Photo-illumination hardening of C60 crystals

Abstract

The effect of light on the hardness of C 60 crystals was investigated. The hardness increased after the crystals were illuminated with white light. Such a photo-illumination hardening was effective in a temperature range of 298-380 K. The photopolymerized C 60 molecules near the crystal surface were responsible for the hardening. The anomalous temperature dependence of the hardness at temperatures higher than 300 K, which we previously have observed, is explained as due to the photo-illumination hardening.

Temperature and photopolymerization effects in microhardness of C70 crystals

“…We have showed that the hardening of C 60 crystals is due to the interactions between dislocations and photoinduced products such as C 60 dimmers. 4,5 According to Rao and co-workers 12,13 such photoinduced polymerization can also occur for C 70 films. The cross section for photopolymerization of C 70 is, however, considerably smaller than that observed for C 60 .…”

“…These results show that C 70 crystals also exhibit photoillumination hardening, similar to the observations in C 60 crystals. 4 When the magnitude ⌬H of the hardening is defined as the change in hardness due to the illumination for 50 h, the values of ⌬H at 300, 343, and 373 K are, respectively, 20, 61, and 43 MPa, as shown in Fig. 4.…”

“…[4][5][6][7] The light effect is a so-called photoillumination hardening. 4,5 The characteristics of the hardening are as follows. ͑1͒ The hardness increases with the development of the illumination time and reaches a constant value.…”

PHOTOINDUCED HARDENING AND REDUCTION OF DISLOCATION MOBILITY IN C60SINGLE CRYSTALS: THE WAVELENGTH DEPENDENCE

“…Photopolymerization of C 60 appears also in air (4)(5)(6). Light-irradiated in air C 60 becomes insoluble in common solvents, exhibits higher hardness compared to pristine fullerite and reverts to pristine fullerite after heat treatment at 400-500 K (4-7).…”

“…The aim of the present work was to investigate the wavelength dependence of phototransformation of C 60 single crystals in air using indentation hardness and dislocation mobility methods. The microindentation as a structure and depth sensitive test has been successfully used earlier in studies of the light-, atmosphere-, pressure and temperature-induced effects in fullerite (4,5,(7)(8)(9)(10)(11)(12). Investigations of the dislocation zone around indents can provide important information about photoinduced processes in the subsurface layer (7,11,13).…”