Scholarly Work - Physics
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/3458
Browse
Search Results
Item Anisotropic 2D excitons unveiled in organic–inorganic quantum wells(Royal Society of Chemistry, 2020-11) Maserati, Lorenzo; Refaely-Abramson, Sivan; Kastl, Christoph; Chen, Christopher T.; Borys, Nicholas J.; Eisler, Carissa N.; Collins, Mary S.; Smidt, Tess E.; Barnard, Edward S.; Strasbourg, Matthew; Schriber, Elyse A.; Shevitski, Brian; Yao, Kaiyuan; Hohman, J. Nathan; Schuck, P. James; Aloni, Shaul; Neaton, Jeffrey B.; Schwartzberg, Adam M.Hybrid layered metal chalcogenide crystalline polymer hosts strongly anisotropic two-dimensional excitons with large binding energies.Item The ultrafast onset of exciton formation in 2D semiconductors(Springer Science and Business Media LLC, 2020-10) Trovatello, Chiara; Katsch, Florian; Borys, Nicholas J.; Selig, Malte; Yao, Kaiyuan; Borrego-Varillas, Rocio; Scotognella, Francesco; Kriegel, Ilka; Yan, Aiming; Zettl, Alex; Schuck, P. James; Knorr, Andreas; Cerullo, Giulio; Dal Conte, StefanoThe equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process.Item Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room(2020-11) Darlington, Thomas P.; Carmesin, Christian; Florian, Matthias; Yanev, Emanuil; Ajayi, Obafunso; Ardelean, Jenny; Rhodes, Daniel A.; Ghiotto, Augusto; Krayev, Andrey; Watanabe, K.; Taniguchi, T.; Kysar, Jeffrey W.; Pasupathy, Abhay N.; Hone, James C.; Jahnke, Frank; Borys, Nicholas J.; Schuck, P. JamesIn monolayer transition-metal dichalcogenides, localized strain can be used to design nanoarrays of single photon sources. Despite strong empirical correlation, the nanoscale interplay between excitons and local crystalline structure that gives rise to these quantum emitters is poorly understood. Here, we combine room-temperature nano-optical imaging and spectroscopic analysis of excitons in nanobubbles of monolayer WSe2 with atomistic models to study how strain induces nanoscale confinement potentials and localized exciton states. The imaging of nanobubbles in monolayers with low defect concentrations reveals localized excitons on length scales of around 10 nm at multiple sites around the periphery of individual nanobubbles, in stark contrast to predictions of continuum models of strain. These results agree with theoretical confinement potentials atomistically derived from the measured topographies of nanobubbles. Our results provide experimental and theoretical insights into strain-induced exciton localization on length scales commensurate with exciton size, realizing key nanoscale structure–property information on quantum emitters in monolayer WSe2.Item Light-Driven Permanent Charge Separation across a Hybrid Zero-Dimensional/Two-Dimensional Interface(2020-04) Kriegel, Ilka; Ghini, Michele; Bellani, Sepastiano; Zhang, Kehao; Jansons, Adam W.; Crockett, Brandon M.; Koskela, Kristopher M.; Barnard, Edward S.; Penzo, Erika; Hutchison, James E.; Robinson, Joshua A.; Manna, Liberato; Borys, Nicholas J.; Schuck, P. JamesWe report the first demonstration of light-driven permanent charge separation across an ultrathin solid-state zero-dimensional (0D)/2D hybrid interface by coupling photoactive Sn-doped In2O3 nanocrystals with monolayer MoS2, the latter serving as a hole collector. We demonstrate that the nanocrystals in this device-ready architecture act as local light-controlled charge sources by quasi-permanently donating ∼5 holes per nanocrystal to the monolayer MoS2. The amount of photoinduced contactless charge transfer to the monolayer MoS2 competes with what is reached in electrostatically gated devices. Thus, we have constructed a hybrid bilayer structure in which the electrons and holes are separated into two different solid-state materials. The temporal evolution of the local doping levels of the monolayer MoS2 follows a capacitive charging model with effective total capacitances in the femtofarad regime and areal capacitances in the μF cm–2 range. This analysis indicates that the 0D/2D hybrid system may be able to store light energy at densities of at least μJ cm–2, presenting new potential foundational building blocks for next-generation nanodevices that can remotely control local charge density, power miniaturized circuitry, and harvest and store optical energy.Item Light-Driven Permanent Charge Separation across a Hybrid Zero-Dimensional/Two-Dimensional Interface(2020-03) Kriegel, Ilka; Ghini, Michele; Bellani, Sebastiano; Zhang, Kehao; Jansons, Adam W.; Crockett, Brandon M.; Koskela, Kristopher M.; Barnard, Edward S.; Penzo, Erika; Hutchison, James E.; Robinson, Joshua A.; Manna, Liberato; Borys, Nicholas J.; Schuck, P. JamesWe report the first demonstration of light-driven permanent charge separation across an ultrathin solid-state zero-dimensional (0D)/2D hybrid interface by coupling photoactive Sn-doped In2O3 nanocrystals with monolayer MoS2, the latter serving as a hole collector. We demonstrate that the nanocrystals in this device-ready architecture act as local light-controlled charge sources by quasi-permanently donating ∼5 holes per nanocrystal to the monolayer MoS2. The amount of photoinduced contactless charge transfer to the monolayer MoS2 competes with what is reached in electrostatically gated devices. Thus, we have constructed a hybrid bilayer structure in which the electrons and holes are separated into two different solid-state materials. The temporal evolution of the local doping levels of the monolayer MoS2 follows a capacitive charging model with effective total capacitances in the femtofarad regime and areal capacitances in the μF cm–2 range. This analysis indicates that the 0D/2D hybrid system may be able to store light energy at densities of at least μJ cm–2, presenting new potential foundational building blocks for next-generation nanodevices that can remotely control local charge density, power miniaturized circuitry, and harvest and store optical energy.