MICROTEXTURE AND MAGNETORESISTANCE OF GLASS-LIKE CARBONS

Microtextures of glass-like carbons commercially available were investigated through scanning electron microscopy and measurement of their magnetoresistance. A field-emission electron gun type SEM, which is characterized by a specimen chamber equipped in its objective lens, was operated with the acceleration voltage of 2 kV, and high fidelity observations were thereby achieved with a resolving power of 2 nm. All the specimens exhibit granular microtextures with the mean grain diameter spanning 6-13 nm. The mean grain diameter correlates to the mean crystallite size L(a)(110) determined by the X-ray powder diffractometry. The density of each sample calculated by using the mean diameter and the X-ray parameters reproduces well its catalog value. Negative magnetoresistance was observed just for the specimens whose average grain sizes are not smaller than 7.3 nm. The crystallite size L(a)(110) of the specimen whose grain size shows the minimum value for appearance of negative magnetoresistance is estimated to be 2.7 nm. The absolute value of negative magnetoresistance under a constant magnetic field increases with increasing the average grain size.