High-yield laser-synthesis of Si-based nanopowders

Amorphous Si3N4, Si/C/N and crystalline SiC nanopowders of 5–50 nm in mean diameter were synthesized via laser-induced gas-phase reactions with yields of 250 g h−1 using low cost hexamethyldisilazane (HMDS) and NH3 (or H2). Reaction flame temperatures, which were controlled by the total gas flow rate, greatly influenced powder composition and crystallinity. Amorphous Si3N4 powders (96 wt.%) were obtained at 1000 °C, with HMDS+NH3; β-SiC (93 wt.%) was formed at 1600 °C with HMDS+H2. Amorphous Si/N/C powders with various N/C ratios (0.1–6) were synthesized at various temperatures. The main impurities in the powders were the organo-ligands such as NHX and CHX (X=1–3), whose existence also resulted in a strong surface absorption of oxygen. Key techniques for commercial production of the abovementioned powders were also stated.