A stoichiometric mixture of evaporating materials for AgGaS2 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, AgGaS2 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were 590oC and 440oC, respectively. The temperature dependence of the energy band gap of the AgGaS2 obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 2.7284 eV . (8.695×10.4 eV/K)T2/(T + 332 K).After the as-grown AgGaS2 single crystal thin films was annealed in Ag-, S-, and Ga-atmospheres, the origin of point
defects of AgGaS2 single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native
defects of VAg, VS, Agint, and Sint obtained by PL measurements were classified as a donors or acceptors type. And we
concluded that the heat-treatment in the Ag-atmosphere converted AgGaS2 single crystal thin films to an optical n-type.
Also, we confirmed that Ga in AgGaS2/GaAs crystal thin films did not form the native defects because Ga in AgGaS2
single crystal thin films existed in the form of stable bonds.
Effects of CH4/H2 flow rate ratio, chuck bias and microwave power on the structural properties and particle
densities of diamond thin films deposited on Ti substrates in microwave plasma CVD were examined. High quality
diamond thin films were deposited on Ti substrates in 2~3 CH4 Vol.% conditions due to the preferential formation of sp3-
bonds and selective removal of sp2-bonds in the CH4/H2 mixtures, and the mechanism for the formation of diamond
particles on Ti was analysed. Diamond particle density increased with increasing negative chuck bias to Ti substrate due to
bias-enhanced nucleation of diamond and the threshold voltage was found at ~.50 V. With increasing microwave power the
evolution from micro-crystalline graphite layer to diamond layer was observed.
In order to improve electrical conductivity and mechanical properties of 8YSZ SOFC electrolyte material, we
used Al2O3 as an additive and applied the spark plasma sintering (SPS) method. The sintered bodies were densified above
96 % of theoretical density at 1200oC and possessed microstructures composed of homogeneous grains less than 1 μm in
size. The addition of Al2O3 improved fracture toughness and bending strength by inhibiting grain growth of 8YSZ and increased
total ionic conductivity because grain interior conductivity appeared to remain constant and grain boundary conductivity
increased. It was assumed that the dissolution of Al2O3 into 8YSZ which was inevitable problem at commercial sintering
method was effectively prohibited by the SPS technique with a relatively low sintering temperature and the reaction
between Al2O3 and SiO2 present at grain boundary to produce the crystalline Al2 − xSi1 − yO5 phase, resulting in the increase
of grain boundary conductivity.
In order to simulate the powder compaction process and to assess the effects of packing randomness and particle arrangement 2-dimensional model of rod array compaction using quasi-random multiparticle array is introduced. The elastic modulus of porous ceramics is computed by the homogenization method. With 3 Al2O3 and 3 Al particles the compaction processes associated with the porosities are simulated by the explicit finite element method, based on the elastic modulus found by the homogenization method. The simulation results are compared with both previous analytical ones and experimental measurements. Finally, in order to find the relationship between the friction coefficient of powder particles and the relative density, the sensitivity analysis is performed.
In this study, the process parameters in ceramics powder compaction are optimized for getting high relative densities of ceramic products. To find optimized parameters, the analytic models of powder compaction are firstly prepared by 2-dimensional rod arrays with random green densities using a quasi-random multiparticle array. Then, using finite element method, the changes in relative densities are analyzed by varying the size of Al2O3 particle, the amplitude of cyclic compaction, and the coefficient of friction, which influence the relative density in cyclic compactions. After the analytic function of relative density associated process parameters are formulated by aid of the response surface method, the optimal conditions in powder compaction process are found by the grid search method. When the particle size of Al2O3 is 22.5 mm, the optimal parameters for the amplitude of cyclic compaction and the coefficient of friction are 75 MPa and 0.1103, respectively. The maximum relative density is 0.9390.
Effects of pH level and slurry particle size on material removal rate and planarization of langasite single crystal wafer have been examined. Higher material removal rate was obtained with lower pH level slurries while the planarization was found to be determined by average particle size of colloidal silica slurries. Slurries containing 0.045 mm amorphous silica particles showed the best polishing effect without any scratches on the surface. Effective particle number has a strong effect on the surface planarization and the removal rate, so that the lower effective particle numbers produced low removal rate but the better planarization results.
A sheet type of green body was made with the mixture of 60 wt% red clay, 20 wt% fly ash, and 20 wt% stone sludge. Indentations were made on the surfaces of sheets to investigate fracture rate of 1 to 5 mm artificial light-weight aggregates by various drying, breaking, and forming methods. Drying methods of green bodies were natural, electric oven, microwave, and fast drying by torch. Breaking methods of green bodies were ballmill I, ballmill II, free dropping in the box, and mechanical breaking with roller mill. The depth and width of indent on the surface of the sheet were varied and the thickness of green bodies was also changed to investigate effects of indentation on fracture rates. The highest fracture rate of 42 % among the various drying methods was obtained by microwave drying for 210 sec and the highest fracture rate of 65 % among the various breaking method was obtained by ballmill II method. In forming method, an yield of larger aggregates than F = 5 mm decreased and that of smaller aggregates than F = 5 mm in creased with increasing depth of indentation (only in 3 mm thick green body)and with increasing thickness of green body. The size of aggregates was most homogeneous (by judging from the measurement of aspect ratio of 1 to 5 mm aggregates.) when 3 mm thick green body was rapidly dried by torch and was broken by ballmill II method.