Our research develops nanoscale spectroscopic imaging techniques with sub 10 nm spatial resolution through deep integration of scanning probe microscopy and infrared optics.  The spectroscopy and chemical imaging at < 10 nm allow access to the nanoscale phenomena that are not possible for traditional diffraction-limited spectroscopy.

The materials that we are interested in are polymers, plasmonic/polaritonic materials, and photovoltaic materials. We hope to unravel the mysteries at the nanoscale with the tools that are developed by our group.

Below are methods that we have developed.

Peak force infrared microscopy (PFIR)


We have developed peak force infrared microscopy at Lehigh University. It is a photo-thermal based infrared microscopy technique. The imaging technique allows infrared imaging, broadband spectroscopy and mechanical property mapping with 10 nm or better spatial resolution. It works for a range of materials from heterogeneous polymers to inorganic particles.

For more information, see our recent paper: Science Advances 3, e1700255 (2017)

The peak force infrared microscopy has been utilized to characterize individual PM2.5 aerosol particles. For more information see our recent publication: Chemical Communications 53, 7397 (2017) 

We have also applied PFIR technique to study biological samples. More research is underway.

 Ultra-broadband light source for Scattering-type scanning near-field optical microscopy


Scattering-type scanning near-field optical microscopy (s-SNOM) is a microscopy based on linear light scattering. The bandwidth of the light source determines its frequency coverage. Current broadband infrared lasers from difference frequency generations are expensive. Here we developed a laser-driven plasma source that provides wide frequency coverage, high brilliance, spatial coherence, and low cost for s-SNOM.  For more information, see our recent publication in ACS Photonics.

Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling


We have discovered a way to combine low repetition rate pulsed laser with scattering-type scanning near-field optical microscopy through sampling in the phase domain. This technique opens the door to combining scattering-type scanning near-field optical microscopy with ultrafast lasers for nanoscale nonlinear and time-resolved processes at high energy regime.

Currently, s-SNOM requires either a continuous wave laser source or a high repetition rate pulsed laser. Pulsed laser sources with a repetition rate < 100 kHz are unable to be used for scattering-type scanning near-field optical microscopy due to the limitation of the sampling rate by Nyquist-Shannon sampling theorem. Our phase-domain sampling technique bypasses this limitation by acquiring near-field interaction from a different and equivalent perspective.

For more information, see our paper: Nature Communications 7, Article number: 13212 (2016) doi:10.1038/ncomms13212

Scattering-type scanning near-field optical microscopy with reconstruction of vertical interaction


Despite the high lateral spatial resolution, conventional scattering-type scanning near-field optical microscopy does not provide simple access to the vertical characteristics of near-field interactions.

We have developed a technique to obtain the vertical interaction characteristics of tip-sample near-field interaction. It is done through reconstruction of near-field response with metric optimization. Three-dimensional tip-sample interactions mapping can be achieved through s-SNOM with this method.

For more details see Nat. Commun. 6:8973 doi: 10.1038/ncomms9973 (2015) and AIP Advances 7, 055118 (2017).