157 research outputs found
Electronic excitation spectrum of doped organic thin films investigated using electron energy-loss spectroscopy
The electronic excitation spectra of undoped, and potassium as well as
calcium doped phenantrene-type hydrocarbons have been investigated using
electron energy-loss spectroscopy (EELS) in transmission. In the undoped
materials, the lowest energy excitations are excitons with a relatively high
binding energy. These excitons also are rather localized as revealed by their
vanishing dispersion. Upon doping, new low energy excitation features appear in
the former gaps of the materials under investigation. In Kpicene and
Kchrysene they are characterized by a negative dispersion while in
Capicene they are dispersionless
Single domain transport measurements of C60 films
Thin films of potassium doped C60, an organic semiconductor, have been grown
on silicon. The films were grown in ultra-high vacuum by thermal evaporation of
C60 onto oxide-terminated silicon as well as reconstructed Si(111). The
substrate termination had a drastic influence on the C60 growth mode which is
directly reflected in the electrical properties of the films. Measured on the
single domain length scale, these films revealed resistivities comparable to
bulk single crystals. In situ electrical transport properties were correlated
to the morphology of the film determined by scanning tunneling microscopy. The
observed excess conductivity above the superconducting transition can be
attributed to two-dimensional fluctuations.Comment: 4 pages, 4 figure
Spin Signatures of Photogenerated Radical Anions in Polymer-[70]Fullerene Bulk Heterojunctions: High Frequency Pulsed EPR Spectroscopy
Charged polarons in thin films of polymer-fullerene composites are
investigated by light-induced electron paramagnetic resonance (EPR) at 9.5 GHz
(X-band) and 130 GHz (D-band). The materials studied were
poly(3-hexylthiophene) (PHT), [6,6]-phenyl-C61-butyric acid methyl ester
(C60-PCBM), and two different soluble C70-derivates: C70-PCBM and
diphenylmethano[70]fullerene oligoether (C70-DPM-OE). The first experimental
identification of the negative polaron localized on the C70-cage in
polymer-fullerene bulk heterojunctions has been obtained. When recorded at
conventional X-band EPR, this signal is overlapping with the signal of the
positive polaron, which does not allow for its direct experimental
identification. Owing to the superior spectral resolution of the high frequency
D-band EPR, we were able to separate light-induced signals from P+ and P- in
PHT-C70 bulk heterojunctions. Comparing signals from C70-derivatives with
different side-chains, we have obtained experimental proof that the polaron is
localized on the cage of the C70 molecule
Strong 3p -T1u Hybridization in Ar@C60
Multilayers of fullerenes with and without endohedral Ar units, C60 and
Ar@C60, were investigated by photoemission and density functional theory. The
stoichiometry and the endohedral nature of Ar is checked by x-ray photoelectron
spectroscopy and x-ray photoelectron diffraction. Valence band ultraviolet
photoemission spectra show a strong hybridisation of the Ar 3p valence shell
with the 6T1u molecular orbital of C60. A hybridisation gap of 1.6 +/- 0.2 eV
is found. This is in agreement with density functional theory (DFT) that
predicts 1.47 eV, and indicates Ar@C60 to be a noble gas compound with a strong
coupling between Ar and the C60 cage. No giant Ar photoemission cross section
as predicted for the gas phase in [Phys. Rev. Lett. 99, 243003 (2007)] was
found
Electronic structure of small GaAs clusters
The electronic structure of small Ga_xAs_y clusters (x+y≤10) are calculated using the local density method. The calculation shows that even‐numbered clusters tend to be singlets, as opposed to odd‐numbered clusters which are open shell systems. This is in agreement with the experimental observations of even/odd alternations of the electron affinity and ionization potential. In the larger clusters, the atoms prefer an alternating bond arrangement; charge transfers are observed from Ga sites to As sites. This observation is also in agreement with recent chemisorption studies of ammonia on GaAs clusters. The close agreement between theoretical calculations and experimental results, together with the rich variation of electronic properties of GaAs clusters with composition makes GaAs clusters an ideal prototype system for the study of how electronic structure influences chemical reactivity
Experimental evidence for high-yield C74 production in an arc periphery plasma
科研費報告書収録論文(課題番号:09358008・基盤研究(A)(2)・H9~H11/研究代表者:畠山, 力三/フラーレンプラズマによる新機能性薄膜形成法の開発
Structure and properties of the stable two-dimensional conducting polymer Mg5C60
We present a study on the structural, spectroscopic, conducting,
and
magnetic properties of Mg5C60, which is a two-dimensional (2D)
fulleride polymer. The polymer phase is stable up to the
exceptionally
high temperature of 823 K. The infrared and Raman studies
suggest the
formation of single bonds between the fulleride ions and
possibly
Mg-C-60 covalent bonds. Mg5C60 is a metal at ambient
temperature, as
shown by electron spin resonance and microwave conductivity
measurements. The smooth transition from a metallic to a
paramagnetic
insulator state below 200 K is attributed to Anderson
localization
driven by structural disorder
Single-particle Excitation Spectra of C Molecules and Monolayers
In this paper we present calculations of single-particle excitation spectra
of neutral and three-electron-doped Hubbard C molecules and monolayers
from large-scale quantum Monte Carlo simulations and cluster perturbation
theory. By a comparison to experimental photoemission, inverse photoemission,
and angle-resolved photoemission data, we estimate the intermolecular hopping
integrals and the C molecular orientation angle, finding agreement with
recent X-ray photoelectron diffraction (XPD) experiments. Our results
demonstrate that a simple effective Hubbard model, with intermediate coupling,
, provides a reasonable basis for modeling the properties of C
compounds.Comment: 6 page
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