Growth and phase transformations of Ir on Ge(111)

摘要

The growth of Ir on Ge(111) as a function of temperature between 23 degrees C and 820 degrees C is characterized with low energy electron microscopy (LEEM), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and x-ray photoemission spectroscopy (XPS). Deposition onto a substrate at 350 degrees C revealed a novel growth mode consisting of multilayer Ir islands with (root 3 x root 3)R30 degrees (abbreviated as root 3) structure interconnected by "bridges" of single-layer Ir several atoms wide. For deposition onto substrates above 500 degrees C, the root 3 Ir phase grows with dendritic morphology, and substrate step bunches act as barriers to root 3 Ir growth. LEEM images showed Stranski-Krastanov growth for 650-820 degrees C: after the root 3 phase covers the surface, corresponding to 2 monolayers (ML) Ir coverage, multilayer hexagonal-shaped Ir islands form, surrounded by regions of IrGe alloy. Hexagonal-shaped Ir islands also formed upon heating 1.2 ML of root 3 Ir beyond 830 degrees C, which resulted in the elimination of root 3 structure from the surface. The transformation from root 3 to (1 x 1) structure upon heating to 830 degrees C was an irreversible surface phase transition. Annealing > 2.0 ML of Ir in the 1/3 phase above the 830 degrees C disorder temperature, followed by cooling, produced a (3 x 1) structure. Subsequent heating and cooling through 830 degrees C give evidence for a reversible (3 x 1) to (1 x 1) phase transition. (C) 2017 Elsevier B.V. All rights reserved.