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Surface Structures Far-from-Equilibrium

Project Leader: Michael Tringides
Principal Investigators: Myron Hupalo, Pat Thiel, Michael Tringides, Cai-Zhuang Wang
Senior/Key Personnel: Kai-Ming Ho

This project focuses on low dimensional surface structures (ultrathin metallic films, islands, wires, etc.), especially in systems exhibiting quantum size effects (QSE). Since such structures are metastable and grown far from equilibrium, it is important to identify the optimal kinetic pathways. In turn, this requires a better understanding of many atomistic processes (e.g. surface diffusion, nucleation, coarsening) that define the kinetic pathway. In addition the properties of the grown structures (e.g. band structure, density-of-states) depend on the structure dimensions. This opens the possibility to control their potential uses in chemical reactivity and energy storage.

This interdisciplinary effort (physics, chemistry) is built upon a close interaction between theorists (Wang, Ho) and experimentalists (Tringides, Thiel, Hupalo). The scientists with the project have a strong background in film growth, coarsening, diffusion, nucleation, and overlayer structure analysis.

This projects objectives include:

• Kinetics of growth. Certain systems with QSE exhibit anomalously fast aggregation kinetics, i.e. deposited atoms assemble very quickly into islands. We study and model the “window” in temperature and coverage parameter space where QSE-driven  self organization is possible. These data are modeled to extract the controlling barriers. This understanding will be used to search for other systems where height uniformity exists. 
• QSE and chemisorption. We test the effect of QSE on chemisorption in several systems, using both experiment (STM/STS, XPS, HRLEED) and theory. These systems include oxygen and hydrocarbons on Ag nanostructures on Si(111); and oxygen and hydrogen on Pb and Mg nanostructures.