| AVS 64th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology Division | Thursday Sessions |
| Session NS+SP+SS-ThA |
| Session: | Advances in Scanning Probe Microscopy |
| Presenter: | Georg Ramer, NIST Center for Nanoscale Science and Technology / University of Maryland |
| Authors: | G. Ramer, NIST Center for Nanoscale Science and Technology / University of Maryland J. Chae, NIST Center for Nanoscale Science and Technology / University of Maryland S. An, NIST Center for Nanoscale Science and Technology / University of Maryland V.A. Aksyuk, NIST Center for Nanoscale Science and Technology A. Centrone, NIST Center for Nanoscale Science and Technology |
| Correspondent: | Click to Email |
Photothermal induced resonance (PTIR) - a hyphenated technique of optical spectroscopy and scanning probe microscopy - allows to perform chemical imaging at nanoscale resolution [1,2]. The signal generation in PTIR consists of illuminating the sample with a pulsed tunable laser and transducing the local thermal expansion using a conventional AFM tip. The rapid expansion of the sample induces a ring down motion in the cantilever with amplitudes proportional to the absorption coefficient. Absorption images can be collected by moving the AFM tip across the sample, local absorption spectra can be collected by keeping the tip still and tuning the laser. PTIR works at ambient conditions and is non-destructive, making for a wide range of possible applications.
PTIR has been successfully applied to range of different samples, from life sciences, to photonics, material science and quality control [1,2]. Recently, PTIR sensitivity down to a monolayer has been demonstrated by using optical field enhancement between a gold tip and gold substrate as well as a mechanical enhancement by resonant excitation of the AFM cantilever.
Here, we present latest advances in improving the sensitivity of PTIR. Our novel AFM tips based on a nanosized picogram scale micromechanical cantilever as a displacement sensor and an optical resonator based near field read out achieve a thermal noise limited deflection measurement in the low fm Hz-0.5 range. Through the high sensitivity and low noise detection of these new probes we obtain PTIR spectra of monolayer samples with high signal to noise ratio, without the need for optical field enhancement or resonant excitation.
Furthermore, low detection noise across the large bandwidth achieved by these probes enables the direct measurement of the sample thermal expansion dynamics after each laser pulse. Leveraging a simple model, the fitting of the thermal expansion dynamics yields the local thermal conductivity at unprecedented, nanoscale lateral resolution.
1 Centrone, A.: ’Infrared Imaging and Spectroscopy Beyond the Diffraction Limit’, Annual Review of Analytical Chemistry, 2015, 8, pp. 101-126
2 Dazzi, A., and Prater, C.B.: ‘AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging’, Chem Rev, 2016