Solid State Phenomena Vols. 121-123

Abstract: We report on room-temperature visible photoluminescence (PL) of B-doped hydrogenated nanocrystalline Si (nc-Si:H) thin films grown by plasma enhanced chemical vapor deposition. It is found that with increasing the boron doing ratio, the PL peak energy blue shifts while the PL intensity first increases and then decreases. The PL profiles can be well reproduced by using the model of Islam and Kumar [J. Appl. Phys. 93, 1753 (2003)] which incorporates the effects of quantum confinement and localized surface states, together with a log-normal rather than normal crystallite size distribution. The yielded microstructural information is in good agreement with the Raman analysis, revealing that B doping tends to reduce the size of Si nanocrystals and the PL intensity is jointly determined by the amount of amorphous Si:H phase and the fraction of B-doped Si nanocrystals. These results also provide implications to realize control of PL properties of nc-Si:H by B doping under optimized growth conditions.

Abstract: Carbon doped titanium dioxide photocatalysts have been synthesized by a precipitation method. Anatase TiO2 was obtained when the precipitate was heat-treated at 400°C when rutile phase appeared at 600°C. The absorption spectra of the powders showed strong absorption in visible region. For the sample calcined at 400 °C , the absorption extended up to 750nm. X-ray photoelectron spectrum (XPS) confirmed that carbon atoms were incorporated into the TiO2 crystal lattice. Photodegradation experiments showed that the powders had visible-light degradation activity.

Abstract: The stress is an important parameter of nano-thin film of the micro-structure. It is essential for the successful design and operation of many micro-machined devices. In this paper, the experiment idea that using Raman spectrometer to quantitate the stress in the nano-thin film of MEMS was put forward and the formula of the stress of Si and GaAs crystal was derived. In the experiment, the Si nano-thin film and AlAs/GaAs nano-thin film on GaAs substrate were grown by MBE (molecular beam epitaxy). The uniaxial pressure is exerted to nano-thin film by using the pressurization instrument designed by ourselves. Raman spectrums of the nano-thin film of MEMS are measured with the pressure exerted varying. Through the processing of the experiment data, the error of measurement to stress in nano-thin film is maximally 0.9% to Si and 7.5% to GaAs. So, Raman spectrum can be used to accurately quantitate stress in nano-thin film of MEMS in order to assessment of the reliability of micromachined structure. And the method can be applied to quantitate the stress in the experiment of testing the piezoresistor effect of double-quantum-well nano-thin film.

Abstract: Nano-structured thin films of amorphous YBa2Cu3Ox were prepared by pulsed laser glancing angle deposition. Ambient oxygen pressure and laser fluence have a strong effect on the microstructure of the films. The films exhibit a structural evolution from isolated nanorods, through network of vertical nanocolumns, to nanoparticles fractal with increasing ambient oxygen pressures. Shadowing effect, surface diffusion and flux scattering by ambient gas play main roles in determining the structural evolution.

Abstract: MCs are produced by cyanobacteria and cause concerns in potable water due to toxicity. Conventional treatments are poor at removing MCs. In the present study, the photocatalytic degradation of MC-LR was conducted using nano-TiO2 thin film, prepared by sol-gel and dip-coating method, with UV 365nm irradiation. According to analysis results from solid-phase extraction combined with HPLC method, the trace-level MC-LR is easily to be removed by photocatalytic system. The degradation efficiency of MC-LR is influenced by the pH conditions, initial concentration due to adsorption of MC-LR on TiO2 thin film. The maximum initial rate of photocatalytic degradation occurs at pH 4 and over 95% of 20μg/L MC-LR is decomposed within 120min. The kinetic equations and parameters revealed that degradation reaction of trace level MC-LR, which depicted by pseudo first order kinetics process in appearance, was in accordance with Langmuir-Hinshelwood kinetics model well, the corresponding rate constant k and Langmuir adsorption constant K were determined to be 19.72μg/l·min-1 and 6.57×10-4l/μg, respectively.

Abstract: Raman scattering from surface optic (SO) phonons has been observed and identified in cylindrical and rectangular cross-section nanowires with lateral dimensions in the range 20-50 nm and lengths of ~ 10 microns. The position of the SO band is found to depend on both the shape of the wire cross section (i. e., circular or rectangular) and on the dielectric constant of the external medium. The position of the SO band in GaP and ZnS nanowires is in good agreement with a dielectric continuum model that takes the shape of the wire cross section into account. We propose that the symmetry breaking mechanism which activates the Raman sacttering of the SO phonon in our nanowires is a quasi-periodic modulation of the cross-sectional area along the nanowire axis. We suggest this modulation stems from an interesting growth instability associated with vapor-liquid-solid (VLS) growth.

Abstract: The perovskite-type nanocrystal LaMnO3 was prepared using sol-gel auto-combustion method with citric acid as the chelating agent. Some analytical methods consisted of FT-IR, XRD, TEM and wave-guide method were used to characterize the gel and the final products. The metal ions coordination compound, obtained from nitrate and citrate, underwent an auto-combustion process and voluminous ashes formed when calcining the complex in the air. From the result of the dielectric properity. It was shown that the dielectric coefficient curves and dielectric loss curve of LaMnO3 nanocrystals were smooth in the range of 8-11MHz. The dielectric loss can be obversed obviously in the measured range.

Abstract: The transparent conducting films have been investigated extensively because of their excellent electrical and optical properties in many applications. For producing the LCD (Liquid Crystal Displays) and OLED (Organic Light-Emitting Diode), the transparent conductive films are mainly deposited on the glass. Using the plastic substrate has the advantages of low cost, light-weighted, and flexible characteristics; it is considered as the candidate substrate material for the portable and flexible LCD. The surface roughness measured by AFM was in the range 2.63~11.1nm. The result shows that the crystallite size increases with increasing the r.f. power. The microstructure of ZnO film has a proud (002) orientation. The average transmittance of ZnO film can be obtained over 80% in the visible spectrum. The lowest resistivity obtained is 4.0×10-3 ohm-cm. The adhesion between ZnO films and PET substrate is good because there is no separate observed in this study.

Abstract: The tribological and mechanical properties of carbon nanofiber (CNF)-filled polytetrafluoroethylene (PTFE) composites with different filler proportions were studied. The worn surfaces of PTFE and carbon nanofiber/PTFE (CNF/PTFE) composites were then examined with scanning electron microscope (SEM). The results show the friction properties of CNF/PTFE composites decreased then increased with the increasing content of CNFs, while the anti-wear properties of CNF/PTFE composites were much higher than that of pure PTFE. The best anti-wear property was obtained with the composite containing 2 wt.% CNFs. The wear volume loss of the composite contained 2 wt.% CNFs was only about 1/700 that of PTFE without CNFs under the condition of 150N and 1.4m/s. Meanwhile, the results also indicate that the mechanical properties of CNF/PTFE composites increased then decreased with the increasing filler concentration, and the composite contained 1 wt.% CNFs has the best mechanical properties. Compare to pure PTFE, the tensile strength and the elongation of CNF/PTFE composites increased about 20% and 70% respectively when the filler content is 1 wt.%. It was seen from the worn surfaces micrographs of PTFE and CNF/PTFE composites that CNFs greatly reduce the adhesive wear of PTFE.

Abstract: The coherent phase equilibria of binary nanoparticles, in which three phases can be formed, were examined by accounting for the particle size effect engendered by the surface stress. Considering the system geometry exhibiting radial symmetry, coherent phase diagrams could be constructed for different particle sizes. The phase diagrams exhibited several characteristics of phase equilibria unique to coherent systems. It was found that a positive surface stress results in a radial compressive stress in the particle that is inversely proportional to the particle radius, thereby increasingly stabilizing the phase having a lower molar volume as the particle size decreases.