Electronic structure and molecular orientation of pentacene thin films on ferromagnetic La0.7 Sr0.3 MnO3

Abstract

Pentacene thin films deposited on a ferromagnetic electrode, La 0.7 Sr0.3 MnO3 (LSMO), have been studied using near-edge x-ray absorption fine structure (NEXAFS), ultraviolet photoemission spectroscopy (UPS), and atomic force microscopy (AFM). Here we present electronic structure and molecular orientation of pentacene thin film on LSMO. No evidence related to covalent bonding or significant charge transfer between pentacene and LSMO has been found in the NEXAFS or UPS results. UPS measurements suggest that the vertical ionization potential of pentacene on LSMO is 4.9 eV. Our results extracted from NEXAFS indicate that molecular long axis of pentacene stands on the LSMO substrate surface with a tilt angle of about 22°±2°between the main molecular axis and the substrate surface normal. AFM images show the terracelike crystalline grain formed by stacking pentacene crystalline layers and a rough crystal-layer spacing of 14-15 Å. Findings deduced from UPS, NEXAFS, and AFM consistently demonstrate that pentacene stands on LSMO with a tilt angle. © 2010 The American Physical Society.