Browsing by Author "Jain, Mitisha"

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Atomistic Simulations of Defects Production under Ion Irradiation in Epitaxial Graphene on SiC
(2023-03) Jain, Mitisha; Kretschmer, Silvan; Höflich, Katja; Lopes, Joao Marcelo Jordao; Krasheninnikov, Arkady V.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Using first-principles and analytical potential atomistic simulations, production of defects in epitaxial graphene (EG) on SiC upon ion irradiation for ion types and energies accessible in helium-ion microscope is studied. Graphene-SiC systems consisting of the buffer (zero) graphene layer and SiC substrate, as well as one (monolayer) and two (bilayer) additional graphene layers, are focused on. The probabilities for single, double, and more complex vacancies to appear upon impacts of energetic ions in each graphene layer as functions of He- and Ne-ion energies are calculated and the data are compared with those obtained for free-standing graphene. The results indicate that the role of the substrate is minimal for He-ion irradiation with energies above 5 keV, which can be associated with a low sputtering yield from this system upon ion irradiation, as compared with the common Si/SiO2 substrate. In contrast, SiC substrate has a significant effect on defect production upon Ne-ion irradiation. The results can serve as a guide to the experiments on ion irradiation of EG to choose the optimum ion beam parameters for defect-mediated engineering of such systems, for example, for creating nucleation centers to grow other 2D materials, such as h-BN, on top of the irradiated EG.
Electron holographic mapping of structural reconstruction at mono- and bilayer steps of h-BN
(2023-07) Subakti, Subakti; Daqiqshirazi, Mohammadreza; Wolf, Daniel; Linck, Martin; Kern, Felix L.; Jain, Mitisha; Kretschmer, Silvan; Krasheninnikov, Arkady V.; Brumme, Thomas; Lubk, Axel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Here, by making use of medium and high resolution autocorrected off-axis electron holography, we directly probe the electrostatic potential as well as in-plane structural reconstruction at edges and steps in multilayer hexagonal boron nitride. In combination with ab initio calculations, the data allows revealing the formation of folded zigzag edges at steps comprising two monolayers and their absence at monolayer steps.
Extrinsic Localized Excitons in Patterned 2D Semiconductors
(2022-08) Yagodkin, Denis; Greben, Kyrylo; Ascunce, Alberto Eljarrat; Kovalchuk, Sviatoslav; Ghorbani-Asl, Mahdi; Jain, Mitisha; Kretschmer, Silvan; Severin, Nikolai; Rabe, Juergen P.; Krasheninnikov, Arkady V.; Koch, Christoph T.; Bolotin, Kirill I.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A new localized excitonic state is demonstrated in patterned monolayer 2D semiconductors. The signature of an exciton associated with that state is observed in the photoluminescence spectrum after electron beam exposure of several 2D semiconductors. The localized state, which is distinguished by non-linear power dependence, survives up to room temperature and is patternable down to 20 nm resolution. The response of the new exciton to the changes of electron beam energy, nanomechanical cleaning, and encapsulation via multiple microscopic, spectroscopic, and computational techniques is probed. All these approaches suggest that the state does not originate from irradiation-induced structural defects or spatially non-uniform strain, as commonly assumed. Instead, it is shown to be of extrinsic origin, likely a charge transfer exciton associated with the organic substance deposited onto the 2D semiconductor. By demonstrating that structural defects are not required for the formation of localized excitons, this work opens new possibilities for further understanding of localized excitons as well as their use in applications that are sensitive to the presence of defects, e.g. chemical sensing and quantum technologies.