Electron transport properties in CoAlO composite antidot arrays

Abstract

A complex disordered system composed of composite material and mesoscopic pore arrays was developed by depositing CoAlO composite thin films on the multiporous anodic aluminum oxide (AAO) membranes. In the disordered antidot arrays, self-connectivity of the metallic phase was dependent on the local conduction geometries. This led to locally variable thresholds for electron percolation. Metallic and semiconductor-like conduction behaviors were simultaneously found in the antidot arrays at thickness less than 15 nm, while the reference continuous films only showed metallic behavior. The observed non-monotonous resistance-temperature relations were explained by configuring a tetragonally oriented random resistor network related to the constrained conduction geometries, where electron conductions controlled by both percolation and tunneling coexisted. The tunneling effect was more evidently manifested in an antidot array with increased structural disorders. In this case the temperature dependence of resistance well followed the typical power law mode, exp [const/Tα] with α = 1/2. It was consistent with the characteristic of highly disordered metallic granular systems, where Coulomb charging energy as well as the aluminum oxide barrier would play a key role for electron tunneling between nanometer-sized granules. Our experimental results indicated that electron conductions in a composite antidot array were closely related to its constrained mesoscopic geometries.