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Applied Surface Science (v.256, #21)

Editorial Board (pp. ii).

Low-nickel stainless steel passive film in simulated concrete pore solution: A SIMS study by S. Fajardo; D.M. Bastidas; M.P. Ryan; M. Criado; D.S. McPhail; J.M. Bastidas (pp. 6139-6143).

Low-nickel and AISI 304 austenitic stainless steel (SS) passive films were studied using secondary ion mass spectrometry (SIMS). An alkaline Ca(OH)₂ saturated test solution containing different chloride additions was used at room temperature. The passive film formed consists mainly of an inner chromium-rich oxide layer and an outer iron-rich oxide layer. The chemistry of the passive film depends strongly on the chloride content in the alkaline solution. Under these exposure conditions nickel was detected in the outer part of the oxide, whereas chloride ions were not found in the passive film for either the low-nickel or AISI 304 SS alloys.

Keywords: SIMS; Passive film; Low-nickel stainless steel; Concrete pore solution; Depth profile

Characterization of inhomogeneous colloidal layers using adapted coherence probe microscopy by Eric Halter; Paul Montgomery; Denis Montaner; Remi Barillon; Mireille Del Nero; Catherine Galindo; Sylvia Georg (pp. 6144-6152).

Colloidal layers play an important role in environmental studies, for example in the movement of radionuclides in nuclear waste management. New characterization techniques are required for studying such complex, porous layers. The purpose of this work is to adapt coherence probe microscopy (CPM), which is typically used for measuring the surface roughness of single surfaces, to the analysis of thick inhomogeneous colloidal layers. Two types of layers, either composed of 80nm or 400nm alumina colloidal particles deposited on glass slides by decantation have been studied. One of the problems in performing routine roughness measurements of colloidal layers using CPM is the appearance of apparent pits below the level of the substrate surface. We demonstrate that this is due to partial detection of the buried colloid/substrate interface. Further, we have developed the “Z-scan” technique, which consists of building up an XYZ image stack by scanning the full depth of the sample. Any point in an XY image can then be investigated to study the local buried internal structure, layer thickness, and effective refractive index. Comparison of results with AFM and SEM confirm the structure found with CPM and the new “Z-scan” technique, which opens up new and useful applications.

Keywords: Inhomogeneous layers; Colloid surfaces; Characterization; Scanning interference microscopy; Layer thickness; Roughness

Improved ultraviolet/visible rejection ratio using MgZnO/SiO₂/n-Si heterojunction photodetectors by Da-Yong Jiang; Xi-Yan Zhang; Quan-Sheng Liu; Zhao-Hui Bai; Li-Ping Lu; Xiao-Chun Wang; Xiao-Yun Mi; Neng-Li Wang; De-Zhen Shen (pp. 6153-6156).

We report on the fabrication and characterization of MgZnO/SiO₂/n-Si structured photodetectors, for the visible–blind monitoring. The current–voltage curve of the heterojunction shows obvious rectifying behaviors. In the visible range, the photocurrent decreased rapidly. In additionally, the ultraviolet/visible rejection ratio (R340nm/R500nm) was about four orders of magnitude at reverse bias, indicating a high degree of visible blindness. The key role of the insulating SiO₂ layer will be discussed in terms of the band diagrams of the heterojunctions.

Keywords: MgZnO; Photodetector; Heterojunction; Ultraviolet/visible rejection ratio

Formation of aligned ZnO nanorods on self-grown ZnO template and its enhanced field emission characteristics by Jai Singh; Sandip S. Patil; Mahendra A. More; Dilip S. Joag; R.S. Tiwari; O.N. Srivastava (pp. 6157-6163).

We report a novel method for producing aligned ZnO nanorods (ANR) on self-grown ZnO template in a single step process involving growth of ZnO by vapor transport, followed by quenching of growing ZnO flux in liquid nitrogen. In the present study Zn powder turns into ZnO sheet under oxygen flow at ∼900°C and bottom surface of the sheet acts as template for the growth of ANR. It is revealed from XRD and EDAX analysis that the bottom of the sheet is Zn rich region and acts as self catalyst for the growth of ANR. The grown nanorods have length up to several tens of micrometers with diameters ranging from ∼100 to 150nm. Microstructural analysis of ANR indicates the fractal like configuration. The field emission properties have been investigated for ANR with fractal geometry using the ANR on self-grown ZnO template as a cathode directly. The turn-on electric field required to draw current density of ∼1.0μA/cm² has been found to be ∼0.98V/μm. The field enhancement factor based on Fowler–Nordheim (F–N) plot was found to be ∼7815 for ANR. The fractal geometry of ANR has been shown to be advantageous for achieving improved field emission features. The present investigations of synthesis involving formation of ANR over self-grown ZnO template, together with fractal configuration of the as-synthesized ANR, are first of their type.

Keywords: Aligned ZnO nanorods (ANR); ZnO template; Field emission; Fractal feature; SEM

Characterization and aging effect study of nitrogen-doped ZnO nanofilm by Javad Karamdel; C.F. Dee; Burhanuddin Yeop Majlis (pp. 6164-6167).

The influence of sputtering and annealing conditions and aging effect on properties of sputtered ZnO:N thin films were investigated. Achieved results confirmed a planar growth of nitrogen-doped ZnO film with a high uniform and smooth surface morphology. Incorporation of nitrogen in the ZnO films made new Raman shifts. X-ray diffraction spectra showed only the ZnO (002) diffraction peak, which was slightly shifted toward lower angels, compared to pure ZnO, which is the result of incorporating nitrogen in the ZnO films. The amount of this shift was proportional to N concentration. In addition, annealed samples showed better crystallinity with lower shift due to dramatically reduction of N atoms during the annealing. The Hall effect measurements exhibited p-type behaviour on annealed ZnO:N thin films while the un-annealed samples showed n-type conductivity. Aging effect studies demonstrated that the N content of thin films decreased dramatically as time passed. The reduction of N concentration in annealed samples was lower than un-annealed ones after 6 months.

Keywords: Thin film; N-doped ZnO; Aging effect; Sputtering

Investigation of magnetic properties for oblique deposited granular films by magnetic field annealing by Bangmin Zhang; Shihui Ge; Huaping Zuo; Yuhua Xiao; Guowei Wang; Li Zhang (pp. 6168-6171).

A series of (Fe₅₇Co₂₄Ni₄Nb₂B₁₃)_x–(SiO₂)1−_x nano-granular thin films were fabricated by magnetron sputtering with different oblique incidence angle θ and excellent soft magnetic properties are achieved. Based on the results of magnetic field anneal at different temperature T_a, it is evidenced that orientation of atomic pairs contributes to the annealing treatment, and could manipulate magnetic anisotropy. The damping coefficient α decreases with increasing angle θ and this is ascribed to the anisotropy dissipation.

Keywords: PACS; 61.46.Df; 68.55.J; 75.40.Gb; 75.70.Ak; 76.50.+gAnnealing; Magnetic thin films; Magnetic anisotropy; Damping coefficient; Magnetic sputtering

Growth of carbon nanofibers on aligned zinc oxide nanorods and their field emission properties by R.N. Gayen; A.K. Pal (pp. 6172-6178).

Carbon nanofibers were grown by electrodeposition technique onto aligned zinc oxide (ZnO) nanorods deposited by hybrid wet chemical route on glass substrates. X-ray diffraction traces indicated very strong peak for reflections from (002) planes of ZnO. The Raman spectra were dominated by the presence of G band at about 1597cm⁻¹ corresponding to the E_2g tangential stretching mode of an ordered graphitic structure with sp² hybridization and a D band at about 1350cm⁻¹ originating from disordered carbon. Fourier transformed infrared studies indicated the presence of a distinct characteristic absorption peak at ∼511cm⁻¹ for Zn–O stretching mode. Photoluminescence spectra indicated band edge luminescence of ZnO at ∼3.146eV along with a low intensity peak at ∼0.877eV arising out of carbon nanofibers. Field emission properties of these films and their dependence on the CNF coverage on ZnO nanorods are reported here. The average field enhancement factor as determined from the slope of the FN plot was found to vary between 1×10³ and 3×10³. Both the values of turn-on field and threshold field for CNF/ZnO were lower than pure ZnO nanorods.

Keywords: PACS; 61.46.+w; 73.63.−b; 79.70.+qCNT; ZnO nanorods; Field emission

Characterization of mesoporous VO_x/MCM-41 composite materials obtained via post-synthesis impregnation by Saeed B. Bukallah; Ali Bumajdad; Kamal M.S. Khalil; Mohamed I. Zaki (pp. 6179-6185).

Spherical-particle MCM-41 was synthesized at room temperature, and, then, impregnated with aqueous solutions of NH₄VO₃ to produce variously loaded VO_x/MCM-41 composite materials. Bulk and surface properties of the materials thus produced were characterized by means of X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), N₂ sorptiometry and X-ray photoelectron spectroscopy (XPS). Results obtained indicated that subsequent calcination at 550°C (for 2h) of the blank and impregnated MCM-41 particles, results in materials assuming the same bulk structure of MCM-41, and exposing uniformly mesporous, high area surfaces ( P_w=2.0–2.3nm; 974–829m²/g), except for the material obtained at 20wt%-V₂O₅ that was shown to suffer a considerable loss on surface area (down to 503m²/g). XPS results implied that the immobilization of the VO_x species occurs via interaction with surface OH/H₂O groups of MCM-41, leading to the formation of vanadate (VO₃⁻) surface species, as well as minor V–O–Si and V₂O₅-like species. However, in all cases, the vanadium sites remained pentavalent and exposed on the surface.

Keywords: MCM-41; VO; _x; /MCM-41 composites; Mesoporous; X-ray diffractometry; X-ray photelectron spectroscopy

Transparent ultrathin conducting carbon films by Martin Schreiber; Tarek Lutz; Gareth P. Keeley; Shishir Kumar; Markus Boese; Satheesh Krishnamurthy; Georg S. Duesberg (pp. 6186-6190).

Ultrathin conductive carbon layers (UCCLs) were created by spin coating resists and subsequently converting them to conductive films by pyrolysis. Homogeneous layers as thin as 3nm with nearly atomically smooth surfaces could be obtained. Layer characterization was carried out with the help of atomic force microscopy, profilometry, four-point probe measurements, Raman spectroscopy and ultraviolet–visible spectroscopy. The Raman spectra and high-resolution transmission electron microscopy image indicated that a glassy carbon like material was obtained after pyrolysis. The electrical properties of the UCCL could be controlled over a wide range by varying the pyrolysis temperature. Variation in transmittance with conductivity was investigated for applications as transparent conducting films. It was observed that the layers are continuous down to a thickness below 10nm, with conductivities of 1.6×10⁴S/m, matching the best values observed for pyrolyzed carbon films. Further, the chemical stability of the films and their utilization as transparent electrochemical electrodes has been investigated using cyclic voltammetry and electrochemical impedance spectroscopy.

Keywords: Conductive carbon films; Transparent films; Pyrolysis; Glassy carbon; Graphene; Electrochemical electrodes

Titania deposited on soft magnetic activated carbon as a magnetically separable photocatalyst with enhanced activity by Shaohua Wang; Shaoqi Zhou (pp. 6191-6198).

Magnetically separable composite photocatalysts, TiO₂ deposited on soft magnetic ferrite activated carbon (TFAC), were prepared by sol–gel and dip-coating technique. The prepared composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectra (FTIR), optical absorption spectroscopy, vibrating sample magnetometer (VSM) and nitrogen adsorption. These photocatalysts exhibited enhanced photocatalytic activity compared to Degussa P25 for the degradation of methyl orange (MO) in aqueous solution. The kinetics of MO degradation was well fitted to the Langmuir–Hinshelwood model. The samples showed good magnetic response and could be completely recovered by an external magnet. Furthermore, the photocatalysts could maintain high photocatalytic activity after five cycles, and the degradation rate of MO was still close to 90%.

Keywords: Composite photocatalyst; Magnetically separable; TiO; ₂; Activated carbon; Soft magnetic ferrite

Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution by Jie Liu; Yuli Tian; Yujia Chen; Jieying Liang (pp. 6199-6204).

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, –COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23–27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.

Keywords: Carbon fibers; Electrochemical oxidation; Interfacial bonding strength; Tensile strength

Influence of plasma pressure on the growth characteristics and ferroelectric properties of sputter-deposited PZT thin films by A. Bose; T. Maity; S. Bysakh; A. Seal; Suchitra Sen (pp. 6205-6212).

PZT thin films of thickness (320–1040) nm were synthesized on Si/SiO₂/Ti/Pt multilayered substrates by radio frequency magnetron sputtering. The influence of plasma pressure in the range of (0.24–4.9) Pa, during deposition, on the structural, electrical and ferroelectric properties of the PZT films was systematically studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and cross-sectional transmission electron microscopy (XTEM) were employed for structural study. Nano-probe Energy Dispersive (EDX) line scanning was employed to investigate the elemental distribution across the film-bottom electrode interface. I– V characteristics and polarization–electric field ( P– E) hysteresis loop of the films were measured. The study reveals that the plasma pressure has a strong influence on the evolution and texture of the ferroelectric perovskite phase and microstructure of the films. At an optimum plasma pressure of 4.1Pa, PZT films are grown with 93% perovskite phase with (111) preferred orientation and uniform granular microstructure. These films show a saturation polarization of 67μC/cm², remnant polarization of 30μC/cm² and coercive field of 28kV/cm which, according to the literature, seem to be suitable for device applications.Transmission electron microscopy (TEM) study shows that at a plasma pressure of 4.1Pa, the PZT/bottom Pt interface is sharp and no amorphous interlayer is formed at the interface. At a higher plasma pressure of 4.9Pa, poor I– V and P– E hysteresis loop are observed which are interpreted as due to an amorphous interlayer at the film-bottom electrode interface which is possibly enriched in Pb, Zr, O and Pt.

Keywords: Thin films; Sputtering; Electron microscopy; Ferroelectricity; PZT

Microscopic observation of laser glazed yttria-stabilized zirconia coatings by M.F. Morks; C.C. Berndt; Y. Durandet; M. Brandt; J. Wang (pp. 6213-6218).

Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2–9μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases.

Keywords: Thermal barrier coating; YSZ; Plasma spraying; Laser glazing; Microstructure; Vickers hardness

Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread by Keun Jung; Won-Kook Choi; Seok-Jin Yoon; Hyun Jae Kim; Ji-Won Choi (pp. 6219-6223).

Ga doped ZnO (GZO) thin films were deposited on glass substrates at room temperature by continuous composition spread (CCS) method. CCS is thin films growth method of various Ga_xZn1−_xO(GZO) thin film compositions on a substrate, and evaluating critical properties as a function position, which is directly related to material composition. Various compositions of Ga doped ZnO deposited at room temperature were explored to find excellent electrical and optical properties. Optimized GZO thin films with a low resistivity of 1.46×10⁻³Ωcm and an average transmittance above 90% in the 550nm wavelength region were able to be formed at an Ar pressure of 2.66Pa and a room temperature. Also, optimized composition of the GZO thin film which had the lowest resistivity and high transmittance was found at 0.8wt.% Ga₂O₃ doped in ZnO.

Keywords: Continuous composition spread; Transparent conducting oxides; Ga doped ZnO; Thin film

Synthesis and separation property of flower-like Cd(OH)₂ microstructures via a simple solution route by DongEn Zhang; Qing Xie; HongXiang Cai; XiaoBo Zhang; ShanZhong Li; GuiQuan Han; AiLing Ying; AiMei Chen; ZhiWei Tong (pp. 6224-6227).

Well-defined flower-like Cd(OH)₂ microstructures have been successfully synthesized via a simple aqueous solution route, using CdCl₂ and NaOH as the reactants, and triethanolamine (TEA) as the modifying agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis spectrometer were used to characterize the products. SEM and TEM images illustrated that the flower-like Cd(OH)₂ bundles consisted of hexagonal nanoplates with thickness of about 50nm. The adsorption of TEA on (001) plane of the growing Cd(OH)₂ crystal leads to the flower petals in appearance. Further experiments evidenced that the positively charged Cd(OH)₂ could effectively adsorb or separate the negatively charged dye molecules.

Keywords: Cd(OH); ₂; microstructures; 3D flower-like; Aqueous solution route; Growth process

Surface segregation in Nb-doped BaTiO₃ films by Emmanuel Arveux; Sandrine Payan; Mario Maglione; Andreas Klein (pp. 6228-6232).

We have used in situ photoemission spectroscopy to investigate Niobium doping in polycristalline BaTiO₃. The valence band maximum position progressively shifts from 2.5eV for undoped to 2.84eV for Nb-doped films. Ceramics and single crystal have been investigated for comparison with thin films. Nb-doped BaTiO₃ ceramics and Nb-doped SrTiO₃ single crystal show higher Fermi level position indicating that our doped films are less conducting regarding their bulk parents. This was confirmed by impedance spectroscopy under variable temperature. Large amount of niobium is clearly observable at surface but the amount of dopant is drastically reduced below the near-surface region, as evidenced by depth profile. Therefore, we provide evidence of surface segregation which would explain the contrasted resistivity values reported in literature for such donor-doped films.

Keywords: BaTiO; ₃; and titanates; Films; PTCR; Segregation; Surfaces; XPS

Electrons diffusion study on the nitrogen-doped nanocrystalline diamond film grown by MPECVD method by Qiang Hu; Rakesh K. Joshi; Ashok Kumar (pp. 6233-6236).

Nitrogen-doped nanocrystalline diamond (NNCD) films were deposited onto p-type silicon substrates with three different layer structures: (i) directly onto the silicon substrate (NNCD/Si), (ii) silicon with undoped nanocrystalline diamond layer which was deposited in the same way as the above mentioned NNCD by the recipe Ar/CH₄/H₂ with a ratio of 98%/1%/1% (NNCD/NCD/Si), and (iii) silicon wafer with 100nm thickness SiO₂ layer (NNCD/SiO₂/Si). Atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy were employed to characterize the morphology and microstructure of the as-grown nitrogen-doped diamond films. Silver colloid/silver contacts were made at to measure the current–voltage ( I– V) characteristics for the three different structures. Electrons from a CVD reactor hydrogen plasma diffuse toward the p-type silicon substrate during a deposition process under the high temperature (∼800°C). The study concluded that the SiO₂ layer could effectively prevents the diffusion of electrons.

Keywords: Electron diffusion; Diamond film; CVD

A theoretical study of c-C₅H₈ adsorption on Ge (001)-2×1 and on dimer vacancies on the surface: Electronic structure and bonding by E. Germán; I. López-Corral; A. Juan; G. Brizuela (pp. 6237-6245).

In this work we analyzed the geometry and the chemical interactions for c-C₅H₈ adsorption on Ge (001), using density functional theory calculations (DFT). We examined the changes in the atomic interactions using a slab model. We considered two cases, the cyclopentene adsorption on Ge(001) and on dimer vacancies on the surface. We found an average distance H–Ge, –C–Ge andC–Ge of 1.50, 1.70 and 1.65Å, respectively, on dimer vacancies; and an averageC–Ge distance of 2.05Å on Ge–Ge dimer. We also computed the density of states (DOS) and the DOS weighted overlap populations (OPDOS) corresponding to C–C, C–Ge, C–H, and Ge–Ge bonds. During adsorption the main contribution are the CC double bond in both cases, and the next C and the H's belonging to this bonds in the case of adsorption on dimer vacancies. The orbital contribution includes participation of the 2p_y and 2p_z orbitals corresponding to unsaturated C atoms, 2p_z corresponding to side saturated C, and the 4p orbitals of Ge for the adsorption on dimer vacancies; 2s and 2p_z orbitals corresponding to double bond C atoms, 4s and 4p_z orbitals of Ge for the adsorption on Ge(001).

Keywords: Cyclopentene; Ge(0; 0; 1); Adsorption; DFT; Bonding

X-ray photoelectron spectroscopy of nano-multilayered Zr–O/Al–O coatings deposited by cathodic vacuum arc plasma by V.N. Zhitomirsky; S.K. Kim; L. Burstein; R.L. Boxman (pp. 6246-6253).

Nano-multilayered Zr–O/Al–O coatings with alternating Zr–O and Al–O layers having a bi-layer period of 6–7nm and total coating thickness of 1.0–1.2μm were deposited using a cathodic vacuum arc plasma process on rotating Si substrates. Plasmas generated from two cathodes, Zr and Al, were deposited simultaneously in a mixture of Ar and O₂ background gases. The Zr–O/Al–O coatings, as well as bulk ZrO₂ and Al₂O₃ reference samples, were studied using X-ray photoelectron spectroscopy (XPS). The XPS spectra were analyzed on the surface and after sputtering with a 4kV Ar⁺ ion gun. High resolution angle resolved spectra were obtained at three take-off angles: 15°, 45° and 75° relative to the sample surface.It was shown that preferential sputtering of oxygen took place during XPS of bulk reference ZrO₂ samples, producing ZrO and free Zr along with ZrO₂ in the XPS spectra. In contrast, no preferential sputtering was observed with Al₂O₃ reference samples. The Zr–O/Al–O coatings contained a large amount of free metals along with their oxides. Free Zr and Al were observed in the coating spectra both before and after sputtering, and thus cannot be due solely to preferential sputtering.Transmission electron microscopy revealed that the Zr–O/Al–O coatings had a nano-multilayered structure with well distinguished alternating layers. However, both of the alternating layers of the coating contained of a mixture of aluminum and zirconium oxides and free Al and Zr metals. The concentration of Zr and Al changed periodically with distance normal to the coating surface: the Zr maximum coincided with the Al minimum and vice versa. However the concentration of Zr in both alternating layers was significantly larger than that of Al. Despite the large free metal concentration, the Knoop hardness, 21.5GPa, was relatively high, which might be attributed to super-lattice formation or formation of a metal–oxide nanocomposite within the layers.

Keywords: Cathodic vacuum arc; Vacuum arc deposition; Nano-multilayered coating; X-ray photoelectron spectroscopy; ZrO; ₂; Al; ₂; O; ₃

Effect of radio frequency power on the inductively coupled plasma etched Al_0.65Ga_0.35N surface by Y. Bai; J. Liu; P. Ma; B. Li; J. Zhu; L.W. Guo; X.Y. Liu (pp. 6254-6258).

The etching effects on the surface and electrical characteristics of high Al mole fraction Al_xGa1−_xN ( x=0.65) have been characterized by X-ray photoelectron spectroscopy (XPS) and transfer length method (TLM) as a function of radio frequency power. XPS results show that the Ga–N and Al–N peaks move to the lower energy after ICP etchings. An increase in the amount of oxygen and a decrease in the amount of nitrogen are observed for the etched samples along with the RF power. The annealing at 450°C is partly effective on removing the oxygen amount which would come from the C–O component and recovering the N deficiencies on the surface of etched sample. The extracted sheet resistance of the AlGaN layer from TLM increases gradually after ICP etching with an increase of RF power. The correlation between the XPS peaks and the electrical properties of the etched samples has been discussed and the annealing effect on the inverse leakage current of the p-i-n AlGaN solar blind UV detector is examined.

Keywords: AlGaN; ICP etching; XPS; Sheet resistance

Band bending at the conducting polymer/indium tin oxide interfaces with and without ultraviolet treatment by Yow-Jon Lin; Yi-Min Chin; Jung-Chung Lin; Yu-Chao Su (pp. 6259-6261).

In this study, the effect of ultraviolet treatment on the band bending at the poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate)/indium tin oxide (PEDOT:PSS/ITO) interfaces were researched. The authors suggested that ultraviolet treatment could lead to a reduction in the band bending at the PEDOT:PSS/ITO interface, owing to the removal of carbon contamination at the ITO surfaces and a decrease in the number of the trap-states at the PEDOT:PSS/ITO interface.

Keywords: Indium tin oxide; Surface treatment; Band bending; Polymer

Effects of N adsorption on the structural and electronic properties of SrTiO₃(001) surface by K.L. Zhao; D. Chen; D.X. Li (pp. 6262-6268).

The atomic configurations, bonding characteristics, and electronic structures of the N-adsorbed (directly and substitutionally) SrTiO₃(001) surface are studied by using first-principles method based on the density functional theory. From the analysis of the energetics and density of states, it is found that the stability of the directly adsorbed N depends on the relative position of N atom to the surface. To better understand the effects of the substitutionally adsorbed N on the surface, as an example, the behavior of Au atoms adsorbed on the N-substituted surface is discussed in detail. There is clearly a synergy effect between the substitution of N for O_s(I) and the adsorption of Au atoms on the SrTiO₃(001) surface.

Keywords: Density functional theory; Electronic structure; Surface structure

Surface modification of an epoxy resin with polyamines via cyanuric chloride coupling by David Schaubroeck; Johan De Baets; Tim Desmet; Peter Dubruel; Etienne Schacht; Luc Van Vaeck; André Van Calster (pp. 6269-6278).

The presence of polyamine groups on the surface of dielectric resins potentially improves the adhesion with electrochemically deposited metals. In this article, first cyanuric chloride is covalently bound to the surface hydroxyl groups of the epoxy resin. The remaining reactive sites on the coupled cyanuric chloride molecule are then used to anchor polyamines. New data on the triazine coupling is presented. The surface reactions are monitored and characterized by means of ATR-IR, SEM-EDS, XPS and ToF-S-SIMS.

Keywords: Surface characterization; Cyanuric chloride; Polyethylenimine; Electroless copper deposition; Adhesion

Microscale steps and micro–nano combined structures by anodizing aluminum by G.Q. Ding; R. Yang; J.N. Ding; N.Y. Yuan; W.Z. Shen (pp. 6279-6283).

In this paper, we firstly present a novel microscale-step structure fabricated by anodizing aluminum in a mixture of 0.05–0.5wt% NaCl (HCl), 2wt% H₃PO₄ and 20wt% ethanol under potentials of 1–40V at room temperature. Then, we present two micro–nano combined structures by integrating the microsteps with nanopores through multi-step anodizations. The microstep–nanopore hierarchical structure was obtained by re-anodizing the sample in oxalic acid, and the regular nanopores can be realized on the microscale patterned aluminum surface. The two-layer porous structure was one layer of nanoporous anodic alumina and another layer of micropores by two-step anodization on sample's both sides. These two novel structures can be useful for surface engineering and high flux filtration, respectively. The current fabrication approach broadens the applications of aluminum anodization, and brings a new method for assembling micro–nano structures.

Keywords: PACS; 62.23.St; 81.16.Rf; 82.45.Yz; 81.16.DnMicrostep; Nanopore; Anodic alumina; Assembly; Pitting

Molecular dynamic simulations of nanoindentation in aluminum thin film on silicon substrate by Ping Peng; Guanglan Liao; Tielin Shi; Zirong Tang; Yang Gao (pp. 6284-6290).

In the present work, the nanoindentation of aluminum thin film on silicon substrate is investigated by three-dimensional molecular dynamic (MD) simulation. The film/substrate system is modeled by taking Lennard–Jones (LJ) potential to describe the interaction at the film–substrate interface. Different loading rate from 50 to 250m/s is carried out in the simulation. The results showed that the hardness of the film increased with the loading rate. In order to study the effect of substrate on the mechanical properties of thin film, nanoindentation process on monolithic Al material is also simulated. The simulation results revealed that indentation pile-up in the aluminum film is significantly enhanced by the substrate. The substrate also affects the loading force during the nanoindentation. At the beginning of the indentation, the loading force is not affected by the substrate. Then, it is getting smaller caused by the interface. As the film is penetrated, the loading force increased rapidly caused by the hard substrate. These results were coincident with the previous reported experiments.

Keywords: Molecular dynamics; Nanoindentation; Al film

Activation of Zr–Co–rare earth getter films: An XPS study by D. Petti; M. Cantoni; M. Leone; R. Bertacco; E. Rizzi (pp. 6291-6296).

Thin films of non-evaporable getters are employed in the field of electronic devices packaging, as they provide a simple and effective solution for pumping in sealed applications. In particular thin films of Zr–Co–rare earth alloys deposited by sputtering have been developed for this purpose and successfully employed in industrial applications. In this paper we present an X-ray photoelectron spectroscopy investigation of the effect of thermal activation of the getter from the point of view of the induced surface chemical modification as seen by such a surface sensitive technique. We find that the activation process reflects in a clear reduction of Zr, accompanied by a decrease of the oxygen concentration at surface, which is fully accomplished already at 350°C; while at 450°C there is a significant increase of the cobalt concentration at surface.

Keywords: Non-evaporable getter; Activation; Zirconium; Oxidation; Carbides; X-ray photoelectron spectroscopy

Fatigue properties of a S45C steel subjected to ultrasonic nanocrystal surface modification by X.J. Cao; Y.S. Pyoun; R. Murakami (pp. 6297-6303).

An ultrasonic nanocrystal surface modification (UNSM) technique, at 3 different vibration strike numbers (34,000times/mm², 45,000times/mm², 68,000times/mm²) was used to modify the surface structure and properties of S45C. These three process conditions respectively produced 2μm, 12μm and 30μm nanocrystal layers. UNSM technique improves the following mechanical properties: microhardness, surface roughness, and compressive residual stress. Also, fatigue life increased with the vibration strike number. UNSM C3 (with the vibration strike number of 68,000times/mm²) has improved the fatigue strength by as much as 33% for S45C. Optical microscope pictures show that cracks usually initiate from intergranular microcracks on the surface and then extend along the tip traces of UNSM which are considered as process defects. A simple math model (tearing adhesive plaster model) has been made to analyze the initiation and growth of cracks. Though most of the cracks initiate at the surface of specimens, surface nanocrystal layers can help to retard crack initiation. In S45C, the efficiency of crack resistance is more than 48%.the vibration strike number

Keywords: Nanocrystal; Surface modification; UNSM; Microhardness; Residual stress; Surface roughness; Fatigue; Crack

Influence of (phospho)lipases on properties of mica supported phospholipid layers by Malgorzata Jurak; Emil Chibowski (pp. 6304-6312).

The effect of enzymes: lipase from Candida cylindracea (L_Cc), phospholipase A₂ from hog pancreas (PLA₂) and phospholipase C from Bacillus cereus (PLC) to modulate wetting properties of solid supported phospholipid bilayers was studied via advancing and receding contact angle measurements of water, formamide and diiodomethane, and calculation of the surface free energy and its components from van Oss et al. (LWAB) and contact angle hysteresis (CAH) approaches. Simultaneously, topography of the studied layers was determined by Atomic Force Microscopy (AFM). The investigated lipid bilayers were transferred on mica plates from subphase of pure water by means of Langmuir–Blodgett and Langmuir–Schaefer techniques. The investigated phospolipid layers were: saturated DPPC (1,2-dipalmitoyl- sn-glycero-3-phosphocholine), unsaturated DOPC (1,2-dioleoyl- sn-glycero-3-phosphocholine), and their mixture DPPC/DOPC. The obtained results revealed that the lipid membrane degradation by the enzymes caused increase in its surface free energy due to the amphiphilic hydrolysis products, which may accumulate in the lipid bilayer. In result activity of the enzymes may increase and then break down the bilayer structure takes place. It is likely that after dissolution of the hydrolysis reaction products in the bulk phase, patches of bare mica surface are accessible, which contribute to the apparent surface free energy changes. Comparison of AFM images and the free energy changes of the layers gives better insight into changes of their properties. The observed gradual increase in the layer surface free energy allows controlling of the hydrolysis process to obtain the surfaces of defined properties.

Keywords: Mixed phospholipid layers; Lipase; Phospholipases; Surface free energy; AFM

Effects of the edge shape and the width on the structural and electronic properties of silicene nanoribbons by Yu-Ling Song; Yan Zhang; Jian-Min Zhang; Dao-Bang Lu (pp. 6313-6317).

Under the generalized gradient approximation (GGA), the structural and electronic properties are studied for H-terminated silicene nanoribbons (SiNRs) with either zigzag edge (ZSiNRs) or armchair edge (ASiNRs) by using the first-principles projector-augmented wave potential within the density function theory (DFT) framework. The results show that the length of the Si–H bond is always 1.50Å, but the edge Si–Si bonds are shorter than the inner ones with identical orientation, implying a contraction relaxation of edge Si atoms. An edge state appears at the Fermi level E_F in broader ZSiNRs, but does not appear in all ASiNRs due to their dimer Si–Si bond at edge. With increasing width of ASiNRs, the direct band gaps exhibit not only an oscillation behavior, but also a periodic feature of Δ3_n>Δ3 n₊₁>Δ3 n₊₂ for a certain integer n. The charge density contours analysis shows that the Si–H bond is an ionic bond due to a relative larger electronegativity of H atom. However, all kinds of the Si–Si bonds display a typical covalent bonding feature, although their strength depends on not only the bond orientation but also the bond position. That is, the larger deviation of the Si–Si bond orientation from the nanoribbon axis as well as the closer of the Si–Si bond to the nanoribbon edge, the stronger strength of the Si–Si bond. Besides the contraction of the nanoribbon is mainly in its width direction especially near edge, the addition contribution from the terminated H atoms may be the other reason.

Keywords: Silicene nanoribbons; Structure; Electronic property; Edge state; First-principles

Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning by R. Nirmala; Ki Taek Nam; Soo-Jin Park; Yu-Shik Shin; R. Navamathavan; Hak Yong Kim (pp. 6318-6323).

In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75–110nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9–28nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.

Keywords: Electrospinning; Polyamide-6; High aspect ratio; Nanofibers; Applied voltage; Polyelectrolyte

Quantitative evaluation of scratch visibility resistance of polymers by Han Jiang; Robert L. Browning; Mohammad M. Hossain; Hung-Jue Sue; Mikihiko Fujiwara (pp. 6324-6329).

Susceptibility of polymer surfaces to acute visibility upon scratching has presented a serious challenge to the polymer industry for quite some time. The ability to design polymers with good scratch visibility resistance requires extensive knowledge about scratch deformation mechanisms and their propensity for light scattering. After examining the physical nature of human vision and surface optical characteristics, a new methodology is developed to quantitatively determine the onset of scratch visibility of polymers via an inexpensive desktop scanner. Taking into account the sample background color, texture, gloss and feature size, the proposed methodology can consistently and reliably determine polymer scratch visibility resistance regardless of the sample surface characteristics. Good correlation is found between this method and actual human perception. Quantitative analysis of the scratched surface is carried out with scanning laser profiling confocal microscopy and strong correlations among scratch visibility, observation angle and various scratch damage features such as roughness and scratch grooves are established. The proposed approach will greatly assist the development of scratch-resistant polymeric materials where surface aesthetics is of primary concern.

Keywords: Polymer scratch resistance; Quantitative visibility determination; Surface roughness; Groove profile; Scanning angle

Assigning chemical configurations to the XPS features observed at pristine (100) Si surface resulting after etching in HF aqueous solution by G.F. Cerofolini; E. Romano; D. Narducci; P. Belanzoni; G. Giorgi (pp. 6330-6339).

While the analysis of the spectra resulting from energy- or angle-resolved X-ray photoelectron spectroscopy allows the in-depth atomic composition in the probed region to be determined even for complex samples, the determination of the bonding configuration is less trivial. In this paper it is shown that a description of the chemical shift in terms of partial charge and Madelung potential (as results from local modelling of the atom) can provide information even in complicate situations, like that characterizing the hydrogen-terminated (100) Si prepared byHFaq etching of the native oxide.

Keywords: PACS; 68.35.Md; 68.45.Da; 82.30.Hk; 82.65.My(1; 0; 0) Si surface; HF-etching of silicon; Inverse problem in XPS; XPS and infrared analysis of silicon surfaces

A new methodology for the near-surface strain measurement on Pd–Ag–Sn alloy by Adele Carradó (pp. 6340-6344).

With the development of modern synchrotron sources, high-energy X-ray diffraction plays an important role in the residual stresses analysis of materials. This paper deals with the development of a new high-energy synchrotron X-ray diffraction (HESXRD) stress evaluation method for improving the near-surface strain measurement. For this purpose a new Monte Carlo simulation program has been developed to modelize any synchrotron radiation instrument. Futhermore conventional X-ray diffraction measurements have also been carried out after chemical etching, to define the surface and in-depth stresses of the sample, thus giving a reference to test the synchrotron radiation measurements. It has been shown that the reliability of this method is better than 5μm. This method has been applied to a machined palladium alloy (Pd–Ag–Sn) plate substrate.

Keywords: Synchrotron; High-energy X-ray diffraction; Near-surface strain measurement; Monte Carlo; Simulation program; Palladium alloy

Ab initio calculations of generalized-stacking-fault energy surfaces and surface energies for FCC metals by Xiao-Zhi Wu; Rui Wang; Shao-Feng Wang; Qun-Yi Wei (pp. 6345-6349).

The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (111) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along〈112〉 (111) direction and〈110〉 (111) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have lowγus/γI value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have largeγus/γI value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.

Keywords: PACS; 61.72.Lk; 71.15.MbFCC metals; Generalized-stacking-fault energy (GSFE) surfaces; Surface energies; Ab initio calculations

Thermal stability of ZnO thin film prepared by RF-magnetron sputtering evaluated by thermal desorption spectroscopy by Tokiyoshi Matsuda; Mamoru Furuta; Takahiro Hiramatsu; Hiroshi Furuta; Chaoyang Li; Takashi Hirao (pp. 6350-6353).

Thermal stability of sputter deposited ZnO thin films was evaluated by thermal desorption spectroscopy (TDS). Desorption of Zn was mainly observed from the films deposited at low O₂/Ar gas ratio and low RF power. In contrast, O₂ desorption was mainly observed from the films deposited at high O₂/Ar gas ratio and high RF power. The amount of desorbed O₂ from the film increased with increasing the O₂/Ar gas flow ratio and the RF power. Furthermore, the desorption temperature of O₂ increased with increasing the RF power during the deposition. Thermal stability of the ZnO films was controlled not only by the O₂/Ar gas flow ratio, but also applied RF power to the target.

Keywords: Thermal desorption spectroscopy (TDS); X-ray diffraction (XRD); RF-magnetron sputtering; Thin film transistor; Post-annealing; Process

Microstructure and corrosion properties of thick WC composite coating formed by plasma cladding by Xie Guozhi; Song Xiaolong; Zhang Dongjie; Wu Yuping; Lin Pinghua (pp. 6354-6358).

The thick Ni-coated WC coatings, in a matrix of Nickel-based alloys, were prepared on AISI 1045 steel using plasma cladding equipment. A pre-placed layer of uniform mixture, with different weight fractions of Ni-coated WC powder and Nickel-based alloy powder, on the steel substrate was melted at the high temperature of the plasma jet. The coating composition, microstructure and microhardness were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and microhardness testing. The experimental results show that the metallurgical bond was formed between the coating and substrate. The XRD results show that the coatings contain γ-Ni, carbides (such as M₂₃C₆ and M₇C₃) and boride (such as Fe₂B, Fe₃B phases). SEM shows that all the coatings are crack-free with lower porosity (<1%). It is found that the microhardness and the electrochemical behavior of the coatings are depended on the content of Ni-coated WC powder. The corrosion mechanism for the coatings may be due to the microgalvance corrosion between the phases in the cladding coatings.

Keywords: Plasma cladding; Microhardness; Tungsten carbide; Electrochemical behavior

Effect of NaAlO₂ concentrations on microstructure and corrosion resistance of Al₂O₃/ZrO₂ coatings formed on zirconium by micro-arc oxidation by Yuanyuan Yan; Yong Han; Dichen Li; Juanjuan Huang; Qin Lian (pp. 6359-6366).

In this study, Al₂O₃/ZrO₂ composite coatings were prepared on Zr substrates by micro-arc oxidation (MAO) in the NaAlO₂-containing electrolytes, and the effect of NaAlO₂ concentration on the microstructure, bond strength, microhardness and corrosion resistance of coatings was systematically investigated. The study reveals that the adequate NaAlO₂ in the electrolyte (>0.2M) is essential to the formation of needle-like α-Al₂O₃ in the coatings, and the amount of α-Al₂O₃ rises with the increase of the NaAlO₂ concentration. m-ZrO₂ and t-ZrO₂ are present in all of the coatings, but their relative amount largely depends on the amount of Al₂O₃. It is also found that as the NaAlO₂ concentration increases from 0.2 to 0.3M, the coating becomes denser and thicker, and its bond strength, maximum microhardness and corrosion resistance increases as well. The coating formed at 0.3M NaAlO₂ demonstrates the highest bond strength of 52MPa, the maximum microhardness of 1600Hv_0.2N and the superior corrosion resistance. However, the overhigh concentration of NaAlO₂ (0.35M) is found harmful to the coating's microstructure and properties.

Keywords: PACS; 62.20.Qp; 68.55.−a; 81.15.Lm; 82.45.Cc; 82.45.BbAl; ₂; O; ₃; /ZrO; ₂; composite coatings; Zirconium; Micro-arc oxidation; Microstructure; Corrosion resistance

GaN grown on Si(111) with step-graded AlGaN intermediate layers by C.C. Huang; S.J. Chang; R.W. Chuang; J.C. Lin; Y.C. Cheng; W.J. Lin (pp. 6367-6370).

The authors report the growth of crack-free GaN on Si(111) substrate with step-graded AlGaN intermediate layers all grown at 1120°C. By preparing all these layers at high-temperature, we can simplify the growth proceduce and minimize the growth time. Using X-ray diffraction and transmission electron microscopy, it was found that the high-temperature step-graded AlGaN intermediate layers can effectively reduce the tensile stress on GaN epitaxial layers. Photoluminescence and Raman measurements also indicate that we can improve the crystal quality of GaN by inserting the step-graded AlGaN intermediate layers.

Keywords: GaN; Graded intermediate layers; Si(1; 1; 1); Photoluminescence; Raman

Formation and growth mechanisms of ion-induced iron–carbon nanocomposites at room temperature by Zhipeng Wang; Mohd Zamri Mohd Yusop; Takehiko Hihara; Akari Hayashi; Yasuhiko Hayashi; Masaki Tanemura (pp. 6371-6374).

The irradiation of graphite surfaces with a simultaneous Fe supply have resulted into the development of various types of carbon nanocomposites. Their morphologies – diameter, density, length and apex angle strongly depend on the ratios of Fe deposition rate ( D_Fe) to ion sputtering rate ( S_ion). By optimizing the ratio of D_Fe/ S_ion (2.40%), the denser and well-aligned Fe–carbon nanocomposite fibers (Fe–CNFs) could be obtained, whose average length and diameter were 0.95μm and 17nm, respectively. As confirmed by energy-dispersive X-ray analysis, the Fe–CNFs with amorphous-like or fine-polycrystalline phase were surely composed of carbon and Fe. Two types of growth models have been employed to explain the formation of metal–carbon nanocomposites.

Keywords: Iron–carbon nanocomposites; Ion irradiation; Growth mechanism

Tough ceramic coatings: Carbon nanotube reinforced silica sol–gel by A.J. López; A. Rico; J. Rodríguez; J. Rams (pp. 6375-6384).

Silica coatings reinforced with carbon nanotubes were produced via sol–gel route using two mixing techniques of the sol–gel precursors, mechanical and ultrasonic mixing, and dip-coating as deposition process on magnesium alloy substrates. Effective incorporation and distribution of 0.1wt.% of carbon nanotubes in the amorphous silica matrix of the coatings were achieved using both techniques. Fabrication procedure determines the morphological aspects of the coating. Only mechanical mixing process produced coatings dense and free of defects. Nanoindentation technique was used to examine the influence of the fabrication process in the mechanical features of the final coatings, i.e. indentation fracture toughness, Young's modulus and hardness. A maximum toughening effect of about 24% was achieved in silica coatings reinforced with carbon nanotubes produced by the mechanical mixing route. Scanning electron microscopy investigation revealed that the toughening of these reinforced coatings was mainly due to bridging effect of the reinforcement.

Keywords: Sol–gel coating; Carbon nanotube; Ceramic matrix composite; Nanoindentation; Toughness

Nitrogen plasma-based ion implantation of poly(tetrafluoroethylene): Effect of the main parameters on the surface properties by K. Kereszturi; A. Tóth; M. Mohai; I. Bertóti; J. Szépvölgyi (pp. 6385-6389).

The surface of poly(tetrafluoroethylene) (PTFE or Teflon) was treated by nitrogen plasma-based ion implantation. Accelerating voltages between 15 and 30kV, fluences between 1×10¹⁷ and 3×10¹⁷cm⁻² and fluence rates between 3×10¹³ and 7×10¹³cm⁻²s⁻¹ were applied. The effects of these main parameters were examined on the evolution of surface chemical composition, mean roughness, abrasive wear, wettability and surface electrical resistance. The aim was to obtain relationships, enabling to control the surface properties examined.The F/C atomic ratio determined by XPS strongly decreased, correlating inversely with voltage. The mean surface roughness characterized by topography measurements, increased, correlating directly with fluence and inversely with voltage. The wear volume obtained by multipass scratch tests did not show clear relationship with the main process parameters, however, it increased upon treatment with the increase of surface roughness and O/C atomic ratio. The water contact angle increased at low voltages and high fluences, due to preferential increase of roughness, and decreased at high voltages and low fluences, owing to intense defluorination and incorporation of N and O. The electrical resistance of the PBII-treated surfaces decreased by several orders of magnitude, showing a significant inverse correlation with fluence. It continued to decrease for samples exposed to air, primarily after treatments performed with low fluences, due to post-treatment type oxidation.

Keywords: Poly(tetrafluoroethylene); Plasma-based ion implantation; XPS; Roughness; Wear; Wettability; Electrical resistance

Enhanced adsorption and visible-light-induced photocatalytic activity of hydroxyapatite modified Ag–TiO₂ powders by Y. Liu; C.Y. Liu; J.H. Wei; R. Xiong; C.X. Pan; J. Shi (pp. 6390-6394).

In order to get a kind of materials with enhanced adsorption and photocatalytic performance, hydroxyapatite modified Ag–TiO₂ powders (Ag–TiO₂–HAP) were prepared by a facile wet chemical strategy. The powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis absorption spectroscopy, N₂ adsorption–desorption measurement (BET), photoluminescence spectroscopy (PL), etc. The photocatalytic activities were evaluated by photocatalytic oxidation decomposition of acetone in air under visible-light illumination. The results showed that the coupled system indicated a highest photocatalytic activity and photochemical stability under visible-light irradiation than all the other catalysts. The intensively improved visible-light-induced photocatalytic activity of the Ag–TiO₂–HAP hybrids could be attributed to its strong absorption in the visible-light region, low recombination rate of the electron–hole pair and large BET specific surface area.

Keywords: Hydroxyapatite modified Ag–TiO; ₂; catalyst; Photocatalytic activity; Acetone; Visible light

Influence of laser power on the orientation and microstructure of CeO₂ films deposited on Hastelloy C276 tapes by laser chemical vapor deposition by Pei Zhao; Akihiko Ito; Rong Tu; Takashi Goto (pp. 6395-6398).

CeO₂ films were prepared on LaMnO₃/MgO/Gd₂Zr₂O₇ multi-coated Hastelloy C276 tapes by laser chemical vapor deposition at different laser power ( P_L) from 46 to 101W. Epitaxial (100) CeO₂ films were prepared at P_L=46–93W (deposition temperature, T_dep=705–792K). Epitaxial CeO₂ films had rectangular-shaped grains at P_L=46–77W ( T_dep=705–754K), while square-shaped grains were obtained at P_L=85–93W ( T_dep=769–792K). CeO₂ films showed a columnar microstructure. Epitaxial (100) CeO₂ films with rectangular grains exhibited full width at half maximum of ω-scan on (200) reflection and ϕ-scan on (220) reflection of 3.4–3.2° and 6.0–7.2°, respectively. The deposition rate of the epitaxial (100) CeO₂ films had a maximum of 4.6μmh⁻¹ at P_L=77W ( T_dep=754K).

Keywords: Laser chemical vapor deposition; CeO; ₂; High deposition rate

Nanocomposite ZnO/Au formation by pulsed laser irradiation by Geetika Bajaj; R.K. Soni (pp. 6399-6402).

The ZnO/Au nanocomposite formation involves synthesis of Au and ZnO colloidal solutions by 532nm pulse laser ablation of metal targets in deionized water followed by laser irradiation of the mixed colloidal solution. The transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images show evolution of spherical particles into ZnO/Au nanonetworks with irradiation time. The formation mechanism of the nanonetwork can be explained on the basis of near resonance absorption of 532nm irradiation by gold nanoparticles which can cause selective melting and fusion of gold nanoparticles to form network. The ZnO/Au nanocomposites show blue shift in the ZnO exciton absorption and red shift in the Au plasmon resonance absorption due to interfacial charge transfer.

Keywords: Laser ablation in liquid; Nanocomposite; ZnO/Au; UV–vis absorption

Characterization of diamond-like carbon films by SEM, XRD and Raman spectroscopy by Hua Pang; Xingquan Wang; Guling Zhang; Huan Chen; Guohua Lv; Size Yang (pp. 6403-6407).

Diamond-like carbon films were deposited by electrolysis of a water–ethanol solution on Cu at low voltages (60–100V) at 2mm interelectrode separation. The films were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Raman spectroscopy. The films were found to be continuous and compact with uniform grain distribution. Raman spectroscopy analysis revealed two broad bands at ∼1350 and ∼1580cm⁻¹. The downshift of the G band of graphite is indicative of the presence of DLC. For XRD analysis, the three strong peaks located at 2 θ values of 43.2°, 74.06° and 89.9° can be identified with reflections form (111), (220) and (311) plane of diamond.

Keywords: Diamond-like carbon; Electrodeposition; SEM; XRD; Raman spectroscopy

Small size TiO₂ nanoparticles prepared by laser ablation in water by F. Barreca; N. Acacia; E. Barletta; D. Spadaro; G. Currò; F. Neri (pp. 6408-6412).

Titanium dioxide nanoparticles in distilled H₂O solvent were prepared by laser ablation. The experiments were performed irradiating a Ti target with a second harmonic (532nm) output of a Nd:YAG laser varying the operative fluence between 1 and 10Jcm⁻² and for an ablation time ranging from 10 to 30min. Electron microscopy measurements have evidenced the predominant presence of nanoparticles with diameter smaller than 10nm together with agglomerations of 100–200nm whose content increases with the laser fluence. At low laser fluence the particles’ size distribution shows that more than 85% of the nanoparticles have a size smaller than 5nm while at mid and high fluences the presence of 5–7nm nanoparticles is predominant. XPS analysis has revealed the presence of different titanium suboxide phases with the prevalence of Ti–O bonds from TiO₂ species. The optical bandgap values, determined by UV–vis absorption measurements, are compatible with the anatase phase.

Keywords: Titanium dioxide nanoparticles; Laser ablation in Liquid; Morphology; Chemical composition; Gas sensing devices

Wear properties of compact graphite cast iron with bionic units processed by deep laser cladding WC by Hong Zhou; Peng Zhang; Na Sun; Cheng-tao Wang; Peng-yu Lin; Lu-quan Ren (pp. 6413-6419).

By simulating the cuticles of some soil animals, the wear resistance of compact graphite cast iron (CGI) processed by laser remelting gets a conspicuous improvement. In order to get a further anti-wear enhancement of CGI, a new method of deep laser cladding was used to process bionic units. By preplacing grooves then filling with WC powders and laser cladding, the bionic units had a larger dimension in depth and higher microhardness. Fe powder with different proportions from 30% (wt.) to 60% (wt.) was added into WC before laser processing for a good incorporation with CGI substrate. The improved laser cladding units turned out to induce higher wear resistance in comparison with laser remelting ones. The depth of the layer reached up to 1mm. The results of dry sliding wear tests indicated that the specimen processed by laser cladding has a remarkable improvement than the ones processed by laser remelting. It should be noted that the wear mass loss was essentially dependent on the increase in WC proportion.

Keywords: Cast iron; Bionic; Laser cladding; Wear properties

Deposition and characterization of TiAlSiN nanocomposite coatings prepared by reactive pulsed direct current unbalanced magnetron sputtering by Harish C. Barshilia; Moumita Ghosh; Shashidhara; Raja Ramakrishna; K.S. Rajam (pp. 6420-6426).

This work reports the performance of high speed steel drill bits coated with TiAlSiN nanocomposite coating at different Si contents (5.5–8.1at.%) prepared using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. The surface morphology of the as-deposited coatings was characterized using field emission scanning electron microscopy. The crystallographic structure, chemical composition and bonding structure were evaluated using X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, respectively. The corrosion behavior, mechanical properties and thermal stability of TiAlSiN nanocomposite coatings were also studied using potentiodynamic polarization, nanoindentation and Raman spectroscopy, respectively. The TiAlSiN coating thickness was approximately 2.5–2.9μm. These coatings exhibited a maximum hardness of 38GPa at a silicon content of approximately 6.9at.% and were stable in air up to 850°C. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions by drilling a 12mm thick 304 stainless steel plate. Under dry conditions the uncoated drill bits failed after drilling 50 holes, whereas, TiAlSiN coated drill bits (Si=5.5at.%) drilled 714 holes before failure. Results indicated that for TiAlSiN coated drill bits the tool life increased by a factor of more than 14.

Keywords: TiAlSiN nanocomposite coatings; Structure and properties; Reactive magnetron sputtering; Performance evaluation

Growth research of Sn nanoparticles deposited on Si(001) substrate by solid phase epitaxy by Xilei Zhao; Ke-Fan Wang; Weifeng Zhang; Mingju Huang; Yanli Mao (pp. 6427-6432).

High density of Sn nanoparticles (NPs) had been obtained directly on Si(001) substrate by solid phase epitaxy. The dependence of the morphology and crystallinity of Sn NPs on Sn coverage, annealing temperature and annealing time was investigated by atomic force microscope (AFM) and X-ray diffraction (XRD). Uniform and densely packed (∼10¹⁰cm⁻²) Sn NPs were obtained at low Sn coverage, low annealing temperature and short annealing time, respectively. The XRD results showed that, the formed Sn NPs were in the form of crystalline β-Sn, with a distinct orientation of Sn(110)//Si(001). The nucleation activation energy of Sn adatoms on Si(001) surface was estimated to be 0.41±0.05eV.

Keywords: PACS; 61.46.Km; 81.15.Np; 07.79.−v; 07.85.−mSn nanoparticles; Solid phase epitaxy; Atomic force microscope; X-ray diffraction

Low-voltage pulse exciting electron emission from ferroelectric copolymer film cathode: Role of film thickness and emission stability by J.J. Li; C. Lu; X.X. Xia; C.Z. Gu (pp. 6433-6436).

Ferroelectric copolymer thin films P(VDF-TrFE) are used as a ferroelectric cathode for investigation of their electron emission properties. This ferroelectric copolymer films with different thicknesses are deposited by spin-coating method, and then the annealing process is carried out to improve the crystallinities of as-deposited copolymer films. The measurement results of ferroelectric electron emission showed that the copolymer P(VDF-TrFE) films had a desired ferroelectric electron emission ability excited at low-voltage pulse, and its peak emission current can reach to be ∼1.3μA when the pulse voltage is 280V. In addition, the effect of film thickness on electron emission property and emission stability of copolymer thin film P(VDF-TrFE) are discussed.

Keywords: Ferroelectric copolymer thin film; Electron emission; Emission stability

Improvement of high-frequency characteristics of FeCoHfO/AlO_x multilayered films by Yu-Ming Kuo; Cheng-Chang Lee; Jenq-Gong Duh (pp. 6437-6440).

High-permeability magnetic films can enhance the inductance of thin-film inductors in dc–dc converters. The FeCoHfO/AlO_x multilayered films were fabricated by dc reactive magnetron co-sputtering. Inserting the AlO_x layers can decrease the anisotropic field of the FeCoHfO magnetic films, which was beneficial to raise the permeability of the FeCoHfO/AlO_x multilayered films. With this optimum configuration of a nine-layer structure [FeCoHfO (133nm)/AlO_x (10nm)]₉, low anisotropic field ( H_K=65Oe) and high permeability (permeability over 170 at 30–50MHz) were obtained. The permeability increased nearly six times from 30 (M1) to 175 (M9). The permeability was evidently improved by the employment multilayered coating.

Keywords: Multilayered films; Anisotropic field; FeCoHfO; Permeability

Synthesis and photoelectric characterization of delafossite conducting oxides CuAlO₂ laminar crystal thin films via sol–gel method by Juan Ding; Yongming Sui; Wuyou Fu; Haibin Yang; Shikai Liu; Yi Zeng; Wenyan Zhao; Peng Sun; Jin Guo; Hui Chen; Minghui Li (pp. 6441-6446).

Thin films of delafossite of CuAlO₂ laminar crystals on metal substrates (Ni plates) were prepared by sol–gel processing and subsequent thermal treatment in vacuum. The influence of annealing treatment on surface morphologies and structure of the samples is discussed. Field-emission scanning electron microscope (FESEM) shows the laminar surface architecture of the as-prepared CuAlO₂ thin films. The electrical property of sample was investigated by current–voltage analysis, which indicates that a rectifying junction between CuAlO₂ film and metal substrate is formed and forward current exceeds reverse current by a factor of up to three. Otherwise, the photoelectrochemical characteristics recorded under 250mW/cm² illumination show that the as-prepared thin film electrode which was annealed at 1150°C for 4h in vacuum possesses the highest photocurrent density, which is 0.7mA/cm² at 0V vs Ag/AgCl.

Keywords: CuAlO; ₂; Delafossite; Sol–gel process; Thin film; Photoelectrochemical activity

Effects of corona discharge on the surface structure, morphology and properties of multi-walled carbon nanotubes by Lihua Xu; Zhengping Fang; Ping’an Song; Mao Peng (pp. 6447-6453).

Multi-walled carbon nanotubes (MWCNTs) were modified by corona discharge and then heat treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive X-ray analysis (EDX) and thermogravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146° to 122° when the time of the corona discharge treatment reached 3min at the processing power of 200W. The enhanced thermomechanical and mechanical properties of epoxy nanocomposites filled with the corona discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy.

Keywords: Multi-walled carbon nanotubes; Corona discharge; Heat treatment; Hydrophobicity; Epoxy

Annealing effects on structural, optical and electrical properties of e-beam evaporated CuIn_0.5Ga_0.5Te₂ thin films by Koray Yılmaz; Hakan Karaagac (pp. 6454-6458).

CuIn_0.5Ga_0.5Te₂ (CIGT) thin films have been prepared by e-beam evaporation from a single crystal powder synthesized by direct reaction of constituent elements in a stoichiometric proportion. Post-depositional annealing has been carried out at 300 and 350°C. The compositions of the films were determined by energy dispersive X-ray analysis (EDXA) and it was found that there was a remarkable fluctuation in atomic percentage of the constituent elements following to the post-depositional annealing. X-ray diffraction analysis (XRD) has shown that as-grown films were amorphous in nature and turned into polycrystalline structure following to the annealing at 300°C. The main peaks of CuIn_0.5Ga_0.5Te₂ and some minor peaks belonged to a binary phase Cu₂Te appeared after annealing at 300°C, whereas for the films annealed at 350°C single phase of the CuIn_0.5Ga_0.5Te₂ chalcopyrite structure was observed with the preferred orientation along the (112) plane. The effect of annealing on and near surface regions has been studied using X-ray photoelectron spectroscopy (XPS). The results indicated that there was a considerable variation in surface composition following to the annealing process. The transmission and reflection measurements have been carried out in the wavelength range of 200–1100nm. The absorption coefficients of the films were found to be in the order of 10⁴cm⁻¹ and optical band gaps were determined as 1.39, 1.43 and 1.47eV for as-grown and films annealed at 300 and 350°C, respectively. The temperature dependent conductivity and photoconductivity measurements have been performed in the temperature range of −73 to 157°C and the room temperature resistivities were found to be around 3.4×10⁷ and 9.6×10⁶ (Ωcm) for the as-grown and annealed films at 350°C, respectively.

Keywords: Chalcopyrite compound; X-ray diffraction; EDXA; e-Beam evaporation; XPS

Study of the adsorption, electronic structure and bonding of C₂H₄ on the FeNi(111) surface by S. Simonetti; G. Brizuela; A. Juan (pp. 6459-6465).

The adsorption of C₂H₄ on the FeNi(111) alloy surface has been studied by ASED-MO tight binding calculations. The C₂H₄ molecule presents its most stable geometry with the CC bond axis parallel to the surface along the [1, −1, 0] direction, bonded on top Fe atom and bonded along a Fe–Fe bridge site. As a consequence, the strength of the local Fe–Fe bond decreases between 37 and 62% of its original bulk value. This bond weakening is mainly due to the new C–Fe interactions however no Fe₃C carbide formation is evidenced on surface. The Fe–Ni and Ni–Ni superficial bonds are only slightly modified.

Keywords: Alloy; Iron; Nickel; Carburization; Modelling studies

Investigating wettability alteration due to asphaltene precipitation: Imprints in surface multifractal characteristics by J. Sayyad Amin; E. Nikooee; Sh. Ayatollahi; A. Alamdari (pp. 6466-6472).

In the present study, multifractality and its formalism were employed to investigate the surface characteristics of an asphaltene deposited heterogeneous solid surface. Wettability alteration of the solid surface was found to affect the multifractal characteristics of an asphaltene deposited heterogeneous surface. Multifractal spectra f( α) show that the more oil wet the surface, the wider the spectrum, and the higher the f_max. The notable distinction between the multifractal spectra associated with different surface wettabilities can be used as a new aspect of wettability alteration.

Keywords: Wettability alteration; Asphaltene precipitation; Multifractal spectra; AFM; Roughness; Wettability classification

Preparation and characteristics of acrylic acid/styrene composite plasma polymerized membranes by Zhongqing Jiang; Zhong-jie Jiang; Yicai Shi; Yuedong Meng (pp. 6473-6479).

Plasma polymerization has gained increasing interest for the deposition of functional plasma-polymerized membranes suitable for a wide range of applications on account of its advantageous features. In this work, acrylic acid/styrene composite plasma polymerized membranes were synthesized by plasma polymerization of a mixture of acrylic acid and styrene monomers in a low-frequency after-glow capacitively coupled plasma (CCP) discharge process. The structure and composition of the plasma polymerized membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that the partial pressure ratio between acrylic acid (AA) and styrene (St), applied discharge power and the energy of the extracted particles have considerable effects on the structure and the content of functional groups of the deposited membranes.

Keywords: Plasma polymerization; Styrene; Acrylic acid; Functionalization of polymers; FTIR

Formation of Si_m⁺ and Si_mC_n⁺ clusters by C₆₀⁺ sputtering of Si by Ian Lyon; Torsten Henkel; Detlef Rost (pp. 6480-6487).

The secondary ion mass spectrum of silicon sputtered by high energy C₆₀⁺ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Si_m⁺ (1≤ m≤15) and various Si_mC_n⁺ clusters (1≤ m≤11 for n=1; 1≤ m≤6 for n=2; 1≤ m≤4 for n=3). The yields of Si_m⁺ clusters up to Si₇⁺ are significant (between 0.1 and 0.6 of the Si⁺ yield) with even numbered clusters Si₄⁺ and Si₆⁺ having the highest probability of formation. The abundances of cluster ions between Si₈⁺ and Si₁₁⁺ are still significant (>1% relative to Si⁺) but drop by a factor of ∼100 between Si₁₁⁺ and Si₁₃⁺. The probability of formation of clusters Si₁₃⁺–Si₁₅⁺ is approximately constant at ∼5×10⁻⁴ relative to Si⁺ and rising a little for Si₁₅⁺, but clusters beyond Si₁₅ are not detected (Si m_≥16⁺/Si⁺<1×10⁻⁴). The probability of formation of Si_m⁺ and Si_mC_n⁺ clusters depends only very weakly on the C₆₀⁺ primary ion energy between 13.5keV and 37.5keV. The behaviour of Si_m⁺ and Si_mC_n⁺ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C₆₀⁺ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Si_m⁺ clusters produced during C₆₀⁺ sputtering of silica (SiO₂) and various silicate minerals. The abundances for clusters heavier than Si₂⁺ are very small compared to the case where Si is the target.The data reported here suggest that Si_m⁺ and Si_mC_n⁺ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3–4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling.

Keywords: TOFSIMS; C; ₆₀; Sputtering; Silicon; Silicon clusters

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Applied Surface Science (v.256, #21)

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Applied Surface Science (v.256, #21)