Thermal phase evolution of Pt-Si intermetallic thin films prepared by the activated adsorption of SiH4 on Pt(100) and comparison to known structural models

We have investigated the growth, morphology, and phase evolution of Pt-Si intermetallic thin films using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). These materials were formed through an "inverted" CVD deposition process that involves the exposure of a Pt(100) crystal to silane (SiH4) followed by flash annealing treatments. Structural studies performed as a function of the annealing temperature reveal a complicated phase behavior that involves the sequential formation of four atomically ordered phases with multilevel character. The nature of this process is analyzed to obtain information about the primary structure-determining interactions responsible for the phase transformations seen in this system. We describe the structure-determining influences seen on the Pt(100) surface and provide a comparison with earlier results obtained on Pt(111) and Ni surfaces. The substrate effects are marked and the differences between the results obtained on Pt(100) and Pt(111) are discussed in detail. A model is presented that relates the structure of the phases obtained on the Pt(100) surface to known bulk Pt silicide phases. Of particular interest is the finding that "inverted" CVD via the thermolytic decomposition of SiH4 on the Pt(100) substrate yields, upon suitable thermal treatment, a(root 17 x root 17)R14.0 degrees overlayer structure exhibiting two chiral surface domains. This multilayer structure is well described by a termination of the bulk Pt-Si intermetallic phase that is isomorphic with the well-known Ni12P5 structure.