Insulator to Semiconductor Transition in Graphene Quantum Dots

TL;DR

This study investigates the insulator to semiconductor transition in graphene quantum dots (GQDs) near 400K, revealing their temperature-dependent electrical properties and dielectric relaxation mechanisms through comprehensive analysis.

Contribution

First observation of insulator to semiconductor transition in GQDs near 400K with detailed dielectric and conductivity analysis.

Findings

Insulator to semiconductor transition occurs near 400K.

GQDs exhibit optical absorption in the visible region.

Dielectric relaxation follows Cole-Cole model.

Abstract

Zero dimensional graphene quantum dots (GQDs) exhibit interesting physical and chemical properties due to the edge effect and quantum confinement. As the number of carbon atoms in edge is more than on basal plane, GQDs are more reactive. Room temperature XRD pattern confirms the formation of the GQDs. UV-Visible spectra confirm that GQDs show optical absorption in the visible region. The emission peaks in the photoluminescence spectra are red shifted with the increase of excitation wavelength. Dynamic light scattering (DLS) analysis shows that the average size of the particles is found to be 65 nm. The frequency dependent electrical transport properties of the GQDs are investigated in a temperature range from 300 to 500 K. Most interestingly, for the first time, the insulator to semiconductor transition of GQD is observed near 400K. The transition mechanism of GQD is discussed with detailed dielectric analysis. The effects of intercalated water on temperature dependent conductivity are clearly discussed. The dielectric relaxation mechanism is explained in the framework of permittivity, conductivity and impedance formalisms. The frequency dependent ac conductivity spectra follows the Jonscher s universal power law. Cole-Cole model is used to investigate the dielectric relaxation mechanism in the sample.