Laser-induced thermal effects in hexagonal MoO3 nanorods

Laser-induced thermal effects on the hexagonal MoO3 nanorods at different power density levels were studied using Raman spectroscopy and scanning electron microscopy techniques. The structural features of the nanorods were accompanied by varying the incident laser power from 8.0 to 600 mW by using a gradual increasing rate and a sudden increasing incident laser power. It was shown that the photoeffects observed on the MoO3 nanorods critically depends on the exposure rate. By gradually increasing the incident laser power up to 600 mW, morphology of the nanorods were completely preserved, and the observed thermal behavior was discussed on the basis of thermal contact at nanoscale. However, when the irradiation intensity was suddenly increased, it was observed that overheating of h-MoO3 nanorods at relatively lower laser powers (80 mW) sublimate the nanorods around the laser spot region. The MoO3 molecules on vapor-phase at high temperatures condense and crystallize next to the laser spot on the orthorhombic (alpha-MoO3) and monoclinic (beta-MoO3) phases. Furthermore, the nanorods closest to the laser spot region undergo a structural phase (and morphological) transition from h-MoO3 phase to alpha-MoO3 phase.