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1. Ultra-low power threshold for laser induced changes in optical properties of 2D Molybdenum dichalcogenides

Author

Cadiz, Fabian, Robert, Cedric, Wang, Gang, Kong, Wilson, Fan, Xi, Blei, Mark, Lagarde, Delphine, Gay, Maxime, Manca, Marco, Taniguchi, Takashi, Watanabe, Kenji, Amand, Thierry, Marie, Xavier, Renucci, Pierre, Tongay, Sefaattin, and Urbaszek, Bernhard

Subjects
Condensed Matter - Materials Science, Physics - Optics
Abstract

The optical response of traditional semiconductors depends on the laser excitation power used in experiments. For two-dimensional (2D) semiconductors, laser excitation effects are anticipated to be vastly different due to complexity added by their ultimate thinness, high surface to volume ratio, and laser-membrane interaction effects. We show in this article that under laser excitation the optical properties of 2D materials undergo irreversible changes. Most surprisingly these effects take place even at low steady state excitation, which is commonly thought to be non-intrusive. In low temperature photoluminescence (PL) we show for monolayer (ML) MoSe2 samples grown by different techniques that laser treatment increases significantly the trion (i.e. charged exciton) contribution to the emission compared to the neutral exciton emission. Comparison between samples exfoliated onto different substrates shows that laser induced doping is more efficient for ML MoSe2 on SiO2/Si compared to h-BN and gold. For ML MoS2 we show that exposure to laser radiation with an average power in the $\mu$W/$\mu$m$^2$ range does not just increase the trion-to-exciton PL emission ratio, but may result in the irreversible disappearance of the neutral exciton PL emission and a shift of the main PL peak to lower energy., Comment: 16 pages, 5 figures

Published
2016
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2. Well separated trion and neutral excitons on superacid treated MoS2 monolayers

Author

Cadiz, Fabian, Tricard, Simon, Gay, Maxime, Lagarde, Delphine, Wang, Gang, Robert, Cedric, Renucci, Pierre, Urbaszek, Bernhard, and Marie, Xavier

Subjects
Condensed Matter - Materials Science
Abstract

Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs the photoluminescence (PL) spectra even at low temperature consists typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here we show that in superacid treated MoS2 MLs the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T=4 K, with linewidth for the neutral exciton of 15 meV, but with similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emission. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton.

Published
2016
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3. The search for manganese incorporation in MoSe$_{{2}}$ monolayer epitaxially grown on graphene

Author

Gay, Maxime, Dau, Minh-Tuan, Vergnaud, Céline, Marty, Alain, Bonell, Frédéric, Boukari, Hervé, Paillet, Colin, Hyot, Bérangère, Okuno, Hanako, Mallet, Pierre, Veuillen, Jean-Yves, Renault, Olivier, and Jamet, Matthieu

Subjects
2D materials, Magnetic doping, Molecular beam epitaxy, Transmission electron microscopy, Scanning tunneling microscopy, Momentum resolved photoemission electron microscopy, Physics, QC1-999
Abstract

The introduction of magnetism in two-dimensional (2D) materials represents an intense field of research nowadays and the quest to reach above-room-temperature ordering temperatures is still underway. Intrinsic ferromagnetism was discovered in 2017 in CrI$_{{3}}$ and Cr$_{{2}}$Ge$_{{2}}$Te$_{{6}}$ in the monolayer form with low Curie temperatures. An alternative method to introduce magnetism into conventional 2D materials is substitutional doping with magnetic impurities similarly to three-dimensional diluted magnetic semiconductors. The case of Mn-doped transition metal dichalcogenide (MoS$_{{2}}$, MoSe$_{{2}}$, WS$_{{2}}$, WSe$_{{2}}$) monolayers is very interesting because combining out-of-plane ferromagnetism and valley contrast leads to ferrovalley materials. In this work, we focus on the incorporation of Mn in MoSe$_{{2}}$ by molecular beam epitaxy on graphene which has been rarely addressed up to now. By using a multiscale characterization approach, we demonstrate that Mn atoms are incorporated into the MoSe$_{{2}}$ monolayer up to 5 atomic percent. However, when incorporated into the film, Mn atoms tend to diffuse to the grain edges forming undefined Mo$_{{{\it x}}}$Mn$_{{{\it y}}}$Se$_{{{\it z}}}$ phase at grain boundaries after completion of the MoSe$_{{2}}$ monolayer. This segregation leaves the crystalline and electronic structure of MoSe$_{{2}}$ unmodified. Above 5%, the saturation of Mn content in MoSe$_{{2}}$ leads to the formation of epitaxial MnSe clusters.

Published
2021
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4. Synthesis of epitaxial monolayer Janus SPtSe

Author

Sant, Roberto, Gay, Maxime, Marty, Alain, Lisi, Simone, Harrabi, Rania, Vergnaud, Céline, Dau, Minh Tuan, Weng, Xiaorong, Coraux, Johann, Gauthier, Nicolas, Renault, Olivier, Renaud, Gilles, and Jamet, Matthieu

Published
2020
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5. The search for manganese incorporation in MoSe 2monolayer epitaxially grown on graphene

Author

Gay, Maxime, primary, Dau, Minh-Tuan, additional, Vergnaud, Céline, additional, Marty, Alain, additional, Bonell, Frédéric, additional, Boukari, Hervé, additional, Paillet, Colin, additional, Hyot, Bérangère, additional, Okuno, Hanako, additional, Mallet, Pierre, additional, Veuillen, Jean-Yves, additional, Renault, Olivier, additional, and Jamet, Matthieu, additional

Published
2022
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7. Van der Waals solid phase epitaxy to grow large-area manganese-doped MoSe 2 few-layers on SiO 2 /Si

Author

Vergnaud, Céline, primary, Gay, Maxime, additional, Alvarez, Carlos, additional, Dau, Minh-Tuan, additional, Pierre, François, additional, Jalabert, Denis, additional, Licitra, Christophe, additional, Marty, Alain, additional, Beigné, Cyrille, additional, Grévin, Benjamin, additional, Renault, Olivier, additional, Okuno, Hanako, additional, and Jamet, Matthieu, additional

Published
2019
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8. Well separated trion and neutral excitons on superacid treated MoS 2 monolayers

Author

Cadiz, Fabian, Tricard, Simon, Gay, Maxime, Lagarde, Delphine, Wang, Gang, Robert, Cédric, Renucci, Pierre, Urbaszek, Bernhard, Marie, Xavier, Laboratoire de physique de la matière condensée (LPMC), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de physique et chimie des nano-objets (LPCNO), Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie de Toulouse (ICT-FR 2599), Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut de Chimie du CNRS (INC), Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information (CEA-LETI), Direction de Recherche Technologique (CEA) (DRT (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Tyndall National Institute [Cork], Institut National des Sciences Appliquées (INSA), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut de Chimie de Toulouse (ICT), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)

Subjects
Condensed Matter::Materials Science, Optical electronics, Semiconductors, Photoluminescence spectroscopy, Condensed Matter::Other, Lasers Excitons, Transition metal chalcogenides, Selection rule, Quasiparticle, [CHIM]Chemical Sciences, Localized states, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Time-resolved photoluminescence
Abstract

International audience; Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs, the photoluminescence (PL) spectra even at low temperature consist typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here, we show that in superacid treated MoS2 MLs, the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T = 4 K, with linewidth for the neutral exciton of 15 meV, but both transitions have similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emissions. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton.

Published
2016

9. Beyond van der Waals Interaction: The Case of MoSe2 Epitaxially Grown on Few-Layer Graphene

Author

Dau, Minh Tuan, primary, Gay, Maxime, additional, Di Felice, Daniela, additional, Vergnaud, Céline, additional, Marty, Alain, additional, Beigné, Cyrille, additional, Renaud, Gilles, additional, Renault, Olivier, additional, Mallet, Pierre, additional, Le Quang, Toai, additional, Veuillen, Jean-Yves, additional, Huder, Loïc, additional, Renard, Vincent T., additional, Chapelier, Claude, additional, Zamborlini, Giovanni, additional, Jugovac, Matteo, additional, Feyer, Vitaliy, additional, Dappe, Yannick J., additional, Pochet, Pascal, additional, and Jamet, Matthieu, additional

Published
2018
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10. Ultra-low power threshold for laser induced changes in optical properties of 2D molybdenum dichalcogenides

Author

Cadiz, Fabian, primary, Robert, Cedric, additional, Wang, Gang, additional, Kong, Wilson, additional, Fan, Xi, additional, Blei, Mark, additional, Lagarde, Delphine, additional, Gay, Maxime, additional, Manca, Marco, additional, Taniguchi, Takashi, additional, Watanabe, Kenji, additional, Amand, Thierry, additional, Marie, Xavier, additional, Renucci, Pierre, additional, Tongay, Sefaattin, additional, and Urbaszek, Bernhard, additional

Published
2016
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12. Well separated trion and neutral excitons on superacid treated MoS2 monolayers.

Author

Cadiz, Fabian, Tricard, Simon, Gay, Maxime, Lagarde, Delphine, Gang Wang, Robert, Cedric, Renucci, Pierre, Urbaszek, Bernhard, and Marie, Xavier

Subjects
OPTOELECTRONICS, PHOTOLUMINESCENCE, EXCITON theory, REFLECTANCE, PICOSECOND pulses, POLARIZATION (Nuclear physics)
Abstract

Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs, the photoluminescence (PL) spectra even at low temperature consist typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here, we show that in superacid treated MoS2 MLs, the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T = 4 K, with linewidth for the neutral exciton of 15 meV, but both transitions have similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emissions. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton. [ABSTRACT FROM AUTHOR]

Published
2016
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13. Beyond van der Waals Interaction: The Case of MoSe2Epitaxially Grown on Few-Layer Graphene

Author

Dau, Minh Tuan, Gay, Maxime, Di Felice, Daniela, Vergnaud, Céline, Marty, Alain, Beigné, Cyrille, Renaud, Gilles, Renault, Olivier, Mallet, Pierre, Le Quang, Toai, Veuillen, Jean-Yves, Huder, Loïc, Renard, Vincent T., Chapelier, Claude, Zamborlini, Giovanni, Jugovac, Matteo, Feyer, Vitaliy, Dappe, Yannick J., Pochet, Pascal, and Jamet, Matthieu

Abstract

Van der Waals heterojunctions composed of graphene and transition metal dichalcogenides have gain much attention because of the possibility to control and tailor band structure, promising applications in two-dimensional optoelectronics and electronics. In this report, we characterized the van der Waals heterojunction MoSe2/few-layer graphene with a high-quality interface using cutting-edge surface techniques scaling from atomic to microscopic range. These surface analyses gave us a complete picture of the atomic structure and electronic properties of the heterojunction. In particular, we found two important results: the commensurability between the MoSe2and few-layer graphene lattices and a band-gap opening in the few-layer graphene. The band gap is as large as 250 meV, and we ascribed it to an interface charge transfer that results in an electronic depletion in the few-layer graphene. This conclusion is well supported by electron spectroscopy data and density functional theory calculations. The commensurability between the MoSe2and graphene lattices as well as the band-gap opening clearly show that the interlayer interaction goes beyond the simple van der Waals interaction. Hence, stacking two-dimensional materials in van der Waals heterojunctions enables us to tailor the atomic and electronic properties of individual layers. It also permits the introduction of a band gap in few-layer graphene by interface charge transfer.

Published
2018
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16. Italy Strikes Relay Gold At MTB Worlds

Abstract

Aug 29, 2013 (SouthAfrica.info/All Africa Global Media via COMTEX) -- Italy claimed the first gold medal of the UCI MTB & Trials World Championships at the Cascades MTB Park in […]

Published
2013

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