Ultralow lattice thermal conductivity and electronic properties of monolayer 1T phase semimetal SiTe2 and SnTe2 (1906.00174v1)

Abstract: 2H phase (trigonal prismatic D3h) of layered two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted a lot of interests due to the superior electronic and optoelectronic properties. However, flexible electronic devices and thermoelectric performances based on 2H phase have been potentially limited by the strain sensitive electronic band gap and high lattice thermal conductivity (kappa_L). Here, we predict and calculate two 1T (octahedral Oh) phase monolayer telluride materials SnTe2 and SiTe2 with soft mechanics, ultralow kappa_L and electronic properties. The calculated in-plane Young's modulus of monolayer SnTe2 is softer than most of 1T-MX2 compounds. Furthermore, monolayer SiTe2 and SnTe2 also have relatively flexible electronic properties under large biaxial strain, indicating potential flexible electrode materials. Meanwhile, monolayer SiTe2 and SnTe2 both exhibit ultralow \k{appa}_L (2.27 W/mK of SiTe2 and 1.62 W/mK of SnTe2) at room temperature. Considering both acoustic and polar optical phonon scattering of the electronic relaxation time, the figure of merit (ZT) can achieve 0.46 at 600 K and 0.71 at 900 K for monolayer SiTe2 and SnTe2 respectively.

• The paper demonstrates that monolayer 1T-phase SiTe2 and SnTe2 exhibit ultralow lattice thermal conductivities of 2.27 W/mK and 1.62 W/mK, respectively, due to flat phonon spectra and heavy atomic masses.
• It employs density functional theory and Boltzmann transport theory to reveal soft mechanical properties and semimetallic band structures that remain stable under ±5% biaxial strain.
• The study suggests potential applications in flexible electronics and thermoelectric devices, with promising figure of merit values (ZT up to 0.71) for enhanced device performance.

Insights into Ultralow Lattice Thermal Conductivity and Electronic Properties of 1T Phase Semimetal Monolayers: SiTe and SnTe

The paper by Yi Wang, Zhibin Gao, and Jun Zhou addresses the mechanical, electronic, and thermoelectric properties of monolayer 1T phase semimetal structures—specifically SiTe and SnTe. Utilizing density functional theory (DFT) computations and Boltzmann transport theory, the paper presents noteworthy findings about these monolayer materials, which have potential applications in the field of nanotechnology and materials science.

Mechanical Properties

The investigation into the mechanical attributes of monolayer SiTe and SnTe reveals significantly soft compositions relative to other 1T phase materials noted in existing literature. The calculated in-plane Young's moduli for SnTe and SiTe are 16.80 N/m and 21.16 N/m, respectively, classifying them among the softest stable monolayer materials. This softness is further augmented by the observed positive in-plane Poisson's ratios. The combination of these mechanical properties indicates the potential of these monolayers in flexible electronics, providing a framework for future research in the engineering of flexible electronic devices.

Lattice Thermal Conductivity

A key focus of the paper is the notably low lattice thermal conductivities (κ_L) of these monolayers. SiTe and SnTe demonstrate lattice thermal conductivities of 2.27 W/mK and 1.62 W/mK at room temperature, respectively, representing lower values compared to their 2H phase counterparts and some known TMDs. Factors contributing to these ultralow lattice thermal conductivities include the lower frequency of acoustic phonon modes, heavy atomic mass, and relatively flat phonon spectra. The lower maximum frequency observed in acoustic phonon modes, compounded by the heavy atomic mass (Te being heavier than Se), contributes to reduced phonon group velocities and enhanced phonon-phonon scattering, thus decreasing κ_L.

Electronic Properties

The paper further elaborates on the electronic characteristics of these materials. The band structure computations indicate semimetallic behavior, maintaining stable electronic structures under varying biaxial strains (ε = ±5%). This attribute marks these monolayers as potential candidates for use as flexible electrodes, capable of maintaining desirable electronic properties even under mechanical deformation.

Thermoelectric Performance

Thermoelectric efficiency, assessed via the dimensionless figure of merit (ZT), reaches values of 0.46 at 600 K for SiTe and 0.71 at 900 K for SnTe. The paper rigorously considers the influence of both acoustic and polar optical phonon scattering on the relaxation time, a critical factor in the calculation of electronic transport properties. The low lattice thermal conductivity coupled with relatively high electronic conductivity affirms their promise as thermoelectric materials.

Implications and Future Directions

The implications of this research span both theoretical and practical domains. The profound understanding of ultralow thermal conductivity in these monolayers could guide the design of efficient thermal management systems in nanoelectronics. Additionally, the flexibility in electronic properties under strain presents significant potential for innovations in the design of malleable electronic devices. Future research endeavors may explore experimental synthesis and characterization of these materials to verify computational predictions and assess their integration into semiconducting devices.

This research enriches the discourse on 1T phase materials, underscoring the potential of SnTe and SiTe to contribute to advanced technological applications and encouraging investigation into further monolayer tellurides.