Feldionenmikroskopische untersuchungen der wechselwirkungen von methan mit wolfram

Abstract The imaging of methane molecules adsorbed on tungsten and the effects of methane as imaging gas are treated in detail. It is possible to image methane molecules or dissociation products with helium as imaging gas in the field range of about 3.3 to 4.0 V A , with a channel plate image intensifier. The adsorption mechanism seems to be different according to the field applied before. For high fields a field adsorption has to be assumed, for low fields a dissociation of CH 4 may occur. When the field strength is increased, the dissociation products remain on the surface. An imaging of metal surfaces with methane is very difficult, because the surface is covered with an adsorption layer of CH x , preventing a stable image with higher degree of order. In the field range of 0.8 V A and temperatures below 78 K a self promotion of methane occurs exactly on the (111)- and (411)-planes. Very bright areas appear on these planes showing dynamical changes in shape and configuration.