Unusual Oxygen Partial Pressure Dependence of Electrical Transport of Single-Crystalline Metal Oxide Nanowires Grown by the Vapor-Liquid-Solid Process.

In general, the electrical conductivities of n-type semiconducting metal oxide nanostructures increase with the decrease in the oxygen partial pressure during crystal growth owing to the increased number of crystal imperfections including oxygen vacancies. In this paper, we report an unusual oxygen partial pressure dependence of the electrical conductivity of single-crystalline SnO2 nanowires grown by a vapor-liquid-solid (VLS) process. The electrical conductivity of a single SnO2 nanowire, measured using the four-probe method, substantially decreases by 2 orders of magnitude when the oxygen partial pressure for the crystal growth is reduced from 10-3 to 10-4 Pa. This contradicts the conventional trend of n-type SnO2 semiconductors. Spatially resolved single-nanowire electrical transport measurements, microstructure analysis, plane-view electron energy-loss spectroscopy, and molecular dynamics simulations reveal that the observed unusual oxygen partial pressure dependence of the electrical transport is attributed to the intrinsic differences between the two crystal growth interfaces (LS and VS interfaces) in the critical nucleation of the crystal growth and impurity incorporation probability as a function of the oxygen partial pressure. The impurity incorporation probability at the LS interface is always lower than that at the VS interface, even under reduced oxygen partial pressures.