Heat transfer at nanoscale contacts investigated with scanning thermal microscopy

This article investigates heat transfer at nanoscale contacts through scanning thermal microscopy (SThM) under vacuum conditions. Measurements were performed using two types of resistive SThM probes operating in active mode on germanium and silicon samples. The experiments measure the heat transfer through the nanoscale point contacts formed between the probe apex, platinum-rhodium alloy, or silicon nitride depending on the probe used, and the samples. The thermal resistance at the probe apex-sample interface becomes extremely important as the contact size becomes smaller or comparable to the phonon mean free path within the materials in contact. This resistance is derived from the measurements using a nanoconstriction model. Consistent to what is expected, the interfacial thermal resistance is found to be dependent on the tip and sample. Assuming perfect interfaces, the thermal boundary resistance Rb is determined for the different contacts. Results obtained for Rb range from 10−9 m2 K W−1 up to 14 × 10−9 m2 K W−1 and have the same order of magnitude of values previously published for other materials. The determination of the averaged phonon transmission coefficient t from the data is discussed, and coefficients t for the Si3N4/Ge and Si3N4/Si contacts are estimated based on the diffuse mismatch model (tSi3N4/Ge = 0.5 and tSi3N4/Si = 0.9).
Studying the heat transfer at nano-sized contacts and within nanostructures is crucial for different related industrial applications.1–6 The thermal resistance at interfaces is necessary parameters to optimize the performance of systems in several technologies where nano/micrometric-sized components are used, such as microelectronics, including molecular junctions3,4 and nanocomposites thermal interface materials.5,6 From a fundamental point of view, understanding the thermal transport between two solids is important when the dimensions for the zones of thermal contact become comparable to the mean free path of the heat carriers of the materials in contact. Only a few experimental results are available to date, where thermal interface resistances at the nanoscale were determined.7–10
Scanning Thermal Microscopy (SThM) is one of the main tools for heat transfer analysis at submicron scales.11,12 In this work, measurements under vacuum conditions were performed using two types of SThM probes. The values of the thermal resistance at the solid-solid contact are determined. Based on these values, the thermal boundary resistance for different contacts is derived, and the phonon transmission coefficient is estimated in specific cases.
Our SThM method is an Atomic Force Microscopy (AFM)-based technique. Two commercialized resistive SThM probes were used: (1) the Wollaston wire probe and (2) the Kelvin NanoTechnology (KNT) probe. Figure 1 shows scanning electronic microscopy (SEM) images of the two probes.

Assy, A., & Gomès, S. (2015). Heat transfer at nanoscale contacts investigated with scanning thermal microscopy. Applied Physics Letters, 107(4), 043105.

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