Measurement Of In-plane Thermal Conductivity Research Articles

Enhancement of ZT in Bi0.5Sb1.5Te3 Thin Film through Lattice Orientation Management.

Thermoelectric power can convert heat and electricity directly and reversibly. Low-dimensional thermoelectric materials, particularly thin films, have been considered a breakthrough for separating electronic and thermal transport relationships. In this study, a series of Bi0.5Sb1.5Te3 thin films with thicknesses of 0.125, 0.25, 0.5, and 1 μm have been fabricated by RF sputtering for the study of thickness effects on thermoelectric properties. We demonstrated that microstructure (texture) changes highly correlate with the growth thickness in the films, and equilibrium annealing significantly improves the thermoelectric performance, resulting in a remarkable enhancement in the thermoelectric performance. Consequently, the 0.5 μm thin films achieve an exceptional power factor of 18.1 μWcm-1K-2 at 400 K. Furthermore, we utilize a novel method that involves exfoliating a nanosized film and cutting with a focused ion beam, enabling precise in-plane thermal conductivity measurements through the 3ω method. We obtain the in-plane thermal conductivity as low as 0.3 Wm-1K-1, leading to a maximum ZT of 1.86, nearing room temperature. Our results provide significant insights into advanced thin-film thermoelectric design and fabrication, boosting high-performance systems.

Simultaneous measurement of in-plane and interfacial thermal conductivity of isotopically labeled bilayer graphene

Simultaneous measurement of in-plane and interfacial thermal conductivity of isotopically labeled bilayer graphene

Direct measurement of in-plane thermal conductivity of microscale suspended thin films using a novel 3ω method

A novel 3ω method has been developed for measuring the in-plane thermal conductivity of microscale suspended thin films. In this method, a heating wire makes contact with the test film using Ampere's force with the assistance of an interstitial material. The thermal impedance is determined by comparing the triple-frequency voltages across the heating wire with and without contact with the test film. The thermal conductivity can be directly obtained from the slope of the real part of the thermal impedance plotted against the logarithm of the heating frequency, even when the thermal contact resistance between the heating wire and the test film is unknown. This method has been successfully applied to determine the in-plane thermal conductivity of various thin films, including stainless-steel and Kapton films. The linear relationship is significantly improved for samples with low thermal conductivity, and its accuracy is verified through repeated measurements under different contact conditions.

Quantitative Characterization of the Anisotropic Thermal Properties of Encapsulated Two-Dimensional MoS2 Nanofilms.

Two-dimensional (2D) semiconductors exhibit unique physical properties at the limit of a few atomic layers that are desirable for optoelectronic, spintronic, and electronic applications. Some of these materials require ambient encapsulation to preserve their properties from environmental degradation. While encapsulating 2D semiconductors is essential to device functionality, they also impact heat management due to the reduced thermal conductivity of the 2D material. There are limited experimental reports on in-plane thermal conductivity measurements in encapsulated 2D semiconductors. These measurements are particularly challenging in ultrathin films with a lower thermal conductivity than graphene since it may be difficult to separate the thermal effects of the sample from the encapsulating layers. To address this challenge, we integrated the frequency domain thermoreflectance (FDTR) and optothermal Raman spectroscopy (OTRS) techniques in the same experimental platform. First, we use the FDTR technique to characterize the cross-plane thermal conductivity and thermal boundary conductance. Next, we measure the in-plane thermal conductivity by model-based analysis of the OTRS measurements, using the cross-plane properties obtained from the FDTR measurements as input parameters. We provide experimental data for the first time on the thickness-dependent in-plane thermal conductivity of ultrathin MoS2 nanofilms encapsulated by alumina (Al2O3) and silica (SiO2) thin films. The measured thermal conductivity increased from 26.0 ± 10.0 W m-1 K-1 for monolayer MoS2 to 39.8 ± 10.8 W m-1 K-1 for the six-layer films. We also show that the thickness-dependent cross-plane thermal boundary conductance of the Al2O3/MoS2/SiO2 interface is limited by the low thermal conductance (18.5 MW m-2 K-1) of the MoS2/SiO2 interface, which has important implications on heat management in SiO2-supported and encased MoS2 devices. The measurement methods can be generalized to other 2D materials to study their anisotropic thermal properties.

Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Highly anisotropic thermal conductive materials are of significance in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with a thickness range from 0.2 μm to 2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional (1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.

Numerical modeling of in-plane thermal conductivity measurement methods based on a suspended membrane setup

A numerical modeling study, based on 3D finite element method (FEM) simulation and 1D analytical solutions, has been carried out to evaluate the capabilities of two ac methods for measuring in-plane thermal conductivity of thin film deposited on the back of a suspended SiNx membrane setup. Two parallel metal strips are present on the top of the dielectric membrane. One strip (S1) serves as both heater and thermometer, while another one (S2) acts as thermometer only. For a modified phase shift (MPS) method, it is crucial to extract the in-plane thermal diffusivity from the phase shift of the temperature oscillation on S2. It was found that the frequency window for carrying out the data fitting became narrower as the in-plane thermal diffusivity of the composite membrane (α∥,C) increased, primarily due to the failure of the semi-infinite width assumption in the low frequency region. To ensure the validity of the method, the upper limit of α∥,C should not exceed ~1.8 × 10−5 m2s−1 for the specific membrane dimension under consideration (1 × 1 mm2). On the other hand, inspired by a modified Ångström method proposed by Zhu recently, we suggest a new data reduction methodology which takes advantage of the phase shift on both S1 and S2 as well as the amplitude on S1. Based on the simulation results, it is expected that the non-ideality associated with the three “observables” may be at least partially canceled out. Therefore, the frequency window selection for carrying out the data fitting is not sensitive to the magnitude of α∥,C and the upper limit of measurable αC,∥ can be further increased with respect to the MPS method. For typical specimen films whose in-plane thermal conductivity ranges from 0.84 W m−1K−1 to 50 W m−1K−1, the method proposed here yields a theoretical measurement uncertainty of less than 5%.

Steady-state methods for measuring in-plane thermal conductivity of thin films for heat spreading applications.

The development of high thermal conductivity thin film materials for the thermal management of electronics requires accurate and precise methods for characterizing heat spreading capability, namely, in-plane thermal conductivity. However, due to the complex nature of thin film thermal property measurements, resolving the in-plane thermal conductivity of high thermal conductivity anisotropic thin films with high accuracy is particularly challenging. Capable transient techniques exist; however, they usually measure thermal diffusivity and require heat capacity and density to deduce thermal conductivity. Here, we present an explicit uncertainty analysis framework for accurately resolving in-plane thermal conductivity via two independent steady-state thermometry techniques: particle-assisted Raman thermometry and electrical resistance thermometry. Additionally, we establish error-based criteria to determine the limiting experimental conditions that permit the simplifying assumption of one-dimensional thermal conduction to further reduce thermal analysis. We demonstrate the accuracy and precision (<5% uncertainty) of both steady-state techniques through in-plane thermal conductivity measurements of anisotropic nanocrystalline diamond thin films.

Heat diffusion imaging: In-plane thermal conductivity measurement of thin films in a broad temperature range.

This work combines the principles of the heat spreader method and the imaging capability of the thermoreflectance measurements to measure the in-plane thermal conductivity of thin films without the requirement of film suspension or multiple thermometer deposition. We refer to this hybrid technique as heat diffusion imaging. The thermoreflectance imaging system provides a temperature distribution map across the film surface. The in-plane thermal conductivity can be extracted from the temperature decay profile. By coupling the system with a cryostat, we were able to conduct measurements from 40 K to 400 K. Silicon thin film samples with and without periodic holes were measured and compared with in-plane time-domain thermoreflectance measurements and literature data as validation for heat diffusion imaging.

Violation of the Wiedemann-Franz law through reduction of thermal conductivity in gold thin films

We present measurements of in-plane thermal and electrical conductivity in thermally evaporated gold thin-film samples ranging in thickness from $\ensuremath{\approx}20$ to $g300\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, performed using a micromachined silicon-nitride membrane thermal isolation platform. In both $\ensuremath{\approx}300$-nm-thick films grown in a single Au deposition and a sample built up to $g300\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ by many sequential depositions of thinner layers, we observe strong ``violations'' of the Wiedemann-Franz law that relates electrical and thermal conductivities. While electrical conductivity behaves essentially as expected, thermal conductivity first rises with growing total film thickness, and then surprisingly drops as the film becomes thicker. The sharp reduction of thermal conductivity decreases the Lorenz number $L$ for $\ensuremath{\approx}300\text{\ensuremath{-}}\mathrm{nm}$-thick samples to less than half the Sommerfeld value over the entire 78--300-K temperature range studied. Such violation near room temperature, in a metal film where electron transport should be well described by Fermi-liquid theory, is previously unreported, even in the presence of disorder introduced by grain boundaries and rough surfaces. This indicates an inelastic-scattering process that we argue, based on detailed characterization of grain size in these films, is likely driven by a combination of modified phonon density of states and structural anisotropy introduced from the strongly columnar grain structure in thicker films. This highly unusual reduction of thermal conductivity while maintaining high electrical conductivity is potentially promising for increasing thermoelectric performance of nanoscale systems.

Accurate measurement of in-plane thermal conductivity of layered materials without metal film transducer using frequency domain thermoreflectance.

Measuring anisotropic thermal conductivity has always been a challenging task in thermal metrology. Although recent developments of pump-probe thermoreflectance techniques such as variable spot sizes, offset pump-probe beams, and elliptical beams have enabled the measurement of anisotropic thermal conductivity, a metal film transducer enabled for the absorption of the modulated pump laser beam and the detection of the thermoreflectance signal. However, the existence of the transducer would cause in-plane heat spreading, suppressing the measurement sensitivity to the in-plane thermal conductivity. In addition, the transducer film also adds complexity to data processing, since it requires careful calibration or fitting to determine extra parameters such as the film thickness and conductivity, and interface conductance between the transducer and the sample. In this work, we discussed the methodology for measuring in-plane thermal conductivity of layered semiconductors and semimetals without any transducer layer. We show that the removal of transducer results in the dominantly large sensitivity to in-plane thermal conductivity compared with other parameters, such as cross-plane thermal conductivity and the absorption depth of the laser beams. Transducerless frequency-domain thermoreflectance (FDTR) measurements are performed on three reference layered-materials, highly ordered pyrolytic graphite, molybdenum disulfide (MoS2), and bismuth selenide (Bi2Se3) and demonstrated using the analytical thermal model that the measured in-plane thermal conductivity showed much-improved accuracy compared with conventional FDTR measurement with a transducer.

Thermoelectric properties of holey silicon at elevated temperatures

Compatibility to the semiconductor industry makes silicon thin-film devices attractive for thermoelectric applications. Silicon has a competitive thermoelectric power factor but a large thermal conductivity, which results in an overall small thermoelectric figure of merit, ZT. By patterning arrays of nano-sized holes with spacing less than the average phonon mean free path into the Si thin films, their thermal conductivity can be greatly suppressed, whereas their electronic properties are less affected. We fabricated and measured the electronic and thermal transport properties of such holey Si devices from 300 K to 650 K. Heat diffusion imaging, a hybrid approach that combines thermoreflectance imaging and the heat spreader method was used for the in-plane thermal conductivity measurement and gives a value of 6.00 ± 1.83 W/mK at room temperature. The power factor times temperature is about 0.52 ± 0.04 W/mK at 300 K and 1.10 ± 0.09 W/mK at 650 K. Therefore, ZT of the holey Si device is approximately 0.09 at room temperature and is at least 0.29 at 650 K. Further improvement is possible by optimizing the feature sizes and using surface doping.

Measurement of in-plane thermal conductivity of self-suspended thin films

A method for in-plane thermal conductivity measurement of self-suspended thin films by steady-state infrared thermal thermography is introduced. Based on the one-dimensional heat conduction equation, a theoretical model of temperature distribution on the surface of thin film at steady state is established. The simulation results show that the error between in-plane thermal conductivity and theoretical value is less than 3% when the temperature rise of the film is less than 5K. By measuring the boundary temperature and thickness of the film, the in-plane thermal conductivity and emissivity can be obtained simultaneously without measuring the absorption of visible light by the film. Polyimide film with the thickness of 550 nm is experimentally investigated by this method. We find that the in-plane thermal conductivity is 2.15W/mK and emissivity is 0.93 by fitting temperature distribution curve. These results validate the method developed.

Fabrication and characterization of graphene-based paper for heat spreader applications

In this work, in-plane thermal conductivity measurement was carried out on graphene-based papers. Graphene-based papers were fabricated using various processing techniques such as chemical vapor deposition (CVD), hot pressing of graphene slurry, and evaporation induced self-assembly. The prepared materials were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. In-plane thermal conductivity measurement was performed via a steady state thin film thermal conductivity apparatus. The in-plane thermal conductivity measurements show that the CVD based sample has the highest thermal conductivity. COMSOL Multiphysics was used to simulate the in-plane thermal conductivity of graphene-based papers.

A suspended 3-omega technique to measure the anisotropic thermal conductivity of semiconducting polymers.

Anisotropic thermal conductivity can complicate the performance of semiconducting polymer thin-films in applications such as thermoelectrics and photovoltaics. Anisotropic measurements of low thermal conductivity polymers are challenging, and there are a limited number of appropriate measurement techniques. Suspended film 3-omega is an appropriate technique but has often required unfavorable microfabrication. Herein, we report on the utility of the suspended 3-omega technique that uses shadow masking, and no other microfabrication techniques, in performing anisotropic (in-plane and through-plane) thermal conductivity measurements of polymer films. We report on the necessary conditions for the validity of the 1D suspended-film heat transfer model and provide experimental guidelines for in-plane thermal conductivity measurements of polymer thin-films. Furthermore, for the first time, we report the anisotropic thermal conductivities of N2200 and a low molecular weight P3HT, which are two common n-type and p-type semiconducting polymers. Measured thermal conductivities are compared with predictions from the conventional Cahill-Pohl model and a recent empirical model that more accurately predicts the temperature dependence.

Anisotropic Thermal Conductivity of Suspended Black Phosphorus Probed by Opto-Thermomechanical Resonance Spectromicroscopy.

Atomic layer semiconducting black phosphorus (P) exfoliated from its bulk crystals offers excellent properties and promises for emerging two-dimensional (2D) electronics, photonics, and transducers. It also possesses unique strong in-plane anisotropy among many 2D semiconductors, stemming from its corrugated crystal structure. As an important thermophysical aspect, probing the anisotropic thermal conductivity of black P is essential for device engineering, especially for energy dissipation and thermal management. Here, we report on measurement and analysis of anisotropic in-plane thermal conductivity of black P crystal, in a mechanically suspended device platform, by exploiting a novel opto-thermomechanical resonance spectromicroscopy (OTMRS) technique. With spatially resolved heating effects and thermomechanical resonance motions of suspended structures, anisotropic in-plane thermal conductivity (κAC and κZZ) is determined for black P crystals of 10-100 nm thick. This study validates a new noninvasive approach to determining anisotropic thermal conductivity without any requirement of preknowledge of crystal orientation or specific configurations of structure and electrodes according to the anisotropy.

Interfacial phonon scattering and transmission loss in &gt;1 µm thick silicon-on-insulator thin films

Scattering of phonons at boundaries of a crystal (grains, surfaces, or solid/solid interfaces) is characterized by the phonon wavelength, the angle of incidence, and the interface roughness, as historically evaluated using a specularity parameter $p$ formulated by Ziman [Electrons and Phonons (Clarendon Press, Oxford, 1960)]. This parameter was initially defined to determine the probability of a phonon specularly reflecting or diffusely scattering from the rough surface of a material. The validity of Ziman's theory as extended to solid/solid interfaces has not been previously validated. To better understand the interfacial scattering of phonons and to test the validity of Ziman's theory, we precisely measured the in-plane thermal conductivity of a series of Si films in silicon-on-insulator (SOI) wafers by time-domain thermoreflectance (TDTR) for a Si film thickness range of 1--10 \ensuremath{\mu}m and a temperature range of 100--300 K. The $\mathrm{Si}/{\mathrm{SiO}}_{2}$ interface roughness was determined to be $0.11\ifmmode\pm\else\textpm\fi{}0.04\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ using transmission electron microscopy (TEM). Furthermore, we compared our in-plane thermal conductivity measurements to theoretical calculations that combine first-principles phonon transport with Ziman's theory. Calculations using Ziman's specularity parameter significantly overestimate values from the TDTR measurements. We attribute this discrepancy to phonon transmission through the solid/solid interface into the substrate, which is not accounted for by Ziman's theory for surfaces. The phonons that are specularly transmitted into an amorphous layer will be sufficiently randomized by the time they come back to the crystalline Si layer, the effect of which is practically equivalent to a diffuse reflection at the interface. We derive a simple expression for the specularity parameter at solid/amorphous interfaces and achieve good agreement between calculations and measurement values.

In-plane Thermal Conductivity Measurement with Nanosecond Grating Imaging Technique

ABSTRACTWe develop a nanosecond grating imaging (NGI) technique to measure in-plane thermal transport properties in bulk and thin-film samples. Based on nanosecond time-domain thermoreflectance (ns-TDTR), NGI incorporates a photomask with periodic metal strips patterned on a transparent dielectric substrate to generate grating images of pump and probe lasers on the sample surface, which induces heat conduction along both cross- and in-plane directions. Analytical and numerical models have been developed to extract thermal conductivities in both bulk and thin-film samples from NGI measurements. This newly developed technique is used to determine thickness-dependent in-plane thermal conductivities (κx) in Cu nano-films, which agree well with the electron thermal conductivity values converted from four-point electrical conductivity measurements using the Wiedemamn–Franz law, as well as previously reported experimental values. The κx measured with NGI in an 8 nm x 8 nm GaAs/AlAs superlattice (SL) is about 10.2 W/m⋅K, larger than the cross-plane thermal conductivity (8.8 W/m⋅K), indicating the anisotropic thermal transport in the SL structure. The uncertainty of the measured κx is about 25% in the Cu film and less than 5% in SL. Sensitivity analysis suggests that, with the careful selection of proper substrate and interface resistance, the uncertainty of κx in Cu nano-films can be as low as 5%, showing the potential of the NGI technique to determine κx in thin films with improved accuracy. By simply installing a photomask into ns-TDTR, NGI provides a convenient, fast, and cost-effective method to measure the in-plane thermal conductivities in a wide range of structures and materials.

Analytical Investigation of the Limits for the In-Plane Thermal Conductivity Measurement Using a Suspended Membrane Setup

An analytical study has been performed on the measurement capabilities of a 100-nm thin suspended membrane setup for the in-plane thermal conductivity measurements of thin film samples using the 3ω measurement technique, utilizing a COSMOL Multiphysics simulation. The maximum measurement range under observance of given boundary conditions has been studied. Three different exemplary sample materials, with a thickness from the nanometer to the micrometer range and a thermal conductivity from 0.4 W/mK up to 100 W/mK have been investigated as showcase studies. The results of the simulations have been compared to a previously published evaluation model, in order to determine the deviation between both and thereby the measurement limit. As thermal transport properties are temperature dependent, all calculations refer to constant room temperature conditions.

(Invited) Review: PEMFC Materials' Thermal Conductivity and Influence on Internal Temperature Profiles

The polymer electrolyte membrane fuel cell (PEMFC) is far from isothermal when in operation. This is well established both from experiments and from mathematical modelling. The latter relies on knowledge of heat transport and local heat generation in the different materials and cell design that constitute the PEMFC. Over the last 15 years the knowledge about thermal conductivity and heat generation in the PEMFC materials as a research field has been established and developed. From first looking at through-plane thermal conductivity of only membranes and gas diffusion layers (GDL), the most recent studies include heat transport dependency on non-isotropic properties, PTFE content, water content, compression, heat pipe effects, and material integration. Depending on the fabric, dry GDL thermal conductivity range from 0.15 to 0.9 W K-1 m-1 when compressed at close to 10 bar compaction pressure. The most common fabrics have thermal conductivity between 0.3 and 0.4 W K-1 m-1. Adding water increases the thermal conductivity by between a factor of two and three, up to 1.5 W K-1 m-1, see ref 1. The in-plane thermal conductivity is larger and more than 10 W K-1 m-1, see ref 2-3. Thermal conductivity of fully humidified Nafion is 0.27 W K-1 m-1, see ref 4. Over the past few years, more attention has been given to the thermal conductivity of the microporous layer (MPL) and the catalyst layer (CL) and the way the MPL interact with the GDL, see ref 5-6. Thermal conductivity of these thin layers (CL and MPL) have been measured to be in the range of 0.1 W K-1 m-1, and in the region where the MPL and the GDL interfere to make a composite material, where the thermal conductivity has been estimated to be as high as 10 W K-1 m-1 . These different values and their historical development leads to a natural selection of 5 reference thermal models at 1 A cm-2 and 0.67 V, leading to temperature profiles under the rib of the current collector, shown i the attached figure. The base case consists of dry materials and no consideration of thin layer effects (CL and MPL), whereas the thin layer effects leads to additional temperature elevation. Accounting for the MPL-GDL interferences, on the other hand leads to a lowered temperature elevation inside the PEMFC. Adding water and accounting for these effects, and in addition considering the GDL with the highest thermal conductivity (wet Toray), the maximum temperature elevation under the polarisation plate land is lowered by a factor of 6 compared the base case of the oldest available thermal conductivity values. The attached figure shows the temperature profiles under the polarisation plate land for these five models and also indicate the regions; GDL, GDL-MPL-comp., MPL, Anode CL, Membrane, Cathode CL, MPL, GDL-MPL-Comp., GDL and the thickness, given by distance from the membrane. A richer and more detailed overview of thermal conductivity of several different materials and their effects on modelling thermal gradients inside the PEMFC is presented in the presentation and following paper at this conference. The take home message is that investigating thermal conductivity of PEMFC components is important for modelling and certainly not a closed chapter. References O. Burheim, H. Lampert, J. Pharoah, P. Vie, S. Kjelstrup, Through-plane thermal conductivity of PEMFC porous transport layers, Journal of Fuel Cell Science and Technology 8 (2011) 021013–1–11. N. Zamel, E. Litovsky, S. Shakhshir, X. Li, J. Kleiman, Measurement of in-plane thermal conductivity of carbon paper diffusion media in the temperature range of -20 ◦c to +120 ◦c, Appl. Energy 88 (2011) 3042–3050.E. Sadeghi, N. Djilali, M. Bahrami, A novel approach to determine the in-plane thermal conductivity of gas diffusion layers in proton exchange membrane fuel cells, J. Power Sources 196 (2011) 3565–3571.O. Burheim, P. Vie, J. Pharoah, S. Kjelstrup, Ex-situ measurements of through-plane thermal conductivities in a polymer electrolyte fuel cell, Journal of Power Sources 195 (2010) 249–256.O. S. Burheim, G. A. Crymble, R. Bock, N. Hussain, S. Pasupathi, A. du Plessis, S. le Roux, F. Seland, H. Su, B. G. Pollet, Thermal conductivity in the three layered regions of micro porous layer coated porous transport layers for the pem fuel cell, International Journal of Hydrogen Energy.R. Bock, A. Shum, T. Khoza, F. Seland, N. Hussain, I. V. Zenyuk, O. S. Burheim, Experimental study of thermal conductivity and compression measurements of the gdl-mpl interfacial composite region, ECS Transactions 75 (14) (2016) 189–199. Figure 1

Elastic and thermal properties of free-standing molybdenum disulfide membranes measured using ultrafast transient grating spectroscopy

Molybdenum disulfide (MoS2), a member of transition-metal dichalcogenide family, is of intense interest due to its unique electronic and thermoelectric properties. However, reports of its in-plane thermal conductivity vary due to the difficulty of in-plane thermal conductivity measurements on thin films, and an experimental measurement of the in-plane sound velocity has not been reported. Here, we use time-resolved transient grating spectroscopy to simultaneously measure the in-plane elastic and thermal properties of free-standing MoS2 membranes at room temperature. We obtain a longitudinal acoustic phonon velocity of 7000 ± 40 m s−1 and an in-plane thermal conductivity of 74 ± 21 W m−1K−1. Our measurements provide useful insights into the elastic and thermal properties of MoS2 and demonstrate the capability of transient grating spectroscopy to investigate the in-plane vibrational properties of van der Waals materials that are challenging to characterize with conventional methods.