We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS₂ crystals. A ≈20 nm thick CoPt multilayer with perpendicular magnetization serves as the heater and thermometer in the experiment. The low thermal conductivity and small thickness of the CoPt transducer improve the sensitivity of the measurement to lateral heat flow in the MoS₂ crystal. The thermal conductivity of MoS₂ is highly anisotropic with basal-plane thermal conductivity varying between 85–110 ${\mathrm{W}\hspace{0.17em}\mathrm{m}}^{-1}{\hspace{0.17em}\mathrm{K}}^{-1}$ as a function of laser spot size. The basal-plane thermal conductivity is a factor of ≈50 larger than the c-axis thermal conductivity, $2.0\pm 0{.3\hspace{0.17em}\mathrm{W}\hspace{0.17em}\mathrm{m}}^{-1}{\hspace{0.17em}\mathrm{K}}^{-1}$ .

Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and compositional disorder. We further show that the ratio of the in-plane to through-plane thermal conductivity of bulk crystal is enhanced by the disorder. These results suggest that stacking disorder and mixture of phases is an effective mechanism to modify the anisotropic thermal conductivity of 2D materials.

The thermal conductivity of thin films and interface thermal conductance of dissimilar materials play a critical role in the functionality and the reliability of micro/nanomaterials and devices. The ultrafast laser-based thermoreflectance techniques, including the time-domain thermoreflectance (TDTR) and the frequency-domain thermoreflectance (FDTR) techniques are excellent approaches for the challenging measurements of interface thermal conductance of dissimilar materials. Both TDTR and FDTR signals on a trilayer structure which consists of a thin film metal transducer, a target thin film, and a substrate are studied by a thermal conduction model. The sensitivity of TDTR signals to the thermal conductivity of thin films is analyzed to show that the modulation frequency needs to be selected carefully for a high precision TDTR measurement. However, such a frequency selection, which is closely related to the unknown thermal properties and consequently hard to make before TDTR measurement, can be avoided in FDTR measurement. We also found out that in FDTR method, the heat transport in a trilayer structure could be divided into three regimes, and the thermal conductivity of thin films and interface thermal conductance can be obtained subsequently by fitting the data in different frequency range of one FDTR measurement, based on the regime map. Both TDTR and FDTR measurements are then conducted along with the analysis to obtain the thermal conductivity of ${\text{SiO}}_2$ thin films and interface thermal conductance between ${\text{SiO}}_2$ and Si. FDTR measurement results agree well with the TDTR measurements, but promises to be a much easier implementation than TDTR measurements.

The low thermal conductivity of polymers will be one of the major roadblocks for the polymer-based microelectronics and macroelectronics due to the limited heat spreading capability. Despite that the thermal conductivity of bulk polymers is usually low, a single extended polymer chain could have very high thermal conductivity. In this paper we present atomistic simulation studies on the phonon transport in single extended polymer chains of various polymers as a function of polymer chain length. The thermal conductivity of single extended polymer chains can be 1–2 orders of magnitude higher than their bulk counterparts. The thermal conductivity of single extended polymer chains is a strong function of monomer type. For example, the thermal conductivity of the extended polymer chains with aromatic backbone can be up to 5 times as that of a polyethylene chain, while the thermal conductivity of the extended polymer chains with bond-strength or mass disorder can be only 1/25 as that of a polyethylene chain. We analyze the phonon transport mechanisms in single extended polymer chains of various polymers and find that the competition between ballistic phonon transport and diffusive phonon transport in a polymer chain leads to a diverging length-dependent thermal conductivity.