Areas of Research

Energy and Charge Exchange for Singly and Multiply Charged Ions

The exchange of energy and charge between ions and target materials (single atoms, molecules, or extended surfaces/solids) is an area of fundamental interest that impacts many fields. For example, the interaction of multiply charged ions with the gases present in stellar environments provides clues about star formation that are relevant to astrophysics and astrochemistry. Furthermore, by developing a fundamental understanding of these processes we can engineer methods to harness the 'potential' of multiply charged ions in standard industrial and applied environments such as thin film growth and radiobiological medicine. In our research, we pursue problems of energy/charge exchange by carrying out absolute and relative cross section measurements using a homebuilt gas jet nozzles and gas cells. In these experiments, a multiply charged beam of ions is fired in a direction orthogonal to a gas jet or cell. X-rays that arise from interactions with the gas are detected and analyzed to determine the particular angular momentum states into which the electrons are transferred. Additionally, a position-sensitive ion detector placed beyond the gas interaction region allows us to determine the distribution of charge states that arise in the beam due to its passage through the gaseous target and its capture of electrons from within that target.

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Tracking Ion Radiation Effects Using Multilayer Devices

Radiation effects testing on devices found its start when high-altitude nuclear detonation tests in the early 1960s led to the failure of a communications satellite, Telstar I. The onboard transistors of this satellite had their operational characteristics altered by the increased radiation from the detonations, and the result was decades of intense study into radiation effects within the semiconductor industry. In our research, we study energy and charge loss effects when singly and multiply charged ions interact with electronic materials imbedded within metal- and semiconductor-based electronic devices. For singly charged ions, the deposition of energy below the surface of electronic materials has been extensively studied at high energies (> 10keV), and computer programs like SRIM can reliably calculate the energy loss functions, or stopping powers, under these conditions. At low energies (< 10keV), however, experiments can be difficult to perform and both data and theoretical predictions are sparse in this regime. Similarly, for multiply charged ions, where both potential and kinetic energy are dissipated, minimal data or predictions exist across all energetic regimes. This is due to lack of access to these ions and because the mechanism of energy dissipation for these ions is inherently complex. For example, charge exchange with the device or material target can begin well above the surface (classical-over-the-barrier-model) and can produce large numbers of secondary electrons and x-rays. As the ions go below the target's surface their energy is lost to both the nuclei and the electronic system of the target. Using multilayer devices, we have demonstrated that this subsurface energy deposition can be tracked via changes in the electrical properties of the device (capacitance-voltage and current-voltage characteristics). This represents a new method for probing energy deposition and we continue to expand it to include different materials and device architectures.

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