Indium nitride from indium iodide at low temperatures: synthesis and their optical properties

In this paper, we present an effective synthetic protocol to produce high quality InN nanocrystals using indium iodide (InI3), one member of the family of indium halides, as the indium source at a low temperature of <250 degrees C (far below the decomposition temperature of InN). Notably, reports on InN synthesized from indium halides are rare due to the lack of well-defined synthetic protocols. Here, indium iodide (InI3), with a stronger covalent ability, can also prevent the In3+ from being reduced to elemental indium, and then InN is formed. This synthetic protocol not only provides an alternative method to successfully synthesize high-quality InN, but is also useful to fabricate other functional materials by using stronger covalent reactants to prevent reduction/oxidation in the oxidation/reduction reaction process, respectively. Furthermore, we also report the first example of an orientation-attachment process occurring between the metal nitride particles. The high purity of the InN nanoparticles can be seen from the XPS and HRTEM results, showing the as-obtained products possess no obvious iodine or amorphous layers on the surface of particles, respectively. By controlling the parameters of reaction temperature and time, nanoparticles with different sizes were obtained as the final products. Raman and IR results indicate that our experimental data were consistent with the theoretical prediction and this gives further evidence that high quality InN nanocrystals were obtained. Moreover, it has been shown that the near-infrared band around 0.7 eV is characteristic of these samples and there were no obvious peaks around 1.9 eV, indicating that these InN nanocrystals exhibit a band gap of 0.7 eV, rather than the previously accepted 1.9 eV.