Heat transfer at nanoscale contacts investigated with scanning thermal microscopy

Abstract

International audienceThis 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 (t Si3N4 /Ge = 0.5 and t Si3N4/Si = 0.9). Heat transfer at nanoscale contacts investigated with scanning thermal microscopy (PDF Download Available). Available from: https://www.researchgate.net/publication/281550668_Heat_transfer_at_nanoscale_contacts_investigated_with_scanning_thermal_microscopy [accessed Mar 8, 2016]

Quantification of probe–sample interactions of a scanning thermal microscope using a nanofabricated calibration sample having programmable size

“…Solving probe temperature from (3) requires parameters of the probe-sample interaction system. With the probe's well-controlled geometry, the same as those used in previous work by Assy et al [3], [54] and Puyoo et al [34], [55], this model can be transferred for use when scanning the JN device. Due to its complex geometry and composition of multiple materials, the probe was split into subregions as denoted by subscript i in (3).…”

“…Furthermore, they have failed to reach agreement on the thermal contact conductance (or resistance) proposing values that range from tens to hundreds of nW/K [25,26,[30][31][32]. Recently, several groups have shown that the DMT (Derjaguin, Muller, and Toporov) model [33] is invalid for analyzing tip-sample nanoscale contact as it fails to match experimental data [3][23] [34]. As a result, recent studies tend to regard the probe's tip radius of curvature (~ 50 nm for the probes in this work [35]) as the real contact radius.…”

“…At the contact point (x = 0), heat transfers from the sample surface to the probe through the tip-surface contact with a thermal conductance defined as Gts. At the base of the cantilever, x = L, the temperature was assumed to be ambient TRT, as the silicon base is treated as a perfect heat sink in common with other studies [3,22,55]. Therefore, two boundary conditions at x = 0 and x = L are: Solving the equation requires knowledge of various thermal properties within the system.…”

“…This is complicated by the fact that many SThM probe structural dimensions are of comparable size to the mean free path (MFP) of heat carriers. Several studies have interrogated the SThM tip-sample contact in order to eliminate the ambiguity of the thermal contact area [3] [23] and estimate the thermal resistance associated with the tip-sample constriction [3][24] [25][26] [27][28] [29]. However, these works are either based on the usage of thermocouple probes with a thermal sensor localized at the end of the tip, or have been carried out under vacuum conditions.…”

“…In recent years scanning thermal microscopy (SThM) has become a widely used tool for the investigation of sub-micron heat transfer [1][2] [3]. It has been applied to the study and development of nanostructured materials, such as superlattices [4] [5], and micro/nano electronic devices, for example, nanowires [6] [7].…”