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Applied Surface Science (v.255, #11)

Novel approach to preparation of LiMn₂O₄ core/LiNi_xMn2−_xO₄ shell composite by Xifei Li; Youlong Xu; Chunlei Wang (pp. 5651-5655).

Combining two methods, coating and doping, to modify spinel LiMn₂O₄, is a novel approach we used to synthesize active material. First we coated the LiMn₂O₄ particles with the nickel oxide particles by means of homogenous precipitation, and then the nickel oxide-coated LiMn₂O₄ was calcined at 750°C to form a LiNi_xMn2−_xO₄ shell on the surface of spinel LiMn₂O₄ particles. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cyclic voltammetry (CV) and charge–discharge test were performed to characterize the spinel LiMn₂O₄ before and after modification. The experimental results indicated that a spinel LiMn₂O₄ core is surrounded by a LiNi_xMn2−_xO₄ shell. The resulting composite showed excellent electrochemical cycling performance with an average fading rate of 0.014% per cycle. This improved cycle stability is greatly attributed to the suppression of Jahn–Teller distortion on the surface of spinel LiMn₂O₄ particles during cycling.

Keywords: Spinel LiMn; ₂; O; ₄; Core; Shell; Jahn–Teller distortion

One-step synthesis of nitrogen-doped ZnO nanocrystallites and their properties by Min Zheng; Jiaqing Wu (pp. 5656-5661).

Nitrogen-doped ZnO nanocrystallites with primary diameter in the range of 30–50nm were synthesized rapidly by self-assembly combustion technique using urea and citric acid as fuels, zinc nitrate as oxidant. The variation of adiabatic flame temperature with the various fuel compounds was calculated theoretically according to the thermodynamic concept. XRD, SEM and XPS were used to characterize the as-synthesized products. The anti-ultraviolet and anti-bacterium ability of the products were estimated by testing the UPF index and repressing-bacterium circle diameter of the cotton fabrics, which were treated using the as-synthesized products. The results show that a small quantity of citric acid has excellent coordinated action with urea and accelerates the nitrogen doping reaction course, obtaining perfect nitrogen-doped ZnO nanocrystallites with uniform color and particles size. The analysis of XPS spectrum shows that the nitrogen incorporation produces an N–O bonding region. The incorporation of nitrogen greatly improves the anti-ultraviolet and anti-bacterium properties of ZnO nanocrystallites, which can be attributed to the change of surface properties of nitrogen-doped ZnO, such as O vacancies and crystal deficiency.

Keywords: Combustion; Nitrogen-doped ZnO; Nanocrystallite; Anti-ultraviolet; Anti-bacterium

Microstructure and wear behavior of γ/Al₄C₃/TiC/CaF₂ composite coating on γ-TiAl intermetallic alloy prepared by Nd:YAG laser cladding by Xiu-Bo Liu; Shi-Hong Shi; Jian Guo; Ge-Yan Fu; Ming-Di Wang (pp. 5662-5668).

As a further step in obtaining high performance elevated temperature self-lubrication anti-wear composite coatings on TiAl alloy, a novel Ni–P electroless plating method was adopted to encapsulate the as-received CaF₂ in the preparation of precursor NiCr–Cr₃C₂–CaF₂ mixed powders with an aim to decrease its mass loss and increase its compatibility with the metal matrix during a Nd:YAG laser cladding. The microstructure of the coating was examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) and the friction and wear behavior of the composite coatings sliding against the hardened 0.45% C steel ring was evaluated using a block-on-ring wear tester at room temperature. It was found that the coating had a unique microstructure consisting of primary dendrites TiC and block Al₄C₃ carbides reinforcement as well as fine isolated spherical CaF₂ solid lubrication particles uniformly dispersed in the NiCrAlTi ( γ) matrix. The good friction-reducing and anti-wear abilities of the laser clad composite coating was suggested to the Ni–P electroless plating and the attendant reduction of mass loss of CaF₂ and the increasing of it's wettability with the NiCrAlTi ( γ) matrix during the laser cladding process.

Keywords: Microstructure; Laser processing; Composite coating; Ni–P electroless plating; γ; -TiAl intermetallic alloy

Room-temperature deposition of transparent conducting Al-doped ZnO films by RF magnetron sputtering method by Weifeng Yang; Zhuguang Liu; Dong-Liang Peng; Feng Zhang; Huolin Huang; Yannan Xie; Zhengyun Wu (pp. 5669-5673).

Transparent conductive Al-doped zinc oxide (AZO) films with highly (002)-preferred orientation were deposited on quartz substrates at room temperature by RF magnetron sputtering. Optimization of deposition parameters was based on RF power, Ar pressure in the vacuum chamber, and distance between the target and substrate. The structural, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The 250nm thickness AZO films with an electrical resistivity as low as 4.62×10⁻⁴Ωcm and an average optical transmission of 93.7% in the visible range were obtained at RF power of 300W, Ar flow rate of 30sccm, and target distance of 7cm. The optical bandgap depends on the deposition condition, and was in the range of 3.75–3.86eV. These results make the possibility for light emitting diodes (LEDs) and solar cells with AZO films as transparent electrodes, especially using lift-off process to achieve the transparent electrode pattern transfer.

Keywords: PACS; 68.55.−a; 73.50.−h; 78.20.−e; 73.61.−r; 81.15.cdAZO film; Transparent conductive oxide; RF magnetron sputtering; Low temperature deposition

Atypical grain growth for (211) CdTe films deposited on surface reconstructed (100) SrTiO₃ substrates by S. Neretina; R.A. Hughes; G.A. Devenyi; N.V. Sochinskii; J.S. Preston; P. Mascher (pp. 5674-5681).

The (100) SrTiO₃ substrate has emerged as the oxide substrate of choice for the deposition of a wide variety of materials. The substrate's unavoidable miscut leads to a step-terrace morphology when heated to high temperatures. This morphological transition is accompanied by an atomic scale repositioning of the uppermost terrace atoms, the nature of which is strongly dependent on the substrate temperature and ambient atmosphere used. Here, we report the deposition of CdTe films on the as-received and reconstructed surfaces of (100) SrTiO₃. The as-received substrate gives rise to a [111] CdTe film with four equally distributed in-plane grain orientations. The surface reconstruction, on the other hand, gives rise to an unprecedented reorientation of the film's grain structure. For this case, a [211] CdTe film emerges having twelve unevenly distributed in-plane orientations. We attribute the film's grain structure to an atomic scale surface reconstruction, with the anisotropic distribution of grain-types arising from a preferential formation due to the step edges.

Keywords: PACS; 61.05.cp; 61.72.Mm; 61.72.uj; 68.37.Ps; 68.47.Gh; 68.55.−a; 68.55.A−Surface reconstruction; Film; (211) CdTe; SrTiO; ₃; Steps and terraces; Miscut; Vicinal; c; (6; ×; 2); c; (4; ×; 2)

The origination of ill-defined layer in organic spin valves by L. Lin; Z.Y. Pang; F.G. Wang; M.S. Lv; T.L. Yang; L.N. Ye; S.H. Han (pp. 5682-5685).

The origination of ill-defined layer in organic spin valves was investigated by using atomic force microscopy (AFM) and Rutherford backscattering (RBS) analysis. It was found that conductive bulges of LSMO film and self-grown pinholes in Alq₃ film other than Co inclusions could lead to the formation of ill-defined layer. The morphology of LSMO substrate had a strong influence on that of Alq₃ film, LSMO/Alq₃ and Alq₃/Co interfaces. Moreover, Alq₃ film with the thickness of 1–4nm could be barriers which was explained by small active area and added insulated layer in organic magnetic tunnel junctions.

Keywords: PACS; 85.75.Ss; 68. 37. Ps; 82.80.YcOrganic electronics; 8-Hydroxyquioline aluminum (Alq; ₃; ); Atomic force microscopy (AFM); Rutherford backscattering (RBS); Interface

Low temperature perovskite phase formation in PCT 90/10 system by modified chemical route by P. Kumar; Sonia; R.K. Patel; Chandra Prakash (pp. 5686-5689).

Perovskite phase development study of PCT 90/10 system was carried out. Modified chemical technique was used for synthesis. Single perovskite phase with a polycrystalline tetragonal structure was obtained in PCT 90/10 ceramic system at 600°C processing temperature. Dense packing of grains with average grain size ∼1μm was observed in PCT 90/10 ceramic samples. Curie transition temperature ( T_c) of PCT 90/10 ceramic samples was found to be ∼180°C with diffuse phase transition.

Keywords: PACS; 77.22.−d; 77.22.Gm; 77.22.Jp; 77.70.+aCalcination; Grain size; Sintering; Dielectric properties

Inactivation of Escherichia coli and properties of medical poly(vinyl chloride) in remote-oxygen plasma by Hu Miao; Chen Jierong (pp. 5690-5697).

This paper reports the germicidal effect (GE) of Escherichia coli on the surface of medical poly(vinyl chloride) (PVC) in remote-oxygen plasma. The concentration of active species in plasma is determined by means of double Langmuir electron probe and electron-spin resonance (ESR) diagnosis. Moreover, surface properties of sterilized PVC are characterized by the water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The distribution of electrons, ions, and radicals in plasma reactor is different. High-purity radicals are obtained at 40cm from the induction coil which is called remote-plasma zone. By remote-oxygen-plasma sterilization, GE value reach 4.12 under the conditions of treatment time of 60s, plasma RF power of 100W and oxygen flux of 60cm³/min. Compared with direct-oxygen-plasma sterilization, remote plasma can enhance the hydrophilic property and limit the degradation of the PVC surface. After remote-plasma sterilization, PVC surface energy is increased more than twice, which mainly resulted from the increase of surface polar forceγLp, and hydrogen bonding forceγLh. Moreover, remote-plasma sterilization can increase oxygenated functional groups on PVC surface. Experimental results show that remote plasma can inactivate E. coli on the medical PVC substrate effectively. Furthermore, it can optimize the surface properties.

Keywords: Remote-oxygen plasma; Escherichia coli; PVC; Inactivation

Effect of different Ge predeposition amounts on SiC grown on Si (111) by Zhongliang Liu; Peng Ren; Jinfeng Liu; Jun Tang; Pengshou Xu (pp. 5698-5701).

The SiC films were grown by solid source molecular beam epitaxy (SSMBE) on Si (111) with different amounts of Ge predeposited on Si prior to the epitaxial growth of SiC. The samples were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results indicate that there is an optimized Ge predeposition amount of 0.2nm. The optimized Ge predeposition suppress the Si outdiffusion and reduce the formation of voids. For the sample without Ge predeposition, the Si outdiffusion can be observed in RHEED and the results of XRD show the worse quality of SiC film. For the sample with excess amount of Ge predeposition, the excess Ge can increase the roughness of the surface which induces the poor quality of the SiC film.

Keywords: PACS; 68.37.Ps; 81.15.Hi; 61.14.Hg; 07.85.JySiC; Si (1; 1; 1); SSMBE; Ge predeposition

Molecular dynamics study on surface structure and surface energy of rutile TiO₂ (110) by Dai-Ping Song; Ying-Chun Liang; Ming-Jun Chen; Qing-Shun Bai (pp. 5702-5708).

The formula for surface energy was modified in accordance with the slab model of molecular dynamics (MDs) simulations, and MD simulations were performed to investigate the relaxed structure and surface energy of perfect and pit rutile TiO₂(110). Simulation results indicate that the slab with a surface more than four layers away from the fixed layer expresses well the surface characteristics of rutile TiO₂ (110) surface; and the surface energy of perfect rutile TiO₂ (110) surface converges to1.801±0.001Jm⁻². The study on perfect and pit slab models proves the effectiveness of the modified formula for surface energy. Moreover, the surface energy of pit surface is higher than that of perfect surface and exhibits an upper-concave parabolic increase and a step-like increase with increasing the number of units deleted along [001] and [110], respectively. Therefore, in order to obtain a higher surface energy, the direction along which atoms are cut out should be chosen in accordance with the pit sizes: [1¯10] direction for a small pit size and [001] direction for a big pit size; or alternatively the odd units of atoms along [110] direction are removed.

Keywords: Molecular dynamics; TiO; ₂; Surface energy; Surface structure; PitPACS; 31.15.xv; 68.35.Md; 68.35.bd; 61.72.Ff

ZnS nanorod arrays synthesized by an aqua-solution hydrothermal process upon pulse-plating Zn nanocrystallines by Wen Yu; Pengfei Fang; Shaojie Wang (pp. 5709-5713).

Via a simple aqua-solution hydrothermal route, uniform ZnS nanorod arrays were fabricated upon pulse-plating Zn nanocrystallines. Particularly, low temperature (95°C) and short time (1h) were employed in the hydrothermal reaction. ZnS nanorods were found to be grown along certain Zn crystalline direction. Control experiments which were performed by replacing Zn nanocrystallines with Zn plate found no one-dimensional ZnS nanostructure on the substrate. Therefore, it was proposed that pulse-plating Zn nanocrystallines acted as both reactant and seed during the hydrothermal process. ZnS nanorod arrays could be theoretically fabricated on almost any raw base plate as long as Zn nanocrystallines could be pulse-plated on the plate. The ZnS nanorod arrays with high length-to-diameter ratio were expected to be a potential candidate for future field-emission devices.

Keywords: PACS; N 62.23.PqZnS; Nanorod; Nanocrystalline; Array; Hydrothermal; Pulse-plating

Polystyrene/magnesium hydroxide nanocomposite particles prepared by surface-initiated in-situ polymerization by Hui Liu; Jianhong Yi (pp. 5714-5720).

In order to avoid their agglomeration and incompatibility with hydrophobic polystyrene substrate, magnesium hydroxide nanoparticles were encapsulated by surface-initiated in-situ polymerization of styrene. The process contained two steps: electrostatic adsorption of initiator and polymerization of monomer on the surface of magnesium hydroxide. It was found that high adsorption ratio in the electrostatic adsorption of initiator could be attained only in acidic region, and the adsorption belonged to typical physical process. Compared to traditional in-situ polymerization, higher grafting ratio was obtained in surface-initiated in-situ polymerization, which can be attributed to weaker steric hindrance. Both Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) indicated that polystyrene/magnesium hydroxide nanocomposite particles had been successfully prepared by surface-initiated in-situ polymerization. The resulting samples were also analyzed and characterized by means of contact angle testing, dispersibility evaluation and thermogravimetric analysis.

Keywords: Surface-initiated in-situ polymerization; Adsorption; Grafting; Polystyrene; Magnesium hydroxide

Effects of half-wave and full-wave power source on the anodic oxidation process on AZ91D magnesium alloy by Ximei Wang; Liqun Zhu; Weiping Li; Huicong Liu; Yihong Li (pp. 5721-5728).

Anodic films have been prepared on the AZ91D magnesium alloys in 1mol/L Na₂SiO₃ with 10vol.% silica sol addition under the constant voltage of 60V at room temperature by half-wave and full-wave power sources. The weight of the anodic films has been scaled by analytical balance, and the thickness has been measured by eddy current instrument. The surface morphologies, chemical composition and structure of the anodic films have been characterized by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the thickness and weight of the anodic films formed by the two power sources both increase with the anodizing time, and the films anodized by full-wave power source grow faster than that by half-wave one. Furthermore, we have fitted polynomial to the scattered data of the weight and thickness in a least-squares sense with MATLAB, which could express the growth process of the anodic films sufficiently. The full-wave power source is inclined to accelerate the growth of the anodic films, and the half-wave one is mainly contributed to the uniformity and fineness of the films. The anodic film consists of crystalline Mg₂SiO₄ and amorphous SiO₂.

Keywords: JEL classification; 81.65.−bAZ91D magnesium alloy; Anodic film; Half-wave; Full-wave; Silica sol

Uniform design and regression analysis of LPCVD boron carbide from BCl₃–CH₄–H₂ system by Yongsheng Liu; Litong Zhang; Laifei Cheng; Qingfeng Zeng; Weihua Zhang; Wenbin Yang; Zude Feng; Siwei Li; Bin Zeng (pp. 5729-5735).

Boron carbide was prepared by low pressure chemical vapor deposition (LPCVD) from BCl₃–CH₄–H₂ system. The deposition process conditions were optimized through using a uniform design method and regression analysis. The regression model of the deposition rate was established. The influences of deposition temperature ( T), deposition time ( t), inlet BCl₃/CH₄ gas ratio ( δ), and inlet H₂/CH₄ gas ratio ( θ) on deposition rate and microstructure of the coatings were investigated. The optimized deposition parameters were obtained theoretically. The morphologies, phases, microstructure and composition of deposits were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman micro-spectroscopy, transmission electron microscopy (TEM), energy dispersive spectra (EDS), and Auger electron spectra (AES), the results showed that different boron carbides were produced by three kinds of deposition mechanisms.

Keywords: Uniform design; CVD; Microstructure; Boron carbide; Deposition mechanisms

Comparative study on structural and optical properties of CdS films fabricated by three different low-cost techniques by K. Ravichandran; P. Philominathan (pp. 5736-5741).

Highly crystalline and transparent cadmium sulphide films were fabricated at relatively low temperature by employing an inexpensive, simplified spray technique using perfume atomizer (generally used for cosmetics). The structural, surface morphological and optical properties of the films were studied and compared with that prepared by conventional spray pyrolysis using air as carrier gas and chemical bath deposition. The films deposited by the simplified spray have preferred orientation along (101) plane. The lattice parameters were calculated as a=4.138Å and c=6.718Å which are well agreed with that obtained from the other two techniques and also with the standard data. The optical transmittance in the visible range and the optical band gap were found as 85% and 2.43eV, respectively. The structural and optical properties of the films fabricated by the simplified spray are found to be desirable for opto-electronic applications.

Keywords: CdS films; Semiconductors; Microstructure; Elemental analysis; Optical properties

Initial growth mechanism of atomic layer deposition of ZnO on the hydroxylated Si(100)-2×1: A density functional theory study by Jie Ren (pp. 5742-5745).

Density functional theory (DFT) is employed to investigate the initial growth mechanism of atomic layer deposition (ALD) of ZnO on the hydroxylated silicon surfaces. Both the diethylzinc (DEZn) and the H₂O half-reactions proceed through an analogous trapping-mediated mechanism. By comparison of the reactions on silicon surfaces with single and double hydroxyl sites, we find that the existence of neighboring hydroxyl can facilitate the adsorption of DEZn and lower the activation barrier. Also, we find that it is both thermodynamically and kinetically more favorable for the reactions on silicon surfaces with double hydroxyl sites. In addition, calculations show that the DEZn half-reaction is more favorable as compared to the H₂O half-reaction.

Keywords: PACS; : 31.15.E; 81.15.AaDensity functional theory; Zinc oxide; Atomic layer deposition; Growth mechanism

Synthesis and morphological study on the nanocomposite hydrophilic coatings by Amir Ershad-Langroudi; Salimeh Gharazi; Azam Rahimi; Diba Ghasemi (pp. 5746-5754).

Hydrophilic nanocomposite coatings based on epoxy silane were prepared with incorporation of aminoethylaminopropyltrimethoxysilane by a sol–gel process. It was found out that the hydrophilicity is affected remarkably in the presence of non-ionic surfactant. Moreover, scanning electron microscopy (SEM) and Si mapping micrographs indicated that there is a uniform distribution of silica particles in the coatings with either lower or higher amounts of aminoethylaminopropyltrimethoxysilane. Furthermore, the effect of aminoethylaminopropyltrimethoxysilane on transparency of the coatings was evaluated in the absence and presence of surfactant. Fourier transform infrared (FT-IR) and attenuated total reflectance infrared spectroscopy (ATR-IR) techniques were employed to study the different steps of nanocomposite hybrid coating synthesis. Surface topography of the coatings investigated by atomic force microscopy (AFM) technique and transmission electron microscopy (TEM) indicated that the silica particles’ dimensions are at the nano-scale.

Keywords: Hydrophilic; Hybrid; Nanocomposite; Coatings; Morphology

Preparation and calibration of ultrathin Zn layers on Pd(111) by M. Kratzer; A. Tamtögl; J. Killmann; R. Schennach; A. Winkler (pp. 5755-5759).

The general assumption that metal vapors stick at any surface with probability one at room temperature is a necessary requirement for the correct metal deposition rate determination by quartz microbalance measurements. In a combined thermal desorption spectroscopy (TDS) and Auger electron spectroscopy (AES) study on clean and sulphur covered Pd(111) surfaces it is shown that Zn exhibits a reduced sticking coefficient on contaminated surfaces which violates the requirements for a proper application of a quartz microbalance. Additional CO titration and AES experiments were applied to calibrate the Zn coverage on Pd(111).

Keywords: Zinc; Palladium; Quartz microbalance; ZnPd; Alloy; Sticking coefficient

Studies on influence of light on fluorescence of Tris-(8-hydroxyquinoline)aluminum thin films by K. Thangaraju; P. Amaladass; K. Shanmuga Bharathi; A.K. Mohanakrishnan; V. Narayanan; J. Kumar (pp. 5760-5763).

Tris-(8-hydroxyquinoline)aluminum (Alq₃) thin films, the most widely used electron transport/emissive material in the organic electroluminescent (EL) devices, have been deposited on glass substrates by thermal evaporation process. Alq₃ thin films were exposed to light for various time periods under normal ambient. The fluorescence of as-prepared and light exposed Alq₃ thin films and formation of luminescent quencher have been studied using fluorescence, Mass, MALDI-ToF-MS,¹H &¹³C NMR, and FT-IR spectroscopy. It is observed that among the three 8-hydroxyquinoline (HQ) units in Alq₃ molecule, one HQ unit is affected during the light exposure in the normal ambient. It is found that the affected resultant Alq₃ molecule containing the carbonyl group acts as fluorescent quencher and the energy of excitons in the Alq₃ molecule in the light exposed Alq₃ thin films can be non-radiatively transferred to the neighboring fluorescent quencher, quenching the fluorescence of light exposed Alq₃ thin films in the normal ambient.

Keywords: PACS; 72.80.Le; 78.66.−w; 33.50.Dq; 33.20.EaTris-(8-hydroxyquinoline)aluminum; Fluorescence; Infrared; Fluorescence quencher

Infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite: DFT study by Shujun Jiang; Shiping Huang; Weixia Tu; Jiqin Zhu (pp. 5764-5769).

The infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag⁺ cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag⁺ cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag–ZSM-5. The free energy changes Δ G, −5.55kcal/mol and 6.52kcal/mol for one and two CO molecules, illustrate that the Ag⁺(CO)₂ complex is unstable at the room temperature. The vibration frequency of C–O stretching of one CO molecule bonded to Ag⁺ ion at 2211cm⁻¹ is in good agreement with the experimental results. The calculated C–O symmetric and antisymmetric stretching frequencies in the Ag⁺(CO)₂ complex shift to 2231cm⁻¹ and 2205cm⁻¹ when the second CO molecule is adsorbed. The calculated C–O stretching frequency in CO–Ag–ZSM-5–H₂O complex shifts to 2199cm⁻¹, the symmetric and antisymmetric O–H stretching frequencies are 3390cm⁻¹ and 3869cm⁻¹, respectively. The Gibbs free energy change(ΔGH2O) is −6.58kcal/mol as a H₂O molecule is adsorbed on CO–Ag–ZSM-5 complex at 298K. The results show that CO–Ag–ZSM-5–H₂O complex is more stable at room temperature.

Keywords: Infrared spectra; Ag–ZSM-5; Density functional theory; CO and H; ₂; O sorption

Laser surface treatment of screen-printed carbon nanotube emitters for enhanced field emission by Chung-Wei Cheng; Chun-Ming Chen; Yung-Chun Lee (pp. 5770-5774).

This paper investigates the surface treatment of screen-printed carbon nanotube (CNT) emitters using a 248nm (KrF) excimer laser. The field emission characteristics of the CNT emitters are measured following irradiation using laser fluences ranging from 80 to 400mJ/cm². The results show that the turn-on electric field, the current density, and the distribution of the emission sites are highly dependent on the value of the laser fluence and are optimized at a fluence of 150mJ/cm². Two distinct laser fluence regimes are identified. In the low fluence regime, i.e. 80–150mJ/cm², the surface treatment process is dominated by a photo ablation mechanism, which results in the gradual removal of the binding material from the cathode surface and leads to an improvement in the emission characteristics of the CNT cathodes with an increasing fluence. However, in the high fluence regime, i.e. 150–400mJ/cm², the thermal ablation mechanism dominates; resulting in a removal of the CNTs from the cathode surface and a subsequent degradation in the emission characteristics.

Keywords: Screen-printed; Carbon nanotube; Excimer laser; Surface treatment

Theoretical study on tailoring symmetric and asymmetric thin films of diblock copolymers by Dapeng Cao; Xianren Zhang; Wenchuan Wang (pp. 5775-5780).

We used density functional theory (DFT) to investigate the formation of symmetric and asymmetric thin film of diblock copolymer melts by tuning the size of the slit confinement. In this work, the DFT contains a modified fundamental measure theory for the excluded volume effect and the first-order thermodynamic perturbation theory for the chain connectivity as well as the mean-field approximation for van der Waals attraction. For the symmetric A₈B₈ linear copolymers, it is observed that with the increase of the width of the slit, morphologies of copolymer in the slits undergo an evolution of “non-layered structure→ABA→ABAB→BABAB→disordered structure”, while the morphologies of asymmetric copolymer with the increase of the width of the slit exhibit a process of “ABA→ABAB→ABABA→ABABAB lamellar structure” in all the cases studied. It suggests that the ratio of two blocks of a copolymer plays an important role on the structure of copolymer film. By adjusting the ratio of two blocks, some copolymer films with novel morphologies, including asymmetric ABAB lamellar structure, can be tailored. Furthermore, it is found that the bonding orientation distribution introduced into the DFT can act as a criterion to identify the disordered and ordered states of copolymers.

Keywords: Diblock copolymer; Density functional theory; Asymmetric film; Slit confinement

Epitaxial growth of Sc-doped ZnO films on Si by sol–gel route by Ruchika Sharma; Kiran Sehrawat; Akihiro Wakahara; R.M. Mehra (pp. 5781-5788).

The epitaxial growth of doped ZnO films is of great technological importance. Present paper reports a detailed investigation of Sc-doped ZnO films grown on (100) silicon p-type substrates. The films were deposited by sol–gel technique using zinc acetate dihydrate as precursor, 2-methoxyethanol as solvent and monoethanolamine (MEA) as a stabilizer. Scandium was introduced as dopant in the solution by taking 0.5wt%¹1Ruchika Sharma, P. K. Shishodia, A. Wakahara and R. M. Mehra, Materials Science-Poland 27 (2009) Ist issue. of scandium nitrate hexahydrate. The effect of annealing on structural and photoluminescence properties of nano-textured Sc-doped films was investigated in the temperature range of 300–550°C. Structural investigations were carried out using X-ray diffraction, scanning electron microscopy and atomic force microscopy. X-ray diffraction study revealed that highly c-axis oriented films with full-width half maximum of 0.21° are obtained at an annealing temperature of 400°C. The SEM images of ZnO:Sc films have revealed that coalescence of ZnO grains occurs due to annealing. Ostwald ripening was found to be the dominant mass transport mechanism in the coalescence process. A surface roughness of 4.7nm and packing density of 0.93 were observed for the films annealed at 400°C. Room temperature photoluminescence (PL) measurements of ZnO:Sc films annealed at 400°C showed ultraviolet peak at about (382nm) with FWHM of 141meV, which are comparable to those found in high-quality ZnO films. The films annealed below or above 400°C exhibited green emission as well. The presence of green emission has been correlated with the structural changes due to annealing. Reflection high energy electron diffraction pattern confirmed the nearly epitaxial growth of the films.

Keywords: PACS; −81.20.Fw; 61.05.cp; 61.05.jh; 68.37.Hk; 68.37.Ps; 68.55.AZinc oxide; Scandium; Sol–gel; Annealing; Morphology; Photoluminescence

Ethylene glycol reflux synthesis of carbon nanotube/ceria core–shell nanowires by Dengsong Zhang; Tingting Yan; Liyi Shi; Chengsi Pan; Jianping Zhang (pp. 5789-5794).

Carbon nanotube (CNT)/ceria core–shell nanowires were prepared facilely on a large scale under the boiling reflux of ethylene glycol. The composites are characterized by transmission electron microscopy, X-ray diffraction as well as Fourier transformed infrared spectra. It is found that the entire outer surface of CNTs is fully sheathed with a dense layer of uniform nanosized CeO₂, and that the thickness of the coating sheath can be readily manipulated by tuning the molar ratio of ceria to CNTs. Finally, a possible formation mechanism has been suggested as follows: with the high reaction temperature, ethylene glycol is partially converted to oxalic acid, and the surface hydroxyl groups of CeO₂ tiny particles react with oxalic acid to form the polymer-like inorganic–organic compounds. Subsequently, in view of the low-energy point, the polymer-like inorganic–organic compounds are coated on the surface of CNTs, and thus CNTs/ceria core–shell composites are obtained.

Keywords: Carbon nanotube; Ceria; Composite; Coating; Nanowire

Electrodeposition of CoWP film by S.M.S.I. Dulal; Hyeong Jin Yun; Chee Burm Shin; Chang-Koo Kim (pp. 5795-5801).

CoWP films were electrochemically deposited on copper-coated silicon wafers from citrate electrolytes containing cobalt sulphate, sodium tungstate and sodium hypophosphite under various deposition conditions and characterisations of the films were carried out using various instrumental techniques. Composition analyses using XPS showed that the surfaces of the films contained large amounts of oxides and hydroxide of tungsten and cobalt, respectively. An AES depth-profile, however, revealed that the bulk of the films predominantly consisted of cobalt, tungsten and phosphorus. Microstructural analyses using XRD showed that, depending on the composition and/or deposition conditions, CoWP films could be amorphous, polycrystalline and crystalline with a strong preferred orientation. Amorphous films were obtained when deposited at higher applied potential and current density or the films contained high amount of phosphorus and/or tungsten, while films deposited by very low applied potential and current density were crystalline with a preferred orientation of [002] of hexagonal cobalt. SEM images showed that the films deposited from neutral or acidic baths at room temperature had typical spherical nodular structures, while the films deposited from basic solution or at elevated temperature had needle-like crystallites. The crystalline films were much rougher than the amorphous films.

Keywords: CoWP film; Electrodeposition; Barrier layer; Coating; Microelectronic devices

Temperature-programmed surface reaction (TPSR) of CH₄ synthesis by Pd_xNi100−_x nanoparticles by Kuan-Wen Wang; Shu-Ru Chung; Yu-Chen Wei; Jyh-Fu Lee; Tsong P. Perng (pp. 5802-5805).

A series of Pd_xNi100−_x nanoparticles were prepared by the co-precipitation method and analyzed using a temperature-programmed surface reaction (TPSR) of their methanation reactions. ESCA measurement suggested that the as-prepared Pd–Ni alloys had Pd-core/Ni-shell structure. Surface Pd segregation occurred during H₂ reduction and resulted in a surface composition close to the nominal value. The TPSR experiments were performed by pre-adsorption of CO with H₂ to form methane. The peak temperature of methanation increased as Pd content increased, indicating that a methanation reaction is favored on Ni and Ni-rich alloy nanoparticles. For physical mixtures of Pd and Ni nanoparticles, methanation behaviors is similar to those of alloy nanoparticles; but the methanation temperatures of physical mixtures are always higher than those of alloy nanoparticles. This may be due to the formation of a Pd-enriched alloy surface layer during reduction in H₂ at 400°C, or because the CO molecules adsorbed on the Pd sites spill over onto the Ni sites for methanation. Using TPSR technique and measuring methanation temperature, the top-most surface of such bimetallic nanoparticles can be probed.

Keywords: Pd; _x; Ni; 100−; _x; nanoparticles; Surface segregation; Temperature-programmed surface reaction; Methanation; Surface composition

Assessing the antimicrobial activity of zinc oxide thin films using disk diffusion and biofilm reactor by Shaun D. Gittard; John R. Perfect; Nancy A. Monteiro-Riviere; Wei Wei; Chunming Jin; Roger J. Narayan (pp. 5806-5811).

The electronic and chemical properties of semiconductor materials may be useful in preventing growth of microorganisms. In this article, in vitro methods for assessing microbial growth on semiconductor materials will be presented. The structural and biological properties of silicon wafers coated with zinc oxide thin films were evaluated using atomic force microscopy, X-ray photoelectron spectroscopy, and MTT viability assay. The antimicrobial properties of zinc oxide thin films were established using disk diffusion and CDC Biofilm Reactor studies. Our results suggest that zinc oxide and other semiconductor materials may play a leading role in providing antimicrobial functionality to the next-generation medical devices.

Keywords: Antimicrobial materials; Pulsed laser deposition; Zinc oxide

The effect of heat treatment on the physical properties of sol–gel derived ZnO thin films by Davood Raoufi; Taha Raoufi (pp. 5812-5817).

Zinc oxide (ZnO) thin films were deposited on microscope glass substrates by sol–gel spin coating method. Zinc acetate (ZnAc) dehydrate was used as the starting salt material source. A homogeneous and stable solution was prepared by dissolving ZnAc in the solution of monoethanolamine (MEA). ZnO thin films were obtained after preheating the spin coated thin films at 250°C for 5min after each coating. The films, after the deposition of the eighth layer, were annealed in air at temperatures of 300°C, 400°C and 500°C for 1h. The effect of thermal annealing in air on the physical properties of the sol–gel derived ZnO thin films are studied. The powder and its thin film were characterized by X-ray diffractometer (XRD) method. XRD analysis revealed that the annealed ZnO thin films consist of single phase ZnO with wurtzite structure (JCPDS 36-1451) and show the c-axis grain orientation. Increasing annealing temperature increased the c-axis orientation and the crystallite size of the film. The annealed films are highly transparent with average transmission exceeding 80% in the visible range (400–700nm). The measured optical band gap values of the ZnO thin films were between 3.26eV and 3.28eV, which were in the range of band gap values of intrinsic ZnO (3.2–3.3eV). SEM analysis of annealed thin films has shown a completely different surface morphology behavior.

Keywords: PACS; 78.20.Ci; 74.25.Gz; 78.20.−eZnO; Sol–gel; Thin film; Structural and optical properties

Chemical modification of silica-gel with diethylenetriamine via an end-group protection approach for adsorption to Hg(II) by Ying Zhang; Rongjun Qu; Changmei Sun; Chunhua Wang; Chunnuan Ji; Hou Chen; Ping Yin (pp. 5818-5826).

Four kinds of silica-gel supported diethylenetriamine adsorbents with different structures, were prepared by so-called “heterogeneous-direct-amination” (hetero-DA), “homogeneous-direct-amination” (homo-DA), “heterogeneous end-group protection” (hetero-EGP), and “homogeneous end-group protection” (homo-EGP) methods, respectively. The obtained products were named SG-HE-dD, SG-HO-dD, SG-HE-pD and SG-HO-pD, respectively (where SG means silica-gel; HE means heterogeneous, HO means homogeneous, d means direct, p means protected and D means diethylenetriamine). Their structures were characterized by FT-IR, elemental analysis, porous structure analysis and thermogravimetric analysis. The adsorption capabilities of such adsorbents towards Hg(II) were studied and evaluated by static method. SG-HE-pD and SG-HO-pD showed higher performance towards Hg(II) adsorption than corresponding counterparts SG-HE-dD and SG-HO-dD, even though the former two possessed lower contents of diethylenetriamine (DETA). The kinetics data indicated that the adsorption process was governed by the film diffusion and followed pseudo-first-order rate model for SG-HE-dD, SG-HO-dD and SG-HE-pD and pseudo-second-order model for SG-HO-pD. The Langmuir model was applied to fit the experimental equilibrium data for all adsorbents. The end-group protection method exhibited its advantage in preparation of effective adsorbent for metal ions uptake compared to the direct-amination method.

Keywords: Chemical modification of silica-gel; Diethylenetriamine; End-group protection; Adsorption; Hg(II)

Synthesis of micron-scale gold nanochains by a modified citrate reduction method by Zhiguo Liu; Yuangang Zu; Songling Guo (pp. 5827-5830).

Gold nanochains ranged from several hundred nanometers to more than 5μm were synthesized by a modified citrate reduction method. The synthesized nanochains have been characterized by TEM, AFM and UV absorption spectrum. The produced nanochains can be transferred onto the mica surface, and can bear the repeating scan by AFM tip, which may have some potential applications in electronics and catalysis.

Keywords: PACS; 61.46.w; 62.23.c; 62.23.StGold nanoparticles; Nanochains; Citrate reduction; AFM

Effects of substrate rotation on the microstructure of metal sheet fabricated by electron beam physical vapor deposition by Yue Sun; Xiu Lin; Xiaodong He; Jiazhen Zhang; Mingwei Li; Guangping Song; Xinyan Li; Yijie Zhao (pp. 5831-5836).

The effects of substrate rotation speed and rotation mode on the microstructure of large-sized metal sheet fabricated by electron beam physical vapor deposition technique were investigated. Helical and columnar microstructures were found in the deposited sheet. Both types of microstructures exhibit no preferential crystallographic orientation. The column inclination under asymmetric vapor incidence pattern was discussed. Integrated vapor incidence angle was found to be effective in evaluating the column inclination.

Keywords: PACS; 68.55.Jk; 81.10.Bk; 81.15.JjPhysical vapor deposition (PVD); Helical microstructure; Film growth

Fabrication of TiO₂ μ-donuts by sol–gel spin coating using a polymer mask by N. Saleema; M. Farzaneh; R.W. Paynter (pp. 5837-5842).

TiO₂ μ-donuts have been fabricated on glass and silicon substrates using polymer masks in combination with a sol–gel technique. Cylindrical poly(methyl methacrylate) (PMMA) nanopillars have been created using a composite polymer of polystyrene (PS) and PMMA followed by careful removal of the PS. Atomic force microscopy (AFM) analyses show that the height and diameter of the PMMA cylinders used as the mask are 440±5nm and 2.1±0.2μm, respectively. The cylindrical PMMA nanopillars have been coated with the sol of the TiO₂ precursor by a spin coating technique and annealed in air at elevated temperature to remove the PMMA mask. Removal of the PMMA mask has resulted in the formation of well ordered μ-donuts of TiO₂ on silicon surfaces. The interior and exterior heights of the TiO₂ μ-donuts are found to be 373±152nm and 457±136nm, respectively; and the interior and exterior diameters of the TiO₂ μ-donuts are found to be 1.33±0.63μm and 2.82±0.50μm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of the TiO₂ μ-donuts as well as the smooth TiO₂ thin film showed signals from Ti and O confirming the presence of TiO₂ with Ti 2p_3/2 and O 1s peaks at 458.8eV and 530.4eV, respectively. The O 1s peak of the TiO₂ μ-donuts shows another peak at binding energy 532.0eV due to SiO₂, as during annealing, the PMMA evaporates and the Si substrate is exposed. The X-ray diffractometer (XRD) pattern of the smooth TiO₂ thin film indicates that the anatase phase is present, with the characteristic peaks observed at 2 θ values of 25.4°, 37.4°, and 48° corresponding to (101), (004), and (200) planes, respectively. UV–vis absorption spectra of TiO₂ μ-donuts on glass showed an unusual absorption of light in the visible region at ∼524nm in addition to the usual UV absorption at ∼337nm.

Keywords: TiO; ₂; μ-donuts; Composite polymer masking; Sol–gel spin coating; Light absorption; Atomic force microscopy; X-ray photoelectron spectroscopy

Post-treatment of mesoporous material with high temperature for synthesis super-microporous materials with enhanced hydrothermal stability by Ke Song; Jingqi Guan; Zhuqian Wang; Chen Xu; Qiubin Kan (pp. 5843-5846).

Super-microporous silicon material with high hydrothermal stability denoted as MCM-48-T has been prepared from mesoporous MCM-48 by high temperature treatment. The structural and chemical property of MCM-48-T has been characterized by variety of techniques such as small-angle X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption–desorption, infrared spectroscopy (IR) and²⁹Si MAS NMR, etc. The results showed that Si–OH groups are forced to condense by the treatment of high temperature and the pore size of MCM-48-T is around 1.03nm in the super-microporous range. Besides, the ratio of Q⁴/Q³ increases considerably. Compared with the original material (MCM-48), the hydrothermal stability of MCM-48-T has significantly enhanced.

Keywords: PACS; 82.75.−z; 81.07.−b; 81.16.−cMCM-48; Mesoporous; Super-microporous; Hydrothermal stability

Sliding tribological properties of untreated and PIII-treated PETP by Gábor Kalácska; László Zsidai; Klára Kereszturi; Miklós Mohai; András Tóth (pp. 5847-5850).

Poly(ethylene terephthalate) (PETP) was treated by plasma immersion ion implantation (PIII or PI³) in nitrogen. The surface changes were characterised by XPS and water contact-angle measurements. Sliding tribological properties of untreated and nitrogen PIII-treated PETP against conventional low carbon structural steel S235 were studied under dry and water-lubricated conditions by a pin-on-disc tribometer.XPS results suggested the evolution of surface composition and bonding towards those of amorphous hydrogenated carbon-nitride. Water contact-angle decreased implying increased surface wettability. At a very low Pv factor (0.0075MPams⁻¹) for the nitrogen PIII-treated PETP the dry friction coefficient was smaller than, while the lubricated friction coefficient was similar to, the corresponding value of the untreated variant. At higher Pv factors (near 0.1MPams⁻¹), however, both the dry and lubricated friction coefficients were higher for the treated sample than for the untreated variant, suggesting an increased adhesion component of friction for the nitrogen PIII-treated PETP in this region.

Keywords: PACS; 68.47.Mn; 52.77.−j; 79.60.−i; 68.08.Bc; 81.40.PqPoly(ethylene terephthalate); Plasma immersion ion implantation; XPS; Contact-angle; Pin-on-disc tribometer; Friction

Co/Mg/Al hydrotalcite-type precursor, promoted with La and Ce, studied by XPS and applied to methane steam reforming reactions by Alessandra Fonseca Lucrédio; Germano Tremiliosi Filho; Elisabete Moreira Assaf (pp. 5851-5856).

Catalysts’ precursor of Co/Mg/Al promoted with Ce and La were tested in the steam reforming of methane (SRM). The addition of promoters was made by anion-exchange. The oxides characterization was made by X-ray Photoelectron Spectroscopy (XPS) analysis that confirmed Co²⁺ species in free form on surface and interacted with Mg and Al in the form of solid solution. In the SRM with high fed molar ratio of H₂O:CH₄=4:1, the catalysts showed a great affinity with water and immediately deactivated by oxidation of the active sites. In the stoichiometric ratio of H₂O:CH₄=2:1 the catalysts were active and presented low carbon deposition during the time reaction tested. Also a test with low fed molar ratio H₂O:CH₄=0.5:1 was carried out to evaluate the stability of the catalysts by CH₄ decomposition and all the catalysts were stable during 6h of reaction. Promoted catalysts presented lower carbon deposition.

Keywords: PACS; 82.65.+rHydrotalcite; Cobalt; Promoter; Reforming; Methane

Formation of As enriched layer by steam oxidation of As⁺-implanted Si by A. Baghizadeh; D. Agha-Aligol; D. Fathy; M. Lamehi-Rachti; M. Moradi (pp. 5857-5860).

Segregation of implanted As during steam oxidation of Si wafers is shown to result in a highly enriched, thin layer of As at the interface between the oxide and the underlying Si. Also, the oxidation rate was found to increase by as much as a factor of ∼2 depending on the depth distribution and fluence of the implanted As impurity. The thin As layer collected at the interface can be used in the design of very shallow junctions. This mechanism enables the formation of a narrow, degenerately doped layer of Si, which can be tailored to have a thickness of only few monolayers depending on the fluence of the implantation used.

Keywords: PACS; 61.72.uf (silicon, doping and ion implantation)Thermal oxidation; Rutherford Backscattering Spectroscopy; Ion implantation; Shallow junction; As impurity

Effects of thermal annealing temperature and duration on hydrothermally grown ZnO nanorod arrays by X.Q. Zhao; C.R. Kim; J.Y. Lee; C.M. Shin; J.H. Heo; J.Y. Leem; H. Ryu; J.H. Chang; H.C. Lee; C.S. Son; B.C. Shin; W.J. Lee; W.G. Jung; S.T. Tan; J.L. Zhao; X.W. Sun (pp. 5861-5865).

In this study, the effects of thermal annealing temperature and duration on ZnO nanorod arrays fabricated by hydrothermal method were investigated. The annealed ZnO/Si(111) substrate was used for ZnO nanorod array growth. The effects of annealing treatment on the structural and optical properties were investigated by scanning electron microscopy, X-ray diffraction, and room-temperature photoluminescence measurements. With the annealing temperature of 750°C and the annealing duration of 10min, both the structural and optical properties of the ZnO nanorod arrays improved significantly, as indicated in the X-ray diffraction and photoluminescence measurement.

Keywords: PACS; 81.05.Dz; 81.16.Be; 81.40.EfZnO; Hydrothermal synthesis; Annealing treatment

Enhancement of the secondary ion emission induced by fast clusters by Fu-Rong Ding; Ping Shi; Rui Nie; Hong-Ji Ma (pp. 5866-5868).

The emission yields of the secondary ions are measured by using a conventional time of flight (TOF) technique under bombardments of Mg and C₂, Ni and Si₂ with different energies, and C_n, Si_n and Ni_n ( n=1–3) with the different charge states and with energy of 1.5MeV per atom, respectively. For the bombardments of C_n, Si_n and Ni_n, the enhancements of the secondary ion emissions increase with increasing cluster sizes and charge states. For the bombardments of Mg and C₂, Ni and Si₂, although the mass and the nuclear charges of C₂ and Si₂ are the same as or equivalent to Mg or Ni, respectively, the enhancements of the secondary ion emissions induced by the clusters of C₂ and Si₂ in a wide energy range are also clearly indicated. The instantaneous collective interaction of the cluster constituents plays an important role in the secondary ion emissions.

Keywords: PACS; 82.80.Ms; 79.20.Rf; 36.40.GkSecondary ion emission; Cluster; Collective interaction

Dopant induced morphology changes in ZnO nanocrystals by K. Jayanthi; Santa Chawla; K.N. Sood; Manisha Chhibara; Sukvir Singh (pp. 5869-5875).

Zinc oxide (ZnO) nanocrystals doped with different groups of impurities, e.g., Li, Na, Cu, Pr and Mg synthesized by solid-state reaction method under similar conditions exhibit different morphology. XRD showed monophasic wurtzite structure but change in lattice parameters and Zn–O bond length indicates incorporation of dopant ion in ZnO lattice. The morphology of ZnO nanocrystals exhibited striking dependence on type of dopant ion with the shape changing from nanorods, spherical to petal like particles. Photoluminescence (PL) shows pronounced UV emission and negligible visible emission for Li, Na and Cu doped ZnO nanocrystals with peak positions coinciding with that of undoped ZnO. Whereas signature emission of Pr³⁺ ion as well as broad visible emission from Mg doped ZnO revealed the role of intra gap metastable states formed by the dopant ion in the emission process.

Keywords: PACS; 71.55.Gs; 78.55.−m; 73.63.BdSolid-state reaction; Photoluminescence; Band edge; Impurities; Nanocrystals

Effects of crystalline quality on the ultraviolet emission and electrical properties of the ZnO films deposited by magnetron sputtering by J.B. You; X.W. Zhang; Y.M. Fan; Z.G. Yin; P.F. Cai; N.F. Chen (pp. 5876-5880).

The ZnO films were deposited on c-plane sapphire, Si (001) and MgAl₂O₄ (111) substrates in pure Ar ambient at different substrate temperatures ranging from 400 to 750°C by radio frequency magnetron sputtering. X-ray diffraction, photoluminescence and Hall measurements were used to evaluate the growth temperature and the substrate effects on the properties of ZnO films. The results show that the crystalline quality of the ZnO films improves with increasing the temperature up to 600°C, the crystallinity of the films is degraded as the growth temperature increasing further, and the ZnO film with the best crystalline quality is obtained on sapphire at 600°C. The intensity of the photoluminescence and the electrical properties strongly depend on the crystalline quality of the ZnO films. The ZnO films with the better crystallinity have the stronger ultraviolet emission, the higher mobility and the lower residual carrier concentration. The effects of crystallinity on light emission and electrical properties, and the possible origin of the n-type conductivity of the undoped ZnO films are also discussed.

Keywords: PACS; 78.55.Et; 81.05.Dz; 68.55.Jk; 73.61.GaCrystal quality; RF magnetron sputtering; Zinc oxide; Semiconducting II–VI materials

Assignment of quantum number for plasmon energies in carbon layer systems by E. Rówiński (pp. 5881-5884).

Electron-emission distribution curves of carbon layer surfaces excited by primary electrons of energies in the 118–534eV range have been measured. The first four peaks in the plasmon spectrum are observed. It is concluded that the oscillator energies are presented to explain the assignment of the quantum number ( n=0,1,2,3) for internal plasmons in carbon layer systems. The preliminary assignment is in good agreement with the experimental results. It is also shown that the existence of limit between internal and surface plasmons. It is pointed out that the plasmon energy does not depend on both the external electrostatic voltage and the sample temperature. Moreover, the quantum number was adopted to the names of internal plasmons in the observed spectra.

Keywords: PACS; 03.67.−a; 07.30.−t; 07.81.+aInternal plasmon; Surface plasmon; Carbon material; Layer

First self-assembly study of large π-conjugated corrole dimers on solid substrates by Xinrui Miao; Aimei Gao; Zhuomin Li; Satoru Hiroto; Hiroshi Shinokubo; Atsuhiro Osuka; Wenli Deng (pp. 5885-5890).

Our study focus on β,β′-doubly linked corrole dimers (CDs) on mica and Au(111) surface using samples prepared by the synthetic method described by Osuka group appeared on recent publication [S. Hiroto, K. Furukawa, H. Shinokubo, A. Osuka, J. Am. Chem. Soc. 128 (2006) 12380]. Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) were used to investigate the self-assembled structure of corrole dimers adsorbed on mica and Au(111) surfaces respectively at room temperature in air. The CDs adopt a dissimilar adsorption modality due to the different surface free energy of the different substrates. These types of molecular layers provide a useful platform for the study of surface and interface phenomena outside a vacuum system. It is potentially useful for practical fabrication of molecular devices because of the simplicity of the sample preparation and the stability of the interface in ambient conditions.

Keywords: PACS; 07.79.Fc; 33.80.−b; 87.15.nr; 33.15.FmScanning tunneling microscope; Atomic force microscope; Corrole dimer; Self-assemble; Aggregation; Hydrogen bonding

A Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) study of oleate adsorbed on magnetite nano-particle surface by Payman Roonasi; Allan Holmgren (pp. 5891-5895).

Magnetite nano-particles were coated with sodium oleate and the spectral behaviour of the coating layer was studied by FTIR spectroscopy after the particles had been heated in air and argon. Magnetite was synthesized by controlled co-precipitation and subsequently coated with sodium oleate. Thermal analysis in combination with mass spectroscopy was carried out to support the FTIR spectroscopic interpretations, but also to monitor the decomposition and surface reaction of oleate adsorbed on the magnetite surface. It was deduced from FTIR and TGA results that the oleate molecules are bonded to iron atoms by a bidentate mononuclear complex and form essentially a single layer with a distance between oleate molecules of ∼36Å². It was shown by IR as well as Raman spectroscopy that oleic acid, when heated in air, undergoes decomposition implying that new carbon–oxygen bonds are formed. Heating the iron oxide–oleate system in air also implies oxidation of the double bond at the C:9 position of the alkyl chain and formation of intermediate oxygen-rich molecules. An enthalpy change of Δ H=49.86J/g was obtained for oleate desorption/decomposition at ∼350°C under argon atmosphere and a carbonaceous graphitic species resulted from this decomposition.

Keywords: Magnetite; Oleic acid; Surface reaction; FTIR spectroscopy; Thermogravimetric analysis

Preparation of nanocrystalline Sn–TiO2−_X via a rapid and simple stannous chemical reducing route by Baifu Xin; Dandan Ding; Yina Gao; Xinghai Jin; Honggang Fu; Peng Wang (pp. 5896-5901).

The Sn–TiO2−_X nanoparticles have been prepared via a rapid and simple stannous chemical reducing method. The as-prepared Sn–TiO2−_X nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), XPS, and DRS technology as well as photocatalytic degradation of RhB were studied under illumination. The experiment results revealed that the reduction of the TiO₂ particles raised their Fermi level, which can enhance the driven force of photoinduced electrons transferring from TiO₂ to adsorbed O₂ and SnO₂ on the surface of TiO₂. On the other hand, the amount of oxygen vacancies of the Sn–TiO2−_X increased after the stannous chemical reduction. The oxygen vacancies can also effectively inhibit the recombination of photoinduced electrons and holes pairs. These factors are favorable to the photocatalytic reaction.

Keywords: TiO; ₂; Stannous; Chemical reduction; Photocatalysis

Some improvement in Fe/Si multilayered neutron polarizor by modified sputtering geometry by A. Ashfaq; J. Stahn (pp. 5902-5904).

Aperture geometry of magnetron sputtering unit was modified by insertion of longitudinal [B] and transverse [A] slits with respect to the motion of substrate. Fe-, Si-mono and Fe/Si multilayer [Fe (70Å)/Si (50Å)]₁₀ (called ML70) were grown with and without modified apertures. Maximum stress anisotropy was found in samples prepared with transverse modified aperture [A]. X-ray reflectometry (XRR) results showed a marked difference in roughness values of interdiffusion layers Fe-_Si and Si-_Fe. Magnetic measurements showed coercive field strength of 50Oe in ML70 prepared by modified aperture geometry Fe[A]/Si[O]. A significant improvement in the neutron polarization efficiency is observed in multilayer ML70 with the use of modified aperture geometry as compared to similar sample prepared by normal aperture.

Keywords: Aperture; X-ray reflectometry; Stress anisotropy; Fe/Si; Multilayer; Magnetic anisotropy; Polarization efficiency

Direct immobilization and hybridization of DNA on group III nitride semiconductors by Xiaobin Xu; Vibhu Jindal; Fatemeh Shahedipour-Sandvik; Magnus Bergkvist; Nathaniel C. Cady (pp. 5905-5909).

A key concern for group III-nitride high electron mobility transistor (HEMT) biosensors is the anchoring of specific capture molecules onto the gate surface. To this end, a direct immobilization strategy was developed to attach single-stranded DNA (ssDNA) to AlGaN surfaces using simple printing techniques without the need for cross-linking agents or complex surface pre-functionalization procedures. Immobilized DNA molecules were stably attached to the AlGaN surfaces and were able to withstand a range of pH and ionic strength conditions. The biological activity of surface-immobilized probe DNA was also retained, as demonstrated by sequence-specific hybridization experiments. Probe hybridization with target ssDNA could be detected by PicoGreen fluorescent dye labeling with a minimum detection limit of 2nM. These experiments demonstrate a simple and effective immobilization approach for attaching nucleic acids to AlGaN surfaces which can further be used for the development of HEMT-based DNA biosensors.

Keywords: PACS; 81.05.Ea; 82.39.PjGroup III–V semiconductors; HEMT; DNA; Sensor; Immobilization

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM by Surendra Singh; Saibal Basu; S.K. Ghosh (pp. 5910-5916).

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air–film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air–film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.

Keywords: PACS; 61.12.Ha; 68.35.Ct; 68.37.PsNeutron reflectometry; AFM; Electrodeposition; Morphology

Photosensitivity of nanocrystalline ZnO films grown by PLD by R. Ayouchi; L. Bentes; C. Casteleiro; O. Conde; C.P. Marques; E. Alves; A.M.C. Moutinho; H.P. Marques; O. Teodoro; R. Schwarz (pp. 5917-5921).

We have studied the properties of ZnO thin films grown by laser ablation of ZnO targets on (0001) sapphire (Al₂O₃), under substrate temperatures around 400°C. The films were characterized by different methods including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS analysis revealed that the films are oxygen deficient, and XRD analysis with θ–2 θ scans and rocking curves indicate that the ZnO thin films are highly c-axis oriented. All the films are ultraviolet (UV) sensitive. Sensitivity is maximum for the films deposited at lower temperature. The films deposited at higher temperatures show crystallite sizes of typically 500nm, a high dark current and minimum photoresponse. In all films we observe persistent photoconductivity decay. More densely packed crystallites and a faster decay in photocurrent is observed for films deposited at lower temperature.

Keywords: PACS; 68.35.Ct; 81.15.Fg; 72.20.Jv; 72.40.+wZnO thin films; Pulsed laser deposition; Persistent photoconductivity; Polycrystalline films

Structure, dielectric and ferroelectric properties of highly (100)-oriented BaTiO₃ grown under low-temperature conditions by J.B. Xu; B. Shen; J.W. Zhai (pp. 5922-5925).

The highly (100)-oriented BaTiO₃ thin films were fabricated on LaNiO₃(100)/Pt/Ti/SiO₂/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400°C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO₃ phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1kHz to 1MHz was obtained. The room temperature remanent polarization (2 P_r) and coercive field were found to be ∼5μC/cm² and 50kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10⁹ switching cycles.

Keywords: PACS; 68.55.Jk; 77.22.Gm; 77.84.s; 81.20.FwThin films; Crystallographic orientation; Dielectric properties; Ferroelectricity

New design of nozzle structures and its effect on the surface and crystal qualities of thick GaN using a horizontal HVPE reactor by Jiejun Wu; Lubing Zhao; Dongyuan Wen; Ke Xu; Zhijian Yang; Guoyi Zhang; Hui Li; Ran Zuo (pp. 5926-5931).

High-quality thick GaN films without cracks were achieved by using a new nozzle structure in the reactor grown by the hydride vapor phase epitaxy on sapphire substrates. Optical contrast microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray double diffraction (XRD) and cathodoluminescence (CL) were carried out to reveal the surface, crystal and optical properties of the GaN epilayer. It was found that the nozzle structure in the reactor has a large effect on the growth rate, surface flat, crystal quality, and the uniformity of the growth. Compared with the old one, the new nozzle structure (denoted as multi-layers nozzle) can improve dramatically the properties of thick GaN. Mirror, colorless and flat GaN thick film was obtained and its (0002) FWHM results were reduced from 1000 to 300arcsec when the new nozzle was used. AFM result revealed a step flow growth mode for GaN layer with the new nozzle. Room-temperature CL spectra on the GaN films showed a strong near-band-edge peak for the new nozzle, but there is only weak emitting peak for the old nozzle. New nozzle structure can improve the uniform of flow field near the surface of substrates compared with the old one, which leads to the improvement of properties of GaN thick film by hydride vapor phase epitaxy (HVPE).

Keywords: PACS; 68.55.−a; 78.55.Cr; 81.15.GhThick GaN; Nozzle structures; Reactor; Hydride vapor phase epitaxy; Surface and crystal qualities

Effects of atomic oxygen irradiation on the surface properties of phenolphthalein poly(ether sulfone) by Xianqiang Pei; Yan Li; Qihua Wang; Xiaojun Sun (pp. 5932-5934).

To study the effects of low earth orbit environment on the surface properties of polymers, phenolphthalein poly(ether sulfone) (PES-C) blocks were irradiated by atomic oxygen in a ground-based simulation system. The surface properties of the pristine and irradiated blocks were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM). It was found that atomic oxygen irradiation induced the destruction of PES-C molecular chains, including the scission and oxidation of PES-C molecular chains, as evidenced by FTIR and XPS results. The scission of PES-C molecular chains decreased the relative concentration of C in the surface, while the oxidation increased the relative concentration of O in the surface. The changes in surface chemical structure and composition also changed the surface morphology of the block, which shifted from smooth structure before irradiation to “carpet-like” structure after irradiation.

Keywords: PACS; 94.05.Dd (Radiation processes)Low earth orbit; Atomic oxygen; Irradiation; Surface property; Polymer

Suspension plasma sprayed composite coating using amorphous powder feedstock by Dianying Chen; Eric H. Jordan; Maurice Gell (pp. 5935-5938).

Al₂O₃–ZrO₂ composite coatings were deposited by the suspension plasma spray process using molecularly mixed amorphous powders. X-ray diffraction (XRD) analysis shows that the as-sprayed coating is composed of α-Al₂O₃ and tetragonal ZrO₂ phases with grain sizes of 26nm and 18nm, respectively. The as-sprayed coating has 93% density with a hardness of 9.9GPa. Heat treatment of the as-sprayed coating reveals that the Al₂O₃ and ZrO₂ phases are homogeneously distributed in the composite coating.

Keywords: Alumina; Zirconia; Suspension plasma spray; Amorphous powders; Nanocomposites

Synthesis of the vertically aligned carbon hexagonal nanoprism arrays and their application for field emission by H.X. Zhang; P.X. Feng (pp. 5939-5942).

A simple approach is demonstrated for effectively growing large-area vertically aligned carbon hexagonal nanoprism arrays on molybdenum substrates by the catalyst-assisted pulsed laser deposition techniques. The carbon hexagonal nanoprisms have uniform shape and length, almost aligned vertically on the substrate, and the average diameters are about 30nm. The internal angles of the nanoprisms present 60°. The vertically aligned nanorods have also been obtained for a comparison in the presence of catalyst Fe. The sample with vertically aligned carbon hexagonal nanoprism arrays exhibits better field emission behaviors than that with aligned carbon nanorod arrays.

Keywords: Hexagonal nanoprism; PLD; SEM; TEM; Field emission

Influence of crystal orientation on copper oxidation failure by Jie Gao; Anmin Hu; Ming Li; Dali Mao (pp. 5943-5947).

The influences of crystal orientation on copper oxidation were investigated. The results indicated that crystal orientation of copper substrate has a great effect on the growth rate, the morphology of oxide film and the extent of oxidation failure. Shear test showed the adhesion strength between Cu(110) and its oxide film was the highest, whereas, the adhesion strength between Cu(311) and its oxide film was the lowest. SEM observations revealed that the oxide film grown on Cu(311) delaminated from substrate seriously, while the oxide film grown on Cu(100) and Cu(110) did not reveal such a phenomenon. Cu(100) and Cu(110) exhibited thinner oxide thickness compared to those on Cu(311) and Cu(111). The activation energy for oxide growth on Cu(100) and Cu(110) was calculated to be the highest while that on Cu(311) was the lowest.

Keywords: Crystal orientation; Copper; Oxidation; Failure

Dry etching characteristics of GaN for blue/green light-emitting diode fabrication by K.H. Baik; S.J. Pearton (pp. 5948-5951).

The etch rates, surface morphology and sidewall profiles of features formed in GaN/InGaN/AlGaN multiple quantum well light-emitting diodes by Cl₂-based dry etching are reported. The chlorine provides an enhancement in etch rate of over a factor of 40 relative to the physical etching provided by Ar and the etching is reactant-limited until chlorine gas flow rates of at least 50 standard cubic centimeters per minute. Mesa sidewall profile angle control is possible using a combination of Cl₂/Ar plasma chemistry and SiO₂ mask. N-face GaN is found to etch faster than Ga-face surfaces under the same conditions. Patterning of the sapphire substrate for improved light extraction is also possible using the same plasma chemistry.

Keywords: GaN; Dry etching

On the optical properties of amorphous Ge–Ga–Se–KBr films prepared by pulsed laser deposition by R.K. Pan; H.Z. Tao; C.G. Lin; H.C. Zang; X.J. Zhao; T.J. Zhang (pp. 5952-5956).

Amorphous thin films (1− x)(4GeSe₂–Ga₂Se₃)– xKBr ( x=0, 0.1, 0.2, 0.3) were prepared by the pulsed laser deposition (PLD) technique. The optical parameters were calculated using the Swanepoel method from the optical transmission spectra. The optical band gap (Egopt) of the studied films increased while the index of refraction decreased when increased the content of KBr. The Tauc slopes were discussed as an indicator of the degree of structural randomness of amorphous semiconductors. The index of refraction decreased andEgopt increased after annealing of as-deposited films below the glass transition temperature. The thermal-bleaching and thermal- contraction effects were observed, which are discussed in relation to the reduction in the density of homopolar bonds confirmed by the Raman spectra analysis and the decreased amount of fragments of the as-deposited films, respectively.

Keywords: Ge–Ga–Se–KBr films; Pulsed laser deposition; Optical properties; Annealing

Preparation of nanocone ZnO thin film and its aging effect of photoluminescence by Linhua Xu; Linxing Shi; Xiangyin Li (pp. 5957-5960).

In this work, a nanocone ZnO thin film was prepared by electron beam evaporation on a Si (100) substrate. The structural properties of the film were investigated by X-ray diffraction (XRD), atomic force microscopy and laser Raman scattering, respectively. The aging effect of the nanocone ZnO thin film was studied by photoluminescence spectra. The structural analyses show that the prepared ZnO thin film has a hexagonal wurtzite structure and is preferentially oriented along the c-axis perpendicular to the substrate surface. The photoluminescence spectra show that with the increase of aging time, the green emission of the nanocone ZnO thin film gradually decreases while the ultraviolet emission somewhat increases. The reason for this phenomenon is likely that the green-emission-related oxygen vacancies in the film are gradually filled up. The Raman scattering analyses also suggest that the intensity of the Raman peak related to oxygen vacancies in the nanocone ZnO thin film declines after the film is aged in air for a year. Therefore, the authors think the green emission is mainly connected with oxygen vacancy defects.

Keywords: PACS; 68.37.Ps; 71.55.Gs; 74.25.Gz; 81.15.−zNanocone ZnO thin film; Electron beam evaporation; Aging effect; Photoluminescence; Raman scattering

Surface modification of cobalt–chromium–tungsten–nickel alloy using octadecyltrichlorosilanes by Gopinath Mani; Marc D. Feldman; Sunho Oh; C. Mauli Agrawal (pp. 5961-5970).

Cobalt–chromium (Co–Cr) alloys have been extensively used for medical implants because of their excellent mechanical properties, corrosion resistance, and biocompatibility. This first time study reports the formation and stability of self-assembled monolayers (SAMs) on a Co–Cr–W–Ni alloy. SAMs of octadecyltrichlorosilanes (OTS) were coated on sputtered Co–Cr–W–Ni alloy thin film and bulk Co–Cr–W–Ni alloy. OTS SAM coated alloy specimens were characterized using contact angle goniometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Contact angle analysis and FTIR suggested that ordered monolayers were coated on both sputtered and bulk alloy. XPS suggested the selective dissolution of cobalt from the alloy during the formation of OTS SAM. The bonding between the alloy and the OTS SAM was mainly attributed to Si–O–Cr and Si–O–W covalent bonds and a smaller contribution from Si–O–Co bonds. AFM images showed the distribution of islands of monolayers coated on the alloy. The height of monolayers in majority of the islands was closer to the theoretical length of fully extended OTS molecules oriented perpendicular to the surface. The stability of OTS SAM was investigated in tris-buffered saline at 37°C for up to 7 days. Contact angle, FTIR, and XPS collectively confirmed that the monolayers remain ordered and bound to the alloy surface under this condition. This study shows that Co–Cr alloys can be surface modified using SAMs for potential biomedical applications.

Keywords: Biomaterials surfaces; Cobalt–chromium alloys; Self-assembled monolayers; Silanes

Structure transformations and hydrogen storage properties of co-sputtered MgNi films by L. Pranevicius; E. Wirth; D. Milcius; M. Lelis; L.L. Pranevicius; A. Bacianskas (pp. 5971-5974).

The quantity of accommodated and distribution profiles of hydrogen in 1.5-μm thick co-sputtered MgNi films after uptake of hydrogen at 800kPa pressure within the temperature range 200–250°C during 1h, 3h, 6h and 72h are measured. The occurring phase changes are followed by X-ray diffraction measurements at room temperature. We conclude that the hydrogenation process involves two stages: (i) the fast nucleation of the initial Mg₂NiH₄ layer near the substrate interface and (ii) the slow random nucleation of the same phase within the remaining part of the film. The growth of the initial hydride layer may be blocked by the surface oxide barrier layer formed during hydrogenation. We find that hydrogen-induced structural transformations are correlated with oxygen contamination and modify hydrogen storage properties.

Keywords: MgNi films; Structure; Hydrogen storage

Preparation and photocatalytic activity of CeO₂/TiO₂ interface composite film by Bangtong Jiang; Shengyi Zhang; Xiaozhu Guo; Baokang Jin; Yupeng Tian (pp. 5975-5978).

The CeO₂/TiO₂ and TiO₂/CeO₂ interface composite films were prepared on glass substrates by the sol–gel process via dip-coating and calcining technique. The scanning electron microscopy (SEM) revealed that the TiO₂ layer has a compact and uniformity glasslike surface with 200nm in thickness, and the CeO₂ layer has a coarse surface with 240nm in thickness. The X-ray diffractometer (XRD) analysis showed that the TiO₂ layer is made up of anatase phase, and the CeO₂ layer is structured by cubic fluorite phase. Through a series of photo-degradation experiments, the relationship of the photocatalytic activity with the constituents of the films was studied. In virtue of the efficient interfacial charge separation via the process of electron transfer from TiO₂ to CeO₂, the photocatalytic activity of the CeO₂/TiO₂ composite film is high. Contrarily, the photocatalytic activity of the TiO₂/CeO₂ composite film is low, due to its inert surface made up of CeO₂ with broad bandwidth. Apart from the effect of the film structure, the effect of film thickness on photocatalytic activity was also discussed.

Keywords: PACS; 68.55.−a; 81.15.−zCeO; ₂; /TiO; ₂; Composite film; Sol–gel; Photocatalysis

Preparation, characterization and surface p K_a values of poly( N-vinyl-2-pyrrolidone)/chitosan blend films by Serkan Demirci; Ali Alaslan; Tuncer Caykara (pp. 5979-5983).

Blend films of poly( N-vinyl-2-pyrrolidone) (PVP) and chitosan (CTS) were prepared by casting method from acetic acid solutions. All blend films obtained are optically clear to the naked eye. The structure and physical properties of the blend films were analyzed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical testing (Instron) and contact-angle measurements. The ATR-FTIR results indicated that there is no detectable band shifts at 1650cm⁻¹. From TGA studies, it was found that the onset degradation temperature of the blends almost unchanged due to the presence of a weak interaction between PVP and CTS chains. The DSC analysis showed a single glass transition temperature for all the blends, indicating that these polymers are miscible over the entire composition range. The mechanical properties of the blends, such as breaking stress and elongation at break and Young modulus were greatly affected with increase of CTS content. In addition, we found that the blends exhibit well defined contact angle titration curves from which the surface p K_a values were determined. In conclusion, these experimental findings provide fundamental knowledge for the preparation of bioreactive surfaces of controlled reactivity on CTS based blends.

Keywords: Poly(; N; -vinyl-2-pyrrolidone); Chitosan; Blends; Contact angle titration

Structural and mechanical characteristics of (103) AlN thin films prepared by radio frequency magnetron sputtering by Ping-Feng Yang; Sheng-Rui Jian; Sean Wu; Yi-Shao Lai; Chung-Ting Wang; Rong-Sheng Chen (pp. 5984-5988).

The (103)-oriented aluminum nitride (AlN) thin film is an attractive piezoelectric material for the applications in surface acoustic wave and film bulk acoustic wave resonator devices. In this work, we repot structural and mechanical characteristics of (103) AlN thin films deposited onto (100) Si substrates with radio frequency magnetron sputtering at different sputtering powers at 150, 250, and 350W. Comparisons were made on their crystalline structures with X-ray diffraction, surface morphologies with atomic force microscopy, mechanical properties with nanoindentation, and tribological responses with nanoscratch. Results indicate that for the sputtering power of 350W, a high-quality (103) AlN thin film, whose hardness is 18.91±1.03GPa and Young's modulus is 242.26±8.92GPa, was obtained with the most compact surface condition.

Keywords: Aluminum nitride; Thin film; Nanoindentation; Nanoscratch

Synthesis, characterization and photodegradation study of mixed-phase titania hollow submicrospheres with rough surface by Rongbo Zheng; Xianwei Meng; Fangqiong Tang (pp. 5989-5994).

Titania hollow submicrospheres with mixed phase (anatase–brookite or anatase–rutile) were synthesized via the combination of hydrothermal treatment and calcination of submicrospheres consisting of a polystyrene core and an amorphous TiO₂ shell. After hydrothermal treatment, amorphous titania shell could be transformed to anatase–brookite shell consisting of loose packed titania nanocrystals, which could be further converted to anatase–brookite (below 700°C) or anatase–rutile titania (700–800°C) hollow spheres with rough surface via calcination. The loose packing of titania nanocrystals not only inhibited the transformation temperature from anatase to rutile, but also provided titania hollow submicrospheres with high photodegradation activity of Rhodamine B. The photocatalytic activity of titania hollow spheres increased firstly then decreased when the calcination temperature was varied in the range of 450–800°C, while hollow spheres obtained via calcinating at 700°C exhibited the highest photocatalytic activity, which was five times higher than that of counterpart without hydrothermal treatment.

Keywords: Hydrothermal; Titania; Hollow spheres; Mixed-phase; Photocatalysis

Composition influence of SiN x gate insulator fabricated by radio frequency (RF) Magnetron sputtering on characteristics of organic thin-film transistors by Guang-Cai Yuan; Zheng Xu; Su-Ling Zhao; Fu-Jun Zhang; Xiao-Yun Jia; Na Xu; Qin-Jun Sun; Xu-Rong Xu (pp. 5995-5998).

To investigate the effect of composition of SiN x on the properties of organic thin-film transistors (OTFTs), we fabricated bottom gate top contact OTFTs devices with different composition SiN x gate insulator. Pentacene based OTFTs with SiN x insulator, prepared using an interface modification process of UV-ozone treatment, exhibited effective mobility of 0.63cm2/Vs and on/off current ratio of 10⁵. Overall improvement in field-effect mobility, threshold voltage was observed as silicon content in SiN x increases. The results demonstrate that the viability of using SiN x for OTFTs and of UV-ozone treatment could be used to improve the properties of organic thin-film transistors. The dependence of the contact angle on the SiN x film composition is evident for the untreated samples, the contact angle increases as the silicon content in the untreated nitride film increases. In contrast, the rise in contact angle across all samples after surface treatment signifies effective surface modification to promote hydrophobicity of the nitride surface. The hydrophobic surface is needed for the organic semiconductor.

Keywords: Organic thin-film transistor; Film composition; Hydrophobicity

Effects of annealing on structural and morphological properties of e-beam evaporated AgGaSe₂ thin films by H. Karaagac; M. Parlak (pp. 5999-6006).

Polycrystalline AgGaSe₂ thin films were deposited by using single crystalline powder of AgGaSe₂ grown by vertical Bridgman-Stockbarger technique. Post-annealing effect on the structural and morphological properties of the deposited films were studied by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDXA) measurements. XRD analysis showed that as-grown films were in amorphous structure, whereas annealing between 300 and 600°C resulted in polycrystalline structure. At low annealing temperature, they were composed of Ag, Ga₂Se₃, GaSe, and AgGaSe₂ phases but with increasing annealing temperature AgGaSe₂ was becoming the dominant phase. In the as-grown form, the film surface had large agglomerations of Ag as determined by EDXA analysis and they disappeared because of the triggered segregation of constituent elements with increasing annealing temperature. Detail analyses of chemical composition and bonding nature of the films were carried out by XPS survey. The phases of AgO, Ag, Ag₂Se, AgGaSe₂, Ga, Ga₂O₃, Ga₂Se₃, Se and SeO₂ were identified at the surface (or near the surface) of AgGaSe₂ thin films depending on the annealing temperature, and considerable changes in the phases were observed.

Keywords: Chalcopyrite compounds; AgGaSe; ₂; X-ray diffraction; Scanning electron microscopy; X-ray photoelectron spectroscopy

Surface-enhanced Raman scattering (SERS) spectra of Methyl Orange in Ag colloids prepared by electrolysis method by M.Z. Si; Y.P. Kang; Z.G. Zhang (pp. 6007-6010).

Polyvinyl alcohol (PVA)-protected Ag colloids were prepared by an electrolysis method. The surface-enhanced Raman scattering (SERS) spectra of Methyl Orange (MO), one of the Azo-dye molecules, in Ag colloids were successfully recorded with good concordance comparing to the theoretical results calculated by the Gaussian’98 program. The MO was adsorbed on the surface of Ag nanoparticles by trans-form which plays an important role for the SERS effect. However, the SERS spectra of MO in Ag colloids prepared by chemical reduction method did not appear which may be because of the competition of the borate or citrate ions with the MO. In order to test the applicability of these colloids, the SERS spectra of Sudan red (III) (SR), another of Azo-dye molecules, were measured and the result was good.

Keywords: SERS; Ag colloids; Electrolysis; MO

Nanoporous carbon spheres and their application in dispersing silver nanoparticles by Shaochun Tang; Yuefeng Tang; Sascha Vongehr; Xiaoning Zhao; Xiangkang Meng (pp. 6011-6016).

Monodisperse NCS with pores of about 0.3nm in diameter were prepared and the effects of reaction parameters on surface roughness, sphere diameter and porosity of NCS were investigated systematically. Silver NP was deposited on the NCS using a facile ultrasonic electrodeposition technique. They have a narrow size range (12–16nm), a well-separated distribution and a high particle density.Monodisperse nanoporous carbon spheres (NCS) were synthesized in large quantities via a facile hydrothermal synthesis. It is found that the NCS have rough surfaces with a large quantity of uniformly distributed protruding and concaving zones. Large quantities of nanopores of about 0.3nm in diameter are distributed uniformly on the whole sphere surfaces. The effects of reaction parameters on the surface roughness, sphere diameter and pore size of NCS were investigated. Taking the NCS as substrates, silver nanoparticles (NPs) were deposited onto their surfaces using a one-step ultrasonic electrodeposition procedure. The deposited silver NP has a uniform distribution, a high particle density and a narrow size range of 12–16nm in diameter. This study demonstrates an efficient approach to fabricate noble-metal/carbon nanocomposites.

Keywords: PACS; 81.07.−b; 81.05.Uw; 82.45.Aa; 68.37.LpNanoporous carbon spheres; Ultrasonic electrodeposition; Ag/C nanocomposite

CF₄ radio frequency plasma surface modification of silicone rubber for use as outdoor insulations by Song-Hua Gao; Ming-Kai Lei; Yang Liu; Li-Shi Wen (pp. 6017-6023).

For further prolonging the serve life of silicone rubber (SIR) for outdoor insulation and increasing its resistance of pollution flashover, surface modifications of SIR were carried out via CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200W for a treatment time up to 20min under CF₄ flow rate of 20sccm. Static contact angle measurement was employed to estimate the change of hydrophobicity of the modified SIR. The variation of the surface functional groups of the modified SIR was observed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). The surface topography was observed by atom force microscopy (AFM). The results indicate that the static contact angle of SIR surface is improved from 100.7° to 150.2° via the CF₄ plasma modification, and the super-hydrophobic surface of modified SIR, which corresponds to a static contact angle of 150.2°, appears at RF power of 200W for a 5-min treatment time. According to the results, it is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of roughness created by the ablation reaction of CF₄ plasma and the formation of [SiF_x(CH₃)2−_xO]_n ( x=1, 2) structure produced by the direct attachment of F atoms to Si.

Keywords: Silicone rubber; Super-hydrophobic; CF; ₄; plasma; XPS; AFM

Transparent conducting Sn-doped Ga1.4In0.6O3 films prepared on α-Al₂O₃ (0001) by MOCVD by Fan Yang; Jin Ma; Caina Luan; Lingyi Kong (pp. 6024-6027).

Sn-doped Ga_1.4In_0.6O₃ films have been prepared on α-Al₂O₃ (0001) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The Sn-doping was varied from 0% to 7% (atomic ratio). Polycrystalline films with resistivity of 4.9×10⁻³Ωcm, carrier concentration of 5.9×10¹⁹cm⁻³ and Hall mobility of 21.4cm²v⁻¹s⁻¹ was obtained at 5at.% of Sn concentration. The average transmittance for the Sn-doped Ga_1.4In_0.6O₃ films in the visible range was over 90%. The bandgap of the films varies from 3.85 to 4.21eV.

Keywords: Sn-doped Ga; _1.4; In; _0.6; O; ₃; thin films; Electrical and optical properties; MOCVD

Growth of carbon nanotubes using nanocrystalline carbon catalyst by Yong Seob Park; Eun Chang Choi; Byungyou Hong (pp. 6028-6032).

The basic growth of carbon nanotubes (CNTs) involves dissociation of hydrocarbon molecules over a metal layer as a catalyst. Generally, the metals used for the catalyst include nickel, cobalt, gold, iron, platinum, and palladium. However, the metal catalyst used with CNTs could have a harmful influence on the electrical properties of electronic devices. Therefore, we propose the use of nanocrystalline carbon (nc-C) as the catalyst for the growth of CNTs. We used a nc-C catalyst layer deposited by the closed-field unbalanced magnetron (CFUBM) sputtering method, and CNTs were grown by the hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH₃) as a pretreatment and acetylene gas (C₂H₂) as a carbon source. The CNTs were grown on the nc-C layers pretreated with a variation of the pretreatment time. The characteristics of the pretreated nc-C layers and the grown CNTs were investigated by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) measurements. Also, the structural variation of the pretreated nc-C layers was investigated by Raman measurement. We used the nc-C catalyst without metal, and we confirmed that our CNTs were composed with only carbon elements through an EDS measurement. Also, the pretreatment time was attributed to the growth of CNTs.

Keywords: Nanocrystalline carbon; Carbon nanotube; Hot filament PECVD; Raman

Effect of filament biasing on nanocrystalline-Si films deposited by hot wire chemical vapor deposition by Bibhu P. Swain; Bhabani S. Swain; Seung M. Yang; Nong M. Hwang (pp. 6033-6037).

Nanocrystalline silicon (nc-Si) films were deposited by hot wire chemical vapor deposition with applying positive or negative filament biases. These films were characterized by Raman spectroscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Plasmon loss of the Si(2p) band region was shifted to higher energy due to dielectric changes with applied filament biases from negative to positive voltage. A semi-quantitative study of the valence band structure was employed to analyze the bias effect of the valance band in nc-Si networks. Nc-Si with a positive filament bias shows better microstructural properties than those with a negative bias and without biasing nc-Si films.

Keywords: Raman spectroscopy; XPS; FESEM; HWCVD

Annealing effects on the plasmonic excitations of metal/metal interfaces by A. Politano; V. Formoso; G. Chiarello (pp. 6038-6042).

The effects of the annealing procedure at 400–450K on the electronic properties of nanoscale thin films of Ca, Au and Ag grown on Cu(111) at room temperature were probed by high-resolution electron energy loss spectroscopy measurements. Ca surface plasmon underwent to a significant red-shift upon annealing, due to the oxidation of the topmost Ca layer. Water strongly interacted with the CaO interface at room temperature. Au surface plasmon disappeared upon annealing the gold film, as a consequence of the formation of an Au–Cu alloy. Ag surface plasmon red-shifted both in the annealed adlayer and with increasing temperature compared with the frequency recorded for the as-deposited silver film.

Keywords: Electron energy loss spectroscopy (EELS); Silver; Gold; Calcium; Thin films

Effect of thermal annealing on nanoimprinted Cu–Ni alloys using molecular dynamics simulation by Te-Hua Fang; Cheng-Da Wu; Win-Jin Chang; Sung-Shui Chi (pp. 6043-6047).

The mechanical behaviors of nanoimprinted Cu–Ni alloys before and after annealing were studied using molecular dynamics simulation with a tight-binding potential. The results showed that when the punch is advancing, the punching force obtained from the simulation with a tight-binding potential is lower than with the Morse potential. During and after withdrawing the punch from the specimen, the adhesive phenomena are observed and the large residual stress in the Cu–Ni alloys is induced. During the annealing process, the internal energy of Cu–Ni alloys decreased with increasing the temperature and the component of Cu. In addition, comparing the maximum residual stress in the Cu–Ni alloys with and without annealing treatment, the stress is significantly released after annealing, especially in the higher component of Ni.

Keywords: Thermal annealing; Nanoimprint; Molecular dynamics; Residual stress; Cu–Ni alloys

Fracture force analysis at the interface of Pd and SrTiO₃ by S. Nazarpour; C. Zamani; A. Cirera (pp. 6048-6053).

The objective of this work is to develop an experimental indentation based method to determine the fracture force at the interface of Pd thin films and SrTiO₃ perovskite substrate. This paper reports on the results obtained for indentation into Pd thin films which were deposited in various thicknesses from 20nm to 200nm under vacuum and 300°C substrate temperature by an electron beam physical vapor deposition. Initially, the relation between grain size, elastic module and hardness was considered as a function of film thickness. Thereafter, in developing new method, oscillating indentation was performed with different applied forces and oscillating times in order to measure the critical fracture force in each thickness. The effect of oscillating time on plastically deformed regions surrounding an indentation was schematically explained in conjunction with variation of oscillating time to determine the interfacial properties of the Pd thin film. Furthermore, the accuracy of the critical fracture force was ensured by applied force versus piling up height plot. The method is validated experimentally for the soft thin films over the hard substrate. However, further study would be essential to measure the film adhesion by means of fracture force at the interface.

Keywords: Soft thin films; Nanoindenter; Fracture force; Oscillating indentation

Low-temperature deposition of transparent conducting ZnO:Zr films on PET substrates by DC magnetron sputtering by Huafu Zhang; Chengxin Lei; Hanfa Liu; Changkun Yuan (pp. 6054-6056).

Transparent conducting zirconium-doped zinc oxide (ZnO:Zr) films were firstly deposited on polyethylene terephthalate (PET) substrates with ZnO buffer layers by DC magnetron sputtering at room temperature. Dependence of physical properties of ZnO:Zr films on deposition pressure was systematically studied. All the deposited films were polycrystalline and (100) oriented. When deposition pressure increases from 1 to 2.5Pa, the crystallinity of the films improves and the resistivity decreases. While deposition pressure increases from 2.5 to 3.5Pa, the crystallinity of the films deteriorates and the resistivity increases. The lowest resistivity of 1.8×10⁻³Ωcm was obtained for the films deposited at the optimum deposition pressure of 2.5Pa. All the films present a high transmittance of above 86% in the wavelength range of the visible spectrum.

Keywords: Zirconium-doped zinc oxide; Polyethylene terephthalate; DC magnetron sputtering; Thin films

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Applied Surface Science (v.255, #11)

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Applied Surface Science (v.255, #11)