Optical and electrical properties of opal carbon replica and effect of pyrolysis

The optical reflection, electrical conductivity, and magnetoconductance of porous opal carbon replicas which have a periodic nanoscale structure have been studied. The temperature dependence of resistivity in green opal carbo n replica is different from that in red opal carbon replica. The electrical properties of replica heat treated up to 3000 degrees C are consistent wit h those of pyrolitic graphite. The periodicity is found to decrease with th is heat treatment by scanning electron microscopy and reflection measuremen ts. Due to alkali metal doping, optical reflection spectra of replica with a heat treatment temperature of 2800 degrees C have changed drastically. Th e occurrence of positive magnetoconductance indicates the existence of quan tum effect at low temperature. These results indicate that the electrical a nd optical properties can be controlled by pyrolysis technique and porous g raphite can be obtained. (C) 2000 American Institute of Physics. [S0021-897 9(00)08014-2].