Applied Surface Science (v.256, #11)
Quality of horizontally aligned single-walled carbon nanotubes: Is methane as carbon source better than ethanol? by Fenglei Gao; Lijie Zhang; Yun Yang; Shaoming Huang (3357-3360).
Chemical vapor deposition (CVD) growth of horizontally aligned single-walled carbon nanotubes (SWNTs) was studied using two representative carbon source sources: ethanol and methane. The resulting SWNTs were compared for similar reaction conditions which were based on the formation of Ni metal nanoparticles selective electrochemical deposition (SED) on the defect sites of SWNTs. The products were analyzed by Raman spectroscopy and SEM. The results demonstrate that methane was much better carbon source for growing high quality horizontal alignment of SWNTs than ethanol due to the etching effects of OH radicals on the SWNTs.
Keywords: Defect; Nanoparticle;
Photoluminescence and field emission properties of Sn-doped ZnO microrods by Lijun Li; Ke Yu; Yang Wang; Ziqiang Zhu (3361-3364).
Sn-doped ZnO (SZO) microrods have been fabricated by a thermal evaporation method. Effect of Sn dopant on the microstructure, morphological and composition of as-prepared SZO microrods have been investigated by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The influence of the doping concentration on the morphological of the microrods has been investigated. Photoluminescence (PL) of these SZO microrods exhibits a weak ultraviolet (UV) emission peak at around 382 nm and the strong green emission peak at around 525 nm at room temperature. Field emission measurements demonstrate that the SZO possess good performance with a turn-on field of ∼1.94 V/μm and a threshold field of ∼3.23 V/μm, which have promising application as a competitive cathode material in FE microelectronic devices.
Keywords: Semiconductors; Crystal growth; Field emission;
Effect of Mn doping on the microstructures and photoluminescence properties of CBD derived ZnO nanorods by Jihui Lang; Qiang Han; Changsheng Li; Jinghai Yang; Xue Li; Lili Yang; Dandan Wang; Hongju Zhai; Ming Gao; Yongjun Zhang; Xiaoyan Liu; Maobin Wei (3365-3368).
Mn-doped ZnO nanorods were synthesized from aqueous solutions of zinc nitrate hexahydrate, manganese nitrate and methenamine by the chemical solution deposition method (CBD). Their microstructures, morphologies and optical properties were studied in detail. X-ray diffraction (XRD) results illustrated that all the diffraction peaks can be indexed to ZnO with the hexagonal wurtzite structure. Scanning electron microscope (SEM) results showed that the average diameter of Mn-doped ZnO nanorods was larger than that of the undoped one. Photoluminescence (PL) spectra indicated that manganese doping suppressed the emission intensity and caused the blue shift of UV emission position compared with the undoped ZnO nanorods. In the Raman spectrum of Mn-doped ZnO nanorods, an additional mode at about 525 cm−1 appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.
Keywords: ZnO nanorods; Mn-doped; Raman spectroscopy; Photoluminescence;
Optimization of porous silicon preparation technology for SERS applications by M.V. Chursanova; L.P. Germash; V.O. Yukhymchuk; V.M. Dzhagan; I.A. Khodasevich; D. Cojoc (3369-3373).
A series of porous silicon samples prepared at different etching parameters, namely etchant composition, etching time and current density, was investigated as substrates for surface-enhanced Raman scattering (SERS). Silver nanostructures were deposited on porous silicon by immersion plating method and Rhodamine 6G was used as analyte. The relation between the etching parameters, morphology of porous silicon surface and its SERS efficiency after silver deposition is examined. We show that a high HF content in the etchant allows the formation of a film with close-packed silver nanocrystals, which possess strong surface enhancement properties.
Keywords: SERS substrate; Porous silicon; Silver crystallites; Rhodamine 6G;
Thin films of molecular materials synthesized from C32H20N10M (M = Co, Pb, Fe): Film formation, electrical and optical properties by A. Rodríguez; M.E. Sánchez Vergara; V. García Montalvo; A. Ortiz; J.R. Alvarez (3374-3379).
In this work, the synthesis of molecular materials formed from metallic phthalocyanines and 1,4-phenylenediamine is reported. The powder and thin film (∼80–115 nm thickness) samples of the synthesized materials, deposited by vacuum thermal evaporation, show the same intra-molecular bonds in the IR spectroscopy studies, which suggests that the thermal evaporation process does not alter these bonds. The morphology of the deposited films was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and their optical and electrical properties were studied as well. The optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range 200–1200 nm. The absorption spectra recorded in the UV–vis region for the deposited samples showed two bands, namely the Q and Soret bands. The optical activation energy was calculated and found to be 3.41 eV for the material with cobalt, 3.34 eV for the material including lead and 3.5 eV for the material with iron. The effect of temperature on conductivity was measured for the thin films and the corresponding conduction processes are discussed in this work.
Keywords: Thin films; Optical properties; Electrical measurements;
Preparation of poly-o-phenylenediamine/TiO2/fly-ash cenospheres and its photo-degradation property on antibiotics by Pengwei Huo; Yongsheng Yan; Songtian Li; Huaming Li; Weihong Huang (3380-3385).
A series of poly-o-phenylenediamine/TiO2/fly-ash cenospheres(POPD/TiO2/fly-ash cenospheres) composites have been prepared from o-phenylenediamine and TiO2/fly-ash cenospheres under various polymerization conditions. The properties of the samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), specific surface area (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and UV–vis diffuse reflectance spectrum (UV–vis DRS). Photocatalytic activity was studied by degradation of antibiotics waste water under visible light. The results indicate that the photo-induced method is viable for preparing modified photocatalysts, and the modified photocatalysts have good absorption in visible light range. The photocatalysts of POPD/TiO2/fly-ash cenospheres which have good performance are prepared at pH 3 and 4, and the polymerized time around 40 min. When the photocatalysts are prepared under the conditions of pH 3 and polymerized time 40 min, the degradation rate of roxithromycin waste water could reach near 60%, and it indicates that the way of POPD modified TiO2/fly-ash cenospheres to degrade the antibiotics waste water is viable.
Keywords: Conducting polymer; TiO2/fly-ash cenospheres; Photo-degradation; Antibiotics; Roxithromycin;
Room-temperature deposition of crystalline patterned ZnO films by confined dewetting lithography by S. Sepulveda-Guzman; B. Reeja-Jayan; E. De la Rosa; U. Ortiz-Mendez; C. Reyes-Betanzo; R. Cruz-Silva; M. Jose-Yacaman (3386-3389).
In this work patterned ZnO films were prepared at room-temperature by deposition of ∼5 nm size ZnO nanoparticles using confined dewetting lithography, a process which induces their assembly, by drying a drop of ZnO colloidal dispersion between a floating template and the substrate. Crystalline ZnO nanoparticles exhibit a strong visible (525 nm) light emission upon UV excitation (λ = 350 nm). The resulting films were characterized by scanning electron microscopy (SEM) and atomic force microscope (AFM). The method described herein presents a simple and low cost method to prepare crystalline ZnO films with geometric patterns without additional annealing. Such transparent conducting films are attractive for applications like light emitting diodes (LEDs). As the process is carried out at room temperature, the patterned crystalline ZnO films can even be deposited on flexible substrates.
Keywords: Confined dewetting lithography; ZnO nanoparticles; Microcontact printing; Nano-patterning;
On the origin of intrinsic donors in ZnO by F. Sun; C.X. Shan; S.P. Wang; B.H. Li; J.Y. Zhang; Z.Z. Zhang; D.X. Zhao; B. Yao; D.Z. Shen; X.W. Fan (3390-3393).
As-grown undoped zinc oxide (ZnO) films have been annealed in zinc-rich, oxygen-rich and vacuum ambient, and the electron concentration varied greatly after the annealing process. It decreased nearly two orders of magnitude after the sample was annealed in oxygen, while increased nearly three times after annealed in metallic zinc ambient, and increased slightly after annealed in vacuum. It was found that the variation trend of the electron concentration is always the same with the expected variation of oxygen vacancy (VO) under the three investigated conditions, it is thus speculated that VO may be the dominant donor source in ZnO. By supplying more oxygen during the growth process to suppress VO, ZnO films with lower electron concentration were obtained, which verifies the above speculation.
Keywords: Zinc oxide; Intrinsic donors; Hall measurement; Carrier concentration;
Micro- to nanoscale surface morphology and friction response of tribological polyimide surfaces by P. Samyn; G. Schoukens; P. De Baets (3394-3408).
Sintered polyimide surfaces that were worn under macroscale conditions at different temperatures, were further characterised by contact-mode atomic force microscopy for getting insight in the tribophysical and -chemical processes at the micro- to nanoscale. Depending on the temperature, either mechanical interaction (23 °C < T < 100 °C), hydrolysis (120 °C < T < 140 °C), or imidisation (180 °C < T < 260 °C) results in different microscale surface characteristics. At low temperatures, surface brittleness and inter-grain fracture has been observed with an almost homogeneous friction pattern. At intermediate temperatures, the formation of a protecting local film leads to smoother surfaces with local lubricating properties. At high temperatures, different topographical and frictional patterns are observed depending on local imidisation or degradation. From AFM scans at the sub-micronscale, local debris depositions are observed and correspond to surface locations with locally reduced friction. From AFM scans at the nanoscale, polymer chain orientation is observed with formation of zig–zag or stretched molecular conformation: the latter is not induced by purely mechanical surface interactions or hydrolysis, but mainly results from tribochemically induced imidisation at high sliding temperatures. The present investigation describes the influences of local tribological interactions onto the macroscale wear behaviour of a polymer, and therefore aims at contributing to a better understanding of scaling between macro- to nanolevel tribological response.
Keywords: Polyimide; Tribochemistry; Atomic force microscopy; Morphology; Friction;
Generalized-stacking-fault energy and surface properties for HCP metals: A first-principles study by Xiaozhi Wu; Rui Wang; Shaofeng Wang (3409-3412).
We present first-principles calculations on the generalized-stacking-fault (GSF) energies and surface properties for several HCP metals on Mg, Be, Ti, Zn, and Zr, employing density functional theory (DFT) within generalized-gradient-approximation (GGA) and spin-polarized GGA (SGGA) using the Vienna ab initio simulation package (VASP). Using a supercell approach, stacking fault energies for the [1 1 2 ¯ 0] and [1 0 1 ¯ 0] slip systems, and surface properties on basal plane (0 0 0 1) have been determined. Our results show that GSF energy is sensitive to the primitive cell volumes and the ratio c / a for HCP metals. A spin-polarized calculations should be considered for transition-metal Ti, Zn, and Zr. The results for Mg from this work are good with ones from the previous ab initio and the experiments.
Keywords: HCP metals; First-principles; Generalized-stacking-fault energy (GSF); Surface properties;
Peak overlaps and corresponding solutions in the X-ray photoelectron spectroscopic study of hydrodesulfurization catalysts by Limei Qiu; Guangtong Xu (3413-3417).
Al2O3-SiO2-based Co(Ni)-Mo(W)-S catalysts are widely investigated hydrodesulfurization (HDS) catalysts in recent decades. XPS is a suitable technique to detect the surface properties of HDS catalysts. Typical overlapping spectra in the XPS analysis of HDS catalysts, such as Mo3d and S2s, Si2p and bremsstrahlung-induced Al KL23L23 using nonmonochromatic AlKα source, W4f and W5p3/2, as well as the disturbance of Auger lines on Ni2p and Co2p, are carefully studied in the present paper. Besides, effective methods to overcome the influence of peak overlaps are illustrated. These results would provide basic and important information in interpreting XPS results of HDS catalysts.
Keywords: XPS; HDS catalyst; Mo3d; Si2p; W4f; Ni2p; Co2p;
Atomic scale mass delivery driven by bend kink in single walled carbon nanotube by Biao Kan; Jianning Ding; Zhiyong Ling; Ningyi Yuan; Guanggui Cheng (3418-3422).
The possibility of atomic scale mass delivery by bend kink in single walled carbon nanotube was investigated with the aid of molecular dynamics simulation. By keeping the bending angle while moving the tube end, the encapsulated atomic scale mass such as atom, molecule and atom group were successfully delivered through the nanotube. The van der Waals interaction between the encapsulated mass and the tube wall provided the driving force for the delivery. There were no dramatic changes in the van der Waals interaction, and a smooth and steady delivery was achieved when constant loading rate was applied. The influence of temperature on the atom group delivery was also analyzed. It is found raising temperature is harmful to the smooth movement of the atom group. However, the delivery rate can be promoted under higher temperature when the atom group is situated before the kink during the delivery.
Keywords: Buckling; Carbon nanotube; Kink; Mass delivery; Molecular dynamics; van der Waals interaction;
Stability of hydrogen-terminated vicinal Si(1 1 1) surface under ambient atmosphere by M. Kolíbal; J. Čechal; M. Bartošík; J. Mach; T. Šikola (3423-3426).
In this paper a comparative study of different wet-chemical etching procedures of vicinal Si(1 1 1) surface passivation is presented. The stability against oxidation under ambient atmosphere was studied by X-ray photoelectron spectroscopy and atomic force microscopy. The best results were achieved by the buffered HF etching and the final smoothing of the surface by hot (72 °C) NH4F. The procedures consisting of a large number of etching steps were unsatisfactory, since the probability of contamination during each step was increasing. The passivated surface was stable against oxidation for at least 3 h under ambient atmosphere.
Keywords: Silicon substrates; Wet-chemical pre-treatment; Etching; Oxidation; X-ray photoelectron spectroscopy;
Investigation on cell biocompatible behaviors of polyaniline film fabricated via electroless surface polymerization by Sheng Liu; Jinqing Wang; Dong Zhang; Puliang Zhang; Junfei Ou; Bin Liu; Shengrong Yang (3427-3431).
Considering for the potential application in tissue engineering, polyaniline (PANi) film was fabricated via a two-step route: a self-assembled monolayer of C6H5NHC3H6Si(OMe)3 was firstly formed on the single-crystal Si substrate; the conducting PANi film was then prepared through electroless surface polymerization of the aniline molecules on the aniline monolayer-bearing silane surface in an acidic aqueous solution. The formation of PANi film on Si surface was confirmed by characterizations of X-ray photoelectron spectroscope (XPS) and specular reflectance Fourier transform infrared (SR-FTIR) spectrum, etc. At last, the proliferation behaviors of PC-12 cells on the PANi film surface were studied by the [3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) colorimetric assays, acridine orange fluorometric staining, and scanning electron microscope (SEM) observation, etc. The results demonstrate that the as-prepared PANi film provides high ability for cell proliferation, exhibiting promising potentials as surface coating to cultivate neuronal cells for applications in the tissue engineering.
Keywords: Polyaniline film; Electroless surface polymerization; PC-12 cell; Cell biocompatibility;
Growth characteristics and properties of ZnO:Ga thin films prepared by pulsed DC magnetron sputtering by W.T. Yen; Y.C. Lin; P.C. Yao; J.H. Ke; Y.L. Chen (3432-3437).
Transparent conductive ZnO:Ga thin films were deposited on Corning 1737 glass substrate by pulsed direct current (DC) magnetron sputtering. The effects of process parameters, namely pulse frequency and film thickness on the structural and optoelectronic properties of ZnO:Ga thin films are evaluated. It shows that highly c-axis (0 0 2) oriented polycrystalline films with good visible transparency and electrical conductivity were prepared at a pulsed frequency of 10 kHz. Increasing the film thickness also enlarged the grain size and carrier mobility which will subsequently lead to the decrease in resistivity. In summary, ZnO:Ga thin film with the lowest electrical resistivity of 2.01 × 10−4 Ω cm was obtained at a pulse frequency of 10 kHz with 500 nm in thickness. The surface RMS (root mean square) roughness of the film is 2.9 nm with visible transmittance around 86% and optical band gap of 3.83 eV.
Keywords: ZnO:Ga; Optoelectronic properties; Pulse frequency; Pulsed DC magnetron sputter;
The role of nitrogen in the preferential chromium segregation on the ferritic stainless steel (1 1 1) surface by J. Yuhara; T. Matsui (3438-3442).
The temperature dependence on the segregation behavior of the ferritic stainless steel single crystal (1 1 1) surface morphology has been examined by scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). AES clearly showed the surface segregations of chromium and nitrogen upon annealing. Nanoscale triangular chromium nitride clusters were formed around 650 °C and were regularly aligned in a hexagonal configuration. In contrast, for the ferritic stainless steel (1 1 1) surface with low-nitrogen content, chromium and carbon were found to segregate on the surface upon annealing and Auger spectra of carbon displayed the characteristic carbide peak. For the low-nitrogen surface, LEED identified a facetted surface with (2 × 2) superstructure at 650 °C. High-resolution STM identified a chromium carbide film with segregated carbon atoms randomly located on the surface. The facetted (2 × 2) superstructure changed into a (3 × 3) superstructure with no faceting upon annealing at 750 °C. Also, segregated sulfur seems to contribute to the reconstruction or interfacial relaxation between the ferritic stainless steel (1 1 1) substrate and chromium carbide film.
Keywords: Surface segregation; Steel; Nitrides; Carbides; Scanning tunneling microscopy;
In situ formation of Al2O3–SiO2–SnO2 composite ceramic coating by microarc oxidation on Al–20%Sn alloy by Zhijiang Wang; Lina Wu; Yulin Qi; Zhaohua Jiang (3443-3447).
In situ formation of Al2O3–SiO2–SnO2 composite ceramic coating on Al–20%Sn alloy was successfully fabricated in aqueous Na2SiO3 electrolyte by microarc oxidation technology. The compositions, structure, mechanical and tribological properties of the composite coating were detailed studied by scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction, hardness tester and ball-on-disc friction tester. It is found that the species originating from the Al–20%Sn alloy substrate and the electrolyte solution both participate in reaction and contribute to the composition of the coating, which results in the generated coating firmly adherent to the substrate. The composite ceramic coating can greatly improve the microhardness and tribological property of Al–20%Sn alloy.
Keywords: Microarc oxidation; Composite materials; Al–Sn alloy; Mechanical properties; Tribological property;
Electron impinging on metallic thin film targets by Z. Rouabah; N. Bouarissa; C. Champion (3448-3452).
Based on the Vicanek and Urbassek theory [M. Vicanek, H.M. Urbassek, Phys. Rev. B 44 (1991) 7234] combined to a home-made Monte Carlo simulation, the present work deals with backscattering coefficients, mean penetration depths and stopping profiles for 1–4 keV electrons normally incident impinging on Al and Cu thin film targets. The cross-sections used to describe the electron transport are calculated via the appropriate analytical expression given by Jablonski [A. Jablonski, Phys. Rev. B 58 (1998) 16470] whose new improved version has been recently given [Z. Rouabah, N. Bouarissa, C. Champion, N. Bouaouadja, Appl. Surf. Sci. 255 (2009) 6217]. The behavior of the backscattering coefficient, mean penetration depth and stopping profiles versus the metallic film thickness at the nanometric scale and beyond is here analyzed and discussed.
Keywords: Electron scattering; Thin films; Transport cross-sections; Nanometric scale;
Laser crystallization of amorphous silicon films investigated by Raman spectroscopy and atomic force microscopy by Jing Jin; Zhijun Yuan; Lu Huang; Sheng Chen; Weimin Shi; Zechun Cao; Qihong Lou (3453-3458).
The intrinsic and phosphorous (P)-doped hydrogenated amorphous silicon thin films were crystallized by laser annealing. The structural properties during crystallization process can be investigated. Observed redshifts of the Si Raman transverse optical phonon peak indicate tensile stress present in the films and become intense with the effect of doping, which can be relieved in P-doped films by introducing buffer layer structures. Based on experimental results, the established correlation between the stress and crystalline fraction (X C) suggests that the relatively high stress can limit the increase in X C and the highest crystalline fraction is obtained by a considerable stress release. At high laser energy density of 1250 mJ/cm2, the poorer crystalline quality and disordered structure of the film originating from the irradiation damage and defects lead to the low electron mobility.
Keywords: Laser annealing; Poly-Si; Crystallization; Stress;
The epoxy-siloxane/Al composite coatings with low infrared emissivity for high temperature applications by Chen Hu; Guoyue Xu; Xingmei Shen; Chunming Shao; Xiaoxing Yan (3459-3463).
Low infrared emissivity coatings with good thermal resistance were prepared by using epoxy-siloxane and aluminum as adhesive and pigment, respectively. The influence of chemical composition, surface texture, roughness and thickness on the infrared emissivity was systematically investigated. The detailed results of experimental investigation indicate that the cured composite coatings could possess low emissivity value. Due to reducing infrared absorption and forming uniform and compact char construction, the infrared emissivity decreases obviously. Both the surface roughness and thickness have a critical value, respectively. Too large roughness or thickness would not contribute to the decrease of the emissivity. Moreover, the composite coatings were tested for thermal stability in air to explore the effect of high-temperature environment on the emissivity. The results indicate that the composite coatings, still possessing low emissivity after the test, exhibit favorable thermal ageing and thermal shock resistance.
Keywords: Infrared emissivity; Thermal resistance; Epoxy-siloxane; Coating;
Nanoindentation characterization of GaN epilayers on A-plane sapphire substrates by Meng-Hung Lin; Hua-Chiang Wen; Chih-Yung Huang; Yeau-Ren Jeng; Wei-Hung Yau; Wen-Fa Wu; Chang-Pin Chou (3464-3467).
Gallium nitride (GaN) epilayers was deposited on a-axis sapphire substrate by means of metal-organic chemical vapor deposition (MOCVD) method. The GaN epilayers has been investigated in their repetition pressure-induced impairment events from nanoindentation technique and, the relative deformation effect was observed from atomic force microscopy (AFM). From the morphological studies, it is revealed that none of crack and particle was found even after the indentation beyond the critical depth on the residual indentation impression. The ‘pop-in’ event was explained by the interaction of the deformed region, produced by the indenter tip, with the inner threading dislocations in the GaN films. Pop-in events indicate the generation and motion of individual dislocation, which is measured under critical depth and, no residual deformation of the GaN films is observed.
Keywords: Gallium nitride; Nanoindentation; Atomic force microscopy;
Low operating temperature of oxygen gas sensor based on undoped and Cr-doped ZnO films by N. Al-Hardan; M.J. Abdullah; A. Abdul Aziz; H. Ahmad (3468-3471).
Undoped and doped ZnO with 1 at.% (atomic percentage) chromium (Cr) was synthesized by RF reactive co-sputtering for oxygen gas sensing applications. The prepared films showed a highly c-oriented phase with a dominant (0 0 2) peak at a Bragg angle of around 34.2°. The operating temperature of the prepared ZnO sensor was around 350 °C and shifted to around 250 °C for the doped ZnO sensor which is lower than that of previously reported work. The sensitivity of the sensor toward oxygen gas was enhanced by doping ZnO with 1 at.% Cr. Good stability and repeatability of the sensor were demonstrated when tested under different concentration of oxygen atmosphere.
Keywords: Gas sensor; Zinc oxide; Oxygen sensors;
Increasing the octane number of gasoline using functionalized carbon nanotubes by Sara Safari Kish; Alimorad Rashidi; Hamid Reza Aghabozorg; Leila Moradi (3472-3477).
The octane number is one of the characteristics of spark-ignition fuels such as gasoline. Octane number of fuels can be improved by addition of oxygenates such as ethanol, MTBE (methyl tert-butyl ether), TBF (tertiary butyl formate) and TBA (tertiary butyl alcohol) as well as their blends with gasoline that reduce the cost impact of fuels. Carbon nanotubes (CNTs) are as useful additives for increasing the octane number. Functionalized carbon nanotubes containing amide groups have a high reactivity and can react with many chemicals. These compounds can be solubilized in gasoline to increase the octane number. In this study, using octadecylamine and dodecylamine, CNTs were amidated and the amino-functionalized carbon nanotubes were added to gasoline. Research octane number analysis showed that these additives increase octane number of the desired samples. X-ray diffraction (XRD), Fourier transforms infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetry analyses (TGA) were used for characterization of the prepared functionalized carbon nanotubes.
Keywords: Multiwall carbon nanotubes; Functionalization; Amidation; Octane number; Gasoline;
Surface defects and their role in the shock sensitivity of cyclotrimethylene-trinitramine by Victor J. Bellitto; Mikhail I. Melnik (3478-3481).
The surface of cyclotrimethylene-trinitramine (RDX), a commonly used crystalline explosive was studied using atomic force microscopy (AFM). A diversity of surface defects was observed in different RDX particles as well as different parts of the same particle. Statistical analysis was undertaken to model the observed surface characteristics with the known shock sensitivities of the material. To quantify the surface defects observed on the crystalline surface of the RDX particles, surface roughness measurements were acquired. It was determined that there exists a statistically significant relationship between surface roughness characteristics and the shock sensitivity of the material.
Keywords: Defect; RDX; Cyclotrimethylene-trinitramine; AFM; Insensitive; Roughness;
The positive charging effect of dielectric films irradiated by a focused electron beam by Wei-Qin Li; Hai-Bo Zhang (3482-3492).
Space charge and surface potential profiles are investigated with numerical simulation for dielectric films of SiO2 positively charged by a focused electron beam. By combining the Monte Carlo method and the finite difference method, the simulation is preformed with a newly developed comprehensive two-dimensional model including electron scattering, charge transport and trapping. Results show that the space charge is distributed positively, like a semi-ellipsoid, within a high-density region of electrons and holes, but negatively outside the region due to electron diffusion along the radial and beam incident directions. Simultaneously, peak positions of the positive and negative space charge densities shift outwards or downwards with electron beam irradiation. The surface potential, along the radial direction, has a nearly flat-top around the center, abruptly decreases to negative values outside the high-density region and finally increases to zero gradually. Influences of electron beam and film parameters on the surface potential profile in the equilibrium state are also shown and analyzed. Furthermore, the variation of secondary electron signal of a large-scale integration sample positively charged in scanning electron microscopic observation is simulated and validated by experiment.
Keywords: Dielectric film; Electron beam irradiation; Charging effect; Space charge; Surface potential; Numerical simulation;
Sunlight photocatalytic activity of CdS modified TiO2 loaded on activated carbon fibers by Wenxia Zhao; Zhipeng Bai; Ailing Ren; Bin Guo; Can Wu (3493-3498).
To improve the photocatalytic application performances of TiO2, in this work, firstly CdS modified Degussa P25 TiO2 (CdS/TiO2) composites were prepared by two methods, sol–gel method and precipitation method. Next they, sol–gel-CdS/TiO2 (sg-CdS/TiO2) and precipitation-CdS/TiO2 (pp-CdS/TiO2), were loaded on activated carbon fibers (ACFs) by dip-coating method using the sodium carboxymethyl cellulose as adhesives. The composites were characterized by XRD, UV–vis absorbance spectra, SEM, EDS and BET. The photocatalytic activities under sunlight were investigated by the degradation of methylene blue. The results showed that CdS/TiO2 composites were mainly composed of anatase-TiO2 and little CdS cubic phases. The absorption wavelengths of sg-CdS/TiO2 and pp-CdS/TiO2 composites were extended to 590 nm and 740 nm, respectively. The absorption edge had a pronounced ‘red shift’. From EDS analysis, the elemental contents of CdS/TiO2 were mainly Ti and O and a small quantity of S and Cd. CdS/TiO2 loaded on ACFs were in the form of small clusters, but not very uniform; compared with the original ACFs, the surface area and pore volume of CdS/TiO2/ACFs decreased slightly, respectively, while the average pore diameter was not changed. The photodegradation rate of methylene blue under sunlight with CdS/TiO2/ACFs composites was markedly higher than that of P25-TiO2/ACFs, and the effect of pp-CdS/TiO2/ACFs composites was better than that of sg-CdS/TiO2/ACFs, when irradiated for 180 min, and the photodegradation rate of methylene blue reached to 90.1%. The photodegradation kinetics of the methylene blue fitted with the Langmuir–Hinshelwood equation. The apparent reaction rate constants of sg-CdS/TiO2/ACFs and pp-CdS/TiO2 were 0.0105 min−1 and 0.0146 min−1, respectively, which were about 1.3–1.7 times as large as that of P25-TiO2/ACFs.
Keywords: TiO2; CdS; Activated carbon fibers; Methylene blue; Photocatalysis; Sunlight;
Strain relaxation in nano-patterned strained-Si/SiGe heterostructure on insulator by XuYan Liu; WeiLi Liu; XiaoBo Ma; ShiLong Lv; ZhiTang Song; ChengLu Lin (3499-3502).
In order to evaluate the strain stability, arrays of strained Si/SiGe nano-stripes and nano-pillars were fabricated by Electron-Beam Lithography (EBL) and Reactive-Ion Etching (RIE). The strain relaxation in the patterned strained Si on SiGe-on-insulator (SGOI) was investigated by high-resolution UV micro-Raman spectroscopy. The Raman measurements before and after patterning indicate that most of the strain in the top strained Si is maintained until scaling down to 300 nm, and relaxation of <15% is observed in pillars with a dimension of 150 nm × 150 nm. In the nano-patterned heterostructure strained Si/SiGe, the observed relaxation is small, which is mainly attributed to the fully relaxed and dislocation-free SiGe virtual substrate fabricated by modified Ge condensation.
Keywords: Strained silicon; SiGe; Strain relaxation; Raman spectroscopy;
Investigation of interface roughness cross-correlation properties of optical thin films from total scattering losses by Yongqiang Pan; Zhensen Wu; Lingxia Hang (3503-3507).
The interface roughness and interface roughness cross-correlation properties affect the scattering losses of high-quality optical thin films. In this paper, the theoretical models of light scattering induced by surface and interface roughness of optical thin films are concisely presented. Furthermore, influence of interface roughness cross-correlation properties to light scattering is analyzed by total scattering losses. Moreover, single-layer TiO2 thin film thickness, substrate roughness of K9 glass and ion beam assisted deposition (IBAD) technique effect on interface roughness cross-correlation properties are studied by experiments, respectively. A 17-layer dielectric quarter-wave high reflection multilayer is analyzed by total scattering losses. The results show that the interface roughness cross-correlation properties depend on TiO2 thin film thickness, substrate roughness and deposition technique. The interface roughness cross-correlation properties decrease with the increase of film thickness or the decrease of substrates roughness. Furthermore, ion beam assisted deposition technique can increase the interface roughness cross-correlation properties of optical thin films. The measured total scattering losses of 17-layer dielectric quarter-wave high reflection multilayer deposited with IBAD indicate that completely correlated interface model can be observed, when substrate roughness is about 2.84 nm.
Keywords: Optical thin films; Cross-correlation properties; Light scattering; Total scattering losses; Surface roughness;
Studies on adhesion characteristics and corrosion behaviour of vinyltriethoxysilane/epoxy coating protective system on aluminium by Jelena B. Bajat; Ingrid Milošev; Željka Jovanović; Vesna B. Mišković-Stanković (3508-3517).
The corrosion stability of vinyltriethoxysilane/epoxy coating protective system on aluminium is strongly related to the strength of bonds forming at the metal/organic coating interface. This article is a study of adhesion, composition, electrochemical and transport properties of epoxy coatings electrodeposited on bare aluminium and aluminium pretreated by vinyltriethoxysilane (VTES) during exposure to 3% NaCl. The VTES film was deposited on aluminium surface from 2% vinyltriethoxysilane solution during 30 s. From the values of adhesion strength (pull-off test), time dependence of pore resistance and coating capacitance of epoxy coating (impedance measurements) and diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements), the influence of VTES sublayer on the corrosion stability of the electrodeposited epoxy coating was shown.The work discusses the role of the VTES pretreatment in the enhanced adhesion and corrosion stability of epoxy cataphoretic coating. The electrochemical results showed that the aluminium pretreatment by VTES film improved barrier properties of epoxy coating (greater pore resistance and lower coating capacitance). The lower value of diffusion coefficient of water through epoxy coating indicates the lower porosity, while the smaller adhesion reduction points to better adhesion of epoxy coating on aluminium pretreated by VTES film. The composition of the deposited coatings investigated by XPS enabled the clarification of the bonding mechanism.
Keywords: Vinyltriethoxysilane; Epoxy coating; Interface; Adhesion; Corrosion; XPS;
Effect of UV lamp irradiation during oxidation of Zr/Pt/Si structure on electrical properties of Pt/ZrO2/Pt/Si structure by Joon Woo Bae; Jae-Won Lim; Kouji Mimura; Masahito Uchikoshi; Takamichi Miyazaki; Minoru Isshiki (3518-3521).
Metal–insulator–metal (MIM) capacitors were fabricated using ZrO2 films and the effects of structural and native defects of the ZrO2 films on the electrical and dielectric properties were investigated. For preparing ZrO2 films, Zr films were deposited on Pt/Si substrates by ion beam deposition (IBD) system with/without substrate bias voltages and oxidized at 200 °C for 60 min under 0.1 MPa O2 atmosphere with/without UV light irradiation (λ = 193 nm, Deep UV lamp). The ZrO2(∼12 nm) films on Pt(∼100 nm)/Si were characterized by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM), capacitance–voltage (C–V) and current–voltage (I–V) measurements were carried out on MIM structures. ZrO2 films, fabricated by oxidizing the Zr film deposited with substrate bias voltage under UV light irradiation, show the highest capacitance (784 pF) and the lowest leakage current density. The active oxygen species formed by UV irradiation are considered to play an important role in the reduction of the leakage current density, because they can reduce the density of oxygen vacancies.
Keywords: ZrO2; MIM capacitor; Substrate bias voltage; Defect; UV light irradiation; C–V; I–V;
Studies on the effect of nozzle-to-substrate distance on the structural, electrical and optical properties of spray deposited CdIn2O4 thin films by R.J. Deokate; A.V. Moholkar; G.L. Agawane; S.M. Pawar; J.H. Kim; K.Y. Rajpure (3522-3530).
The physical, chemical, electrical and optical properties of as-deposited and annealed CdIn2O4 thin films deposited using spray pyrolysis technique at different nozzle-to-substrate distances are reported. These films are characterized by X-ray diffraction, XPS, SEM, PL, Hall effect measurement techniques and optical absorption studies. The average film thickness lies within 600–800 nm range. The X-ray diffraction study shows that films exhibit cubic structure with orientation along (3 1 1) plane. The XPS study reveals that CdIn2O4 films are oxygen deficient. Room temperature PL indicates the presence of green shift with oxygen vacancies. The typical films show very smooth morphology. The best films deposited with optimum nozzle-to-substrate distance (NSD) of 30 cm, has minimum resistivity of 1.3 × 10−3 Ω cm and 2.6 × 10−4 Ω−1 figure of merit. The band gap energy varies from 3.04 to 3.2 eV with change in NSD for annealed films. The effect of NSD as well as the annealing treatment resulted into the improvement of the structural, electrical and optical properties of the studied CdIn2O4 thin films.
Keywords: Chemical spray pyrolysis; X-ray diffraction; XPS and PL measurements; Electrical properties; Optical absorption;
Influence of Cu substrate surface oxides and heating rates during reflow on melting point of Sn–3.5Ag solder by Jagjiwan Mittal; Yu Wei Lin; Kwang Lung Lin (3531-3540).
Three types of copper substrates, fresh, aged (kept for years in open atmosphere) and acid washed aged, were investigated for the reflow behaviour of a solder using different heating rates. Melting point of the Sn–3.5Ag solder was lowered on the aged Cu substrate. Reduction was found to be higher in high heating rate and declined with the decrease in the heating rate. Melting point was lowered from 221 °C to 175 °C with the heating rate of 180 °C/min, but recovered to 210 °C when aged Cu substrate was washed with sulphuric acid. XPS depth profile revealed the presence of Cu2O up to the greater depth in the aged substrate compared to the fresh and acid washed aged substrates. Study showed the relation of reduction in melting point with the depth of Cu2O on the surface of aged Cu substrates. It was proposed that lower dissipation of heat generated in high heating rates by the oxidation of the flux carbon during reduction of high Cu2O amount in aged carbon was responsible for the variations in melting points.
Keywords: Oxidation of Cu surfaces; Reflowing; Melting point; Heating rates; XPS;
The influence of the substrate temperature on the photovoltaic properties of spray-deposited CdS:In thin films by Shadia. J. Ikhmayies; Riyad N. Ahmad-Bitar (3541-3545).
Polycrystalline and highly transparent CdS:In thin films were produced by the spray pyrolysis (SP) technique at different substrate temperatures ranging from 350 to 490 °C on glass substrates. The effect of the substrate temperature on the photovoltaic properties of the films was investigated by studying the transmittance measurements, X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) observations and the I–V plots. The transmittance measurements were used to estimate the band gap energy by the linear fit of (αhν)2 versus hν. The band gap energy was found to be slightly increasing with the substrate temperature. XRD diffractograms show that a phase transition from the cubic to the hexagonal phase occurs by increasing the substrate temperature, beside more orientation of crystal growth. Also they show that complex cadmium compounds are still present till T s ≈ 460 °C after which they practically disappear. From the linear I–V plots the resistivity was estimated and found to be strongly decreasing with the substrate temperature.
Keywords: Thin films; Semiconductors; Spray pyrolysis; X-ray diffraction;
Properties of mesoporous tungstosilicic acid/titania composites prepared by sol–gel method by Mirta N. Blanco; Luis R. Pizzio (3546-3553).
The tungstosilicic acid/titania composites were prepared by the sol–gel method. Titanium isopropoxide was used as titania precursor, and urea as a low-cost template. The tungstosilicic acid (TSA) was added in the same step as that in which titania hydrogel is formed. The TSA-modified samples only showed the characteristic peaks of anatase phase of titanium oxide in the XRD patterns, indicating that the presence of TSA retarded the crystallization of the anatase phase and its transformation into the rutile phase. Spherical particles with sizes between 200 and 700 nm, formed by aggregation of nanoparticle aggregates (4–50 nm in size), were observed. The particle size increased when the TSA content was raised and also increased slightly with the thermal treatment temperature. Mesoporous materials were obtained, with a mean pore diameter higher than 3.1 nm. Both the increase of the TSA concentration in the solid and the calcination temperature led to a decrease in the specific surface area of the samples. The main heteropolyoxometallate species present in the composites is the [SiW12O40]4− anion for the composites calcined up to 500 °C. The band gap energy decreased as a result of the introduction of TSA into the titania matrix, though it remained almost constant with the calcination temperature increase.
Keywords: Titania; Tungstosilicic acid; Urea template; Mesoporous solid;
Improvement of copper plating adhesion on silane modified PET film by ultrasonic-assisted electroless deposition by Yinxiang Lu (3554-3558).
Copper thin film on silane modified poly(ethylene terephthalate) (PET) substrate was fabricated by ultrasonic-assisted electroless deposition. The composition and topography of copper plating PET films were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Peel adhesion strength, as high as 16.7 N/cm, was achieved for the planting copper layer to the modified PET substrate with ultrasonic-assisted deposition; however, a relative low value as 11.9 N/cm was obtained for the sample without ultrasonic vibration by the same measurement. The electrical conductivity of Cu film was changed from 7.9 × 104 to 2.1 × 105 S/cm by using ultrasonic technique. Ultrasonic operation has the significant merits of fast deposition and formation of good membranes for electroless deposition of Cu on PET film.
Keywords: Poly(ethylene terephthalate) film; Electroless copper plating; Ultrasonic assisted; Adhesion strength;
Effect of annealing temperature on structure, magnetic properties and optical characteristics in Zn0.97Cr0.03O nanoparticles by Yang Liu; Jinghai Yang; Qingfeng Guan; Lili Yang; Huilian Liu; Yongjun Zhang; Yaxin Wang; Dandan Wang; Jihui Lang; Yanting Yang; Lianhua Fei; Maobin Wei (3559-3562).
The Cr-doped zinc oxide (Zn0.97Cr0.03O) nanoparticles were successfully synthesized by sol–gel method. The relationship between the annealing temperature (400 °C, 450 °C, 500 °C and 600 °C) and the structure, magnetic properties and the optical characteristics of the produced samples was studied. The results indicate that Cr (Cr3+) ions at least partially substitute Zn (Zn2+) ions successfully. Energy dispersive spectroscopy (EDS) measurement showed the existence of Cr ion in the Cr-doped ZnO. The samples sintered in air under the temperature of 450 °C had single wurtzite ZnO structure with prominent ferromagnetism at room temperature, while in samples sintered in air at 500 °C, a second phase-ZnCr2O4 was observed and the samples were not saturated in the field of 10000 Oe. This indicated that they were mixtures of ferromagnetic materials and paramagnetic materials. Compared with the results of the photoluminescence (PL) spectra, it was reasonably concluded that the ferromagnetism observed in the studied samples was originated from the doping of Cr in the lattice of ZnO crystallites.
Keywords: Cr-doped ZnO; Ferromagnetism; Photoluminescence; Sol–gel;
Titanium buffer layer for improved field emission of CNT based cold cathode by S. Srividya; S. Gautam; P. Jha; P. Kumar; A. Kumar; U.S. Ojha; J.S.B.S. Rawat; S. Pal; P.K. Chaudhary; Harsh; R.K. Sinha (3563-3566).
Carbon nanotube (CNT) based cold cathodes are considered to be the most promising material for fabrication of next generation high-performance flat panel displays and vacuum microelectronic devices. Adhesion of CNTs with the substrate and the contact resistance between them are two of the important issues to be addressed in CNT based field emission (FE) devices. Here in this work, a buffer layer of titanium (Ti) is deposited prior to the catalyst deposition and the growth was carried out using chemical vapor deposition (CVD) technique. There was significant increase in emission current density from 10 mA/cm2 to 30 mA/cm2 at the field of 4 V/μm by the use of titanium buffer layer due to much less dense growth of CNTs of smaller diameter. Field emission results suggest that the adhesion of the CNTs to the substrate has improved. The titanium buffer layer has also lowered the contact resistance between the CNTs and the substrate because of which a stable emission of 30 mA for a longer duration was obtained.
Keywords: Carbon nanotube (CNT); Chemical vapor deposition (CVD); Photolithography; Field emission;
Surface modification of plasticized PVC by dry cleaning methods: Consequences for artworks by C. Morales Muñoz (3567-3572).
A study of dry cleaning methods for plasticized PVC has been undertaken using three commercial cloths recommended for plastics artworks, in addition to cotton swabs traditionally used in art conservation. The evaluation of the cleaning has focussed on the efficiency of the cleaners, and the physical and chemical damages caused by the cleaning. The physical and chemical modifications of the PVC surface have been studied by optical microscopy, non-contact profilometry and ATR-FTIR spectroscopy, while spectrocolorimetry and non-contact profilometry have been used for evaluating the cleaning efficiency. The results have shown that the cleaner's composition and the cleaning time play an important role in damaging the plasticized PVC surface. On the contrary, it has not been completely determined if the texture of the cleaning agents’ surface had an influence on the cleaning efficiency.
Keywords: Plasticized PVC; Plastics conservation; Dry cleaning; Surface analysis;
Synthesis and characterization of a hexagonal mesoporous silica with enhanced thermal and hydrothermal stabilities by Zeid A. AlOthman; Allen W. Apblett (3573-3580).
A synthetic route was developed for a novel hexagonal mesoporous silica that has remarkably wide channel diameters and thick walls. The procedure involved the acid-catalyzed hydrolysis of tetraethylorthosilicate in a water/ethanol/isopropoanol solvent mixture while employing 1-hexadecylamine as a templating agent and mesitylene as an auxiliary agent. After removal of the template by either extraction with ethanolic hydrochloric acid or by calcination at 550 °C, the resulting mesoporous materials had surface areas of 1283 and 1211 m2/g. The channel diameters were found to be 47.2–51.1 Å, while the wall thicknesses were 20.9–21.1 Å. X-ray powder diffraction demonstrated that the novel mesoporous silica belonged to the MCM-41 structural family. Notably, they displayed higher thermal and hydrothermal stabilities, and have higher surface areas than conventionally prepared MCM-41 silica. The thickest channel walls (21.1 Å) can withstand calcination to nearly 850 °C with minimal structural damage. The calcined sample was more resistant to hydrothermal treatment in boiling water than was the solvent-extracted product but both materials showed minimal change after 25 h of hydrothermal treatment.
Keywords: MCM-41; Hexagonal mesoporous silica; X-ray diffraction; NMR; Thermal and hydrothermal stabilities;
Numerical analysis of partially molten splat during thermal spray process using the finite element method by M. Zirari; A. Abdellah El-Hadj; N. Bacha (3581-3585).
A finite element method is used to simulate the deposition of the thermal spray coating process. A set of governing equations is solving by a volume of fluid method. For the solidification phenomenon, we use the specific heat method (SHM). We begin by comparing the present model with experimental and numerical model available in the literature. In this study, completely molten or semi-molten aluminum particle impacts a H13 tool steel substrate is considered. Next we investigate the effect of inclination of impact of a partially molten particle on flat substrate. It was found that the melting state of the particle has great effects on the morphologies of the splat.
Keywords: Coating; Impact; Splat; VOF; Partially molten particle; Solidification;
In situ Raman spectroscopy of phase transformation in CrO x -Y2O3 system at elevated temperatures by Liqiong Xing; Jiqing Lu; Qingyuan Bi; Zhiying Pu; Ming Guo; Yuejuan Wang; Mengfei Luo (3586-3591).
A CrO x -Y2O3 sample was prepared by a deposition–precipitation method and phase transformation of the sample under N2 and air atmospheres was characterized by in situ Raman spectroscopy and X-ray diffraction (XRD) techniques. It was found that when the CrO x -Y2O3 sample was heated, CrO3 transformed to YCrO4 and then to YCrO3 and Cr2O3. Also, the transformation started from the surface region of the sample and then extended to the bulk, due to the fact that the phase transformation was detected by Raman spectroscopy at lower temperature compared to that by XRD. In addition, both atmosphere and temperature had influence on the phase transformation in the surface region, while the phase transformation in the bulk was merely dependent on the temperature. It was also found that low oxidation state Cr(III) species on the surface could be re-oxidized to high oxidation state Cr(V) or Cr(VI) species when the thermal treated sample was exposed to ambient air.
Keywords: CrO x –Y2O3; Raman spectroscopy; X-ray diffraction; Phase transformation; Cr species;
Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy by L.L. Yang; Q.X. Zhao; M. Willander; X.J. Liu; M. Fahlman; J.H. Yang (3592-3597).
The surface composition of as-grown and annealed ZnO nanorods arrays (ZNAs) grown by a two-step chemical bath deposition method has been investigated by X-ray photoelectron spectroscopy (XPS). XPS confirms the presence of OH bonds and specific chemisorbed oxygen on the surface of ZNAs, as well as H bonds on ( 1 0 1 ¯ 0 ) surfaces which has been first time observed in the XPS spectra. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Annealing can largely remove the OH and H bonds and transform the composition of the other chemisorbed oxygen at the surface to more closely resemble that of high temperature grown ZNAs, all of which suppresses surface recombination according to time-resolved photoluminescence measurements.
Keywords: ZnO nanorods; Optical properties; Surface recombination; X-ray photoelectron spectroscopy;
Molecular assembly of tetracene on the (2 × 1)O reconstructed Cu(1 1 0) surface by Hongying Mao; Weidong Dou; Ateeq ur Rehman; Qing Liao; Hanjie Zhang; Haiyang Li; Pimo He; Shining Bao (3598-3602).
Using a combination of scanning tunneling microscopy (STM) and density functional theory calculations, we have studied the adsorption of tetracene on the Cu(1 1 0) (2 × 1)O substrate. At monolayer coverage the adsorbed molecules are in the flat-laying geometry with their long axis along the close-packed [0 0 1] direction of the substrate and a long-range ordered structure on the length scale up to 100 nm has been observed. DFT calculation results indicate a stronger interaction between tetracene molecules and Cu(1 1 0) substrate than Cu(1 1 0) (2 × 1)O substrate. The preferential adsorption sites have also been pointed out on both substrates. The observed wavelike structure is explained by the interdigitation of C–H bonds of adjacent molecules.
Keywords: Organic semiconductor; Scanning tunneling microscopy; Nanotemplate; DFT;
Surface-stress-induced elongation of β -Sn metal nanowires: A density-functional study by Yong-Sung Kim; Seung Mi Lee; Jae Yong Song (3603-3606).
We investigated surface stabilities and stresses of β -Sn and their consequences to the nanowire structure through density-functional theory calculations. β -Sn nanowires are well known to grow along the [1 0 0] direction. Even though the (1 0 0) and (0 1 0) planes are equivalent in bulk, the surface stresses are found to induce the anisotropic deformation. Along the surface zigzag bond chain direction, large negative surface tensions are found, combined with a linearization tendency of the zigzag bond chains. The negative surface tensions are not typical on metal surfaces and results in the elongation of the β -Sn metal nanowires.
Keywords: β -Sn; Surface stress; Nanowire; Density-functional calculations;
Synthesis and characterization of nano-sepiolite by solvothermal method by Zahra Darvishi; Ali Morsali (3607-3611).
Nano-sepiolite with novel morphology has been fabricated by solvothermal method in different conditions. The nano-sepiolite was characterized by X-ray fluorescence analysis, X-ray powder diffraction, thermal gravimetry analysis, differential thermal analysis and infrared spectroscopy. Scanning electron microscopy observations revealed that using of solvothermal route led to nano-wires of sepiolite. The reactions have been performed in several conditions to find out the role of different factors such as the aging time and temperature of the reaction in the solvothermal on the size and morphology of the nano-structures.
Keywords: Solvothermal; X-ray diffraction; Nano-sepiolite; Electron microscopy;
Damage mechanism and morphology characteristics of chromium film in femtosecond laser rear-side ablation by Wenjun Wang; Gedong Jiang; Xuesong Mei; Kedian Wang; Jinyou Shao; Chengjuan Yang (3612-3617).
In this paper, damage mechanism and morphology characteristics of chromium film in femtosecond laser rear-side ablation are investigated. The film removing process includes two key sub-processes: the laser ablation dynamic process and subsequent breaking and ejecting dynamic process. Film morphology in rear-side ablation is determined by the interrelation between the laser energy and the film strength. When lower laser energy is used, residual out-layer film is relative thick and tends to break into some large fragments, which results in an irregular ablation shape. While when higher pulse energy is used, thinner residual film with weaker break strength breaks into small fragments, the ablation quality improves correspondingly. Besides laser energy and film property, energy distribution of laser beam also affects the ablation quality. In experiments, this kind of effect is researched by changing the focal position. It is found that ripples, which are familiar nano-structures in front-side ablation, also exist in rear-side ablation. These ripples are formed initially at the interface between quartz substrate and film, and their coverage varies with the energy distribution. Additionally, increasing number of scans is an effective method to shorten the period of ripples.
Keywords: Femtosecond laser; Rear-side ablation; Damage mechanism; Morphology characteristics; Nano-ripples;
The effect of Al and Cr additions on pack cementation zinc coatings by D. Chaliampalias; M. Papazoglou; S. Tsipas; E. Pavlidou; S. Skolianos; G. Stergioudis; G. Vourlias (3618-3623).
Zinc is widely used as a protective coating material due to its corrosion resistant properties. The structure and oxidation resistance of Al and Cr mixed zinc coatings, deposited by pack cementation process, is thoroughly examined in this work. The morphology and chemical composition of the as-deposited and oxidized samples was accomplished by electron microscopy while the phase identification was performed by XRD diffraction analysis. The experimental results showed that the addition of aluminum or chromium in the pack mixture forms only Al and Cr rich phases on the surface of the specimens without affecting significantly the phase composition of the rest zinc coatings. In the case of Zn–Al coatings, the overlying layer contains high concentrations of Al together with lower amounts of zinc and iron and in Zn–Cr coatings this layer contains Cr, Fe and Zn atoms and has much smaller thickness. The presence of these additional layers promotes significantly the oxidation resistance of the zinc pack coatings and they preserve most of their initial thickness and chemical content when exposed to an aggressive environment while their oxidation mass gain was measured at low levels during the oxidation tests.
Keywords: Coatings; Zinc; Aluminum; Chromium; Pack cementation; Oxidation;
Transparent water repellent silica films by sol–gel process by Sunetra L. Dhere; Sanjay S. Latthe; Charles Kappenstein; G.M. Pajonk; V. Ganesan; A. Venkateswara Rao; Pratap B. Wagh; Satish C. Gupta (3624-3629).
Non-wettable surfaces with high contact angles and facile sliding angle of water droplets have received tremendous attention in recent years. The present paper describes the room temperature (∼27 °C) synthesis of dip coated water repellent silica coatings on glass substrates using iso-butyltrimethoxysilane (iso-BTMS) as a co-precursor. Emphasis is given to the influence of the hydrophobic reagent (iso-BTMS) on the water repellent properties of the silica films. Silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS) precursor, methanol (MeOH) solvent, water (H2O) constant at 1:16.53:8.26 respectively, with 0.01 M NH4F throughout the experiment and the molar ratio of iso-BTMS/TEOS (M) was varied from 0 to 0.965. The effect of M on the surface structure and hydrophobicity has been researched. The static water contact angle values of the silica films increased from 65° to 140° and water sliding angle values decreased from 42° to 16° with an increase in the M value from 0 to 0.965. The water repellent silica films are thermally stable up to a temperature of 280 °C and above this temperature the film shows hydrophilic behavior. The water repellent silica films were characterized by the Fourier Transform Infrared (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), % of optical transmission, thermal and chemical aging tests, humidity tests, static and dynamic water contact angle measurements.
Keywords: Sol–gel process; Hydrophobic; Wetting phenomena; Transparent; Humidity; Coatings;
Effect of laser irradiation on the structure and valence states of copper in Cu-phosphate glass by XPS studies by G.D. Khattak; A. Mekki; M.A. Gondal (3630-3635).
The effect of laser irradiation using three different wavelengths (IR, visible and UV) generated from Nd:YAG laser on the local glass structure as well as on the valence state of the copper ions in copper phosphate glass containing CuO with the nominal composition 0.30(CuO)–(0.70)(P2O5), has been investigated by X-ray photoelectron spectroscopy (XPS). The presence of asymmetry and satellite peaks in the Cu 2p spectrum for the unirradiated sample is an indication of the presence of two different valence states, Cu2+ and Cu+. Hence, the Cu 2p3/2 spectrum was fitted to two Gaussian–Lorentzian peaks and the corresponding ratio, Cu2+/Cutotal, determined from these relative areas clearly shows that copper ions exist predominately (>86%) in the Cu2+ state for the unirradiated glass sample under investigation. For the irradiated samples the symmetry and the absence of satellite peaks in the Cu 2p spectra indicate the existence of the copper ions mostly in Cu+ state. The O 1s spectra show slight asymmetry for the irradiated as well as unirradiated glass samples which result from two contributions, one from the presence of oxygen atoms in the P–O–P environment (bridging oxygen BO) and the other from oxygen in an P–O–Cu and P＝O environment (non-bridging oxygen NBO). The ratio of NBO to total oxygen was found to increase with laser power.
Keywords: XPS; Phosphate glasses; TM oxide glasses; Laser effect on glass;
Formation of copper islands on a native SiO2 surface at elevated temperatures by Jan Čechal; Josef Polčák; Miroslav Kolíbal; Petr Bábor; Tomáš Šikola (3636-3641).
A combination of in situ X-ray photoelectron spectroscopy analysis and ex situ scanning electron- and atomic force microscopy has been used to study the formation of copper islands upon Cu deposition at elevated temperatures as a basis for the guided growth of copper islands. Two different temperature regions have been found: (I) up to 250 °C only close packed islands are formed due to low diffusion length of copper atoms on the surface. The SiO2 film acts as a barrier protecting the silicon substrate from diffusion of Cu atoms from oxide surface. (II) The deposition at temperatures above 300 °C leads to the formation of separate islands which are (primarily at higher temperatures) crystalline. At these temperatures, copper atoms diffuse through the SiO2 layer. However, they are not entirely dissolved in the bulk but a fraction of them forms a Cu rich layer in the vicinity of SiO2/Si interface. The high copper concentration in this layer lowers the concentration gradient between the surface and the substrate and, consequently, inhibits the diffusion of Cu atoms into the substrate. Hence, the Cu islands remain on the surface even at temperatures as high as 450 °C.
Keywords: Copper (Cu); Silicon (Si); Silicon dioxide (SiO2); Photoelectron spectroscopy (XPS); Scanning electron microscopy (SEM); Diffusion; Surface structures;
Effect of silver on antibacterial properties of stainless steel by Kuo-Hsing Liao; Keng-Liang Ou; Hsin-Chung Cheng; Che-Tong Lin; Pei-Wen Peng (3642-3646).
The microstructural variation and antibacterial properties of the AISI 304 stainless steel containing silver (Ag) element have been investigated by means of optical microscopy (OM), grazing incidence X-ray diffractometry (GIXRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). Furthermore, the antibacterial testing was performed according to JIS Z2801:2000 specification. As the alloy contained Ag elements, the microstructure of the alloys was a mixture of (α + γ + Ag-rich compound)-phases. The amounts of α phase and Ag-rich compound increased as Ag contents increased. The Ag-rich compound has FCC structure with the lattice parameter a = 0.251 nm. No precipitates were found within the matrix and grain boundaries in the present alloys after SHT. Moreover, when the alloy is added to Ag element, antibacterial property was seen obvious against E. coli. It has an AR nearly of 100%.
Keywords: AISI 304 stainless steel; Silver; Antibacterial property; Microstructure;
Surface characterization of Ag/Titania adsorbents by Alexander Samokhvalov; Sachin Nair; Evert C. Duin; Bruce J. Tatarchuk (3647-3652).
The Ag/Titania adsorbent for selective removal of the desulfurization-refractive polycyclic aromatic sulfur heterocycles (PASHs) from liquid hydrocarbon fuels was prepared, its total and the Ag specific surface area were determined and the surface reaction sites in the sorbent that may be active in the adsorptive selective desulfurization were characterized by several spectroscopic and surface science techniques. The sorbent contains Ag, Ti, O and spurious C on its surface, as by the XPS measurements. Silver is present as an oxide, as judged by the XPS Auger parameter (AP). The complementary electron spin resonance (ESR) spectroscopy confirms that the majority of Ag is present in the diamagnetic Ag1+ form, with the minor concentration (∼0.1% of total Ag) present as Ag2+. The findings by XPS and ESR are confirmed by the XRD, UV–vis spectroscopy and thermodynamic considerations. The supported Ag is highly dispersed on the surface of the titania support, with the particle size of ∼30–60 Å depending on Ag content, with an Ag specific surface area of ∼7–14 m2/g, vs. the total surface area of ∼114–58 m2/g.
Keywords: Desulfurization; Fuel; Sorbent; Silver; XPS; ESR;
Femtosecond laser-induced concentric ring microstructures on Zr-based metallic glass by Fengxu Ma; Jianjun Yang; XiaonongZhu; Chunyong Liang; Hongshui Wang (3653-3660).
Surface morphological evolution of Zr-based metallic glass ablated by femtosecond lasers is investigated in atmosphere condition. Three types of permanent ring structures with micro-level spacing are observed for different laser shots and fluences. In the case of low laser fluences, the generation of annular patterns with nonthermal features is observed on the rippled structure with the subwavelength scale, and the ring spacing shows a decrease tendency from the center to the margin. While in the case of high laser fluences, the concentric rings formation within the laser spot is found to have evident molten traces and display the increasing ring spacing along the radial direction. Moreover, when the laser shots accumulation becomes large, the above two types of ring microstructures begin to develop into the common ablation craters. Analysis and discussion suggests that the stress-induced condensation of ablation vapors and the frozen thermocapillary waves on the molten surfaces should be responsible for the formation of two different types of concentric ring structures, respectively. Eventually, a processing window for each resulting surface microstructure type is obtained experimentally and indicates the possibility to control the morphological transitions among different types.
Keywords: Femtosecond lasers; Metallic glasses; Microstructuring;
Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition by Z.H. Xu; L.M. He; R.D. Mu; S.M. He; G.H. Huang; X.Q. Cao (3661-3668).
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and La2Ce2O7 (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO3 is formed due to the chemical reaction between LC and Al2O3 which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.
Keywords: Thermal barrier coatings; EB-PVD; Double-ceramic-layer; La2(Zr0.7Ce0.3)2O7; La2Ce2O7; Thermal cycling;
Microstructures, surface bonding states and room temperature ferromagnetisms of Zn0.95Co0.05O thin films doped with copper by Zuci Quan; Dan Li; Bobby Sebo; Wei Liu; Shishang Guo; Sheng Xu; Huiming Huang; Guojia Fang; Meiya Li; Xingzhong Zhao (3669-3675).
Zn0.95−x Co0.05Cu x O (ZCCO, where x = 0, 0.005, 0.01 and 0.015) thin films were deposited on Si (1 0 0) substrates by pulsed laser deposition technique. Crystal structures, surface morphologies, chemical compositions, bonding states and chemical valences of the corresponding elements for ZCCO films were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD and FESEM results indicate that crystallite sizes of the highly (0 0 2)-oriented ZCCO films slightly decrease with increasing Cu content. When the Cu content increases from 0 to 0.015, Zn 2p 3/2, Co 2p, Cu 2p 3/2 and O 1s peaks of the ZCCO film shift towards higher or lower binding energy regions, and the reasons for these chemical shifts are investigated by fitting the corresponding XPS narrow-scan spectra. Both in-plane and out-of-plane magnetization-magnetic field hysteresis loops of the ZCCO films reveal that all the films have room temperature ferromagnetisms (RTFMs). The conceivable origin of the RTFM is ascribed to the combined effects of the local structural disorder resulted from (Co2+, Cu2+, Cu1+)-cations which substitute Zn2+ ions in the ZnO matrices, ferromagnetic coupling between coupled dopant atoms caused by Co2+ (3d 74s 0) and Cu2+ (3d 94s 0) spin states, and exchange interactions between the unpaired electron spins originating from lattice defects induced by Cu doping in the Zn0.95Co0.05O matrices.
Keywords: Cu-doped Zn0.95Co0.05O thin films; Microstructures; Bonding states; Room temperature ferromagnetisms;
The control of the diameter of the nanorods prepared by dc reactive magnetron sputtering and the applications for DSSC by Lijian Meng; Tong Ren; Can Li (3676-3682).
The TiO2 nanorod arrays, with about 1.8 μm lengths, have been deposited on ITO substrates by dc reactive magnetron sputtering at different target-substrate distances. The average diameter of these nanorods can be modified from about 45 to 85 nm by adjusting the target-substrate distance from 90 to 50 mm. These nanorods are highly ordered and perpendicular to the substrate. Both XRD and Raman measurements show that the nanorods prepared at different target-substrate distances have only an anatase TiO2 phase. The nanorods prepared at the target-substrate distance less than 80 mm have a preferred orientation along the (2 2 0) direction. However, this preferred orientation disappears as the target-substrate distance is more than 80 mm. These TiO2 nanorods have been used as the electrodes for dye-sensitized solar cells (DSSCs). The highest conversion efficiency, about 4.78%, has been achieved for TiO2 nanorods prepared at 80 mm target-substrate distance.
Keywords: TiO2; Nanorod; Sputtering; DSSC;
Study on wetting properties of periodical nanopatterns by a combinative technique of photolithography and laser interference lithography by Yung-Lang Yang; Chin-Chi Hsu; Tien-Li Chang; Long-Sheng Kuo; Ping-Hei Chen (3683-3687).
This study presents the wetting properties, including hydrophilicity, hydrophobicity and anisotropic behavior, of water droplets on the silicon wafer surface with periodical nanopatterns and hierarchical structures. This study fabricates one- and two-dimensional periodical nanopatterns using laser interference lithography (LIL). The fabrication of hierarchical structures was effectively achieved by combining photolithography and LIL techniques. Unlike conventional fabrication methods, the LIL technique is mainly used to control the large-area design of periodical nanopatterns in this study. The minimum feature size for each nanopattern is 100 nm. This study shows that the wetting behavior of one-dimensional, two-dimensional, and hierarchical patterns can be obtained, benefiting the development of surface engineering for microfluidic systems.
Keywords: Laser interference lithography; Periodical nanostructures; Hierarchical structures; Hydrophilic; Hydrophobic;
Photoluminescence properties of a single tapered CuO nanowire by C.-Y. Huang; A. Chatterjee; S.B. Liu; S.Y. Wu; C.-L. Cheng (3688-3692).
Photoluminescence spectroscopy has been employed in order to explore the optical emission properties of a single CuO nanowire, grown on a copper grid in static air by simple thermal oxidation method. As the diameter of the single tapered CuO nanowire decreases, the green emission of the nanowire gradually shifts towards the higher energy side. A steady blue shift of 20 nm of the photoluminescence (PL) peak has been attributed to nanosize effect. Higher surface to volume ratio and enhanced surface defects along the growth direction of the nanowire might be responsible for the observed PL behavior. In addition, crystallization process along the length of the nanowire during growth to form pure CuO structure from the precursor state may also have some role in observed shift in the PL peak.
Keywords: Nanowire (NW); CuO; Growth; Photoluminescence;
Influence of surface topography and pore architecture of alkali-treated titanium on in vitro apatite deposition by Matthieu Ravelingien; Anne-Sophie Hervent; Steven Mullens; Jan Luyten; Chris Vervaet; Jean Paul Remon (3693-3697).
Alkali-treated titanium surfaces have earlier shown to induce bone-like apatite deposition. In the present study, the effect of surface topography of two-dimensional and pore architecture of three-dimensional alkali-treated titanium substrates on the in vitro bioactivity was investigated. Titanium plates with a surface roughness of R a = 0.13 μm, 0.56 μm, 0.83 μm, and 3.63 μm were prepared by Al2O3 grit-blasting. Simple tetragonal and face-centered Ti6Al4V scaffolds with spatial gaps of 450–1100 μm and 200–700 μm, respectively, were fabricated by a three-dimensional fiber deposition (3DFD) technique. After alkali treatment, the titanium plates with a surface roughness of R a = 0.56 μm were completely covered with hydroxyapatite globules after 7 days in simulated body fluid (SBF), while the coverage of the samples with other surface roughness values remained incomplete. Similarly, face-centered Ti6Al4 scaffolds with spatial gaps of 200–700 μm exhibited a full surface coverage after 21 days in SBF, while simple tetragonal scaffolds with spatial gaps of 450–1100 μm were only covered for 45–65%. This indicates the importance of surface topography and pore architecture for in vitro bioactivity.
Keywords: Titanium; Alkali treatment; Bioactivity; Surface roughness; Spatial gap;
Wetting and superhydrophobic properties of PECVD grown hydrocarbon and fluorinated-hydrocarbon coatings by D.K. Sarkar; M. Farzaneh; R.W. Paynter (3698-3701).
Wetting characteristics of micro-nanorough substrates of aluminum and smooth silicon substrates have been studied and compared by depositing hydrocarbon and fluorinated-hydrocarbon coatings via plasma enhanced chemical vapor deposition (PECVD) technique using a mixture of Ar, CH4 and C2F6 gases. The water contact angles on the hydrocarbon and fluorinated-hydrocarbon coatings deposited on silicon substrates were found to be 72° and 105°, respectively. However, the micro-nanorough aluminum substrates demonstrated superhydrophobic properties upon coatings with fluorinated-hydrocarbon providing a water contact angle of ∼165° and contact angle hysteresis below 2° with water drops rolling off from those surfaces while the same substrates showed contact angle of 135° with water drops sticking on those surfaces. The superhydrophobic properties is due to the high fluorine content in the fluorinated-hydrocarbon coatings of ∼36 at.%, as investigated by X-ray photoelectron spectroscopy (XPS), by lowering the surface energy of the micro-nanorough aluminum substrates.
Keywords: Superhydrophobic; Fluorinated-hydrocarbon coatings; AFM; SEM;
Erratum to “Improving the stability of organic light-emitting devices using a solution-processed hole-injecting layer” [Appl. Surf. Sci. 255 (2009) 7970–7973] by Xinwen Zhang; Zhaoxin Wu; Dongdong Wang; Dawei Wang; Xun Hou (3702-3703).
Erratum to “Studies on electrodeposition of Fe-W alloys for fuel cell applications” [Appl. Surf. Sci. 253 (2006) 2031–2037] by C.N. Tharamani; Parthasarathi Bera; V. Jayaram; Noor Shahina Begum; S.M. Mayanna (3704).