Tailor Synthesis of 0D, 1D and 2D Transition Metal Dichalcogenide Nanostructures PDF Download
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Author: Faegheh Hoshyargar
Publisher:
ISBN:
Category :
Languages : en
Pages : 146
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Author: Faegheh Hoshyargar
Publisher:
ISBN:
Category :
Languages : en
Pages : 146
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Author: Yifan Sun
Publisher:
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Category :
Languages : en
Pages :
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Layered transition metal dichalcogenides (TMDs) are particularly intriguing targets due to unique anisotropic quantum confinement, phase engineering enabled by rich polymorphism, and favorable properties for optical, electronic, magnetic and catalytic applications. Colloidal synthesis has been developed as a powerful and scalable solution-phase tool to access free-standing TMD nanostructures. While several colloidal TMD nanostructures have been prepared, questions remain at establishing universal synthetic protocols to directly access well-defined nanostructures without post-annealing, delicate adjustment over chemical composition, structure and morphology associated with vertical thickness and lateral size, as well as understanding formation and transformation for the two-dimensional nanosheets. More challenges, from both synthesis and characterization perspectives, emerge for the colloidal synthesis of complex TMD species including atomically-mixed alloys and mixed-dimensional heterostructures. In this dissertation, I focus on the colloidal synthesis of group 6 TMD (MX2, M = Mo, W and X = S, Se, Te) nanostructures, alloys and heterostructures, as well as systematic study with a suite of spectroscopic and microscopic techniques. Moreover, I aim to extract novel fundamental insights through exploring the structure-property relationship, which can trigger a wider range of applications based on the dimension-confined TMD nanostructures.I start with the colloidal synthesis of few-layer 1T-MoTe2 nanostructures (Chapter 2). Uniform 1T-MoTe2 nanoflowers comprised of few-layer nanosheets form directly in colloidal solution, with approx. 1 % lateral lattice compression compared with the bulk analogue. It is interesting to directly obtain the metastable monoclinic (1T) polymorph at low temperatures where the 2H phase should be preferred. Besides a small energy difference between 1T- and 2H-MoTe2, and modification of the surface energy and formation barrier by organic ligands, grain boundary pinning facilitated by polycrystallinity and small domain size also contributes to the stabilization of the metastable 1T phase as revealed by computational studies. This study demonstrates the capability of colloidal approaches to obtain synthetically challenging TMD systems. I then target nanostructured TMD alloys to elucidate the relationship between continuous adjustment of elemental composition and tunable optical properties (Chapter 3). Few-layer TMD alloys, MoxW1-xSe2 and WS2ySe2(1-y), exhibiting tunable metal and chalcogen compositions spanning the MoSe2-WSe2 and WS2-WSe2 solid solutions, respectively, are directly synthesized in colloidal solution. Comprehensive structural characterization of the composition-tunable TMD samples are presented, together with instructive chemical synthetic guidelines. Importantly, we are able to identify a random distribution of the alloyed elements and various types of vacancy sites with high-resolution microscopic imaging. The A excitonic transition of the solution-dispersible TMD samples can be readily tuned between 1.51 and 1.93 eV via metal and chalcogen alloying, correlating composition modification with tunable optical properties. In Chapter 4, I further modify the colloidal synthetic approach to access tungsten ditelluride (WTe2), which exhibits exotic properties in magnetic and topological devices. Nanostructured WTe2 with the orthorhombic (Td) structure is directly synthesized in colloidal solution. Microscopic imaging monitors the anisotropic pathway by which the few-layer WTe2 nanoflowers grow, and captures the co-existence of multiple stacking patterns of the atomically-thin layers. In addition, nanostructured transition metal ditelluride alloys (MoxW1-xTe2) with 1T-MoTe2 and Td-WTe2 as end members are obtained. Using the variety of TMD nanostructures now accessible based on our studies and previous reports, we investigate the solution-phase deposition of noble metals (Au and Ag) on transition metal disulfides (1T- and 2H-WS2), diselenides (MoSe2 and WSe2) and ditellurides (1T-MoTe2 and WTe2) in Chapter 5. Au3+ and Ag+ are reduced on the surface of the TMD nanostructures at room temperature via a spontaneous charge transfer process, and the nucleation, growth, structure, and morphology of the deposited Au and Ag are highly dependent on the noble metal/chalcogen interface. In particular, efficient electron transfer and strong interactions between silver and tellurium through interfacial Ag-Te bonding lead to the deposition of single-atom-thick Ag layers on nanostructured 1T-MoTe2 and WTe2, producing unique monolayer coatings with distinct structural and energetic features. Construction of the interface-tunable hybrids indicates that colloidal TMD nanosheets provide a diverse platform to probe charge transfer as well as interfacial coupling at the atomic scale. In Chapter 6, I expand the knowledge gained from previous synthetic studies and exploit structure-property relationships of colloidal TMD nanostructures to identify new heterogeneous catalysts. Colloidally synthesized 2H-WS2 nanostructures are identified as active and robust catalysts to selectively hydrogenate nitroarenes to their corresponding anilines with molecular hydrogen. A broad scope of molecular substrates with reducible functional groups including alkynes, alkenes, nitriles, ketones, aldehydes, esters, carboxylic acids, amides, and halogens are tested to demonstrate the wide applicability of the 2H-WS2 nanostructures for chemoselective transformation of substituted nitroarenes. In addition, microscopic evidence indicates that the improved performance for the nanostructured 2H-WS2 compared with the inactive bulk counterparts is due to the existence of sulfur vacancies situated on the high surface area nanosheets.
Author: Jessica Quinn Geisenhoff
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Transition metal dichalcogenides are a class of materials that are built from two-dimensional layers held together via Van der Waals interactions. These materials are structurally diverse and can adopt multiple phases. In particular, the group VI TMDs (MoS2, MoSe2, WS2, WSe2) exist in either a metastable 2M phase or the thermodynamically favored 2H phase. Material properties can be tuned by controlling the phase or the number of layers in the crystal, making controllable syntheses of these materials highly desired. Colloidal synthesis offers a solution-phase route to solid-state materials. Conducting the synthesis in the solution phase allows a synthetic chemist to access a diverse parameter space that is usually not afforded with more traditional solid-state syntheses. This includes being able to tune reaction temperature, ligand environment, and precursor reactivity, which can easily lead to kinetically controlled reaction regimes and direct synthesis of metastable phases. This dissertation demonstrates that colloidal synthesis is a viable tool for phase tunable syntheses of TMDs, as well as investigating aspects that govern phase conversion.The coordination and reactivity of the tungsten precursor used can be influenced via the ligands used. Reactions performed in solutions of either the strongly coordinating oleic acid, or the weakly coordinating trioctylphosphine oxide are detailed in chapter 2. The size and phase of the nanocrystals are tuned, where increased amounts of oleic acid decrease the reactivity leading to large nanocrystals of the metastable 2M phase. Building upon the work outlined in chapter 2, chapter 3 leverages the reduced reactivity of the metal precursor in great amounts of oleic acid to synthesize metal selenide/tungsten diselenide heterostructures via a one-pot method. The delayed reactivity in oleic acid allows for the nucleation of other metal selenides prior to the secondary growth of WSe2. How the coordination environment of tungsten influences reactivity and nanocrystal formation is more rigorously evaluated in chapter 4. Heating W(CO)6 in the presence of either trioctylphosphine oxide or trioctylphosphine forms W(CO)6-x(L)x intermediates. Phosphine oxides promote CO labilization while phosphines hinder this process. Thus, performing reactions in TOPO lead to low-temperature syntheses of the metastable 2M phase, while those with TOP require additional heating. Insights into how morphology impacts phase conversion from the metastable 2M phase to the thermodynamically favored 2H phase are investigated in chapter 5. Reactions performed in trioctylphosphine oxide with differing concentration results in WSe2 nanocrystals with differing layer numbers. Here, high precursor concentrations lead to nanocrystals with increased number of layers without changing the lateral size of the nanocrystals. This change in nanocrystal morphology is accompanied by a reduction in the phase conversion rate from the 2M phase to the 2H phase. Phase conversion is likely slowed with increased interlayer binding energies. Finally, a synthetic route to monolayer TMD nanocrystals is outlined in chapter 6. Controlled heat-ups in the presence of excess trioctylphosphine result in ligands tightly bound to the basal plane of the TMDs. These ligands permanently separate the layers from one another, producing monolayers, and influence the electronic properties of the nanocrystals. Additionally, phase conversion is rapid in these monolayer-like systems.
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Category :
Languages : en
Pages :
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Abstract : The rapid development of two-dimensional (2D) materials has led to tremendous interest in the study of graphene and a series of mono- and few-layered transition metal dichalcogenides (TMDCs). One major attraction of TMDCs is their semiconducting nature with indirect to direct bandgap transition, when thinned from bulk to few- and mono- layers. Molybdenum disulfide (MoS2) is one of the 2D TMDCs that has gained increasing attention due to its promising optical, electronic, and optoelectronic properties. In this thesis, I will discuss my research on the synthesis of 2D MoS2 and the characterization of its optical properties by Raman, Photoluminescence (PL) and UV-Vis spectroscopy. Next, the application of 2D TMDCs for FETs and solar cells will be reviewed. Finally, my extended work on the oxide form (transition metal oxides) and zero-dimensional (0D) form of TMDCs will be discussed. Efficient solar cells constructed by MoO3 and other oxides, and the future application of 0D TMDCs will also be evaluated.
Author: Narayanasamy Sabari Arul
Publisher: Springer
ISBN: 9811390452
Category : Technology & Engineering
Languages : en
Pages : 355
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Book Description
This book presents advanced synthesis techniques adopted to fabricate two-dimensional (2D) transition metal dichalcogenides (TMDs) materials with its enhanced properties towards their utilization in various applications such as, energy storage devices, photovoltaics, electrocatalysis, electronic devices, photocatalysts, sensing and biomedical applications. It provides detailed coverage on everything from the synthesis and properties to the applications and future prospects of research in 2D TMD nanomaterials.
Author: Pramoda Kumar Nayak
Publisher: BoD – Books on Demand
ISBN: 9535125540
Category : Technology & Engineering
Languages : en
Pages : 282
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Book Description
There are only a few discoveries and new technologies in materials science that have the potential to dramatically alter and revolutionize our material world. Discovery of two-dimensional (2D) materials, the thinnest form of materials to ever occur in nature, is one of them. After isolation of graphene from graphite in 2004, a whole other class of atomically thin materials, dominated by surface effects and showing completely unexpected and extraordinary properties, has been created. This book provides a comprehensive view and state-of-the-art knowledge about 2D materials such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMD) and so on. It consists of 11 chapters contributed by a team of experts in this exciting field and provides latest synthesis techniques of 2D materials, characterization and their potential applications in energy conservation, electronics, optoelectronics and biotechnology.
Author: Zishan Husain Khan
Publisher: Springer Nature
ISBN: 9811599041
Category : Technology & Engineering
Languages : en
Pages : 382
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Book Description
This book discusses new trends in nanotechnology. It covers a wide range of topics starting from applications of nanomaterials in perovskite solar cells, pharmacy, and dentistry to self-assembled growth of GaN nanostructures on flexible metal foils by laser molecular beam epitaxy. It also includes other interesting topics such as advancement in carbon nanotubes; processing techniques, purification and industrial applications, metal di-chalcogenides for waste water treatment and recent advancement in nanostructured-based electrochemical genosensors for pathogen detection and many more. The book will be of great interest to researchers, professionals and students working in the areas of nanomaterials and nanotechnology.
Author: F.A. Lévy
Publisher: Springer Science & Business Media
ISBN: 9401014337
Category : Science
Languages : en
Pages : 374
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Book Description
In the last ten years, the chemistry and physics of materials with layered structures became an intensively investigated field in the study of the solid state. Research into physical properties of these crystals and especially investigations of their physical anisotropy related to the structural anisotropy has led to remarkable and perplexing results. Most of the layered materials exist in several polytypic modifications and can include stacking faults. The crystal structures are therefore complex and it became apparent that there was a great need for a review of the crystallographic data of materials approximating two-dimensional solids. This second volume in the series 'Physics and Chemistry of Materials with Layered Structures' has been written by specialists of different classes of layered materials. Structural data are reviewed and the most important relations between the structure and the chemical and physical properties are emphasized. The first three contributions are devoted to the transition metal dichalcogenides whose physical properties have been investigated in detail. The crystallographic data and crystal growth conditions are presented in the first paper. The second paper constitutes an incisive review of the phase transformations and charge density waves which have been observed in the metallic dichalcogenides. In two contributions the layered structures of newer ternary compounds are de scribed and the connection between structure and non-stoichiometry is discussed.
Author: Xin Tong
Publisher: Springer Nature
ISBN: 3030465969
Category : Science
Languages : en
Pages : 331
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Book Description
This book outlines various synthetic approaches, tuneable physical properties, and device applications of core/shell quantum dots (QDs). Core/shell QDs have exhibited enhanced quantum yield (QY), suppressed photobleaching/blinking, and significantly improved photochemical/physical stability as compared to conventional bare QDs. The core-shell structure also promotes the easy tuning of QDs’ band structure, leading to their employment as attractive building blocks in various optoelectronic devices. The main objective of this book is to create a platform for knowledge sharing and dissemination of the latest advances in novel areas of core/shell QDs and relevant devices, and to provide a comprehensive introduction and directions for further research in this growing area of nanomaterials research.
Author: Md Nurunnabi
Publisher: Elsevier
ISBN: 0128162694
Category : Technology & Engineering
Languages : en
Pages : 399
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Book Description
Biomedical Applications of Graphene and 2D Nanomaterials provides a much-needed reference on the biomedical applications of 2D nanomaterials, as well as theoretical knowledge on their structure, physicochemical properties and biomedical applications. Chapters are dedicated to growth areas, such as size and shape-dependent chemical and physical properties and applications, such as in diagnostic and therapeutic products. The book also discusses the concept, development and preclinical studies of 2D nanomaterials-based biomedical tools, such as biosensors, artificial organs and photomedicine. Case studies and reports form the core of the book, making it an ideal resource on potential applications in biomedical science and engineering. This timely resource for scientists and engineers in this rapidly advancing field features contributions from over 30 leaders who address advanced methods and strategies for controlling the physical-chemical properties of 2D nanomaterials, along with expert opinions on a range of 2D nanomaterials that have therapeutic and diagnostic applications. Presents advanced methods and strategies for controlling the physical-chemical properties of 2D nanomaterials Provides state-of-the-art biomedical applications for 2D nanomaterials, including graphene and boron nitride Includes key information from a broad selection of subject areas for researchers in both materials, engineering and medicine
