Event

Title: Peak Force Infrared Microscopy for Chemical Imaging and Spectroscopy at < 6 nm Spatial Resolution With Correlative Mapping on Mechanical and Electrical Properties

Abbe’s diffraction limit set a boundary to the spatial resolution of optical microscopy and laser spectroscopy and prevents easy access to the nanoscale. Spectroscopic characterizations and chemical identifications become difficult when their characteristic features are below 100 nm. In this presentation, I will describe a new type of atomic force microscopy (AFM) developed in my research group that achieves label-free infrared microscopy spectroscopy at < 6 nm spatial resolution. The peak force infrared (PFIR) microscopy detects the transient photothermal mechanical responses of the sample due to laser pulse illumination and measure signal that is proportional to the infrared absorption. We demonstrate chemical sensitive imaging and nano-spectroscopy with PFIR on a range of samples across many disciplines. Nanophase separations of the block copolymers are mapped by their chemical identities. Disorders of secondary structures of amyloid fibrils are revealed by PFIR spectra. Secondary organic aerosols are identified by the presence of oxidized chemical compositions at the nanoscale. Zymosan particles from yeast are imaged to reveal the peptidoglycan and embedded proteins. Chemical compositions of organic matters in the source rock of oil shale are obtained in situ. Phonon polaritons of hexagonal boron nitride are revealed by PFIR in polaritonic nanostructures. We have demonstrated a consistent spatial resolution of 6 nm and found the detection limit on the zeptomole level of infrared oscillators. In addition, PFIR also provides complimentary mechanical property mapping simultaneously with the infrared responses for correlative measurement. The types of organic matters in oil shale is found to correlate with the moduli of the surrounding inorganic matrix. Further extension of the PFIR microscopy also includes combination with simultaneous Kelvin probe force measurement on surface work functions of materials, providing correlative chemical and electrical information at < 10 nm spatial resolution.  The PFIR microscopy provides a new platform for correlative measurement to decipher the relationships among compositions, structures, and functions of materials.

Biography

Dr. Xiaoji Xu established his research group since 2014 as an assistant professor in the Department of Chemistry at Lehigh University in Bethlehem, Pennsylvania. Before at Lehigh University, he was a postdoctoral fellow at the University of Toronto (2012-2014) and University Colorado Boulder (2009-2011). He received his B.S. in Chemistry from Peking University in 2004 and Ph.D. from The University of British Columbia, Vancouver, Canada in 2009. His current research focuses are on nanoscale chemical imaging, laser spectroscopy, and development of new analytical instrumentation for chemical and material measurement. He holds several patents and patent applications on nanoscale AFM-based infrared microscopy. Dr. Xu was featured as one of Emerging Investigators by Chemical Communications in 2017. He was selected as a Beckman Young Investigator by Arnold and Mabel Beckman Foundation in 2018. He is also a recipient of the NSF CAREER award in 2019.