No abstract

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 carbon replica is different from that in red opal carbon replica. The electrical properties of replica heat treated up to 3000 °C are consistent with those of pyrolitic graphite. The periodicity is found to decrease with this heat treatment by scanning electron microscopy and reflection measurements. Due to alkali metal doping, optical reflection spectra of replica with a heat treatment temperature of 2800 °C have changed drastically. The occurrence of positive magnetoconductance indicates the existence of quantum effect at low temperature. These results indicate that the electrical and optical properties can be controlled by pyrolysis technique and porous graphite can be obtained.

No abstract

No abstract

Carbon inverse opals with three-dimensional nanoporous structures are fabricated by a template method using synthetic opals formed by the sedimentation of SiO 2 spheres. The pore size of the carbon inverse opals ranges widely from approximately 11 nm to 1 mm depending on the diameter of the SiO 2 spheres. The nanostructure size and the degree of graphitization of carbon are also controlled by the change in pyrolysis technique. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations of the carbon inverse opals prepared by pyrolysis at a heat-treatment temperature (HTT) of 2800 C revealed that the graphite layers are formed in the area surrounding the pore and the degree of graphitization depends on the pore size. The electronic properties of the carbon inverse opals are dependent on pore size and the conditions of pyrolysis and are interpreted to be influenced by weak localization effect by taking into consideration the degree of graphitization depending on pore size.