Graduate Student Qing Zie

"Expanding Infrared Information at Nanoscale: From Multi-Color Imaging to Broadband and Multi-dimensional Nanospectroscopy"

Infrared (IR) spectroscopy provides label-free determination of molecules and materials. However, it is constrained by Abbe’s diffraction limit, which limits tiny feature resolvability to incident light wavelength. Many nanomaterials and biological objects have significantly smaller spatial features than IR spectroscopy can resolve. The use of atomic force microscopy (AFM) in conjunction with IR radiation is an effective way to overcome this limitation. The fast-growing AFM-based IR technology avoids the diffraction limit to image at the nanoscale.1-2 However, it suffers from the major limitation that only one IR frequency can be scanned at a time. To tackle this challenge, we developed a dual-color peak force infrared (PFIR) microscopy technique that allows for the simultaneous imaging of two IR frequencies at the nanoscale level in a single AFM scan.3 This method eliminates AFM frame drift and distortion when comparing multiple infrared images. It enables simultaneous nondestructive chemical nanoimaging of multiple chemical components and can be beneficial for applications such as in situ dual-channel monitoring of chemical processes. Based on this idea, we later introduced dual-frequency peak force photothermal microscopy.4 IR and visible information are provided simultaneously for nanoscale chemical distribution and energy dissipation mapping at the surface.

Moving to a broadband laser source, we developed a Fourier transform AFM-IR technique with PFIR and broadband femtosecond IR pulses.5 Through a Fourier transform, we demonstrated it is possible to retrieve IR absorption spectra from the photothermal detection of broadband IR absorption by an AFM tip on a polymer mixture and hexagonal boron nitride. Our work revealed the feasibility of time-domain detection of the AFM-IR signal in the mid-IR regime and paves the way toward multiphoton vibrational spectroscopy below the diffraction limit. Further, we developed time domain AFM-based two-dimensional (2D) IR nano-spectroscopy for the first time.6 This technology integrates the current research horizon of 2D IR spectroscopy with AFM-IR, allowing rich spectroscopic data to be gathered locally on a heterogeneous sample surface under super spatial resolution. The AFM-based 2DIR allows for in situ examinations of vibrational anharmonicity, coupling, and energy transfers in materials and nanostructures, making it particularly effective for understanding the relaxation dynamics at the IR range in 2D materials.

References:
1. Xie, Q.; Xu, X. G., What Do Different Modes of AFM-IR Mean for Measuring Soft Matter Surfaces? Langmuir 2023, 39 (49), 17593-17599.
2. Wang, H.; Xie, Q.; Xu, X. G., Super-resolution mid-infrared spectro-microscopy of biological applications through tapping mode and peak force tapping mode atomic force microscope. Advanced Drug Delivery Reviews 2022, 180, 114080.
3. Xie, Q.; Wiemann, J.; Yu, Y.; Xu, X. G., Dual-Color Peak Force Infrared Microscopy. Analytical Chemistry 2022, 94 (2), 1425-1431.
4. Xie, Q.; Wang, H.; Xu, X. G., Dual-Frequency Peak Force Photothermal Microscopy for Simultaneously Spatial Mapping Chemical Distributions and Energy Dissipation. The Journal of Physical Chemistry C 2022, 126 (19), 8393-8399.
5. Xie, Q.; Xu, X. G., Fourier-Transform Atomic Force Microscope-Based Photothermal Infrared Spectroscopy with Broadband Source. Nano Letters 2022, 22 (22), 9174-9180.
6. Xie, Q.; Zhang, Y.; Janzen, E.; Edgar, J. H.; Xu, X. G., Atomic Force Microscopy-Based Time-Domain 2D Infrared Nanospectroscopy. Nature Nanotechnology 2024, accepted.