Electronic structure of organic/metal interfaces

In this article, studies of two subjects recently carried out in our group on organic/metal interfaces are reported. The first is the examination of the change of the work function of various metals (Ca, Mg, Cu, Ag and Au) at the deposition of TPD [N,N ' -bis(3-methylphenyl)-N,N ' -diphenyl-[1,1 ' -biphenyll-4,4 ' -diamine (TPD)], which is used as a typical hole-injection layer. The work function change was pursued using Kelvin probe method and UV photoelectron spectroscopy (UPS) up to the film thickness of 100 nm. The results clearly showed that band bending leading to Fermi level alignment is not achieved, at least for systems prepared and measured under ultra high vacuum (UHV) conditions. The results of the exposure of the metal substrate to air was also examined. In the second work, we studied the mode of film growth, chemical interaction and electronic structure for interfaces formed by depositing p-sexiphenyl (6P) on metals (Au and Mg) and metals on 6P, using metastable atom electron spectroscopy (MAES), UPS and X-ray photoelectron spectroscopy MPS). The results strongly depended on the metal and the order of deposition. The Au surface was easily covered by 6P deposition (equivalent to 0.3 nm thickness), while Mg surface requires much larger amount of 6P. In contrast, metal atoms deposited on 6P diffused into the organic layer. In particular, the surface of 6P was exposed even after depositing Au equivalent to 200-nm thickness. The change of work function in these cases is interpreted based on these modes of interface formation. (C) 2001 Elsevier Science B.V. All rights reserved.