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Applied Surface Science (v.253, #16)

Preface by Toshiaki Makabe; Seiji Samukawa (pp. 6617-6617).

Data and modeling of negative ion transport in gases of interest for production of integrated circuits and nanotechnologies by Z.Lj. Petrović; Z.M. Raspopović; V.D. Stojanović; J.V. Jovanović; G. Malović; T. Makabe; J. de Urquijo (pp. 6619-6640).

We review techniques to prepare, evaluate and apply sets of cross section and transport data for negative ions that are required for the modeling of collisional non-equilibrium plasmas used for processing of microelectronic circuits. We collect and discuss the transport coefficients and cross section sets.We have compiled data for negative ions in CF₄ and CF₄-related negative ions in rare gases. In addition, we consider data for F⁻ and CF₃⁻ in rare gases. Furthermore, we analyze the cross sections of halogen negative ions in rare gases and other molecules. This is followed by the data for SF₆ related ions in SF₆ and in rare gases. The cross section for scattering of O⁻ in O₂ has been derived from the transport data and used to make calculations of the transport properties. Finally we give a brief discussion of the availability of the data for H⁻ ions in H₂. We have derived cross sections in several cases but the basic aim is to show the basic features of transport coefficients. In particular we discuss the need to represent properly some details such as the non-conservative nature of transport coefficients and the anisotropy of diffusion. Application of approximate theories and representations of cross sections are also discussed.

Keywords: Negative ions; Monte Carlo; Transport coefficients; Swarm data; Plasma processing; Plasma modeling; Halogen ions; SF; ₆; Oxygen; Hydrogen; Molecular ions

Negative-ion formation and mutual neutralization in atom–atom and ion–ion collisions below keV energies by Mineo Kimura (pp. 6641-6645).

Dynamics and cross-section values for ion-pair formation and its reverse process, mutual neutralization in atom–atom and ion–ion collisions are reviewed for hydrogen–hydrogen atom collisions and hydrogen–alkali atom collisions. For ion-pair formation process, the initial state shows a weak polarization potential, while the final ion-pair state arises from a strong Coulomb potential. Hence, the final state shows a series of avoided crossings with many intermediate states which correspond to electronic excited states of one of pairs. Therefore, the ladder climbing mechanism is the driving dynamics for ion-pair formation. This fact, that is, many sates are involved in dynamics, makes theoretical treatments more complex and cumbersome for an accurate description. We overview the current experimental and theoretical status of these processes.

Keywords: Ion-pair; Neutralization; Collisions

Inelastic electron scattering and energy-selective negative ion reactions in molecular films on silicon surfaces by Chirstopher D. Lane; Thomas M. Orlando (pp. 6646-6656).

Careful control of plasma chemistry, particularly the negative ion production and reaction channels, could lead to nanoscale patterning, growth, and etching strategies. Since the energies of anion and electron surface collisions are relatively low (<10eV) in plasmas, these interactions are essentially damage free with respect to the buried interface and subsurface region. Thus, renewed interest has arisen that takes advantage of negative ion surface chemistry in film deposition and nanopatterning. We review (i) the transient negative ion states such as shape and dissociative electron attachment resonances produced during electron molecule scattering, (ii) the many body interactions and substrate-effects on the resonance energies, widths and cross sections and (iii) examples of post-dissociation interactions of the reactive fragments and anions that may lead to controlled etching or growth. Specifically, we summarize past and recent studies on electron scattering with gas- and condensed-phase H₂O, CF₄, SiCl₄ and O₂ targets. We then discuss recent examples of energy selective oxidation and fluorination of hydrogen terminated silicon surfaces and comment on the general applicability of low-energy electrons and negative ion surface chemistry in film deposition, nanopatterning and growth strategies.

Keywords: Plasma processing; Electron-solid interactions; Electron-stimulated desorption; Growth; Silicon

Insights into sticking of radicals on surfaces for smart plasma nano-processing by Masaru Hori; Toshio Goto (pp. 6657-6671).

In reactive plasma processing, species produced in the plasma reach the surface of a substrate and cause etching, deposition and surface modification through surface reactions. These reactions are characterized by the densities and energies of species incident on the surfaces. In order to realize nano-scale plasma processing, important species for plasma processing have been identified and characterized, and their behavior, not only in the gas phase, but also on the surface, have been clarified and controlled. One of the most critical parameters for insights into surface reaction kinetics of radicals is sticking and surface loss probability. On the basis of radical densities measured by various methods, the sticking and surface reaction loss probabilities have been compiled, and they enable the quantitative understanding of the kinetics of radicals on the surface in the plasma. In this article, the sticking and surface reaction loss probabilities measured thus far are reviewed focusing on fluorocarbon gas, silane gas and methane gas based plasma processes. The establishment of a smart plasma process and the development of an autonomous production device with control of radicals on the basis of insights into the surface reactions for nano-scale plasma processing are presented.

Keywords: Radical; Sticking; Loss probability; Plasma processing

Fundamentals and applications of ion–ion plasmas by Demetre J. Economou (pp. 6672-6680).

Ion–ion plasmas can form in the late afterglow of pulsed discharges or downstream of continuous wave discharges in electronegative gases. In ion–ion plasmas, negative ions replace electrons as the negative charge carriers. In the absence of electrons, ion–ion plasmas behave quite differently compared to conventional electron–ion plasmas. Application of a radio frequency bias to a substrate immersed in an ion–ion plasma can be used to extract alternately positive and negative ions, thereby minimizing charging on device features during micro-device fabrication. Ion–ion plasmas are also important in negative ion sources, dusty plasmas, and the D-layer of the earth's atmosphere.

Keywords: Pulsed plasma; Afterglow; Charging damage; Negative ions; Simulation

High-performance and damage-free neutral-beam etching processes using negative ions in pulse-time-modulated plasma by Seiji Samukawa (pp. 6681-6689).

For the past 30 years, plasma-etching technology has led efforts to shrink the patterns of ultralarge-scale integrated (ULSI) devices. However, inherent problems with plasma processes, such as charge build-up and UV photon radiation, have limited etching in the future devices. To overcome these and fabricate sub-50nm devices in practice, neutral-beam etchings have been proposed. In this paper, we introduce damage-free etching processes using neutral beam with negative ions in pulse-time-modulated plasmas. These techniques can achieve damage-free etching processes. They are promising candidates for the practical technology that will be required to fabricate future devices.

Keywords: Neutral beam; ULSI; Plasma etching

Designable formation of metal nanoparticle array with the deposition of negatively charged nanoparticles by Sayuri Kawabata; Yasutomo Naono; Yosuke Taguchi; Seung H. Huh; Atsushi Nakajima (pp. 6690-6696).

Ultrafine gold and platinum nanoparticles (NPs) were fabricated by pulsed laser ablation in helium gas and the NPs 2–15nm in diameter were selectively classified by an electrostatic size-selection technique employing a low-pressure differential mobility analyzer (LP-DMA). The spherical NPs obtained showed a narrower distribution of diameters of anionic NPs over cationic NPs. With this knowledge, the anionic NPs were deposited onto silicon substrates designed by electron beam lithography processing, and designable patterns of arrayed NPs were produced by removing the photoresist layer.

Keywords: Pulsed laser ablation; Nanoparticles; LP-DMA; Nanodevices

On interface properties of ultra-thin and very-thin oxide/a-Si:H structures prepared by oxygen based plasmas and chemical oxidation by Emil Pinčík; Hikaru Kobayashi; Rudolf Hajossy; Helena Glesková; Masao Takahashi; Matej Jergel; Róbert Brunner; Luc Ortega; Michal Kučera; Martin Kráľ; Jaroslav Rusnák (pp. 6697-6715).

Amorphous hydrogenated silicon (a-Si:H) belongs still to most promising types of semiconductors for its utilization in fabrication of TFTs and thin film solar cell technology due to corresponding cheap a-Si:H-based device production in comparison with, e.g. crystalline silicon (c-Si) technologies. The contribution deals with both two important modes of preparation of very-thin and ultra-thin silicon dioxide films in the surface region of a-Si:H semiconductor (oxygen plasma sources and liquid chemical methods) and electrical, optical and structural properties of produced oxide/semiconductor structures, respectively. Dominant aim is focused on investigation of oxide/semiconductor interface properties and their comparison and evaluation from view of utilization of used technological modes in the nanotechnological industry. Following three basic types of oxygen plasma sources were used for the first time in our laboratories for treatments of surfaces of a-Si:H substrates: (i) inductively coupled plasma in connection with its applying at plasma anodic oxidation; (ii) rf plasma as the source of positive oxygen ions for plasma immersion ion implantation process; (iii) dielectric barrier discharge ignited at high pressures.The liquid chemical manner of formation SiO₂/a-Si:H structures uses 68wt% nitric acid aqueous solutions (i.e., azeotropic mixture with water). Their application in crystalline Si technologies has been presented with excellent results in the formation of ultra-thin SiO₂/c-Si structures [H. Kobayashi, M. Asuha, H.I. Takahashi, J. Appl. Phys. 94 (2003) 7328].Passivation of surface and interface states by liquid cyanide treatment is additional original technique applied after (or before) formation of almost all formed thin film/a-Si:H structures. Passivation process should be used if high-quality electronical parameters of devices can be reached.

Keywords: Plasma interaction; Very-thin oxides; Interface; Cyanide treatment

Control of reactive plasmas for low- k/Cu integration by Tetsuya Tatsumi (pp. 6716-6737).

We proposed models for controlling surface reactions during etching of SiOCH and organic material. The etch rate of each material can be determined by the balance between the total atom fluxes of O, C, F, N, and H that were supplied from both the plasma and the etched material to the reactive layer. Low- k films (SiOCH, porous SiOCH, and organic material) have narrow process windows for obtaining good etching properties, such as selectivity, because the polymer and reactive layers on these films can be changed by only slight changes in the plasma parameters. Therefore, the partial pressure and dissociation of parent gas molecules in fluorocarbon or N–H plasma as well as plasma–wall interaction must be controlled. To create highly reliable interconnects, the interfaces between the metal and low- k must be optimized during the etching of stopper material and ashing. The surface of Cu is very reactive, the remaining F induces degradation of Cu. SiOCH can easily be oxidized during ashing processes, and the adsorption of H₂O on damaged SiOCH causes interconnect failure during electrical tests. To suppress problems in the etching and ashing processes, the balance of the total atom fluxes should be quantitatively and instantaneously controlled to the optimum point for each material.

Keywords: Plasma; Dry etching; Low-; k; SiOCH; Cu; Damage

Effect of hydrazine and hydroxylaminophosphate on chrome plating from trivalent electrolytes by S. Survilienė; V. Jasulaitienė; O. Nivinskienė; A. Češūnienė (pp. 6738-6743).

The influence of hydrazine and hydroxylaminophosphate on solution chemistry and quality of chromium coatings deposited from Cr(III) formate–urea baths has been studied by FT-IR, XPS and AFM. The results have shown that hydrazine and hydroxylaminophosphate differently affect Cr plating. The morphology of Cr deposits obtained in the formate–urea electrolytes is a typical nodular structure with a less nodular and smoother fine-grained structure of Cr obtained in the presence of hydroxylaminophosphate. Hydrazine, in contrast, worsened the quality and lowered the hardness of the deposits. The current efficiency of chromium increases in the presence of both hydrazine and hydroxylaminophosphate. This may be related with the ability of these ligands to reduce the CrH content in the growing Cr deposit. The data obtained suggest that hydroxylaminophosphate improves the stability of the active [Cr(carbamide)_n(H₂O)6−_n]³ complexes providing good quality of the deposits and prolonged working lifetime in the formate–urea bath.

Keywords: Chromium; Formate; Urea; Hydrazine; Hydroxylaminophosphate; Electrodeposition; XPS; FT-IR

Plasma oxynitrocarburizing of 40Cr steel in an atmosphere of gasoline and air by L.F. Liu; S.Q. Zhou; Q. Ren (pp. 6744-6748).

A new plasma oxynitrocarburizing process in an air and gasoline atmosphere was developed. The influences of the atmosphere with different ratios of gasoline/air on the microstructure, surface hardness, and phase composition of 40Cr steel were characterized using optical microscope, scanning electron microscope (SEM), microhardness tester, and X-ray diffractometer (XRD), respectively. The experimental results showed that the plasma oxynitrocarburized layer was composed of bright layer and diffusion layer. It was found that the thickness, hardness, and Fe₃N concentration of the plasma oxynitrocarburized layer increased with the increment of ratio of gasoline/air.

Keywords: Oxynitrocarburizing; Air; Gasoline

Preparation of nanosized ZnO using α brass by W.J. Chen; W.L. Liu; S.H. Hsieh; T.K. Tsai (pp. 6749-6753).

Nanosized ZnOs were synthesized on the surface of α brass coated a film of nickel catalyst at 500–700°C under atmosphere of O₂ and CH₄ gases. The nanosized ZnOs have shapes including pillar, leaf, sheet and rod, which were determined by the synthesis temperature and the flow rates of O₂ and CH₄ gases. The nanosized ZnOs were characterized by electron microscopy including transmission electron microscope for crystal structure, morphology and high resolution images, both field emission scanning electron microscope and scanning electron microscope for morphology, and energy dispersive X-ray spectroscope equipped in electron microscope for chemical composition. A mechanism was proposed for the growth of nanosized ZnO obtained in this work.

Keywords: Nanosized ZnO; Ni catalyst; Brass; Carbon nanotube

An investigation of nanoscale tribological characteristics under different interaction forces by Yeau-Ren Jeng; Chien-Chan Su; Yeong-Tsyh Lay (pp. 6754-6761).

The present study employs a Finite Element Method (FEM) atomic approach to investigate the nanoscale mechanisms of sliding friction. The current investigation chooses diamond-like carbon as the hard material, and copper as the soft material. The atomic configurations following sliding under non-interactive, attractive, and repulsive interaction forces are observed for soft-to-soft, hard-to-soft, and hard-to-hard sliding systems. The relationships between the normal force, the friction force, and the sliding distance are discussed. The current simulation results exhibit a similar trend with the findings of previous studies using molecular dynamics approach.

Keywords: Friction; Wear; Nanoscale sliding

Characterization and corrosion studies of titania-coated NiTi prepared by sol–gel technique and steam crystallization by K.Y. Chiu; M.H. Wong; F.T. Cheng; H.C. Man (pp. 6762-6768).

Nickel titanium (NiTi) was dip-coated with titania via the sol–gel route using titanium butoxide (Ti(OC₄H₉)₄) as precursor. The as-coated titania film was crystallized to form anatase by treatment in steam at 105°C. The crystallized film was relatively thick (about 750nm) and even. Atomic force microscopy (AFM) revealed that the film was dense with a surface roughness of about 3nm, and was composed of particles of about 100nm. X-ray diffractometry (XRD) showed that these particles were composed of nanocrystallites of a few nanometers. Nanoindentation tests of the titania film indicated that the film was tough, possibly due to the nano-size of the crystallites. The mean hardness H and elastic modulus E of the coating were about 1.5 and 70GPa, respectively. Direct pull-off test recorded a mean coating–substrate bonding strength larger than 17MPa. Electrochemical impedance spectroscopic (EIS) study and cyclic polarization tests showed that the corrosion resistance of the coated NiTi samples in Hanks’ solution was increased by about two orders of magnitude compared with the substrate. Taken together, the present study showed that steam crystallization is a feasible low-temperature treatment method for sol–gel derived titania coating on NiTi in biomedical applications.

Keywords: TiO; ₂; NiTi; Corrosion resistance; Sol–gel coating; Crystallization

On texture, corrosion resistance and morphology of hot-dip galvanized zinc coatings by H. Asgari; M.R. Toroghinejad; M.A. Golozar (pp. 6769-6777).

Texture is an important factor which affects the coating properties. Chemical composition of the zinc bath can strongly influence the texture of hot-dip galvanized coatings. In this study, lead content of the zinc bath was changed from 0.01wt.% to 0.11wt.%. Specimens were prepared from zinc baths of different lead content and its texture was evaluated using X-ray diffraction. Corrosion behaviour was analyzed by Tafel extrapolation and linear polarization tests. To study the corrosion products of the specimens, salt spray test was employed. Also, the spangle size of the specimens was determined using line intercept method. From the experimental results it was found that (00.2) basal plane texture component would be weakened by increasing the lead content of the zinc and conversely, (20.1) high angle pyramidal texture components strengthened. Besides, coatings with strong (00.2) texture component and weaker (20.1) component have better corrosion resistance than the coatings with weak (00.2) and strong (20.1) texture components. In addition, surface morphology would be changed and presence of basal planes decreases at the coating surface due to the increase of lead in the zinc bath. Furthermore, spangle size would be increased by increasing the lead content of the zinc bath. Investigation on the effects of skin pass rolling showed that in this case, (00.2) basal texture component and corrosion resistance of the skin passed specimens, in comparison with non-skin passed specimens, have been decreased.

Keywords: Texture; Corrosion resistance; Skin pass rolling; Tafel/linear polarization test; Morphology; Hot-dip galvanizing

Effects of duty ratio at low frequency on growth mechanism of micro-plasma oxidation ceramic coatings on Ti alloy by Zhongping Yao; Ruihai Cui; Zhaohua Jiang; Fuping Wang (pp. 6778-6783).

The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti–6Al–4V alloy prepared by pulsed single-polar MPO at 50Hz in NaAlO₂ solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. The changes of the duty ratio ( D) of the anode process led to the changes of the mode of the spark discharge during the pulsed single-polar MPO process, which further influenced the structure and the morphology of the ceramic coatings. The coatings prepared at D=10% were composed of a large amount of Al₂TiO₅ and a little γ-Al₂O₃ while the coatings prepared at D=45% were mainly composed of α-Al₂O₃ and γ-Al₂O₃. The coating thickness and the roughness were both increased with the increasing D due to the formation of Al₂O₃. The formation of Al₂TiO₅ resulted from the spark discharge due to the breakdown of the oxide film, while the formation of Al₂O₃ resulted from the spark discharge due to the breakdown of the vapor envelope. The ceramic coatings improved the corrosion resistance of Ti–6Al–4V alloy. And the surface morphology and the coating thickness determined the corrosion resistance of the coated samples prepared at D=45% was better than that of the coated samples prepared at D=10%.

Keywords: Ceramic coatings; Micro-plasma oxidation; Growth mechanism; Duty ratio

High sensitivity IR spectroscopic methods of self-assembling monolayers (SAM) measurements by A. Inberg; N. Croitoru; G. Revzin (pp. 6784-6786).

New systems of coupling the FTIR spectrum signal amplification, mainly for self-assembling monolayers (SAMs) investigation, were developed. These systems based on hollow waveguide (HW) or half cylinder mirror, which have negligible attenuation in the mid infrared; enable to obtain high signal sensitivity of the samples absorption due to the very high signal to noise ratio. This has lead more detailed characterization of the SAMs molecular structure and its modifications. In addition, a linear dependence of the signal on the number of IR radiation rays incidents on length of HW, which has resulted in simple interpretation of results, was obtained.

Keywords: Spectral absorption; FTIR spectroscopy; Sensitivity; SAM; Thiol

Relative performances of effective medium formulations in interpreting specific composite thin films optical properties by N.K. Sahoo; S. Thakur; R.B. Tokas; N.M. Kamble (pp. 6787-6799).

Several powerful effective medium formulations/approximation (EMA) and associated theories with different origins and concepts have been discussed and utilized here in order to model the experimental refractive index evolutions of ZrO₂–SiO₂ and Gd₂O₃–SiO₂ composite films with respect to their compositional mixings. Amongst these formulations, the Böttcher's generalized theory has been noticed to have more versatility and can simulate varieties of experimental observations incorporating a form factor parameter to account for the grain structure and morphology to a great extent. The refractive index modeling results of most of the available theories were compared with respect to their functional evolutions and limitations. It was noticed that at higher silica fractions (>20%) in our composite films, the effective experimental refractive index parameters have remained close to the most modeling results and Böttcher's expression has shown to fit the observable parameters very accurately. However, under low silica compositions (<20%) the refractive index values of the composite films depicted different functional evolutions. Such deviations have been attributed to the various morphological, grain structure and band gap supremacies observed in these specific composite films which are not accounted by the effective medium formulations and approximations. These observations are well supported by the atomic force microscopy results.

Keywords: PACS; 42.79.Wc, 78.66.−w, 78.20.Ci, 61.16.Ch, 51.70.+f, 52.70.KzEffective medium approximation; Optical coatings; Codeposition; Oxide thin films; Binary composites; Ellipsometry; Scanning probe microscopy; Thin film morphology; Band gap

Tribological behaviors of lanthanum-based phosphonate 3-aminopropyltriethoxysilane self-assembled films by Gu Qinlin; Cheng Xianhua (pp. 6800-6806).

Lanthanum-based thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated glass substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of the films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. The tribological results show that lanthanum-based thin films are superior in reducing friction and resisting wear compared with APTES-SAM and phosphorylated APTES-SAM. SEM observation of the morphologies of worn surfaces indicates that the wear of APTES-SAM and the phosphorylated APTES-SAM is characteristic of brittle fracture and severe abrasion. Differently, slight abrasion and micro-crack dominate the wear of lanthanum-based thin films. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate.

Keywords: 3-Aminopropyltriethoxysilane (APTES); Self-assembled monolayer (SAM); Friction; Adhesion

Synthesis and characterization of carbon nanotubes on carbon microfibers by floating catalyst method by Yuxue Xia; Leyong Zeng; Weibiao Wang; Jingqiu Liang; Da Lei; Song Chen; Haifeng Zhao (pp. 6807-6810).

In this paper, carbon nanotubes were synthesized on carbon microfibers by floating catalyst method with the pretreatment of carbon microfibers at the temperature of 1023K, using C₂H₂ as carbon source and N₂ as carrier gas. The morphology and microstructure of carbon nanotubes were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The composition of carbon nanotubes was determined by energy dispersive X-ray spectroscopy (EDX). The results showed that the surface of treated carbon microfibers was thickly covered by carbon nanotubes with diameters of about 50nm. EDX image indicated that the composition of carbon nanotubes was carbon. In comparison with the sample grown on untreated carbon microfibers surface, it was found that after carbon microfibers were boiled in the solution of sulfur acid and nitric acid (VH2SO4:VHNO3=1:3) and immersed in the solution of iron nitrate and xylene, carbon nanotubes with uniform density can be grown on carbon microfibers surface. Based on the results, we concluded that the pretreatment of carbon microfibers had great effect on the growth of carbon nanotubes by floating catalyst method.

Keywords: Carbon nanotubes; Carbon microfibers; Floating catalyst

Synthesis and electrochemical characteristics of Ta–N thin films fabricated by cathodic arc deposition by Li Li; Erwu Niu; Guohua Lv; Xianhui Zhang; Huan Chen; Songhua Fan; Chizi Liu; Si-Ze Yang (pp. 6811-6816).

Ta–N thin films were deposited on AISI 317L stainless steel (SS) substrates by cathodic arc deposition (CAD) at substrate biases of −50 and −200V. The as-deposited films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The results show that stoichiometric TaN with hexagonal lattice (300) preferred orientation was achieved at the bias of −200V. On the other hand, Ta-rich Ta–N thin film deposited at −50V shows amorphous nature. According to the XPS result, Ta element in the films surface exist in bonded state, including the Ta–N bonds characterized by the doublet (Ta 4f_7/2=23.7eV and Ta 4f_5/2=25.7eV). Electrochemical properties of the Ta–N coated stainless steel systems were investigated using potentiodynamic polarization and electrochemical impedance spectroscope (EIS) in Hank's solution at 37°C. For the Ta–N coated samples, the corrosion current ( i_corr) is two or three orders of magnitude lower than that of the uncoated ones, indicating a significantly improved corrosion resistance. Growth defects in the Ta–N thin films produced by CAD, however, play a key role in the corrosion process, especially the localised corrosion. Using the polarization fitting and the EIS modelling, we compared the polarization resistance ( R_p) and the porosity ( P) of the Ta–N coatings deposited at different biases. It seems that Ta–N film with comparatively lower bias (−50V) shows better corrosion behavior in artifical physiological solution. That may be attributed to the effect of ion bombarding, which can be modulated by the substrate bias.

Keywords: PACS; 52.75.−d; 68.55.−a; 81.65.KnTantalum nitride; Cathodic arc deposition; Microstructure; Corrosion

Fluram labeling of high density NH₂ surfaces by F. Pippig; A. Holländer (pp. 6817-6823).

Some surface bonded and fluram labeled primary amines show a new red-shifted emission in their fluorescence spectrum. We compared the fluorescence of fluram bonded to various amine functionalized surfaces including tetraethylene pentamine (TEPA), 1,2-ethylene diamine (EDA), 3-aminopropyltriethoxy silane (APTES) and trimetylol-propanetris-(beta-aziridino)-propionate (ATA). All reactions were also monitored using XPS. It was found that the new spectral features seem to be related to the local density of amino groups on the surface. In order to verify this hypothesis we synthesized a surface bonded dendrimer with a step-wise increasing NH₂ density. Using molecules with different lengths as branches in the dendrimer, the amine density can be varied. Only in the case of the highest density, the new fluorescence emission was detected. Consequently, the fluorescence of fluram coupled to amines at a surface can be used to quantify the concentration of these amines and the appearance of the red-shifted emission indicates a high local density of the amino groups.

Keywords: Fluram; Labeling; Fluorescence; Polyethylene-surface; Red shift; Dendrimer

Nano- and micro-scale patterning of Si (100) under keV ion irradiation by Yashpal S. Katharria; Sandeep Kumar; A. Tarun Sharma; Dinakar Kanjilal (pp. 6824-6828).

Evolution of Si (100) surface under 100keV Ar⁺ ion irradiation at oblique incidence has been studied. The dynamics of surface erosion by ion beam is investigated using detailed analysis of atomic force microscopy (AFM) measurements. During an early stage of sputtering, formation of almost uniformly distributed nano-dots occurs on Si surface. However, the late stage morphology is characterized by self-organization of surface into a regular ripple pattern. Existing theories of ripple formation have been invoked to provide an insight into surface rippling.

Keywords: PACS; 61.80.Jh; 68.37.Ps; 68.49.Sf; 81.65.CfSputtering; Nano-dots; Ripples; Atomic force microscopy

A study of direct- and pulse-current chromium electroplating on rotating cylinder electrode (RCE) by J.H. Chang; F.Y. Hsu; M.J. Liao; C.A. Huang (pp. 6829-6834).

Direct- and pulse-current (DC and PC) chromium electroplating on Cr–Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50°C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60Adm⁻², respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit.

Keywords: Chromium electroplating; Rotating speed; RCE; TEM microstructure

Fabrication of highly ordered and stepped ZnO comb-like structures by Wei Bai; Ke Yu; Qiuxiang Zhang; Feng Xu; Deyan Peng; Ziqiang Zhu (pp. 6835-6839).

Highly ordered and stepped ZnO comb-like structures were fabricated using conventional thermal evaporation method. Zn powder covered by a layer of a mixture of ZnO and graphite was employed as the Zn source. The obtained ZnO comb-like structures are several tens of micrometers and some of them are even up to 100μm. Both the widths of the belts and the lengths of the branches gradually decrease along the growth direction of ZnO comb-like structures. Under the most suitable condition, ZnO nanorods branches have uniform diameters and are evenly distributed on the belt-like stem. Possible growth process of ZnO comb-like structures was discussed. The effect of growth temperature on the morphology of the obtained products was also investigated. Room-temperature photoluminescence spectra from the ZnO comb-like structures and the nanorods film reveal weak UV emission and strong green emission.

Keywords: PACS; 78.30.Fs; 61.46.−w; 78.67.−nZinc oxide (ZnO); Comb-like structures; PL spectroscopy

Template synthesis and characterization of highly ordered lamellar hydroxyapatite by Chao Liu; Xiujie Ji; Guoxiang Cheng (pp. 6840-6843).

Surfactant template synthesis attracts great attention in the fields of biomaterials and functional materials. In this study, highly ordered lamellar hydroxyapatite (Lα-HA) powder was synthesized by a surfactant templating method in water–ethanol. Ca(NO₃)₂ and (NH₄)₂HPO₄ were used as calcium and phosphorus sources, respectively. Sodium dodecyl sulphonate (SDS, C₁₂H₂₅SO₃Na) acted as the template. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses showed that HA is the only crystal phase in Lα-HA. Transmission electron microscope (TEM) observation further proved this regular lamellar structure detected by XRD. The repeat periodicity of the structure is about 3.6nm observed by TEM, which is in well accordance with the XRD data (3.16nm). The selected area electron diffraction (SAED) results indicated that Lα-HA was a polycrystalline structure. The formation of Lα-HA could be explained by a surfactant template.

Keywords: Lamellar; Hydroxyapatite; Nanostructure; Surfactant; Template

X-ray photoelectron spectroscopic study on initial oxidation of hafnium hydride fractured in an ultra-high vacuum by Naofumi Ohtsu; Bun Tsuchiya; Masaoki Oku; Tatsuo Shikama; Kazuaki Wagatsuma (pp. 6844-6847).

The initial oxidation of hafnium hydride was studied by X-ray photoelectron spectroscopy (XPS). The clean surface of hafnium hydride was obtained by fracturing the specimen in an XPS measurement chamber under a background pressure of 2.7×10⁻⁶Pa. The fractured surface was oxidized in situ with the exposure to high-purity oxygen and the residual gases in an ultra-high vacuum chamber. The XPS spectra for the oxidized surfaces had the shoulder due to the oxidation, and the shoulder grew up with increase in exposure time even in the ultra-high vacuum. The factor analysis for the XPS spectra of the oxidized surface showed that the oxide formed in the chamber consists of only the hafnium dioxide, and no suboxide states are contained. The result corresponded to the oxide observed on hafnium hydride fractured in air.

Keywords: X-ray photoelectron spectroscopy; Hafnium hydride; Initial oxidation; Fracturing; Factor analysis

Investigations of environmental induced effects on AlQ₃ thin films by AFM phase imaging by Vivek Kumar Shukla; Satyendra Kumar (pp. 6848-6853).

Tris(8-hydroxyquinoline) metal complex (AlQ₃) is a widely used light-emitting material in organic light emitting devices (OLEDs). The environmental stability is still a major problem with OLEDs and needs further improvement. In this report, an additional feature of Atomic Force Microscopy (AFM) was exploited with the aim to understand the environmental induced effects and physical phenomenon involved on AlQ₃ thin films. We have used phase imaging to identify the presence of other aggregation phases formed after annealing the thin film in different ambient and after white light exposure. An enhanced photoluminescence intensity is observed for the samples annealed in oxygen near 100°C. The enhanced photoluminescence is understood in terms of formation of a new aggregation phase. The phase change and the fraction of new phase is estimated by phase images taken by atomic force microscopy (AFM). Light induced effects on AlQ₃ films exposed to white light in air and vacuum are characterized by atomic force microscopy (AFM) for surface morphology and phases present. The AFM images indicate enhanced crystallinity for the vacuum exposed samples. The phase with increased lifetime and hence enhanced crystallinity for vacuum exposed films has also been found by time correlated single photon counting (TCSPC) measurements. To the best of our knowledge, this study is applied for the first time on this material with the combination of topography and phase imaging in atomic force microscopy (AFM). The major aim was to take advantage of the additional feature of AFM-mode over the conventionally used.

Keywords: PACS; 78.66Qn Polymers; Organic compoundsOrganic light emitting devices (OLEDs); Photoluminescence (PL); Tris(8-hydroxyquinoline)aluminium (AlQ; ₃; ); Atomic force microscopy (AFM)

Composition, structure and morphology of oxide layers formed on austenitic stainless steel by oxygen plasma immersion ion implantation by C. Anandan; K.S. Rajam (pp. 6854-6859).

Oxygen ions were implanted in to austenitic stainless steel by plasma immersion ion implantation at 400°C. The implanted samples were characterized by XPS, GIXRD, micro-Raman, AFM, optical and scanning electron microscopies. XPS studies showed the presence of Fe in elemental, as Fe²⁺ in oxide form and as Fe³⁺ in the form of oxyhydroxides in the substrate. Iron was present in the oxidation states of Fe²⁺ and Fe³⁺ in the implanted samples. Cr and Mn were present as Cr³⁺ and Mn²⁺, respectively, in both the substrate and implanted samples. Nickel remained unaffected by implantation. GIXRD and micro-Raman studies showed the oxide to be a mixture of spinel and corundum structures. Optical and AFM images showed an island structure on underlying oxide. This island structure was preserved at different thicknesses. Further, near the grain boundaries more oxide growth was found. This is explained on the basis of faster diffusion of oxygen in the grain boundary regions. Measurement of total hemispherical optical aborptance, α and emittance, ɛ of the implanted sample show that it has good solar selective properties.

Keywords: PACS; 52.77.Dq; 81.65.Mq; 68.55.JkPlasma immersion ion implantation; Iron oxide; XPS; AFM

The acid–base properties of the surface of native zinc oxide layers: An XPS study of adsorption of 1,2-diaminoethane by G. Ballerini; K. Ogle; M.-G. Barthés-Labrousse (pp. 6860-6867).

The acid–base properties of native zinc oxide surfaces have been studied using X-ray photoelectron spectroscopy (XPS). The native layers of zinc oxide have been obtained by ageing mechanically polished pure zinc disks in a glass dryer for 1 month. Such a treatment lead to the formation of an unstable oxide layer and dehydroxylation has been observed during storage in vacuum. By following adsorption in ultrahigh vacuum of 1,2-diaminoethane (DAE) several types of active sites have been evidenced. Zinc cations react with the probe molecule following a Lewis acid/base interaction, while the hydroxyl and the carbonate-like species react following a Brønsted acid/base reaction. Although initial interaction via the Brønsted-like mechanisms is favoured, it has been shown that the resulting complexes are not stable. Under vacuum conditions, the adsorbed DAE molecules either partly desorb or modify their interaction mode with the surface to form additional Lewis-like bonded stable complexes. In addition, a cleaning effect of the molecule has been observed which lead to partial removal of the carbonate-like contamination.

Keywords: PACS; 82.65.+r; 82.80.Pv; 82.45.JnEthylenediamine; Acid–base interactions; Zinc oxide layers; Adhesion; Bonding stability; X-ray photoelectron spectroscopy

Slow positron beam study of nitrogen implanted CZ-Si subjected to rapid thermal processing by X.P. Hao; R.S. Yu; B.Y. Wang; H.L. Chen; D.N. Wang; C.X. Ma; L. Wei (pp. 6868-6871).

In this experiment, nitrogen ions were implanted into CZ-silicon wafer at 100keV at room temperature with the fluence of 5×10¹⁵N₂⁺/cm², followed by rapid thermal processing (RTP) at different temperatures. The single detector Doppler broadening and coincidence Doppler broadening measurements on slow positron beam were carried out to characterize the defects in the as-implanted silicon and RTP-treated samples. It is found that both nitrogen-vacancy complexes (N-Vsi) and oxygen-vacancy complexes (O-Vsi) produced by nitrogen implantation diffuse back to the sample surface upon annealing. But the N-Vsi and the O-Vsi complete with each other and give a summed effect on positron annihilation characteristics. It is shown that the N-Vsi win out the O-Vsi in as-implanted sample and by RTP at 650°C, 750°C, which make the S-parameter increase; O-Vsi plays a dominant role after annealing above 850°C, which makes the S parameter decrease.

Keywords: Slow positron beam; Nitrogen ion implantation; Rapid thermal processing

Imaging characterization of carbon nanotube tips modified using a focused ion beam by Young-Hyun Shin; Jin-Won Song; Eung-Sug Lee; Chang-Soo Han (pp. 6872-6877).

A carbon nanotube (CNT) tip, which assembled on the sharp end of a Si tip by dielectrophoresis, was structurally modified using focused ion beam (FIB). We described the imaging characterization of the FIB-modified CNT tip in noncontact AFM mode in terms of wear, deep trench accessibility, and imaging resolution. Compared to a conventional Si tip, the FIB-modified CNT tip was superior, especially for prolonged scanning over 10h. We conclude that modified CNT tips have the potential to obtain high-quality images of nanoscale structures.

Keywords: Carbon nanotube; Atomic force microscopy; Wear; Imaging

The water–silicas interfacial interaction energies by Ahmed K. Helmy; Silvia G. de Bussetti; Eladio A. Ferreiro (pp. 6878-6882).

The water–silicas interfacial interaction energies were calculated for samples of quartz, silicas and silicas outgassed at high temperatures using own and published data of the spreading pressure of water, its surface tension, its contact angle and using formulas obtained by the combination of the Young equation with a general equation of pair interaction. The values obtained for 18 different samples were in the range 7.80–6.92kJmol⁻¹. Lower values of energies are for samples that contain relatively less amounts of water at P/ P₀=0.25 and are characterized also by relatively low values of surface pressures.

Keywords: Water–silica interfacial interaction energy; Quartz; Silicas; Surface energy; Surface tension

XPS and ToF-SIMS analysis of natural rubies and sapphires heated in an inert (N₂) atmosphere by S. Achiwawanich; B.D. James; J. Liesegang (pp. 6883-6891).

Advanced surface analysis techniques: X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, have been employed in the study of heat treatment of natural corundum as ruby and sapphire. The stones were heat treated in an inert (N₂) atmosphere. The setting temperatures were: 1000, 1100, 1200, 1300, 1400, 1500 and 1600°C. The XPS studies and the parallel ToF-SIMS experiments revealed diffusion behavior of Fe and Ti in the as-mined stones as evidenced by surface observations. Both metals exhibited broad maxima in surface concentration near 1300°C. Owing to its superlative detection limit, ToF-SIMS spectra are able to provide the temperature-dependent concentration profiles of trace transition metals such as Cr, Cu and V at a level not detectable by XPS. Visible appearance of the stones is clearly affected by heat treatment. Interestingly, the ruby stones did not exhibit cloudy inclusion (“silk”) on heating, contrary to previous experiments under atmospheric conditions.

Keywords: PACS; 79.60.-i; 82.80.Pv; 82.80.RtPhotoelectron spectroscopy; Secondary ions mass spectrometry; Ruby; Sapphire; Heat treatment; Diffusion

Great influence of the oxygen vacancies on the ferromagnetism in the Co-doped ZnO films by Bao Huang; Deliang Zhu; Xiaocui Ma (pp. 6892-6895).

The ZCO (Co-doped ZnO) films were prepared by using submolecule-doping technique, where the magnetic sputtering of Co and ZnO were alternatively performed onto silicon substrates. The prepared ZCO films were then annealed at different temperatures, and the dependence of the ferromagnetism on annealing temperature was studied. It is found that the saturation magnetization of our samples decreases with the increase of annealing temperature. This behavior is possibly due to the decrease of oxygen vacancies with the increase of the annealing temperature.

Keywords: PACS; 75.50.Pp; 81.05.Dz; 81.15.CdZnO; XPS; Oxygen vacancy; Ferromagnetism

Association of polyethylene friction and thermal unfolding of interfacial albumin molecules by Hsu-Wei Fang; Meng-Lin Shih; Jian-Hua Zhao; Huei-Ting Huang; Hsin-Yi Lin; Hsuan-Liang Liu; Chih-Hung Chang; Charng-Bin Yang; Hwa-Chang Liu (pp. 6896-6904).

Under the articulation of artificial joints, ultra-high molecular weight polyethylene (UHMWPE) acts as a bearing surface under the lubrication of synovial fluid containing various proteins. Albumin is the most abundant composition and acts as the interfacial molecule in the boundary lubrication regime. The dissipated energy including thermal energy from the tribological process may lead to the conformational change of albumin molecules.In this study, a series of experiments were designed and carried out to investigate the association of thermal unfolding albumin and the frictional characteristics of highly-crosslinked UHMWPE (x-UHMWPE). An accelerated oxidation experiment was used to prepare x-UHMWPE with an oxidized surface. Analysis of the albumin protein by circular dichroism (CD) spectroscopy was performed to detect the conformational changes during a thermal process. In addition, a molecular simulation was performed to understand the structural change of albumin at various temperatures and the exposed hydrophobic contact areas. Linear reciprocating frictional tests were carried out to obtain the start-up friction coefficients. The results indicate that a decrease of α-helix content and an unfolding of the secondary structure of albumin were observed with increasing temperatures which may come from the frictional heat of joint articulation process. The conformational change of albumin differentiates the frictional characteristics for x-UHMWPE with different oxidation levels. A model, describing that the properties of the lubricating molecules and articulating surfaces may affect the adsorption of the boundary lubrication thin film which is critical to the tribological behavior, is proposed.

Keywords: UHMWPE; Albumin; Friction; Conformation

Photoluminescence and Raman scattering of Cu-doped ZnO films prepared by magnetron sputtering by X.B. Wang; C. Song; K.W. Geng; F. Zeng; F. Pan (pp. 6905-6909).

The Cu-doped ZnO films were prepared by direct current reactive magnetron sputtering using a zinc target with various Cu-chips attached. The influences of Cu-doping on the microstructure, photoluminescence, and Raman scattering of ZnO films were systematically investigated. The results indicate that ZnO films doped with moderate Cu dopant (2.0–4.4at.%) can obtain wurtzite structure with strong c-axis orientation. The near band edge (NBE) emission of ZnO film can be enhanced by Cu dopant with a concentration of 2.0at.% and quench quickly with further increase of doping concentration. Two additional modes at about 230 and 575cm⁻¹, which could be induced by Cu dopant, can be observed in Raman spectra of the Cu-doped ZnO films.

Keywords: PACS; 78.30.Fs; 78.55.Et; 78.66.HfZnO film; Cu doping; Photoluminescence; Raman scattering

The characteristics of platinum diffusion in n-type GaN by Der-Hwa Yeh; Li-Zen Hsieh; Liann-Be Chang; Ming-Jer Jeng (pp. 6910-6914).

The electrical and optical characteristics of platinum (Pt) diffusion in n-type gallium nitride (GaN) film are investigated. The diffusion extent was characterized by the SIMS technique. The temperature-dependent diffusion coefficients of Pt in n-GaN are 4.158×10⁻¹⁴, 1.572×10⁻¹³ and 3.216×10⁻¹³cm²/s at a temperature of 650, 750 and 850°C, respectively. The Pt diffusion constant and activation energy in GaN are 6.627×10⁻⁹cm²/s and 0.914eV, respectively. These results indicate that the major diffusion mechanism of Pt in GaN is possibly an interstitial diffusion. In addition, it is also observed that the Pt atom may be a donor because the carrier concentration in Pt-diffused GaN is higher than that in un-diffused GaN. The optical property is studied by temperature-dependent photoluminescence (PL) measurement. The thermal quenching of the PL spectra for Pt-diffused GaN samples is also examined.

Keywords: PACS; 66.30.JtGaN; Platinum diffusion; SIMS; Diffusion coefficient; Activation energy; PL

Surface modification of Angora rabbit fibers using dielectric barrier discharge by N. Danish; M.K. Garg; R.S. Rane; P.B. Jhala; S.K. Nema (pp. 6915-6921).

Dielectric barrier discharge (DBD) of Helium and Helium+air modify the surface of Angora rabbit fibers. DBD treatment carried out at different power densities, changes the morphology and chemical composition of the surface of Angora fiber. Scanning electron microscopy (SEM) results reveal that the DBD treatment eliminates fibrosity from the fiber surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer (FTIR) spectrum confirm the increase in oxygen bonding at the surface. These changes reduce shedding of the fibers and improve dye-uptake property. However, even after 10min of plasma exposure the thermal insulation (heat keeping ratio) of Angora fibers nearly remain unchanged. It has been noticed that DBD treatment (10min) reduces whiteness of the fiber.

Keywords: Dielectric barrier discharge; Atmospheric pressure plasma; Angora fiber; X-ray photoelectron spectroscopy; SEM; Thermal insulation

Characterization of rare-earth conversion films formed on the AZ31 magnesium alloy and its relation with corrosion protection by M.F. Montemor; A.M. Simões; M.J. Carmezim (pp. 6922-6931).

Two pre-treatments were studied for AZ31 Mg alloy substrates, consisting of immersion in cerium nitrate and lanthanum nitrate solutions for various immersion times. The surface composition was investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy that revealed the presence of a surface film containing the rare-earth cation, with a composition which was time dependent in the case of the cerium pre-treatment.The corrosion behaviour of the pre-treated substrates in 0.005M NaCl solutions was assessed by potentiodynamic polarization, open circuit potential monitoring and the scanning vibrating electrode technique (SVET). The electrochemical results show that the pre-treatments reduced the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions. The corrosion protection efficiency is dependent on the treatment time.

Keywords: Magnesium; Cerium; Lanthanum; XPS; AES; Corrosion

An exploratory study of the effects of the dielectric-barrier-discharge surface pre-treatment on the self-assembly processes of a (3-Aminopropyl) trimethoxysilane on glass substrates by Nai-Yi Cui; Chaozong Liu; Norman M.D. Brown; Brian J. Meenan (pp. 6932-6938).

X-ray photoelectron spectrometry (XPS), Fourier transform infrared spectrometry (FTIR), secondary-ion-mass spectrometry (SIMS) and contact angle measurement have been used in study of the enhancement effect of substrate pre-treatment by dielectric-barrier-discharge (DBD) for the self-assembly of a (3-Aminopropyl) trimethoxysilane (APTS) on glass substrates. In results, the concentration of the APTS molecules self-assembled on the surfaces of both the acetone-washed and the DBD-treated substrates were more than three times of that on the as-supplied substrate. Meanwhile, the self-assembly (SA) layers grown on the DBD-treated substrates have the best quality compared to those grown on the substrates pre-treated in other ways in terms of the silane-substrate bonding and the order of arrangement of the silane molecules.

Keywords: Dielectric-barrier-discharge; Self-assembly; Silane

Improvement of corrosion properties of microarc oxidation coating on magnesium alloy by optimizing current density parameters by Jun Liang; Litian Hu; Jingcheng Hao (pp. 6939-6945).

The microstructure, composition and corrosion performance of oxide coatings formed on AM60B alloy using microarc oxidation techniques at different waveforms of applied current densities were investigated within this study. It is found that the use of optimizing current density waveforms, i.e. decaying freely current density in the later stage and stepped decreasing current density, significantly improved the microstructure of oxide coatings compared with the constant current density mode, which are connected with changes in behaviors of spark discharges on the surface in oxidation process. The optimal waveform of current density is showed to be decaying freely current density in the later stage, which results in sealing the originally formed large micropores. The optimisation of the microstructure results in a significant improvement of the corrosion resistance of oxide coating.

Keywords: Magnesium alloy; Microarc oxidation; Current density; Corrosion resistance

Molecular beam epitaxy of CdSe epilayers and quantum wells on ZnTe substrate by Y.M. Park; R. Andre; J. Kasprzak; Le Si Dang; E. Bellet-Amalric (pp. 6946-6950).

We have grown zinc-blende cadmium selenide (CdSe) epilayers on ZnTe-(001) substrate by molecular beam epitaxy (MBE). By controlling the substrate temperature and beam-equivalent pressure (BEP) ratio, of Se to Cd, we determined the most suitable growth condition based on reflection high-energy electron diffraction (RHEED) pattern. At a substrate temperature of 280°C and a BEP ratio of 3.6, the RHEED pattern showed a V-like feature, indicating a rough surface with facets. As the substrate temperature was increased to 360°C at the same BEP ratio, a V-like RHEED pattern moved to a clear streaky pattern. Moreover when the BEP ratio was increased to 4.8 at 360°C of substrate temperature, a clear (2×1) reconstruction of the CdSe layer was observed. A CdSe/CdMgSe single quantum well structure was also grown on ZnTe-(001) substrate by MBE. The RHEED pattern showed a clear (2×1) surface reconstruction during the growth. By photoluminescence measurement, a good optical property of the structure was obtained.

Keywords: CdSe epilayers; RHEED patterns; CdSe/CdMgSe quantum well; ZnTe substrate; XRD

Study on formation and shape of carbon nanotips depending on ion bombardment by B.B. Wang; X.Z. Xu; B. Zhang (pp. 6951-6956).

Carbon nanotips were grown from carbon film deposited on silicon substrate by plasma-enhanced hot filament chemical vapor deposition. The carbon film and carbon nanotips were investigated by scanning electron microscopy and micro-Raman spectrometry, respectively. The results indicate that the carbon film is composed of amorphous carbon and the carbon nanotips are characteristic of nanographite, and their formation and shapes depend on ion bombardment strongly. Simultaneously, the number of forming the carbon nanotips is increased by the ion bombardment. Because there are ion deposition and sputtering-etching in the process of growing of the carbon nanotips, the theory related to ion deposition and sputtering was used to obtain their formation condition and analyze effects of the ion bombardment on their shapes and the number of forming them.

Keywords: PACS; 52.77.Bn; 81.07.Bc; 81.15.GhIon bombardment; Carbon nanotips; Chemical vapor deposition

Raman spectroscopy of a-C:H:N films deposited using ECR-CVD with mixed gas by Fan-Xin Liu; Kai-Lun Yao; Zu-Li Liu (pp. 6957-6962).

Ultraviolet (UV) and visible Raman spectroscopy were used to study a-C:H:N films deposited using ECR-CVD with a mixed gas of CH₄ and N₂. Small percentage of nitrogen from 0 to 15% is selected. Raman spectra show that CN bonds can be directly observed at 2220cm⁻¹ from the spectra of visible and UV Raman. UV Raman enhances the sp¹ CN peak than visible Raman. In addition, the UV Raman spectra can reveal the presence of the sp³ sites. For a direct correlation of the Raman parameter with the N content, we introduced the G peak dispersion by combining the visible and UV Raman. The G peak dispersion is directly relative to the disorder of the sp² sites. It shows the a-C:H:N films with higher N content will induce more ordered sp² sites. In addition, upper shift of T position at 244nm excitation with the high N content shows the increment of sp² fraction of films. That means the films with high N content will become soft and contain less internal stress. Hardness test of films also confirmed that more N content is with less hardness.

Keywords: a-C:H:N; Raman spectroscopy; G peak dispersion; Hardness

Molecular dynamics analysis of nanoimprinted Cu–Ni alloys by Te-Hua Fang; Cheng-Da Wu; Win-Jin Chang (pp. 6963-6968).

The nanoimprinted behaviors of Cu–Ni alloys were studied through molecular dynamics simulation. The results from the simulations showed that the punching force and the internal energy of the specimen increased rapidly with increasing punch position and both of they at the elevated temperature were lower than that at the low temperature. The punching force of the specimen with a lower Ni content was higher than that with a higher Ni content, while the internal energy of specimen was reverse. In addition, the spring-back phenomenon was more obvious with increasing Ni components of Cu–Ni alloy after the punch was retrieved during the nanoimprinting process and that induced a smaller residual stress within the specimens.

Keywords: Nanoimprint; Molecular dynamics; Spring-back; Residual stress; Cu–Ni

Surface properties, textural features and catalytic performance for NO+CO abatement of spinels MAl₂O₄ (M=Mg, Co and Zn) developed by reverse and bicontinuous microemulsion method by A.E. Giannakas; A.K. Ladavos; G.S. Armatas; P.J. Pomonis (pp. 6969-6979).

Three typical spinels of general formula MAl₂O₄ (M=Mg, Co and Zn) have been successfully prepared via a microemulsion method both in the reverse and bicontinuous state. The final solids were characterized by X-ray diffraction followed by Rietveld analysis, N₂ adsorption–desorption porosimetry and SEM. Pore connectivity ( c) was also calculated with Seaton's method. The analysis of all these properties shown that spinels prepared via reverse microemulsion route have better surface and textural properties than bicontinuous ones. The spinels were tested for NO+CO reaction and reverse spinels shown better catalytic activity than bicontinuous ones while the full sequence of catalytic activity is: ZnAl₂O₄-r>ZnAl₂O₄-b>MgAl₂O₄-r>MgAl₂O₄-b>CoAl₂O₄-r>CoAl₂O₄-b. The Rietveld analysis helped us to give an explanation about the catalytic activity and shown that the configuration of inverse spinel phase is the critical factor for the catalytic behavior of final solids. The reactants NO and CO react in a 2:1 ratio at low temperature but they convert in a 1:1 ratio at high temperatures. From the kinetic analysis the heats of NO adsorption are estimated and are in full agreement with the results of catalytic activity.

Keywords: Microemulsion; Spinels; Catalysis; NO; +; CO

Preparation and tribological performance of perfluoropolyether derived coatings by Guotuan Gu; Xueqiang Shen; Feng-ling Qing (pp. 6980-6986).

A series of perfluoropolyether (PFPE) functional derivatives terminated with different amide groups (FD-As) were synthesized. The chemical structures of the FD-As were determined by FTIR,¹H and¹⁹F NMR spectra, and the thermo stability was determined by TG analysis. Thin films of FD-As were fabricated by strongly adsorbing FD-As molecules on the surfaces of metals such as aluminum plates and steel balls. The thin films of FD-As prepared possessed very low surface free energy about 12mN/m. Tribological performance of these thin films was characterized using a UMT-2 model micro-tribometer and a four-ball tribotester using paraffin liquid as lubricant. Thin films of FD-As at both states of UMT and four-ball tribo analysis can reduce the friction coefficient. And the anti-wear property of the liquid lubricant can also be improved.

Keywords: Low surface free energy; Functional derivatives; PFPE; Boundary lubrication; Anti-wear coatings

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Applied Surface Science (v.253, #16)

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Applied Surface Science (v.253, #16)