Yang Jiong, Mayyas Mohannad, Tang Jianbo, Ghasemian Mohammad B, Yang Honghua, Watanabe Kenji, Taniguchi Takashi, Ou Qingdong, Li Lu Hua, Bao Qiaoliang, Kalantar-Zadeh Kourosh
School of Chemical Engineering , University of New South Wales (UNSW) , Sydney Campus, NSW 2052 Australia.
Bruker Nano , 112 Robin Hill Road , Santa Barbara , California 93117 United States.
ACS Nano. 2020 Jan 28;14(1):1123-1132. doi: 10.1021/acsnano.9b08895. Epub 2019 Dec 23.
Phonon-polaritons (PhPs) in layered crystals, including hexagonal boron nitride (hBN), have been investigated by combined scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. Nevertheless, many of such s-SNOM-based FTIR spectra features remain unexplored, especially those originated from the impact of boundaries. Here we observe real-space PhP propagations in thin-layer hBN sheets either supported or suspended by s-SNOM imaging. Then with a high-power broadband IR laser source, we identify two major peaks and multiple auxiliary peaks in the near-field amplitude spectra, obtained using scattering-type near-field FTIR spectroscopy, from both supported and suspended hBN. The major PhP propagation interference peak moves toward the major in-plane phonon peak when the IR illumination moves away from the hBN edge. Specific differences between the auxiliary peaks in the near-field amplitude spectra from supported and suspended hBN sheets are investigated regarding different boundary conditions, associated with edges and substrate interfaces. The outcomes may be explored in heterostructures for advanced nanophotonic applications.
包括六方氮化硼（hBN）在内的层状晶体中的声子极化激元（PhPs），已通过散射型扫描近场光学显微镜（s-SNOM）和傅里叶变换红外（FTIR）光谱相结合的方法进行了研究。然而，许多基于s-SNOM的FTIR光谱特征仍未被探索，尤其是那些源于边界影响的特征。在此，我们通过s-SNOM成像观察了支撑或悬浮的薄层hBN片中的实空间PhP传播。然后，使用高功率宽带红外激光源，我们在通过散射型近场FTIR光谱获得的支撑和悬浮hBN的近场振幅光谱中识别出两个主要峰和多个辅助峰。当红外照明远离hBN边缘时，主要的PhP传播干涉峰向主要的面内声子峰移动。针对与边缘和衬底界面相关的不同边界条件，研究了支撑和悬浮hBN片近场振幅光谱中辅助峰的具体差异。这些结果可用于先进纳米光子学应用的异质结构研究。
