Dissertations / Theses on the topic 'Two-Dimensional Metals'
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1
Grigoriev, Pavel. "Magnetic quantum oscillations in quasi-two-dimensional metals." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965616142.
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Wang, Dapeng. "Electronic transport and potential applications of one-dimensional and two-dimensional granular nanotubes and metals." View abstract/electronic edition; access limited to Brown University users, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3318367.
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Qawasmeh, Yasmeen Jamal [Verfasser]. "Two-Dimensional Potential Energy Surfaces of Binding CO/NO with Coinage Metals / Yasmeen Qawasmeh." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1212435400/34.
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Qawasmeh, Yasmeen [Verfasser]. "Two-Dimensional Potential Energy Surfaces of Binding CO/NO with Coinage Metals / Yasmeen Qawasmeh." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1212435400/34.
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Holder, Tobias [Verfasser], and Walter [Akademischer Betreuer] Metzner. "Quantum fluctuations in two-dimensional metals with singular forward scattering / Tobias Holder. Betreuer: Walter Metzner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1082238155/34.
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Drukier, Casper [Verfasser], Peter [Akademischer Betreuer] Kopietz, and Walter [Akademischer Betreuer] Hofstetter. "Aspects of electron correlations in two-dimensional metals / Casper Drukier. Gutachter: Peter Kopietz ; Walter Hofstetter." Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2015. http://d-nb.info/1067918221/34.
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Solanki, Kiran N. "TWO AND THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF PLASTICITY-INDUCED FATIGUE CRACK CLOSURE ? A COMPREHENSIVE PARAMETRIC STUDY." MSSTATE, 2002. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11102002-143748/.
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Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. Two-dimensional, elastic-perfectly plastic finite element analyses of middle-crack tension (M(T)), bend (SEB), and compact tension (C(T)) geometries were conducted to study fatigue crack closure and to calculate the crack opening values under plane-strain and plane-stress conditions. The loading was selected to give the same maximum stress intensity factor in both geometries, and thus similar initial forward plastic zone sizes. Mesh refinement studies were performed on all geometries with various element types. For the C(T) geometry, negligible crack opening loads under plane-strain conditions were observed. In contrast, for the M(T) specimen, the plane-strain crack opening stresses were found to be significantly larger. This difference was shown to be a consequence of in-plane constraint. Under plane-stress conditions, it was found that the in-plane constraint has negligible effect, such that the opening values are approximately the same for the C(T), SEB, and M(T) specimens. Next, the crack opening values of the C(T), SEB and M(T) specimens were compared under various stress levels and load ratios. The effect of a highly refined mesh on crack opening values was noted and significantly lower crack opening values than those reported in literature were found. A new methodology is presented to calculate crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses. The calculated crack opening values are compared with values obtained using finite element analysis and more conventional crack opening assessment methodologies. It is shown that the new method is independent of loading increment, integration method (normal and reduced integration), and crack opening assessment location. The compared opening values were in good agreement with strip-yield models.
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Wang, Mingchao, Marco Ballabio, Mao Wang, Hung-Hsuan Lin, Bishnu P. Biswal, Xiaocang Han, Silvia Paasch, et al. "Unveiling Electronic Properties in Metal–Phthalocyanine-Based Pyrazine-Linked Conjugated Two-Dimensional Covalent Organic Frameworks." American Chemical Society, 2019. https://tud.qucosa.de/id/qucosa%3A72450.
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π-Conjugated two-dimensional covalent organic frameworks (2D COFs) are emerging as a novel class of electro-active materials for (opto-)electronic and chemiresistive sensing applications. However, understanding the intricate interplay between chemistry, structure and conductivity in π-conjugated 2D COFs remains elusive. Here, we report a detailed charac-terization for the electronic properties of two novel samples consisting of Zn- and Cu-phthalocyanine-based pyrazine-linked 2D COFs. These 2D COFs are synthesized by condensation of metal-phthalocyanine (M=Zn and Cu) and pyrene derivatives. The obtained polycrystalline-layered COFs are p-type semiconductors both with a band gap of ~1.2 eV. Mobilities up to ~5 cm²/Vs are resolved in the dc limit, which represent a lower threshold induced by charge carrier localization at crystalline grain boundaries. Hall Effect measurements (dc limit) and terahertz (THz) spectroscopy (ac limit) in combination with den-sity functional theory (DFT) calculations demonstrate that varying metal center from Cu to Zn in the phthalocyanine moiety has a negligible effect in the conductivity (~5×10⁻⁷ S/cm), charge carrier density (~10¹² cm⁻³), charge carrier scattering rate (~3×10¹³ s⁻¹), and effective mass (~2.3m₀) of majority carriers (holes). Notably, charge carrier transport is found to be aniso-tropic, with hole mobilities being practically null in-plane and finite out-of-plane for these 2D COFs.
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Yuhara, J., M. Schmid, and P. Varga. "Two-dimensional alloy of immiscible metals: Single and binary monolayer films of Pb and Sn on Rh(111)." The American Physical Society, 2003. http://hdl.handle.net/2237/7113.
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Murdock, Adrian T. "Chemical vapour deposition growth of large-area graphene on metals." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:07fa91ef-0d61-4086-a7d8-a53537dcb54b.
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Graphene has unrivalled properties and is heralded as a revolutionary material for the 21st century. Chemical vapour deposition (CVD) on metals is a promising method to produce large-area graphene. Controlling the properties of CVD graphene is vital for its integration in a wide-range of future applications. Many factors can influence the CVD growth of graphene and its properties, therefore further investigations will be beneficial to fully understand and control this technique. In this thesis I expand the knowledge about the growth of pure and heteroatom-doped graphene by low pressure chemical vapour deposition (LPCVD) and atmospheric pressure chemical vapour deposition (APCVD) on commercially available Cu and Pt foils. Using a range of characterisation techniques, I investigate the influence of the substrate’s properties and the synthesis conditions on the growth of graphene, in pursuit of improved, controlled or optimised production, which can promote high quality, large-area, single-layer graphene, or other as desired. By characterising the topography, surface roughness, crystallographic orientations, and chemical composition of six Cu foils, I find that their properties vary greatly and this influences the growth of CVD graphene. I elucidate that the commonly used 99.8 % Alfa Aesar Cu foil has a surface coating composed of calcium, chromium, and phosphorus, which detrimentally influences graphene growth. Cleaning Cu foils with CH3COOH is shown to reduce the concentration of surface contaminants, consequently reducing the nucleation density and increasing the growth rate of CVD graphene. I also demonstrate that the shape, orientation, edge-geometry and thickness of CVD graphene domains can be controlled by the Cu crystallographic orientations. Single layer LPCVD graphene domains align with zigzag edges parallel to a single <101> direction on Cu{111} and Cu{101}, while bilayer domains align to two directions on Cu{001}. Hexagonal APCVD domains also preferentially align with edges parallel to the <101> direction(s). This discovery resolves a key challenge of controlling the orientation of individual graphene domains and opens a new avenue for tailored production of large-area CVD graphene with improved properties. By controlling the synthesis conditions of APCVD graphene on Pt foils I optimise production of ~0.5 mm single layer graphene domains with reduced nucleation density and increased growth rate of ~100 μm/min by synthesis at 1150°C, a higher temperature than previously reported. The absence of large, hexagonal, single-crystal domains on pristine Pt foil, and observation of a reaction between quartz and Pt that promotes hexagonal domains, suggests that a silicon or platinum silicide surface layer may be advantageous for improved growth of graphene. Finally, I demonstrate that the dopant concentration of nitrogen-doped graphene is increased at lower synthesis temperatures and higher NH3 concentration, up to 1.3 %, but with an associated decrease in the growth rate. Direct visualisation, elemental confirmation, and electronic characterisation of individual nitrogen atoms is shown for the first time using aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy. Boron-doped graphene is also synthesised. The implications of these findings, and many additional minor contributions, are wide-ranging and of considerable importance for the future understanding of CVD growth of graphene on metals, and more generally for the advancement of scientific knowledge for manufacturing large-area graphene. Collectively, these discoveries represent a significant body of work that can improve the efficiency of production and assist with controlling the properties of large-area CVD graphene.
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Ismer, Jan-Peter [Verfasser], Ilya [Gutachter] Eremin, and Dirk [Gutachter] Manske. "Coexistence of superconductivity and density waves in quasi-two-dimensional metals / Jan-Peter Ismer ; Gutachter: Ilya Eremin, Dirk Manske ; Fakultät für Physik und Astronomie." Bochum : Ruhr-Universität Bochum, 2011. http://d-nb.info/1223171779/34.
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Dai, Ji. "Low-dimensional electron systems studied by angle- and spin-resolved photoemission spectroscopy." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS345.
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Les matériaux dans lesquels des interactions à plusieurs particules, un confinement de faible dimension et/ou un fort couplage spin-orbite sont présents témoignent d’une grande variété de phénomènes, mais sont encore mal compris. Des informations essentielles sur l’origine de tels phénomènes peuvent être obtenues en mesurant leur structure électronique. Cette thèse présente une étude expérimentale de la structure électronique de matériaux de faible dimension et/ou fortement corrélés présentant un intérêt fondamental actuel, en utilisant la spectroscopie par photoémission résolue en angle et en spin (ARPES et SARPES).Dans la partie introductive, je présente mon travail sur deux exemples de type "livre de texte", mais innovants, montrant comment les interactions affectent la structure de bande d'un matériau: le couplage des électrons avec des phonons dans une distribution de Debye dans un système électronique à deux dimensions (2DES) dans ZnO, semi-conducteur à oxyde à bande interdite large utilisé dans les applications photovoltaïques, et le dédoublement induit par un fort couplage spin-orbite (SOC) dans la bande de valence du ZnTe, un autre semi-conducteur important utilisé dans les dispositifs optoélectroniques. Ensuite, dans la suite de cette thèse, je discute de mes résultats originaux dans trois systèmes différents de basse dimensionnalité et d'intérêt actuel en recherche : 1.La réalisation d'un 2DES à la surface (110) de SnO₂, le premier du genre dans une structure rutile. L'ajustabilité de la densité de ses porteurs au moyen de la température ou du dépôt d'Eu, et la robustesse vis-à-vis les reconstructions de surface et l'exposition aux conditions ambiantes rendent ce 2DES prometteur pour les applications. Au moyen d'une simple réaction redox à la surface, ces travaux ont prouvé que les lacunes en oxygène pouvaient doper la bande de conduction à la surface de SnO₂, résolvant ainsi un problème longtemps débattu concernant le rôle desdites lacunes dans le dopage de type n dans SnO₂. 2.L'étude des états de surface topologiques dans M₂Te₂X (avec M = Hf, Zr ou Ti; et X = P ou As), une nouvelle famille de métaux topologiques en trois dimensions, provenant du SOC et étant protégés par la symétrie du renversement du temps. Leur structure électronique et leur texture de spin, étudiées par ARPES et SARPES, révèlent la présence de fermions de Dirac sans masse donnant naissance à des arcs de nœuds de Dirac. 3.L'étude du matériau YbNi₄P₂ à fermions lourds quasi unidimensionnel, qui présente une transition de phase quantique de second ordre d’une phase ferromagnétique à une phase paramagnétique de liquide de Fermi lors de la substitution partielle du phosphore par l'arséniure. Une telle transition ne devrait se produire que dans les systèmes zéro ou unidimensionnels, mais la mesure directe de la structure électronique des matériaux ferromagnétiques quantiques critiques faisait jusqu'à présent défaut. Grâce à une préparation et nettoyage méticuleux in situ de la surface des monocristaux YbNi₄P₂, qui sont impossibles à cliver, leur structure électronique a été mesurée avec succès au moyen de l'ARPES, dévoilant ainsi le caractère quasi-1D, nécessaire à la compréhension de la criticité quantique ferromagnétique, dans YbNi₄P₂. Le protocole utilisé pour rendre ce matériau accessible à l'ARPES peut être facilement généralisé à d'autres matériaux exotiques dépourvus de plan de clivageMaterials in which many-body interactions, low-dimensional confinement, and/or strong spin-orbit coupling are present show a rich variety of phenomena, but are still poorly understood. Essential information about the origin of such phenomena can be obtained by measuring their electronic structure. This thesis presents an experimental study of the electronic structure of some low-dimensional and/or strongly correlated materials of current fundamental interest, using angle- and spin-resolved photoemission spectroscopy (ARPES and SARPES). In the introductory part, I present my work on two innovative textbook examples showing how interactions affect the band structure of a material: the coupling of electrons with phonons in a Debye distribution in a two-dimensional electron system (2DES) in ZnO, a wide-band-gap oxide semiconductor used in photovoltaic applications, and the splitting induced by strong spin-orbit coupling (SOC) in the bulk valence band of ZnTe, another important semiconductor used in optoelectronic devices. Then, in the rest of this thesis, I discuss my original results in three different low-dimensional systems of current interest: 1.The realisation of a 2DES at the (110) surface of SnO₂, the first of its kind in a rutile structure. Tunability of its carrier density by means of temperature or Eu deposition and robustness against surface reconstructions and exposure to ambient conditions make this 2DES promising for applications. By means of a simple redox reaction on the surface, this work has proven that oxygen vacancies can dope the conduction band minimum at the surface of SnO₂, solving a long-debated issue about their role in n-type doping in SnO₂. 2.The study of topological surface states in M₂Te₂X (with M = Hf, Zr, or Ti; and X = P or As), a new family of three-dimensional topological metals, originating from SOC and being protected by time-reversal symmetry. Their electronic structure and spin texture, studied by ARPES and SARPES, reveal the presence of massless Dirac fermions giving rise to Dirac-node arcs. 3.The investigation of the quasi-one-dimensional heavy-fermion material YbNi₄P₂, which presents a second-order quantum phase transition from a ferromagnetic to a paramagnetic phase upon partial substitution of phosphorous by arsenide. Such a transition is expected to occur only in zero- or one-dimensional systems, but a direct measurement of the electronic structure of ferromagnetic quantum-critical materials was missing so far. By careful in-situ preparation and cleaning of the surface of YbNi₄P₂ single crystals, which are impossible to cleave, their electronic structure has been successfully measured by ARPES, thus effectively unveiling the quasi-one-dimensionality of YbNi₄P₂. Moreover, the protocol used to make this material accessible to ARPES can be readily generalised to other exotic materials lacking a cleavage plane
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Danovich, Mark. "Optoelectronics of two dimensional transition metal dichalcogenides." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/optoelectronics-of-two-dimensional-transition-metal-dichalcogenides(7f280bf3-2591-429f-84f5-c89971db0e00).html.
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Two dimensional transition metal dichalcogenides provide a host of unique optoelectronic properties, attributed to their two dimensional nature and unique band structure, making them promising for future optoelectronics device applications. In the work presented in this thesis, we focus on the theoretical understanding and modelling of the optoelectronic properties of monolayer transition metal dichalcogenides, their heterostructures and multilayers. We studied the relaxation rates of photo-excited carriers leading to the formation of electron-hole pairs and their subsequent radiative recombination, resulting in emission of light. We find sub-ps relaxation times, attributed to the strong coupling of carriers with optical phonons, allowing the efficient formation of strongly bound multi-particle complexes such as excitons, trions and biexcitons, which can recombine radiatively if allowed by selection rules. We classify the various complexes according to their optical activity, and predict using diffusion quantum Monte Carlo calculations the resulting photoluminescence spectra in these materials. We proposed a novel, material specific, Auger process in WS2 and WSe2 involving dark excitons, which dominates over radiative processes for relatively low carrier densities, providing an explanation to the observed low quantum efficiencies in these materials. In the same pair of materials, we have shown how the ground state dark trions and biexcitons can become bright and recombine radiatively through an electron-electron intervalley scattering process, resulting in new observable lines in the photoluminescence spectra of these materials. The ability to form van der Waals heterostructures of two or more layers of these materials, allows for new degrees of freedom to be explored and utilised. The heterobilayer system made of MoSe2/WSe2 has a type-II band alignment, allowing for the formation of interlayer bound complexes with carriers localized on opposite layers. We studied the bound complexes formed in this bilayer system, localized on donor impurities. We used quantum Monte Carlo methods to obtain binding energies and wave functions, and calculated the radiative rates and doping dependent photoluminescence spectra of these complexes for closely aligned layers, and asymptotic behaviour for strongly misaligned layers. Finally, we studied few-layers of 2H-stacked transition metal dichalcogenides. The van der Waals quantum well structure results in the splitting of the conduction and valence bands into multiple subbands with energy spacings covering densely the infrared to far-infrared spectral range. We developed a hybrid k.p-tight binding model parameterised by DFT calculations of monolayer and bulk crystals of the studied materials. We used the model to describe the subband dispersions, transition energies, phonon induced broadening and resulting absorption lineshapes for both p-doped and n-doped few-layer films.
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Golla, Dheeraj, and Dheeraj Golla. "Ultrafast Dynamics of Two Dimensional Materials." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626303.
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Two dimensional (2D) materials are poised to revolutionize the
future of optics and electronics. The past decade saw intense research
centered around graphene. More recently, the tide has shifted to a bigger
class of two-dimensional materials including graphene but more
expansive in their capabilities. The so called ‘2D material zoo’ includes
metals, semi-metals, semiconductors, superconductors and insulators.
The possibility of mixing and matching 2D materials to fabricate
heterostructures with desirable properties is very exciting.
To make devices with superior electronic, optical and thermal
properties, we need to understand how the electrons, phonons and other
quasi particles interact with each other and exchange energy in the
femtosecond and nanosecond timescales. To measure the timescales of
energy distribution and dissipation, I used ultrafast pump-probe
spectroscopy to perform time-domain measurements of optical
absorption. This approach allows us to understand the impact of manybody
interactions on the bandstructure and carrier dynamics of 2D
materials.
After a brief introduction to femtosecond laser spectroscopy, I will
explore the transient absorption dynamics of three classes of 2D
materials: intrinsic graphene, graphene-hBN heterostructures and
Transition Metal Dichalcogenides (TMDs). We will see that using pumpprobe
measurements around the high energy M-point of intrinsicgraphene, we can extract the value of the acoustic deformation potential
which is vital in characterizing the electron-acoustic phonon
interactions. In the next part of the thesis, I will delineate the role of the
substrate in the cooling dynamics in graphene devices. We will see that
excited carriers in graphene on hBN substrates cool much faster that on
SiO2 substrates due to faster decay of the optical phonons in graphenehBN
heterostructures. These results show that graphene-hBN
heterostructures can solve the hot phonon bottleneck that plagues
graphene devices at high power densities. In the last part, I will
demonstrate the role of phonon induced bandgap renormalization in the
carrier dynamics of TMD materials and measure the timescale of
phonon decay through the generation of low-energy phonons and
transfer to the substrate. This study will help us understand carrier
recombination in TMD devices under high-bias conditions which show
great potential in opto-electronic applications such as photovoltaics,
LEDs etc.
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Zhu, Bairen, and 朱柏仁. "Optical study on two dimensional transition metal dichalcogenides." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208045.
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Atomically thin group-VI transition metal dichalcogenides (TMDC) has been emerging as a family of intrinsic 2-dimensional (2D) crystals with a sizeable bandgap in the visible and near infrared range, satisfying numerous requirements for ultimate electronics and optoelectronics. This intrinsic 2D crystal also provides a perfect platform for physics study in 2D semiconductors. The characteristic inversion symmetry breaking presented in monolayer TMDCs leads to non-zero but contrasting Berry curvatures and orbital magnetic moments at K/K’ valleys located at the corners of the first Brillouin zone. These features provide an opportunity to manipulate electrons’ additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDC a promising candidate for the conceptual valleytronics. Besides, the strong spin-orbit interactions and the subsequent spin-valley coupling demonstrated in 2D TMDCs open potential new routes towards quantum manipulation.
In this thesis, I give a brief review on the background and our progress of the physics study in 2D TMDCs (MoS2, WS2) via optical spectroscopy. Particularly, our experimental approach on the excitonic effect, valley dependent circular dichroism, and the spin-valley coupling in monolayer and bilayer TMDCs are elaborated in individual chapters.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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Lin, Yuxuan S. M. Massachusetts Institute of Technology. "Optical properties of two-dimensional transition metal dichalcogenides." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93059.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 91-115).
The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the research on their potential applications in the fields of logic nanoelectronics and high-performance nanophotonics. Many body effects are of great significance in 2-dimensional TMDs, especially when thinned down to a monolayer. As a result, the exciton-related phenomena are prominent in TMD monolayers, which distinguish the monolayers significantly from their bulk counterparts. This thesis systematically studies the optical properties in semiconducting, monolayer TMDs, including Raman spectroscopy, photoluminescence (PL), and optical absorption. In order to further understand the excitononic properties in 2-dimensional TMDs, we took monolayer MoS2 as an example, and studied its exciton behaviors with different carrier densities and dielectric environments through PL measurements with the help of electrochemical gating and non-ionic solvent immersion. Our findings are helpful to understand better the tightly bound excitons in low-dimensional systems and to provide a simple approach to controlling the generation of excitons and trions (charged excitons) selectively and separately.
by Yuxuan Lin.
S.M.
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Esche, Sven Karsten. "Developments for two-dimensional sheet metal forming analysis /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487946103566303.
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Johnson, Mark Thomas. "Photoelectron spectroscopy of two-dimensional materials and surfaces." Thesis, University of Cambridge, 1987. https://www.repository.cam.ac.uk/handle/1810/250898.
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Klein, R. "MHD experiments on quasi two-dimensional and three-dimensional liquid metal flows." Thesis, Coventry University, 2010. http://curve.coventry.ac.uk/open/items/a96c047e-3fe7-4408-967d-a0d32fa95e47/1.
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This dissertation reported an experimental answer to the long-standing question of how three-dimensionality appears in wall-bounded magnetohydrodynamic flows and presented also an experimental study on the transition to turbulence in a confined, mostly quasi two-dimensional flow. Accordingly, it was shown the analysis of a vortex array with susceptibility to three-dimensionality, enclosed in a cubic container and a mostly, quasi two-dimensional vortex pair confined by the walls of a shallow, cylindrical container. Both containers were hermetically filled by a liquid metal fluid and subject to a constant, homogeneous magnetic field. The flow forcing was made by injecting constant electric current from one wall that intersects magnetic field lines (Hartmann wall). Flow characteristics and the presence of three-dimensionality were monitored by measuring electric potentials on either Hartmann walls that confined the liquid metal. A form of three-dimensionality termed as weak appeared through differential rotation along the axis of individual vortices, while a strong form manifested itself in vortices that do not extend from one to the other Hartmann wall. In the cubic container, this resulted into an array of novel, spectacular flow structures that were both steady and strongly three-dimensional, and, yielded to a frequency-selective breakdown of quasi two-dimensionality in chaotic and turbulent flow regimes. The mostly quasi two-dimensional flow in the shallow, cylindrical container was shown to undergo a sequence of supercritical bifurcations to turbulence triggered by boundary layer separations from the circular wall. For very high forcing, the flow reached a turbulent regime where the dissipation increased drastically. This was related to a possible transition from a laminar to a turbulent Hartmann layer.
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He, Keliang. "Optical Spectroscopy of Two-Dimensional Transition Metal Dichalcogenides (TMDCs)." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1387468973.
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Ha, Dong-Gwang. "Growth and characterizations of two-dimensional metal-organic frameworks." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122155.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 123-132).
Metal-Organic Frameworks (MOFs) are a class of porous materials with a crystalline structure that can be designed based on extremely tunable building blocks of organic molecules and metal ions. They are typically insulators but making them [pi]-conjugated with two-dimensional structure results in high electrical conductivity. This makes the two-dimensional a-conjugated MOFs (2D [pi]MOFs) good candidates for applications that need porous conductors such as supercapacitors and batteries. More importantly, tunability of the crystal structure enables us to explore exotic physical properties, including topological protection. This great potential has inspired the synthesis of various 2D [pi]MOFs, but their crystal growth remains challenging, preventing the characterization of intrinsic electrical properties. In this thesis, I will explain the growth mechanisms of 2D [pi]MOFs and the limitations of conventional growth methods.
Based on the analysis, I developed a novel growth method that generates single-crystal plates of a 2D [pi]MOF, Ni₃(HHTP)₂ (HHTP= 2,3,6,7,10,11 hexahydroxytriphenylene), over 10 [mu]m in lateral dimension, two orders of magnitude larger than previous reports. The growth mechanism of the new method is also studied by varying multiple growth parameters. The properties of the single crystals are characterized by various spectroscopic techniques. Among assorted characteristics, the electrical properties are explored closely. The large single-crystal plates enable us to study in-plane properties of a 2D [pi]MOF for the first time. The in-plane conductivity of Ni₃(HHTP)₂ is up to 2 S/cm, two orders of magnitude higher than pressed pellet, and shows a clear temperature dependence. Hall measurements reveal that the origin of the high conductivity is a high charge carrier density rather than high charge carrier mobility.
We anticipate our demonstration will facilitate the discovery of fundamental properties of various 2D [pi]MOFs and further our realization of their potential as electronic materials.
Kwangjeong educational foundation for financial support
by Dong-Gwang Ha.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Bogaert, Kevin Christopher. "Defect-driven processing of two-dimensional transition metal dichalcogenides." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122072.
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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 149-161).
Two-dimensional transition metal dichalcogenides (TMDs) are an emerging class of semiconductor materials that offer exciting new properties for future electronic and optoelectronic applications. However, many ongoing challenges related to synthesis and processing must be overcome before this nascent technology can become industrially viable. In this thesis, processing-related phenomena relevant to the fabrication of TMD heterostructures, alloys, and nanoporous membranes are presented. This thesis begins with an investigation of the role of substrate temperature in two-step chemical vapor deposition (CVD) growth of MoS₂/WS₂ heterostructures. We demonstrate diffusion-mediated synthesis of inverted lateral heterostructures following low MoS2 growth temperatures in the second CVD step and homogeneous Mo[subscript x]W[subscript 1-x]S₂ alloyed crystals following higher MoS₂ growth temperatures.
Investigating the nature of this diffusion-mediated process, we identify an energetically favorable atomistic model proposing that transition metal diffusion is driven by a heterogeneous distribution of sulfur vacancies. This model is corroborated by the synthesis of a composition-graded Mo[subscript x]W[subscript 1-x]S₂ alloy crystals in which the final-stage spatial distribution of transition metal atoms correlates with intermediate-stage distribution of point defects. These heterogeneous crystals allow for correlation of the local optical properties with the local composition, demonstrating a variation in photoluminescence intensity spanning two orders of magnitude and reaching the maximum value for equicompositional alloy Mo₀.₅W₀.₅S₂ (x=0.5). Furthermore, the correlation between intermediate-stage distribution of point defects and final-stage spatial distribution of transition metal atoms enables the opportunity for bespoke patterning.
Utilizing a laser annealing technique, we demonstrate the ability to locally induce defects that define the regions of preferential nucleation during subsequent CVD growth. Finally, defect processing is also demonstrated in nanoporous TMD membrane applications. Combining modeling with experimentation, we demonstrate the relationship between vacuum annealing time and temperature with nanopore properties such as average radius and edge structure. Control of these properties is essential for the fabrication of functional nanoporous membrane devices for sensing, filtration, and energy applications. This thesis motivates further work on TMD processing in pursuit of developing a fundamental understanding of the defect-driven diffusion mechanism, a larger library of interesting TMD compositions and structures, as well as industrially viable TMD devices.
by Kevin Christopher Bogaert.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Long, Zhenyi. "Studies of two dimensional superconductor-normal metal hybrid thin films /." View online version; access limited to Brown University users, 2005. http://wwwlib.umi.com/dissertations/fullcit/3174641.
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Tsang, Ka-yi, and 曾家懿. "Two dimensional transition metal dichalcogenides grown by chemical vapor deposition." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/212604.
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An atomically thin film of semiconducting transition metal dichalcogenides (TMDCs) is emerging as a class of key materials in chemistry and physics due to their remarkable chemical and electronic properties. The TMDCs are layered materials with weak out-of-plane van der Waals (vdW) interaction and strong in-plane covalent bonding enabling scalable exfoliation into two-dimensional (2D) layers of atomic thickness. The growth techniques to prepare these 2D TMDC materials in high yield and large scale with high crystallinity have attracted intensive attention recently because of the new properties and potentials in nano-elctronic, optoelectronic, spintronic and valleytronic applications.
In this thesis, I develop methods for the chemical synthesis of 2D TMDCs films. The relevant growth mechanism and material characteristics of these films are also investigated. Molybdenum disulfide (MoS2) is synthesized by using molybdenum trioxide (MoO3) and sulfur (S) powder as the precursor. The films are formed on substrate pre-treated with reduced graphene oxide as the catalyst. However, this method cannot be extended to other TMDC materials such as molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) because reduced graphene oxide (rGO) reacts with selenium to form alloy materials rather than TMDC films. At the same time, the conversion of MoO3 to MoSe2 or that of tungsten trioxide (WO3) to WSe2 without the assistance of hydrogen in the chemical reaction is not thermodynamically feasible because the oxygen in the metal oxide cannot be replaced by selenium due to lower reactivity of the latter. On the other hand, I demonstrate that MoSe2 film can be synthesized directly by using MoSe2 and Se powder. Furthermore, the method of sulfurization or selenization of pre-deposited metal film can be promising due to precise thickness/size controls. Finally, some perspectives on the engineering challenges and fabrication methods of this family of materials will be given.published_or_final_version
Physics
Master
Master of Philosophy
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Wu, Ziyang. "Rational design of two-dimensional architectures for efficient electrocatalysis." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235888/1/ziyang%2Bwu%2Bthesis%284%29.pdf.
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In this thesis, the principal focus is the rational design and fabrication of two-dimensional (2D) nanoarchitectures, e.g., low-cost metal oxide nanosheets and earth-abundant transition metal layered double hydroxides (LDHs) for enhanced electrocatalysis. The related hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance not only demonstrated the advances of 2D nanomaterials, such as unique physical and mechanical properties, unprecedented electronic features, and ultrahigh surface areas but also indicated the possible mechanisms behind boosted activity and stability, e.g., phase engineering function and oxygen vacancies influence.
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Yen, Chi-min 1949. "Two-dimensional simulation of power MOSFET near breakdown." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276695.
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A simulation program has been developed to facilitate the investigation and analysis of power semiconductor devices under the reverse-bias condition. The electrostatic potential distribution is solved by using Poisson's equation alone, with particular attention to the neighborhood of avalanche breakdown. Because of its generality and efficiency, the program emerges as a powerful engineering tool for the design of power devices incorporating special junction termination techniques. Results are presented for a DMOS structure to illustrate the improvement in breakdown voltage when a field plate is applied. Numerical solution techniques for solving elliptic partial differential equations in a multi-material domain are discussed. The discretization of this domain is nonuniform in general due to its highly nonuniform physical parameters. By careful selection of grid lines near interfaces, the difference equation coefficients are considerably simplified. The resultant matrix of coefficients is symmetric even though Neumann boundary conditions are specified.
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McCormick, Elizabeth Joan McCormick. "Optical Properties of Two Dimensional Semiconductors." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531907387651019.
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Pezo, Lopez Armando Arquimedes [UNESP]. "Electronic structure of two dimensional systems with spin-orbit interaction." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/151633.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A realização experimental do grafeno em 2004 abriu as portas para os estudos de uma nova geração de materiais, estes chamados materiais bidimensionais são a expressão final do que poderíamos pensar em material plano (monocamada) que, eventualmente, podem ser empilhados para formar o bulk. O grafeno oferece uma grande variedade de propriedades físicas, em grande parte, como o resultado da dimensionalidade de sua estrutura, e pelas mesmas razões, materiais como Fosforeno (P), Siliceno (S), Nitreto de Boro hexagonal (hBN), dicalcogenos de metais de transição (TMDC), etc. São muito interessantes para fins teóricos, como para futuras aplicações tecnológicas que podem-se desenvolver a partir deles, como dispositivos de spintrônica e armazenamento. Neste trabalho o estudo desenvolvido são as propriedades eletrônicas dos materiais apresentados acima (grafeno, fosforeno e MoTe 2 ), e além disso, ja que o acoplamento spin-órbita aumenta à medida que o número atômico tambem aumenta, espera-se que este parâmetro desempenhe um papel na estrutura eletrônica, particularmente para os TMDC’s. Começamos descrevendo genéricamente esses três sistemas, isto é, para o grafeno, podemos usar uma abordagem tipo tight binding, a fim de encontrar a dispersão de energia para as quase-particulas perto do nível de Fermi (Equação de Dirac). Usando cálculos DFT estudou-se de forma geral as propriedades desses sistemas com a inclusão do espin órbita. Abordou-se cálculos para descrever os efeitos do acoplo spin órbita sobre os materiais isolados, tambem nas heterostruturas (duas camadas formadas por eles). Finalmente, tambem estudou-se a possibilidade de defeitos e sua possível influência sobre a estrutura eletrônica das heterostruturas.
The experimental realization of graphene in 2004 opened the gates to the studies of a new generation of materials, these so-called 2 dimensional materials are the final expression of what we could think of a plane material (monolayer) that eventually can be stacked to form a bulk. Graphene, the wonder material, offers a large variety of physical properties, in great part, as the result of the dimensionality of its structure, and for the same reasons, materials like phosphorene(P), silicene(S), hexagonal Boron Nitride (hBN), transition metal dichalcogenides(TMDC), etc. are very interesting for theoretical purposes, as for the future technological applications that we can develope from them, such as Spintronics and Storage devices. In this dissertation we theoretically study the electronic properties of the materials presented above (graphene, Phosphorene and MoTe2), and besides that, since the spin-orbit coupling strength increases as the atomic number does, we expect that this paremeter plays a role in the electronic structure, particularly for the TMDC. We start describing generically those three systems using density functional theory including the effect of spin orbit. We address calculations to describe the effects of spin orbit on the isolated materials as well as the heterostructures. Finally we also include the possibility of defects in graphene and their possible influence on the electronic structure of heterostructures.
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Mei, Jun. "Optimization of two-dimensional nanostructures for rechargeable batteries." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/135045/1/Jun%20Mei%20Thesis.pdf.
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This research aims to explore the optimization strategies of two-dimensional (2D) nanostructures for high-performance rechargeable batteries. Three effective strategies, including 2D-based phase engineering, component engineering and van der Waals (vdW) heterostructures, were proposed for improving electrochemical properties of 2D nanomaterials. These effective strategies will offer good references for researchers to develop practical next-generation rechargeable batteries using the emerging 2D nanomaterials.
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Lewalle, Alexandre. "Metallic behaviour and the metal-insulator transition in two-dimensional systems." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619842.
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York, Ethan Cole. "Numerical Simulation of Quasi-Two-Dimensional Corrosion of a Coated Metal." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1429032542.
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Rai, Rachel H. "Crystallization of Two-Dimensional Transition Metal Dichalcogenides for Tailored Optical Properties." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1565191101735252.
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Docherty, Callum James. "Terahertz spectroscopy of graphene and other two-dimensional materials." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:98c03952-dc3f-442b-bbc0-d8397645cc1b.
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In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.
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Plumadore, Ryan. "Study of Two Dimensional Materials by Scanning Probe Microscopy." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38637.
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This thesis explores structural and electronic properties of layered materials at the nanometre scale. Room temperature and low temperature ultrahigh vacuum scanning probe microscopy (scanning tunneling microscopy, scanning tunneling spectroscopy, atomic force microscopy) is used as the primary characterization method. The main findings in this thesis are: (a) observations of the atomic lattice and imaging local lattice defects of semiconducting ReS2 by scanning tunneling microscopy, (b) measurement of the electronic band gap of ReS2 by scanning tunneling spectroscopy, and (c) scanning tunneling microscopy study of 1T-TaS2 lattice and chemically functionalizing its defects with magnetic molecules.
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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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Reifler, Ellen Sarah. "Investigation of Intrinsic and Tunable Properties of Two-Dimensional Transition-Metal Dichalcogenides for Optical Applications." Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1182.
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Since the scotch-tape isolation of graphene, two-dimensional (2D) materials have been studied with increasing enthusiasm. Two-dimensional transition-metal dichalcogenides are of particular interest as atomically thin semiconductors. These materials are naturally transparent in their few-layer form, have direct band gaps in their monolayer form, exhibit extraordinary absorption, and demonstrate unique physics, making them promising for efficient and novel optical devices. Due to the two-dimensional nature of the materials, their properties are highly susceptible to the environment above and below the 2D films. It is critical to understand the influences of this environment on the properties of 2D materials and on the performance parameters of devices made with the materials. For transparent optical devices requiring electrical contacts and gates, the effect of transparent conducting oxides on the optical properties of 2D semiconductors is of particular importance. The ability to tune the optical properties of 2D transition-metal dichalcogenides could allow for improved control of the emission or absorption wavelength of optical devices made with the materials. Continuously tuning the optical properties of these materials would be advantageous for variable wavelength devices such as photodetectors or light emitters. This thesis systematically investigates the intrinsic structural and optical properties of two-dimensional transition-metal dichalcogenide films, the effect of substrate-based optical interference on the optical emission properties of the materials, and demonstrates methods to controllably tune the luminescence emission of the materials for future optical applications. This thesis advances the study of these materials toward integration in future efficient and novel optical devices. The specific transition metal dichalcogenides investigated here are molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), and tungsten diselenide (WSe2). The thickness-dependence of the intrinsic in-plane crystal structure of these materials is elucidated with high-resolution transmission electron microscopy; thickness-dependent optical properties are studied using Raman and photoluminescence spectroscopies. This thesis investigates the optical interference effects from substrates with transparent conducting oxide layers on the optical properties of few-layer MoS2 films. An understanding of these effects is critical for integrating MoS2 into efficient optical devices. We predict contributions of optical interference effects to the luminescence emission of few-layer MoS2 films. The predictions are experimentally verified. We also demonstrate the use of optical interference effects to tune the wavelength and intensity of the luminescence emission of few-layer MoS2. This thesis explores the use of electric fields applied perpendicular to the films to continuously and reversibly tune the band gap of few-layer MoS2 for future variable wavelength devices. To facilitate integration into devices, we demonstrate electric fieldinduced band gap tuning by applying electric fields with a pair of transparent or semitransparent conducting layers, and without the need for direct electrical contact to the MoS2 films. The observed band gap tuning is attributed to the Stark Effect. We discuss challenges to maximizing the effect of electric field-induced band gap tuning. We demonstrate that optical interference effects do not prevent observation of band gap tuning via applied electric fields. We successfully combine two luminescence emission tuning methods: optical interference effects and electric field effects.
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Gorini, Lorenzo. "Electrical contact properties of ultrathin transition metal dichalcogenide sheets." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16884/.
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The graphene discovery led to advances in exfoliation and synthetic techniques, and the lack of a bandgap in graphene has stimulated the research for new 2D semiconducting materials. Transition metal dichalcogenides (TMDCs), semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), have recently been isolated. TMDCs exhibit a unique combination of atomic-scale thickness, strong spin–orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, valleytronics and optoelectronics.
According to optical measurements, single-layer WS2 sheets exhibit a direct band gap of at least 2.0 eV. Because of its strong spin-orbit coupling induced valence band splitting, WS2 shows spin-valley coupling, even in few-layer sheets , which may allow easier observation of the valley Hall effect than in the other TMDCs.
The thesis reviews the theoretical background of TMDCs and their optoelectronic properties. It also reports on the fabrication of field-effect transistors based on few-layer sheets of WS2 and the investigation of their electronic transport properties. Particularly the project focuses on improving the interface between the metal contact and WS2 sheet, where annealing improves the contact transparency. Together with van der Pauw geometry, annealing allows four-terminal measurements to be performed and the pristine properties of the material to be recovered at room temperature, where the devices show n-type behaviour and a linear I-V curve.
The promising improvements and the electronic properties shown in this thesis make WS2 interesting for future applications in valleytronic devices.
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Shelley, Valerie Anderson 1957. "Validity of the Jain and Balk analytic model for two-dimensional effects in short channel MOSFETS." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276801.
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The Jain and Balk analytic model for two-dimensional effects in short channel MOSFETS is investigated. The effects considered are Drain Induced Barrier Lowering, DIBL, and the maximum electric field, Emax, which influences Drain Induced High Field, DIHF. A scaled short channel design is used as the basis for the investigation. Cases are numerically simulated using the MINIMOS program. DIBL and Emax are calculated using the Jain and Balk model. Model values are compared to numerical simulation values. Results show the model consistently overestimates DIBL. Also, the range for which the model closely estimates Emax is found. Variation in Emax with change of junction depth Xj is investigated. The electric field, Ex, as it varies with depth in the channel is investigated, and compared to the Jain and Balk approximation. The deviations suggest that the model must break down for short channels.
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Cudzilo, Bogdan E. "Two-dimensional BEM analysis of cracked fibre-metal laminates with circular cut-outs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ57751.pdf.
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Ziegler, Christian [Verfasser], and Bettina [Akademischer Betreuer] Lotsch. "Two-dimensional transition metal oxide nanosheets for nanoarchitectonics / Christian Ziegler ; Betreuer: Bettina Lotsch." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1124395814/34.
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Proskuryakov, Yuri. "Interactions, localisation and the metal to insulator transition in two-dimensional semiconductor systems." Thesis, University of Exeter, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288367.
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Cattelan, Mattia. "Graphene and beyond: development of new two-dimensional materials." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424752.
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During the three years of my PhD project, I explored part of the world of two-dimensional materials. My activity has been focused on the growth and analysis of two-dimensional materials by means of Surface Science techniques. For the growth both chemical methods, such as decomposition of gaseous precursors, as well as physical methods, such as evaporation of metals under ultra-high vacuum conditions, were used. The main method for studying the properties of these materials was photoemission spectroscopy from core levels and valence band.
The materials were mostly grown and analysed directly in-situ, avoiding air exposure, which is known to alter their properties. Taking the cue from the results on single materials, I further widened my investigation toward complex heterostructures, i.e. artificial architectures of two-dimensional materials. Systems stemming from different combinations among graphene, hexagonal boron nitride and two-dimensional chalcogenides were produced and investigated with the aim to unravel the structure-activity relationships in heterostructures.
The thesis is divided into four main chapters.
The first is an introduction to the world of two-dimensional materials and summarized the main themes and the general structure of the thesis.
The second chapter is dedicated to the growth and study of graphene, which is the archetype of this class of materials. After an introduction on its electrical properties and on its growth on conventional metal single crystals, the chapter is divided into four sections that cover specific issues. Paragraphs 2.1.1 and 2.1.2 examine the properties of graphene and nitrogen doped graphene in contact with ultra-thin layers of iron. The section 2.2 studies the reaction of water with graphene grown on nickel single crystal, for the production of hydrogen. The paragraph 2.3 describes the growth of graphene on an unconventional substrate: platinum nickel alloy (Pt3Ni).
The third chapter is devoted to the study of other two-dimensional materials firstly introducing the studied materials: hexagonal boron nitride, transition metals dichalcogenides, other layered chalcogenides and heterostructures. Afterward, this chapter continues with three specific sections: paragraphs 3.1.1 and 3.1.2 are dedicated to two innovative methods for preparing heterostructures under ultra-high vacuum conditions. The section 3.1.1 presents a new strategy to synthesize monolayer in-plane heterostructure composed by graphene and hexagonal boron nitride, the 3.1.2 discusses a versatile route to create vertically stacked heterostructures of various two-dimensional materials. The last paragraph, 3.2, reports a detailed investigation of the electronic and chemical properties of a bulk layered chalcogenide, indium selenide.
The fourth chapter summarizes the main conclusions of the work.In questi tre anni di progetto di dottorato ho esplorato parte del mondo dei materiali bidimensionali. Il mio lavoro si è concentrato sull’analisi e la crescita di materiali bidimensionali con tecniche della Scienza delle Superfici. Per la crescita sono stati utilizzati sia metodi chimici, come la decomposizione di precursori gassosi, che fisici, come l’evaporazione di metalli in condizioni di ultra alto vuoto. Il metodo principale usato per studiare le proprietà di questi materiali è stata la fotoemissione da livelli di core e dalla banda di valenza. I materiali sono stati in gran parte cresciuti e analizzati direttamente in-situ, cioè evitando l’esposizione all’aria che ne altera le loro proprietà. Prendendo spunto dai risultati sui singoli materiali ho ulteriormente ampliato le mia ricerca verso complesse eterostrutture, ossia delle architetture artificiali di materiali bidimensionali. I sistemi derivanti da diverse combinazioni di grafene, nitruro di boro esagonale e calcogenuri bidimensionali sono stati prodotti e analizzati con lo scopo di rivelare la relazioni tra struttura e attività nelle eterostrutture. La tesi è divisa in quattro capitoli principali. Il primo è un’introduzione al mondo dei materiali bidimensionali e riassume i temi principali e la struttura generale della tesi. Il secondo capitolo è dedicato alla crescita e allo studio del grafene, archetipo di questa classe di materiali. Dopo un’introduzione sulle sue proprietà elettriche e sulla sua crescita su monocristalli metallici convenzionali il capitolo si suddivide in quattro sezioni che trattano tematiche specifiche. I paragrafi 2.1.1 e 2.1.2 esaminano le proprietà di grafene e grafene drogato azoto in contatto con strati ultrasottili di ferro. La sezione 2.2 studia la reazione dell’acqua con grafene cresciuto su monocristallo di nickel, per la produzione di idrogeno. Il paragrafo 2.3 descrive la crescita di grafene su un substrato non convenzionale: una lega di platino e nickel (Pt3Ni). Il terzo capitolo è rivolto allo studio di altri materiali bidimensionali, innanzitutto introduce i materiali trattati: nitruro di boro esagonale, dicalcogenuri di metalli di transizione, altri calcogenuri stratificati e le eterostrutture. Poi prosegue con tre sezioni specifiche; i paragrafi 3.1.1 e 3.1.2 sono dedicati a due metodi innovativi per formare eterostrutture in condizioni di ultra alto vuoto. La sezione 3.1.1 presenta un nuovo metodo per sintetizzare l’eterostruttura nel piano composta da grafene e nitruro di boro esagonale, la 3.1.2 propone un metodo versatile per creare eterostrutture impilate verticalmente di vari materiali bidimensionali. L’ultimo paragrafo, 3.2, riporta una ricerca dettagliata sulle proprietà elettroniche e chimiche di un calcogenuro stratificato massivo, l’indio seleniuro. Il quarto capitolo riassume le conclusioni del lavoro.
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Rahneshin, Vahid. "Versatile High Performance Photomechanical Actuators Based on Two-dimensional Nanomaterials." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-dissertations/549.
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The ability to convert photons into mechanical motion is of significant importance for many energy conversion and reconfigurable technologies. Establishing an optical-mechanical interface has been attempted since 1881; nevertheless, only few materials exist that can convert photons of different wavelengths into mechanical motion that is large enough for practical import. Recently, various nanomaterials including nanoparticles, nanowires, carbon nanotubes, and graphene have been used as photo-thermal agents in different polymer systems and triggered using near infrared (NIR) light for photo-thermal actuation. In general, most photomechanical actuators based on sp bonded carbon namely nanotube and graphene are triggered mainly using near infra-red light and they do not exhibit wavelength selectivity. Layered transition metal dichalcogenides (TMDs) provide intriguing opportunities to develop low cost, light and wavelength tunable stimuli responsive systems that are not possible with their conventional macroscopic counterparts. Compared to graphene, which is just a layer of carbon atoms and has no bandgap, TMDs are stacks of triple layers with transition metal layer between two chalcogen layers and they also possess an intrinsic bandgap. While the atoms within the layers are chemically bonded using covalent bonds, the triple layers can be mechanically/chemically exfoliated due to weak van der Waals bonding between the layers. Due to the large optical absorption in these materials, they are already being exploited for photocatalytic, photoluminescence, photo-transistors, and solar cell applications. The large breaking strength together with large band gap and strong light- matter interaction in these materials have resulted in plethora of investigation on electronic, optical and magnetic properties of such layered ultra-thin semiconductors. This dissertation will go in depth in the synthesis, characterization, development, and application of two- dimensional (2D) nanomaterials, with an emphasis on TMDs and molybdenum disulfide (MoS2), when used as photo-thermal agents in photoactuation technologies. It will present a new class of photo-thermal actuators based on TMDs and hyperelastic elastomers with large opto-mechanical energy conversion, and investigate the layer-dependent optoelectronics and light-matter interaction in these nanomaterials and nanocomposites. Different attributes of semiconductive nanoparticles will be studied through different applications, and the possibility of globally/locally engineering the bandgap of such nanomaterials, along with its consequent effect on optomechanical properties of photo thermal actuators will be investigated. Using liquid phase exfoliation in deionized water, inks based on 2D- materials will be developed, and inkjet printing of 2D materials will be utilized as an efficient method for fast fabrication of functional devices based on nanomaterials, such as paper-graphene-based photo actuators. The scalability, simplicity, biocompatibility, and fast fabrication characteristics of the inkjet printing of 2D materials along with its applicability to a variety of substrates such as plastics and papers can potentially be implemented to fabricate high-performance devices with countless applications in soft robotics, wearable technologies, flexible electronics and optoelectronics, bio- sensing, photovoltaics, artificial skins/muscles, transparent displays and photo-detectors.
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Thulasi, Sunita. "Theory of the two-dimensional airy electron gas Hartee-Fock and density-functional studies /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4111.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 17, 2007) Vita. n following parenthesis in formula (LaTiO₃) should be subscript. Includes bibliographical references.
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Grechnyev, Oleksiy. "Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4815.
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Nur, Baizura Binti Mohamed. "Study on photoluminescence quantum yields of atomically thin-layered two-dimensional semiconductors transition metal dichalcogenides." Kyoto University, 2018. http://hdl.handle.net/2433/233854.
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Melton, Darren Landon. "Metal ion complexing properties of the two-dimensional, highly preorganized ligand 1, 10-Phenanthroline-2, 9-Dicarboxylic acid /." Electronic version (PDF), 2005. http://dl.uncw.edu/etd/2005/meltond/darrenmelton.pdf.
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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.
Full textAbstract:
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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Brewer, Darcy M. J. "Electrodeposited metal nanocomposite catalysts utilizing the hexagonally ordered two-dimensional nanochannel arrays of anodic alumina." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0007/MQ45924.pdf.
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Blowey, Phil J. "Probing the geometrical and electronic structure of two-dimensional charge transfer networks on metal surfaces." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/111281/.
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Due to its ability to form conductive organic salts, the prototypical electron acceptor molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ) has attracted considerable interest in the field of organic electronics. This has motivated numerous surface science studies of TCNQ and related molecules, with an aim to understand the molecule-substrate interface and, in particular, the nature of any charge transfer. Although charge transfer is strongly dependent on subtle aspects of the molecular adsorption geometry, there is a dearth of detailed structural investigations for these systems. In this thesis, a variety of surface science techniques were used to characterise model systems of TCNQ adsorbed on coinage metal substrates with the aim to identify key relationships between the adsorption structure and the electronic properties of the surface. Particular focus was given to studying two-dimensional charge-transfer networks formed by TCNQ and alkali metals on the surface of Ag. Scanning tunnelling microscopy and low energy electron diffraction were used to characterise the packing and ordering of molecules and to ascertain whether the adsorbed layer is commensurate with respect to the underlying substrate. X-ray and ultraviolet photoelectron spectroscopy were used to provide complementary information on the chemical composition and electronic properties of the surface. Most significantly, the normal incident X-ray standing wave (NIXSW) technique was used to obtain precise quantitative structural measurements of the surface. On the surfaces of coinage metals, TCNQ is generally believed to adsorb in a significantly bent conformation, with all four cyano groups pointing down towards the substrate. The NIXSW measurements in this thesis show that the conformation adopted by TCNQ on Ag(100) is consistent with this, but on Ag(111), TCNQ adopts a considerably different conformation that was found, through comparison with density functional theory calculations, to result from the participation of Ag adatoms within the surface structure. These results also highlight the need for using both experimental and theoretical quantitative structural methods to obtain a reliable understanding of metal-organic interfaces and that some previously studied systems may need to be re-investigated. On both the (111) and (100) surfaces of Ag, a wide variety of TCNQ/alkali metal network structures were formed with Cs, K and Na. NIXSW measurements obtained from a subset of these structures show that the alkali metals adsorb at elevated heights above the TCNQ molecules. In comparable structures, K adsorbs closer to the surface than Cs and causes a smaller shift to the surface work function. The alkali metal adsorption height was also found to decrease as its coverage relative to TCNQ increased.