Peak Force Infrared Microscopy

Peak force infrared (PFIR) microscopy is a new infrared imaging technique developed in Dr. Xu’s lab at Lehigh University in collaboration with an industrial partner. The PFIR microscopy measures the photo-thermal expansion of the sample with an atomic force microscope (AFM) operated in the peak force tapping mode or pulsed force mode. PFIR can operate in both air and fluid phase. 

For more information, please see our first paper Science Advances 3, e1700255 (2017)

 For the multiple pulse excitation PFIR, please see our paper Advanced Optical Materials 1901084 (2019).

 For total internal reflection geometry of PFIR, please see our paper Analytical Chemistry  93, 2, 731–736 (2020) .

 For PFIR microscopy in the fluid phase , please see our paper Analytical Chemistry 93, 7, 3567 (2021)  and Nano Letters 20, 5, 3986 (2020).

We are open to research collaborations on the applications of the PFIR microscopy, please contact


In PFIR, the atomic force microscope is operated in the peak force tapping mode or the pulsed force mode. Infrared laser pulses illuminate the AFM tip and the sample when they are in contact and at every other peak force tapping cycle.  Consequently, the subtraction of the cantilever deflection waveforms leads to the pure response from the laser-induced photo-thermal expansion. Subsequent analysis on the photo-thermal expansions extracts mechanical signals that correspond to the infrared absorption. Figure_1.pngPFIR microscopy has two operation modes: imaging mode and spectroscopy mode. In imaging mode, the laser-induced mechanical responses are mapped when the AFM tip is scanned over the surface of the sample at a fixed infrared frequency. In spectroscopy mode, the frequency of the infrared light source is scanned at a fixed spatial location, while the photo-thermal mechanical responses are recorded.

The spatial resolution of PFIR microscopy is found to be 6 nm. Block copolymers form nanoscale phase separation. We used PFIR microscopy to reveal individual chemical compositions of PS-b-PMMA block copolymer. The spatial resolution was found to be as high as 6 nm.


PFIR microscopy provides simultaneous spectral imaging and mechanical information. The infrared image and mechanical properties (modulus and adhesion) are simultaneously collected from the same area. PFIR allows naturally correlative imaging. By placing the AFM tip at one location, PFIR microscopy also allows the collection of the infrared absorption spectrum.


In order to further improve the signal of PFIR, we also implemented a multipulse excitation configuration for PFIR. Per one peak force tapping cycle, multiple laser pulses are used to further increase the signal quality. Such an implementation is particularly good for imaging thin material, such as 2D materials.

Figure MultipulsePFIR.png

Applications of PFIR microscopy:

  1. Nanoscale polymer characterizations. For example, nanophase separation of block-copolymers.

  2. Characterization of individual PM2.5 urban aerosol particles.

  3. Characterization of organic compositions in oil shale.

  4. Characterization of organic photovoltaic domains; characterization of perovskite solar cell.

  5. Imaging biological samples, such as cell wall particles, peptide aggregates

  6. Polaritonic materials and inorganic materials

  7. Determination of exciton diffusion length in organic photovoltaics 

  8. Label-free infrared nanoscopy in the fluid phase