Metal Organic Frameworks (MOFs) are highly porous, crystalline frameworks composed of an organic linker and a metal oxide cluster. Covalent Triazine Frameworks (CTFs) are a subclass of MOFs and similarly are highly porous crystalline frameworks, but unlike MOFs, are composed of purely organic building units. Since the initial reports of a successful synthesis and characterization of MOF-5 in 1995, the interest in these frameworks has exploded. The ability to design the MOF properties and functionality by simply selecting the starting precursors make MOFs optimal materials for a multitude of fields. However, even with all of the research being conducted, there are many MOF applications yet to be discovered. In the first part of this thesis we explore the application of MOFs as templates for the synthesis of metallic nanostructures based on the size and the shape of the MOF pores. The limitless number of MOF structures with different pore shapes and sizes allow for the synthesis of nanostructures with any desired shape or size. It is shown that by using MOF-545 with one dimensional pores, well aligned, ultra-thin gold and platinum nanowires are grown. The nanowires inside the MOF pores are confirmed by imaging the focus-ion beam cross-section of the metal loaded MOF-545 using a transmission electron microscope. In the second part of this thesis, the use of MOFs as a precursor to fabricate nitrogen and metal co-doped carbons is discussed. MOF-545 is an excellent precursor for one-pot synthesis of metal and nitrogen co-doped carbon wires. Two different annealing methods are studied, either under pure argon or argon mixed with air impurities, and the resulting carbon wires are tested as an electro-catalyst for oxygen reduction reaction (ORR). Surprisingly, the air treated carbon wires show much higher ORR activity, comparable to that of platinum in basic electrolyte. Finally, the last part of this thesis will discuss controlling the surface area and porosity of carbon frameworks fabricated from CTFs. By using three different precursors, 12 carbon networks are synthesized and analyzed for porosity, surface area and capacitance. By varying the precursor composition and ratio, as well as the temperature, we are able to control the average pore size distribution between 1-17 nm, while the samples treated at 900�C show the best capacitance of 130 F/g.

Covalent Triazine Frameworks (CTFs) are highly porous materials with two- dimensional or three-dimensional architectures, which can be synthesized with tunable porosity and a variety of functionalities. Their synthesis and characterization has been studied extensively in many prior works. However, ionic functionalities built into CTFs are new and have not been investigated, especially those containing an imidazolium ring and capable of being deprotonated into an active N-heterocyclic carbene. Chapter 1 introduces different chemical architectures developed by chemists, highlighting one of the most investigated topics being Covalent Organic Frameworks. The theory of absorption of gasses on porous solids is also discussed. Chapter 2 outlines the detailed synthesis and characterization of a unique CTF with Reuleaux Triangle shaped pores, which forms by harnessing the geometry of the N-heterocyclic carbene. Aside from nitrogen uptake, we studied absorption of carbon dioxide on an ionically charged framework. Chapter 3 illustrates a method of exfoliating two-dimensional CTFs. Most CTFs are two dimensionally stacked, which have full conjugation, and π-π stacking similar to that of graphite. Yet, their thin film characteristics have never been studied. Here we developed a method to peel these stacked layers apart, characterize the sheets, and produced thin-film devices along with conductivity measurements. Due to CTFs exceptional stability, and intrinsic nitrogen doping, their electrochemical applications are just beginning to be explored. The electrochemical reduction of oxygen, a very important reaction, is one of the main limiting factors to widespread use of fuel cells. In Chapter 4 we create oxygen reduction catalysts using super-acid derived CTF polymers and cobalt salts as precursors. The CTF polymers readily absorb cobalt from solution and are then annealed at 900 �C. The resultant porous catalyst reduces oxygen to water with performance comparable to the industrial standard platinum. Chapter 5 discusses molecular control of porous carbons. We have developed a new pathway by designing molecular precursors to tune the porosity of CTF-derived porous carbon materials. Using CTFs as precursors, while controlling their monomeric length results in a high degree of pore size control. In this process, by choosing using different ratios of long and short monomers we can be tune the size of the CTFs. The resultant framework is heated to desired temperatures of 700 to 900 �C to yield porous carbon materials. The incremental pore size and volumes from molecular tuning these frameworks remains consistent from both pre annealing to post annealing, though some pore expansions can exist. This is the first demonstration of molecular tuning the pore size of porous carbons, and a powerful way of bringing a certain degree of order to traditionally disordered carbon materials. We apply these characteristics of molecular tuning to investigate capacitive related performance as well as oxygen reduction reaction. Through pore tuning, we create different porous carbons with surface areas ranging from 450 m2 g-1 all the way to 2400 m2 g-1 while controlling pore sizes within a few nanometers of each other. Capacitive values rise over ten fold from 14 F g-1 to 180 F g-1. When different size frameworks are loaded with cobalt and used for oxygen reduction, we observe five-fold increases in kinetic current density, and reach overpotentials of 38 mV less than that of platinum on carbon. These electrocatalysis experiments demonstrate the significance of ample reactant delivery to the catalyst.

Plasmonic hot electrons are electrons with high kinetic energy, generated from the

plasmonic nanostructures. The application of hot electrons has been widely studied in the

community of photochemistry and optoelectronics. Many applications like photoelectrochemistry

and photodetector involve semiconductors, and these applications are plagued by low hot

electron injection efficiency in the metal-semiconductor junctions which hinders the wider

applications for the hot electrons.

Since the exfoliation of graphene with scotch tape in 2004, two dimensional (2D) materials

have been widely studied for their unique properties when the thickness scales down to atomically

thin. Transition metal dichalcogenides are a class 2D materials, they are semiconductors, and

they have the different band structures with different material compositions. For each type of the

transition metal dichalcogenide, its few-layer counterparts have both direct band transition and

the indirect band transition, this unique band structure of the few-layer 2D transition metal

dichalcogenides opens up the possibilities for studying the relationship between the hot electron

injection and the band structure in the metal-semiconductor junction.

Inspired by the unique band structure of the 2D semiconductors, we design the structure

formed with plasmonic nanostructures and 2D semiconductors as a model system to explore

plasmonic hot electron injection process at the metal-semiconductor junction, in which we employ

high mobility 2D semiconductor to capture the hot electrons. Due to the high photoluminescence

quantum yield WSe2, photoluminescence spectra are sued to probe the hot electron injection

mechanism between the gold and few-layer WSe2. We demonstrated that the hot electrons tend

to at first inject into the energy lower L point, and then to the K point of the of the few-layer WSe2.

Another question considered in this dissertation is how to modulate the hot electron

injection to improve hot electron collection in the semiconductor. We employed self-assembled

monolayer alkane thiols with different chain lengths as the interlayer, and polymethyl methacrylate

(PMMA) as protection layer to tune hot electron transfer process. The insight derived provides

valuable guidance for the rational design and performance optimization of the relevant plasmonic

hot electron devices.

The continued miniaturization of the silicon-based electronics has been the core of the information technology revolution, but such efforts are quickly approaching the fundamental material limit, which has motivated considerable efforts in exploring a new generation of electronic materials and device architectures. Among many material systems explored, two-dimensional (2D) atomic crystals, wide bandgap semiconductors and halide perovskite have attracted considerable interests for their unique physical geometry or excellent electronic, optoelectronic properties, offering a pathway for further miniaturization of digital devices or diversified function integration for Internet of Things and artificial intelligence. However, to probe the fundamental transport of these materials and capture their intrinsic merits in functional devices is a nontrivial challenge since these materials are usually rather delicate and may readily degrade during the material integration and device fabrication steps. To this end, a physical transfer process exploiting the weak van der Waals (vdW) force to combine disparate materials to form heterojunction interfaces with atomically clean and electronically sharp vdW interfaces, allowing creating high-performance devices for probing and pushing the limit of these emerging electronic materials. Here in this dissertation, we explore and optimize vdW integration of high-quality and uniquely designed device architectures for creating and investigating high performance devices of emerging electronic materials including 2D atomic crystals, bulk β-Ga2O3 and single crystalline lead halide perovskites. We first show the potential of integrating metal contacts with sub-10 nm channel length to 2D materials for probing quantum transport and pushing the on-current for breaking the miniaturization limit of silicon. Then we demonstrated various high-performance vdW heterojunctions based on 3D semiconductors including Schottky diode, p-n diode, metal semiconductor field effect transistors and junction field effect transistors to unlock a rich material library for vdW integration. We also design a feedback gate structure to suppress the threshold voltage roll-off and undesired ambipolar transport in 2D semiconductors, which are crucial for stable device operation for integrated circuits but have seldomly been explored. Finally, we develop a convenient and scalable vdW plug-and-probe technique to integrate top-gate and contact structures on 2D materials and halide perovskite in one step to form ideal transistors for intrinsically probing these novel materials and fabricating high-performance devices. By increasing both complicity of device architectures and the variety of channel material choices while still capturing the merits of these emerging electronic materials, we prove the vdW integration as a universal approach providing prominent opportunities to both fundamental study for novel materials as well as the design of next-generation devices in future semiconductor industry.

High performance energy storage technologies are being developed to more effectively utilize renewable energies, as a result of the steadily expanding energy consumption for portable electronics and electric cars. Batteries with sulfur cathodes have attracted a lot of attention due to their inexpensive cost and great charge storage capacity. Polysulfide shuttling, the main issue in metal sulfur batteries, results in significant sulfur loss and quick deterioration. Despite significant efforts being devoted to improving their performance, the chemical pathway and shuttling mechanism in lithium/sodium sulfur batteries are still up for debate. In order to better mitigate the polysulfide shuttling issue, this work intends to examine the sulfur reaction mechanism and deposition behavior from a fundamental perspective. Additionally, effective catalysts can offer adequate active sites to improve the kinetics of sulfur reactions during charge/discharge, speeding up the conversion of polysulfides and reducing polysulfide accumulation that results in shuttling. To determine how catalysts affect the reaction network and battery performance, various catalysts are examined. This information could be employed to guide the rational design of the catalysts for sulfur cathodes in the future. In this work, Chapter 1 provides a background introduction for the tasks that follow. The behavior of sulfur deposition and basic reaction mechanisms such as the shuttling mechanism and molecular pathway in lithium sulfur batteries, were studied in Chapter 2 and Chapter 3 using heteroatom doped holey graphene frameworks as the modeling system. After building a systematic methodology to comprehend the reaction mechanism by combining electrochemistry (cyclic voltammetry), in situ Raman, and density functional theory, we further analyzed different catalysts in Chapter 4 and Chapter 5, including different heteroatom doped holey graphene frameworks and nitrogen doped mesoporous carbon materials. Finally, in Chapter 6, we took a step forward from lithium to sodium, and demonstrated a useful technique for separator modification to reduce polysulfide shuttling in sodium sulfur batteries. These findings attempt to address the shuttling issue by studying the fundamental reaction mechanism in metal sulfur batteries and would be very helpful as a blueprint for creating the next generation high energy density batteries.

Portable energy storage is of critical importance for the advance of renewable energy storage, consumer electronics, electric vehicles, and electric aviation, due to the increasingly complex and energy intensive products. Most of the mobile energy market relies on and is dominated by Li-ion battery technology, since its commercial introduction during the 1990s. However, the commercial Li-ion battery does not use lithium metal (3840 mA h g -1) as anode, but instead uses graphite anode or LiC6 (372 mA h g -1) when fully charged with only ~10% capacity compared to solid lithium metal. Thus, to increase the energy density of the battery and keep up with the improvement of future electronics, incorporation of lithium metal anode will have to be realized. However, the holy grail that is lithium metal anode is plagued by numerous hindrances. The chief problem being lithium dendrite growth as the result of charge and discharge during battery usage. The formation of lithium dendrite can result in the capacity fade of the battery due to electrode detachment, and severe safety concerns of battery short from dendrite penetrating the thin separator, and unwanted side reaction with the volatile electrolytes. These inherent problems can be addressed by incorporating solid-state electrolytes, where higher modulus can suppress the danger associated with lithium metal anode. In the first part of this thesis, we discuss the background and electrochemistry of a battery and the role of solid electrolytes compared to its liquid counterpart. In the second portion, we examine the application of nanomaterials and nanostructures in solid state electrolyte to enhance the low ionic conductivity of solid electrolyte to realize the effects of percolation pathways. In the third part, we examine the high surface area 3D network nanostructure with electronegative surface atoms that enhances ionic conductivity at the interface between the network and polymer. Lastly, we demonstrate the use of lithium trifluoromethane-bis-(sulfonyl)imide (LiTFSI) surface functionalized silica aerogel/polyethylene oxide (PEO) composite electrolyte. And its ionic conductivity (2 x 10 –3 S/cm) compared to the liquid and solid counterparts. In addition, we unravel the typically neglected ionic conductivity at extremely low temperature regime.

All-inorganic perovskites have attracted tremendous interest for their tunable optical properties and remarkable stability when compared with its hybrid counterpart. Although considerable efforts have been devoted to synthesizing micro-crystalline domains and various nanostructures, it remains a considerable challenge to produce high-quality monocrystalline thin films that are indispensable for functional electronics and optoelectronics. Furthermore, due to the fragility of metal halide perovskites, it remains a standing challenge to use conventional lithography to create reliable electrical contacts, rendering the intrinsic electrical transport properties of such perovskite materials are often seriously convoluted/plagued by poor electrical contacts. Starting from the vapor phase deposition of cesium lead halide CsPbX3 (X=Cl, Br, I) microplates, we demonstrated the growth of large-area monocrystalline all-inorganic perovskite thin films on muscovite mica. We show highly oriented CsPbBr3 square microplates can be readily grown on the (001) surface of muscovite with an epitaxial relationship of CsPbBr3-(001) paralleled to muscovite-(001), CsPbBr3-[100] paralleled to muscovite-[100] and CsPbBr3-[010] paralleled to muscovite-[010], which eventually merge together to form a continuous monocrystalline thin film. Time resolved photoluminescence (TRPL) decay measurements give a carrier lifetime of 170 ns, considerably longer than that in spin-coated thin films and well comparable to that in the highest quality bulk crystals. Aiming to resolve the problem of poor electrical contacts, we have further developed a simple physical transfer approach to create high-quality van der Waals (vdW) contacts, where the prefabricated thin film gold electrodes are directly laminated onto the perovskite thin films with minimum interfacial damage to produce electrical contacts for functional devices. The electrical and photoelectrical transport studies demonstrated an extraordinary photocurrent gain exceeding 106. The van der Waals contacts enable not only accurate measurements at room temperature but also the exploration of electrical properties at cryogenic conditions. A record-high carrier mobility exceeding 2,000 cm2/Vs has been achieved at 80 K and a quantum interference induced weak localization behavior in halide perovskite materials with a coherence length up to 49 nm has also been revealed for the first time by magnetotransport studies at 3.5 K. The growth of large-area high-quality perovskite thin films and the integration of the damage-free metal integration approach mark important steps for both the fundamental investigation and potential applications of the perovskite materials in integrated optoelectronics.

Here I describe the synthesis and characterization of a new Covalent Triazine Framework (CTF) with the potential to coordinatively link organometallic complexes inside the pores for enhanced carbon dioxide (CO2) adsorption and for control of the electronic transport properties of the framework. An N-heterocyclic Carbene (NHC) precursor is synthesized and then used to construct a CTF through the trimerization of 1,3-bis(4-cyanophenyl)-1H-imidazol-3-ium in molten ZnCl2. X-ray Diffraction (XRD) studies and Selective Area Electron Diffraction (SAED) reveal the highly crystalline nature of the resulting framework, and the Brunauer-Emmett-Teller (BET) analysis demonstrates a high specific surface area up to 850 m2/g with high H2 and CO2 uptakes.

The ability to deposit and modulate conducting and semiconducting bulk materials and films on various substrates, including silicon and plastics, is of central importance for contemporary and future solid-state electronics, thermoelectrics and photovoltaics. Current approaches, such as chemical vapor deposition (CVD) or high vacuum physical vapor deposition (PVD) processes, are usually too costly and require too high processing temperature, and are not typically compatible with the growing demand of low-cost and large-area electronics, such as the emerging wearable devices. As a result, solution processes, with the potential advantages of low cost, low temperature and compatibility with plastic substrate, have emerged as an attractive approach for next-generation flexible electronic devices and thermoelectrics, wearable computers and large-area displays/photovoltaics. The key component of the solution process is the formulation of an easy-to-handle ink. Therefore, in my dissertation, I mainly investigated two types of method to prepare semiconducting or conducting ink solution, including utilizing two-dimensional (2D) nanoplates dispersion and a formulated co-solvent. In the first part, 2D nanoplates (Bi2Se3, Bi2Te3, SnS2, SnSe2, etc.) were synthesized with a ultra-small thickness (~ 6-15 nm) to form a stable ink solution which could be processed into highly uniform thin films with superior electrical performance. Taking a step further, I have also developed a new solution epitaxial approach for the growth of van der Waals heterostructures, which can be further used to create a quasi-superlattice structure with superior thermoelectric properties. The following chapters discuss the preparation of a co-solvent which could directly dissolve a variety of semiconductor solid to form ink solution at room temperature with a greatly simplified procedure. The ink solution could be used to fabricate highly uniform electronic thin films with excellent performance via conventional solution deposition approaches. And such ink solution could produce a flexible high-performance thermoelectric Cu2Se thin film. The development of those new fabrication strategies for the solution processable ink is an exciting advancement and offers great opportunities in the facile fabrication of semiconducting and conducting thin films/bulk for large-area high-performance flexible electronics, thermoelectrics and photovoltaics with high throughput, greatly reduced cost and improved safety.

The development of graphene and the nanotechnology revolution brought new interest in Layered transition metal dichalcogenides (TMDs). First explored in the 1960s, these TMDs are a subject of interest due to their wide range of material properties form semiconductor, metals, to superconductor. Through intercalation chemistry, there is additional flexibility to tune the materials’ parameters to the desired property. Naturally semiconducting, Group 6 TMDs (i.e. MoS2) have the most potential for future electronic application. Yet these Group 6 TMDs are also the most chemically inert. While over 240 organic-TMD complexes have been made reported for Group 4 (i.e. TiS2) and Group 5 (i.e. TaS2) TMDs, for 50 years, organic complexes of Group 6 TMDs remained unexplored.

With the goal of tailoring the properties of Group 6 TMDs, we followed three different experimental approaches. We begin by pursuing liquid phase exfoliation to produce few/mono layer products and use contact angle measurement to infer the thermodynamic of the exfoliated materials in mixed solvents. We expanded a pen-paper vibrational model of 2H-MoS2 to analyze the vibrational spectra of WS2-xSex alloy with a tunable optical gap. Inspired by Lithium based intercalation methods, we propose a new and direct electrochemical intercalation route to produce Organic-MoS2 complexes using quaternary ammonium compounds. We use the same electrochemical concept and show that the theory is sufficiently robust, allowing intercalation onto Layered Black Phosphorus (BP).