Evidence of dynamic Jahn-Teller distortions in two-dimensional crystalline molecular films

Abstract

Borca, C.N.; Adenwalla, Shireen; Bune, A.V.; Ducharme, Stephen; Fridkin, V.M.; Palto, S.P.; and Petukhova, N., "Evidence of dynamic Jahn-Teller distortions in two-dimensional crystalline molecular films" (1999 The surface electronic structure in crystalline copolymer films of vinylidene fluoride ͑70%͒ with trifluoroethylene ͑30%͒ has been studied by photoemission and inverse photoemission as a function of alkali metal ͑sodium͒ doping. Sodium doping introduces at least two new states into the band ͑HOMO-LUMO͒ gap well away from the Fermi level. While the sodium-doped copolymer is observed to resemble an n-type semiconductor, the change in electronic structure with temperature suggests that dynamic distortions lead to a photoemission initial state splitting of the lower Hubbard-like bands. There is a decrease in the effective Debye temperature with sodium doping which may, in turn, enhance the dynamic Jahn-Teller distortion.

Different approaches to adjusting band offsets at intermolecular interfaces

“…Both the occupied and unoccupied molecular orbitals of the freshly evaporated polyaniline thin films shift to greater or smaller binding energies (with respect to the Fermi level) when doped with sodium or iodine, respectively [21]. This is very different from sodiumdoped poly(p-pyridine) [41] and other polymeric systems [1,4], where sodium-doping induces new states in the otherwise empty band gap.…”

“…These new bands can appear well away from the Fermi level (both above and below the Fermi level) as a result of the on site correlation energies. These Hubbard bands have been observed with the alkali metal doping of a number of molecular systems with a large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) [1,3,4]. If the molecular orbitals are sufficiently delocalized, organic conductors provide an avenue for the direct investigation of systematic shifts of the valence and conduction band states as a result of charge transfer.…”

The coadsorption and interaction of molecular icosahedra with mercury

“…The evidence for metallic mercury, from the Hg 5d 5/2 core level widths does not suggest that mercury atoms may form a lattice which weakly interacts with orthocarborane lattice, or Hg may form a wetting surfactant layer and a layer between the Cu substrate and orthocarborane molecular fi lm which would easily explain a uniform shift in the molecular orbital photoemission binding energies. In this regard, Hg is very different from the more homo geneous mixtures formed with some metals and molecularly chemisorbed species [14][15][16][38][39][40][41][42][43][44][45][46][47][48][49].…”

Aluminum doping of poly(vinylidene fluoride with trifluoroethylene) copolymer

“…Conduction band spectroscopy 9,17,18 provides strong evidence that the density of states near E F , in the surface region, is greater than in the bulk near room temperature. We can reasonably anticipate that screening of a core photohole at the surface would be better at the surface than in the bulk.…”

“…1,[5][6][7] The appearance of states in the region near the chemical potential, between the highest occupied state and lowest unoccupied state ͑the HOMO-LUMO gap͒, has been reported for alkali doping of poly͑para-phenylenevinylene͒, 6 ␣, -diphyltetrahecaheptaene, 1,7 poly͑pyridine-2,5-diyl͒, 8 poly͑2,2Ј-bipyridine-5,5Ј -diyl͒, 8 and the copolymer vinylidene fluoride ͑70%͒ with trifluoroethylene ͑30%͒. 9 These alkali-induced states have been variously ascribed to the formation of lower Hubbard bands, 9 bipolaron states, 6,8 and a soliton-antisoliton pair, 1,7 and the alkali metals generally act and are perceived as doping agents, inducing new states in the otherwise forbidden band gap.…”