Phase transitions at Al and Au surfaces: Deconstruction, roughening and premelting

Abstract

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 Al and Au surfaces. We have studied Au(111)‐, Au(110)‐ and Au(100)‐surfaces by medium energy ion scattering (MEIS) experiments and Au(110)‐ as well as Al(110)‐surfaces by low energy electron diffraction (LEED) experiments. At the Au(110) (2×1)‐surface deconstruction is accompanied by the disappearance of monoatomic steps. At about 40 K above the deconstruction temperature roughening sets in. The rough surface begins to smoothen if due to the increasing diffusion the outermost layers start to transform into a quasi‐liquid state. The growth of the quasi‐liquid layer with increasing temperature follows a logarithmic law. Preroughening, roughening and premelting transitions have been detected at the Al(110)‐surface. Open questions regarding these phase transitions will be discussed.

Solid-Liquid Interfacial Premelting

“…Figure 2 shows that solid-liquid premelting occurs in this system for all orientations studied, with nearly identical behavior. This is in contrast to surface premelting in many fcc metal surfaces, in which (110) surfaces are prone to premelting, while premelting is not seen in the other orientations [7,14].…”

“…This is in contrast to surface premelting in many fcc metal surfaces, in which (110) surfaces are prone to premelting, while premelting is not seen in the other orientations. [7,14] Note that, we have examined the local structure of the Al liquid within the premelting layer and found it to be consistent with that of bulk liquid, showing little influence of either confinement or the nearby presence of the liquid Pb phase. [44] Our previous simulations at 625K [40] suggested that the (100) and (110) interfaces are rough at that temperature, while the (111) interface is faceted.…”

“…Since then, advances in experimental techniques have provided powerful tools for direct atomicresolution observations of this surface phase transition. [4][5][6][7][8][9][10] These experimental studies have been complemented by a number of detailed atomistic simulations probing the existence and atomic-level mechanisms of SP (Refs. 11-18 and references therein).…”

“…Surface premelting (SP), the formation of a premelting layer at a solid-vapor interface, was first observed experimentally by Frenken and van der Veen [3] using proton scattering. Since then, advances in experimental techniques have provided powerful tools for direct atomic-resolution observations of this surface phase transition [4][5][6][7][8][9][10] These experimental studies have been complemented by a number of detailed atomistic simulations probing the existence and atomic-level mechanisms of SP (Refs. 11-18 and references therein).…”