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Applied Surface Science (v.256, #5)

Editorial Board (pp. ii).

Festschrift for Prof. Şefik Süzer's 60th birthday by Gülay Ertaş Guest Editor (pp. 1269-1271).

Enhancement of catalytic activity by increasing surface area in heterogeneous catalysis by Saim Özkar (pp. 1272-1277).

The use of nanoclusters in systems with confined void spaces such as inside mesoporous or microporous solids appears to be an efficient way of preventing aggregation of nanoclusters in their catalytic application. Zeolite-Y is considered as a suitable host providing highly ordered supercages with a diameter of 1.3nm. Intrazeolite metal(0) nanoclusters were prepared at room temperature by ion-exchange of metal cations with the extra framework Na⁺ ions in Zeolite-Y, followed by the reduction of the metal cations in the cavities of Zeolite-Y with sodium borohydride in aqueous solution, whereby the Zeolite-Y is reloaded with Na⁺ ions. Hence, host framework remains intact as shown by using a multi-prong approach. Intrazeolite transition-metal(0) nanoclusters were isolated by suction filtration and drying in vacuum at room temperature and characterized by a combination of analytical methods. Intrazeolite metal(0) nanoclusters were tested as catalyst in the hydrolysis of sodium borohydride and ammonia-borane, both of which have been considered as a promising hydrogen storage materials. High catalytic activity and the outstandingly long lifetime of intrazeolite transition-metal(0) nanoclusters catalyst in the hydrogen generation from the hydrolysis of both sodium borohydride and ammonia-borane is demonstrated. The results are attributed to the small size of the nanoclusters within the zeolite cages as well as prevention of agglomeration of the nanoclusters.

Keywords: Heterogeneous; Nanoclusters; Catalyst; Catalysis; Hydrolysis; Sodium borohydride; Amine-borane; Zeolite; Hydrogenation

Evaporation rate of PTFE liquid marbles by A. Tosun; H.Y. Erbil (pp. 1278-1283).

Liquid marbles are hydrophilic liquid drops encapsulated with a hydrophobic powder. They behave as micro-reservoirs of liquids able to move rapidly without any leakage and are promising candidates to be applied in genetic analysis where 2D microfluidics and lab-on-a-chip methods are used. The manipulation of liquid marbles using gravitational, electrostatic and magnetic fields were recently investigated. In this work, we determined the evaporation rates of PTFE marbles formed by encapsulating PTFE micropowder on a water droplet in a closed chamber where relative humidity and temperature was kept constant. Evaporation rates of PTFE marbles were compared with the rates of pure water droplets in terms of evaporation resistance, ϕ parameter and it was found that PTFE marbles have longer life-time than water droplets so that ϕ values were found to increase regularly from 0.365 to 0.627 with the increase of RH of the evaporating medium. The barrier effect of PTFE microparticles at the water–air interface was more effective when water was evaporating slowly. PTFE water marbles have life-time of 26–60min to retain their spherical shape under normal atmospheric conditions which is suitable for many promising applications in microfluidics, genetic analysis, electromagnetic actuators and valves.

Keywords: PACS; 47.55.D; 68.03.Fg; 68.08.BcLiquid marbles; Super-hydrophobicity; Drop evaporation; Non-wetting

Nanoepitaxy on quasicrystal surfaces by M. Erbudak; M. Mungan; S. Burkardt (pp. 1284-1288).

In film growth on quasicrystalline surfaces, the epitaxy-imposed ordering cannot compete with the stable bulk phases of thick films due to absence of translational order in the structure of the substrate. Energetically, this renders the formation of crystalline domains in the native structure of the film material more favorable, while their global orientation is prescribed by the quasicrystalline order. We present experimental results on the dissociative chemisorption of oxygen at the decagonal surface of Al₇₀Co₁₅Ni₁₅ as well as molecular-dynamics simulations of the diffusion of adatoms on the surface of the partially covered substrate.

Keywords: PACS; 61.44.Br; 68.47.Gh; 68.43.; −; h; 61.46.HkQuasicrystals; Epitaxy; Oxidation; LEED; Molecular-dynamics simulations; Nanocrystals

Lineshapes, shifts and broadenings in dynamical X-ray photoelectron spectroscopy by Aykutlu Dâna (pp. 1289-1295).

We describe in detail a model that can be used to estimate the X-ray photoelectron spectroscopic data of surfaces when a time varying bias or a modulation of the electrical properties of the surface is applied by external stimulation, in the presence of a neutralizing electron beam. Using the model and spectra recorded under periodic sample bias modulation, certain electronic properties related to charging dynamics of the surface can be estimated. The resulting technique is a non-contact impedance measurement technique with chemical specificity. Typical behavior of spectra under a square wave bias is given. Alternative modulation schemes are investigated, including small-signal square wave modulation, sinusoidal modulation and modulation of sample resistivity under fixed bias.

Impedance-type measurements using XPS by Sefik Suzer; Esta Abelev; Steven L. Bernasek (pp. 1296-1298).

An impedance type of measurement using X-ray photoelectron spectroscopy is applied for probing charging/discharging dynamics of a sample containing Rb deposited on a SiO₂/Si substrate containing an octadecyltrichlorosilane (OTS) bilayer coating. The OTS bilayer coatings have possible use as anti-relaxation wall coatings for alkali atom vapor cells in miniaturized instruments such as chip-scale atomic clocks, and/or magnetometers. The measurement consists of the application of bipolar square wave pulses of ±10.0V amplitude to the sample with varying frequencies in the range of 10⁻² to 10²Hz while recording X-ray photoemission data. For a conducting sample this type of measurement twins all the photoemission peaks at −10.0 and +10.0eV positions at all frequencies with exactly 20.0eV difference between them. However, for samples amenable to charging, the difference between the twinned peaks is less than 20.0eV, and gradually decreases at correspondingly lower frequencies. For the sample under consideration here at 0.01Hz, the twinned O1s and Si2p peaks, representing the SiO₂ substrate, are separated by 18.2eV, displaying a 1.8eV charging shift. These positions differ from those of the C1s (18.0eV) representing the OTS bilayer and the Rb3d peaks (18.1eV). These results reveal that the Rb is electrically (perhaps also chemically) isolated from the OTS bilayer, which may be correlated with the improved performance of the OTS bilayers as anti-relaxation coatings in these alkali atom magnetometer cells.

Keywords: XPS; Charging; Impedance; Bilayer OTS; Rb-atom

Sub-Angstrom oscillation amplitude non-contact atomic force microscopy for lateral force gradient measurement by Mehrdad Atabak; Özhan Ünverdi; H. Özgür Özer; Ahmet Oral (pp. 1299-1303).

We report the first results from novel sub-Angstrom oscillation amplitude non-contact atomic force microscopy developed for lateral force gradient measurements. Quantitative lateral force gradients between a tungsten tip and Si(111)–(7×7) surface can be measured using this microscope. Simultaneous lateral force gradient and scanning tunnelling microscope images of single and multi atomic steps are obtained. In our measurement, tunnel current is used as feedback. The lateral stiffness contrast has been observed to be 2.5N/m at single atomic step, in contrast to 13N/m at multi atomic step on Si(111) surface. We also carried out a series of lateral stiffness–distance spectroscopy. We observed lateral stiffness–distance curves exhibit sharp increase in the stiffness as the sample is approached towards the surface. We usually observed positive stiffness and sometimes going into slightly negative region.

Keywords: Non-contact lateral atomic force microscopy; Small oscillation amplitude; Lateral force gradient–distance spectroscopy

A new interpretation of electrochemical impedance spectroscopy to measure accurate doping levels for conducting polymers: Separating Faradaic and capacitive currents by Burak Ulgut; Jacob E. Grose; Yasuyuki Kiya; Daniel C. Ralph; Héctor D. Abruña (pp. 1304-1308).

We report an electrochemical impedance spectroscopy (EIS) based method to measure the doping level of conducting polymers. Using EIS the Faradaic current and the capacitive charging current can be separated without relying on any unverifiable assumptions. We demonstrate the method for three types of conducting polymer thin films that are the basis for many commercial applications (poly(3,4-ethylenedioxythiophene), poly-3-hexylthiophene and polypyrrole).

Keywords: Electrochemical Impedance Spectroscopy; Conducting Polymers; PEDOT; Doping level; Capacitive charging

Cobalt coated substrate for matrix-free analysis of small molecules by laser desorption/ionization mass spectrometry by Talat Yalcin; Liang Li (pp. 1309-1312).

Small molecule analysis is one of the most challenging issues in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. We have developed a cobalt coated substrate as a target for matrix-free analysis of small molecules in laser desorption/ionization mass spectrometry. Cobalt coating of 60–70nm thickness has been characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and laser induced breakdown spectroscopy. This target facilitates hundreds of samples to be spotted and analyzed without mixing any matrices, in a very short time. This can save a lot of time and money and can be a very practical approach for the analysis of small molecules by laser desorption/ionization mass spectrometry.

Keywords: Cobalt-coated substrate; Matrix-free target; Laser; Desorption/ionization; Small molecule analysis

Electron spectroscopies for simultaneous chemical and electrical analysis by Robert L. Opila (pp. 1313-1315).

Electrons are used as spectroscopic probes to determine elemental composition and chemistry, and are also useful as probes of the electrical properties of devices and materials. In this paper, four examples with incident and emitted electrons were used to evaluate the electrical and chemical properties of samples. These examples were the electrical conductivity of an Ag-epoxy composite, the electric field in an avalanche photodiode near breakdown, the mechanism of conductivity of semi-insulating polycrystalline films, and the charge at an oxide/semiconductor interface for high-k applications. This kind of work is very much in the spirit of the work done by Prof. Sefik Suzer.

Keywords: Auger electron spectroscopy; X-ray photoelectron spectroscopy; Electrical potential; High-k; Avalanche photodiode; Semi-insulating polycrystalline silicon (SIPOS)

Synthesis and optical properties of tetragonal KTa_0.6Nb_0.4O₃ nanoparticles by Zheng Keyu; Zhang Duanming; Zhong Zhicheng; Yang Fengxia; Xiangyun Han (pp. 1317-1321).

Tetragonal phase KTa_0.6Nb_0.4O₃ (KTN) nanoparticles have been prepared by hydrothermal method. The obtained particles were characterized by X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV–vis absorption spectrum techniques. A systematic change in crystal structure from cubic to tetragonal is observed with the increase of reaction temperature and KOH concentration. Room temperature UV–vis absorption spectrums of KTN particles show that the band gap changes from 3.24 to 3.34eV with grain size diminished, which reveals the existence of blue-shift phenomenon of absorption bands.

Keywords: PACS; 73.63.Bd; 78.67BfKTa; _0.6; Nb; _0.4; O; ₃; Nanoparticle; Tetragonal phase; Hydrothermal; Band gap; Blue-shift

The effects of temperature on nanocrystalline diamond films deposited on WC–13wt.% Co substrate with W–C gradient layer by Q.P. Wei; Z.M. Yu; L. Ma; D.F. Yin; J. Ye (pp. 1322-1328).

A tungsten-carbide gradient coating (WCGC) was prepared by reactive sputtering as an intermediate layer on the cemented carbide, WC–13wt.% Co, substrate to improve the nucleation, smoothness and adhesion of diamond film. The diamond film was deposited by hot filament chemical vapor deposition (HFCVD). The effects of the substrate temperature on the WCGC and the diamond film were investigated. The characterization of the WCGC and the diamond films was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), micro-Raman spectroscopy and Rockwell hardness indentation. It is found that the WCGC plays an important role in improving the nucleation, smoothness and adhesion of diamond film; and the diamond films exhibit better quality and adhesion as substrate temperature increases during the CVD processes.

Keywords: Cemented carbide; Diamond film; HFCVD; Nanocrystalline; Interlayer

Formation of Al–N co-doped p-ZnO/n-Si (100) heterojunction structure by RF co-sputtering technique by Manoj Kumar; Sang-Kyun Kim; Se-Young Choi (pp. 1329-1332).

Al–N co-doped ZnO (ZnO:Al–N) thin films were grown on n-Si (100) substrate by RF co-sputtering technique. As-grown ZnO:Al–N film exhibited n-type conductivity whereas on annealing in Ar ambient the conduction of ZnO:Al–N film changes to p-type, typically at 600°C the high hole concentration of ZnO:Al–N co-doped film was found to be 2.86×10¹⁹cm⁻³ and a low resistivity of 1.85×10⁻²Ω-cm. The current–voltage characteristics of the obtained p-ZnO:Al–N/n-Si heterojunction showed good diode like rectifying behavior. Room temperature photoluminescence spectra of annealed co-doped films revealed a dominant peak at 3.24eV.

Keywords: PACS; 81.05.Dz; 81.15.Cd; 85.30.Kk; 78.55.EtAl and N co-doping; RF co-sputtering; ZnO II–VI semiconductor material; Heterojunction semiconductor device

The role of process parameters in plasma surface chromising of Ti₂AlNb-based alloys by Hongyan Wu; Pingze Zhang; Ling Wang; Haofeng Zhao; Zhong Xu (pp. 1333-1340).

In order to enhance the wear resistance of Ti₂AlNb-based alloy (O-phase), surface chromising was performed by double glow plasma process in this study. The effect of process parameters, such as temperature, time and pressure, on the microstructure, thickness, and micro-hardness of the alloyed layers was investigated. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were employed to analyze the composition distribution and microstructure of the alloy. The results showed that the optimum process parameters were as follows: 970°C for temperature, 4h for chromising time, and 30Pa for pressure. Following the optimization the thickness, microstructure and micro-hardness of the modified layer achieved the designed requirements. The results of tribological tests showed that the friction coefficient of the chromised layer was lower than that of the matrix at the room temperature or 500°C, and the specific wear rate of samples with plasma chromising at either room temperature or high temperature was decreased markedly.

Keywords: Plasma surface chromising; The double glow plasma alloying; Ti; ₂; AlNb-based alloy; Wear; Friction

Protein imprinting and recognition via forming nanofilms on microbeads surfaces in aqueous media by Yan Lu; Chang-Ling Yan; Xue-Jing Wang; Gong-Ke Wang (pp. 1341-1346).

In this paler, we present a technique of forming nanofilms of poly-3-aminophenylboronic acid (pAPBA) on the surfaces of polystyrene (PS) microbeads for proteins (papain and trypsin) in aqueous. Papain was chosen as a model to study the feasibility of the technique and trypsin as an extension. Obtained core–shell microbeads were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and BET methods. The results show that pAPBA formed nanofilms (60–100nm in thickness) on the surfaces of PS microbeads. The specific surface area of the papain-imprinted beads was about 180m²g⁻¹ and its pore size was 31nm. These imprinted microbeads exhibit high recognition specificity and fast mass transfer kinetics. The specificity of these imprinted beads mainly originates from the spatial effect of imprinted sites. Because the protein-imprinted sites were located at, or close to, the surface, the imprinted beads have good site accessibility toward the template molecules. The facility of the imprinting protocol and the high recognition properties of imprinted microbeads make the approach an attractive solution to problems in the field of biotechnology.

Keywords: PACS; 68.43._h; 68.43.Fg; 87.85.jfMolecularly imprinted polymers; Nanofilm; Protein; 3-Aminophenylboronic acid

The effect of surface modification on heavy metal ion removal from water by carbon nanoporous adsorbent by M.J. Baniamerian; S.E. Moradi; A. Noori; H. Salahi (pp. 1347-1354).

In this work, chemically oxidized mesoporous carbon (COMC) with excellent lead adsorption performance was prepared by an acid surface modification method from mesoporous carbon (MC) by wet impregnation method. The structural order and textural properties of the mesoporous materials were studied by XRD, SEM, and nitrogen adsorption. The presence of carboxylic functional groups on the carbon surface was confirmed by FT-IR analysis. Batch adsorption experiments were conducted to study the effect of adsorbent dose, initial concentration and temperature for the removal of Pb(II) from aqueous systems. The adsorption was maximum for the initial pH in the range of 6.5–8.0. The kinetic data were best fitted to the pseudo-second order model. The adsorption of chemically oxidized mesoporous carbon to Pb(II) fits to the Langmuir model. The larger adsorption capacity of chemically oxidized mesoporous carbon for Pb(II) is mainly due to the oxygenous functional groups formed on the surface of COMC which can react with Pb(II) to form salt or complex deposited on the surface of MC.

Keywords: Lead; Chemically oxidized mesoporous carbon; Adsorption; Langmuir isotherm

XPS characterization of naturally aged wood by Carmen-Mihaela Popescu; Carmen-Mihaela Tibirna; Cornelia Vasile (pp. 1355-1360).

Wood deterioration over time (by a simultaneously biological, chemical or physical attack) is an inevitable continuous process in the environment. This process destroys all heritage resulting in a loss of valuable old wooden structures and their properties. What type of deterioration occurs and how these processes impact the wood are important questions that need consideration if old wooden structures are to be studied and properly preserved.X-ray photoelectron spectroscopy (XPS) was employed to analyze the undegraded (sound wood of ∼6 years) and degraded lime wood (∼150 years, ∼180 years, ∼250 years) from painting supports, differing in terms of the provenance, conservation status and environmental conditions of storage. Elaborated XPS analysis (comparison of C and O individual spectra, decomposition for each atomic component, calculation of O/C ratio) provided a view of the composition of the sample surfaces analyzed. On the basis of these results, it was confirmed that significant changes occurred in the first period of ageing, the ∼150 years lime wood sample having the highest percent of the carbon atoms and the lowest percentage of oxygen atoms and, respectively O/C ratio. According to our previous studies (X-ray diffraction, FTIR spectroscopy, analytical pyrolysis combined with gas chromatography/mass spectrometry and ESR-spectroscopy results), these features could be attributed to the fact that hemicelluloses and amorphous cellulose are degraded in time, whereas the crystalline fraction of cellulose decreases more slowly than the amorphous one. Consequently, the observation may be made that lignin is not so easily degraded under the environmental conditions where paintings are frequently exposed.

Keywords: Lime wood; Environmental deterioration; X-ray photoelectron spectroscopy

Structural, morphological, and magnetic characteristics of Cu-implanted nonpolar GaN films by Lili Sun; Fawang Yan; Huixiao Zhang; Junxi Wang; Yiping Zeng; Guohong Wang; Jinmin Li (pp. 1361-1364).

Diluted magnetic nonpolar GaN:Cu films have been fabricated by implanting Cu ions into unintentionally doped nonpolar a-plane(112¯0) GaN films and a subsequent thermal annealing process. The structural, morphological and magnetic characteristics of the samples have been investigated by means of high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and superconducting quantum interference device (SQUID). The sample shows a clear ferromagnetism behavior at room temperature. It is significantly shown that with a Cu concentration as low as 0.75% the sample exhibits a saturation magnetization about 0.65μ_B/Cu atom. Moreover, the possible origin of the ferromagnetism for the sample was also discussed briefly.

Keywords: PACS; 75.50.Pp; 81.05.Ea; 81.15.Gh; 85.40.RyDiluted magnetic semiconductors (DMSs); Ion implantation; Nonpolar a-plane GaN:Cu films; Room-temperature ferromagnetic properties

Hot filament CVD of Fe–Cr catalyst for thermal CVD carbon nanotube growth from liquid petroleum gas by M. Akbarzadeh Pasha; A. Shafiekhani; M.A. Vesaghi (pp. 1365-1371).

A hot filament chemical vapor deposition (HFCVD) method was used to prepare Fe–Cr thin film on Si substrate. The produced layers were used as catalysts for growing carbon nanotubes (CNTs) from liquid petroleum gas (LPG) at 825°C by thermal CVD (TCVD) method. To characterize the obtained catalysts or CNTs, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman spectroscopy were used. CNTs were grown on HFCVD derived Fe–Cr catalyst with the LPG as carbon source successfully. It was found that an annealing process on catalysts enhances the surface concentration of Cr atoms and reduces the sizes of catalyst particles. The grown CNTs on annealed sample were morphologically denser with smaller diameters compared to the as deposited one. In addition, the effect of filament temperature on CNTs was investigated. By increasing the filament temperature from 850 to 1050°C the surface density and diameters of CNTs were improved.

Keywords: Carbon nanotube; HFCVD; TCVD; Metal catalyst; SEM

Self-assembling of cyano- and carboxyl-terminated monolayers using short-chain alkylsiloxane by Zhe Kong; Qi Wang; Liang Ding (pp. 1372-1376).

A simple method was developed for the preparation of cyano- and carboxyl-terminated alkylsiloxane monolayers on the hydroxylated surface of the SiO₂/Si substrate through using adsorption and hydrolysis reaction of a short-chain 2-cyanoethyl triethoxysilane [(CH₃CH₂O)₃SiCH₂CH₂CN]. The contact angle and the X-ray photoelectron spectroscopy (XPS) measurements have proved that the cyano terminal group indeed formed on the substrate and was transformed into the carboxylic terminal group after hydrolysis. The ellipsometry shows the presence of an intact monolayer with thickness of around 0.7nm before and during the hydrolysis reaction. The surface morphology was observed with atomic force microscopy (AFM) imaging. Those all indicate that uniform and ordered self-assembled monolayers (SAMs) were formed on the substrate.

Keywords: Self-assembled monolayers (SAMs); Short-chain alkylsiloxane; Cyano-terminated SAM; Carboxyl-terminated SAM; Hydrolysis reaction

Plasma dynamics study by fast imaging and Sm1−_xNd_xNiO₃ thin film deposition by S. Lafane; T. Kerdja; S. Abdelli-Messaci; S. Malek; M. Maaza (pp. 1377-1381).

The plume expansion dynamics of an ablated target of Sm₂O₃, Nd₂O₃ and NiO mixture oxides by KrF laser into 0.2mbar oxygen atmosphere has been investigated using fast imaging. The study was carried out for two different laser fluences 2 and 3Jcm⁻². It was found that at early time delays, the expansion is still linear, independently of the laser fluence. However, as time evolves, the plume is decelerated and comes to rest. The plasma plume dynamics was analysed in the framework of Predtechensky and Mayorov model and drag model. It was found that Predtechensky and Mayorov model gives a general description of the plume expansion. However, at later time delays, it is rather the drag model which is valid. Furthermore, under the same conditions of pressure and fluences used for the plasma study, thin films were deposited at 4cm from target surface and at temperature of 500°C on (100) silicon substrates. The obtained layers were characterized by atomic force microscopy and electron dispersive X-ray spectroscopy diagnostics. A correlation between the films properties and the plasma plume dynamics was found.

Keywords: PACS; 52.38.Mf; 52.50.Jm; 52.70.Kz; 68.55.−aLaser ablation; Fast imaging; Plume dynamics; Sm; 1−; _x; Nd; _x; NiO; ₃; thin films

Low-pressure plasma cleaning of Au and PtIr noble metal surfaces by P. Fuchs (pp. 1382-1390).

The effect of low-pressure hydrogen and oxygen plasma cleaning of Au and PtIr was investigated by X-ray photoelectron spectroscopy. Hydrocarbon contamination was efficiently removed by hydrogen and oxygen plasma. Hydrogen plasma additionally reduces oxygen compounds, especially metal oxides, while oxygen plasma results in the formation of a surface layer of Au₂O₃ and PtO, respectively. Both noble metal oxides are unstable and decompose with time. The decomposition of metal oxides occurs in parallel with the recontamination of the surface. Metal oxides can be removed completely for Au and partially for PtIr by an additional cleaning with hydrogen plasma. Hydrogen plasma treatment is very promising for noble metal surface cleaning.

Keywords: Low-pressure plasma; Plasma cleaning; Hydrogen plasma; Oxygen plasma; X-ray photoelectron spectroscopy; Noble metals; Mass standards

Growth of ultra-thin TiO₂ films by spray pyrolysis on different substrates by I. Oja Acik; A. Junolainen; V. Mikli; M. Danilson; M. Krunks (pp. 1391-1394).

In the present study TiO₂ films were deposited by spray pyrolysis method onto ITO covered glass and Si (100) substrates. The spray solution containing titanium(IV) isopropoxide, acetylacetone and ethanol was sprayed at a substrate temperature of 450°C employing 1–125 spray pulses (1s spray and 30s pause). According to AFM, continuous coverage of ITO and Si substrates with TiO₂ layer is formed by 5–10 and below 5 spray pulses, respectively. XPS studies revealed that TiO₂ film growth on Si substrate using up to 4 spray pulses follows 2D or layer-by-layer-growth. Above 4 spray pulses, 3D or island growth becomes dominant irrespective of the substrate. Only 50 spray pulses result in TiO₂ layer with the thickness more than XPS measurement escape depth as any signal from the substrate could not be detected. TiO₂ grain size remains 30nm on ITO and increases from 10–20nm to 50–100nm on Si substrate with the number of spray pulses from 1 to 125.

Keywords: TiO; ₂; Spray pyrolysis; Film growth; Thin film; AFM; XPS

Impact and spreading behavior of cluster atoms bombarding substrates by Te-Hua Fang; Shao-Hui Kang; Jia-Hung Liao (pp. 1395-1398).

The purpose of this study is to investigate the behavior of copper cluster atoms bombarding a substrate using molecule dynamics based on tight-binding second moment approximation (TB-SMA) potential. The simulated results show that a crater on the substrate surface was created by the impact of the clusters. The variations of kinetic energy of cluster bombardments can be divided into three stages. At the initial impact level, the kinetic energies of the clusters and the substrate were constant. Then, the system went into a sluggish stage of energy variation, in which the kinetic energy of the clusters reduced. In the final stage, the kinetic energy of the system became stable. The high slip vector region around the crater had a disorder damage zone. The symmetry-like cross-slip occurred beneath the top layer of the substrate along the 〈110〉 orientations. The spreading index, temperature, and potential functions that affect the bombardments are also discussed.

Keywords: Molecular dynamics; Spreading; Cluster; Bombardment; Craters

Application of thermodynamics and Wagner model on two problems in continuous hot-dip galvanizing by Huachu Liu; Yanlin He; Lin Li (pp. 1399-1403).

Firstly in this paper, the influence of H₂ and water vapor content on selective oxidation occurred in continuous hot-dip galvanizing has been studied by thermodynamics and Wagner model, then, the Gibbs energy of each possible aluminothermic reducing reaction in zinc bath was calculated in order to judge the possibility of these reactions. It was found that oxides’ amounts and oxidation type were greatly related to the H₂ and water content in the annealing atmosphere. And from the view of thermodynamics, surface oxides (MnO, Cr₂O₃, SiO₂ etc.) can be reduced by the effective Al in Zn bath.

Keywords: Hot-dip galvanizing; Selective oxidation; Thermodynamics; Wagner model; Aluminothermic reduction

Preparation, characterization and infrared emissivity study of helical polyurethane@SiO₂ core-shell composite by Zhiqiang Wang; Yuming Zhou; Qingzhao Yao; Yanqing Sun (pp. 1404-1408).

Helical polyurethane@SiO₂ (HPU@SiO₂) core-shell composite was prepared after surface modification of SiO₂ nanoparticles. HPU@SiO₂ was characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified SiO₂. HPU@SiO₂ composite exhibits clearly core-shell structure. The ultraviolet absorption and crystallizability of HPU@SiO₂ are changed due to the shell of helical polyurethane, which possesses regular single-handed conformation and inter-chain hydrogen bonds. The infrared emissivity of HPU@SiO₂ was also investigated. The result indicates that the interfacial interactions between organic shell and inorganic core induce the infrared emissivity value being reduced from 0.781 for SiO₂ to 0.503 for HPU@SiO₂.

Keywords: PACS; 81.07.Pr; 82.35.Np; 64.60.Qb; 78.66.Sq; 68.55.AcPolyurethane; Silica; Helical structure; Infrared emissivity

The effect of the excitation and of the temperature on the photoluminescence circular polarization of AlInAs/AlGaAs quantum dots by N. Sellami; A. Melliti; A. Sahli; M.A. Maaref; C. Testelin; R. Kuszelewiez (pp. 1409-1412).

In this paper, we present a study of photoluminescence (PL) from AlInAs/AlGaAs quantum dots (QDs) structures grown by molecular beam epitaxy. Specifically, we describe the effects of the temperature and of the excitation density on the photoluminescence circular polarization. We have found that the circular polarization degree depends on temperature. On the other hand, the study of the excitation density dependent circular polarization PL degree shows that the last increases in the case of the sample of weak dot density. However, in the case of large dot density, it is almost constant in the excitation density range from 0.116Wcm⁻² to 9Wcm⁻².

Keywords: PACS; 78.20.Ls; 78.47.+p; 78.55.Cr; 78.66.Fd; 78.67.HcCircular polarization; Photoluminescence; InAlAs/AlGaAs quantum dots

Highly hydrophobic and oleophilic foam for selective absorption by Changhong Su (pp. 1413-1418).

In this article, both highly hydrophobic and oleophilic foam were fabricated by coating inner surface of polyurethane (PU) foam with a super-hydrophobic film. The contact angle of the foam is large as 152.2° for water, and 0° for kerosene. The foam can absorb kerosene selectively from kerosene–water mixture and be regenerated easily. The foam may be used to reclaim oil from polluted natural water area resulted from shipwreck or leakage.

Keywords: Hydrophobic; Oleophilic; Foam; Selective wetting; Oil–water separation

Surface evaluation of cardiac angiographic catheters after simulated use and reprocessing by Thabata Coaglio Lucas; Rodrigo Lambert Oréfice; Marcos Pinotti; Rudolf Huebner (pp. 1419-1425).

Reprocessing of single-use intravascular catheters is a common practice in public health services and hospitals. The determination of safe number of reprocessing cycles before the catheter integrity becomes compromised has been a priority issue. The present paper addresses the evaluating molecular and micro-structural integrity of reprocessed cardiac angiographic catheters. The Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy were carried out to elucidate morphological changes. The tensile test was performed on catheters to examine changes in bulk characteristics. In this work, samples of catheters were reprocessed until nine times and sterilized by hydrogen peroxide plasma. It was observed that the number of hydrogen-bonded carbonyls groups increased in 0.05u.a. ( p<0.001) after each reprocessing cycle. The spectra indicated degradation products included acids, esters, alcohols, and small amounts of other products containing a carbonyl functional group. The micrographs revealed that only after the fourth reprocessing cycle the effect increased in the surface roughness was more pronounced. On the other hand, after each reprocessing cycle and as consequence of extensive aging of polyamide/polyurethane blends of the catheters surface, it was observed that the micro-fissures, micro-scratches and micro-pores increased in quantity and length. The mechanical test proved that the Young modulus increased in average 3.26MPa ( p=0.0003) at increasing number of reprocessing cycles, also suggestive of crosslinking in this material.

Keywords: Catheter reuse; Reprocessing cycle; Molecular structure; Diagnostic techniques; Cardiovascular; Surface characterization

Surface modification of copper with 2-dodecylpropane-1,3-dithiol: The key effect of the solvent by J. Denayer; J. Delhalle; Z. Mekhalif (pp. 1426-1430).

Self-assembly of alkanethiol on gold in various solvents (alkane, alcohol, etc) leads to monolayers with similar properties. However when the self-assembly is performed on copper substrates, the nature of the solvent has an effect on the properties of the monolayer. This phenomenon arises from the chemical interaction of copper with the solvent, which is not the case of gold.Ethanol is a solvent widely used for self-assembly, however some studies pointed out its negative effect due to its significant chemical reactivity towards copper and its ability to chemisorb on the surface.The aim of this work consists in a comparative investigation of 2-dodecylpropane-1,3-dithiol (or R(SH)₂) in various solvents and its ability to form stable SAMs, densely packed and well ordered. Characterizations of the SAMs are carried out using X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and cyclic voltammetry (CV).

Keywords: Self-assembled monolayers; 2-Monoalkylpropane-1,3-dithiol; Copper; Solvent effect

Microstructure and mechanical properties of Ag-containing diamond-like carbon films in mid-frequency dual-magnetron sputtering by Chengbiao Wang; Xiang Yu; Meng Hua (pp. 1431-1435).

Seven diamonds-like carbon (Ag-DLC) films with different Ag contents were deposited on (100) Si substrate in a mid-frequency dual-magnetron system. Studies were performed to investigate the influence of the Ag content and nanograin size on the microstructure and mechanical properties of the films. Results showed: (i) the dispersion of Ag nanocrystallites within the amorphous DLC matrix, and the tendency for the size of the Ag nanocrystallite to increase with the Ag content; (ii) the exhibition of higher hardness, lower intrinsic stress and better adhesion for the films with Ag content ranging between 7.4 and 12.5at% when compared with the films of Ag content in range of 16.8–24.7at%; and (iii) the achievement of the best mechanical properties for the film deposited with 9.6at% Ag.

Keywords: Ag-containing diamond-like carbon film; Ag content; Microstructure; Mechanical behavior

Synthesis of CuS thin films by microwave assisted chemical bath deposition by Mudi Xin; KunWei Li; Hao Wang (pp. 1436-1442).

In this study, oriented CuS nanoplates standing perpendicularly on F: SnO₂ (FTO) coated glass substrates have been prepared through a mild microwave assisted chemical bath deposition process in which copper acetate reacted with ethylenediamine tetraacetate acid disodium and thioacetamide in aqueous solution within 40min. The effects of reaction time and microwave radiation on the treatment process were investigated. The morphology, structure, and composition of the yielded nanostructures have been confirmed by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), and scanning electron microscope (SEM). Also, the correlation between the reflectance, transmittance coefficient in the UV and the thickness of films was established. Furthermore, a two-point probe was used for resistivity measurements. We believe this simple chemical conversion technique can be further extended to the synthesis of other semiconductors with various morphologies.

Keywords: CuS; Microwave assisted chemical bath deposition; Thin films

D₂ layers on MgO(001): Simulation study by J.N. Dawoud; D.B. Jack (pp. 1443-1451).

In response to recent helium atom scattering (HAS) and neutron scattering results, Monte Carlo simulations and perturbation theory calculations have been performed for D₂ on MgO(001). Monte Carlo simulations predict that D₂ molecules form a series of interesting structures, p(2×2)→ p(4×2)→ p(6×2), with coverages Θ=0.5, 0.75, 0.83 respectively, and followed by a formation of a top layer of p(6×2) unit cell symmetry. The three types of mono-layers are stable up to 13K, whereas the top layer still exists up to 10K. This is in partial agreement with the neutron scattering and HAS results that report c(2×2), c(4×2) and c(6×2); they agree in terms of coverage and stability, but disagree in terms of symmetry. A quantum mechanical examination of the D₂ molecules’ rotational motion shows the molecular axes are azimuthally delocalized and hence the simulated structures are c-type rather than p-type. These calculations also indicate that ortho-D₂ and helicoptering para-D₂ prefer cationic sites, while cartwheeling para-D₂ prefers anionic sites.

Keywords: Deuterium; Monte Carlo simulations; Potential energy surface; Physical adsorption; MgO

Preparation of ZnMgO:Ga thin films on flexible substrates by pulsed laser deposition by W. Yuan; L.P. Zhu; Z.Z. Ye; X.Q. Gu (pp. 1452-1454).

Transparent conducting ZnMgO:Ga films were deposited on flexible PET substrates by pulsed laser deposition (PLD). Effects of deposition pressure and time on the structural, electrical and optical properties of ZnMgO:Ga films were investigated. The films showed a low resistivity about 7.68×10⁻⁴Ωcm when deposited at the pressure of 0.03Pa for 40min. All the films exhibited a high transmittance over 80% in the visible and near-ultraviolet region. The band gap of as-grown films was about 3.50eV.

Keywords: Pulsed laser deposition; Flexible substrates; ZnMgO:Ga thin film; Transparent conducting

Structural, electrical and piezoelectric properties of LiNbO₃ thin films for surface acoustic wave resonators applications by V. Edon; D. Rèmiens; S. Saada (pp. 1455-1460).

In this work, 0.30μm thick LiNbO₃ layers have been deposited by sputtering on nanocrystalline diamond/Si and platinised Si substrates. The films were then analyzed in terms of their structural and optical properties. Crystalline orientations along the (012), (104) and (110) axes have been detected after thermal treatment at 500°C in air. The films were near-stoichiometric and did not reveal strong losses or diffusion in lithium during deposition or after thermal annealing. Pronounced decrease of the roughness on top of the LiNbO₃ layer and at the interface between LiNbO₃ and diamond was also observed after annealing, compared to the bare nanocrystalline diamond on Si substrate. Furthermore, ellipsometry analysis showed a better density and a reduced thickness of the surface layer after post-deposition annealing. The dielectric constant and losses have been measured to 50 and less than 3.5%, respectively, for metal/insulator/metal structures with 0.30μm thick LiNbO₃ layer. The piezoelectric coefficient d₃₃ was found to be 7.1pm/V. Finally, we succeeded in switching local domain under various positive and negative voltages.

Keywords: PACS; 77.84.Dy; 61.05.Cp; 82.80.Yc; 68.37.Ps; 68.37.Hk; 78.20.Ci; 77.22.Ch; 77.65.Bn; 77.80.FmLithium niobate; Nanocrystalline diamond; Thin films; Piezoelectric properties

Tribological changes on SS304 stainless steel induced by nitrogen plasma immersion ion implantation with and without auxiliary heating by C.B. Mello; M. Ueda; C.M. Lepienski; H. Reuther (pp. 1461-1465).

In order to achieve quite thick treated layers with reasonable thickness uniformity in SS304 steel, the plasma immersion ion implantation (PIII) process was run in high-temperature, up to 350°C, to induce high thermal diffusion but avoid the white layer formation. In these experiments, we heated the sample-holder with a shielded resistive wire properly wound around it and subjected the SS samples to nitrogen glow discharge PIII with relatively low voltages (10kV) in different temperatures. We also treated the SS samples by the traditional PIII method, slowly increasing the high voltage pulse intensities, until 14kV at the end of processing, reaching temperatures of up to 350°C. These modes of treatments were compared with respect to nitrogen implantation profiles, X-ray diffraction, tribology and mechanical properties. X-ray diffraction results indicated a much higher efficiency of auxiliary heated PIII mode compared to the ordinary PIII. Very prominent γ_N peaks were observed for the first mode, indicating large concentration of nitrogen in thick layers, confirmed by the nitrogen profiles measured by GDOS and AES. Improved mechanical and tribological properties were obtained for SS304 samples treated by the PIII with auxiliary heating, more than for ordinary PIII. Hardness was enhanced by up to 2.77 times, as seen by nanoindentation tests.

Keywords: PACS; 52.77.Dq; 85.40.Ry; 62.20.QpPlasma immersion ion implantation; SS304; Tribology

Comparison of diamond film adhesion on molybdenum substrates with different surface morphologies by Hitoshi Wako; Toshihiko Abe; Toshiyuki Takagi; Toshiaki Ikohagi (pp. 1466-1471).

To evaluate the effect of substrate morphology on the adhesion of diamond film, two types of substrate morphology of molybdenum (Mo) were compared. The two morphology types were formed by polishing a Mo substrate with SiC abrasive paper along one direction (anisotropic morphology) and by polishing the Mo substrate with diamond powder in a random direction (isotropic morphology).Ultrasonic cavitation tests were conducted to evaluate the adhesion of the diamond films on these Mo substrates. In the case of low surface roughness, there was very little difference between the effects of SiC abrasive paper polishing and diamond powder polishing. In the case of high surface roughness, the adhesion of the diamond film on the SiC paper polished Mo substrate was larger than that of the diamond film on the diamond powder polished Mo substrate. Detachment of the diamond film from the SiC paper polished Mo substrate progressed along the polishing direction; while detachment of the diamond film from the diamond powder polished Mo substrate progressed in a random direction. It was thought that the detachment of the diamond film from a Mo substrate having an anisotropic polishing trace was suppressed because the anisotropic grooves restricted the formation of connections between the points of detachment at right angles to the groove direction. Therefore, the anisotropic surface morphology of the Mo substrate is effective for improving the adhesion of diamond film.

Keywords: Adhesion; Cavitation test; Morphology; Surface roughness; CVD diamond

Size effect on the SHG properties of Cu-doped CdI₂ nanocrystals by M. Idrish Miah (pp. 1472-1475).

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI₂ layered nanocrystal structures from the mixture of CdI₂ and CuI using the standard Bridgman–Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83pmV⁻¹ for the thicknesses of 10–0.8nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron–phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI₂ layered nanocrystals are promising materials for applications in optoelectronic nano-devices.

Keywords: Keyword; Nanomaterials

Fabrication of chain-like Mn₂O₃ nanostructures via thermal decomposition of manganese phthalate coordination polymers by Masoud Salavati-Niasari; Fatemeh Mohandes; Fatemeh Davar; Kamal Saberyan (pp. 1476-1480).

A novel manganese coordination polymer [Mn(Pht)(H₂O)]_n as a precursor was obtained by chemical precipitation involving an aqueous solution of anhydrous manganese acetate and phthalate anion as a potential O-banded ligand. Fourier transform infrared (FT-IR) results proved that phthalate anions coordinate to metal cations as a chelating bidentate ligand, making polymeric structure. The Mn₂O₃ nanostructures have been prepared via thermal decomposition of as-prepared manganese phthalate polymers as precursor in the presence of oleic acid (OA) and triphenylphosphine (TPP) as a stabilizer and capping. Different approaches such as FT-IR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the products. TEM images and XRD analysis indicated that the as-synthesized chain-like Mn₂O₃ has a crystal phase of cubic syngony with a mean size of ∼40nm.

Keywords: Nanostructure; Mn; ₂; O; ₃; Oleic acid; Thermal decomposition; Chelating bidentate ligand

Fabrication of well ordered Zn nanorod arrays by ion irradiation method at room temperature and effect on crystal orientations by Masaki Kutsuna; Pradip Ghosh; Masato Kudo; Masaki Tanemura; Yasuhiko Hayashi (pp. 1481-1485).

Highly oriented and densely packed one-dimensional (1D) polycrystalline Zn nanorods were fabricated on zinc plate without any catalyst at room temperature by bombardment with obliquely incident Ar⁺ ion via ion irradiation method. The sputtered surfaces were fully covered with Zn nanostructures with diameter and the length around 60nm and 1.3μm, respectively, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal orientation of the Zn plate was investigated by electron back scattering pattern method (EBSP). The numerical density and morphology of Zn nanostructures (nanoneedle or nanorods) were found to be 2.1×10⁶ to 9×10⁶/mm² depending upon the crystal orientation and the atomic density on different crystallographic faces. (21¯1¯0) faces of Zn polycrystal tended to form more dense nanostructures compared to (0001¯) faces. This is because of lower atomic density on (21¯1¯0) faces in comparison with (0001¯) faces. This indicates that lower atomic density on any crystallographic faces is favorable to form nanostructure of higher density. The outstanding feature of this growth technique is that it provides a new direction for the controllable growth of desired nanostructures of variable density at room temperature without any catalyst. These well-aligned arrays of Zn nanorods/nanoneedle might be a promising material for the future application in nanodevices.

Keywords: PACS; 61.46.Km; 61.82.RxZn nanostructures; Ion beam sputtering; Electron back scattering pattern

Synthesis of a composite consisting of carbon nanotubes and graphite shell-encapsulated cobalt nanoparticles using plasma-enhanced chemical vapor deposition by J.L. Qi; X. Wang; H.W. Tian; C. Liu; Y.L. Lu; W.T. Zheng (pp. 1486-1491).

We report a simple and effective one-step synthesis route for synthesizing a composite consisted of carbon nanotubes (CNTs) and graphite shell-encapsulated cobalt nanoparticles using plasma-enhanced chemical vapor deposition on Si (100) substrate covered with catalyst Co particles, discharging a mixture of H₂ and CH₄ gas, and characterize the obtained composite by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscope, and X-ray photoelectron spectroscopy. The results show that CNTs align perpendicularly to the substrate and graphite shell-encapsulated Co nanoparticles clung to the external surfaces of aligned CNTs. The diameter of the graphite shell-encapsulated Co nanoparticles increases with increasing the H₂ content in H₂ and CH₄ carbonaceous gas. A possible growth mechanism of the CNTs and graphite shell-encapsulated cobalt nanoparticles composite has been explored.

Keywords: Carbon nanotube; Graphite encapsulated nanoparticles; PECVD

Effect of amorphous C films deposited by RF magnetron sputtering on smoothing K9 glass substrate by Songwen Deng; Hongji Qi; Chaoyang Wei; Kui Yi; Zhengxiu Fan; Jianda Shao (pp. 1492-1495).

Soft X-ray multilayer reflectors must be deposited on super-smooth surface such as super-polished silicon wafers or glasses, which are complicate, time-consuming and expensive to produce. To overcome this shortage, C films deposited by RF magnetron sputtering were considered to smooth the K9 glass substrates’ surface in the present paper. The structure of C films was systematically studied by XRD and Raman spectrum. The surface morphology and rms-roughness were obtained by AFM. Then, we calculated the impact of the C layers on the reflectivity curve of Mo/Si soft X-ray multilayer reflector around 13.5nm. The C films exhibit typical amorphous state. With the increasing of power and thickness, the content of sp3 hybrid bonding decreases while the amount or size of well-organized graphite clusters increases. The surface rms-roughness decreases from 2.4nm to 0.62nm after smoothed by an 80nm thick C layer deposited in 500W, which is the smoothest C layer surface we have obtained. The calculation results show that the theoretical normal incidence reflectivity of Mo/Si multilayer at 13.5nm increases from 7% to 63%.

Keywords: Roughness; Smoothing effect; C film; Soft X-ray multilayer reflector

Surface modification of a polyamide 6 film by He/CF₄ plasma using atmospheric pressure plasma jet by Zhiqiang Gao; Jie Sun; Shujing Peng; Lan Yao; Yiping Qiu (pp. 1496-1501).

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.

Keywords: PACS; 52.40.Hf; 81.05.Lg; 81.65.MqPolyamide; Atmospheric pressure plasma; Surface; XPS; AFM

Reliable lateral manipulation of a single Ag adatom on a Ag(111) surface with a trimer-apex tip by Yiqun Xie; Wangzhou Shi; Guoping Du (pp. 1502-1506).

We study the reliability of the lateral manipulation of a single Ag adatom on a Ag(111) surface with the single-atom and trimer-apex tips based on molecular statics simulations using surface embedded-atom-method potential. The dependence of the manipulation reliability on tip height and orientation is investigated. For the single-atom tip the manipulation reliability increases monotonically with decreasing tip height, which is owing to the strengthened lateral tip–adatom interaction as the tip height lowers. For the trimer-apex tip, the manipulation reliability is sensitive to the tip orientation in the lower tip-height range, while in the higher tip-height range the manipulation reliability is independent of the tip orientation and moreover can be greatly improved due to the strong vertical attraction of the tip on the adatom as compared to the single-atom tip. We also compare these results to those for manipulating single Cu adatoms on the Cu(111) surface, reveal the underlying physics, and propose the method to improve the manipulation reliability for different systems.

Keywords: Lateral atom manipulation; Single crystal surface; Adatom; Silver; Computing simulations

Organosilane self-assembled multilayer formation based on activation of methyl-terminated surface with reactive oxygen species generated by vacuum ultra-violet excitation of atmospheric oxygen molecules by Young-Jong Kim; Jiwon Han; Hikaru Sano; Kyung-Hwang Lee; Kei Noda; Takashi Ichii; Kuniaki Murase; Kazumi Matsushige; Hiroyuki Sugimura (pp. 1507-1513).

A xenon excimer lamp which irradiates vacuum ultra-violet (VUV) light at 172nm in wavelength was applied to the photochemical surface conversion of n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) in the presence of atmospheric oxygen and subsequent multilayer fabrication. The terminal functional groups of ODS-SAM, –CH₃ groups, were converted into polar functional groups, like –COOH, by the reaction with atomic oxygen species generated photochemically through VUV excitation of atmospheric oxygen molecules. The structure of the resulting organosilane multilayer with different numbers of superimposed monolayers (from 1 to 11), prepared on a smooth and hydrophilic silicon substrate by the layer-by-layer (LbL) approach, was examined in terms of molecular organization as well as the intra- or interlayer binding modes in such novel films. Ellipsometry and grazing angle X-ray reflectivity measurements revealed that multilayer films of up to 11 discrete monolayers were successfully obtained, indicating that the self-assembly is a viable technique for the construction of relatively thick (16nm and above) multilayer films.

Keywords: Self-assembled monolayer (SAM); Multilayer; Photochemical surface modification; Vacuum ultra-violet (VUV); Active oxygen species; Layer-by-layer approach

Effects of laser operating parameters on metals micromachining with ultrafast lasers by J. Cheng; W. Perrie; S.P. Edwardson; E. Fearon; G. Dearden; K.G. Watkins (pp. 1514-1520).

180 femtoseconds (1kHz) and 10 picoseconds (1–50kHz) ultrafast laser micro-structuring of the metals Ti alloy, Al and Cu have been studied for the purpose of industrial application. The effects of some key laser operating parameters were investigated. The evolution of surface morphology revealed that laser pulses overlap in a range around the spatial FWHM can help to achieve optimal residual surface roughness. While observed ablation rate (unit: μm³ per pulse) changed dramatically with repetition rate due to the combined effects of plasma absorption, residual thermal energy and phase transition, higher throughput can be achieved with higher repetition rate. This study also indicated that residual surface roughness is almost independent of repetition rate at 10ps temporal pulse length. The ablation depth is approximately proportional to the number of overscan; however, machining accuracy deteriorates, especially for femtosecond laser processing and metals with low thermal conductivity and short electron–phonon coupling time.

Keywords: PACS; 52.38.Mf; 79.20.Ds; 79.60.BmLaser micromachining; Metals and alloys

Diffusion of single adatom Cu on Cu (001) and (110) surfaces by Yan-Ni Wen; Jian-Min Zhang; Ke-Wei Xu (pp. 1521-1525).

With static relaxation, the surface diffusion activation energies of a single Cu adatom migrated by both atomic exchange and hopping mechanisms and the forces acted on the diffusing adatom from other atoms of Cu (001) or (110) surface are calculated by using the MAEAM. When adatom migrated on Cu (001) or (110) surface, the increment curves of the system energy by hopping mechanism are symmetrical and the saddle points are in the midpoints of the migration path, but the ones by the exchange mechanism are dissymmetrical and the saddle points are always close to the initial hole positions of the adatom and away from the initial equilibrium positions of the exchanged atom. From minimization of both the diffusion activation energy and the force acted on the diffusing adatom from other atoms, we found that, on Cu (001) surface the favorable diffusion mechanism is hopping mechanism, however, on Cu (110) surface, hopping via long bridge is easier than the exchange mechanism but the hopping via short bridge is more difficult than the exchange mechanism.

Keywords: Cu; Surface; Diffusion; MAEAM

A highly effective method for synthesizing hybrid Pt–CdSe nanocomposite by Jing Chen; D.W. Zhao; Wei Lei; X.W. Sun; Junling Song; Weiqiao Deng (pp. 1526-1529).

Hybrid Pt–CdSe nanocomposite was fabricated by a two-step chemical route. Cadmium selenide (CdSe) quantum rods (QRs) were prepared by a one-pot approach with tunable size. After ligand exchange, CdSe QRs were loaded with monodisperse 1.9nm Pt nanopaticles in aqueous solution. Transmission electron microscopy (TEM) revealed the morphology of the Pt–CdSe nanostructure, and the decreased photoluminescence (PL) intensity demonstrated that electron and hole separation can be enhanced after loading Pt on CdSe QRs. X-ray photoelectron energy spectrum (XPS) was applied to confirm the existence of Pt and detect the Pt mass concentration of 3%.

Keywords: PACS; 81.10.Dn; 81.16.BeCadmium selenide; Platinum; Solar cell

Hybrid ultraviolet photodetectors with high photosensitivity based on TiO₂ nanorods array and polyfluorene by Yangang Han; Gang Wu; Mang Wang; Hongzheng Chen (pp. 1530-1533).

The highly oriented array composed of rutile TiO₂ nanorods is synthesized by the hydrothermal method on the SnO:F (FTO) substrate. The hybrid UV detector is fabricated via spin-coating a thin layer of poly (9,9-dihexylfluorene) (PFH) on the array. The device characteristics, including I– V curves under UV illumination and time response are studied. Obvious UV photoconductive effect is observed in the device and the response is fast to the switching on and off UV light illumination, which can be repeated for at least 50 times. The quick enhancement of the current origins from the large contact area between TiO₂ nanorods and PFH and the convenient charge transport in TiO₂ nanorods.

Keywords: TiO; ₂; nanorod; Array; PFH; UV detector; Surface photoconductivity

Effect of post-deposition annealing on structural and electrical properties of high- k HoTiO₃ gate dielectrics by Tung-Ming Pan; Li-Chen Yen; Sheng-Han Su (pp. 1534-1537).

In this article, the authors developed a high- k HoTiO₃ gate dielectric deposited on Si (100) through reactive cosputtering. They found that the HoTiO₃ dielectrics annealed at 800°C exhibited excellent electrical properties such as high capacitance value, small density of interface state, almost no hysteresis voltage, and low leakage current. This phenomenon is attributed to the decrease in intrinsic defect (related to oxygen vacancy) due to a rather well-crystallized HoTiO₃ structure and composition observed by X-ray diffraction, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy, respectively.

Keywords: High-; k; HoTiO; ₃; Gate dielectric

Effect of substrate temperature on properties of multilayer thin film based on ZnO and Mo-doped indium oxide by R.K. Gupta; K. Ghosh; P.K. Kahol (pp. 1538-1541).

Zinc oxide/molybdenum-doped indium oxide/zinc oxide (ZnO/IMO/ZnO) multilayer thin films are grown using pulsed laser deposition technique. The effect of substrate temperature on structural, optical, and electrical properties of multilayer films is studied. It is observed that films grown at high substrate temperature are oriented along (002) and (222) direction for ZnO and IMO respectively. The crystallinity of these films increases with increase in substrate temperature. It is also seen that conductivity, carrier concentration, and mobility increase with increase in temperature. The multilayer film grown at 500°C has low resistivity (7.67×10⁻⁵Ωcm), high carrier concentration (3.90×10²⁰cm⁻³), and high mobility (209cm²/Vs).

Keywords: PACS; 72.20; 78.66; 73.50J; 61.16CZinc oxide; Indium oxide; Pulsed laser deposition; Transparent electrode; Hall effect; Multilayer

Effects of total CH₄/Ar gas pressure on the structures and field electron emission properties of carbon nanomaterials grown by plasma-enhanced chemical vapor deposition by J.L. Qi; X. Wang; W.T. Zheng; H.W. Tian; C. Liu; Y.L. Lu; Y.S. Peng; G. Cheng (pp. 1542-1547).

The effects of total CH₄/Ar gas pressure on the growth of carbon nanomaterials on Si (100) substrate covered with CoO nanoparticles, using plasma-enhanced chemical vapor deposition (PECVD), were investigated. The structures of obtained products were correlated with the total gas pressure and changed from pure carbon nanotubes (CNTs) through hybrid CNTs/graphene sheets (GSs), to pure GSs as the total gas pressure changed from 20 to 4Torr. The total gas pressure influenced the density of hydrogen radicals and Ar ions in chamber, which in turn determined the degree of how CoO nanoparticles were deoxidized and ion bombardment energy that governed the final carbon nanomaterials. Moreover, the obtained hybrid CNTs/GSs exhibited a lower turn-on field (1.4V/μm) emission, compared to either 2.7V/μm for pure CNTs or 2.2V/μm for pure GSs, at current density of 10μA/cm².

Keywords: PECVD; Carbon nanotubes; Graphene sheets; Field emission

Influence of alkali metallization (Li, Na and K) on photoluminescence properties of porous silicon by Kadir Esmer; Ersin Kayahan (pp. 1548-1552).

We present results for alkali metallization effects on photoluminescence (PL) properties of porous silicon (PS). The metallization of PS was realized by immersion plating in solutions containing 3mM LiNO₃, KNO₃ and NaNO₃ metal salts. The surface bond configuration of PS was monitored by Fourier transmission infrared spectroscopy (FTIR) and it was found that the PS surface was oxidized after metallization. Surface properties of PS were investigated by field emission scanning electron microscopy (FE-SEM) and it was found that the PS surface was covered by alkali metals for short immersion times. The PL intensity increased for critical immersion times and PL spectrum shifted to high energy region with the metallization. The experimental results suggest a possibility that the metallization provides a relatively easy way to achieve an increase in the PL intensity and oxidation of the PS surface.

Keywords: Porous silicon; Immersion plating; Electrochemical etching; Spectral response

Studies on interdiffusion in Pd/Mg/Si films: Towards improved cyclic stability in hydrogen storage by Y. Sunitha; G.L.N. Reddy; Sanjiv Kumar; V.S. Raju (pp. 1553-1559).

The paper reports the diffusion coefficients of grain boundary diffusion and grain boundary assisted lattice diffusion of Pd in Mg in Pd/Mg/Si system, a useful material for hydrogen storage, at 473K in vacuum. The grain boundary diffusivity is measured by Whipple model and grain boundary assisted lattice diffusivity by plateau rise method using Pd depth profiles constructed by Rutherford backscattering spectrometry. It is established that grain boundary diffusivities are about six orders of magnitude faster than lattice diffusivities. Fine grained microstructure of Pd film, high abundance of defects in Mg film and higher stability associated with Pd–Mg intermetallics are responsible for the diffusion of Pd into grain boundaries and subsequently in the interiors of Mg. Besides the indiffusion of Pd, annealing also brings about an outdiffusion of Mg into Pd film. Examination by nuclear reaction analysis involving²⁴Mg(p,p′γ)²⁴Mg resonance reaction shows the occurrence of Mg outdiffusion. Minimization of surface energy is presumably the driving force of the process. In addition to Pd/Mg interface, diffusion occurs across Mg/Si (substrate) interface as well on increasing the annealing temperature above 473K. These studies show that dehydrogenation of films accomplished by vacuum annealing should be limited to temperatures less than 473K to minimize the loss of surface Pd, the catalyst of the hydrogen absorption–desorption process and Mg, the hydrogen storing element, by way of interfacial reactions.

Keywords: Palladium; Magnesium; Hydrogen storage; Interdiffusion; Rutherford backscattering spectrometry; Nuclear resonance reaction analysis

Improvement of depth resolution in XPS analysis of fluorinated layer using C₆₀ ion sputtering by Takuya Nobuta; Toshio Ogawa (pp. 1560-1565).

Depth profile of C₆₀ ion-used X-ray photoelectron spectroscopy (XPS) was studied on fluorinated organic layers with different thicknesses. We found that the depth resolution decreased, the sputtering rate went down and the surface turned rough as the layer thickness increased. This is because carbon-rich layer was formed on the surface by cross-linking reaction of the polymer and/or accumulation of degraded C₆₀ through continuous sputtering. Surprisingly, the high sputtering rate drastically improved the resolution of the analysis. The rate over 48.7nm/min did not show any deterioration on the depth resolution, the sputtering rate and surface smoothness.

Keywords: Depth profile XPS analysis; Fluorinated layer; C; ₆₀; ion; Sputtering rate; Depth resolution

The influence of substrate temperature on the morphology, optical and electrical properties of thermal-evaporated ZnTe Thin Films by E. Bacaksiz; S. Aksu; N. Ozer; M. Tomakin; A. Özçelik (pp. 1566-1572).

The structural, morphological, optical and electrical properties of ZnTe films deposited by evaporation were investigated as a function of substrate temperature (at −123 and 27°C) and post-deposition annealing temperature (at 200, 300 and 400°C). It was determined that films deposited at both substrate temperatures were polycrystalline in nature with zinc-blende structure and a strong (111) texture. A small Te peak was detected in XRD spectra for both substrate temperatures, indicating that as-deposited ZnTe films were slightly rich in Te. Larger grains and a tighter grain size distribution were obtained with increased substrate temperature. Scanning electron microscopy (SEM) studies showed that the microstructures of the as-deposited films agreed well with the expectations from structure zone model. Post-deposition annealing induced further grain growth and tightened the grain size distribution. Annealing at 400°C resulted in randomization in the texture of films deposited at both substrate temperatures. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.13 to 2.16eV with increased substrate temperature. Increasing the annealing temperature sharpened the band-edge. Resistivity measurements showed that the resistivity of films deposited at substrate temperatures of −123 and 27°C were 32Ωcm, and 1.0×10⁴Ωcm, respectively with corresponding carrier concentrations of 8.9×10¹⁵cm⁻³ and 1.5×10¹⁴cm⁻³. Annealing caused opposite changes in the film resistivity between the samples prepared at substrate temperatures of −123 and 27°C.

Keywords: ZnTe thin films; Vacuum evaporation; Substrate temperature; Annealing temperature; Microstructure; Optical band gap; Electrical resistivity

Surface free energy of polypropylene and polycarbonate solidifying at different solid surfaces by Emil Chibowski; Konrad Terpilowski (pp. 1573-1581).

Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energiesγstot of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction (γs−=1.91mJ/m2), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8–10mJ/m² for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the sameγs−=6.56.7mJ/m2. No electron acceptor interaction is found on the surfaces.Theγstot of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PPγstot values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed betweenγstot and dielectric constant or dipole moment of the polar probe liquids. The changes inγstot of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images.

Keywords: Polypropylene; Polycarbonate; Contact angles; Surface free energy

Analysis of oxide formation induced by UV laser coloration of stainless steel by Z.L. Li; H.Y. Zheng; K.M. Teh; Y.C. Liu; G.C. Lim; H.L. Seng; N.L. Yakovlev (pp. 1582-1588).

Laser-induced coloration on metal surfaces has important applications in product identification, enhancing styles and aesthetics. The color generation is the result of controlled surface oxidation during laser beam interaction with the metal surfaces. In this study, we aim to obtain in-depth understanding of the oxide formation process when an UV laser beam interacts with stainless steel in air. The oxide layer is analysed by means of optical microscopy, scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometer (TOF-SIMS). TOF-SIMS results clearly show the formation of duplex oxide structures. The duplex structure includes an inner layer of Cr oxide solution and an outer layer of Fe oxide solution. The oxide layer thickness increased as the results of Fe diffusion to surface during multiple laser scanning passes.

Keywords: Laser color marking; Stainless steel oxidation; Element diffusion

Growth and characteristics of hydrogenated In-doped ZnO thin films by pulsed DC magnetron sputtering by Young Ran Park; Juho Kim; Young Sung Kim (pp. 1589-1594).

We investigated the role of hydrogen impurities in highly oriented In-doped ZnO (IZO:H) films. The conductivity of ZnO:H films exhibit small variation despite the increase of hydrogen ratio. The small variation of the carrier concentration in IZO:H films can be explained by the reduction of the oxygen deficiency for the charge neutrality and the increase of Vzn–H bonding for partially charge compensation in the films. The additional mode at 573cm⁻¹ is interpreted as vacancy clusters. The discrepancy between the increase of vacancy clusters (573cm⁻¹) and small variation of carrier concentration is attributed to the different physical characteristics of the IZO:H films due to the hydrogen existence between bulk and surface. The measured FT-IR peak at 3500cm⁻¹ exhibits typical characteristic of O–H bonding.

Keywords: Zinc oxide (ZnO); In-doped; Hydrogen effect; Film; FT-IR; Micro Raman

Characterization of N,C-codoped TiO₂ films prepared by reactive DC magnetron sputtering by Kee-Rong Wu; Chung-Hsuang Hung (pp. 1595-1603).

Titanium dioxide (TiO₂) films are deposited by codoping nitrogen and carbon on indium tin oxide-coated substrates as visible light (Vis)-enabled catalysts. The X-ray diffraction peak intensity of the preferential orientation in (211) plane declines when the topmost 1.0μm layer of the film is ground off. The decrease in the crystallite size and the crystallinity of anatase TiO₂ film is also evidenced by a shift towards the high wave number and broadening of the Raman spectra. Low doping concentrations of N (1.3%) and C (1.8%) are estimated by X-ray photoelectron spectroscopy (XPS) which displays an N 1 s peak at 396.8eV and a C 1 s peak at 282.1eV, respectively. This is attributed to the substitution of the oxygen sites with nitrogen and carbon, which is believed to be responsible for the Vis photocatalytic activity into a wavelength of >500nm. The cross-sectional transmission electron microscopy images show larger pores at the grain boundaries and in larger columnar crystals than in the undoped TiO₂ film. All of these results indicate that porosity, crystallinity and shift in the preferential orientation are more pronounced close to the surface than close to the bottom of the sample. Wettability upon measurement of the water contact angle, methylene blue degradation and radical formation tests under both ultraviolet and Vis irradiation demonstrate that the topmost surface renders not only a larger reactive surface area but also a better carrier transport route than the rest of the film, improving its photocatalytic activity. These results show that surface porosity of the film is dominant than the tailoring of the photocatalytic activities of N,C-codoped TiO₂ catalysts.

Keywords: Titanium dioxide film; Hardness; Sputtering; Photocatalytic activity

Surface characterization of plasma-modified resist patterns by ToF-SIMS analysis by Jong S. Park; Hyung-jun Kim (pp. 1604-1608).

We report the use of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) technique to determine whether the patterned bank is suitable for inkjet printing, by evaluating the phobicity contrast between two regions, the glass substrate inside pixels and the surface of the resist bank. We first examined the effect of plasma treatment on the ink spreading behavior inside pixels. The phobicity contrast was optimized by removing residues inside the pixels and by providing high phobicity on the bank surface. We show that ToF-SIMS spectra and mass-resolved images are effective tools in examining the existence of organic contaminants inside pixels and predicting the actual inkjet printing behavior. The ToF-SIMS technique will find promising applications that are related to surface characteristics where conventional contact angle measurement is hard to apply due to geometrical and technical restrictions.

Keywords: Plasma; Inkjet; ToF-SIMS; Resist; Bank; Pixel

Composition design and laser cladding of Ni–Zr–Al alloy coating on the magnesium surface by Cunshan Wang; Yongzhe Chen; Ting Li; Biao Yao (pp. 1609-1613).

The cluster line criterion was used for optimized design of a Ni–Zr–Al alloy used as coating on the AZ91HP magnesium alloy by laser cladding. Results show that the coating mainly consists of an amorphous, two ternary intermetallic phases with Ni₁₀Zr₇ and Ni₂₁Zr₈ type structures resulting in high hardness, good wear resistance and corrosion resistance. The interface between the clad layer and the substrate has good metallurgical bond.

Keywords: Composition design; Laser cladding; Ni-based alloy; Magnesium alloy

Composite electroplating of Cu–SiO₂ nano particles on carbon fiber reinforced epoxy composites by Hao Li; Yizao Wan; Hui Liang; Xiaolei Li; Yuan Huang; Fang He (pp. 1614-1616).

The main purpose of this work is to co-deposit nano-SiO₂ particles into the copper coatings on carbon fiber reinforced epoxy (C/EP) composite surface by electrodeposition method in order to improve the micro hardness of coatings. C/EP composites are copper plated with sulfuric acid based solution, and the effects of nano-SiO₂ and C₆H₁₂O₆ in the electrolyte contents on the copper coatings are investigated. It is found that crystalline grains of coatings are markedly refined by nano-SiO₂ in the acidic sulfate copper plating bath and the ceramic particles cause an increase in hardness of coatings though nano-SiO₂ results in a decline of deposition rate and a decrease in electrical conductivity of electroplating layers. Otherwise, C₆H₁₂O₆ in the plating bath is indispensable to the layer formation even though nano-SiO₂ added. These results demonstrate that the hardness of coatings will be increased with appropriate contents of co-deposited SiO₂ and C₆H₁₂O₆ in the plating bath.

Keywords: Epoxy resin; Composites; Nano-particles; Electroplating; Composite coatings

Erratum to “Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings” [Appl. Surf. Sci. 255 (2009) 9132–9138] by G.E. Stan; C.O. Morosanu; D.A. Marcov; I. Pasuk; F. Miculescu; G. Reumont (pp. 1617-1617).

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Applied Surface Science (v.256, #5)