Giant Optical Anisotropy and High Refractive Index in van der Waals Materials

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Two-dimensional materials are at the core of many fields of modern optoelectronics [1] and nanophotonics [2]. However, relatively small research attention is devoted to their bulk counterparts [3,4]. In this webinar, we demonstrate that bulk van der Waals crystals (MoS2, WS2, MoSe2, WSe2, hBN, and many others) are even more promising material platforms for optical applications than two-dimensional materials thanks to unprecedented giant optical anisotropy (around 2) and high refractive index (around 4) in a broad spectral range from ultraviolet (for hBN) to visible (for MoS2 and WS2) and near-infrared (for MoSe2 and WSe2) wavelengths. These outstanding properties allow us to design next-generation integrated circuits and optical elements [4-7].

In detail, we managed to achieve unmatched lateral dimensions for van der Waals-based waveguides with only several tens of nanometers footprint. In other words, it gives a unique opportunity to place around 10000 waveguides on an mm-scale photonic chip. These characteristics make us a step closer to electronic integrated circuits. Hence, van der Waals-based photonic integrated circuits can become a decisive platform for an electronic-to-photonic replacement to increase computer data processing. The idea behind the use of van der Waals materials has four advantages. First, van der Waals crystals have larger optical bandgap in comparison with conventional high refractive index materials (TiO2, GaP, Si, Ge, and many others) and, therefore, smaller operation wavelength without dissipative losses [4]. Secondly, van der Waals materials have one of the largest refractive indices among known materials [4]. Thirdly, the record-breaking optical anisotropy of van der Waals gives an additional degree of freedom for the design optimization of integrated photonic elements [4]. Finally, van der Waals materials have dangling bonds-free surfaces and atomically sharp edges after the lithography process, which results in minimum scattering losses in photonic waveguides and high-intensity nonlinear properties in addition to superior linear response [7-9]. From a broader perspective, we would like to note that these van der Waals features are also beneficial for countless optical devices (resonators, dielectric mirrors, waveplates, and many others) beyond on-chip integration.

References
[1] S. Manzeli, D. Ovchinikov, D. Pasquier, O.V. Yazyev, and A. Kis, “2D transition metal dichalcogenides”, Nature Reviews Materials 2, 17033 (2017).
[2] F. Xia, H. Wang, D. Xiao, M. Dubey, and A. Ramasubramaniam, “Two-dimensional material nanophotonics”, Nature Photonics 8, 899-907 (2014).
[3] R. Verre, D.G. Baranov, B. Munkhbat, J. Cuadra, M. Kall, and T. Shegai, “Transition metal dichalcogenide nanodisks as high-index dielectric Mie nanoresonators”,Nature Nanotechnology 14, 679-683 (2019).
[4] G.A. Ermolaev, D.V. Grudinin, Y.V. Stebunov, K.V. Voronin, V.G. Kravets, J. Duan, A.B. Mazitov, G.I. Tselikov, A. Bylinkin, D.I. Yakubovsky, S.M. Novikov, D.G. Baranov, A.Y. Nikitin, I.A. Kruglov, T. Shegai, p. Alonso-Gonzalez, A.N. Grigorenko, A.V. Arsenin, K.S. Novoselov, V.S. Volkov, “Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics”, Nature Communications 12, 854 (2021).
[5] G. Ermolaev, D. Grudinin, K. Voronin, A. Vyshnevyy, A. Arsenin, and V. Volkov, “Van der Waals materials for subdiffractional light guidance”, Photonics 9, 744 (2022).

[6] G.I. Tselikov, G.A. Ermolaev, A.A.Popov, G.V. Tikhonowski, D.A. Panova, A.S. Taradin, A.A. Vyshnevyy, A.V. Syuy, S.M. Klimentov, S.M. Novikov, A.B. Evlyukhin, A.V. Kabashin, A.V. Arsenin, K.S. Novoselov, and V.S. Volkov, “Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics”, PNAS 119, e2208830119 (2022).
[7] A.A. Popkova, I.M. Antropov, G.I. Tselikov, G.A. Ermolaev, I. Ozerov, R.V. Kirtaev, S.M. Novikov, A.B. Evlyukhin, A.V. Arsenin, V.O. Bessonov, V.S. Volkov, and A.A. Fedyanin, “Nonlinear exciton‐Mie coupling in transition metal dichalcogenide nanoresonators”, Laser and Photonics Reviews 16, 2100604 (2022).
[8] B. Munkhbat, A.B. Yankovich, D.G. Baranov, R. Verre, E. Olsson, and T.O. Shegai, “Transition metal dichalcogenide metamaterials with atomic precision”, Nature Communications 11, 4604 (2020).
[9] B. Munkhbat, B. Kucukoz, D.G. Baranov, T.J. Antosiewicz, and T.O. Shegai, “Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics”, Laser and Photonics Reviews 17, 2200057 (2022).

Atomic force microscope image of unidirectionally directionally controlled grown nanofibers

Electron microscope image and structural model of TMC atomic wire nanofibers aggregated in the same direction

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Ferroelectricity is observed in hexagonal boron nitride(hBN) through control of the registry of stacked layers, which we explore through both amplitude-modulated and sideband Kelvin probe force microscopy (KPFM) on the Park FX40 automatic AFM.

A schematic of the formation of parallel stacked bilayer hBN is shown in addition to a contact potential difference map measured using sideband KPFM.

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Georgy Ermolaev

Emerging Technologies Research Center, XPANCEO, Dubai00000, United Arab Emirates

Georgy Ermolaev received a Ph.D. in “Broadband optical properties of MoS2 for photonic applications” in 2022 from the Moscow Institute of Physics and Technology. After receiving a Ph.D. Georgy Ermolaev became Research Studies Manager in Xpanceo (Dubai, United Arab Emirates), a deep tech company specializing in next-generation optoelectronic devices. In 2023 Georgy Ermolaev also joined the University of Rome Tor Vergata (Rome, Italy) as a Visiting Researcher. His research interest encompasses various areas, such as ellipsometry, 2D and quantum materials, integrated nanophotonics, biosensors, plasmonics, scanning near-field optical microscopy, and smart contact lenses. Georgy Ermolaev has an impressive publication record, with over 50 published papers and more than 1500 citations during the last 5 years.

Enriching your AFM data: KPFM high resolution imaging of ferroelectric domains with automated AFM

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