Photoemission from the negative electron affinity (100) natural hydrogen terminated diamond surface

We reported recently about the cleaning and polishing of natural doped (100) and (111) diamond surfaces in a hydrogen plasma at 870 degrees C and 40 mbar [Kuttel et al., Surf. Sci. 337 (1995)L812]. This smooth (100) surface shows a sharp negative electron affinity (NEA) peak for the 2 x 1 monohydride terminated surface upon annealing to 300 degrees C, experimentally observed by ultraviolet photoemission spectroscopy (UPS). The effect of annealing the crystal up to 1000 degrees C in an UHV environment (p < 3 x 10(-9) mbar) results in a positive electron affinity (PEA) whereas a subsequent atomic hydrogen adsorption from a heated filament leads to an 1 x 1 reconstruction and to the reappearance of the NEA peak with a lower intensify than the plasma exposed surface. Upon annealing the surface up to 1000 degrees C at a pressure of 5 x 10(-8) mbar, a NEA is observed which probably is caused by remaining hydrogen at the surface. The hydride terminated surface seems to be responsible for the NEA property. The link between the NEA property and the band bending of the (100) surface are elucidated by photoemission spectroscopy of the core level and the valence band and we measured the spatial distribution of the NEA peak for the plasma exposed surface by angle resolved UPS. Finally, we show photoelectron current measurements and the influence of the bias applied to the surface.