MORPHOLOGY AND CRYSTALLOGRAPHY OF ALUMINUM NITRIDE WHISKERS

Highly pure and dense AlN whiskers were produced by carbothermal reaction of an alumina and a carbon source at 1800-degrees-C under flowing nitrogen. The whiskers grew via a VLS mechanism where there is a strong interaction between the liquid catalyst and the substrate/support, resulting in a complete lack of droplets at the whisker tips. The whiskers can be described as long and straight single crystals, free of planar defects, having a diameter of 2-30 mum and a length of 0.5-10 cm. They exhibited two different morphologies, planar and serrated. SADPs indicate that their lateral surfaces fall in a great circle of a stereographic projection, joining two pyramidal poles such as the (1101BAR)-(1011BAR). It is suggested that branching in these whiskers occurs by keeping active one of the pyramidal planes and activating a new one.