Heat-induced ultrathin oxide layer blocks the current generation of Schottky nanogenerators

Abstract

Schottky nanogenerators (SNGs) are very simple power generation devices that can generate a direct current with a high current density of 104–107 Am−2 by sliding a metal-coated nanotip on semiconductor wafers. However, the current generation of SNGs has a rapid degradation if the sliding between metal and semiconductor is repeatedly performed over the same area. Although it is widely guessed that the oxidization during sliding on the semiconductor side induces the current attenuation, there is no reported in situ direct characterization of the ultrathin oxide layer (thickness <0.5 nm) in the SNGs as a demonstration of the aforementioned attenuation mechanism, and no reason for the oxidation is given. Here, we performed meticulous characterization and then illustrated that the current attenuation is mainly derived from the growth of an ultra-thin oxide layer in the semiconductor side contact region, which is mainly caused by friction heating and Joule heating. This understanding may guide the design and development of Schottky generators with a high current density as well as sufficient long life.