Electron-doped α-rhombohedral boron (α-r-B) crystals were synthesized by Li- and Mg-dopings. The doped α-r-B particles showed a shiny metallic colour, though non-doped α-r-B crystals showed a dark red colour (red boron). The electronic structures of doped α-r-B single crystals were examined by a high energy-resolution electron energy-loss spectroscopy microscope. Boron Is electron-excitation spectra, which show the density of states of the conduction bands, of Li-doped α-r-B showed a chemical shift toward a smaller binding-energy side, indicating a charge transfer from the doped atoms to α-r-B. These spectra also showed a sharp intensity increase at the onset with a width of an energy resolution of the experiment. The sharp intensity increase may be assigned to a Fermi edge produced by the electron doping. The spectra of Mg-doped α-r-B showed a chemical shift indicating an electron doping, but did not show the presence of a Fermi edge.
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