PHASE-TRANSITIONS AT AL AND AU SURFACES - DECONSTRUCTION, ROUGHENING AND PREMELTING

A short outline of structural phase transitions at surfaces and their experimental verification will be given as an introduction, which will be followed by a review of experimental and theoretical results for A l and Au surfaces. We have studied Au(111)-, Au(110)- and Au(100)-surf aces by medium energy ion scattering (MEIS) experiments and Au(110)- a s weil as Al(110)-surfaces by low energy electron diffraction (LEED) e xperiments. At the Au(110) (2 x 1)-surface deconstruction is accompani ed by the disappearance of monoatomic steps. At about 40 K above the d econstruction temperature roughening sets in. The rough surface begins to smoothen if due to the increasing diffusion the outermost layers s tart to transform into a quasi-liquid state. The growth of the quasi-l iquid layer with increasing temperature follows a logarithmic law. Pre roughening, roughening and premelting transitions have been detected a t the Al(110)-surface. Open questions regarding these phase transition s will be discussed.