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>Scanning probe microscopy studies of the highly strained epitaxy of indium arsenide on gallium arsenide(001) and scanning probe based imaging and manipulation of nanoscale three-dimensional objects.
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Scanning probe microscopy studies of the highly strained epitaxy of indium arsenide on gallium arsenide(001) and scanning probe based imaging and manipulation of nanoscale three-dimensional objects.
This Dissertation contributes to three mainstream areas of current research: (a) the nature of two-dimensional (2D) to three-dimensional (3D) morphology change in the highly strained epitaxy of InAs on GaAs(001) and the formation and evolution of the InAs nanoscale 3D islands, (b) the understanding of scanning tunneling microscope (STM), and contact- and noncontact atomic force microscope (C-AFM and NC-AFM) imaging of nanoscale 3D islands/objects, and (c) the direct manipulation of nanoscale 3D objects in air, and at room temperature, using the NC-AFM.; A remarkable re-entrant behavior of the 2D → 3D morphology transition in InAs/GaAs(001) is found in which small quasi-3D (Q3D) clusters of heights 2–4 monolayers (ML) act as a kinetic pathway towards InAs 3D (>4 ML high) island formation. The 2D → 3D transition is gradual, with a varying material transfer between the 2D and 3D features. The 3D islands exhibit a tendency towards lateral size (and to some extent, volume) equalization with increasing InAs delivery, &thetas;. The combined STM/AFM results point to models for 3D island formation (from small Q3D clusters) and for 3D island evolution, that reveal the importance of various kinetic processes. Growth condition dependence of the InAs 3D morphology reveals the significance of kinetic processes such as arsenic incorporation and interplanar and intraplanar In migration.; Some similarities and significant differences are found between in-situ UHV C-AFM, STM, and NC-AFM images of InAs nanoscale 3D islands. In particular, NC-AFM images show a remarkable contrast-reversal of the images of 3D nanofeatures. This behavior is partly attributed to a feedback instability related to the tip-sample interaction force gradient curve, based on our simple model of NC-AFM imaging. We find that the differences in the STM/C-AFM/NC-AFM images can be reconciled with the corresponding mechanism(s) of operation of the microscopes.; Finally, we have developed protocols for nanomanipulation using the NC-AFM and demonstrate the first direct and controlled manipulation of nanoparticles (of gold) as small as 5 nm in diameter, in air and at room temperature using the NC-AFM. We also show how simple experiments based on variation of the manipulation window can provide much information on the manipulation mechanism and tip-sample-substrate interactions.
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