Measuring chemical composition, optical and thermal properties at the nanoscale with AFM probes

Session

Nanoscale Probing of Physical Properties via AFM & SPM

Authors

Dr Andrea Centrone (1)

Affiliations

1. National Institute of Standards and Technology

Keywords

AFM-IR, PTIR, optomechanics, nanoscale composition, nanoscale thermal conductivity, interfacial thermal conductance

Abstract text

Photothermal induces resonance (PTIR) [1,2,3], also known as AFM-IR, is a scanning probe technique that uses the tip on an AFM to transduce the sample photothermal expansion and measure IR (or visible) spectra at the nanoscale. In practice, conventional AFM probes are kicked into oscillation (like a struck tuning fork) with amplitude proportional to the absorbed energy and to the sample absorption coefficient. This way PTIR enables identification and mapping of the sample composition, molecular conformation, and bandgap at the nanoscale. However, conventional AFM probes do not have sufficient sensitivity or bandwidth to capture the fast sample thermalization linked to the sample thermal conductivity (η) and interfacial thermal conductance (G). Measuring η and G at the nanoscale is critical for engineering thermoelectrics, advanced electronics and for studying thermal transport. Time-domain thermoreflectance (TDTR) is a pump-probe technique that measures η and G by reconstructing the sample time-domain photothermal expansion as a function of the probe delay time. However, the spatial resolution of conventional TDTR is limited to the micrometer scale and requires long measurement times (≈120 s per pixel).   

In this talk, I will introduce the PTIR working principles and measurements modalities,[1,2,3] followed and a few representative chemical imaging characterization examples, including on 2D materials and on single polypeptides aggregates in water. Next, I will discuss recent critical advances in my lab that increase the sensitivity, throughput, and time resolution of the PTIR technique many folds.[4,5]   

Specifically, I will introduce new optomechanical nanosized AFM cantilever probes,[4,5] developed at NIST, and a customized PTIR setup that captures the entire, time-domain, thermal expansion dynamic of the sample with high spatial (≈ 10 nm) and temporal (≈ 4 ns) resolutions, thanks to a very low detection noise (≈ 1 fm/Hz^1/2) over a wide (> 100 MHz) bandwidth. This setup enables measuring IR spectra and nanoimaging of composition, η and G with a throughput ≈ 6000× faster (20 ms per pixel) than macroscale-resolution TDTR and ≈ 500000× faster than PTIR ringdown measurements with conventional AFM cantilevers. As a proof-of-principle demonstration, we obtain 100×100 pixels maps of η and G in 200 s with a small relative uncertainty (5%) on a ≈ 3 µm wide polymer particle and measure IR spectra of a molecular monolayer [3]. This work paves the way to study composition along fast thermal dynamics in materials and devices with nanoscale resolution. Finally, I will discuss why the high resonance frequency (10 MHz) of the optomechnical probe developed here is ideal for obtaining IR spectra and images with improved spatial resolution.[6]

References

[1] Centrone, A., Infrared Imaging and Spectroscopy Beyond the Diffraction Limit, Annu. Rev. Anal. Chem. 2015, 8 (1), 101-126.

[2] Kurouski, D. ; Dazzi, A; Zenobi, R. ; Centrone, A, , Infrared and Raman chemical imaging and spectroscopy at the nanoscale, Chem. Soc. Rev., 2020, 49, 3315-3347.

[3] Schwartz, J.J., Jakob D.S., Centrone A., A guide to nanoscale IR spectroscopy: resonance enhanced transduction in contact and tapping mode AFM-IR Chem. Soc. Rev., 2022, 51, 5248-5267.

[4] Chae, J, et al, Nanophotonic Atomic Force Microscope Transducers Enable Chemical Composition and Thermal Conductivity Measurements at the Nanoscale Nano Lett. 2017, 17, 5587–5594.

[5] Wang M, et al. High Throughput Nanoimaging of Thermal Conductivity and Interfacial Thermal Conductance Nano Lett. 2022, 22, 11, 4325–4332

[6] Schwartz, J.J., Pavlidis G.,, Centrone A., Understanding Cantilever Transduction Efficiency and Spatial Resolution in Nanoscale Infrared Microscopy, Anal. Chem. 2022, 94, 38, 13126–13135