Low energy electron diffraction study of low index platinum single crystal surfaces

Abstract

The post-acceleration technique of Low Energy Electron Diffraction has been used to examine the three low index (100), (110), (111) crystal faces of platinum. The single crystal samples were subjected to ion bombardment, ultra-high vacuum anneal (p = 5Xl0(-10) torr) 25°C < T < 1450°C) and exposure to different gases (0(2), CO, H(2), CH(4), C(2)H(4), NH(3), N(2)). The changes in the diffraction features of platinum were correlated to these treatments in an attempt to explain the appearance of new surface structures. Several distinct sets of new diffraction patterns were observed as a function of these different treatments. These were characterized by the appearance of new periodicities in the diffraction pattern at well-defined ranges of electron beam energy. A high temperature anneal (T > 1000 °K) in ultra high vacuum will generally lead to the formation of a disordered, highly unreactive structure which is the same for all three faces of platinum. The specular intensity was measured as a function of beam voltage. The Debye temperatures which characterize the mean displacement of the surface atoms perpendicular to the surface planes were measured for all three faces. The average value of the surface Debye temperature is 110°K and shows little variation from face to face. The Debye tempera­ture of bulk platinum is 234°K.