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Applied Surface Science (v.255, #9)

Growth and interconversion of ZnO nanostructure films on different substrates by Zhiguang Wang; Minqiang Wang; Zhonghai Lin; Yaohui Xue; Ge Huang; Xi Yao (pp. 4705-4710).

Hexagonal c-axis oriented ZnO nanorod (NR) arrays were grown on ZnO-coated glass substrates by chemical bath deposition (CBD). By varying the concentration of the precursor solutions, NRs’ mean diameter was controlled from about 100–400nm. With increasing the growing time, the morphology of as-synthesized ZnO NRs evolved: the top center of the ZnO NRs was eroded into volcano-like structures which developed into ZnO nanotubes (NT) and finally the ZnO NTs split to form ZnO nanosheets (NS). We have also introduced Al to the fabrication of some different ZnO nanostructures: on Al substrate, freestanding ZnO NSs formed a flower-like structure at the early growing period and these ZnO NSs reassembled into ZnO NTs as growing time increased; while on ZnO-coated glass substrate with an Al foil dipped in the growing precursor solution ZnO NR–NS composited arrays were synthesized.

Keywords: ZnO; Nanosheet; Nanotube; CBD; Growth mechanism

The structure and photoluminescence properties of Cr-doped SiC films by C.G. Jin; X.M. Wu; L.J. Zhuge (pp. 4711-4715).

Cr-doped SiC films are prepared by the RF-magnetron sputtering technique on Si substrates with a composite target of a single-crystalline SiC containing several Cr pieces on the surface. The as-deposited films are annealed in the temperature of 1000°C under nitrogen ambient. The structure of the samples has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and Raman scattering measurement. The results show that the SiC crystal is formed and that majority of Cr doped in the SiC resulted in the formation of the C clusters. Then the photoluminescence (PL) spectra of the samples are observed in the visible range at room temperature. The optical properties of the samples have also been discussed briefly. We attribute the origin of the 412-nm PL band to a kind of C cluster center.

Keywords: PACS; 78.66.−w; 78.68.+m; 78.55.−m; 78.40.−qCr-doped SiC films; Photoluminescence; Raman spectra; XRD

Study of the luminescence of H₂O and D₂O ices induced by charged-particle bombardment by Chinshuang Lee; Yuling Fong; Mingtsong Tsai; Wing Ip; Robert Wu; Shyong Lee (pp. 4716-4719).

We measured the optical emission of H₂O and D₂O ices in visible region (300–500nm) induced by energetic hydrogen ions (H⁺, H₂⁺, and H₃⁺) irradiation. Our analysis of the data of ion-stimulated luminescence (ISL) shows that all spectra of ISL emission are identical, independent of projectile. We show that all lines in the ISL emission spectrum may be assigned to decays from excited particles and/or fragments of H, H₂, OH, and H₂O. From the independence of emission spectrum on projectile we conclude that the final process causing the emissions may be attributed to the interaction between H⁺ (and/or H) and the water molecules.

Keywords: Ionbardment; Ion irradiation on ice; Ion-stimulated luminescence (ISL)

Synthesis of Ti–Si–N nanocomposite coatings by a novel cathodic arc assisted middle-frequency magnetron sputtering by Z.T. Yang; B. Yang; L.P. Guo; D.J. Fu (pp. 4720-4724).

Ti–Si–N nanocomposite coatings were synthesized by using a cathodic arc assisted middle-frequency magnetron sputtering system in an industrial scale. X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy were employed to investigate the chemical bonding and microstructure of the coatings. Atomic force microscope and scanning electron microscope were used to characterize the surface and cross-sectional morphologies of the samples. The coating was found to be nc-TiN/a-Si₃N₄ structure and exhibit a high hardness of 40GPa when the Si content was 6.3at.%.

Keywords: Ti–Si–N nanocomposite coatings; Cathodic arc; Middle-frequency magnetron sputtering; Hardness

Effect of TiO₂ nanoparticles on the surface morphology and performance of microporous PES membrane by Jing-Feng Li; Zhen-Liang Xu; Hu Yang; Li-Yun Yu; Min Liu (pp. 4725-4732).

PES–TiO₂ composite membranes were prepared via phase inversion by dispersing TiO₂ nanopaticles in PES casting solutions. The crystal structure, thermal stability, morphology, hydrophilicity, permeation performance, and mechanical properties of the composite membranes were characterized in detail. XRD, DSC and TGA results showed that the interaction existed between TiO₂ nanopaticles and PES and the thermal stability of the composite membrane had been improved by the addition of TiO₂ nanopaticles. As shown in the SEM images, the composite membrane had a top surface with high porosity at low loading amount of TiO₂, which was caused by the mass transfer acceleration in exposure time due to the addition of TiO₂ nanopaticles. At high loading amount of TiO₂, the skinlayer became much looser for a significant aggregation of TiO₂ nanopaticles, which could be observed in the composite membranes. EDX analysis also revealed that the nanoparticles distributed in membrane more uniformly at low loading amount. Dynamic contact angles indicated that the hydrophilicity of the composite membranes was enhanced by the addition of TiO₂ nanopaticles. The permeation properties of the composite membranes were significantly superior to the pure PES membrane and the mean pore size also increased with the addition amount of TiO₂ nanopaticles increased. When the TiO₂ content was 4%, the flux reached the maximum at 3711Lm⁻²h⁻¹, about 29.3% higher than that of the pure PES membrane. Mechanical test also revealed that the mechanical strength of composite membranes enhanced as the addition of TiO₂ nanopaticles.

Keywords: Poly(ethersulfones) (PES); Microporous membrane; Titanium dioxide; Phase inversion

Effects of deposition rates on laser damage threshold of TiO₂/SiO₂ high reflectors by Jianke Yao; Cheng Xu; Jianyong Ma; Ming Fang; Zhengxiu Fan; Yunxia Jin; Yuanan Zhao; Hongbo He; Jianda Shao (pp. 4733-4737).

TiO₂ single layers and TiO₂/SiO₂ high reflectors (HR) are prepared by electron beam evaporation at different TiO₂ deposition rates. It is found that the changes of properties of TiO₂ films with the increase of rate, such as the increase of refractive index and extinction coefficient and the decrease of physical thickness, lead to the spectrum shift and reflectivity bandwidth broadening of HR together with the increase of absorption and decrease of laser-induced damage threshold. The damages are found of different morphologies: a shallow pit to a seriously delaminated and deep crater, and the different amorphous-to-anatase-to-rutile phase transition processes detected by Raman study. The frequency shift of Raman vibration mode correlates with the strain in film. Energy dispersive X-ray analysis reveals that impurities and non-stoichiometric defects are two absorption initiations resulting to the laser-induced transformation.

Keywords: TiO; ₂; /SiO; ₂; high reflectors; Laser damage; Deposition rate; Electron beam evaporation; Raman spectra; Energy dispersive X-ray analysis

Evaluation of the barrier capability of Zr–Si films with different substrate temperature for Cu metallization by Ying Wang; Fei Cao; Ming-hui Ding; Lei Shao (pp. 4738-4741).

Barrier capability of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. An increase in substrate temperature results in a slightly decreased deposition rate together with an increase in mass density. An increase in substrate temperature also results in grain growth as deduced from field emission scanning electron microscopy (FE-SEM) micrographs. X-ray diffraction (XRD) spectra and Auger electron spectroscopy (AES) depth profiles for Cu/Zr–Si(RT)/Si and Cu/Zr–Si(300°C)/Si samples subjected to anneal at various temperatures show that the thermal stability was strongly correlated with the deposition temperature (consequently different density and chemical composition etc.) of the Zr–Si barrier layers. ZrSi(300°C) with higher mass density make the Cu/Zr–Si(300°C)/Si sample more stable. The appearance of Cu₃Si in the Cu/Zr–Si/Si sample is attributed to the failure mechanism which may be associated with the diffusion of Cu and Si via the grain boundaries of the Zr–Si barriers.

Keywords: Diffusion barrier; Cu interconnection; Sputtering; Substrate temperature; Zr–Si

Photoluminescence and secondary ion mass spectroscopy characterization of GaAs–AlGaAs quantum wells grown on GaAs (100) substrates with different surface treatments by A. Guillén-Cervantes; Z. Rivera-Álvarez; M. López-López; I. Koudriavtsev; V.M. Sánchez-Reséndiz (pp. 4742-4746).

GaAs (100) substrates prepared in a quartz chamber under a H₂/As₄ flux, and then exposed to air were used for the subsequent growth of GaAs–AlGaAs single quantum wells by molecular beam epitaxy. The substrates prepared by this method showed atomically flat surfaces corroborated by atomic force microscopy analysis. Quantum wells grown directly on these substrates without a GaAs buffer layer exhibited narrow and intense photoluminescence peaks, an indication of a high quality material. The secondary ion mass spectroscopy analysis showed oxygen and carbon traces on the first AlGaAs barrier layer grown after air exposure with no effects on the quantum wells optical emissions. From the results we conclude that the prepared GaAs surfaces are useful for the epitaxial growth of high quality quantum structures.

Keywords: GaAs substrates; AlGaAs–GaAs quantum wells; Molecular beam epitaxy

The influence of ligands on the preparation and optical properties of water-soluble CdTe quantum dots by Yao-hai Zhang; Hua-shan Zhang; Ming Ma; Xiao-feng Guo; Hong Wang (pp. 4747-4753).

In a systematic investigation has been found that ligands play an important role in both the water-phase preparation and optical properties of CdTe quantum dots. Experiments were performed using three typical thioalkyl acids as ligands, namely mercaptoacetic acid (MAA),l-cysteine (Cys) and reduced glutathione (GSH). The growth rate and size-distribution of CdTe quantum dots (QDs) are shown to depend on the type of ligands. A proper choice of ligand enables to make lager nanocrystals with narrower size-distribution. The effects of pH (buffer solution), illumination, heating and cations on the spectroscopic properties of CdTe QDs for the three ligands are reported. In addition, three same-size CdTe QDs were individually characterized by micellar electrokinetic capillary electrophoresis with laser-induced fluorescent detection, which proved their monodisperse size-distribution and different electric charge distribution on the surface for each of the three different type of QDs.

Keywords: PACS; 78.67.Hc; 81.07.TaCdTe quantum dots; Water-phase preparation; Thioalkyl acid; Ligand; Capillary electrophoresis

Effect of deposition voltage on the field emission properties of electrodeposited diamond-like carbon films by R.S. Li; B. Liu; M. Zhou; Z.X. Zhang; T. Wang; B.A. Lu; E.Q. Xie (pp. 4754-4757).

Diamond-like carbon (DLC) films were deposited on Al substrates by electrodeposition technique under various voltages. The surface morphology and compositions of synthesized films were characterized by scanning electron microscopy and Raman spectroscopy. With the increase of deposition voltage, the sp² phase concentration decreased and the surface morphology changed dramatically. The influence of deposition voltage on the field electron emission (FEE) properties of DLC films was not monotonic due to two adverse effects of deposition voltage on the surface morphology and compositions. The DLC film deposited under 1200V exhibited optimum FEE property, including a lowest threshold field of 13V/μm and a largest emission current density of 904.8μA/cm² at 23.5V/μm.

Keywords: Electrodeposition; Diamond-like carbon; Field electron emission

Cross-sectional analysis of the graded microstructure in an AISI D2-steel treated with low energy high-current pulsed electron beam by J.X. Zou; T. Grosdidier; K.M. Zhang; C. Dong (pp. 4758-4764).

A detailed analysis from cross-section of the rapidly solidified layer of a steel formed by low energy high-current pulsed electron beam (LEHCPEB) treatment has been successfully carried out. The results of electron backscattering diffraction (EBSD) measurements revealed that the microstructures and phase components vary dramatically through the melted layer and the heat-affected zone. The exact nature of such a graded structure also changes with the number of pulses. The phase transformation paths vary at different depth and different areas (close to or far away from the carbides). They are determined both by (i) the temperature gradients and (ii) the composition gradients in the surface layers induced by the LEHCPEB treatment.

Keywords: Low energy high-current pulsed electron beam (LEHCPEB); AISI D2-steel; Electron backscattered diffraction (EBSD); Phase transformation

Molecular functionalization of tantalum oxide surface towards development of apatite growth by D. Aubry; C. Volcke; Ch. Arnould; C. Humbert; P.A. Thiry; J. Delhalle; Z. Mekhalif (pp. 4765-4772).

We have studied the apatite growth dynamics on tantalum oxide surfaces. This nucleation is obtained via an organosilane intermediate layer between the apatite and the substrate surface. Four organosilane layers (differing by their terminal functionality) were investigated. Their characterization with atomic force microscopy and other techniques such as X-ray photoelectron spectroscopy (XPS) and wetting measurements highlighted the influence of the organosilane terminal groups on the apatite growth rates. Results revealed that apatite is indeed growing faster on phosphate terminal groups than on the three other groups studied (vinyl, hydroxyl and carboxyl).

Keywords: Biomaterials; Apatite; Tantalum; X-ray photoelectron spectroscopy; Atomic force microscopy; Self-assembled monolayers

Grand canonical Monte Carlo simulation of isotherm for hydrogen adsorption on nanoporous siliceous zeolites at room temperature by Mahmoud Rahmati; Hamid Modarress (pp. 4773-4778).

Zeolites belong to a most prominent class of nanoporous materials which have been considered as potential sorbents for hydrogen storage. The adsorption of hydrogen molecules on purely siliceous zeolites such as ACO, MEP, ASV, ANA, RWY, and RHO, which encompass a range of different pore structures and their chemical compositions has been simulated employing Grand Canonical Monte Carlo (GCMC) procedure for a temperature range of 250–325K, and a pressure range of 0–10kbar. The effects of pore structure of zeolites, temperature and pressure on the hydrogen adsorption has been examined. The results clearly show that the number of adsorbed hydrogen molecules at high pressure, only depends on pore diameter, and the temperature effect on the adsorption decreases with decrease in the number of adsorbed of hydrogen molecules.

Keywords: Hydrogen; Zeolite; Adsorption; Pore structure; Monte Carlo simulation

Charge kinetics in spinel and yttria-stabilized zirconia by Aicha Boughariou; Fekri Karray; Ali Kallel; Guy Blaise (pp. 4779-4781).

Spinel and zirconia were studied by measuring the total secondary electron emission (SEE) yield σ in a dedicated scanning electron microscope (SEM) especially equipped to study the fundamental aspects of the charge trapping in insulating materials during a 1.1keV electron irradiation at room temperature. The variation of the total SEE yield with the injected dose for both spinel and zirconia is different. In spinel the coefficient σ starts from its intrinsic value σ₀=4 and reaches a plateau at σ=1 at the end of irradiation, which corresponds to the self-regulated regime. The continuity of the curves, shot after shot, proves that the trapped charges are stable and does not spread out in the material as injection proceeds. In this case spinel is called “trapper insulator”. In contrast with the spinel, σ in zirconia, never reaches unity while the injected charge increases: it evolves from its intrinsic yield σ₀=2.3 to a steady value a few percent above 1. The curve shows the relaxation of the positive generated charge. In this case zirconia is called “conductive insulator”. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities.

Keywords: PACS; 72.20.Jv: charges carriers generation, recombination, lifetime and trapping; 72.80.SK: insulators; 79.20.Hx: electron impact: secondary emissionSpinel; Zirconia; The total secondary electron emission; Trapper insulator; Conductive insulator

The HSAB principle as a means to interpret the reactivity of carbon nanotubes by Marek Wiśniewski /; Piotr A. Gauden (pp. 4782-4786).

Polycyclic curved aromatic fragments (C₂₄H₁₂) have been employed as models of the single-walled carbon nanotubes ( n,0), where n varies from 4 up to 30. Those structures were chosen on the basis of the analysis of the strain energy values calculated for the models possessing various sizes. The flat coronene structure has been chosen as a molecular fragment topologically resembling the honeycomb lattice in order to investigate the relation between the curvature and reactivity of the sidewalls of SWNTs. In the current study we took into account the interaction of CO andNH₂ (treated as probe molecules) with the exterior surface of nanotubes. Obtained results illustrate that both total as well as local hardness and/or molecular electrostatic potential (MEP) can be a good measure for the reactivity if the influence of geometrical changes is considered. The systematic theoretical studies also show that the calculated interaction energies of sorbed CO on those models are related to the both types of hardness. On the other hand, in the case of amidogen sorbed on the nanotube surface the correlation between the binding energy and MEP is visible. Those differences can be explained by various kinds of the adsorption mechanism, i.e. physical or chemical adsorption, respectively.

Keywords: Sorption; SWNT; Reactivity; HSAB; Carbon monoxide; Amidogene radical

Synthesis of silica-pillared clay (SPC) with ordered mesoporous structure by one-step method without preswelling process by Huihui Mao; Baoshan Li; Xiao Li; Zhengxing Liu; Wei Ma (pp. 4787-4791).

The simultaneous intercalation of surfactants and TEOS into clay interlayers and subsequent intragallery ammonia-catalyzed hydrolysis of TEOS resulted in mesoporous silica-pillared clay (SPC). These SPC materials exhibited refractions corresponding to a basal spacing of 3.7–4.3nm, a uniform pore size of 2.5–3.16nm and large surface areas of 567–576m²/g. Our results indicate that surfactants play a decisive role in pore formation, because they act as micelle-like template during the hydrolysis of TOES. Moreover, the pore size of SPC derivatives is controllable by the molecular length of surfactant. All of the SPC materials reported here exhibit high catalytic activity and selectivity for coker gas oil (CGO) cracking reaction in comparison to parent MCM-41 and Al-MCM-41. The excellent acid catalytic activity, together with their sable, well-organized porous structure, opens up new opportunities for applications in catalysis.

Keywords: Silica-pillared clay (SPC); Mesoporous structure; Preswelling process; Simultaneous intercalation; Intragallery

MOCVD of zirconium oxide thin films: Synthesis and characterization by A.M. Torres-Huerta; M.A. Domínguez-Crespo; E. Ramírez-Meneses; J.R. Vargas-García (pp. 4792-4795).

The synthesis of thin films of zirconia often produces tetragonal or cubic phases, which are stable at high temperatures, but that can be transformed into the monoclinic form by cooling. In the present study, we report the deposition of thin zirconium dioxide films by metalorganic chemical vapor deposition using zirconium (IV)-acetylacetonate as precursor. Colorless, porous, homogeneous and well adherent ZrO₂ thin films in the cubic phase were obtained within the temperature range going from 873 to 973K. The deposits presented a preferential orientation towards the (111) and (220) planes as the substrate temperature was increased, and a crystal size ranging between 20 and 25nm. The kinetics is believed to result from film growth involving the deposition and aggregation of nanosized primary particles produced during the CVD process. A mismatch between the experimental results obtained here and the thermodynamic prediction was found, which can be associated with the intrinsic nature of the nanostructured materials, which present a high density of interfaces.

Keywords: ZrO; ₂; CVD; Thin films

Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation by S. Mathew; U.M. Bhatta; A.K.M. Maidul Islam; M. Mukherjee; N.R. Ray; B.N. Dev (pp. 4796-4800).

Diamond-like carbon (DLC) films were deposited on Si(100) substrates using plasma deposition technique. The deposited films were irradiated using 2MeV N⁺ ions at fluences of1×1014,1×1015 and5×1015ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/ I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of5×1015ions/cm² show the lattice image with an average interplanar spacing of 0.34nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.

Keywords: PACS; 81.05.Uw; 78.70; −; g; 82.80.Pv;; 78.30.; −; jDiamond; Interactions of particles and radiation with matter; X-ray photoelectron spectroscopy (XPS); Raman spectroscopy

Effect of annealing atmosphere on the photoluminescence of ZnO nanospheres by Yongzhe Zhang; Yanping Liu; Lihui Wu; Hui Li; Lizhong Han; Bochong Wang; Erqing Xie (pp. 4801-4805).

ZnO nanospheres were synthesized by a wet-chemical method. X-ray diffraction and field-emission scanning electron microscopy confirmed the formation of wurtzite-structured ZnO with regular sphere shape. Two Raman modes located at 333cm⁻¹ and 437cm⁻¹ with two additional Raman humps centered at 577cm⁻¹ and 1077cm⁻¹ were observed. Photoluminescence spectra showed ultraviolet, green, orange and red emissions, which changed significantly after the samples were annealed in air, oxygen, argon and forming gas four different ambiences. All the evidence indicates that surface states are responsible to orange and red emissions in addition to excitonic recombination (3.18eV) and oxygen vacancy (2.25eV) emission.

Keywords: PACS; 78.20.Ek; 78.30.Fs; 78.55.Et; 78.66.hf; 81.15.CodZinc oxide; Nanospheres; Photoluminescence; Annealing atmosphere; Surface states; Broad emission range

Functionalization of carbon nanofibers with elastomeric block copolymer using carbodiimide chemistry by Javed A. Mapkar; Ganesh Iyer; Maria R. Coleman (pp. 4806-4813).

Surface functionalization of carbon nanofibers (CNFs) with aminopropyl terminated polydimethylsiloxane [(PDMS-NH₂)] and other organic diamines was achieved using carbodiimide chemistry. The carbodiimide chemistry provides faster reaction rate so that the reaction occurs at lower temperature compared to amidation and acylation–amidation chemistry. CNF functionalized with PDMS-NH₂ fibers were further functionalized with oligomer of polyimide (6FDA-BisP) using imidization reaction. The formation of block copolymer on the surface of CNF is proposed as an effective method to engineer the interphase between the fiber and the polymer, which is essential to modulate and enhance the properties of the nanocomposite. The efficiency of the carbodiimide chemistry to functionalize amine terminated groups on CNF and the functionalization of block copolymer was characterized using thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and UV–vis spectroscopy.

Keywords: PACS; 81.05.Tp; 82.65.+r; 61.46.−w; 79.60.−iCarbon nanofiber; Surface functionalization; XPS; EDC

Investigation of impurity phase formation for (ZnO)1−_x(TMO)_x bulk samples formed by ball milling by S. Karamat; C. Ke; T.L. Tan; W. Zhou; P. Lee; R.S. Rawat (pp. 4814-4820).

Structural, compositional, optical and magnetic properties have been studied for polycrystalline (ZnO)_0.90(TMO)_0.10 bulk samples, where TM (transition metal ions)=Mn, Fe, and Co. The quantitative Rietveld analysis showed relatively higher percentage of impurity (spinel and oxide) phases of about 33.76, 52.38 and 55.61% for Mn, Fe and Co doped ZnO samples, respectively. The de-convolution of XPS spectra indicated the presence of different phases. The appearance of shaking satellites in XPS spectra confirmed the presence of different valence states of dopant ions. The red shift in energy band gap, estimated from reflectance UV–vis spectroscopy, was observed for all TM doped bulk samples. For Mn doping, paramagnetic behavior was obtained while for Co and Fe, weak ferromagnetic behavior was observed at room temperature.

Keywords: Dilute magnetic semiconductors; Ball milling; Rietveld refinement

Bio-inspired dual surface modification to improve tribological properties at small-scale by R. Arvind Singh; Duc-Cuong Pham; Jinseok Kim; Sungwook Yang; Eui-Sung Yoon (pp. 4821-4828).

In miniaturized devices like micro/nano-electro-mechanical systems (MEMS/NEMS), the critical forces, namely adhesion and friction restrict the smooth operation of the elements that are in relative motion. MEMS/NEMS are traditionally made of silicon, whose tribological properties are not good. In this paper, we present an investigation on the approach of dual surface modification of silicon surfaces and their tribological properties at micro-scale. The dual surface modification is a combination of topographical and chemical modifications. As the topographical modification, micro-patterns with varying shapes of pillars and channels were fabricated on Si(100) wafer surfaces using photolithography method. Chemical modification included the coating of micro-patterns with diamond-like carbon (DLC) and Z-DOL (perfluoropolyether, PFPE) thin films. The surfaces with combined modification were evaluated for their micro-friction behavior in comparison with those of bare Si(100) flat surfaces and the topographically/chemically modified silicon surfaces. Results showed that the surfaces with dual modification exhibited superior tribological properties. These results indicate that a combination of topographical and chemical modification is very effective in enhancing tribological properties at small-scale. The combined surface treatments such as the ones investigated in the current work could be useful for tribological applications in small-scale devices such as MEMS/NEMS. The motivation for undertaking the dual modification approach comes from an earlier observation made on the significant influence of the surface characteristics of lotus leaf on its micro-friction behavior.

Keywords: PACS; 81.40.Pq; 81.65.Cf; 85.40.Hp; 85.85.+jMicro; Friction; Wear; Tribology; Surface modification; Photolithography

Structure and optical analysis of Ta₂O₅ deposited on infrasil substrate by Osama A. Azim; M.M. Abdel-Aziz; I.S. Yahia (pp. 4829-4835).

Electron beam gun technique was used to prepare Ta₂O₅ thin films onto infrasil substrates of thicknesses 333 and 666nm. The structure characterization was investigated using X-ray diffraction patterns. Transmittance measurements in the wavelength range (240–2000nm) were used to calculate the refractive index n and the absorption index k depending on Swanepole's method. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal one in the transparent region. The analysis of the optical absorption data revealed that the optical band gap E_g was indirect transition. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters ( E_o and E_d) and the high frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration to the effective mass ratio were estimated according to the model of Spitzer and Fan. Graphical representation of the relaxation time as a function of photon energy was also presented.

Keywords: Ditantalum pentoxide (Ta; ₂; O; ₅; ); Optical dispersion parameters; Dielectric constant; The electric free carrier susceptibility

The preparation of lotus-like super-hydrophobic copper surfaces by electroplating by Wenjun Xi; Zhenmei Qiao; Chunlei Zhu; Ao Jia; Ming Li (pp. 4836-4839).

The preparation of super-hydrophobic metal surfaces had to combine rough structures and the surface modifications with low surface energy materials. Although there were different views on it, no experiment was done to prove it yet. In this paper, the structure of natural lotus leaf was observed and the lotus-like surfaces on hydrophilic copper substrates were fabricated via electroplating in large current density. These surfaces were super-hydrophobic without any chemical modification. The hydrophobic mechanism was analyzed. It is believed that this was a meta-stable state in Cassie model. As long as the surface structure was suitable, hydrophobic surface, even super-hydrophobic surface, could be got on hydrophilic substrate.

Keywords: Super-hydrophobic; Electroplating; Rough surface; Lotus leaves structure; Hydrophilic materials

Photoluminescence investigation of ferromagnetic Ga1−_xMn_xN layers with GaN templates grown on sapphire (0001) substrates by I.T. Yoon; M.H. Ham; J.M. Myoung (pp. 4840-4843).

We have investigated the temperature and composition dependent photoluminescence (PL) spectra in Ga1−_xMn_xN layers (where x≈0.1–0.8%) grown on sapphire (0001) substrates using the plasma-enhanced molecular beam epitaxy technique. The efficient PL is peaked in the red (1.86eV), yellow (2.34eV), and blue (3.29eV) spectral range. The band-gap energy of the Ga1−_xMn_xN layers decreased with increasing temperature and manganese composition. The band-gap energy of the Ga1−_xMn_xN layers was modeled by the Varshni equation and the parameters were determined to be α=2.3×10⁻⁴, 2.7×10⁻⁴, 3.4×10⁻⁴eV/K and β=210, 210, and 230K for the manganese composition x=0.1%, 0.2%, and 0.8%, respectively. As the Mn concentration in the Ga1−_xMn_xN layers increased, the temperature dependence of the band-gap energy was clearly reduced.

Keywords: PACS; 71.55.Ak; 75.50.Pp; 78.55.CrFerromagnetic semiconductor; Photoluminescence

Silver grain boundary diffusion in Pd by Z. Balogh; Z. Erdélyi; D.L. Beke; A. Portavoce; C. Girardeaux; J. Bernardini; A. Rolland (pp. 4844-4847).

Two to ten nanometer thick polycrystalline Pd films were prepared on the (111) surface of Ag single crystal and investigations of the Ag diffusion along Pd grain boundaries were carried out using the Hwang–Balluffi method. The samples were monitored by Auger electron spectroscopy (AES) during isothermal heat treatments in the 438–563K temperature range. Using plausible simplifying assumptions, the activation energy of the product of the grain boundary (GB) diffusion coefficient and k′ ( k′= c_s/ c_gb; c_s and c_gb are the surface and GB concentration, respectively) was calculated (0.99±0.08eV) from the evaluated saturation coefficients of the surface accumulation. This energy, for weak temperature dependence of k′, is approximately equal to the activation energy of the GB diffusion.

Keywords: PACS; 66.10C; 61.72Mn; 82.80PvC kinetics; Grain boundary diffusion; Auger electron spectroscopy; Hwang–Balluffi method

The effect of substrate material on pulsed laser deposition of HgCdTe films by M. Liu; B.Y. Man; X.C. Lin; X.Y. Li; J. Wei (pp. 4848-4851).

This paper describes some recent results of the HgCdTe thin film grown directly on different substrates (sapphire, GaAs and Si) by pulsed laser deposition (PLD). The influences of the substrate material on the properties of HgCdTe thin films were investigated by X-ray diffraction (XRD), selected area electron diffraction (SAED), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). It was found that the quality of the HgCdTe film has a strong relation to the structure and properties of the substrate. The experiment results indicate that the HgCdTe epitaxial thin films grown directly on the sapphire substrates have a high quality, and the composition of the films is close to that of the target. While the quality of the HgCdTe films deposited on the Si and GaAs substrates are not very good.

Keywords: PACS; 68.55.a; 73.40.Sx; 81.15.−zPLD; HgCdTe thin film; Different substrates

Investigation of thin TiO₂ films cosputtered with Si species by Jin-Cherng Hsu; Cheng-Chung Lee; Huang-Lu Chen; Chien-Cheng Kuo; Paul W. Wang (pp. 4852-4858).

Titanium dioxide (TiO₂) films were fabricated by cosputtering titanium (Ti) target and SiO₂ or Si slice with ion-beam-sputtering deposition (IBSD) technique and were postannealed at 450°C for 6h. The variations of oxygen bonding, which included high-binding-energy oxygen (HBO), bridging oxygen (BO), low-binding-energy oxygen (LBO), and three chemical states of titanium (Ti⁴⁺, Ti³⁺ and Ti²⁺) were analyzed by X-ray photoelectron spectroscopy (XPS). The enhancement of HBO and reduction of BO in O 1s spectra as functions of SiO₂ or Si amount in cosputtered film imply the formation of Si–O–Ti linkage. Corresponding increase of Ti³⁺ in Ti 2p spectra further confirmed the property modification of the cosputtered film resulting from the variation of the chemical bonding. An observed correlation between the chemical structure and optical properties, refractive index and extinction coefficient, of the SiO₂ or Si cosputtered films demonstrated that the change of chemical bonding in the film results in the modification of optical properties. Furthermore, it was found that the optical properties of the cosputtered films were strongly depended on the cosputtering targets. In case of the Si cosputtered films both the refractive indices and extinction coefficients were reduced after postannealing, however, the opposite trend was observed in SiO₂ cosputtered films.

Keywords: PACS; 68.37.ps; 68.55.−at; 78/20.−e.; and 79.60.−iTitanium dioxide; X-ray photoelectron spectroscopy; Cosputtering; Ion-beam-sputtering deposition; High-binding-energy oxygen; Bridging oxygen; Low-binding-energy oxygen

ZnO–ionic liquid nanostructures by José Sanes; Francisco-José Carrión; María-Dolores Bermúdez (pp. 4859-4862).

The mixture of nanostructures derived from the surface interactions and reactivity of ZnO nanoparticles with the room-temperature ionic liquid (IL1) 1-hexyl, 3-methylimidazolium hexafluorophosphate has been studied. Results are discussed on the basis of transmission electron microscopy (TEM) observations, energy dispersive spectroscopy (EDS) analysis, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) determinations. Size and morphology changes in ZnO nanoparticles by surface modification with IL1 are observed. ZnF₂ crystalline needles due to reaction with the hexafluorophosphate anion are also formed.

Keywords: Zinc oxide; Nanoparticles; Ionic liquid; Surface chemistry; Nanostructures

Preparation of Ru-loaded CdS/Al-HMS nanocomposites and production of hydrogen by photocatalytic degradation of formic acid by Yao Jun Zhang; Li Zhang (pp. 4863-4866).

The composite of aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS (CdS/Al-HMS) was prepared by template, ion exchange and sulfurization reactions. The result of low angle XRD patterns showed that the low content of 2.5wt% CdS is incorporated inside Al-HMS channels. The results of diffuse reflectance UV–visible spectra and fluorescence emission spectra exhibited that the absorption edge and photoluminescence peak for CdS/Al-HMS are blue-shifted about 75nm and 40nm in comparison to bulk CdS, respectively. The activities of hydrogen production by photocatalytic degradation of formic acid were evaluated under visible light irradiation ( λ≥420nm) and the CdS/Al-HMS loaded 0.07wt% Ru showed the highest H₂ evolution at a rate of 3.7mLh⁻¹ with an apparent quantum yield of 1.2% at 420nm.

Keywords: PACS; 81.07.Ta; 82.65.+rNanocomposite; Surface technology; Hydrogen production; Degradation formic acid

Effects of sputtering pressure on the field emission properties of N-doped SrTiO₃ thin films coated on Si tip arrays by H.J. Bian; X.F. Chen; J.S. Pan; W. Zhu; Chang Q. Sun (pp. 4867-4872).

The influence of sputtering pressure on the electron emission properties of Si tips coated with N-doped SrTiO₃ ultrathin films was investigated. X-ray diffraction studies revealed that the N-doped SrTiO₃ films deposited at different pressures remain the perovskite structure. However, the threshold electric field of electron emission decreased markedly when the sputtering pressure is increased, and reached a minimum value of 17.37V/μm while deposited at 1.6Pa. The decrease in the threshold field is attributed to the narrowed band gap and the lowered surface energy of SrTiO₃ thin films with nitrogen doped, as confirmed using spectroscopic ellipsometry and water contact angle measurement. Furthermore, it is revealed using XPS that such sputtering pressure dependence is accompanied with the change of nitrogen bonding state in the films, which changes from poorly screened γ-N₂ state to atomic β-N state when the sputtering pressure is increased. A mechanism of bonding and band-forming was proposed for the enhanced electron emission with nitrogen incorporation in the sputtered SrTiO₃ films.

Keywords: Field emission; N doping; SrTiO; ₃; thin film; Sputtering pressure

The use of contact angle measurements to estimate the adhesion propensity of calcium carbonate to solid substrates in water by Sameer Bargir; Steve Dunn; Bruce Jefferson; Jitka Macadam; Simon Parsons (pp. 4873-4879).

We have studied a series of solids using contact angle measurements; stainless steel, gold, aluminium, titanium nitride and PTFE that are frequently used in domestic water environments. It was found the influence of electron-donor ( γ⁻) and electron-acceptor ( γ⁺) free energies on material scaling rate was dominated by water wetting angles, providing materials exhibit an average roughness below 100nm. The γ⁻ component had the greatest influence on theoretical adhesion, while γ^LW, (Lifshitz-van der Waals) γ⁺ and γ^AB (acid-base) had little effect. From the materials analysed, amorphous carbon coatings were least adhesive, while ‘kettle coating’ and highly roughened steel the most adhesive. The size and distribution of asperities also influenced the polar free energies and subsequent adhesion due to fluctuations in the wetting angle. The results obtained indicate works of adhesion can be used as a complementary technique with Lewis acid–base theory to deliver useful information about the propensity of scale to deposit on solids.

Keywords: Contact angle; Surface free energy; Acid–base theory; Adhesion; Roughness; Scanning probe microscopy

Phase-oriented surface segregation in an aluminium casting alloy by Chuong L. Nguyen; Armand Atanacio; Wei Zhang; Kathryn E. Prince; Margaret M. Hyland; James B. Metson (pp. 4880-4885).

There have been many reports of the surface segregation of minor elements, especially Mg, into surface layers and oxide films on the surface of Al alloys. LM6 casting alloy (Al–12%Si) represents a challenging system to examine such segregation as the alloy features a particularly inhomogeneous phase structure. The very low but mobile Mg content (approximately 0.001wt.%), and the surface segregation of modifiers such as Na, mean the surface composition responds in a complex manner to thermal treatment conditions. X-ray photoelectron spectroscopy (XPS) has been used to determine the distribution of these elements within the oxide film. Further investigation by dynamic secondary ion mass spectrometry (DSIMS) confirmed a strong alignment of segregated Na and Mg into distinct phases of the structure.

Keywords: PACS; 68.35; DvSurface segregation; SIMS; XPS; Aluminium alloys

Controlling the orientation and coverage of silica-MFI zeolite films by surface modification by Lin Lang; Xiufeng Liu; Baoquan Zhang (pp. 4886-4890).

The silica-MFI (Si-MFI) zeolite films are fabricated on α-Al₂O₃ supported silica–zirconia layers. The roughness and chemistry of the substrate surface are changed by surface modification with hydrogen peroxide and carboxymethyl chitosan (CMCS) solution to investigate their effects on the formation and orientation control of Si-MFI zeolite films. The AFM images reveal that the roughness of the silica–zirconia surface can be increased under the treatment of hydrogen peroxide. The Si-MFI zeolite films grown on the rough substrate surface are also b-oriented. Diffuse-reflectance FT-IR studies demonstrate that the abundance of functional groups such as –OH and –COOH can be successfully seeded onto the α-Al₂O₃ supported silica–zirconia layer through modification with CMCS solution. Continuous b-oriented Si-MFI zeolite films can be fabricated on the CMCS-modified α-Al₂O₃ supported silica–zirconia layer. It is evident that the orientation and microstructure of Si-MFI zeolite films on α-Al₂O₃ supported silica–zirconia layers are dominantly controlled by the chemical nature of the substrate surface, where the functional groups serve as the structure-directing matrix to induce the orientation and growth of the zeolite crystals with their b-axes perpendicular to the substrate surface.

Keywords: PACS; 68.55.−a; 81.15.Aa; 81.10.−hMFI zeolite film; Orientation; Surface modification

The role of pH variation on the growth of zinc oxide nanostructures by Rizwan Wahab; S.G. Ansari; Young Soon Kim; Minwu Song; Hyung-Shik Shin (pp. 4891-4896).

In this paper we present a systematic study on the morphological variation of ZnO nanostructure by varying the pH of precursor solution via solution method. Zinc acetate dihydrate and sodium hydroxide were used as a precursor, which was refluxed at 90°C for an hour. The pH of the precursor solution (zinc acetate di hydrate) was increased from 6 to 12 by the controlled addition of sodium hydroxide (NaOH). Morphology of ZnO nanorods markedly varies from sheet-like (at pH 6) to rod-like structure of zinc oxide (pH 10–12). Diffraction patterns match well with standard ZnO at all pH values. Crystallinity and nanostructures were confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) pattern, which indicates structure grew along [0001] direction with an ideal lattice fringes distance 0.52nm. FTIR spectroscopic measurement showed a standard peak of zinc oxide at 464cm⁻¹. Amount of H⁺ and OH⁻ ions are found key to the structure control of studied material, as discussed in the growth mechanism.

Keywords: ZnO; Solution method; Nanostructures; pH variation; Hydroxyl ion

¹H and³¹P solid-state NMR of trimethylphosphine adsorbed on heteropolytungstate supported on silica by J. Deleplanque; R. Hubaut; P. Bodart; M. Fournier; A. Rives (pp. 4897-4901).

Trimethylphosphine (TMP) has been used as an NMR probe in order to determine the acidity of Keggin-type 12-tungstophosphoric heteropolyacid (HPW), pure and supported on silica, dehydrated at 473K. Adsorption of TMP on pure dehydrated HPW leads to the formation of trimethylphosphonium ions (TMPH⁺) characteristic of the presence of strong Brönsted acid sites. TMP replaces the water molecules lost by dryness and allows the Keggin secondary structure to recover.Silica interacts with TMP by two kinds of acid sites: with weak acid support sites through the isolated silanol groups and with strong Brönsted acid, which lead to the formation of TMPH⁺, through the hydrogen-bonded silanol groups. Silica only interacts with HPW through its isolated silanol groups.

Keywords: PACS; 82.56−Dj; 68.43.−h; 82.65.+rSolid-state NMR; Chemisorption; Brönsted acidity; Polyoxometalates; Silica

Modulation of field emission properties of vertically aligned ZnO nanorods with aspect ratio and number density by R.N. Gayen; S. Dalui; A. Rajaram; A.K. Pal (pp. 4902-4906).

Vertically aligned ZnO nanorod arrays with different aspect ratios were synthesized by hybrid wet chemical route. Modulation of the field emission properties (FE) with aspect ratio of ZnO nanorods was examined. With the increase in the aspect ratio, the emission current density increases from 0.02 to 8μA/cm² at 7.0V/μm. Turn-on voltage was seen to decrease from 9.6 to 7V/μm at a current density of 10μA/cm² with the increase in aspect ratio in the ZnO films. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure of the ZnO nanostructure obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) was discussed. Quality of the ZnO nanorods was also examined by using Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). It was found that the observed enhancements of FE characteristics could mainly be attributed to the increase in aspect ratio and associated number density of ZnO nanorods.

Keywords: PACS; 73.63.−b; 79.70.+qZnO nanorods; Field emission

Controllable synthesis and highly efficient electrocatalytic oxidation performance of SnO₂/CNT core-shell structures by Dengsong Zhang; Chengsi Pan; Liyi Shi; Hailing Mai; Xiaohong Gao (pp. 4907-4912).

In this work, the nanocomposites, carbon nanotubes (CNTs) coated with nanosized uninterrupted SnO₂, were prepared controllably by a facile solvothermal method. The obtained nanocomposites have a thin overlayer which is made of nanoparticles with a diameter of ∼3nm. The products were characterized by X-ray diffraction and transmission electron microscopy. The obtained SnO₂/CNTs have an excellent electrocatalytic oxidation performance for the X-3B, a kind of dye. The parameters affecting the electrocatalytic activity were investigated in details. The excellent catalytic property of the SnO₂/CNT electrodes can be explained as follows: (1) high specific surface area gives more active sites for X-3B oxidation; (2) the formation of thin, uniform, and uninterrupted coverage of SnO₂ nanoparticles on CNTs raises the potential of oxygen evolution and the current efficiency; and (3) the CNTs increase the conductivity of the electrodes, which results in the increase of the current efficiency.

Keywords: Carbon nanotubes; SnO; ₂; Composite; Coating; Electrocatalytic performance

Electrical and optical properties of ZnO films grown by molecular beam epitaxy by S.P. Wang; C.X. Shan; B. Yao; B.H. Li; J.Y. Zhang; D.X. Zhao; D.Z. Shen; X.W. Fan (pp. 4913-4915).

Zinc oxide (ZnO) films have been grown on sapphire by molecular beam epitaxy (MBE), and it is found that the grain size of the ZnO films increased with increasing the growth temperature. Photoluminescence (PL) study shows that the intensity ratio of near-band-edge emission to deep-level-related emission (NBE/DL) of the ZnO is significantly enhanced with increasing the growth temperature, and the dependence of the carrier mobility on the growth temperature shows very similar trend, which implies that there is a community factor that determines the optical and electrical properties of ZnO, and this factor is suggested to be the grain boundary. The results obtained in this paper reveal that by reducing the grain boundaries, ZnO films with high optical and electrical properties may be acquired.

Keywords: PACS; 61.72.Mm; 72.80.Ey; 73.61.Ga; 78.55.EtZinc oxide; Molecular beam epitaxy; Hall mobility; Grain boundary

Preparation and study on radar-absorbing materials of cupric oxide-nanowire-covered carbon fibers by Zeng Jun; Tao Peng; Wang Sen; Xu Jincheng (pp. 4916-4920).

This paper firstly reports that cupric oxide nanowires (CNWs) were synthesized by thermal oxidation of copper coated carbon fibers (Cu/CFs). The results of transmission electron microscope images indicate that the nanowires are about 50nm in diameter and several microns in length. The optimum growth conditions of the nanowires are found when the film of Cu/CFs is annealed at 400°C for 4h in air. The results show that the reflectivity of cupric oxide-nanowire-covered carbon fibers (1–1.3mm in thickness) is less than −4dB over the range of 8.6–18GHz. Furthermore, the possible growth mechanism of CNWs is discussed.

Keywords: Carbon fibers; Nanostructures; Oxides; Surface treatments; Radar-absorbing materials

Reactive plasma cladding of TiC/Fe cermet coating using asphalt as a carbonaceous precursor by Junbo Liu; Limei Wang; Huiqi Li (pp. 4921-4925).

A new process of preparing Ti–Fe–C composites powder for reactive plasma cladding, precursor carbonization–composition process, was developed. TiC/Fe cermet coatings were synthesized by reactive plasma cladding of the composite powder. XRD and SEM were employed to analyze the phase composition and microstructure of the composite powder and coating. The hardness and wear resistance of the coating was tested. Results show that: The compound powder prepared by precursor carbonization–composition process has very tight structure, which can avert the question of raw powder breaking-up in cladding process. The TiC/Fe cermet coating by reactive plasma cladding consists of alternate, laminated layers as following: the layers in which the round nanoscale TiC particles are dispersed within the α-Fe matrix and the layers of TiC accumulation. The TiC/Fe cermet coating by reactive plasma cladding shows superior hardness and wear resistance: The surface hardness of the TiC/Fe cermet coating is 68±6 (HR30N). In the same fretting conditions, the wear resistance of Ni60 coating is twelve times than that of the TiC/Fe cermet coating.

Keywords: Cermet coating; Reactive plasma cladding; TiC/Fe; Precursor

Electrodeposition of Al–Mn alloy on AZ31B magnesium alloy in molten salts by Jifu Zhang; Chuanwei Yan; Fuhui Wang (pp. 4926-4932).

The Al–Mn alloy coatings were electrodeposited on AZ31B Mg alloy in AlCl₃–NaCl–KCl–MnCl₂ molten salts at 170°C aiming to improve the corrosion resistance. However, in order to prevent AZ31B Mg alloy from corrosion during electrodeposition in molten salts and to ensure excellent adhesion of coatings to the substrate, AZ31B Mg alloy should be pre-plated with a thin zinc layer as intermediate layer. Then the microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). It was indicated that, by adjusting the MnCl₂ content in the molten salts from 0.5wt% to 2wt%, the Mn content in the alloy coating was increased and the phase constituents were changed from f.c.c Al–Mn solid solution to amorphous phase. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was confirmed that the Al–Mn alloy coatings exhibited good corrosion resistance with a chear passive region and significantly reduced corrosion current density at anodic potentiodynamic polarization. The corrosion resistance of the alloy coatings was also related with the microstructure and Mn content of the coatings.

Keywords: Magnesium alloy; Electrodeposition; Al–Mn alloy; Zn intermediate layer; Corrosion resistance

Thin films of silver nanoparticles deposited in vacuum by pulsed laser ablation using a YAG:Nd laser by J.C. Alonso; R. Diamant; P. Castillo; M.C. Acosta–García; N. Batina; E. Haro-Poniatowski (pp. 4933-4937).

We report the deposition of thin films of silver (Ag) nanoparticles by pulsed laser ablation in vacuum using the third line (355nm) of a YAG:Nd laser. The nanostructure and/or morphology of the films was investigated as a function of the number of ablation pulses, by means of transmission electron microscopy and atomic force microscopy. Our results show that films deposited with a small number of ablation pulses (500 or less), are not continuous, but formed of isolated nearly spherical Ag nanoparticles with diameters in the range from 1nm to 8nm. The effect of increasing the number of pulses by one order of magnitude (5000) is to increase the mean diameter of the globular nanoparticles and also the Ag areal density. Further increase of the number of pulses, up to 10,000, produces the formation of larger and anisotropic nanoparticles, and for 15,000 pulses, quasi-percolated Ag films are obtained. The presence of Ag nanoparticles in the films was also evidenced from the appearance of a strong optical absorption band associated with surface plasmon resonance. This band was widened and its peak shifted from 425nm to 700nm as the number of laser pulses was increased from 500 to 15,000.

Keywords: PACS; (Ablation film deposition) 81.15.Fg; (Metal thin films optical properties of) 78.66.Bz; (Nanoparticles optical properties of) 78.67.Bf; (Structure of thin films) 68.55.−a; 68.55.J−Silver; Nanoparticles; Laser; Ablation; Films; Deposition

Electrical and photovoltaic characteristics of sodium copper chlorophyllin/n-type silicon heterojunctions by A.A.M. Farag (pp. 4938-4943).

Heterojunctions of p-type sodium copper chlorophyllin (p-SCC)/n-type silicon (n-Si) were prepared by deposition of p-SCC film on n-Si wafers using spray-pyrolysis technique. Current–voltage and capacitance–voltage measurements of Au/p-SCC/n-Si/In heterojunctions were performed to discuss the electrical properties of these heterostructures. Rectifying characteristics were observed, which are definitely of the diode type. The current–voltage measurements suggest that the forward current in these junctions involves tunnelling and the results showed that the forward current can be explained by a multi-tunnelling capture–emission model in which the electron emission process dominates the carrier transport mechanism. On the other hand, the reverse current is probably limited by the same conduction process. The capacitance–voltage behavior indicates an abrupt heterojunction model is valid for Au/p-SCC/n-Si/In heterojunctions and the junction parameters such as, built-in potential, V_D, carrier concentration, N, the width of depletion layer, W, were obtained. The temperature and frequency dependence of the measured capacitance were also studied. The loaded I– V characteristics under white illumination provided by tungsten lamp (80mW/cm²) give values of 400mV, 0.9mA, 0.38 and 1.7% for the open-circuit voltage, V_oc, the short-circuit current, I_sc, the fill factor, FF, and conversion efficiency, η, respectively.

Keywords: Sodium copper chlorophyllin; Conduction mechanism; Photovoltaic properties

Ultra-fast spreading on superhydrophilic fibrous mesh with nanochannels by Lifang Wang; Yong Zhao; Jingming Wang; Xia Hong; Jin Zhai; Lei Jiang; Fosong Wang (pp. 4944-4949).

In this paper, we fabricated a TiO₂ mesh with ultra-fast spreading superhydrophilic property without UV irradiation. Through electrospinning process followed by calcinations, we obtained meshes with special micropores and nanochannels composite hierarchical structures. Each fiber exhibits a bundle structure of aligned elementary filaments with nanochannels, which should be resulted from phase separation and stretch of electrostatic force during electrospinning process. The mesh shows ultra-fast spreading property within only tens of milliseconds (ms). It is concluded that the special topography offered a multi-scale 3D capillary effect that play crucial role in ultra-fast spreading superhydrophilic property of the mesh. This study provides interesting insights to design novel materials concerning liquid transport and dissipation, which may find its way in various applications.

Keywords: Superhydrophilic; Ultra-fast spreading; Titanium dioxide; Electrospinning; Capillary effect

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films by Zhe Zhang; Shenhao Chen; Haipeng Ren; Juanjuan Zhou (pp. 4950-4954).

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods – electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.

Keywords: EIS; Iron; Polarization; Nanoparticle; Mixed films

Laser assisted removal of synthetic painting-conservation materials using UV radiation of ns and fs pulse duration: Morphological studies on model samples by P. Pouli; A. Nevin; A. Andreotti; P. Colombini; S. Georgiou; C. Fotakis (pp. 4955-4960).

In an effort to establish the optimal parameters for the cleaning of complex layers of polymers (mainly based on acrylics, vinyls, epoxys known as Elvacite, Laropal, Paraloid B72, among others) applied during past conservation treatments on the surface of wall paintings, laser cleaning tests were performed with particular emphasis on the plausible morphological modifications induced in the remaining polymeric material. Pulse duration effects were studied using laser systems of different pulse durations ( ns and fs) at 248nm. Prior to tests on real fragments from the Monumental Cemetery in Pisa (Italy) which were coated with different polymers, attention was focused on the study of model samples consisting of analogous polymer films cast on quartz disks. Ultraviolet irradiation is strongly absorbed by the studied materials both in ns and fs irradiation regimes. However, it is demonstrated that ultrashort laser pulses result in reduced morphological alterations in comparison to ns irradiation. In addition, the dependence of the observed alterations on the chemical composition of the consolidation materials in both regimes was examined. Most importantly, it was shown that in this specific conservation problem, an optimum cleaning process may rely not only on the minimization of laser-induced morphological changes but also on the exploitation of the conditions that favour the disruption of the adhesion between the synthetic material and the painting.

Keywords: PACS; 79.20.Ds; 52.38.Mf (Laser ablation)Femtosecond; Conservation; Wall paintings; Ablation; Consolidation polymers

Benzothiazole sulfide compatibilized polypropylene/halloysite nanotubes composites by Mingxian Liu; Baochun Guo; Yanda Lei; Mingliang Du; Demin Jia (pp. 4961-4969).

Clay-philic benzothiazole sulfide, capable of donating electrons, is grafted onto polypropylene (PP) backbones when N-cyclohexyl-2-benzothiazole sulfonamide (CBS), a commonly used accelerator in the tire industry, is included in the processing of PP/halloysite nanotubes (HNTs) composites. CBS decomposes at elevated temperature and yields benzothiazole sulfide radicals, which react with the PP polymeric free radicals generated during the processing of the composites. On the other hand, the benzothiazole group of CBS is reactive to HNTs via electron transferring. The compatibilization between HNTs and PP is thus realized via interfacial grafting and electron transferring mechanism. The interfacial interactions in the compatibilized systems were fully characterized. Compared with the control sample, the dispersion of HNTs and the interfacial bonding are enhanced substantially in the compatibilized composites. The significantly improved mechanical properties and thermal properties of benzothiazole sulfide compatibilized PP/HNTs composites are correlated to the enhanced interfacial property. The present work demonstrates a novel interfacial design via interfacial grafting/electron transferring for the compatibilization of PP/clay composites.

Keywords: Halloysite; Polypropylene; Rubber accelerator; Compatibilization; Grafting; Electron transfer

Novel W-shaped and straight porous ZnO nanobelts by Zhuang Huizhao; Shen Jiabing; Xue Chengshan; Wang Dexiao; Zhang Xiaokai; Liu Hang (pp. 4970-4973).

Novel W-shaped porous ZnO nanobelt with the periodical junction angles of about 118° and straight porous ZnO nanobelt have been successfully synthesized. The W-shaped structure growth changes from [0001] to[011¯1] periodically. The straight nanobelt grows along [0001] direction. Both of the structures have smooth surfaces with high porous density. Based on our X-ray diffraction (XRD), electron microscopy and photoluminescence (PL) spectrum study, the growth mechanism of the special ZnO nanostructures is discussed, emphasizing the effect of alteration of the reactant concentration for two different morphologies.

Keywords: PACS; 81.07.−b; 81.10.−h; 81.10.BkZnO nanomaterials; Methods of crystal growth; Growth from vapor

Measurement of UV absorption of single living cell for cell manipulation using NIR femtosecond laser by Sung-Hak Cho; Won-Seok Chang; Kwang-Ryul Kim; Jong Wook Hong (pp. 4974-4978).

Optical UV absorption of single human living cells ranging from 200nm to 360nm was measured in situ for the study of cell manipulation using the near-infrared (NIR) femtosecond laser . Human breast living cells of MCF-10A, MCF-7, and MDA-MB-231 were used in this experiment. The selective photo-disruptions of single living cell and its sub-organelle (nucleus) were also demonstrated using the tightly focused 790nm wavelength femtosecond laser with pulse duration of 110fs. It was found that each living cell has its own absorption spectrum in UV wavelength ranges. It was also inferred that intrinsic absorption spectrum is attributed to the amount of DNA and protein of living cell. For the study of photo-disruption of single cell using the multi-photon absorption excited by the NIR femtosecond laser pulse, the origin UV absorption spectrum of targeted living cell is important and fundamental information to understand nonlinear interaction between NIR ultrashort, high-intensity laser light and transparent living cell.

Keywords: PACS; 87.17.−d; 52.38.Mf; 42.62.BeCell manipulation; UV absorption; Living cell; Femtosecond laser; Photo-disruption; Laser internal processing

Physical and electrical characteristics of a high- k Yb₂O₃ gate dielectric by Tung-Ming Pan; Wei-Shiang Huang (pp. 4979-4982).

High- k ytterbium oxide (Yb₂O₃) gate dielectrics were deposited on Si substrate by reactive sputtering. The structural features of these films after postdeposition annealing treatment were studied by X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the Yb₂O₃ gate dielectrics annealed at 700°C exhibit a larger capacitance value, a lower frequency dispersion and a smaller hysteresis voltage in C– V curves compared with other annealing temperatures. They also show negligible charge trapping under high constant voltage stress. This phenomenon is mainly attributed to the decrease in the amorphous silica thickness.

Keywords: High-; k; Yb; ₂; O; ₃; Postdeposition annealing treatment; Amorphous silica

Kinetics, thermodynamics and surface heterogeneity assessment of uranium(VI) adsorption onto cation exchange resin derived from a lignocellulosic residue by T.S. Anirudhan; P.G. Radhakrishnan (pp. 4983-4991).

A new cation exchange resin (PGTFS–COOH) having a carboxylate functional group at the chain end was prepared by grafting poly(hydroxyethylmethacrylate) onto tamarind fruit shell, TFS (a lignocellulosic residue) using potassium peroxydisulphate–sodium thiosulphate redox initiator, and in the presence of N,N′-methylenebisacrylamide (MBA) as a crosslinking agent, followed by functionalisation. The adsorbent was characterized with the help of FTIR, XRD, scanning electron micrographs (SEM), and potentiometric titrations. The kinetic and isotherm data, obtained at optimum pH value 6.0 at different temperatures could be fitted with pseudo-second-order equation and Sips isotherm model, respectively. An increase in temperature induces positive effect on the adsorption process. The calculated activation energy of adsorption ( E_a, 18.67kJ/mol) indicates that U(VI) adsorption was largely due to diffusion-controlled process. The values of adsorption enthalpy, Gibbs free energy, and entropy were calculated using thermodynamic function relationships. The decrease in adsorption enthalpy with increasing U(VI) uploading on the adsorbent, reflects the surface energetic heterogeneity of the adsorbent. The isosteric heat of adsorption was quantitatively correlated with the fractional loading for the U(VI) ions adsorption onto PGTFS–COOH. The results showed that the PGTFS–COOH possessed heterogeneous surface with sorption sites having different activities.

Keywords: U(VI) ions; Tamarind fruit shell; Isotherms; Thermodynamics; Surface heterogeneity

Influence of Co doping content on its valence state in Zn1−_xCo_xO (0≤ x≤0.15) thin films by Ling Wei; Zonghui Li; W.F. Zhang (pp. 4992-4995).

Zn1−_xCo_xO (0≤ x≤0.15) thin films grown on Si (100) substrates were prepared by a sol–gel technique. The effects of Co doped on the structural, optical properties and surface chemical valence states of the Zn1−_xCo_xO (0≤ x≤0.15) films were investigated by X-ray diffraction (XRD), ultraviolet–visible spectrometer and X-ray photoelectron spectroscopy (XPS). XRD results show that the Zn1−_xCo_xO films retained a hexagonal crystal structure of ZnO with better c-axis preferred orientation compared to the undoped ZnO films. The optical absorption spectra suggest that the optical band-gap of the Zn1−_xCo_xO thin films varied from 3.26 to 2.79eV with increasing Co content from x=0 to x=0.15. XPS studies show the possible oxidation states of Co in Zn1−_xCo_xO (0≤ x≤0.05), Zn_0.90Co_0.10O and Zn_0.85Co_0.15O are CoO, Co₃O₄ and Co₂O₃, with an increase of Co content, respectively.

Keywords: PACS; 73.61.Ga; 61.72.Vv; 82.80.Ej; 31.15.RhZinc oxide; Cobalt doping; XPS; Valence state

A simplified predictive model for high-fluence ultra-short pulsed laser ablation of semiconductors and dielectrics by Benxin Wu; Yung C. Shin (pp. 4996-5002).

Ultra-short pulsed laser ablation is a very complicated process and a predictive model is very desirable for process design and optimization in practical applications. However, the molecular dynamics or hydrodynamic models, although they are powerful and necessary tools for the study of the fundamental physics, are time-consuming and difficult to apply for practical applications. In this paper, a predictive, simplified and easy to apply model has been developed for high-fluence ultra-short laser ablation of semiconductors and dielectrics. Unlike many other simplified models, this model does not involve any free adjustable variables. The model predictions agree well with experimental measurements for femtosecond laser ablation, while the model is not very applicable for pulse durations more than ∼10ps.

Keywords: Keyword; Femtosecond laser ablation

Integration and characterization of aligned carbon nanotubes on metal/silicon substrates and effects of water by Yong Zhang; Ruying Li; Hao Liu; Xueliang Sun; Philippe Mérel; Sylvain Désilets (pp. 5003-5008).

We report here a facile way to grow aligned multi-walled carbon nanotubes (MWCNTs) on various metal (e.g. gold, tungsten, vanadium and copper)/silicon electrically conductive substrates by aerosol-assisted chemical vapor deposition (AACVD). Without using any buffer layers, integration of high quality MWCNTs to the conductive substrates has been achieved by introducing appropriate amount of water vapor into the growth system. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) determination indicate tidy morphology and narrow diameter distribution of the nanotubes as well as promising growth rate suitable for industrial applications. Raman spectra analysis illustrates that the structural order and purity of the nanotubes are significantly improved in the presence of water vapor. The growth mechanism of the nanotubes has been discussed. It is believed that water vapor plays a key role in the catalyst-substrate interaction and nucleation of the carbon nanotubes on the conductive substrates. This synthesis approach is expected to be extended to other catalyst-conductive substrate systems and provide some new insight in the direct integration of carbon nanotubes onto conductive substrates, which promises great potential for applications in electrical interconnects, contacts for field emitters, and other electronic nanodevices.

Keywords: PACS; 61.48.De; 81.07.De; 81.07.Lk; 81.15.GhCarbon nanotubes; Chemical vapor deposition; Metal/Silicon substrate; Water vapor

Improved biological performance of low modulus Ti–24Nb–4Zr–7.9Sn implants due to surface modification by anodic oxidation by Y. Gao; B. Gao; R. Wang; J. Wu; L.J. Zhang; Y.L. Hao; X.J. Tao (pp. 5009-5015).

Dental implants are usually made from commercially pure titanium or titanium alloys. The purpose of this study was to evaluate the influence of surface treatment to low modulus Ti–24Nb–4Zr–7.9Sn (TNZS) on cell and bone responses. The TNZS alloy samples were modified using anodic oxidation (AD). Surface oxide properties were characterized by using various surface analytic techniques, involving scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), X-ray diffractometry (XRD) and surface profilometer. During the AD treatment, porous titanium oxide layer was formed and Ca ions were incorporated into the oxide layer. The viability and morphology of osteoblasts on Ca-incorporated TNZS were studied. The bone responses of Ca-incorporated TNZS were evaluated by pull-out tests and morphological analysis after implantation in rabbit tibiae. The non-treated Ti and TNZS samples were used as the control. Significant increases in cell viability and pull-out forces ( p<0.05) were observed for Ca-incorporated TNZS implants compared with those for the control groups. Porous structures supplied positive guidance cues for osteoblasts to attach. The enhanced cell and bone responses to Ca-incorporated TNZS implants could be explained by the surface chemistry and microtopography.

Keywords: PACS; 87.85.−JTitanium alloy; Anodic oxidation; Biocompatibility; Osteoblast; Osseointegration

Photoluminescence and optical properties of He ion bombarded ultra-high molecular weight polyethylene by A.M. Abdul-Kader (pp. 5016-5020).

Ion bombardment is a suitable tool to improve the physical and chemical properties of polymer surface. In this study UHMWPE samples were bombarded with 130keV He ions to the fluences ranging from 1×10¹² to 1×10¹⁶cm⁻². The untreated and ion beam modified samples were investigated by photoluminescence, and ultraviolet-visible (UV–vis) spectroscopy. Remarkable decrease in integrated luminescence intensity with increasing ion fluences was observed. The reduction in PL intensity with increase of ion fluence might be attributed to degradation of polymer surface and formation of defects. The effect of ion fluence on the optical properties of the bombarded surfaces was characterized. The values of the optical band gap E_g, and activation energy E_a were determined from the optical absorption. The width of the tail of the localized states in the band gap (E_a) was evaluated using the Urbach edge method. With increasing ion fluences a decrease in both the energy gap and the activation energy were observed. Increase in the numbers of carbon atoms ( N) in a formed cluster with increasing the He ion fluence was observed.

Keywords: Ultra-high molecular weight polyethylene; Ion beam bombardment; Photoluminescence; Optical energy gap; Activation energy

Growth and properties of YAlO film synthesized by RF magnetron sputtering by Keiko Matsunouchi; Naoyoshi Komatsu; Chiharu Kimura; Hidemitsu Aoki; Takashi Sugino (pp. 5021-5024).

YAlO films are synthesized on (100)-oriented Si substrates by RF magnetron sputtering method. Al₂O₃ wafer is used as a target material, and some small pieces of Y bulk material are put on the Al₂O₃ target to synthesize YAlO films. Y composition ratio is varied from 0 to 34%. Amorphous YAlO films are characterized. An electrical resistivity as high as 3.4×10¹⁴Ω-cm is achieved for the YAlO film with Y composition ratio of 10%. The dielectric constant increases with increasing Y composition ratio, and the YAlO film with Y composition ratio of 34% has a dielectric constant of 10.2. The bandgap energy of the YAlO film is suggested to be wider than 6.5eV. YAlO films with a surface roughness of 0.4–1.3nm are obtained irrespective of the Y composition ratio.

Keywords: YAlO film; Al; ₂; O; ₃; Y; ₂; O; ₃; High-K; Wide bandgap semiconductor

Characterization of ultra-fast deposited polycrystalline graphite by a CO₂ laser-assisted combustion-flame method by Travis McKindra; Sandeep Patil; Matthew J. O’Keefe; Yaoxuan Han; Hao Ling; Yongfeng Lu (pp. 5025-5030).

High deposition rate, 750μm/min, crystalline graphite was deposited on WC substrates by a CO₂ laser-assisted combustion-flame method at laser powers between 300 and 800W. The structures, which were identified as pillars, were characterized by various methods. The pillars were cylindrical in shape and grew to a size of approximately 3mm in length and in a few minutes. The laser power did not affect the overall length of the pillar, but caused changes in the physical shape. X-ray and electron diffraction results revealed the pillars to be crystalline graphite regardless of the laser power. Investigation of the pillars by scanning electron microscopy showed two distinct microstructural areas: an inner core of dense material surrounded by an outer shell of lamellar-like material. The core/shell microstructure was unaffected by the level of CO₂ laser power.

Keywords: PACS; 81.05.Uw; 81.16.Mk; 68.37.HkHigh deposition rate; Crystalline graphite; Laser-assisted combustion-flame deposition

Adsorption performance and mechanism of 2,4,6-trinitrotoluene on a novel adsorption material polyvinylbenzyl acid/SiO₂ by Fuqiang An; Baojiao Gao; Xiaoqin Feng (pp. 5031-5035).

Polyvinylbenzene (PVB, namely polystyrene, PSt) was grafted on the surface of silica gel particles by “grafting from” in solution polymerization system, and grafting particles PVB/SiO₂ were obtained. The chloromethylation reaction of the grafted polyvinylbenzene was performed using a novel chloromethylation reagent, 1,4-bis (chloromethyoxy) butane that is un-carcinogenic, and grafting particles CMPVB/SiO₂ were obtained. Subsequently, chloromethyl groups on grafting particles CMPVB/SiO₂ were hydrolyzed and oxidized, and finally adsorption material polyvinylbenzyl acid/SiO₂ (PVBA/SiO₂) was prepared. The adsorption performances and mechanism of 2,4,6-trinitrotoluene (TNT) on PVBA/SiO₂ were investigated through static methods. The experimental results showed that PVBA/SiO₂ possessed strong adsorption ability for TNT with adsorption amount of 26.84mgg⁻¹. The empirical Freundlich isotherm was also found to agree well with the equilibrium adsorption data. In addition, pH was found to have great influence on the adsorption amount. Finally, PVBA/SiO₂ was observed to possess excellent reusability as well.

Keywords: PACS; 68.43.−hPolyvinylbenzyl acid; Silica gel; Adsorption; 2,4,6-Trinitrotoluene (TNT)

Ablation properties of carbon/carbon composites with tungsten carbide by Jian Yin; Hongbo Zhang; Xiang Xiong; Baiyun Huang; Jinlv Zuo (pp. 5036-5040).

The ablation properties and morphologies of carbon/carbon (C/C) composites with tungsten carbide (WC) filaments were investigated by ablation test on an arc heater and scanning electron microscopy. And the results were compared with those without tungsten carbide (WC) filaments tested under the same conditions. It shows that there is a big difference between C/C composites with and without WC filaments on both macroscopic and microscopic ablation morphologies and the ablation rates of the former are higher than the latter. It is found that the ablation process of C/C composites with WC filaments includes oxidation of carbon fibers, carbon matrices and WC, melting of WC and WO₃, and denudation of WC, WO₃ and C/C composites. Oxidation and melting of WC leads to the formation of holes in z directional carbon fiber bundles, which increases the coarseness of the ablation surfaces of the composites, speeds up ablation and leads to the higher ablation rate. Moreover, it is further found that the molten WC and WO₃ cannot form a continuous film on the ablation surface to prevent further ablation of C/C composites.

Keywords: Carbon/carbon composites; WC filament; Ablation morphology; Ablation property

Removal of naphthalene from petrochemical wastewater streams using carbon nanoporous adsorbent by Mansoor Anbia; Seyyed Ershad Moradi (pp. 5041-5047).

Ordered mesoporous carbon, OMC, was synthesized using ordered mesoporous silica MCM-48 as hard template, the structural order and textural properties of the synthesized materials were studied by XRD, SEM, and nitrogen adsorption–desorption analysis. Adsorption of naphthalene over various porous adsorbents such as OMC, MCM-48, and commercial activated carbon was studied from solutions with different concentration at ambient temperature (25±2°C) and pH 7. The adsorption isotherms of naphthalene were in agreement with a Langmuir model, moreover, the uptake capacity of naphthalene followed the order: OMC>commercial activated carbon>mesoporous silica (MCM-48).

Keywords: Naphthalene; Mesoporous carbon; Adsorption; Langmuir isotherm; Wastewater

Activation energies of the acceptor-bound excitons and the donor-acceptor pairs in nitrogen-doped p-type ZnSe, p-type ZnS_ySe1−_y, and p-type Zn1−_xMg_xS_ySe1−_y epitaxial films grown on GaAs (100) substrates by H.J. Kim; B.J. Kim; T.W. Kim; K.H. Yoo (pp. 5048-5051).

Nitrogen-doped p-type ZnSe, p-type ZnS_ySe1−_y, and p-type Zn1−_xMg_xS_ySe1−_y epilayers were grown on n-type GaAs (100) substrates by molecular beam epitaxy. Photoluminescence (PL) spectra for the p-type ZnSe and the lattice-matched p-type ZnS_0.06Se_0.94, and p-type Zn_0.92Mg_0.08S_0.12Se_0.88 epilayers showed a deep acceptor bound exciton emission and a donor–acceptor pair emission. Temperature-dependent PL measurements were carried out to determine the activation energies of these states. The activation energies of the acceptor-bound excitons and the donor–acceptor pairs were determined to be 40 and 65 meV in the p-type ZnSe epilayer, 20 and 45 meV in the p-type ZnS_0.06Se_0.94, and 45 and 43 meV in the p-type Zn_0.92Mg_0.08S_0.12Se_0.88 epilayers.

Keywords: PACS; 61. 70. Tm; 68. 55. Bd; 71. 35. +; z; and 78. 55. EtActivation energy; exciton; p-type ZnSe; p-type ZnS; _y; Se; 1−; _y; p-type Zn; 1−; _x; Mg; _x; S; _y; Se; 1−; _y

XPS characterisation of plasma treated and zinc oxide coated PET by S. Ben Amor; M. Jacquet; P. Fioux; M. Nardin (pp. 5052-5061).

At first, X-ray photoelectron spectroscopy (XPS) analyses of reference and carbon dioxide plasma treated polyethylene terephthalate (PET) were carried out. Significant chemical modifications were outlined in the treated PET surface in comparison with the reference one. The formation of new oxygenated groups was evidenced. These modifications heighten the level of interactions between the polymer substrate and the deposited coating.In a second stage, zinc oxide thin films were elaborated by r.f. magnetron sputtering from a ceramic target and with a reactive gas (mixture of argon–1% oxygen) under optimised conditions on CO₂ plasma treated PET. The interfacial chemistry between the plasma treated PET and the zinc oxide was also studied by XPS. The line shape changes in the high-resolution core level spectra of carbon C1s, oxygen O1s, and zinc (Zn2p3/2, Zn3p), with the progressive deposition of zinc oxide coatings being recorded. The obtained spectra were fitted to mixed Gaussian–Lorentzian components using XPS CASA software.An interaction scheme between the zinc oxide thin layer and its polymer substrate, in the first stage of deposition, was proposed and checked by corroborating the findings of the different XPS spectra and their decompositions. It suggests the formation of ZnOC complexes at the interface, which are promoted by an electron transfer from zinc to oxygen in oxygenated species, mainly alcohol groups, generated by the CO₂ plasma treatment of PET.

Keywords: PACS; 52.77.Bn; 68.47.Mn; 81.15.Cd; 82.80.Pv; 68.35.NpPET; Plasma processing and deposition; Zinc oxide; Interface; XPS

Luminescent characteristics of CaTiO₃:Pr³⁺ thin films prepared by pulsed laser deposition method with various substrates by Hyun Kyoung Yang; Jong Won Chung; G. Seeta Rama Raju; Byung Kee Moon; Byung Chun Choi; Jung Hyun Jeong; Jung Hwan Kim (pp. 5062-5066).

CaTiO₃:Pr³⁺ films were deposited on different substrates such as Al₂O₃ (0001), Si (100), MgO (100), and fused silica using pulsed laser deposition method. The crystallinity and surface morphology of these films were investigated by XRD and SEM measurements. The films grown on the different substrates have different crystallinity and morphology. The FWHM of (200) peak are 0.18, 0.25, 0.28, and 0.30 for Al₂O₃ (0001), Si (100), MgO (100), and fused silica, respectively. The grain sizes of phosphors grown on different substrates were estimated by using Scherrer's formula and the maximum crystallite size observed for the thin film grown on Al₂O₃ (0001). The room temperature PL spectra exhibit only the red emission peak at 613nm radiated from the transition of (¹D₂→³H₄) and the maximum PL intensity for the films grown on the Al₂O₃ (0001) is 1.1, 1.4, and 3.7 times higher than that of the CaTiO₃:Pr³⁺ films grown on MgO (100), Si (100), and fused Sillica substrates, respectively. The crystallinity, surface morphology and luminescence spectra of thin-film phosphors were highly dependent on substrates.

Keywords: PACS; 78.20.−e; 78.55.−m; 78.66.−wSubstrate; X-ray diffraction; Oxides; Phosphors

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−_xC_x nanocomposites mixed with Si nanoparticles and C atoms by J.W. Shin; D.H. Oh; T.W. Kim; W.J. Cho (pp. 5067-5070).

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si1−_xC_x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO₂ layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si1−_xC_x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO₂ layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−_xC_x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.

Keywords: PACS; 68. 43.Hn; 68. 55.NqSi; 1−; _x; C; _x; nanocomposite; Si nanoparticle; Microstructural property; Formation mechanism; Transformation mechanism

Coating formation by plasma electrolytic oxidation on ZC71/SiC/12p-T6 magnesium metal matrix composite by R. Arrabal; E. Matykina; P. Skeldon; G.E. Thompson (pp. 5071-5078).

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350mAcm⁻² (rms) and 50Hz with a square waveform in stirred 0.05M Na₂SiO₃.5H₂O/0.1M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4GPa, formed at an average rate of ∼1μmmin⁻¹ for treatment times up to 100min and ∼0.2μmmin⁻¹ for later times. The coatings are composed mainly of MgO and Mg₂SiO₄, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.

Keywords: PACS; 81.65.−b; 81.65.MqMagnesium; Matrix matrix composite; Plasma electrolytic oxidation; Corrosion; Nanoindentation

Influence of nitrogen ion implantation fluences on surface structure and tribological properties of SiC ceramics in water-lubrication by Fei Zhou; Yingguang Yuan; Xiaolei Wang; Meiling Wang (pp. 5079-5087).

Nitrogen ions were implanted into SiC ceramics by using ion implantation technology (N⁺-SiC). The surface structure and chemical bonds of N⁺-SiC ceramics were determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their nanohardness was measured by nanoindenter. The friction and wear properties of the N⁺-SiC/SiC tribo-pairs were investigated and compared with those of SiC/SiC tribo-pairs in water using ball-on-disk tribo-meters. The wear tracks on the N⁺-SiC ceramics were observed by non-contact surface profilometer and scanning electron microscope (SEM) and their wear volumes were determined by non-contact surface profilometer. The results show that the N⁺-SiC ceramics were mainly composed of SiC and SiCN phase and SiN, CC, CN and CN bonds were formed in the implantation layer. The highest hardness of 22.3GPa was obtained as the N⁺-SiC ceramics implanted at 50keV and 1×10¹⁷ions/cm². With an increase in nitrogen ion fluence, the running-in period of N⁺-SiC/SiC tribo-pairs decreased, and the mean stable friction coefficient decreased from 0.049 to 0.024. The N⁺-SiC ceramics implanted at 50keV and 5×10¹⁷ions/cm² exhibited the excellent tribological properties in water. In comparison of SiC/SiC ceramic tribo-pairs, the lower friction coefficient and lower wear rate for the N⁺-SiC/SiC tribo-pairs were acquired.

Keywords: Silicon carbide ceramics; Ion implantation; Nanohardness; Friction; Wear; Water-lubrication

Facile fabrication of novel cyclomatrix-type polyphosphazene nanotubes with active hydroxyl groups via an in situ template approach by Jianwei Fu; Xiaobin Huang; Yan Zhu; Yawen Huang; Xiaozhen Tang (pp. 5088-5091).

Novel polyphosphazene nanotubes with active hydroxyl groups were fabricated via an in situ template approach under ultrasonic irradiation. SEM and TEM results indicated that the nanotubes were uniform with length of several micrometers, inner diameter of ca. 20nm and outer diameter of 60–80nm. FTIR spectra revealed that the content of the hydroxyl groups on the nanotube surface was dependent on the feed ratio of hexachlorocyclotriphosphazene (HCCP) to 4,4′-sulfonyldiphenol. The successful esterification of polymer nanotubes with benzoxy chloride demonstrated the high reactivity of the hydroxyl groups. The method employed here might provide a simple and effective way to prepare functional nanotubes used for biological applications.

Keywords: Nanotube; Hydroxyl group content; Polymer; Surface modification; In situ template

Multiferroic properties of Bi_0.8La_0.2FeO₃/CoFe₂O₄ multilayer thin films by Shan-Tao Zhang; Yi Zhang; Zhen-Lin Luo; Ming-Hui Lu; Zheng-Bin Gu; Yan-Feng Chen (pp. 5092-5095).

Bi_0.8La_0.2FeO₃/CoFe₂O₄ (BLFO/CFO) multilayer thin films (totally 20 layers BLFO and 19 layers CFO) were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. X-ray diffraction and transmission electron microscope measurements show that the films are polycrystalline and consisted of multilayered structure. Ferroelectric hysteresis loops with remnant polarization and saturated polarization of 4.2 and 13.3μC/cm², respectively, were observed. On the other hand, the films show well-shaped magnetization hysteresis loops with saturated and remnant magnetization of 34.7 and 11.4emu/cm³, respectively, which are significantly larger than pure BLFO thin films deposited under the same conditions. These results indicate that constructing epitaxial superlattice might be a promising way to fabricate multiferroics with improved properties.

Keywords: PACS; 77.84.−s; 77.80.−e; 75.80.+qMultiferroics; Multilayer thin films; Bi; _0.8; La; _0.2; FeO; ₃; CoFe; ₂; O; ₄

Enhancement of carrier mobility in pentacene thin-film transistor on SiO₂ by controlling the initial film growth modes by Qiong Qi; Aifang Yu; Peng Jiang; Chao Jiang (pp. 5096-5099).

Pentacene thin-film transistors (TFTs) were fabricated on thermally grown SiO₂ gate insulator under the conditions of various pre-cleaning treatments. Initial nucleation and growth of the material films on treated substrates were observed by atomic force microscope. The performance of fabricated TFT devices with different surface cleaning approaches was found to be highly related to the initial film morphologies. In contrast to the three-dimensional island-like growth mode on SiO₂ under an organic cleaning process, a layer-by-layer initial growth occurred on the SiO₂ insulator cleaned with ammonia solution, which was believed to be the origination of the excellent electrical properties of the TFT device. Field effect mobility of the TFT device could achieve as high as 1.0cm²/Vs on the bared SiO₂/Si substrate and the on/off ratio was over 10⁶.

Keywords: PACS; 85.30.Tv; 72.20.Jv; 72.80.LeOrganic thin-film transistor; Pentacene; Surface treatment; Initial growth mode

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Applied Surface Science (v.255, #9)