(310c) Modeling Plasma-Surface Interactions and Their Role In Inducing Structural Transitions In Materials

Plasma-surface interactions play a crucial role in determining the structure and properties of thin films and nanostructures grown by plasma deposition processes. Such thin films and nanostructures of electronic materials are used widely in numerous technological applications. For example, thin films of hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon grown by plasma-enhanced chemical vapor deposition from silane-containing discharges are important materials in the fabrication of optoelectronic and photovoltaic devices. Film properties, such as crystallinity and surface roughness, are determined by the surface reactivities and mobilities of reactive species from the plasma that impinge on the growth surfaces; these properties are key factors in determining device performance.

In this presentation, we discuss a hierarchical modeling approach for the fundamental understanding of plasma-surface interactions and the first-principles-based simulation of plasma deposition and other plasma treatment processes. The approach combines first-principles density functional theory calculations of surface reaction and diffusion phenomena that occur during deposition or post-deposition plasma treatment, molecular-dynamics simulations of radical-surface interactions for radicals originating from the plasma, and kinetic Monte Carlo simulations of the long-time dynamics that govern film growth during plasma deposition processes. Representative results are presented for a-Si:H growth under conditions that make the silyl radical the dominant deposition precursor. The results are used to discuss issues of surface reactivity during deposition, film smoothening mechanisms, and film surface composition as a function of temperature.

We place special emphasis on understanding structural transitions induced upon processing of plasma deposited thin films and nanostructures with dihydrogen plasmas. Specifically, we discuss the mechanism of hydrogen-induced crystallization of a-Si:H films when they are exposed to hydrogen atom fluxes, which triggers an amorphous-to-nanocrystalline phase transformation. Furthermore, we present recent results of interactions of multi-walled carbon nanotubes (MWCNTs) with H atoms from a dihydrogen plasma and demonstrate a H-induced MWCNT-to-diamond transition that leads to formation of diamond nanocrystals even at room temperature.