Band alignment at the organic-inorganic interface

The band alignment of the bithiophene interface with a diverse range of sub strates has been determined by a combination of ultraviolet photoemission a nd work function measurements. Not only is vacuum level alignment clearly s hown to be invalid but also any sort of linear relationship between band al ignment and substrate work function is shown not to be the case. Rather, th e alignment is determined by the interface dipole, which is specific to the interaction at the inorganic-organic interface. The interface dipoles, whi ch always appear, while dominated by the first monolayer interaction, are c ompleted after two to three monolayers. As the ionization potentials of the films are shown to be constant, it is argued that a simple work function m easurement, for an organic film on a particular substrate, quantifies the b and alignment. (C) 2000 American Institute of Physics. [S0003-6951(00)00407 -1].