S. Xie

Rate-limiting process and growth kinetics of AlN thin films by microwave plasma CVD with AlBr3-NH3-N2 system

Abstract Microwave plasma enhanced CVD with AlBr 3 -NH 3 -N 2 system is developed for the preparation of AlN thin films. The growth rate and morphology of the films on Si(111) substrate as a function of the operation parameters were systematically studied. (002) oriented AlN thin films have been obtained. The growth rate vs. temperature showed a two-regime behavior with activation energies of 3.12 kJ/mol and 15.6 kJ/mol, respectively. The dependence of the growth rate on AlBr 3 precursor temperature well fitted the prediction from thermodynamic analysis of the CVD system, indicating the deposition rate limited by the mass feeding process. A surface kinetic model was proposed to interpret the (002) oriented growth behavior.

Highly Porous Spongelike Ceramic Films with Bimodal Pore Structure Prepared by Electrostatic Spray Deposition Technique

With a high feeding rate of the precursor solution, highly porous spongelike lithium–cobalt–oxide films with bimodal pore structure and porosity over 90% were fabricated at 235°C by the electrostatic spray deposition (ESD) technique. The metal acetates were used as the precursors dissolved in a mixed solvent of ethanol and butyl carbitol. Scanning electron microscopy (SEM) and X–ray diffraction were used to analyze the structure of the as–deposited films. The growth rate was found to be 7.8 μm/h and 0.24 mg/(cm2 h). At a relatively long deposition time, this bimodal porous structure may evolve into a porous columnar structure. Other morphologies such as flattened reticular structure and rather dense structure can be obtained at deposition temperatures between 270 and 320°C.

〈0001〉-oriented growth of AlN films on Si(111) by microwave plasma CVD with AlBr3NH3N2 system

Abstract AlN thin films on Si(111) substrates were prepared by a microwave plasma activated chemical vapour deposition using NH 3 and AlBr 3 precursors. The films were highly (0002)-oriented on Si(111) properly pre-treated, and amorphous polycrystalline on non-treated surfaces. The growth rate and morphology of the films as a function of deposition parameters such as AlBr 3 source and deposition temperatures, carrier gas flow rate, and system pressure were studied. The 〈0001〉-oriented growth behaviour is discussed in terms of the system thermodynamics and surface adsorption-gas reaction growth model, associated with the effect of plasma ambient.

Preparation and characterization of perovskite ceramic powders by gelcasting

Perovskite La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) powders have been successfully synthesized from oxide and carbonates based on the principle of gelcasting. Phase-forming temperature is very dependent on the ball-milling process during the suspension preparation. As the ball-milling time is increased, the temperature of phase formation decreases, therefore the perovskite powder obtained has a larger Brunaver–Emmett–Teller (BET) specific surface area. The grain sizes were around 1 μm at 1000°C and 2 μm at 1100°C from scanning electron microscopy (SEM) photographs. The perovskite powders have good sinterability: the sintering densities of ceramic bodies shaped with as-prepared powders were investigated. SEM photos show that sintered ceramics exhibit a well defined morphology in the packing and sintering of particles. The oxygen permeance of disc shaped samples, with a thickness ranging from 1.02 to 1.98 mm was 6.39 × 10−8–1.99 × 10−8 mol cm−2 s−1 at 900°C indicating that LSCF ceramics have high oxygen permeation. It can be concluded that gelcasting is a simple and effective method for preparing practical multicomponent perovskite powders.

Electrical conduction and oxygen transport in SrFeCo0.5Ox oxide membranes

Abstract Electrical and oxygen transport properties of SrFeCo 0.5 O x oxide were investigated at elevated temperatures. The electrica1 conductivity was found in the order of 20–10 S/cm in the temperature range of 1100–600°C. An abnormal region was observed at temperatures around 900°C in which electrical conductivity increased with decreasing temperature, which may be related to the undergoing of phase transformation. An oxygen permeation flux of 159×10 −8 mol/cm 2 ·s was measured in an air/helium gradient at 900°C. The acid treatment on the sintered oxide resulted in a considerable improvement of the oxygen permeability, indicating that the surface oxygen exchange limits the overall oxygen permeation process.