Scanning probe microscopy methods that provide chemical maps of the surface of objects hold promise for revealing information that is useful for making chemical reactions more efficient and developing faster electronic and optical devices. Scanning probe microscopes may one day yield chemical images of individual molecules in a variety of environments, but this potential to visualize such small objects has been stymied due to limitations associated with effectively and simply integrating the probe element into the microscope system. With support from the Chemical Measurement and Imaging Program and partial co-funding from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Zhenrong Zhang and Howard Lee at Baylor University are developing tip-enhanced Raman spectroscopy techniques that allow for imaging of individual nanometer-sized objects in their native environments, as a result of novel, integrated fiber optic probe tips made by sophisticated microfabrication methods. This new approach to building chemical imaging systems significantly simplifies microscope operation and yields a method for visualizing tiny amounts of sample. The Baylor team readily investigates chemical reactions on catalyst surfaces in gas and liquid environments. Due to the practical and accessible nature of the new nanoscale chemical imaging tool, the research may impact research in materials, biomedical, and optoelectronic sciences. Professors Zhang and Lee are providing undergraduate and technical college students new learning and research opportunities in optics and scanning probe microscopy. Such student skill sets are valuable for the students' future careers. The Baylor team is also providing broad, public education and outreach to the Waco community through frequent hands-on optics and spectroscopy events at the Mayborn Museum.
This project develops a user-friendly, tip-enhanced, Raman spectroscopy nanoscale chemical imaging system that is based on an optical alignment-free design, namely, an integrated plasmonic fiber-tip assembly. The fiber-tip assembly can be easily integrated into existing scanning probe microscope designs. This unique approach provides a simple path for independent delivery of excitation light to and collection of light from a sample, which offers high light coupling efficiency and virtually nonexistent far-field background interference. As a result, sample signals are highly sensitive and provide detection limits approaching that of single molecules. The plasmonic nanostructured optical fibers merge the fields of plasmonics and fiber optics, thereby enabling tip-enhanced Raman spectroscopy imaging applications in numerous gaseous and liquid environments. The specific objectives of this proposal are to demonstrate nanoscale mapping using fiber-tip-enhanced Raman spectroscopy imaging and study the photochemistry of molybdenum sulfide (MoS2) at the nanometer scale in a controlled ambient pressure environment. The team also seeks to demonstrate fiber-tip-enhanced Raman spectroscopy imaging in a liquid environment via the use of field-tunable plasmonic materials.
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.
