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In-situ transmission electron microscopy studies of dislocations in thin film systems

Abstract

In-situ transmission electron microscopy of thin films systems provides an ideal experimental laboratory for the study of dislocation motion and dislocation defect interactions in materials. Through careful consideration of the sample geometry and calibration of the experimental conditions it is possible to obtain accurate quantitative information about dislocation velocities, interaction stresses and overall strain relaxation behavior. A model materials system for studies of dislocation behavior is heteroepitaxial SiGe layers grown on Si substrates. In this case the difference in lattice parameter between the layers results in mismatch strains and stresses whose magnitude can be directly controlled by the choice of germanium concentration and sample thickness. During growth and annealing within the microscope, dislocations nucleate and grow in order to relieve this mismatch strain. Quantitative observations of the interaction between moving threading dislocations and other interfacial misfit dislocations will be presented. These observations are amenable to direct comparison with mesoscale modeling of dislocation dynamics, and we will discuss in particular the interplay between experimental observation and computational modeling that has lead to understanding of the important phenomenon of reactive blocking in heteroepitaxial strain relaxation. Additionally, it is possible to use thermal mismatch strains to move dislocations through thin films. Results from in-situ thermal cycling of sputter-deposited aluminum films grown on silicon-on-insulator wafers will also be discussed. Use of selective etching techniques permits observation of free standing Al/Si layers in-situ, allowing one to identify the dislocation mechanisms that control strain relaxation in these films. These observations can be correlated with direct measurements of strain relaxation made by wafer curvature and bulge testing techniques, providing an important cross-link with other experimental methods

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