Internal structure of a molecular junction device: Chemical reduction of PtO2 by Ti evaporation onto an interceding organic monolayer

Abstract

We present a physical and chemical characterization study of molecular electronic junctions previously shown1,2 to display tunable hysteric electrical switching behavior useful for nanoscale memory and logic circuitry applications.3-6 X-ray photoelectron spectroscopy (XPS) data were acquired from the internal buried interfaces in a series of related device structures. This was accomplished using a new technique based on stripping (delaminating) the molecular device stacks at the molecular layer for XPS examination in ultrahigh vacuum (UHV). These data reveal that evaporative deposition of titanium onto the organic monolayers in these junctions results in the chemical reduction of the 2.5 nm platinum oxide film underlying the monolayers. This understanding allows us to construct an improved model for the internal chemical structure of these electrically well-studied molecular junctions, and to suggest a new model for how the evaporation of titanium as the top contact in molecular electronic devices prevents electrical shorts in these devices. © 2007 American Chemical Society.