Porosity control in pre-ceramic molecular precursor-derived GaN based materials

Ga2(NMe2)6 is transformed into highly porous GaN based materials via ammonolysis in solution and subsequent pyrolysis at 673 K in an ammonia stream. The addition of long chain aliphatic amines (n-C6H13NH2-n-C12H25NH2) in solution allows the condensation reaction to be directed and results in microporous GaN based materials (GaN1.21-1.31O0.0-0.04C0.03-0.09H0.83-01.57) with type I isotherms. Materials prepared without long chain amine show type II isotherms with a broad interparticle pore size distribution. Three different processing pathways and critical parameters such as precursor concentration, amine concentration, amine chain length, and processing temperature are evaluated. Heat treatments above 673 K lead to enhanced mass transfer, a decrease in the N/Ga ratio from 1.25 to 1.0, and crystallisation of hexagonal GaN. According to TEM and physisorption studies, materials prepared without amine additive are transformed into micron-sized GaN crystals at 1073 K, whereas nonylamine-templated materials afford nanocrystalline GaN (dav = 9 nm). 28 refs.