Preferential orientation growth of AIN thin films on Si (111) substrates by LP-MOCVD

Aluminum nitride (AIN) thin films were deposited on Si (111) substrates by low pressure metalorganic chemical vapor deposition system. The effects of the V/III ratios on the film structure and surface morphology were systematically studied. The chemical states and vibration modes of AIN films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The optical absorption property of the AIN films, characterized by ultraviolet-visible-near infrared spectrophotometer, exhibited a sharp absorption near the wavelength of 206 mm. The AIN (002) preferential orientation growth was obtained at the V/III ratio of 10,000 and the preferential growth mechanism is presented in this paper according to the thermodynamics and kinetics process of the AIN growth.

Fabrication and Infrared Optical Properties of Nano Vanadium Dioxide Thin Films

Vanadium dioxide thin films were fabricated by ion beam sputtering on Si3N4/SiO2/Si after a post reductive annealing process in a nitrogen atmosphere. X-ray Diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the effects of post annealing temperature on crystallinity, morphology, and composition of the vanadium oxide thin films. Transmission properties of vanadium dioxide thin films were measured by Fourier transform-infrared (FT-IR) spectroscopy. The results showed that the as-deposited vanadium oxide thin films were composed of non-crystalline V2O5 and a tetragonal rutile VO2. After annealing at 400 degrees C for 2 h, the mixed phase vanadium oxide (VOx) thin film changed its composition and structure to VO2 and had a (011) oriented monoclinic rutile structure. When increasing the temperature to 450 degrees C, nano VO2 thin films with smaller grains were obtained. FT-IR results showed that the transmission contrast factor of the nano VO2 thin film was more than 0.99 and the transmission of smaller grain nano VO2 thin film was near zero at its switched state. Nano VO2 thin film with smaller grains is an ideal material for application in optical switching devices.

Characterization of silicon carbide thin films and their use in colour sensor

A series of hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were prepared by plasma-enhanced chemical vapour deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source. The previous results show that a high excitation frequency, together with a high hydrogen dilution ratio of the reactive gases, allow an easier incorporation of the carbon atoms into the silicon-rich a-Si1-xCx:H film, widen the valence controllability. The data show that films with optical gaps ranging from about 1.9 to 3.6 eV could be produced. In this work the influence of the hydrogen dilution ratio of the reactive gases on the a-Si1-xCx:H film properties was investigated. The microstuctural and photoelectronic properties of the silicon carbide films were characterized by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), and FT-IR spectrometry. The results show that a higher hydrogen dilution ratio enhances the incorporation of silicon atoms in the amorphous carbon matrix for carbon-rich a-Si1-xCx:H films. One pin structure was prepared by using the a-Si1-xCx:H film as the intrinsic layer. The light spectral response shows that this structure fits the requirement for the top junction of colour sensor. (c) 2004 Elsevier B.V. All rights reserved.

The microstructure of hydrogenated microcrystalline silicon thin films studied by small-angle x-ray scattering

The microstructures of hydrogenated microcrystalline silicon (tic-Si: H) thin films, prepared by plasma-enhanced chemical vapor deposition (PECVD), hot wire CVD(HWCVD) and plasma assisted HWCVD (PE-HWCVD), have been analyzed by the small angle x-ray scattering(SAXS) measurement. The SAXS data show that the microstructures of the μ c-Si: H films display different characteristics for different deposition techniques. For films deposited by PECVD, the volume fraction of micro-voids and mean size are smaller than those in HWCVD sample. Aided by suitable ion-bombardment, PE-HWCVD samples show a more compact structure than the HWCVD sample. The microstructure parameters of the μ c-Si: H thin films deposited by two-steps HWCVD and PE-HWCVD with Ar ions are evidently improved. The result of 45° tilting SAXS measurement indicates that the distribution of micro-voids in the film is anisotropic. The Fouriertransform infrared spectra confirm the SAXS data.

Anisotropic strain relaxation of thin Fe film on c(4 x 4) reconstructed GaAs (001) surface

National Natural Science Foundation of China 60836002 10674130 60521001;Major State Basic Research of China 2007CB924903;Chinese Academy of Sciences KJCX2.YW.W09-1

V5+-doped Bi3.4Yb0.6Ti3O12 fatigue resistant ferroelectric thin films

In this paper, a serial of Bi3.4Yb0.6Ti3-xVxO12 (BYTV) thin film with different V5+ contents were deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD). The crystallized phase and electrical properties of the films were investigated using X-ray diffraction, polarization hysteresis loops, leakage current-voltage, and fatigue test. From our experimental results, it can be found that the ferroelectric properties can be improved greatly using V5+-doped in Bi3.4Yb0.6Ti3O12 (BYT) thin film, compared with the reported BYT thin film. The remanent polarization was enhanced and excellent leakage current characteristic with 10(-11)A at the bias voltage of 4V, which is much lower than the BYT thin film or some reported bismuth layer-structure ferroelectric films. Fatigue test shows that the fabricated films have good anti-fatigue characteristic after 10(10) switching cycles. (c) 2008 Published by Elsevier B.V.

Influence of catalyst layer structure on the current distribution of PEMFCs

A modified subcell approach was adopted to evaluate the current density distributions of proton exchange membrane fuel cells (PEMFCs) with different electrodes. Conventional hydrophobic electrodes showed better performance under flooding conditions compared to hydrophilic electrodes. The thin-film hydrophilic electrode performed better in the absence of liquid water, but it was more readily flooded. A composite catalyst layer was designed with 2/3 of the area from the inlet prepared hydrophilic and the remaining 1/3 area hydrophobic. The composite catalyst layer with commercial scale dimension showed notable enhanced performance in the concentration polarization region. (C) 2004 The Electrochemical Society.

Microstructure and NO2 sensing properties of Fe2O3 thin films

W-doped Fe2O3 films have been fabricated on polycrystalline alumina substrates by the RF magnetron sputtering method, and effects of annealing temperature on the NO2 sensing properties have been examined. The crystal structure of the obtained film changed from Fe3O4 to α-Fe2O3 after annealing at temperatures of 500 to 500°C in air. An increase in the annealing temperature increased the particle size, resulting in a decrease in the NO2-gas sensitivity. These results suggest that the NO2 sensitivity of W-doped Fe2O3 film depends on the particle size.

Effect of the nature of annealing solvent on the morphology of diblock copolymer blend thin films

The morphologies and structures for the thin film of blend systems consisting of two asymmetric polystyrene-block-polybutadiene (SB) diblock copolymers induced by annealing in the vapor of different solvents, namely, cyclohexane, benzene, and heptane, which have different selectivity or preferential affinity for a certain block, were investigated by tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results revealed that even a slight preferential affinity of good solvent for one block would strongly alter the morphology of the blend thin film.

Ring-shaped morphology in H-shaped block copolymer thin films

The formation of ring-shaped structures in an H-shaped block copolymer [a poly(ethylene glycol) backbone with polystyrene branches, i.e., (PS)(2)PEG(PS)(2)] thin film was investigated when it was annealed in saturated PEG-selective acetonitrile vapor. Our results clearly indicate that ring formation is determined by the initial morphology of the spin-coated film, the solvent vapor selectivity and the environmental temperature of the solvent-annealing process. Only the films with the initial core-shell cylindrical structure in strongly PEG-selective acetonitrile vapor could form the ring-shaped structures.

Vertical structure p-type permeable metal-base organic transistors based on N,N '-diphentyl-N,N '-bis(1-naphthylphenyl)-1,1 '-biphenyl-4,4 '-diamine

In this article, vertical structure p-type permeable-base organic transistors were proposed and demonstrated. A hole-type organic semiconductor N,N-'-diphentyl-N,N-'-bis(1-naphthylphenyl)-1,1(')-biphenyl-4,4(')-diamine was used as emitter and collector. In the permeable-base transistors, the metal base was formed by firstly coevaporating Al and Ca in vacuum and then annealing at 120 degrees C for 5 min in air, followed by a thin Al deposition. These devices show a common-base current gain of near 1.0 and a common-emitter current gain of similar to 270.

Electrostatic layer-by-layer a of platinum-loaded multiwall carbon nanotube multilayer: A tunable catalyst film for anodic methanol oxidation

A simple layer-by-layer (LBL) electrostatic adsorption technique was developed for deposition of films composed of alternating layers of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged multiwall carbon nanotubes bearing platinum nanoparticles (Pt-CNTs). PDDA/Pt-CNT film structure and morphology up to six layers were characterized by scanning electron microscopy and ultraviolet-visible spectroscopy, showing the Pt-CNT layers to be porous and uniformly deposited within the multilayer films.

GIUSAXS and AFM Studies on Surface Reconstruction of Latex Thin Films during Thermal Treatment

The structural evolution of a single-layer latex film during annealing was studied via grazing incidence ultrasmall-angle X-ray scattering (GIUSAXS) and atomic force microscopy (AFM). The latex particles were composed of a low-T-g (-54 degrees C) core (n-butylacrylate, 30 wt %) and a high-T-g (41 degrees C) shell (t-butylacrylate, 70 wt %) and had an overall diameter of about 500 nm. GIUSAXS data indicate that the q(y) scan at q(z) = 0.27 nm(-1) (out-of-plane scan) contains information about both the structure factor and the form factor. The GIUSAXS data on latex films annealed at various temperatures ranging from room temperature to 140 degrees C indicate that the structure of the latex thin film beneath the surface changed significantly. The evolution of the out-of-plane scan plot reveals the surface reconstruction of the film. Furthermore, we also followed the time-dependent behavior of structural evolution when the latex film was annealed at a relatively low temperature (60 degrees C) where restructuring within the film can be followed that cannot be detected by AFM, which detects only surface morphology.

Electronic structure of interfaces between copper-hexadecafluoro-phthalocyanine and 2,5-bis(4-biphenylyl) bithiophene

The interfaces formed between copper-hexadecafluoro-phthalocyanine (F16CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T) were examined using photoemission and inverse photoemission spectroscopy. It is observed that in F16CuPc/BP2T the heterojunction is characterized by band bending in both materials, while in BP2T/F16CuPc the band bending is confined in BP2T only. The combination of the band bending and finite Debye lengths provides an explanation to the observed ambipolar behavior of the organic thin film transistors based on such heterojunctions.

Tunable ordered droplets induced by convection in phase-separating P2VP/PS blend film

Ordered hexagonal droplets patterns in phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/PVP) formed due to the convection effect by solvent evaporation. The influences of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to PVP on the PVP-rich domains pattern formation and distributions were investigated by atomic force microscope (AFM). Only in an appropriate range of molecular weight of PS, can the ordered pattern form. Too low or too high molecular weight of PS led no ordered pattern due to the viscosity effects. The increase of solvent evaporation rate decreased the mean radius of the PVP-rich domains and the intervals between the centers of the domains due to the enhancement of the viscosity on the top layer of the fluid film. The increase of the weight ratio of PS to PVP decreased mean radius of the PVP-rich domains whereas the intervals between the centers of droplets remained constant. Therefore, the size and the distributions of ordered patterns can be tuned by the polymer molecular weight, the weight ratio of the two components and the solvent evaporation rate.