School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
Nanotechnology. 2018 Jan 5;29(1):015204. doi: 10.1088/1361-6528/aa99ba.
Using first-principle calculations combined with Boltzmann transport theory, we investigate the biaxial strain effect on the electronic and phonon thermal transport properties of a 1 T (CdI-type) structural TiS monolayer, a recent experimental two-dimensional (2D) material. It is found that the electronic band structure can be effectively modulated and that the band gap experiences an indirect-direct-indirect transition with increasing tensile strain. The band convergence induced by the tensile strain increases the Seebeck coefficient and the power factor, while the lattice thermal conductivity is decreased under the tensile strain due to the decreasing group velocity and the increasing scattering chances between the acoustic phonon modes and the optical phonon modes, which together greatly increase the thermoelectric performance. The figure of merit can reach 0.95 (0.82) at an 8 percent tensile strain for the p-type (n-type) doping, which is much larger than that without strain. The present work suggests that the TiS monolayer is a good candidate for 2D thermoelectric materials, and that biaxial strain is a powerful tool with which to enhance thermoelectric performance.
利用第一性原理计算结合玻尔兹曼输运理论，我们研究了双轴应变对最近实验二维（2D）材料 1T（CdI 型）结构 TiS 单层的电子和声子热输运性质的影响。研究发现，电子能带结构可以得到有效调节，带隙随拉伸应变的增加经历间接-直接-间接转变。拉伸应变引起的能带收敛增加了 Seebeck 系数和功率因子，而晶格热导率由于声子模式和光学声子模式之间的群速度降低和散射机会增加而在拉伸应变下降低，这共同极大地提高了热电性能。在 8%的拉伸应变下，p 型（n 型）掺杂的品质因数可达到 0.95（0.82），远大于无应变时的值。本工作表明 TiS 单层是二维热电材料的良好候选材料，双轴应变是增强热电性能的有力工具。
