Valence electronic structure of cross-linked C60 polymers: In situ high-resolution photoelectron spectroscopic and density-functional studies (original) (raw)
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Surface Science, 2002
The electronic valence band structures of polymerized thin films of C 60 and La 0:1 C 60 have been studied by using ultra-violet photoelectron spectroscopy. Additionally, the films have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The valence band of the C 60 film shows major peaks at binding energies of 2.6, 7.2, 10.3, and 12.6 eV. In the case of the doped film, we observe (i) an additional peak with a binding energy of 13.7 eV, (ii) evidence for redistribution of the density of electronic states due to hybridization between the 5d orbitals of La and the C 60 cage, and (iii) significantly higher density of the electronic states near the Fermi energy. The valence band spectra of the doped film are in good agreement with recent results of the density functional theory that support strong hybridization between the d-valence orbitals of La and the C 60 cage.
The electron transport properties of photo- and electron-beam-irradiated C 60 films
Journal of Physics and Chemistry of Solids, 2004
The electron transport properties of photo- and electron-beam-induced C60 polymers, in which the former is a dumbbell-type two-dimensional (2D) polymer and the latter is a new polyhedral structured (peanut-shaped) carbon nanomaterial, have been investigated. Using a four-probe measurement, we found that the 2D photopolymer and the peanut-shaped polymer exhibit semiconducting and metallic characters in air at room temperature, respectively. In order to elucidate the origin of these electron transport properties, we have performed density-functional calculations of the dumbbell-shaped and peanut-shaped C120 dimers that can be regarded as a basic unit of each polymer. It was found that the HOMO consisting of π-electrons orbital, which is related to the electron transport property, has a node on the [2+2] cyclo-bond for the dumbbell-shaped dimer, while that the HOMO has no node on the cross-linkage and spreads over the peanut-shaped dimer.
First-principles calculations of the electronic structure of one-dimensionalC60polymers
Physical Review B, 2005
The geometrical and electronic properties of two dimers ͑one with C 2h symmetry͒ from the Stone-Wales rearrangement sequence of C 60 dimers ͓described by E. Osawa and K. Honda, Full Sci. Technol. 4, 939 ͑1996͔͒ are investigated by density functional and tight-binding calculations. The trimer and the infinite periodic polymer derived from the C 2h symmetry dimer are shown to continue a decreasing trend of the energy gap between the highest occupied ͑HOMO͒ and the lowest unoccupied ͑LUMO͒ molecular orbitals to values smaller than 0.1 eV. The very small energy gap, in conjunction with the extension of the HOMO orbital over the whole cross-linkage region, provides an explanation for the observed conducting properties of electron beam irradiated C 60 films.
Stability and Electronic Properties of C60Chain Polymer: DFT Study
Journal of Natural Sciences Research, 2014
Interfullerene C 60 cages polymers have been investigated by density functional theory in general gradient approximation PBE calculations based on DZP basis set. The electronic spectra of these systems are carried out by using TDDFT (PBE/DZP) method. The heat of formation, electronic levels and electronic density of states are explored. The integrated polymer (polymer-A) has a high heat of formation and a very low band gap (like a semi-metallic), while the inter-bonded cyclo addition polymer (polymer-B) has moderate heat of formation and a semiconductor band gap. C 60 polymers have strong electron correlation, which increases the localization of electrons. The electron excitations have two peaks for polymer-A, one is strong and the other is weak. Polymer-B has a single band of absorption with higher energy than that of polymer-A.
Electronic properties of polymers including C60
Chemical Physics Letters, 1995
The electronic properties of the polymer models involving C6o molecules incorporated into either polymer skeleton or side chain are first examined based on the one-dimensional (1D) tight-binding crystal orbital method in the framework of the extended Hiickel approximation. The band structure characteristic of each polymer model is discussed particularly with respect to the interruption of the w-conjugation of the rest of the main chain. * Corresponding author. tronic properties of polymers including C6o based on the one-dimensional (1D) tight-binding calculation. The model polymers A-C considered are shown in Figs. 2a-c, where 2a and 2b are those including C60 in the main chain with a possible w-conjugation and 2c has a conjugated trans-polyacetylene (PA) as a main chain with C6oH molecules as pendant groups. .
Structural and electrical properties of an electron-beam-irradiated C60 film
Applied Physics Letters, 2003
The structural and electrical properties of an electron-beam (EB)-irradiated C60 film have been examined at room temperature, using in situ infrared (IR) spectroscopy and ex situ four-probe measurements. IR results show that the irradiated film is neither graphite nor carbon nanotube-like but a peanut-shaped C60 polymer. Current–voltage curve shows that the polymer exhibits a metallic property with a drastically reduced resistivity of 7 Ω cm in comparison with 108–1014 Ω cm for solid C60. This indicates the possibility of applying C60 molecules in EB nanofabrication processes and large potential for developing carbon-based nanodevices.
Metal-Insulator Transition in C60-Polymers
1995
Variations in the band structures of C 60 -polymers are studied, when π-conjugation conditions are changed. We look at band structures in order to discuss a metal-insulator transition, using a semi-empirical model with the Su-Schrieffer-Heeger type electron-phonon interactions. We find that electronic structures change among direct-gap insulators and the metal, depending on the degree of π-conjugations. High pressure experiments could observe such pressureinduced metal-insulator transitions.
IR Spectra of Photopolymerized C60 Films. Experimental and Density Functional Theory Study
The Journal of Physical Chemistry B, 2006
IR spectra of photopolymerized fullerene films obtained by simultaneous deposition and UV irradiation were measured in the range of 1500-450 cm-1. The degree of the polymerization of the C 60 films was estimated to be about 95%. To assist the assignment of the experimental IR spectra of the films, quantum chemical calculations of the equilibrium structures of the C 60 dimers and trimers were performed at the DFT(B3LYP)/ 3-21G level of theory. Next, IR frequencies and intensities for those structures were calculated. For the fivetrimer structures found in the calculations, the relative stabilities were determined at the B3LYP/4-31G* and B3LYP/6-31G* levels and used to select the lowest-energy trimers, which are Trimer A (angle between monomer centers is 90°) and Trimer B (angle between monomer centers is 120°). Next, the IR spectra of the polymerized fullerene films were compared with the calculated frequencies of the lowest-energy dimer and the two lowest-energy trimers. On the basis of this analysis and on the comparison of the film spectra with the IR spectra of the C 60 dimer and trimer spectra obtained by other methods, it was shown that the main components of the films are C 60 dimers and the orthorhombic (O) polymer phase. The tetragonal (T) and rhombohedral (R) polymers, as well as small amounts of monomers, were also found. Although vibrational frequencies of different C 60 phases are similar in most cases, we found several unique spectral features of the C 60 dimer and other polymers that may be used to determine the composition of the polymerized C 60 film.
Physica B: Condensed Matter, 2002
Compton profile measurements on K 1 C 60 and Rb 1 C 60 and C 60 powders have been carried out using inelastically scattered photons. We compare experimental Compton Profile Difference (CPD) of K 1 C 60 and that of C 60 with the corresponding calculated results, obtained from ab initio self-consistent field calculations of the energy band structure. This permits us to isolate the contribution of the distortion of the C 60 orbitals for each compound and to compare them. In previous paper, we have shown that for A n C 60 compounds this approach leads to a good agreement between theory and experiment. In this paper, we show that it is not the case for K 1 C 60 . The distortion contribution is overestimated by calculations leading to a CPD narrower than the experimental one. Furthermore similar measurements performed on heavy ions intercalated compounds (Rb 1 C 60 ) show clearly that CPD depends on the number of ions and not on their nature. We think that our results corroborate the conclusions of a very small distortion of C 60 molecules in the polymerized phase obtained by neutron diffraction experiments by Fox et al. (Chem. Phys. Lett. 249 (1996) 195). r