Thermoelectric properties of the SnS monolayer: Fully ab initio and accelerated calculations

Abstract

An energetic and dynamical stability analysis of five candidate structures—hexagonal, buckled hexagonal, litharge, inverted litharge, and distorted-NaCl—of the SnS monolayer is performed using density functional theory. The most stable is found to be a highly distorted-NaCl-type structure. The thermoelectric properties of this monolayer are then calculated using the density functional theory and the Boltzmann transport equation. In terms of phonon scattering, there is a sharp contrast between this monolayer and bulk materials, where normal processes are more important. The calculations reveal that the SnS monolayer has enhanced electrical performance as compared to the bulk phase. As a consequence, high figures of merit ZT∼5 and ZT∼1.36 are predicted at 600 and 300 K, respectively, for the monolayer, ∼33 times higher than the ZT of its bulk analog. Therefore, this structure is an interesting candidate for room-temperature thermoelectric applications. A comparison between the fully ab initio results and simpler models based on relaxation times for electrons and phonons highlights the efficiency of computationally inexpensive models. However, ab initio calculations are found to be very important for the prediction of thermal transport properties.

Pure spin current injection of single-layer monochalcogenides

“…But all this is beyond the scope of this work and this approximation can still give in general a reasonable estimate in most of the cases of our interest, where temperature, anisotropy and hole-electron differences are neglected [17,36,45,46]. Several papers tried to evaluate the momentum relaxation time of monochalcogenides, both bulk [47,46,48,49], and 2D systems [17,36,50,51]. Moreover, theoretical calculations based on simple models or more refined ab initio approaches on single-layer SnS [36], SnSe [50], and GeSe [51], take into account a range of values for τ spanning from roughly 10 to 1000 fs, depending on the calculated band energies (ab initio, at T = 0), up to 3eV above the Fermi level, and lattice temperatures (to which the relaxation time is inversely proportional) roughly considered between 300 to 600 K. Thus, keeping all this in mind and considering for τ the range 10-1000 fs, from figure 3 we see that  , 90 500 z ( ) w a =  ~Km s −1 for ÿω = 2.160 eV and then d ∼ 20 − 2000 nm.…”

“…More in general, the relaxation time varies with the band energy and the quasimomentum. But all this is beyond the scope of this work and this approximation can still give in general a reasonable estimate in most of the cases of our interest, where temperature, anisotropy and hole-electron differences are neglected [17,36,45,46]. Several papers tried to evaluate the momentum relaxation time of monochalcogenides, both bulk [47,46,48,49], and 2D systems [17,36,50,51].…”

“…Several papers tried to evaluate the momentum relaxation time of monochalcogenides, both bulk [47,46,48,49], and 2D systems [17,36,50,51]. Moreover, theoretical calculations based on simple models or more refined ab initio approaches on single-layer SnS [36], SnSe [50], and GeSe [51], take into account a range of values for τ spanning from roughly 10 to 1000 fs, depending on the calculated band energies (ab initio, at T = 0), up to 3eV above the Fermi level, and lattice temperatures (to which the relaxation time is inversely proportional) roughly considered between 300 to 600 K. Thus, keeping all this in mind and considering for τ the range 10-1000 fs, from figure 3 we see that  , 90 500 z ( ) w a =  ~Km s −1 for ÿω = 2.160 eV and then d ∼ 20 − 2000 nm. This value of d could be ∼1 and up to ∼100 times larger than those experimentally measured values of d = 20 nm for GaAs [16], AlGaAs [16] and d = 24 nm for ZnSe [17],.…”

Theoretical Prediction of the Monolayer Hf2Br4 as Promising Thermoelectric Material

“…Under a moderate hole concentration, the ZT value of the Sb 2 Si 2 Te 6 monolayer reaches 9.62 at 700 K, which is nearly nine times that of the bulk structure [18]. Gupta et al [19] theoretically predicted that the maximum ZT value of SnS monolayer is 1.36 at room temperature, which is almost 33 times higher than the ZT of its bulk form.…”

Monolayer SnX (X = O, S, Se): Two-Dimensional Materials with Low Lattice Thermal Conductivities and High Thermoelectric Figures of Merit

“…The p-doped heterojunction achieved the optimized PF with the carrier concentration ranging from 10 19 to 5 × 10 20 cm –3 , which could be lower than other monolayers. Also, other 2D materials SnX (e.g., the d -NaCl ( Pmn 21) phase SnS, SnSe with symmetries of P 3 m 1, P 21 mn , and P 21 ca , and SnS with a symmetry group of P 4/ nmm ) have been investigated, and all of them exhibited high thermoelectric properties.…”