Evidence for solid-state effects in the electronic structure of C60 films: a resonance-Raman study

Sinha, K.; Menéndez, José; Hanson, R. C.; Adams, G. B.; Page, J. B.; Sankey, Otto F.; Lamb, Lowell D.; Huffman, Donald R.

doi:10.1016/s0009-2614(91)85143-k

Cited by 40 publications

(11 citation statements)

References 15 publications

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“…Several strong transitions were identified in a range between 0.2 eV and 0.7 eV above the absorption threshold, which was found at 1.46 eV. When the experimental value of 1.72 eV [147,148] is used, these strongest "forbidden" transitions are predicted to occur between 1.9 eV and 2.4 eV, overlapping the energy range within which the Raman resonance was observed by Sinha et al [136] and Guha et al [138] An alternative explanation for the visible Raman resonance was proposed by Matus et al [137]. These investigators suggested an interpretation based on the "A-term" in Albrecht's molecular theory of resonance Raman scattering [149], with the resonant optical transition occurring between bands derived from the h u and t 1g molecular orbitals.…”

Section: Resonance Raman Scatteringmentioning

confidence: 55%

“…These transitions are optically forbidden in the icosahedral molecule, but it was argued that they should become allowed in the solid state. The mechanism proposed by Sinha et al [136] was supported by the fact that no resonance enhancement was observed in solutions of C 60 in CS 2 . Theoretical calculations of the dielectric function of C 60 crystals confirmed that "forbidden" HOMO → LUMO transitions make a significant contribution to the optical absorption at low energies [146].…”

Section: Resonance Raman Scatteringmentioning

confidence: 83%

“…Sinha et al [136] carried out resonance Raman experiments in C 60 films using laser lines in the visible. At room temperature, they found a maximum at 2.4 eV in the Raman excitation profile for the A g (2) mode.…”

Section: Resonance Raman Scatteringmentioning

confidence: 99%

“…Two explanations have been offered for the resonance in the excitation profile of the A g (2) mode in C 60 . Sinha et al [136] argued that the energy of the resonance was too low to be assigned to optically allowed transitions. Detailed studies of C 60 in solution show that the first allowed transitions correspond to a broad structure with a maximum at 3.7 eV.…”

Section: Resonance Raman Scatteringmentioning

confidence: 99%

“…According to theoretical calculations [145], the first allowed transitions involve excited states derived from the h u (HOMO) and t 1g (LUMO+1) molecular orbitals. Thus Sinha et al [136] assigned the observed Raman resonance at 2.4 eV to transitions between crystalline electronic bands derived from the h u (HOMO) and t 1u (LUMO) molecular orbitals. These transitions are optically forbidden in the icosahedral molecule, but it was argued that they should become allowed in the solid state.…”

Section: Resonance Raman Scatteringmentioning

confidence: 99%

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Vibrational spectroscopy of C60

Menéndez¹,

Page²

Topics in Applied Physics

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The fullerene era was started in 1985 with the discovery of the stable C 60 cluster and its interpretation as a cage structure with the familiar shape of a soccer ball [1]. An explosive growth in fullerene research was triggered in 1990 by the development of a method to produce fullerenes in bulk quantities [2]. Subsequently, the structural, electronic, and vibrational properties of many fullerenes have been studied in detail. The importance and potential of this new class of materials is exemplified by the discovery of intermediatetemperature superconductivity in doped C 60 [3]. Carbon nanotubes, a novel form of carbon which combines the properties of graphite and fullerenes, were discovered in 1991 [4]. Because of their intriguing properties and potential for applications, nanotubes are currently the subject of very intense research. Polymerization of C 60 molecules, particularly by photoexcitation [5] but by several other techniques as well, also results in a variety of interesting new structures, which contain both 4-coordinated and 3-coordinated carbon atoms [6]. The burgeoning field of fullerene research has been reviewed by several authors [7][8][9][10][11][12], most notably by Dresselhaus et al. [11] in an extensive monograph that appeared in 1996.In spite of the rapidly increasing interest in new forms of fullerenes, icosahedral C 60 , the "most beautiful molecule" [13], remains the focus of vigorous research as the prototype fullerene system. The present chapter concerns the vibrational structure of C 60 and the efforts to unravel its details using spectroscopic techniques. This remains a work in progress, but we hope to show that a look at the existing body of experimental and theoretical research from the broader perspective of an extended article provides a deeper understanding of the vibrational properties of C 60 .

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Section: Resonance Raman Scatteringmentioning

confidence: 55%

Section: Resonance Raman Scatteringmentioning

confidence: 83%

Section: Resonance Raman Scatteringmentioning

confidence: 99%

Section: Resonance Raman Scatteringmentioning

confidence: 99%

Section: Resonance Raman Scatteringmentioning

confidence: 99%

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Vibrational spectroscopy of C60

Menéndez¹,

Page²

Topics in Applied Physics

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Optical Excitations near the Fundamental Gap of Solid C₆₀

Feldmann

Fischer

Göbel

et al. 1992

Physica Status Solidi (b)

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Optical studies of solid C,@ employing time-integrated as well as time-resolved photoluminescence spectroscopy are reported. At low excitation intensity, a richly structured luminescence spectrum is observed. Increasing the excitation intensity leads to pronounced carrier accumulation and to the emission of intense and spectrally broad luminescence. It is concluded that multiple-step absorption processes lead to carrier recombination originating from higher conduction or lower valence band states. and electrically [8] excited, spectrally broad ('white') luminescence have been reported. These optical features of C,, may find important applications, e.g., for second-harmonic light generation, for optical-limiting purposes, and for the realization of white-light emitting electroluminescence diodes.In order to understand the optical properties of the c 6 0 molecule, the character of the chemical bonds between the C atoms has to be considered. The valence electrons of the C atoms undergo a sp2 hybridization, i.e., three electrons of each C atom contribute to the o-bonds, which stabilize the mechanical framework of the soccerball molecule. The remaining p-electron per C atom participates in the formation of n-bonds with orbitals perpendicular to the spherical surface. These delocalized n-states determine the electronic as well as the optical properties of the C 6 , molecule [9, 101. The quantized energy states for the n-electrons are mainly determined by their angular momentum 011 the C,, molecule surface. The energy difference EMo between the highest occupied molecular orbital (HOMO) 11, and the lowest unoccupied molecular orbital (LUMO) t , , amounts to about 1.9eV. However, the corresponding optical transition is dipole forbidden due to the fact that the initial and final wave functions have the same 'ungerade' parity.Solid C,, is normally prepared as a polycrystalline powder, but also large single crystals can be grown [ 111. The C60 molecules occupy the sites of an f.c.c. lattice with a lattice constant of about 14.2 nm. The cohesive energy of the crystal is due to van der Waals interactions between the n-electron systems of the individual c 6 0 units. This intermolecular interaction changes the sharp molecular energy levels of the n-electrons into bands with widths of about 0.5 eV [9, 101. As a consequence, the band gap E, between the 'h,' valence band and the 't,,' conduction band is red-shifted in comparison to the lowest optical transition

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