弯曲声子在石墨烯晶界的衍射和近零透射

Valley filtering effect of phonons in graphene with a grain boundary

Due to their possibility to encode information and realize low-energy-consumption quantum devices, control and manipulation of the valley degree of freedom have been widely studied in electronic systems. In contrast, the phononic counterpart--valley phononics--has been largely unexplored, despite the importance in both fundamental science and practical applications. In this work, we demonstrate that the control of "valleys" is also applicable for phonons in graphene by using a grain boundary. In particular, perfect valley filtering effect is observed at certain energy windows for flexural mode…

揭示化学气相沉积法生长的石墨烯的晶粒结构

Revealing the grain structure of graphene grown by chemical vapor deposition

在存在无序的情况下发生的物理过程：点缺陷、晶界等可能对石墨烯的电子性质具有不利影响。在这里，我们提出了一种方法来揭示石墨烯的颗粒结构的缺陷的选择性氧化和随后的原子力显微镜分析。这种技术提供了一种快速简便的替代不同的电子显微镜和衍射方法，并可用于快速反馈化学气相沉积生长的石墨烯样品的质量。

Phononic thermal transport along graphene grain boundaries

We reveal that phononic thermal transport in graphene is not immune to grain boundaries (GBs) aligned along the direction of the temperature gradient. Non-equilibrium molecular dynamics simulations uncover a large reduction in the phononic thermal conductivity ($κ_p$) along linear ultra-narrow GBs comprising periodically-repeating pentagon-heptagon dislocations. Green's function calculations and spectral energy density analysis indicate that $κ_p$ is the complex manifestation of the periodic strain field, which behaves as a reflective diffraction grating with both diffuse and specular phonon r…

石墨烯中的准周期纳米突起及其对电荷输运的影响

Quasi-Periodic Nanoripples in Graphene Grown by Chemical Vapor Deposition and Its Impact on Charge Transport

通过化学气相沉积方法（CVD）合成石墨烯的技术突破为大规模器件应用开辟了巨大的机会。为了改善在铜上生长的CVD石墨烯（Cu-CVD石墨烯）的电性能，最近的努力集中在将这种多晶石墨烯膜的晶粒尺寸增加到100微米和更大。虽然晶粒尺寸的增加以及因此晶界密度的降低预计会大大提高器件性能，但在这里，我们表明Cu-CVD石墨烯的电荷迁移率和薄层电阻已经限制在单个晶粒内。我们发现目前CVD石墨烯的高温生长和湿转移方法导致准周期纳米波纹阵列（NRA）。在这种部分悬浮的石墨烯器件中的电子弯曲声子散射引入了各向异性电荷传输，并对最高可能的电荷迁移率和最低可能的薄层电阻值设置了限制。我们的研究结果为进一步改善CVD石墨烯生长和转移过程提供了指导。

合成单层二硫化钼中边缘和晶界缺陷诱导激子性质的可视化

Visualization of defect-induced excitonic properties of the edges and grain boundaries in synthesized monolayer molybdenum disulfide

原子薄的二维过渡金属二硫属化合物（TMDC）是下一代纳米光电应用的重要材料。了解合成生长的TMDC的边缘和晶界的纳米级光学行为对于优化其光电性能至关重要。通过远场光学显微镜来阐明二维材料的纳米级光学特性需要衍射受限的光束直径亚微米尺寸。在这里，我们提出了我们的实验工作的空间光致发光（PL）扫描的大尺寸（$\geq 50$微米）单层MoS $_2$生长的化学气相沉积（CVD）使用衍射限制的蓝色激光束斑（波长405 nm）的光束直径小至200 nm，使我们能够探测纳米级激子现象，这是以前没有观察到的。我们发现了几个重要的特征：（i）存在亚微米宽度的条带（ii）存在另一个较亮的宽区域，其由终止于锯齿形外围边缘的拐角处的平行荧光线组成;（iii）在PL谱的边缘处存在一个巨大的蓝移A激子峰，其能量可达$\sim 120$ meV。利用密度泛函理论计算，我们将这种巨大的蓝移归因于氧二聚体在边缘的吸附，这降低了激子结合能。我们的研究结果不仅揭示了缺陷诱导的激子性质，但也提供了一个有吸引力的路线，通过缺陷工程定制的光学性能在TMDC边缘。

Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

The electronic Seebeck response in a conductor involves the energy-dependent mean free path of the charge carriers and is affected by crystal structure, scattering from boundaries and defects, and strain. Previous photothermoelectric (PTE) studies have suggested that the thermoelectric properties of polycrystalline metal nanowires are related to grain structure, though direct evidence linking crystal microstructure to the PTE response is difficult to elucidate. Here, we show that room temperature scanning PTE measurements are sensitive probes that can detect subtle changes in the local Seebeck…

Formation process of skyrmion lattice domain boundaries: The role of grain boundaries

We report on the formation process of skyrmion lattice (SkL) domain boundaries in FeGe using Lorentz transmission electron microscopy and small-angle electron diffraction. We observed that grain boundaries and edges play an important role in the formation of SkL domain boundaries; The SkL domain boundary is stabilized at the intersection of two grains. A micromagnetic simulation using the Landau-Lifshitz-Gilbert equation revealed that the SkL domains separated by a boundary represent the lowest energy configuration. Conversely, in a wide area, SkL domain boundaries were not formed and SkL doma…