Abstract
Low-dimensional nanostructures of electronic and/or optical materials possess a large number of new properties due to space quantization, thus exceeding the bulk "parent" materials. Similarly, nanoheterostructures of these materials provide even better control of properties and allow to explore new physics and utilize novel phenomena for device applications. In such systems, the materials properties can vary at the size scale of several nanometers.
To meet the challenge of studying nanoheterostructures, the optical materials characterization tools have been recently extended beyond bulk spectroscopy or imaging. A number of Near-Field Optical Microscopy methods were developed. In this online presentation, we will report on a new approach to hyperspectral imaging with scattering Scanning Near-Field Optical Microscopy (sSNOM) which allowed us to perform materials spectroscopy with resolution not restricted by Abbe (diffraction) limit.
In 2020, a new class of low-dimensional nanoheterostructure materials – two-dimensional sandwich materials (semiconductor and insulator van der Waals heterostructures) wrapped around carbon nanotube – has been synthesized [1]. Although confirmed by the structural studies (TEM) and elemental analysis (macro- to micro-scale), the heterostructures themselves or their devices were hardly imaged, except for AFM or SEM, not giving materials information. This is due to the diameter of the smallest part ca. 1-2 nm, much beyond the limitations of typical analytical methods.
Here we present results on imaging different materials containing the nanoheterostructure with the sSNOM hyperspectral mapping [2]. The maximum resolution (imaging of 2 nm heteronanotube) achieved in these experiments exceeds the inverse wavelength of excitation mid-IR laser ~3,700 times, thus beating diffraction limits of regular optical spectroscopy. Heteronanotubes have been studied on the substrate as well as in real devices (diodes). Imaging of the heteronanotubes through the over-deposited metal electrodes was demonstrated.
Acknowledgments: sSNOM work was supported by the National Science Foundation (Grant DMR-2011839). Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan. Part of this work was conducted at Takeda Sentanchi Supercleanroom, supported by "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, Grant number JPMXP09F19UT0006.
[1] Xiang, R.; Inoue, T.; Zheng, Y.; Kumamoto, A.; Qian, Y.; Sato, Y.; Liu, M.; Tang, D.; Gokhale, D.; Guo, J.; Hisama, K.; Yotsumoto, S.; Ogamoto, T.; Arai, H.; Kobayashi, Y.; Zhang, H.; Hou, B.; Anisimov, A.; Maruyama, M.; Miyata, Y.; Okada, S.; Chiashi, S.; Li, Y.; Kong, J.; Kauppinen, E. I.; Ikuhara, Y.; Suenaga, K.; Maruyama, S., One-dimensional van der Waals heterostructures. Science 2020, 367 (6477), 537.
[2] Y. Feng, H. Li, T. Inoue, S. Chiashi, S. V. Rotkin, R. Xiang, and S. Maruyama, "One-dimensional van der waals hetero-junction diode", (2020), arXiv:2012.03180.