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Applied Surface Science (v.253, #10)

Influence of the deposition temperature on the structure and performance of tris(8-hydroxyquinoline) aluminum based flexible organic light-emitting devices by Guang Feng Wang; Xiao Ming Tao; Hong Min Huang (pp. 4463-4466).

Based on indium tin oxide (ITO)/ N, N′diphenyl- N- N′-di( m-tdyl) benzidine (TPD)/Alq₃/Al structure, flexible OLEDs on polyethylene terephthalate (PET) substrates were fabricated by physical vapor deposition (PVD) method. Tris(8-hydroxyquinoline)aluminum (Alq₃) films were deposited at 90, 120 and 150°C to examine the influence of the deposition temperature on the structure and performance of OLEDs. Electroluminescence (EL) spectra and current–voltage–luminance ( I– V– L) characteristics of the OLEDs were examined. It was found that the device fabricated at a high temperature had a higher external efficiency and longer lifetime. Atomic force microscope (AFM) was adopted to characterize the surface morphology of ITO/TPD/Alq₃. The higher uniform morphology of the Alq₃ formed at high temperature might contribute to the performance improvement of the OLEDs.

Keywords: Organic light-emitting device; AFM; PVD; Alq; ₃

Synthesis of crystalline SiC nanofiber through the pyrolysis of polycarbomethylsilane coated platelet carbon nanofiber by W.M. Qiao; S.Y. Lim; S.H. Yoon; I. Mochida; L.C. Ling; J.H. Yang (pp. 4467-4471).

SiC nanofiber with high crystallinity was synthesized through the pyrolysis of polycarbomethylsilane (PS) coated platelet carbon nanofiber (PCNF) over 700°C and burning PCNF under the oxidative atmosphere. The as-prepared β-SiC nanofiber exhibited a diameter less than 100nm and a medium surface area of 50m²/g. The crystallinity of silicon carbide (SiC) nanofiber increases with increasing heat-treatment temperature, showing the formation of high crystalline SiC nanofiber at 1400°C. PCNF can be used as a unique template to govern the shape, crystallinity and morphology of SiC.

Keywords: Carbon nanofibers; Pyrolysis; X-ray diffraction; Microstructure; SiC nanofiber

Relaxed SiGe-on-insulator with high Ge fraction obtained by oxidation of SiGe/Si-on-insulator with hydrogen ions implantation by Xinli Cheng; Hong Liu; Feng Zhang (pp. 4472-4476).

The SiGe-on-insulator (SGOI) materials were obtained by thermal oxidation of SiGe layers on SOI wafers. As a comparison, H ions were implanted into SiGe layer of some samples before oxidation. The high degree relaxed SGOI materials with high Ge fraction were fabricated by two kinds of samples, including the samples without and with H ions implantation, and relaxation degree of SiGe layers is above 93%. The different result is that implantation of H ions decreased the oxidation rate of SiGe layer and decreased the loss of Ge in SiGe layer during oxidation. The effect of implantation of H ions is discussed in the paper.

Keywords: PACS; 61.72.Tt; 68.55.Ln; 81.65.MqSGOI; Thermal oxidation; H ions

Efficiency and resistance of the artificial oxalate protection treatment on marble against chemical weathering by B. Doherty; M. Pamplona; R. Selvaggi; C. Miliani; M. Matteini; A. Sgamellotti; B. Brunetti (pp. 4477-4484).

The artificial oxalate protection method was analyzed in laboratory experiments in order to achieve an optimum treatment application and concentration giving rise to its most effective protective nature. Spectroscopic (Fourier transform infrared, Micro-Raman and UV–vis colorimetry), microscopic (scanning electron microscope) and contact-angle analyses were carried out to characterize Carrara marble samples before and after application of the treatment to validate its efficiency. The resistance effects against chemical weathering were subsequently observed in a lab-controlled weak acid rain experiment. An acid spray at pH 5.5, representative of normal rain was used to provoke degrade of natural marble, marble treated with the artificial oxalate protective at concentrations of 0.4 and 5% and marble treated with a commercial organic silicon product. Run-off solutions sampled at timely intervals were tested for any change in pH followed by ion chromatography measurements for the presence of calcium ions in solution. The chromatography results of the oxalate treatment applied at a 5% concentration are analogous to an organic commercial product indicating its validity as a method for the conservation of carbonate substrates conferring protection to stone materials against acid environments.

Keywords: Marble; Protection; Calcium oxalate; Durability; Artificial weathering

Ab initio investigation of hydrogenation of (BN)₁₂ by Jian-Feng Jia; Hong Wang; Xiao-Qin Pei; Hai-Shun Wu (pp. 4485-4489).

Ab initio molecular orbital theory was used to examine the hydrogenation of a B₁₂N₁₂ molecule. The 1,2 addition of the 4,6 bond is an energetically favorable adsorption site in one-hydrogen-molecule adsorption. We found that the averaged bind energy of hydrogen molecule is maximized in B₁₂N₁₂H₁₂. The largest energy gaps of B₁₂N₁₂H₁₂ and B₁₂N₁₂H₂₄ suggest they have special stability. Moreover, calculation of the Gibbs free energy of the B₁₂N₁₂+12H₂→B₁₂N₁₂H₂₄ reaction showed that this reaction becomes endothermic above 320K.

Keywords: PACS; 33.15.−e; 31.15.EwDensity functional theory; Averaged bind energy; Stability

Characterization of microarc oxidation coatings formed on AM60B magnesium alloy in silicate and phosphate electrolytes by Jun Liang; Litian Hu; Jingcheng Hao (pp. 4490-4496).

Microarc oxidation coatings on AM60B magnesium alloy were prepared in silicate and phosphate electrolytes. Structure, composition, mechanical property, tribological, and corrosion resistant characteristics of the coatings was studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness analyses, and by ball-on-disc friction and potentiodynamic corrosion testing. It is found that the coating produced from the silicate electrolyte is compact and uniform and is mainly composed of MgO and forsterite Mg₂SiO₄ phases, while the one formed in phosphate electrolyte is relatively porous and is mainly composed of MgO phase. The thick coating produced from a silicate electrolyte possesses a high hardness and provides a low wear rate (3.55×10⁻⁵mm³/Nm) but a high friction coefficient against Si₃N₄ ball. A relatively low hardness and friction coefficient while a high wear rate (8.65×10⁻⁵mm³/Nm) is recorded during the testing of the thick coating produced from a phosphate electrolyte. Both of these types of coatings provide effective protection for the corrosion resistance compared with the uncoated magnesium alloy. The coating prepared from the silicate electrolyte demonstrates better corrosion behavior due to the compacter microstructure.

Keywords: Magnesium alloy; Microarc oxidation; Oxide coating; Friction and wear; Corrosion resistance

The effect of Ehrlich–Schwoebel step-edge barrier on the formation of self-organized Si nanodots by ion-sputter erosion by Li Liu; Jing Zhou; Wen-bin Fan; You-yuan Zhao; Chang-xin Gu; Ming Lu (pp. 4497-4500).

The ion flux dependence of the self-organized Si nanodots induced by 1.5keV Ar⁺ ion sputter erosion has been studied. It shows that for the regime with ion flux >∼280μA/cm², the currently adopted Bradley–Harper (BH) model, which is incorporated in a dynamic continuum equation holds valid. However, for ion flux <∼280μA/cm², the measured dot size and surface roughness deviate drastically from the BH model. To interpret the data for this lower ion flux regime, the effect of the Ehrlich–Schwoebel (ES) step-edge barrier was introduced into the continuum equation. A consistency between the calculated and the experimental results was reached, furthermore, a reasonable trend was found, that is, the effective ES diffusion decreases steadily with the increasing ion flux, and at ∼280μA/cm², it became negligibly small.

Keywords: PACS; 68. 49. Sf; 68. 37. Ps; 68. 35. BsSilicon; Surface structure; Morphology; Roughening and topography; Ion bombardment; Atomic force microscopy

STM image visualization of Si(111) 7×7 surface (graphic simulation and implementation) by Karlo T. Raić; Rajko M. Šašić (pp. 4501-4506).

The possibilities of graphic STM image simulation of a clean Si(111) 7×7 surface at atomic level are indicated. The presented procedure takes into account various types of deformation on the surface near the Fermi level in order to classify them and explain their origin. It also gives a clear hint to insert relevant physical phenomena in a suggested analysis. This goal is achieved exploiting the results of DAS (dimmer adatom stacing fault) model by means of standard mathematical programmes. A clean Si(111) 7×7 surface is considered as the representative example, but similar evaluation is possible for another non-metal and metal surfaces.

Keywords: STM; Tunneling; Si(1; 1; 1) 7; ×; 7; Surface defects; Computer simulation

Fractal microstructures of light-emitting porous silicon films by Fufang Zhou; Yuan Ming Huang (pp. 4507-4511).

By means of scanning electron microscopy and computer simulation, we have investigated the microstructures of a 23-μm-thick porous silicon (PS) film and a 6-μm-thick PS film. The two films give off strong visible emissions when excited by the 254nm light. For the 23-μm-thick PS film, both of its cross-sectional and top-surface morphologies exhibit self-similarity whose small-scale and large-scale microstructures resemble one another. For the 6-μm-thick PS film, self-similar cracks are developed on its top surface. Our results have demonstrated that the microstructures of PS films exhibit the characteristics of fractals. With box counting method, the fractal dimensions of the PS films are calculated to be about 2.3–2.6. Based on the model of diffusion-limited aggregation, the fractal growth processes have been simulated for the PS films.

Keywords: PACS; 61.43.Gt; 61.43.Hv; 68.03.Hj; 61.46.+w; 68.65.–kPorous silicon; Fractals; Nanoscale systems; Simulation

Surface modification of silicate glasses by nanoimprint using nanostriped NiO thin film molds by Shusaku Akiba; Wakana Hara; Takahiro Watanabe; Akifumi Matsuda; Masayasu Kasahara; Mamoru Yoshimoto (pp. 4512-4514).

Nanoscale surface modification of silicate glasses was examined by applying nanoimprint technique using a nanostriped NiO thin film mold. The mold had the pattern composed of regularly arranged straight nanogrooves, which was formed by high-temperature annealing of the Li-doped NiO epitaxial thin film deposited on the atomically stepped sapphire (α-Al₂O₃ single crystal) substrate. The glass imprint was proceeded through the simple steps of heating (∼600°C), pressing (∼1kPa) and then cooling in air. The nanoimprinted glass surface transferred reversely from the mold exhibited the multi nanowire array having an interval of ∼80nm, wire width of ∼70nm, and wire height of ∼20nm.

Keywords: PACS; 61.43.Fs; 61.46.−w; 61.66.Fn; 81.65.CfOxide glass nanopattern; Nanogroove; Imprint; Oxide glass; Oxide thin film mold

Spectral diffuse reflectance measurements of gadolinia, silica thin film systems using synchrotron radiation by N.K. Sahoo; S. Thakur; R.B. Tokas; B.N. Raja Sekhar (pp. 4515-4523).

Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic.

Keywords: PACS; 42.79.Wc; 52.70.Kz; 78.66.-w; 78.40.-q; 43.30.Hw; 07.85.Qe; 41.60.ApOptical coating; Thin films; Diffuse reflectance; Light scattering; Synchrotron radiation; Phase coherent delay; Spectral interference; Optical multilayers

Improvement in the corrosion resistance of Al₁₈B₄O₃₃w/2024Al composite by laser surface treatment by J. Hu; G. Liu; Z.J. Li; L.C. Kong (pp. 4524-4530).

Aluminum metal-matrix composites (MMCs) show great potential for aircraft industries. Nevertheless, the composites can be affected by different forms of corrosion such as pitting and galvanic corrosion. A pulsed YAG laser installation was used to produce surface treatment on Al₁₈B₄O₃₃w/2024Al composite. Results indicate that laser power has significant influences on both of the microstructure and the corrosion resistance. The difference in morphological transformations was observed on the surfaces of the laser-treated specimens. An increase in E_pit was obtained after laser treatment for the composite. The improvement was considered primarily due to the reduction both of reinforcement Al₁₈B₄O₃₃ whisker and intermetallics CuAl₂ on the surfaces of the laser-treated composites, which were found to be sites for pits nucleation. Moreover, the specimen with 700W laser treatment exhibited a much greater resistance to corrosion than the other specimens with laser treatment. This was attributed to the formation of the homogeneous and defect free microstructure in the laser-modified layer.

Keywords: Al; ₁₈; B; ₄; O; ₃₃; w/2024Al composite (MMCs); Microstructure; Corrosion; X-ray diffraction (XRD); Scanning electron microscope

Morphological and micro-Raman investigations on Ar⁺-ion irradiated nanostructured GaAs surface by S.K. Mohanta; R.K. Soni; N. Gosvami; S. Tripathy; D. Kanjilal (pp. 4531-4536).

Low energy Ar⁺-ion irradiation at normal incidence is used to fabricate nanostructured GaAs surface. Atomic force microscopy (AFM) images reveal the formation of GaAs surface nanodots with an average size of about 25–35nm. The swelling of irradiated surface is observed at a higher energy due to the ion beam-induced porosity in the amorphized GaAs surface. Micro-Raman scattering shows a gradual increase in the downward shift and line shape broadening of optical phonon modes from the nanostructured GaAs prepared with increasing ion dose and beam energy. The rapid broadening of the transverse-optical phonon mode at a higher energy and dose represents the onset of plastic deformation of the irradiated surface. Furthermore, the influence of rapid thermal annealing (RTA) shows a reverse LO and TO phonon peakshift and the change in the lineshape due to reduction of the amorphous disorder.

Keywords: PACS; 81.65Rf; 68.55Jk; 78.30FsNanostructuring; Low energy ion irradiation; GaAs; Raman scattering; Rapid thermal annealing

Hydrocarbon molecules deposited onto monolayer steps on Si(100): A study of adsorption and conductance by A.M. Mazzone; R. Rizzoli (pp. 4537-4541).

In this study, the interactions of small hydrocarbon molecules with monolayer SA steps are considered. The purpose of the calculations is a systematic description of the adsorption capability of the silicon steps in dependence of the type of the incident molecule. The study deals with both the electronic configuration of the deposited system and with its transport properties and the flat, dimerized surface is used as reference. The calculations are based on a semi-empirical Hamiltonian which is applied to the evaluation of the total energy and of the conductance and this last quantity is obtained from the scattering theory. It has been found that, though the step is a weaker sink than the flat surface, adsorption is possible and the molecules are bonded to the step. The functional relationship between the binding energy and the type of the adsorbed molecule is reminiscent of the intrinsic binding energy of the molecule itself and is therefore similar for the flat surface and for the step. The transmission function depends on the type of molecule and of the substrate and on the allowed energy levels of the deposited system. Depending on the channel type, a direct, or reverse, proportionality exists between the conductance and the binding energy.

Keywords: Silicon steps; Organic molecules; Semi-empirical calculations

Luminescence properties of type-II quantum well light-emitting diodes formed with NPB and Alq₃ by Jin-Zhao Huang; Zheng Xu; Su-Ling Zhao; Fu-Jun Zhang; Yong Wang (pp. 4542-4545).

The organic quantum well devices which are similar to the type-II quantum well of inorganic semiconductor have been fabricated. In the electroluminescence, the blue shift of spectrum with increasing applied voltage is observed, which is interpreted by exciton confinement effect and polarization effect, and the generation of exciton, including carrier injection and energy transfer, is discussed. This energy transfer from barrier to well is studied by photoluminescence and is interpreted in terms of Förster energy transfer. The electromodulation of photoluminescence demonstrates the quenching mainly comes from the dissociation of exciton in NPB and that in Alq₃ is very stable.

Keywords: Organic quantum well; Energy transfer; Electroluminescence; Photoluminescence; Electromodulation

Electroless synthesis of large scale Co–Zn–P nanowire arrays and the magnetic behaviour by Xiaoyou Yuan; Chunsheng Du; Gang Sun; Ning Pan (pp. 4546-4549).

Co–Zn–P nanowire arrays have been synthesized by electroless deposition in an anodic alumina membrane (AAM). The images of Co–Zn–P nanowire arrays and single nanowires are obtained by both scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that Co–Zn–P nanowire arrays are amorphous in structure. The hysteresis loops characterized by a vibrating sample magnetometer (VSM) show that the easily magnetized direction of Co–Zn–P nanowire arrays is parallel to the nanowire arrays and that there exhibits clearly a magnetic anisotropy as a result of the shape anisotropy.

Keywords: PACS; 81.07.−b; 47.54.Jk; 81.16.BeElectroless deposition; Co–Zn–P alloy; Magnetic; Nanowire arrays

Ultraviolet irradiation induced changes in the surface of phenolphthalein poly(ether sulfone) film by Xianqiang Pei; Qihua Wang (pp. 4550-4553).

Changes in surface characteristics of phenolphthalein poly(ether sulfone) (PES-C) film induced by ultraviolet (UV) irradiation were investigated. The surface properties of the pristine and irradiated films were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). It was found that photooxidation degradation took place on the sample surface after irradiation and the oxygen content in the surface increased as evidenced by FTIR-ATR and XPS results. The water contact angle of the irradiated films decreased with increasing irradiation time, which was ascribed to the increased polarity of the surface induced by photooxidation. The etching of ultraviolet irradiation induced the roughening of PES-C surface after irradiation with its root-mean-square roughness (RMS) determined by AFM increased from 2.097nm before irradiation to 7.403nm in the area of 25μm×25μm.

Keywords: PACS; 94.05.DdPhenolphthalein poly(ether sulfone) (PES-C); Ultraviolet (UV) irradiation; Surface characteristic; Photooxidation

Adsorption and thermal decomposition of C₆₀ on Co/Si(111)-7×7 by M.A.K. Zilani; H. Xu; Y.Y. Sun; X.-S. Wang; A.T.S. Wee (pp. 4554-4559).

We present a study on the adsorption and thermal decomposition of C₆₀ on Co covered Si(111)-7×7 using scanning tunneling microscopy and X-ray photoelectron spectroscopy. Co-induced magic clusters grown on Si(111)-7×7 are identified as a possible adsorption site where 51±3% of C₆₀ molecules adsorb at room temperature. On Co/Si(111)-7×7, C₆₀ molecules start to decompose at 450°C, and are completely dissociated to form SiC by 720°C. This temperature is significantly lower than 910°C at which C₆₀ completely dissociates on clean Si(111)-7×7. This is a possible low temperature method for growing crystalline SiC films using C₆₀ as a precursor molecule.

Keywords: Scanning tunneling microscopy; X-ray photoelectron spectroscopy; Fullerenes; Cobalt; Silicon; Silicon carbide; Catalysis

Deposition and characterization of La₂Ti₂O₇ thin films via spray pyrolysis process by D.S. Todorovsky; R.V. Todorovska; M.M. Milanova; D.G. Kovacheva (pp. 4560-4565).

Thin films of La₂Ti₂O₇ have been deposited on fused silica and Si substrates by a spray pyrolysis method using ethylene glycol solution of La(III)-Ti(IV)-citrate complexes as starting material and O₂ as a carrier gas. The composition, crystal structure and morphology of the films are studied.

Keywords: PACS; 81.15.-z; 81.15.Rs; 81.20.Fw; 81.40Tv; 68.37Hu; 68.55-aCitrates; Deposition; Lanthanum titanates; Spray pyrolysis; Thin films

Study of photoconductivity and photoluminescence of organic/porous silicon complexes by Yue Zhao; Dongsheng Li; Wenbin Sang; Deren Yang; Minhua Jiang (pp. 4566-4569).

In this paper, time-varying photoconductivity (PC) and the photoluminescence (PL) of different complexes were studied. Due to thick polymer layer hindering light penetrating into porous silicon (PS) layer, intrinsic PS luminescence in polymer/PS system disappeared. The physical origin of PL may be related to the recombination mechanisms involving surface defect states such as silicon oxide, siloxene. Due to carrier transfer controlled by different energy barrier, different devices prepared from different doped Si wafer showed opposite current–voltage characteristic.

Keywords: Porous silicon; Complexes; Photoconductivity; Photoluminescence

Thermodynamic and quantum chemistry characterization of the adsorption of triazole derivatives during Muntz corrosion in acidic and neutral solutions by Nageh K. Allam (pp. 4570-4577).

Some triazole derivatives (4-amino-5-mercapto-3-methyl 1,2,4-triazole (AMMT), 4-amino-5-mercapto-3-ethyl 1,2,4-triazole (AMET) and 4-amino-5-mercapto-3-propyl 1,2,4-triazole (AMPT)) have been evaluated as new corrosion inhibitors for the corrosion of muntz alloy (60Cu–40Zn) in acidic and neutral solutions. The adsorption of these compounds has been tested thermodynamically which was found to be of a physisorption mode. Furthermore, some activation thermodynamic parameters such as Δ H^*, Δ S^* and Δ G^* of activation have been estimated. In addition, a trial to find a quantitative relationship between the inhibition efficiency and the electronic properties of the inhibitor molecules was carried out.

Keywords: Triazole; Muntz; Corrosion; Inhibition; Adsorption; Quantum

Monolayer passivation of silicon(001) surface by selenium by M. Tao; E. Maldonado; W.P. Kirk (pp. 4578-4580).

Monolayer passivation of the silicon(001) surface by selenium is investigated in an ultrahigh vacuum environment with a solid selenium source by reflection high-energy electron diffraction and residual gas analysis. It is found that precisely one monolayer of selenium is deposited on silicon(001) when the silicon substrate temperature is set slightly above the selenium source temperature and the passivation time ensures a little overdose of selenium above one monolayer. The temperature settings prevent selenium condensation on silicon(001), which makes selenium deposition on silicon(001) a thermodynamically self-limited process to exactly one monolayer.

Keywords: PACS; 81.65.Rv; 68.03.Fg; 68.47.FgSilicon(0; 0; 1) surface; Surface passivation; Selenium; Monolayer

Surface modification of SnO₂ nanoparticles containing Mg or Fe: Effects on sintering by Ricardo H.R. Castro; Gilberto J. Pereira; Douglas Gouvêa (pp. 4581-4585).

Controlling the surface chemistry of oxide systems has emerged an effective tool to obtain desirable nanostructures and macro properties. A relatively simple way to achieve this is by using dopants that are prone to segregate to the surfaces of the powders. In this work, we delineate the effect of Mg and Fe on SnO₂ nanopowders focusing on the surface modifications caused by surface segregation. The effects of increasing the temperature of calcinations are particularly addressed to evaluate the surface modifications at high temperatures. The powders were studied by infrared spectroscopy, zeta potential measurements, X-ray diffraction, and specific surface area measurements. Since sintering is a high-temperature process strongly dependent on surface characteristics, we drawn a relationship between the final densities after sintering and the surface chemistry of the doped powders. Doped SnO₂ pellets were sintered to over 95% of the theoretical density within a few seconds (fast firing) when significant surface modifications were observed.

Keywords: PACS; 81.20.Ev; 68.35.Dv; 61.72.−y; 68.35.FxSnO; ₂; Surface excess; Additives; Sintering

Surface diffusion of carbon atom and carbon dimer on Si(001) surface by J. Zhu; Z.Y. Pan; Y.X. Wang; Q. Wei; L.K. Zang; L. Zhou; T.J. Liu; X.M. Jiang (pp. 4586-4592).

Carbon (C) atom and carbon dimer (C2) are known to be the main projectiles in the deposition of diamond-like carbon (DLC) films. The adsorption and diffusion of the C adatom and addimer (C2) on the fully relaxed Si(001)-(2×1) surface was studied by a combination of the molecular dynamics (MD) and Monte Carlo (MC) simulation. The adsorption sites of the C and C2 on the surface and the potential barriers between these sites were first determined using the semi-empirical many-body Brenner and Tersoff potential. We then estimated their hopping rates and traced their pathways. It is found that the diffusion of both C and C2 is strongly anisotropic in nature. In addition, the C adatom can diffuse a long distance on the surface while the adsorbed C2 is more likely to be confined in a local region. Thus we can expect that smoother films will be formed on the Si(001) surface with single C atoms as projectile at moderate temperature, while with C2 the films will grow in two-dimensional islands. In addition, relatively higher kinetic energy of the projectile, say, a few tens of eV, is needed to grow DLC films of higher quality. This is consistent with experimental findings.

Keywords: PACS; 79.20.Rf; 68.35.Fx; 81.05.UwSurface diffusion; Monte Carlo simulation; Diamond-like carbon film

Microstructure and optical properties of nanocrystalline ZnO and ZnO:(Li or Al) thin films by A. Yavuz Oral; Z. Banu Bahşi; M. Hasan Aslan (pp. 4593-4598).

Zinc oxide thin films (ZnO, ZnO:Li, ZnO:Al) were deposited on glass substrates by a sol–gel technique. Zinc acetate, lithium acetate, and aluminum chloride were used as metal ion sources in the precursor solutions. XRD analysis revealed that Li doped and undoped ZnO films formed single phase zincite structure in contrast to Al:ZnO films which did not fully crystallize at the annealing temperature of 550°C. Crystallized films had a grain size under 50nm and showed c-axis grain orientation. All films had a very smooth surface with RMS surface roughness values between 0.23 and 0.35nm. Surface roughness and optical band tail values increased by Al doping. Compared to undoped ZnO films, Li doping slightly increased the optical band gap of the films.

Keywords: Doped zinc oxide; Sol–gel; Thin film; Transparent-conductive oxide

Studies on surface graft polymerization of acrylic acid onto PTFE film by remote argon plasma initiation by Chen Wang; Jie-Rong Chen (pp. 4599-4606).

The graft polymerization of acrylic acid (AAc) was carried out onto poly(tetrafluoroethylene) (PTFE) films that had been pretreated with remote argon plasma and subsequently exposed to oxygen to create peroxides. Peroxides are known to be the species responsible for initiating the graft polymerization when PTFE reacts with AAc. We chose different parameters of remote plasma treatment to get the optimum condition for introducing maximum peroxides (2.87×10⁻¹¹mol/cm²) on the surface. The influence of grafted reaction conditions on the grafting degree was investigated. The maximum grafting degree was 25.2μg/cm². The surface microstructures and compositions of the AAc grafted PTFE film were characterized with the water contact angle meter, Fourier-transform infrared spectroscopy (ATR–FTIR) and X-ray photoelectron spectroscopy (XPS). Contact angle measurements revealed that the water contact angle decreased from 108° to 41° and the surface free energy increased from 22.1×10⁻⁵ to 62.1×10⁻⁵Ncm⁻¹ by the grafting of the AAc chains. The hydrophilicity of the PTFE film surface was greatly enhanced. The time-dependent activity of the grafted surface was better than that of the plasma treated film.

Keywords: Poly(tetrafluoroethylene); Remote argon plasma; Acrylic acid; Graft polymerization

Thermodynamic and kinetic aspects on the selective surface oxidation of binary, ternary and quarternary model alloys by Srinivasan Swaminathan; Michael Spiegel (pp. 4607-4619).

Segregation and selective oxidation phenomena of minor alloying elements during annealing of steel sheets lead to the formation of bare spots after hot dip galvanizing. In order to understand the influence of common alloying elements on the surface chemistry after annealing, model alloys of binary (Fe–2Si, Fe–2Mn and Fe–0.8Cr), ternary (Fe–2Mn–2Si, Fe–2Mn–0.8Cr and Fe–2Si–0.8Cr) and quarternary (Fe–2Mn–2Si–0.8Cr) systems were investigated. The specimens were annealed for 60s at 820°C in N₂–5% H₂ gas atmospheres with different dew points −80 and −40°C, respectively. Surface chemistry of the annealed specimens was obtained by using X-ray photoelectron spectroscopy (XPS). The field emission scanning electron microscopy (FE-SEM) was used to view surface morphology. At low dew point −80°C, apart from the thermodynamical calculations such as solubility product of oxides and their critical solute concentrations, kinetics play a decisive role on the selective oxidation, i.e. oxygen competition. As expected, the amount of external selective oxidation of alloying elements are well pronounced at higher dew point −40°C. An attempt has been made to explain the dominant process of Si and Mn on Cr-oxidation and segregation. It is observed that annealing of quarternary system at higher dew point shifts the Cr-oxidation from external to internal.

Keywords: PACS; 64.75.+g (segregation); 81.65.Mq (oxidation); 79.60.−i (XPS); 68.37.Hk (SEM); 68.37.−d (microscopy of surfaces); 68.35.Fx (diffusion)Segregation; Selective oxidation; Model alloys; Short-term annealing

Nucleation control for ZnO nanorods grown by catalyst-driven molecular beam epitaxy by L.C. Tien; D.P. Norton; S.J. Pearton; Hung-Ta Wang; F. Ren (pp. 4620-4625).

We report a study of the annealing temperature and time on Ag catalyst size and density for subsequent growth of ZnO nanorods by catalyst-driven molecular beam epitaxy (MBE). Two different substrates (SiO₂ and SiN_X) for the Ag deposition were used and the thickness of the Ag held constant at 25Å. Annealing between 600 and 800°C produced Ag cluster sizes in the range 8–30nm diameter on SiO₂ and 10–65nm on SiN_X with a cluster density from 100 to 2500mm⁻² for SiO₂ and 30 to 1900mm⁻² for SiN_X. ZnO nanorods grown on these clusters show single-crystal, wurtzite-phase nature and strong band-edge photoluminescence at 380nm. The nanorods can also be grown selectively on lithographically-patterned dielectric stripes with Ag clusters formed on top by e-beam evaporation and annealing.

Keywords: ZnO; Nanorods

Synthesis, structure, microstructure and mechanical characteristics of MOCVD deposited zirconia films by O. Bernard; A.M. Huntz; M. Andrieux; W. Seiler; V. Ji; S. Poissonnet (pp. 4626-4640).

Zirconia (ZrO₂) thin films were deposited by metal organic chemical vapor deposition (MOCVD) on (100) Si over temperature and pressure ranges from 700 to 900°C and 100 to 2000Pa, respectively. The oxide films were characterized by field emission microscopy and X-ray diffraction so that microstructure and ratios of monoclinic and tetragonal phases could be estimated according to the process conditions. The mechanical behaviour of the substrate-film systems was investigated using Vickers micro-indentation and Berkovitch nano-indentation tests. The characteristics of silicon are not modified by the presence of a thin film of silicon oxide (10nm), formed in the reactor during heating. Young's modulus and the hardness of tetragonal zirconia phase, 220 and 15GPa, respectively, are greater than values obtained for monoclinic phase, 160 and 7GPa, respectively. The zirconia films are well adherent and the toughness of tetragonal zirconia phase is greater than that of monoclinic phase.

Keywords: Thin films; Zirconia; Monoclinic phase; Tetragonal phase; Mechanical properties; Micro- and nano-indentation

Investigation of chemisorbed oxygen, surface segregation and effect of post-treatments on La_0.8Sr_0.2MnO₃ powder and screen-printed layers for solid oxide fuel cell cathodes by N. Caillol; M. Pijolat; E. Siebert (pp. 4641-4648).

In order to better understand the mechanism of the reaction of oxygen reduction at the surface of strontium doped lanthanum manganites (LSM) cathodes in solid electrolyte fuel cells (SOFC), the surface properties of La_0.8Sr_0.2MnO₃ powders and screen-printed layers have been characterised by various techniques.Strontium enrichment at the surface has been evidenced by X-ray photoelectron spectroscopy according to the conditions of annealing (temperature, oxygen pressure) and polarisation treatments of the samples.The interaction between oxygen and La_0.8Sr_0.2MnO₃ for SOFC cathodes has been studied by thermo-programmed desorption, in situ infrared spectrometry and calorimetry. The results indicate that various adsorbed oxygen species may exist on the surface of LSM depending on temperature.The presence of various adsorbed oxygen species and the surface Sr segregation are important factors to consider in the mechanism of oxygen reduction at LSM SOFC cathodes since they could be responsible for many discrepancies between the interpretations that can be found in the literature data.

Keywords: PACS; 82.47.−aLSM; SOFC; Adsorbed oxygen species; Screen-printing; Segregation

Surface characteristics of self-assembled microporous Ti-6Al-4V compacts fabricated by electro-discharge-sintering in air by W.H. Lee; C.Y. Hyun (pp. 4649-4651).

A single electro-discharge-sintering (EDS) pulse (1.0kJ/0.7g), from a 300(F capacitor, was applied to atomized spherical Ti-6Al-4V powder in air to produce microporous compact. A solid core surrounded by a porous layer was self-assembled by a discharge in the middle of the compact. X-ray photoelectron spectroscopy was used to study the surface characteristics of the compact material. C, N, O and Ti were the main constituents, with smaller amounts of Al and V. The surface was lightly oxidized and was primarily in the form of TiO₂. A lightly etched EDS sample showed the surface form of metallic Ti, indicating that EDS breaks down the oxide film of the as-received Ti-6Al-4V powder during the discharge process. The EDS Ti-6Al-4V compact surface also contained small amounts of TiN in addition to TiO₂, resulting in the reaction between nitrogen in air and the Ti substrate in times as short as 125μs.

Keywords: Ti-6Al-4V; Implant; Porous; Sintering; XPS

Photoelectron spectroscopic investigation of transformation of trifluoroacetate precursors into superconducting YBa₂Cu₃O7−_δ films by J.H. Su; P.P. Joshi; V. Chintamaneni; S.M. Mukhopadhyay (pp. 4652-4658).

X-ray photoelectron spectroscopy (XPS) has been used to investigate the evolution of surface chemistry of YBa₂Cu₃O7−_δ (Y123) films prepared by the metalorganic deposition (MOD) process using trifluoroacetate (TFA) precursors. Detailed XPS core-level spectra obtained from the samples quenched from various points during the calcining and firing stages have been reported for the first time and are used to identify surface species. The XPS data show evidence of formation of intermediate phases such as Y–O–F, BaF₂, and CuO during the calcining process, which are the decomposition products of yttrium, barium, and copper trifluoroacetates, respectively. The TFA precursors are completely decomposed at the end of calcination. The change of binding energies for Y 3d_5/2, Ba 3d_5/2, and O 1s during the firing process indicates that Y123 starts to form at 800°C after 0.5h firing. Based on the experimental results, an alternative mechanism of the chemical evolution from precursor to final film in the TFA-MOD process is proposed.

Keywords: PACS; 79.60.Dp; 74.72.BkX-ray photoelectron spectroscopy; YBCO; Thin film; TFA-MOD

Effect of the surface-modifying macromolecules on the duration of the surface functionalization by Hao Qian; Ying Xue Zhang; Sheng Mei Huang; Zhi Yong Lin (pp. 4659-4667).

Functionalization of polystyrene films by the preferential surface enrichment of surface-modifying macromolecules (SMM) to achieve a hydrophilic surface with long effective duration is described. The comb-like amphiphilic copolymers (PKG-g-PS) based on styrene-maleic anhydride copolynier (SMA) backbone was synthesized by esterification of SMA with poly(ethylene glycol) (PEG). When PEG-g-PS was melt blended with polystyrene, the preferential surface enrichment of PEG-g-PS was much evident resulting in the large increase of the surface polarity. The effective duration of the surface functionalizatoin was also hugely extended as SMMs were added into the blends. Furthermore, more polyether chain segments on PEG-g-PS could selectively migrate to the surface by the inducement of polar solvent. Compared with the PEG-g-PS/PS and PEG/PEG-g-PS/PS blends, the surface polarity and the effective duration of surface modification both increased greatly when PEG-g-PS was used as the compatibilizer of PEG/PS blends. It was an effective solution to balance the conflict between the duration and efficiency of the surface-modifying additives.

Keywords: Surface migration; Maleic anhydride-styrene copolymer; The duration of the surface modification; Surface-modifying macromolecules

Effect of growth temperature on the morphology and bonded states of SnO₂ nanobaskets by S.G. Ansari; M.A. Dar; Young-Soon Kim; Gil-Sung Kim; Hyung-Kee Seo; Gilson Khang; Hyung-Shik Shin (pp. 4668-4672).

The nanobaskets of SnO₂ were grown on in-house fabricated anodized aluminum oxide pores of 80nm diameter using plasma enhanced chemical vapor deposition at an RF power of 60W. Hydrated stannic chloride was used as a precursor and O₂ (20sccm) as a reactant gas. The deposition was carried out from 350 to 500°C at a pressure of 0.2Torr for 15min each. Deposition at 450°C results in highly crystalline film with basket like (nanosized) structure. Further increase in the growth temperature (500°C) results in the deterioration of the basket like structure and collapse of the alumina pores. The grown film is of tetragonal rutile structure grown along the [110] direction. The change in the film composition and bonded states with growth temperature was evident by the changes in the photoelectron peak intensities of the various constituents. In case of the film grown at 450°C, Sn 3d_5/2 is found built up of Sn⁴⁺ and O–Sn⁴⁺ and the peaks corresponding to Sn²⁺ and O–Sn²⁺ were not detected.

Keywords: PACS; 82.45.Cc; 81.15.Gh; 61.46.Hk; 52.25.−bSnO; ₂; Nanobaskets; AAO pores; PECVD; Bonded states

Nonlinear optical properties of periodic gold nanoparticle arrays by Weitian Wang; Yanmin Wang; Zhenhong Dai; Yuming Sun; Yuanping Sun (pp. 4673-4676).

Periodic Au nanoparticle arrays were fabricated on silica substrates using nanosphere lithography. The identical single-layer masks were prepared by self-assembly of polystyrene nanospheres with radius R=350nm. The structural characterization of nanosphere masks and periodic particle arrays was investigated by atomic force microscopy. The nonlinear optical properties of the Au nanoparticle arrays were determined using a single beam z-scan method at a wavelength of 532nm with laser duration of 55ps. The results show that periodic Au nanoparticle arrays exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂=6.09×10⁻⁶cm²/kW and β=−1.87×10⁻⁶m/W, respectively.

Keywords: PACS; 42.70.−a; 61.46.+w; 81.07.−b; 78.67.−nNanoparticle arrays; Optical nonlinearity; Pulsed laser deposition; Z; -scan

Preparation of high quality Ag film from Ag nanoparticles by Ya Yan; Shi-Zhao Kang; Jin Mu (pp. 4677-4679).

A simple route to the high quality Ag film was developed at room temperature by using Ag nanoparticles stabilized by polyvinylpyrrolidone (PVP) as Ag source. The scanning electron microscopy (SEM) images indicate that the silver film prepared on the quartz substrate is smooth and dense. Meanwhile, the X-ray diffraction (XRD) of the film shows a face-centered cubic (fcc) phase of Ag.

Keywords: PACS; 81.15.−Z; 81.05.Bx; 81.07.BcAg; Nanoparticles; Film; PVP

Electronic properties of electrolyte/anodic alumina junction during porous anodizing by I. Vrublevsky; A. Jagminas; J. Schreckenbach; Werner A. Goedel (pp. 4680-4687).

The growth of porous oxide films on aluminum (99.99% purity), formed in 4% phosphoric acid was studied as a function of the anodizing voltage (23–53V) using a re-anodizing technique and transmission electron microscopy (TEM) study. The chemical dissolution behavior of freshly anodized and annealed at 200°C porous alumina films was studied. The obtained results indicate that porous alumina has n-type semiconductive behavior during anodizing in 4% phosphoric acid. During anodising, up to 39V in the barrier layer of porous films, one obtains an accumulation layer (the thickness does not exceed 1nm) where the excess electrons have been injected into the solid producing a downward bending of the conductive and valence band towards the interface. The charge on the surface of anodic oxide is negative and decreases with growing anodizing voltage. At the anodizing voltage of about 39V, the charge on the surface of anodic oxide equals to zero. Above 39V, anodic alumina/electrolyte junction injects protons from the electrolyte. These immobile positive charges in the surface layer of oxide together with an ionic layer of hydroxyl ions concentrated near the interface create a field, which produces an upward bending of the bands.

Keywords: Porous alumina; Electronic properties; Semiconductive behavior; Anodic alumina/electrolyte junction; Embedded space charges

Thickness determination of molecularly thin lubricant films by angle-dependent X-ray photoelectron spectroscopy by Chongjun Pang; Mingwu Bai (pp. 4688-4693).

An angle-dependent X-ray photoelectron spectroscopy (XPS) method used to measure the thickness of molecularly thin lubricants was developed. The method was built based on an island model of patched overlayer on a flat substrate by using the photoemission signal solely from the lubricant film. Typical molecularly thin Zdol films on the CHx overcoat of unused commercial magnetic disks were measured to verify the metrology. The lubricant thickness determined by the metrology was equal to the recent result by thermostatic high vacuum atomic force microscopy. The measured deduction in the thickness of the molecularly thin lubricant films, successively irradiated by the monochromatic source operated at 14kV/250W, was as low as 1Ǻ during the first irradiation hour. XPS spectra showed that no hydrocarbons, water or oxygen were adsorbed over the Zdol outer surfaces in the tested XPS conditions. The inelastic mean free path (IMFP) of C 1s in Zdol or in CHx was found to be independent of take off angle (TOA) when TOA<40°. The IMFP of C 1s in Zdol was ∼63.5Ǻ and the lubricant island thickness was ∼35Ǻ.

Keywords: PACS; 82.80.Pv; 06.60Mr; 68.55.Jk; 68.08.DeThickness determination; Metrology; Angle-dependent XPS; Lubricant; Perfluoropolyether

Activation of Mg-doped P-GaN by using two-step annealing by Jun-Dar Hwang; Gwo-Huei Yang (pp. 4694-4697).

One- and two-step rapid thermal annealing (RTA) for activating Mg-doped p-type GaN films had been performed to compare with conventional furnace annealing (CFA). The two-step annealing process consists of two annealing steps: the first step is performed at 750°C for 1min and the second step is performed at 600°C for 5min in pure O₂ or air ambient. It is found that the samples annealed in air ambient exhibit poor electrical properties as compared to those annealed in pure O₂. Compared to one-step RTA annealing and CFA annealing, the samples with two-step annealing exhibit higher hole concentration and lower resistivity. This means that the two-step annealing is a powerful method to enhance the electrical performance of Mg-doped p-type GaN films. Similar results were also evidenced by photoluminescence (PL) measurement. Possible mechanism was confirmed by secondary ion mass spectrometry analysis.

Keywords: Optoelectronic device; Rapid thermal annealing; Mg-doped p-type GaN film; Photoluminescence; Conventional furnace annealing

Application of Ru(bpy)₃²⁺ in control and formation of gold surface nanostructure through oxidation–reduction cycling by Bin Qi; Zhikun Zheng; Xiurong Yang (pp. 4698-4703).

It was studied that the nanostructure formed on a gold surface via a simple oxidation–reduction cycles (ORC) in 0.1M KCl containing Ru(bpy)₃²⁺ with different concentrations. Atomic force microscopy (AFM) and energy-dispersed spectroscopy (EDS) were used to characterize the nanostructure formed on the gold surface. Sweep-step voltammetry and corresponding electroluminescence (ECL) response, in situ electrochemical quartz crystal microbalance (EQCM) measurement were used to monitor the ORC procedure. It was found that the surface structure became more uniform in the presence of Ru(bpy)₃²⁺, and the surface roughness was decreasing with the increasing of Ru(bpy)₃²⁺ concentration, suggesting a simple and effective method to control the formation of nanostructure on the gold surface.

Keywords: PACS; 78.60.FGold; Ru(bpy); ₃; ²⁺; Nanostructure; Oxidation–reduction cycles; Electroluminescence; QCM

Nanoscale structuring of SrRuO₃ thin film surfaces by scanning tunneling microscopy by C.C. You; N.V. Rystad; A. Borg; T. Tybell (pp. 4704-4708).

Surface modifications through line etching of SrRuO₃ thin films have been carried out using a scanning tunneling microscope under ambient conditions. The line etching is found to be dependent on both bias voltage and scan speed for a given number of scan repetitions. We observe that an applied voltage above a threshold value is required for successful line etching. The depth of the etched lines is increasing with increasing bias voltage and scan repetitions as well as with decreasing scan speed. Moreover, sub-50 nm laterally confined mesa structures could be reproducibly etched on the SrRuO₃ thin film surfaces.

Keywords: Nanostructuring; Scanning tunneling microscopy; Sputtering; SrRuO; ₃

Surface modification of polyethylene film by acrylamide graft and alcoholysis for improvement of antithrombogenicity by Guowei Zhao; Yashao Chen; Xiaoli Wang (pp. 4709-4714).

To improve antithrombogenicity of polyethylene (PE) films, the films pretreated by Ar plasma were radiated by ultraviolet light to initiate grafting polymerization with acrylamide (AAm) in absence of photo-initiator, then the AAm-grafted PE films (PE-g-AAm) were alcoholized with octadecyl alcohol. Effects of Ar plasma composite parameter ( W/ FM), pretreated time, AAm monomer concentration, and UV irradiation time on grafting rate were investigated systematically. AAm-grafted PE film and alcoholized PE film (PE-g-SAAm) were characterized by contact angle, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transfer infrared (ATR-FT-IR) spectroscopy and atomic force microscope (AFM), respectively. The results indicated that the moieties of AAm and stearyl were successively immobilized onto the PE surface. The platelet adhesion experiment showed that antithrombogenicity of the modified PE films was improved in comparison with PE films. The change in antithrombogenicity is attributed to the surface of the modified film in presence of tail-like structure which consists of polyacrylamide as spacer and stearyl as end groups.

Keywords: PACS; 81.05.Qk; 81.05.LgPE film; Plasma; UV-induced grafting; Acrylamide; Stearyl groups; Antithrombogenicity

STM studies of the reconstructed Au(111) thin-film at elevated temperatures by P. Kowalczyk; W. Kozlowski; Z. Klusek; W. Olejniczak; P.K. Datta (pp. 4715-4720).

High temperature scanning tunneling microscope (HT-STM) was used to investigate a reconstructed Au(111) film evaporated on mica. The experiment was carried out at elevated temperatures in the range of 300–500K. A herringbone reconstruction was observed at a wide range of temperatures. However, at the highest temperatures studied a break down of the reconstruction long range order was noticed. Finally, the presence of a triangular-like reconstruction was reported. Changes in the reconstruction were explained in terms of the change in surface stress arising as a result of the tension at the gold–mica interface.

Keywords: PACS; 62.40.+i; 68.37.Ef; 68.35.Bs; 68.35.GyHigh temperature scanning tunneling microscopy; Gold; Surface stress; Reconstruction

Surface morphology and the phase formation at Cr/Si system by Shivani Agarwal; Ankur Jain; Chhagan Lal; V. Ganesan; I.P. Jain (pp. 4721-4726).

Metal silicide technology has been attracting attention worldwide and it constitutes an active, frontier area of research. Research in this area has not only stimulated the exploration of new phenomena, but is also leading to a technological revolution. Electron beam evaporation in ultra high vacuum (UHV) environment is one of the best techniques to grow thin metal film on Si substrate. Metal silicide contact is an interesting and important part of integrated circuit. Due to selective growth and high thermal stability metal silicides are used in very large scale integrated (VLSI) and ultra large scale integrated (ULSI) applications. In this paper our interest is to show GIXRD, XRR and SPM measurement on C (2nm)/Cr (25nm)/Si (100) system in which thin films were deposited using electron beam evaporation technique at 2×10⁻⁸Torr vacuum. The capping layer of 2nm carbon is deposited to stop contamination. The C (2nm)/Cr (25nm)/Si (100) system were annealed in 10⁻⁵Torr vacuum at temperatures 300–600°C to study the formation of chromium silicide. Structural properties at the interface has been studied by grazing incidence X-ray diffraction (GIXRD), which shows formation of Cr₃Si and CrSi₂ as a result of interface mixing due to annealing. The morphology of the system was investigated by AFM in tapping mode. It was found that nano-rod type structures were formed with annealing at 600°C temperature.

Keywords: Solid state mixing; Metal silicide; Nanorods; GIXRD; XRR; AFM

Removal of lead(II) by adsorption onto Viscum album L.: Effect of temperature and equilibrium isotherm analyses by Saliha Erentürk; Emine Malkoç (pp. 4727-4733).

The removal efficiency of Viscum album L. from lead containing aqueous solutions was investigated. The effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature was investigated using a batch adsorption technique. The optimum pH for Pb(II) adsorption was found as 3.0 for Viscum album L. Results were analyzed by the Langmuir, Freundlich, Temkin and Harkins–Jura, equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. The Langmuir model agrees very well with experimental data than the other models. According to Langmuir isoterm, the monolayer saturation capacity ( Q_o) is 769.23mg/g at 25°C. Models and the isotherm constant were evaluated depending on temperature. Thermodynamic parameters such as Δ H^o, Δ S^o and Δ G^o were calculated. The adsorption process was found to be endothermic and spontaneous. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data.

Keywords: Adsorption; Lead; Viscum; album; L.; Adsorption isotherms; Thermodynamics

Crystallization of amorphous SiC and superhardness effect in TiN/SiC nanomultilayers by Ming Kong; Jiawei Dai; Jijun Lao; Geyang Li (pp. 4734-4739).

TiN/SiC nanomultilayers with various constituent layer thicknesses were prepared by magnetron sputtering using TiN and SiC ceramic targets. X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer, high-resolution transmission electron microscope, atomic force microscope and nanoindenter were employed to study the growth, microstructure and mechanical properties of these films. Experimental results revealed that amorphous SiC, which is more favorable under normal sputtering conditions, was forced to crystallize and grew epitaxially with TiN layers at thicknesses of less than 0.8nm. The resultant films were found to form strong columnar structures, accompanied with a remarkable hardness increment. Maximal nanoindentation hardness as high as 60.6GPa was achieved when SiC thickness was ∼0.6nm. A further increase of SiC thickness caused the formation of amorphous SiC, which blocked the epitaxial growth of the multilayers, resulting in the decline of film's hardness. Additionally, investigations on multilayers different in TiN layer thicknesses showed that they are insensitive in both microstructure and hardness to the fluctuation of TiN layer thickness. The formation of epitaxially grown structure between crystalline SiC and TiN layers was found to be responsible for the obtained superhardness in multilayers.

Keywords: PACS; 68.65.Ac; 81.16.−c; 68.35.Rh; 68.55.−a; 61.50.−f; 62.25.+gTiN/SiC nanomultilayers; Crystallization; Epitaxial growth; Superhardness effect

Femtosecond laser patterning of Ta_0.1W_0.9O_x/ITO thin film stack by Seongkuk Lee; Dongfang Yang; Suwas Nikumb (pp. 4740-4747).

Selective laser patterning of thin films in a multilayered structure is an emerging technology for process development and fabrication of optoelectronics and microelectronics devices. In this work, femtosecond laser patterning of electrochromic Ta_0.1W_0.9O_x film coated on ITO glass has been studied to understand the selective removal mechanism and to determine the optimal parameters for patterning process. A 775nm Ti:sapphire laser with a pulse duration of 150fs operating at 1kHz was used to irradiate the thin film stacks with variations in process parameters such as laser fluence, feedrate and numerical aperture of objective lens. The surface morphologies of the laser irradiated regions have been examined using a scanning electron microscopy and an optical surface profiler. Morphological analysis indicates that the mechanism responsible for the removal of Ta_0.1W_0.9O_x thin films from the ITO glass is a combination of blistering and explosive fracture induced by abrupt thermal expansion. Although the pattern quality is divided into partial removal, complete removal, and ITO film damage, the ITO film surface is slightly melted even at the complete removal condition. Optimal process window, which results in complete removal of Ta_0.1W_0.9O_x thin film without ablation damage in the ITO layer, have been established. From this study, it is found that focusing lens with longer focal length is preferable for damage-free pattern generation and shorter machining time.

Keywords: PACS; 42.62.Cf; 79.20Ds; 81.20.WkFemtosecond laser; Selective removal; Thin film; Electrochromic display

Detection of hydrogen with SnO₂-coated ZnO nanorods by L.C. Tien; D.P. Norton; B.P. Gila; S.J. Pearton; Hung-Ta Wang; B.S. Kang; F. Ren (pp. 4748-4752).

SnO₂-coated ZnO nanorods on c-plane sapphire substrates were synthesized by pulsed laser deposition. The thickness of the polycrystalline SnO₂ was ∼10nm, as determined by high-resolution transmission electron microscopy, while the diameter of the ZnO nanorods was ∼30nm. The sensitivity of the SnO₂/ZnO structures to hydrogen was tested by depositing Ti/Au Ohmic contacts on a random array of the nanorods and measuring the current at fixed voltage. There was no response to 500ppm H₂ in N₂ at room temperature, but we obtained a sensitivity of ∼70% at 400°C. The SnO₂/ZnO structures exhibit drift in their recovery characteristics and for sequential detection of hydrogen, as generally reported for SnO₂ thin film sensors.

Keywords: Hydrogen; Sensors; ZnO; Nanorods

Roughness and fibre reinforcement effect onto wettability of composite surfaces by Quentin Bénard; Magali Fois; Michel Grisel (pp. 4753-4758).

Wettability of glass/epoxy and carbon/epoxy composites materials has been determined via sessile drop technique. Good–Van Oss approach has been used to evaluate surface free energy parameters of smooth and rough surfaces. Results obtained point out the influence of fibre reinforcement on surface free energy of composite materials. In addition, the interest of surface treatment to increase surface roughness has been discussed in terms of wettability. To sum up, results obtained clearly demonstrate the necessity of considering properties of a given composite surface not only as a polymer but a fibre/polymer couple. The drawn conclusions are of great interest as it may have numerous consequences in applications such as adhesion.

Keywords: PACS; 81.05 Qk (reinforced polymer and polymer-based composites); 81.70 Jb (chemical composition analysis, chemical depth and dopant profiling); 82.35 Gk (polymers on surface, adhesion)Polymer matrix composites; Wettability; Surface treatment; Interface

The effect of melting-induced volumetric expansion on initiation of laser-induced forward transfer by David A. Willis; Vicentiu Grosu (pp. 4759-4763).

A numerical model was developed to investigate thermal processes that initiate laser-induced forward transfer (LIFT). The model included laser absorption, conduction, melting, and volumetric expansion in a thin film. The model was used to investigate the role of volumetric expansion associated with the melting process and was used to help explain surface deformations observed in previous studies of LIFT. The results of the model indicated that volumetric expansion initiated fluid motion that was directed away from the substrate, and the fluid motion was sufficient to induce surface deformations that remained after solidification. The resulting textured surface was similar to that observed experimentally below the droplet expulsion threshold. The fluid motion away from the substrate may explain the mechanism by which droplet formation occurs.

Keywords: PACS; 81.16.Mk; 42.62−b; 44.05.+e; 68.18.JkLaser-induced forward transfer; Microfabrication; Thin film; Phase change

Improved optical response and photocatalysis for N-doped titanium oxide (TiO₂) films prepared by oxidation of TiN by L. Wan; J.F. Li; J.Y. Feng; W. Sun; Z.Q. Mao (pp. 4764-4767).

In order to improve the photocatalytic activity, N-doped titanium oxide (TiO₂) films were obtained by thermal oxidation of TiN films, which were prepared on Ti substrates by ion beam assisted deposition (IBAD). The dominating rutile TiO₂ phase was found in films after thermal oxidation. According to the results of X-ray photoelectron spectroscopy (XPS), the residual N atoms occupied O-atom sites in TiO₂ lattice to form TiON bonds. UV–vis spectra revealed the N-doped TiO₂ film had a red shift of absorption edge. The maximum red shift was assigned to the sample annealed at 750°C, with an onset wavelength at 600nm. The onset wavelength corresponded to the photon energy of 2.05eV, which was nearly 1.0eV below the band gap of pure rutile TiO₂. The effect of nitrogen was responsible for the enhancement of photoactivity of N-doped TiO₂ films in the range of visible light.

Keywords: PACS; 61.72.Ww; 78.68.+m; 81.15.JjThermal oxidation; N-doped TiO; ₂; films; Band gap; Photocatalysis

Biomimetic nucleation and growth of hydrophobic vaterite nanoparticles with oleic acid in a methanol solution by Chengyu Wang; Xu Zhao; Jingzhe Zhao; Yanhua Liu; Ye Sheng; Zichen Wang (pp. 4768-4772).

Hydrophobic vaterite nanoparticles were prepared via crystallization of CaCO₃ with oleic acid in methanol by mimicking the process of biomineralization. The molar ratio of oleic acid to calcium ion was varied from 0.1 to 0.5. By changing the concentration of the oleic acid, CaCO₃ particles with different shapes and polymorphism were obtained. High concentration of the oleic acid gave stable vaterite crystals, the polymorph of which did not change when the composite was kept in water for more than one week. Fourier transform infrared spectroscopy (FT-IR) and TGA analysis of the obtained product indicated that the oleic acid was bound to the crystalline CaCO₃. The contact angle of the modified vaterite reached 122°. We have succeeded in crystallization of hydrophobic CaCO₃ nanoparticles in situ.

Keywords: Calcium carbonate; Oleic acid; Hydrophobic; Nanoparticle

Triangular pattern formation on silicon through self-organization of GaN nanoparticles by Kuniyil Prabhakaran; Birgit Schwenzer; Steven P. DenBaars; Umesh K. Mishra (pp. 4773-4776).

Nanoparticles of gallium nitride, synthesized by a low-temperature reaction between triethyl gallium and ammonia, were introduced onto silicon wafers containing a thin layer of chemically prepared silicon dioxide. At room temperature, the nanoparticles form unstructured agglomerates on the surface. However, upon annealing the samples beyond the decomposition temperature of the silicon dioxide layer, the gallium nitride particles self-organize to form triangular structures. The pattern formation is attributed to the domain separation associated with the (1×1)–(7×7) surface phase transformation followed by selective incorporation of the nanoparticles.

Keywords: Triangular pattern; Self-organization; Nanoparticles; Luminescent; Silicon; GaN

Microstructure and mechanical properties of neoprene–montmorillonite nanocomposites by Meng-Heng Yeh; Weng-Sing Hwang; Lin-Ri Cheng (pp. 4777-4781).

To investigate the microstructure and mechanical properties of neoprene–montmorillonite nanocomposite, three modified montmorillonite are used. An X-ray diffractometer is used to measure the corresponding change in d-spacing. Scanning electron microscopy is employed to investigate the morphology of the various composites. Transmission electron microscopy is employed to investigate the composite of montmorillonite and neoprene. The results indicate that the addition of montmorillonite enhances the mechanical properties of neoprene significantly.

Keywords: Nanocomposite; Montmorillonite; Neoprene; Neoprene; Mechanical properties

Surface properties of LiCoO₂, LiNiO₂ and LiNi1−_xCo_xO₂ by Anthony W. Moses; Harry G. Garcia Flores; Jong-Gyu Kim; Marjorie A. Langell (pp. 4782-4791).

The surface composition and chemical environment of LiCoO₂, hexagonal LiNiO_2, cubic LiNiO₂, and the mixed transition metal oxide LiNi_0.5Co_0.5O₂ have been determined by Auger electron and X-ray photoelectron spectroscopies. While the LiCoO₂ surface properties can easily be extrapolated from bulk composition, the nickel-containing materials are less straightforward. Their surface concentration tends to be depleted in lithium relative to that of the bulk and shows an atypical chemical environment for the constituent elements. The Ni 2p XPS photoemission suggests a near “ NiO-like” selvedge through the XPS binding energies and satellite structure which are essentially identical to that of NiO; the spectrum appears fairly insensitive to lithium concentration. Although there is little evidence for higher binding energy Ni³⁺ species or for an electron poor Ni^2.δ+-derived band structure in the XPS, the lattice oxygen is very electron-rich and yields among the lowest binding energies reported for a transition metal oxide. The nickel-containing lithium oxide selvedge is thus not simply “NiO” and the surface lithium cations have a measurable effect on the electronic structure even in their more highly depleted levels. This is explained in the context of the charge-transfer model of the oxide band structure.

Keywords: Lithium cobalt oxide; Lithium nickel oxide; XPSPACS; 68.35Dv; 68.476h; 79.60.Bm

The effects of thermal annealing in self-assembled Ge/Si quantum dots by QiJia Cai; Hao Zhou; Fang Lu (pp. 4792-4795).

The effects of thermal annealing in Si base self-assembled Ge dots have been investigated by Raman spectra and PL spectra. An obvious Raman frequency shift under different annealing temperature can be observed. There are two main effects during the annealing procession: one is the inter-diffusion of the Si and Ge quantum dots; the other is the relaxation of the elastic strain. With the calculated results, PL blue shift can be related to strain relaxation effects, and/or a general decrease of Ge content due to the Ge–Si intermixing.

Keywords: Quantum dots; Thermal annealing; Raman spectra; PL spectra; Strain relaxationPACS; 78.67.Hc; 81.40.Ef; 81.40.Jj

Thiolated polyethylene oxide as a non-fouling element for nano-patterned bio-devices by Patrícia Lisboa; Andrea Valsesia; Pascal Colpo; Douglas Gilliland; Giacomo Ceccone; Andri Papadopoulou-Bouraoui; Hubert Rauscher; Fabiano Reniero; Claude Guillou; François Rossi (pp. 4796-4804).

This work describes the synthesis of a thiolated polyethylene oxide that self-assembles on gold to create a non-fouling surface. Thiolated polyethylene oxide was synthesised by reacting 16-mercaptohexadecanoic acid with polyethylene glycol mono methyl ether. The coverage of the thiolated polyethylene oxide on gold was studied by cyclic voltammetry, and the modified surfaces were characterised by X-ray photoelectron spectroscopy and ellipsometry. Protein resistance was assessed using quartz crystal microbalance. Results showed a non-fouling character produced by the thiolated polyethylene oxide. The synthesised product was used as the passivation layer on nano-patterned surfaces consisting of arrayed nano-spots, fabricated by plasma based colloidal lithography. The specific adsorption of anti-bovine serum albumin in the mercaptohexadecanoic acid spots was verified by atomic force microscopy.

Keywords: PACS; 87.68. +z; 81.16.Dd; 81.16.NdPolyethylene oxide; Thiol; Nanotopography; Protein adsorption

Influence of modifiers on the performance of Ru-supported catalysts on the stereoselective hydrogenation of 4-acetamidophenol by B. Bachiller-Baeza; A. Guerrero-Ruiz; I. Rodríguez-Ramos (pp. 4805-4813).

Ruthenium-supported catalysts modified by the addition of Mg, Na or Ce were studied in the selective hydrogenation of paracetamol (4-acetamidophenol) to cis- and trans-4-acetamidocyclohexanol. In both series, catalysts supported on carbon or on alumina, the modified catalysts were more selective to the trans isomer than the corresponding monometallic catalysts. However, the modified catalysts, particularly the supported on carbon, were less active. Moreover, there is a reduction in the hydrogenolysis reaction of the OH group on carbon-supported catalysts. The enhancement observed in the stereoselectivity for the modified catalysts may be explained by an alteration in the acid–base properties of the catalyst surface, which eventually control the mode of adsorption of the molecule of paracetamol and probably the tautomeric equilibrium of the 4-acetamidocyclohexene-1-ol intermediate. The optimum amount of promoter to improve the stereoselectivity seems to depend on the inherent acid–base characteristics of both the modifier and the support. Therefore, the proper adjustment or fine tuning of these parameters is crucial for obtaining the best results in terms of stereoselectivity.

Keywords: Ru catalysts; Stereoselective hydrogenation; Paracetamol; Modifier oxides; CO; ₂; adsorption; NH; ₃; adsorption; Microcalorimetry

Comment on Lihua Liu et al. “Preparation of boron carbon nitride thin films by radio frequency magnetron sputtering” [Appl. Surf. Sci. 252 (2006) 4185–4189] by V. Linss (pp. 4814-4815).

Reply by Liu et al. by Lihua Liu; Yuxin Wang; Kecheng Feng; Yingai Li; Weiqing Li; Chunhong Zhao; Yongnian Zhao (pp. 4816-4817).

The experimental results indicate that the composition of our samples is homogeneous. We have explained the reason why the composition of the BCN film is influenced by the r.f. power. The Fourier transformed infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements suggest that the samples are atomic-level hybrids of B, C and N.

Keywords: Homogeneity; Hybrids; Peak

Corrigendum to “Corrosion resistance and lubricated sliding wear behaviour of novel Ni–P graded alloys as an alternative to hard Cr deposits” [Appl. Surf. Sci. 252 (2006) 7361–7372] by Liping Wang; Yan Gao; Tao Xu; Qunji Xue (pp. 4818-4818).

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Applied Surface Science (v.253, #10)