Determining phonon transport properties of bismuth telluride thin films with extremely small grain size using nanoindentation and 3ω method

Abstract

The phonon transport properties of Bi2Te3 thin films with extremely small grain size (3.4 nm) is investigated in this study using radio-frequency magnetron sputtering. The films exhibited an average group velocity of 2083 m/s and lattice thermal conductivity of 0.42 W/(m∙K), as determined by nanoindentation and 3ω method, respectively. The phonon mean free path (MFP) was 0.49 nm, determined from the group velocity and lattice thermal conductivity. The lattice thermal conductivity decreased to 35% for single-crystal Bi2Te3 owing to the decrease in the phonon MFP, whereas the group velocity hardly changed in the region of extremely small grain size.

Ultralow thermal conductivity of amorphous silicon–germanium thin films for alloy and disorder scattering determined by 3ω method and nanoindentation

“…41) In our previous studies, we developed a method to estimate thermal conductivity, group velocity, and phonon MFP by combining thermal conductivity measurements and nanoindentation. [42][43][44][45][46] Consequently, we showed that the primary cause of the ultralow thermal conductivity of amorphous materials is a notable reduction in phonon MFP. 47) One approach to further decreasing the lattice thermal conductivity of amorphous materials is to alloy them.…”

“…The process of determining group velocity through nanoindentation has been described in our previous reports. 44,45) The surface morphologies of the amorphous thin films analyzed using SPM are shown in Fig. 1.…”

Determination of Seebeck coefficient originating from phonon-drag effect using Si single crystals at different carrier densities

“…In this study, Si single crystals with different amounts of phosphorus doping were used because the crystals were perfectly oriented with no grain boundaries, and the carrier density could be easily varied. For the evaluation of phonon transport properties, we determined group velocities and phonon MFP of various materials using nanoindentation and thermal conductivity measurements 17 , 18 . The effect on the crystal orientation of the Si single crystals was investigated using the same technique 19 .…”

Origin of ultralow thermal conductivity in amorphous Si thin films investigated using nanoindentation, 3ω method, and phonon transport analysis

“…17) In our previous studies, we proposed a combined method of thermal conductivity and nanoindentation to estimate the lattice thermal conductivity, group velocity, and phonon MFP in single-crystal Si and nanocrystalline bismuth telluride films. [18][19][20][21] In addition, the phonon frequency in singlecrystal Si was estimated using the combined method and modeling. 22) Nanoindentation is frequently used to measure the elastic modulus and hardness of structural materials, 23,24) and group velocity can be estimated from the elastic modulus.…”