A Journey through Flatlands: Defects, Interfaces, and Properties of 2D-Materials
Department of Physics, University of South Florida, USA
Two dimensional materials, i.e. materials with strong in-plane covalent bonds, but only weak, mainly van der Waals interactions, between molecular planes, have promise for novel heterostructure materials and devices. The weak interlayer interactions enable the combination of materials with diverse properties with atomically sharp interfaces. However, even the weak interlayer interactions may decisively modify the materials properties. Consequently, the lack of interlayer interactions can give rise to different properties in monolayers compared to bulk materials. Moreover, in heterostructures of 2D materials interfaces also play an important role for modifying properties in these materials . In this talk, we examine how monolayers may be different from bulk materials and on how the materials properties of monolayers can be tuned by interfacing them with dissimilar materials. This is shown on the example of the opening of hybridization gaps in graphene if interfaced with bulk-MoS2 , as well as a tuning of the charge density wave transition in monolayer TiSe2 by growing monolayers on different van der Waals substrates [3,4]. In the second part of the talk, we address the formation and properties of grain boundaries in 2D Materials [5, 6, 7, 8, 9]. In particular, we show the first ARPES studies of the electronic structure of grain boundaries. In MoSe2these grain boundaries are 1D metallic materials and consequently are expected to exhibit Tomonaga Luttinger liquid (TLL) behavior. We discuss indication of TLL properties. Specifically, we demonstrate evidence for spin-charge separation in ARPES studies. Lastly, we discuss properties in monolayer VSe2 . MBE grown monolayers exhibit ferromagnetic properties, which were also predicted by DFT simulations. In contrast to DFT, however, ARPES measurements do not show any spin-split bands indicating that the observed magnetism is not well described by DFT and the magnetism must have a different origin.
Prof. Batzill graduated in Physics from the University of Goettingen, Germany and obtained a PhD in Physics in 1999 from the University of Newcastle upon Tyne, UK. He went on to do post-doc research at the Universities of Southern California in Los Angeles and Tulane University in New Orleans, before starting his independent research group at the University of South Florida (USF) in Tampa, USA in 2006. He is currently a full Professor of Physics. He received an NSF-CAREER award and NSF creative extension award. He also has been a Hans-Fischer Fellow of the Technical University of Munich, Germany and won several outstanding research achievement and faculty awards at USF. He gave over 70 invited talks and published more than 120 publications with an H-index of 41.
 H.C. Diaz, Y. Ma, S. Kolekar, J. Avila, C. Chen, M.C. Asensio, M.s Batzill. Substrate dependent electronic structure variations of van der Waals heterostructures of MoSe2 or MoSe2 (1-x) Te2x grown by van der Waals epitaxy. 2D Mater. 4, 025094 (2017).
 H.C. Diaz, J. Avila, C. Chen, R. Addou, M.C. Asensio, M. Batzill. Direct observation of interlayer hybridization and Dirac relativistic carriers in graphene/MoS2 van der Waals heterostructures. Nano Lett. 15, 1135-1140 (2015).
 S. Kolekar, M. Bonilla, Y. Ma, H.C. Diaz, M. Batzill. Layer-and substrate-dependent charge density wave criticality in 1T–TiSe2. 2D Mater. 5, 015006 (2017).
 S. Kolekar, M. Bonilla, H.C. Diaz, M. Hashimoto, D. Lu, M. Batzill. Controlling the Charge Density Wave Transition in Monolayer TiSe2: Substrate and Doping Effects. Adv. Quantum Technol. (2018) |https://doi.org/10.1002/qute.201800070
 J. Lahiri, Y. Lin, P. Bozkurt, I.I. Oleynik, M. Batzill. An extended defect in graphene as a metallic wire. Nat. Nano. 5, 326 (2010).
 P.M. Coelho, H.-P. Komsa, H.C. Diaz, Y. Ma, A.V. Krasheninnikov, M. Batzill. Post-Synthesis Modifications of Two-Dimensional MoSe2 or MoTe2 by Incorporation of Excess Metal Atoms into the Crystal Structure. ACS Nano 12, 3975-3984 (2018).
 H.C. Diaz, Y. Ma, R. Chaghi, M. Batzill. High density of (pseudo) periodic twin-grain boundaries in molecular beam epitaxy-grown van der Waals heterostructure: MoTe2/MoS2. Appl. Phys. Lett. 19, 191606 (2016).
 Y. Ma, H.C. Diaz, J. Avila, C. Chen, V. Kalappattil, R. Das, M.-H. Phan, T. ？ade？, J.M.P. Carmelo, M.C. Asensio, M. Batzill. Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe2 grain boundary. Nat. Commun. 8, 14231 (2107).
 M. Batzill. Mirror twin grain boundaries in molybdenum dichalcogenides. J. Phys: Condensed Matt. (2018) http://iopscience.iop.org/article/10.1088/1361-648X/aae9cf
 M. Bonilla, S. Kolekar, Y. Ma, H.C. Diaz, V. Kalappattil, R. Das, T. Eggers, H.R. Gutierrez, M.-H. Phan, M. Batzill. Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates. Nat. Nanotechnol. 13, 289 (2018).