Valence band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

TL;DR

This study investigates how thermal annealing affects the valence band electronic structure of graphene oxide, revealing band gap closure and enhanced optoelectronic properties at specific annealing temperatures.

Contribution

It provides real-time spectroscopic insights into the electronic structure evolution of graphene oxide during thermal reduction, identifying optimal annealing conditions for optoelectronic applications.

Findings

Band gap closes after annealing at ~600°C.

Enhanced photocurrent observed at ~500°C.

Density of states increases near the Fermi level after annealing.

Abstract

We report valence band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. Degree of oxygen functionalization was controlled by annealing temperatures, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in density of states around the Fermi level upon thermal annealing at ~600 oC. The result indicates that while there is an apparent band gap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of band gap closure was correlated with electrical, chemical, and structural properties to determine a set of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of ~500 oC leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to as-synthesized counterpart.