Large Area Periodically Modulated 2D Transition Metal Dichalcogenide Layers Featuring Flat-Optics Light Harvesting

Transition Metal Dichalcogenides (TMDs) are two-dimensional semiconductors featuring high optical absorption coefficient combined with good transport and mechanical properties. Although mechanically exfoliated TMD flakes ensure the best opto-electronic properties, homogeneous large area growth techniques are mandatory for real world applications [1,2]. At the same time, in view of light conversion applications in the extreme thickness regime of 2D-TMDs it is essential to develop effective photon harvesting strategies.<br/>Here we demonstrate that periodic modulation of MoS₂ layers on large area nanostructured samples (either MoS₂ nanostripes arrays or conformal MoS₂ layers grown on top of nanogrooved silica templates) efficiently steers light parallel to the 2D material, exploiting photonic anomalies in the flat-optics regime [3,4].<br/>As a case study, we demonstrate that flat-optics light harvesting in periodically corrugated MoS₂ layers employed as photocatalysts boosts photodissociation of Methylene Blue (MB), a polluting dye molecule commonly used in the textile industry. When illumination occurs at the optimized angles which couple light to the photonic anomalies a two-fold faster photodissociation rate is observed with respect to planar MoS₂ films [6].<br/>In a recent development of our TMD platform, we demonstrated the possibility to stack different 2D-TMDs layers forming large area arrays of van der Waals heterostructures. For this purpose, we developed a custom prototype setup which allows sequential deposition of different TMD layers, MoS₂ and WS₂, by Ion Beam Sputtering. Physical deposition of WS₂ at glancing angles on the nanogrooved silica templates leads to the formation of laterally confined nanostripes which are subsequently coated by a MoS₂ layer, thus achieving maskless deposition of large area arrays of TMD heterostructures.<br/>Our preliminary results demonstrate the higher light trapping potential of the TMD heterostructures with respect to single component MoS₂ layers, to be employed as optical sensitizers in water remediation and photocatalytic applications [7].<br/><br/>[1] C. Martella et al., Adv. Mater. 2018, 30, 1705615<br/>[2] C. Martella et al., Adv. Mater. 2017, 1605785<br/>[3] M. Bhatnagar et al., Nanoscale, 2020, 12, s24385-24393<br/>[4] M. Bhatnagar et al., ACS Appl. Mater. Interfaces 2021, 13, 13508−13516<br/>[5] M.C. Giordano et al., under review<br/>[6] G. Ferrando et al., submitted<br/>[7] M. Gardella et al., manuscript in preparation