Ion beams: creating functionalities and probing interfaces in materials

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The central theme of my proposed research is unravelling the mystery of materials on the electronic level, with focus on quantum structures and other nanoscale materials, with the electronic properties modified from their bulk analogues. My group studies atomic-scale behavior of semiconductor quantum dots (QD) with emphasis on their interfaces. Advanced fabrication methods such as ion beam modification (IBM) and molecular beam epitaxy (MBE) combined with nanofabrication are used. Surface and interface characterization tools with sub-nanometer depth resolution, and the atomic lateral resolution as well as time-domain optical spectroscopy are employed. Three major themes will be pursued in the next five years: 1. Semiconductor quantum structures: interplay of quantum confinement, interface and defect states. We have established expertise in the fabrication of silicon QDs using ion beams and will further explore the difference in optical and electronic properties of these systems when doped. We are interested in the interactions of photons (visible or X-ray) with these QD assemblies studied using photoluminescence (PL), time-resolved PL and X-ray excited optical luminescence (XEOL). Special effort will be given to characterization of the QDs/matrix interfaces and description of the transport properties using various transport models. These studies will be extended to device response under non-equilibrium conditions, e.g., with applied voltage or under illumination. The results of this work will have immediate impact on semiconductor science and technology, light-emitting structures and the future generation of ultra-fast devices for signal transmission and processing. 2. Plasmonic effects. Our goal is to achieve controllable plasmonic responses for metal nanoparticles (Al, Au) and non-metal group IV plasmonic systems. By using MBE and IBM, we will design and fabricate plasmonic structures that will be optimized to operate in the UV/visible and short wavelength IR range. We will focus on the following key questions. Can plasma frequency be controlled through MBE growth combined with nanofabrication and IBM? What are the effects of geometry on plasmonic structures? How to better control the confined modes? The outcome of these studies will be applicable in quantum and chemical sensing. 3. Ultra-high resolution ion depth profiling and in-situ capabilities. We will focus on in-situ application of high-resolution ion beam analysis to electrochemical processes. New in-situ devices will be designed and employed to study the mechanisms of passive film growth on metals, corrosion in multilayer metal structures and interface effects in Li- and Na-ion batteries. New designs of in-situ cells give us opportunities to perform high-resolution depth analysis while cycling the electrochemical cells. An improved understanding of reaction mechanisms will lead to higher performance of electrodes, better passive films, more advanced corrosion protection.