Overview

InFocus BB-FDTR is a frequency-domain thermoreflectance microscope that exploits the phenomenon where the reflectance of light on the surface of a sample changes with respect to the temperature (i.e., thermoreflectance) to measure the thermal properties of thin films and nanostructures and observe their distribution. The pump CW laser periodically heats the sample surface at a high frequency of up to 200 MHz, and the phase delay of the temperature response is detected using the probe CW laser to measure the thermal properties of the sample.

Similar to the time-domain thermoreflectance (TDTR) method, InFocus BB-FDTR can analyze not only bulk materials but also thin films and nanostructures with sizes on the order of submicrons to several microns. By selecting the measurement conditions, various thermal properties, ​​such as the cross-plane thermal conductivity K_z, in-plane thermal conductivity K_r, interface thermal conductance G, and heat capacity C, can be evaluated. In contrast to the TDTR method, an expensive pulsed laser and cumbersome mechanical moving stage are not necessary.

(Click "Introduction to broadband frequency-domain thermoreflectance (BB-FDTR)" for further information on BB-FDTR.)

In addition, high-resolution Raman spectroscopy can be used as an option. Raman spectroscopy facilitates multifaceted material analysis with a single device by providing additional information such as the sample crystallinity and residual stress.

Evaluation of phonon MFP spectrum

The most significant feature of the InFocus BB-FDTR is heterodyne detection, which realizes broadband periodic heating at a modulation frequency of up to 200 MHz. Changing the modulation frequency of the pump beam changes the thermal penetration depth d_p from the sample surface (a). When d_p is as long as the MFP of phonons, a quasi-ballistic heat transport effect appears, and the cumulative thermal conductivity k_accum for phonons with an MFP shorter than d_p is selectively measured (b).

By utilizing this characteristic, we can deepen our understanding of quasi-ballistic heat transport in nanodevice engineering and thermoelectric conversion materials.

Intuitive control of laser spots using laser beam scanning technology

Using a laser scanning optical system, which is the specialized capability of ScienceEdge, the positions of the pump and probe beams can be instantly changed by simply clicking anywhere on the software’s microscope image. The incident light on the sample surface is kept vertical; thus, spot-shape distortion will not be a cause for concern.

Lineup and specifications

Lineup

• Broadband frequency-domain thermoreflectance microscope　（InFocus BB-FDTR）
• Frequency-domain thermoreflectance microscope　（InFocus FDTR）

Specifications

Applications

Thermal conductivity measurement of amorphous Ge_1-xSn_x thin films using frequency-domain thermoreflectance

The thermal conductivities of amorphous Ge_1-xSn_x thin films with different Sn compositions were measured using InFocus FDTR. The results show that the thermal conductivity of the thin films decreases from 0.50 W/mK to 0.44 W/mK with increasing Sn composition, consistent with the amorphous limit calculated by the minimum thermal conductivity model.

Papers

Jun Hirotani, Taisuke Ota
“Measurement Error Reduction in Frequency-Domain Thermoreflectance Techniques”
The 69th JSAP spring meeting 2022, 22p-P03-23 (2022) (Japanese only)