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 t he 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 U V photoelectron spectroscopy (UPS) up to the film thickness of 100 nm. The results clearly showed that band bending leading to Fermi level alignment i s not achieved, at least for systems prepared and measured under ultra high vacuum (UHV) conditions. The results of the exposure of the metal substrat e to air was also examined. In the second work, we studied the mode of film growth, chemical interaction and electronic structure for interfaces forme d by depositing p-sexiphenyl (6P) on metals (Au and Mg) and metals on 6P, u sing metastable atom electron spectroscopy (MAES), UPS and X-ray photoelect ron spectroscopy MPS). The results strongly depended on the metal and the o rder of deposition. The Au surface was easily covered by 6P deposition (equ ivalent 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 l ayer. 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 Elsev ier Science B.V. All rights reserved.