The effect of 1 MeV electron irradiation on charge carrier localization in graphene quantum dot array of reduced graphene oxide

Abstract

This paper presents a study of the effect of 1 MeV electron irradiation on the localization of charge carriers in graphene quantum dots (GQDs) located in a reduced graphene oxide (RGO). The electrical properties were analyzed in a wide temperature range of 4.2–340 K for fluences of 0–160 × 1015 cm−2. The localization length, dielectric permittivity, and density of localized states were estimated. It was found that the conductivity and charge localization parameters exhibit non-monotonic behavior depending on the electron fluences. It can change several times in the vicinity of a fluence of 10 × 1015 cm−2 compared to the higher or lower fluence. It is shown that electron irradiation affects the disordered surrounding matrix, which leads to an increase in the content of oxygen and functional groups. At the same time, the size of the sp2‑carbon domains does not depend on the fluence. It is assumed that electron irradiation indirectly affects the properties of GQDs. The transformation of the surrounding disordered matrix leads to a modification of the electronic properties of the GQDs array and the RGO as a whole. The non-monotonic behavior of the RGO conductivity upon irradiation is due to the features of the energy spectrum of the GQDs array, which is characterized by the presence of periodic peaks in the density of states. The irradiation-induced structural modification likely leads to a shift in the Fermi level and a change in the density of states. It is shown that the RGO behaves like a wide-band doped semiconductor. The difference is that the impurity level was formed by GQDs. At temperatures above 310 K, the RGO conductivity exhibits an Arrhenius behavior with an activation energy of about 60 meV due to charge carrier delocalization at thermal ejection into the extended band.