Oxygen induced molecular reorientation on aluminum

Abstract

Para-sexiphenyl films grow on Al(111) at room temperature such that the molecules are oriented with their molecular axes parallel to the Al surface. Here we demonstrate that the presence of oxygen on the Al substrate prior to deposition leads to a reorientation of the molecules in which their axes are nearly perpendicular to the Al surface. This reorientation also leads to a difference in the electronic structure and an improvement in the band alignment of 1.0eV. The contribution of substrate order to molecular orientation in organic films is discussed.