Terahertz (THz) waves are genarally in the frequency range of 0.1 to 10 THz. Due to the characteristics of spectral resolution, good perspective and security, THz technology has important application prospects in the field of materials detection, quality and quantity analyse of materials, and biomedical imaging. However, most of natural materials have no electromagnetic response in THz region, resulting in a lack of THz materials and devices. The development of THz functional devices will greatly promote the development and practical application of THz technology. Metamaterials (MMs), as a kind of electromagnetic material with controllable properties, can be designed artificially, providing an effective method for developing THz functional devices. In this thesis, we carry out research work concerning the mechanism and characteristics of THz MM functional devices; and various THz MM functional devices were proposed. The main work are summarized and listed as follows:1. A multiband THz MM absorber with three absorption peaks was proposed, with all absorption intensity more than 85%. The proposed structure has the feature of polarization independent, and has potential application in THz spectroscopy, sensing and other fields. Furthermore, a multiband THz MM filter was proposed, and all pass bands have the fearture of low average insertion loss, steep skirts, high out-of-band rejection and polarization independent. This filter has broad application prospects in THz photodetectors, imaging, and communications. 2. A planar THz MM structure with electromagnetically induced transparency (EIT) effect was proposed, and the unit cell of the proposed structure consists of two different split ring resonantors (SRRs). Due to the destructive interference between these two SRRs, the proposed structure generates a very narrow transparent window in the transmission spectrum, which is a typical EIT-like effect. In addititon, a graphene-based THz MM structure composed of multilayer gr
Incorporation of fluoroalkyl groups into porphyrin macrocycles can profoundly change their physical, chemical, and biological properties. Based on our previous work, we investigated the synthesis, properties and applications of various fluoroalkylporphyrins. Various trifluoromethyl-substituted porphyrin cobalt complexes were synthesized by using Chen’s reagent (FSO2CF2COOMe), and their physical and chemical properties were investigated systemetically. A series of perfluoroalkylated porphyrins were synthesized by the second generation click chemistry sulfur(VI) fluoride exchange (SuFEx) reaction, and their catalytic oxidation reactivity was preliminarily estimated. We also studied the transfer reactions of fluoroalkyl carbenes catalyzed by metalloporphyrins. In addition, fluorinated porphyrin covalently functionalized graphene nanocomposite was built and its application on photocatalytic hydrogen production was preliminarily investigated. Specifically, the contents mainly consist of the following four chapters:1. Synthesis and properties of perfluoroalkylated metalloporphyrins. When we studied the trifluoromethylation of cobalt(II) porphyrin, Co-CF3] metalloporphyrin was unexpectedly obtained. Then a series of cobalt porphyrins substituted with different numbers of trifluoromethyl groups at different positions were synthesized. Systematic study on the UV-Vis spectra, fluorescence quenching spectra, redox potential as well as the various physical and chemical properties of the resulting porphyrins were made. Furthermore, a number of perfluoroalkylated porphyrins via the second-generation click chemistry SuFEx reaction was synthesized and applied to catalyze the oxidation of inert C(sp3)-H bonds. Reaction selectivity and the catalyst stability were mainly studied.2. Iron(III) porphyrin complex-catalyzed olefination of aldehydes with 2,2,2-trifluorodiazoethane (CF3CHN2) . Metalloporphyrin-catalyzed Wittig reaction of diazo compounds with aldehydes has been extensively
As a kind of the new material with great interest, carbon based 2D materials (such as graphene) have been widely researched. Recently, carbon based 2D materials have been widely applied in new energy, photocatalysis, microelectronics, biomedical, new functional devices and a series of other application areas. The carbon based 2D materials have shown really broad application prospects. However, due to the boundedness of the preparation methods, the structure of carbon based 2D materials always seemed complicated. This makes it hard to point out the relationship between the structure and basic properties of carbon based 2D materials. However, the deep understanding of the relationship between the structure and the basic properties of carbon based 2D materials is the theoretical basis for further research on the related applications of such materials.In this work, the bottom-up synthesis, shearing, pore-forming, welding, doping, surface/edge groups modification of carbon based 2D materials are realized by diversified controllable methods. Modification and conversion and composite construction. In Chapter 1, we use the bottom-up synthesis method to prepare a new carbon based 2D material: C3N. At the same time, we have carried out theoretical and experimental research on the bottom-up synthesis process. In Chapter 2, we explored the oxidation and shear method of 2D and 3D carbon materials which realized the effective oxidation shearing of the hydroxyl radicals produced by H2O2 catalyzed decomposition of graphene. At the same time, we use cheap and readily available carbon black as raw material, to achieve the 3D carbon material oxidation shearing and the successful preparation of graphene quantum dots. In Chapter 3, we have developed a new method for the preparation of porous graphene based on the chemical oxidation process between hydroxyl radical and graphene. At the same time, the mechanism of free radical oxidation was further analyzed. In Chapter 4, we show the effective welding of reduced graphene oxide by coupling reaction in FeCl3 nitromethane solution. In Chapter 5, we mainly discuss the doping of graphene quantum dots and g-C3N4 quantum dots. We achieved the controllable N-doping of the graphene quantum dots by the bottom-up synthesis method based on the ultrahigh-pressure or the electrochemical technique. The doping of N, S, Se in graphene quantum dots and the doping of P in g-C3N4 quantum dots was achieved by solvothermal methods. In Chapter 6, we use high-pressure homogeneous equipment in alkaline environment successfully prepared a new graphene derivatives: hydroxylated graphene. Further studies have shown that hydroxyl groups in hydroxylated graphene can reversibly convert between hydroxyl-halogen atoms by halogenation. On the other hand, we achieved the modification of the edge groups of graphene quantum dots by hydrothermal or solvothermal methods which successfully obtained the polyethylene glycol-modified graphene quantum dots and the triphenylphosphine-modified graphene quantum dots. Finally, we achieved the surface hydrogenation of the new carbon based 2D material C3N. In Chapter 7, we used a freeze-dried tungsten oxide-reduced graphene oxide aqueous dispersion and then chemically reduced the tungsten oxide-reduced graphene oxide aerogel using hydrazine hydrate. This method not only realizes the preparation of tungsten oxide nanowire - graphene composite aerogel, but also provides a new idea for the preparation of other inorganic materials-reduced graphene oxide aerogel.Based on the controllable preparation of carbon based 2D materials, we have realized the relationship between the bandgap, photoluminescence/interfacial properties and the structure of carbon based 2D materials. In Chapter 1, we show the new carbon based 2D material C3N has an indirect band gap of 0.39 eV. At the same time, we proved the mechanism and relationship between heteroatom species and doping concentration on the energy band of carbon based 2D materials. In Chapter 2, we discussed the effect of size, heteroatom and edge groups on the photoluminescence wavelength of carbon based 2D materials. On the edge group, we proved that the edge groups can have a significant effect on the photoluminescence wavelengths of the carbon based 2D materials by the electron induced effect which is just like the hetero atoms in lattice. In terms of excitation wavelength dependence, we confirm the edge, the complexity of surface groups is the main factor leading to excitation wavelength dependence. In terms of quantum yield, we demonstrate the advantages of direct bandgap carbon based 2D materials in the process of photoluminescence and the exciton process of indirect bandgap carbon-based two-dimensional quantum production by means of band structure and transition model. We also proved that the n-π* transition in carbon-based 2D materials can greatly improve the quantum yield of graphene quantum dots. In addition, we studied the mechanism of the lattice heteroatom and the edge groups through the coordination and redoxing of the carbon-based 2D materials in the fluorescence quenching process. Furthermore, we analyzed the influence of the chain length and the size of the edge groups of graphene quantum dots on their ion selectivity and detection limit. Finally, in Chapter 3, we demonstrated the effect of the surface groups on the wettability of the carbon-based 2D materials, and the effect of the electron-hole pair separation on the photocatalytic ability of the composite structure. Our work not only has some reference for the controllable preparation and structural control of carbon-based 2D materials, but also is helpful for the further understanding of the basic properties of carbon based 2D materials. The basic understanding of the basic properties of carbon based 2D materials will further promote the carbon based 2D materials in a variety of practical applications of the rapid development.
Electronic skin based on multimodal sensing array is ready to detect various stimuli in different categories by utilizing highly sensitive materials, sophisticated geometry designs, and integration of multifunctional sensors. However, it is still difficult to distinguish multiple and complex mechanical stimuli in a local position by conventional multimodal E-skin, which is significantly important in the signals feedback of robotic fine motions and human-machine interactions. Here, we present a transparent, flexible and self-powered multi-stage sensation matrix based on piezoelectric nanogenerators (NGs) constructed in a crossbar design. Each sensor cell in the matrix comprises of a layer of piezoelectric polymer sandwiched between two graphene electrodes. The simple lamination design allows sequential multi-stage sensation in one sensing cell, including compressive/tensile strain and detaching/releasing area. In order to improve the sensitivity of the sensor cell, PDMS substrate was further structure engineered. The experimental results show that the sensor cell was highly sensitive to the applied pressures than before. And the minimum sensing pressure was lower than 1kPa. As the basic combinations of compressive/tensile strains or detaching/releasing represent individual output signals, the proposed multi-stage sensors are capable of decoding to distinguish external complex motions. The proposed self-powering multi-stage sensation matrix can be used universally as an autonomous invisible sensory system to detect complex motions of human body in local position, which has promising potential in movement monitoring, human-computer interaction, humanoid robots, and E-skins.
Graphene is the name given to a ?at monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, as well as many other supreme properties, all of which justify its nickname of a miracle “omnipotent material”. Recent years have witnessed the progresses of the synthesis of large area graphene with high crystallinity and controllable layers by chemical vapor deposition, significantly advanced its applications in nano-electronic devices, biomedicine, solar cells, supercapacitors, Li-ion battery and many others. However, until now, the controllable graphene growth and its structural refinement through chemical vapor deposition are still mainly on the basis of “trial-and-error approach”, with limited researches focus on the in-situ thermodynamics, kinetics, growth mechanism(s), real-time structure regulations and the structure-performance relationship in graphene applications. Those researches are blocked by the lack of in-situ experimental setup and corresponding time-resolved characterization techniques. On the other hand, the high brightness, tunable energy, coherence, high collimation, large equipment integrated space of synchrotron radiation can provide multiple technologies that enable the real-time dynamics study of materials. Thus, here, based on the hard X-ray diffraction and absorption spectrum beamlines in Shanghai Synchrotron Radiation Facility, we construct a universal in-situ chemical vapor deposition platform, battery cells and moisture cells, toward the in-situ study of graphene growth, refinement and electrochemical application. The main studies include the following aspects:1.Using the home-made chemical vapor deposition (CVD) chamber, we demonstrated the direct growth of graphene on a single-crystal silicon surface. In-plane propagation, edge-propagation, and core-propagation processes were proposed to
Fuel cell is a device that converts the chemical energy from fuel into electricity. As the energy conversion in fuel cell is not a combustion process, Thus it is not subject to the Carnot cycle limit. With higher energy conversion efficiency, less environmental pollution and other significant advantages, the fuel cell technology meets the demand for increasing energy utilization efficiency without polluting the environment. Oxygen reduction reaction (ORR) is the core reaction in the fuel cell, but since this is involved in four electrons transfer and multi-reaction steps, the reaction path is complex, the intermediate species are various, and the rate determining step is difficult to determine. The oxygen reduction reaction study on fuel cell cathode is considered to be the key to the design of fuel cell.Carbon materials directly as catalysts have been studied in the many reactions. They become the alternatives to replace the conventional metal catalysts due to the promising performance in some of the reactions. The oxygen reduction reaction on sulfur and nitrogen dual doped graphene has been studied by the period density functional theory calculation to investigate the key factors determining the catalytic properties of the carbon catalyst, through exploring the physisorption of the reactants, the identification of active site, the reaction pathway and the effect of heteroatom doping. The main results are listed as follows:Structure optimization results show that sulfur and nitrogen atoms in sulfur and nitrogen dual doped graphene are in ortho-position, sulfur and nitrogen atoms are not bonded with each other. But sulfur and nitrogen atoms form a chemical bond after the oxygen adsorption, single sulfur or nitrogen doped graphene can only achieve physical adsorption of oxygen. Sulfur and nitrogen dual doped graphene has better activity of oxygen reduction. The charge analysis results show that the high charge density and spin density in sulfur atom are the main reas
Since the first fabrication of monolayer graphene by A. K. Geim and K. S. Novoselov in 2004, graphene has attracted enormous interest of researchers due to its distinctive and intriguing optical and electronic properties as diverse as zero-band gap, tunable Fermi level, high carrier mobility and optical transparency. In photonics and optoelectronics, a variety of high-performance graphene-integrated optoelectronic devices have been successively reported, for example, electro-optical modulators, photodetectors, and saturable absorbers. Recently, graphene has been experimentally proved to support the surface plasmons with flexible tunability at deep subwavelength scale, called graphene plasmons (GPs), which provides the opportunities and also challenges for the development of integrated photonics. Additionally, as a highly designable technique for exploiting artificial materials, metamaterials (MMs) possess exotic properties that can never be achieved by materials and devices in nature, such as negative refraction, invisible cloak, rainbow trapping, and metalens. In this dissertation, for the purpose of the functionalities and applications of grapheme-integrated photonic devices, the optical properties of GPs have been systematically investigated, and then the design methods of 1D, 2D, and 3D graphene plasmonic metamaterials are proposed and demonstrated theoretically and numerically, which successively inherit the unique advantages of GPs and MMs. Finally, on the basis of the proposal, several types of graphene metamaterial photonic devices operating at mid-infrared (MIR) and terahertz (THz) range are investigated in details, including Bragg gratings, transformation optical lenses, electro-optical switches, dual-polarization optical modulators, and tunable multi-channel optical filters.The main contents of this dissertation are shown as follows:1. The optical properties of GPs are systematically investigated. According to the carrier transition processes in energy
The study of topological states is a hot topic in condensed matter physics. It is a novel electronic state generated by integral topological property of system. Quantum Hall effect, quantum spin Hall effect and topological insulator all have topological states. Their characteristics are insulated in its interior and protected by topology at the surface. Recently, many theoretical and experimental studies have demonstrated photonic analogues of topological states, based on the fact that these states are a manifestation of one-particle wave behavior, and this has further stimulated research on photonic topological states. Photonic crystals and metamaterials provide a flexible platform for simulating topological phases. The introduction of topology makes traditional photonic system have some new features, including unidirectional transport edge states, robustness of immunizing defects and no backscattering. Topological photonic is hopeful to provide huge revolution for photonic integration chip and optic communication devices. However, the application of topological photonic device is still facing much challenge. It is difficult to achieve topological photonic device at optical frequency. Devices are complex and big, so it is difficult to fabricate and integration. In this paper, we propose a graphene-based dielectric topological photonic crystal slab. Nontrival topological photonic cystal can be construct by lattice perturbation and deformation. We can achieve topological edge state waveguide transport. Our proposed structure has smaller dimension and is convenient for integration. Furthermore, the achievement of topological photonic states at optical frequencies is much easier in this designed structure. At the same time, it has simple design and is easier to fabricate. Most of all, topological edge state in the structure is continuously and dynamically tunable. The main works are as follows: 1. Introduce the concept of photonic crystals and topologica
AbstractNano materials are a series of materials whose dimensionality is limited to nanoscale. Nano materials can be divided into zero-dimensional, one-dimensional and two-dimensional materials. Graphene is two-dimensional Nano carbon material with unique optical and electronic properties, and one of most promising emerging materials. The compatibility of graphene preparation with silicon-based fabrication process is one of challenges that hinders massive applications of graphene. Besides, the preparation of unnatural atomically thin metal oxides is another important research field. Bulk Magnetite is an important ferromagnetic material and is used widely. Magnetite is theoretically predicted to be 100% Spin polarization at room temperature, which is ideal half-metallic material for spin injection in spin electronics. However, besides molecular beam epitaxy and energy-assisted deposition, the breakthrough of magnetite preparation is rare. The main topics of the thesis focus on silicon-intercalation graphene synthesis and controlled synthesis and characterizations of quasi-two-dimensional magnetite on liquid copper surface. The thesis is divided into two parts:1.Preparation of graphene/silica/copper heterostructure via chemical vapor deposition（CVD）. Although graphene preparation contains mechanical exfoliation, epitaxial growth and CVD, CVD is a cost-effective method in massive production of electronics-grade graphene. Metal substrate is necessary for CVD graphene growth. However, the subsequent transfer process usually causes defects, wrinkles and metal ions pollution on graphene which affect graphene electronic performance. The size and cost of graphene grown on dielectric is largely different from graphene grown on metal. The work focuses on directly co-growth graphene/silica heterostructure via CVD. Our experiments confirm the formation of graphene/silicon oxides/metal structure on Cu surface. Silica growth on Cu-Fe/W alloy substrates are systematically investi
AbstractLithium-ion capacitor (LIC) is a new type of electrochemical energy storage device developed rapidly in this century. It’s feature is between the traditional double-layer supercapacitor and lithium-ion battery, so that it has the advantages of both, with high energy density, high power density, long cycle life, green and other advantages at the same time. There is a wide range of applications in the new energy power generation, electric vehicles, aerospace and other fields. High-performance electrode material is the core of lithium-ion capacitor, so it has become the focus of research, and a variety of systems of lithium-ion capacitors are emerging, its performances are also different. In the industrial research, the work is mainly concentrated in the prelithiation technology, production process optimization and other direction.In this paper, the core content of our work is cathode electrode material. We studied the performance of lithium-ion capacitor with different anode material and activated carbon cathode. We also researched the effect of different prelithiation capacity on the performance of lithium-ion capacitor. A kind of high-performance composite material, consisting of Fe3O4 nanocrystallites and graphene (Fe3O4-G), was synthesized and applied as anode material in lithium-ion capacitor. We characterized and tested a commercial silicon-carbon composite and applied it into lithium-ion capacitor. The main research contents are as follows:1. The activated carbon and mesocarbon microbeads system were used to assemble the lithium-ion capacitor. The influence of the prelithiation capacity on the electrochemical performance of lithium-ion capacitor was investigated. The prelithiation capacity was set as 100, 200 and 300 mAh·g-1, respectively. The optimal electrochemical performance happened in 200 mAh·g-1, the energy density is 83.7 Wh·kg-1 and the power density is 8.8 kW·kg-1. The cycle life was tested at 20C rate, the capacity is maintained at 91.6%