Electronic structure of fluorinated multiwalled carbon nanotubes studied using x ray absorption and photoelectron spectroscopy

This paper presents the results of combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes (MWCNTs) with different fluorine contents (10-55 wt %) and reference compounds (highly oriented pyrolytic graphite crystals and "white" graphite fluoride) using x-ray absorption and photoelectron spectroscopy at C 1s and F 1s thresholds. Measurements were performed at BESSY II (Berlin, Germany) and MAX-laboratory (Lund, Sweden). The analysis of the soft x-ray absorption and photoelectron spectra points to the formation of covalent chemical bonding between fluorine and carbon atoms in the fluorinated nanotubes. It was established that within the probing depth (similar to 15 nm) of carbon nanotubes, the process of fluorination runs uniformly and does not depend on the fluorine concentration. In this case, fluorine atoms interact with MWCNTs through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton (phase 1) and this bonding is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp(2)) to tetrahedral (sp(3)) hybridization and by a large electron transfer between carbon an fluorine atoms. In the MWCNT near-surface region the second fluorine-carbon phase with weak electron transfer is formed; it is located mainly within two or three upper graphene monolayers, and its contribution becomes much poorer as the probing depth of fluorinated multiwalled carbon nanotubes (F-MWCNTs) increases. The defluorination process of F-MWCNTs on thermal annealing has been investigated. The conclusion has been made that F-MWCNT defluorination without destruction of graphene layers is possible

Features of metal atom 2p excitations and electronic structure of 3d metal phthalocyanines studied by X ray absorption and resonant photoemission

The metal atom 2p core excitations in 3d metal phthalocyanines MPc s, M Ni, Co, Fe have been studied via a combination of near edge X ray absorption fine structure NEXAFS and resonant photoemission ResPE spectroscopy. On the basis of comparison of the corresponding spectra of NiPc, CoPc and FePc it has been shown that the presence of a partly filled molecular orbital MO dramatically affects the formation and decay processes of the M 2p core excitation in CoPc and, to a greater extend, in FePc due to the significant 3d 3d exchange interaction. It has been found that the low lying unoccupied electronic states of NiPc, CoPc and FePc are strongly localized within the MN4 quasi molecule and have nearly pure 3d character. Moreover, mainly 3d metallic character of the high lying occupied MOs of NiPc, CoPc and FePc has been prove

Electronic properties of potassium doped FePc

The evolution of electronic structure of the organic semiconductor iron-phthalocyanine with potassium doping has been studied by means of photoemission spectroscopy, near-edge X-ray absorption fine structure and density functional theory (DFT) calculations. The DFT study and detailed analysis of the core-level spectra permit us to suggest possible lattice sites for the potassium ions. The data disclosed filling of the lowest unoccupied molecular orbital upon doping and associated changes of the core level absorption spectra. None of the films prepared in our studies showed a finite electronic density of states at the Fermi level. (C) 2010 Elsevier B.V. All rights reserved

Electronic Structure of Genomic DNA A Photoemission and X ray Absorption Study

The electronic structure of genomic DNA has been comprehensively characterized by synchrotron-based X-ray absorption and X-ray photoelectron spectroscopy. Both unoccupied and occupied states close to the Fermi level have been unveiled and attributed to particular sites within the DNA structure. A semiconductor-like electronic structure with a band gap of approximately 2.6 eV has been found at which the pi and pi* orbitals of the nucleobase stack make major contributions to the highest occupied and lowest unoccupied molecular orbitals, respectively, in agreement with previous theoretical predictions