-
Engineering deterministic, tunable, and reversible folds in graphene with the use of ultrafast laser micro-patterned stretchable polymer substrate
Authors:
A. F. Juarez Saborio,
F. Bourquard,
R. Galafassi,
A. Claudel,
L. Marty,
A. Piednoir,
M. Mercury,
R. Fulcrand,
C. Albin,
V. Barnier,
F. Garrelie,
A. San-Miguel,
F. Vialla
Abstract:
The unique atomic monolayer structure of graphene gives rise to a broad range of remarkable mechanical folding properties. However, significant challenges remain in effectively harnessing them in a controllable and scalable manner. In this study, we introduce an innovative approach that employs micron-scale cavities, fabricated through ultrafast laser patterning, in a stretchable polymer substrate…
▽ More
The unique atomic monolayer structure of graphene gives rise to a broad range of remarkable mechanical folding properties. However, significant challenges remain in effectively harnessing them in a controllable and scalable manner. In this study, we introduce an innovative approach that employs micron-scale cavities, fabricated through ultrafast laser patterning, in a stretchable polymer substrate to locally modulate adhesion and strain transfer to a graphene monolayer. This technique enables the deterministic induction of single folds in graphene with fold dimensions, width and height in the hundreds of nanometers, tunable through the geometry of the polymer cavities and the applied strain. Importantly, these folds are reversible, returning to a flat morphology with minimal structural damage, as confirmed by Raman spectroscopy. Additionally, our method allows for the creation of fields of folds with reproducible periodicity, defining clear potential for practical applications. These findings pave the way for the development of advanced devices that would leverage the strain and morphology-sensitive properties of graphene.
△ Less
Submitted 23 June, 2025;
originally announced June 2025.
-
Strain and doping transfer between suspended and supported bilayer graphene
Authors:
Riccardo Galafassi,
Fabien Vialla,
V. Rajaji,
Alexis Forestier,
Bruno Sousa Araújo,
Hatem Diaf,
Natalia Del Fatti,
Antonio Gomes Souza Filho,
Arnaud Claudel,
Laëtitia Marty,
Alfonso San-Miguel
Abstract:
Due to their unique dimensionality, the physical properties of two-dimensional materials are deeply impacted by their surroundings, calling for a thorough understanding and control of these effects. We investigated the influence of the substrate and the pressure transmitting medium on bilayer graphene in a unique high-pressure environment where the sample is partially suspended and partially suppo…
▽ More
Due to their unique dimensionality, the physical properties of two-dimensional materials are deeply impacted by their surroundings, calling for a thorough understanding and control of these effects. We investigated the influence of the substrate and the pressure transmitting medium on bilayer graphene in a unique high-pressure environment where the sample is partially suspended and partially supported. By employing Raman spectroscopy with a sub-micron spatial resolution, we explored the evolution of strain and doping, and demonstrated that they are both similarly induced in the suspended and supported regions of the bilayer graphene within the studied pressure range. Almost full strain and doping transfer between the supported and suspended regions is concluded. We observed that charge carrier density saturates quickly at low pressures (2 GPa) while biaxial strain continuously increases with pressure. Additionally, Raman spatial mapping highlights a rather uniform doping and strain distribution, yet with significant local variations revealing a more complex scenario than previously documented by single-point studies at high pressure.
△ Less
Submitted 10 March, 2025;
originally announced March 2025.
-
Laser patterning of the room temperature van der Waals ferromagnet 1$T$-CrTe$_2$
Authors:
Tristan Riccardi,
Suman Sarkar,
Anike Purbawati,
Aloïs Arrighi,
Marek Kostka,
Abdellali Hadj-Azzem,
Jan Vogel,
Julien Renard,
Laëtitia Marty,
Amit Pawbake,
Clément Faugeras,
Kenji Watanabe,
Takashi Taniguchi,
Aurore Finco,
Vincent Jacques,
Lei Ren,
Xavier Marie,
Cedric Robert,
Manuel Nuñez-Regueiro,
Nicolas Rougemaille,
Nedjma Bendiab,
Johann Coraux
Abstract:
Lamellar crystalline materials, whose layers are bond by van der Waals forces, can be stacked to form ultrathin artificial heterostructures, and in particular vertical magnetic junctions when some of the stacked materials are (ferro)magnetic. Here, using the room temperature van der Waals ferromagnet 1$T$-CrTe$_2$, we report a method for patterning lateral magnetic junctions. Exploiting the heat-i…
▽ More
Lamellar crystalline materials, whose layers are bond by van der Waals forces, can be stacked to form ultrathin artificial heterostructures, and in particular vertical magnetic junctions when some of the stacked materials are (ferro)magnetic. Here, using the room temperature van der Waals ferromagnet 1$T$-CrTe$_2$, we report a method for patterning lateral magnetic junctions. Exploiting the heat-induced phase transformation of the material into Cr$_x$Te$_y$ compounds ($x/y>1/2$), we use local laser heating to imprint patterns at the micron-scale. Optimizing laser heat dissipation, we further demonstrate the crucial role of the substrate to control the phase transformation. If plain, unstructured poorly heat-conducting substrates allow for direct writing of magnetic patterns, structured $h$-BN layers can serve as heat stencils to draw potentially thinner patterns. Besides, $h$-BN encapsulation turns out to be heat-protective (in addition from protecting against oxidation as it is generally used for), allowing the demonstration of room temperature ferromagnetism in $<$7~nm-thick 1$T$-CrTe$_2$.
△ Less
Submitted 28 January, 2025;
originally announced January 2025.
-
Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe$_2$ Compounds
Authors:
Anike Purbawati,
Suman Sarkar,
Sébastien Pairis,
Marek Kostka,
Abdellali Hadj-Azzem,
Didier Dufeu,
Priyank Singh,
Daniel Bourgault,
Manuel Nuñez-Regueiro,
Jan Vogel,
Julien Renard,
Laëtitia Marty,
Florentin Fabre,
Aurore Finco,
Vincent Jacques,
Lei Ren,
Vivekanand Tiwari,
Cedric Robert,
Xavier Marie,
Nedjma Bendiab,
Nicolas Rougemaille,
Johann Coraux
Abstract:
Van der Waals magnetic materials are building blocks for novel kinds of spintronic devices and playgrounds for exploring collective magnetic phenomena down to the two-dimensional limit. Chromium-tellurium compounds are relevant in this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to have a Curie temperature above 300~K, a rare and desirable property in the class of lamell…
▽ More
Van der Waals magnetic materials are building blocks for novel kinds of spintronic devices and playgrounds for exploring collective magnetic phenomena down to the two-dimensional limit. Chromium-tellurium compounds are relevant in this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to have a Curie temperature above 300~K, a rare and desirable property in the class of lamellar materials, making it a candidate for practical applications. However, recent literature reveals a strong variability in the reported properties, including magnetic ones. Using electron microscopy, diffraction and spectroscopy techniques, together with local and macroscopic magnetometry approaches, our work sheds new light on the structural, chemical and magnetic properties of bulk 1$T$-CrTe$_2$ exfoliated in the form of flakes having a thickness ranging from few to several tens of nanometers. We unambiguously establish that 1$T$-CrTe$_2$ flakes are ferromagnetic above room temperature, have an in-plane easy axis of magnetization, low coercivity, and we confirm that their Raman spectroscopy signatures are two modes, $E_{2\text{g}}$ (103.5~cm$^{-1}$) and $A_{1\text{g}}$ (136.5~cm$^{-1}$). We also prove that thermal annealing causes a phase transformation to monoclinic Cr$_5$Te$_8$ and, to a lesser extent, to trigonal Cr$_5$Te$_8$. In sharp contrast with 1$T$-CrTe$_2$, none of these compounds have a Curie temperature above room temperature, and they both have perpendicular magnetic anisotropy. Our findings reconcile the apparently conflicting reports in the literature and open opportunities for phase-engineered magnetic properties.
△ Less
Submitted 3 March, 2023; v1 submitted 22 January, 2023;
originally announced January 2023.
-
Fermi resonance in the Raman spectrum of graphene
Authors:
Dipankar Kalita,
Michele Amato,
Alexandre Artaud,
Laëtitia Marty,
Vincent Bouchiat,
Johann Coraux,
Christian Brouder,
Michele Lazzeri,
Nedjma Bendiab
Abstract:
We report the observation of an intense anomalous peak at 1608 cm$^{-1}$ in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D$'$ peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bondin…
▽ More
We report the observation of an intense anomalous peak at 1608 cm$^{-1}$ in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D$'$ peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bonding of chromium atoms with carbon atoms softens the out-of-plane optical (ZO) phonon mode, in such a way that the frequency of its overtone decreases to $2ω_{\rm ZO}\simω_{\rm G}$, where $ω_{\rm G}$=1585~cm$^{-1}$ is the frequency of the Raman-active E$_{\rm 2g}$ mode. Thus, the observed new peak is attributed to the 2ZO mode which becomes Raman-active following a mechanism known as Fermi resonance. First-principles calculations on vibrational and anharmonic properties of the graphene/Cr interface support this scenario.
△ Less
Submitted 18 November, 2020;
originally announced November 2020.
-
Anharmonicity in Raman-active phonon modes in atomically thin MoS$_2$
Authors:
Suman Sarkar,
Indrajit Maity,
H. L. Pradeepa,
Goutham Nayak,
Laetitia Marty,
Julien Renard,
Johann Coraux,
Nedjma Bendiab,
Vincent Bouchiat,
Sarthak Das,
Kausik Majumdar,
Manish Jain,
Aveek Bid
Abstract:
Phonon-phonon anharmonic effects have a strong influence on the phonon spectrum; most prominent manifestation of these effects are the softening (shift in frequency) and broadening (change in FWHM) of the phonon modes at finite temperature. Using Raman spectroscopy, we studied the temperature dependence of the FWHM and Raman shift of $\mathrm{E_{2g}^1}$ and $\mathrm{A_{1g}}$ modes for single-layer…
▽ More
Phonon-phonon anharmonic effects have a strong influence on the phonon spectrum; most prominent manifestation of these effects are the softening (shift in frequency) and broadening (change in FWHM) of the phonon modes at finite temperature. Using Raman spectroscopy, we studied the temperature dependence of the FWHM and Raman shift of $\mathrm{E_{2g}^1}$ and $\mathrm{A_{1g}}$ modes for single-layer and natural bilayer MoS$_2$ over a broad range of temperatures ($8 < $T$ < 300$ K). Both the Raman shift and FWHM of these modes show linear temperature dependence for $T>100$ K, whereas they become independent of temperature for $T<100$ K. Using first-principles calculations, we show that three-phonon anharmonic effects intrinsic to the material can account for the observed temperature-dependence of the line-width of both the modes. It also plays an important role in determining the temperature-dependence of the frequency of the Raman modes. The observed evolution of the line-width of the A$_{1g}$ mode suggests that electron-phonon processes are additionally involved. From the analysis of the temperature-dependent Raman spectra of MoS$_2$ on two different substrates -- SiO$_2$ and hexagonal boron nitride, we disentangle the contributions of external stress and internal impurities to these phonon-related processes. We find that the renormalization of the phonon mode frequencies on different substrates is governed by strain and intrinsic doping. Our work establishes the role of intrinsic phonon anharmonic effects in deciding the Raman shift in MoS$_2$ irrespective of substrate and layer number.
△ Less
Submitted 9 September, 2020;
originally announced September 2020.
-
In-plane magnetic domains and Néel-like domain walls in thin flakes of the room temperature CrTe$_2$ van der Waals ferromagnet
Authors:
Anike Purbawati,
Johann Coraux,
Jan Vogel,
Abdellali Hadj-Azzem,
NianJheng Wu,
Nedjma Bendiab,
David Jégouso,
Julien Renard,
Laetitia Marty,
Vincent Bouchiat,
André Sulpice,
Lucia Aballe,
Michael Foerster,
Francesca Genuzio,
Andrea Locatelli,
Tevfik Onur Menteş,
Zheng Vitto Han,
Xingdan Sun,
Manuel Núñez-Regueiro,
Nicolas Rougemaille
Abstract:
The recent discovery of magnetic van der Waals materials has triggered a wealth of investigations in materials science, and now offers genuinely new prospects for both fundamental and applied research. Although the catalogue of van der Waals ferromagnets is rapidly expanding, most of them have a Curie temperature below 300 K, a notable disadvantage for potential applications. Combining element-sel…
▽ More
The recent discovery of magnetic van der Waals materials has triggered a wealth of investigations in materials science, and now offers genuinely new prospects for both fundamental and applied research. Although the catalogue of van der Waals ferromagnets is rapidly expanding, most of them have a Curie temperature below 300 K, a notable disadvantage for potential applications. Combining element-selective x-ray magnetic imaging and magnetic force microscopy, we resolve at room temperature the magnetic domains and domains walls in micron-sized flakes of the CrTe$_2$ van der Waals ferromagnet. Flux-closure magnetic patterns suggesting in-plane six-fold symmetry are observed. Upon annealing the material above its Curie point (315 K), the magnetic domains disappear. By cooling back down the sample, a different magnetic domain distribution is obtained, indicating material stability and lack of magnetic memory upon thermal cycling. The domain walls presumably have Néel texture, are preferentially oriented along directions separated by 120 degrees, and have a width of several tens of nanometers. Besides microscopic mapping of magnetic domains and domain walls, the coercivity of the material is found to be of a few mT only, showing that the CrTe$_2$ compound is magnetically soft. The coercivity is found to increase as the volume of the material decreases.
△ Less
Submitted 25 June, 2020;
originally announced June 2020.
-
Magneto-spectroscopy of exciton Rydberg states in a CVD grown WSe2 monolayer
Authors:
A. Delhomme,
G. Butseraen,
B. Zheng,
L. Marty,
V. Bouchiat,
M. R. Molas,
A. Pan,
K. Watanabe,
T. Taniguchi,
A. Ouerghi,
J. Renard,
C. Faugeras
Abstract:
The results of magneto-optical spectroscopy investigations of excitons in a CVD grown monolayer of WSe2 encapsulated in hexagonal boron nitride are presented. The emission linewidth for the 1s state is of 4:7 meV, close to the narrowest emissions observed in monolayers exfoliated from bulk material. The 2s excitonic state is also observed at higher energies in the photoluminescence spectrum. Magne…
▽ More
The results of magneto-optical spectroscopy investigations of excitons in a CVD grown monolayer of WSe2 encapsulated in hexagonal boron nitride are presented. The emission linewidth for the 1s state is of 4:7 meV, close to the narrowest emissions observed in monolayers exfoliated from bulk material. The 2s excitonic state is also observed at higher energies in the photoluminescence spectrum. Magneto-optical spectroscopy allows for the determination of the g-factors and of the spatial extent of the excitonic wave functions associated with these emissions. Our work establishes CVD grown monolayers of transition metal dichalcogenides as a mature technology for optoelectronic applications.
△ Less
Submitted 7 June, 2019;
originally announced June 2019.
-
Interlayer Charge Transfer and Defect Creation in Type I van der Waals Heterostructures
Authors:
G. Nayak,
S. Lisi,
W-L. Liu,
T. Jakubczyk,
P. Stepanov,
F. Donatini,
K. Watanabe,
T. Taniguchi,
A. Bid,
J. Kasprzak,
M. Richard,
V. Bouchiat,
J. Coraux,
L. Marty,
N. Bendiab,
J. Renard
Abstract:
Van der Waals heterostructures give access to a wide variety of new phenomena that emerge thanks to the combination of properties brought in by the constituent layered materials. We show here that owing to an enhanced interaction cross section with electrons in a type I van der Waals heterostructure, made of single layer molybdenum disulphide and thin boron nitride films, electrons and holes creat…
▽ More
Van der Waals heterostructures give access to a wide variety of new phenomena that emerge thanks to the combination of properties brought in by the constituent layered materials. We show here that owing to an enhanced interaction cross section with electrons in a type I van der Waals heterostructure, made of single layer molybdenum disulphide and thin boron nitride films, electrons and holes created in boron nitride can be transferred to the dichalcogenide where they form electron-hole pairs yielding luminescence. This cathodoluminescence can be mapped with a spatial resolution far exceeding what can be achieved in a typical photoluminescence experiment, and is highly valuable to understand the optoelectronic properties at the nanometer scale. We find that in heterostructures prepared following the mainstream dry transfer technique, cathodoluminescence is locally extinguished, and we show that this extinction is associated with the formation of defects, that are detected in Raman spectroscopy and photoluminescence. We establish that to avoid defect formation induced by low-energy electron beams and to ensure efficient transfer of electrons and holes at the interface between the layers, flat and uniform interlayer interfaces are needed, that are free of trapped species, airborne ones or contaminants associated with sample preparation. We show that heterostructure fabrication using a pick-up technique leads to superior, intimate interlayer contacts associated with significantly more homogeneous cathodoluminescence.
△ Less
Submitted 3 June, 2019;
originally announced June 2019.
-
Coherence and density dynamics of excitons in a single-layer MoS$_2$ reaching the homogeneous limit
Authors:
Tomasz Jakubczyk,
Goutham Nayak,
Lorenzo Scarpelli,
Francesco Masia,
Wei-Lai Liu,
Sudipta Dubey,
Nedjma Bendiab,
Laëtitia Marty,
Takashi Taniguchi,
Kenji Watanabe,
Gilles Nogues,
Johann Coraux,
Vincent Bouchiat,
Wolfgang Langbein,
Julien Renard,
Jacek Kasprzak
Abstract:
We measure the coherent nonlinear response of excitons in a single-layer of molybdenum disulphide embedded in hexagonal boron nitride, forming a $h$-BN/MoS$_2$/$h$-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton homogeneous and inhomogeneous broadenings. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal pro…
▽ More
We measure the coherent nonlinear response of excitons in a single-layer of molybdenum disulphide embedded in hexagonal boron nitride, forming a $h$-BN/MoS$_2$/$h$-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton homogeneous and inhomogeneous broadenings. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultra-fast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the $h$-BN and imperfections in the encapsulation process.
△ Less
Submitted 28 September, 2018;
originally announced October 2018.
-
Weakly Trapped, Charged, and Free Excitons in Single-Layer MoS2 in the Presence of Defects, Strain, and Charged Impurities
Authors:
Sudipta Dubey,
Simone Lisi,
Goutham Nayak,
Felix Herziger,
Van-Dung Nguyen,
Toai Le Quang,
Vladimir Cherkez,
César González,
Yannick J. Dappe,
Kenji Watanabe,
Takashi Taniguchi,
Laurence Magaud,
Pierre Mallet,
Jean-Yves Veuillen,
Raul Arenal,
Laëtitia Marty,
Julien Renard,
Nedjma Bendiab,
Johann Coraux,
Vincent Bouchiat
Abstract:
Few- and single-layer MoS2 host substantial densities of defects. They are thought to influence the doping level, the crystal structure, and the binding of electron-hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local environment. We do so by using diffe…
▽ More
Few- and single-layer MoS2 host substantial densities of defects. They are thought to influence the doping level, the crystal structure, and the binding of electron-hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local environment. We do so by using different sources of MoS2 -- a natural one and one prepared at high pressure and high temperature -- and different substrates bringing varying amounts of charged impurities and by separating the contributions of internal strain and doping in Raman spectra. Photoluminescence unveils various optically active excitonic complexes. We discover a defect-bound state having a low binding energy of 20 meV that does not appear sensitive to strain and doping, unlike charged excitons. Conversely, the defect does not significantly dope or strain MoS2. Scanning tunneling microscopy and density functional theory simulations point to substitutional atoms, presumably individual nitrogen atoms at the sulfur site. Our work shows the way to a systematic understanding of the effect of external and internal fields on the optical properties of two-dimensional materials.
△ Less
Submitted 7 May, 2018;
originally announced May 2018.
-
High-Yield Proximity-Induced Chemical Vapor Deposition of Graphene Over Millimeter-Sized Hexagonal Boron Nitride
Authors:
Hadi Arjmandi-Tash,
Dipankar Kalita,
Zheng Han,
Riadh Othmen,
Cecile Berne,
John Landers,
Kenji Watanabe,
Takashi Taniguchi,
Laetitia Marty,
Johann Coraux,
Nedjma Bendiab,
Vincent Bouchiat
Abstract:
We present a transfer-free preparation method for graphene on hexagonal boron nitride (h-BN) crystals by chemical vapor deposition of graphene via a catalytic proximity effect, i.e. activated by a Cu catalyst close-by . We demonstrate the full coverage by monolayer graphene of half-millimeter-sized hexagonal boron nitride crystals exfoliated on a copper foil prior to growth. We demonstrate that th…
▽ More
We present a transfer-free preparation method for graphene on hexagonal boron nitride (h-BN) crystals by chemical vapor deposition of graphene via a catalytic proximity effect, i.e. activated by a Cu catalyst close-by . We demonstrate the full coverage by monolayer graphene of half-millimeter-sized hexagonal boron nitride crystals exfoliated on a copper foil prior to growth. We demonstrate that the proximity of the copper catalyst ensures high yield with the growth rate estimated between of 2μm/min to 5μm/min . Optical and electron microscopies together with confocal micro-Raman mapping confirm that graphene covers the top surface of h-BN crystals that we attribute to be a lateral growth from the supporting catalytic copper substrate. Structural and electron transport characterization of the in-situ grown graphene present an electronic mobility of about 20, 000cm2/(V.s). Comparison with graphene/h-BN stacks obtained by manual transferring of similar CVD graphene onto h-BN, confirms the better neutrality reached by the self-assembled structures.
△ Less
Submitted 21 January, 2017;
originally announced January 2017.
-
Deviation from the normal mode expansion in a coupled graphene-nanomechanical system
Authors:
Cornelia Schwarz,
Benjamin Pigeau,
Laure Mercier de Lépinay,
Aurélien Kuhn,
Dipankar Kalita,
Nedjma Bendiab,
Laëtitia Marty,
Vincent Bouchiat,
Olivier Arcizet
Abstract:
We optomechanically measure the vibrations of a nanomechanical system made of a graphene membrane suspended on a silicon nitride nanoresonator. When probing the thermal noise of the coupled nanomechanical device, we observe a significant deviation from the normal mode expansion. It originates from the heterogeneous character of mechanical dissipation over the spatial extension of coupled eigenmode…
▽ More
We optomechanically measure the vibrations of a nanomechanical system made of a graphene membrane suspended on a silicon nitride nanoresonator. When probing the thermal noise of the coupled nanomechanical device, we observe a significant deviation from the normal mode expansion. It originates from the heterogeneous character of mechanical dissipation over the spatial extension of coupled eigenmodes, which violates one of the fundamental prerequisite for employing this commonly used description of the nanoresonators' thermal noise. We subsequently measure the local mechanical susceptibility and demonstrate that the fluctuation-dissipation theorem still holds and permits a proper evaluation of the thermal noise of the nanomechanical system. Since it naturally becomes delicate to ensure a good spatial homogeneity at the nanoscale, this approach is fundamental to correctly describe the thermal noise of nanomechanical systems which ultimately impact their sensing capacity.
△ Less
Submitted 2 January, 2016;
originally announced January 2016.
-
Strain superlattices and macroscale suspension of Graphene induced by corrugated substrates
Authors:
Antoine Reserbat-Plantey,
Dipankar Kalita,
Laurence Ferlazzo,
Sandrine Autier-Laurent,
Katsuyoshi Komatsu,
Chuan Li,
Raphaël Weil,
Zheng Han,
Sandrine Autier-Laurent,
Arnaud Ralko,
Laetitia Marty,
Sophie Guéron,
Nedjma Bendiab,
Hélène Bouchiat,
Vincent Bouchiat
Abstract:
We investigate the organized formation of strain, ripples and suspended features in macroscopic CVD-prepared graphene sheets transferred onto a corrugated substrate made of an ordered arrays of silica pillars of variable geometries. Depending on the aspect ratio and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lay, fakir-like, fully suspended…
▽ More
We investigate the organized formation of strain, ripples and suspended features in macroscopic CVD-prepared graphene sheets transferred onto a corrugated substrate made of an ordered arrays of silica pillars of variable geometries. Depending on the aspect ratio and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lay, fakir-like, fully suspended between pillars over tens of micrometers. Upon increase of pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to ripples linking nearest neighboring pillars organized in domains of given orientation. Spatially-resolved Raman spectroscopy, atomic force microscopy and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the transition between suspended and collapsed graphene. For the arrays with high aspect ratio pillars, graphene membranes stays suspended over macroscopic distances with minimal interaction with pillars tip apex. It offers a platform to tailor stress in graphene layers and open perspectives for electron transport and nanomechanical applications.
△ Less
Submitted 24 April, 2014; v1 submitted 23 April, 2014;
originally announced April 2014.
-
Time- and Space-Modulated Raman Signals in Graphene-based Optical Cavities
Authors:
Antoine Reserbat-Plantey,
Svetlana Klyatskaya,
Valerie Reita,
Laetitia Marty,
Olivier Arcizet,
Mario Ruben,
Nedjma Bendiab,
Vincent Bouchiat
Abstract:
We present fabrication and optical characterization of micro-cavities made of multilayer graphene (MLG) cantilevers clamped by metallic electrodes and suspended over Si/Si02 substrate. Graphene cantilevers act as a semi-transparent mirrors closing an air-wedge optical cavity. This simple geometry implements a standing-wave optical resonator along with a mechanical one. Equal thickness interference…
▽ More
We present fabrication and optical characterization of micro-cavities made of multilayer graphene (MLG) cantilevers clamped by metallic electrodes and suspended over Si/Si02 substrate. Graphene cantilevers act as a semi-transparent mirrors closing an air-wedge optical cavity. This simple geometry implements a standing-wave optical resonator along with a mechanical one. Equal thickness interference fringes are observed in both Raman and Rayleigh backscattered signals with interfringe given by their specific wavelength.Chromatic dispersion within the cavity makes possible spatial modulation of graphene Raman lines and selective rejection of the silicon background signals. Electrostatic actuation of the multilayer graphene cantilever by gate voltage tunes the cavity length and induces space and time modulation of backscattered light including Raman lines. We demonstrate the potential of those systems for high sensitivity Raman measurements of generic molecular species grafted on multilayer graphene surface. The Raman signal of the molecular layer can be modulated both in time and in space in a similar fashion and show enhancement with respect to a collapsed membrane.
△ Less
Submitted 13 June, 2013;
originally announced June 2013.
-
Local Optical Probe of Motion and Stress in a multilayer graphene NEMS
Authors:
Antoine Reserbat-Plantey,
Laetitia Marty,
Olivier Arcizet,
Nedjma Bendiab,
Vincent Bouchiat
Abstract:
Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the crossroads between mechanics, optics and electronics, with significant potential for actuation and sensing applications. The reduction of dimensions compared to their micronic counterparts brings new effects including sensitivity to very low mass, resonant frequencies in the radiofrequency range, mechanical non-linearitie…
▽ More
Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the crossroads between mechanics, optics and electronics, with significant potential for actuation and sensing applications. The reduction of dimensions compared to their micronic counterparts brings new effects including sensitivity to very low mass, resonant frequencies in the radiofrequency range, mechanical non-linearities and observation of quantum mechanical effects. An important issue of NEMS is the understanding of fundamental physical properties conditioning dissipation mechanisms, known to limit mechanical quality factors and to induce aging due to material degradation. There is a need for detection methods tailored for these systems which allow probing motion and stress at the nanometer scale. Here, we show a non-invasive local optical probe for the quantitative measurement of motion and stress within a multilayer graphene NEMS provided by a combination of Fizeau interferences, Raman spectroscopy and electrostatically actuated mirror. Interferometry provides a calibrated measurement of the motion, resulting from an actuation ranging from a quasi-static load up to the mechanical resonance while Raman spectroscopy allows a purely spectral detection of mechanical resonance at the nanoscale. Such spectroscopic detection reveals the coupling between a strained nano-resonator and the energy of an inelastically scattered photon, and thus offers a new approach for optomechanics.
△ Less
Submitted 18 March, 2012;
originally announced March 2012.
-
First order $0/π$ quantum phase transition in the Kondo regime of a superconducting carbon nanotube quantum dot
Authors:
Romain Maurand,
Tobias Meng,
Edgar Bonet,
Serge Florens,
Laëtitia Marty,
Wolfgang Wernsdorfer
Abstract:
We study a carbon nanotube quantum dot embedded into a SQUID loop in order to investigate the competition of strong electron correlations with proximity effect. Depending whether local pairing or local magnetism prevails, a superconducting quantum dot will respectively exhibit positive or negative supercurrent, referred to as a 0 or $π$ Josephson junction. In the regime of strong Coulomb blockade,…
▽ More
We study a carbon nanotube quantum dot embedded into a SQUID loop in order to investigate the competition of strong electron correlations with proximity effect. Depending whether local pairing or local magnetism prevails, a superconducting quantum dot will respectively exhibit positive or negative supercurrent, referred to as a 0 or $π$ Josephson junction. In the regime of strong Coulomb blockade, the 0 to $π$ transition is typically controlled by a change in the discrete charge state of the dot, from even to odd. In contrast, at larger tunneling amplitude the Kondo effect develops for an odd charge (magnetic) dot in the normal state, and quenches magnetism. In this situation, we find that a first order 0 to $π$ quantum phase transition can be triggered at fixed valence when superconductivity is brought in, due to the competition of the superconducting gap and the Kondo temperature. The SQUID geometry together with the tunability of our device allows the exploration of the associated phase diagram predicted by recent theories. We also report on the observation of anharmonic behavior of the current-phase relation in the transition regime, that we associate with the two different accessible superconducting states. Our results ultimately reveal the spin singlet nature of the Kondo ground state, which is the key process in allowing the stability of the 0-phase far from the mixed valence regime.
△ Less
Submitted 10 October, 2011;
originally announced October 2011.
-
Self-assembly of carbon-nanotube-based single electron memories
Authors:
L. Marty,
A. -M. Bonnot,
A. Iaia,
C. Naud,
A. Bonhomme,
E. Andre,
V. Bouchiat
Abstract:
We demonstrate wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (cnfets) by a complete self assembly process. First, a dry self assembly based on a Hot Filament assisted Chemical Vapor Deposition technique allows both localized growth and in situ electrical connection of carbon nanotubes on predefined catalytic electrodes. The semiconducting c…
▽ More
We demonstrate wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (cnfets) by a complete self assembly process. First, a dry self assembly based on a Hot Filament assisted Chemical Vapor Deposition technique allows both localized growth and in situ electrical connection of carbon nanotubes on predefined catalytic electrodes. The semiconducting carbon nanotubes integration yield can exceed 50% for a batch. Secondly, a wet self-assembly attaches single 30 nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead acts as the memory storage node while the cnfet operated in the subthreshold regime is an electrometer having exponential gain. Below 50 K, the transfer characteristics of some functionalized cnfets show highly reproducible hysteretical steps whose height can reach one decade of current. Evaluation of the capacitance confirms these current steps originate from single electron transfers between the bead and the nanotubes with a time retention exceeding 550s at 1.5K.
△ Less
Submitted 26 June, 2006; v1 submitted 18 March, 2005;
originally announced March 2005.