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Applied Surface Science (v.256, #23)

Editorial Board (pp. ii).

Amino functionalization of carbon nanotube surfaces with NH₃ plasma treatment by Ju Young Yook; Jaeho Jun; Soonjong Kwak (pp. 6941-6944).

NH₃ plasma treatment of carbon nanotube (CNT) surfaces was performed with the purpose of incorporating amino groups onto the surface. Amino groups incorporated onto the CNT surface were indentified and quantified using chemical derivatization with pentafluorobenzaldehyde and subsequent characterization with X-ray photoelectron spectroscopy (XPS). The amount of incorporated amino groups reached a maximum value with increasing plasma power. The incorporation of amino groups was seriously affected by the degradation of the CNT surface during the plasma treatment, which became very serious at high plasma power, as verified with optical emission spectroscopy (OES) and FT-IR analyses. The type of species present in the plasma discharge also seems to be important for amino group functionalization; partially decomposed ammonia species are considered to be more favorable than fully decomposed atomic species.

Keywords: Carbon nanotube; Plasma treatment; Amino group; Functionalization; Derivatization

Silane treatment of Fe₃O₄ and its effect on the magnetic and wear properties of Fe₃O₄/epoxy nanocomposites by J.O. Park; K.Y. Rhee; S.J. Park (pp. 6945-6950).

In this study, the effect of silane treatment of Fe₃O₄ on the magnetic and wear properties of Fe₃O₄/epoxy nanocomposites was investigated. Fe₃O₄ nanopowders were prepared by coprecipitation of iron(II) chloride tetrahydrate with iron(III) chloride hexahydrate, and the surfaces of Fe₃O₄ were modified with 3-aminopropyltriethoxysilane. The magnetic properties of the powders were measured on unmodified and surface-modified Fe₃O₄/epoxy nanocomposites using SQUID magnetometer. Wear tests were performed on unmodified and surface-modified Fe₃O₄/epoxy nanocomposites under the same conditions (sliding speed: 0.18m/s, load: 20N).The results showed that the saturation magnetization ( M_s) of surface-modified Fe₃O₄/epoxy nanocomposites was approximately 110% greater than that of unmodified Fe₃O₄/epoxy nanocomposites. This showed that the specific wear rate of surface-modified Fe₃O₄/epoxy nanocomposites was lower than that of unmodified Fe₃O₄/epoxy nanocomposites. The decrease in wear rate and the increase in magnetic properties of surface-modified Fe₃O₄/epoxy nanocomposites occurred due to the improved dispersion of Fe₃O₄ into the epoxy matrix.

Keywords: Fe; ₃; O; ₄; Nanocomposites; Silane; Wear test; Magnetization

Effect of change in pulsed DC frequency on indium–tin oxide anode on J– V– L performance of built-up organic light emitting diode during facing-target sputtering by Chul Yoon; Sang-Ho Kim (pp. 6951-6955).

Investigations were carried out on the changes in the electrical and optical properties and surface roughness of the indium–tin oxide (ITO) anode as a function of DC pulse frequency during facing-target sputtering. The current density–voltage–luminescence ( J– V– L) characteristics of organic light emitting diodes (OLEDs) developed on the anodes were measured and analyzed in relation to the properties of ITO. When the pulsed DC frequency was less than 120kHz, the resistivity of ITO was maintained well below 4.3×10⁻⁴Ωcm and the optical energy band gap was greater than 4.1eV, but these properties changed abruptly at 150kHz with the morphological transition from columnar to equi-axed. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 150kHz. The J– V characteristics of the built-up OLED deteriorated slightly as the pulsed DC frequency increased to 120kHz and then deteriorated rapidly at 150kHz. The L– V curves, however, showed an improvement of luminescence as the frequency increased up to 120kHz. These J– V– L characteristics imply that ITO which is more conductive and with a higher band gap can be obtained at the lower pulsed DC frequencies, which is desirable for higher current flow; however, better luminescence is closely related to smoother surfaces. Therefore, for the optimized J– V– L performance of OLEDs, a moderate pulse DC frequency, below the morphological transition of ITO, is desirable.

Keywords: ITO; OLED; Pulsed DC frequency; Facing-target sputtering

Iron and aluminium based mixed hydroxides: A novel sorbent for fluoride removal from aqueous solutions by M. Gude Sujana; S. Anand (pp. 6956-6962).

In our previous studies, iron and aluminium based mixed hydroxides were prepared in different molar ratios and fluoride removal efficiencies were evaluated. It was found that the Fe/Al sample with 1:1 molar ratio exhibited maximum adsorption capacity for fluoride. In the present work detailed studies were carried out to understand the effect of fluoride concentration on kinetics, adsorbent dose and competing anion concentrations. Characterisation studies on the adsorbent by XRD, TGA, SEM-EDX, TEM and FT-IR analysis before and after fluoride adsorption were carried out to understand the adsorption mechanism. The particles were irregular in shape, <0.5μm in size, highly porous and showed specific surface area of 268m²g⁻¹. XRD and FT-IR studies revealed significant changes after fluoride adsorption and showed formation of new complexes on adsorbent surface. Applicability of different sorption kinetic models was studied. The surface sites are heterogeneous in nature and followed heterogeneous site binding model. The presence of phosphate, sulphate and arsenate showed adverse effect on fluoride removal efficiency of Fe/Al adsorbent. The efficiency of material towards ground water samples treatment was tested with and without adjusting pH, and the results are discussed.

Keywords: Fe/Al mixed hydroxides; Fluoride; Adsorption; Hot water spring; Ground water

Template occluded SBA-15: An effective dissolution enhancer for poorly water-soluble drug by Fu Tingming; Guo Liwei; Le Kang; Wang Tianyao; Lu Jin (pp. 6963-6968).

The aim of the present work was to improve the dissolution rate of piroxicam by inclusion into template occluded SBA-15. Our strategy involves directly introducing piroxicam into as-prepared SBA-15 occluded with P123 (EO₂₀PO₇₀EO₂₀) by self assembling method in acetonitrile/methylene chloride mixture solution. Ultraviolet spectrometry experiment and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) profiles show that the piroxicam and P123 contents in the inclusion compound are 12wt% and 28wt%, respectively. X-ray powder diffraction and DSC analysis reveal that the included piroxicam is arranged in amorphous form. N₂ adsorption–desorption experiment indicates that the piroxicam has been introduced to the mesopores instead of precipitating at the outside of the silica material. The inclusion compound was submitted to in vitro dissolution tests, the results show that the piroxicam dissolve from template occluded inclusion compound more rapidly, than these from the piroxicam crystalline and template removed samples in all tested conditions. Thus a facile method to improve the dissolution rate of poorly water-soluble drug was established, and this discovery opens a new avenue for the utilization of templates used for the synthesis of mesoporous materials.

Keywords: Dissolution rate; Piroxicam; Mesoporous silica; Template occluded

SERS-active substrates based on n-type porous silicon by A. Yu. Panarin; S.N. Terekhov; K.I. Kholostov; V.P. Bondarenko (pp. 6969-6976).

Porous silicon (PS) prepared from n-type Si crystal is proposed as a new material for the fabrication of sensitive substrates for surface-enhanced Raman scattering (SERS). The formation procedure for nanostructured silver films on the surface of PS was optimized. Maximum of SERS enhancement for rhodamine 6G probing molecule is observed for samples obtained by the immersion plating from the water solution of AgNO₃ with the 10mM concentration during 5min. The dependence of morphological parameters of PS and corresponding silvered surfaces on the anodization current density has been studied. It is shown that the most SERS activities possess substrates produced from PS with lower porosity. The optimum of the PS layer thickness for high Raman signal is about 5μm. The detection limit for rhodamine 6G adsorbed on Ag-coated PS from the 100pM solution is established to be comparable with that for p-type PS-based substrates. Thus, the n-type porous silicon is suitable material for the preparation of sensitive SERS-active substrates.

Keywords: SERS-active substrates; n-type porous silicon; Rhodamine 6G

A study of modified Fe₃O₄ nanoparticles for the synthesis of ionic ferrofluids by Jian Li; Xiaoyan Qiu; Yueqiang Lin; Xiaodong Liu; Rongli Gao; Anrong Wang (pp. 6977-6981).

XRD and XPS analyses revealed that a Fe(NO₃)₃·9H₂O layer formed outside γ-Fe₂O₃ particles when Fe₃O₄ nanoparticles were treated with ferric nitrate. The particle density differed for untreated and treated particles and was not uniform for the latter. The specific saturation magnetization of both treated and untreated particles was used to estimate the thickness of the Fe(NO₃)₃·9H₂O layer and the average density of the treated particles. The density of the treated particles was used to calculate the density of ferrofluids of different particle volume fractions. These values are in agreement with measured results. Therefore, the particle volume fraction can be designed to synthesize acid ionic ferrofluids based on Fe₃O₄ nanoparticles using Massart's method.

Keywords: Magnetic materials; Nanoparticles; Ferrofluids

Surface effect on the coalescence of Pt clusters: A molecular dynamics study by K. Kayhani; K. Mirabbaszadeh; P. Nayebi; A. Mohandesi (pp. 6982-6985).

We have performed molecular dynamics simulations for Pt_N+Pt_N→Pt2_N ( N=147, 324, 500,792), to investigate the effect of size and substrate on coalescence temperature. Our simulations show that platinum nanoclusters coalesce at the temperatures lower than the cluster melting point. The difference between coalescence and melting temperatures decreases with the increase in cluster size and presence of substrate. These thermal behaviors affect catalytical properties of nanoclusters and the substrate, as an environment, has major effect on activity of metal nanoclusters.

Keywords: Nanocluster; Molecular dynamics; Platinum clusters; Coalescence temperature

Surface characterization and growth mechanism of laminated Ti₃SiC₂ crystals fabricated by hot isostatic pressing by Qiong Wu; Changsheng Li; Hua Tang (pp. 6986-6990).

Laminated Ti₃SiC₂ crystals were prepared by hot isostatic pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1350°C. The morphology and microstructure of Ti₃SiC₂ crystals were investigated by means of XRD, SEM, and TEM. The high symmetry and crystalline was revealed by high resolution transmission electronic microscope (HRTEM) and selected area electron diffraction (SAED). The growth mechanism of Ti₃SiC₂ crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (002) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces.

Keywords: Ti; ₃; SiC; ₂; Hot isostatic pressing; Growth mechanism

Roles of γ-Fe₂O₃ in fly ash for mercury removal: Results of density functional theory study by Pan Guo; Xin Guo; Chuguang Zheng (pp. 6991-6996).

First-principle calculations based on density function theory (DFT) are used to clarify the roles of γ-Fe₂O₃ in fly ash for removing mercury from coal-fired flue gases. In this study, the structure of key surface of γ-Fe₂O₃ is modeled and spin-polarized periodic boundary conditions with the partial relaxation of atom positions are employed. Binding energies of Hg on γ-Fe₂O₃ (001) perfect and defective surfaces are calculated for different adsorption sites and the potential adsorption sites are predicted. Additionally, electronic structure is examined to better understand the binding mechanism. It is found that mercury is preferably adsorbed on the bridge site of γ-Fe₂O₃ (001) perfect surface, with binding energy of −54.3kJ/mol. The much stronger binding occurs at oxygen vacancy surface with binding energy of −134.6kJ/mol. The calculations also show that the formation of hybridized orbital between Hg and Fe atom of γ-Fe₂O₃ (001) is responsible for the relatively strong interaction of mercury with the solid surface, which suggests that the presently described processes are all noncatalytic in nature. However, this is a reflection more of mercury's amalgamation ability.

Keywords: Mercury; γ-Fe; ₂; O; ₃; Density functional theory; Amalgamation

Effects of in situ plasma treatment on optical and electrical properties of index-matched transparent conducting oxide layer by Yong Hwan Lim; Hana Yoo; Bum Ho Choi; Young Baek Kim; Jong Ho Lee; Dong Chan Shin (pp. 6997-7000).

We investigated the effects of in situ plasma-treatment on optical and electrical properties of index-matched indium tin oxide (IMITO) thin film. To render the IMITO-coated surface hydrophilic and study the optical and electrical characteristics, we performed in situ oxygen plasma post-treatment without breaking vacuum. The 94.6% transmittance in the visible wavelength range (400–700nm) increased on average to 96.4% and the maximum transmittance reached 98% over a broad wavelength range. The surface roughness and sheet resistance improved from 0.9nm and 200Ω/sq to 0.0905nm and 100Ω/sq, respectively, by in situ plasma post-treatment. We confirmed by contact angle measurement that the hydrophobic IMITO surface was altered to hydrophilic. The improved optical and electrical characteristics of in situ plasma-treated IMITO makes it adequate for high-resolution liquid crystal on silicon displays.

Keywords: IMITO; LCoS; In situ plasma treatment

Microstructure and wear resistance of composite layers on a ductile iron with multicarbide by laser surface alloying by Hua Yan; Aihua Wang; Zhaoting Xiong; Kaidong Xu; Zaowen Huang (pp. 7001-7009).

Multicarbide reinforced metal matrix composite (MMC) layers on a ductile iron (QT600-3) were fabricated by laser surface alloying (LSA) using two types of laser: a 5kW continuous wave (CW) CO₂ laser and a 400W pulsed Nd:YAG laser, respectively. The research indicated that LSA of the ductile iron with multicarbide reinforced MMC layers demonstrates sound alloying layers free of cracks and porosities. The microstructure, phase structure and wear properties of MMC layers were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), as well as dry sliding wear testing. The microstructure of the alloyed layer is composed of pre-eutectic austenite, ledeburite, spherical TiC, Cr₇C₃ and Cr₂₃C₆ with various morphologies. TiC particles are dispersed uniformly in the upper region of MMC layers. The average hardness of LSA layers by CO₂ laser and pulsed Nd:YAG laser is 859 HV_0.2 and 727 HV_0.2, respectively. The dry sliding wear testing shows the wear resistance of ductile iron is significantly improved after LSA with multicarbide.

Keywords: Laser surface alloying; MMC layers; Multicarbide; Microstructure; Wear resistance

Properties of Cu film and Ti/Cu film on polyimide prepared by ion beam techniques by Jie Ran; Jizhong Zhang; Wenqing Yao; Yueteng Wei (pp. 7010-7017).

Cu film and Ti/Cu film on polyimide substrate were prepared by ion implantation and ion beam assisted deposition (IBAD) techniques. Three-dimension white-light interfering profilometer was used to measure thickness of each film. The thickness of the Cu film and Ti/Cu film ranged between 490nm and 640nm. The depth profile, surface morphology, roughness, adhesion, nanohardness, and modulus of the Cu and Ti/Cu films were measured by scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindenter, respectively. The polyimide substrates irradiated with argon ions were analyzed by scanning electron microscopy (SEM) and AFM. The results suggested that both the Cu film and Ti/Cu film were of good adhesion with polyimide substrate, and ion beam techniques were suitable to prepare thin metal film on polyimide.

Keywords: PACS; 52.77.Dq; 68.55.Jk; 68.35.Np; 68.60.WmMetal film; Polyimide; Ion implantation; Ion beam assisted deposition; Adhesion

Surface characteristic of stainless steel sheet after pulsed laser forming by L.J. Yang; J. Tang; M.L. Wang; Y. Wang; Y.B. Chen (pp. 7018-7026).

Laser forming is a non-contact and die-less forming technique of producing bending, spatial forming, modifying and adjusting the curvature of the metallic sheet by using the controlled laser beam energy. One of the problems in laser forming is controlling the characteristic of laser scanned surface. The aim of the investigation is to explore the relation between the surface behaviors of heat affected zone (HAZ) scanned by pulse laser and the pulse parameters of the laser. This paper illustrated the fundamental theory of pulsed laser affected material, and pays attention to the microstructure, micro-hardness and the anticorrosion in the HAZ generated by the laser scanning. Metallographic microscope, scanning electron microscope (SEM), micro-hardness testing system are used to examine the surface characteristics. The work presented in this paper is beneficial to understand the mechanism of pulse laser affect to materials and improve controlling the surface behaviors scanned by pulsed laser.

Keywords: Heat affected zone (HAZ); Microstructure; Micro-hardness; Pulse parameter; Laser forming

Influence of the hydrothermal temperature and pH on the crystallinity of a sputtered hydroxyapatite film by K. Ozeki; H. Aoki; T. Masuzawa (pp. 7027-7031).

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the sputtered films were crystallized under hydrothermal conditions at 110–170°C at pH values of 7.0 and 9.5. The crystallite size, the remnant film thickness, and the surface morphology of the films were observed using X-ray diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy, respectively.The crystallite size increased with the process temperature, and reached 123.6nm (pH 9.5 and 170°C) after 24h. All of the crystallite sizes of the film treated at pH 9.5 were higher than those treated at pH 7.0 at each process temperature. The film treated at pH 9.5 retained more than 90% of the initial film thickness at any process temperature. The ratio of the film treated at pH 7.0 did not reached 90% at less than 150°C, and tended to increase with the process temperature.

Keywords: Hydroxyapatite; Sputtering; Hydrothermal; Crystallinity

The effect of Ar flow rate in the growth of SiGe:H thin films by PECVD by Zeguo Tang; Wenbin Wang; Desheng Wang; Dequan Liu; Qiming Liu; Min Yin; Deyan He (pp. 7032-7036).

In this article, by investigating the influence of Ar flow rate on deposition rate and structural properties of hydrogenated silicon germanium (SiGe:H) films, we showed that the addition of Ar in the diluted gas efficiently improve the deposition rate and crystallinity due to an enhanced dissociation of source gases and bombardment on growth surface. The hydrogen content and SE results suggest that the defect density and void volume fraction increases with increasing Ar flow rate, which is attributed to the injection of higher energy Ar⁺ ions into the film led to a displacement of the atoms and an increased possibility of argon being trapped with the films. The optoelectronic properties are investigated by absorption coefficient and dark conductivity measurements and a reasonable explanation is presented.

Keywords: PACS; 7360F; 7820D; 8115HSiGe:H thin films; PECVD; Ar diluted gas; Optoelectronic properties

Synthesis of highly stable silver colloids stabilized with water soluble sulfonated polyaniline by Yu.A. Krutyakov; A.A. Kudrinsky; A.Yu. Olenin; G.V. Lisichkin (pp. 7037-7042).

A simple technique was developed for the synthesis of silver nanoparticles (NPs) in an aqueous medium using water soluble sulfonated polyaniline as a new non-covalent effective stabilizer. The narrow size distribution of the NPs was achieved through the synthesis. In neutral and basic solutions the as-prepared silver NPs demonstrated resistance toward aggregation over several months and at least a few days at pH 1. The versatility of the procedure was demonstrated also for the preparation of gold nanoparticles. Transmission electron microscopy with electron microdiffraction, UV–vis spectroscopy, XRD, XPS and FTIR analyses were used to characterize the structure and chemical composition of as obtained silver NPs.

Keywords: Silver nanoparticles; Sulfonated polyaniline; Chemical stability; Water soluble

Wetting and evaporation behaviors of molten Mg on partially oxidized SiC substrates by Dan Zhang; Ping Shen; Laixin Shi; Qiaoli Lin; Qichuan Jiang (pp. 7043-7047).

The wetting and evaporation behaviors of molten Mg drops on pressureless-sintered SiC surfaces were studied in a flowing Ar atmosphere at 973–1173K by an improved sessile drop method. The initial contact angles are between 83° and 76°, only mildly depending on temperature. The formation of a ridge at the triple junction as a result of reaction between molten Mg and the SiO₂ film on the SiC surface pins the triple line and leads to a constant contact diameter mode during the entire evaporation process. Moreover, the diffusion coefficients of the Mg vapor at different temperatures were evaluated based on a simple model.

Keywords: Wetting; Evaporation; Mg; Diffusion

Functionalization of carbon nanotubes with silver clusters by Jelena Cveticanin; Aleksandra Krkljes; Zorica Kacarevic-Popovic; Miodrag Mitric; Zlatko Rakocevic; Djordje Trpkov; Olivera Neskovic (pp. 7048-7055).

In this paper, an advanced method of one-step functionalization of single and multi walled carbon nanotubes (SWCNTs and MWCNTs) using γ-irradiation was described. Two synthesis procedures, related with different reduction species, were employed. For the first time, poly(vinyl alcohol) PVA is successfully utilized as a source to reduce silver (Ag) metal ions without having any additional reducing agents to obtain Ag nanoparticles on CNTs. The decoration of carbon nanotubes with Ag nanoparticles takes place through anchoring of (PVA) on nanotube's surface. Optical properties of as-prepared samples and mechanism responsible for the functionalization of carbon nanotubes were investigated using UV–vis and FTIR spectroscopy, respectively. Decorated carbon nanotubes were visualized using microscopic techniques: transmission electron microscopy and scanning tunneling microscopy. Also, the presence of Ag on the nanotubes was confirmed using energy dispersive X-ray spectroscopy. This simple and effective method of making a carbon nanotube type of composites is of interest not only for an application in various areas of technology and biology, but for investigation of the potential of radiation technology for nanoengineering of materials.

Keywords: Carbon nanotubes; Functionalization; Silver clusters

Fabrication of hydroxyapatite and TiO₂ nanorods on microarc-oxidized titanium surface using hydrothermal treatment by Ho-Jun Song; Ji-Woo Kim; Min-Suk Kook; Won-Jin Moon; Yeong-Joon Park (pp. 7056-7061).

AC-type microarc oxidation (MAO) and hydrothermal treatment techniques were used to enhance the bioactivity of commercially pure titanium (CP-Ti). The porous TiO₂ layer fabricated by the MAO treatment had a dominant anatase structure and contained Ca and P ions. The MAO-treated specimens were treated hydrothermally to form HAp crystallites on the titanium oxide layer in an alkaline aqueous solution (OH-solution) or phosphorous-containing alkaline solution (POH-solution). A small number of micro-sized hydroxyapatite (HAp) crystallites and a thin layer composed of nano-sized HAps were formed on the Ti-MAO-OH group treated hydrothermally in an OH-solution, whereas a large number of micro-sized HAp crystallites and dense anatase TiO₂ nanorods were formed on the Ti-MAO-POH group treated hydrothermally in a POH-solution. The layer of bone-like apatite that formed on the surface of the POH-treated sample after soaking in a modified simulated body fluid was thicker than that on the OH-treated samples.

Keywords: Titanium; Hydroxyapatite; Nanorod; Microarc oxidation; Hydrothermal treatment; Bone-like apatite

Preparation and photo-induced superhydrophilicity of composite TiO₂–SiO₂–In₂O₃ thin film by A. Eshaghi; M. Pakshir; R. Mozaffarinia (pp. 7062-7066).

In this work, TiO₂–SiO₂–In₂O₃ composite thin films on glass substrates were prepared by the sol–gel dip coating process. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. UV–vis spectrophotometer was used to measure the transmittance spectra of thin films. The water contact angle (WCA) of thin films during UV/vis irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicated that fabrication of composite film has a significant effect on transmittance and superhydrophilicity of TiO₂ films.

Keywords: Sol–gel processes; TiO; ₂; Superhydrophilicity

Preparation and characterization of SnO₂ nanoparticles using high power pulsed laser by M.A. Gondal; Q.A. Drmosh; T.A. Saleh (pp. 7067-7070).

Tin dioxide (SnO₂) nanoparticles having 3nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO₂ crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV–vis absorption spectral studies showed a peak at 240nm. FTIR spectrum showed a band in the range of 400–700cm⁻¹ which was assigned to Sn–O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO₂ nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613eV respectively.

Keywords: SnO; ₂; Nanoparticles; Characterization; Optical properties; Laser ablation

Polypropylene modified with 2-hydroxyethyl acrylate-g-2-methacryloyloxyethyl phosphorycholine and its hemocompatibility by Jie Zhao; Qiang Shi; Ligang Yin; Shifang Luan; Hengchong Shi; Lingjie Song; Jinghua Yin; Paola Stagnaro (pp. 7071-7076).

Polypropylene (PP) was modified with 2-hydroxyethyl acrylate (HEA) by solution radical grafting to introduce active hydroxyl groups on polypropylene backbone (PP-g-HEA). Then the biomimic monomer, 2-methacryloyloxyethyl phosphorycholine (MPC), was grafted onto the surface of PP-g-HEA film (PP-g-HEA-g-MPC) by redox graft polymerizations with ceric(IV) ammonium nitrate as an initiator. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed that the HEA and MPC were introduced onto PP molecular chains and the copolymer, PP-g-HEA-g-MPC were formed. The water contact angle measurements demonstrated that the final modified PP film exhibited a better hydrophilic surface compared to the neat PP film. The platelets adhesion on the neat PP, PP-g-HEA and PP-g-HEA-g-MPC film was examined by scanning electron microscopy (SEM). It was found that a large number of platelets were adhered and activated on the surface of neat PP and PP-g-HEA films, while the number of platelets on PP-g-HEA-g-MPC surface was decreased remarkably. The result revealed that the introduction of poly(MPC) onto the PP surface improved the hemocompatibility of PP substantially.

Keywords: Hemocompatibility; Redox polymerization; 2-Hydroxyethyl acrylate; 2-Methacryloyloxyethyl phosphorylcholine

Effect of citric acid on photoelectrochemical properties of tungsten trioxide films prepared by the polymeric precursor method by Wenzhang Li; Jie Li; Xuan Wang; Jun Ma; Qiyuan Chen (pp. 7077-7082).

Effect of citric acid (CA) on microstructure and photoelectrochemical properties of WO₃ films prepared by the polymeric precursor method was investigated. The obtained materials were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The results showed that samples prepared with adding different amounts of citric acid had a pure phase of cubic. The addition of citric acid could significantly increase the particle size and change the surface of WO₃ films. The photoelectrochemical measurements were performed using a standard three-electrode system cell. The films prepared from mass ratios of CA/PEG ( R=0, 0.2, 0.4, 0.6 and 1) showed 1.0, 1.4, 1.7, 2.1 and 0.9mAcm⁻² at 1.2V under illumination with a 500W xenon lamp ( I₀=100mW/cm²), respectively.

Keywords: Citric acid; WO; ₃; thin films; Polymeric precursor method; Photoelectrochemistry

Structural properties and diffusion processes of the Cu₃Au (001) surface by Fang Wang; Jian-Min Zhang; Yan Zhang; Vincent Ji (pp. 7083-7087).

The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu₃Au (001) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu₃Au (001) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer.

Keywords: Cu; ₃; Au; Surface relaxation; Surface diffusion; MAEAM

Room temperature synthesis of water-repellent polystyrene nanocomposite coating by Yonggang Guo; Dong Jiang; Xia Zhang; Zhijun Zhang; Qihua Wang (pp. 7088-7090).

A stable superhydrophobic polystyrene nanocomposite coating was fabricated by means of a very simple and easy method. The coating was characterized by scanning electron microscopy and X-ray photoelectron spectrum. The wettability of the products was also investigated. By adding the surface-modified SiO₂ nanoparticles, the wettability of the coating changed to water-repellent superhydrophobic, not only for pure water, but also for a wide pH range of corrosive liquids. The influence of the drying temperature and SiO₂ content on the wettability of the nanocomposite coating was also investigated. It was found that both factors had little or no significant effect on the wetting behavior of the coating surface.

Keywords: Coating; Superhydrophobicity; Water contact angle

Growth dynamics of pulsed laser deposited indium oxide thin films: a substrate dependent study by Neeti Tripathi; Shyama Rath; V. Ganesan; R.J. Choudhary (pp. 7091-7095).

Indium oxide films are deposited by pulsed laser deposition in the presence of oxygen atmosphere, on different substrates, namely GaAs, Si, quartz, and glass. The structural, morphological, and interface characteristics are studied. Cubic In₂O₃ phase is confirmed by high resolution X-ray diffraction measurements. While the films on Si, glass, and quartz substrates are polycrystalline, the films on GaAs exhibit a preferred orientation along (222) plane. The structure and crystalline nature of the films are also confirmed by Raman spectroscopy. Furthermore, Raman spectra show the appearance of gallium oxide modes arising due to Ga diffusion from the substrate. The morphology of the films deposited on different substrates is studied by atomic force microscopy and rms roughness values are obtained. A two-dimensional power spectral density analysis has been used to calculate the growth exponent ( α). A value of α>1 ( α<1) for films grown on GaAs/Si (quartz/glass) substrates suggests that the growth on crystalline substrates is governed by the linear diffusion model, whereas the growth on amorphous substrates follows the dynamic scaling behaviour. UV–visible study shows a high optical transmittance of >90% and a band gap value of 3.64 and 3.79eV for the films deposited on quartz and glass substrates, respectively.

Keywords: Indium oxide; Pulsed laser deposition; XRD; Raman spectroscopy; AFM; Power spectral density

Deposition of Ag nanostructures on TiO₂ thin films by RF magnetron sputtering by J. Zuo (pp. 7096-7101).

Ag nanostructures on TiO₂ films were deposited by RF magnetron sputtering under variable deposition parameters, such as DC potential, RF-power and total pressure. The concentration, shape, and distribution of the deposited nanostructures and continuous Ag films on thin films of TiO₂ can be tailored by careful variation of the deposition parameters. Controllable clusterlike, islandlike and film Ag structures on TiO₂ film were obtained, respectively. DC potential was found as an appropriate parameter to tailor the change of Ag nanostructure and the overall Ag amount. The compositions, nanostructures and morphologies of nanocomposite films appreciably influence the optical response.

Keywords: PACS; 68.55.J−; 81.15.Cd; 64.70.Nd; 78.67.BfTiO; ₂; Nanocomposite film; RF magnetron sputtering; Ag nanostructure

Bioactive glass thin films deposited by magnetron sputtering technique: The role of working pressure by G.E. Stan; D.A. Marcov; I. Pasuk; F. Miculescu; S. Pina; D.U. Tulyaganov; J.M.F. Ferreira (pp. 7102-7110).

Bioglass coatings were prepared by radio frequency magnetron sputtering deposition at low temperature (150°C) onto silicon substrates. The influence of argon pressure values used during deposition (0.2Pa, 0.3Pa and 0.4Pa) on the short-range structure and biomineralization potential of the bioglass coatings was studied. The biomineralization capability was evaluated after 30 days of immersion in simulated body fluid. SEM-EDS, XRD and FTIR measurements were performed. The tests clearly showed strong biomineralization features for the bioglass films. The thickness of the chemically grown hydroxyapatite layers was more than twice greater for the BG films deposited at the highest working pressure, in comparison to those grown on the films obtained at lower working pressures. The paper attempts to explain this experimental fact based on structural and compositional considerations.

Keywords: Magnetron sputtering; Bioglass thin films; SBF; Biomineralization; Carbonated hydroxyapatite

Changing the adsorption capacity of coal-based honeycomb monoliths for pollutant removal from liquid streams by controlling their porosity by José M. Gatica; Sanae Harti; Hilario Vidal (pp. 7111-7117).

Coal-based honeycomb monoliths extruded using methods developed for ceramic materials have been used to retain methylene blue and p-nitrophenol from aqueous solutions. The influence of the filters’ thermal treatment on their textural properties and performance as adsorbents was examined. Characterization by N₂ physisorption, mercury porosimetry and scanning electron microscopy along with adsorption tests under dynamic conditions suggest that, depending on the pollutant and its initial concentration, it can be more convenient to previously submit the monoliths to a simple carbonization or to an additional activation, with or without preoxidation, as a consequence of their different resulting pore structures. Infrared spectroscopy indicates that their different adsorption behaviour seems not to be related to differences in their surface chemical groups. In addition, axial crushing tests show that the monoliths have an acceptable mechanical resistance for the application investigated.

Keywords: Coal; Honeycomb monoliths; Adsorption; Porosity; Water pollutant removal

Two routes to polycrystalline CoSi₂ thin films by co-sputtering Co and Si by Yukie Tsuji; Yoshiko Tsuji; Shinichi Nakamura; Suguru Noda (pp. 7118-7124).

Two processes for the fabrication of polycrystalline CoSi₂ thin films based on the codeposition of Co and Si by sputtering were studied and compared. The first process involved “annealing after deposition”, where Co and Si are codeposited at ambient temperature and then crystallized by annealing. This process yielded randomly oriented plate-like CoSi₂ grains with a grain size that is governed by the nanostructure of the as-deposited film. Polycrystalline CoSi₂ thin films were obtained at a process temperature of 170°C, which was much lower than the annealing temperature of 500°C needed for Co/Si bilayers. The second process involved “heating during deposition”, where Co and Si are codeposited on heated substrates. This process yielded CoSi₂ grains with a columnar structure, and the grain size and degree of (111) orientation are temperature dependent. The sheet resistance of the resulting films was determined by the preparation temperature regardless of the deposition process used, i.e. “annealing after deposition” or “heating during deposition”. Temperatures of 500°C and higher were needed to achieve CoSi₂ resistivity of 40μΩcm or lower for both processes.

Keywords: CoSi; ₂; Sputtering; Crystal growth; Transmission electron microscopy; X-ray diffraction

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO₂ hollow nanorod arrays with enhanced photocatalytic activity by Min Wu; Beifang Yang; Yan Lv; Zhengping Fu; Jiao Xu; Ting Guo; Yongxun Zhao (pp. 7125-7130).

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N–THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet–vis (UV–vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).

Keywords: Ag loading and N doping; Phase transformation; TiO; ₂; hollow nanorod arrays; Liquid phase deposition (LPD); Photocatalysis; Methylene blue (MB)

Self-assembled bilayers based on organothiol and organotrimethoxysilane on zinc platform by François Berger; Joseph Delhalle; Zineb Mekhalif (pp. 7131-7137).

This study describes the formation of a bilayer system developed on electrodeposited zinc. In a first step, a monolayer of 11-mercapto-1-undecanol is grafted on zinc, optimization of the conditions of elaboration have been performed. In a second step, organotrimethoxysilane have been grafted on the zinc modified with the hydroxyl terminated self-assembled monolayer (SAM) to finalize the bilayer system. X-ray photoelectron spectroscopy (XPS), polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) and contact angle measurements are used to characterize each step of modification. An electrochemical evaluation of the different created systems is carried out by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and scanning vibrating electrode technique (SVET). The impact of the modification of zinc using SAM and self-assembled bilayer (SAB) on the electrochemical activity of the surface is highlighted.

Keywords: Self-assembled bilayer; Zinc; Organothiol; Organosilane

In situ deposition behavior of silica-based layers and its effect on thermal degradation of IN713 turbine blades during operation of a micro-gas turbine by Min Tae Kim; Doo Soo Kim; Won Young Oh (pp. 7138-7145).

This study examined the in situ deposition behavior of silica-based layers on IN713 turbine blades during the operation of a 13kgf-class gas turbine at a rotation speed of 20,000/min as well as its effect on the degradation of the metallic substrate. Tetraethylorthosilicate (TEOS) was mixed with the fuel (liquid petroleum gas, LPG) and burned to generate silica-based coating precursors for deposition from the flame. Two deposition conditions were adopted. For condition 1 (C1), the silicon-to-carbon ratio in the mixed fuel was set at 0.1mol% for the first 5min and at zero mol% for the final 95min in a 100-min operation. For condition 2 (C2), the ratio was set at 0.005mol% during the entire 100min operation. The total TEOS feed was the same under both conditions. C1 resulted in a rather uniform and thicker (5–10μm on the pressure side) porous silica-based coating on the blade than C2. The in situ deposited layer of C1 was well preserved on the blade and protected the underlying metallic substrate from oxidation during the entire 100min operation. The layer on the C2 blades was ∼5μm thick at the region near to root, but was too thin in the other areas on the blade to be protective. The early build-up of a porous layer to an effective thickness on the blades produced a thermal barrier toward the substrate as well as a diffusion barrier toward the oxidizing elements during operation.

Keywords: Nickel-based superalloy; Micro-gas turbine; In situ coating; Silica; Tetraethylorthosilicate; Oxidation

Passivation of aluminum with alkyl phosphonic acids for biochip applications by Sachin Attavar; Mohit Diwekar; Matthew R. Linford; Mark A. Davis; Steve Blair (pp. 7146-7150).

Self-assembly of decylphosphonic acid (DPA) and octadecylphosphonic acid (ODPA) was studied on aluminum films using XPS, ToF-SIMS and surface wettability. Modified aluminum films were tested for passivation against silanization and subsequent oligonucleotide attachment. Passivation ratios of at least 450:1 compared to unprotected aluminum were obtained, as quantified by attachment of radio-labeled oligos.

Keywords: Biosenor; DNA metallic microarray; Phosphonic acid self-assembled monolayer

Multifractal analysis of fracture morphology of poly(ethylene-co-vinyl acetate)/carbon black conductive composite by Yong-Hai Zhang; Bao-Feng Bai; Jing-Bo Chen; Chang-Yu Shen; Jian-Qiang Li (pp. 7151-7155).

In this paper, based on scanning electron microscope (SEM), the fracture morphology of poly(ethylene-co-vinyl acetate)/carbon black (EVA/CB) conductive composite with various cross-linkers 2,4-di(2-phenylisopropyl) phenol (DCP) contents were analysed by multifractal analysis. The relationship among the multifractal spectrum, cross-linker DCP content, the fracture morphology, fracture process and some mechanical property were discussed. The results showed that the larger the width Δ α (Δ α= α_max− α_min) of the multifractal spectra f( α), the more nonuniform the fracture surface morphology, in other words, the more the roughness. Moreover, the width Δ α (Δ α= α_max− α_min) of the multifractal spectra f( α) is the result of competition between ductile fracture and brittle fracture. Also, some mechanical property will correspondingly change when various cross-linker DCP contents were added. Multifractal analysis showed that the spectrum width Δ α (Δ α= α_max− α_min) of the multifractal spectra f( α) could be used to characterize the surface morphology and mechanical property of EVA/CB conductive composite, quantitatively.

Keywords: Multifractal spectrum; EVA/CB conductive composite; Cross-linker DCP; Fracture morphology; Mechanical property; Fracture process

Surface acoustic wave device properties of (B, Al)N films on 128° Y– X LiNbO₃ substrate by Jen-Hao Song; Jow-Lay Huang; Sean Wu; Sheng-Chang Wang; Jian-Long Ruan; Ding-Fwu Lii (pp. 7156-7159).

A c-axis orientated aluminium nitride (AlN) film on a 128° Y– X lithium niobate (LiNbO₃) surface acoustic wave (SAW) device which exhibit a large electromechanical coupling coefficient ( k²) and a high SAW velocity property, is needed for future communication applications. In this study, a c-axis orientated (B, Al)N film (with 2.6at.% boron) was deposited on a 128° Y– X LiNbO₃ substrate by a co-sputtering system to further boost SAW device properties. The XRD and TEM results show that the (B, Al)N films show highly aligned columns with the c-axis perpendicular to the substrate. The hardness and Young's modulus of (B, Al)N film on 128° Y– X LiNbO₃ substrates are at least 17% and 7% larger than AlN films, respectively. From the SAW device measurement, the operation frequency characteristic of (B, Al)N film on 128° Y– X LiNbO₃ is higher than pure AlN on it. The SAW velocity also increases as (B, Al)N film thickness increases (at fixed IDT wavelength). Furthermore, the k² of (B, Al)N on the IDT/128° Y– X LiNbO₃ SAW device shows a higher value than AlN on it.

Keywords: Lithium niobate; Aluminum nitride; Boron nitride; Surface acoustic wave

Study of AFM-based nanometric cutting process using molecular dynamics by Peng-zhe Zhu; Yuan-zhong Hu; Tian-bao Ma; Hui Wang (pp. 7160-7165).

Three-dimensional molecular dynamics (MD) simulations are conducted to investigate the atomic force microscope (AFM)-based nanometric cutting process of copper using diamond tool. The effects of tool geometry, cutting depth, cutting velocity and bulk temperature are studied. It is found that the tool geometry has a significant effect on the cutting resistance. The friction coefficient (cutting resistance) on the nanoscale decreases with the increase of tool angle as predicted by the macroscale theory. However, the friction coefficients on the nanoscale are bigger than those on the macroscale. The simulation results show that a bigger cutting depth results in more material deformation and larger chip volume, thus leading to bigger cutting force and bigger normal force. It is also observed that a higher cutting velocity results in a larger chip volume in front of the tool and bigger cutting force and normal force. The chip volume in front of the tool increases while the cutting force and normal force decrease with the increase of bulk temperature.

Keywords: Molecular dynamics; Nanometric cutting; AFM

The effect of electric current and surface oxidization on the growth of Sn whiskers by Kyung-Seob Kim; Jun-Mo Yang; Jae-Pyoung Ahn (pp. 7166-7174).

Electric current was applied on pure Sn-plated leadframes to evaluate the effects of current-induced stress on the growth of Sn whiskers. The samples were stored at room temperate and 55°C/85% relative humidity (RH) conditions with an induced current range of 0.1 A to 0.5 A. The samples stored at the room temperature did not grow the whiskers at any of the current conditions until 3000 hrs. As the current flow increased, irregular intermetallic compounds (IMCs) grew at the interface between the Sn finish and Cu substrate. However, various lengths of columnar and bent whiskers were observed under all current conditions, after exposure to 55°C/85% RH conditions for 1000hours. At the same temperature, the higher current levels showed longer whiskers than lower current levels. The Sn oxide had the α-SnO₂ structure of the rutile phase which was non-uniformly formed on the surface of the Sn finish. The grain size of the SnO₂ was estimated to be several nanometers. The SnO₂ film was up to a thickness of ∼23nm on the Sn whisker surface stored at 55°C/85% RH conditions for 3000hours.

Keywords: Tin whisker; Current; Tin oxide; Intermetallic compounds; Transmission electron microscopy

Structure and surface characterization of ZrO₂-Y₂O₃-Cr₂O₃ system by I.A. Yashchishyn; A.M. Korduban; T.E. Konstantinova; I.A. Danilenko; G.K. Volkova; V.A. Glazunova; V.O. Kandyba (pp. 7175-7177).

3-mol% Y₂O₃ and 0.3 to 3-mol % Cr₂O₃ co-doped ZrO₂ nanopowders were synthesized using co-precipitation technique and investigated by terms of X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Structural analysis shows no significant impact of chromium on powders structure except of presence of small amount of m-phase. Surface analysis reveals segregation of yttrium and chromium atoms to the surface along with surface enrichment by oxygen that can be attributed to residual water. Chromium surface atoms present in three oxidation states with catalytically active Cr²⁺ sites possibly controlling m-phase appearance through lattice distortion.

Keywords: PACS; 61.46.Df; 79.60.Jv; 81.07.Wxnanopowders; zirconium; chromium; yttrium; XPS; segregation; oxidation states

X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings by K. McLeod; S. Kumar; N.K. Dutta; R.St.C. Smart; N.H. Voelcker; G.I. Anderson (pp. 7178-7185).

Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13h without SBF replenishment; (ii) thicker HA coatings about 1μm in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).

Keywords: Hydroxyapatite coatings; Simulated body fluid; Growth kinetics; X-ray photoelectron spectroscopy; Bone implants

Effects of oxygen content and postdeposition annealing on the physical and electrical properties of thin Sm₂O₃ gate dielectrics by Tung-Ming Pan; Chun-Chin Huang (pp. 7186-7193).

In this paper, we describe the physical properties and electrical characteristics of thin Sm₂O₃ dielectric films deposited on Si (100) by means of rf reactive sputtering. The structural and morphological features of these films were studied, as a function of the growth conditions (three various argon-to-oxygen flow ratios: 10/15, 15/10 and 20/5, and temperature from 600 to 800°C), by x-ray diffraction, atomic force microscopy, and x-ray photoelectron spectroscopy. It is found that Sm₂O₃ dielectric prepared under 15/10 flow ratio and annealed at 700°C exhibits a thinner capacitance equivalent thickness and excellent electrical properties, including the interface trap density, the hysteresis and frequency dispersion in the capacitance–voltage curves. This condition is attributed to the reduction of the interfacial SiO₂ and silicate formation, and the small of surface roughness due to the optimization of oxygen in the Sm₂O₃ film.

Investigation the effects of nano golds on the fluorescence properties of the sectorial poly(amidoamine) (PAMAM) dendrimers by Zhijuan Zhang; Fei Rong; Shuhua Niu; Yibing Xie; Yong Wang; Haiyan Yang; Degang Fu (pp. 7194-7199).

The influence of nano golds on fluorescence properties of sectorial Polyamidoamine dendrimers (G4 s-PAMAM) was investigated in this paper. It was found that gold nanoparticles (GNPs) with definite surface plasmon absorption can quench the fluorescence of G4 s-PAMAM dendrimers. With the increasing of the concentration of GNPs, the fluorescence intensity of G4 s-PAMAM decreased correspondingly, and varied linearly at low concentration of GNPs. This phenomenon was owing to the fluorescence resonance energy transfer (FRET) between the dendrimers and GNPs. In contrast, the complex with smaller gold nanodots (GNDs) encapsulated in the interior of the G4 s-PAMAM presented greatly enhanced emission. Those results show that the size of nano golds may be used to adjust the fluorescence properties of sectorial PAMAM dendrimers and may extend potential applications of PAMAM dendrimers and nano golds.

Keywords: PAMAM; fluorescence; nano golds

Fabrication and characterization of magnetron sputtered arsenic doped p-type ZnO epitaxial thin films by Amit Kumar; Manoj Kumar; Beer Pal Singh (pp. 7200-7203).

Arsenic doped p-type ZnO thin films were grown on sapphire substrate by magnetron sputtering. As grown films reveal p-type conduction confirmed by Hall-effect and photoluminescence measurements. The p-type film with a hole concentration of 2.16× 10¹⁷ cm⁻³, mobility of 1.30cm²/V.s and resistivity of 22.29Ω-m were obtained at substrate temperature of 700°C. ZnO homojunction synthesized by in-situ deposition of As doped p-ZnO layer on Al doped n-ZnO layer showed p-n diode like characteristics. X-ray pole figure and Transmission Electron Microscope studies confirm epitaxial nature of the films. Photoluminescence results exhibit the peaks associated with donor acceptor pair emission.

Keywords: ZnO; As-doping; Sputtering; Epitaxial growth

Sn doping effects on the electro-optical properties of sol gel derived transparent ZnO films by Saliha Ilican; Mujdat Caglar; Yasemin Caglar (pp. 7204-7210).

Undoped and tin (Sn) doped ZnO films have been deposited by sol gel spin coating method. The Sn/Zn nominal volume ratio was 1, 3 and 5% in the solution. The effect of Sn incorporation on structural and electro-optical properties of ZnO films was investigated. All the films have polycrystalline structure, with a preferential growth along the ZnO (002) plane. The crystallite size was calculated using a well-known Scherrer's formula and found to be in the range of 26-16nm. X-ray diffraction patterns of the films showed that Sn incorporation leads to substantial changes in the structural characteristics of ZnO films. The SEM measurements showed that the surface morphology of the films was affected from the Sn incorporation. The highest average optical transmittance value in the visible region was belonging to the undoped ZnO film. The optical band gap and Urbach energy values of these films were determined. The absorption edge shifted to the lower energy depending on the Sn dopant. The shift of absorption edge is associated with shrinkage effect. The electrical conductivity of the ZnO film enhanced with the Sn dopant. From the temperature dependence of conductivity measurements, the activation energy of ZnO film increased with Sn incorporation.

Keywords: Sn doped ZnO; sol gel spin coating; structural properties; absorption edge; electrical conductivity

Natural rubber nanocomposites using polystyrene-encapsulated nanosilica prepared by differential microemulsion polymerization by Saowaroj Chuayjuljit; Anyaporn Boonmahitthisud (pp. 7211-7216).

In this study, nanocomposites of natural rubber (NR) and polystyrene (PS)-encapsulated nanosilica were prepared by latex compounding method. The nanolatex of PS-encapsulated silica was synthesized via in situ differential microemulsion polymerization. The resulted hybrid nanoparticles showed core-shell morphology with an average diameter of 40nm. The silica hybrid nanoparticles were subsequently used as filler for the NR nanocomposite. The properties of NR were found to be improved as a result of the incorporation of PS-encapsulated nanosilica at 3 and 3–9 parts per hundred rubber (phr) for tensile strength and modulus at 300% strain, respectively, except the elongation at break, and up to 9phr for flammability. The results from dynamic mechanical analyzer showed that the elastic properties of NR near the glass transition temperature increased with the inclusion of increasing concentration of the PS-encapsulated nanosilica, causing by the semi-interpenetrating nanostructure in the NR nanocomposites.

Keywords: Natural rubber; Polystyrene-encapsulated nanosilica; Differential microemulsion polymerization; Mechanical properties; Flammability

A study on photo-generated charges property in highly ordered TiO₂ nanotube arrays by Yu Zhang; Dejun Wang; Shan Pang; Yanhong Lin; Tengfei Jiang; Tengfeng Xie (pp. 7217-7221).

In this study TiO₂ nanotube arrays were fabricated by potentiostatic anodization of titanium sheet. The X-ray diffraction (XRD) pattern and field emission scanning electron microscopy (FE-SEM) image indicated the TiO₂ nanotube arrays were of pure anatase form and highly ordered. The properties of the photo-generated charges in the nanotube arrays were investigated by transient photovoltage (TPV) technique and surface photovoltage (SPV) technique based on lock-in amplifier with dc bias, in comparison with the commercial powder derived film. The separation processes of the photo-induced charges in the system of TiO₂ nanotubes on Ti have been demonstrated to be correlated with the incident light intensity, surface trapping states, and the interfacial electric field between Ti and TiO₂. The results also show that the highly ordered nanotube film could generate much stronger SPV responses under external electric field than the commercial powder derived film.

Keywords: Titania nanotube array; Photo-generated charge; Surface photovoltage

Microstructuring of fused silica by laser-induced backside wet etching using picosecond laser pulses by M. Ehrhardt; G. Raciukaitis; P. Gecys; K. Zimmer (pp. 7222-7227).

The laser-induced backside wet etching (LIBWE) is an advanced laser processing method used for structuring transparent materials. LIBWE with nanosecond laser pulses has been successfully demonstrated for various materials, e.g. oxides (fused silica, sapphire) or fluorides (CaF₂, MgF₂), and applied for the fabrication of microstructures. In the present study, LIBWE of fused silica with mode-locked picosecond ( t_p=10ps) lasers at UV wavelengths ( λ₁=355nm and λ₂=266nm) using a (pyrene) toluene solution was demonstrated for the first time. The influence of the experimental parameters, such as laser fluence, pulse number, and absorbing liquid, on the etch rate and the resulting surface morphology were investigated. The etch rate grew linearly with the laser fluence in the low and in the high fluence range with different slopes. Incubation at low pulse numbers as well as a nearly constant etch rate after a specific pulse number for example were observed. Additionally, the etch rate depended on the absorbing liquid used; whereas the higher absorption of the admixture of pyrene in the used toluene enhances the etch rate and decreases the threshold fluence. With a λ₁=266nm laser set-up, an exceptionally smooth surface in the etch pits was achieved. For both wavelengths ( λ₁=266nm and λ₂=355nm), LIPSS (laser-induced periodic surface structures) formation was observed, especially at laser fluences near the thresholds of 170 and 120mJ/cm², respectively.

Keywords: PACS; 81.55.Xi; 81.65.Cf; 42.62.Cf; 79.20.Ds; 81.05.JLaser; Fused silica; Etching; LIBWE; Picosecond; Toluene; Structuring

New bioactive hybrid material of nano-hydroxyapatite based on N-carboxyethylchitosan for bone tissue engineering by Yan Lu; Aiping Zhu; Wanpeng Wang; Hongchan Shi (pp. 7228-7233).

N-carboxyethylchitosan/nano-hydroxyapatite (NCECS/HA) composite films were fabricated and their potential applications in guiding bone regeneration were investigated in terms of their in vitro cellular activity. Fourier ransform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to investigate the structure and composition of the composite film. Field Emission scanning electron microscopy (FESEM) revealed that HA nanoparticles were dispersed homogeneously in NCECS matrix. The composite film has sufficient mechanical properties for tissue engineering scaffold. The composite film was found to have better cartilage cell adhesion and growth than pure NCECS film.

Keywords: Nano-hydroxyapatite; N-carboxyethylchitosan; Composite; Cartilage cells

Combined effects of hydrostatic pressure and electric field on the donor binding energy and polarizability in laterally coupled double InAs/GaAs quantum-well wires by E. Tangarife; C.A. Duque (pp. 7234-7241).

This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a nonlinear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum well wires.

Keywords: PACS; 73.61.Ey; 62.50.-p; 78.67.Lt

Activation energy of water vapor and oxygen transmission through TiN_xO_y/PET gas barrier films by M.C. Lin; M.-J. Chen; L.-S. Chang (pp. 7242-7245).

Titanium oxynitride (TiN_xO_y) films were deposited on polyethylene terephthalate (PET) substrates by means of a reactive radio frequency (RF) magnetron sputtering system in which the power density was the varied parameter. Experimental results show that the deposited TiN_xO_y films with a thickness of about 55nm have similar contents of TiN, TiN_xO_y and TiO₂ bonds, although they are deposited at different power densities. The TiN_xO_y films deposited at a lower power density have fewer internal defects and grain boundaries and possess higher activation energy and a lower rate of water vapor and oxygen transmission through TiN_xO_y/PET films.

Keywords: Titanium oxynitride film; Reactive magnetron sputtering; Polyethylene terephthalate; Gas permeation; Activation energy

Kinetics, equilibrium and thermodynamics of the sorption of tetrabromobisphenol A on multiwalled carbon nanotubes by Ismail I. Fasfous; Enas S. Radwan; Jamal N. Dawoud (pp. 7246-7252).

Tetrabromobisphenol A (TBBPA) is widely used as a flame retardant and is relatively persistent in the environment. This study reports the sorption kinetics, equilibrium and thermodynamics of TBBPA on multiwalled carbon nanotubes (MWCNTs). The equilibrium sorption capacity has been significantly improved by increasing the initial TBBPA concentration and contact time. In alkaline conditions and at high temperatures, a large reduction of TBBPA uptake was observed. The equilibrium between TBBPA and MWCNTs was achieved in approximately 60min with removal of 96% of the TBBPA. The sorption kinetics were well described by a pseudo-second-order rate model, while both Langmuir and Freundlich models described the sorption isotherms well at different temperatures. Thermodynamic parameters suggested that the sorption of TBBPA is exothermic and spontaneous at the temperatures studied.

Keywords: Sorption; Thermodynamic; Tetrabromobisphenol A; Carbon nanotube; Flame retardants

Sliding behavior of oil droplets on nanosphere stacking layers with different surface textures by Chien-Te Hsieh; Fang-Lin Wu; Wei-Yu Chen (pp. 7253-7259).

Two facile coating techniques, gravitational sediment and spin coating, were applied for the creation of silica sphere stacking layers with different textures onto glass substrates that display various sliding abilities toward liquid drops with different surface tensions, ranged from 25.6 to 72.3 mN/m. The resulting silica surface exhibits oil repellency, long-period durability>30 days, and oil sliding capability. The two-tier texture offers a better roll-off ability toward liquid drops with a wide range of γ_L, ranged from 30.2 to 72.3 mN/m, i.e., when the sliding angle (SA)<15°, the oil droplet start to roll off the surface. This improvement of sliding ability can be ascribed to the fact that the two-tier texture allows for air pockets (i.e., referred to as the Cassie state), thus favoring the self-cleaning ability. Taking Young–Duprè equation into account, a linearity relationship between sine SA and work of adhesion ( W_ad) appears to describe the sliding behavior within the W_ad region: 2.20–3.03 mN/m. The smaller W_ad, the easier drop sliding (i.e., the smaller SA value) takes place on the surfaces. The W_ad value ∼3.03 mN/m shows a critical kinetic barrier for drop sliding on the silica surfaces from stationary to movement states. This work proposes a mathematical model to simulate the sliding behavior of oil drops on a nanosphere stacking layer, confirming the anti-oil contamination capability.

Keywords: Sliding angle; Work of adhesion; Contact angle; Silica spheres; Oil repellency; Superhydrophobic behavior

Wetting of liquid droplets on two parallel filaments by Amol Bedarkar; Xiang-Fa Wu; Abe Vaynberg (pp. 7260-7264).

Droplet wetting on two parallel filaments may assume a barrel-shaped morphology or a liquid bridge depending upon the filament diameter and spacing, droplet volume, and contact angle. This paper is aimed to examine the dependency of droplet wetting length upon the above parameters. In the process, morphology of either a barrel-shaped droplet or a liquid bridge sitting on two parallel filaments is determined numerically by using surface finite element method (SFEM). Variation of wetting length with contact angle is examined at varying droplet volume, filament spacing, and droplet morphology. It is found that the droplet wetting length increases with decreasing filament spacing ratio as well as contact angle while it also increases with the growth of droplet volume. The dependency of wetting length upon contact angle behaves sensitive to filament spacing in the case of stable liquid bridges, while it exhibits nearly constant sensitivity to the contact angle in the case of barrel-shaped droplets. The quantitative relations yielded in this study can be considered as characteristic curves applicable for a variety of droplet-on-filament systems, particularly useful to wetting property characterization of filaments, micro liquid delivery, biological cell manipulation, etc.

Keywords: surface wetting; wetting length; droplets; filaments; contact angle

The structural formation of methylthiolate SAMs on Au(111) for short deposition times from solution by P. Mehring; A. Beimborn; C. Westphal (pp. 7265-7269).

Scanning tunnelling microscopy was used to investigate the structural formation of methylthiolate self-assembled monolayers on Au(111). SAMs were prepared by exposing the gold crystal to an ethanol–dimethyldisulfide solution for immersion times of 12 min, 12 h, and 24 h. After preparation the formation of a (4×3) rect. striped phase was found. For this phase, the immersion time is the key parameter determining the size and number of ordered domains. Annealing induced a phase transition leading to large domains in a(3×4) structure. The annealing temperature determines whether a mixed phase of both structures or only the(3×4) structure are formed. We find no influence of the immersion time on the formation of the second structure. A structure model is presented for both phases on the basis on the same building block containing two methylthiolate molecules and a gold ad-atom.

Keywords: PACS; 68.37.Ef; 68.43.Fg; 68.43.HnSelf-assembled monolayers; Alkanethiol; STM

Preparation and fluorescent sensing applications of novel CdSe–chitosan hybrid films by Huiyun Xia; Gang He; Junxia Peng; Weiwei Li; Yu Fang (pp. 7270-7275).

A novel CdSe–chitosan hybrid fluorescent film has been fabricated by dipping a chitosan film containing Cd(Ac)₂ into NaHSe aqueous solution under a nitrogen atmosphere at room temperature. It has been demonstrated that utilization of a chitosan film as a substrate prohibits the aggregation of the as formed CdSe micro-nano-particles, and enhances the sensing performance of the inorganic–organic hybrid film. It has been also revealed that the amount of CdSe embedded in the hybrid film can be altered by varying the initial concentration of Cd(Ac)₂. Importantly, the photoluminescence emission of the hybrid film is selectively sensitive to the presence of polyamines. Furthermore, the response is reversible. Accordingly, it is anticipated that the film may be developed into a polyamine sensor.

Keywords: CdSe; Polyamines; Chitosan; Hybrid films; Fluorescence sensing

A study of stitch line formation during high speed laser patterning of thin film indium tin oxide transparent electrodes by Paul M. Harrison; Nick Hay; Duncan P. Hand (pp. 7276-7284).

High speed laser patterning of indium tin oxide thin films on glass is part of the production method used to produce transparent conductive electrodes for plasma display panels. Such a design consists of rows of repeating electrode structures which cover the active area of the display. Whilst the patterning process for such electrode structures exceeds the industrial acceptance criteria there are certain features that are yet to be fully understood. The visible line that occurs in-between two adjacent laser processed areas, commonly known as a stitch line, is one such feature. Previously published research claimed that the stitch line was caused by incomplete removal of the thin film however experimental results presented within this paper demonstrate that this cannot be the case and show that the stitch line is formed by redeposition of the plume of ablated material within the area of overlap with the previous pulse, and that heating of the sample by the second pulse plays a key role in stitch line formation.

Keywords: ITO thin film; PDP transparent electrode; Laser patterning; Stitch line; Redeposition; Transparent conductive oxide

Oxygen pressure dependent interfacial polarization of perovskite oxide multilayers on Si substrates by Yingtang Zhang; Yiming Zhang; Xiaoming Feng; Xinqiang Yuan; Lei Fu; Taotao Ai (pp. 7285-7288).

The SrTiO₃/La_0.9Sr_0.1MnO₃ (STO/LSMO) multilayers were fabricated on n-Si (100) substrates using a computer-controlled laser molecular-beam epitaxy (MBE) technique at 1×10⁻²Pa and 2×10⁻⁴Pa oxygen partial pressures, respectively. The dielectric properties of the multilayers (MLs) were investigated. The differences of the dielectric properties of the two samples were explained by an impedance analysis technique, which indicates that the interfacial polarization has a close relationship with the oxygen pressure.

Keywords: PACS; 68.37.−d; 73.30.+y; 77.55f; 81.15.NpSTO/LSMO/Si; Interfacial polarization; Oxygen pressure; MBE

The interaction effects between adsorbed molecules in the Statistical Rate Theory approach to the kinetics of mixed-gas adsorption by Krzysztof Nieszporek; Tomasz Banach (pp. 7289-7299).

Kinetics of adsorption of single gases and their binary mixture on an energetically homogeneous surface are studied theoretically using the Statistical Rate Theory (SRT) of interfacial transport. Additionally, the influence of intermolecular interactions on the rate of adsorption is modeled using the Regular Adsorbed Solution Theory. The theoretical results are classified and assigned to different types of experimental conditions under which the changes of the adsorbate concentration near the adsorbing surface are considerable or they are negligible. Predictions of the theory are verified using adsorption data measured in real systems.

Keywords: Kinetics; Mixed-gas adsorption; Statistical Rate Theory

Element segregation on the surfaces of pure aluminum foils by Xinming Zhang; Jiancai Liu; Jianguo Tang; Li Li; Mingan Chen; Shengdan Liu; Bing Zhu (pp. 7300-7304).

The surface segregation trend of trace elements in pure aluminum foils was investigated by density functional theory. The model of nine-layer Al(100) slab substituted partially by trace element atoms was proposed for calculating surface segregation energy. The calculating results show that (i) B, Mg, Si, Ga, Ge, Y, In, Sn, Sb, Pb and Bi exhibit negative segregation energy and possibly move to the surface, while Be, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zr exhibit positive segregation energies and migrated into the bulk; (ii) the segregation energy was found to be related with the covalent radius, the relaxed position at the surface of the substituting atom and the surface energy; (iii) the segregation behavior of trace element generates lots of defects and dislocation, which can increase the initial pitting nucleation sites in the surface of aluminum foils; (iv) the impurity atom concentration was tested with Pb-doped surfaces, the calculated negative segregation energies in all coverage increases rapidly with the Pb coverage. These conclusions are helpful for designing of the chemical composition and to advance the tunnel etching of aluminum foils.

Keywords: Density functional theory; Surface segregation; Surface energy; Aluminum foil

Morphology transition of ZnO films with DMZn flow rate in MOCVD process by J.H. Liang; H.Y. Lai; Y.J. Chen (pp. 7305-7310).

We used a metal-organic chemical vapor deposition (MOCVD) method to grow ZnO films on MgAl₂O₄ (111) substrate, and succeeded in preparing films with microstructures from well-aligned ZnO nanorods to continuous and dense films by adjusting the ratio of the input rates of oxygen and zinc sources (VI/II). At the growth temperature of 350°C, the ZnO nanorods were formed under a low flow rate of a zinc precursor. On the other hand, continuous and dense ZnO films were formed under a high flow rate of the zinc precursor. There is a transition zone at medium zinc precursor flow rate, where nanorods transform to dense films. We proved that the height of ZnO nanorods and the thickness of ZnO dense films both increase with zinc flow rate, and are consistent with the mass-transport mechanism for ZnO growth. The XRD spectra of the sample in the transition zone show both (002) and (101) peaks, where (101) peaks are formed only in the transition zone. We consider that there are (002) and (101) ZnO grains in the early growth stage of dense ZnO films.

Keywords: Zinc oxide; MOCVD; Transition zone; Growth mechanism; MgAl; ₂; O; ₄; VI/II ratio

Effect of Young's modulus evolution on residual stress measurement of thermal barrier coatings by X-ray diffraction by Q. Chen; W.G. Mao; Y.C. Zhou; C. Lu (pp. 7311-7315).

Subjected to thermal cycling, the apparent Young's modulus of air plasma-sprayed (APS) 8wt.% Y₂O₃-stabilized ZrO₂ (8YSZ) thermal barrier coatings (TBCs) was measured by nanoindentation. Owing to the effects of sintering and porous microstructure, the apparent Young's modulus follows a Weibull distribution and changes from 50 to 93GPa with an increase of thermal cycling. The evolution of residual stresses in the top coating of an 8YSZ TBC system was determined by X-ray diffraction (XRD). The residual stresses derived from the XRD data are well consistent with that obtained by the Vickers indention. It is shown that the evolution of Young's modulus plays an important role in improving the measurement precision of residual stresses in TBCs by XRD.

Keywords: Thermal barrier coatings; X-ray diffraction; Residual stress; Young's modulus

Preparation and characterization of patterned copper sulfide thin films on n-type TiO₂ film surfaces by Yongjuan Lu; Gewen Yi; Junhong Jia; Yongmin Liang (pp. 7316-7322).

Micro-arrayed patterns of p-type copper sulfide (Cu_xS) thin films with positive and negative features were deposited onto the surfaces of n-type TiO₂ semiconductor films via a selective nucleation and growth process from aqueous solution. The surface functional molecules of the UV photo-oxidised patterned SAMs were utilized to direct the nucleation and growth of Cu_xS crystallites. The resultant Cu_xS/TiO₂ composite films with negative and positive Cu_xS patterns on the TiO₂ film surface were investigated using SEM, XRD, XPS and a 3D Surface Profiler. It is demonstrated that regular and compact patterned films of Cu₂S crystallites had been deposited onto the n-type TiO₂ surface, with sharp edges demarcating the boundaries between the patterned Cu₂S region and the TiO₂ film region. The UV–vis spectra for three Cu₂S/TiO₂ films exhibit a wide absorption between 300nm and 450nm. The maximum wavelength differences in the spectra of Cu₂S/TiO₂ films and TiO₂ film were attributed to the added absorption of Cu₂S films at 302nm and the unchanged adsorption of TiO₂ films. The absorption intensities of the Cu₂S/TiO₂ films could be varied in the UV–vis range using the Cu₂S patterned features (positive, negative).

Keywords: Copper sulfide; Thin film; Micropattern; Characterization; Optical property

Improved electron emission characteristics of ZnO nano-gap with Pd films by Siliang Xiong; Zhongxiao Song; Shengli Wu; Lingguo Zhao; Yanhuai Li; Jintao Zhang (pp. 7323-7326).

The properties of the surface-conduction electron-emitter display (SED) are mainly decided by the surface-conduction electron emitters (SCEs). Pd is mostly used to fabricate the surface-conduction electron emitters, which are normally obtained by generating a nano-scale gap from PdO conductive film. ZnO is a potential material for electron emission and the research work has proved that ZnO film can act as the electron-emitter material. In this study, we propose to use the ZnO–Pd two-layer film as the conductive film. Both the multi-layer device electrode film and conductive film were deposited by a magnetron sputter, and SCEs are formed by the electro-forming process as used in SED. The results revealed that the Pd film on ZnO film surface increases the electron emission efficiency from 0.36‰ to 3.85‰.

Keywords: Surface-conduction electron emission; Nano-scale gap; Multi-layer films

Valence band offset of MgO/TiO₂ (rutile) heterojunction measured by X-ray photoelectron spectroscopy by Gaolin Zheng; Jun Wang; Xianglin Liu; Anli Yang; Huaping Song; Yan Guo; Hongyuan Wei; Chunmei Jiao; Shaoyan Yang; Qinsheng Zhu; Zhanguo Wang (pp. 7327-7330).

The valence band offset (VBO) of MgO/TiO₂ (rutile) heterojunction has been directly measured by X-ray photoelectron spectroscopy. The VBO of the heterojunction is determined to be 1.6±0.3eV and the conduction band offset (CBO) is deduced to be 3.2±0.3eV, indicating that the heterojunction exhibits a type-I band alignment. These large values are sufficient for MgO to act as tunneling barriers in TiO₂ based devices. The accurate determination of the valence and conduction band offsets is important for use of MgO as a buffer layer in TiO₂ based field-effect transistors and dye-sensitized solar cells.

Keywords: MgO; Rutile; Band offset; X-ray photoelectron spectroscopy; Gate dielectric; Dye-sensitized solar cells

Migration of CrSi₂ nanocrystals through nanopipes in the silicon cap by N.G. Galkin; L. Dózsa; E.A. Chusovitin; B. Pécz; L. Dobos (pp. 7331-7334).

CrSi₂ nanocrystals (NC¹1NC – nanocrystal.) were grown by reactive deposition epitaxy of Cr at 550°C. After deposition the Cr is localized in about 20–30nm dots on the Si surface. The NCs were covered by silicon cap grown by molecular beam epitaxy at 700°C. The redistribution of NCs in the silicon cap was investigated by transmission electron microscopy and atomic force microscopy. The NCs are partly localized at the deposition depth, and partly migrate near the surface. A new migration mechanism of the CrSi₂ NCs is observed, they are transferred from the bulk toward the surface through nanopipes formed in the silicon cap. The redistribution of CrSi₂ NCs strongly depends on Cr deposition rate and on the cap growth temperature.

Keywords: Chromium disilicide; Quantum dots; Diffusion of Cr in silicon; Si cap growth; Defects in Si

Room temperature preparation of cuprous oxide hollow microspheres by a facile wet-chemical approach by Ning Wang; Hongcai He; Li Han (pp. 7335-7338).

Cuprous oxide hollow spheres have potential applications in drug-delivery carriers, biomedical diagnosis agents, and cell imaging. From a commercial point of view, the low-temperature, template-free, facile method is widely popular synthetic method for the synthesis of cuprous oxide hollow spheres. In this letter, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. XRD patterns and SEM images revealed that pure crystallized cuprous oxide hollow microspheres were successfully obtained at room temperature. The diameter of cuprous oxide hollow sphere can be adjusted (0.7–7μm) by concentration control of hydrazine hydrate. Generated N₂ gas bubbles in the aqueous solution, serving as “soft” templates, play a key role in the formation of hollow microspheres.

Keywords: Cuprous oxide; Hollow microsphere; Nanomaterials; Crystal growth

Controlling growth density and patterning of single crystalline silicon nanowires by Tung-Hao Chang; Yu-Cheng Chang; Fu-Ken Liu; Tieh-Chi Chu (pp. 7339-7343).

This study examines the usage of well-patterned Au nanoparticles (NPs) as a catalyst for one-dimensional growth of single crystalline Si nanowires (NWs) through the vapor-liquid-solid (VLS) mechanism. The study reports the fabrication of monolayer Au NPs through the self-assembly of Au NPs on a 3-aminopropyltrimethoxysilane (APTMS)-modified silicon substrate. Results indicate that the spin coating time of Au NPs plays a crucial role in determining the density of Au NPs on the surface of the silicon substrate and the later catalysis growth of Si NWs. The experiments in this study employed optical lithography to pattern Au NPs, treating them as a catalyst for Si NW growth. The patterned Si NW structures easily produced and controlled Si NW density. This approach may be useful for further studies on single crystalline Si NW-based nanodevices and their properties.

Keywords: Nanoparticles; Nanowires; Self-assembly

Erratum to “Microstructure evolution during surface alloying of ductile iron and austempered ductile iron by electron beam melting” [Appl. Surf. Sci. 255 (2009) 8527-8532] by A. Gulzar; J.I. Akhter; M. Ahmad; G. Ali; M. Mehmood; M. Ajmal (pp. 7344-7344).

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Applied Surface Science (v.256, #23)

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Applied Surface Science (v.256, #23)