We have investigated using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) the growth and structural evolution of Pt-Si intermetallic phases formed via a chemical vapor deposition (CVD) mediated process. The Pt silicide thin films were prepared though the exposure of a Pt(111) crystal to silane (SiH4) followed by various annealing treatments. The deposition of Si via the decomposition of silane at room temperature preferentially forms clusters at step edges that avoid the centers of Pt terraces. The sizes and coverages of the clusters increases with silane exposure. The clusters are of intermetallic character (composed of both Si and Pt) and coarsen to give cluster heights much larger than a Pt(111) step height. These observations implicitly establish that Si interdiffusion in the near-surface region is weakly activated. Studies performed as a function of the silane exposure and annealing temperature reveal a complicated phase behavior that incorporates seven separate atomically ordered phases in addition to large-scale surface features such as three-dimensional islands. The ordered overlayers we have characterized include a complex, multilayer (√7×√7)R19.1° phase, at least one and perhaps two separate overlayers with (√19×√19)R23.4° symmetry, and a centered, rectangular overlayer. The structure of the adlayers observed by STM generally confirm but expand upon earlier structural studies based primarily on low-energy electron diffraction (LEED), which explored a more restricted sampling of the Pt(111)-Si compositional phase space. In this paper, we also describe several dynamical phenomena that have heretofore not been appreciated as making important contributions to silicide growth processes. They include progressive degradation and incomplete phase formation behaviors, the coexistence of ordered phases, and the metastable growth of multiple hexagonal (i.e., nonbulk) structures. Large-scale growth behavior involving step edge evolution and bunching as well as island structural evolution and coarsening have also been characterized. Notable is that fact that qualitative features of the island structure (e.g., size, angularity, and arrangement) appear to depend only weakly on the method of formation but rather strongly on the elemental composition. Growth and degradation mechanisms have been constructed, and the phenomena observed are contrasted with standard kinetic models based on sequential phase growth.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry