Quantitative Characterization of Local Thermal Properties in Thermoelectric Ceramics Using “Jumping‐Mode” Scanning Thermal Microscopy

Abstract

Thermoelectric conversion may take a significant share in future energy technologies. Oxide‐based thermoelectric composite ceramics attract attention for promising routes for control of electrical and thermal conductivity for enhanced thermoelectric performance. However, the variability of the composite properties responsible for the thermoelectric performance, despite nominally identical preparation routes, is significant, and this cannot be explained without detailed studies of thermal transport at the local scale. Scanning thermal microscopy (SThM) is a scanning probe microscopy method providing access to local thermal properties of materials down to length scales below 100 nm. To date, realistic quantitative SThM is shown mostly for topographically very smooth materials. Here, methods for SThM imaging of bulk ceramic samples with relatively rough surfaces are demonstrated. “Jumping mode” SThM (JM‐SThM), which serves to preserve the probe integrity while imaging rough surfaces, is developed and applied. Experiments with real thermoelectric ceramics show that the JM‐SThM can be used for meaningful quantitative imaging. Quantitative imaging is performed with the help of calibrated finite‐elements model of the SThM probe. The modeling reveals non‐negligible effects associated with the distributed nature of the resistive SThM probes used; corrections need to be made depending on probe‐sample contact thermal resistance and probe current frequency.

Nanoscale Imaging and Measurements of Grain Boundary Thermal Resistance in Ceramics with Scanning Thermal Wave Microscopy

“…The maps of thermal wave amplitudes were acquired in the "jumping" mode SThM, which is described in detail elsewhere. 37 In this mode, the measurements are performed with the probe in contact with a sample. However, the probe is lifted above the sample surface to be moved between pixels.…”

“…A "jumping mode" SThM was employed to minimize the degradation of the resistive probe when interacting with surface topography. 37 Complementary topographic images of the ceramic surface were acquired in the tapping mode at higher-order noncontact flexural resonances using the same SThM cantilevers as were used for corresponding STWM images. High-resolution AFM images were obtained in the tapping mode with sharp silicon cantilevers (Nanosensors PPP-NHCR, Switzerland) with a nominal tip apex radius below 10 nm.…”

Local Heat Dissipation and Elasticity of Suspended Silicon Nanowires Revealed by Dual Scanning Electron and Thermal Microscopies

“…The vacuum conditions achieved here are likely to be responsible for the comparatively-larger Ω C observed, [36] and closer to those performed under vacuum conditions. [17,27,37,38] Noteworthy, a new version of the commonly used Pd/nitride probes was used in this work. This probe features a convex angle across the symmetry line on the tilted section of the tip and a smaller apex angle respect to the previous models (see Figure 1).…”

“…This issue has been partially solved by the development of finite element method (FEM) models of the probes. [15][16][17] A limitation of this technique is that most commonly used commercial SThM probes such as the micrometric Wollaston or the nanometric Pd/nitride thin film one present large apex angles (≈45°) [18][19][20] and thus they easily suffer of lateral interaction over high aspect ratio samples. [21] Over these types of samples, the signal change due to variations in the contact area can be of the same order of magnitude as the signal of the nano/microstructure of interest as it will be discussed along this work.…”

“…This issue has been partially solved by the development of finite element method (FEM) models of the probes. [ 15–17 ]…”