Thermodynamic equilibrium and metal-organic interface dipole

We determined the interface dipoles at a number of metal-organic interfaces using ultraviolet and x-ray photoelectron spectroscopy. A linear dependence of the dipole on the metal work function is observed. This is consistent with the theory based on the charge transfer and thermodynamic equilibrium across the interface. The agreement suggests that charge transfer is one major factor in the formation of interface dipole. In addition, we find that the pushing back of the electron cloud tail that extends out of the metal surface and the permanent dipole moment of the organic molecule affect the interface dipole. (C) 2002 American Institute of Physics.