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Applied Surface Science (v.253, #23)

Using a chemical concept for reactivity for the interpretation of STM images of physisorbed molecules by Heiko Gawronski; Jörg Henzl; Violeta Simic-Milosevic; Karina Morgenstern (pp. 9047-9053).

The electrostatic potential mapped on the electron density contour of gas phase molecules is used to identify several molecules physisorbed on transition metals imaged by scanning tunnelling microscopy within the molecular HOMO–LUMO gap. It is rationalized that the inverted of this potential, representing the potential energy felt by a negative test charge, is a good concept to interpret changes in the dielectricity constant through the influence of physisorbed molecules and thus to understand their submolecular resolution images. The validity of the concept is demonstrated on dichlorobenzene, chloronitrobenzene, and two azobenzene derivates on the surfaces of Au(111), Ag(111), and Cu(111).

Keywords: PACS; 68.37.Ef; 68.43.De; 82.20.Kh; 72.40.GkSTM imaging of molecules; Electrostatic potential mapped electron density

Stable highly hydrophobic and oleophilic meshes for oil–water separation by Qingjun Wang; Zhe Cui; Yi Xiao; Qingmin Chen (pp. 9054-9060).

This paper describes a simple method for fabricating both highly hydrophobic and oleophilic meshes by coating thin fluoro-containing films. The static contact angle of such meshes is greater than 150° for water, and close to 0° for kerosene, xylene and toluene. These meshes can separate water from oil effectively without resorting to any extra power or chemical agent. Moreover, they exhibited stable water resisting, anti-chemical erosion and anti-hot aging properties. It promises as a candidate for the separation of oil and water.

Keywords: PACS; 68.08.Bc, Wetting; 82.70.Gg, Gels and sols; 68.08De, Structure/measurements and simulations; 47.32.Ff, Separated flowSurface; Morphology; Contact angle; Hydrophobic; Oleophilic; Mesh; Wetting; Sol–gel process; Perfluoroalkyltriethoxysilane

Corrosion behavior of boride layers evaluated by the EIS technique by I. Campos; M. Palomar-Pardavé; A. Amador; C. VillaVelázquez; J. Hadad (pp. 9061-9066).

The corrosion behavior of boride layers at the AISI 304 steel surface is evaluated in the present study. Electrochemical impedance spectroscopy (EIS) technique was used for the evaluation of the polarization resistance at the steel surface, with the aid of AUTOLAB potentiostat. Samples were treated with boron paste thickness of 4 and 5mm, in the range of temperatures 1123≤ T≤1273K and exposed time of 4 and 6h. The electrochemical technique employed 10mV AC with a frequency scan range from 8kHz to 3mHz in deaerated 0.1M NaCl solution. Nyquist diagrams show that the highest values of corrosion resistance are present in the samples borided at the temperature of 1273K, with treatment time of 4h and 4mm of boron paste thickness. The values of corrosion resistance on borided steels are compared with the porosity exhibited in the layers.

Keywords: Boriding; EIS technique; Boride layers; Polarization resistance; Borided stainless steel

Surface improvement and biocompatibility of TiAl₂₄Nb₁₀ intermetallic alloy using rf plasma nitriding by A.M. Abd El-Rahman; M.F. Maitz; M.A. Kassem; F.M. El-Hossary; F. Prokert; H. Reuther; M.T. Pham; E. Richter (pp. 9067-9072).

The present work describes the surface improvement and biocompatibility of TiAl₂₄Nb₁₀ intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400W to 650W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400W.

Keywords: Radio frequency (rf) plasma power; Auger electron spectroscopy (AES); Surface hardness; Corrosion resistance; Wear rate; Biocompatibility

Field emission from nano-patterned amorphous carbon by Zengmei Wang; Jian Wang; Dejie Li (pp. 9073-9076).

Electron emission from nano-patterned amorphous carbon is realized in this paper. The patterned carbon consists of islands with size of tens of nanometers, and is formed by etching uniform carbon film in oxygen plasma using a bismuth island-like film as the mask. Uniform and stable electron emission is reproducibly obtained, and the emission efficiency is above 2% at an anode voltage of 3kV. Small carbon particles between large islands are supposed to be necessary for stable electron emission.

Keywords: PACS; 79.70.+q; 73.40.Gk; 78.55.QrElectron emission; Amorphous carbon film; Bismuth film

GaN films deposited by middle-frequency magnetron sputtering by C.W. Zou; M.L. Yin; M. Li; L.P. Guo; D.J. Fu (pp. 9077-9080).

GaN films were deposited on Si (111) substrates by middle-frequency magnetron sputtering. X-ray diffraction revealed preferential GaN (0002) orientation normal to the substrate surface for all the films deposited. The diffraction intensity and N contents were found to depend strongly on the total gas pressure. Good quality films were only obtained at pressures in the range of 0.4–1.0Pa. Little diffraction of GaN (0002) could be observed either at total pressures below 0.4Pa or above 1.0Pa. The GaN films produced under the optimized conditions have an N:Ga ratio of 1:1 as determined by energy-dispersive X-ray spectroscopy.

Keywords: GaN; Middle-frequency; Magnetron sputtering; Structure

Modification of the organic/La_0.7Sr_0.3MnO₃ interface by in situ gas treatment by X.Z. Wang; X.M. Ding; Z.S. Li; Y.Q. Zhan; I. Bergenti; V.A. Dediu; C. Taliani; Z.T. Xie; B.F. Ding; X.Y. Hou; W.H. Zhang; F.Q. Xu (pp. 9081-9084).

La_0.7Sr_0.3MnO₃ (LSMO) can act as a spin injection electrode in organic spin-valves and organic light-emitting devices. For the latter application, good control of the electronic structure of the organic/LSMO interface is a key issue to ensure sufficient current injection in the device. By exposing cleaned LSMO surfaces to activated oxygen and hydrogen, the work function of the samples can reach 5.15 and 4.3eV, respectively, as shown by in situ photoemission measurements. The initial stage of formation of the organic/LSMO interface upon deposition of N, N′-bis-(1-naphyl)- N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) onto the oxygen-treated LSMO surface is examined. We find that the NPB molecules evenly cover the LSMO surface and that the interface barrier height is 0.8eV, which is comparable to that at the NPB/indium tin oxide (ITO) interface with the ITO surface pretreated in situ by oxygen plasma.

Keywords: Spin injection; Organic/magnetic interface; Synchrotron radiation; Surface treatment

Surface characterization and microstructure of ITO thin films at different annealing temperatures by Davood Raoufi; Ahmad Kiasatpour; Hamid Reza Fallah; Amir Sayid Hassan Rozatian (pp. 9085-9090).

In this study, the electron beam evaporation method is used to generate an indium tin oxide (ITO) thin film on a glass substrate at room temperature. The surface characteristics of this ITO thin film are then investigated by means of an AFM (atomic force microscopy) method. The influence of postgrowth thermal annealing on the microstructure and surface morphology of ITO thin films are also examined. The results demonstrate that the film annealed at higher annealing temperature (300°C) has higher surface roughness, which is due to the aggregation of the native grains into larger clusters upon annealing. The fractal analysis reveals that the value of fractal dimension D_f falls within the range 2.16–2.20 depending upon the annealing temperatures and is calculated by the height–height correlation function.

Keywords: PACS; 68.55.Jk; 68.55.−aElectron beam evaporation; ITO thin film; Thermal annealing; Fractal analysis; Morphology

Perovskite thin films grown by direct liquid injection MOCVD by M. Andrieux; C. Gasquères; C. Legros; I. Gallet; M. Herbst-Ghysel; M. Condat; V.G. Kessler; G.A. Seisenbaeva; O. Heintz; S. Poissonnet (pp. 9091-9098).

The continuous scaling down of devices dimensions, in silicon technology, imposes to replace silicon dioxide. Among the potential candidates for new capacitors, some perovskite structure materials (such as titanate or zirconate) show interesting characteristics. The first way to develop perovskite films is to use a mixture of two β-diketonates by varying the solution's cationic ratio. However, our previous results on SrZrO₃ showed that a wide parametric study had to be carried on. Another way is to design novel heterometallic precursors that contain both cations on the same molecule. The ligands could be chosen so that peculiar evaporation and decomposition temperatures could be obtained.Thus, perovskite films (SrZrO₃) were deposited on plane Si(100) substrates by direct liquid injection MOCVD from two original heterometallic precursors Sr₂Zr₂(OⁿPr)₈(thd)₄(ⁿPrOH)₂ and Sr₂Zr₂(thd)₄(OⁱPr)₈. The oxide films were deposited at substrate temperature ranging from 550 to 900°C. At the lowest temperatures (550 and 600°C) the as-deposited films were amorphous. After a postannealing at 700°C for 1h under N₂/O₂, the films deposited at 550°C were crystallized in the SrZrO₃ orthorhombic phase. Crystallographic and chemical structures were controlled applying grazing X-ray diffraction and infrared spectroscopy measurements. Results are discussed with respect to experimental synthesis conditions.

Keywords: Perovskite oxide; Strontium zirconate; MOCVD; Single-source precursor

The influence of preparative parameters on the adhesion of alumina washcoats deposited on metallic supports by Jingsheng Jia; Jin Zhou; Jianguo Zhang; Zhongshan Yuan; Shudong Wang (pp. 9099-9104).

Well-adhered alumina washcoats on FeCrAl metallic supports were prepared using boehmite sols and alumina slurries. The microstructure and the surface performance of the washcoat/support were investigated by SEM, XRD, and ultrasonic vibration. The effects of the main preparative parameters on the coating adherence were studied. The optimal coating conditions are presented as follows: pre-oxidation of the metallic supports was performed at 900°C for 10h, the sol layer loadings were 2.0–6.6wt.%, and the slurry layer loadings were less than 25.3wt.%. The sol layer drying was performed at 30°C for 1h and that for the slurry layer the drying was performed at 120°C for 2h, and the coating calcining was performed at 900°C for 2h. The SEM photographs of coated samples show that alumina washcoats were well deposited on the metallic supports.

Keywords: Adhesion; Alumina coating; Metallic support

Ferrite stabilization induced by molybdenum enrichment in the surface of unalloyed iron sintered in an abnormal glow discharge by H.C. Pavanati; J.M. Lourenço; A.M. Maliska; A.N. Klein; J.L.R. Muzart (pp. 9105-9111).

Unalloyed iron was sintered using an abnormal glow discharge with confined anode–cathode configuration. This electrode arrangement allows heating the component as well as enriching the surface with atoms from the cathode. In order to sinter unalloyed iron with molybdenum enrichment, the samples were placed on a holder acting as the discharge anode, inside a cylindrical cathode of Mo. The cathode was heated by the bombardment of ions and fast neutrals accelerated in the cathode sheath and as a consequence of the confined geometry the sample was efficiently heated by thermal radiation. On heating, the ion and neutral species bombardment produces sputtering of atoms of the cathode, which by diffusion in the gas phase deposit on the sample surface. During sintering the deposited atoms diffuse into the sample, resulting in a layer enriched with elements sputtered out from the cathode. Mo enrichment was observed on the sample surface (more than 4wt%), which resulted in stabilization of the Fe α-phase at the treatment temperature. Under these conditions, as the diffusion coefficient in the Fe α-phase is about 10² times higher than in the γ-phase, the sintering of this enriched phase is activated.

Keywords: Powder metallurgy; Plasma sintering; Surface enrichment

In situ measurement of the surface stress evolution during magnetron sputter-deposition of Ag thin film by Seung Hyun Lee; Joong Keun Park (pp. 9112-9115).

We measured the evolution of in situ surface stress of Ag thin film during the magnetron sputter deposition. The measurement of force per width of Ag thin film showed that both the surface state and surface stress of Ag layer can be controlled through the variation of the deposition conditions such as the deposition temperature and rate. At room temperature, the force per width curve of Ag film deposited to 1Å/s showed a typical curve consisting of three stages of surface stress. A brief presence of initial compressive stage and broad tensile maximum resulting in a compressive state had a tendency to disappear with increasing the deposition temperature. Meanwhile, a development of final compressive stage was more at higher temperature. Similar effect was observed but less obvious on increasing the deposition rate.

Keywords: PACS; 68.60.−p; 68.55.−aAg thin film; Magnetron sputter deposition; Surface stress; Surface structure

Layer uniformity in glucose oxidase immobilization on SiO₂ surfaces by Sebania Libertino; Antonino Scandurra; Venera Aiello; Filippo Giannazzo; Fulvia Sinatra; Marcella Renis; Manuela Fichera (pp. 9116-9123).

The goal of this work was the characterization, step by step, of the enzyme glucose oxidase (GOx) immobilization on silicon oxide surfaces, mainly by means of X-Ray photoelectron spectroscopy (XPS). The immobilization protocol consists of four steps: oxide activation, silanization, linker molecule deposition and GOx immobilization. The linker molecule, glutaraldehyde (GA) in this study, must be able to form a uniform layer on the sample surface in order to maximize the sites available for enzyme bonding and achieve the best enzyme deposition. Using a thin SiO₂ layer grown on Si wafers and following the XPS Si2p signal of the Si substrate during the immobilization steps, we demonstrated both the glutaraldehyde layer uniformity and the possibility to use XPS to monitor thin layer uniformity. In fact, the XPS substrate signal, not shielded by the oxide, is suppressed only when a uniform layer is deposited. The enzyme correct immobilization was monitored using the XPS C1s and N1s signals. Atomic force microscopy (AFM) measurements carried out on the same samples confirmed the results.

Keywords: PACS; 87.64.Gb; 87.64.Je; 68.37.Nq; 81.15.-z; 81.70.-q; 87.15.ByX-ray photoelectron spectroscopy; Glucose oxidase; Immobilization; Glutaraldehyde; Silicon oxide; Biosensor

Correlation between substrate bias, growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon films by Aiping Liu; Jiaqi Zhu; Jiecai Han; Huaping Wu; Zechun Jia (pp. 9124-9129).

We investigate the growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films which are deposited at different substrate biases by filtered cathodic vacuum arc technique with PH₃ as the dopant source. The films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Raman spectroscopy, residual stress measurement, UV/VIS/NIR absorption spectroscopy and temperature-dependent conductivity measurement. The atomic fraction of phosphorus in the films as a function of substrate bias is obtained by XPS analysis. The optimum bias for phosphorus incorporation is about −80V. Raman spectra show that the amorphous structures of all samples with atomic-scaled smooth surface are not remarkably changed when PH₃ is implanted, but some small graphitic crystallites are formed. Moreover, phosphorus impurities and higher-energetic impinging ions are favorable for the clustering of sp² sites dispersed in sp³ skeleton and increase the level of structural ordering for ta-C:P films, which further releases the compressive stress and enhances the conductivity of the films. Our analysis establishes an interrelationship between microstructure, stress state, electrical properties, and substrate bias, which helps to understand the deposition mechanism of ta-C:P films.

Keywords: PACS; 81.15.Ef; 78.30.Ly; 78.66.Jg; 68.37; 62.40.+iPhosphorus incorporated tetrahedral amorphous carbon; Filtered cathodic vacuum arc; Substrate bias; Microstructure; Residual stress; Optical gap

Poly-benzyl domains grown on porous silicon and their I– V rectification by Jie Chao; Huan-Mei Han; Bing Xia; Long Ba; Hong-Bo Liu; Shou-Jun Xiao (pp. 9130-9136).

Microwave-irradiated polymerization of benzyl chloride and triphenyl chloromethane on hydride-terminated porous silicon (PS) was achieved through the use of Zn powder as a catalyst. Transmission infrared Fourier-transform spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the poly-benzyl membranes grafted on PS. Topographical images by AFM revealed crystal-like domains rather than homogenous monolayers on the surface. The current–voltage measurements in nano-scale by current sensing atomic force microscopy (CS-AFM) showed the rectification behavior of this polymer membrane. Finally, mechanism of a radical initiation on the surface and a following Friedel-Crafts alkylation was proposed for the covalent assembly of poly-benzyl domains.

Keywords: PACS; 68.43.Hn; 68.55.Jk; 73.40.EiPorous silicon; Poly-benzyl domain; I; –; V; rectification

Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale by Yongguang Wang; Yongwu Zhao; Wei An; Jun Wang (pp. 9137-9141).

This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale.

Keywords: Chemical mechanical polishing; Binding energy; Modeling; Atomic scale

Coexistent compressive and tensile strain in Ag thin films on Si(1 1 1)-(7×7) surfaces by D.K. Goswami; K. Bhattacharjee; B. Satpati; S. Roy; G. Kuri; P.V. Satyam; B.N. Dev (pp. 9142-9147).

Growth and strain behavior of thin Ag films on Si substrates have been investigated by scanning tunneling microscopy, cross-sectional transmission electron microscopy and high resolution X-ray diffraction studies. Ag islands formed on Si at room temperature growth show strongly preferred heights and flat top. At low coverage [≳1 monolayer (ML)], Ag islands with (1 1 1) orientation containing two atomic layers of Ag are overwhelmingly formed [D.K. Goswami, K. Bhattacharjee, B. Satpati, S. Roy, P.V. Satyam, B.N. Dev, Surf. Sci. 601 (2007) 603]. A thicker (40 ML) annealed film shows two closely spaced Ag(1 1 1) diffraction peaks—one weak and broad and the other narrow and more intense. The broad peak corresponds to an average expansion (0.21%) and the narrow intense peak corresponds to a contraction (0.17%) of the Ag(1 1 1) planar spacing compared to the bulk value. This coexistence of compressive and tensile strain can be explained in terms of changes in the Ag lattice during the heating–cooling cycle due to thermal expansion coefficient mismatch between Ag and Si.

Keywords: PACS; 68.55.Jk; 61.16.Ch; 68.37.Ef; 68.60.DvAg films on Si; Coexistent compressive and tensile strain; Si(1 1 1)-(; 7; ×; 7; ) surface; High resolution X-ray diffraction

Density functional study of initial HfCl₄ adsorption and decomposition reactions on silicon surfaces with SiON interfacial layer by Jie Ren; Bao Sun; David Wei Zhang (pp. 9148-9153).

The initial adsorption and decomposition of HfCl₄ on silicon surfaces with different types of SiON interfacial layers are investigated using density functional theory. We find that the reactions of HfCl₄ on both the hydroxylated and nitrided silicon surfaces proceed through similar reaction pathways. By comparison of the reaction energies of HfCl₄ with the hydroxyl and amino surface sites, we find that it is both kinetically and thermodynamically favorable for the reactions of HfCl₄ on hydroxyl site of silicon substrates. Comparing with the adjacent bridging oxygen, we also find that the neighboring hydroxyl can facilitate the adsorption of HfCl₄ on the amido surface site. Also, it is more kinetically and thermodynamically favorable for the reaction of HfCl₄ with bridging NH site than that with NH₂ site.

Keywords: Density functional theory; Dielectrics; Hafnium; Atomic layer deposition

Synthesis, characterization and infrared emissivity study of polyurethane/TiO₂ nanocomposites by Jing Chen; Yuming Zhou; Qiuli Nan; Yanqing Sun; Xiaoyun Ye; Zhiqiang Wang (pp. 9154-9158).

In this study, polyurethane/titania (PU/TiO₂) nanocomposites were prepared in ultrasonic process and characterized by fourier transform IR spectroscopy (FT-IR), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissivity analysis. The TEM and SEM results indicated that the nanoparticles were dispersed homogeneously in PU matrix on nanoscale. TGA-DSC confirmed that the heat stability of the composite was improved. Infrared emissivity study showed that the nanocomposite possessed lower emissivity value than those values of pure polymer and nanoparticles.

Keywords: Polyurethane; Nano-TiO; ₂; Nanocomposites; Polymers; Emissivity

Field emission investigations of RuO₂-doped SnO₂ wires by Ashok B. Bhise; Dattatray J. Late; Niranjan S. Ramgir; Mahendra A. More; Imtiaz S. Mulla; Vijayamohanan K. Pillai; Dilip S. Joag (pp. 9159-9163).

Field emission studies of a bunch and a single isolated RuO₂:SnO₂ wire have been performed. A current density of 5.73×10⁴A/cm² is drawn from the single wire emitter at an applied field of 8.46×10⁴V/μm. Nonlinearity in the Fowler–Nordheim (F–N) plot has been observed and explained on the basis of electron emission from both the conduction and the valence bands of the semiconductor. The current stability recorded at the preset value of 1.5μA is observed to be good. Overall the high emission current density, good stability and mechanically robust nature of the RuO₂:SnO₂ wires offer advantages as field emitters for many potential applications.

Keywords: Field emission; Doped semiconductor; Field enhancement factor; SnO; ₂; RuO; ₂

Corrosion behaviour of AISI 304 stainless steel with Cu coatings in H₂SO₄ by A. Pardo; M.C. Merino; A.E. Coy; R. Arrabal; F. Viejo; A. M’hich (pp. 9164-9176).

The work addresses the influence of cementation and electrodeposition of copper coatings on the corrosion resistance of AISI 304 stainless steel immersed in 30wt.% H₂SO₄ at temperatures of 25 and 50°C. Corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The specimen surfaces were analysed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The corrosion performance of AISI 304 stainless steel in sulphuric acid solution was greatly improved by copper coatings. The amount of copper deposited by the cementation process was sufficient to protect the stainless steel of corrosion. A greater amount of copper obtained by electrodeposition treatments does not supply further improvement in the corrosion behaviour. The improved corrosion resistance is related to copper dissolution at the initial stages of immersion tests and the presence of Cu²⁺ in the solution, which makes the medium more oxidizing, increasing the stability of the passive layer. In addition, the presence of copper at the surface reduces the overpotential of cathodic reaction, enabling the transition from an active region to the passive one.

Keywords: Stainless steel; Acid corrosion; General corrosion; Coatings

Laser-assisted modification of polystyrene surfaces for cell culture applications by Wilhelm Pfleging; Michael Bruns; Alexander Welle; Sandra Wilson (pp. 9177-9184).

Laser-assisted patterning and modification of polystyrene (PS) was investigated with respect to applications in micro-fluidics and cell culture. For this purpose the wettability, the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local formation of chemical structures suitable for improved cell adhesion was realized on PS surfaces by UV laser irradiation. Above and below the laser ablation threshold two different mechanisms affecting cell adhesion were detected. In the first case the debris deposited on and along laser irradiated areas was responsible for improved cell adhesion, while in the second case a photolytic activation of the polymer surface including a subsequent oxidization in oxygen or ambient air is leading to a highly localized alteration of protein adsorption from cell culture media and finally to increased cell adhesion. Laser modifications of PS using suitable exposure doses and an appropriate choice of the processing gas (helium or oxygen) enabled a highly localized control of wetting. The dynamic advancing contact angle could be adjusted between 2° and 150°. The hydrophilic and hydrophobic behaviour are caused by chemical and topographical surface changes.

Keywords: Polystyrene; Laser; Modification; Ablation; Wetting; Cell adhesion

Post-deposition atomic terraces growth of ZnO thin films deposited on epi-GaN templates by Takeshi Okato; Tatsunori Sakano; Minoru Obara; Menno J. Kappers; Mark G. Blamire (pp. 9185-9190).

We demonstrate how growth processes affect on ZnO film properties, which are to be essential guides to prevent defect formation in order to synthesize reproducible high quality ZnO films. First, we reveal that deposition at a low temperature is indispensable to transfer underlying GaN atomic terraces to ZnO surface. As the film thickness is increased, however, the terraces disappear to develop island morphology. It is found that the thick film surface is smoothed to the extent that atomic terraces can be seen after an appropriate thermal treatment. Adverse effects associated with high annealing temperatures are then demonstrated as evidenced by cracks formation, increased yellow cathode-luminescence and intermixing at the interface.

Keywords: PACS; 68.55.−a; 78.66.−w; 81.15.FgZinc oxide; Gallium nitride; Pulsed-laser deposition; Annealing

Amorphous hydrogenated carbon coatings on IC packaging mold by ECR-CVD system by C.T. Guo; P.C. Chen (pp. 9191-9197).

The surface properties of IC packaging molds such as anti-sticking, wear, and corrosion resistances can be improved by hard surface coating. In this study, Ti/TiN/TiCN/a-C:H thin film coatings were deposited on IC cavity bar molds in a hybrid PVD-ECR-CVD coating system. The structure of the a-C:H films was delineated by a function of bias voltages by Raman spectroscopy. Excellent adhesion and lower friction coefficients of a-C:H films were also assessed. According to the normal adhesion force measurement, a-C:H coating was superior to that of typical electroplated hard chromium (Ep-Cr). Performance evaluation showed that the a-C:H coating could increase the number of molding injections in IC package production lines by 216%.

Keywords: Amorphous hydrogenated carbon (a-C:H); Raman spectrum; ECR-CVD; IC cavity bar mold

Influence of laser treatment on the corrosion properties of plasma-sprayed Ni-coated WC coatings by Guozhi Xie; Jinxian Zhang; Yijun Lu; Ziyi He; Bing Hu; Dongjie Zhang; Keyu Wang; Pinghua Lin (pp. 9198-9202).

The electrochemical corrosion of plasma spray Ni-coated WC cermet coatings, after laser treatment, has been studied in 3.5% NaCl solution through immersion test. The main corrosion mechanism for as-sprayed coating is the galvanic corrosion between coating and substrate, resulting in the detachment of coating from substrate, while the homogeneous corrosion occurs for the laser treatment coating. However, the corrosion trace for the as-sprayed pure coating could not be found. It is found that the electrochemical corrosion has been found heavily depending on the galvanic corrosion between the coating and the substrate. The defects, such as pores and laminar structures in the coating, could act as the infiltration paths of the electrolyte.

Keywords: Immersion test; Plasma spraying; WC; Corrosion mechanism

Surface modification of Ti dental implants by Nd:YVO₄ laser irradiation by Francisco J.C. Braga; Rodrigo F.C. Marques; Edson de A. Filho; Antonio C. Guastaldi (pp. 9203-9208).

Surface modifications have been applied in endosteal bone devices in order to improve the osseointegration through direct contact between neoformed bone and the implant without an intervening soft tissue layer. Surface characteristics of titanium implants have been modified by addictive methods, such as metallic titanium, titanium oxide and hydroxyapatite powder plasma spray, as well as by subtractive methods, such as acid etching, acid etching associated with sandblasting by either AlO₂ or TiO₂, and recently by laser ablation. Surface modification for dental and medical implants can be obtained by using laser irradiation technique where its parameters like repetition rate, pulse energy, scanning speed and fluency must be taken into accounting to the appropriate surface topography. Surfaces of commercially pure Ti (cpTi) were modified by laser Nd:YVO₄ in nine different parameters configurations, all under normal atmosphere. The samples were characterized by SEM and XRD refined by Rietveld method. The crystalline phases αTi, βTi, Ti₆O, Ti₃O and TiO were formed by the melting and fast cooling processes during irradiation. The resulting phases on the irradiated surface were correlated with the laser beam parameters. The aim of the present work was to control titanium oxides formations in order to improve implants osseointegration by using a laser irradiation technique which is of great importance to biomaterial devices due to being a clean and reproducible process.

Keywords: PACS; 61.80.Ba; 79.20.Ds; 61.66.BiSurface modification; Titanium; Laser ablation; Dental implant; Biomaterial

AFM study of BSA adlayers on Au stripes by Michal Tencer; Robert Charbonneau; Nancy Lahoud; Pierre Berini (pp. 9209-9214).

Thin narrow Au stripes suitable for propagating long-range surface plasmon–polaritons were deposited by evaporation and lift-off on a thermal oxide layer on a silicon substrate, and modified by direct adsorption of bovine serum albumin (BSA). Atomic force microscopy (AFM) measurements reveal that BSA adsorbs onto the Au stripes from phosphate buffer solutions forming an adlayer having an average thickness of about 2nm (surface mass density of about 2ng/mm²). Comparisons with a simple adsorption model suggest the side-on adsorption of a single monolayer of BSA followed by denaturation and flattening. The BSA-coated stripes have an increased surface roughness compared to a virgin stripe.

Keywords: Surface; Plasmon; Waveguide; Protein; AFM

Tin-Platinum catalysts interactions on titania and silica by N. Nava; P. Del Angel; J. Salmones; E. Baggio-Saitovitch; P. Santiago (pp. 9215-9220).

Pt-Sn was supported on titania and silica, and the resulting interactions between the components in prepared samples and the resulting interactions between the components before and after treatment with hydrogen were characterized by Mössbauer spectroscopy, X-ray diffraction, Rietveld refinement, high-resolution transmission electron microscopy (HRTEM) and catalytic tests data. Results show the presence of Pt and SnO₂ after calcinations, and Pt₃Sn, PtSn and PtSn₃ after reduction. Rietveld analysis shows that some Ti⁴⁺ are replaced by Sn⁴⁺ atoms in the titania structure. Finally, HRTEM and the practically absence of activity observed confirms that metallic platinum is encapsulated.

Keywords: Platinum-tin catalysts; Pt-Sn interactions on titania and silica; Mössbauer spectroscopy; HRTEM

Dissociative adsorption and thermal evolution of dichloroethylenes on Ni(100) by S.H. Xu; X. Yang; Z.H. He; K.T. Leung (pp. 9221-9227).

The room temperature (RT) adsorption and thermal evolution of cis- and trans-dichloroethylene (DCE) and their structural isomer, iso-DCE, on Ni(100) have been studied by vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS). For RT adsorption, both cis- and trans-DCE exhibit very similar EELS features that are different from those found for iso-DCE. These differences indicate the formation of different fragments upon RT adsorption. In particular, the primary adspecies for cis- and trans-DCE are ethane-1,1,2,2-tetrayl (HC¨–C¨H) and acetylide-like (▪) adspecies along with a small amount of chlorovinyl adspecies, while ethylylidyne (▪) is the more plausible adspecies for iso-DCE. The differences in the adstructures upon dissociative adsorption at RT underline the important isomeric effects. Furthermore, both AES and TDS results for all three DCE isomers show that most of the Cl atoms produced by dechlorination remain on the surface and its surface concentration remains unchanged upon annealing the samples above 500K. Upon further annealing to 550K, the EELS spectra of all three isomers exhibit a broad feature near 1600cm⁻¹, which suggests the formation of carbon clusters on the surface. The presence of surface Cl atoms therefore appears to prevent the CC bond cleavage during thermal evolution of the adspecies on Ni(100).

Keywords: Dissociative adsorption; Dichloroethylenes; Ni(1; 0; 0)

Comparison of plasma chemistries for the dry etching of bulk single-crystal zinc-oxide and rf-sputtered indium–zinc-oxide films by W.T. Lim; L. Stafford; J.S. Wright; L.F. Vossa; R. Khanna; Ju-Il Song; Jae-Soung Park; Young Woo Heo; Joon-Hyung Lee; Jeong-Joo Kim; D.P. Norton; S.J. Pearton (pp. 9228-9233).

The dry etching characteristics of bulk, single-crystal zinc-oxide (ZnO) and rf-sputtered indium–zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma with different plasma chemistries. The introduction of interhalogens such as ICl, IBr, BI₃, and BBr₃ to the Ar plasma produced no enhancement of the ZnO and IZO etch rates with respect to physical sputtering in a pure argon atmosphere under the same experimental conditions. In these plasma chemistries, the etch rate of both materials increased with source power and ion energy, indicating that ion bombardment plays an important role in enhancing desorption of etch products. Except in Ar/CH₄/H₂ discharges, the ZnO etch rate was very similar to that of IZO, which indicates that zinc and indium atoms are driven by a similar plasma etching dynamic. CH₄/H₂-containing plasmas produced higher etch rates for IZO than for ZnO due to the preferential desorption of the group III etch products. Application of the CH₄/H₂/Ar plasma to the etching of deep features in bulk, single-crystal ZnO produced highly anisotropic profiles although some trenches were observed near the sidewalls.

Keywords: ZnO; Etching

Residual stresses and white layer in electric discharge machining (EDM) by Bülent Ekmekci (pp. 9234-9240).

The effect of dielectric liquid and electrode type on white layer structure in electric discharge machined surfaces has been studied in terms of retained austenite and residual stresses using X-ray diffraction method. The machining tests were conducted by using two different tool electrodes (copper and graphite) and dielectric liquid (kerosene and de-ionized water) under same operational conditions. The present work suggests that the surface is saturated with carbon irrespective of the tool electrode material when machining with kerosene dielectric liquid. But, retained austenite is formed on the surface due to carbon uptake from graphite tool electrode when machining with de-ionized water dielectric liquid. On the other hand, even though surface residual stresses increase with structural non-homogeneities in the white layer, no clear consequences have been observed in residual stress distribution beneath the white layer.

Keywords: Electric discharge machining; EDM; Residual stresses; White layer; Retained austenite

Characterisation of porous doped ZnO thin films deposited by spray pyrolysis technique by F. Kadi Allah; S. Yapi Abé; C.M. Núñez; A. Khelil; L. Cattin; M. Morsli; J.C. Bernède; A. Bougrine; M.A. del Valle; F.R. Díaz (pp. 9241-9247).

Al or Sn doped ZnO films were deposited by spray pyrolysis using aqueous solutions. The films were deposited on either indium tin oxide coated or bare glass substrates. ZnCl₂, AlCl₃ and SnCl₂ were used as precursors. The effect of ZnCl₂ molar concentration (0.1–0.3M) and doping percentage (2–4% AlCl₃ or SnCl₂) have been investigated. The main goal of this work being to grow porous ZnO thin films, small temperature substrates (200–300°C) have been used during the spray pyrolysis deposition. It is shown that, if the X-ray diffraction patterns correspond to ZnO, the films deposited onto bare glass substrate are only partly crystallized while those deposited onto ITO coated glass substrate exhibit better crystallization. The homogeneity of the films decreases when the molar concentration of the precursor increases, while the grain size and the porosity decrease when the Al doping increases. The optical study shows that band tails are present in the absorption spectrum of the films deposited onto bare glass substrate, which is typical of disordered materials. Even after annealing 4h at 400°C, the longitudinal resistivity of the films is quite high. This result is attributed to the grain boundary effect and the porosity of the films. Effectively, the presence of an important reflection in the IR region in samples annealed testifies of a high free-carriers density in the ZnO crystallites. Finally it is shown that when deposited in the same electrochemical conditions, the transmission of a polymer film onto the rough sprayed ZnO is smaller than that onto smooth sputtered ZnO.

Keywords: Zinc oxide; Spray pyrolysis; X-ray diffraction; Scanning electron microscopy; Optical and electrical properties

The effects of hydrogen plasma pretreatment on the formation of vertically aligned carbon nanotubes by Wen-Pin Wang; Hua-Chiang Wen; Sheng-Rui Jian; Jenh-Yih Juang; Yi-Shao Lai; Chien-Huang Tsai; Wen-Fa Wu; Kuan-Ting Chen; Chang-Pin Chou (pp. 9248-9253).

The effects of H₂ plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H₂ and CH₄ with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(100) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands ( I_D/ I_G) is decreased with increasing gas flow rate. TEM results suggest H₂ plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures.

Keywords: PACS; 61.46.+w; 68.37.Hk; 68.37.Lp; 81.20.−nCarbon nanotubes; H; ₂; pretreatment; Raman spectroscopy; Scanning electron microscopy; Transmission electron microscopy

The effects of activated carbon supports on the structure and properties of TiO₂ nanoparticles prepared by a sol–gel method by Youji Li; Shiying Zhang; Qumin Yu; Wenbin Yin (pp. 9254-9258).

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol–gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.

Keywords: Crystallites; Sol–gel method; Nanomaterials; Titanium composites; Activated carbon

Thioglycolic acid (TGA) assisted hydrothermal synthesis of SnS nanorods and nanosheets by Subhajit Biswas; Soumitra Kar; Subhadra Chaudhuri (pp. 9259-9266).

Nanorods and nanosheets of tin sulfide (SnS) were synthesized by a novel thioglycolic acid (TGA) assisted hydrothermal process. The as prepared nanostructures were characterized by X-ray diffraction (XRD) study, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD study reveals the formation of well-crystallized orthorhombic structure of SnS. Diameter of the SnS nanorods varied within 30–100nm. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns identify the single crystalline nature for the SnS nanocrystals. The mechanism for the TGA assisted growth for the nanosheets and nanorods have been discussed.

Keywords: Tin sulfide; Nanorods; Nanosheets; Solvothermal; Scanning and transmission electron microscopy

Enhanced corrosion resistance of mild steel in normal sulfuric acid medium by 2,5-bis( n-thienyl)-1,3,4-thiadiazoles: Electrochemical, X-ray photoelectron spectroscopy and theoretical studies by M. Lebrini; M. Lagrenée; M. Traisnel; L. Gengembre; H. Vezin; F. Bentiss (pp. 9267-9276).

The inhibitive action of some thiadiazole derivatives, namely 2,5-bis(2-thienyl)-1,3,4-thiadiazole (2-TTH) and 2,5-bis(3-thienyl)-1,3,4-thiadiazole (3-TTH) against the corrosion of mild steel in 0.5M H₂SO₄ solution has been investigated using weight loss measurements, Tafel polarisation and electrochemical impedance spectroscopy (EIS) techniques. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution. The protection efficiency increased with increasing inhibitors concentration and the ability of the molecule to adsorb on the steel surface was dependent on the position of the sulphur atom on the thienyl substituent. Inhibition efficiency values obtained from various methods employed were in reasonable agreement. Potentiodynamic polarisation studies clearly showed that 2-TTH and 3-TTH acted as mixed inhibitors. Adsorption of these inhibitors on steel surface obeyed to Langmuir adsorption isotherm. X-ray photoelectron spectroscopy and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal sulphuric solution by n-TTH is due to the formation of a chemisorbed film on the steel surface. Molecular modelling was used to gain some insight, about structural and electronic effects in relation to the inhibiting efficiencies.

Keywords: Acid corrosion inhibitors; Thiadiazoles; Mild steel; Adsorption; XPS; Quantum chemical approach

Effects of organic acids on the size-controlled synthesis of rutile TiO₂ nanorods by Yinhua Jiang; Hengbo Yin; Yueming Sun; Hui Liu; Lixu Lei; Kangmin Chen; Yuji Wada (pp. 9277-9282).

Size-controlled synthesis of pure rutile-phase TiO₂ nanorods was carried out by a hydrothermal method using different organic acids as modifiers, and metatitanic acid and concentrated sulfuric acid as raw materials. The synthesized rutile TiO₂ nanorods were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of organic acid modifiers on the sizes of rutile TiO₂ nanorods were investigated. It was found that the steric effect occurred by the organic modifiers and non-polarity of organic acids were beneficial to the formation of small-sized rutile TiO₂ nanorods. The strongly coordinative interaction between the carboxyl (or hydroxyl) group of the modifier and the surface of TiO₂ nanoparticles effectively inhibited the crystal growth.

Keywords: PACS; 81.05.Hd; 81.07.Bc; 81.16.BeRutile TiO; ₂; Nanorods; Organic acid modifiers; Metatitanic acid

Influence of aramid fiber moisture regain during atmospheric plasma treatment on aging of treatment effects on surface wettability and bonding strength to epoxy by Yu Ren; Chunxia Wang; Yiping Qiu (pp. 9283-9289).

One of the main differences between a low-pressure plasma treatment and an atmospheric pressure plasma treatment is that in atmosphere, the substrate material may absorb significant amount of water which may potentially influence the plasma treatment effects. This paper investigates how the moisture absorbed by aramid fibers during the atmospheric pressure plasma treatment influences the aging behavior of the modified surfaces. Kevlar 49 fibers with different moisture regains (MR) (0.5, 3.5 and 5.5%, respectively) are treated with atmospheric pressure plasma jet (APPJ) with helium as the carrier gas and oxygen as the treatment gas. Surface wettability and chemical compositions, and interfacial shear strengths (IFSS) to epoxy for the aramid fibers in all groups are determined using water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and micro-bond pull out tests, respectively. Immediately after the plasma treatment, the treated fibers have substantially lower water contact angles, higher surface oxygen and nitrogen contents, and larger IFSS to epoxy than those of the control group. At the end of 30 day aging period, the fibers treated with 5.5% moisture regain had a lower water contact angle and more polar groups on the fiber surface, leading to 75% improvement of IFSS over the control fibers, while those for the 0.5 and 3.5% moisture regain groups were only 30%.

Keywords: PACS; 52.77.Bn; 92.60.Jq; 33.60.Fy; 81.40.CdAramid fibers; Atmospheric pressure plasma treatment; Moisture regain; XPS; Interfacial shear strength; Aging effect

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Applied Surface Science (v.253, #23)