Band Edge at the (111) Surface of Copper Measured by the Total Energy Distribution of Field-Emitted Electrons

The upper limit of the conduction band was found to be 0.4±{}0.05 eV below the Fermi level in the $〈111〉$ direction of a copper crystal, in good agreement with theoretical predictions. The crystal was grown on the end of a tungsten field-emission tip and exhibited a central dark (111) region about 1000 {} in diameter. With the maximum permissible total emission, a current of 300 electrons/sec was observed from a region about 30 {} in diameter positioned on the $〈111〉$ pole.