CRITICAL BEHAVIOR OF THE AU/SI(111)-(5X1) SURFACE

Abstract

We have investigated the critical behavior of the order-disorder phase transitions of the Au/Si(lll)-(5x1) surface for three different Au coverages theta(1)<theta(2)<theta(3). The temperature dependence of a (0 1/5) low-energy electron diffraction spot reveals a commensurate-solid-fluid transition (CFT) at theta(1) and incommensurate-solid-fluid transitions (IFT&apos;s) at theta(2) and theta(3) upon increasing temperature. The measured T-theta phase diagram is compared with a theoretical prediction where a Lifshitz point exists at a nonzero theta. We notice two distinct features that are different from theory: the slightly higher transition temperatures of IFT&apos;s than that of CFT&apos;s and the seemingly second-order nature of CFT&apos;s which might well be a smeared out first order. The former is understood by the enhanced core energy of dislocations in the I phase, while the latter reflects the nonideal conditions of the sample surface. The critical behavior of CFT&apos;s produces critical exponents close to a four-state Potts universality class.