Electrostatic modulation of thermoelectric transport properties of 2H-MoTe2 (original) (raw)
Related papers
Very high thermoelectric figure of merit found in hybrid transition-metal- dichalcogenides
The search for thermoelectrics with higher figures of merit (ZT) will never stop due to the demand of heat harvesting. Single layer transition metal dichalcogenides (TMD), namely, MX 2 (where M is a transition metal and X is a chalcogen), that have electronic band gaps are among the new materials that have been the focus of such research. Here, we investigate the thermoelectric transport properties of hybrid armchair-edged TMD nanoribbons, by using the nonequilibrium Green's function technique combined with the first principles and molecular dynamics methods. We find a ZT as high as 7.4 in hybrid MoS 2 /MoSe 2 nanoribbons at 800 K, creating a new record for ZT. Moreover, the hybrid interfaces by substituting X atoms are more efficient than those by substituting M atoms to tune the ZT. The origin of such a high ZT of hybrid nanoribbons is the high density of the grain boundaries: the hybrid interfaces decrease thermal conductance drastically without a large penalty to electronic conductance. Published by AIP Publishing. [http://dx.
In-Plane and Interfacial Thermal Conduction of Two-Dimensional Transition-Metal Dichalcogenides
Physical Review Applied
We elucidate the dependence of the in-plane and interfacial thermal conduction of twodimensional (2D) transition metal dichalcogenide (TMDC) materials (including MoS2, WS2, and WSe2) on the materials' physical features, such as size, layer number, composition, and substrates. The in-plane thermal conductivity k is measured at suspended 2D TMDC materials and the interfacial thermal conductance g measured at the materials supported onto substrates, both with Raman thermometry techniques. The thermal conductivity k increases with the radius R of the suspended area following a logarithmic scaling as k ~ log(R). k also shows a substantial decrease from monolayer to bilayer, but only changes mildly with further increase in the layer number. In contrast, the interfacial thermal conductance g bears negligible dependence on the layer number. But g increases with the strength of the interaction between 2D TMDC materials and the substrate, substantially varying among different substrates. The result is consistent with theoretical predictions and clarifies much inconsistence in references. This work provides useful guidance for the thermal management in 2D TMDC materials and devices.
Cross-plane thermal properties of transition metal dichalcogenides
Applied Physics Letters, 2013
Thermal conductivity predictions of herringbone graphite nanofibers using molecular dynamics simulations J. Chem. Phys. 138, 084708 (2013) Thermoelectric properties of p-type (Bi2Te3)x(Sb2Te3)1−x single crystals doped with 3wt. % Te J. Appl. Phys. 113, 073709 Effect of grain boundaries on thermal transport in graphene Appl. Phys. Lett. 102, 033104 Nonlinear thermal conductance in single-wall carbon nanotubes: Negative differential thermal resistance J. Chem. Phys. 138, 034708 Sensitivity of thermal conductivity of carbon nanotubes to defect concentrations and heat-treatment J. Appl. Phys. 113, 034312 (2013) Additional information on Appl. Phys. Lett.
Science Advances
Two-dimensional (2D) materials have enabled promising applications in modern miniaturized devices. However, device operation may lead to substantial temperature rise and thermal stress, resulting in device failure. To address such thermal challenges, the thermal expansion coefficient (TEC) needs to be well understood. Here, we characterize the in-plane TECs of transition metal dichalcogenide (TMD) monolayers and demonstrate superior accuracy using a three-substrate approach. Our measurements confirm the physical range of 2D monolayer TECs and, hence, address the more than two orders of magnitude discrepancy in literature. Moreover, we identify the thermochemical electronegativity difference of compositional elements as a descriptor, enabling the fast estimation of TECs for various TMD monolayers. Our work presents a unified approach and descriptor for the thermal expansion of TMD monolayers, which can serve as a guideline toward the rational design of reliable 2D devices.
Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS 2 /WS 2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green's function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS 2 and WS 2 nanoribbons due to the fact that the MoS 2 /WS 2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS 2 /WS 2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS 2 /WS 2 hybrid nanoribbons have promising applications in thermal energy harvesting. Environmental pollution and energy shortages are two big concerns in modern society. Thermoelectric materials, which can convert waste heat in the environment to electricity, are expected to be helpful in resolving these two issues 1–4. The energy conversion efficiencies of thermoelectric materials are measured by the so-called figure of merit ZT which is defined as σ = / ZT S T k 2 , where S is the Seebeck coefficient, σ is the electronic conductance, and k (= + k k k e p) is the total thermal conductance including contributions of electrons (k e) and phonons (k p). Therefore, a high-performance thermoelectric material should have high electron conductance and low thermal conductance, i.e., electron crystals and thermal glasses. However, the ZT values of most bulk materials are very small (much less than 1.0) because their electronic and thermal properties always have the same trends 5–8. There are extensive studies to search for high ZT materials. It is reported that the ZT values of some materials are improved significantly after nanocrystallization due to drastic changes of electronic and thermal properties 9–16. For example, theoretical calculations proved that the ZT values of quasi-one nanowires have a larger increase than those of bulk and two-dimensional structures 2 nanostructured bismuth antimony telluride showed experimentally higher ZT values than the bulk because of a sharp reduction in k p 6. Beyond the intrinsic improvement, the ZT values of nanostructures can be further enhanced by various modifications, such as hybridization 10–12 , doping 13,14 , absorption 15,16 , etc. Previous theoretical studies indicated that hybrid nanostructures, such as SiGe alloys and hybrid BN/graphene nanoribbons, possess higher thermoelectric properties than single nanostructures 11,12. Even if the thermoelectric performances of nanostructures are much better than those of bulk, most of them still cannot meet the requirements for real world applications. As such, the search for high-performance thermoelectric materials for energy harvesting applications has become a main focus in the thermoelectric field. Recently, the thermoelectric properties of single-layer or few-layer transition metal dichalcogenides (TMD) MX 2 (M = Mo, W, while X = S, Se etc.) have attracted attention 17–21. MoS 2 and WS 2 are two typical TMDs, which are considered as excellent electronic materials because of direct band gaps and high carrier mobility. Electron transistors based on MoS 2 and WS 2 have been reported and show high electronic performance, while the thermal conductivities of the two nanosheets are relatively low 22–26. Therefore, MoS 2 and WS 2 monolayer should have high ZT values, which have been proven by previous theoretical studies 18,19,21. Meanwhile, some interesting MoS 2 /WS 2
Effect of Metal Doping and Vacancies on the Thermal Conductivity of Monolayer Molybdenum Diselenide
ACS applied materials & interfaces, 2018
It is well understood that defect engineering can give rise to exotic electronic properties in transition-metal dichalcogenides, but to this date, there is no detailed study to illustrate how defects can be engineered to tailor their thermal properties. Here, through combined experimental and theoretical approaches based on the first-principles density functional theory and Boltzmann transport equations, we have explored the effect of lattice vacancies and substitutional tungsten (W) doping on the thermal transport of the suspended molybdenum diselenide (MoSe2) monolayers grown by chemical vapor deposition (CVD). The results show that even though the isoelectronic substitution of the W atoms for Mo atoms in CVD-grown Mo0.82W018Se2 monolayers reduces the Se vacancy concentration by 50% compared to that found in the MoSe2 monolayers, the thermal conductivity remains intact in a wide temperature range. On the other hand, Se vacancies have a detrimental effect for both samples and more ...
Orientation dependent thermal conductance in single-layer MoS 2
Scientific Reports, 2013
We investigate the thermal conductivity in the armchair and zigzag MoS 2 nanoribbons, by combining the non-equilibrium Green's function approach and the first-principles method. A strong orientation dependence is observed in the thermal conductivity. Particularly, the thermal conductivity for the armchair MoS 2 nanoribbon is about 673.6 Wm 21 K 21 in the armchair nanoribbon, and 841.1 Wm 21 K 21 in the zigzag nanoribbon at room temperature. By calculating the Caroli transmission, we disclose the underlying mechanism for this strong orientation dependence to be the fewer phonon transport channels in the armchair MoS 2 nanoribbon in the frequency range of [150, 200] cm 21 . Through the scaling of the phonon dispersion, we further illustrate that the thermal conductivity calculated for the MoS 2 nanoribbon is esentially in consistent with the superior thermal conductivity found for graphene.
The Journal of Physical Chemistry C, 2018
Thermal transport in a material is governed by anharmonicity of crystal potential, which depends on the type of inter-atomic interaction. Using first-principles calculations, we report that lattice thermal conductivity (κ latt) and its anisotropy (κ x,y − κ z) of transition metal dichalcogenides (TMDs) increase by orders of magnitude with the change of constituent metal atom from Zr/Hf to Mo/W. This unprecedented difference in κ latt is substantiated by lower phonon group velocity, and four times larger anharmonicity of Zr/Hf based TMDs compared to Mo/W based TMDs. The sign and the absolute value of the Born effective charges, which emerges from the ionicity of the bonds, are found to be different for these two classes of materials. This leads to a significant difference in their interlayer van der Waals (vdW) interaction strengths, which are shown to be inversely related to the anisotropy in κ latt .