Characterization of microporosity and mesoporosity in carbonaceous materials by scanning tunneling microscopy

Scanning tunneling microscopy has been employed to characterize the micropo rous and mesoporous structure of different carbon materials. First, model m icropores artificially created on a highly oriented pyrolytic graphite subs trate by plasma treatment were studied at the atomic scale: the observed in crease in electronic density near the Fermi level around the defect implies an increased adsorptivity of the model micropore region. Second, activated carbon fibers were studied. A spongy mesoporous texture along with slit-sh aped microporosity (similar to1 nm) was observed, accounting for the high a dsorption properties of this material. For comparison, nonporous thermally treated carbon black and nonactivated carbon fibers with a ultramicroporous texture were also investigated. In the former case, as expected, no sign o f extensive microporosity or mesoporosity such as that of the activated car bon fibers was encountered, in agreement with its poor sorptive capability. In the latter case, the interpretation of the results was rather troubleso me, since the minute pore size rendered a reasonably accurate STM imaging d ifficult.