Temperature-dependent (5 K to 300 K) Raman scattering study of A$_{1g}$/A'$_1$ phonon modes in mono-layer (1L), bilayer (2L), trilayer (3L), and tetralayer (4L) MoTe$_2$ is reported. The temperature evolution of the modes' intensity critically depends on the flake thickness. In particular with $λ$=632.8 nm light excitation, a strongly non-monotonic dependence of the A$_{1g}$ mode intensity is observed in 2L MoTe$_2$. The intensity decreases with decreasing temperature down to 220 K and the A$_{1g}$ mode almost completely vanishes from the Stokes scattering spectrum in the temperature range between 160 K and 220 K. The peak recovers at lower temperatures and at T=5 K it becomes three times more intense that at room temperature. Similar non-monotonic intensity evolution is observed for the out-of-plane mode in 3L MoTe$_2$ in which tellurium atoms in all three layers vibrate in-phase. The intensity of the other out-of-plane Raman-active mode, (with vibrations of tellurium atoms in the central layer shifted by 180$^o$ with respect to the vibrations in outer layers), only weakly depends on temperature. The observed quenching of the Raman scattering in 2L and 3L MoTe$_2$ is attributed to a destructive interference between the resonant and non-resonant contributions to the Raman scattering amplitude. The observed "antiresonance" is related to the electronic excitation at the M point of the Brillouin zone in few-layer MoTe$_2$.
Structural Phase Transition and Interlayer Coupling in Few-Layer 1T' and Td MoTe2
我们对机械剥离的少层MoTe_2样品进行了偏振拉曼光谱分析，在室温下观察到了1 T '和Td相。少层1 T '和Td MoTe 2表现出显着的差异，特别是在层间振动模式，从中提取的层间耦合强度使用线性链模型：在两个阶段中观察到强的面内各向异性。此外，温度相关的拉曼光谱测量揭示了一个特殊的相变行为在少层1 T 'MoTe 2。与在~250 K下发生向Td相的相变的大块1 T 'MoTe 2晶体相比，随着厚度的减小，温度驱动的向Td相的相变越来越受到抑制，并且即使对于相同的厚度，从样品到样品的转变和临界温度也显著变化。观察到了既不对应于1 T '相也不对应于Td相的中间相的Raman光谱，这些中间相具有不同的层间振动模式，这表明存在几个亚稳相，它们的总能量相似。
Field-Effect Transistors Based on Few-Layered alpha-MoTe_2
本文报道了在SiO_2上用机械剥离法生长的几层化学气相传输法生长的α- MoTe_2晶体的场效应晶体管的特性。我们进行了场效应和霍尔迁移率测量，以及拉曼散射和透射电子显微镜。与MoS_2和MoSe_2相比，我们的MoTe_2场效应晶体管（FET）被观察到是空穴掺杂的，显示超过106的开/关比和典型的亚阈值摆幅为每十倍约140 mV。场效应迁移率和霍尔迁移率的最大值接近或超过10 cm ^2/Vs，这与以前报道的室温下单层或双层MoS_2和/或MoSe_2在SiO_2上剥离的数据相当。拉曼散射揭示了尖锐的模式与以前的报告，其频率被发现显示很少或没有依赖于层数。由于两种MoS_2都是电子掺杂的，MoTe_2在MoS_2上的堆叠可以产生双极场效应晶体管和间隙调制。尽管MoTe_2的总体电子性能与MoS_2和MoSe_2相当，但较重的元素Te应该会导致更强的自旋轨道耦合，并可能伴随着更长的激子谷和自旋指数的退相干时间。
University of Warsaw（华沙大学）；Wrocław University of Science and Technology（弗罗茨瓦夫科技大学）；Peking University Shenzhen Graduate School（北京大学深圳研究生院）；CNRS（法国国家科学研究中心）
Enhancement of the WS$_2$ A$_{1\text{g}}$ Raman Mode in MoS$_2$/WS$_2$ Heterostructures
Institute of Physics, Rostock University（罗斯托克大学物理研究所）；Institute of Theoretical Physics, University of Warsaw（华沙大学理论物理研究所）；Institute of Theoretical Physics, Wrocław University of Science and Technology（弗罗茨瓦夫科技大学理论物理研究所）；Department of Physics, Freie Universität Berlin（柏林自由大学物理系）；Institute of Physical Chemistry, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学物理化学研究所）；Department of Physics and Materials Science, University of Luxembourg（卢森堡大学物理与材料科学系）
