Applied Surface Science (v.254, #10)
The stability of superhydrophobic surfaces tested by high speed current scouring by Zhe Cui; Qingjun Wang; Yi Xiao; Changhong Su; Qingmin Chen (2911-2916).
In this paper, on the basis of our former work, we fabricate four kinds of superhydrophobic surfaces by simple means, and adopt high-speed-current-scouring method to test the durability of the as-prepared samples against external force. There exists obvious difference between these four samples in the durability. Finally, we find that the sample with chemical etching and aminosiloxane coating presents best stability, and its contact angle still maintains 141° even after 32-h scouring by current at a speed of 10 m/s. SEM and XPS are utilized to analyze and explain the difference in the durability of the four samples.
Keywords: Superhydrophobic; Micro–nano-structure; Stability; High speed current scouring;
Well-aligned ZnO rod arrays grown on glass substrate from aqueous solution by Mei Yang; Guangfu Yin; Zhongbing Huang; Xiaoming Liao; Yunqing Kang; Yadong Yao (2917-2921).
Well-aligned ZnO rod arrays have been successfully synthesized on glass substrate from the aqueous solution of Zn(NO3)2·6H2O and C6H12N4 (HMT). Some critical issues such as seed layers, concentration and reaction time were investigated. The results show that ZnO seed layers were pre-requisite for the aligned growth of ZnO rod arrays. The length of rods is tunable in a range from 2 μm to 3 μm by varying the solution concentration and reaction time. X-ray diffraction results demonstrate that ZnO rods are wurtzite crystal structures preferentially orienting in the direction of the c-axis. Microstructure observation by scanning electron microscope confirms that ZnO rods grew up perpendicular to the substrate. Room-temperature photoluminescence (PL) spectrum of rod arrays shows a strong emission band at about 396 nm.
Keywords: ZnO; Rod arrays; Aqueous solution; Photoluminescence;
Optical properties of Al-doped ZnO thin films by ellipsometry by Qing Hua Li; Deliang Zhu; Wenjun Liu; Yi Liu; Xiao Cui Ma (2922-2926).
Al-doped ZnO thin films (AZO) were prepared on Si (1 0 0) substrates by using sub-molecule doping technique. The Al content was controlled by varying Al sputtering time. The as-prepared samples were annealed in vacuum chamber at 800 °C for 30 min. From the XRD observations, it is found that all films exhibit only the (0 0 2) peak, suggesting that they have c-axis preferred orientation. The average transmittance of the visible light is above 80%. Spectroscopic ellipsometry was used to extract the optical constants of the films. The absorption coefficient and the energy gap were then calculated. The results show that the absorption edge initially blue-shifts and then red-shifts with increase of Al content.
Keywords: Al-doped ZnO (AZO); Optical properties; Ellipsometry;
Influence of the synthesis conditions of silicon nanodots in an industrial low pressure chemical vapor deposition reactor by V. Cocheteau; E. Scheid; P. Mur; T. Billon; B. Caussat (2927-2933).
Experiments conducted in an industrial tubular low pressure chemical vapor deposition (LPCVD) reactor have demonstrated the reproducibility and spatial uniformity of silicon nanodots (NDs) area density and mean radius. The wafer to wafer uniformity was satisfactory (density and radius standard deviations <10%) for the whole conditions tested except for low silane flow rates, high silane partial pressures and short run durations (<20 s). Original synthesis conditions have then been searched to reach both excellent wafer to wafer uniformities along the industrial load of wafers and high NDs densities. From previous results, it was deduced that the key was to markedly increase run duration in decreasing temperature and in increasing silane pressure. At 773 K, run durations as long as 180 and 240 s have thus allowed to reach NDs densities respectively equal to 9 × 1011 and 6.5 × 1011 NDs/cm2 for the two highest silane pressures tested in the range 60–150 Pa.
Keywords: Silicon nanodots; Chemical vapor deposition; Area density; Ellipsometry; SEM;
Functional multi-walled carbon nanotube/polyaniline composite films as supports of platinum for formic acid electrooxidation by Zan-Zan Zhu; Zhe Wang; Hu-Lin Li (2934-2940).
Embedding of carbon nanotubes in conducting polymeric matrices for various nanocomposites material is now a popular area. In this article, a concise chemical method has been described for the preparation of homogeneous nanocomposite of multi-walled carbon nanotube (MWNT)/polyaniline (PANI) by electrochemical codeposition. For this we functionalized the MWNTs via the diazotization reaction. This helped to disperse the nanotubes in aniline. The composite films were dispersed Pt by electrodeposition technique. The presence of MWNTs and platinum in the composite films was confirmed by XRD analysis and transmission electron microscopy (TEM). Four-point probe investigations revealed that the MWNT/PANI composite films exhibited a good conductivity. Cyclic voltammograms (CV) showed that Pt-modified MWNT/PANI composite films perform higher electrocatalytic activity and better long-term stability than Pt-modified pure PANI film toward formic acid oxidation. The results imply that the MWNT/PANI composite films as a promising support material improves the electrocatalytic activity for formic acid oxidation greatly.
Keywords: Multi-walled carbon nanotubes; Polyaniline; Composite film; Formic acid electrooxidation; Electrocatalytic activity;
Antibody and DNA dual-labeled gold nanoparticles: Stability and reactivity by Fei-Yan Qiao; Jun Liu; Fu-Rong Li; Xiao-Li Kong; Hao-Li Zhang; Han-Xin Zhou (2941-2946).
Gold nanoparticles labeled by both antibody (IgG) and single stranded DNA (ss-DNA) have been synthesized and characterized. The stability and reactivity of the dual-labeled nanoparticles were compared with the conventional IgG or ss-DNA modified nanoparticles. It was found that the IgG adsorption significantly improved the stability of the nanoparticles in aqueous solution, which is beneficial for attaching ss-DNA. The presence of IgG also effectively prohibits the desorption of ss-DNA against dithiothreitol (DTT) displacement. The coverage on dual-labeled nanoparticles was found to be 50 ± 15 ss-DNA/nanoparticle and 10 ± 2 IgG/nanoparticle, respectively, compared to the value of 70 ± 15 ss-DNA/nanoparticle of only ss-DNA-labeled gold nanoparticles. Dot-immuno and cross-linking experiments confirmed that both the IgG and ss-DNA retained their bioactivity on the nanoparticle surface. The dual-labeled nanoparticles have potential to be used as novel bio-probes for ultrasensitive detection.
Keywords: Gold nanoparticle; Self-assembly; DNA; Antibody;
Crystallizaion and surface morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) films by solution casting on different substrates by Wenzhong Ma; Jun Zhang; Xiaolin Wang (2947-2954).
The dependence of surface structure of the poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) films by solution casting on properties of seven substrates was investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). It was revealed that the polyblend films obtained by casting onto each substrate contained exclusively β phase PVDF. Higher crystallinity of the film was obtained by casting onto ceramic, polytetrafluoroethylene (PTFE), copper (Cu), stainless steel and glass substrates than that by casting onto aluminium (Al) and polypropylene (PP) substrates, depending on the degree of close lattice matching. The surface crystalline structure of PVDF was strongly affected by the wettability of substrate. The largest size of PVDF spherulitic crystal structure with about 6 μm presented in the casting film grown at the air/solution interface on glass substrate, while the smallest spherulite size with about 3 μm was generated by casting onto PTFE, stainless steel and PP substrates. It implied that the higher surface tension the substrate had, the larger PVDF spherulite grew at the air/solution interface.
Keywords: Poly(vinylidene fluoride); Crystallinity; Surface morphology; Substrate;
Anti-sticking treatment for a nanoimprint stamp by Hongwen Sun; Jingquan Liu; Pan Gu; Di Chen (2955-2959).
Nanoimprint lithography (NIL), as a low-cost and mass production technique, has played an important role in micro/nano fabrication. However, the sticking problem between the stamp and resist blocks its further application. In order to modify the contact surface, a molecular dynamics (MD) method was used to choose the proper material to coat on the surface of the stamp. According to the MD analysis, CF2 was found to be a good choice for this purpose. It was applied to the nanoimprint stamp by using the gases in reactive ion etching (RIE). A self-assembly monolayer (SAM) layer was also used in the experiment to release the contact surface energy. Both dry and wet methods were demonstrated as excellent anti-sticking approaches by measuring the contact angles and calculating the surface energy. Both the stamps after anti-sticking treatment can be used more times than the untreated stamps.
Keywords: Nanoimprint; Anti-sticking; Molecular dynamics; RIE; SAM;
Attenuated total reflectance spectroscopy of simultaneous processes: Corrosion inhibition of cuprous oxide by benzotriazole by Maria Antoaneta Bratescu; Daniel B. Allred; Nagahiro Saito; Mehmet Sarikaya; Osamu Takai (2960-2966).
Attenuated total reflectance (ATR) spectroscopy was used to perform in situ studies of the corrosion inhibition of cuprous oxide (Cu2O) by benzotriazole (BTA) in aqueous solution at concentrations from 1 to 20 μM. Because two separate processes occur simultaneously, that of Cu2O corrosion and corrosion inhibition by BTA adsorption, the spectral information was subjected to deconvolution by a conjugate gradient minimization algorithm. Under these conditions, a solution phase concentration of 7–10 μM BTA nearly completely inhibited the corrosion of Cu2O in deionized water. Using a Langmuir adsorption model, this represented only 25% of the maximally covered surface area.
Keywords: Total internal reflection; Attenuated total reflectance spectroscopy; Benzotriazole; Corrosion inhibition; Ultraviolet evanescent wave; Cuprous oxide; ATR-UV;
Evaluation of the tool life and fracture toughness of cutting tools boronized by the paste boriding process by I. Campos; M. Farah; N. López; G. Bermúdez; G. Rodríguez; C. VillaVelázquez (2967-2974).
The present study evaluates the tool life and the fracture toughness of AISI M2 steel cutting tools boronized by the paste boriding process. The treatment was done in selective form on the tool tips of the steels. The temperatures were set at 1173 and 1273 K with 4 h of exposure time and modifying the boron carbide paste thicknesses in 3 and 4 mm. Microindentation fracture toughness method was used on the borided tool at the temperature of 1273 K and a 4 mm paste thickness, with a 100 g load at different distances from the surface. Also, the borided cutting tools were worn by the turning process that implied the machining of AISI 1018 steel increasing the nominal cutting speed, of 55 m/min, in 10 and 25% and maintaining the feed and the depth cut constants. The tool life was evaluated by the Taylor's equation that shows the dependence of the experimental parameters of the boriding process.
Keywords: Boriding; Tool life; Fracture toughness; Borided layers; Wear resistance; Cutting tools;
Biomimetic, hierarchical structures on polymer surfaces by sequential imprinting by Fengxiang Zhang; Jennifer Chan; Hong Yee Low (2975-2979).
Thermal nanoimprint lithography (NIL) is based on the thermo-mechanical deformation of a polymer film above the glass transition temperature (T g) and at an applied pressure. Sequential imprinting extends the process of thermal NIL to create hierarchical structures by carrying out secondary and tertiary imprintings at temperatures below the T g of a polymer. In this work, we demonstrate the use of sequential imprinting technique to fabricate two- and three-level hierarchical structures on polystyrene (PS) and poly(methyl methacrylate) (PMMA) films over a temperature range of 70–130 °C, with the aim to mimic the hierarchical structures found in biological systems. By mimicking the hierarchical structure in a plant leaf, the water contact angle of PS film was increased from 95° to 128°, while the water contact angle of PMMA film was increased from 71° to 104°, without any chemical treatment.
Keywords: Sequential imprinting; Hierarchical; Biomimetic; Wettability; Polymer;
Microstructure and surface morphology of YSZ thin films deposited by e-beam technique by G. Laukaitis; J. Dudonis; D. Milčius (2980-2987).
In present study yttrium-stabilized zirconia (YSZ) thin films were deposited on optical quartz (amorphous SiO2), porous Ni–YSZ and crystalline Alloy 600 (Fe–Ni–Cr) substrates using e-beam deposition technique and controlling technological parameters: substrate temperature and electron gun power which influence thin-film deposition mechanism. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin-film structure and surface morphology depend on these parameters. It was found that the crystallite size, roughness and growth mechanism of YSZ thin films are influenced by electron gun power. To clarify the experimental results, YSZ thin-film formation as well evolution of surface roughness at its initial growing stages were analyzed. The evolution of surface roughness could be explained by the processes of surface mobility of adatoms and coalescence of islands. The analysis of these experimental results explain that surface roughness dependence on substrate temperature and electron gun power non-monotonous which could result from diffusivity of adatoms and the amount of atomic clusters in the gas stream of evaporated material.
Keywords: YSZ thin films; Electron beam deposition; Electron gun power; Thin-film growth; Microstructure; Surface morphology and surface roughness;
Surface modification and properties of Bombyx mori silk fibroin films by antimicrobial peptide by Liqiang Bai; Liangjun Zhu; Sijia Min; Lin Liu; Yurong Cai; Juming Yao (2988-2995).
The Bombyx mori silk fibroin films (SFFs) were modified by a Cecropin B (CB) antimicrobial peptide, (NH2)-NGIVKAGPAIAVLGEAAL-CONH2, using the carbodiimide chemistry method. In order to avoid the dissolution of films during the modification procedure, the SFFs were first treated with 60% (v/v) ethanol aqueous solution, resulting a structural transition from unstable silk I to silk II. The investigation of modification conditions showed that the surface-modified SFFs had the satisfied antimicrobial activity and durability when they were activated by EDC·HCl/NHS solution followed by a treatment in CB peptide/PBS buffer (pH 6.5 or 8) solution at ambient temperature for 2 h. Moreover, the surface-modified SFFs showed the smaller contact angle due to the hydrophilic antimicrobial peptides coupled on the film surface, which is essential for the cell adhesion and proliferation. AFM results indicated that the surface roughness of SFFs was considerably increased after the modification by the peptides. The elemental composition analysis results also suggested that the peptides were tightly coupled to the surface of SFFs. This approach may provide a new option to engineer the surface-modified implanted materials preventing the biomaterial-centered infection (BCI).
Keywords: Bombyx mori silk; Silk fibroin film; Surface modification; Cecropin B; Antimicrobial activity; Antimicrobial peptide;
Femtosecond laser micromilling of Si wafers by Seongkuk Lee; Dongfang Yang; Suwas Nikumb (2996-3005).
Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2–8 J/cm2 and the milling efficiency attains its maximum between 10 and 20 J/cm2.
Keywords: Femtosecond laser; Ablation; Micromilling; Silicon;
Manganese cryptomelane-type oxides: A thermo-kinetic and morphological study by J.S. Valente; D. Frías; P. Navarro; M. Montes; J.J. Delgado; E. Fregoso-Israel; E. Torres-García (3006-3013).
In the present work, a detailed study on structural and textural properties, as well as a thermo-kinetic characterization of two manganese cryptomelane-type oxides, was carried out. A suitable methodology was stated for determining the several stages taking place during the surface molecules’ removal. Thus, further insights were provided about the chemical nature of the sites present at the solid's surface. Relative strengths and the number of basic sites at the surface were estimated. The results show that the removal of the adsorbed (H2O, CO2) molecules from the surface is essential to disclose the oxide surface features. The morphological properties and thermo-kinetic characterization indicate the existence of at least three types of basic sites, owing activation energy values ranging from 140 to 190 kJ/mol. The dispersion observed in the activation energy data, during the CO2 loss, suggests that the interaction occurs on different sites. Therefore, both samples showed a heterogeneous surface; this is related to the energetic nature of the sites, as well as the basic strengths of the surface manganese cryptomelane oxides.
Keywords: Manganese cryptomelane oxides; Hi-Res TGA; Kinetics in solid; Thermal analysis; Isoconversion method;
Plasma electrolytic oxidation coating on AZ91 magnesium alloy modified by neodymium and its corrosion resistance by Y.L. Song; Y.H. Liu; S.R. Yu; X.Y. Zhu; Q. Wang (3014-3020).
Ceramic coatings on the surfaces of Mg-9Al-1Zn (AZ91) magnesium alloy and Mg-9Al-1Zn-1Nd magnesium alloy (AZ91 magnesium alloy modified by neodymium, named as AZ91Nd in this paper) are synthesized in aluminate electrolyte by plasma electrolytic oxidation (PEO) process, respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses show the PEO coating on the Mg-9Al-1Zn-1Nd alloy comprises not only MgO and Al2O3, which are found in the coating on the AZ91 alloy, but also a trace amount of Nd2O3. Microstructure observations indicate the addition of Nd can decrease the sizes of β phases and form Al2Nd intermetallics in the AZ91 alloy. The fine β phases can effectively restrain the formation of unclosed-holes and greatly decrease the sizes of pores in the coating during the PEO process. In addition, the Al2Nd intermetallics can be completely covered due to the lateral growth of the PEO coatings formed on the α and β phases. As a result, the coating on the AZ91Nd alloy possesses a dense microstructure compared with that on the AZ91 alloy. The following corrosion tests indicate the corrosion resistance of the PEO coating on the AZ91Nd alloy is evidently higher than that of the PEO coating on the AZ91 alloy.
Keywords: Magnesium alloys; Neodymium; Plasma electrolytic oxidation; Microstructure; Corrosion resistance;
Electrochemical corrosion behaviors of a-C:H and a-C:N X :H films by Zhou Wang; Chengbing Wang; Qi Wang; Junyan Zhang (3021-3025).
The a-C:H and a-C:N X :H films were deposited onto silicon wafers using radio frequency (rf) plasma enhanced chemical vapor deposition (PECVD) and pulsed-dc glow discharge plasma CVD, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize chemical nature and bond types of the films. The results demonstrated that the a-C:H film prepared by rf-CVD (rf C:H) has lower I D/I G ratio, indicating smaller sp2 cluster size in an amorphous carbon matrix. The nitrogen concentrations of 2.9 at.% and 7.9 at.% correspond to carbon nitride films prepared with rf and pulse power, respectively.Electrochemical corrosion performances of the carbon films were investigated by potentiodynamic polarization test. The electrolyte used in this work was a 0.89% NaCl solution. The corrosion test showed that the rf C:H film exhibited excellent anti-corrosion performance with a corrosion rate of 2 nA cm−2, while the carbon nitride films prepared by rf technique and pulse technique showed a corrosion rate of 6 nA cm−2 and 235 nA cm−2, respectively. It is reasonable to conclude that the smaller sp2 cluster size of rf C:H film restrained the electron transfer velocity and then avoids detriment from the exchange of electrons.
Keywords: Electrochemical corrosion; CVD; a-C:H films; a-C:N X :H films;
Phase evolution of an aluminized steel by oxidation treatment by Wang Deqing (3026-3032).
Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe2Al5. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe2Al5 phase remains at the temperature below 950 °C in 2-h, and the Fe2Al5 phase is completely transformed into low iron content Fe–Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe2Al5 phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al2O3 and the intermetallic Fe2Al5, FeAl2, FeAl and Fe3Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.
Keywords: Fe–Al intermetallics; Aluminum diffusion; Phase transition; Oxidation; Thermal shock;
Low-temperature preparation of F-doped TiO2 film and its photocatalytic activity under solar light by Jingjing Xu; Yanhui Ao; Degang Fu; Chunwei Yuan (3033-3038).
A novel and simple method for preparing F-doped anatase TiO2 (defined as FTO) film with high photocatalytic activity was developed using titanium-n-butoxide and NH4F as TiO2 and fluorine precursors under mild condition, i.e. low temperature (lower than 373 K) and ambient pressure. The prepared samples were characterized by XRD, SEM, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectrum (DRS), photoluminescence spectrum (PL) and TG–DSC analysis. The photocatalytic activity was evaluated by decomposing X-3B under artificial solar light. The results showed that the crystallinity of TiO2 was improved by F-doping. F− ions can prevent the grain growth, and the transformation of anatase to rutile phase was also inhibited. The doped fluorine atoms existed in two chemical forms, and the ones incorporated into TiO2 lattice might take a positive role in photocatalysis. Compared with surface fluorination samples, FTO film exhibited better photocatalytic activity. The high photocatalytic activity of FTO may due to extrinsic absorption through the creation of oxygen vacancies rather than the excitation of the intrinsic absorption band of bulk TiO2. Furthermore, the FTO can be recycled with little photocatalytic activity depression. Without any further treatment besides rinsing, after 6 recycle utilization, the photocatalytic activity of FTO film was still higher than 79%.
Keywords: Fluorine-doped; Photocatalysis; Low-temperature; Recycle;
Laterally inhomogeneous barrier analysis of the methyl violet/p-Si organic/inorganic hybrid Schottky structures by Ö. Güllü; Ö. Barış; M. Biber; A. Türüt (3039-3044).
In this work, we have investigated the electrical characteristics, such as current–voltage (I–V) and capacitance–voltage (C–V) measurements, of identically prepared crystal violet/p-Si Organic/Inorganic (OI) Schottky structures formed by evaporation of organic compound solution to directly p-Si semiconductor substrate. It has been seen that the crystal violet organic dye thin film on the p-Si substrate has exhibited a good rectifying behavior. The barrier heights (BHs) and ideality factors of all devices have been calculated from the electrical characteristics. Although the diodes were all identically prepared, there was a diode-to-diode variation: the effective barrier heights ranged from 0.6 ± 0.1 to 0.8 ± 0.1 eV, and the ideality factor from 1.6 ± 0.4 to 3.5 ± 0.4. The barrier height versus ideality factor plot has been plotted for the OI devices. Lateral homogeneous BH was calculated as a value of 0.7 eV from the observed linear correlation between BH and ideality factor, which can be explained by laterally inhomogeneities of BHs. The values of barrier height and acceptor doping concentration yielded from the reverse bias C–V measurements ranged from 0.7 ± 0.1 to 1.3 ± 0.1 eV and from (4.7 ± 0.8) × 1014 to (8.1 ± 0.8) × 1014 cm−3, respectively. The mean barrier height and mean acceptor doping concentration from C–V characteristics has been calculated 1.0 eV and 5.9 × 1014 cm−3, respectively. It has been seen that the mean BH value of 0.7 eV obtained for the Al/methyl violet/p-Si contact is significantly larger than BH values of the conventional Al/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for metal/Si diodes has been achieved using a thin interlayer of the methyl violet organic semiconductor; this has been ascribed to the fact that the methyl violet interlayer increases the effective barrier height by influencing the space charge region of Si.
Keywords: Schottky barrier; Organic–inorganic semiconductor contact; Methyl violet;
Al2O3/SiO2 films prepared by electron-beam evaporation as UV antireflection coatings on 4H-SiC by Feng Zhang; Huili Zhu; Weifeng Yang; Zhengyun Wu; Hongji Qi; Hongbo He; Zhengxiu Fan; Jianda Shao (3045-3048).
Al2O3/SiO2 films have been deposited as UV antireflection coatings on 4H-SiC by electron-beam evaporation and characterized by reflection spectrum, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reflectance of the Al2O3/SiO2 films is 0.33% and 10 times lower than that of a thermally grown SiO2 single layer at 276 nm. The films are amorphous in microstructure and characterize good adhesion to 4H-SiC substrate. XPS results indicate an abrupt interface between evaporated SiO2 and 4H-SiC substrate free of Si-suboxides. These results make the possibility for 4H-SiC based high performance UV optoelectronic devices with Al2O3/SiO2 films as antireflection coatings.
Keywords: UV antireflection coatings; 4H-SiC; Al2O3/SiO2 films; Electron-beam evaporation;
Characterization of chemically modified carbon black for sorption application by Dipu Borah; Shigeo Satokawa; Shigeru Kato; Toshinori Kojima (3049-3056).
A commercial grade carbon black was chemically modified using mineral acids (either with HNO3 or H2SO4 or mixture) and the sorption performance of the virgin and modified forms were investigated. Chemical modification resulted in the creation of surface acidic functional groups (―COOH, ―SO2OH) and was verified by FTIR spectra. This was further verified by TGA analysis revealing higher weight loss characteristics of the modified carbons in comparison to virgin carbon black. Morphological changes were observed from BET surface area measurements and SEM analysis. XRD study revealed the change of graphitic crystallite size as a result of modification. The suspension pH of the materials in deionized water and the point of zero charge (pHpzc) in inert electrolyte were determined. The measured values of suspension pH and pHpzc for all the carbons were found to be acidic with more acidic character in the modified carbons. These materials were used as sorbents for the removal of arsenic from aqueous medium and showed excellent adsorption performance.
Keywords: Carbon black; Chemical modification; Characterization; Suspension pH; Point of zero charge; Arsenic adsorption;
Synthesis and characterization of β-Ga2O3 nanorods by Huizhao Zhuang; Shiying Zhang; Xiaokai Zhang; Chengshan Xue; Baoli Li; Dexiao Wang; Jiabing Shen (3057-3060).
A novel method was applied to prepare β-Ga2O3 nanorods. In this method, β-Ga2O3 nanorods have been successfully synthesized on Si(1 1 1) substrates through annealing sputtered Ga2O3/Mo films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The results show that the nanorod is single-crystalline Ga2O3 with monoclinic structure. The β-Ga2O3 nanorods are straight and smooth with diameters in the range of 200–300 nm and lengths typically up to several micrometers. The growth process of the β-Ga2O3 nanorods is probably dominated by conventional vapor–solid (VS) mechanism.
Keywords: β-Ga2O3; Nanorods; Magnetron sputtering; Annealing;
Catalysis of dispersed silver particles on directional etching of silicon by Y.M. Yang; Paul K. Chu; Z.W. Wu; S.H. Pu; T.F. Hung; K.F. Huo; G.X. Qian; W.J. Zhang; X.L. Wu (3061-3066).
Silver particles are dispersed on silicon by magnetron sputtering and post-annealing to investigate the catalytic effects of individual silver particles on wet etching of silicon surface. According to scanning electron microscopy, dispersed deep holes are present and the major etching direction is vertical to the surface of a Si(1 0 0) wafer or inclined to that on a Si(1 1 1) wafer. Our experiments indicate that the effect of the anisotropy of Si on directional etching is fundamental and the wafer resistivity and experimental process have important influence on the etching results. In addition, aggregation of silver particles and random horizontal etching on the surface of the wafer are caused by the local imbalance between the oxidant and HF. Our results enable better understanding of the catalytic effects of metal particles on silicon and are helpful to the preparation new silicon nanostructures.
Keywords: Metal catalysis; Directional etching; Porous silicon;
Laser-irradiated thermodynamic behaviors of spallation and recombination at solid-state interface by Hsin-Yi Lai; Pei-Hsing Huang (3067-3073).
A microscopic insight of interfacial spallation and recombination behaviors at multilayer thin-film interface induced by incident femtosecond pulsed laser is presented in this paper. Such two different aforementioned behaviors are investigated via the thermodynamic trajectories obtained by using standard Lennard–Jones (L–J) molecular dynamics (MD) simulation. Based on the simulation results, the interfacial damages of multilayer thin film are dominated by a critical threshold that induces an extraordinary expansive dynamics and phase transitions leading to the structural softened and tensile spallation at interface. The critical damage threshold is evaluated at around 8.5 J/m2 which governs the possible occurrence of two different regimes, i.e. interfacial spallaiton and recombination. In interfacial damage region, quasi-isothermal thermodynamic trajectories can be observed after the interfacial spallation occurs. Moreover, the result of thermodynamic trajectories analyses indicates that, the relaxation of pressure wave may cause the over-heated interfacial zone to reduce volumetric density, thus leading to structural softness and even weaken interfacial structural strength. The crucial effect leading to the phenomenon of low tension spallation is identified.
Keywords: Molecular dynamics; Femtosecond pulses laser; Interfacial spallation;
Field electron emission from HfN x O y thin films deposited by direct current sputtering by Xing-Min Cai; Fan Ye; Er-Qing Xie; Dong-Ping Zhang; Ping Fan (3074-3077).
HfN x O y thin films were deposited on Si substrates by direct current sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). SEM indicates that the film is composed of nanoparticles. AFM indicates that there are no sharp protrusions on the surface of the film. XRD pattern shows that the films are amorphous. The field electron emission properties of the film were also characterized. The turn-on electric field is about 14 V/μm at the current density of 10 μA/cm2, and at the electric field of 24 V/μm, the current density is up to 1 mA/cm2. The field electron emission mechanism of the HfN x O y thin film is also discussed.
Keywords: Sputtering; HfN x O y thin film; Field electron emission;
Influence of substitution on dielectric and impedance spectroscopy of Sr1 − x Bi2 + y Nb2O9 ferroelectric ceramics synthesized by chemical route by D. Dhak; P. Dhak; P. Pramanik (3078-3092).
Nanocrystalline powders of Sr1 − x Bi2 + y Nb2O9 (SBN, x = 0.0, 0.1, 0.2, 0.3, and 0.4; y = 0, 0.066, 0.133, 0.200, and 0.266) were prepared by aqueous solution method using water-soluble Sr–EDTA, Bi–EDTA and Nb–tartarate as the starting materials. XRD showed that the samples were free from fluorite or pyrochlore phase within heat-treatment temperature from 550 to 600 °C. Average crystallite size and particle diameter were observed to be between 10 and 25 nm, which were analyzed through XRD and TEM, respectively. Bi-substitution has substantially improved the sinterability of SBN and enabled to achieve high density (96%), which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Sr2+ ions by the trivalent bismuth ions. The complex impedance diagrams of Bi-substituted SBN, x = 0.4 ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for pure and other substituted SBN ceramics show an additional low-frequency semicircle, which was attributed to the blocker size effects. The dielectric behavior of pure and Bi-substituted SBN ceramics was rationalized using the impedance and modulus data.
Keywords: Ferroelectrics; Chemical route; Impedance;
Analysis of mechanically induced processes in the Langmuir film by Martin Weis; Ján Vajda (3093-3099).
The understanding of processes in the monolayer at the air–water interface induced by mechanical compression is important as a part of basic research of the system with reduced dimensionality as well as for the investigation of processes during the Langmuir–Blodgett deposition. The Maxwell displacement current technique provides a substantial contribution for the study of structural and electrical properties. Analysis based on imperfect gas approximation with semi-empirical intermolecular potentials is used. Detail theoretical study of molecular tilt in a continual lateral compression and dielectric relaxation phenomena (step-compression) is presented. Obtained results are confronted with standard surface pressure analysis and surface potential measurement.
Keywords: Langmuir–Blodgett film; Monolayers; Electrical properties and measurements; Dielectric properties;
Substrate effects on ZnO nanostructure growth via nanoparticle-assisted pulsed-laser deposition by Ruiqian Guo; Jun Nishimura; Mitsuhiro Higashihata; Daisuke Nakamura; Tatsuo Okada (3100-3104).
The effects of various substrate conditions on the morphology, crystal structure and photoluminescence of ZnO nanostructures synthesized by nanoparticle-assisted pulsed-laser ablation deposition were investigated. It is concluded that the sapphire substrate with a 1 h anneal at 1000 °C is the most favorable to the vertical growth of ZnO nanostructures. SEM analysis indicates that the well-aligned diameter-modulated ZnO nanonails with unique shape were successfully synthesized on the annealed sapphire substrate. The as-synthesized ZnO nanostructures exhibit an ultraviolet emission at around 390 nm and the absent green emission under room temperature, indicating that there is a very low concentration of deep-level defects inside ZnO lattices. The novel ZnO nanostructures could offer novel opportunities for both fundamental research and technological applications.
Keywords: ZnO; Nanostructures; Pulsed-laser deposition; Optical properties;
Effect of annealing temperature for Si0.8Ge0.2 epitaxial thin films by Yuan-Ming Chang; Ching-Liang Dai; Tsung-Chieh Cheng; Che-Wei Hsu (3105-3109).
This study investigates the effect of annealing temperature on the Si0.8Ge0.2 epitaxial layers. The Si0.8Ge0.2 epitaxial layers were deposited by using ultrahigh vacuum chemical vapor deposition (UHVCVD) with different annealing temperatures (400–1000 °C). Various measurement technologies, including high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM) and interfacial adhesion tester, were used to characterize the materials properties of the SiGe epilayers. The experimental results showed that the SiGe epilayers gradually reduced lattice-mismatch to the underlying substrate as annealing temperature increased (from 400 to 800 °C), which resulted from a high temperature enhancing interdiffusion between the epilayers and the underlying substrate. In addition, the average grain size of the SiGe films increased from 53.3 to 58 nm with increasing annealing temperature. The surface roughness in thin film annealed at 800 °C was 0.46 nm. Moreover, the interfacial adhesion strength increased from 476 ± 9 to 578 ± 12 kg/cm2 with increasing the annealing temperature.
Keywords: SiGe epilayers; Annealing; Adhesion strength; UHVCVD;
A study of Ni-based WC composite coatings by laser induction hybrid rapid cladding with elliptical spot by Shengfeng Zhou; Yongjun Huang; Xiaoyan Zeng (3110-3119).
Ni-based WC composite coatings by laser induction hybrid rapid cladding (LIHRC) with elliptical spot were investigated. Results indicate that the efficiency using the elliptical spot of 6 mm × 4 mm (the major and minor axis of laser beam are 6 mm and 4 mm, respectively, the major axis is parallel to the direction of laser scanning) is higher than that using the elliptical spot of 4 mm × 6 mm (the major axis is perpendicular to the direction of laser scanning). The precipitated carbides with the blocky and bar-like shape indicate that WC particles suffer from the heat damage of “the disintegration pattern + the growth pattern”, whichever elliptical spot is used at low laser scanning speed. However, at high laser scanning speed, the blocky carbides are only formed if the elliptical spot of 6 mm × 4 mm is adopted, showing that WC particles present the heat damage of “the disintegration pattern”, whereas the fine carbides are precipitated when the elliptical spot of 4 mm × 6 mm is used, showing that WC particles take on the heat damage of “the radiation pattern”. Especially, the efficiency of LIHRC is increased much four times higher than that of the general laser cladding and crack-free ceramic-metal coatings can be obtained.
Keywords: Laser cladding; Composite coatings; Laser induction hybrid rapid cladding (LIHRC); Elliptical spot; Cracks;
The effect of hydrogen irradiation and annealing on the low-temperature growth of homoepitaxial ZnO layers grown on (0 0 0 1) ZnO substrates by plasma-assisted molecular beam epitaxy by S.H. Park; H. Suzuki; J.H. Chang; T. Minegishi; J.S. Park; I.H. Im; G. Fujimoto; T. Hanada; D.C. Oh; M.W. Cho; T. Yao (3120-3124).
Low-temperature growth of high quality homoepitaxial ZnO is realized by using hydrogen irradiation and annealing processes (modified method). By modified method, two-dimensional growth and atomically smooth surface with steps (terrace length ∼75 nm) are achieved at 400 °C. Furthermore, FWHMs of high resolution X-ray rocking curves for (0 0 0 2) and (10–11) reflections are evaluated as narrow as 21 arcsec, which indicates that high crystallinity of the ZnO grown at 400 °C by modified method is almost similar to that grown at 600 °C by conventional method. Photoluminescence results show the considerable improvement of optical properties, such as an emersion of free exciton (FX) and a decrease of donor bound exciton (D°X) linewidth, by using modified method, even at growth temperature as low as 400 °C.
Keywords: Hydrogen; Surfactant; Low-temperature growth;
Observation of many-body Coulomb interaction effects on the photoluminescence spectra of InAs/GaAs quantum dots by J. Rihani; N.B. Sedrine; V. Sallet; M. Oueslati; R. Chtourou (3125-3129).
InAs quantum dots (QDs) on GaAs (0 0 1) substrates were grown by Molecular Beam Epitaxy (MBE) using two growth temperatures. Photoluminescence (PL) pump power dependence measurements at low temperature were carried out for sample grown at higher temperature (520 °C). With increasing excitation density, the ground-state transition energy is found to decrease by 8 meV, while the excited-state transition energies exhibit resonance behaviour. The redshift of the ground-state emission was related to the band-gap renomalization (BGR) effect whereas the blueshift of the excited-state emissions was assigned to the compensation between filling of fine structure states and BGR effects. Using a quasi-resonant PL measurement, we have shown that the renormalization of the band-gap had to occur in the QD barrier.
Keywords: InAs QDs; Molecular beam epitaxy; Photoluminescence spectroscopy; Band-gap renormalization; AFM analysis;
Deposition of TiSiN coatings by arc ion plating process by C.T. Guo; D. Lee; P.C. Chen (3130-3136).
Titanium silicon nitride (TiSiN) thin films were deposited on tungsten cemented carbide tools by cathode arc ion plating (AIP) process using alloy TiSi targets. The effects of silicon addition and negative substrate bias on the development of the textures of films were studied systematically by varying the bias voltage from −20 to −200 V. The structural features of the films were investigated in detail using X-ray diffraction. The effect of the texture on such mechanical properties as hardness and adhesion of the films was also studied. A maximum hardness of 42 GPa was obtained at a DC substrate bias of −150 V. The characteristics of TiSiN thin films exhibited excellent adhesion of over 150 N. The cutting performance of end-mills and drillers was evaluated by milling and drilling of highly hardened material under high-speed cutting conditions. The results reveal that cutting tools with TiSiN coatings markedly outperformed those with TiN coatings, and the uncoated cutting tools. TiSiN coating increased the cutting lifetime to seven times that of the uncoated one.
Keywords: TiSiN; Arc ion plating (AIP); XRD;
Ultrafast laser ablation for restoration of heritage objects by A.V. Rode; K.G.H. Baldwin; A. Wain; N.R. Madsen; D. Freeman; Ph. Delaporte; B. Luther-Davies (3137-3146).
Powerful ultrafast laser pulses have a unique capability to ablate material from the surface without heat propagation into the bulk due to the non-linear nature of the laser-surface interaction. This quality offers a new application of ultrafast lasers for restoration of objects of art and heritage artefacts. We discuss the laser-based cleaning methods used in art restoration, analyse the potential advantages and challenges of using ultrafast laser pulses, and present new encouraging results on using ultrafast lasers in the field of heritage conservation.
Keywords: Femtosecond laser-matter interaction; Laser ablation; Art restoration; Heritage conservation;
Elaboration of self-organized magnetic nanoparticles by selective cobalt silicidation by A. Fleurence; G. Agnus; T. Maroutian; B. Bartenlian; P. Beauvillain; E. Moyen; M. Hanbücken (3147-3152).
Self-organized magnetic nanoparticles are obtained through selective silicidation of cobalt using a silicon substrate pre-structured with tri-dimensional gold islands as template. On the step bunches array of a vicinal Si(1 1 1) surface, gold deposition results in the formation of nanodroplets aligned along the step bunches. A subsequent cobalt deposition is performed onto this gold islands-covered Si surface, with two silicidation processes investigated: reactive deposition (RD) and solid phase reaction (SPR). The cobalt is converted into a non-magnetic silicide film except where the surface is locally masked by the gold islands, giving rise to cobalt nanomagnets which can be capped by a gold layer. A scanning tunneling microscopy comparative study of RD and SPR processes demonstrates that the former induces strong surface morphology changes while the latter preserves the pristine islands. Magnetic measurements performed with alternating gradient force magnetometry at room temperature are used to demonstrate the presence of ferromagnetic cobalt nanoparticles on SPR-processed samples. These nanomagnets show a clear in-plane anisotropy behavior.
Keywords: Nanoparticles; Self-organization; Magnetism;
Effects of γ-ray radiation grafting on aramid fibers and its composites by Y.H. Zhang; Y.D. Huang; L. Liu; K.L. Cai (3153-3161).
Armos fiber was modified by Co60 γ-ray radiation in the different concentrations’ mixtures of phenol–formaldehyde and ethanol. Interlaminar shear strength (ILSS) was examined to characterize the effects of the treatment upon the interfacial bonding properties of Armos fibers/epoxy resin composites. The results showed that the ILSS of the composite, whose fibers were treated by 500 kGy radiation in 1.5 wt% PF, was improved by 25.4%. Nanoindentation technique analysis showed that the nanohardnesses of the various phases (the fiber, the interface and the matrix) in the composite, whose fibers were treated, were correspondingly higher than those in the composite, whose fibers were untreated. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectrum confirmed the increase in the polar groups at the fibers’ surface. Atomic force microscopy (AFM) results revealed that the surface of the fibers treated was rougher than that of the fibers untreated. The wettability of the fibers’ surface was also enhanced by the treatment. The conclusion that γ-ray irradiation grafting significantly improved the surface properties of Armos fibers could be drawn.
Keywords: Armos fibers; Surface modification; γ-Ray radiation grafting; Surface properties; Mechanical properties;
One-dimensional and quasi-one-dimensional ZnO nanostructures prepared by spray-pyrolysis-assisted thermal evaporation by Wen-Cheng Liu; Wei Cai (3162-3166).
One-dimensional (1D) and quasi-1D ZnO nanostructures have been fabricated by a kind of new spray-pyrolysis-assisted thermal evaporation method. Pure ZnO powder serves as an evaporation source. Thus-obtained products have been characterized by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM). The room temperature photoluminescence spectrum of these ZnO nanostructures is presented. The results show that as-grown ZnO nanomaterials have a hexagonal wurtzite crystalline structure. Besides nanosaws, nanobelts and nanowires, complex ZnO nanotrees have also been observed in synthesized products. The study provides a new simple route to construct 1D and quasi-1D ZnO nanomaterials, which can probably be extended to fabricate other oxide nanomaterials with high melting point and doped oxide nanomaterials.
Keywords: Zinc oxides; Nanostructures; Semiconductors; Chemical vapor deposition;
Substrate orientation-induced distinct ferromagnetic moment in Co:ZnO films by X.J. Liu; C. Song; P.Y. Yang; F. Zeng; F. Pan (3167-3174).
Dilute (3.8 at.%) cobalt-doped ZnO thin films are deposited on LiTaO3 (LT) substrates with three different orientations [LT(1 1 0), LT(0 1 2) and LT(0 1 8)] by direct current reactive magnetron co-sputtering. The experimental results indicate that Co atoms with 2+ chemical valence are successfully incorporated into the ZnO host matrix on various oriented substrates, and the substrate orientations have a profound influence on the crystal growth and magnetization of Co:ZnO films. A large magnetic moment of 2.42μ B/Co at room temperature is obtained in the film deposited on LT(0 1 2), while the corresponding values of the other films deposited on LT(1 1 0) and LT(0 1 8) are 1.21μ B/Co and 0.65μ B/Co, respectively. Furthermore, the crystal growth mode of Co:ZnO films on various oriented LT, the relationship between the microstructures and corresponding ferromagnetic properties are also discussed.
Keywords: Co:ZnO; Substrate orientation; Ferromagnetism; Bound magnetic polarons;
Effects of interface on the dielectric properties of Ba0.6Sr0.4TiO3 thin film capacitors by Hongwei Chen; Chuanren Yang; Chunlin Fu; Jihua Zhang; Jiaxuan Liao; Liye Hu (3175-3179).
Ba0.6Sr0.4TiO3 thin films were deposited on Pt/SiO2/Si substrate by radio frequency magnetron sputtering. High-resolution transmission electron microscopy (HRTEM) observation shows that there is a transition layer at BST/Pt interface, and the layer is about 7–8 nm thickness. It is found that the transition layer was diminished to about 2–3 nm thickness by reducing the initial RF sputtering power. X-ray photoelectron spectroscopy (XPS) depth profiles show that high Ti atomic concentration results in a thick interfacial transition layer. Moreover, the symmetry ν of ɛ r–V curve of BST thin film is enhanced from 52.37 to 95.98%. Meanwhile, the tunability, difference of negative and positive remanent polarization (P r), and that of coercive field (E C) are remarkably improved.
Keywords: Barium strontium titanate; Thin film; Interface; Dielectric properties;
Simultaneous imaging for surface and internal structure of polymer blend thin films by Hideki Sugihara; Kazuyuki Oya; Hiroki Murase; Keiichi Akabori; Keiji Tanaka; Tisato Kajiyama; Atsushi Takahara (3180-3183).
A novel experimental technique for three-dimensional (3D) visualization of phase-separated structure of polymer blend thin film was proposed. Polystyrene/poly(methyl methacrylate) (PS/PMMA) blend thin films with the thickness of approximately 100 nm were cut at extremely low angle by utilizing surface and interface cutting analysis system (SAICAS), and the cross-section was exposed as gradient surface with the width of approximately 2.5 μm. SFM investigation for the grazing cross-section imaged the detailed internal and surface phase separated structure of the (PS/PMMA) blend thin films on one image.
Keywords: Surface; Internal structure; Phase-separated structure; Scanning force microscopy; Polymer blend; Thin film;
Oxidation of epitaxial Y(0 0 0 1) films by M. Ay; O. Hellwig; H.W. Becker; B. Hjörvarsson; H. Zabel (3184-3190).
We have investigated the oxidation behavior of MBE grown epitaxial Y(0 0 0 1)/Nb(1 1 0) films on sapphire ( 1 1 2 ¯ 0 ) substrates at elevated temperatures under atmospheric conditions with a combination of experimental methods. At room temperature X-ray diffraction (XRD) reveals the formation of a 25 Å thick YO x H x layer at the surface, while simultaneously oxide growth proceeds along defect lines normal to the film plane, resulting in the formation of a single crystalline cubic Y2O3 (2 2 2) phase. Furthermore, nuclear resonance analysis (NRA) reveals that hydrogen penetrates into the sample and transforms the entire Y film into the hydride YH2 phase. Additional annealing in air leads to further oxidation radially out from the already existing oxide channels. Finally material transport during oxidation results in the formation of conically shaped oxide precipitations at the surface above the oxide channels as observed by atomic force microscopy (AFM).
Keywords: Oxidation; X-ray scattering; Nuclear resonance analysis;
Stability of MgO(1 1 1) films grown on 6H-SiC(0 0 0 1) by molecular beam epitaxy for two-step integration of functional oxides by T.L. Goodrich; Z. Cai; K.S. Ziemer (3191-3199).
Crystalline magnesium oxide (MgO) (1 1 1), 20 Å thick, was grown by molecular beam epitaxy (MBE) on hydrogen cleaned hexagonal silicon carbide (6H-SiC). The films were further heated to 740 °C and 650 °C under different oxygen environments in order to simulate processing conditions for subsequent functional oxide growth. The purpose of this study was to determine the effectiveness and stability of crystalline MgO films and the MgO/6H-SiC interface for subsequent heteroepitaxial deposition of multi-component, functional oxides by MBE or pulsed laser deposition processes. The stability of the MgO films and the MgO/6H-SiC interface was found to be dependent on substrate temperature and the presence of atomic oxygen. The MgO films and the MgO/6H-SiC interface are stable at temperatures up to 740 °C at 1.0 × 10−9 Torr for extended periods of time. While at temperatures below 400 °C exposure to the presence of active oxygen for extended periods of time has negligible impact, exposure to the presence of active oxygen for more than 5 min at 650 °C will degrade the MgO/6H-SiC interface. Concurrent etching and interface breakdown mechanisms are hypothesized to explain the observed effects. Further, barium titanate was deposited by MBE on bare 6H-SiC(0 0 0 1) and MgO(1 1 1)/6H-SiC(0 0 0 1) in order to evaluate the effectiveness of the MgO as a heteroepitaxial template layer for perovskite ferroelectrics.
Keywords: MgO; SiC; Heteroepitaxy; Functional oxides; MBE; Wide bandgap semiconductor;
On the structure, morphology, and optical properties of chemical bath deposited Sb2S3 thin films by B. Krishnan; A. Arato; E. Cardenas; T.K. Das Roy; G.A. Castillo (3200-3206).
In the present paper, we have reported the room temperature growth of antimony sulphide (Sb2S3) thin films by chemical bath deposition and detailed characterization of these films. The films were deposited from a chemical bath containing SbCl3 and Na2S2O3 at 27 °C. We have analysed the structure, morphology, composition and optical properties of as deposited Sb2S3 films as well as those subjected to annealing in nitrogen atmosphere or in air. As-deposited films are amorphous to X-ray diffraction (XRD). However, the diffused rings in the electron diffraction pattern revealed the existence of nanocrystalline grains in these films. XRD analysis showed that upon annealing in nitrogen atmosphere these films transformed into polycrystalline with orthorhombic structure. Also, we have observed that during heating in air, Sb2S3 first converts into orthorhombic form and then further heating results in the formation of Sb2O3 crystallites. Optical bandgap energy of as deposited and annealed films was evaluated from UV–vis absorption spectra. The values obtained were 2.57 and 1.73 eV for the as-deposited and the annealed films respectively.
Keywords: Antimony sulphide; Thin films; Chemical bath deposition; XRD;
Effects of carbonization and substrate temperature on the growth of 3C–SiC on Si(1 1 1) by SSMBE by Zhongliang Liu; Jinfeng Liu; Peng Ren; Yuyu Wu; Pengshou Xu (3207-3210).
The growth of 3C–SiC on Si(1 1 1) substrate was performed at different carbonization temperatures and substrate temperatures by solid-source molecular beam epitaxy (SSMBE). The properties of SiC film were analyzed with in situ reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The best carbonization temperature of 810 °C was found to be optimal for the surface carbonization. The quality of SiC film grown on Si at substrate temperature of 1000 °C is best. The worse crystalline quality for the sample grown at higher temperature was attributed to the large mismatch of thermal expansion coefficient between SiC and Si which caused more dislocation when sample was cooled down to room temperature from higher substrate temperature. Furthermore, the larger size of single pit and the total area of the pits make the quality of SiC films grown at higher temperature worse. More Si atoms for the sample grown at lower temperature were responsible for the degradation of crystalline quality for the sample grown at lower temperature.
Keywords: 3C–SiC; Si(1 1 1); SSMBE; Carbonization; Substrate temperature;
Surface functionalization of porous ZrO2–TiO2 membranes using γ-aminopropyltriethoxysilane in palladium electroless deposition by M. Williams; C.A. Pineda-Vargas; E.V. Khataibe; B.J. Bladergroen; A.N. Nechaev; V.M. Linkov (3211-3219).
A pre-treatment technique was developed to facilitate the electroless deposition of Pd layers onto ZrO2–TiO2 ceramic membrane surfaces in the preparation of novel multi-functional porous membranes. Surface functionalization using an aqueous solution of γ-aminopropyltriethoxysilane (γ-APTES) aided the surface immobilization of the Pd activation particles and the subsequent electroless deposition of metal layers onto the hydroxyl-rich membrane surface. The attractiveness of γ-APTES functionalization, in the electroless deposition of metal layers, was thus demonstrated. Characterization techniques employed in the structural study of the surface-modified membranes included SEM, EDS, dynamic analysis in micro-PIXE, and XRD. Special membrane techniques such as electrokinetic analysis and single-gas permeation measurements were also used in the study of surface modification. These membranes were developed for application in tasks associated with the hydrogen economy.
Keywords: ZrO2–TiO2; γ-Aminopropyltriethoxysilane; Electroless deposition; Palladium;
Characteristics of adsorption phase with water/organic mixtures at a surface of activated carbons possessing intraparticle and textural porosities by V.M. Gun’ko; V.V. Turov; O.P. Kozynchenko; D. Palijczuk; R. Szmigielski; S.V. Kerus; M.V. Borysenko; E.M. Pakhlov; P.P. Gorbik (3220-3231).
The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and 1H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190–273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the 1H NMR and adsorption methods.
Keywords: Activated carbon; Multicomponent adsorption; Water; Organic solvents; Methane; Porosity; 1H NMR spectroscopy; NMR-cryoporometry;
Electrochemical oxidation of methanol on Pt nanoparticles composited MnO2 nanowire arrayed electrode by Guang-Yu Zhao; Hu-Lin Li (3232-3235).
By use of the membrane-template synthesis route, MnO2 nanowire arrayed electrodes are successfully synthesized by means of the anodic deposition technique. The Pt nanoparticles composited MnO2 nanowire arrayed electrodes (PME) are obtained through depositing Pt on MnO2 nanowire arrayed electrode by cathode deposition technique. For comparison of electrochemical performance, Pt nanowire arrayed electrodes which have the same amount of Pt with PME are also prepared. The electro-oxidation of methanol on PME and Pt nanowire arrayed electrodes is investigated at room temperature by cyclic voltammetry, which show that about 110 mV decreased overpotential and 2.1-fold enhanced votammetric current are achieved on PME. The chronoamperometry result demonstrates that the resistance to carbon monoxide for PME is improved.
Keywords: Electrodeposition; MnO2 nanowire arrayed electrode; Pt nanoparticles; Methanol oxidation;
Preparation and characterization of visible-light-driven titania photocatalyst co-doped with boron and nitrogen by Qincai Ling; Jianzhong Sun; Qiyun Zhou (3236-3241).
In order to improve the photocatalytic performance of titania under visible light, a boron and nitrogen co-doped titania photocatalyst was prepared. Its photoabsorbance was measured by UV–vis diffusive reflectance spectroscopy (DRS). The microstructure of photocatalyst was characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The microcrystal of the co-doped photocatalyst consisted of anatase phase and was approximately present in the form of spherical particle. The particle size was in correlation with the calcination temperature. Degradation of phenol under visible light illumination was used to evaluate the photocatalytic performance. The calcination temperature and the component influenced the photoactivity. The results showed that the co-doping of boron and nitrogen played an important role in the band gap decrease, which led to the rise of the photocatalytic activity.
Keywords: Visible light photocatalysis; Titania; Boron; Nitrogen; Co-doped;
Adsorption equilibrium and kinetics of dibenzothiophene from n-octane on bamboo charcoal by Dishun Zhao; Juan Zhang; Erhong Duan; Jinlong Wang (3242-3247).
The adsorption of the model sulfur compound dibenzothiophene (DBT) from n-octane solution on to bamboo charcoal (BC) was investigated. The equilibrium and kinetics of DBT adsorption on BC were examined. Adsorption isotherm of DBT on BC was determined and correlated with two well-known isotherm equations (Langmuir and Freundlich). The equilibrium data for DBT adsorption fitted the Freundlich model well. Two simplified kinetic models including pseudo first-order and pseudo second-order equations were selected to follow the adsorption processes. The adsorption of DBT on BC can be best described by a pseudo second-order equation. The parameters of this best-fit kinetic model were calculated and discussed.
Keywords: Adsorption; Dibenzothiophene; Isotherm equations; Kinetics;