LEED and XPS studies of ZrOW(100) surface in comparison with W(110) surface

Because the ZrOW(100) surface has a remarkably low work function, it has been widely applied to thermal field emitters for electron microscopes. Nevertheless, it seems that the lowering mechanism of the low work function has not been clearly understood. Especially, the question “why the lowering occurs only on the (100) surfaces” is left without answer. In situ analyses of LEED, XPS and work function measurement have been systematically performed under an intention to understand the lowering mechanism of the work function. In this study, a comparative analyses of the behaviours between (100) and (110) tungsten surfaces, due to the deposition of zirconium and the following heat treatment in oxygen ambient, will be given. Several monolayers of Zr were vacuum deposited on clean tungsten single crystal surfaces, followed by heat treatment in an oxygen ambient. In the case of the (100) surface, the work function once increased to 5.5 eV and dramatically decreased to 2.8 eV by the following heat treatment in UHV. The heat treatment in oxygen ambient once shifted the XPS peak for Zr3d52 to a high binding energy and the following heat treatment in UHV shifted back the peak to an intermediate position. In the case of the (110) surface, the XPS peak for Zr showed almost the same behaviour as the (100) surface, but the work function decreased hardly. The results of a LEED study will be given also.