Design and Implementation of Hyperdimensional Scanning Tunneling Microscopy

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Shaowei Li of the University of California, San Diego is developing a method to measure how electrons move and molecular vibrations change as a function of both space and time when excited by short laser pulses in molecules and two-dimensional materials. These low-dimensional systems exhibit unique dynamics that are sensitive to nanoscale chemical variations, which are difficult to observe using existing microscopic techniques. The Li group is developing a new microscopy called hyperdimensional scanning tunneling microscopy (HD-STM) to study these materials with Angstrom spatial resolution and femtosecond temporal resolution. This approach has the potential to uniquely reveal details about atomic-scale ultrafast dynamics and potentially enable the manipulation of these dynamics on-demand. Dr. Li will also develop a five-week summer research program for high school and undergraduate students that focuses on increasing student interest in science. Hyperdimensional scanning tunneling microscopy (HD-STM) couples STM with visible-infrared pump frequencies, THz (terahertz)-probe frequencies, and optical/photoluminescence spectroscopy to extract structure, chemical, and reactivity details about interfacial samples across a wide scale of space, time, and frequency. The Li group will work to develop this instrumentation so that electron transfer and nuclear motion in molecules and low-dimensional materials can be observed with high resolution in the space, time, and frequency domains. By coupling high resolution STM with optical spectroscopy to do high spatial resolution visible-pump THz-probe spectroscopy, there is the potential to examine chemical structure and reactivity at surfaces down to a single atom or bond, with implications for a broad range of science. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.