Littérature scientifique sur le sujet « Hétérostructure du graphène »
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Thèses sur le sujet "Hétérostructure du graphène"
Arezki, Hakim. « Ingénierie des propriétés optoélectroniques du graphène ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS095/document.
Texte intégralThis work was structured around the modulation of the electronic properties of graphene obtained via the CVD growth on copper substrate and/or the graphitization of the carbon atoms in the SiC substrate. One of the objectives was the design of electrodes (front or rear) for photovoltaic cells, among other applications. Different doping techniques have been implemented for modulating the work function (WF) and the electron mobility i.e. the incorporation of nitrogen in-situ during the growth, ex-situ incorporation by nitric acid and/or nano gold colloids (AuCl3). In this work, various characterization techniques were employed including atomic force microscopy (AFM), Raman spectroscopy, photoelectron spectroscopy (XPS and UPS), electrical transport measurements by Hall and field effect. These techniques have enabled us to determine the homogeneity , thecrystalline quality of the material, the carrier density, the electrical resistance and the electron mobility of different intrinsic and doped samples. Furthermore, we showed that it is possible to modulate the WF graphene by fabricating a heterostructure composed of PECVD amorphous silicon doped N or P deposited onto the graphene. This approach is of particular interest for replacement of ITO with graphene as transparent electrode. This result was confirmed by the study detailed spectra of the XPS and Raman vibrational states. The electronic transport measurements showed a charge transfer at the interface of the heterojunction graphene/amorphous silicon. The variation observed depends not only on the type of doping of the amorphous silicon but also on the crystallinity of the latter. This approach can readily be adapted to photovoltaic devices
Courtin, Jules. « Hétérostructure graphène / silicium : de la formation de l'interface aux propriétés de transport électronique ». Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S048.
Texte intégralThe graphene / silicon interface is of interest to diverse fields such as photovoltaics, electronics and spin electronics to name a few. This thesis work, based on the combination of photoemission measurements, transport and DFT calculations, allows a better understanding of the electronic properties of this interface as well as of the mechanisms associated with the formation of the Schottky barrier. We show a de-anchoring of the closure level at the graphene/silicon or metal/graphene/silicon interface. This implies that the height of the Schottky barrier can be controlled by modifying the work of exiting the graphene. DFT calculations reveal that this non-anchoring of the closure level at the graphene/silicon interface describes a low density of states induced in the bandgap of silicon by graphene. We show that this phenomenon is mainly associated with the structure of the graphene band whose electrons close to the closing level are at the edge of the Brillouin zone, leading to a low evanescence length of electronic functions compared to classical metals. The removal of the anchoring of the closure level at the metal / silicon interface by addition to the interface of a graphene sheet has enabled us to obtain interesting metal/graphene/silicon structures for spin electronics
Hong, Yuanzhuo. « Charge transport properties of graphene and its aligned heterostructures ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP020.
Texte intégralGraphene has unique band structure that conduction band and valence band touch at the Dirac points K and K', making it a zero gap semiconductor. The band structure can be modified by introducing periodic potential (superlattice) that place graphene on top of BN to crystallographic alignment. In this thesis, I mainly discuss the charge transport properties of graphene and its heterostructures. Different sample fabrication methods are introduced to make stacks depending on experiment purpose. We use different transport techniques in monolayer/bilayer graphene and their alignment heterostructures to study different scattering mechanisms in order to understand if these are modified by the presence of the superlattice. We found that small angle scattering is dominant in both monolayer and bilayer graphene samples. Through the transverse magneto focusing (TMF) measurements, we have the conclusion that electron-electron scattering is in dominance of TMF suppression. However, we observe nonidentical response in 0 ̊ and 60 ̊ alignment for bilayer graphene in TMF. This shows the different band structure of two alignments and tell us that the symmetry of bilayer graphene/BN heterostructure is not 60 ̊.We further observe the same nonidentical response in valley Hall effect (VHE) that 60 ̊ alignment doesn't give us the cubic relation which represents the VHE. This fact tells us the three fold symmetry of bilayer graphene/BN and also show that Berry curvature is not the only explanation of VHE. Here we propose a possible explanation about atomic structure relaxation. The strain on the second layer of graphene is different and create gauge fields that act as different pseudo magnetic field and indeed affect the VHE
Henni, Younes. « Etudes magnéto-Raman de systèmes - graphène multicouches et hétérostructures de graphène-nitrure de bore ». Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY060/document.
Texte intégralAs the fourth most abundant element in the universe, Carbon plays an important rolein the emerging of life in earth as we know it today. The industrial era has seen this element at the heart of technological applications due to the different ways in which carbon forms chemical bonds, giving rise to a series of allotropes each with extraordinary physical properties. For instance, the most thermodynamically stable allotrope of carbon, graphite crystal, is known to be a very good electrical conductor, while diamond very appreciated for its hardness and thermal conductivity is nevertheless considered as an electrical insulator due to different crystallographic structure compared to graphite. The advances in scientific research have shown that crystallographic considerations are not the only determining factor for such a variety in the physical properties of carbon based structures. Recent years have seen the emergence of new allotropes of carbon structures that are stable at ambient conditions but with reduced dimensionality, resulting in largely different properties compared to the three dimensional structures. Among these new classes of carbon allotropes is the first two-dimensional material: graphene.The successful isolation of monolayers of graphene challenged a long established belief in the scientific community: the fact that purely 2D materials cannot exist at ambient conditions. The Landau-Peierls instability theorem states that purely 2D materials are very unstable due to increasing thermal fluctuations when the material in question extends in both dimensions. To minimize its energy, the material will break into coagulated islands, an effect known as island growth. Graphene happens to overcome such barrier by forming continuous ripples on the surface of its substrate and thus is stable even at room temperature and atmospheric pressure.A great intention from the scientific community has been given to graphene, since 2004. Both fundamental and mechanical properties of graphene are fascinating. Thanks to its carbon atoms that are packed in a sp2 hybridized fashion, thus forming a hexagonal lattice structure, graphene has the largest young modulus and stretching power, yet it is hundreds of times stronger than steel. It conducts heat and electricity very efficiently, achieving an electron mobility as high as 107 cm−2V−1 s−1 when suspended over the substrate. The most fascinating aspect about graphene is the nature of its low energy charge carriers. Indeed, graphene has a linear energy dispersion at the charge neutrality, giving the charge carriers in graphene a relativistic nature. Many phenomena observed in this material are consequences of this relativistic nature of its carriers. Ballistic transport, universal optical conductivity, absence of back-scattering, and a new class of room temperaturequantum Hall effect are good examples of newly discovered phenomena in thismaterial. Graphene has become an active research area in condensed matter physics since 2004. It is however still early to state that all the physical properties of this material are well understood. In this thesis we conducted magneto-Raman spectroscopy experiments to address some of the open questions in the physics of graphene, such as the effect of electron-electron coupling on the energy spectrum of monolayer graphene, and the change in the physical properties of multilayer graphene as a function of the crystallographic stacking order. In all our experiments, the graphene-based systems have been subject to strong continuous magnetic fields, applied normal to the graphene layers. We study the evolution of its energy excitation spectra in the presence of the magnetic field, and also the coupling between these excitations and specific vibrational modes that are already in the system. This experimental approach allows us to deduce the band structure of the studied system at zero field, as well as many other lowenergy properties
Di, Felice Daniela. « Electronic structure and transport in the graphene/MoS₂ heterostructure for the conception of a field effect transistor ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS267/document.
Texte intégralThe isolation of graphene, a single stable layer of graphite, composed by a plane of carbon atoms, demonstrated the possibility to separate a single layer of atomic thickness, called bidimensional (2D) material, from the van der Waals (vdW) solids. Thanks to their stability, 2D materials can be used to form vdW heterostructures, a vertical stack of different 2D crystals maintained together by the vdW forces. In principle, due to the weakness of the vdW interaction, each layer keeps its own global electronic properties. Using a theoretical and computational approach based on the Density Functional Theory (DFT) and Keldish-Green formalism, we have studied graphene/MoS₂ heterostructure. In this work, we are interested in the specific electronic properties of graphene and MoS₂ for the conception of field effect transistor: the high mobility of graphene as a basis for high performance transistor and the gap of MoS₂ able to switch the device. First, the graphene/MoS₂ interface is electronically characterized by analyzing the effects of different orientations between the layers on the electronic properties. We demonstrated that the global electronic properties as bandstructure and Density of State (DOS) are not affected by the orientation, whereas, by mean of Scanning Tunneling Microscope (STM) images, we found that different orientations leads to different local DOS. In the second part, graphene/MoS₂ is used as a very simple and efficient model for Field Effect Transistor. The role of the vdW heterostructure in the transistor operation is analyzed by stacking additional and alternate graphene and MoS₂ layers on the simple graphene/MoS₂ interface. We demonstrated that the shape of the DOS at the gap band edge is the fundamental parameter in the switch velocity of the transistor, whereas the additional layers do not improve the transistor behavior, because of the independence of the interfaces in the vdW heterostructures. However, this demonstrates the possibility to study, in the framework of DFT, the transport properties of more complex vdW heterostructures, separating the single interfaces and reducing drastically the calculation time. The 2D materials are also studied in the role of a tip for STM and Atomic Force Microscopy (AFM). A graphene-like tip, tested on defected MoS₂, is compared with a standard copper tip, and it is found to provide atomic resolution in STM images. In addition, due to vdW interaction with the sample, this tip avoids the contact effect responsible for the transfer of atoms between the tip and the sample. Furthermore, the analysis of defects can be very useful since they induce new peaks in the gap of MoS₂: hence, they can be used to get a peak of current representing an interesting perspective to improve the transistor operation
Arjmandi-Tash, Hadi. « Graphene based mechanical and electronic devices in optimized environments : from suspended graphene to in-situ grown graphene/boron nitride heterostructures ». Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY043/document.
Texte intégralCharge carriers in graphene form stable two-dimensional gases which are fully exposed to the environment. As a consequence, the electrical performance of graphene is strongly affected by surface charged impurities as well as topographic perturbations inherited from the underlying substrate.This thesis addresses several methods to circumvent that issue.The first method consists in embedding graphene in an optimized environment by depositing graphene onto some neutral and crystalline material. Novel 2D insulating materials such as hexagonal boron nitride buffer layer (BN) appears as ideal substrates to get rid of detrimental effect of interfacial charges and corrugation. Several fabrication schemes of Graphene/BN stacks are shown including some direct in-situ growth of graphene on BN crystal using an innovative proximity-driven chemical vapour growth based on BN exfoliation on copper. In order to explore the effects of the improved substrate on the transport properties of graphene, we have performed low temperature magneto-transport studies on these stacks. We present a direct comparison of weak localization signals with those acquired on a graphene/silica reference device. A clear increase of the coherence length is shown on Graphene/BN stacks together with improved electronic mobility and charge neutrality.Removing the substrate and suspending graphene is another approach for optimization of the graphene environment which forms the second topic covered in this thesis. After introducing an improved recipe for preserving the quality of graphene throughout an elaborate fabrication process, we probe the room- and low-temperature performance of the nano-electro-mechanical devices based on doubly clamped suspended graphene ribbons. The obtained data are used for characterizing the thermal expansion of CVD graphene
Tran, Van Truong. « Propriétés électroniques et thermoélectriques des hétérostructures planaires de graphène et de nitrure de bore ». Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS133/document.
Texte intégralGraphene is a fascinating 2-dimensional material exhibiting outstanding electronic, thermal and mechanical properties. Is this expected to have a huge potential for a wide range of applications, in particular in electronics. However, this material also suffers from a strong drawback for most electronic devices due to the gapless character of its band structure, which makes it difficult to switch off the current. For thermoelectric applications, the high thermal conductance of this material is also a strong limitation. Hence, many challenges have to be taken up to make it useful for actual applications. This thesis work focuses on the theoretical investigation of a new strategy to modulate and control the properties of graphene that consists in assembling in-plane heterostructures of graphene and Boron Nitride (BN). It allows us to tune on a wide range the bandgap, the thermal conductance and the Seebeck coefficient of the resulting hybrid nanomaterial. The work is performed using atomistic simulations based on tight binding (TB), force constant (FC) models for electrons and phonons, respectively, coupled with the Green's function formalism for transport calculation. The results show that thanks to the tunable bandgap, it is possible to design graphene/BN based transistors exhibiting high on/off current ratio in the range 10⁴-10⁵. We also predict the existence hybrid quantum states at the zigzag interface between graphene and BN with appealing electron transport. Finally this work shows that by designing properly a graphene ribbon decorated with BN nanoflakes, the phonon conductance is strongly reduced while the bandgap opening leads to significant enhancement of Seebeck coefficient. It results in a thermoelectric figure of merit ZT larger than one at room temperature
Cazayus-Claverie, Emmanuelle. « Matériaux pour les batteries Li-AIR : nouvelles approches vers des nano-hétérostructures spinelles/graphène pour électrode à air ». Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066508/document.
Texte intégralThis research work is focused on the design and characterisation of cobalt based oxides nanospinels anchored onto the surface of reduced graphene oxides (RGO) nanosheet, which will serve as bifunctional catalysts for the new generation lithium-air batteries. Whereas nanospinels are relatively simple to synthesize by conventional colloidal routes as nanoparticles dispersed into an aqueous solution, the synthesis we developed relies on a hydrothermal microwave treatment in the 100°C-200°C range. The main challenges of this nano-heterostructures synthesis was to create the interface between the nanoparticles and the RGO directly during the nanoparticles nucleation. RGO are very efficient microwave absorbers and could then convert microwave irradiation into heat in order to trigger precipitation of the spinel at the surface of the RGO sheet.Starting from Co3O4 as proof-of-concept material, the synthesis protocol has been successfully adapted to address binary oxides by substituting cobalt with first row transition metals such as nickel, manganese or iron. The precipitation of binary and ternary oxides was achievable thanks to a good understanding of the Pourbaix diagrams of all cations to adjust the acido-basic and redox conditions.Finally, the electrocatalytic activity of these supported spinel oxides was measured for both the oxygen reduction and oxygen evolution reactions (ORR and OER). The gap between the ORR and the OER potentials was significantly lowered by the presence of Co3O4 nanoparticles on the RGO, thus assuring the reversibility of this catalytic system, which is to be integrated in future scale-up test
Cazayus-Claverie, Emmanuelle. « Matériaux pour les batteries Li-AIR : nouvelles approches vers des nano-hétérostructures spinelles/graphène pour électrode à air ». Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066508.pdf.
Texte intégralThis research work is focused on the design and characterisation of cobalt based oxides nanospinels anchored onto the surface of reduced graphene oxides (RGO) nanosheet, which will serve as bifunctional catalysts for the new generation lithium-air batteries. Whereas nanospinels are relatively simple to synthesize by conventional colloidal routes as nanoparticles dispersed into an aqueous solution, the synthesis we developed relies on a hydrothermal microwave treatment in the 100°C-200°C range. The main challenges of this nano-heterostructures synthesis was to create the interface between the nanoparticles and the RGO directly during the nanoparticles nucleation. RGO are very efficient microwave absorbers and could then convert microwave irradiation into heat in order to trigger precipitation of the spinel at the surface of the RGO sheet.Starting from Co3O4 as proof-of-concept material, the synthesis protocol has been successfully adapted to address binary oxides by substituting cobalt with first row transition metals such as nickel, manganese or iron. The precipitation of binary and ternary oxides was achievable thanks to a good understanding of the Pourbaix diagrams of all cations to adjust the acido-basic and redox conditions.Finally, the electrocatalytic activity of these supported spinel oxides was measured for both the oxygen reduction and oxygen evolution reactions (ORR and OER). The gap between the ORR and the OER potentials was significantly lowered by the presence of Co3O4 nanoparticles on the RGO, thus assuring the reversibility of this catalytic system, which is to be integrated in future scale-up test
Berthou, Simon. « Etude opto-électronique des mécanismes de relaxation des électrons de haute énergie dans les hétérostructures en graphène ». Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC133/document.
Texte intégralIn this thesis we study the electron-phonon coupling in graphene and in particular theinfluence of the substrate in the aforementioned coupling. We want to quantify by optoelectronicalmeasurements the coupling between the phonon modes of the substrate. It might be the couplingwith Surface Phonon Polaritons (SPPs) in case of isotropic substrates as SiO2 or Hyperbolic PhononPolaritons (HPPs) in case of highly anisotropic substrates. We start by a review about the state of theart on electron phonon coupling in graphene. Then we introduce the different experimental methodsused during this thesis. We present experimental results on an graphene on SiO2 sample. We identifythe different coupling regimes and point out the necessity of working on ultra clean samples toinvestigate the high energy regimes. Finally we prensent experimental results on a graphene on BNsample where we identify a new coupling regime consisting in HPP emission in a Zener-Klein transportregime