Joshi Prakriti P, Li Ruiyu, Spellberg Joseph L, Liang Liangbo, King Sarah B
James Franck Institute, University of Chicago, Chicago, Illinois 60637 United States.
Department of Chemistry, University of Chicago, Chicago, Illinois 60637 United States.
Nano Lett. 2022 Apr 27;22(8):3180-3186. doi: 10.1021/acs.nanolett.1c03849. Epub 2022 Apr 5.
The electronic structure and functionality of 2D materials is highly sensitive to structural morphology, not only opening the possibility for manipulating material properties but also making predictable and reproducible functionality challenging. Black phosphorus (BP), a corrugated orthorhombic 2D material, has in-plane optical absorption anisotropy critical for applications, such as directional photonics, plasmonics, and waveguides. Here, we use polarization-dependent photoemission electron microscopy to visualize the anisotropic optical absorption of BP with 54 nm spatial resolution. We find the edges of BP flakes have a shift in their optical polarization anisotropy from the flake interior due to the 1D confinement and symmetry reduction at flake edges that alter the electronic charge distributions and transition dipole moments of edge electronic states, confirmed with first-principles calculations. These results uncover previously hidden modification of the polarization-dependent absorbance at the edges of BP, highlighting the opportunity for selective excitation of edge states of 2D materials with polarized light.
二维材料的电子结构和功能对结构形态高度敏感，这不仅为操纵材料特性提供了可能性，也使可预测和可重复的功能具有挑战性。黑磷（BP）是一种具有波纹状的正交晶系二维材料，其面内光学吸收各向异性对于诸如定向光子学、等离子体激元学和波导等应用至关重要。在此，我们使用偏振依赖光发射电子显微镜以54纳米的空间分辨率可视化BP的各向异性光学吸收。我们发现，由于一维限制以及薄片边缘处对称性降低，改变了边缘电子态的电荷分布和跃迁偶极矩，BP薄片边缘的光学偏振各向异性相对于薄片内部发生了偏移，这一点通过第一性原理计算得到了证实。这些结果揭示了BP边缘处偏振依赖吸光度先前隐藏的变化，突出了用偏振光选择性激发二维材料边缘态的机会。
