Dynamic Modification of Fermi Energy in Single-Layer Graphene by Photoinduced Electron Transfer from Carbon Dots.

Angelo Armano,Alice Sciortino,Fabrizio Messina,Marco Cannas,Emanuela Schilirò,Simonpietro Agnello,Franco Mario Gelardi,Gianpiero Buscarino,Filippo Giannazzo

doi:10.3390/nano10030528

Abstract

Graphene (Gr)—a single layer of two-dimensional sp2 carbon atoms—and Carbon Dots (CDs)—a novel class of carbon nanoparticles—are two outstanding nanomaterials, renowned for their peculiar properties: Gr for its excellent charge-transport, and CDs for their impressive emission properties. Such features, coupled with a strong sensitivity to the environment, originate the interest in bringing together these two nanomaterials in order to combine their complementary properties. In this work, the investigation of a solid-phase composite of CDs deposited on Gr is reported. The CD emission efficiency is reduced by the contact of Gr. At the same time, the Raman analysis of Gr demonstrates the increase of Fermi energy when it is in contact with CDs under certain conditions. The interaction between CDs and Gr is modeled in terms of an electron-transfer from photoexcited CDs to Gr, wherein an electron is first transferred from the carbon core to the surface states of CDs, and from there to Gr. There, the accumulated electrons determine a dynamical n-doping effect modulated by photoexcitation. The CD–graphene interaction unveiled herein is a step forward in the understanding of the mutual influence between carbon-based nanomaterials, with potential prospects in light conversion applications.

Highlights

Nanomaterials have rapidly attracted the interest of frontiers research in material science [1]
We proposed a similar process in order to describe the interaction between Carbon Dots (CDs) and Gr supported on SiO2 in a solid composite, wherein the CD emission efficiency was affected by the surface of deposition [30], noting the lack of structural modification of Gr decorated with CDs [31] and the stability of CDs to soft thermal treatment [30]
As discussed in previous works by Sciortino et al, optical absorption of CDs is characterized by two main contributions: an edge below 300 nm due to band-to-band transition of the crystalline core; and a composite band between 300 and 500 nm related to transition towards midgap levels belonging to surface states

Summary

Introduction

Nanomaterials have rapidly attracted the interest of frontiers research in material science [1]. The large surface area of Gr and the presence of delocalized electrons result in a strong interaction between Gr and surrounding species which allows charge–exchange related processes, such as doping processes involving molecular adsorption [18,19] and charge transfer to/from other nanosystems [13,20,21,22,23] In regard to these Gr composites, most of literature works concern the interaction of graphene with metal nanoparticles [24,25,26,27], transition metal oxides [28,29] or transition metal calchogenide quantum dots [12], and graphene oxide—mainly investigated in liquid phase. Despite that such composite nanomaterials are of cross-disciplinary interest for application in photocatalysis, molecular detection, and microelectronics, most of them are hindered by severe practical limitations, such as lack in visible emission, toxicity of materials, and inapplicability in solid-state microelectronics

Methods

Results

Conclusion