Combined synthesis and in situ coating of nanoparticles in the gas phase

Ga₂O₃ was-synthesized by doping a premixed H₂/O₂/Ar flat flame with diluted trimethyl gallium Ga(CH₃)₃ in a low-pressure reactor. The mean particle diameter d _p of the resulting metal oxide was characterized in-situ with a particle mass spectrometer (PMS), and was observed to range between 2.5 nm ≤ d _p ≤ 6.5 nm. XRD results show that the as-synthesized Ga₂O₃ nanoparticles are mostly amorphous, although, a few broad reflexes were observed that indicate the presence of some degree of crystallinity. Thermal annealing of the as-synthesized material at 1000 °C for 5 min yielded β-Ga₂O₃ with a monoclinic structure. UV–VIS measurements indicate strong absorption in the UV range (4.8 eV), which corresponds quite well to the direct band gap of bulk Ga₂O₃. Photoluminescence (PL) measurements of the as-synthesized metal oxide show a broad emission ranging from 350 nm to 600 nm with a maximum at 460 nm. Crystalline β-Ga₂O₃ exhibited stronger luminescence than as-synthesized particles.