Since it was first discovered in 2004, graphene has been a rapidly rising star on the horizon of materials science and condensed-matter physics. Unique two-dimensional structure and excellent electrical, optical, mechanical, thermal characteristics make graphene a broad prospect of application in theoretical researches, nanoelectronic devices, energy storages, transparent conductive films, sensors and composite materials. Since the preparation of material is the premise and basis for the systematic study of its properties and applications, we study on the synthesis and transfer of graphene grown by chemical vapor deposition in this paper. The main results are summarized as follows: 1. Few-layer graphene films on Ni films and Cu foils have been successfully synthesised by the self-built CVD equipment. 2. The correlation between the annealing time, surface treatment, gas flow and the quality of graphene has been studied. The results indicate that the size of Ni crystalline grain and the area of fewer layers graphene increase with the annealing time, but the amount of hydrogen blisters also increases. On the other hand, surface treatment of Cu foil can improve the crystallization of graphene, and gas flow rate optimizing makes the graphene film more homogeneous, more orderly and fewer layers. Finally, we obtained homogeneous graphene films under two layers on the condition of CH4 : H2 = 200 : 0 sccm on surface treated Cu foil. 3. The graphene films synthesised on Ni films and Cu foils have been successfully transferred to SiO2, glasses, surface treated-glasses and PET films by self-designed method. 4. The correlation between the pressure duration, heating temperature, target substrates’ surface treatment and the transfer percentage has been reserched, finding that longer pressure duration, higher heating temperature and surface treatment can improve the transfer percentage of graphene. 5. The graphene films synthesised on Ni films exhibit a high optical transmittance of more than 90%, which is superior to commercial transparent electrodes such as indium tin oxides.
Graphene, a perfect two-dimensional atomic material with compact honeycomb structures, has attracted enormous interests due to its exceptional physical, mechanical, and electronic properties. Since the first discovery by mechanical exfoliation from highly oriented pyrolytic graphite, numerous methods have been developed to fabricate large-scale and high-quality graphene for basic research and wide applications. Among them, chemical vapour deposition (CVD) has achieved successful growth of large-area graphene on metals. Novel catalysts need to be developed to realize the industrialization of graphene in the future in the CVD graphene field. Recently, the liquid Cu has been introduced into the growth of high-quality graphene, posing great advantages over conventional solid Cu catalyst. This dissertation is mainly focused on the controlled growth and etching of graphene on liquid copper surface by chemical vapor deposition. This dissertion contains the four following parts: 1. We report the use of liquid Cu to precisely control growth of self-aligned hexagonal graphene grains by methane CVD at ambient pressure. By controlling the growth parameters, for example, methane ?ow rate, well-dispersed and single-crystal graphene arrays were prepared. 2. The controlled fabrication of single-crystal twelve-pointed graphene grains is demonstrated for the first time by ambient pressure chemical vapor deposition on a liquid Cu surface. The shape evolution among hexagonal graphene, twelve-pointed graphene and round graphene is investigated. 3. We demonstrate for the first time that the graphene etching process can follow a novel fractal mode. Further we show that the etched graphene pattern can be modulated from a simple hexagonal pattern to complex fractal geometric patterns with six-fold symmetry by varying the Ar/H2 flow rate ratio. 4. We demonstrate for the first time a CVD process to directly fabricate hexagon graphene flake arrays with high control over the size, location and edge orientation. Controlled micro and nano-cutting of graphene film and single crystals is realized by introduction of hydrogen gas for etching. 5. We show the complex and regular silicane oxide patterns induced by graphene etching on liquid Cu surface. Numerous patterns have been controlled prepared by varing the etching conditons.
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
In this thesis, we have prepared n-layer graphenes through several approaches and studied Raman features of graphenes with strain, deposited with gold particles or covered by crystal violet molecules. The thesis includes the following parts:
The 2-D materials, such as graphene (G), have the unique physical and chemical properties. They arouse so much attentions due to the huge influence in the physics, chemistry and biology as well as the potential applications in the flexible flat-panel displays and integrated circuits. In this thesis, we mainly investigate the basic structures and their electronic properties of some 2-D films on metal surfaces by using the first-principle density function theory calculations. The main results are summarized as follows: I, We investigate the structures and electronic properties of the G/Ru(0001) and the G/Ir(111) moiré patterns. For the G/Ru(0001) moiré pattern, graphene is divided into three different regions due to the interactions between carbon atom of graphene andmetal atoms in the substrate: the fcc, hcp and atop region. These regions have different structures and electronic properties, where atop region is the highest, hcp region is the lowest, and fcc region has the strongest sp3 hybridization. For the six kinds of G/Ir(111) moiré patterns in the experiment, our calculation shows that graphenes are very flat in these systems, and they also have tiny p doping. Except for the R0 structure, the influences of the Ir(111) substrate to the electronic structures of the graphene are very small. Due to the difference of the electronic structures for different regions of the G/Ru(0001), we investigate the selective adsorption for the metal atoms and the organic molecules on this moiré pattern. For the metal atoms, which have the stronger interaction with G/Ru(0001) substrate, we find the selective growth mechanism of them on G/Ru(0001): The metal atoms which locate at the fcc region have the largest binding energy because of the strongest sp3 hybridization in this region, the metal atoms with the partially-occupied d orbit have larger binding energy differences and they can form the selective nano clusters.
Since it was first discoveredin 2004, graphene has been rapidly developed in the areas of materials science, microelectronicsand condensed-matter physics for its unique two-dimensional structure and excellent electrical, mechanical, optical,thermal characteristics. Till now, graphene has a broad prospect of application in transparent conductive films, nanoelectronicdevices, resonator,sensor, composite materials and so on. Thepreparation ofhigh-quality graphene material is the premise andbasis for the systematic study of its properties and application. In this work, we firstly studyon the synthesis of graphene by chemical vapor deposition (CVD), and then westudy the process technology of graphene transfer, graphene imaging, metalelectrodes fabraction and high-k material deposition, finally we fabricate andstudy the mechanisms of graphene-based field effect transistor (G-FET),photonic device, biosensor and gas sensor. The main results are summarized asfollows:
Based on non-covalent functionalization of graphene, the thesis has prepared smart responsive as well as functional graphene/polymer composites and studied its properties wihtout destroying or changing the chemical structure of graphene. The main contents and conclusions were described as follows: The atoms transfer radical polymerization (ATRP) initiator containing pyrene group was designed and synthesized, which could anchor on surface of graphene oxide (GO) via π-π interaction between pyrene groups and sp2 -hybridized carbon structure. Then, GO/PDMAEMA composites were prepared by surface initiated-atom transfer radical polymerization (SI-ATRP) method. Studies indicate that the composite exihibits zwitterionic property and its charging state could be altered by changing solution with different pH values. By using zwitterionic property of the composite, through anion and cation ion exchanging respectively and following in-situ reduction method, the noble Pd-Au bimetal nanoparticle loaded graphene-based organic/ inorganic nanocomposites were prepared, which could effectively catalyze the reaction that reduction of p-nitrophenol by NaBH4. Using initiators which contain pyrene or catechol structure as anchoring ink, through non-covalent micro-contact printing and following SI-ATRP method, patterned polymer brushes with different functionalities (including pH, temperature responsive and positive/negative ionic polymer brushes) as well as binary polymer brush patterns on graphene substrate were successfully prepared. It was proved to be a general method for preparing polymer brush patterns on graphene surface. In this way, patterned POEGMA-OH brushes were grafted onto graphene surface, and were successfully used for anchoring proteins. The quasi-2D polymer brushes@graphene film with excellent properties such as different functionalities, freestanding, high transmistance, flexibility, was prepared, which could be used for a one-step, non-destructive modification of a variety of planar substrates. Using self-assembled reduced graphene oxide (rGO) film as substrate electrode, anodic aluminum oxide (AAO) as template, ordered PANI nanoarrays on rGO surface were prepared via potentiostatic method. The PANI nanoarray could firmly anchor on rGO surface via non-covalent interaction between conjugated polyaniline (PANI) and graphene. The results of the electrochemical test of PANI nanoarray indicate that PANI array has a higher specific capacitance than the PANI film; and its specific capacitance could reach up to 990 F/g. Keywords: Graphene, Atom transfer radical polymerization, Pyrene, Polymer brush, Noncovalent modification
Owing to its unique properties which different from other waveband such as microwave，infrared radiation，and X-rays, Terahertz (THz) electromagnetic wave has a wide variety of applications in materials science, communication, environmental detection, health, national defense, and so on. THz sources and detectors are the two main research focuses in THz technology. The two-dimensional electron gas (2DEG) system based on semiconductor heterostructure, as it is convenient for controlling by external fields, mature processing technology and simple device structure, which has been studied extensively aiming to develop continuously adjustable, operation at room temperature, and small volume THz source and detector devices. In the present work, the energy bandstructure, electronic transport properties, the electric field driven plasmon modes and blackbody-like emission of 2DEG in AlGaN/GaN heterojunction have been theoretically investigated in detail. In the second part of this work, we modeled an antenna-coupled graphene field effect terahertz (GFET) detector based on self-mixing detection principle. The main contents and innovations are presented as follows:
er of carbon atoms arranged in honeycomb lattice, is a newly discovered allotrope form of carbon after fullerene and carbon nanotubes. As a strictly 2D atomic crystal, graphene possess peculiar electronic structures and on this basis holds fundamental importance for condensed-matter physics research. In the meanwhile, the remarkable material properties of graphene, ranging from ultra-high carrier nobilities to extreme mechanical stiffness, also lend itself to a plethora of potential applications such as post-silicon nanoelectronics, optoelectronics, reinforced nanocomposite materials, energy storage materials and so on.
We focus on the in-plane optical properties of graphene-like two-dimensional materials irradiated by near infrared laser. The Microscopic Reflection Difference Spectroscopy (micro-RDS) and polarized Raman spectroscopy was used to probed the in-plane optical anisotropic properties in graphene. The micro-RDS is also applied to identification of graphene-like two dimensional materials thickness and imaging of the materials surface topography. We further studied the polarized photogalvanic effect in CVD graphene samples. The content of this thesis is divided into the following parts: 1. We present the first directly observation of in-plane optical anisotropy in graphene investigated by the Microscopic Reflection Difference Spectroscopy (micro-RDS) in the visible-frequency range. The complex reflectivity of two perpendicular crystallographic directions was found to be different. After angle-dependent scanning measurement, we found there was a principal axis of the reflectivity. The optical anisotropic properties in graphene cannot be explained by classical theory of condensed matter physics but easily understood in the SN structure model, in which carbon dimer (C2) is considered to be the basic unit of graphene lattice. The employed techniques allows a detailed study of anisotropic properties in graphene-like two dimensional materials. 2. We introduced the specially designed polarized Raman spectroscopy to study the in-plane anisotropic properties in graphene. The results of polarized Raman spectroscopy show the similar angle dependence of two samples, which also confirms the discovery made by micro-RDS . 3. We employed the micro-RDS to determine the layer-number and microscopically image the surface topography of graphene and MoS2 samples. The contrast image shows efficiency and reliability of this new clipping technique. As a low-cost, quantifiable, no-contact and non-destructive method, it is not concerned with the characteristic signal of certain materials and can be applied to arbitrary substrate. Therefore it is a perfect candidate for characterizing the thickness of graphene-like two-dimensional (2D) materials. In addition, the technique can also be used to probe the in-plane anisotropic properties in these materials. 4. We utilized the quarter-wave plate and amplitude Electro-optic modulator (A-EOM) techniques to study the polarized photogalvanic effect in CVD graphene samples under the irradiation of 1064nm laser beam. The tested linear polarized photocurrent of two methods agrees well with each other.