Laser heating of scanning probe tips for thermal near-field spectroscopy and imaging

Abstract

Spectroscopy and microscopy of the thermal near-field yield valuable insight into the mechanisms of resonant near-field heat transfer and Casimir and Casimir-Polder forces, as well as providing nanoscale spatial resolution for infrared vibrational spectroscopy. A heated scanning probe tip brought close to a sample surface can excite and probe the thermal near-field. Typically, tip temperature control is provided by resistive heating of the tip cantilever. However, this requires specialized tips with limited temperature range and temporal response. By focusing laser radiation onto AFM cantilevers, we achieve heating up to ∼1800 K, with millisecond thermal response time. We demonstrate application to thermal infrared near-field spectroscopy (TINS) by acquiring near-field spectra of the vibrational resonances of silicon carbide, hexagonal boron nitride, and polytetrafluoroethylene. We discuss the thermal response as a function of the incident excitation laser power and model the dominant cooling contributions. Our results provide a basis for laser heating as a viable approach for TINS, nanoscale thermal transport measurements, and thermal desorption nano-spectroscopy.

Apparent Spectral Shift of Thermally Generated Surface Phonon-Polariton Resonance Mediated by a Nonresonant Film

“…Near-field thermal spectroscopy, a promising method for characterizing near-field thermal spectra [27][28][29][30][31][32][33][34], also involves dissimilar materials. In this paradigm, a probing tip is brought within a sub-wavelength distance from a sample.…”

Spectral redshift of the thermal near field scattered by a probe

“…The collected signal is interpreted as a measurement of the spectral near-field energy density of the heat source. However, all near-field thermal spectroscopy experiments performed with heat sources supporting SPhPs in the infrared (SiC, silicon dioxide, hexagonal boron nitride) have reported resonance redshifts of varying magnitude, from ~ 5 cm -1 to ~ 65 cm -1 , using probing tips made of intrinsic Si [19,21], tungsten [20] and platinum-iridium [22]. The mechanism causing SPhP resonance redshift, experimental or physical, is still unclear.…”

Measurement of near-field thermal emission spectra using an internal reflection element

“…The measured peaks using this technique are redshifted (from 3 cm -1 to 63 cm -1 ) and broadened relative to the theoretical predictions using the fluctuational electrodynamics [48][49][50][51][52][53][54]. It is shown experimentally [51], and theoretically [54], that the spectral redshift and broadening of the peaks are strongly dependent on the geometry of the probe.…”

“…Measuring the spectrum of near-field thermal emission is challenging because the evanescent waves in the near-field need to be converted to propagating waves to reach a Fourier-transform infrared (FTIR) spectrometer located in the far zone. So far, the SPhP modes of near-field thermal emission have been measured for silica [48,49], quartz [50], silicon carbide (SiC) [48,[50][51][52], and for a thin film of hexagonal boron nitride (hBN) on gold and silica substrates [52]. The frustrated total-internal-reflection modes thermally emitted by polytetrafluoroethylene (PTFE) have also been measured [50,52].…”

“…Most of the measured near-field spectra are obtained using scanning optical microscopes [48,[50][51][52]. In this spectroscopic technique, the thermal near field of an emitting sample is scattered to the far zone by bringing the sharp tip of the microscope to a sub-wavelength distance from the sample.…”