Dissertations / Theses on the topic 'Liquid phase exfoliation (LPE)'

Cette thèse est consacrée à la production de matériaux 2D en phase liquide, en utilisant des approches pouvant permettre la production en masse de graphène et de matériaux apparentés. Notre objectif est de surmonter certains problèmes critiques pour le traitement et l'utilisation pratique des encres à base de matériaux 2D et de fournir une compréhension approfondie de la relation structure-propriétés dans ces matériaux, constituant des étapes obligatoires pour leurs applications futures. Cette thèse porte principalement sur l'UILPE et l'exfoliation électrochimique du graphène et du disulfure de molybdène (MoS2), qui ont été choisis comme matériaux prototypes à 2 dimensions. Les approches synthétiques sont combinées à une caractérisation physico-chimique des matériaux produits, à l'aide de techniques telles que l'AFM, la microscopie électronique, la spectroscopie XPS et Raman, ainsi qu'à une caractérisation électrique. Des applications dans le domaine de la détection et de l'électronique ont été explorées et ont permis de démontrer que des approches d'exfoliation en phase liquide pouvaient être utilisées pour obtenir un contrôle précis des propriétés des matériaux 2D ouvrant la voie à leur intégration en tant que matériaux actifs dans de nouveaux dispositifs multifonctionnels
This thesis is devoted to the production in liquid-phase of two-dimensional materials, by using approaches that may enable mass production of graphene and related materials. We aim to overcome some issues that are critical for the processing and practical use of 2D materials-inks and to provide a deep understanding of the structure-properties relationship in such materials being mandatory steps toward their future applications. This thesis mainly focuses on ultrasound-induced liquid-phase exfoliation and electrochemical exfoliation of graphene and molybdenum disulfide, which have been chosen as prototypical 2D materials. The synthetic approaches have been combined with a multiscale physico-chemical and electrical characterization of the produced materials, by employing techniques such as AFM, XPS and Raman spectroscopy. Applications in the field of sensing and electronics have been explored and allowed to demonstrate that liquid-phase exfoliation approaches can be conveniently employed to achieve a fine control on the properties of 2D materials paving the way to their integration as active materials in novel multifunctional devices

In this work, several materials possessing a layered structure were investigated using a technique of exfoliation in liquid phase to produce few- to mono-layers of the material. Materials exfoliated in such a way included graphite, boron nitride, molybdenum disulfide and tungsten disulfide. Subsequent transmission electron microscopy and accompanying electron diffraction patterns revealed that few and mono layer forms of these materials have been realized through this exfoliation method. Ultraviolet-visible spectroscopy confirmed the shifting of the band gaps in molybdenum and tungsten disulfides that is predicted in reducing the number of layers of these materials and was also used to confirm the band gap of the boron nitride. As a potential application, exfoliated molybdenum disulfide was used in the construction of electrodes for electrical charge storage in an electrochemical double layer capacitor, or supercapacitor, style device. Cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy measurements were performed using three different electrolytes, which showed good capacitive behavior for these devices. Using the data from electrochemical impedance spectroscopy, equivalent circuit models were generated to represent the systems in different electrolytes. From this, it was determined that the capacitive behavior of these systems was partially diffusion limited.

Cette thèse démontre le potentiel dont dispose l’exfoliation en phase liquide du graphite dans le but d’obtenir des feuillets de graphène dispersés dans un solvant organique. Ainsi le mécanisme d’exfoliation a été étudié en profondeur, en particulier, l’influence de plusieurs paramètres (température, puissance et solvants). Le choix de ses paramètres se montre crucial dans le contrôle du procédé, et pour l’obtention des feuillets de graphène ayant une taille ciblée. Il est donc possible de fabriquer des nano-feuillets de quelques dizaines de nanomètre qui en plus possèdent des propriétés de photoluminescence.Dans le but de comprendre le mécanisme d’exfoliation en phase liquide assistée par des molécules, une nouvelle approche a été mise au point : l’approche supramoléculaire. Cette approche se base sur l’utilisation de surfactants d’un nouveau type. En effet, les molécules sélectionnées possèdent une longue chaine alkyle. Cette chaine s’adsorbe sur la surface du graphène et permet de stabiliser les feuillets lors de l’exfoliation. L’influence de la taille de la chaine alkyle de ces molécules lors de l’exfoliation a été vérifiée. De plus, ces molécules ont été équipées de différentes fonctions supramoléculaires afin qu’elles puissent former des dimères sur la surface du graphène. L’ajout de ces molécules augmente non seulement le rendement d’exfoliation mais aussi le nombre de mono-feuillets présents dans ces dispersions. Ces dispersions présentent des propriétés conductrices lorsqu’elles sont déposées sur des substrats. Une nouvelles méthode de déposition a été mise au point afin d’améliorer et d’augmenter la conductivité mais aussi le pourcentage de transparence
This thesis demonstrates the potential of exfoliation of the graphite in the liquid phase in order to obtain graphene sheets dispersed in an organic solvent. Thus the exfoliation mechanism has been studied, in particular, the influence of several parameters (temperature, power and solvents). The choice of parameters is actually crucial for the control of the process, and to obtain graphene sheets having a targeted size. It is therefore possible to manufacture nanosheets of several tens of nanometers, which in addition exhibit photoluminescence properties.In order to understand the exfoliation mechanism in liquid phase assisted by molecules, a new approach has been developed: the supramolecular approach. This approach is based on using a new type of surfactant. Indeed, the selected molecules carry a long alkyl chain. This chain is adsorbed on the surface of graphene and can stabilize the sheets during exfoliation. The influence of the size of the alkyl chain of these molecules during exfoliation was verified. Furthermore, these molecules have been equipped with various supramolecular functions, which can form dimers on the surface of graphene. The addition of these molecules not only increases exfoliation performance but also the number of mono-layers present in these dispersions. These dispersions have conductive properties when deposited on substrates. A new deposition method was developed to enhance and increase conductivity but also the percentage of transparency

Graphene, a single layer of graphite, owing to its excellent mechanical, electrical, and thermal properties, has evolved as an exceptional nanomaterial in the past decade. It holds great promise in developing various novel applications from biomedical to structural composites. However, several challenges remain in realising the great potential of this material; one being the bulk scale production of graphene. This thesis has been concerned with production of pristine few-layer graphene (FLG) using liquid phase exfoliation (LPE) of graphite in various solvent media and exploring the applications of graphene-based composite coatings as optical Raman-strain sensors. LPE of natural graphite using bath sonication was used to produce highly stable pristine FLG in 1-methyl-2-pyrrolidinone (NMP) and N,N-dimethylformamide (DMF). Atomic force microscope (AFM) was used to analyse the exfoliation efficiency and lateral dimensions, while Raman spectroscopy provided an insight about the quality of the graphene flakes. Moreover, the potential for dynamic light scattering (DLS) as an efficient in situ characterisation technique for estimating the lateral dimensions of graphene flakes in dispersions was demonstrated. LPE was also employed to explore various routes to produce pristine graphene in aqueous media which can be used for toxicity studies. Aqueous dispersions were prepared by a solvent exchange method of graphene originally in organic solvents (NMP and DMF) using dialysis, achieving 0.1 v/v% organic solvent levels. Pristine aqueous graphene dispersions were also prepared by directly exfoliating graphite in biocompatible surfactant (TDOC- Sodium taurodeoxycholate) and biomolecules (Phosphatidylcholine and human serum albumin) solutions. Cell culture studies by collaborators revealed that solvent-exchanged and TDOC-exfoliated pristine FLG displayed minimal toxicity and albumin-exfoliated FLG hardly any cytotoxicity, whereas phosphatidylcholine-exfoliated FLG was cytotoxic. Raman spectroscopy is a well-established technique used to study the local deformation of carbon-based composites by following the shift rates of the Raman 2D band with strain. Raman active strain coatings were produced from epoxy composites made with the FLG produced by LPE in organic solvents and by electrochemical exfoliation method. The deformation experiments on these coatings revealed little or no strain sensitivity, due to several factors such as length of flakes, processing history, graphene loading, defects in graphene and alignment of flakes within the composites. As an alternative, composite coatings made from chemical vapour deposition (CVD) graphene were investigated. Excellent strain sensitivity was observed upon various cyclic deformational sequences and Raman mapping over 100 × 100 µm area. In comparison to the commercially available wide area strain sensors, CVD graphene composite coatings with a calculated absolute accuracy of ~ ± 0.01 % strain and absolute resolution of ~ 27 microstrains show promise for wide area Raman-based strains sensors.

Depuis la découverte des propriétés physiques et électroniques du graphène, un très grand nombre de méthodes visant à produire et modifier chimiquement le graphène ont été développées afin d'étendre et améliorer ses capacités en vue de futures applications. Les travaux réalisés au cours de cette thèse ont portés sur une méthode exfoliation du graphite en phase liquide assistée d'une réaction de cycloaddition réversible. Cette approche repose sur la réaction de Diels-Alder entre le graphite et un diène masqué très réactif, et se révèle être très efficace dans des solvants organiques volatils qui ne permettent pas l'exfoliation directe du graphite. L'introduction de groupements fonctionnels sur le diène a permis de moduler les propriétés de surface de films de graphène, ainsi que de post-fonctionnaliser les feuillets de graphène afin d'apporter une plus-value au matériau
Since the discovery of the exciting properties of graphene, many techniques to produce and chemically modify graphene have been developed in order to expand and improve its properties in view of future applications. The study presented in this thesis focus on a process for the chemically-assisted exfoliation of graphite based on a reversible cycloaddition reaction. It relies on the Diels-Alder reaction between graphite and highly reactive masked diene, and it is effective even in solvents that are otherwise ineffective for exfoliation of graphite. Furthermore, it is possible to introduce functional groups on the diene, thereby enabling the tuning of the surface properties of graphene, as well as the post-functionalization of graphene sheets

This master thesis work is performed at ABB Corporate Research Center inVästerås. The aim of this study is to investigate Ag:graphene composites as slidingelectrical contacts, suitable for use in e.g. tap-changers. Three different graphenematerials, all produced by a low-cost exfoliation process, are evaluated in this study. The results are compred to an ongoing work on Ag:GO (graphene oxide) composites. This material has shown very good tribological properties, however it hasbeen difficult to handle during sintering processing. The goal of this study is to geteven better tribological, electrical and mechanical properties than Ag:GO, and also todevelop a new powder-metallurgical method to produce the Ag:graphene composites.The study also investigates the influence of graphene flake size and concentration aswell as microstructure of the Ag:graphene composites. This report focuses on aninvestigation of the graphene raw material quality from the suppliers, and friction,wear and resistance analysis of the composites. This is done by using Ramanspectroscopy, SEM with EDS, LOM, tribometer tests and resistivity analysis. Raman and SEM analyses show that none of the supplied LEG materials are ofhigh-quality G (single or bilayer), but rather multi-layer graphene or even graphite.Small amounts of graphene added to Ag gave extremly low friction (μ<0.2 vs. pureAg μ~1.3, 5 N load and 5 cm/s speed). The composite manufacturing process hadcritical steps, which have to be optimized, to obtain low values of friction. Severedegassing of the composites was observed for some sampes, but the samples stillmaintained good friction values. SEM and EDS analyses of 2dfab’s wear track show abuild-up thin carbon-containing tribofilm on the Ag surface. Indicating that G ispresent, and works as a lubricant, creating good tribological properties. The resultsfrom this project may for sure be of importance for future ABB products in specificindustrial applications.

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The different methods of obtaining two-dimensional materials are being researched intensively, due to their promising physical and chemical properties. Among the methods of obtaining graphene, the liquid phase exfoliation (LPE) of graphite is proving to be a relatively simple and efficient process for the production of flakes of high quality and large scale. It is primarily based on the separation of the layers of graphite in liquids, such as common organic solvents and aqueous surfactant solutions. In this work the exfoliation of graphite was performed in liquid phase by sonication in aqueous suspension in the presence of an industrial reagent. A comparison with suspensions not using the polymeric surfactant indicates that its presence is necessary, because it prevents the re-agglomeration of the layers after sonication, through the multipolar and electrostatic repulsion mechanism. This result coincides with the reports of most recent works on liquid-phase exfoliation of graphite.
Os diferentes métodos de obtenção de materiais bidimensionais estão sendo pesquisados intensamente, devido a suas promissoras propriedades físicas e químicas. Entre os métodos de obtenção de grafeno, a esfoliação em fase líquida (LPE) de grafite está demonstrando ser um processo relativamente simples e eficaz de produção de flocos de alta qualidade e em larga escala. Ela se baseia principalmente na separação das camadas de grafite em líquidos, tais como solventes orgânicos comuns e soluções surfactantes aquosas. Neste trabalho foi realizada a esfoliação de grafite em fase líquida através da sonificação em suspensão aquosa em presença um reagente industrial. A comparação com resultados usando suspensões sem o agente surfactante polimérico indica que a presença deste é necessária, pois evita a reaglomeração das camadas após a sonificação, através do mecanismo de multipolo e repulsão eletrostática. Este resultado coincide com os reportes dos trabalhos mais recentes realizados sobre esfoliação em fase líquida de grafite.

Grafen v kombinaci s komplexy kovů by mohl poskytnout nové přísutpy v hybridních materiálech založených na grafenové bázi a v oblasti molekulárního magnetismu. Obě témata jsou velmi diskutovaná jako taková, nicméně, výzkumu vedoucího k možnosti jejich míchání není mnoho. Vzorky byly připraveny sonikací grafitu v kapalné fázi, což vedlo k exfoliaci grafenu. Následně byly nadeponovány pomocí modiikované Lagmuirovy– Schaeferovy depoziční metody různé komplexy kovů na substrát pokrytý grafenem. Klíčovým krokem bylo určení vlastností takto připraveného materiálu. Proto byly následně vlastnosti takového hybridního materiálu charakterizovány pomocí vysokofrekvenční elektronové paramagnetické rezonance (angl. HFEPR), rastrovacího elektronového mikroskopu, (angl. SEM), Ramanovou spektroskopií a čtyř bodovou metodou měření odporu. V této práci jsme potvrdili naši presumpci, že je možné vytvořit hybridní materiál smícháním exfoliovaného grafenu s molekulárními magnety pro získání nových magnetických a elektronických vlastností, které by mohly být využity v další generaci detektorů a elektroniky.

Une solution pour réduire la consommation de Si de haute pureté dans les cellules solaires à base de Si cristallin est de faire croître une couche active mince de haute qualité sur un substrat à faible coût. L'Epitaxie en Phase Liquide (EPL) est l'une des techniques les plus appropriées, car la croissance est réalisée dans des conditions proches de l'équilibre. On s'intéresse plus particulièrement au développement et l'optimisation d'une technique de croissance stationnaire et isotherme basée sur l'évaporation du solvant : l'Epitaxie en Phase Liquide par Evaporation d'un Solvant métallique (EPLES). Les principaux critères concernant le choix du solvant, de l'atmosphère de croissance et du creuset sont d'abord présentés et permettent de concevoir une première configuration d'étude. Un modèle analytique est ensuite développé pour comprendre les mécanismes mis en œuvre et étudier la cinétique d'évaporation du solvant et de croissance. Les différentes étapes du procédé de croissance dans le cas de l'EPLES de Si sont examinées et mettent en évidence un certain nombre de difficultés technologiques liées à cette technique : contrôle de la convection dans le bain, réactivité du bain Si-M avec le creuset, transport par différence de température et dépôt pendant la phase de refroidissement. Des solutions techniques sont proposées et mise en place pour contourner les difficultés rencontrées. Des couches épitaxiées de Si uniformes comprises entre 20 et 40 µm sont alors obtenues par EPLES avec des bains Sn-Si et In-Si sur substrat Si monocristallin entre 900 et 1200°C sous vide secondaire. Les vitesses de croissance expérimentales atteintes sont comprises entre 10 et 20 µm/h et sont conformes aux prédictions du modèle cinétique. La qualité structurale obtenue est comparable à celle des couches obtenues par EPL. Des couches de type P, avec un bain dopé In et In(Ga) sont obtenues avec une concentration en dopants proches de 1017 at.cm3 compatible avec une application PV. Enfin le potentiel de l'application de cette technique est évalué en basant la discussion sur la réalisation d'une couche de Si obtenue par EPLES sur substrat multicristallin avec un bain In-Si
Crystalline Si thin films on low-cost substrates are expected to be alternatives to bulk Si materials for PV applications. Liquid Phase Epitaxy (LPE) is one of the most suitable techniques for the growth of high quality Si layers since LPE is performed under almost equilibrium conditions. We investigated a growth technology which allows growing Si epitaxial thin films in steady temperature conditions through the control of solvent evaporation from a metallic melt saturated with silicon: Liquid Phase Epitaxy by Solvent Evaporation (LPESE). We studied the main requirements regarding selection of solvent, crucible and growth ambient, and a first experimental set up is designed. An analytical model is described and discussed, aiming to predict solvent evaporation and Si crystallization rate. Growth experiments are implemented with a vertical dipping system. Growth procedure is presented and the influence, on Si growth, of melt convection, temperature gradient in the melt and Si-M reactivity with the material crucible are discussed. Solutions are proposed to improve and optimise the growth conditions. Experimentally, Si thin films were grown from Sn-Si and In-Si solution at temperatures between 900 and 1200°C under high vacuum. We are able to achieve epitaxial layers of several micrometers thickness (20-40µm). The predicted solvent evaporation rate and Si growth rate are in agreement with the experimental measurements. Regarding the structural quality, it is comparable to the crystal quality of layers grown by LPE. With In and In(Ga) melts, we can obtain P-type epitaxial layers with doping level in the range 1017 at.cm3, which is of great interest for the fabrication of solar cells. Finally, the growth of Si thin films on multicrystalline Si substrates by LPESE is discussed to assess the potential application of this technique

Mit der vorliegenden Arbeit wird das Wachstum von polykristallinem Silicium auf Glas bei niedrigen Temperaturen aus metallischen Lösungen in einem Zweistufenprozess untersucht. Im ersten Prozessschritt werden nanokristalline Siliziumschichten (nc-Si) hergestellt, entweder durch die direkte Abscheidung auf geheizten Substraten oder durch als ''Amorphous-Liquid-Crystalline''(ALC)-Umwandlung bezeichnete metall-induzierte Kristallisation. Im zweiten Prozessschritt dienen die Saatschichten als Vorlage für das Wachstum von deutlich größeren Kristalliten durch stationäre Lösungszüchtung. Die ALC-Prozessdauer konnte durch umfassende Parameterstudien signifikant reduziert werden. Die Charakterisierung der durch direkte Abscheidung auf geheizten Substraten entstehenden nc-Si Saatschichten offenbarte, dass es sich dabei um individuelle Saatkörner handelt, die in eine quasi-amorphe Matrix eingebettet sind. Die Oxidation der Saatschichten vor dem zweiten Prozessschritt wurde als ein wesentliches Hindernis für das Wachstum identifiziert. Als erfolgreichste Lösung zur Überwindung dieses Problems hat sich ein anfänglicher Rücklöseschritt erwiesen. Da diese Methode jedoch schwierig zu kontrollieren ist, wurde ein UV-Laser-System entwickelt und installiert. Erste Resultate zeigen epitaktisches Wachstum an den Stellen, an denen das Oxid entfernt wurde. Bei der Lösungszüchtung auf ALC-Schichten beginnt das Wachstum an einigen größeren Saatkristallen, von wo aus umliegende Gebiete lateral überwachsen werden. Obwohl Kristallitgrößen bis zu 50 Mikrometern erreicht wurden, war es noch nicht möglich, geschlossene Schichten zu erzielen. Durch Lösungszüchtung auf nc-Si Saatschichten hingegen konnte dieses Ziel erreicht werden. Geschlossene, polykristalline Si-Schichten wurden erzeugt, auf denen alle Si-Kristallite miteinander verbunden sind. Neben den Wachstumsexperimenten wurden 3D-Simulationen durchgeführt, in denen u.a. unterschiedliche Heizerkonfigurationen simuliert wurden.
The subject of this thesis is the investigation of the growth of polycrystalline silicon on glass at low temperatures from metallic solutions in a two-step growth process. In the first process step, nanocrystalline Si (nc-Si) films are formed either by direct deposition on heated substrates, or by a metal-induced crystallization process, referred to as amorphous-liquid-crystalline (ALC) transition. In the second process step, these seed layers serve as templates for the growth of significantly larger Si crystallites by means of steady-state solution growth. Extensive parameter studies for the ALC process helped to bring down the process duration significantly. Characterization of the nc-Si seed layers, formed by direct deposition on heated substrates, showed that the layer is composed of individual seeds, embedded in a quasi-amorphous matrix. The oxidation of the seed layers prior to the second process step was found to be a major obstacle. The most successful solution has been an initial melt-back step. As the process is hard to control, though, a UV laser system has been developed and installed. First promising results show unobstructed epitaxial growth where the oxide has been removed. Steady-state solution growth on ALC seed layers was found to start from a few larger seed crystals, and then cover the surrounding areas by lateral overgrowth. Although crystallites with sizes of up to 50 micrometers were obtained, it was not yet possible to achieve full surface coverage with a continuous layer. By solution growth on nc-Si seed layers, however, it was eventually possible to achieve this goal. Continuous, polycrystalline Si layers were grown, on which all Si crystallites are interlocked. The growth experiments were accompanied by 3D simulations, in which e.g. different heater configurations have been simulated.

This thesis explores the application of two-dimensional (2D) materials such as graphene and single layer hexagonal boron nitride (h-BN) which are produced by liquid phase exfoliation for use in printed electronics and energy composite applications. In Chapter 2 I give a broad overview of the electrical, mechanical and optical properties of 2D materials among other nanomaterials that were used in the thesis such as carbon nanotubes and conductive polymers. Additionally I review the techniques and theory behind the exfoliation and dispersion of functional layered materials. In Chapter 3 I present the coating and printing techniques which were used in this thesis along with the experimental techniques and methods which I use to characterise my inks, films and devices. Chapter 4 is the first experimental chapter of the thesis and demonstrates the printing of 2D material heterostructures to create fully printed dieletrically gated field effect transistors with 2D materials on textile and polymer substrates. In this chapter I also demonstrate reprogrammable volatile memory, p and n type inverters, complementary inverters, and logic gates which pave the way to fully printed integrated circuits, operational at room temperature and pressure with 2D materials processed in liquid. In Chapter 5, I review spray coating (a highly industrial scalable printing technique), in terms of the optimisation of its parameters to achieve thin films of nanomaterials on three-dimensional (3D) surfaces. I then demonstrate that it is possible to create large area (∼750 cm2) transparent conducting films around curved surfaces with spray coating enabling a semi-transparent (around 360°) spherical touch sensor for interactive devices. Chapter 6 explores printed photonics for applications in terahertz (THz) frequencies. Here I demonstrate the feasibility of liquid phase exfoliated graphene to create THz saturable absorbers (SAs) which could enable many applications in THz frequencies such as tomography or time-resolved spectroscopy that require mode-locked (i.e. enabling a train of short pulses to be derived from continuous-wave operation) THz pulses. I also demonstrate that these SAs can be inkjet printed on demand providing unprecedented compactness in a quantum cascade laser system. Finally in Chapter 7, I look at the application of graphene in microbial fuel cells (MFC). I demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of a graphene based electrode. As a final step graphene based anodes and cathodes which were entirely platinum free were combined to create an environmentally sustainable energy source.

碩士
國立成功大學
物理研究所
76
AlxGa(1-x)Sb半導體其能隙隨ｘ值不同而從０．７eV改變至１．４eV，此種材料在光 電元件上之應用有極大的潛力。 本文討論以液相磊晶（LPE ）技術中的超冷降溫法於銻化鎵基片上成長三種不同組成 的AlxGa(1-x)Sb，利用SEM （Scanning Electron Mircoscopy），EDAX（Energy Dis persion Analysis X-ray），測量磊晶層的特性並得到成長過程的最佳溫度曲線。Ｘ ＝０．１２的樣品表面經１：１的鹽酸和甲醇處理得可得如鏡面般的平坦，從剖面的 SEM 相片中得知鋁之莫耳分率愈高時成長速率愈慢。經XPS（X-ray Photolectron Sp ectroscopy）的測量結果指出磊晶的表面是以氧化狀態存在。由PL（Photoluminesce nce） 的測試得知在不同組成下能隙的大小分別為Ｘ＝０．０６時Ｅg ＝０．８５eV ，Ｘ＝１．１２４，Ｅg ＝０．９０８eV；Ｘ＝０．１２８，Ｅg ＝０．９１２eV； Ｘ＝０．２４２，Ｅg ＝１．０３１eV，銻化鎵的Ｅg ＝０．８eV。

碩士
國立中央大學
機械工程學系
105
Black phosphorus is one of the most stable allotropes of phosphorus, and its unique two-dimensional lamellar structure makes it have many excellent properties. The two-dimensional multilayer crystal structure of black phosphorus is similar to graphene, and the lamellar layer is bonded to each other by Van der Waals bonding. In early research, it is easy to tear off the nano-level black phosphorus by mechanical exfoliation process and the nano-level black phosphorus is called phosphorene. The band gap of phosphorene changes because of different numbers of its layers, and the adjustable range of band gap is greater than any of today’s transitional metal disulfide. Meanwhile, phosphorene is applied to electronic components with a high on-off ratio of 105, and carrier mobility of ~ 1000 cm2/Vs, both of which are excellent features required as logic devices. Phosphorene is a remarkable and novel two-dimensional material expected to replace silicon as the transporting channel of the semiconducting device. However, in the past studies, black phosphorus was prone to be oxidized easily in the atmosphere and this phenomenon was obviously observed on the few layers phosphorene, which results in deterioration of its intrinsic electrical transport properties. How to protect the black phosphorus without oxidation and maintain the excellently electrical property is an important issue. In addition, the process to quantify the synthesis of phosphorene is few to be researched, while the material properties are still at the researching stage. In this study, we obtained phosphorene by liquid phase exfoliation, and analyzed its material properties and stability. We used different solvents as exfoliation medium, and found that 1% sodium dodecyl sulfate (SDS) dissolved in deoxygenated water solvent can get a high productivity. The thickness of few layered phosphorene is about 6 nm. The uniformity in thickness of exfoliated phosphorene with SDS solvent is better than it with other solvents. In addition, the deterioration rate of phosphorene could be restrained by encapsulating electrochemical graphene with its excellent resistance of water and oxygen. The solution was prepared by mixing the solution with dimethylformamide (DMF) as the dispersion of phosphorene and graphene. Therefore, high quality phosphorene can be obtained by optimizing this synthesis method, the production of. Our study also demonstrates a process for the assembly of the phosphorene into a continuous film which is effective in retarding the oxidation of the phosphorene. The surface of the phosphorene film can maintain the intrinsic state, so that phosphorene can be protected within 60 days from the impact of oxidation. It is attractive and has benefit to form the continuous and large area film with a few layers of phosphorene for the applications of electrical devices in the future.

碩士
國立成功大學
地球科學系
104
Graphene dispersions were produced by liquid-phase exfoliation method. Sonication of graphite powder in alcohol solution can yield graphene dispersions which contains numerous few-layers graphene sheets at micrometer scale, and they can be identified by the Raman spectroscopy and atomic force microscope (AFM). Raman spectroscopy analysis revealed two peaks at ~1580cm-1 and 2600~2700cm-1 called G peak and 2D peak, we focus on shape difference of 2D peak that can use to determine the graphene layers. The conductivity and concentration of dispersions is determined by the conductivity meter and visible absorbance via Lambert – Beer’s law (A=abc). It shows the yield of graphene is about 0.63%. In order to examine the stability of the graphene dispersions, the solution was placed for a month and the concentration variation was measured every interval. The experimental parameters are optimized by adjusting alcohol-water mixture proportion, sonication time, graphite mass and centrifugation speed. This study provides a green liquid-phase exfoliation method to prepare few-layers graphene with alcohol-water mixture.

abstract: Ultrasonication-mediated liquid-phase exfoliation has emerged as an efficient method for producing large quantities of two-dimensional materials such as graphene, boron nitride, and transition metal dichalcogenides. This thesis explores the use of this process to produce a new class of boron-rich, two-dimensional materials, namely metal diborides, and investigate their properties using bulk and nanoscale characterization methods. Metal diborides are a class of structurally related materials that contain hexagonal sheets of boron separated by metal atoms with applications in superconductivity, composites, ultra-high temperature ceramics and catalysis. To demonstrate the utility of these materials, chromium diboride was incorporated in polyvinyl alcohol as a structural reinforcing agent. These composites not only showed mechanical strength greater than the polymer itself, but also demonstrated superior reinforcing capability to previously well-known two-dimensional materials. Understanding their dispersion behavior and identifying a range of efficient dispersing solvents is an important step in identifying the most effective processing methods for the metal diborides. This was accomplished by subjecting metal diborides to ultrasonication in more than thirty different organic solvents and calculating their surface energy and Hansen solubility parameters. This thesis also explores the production and covalent modification of pristine, unlithiated molybdenum disulfide using ultrasonication-mediated exfoliation and subsequent diazonium functionalization. This approach allows a variety of functional groups to be tethered on the surface of molybdenum disulfide while preserving its semiconducting properties. The diazonium chemistry is further exploited to attach fluorescent proteins on its surface making it amenable to future biological applications. Furthermore, a general approach for delivery of anticancer drugs using pristine two-dimensional materials is also detailed here. This can be achieved by using two-dimensional materials dispersed in a non-ionic and biocompatible polymer, as nanocarriers for delivering the anticancer drug doxorubicin. The potency of this supramolecular assembly for certain types of cancer cell lines can be improved by using folic-acid-conjugated polymer as a dispersing agent due to strong binding between folic acid present on the nanocarriers and folate receptors expressed on the cells. These results show that ultrasonication-mediated liquid-phase exfoliation is an effective method for facilitating the production and diverse application of pristine two-dimensional metal diborides and transition metal dichalcogenides.
Dissertation/Thesis
Doctoral Dissertation Chemistry 2018

In order to meet the demand for a highly profitable, versatile and environmentally friendly graphene production method, Graphenest developed a methodology based on liquid phase exfoliation that was now tested using a different raw material: highly oriented pyrolytic graphite (HOPG). After the exfoliation, the obtained multilayer graphene dispersion underwent to a step of atomization using a mixture of air-ozone, in order to achieve a material having a higher oxidation level. To accomplish this, the exfoliation process was carried out applying a Design of Experiments (DoE) that allowed to understand the effect of four different variables on the yield of graphene’s production: 1) temperature; 2) power density of ultrasound equipment; 3) frequency of ultrasound equipment; and 4) initial concentration of dispersed graphite. All the samples were characterized by Raman spectroscopy and Dynamic Light Scattering (DLS) in order to determine which processual conditions allow the obtaining of graphene particles with the smallest lateral size and thickness. Additionally, the concentration of graphene dispersed obtained in each of the exfoliation Runs was determined by UV-Vis spectroscopy after a centrifugation step at different speeds (1000, 2000 and 4000 rpm). Before the atomization step, the samples with the desired characteristics (smaller lateral size and thickness) were characterized by transmission electron microscopy TEM. Regarding the processual conditions, the DoE revealed that the combination of the lowest level of each variable under analysis allowed the production of more quantity (higher yield) and better quality (smaller lateral size and thickness) of graphene particles. The crystalline graphene samples showed ultrafine nature and good flexibility. In order to obtain a fast and efficient way for the functionalization of this nanomaterial, the production of graphene oxide was tested relying on the usage of an air-ozone gas mixture during the atomization process. To verify the validity of the oxidation, a selected sample was atomized exclusively with air and in paralell with a mixture of air-ozone. These samples were then characterized by Xray photoelectron spectroscopy (XPS) and the results, although to some extent inconclusive, revealed a residual oxidation.
Com vista a responder à procura de um método de produção de grafeno altamente rentável, versátil e amigo do ambiente, a Graphenest desenvolveu uma metodologia baseada numa exfolição em fase líquida que foi agora testada com recurso ao uso de uma matéria-prima diferente: grafite pirolitica altamente orientada (HOPG). Após a exfoliação, a dispersão de grafeno de multicamadas passou por uma etapa de atomização utilizando uma mistura de ar-ozono, por forma a se obter um material com um nível de oxidação superior. Para tal, o processo de exfoliação foi realizado, efetuando um desenho de experiências (DoE) que permitisse compreender o efeito de quatro variáveis distintas no rendimento da produção de grafeno: 1) temperatura; 2) densidade de potência do equipamento de ultrassons; 3) frequência do equipamento de ultrassons; e 4) concentração inicial de grafite dispersa. Todas as amostras foram caracterizadas por espectroscopia Raman e por Dispersão Dinâmica de Luz (DLS) com o objetivo de determinar as condições processuais que permitem a obtenção de particulas com tamanho lateral e espessura mais pequenas. Adicionalmente, a concentração de grafeno disperso após cada uma das corridas de exfoliação foi determinada por espectroscopia UVVis, após centrifugação com diferentes velocidades (1000, 2000 e 4000 rpm). Antes da etapa de atomização, as amostras com as caracteristicas pretendidas (menor dimensão lateral e espessura) foram caracterizadas por microscopia eletrónica de trasmissão (TEM). Relativamente às condições processuais, o DoE revelou que a combinação do nível mais baixo de cada variável em análise permitiu a produção de maior quantidade (maior rendimentos) e melhor qualidade (menor dimensão lateral e espessura) de partículas de grafeno. As amostras cristalinas de grafeno manifestaram natureza ultrafina e boa flexibilidade. De modo a se obter uma forma rápida e eficiente para a funcionalização deste nanomaterial, a produção de óxido de grafeno foi testada, recorrendo a uma mistura de gás ar-ozono durante o processo de atomização. Para avaliar a oxidação, uma determinada selecção de amostras foi atomizada com ar e paralelamente com uma mistura de ar-ozono. Essas amostras foram, de seguida, caracterizadas por espectroscopia de fotoeléctrones excitados por raios-X (XPS) e os resultados, embora, de certa forma, inconclusivos, revelaram uma oxidação residual.
Mestrado em Engenharia Química

碩士
國立成功大學
材料科學及工程學系
104
This study investigates room temperature gas sensing of MoS2 nanosheets synthesized by liquid phase exfoliation followed by annealing in oxygen atmosphere. Scanning electron microscopy images clearly showed that 45vol% ethanol could exfoliate bulk MoS2 into nanosheets. Raman spectrometry and ultraviolet-visible spectrometry also showed that 45vol% ethanol successfully exfoliated bulk MoS2 into few layers. The structure of MoS2 nanosheets was analyzed using Transmission electron microscopy. X-ray photoelectron spectroscopy clearly showed that Mo and S were partially oxidized. Using annealing in oxygen atmosphere, as surface modification, the performance of MoS2 gas sensing could be improved. Using oxidized MoS2 nanosheets, the sensitivity of 0.7ppm NH3 was enhanced from 8.1% to 8.6% at room temperature.

by Clive Hau Ming Shiu.
On t.p., "x" and "1-x" are subscript.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.
Includes bibliographical references (leaves [126]-[130]).
ACKNOWLEDGEMENT --- p.i
ABSTRACT --- p.ii
TABLE OF CONTENTS --- p.iii
Chapter Chapter 1 --- INTRODUCTION --- p.1
Chapter Chapter 2 --- THEORY --- p.3
Chapter 2.1 --- Fundamentals of GaAs and AlGaAs --- p.3
Chapter 2.1.1 --- Crystal structure and properties of GaAs --- p.4
Chapter 2.1.2 --- General properties of GaAs at 300K --- p.5
Chapter 2.1.3 --- Temperature dependence of bandgap for GaAs --- p.6
Chapter 2.1.4 --- Dopants of GaAs --- p.7
Chapter 2.1.5 --- Properties of AlGaAs --- p.8
Chapter 2.2 --- Phase Equilibrium of GaAs and AlGaAs --- p.10
Chapter 2.2.1 --- Phase diagram of Ga-As binary system --- p.11
Chapter 2.2.2 --- Phase diagram of Al-Ga-As ternary system --- p.13
Chapter 2.3 --- Principle of LPE growth --- p.17
Chapter 2.3.1 --- General concept of liquid phase epitaxy --- p.17
Chapter 2.3.2 --- Fundamental methods of LPE growth --- p.19
Chapter 2.4 --- Dopants in GaAs and AlGaAs system --- p.21
Chapter 2.4.1 --- Common dopants in GaAs --- p.22
Chapter 2.4.2 --- Tellurium in GaAs --- p.23
Chapter 2.4.3 --- Silicon in GaAs --- p.24
Chapter 2.4.4 --- Tellurium and Tin in AlGaAs --- p.26
Chapter Chapter 3 --- LPE SYSTEM FOR GaAs AND AlGaAs --- p.28
Chapter 3.1 --- Basic requirements for horizontal sliding LPE system --- p.30
Chapter 3.2 --- Cleaning process of the LPE system --- p.37
Chapter 3.2.1 --- Cleaning procedures of the quartz parts --- p.37
Chapter 3.2.2 --- Cleaning procedures of the stainless steel tubing --- p.38
Chapter 3.2.3 --- Cleaning procedures of the graphite boat --- p.39
Chapter 3.3 --- Final examination for LPE growth --- p.41
Chapter 3.3.1 --- Examining the sealing of the system --- p.41
Chapter 3.3.2 --- Examining the palladium hydrogen purifier --- p.41
Chapter 3.3.2.1 --- Measuring the dew point --- p.41
Chapter 3.3.2.2 --- Measuring the content of oxygen and nitrogen --- p.42
Chapter 3.3.3 --- Adjusting and measuring the isothermal zone in the fumace --- p.42
Chapter 3.3.4 --- Measuring of background impurity --- p.43
Chapter 3.3.5 --- Inspection of the operating chamber --- p.44
Chapter Chapter 4 --- EXPERIMENTALS --- p.45
Chapter 4.1 --- Determination of GaAs and AlGaAs content in the source melt --- p.45
Chapter 4.2 --- Calculation of GaAs and AlGaAs content in the source melt --- p.45
Chapter 4.3 --- Experimental determination of source melt composition --- p.48
Chapter 4.4 --- LPE growth method --- p.49
Chapter 4.5 --- Thickness control of LPE epilayers --- p.49
Chapter 4.6 --- Experimental procedures --- p.50
Chapter Chapter 5 --- RESULTS AND DISCUSSIONS --- p.63
Chapter 5.1 --- Growth condition studies of GaAs --- p.63
Chapter 5.1.1 --- Experimental --- p.63
Chapter 5.1.2 --- Phase equilibrium of GaAs in the range of 780 to 840 °C --- p.63
Chapter 5.1.3 --- Results of undoped GaAs epilayers --- p.67
Chapter 5.1.4 --- Results of Si doped GaAs epilayers --- p.72
Chapter 5.2 --- Growth condition studies of AlxGa1-xAs for x=0.1 to 09 --- p.73
Chapter 5.2.1 --- Phase equilibrium of AlxGa1-xAs for x=0.1 to 09 --- p.73
Chapter 5.2.2 --- Relation between saturation of solution and he flatness of interface between epilayer and substrate --- p.79
Chapter 5.2.3 --- Determination of composition x in AlxGa1-xAs --- p.82
Chapter 5.2.4 --- Relation between epilayer thickness and x in AlxGa1-xAs --- p.84
Chapter 5.3 --- High AlxGa1-xAs with x ´ 0.9 ° at 780 °C --- p.87
Chapter 5.3.1 --- Deposition rate of high AlxGa1-xAs epilayer versus cooling rate --- p.87
Chapter 5.3.2 --- Thickness profiles of epilayers versus cooling rate --- p.89
Chapter 5.3.3 --- Spectroscopic refractive index of high AlxGa1-xAs in the visible light spectrum --- p.94
Chapter 5.3.4 --- Rocking curves of high AlxGa1-xAs --- p.96
Chapter 5.4 --- Tellurium doped AlxGa1-xAs with x ranging from 0.1 to 09 --- p.98
Chapter 5.4.1 --- Carrier concentration versus composition x in AlxGa1-xAs --- p.98
Chapter 5.4.2 --- Carrier concentration of Al0.3Ga0.7As versus Te mole fraction --- p.100
Chapter 5.4.3 --- Donor activation energy of Te Versus x in AlxGa1-xAs --- p.102
Chapter 5.4.4 --- Refractive index of Te doped AlxGa1-xAs at 300K --- p.105
Chapter 5.4.5 --- Dependence of solubility upon Te doping level --- p.106
Chapter 5.5 --- Heavily tellurium doped Al0.3Ga0.7As --- p.107
Chapter 5.5.1 --- Diffractometry study of heavily Te doped Al0.3Ga0.7As --- p.108
Chapter 5.5.2 --- Morphological studies and interface studies of heavily Te doped Al0.3Ga0.7As --- p.112
Chapter Chapter 6 --- CONCLUSION --- p.119
APPENDIX Photoluminance Analysis at room temperature
REFERENCE

碩士
國立中正大學
化學工程研究所
106
The study is divided into two parts. In the first part, we used liquid phase exfoliation to produce graphene. According to distinct operating time, we can observe different ultraviolent/visible spectrum, and linear relationship between operating time and the intensity of absorbance. By diluting the supernatant and comparing the results of uv-vis characterization, a calibration curve was obtained, and it can be served as quantitative indicator. From the results of TEM and AFM, the size of graphene was approximately 500 nm to 5 um, and height was about 1-10 layers graphene. In the second part, graphene quantum dots（GQDs） were derived from carbon black by ball-milling technique. A simple and innovative method was obtained, and we used the mixture of sodium carbonate and carbon nano-capsule to synthesize nanoscale carbon structure. From the observation of TEM, the size of GQDs ranged from 1 to 3.5 nm. GQDs exhibited lots of unique optical properties compared to graphene flakes, particular in PL performance. By PLE analysis, we realized that the band-gap of GQDs were about 3.95 eV.

abstract: Liquid-phase exfoliation (LPE) is a straightforward and scalable method of producing two-dimensional nanomaterials. The LPE process has typical been applied to layered van der Waals (vdW) solids, such as graphite and transition metal dichalcogenides, which have layers held together by weak van der Waals interactions. However, recent research has shown that solids with stronger bonds and non-layered structures can be converted to solution-stabilized nanosheets via LPE, some of which have shown to have interesting optical, magnetic, and photocatalytic properties. In this work, two classes of non-vdW solids – hexagonal metal diborides and boron carbide – are investigated for their morphological features, their chemical and crystallographic compositions, and their solvent preference for exfoliation. Spectroscopic and microscopic techniques are used to verify the composition and crystal structure of metal diboride nanosheets. Their application as mechanical fillers is demonstrated by incorporation into polymer nanocomposite films of polyvinyl alcohol and by successful integration into liquid photocurable 3D printing resins. Application of Hansen solubility theory to two metal diboride compositions enables extrapolation of their affinities for certain solvents and is also used to find solvent blends suitable for the nanosheets. Boron carbide nanosheets are examined for their size and thickness and their exfoliation planes are computationally analyzed and experimentally investigated using high-resolution transmission electron microscopy. The resulting analyses indicate that the exfoliation of boron carbide leads to multiple observed exfoliation planes upon LPE processing. Overall, these studies provide insight into the production and applications of LPE-produced nanosheets derived from non-vdW solids and suggest their potential application as mechanical fillers in polymer nanocomposites.
Dissertation/Thesis
Doctoral Dissertation Chemistry 2020

Nowadays we’re living in a wireless connected world. Our phones, computers, and even everyday appliances such as clocks, cameras, etc. are getting out of the grid using batteries as its main source of energy. It’s becoming more and more demanding to sustain an increase in energy consumption of these devices while maintaining a good battery life. As a result, we must develop batteries that are cheaper, better and smaller than ever before. Many batteries have been developed in the past few years, such as Nickel and sulfur batteries. But it is the lithium-ion batteries that has the most significant improve in use, due to its high stability and easiness to produce. There are plenty of ways to improve a Lithium-ion battery, and the most effective and useful is improving the cathode. For this, Nanostructured Vanadium Pentoxide, an earth rich, cheap and with higher energy density than traditional materials was used in this present work. Liquid-phase exfoliation was used to produce the nanostructure, while XRD, SEM, BET and XPS were used to confirm its structure. For the batteries, galvanostatic charge-discharge and cyclic voltammetry were used to test its performance as a cathode material.