Youngji Kim
Vanderbilt University – Nashville, Tennessee, USA
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Twisted two-dimensional van der Waals heterostructures have been widely investigated for their ability to manipulate light-matter interactions. Optical observation of the moirélattice is crucial for understanding the induced long-range periodicity and its impact on the optical and electronic behavior of these heterostructure devices. Furthermore, moiré studies to date have focused on twisted individual monolayers, thus, the extent of the moiré interactions out of plane have not been quantitatively investigated. In this study, we experimentally investigate the optical moirépatterns of twisted hBN structures using scattering-type scanning near-field optical microscopy (s-SNOM) within non-monolayer systems. A distinct variation in the frequency-dependent moirépattern is clearly observed in each isotope twisted structure near the transverse optic (TO) phonon resonance, with the moiré pattern observed in structures up to 5 monolayers each. Further analysis and comparison of local TO phonon frequency shifts and domain wall variations as a function of isotope composition and structure thickness using nano-FTIR measurements and superlattice calculations will also be discussed. This work provides experimental evidence of isotope dependency in optical moirépatterns, revealing how isotope composition affects lattice dynamics and phonon-mediated optical properties in twisted heterogeneous moiré, as well as providing insight into the vertical extent of the moiré interactions in the atomic-scale limit.
Email: youngji.kim@vanderbilt.edu