Abstract
Tetragonal rutile TiO 2 /Ti 1-x Sn x O 2 heterojunction nanowires were successfully fabricated through carbothermal reaction with hydrogen gas at 1050 °C. These heterojunction nanowires partially formed Ti 1-x Sn x O 2 superlattice structures and SnO 2 nanocrystals epitaxially grew on the TiO 2 nanowire surfaces. Based on the evaluations of Gibbs free energy, all reaction processes were governed by spontaneous reactions with vapor-solid-liquid (VLS). The nanowires exhibited many defect states, such as dislocations, stacking faults, and vacancies, revealed by high-resolution transmission microscopy (HRTEM) and the cathodoluminescence spectrum. The Raman spectrum revealed obvious redshift and asymmetric broadening effects, especially in the position of A 1g (604 cm -1 ) and E g (427 cm -1 ) modes when compared with a previous study (J. M. Wu et al., J. Cryst. Growth, 2005, 281, 384.). The size-induced phonon confinement effect and the presence of dislocations with internal strain in the vicinity of the nanowire surfaces led to a downshift and broadening of the first order Raman line. The results are consistent with our observations from the HRTEM images. Operating temperatures of ∼160 °C with a gas sensitivity of ∼350% were achieved when detecting an ethanol concentration of ∼300 ppm. The material characterizations and formation mechanism are investigated in detail. © 2011 The Royal Society of Chemistry.