Quantitative Structural Determination of Metallic Film Growth on a Semiconductor Crystal:(3×3)R30°→(1×1

New(3×3)R30°Phase of Pb on Ge(111) and Its Consequence for the Melting Transition

“…The phase diagram of this system as derived by Ichikawa [10] and Grey et al [6,11] shows two 3 p 3 p R30 ( 3 p in short) phases, a low-coverage phase at 1 3 monolayer (ML) known as the phase and a dense phase at 4 3 ML. de Vries et al [7] confirmed that the saturation coverage of the phase is 4 3 ML, with one Pb atom located at an H 3 site and the other three located on off-center bridge positions between the T 1 and T 4 sites (''OCT 1 ''), see Fig. 1.…”

“…If at least 4 3 ML of Pb is deposited, a 3 p phase forms (that we will call the 0 phase) that exhibits a phase transition to a 1 1 phase at 330 C. This is an irreversible transition, and after cooling down the well-known phase emerges with a lower transition temperature of 270 C. The latter transition is reversible; thus the phase is stable.…”

“…(Received 17 July 2002; published 6 February 2003) Depending on the preparation method, we find two different structures of the Pb=Ge111 system at a nominal coverage of 4 3 monolayer that exhibit different melting points. One is the well studied phase that melts at 270 C, but the other is a new and metastable phase that melts at 330 C. Using surface x-ray diffraction the atomic structure of both phases is found to be surprisingly similar.…”

“…In the course of investigating the phase transition at a coverage of 4 3 ML [12], we found a difference between the as-deposited structure and the annealed structure. If at least 4 3 ML of Pb is deposited, a 3 p phase forms (that we will call the 0 phase) that exhibits a phase transition to a 1 1 phase at 330 C. This is an irreversible transition, and after cooling down the well-known phase emerges with a lower transition temperature of 270 C. The latter transition is reversible; thus the phase is stable.…”

“…Owing to the low dimensionality, the local structure, defects, and thermal fluctuations are more important than in bulk material [1,2]. One type of system that has been found to be particularly rich is the metal-semiconductor interface, of which a lot is known thanks to their importance in electronics [3,4]. Prime examples are Pb and Sn monolayers on Si(111) and Ge(111).…”