Insulator to semiconductor transition in graphene quantum dots

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.

Dielectric properties of nano‐MMT and graphene quantum dots embedded poly (vinylidene fluoride‐co‐hexafluoropropylene) nanocomposite films

“…A broad peak of pure PVDF‐HFP displayed at 2θ = 20.17° corresponds to the (020) crystal plane indicating the semi‐crystalline nature of the polymer (Figure 4b). The XRD peak in Figure 4c reveals the existence of GQDs at 2θ = 25.3° attributed to the (002) crystal plane 31,32 . The characteristic peaks of nano‐additives in PVDF‐HFP/MMT/GQDs nanocomposite films were also observed as depicted in Figure 5a–f.…”

“…30 A broad peak of pure PVDF-HFP displayed at 2θ = 20.17 corresponds to the (020) crystal plane indicating the semi-crystalline nature of the polymer (Figure 4b). The XRD peak in 31,32 The characteristic peaks of nano-additives in PVDF-HFP/MMT/GQDs nanocomposite films were also observed as depicted in Figure 5a-f. There are no significant differences in the intensities of the XRD peaks of the nanocomposite films.…”

“…Figure4creveals the existence of GQDs at 2θ = 25.3 attributed to the (002) crystal plane 31,32. The characteristic peaks of nano-additives in PVDF-HFP/MMT/GQDs…”

Graphene quantum dots: preparations, properties, functionalizations and applications

“…Figure 9(e) shows a plot of several electrical parameters against the number of GQD layers. Interestingly, GQDs can be converted from insulators to semiconductors at a certain critical temperature, as discovered by Sinha et al [247]. They recorded a large change in the electrical conductivity of the GQDs when the temperature was approximately 400 K, as shown in figure 9(h).…”

“…When energy is incident on the GQDs, electrons are confined within the GQDs, with their edges as boundaries. Reprinted from [247] with permission from AIP Publishing. (i) Schemes of GQDs/SWCNTs.…”