Anisotropic Thermal Conductivity of Crystalline Layered SnSe₂

Abstract

The degree of thermal anisotropy affects critically key device-relevant properties of layered two-dimensional materials. Here, we systematically study the in-plane and cross-plane thermal conductivity of crystalline SnSe2 films of varying thickness (16–190 nm) and uncover a thickness-independent thermal conductivity anisotropy ratio of about ∼8.4. Experimental data obtained using Raman thermometry and frequency domain thermoreflectance showed that the in-plane and cross-plane thermal conductivities monotonically decrease by a factor of 2.5 with decreasing film thickness compared to the bulk values. Moreover, we find that the temperature-dependence of the in-plane component gradually decreases as the film becomes thinner, and in the range from 300 to 473 K it drops by more than a factor of 2. Using the mean free path reconstruction method, we found that phonons with MFP ranging from ∼1 to 53 and from 1 to 30 nm contribute to 50% of the total in-plane and cross-plane thermal conductivity, respectively.

Ultrasensitive, Ultrafast, and Gate-Tunable Two-Dimensional Photodetectors in Ternary Rhombohedral ZnIn2S4 for Optical Neural Networks

“…It is found that the P2 mode is more sensitive to temperature, which may be related to the vdW force between layers. These χ values are greater than those of MoS 2 , graphene and SnSe 2 , indicating that R-ZIS flakes possess relatively strong interlayer interactions.…”

Effect of crystallinity and thickness on thermal transport in layered PtSe2

“…For the thermal measurements, we used a custom-built frequencydomain thermo-reflectance (FDTR) setup, a well-established optical pump-probe technique, capable of measuring heat transport in thin films and across interfaces [31][32][33][34][35][36] . A schematic representation of the experimental setup is shown in Fig.…”

“…We used a lock-in amplifier (Zurich Instruments HF2LI) to record the amplitude and phase response of the reflected probe beam to the thermal wave, and the phase lag between the pump and probe beam as the observable quantity. More details on the experimental setup can be found elsewhere 35 .…”

Excitation and detection of acoustic phonons in nanoscale systems

“…45 These low-dimensional materials are particularly interesting in nanophononics due to their ability to confine phonons as they approach length scales in which their finite size or thickness begins to have a strong effect on material properties such as the thermal conductivity. 22,46 For example, in the case of nanoparticles, the confinement resulting from the edges of the nanoparticle leads to a break in translational symmetry in the crystal (i.e., absence of periodicity beyond the limits of the particle). This loss of symmetry leads to a shift of the optical Raman modes and an asymmetric broadening of the signal, usually observed as a "shoulder" at lower wavenumber as shown in Fig.…”

“…Rather, the modification of the thermal conductivity is mainly attributed to diffuse scattering of phonons at boundaries. Although this mechanism has been widely explored and exploited, [22][23][24] recent works propose using phonon coherence to control heat flow. [25][26][27] In this scenario, modification of the phonon dispersion relation by adding additional periodicity to the system by alternating thin layers of dissimilar materials (superlattices), 28 patterning holes in a suspended system, 29,30 or by self-assembling colloidal particles, 31,32 offers a simple strategy to manipulate phonon waves.…”