Semimetal to Semiconductor Transition in Carbon Nanoparticles

Electron energy loss spectroscopy (EELS) has been used to observe size dependent changes in the electronic states of isolated, nanocrystalline carbon particles supported on ${\mathrm{SiO}}_2$ substrates. The structure and size distribution of the particles have been characterized by Raman scattering, Auger electron spectroscopy, and electron microscopy. EELS observations indicate that a semimetal to semiconductor transition occurs for particles smaller than 1 nm. In addition, hydrogen adsorption is found to significantly alter the electronic states, demonstrating that both finite size and dangling bond effects modify the properties of small carbon nanocrystallites.