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1. Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects

Author

Griffin, Eoin, Mogg, Lucas, Hao, Guang-Ping, Kalon, Gopinadhan, Bacaksiz, Cihan, Lopez-Polin, Guillermo, Zhou, T. Y., Guarochico, Victor, Cai, Junhao, Neumann, Christof, Winter, Andreas, Mohn, Michael, Lee, Jong Hak, Lin, Junhao, Kaiser, Ute, Grigorieva, Irina V., Suenaga, Kazu, Ozyilmaz, Barbaros, Cheng, Hui-Min, Ren, Wencai, Turchanin, Andrey, Peeters, Francois M., Geim, Andre K., and Lozada-Hidalgo, Marcelo

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Defect-free graphene is impermeable to gases and liquids but highly permeable to thermal protons. Atomic-scale defects such as vacancies, grain boundaries and Stone-Wales defects are predicted to enhance graphene's proton permeability and may even allow small ions through, whereas larger species such as gas molecules should remain blocked. These expectations have so far remained untested in experiment. Here we show that atomically thin carbon films with a high density of atomic-scale defects continue blocking all molecular transport, but their proton permeability becomes ~1,000 times higher than that of defect-free graphene. Lithium ions can also permeate through such disordered graphene. The enhanced proton and ion permeability is attributed to a high density of 8-carbon-atom rings. The latter pose approximately twice lower energy barriers for incoming protons compared to the 6-atom rings of graphene and a relatively low barrier of ~0.6 eV for Li ions. Our findings suggest that disordered graphene could be of interest as membranes and protective barriers in various Li-ion and hydrogen technologies.

Published
2020
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2. Lateral heterostructures of two-dimensional materials by electron-beam induced stitching

Author

Winter, Andreas, George, Antony, Neumann, Christof, Tang, Zian, Mohn, Michael J., Biskupek, Johannes, Masurkar, Nirul, Arava, Leela Mohana Reddy, Weimann, Thomas, Hübner, Uwe, Kaiser, Ute, and Turchanin, Andrey

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We present a novel methodology to synthesize two-dimensional (2D) lateral heterostructures of graphene and MoS2 sheets with molecular carbon nanomembranes (CNMs), which is based on electron beam induced stitching. Monolayers of graphene and MoS2 were grown by chemical vapor deposition (CVD) on copper and SiO2 substrates, respectively, transferred onto gold/mica substrates and patterned by electron beam lithography or photolithography. Self-assembled monolayers (SAMs) of aromatic thiols were grown on the gold film in the areas where the 2D materials were not present. An irradiation with a low energy electron beam was employed to convert the SAMs into CNMs and simultaneously stitching the CNM edges to the edges of graphene and MoS2, therewith forming a heterogeneous but continuous film composed of two different materials. The formed lateral heterostructures possess a high mechanical stability, enabling their transfer from the gold substrate onto target substrates and even the preparation as freestanding sheets. We characterized the individual steps of this synthesis and the structure of the final heterostructures by complementary analytical techniques including optical microscopy, Raman spectroscopy, atomic force microscopy (AFM), helium ion microscopy (HIM), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) and find that they possess nearly atomically sharp boundaries.

Published
2018
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3. Heterocontact-Triggered 1H to 1T′ Phase Transition in CVD-Grown Monolayer MoTe2: Implications for Low Contact Resistance Electronic Devices.

Author

Khaustov, Vladislav O., Convertino, Domenica, Köster, Janis, Zakharov, Alexei A., Mohn, Michael J., Gebeyehu, Zewdu M., Martini, Leonardo, Pace, Simona, Marini, Giovanni, Calandra, Matteo, Kaiser, Ute, Forti, Stiven, and Coletti, Camilla

Abstract

Single-layer molybdenum ditelluride (MoTe2) has attracted attention due to the smaller energy difference between the semiconducting (1H) and semimetallic (1T′) phases with respect to other two-dimensional transition metal dichalcogenides (TMDs). Understanding the phenomenon of polymorphism between these structural phases is of great fundamental and practical importance. In this paper, we report a 1H to 1T′ phase transition occurring during the chemical vapor deposition (CVD) synthesis of single-layer MoTe2 at 730 °C. The transformation originates at the heterocontact between monoclinic and hexagonal crystals and progresses to either yield a partial or complete 1H to 1T′ phase transition. Microscopic and spectroscopic analyses of the MoTe2 crystals reveal the presence of Te vacancies and mirror twin boundaries (MTB) domains in the hexagonal phase. The experimental observations and theoretical simulations indicate that the combination of heterocontact formation and Te vacancies are relevant triggering mechanisms in the observed transformation. By advancing in the understanding and controlling of the direct synthesis of lateral 1T′/1H heterostructures, this work contributes to the development of MoTe2-based electronic and optoelectronic devices with low contact resistance. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Heterocontact-Triggered 1H to 1T′ Phase Transition in CVD-Grown Monolayer MoTe2: Implications for Low Contact Resistance Electronic Devices

Author

Khaustov, Vladislav O., primary, Convertino, Domenica, additional, Köster, Janis, additional, Zakharov, Alexei A., additional, Mohn, Michael J., additional, Gebeyehu, Zewdu M., additional, Martini, Leonardo, additional, Pace, Simona, additional, Marini, Giovanni, additional, Calandra, Matteo, additional, Kaiser, Ute, additional, Forti, Stiven, additional, and Coletti, Camilla, additional

Published
2023
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9. Energy-filtered TEM and low-loss EELS of 2D materials

Author

Mohn, Michael Johannes, Kaiser, Ute, Koch, Christoph T., European Union (EU), and Horizon 2020

Subjects
Low-dimensional semiconductors, DDC 530 / Physics, Plasmon, Graphen, Niederdimensionales System, Condensed Matter::Materials Science, Durchstrahlungselektronenmikroskopie, Heterostructures, ddc:530, Dielectrics, Dichtefunktionalformalismus, Graphene, Electron energy loss spectroscopy, Elektronen-Energieverlustspektroskopie, Heterostruktur, Dielektrische Eigenschaft, Transmission electron microscopy, Density functionals
Abstract

In this work, we perform aberration-corrected energy-filtered TEM (EFTEM) and low-loss electron energy-loss spectroscopy (EELS) with two-dimensional (2D) materials. In particular, the carbon K-edge EFTEM signal is analyzed for a monolayer of graphene, and the low-loss EELS spectra of graphene and molybdenum disulfide (MoS���) heterostructures are investigated by the technique of momentum-resolved EELS. With EFTEM in the Cc/Cs-corrected ���SALVE III��� low-voltage transmission electron microscope, we demonstrate lattice contrast in zero-loss, plasmon-loss, and C-K-edge images. Both bright-atom contrast and dark-atom contrast are observed in all three cases, and focus series show that even for the C-K edge, contrast inversions can be caused by a change in the defocus. For an analysis of the image contrast in direct space, all raw EFTEM data are averaged over a large number of unit cells to improve the signal-to-noise-ratio. In the low-loss regime of EELS (0���50 eV), our momentum-resolved experimental data for 2D heterostructures of graphene and MoS��� can be understood by a combination of ab initio simulations and dielectric model calculations. Therefore, the low-loss EELS signals of 2D multilayers and heterostructures are described on the basis of time-dependent density functional theory calculations for the constituent monolayers. Expanding on a layered-electron gas model for graphene, multilayers and heterostructures with MoS��� are eventually modeled by microscopic dielectric calculations that are in good agreement with our experimental EELS data. The necessity of models beyond the layered electron-gas model is demonstrated by calculations for multilayer and bulk MoS���.

Published
2020

10. Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects

Author

Griffin, Eoin, primary, Mogg, Lucas, additional, Hao, Guang-Ping, additional, Kalon, Gopinadhan, additional, Bacaksiz, Cihan, additional, Lopez-Polin, Guillermo, additional, Zhou, T.Y., additional, Guarochico, Victor, additional, Cai, Junhao, additional, Neumann, Christof, additional, Winter, Andreas, additional, Mohn, Michael, additional, Lee, Jong Hak, additional, Lin, Junhao, additional, Kaiser, Ute, additional, Grigorieva, Irina V., additional, Suenaga, Kazu, additional, Özyilmaz, Barbaros, additional, Cheng, Hui-Min, additional, Ren, Wencai, additional, Turchanin, Andrey, additional, Peeters, Francois M., additional, Geim, Andre K., additional, and Lozada-Hidalgo, Marcelo, additional

Published
2020
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11. Dielectric properties of graphene/MoS2 heterostructures from ab initio calculations and electron energy-loss experiments

Author

Mohn, Michael Johannes, Hambach, Ralf, Wachsmuth, Philipp, Giorgetti, Christine, Kaiser, Ute, European Union (EU), and Horizon 2020

Subjects
DDC 530 / Physics, Physics::Optics, 2-dimensional systems, Time-dependent DFT, Plasmons (Physics), Niederdimensionales System, Condensed Matter::Materials Science, Two-dimensional systems, Dielectric properties, Dichtefunktionaltheorie, Density functional theory, Heterostructures, ddc:530, Dichtefunktionalformalismus, Electron energy loss spectroscopy, Heterostruktur, Dielektrische Eigenschaft, Density functionals
Abstract

High-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS2/graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack., acceptedVersion

Published
2018

12. Dielectric properties of graphene/ MoS 2 heterostructures from ab initio calculations and electron energy-loss experiments

Author

Mohn, Michael, Hambach, Ralf, Wachsmuth, Philipp, Giorgetti, Christine, Kaiser, Ute, Electron Microscopy Group of Materials Science, Universität Ulm - Ulm University [Ulm, Allemagne], Laboratoire des Solides Irradiés (LSI), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), ETSF, Palaiseau, France, and affiliation inconnue

Subjects
Condensed Matter::Materials Science, [PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other], Physics::Optics, [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat]
Abstract

International audience; High-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS2/graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack.

Published
2018

19. Steering LCS off the shoals: how to keep U.S. program from failing

Author

Mohn, Michael, Murray, Stephen, and Singer P.W.

Subjects
United States. Navy -- Equipment and supplies, United States. Navy -- Contracts, United States -- Military aspects, Warships -- Contracts, Contract agreement, Aerospace and defense industries, History, Military and naval science
Abstract

The possible reasons that defense contractors are reluctant to bid for the Littoral Combat Ship (LCS) of the U.S. Navy are discussed. Some remedial measures that could be used to solve the problem are suggested.

Published
2008

20. High Growth For Digital TV in Sweden, But Still Many Refusenicks

Author

Mohn, Michael

Subjects
Cable television broadcasting industry -- Growth -- Forecasts and trends, Consumer preferences -- Research -- Forecasts and trends, Digital television -- Forecasts and trends -- Research, Company growth, Digital television, Market trend/market analysis, Business, Electronics and electrical industries, High technology industry, Mass communications, Telecommunications industry
Abstract

Michael Mohn, Mediavision New research about the digital TV market in Sweden shows that more than 26 per cent of all individuals between the ages of 15 and 74 had [...]

Published
2004

21. Consumer Behaviour Focus: Interactive Usage Still Slow In Sweden

Author

Mohn, Michael

Subjects
Digital television -- User statistics, Consumer behavior, Digital television
Abstract

By Michael Mohn, Mediavision Mediavision has recently released new research on the digital TV market in Sweden. In the third quarter, there was an average digital TV penetration rate amongst […]

Published
2003

22. FORUM.

Author

Keim, Bernhard, Gade, Bianca, Mohn, Michael, and Happich, Gudrun

Published
2013

23. How to save the LCS.

Author

Mohn, Michael, Murray, Stephen, and Singer, Peter

Subjects
LITTORAL combat ships, GOVERNMENT purchasing, DEFENSE industries
Abstract

The article focuses on the Littoral Combat Ship program of the U.S. Navy. It states that as of June 2008, the program is experiencing some problems in acquisitions. The author claims that cost overruns and shifting requirements have driven big industry players, like Lockheed Martin and General Dynamics, to shy away from bidding in the program. Presented are five steps which the author believes will help in saving the program.

Published
2008

24. Heterocontact-Triggered 1H to 1T' Phase Transition in CVD-Grown Monolayer MoTe 2 : Implications for Low Contact Resistance Electronic Devices.

Author

Khaustov VO, Convertino D, Köster J, Zakharov AA, Mohn MJ, Gebeyehu ZM, Martini L, Pace S, Marini G, Calandra M, Kaiser U, Forti S, and Coletti C

Abstract

Single-layer molybdenum ditelluride (MoTe 2 ) has attracted attention due to the smaller energy difference between the semiconducting (1H) and semimetallic (1T') phases with respect to other two-dimensional transition metal dichalcogenides (TMDs). Understanding the phenomenon of polymorphism between these structural phases is of great fundamental and practical importance. In this paper, we report a 1H to 1T' phase transition occurring during the chemical vapor deposition (CVD) synthesis of single-layer MoTe 2 at 730 °C. The transformation originates at the heterocontact between monoclinic and hexagonal crystals and progresses to either yield a partial or complete 1H to 1T' phase transition. Microscopic and spectroscopic analyses of the MoTe 2 crystals reveal the presence of Te vacancies and mirror twin boundaries (MTB) domains in the hexagonal phase. The experimental observations and theoretical simulations indicate that the combination of heterocontact formation and Te vacancies are relevant triggering mechanisms in the observed transformation. By advancing in the understanding and controlling of the direct synthesis of lateral 1T'/1H heterostructures, this work contributes to the development of MoTe 2 -based electronic and optoelectronic devices with low contact resistance., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Published
2023
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25. Evaluation of TEM methods for their signature of the number of layers in mono- and few-layer TMDs as exemplified by MoS 2 and MoTe 2 .

Author

Köster J, Storm A, Gorelik TE, Mohn MJ, Port F, Gonçalves MR, and Kaiser U

Abstract

In mono- and few-layer 2D materials, the exact number of layers is a critical parameter, determining the materials' properties and thus their performance in future nano-devices. Here, we evaluate in a systematic manner the signature of exfoliated free-standing mono- and few-layer MoS 2 and MoTe 2 in TEM experiments such as high-resolution transmission electron microscopy, electron energy-loss spectroscopy, and 3D electron diffraction. A reference for the number of layers has been determined by optical contrast and AFM measurements on a substrate. Comparing the results, we discuss strengths and limitations, benchmarking the three TEM methods with respect to their ability to identify the exact number of layers., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Published
2022
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