Thickness-dependent electronic properties and molecular orientation of diradical metal complex thin films grown on SiO 2

Abstract

We studied the thickness dependence of electronic structure and molecular orientation of neutral, square planar, diamagnetic diradical metal complex, bis( o-diiminobenzosemiquinonate) nickel(II) complexes (Ni(DIBSQ) 2), thin films grown on a SiO 2 substrate by using ultraviolet photoelectron spectroscopy in combination with metastable atom electron spectroscopy. We observed that the small hole-injection barrier of 0.46 eV for the monolayer film, and the barrier increases continuously with the film thickness and becomes larger than the electron-injection barrier. We further found that molecules are oriented with their long-axes nearly perpendicular to the surface both in the monolayer and multilayer films independent of the film thickness.