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The dielectric constant of TCNQ single crystals as deduced by reflection electron energy loss spectroscopy

Published online by Cambridge University Press:  03 March 2011

G. Mondio
Affiliation:
Istituto di Struttura della Materia dell'Universitá di Messina and Centro Siciliano per le Ricerche Atmosferiche e di Fisica dell'Ambiente, Salita Sperone 31, 98166 S. Agata, Messina, Italy
F. Neri
Affiliation:
Istituto di Struttura della Materia dell'Universitá di Messina, Salita Sperone 31, 98166 S. Agata, Messina, Italy
G. Curró
Affiliation:
Istituto di Struttura della Materia dell'Universitá di Messina, Salita Sperone 31, 98166 S. Agata, Messina, Italy
S. Patané
Affiliation:
Istituto di Struttura della Materia dell'Universitá di Messina, Salita Sperone 31, 98166 S. Agata, Messina, Italy
G. Compagnini
Affiliation:
Dipartimento di Fisica dell'Universitá di Catania, Corso Italia 57, 95129 Catania, Italy
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Abstract

The dielectric constant of tetracyanoquinodimethane (TCNQ) single crystals has been obtained by reflection electron energy loss spectroscopy (REELS) over the 0–60 eV energy range, using primary electron energies ranging from 0.5 to 1.5 keV at an incidence angle of about 40°. A self-consistent method is discussed concerning the evaluation of the surface and bulk contributions to the loss spectra. As a result, for the first time, the Im(−1/∊) function and the dielectric constant of TCNQ have been deduced in such a wide energy range. According to the results obtained by other authors, the low-energy loss spectral profile is characterized by two main structures ascribed to the π → π dipole-allowed transitions located at about 3.5 and 6.5 eV while, at higher energy loss, the π + σ plasmon, centered at about 21.5 eV, dominates the spectrum. The differences among the spectra taken at different primary energies are interpreted as due only to surface effects, more evident in the low-energy-loss spectral region. The results are in good agreement with those obtained by recent transmission-mode (TEELS) experiments.

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Articles
Copyright
Copyright © Materials Research Society 1993

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References

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