Journal
LIGHT-SCIENCE & APPLICATIONS
Volume 7, Issue -, Pages -Publisher
SPRINGERNATURE
DOI: 10.1038/lsa.2018.5
Keywords
armchair orientation mapping; atomically thin transition metal dichalcogenides; crystal quality marker; graphene-related materials; polarization-resolved second-harmonic generation
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Funding
- European Research Infrastructure NFFA-Europe - EU [654360]
- Stavros Niarchos Foundation
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We used nonlinear laser scanning optical microscopy to study atomically thin transition metal dichalcogenides (TMDs) and revealed, with unprecedented resolution, the orientational distribution of armchair directions and their degree of organization in the two-dimensional (2D) crystal lattice. In particular, we carried out polarization-resolved second-harmonic generation (PSHG) imaging for monolayer WS2 and obtained, with high-precision, the orientation of the main crystallographic axis (armchair orientation) for each individual 120 x 120 nm(2) pixel of the 2D crystal area. Such nanoscale resolution was realized by fitting the experimental PSHG images, obtained with sub-micron precision, to a new generalized theoretical model that accounts for the nonlinear optical properties of TMDs. This enabled us to distinguish between different crystallographic domains, locate boundaries and reveal fine structure. As a consequence, we can calculate the mean orientational average of armchair angle distributions in specific regions of interest and define the corresponding standard deviation as a figure-of-merit for the 2D crystal quality.
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