While Abbe’s optical diffraction limit prevents nanometer-scale spatial resolution for conventional microscopy and spectroscopy, the combination of optics and scanning probe microscopy provides a way to bypass the diffraction limit. One type of imaging technique is to utilize the near-field light scattering from a metallic AFM tip to locally probe the optical properties of the sample. The other type of high spatial resolution imaging technique is to measure the light-induced thermal expansions in the sample and related that to the local optical or infrared absorption. In the presentation, I will first describe our recent development of the scattering-type infrared near-field microscopy for three-dimensional mapping of near-field responses1 and a route to incorporate scattering-type infrared near-field microscopy with ultrafast lasers.2 Then, I will present our latest invention of peak force infrared (PFIR) microscopy that provides infrared imaging, broadband spectroscopy, and mechanical property mapping at a spatial resolution as high as 6 nm.3 In the end, I will describe applications of PFIR microscopy on the characterization of urban aerosols (particulate matter PM2.5)4 as well as the characterization of biological samples. The exploration of nanoscale phenomena will be facilitated by these nanoscale infrared imaging techniques in revealing hidden secrets of the nanoworld. References:

1.Wang, L.; et al., Nature Communications 2015, 6, 8973. 2.Wang, H.; et al., Nature Communications 2016, 7, 13212. 3.Wang, L.; et al., Science Advances 2017, 3 (6), e1700255. 4.Wang, L.; et al., Chem Commun 2017, 53 (53), 7397-7400.