Atom probe and field emission electron spectroscopy studies of semiconductor films on metals

The surface morphology and the electronic states of Ge overlayers deposited on Ir-and Mo-tips were investigated by a combined instrument of an atom probe (AP) and a field emission electron spectroscope (FEES). The overlayers were deposited on the tips while observing field emission microscope (FEM) images of the surfaces. The FEM images of thin Ge overlayers on the Ir-tips show layer-like structures. In field emission electron distribution (FEED) of a Ge overlayer on the Ir-tip, about 5 ML thick, an energy gap near the Fermi level was clearly widened by low temperature annealing. After the thickness was reduced to 3 ML by field evaporation, the energy gap still remained wide. The FEEDs of the Ge overlayers on the Mo-tips exhibit several peaks distinct from those on the Ir-tip. This may be attributed to the local strong electric field surrounding the Ge clusters formed on the Mo-tips.