G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, Georgia 30313, United States.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37830, United States.
ACS Appl Mater Interfaces. 2018 Feb 7;10(5):4921-4928. doi: 10.1021/acsami.7b14310. Epub 2018 Jan 23.
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 (MoSe) 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 MoWSe monolayers reduces the Se vacancy concentration by 50% compared to that found in the MoSe 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 so in the MoWSe monolayers, which results in thermal conductivity reduction up to 72% for a vacancy concentration of 4%. This is because the mass of the W atom is larger than that of the Mo atom, and missing a Se atom at a vacancy site results in a larger mass difference and therefore kinetic energy and potential energy difference. Furthermore, the monotonically increasing thermal conductivity with temperature for both systems at low temperatures indicates the importance of boundary scattering over defects and phonon-phonon scattering at these temperatures.
人们深知，在过渡金属二卤族化合物中，通过缺陷工程可以产生奇特的电子特性，但迄今为止，还没有详细的研究来阐明如何通过工程缺陷来调整它们的热性能。在这里，我们通过基于第一性原理密度泛函理论和玻尔兹曼输运方程的组合实验和理论方法，研究了晶格空位和替代钨（W）掺杂对化学气相沉积（CVD）生长的悬空二硒化钼（MoSe）单层热输运的影响。结果表明，尽管 CVD 生长的 MoWSe 单层中 W 原子的等电子替代将 Se 空位浓度降低了 50%，但在很宽的温度范围内，热导率保持不变。另一方面，Se 空位对两种样品都有不利影响，对 MoWSe 单层的影响更大，空位浓度为 4%时，热导率降低了 72%。这是因为 W 原子的质量大于 Mo 原子的质量，而在空位处缺少一个 Se 原子会导致质量差异更大，从而导致动能和位能差异更大。此外，在低温下，两种体系的热导率随温度单调增加，这表明在这些温度下，边界散射比缺陷和声子-声子散射更为重要。
