Geschichtete bzw. 2D Materialien bieten interessante Eigenschaften für Halbleiteranwendungen, wie Photonik durch direkte Bandlücken und Miniaturisierung durch atomar dünne Schichten. Diese Arbeit behandelt die Isolierung von 2D-Materialien und die Kontrolle über ionische Modulation in den resultierenden Bauteilen. Im ersten Kapitel wird eine silbervermittelte Exfoliation für MoS₂ eingeführt, die Monolagen mit großer Fläche liefert. Diese Technik ist ebenso leistungsfähig wie goldvermittelte Prozesse und erfordert nur einen einfachen Heizschritt, was zukünftige Exfoliationen erleichtern könnte. Die folgenden Kapitel befassen sich mit Funktionen, die durch kontrolliertes ionisches Gating ermöglicht werden. Im zweiten Kapitel wird die kontrollierte Li-Interkalation in LixZrNCl genutzt, um Supraleitung bei niedriger Ladungsträgerdichte zu untersuchen (BCS-BEC-Übergang). Durch Steuerung der Li-Menge wurden Veränderungen in der Vortex-Dynamik aufgedeckt, z.B. ein Vorzeichenwechsel im Vortex-Hall-Effekt, was auf eine Veränderung der Vortex-Flussdynamik in BEC-ähnlicher Supraleitung zurückgeführt wurde. Diese Erkenntnisse sind relevant für die Entwicklung von Supraleitern. Das dritte Kapitel wechselt zu Bauteilen auf Basis der elektrochemischen Doppelschicht (EDL). Ein 2D MoS₂-synaptischer Transistor wurde demonstriert, wobei gezeigt wurde, dass die Hysterese auf Ionenretention an der EDL zurückzuführen ist. Diese Kombination eines 2D-Materials mit einem Polymerelektrolyten emuliert synaptische Lernprozesse wie gepaarte Puls-Fazilitation und arbeitet energieeffizient. Das letzte Kapitel verlagert das ionische Gating auf das Substrat mittels Li-Ionen-leitender Keramiken für operando-Messungen an 2D-Materialien. Zusammenfassend demonstriert diese Arbeit neben der Exfoliation die vielfältigen Funktionen, die durch kontrolliertes ionisches Gating verfügbar sind, einschließlich Supraleitung bei niedriger Ladungsträgerdichte, neuromorphe Bauteile und operando-Plattformen. / Layered materials and their 2D single-layer forms offer interesting properties for semiconductor applications, such as photonics due to direct band gaps and miniaturization through atomically thin layers. This work addresses the isolation of 2D materials and the control via ionic modulation in the resulting devices. In the first chapter, a silver-mediated exfoliation for MoS₂ is introduced, yielding large-area monolayers. This technique is as effective as gold-mediated processes and requires only a simple heating step, potentially simplifying future exfoliations. The following chapters explore functions enabled by controlled ionic gating. The second chapter utilizes controlled Li intercalation in LixZrNCl to investigate superconductivity at low charge carrier densities to investigate superconductivity within the BCS-BEC crossover. By adjusting the Li content, changes in vortex dynamics were revealed, such as a sign reversal in the vortex Hall effect, attributed to altered vortex flow in increasingly BEC-like superconductivity. These findings are relevant for the development of future superconductors. The third chapter shifts to devices based on the electric double layer (EDL). A 2D MoS₂ synaptic transistor was demonstrated, showing that hysteresis and hence the short-term memory effect stems from ion retention in the EDL formed at the 2D material electrolyte interface. This combination of a 2D material with a polymer electrolyte emulates synaptic learning processes like paired-pulse facilitation and operates in an energy-efficient manner. The final chapter translates the ionic gating to the substrate using Li-ion-conducting ceramics for operando measurements on 2D materials in “open-hood” devices. In summary, besides exfoliation, this work demonstrates the diverse functions achievable through controlled ionic gating applied to 2D and layered materials, including superconductivity at low charge carrier densities, neuromorphic devices, and operando platforms.

In-situ polymerization is one of the most efficient methods for production of polymer clay nanocomposites. In-situ polymerization of olefins using coordination catalysts is a type of heterogeneous polymerization. In order to achieve acceptable clay nanolayer dispersion in the polyolefin matrix, the clay layer exfoliation and particle break up during the polymerization are essential requirements. A literature review on polyolefin/clay nanocomposite is given in Chapter 2. In Chapter 3, we present a new mathematical model, which is as an extension of the multigrain model (MGM), to describe the intercalative polymerization and expansion of clay interlayer spaces during polymerization using clay-supported metallocenes. The results from the model show that, under the studied conditions, mass transfer is not a strong factor controlling clay exfoliation and particle break up. If the polymerization active sites are supported uniformly on all clay surfaces, effective exfoliation will be achieved after a relative short polymerization time. In practice, obtaining good dispersion of clay nanolayers with uniform properties requires that the active sites be exclusively located on the clay nanolayer surfaces, and not extracted by the solvent to form a homogeneous solution. Factors favouring active site extraction would result in nanocomposites with poor properties. In addition, high polymerization activities, stable polymerization runs, and ease of supporting are other criteria for a successful in-situ polymerization. For this purpose we established a catalyst supporting method by which most of these requirements were met. In this method, the water content on the clay surface, which is considered as poison for the metallocene catalyst, was used to produce MAO upon reaction with trimethylaluminum (TMA). Using this method, polymerization was highly active in absence of MAO cocatalyst, knowing that MAO cocatalyst promotes active site extraction from the clay surface and results in poor powder morphology. Chapter 4 describes the development of this supporting methodology. Chapter 4 also investigates the effect of the organic modification type existing on the clay surface on the success of catalyst supporting and in-situ polymerization. We found that using the proposed supporting procedure, only tertiary ammonium type modification enhanced the in-situ polymerization, whereas the quaternary ammonium worsened the catalyst supporting efficiency and led to catalyst with poor or no polymerization activity. It is suggested that, in addition to enhancing clay surface-organic solvent compatibility (which facilitates catalyst supporting), the tertiary ammonium cation reacts with the in-situ produced MAO and increases the stability of the cocatalyst bonded to the clay surface. The effect of different polymerization conditions on the polymerization behavior and nanocomposite structural properties, such as catalyst loading during supporting, polymerization temperature and triisobutylaluminum (TIBA) concentration, were studied in Chapter 5. It was found that TIBA acts merely as scavenger. High polymerization activities were obtained with low Al/Zr ratios (Al from TIBA) and increased Al concentration decreased the polymerization activity and also the quality of powder morphology. Catalyst loading in the supporting step showed to have an important role in determining the final properties. The clay particles with higher catalyst loading resulted in better exfoliation and powder morphologies The effect of solvent type during catalyst supporting and polymerization was studied in Chapter 6. It was shown that catalyst supporting in n-hexane resulted in polymerizations with higher activities and polymers with higher molecular weight were produced. Polymerization with catalyst supported in hexane showed different ethylene uptake profiles, suggesting different mechanism of exfoliation. It is suggested that using this catalyst, the clay is mostly exfoliated before polymerization started. Similar to the original clay, the catalyst supporting efficiency on the organically modified clay was close to 100 percent. However, comparing the polymerization activities of these catalysts to those that were supported directly in the reactor just before the polymerization (in-reactor, or in-situ, supported catalysts) shows that a considerable fraction of the active sites are deactivated during the prolonged contact between catalyst and clay support surface. In Chapter 5, it was shown that the in-reactor supported catalyst had considerably higher polymerization activities, up to 40 percent of that of the homogeneous catalyst. Nanocomposites made with in-reactor supported catalysts had powder morphology and nanaolayer dispersion comparable to those made with clay-supported catalysts.

In-situ polymerization is one of the most efficient methods for production of polymer clay nanocomposites. In-situ polymerization of olefins using coordination catalysts is a type of heterogeneous polymerization. In order to achieve acceptable clay nanolayer dispersion in the polyolefin matrix, the clay layer exfoliation and particle break up during the polymerization are essential requirements. A literature review on polyolefin/clay nanocomposite is given in Chapter 2. In Chapter 3, we present a new mathematical model, which is as an extension of the multigrain model (MGM), to describe the intercalative polymerization and expansion of clay interlayer spaces during polymerization using clay-supported metallocenes. The results from the model show that, under the studied conditions, mass transfer is not a strong factor controlling clay exfoliation and particle break up. If the polymerization active sites are supported uniformly on all clay surfaces, effective exfoliation will be achieved after a relative short polymerization time. In practice, obtaining good dispersion of clay nanolayers with uniform properties requires that the active sites be exclusively located on the clay nanolayer surfaces, and not extracted by the solvent to form a homogeneous solution. Factors favouring active site extraction would result in nanocomposites with poor properties. In addition, high polymerization activities, stable polymerization runs, and ease of supporting are other criteria for a successful in-situ polymerization. For this purpose we established a catalyst supporting method by which most of these requirements were met. In this method, the water content on the clay surface, which is considered as poison for the metallocene catalyst, was used to produce MAO upon reaction with trimethylaluminum (TMA). Using this method, polymerization was highly active in absence of MAO cocatalyst, knowing that MAO cocatalyst promotes active site extraction from the clay surface and results in poor powder morphology. Chapter 4 describes the development of this supporting methodology. Chapter 4 also investigates the effect of the organic modification type existing on the clay surface on the success of catalyst supporting and in-situ polymerization. We found that using the proposed supporting procedure, only tertiary ammonium type modification enhanced the in-situ polymerization, whereas the quaternary ammonium worsened the catalyst supporting efficiency and led to catalyst with poor or no polymerization activity. It is suggested that, in addition to enhancing clay surface-organic solvent compatibility (which facilitates catalyst supporting), the tertiary ammonium cation reacts with the in-situ produced MAO and increases the stability of the cocatalyst bonded to the clay surface. The effect of different polymerization conditions on the polymerization behavior and nanocomposite structural properties, such as catalyst loading during supporting, polymerization temperature and triisobutylaluminum (TIBA) concentration, were studied in Chapter 5. It was found that TIBA acts merely as scavenger. High polymerization activities were obtained with low Al/Zr ratios (Al from TIBA) and increased Al concentration decreased the polymerization activity and also the quality of powder morphology. Catalyst loading in the supporting step showed to have an important role in determining the final properties. The clay particles with higher catalyst loading resulted in better exfoliation and powder morphologies The effect of solvent type during catalyst supporting and polymerization was studied in Chapter 6. It was shown that catalyst supporting in n-hexane resulted in polymerizations with higher activities and polymers with higher molecular weight were produced. Polymerization with catalyst supported in hexane showed different ethylene uptake profiles, suggesting different mechanism of exfoliation. It is suggested that using this catalyst, the clay is mostly exfoliated before polymerization started. Similar to the original clay, the catalyst supporting efficiency on the organically modified clay was close to 100 percent. However, comparing the polymerization activities of these catalysts to those that were supported directly in the reactor just before the polymerization (in-reactor, or in-situ, supported catalysts) shows that a considerable fraction of the active sites are deactivated during the prolonged contact between catalyst and clay support surface. In Chapter 5, it was shown that the in-reactor supported catalyst had considerably higher polymerization activities, up to 40 percent of that of the homogeneous catalyst. Nanocomposites made with in-reactor supported catalysts had powder morphology and nanaolayer dispersion comparable to those made with clay-supported catalysts.

2D molybdenum disulfide (MoS₂) gives a new inspiration for the field of nanoelectronics, photovoltaics, and sensorics. However, the most common processing technology, e.g., liquid‐phase based scalable exfoliation used for device fabrication, leads to the number of shortcomings that impede their large area production and integration. Major challenges are associated with the small size and low concentration of MoS₂ flakes, as well as insufficient control over their physical properties, e.g., internal heterogeneity of the metallic and semiconducting phases. Here it is demonstrated that large semiconducting MoS₂ sheets (with dimensions up to 50 µm) can be obtained by a facile cathodic exfoliation approach in nonaqueous electrolyte. The synthetic process avoids surface oxidation thus preserving the MoS₂ sheets with intact crystalline structure. It is further demonstrated at the proof‐of‐concept level, a solution‐processed large area (60 × 60 µm) flexible Ebola biosensor, based on a MoS₂ thin film (6 µm thickness) fabricated via restacking of the multiple flakes on the polyimide substrate. The experimental results reveal a low detection limit (in femtomolar–picomolar range) of the fabricated sensor devices. The presented exfoliation method opens up new opportunities for fabrication of large arrays of multifunctional biomedical devices based on novel 2D materials.

This work deals with issues of application of the graphene material in the field of electrochemical energy storage. It includes basic graphene properties, the overview of methods for the production of lithium-iron-phosphate/graphene composites and results of different research approaches. The general aim is to present growing opportunity of application of graphene based composites in the electrochemical energy storage field. In the experimental part of this work, a electrochemical exfoliation of graphite and a production of LFP/G composites with different amount of graphene material and with different types of graphene material are carried out. This work includes also x-ray diffraction spectroscopy measurements and the evaluation of impacts of graphene additives on final properties of the electrochemical energy storage.

Monolayer two-dimensional (2D) materials have been regarded as a hot topic in the fields of condensed matter physics, materials science, and chemistry due to their unique physical, chemical, and electronic properties. However, the research on the preparation method and properties understanding of the 2D monolayer are inadequate. In this dissertation, taking 2D nickel-iron layered double hydroxides (NiFe LDHs) and molybdenum disulfide (MoS2) as examples, the practicability of the direct synthesis of NiFe LDHs monolayer and the thermal enhancement catalytic performance of 2D MoS2 monolayer (MoS2 ML) are discussed. First, a one-pot synthetic strategy (bottom-up method) is presented to synthesize 2D NiFe-based LDHs monolayers, including NiFe, Co-, Ru-, doped, and Au-modified NiFe LDHs. The prerequisite and universality of this strategy are investigated and confirmed. The features of LDHs are characterized by advanced technologies. The obtained LDH bulks own a large interlayer spacing up to 8.2 Å, which can be facilely exfoliated into monolayers in water by hand-shaking within 10 s. As a result, the as-prepared NiFe-based LDH monolayers display a good electrocatalytic oxygen evolution reaction (OER) performance. This facile strategy paves the way for designing easily exfoliated LDHs for highly active catalysts and energy conversion devices based on other monolayer LDHs. Second, with gold-modified tape, 2D MoS2 ML is exfoliated from the bulk crystal through a micromechanical exfoliation method (top-down strategy). The thermal effects of MoS2 ML are confirmed by Raman and photoluminescence (PL) spectra. Moreover, an on-chip MoS2 ML hydrogen evolution reaction (HER) reactor is designed and fabricated. The thermal effects generate efficient electron transfer in the MoS2 ML and at the electrolyte-catalyst (MoS2 ML) interface, leading to an enhanced HER performance. Compared to the results obtained at room temperature, the MoS2 ML shows a direct thermal enhanced HER performance at higher temperatures. In summary, the findings and understandings, the direct synthesis and direct thermal enhancement catalytic performance, of 2D monolayers offer a guideline for synthesizing and catalyst application of other 2D monolayers.

The demand for today's material resources for energy storage is rapidly increasing and can result in both environmental and political conflicts that can affect the development of electronic devices due to high prices and limitations of raw materials for batteries. In this study, potential future composite electrodes were synthesised with an ex-situ approach by compositing redox-active 2,6-Diaminoanthraquinone and 1,3,5-Triformylphloroglucinol covalent organic framework (DAAQ-TFP COF) with conductive delaminated Ti3C2Tx MXene to maximise the number of redox-active moieties during cycling. In addition, solvothermal synthesis with the implementation of mechanical grinding as an exfoliation method was used to try to obtain DAAQ-TFP nanosheets to increase both the contact area between the two materials and the number of charge carriers. The sample was analysed with PXRD and BET surface analysis to characterise the crystallinity meanwhile SEM was utilised to study the morphology of the COF and the composite material. The specific capacitance of each electrode was estimated by cyclic voltammetry. The study showed a decrease in reduced specific capacitance with lower MXene content. Hence, this concludes pure Ti3C2Tx sheets have the highest capacitance contribution with a value of 48.79 Fg-1 meanwhile the composite electrode with a ratio of 1:1 was estimated to 32.26 Fg-1 with 0.0928 % of its moieties undergoing a redox reaction. A reduced capacitance with an increased COF-MXene ratio indicates that MXene contributes with more capacity relative to the COF, in combination with a non-successful exfoliation of DAAQ-TFP to single-layered nanosheets, reducing the interactions between the two materials.

Inkjet-printing of graphene is a desirable additive-manufacturing process for rapid-prototyping and centers around the readily scalable process of liquid-phase exfoliation of graphene. Unfortunately, most common solvents for this process such as N-methyl-2-pyrrolidone (NMP) or cyclohexanone/terpineol (C/T) are toxic. Dihydrolevoglucosenone, commonly known as Cyrene, is a renewable and fully biodegradable non-toxic solvent that represents an ideal alternative. Here, we demonstrate the potential of Cyrene-based graphene inks through few-layer inkjet printing on flexible substrates to produce non-toxic conductors a strain-mediated mechanism for biosensing. These strain-sensors were used to detect bodily motion for wearable electronics, where gel-based, wet-electrodes are a common feature within the broader class of sensors used in electromyography (EMG). The environmentally friendly and non-toxic nature of this solvent has promise not only for wearables, but also in agricultural and food industries where sensors need to be safe for potential contacts made to food supplies. Moreover, it has demonstrated superior suspension of graphene flakes compared to traditional solvents.