Scanning thermal microscopy on samples of varying effective thermal conductivities and identical flat surfaces

Abstract

We propose an approach for the characterization of scanning thermal microscopy (SThM) probe response using a sample with silicon dioxide steps. The chessboard-like sample provides a series of nine surfaces made of the same material, with identical roughness, but consisting of different thicknesses of silica layers standing on a single silicon wafer. The nine regions have different effective thermal conductivities, allowing calibration of SThM probes within a given set of surface conditions. A key benefit is the possibility of comparing the spatial resolution and the sensitivity to vertical inhomogeneities of the sample for different probes. A model is provided to determine the thermal contact area and contact thermal resistance from the experimental data. The results underline that ballistic heat conduction can be significant in crystalline substrates below the top thin films, especially for film thicknesses lower than 200 nm and effective thermal contact radius lower than 200 nm. They also highlight the sensitivity of SThM to ultrathin films, as well as the substrate below micrometric films under in-air conditions but not when in vacuum. This work advances quantitative nanometer-scale thermal metrology, where usual photothermal methods are more difficult to implement.

Thermal boundary conductance of CVD-grown MoS2 monolayer-on-silica substrate determined by scanning thermal microscopy

“…Assuming similar thermal conductivity for the oxide in the SiO2/Si substrate here and that of Ref. [31], we find that the decrease of probe thermal conductance when locating the probe on MoS2 is the same as that while bringing it over an oxide layer thicker by 95 nm. This thickness is more than hundred times than that of MoS2, underlining the potential of the TMDC as thin but efficient heat barrier.…”

“…In Ref. [31], some of us reported, with a similar Wollaston SThM probe, how 𝐺 probe varies with SiO2 thickness (see Suppl. Sec.…”

“…It is obtained by first comparing the probe thermal conductance with that obtained as a function of the silica thickness in Ref. [31]. The effective thermal conductivity (that of a bulk leading to the same 𝐺 probe ) determined for a layer of 300 nm of SiO2 over Si is around 𝜆 𝑒𝑓𝑓 ≈ 2 W.m -2 .K -1 (see Suppl.…”

“…This simplification is possible because the current work builds on the previous calibration in Ref. [31]. The final step is also performed with a FE simulation.…”

Button shear testing for adhesion measurements of 2D materials

“…We performed scanning thermal microscopy (SThM) to determine the thermal conductivity (or thermal resistance) 83 – 85 of the multilayer hBN on thermal SiO 2 samples before and after annealing as a measure of the conformal contact of the 2D material with its substrate 9 , 82 . In SThM, the measured thermal signal in Volt corresponds to the thermal interface resistances (TIRs) between the layers for a system of ultrathin layers 86 . This, in turn, correlates with high adhesion as shown for other material systems 87 – 89 .…”