Shenda M. Baker1, George R. Rossman2, and John D. Baldeschwieler1
1Division of Chemistry and Chemical Engineering
2Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, California 91125
Spectroscopic current-voltage (I V) curves taken with a scanning tunneling microscope on a synthetic, boron-doped diamond single crystal indicate that the diamond, boiled in acid and baked to 500°C in vacuum, does not exhibit ideal Schottky characteristics. These I-V curves taken in ultrahigh vacuum do not fit the traditional theory of thermionic emission; however, the deviation from ideal can be accounted for by charge screening at the diamond surface. At ambient pressure, the I-V curves have a sharp threshold voltage at 1.7 eV above the valence band edge indicating pinning of the Fermi energy. This measurement is in excellent agreement with the 4 band gap rule of Mead and Spitzer [Phys. Rev. 134, A7 13 (1964)].