Probing Surface Band Bending of Surface-Engineered Metal Oxide Nanowires

We in situ probed the surface band bending (SBB) by ultraviolet photoelectron spectroscopy (UPS) in conjunction with field-effect transistor measurements on the incompletely depleted ZnO nanowires (NWs). The diameter range of the NWs is ca. 150-350 nm. Several surface treatments (i.e., heat treatments and Au nanoparticle (NP) decoration) were conducted to assess the impact of the oxygen adsorbates on the SBB. A 100 degrees C heat treatment leads to the decrease of the SBB to 0.74 +/- 0.15 eV with 29.9 +/- 3.0 nm width, which is attributed to the removal of most adsorbed oxygen molecules from the ZnO NW surfaces. The SBB of the oxygen-adsorbed ZnO NWs is measured to be 1.53 +/- 0.15 eV with 43.2 +/- 2.0 nm width. The attachment of Au NPs to the NW surface causes unusually high SBB (2.34 +/- 0.15 eV with the wide width of 53.3 +/- 1.6 nm) by creating open-circuit nano-Schottky junctions and catalytically enhancing the formation of the charge 02 adsorbates. These surface-related phenomena should be generic to all metal oxide nanostructures. Our study is greatly beneficial for the NW-based device design of sensor and optoelectronic applications via surface engineering.