Cold Plasma Cathode for High Resolution Condensed Matter Electron Spectroscopy

STATEMENT OF THE PROBLEM Many of the quantum phenomena most relevant to ongoing research in nanotechnology and microelectronics occur at a spatial scale of nanometers and an energetic scale of 100 µeV. This unique combination makes them extremely difficult to study experimentally. Most existing methods of spectroscopy can reach either the spatial or energetic resolution but not both. In other cases, like X-ray spectroscopy, the probe particle has such low interaction cross-sections that many nanostructures cannot be effectively studied. Improvements on existing spectroscopy methods are needed to support ongoing computing and semiconductor research. TECHNICAL APPROACH A cold plasma cathode (CPC) is proposed to extend the energy resolution of electron energy loss spectroscopy (EELS), which has nanometer spatial resolution, to the 100 µeV level. CPC is based on the continuous, shaped, two-photon ionization of alkali gas in molecular flow. The ionization of low-density gas by narrow bandwidth laser allows for a near-uniform emission process. The shaping of the plasma to a quasi-2D region by controlling laser optics leverages nonlinear space-charge behavior to limit scattering, achieving, in particle-tracking simulations, an energy spread of ˜1 µeV/pA. PHASE I PLANS The Phase I project aims to develop a prototype CPC. In this proposal, an alkali gas source, laser system, and accelerating plate setup will be constructed using the precision machining capability and vacuum infrastructure at RadiaBeam. Extraction of charges from shaped ionization regions will be demonstrated, by controlling the path of the lasers and the gas, and characterized to compare with simulation results. Further computational studies on the geometric dependence of space-charge effects in a cold plasma cathode will be performed. Phase II subsystems, such as an appropriate energy resolution characterization system will be designed. In Phase II, an ultra-high resolution EELS beamline will be constructed with the CPC as its electron source. COMMERCIAL APPLICATIONS AND OTHER BENEFITS The program results will yield a prototype cold plasma cathode that will enable EELS at a previously inaccessible energy resolution for both academic and commercial condensed matter physics research. Among other things, it can be used to further understand quantum materials, superconductors, and semiconductor nanostructures. In addition to aiding nanotechnology and microelectronics research, the improved EELS capability will support research in material science, surface chemistry, and even structural biology.