ELECTRON-AFFINITY AND SCHOTTKY-BARRIER HEIGHT OF METAL-DIAMOND (100),(111), AND (110) INTERFACES

The electron emission properties of metal-diamond (100), (111), and (1 10) interfaces were characterized by means of UV photoemission spectro scopy (UPS) and field-emission measurements. Different surface cleanin g procedures including annealing in ultrahigh vacuum (UHV) and rf plas ma treatments were used before metal deposition. This resulted in diam ond surfaces terminated by oxygen, hydrogen, or free of adsorbates. Th e electron affinity and Schottky barrier height of Zr or Co thin films were correlated by means of UPS. A negative electron affinity (NEA) w as observed for Zr on any diamond surface. Co on diamond resulted in N EA characteristics except for oxygen-terminated surfaces. The lowest S chottky barrier heights were obtained for the clean diamond surfaces. Higher values were measured for H termination, and the highest values were obtained for O on diamond. For Zr, the Schottky barrier height ra nged from 0.70 eV for the clean to 0.90 eV for the O-terminated diamon d (100) surface. Values for Co ranged from 0.35 to 1.40 eV for clean- and O-covered (100) surfaces, respectively. The metal-induced NEA prov ed to be stable after exposure to air. For the oxygen-terminated diamo nd (100) surface a field-emission threshold of 79 V/mu m was measured. Zr or Co deposition resulted in lower thresholds. Values as low as 20 V/mu m were observed for Zr on the clean diamond (100) surface. Resul ts for Zr or Co on H- or O-terminated surfaces were higher. H or O lay ers on diamond tend to cause an increase in the Schottky barrier heigh t and the field-emission threshold field of Zr- and Go-diamond interfa ces. The value of the electron affinity and Schottky barrier were corr elated with work function and different initial surface preparation. T he results were largely consistent with a model in which the vacuum le vel was related to the metal work function and the measured Schottky b arrier. (C) 1998 American Institute of Physics.