Applied Surface Science (v.207, #1-4)
Publisher's Note (viii).
Author Index (I-III).
Subject Index (IV-XI).
Editorial Board (ii).
Cu cluster adhesion enhancement on the modified Dow Cyclotene surface through low energy N2 + beam irradiation at grazing angles by D.-Q Yang; E Sacher (1-5).
In order to enrich the N content at the outer surface of Dow Cyclotene, a low permittivity polymer, a 3 keV N2 + beam was used to implant N at various angles. Both in situ XPS analysis of the modified surface and the initial coalescence behavior of Cu clusters deposited by evaporation demonstrated that a lower angle between the beam and the surface led to N enrichment at the surface but not to the extent offered by a N2 + plasma. The reason for this is discussed.
Keywords: Adhesion; Copper clusters; Dow Cyclotene; Metallization; Nitrogen ion implantation; Nitrogen plasma treatment;
Photocurrent and photothermal current of polypyrrole (PPy) film by Chongjun Zhao; Haihong Wang; Zhiyu Jiang (6-12).
The photoelectrochemical properties of polypyrrole (PPy) film in aqueous solutions in the potential region of −0.7 to 0.5 V (versus Ag/AgCl) were investigated by using photocurrent, photothermal and photothermal current methods under the irradiation of laser beams with wavelength of 532 and 632.8 nm, respectively. It was found that the photocurrent at more negative potential was caused by the p-type semiconductor properties, while the photocurrent at more positive potential was caused by the local temperature rather than the semiconductor properties of the films. The effect of the film thickness on the photocurrent of PPy films was studied in detail.
Keywords: Polypyrrole (PPy); Photocurrent; Photothermal; Photothermal current; Thickness;
Ultra-thin titanium oxide film with a rutile-type structure by Masahiko Hiratani; Masaru Kadoshima; Tatsumi Hirano; Yasuhiro Shimamoto; Yuichi Matsui; Toshihide Nabatame; Kazuyoshi Torii; Shinichiro Kimura (13-19).
A titanium oxide film was deposited on a silicon substrate by RF-magnetron sputtering using a sintered oxide target in an argon-gas atmosphere. Phase transition and crystallization during the post-heat treatment were investigated. The thermodynamic stability of phase, oxygen diffusion through the film to form an interfacial SiO2 layer, and the reaction process in which the rutile-type TiO2 is crystallized were investigated. Rock-salt-type TiO with large deficiency of titanium ions is quenched in the as-deposited film in non-equilibrium. The following post-heat treatment in nitrogen gas transforms the film to Ti3O5, while post-oxidation transforms the film into rutile-type TiO2, even in an ultra-thin film of 5 nm, at the expense of the growth of interfacial SiO2 with a thickness of 2.5 nm. The growth of the interfacial oxide is explained in terms of three origins: oxygen defects incorporated into the rutile-type TiO2, fast oxygen diffusion via the defects, and the fact that non-stoichiometric TiO2 − x is less stable than SiO2. We also discuss the main criteria that must be satisfied in order to apply the high-permittivity oxide to a gate insulator.
Keywords: Gate dielectric; High-κ; Rutile; Titanium oxide; TiO2;
Photoluminescence of ZnO films excited with light of different wavelength by D.H. Zhang; Q.P. Wang; Z.Y. Xue (20-25).
Different photoluminescence (PL) spectra were observed for rf sputtered ZnO films when excited with light of different wavelength. When the wavelength of the excitation light was 270 nm, a UV emission peak (356 nm) and a blue peak (446 nm) were generated for the films on sapphire, silicon and quartz substrates. For the films on glass substrates only the 446 nm blue emission appeared. With increasing the wavelength of the excitation light up to 300 and 320 nm, the UV emission disappeared for films on various substrates and the wavelength of the PL peaks increased up to 480 and 510 nm, respectively. When the wavelength of the excitation light increased to 340–395 nm, the PL spectrum became a wide band which was consistent with three emission peaks.
Keywords: ZnO films; Photoluminescence; rf sputtering; Excitation light;
Role of excess cadmium in the electrical properties of devices made of chemically deposited nano-CdS by K.B. Jinesh; C. Sudha Kartha; K.P. Vijayakumar (26-32).
Effects of excess cadmium in chemically deposited cadmium sulfide (CdS) nanoclusters are investigated here. This was done by fabricating a bulk-nano (bn) junction of CdS and observing the alterations in the junction characteristics under different conditions. The I–V characteristics of such junctions clearly depict changes even with incident photon energy lesser than the HOMO-LUMO separation of nano-CdS, that are not stimulating the original electronic properties of either bulk or nano-CdS. Alterations of characteristics under such conditions assures the role of impurities like excess cadmium and oxygen in the sample. From the different junctions of bulk and nano-CdS, it is studied here that the excess Cd present in the sample could have raised the Fermi level of the nano layer and is responsible for the ohmic contact between nano-CdS and the tin oxide layer. The raise of the conduction level of nano-CdS roughly estimated here is in agreement with the suggestion that the excess cadmium in the chemically deposited nano-CdS causes a larger shift in the conduction band than that of its valance band.
Keywords: Cadmium sulfide; Bulk-nano junctions; I–V characteristics; Unstable bonds;
Surface morphology of Hg0.8Cd0.2Te epilayers grown by LPE using horizontal slider by J.K. Radhakrishnan; S. Sitharaman; S.C. Gupta (33-39).
The surface morphology of Hg0.8Cd0.2Te epilayers on (111)±0.5° oriented Cd0.96Zn0.04Te substrates grown from Te-rich solution by LPE using horizontal slider has been studied. The surface morphology, apart from exhibiting the terrace patterns typical of LPE growth, shows other surface features like pin holes/voids, Hg-evaporation points, slider scratch marks and some long-distance perturbations in the layer thickness visible to the naked eye. Also, discussed are the surface morphology of the layer at edge regions and the effect of non-smooth slide-out of the layer on its surface morphology.
Keywords: LPE; Surface morphology; Horizontal slider; HgCdTe;
Adsorption of BTSE and γ-APS organosilanes on different microstructural regions of 2024-T3 aluminum alloy by D. Susac; X. Sun; K.A.R. Mitchell (40-50).
The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and γ-aminopropyltriethoxysilane (γ-APS) has been studied on 2024-T3 aluminum alloy samples using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The thickness and coverage of the BTSE film formed on a mechanically polished sample was found to be strongly affected by the distribution of second-phase particles on the alloy surface. Specifically, although the adsorption occurs on the alloy matrix away from the particles, and on the particles themselves, the regions immediately surrounding the particles had less BTSE. The amounts of this adsorption on an air-oxidized sample is increased on average, although the coating is non-uniform with regions (∼100 μm) of higher and lower coverages. There appears to be a competition between the silane deposition and etching of the underlying oxide film for the initially oxidized sample. The adsorption of γ-APS is different with films of relatively even thickness formed over large areas of the polished sample; hydrogen bonding through the amino groups probably helps the distribution in this case.
Keywords: Aluminum alloy; Silane adsorption; Surface microstructure;
Surface wettability and platelet adhesion studies on Langmuir–Blodgett films by Yuh-Lang Lee; Chi-Yun Chen (51-62).
Because Langmuir–Blodgett (LB) deposition technique is known to be capable of preparing highly ordered monomolecular films with densely packed structure, LB technique is used to prepare films of DPPC, DMPC, cholesterol, octadecylamine (ODA), and stearic acid, with thickness of one molecular layer. The film surfaces were characterized by dynamic contact angle measurement and the interaction between blood and these materials were investigated. The properties of LB films were also compared with the results obtained on continuous films prepared by solution dipping. The results show that the contact angles of water on LB films of the five compounds decreases as the following order: ODA>DMPC≈DPPC>stearic acid>cholesterol . The hydrophobic property reflects the highest organization of ODA molecules on the substrate, which is related to its interaction between the molecule and substrate. The advancing contact angle of ODA is equivalent to that of a methyl-terminated SAM, but its receding contact angle is smaller which implies the exposing of hydrophilic pole or glass substrate on LB film. The irregular orientation of molecules on LB film increases with decreasing of contact angle and is especially significant on LB film of cholesterol which has highest hydrophilic property. The plate adhesion experiments on the continuous films show that the hemocompatibility of the five materials decreases as the order: DPPC≈DMPC>ODA>cholesterol>stearic acid≈glass . This result implies that the lipid has highest blood compatibility, and then –NH2, and then –OH functionality. On the contrary, the glass surface, –COOH and –CH3 functionalities have high reactivity to platelet. Due to the possibility of glass exposure on LB films, as estimated from the surface wettability, the LB films have higher platelet reactivity, especially for the cholesterol, compared with the continuous films. Because the interaction of the LB film to the substrate is physical force, the deposited molecules may be peeled off from the substrate by dipping in Hepes–Tyrodes buffer solution. As a consequence, the LB films after equilibrating with Hepes–Tyrodes buffer solution have high platelet reactivity as that on glass surface.
Keywords: Langmuir–Blodgett film; Surface modification; Wettability; Platelet adhesion; Hemocompatibility;
Electrical properties of (Pb0.76Ca0.24)TiO3 thin films on LaNiO3 coated Si and fused quartz substrates prepared by a sol–gel process by X.G. Tang; H.L.W. Chan; A.L. Ding (63-68).
Ferroelectric (Pb0.76Ca0.24)TiO3 (PCT) thin films were grown on LaNiO3 (LNO) coated Si(1 1 1) and fused quartz substrates by using a sol–gel process. The highly (1 0 0)-oriented PCT films on LNO coated Si(1 1 1) substrates, and random oriented pervoskite PCT thin films on fused quartz substrates have been obtained, respectively. Atomic force microscopy (AFM) revealed that the surface morphology smooth. PCT films on LNO coated Si(1 1 1) and fused quartz substrates, the grain sizes were about 60–120 and 40–60 nm, respectively. The PCT thin films on LNO coated Si(1 1 1) and fused quartz substrates annealed at 600 °C have the remanent polarization (P r) and coercive electric field (E c) values were 9.3 μC/cm2 and 64 kV/cm, 1.4 μC/cm2 and 28 kV/cm, respectively. At 100 kHz, the dielectric content and dielectric loss of the PCT films on LNO coated Si(1 1 1) and fused quartz substrates were 231 and 0.045, 160 and 0.061, respectively.
Keywords: PCT thin films; LaNiO3 electrode; Orientation; Sol–gel; Electrical properties;
The influence of carbon steel microstructure on corrosion layers by D.A López; W.H Schreiner; S.R de Sánchez; S.N Simison (69-85).
Corrosion related failures in the oil and gas industry represent a very serious and costly problem. The successful application of carbon steels in oil and gas pipelines and production tubulars in CO2 containing environments depends mainly on either the formation of protective corrosion product film or the use of corrosion inhibitors.Both laboratory experiments and field experience have shown that the protective properties and adherence of the film may vary significantly for carbon steels with apparently the same composition and microstructure.In the present work, characteristics such as morphology, thickness and composition of corrosion layers formed on carbon steel with two different microstructures (annealed, and quenched and tempered) have been studied by means of scanning electron microscopy (SEM), electron dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The corrosive media was a deoxygenated 5% NaCl solution, saturated with CO2 at 40 °C and pH 6. The effect of the addition of benzimidazol as a corrosion inhibitor has also been analyzed.It is concluded that the microstructure of steel influences the inhibitor efficiency and the properties of the corrosion layers, such as morphology and proportion of the various chemical compounds present.
Keywords: Carbon dioxide; Corrosion layers; Steel microstructure; XPS; EDX; SEM;
Cleaning graffitis on urban buildings by use of second and third harmonic wavelength of a Nd:YAG laser: a comparative study by A Costela; I Garcı́a-Moreno; C Gómez; O Caballero; R Sastre (86-99).
The present article focuses on the cleaning of graffitis on urban buildings by using laser radiation. A comparison between cleaning results obtained with second and third harmonic wavelengths of a Q-switched Nd:YAG laser is presented. Ablation rate studies have been carried out and elemental analysis by laser-induced breakdown spectroscopy (LIBS) has been applied as a real-time diagnostic technique for the cleaning process, with the aim of preventing potential damage of the surface. To remove graffitis on urban buildings the third harmonic was observed to be the most efficient wavelength, supporting the best result.
Keywords: Laser cleaning; Nd:YAG; Laser-induced breakdown spectroscopy; Graffitis;
Electron-accepting surface properties of ceria–(praseodymia)–zirconia solids modified by Y3+ or La3+ studied by paramagnetic probe method by Larisa N Ikryannikova; Goar L Markaryan; Andrey N Kharlanov; Elena V Lunina (100-114).
EPR paramagnetic probe method with 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO) as a probe has been applied to study of electron-accepting properties of the surface of (Y, La0.1)Ce x Zr1−x O2−y (x=0.1–0.7), Y0.1Pr0.3Zr0.6O2−y and Y0.1Pr0.15Ce0.15Zr0.7O2−y mixed oxides. Two types of acceptor sites—coordinatively unsaturated (cus) cations Zr4+ and Ce4+—have been revealed on the CeO2–ZrO2 surface after thermovacuum treatment (820 K). The relative amounts and “strength” of these centers were evaluated on the basis of EPR spectra analysis. An introduction of trivalent Y3+ or La3+ cations reduces the amount of electron-acceptor sites belonging to cerium cations, stabilizing ones as Ce3+. A formation of very strong electron-accepting sites (Pr4+ cus cations) able to form charge transfer complexes with adsorbed TEMPO on the surface of praseodymia-containing samples after thermovacuum treatment was found out. At the same time electron-accepting ability of Zr4+ cationic sites on Y0.1Pr0.3Zr0.6O2−y and Y0.1Pr0.15Ce0.15Zr0.7O2−y surfaces decreases in comparison with ceria–zirconia one. The generally used IR spectroscopy technique with CO as a probe molecule appeared to be considerably less informative for such systems characterization, due to their high catalytic activity to carbon monoxide. A formation of paramagnetic Zr3+ ions in ceria–zirconia mixed oxides has been investigated by EPR spectroscopy technique. The different states of this paramagnetic ion are realized in the complex oxides depending on Ce/Zr ratio.
Keywords: Ceria; Zirconia; Praseodymia; Surface; Electron-acceptor sites; EPR spectroscopy; Paramagnetic probe;
Investigation of the adsorption and decomposition of Fe(CO)5 on fcc and bcc iron films by infrared reflection absorption spectroscopy by T. Tanabe; K. Kubo; T. Ishibashi; T. Wadayama; A. Hatta (115-120).
The adsorption and decomposition of Fe(CO)5 on fcc and bcc iron films at 90 K were investigated using infrared reflection absorption spectroscopy (IRRAS). The fcc film was epitaxially grown on a Cu(1 0 0) crystal at room temperature, whereas the bcc film was deposited as polycrystalline by electron-beam evaporation onto a Si(1 1 1) wafer. The saturated adsorption of Fe(CO)5 on the fcc Fe(1 0 0) surface yielded a dominant IRRAS band at 2060 cm−1 due to the axial CO stretch mode of Fe(CO)5. Upon UV (254 nm) irradiation to the adsorbed layer, the 2060 cm−1 band decreased in intensity and a new band appeared at 2072 cm−1, indicating the photolytic decomposition of the adsorbed Fe(CO)5. Fe(CO)5 adsorption on the polycrystalline bcc surface gave rise to a single intense band at 2072 cm−1 which was not changed in position by UV irradiation. We conclude from these results that the fcc(1 0 0) surface is inactive for the decomposition of Fe(CO)5 in comparison to the polycrystalline bcc surface.
Keywords: Iron films; Pentacarbonyliron; Chemisorption; Infrared absorption spectroscopy; Molecular beam epitaxy;
A simple method to grow textured (1 1 1) diamond thin films in a hot-filament CVD system by G.F. Zhang; V. Buck (121-127).
A simple and new method for synthesizing (1 1 1)-textured diamond films in a hot-filament CVD reactor has been developed by adopting a lower-than-normal filament temperature pretreatment. The (1 1 1) facets are always dominant in the resulting diamond films using a low filament temperature range of 1300–1600 °C. This growth habit is insensitive to the change in deposition parameters, such as substrate temperature, methane concentration, and even addition of a small amount of nitrogen. High-quality and high-textured (1 1 1) diamond films can be easily achieved by a subsequent growth at a normal filament temperature of 2000 °C.
Keywords: Hot-filament CVD; Diamond film; (1 1 1)-textured growth; Filament temperature;
Quantification of AES depth profiles by the MRI model by Janez Kovač; Anton Zalar; Borut Praček (128-134).
The main physical effects that contribute to interface broadening in the sputter depth profiles of polycrystalline metallic multilayer structures were studied by comparison of measured and simulated AES depth profiles. An algorithm based on the so-called mixing–roughness-information depth (MRI) model was used to simulate AES depth profiles of Ni/Cr multilayer structures with different roughnesses of the initial surfaces. The simulated depth profiles were compared with measurements performed at two different depth profiling parameters on the Ni/Cr and Al/Ni/Cr multilayer structures with an initial surface roughness of about 1.0 and 21.5 nm, respectively.The comparison of simulated and measured depth profiles enabled us to separate and estimate different contributions to the interface broadening, as well as their dependence on the sputter depth. We found that roughness was the dominant factor related to depth resolution with respect to the information depth and atomic mixing contribution. The values of roughness introduced into the simulation algorithm coincided well with the values measured by AFM at the initial surface and after depth profiling. The results showed the capability of the simulation procedure based on the MRI model to separate and evaluate different contributions to the depth resolution.
Keywords: Ni/Cr multilayer; AES depth profiling; MRI model; Depth resolution; Surface roughness;
Microstructural features of pulsed-laser deposited V2O5 thin films by C.V. Ramana; O.M. Hussain; R. Pinto; C.M. Julien (135-138).
Vanadium pentoxide (V2O5) thin films were grown onto amorphous glass substrates by pulsed-laser deposition (PLD). The surface morphology and structural features were studied by XRD, XPS, AFM, and FTIR to ensure the growth of V2O5 films. These investigations revealed that stoichiometric V2O5 films can be grown with a layered structure onto amorphous glass substrates at temperature as low as 200 °C and oxygen partial pressure of 100 mTorr.
Keywords: V2O5 films; Pulsed-laser deposition; Microstructure;
Mechanism about improvement of NiSi thermal stability for Ni/Pt/Si(1 1 1) bi-layered system by R.N. Wang; J.Y. Feng; Y. Huang (139-143).
A thin interlayer of Pt can greatly enhance the thermal stability of NiSi films formed by rapid thermal annealing (RTA) on Si(1 1 1) substrates, as was revealed by X-ray diffraction (XRD) data and sheet resistance measurement. One possible reason for the enhanced NiSi thermal stability is attributed to the formation of the Ni0.945Pt0.055Si solid solution and its preferred orientation, leading to the decrease in the driving force and the increase in the interfacial energy change, respectively. Both of them increase the activation energy for the NiSi2 nucleation, improving the NiSi thermal stability.
Keywords: NiSi; Thermal stability; The solid solution;
The influence of ablation carrier gasses Ar, He and Ne on the particle size distribution and transport efficiencies of laser ablation-induced aerosols: implications for LA–ICP–MS by Ingo Horn; Detlef Günther (144-157).
The influence of ablation cell carrier gasses He, Ne and Ar on the particle size distribution generated and subsequently transported during the laser ablation process of silicate glasses was investigated using 266 and 193 nm wavelengths for ablation. The particle size distributions was determined for the NIST 600 series glasses and synthetic quartz glass using an optical particle counter within the size range of 0.1 to >2 μm. The results illustrate that the ablation carrier gas strongly influences the particle size distribution for λ=193 nm while this effect is far less pronounced for ablations using λ=266 nm. The experiments also show that 266 nm produces to a larger degree primary particles which are not largely influenced by the ablation carrier gas environment while 193 nm produces a larger amount of vapour during impact of the laser beam which subsequently condenses to form larger aggregates. These results verify and give the reason for the large increase in sensitivity obtainable by inductively coupled plasma mass spectrometry (ICP–MS) when using helium together with 193 nm ablation systems while only a minor increase will be observable when using 266 nm under similar conditions. Furthermore the influences of the laser energy density, on the particle size distribution as well as values for the transport efficiency were investigated.
Keywords: Laser ablation; ICP–MS; Spatial resolution;
Thermodynamic equilibrium calculation of Cu(s)–Cl2(g) reaction by Myoung Seok Kwon; Jeong Yong Lee (158-168).
Thermodynamic calculations of the equilibrium compositions of condensed- and gaseous-reaction products from the reaction between Cu(s) and Cl2(g) has been performed to understand the fundamental reactions during the Cl-based dry etching of Cu thin film. Total pressure was fixed at 5 mTorr, which is typical for high-density plasma etching. The final phase equilibrium state of Cu(s)–Cl2(g) system was determined by using the minimization of the total free energy of the system as a function of temperature and initial Cl2(g)/Cu(s) molar ratio, and the calculated phase equilibrium results were discussed in relation to the Cl-based Cu dry etch reaction.
Keywords: Cu; Chlorine; Reaction; Equilibrium; Phase;
The influence of C60 as intermediate on the diamond nucleation on copper substrate in HFCVD by C. Li; K.C. Feng; Y.J. Fei; H.T. Yuan; Y.Y. Xiong; K. Feng (169-175).
The diamond films on copper substrates using C60 as intermediate have been grown by the hot filament chemical vapor deposition (HFCVD) technique. Scanning electron microscopy (SEM) and micro-Raman spectra were used to study the process of diamond nucleation. The UV-light pretreatment was beneficial for improving the diamond nucleation. The temperature of the substrate is very important. The C60 molecule layers with UV-light pretreatment could increase the density of diamond nuclei on copper substrates and enhance the adherence between the copper substrates and diamond films. The long induction time for forming graphite intermediate is not necessary.
Keywords: Diamond; CVD; Nucleation; SEM; Raman spectra;
In situ ellipsometric investigation of stainless steel corrosion behavior in buffered solutions with amino acids by M.V. Vinnichenko; M.T. Pham; T. Chevolleau; L.V. Poperenko; M.F. Maitz (176-182).
The corrosion of metals is associated both with a release of ions and changes in optical surface properties. In this study, these two effects were correlated by a potentiodynamic corrosion test and in situ probing of the surface by ellipsometry. The studies were carried out with stainless steel (SS) AISI 304 and 316 in phosphate buffered saline (PBS) and in Dulbecco’s modified minimal essential medium (DMEM) at pH 7.4. In both media, 304 steel is more susceptible to corrosion than 316 grade. The 316 steel shows a higher corrosion potential and higher corrosion current density in PBS than in DMEM, for 304 steel this behavior is vice versa. Ellipsometry demonstrated a higher sensitivity than potentiodynamics to surface modification in the cathodic area. In DMEM the removal of a surface layer at negative potential and a further repassivation with increasing potential was characteristic. In PBS a surface layer started to grow immediately. X-ray photoelectron spectra of this layer formed in PBS are consistent with iron phosphate. Its formation is inhibited in DMEM; the presence of amino acids is discussed as the reason.
Keywords: Stainless steel; Electrochemical corrosion; In situ ellipsometry; X-ray photoelectron spectroscopy; Atomic force microscopy;
Surface energy for electroluminescent polymers and indium-tin-oxide by Zhiyou Zhong; Sheng Yin; Chen Liu; Youxin Zhong; Wuxing Zhang; Dufang Shi; Chang’an Wang (183-189).
The contact angles on the thin films of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and indium-tin-oxide (ITO) were measured by the sessile-drop technique. The surface energies of the films were calculated using the Owens–Wendt (OW) and van Oss–Chaudhury–Good (vOCG) approaches. The overall total surface energies of MEH-PPV and the as-received ITO were 30.75 and 30.07 mJ/m2, respectively. Both approaches yielded almost the same surface energies. The surface energies were mainly contributed from the dispersion interactions or Lifshitz–van der Waals (LW) interactions for both MEH-PPV and ITO. The changes in the contact angles and surface energies of the ITO films, due to different solvent cleaning processes and oxygen plasma treatments, were analyzed. Experimental results revealed that the total surface energy of the ITO films increased after various cleaning processes. In comparison with different solvents used in this study, we found that methanol is an effective solvent for ITO cleaning, as a higher surface energy was observed. ITO films treated with oxygen plasma showed the highest surface energy. This work demonstrated that contact angle measurement is a useful method to diagnose the cleaning effect on ITO films.
Keywords: Electroluminescent polymer; Indium-tin-oxide; Contact angle; Surface energy;
The energy distribution of the interface state density of Pb/p-Si Schottky contacts exposed to clean room air by H.A Çetinkara; A Türüt; D.M Zengı̀n; Ş Erel (190-199).
Pb/p-Si Schottky barrier diodes (SBDs) with and without thin native oxide layer have been fabricated. The previously polished p-Si wafer has been cleaned by using a traditional RCA clean with the final dip in diluted HF for 30 s. The ohmic contact on the back surface of the wafer was made by evaporation of Aluminium metal and then the wafer was cut into pieces of 5 mm×5 mm. Other than the sample PbD1, before Schottky contact formation, these pieces with ohmic contact were exposed to clean room air for 1, 5, 10, 15, 30, 45 and 60 days at room temperature to obtain the samples with the native oxide layer on the clean Si surface. The value of the barrier height (BH), Φ b first increases with the increasing exposure time to air and then tends to that of the initial sample PbD1. Furthermore, the energy distribution curves of the interface states localized at the native oxide layer–semiconductor interface were determined from the forward bias current–voltage (I–V) characteristics by taking into account the bias dependence of the barrier height. It was seen that the density value of the interface states for the samples with the native oxide layer at all energy positions is lower than that for the initial sample. This is attributed to the passivation of the cleaned Si surface due to the formed native oxide layer.
Keywords: Schottky barrier diodes; Exposure; Passivation;
Nature effect of the gas during high temperature treatments of 4H-SiC substrates by Ghassan Younes; Gabriel Ferro; Christophe Jacquier; Jacques Dazord; Yves Monteil (200-207).
4H-SiC seeds have been treated at high temperatures (1650–1900 °C) under Ar or N2 in a sublimation like graphite crucible with SiC powder at the hotter part. It was found that the surface morphology is significantly altered by the nature of the atmosphere. Surfaces without step bunching under 1 bar of N2 appear for low temperature range (≤1700 °C) whereas at higher temperature or lower pressure a step bunch morphology appears. Ar always gives step bunched surfaces but with more regular and parallel steps. Thermodynamical calculations performed on the SiCN (Ar) system show that N2 plays an important role on the gas phase chemistry of decomposition of SiC by forming gaseous species of nitrides. The theoretical results correlate well with the observations of surface morphology and graphitisation of the SiC powder.
Keywords: 4H-SiC; High temperature treatment; Surface morphology; Thermodynamic calculations; Nitrogen;
The application of NIAS approach to describe enthalpic effects accompanying mixed-gas adsorption by K. Nieszporek (208-218).
The possibilities of the non-ideal adsorbed solution (NIAS) approach to study enthalpic effects accompanying mixed-gas adsorption equilibria is presented. Besides heterogeneity the interaction effects are taken into account. The obtained theoretical expressions for predicting isosteric heats of adsorption in the gas mixture are relatively simple and accurate. To predict phase diagrams and calorimetric effects in the mixed-gas adsorption only the knowledge of single-gas adsorption isotherms and accompanying calorimetric effects is required.
Keywords: Adsorption; Isotherms; Enthalpic effects; Isosteric heats of adsorption; Heterogeneity; Ideal adsorbed solution approach;
Modified Poole–Frenkel mechanisms in Ge25Bi x Sb15−x S60 thin films by M.M El-Samanoudy (219-226).
The current–voltage (I–V) characteristics of amorphous Ge25Bi x Sb15−x S60 (x=0, 5, 10 and 15) thin film samples sandwiched between metal electrodes have been investigated as a function of composition, deposition rate (0.61–2.65 nm s−1), film thickness (128.6–598.2 nm) and temperature (130–373 K). The current–voltage characteristics are ohmic in the lower field regime followed by non-ohmic behavior in the higher voltage regime, which has been satisfactorily explained by the modified Poole–Frenkel effect. The experimentally determined values of Poole–Frenkel factor (β PF) for different film composition, deposition rate and thicknesses are in good agreement with the theoretically calculated values. Fitting the room temperature data with Jonscher’s field-independent re-trapping model is an indication that a modified Poole–Frenkel process is operating. The Hall model can account for the low-temperature dielectric constant, and gives an indication of modified Poole–Frenkel emission.
Keywords: Chalcogenide films; Poole–Frenkel effects; Schottky mechanism;
Study of the plasma produced from laser ablation of a KTP crystal by Minju Ying; Yueyuan Xia; Yuming Sun; Qingming Lu; Mingwen Zhao; Xiangdong Liu (227-235).
Optical emission spectra of the plasma produced by 1.06 μm Nd:YAG laser irradiation of a potassium titanium phosphate (KTP) crystal in vacuum and in air were recorded and analyzed in a spatially resolved manner. Electron temperatures and densities in the plasma in vacuum were determined with the Boltzmann plot method using five Ti(II) emission lines and the Stark-broadened linewidths of neutral K atoms, respectively. The dependence of the electron densities and temperatures on distance from the target surface and on laser irradiance were manifested. In order to see the effect of backing gas, we also performed laser ablation of a KTP crystal in air and compared the results with that of the ablation in vacuum. Gas dynamical parameters of the laser-induced KTP evaporation wave were simulated using a hydrocode developed in our group based on the self-similar solutions of the gas dynamical equations. Moreover, the velocity of the evaporating wave and the vapor pressure were calculated under different laser power densities.
Keywords: Laser ablation; Laser-induced breakdown spectroscopy; Plasma diagnosis;
Surface modification during Nd:YAG (1064 nm) pulsed laser cleaning of organic fibrous materials by Matija Strlič; Jana Kolar; Vid-Simon Šelih; Marko Marinček (236-245).
Formation of yellow chromophores on artificially soiled surfaces of cellulose sheets, rag paper, linen, cotton, wool and silk during Nd:YAG (1064 nm) pulsed laser cleaning was followed using Vis and FTIR diffuse reflectance spectrometry. Content of reducing carbonyl groups and changes in FTIR reflectance spectra of cellulose are indicative of surface chemical modifications typical of thermal degradation at elevated temperatures. Two types of soiling were used: well-characterised natural dust and carbon powder and no difference in laser-induced formation of chromophores on material surface was observed at low deposit densities. The influence of laser fluence and number of repetitions was studied and a single pulse of a higher fluence (1 J cm−1) is in general more advisable. No bleaching of the chromophores formed was noticed after repeated treatments.
Keywords: Artwork conservation; Surface modification; Nd:YAG pulsed laser; Organic fibrous material;
Oxidation behaviour of Kanthal A1 and Kanthal AF at 1173 K: effect of yttrium alloying addition by R Cueff; H Buscail; E Caudron; C Issartel; F Riffard (246-254).
The oxidation behaviour of two commercial FeCrAl alloys, Kanthal A1 and Kanthal AF (containing alloying additions of yttrium), has been investigated during isothermal exposures in air at 1173 K. Mass gains were measured by thermogravimetry and identification of the oxidation products determined by in situ high temperature X-ray diffraction. The morphology of the oxide layer surfaces was studied by SEM, the elemental distribution inside the scales being carried out by EDXS analysis. The study revealed that yttrium markedly influences the composition and growth rate of the oxide scale during the steady-state stage of oxidation. The lower oxidation rate resulting from the presence of the reactive element reflects the influence of yttrium in suppressing the formation of transition alumina and promoting the earlier formation of a protective α-Al2O3 scale.
Keywords: FeCrAl alloys; Yttrium; Reactive element effect; High temperature oxidation; X-ray diffraction;
Effect of silicon on the oxidation resistance of 9% Cr steels by A.M Huntz; V Bague; G Beauplé; C Haut; C Sévérac; P Lecour; X Longaygue; F Ropital (255-275).
The oxidation resistance of 9% chromium steels, either with 0.5% Si or doped up to 4% Si, was studied at 600 and 950 °C under either 1 atm oxygen or Ar–H2 mixture to elucidate the influence of silicon and oxygen pressure. Particular attention was paid to the initial stages of oxidation, using “in situ” monitoring of oxidation in an X-photoelectron spectroscopy (XPS) apparatus at 600 °C and under a low oxygen pressure.In 1 atm oxygen, the oxide film formed on the undoped steel mainly consists of iron oxides, while a chromia film grows on the steels containing 2–4% Si. In Ar–H2/H2O, the scale on the undoped steel is heterogeneous and made up of both iron and chromium oxides while the pO2 decrease has no significant influence on the Si-doped steels.During heating of the doped steels, silicon segregates at the outer surface and forms a thin SiO2 film. During further oxidation, the silica film only allows the formation of chromia (with Mn). Under the same conditions, no silicon segregation occurs on the surface of the undoped steel and iron oxides formed when oxygen is introduced.These results clearly demonstrate the beneficial influence of Si on the oxidation resistance of 9% Cr steels.
Keywords: Oxidation resistance; 9% Cr steels; Silicon doping; Cr2O3; SiO2; In situ XPS;
Modification of the micro- and nanotopography of several polymers by plasma treatments by Martine Collaud Coen; Roland Lehmann; Pierangelo Groening; Louis Schlapbach (276-286).
Major topographical modifications of polypropylene (PP), polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE) and polyethyleneterephthalate (PET) can be induced by plasma treatments. If only non-specific topographical changes are observed on most of the polymers, characteristic nanostructures are created on PP and PMMA by noble gases plasma treatments. These nanostructures do not depend on the crystallinity and on the stretching of the polymers, but can be related to the chemistry of the polymers after the plasma treatment. He plasma treated PMMA also shows microstructures superposed on the nanostructures. These greater grooves are oriented along the stretching direction of the polymer foil. Etching is the main phenomenon induced by plasma treatments on PTFE and PET, leading to different final surface features for both polymers. Atomic force microscopy (AFM) associated with X-ray photoelectron spectroscopy (XPS) results provides a good estimation of phenomena occurring during plasma treatments.
Keywords: Polymer topography; Nanostructures; Plasma treatment; Atomic force microscopy; X-ray photoelectron spectroscopy;
Element sensitive atom beam etching based on projectile mass by Y. Watanabe; M. Tanamura (287-294).
A new approach of ion/atom beam etching is proposed, which utilizes the projectile mass dependence of the sputtering process. As a model experiment, we etch YBa2Cu3O7−δ films using inert gases having different masses. Various etching characteristics are found to depend evidently on the mass of the gases. Substantial improvements such as 2.5-fold increase of the etching selectivity and the reduction of the etching damage of the etched area are demonstrated by using Kr. A primitive semi-empirical extension of Sigmund theory is proposed, which explains the results indeed as a mass effect and suggests the directions of further improvements. The results show a new important factor in plasma and ion/atom beam etching, which can be useful for realizing artificial structures of metal oxides.
Keywords: Etching; Ion beam; Oxide; Selectivity; YBCO; Theory; Experiment;
Synthesis and properties of ZnO films with (1 0 0) orientation by SS-CVD by Jianguo Lu; Zhizhen Ye; Jingyun Huang; Lei Wang; Binghui Zhao (295-299).
ZnO films with (1 0 0) preferred orientation have been synthesized on Si (1 0 0) and α-Al2O3 (0 0 0 1) substrates by single-source chemical vapor deposition (SS-CVD) using zinc acetate dihydrate (solid) as a precursor. X-ray diffraction (XRD) reveals that a lower growth temperature and a higher deposition rate will facilitate the forming of (1 0 0) orientation. X-ray photoelectron spectroscopy (XPS) indicates that the O 1s peak in the surface of films can be consistently fitted by two nearly Gaussian curves centered at 530.08 and 531.67 eV, respectively. Transmittance about 90% in visible region and near 100% absorption in UV region for (1 0 0) oriented ZnO films are confirmed by the optical transmission spectra, which are better than those of randomly oriented films. The optical band gap is evaluated to be around 3.31 eV for the (1 0 0) oriented ZnO.
Keywords: ZnO films; (1 0 0) orientation; SS-CVD; Properties;
Spectroscopic ellipsometric characterization of approximant thin films of Al–Cr–Fe by L. Johann; A. En Naciri; L. Broch; V. Demange; J. Ghambaja; F. Machizaud; J.M. Dubois (300-305).
The reflection spectroscopic ellipsometric study of optical properties of thin films of Al–Cr–Fe is presented. Glass substrates were used for the optical characterization of Al–Cr–Fe thin films. Polarizer, rotating polarizer spectroscopic ellipsometer (PRPSE) equipped with an achromatic quarter wave was used for thin films/glasses analysis. Al–Cr–Fe approximant thin films were deposited from the vapor phase on the glass substrates. The optical constants were determined at room temperature in the spectral range from 500 to 800 nm. The best glass/layer/Al2O3 model using for the regression procedure is validated by the transmittance technique. The refractive index and extinction coefficient vary with the wavelength from 3.8 to 5.3 and 4.3 to 3.5, respectively. Surface layer on the glass substrates was treated as a mixture of air and Al–Cr–Fe compound by using the Bruggeman effective medium approximation. The oxide thickness derived as an independent parameter in the best model is in agreement with the oxide thickness derived from X-ray photoelectron spectroscopy measurements.
Keywords: Ellipsometry; Al–Cr–Fe; Approximant; Optical constants; TEM; Transmission;
Silicon dioxide thin film removal using high-power nanosecond lasers by J. Magyar; A. Sklyarov; K. Mikaylichenko; V. Yakovlev (306-313).
High intensity nanosecond laser pulses of different wavelengths are used to remove thin film silicon dioxide coatings from the silicon surface. Films as thick as 0.7 μm can be removed from the surface in one shot with very minor or no damage to the bare silicon surface. The accumulated effect of multiple-pulse irradiation is studied. It is found that multiple-pulse irradiation results in some reduction of the threshold for coating removal. However, the surface quality gets significantly worse with the increasing number of shots.
Keywords: Silicon dioxide; Thin film; High-power nanosecond lasers;
Lattice deformation in laser-irradiated silicon crystal studied by picosecond X-ray diffraction by Hiroaki Kishimura; Akio Yazaki; Yoichiro Hironaka; Kazutaka G. Nakamura; Ken-ichi Kondo (314-317).
Lattice deformation in laser-irradiated Si(1 1 1) has been studied by picosecond X-ray diffraction at a delay time of 350 ps. The rapid thermal expansion (0.24% at maximum) was observed at 2.0 GW/cm2 irradiation. By irradiation above dielectric breakdown threshold (10.0 GW/cm2), the intense lattice compression (2.1% at maximum) was observed. The compression is caused by the laser ablation due to dielectric breakdown.
Keywords: Time-resolved X-ray diffraction; Silicon; Laser ablation; Picosecond;
Adsorption on transition aluminas from in situ capacitance measurements by Monica Caldararu; Georgeta Postole; Mariana Carata; Cristian Hornoiu; Niculae I Ionescu; Tatiana Ioujakova; Akos Redey (318-326).
The interaction of water or propylene dipoles with surface of γ-Al2O3 and of a boehmite type alumina between room temperature and 400 °C was evaluated from evolution of the apparent capacity/dielectric constant during thermal cycling and under flushing with dry or humid gases (argon, oxygen) and with a mixture containing propylene and air (i.e. in conditions which mimic the catalytic experiment). Data allowed to stipulate that the extent of weak adsorption was higher on γ-Al2O3, in relation with the higher amount of surface OH groups, as supported by IR data.
Keywords: 82.65.Jv; 77.22.-d; 82.80.-ch; Alumina; Capacity; Dielectric constant; Dehydration; Water adsorption; Propylene adsorption;
Surface heterogeneity and ionization of Cs promoter in carbon-based ruthenium catalyst for ammonia synthesis by Andrzej Kotarba; Jaromir Dmytrzyk; Wioletta Raróg-Pilecka; Zbigniew Kowalczyk (327-333).
Second-generation ammonia synthesis cesium-doped ruthenium catalyst supported on turbostratic carbon was investigated by the species resolved thermal alkali desorption method (SR-TAD). Energetic barriers for cesium ions (2.86 eV), ground state (1.96 eV) and electronically excited atoms (5.76 eV) desorbing from the Cs-Ru/C catalyst were determined. In the case of ruthenium-free Cs/C system, cesium desorbs as ground state atoms only, with an energy barrier of 2.87 eV. The work functions determined by the thermionic emission of electrons from Cs/C and Cs-Ru/C were of the same value (2.9 eV). It was concluded that ruthenium induces heterogeneous distribution of cesium on the catalyst surface. The promoter stability is reduced on low work function areas and its surface ionization on high work function areas opens the ionic desorption channel. The Cs desorption from the catalyst is discussed in terms of the literature data for the cesium/graphite system.
Keywords: Cesium; Surface stability; Surface ionization; Electronic excitation; Catalyst; Thermal desorption;
Ion beam induced formation of metastable alloy phases in Cu–Mo system during ion beam assisted deposition by B. Zhao; D.M. Li; F. Zeng; F. Pan (334-340).
The Cu–Mo alloy film with positive heat of mixing was prepared by ion beam assisted deposition (IBAD) technique. When the energy of Ar+ ions was 2 keV during IBAD, metastable bcc Cu was formed in the Cu20Mo80 film. A Mo-based bcc supersaturated solid solution was obtained within the composition range of 0–50% Cu fraction. An fcc supersaturated solid solution was also formed around the composition of 15 at.% Mo. The formation mechanisms of the metastable alloy phases were discussed in terms of the process far from equilibrium.
Keywords: Microstructure evolution; Solid solution; Ion beam assisted deposition; Metastable bcc Cu;
Studies on ZnO:Al thin films deposited by in-line reactive mid-frequency magnetron sputtering by R.J. Hong; X. Jiang; B. Szyszka; V. Sittinger; A. Pflug (341-350).
Al-doped ZnO (ZnO:Al or AZO) films were deposited on glass substrates using an in-line reactive mid-frequency (MF) magnetron sputtering process. The influence of the deposition parameters including oxygen partial pressure and substrate temperature on the surface morphology and electrical, optical and mechanical properties of the films were investigated. The film hardness as determined by a nano-indenter indicate that the crystallinity of the ZnO:Al films was improved with increasing substrate temperature. The films with minimum resistivity could only be deposited under a narrow range of oxygen partial pressure. The carrier concentration, Hall mobility and optical band gap of the ZnO:Al films increased when the substrate temperature was raised from room temperature to 150 °C, and then decreased when the temperature was higher than 150 °C. The film prepared at the substrate temperature of 150 °C exhibited columnar structure with a RMS roughness of 4.4 nm and a lowest resistivity of 4.6×10−4 Ω cm. The transmittance and reflectance spectra with the ellipsometric data were analyzed by using a Drude–Lorentz–Gauss model.
Keywords: Transparent conductive oxides; Reactive deposition; Al-doped ZnO (AZO);
H+, Na+, and K+ ion sensing properties of sodium and aluminum coimplanted LPCVD silicon oxynitride thin films by Paik-Kyun Shin; Thomas Mikolajick (351-358).
Three different silicon oxynitride layers were fabricated by varying NH3/N2O flow rate ratios in low pressure chemical vapor deposition (LPCVD) process. Sodium and aluminum were then coimplanted by implanting sodium ions with the energy of 100 keV and dose of 5×1016 cm−2 into an aluminum buffer layer on silicon dioxide and three different silicon oxynitride layers. The composition of the as-deposited silicon oxynitride layers was analyzed by sputtered neutral mass spectroscopy (SNMS). Sodium, potassium and pH-sensing properties of the layers were investigated on an electrolyte-isolator-silicon (EIS) structure using high frequency capacitance–voltage (HF-CV) measurements. Differences of pH, sodium and potassium sensing properties between the as-deposited silicon oxynitride layers and the coimplanted silicon oxynitride layers were investigated. The sodium and aluminum coimplanted layers showed better sodium and potassium sensitivity as well as a lower sensitivity towards hydrogen ions. The effect is more pronounced for higher oxygen concentration in the layers. On the other hand the stability of ion response of the layers, in contrast, is better for the higher nitrogen content of the layers.
Keywords: Silicon oxynitride; Ion implantation; Ion sensitivity; ISFET;
Effects of ZnO buffer layer thickness on properties of ZnO thin films deposited by radio-frequency magnetron sputtering by Kyu-Hyun Bang; Deuk-Kyu Hwang; Jae-Min Myoung (359-364).
A series of ZnO films were deposited on c-plane sapphire substrates having different buffer layer thicknesses between 50 and 500 Å by radio-frequency (rf) magnetron sputtering. Scanning electron microscopy (SEM) was utilized to investigate the surface morphology of ZnO films. The crystallinity of ZnO films was investigated by the double-crystal X-ray diffractometry (DCXRD). The optical properties of ZnO films were also investigated using low-temperature (LT) photoluminescence (PL). It was found that the surface morphology, structural and optical properties of the films depended on the thickness of the buffer layer. The films deposited on the 100 Å thick ZnO buffer layer exhibit the good structural and optical properties with a very smooth surface.
Keywords: ZnO; Buffer layer; Sapphire substrate; rf Magnetron sputtering; SEM; PL;
Selective surface texturing using femtosecond pulsed laser induced forward transfer by B Tan; K Venkatakrishnan; K.G Tok (365-371).
Microdeposition of metal structure on quartz substrate using femtosecond pulsed laser induced forward transfer has been studied. A femtosecond laser having pulse duration of 150 fs and central wavelength spectrum of 400 nm was coupled to a two-axis acousto-optical deflector micromachining system, which provides selective deposition with spatial resolution of 2 μm. Experiments were conducted with air ambient. The laser irradiation spot was focused on the gold thin film (donor) through supporting quartz substrate. The removed material was transferred onto an acceptor, a quartz substrate, which was placed in near contact with the donor substrate. The transferred patterns were measured and investigated by the images obtained from scanning electron microscope and atomic force microscope. The results reveal that to obtain the best deposition with maximum thickness, the laser fluency must be precisely controlled just above the ablation threshold.
Keywords: Microdeposition; Texturing; Laser induced forward transfer; Femtosecond pulsed laser;
Transmission electron microscopy study of plasma nitriding of electroplated chromium coating by L Wang; K.S Nam; S.C Kwon (372-377).
In this paper, the influence of plasma nitriding at temperature 720 °C for 20 h on the surface microstructure and interface microstructure of electroplated chromium coating was investigated. In these conditions, interdiffusion, mixing and reaction phenomena of elements originating from the substrate and coating material are more likely to occur, thus increasing the bonding strength between the coating and carbon steel substrate. The change of the structures from the substrate side to the coating surface, and the effect of the substrate steel on the interface structure were studied by cross-sectional transmission electron microscope observation (XTEM). The nitride layer formed on the surface was analyzed by X-ray diffraction method (XRD). After treatment at above conditions a 6–7 μm thick nitride compound layer was formed in surface region and the same thick carbide compound layer was also formed in the interface region between electroplated chromium coating and mild carbon steel substrate.
Keywords: Interdiffusion; X-ray diffraction; Scanning electron microscopy;
Polyaniline on surface modification of diatomite: a novel way to obtain conducting diatomite fillers by Xingwei Li; Chaoqing Bian; Wei Chen; Jinbo He; Zhaoquen Wang; Ning Xu; Gi Xue (378-383).
A conducting diatomite was obtained by polyaniline on surface modification of diatomite, and was characterized via Fourier-transform Raman spectra, UV-Vis absorption spectra, thermogravimetric analysis and scanning electron microscope, as well as conductivity. The results of spectroanalysis illustrate that polyaniline is not simply blended with diatomite. An interaction exists at the interface of diatomite and polyaniline, which may associate with hydrogen bond formed between the surface of diatomite with electronegativity and NH bond in polyaniline macromolecule. The results of thermogravimetric analysis suggest that the conducting diatomite only contains 8% polyaniline by mass, but its conductivity has reached 2.8×10−2 S cm−1 at 20 °C.
Keywords: Polyaniline; Diatomite; Interface;