Nucleation and growth of noble metals on transition-metal ditellurides PDF Download
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Author: Saw Wai Hla
Publisher:
ISBN:
Category :
Languages : en
Pages : 134
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Author: Saw Wai Hla
Publisher:
ISBN:
Category :
Languages : en
Pages : 134
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Author: Keyna O'Reilly
Publisher:
ISBN:
Category : Nucleation
Languages : en
Pages : 220
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Author: Keyna O'Reilly
Publisher:
ISBN:
Category : Nucleation
Languages : en
Pages : 0
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Author: Yifan Sun
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
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:
Publisher:
ISBN:
Category : Metallurgy
Languages : en
Pages : 1076
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Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2664
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Author: Alexander V. Kolobov
Publisher: Springer
ISBN: 3319314505
Category : Technology & Engineering
Languages : en
Pages : 545
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Book Description
This book summarizes the current status of theoretical and experimental progress in 2 dimensional graphene-like monolayers and few-layers of transition metal dichalcogenides (TMDCs). Semiconducting monolayer TMDCs, due to the presence of a direct gap, significantly extend the potential of low-dimensional nanomaterials for applications in nanoelectronics and nano-optoelectronics as well as flexible nano-electronics with unprecedented possibilities to control the gap by external stimuli. Strong quantum confinement results in extremely high exciton binding energies which forms an interesting platform for both fundamental studies and device applications. Breaking of spatial inversion symmetry in monolayers results in strong spin-valley coupling potentially leading to their use in valleytronics. Starting with the basic chemistry of transition metals, the reader is introduced to the rich field of transition metal dichalcogenides. After a chapter on three dimensional crystals and a description of top-down and bottom-up fabrication methods of few-layer and single layer structures, the fascinating world of two-dimensional TMDCs structures is presented with their unique atomic, electronic, and magnetic properties. The book covers in detail particular features associated with decreased dimensionality such as stability and phase-transitions in monolayers, the appearance of a direct gap, large binding energy of 2D excitons and trions and their dynamics, Raman scattering associated with decreased dimensionality, extraordinarily strong light-matter interaction, layer-dependent photoluminescence properties, new physics associated with the destruction of the spatial inversion symmetry of the bulk phase, spin-orbit and spin-valley couplings. The book concludes with chapters on engineered heterostructures and device applications such as a monolayer MoS2 transistor. Considering the explosive interest in physics and applications of two-dimensional materials, this book is a valuable source of information for material scientists and engineers working in the field as well as for the graduate students majoring in materials science.
Author: Babak Anasori
Publisher: Springer Nature
ISBN: 3030190269
Category : Technology & Engineering
Languages : en
Pages : 534
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Book Description
This book describes the rapidly expanding field of two-dimensional (2D) transition metal carbides and nitrides (MXenes). It covers fundamental knowledge on synthesis, structure, and properties of these new materials, and a description of their processing, scale-up and emerging applications. The ways in which the quickly expanding family of MXenes can outperform other novel nanomaterials in a variety of applications, spanning from energy storage and conversion to electronics; from water science to transportation; and in defense and medical applications, are discussed in detail.
Author: Zongyu Huang
Publisher: CRC Press
ISBN: 1000562840
Category : Science
Languages : en
Pages : 166
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Book Description
Monoelemental 2D materials called Xenes have a graphene-like structure, intra-layer covalent bond, and weak van der Waals forces between layers. Materials composed of different groups of elements have different structures and rich properties, making Xenes materials a potential candidate for the next generation of 2D materials. 2D Monoelemental Materials (Xenes) and Related Technologies: Beyond Graphene describes the structure, properties, and applications of Xenes by classification and section. The first section covers the structure and classification of single-element 2D materials, according to the different main groups of monoelemental materials of different components and includes the properties and applications with detailed description. The second section discusses the structure, properties, and applications of advanced 2D Xenes materials, which are composed of heterogeneous structures, produced by defects, and regulated by the field. Features include: Systematically detailed single element materials according to the main groups of the constituent elements Classification of the most effective and widely studied 2D Xenes materials Expounding upon changes in properties and improvements in applications by different regulation mechanisms Discussion of the significance of 2D single-element materials where structural characteristics are closely combined with different preparation methods and the relevant theoretical properties complement each other with practical applications Aimed at researchers and advanced students in materials science and engineering, this book offers a broad view of current knowledge in the emerging and promising field of 2D monoelemental materials.
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.
