Yuezhong Wang

Light extinction by pores in AlON ceramics: the transmission properties

The transmission properties of aluminium oxynitride (AlON) ceramics were studied. AlON samples with different transmittances were prepared. SEM detected two types of pores with a different range of diameters in the samples; the porosity was obtained by counting the number of pores in a certain area. Mie theory was applied to illuminate the effects of pores on the transmittances. The calculated transmittances were compared with the experiments. The existence of pores with sizes in the 1.1-1.6 mu m range and porosities above 10(-4) accounted for the degradation of the transmittance spectra at 2.5 mu m. Discrepancies of the spectra between the samples were caused mainly by different densities of the A-type pores with sizes above 1 mu m. The concepts of critical size and critical concentration were proposed and were quantitatively characterized by critical curves, which divided the regions of translucency and transparency into three parts: R(1), R(2) and R(3) depending on porosity. New approaches on how to control the pore sizes and porosities quantitatively for transparent ceramics design were presented.

Effects of Al2O3 phase composition on AlON powder synthesis via aluminothermic reduction and nitridation

Abstract Using micro-sized aluminum powder (11 wt.%) and nano-sized Al2O3 powder (89 wt.%) with five different phase compositions, AlON powders were synthesized at different temperatures in flowing-nitrogen atmosphere. Our results suggest that for starting materials with low γ-Al2O3/total Al2O3 ratio R (0 and 0.15), a calcination temperature of 1 750 °C is required to obtain single-phase AlON. This temperature is about 50 °C higher than for other batches starting with larger R values (0.5, 0.85, and 1.0). The AlON powders fabricated from reactants with a high R value in this work show narrower particle size distribution and better particle homogeneity than those prepared from batches with lower R values.

Design and fabrication of ultrathin and highly thermal-stable α-Ta/graded Ta(N)/TaN multilayer as diffusion barrier for Cu interconnects

A one-step strategy of magnetron sputtering deposition with dynamic regulation of sputtering atmosphere was developed to prepare α-Ta/graded Ta(N)/TaN multilayer films on the Si substrate. The evolution of Ta clusters shows a significant effect on the crystal structure of the Ta film. The experimental results validate that the formation of α-Ta was attributed to the nucleation of larger Ta clusters. After being annealed at 600 °C, the α-Ta/graded Ta(N)/TaN multilayer film can still effectively block the diffusion of Cu. The mechanisms of the forming of the α-Ta and the thermal stability of the film stacks are characterized in detail.