"Effect of Rotational Motion on the Conduction Properties of Molecular Semiconductors"

Mikhail Strzhemechny
Institute for Low Temperature Physics and Engineering
Ukrainian Academy of Science, Kharkov

Abstract: The topic of this talk concerns the strong effect of the orientational (rotational) state of the molecules that constitute fullerite (solid fullerene) C60 on the electron transport in this molecular semiconductor. This phenomenon is more pronounced in C60 films than in single crystals. The sign and magnitude of the effect depend on the morphology and purity of the film. Dark and photo current measurements as well as surface photo voltage spectra versus temperature-resolved XRD data are used to characterize the phenomenon. In particular, in highly crystalline films a large positive surge in the dark (or photo) current vs. temperature appears close to the orientational phase transition point against the negative-slope Ahrrenius relationship. In samples with high concentrations of defects and/or poisoned by air oxygen the effect is strongly suppressed or even shows a tendency of an opposite-sign effect. A new mechanism of dynamical disorder, which is applicable for materials in which the charge jump frequency between (molecular) centers depends on their mutual orientation, is suggested in an attempt to phenomenologically explain the experimental data.

Some references:

A. Katz, D. Faiman, B. Mishori, Yoram Shapira, A. P. Isakina, and M.A. Strzhemechny/ Disorder/Order Phase Transition in C60 thin films studied by surface photovoltage spectroscopy/ J. Appl. Phys. 94, 7173-7177 (2003).

E.A. Katz, D. Faiman, K. Iakoubovskii, A. Isakina, K.A. Yagotintsev, M.A. Strzhemechny, and I. Balberg, Effect of the disorder/order phase transition on the electrical and photoelectrical properties of C60 thin films, J. Appl. Phys. 93, 3401-3406 (2003).

M. A. Strzhemechny and E. A. Katz/ On the effect of the rotational state of C60 molecules on electronic transport in the C60 fullerite/ Fullerenes, Nanotubes, and Carbon Nanostructures 12, 281-286 (2004).

E. A. Katz, D. Faiman, S. Shtutina, N. Froumin, M. Polak, A. P. Isakina, K. A. Yagotintsev, M. A. Strzhemechny, Y. M. Strzhemechny, V. V. Zaitsev and S. A. Schwarz/ Structural and chemical modifications in Cu-supported C60 thin films exposed to an atmosphere of air or iodine/ Physica B, 304, 348-356 (2001).