Electron-Beam Retardation Contact Potential of Cuprous Oxide

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Lindle, James
Physical Sciences and Mathematics; Physics
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The purpose of this research is to determine the contact potential of cuprous oxide, Cu2O, with respect to gold. A band model for cuprous oxide is presented. Single-crystal cuprous oxide is prepared from Oxygen Free High Conductivity copper equilibrated at 120°C and at atmospheric pressure. The contact potential difference of cuprous oxide (using gold as a reference) is measured in a bakeable ultrahigh vacuum system using a modified version of Nelson's electron beam retardation method. Measurements made at 10-6 torr and at room temperature give a value of 0.1 +/-0.05 eV for the contact potential difference of cuprous oxide with respect to gold. Photoelectric emission from the gold reference is approximately 4.9 eV. Hence, the Fermi level resides at approximately 5 eV below vacuum zero. This places the Fermi level between the valence band which was found to be at approximately 5.1 eV and the acceptor levels which reside somewhere between 0.3 eV and 0.6 eV above the valence band. From optical experiments the band width has been determined to be approximately 2.3 eV. If 5.1 eV is taken as the top of the valence band and 2.3 eV is the band gap, then the electron affinity of cuprous oxide is approximately 2.8 eV.