Thin polymer films on metal: assessment of a conductivity mechanism via valence band spectra

When prepared as very thin layers on a conducting substrate, organic and polymer films are generally not prone to the charging effect when studied for example with XPS, HREELS or STM. For Langmuir-Blodgett layers of Arachic Acid, Behenic Acid, and Polyvinylstearate, it is shown that XPS valence band spectra exhibit an increased density of states just below the Fermi level. It is suggested that this effect is due to an electronic interaction with the substrate, allowing for electrical conductivity in the adsorbate layer.