Laser ablation synthesis of indium oxide quantum dots and a kinetic study of the oxide to nitride conversion

Indium oxide (IO) nanoparticles were synthesized by reactive laser ablation technique with the objective of demonstrating the formation of nanoparticles of transparent conducting oxides. The microstructure and phase chemistry of the products were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM), and the optical properties were characterized by photoluminescence (PL) and absorption spectroscopy. XRD data confirmed the presence of indium oxide, and TEM results showed an average particle size of 6.6 nm. The optical data showed weak confinement effects. The peak of the laser ablated sample was blue shifted from the bulk by 110 meV.; IO nanoparticles thus formed were nitrided inside xerogel cavities with the goal of forming composites of InN nanoparticles embedded in a silicate matrix. In order to study the kinetics of the nitridation process, indium oxide commercial powder was reacted in flowing ammonia at various temperatures and time. The kinetics was determined quantitatively by X-ray diffraction analysis of the product. The conversion of indium oxide to indium nitride increased with the reaction temperature and time following a stretched exponential curve. The reaction rate constant at a given temperature was determined using the Avrami equation. The activation energy for the reaction was calculated to be 164.5 KJ/mol in the temperature range of 580°–650°C. The Avrami constant varied between 1.56 and 2.8 for the same temperature range. These values suggest that the reaction is diffusion controlled with increasing nucleation rate for 580°C and decreasing nucleation rate for other temperatures. After determining the optimum conditions, IO nanoparticles formed from laser ablation were nitrided inside xerogel cavities. The resulting product was characterized using XRD and photoluminescence spectroscopy. The XRD data confirmed the presence of InN and the PL spectroscopy showed emission peaks matching the bulk value of InN (1.9eV).