Chaudhary Kundan, Tamagnone Michele, Rezaee Mehdi, Bediako D Kwabena, Ambrosio Antonio, Kim Philip, Capasso Federico
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Department of Electrical Engineering, Howard University, Washington, DC 20059, USA.
Sci Adv. 2019 Apr 12;5(4):eaau7171. doi: 10.1126/sciadv.aau7171. eCollection 2019 Apr.
Van der Waals (vdW) heterostructures assembled from layers of two-dimensional materials have attracted considerable interest due to their novel optical and electrical properties. Here, we report a scattering-type scanning near-field optical microscopy study of hexagonal boron nitride on black phosphorus (h-BN/BP) heterostructures, demonstrating the first direct observation of in-plane anisotropic phonon polariton modes in vdW heterostructures. Notably, the measured in-plane optical anisotropy along the armchair and zigzag crystal axes exceeds the ratio of refractive indices of BP in the - plane. We explain that this enhancement is due to the high confinement of the phonon polaritons in h-BN. We observe a maximum in-plane optical anisotropy of α = 1.25 in the frequency spectrum at 1405 to 1440 cm. These results provide new insights into the behavior of polaritons in vdW heterostructures, and the observed anisotropy enhancement paves the way to novel nanophotonic devices and to a new way to characterize optical anisotropy in thin films.
由二维材料层组装而成的范德华（vdW）异质结构因其新颖的光学和电学性质而引起了广泛关注。在此，我们报道了对黑磷上的六方氮化硼（h-BN/BP）异质结构进行的散射型扫描近场光学显微镜研究，首次直接观察到了vdW异质结构中的面内各向异性声子极化激元模式。值得注意的是，沿扶手椅型和锯齿型晶轴测量的面内光学各向异性超过了BP在面内的折射率之比。我们解释这种增强是由于声子极化激元在h-BN中的高度限制。我们在1405至1440厘米的频谱中观察到面内光学各向异性的最大值α = 1.25。这些结果为vdW异质结构中极化激元的行为提供了新的见解，并且观察到的各向异性增强为新型纳米光子器件以及表征薄膜光学各向异性的新方法铺平了道路。
