The objectives of this project are to conduct research on break-through sub-surface structural defect characterization based on laser-coupled scanning probe photothermal concept to achieve depth profiling with nanoscale spatial resolution. The proposed sub-surface characterization features nanoscale spatial resolution using frequency-modulated near-field laser focusing and thermal expansion sensing. Research will be carried out to study the physical phenomena in sub-surface characterization, including near-field laser focusing, nanoscale heating, thermal transport, and elastic surface displacement. A physical model will be developed for dynamic surface displacement under periodical nanoscale laser heating.
Upon accomplishment, the proposed research will open a new compelling way for sub-surface structural defect characterization with nanoscale spatial resolution while most of the existing scanning probe technologies are for characterizing surface properties. The surface displacement sensing in the proposed characterization takes advantage of the atomic force acoustic mechanism and features fast response. By varying the modulation frequency of the laser beam incident on the scanning probe tip, we will be able to vary the characterization length and diagnose sub-surface defect of different depth. Furthermore, deliverables will include a comprehensive physical model to interpret the characterization data to obtain quantitative information about the size and depth of structural defect. The strong capability of the proposed sub-surface characterization will make it have broad applications in structural diagnostics of nanostructured materials and evaluation of sub-surface structure in nanoscale material processing. Results of the proposed research will be disseminated through broad publications. Furthermore, the research results will be integrated into new course development and conventional class teaching at Iowa State University. Extensive undergraduate participation via summer research will be arranged. Outreach services to K-12 students will be facilitated through the ESPP program of Iowa State University.
