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<p dir="ltr">The technological drive of humanity to explore the cosmos, travel at hypersonic speeds, and pursue clean energy solutions requires ceramic scientists and engineers to constantly push materials to their functional, behavioral, and chemical extremes. Ultra-high temperature ceramics, and particularly transition metal carbides, are promising materials to meet the demands of extreme environment materials with their >4000 °C melting temperature and impressive thermomechanical behaviors in extreme conditions. The advent of the 2D version of these transition metal carbides, known as MXenes, added a new direction to design transition metal carbides for energy, catalysis, flexible electronics, and other applications. Toward extreme conditions, although MXenes remain yet unexplored, we believe that the ~1 nm flakes of MXenes gives ceramics scientists and engineers the ability to truly engineer transition metal carbides layer-by-layer at the nanoscale to endure the extreme conditions required by future harsh environment technology. Although MXenes have this inherent promise, fundamental study of their behavior in high-temperature environments is necessary to understand how their chemistry and 2D nature affects the high-temperature stability and phase behavior of MXenes toward application in extreme environments.</p><p dir="ltr">In this dissertation, we investigate the high-temperature phase behavior of 2D MXenes in high temperature inert environments to understand the stability and phase transition behavior of MXenes. In this work, we demonstrate that 1) MXenes’ transition at high-temperatures is to highly textured transition metal carbides is due to the homoepitaxial growth of these phases onto ~1-nm-thick MXenes’ highly exposed basal plane, 2) the MXene to MXene interface plays a major role in the phase behavior of MXenes, particularly toward building layered transition metal carbides using MXenes as ~1-nm-thick building blocks, and 3) Defects are the primary site at which atomic migration begins during phase transition of MXenes into these highly textured transition metal carbides, and these defects can be engineered for different phase stability of MXenes. To do so, we investigate the phase behavior of Ti₃C₂T_<em>x</em>, Ta₄C₃T_<em>x</em>, Mo₂TiC₂T_<em>x</em>, and other MXenes using a combination of <i>in situ</i> x-ray diffraction and scanning transmission electron microscopy and other <i>ex situ</i> methods, such as secondary ion mass spectrometry and x-ray photoelectron spectroscopy, with other methods. By investigating the fundamentals of the high-temperature phase behavior of MXenes, we hope to establish the basic principles behind use of MXenes as the ideal material for application in future extreme environments.</p>

Molecules adsorbed on two-dimensional (2D) materials can show interesting physical and chemical properties. This thesis presents scanning probe microscopy (SPM) investigation of emerging 2D materials, molecular nanostructures on 2D substrates at the nanometer scale, and biophysical processes on the biological membrane. Two main techniques of nano-probing are used: scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The study particularly emphasizes on self-assembled molecules on flat 2D materials and quasi-1D wrinkles. First, we report the preparation of novel 1D C60 nanostructures on rippled graphene. Through careful control of the subtle balance between the linear periodic potential of rippled graphene and the C60 surface mobility, we demonstrate that C60 molecules can be arranged into a 1D C60 chain structure of two to three molecules in width. At a higher annealing temperature, the 1D chain structure transitions to a more closely packed, quasi-1D hexagonal stripe structure. The experimental realization of 1D C60 structures on graphene is, to our knowledge, the first in the field. It could pave the way for fabricating new C60/graphene hybrid structures for future applications in electronics, spintronic and quantum information. Second, we report a study on nano-morphology of potential operative donors (e.g., C60) and acceptors (e.g., perylenetetracarboxylic dianhydride, aka. PTCDA) on wrinkled graphene supported by copper foils. We realize sub-monolayer C60 and PTCDA on quasi-1D and quasi-2D real periodic wrinkled graphene, by carefully controlling the deposition parameters of both molecules. Our successful realization of acceptor-donor binary nanostructures on wrinkled graphene could have important implications in future development of organic solar cells. Third, we report an STM and spectroscopy study on atomically thin transition-metal dichalcogenides (TMDCs) material. TMDCs are emerging 2D materials recently due to their intriguing physical properties and potential applications. In particular, our study focuses on molybdenum disulfide (MoS2) mono- to few-layers and pyramid nanostructures synthesized through chemical vapor deposition. On the few-layered MoS2 nanoplatelets grown on gallium nitride (GaN) and pyramid nanostructures on highly oriented pyrolytic graphite (HOPG), we observe an intriguing curved region near the edge terminals. The measured band gap in these curved regions is consistent with the direct band gap in MoS2 monolayers. The curved features near the edge terminals and the associated electronic properties may contribute to understanding catalytic behaviors of MoS2 nanostructures and have potential applications in future electronic devices and catalysts based on MoS2 nanostructures. Finally, we report a liquid-cell AFM study on the endosomal protein sorting process on the biological lipid membrane. The sorting mechanism relies on complex forming between Tom1 and the cargo sorting protein, Toll interacting protein (Tollip). The induced conformational change in Tollip triggers its dissociation from the lipid membrane and commitment to cargo trafficking. This collaborative study aims at characterizing the dynamic interaction between Tollip and the lipid membrane. To study this process we develop the liquid mode of AFM. We successfully demonstrate that Tollip is localized to the lipid membrane via association with PtdIns3P (PI(3)P), a major phospholipid in the cell membrane involved in protein trafficking. / Ph. D. / Two-dimensional (2D) materials are layered materials with thickness of single atom or few atoms. The ultimate thickness leads to novel properties that are useful for a wide range of applications in photovoltaics, electronics and quantum information. In order to explore these properties at the nanometer scale, we used scanning probe techniques, i.e., scanning tunneling microscopy (STM) and atomic force microscopy (AFM), to perform comprehensive investigations on these emerging materials. 2D materials, such as graphene and atomically thin transition-metal dichalcogenides (TMDCs), are promising candidates for building economic, safe and mechanically flexible solar cells with desirable optical and electronic properties, e.g. tunable sunlight absorption. The first part of the thesis focuses on graphene, a single-atom-thick carbon sheet. We deposited key components in organic solar cells, such as perylenetetracarboxylic dianhydride (PTCDA) and C₆₀ molecules, on graphene. On these materials we observed various novel nanostructures, like quasi-1D C₆₀ nanochains. The second part of the thesis focuses on mono- to few-layered MoS₂, which can be used as an active layer in high-efficiency solar cells. Our study has important implications in improving efficiency of organic solar cells in the future. In the final part of the thesis, we extended our subject to the biological lipid membrane, a 2D material critical in biology, and biophysical processes occurring on the membrane. Using a liquid-cell AFM, we investigated the endosomal protein sorting process on the biological membranes. Our study contributes to understanding of the interactions between the adaptor proteins and cell membranes in the protein sorting process that guides proteins to their proper destinations.

Die optischen Eigenschaften von Übergangsmetall-Dichalcogeniden (TMDC) werden durch Exzitonen (exc) dominiert, was auf den Quanteneinschluss und die reduzierte Abschirmung zurückzuführen ist, die für ihre 2D-Natur charakteristisch sind. Das Coulomb-Screening spielt eine grundlegende Rolle bei der Bestimmung der stationären und dynamischen Eigenschaften solcher Materialien. Zeitaufgelöste optische Spektroskopie ist ein grundlegendes Instrument, um die Rolle der Abschirmung in der Nicht-Gleichgewichtsphysik von TMDC zu untersuchen. Ich untersuche WS2-Monoschichten auf verschiedenen Substraten mit zeitaufgelöstem Transmissions-/Reflexionskontrast. Ich stelle einen Formalismus vor, der einen zuverlässigen Vergleich der dynamischen Reaktion der Exzitonen unabhängig von Probe, Substrat und Messtechnik ermöglicht. Mit diesem Formalismus werden die von der Pump-Photonen-Energie und der Fluenz abhängige Verschiebung und Verbreiterung des Exziton-Peaks extrahiert und mit Hilfe eines Zwei-/Drei-Niveau-Modells reproduziert. Mit Hilfe dieses Modells konnte die Konkurrenz zwischen dynamischer Abschirmung der Quasiteilchen, Streuung und thermischen Effekten entschlüsselt werden. Die Verbreiterung wird durch QFC-exc (exc-exc) Streuung bestimmt, wenn QFC (exc) im System vorhanden sind. Darüber hinaus induzieren QFC (exc) eine globale Rot-(Blau-)Verschiebung der Exzitonenresonanz, die mit einer effektiven QFC (exc) dynamischen, abschirmungsinduzierten Renormalisierung der Bandlücke (Verringerung der Bindungsenergie) reproduziert wird. Schließlich wird der Einfluss der statischen Abschirmung auf die Reaktion der Exzitonen untersucht. Die dynamische exc-Abschirmung ist bei höherer Substratpermittivität verstärkt und wird versuchsweise auf einen höheren Grad der Delokalisierung des Exzitons zurückgeführt. Letztlich trägt diese Arbeit zu einem umfassenden Bild der Nicht-Gleichgewichtsdynamik und der Rolle der Abschirmung in TMDC bei. / The optical properties of transition metal dichalcogenides (TMDC) are dominated by excitons, due to quantum confinement and reduced screening characteristic of their 2D nature. Exactly the screening of the Coulomb interaction has a fundamental role in determining the steady-state and dynamic properties of such materials. Time-resolved optical spectroscopies are a fundamental tool to investigate the phenomena governing the non-equilibrium physics of TMDC materials. Nevertheless, the quantitative role of the screening in the non-equilibrium response of the TMDC is yet to be understood. I investigate monolayers WS2 placed on various substrates with time-resolved transmittance/reflectance contrast. I report a formalism that allows the reliable comparison of the exciton dynamic response independently of sample, substrate and measurement technique. With this formalism, the pump-photon energy and fluence-dependent exciton peak shift and broadening are extracted and reproduced using a basic two/three-level model. Through this model the competition of quasiparticle dynamic screening, scattering and thermal effects was unravelled. The broadening is governed by QFC-exciton (exciton-exciton) scattering when QFC (excitons) are present in the system. Furthermore, QFC (excitons) induce a global red-(blue-)shift of the exciton resonance, reproduced with an effective QFC (excitons) dynamic screening-induced bandgap renormalization (binding energy reduction). Finally, the static screening influence on the non-equilibrium exciton response is addressed. Scattering and QFC dynamic screening are unaffected in different dielectric environments. On the contrary, the exciton dynamic screening is enhanced for higher substrate permittivity and possibly due to a higher degree of delocalization of the exciton. Ultimately, this thesis contributes to a comprehensive picture of the non-equilibrium dynamics and the role of screening in TMDC.

In this work, we have explored 2D semiconducting transition metal dichalcogenides (TMDs), black phosphorus (BP), and graphene for various applications using liquid and mechanical exfoliation routes. The topical areas of interest that motivate our work include considering factors such as device integration, stability, doping, and the effect of gasses to modulate the electronic transport characteristics of the underlying 2D materials. In the first area, we have integrated solution-processed transparent conducting oxides (TCOs), specifically indium-doped tin oxide (ITO) with BP, which is a commonly used TCO for solar cell devices. Here we have found surface treatment of glass substrates with a plasma before spin-coating the solution-processed ITO, to be effective in improving coverage and uniformity of the ITO film by promoting wettability and film adhesion. The maximum transmittance obtained was measured to be ~75% in the visible region, while electrical measurements made on BP/ITO heterostructures showed improved transport characteristics compared to the bare ITO film. Within the integration realm, inkjet-printing of BP and MoS2 p-n hetero-junctions on standard ITO glass substrates in a vertical architecture was also demonstrated. To address the issue of stability which some 2D materials such as BP face, we experimented with ionic liquids (ILs) to passivation the hydrophilic surface of BP to minimize its oxidative degradation. The enhanced stability of BP was inferred through Raman spectroscopy and scanning probe microscopy techniques, where no observable changes in the A1g and A2g Raman vibrational modes were observed for the BP films passivated with ILs over time under ambient conditions. On the other hand, a blue-shift in these Raman modes was evident for unpassivated samples. Atomic force microscopy measurements on the unpassivated samples clearly revealed the difference in surface characteristics through localized regions of degradation that intensified with time which was absent in IL passivated BP samples. The electronic device measurements for IL coated BP devices showed a more stabilized Ids−Vds characteristic in the 5.4 K to 335 K temperature range. Prototypical demonstrations of stabilized ILs/BP devices at ambient printed on flexible polyimide substrates were also successfully made. At the same time, doping is one of the essential steps required for the modulation of carrier density and electronic transport in electronic and optoelectronic devices, which is the third topical area we have addressed in this work with semiconducting TMDs. Of the conventional approaches used to dope 3D semiconductors, ion-implantation is commonly adopted but given the ultra-thin nature of 2D materials, this approach is not feasible as it causes severe damage to the delicate crystalline lattice of ultra-thin 2D membranes. Instead, we have used plasma-based doping routes with UV-ozone treatement and solution processing using 1,2 dichloroethane, to characterize the temperature-dependent two-terminal and three-terminal electronic and optoelectronic transport of mechanically exfoliated 2D MoS2 and WSe2. A significant difference was seen in the optoelectronic properties between the two dopants, owing to differences in their respective doping mechanisms and the intrinsic structural attributes of the exfoliated flakes. A significant reduction in barrier height was evident after doping using both techniques in MoS2, while an increase in barrier height after soaking in 1,2 dichloroethane was seen in WSe2. Lastly, in the fourth topical area for sensing devices, we have studied the effect of gas-flow in inkjet-printed and spin-coated graphene and MoS2 to modulate the electronic transport for the 2D materials since their increased surface area is an ideal platform to observe interactions with external stimuli, in this case, in-coming gas species. Here, the chamber pressure and change in current with flow of gas was measured in the steady-state, as well as time-dependent dynamic transport toward nitrogen and carbon dioxide. We observed significant differences in the electrical response of mono-elemental graphene and binary MoS2, owing to differences in microstructure and joule heating response to the ambient gas. In conclusion, the findings obtained from our work will provide an important framework to help guide strategies in further improving integration schemes, stability, doping and sensing behavior driven by the unique structural attributes inherent to 2D materials for high-performance devices in the future.

Die rasanten Fortschritte bei der Entwicklung neuartiger 2D-Materialien haben in den letzten Jahren auch das Forschungsfeld der Spintronik stetig bereichert aufgrund der vielseitigen physikalischen Eigenschaften und der Flexibilität hinsichtlich der Realisierung von Heterostrukturen. Das erst kürzlich entdeckte metastabile und geschichtete Material alpha-FeGe2 trägt das Potenzial, in die Klasse der bekannten 2D Materialien aufgenommen zu werden. In dieser Dissertation werden die elektrischen und magnetischen Eigenschaften von alpha-FeGe2 diskutiert, basierend auf elektrischen Transportmessungen bei unterschiedlichen äußeren Magnetfeldern und Temperaturen. Zur Untersuchung von magnetoresistiven Effekten wurden Spinventilstrukturen mit alpha-FeGe2 als Trennmaterial zwischen zwei metallische Ferromagnete verwendet. Es wird gezeigt, dass alpha-FeGe2 eine dickenabhängige kritische Temperatur besitzt, die bei etwa 100 K liegt und mit einem magnetischen Phasenübergang von der antiferromagnetischen Phase für T > 100 K in die ferromagnetische Phase bei T < 100 K verknüpft ist. Dieser Phasenübergang wird von Berechnungen aus der Dichtefunktionaltheorie (DFT) gestützt. Es wird gezeigt, dass die magnetische Ordnung in der alpha-FeGe2-Trennschicht einen starken Einfluss auf die Spinventilsignale ausübt. Insbesondere spielt hierbei die Auswirkung auf die magnetische Interschichtkopllung zwischen den ferromagnetischen Elektroden aus Fe3Si oder Co2FeSi eine entscheidende Rolle. Die magnetische Kopplung an der Grenzfläche zwischen antiferromagnetischem alpha-FeGe2 und Fe3Si führt zu einer Anisotropie in den Spinventilsignalen hinsichtlich der Orientierung des externen Magnetfeldes. Diese Anisotropie wird durch ein komplexes Zusammenspiel zwischen der Magnetisierung der ferromagnetischen Elektroden und der magnetischen Vorzugsrichtung des antiferromagnetischen alpha-FeGe2, die durch den sog. Néelvektor beschrieben wird, diskutiert. / The rapid progress in the development of new 2D materials have also enriched spintronic research in recent years, thanks to their versatile physical properties and flexibility with regard to the design of heterostructures. The prominent examples graphene and transition metal dichalcogenides (TMDs) have the prospect to represent the basis of future spintronic applications, in particular due to their tunability and multifunctionality. The recently discovered metastable layered material alpha-FeGe2 is a potential candidate for being added to this class of materials. In this work, the electrical and magnetic properties of alpha-FeGe2 are studied, based on results from electrical transport measurements at different external magnetic fields and temperatures. For the investigation of magnetoresistive effects, spin valve devices containing alpha-FeGe2 as a spacer layer between two metallic ferromagnets have been utilized. It is shown that alpha-FeGe2 exhibits a thickens dependent critical temperature around 100 K at which it undergoes a magnetic phase transition from an antiferromagnetic state at T > 100 K to a ferromagnetic state at T < 100 K. This phase transition is also predicted by density functional theory (DFT) calculations and reflected in a disappearing spin valve signal at low temperatures. It is demonstrated that the magnetic phase of the alpha-FeGe2 spacer strongly influences the performance of spin valves, particularly via the impact on the magnetic interlayer coupling between the ferromagnetic electrodes made of Fe3Si or Co2FeSi. The magnetic coupling at the interface between antiferromagnetic alpha-FeGe2 and Fe3Si was found to induce anisotropies in the spin valve signal with regard to the external magnetic field orientation. This anisotropy is explained in terms of a complex interplay between the misalignment between the ferromagnetic electrodes and the magnetically preferred direction of the antiferromagentic alpha-FeGe2 described by the Néel vector.

In this thesis, two-dimensional (2D) van der Waals materials have been explored, focusing on the encapsulation of graphene with hexagonal boron nitride (hBN), as well as detailed study of 2D magnets Cr2Ge2Te6 and CuCrP2S6. Graphene has been studied to establish the connection between its quantum Hall phase with the non-hermitian Hatano-Nelson model. Additionally, the thickness-dependent magnetism of Cr2Ge2Te6 has been studied and the exfoliation and oxidation study of CuCrP2S6 has been carried out. Through the tunable electronic properties of graphene, specifically its ability to move between electron and hole side by applying back gate voltage, we demonstrate how the quantum Hall effect in graphene can proove a physical realization of non-Hermitian topological phase. By systematically measuring the resistance matrices of graphene in the quantum Hall regime and inverting them to the conductance matrices, it has been shown that the quantum Hall phase in graphene corresponds to the conductance matrix in Hatano-Nelson model, with the electron and hole side exhibiting chirality or non-chirality. For Cr2Ge2Te4, the thickness-dependent magnetism has been studied through exfoliation and succesfully reached a thickness down to 4 nm. Using the magnetooptical Kerr method (MOKE), distinct variations in the hysteresis curve across different thicknesses have been observed. Notably, 8nm thick part of the flake exhibit highly coercive hysteresis, while down-to-a few layer part show no signal. For CuCrP2S6, a systematic degradation study has been conducted. Flakes were observed over the course of the year. AFM analysis confirmed the thickness remained stable for the first month, with no noticeable degradation. However, after a year, significant degradation was visible in optical images, indicating that Cu-CrP2S6 oxidizes in air over a long time scale.

This thesis investigates the structural, energetic, and electronic properties of two-dimensional (2D) materials, focusing on graphene, hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDCs), and arsenic phosphide (AsP) bilayers, using dispersion-corrected density functional theory (DFT) and random Phase Approximation (RPA). Central to our analysis is the use of dispersion-corrected DFT methods, particularly the SCAN-rVV10 and PBE-rVV10L functionals, to accurately predict interlayer distances, interaction energies, and electronic properties. We assess these properties across a wide range of 2D materials in both homogeneous and heterostructured forms. This thesis demonstrates the effectiveness of standard DFT methods in predicting intralayer properties like bond lengths and lattice constants. However, it is the advanced London dispersion-corrected functionals, such as SCAN-rVV10, that are particularly effective in detailing interlayer distances and interactions. These interlayer phenomena are crucial for accurate material characterization and application. For instance, in homogeneous and heterostructured layered systems, SCAN-rVV10 accurately predicts interlayer distances and interaction energetics, aligning closely with experimental and higher-level theoretical RPA results. Moreover, in studying binding behavior, particularly for {Mo,Ti}S2 nanostructures interacting with organic molecules, we illustrate how molecular orientation and surface structure influence binding characteristics. This research emphasizes that molecule interactions at edge and basal plane sites are crucial for controlling the shape and growth of these nanostructures. Molecules often bind more strongly to edge sites, promoting edge passivation and vertical stacking, while basal plane interactions, especially with thiophene, favor lateral growth. In conclusion, this thesis not only advances our understanding of the fundamental properties of 2D materials but also provides crucial insights into the accuracy of DFT methods in predicting these properties. By identifying the strengths and limitations of different dispersion-corrected DFT methods, we open the way for more accurate computational research and practical applications of these materials. This comprehensive analysis bridges theoretical predictions with potential industrial applications, underscoring the transformative impact of 2D materials in science and technology.

Since the discovery of graphene, substantial effort has been put toward the synthesis and production of 2D materials. Developing scalable methods for the production of high-quality exfoliated nanosheets has proved a significant challenge. To date, the most promising scalable method for achieving these materials is through the liquid-based exfoliation (LBE) of nanosheetsin solvents. Thin films of nanosheets in dispersion can be modified with additives to produce 2D inks for printed electronics using inkjet printing. This is the most promising method for the deposition of such materials onto any substrate on an industrial production level. Although well-developed metallic and organic printed electronic inks exist on the market, there is still a need to improve or develop new inks based on semiconductor materials such as transition metal dichalcogenides (TMDs) that are stable, have good jetting conditions and deliver good printing quality.The inertness and mechanical properties of layered materials such as molybdenum disulfide (MoS2) make them ideally suited for printed electronics and solution processing. In addition,the high electron mobility of the layered semiconductors, make them a candidate to become a high-performance semiconductor material in printed electronics. Together, these features make MoS2 a simple and robust material with good semiconducting properties that is also suitable for solution coating and printing. It is also environmentally safe.The method described in this thesis could be easily employed to exfoliate many types of 2D materials in liquids. It consists of two exfoliation steps, one based on mechanical exfoliation of the bulk powder utilizing sand paper, and the other inthe liquid dispersion, using probe sonication to liquid-exfoliate the nanosheets. The dispersions, which were prepared in surfactant solution, were decanted, and the supernatant was collected and used for printing tests performed with a Dimatix inkjetprinter. The printing test shows that it is possible to use the MoS2 dispersion as a printed electronics inkjet ink and that optimization for specific printer and substrate combinations should be performed. There should also be advances in ink development, which would improve the drop formation and break-off at the inkjet printing nozzles, the ink jetting and, consequently, the printing quality. / Sedan upptäckten av grafen har mycket arbete lagts på framställning och produktion av 2D-material. En viktig uppgift har varit att ta fram skalbara metoder för produktion av högkvalitativa  nanosheets via exfoliering. Den mest lovande skalbarametoden hittills har varit vätskebaserad exfoliering av nanosheets i lösningsmedel. Tunna filmer av nanosheets i dispersion kan anpassas med hjälp av tillsatser och användas för tillverkning av halvledare strukturer med inkjet-skrivare, vilket är den mest lovande metoden för på en industriell produktions nivå beläggaden typen av material på substrat. Även om det finns välutvecklade metalliska och organiskabläck för tryckt elektronik, så finns det fortfarande ett behov av att förbättra eller utveckla nya bläck baserade på halvledarmaterial som t.ex. TMD, som är stabila, har goda bestryknings  egenskaper och ger bra tryckkvalitet. Den inerta naturen tillsammans med de mekaniska egenskaperna som finns hosskiktade material, som t.ex. molybdendisulfid (MoS2), gör demlämpliga för flexibel elektronik och bearbetning i lösning. Dessutom gör den höga elektronmobiliteten i dessa 2D-halvledaredem till en stark kandidat som halvledarmaterial inom trycktelektronik. Det betyder att MoS2 är ett enkelt och robust material med goda halvledaregenskaper som är lämpligt för bestrykning från lösning och tryck, och är miljömässigt säker.Den metod som beskrivs här kan med fördel användas föratt exfoliera alla typer av 2D-material i lösning. Exfolieringensker i två steg; först mekanisk exfoliering av torr bulk med sandpapper, därefter används ultraljudsbehandling i lösning för att exfoliera nanosheets. De dispersioner som framställts i lösning med surfaktanter dekanterades och det övre skiktetanvändes i trycktester med en Dimatix inkjet-skrivare.Tryckprovet visar att det är möjligt att använda MoS2 -dispersion som ett inkjet-bläck och att optimering för särskildaskrivar- och substratkombinationer borde göras, såsom förbättringav bläcksammansättningen med avseende på droppbildning och break-off vid skrivarmunstycket, vilket i sin tur skulleförbättra tryckkvaliteten. / KM2 / Paper Solar Cells

The ability to convert photons into mechanical motion is of significant importance for many energy conversion and reconfigurable technologies. Establishing an optical-mechanical interface has been attempted since 1881; nevertheless, only few materials exist that can convert photons of different wavelengths into mechanical motion that is large enough for practical import. Recently, various nanomaterials including nanoparticles, nanowires, carbon nanotubes, and graphene have been used as photo-thermal agents in different polymer systems and triggered using near infrared (NIR) light for photo-thermal actuation. In general, most photomechanical actuators based on sp bonded carbon namely nanotube and graphene are triggered mainly using near infra-red light and they do not exhibit wavelength selectivity. Layered transition metal dichalcogenides (TMDs) provide intriguing opportunities to develop low cost, light and wavelength tunable stimuli responsive systems that are not possible with their conventional macroscopic counterparts. Compared to graphene, which is just a layer of carbon atoms and has no bandgap, TMDs are stacks of triple layers with transition metal layer between two chalcogen layers and they also possess an intrinsic bandgap. While the atoms within the layers are chemically bonded using covalent bonds, the triple layers can be mechanically/chemically exfoliated due to weak van der Waals bonding between the layers. Due to the large optical absorption in these materials, they are already being exploited for photocatalytic, photoluminescence, photo-transistors, and solar cell applications. The large breaking strength together with large band gap and strong light- matter interaction in these materials have resulted in plethora of investigation on electronic, optical and magnetic properties of such layered ultra-thin semiconductors. This dissertation will go in depth in the synthesis, characterization, development, and application of two- dimensional (2D) nanomaterials, with an emphasis on TMDs and molybdenum disulfide (MoS2), when used as photo-thermal agents in photoactuation technologies. It will present a new class of photo-thermal actuators based on TMDs and hyperelastic elastomers with large opto-mechanical energy conversion, and investigate the layer-dependent optoelectronics and light-matter interaction in these nanomaterials and nanocomposites. Different attributes of semiconductive nanoparticles will be studied through different applications, and the possibility of globally/locally engineering the bandgap of such nanomaterials, along with its consequent effect on optomechanical properties of photo thermal actuators will be investigated. Using liquid phase exfoliation in deionized water, inks based on 2D- materials will be developed, and inkjet printing of 2D materials will be utilized as an efficient method for fast fabrication of functional devices based on nanomaterials, such as paper-graphene-based photo actuators. The scalability, simplicity, biocompatibility, and fast fabrication characteristics of the inkjet printing of 2D materials along with its applicability to a variety of substrates such as plastics and papers can potentially be implemented to fabricate high-performance devices with countless applications in soft robotics, wearable technologies, flexible electronics and optoelectronics, bio- sensing, photovoltaics, artificial skins/muscles, transparent displays and photo-detectors.