Polymorph-Tuned Synthesis of alpha- and beta-Bi2O3 Nanowires and Determination of Their Growth Direction from Polarized Raman Single Nanowire Microscopy

We report polymorph-tuned synthesis of alpha- and beta-Bi2O3 nanowires and their single nanowire micro-Raman study. The single crystalline Bi2O3 nanowires in different phases (alpha and beta) were selectively synthesized by adjusting the heating temperature of Bi precursor in a vapor transport process. No catalyst was employed. Furthermore, at an identical precursor evaporation temperature, alpha- and beta- phase Bi2O3 nanowires were simultaneously synthesized along the temperature gradient at a substrate. The growth direction of alpha-Bi2O3 nanowires was revealed by polarized Raman single nanowire spectra. For thin beta-Bi2O3 nanowires with a very small diameter, the polarized Raman single nanowire spectrum was strongly influenced by the shape effect.