In this study, the evolution from diamond surfaces to metal-diamond interfaces has been examined. The electron affinity and the Schottky barrier height of a few Angstrom thick films of Zr and Cu deposited in ultrahigh vacuum (UHV) onto IIb substrates were correlated. Prior to metal deposition, the diamond surfaces have been cleaned by different anneals and plasma treatments in UHV, and the surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The initial surfaces were terminated with oxygen, or free of chemisorbed species. Ultraviolet photoemission spectroscopy was employed to determine whether the samples exhibited a positive electron affinity or a negative electron affinity (NEA) before and after metal deposition. For Zr, the Schottky barrier height was found to change very little with the presence or absence of chemisorbed species at the interface. A NEA was observed for Zr on diamond independent of the surface termination. However, for Cu, the surface cleaning prior to metal deposition had a more significant effect. The Schottky barrier height changed strongly depending on the chemical species at the interface. A NEA was only detected for Cu on clean diamond surfaces. The differences between Zr on the one hand and Cu on the other are correlated with differences in interface chemistry and structure.