Thermal expansion of thin C60 films |
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Authors: | A T Pugachev N P Churakova N I Gorbenko Kh Saadli E S Syrkin |
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Institution: | (1) Khar’kov State Polytechnical University, 310002 Khar’kov, Ukraine;(2) Physicotechnical Institute of Low Temperatures, Ukrainian National Academy of Sciences, 310164 Khar’kov, Ukraine |
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Abstract: | The thermal expansion coefficient a and structure of C60 films with thickness t∼3–10 nm were investigated in the temperature interval from room to liquid-nitrogen temperature by electron-optical methods.
The thermal expansion coefficient was determined from the temperature shift of the diffraction maxima in the electron diffraction
patterns. The objects of investigation were epitaxial C60 films condensed in vacuum on a (100) NaCl cleavage surface and oriented in the (111) plane. A surface-induced size effect
in the thermal expansion coefficient was observed. It was established that as t decreases α
f increases and is described well by the relation α
f=17·10−6 K−1+8.3·10−5 nm K−1
t
−1. This relation was used to estimate the linear expansion coefficient α
s of the C60 surface in the (111) plane as α
s=60·10−6K−1, which is several times larger than the bulk value. The experimental results agree satisfactorily with the theoretical calculations
of the mean-square displacements of molecules located in a region near the surface.
Zh. éksp. Teor. Fiz. 114, 1868–1875 (November 1998) |
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