Lowering of the work function on carbon surfaces due to hydrogen plasma treatment

It is known that exposure of smooth [111] and [100] diamond surfaces to atomic hydrogen leads to negative electron affinity. A common explanation is the assumption of a dipole layer leading to a reduction of the work function. However, it is not so clear whether such a dipole layer is beneficial for field electron emission. We investigated by STM, AFM, X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) the effect of a hydrogen plasma treatment on different carbon surfaces (HOPG, diamond, amorphous carbon).