Surface Self-diffusion of Erbium

The activation energy for the surface self-diffusion of epitaxial erbium crystals grown on a tungsten field emitter tip has been examined. It was found to be strongly dependent both on the crystallographic orientation of the tip and the direction of electric field applied. The values of the activation energy, calculated from Arrhenius-type plots, and also field emission patterns of epitaxial Er crystals are presented. I INTRODUCTION The procedure of growing epitaxial single crystals of erbium [ l ] made possible to measure the activation energy for self-diffusion of erbium. Erbium crystals were grown by vapour deposition onto a tungsten substrate in the ultra-high vacuum environment of a field electron microscope. This method growth [21 assures a very good surface cleanness and eliminates the necessity of additional cleaning before the measurements. I1 -EXPERIMENTAL, METHOD The measurements were done in a glass field emission microscope connected to a sputter-ion pumped metal vacuum system. Base pressure in the microscope was about 1 0 ~ Pa, estimated from the rate of the specimen surface contamination time. The erbium used for vapour source was of about 99.9% purity. The conventional methods of field emission microscopy were used [ 3 , 4 ] . Zero-field activation energy was determined 151 first by establishing a reproducible small deformation of the crystal shape at a certain temperature with an electric field applied and then measuring the time required to smooth the surface at various temperatures with no field applied. The deformation has to be small enough in order to make the surface diffusion be the main mechanism of transport during the course of smoothing and to avoid the influence of the bulk diffusion. The initial and the final states of the crystal shape were characterized by the relevant values of the Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986251