Crystallographic Disorder in Surfaces and Thin Films

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9304912 Lagally The proposed effort aims to combine scanning tunneling microscopy (STM) with diffraction techniques to investigate diffusion, interactions with steps, initial film formation, and a number of other aspects of the kinetics and thermodynamics of film formation. Measurements are planned both in real time and in a quench-and-look mode. Epitaxial, Stranski-Krastanov, and Volmer-Weber systems will be investigated. From a combination of theoretical and experimental effort, quantitative values of energies, barriers, and rates will be extracted. Systems include Si, Ge, and a number of metals on SI(001) substrates. Stress effects will be investigated using also Si whiskers as substrates. Because in STM measurements the electric field from the tip may influence rates of kinetic mechanisms, a comprehensive investigation of this phenomenon will be undertaken. %%% In this research diffraction methods and scanning tunneling microscopy are used to investigate atomic scale mechanisms involved in film growth. These mechansisms all have some sort of morphological or microstructural consequence. An analysis of the changing morphology can be interpreted in terms of the responsible mechanisms. There are in principle two ways of doing this: 1) real-time measurements or 2) quench-and-look measurements. In the former, one attempts to follow the changing positions of atoms or the shape and size of particular structures. The latter is effectively a series of snapshots of the morphologies that are frozen in at different times. The proposed work is important because crystal growth is at the basis of all thin-film technology. ***