Electron spectroscopy of the main allotropes of carbon

Abstract

Recently, carbon spectroscopy became very important due to the growing interest in the applications of new carbon allotropes, especially of 2D structures such as graphene and nanotubes. It is well known that the hybridization of carbon electrons defines most of the properties of these materials. Among the analytical techniques used for the identification of carbon allotropes is the spectroscopy of carbon Auger line, which involves the transitions of valence band electrons and can be excited by electron beam (AES) or X‐ray photons (XAES). From the shape of C KVV spectrum, it is possible not only to recognize the cases of pure sp2 and sp3 configurations but also to quantify their ratio in amorphous carbon films. In present work, an experimental study of three main allotropes of carbon: graphite, diamond, and graphene is reported. The average thickness of graphene was evaluated from the ratio of C 1s and substrate photoelectron peaks, registered at grazing angle. Carbon KVV spectra were investigated by using XAES and AES techniques. Obtained results were compared with the ones acquired for reference samples of graphite and monocrystalline diamond. In addition, some samples of hydrogenated diamond were analyzed. It was demonstrated that the comparison of C KVV spectra excited by electrons and X‐rays can be used for identification of graphene. Diamond‐like C KVV spectrum, observed in XAES experiments, is a very promising fingerprint of graphene. Obtained results are also compared with valence band spectra of graphene, diamonds and graphite that were acquired by using ultraviolet photoemission spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

Investigation of graphene layers on electrodeposited polycrystalline metals

“…The values of D parameter for the same samples, determined by using electron source (AES), were identical to graphite: 21.5– 22.1 eV. The change of the D parameter from the diamond‐like (XAES) to graphitic (AES) value is a fingerprint of graphene . In fact, this effect can be explained considering that the XAES spectra are originating from a convolution of π and mixed π–σ holes in the valence band (VB) of carbon, which is strongly influenced by the screening in proximity of the Fermi level .…”

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

“…However, the validity of the methodology for the quantitative evaluation of the hybridization state of carbon on the basis of the C1s signal, which relies on fitting it with two distinct features for sp 2 -and sp 3 -bonded carbon 16,26,27 , has been refuted 17,18 , since the binding energy values of the C1s transition for graphite (100% sp 2 -bonded carbon), diamond (100% sp 3 -bonded carbon), and ultrananocrystalline diamond (94±1% sp 3 -bonded carbon 21 ) are not significantly different 17,18 . Instead, insights into the carbon hybridization state in the near-surface region of a-C materials can be gained by XPS through the analysis of the plasmon band near the C1s signal 18,24 , the π-π* shake-up satellites 42,43 , or the X-ray induced C KVV Auger spectrum 17,18,22,23,25,28 .…”

In situ fabrication of graphene oxide supported nano silica for the preparation of rubber composites with high mechanical strength and thermal conductivity

“…a. For GO, it shows strong D‐band and G‐band at 1354 cm −1 and 1593 cm −1 , respectively . For SiO 2 ‐GO nano hybrid, it shows a similar D‐band position as GO at 1354 cm −1 , while the position of G‐band for SiO 2 ‐GO shifts to higher wavenumber at 1600 cm −1 than that for GO.…”