Dissertations / Theses on the topic 'Van der Waal materials'
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Boddison-Chouinard, Justin. "Fabricating van der Waals Heterostructures." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38511.
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The isolation of single layer graphene in 2004 by Geim and Novoselov introduced a
method that researchers could extend to other van der Waals materials. Interesting and new properties arise when we reduce a crystal to two dimensions where they are often different from their bulk counterpart. Due to the van der Waals bonding between layers, these single sheets of crystal can be combined and stacked with diferent sheets to create novel materials.
With the goal to study the interesting physics associated to these stacks, the focus of this work is on the fabrication and characterization of van der Waals heterostructures.
In this work, we first present a brief history of 2D materials, the fabrication of heterostructures, and the various tools used to characterize these materials. We then give a description of the custom-built instrument that was used to assemble various 2D heterostructures followed by the findings associated with the optimization of the cleanliness of the stack's interface and surface. Finally, we discuss the results related to the twisting of adjacent layers of stacked MoS2 and its relation to the interlayer coupling between said layers.
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Schofield, Robert Christopher. "Raman studies of 2-dimensional van der Waals materials." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21313/.
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Presented herein are results of optical studies with emphasis on the Raman response, providing significant contribution to the knowledge of the field. In Mox W(1−x) S2 , confirmation of the behaviour of the excitonic properties is made. Raman measurements performed in this system allow investigation with unprecedented resolution, highlighting deviations in the high frequency A1g optical phonon mode from theoretical predictions, and previous experimental studies. In the low frequency, data confirms the trends in the shear and breathing interlayer modes in alloys between WS2 and MoS2 are well described by the modification in the square density. Resonant excitation for [Mo] < 0.4, highlights new evidence for the understanding of the hitherto unexplained ‘Peak X’ resonant feature. Diverse indium-selenium compounds isolated by novel means are studied. The ULF Raman modes of PDMS exfoliated InSe are documented for the first time, demonstrating the ε-phase with ABA stacking, with flake of thickness N manifesting (N − 1) shear modes owing to resonant excitation of few layer samples. InSe flakes encapsulated in hexagonal boron nitride manifest different stacking orders to those of PDMS exfoliated InSe, and were found to have significant contamination, with crystalline degradation of the monolayer flake, and peaks corresponding N2 & O2 rotational modes present. In2Se3 films grown epitaxially on GaSe display substrate-selective polymorphism, where α-, β-, & γ- phases are identified, in addition to regions of InSe. Laser photo-annealing is shown to drive a phase change from the groundstate β → α phase, which is against the thermodynamic gradient. MoSe2/WS2 twisted hetero-bi-layer structures are studied, where shear modes showing a linear softening from AA′ stacking towards the AB at 60° indicating reduced interlayer coupling, as expected from the difference in interlayer spacing of AA′ and AB ordering. High frequency modes in the heterobilayer also demonstrate some sensitivity in the relative angle, and are analysed in detail.
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Zheng, Zhikun, Xianghui Zhang, Christof Neumann, Daniel Emmrich, Andreas Winter, Henning Vieker, Wei Liu, Marga Lensen, Armin Gölzhäuser, and Andrey Turchanin. "Hybrid van der Waals heterostructures of zero-dimensional and two-dimensional materials." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-188567.
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van der Waals heterostructures meet other low-dimensional materials. Stacking of about 1 nm thick nanosheets with out-of-plane anchor groups functionalized with fullerenes integrates this zero-dimensional material into layered heterostructures with a well-defined chemical composition and without degrading the mechanical properties. The developed modular and highly applicable approach enables the incorporation of other low-dimensional materials, e.g. nanoparticles or nanotubes, into heterostructures significantly extending the possible building blocks.
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Hadland, Erik. "Thin Film van der Waals Heterostructures containing MoSe2 from Modulated Elemental Precursors." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24520.
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Transition metal dichalcogenides (TMDs) are naturally occurring layered materials that have attracted immense research interest due to their high degree of chemical tunability. In particular, MoSe2 has been the focus of significant investigation stemming from reports that it converts to a direct band gap semiconductor material at ultralow dimensions. Yet, as more and more is learned about increasingly thin MoSe2, efforts are now aimed at imparting the novel functionality of MoSe2 into van der Waals heterostructures. This dissertation focuses on synthesis and characterization of novel MoSe2-based nanolaminate structures that have been self assembled from modulated elemental precursors.
The first section describes a new treatment of x-ray fluorescence spectroscopy data and its use as a powerful probe for determining the absolute composition per unit area of a thin film with sub-monolayer accuracy. While this has widespread application in the thin film world, it is particularly useful for MER synthesis in the calibration of modulated elemental precursors. In order to crystallize a target structure, it is imperative to deposit the correct number of atoms, which is now possible with greater precision.
The second section shows the importance of rotational (i.e. “turbostratic”) disorder on lowering cross-plane thermal conductivity in two systems—MoSe2 and the (SnSe2)1(MoSe2)1.32 heterostructure. The binary systems exhibits ultralow thermal conductivity that rivals that of WSe2, yet some interlayer atomic registry was noted in TEM images. By interleaving layers of MoSe2 with SnSe2—which also possesses hexagonal symmetry, but has a significantly larger basal plane—the cross-plane thermal
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conductivity was depressed to the lowest reported value in the literature for a fully dense solid.
The final section presents the synthesis and characterization of a new, ternary phase of Bi|Mo|Se. The structure consists of alternating layers of a “puckered” rock salt BiSe lattice and nanosheets of MoSe2. Notably, the MoSe2 sublattice consists of a mixture of the semiconducting 2H phase (~60%) and the metallic 1T phase (~40%). This is the result of electron injection from the BiSe into the conduction band of the MoSe2, which is known to undergo a rearrangement upon reduction.
This dissertation includes previously published and unpublished coauthored materials.2021-04-30
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Rajter, Richard F. "Chirality-dependent, van der Waals-London dispersion interactions of carbon nanotube systems." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46670.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Includes bibliographical references (p. 185-192).
The Lifshitz formulation is a quantum electrodynamic, first principals formulation used to determine van der Waals - London dispersion interactions in the continuum limit. It has many advantages over crude, pairwise potential models. Most notably, it can solve for complex interactions (e.g. repulsive and multi-body effects) and determine the vdW-Ld interaction magnitude and sign a priori from the optical properties rather than by parameterization. Single wall carbon nanotubes (SWCNTs) represent an ideal class of materials to study vdW-Ld interactions because very small changes in their geometrical construction, via the chirality vector [n,m], can result in vastly different electronic and optical properties. These chirality-dependent optical properties ultimately lead to experimentally exploitable vdW-Ld interactions, which already exist in the literature.Proper use of the Lifshitz formulation requires 1) An analytical extension for the geometry being studied 2) The optical properties of all materials present and 3) A method to incorporate spatially varying properties. This infrastructure needed to be developed to study the vdW-Ld interactions of SWCNTs systems because they were unavailable at the onset. The biggest shortfall was the lack of the E" optical properties out to 30+ eV.
(cont.) This was solved by using an ab initio method to obtain this data for 63 SWCNTs and a few MWCNTs. The results showed a clear chirality AND direction dependence that is unique to each [n,m]. Lifshitz and spectral mixing formulations were then derived and introduced respectively for obtaining accurate Hamaker coefficients and vdW-Ld total energies for these optically anisotropic SWCNTs at both the near and far-limits. With the infrastructure in place, it was now possible to study the trends and breakdowns over a large population as a function of SWCNT class and chirality. A thorough analysis of all these properties at all levels of abstraction yielded a new classification system specific to the vdW-Ld properties of SWCNTs. Additionally, the use of this data and an understanding of the qualitative trends makes it straightforward to design experiments that target, trap, and/or separate specific SWCNTs as a function of SWCNT class, radius, etc.
by Richard F. Rajter.
Ph.D.
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Wood, Cody. "A Continuum Model for the van der Waals Interaction Energy of Carbon Nanotubes." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493376354522434.
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Yankowitz, Matthew Abraham. "Local Probe Spectroscopy of Two-Dimensional van der Waals Heterostructures." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/594649.
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A large family of materials, collectively known as "van der Waals materials," have attracted enormous research attention over the past decade following the realization that they could be isolated into individual crystalline monolayers, with charge carriers behaving effectively two-dimensionally. More recently, an even larger class of composite materials has been realized, made possible by combining the isolated atomic layers of different materials into "van der Waals heterostructures," which can exhibit electronic and optical behaviors not observed in the parent materials alone. This thesis describes efforts to characterize the atomic-scale structural and electronic properties of these van der Waals materials and heterostructures through scanning tunneling microscopy measurements. The majority of this work addresses the properties of monolayer and few-layer graphene, whose charge carriers are described by massless and massive chiral Dirac Hamiltonians, respectively. In heterostructures with hexagonal boron nitride, an insulating isomorph of graphene, we observe electronic interference patterns between the two materials which depend on their relative rotation. As a result, replica Dirac cones are formed in the valence and conduction bands of graphene, with their energy tuned by the rotation. Further, we are able to dynamically drag the graphene lattice in these heterostructures, owing to an interaction between the scanning probe tip and the domain walls formed by the electronic interference pattern. Similar dragging is observed in domain walls of trilayer graphene, whose electronic properties are found to depend on the stacking configuration of the three layers. Scanning tunneling spectroscopy provides a direct method for visualizing the scattering pathways of electrons in these materials. By analyzing the scattering, we can directly infer properties of the band structures and local environments of these heterostructures. In bilayer graphene, we map the electrically field-tunable band gap and extract electronic hopping parameters. In WSe₂, a semiconducting transition metal dichalcogenide, we observe spin and layer polarizations of the charge carriers, representing a coupling of the spin, valley and layer degrees of freedom.
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Coy, Diaz Horacio. "Preparation and Characterization of Van der Waals Heterostructures." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6212.
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In this dissertation different van der Waals heterostructures such as graphene-MoS2 and MoTe2-MoS2 were prepared and characterized. In the first heterostructure, polycrystalline graphene was synthesized by chemical vapor deposition and transferred on top of MoS2 single crystal. In the second heterostructure, MoTe2 monolayers were deposited on MoS2 by molecular beam epitaxy.
Characterization of graphene-MoS2 heterostructures was conducted by spin and angle resolve spectroscopy which showed that the electronic structure of the bulk MoS2 and graphene in this van der Waals heterostructures is modified. For MoS2 underneath the graphene, a band structure renormalization and spin polarization are observed. The band structure of MoS2 is modified because the graphene induces screening which shifts the Г-point ~150 meV to lower binding compared to the sample without graphene. The spin polarization is explained by the dipole arising from band bending which breaks the symmetry at the MoS2 surface. For graphene, the band structure at lower binding energy shows that the Dirac cone remains intact with no significant doping. Instead, away from the Fermi level the formation of several gaps in the pi-band due to hybridization with states from the MoS2 is observed.
For the heterostructures made depositing monolayer of MoTe2 on MoS2, the morphology, structure and electronic structure were studied. Two dimensional growth is observed under tellurium rich growth conditions and a substrate temperature of 200 °C but formation of a complete monolayer was not achieved. The obtained MoTe2 monolayer shows a high density of the mirror-twins grain boundaries arranged in a pseudo periodic wagon wheel pattern with a periodicity of ~2.6 nm. These grain boundary are formed due to Te-deficiency during the growth. The defect states from these domain boundary pin the Fermi level in MoTe2 and thus determine the band alignment in the MoTe2-MoS2 heterostructures.
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Henck, Hugo. "Hétérostructures de van der Waals à base de Nitrure." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS319/document.
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Le sujet de cette thèse est à l’interface entre l’étude de composés à base de nitrure et des structures émergeantes formées par les matériaux bidimensionnels (2D) d’épaisseur atomique. Ce travail se consacre sur l’hybridation des propriétés électriques et optiques des semi-conducteurs à larges bandes interdites que sont les nitrures et des performances mécaniques, électriques et optiques des matériaux lamellaires, récemment isolé à l’échelle d’un plan atomique, qui sont aujourd’hui considérées avec attention aux regards de futures applications et d’études plus fondamentales. En particulier, une étude des propriétés électroniques, optiques et structurelles d’hétérostructures composées de plusieurs matériaux lamellaires et d’interfaces entre matériaux 2D et 3D a été réalisé par des moyens de microscopie et de spectroscopie tel que la spectroscopie Raman, de photoémission et d’absorption.Ce manuscrit traite dans un premier temps des propriétés structurelles et électroniques du nitrure de bore hexagonal (h-BN), matériau isolant aux propriétés optiques exotiques et essentiel dans la future intégration de ce type de matériaux 2D permettant de mettre en valeur leurs propriétés intrinsèques.En utilisant le graphène comme substrat les problèmes de mesures par photoémission rencontrés pour des matériaux isolant ont pu être surmonté dans le cas du h-BN et une étude des défauts structurels a pu être réalisée. Par conséquent, les premières mesures directes de la structure de bande électronique de plusieurs plans de h-BN sont présentées dans ce manuscrit.Dans un second temps, une approche d’intégration de ces matériaux 2D différente a été étudiée en formant une hétérostructure 2D/3D. L’interface de cette hétérojonction, composée d’un plan de disulfure de molybdène (MoS2) de dopage intrinsèque N associé à 300 nm de nitrure de gallium (GaN) intentionnellement dopé P à l’aide de magnésium, a été caractérisée. Un transfert de charge du GaN vers le MoS2 a pu être identifié suggérant un contrôle des propriétés électroniques de ce type de structure par le choix de matériaux.Ces travaux ont permis de révéler les diagrammes de bandes électroniques complet des structures étudiées a pu être obtenu permettant une meilleur compréhension de ces systèmes émergeantsThis thesis is at the interface between the study of nitride based compounds and the emerging structures formed by atomically thin bi-dimensional (2D) materials. This work consists in the study of the hybridization of the properties of large band gap materials from the nitride family and the mechanical, electronic and optical performances of layered materials, recently isolated at the monolayer level, highly considered due to their possible applications in electronics devices and fundamental research. In particular, a study of electronics and structural properties of stacked layered materials and 2D/3D interfaces have been realised with microscopic and spectroscopic means such as Raman, photoemission and absorption spectroscopy.This work is firstly focused on the structural and electronic properties of hexagonal boron nitride (h-BN), insulating layered material with exotic optical properties, essential in in the purpose of integrating these 2D materials with disclosed performances. Using graphene as an ideal substrate in order to enable the measure of insulating h-BN during photoemission experiments, a study of structural defects has been realized. Consequently, the first direct observation of multilayer h-BN band structure is presented in this manuscript. On the other hand, a different approach consisting on integrating bi-dimensional materials directly on functional bulk materials has been studied. This 2D/3D heterostructure composed of naturally N-doped molybdenum disulphide and intentionally P-doped gallium nitride using magnesium has been characterised. A charge transfer from GaN to MoS2 has been observed suggesting a fine-tuning of the electronic properties of such structure by the choice of materials.In this work present the full band alignment diagrams of the studied structure allowing a better understanding of these emerging systems
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Froehlicher, Guillaume. "Optical spectroscopy of two-dimensional materials : graphene, transition metal dichalcogenides and van der Waals heterostructures." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE033/document.
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Au cours de ce projet, nous avons utilisé la microspectroscopie Raman et de photoluminescence pour étudier des matériaux bidimensionnels (graphène et dichalcogénures de métaux de transition) et des hétérostructures de van der Waals. Tout d’abord, à l’aide de transistors de graphène munis d’une grille électrochimique, nous montrons que la spectroscopie Raman est un outil extrêmement performant pour caractériser précisément des échantillons de graphène. Puis, nous explorons l’évolution des propriétés physiques de N couches de dichalcogénures de métaux de transition semi-conducteurs, en particulier de ditellurure de molybdène (MoTe2) et de diséléniure de molybdène (MoSe2). Dans ces structures lamellaires, nous observons la séparation de Davydov des phonons optiques au centre de la première zone de Brillouin, que nous décrivons à l’aide d’un modèle de chaîne linéaire. Enfin, nous présentons une étude toute optique du transfert de charge et d’énergie dans des hétérostructures de van der Waals constituées de monocouches de graphène et de MoSe2. Ce travail de thèse met en évidence la riche photophysique de ces matériaux atomiquement fins et leur potentiel en vue de la réalisation de nouveaux dispositifs optoélectroniquesIn this project, we have used micro-Raman and micro-photoluminescence spectroscopy to study two-dimensional materials (graphene and transition metal dichalcogenides) and van der Waals heterostructures. First, using electrochemically-gated graphene transistors, we show that Raman spectroscopy is an extremely sensitive tool for advanced characteri-zations of graphene samples. Then, we investigate the evolution of the physical properties of N-layer semiconducting transition metal dichalcogenides, in particular molybdenum ditelluride (MoTe2) and molybdenum diselenide (MoSe2). In these layered structures, theDavydov splitting of zone-center optical phonons is observed and remarkably well described by a ‘textbook’ force constant model. We then describe an all-optical study of interlayer charge and energy transfer in van der Waals heterostructures made of graphene and MoSe2 monolayers. This work sheds light on the very rich photophysics of these atomically thin two-dimensional materials and on their potential in view of optoelectronic applications
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Graziano, G. "The role of van der Waals interactions and nuclear quantum effects in soft layered materials." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1463160/.
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Recent years have seen a surge of interest in layered materials, mainly because of their numerous applications, prominently in gas sorption. These materials are highly anisotropic, because of the coexistence of covalent bonds within the individual layers and weak van der Waals (vdW) interactions between layers. Although the anisotropy makes layered materials appealing for many technological applications, it also makes their full theoretical and experimental description difficult. This study has addressed some of the major gaps in our understanding of layered materials using a combination of theoretical and experimental techniques. Computationally, newly developed functionals able to treat both short and long range interactions within density functional theory have been used to look at the structure, energetics, dynamics and adsorption properties of layered materials. Neutron scattering experiments have been used to further our understanding of the atomic dynamics in graphite and to set up a preliminary study of the hydrogen adsorption in doped graphite. The present results underline strong similarities of the vdW-dominated properties of the systems examined. The interlayer binding energies and the hydrogen adsorption capabilities have been found to be surprisingly similar. Analysis shows that this is due to a fine balance between attractive and repulsive forces and, more specifically between atomic polarizabilities and volumes of the material components. The comparison between experimental and predicted atomic displacements in graphite highlights that the carbon dynamics is affected by nuclear quantum effects at temperatures lower than 300 K. These temperatures are common for many technological applications, especially those related to gas adsorption. Thus, the presented results pose some questions on what could be the correct model and computational technique to use in order to gain a better understanding of the sorptive properties of layered materials, especially carbon based, and move forward in the design of new gas storage materials.
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Khestanova, Ekaterina. "Van der Waals heterostructures : fabrication, mechanical and electronic properties." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/van-der-waals-heterostructures-fabrication-mechanical-and-electronic-properties(047ce24b-7a58-4192-845d-54c7506f179f).html.
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The fast progress in the exploration of 2D materials such as graphene became possible due to development of fabrication techniques that allowed these materials to be protected from e.g. undesirable doping and gave rise to new functionalities realized within van der Waals heterostructures. Attracted by van der Waals interaction the constituent layers of such heterostructures preserve their exceptional electronic quality and for example in graphene allow for high electron mobility to be achieved. However, the studies of atomically thin layers such as NbSe2 that exhibit metallic behavior have been impeded by their reactivity and hence oxidation during exposure to ambient or oxidizing agents such as solvents. In this thesis, the existing heterostructure assembly technique was improved by the introduction of exfoliation and re-stacking by a fully motorized system placed in an inert atmosphere. This approach allowed us to overcome the problem of environmental degradation and create Hall bars and planar tunnel junctions from atomically thin superconducting NbSe2. Furthermore, this versatile approach allowed us to study the thickness dependence of the normal and superconducting state transport properties of NbSe2, uncovering the reduction of the superconducting energy gap and transition temperature in the thinnest samples. On the other hand, 2D materials being just 1-3 atoms thick represent an ultimate example of a membrane - thin but laterally extended object. Consisting of such atomically thin membranes the van der Waals heterostructures can be used for purposes other than the studies of electronic transport. In this work, ubiquitous bubbles occurring during van der Waals heterostructure assembly are employed as a tool to explore 2D materials' mechanical properties and mutual adhesion. This allowed us to measure Young's modulus of graphene and other 2D materials under 1-2% strain and deduce the internal pressure that can reach up to 1 GPa in sub-nanometer size bubbles.
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Nayak, Goutham. "Amélioration des propriétés physiques de matériaux de basse-dimensionnalité par couplage dans des hétérostructures Van der Waals." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY084/document.
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Les propriétés intrinsèques extraordinaires de ces matériaux de faible dimension dépendent fortement de l'environnement auquel ils sont soumis. Par conséquent, ils doivent être préparés, traités et caractérisés sans défauts. Dans cette thèse, je discute de la manière de contrôler l'environnement des nanomatériaux de faible dimension tels que le graphène, le MoS$_{2}$ et les nanotubes de carbone afin de préserver leurs propriétés physiques intrinsèques. De nouvelles solutions pour l'amélioration des propriétés sont discutées en profondeur. Dans la première partie, nous fabriquons des dispositifs d'hétérostructure à base de graphène de Van der Waals (VdW) de dernière génération, en contact avec les bords, encapsulés dans du nitrure de bore hexagonal (hBN), afin d'obtenir un transport balistique. Nous utilisons une technique basée sur des mesures de bruit 1 / f pour sonder le transport de masse et de bord lors de régimes Quantum Hall entiers et fractionnaires. Dans la deuxième partie, le même concept de fabrication des hétérostructures VdW a été étendu pour encapsuler la couche monocouche MoS $_{2}$ dans le hBN afin d'en modifier les propriétés optiques. À cet égard, nous présentons une étude approfondie sur l'origine et la caractérisation des défauts intrinsèques et extrinsèques et leur incidence sur les propriétés optiques. En outre, nous décrivons une technique pour sonder le couplage entre couches ainsi que la génération de lumière avec une résolution spatiale inférieure à la limite de diffraction de la lumière. Enfin, nous discutons d'un processus systémique naturel visant à améliorer les propriétés mécaniques de la soie polymérique naturelle à l'aide d'une nanotubes de carbone à paroi unique fabriqués par HipCO comme aliment pour le ver à soieThe extraordinary intrinsic properties of low dimensional materials depend highly on the environment they are subjected to. Hence they need to be prepared, processed and characterized without defects. In this thesis, I discuss about how to control the environment of low dimensional nanomaterials such as graphene, MoS2 and carbon nanotubes to preserve their intrinsic physical properties. Novel solutions for property enhancements are discussed in depth. In the first part, we fabricate state-of-the-art, edge-contacted, graphene Van der Waals(VdW) heterostructuredevices encapsulated in hexagonal-boron nitride(hBN), to obtain ballistic transport. We use a technique based on 1/f-noise measurements to probe bulk and edge transport during integer and fractional Quantum Hall regimes. In the second part, the same fabrication concept of VdW heterostructures has been extended to encapsulate monolayer MoS2 in hBN to improve optical properties. In this regard we present an extensive study about the origin and characterization of intrinsic and extrinsic defects and their affect on optical properties. Further, we describe a technique to probe the interlayer coupling along with the generation of light with spatialresolution below the diffraction limit of light. Finally, we discuss a natural systemic process to enhance the mechanical properties of natural polymer silk using HipCO-made single walled carbon nanotubes as a food for silkworm
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Forrer, Daniel. "Role and Eective Treatment of Dispersive Forces in Materials." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3427094.
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DFT and DFT-D calculations have been carried out on several chemical systems, ranging from molecules to crystalline polymers, bulk graphite, self-assembled phases of large molecules on metal surfaces and small molecules absorbed in porous organic-inorganic materials.
Joining insights from calculations with experimental outcomes, the structural and electronic behavior of complex chemical systems have been described and explained, allowing a deeper understanding of the studied phenomena. Thanks to the implementation of a correction scheme to DFT, allowing the effective treatment of dispersion forces in materials, accurate calculations on previously unaffordable problems have been performed at a reasonable computational effort. This allowed, e.g., to understand the coverage-dependent phase transition of iron phthalocyanine on Ag(110) and the successful modeling of water absorption in a bispyrazolato copper(II) polymer.In questa tesi è presentata un'indagine computazionale basata sulla Teoria del Funzionale Densità (DFT), eseguita su un ampio range di sistemi che spazia da molecole a polimeri cristallini, grafite, fasi auto-organizzate di molecole organiche su supporti metallici e piccole molecole assorbite in materiali porosi a base organica-inorganica. Combinando le informazioni ottenute per mezzo di metodi computazionali con i risultati sperimentali, prevalentemente di microscopia a scansione ad effetto tunnel, è stato possibile descrivere il comportamento elettronico e strutturale di tali sistemi e raggiungere una compresione dettagliata del loro comportamento chimico-fisico. Grazie all'implementazione di uno schema correttivo per l'inclusione delle forze di dispersione nella DFT, sono stati effettuati calcoli accurati su sistemi altrimenti inaccessibili, pur contendo lo sforzo computazionale. Questo ha permesso, ad esempio, di capire il ruolo giocato dal ricoprimento della superficie nella transizione di fase osservata per le ftalocianine di ferro depositate su Ag(110) e di modellare con successo l'assorbimento di H20 in un polimero di Cu(II) bispirazolato.
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Constantinescu, Gabriel Cristian. "Large-scale density functional theory study of van-der-Waals heterostructures." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274876.
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Research on two-dimensional (2D) materials currently occupies a sizeable fraction of the materials science community, which has led to the development of a comprehensive body of knowledge on such layered structures. However, the goal of this thesis is to deepen the understanding of the comparatively unknown heterostructures composed of different stacked layers. First, we utilise linear-scaling density functional theory (LS-DFT) to simulate intricate interfaces between the most promising layered materials, such as transition metal dichalcogenides (TMDC) or black phosphorus (BP) and hexagonal boron nitride (hBN). We show that hBN can protect BP from external influences, while also preventing the band-gap reduction in BP stacks, and enabling the use of BP heterostructures as tunnelling field effect transistors. Moreover, our simulations of the electronic structure of TMDC interfaces have reproduced photoemission spectroscopy observations, and have also provided an explanation for the coexistence of commensurate and incommensurate phases within the same crystal. Secondly, we have developed new functionality to be used in the future study of 2D heterostructures, in the form of a linear-response phonon formalism for LS-DFT. As part of its implementation, we have solved multiple implementation and theoretical issues through the use of novel algorithms.
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Rooney, Aidan. "Characterisation of buried interfaces in van der Waals materials by cross sectional scanning transmission electron microscopy." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/characterisation-of-buried-interfaces-in-van-der-waals-materials-by-cross-sectional-scanning-transmission-electron-microscopy(dd5565b9-1709-4d28-b4ce-9cd675fb36eb).html.
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Graphene and other two-dimensional materials can be stacked together to form vander Waals heterostructures: synthetic crystals composed of different atomically thin layers with a bespoke electronic band structure. Structural characterisation of vander Waals heterostructures is difficult using conventional methods as the properties are almost entirely defined by the nature of the buried interfaces between dissimilar crystals. These methods also fall short of resolving the atomic structure of buried defects in van der Waals materials such as graphite. This work demonstrates the refinement and successful application of ion beam specimen preparation to produce cross sectional slices through these unique crystals so that they can be characterised by high resolution scanning transmission electron microscopy (STEM). Cross sectional specimen were prepared using in situ lift-out in a focused ion beam (FIB) dual-beam instrument. The fine polishing steps were optimised to prevent damage to the core of the specimen. High resolution STEM imaging of twin defects in graphene, hexagonal boron ni-tride and MoSe2 revealed that the boundaries are not atomically sharp but extended across many atoms. Advanced processing and analysis of these images uncovered fundamental mechanics which govern their geometry. This technique was further applied to complex transition metal dichalcogenide heterostructures to quantitatively determine the properties of buried interfaces between atomically thin crystals.
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Zhao, Liang. "Optical properties of two-dimemsional Van der Waals crystals: from terahertz to visible." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1433378350.
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Saenz, Saenz Gustavo Alberto. "High-Performance Detectors Based on the Novel Electronic and Optoelectronic Properties of Crystalline 2D van der Waals Solids." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703294/.
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In this work, we study the properties and device applications of MoS2, black phosphorus, MoOx, and NbSe2. We first start with the design, fabrication, and characterization of ultra-high responsivity photodetectors based on mesoscopic multilayer MoS2. The device architecture is comprised of a metal-semiconductor-metal (MSM) photodetector, where Mo was used as the contact metal to suspended MoS2 membranes. The dominant photocurrent mechanism was determined to be the photoconductive effect, while a contribution from the photogating effect was also noted from trap-states that yielded a wide spectral photoresponse from UV-to-IR with an external quantum efficiency (EQE) ~ 104. From time-resolved photocurrent measurements, a fast decay time and response time were obtained with a stream of incoming ON/OFF white light pulses. Another interesting semiconductor 2D material that has attracted special attention due to its small bandgap and ultra-high hole mobility is the black phosphorus. An analysis of the optoelectronic properties and photocurrent generation mechanisms in two-dimensional (2D) multilayer crystallites of black phosphorus (BP) was conducted from 350 K down to cryogenic temperatures using a broad-band white light source. The Mo-BP interface yielded a low Schottky barrier "φ" _"SB" ~ -28.3 meV and a high photoresponsivity R of ~ 2.43 x 105 A/W at a source-drain bias voltage of ~ 0.5 V (300 K, and incident optical power ~ 3.16 μW/cm2). Our report is the first to highlight the empirical use of Mo as a contact metal with BP. From the analysis conducted on the BP devices, the thermally driven photocurrent generation mechanism arising from the photobolometric effect (PBE) dominated the carrier dynamics for T > 181 K since the photocurrent Iph and the bolometric coefficient β undergo a transition in polarity from positive to negative. Our results show the promise of BP to potentially advance thermoelectric and optoelectronic devices stemming from this mono-elemental, direct bandgap 2D van der Waals solid. Another intriguing metallic 2D material is superconducting 2H-NbSe2. Here we present the temperature-dependent Raman spectroscopy and electronic transport on bulk NbSe2, carried out to investigate the scattering mechanisms. We report on the photoresponse of direct probed mesoscopic 2H-NbSe2 as a function of laser energy for lasers at 405 nm, 660 nm, and 1060 nm wavelengths used to irradiate the device, where the modulation from the superconducting-to-normal-state is detected through photomodulation. Additionally, the various oxidation levels of molybdenum oxide have interesting optical and electrical properties as a function of the oxygen vacancy and stoichiometry. The substoichiometric MoOx (2 < x < 3) behaves as a high work function conductor due to its metallic defect band. As a result, one of the potential applications of MoOx is for electrical contacts providing high hole injection or extraction. In this work, we have synthesized MoOx nanosheets via chemical vapor deposition and a four-terminal device was fabricated via e-beam lithography and electronic transport was measured as a function of temperature. Outstanding properties were obtained from our MoOx nanosheets, including a high conductivity of ~ 6,680.3 S cm-1, a superior temperature coefficient of resistance ~ -0.10%, and a high sensitivity based on the bolometric coefficient β of ~ 0.152 mS K-1. In summary, this work pushes the state-of-the-art in enabling 2D van der Waals materials for next-generation high-performance detectors.
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Cohen, Liam Augustus. "Fabricating Van der Waals heterostructures with air sensitive materials : a study of flake Bi₂Sr₂CaCu₂08₊x." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/118024.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, June 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages [96]-[97]).
by Liam Augustus Cohen.
S.B.
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Ma, Yingfang. "Long-range Interactions and Second Virial Coefficients of Biomolecular Materials." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1416915622.
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Bradford, Jonathan. "Growth and characterisation of two-dimensional materials and their heterostructures on sic." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134400/1/Jonathan_Bradford_Thesis.pdf.
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Atomically thin two-dimensional materials and their hybrids represent an elegant approach to designing and synthesizing functional nanomaterials and are expected to find applications across a broad range of new technologies. This project explored scalable synthesis of various two-dimensional layered materials and their hybrid counterparts on silicon carbide, an industrially relevant device substrate. It demonstrates the integration of graphene, hexagonal boron nitride and transition metal dichalcogenide layers which were characterised by high resolution scanning probe microscopy and electron spectroscopy. The procedures developed in this work are expected to facilitate a route towards large-scale synthesis of novel nanoscale devices directly on-chip.
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Harnish, Peter Karl. "Electron Correlation Effects in Strained Dual-Layer Graphene Systems." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/300.
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In low dimensional systems, electron correlation effects can often be enhanced. This can be vital since these effects not only play an important role in the study of many-electron physics, but are also useful in designing new materials for various applications. Since its isolation from graphite in 2004, graphene, a two dimensional sheet of carbon atoms, has drawn considerable interest due to its remarkable properties. In the past few years, research has moved on from single to bi-, dual- and multi-layer graphene systems, each displaying their own multitudes of intriguing properties. In particular, multi-layer systems that are electronically decoupled, but still coupled via the long-range Coulomb interaction, are very fascinating as they provide an opportunities to study phenomena like excitonic condensates, non-zero band gaps and van der Waals (vdW) interactions.
In this thesis, I shall discuss our recent work on two different physical aspects of dual- layer graphene systems under uniaxial strain. Firstly, I shall present results on the vdW correlation energy evaluated, within the Random Phase Approximation, at zero temperature between two undoped graphene layers separated by a finite distance. The correlation energy is obtained for three anisotropic models with variations in the strength of the effective coupling constant. We find that the vdW interaction energy increases with increasing anisotropy and the many-body contributions to the correlation energy are non-negligible. In the second part, I shall talk about the formation of inter-layer electron-hole (excitonic) pairings, caused by the inter-layer Coulomb interaction between two uniaxially strained graphene sheets which are appropriately doped with electrons/holes and our studies of the dependence of strain on the effective interaction. We find that strain, in combination with precise control of the initial momentum can effectively overcome the suppression due to inter-layer screening effects.
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Lorchat, Étienne. "Optical spectroscopy of heterostructures based on atomically-thin semiconductors." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE035.
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Au cours de cette thèse, nous avons fabriqué et étudié par spectroscopie optique, des hétérostructures de van der Waals, composées de monofeuillets semi-conducteurs (dichalcogénures de métaux de transition, DMT) couplés à une monocouche de graphène ou à un résonateur plasmonique. Nous avons observé des modifications importantes de la dynamique des états excités optiquement dans le DMT (excitons) lorsque celui-ci est en contact avec le graphène. Le graphène neutralise la couche de DMT et permet un transfert non-radiatif d’excitons en moins de quelques picosecondes. Ce transfert d’énergie peut s’accompagner d’un photodopage extrinsèque considérablement moins efficace. La réduction de la durée de vie des excitons du DMT en présence de graphène a été exploitée pour montrer que leur pseudo-spin de vallée maintenait un degré de polarisation et de cohérence important jusqu’à température ambiante. Enfin, en couplant fortement les excitons d’un DMT aux modes d’un résonateur plasmonique à phase géométrique, nous avons mis en évidence, à température ambiante, le verrouillage du pseudo-spin de vallée sur la direction de propagation des polaritons chiraux (chiralitons) issus du couplageDuring this thesis, we have fabricated and studied by optical spectroscopy, van der Waals heterostructures composed of semiconductor monolayers (transition metal dichalcogenides, TMD) coupled to a graphene monolayer or to a plasmonic resonator. We have observed significant changes in the dynamics of the TMD optically excited states (excitons) when it is in direct contact with graphene. Graphene neutralizes the TMD monolayer and enables non-radiative transfer of excitons within less than a few picoseconds. This energy transfer process may be accompanied by a considerably less efficient, extrinsic photodoping. The reduced lifetime of TMD excitons in the presence of graphene has been exploited to show that their valley pseudo-spin maintains a high degree of polarization and coherence up to room temperature. Finally, by strongly coupling TMD excitons to the modes of a geometric phase plasmonic resonator, we have demonstrated, at room temperature, that the momentum of the resulting chiral polaritons (chiralitons) is locked to their valley pseudo-spin
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Mouafo, Notemgnou Louis Donald. "Two dimensional materials, nanoparticles and their heterostructures for nanoelectronics and spintronics." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE002/document.
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Cette thèse porte sur l’étude du transport de charge et de spin dans les nanostructures 0D, 2D et les hétérostructures 2D-0D de Van der Waals (h-VdW). Les nanocristaux pérovskite de La0.67Sr0.33MnO3 ont révélé des magnétorésistances (MR) exceptionnelles à basse température résultant de l’aimantation de leur coquille indépendamment du coeur ferromagnétique. Les transistors à effet de champ à base de MoSe2 ont permis d’élucider les mécanismes d’injection de charge à l’interface metal/semiconducteur 2D. Une méthode de fabrication des h-VdW adaptés à l’électronique à un électron est rapportée et basée sur la croissance d’amas d’Al auto-organisés à la surface du graphene et du MoS2. La transparence des matériaux 2D au champ électrique permet de moduler efficacement l’état électrique des amas par la tension de grille arrière donnant lieu aux fonctionnalités de logique à un électron. Les dispositifs à base de graphene présentent des MR attribuées aux effets magnéto-Coulomb anisotropiquesThis thesis investigates the charge and spin transport processes in 0D, 2D nanostructures and 2D-0D Van der Waals heterostructures (VdWh). The La0.67Sr0.33MnO3 perovskite nanocrystals reveal exceptional magnetoresistances (MR) at low temperature driven by their paramagnetic shell magnetization independently of their ferromagnetic core. A detailed study of MoSe2 field effect transistors enables to elucidate a complete map of the charge injection mechanisms at the metal/MoSe2 interface. An alternative approach is reported for fabricating 2D-0D VdWh suitable for single electron electronics involving the growth of self-assembled Al nanoclusters over the graphene and MoS2 surfaces. The transparency the 2D materials to the vertical electric field enables efficient modulation of the electric state of the supported Al clusters resulting to single electron logic functionalities. The devices consisting of graphene exhibit MR attributed to the magneto-Coulomb effect
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Bezzi, Luca. "Materiali 2D van der Waals." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Dalla scoperta del grafene, molte ricerche sono state condotte sui cosiddetti “materiali 2D”. Questo elaborato si focalizza sulle proprietà strutturali, elettroniche, ottiche ed eccitoniche di due materiali bidimensionali, ossia il grafene il disolfuro di molibdeno (MoS2-1H), quest’ultimo un importante semiconduttore. Le proprietà di questi materiali sono diverse rispetto alla loro controparte massiva (bulk) grafite e MoS2-2H, e un loro confronto è stato preso in considerazione. Come metodo di indagine sono state scelte simulazioni quanto- meccaniche ab initio dei sistemi in esame, un approccio che, negli ultimi decenni, sta avendo un impatto sempre più importante sulla fisica, sulla chimica dello stato solido e sulla scienza dei materiali, promuovendo non solo una comprensione più profonda, ma anche la possibilità di contribuire in modo significativo alla progettazione di materiali per nuove tecnologie. Questo importante passo avanti è stato possibile grazie a: (i) una descrizione migliorata ed efficiente degli effetti elettronici a molti corpi (many-body) nella teoria del funzionale della densità (DFT), nonché lo sviluppo di metodi post-DFT per lo studio di proprietà specifiche; (ii) un’accurata implementazione di questi metodi in software altamente efficienti, stabili e versatili, capaci di sfruttare il potenziale delle architetture informatiche moderne. Tra i possibili software ab initio basati su DFT, abbiamo scelto il pacchetto di simulazione di Vienna ab initio VASP, considerato un gold standard per questo tipo di indagini. I risultati ottenuti per le varie proprietà di bulk e di superficie (bidimensionale) dei materiali scelti sono in ottimo accordo con dati ottenuti in precedenza, sia a livello teorico, sia sperimentale. Questo elaborato getta quindi le basi per futuri studi nel campo dei materiali 2D per comprendere, analizzare, ingegnerizzare nuovi materiali con proprietà desiderabili e per sviluppare nuove applicazioni degli stessi.
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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.
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L'isolement du graphène, une monocouche de graphite composée d'un plan d’atomes de carbone, a démontré qu'il est possible de séparer un seul plan d'épaisseur atomique, que l'on appelle matériau bidimensionnel (2D), à partir des solides de Van de Waals (vdW). Grâce à leur stabilité, différents matériaux 2D peuvent être empilés pour former les hétérostructures de vdW. L'interaction vdW à l'interface étant suffisamment faible, les propriétés spécifiques de chaque matériau demeurent globalement inchangées dans l’empilement. En utilisant une démarche théorique et computationnelle basée sur la théorie de la fonctionnelle de la densité (DFT) et le formalisme de Keldysh-Green, nous avons étudié l'hétérostructure graphène/MoS₂ . Le principal intérêt des propriétés spécifiques du graphène et du MoS₂ pour la conception d'un transistor à effet de champ réside dans la mobilité du graphène, à la base d'un transistor haute performance et dans le gap électronique du MoS₂, à la base de la commutation du dispositif. Tout d'abord, nous avons étudié les effets de la rotation entre les deux couches sur les propriétés électroniques à l'interface, en démontrant que les propriétés électroniques globales ne sont pas affectées par l'orientation. En revanche, les images STM (microscope à effet tunnel) sont différentes pour chaque orientation, en raison d'un changement de densité de charge locale. Dans un deuxième temps, nous avons utilisé l’interface graphène/MoS₂ en tant que modèle très simple de Transistor à Effet de Champ. Nous avons analysé le rôle des hétérostructures de vdW sur la performance du transistor, en ajoutant des couches alternées de graphène et MoS₂ sur l'interface graphène/MoS₂. Il a ainsi été démontré que la forme de la DOS au bord du gap est le paramètre le plus important pour la vitesse de commutation du transistor, alors que si l’on ajoute des couches, il n’y aura pas d’amélioration du comportement du transistor, en raison de l'indépendance des interfaces dans les hétérostructures de vdW. Cependant, cela démontre que, dans le cadre de la DFT, on peut étudier les propriétés de transport des hétérostructures de vdW plus complexes en séparant chaque interface et en réduisant le temps de calcul. Les matériaux 2D sont également étudiés ici en tant que pointe pour STM et AFM (microscope à force atomique) : une pointe de graphène testée sur MoS₂ avec défauts a été comparée aux résultats correspondants pour une pointe en cuivre. La résolution atomique a été obtenue et grâce à l'interaction de vdW entre la pointe et l’échantillon, il est possible d’éviter les effets de contact responsables du transfert d'atomes entre la pointe et l'échantillon. En outre, l'analyse des défauts est très utile du fait de la présence de nouveaux pics dans le gap du MoS₂ : ils peuvent ainsi être utilisés pour récupérer un pic de courant et donner des perspectives pour améliorer la performance des transistorsThe 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
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Tenasini, Giulia. "Quantum transport in monolayer WTe2." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14897/.
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Il ditellurio di tungsteno (WTe2) appartiene alla classe dei dicalcogenuri di metalli di transizione (TMDs), che rappresentano attualmente i materiali più promettenti, insieme al grafene, nel campo di ricerca dei cristalli bidimensionali (2D). Grazie ad una caratteristica struttura stratificata, con differenti piani atomici legati da forze di van der Waals, mediante esfoliazione è possibile isolare strati di spessore quasi-atomico di TMDs, detti “monostrati”, con proprietà spesso molto diverse dal materiale bulk originario. Il WTe2 nella sua forma a monostrato, è stato recentemente oggetto di interesse scientifico, in quanto teoricamente predetto essere un isolante topologico (TI) bidimensionale. Un TI è un materiale che internamente si comporta come un isolante elettrico ma che sulla superficie manifesta stati conduttivi. Lo scopo di questa tesi è studiare le proprietà si trasporto di monostrati di WTe2 in micro-dispositivi realizzati con opportune tecniche di nanofabbricazione. L'ossidazione della superficie esterna del WTe2, dovuta ad una non-perfetta stabilità in aria, influenza significativamente il trasporto elettronico in cristalli costituiti da pochi strati atomici ed è causa di una transizione metallo-isolante. Una possibile soluzione per evitare la degradazione del materiale consiste nell' “incapsulamento” di un monostrato di WTe2 fra materiali 2D chimicamente inerti, come il nitruro di boro esagonale. A tale proposito, si è sviluppata una tecnica di “trasferimento” che permette di sollevare e allineare con precisione micrometrica strati di spessore atomico di differenti materiali, assemblando eterostrutture di van der Waals. Campioni selezionati sono studiati mediante misure di magneto-transporto a bassa temperatura (fino a 0.250 K). I dati analizzati evidenziano l'esistenza di un gap di energia in monostrati di WTe2 e la presenza di una corrente localizzata ai bordi del sistema, coerentemente con l'ipotesi di un isolante topologico 2D.
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Ryan, Shawn David. "Bifurcation and Boundary Layer Analysis for Graphene Sheets." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1239646272.
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Ferri, Nicola [Verfasser], Alexandre [Akademischer Betreuer] Tkatchenko, Andreas [Gutachter] Knorr, and Alexandre [Gutachter] Tkatchenko. "The role of van der Waals interactions on the electronic properties of molecules and materials / Nicola Ferri ; Gutachter: Andreas Knorr, Alexandre Tkatchenko ; Betreuer: Alexandre Tkatchenko." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156013631/34.
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Huang, Shengqiang, and Shengqiang Huang. "Electronic and Optical Properties of Twisted Bilayer Graphene." Diss., The University of Arizona, 2018. http://hdl.handle.net/10150/626686.
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The ability to isolate single atomic layers of van der Waals materials has led to renewed interest in the electronic and optical properties of these materials as they can be fundamentally different at the monolayer limit. Moreover, these 2D crystals can be assembled together layer by layer, with controllable sequence and orientation, to form artificial materials that exhibit new features that are not found in monolayers nor bulk. Twisted bilayer graphene is one such prototype system formed by two monolayer graphene layers placed on top of each other with a twist angle between their lattices, whose electronic band structure depends on the twist angle. This thesis presents the efforts to explore the electronic and optical properties of twisted bilayer graphene by Raman spectroscopy and scanning tunneling microscopy measurements.
We first synthesize twisted bilayer graphene with various twist angles via chemical vapor deposition. Using a combination of scanning tunneling microscopy and Raman spectroscopy, the twist angles are determined. The strength of the Raman G peak is sensitive to the electronic band structure of twisted bilayer graphene and therefore we use this peak to monitor changes upon doping. Our results demonstrate the ability to modify the electronic and optical properties of twisted bilayer graphene with doping.
We also fabricate twisted bilayer graphene by controllable stacking of two graphene monolayers with a dry transfer technique. For twist angles smaller than one degree, many body interactions play an important role. It requires eight electrons per moire unit cell to fill up each band instead of four electrons in the case of a larger twist angle. For twist angles smaller than 0.4 degree, a network of domain walls separating AB and BA stacking regions forms, which are predicted to host topologically protected helical states. Using scanning tunneling microscopy and spectroscopy, these states are confirmed to appear on the domain walls when inversion symmetry is broken with an external electric field. We observe a double-line profile of these states on the domain walls, only occurring when the AB and BA regions are gaped. These states give rise to channels that could transport charge in a dissipationless manner making twisted bilayer graphene a promising platform to realize controllable topological networks for future applications.
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De, Waal Alda. "Die regte van die leerling as regsubjek / Elda de Waal." Thesis, Potchefstroom University for Christian Higher Education, 1994. http://hdl.handle.net/10394/10319.
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Mindful of the imminent introduction of a South African Bill of
Rights, this study has been undertaken to define the rights and
duties of the South African pupil by means of a literature
study and an elementary study of comparative law with a view to
promoting pedagogical education.
Various legal terms which influence the classification of the
rights of the pupil significantly are defined.
In conjunction with the three sources of educational law (viz
common law, legislation and case law), the status of the minor
personality, the administrative educational procedure and the
legal status of the pupil as determinants for pedagogical
education are identified and dealt with in so far as they have
any bearing on the rights of the pupil. In addition to the
exposition of the existing legal status of the pupil, a survey
is made of the pupil, as determinant for pedagogical education
in order to draw conclusions by means of similarities, differences
and shortcomings.
Important concepts concerning the teacher's rights and duties
toward the pupil that come to light in this script are bona
fides, quasi-judicial competence, rules of natural justice,
ultra vires and in loco parentis. Important concepts that
come to light concerning the rights and duties of the pupil
toward others are legal capacity, personality rights, correct
information, authority and discipline, procedural rights
and duties
The concept "the rights of the child" is shown to imply certain
duties that should be performed by the pupil. Pedagogical
education is shown to be impracticable unless not only the
teacher and the parents, but also the pupil performs his
duties.
Attention is paid to the necessity of informing teachers,
parents and especially pupils concerning their respective
rights and duties, so that pedagogical education can reach its
optimum development in South Africa.Skripsie (MEd)--PU vir CHO, 1994
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De, Waal Johannes Joachim Prinsloo. "Dekonstruksie van beperkende narratiewe in die lewe van individue / Johannes Joachim Prinsloo De Waal." Thesis, North-West University, 2004. http://hdl.handle.net/10394/2406.
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Dryden, Daniel M. "Long-Range Interactions in Biomolecular-Inorganic Assemblies." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1405078771.
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Tesař, Jan. "Příprava a charakterizace atomárně tenkých vrstev." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417143.
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Tato práce se zabývá oblastí dvourozměrných materiálů, jejich přípravou a analýzou. Pravděpodobně nejznámějším zástupcem dvourozměrných materiálů je grafen. Tento 2D allotrop uhlíku, někdy nazývaný „otec 2D materiálů“, v sobě spojuje neobyčejnou kombinaci elektrických, tepelných a mechanických vlastností. Grafen získal mnoho pozornosti a byl také připraven mnoha metodami. Jedna z těchto metod však stále vyniká nad ostatními kvalitou produkovaného grafenu. Mechanická exfoliace je ve srovnání s jinými technikami velmi jednoduchá, takto připravený grafen je však nejkvalitnější. Práce je také zaměřena na optimalizaci procesu tvorby heterostruktur složených z vrstev grafenu a hBN. Dle prezentovaného postupu bylo připraveno několik van der Waalsových heterostruktur, které byly analyzovány Ramanovskou spektroskopií, mikroskopií atomových sil a nízkoenergiovou elektronovou mikroskopií. Měření pohyblivosti nosičů náboje bylo provedeno v GFET uspořádání. Získané hodnoty pohyblivosti prokázaly vynikající transportní vlastnosti exfoliovaného grafenu v porovnání s grafenem připraveným jinými metodami. V práci popsaný proces přípravy je tedy vhodný pro výrobu kvalitních heterostruktur.
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Avalos, Ovando Oscar Rodrigo. "Magnetic Interactions in Transition Metal Dichalcogenides." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166.
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Sant, Roberto. "Exploration par rayonnement synchrotron X de la croissance et de la structure de dichalcogénures 2D." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY075.
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Les dichalcogenures de métaux de transition bidimensionnels (2D) suscitent un grand intérêt pour des applications variées, principalement en optoelectronique. Toutefois, la faible compréhension des mécanismes liés à leur épitaxie, de leur microstructure et de la nature de leur interaction avec le substrat représentent encore des problèmes ouverts. Nous avons exploré un certain nombre de croissances épitaxiales des dichalcogenures 2D préparés par épitaxie à jets moléculaires sur des substrats différents. Nous en avons examiné la structure atomique et essayé d’en modifier certains in situ. Plusieurs systèmes et processus ont été étudiés: (i) des tellurures de métaux de transition, ZrTe2, MoTe2 et TiTe2, épitaxiés sur un substrat de InAs(111), (ii) l’intercalation d’espèces atomique alcalines entre une monocouche de MoS2 et son substrat d’Au(111), (iii) la croissance et le traitement thermique sous atmosphère de H2S d’une monocouche de PtSe2 sur Pt(111). Notre travail s’appuie sur des approches à la fois phénoménologiques et quantitatives de diffraction de rayons X de surface, souvent complétées par ses analyses effectuées à l’aide d’autres techniques (STM, TEM, XPS et ARPES). Les principaux résultats sont que: (i) une phase orthorhombique et une onde de densité de charge sont stabilisées à température ambiante dans les couches de MoTe2 et TiTe2 par un effet de déformation induite par l’épitaxie; (ii) l’intercalation de césium (Cs) au-dessous du MoS2 induit un découplage structurel mais aussi électronique de la monocouche de son substrat; (iii) la sulfurisation de PtSe2 à chaud en conditions contrôlées permet de substituer des atomes de Se par des atomes de S dans la couche supérieure du dichalcogenure, formant ainsi un alliage ordonné de SPtSe, structure de type JanusTwo-dimensional transition metal dichalcogenides (TMDCs) are promising materials for a variety of applications, especially in optoelectronics. However, the lack of understanding of their epitaxy - i.e. growth mechanism, microscopic structure, nature of the 2D layer-substrate interaction, etc. - is still a crucial issue to address. In this PhD thesis we explored a series of epitaxial growths of monolayer and thin film TMDCs grown by molecular beam epitaxy (MBE) on a variety of substrates. We studied their atomic structures and we attempted the modifications of some of them with various in situ methods. Several systems and processes have been investigated: (i) transition metal ditellurides, ZrTe2 , MoTe2 and TiTe2 on InAs(111) substrate, (ii) the intercalation of alkali metal species between single layer MoS2 and its Au(111) substrate, (iii) the growth and the thermal treatments in H2S atmosphere of monolayer PtSe2 on Pt(111). Our work relies on both phenomenological and quantitative methods based on surface X-ray diffraction, often complemented by parallel analysis performed with other probes, e.g. STM, TEM, XPS, ARPES. Most notably, we found that: (i) a metastable orthorhombic phase and a charge density wave phase can be stabilized at room temperature in MoTe2 and TiTe2 owing to the epitaxial strain in the materials; (ii) the intercalation of Cs atoms under MoS2 induces structural and electronic decoupling of the 2D MoS2 layer from its Au(111) substrate; (iii) the sulfurization of PtSe2 promotes the Se-by-S substitution in one (or both) of its two chalcogen layers, leading either to the full conversion of the selenide into a sulfide or even to an ordered Janus alloy
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De, Waal Esther Aletta Susanna. "Tuisonderwys as alternatiewe vorm van onderwysvoorsiening in Suid-Afrika / Esther Aletta Susanna de Waal." Thesis, Potchefstroom University for Christian Higher Education, 2000. http://hdl.handle.net/10394/1237.
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This study investigated home schooling as alternative form of educational provision in South Africa by focussing on the following aspects: • the nature of home schooling as alternative form of educational provision; • home schooling as alternative form of educational provision in the USA;
and • the position of home schooling as alternative form of educational provision in South Africa.
The nature of home schooling as alternative form of educational provision has been researched by means of a literature study. Home schooling within a system of educational provision has been investigated and it has been found that home schooling cannot be categorised within existing terms because it includes aspects of both formal and non-formal education and excludes aspects of both. Home schooling has moved from an initially traditional form of education to an alternative form of education, enjoying growing support at an international level.
As an alternative form of educational provision in the USA home schooling has a sound legal foundation and has become an acceptable educational alternative. Home schoolers in the USA are very diverse with regard to various aspects, including reasons for home schooling. In regard of the structure of home schooling there are two extremes, namely the orthodox structuralists and the proponents of unstructured learning, with the largest group of home schoolers somewhere between these extremes. Available research indicates clearly that academically home schoolers perform very well and home schooling does not in any way disadvantage them with regard tosocial-emotional development or socialisation. Policy makers in the USA seem to be increasingly of the opinion that there should be some form of cooperation between public schools and home schoolers.
The literature study on the origin and development of home schooling as alternative form of educational provision in South Africa revealed that, although the Constitution does not contain a stipulation granting parents an explicit right to home schooling, it does not make homeschooling
unconstitutional. New regulations regarding home schooling have been announced by the government in November 1999 and are already operative. The empirical research revealed that home schooling in South Africa has grown phenomenally over the past two years. In South Africa home schoolers are also diverse regarding various aspects, but generally spend much time on formal lessons and mostly use previously prepared curricula. It seems as if educational reasons are the most important and religious beliefs the second most important reason for home schooling in South Africa. Some of the most important recommendations of this study are firstly that a partnership should be established between government and home schoolers. The government should take notice of research on home schooling and the opportunities that home schooling presents. Home schooling as alternative form of educational provision can be supplementary to the existing system of educational provision. Finally, education policy makers should also reconsider legislation regarding compulsory education rather than compulsory schooling.Thesis (Ph.D.)--Potchefstroom University for Christian Higher Education, 2000
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Matope, Stephen. "Application of Van-der-Waals forces in micro-material handling." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71608.
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Thesis (PhD)--Stellenbosch University, 2012.This doctoral dissertation focuses on the application of Van-der-Waals’ forces in micromaterial handling. A micro-material handling system consists of four main elements, which include: the micro-gripper, the micro-workpart, the picking up position and the placement position. The scientific theoretical frameworks of Van-der-Waals’ forces, presented by Van der Waals, Hamaker, London, Lifshitz, Israelachvilli, Parsegian, Rumpf and Rabinovich, are employed in exploring the extent to which these forces could be applied in a micromanufacturing situation. Engineering theoretical frameworks presented by Fearing, Bohringer, Sitti, Feddema, Arai and Fukuda, are employed in order to provide an in-depth synthesis of the application of Van-der-Waals’ forces in micro-material handling. An empirical or pragmatic methodology was adopted in the research. The Electron Beam Evaporation (e-beam) method was used in generating interactive surfaces of uniform surface roughness values. E-beam depositions of copper, aluminum and silver on silicon substrates were developed. The deposition rates were in the range of 0.6 – 1.2 Angstrom/s, at an average vacuum pressure of 2 x 10-6 mbar. The topographies were analysed and characterised using an Atomic Force Microscope and the corresponding rms surface roughness values were obtained. The Rumpf-Rabinovich equation, which gives the relationship of the exerted Van-der-Waals’ forces and the rms surface roughness values, is used to numerically model the results. In the final synthesis it is observed that the e-beam depositions of copper are generally suited for the pick-up position. Aluminum is suited for the micro-gripper and silver is suited for the placement position in an optimised micro-material handling system. Another Atomic Force Microscope was used in order to validate the numerically modelled results of the exerted Van- der-Waals’ forces. The aim was to measure the magnitude of Vander- Waals’ forces exerted by the e-beam depositions and to evaluate their applicability in micro-material handling operations. The measurements proved that Van-der-Waals’ forces exerted by the samples could be used for micro-material handling purposes on condition that they exceeded the weight of the micro-part being handled. Three fundamental parameters, ie: material type, geometrical configuration and surface topography were used to develop strategies of manipulation of micro-materials by Van-der- Waals’ forces. The first strategy was based on the material type variation of the interactive surfaces in a micro-material handling operation. This strategy hinged on the fact that materials have different Hamaker coefficients, which resulted in them experiencing a specific Van-der- Waals’ forces’ intensity during handling. The second strategy utilised variation in the geometrical configuration of the interacting surfaces. The guiding principle in this case was that, the larger the contact area was, the greater the exerted Van-der-Waals’ forces would be In the analytical modelling of Van-der-Waals’ forces with reference to geometrical configuration, a flat surface was found to exert more force than other configurations. The application of the design, for purposes of manufacturing and assembling (DFMA) criteria, also proved that flat interactive surfaces have high design efficiency. The third strategy was based on surface roughness. The rougher the topography of a given surface was, the lesser the Van-der-Waals’ forces exerted were. It was synthesised that in order for a pick-transfer-place cycle to be realised, the root-mean-square (rms) interactive surface roughness values of the micro-part (including the picking position, the micro-gripper, and the placement position) should decrease successively. Hybrid strategies were also identified in this research in order to deal with some complex cases. The hybrids combined at least two of the aforementioned strategies.
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Matope, S., and Der Merwe A. Van. "The application of Van der Waals forces in micro-material handling." Journal for New Generation Sciences, Vol 8, Issue 1: Central University of Technology, Free State, Bloemfontein, 2010. http://hdl.handle.net/11462/554.
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Published ArticleThis paper investigates the challenges of employing Van der Waals forces in micro-material handling since these forces are dominant in micro-material handling systems. The problems include the creation of a dust-free environment, accurate measurement of the micro-force, and the efficient picking and placing of micro-work pieces. The use of vacuum suction, micro-gripper's surface roughness, geometrical configuration and material type are presented as alternatives to overcome the challenges. An atomic force microscope is proposed for the accurate measurement of the Van der Waals force between the gripper and the micro-work piece.
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Simpson, William M. R. "Surprises in theoretical Casimir physics : quantum forces in inhomogeneous media." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/6338.
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This thesis considers the problem of determining Casimir-Lifshitz forces in inhomogeneous media. The ground-state energy of the electromagnetic field in a piston-geometry is discussed. When the cavity is empty, the Casimir pressure on the piston is finite and independent of the small-scale physics of the media that compose the mirrors. However, it is demonstrated that, when the cavity is filled with an inhomogeneous dielectric medium, the Casimir energy is cut-off dependent. The local behavior of the stress tensor commonly used in calculations of Casimir forces is also determined. It is shown that the usual expression for the stress tensor is not finite anywhere within such a medium, whatever the temporal dispersion or index profile, and that this divergence is unlikely to be removed by modifying the regularisation. These findings suggest that the value of the Casimir pressure may be inextricably dependent on the detailed behavior of the mirror and the medium at large wave vectors. This thesis also examines two exceptions to this rule: first, the case of an idealised metamaterial is considered which, when introduced into a cavity, reduces the magnitude of the Casimir force. It is shown that, although the medium is inhomogeneous, it does not contribute additional scattering events but simply modifies the effective length of the cavity, so the predicted force is finite and can be stated exactly. Secondly, a geometric argument is presented for determining a Casimir stress in a spherical mirror filled with the inhomogeneous medium of Maxwell's fish-eye. This solution questions the idea that the Casimir force of a spherical mirror is repulsive, but prompts additional questions concerning regularisation and the role of non-local effects in determining Casimir forces.
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Crowley, Kyle McKinley. "Electrical Characterization, Transport, and Doping Effects in Two-Dimensional Transition Metal Oxides." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1597327584506971.
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Van, der Merwe A., and S. Matope. "Manipulation of Van der Waals' forces by geometrical parameters in micro-material handling." Journal for New Generation Sciences, Vol 8, Issue 3: Central University of Technology, Free State, Bloemfontein, 2010. http://hdl.handle.net/11462/574.
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Published ArticleThis paper explores the manipulation of Van der Waals' forces by geometrical parameters in a micro-material handling system. It was observed that the flat-flat interactive surfaces exerted the highest intensity of Van der Waals' forces followed by cone-flat, cylinder-flat, sphere-flat and sphere-sphere interactive surfaces, respectively. A conical micro-gripper proved to be versatile in manipulating the Van der Waals' forces efficiently in a 'picking up' and 'releasing' mechanism of micro-work parts. It was deduced that the pick-up position should be rough and spherical, and the placement position should be smooth and flat for an effective 'pick-and-place' cycle to be realised.
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Weststrate, Job. "In het kielzog van moderne markten : handel en scheepvaart op de Rijn, Waal en IJssel, ca. 1360-1560 /." Hilversum : Verloren, 2008. http://catalogue.bnf.fr/ark:/12148/cb41271581v.
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Dou, Ziwei. "Investigation on high-mobility graphene hexagon boron nitride heterostructure nano-devices using low temperature scanning probe microscopy." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283618.
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This thesis presents several experiments, generally aiming at visualising the ballistic and topological transport on the high-mobility graphene/boron nitride heterostructure using the scanning gate microscope. For the first experiment, we use the scanning gate microscopy to map out the trajectories of ballistic carriers in high-mobility graphene encapsulated by hexagonal boron nitride and in a weak perpendicular magnetic field. We employ a magnetic focusing transport configuration to image carriers that emerge ballistically from an injector, follow a cyclotron path due to the Lorentz force from an applied magnetic field, and land on an adjacent collector probe. The local potential generated by the scanning tip in the vicinity of the carriers deflects their trajectories, modifying the proportion of carriers focused into the collector. By measuring the voltage at the collector while scanning the tip, we are able to obtain images with arcs that are consistent with the expected cyclotron motion. We also demonstrate that the tip can be used to redirect misaligned carriers back to the collector. For the second experiment, we investigate the graphene van der Waals structures formed by aligning monolayer graphene with insulating layers of hexagonal boron nitride which exhibit a moiré superlattice that is expected to break sublattice symmetry. However, despite an energy gap of several tens of millielectronvolts opening in the Dirac spectrum, electrical resistivity remains lower than expected at low temperature and varies between devices. While subgap states are likely to play a role in this behaviour, their precise nature is still unclear in the community. We therefore perform a scanning gate microscopy study of graphene moiré superlattice devices with comparable activation energy but with different charge disorder levels. In the device with higher charge impurity ($\sim$ 10$^-$ cm$^{-2}$) and lower resistivity ($\sim$ 10 k$\Omega$) at the Dirac point we observe scanning gate response along the graphene edges. Combined with simulations, our measurements suggest that enhanced edge doping is responsible for this effect. In addition, a device with low charge impurity ($\sim$ 10$^{9}$ cm$^{-2}$) and higher resistivity ($\sim$ 100 k$\Omega$) shows subgap states in the bulk. Our measurements provide alternative model to the prevailing theory in the literature in which the topological bandstructures of the graphene moiré superlattices entail an edge currents shunting the insulating bulk. In the third experiment, we continue our study in the graphene moir$\acute e$ superlattices with the newly reported non-local Hall signals at the main Dirac point. It has been associated with the non-zero valley Berry curvature due to the gap opening and the nonlocal signal has been interpreted as the signature of the topological valley Hall effects. However, the nature of such signal is still disputed in the community, due to the vanishing density of states near the Dirac point and the possible topological edge transport in the system. Various artificial contribution without a topological origin of the measurement scheme has also been suggested. In connection to the second experiment, we use the scanning gate microscope to image the non-local Hall resistance as well as the local resistance in the current path. By analysing the features in the two sets of images, we find evidence for topological Hall current in the bulk despite a large artificial components which cannot be distinguished in global transport measurement. In the last experiment, we show the development of a radio-frequency scanning impedance microscopy compatible with the existing scanning gate microscopy and the dilution refrigerator. We detailed the design and the implementation of the radio-frequency reflectometry and the specialised tip holder for the integration of the tip and the transmission lines. We demonstrate the capability of imaging local impedance of the sample by detecting the mechanical oscillation of the tip, the device topography, and the Landau levels in the quantum Hall regime at liquid helium temperature and milli-Kelvin temperature.
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Rhoads, Daniel Joseph. "A Mathematical Model of Graphene Nanostructures." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1438978423.
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Woods, Colin. "Investigations into the interfacial interaction of graphene with hexagonal boron nitride." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/investigations-into-the-interfacial-interaction-of-graphene-with-hexagonal-boron-nitride(de99f43b-790f-4a32-b696-060ed700a5bd).html.
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This thesis, submitted to the University of Manchester, covers a range of topics related to current research in two-dimensional materials under the title: 'Investigations into the interfacial interaction of graphene with hexagonal boron nitride.'In the last decade, two-dimensional materials have become a rich source of original research and potential applications. The main advantage lies in the ability to produce novel composite structures, so-called 'layered heterostructures', which are only a few atomic layers thick. One can utilise the unique properties of several species of crystal separately, or how they interact to realise a diverse range of uses. Two such crystals are graphene and hexagonal boron nitride. Hexagonal boron nitride has, so far, been used primarily as a substrate for graphene, allowing researchers to get the most out of graphene's impressive individual properties. However, in this thesis, the non-trivial van der Waals interaction between graphene and hexagonal boron nitride is examined. The interface potential reveals itself as a relatively large-scale, orientation-dependant superlattice, which is described in chapters 1 and 2.I In Chapter 4, the effect of this superlattice is examined by measurement of its effect upon the electrons in graphene, where its modulation leads to the creation of second and third generation Dirac points, revealing Hofstadter's Butterfly. As well as an excellent example of the physics possible with graphene, it also presents a new tool with which to create novel devices possessing tailored electronic properties. II In chapter 5, the consequential effect of the superlattice potential on the structure of graphene is studied. Results are discussed within the framework of the Frenkel-Kontorova model for a chain of atoms on a static background potential. Results are consistent with relaxation of the graphene structure leading to the formation of a commensurate ground state. This has exciting consequences for the production of heterostructures by demonstrating that alignment angle can have large effects upon the physical properties of the crystals. III In chapter 6, the van der Waals potential is shown to be responsible for the self-alignment of the two crystals. This effect is important for the fabrication of perfectly aligned devices and may lead to new applications based on nanoscale motion.
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Ma, Yingfang. "Electronic Structure, Optical Properties and Long-Range-Interaction Driven Mesoscale Assembly." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1497049273517057.
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Nicely, Clinton R. "Transverse Vibrations of Multi-Walled Nanotubes with Visco-Elastic Layers." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1227460546.
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Stark, Alyssa Yeager. "The Effect of Water on the Gecko Adhesive System." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1405334677.
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Stanek, Lucas James. "Deformation of a Graphene Sheet Driven by Lattice Mismatch with a Supporting Substrate." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493999094753307.
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