of the mask was about 145nm. The SR irradiation with flowing SF6 and O2 could effectively etch the silicon dioxide and the etching process stopped at the SiO2/Si interface. The etching rate at room temperature was about 2.7nm per 100mAmin. The etched pattern was evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profile meter. Area-selective and anisotropy etching were achieved and the roughness ( Ra) with a line profile on the etched surface was about 0.05nm.
Keywords: PACS; 81.65.Cf; 87.80.Mj; 82.50.KxSynchrotron radiation stimulated etching; SiO; 2; thin films; Cobalt masks
Preparation of silica encapsulated CdSe quantum dots in aqueous solution with the improved optical properties by Xingping Zhou; Yoshio Kobayashi; Volodya Romanyuk; Noriaki Ochuchi; Motohiro Takeda; Shin Tsunekawa; Atsuo Kasuya (pp. 281-286).
Silica encapsulated CdSe quantum dots (QDs) have been prepared by the use of 3-mercaptopropyl trimethoxysilane (MPS) in a weak alkaline solution in ambient atmosphere at room temperature. The average size of the multicore-shell structured CdSe/SiO2 is 28.0nm and that of the CdSe QDs is 3.4nm from the observation of the transmission electron micrographs (TEMs). The enhanced photoluminescence (PL) intensity of the QDs has been observed by passivation of silica shell. The increased photo-chemical and -physical stability of the encapsulated CdSe/SiO2 QDs has also been demonstrated.
Keywords: PACS; 8.20.n; 72.80.Tm; 74.25.GzEncapsulation; CdSe; Quantum dots; SiO; 2; Passivation; Photoluminescence (PL); Stability
Tribological behavior of self-assembled double layer measured by a pin-on-plate method by Miki Nakano; Takao Ishida; Toshimitsu Numata; Yasuhisa Ando; Shinya Sasaki (pp. 287-294).
We investigated the frictional properties and the durability of self-assembled double layers using pin-on-plate methods and X-ray photoelectron spectroscopy (XPS). We found that double layers made from octadecanethiol (ODT) and mercaptohexadecanoic acid (MHA) connected via Cu ions exhibited lower frictional coefficients (approximately 0.1–0.15) than that of ODT monolayer (∼0.2). XPS measurements revealed that ratios of C(1s)/Au(4f) after friction tests were lower than that before friction but was higher than that measured on ODT monolayer, suggesting that some of ODT molecules were desorbed from the surface, i.e. formation of loosely packing molecular layers after friction. These findings suggest that the loosely packed molecular layer contributed to decrease the friction.
Keywords: PACS; PACS: 81.40.PqMultilayer; Frictional properties; Pin-on-plate methods; XPS
Direct growth of CdTe(100) epilayers on Si(100) substrate by hot wall epitaxy by Georgi M. Lalev; Jifeng Wang; Jae-Won Lim; Seishi Abe; Katashi Masumoto; Minoru Isshiki (pp. 295-303).
Strong preferential (100) orientation is observed for the first time in the CdTe thin films directly grown on Si(100) substrates without any buffer layers. This result is attributed to the fact that the epilayer is grown directly on the hydrogen-terminated Si substrate without any preheating treatment. The crystal qualities of CdTe(100)/Si(100) and CdTe(111)/Si(111) epilayers obtained at the same growth conditions were compared. Atomic force microscopy observations reveal different surface morphology at the early stages of the crystal growth for CdTe(111)/Si(111) and CdTe(100)/Si(100) epilayers, implying that they are governed by different growth mechanisms. The nucleation of CdTe(100)/Si(100) starts with 3D islands having a dome shape. It is demonstrated that the height and diameter distributions narrow and the aspect ratio decreases with decreasing the growth time. The crystallinity of CdTe(100)/Si(100) epilayers is inferior to that of CdTe(111)/Si(111) due to a double-domain structure.
Keywords: PACS; 81.15; 81.10; 78.EtHot wall epitaxy; Semiconducting II–VI materials
Investigation of lattice defects in the early stage of fatigue in iron by positron annihilation techniques by F. Hori; K. Koike; R. Oshima (pp. 304-312).
Positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques have been performed to identify defects, such as vacancy clusters and dislocations, and to study their distributions on the sample in the early stage of fatigue cycle (0–10% of cycles to failure) in pure Fe. From two-lifetime component analysis, the component of the longer lifetime of about 130ps, corresponding to a mono-vacancy on edge dislocation, has been observed from 0.01% Nf fatigue. However, the long lifetime component of about 200ps appears in 10% Nf fatigue at a certain position of the sample. Vacancy clusters have possibly been formed to some extent at this fatigue life. The results suggest that the generation of micro-cracks during fatigue test is related to the formation of three-dimensional vacancy clusters.
Keywords: PACS; 61.72.FJ; 78.70.BPositron annihilation; Iron; Vacancy; Dislocation; Fatigue
Electrical and reliability characteristics of HfO2 gate dielectric treated in N2 and NH3 plasma atmosphere by Jeon-Ho Kim; Kyu-Jeong Choi; Soon-Gil Yoon (pp. 313-317).
As-grown HfO2 films by plasma-enhanced chemical vapor deposition (PECVD) were treated by N2 and NH3 plasma at 70W and 300°C. The films treated by either N2 or NH3 plasma were crystallized at annealing temperature above 800°C, resulting in 200°C higher crystallization temperature than that of HfO2 films without plasma treatment. The capacitors treated at the bottom side of HfO2 by NH3 plasma exhibited the lowest leakage current density, but the highest interface trap density. The capacitors treated at the bottom side of HfO2 by N2 plasma showed a comparable leakage current density to samples treated by NH3 plasma and the lowest interface trap density. The N2 plasma-treatment instead of NH3 is a suitable method to improve the reliable characteristics of HfO2 gate dielectric.
Keywords: Electrical and reliability characteristics; HfO; 2; gate dielectric; Plasma-enhanced chemical vapor deposition
X-ray photoelectron spectroscopy study on Ba1− xEu xTiO3 by Da-Yong Lu; Mikio Sugano; Xiu-Yun Sun; Wen-Hui Su (pp. 318-325).
X-ray photoelectron spectroscopy is employed to study inner-shell core-level binding energies Eu 4d, Ti 2p and O 1s, Ba 3d for new single-phase Ba1− xEu xTiO3 (0.1 ≤ x ≤ 0.4) samples prepared by solid state reaction at 4.0GPa and 1090°C. The peak positions of binding energies determined by linear background subtraction and Gaussian fit are presented. XPS analysis indicates that the mixed-valent Eu3+/Eu2+ ions at A-site and Ti4+/Ti3+ ions at B-site coexisted in the Ba1− xEu xTiO3 powder surface, and the amount of Eu2+ ions is equal to Eu3+ ions.
Keywords: PACS; 79.60; 74.25; 74.62X-ray photoelectron spectroscopy; Ba; 1−; x; Eu; x; TiO; 3; Mixed-valence
Microstructure and tribological properties of electrodeposited Ni–Co alloy deposits by Liping Wang; Yan Gao; Qunji Xue; Huiwen Liu; Tao Xu (pp. 326-332).
Ni–Co alloys with different compositions and microstructures were produced by electrodeposition. The effects of Co content on the composition, surface morphology, phase structure, hardness and tribological properties of Ni–Co alloys were investigated systemically. Results showed that the morphology and grain size of alloys are mainly influenced by the Co content and the phase structure of Ni–Co alloys gradually changed from fcc into hcp structure with the increase of Co content. The hardness of Ni–Co alloys with a maximum around 49wt.% Co followed the Hall–Petch effect. It was found that the improvement of wear resistance of Ni-rich alloys with hardness increase fits Archard's law. In addition, the Co-rich alloys exhibited much lower friction coefficient and higher wear resistance when compared with Ni-rich alloys. It has been concluded that hcp crystal structure in Co-rich alloys contributed to the remarkable friction–reduction effect and better anti-wear performance under the dry sliding wear conditions.
Keywords: Ni–Co alloy; Electrodeposition; Structure; Tribological properties
Analysis of porous oxide film growth on aluminum in phosphoric acid using re-anodizing technique by I. Vrublevsky; V. Parkoun; J. Schreckenbach (pp. 333-338).
The effects of the anodizing voltage on the porous alumina film formation on Al foil in 4% phosphoric acid at 20°C have been studied. The barrier layer thickness of porous films was determined by a re-anodizing technique. A digital voltmeter with a computer system was used to record the change in the anode potential with re-anodizing time. It was established that the change in the porous film growth mechanism occurred at 38V in phosphoric acid. We explained this phenomenon by the surface charge of anodic oxide film and its dependence on the anodizing voltage in the electrolyte. It was shown that the surface charge of oxide film during anodizing in phosphoric acid to 38V was negative. The charge was equal to zero at 38V. Above 38V, the surface of oxide film had a positive charge and this charge increased with the anodizing voltage.
Keywords: Aluminum; Porous alumina; Electrical double layer; Injecting junction; Surface charge; Re-anodizing
Wettability of porous polydimethylsiloxane surface: morphology study by M.T. Khorasani; H. Mirzadeh; Z. Kermani (pp. 339-345).
Two methods used for producing porous polydimethylsiloxane (PDMS) surfaces. In the first method, PDMS films without photosensitizer was exposed to CO2-pulsed laser at room temperature, as the excitation source. In the second method applying NaCl solid particles to the external surface layer before it is cured. In this study the morphology, wettability and surface chemical characteristics have been investigated. These surfaces have been studied by performing scanning electron microscopy (SEM) and attenuated total reflectance infrared (ATR-FTIR) spectroscopy. To evaluate the surface wettability, the water drop contact angle was measured. SEM photomicrographs and ATR-FTIR spectra and water drop contact angle measurement show that the morphology of these surfaces change to a uniform porous surface and wettability decreased. Results indicated that the porosity and morphology are important factor in wettability of PDMS surface and laser irradiation cause ordering in molecular chains onto the PDMS surface and this surface is a superhydrophobic compared to the virgin PDMS surface.
Keywords: PDMS; Porosity; Chain ordering; Hydrophobic; Laser treatment
Influence of different post-treatments on the structure and optical properties of zinc oxide thin films by Ruijin Hong; Jianbing Huang; Hongbo He; Zhengxiu Fan; Jianda Shao (pp. 346-352).
Zinc oxide (ZnO) films with c-oriented were grown on fused quartz glass substrates at room temperature using dc reactive magnetron sputtering. The as-grown films were annealed at 700°C in air and bombarded by ion beam, respectively. The effects of post-treatments on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. The XRD spectra indicate that the crystal quality of ZnO films has been improved by both the post-treatments. Compared with the as-grown sample, both annealed and bombarded samples exhibited blueshift in the UV emission peaks, and a strong green emission was found in the annealed ZnO film. In both optical transmittance and absorption spectra, a blueshift of the band-gap edge was observed in the bombarded film, while a redshift was observed in the annealed film.
Keywords: PACS; 78.66.Db; 71.20.Mq; 78.55.ApZinc oxide; Thin films; Annealing; Ion beam bombardment
Water formation on Pt(111) surfaces at high temperatures studied by kinetic Monte Carlo simulations by Rui Hu; Shiping Huang; Zhiping Liu; Wenchuan Wang (pp. 353-361).
By introducing finite diffusion of absorbed hydrogen atoms, adsorption, desorption and reaction patterns in H2O formation on the Pt(111) surface were simulated with the kinetic Monte Carlo (KMC) method. The results of the finite diffusion model proposed, show clearly the variation of OH desorption, which has not been observed in both the infinite diffusion model and the mean field theory. The simulation results indicate that diffusion of hydrogen atoms on the surface is essential for the reaction pattern, as the total coverage is low, and OH desorption occurs above 900K at the value of the partial pressure ratio between hydrogen and oxygen molecules,α=PH2/PO, about 0.08.
Keywords: Kinetic Monte Carlo; Diffusion; Desorption; Adsorption; Water formation
CO2 laser cutting of advanced high strength steels (AHSS) by A. Lamikiz; L.N. López de Lacalle; J.A. Sánchez; D. del Pozo; J.M. Etayo; J.M. López (pp. 362-368).
This article demonstrates the optimum working areas and cutting conditions for the laser cutting of a series of advanced high strength steels (AHSS). The parameters that most influence the cutting of sheet metal have been studied and the results have been divided into two large groups with thickness of more and less than 1mm.The influence of the material and, more important, the effect of coating have been taken into account. The results, have demonstrate very different behaviours between the thinnest and thickest sheets, whilst the variation of the cutting parameters due to the influence of the material is less relevant.The optimum cutting areas and the quality of the cut evaluated with different criteria are presented. Finally, the best position for the laser beam has been observed to be underneath the sheet.
Keywords: PACS; Lasers-applications; 42.62; Machining-materials; 81.20.WLaser cutting; AHSS; CO; 2; laser
A simple diffusion model for the growth kinetics of γ′ iron nitride on the pure iron substrate by M. Keddam; M.E. Djeghlal; L. Barrallier (pp. 369-374).
A simplified diffusion model designed to predict the thickness, microstructure of nitrided layer on the pure iron, and the nitrogen profile is reported. The error function model based on Fick's laws was used to study the growth kinetics of γ′ phase during the gas nitriding process. The validity of the generated computer program was checked by comparing our simulation results with the experimental data taken from the literature and a fairly good agreement is achieved between calculated and experimentally measured values.
Keywords: Fe–N binary system; Fick's laws; Nitrogen diffusion; Growth kinetics; Iron nitride
Ion bombardment induced interface broadening in Co/Cu system as a function of layer thickness by A. Barna; M. Menyhard; A. Zalar; P. Panjan (pp. 375-379).
It has been shown recently that in case of bilayers ion bombardment induced interface roughening occurs if the sputtering yields of the adjacent layers are strongly different. Now we checked the effect of this mechanism on AES depth profiling if the thickness at least one of the layers is small compared to the thickness of ion mixed layer. It turned out that in this case the ion bombardment induced interface roughening is negligible, since the ion mixing eliminates the differences of the sputtering yields.
Keywords: AES depth profiling; Thin film analysis; Co/Cu system; Ion bombardment induced interface broadening; TRIM simulation
AuPd alloy formation in Au-Pd/Al2O3 catalysts and its role on aromatics hydrogenation by B. Pawelec; A.M. Venezia; V. La Parola; E. Cano-Serrano; J.M. Campos-Martin; J.L.G. Fierro (pp. 380-391).
Alumina-supported bimetallic Au-Pd catalysts were prepared by the simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polyvinylpyrrolidone (PVP) and classical incipient wetness co-impregnation method (iwi). The catalysts were characterized by a variety of techniques (AAS, N2 adsorption–desorption, XRD, TEM, CO chemisorption, TGA, FTIR-CO, DRIFTS-NH3, and XPS). According to X-ray diffraction measurements and FTIR-CO spectra, an AuPd alloy formed on the sample prepared by the PVP method, whereas distinct phases of gold and palladium metals formed on the iwi samples. The effect of the presence of the AuPd alloy on the catalytic activity was investigated in the simultaneous hydrogenation (HYD) of toluene (T) and naphthalene (NP) in the presence of dibenzothiophene (DBT) at P=5.0MPa, T=523K, WHSV=41.2h−1. Under the selected conditions, all the catalysts were resistant to poisoning with 113ppm of S (as DBT). The enhancement in activity observed for the sample prepared by PVP method as compared to those prepared by impregnation is related to the geometric effect resulting from the dilution of the Pd ensemble in the AuPd alloy and also to the presence of smaller Pd0 particles.
Keywords: Au-Pd catalysts; AuPd alloy; Aromatics hydrogenation
In-situ monitoring and analysis of GaSb(100) substrate deoxidation by K. Möller; L. Töben; Z. Kollonitsch; Ch. Giesen; M. Heuken; F. Willig; T. Hannappel (pp. 392-398).
The thermal deoxidation procedure of GaSb(100) substrates has been investigated with in-situ reflectance difference spectroscopy (RDS). The “epi-ready� substrates were loaded in a metal-organic vapor phase epitaxy (MOVPE) reactor either “as-supplied� or after etching with HCl to remove the native oxide layer. Annealing between 475–575°C and in-situ monitoring reveals RDS features associated with the surface morphology and the development of oxide desorption. This process is supported by molecular hydrogen utilized as carrier gas. Photoemission spectroscopy was applied to benchmark the surface of selected samples with regard to the electronic structure and the chemical composition during the deoxidation of GaSb(100) substrates. Based on the in-situ and UHV data, a model of the oxide desorption process and recommendations for the GaSb substrate deoxidation procedure in MOVPE environment are proposed.
Keywords: PACS; 68.47.Gh; 68.55.Jk; 78.40.Fy; 78.66.Fd; 79.60.Jv; 81.05.Ea; 82.20.PmGaSb oxides; Ga; 2; O; 3; Ga; 2; O; Surface structure; RDS; RAS; XPS
A pyrazine derivative as corrosion inhibitor for steel in sulphuric acid solution by M. Bouklah; A. Attayibat; S. Kertit; A. Ramdani; B. Hammouti (pp. 399-406).
The influence of diethyl pyrazine-2,3-dicarboxylate (P1) on the corrosion of steel in 0.5M H2SO4 solution has been studied by weight loss measurements, potentiodynamic polarisation and linear polarisation resistance (Rp) and impedance spectroscopy (EIS) methods. The inhibiting action increases with the concentration of pyrazine compound to attain 82% at 10−2M. We note good agreement between gravimetric and electrochemical methods (potentiodynamic and Rp polarisation and electrochemical impedance spectroscopy (EIS)). Polarisation measurements also show that the pyrazine acts essentially as a cathodic inhibitor. The cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism. The yellow deposit on the steel surface was analysed by infrared method. P1 adsorbs on the steel surface according to Langmuir adsorption model. Effect of temperature is also made in the 298–353K range.
Keywords: Pyrazine; Inhibition; Corrosion; Steel; Acid
Field emission from hafnium oxynitride films prepared by ion beam-assisted deposition by Yongjin Wang; Jihua Zhang; Fumin Zhang; Feng Zhang; Shichang Zou (pp. 407-411).
HfN xO y films are deposited by ion beam-assisted deposition on (100) silicon substrates at room temperature. According to X-ray diffraction analysis, at least two phases exist in HfN xO y film, and X-ray photoelectron spectroscopy results are in good agreement with these analysis. Both annealing and increasing assisting ion beam current increase the concentration of the β-Hf7O8N4 phase in HfN xO y films. Field emission with low turn on field is reported. Field emission results suggest that the concentration of β-Hf7O8N4 plays an important role in field emission properties. Hydrogen plasma treatment also enhances field emission properties. These results indicate that the HfN xO y film is an excellent material for field emitter.
Keywords: PACS; 79.70.; +; q; 81.15.Jj; 77.55.; +; fField emission; Ion beam-assisted deposition; HfN; x; O; y; thin film
Temperature dependence of current–voltage characteristics of Ag/p-SnS Schottky barrier diodes by Mehmet Şahin; Haluk Şafak; Nihat Tuğluoğlu; Serdar Karadeniz (pp. 412-418).
The current–voltage ( I– V) measurements on Ag/p-SnS Schottky barrier diodes in the temperature range 100–300K were carried out. It has been found that all contacts are of Schottky type. The ideality factor and the apparent barrier height calculated by using thermionic emission (TE) theory were found to be strongly temperature dependent. The I– V curves is fitted by the equation based on thermionic emission theory, but the zero-bias barrier height ( ΦB0) decreases and the ideality factor ( n) increases with decreasing temperature. The conventional Richardson plot exhibits non-linearity below 200K with the linear portion corresponding to activation energy of 0.32eV. It is shown that the values of Rs estimated from Cheung's method were strongly temperature dependent and decreased with increasing temperature. From the reverse-bias I– V graphs, it is found that the experimental carrier density ( NA) values increased with increasing temperature.
Keywords: PACS; 73.30.+y; 73.40.QvSchottky barrier diode; IV–VI layered semiconductor compounds; I; –; V; characteristics
Microscale chemical and electrostatic surface patterning of Dow Cyclotene by N2 plasma by D.-Q. Yang; S. Poulin; L. Martinu; J.E. Klemberg-Sapieha; O. Zabeida; E. Sacher (pp. 419-427).
Using TEM grids as masks, we have chemically modified selected areas of the surface of Dow Cyclotene, a low permittivity polymer, by a N2 plasma (chemical surface patterning), grafting a maximum of ∼3% N; this was verified by XPS (X-ray photoelectron spectroscopy) and TOF-S-SIMS (time-of-flight static secondary ion mass spectrometry) chemical imaging. Contact mode AFM (atomic force microscopy) studies of the modified surface morphology show unexpected, initially large, values of both etch depth and friction in the treated areas, which decrease on exposure to atmosphere; similar results were absent in tapping mode images. When Cu, which forms nanoclusters on Cyclotene, was deposited by evaporation onto freshly etched Cyclotene, the large etch depth and friction in the etched areas decreased to much lower values.The depth and friction differences occurring on surface modification, which were revealed through our use of patterning, are apparent, and are, in fact, caused by enhanced electrostatic interaction of the chemically modified surface with the AFM tip, as confirmed by the tapping mode data. Some of the electrostatic surface charge, introduced by the positively charged species chemically modifying the Cyclotene surface, is reduced by subsequent charge neutralization. XPS has shown this to be due to the oxidation of these surface charges on atmospheric exposure, initially ∼70%, to form alcohol, carbonyl and carboxylic acid groups. Contact mode AFM imaging of plasma-patterned surfaces is revealed as an excellent tool for the high-resolution characterization of such surfaces.
Keywords: PACS; 52.77.Bn; 68.37.Ps; 68.47.Mn; 81.07.−b; 81.65.Cf; 81.65.−bAFM; Dow Cyclotene; Microscale chemical and electrostatic patterning; N; 2; plasma treatment; Surface chemical modification; TOF-S-SIMS; XPS
Photo-electron emission and atomic force microscopies of the hydrogen etched 6H-SiC(0001) surface and the initial growth of GaN and AlN by J.D. Hartman; K. Naniwae; C. Petrich; R.J. Nemanich; R.F. Davis (pp. 428-436).
Photo-emission electron microscopy (PEEM) and atomic force microscopy (AFM) have been used to characterize the surfaces of hydrogen etched 6H-SiC(0001) wafers and the microstructure of the initial stages of growth of GaN and AlN on these surfaces via molecular beam epitaxy. The PEEM images were obtained using a free electron laser as the photon source. A stepped structure was evident in these images of the surfaces etched at 1600–1700°C for 15min. Comparison with the AFM images revealed that emission was occurring from the intersection of the steps and the terraces. Images of the initial stages of deposition of the GaN thin films at 700 and 800°C revealed three-dimensional island growth. The degree of coalescence of these films was dependent upon the step structure: regions containing steps having unit cell height exhibited complete or nearly complete coalescence; regions containing steps with half unit cell height showed voids in the films parallel to the steps. PEEM of the initial stages of growth of AlN revealed immediate nucleation and rapid coalescence during deposition at 900°C, except in areas on the substrate surface containing steps having half unit cell height. Incomplete coalescence and pits were also observed in the latter areas.
Keywords: PACS; 61.16.MPhoto-emission electron microscopy; Gallium nitride; Aluminum nitride; Silicon carbide; Molecular beam epitaxy; Stepped single crystal surfaces
Annealing effects on electron-beam evaporated Al2O3 films by Shang Shuzhen; Chen Lei; Hou Haihong; Yi Kui; Fan Zhengxiu; Shao Jianda (pp. 437-442).
The effects of post-deposited annealing on structure and optical properties of electron-beam evaporated Al2O3 single layers were investigated. The films were annealed in air for 1.5h at different temperatures from 250 to 400°C. The optical constants and cut-off wavelength were deduced. Microstructure of the samples was characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness.It was found that the cut-off wavelength shifted to short wavelength as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400°C temperature and the samples annealed at higher temperature had the higher rms surface roughness. The decreasing total optical loss with annealing temperature was attributed to the reduction of absorption owing to oxidation of the film by annealing. Guidance to reduce the optical loss of excimer laser mirrors was given.
Keywords: Ultraviolet; Annealing; Al; 2; O; 3; Optical loss; Microstructure