Interfacial Engineering on Electronic States and Gas Sensing Performances of Metal Oxide/Graphene Composites

Abstract

Heterojunctions of two-dimensional materials have been attracting considerable attention because of their outstanding tunable optical and electrical properties. Taking the composites of CeO2/graphene and SnO2/graphene as examples, the interfacial effects on the electronic states and gas sensing properties are studied. For the CeO2/graphene composites, the electron is transferred from graphene onto CeO2 {111} facets showing the Schottky contact, but from CeO2 {100} facets onto graphene resulting in Ohmic contact. Furthermore, since CeO2{100} surface is the polar surface, and NO2 is a polar molecule, the interactions between NO2 and CeO2 with {100} polar facets should be stronger thus promoting adsorption of NO2. The internal electric field near the polar surface promotes charge separation and accelerates charge exchange between NO2 and the composites. As a result, the CeO2 {100}/graphene composites deliver substantially enhanced gas sensing performance to NO2, as compared to CeO2 {111}/graphene composites. It was also found that oxygen vacancies (Ov) have significant influences on the gas sensing performance. According to the first-principle calculations, the tunable electronic states and enhanced gas sensing performances owing to interfacial effects can be well understood.