Materials Science and Nanotechnology I

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Authors: Mei Fen Wang, Guo Jun Du, Dong Yu Xia
Abstract: The molecular dynamics method is used to simulate microcrack healing in copper nano-plate during heating. During microcrack healing, the tip of microcrack is blunted and deforms to round shape, the microcrack becomes smaller and smaller until it is healed through slip bands emitting from the pre-crack tip and expanding to the top and bottom of the copper nano-plate. The healing time is different in different temperature. The healing processes in different temperature present different slip bands for crack healing. When temperature is below 650K, the healing time decreases dramatically with temperature increase. When temperature is above 650K, the healing time decreases smoothly with temperature increase. The critical temperature of microcrack healing in copper nano-plate without pre-existing dislocations is about 400K.
454
Authors: Jian Jun Fang, Rong Fa Guan, Jie Qing Ma, Chang Rui, Hai Tao Shen, Jin Jie Zhang
Abstract: The fuzzy orthogonal design is a method that the orthogonal results were fuzzed and then analyzed using fuzzy mathematical theory. It took the full advantage of the information from orthogonal experiments to obtain the optimal liposome preparation conditions by considering all the evaluation indexes. With the fuzzy comprehensive evaluation for the objective function, main technological parameters of process in liposome preparation were optimized using fuzzy orthogonal design. The optimal processing parameters were pH values of phosphate-buffer solution of 7,soybean phosphatidyl-choline and cholesterol proportion of 1:1,the concentration of Catechin of 5mg/mL,Oil­water proportion of 3:1.The catechin-loaded liposomes prepared under the optimized conditions has high encapsulation efficiency. The entrapment rate of catechin nanoliposome measured by validated test was 61.7%±0.015,while the mean diameter was 193.6±0.119 nm.
458
Authors: Chao Song, Yan Qing Guo, Xiang Wang, Jie Song, Rui Huang
Abstract: Series of a-Si:H/a-SiNx multilayers were prepared by very high frequency plasma enhanced chemical vapor deposition system. As-deposited samples were thermally annealed at the various temperatures. The effects of thermal annealing on the properties of luminescence were investigated. The photoluminescence intensity of the film annealed at 600 °C is found to be higher than that of the film without annealing. However, with further increasing the annealing temperature from 600 °C to 800 °C, the photoluminescence intensity of the film rapidly decreases. Fourier transform infrared spectroscopy and Raman-scattering spectroscopy were used to study the changes of the microstructures and bonding configurations. Based on the measurements of structural and bonding configurations, the improved photoluminescence intensity is attributed to the forming of radiative defect states caused by the effusion of hydrogen in the films.
465
Authors: Yan Qing Guo, Xiang Wang, Chao Song, Rui Huang, Jie Song
Abstract: In recent years, hydrogenated nanocrystalline silicon (nc-Si:H) film has received much attention due to its potential application in various optoelectronic devices. In the present work, nanocrystalline silicon (nc-Si) films were fabricated from SiH4 diluted with H2 in very high frequency (40.68 MHz) plasma enhanced chemical vapor deposition system. The influence of radio frequency (rf) power on the structural properties of nanocrystalline silicon films has been studied. Raman spectra show that the crystallinity of the nc-Si films can be increased by promoting the rf power. But over high rf power leads to the structural deterioration of nc-Si:H film. AFM images manifest that, with the increase of deposition time, the grain size becomes larger accompanied by the decrease of the number density.
469
Authors: Hai Feng Chen, Ting Yan
Abstract: Using Bi(NO3)3•5H2O, Na2WO4•2H2O and Ti• (OC4H9)4 as the main raw materials, different alcohol solvent as medium, hexamethylene tetramine as sink set agent, tungsten bismuth and titanium dioxide composite powder were prepared by hydrothermal synthesis. It was characterized by XRD and DRS. The methyl orange imitated sewage, we study the impacts of calcinations’ temperature, catalyst amount, concentration, illumination time and pH on photocatalytic performance of Bi2WO6/TiO2 samples under visible light. The results showed that calcinations’ temperature 400 oC was the best, because the forbidden band gap decreased with temperature increased, but phase transition or decomposition exothermic of the samples would occurre at higher than 400 degree. The Bi2WO6/TiO2 prepared under acidic condition had only 2.41 eV as the smallest forbidden band gap of the samples.
473
Authors: Chao Chen, Ya Dong Jiang, Hong Xi Zhou
Abstract: Thermal conductance of microbolometer has a directly impact on Noise Equivalent Temperature Difference (NETD) and thermal time constant which are the key indicators of uncooled IR detector. It is of great significance to calculate and evaluate thermal conductance. A calculate approach of thermal conductance for uncooled microbolometer detectors is introduced in this paper. Accurate three-dimensional modeling of microbolometer is found by using MEMS analysis software Intellisuite. Dynamic thermal analysis of this model is solved and then thermal time constant can be read from thermal time curve of the analysis mentioned above. Combined with the calculation of thermal capacitance, more precisely thermal conductance value can be reached which is more accurate than theoretical calculations result and meaningful for design and fabrication of the device.
477
Authors: Yue Wu, Xiao Hong Meng
Abstract: The single crystalline Si target with high resistivity was ablated by a XeCl excimer laser (laser fluence 4 J/cm2, repetition rate 1 Hz), and at ambient pressure of 10Pa of pure Ar gas, the nanocrystalline silicon film was deposited on a glass or single crystalline Si substrate located at a distance of 3 cm from the Si target in 30 and 10min, respectively. The Raman and X-ray diffraction spectra of the film deposited on the glass substrate indicate the film is nanocrystalline, which means that it is composed of Si nanoparticles. Scanning electron microscope of the film on the Si substrate shows that the film has the mosaic structure of Si nano-crystallites of uniform size. The photoluminescence peak wavelength is 599nm with full width at half maximum of 56nm.
481
Authors: Chao Ding, Li Bao An, Xiao Xia Yang, Yan Yan Liu
Abstract: Carbon nanotubes (CNTs) have drawn extensive research interest for a variety of applications in single electron transistors, field emission displays, interconnects, sensors, energy storage, composites, and many others due to their excellent electrical, mechanical, and thermal properties. One requirement for many of these applications is the need to integrate CNTs into various devices or circuits as functional components and different manipulation methods have been developed. This paper addresses the assembly of CNTs by dielectrophoresis (DEP) and reviews recent research progress of controlled assembly of CNTs. Totally six approaches are introduced in which different techniques including impedance measurement, optical induced DEP, floating electrode DEP, self-limiting resistor, fluidic assisted deposition, and real-time gap impedance monitoring of DEP are respectively used to control the yield of the DEP process. The advantages and disadvantages of these methods are analysed. The purpose is to help automating the DEP process of CNTs and other one-dimensional nanomaterials by presenting these advanced control techniques.
485
Authors: Jun Hong Zhang, Guo Hui Xu, Ya Juan Xu, Yue Hui He
Abstract: Blended elemental powders with the nominal compositions (at%) of Ti50Al50, was mechanically alloyed in a planetary ball milling system for up to 100h, an amorphous Ti50Al50 phase was obtained in the process. The amorphization process as a function of time of milling was monitored by scanning electron microscope, X-ray diffraction and transmission electron microscope. It is shown that, as first, Al atoms diffuse into the host lattice of hexagonal Ti; subsequently, the milling accumulates a critical density of disorder that causes the Ti (Al) crystalline phase to collapse into an amorphous phase, it is suggested the grain size condition for formation of amorphous phase is 12nm. On the basis of thermodynamic models, the formation of the amorphous phase is discussed.
490
Authors: Shu Min Ma, Chao Chen, Tao Wang, Huan Zhang, Hong Xi Zhou
Abstract: An accelerometer is a micro- electromechanical device which can sensitive to acceleration . The sensing mechanism of accelerometer is that when accelerated , the mass moves in Z-axis, and the gap between parallel plates changed with the loads, which causes vary of the capacitance of the estimation. This paper presents a newly devel oped sensor for the conventional capacitive MEMS accelerometer in Z-axis . The principle of capacitive acceleration is based on the detection the change of capacitance which results from acceleration changes. The sensor is used for estimation of the size a nd loads variations for accelerometer. This paper has been focused on the design of the MEMS accelerometer and calculation of the major parameters of the sensor.
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