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1. Configurable phonon polaritons in twisted α-MoO3

   https://doi.org/10.1038/s41563-020-0732-6  

   Chen, Mingyuan; Lin, Xiao; Dinh, Thao H.; Zheng, Zhiren; Shen, Jialiang; Ma, Qiong; Chen, Hongsheng; Jarillo-Herrero, Pablo; Dai, Siyuan (December 2020, Nature Materials)

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2. Charge-transfer hyperbolic polaritons in α-MoO3/graphene heterostructures

   https://doi.org/10.1063/5.0173562  

   Shen, J.; Chen, M.; Korostelev, V.; Kim, H.; Fathi-Hafshejani, P.; Mahjouri-Samani, M.; Klyukin, K.; Lee, G.-H.; Dai, S. (April 2024, Applied Physics Reviews)

   Charge transfer is a fundamental interface process that can be harnessed for light detection, photovoltaics, and photosynthesis. Recently, charge transfer was exploited in nanophotonics to alter plasmon polaritons by involving additional non-polaritonic materials to activate the charge transfer. Yet, direct charge transfer between polaritonic materials has not been demonstrated. We report the direct charge transfer in pure polaritonic van der Waals (vdW) heterostructures of α-MoO3/graphene. We extracted the Fermi energy of 0.6 eV for graphene by infrared nano-imaging of charge transfer hyperbolic polaritons in the vdW heterostructure. This unusually high Fermi energy is attributed to the charge transfer between graphene and α-MoO3. Moreover, we have observed charge transfer hyperbolic polaritons in multiple energy–momentum dispersion branches with a wavelength elongation of up to 150%. With the support from the density functional theory calculation, we find that the charge transfer between graphene and α-MoO3, absent in mechanically assembled vdW heterostructures, is attributed to the relatively pristine heterointerface preserved in the epitaxially grown vdW heterostructure. The direct charge transfer and charge transfer hyperbolic polaritons demonstrated in our work hold great promise for developing nano-optical circuits, computational devices, communication systems, and light and energy manipulation devices. 

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3. Tuning of Optical Phonons in α-MoO3–VO2 Multilayers

   https://doi.org/doi.org/10.1021/acsami.1c12320  

   Dereshgi, Sina; Larciprete, Maria; Centini, Marco; Murthy, Akshay; Tang, Kechao; Wu, Junqiao; Dravid, Vinayak; Aydin, Koray (October 2021, ACS applied materials interfaces)

   Merging the properties of VO2 and van der Waals (vdW) materials has given rise to novel tunable photonic devices. Despite recent studies on the effect of the phase change of VO2 on tuning near-field optical response of phonon polaritons in the infrared range, active tuning of optical phonons (OPhs) using far-field techniques has been scarce. Here, we investigate the tunability of OPhs of α-MoO3 in a multilayer structure with VO2. Our experiments show the frequency and intensity tuning of 2 cm–1 and 11% for OPhs in the [100] direction and 2 cm–1 and 28% for OPhs in the [010] crystal direction of α-MoO3. Using the effective medium theory and dielectric models of each layer, we verify these findings with simulations. We then use loss tangent analysis and remove the effect of the substrate to understand the origin of these spectral characteristics. We expect that these findings will assist in intelligently designing tunable photonic devices for infrared applications, such as tunable camouflage and radiative cooling devices. 

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4. Oxidation state of Mo affects dissolution and visible-light photocatalytic activity of MoO3 nanostructures

   https://doi.org/10.1016/j.jcat.2019.11.035  

   Peña-Bahamonde, Janire; Wu, Chunzheng; Fanourakis, Sofia K.; Louie, Stacey M.; Bao, Jiming; Rodrigues, Debora F. (January 2020, Journal of Catalysis)
5. CIRCULARLY POLARIZED THERMAL RADIATION IN α-MoO3/β-Ga2O3 TWISTED LAYERS

   https://doi.org/10.1615/RAD-23.180  

   Centini, Marco; Yang, Chiyu; Larciprete, Maria Cristina; Antezza, Mauro; Zhang, Zhuomin M. (January 2023, Proceedings of the 10th International Symposium on Radiative Transfer, RAD-23 Thessaloniki, Greece, 12–16 June 2023)

   We numerically investigated the possibility to obtain circularly polarized infrared thermal emission from a bilayer scheme taking advantage of the strong anisotropy of low symmetry materials such as -Ga2O3 and -MoO3. Our results show that it is possible to achieve a high degree of circular polarization over 0.85 at two typical emission frequencies related to the excitation of -Ga2O3 optical phonons. Our simple but effective scheme could set the basis for a new class of lithography-free thermal sources for IR bio-sensing. 

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