X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge

Carla Bittencourt,Xiaoxing Ke,Chris P Ewels,Gustaaf Van Tendeloo,Peter Guttmann,Adam P Hitchock

doi:10.3762/bjnano.3.39

Abstract

We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV.

Highlights

The demonstration of the remarkable transport properties of graphene in 2004 by Geim and Novoselov triggered intense interest in its electronic structure [1,2,3,4,5,6,7,8,9,10,11]
We use near-edge X-ray-absorption fine-structure technique (NEXAFS) spectromicroscopy, performed with the Helmholtz Zentrum Berlin (HZB) full-field transmission X-ray microscope (TXM) installed at the electron storage ring BESSY II [19], to image and to study the electronic structure of a freestanding thin graphite flake produced by means of densitygradient ultracentrifugation (DGU) [20]
We examined several different flakes to ensure that we had selected a typical specimen; electron microscopy images are given in Supporting Information File 1

Summary

Introduction

The demonstration of the remarkable transport properties of graphene in 2004 by Geim and Novoselov triggered intense interest in its electronic structure [1,2,3,4,5,6,7,8,9,10,11]. We use NEXAFS spectromicroscopy, performed with the Helmholtz Zentrum Berlin (HZB) full-field transmission X-ray microscope (TXM) installed at the electron storage ring BESSY II [19], to image and to study the electronic structure of a freestanding thin graphite flake produced by means of densitygradient ultracentrifugation (DGU) [20].

Results

Conclusion