In the last decade, the emerging classes of two-dimensional (2D) materials have been studied as potential candidates for various sensing technologies, including magnetic and optoelectronic detectors. Within the quickly growing portfolio of 2D materials, graphene and semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive candidates for various sensor applications because of their unique properties such as extreme thickness, excellent electrical and optical properties. In this thesis, I have exploited the unique properties of graphene and TMDs materials to develop 2D detectors based on field effect transistors for sensing magnetic field and light. In the first part of this thesis I have shown how the sensitivity of the properties of 2D materials to their surrounding environment can be turned into a feature useful to create new types of magnetic field sensors. The first experimental demonstration of this concept involved the use of graphene deposited on hexagonal Boron Nitride (h-BN), where the inevitable contaminations occurring at the interface of the two materials was used to generate a large magnetoresistance (MR) for a magnetic field sensor. Specifically, I have demonstrated that the contaminations generate an inhomogeneity in the carrier mobility throughout the channel, which is a required ingredient for magnetic field sensing based on linear magnetoresistance (LMR). Another approach I used to make a LMR sensor was by exploiting the large dependence of the mobility in graphene on the Fermi level position. This concept was used to generate two parallel electron gases with different mobility by tuning the Fermi level with an electrical field employing a field effect transistor. The second part of the thesis is focussed on strategies to reduce the impact of the surrounding environment on the properties of 2D materials in order to improve their performance. In particular, I used a 2D heterostructure encapsulated in an ionic polymer to makeii a highly responsive graphene-TMD photodetector. In this device, the ionic polymer covering the heterostructure was employed to screen the long-lived charge traps that limit the speed of such detectors, resulting in a drastic improvement of the detector responsivity properties. Finally, some of the 2D materials properties are very sensitive to the configuration of the electronics measurement setup. For example, effects behind spintronic and valleytronic concepts require non-local electrical transport measurement. We built a novel circuit that enables the detection of such effects without concern about the spurious contributions.

Wearables for health monitoring are rapidly advancing as evidenced by the number of wearable products on the market. More recently, the US Food and Drug Administration approved the Apple Watch for heart monitoring, indicating that wearables are going to be a part of our lives sooner than expected. However, wearables are still based on rigid, conventional electronic materials and fabrication procedures. The use of flexible conducting materials fabricated on flexible substrates allows for more comprehensive health monitoring because of the seamless integration and conformability of such devices with the human skin. Many materials can be used to fabricate flexible electronics such as thin metals, liquid metals, conducting polymers, and 1D and 2D materials. Ti3C2 MXene is a promising 2D material that shows flexibility as well as desirable electronic properties. Ti3C2 MXene is easily processable in aqueous solutions and can be an excellent functional ink for inkjet printing. Here we report the fabrication and the properties of Ti3C2 MXene films inkjet-printed from aqueous dispersions with a nonionic surfactant. The films are uniform and formed with only a few layers on glass and tattoo paper. The MXene films printed on tattoo are used to record ECG signals with comparable signal-to-noise ratio to commercial Ag/AgCl electrodes despite the absence of gels to lower skin-contact impedance. Due to their high charge storage capacity and mixed (ionic and electronic) conductivity, inkjet-printed MXene films open up a new avenue for applications beyond health monitoring.

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En esta Tesis Doctoral, las heterouniones de grafeno con otros materiales 2D y nanopartículas metálicas, incluyendo (N)grafeno/h-BN, grafeno/MoS2 y grafeno depositado Fe/Co, se sintetizaron en base al uso de polisacáridos naturales como precursors de grafeno. Estos materials se caracterizaron usando diversos métodos analíticos y se ensayaron para determinar el acoplamiento C-N oxidativo de las amidas, la hidrogenación de CO2 o la aplicación catalítica fotoeléctrica y física. En la primera etapa de la tesis, se estudió la influencia de la temperatura y la presencia de H2 durante la pirólisis en la calidad del grafeno. Se observó que una disminución significativa en la densidad de defectos relacionados con la presencia de oxígeno residual se puede lograr cuando el producto se preparó a la temperatura óptima (1100 oC) bajo un bajo porcentaje de H2 (5%). Esta mejora en la calidad del grafeno defectuoso resultante se reflejó en una disminución de la resistencia eléctrica y una mayor actividad fotoeléctrica. En el caso de las heteroestructuras de grafeno dopadas con N/h-BN, se ha revelado que se produjeron capas de segregación espontánea (N)grafeno y nitruro de boro durante la pirólisis. Aunque las heteroestructuras resultantes no mostraron una mejora en la conductividad, el material podría comportarse como un condensador que almacena carga en el rango de voltajes positivos. El grafeno/MoS2 se preparó por pirólisis de ácido algínico que contenía (NH4)2MoS4 adsorbido. Las nanopartículas de MoS2 exhibieron una orientación preferencial en la cara 002, como resultado del efecto de plantilla de las capas de grafeno. Este material exhibió actividad para la reacción de evolución H2, aunque se ha observado alguna variación de la actividad electrocatalítica de un lote a otro. También se prepararon Fe, Co NP o aleaciones Fe-Co incrustadas en matriz carbonosa por pirólisis de polvos de quitosano que contenían iones Fe2+ y Co2+ a 900 oC en atmósfera de Ar y se usaron para el acoplamiento oxidativo de C-N de amidas y compuestos aromáticos de N-H. Se observó que la adición secuencial de dos alícuotas de hidroperóxido de terc-butilo (TBHP) en un exceso de N,N-dimetilacetamida (DMA) como disolvente proporcionaba el correspondiente producto de acoplamiento en altos rendimientos, y el catalizador más eficiente era FeNP@C con alta reutilización y un amplio alcance. Finalmente, las perlas de matriz de carbono grafítico que contienen Fe, Co NPs o aleaciones de Fe-Co se sintetizaron secuencialmente mediante pirólisis en una etapa a 900 oC de perlas de quitosano que tenían acetatos de hierro y cobalto adsorbidos. La mejor muestra, Fe-Co aleación/G (Fe/Co alrededor de 0.4), mostró alta actividad para la hidrogenación de CO2 a isobutano con una selectividad superior al 92% y una conversión de CO2 de aproximadamente el 87%. / In this Doctoral Thesis, the heterojunctions of graphenes with other 2D materials and metal nanoparticles, including (N)graphene/h-BN, graphene/MoS2 and Fe/Co deposited graphene, were synthesized based on using natural polysaccharides as graphene precursors. These materials were characterized using various analytical methods and were tested for oxidative C-N coupling of amides, CO2 hydrogenation or physical and photoelectric catalytic application. In the first stage of the thesis, the influence of temperature and the presence of H2 during pyrolysis on the quality of graphene was studied. It was observed that a significant decrease in the density of defects related to the presence of residual oxygen can be achieved when the produce was performed at the optimal temperature (1100 oC) under a low percentage of H2 (5%). This improvement in the quality of the resulting defective graphene was reflected in a decrease in the electrical resistance and increased photoelectric activity. In the case of N-doped graphene/h-BN heterostructures, it has been revealed that a spontaneous segregation (N)graphene and boron nitride layers took place during the pyrolysis. Although the resulting heterostructures did not show an improvement in the conductivity, the material could behavior as capacitor storing charge in the range of positive voltages. Graphene/MoS2 was prepared by pyrolysis of alginic acid containing adsorbed (NH4)2MoS4. The MoS2 nanoparticles exhibited a preferential 002 facet orientation, as a result of the template effect of graphene layers. This material exhibited activity for H2 evolution reaction, although some variation of the electrocatalytic activity has been observed from batch to batch. Fe, Co NPs or Fe-Co alloys embedded in carbonaceous matrix were also prepared by pyrolysis of chitosan powders containing Fe2+ and Co2+ ions at 900 oC under Ar atmosphere and used for the oxidative C-N coupling of amides and aromatic N-H compounds. It was observed that sequential addition of two aliquots of tert-butyl hydroperoxide (TBHP) in an excess of N,N-dimethylacetamide (DMA) as solvent afforded the corresponding coupling product in high yields, and the most efficient catalyst was FeNP@C with high reusability and a wide scope. Finally, beads of graphitic carbon matrix containing Fe, Co NPs or Fe-Co alloys were sequentially synthesized by one-step pyrolysis at 900 oC of chitosan beads having adsorbed iron and cobalt acetates. The best sample, Fe-Co alloy/G (Fe/Co about 0.4), showed high activity for the hydrogenation of CO2 to isobutane with a selectivity higher than 92 % and a CO2 conversion about 87%. / En esta Tesi Doctoral, les heterounions de grafeno amb altres materials 2D i nanopartícules metàl·liques, incloent (N)grafé/h-BN, grafé/MoS2 i grafé depositat Fe/Co, es van sintetitzar basant-se en l'ús de polisacàrids naturals com precursors de grafé. Estos materials es van caracteritzar usant diversos mètodes analítics i es van assajar per a determinar l'adaptament C-N oxidatiu de les amides, la hidrogenació de CO2 o l'aplicació catalítica fotoelèctrica i física. En la primera etapa de la tesi, es va estudiar la influència de la temperatura i la presència de H2 durant la piròlisi en la qualitat del grafé. Es va observar que una disminució significativa en la densitat de defectes relacionats amb la presència d'oxigen residual es pot aconseguir quan el producte es va preparar a la temperatura òptima (1100 oC) davall un baix percentatge de H2 (5%) . Esta millora en la qualitat del grafé defectuós resultant es va reflectir en una disminució de la resistència elèctrica i una major activitat fotoelèctrica. En el cas de les heteroestructures de grafé dopades amb N/h-BN, s'ha revelat que es van produir capes de segregació espontània (N)grafé i nitrur de bor durant la piròlisi. Encara que les heteroestructures resultants no van mostrar una millora en la conductivitat, el material podria comportar-se com un condensador que emmagatzema càrrega en el rang de voltatges positius. El grafé/MoS2 es va preparar per piròlisi d'àcid algínic que contenia (NH4)2MoS4 adsorbit. Les nanopartícules de MoS2 van exhibir una orientació preferencial en la cara 002, com resultat de l'efecte de plantilla de les capes de grafé. Este material va exhibir activitat per a la reacció d'evolució H2, encara que s'ha observat alguna variació de l'activitat electrocatalítica d'un lot a un altre. També es van preparar Fe, Co NP o aliatges Fe-Co incrustades en matriu carbonosa per piròlisi de pols de quitosano que contenien ions Fe2+ i Co2+ a 900 oC en atmosfera d'Ar i es van usar per a l'acoblament oxidatiu de C-N d'amides i compostos aromàtics de NH. Es va observar que l'addició seqüencial de dos alíquotes de hidroperóxid de terc-butil (TBHP) en un excés de N,N-dimetilacetamida (DMA) com a dissolvent proporcionava el corresponent producte d'acoblament en alts rendiments, i el catalitzador més eficient era FeNP@C amb alta reutilització i un ampli abast. Finalment, les perles de matriu de carboni grafític que contenen Fe, Co NPs o aliatges de Fe-Co es van sintetitzar seqüencialment per mitjà de piròlisi en una etapa a 900 oC de perles de quitosano que tenien acetats de ferro i cobalt adsorbits. La millor mostra, Fe-Co aliatge/G (Fe/Co al voltant de 0.4), va mostrar alta activitat per a la hidrogenació de CO2 a isobutà amb una selectivitat superior al 92% i una conversió de CO2 d'aproximadament el 87%. / He, J. (2018). Heterojunctions of defective graphenes with 2D materials and metal nanoplatelets: preparation and catalytic applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/111923

The present work investigates the synthesis and nanocrystal deposition of some selected solid solutions of transition metal trihalides with 2-dimensional crystal structure - specifically, the solutions of CrCl3 – CrBr3, CrBr3 – CrI3, RhCl3 – RhBr3, RhBr3 – RhI3, CrCl3 – RuCl3, and CrCl3 – MoCl3. Theoretical simulations of phase equilibria and partial pressures were applied to estimate suitable synthesis conditions for phase-pure solid solutions, before the syntheses were subsequently performed practically. It was found that for most of the systems investigated, special conditions, such as an appropriate excess of halogen or a specific temperature range, are crucial for successful synthesis. The purity of the corresponding products was confirmed by X-ray powder diffraction. These measurements were further used to investigate the course of the lattice parameters within the series of mixtures in order to be able to observe potential deviations from ideal mixing behavior of the parent compounds. These investigations revealed only small or no deviation from Vegard’s law for all investigated systems except CrCl3 – MoCl3. For CrCl3 – CrBr3, CrBr3 – CrI3, RhCl3 – RhBr3, RhBr3 – RhI3 and CrCl3 – RuCl3, the prepared powder material with different compositions was further used for the deposition of high-quality nanocrystals on a substrate. For this purpose, chemical vapor transport was applied. Suitable deposition conditions were also previously estimated by simulations before finally performing an experimental optimization of the transport conditions. The 2D nanocrystals thus obtained generally exhibit heights in the low 2-digit nm range, while monolayers were also observed in the case of RhCl3 – RhBr3. The compositions of the deposited structures were analyzed by energy dispersive X-ray spectroscopy to detect possible enrichment effects of the solid solutions during vapor transport. With the knowledge of these relationships, nanocrystals with controllable composition can be deposited by the developed method. The high quality of the deposited nanocrystals was ensured by transmission electron microscopy, selected area electron diffraction, and X-ray photoemission spectroscopy. Depending on the system, selected material properties were determined using powder samples, bulk or nanocrystals, such as the photoluminescence behavior of the CrCl3 – CrBr3 and CrBr3 – CrI3 series or the optical band gap characteristics of the RhCl3 – RhBr3 and RhBr3 – RhI3 systems. Unlike for the previously mentioned systems, in the case of CrCl3 – MoCl3, strong deviations from an ideal linear course of the lattice parameters were observed, where several phase regions can be distinguished within the series. To explain these anomalies, structural models were developed that explain the anomalies with the formation of differently arranged Mo-Mo dimers within the crystal structure. These hypotheses were investigated by different characterization methods such as IR spectroscopy or SQUID measurements and confirmed the hypotheses within the limits of the validity of the applied methods. The simulative and experimental methods developed in this work can be applied to numerous similar systems of transition metal trihalides, but should also work for other classes of compounds. The nanocrystals thus made available are suitable for follow-up studies with respect to property changes upon downscaling.:1. Introduction 1 2. Theoretical Background 3 2.1. Properties of Selected Transition Metal Trihalides and Their Solid Solutions . . . 3 2.1.1. Crystal Structures of 2D Transition Metal Trihalides . . . . . . . . . . . . . 4 2.1.2. CrX3 (X = Cl, Br, I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.3. RhX3 (X = Cl, Br, I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.4. RuCl3 and CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.5. MoCl3 and CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Solid Solution Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.1. Structural Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.2. Chemical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.3. Thermodynamic Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3. Chemical Vapor Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3.1. Bulk and Nanocrystal Growth by CVT . . . . . . . . . . . . . . . . . . . . . . 11 2.3.2. CVT of Solid Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3.3. Simulation of CVT Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4. Vapor Phase Chemistry of Selected Transition Metal Trihalides . . . . . . . . . . . 15 2.4.1. CrCl3, CrBr3 and CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4.2. RhCl3, RhBr3 and RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.4.3. RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.4.4. MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3. Material and Methods 19 3.1. Chemicals and Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2. Synthesis, Purification and CVT of Materials . . . . . . . . . . . . . . . . . . . . . . 20 3.2.1. General Aspects of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.2.2. CrX3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.3. CrCl3-CrBr3 and CrBr3-CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.4. RhX3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 X Table of Contents 3.2.5. RhCl3-RhBr3 and RhBr3-RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.6. Purification of commercial RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.7. CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.8. MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.9. CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.10. Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3. Thermodynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3.1. Estimation of Unknown Thermodynamic Data . . . . . . . . . . . . . . . . 26 3.3.2. Simulations with Tragmin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4. Instrumental Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.1. Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.2. Powder X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.3. Single-Crystal X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.4.4. Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy 27 3.4.5. Transmission Electron Microscopy and Selected Area Electron Diffraction 28 3.4.6. Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.4.7. Raman Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.8. Infrared Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.9. Diffuse Reflection Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.10. Photoluminescence Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.11. X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.12. Inductively Coupled Plasma Optical Emission Spectroscopy . . . . . . . . 30 3.4.13. Simultaneous Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.4.14. Electron Energy-Loss Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 31 3.4.15. Superconducting Quantum Interference Device Measurements . . . . . . 31 4. Results and Discussion 32 4.1. CrCl3 – CrBr3 and CrBr3 – CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.1.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 32 4.1.2. Solid Solution Synthesis and Basic Properties . . . . . . . . . . . . . . . . . 37 4.1.3. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.1.4. Nanocrystal Growth, Enrichment Effects and Delamination . . . . . . . . . 45 4.1.5. Further Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.2. RhCl3-RhBr3 and RhBr3-RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.2.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 55 4.2.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.2.3. Thermochemical Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2.4. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.2.5. Crystal Growth and Delamination . . . . . . . . . . . . . . . . . . . . . . . . 65 4.2.6. Further Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4.3. CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.3.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 73 4.3.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 XI Table of Contents 4.3.3. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.3.4. Nanocrystal Growth, Enrichment Effects and Delamination . . . . . . . . . 78 4.3.5. Further Characterization of As-Grown Nanocrystals . . . . . . . . . . . . . 81 4.4. CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.4.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 84 4.4.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 4.4.3. Structural Investigation by pXRD . . . . . . . . . . . . . . . . . . . . . . . . . 88 4.4.4. Further Structural Characterization . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.5. Magnetic Investigations of Powder Samples by SQUID . . . . . . . . . . . . 98 4.4.6. Summary of Characterization Results . . . . . . . . . . . . . . . . . . . . . . 101 4.4.7. CVT Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5. Summary and Outlook 104 References 107 List of Figures 120 List of Tables 121 Abbreviations 122 Used Symbols 124 A. Appendix 126 A.1. Atom Positions and Space Group Transformations of 2D TMTH . . . . . . . . . . 126 A.2. Raw pXRD Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 A.3. Refined Lattice Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 A.4. Additional Data of Characterizations . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 A.5. EDX-Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 A.6. Thermodynamic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 / Die vorliegende Arbeit beschäftigt sich mit der Synthese und Nanokristallabscheidung von einigen ausgewählten Festkörperlösungen von Übergangsmetalltriahlogeniden mit 2-dimensionaler Kristallstruktur - konkret die Lösungen von CrCl3 – CrBr3, CrBr3 – CrI3, RhCl3 – RhBr3, RhBr3 – RhI3, CrCl3 – RuCl3 und CrCl3 – MoCl3. Dabei wurden theoretische Simulationen der Phasengleichgewichte und Partialdrücke angewandt um geeignete Synthesebedingungen für phasenreine Festkörperlösungen abzuschätzen und diese Synthesen im Anschluss entsprechend zu realisieren. Dabei zeigte sich, dass für die meisten der untersuchten Mischphasen spezielle Bedingungen, wie z.B. ein entsprechender Halogenüberschuss oder ein enges Temperaturfenster entscheidend für die erfolgreiche Synthese sind. Die Phasenreinheit der entsprechenden Produkte wurde mittels Röntgenpulverdiffraktometrie bestätigt. Diese Messungen wurden weiterhin zur Untersuchung des Verlaufs der Gitterparameter innerhalb der Mischungsreihen verwendet um potenzielle Abweichungen von idealem Mischungsverhalten der Randverbindungen beobachten zu können. Dabei zeigte sich für alle Mischungen außer CrCl3 – MoCl3 nur geringe oder keine Abweichungen von der Vegard’schen Regel. Für CrCl3 – CrBr3, CrBr3 – CrI3, RhCl3 – RhBr3, RhBr3 – RhI3 und CrCl3 – RuCl3 wurde das hergestellte Pulvermaterial mit verschiedenen Zusammensetzungen für die Abscheidung von hochqualitativen Nanokristallen auf einem Substrat verwendet. Dafür wurde die Methode des chemischen Gasphasentransports angewandt, wobei ebenfalls geeignete Abscheidungsbedingungen zuvor mittels Simulationen ermittelt wurden, bevor schlussendlich eine experimentelle Optimierung der Transportbedingungen durchgeführt wurde. Die damit erhaltenen 2D Nanokristalle weisen in der Regel Höhen im niedrigen 2-stelligen nm-Bereich auf, wobei im Fall von RhCl3 – RhBr3 auch direkt abgeschiedene Monolagen beobachtet wurden. Die Zusammensetzungen der abgeschiedenen Strukturen wurden intensiv mittels energiedispersiver Röntgenspektroskopie analysiert um mögliche Anreicherungseffekte der Festkörperlösungen während des Gasphasentransports zu detektieren. Dabei zeigte sich, dass eine Anreicherung insbesondere im Fall der kationischen Festkörperlösungen auftritt, während bei anionischen Lösungen ein kongruenter Transport vorherrscht. Mithilfe der Kenntnisse dieses Zusammenhangs lassen sich Nanokristalle mit kontrollierbarer Zusammensetzung über die entwickelte Methode abscheiden. Die hohe Qualität der abgeschiedenen Nanostrukturen wurde mittels Transmissionselektronmikroskopie, Feinbereichselektronenbeugung und Röntgenphotoelektronenspektroskopie sichergestellt. Je nach System wurden weitere ausgewählte Materialeigenschaften anhand von Pulver-Proben, bulk- oder Nanokristallen ermittelt, wie beispielsweise das Photolumineszenzverhalten der CrCl3 – CrBr3 und CrBr3 – CrI3 Reihen oder den Verlauf der optischen Bandlücke der RhCl3 – RhBr3 und RhBr3 – RhI3 Systeme. Anders als für die zuvor beschriebenen Systeme wurden im Fall von CrCl3 – MoCl3 starke Abweichungen von idealem Verlauf der Gitterparameter beobachtet, wobei innerhalb der Mischungsreihe mehrere Phasengebiete unterschieden werden können. Zur Erklärung dieser Anomalien wurden verschiedene Strukturmodelle erdacht, welche die Bildung von unterschiedlich angeordneten Mo-Mo-Dimeren innerhalb der Kristallstruktur beschreiben. Diese Hypothesen wurden mittels verschiedener Charakterisierungsmethoden wie z.B. IR-Spektroskopie oder SQUID-Messungen untersucht und im Rahmen der Aussagekraft der Messmethoden bestätigt. Die in dieser Arbeit entwickelten simulativen und experimentellen Methoden lassen sich auf zahlreiche ähnliche Systeme von Übergangsmetalltrihalogeniden übertragen, sind aber auch auf andere Verbindungsklassen anwendbar. Die damit verfügbar gemachten Nanokristalle sind für Folgeuntersuchungen im Hinblick auf die Eigenschaftsveränderungen bei der Nanoskalierung geeignet.:1. Introduction 1 2. Theoretical Background 3 2.1. Properties of Selected Transition Metal Trihalides and Their Solid Solutions . . . 3 2.1.1. Crystal Structures of 2D Transition Metal Trihalides . . . . . . . . . . . . . 4 2.1.2. CrX3 (X = Cl, Br, I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.3. RhX3 (X = Cl, Br, I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.4. RuCl3 and CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.5. MoCl3 and CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Solid Solution Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.1. Structural Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.2. Chemical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.3. Thermodynamic Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3. Chemical Vapor Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3.1. Bulk and Nanocrystal Growth by CVT . . . . . . . . . . . . . . . . . . . . . . 11 2.3.2. CVT of Solid Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3.3. Simulation of CVT Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4. Vapor Phase Chemistry of Selected Transition Metal Trihalides . . . . . . . . . . . 15 2.4.1. CrCl3, CrBr3 and CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4.2. RhCl3, RhBr3 and RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.4.3. RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.4.4. MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3. Material and Methods 19 3.1. Chemicals and Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2. Synthesis, Purification and CVT of Materials . . . . . . . . . . . . . . . . . . . . . . 20 3.2.1. General Aspects of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.2.2. CrX3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.3. CrCl3-CrBr3 and CrBr3-CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.4. RhX3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 X Table of Contents 3.2.5. RhCl3-RhBr3 and RhBr3-RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.6. Purification of commercial RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.7. CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.8. MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.9. CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.10. Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3. Thermodynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3.1. Estimation of Unknown Thermodynamic Data . . . . . . . . . . . . . . . . 26 3.3.2. Simulations with Tragmin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4. Instrumental Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.1. Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.2. Powder X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4.3. Single-Crystal X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.4.4. Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy 27 3.4.5. Transmission Electron Microscopy and Selected Area Electron Diffraction 28 3.4.6. Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.4.7. Raman Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.8. Infrared Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.9. Diffuse Reflection Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.10. Photoluminescence Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.11. X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.12. Inductively Coupled Plasma Optical Emission Spectroscopy . . . . . . . . 30 3.4.13. Simultaneous Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.4.14. Electron Energy-Loss Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 31 3.4.15. Superconducting Quantum Interference Device Measurements . . . . . . 31 4. Results and Discussion 32 4.1. CrCl3 – CrBr3 and CrBr3 – CrI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.1.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 32 4.1.2. Solid Solution Synthesis and Basic Properties . . . . . . . . . . . . . . . . . 37 4.1.3. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.1.4. Nanocrystal Growth, Enrichment Effects and Delamination . . . . . . . . . 45 4.1.5. Further Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.2. RhCl3-RhBr3 and RhBr3-RhI3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.2.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 55 4.2.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.2.3. Thermochemical Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2.4. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.2.5. Crystal Growth and Delamination . . . . . . . . . . . . . . . . . . . . . . . . 65 4.2.6. Further Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4.3. CrCl3-RuCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.3.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 73 4.3.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 XI Table of Contents 4.3.3. Structural Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.3.4. Nanocrystal Growth, Enrichment Effects and Delamination . . . . . . . . . 78 4.3.5. Further Characterization of As-Grown Nanocrystals . . . . . . . . . . . . . 81 4.4. CrCl3-MoCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.4.1. Thermodynamic and CVT Simulations . . . . . . . . . . . . . . . . . . . . . 84 4.4.2. Solid Solution Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 4.4.3. Structural Investigation by pXRD . . . . . . . . . . . . . . . . . . . . . . . . . 88 4.4.4. Further Structural Characterization . . . . . . . . . . . . . . . . . . . . . . . 93 4.4.5. Magnetic Investigations of Powder Samples by SQUID . . . . . . . . . . . . 98 4.4.6. Summary of Characterization Results . . . . . . . . . . . . . . . . . . . . . . 101 4.4.7. CVT Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5. Summary and Outlook 104 References 107 List of Figures 120 List of Tables 121 Abbreviations 122 Used Symbols 124 A. Appendix 126 A.1. Atom Positions and Space Group Transformations of 2D TMTH . . . . . . . . . . 126 A.2. Raw pXRD Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 A.3. Refined Lattice Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 A.4. Additional Data of Characterizations . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 A.5. EDX-Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 A.6. Thermodynamic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Clean air is an indispensable prerequisite for human health. The capture of small toxic molecules requires the development of advanced materials for air filtration. Two-dimensional nanomaterials offer highly accessible surface areas but for real-world applications their assembly into well-defined hierarchical mesostructures is essential. DUT-134(Cu) ([Cu2(dttc)2]n, dttc=dithieno[3,2-b : 2′,3′-d]thiophene-2,6-dicarboxylate]) is a metal–organic framework forming platelet-shaped particles, that can be organized into complex structures, such as millimeter large free-standing layers (carpets) and tubes. The structured material demonstrates enhanced accessibility of open metal sites and significantly enhanced H2S adsorption capacity in gas filtering tests compared with traditional bulk analogues.

No description available.

In this work, we performed an experimental analysis using a two-dimensional semiconducting transition metal dichalcogenide (TMD), specifically tungsten diselenide (WSe2), for gas sensor applications. Our method entailed building a chemically liquid exfoliated WSe2 gas sensing device with gold (Au) electrodes to measure its reaction and sensitivity to environmental gasses such as CO2 and N2. The 2D thin film was created through a solution processing method and electrically coupled in a two-terminal configuration; photonic curing system along with the hot plate annealing process was used on the thin film for rapid annealing, enhancing particle connectivity, stable crystal structure, and increasing overall electrical conductivity. The inkjet printing technology is used to explore the potential of the 2D thin film fabrication process that defines a well-controlled and scalable additive manufacturing process at the nano level that makes it possible to develop next-generation flexible devices. The additive nano-manufacturing process allowed us to establish the film's structure and chemical properties before measuring the electrical characteristics of the films when exposed to CO2 and N2 gases at room temperature. To explore and validate the sensitivity to human interaction with the gas-sensing device, we carried out further experiments with direct exposure to human breath in an open environmental space which shows a promising landmark for developing a next-generation flexible breath-sensing device.

The aim of this project is to examine the electric and magneticproperties of three monolayer chromium trihalides when doped withdifferent transitions metals, that is CrXY_6, where X=(Mn,Fe,Co,Ni,V)and Y=(Cl,Br,I). The calculations were made using the software programQuantum Espresso that used density functional theory to solveSchrödinger’s equation. The first step of the calculations was to optimize the atomic positionsand the lattice parameters to find the ground state energy of thecompounds. The magnetic configuration was also examined to find thefavorable configuration. With the optimized values for each compound,the band structure, density of states and the projected density ofstates was calculated. The results confirmed the ferromagnetic behaviorof non-doped compounds, however for some of the doped compounds themagnetic configurations changed to anti-ferromagnetic. Most of thecompounds retained their semiconductor properties when doped and had aband gap near the fermi-energy, while other changed to metallic or halfmetallic and had available electron states at fermi-energy.