Advanced Functional Materials & Optoelectronics Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha, Saudi Arabia.
Phys Chem Chem Phys. 2019 Feb 20;21(8):4624-4632. doi: 10.1039/c8cp07645f.
Advanced computational approaches have made the design and characterization of novel two-dimensional (2D) materials possible for applications in cutting-edge technologies. In this work, we designed five polymorphs of 2D tin sulfide (namely, α-SnS, β-SnS, γ-SnS, δ-SnS, and ε-SnS) and explored their potential for thermoelectric applications using density functional theory-based computational approaches. Investigations of the energetic stability showed that the generated monolayers were as stable as parent α-SnS and exhibited cohesive and formation energies comparable to those of other stable 2D materials. These monolayers demonstrated high structural anisotropy (except β-SnS), which resulted in interesting features in the effective mass of the charge carriers and the subsequent thermoelectric properties. The in-plane anisotropy yielded different effective masses of charge carriers along the 100- and 010-directions. The x- and y-components of the electrical conductivity tensors were accordingly enhanced by the p-type doping and n-type doping, respectively. We estimated the maximum thermoelectric power factors along the x- and y-axes and the corresponding optimal doping levels were recognized; this suggested that the thermoelectric performance of these monolayers along the x-direction can be improved by p-type doping and that along the y-direction can be improved by n-type doping. Moreover, the thermoelectric figures of merit of the SnS monolayers approached a benchmark value of unity at room temperature. Our results suggested that these novel polymorphs of 2D SnS are promising materials for applications in direction-dependent thermoelectric devices. The present study can provide valuable guidance for generating low-cost and non-toxic polymorphs of other layered-structure materials.
先进的计算方法使得设计和表征新型二维（2D）材料成为可能，这些材料可应用于前沿技术中。在这项工作中，我们设计了五种二维锡硫化物（即α-SnS、β-SnS、γ-SnS、δ-SnS 和 ε-SnS）的多晶型物，并使用基于密度泛函理论的计算方法探索了它们在热电应用中的潜力。对能量稳定性的研究表明，生成的单层与母体α-SnS 一样稳定，并表现出与其他稳定的 2D 材料相当的内聚能和形成能。这些单层表现出高结构各向异性（除了β-SnS），这导致了载流子有效质量和后续热电性质的有趣特征。面内各向异性导致载流子沿 100-和 010-方向的有效质量不同。相应地，通过 p 型掺杂和 n 型掺杂，分别增强了面内电导率张量的 x-和 y-分量。我们沿着 x-和 y-轴估计了最大热电功率因子，并识别了相应的最佳掺杂水平；这表明这些单层在 x 方向上的热电性能可以通过 p 型掺杂来提高，而在 y 方向上的热电性能可以通过 n 型掺杂来提高。此外，SnS 单层的热电优值在室温下接近单位值。我们的结果表明，这些新型二维 SnS 多晶型物是应用于方向依赖性热电设备的有前途的材料。本研究可为生成低成本、无毒的其他层状结构材料的多晶型物提供有价值的指导。
