New Epitaxial Nanostructures in the Limited Adatom Mobility Regime

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Technical: The thesis of this research is that by reducing ad-atom mobility during epitaxial growth, formation of new localized nanostructures are possible. The approach focuses on the GeSi/Si system, although fundamental mechanisms uncovered may be transferable to other systems. Under study is how growth conditions determine kinetically limited local formation of islands as a function of strain. Kinetic parameters will be explored for molecular beam epitaxy (MBE) and chemical vapor deposition growth methods. The project is collaborative including researchers at national laboratories, enabling access to unique instruments and methods. Both continuum and atomistic modeling is coupled to experiment to predict where in growth parameter space, and why, such assembly of new kinetically limited nanostructures might be expected. Another focus is on understanding initial surface perturbations that lead to localized islanding. Combined in-situ microscopy and deposition techniques based upon scanning tunneling microscopy (STM) and low energy electron microscopy (LEEM) systems will be employed to study the early stages of morphology evolution and to determine controlling factors. Once fundamental behavior is understood, the controlling factors will be utilized to achieve novel device structures. This includes control of size, composition, and lateral positioning of the nanostructures. To control positioning, a focused ion beam (FIB) will be employed for creating initial perturbation sites in pre-defined substrate locations, both in-situ and ex-situ to deposition/imaging. Non-technical: This project builds upon previous work on a complex nanostructure, the Quantum Dot Molecule, that forms under kinetically limited growth conditions in the GeSi/Si system. Such nanostructures may be relevant to novel quantum dot based device architectures. Thus this research could lead to advances in fundamental knowledge of thin film growth and potential building blocks of novel nanoelectronic device structures. This interdisciplinary project and the related collaborations provide graduate students with opportunities to work closely with researchers at national labs and other institutions in a field at the cutting edge of materials research. Also special opportunities are provided for undergraduate research experience, including extension of a MS transfer program for students from Longwood University in Virginia. Additional outreach activities include development of a website aimed at informing the general public about materials science research.