Longuinhos R, Ribeiro-Soares J
Departamento de Física, Universidade Federal de Lavras, PO Box 3037, Lavras, MG 37200-000, Brazil.
Phys Chem Chem Phys. 2016 Sep 14;18(36):25401-25408. doi: 10.1039/c6cp03806a.
Beyond-graphene two-dimensional (2D) materials are envisioned as the future technology for optoelectronics, and the study of group IIIA metal monochalcogenides (GIIIAMMs) in 2D form is an emerging research field. Bulk gallium selenide (GaSe) is a layered material of this family which is widely used in nonlinear optics and is promising as a lubricant. The interlayer coupling in few-layer GaSe is currently unknown, and the stability of different polytypes is unclear. Here we use symmetry arguments and first-principles calculations to investigate the phase stability, interlayer coupling, and the Raman and infrared activity of the low-frequency shear and breathing modes expected in few-layer GaSe. Strategies to distinguish the number of layers and the β and ε polytypes are discussed. These symmetry results are valid for other isostructural few-layer GIIIAMM materials. Most importantly, by using a linear chain model, we show that the shear and breathing force constants reveal an ultra-weak interlayer coupling at the nanoscale in GaSe. These results suggest that β and ε few-layer GaSe show similar lubricant properties to those observed for few-layer graphite. Our analysis opens new perspectives about the study of interlayer interactions and their role in the mechanical and electrical properties of these new 2D materials.
超越石墨烯的二维（2D）材料被视为光电子学的未来技术，对二维形式的IIIA族金属硫属化物（GIIIAMMs）的研究是一个新兴的研究领域。块状硒化镓（GaSe）是该家族的一种层状材料，广泛应用于非线性光学领域，并且有望用作润滑剂。目前尚不清楚少层GaSe中的层间耦合情况，不同多型体的稳定性也不明确。在此，我们运用对称性论证和第一性原理计算，来研究少层GaSe中预期的低频剪切和呼吸模式的相稳定性、层间耦合以及拉曼和红外活性。讨论了区分层数以及β和ε多型体的策略。这些对称性结果对于其他同构的少层GIIIAMM材料也是有效的。最重要的是，通过使用线性链模型，我们表明剪切力常数和呼吸力常数揭示了GaSe在纳米尺度上存在超弱的层间耦合。这些结果表明，β和ε少层GaSe表现出与少层石墨类似的润滑特性。我们的分析为研究层间相互作用及其在这些新型二维材料的机械和电学性质中的作用开辟了新的视角。
