Dissertations / Theses on the topic 'MoS2 material'
To see the other types of publications on this topic, follow the link: MoS2 material.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'MoS2 material.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Singh, Harpal. "An Investigation of Material Properties and Tribological Performance of Magnetron Sputtered Thin Film Coatings." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1449850005.
Full text
2
Ma, Lu. "Synthesis and Characterization of Large Area Few-layer MoS2 and WS2 Films." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1388149255.
Full text
3
Ma, Lu. "Mo-S Chemistry: From 2D Material to Molecular Clusters." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480268313180315.
Full text
4
Nasseri, Mohsen. "NANOSCALE DEVICES CONSISTING OF HETEROSTRUCTURES OF CARBON NANOTUBES AND TWO-DIMENSIONAL LAYERED MATERIALS." UKnowledge, 2018. https://uknowledge.uky.edu/physastron_etds/59.
Full textAbstract:
One dimensional carbon nanotubes (CNTs) and two-dimensional layered materials like graphene, MoS2, hexagonal boron nitride (hBN), etc. with different electrical and mechanical properties are great candidates for many applications in the future. In this study the synthesis and growth of carbon nanotubes on both conducting graphene and graphite substrates as well as insulating hBN substrate with precise crystallographic orientation is achieved. We show that the nanotubes have a clear preference to align to specific crystal directions of the underlying graphene or hBN substrate. On thicker flakes of graphite, the edges of these 2D materials can control the orientation of these carbon nanotubes. This integrated aligned growth of materials with similar lattices provides a promising route to achieving intricate nanoscale electrical circuits. Furthermore, short channel nanoscale devices consisting of the heterostructure of 1D and 2D materials are fabricated. In these nanoscale devices the nanogap is created due to etching of few layer graphene flake through hydrogenation and the channel is either carbon nanotubes or 2D materials like graphene and MoS2. Finally the transport properties of these nanoscale devices is studied.
5
Chen, Zhesheng. "Novel two dimensional material devices : from fabrication to photo-detection." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066595/document.
Full textAbstract:
Au delà du graphène, de nouveaux semiconducteurs 2D tels que MoS2, GaS, GaSe et InSe deviennent pertinents pour les applications et dispositifs émergents. Dans cette thèse, nous fabriquons des échantillons de quelques feuillets atomiques de ces matériaux pour des dispositifs de photo-détecteurs et les caractérisons par microscopie optique, AFM et TEM. L'interaction de la lumière avec le substrat et le dispositif ultra-mince étant critique pour son fonctionnement, nous calculons et mesurons le contraste et l'intensité de la lumière diffusée par le dispositif. Nous caractérisons également la réponse Raman et la photoluminescence en fonction du nombre de couches pour étudier les propriétés vibrationnelles et électroniques. Plusieurs dispositifs ont été fabriqués et analysés. Nous examinons d'abord les dispositifs homogènes basés sur MoS2, GaSe ou InSe, et trouvons une excellente photosensibilité pour notre photo-détecteur MoS2. Nous examinons ensuite plusieurs hétéro-structures pour combiner les propriétés de chaque matériau et atteindre de meilleures performances. Le premier exemple est un photo-détecteur graphène/InSe dont la photosensibilité augmente de quatre ordres de grandeur par rapport à un dispositif basés sur InSe seul. Nous montrons également que la couche supérieure de graphène prévient la dégradation de couches atomiques ultra-minces dans l'air. Des hétéro-structures plus complexes graphène/InSe/graphène et graphène/InSe/Au montrent un effet photovoltaïque. Enfin, nous combinons InSe avec MoS2 et obtenons un dispositifs avec photo-réponse rapide, un comportement de type photo-diode, une distribution de photo-courant uniforme et un fort effet photovoltaïqueNovel two dimensional (2D) semiconductors beyond graphene such as MoS2, GaS, GaSe and InSe are increasingly relevant for emergent applications and devices. In this thesis, we fabricate these 2D samples for photo-detector applications and characterize them with optical microscopy, atomic force microscopy, Raman and photoluminescence (PL) spectroscopy and transmission electron microscopy. Since the interaction of light with the substrate and the ultra-thin photodetector device is critical for its functioning we calculate and measure optical contrast and intensity of light scattered from the device. We also characterize the Raman and PL response as a function of number of layers to study both vibrational properties and the band gap transition. For the device application, we first examine homogenous devices based on few-layer MoS2, GaSe and InSe respectively and find an excellent photoresponsivity in our few-layer MoS2 photo-detector. We then examine several geometries for heterostructure devices, which have the advantage of combining favorable properties of each material to reach better performances. The first example is a graphene/InSe photo-detector where the photoresponsivity increases by four orders of magnitude with respect to a few-layer InSe device while the top graphene layer is also shown to prevent degradation of ultra-thin atomic layers in air. Still more complex graphene/InSe/graphene and graphene/InSe/Au heterostructures show a photovoltaic effect. Finally for the first time, we combine InSe with MoS2 and obtain a high performance device with fast photo-response, photodiode like behavior, uniform photocurrent distribution and high photovoltaic effect
6
Mosconi, Dario. "Crashing flatland: defective and hybrid 2D-materials for (Electro) catalysis." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3426844.
Full textAbstract:
This Ph.D. project is aimed to discover new strategies to develop materials to utilize in the fields of Green Energy and Green Chemistry and it was directed at the application of 2D Materials in particular. This thesis is divided into five main chapters where we presented five exemplary systems in which we focused our attention on different aspects of materials design. Each chapter comprises an introduction and a conclusion section, in which we tried to go into the details of each targeted application and of the specific design strategy employed. However, at the beginning and at the end of the thesis, the reader can find an Introduction and a Conclusion section where we tried to collocate the goals and challenges of this work within a broader context of materials science and catalysis/electrocatalysis.
In our studies in the Green Energy area, we focused on the use of MoS2-based materials in water splitting cathodic half-reaction in order to obtain the best possible performance in hydrogen generation in different conditions. To do that, different strategies were developed to drive the original material to adapt to specific application. In detail, in Chapter Two we investigated the design of three-dimensional MoS2 structures doped with different amount of Ni in order to activate MoS2 for the Hydrogen Evolution Reaction (HER) performed in alkaline environment, which typically hinder this reaction. We carried out an extensive structural characterization in order to establish the role of each type of active sites formed on the material in the HER activity and kinetics. In Chapter Three, we developed an electrodeposition method for preparing amorphous MoS2/Ag2S hybrid using recycled DVD as the support; this revealed as a viable opportunity to turn an abundant waste into an added-value material. After a suitable investigation to understand what kind of material was formed upon electrodeposition, MoS2/Ag2S/DVD was tested for HER in acidic medium. In Chapter Four another kind of hybrid was prepared by designing a one-pot solvothermal synthesis of MoS2(1-x)Se2x nanosheets grown on N-doped reduced Graphene Oxide (N-rGO). The goal was the control of the optoelectronic properties of the final material, since the combination of MoS2(1-x)Se2x and N-rGO allows to form p-n nanojunctions, which induce an enhancement of HER activity upon illumination with visible light. Then we used different techniques to prove what was the best Se:S ratio to optimize both the absolute performances in HER and the enhancement upon light irradiation.
Regarding Green Chemistry area, we used Graphene Acid (GA) as starting material and we exploited its uniform surface functionalization to prepare materials for heterogeneous catalysis for different reactions, comparing them with the benchmark Graphene Oxide (GO), modified with the same protocol. In Chapter Five, we synthesized a heterogeneous catalyst by covalently grafting Ferrocene (Fc) moieties to –COOH surface groups of GA and GO. The resulting Fc-modified graphene derivatives have been tested as heterogeneous catalysts for the C-H insertion of aryl diazonium salts into several arene substrates. The tests revealed a strong influence of the support, which we could attribute the intrinsic properties of GA. In Chapter Six, we have grown Pd nanoparticles on GA to prepare a catalyst for Suzuki-Miyaura cross coupling reaction. We have studied the effect of surface functionalization on the nanoparticles formation process and on the derived capability on the controlling the size distribution. The catalysts were tested in Suzuki cross coupling in green conditions and we could highlight the influence of nanoparticles size on activity. Moreover, we studied the same catalysts also for boronic acid homocoupling reaction, that can provide similar final products, but in a more atom economically way.Questo progetto di dottorato è mirato alla scoperta di nuove strategie per lo sviluppo di materiali da utilizzare nei campi della Green Energy e della Green Chemistry ed è rivolto all’applicazione dei materiali 2D in particolare. Questa tesi è divisa in cinque capitoli principali dove presentiamo cinque sistemi esemplificativi in cui ci siamo focalizzati su diversi aspetti del design del materiale. Ogni capitolo comprende una sezione di introduzione e una di conclusione, in cui abbiamo provato ad andare nel dettaglio di ogni applicazione e della specifica strategia di design utilizzata. In ogni caso, all’inizio e alla fine della tesi, il lettore può trovare una sezione di Introduzione e una di Conclusione dove abbiamo provato a collocare gli obbiettivi e le sfide di questo lavoro in un contesto più ampio della scienza dei materiali e della catalisi/elettrocatalisi. Nei nostri studi nell’area della Green Energy, ci siamo focalizzati sull’utilizzo di materiali a base MoS2 per la riduzione dell’acqua così da ottenere le migliori performance possibile nella generazione di idrogeno in diverse condizioni. Abbiamo sviluppato diverse strategie per indurre il materiale originale ad adattarsi alla specifica applicazione. Nel Capitolo Due abbiamo investigato il design di strutture 3D di MoS2 drogato con diverse quantità di Ni, con lo scopo di attivare il MoS2 per Hydrogen Evolution Reaction (HER) in ambiente alcalino, che di solito ostacola la reazione. Abbiamo eseguito un’estensiva analisi strutturale per stabilire il ruolo di ogni tipo di sito attivo formato sul materiale nell’attività e nella cinetica della HER. Nel Capitolo Tre, abbiamo sviluppato un metodo di elettrodeposizione per preparare un ibrido MoS2/Ag2S amorfo usando DVD riciclati come supporto, rivelandosi un’ottima strada per ridare valore a un materiale di scarto. Dopo un’adeguata analisi per capire il tipo di materiale formato, MoS2/Ag2S/DVD è stato testato per la HER in ambiente acido. Nel Capitolo Quattro abbiamo preparato un ibrido ottimizzando una sintesi solvotermale di nanofogli di MoS2(1-x)Se2x su Grafene Ossido ridotto drogato-N (N-rGO). L’obiettivo era il controllo delle proprietà optoelettroniche del materiale, dato che la combinazione di MoS2(1-x)Se2x e N-rGO permette di formare nanogiunzione p-n, che inducono un aumento dell’attività HER sotto illuminazione. Abbiamo utilizzato differenti tecniche per provare quale fosse il miglior rapporto Se:S per ottimizzare sia la performance assoluta in HER sia l’incremento dovuto all’irradiamento. Riguardo all’area della Green Chemistry, abbiamo utilizzato il Grafene Acido (GA) come materiale di partenza e abbiamo sfruttato la sua funzionalizzazione superficiale uniforme per preparare materiali per catalisi eterogenea di diverse reazioni, comparandoli con il riferimento Grafene Ossido (GO), modificato con la stessa procedura. Nel Capitolo Cinque, abbiamo sintetizzato un catalizzatore eterogeneo attaccando unità di Ferrocene (Fc) a GA e GO. I risultanti derivati grafenici modificati con Fc sono stati testati come catalizzatori eterogenei per l’inserimento di sali di diazonio aromatici in substrati arenici. I test hanno rivelato una forte incidenza del supporto, attribuibile alle proprietà intrinseche del GA. Nel Capitolo Sei, abbiamo cresciuto nanoparticelle di Pd sul GA per preparare un catalizzatore per la reazione di cross coupling Suzuki-Miyaura. Abbiamo studiato gli effetti della chimica superficiale sul processo di formazione delle nanoparticelle e sulla conseguente capacità di controllare la taglia. I catalizzatori sono stati testati nella Suzuki-Miyaura in condizioni green e abbiamo potuto evidenziare l’influenza della taglia delle nanoparticelle sull’attività. In aggiunta, abbiamo studiato gli stessi catalizzatori anche per la reazione di homocoupling di acidi boronici, la quale può fornire simili prodotti finali, ma con un migliore economia atomica.
7
Curcella, Alberto. "Looking for silicene: studies of silicon deposition on metallic and semiconductor substrates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9314/.
Full textAbstract:
Nel presente lavoro espongo i risultati degli esperimenti svolti durante la mia internship all’Institut des NanoSciences de Paris (INSP), presso l’Università Pierre et Marie Curie (Paris VI), nel team "Phisico-Chimie et Dynamique des Surfaces", sotto la supervisione del Dott. Geoffroy Prévot. L’elaborato è stato redatto e in- tegrato sotto la guida del Dott. Pasquini, del dipartimento di Fisica e Astronomia dell’Università di Bologna. La tesi s’inserisce nel campo di ricerca del silicene, i.e. l’allotropo bidimensionale del silicio. Il cosidetto free-standing silicene è stato predetto teoricamente nel 2009 utilizzando calcoli di Density Functional Theory, e da allora ha stimolato un’intensa ricerca per la sua realizzazione sperimentale. La sua struttura elettronica lo rende particolarmente adatto per eventuali appli- cazioni tecnologiche e sperimentali, mentre lo studio delle sue proprietà è di grande interesse per la scienza di base.
Nel capitolo 1 presento innanzitutto la struttura del silicene e le proprietà previste dagli studi pubblicati nella letteratura scientifica. In seguito espongo alcuni dei risultati sperimentali ottenuti negli ultimi anni, in quanto utili per un paragone con i risultati ottenuti durante l’internship.
Nel capitolo 2 presento le tecniche sperimentali che ho utilizzato per effettuare le misure. Molto tempo è stato investito per ottenere una certa dimistichezza con gli apparati in modo da svolgere gli esperimenti in maniera autonoma.
Il capitolo 3 è dedicato alla discussione e analisi dei risultati delle misure, che sono presentati in relazione ad alcune considerazioni esposte nel primo capitolo.
Infine le conclusioni riassumono brevemente quanto ottenuto dall’analisi dati. A partire da queste considerazioni propongo alcuni esperimenti che potrebbero ulteriormente contribuire alla ricerca del silicene. I risultati ottenuti su Ag(111) sono contenuti in un articolo accettato da Physical Review B.
8
Stoyanov, Pantcho. "Micro-tribological performance of metal-doped MoS2 coatings." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103709.
Full textAbstract:
The mechanical and tribological properties of pure MoS2, pure Au, Au-MoS2 and Ti-MoS2 coatings were evaluated and examined at a microscopic scale. The metal doped MoS2 coatings had varying metal content, 5-10at% for Ti and 10-90% for Au. Reciprocating sliding wear tests were performed with a range of initial Hertzian contact pressures from 0.41 to 3.5 GPa and in air at two humidity levels (i.e. "low" being 3-5%RH and "high" being 30-40%RH). Titanium and gold were chosen for this study as metal additives due to their positive influence on the mechanical properties of the coating. The friction and wear behavior at the micro-scale were directly compared to tribological properties at the macro-scale, which were performed using an in situ tribometer. Reciprocating micro- and macro- wear tests were performed with spherical diamond tip (with 10 and 50 µm radii) and a sapphire tip (with a radius of 3.175 mm), respectively. The range of initial Hertzian contact pressures for macro-scale (i.e. between 0.41GPa and 1.2GPa) overlapped with that for micro-scale. However, the initial Hertzian contact diameters (2*a) were very different (i.e. 0.8-2.3 µm for micro-scale and 60-180 µm for macro-scale). It was observed that the small addition of Ti or Au to MoS2 improved the microtribological properties (i.e. lower friction and less wear) compared to pure MoS2 coatings. The improved microtribological properties with metal additions were attributed to an increase in the mechanical properties, decrease in adhesion, and a decrease in the interfacial shear strength. In terms of the different length scales, lower steady state friction was observed for macrotribology compared to microtribology. The higher friction at the micro-scale was explained by the greater adhesion effects and additional velocity accommodation modes (e.g. microplowing or plowing). The microplowing or plowing at the microscopic scale was attributed to the tip roughness and the inability to sustain a stable transfer film throughout the tests at high humidity. In addition, using in situ and ex situ techniques, three different stages for solid lubrication were identified based on differences in contact area, tip shapes, and environmental conditions. The first stage has been previously observed with macrotribology on MoS2 coatings at low humidity levels. The second stage, on the other hand, was observed for micro-tribology where the contact size is significantly smaller compared to stage one. The main wear mechanism is still adhesion, but there is also some micro-plowing. The final stage was observed for humid sliding in microtribology, where no transfer films were observed and therefore the main wear mechanism was plowing.Les propriétés mécaniques et tribologiques de revêtements de MoS2 pur, d'Au pur, de Au-MoS2 et de Ti-MoS2 ont été évaluées et examinées à l'échelle microscopique. Les revêtements nanocomposites étudiés contenaient 5-10 % at. de Ti et 10-90 % at. d'Au. Des tests d'usure par glissement alternatif ont été mis en œuvre, l'échelle de pression Hertzienne de contact initiale variant de 0.41 à 3.5 GPa, dans une atmosphère d'air avec deux niveaux d'humidité contrôlée (le niveau le moins élevé se situant entre 3 et 5 % HR et le plus élevé entre 30 et 40 % HR). Pour cette étude, le titane et l'or ont été choisis comme additifs métalliques pour leur influence positive sur les propriétés mécaniques des revêtements. Les comportements de friction et d'usure des revêtements à l'échelle microscopique ont été directement comparés à leurs propriétés tribologiques à l'échelle macroscopique, dont les tests étaient effectués à l'aide d'un tribomètre in situ. Des tests sclérométriques alternatifs ont été réalisés aux échelles microscopiques et macroscopiques avec des pointes de diamant sphérique (10 et 50 µm de rayon) et une pointe de saphir (ayant un rayon de 3.175 mm). La gamme de pression Hertzienne de contact utilisée à l'échelle microscopique (entre 0.41 GPa et 1.2 GPa) était très proche de celle utilisée à l'échelle macroscopique. Cependant, le diamètre de contact Hertzien initial (2*a) était très différent, soit 0.8 – 2.3 µm à l'échelle microscopique et 60 – 180 µm à l'échelle macroscopique. Les résultats montrent que l'ajout de faibles quantités de Ti ou d'Au au MoS2 améliore les propriétés micro-tribologiques (comportements à la friction et à l'usure atténués) en comparaison avec des revêtements de MoS2 pur. L'amélioration des propriétés micro-tribologiques due à l'addition de métaux a été attribuée au renforcement des propriétés mécaniques, une adhésion plus faible et une baisse des contraintes de cisaillement interfaciales. Si l'on compare des tests micro- et macro-tribologiques effectués sur des étendues de longueur variées, ces derniers étaient caractérisés par une friction en régime permanent moins élevée. Le comportement de friction plus accentué dans le cas des tests réalisés à l'échelle microscopique s'explique sur la base d'effets d'adhésion plus importants et des modes additionnels de compensation de vitesse (labourage ou micro-labourage). Les tendances au labourage ou micro-labourage observées à l'échelle microscopique ont été attribuées à la rugosité de la pointe de diamant et à la difficulté de maintenir une couche de film de transfert en place lors de tests effectués dans des conditions d'humidité élevée. L'utilisation de techniques in situ et ex situ a également permis de déterminer trois stades de lubrification solide, en se basant sur des différences observées à la zone de contact, dues aux formes des différentes pointes et aux conditions environnementales appliquées. Le premier stade, avait été identifié auparavant, lors de tests de macro-tribologie sur des revêtements de MoS2, à un niveau d'humidité faible. Par contre, le deuxième stade n'a été observé que lors de tests de micro-tribologie où la taille de la zone de contact était bien plus petite que dans le cas du premier stade. A ce stade, le mécanisme d'usure est principalement relié au comportement d'adhésion du revêtement, avec une influence possible de l'effet de micro-labourage. Le stade final de lubrification a été observé lors de tests de micro-tribologie réalisés dans des conditions d'humidité élevée et caractérisés par l'absence du film de transfert. De cette observation, il a été déduit que le principal mécanisme d'usure du film à ce stade de lubrification correspondait au labourage.
9
Thorat, Ruhi P. "Opto-Electronic Properties of Self-Contacted MoS2 Monolayer Devices." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1512731597427663.
Full text
10
Furlan, Kaline Pagnan. "Desenvolvimento de compósito autolubrificante de matriz ferrosa contendo MoS2." reponame:Repositório Institucional da UFSC, 2016. https://repositorio.ufsc.br/xmlui/handle/123456789/169081.
Full textAbstract:
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2016.Made available in DSpace on 2016-10-11T04:03:50Z (GMT). No. of bitstreams: 1 342186.pdf: 10392257 bytes, checksum: 8c1c5b44f4e3bee87886782ff84656eb (MD5) Previous issue date: 2016
Esta tese visou o desenvolvimento de um material autolubrificante volumétrico de matriz ferrosa contendo MoS2 como elemento lubrificante majoritário. Estudos demonstram a dificuldade em se produzir este tipo de compósito, devido a reação do MoS2 com a matriz ferrosa durante a sinterização. Desta forma, a pesquisa desenvolvida nesta tese buscou soluções para evitar ou reduzir esta reação, avaliando a influência de parâmetros da matéria-prima da matriz e da fase lubrificante (tamanho de partícula, adição de outros elementos e teor de lubrificantes), bem como parâmetros de processamento (taxa de aquecimento, temperatura, formação de fase líquida, tempo de patamar e atmosfera de sinterização). Os resultados mostraram que a temperatura influiu de forma preponderante na reação, mas não a taxa de aquecimento e que o uso de um pó de Fe de menor tamanho de partícula acelera-a; o melhor desempenho está associado ao MoS2 de maior tamanho de partícula (d50=32µm) e 9% em volume é o teor limite; a adição de grafite ou h-BN retarda a reação, porém apenas compósitos com MoS2+grafite apresentaram coeficiente de atrito abaixo de 0,2 associado a um baixo desgaste. A adição de elementos de liga modificou a forma como o MoS2 reagiu com a matriz ferrosa e o desempenho tribológico do compósito, sendo que alguns apresentaram resultados similares ao Fe puro (Ni misturado e P pré-misturado), outros possuem caráter deletério (Cr e Mo misturados e Mo pré-ligado) e alguns apresentaram caráter benéfico (C e P misturados e Cr pré-ligado). É viável sinterização de amostras em temperaturas entre 800 e 850 °C, porém as abordagens visando a intensificação da densificação e propriedades mecânicas não foram bem sucedidas. Através da definição e controle da matéria prima inicial (nomeadamente tamanho de partícula da matriz e do MoS2), composição do compósito e parâmetros de processamento (temperatura, tempo e atmosfera de sinterização) foi possível a produção de materiais autolubrificantes de matriz ferrosa contendo MoS2 como elemento lubrificante majoritário que apresentam baixo coeficiente de atrito a seco (0,06-0,08) associado a uma baixa taxa de desgaste (2,0-3,5 x 10-6 mm³.N-1.m-1).
Abstract : This thesis aimed the development of a self-lubricating composite containing MoS2 dispersed in an iron matrix produced by powder metallurgy. Previous studies demonstrate that MoS2 reacts with iron matrices during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore the research developed within this thesis focused on the possible solutions to avoid or reduce this reaction, evaluating the influence of raw material (particle size, amount and type of lubricants) and processing (heating rate, temperature, dwell time, liquid phase formation and atmosphere) parameters. The results have shown that temperature has a major influence on the reaction, but not the heating rate; the use of a small Fe particle size accelerates the reaction; better performance was achieved by using the d50=32µm MoS2 and 9% in volume is the limit amount; the addition of graphite or h-BN slows the reaction, but only MoS2+graphite composites presents friction coefficient below 0,2 associated with low wear rate. The addition of alloying elements modified how MoS2 interacts with the iron matrix and the composite friction coefficient, some of which had a beneficial effect (admixed C and P, and pre-alloyed Cr alloy), while others (admixed Cr and Mo, and pre-alloyed Mo alloy) are harmful. It is possible to produce iron samples by low temperature sintering (800-850 °C), however the approaches to improve densification and mechanical properties were not successful. By means of defining and adequate control of the raw material (namely particle size of matrix and lubricants), composition and processing parameters (sintering temperature, time and atmosphere) it was possible to produce self-lubricating iron based composites containing MoS2, which presented low dry friction coefficient (0,06-0,08) and low wear rate (2,0-3,5 x 10-6 mm³.N-1.m-1).
11
Huang, Puxi. "Hygrothermal performance of Moso bamboo-based building material." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715306.
Full textAbstract:
This study focuses on the hygrothermal performance of Moso bamboo. The knowledge in this aspect is remarkable important for the research of building energy saving and the low carbon building design. However, the detailed hygrothermal properties of Moso bamboo are fairly rare. To obtain these data, a series of experimental works have been done for measurement of density, porosity, thermal conductivity, specific heat capacity, water vapour permeability, hygrothermal expansion and sorption isotherm of Moso bamboo. To obtain further understanding on the hygrothermal performance of Moso bamboo, a number of dynamic heat and moisture transfer experiments were conducted. These experiments simulated two extreme outdoor environments and one indoor environment. The temperature and RH responses of Moso bamboo panels were monitored. Then a coupled transient heat and moisture transfer numerical simulation at the material level was conducted to predict and validate the hygrothermal performance of Moso bamboo. A sensitivity study of the hygrothermal properties of bamboo was also presented to indentify the influence of each hygrothermal property of Moso bamboo. Major findings include the following aspects. Both experiment and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters. The parametric study found that density can be regarded as the most sensible parameter to influence the temperature simulation results at the transient state, while the thermal conductivity dominated the temperature variation at the steady state. The water vapour diffusion resistance factor can be regarded as the most critical parameter to influence the RH simulation results. The influence of liquid water diffusivity is negligible in this study. The parametric study results indicated that the simulation with moisture is more accurate than the simulation without moisture in both equilibrium and transient state. The results also imply that the existence of moisture could increase the heat capacity and reduce the thermal conductivity. The results of this study recommend that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part of the bamboo culm wall is suitable to increase the thermal insulation performance of the panel. To avoid hygroexpansion, the implementation of external part of bamboo culm wall needs to be minimised.
12
Blumer, Ari Nathan. "Few-layer MoS2 Flakes and Carbon Quantum Dots as Supercapacitor Electrode Materials." Ohio University Honors Tutorial College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1524839175902206.
Full text
13
Lindquist, Miles T. "Investigation of growth parameters for as-grown 2D materials- based devices." Ohio University Honors Tutorial College / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1492781232538674.
Full text
14
Jyah, Strachan. "On Molybdenum Sulfides and Other Active Materials for Sustainable Energy Systems." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/25375.
Full textAbstract:
To respond to the approaching climate crisis, the current energy landscape must shift towards sustainable, decarbonised systems. This shift will require the development of inexpensive and active energy conversion materials. The work within this thesis reports the investigation of several candidate materials, i.e. molybdenum sulfides and carbides, for use as catalysts and electrodes in energy conversion processes. These materials were chosen for their natural abundance, controllable morphologies, and varied chemistries.
Chapter 1 focuses on the scope and potential of Chevrel phases (MxMo6S8) as catalytic materials. It includes both a critical literature review and original research on nanoparticulate catalysts that exhibited excellent performance for the hydrogen evolution reaction.
Chapter 2 focuses on the various morphologies of MoS2 and incorporates two reviews: the first review summarises all known reports of 3R-MoS2 and clarifies inconsistencies with the literature. The second review rectifies the errors in the literature on hydrothermally produced 1T-MoS2 and provides best practice analysis instructions. The final section of Chapter 2 is an investigation into the effect of crystal disorder on the electrochemical performance of MoS2 in hybrid batteries in order to aid the optimisation of MoS2 electrodes.
Chapter 3 is comprised of a study that elucidates the structure of a highly active lignin valorisation catalyst, Mo2CxNx-1/TiN. The analyses show that the titanium nitride and molybdenum carbide phases are intimately mixed and that the catalyst incorporates terminal Mo≡N motifs.
Chapter 4 includes studies on the silver catalysed reduction of 4-nitrophenol; a ubiquitous model reaction. A detailed kinetic analysis of the reaction mechanism elucidates the role of oxygen during the induction period of the reaction. The research-level chemistry and protocols were then adapted to be used as a pedagogical tool.
15
Sirota, Benjamin. "Investigation into the Semiconducting and Device Properties of MoTe2 and MoS2 Ultra-Thin 2D Materials." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157626/.
Full textAbstract:
The push for electronic devices on smaller and smaller scales has driven research in the direction of transition metal dichalcogenides (TMD) as new ultra-thin semiconducting materials. These ‘two-dimensional' (2D) materials are typically on the order of a few nanometers in thickness with a minimum all the way down to monolayer. These materials have several layer-dependent properties such as a transition to direct band gap at single-layer. In addition, their lack of dangling bonding and remarkable response to electric fields makes them promising candidates for future electronic devices. For the purposes of this work, two 2D TMDs were studied, MoS2 and MoTe2. This dissertation comprises of three sections, which report on exploration of charge lifetimes, investigation environmental stability at elevated temperatures in air, and establishing feasibility of UV laser annealing for large area processing of 2D TMDs, providing a necessary knowledge needed for practical use of these 2D TMDs in optoelectronic and electronic devices.
(1) A study investigating the layer-dependence on the lifetime of photo-generated electrons in exfoliated 2D MoTe2 was performed. The photo-generated lifetimes of excited electrons were found to be strongly surface dependent, implying recombination events are dominated by Shockley-Read-Hall effects (SRH). Given this, the measured lifetime was shown to increase with the thickness of exfoliated MoTe¬2; in agreement with SRH recombination. Lifetimes were also measured with an applied potential bias and demonstrated to exhibit a unique voltage dependence. Shockley-Read-Hall recombination effects, driven by surface states were attributed to this result. The applied electric field was also shown to control the surface recombination velocity, which lead to an unexpected rise and fall of measured lifetimes as the potential bias was increased from 0 to 0.5 volts.
(2) An investigation into the environmental stability of exfoliated 2D MoTe2 was conducted using a passivation layer of amorphous boron nitride as a capping layer for back-gated MoTe2 field effect transistor (FET) devices. A systematic approach was taken to understand the effects of heat treatment in air on the performance of FET devices. Atmospheric oxygen was shown to negatively affect uncoated MoTe2 devices while BN-covered FETs showed remarkable chemical and electronic characteristic stability. Uncapped MoTe2 FET devices, which were heated in air for one minute, showed a polarity switch from n- to p-type at 150 °C, while BN-MoTe2 devices switched only after 200 °C of heat treatment. Time-dependent experiments at 100 °C showed that uncapped MoTe2 samples exhibited the polarity switch after 15 min of heat treatment while the BN-capped device maintained its n-type conductivity. X-ray photoelectron spectroscopy (XPS) analysis suggests that oxygen incorporation into MoTe2 was the primary doping mechanism for the polarity switch.
(3) The feasibility of UV laser annealing as a post-process technique to sinter 2D crystal structures from sputtered amorphous MoS2 was explored. Highly crystalline materials are sought after for their use in electron and opto-electronic devices. Sputtered MoS2 has the advantage of potential for large area deposition and high scalability, however, it requires high temperatures (>350 °C) for their crystalline growth. Which creates difficulty for devices grown on polymer substrates. Low-temperature and room temperature deposition results in amorphous films which is detrimental for electric devices. A one-step lase annealing procedure was developed to provide amorphous to crystalline conversion of nanometer thin MoS2 films. Samples were annealed using an unfocused laser beam from a KrF (248 nm) excimer source. The power density was found to be 1.04 mJ/mm2. Raman analysis of laser annealed MoS2 was shown to exhibit a significant improvement of the 2D MoS2 crystallinity compared to as-deposited films on both SiO2/Si, as well as polydimethylsiloxane (PDMS) substrates. Annealed samples showed improvement of their conductivity on an order of magnitude. A top-gated FET device was fabricated on flexible PDMS substrates using Al2O3 as a gate oxide. Measured field effect mobility of annealed samples showed significant improvement over as-deposited devices.
16
Kuba, Jakub. "Studium fotoluminiscence tenkých vrstev MoS2." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254284.
Full textAbstract:
The thesis deals with study of thin layers of transition metal dichalcogenides, especially of molybdenum disulfide. Nanostructures were fabricated on two-dimensional crystals of MoS2 and WSe2. Within followed analysis attention was paid to the photoluminescence properties. In the thesis transition metal dichalcogenides are reviewed and description of the modified process of preparation by micromechanical exfoliation is given.
17
Bizhani, Maryam. "Thermal Annealing Effects on 2D Materials." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575627966654889.
Full text
18
Brent, John. "Exfoliation and synthesis of two-dimensional semiconductor nanomaterials." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/exfoliation-and-synthesis-of-twodimensional-semiconductor-nanomaterials(289ba930-19ff-4fae-8d84-e46560620c18).html.
Full textAbstract:
2-Dimensional (2D) materials are characterised by atomic thickness and significantly larger edge-lengths, producing particles which are highly confined in 1 direction. Reducing a material to one or few atomic layers gives rise to structural and electronic properties that deviate significantly from those of the bulk crystal. For this reason 2D nanosheets have been investigated for potential application in sensing, catalysis, capacitance, photovoltaics and for flexible circuits (among others).Despite rapid progress in understanding the synthesis and properties of 2D nanosheets in recent years, there remain significant problems surrounding the development of scalable production methods, understanding and tuning fundamental properties, and controlling the size and monodispersity of semiconductor crystals. In addition, new materials with novel properties are constantly sought in order to meet specific requirements. Although the tools developed over the last 12 years can often be applied to the fabrication of these materials, understanding their behaviour and limitations is ongoing. The following thesis discusses the routes to the fabrication of 2-dimensional materials and explores the production of MoS2, black phosphorus and tin(II) sulfide nanosheets. The aim of each piece of work is determined by the level of development of the field; MoS2 nanosheets have been known for several years and therefore the work presented was motivated by a desire to impart size control for specific applications. The study of phosphorene and 2D tin(II) sulfide is in its infancy; as such the focus remains on scalable nanosheet exfoliation and developing an understanding of their properties. The following studies on phosphorene report the exfoliation of nanosheets in organic and aqueous surfactant solutions and an investigation of the stability and breakdown products of the resulting colloidal suspensions. The stabilisation of phosphorene in aqueous media paves the way for its use in biological systems. Band-gap tuning in IV-VI analogues of phosphorene is demonstrated by size-selection of exfoliated SnS nanosheets. Although the physical characteristics of nanosheets and their incorporation into devices receive some attention, this thesis will focus mainly on the synthetic aspects of 2D materials research.
19
Furlan, Kaline Pagnan. "Estudo da sinterização e evolução microestrutural de misturas de Fe-MoS2." reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/handle/123456789/106883.
Full textAbstract:
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2013Made available in DSpace on 2013-12-05T22:38:40Z (GMT). No. of bitstreams: 1 319276.pdf: 3826214 bytes, checksum: fae2266a33be0465ab0f95e7a05cec4f (MD5) Previous issue date: 2013
20
Tsai, I.-Ling. "Magnetic properties of two-dimensional materials : graphene, its derivatives and molybdenum disulfide." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/magnetic-properties-of-twodimensional-materials-graphene-its-derivatives-and-molybdenum-disulfide(59dcba1b-332e-4a58-86f6-80ed56c7fdd1).html.
Full textAbstract:
Graphene, an atomically thin material consisting of a hexagonal, highly packed carbon lattice, is of great interests in its magnetic properties. These interests can be categorized in several fields: graphene-based magnetic materials and their applications, large diamagnetism of graphene, and the heterostructures of graphene and other two dimensional materials. In the first aspect, magnetic moments can be in theory introduced to graphene by minimizing its size or introducing structural defects, leading to a very light magnetic material. Furthermore, weak spin-orbital interaction, and long spin relaxation length make graphene promising for spintronics. The first part of this thesis addressed our experimental investigation in defect-induced magnetism of graphene. Non-interacted spins of graphene have been observed by intentionally introducing vacancies and adatoms through ion-irradiation and fluorination, respectively. The defect concentration or the magnetic moments introduced in this thesis cannot provide enough interaction for magnetic coupling. Furthermore, the spins induced by vacancies and adatoms can be controlled through shifting the Fermi energy of graphene using molecular doping, where the adatoms were alternatively introduced by annealing in the inert environment. The paramagnetic responses in graphene induced by vacancy-type defects can only be diverted to half of its maximum, while those induced by sp3 defects can be almost completely suppressed. This difference is supposed that vacancy-type defects induced two localized states (pie and sigma). Only the latter states, which is also the only states induced by sp3 defects, involves in the suppression of magnetic moments at the maximum doping achieved in this thesis. The observation through high resolution transmission electron microscope (HR-TEM) provides more information to the hypothesis of the previous magnetic findings. Reconstructed single vacancy is the majority of defects discovered in proton-irradiated graphene. This result verifies the defect-induced magnetic findings in our results, as well as the electronic properties of defected graphene in the literatures. On the other hand, the diamagnetic susceptibility of neutral graphene is suggested to be larger than that of graphite, and vanish rapidly as a delta-like function when graphene is doped. In our result, surprisingly, the diamagnetic susceptibility varies little when the Fermi level is less than 0.3 eV, in contrast with the theory. When the Fermi energy is higher than 0.3 eV, susceptibility then reduces significantly as the trend of graphite. The little variation in susceptibility near the Dirac point is probably attributed to the spatial confinement of graphene nanoflakes, which are the composition of graphene laminates. In the end of this thesis, we discuss the magnetic properties in one of the other two dimensional materials, molybdenum disulfide (MoS2). It is a potential material for graphene-based heterostructure applications. The magnetic moments in MoS2 are shown to be induced by either edges or vacancies, which are introduced by sonication or proton-irradiation, respectively, similar to the suggestions by theories. However, no significant ferromagnetic finding has been found in all of our cases.
21
Samadzadeh, Seyed Mostafa. "Comparative studies of the oxidation of MoSi₂ based materials." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55050.
Full textAbstract:
Molybdenum disilicide (MoSi₂) is a promising intermetallic material for high temperature applications (above 1000°C). However, it rapidly oxidizes at temperatures ranging from 400 to 600°C, which given enough time, can lead to its disintegration. Above 1000°C, MoSi₂ exhibits better oxidation resistance due to the formation of a continuous SiO₂ layer (or alumina layer for the materials doped with aluminum). The experiments in this study were divided into two main categories: low temperature oxidation (300 to 900°C; high oxidation rate expected) and high temperature oxidation (1000 to 1600°C; lower oxidation rate expected due to rapid formation of the protective oxide films). The isothermal exposure time in the low temperature oxidation experiments was from 4 to 240 hrs while it was from 2 to 144 hrs for the high temperature oxidation experiments. Five different, commercially available, MoSi₂ based heating elements, i.e. Kanthal Super (labelled by the manufacturer as KS-1700, KS-1800, KS-1900, KS-ER and KS-HT) were used in the experiments. It was found that the oxidation behavior of different materials under investigation depended strongly on their chemical and phase composition, exposure time and temperature. KS-ER and KS-1800 showed excellent resistance against the low temperature (300 to 900°C) degradation for up to 240 hrs, while KS-HT and KS-1900 underwent significant degradation after 240 hrs of air exposure within the same temperature range. In high temperature oxidation experiments, a dense barrier alumina film (1.5 µm thick at 1000°C to 50 µm thick at 1500°C for up to 144 hrs) formed on KS-ER samples. A dense glassy SiO₂ film (3 µm thick at 1000°C to 50 µm thick at 1600°C for up to 144 hrs) formed on the other types of samples. The glass scale on the surface of KS-1700, KS-1800 and KS-HT was significantly thicker (~3 times) than that on KS-HT over the temperature range of 1200°C to 1600°C after 144 hrs. The rate of alumina formation of KS-ER was relatively higher than the glass film formation of the other types of composite MoSi₂ materials. The differences in the oxidation behavior of various MoSi₂-based materials were linked to their chemistry and phase compositions.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
22
Hudson, David Christopher. "Two dimensional atomically thin materials and hybrid superconducting devices." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/16034.
Full textAbstract:
In this thesis a variety of topics concerning 2D materials that have been separated from bulk layered crystals are discussed. Throughout the thesis, single and few layers of graphene, fluorinated graphene, MoS2 and WS2 are used. Two new methods of freely suspending 2D materials are presented as well as a method of removing the background from optical images. This aids contrast measurements for the determination of the number of layers. Fluorinated graphene is found to be sensitive to beta radiation; the resistance of fluorinated graphene transistors is shown to decrease upon exposure to the radiation. This happens due to the carbon-fluorine bond breaking. The sp3 hybridised structure of the fluorinated graphene is reduced back into the sp2 hybridised structure of pristine graphene. The superconducting properties of molybdenum-rhenium are characterised. It is shown to have a transition temperature of 7.5 K. It is also discovered that the material has a resistance to hydrofluoric acid; the acid etches nearly all other superconducting materials. This makes MoRe a possible candidate to explore superconductivity in conjunction with high mobility suspended graphene. To see if the material is compatible with graphene, a supported Josephson junction is fabricated. A proximity induced super current is sustained through the junction up to biases of ∼ 200 nA. The temperature dependence of the conductivity is measured for both suspended MoS2 and WS2 on a hexagonal boron nitride substrate. The dominant hopping mechanism that contributes to the conductivity at low temperatures is found to be Mott variable range hopping, with the characteristic T−1/3 dependence. The hopping transport is due to impurities that are intrinsic to the crystals, this is confirmed by comparing the results with those of supported devices on SiO2.
23
Young, Justin R. "Synthesis and Characterization of Novel Two-Dimensional Materials." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468925594.
Full text
24
Zhang, Nan. "Propriétés électroniques de MoS2 / MoSe2van der Waals heterostructures." Thesis, Toulouse, INSA, 2020. http://www.theses.fr/2020ISAT0017.
Full textAbstract:
Le sujet de ma thèse concerne l’étude des propriétés optiques fon-damentales des dichalcogénures des métaux de transition (DCMT)des couches ultra-mince et plus précisément les hétérostuctures con-stituées de matériaux MX2(où M est du molybdène (Mo) et X dusoufre (S) ou du sélénium (Se)), liées entre elles par des interactionsde type Van der Waals. Le premier chapitre de la thèse a été con-sacré pour la description des propriétés fondamentales générales des(DCMT) exfolié et amincie jusqu’une monocouche. Egalement, leshétérostuctures à base des DCMT ont été largement décrites.Le chapitre 2 décrit les techniques expérimentales mises à dispo-sition pour servir mon projet de recherche soit en terme de mesuresou en terme de préparation des échantillons.Dans le chapitre 3, je présente l’effet de la photo-génération surles propriétés des exciton émis inter-couche. La photo-générationétant identifié à partir une augmentation de l’énergie de dissociationdes trions (via luminescence) accompagnée par un changement carac-téristique du rapport d’intensité de photoluminescence d’exciton etde trion dans le MoS2. Simultanément, j’ai observé une diminutionde l’intensité de PL de l’exciton généré inter-couche. Par contre lesignal PL composé des excitons et trions dans la couche de MoSe2aété amélioré montrant que le transfert de charges inter-couche peutêtre contrôlé en contrôlant le niveau de dopage. Cet effet observéest persistant sur une échelle de temps de plusieurs heures, tant quel’échantillon est maintenu sous vide. Ceci indique un mécanisme im-pliquant la désorption, induite par un laser, des molécules physisor-bées à la surface de l’hétérostructure. Je soutiens cette hypothèse endévoilant la sensibilité du taux de photo-génération sur la longueurd’onde d’excitation. Le processus de photo- génération se produitbeaucoup plus rapidement pour les photons ayant une énergie plusélevée.Dans le chapitre 4, je présente le résultat de l’impact du motifmoiré sur le spectre d’exciton inter-couche dans l’hétérostructureMoS2/ MoSe2. La formation du motif moiré est un phénomène car-actéristique des empilements de van der Waals où, en raison de lafaible interaction entre les couches chacune conservent ses propresparamètres de réseau. Par conséquent, en raison d’un petit anglede torsion ou d’une discordance de réseau entre les monocouches, unpotentiel variable dans l’espace périodique peut être induit. Ce po-tentiel peut avoir un impact non trivial sur les propriétés optiques desexcitons intra et inter-couche des hétérostructures de dichalcogénurede métaux de transition. Ici, je montre des preuves expérimentalesde l’impact du motif de moiré sur l’émission intra-couche dans unehétérostructure de MoSe2/ MoS2encapsulée avec du nitrure de borehexagonal (h-BN). Le potentiel périodique dans le plan se traduit par une clivage de spectre d’émission et ou d’absorption de l’excitonet du trion dans la couche de MoSe2. La différence d’énergie ob-servée entre les pics clivés est tout à fait conforme aux prévisionsthéoriques. De plus, ce chapitre contient une description détailléede la manière dont l’orientation relative des flocons dans une tellehétérostructure peut être révélée par la spectroscopie de générationdu deuxième harmonique.Le chapitre 5 contient les résultats des études préliminaires surl’impact de la qualité des échantillons et la possibilité de générerune polarisation de vallée via l’application d’un champ magnétique.Dans ces études, trois types de structures sont comparés, à savoirle MoSe2préparé par CVD et le MoSe2encapsulé par h-BN, ainsique l’hétérostructure MoSe2 / MoS2. De plus, j’ai trouvé que laformation d’un motif moiré a un impact négligeable sur le facteur gde Landé sur la transition excitonique intra-layerIn my thesis, I concluded results of my three years investigation of the optical properties of MoSe2/MoS2 transition metal dichalcogenides heterostructures. Thesis starts with the general overview of the properties of transition metal dichalcogenides monolayers and their heterostucers. This is followed by the detailed description experimental techniques which wear used to characterize photoresponse of heterostructures and their preparation. Next three paragraphs are devoted to the rustles of my investigations:In chapter 3 the impact of characteristic for transition metal dichalcogenides effect photodoping on the interlayer exciton emission properties is presented. The photodoping isidentified by the increasing (upon illumination) trion dissociation energy, accompanied by a characteristic change of the exciton/trion photoluminescence intensity ratioin MoSe2. At the same time, I observe decreasing photoluminescence intensity of the interlayer exciton. In the same time the combined PL intensity of the exciton and the trion in MoSe2 is enhanced, showing that the interlayer charge transfer can be controlled by the doping level. This observed effect is persistent on a timescale of several hours, as long as the sample is maintained under vacuum. This indicate a mechanism involving laser induced desorption of molecules physisorbed on the surface of the heterostructure. I support this hypothesis by revealed sensitivity of the photodoping rate on the excitation wavelength. The process of photodoping occurs much faster for higher energy photons.In chapter 4 I present result of the impact of moiré pattern on the intralayer exciton spectrum in MoS2/MoSe2 heterostructure. The moiré pattern formation is a phenomenon characteristic for van der Waals stacks where due to the weak interlayer interaction the ingredient layers preserve their own lattice parameters. Therefore due to small twist angle or of lattice mismatch between the monolayers periodic spatially varying potential is induced. This potential can have nontrivial impact on the optical properties of both intra- and interlayer excitons of transition metal dichalcogenide heterostructures. Here, I show experimental evidences of the moiré pattern impact on intralayer emission in a MoSe2/MoS2 heterobilayer encapsulated in hexagonal boron nitride. The periodic in-plane potential results in a splitting of the MoSe2 exciton and trion in emission and (for the exciton) absorption spectra. The observed energy difference between the split peaks is fully consistent with theoretical predictions. Moreover this chapter contain detailed description how the relative orientation of the flakes in such heterostructure can be revealed by second harmonic generation spectroscopy.Chapter 5 contains result of the initial studies about the impact of sample quality and possibility to generate valley polarization by the magnetic field. In this studies three type of structures are compared namely CVD grown and h-BN encapsulated MoSe2, together with MoSe2/MoS2 heterostructure. In addition I found that the formation of moire pattern has negligible impact on the Lande g-factor on intralayer excitonic transition
25
Dantu, Srilakshmi V. (Srilakshmi Venkata) Carleton University Dissertation Engineering Electronics. "In-situ doped p+ polysilicon as a MOS gate material." Ottawa, 1994.
Find full text
26
Mgeta, Frank. "Most maternal deaths in sub-saharan africa could be avoided." Thesis, Буковинський державний медичний університет, 2012. http://dspace.bsmu.edu.ua:8080/xmlui/handle/123456789/1420.
Full text
27
Ullberg, Nathan. "Field-effect transistor based biosensing of glucose using carbon nanotubes and monolayer MoS2." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-397719.
Full textAbstract:
As part of the EU SmartVista project to develop a multi-modal wearable sensor for health diagnostics, field-effect transistor (FET) based biosensors were explored, with glucose as the analyte, and carbon nanotubes (CNTs) or monolayer MoS2 as the semiconducting sensing layer. Numerous arrays of CNT-FETs and MoS2-FETs were fabricated by photolithographic methods and packaged as integrated circuits. Functionalization of the sensing layer using linkers and enzymes was performed, and the samples were characterized by atomic force microscopy, scanning electron microscopy, optical microscopy, and electrical measurements. ON/OFF ratios of 102 p-type and < 102 n-type were acheived, respectively, and the work helped survey the viability of realizing such sensors in a wearable device.EU Horizon 2020 - SmartVista (825114)
28
Poehler, Scott A. "Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154.
Full text
29
Paulin, Christophe. "Etude de l'endommagement du contact multicouche aube/disque sous chargement de fretting : impact des sollicitations variables et de la dimension du contact." Ecully, Ecole centrale de Lyon, 2006. http://www.theses.fr/2006ECDL0001.
Full textAbstract:
Dans le contexte des assemblages mécaniques, et plus particulièrement pour le contact en queue d'aronde alvéolé aube/disque de turbine, la combinaison d'un chargement normal (force centrifuge) et tangentiel (vibrations) se traduit par des sollicitations de fretting dégradant ainsi le bon fonctionnement de la liaison. Du fait d'une problématique industrielle spécifique Snecma utilise, sur une des deux pièces en Ti-6AI-4V, un revêtement mou et rugueux à base de Cu-Ni-In sur lequel est déposé un film de lubrifiant solide polymérisé à base de MoS2. Le but de cette recherche est alors de comprendre et de formaliser les phénomènes d'usure des différents matériaux en contact pour des conditions variables de sollicitations ainsi que d'en évaluer l' effet de la dimension du contact. Premièrement， pour le couple MoS2/lTi-6AI-4V, nous proposons une cartographie de l'endommagement de ce contact, puis, à partir d'un comportement élasto-plastique, l’établissement de la courbe maîtresse de la durée de vie du dépôt. On montre la stabilité de cette approche quelle que soit la dimension du contact et la géométrie de l'indenteur toutefois celle-ci reste sensible au chargement local appliqué au contact ce qui se traduit par la présence d'un régime d'usure sévère. Concernant l’ usure des matériaux métalliques (Cu-Ni-In et Ti-6AI-4V) un concept spécifique de cinétique d'usure qui prend en compte les phénomènes d'adhésion à l’interface de frottement est introduit. Cette propriété est alors validée pour différentes configurations de contact ainsi que pour des sollicitations variables de glissement. Enfin, la validation d'un modèle éléments finis de l'usure par modification de la surface de contact, qui montre une bonne corrélation avec les tests expérimentaux, permet d'ouvrir la voie à la prédiction de l’endommagement du contact completIn mechanical assemblies and especially for the aeronautical blade on disk contact, the combination between a normal load (centrifugal force) and a tangential load (vibrations) involves fretting solicitations. Resulting contact damages modify contacting surfaces and hinder the good working of the joint. Thus, from this specific industrial problem Snecma is performing a double coating process on one of the two Ti-6Al-4V parts. Lt consists of a soft and rough plasma sprayed layer (Cu-Ni-In) and a polymer bonded MoS2 solid lubricant. The aim of this research is to describe and formalize wear phenomena for variable amplitude conditions as well as the impact of the contact size for each contacting material. Firstly, for the MoS2/lTi-6Al-4V contact, we propose a map of the contact damages encountered ,then, from an elasto-plastic description of the materials we formalize the lifetime master curve. However, this technique reveals that for overcharged contacts the wear regime becomes severe. Then, concerning the wear behaviour of metallic materials, we propose wear kinetics which can take into account adhesion phenomena. This property has been validated for variable amplitude configurations as well as for different contact size and reveals a rather good stability. Finally, the development of an original finite element model of wear, which shows a very good correlation with experimental tests, encourages the way to formalize the global and successive damage of the entire contact
30
Jia, Tiantian. "Photocatalytic hydrogen production over layered materials." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6426c02b-f2b1-4326-a767-2384c303faf3.
Full textAbstract:
The technology of semiconductor-based photocatalytic water splitting to produce hydrogen using solar energy has been considered as one of the most important approaches to solve the world energy crisis. Therefore, the development of the effective semiconductor photocatalysts has undergone considerable research. However, the traditional photocatalysts suffer from the negative effects from rapid charge recombination, which reduces the excited charges by emitting light or generating phonons. Efficient charge separation and fast charge transport, avoiding any bulk/surface recombination, are fundamentally important for photocatalytic hydrogen generation through water splitting. Here, we have introduced assembled layered materials as photocatalyst systems with their unique physicochemical properties to realize the effective charge separation and high photocatalytic activity. Using graphene as a two-dimensional supporting matrix, we have succeeded in selective anchoring of semiconductor and metal nanoparticles as separate catalytically active sites on the graphene surface. The ability of graphene to capture, transfer and store electrons and its potential to serve as a conductive support are demonstrated. The TiO2 semiconductor/metals nanocrystals-graphene ensemble makes it possible to carry out selective catalytic processes at the separate sites and provides the potentials for applications in water splitting reactions. After demonstrating the positive role of graphene in such photocatalytic system, we then fabricate a simple but highly cooperative ensemble with CdS and MoS2 nanocrystals dispersed on graphene sheets. It is demonstrated that CdS nanocrystals can also capture visible light energy and facilitate excited electron transfer to MoS2 (as metal substituent) for catalytic hydrogen production via the 2-D graphene which plays a key role as an efficient electron mediator. Hexagonal multilayer MoS2 with a layered structure in this system serves to provide active sites for hydrogen evolution by its exposed Mo edges. Hence, multilayer MoS2 is an ideal cocatalyst of semiconductors for hydrogen generation. This crystalline-layered structure also shows semiconducting properties, however, its characteristic indirect band gap displays a poor light capture and emission ability with excited electrons and holes with different momentum. In contrast, single layer MoS2 shows a direct band gap behavior. Our studies have clearly shown that single layer MoS2 prepared with lithium intercalation indeed displays encouraging results in hydrogen evolution due to the direct band gap and quantum confinement effects. In addition, the exfoliated single layer MoS2 exhibits extraordinary enhanced activity and stability in combination with the Eosin Y sensitized system when compared to those of multilayer MoS2 and bulk MoS2 counterparts, which is attributed to the improvement of the density of surface active sites with stronger adsorption for the Eosin Y molecules on the single layer MoS2. In addition, this multifunctional catalyst on graphene sheet can also create adsorption sites on a defective basal surface of single layer MoS2 through adsorption of Eosin Y where electron transfer from photoexcited Eosin Y molecule to graphene via the 2-D MoS2 mainly takes place. Thus, the photo-generated electrons are then effectively transported to the exposed active sites of MoS2 for the proton reduction to hydrogen molecule. It is believed the above novel assembled molecular layered systems may be applicable for a wide range of catalytic,photocatalytic and electrocatalytic reactions.
31
Shulruff, S., and Michele R. Moser. "Help for Tennessee’s Most Vulnerable Children." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etsu-works/4999.
Full text
32
Teixeira, André Messias. "Estudo da produção em escala aumentada de nanopartículas de dissulfeto de molibdênio (2H-MoS2) pelo método hidrotérmico." reponame:Repositório Institucional da UFSC, 2012. http://repositorio.ufsc.br/xmlui/handle/123456789/100373.
Full textAbstract:
Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2012Made available in DSpace on 2013-06-25T18:34:10Z (GMT). No. of bitstreams: 1 313603.pdf: 2133318 bytes, checksum: b7be309203777ea9c96db6d4e4a8d521 (MD5)
No presente trabalho foi desenvolvido um método de produção em escala aumentada de nanopartículas de dissulfeto de molibdênio (MoS2). Foi utilizada a rota hidrotérmica para sua produção, sendo projetado um forno de aquecimento resistivo com capacidade para 9 autoclaves. Estas foram confeccionadas em aço SAE 310, revestidas internamente com politetrafluoretileno (PTFE), tendo 120 ml de volume interno cada. Este forno conta com um assoalho vibratório capaz de manter as autoclaves sob agitação constante, alcançando até dois modos vibracionais fundamentais do conteúdo líquido no interior delas. As sínteses foram desenvolvidas na temperatura de 220°C em períodos de 6, 12 e 24 horas, tendo como reagentes o molibdato de amônio tetrahidratado, hidroxilamina cloridrato e tioureia, sendo a reação dada em água bidestilada. As amostras foram caracterizadas quanto ao seu rendimento químico, estrutura cristalina por Difração de Raios X (DRX), morfologia por Microscopia Eletrônica de Varredura por Emissão de Campo (FEG), Termogravimetria e Infravermelho por Transformada de Fourier (TG-IR) simultaneamente, Espectroscopia Raman, Interferometria Óptica e, com enfoque maior, Tribologia. Foram obtidas nanopartículas na morfologia de nanoflores com cerca de 200 nm de diâmetro com estrutura cristalina hexagonal lamelar (2H-MoS2) parcialmente amorfizadas. Estas formam dispersões relativamente estáveis com os três óleos sintéticos testados (fortemente polar, de média polaridade e apolar) e com água bidestilada. Obteve-se um rendimento médio de reação de 71,3% em relação ao Mo e foi verificado um aumento de 10% neste quando comparado com amostras estáticas, sem a aplicação da agitação por vibração. Desta forma, valores para uma produção industrial utilizando o sistema desenvolvido ficam em torno de 300 g/mês.
Abstract : In the present work was developed a method for scaling up the production of molybdenum disulfide (MoS2) nanoparticles. It was used a hydrothermal route to its production, being designed a resistive heating furnace with capacity for 9 autoclaves. They were designed in SAE 310 stainless steel, internally coated with polytetrafluoroethylene (PTFE), having 120 ml internal volume each. This furnace has a vibratory floor capable of maintaining the autoclaves under stirring, reaching until two fundamental vibrational modes of the liquid contents inside them. The syntheses were developed at temperature of 220 °C in periods of 6, 12 and 24 hours, with the reagents of ammonium molybdate tetrahydrate, hydroxylamine hydrochloride and thiourea, the reaction is given in bidistilled water. The samples were characterized according to their chemical yield, crystalline structure by X-ray Diffraction (XRD), morphology by Field Emission Scanning Electron Microscopy (FEG), Thermogravimetry and Fourier Transform Infrared (TG-IR) simultaneously, Raman Spectroscopy, Optical Interferometry and, with increased focus, Tribology. Nanoparticles were obtained on the morphology of nanoflowers about 200 nm diameter with lamellar hexagonal crystalline structure (2H-MoS2) partially amorphous. These form relatively stable dispersions with the three synthetic oils tested (strongly polar, medium polarity and nonpolar) and with bidistilled water. It was obtained an average reaction yield of 71.3% in relation to Mo and there was verified an increment of 10% in it in comparison with static samples, without the application of stirring by vibration. Thus, values for an industrial production using the developed system are around 300 g / month.
33
Hadland, Erik. "Thin Film van der Waals Heterostructures containing MoSe2 from Modulated Elemental Precursors." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24520.
Full textAbstract:
Transition metal dichalcogenides (TMDs) are naturally occurring layered materials that have attracted immense research interest due to their high degree of chemical tunability. In particular, MoSe2 has been the focus of significant investigation stemming from reports that it converts to a direct band gap semiconductor material at ultralow dimensions. Yet, as more and more is learned about increasingly thin MoSe2, efforts are now aimed at imparting the novel functionality of MoSe2 into van der Waals heterostructures. This dissertation focuses on synthesis and characterization of novel MoSe2-based nanolaminate structures that have been self assembled from modulated elemental precursors.
The first section describes a new treatment of x-ray fluorescence spectroscopy data and its use as a powerful probe for determining the absolute composition per unit area of a thin film with sub-monolayer accuracy. While this has widespread application in the thin film world, it is particularly useful for MER synthesis in the calibration of modulated elemental precursors. In order to crystallize a target structure, it is imperative to deposit the correct number of atoms, which is now possible with greater precision.
The second section shows the importance of rotational (i.e. “turbostratic”) disorder on lowering cross-plane thermal conductivity in two systems—MoSe2 and the (SnSe2)1(MoSe2)1.32 heterostructure. The binary systems exhibits ultralow thermal conductivity that rivals that of WSe2, yet some interlayer atomic registry was noted in TEM images. By interleaving layers of MoSe2 with SnSe2—which also possesses hexagonal symmetry, but has a significantly larger basal plane—the cross-plane thermal
iv
conductivity was depressed to the lowest reported value in the literature for a fully dense solid.
The final section presents the synthesis and characterization of a new, ternary phase of Bi|Mo|Se. The structure consists of alternating layers of a “puckered” rock salt BiSe lattice and nanosheets of MoSe2. Notably, the MoSe2 sublattice consists of a mixture of the semiconducting 2H phase (~60%) and the metallic 1T phase (~40%). This is the result of electron injection from the BiSe into the conduction band of the MoSe2, which is known to undergo a rearrangement upon reduction.
This dissertation includes previously published and unpublished coauthored materials.2021-04-30
34
Wen, Yuming. "Study of the Performance of Peat Moss Pyrolysis." Thesis, KTH, Materialens processteknologi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256027.
Full textAbstract:
Peat moss, also called sphagnum, has become a big problem in many countries such as China and Sweden due to its high green-house gas emission from chemical and biological degradation. In this work, the performance of peat moss pyrolysis has been studied, to investigate the potential of application of peat moss pyrolysis on fuel and chemical production. Thermalgravimetric analysis (TGA), differential thermal analysis (DTA), and pyrolysis experiments in a bench-scale reactor have been conducted. Kinetic parameters were calculated based on the results of TG and DTG by Kissinger-Akahira-Sunose (KAS) method and Coats-Redfern method. 450, 500, 550, 600 °C were chosen as the pyrolytic peak temperatures and four phases of products (char, aqueous phase, tar, and gas) were collected. It was found that the peat moss pyrolysis from room temperature to 900 °C could be classified as a six stages reaction. Stage 1 to stage 5 were estimated to be the results of the removal or decomposition of moisture content, hemicellulose, cellulose, lignin, and CaCO3, respectively. The results of activation energies calculated by Coats-Redfern method revealed that, when the heating rate different from 10, 15, and 20 °C/min: stage 3 had the activation energy of 276389, 262587, and 239049 J/mol; stage 4 had the activation energy of 252851, 248918, and 307427 J/mol; stage 5 had the activation energy of 1108268, 814402, and 857437 J/mol, respectively. When the peak pyrolytic temperature raised from 450 to 600 °C: the production of char would decrease; the 500 °C one had the highest production of tar; the aqueous phase produced had the highest TAN value at 500 °C.Torvmossa, även kallad sphagnum, har blivit ett stort problem i många länder som Kina och Sverige på grund av dess stora utsläpp av växthusgaser från kemisk och biologisk nedbrytning. I detta arbete har torvmossans egenskaper vid pyrolys studerats för att undersöka dess potential att användas inom bränsle- och kemisk produktion.Termogravimetrisk analys (TGA), differentiell termisk analys (DTG) och pyrolysförsök i en bench-scale reaktor har genomförts. Kinetiska parametrar beräknades baserat på resultaten av TGA och DTG med Kissinger-Akahira-Sunose (KAS) metoden och Coats-Redfern metoden. 450, 500, 550, 600 °C valdes som temperaturer vid pyrolys och fyra olika produkter (kol, vattenfas, tjära och gas) uppsamlades. Det visade sig att torvmosspyrolysen från rumstemperatur till 900 °C kunde klassificeras som en reaktion på sex steg. Steg 1 till steg 5 uppskattades vara resultaten av avlägsnande eller sönderdelning av fuktinnehåll, hemicellulosa, cellulosa, lignin respektive CaCO3. Resultaten av aktiveringsenergier beräknade med CoatsRedfern-metoden och visade att: när uppvärmningshastigheten skiljer sig från 10, 15 och 20 °C/min; steg 3 hade aktiveringsenergin 276389, 262587 och 239049 J/mol; steg 4 hade aktiveringsenergin 252851, 248918 och 307427 J/mol; steg 5 hade aktiveringsenergin 1108268, 814402 respektive 857437 J/mol. När den högsta pyrolytiska temperaturen höjdes från 450 till 600 °C: minskade produktionen av kol; 500 °C hade den högsta produktionen av tjära; den producerade vattenfasen hade det högsta TAN-värdet vid 500 °C.
35
Lee, Edwin Wendell II. "Growth and Nb-doping of MoS2 towards novel 2D/3D heterojunction bipolar transistors." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480686917234143.
Full text
36
Bernardi, Cristian. "Produção e caracterização de nanopartículas de MoS2 e sua estabilização em óleos visando a lubrificação limite." Florianópolis, SC, 2011. http://repositorio.ufsc.br/xmlui/handle/123456789/95523.
Full textAbstract:
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2011Made available in DSpace on 2012-10-26T02:59:24Z (GMT). No. of bitstreams: 1 294797.pdf: 4976680 bytes, checksum: 6e9a43f87decd9c4c4ae69ed22325f3e (MD5)
Neste trabalho foi realizado um amplo estudo, explorando vários protocolos de sínteses de partículas de MoS2, procurando a melhor morfologia para ser utilizada como aditivo em óleos lubrificantes para compressores herméticos. Foram sintetizadas micro e nanopartículas de MoS2 em diferentes morfologias (esferas, nanoesferas, tubos, nanotarugos e nanoflores) pelos métodos hidrotérmicos e solvotérmicos. Também foram sintetizadas partículas híbridas de carbono (esferas e nanotubos) impregnadas com nanopartículas de MoS2. A morfologia das nanopartículas é fortemente influenciada pelos parâmetros de sínteses (temperatura, tempo, solvente e concentração dos reagentes) e também pela adição de agentes modificadores (surfactantes e polímeros). A morfologia adotada para utilizar como aditivo em óleos lubrificantes foi a de nanoflores com diâmetros aproximados de 250 nm. Para funcionar como aditivo lubrificante as nanoflores passaram por um tratamento com etanol absoluto em autoclave, que promove sua desidratação e torna suas superfícies lipofílicas, permitindo formar suspensões em óleos lubrificantes que apresentam boa estabilidade. Serão apresentados vários testes tribológicos de óleos lubrificantes para compressores aditivados com nanoflores de MoS2 com bons resultados. Para o caso de um óleo naftênico após aditivado com nanoflores de MoS2, observa-se uma redução excepcional de 200 % no coeficiente de atrito em relação ao óleo não aditivado.
37
Beyer, Griffin Joseph. "Large Area 2D Electronic Molecular Sensor Arrays via Photonic Annealing of Amorphous Sputtered Mos2." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1582624657416084.
Full text
38
Ellison, Rachel (Rachel M. ). "Mode II fracture mechanics of moso bamboo for application in novel engineering materials." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98653.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 32-34).
Bamboo has been used as a structural material for thousands of years. Recently there has been increasing interest in its use as a modem construction material. In this study, as part of a larger project to characterize the mechanical properties of Moso bamboo for application in the production of structural bamboo products (SBP), end-notched flexure (ENF) tests and three-point bending tests were performed to obtain the mode II interlaminar toughness (GIIc) and longitudinal Young's modulus (EL). It was found that known values for GIIc, include the pith (innermost layer) and cortex (outermost layer) of the bamboo culm in their calculations. The resulting value is, to a statistically significant degree (t = 5.0 x 10⁶), higher than that with the pith and cortex removed, as they typically will be in processing SBP. A new value, GIIc, = 630 +/- 155 J/m² , was established for specimens lacking the pith and cortex. Although no correlation was found between GIIc, and specimen density, it is suspected that a relationship does exist, and recommendations for further investigation are given.
by Rachel Ellison.
S.B.
39
Lai, Diane Wenbi. "Aerosol Jet Printing of Selective Molecular Inks for Patterning of 2D MoS2." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton151335729815385.
Full text
40
Ries, Lucie. "Functionalized two-dimensional (2D) MoS2 nanosheets as building blocks for water purification membranes." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2019. http://www.theses.fr/2019ENCM0009.
Full textAbstract:
Les technologies de séparation par membranes jouent un rôle important dans divers domaines tels que le traitement de l’eau, la séparation de produits chimiques et de gaz dans de nombreux domaines industriels ou encore l’industrie alimentaire. L’accent a récemment été mis sur les matériaux bidimensionnels(2D) pour les applications membranaires, car leur épaisseur atomique et leur espacement limité entre les couches pourraient théoriquement améliorer les performances de séparation. Les nanofeuillets eux-mêmes ou l’empilement de plusieurs feuillets peuvent former des membranes sélectives. L’empilement multicouche de monofeuillets sous forme de membrane nanolaminée crée des capillaires 2D (ou nanocanaux) capables de tamiser efficacement les espèces chimiques en fonction de leur taille. Des exemples récents ont été rapportés dans la littérature démontrant le potentiel des matériaux 2D en tant que membranes multicouches ou monocouches pour le tamisage moléculaire (222; 260; 466; 204), la séparation de gaz (219; 246; 190),la production d’énergie (467) et le dessalement de l’eau de mer (198; 194). Parmi les différentes membranes 2D nanolaminées, l’oxyde de graphène (GO) est le matériau le plus étudié, et le tamisage moléculaire au sein de sa structure est principalement dicté par la taille de ses capillaires 2D (222). Malheureusement,l’hydrophilie importante des nanofeuillets rend les membranes de GO instables en milieu aqueux, et la difficulté de contrôler la largeur des capillaires entre les nanofeuillets limite l’utilisation de ces membranes pour le traitement des eaux. D’autres matériaux 2D tels que les nanofeuillets exfoliées de dichalcogénures de métaux de transition (TMD) constituent des plateformes attrayantes pour la réalisation de membranes nanolaminées.Des travaux récents menés sur des membranes nanolaminées en disulfure de molybdène (MoS2) ont montré sa stabilité améliorée (3). Dans le cadre de cette thèse, nous avons étudié les performances d’un nouveau type de membranes nanolaminées en MoS2 pour lesquelles la chimie de surface des feuillets est précisément contrôlée (14). Afin d’évaluer le rôle de la chimie de surface,nous avons exploré l’impact de la fonctionnalisation covalente sur le tamisage moléculaire pour la purification de l’eau (plus particulièrement le dessalement et l’élimination des micropolluants) (14). Nos résultats ouvrent de nouvelles voies pour ajuster avec précision les capacités de séparation des membranes à base de matériaux 2DMembrane separation technology plays an important role in various fields including water treatment, chemicals and gas separation for numerous industrial fields, and food processing. There has been a renewed focus on two-dimensional(2D) materials for membrane application since their atomic thicknessand confined interlayer spacing could theoretically lead to enhanced separative performances. Either the single nanosheets themselves, or the stackingof multiple sheets can form selective membranes. The multilayer assembly of single nanosheets – forming nanolaminate membranes – creates 2D capillaries(or nanochannels) that can efficiently sieve chemical species depending ontheir size.Recent examples have been reported in the literature demonstrating the potential of 2D materials as multi- or single-layer membranes for molecular sieving(222; 260; 466; 204), gas separation (219; 246; 190), energy harvesting (467)and water desalination (198; 194).Among the different building blocks of nanolaminate membranes made of two-dimensional materials (2D), graphene oxide (GO) has been studied as a candidate for molecular sieving via size-limited diffusion in the 2D capillaries (222). Unfortunately the high hydrophilicity of GO nanosheets makes GO membranes unstable in water, while the poor control of the capillary width between the nanosheets limits the water permeance of the membranes. Other 2D materials such as exfoliated nanosheets of transition metal dichalcogenides (TMDs)constitute attractive platforms for the realization of nanolaminate membranes.Recent works carried out on nanolaminate membranes made of molybdenum disulfide (MoS2) have demonstrated improved stability (3). Within this thesis we have studied the performance of a novel type of MoS2 nanolaminate membranes with well-controlled surface chemistry of the nanosheets (14). Inorder to assess the role of surface chemistry, we explored the impact of covalent functionalization on molecular sieving toward water purification (i.e. desalination and micropollutant removal) (14). Our results open novel directions to finely tune the sieving behavior of membranes based on 2D materials
41
He, Ruicong, and 何锐聪. "Photocurrent study on bulk and few layers MoS₂ field effect transistors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/212610.
Full textAbstract:
Atomically thin Molybdenum disulfide, MoS2, a star member of the group VI transition metal dichalcogenide(TMDC) family has been attracting rising interests for its potential applications in emerging electronics and optoelectronics. Bulk MoS2is a semiconductor with an indirect gap located between the top of valence band at Γ points and the bottom of conduction band in mid of K and Γ points in its Brillouin zone. Atomically thin MoS2 films including monolayers and multilayers, being chemically inert, present a class of intrinsic 2D semiconductors which are widely regarded as a platform for ultimate electronics.
As yet tremendous efforts focus on the optical properties and electric transport study. In this thesis, we report the experimental study of photocurrent measurements on MoS2thin films. The sample preparation, device fabrication, optical and electric characterizations are introduced. The experiments have been carried out on a field effect transistor (FET) structured MoS2 device. The photocurrent spectroscopy reveals the interband excitonic transitions at spin-split bands around K valleys. The results demonstrate that MoS2has potential applications in optoelectronics.published_or_final_version
Physics
Master
Master of Philosophy
42
YESMIN, Panecatl Bernal. "Síntese e caracterização do material mesoporoso MCM-41 para o desenvolvimento de capacitores MOS." Universidade Federal de Pernambuco, 2015. https://repositorio.ufpe.br/handle/123456789/15471.
Full textAbstract:
Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-02-26T16:11:44Z
No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5)Made available in DSpace on 2016-02-26T16:11:44Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 5.-Tesis doutorado Yesmin 2015 UFPE Bibliot.pdf: 2813580 bytes, checksum: c994d000e414c2f79bd7b8711d5f2714 (MD5) Previous issue date: 2015-06-05
CAPES
CNPq
FACEPE
Neste trabalho, apresentamos a síntese e caracterização do material mesoporoso MCM-41 para o desenvolvimento de capacitores MOS. A motivação deste trabalho deve-se às propriedades interessantes que MCM-41 apresenta, tais como: área superficial e volume de poro grande e estrutura ordenada de poros. Inicialmente apresentamos a síntese do material mesoporoso MCM-41 pelo método Sol-Gel, e sua caracterização estrutural (DRX e IV), morfológica (MEV e TEM) e texturais (Análise de Adsorção e Dessorção de Nitrogênio), e fazemos uma comparação de resultados com o mesmo material produzido pela Sigma-Aldrich. Também foram obtidos filmes pelo método químico, que foram caracterizados por MEV e DRX e em seguida foram fabricados capacitores MOS. As medidas elétricas do capacitor MOS com dielétrico de MCM-41 foram comparadas com capacitores com dielétrico de SiO2 térmico. Os resultados mostraram uma clara diferença nas curvas de Corrente-Tensão. Conclui-se que a água confinada dentro do filme dielétrico é associada com os valores elevada de capacitância por unidade de área, estes valores permanecem altos depois do aquecimento, indicando que a resposta dielétrica é devida á água ligada ao material dielétrico, formando camadas paralelas á superfície do substrato. Capacitores de MCM-41 foram expostos a vários solventes polares e apolares, assim como á radiação gama e apresentaram distorção na resposta da capacitância e deslocamento nas curvas de corrente – tensão. Finalmente, capacitores de MCM-41 foram hidrolisados com o objetivo de aumentar a concentração dos grupos silanol na superfície do MCM-41 e como consequência alterar a capacitância do dispositivo.
In this work, we report the synthesis and characterization of MCM-41 mesoporous material for the development of devices types MOS capacitors. The motivation of this work is due to the MCM-41 interesting properties such as: surface area and pore volume large and pore ordered structure. Initially, we present a synthesis of MCM-41 mesoporous material by sol-gel method and their structural characterization (XRD and IR), morphological (SEM and TEM) and texture (Nitrogen Desorption and Adsorption Analysis) and make a comparison with the same material produced by Sigma. Also, films were obtained by chemical method, which were characterized by SEM and XRD, and then MOS capacitors were fabricated. The electrical characteristics MCM-4 MOS capacitors were compared with thermal SiO2, the results showing a clear difference in the voltage-current curves. It concludes that water confined within the dielectric film is associated with high values of capacitance per unit area these values remain high even after heating, indicating a dielectric response due to water strongly bonded to the dielectric material forming layers parallel to the substrate surface. The MCM-41 capacitors were exposed to various polar and nonpolar solvents and gamma radiation and showed good results were due to variations in the response to capacitance and the voltage-current curves showed displacement and distortion. Finally, the MCM-41 capacitors were hydrolyzed in order to be able to increase the concentration of silanol groups on the surface of MCM-41; as a consequence the material is more sensitive to moisture and therefore, the capacitance of the device response.
43
Silva, G. M. "Efeitos do autoaquecimento em transistores SOI-MOS tridimensionais nanométricos/." reponame:Biblioteca Digital de Teses e Dissertações da FEI, 2016. https://doi.org/10.31414/EE.2016.T.128531.
Full text
44
Strapasson, Gilmara. "Estudo da influência do lubrificante sólido MoS2 nas propriedades de revestimentos protetores de TiN." reponame:Repositório Institucional da UCS, 2010. https://repositorio.ucs.br/handle/11338/563.
Full textAbstract:
Neste trabalho investigou-se o revestimento protetor nitreto de titânio com a incorporação de dissulfeto de molibdênio como lubrificante sólido, visando aplicação em peças e ferramentas de corte na indústria metal-mecânica. Este revestimento foi obtido na forma de filme fino pela técnica de magnetron sputtering reativo modificando a quantidade de MoS2 de 2,9 a 40,3 % . As propriedades estruturais, físico-químicas, morfológicas, mecânicas e elementares foram analisadas observando a variação na quantidade de dissulfeto de molibdênio nos filmes finos. Estas propriedades foram analisadas por diferentes métodos, tais como espectrometria de retroespalhamento Rutherford, espectroscopia de fotoelétrons induzidos por raios X, difração de raios X de ângulo rasante, nanoindentação e microscopia eletrônica de transmissão. O MET revela que o composto MoS2 está estruturado na forma de partículas formadas durante a deposição na matriz de TiN. As análises de XPS revelam apenas ligações químicas de Ti-N, Mo-S e não o composto Ti-S pôde ser detectado. Na análise de DRX pode ser observado que em quantidades de MoS2 superiores a 40% sugere um stress compressivo e trativo entre os grãos de MoS2 e TiN causando um deslocamento dos picos para ambas as estruturas. Com o desgaste mecânico não se observou nenhuma modificação nos resultados de XPS e DRX. As propriedades mecânicas tiveram melhores resultados para amostras que contém o percentual de MoS2 abaixo de 12%.Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-06-03T18:51:53Z No. of bitstreams: 1 Dissertacao Gilmara Strapasson.pdf: 6933686 bytes, checksum: f899af08e7e81dde6373ff00102fc235 (MD5)
Made available in DSpace on 2014-06-03T18:51:53Z (GMT). No. of bitstreams: 1 Dissertacao Gilmara Strapasson.pdf: 6933686 bytes, checksum: f899af08e7e81dde6373ff00102fc235 (MD5)
In this study we investigated the protective coating of titanium nitride using incorporation of molybdenum disulfide as a solid lubricant, seeking application in parts and cutting tools in the metal working industry. This coating was obtained in the form of thin film by dc magnetron reactive sputtering technique. The structural, physicochemical, morphological, mechanical and quantitative elemental analysis were observing the different amounts of molybdenum disulfide in thin films (2,9 to 40,3%). These properties were analyzed using different methods such as Rutherford backscattering spectrometry, photoelectron spectroscopy induced by X-rays, X-ray diffraction, nanoindentation and transmission electron microscopy. TEM reveals a MoS2 compound structured as clusters formed during depositions into TiN matrix; XPS analysis show just Ti-N and Mo-s chemical bindings and no Ti-S compound could be detected; XRD analysis can be observed that amounts of MoS2 over 40% suggests a compressive stress and tractive between the grains of TiN and MoS2 causing a shift of the peaks for both structures. With the mechanical stress that there was no change in the results of XPS and XRD. The mechanical properties showed best results for samples containing a value of MoS2 below 12%.
45
Lee, Jaesung. "Optically Transduced Two-Dimensional (2D) Resonant Nanoelectromechanical Systems and Their Emerging Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1474972552266241.
Full text
46
Lander, Robert James Pascoe. "Electronic and material properties of MOS-gated Si/Siâ†1â†-â†xGeâ†x P-channel heterostructures." Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263117.
Full text
47
John, Soji. "UHVCVD growth of Si₁-x-yGexCy epitaxial materials and application in heterostructure MOS devices /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Full text
48
Hagerty, Phillip. "Physical Vapor Deposition of Materials for Flexible Two Dimensional Electronic Devices." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1460739765.
Full text
49
Alwardi, Milad 1958. "ANALYSIS AND DESIGN OF N-CHANNEL MOS TRANSISTORS FOR CRYOGENIC SWITCHING APPLICATIONS." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/291980.
Full text
50
Wu, Min. "Adhesion and Surface Energy Profiles of Large-area Atomic Layers of Two-dimensional MoS2 on Rigid Substrates by Facile Methods." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849762/.
Full textAbstract:
Two-dimensional (2D) transition metal dichalcogenides (TMDs) show great potential for the future electronics, optoelectronics and energy applications. But, the studies unveiling their interactions with the host substrates are sparse and limits their practical use for real device applications. We report the facile nano-scratch method to determine the adhesion energy of the wafer scale MoS2 atomic layers attached to the SiO2/Si and sapphire substrates. The practical adhesion energy of monolayer MoS2 on the SiO2/Si substrate is 7.78 J/m2. The practical adhesion energy was found to be an increasing function of the MoS2 thickness. Unlike SiO2/Si substrates, MoS2 films grown on the sapphire possess higher bonding energy, which is attributed to the defect-free growth and less number of grain boundaries, as well as less stress and strain stored at the interface owing to the similarity of Thermal Expansion Coefficient (TEC) between MoS2 films and sapphire substrate. Furthermore, we calculated the surface free energy of 2D MoS2 by the facile contact angle measurements and Neumann model fitting. A surface free energy ~85.3 mJ/m2 in few layers thick MoS2 manifests the hydrophilic nature of 2D MoS2. The high surface energy of MoS2 helps explain the good bonding strength at MoS2/substrate interface. This simple adhesion energy and surface energy measurement methodology could further apply to other TMDs for their widespread use.