Effect of oxygen on electric conductivities Of C60 and higher fullerene thin films

The dark conductivities and photoconductivities of C-60 and higher fullerene (C-70, C-76, C-78 and C-84) thin films in oxygen gas at room temperature have been investigated. It was found that the time dependences of both the dark conductivities and photoconductivities of higher fullerene films are of the same pattern as those of a C-60 film in oxygen gas. These electric conductivities quickly decrease after the films are exposed to oxygen gas or air. Both the dark and photoconductivities of C-60 and C-70 films are much higher than those of higher fullerene (C-76, C-78 and C-84) films in vacuum. However, the dark conductivities of these fullerene films after 24-h treatment in oxygen gas become of the same order of magnitude. The degree of reduction and saturation times of the electric conductivities of higher fullerene films in oxygen gas are smaller and longer, respectively, than those of C-60 and C-70 films. (C) 2003 Elsevier B.V. All rights reserved.