Interface Electronic Structures of the L-Cysteine on Noble Metal Surfaces Studied by Ultraviolet Photoelectron Spectroscopy

Abstract

L-cysteine, one of amino acids, is well known in the bioelectronics field as a linker between proteins and metal electrodes. The interface electronic structures between L-cysteine and metals are therefore very crucial because they dominate the charge carrier injection characteristics into such biological systems. However the interface electronic structures of L-cysteine and metals have been not well understood. In this study, the electronic structures at the interfaces of sequentially deposited L-cysteine layers on the metal surfaces of Au(111), Ag(111), and Cu(111) were investigated by thickness-dependent ultraviolet photoelectron spectroscopy (UPS). At the contact regions, the electronic structures of L-cysteine revealed modification with respect to its bulk phase and significant variation depending on the substrate. The electronic structure at the interfaces including work function, secondary electron cutoff (SECO), highest occupied molecular orbital (HOMO) onset, position of an interface state, charge injection barrier, and ionization energy were estimated for each case. [DOI: 10.1380/ejssnt.2015.373]