Phase Transitions Near Surfaces Studied By Grazing Incidence Diffraction of X-Rays

Abstract

ABSTRACTWe review two different experiments in order to demonstrate the power of grazing incidence diffraction of x-rays in studying phase transitions near surfaces and to show that it is well suited to get information on structural details even from subsurface layers: We have measured the near surface critical scattering at the continuous order disorder transition of an Fe3Al single crystal which provides information on modifications of critical behavior of a bulk transition near a surface. These modifications are detectable to a considerable depth due to the diverging range of correlations. We determined three different critical surface exponents which allow, for the first time, to confirm scaling laws for near surface critical behavior.- The experiment at a (100) surface of a discontinuous ordering Cu3Au single crystal shows that the surface is wetted by a disordered layer below the transition temperature. By means of the adjustable depth sensitivity of grazing incidence scattering we were able to demonstrate that the thickness of this layer increases logarithmically when approaching the transition temperature.