Plasmonic Tip-Enhanced Probing of Excitonic Materials and Heterostructures

Two-Dimensional (2D) chalcogenides of Mo and W are semiconductors that show strong excitonic responses due to their highly quantum-confined character. ^{1, 2}^,^{3, 4} This talk will discuss our recent work on optical phenomena and electronic phenomena in 2D semiconductors when they are placed in close proximity on plasmonic substrates such as Au, Ag and Al.<br/>For a bulk of this talk, I will be presenting our work on near-field optical spectroscopy using a plasmonic tip. I will also show how using a plasmonic tip once can use near-field tip based micro-spectroscopy to probe defects,^{5, 6} interfaces^{7, 8} and hybrid states in 2D excitonic semiconductors. I will start by showing how tip-enhanced micro-spectroscopy can be used to probe buried metal-semiconductor interfaces in 2D MoS₂.⁷ Specifically, I will focus on how scanning potential probe and scanning conductance probe can be correlated with near-field photoluminescence (PL) to understand the nature of contact between metal and the semiconductor. Next, I will show that the same technique can be used to probe defects,⁵ heterointerfaces, heterogeneities and strain⁹ in 2D semiconductor layers. I will also show how strong-light matter coupling between excitons and plasmonic gap modes can be probed directly using this technique¹⁰ including observation of interlayer excitons.^{11, 12}<br/><b>References:</b><br/>1. Jariwala, D.; Marks, T. J.; Hersam, M. C., Mixed Dimensional van der Waals Heterostructures. <i>Nature Materials </i><b>2017,</b> <i>16</i>, 170-181.<br/>2. Jariwala, D.; Sangwan, V. K.; Lauhon, L. J.; Marks, T. J.; Hersam, M. C., Emerging device applications for semiconducting two-dimensional transition metal dichalcogenides. <i>ACS Nano </i><b>2014,</b> <i>8</i> (2), 1102–1120.<br/>3. Brar, V. W.; Sherrott, M. C.; Jariwala, D., Emerging photonic architectures in two-dimensional opto-electronics. <i>Chemical Society Reviews </i><b>2018,</b> <i>47</i> (17), 6824-6844.<br/>4. Jariwala, D.; Davoyan, A. R.; Wong, J.; Atwater, H. A., Van der Waals Materials for Atomically-Thin Photovoltaics: Promise and Outlook. <i>ACS Photonics </i><b>2017,</b> <i>4</i>, 2692-2970.<br/>5. Moore, D.; Jo, K.; Nguyen, C.; Lou, J.; Muratore, C.; Jariwala, D.; Glavin, N. R., Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes. <i>npj 2D Materials and Applications </i><b>2020,</b> <i>4</i> (1), 44.<br/>6. Chowdhury, T.; Kim, J.; Sadler, E. C.; Li, C.; Lee, S. W.; Jo, K.; Xu, W.; Gracias, D. H.; Drichko, N. V.; Jariwala, D.; Brintlinger, T. H.; Mueller, T.; Park, H.-G.; Kempa, T. J., Substrate-directed synthesis of MoS2 nanocrystals with tunable dimensionality and optical properties. <i>Nature Nanotechnology </i><b>2020,</b> <i>15</i> (1), 29-34.<br/>7. Jo, K.;et al. Jariwala, D., Direct Optoelectronic Imaging of 2D Semiconductor–3D Metal Buried Interfaces. <i>ACS Nano </i><b>2021,</b> <i>15</i> (3), 5618-5630.<br/>8. Krayev, A.; et al. Jariwala, D., Dry Transfer of van der Waals Crystals to Noble Metal Surfaces To Enable Characterization of Buried Interfaces. <i>ACS Applied Materials & Interfaces </i><b>2019,</b> <i>11</i> (41), 38218-38225.<br/>9. Kim, G.; et al. Jariwala, D., High Density, Localized Quantum Emitters in Strained 2D Semiconductors. <i>ACS Nano </i><b>2022,</b> <i>16</i> (6), 9651–9659.<br/>10. Jo, K.;et al. Jariwala, D., Direct Nano-Imaging of Light-Matter Interactions in Nanoscale Excitonic Emitters. <i>Nature Communications </i><b>2023,</b> <i>14</i>, 2469.<br/>11. Rahaman, et al. Jariwala, D., Tunable Localized Charge Transfer Excitons in a Mixed Dimensional van der Waals Heterostructure. <i>arXiv preprint arXiv:2210.12608 </i><b>2022</b>.<br/>12. Rahaman, M.; Kim, G.; Ma, K. Y.; Song, S.; Shin, H. S.; Jariwala, D., Tailoring Exciton Dynamics in TMDC Heterobilayers in the Quantum Plasmonic Regime.<i> arXiv:2306.06337 </i><b>2023</b>.