Reflection High Energy Electron Diffraction (RHEED) has become a commonplace tech- nique for probing the atomic surface structures of materials. Under vacuum conditions an elec- tron beam is made to strike the surface of the sample under test at a glancing angle(theta<=100). Thc beam reflects off thc surface of the matcrial and subsequently strikes a phosphorescent screen. Because of the wave-like nature of the electrons, a diffraction pattern charactcristic of the first few atomic layers is observed on the scrcen if the surface is flat and the material

is crystalline. With a distance between atomic planes ofd=5A,a glancing angle of 1 and an operating de Broglie wavelength for the electrons of 2dsin(theta), compute the electron energy employed in the technique.