Hydrogen-induced metallization of zinc oxide (2 1̄ 1̄ 0) surface and nanowires: The effect of curvature

We have comparatively studied the hydrogen (H)-induced metallization mechanism and characteristics for zinc oxide (ZnO) nanowires with (2 1̄ 1̄ 0) side surface and the ZnO surface with the same index by density functional theory calculations. It is found that the ZnO surfaces and nanowires with only surface oxygen (O) atoms saturated by H (denoted as ZnO-H) become metallic, while the pristine and heterolytically chemisorbed systems are semiconducting. For the ZnO-H (2 1̄ 1̄ 0) surface, the 4s states of surface Zn atoms contribute to the sawtoothlike conducting pathways along the [0001] direction, rendering the surface metallic. By contrast, in the ZnO-H (2 1̄ 1̄ 0) nanowire, apart from the 4s states of side surface Zn atoms, both the Zn-4s and O-2p states of the corner atoms also significantly contribute to H-induced metallization due to the curvature effect. In this case, the linear and sawtoothlike conducting pathways exist in the corner and the sides, respectively. With the semiconductor-to-metal transition dependent on hydrogen concentration, ZnO (2 1̄ 1̄ 0) nanowire is proposed to be a good candidate for nanoscale chemical sensors or electronic devices for miniaturization.