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

Abstract

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 (GaN_1.21–1.31O_0.0–0.04C_0.03–0.09H_0.83–01.57) 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 (d_av = 9 nm).