Fabrication of Pristine and Doped Graphene Nanostripes and their Application in Energy Storage

Fossil fuel usage causing rising CO2 levels and leading to climate change is, perhaps, the most pressing issue of our time. However, our economic dependence on energy necessitates its usage such that reducing energy usage is not possible leaving transitioning to renewable energy technologies as the only sustainable option. Currently, the largest barrier to large scale incorporation of renewable energy sources (e.g., solar, wind) is the high cost of energy storage technologies. Electrochemical energy storage technologies (e.g., lithium-ion batteries and supercapacitors) have been identified as a key approach for enabling the transition to renewable energy technologies. Graphene is a material with exceptional properties that is receiving much attention for application in various energy storage technologies and could help reduce the cost of energy storage technologies. This thesis describes a novel fabrication procedure for low-cost and efficient synthesis of high-quality graphene nanostripes (GNSPs) and their application in lithium-ion battery and supercapacitor electrodes. This thesis is structured as follows. Chapter 1 outlines the motivation and technical background of this research. Chapter 2 describes the instrumentation and procedures for fabricating GNSPs. Chapter 3 describes in situ exfoliation of GNSPs as electrodes in supercapacitors to increase the capacitance. Chapter 4 describes synthesis and application of pyridinic-type nitrogen-doped GNSPs as a lithium-ion battery anode. Chapter 5 describes the synthesis and application of silicon-, germanium-, and tin-doped GNSPs and their application in lithium-ion battery anodes. Chapter 6 concludes and synthesizes the findings of the thesis holistically. Additionally, future outlook and potential research objectives are presented.</p

Single-step growth of graphene and graphene-based nanostructures by plasma-enhanced chemical vapour deposition

The realization of many promising technological applications of graphene and graphene-based nanostructures depends on the availability of reliable, scalable, high-yield and low-cost synthesis methods. Plasma enhanced chemical vapor deposition (PECVD) has been a versatile technique for synthesizing many carbon-based materials, because PECVD provides a rich chemical environment, including a mixture of radicals, molecules and ions from hydrocarbon precursors, which enables graphene growth on a variety of material surfaces at lower temperatures and faster growth than typical thermal chemical vapor deposition. Here we review recent advances in the PECVD techniques for synthesis of various graphene and graphene-based nanostructures, including horizontal growth of monolayer and multilayer graphene sheets, vertical growth of graphene nanostructures such as graphene nanostripes with large aspect ratios, direct and selective deposition of monolayer and multi-layer graphene on nanostructured substrates, and growth of multi-wall carbon nanotubes. By properly controlling the gas environment of the plasma, it is found that no active heating is necessary for the PECVD growth processes, and that high-yield growth can take place in a single step on a variety of surfaces, including metallic, semiconducting and insulating materials. Phenomenological understanding of the growth mechanisms are described. Finally, challenges and promising outlook for further development in the PECVD techniques for graphene-based applications are discussed

Generating summary documents for a variable-quality PDF document collection

The Cochrane Schizophrenia Group’s Register of studies details all aspects of the effects of treating people with schizophrenia. It has been gathered over the last 20 years and consists of around 20,000 documents, overwhelmingly in PDF. Document collections of this sort – on a given theme but gathered from a wide range of sources – will generally have huge variability in the quality of the PDF, particularly with respect to the key property of text searchability. Summarising the results from the best of these papers, to allow evidence-based health care decision making, has so far been done by manually creating a summary document, starting from a visual inspection of the relevant PDF file. This labour-intensive process has resulted, to date, in only 4,000 of the papers being summarised – with enormous duplication of effort and with many issues around the validity and reliability of the data extraction. This paper describes a pilot project to provide a computer-assisted framework in which any of the PDF documents could be searched for the occurrence of some 8,000 keywords and key phrases.Once keyword tagging has been completed the framework assists in the generation of a standard summary document, thereby greatly speeding up the production of these summaries. Early examples of the framework are described and its capabilities illustrated

Laser-induced plasma generation of terahertz radiation using three incommensurate wavelengths

We present the generation of THz radiation by focusing ultrafast laser pulses with three incommensurate wavelengths to form a plasma. The three colors include 800 nm and the variable IR signal and idler outputs from an optical parametric amplifier. We observe that stable THz is generated when all three colors are present, with a peak-to-peak field strength of ~200 kV cm^(−1) and a relatively broad, smooth spectrum extending out to 6 THz, without any strong dependence on the selection of signal and idler IR wavelengths (in the range from 1300 to 2000 nm). We confirm that three colors are indeed needed, and we present plasma current modeling that corroborates our observations

Laser-induced plasma generation of terahertz radiation using three incommensurate wavelengths

We present the generation of THz radiation by focusing ultrafast laser pulses with three incommensurate wavelengths to form a plasma. The three colors include 800 nm and the variable IR signal and idler outputs from an optical parametric amplifier. We observe that stable THz is generated when all three colors are present, with a peak-to-peak field strength of ~200 kV cm^(−1) and a relatively broad, smooth spectrum extending out to 6 THz, without any strong dependence on the selection of signal and idler IR wavelengths (in the range from 1300 to 2000 nm). We confirm that three colors are indeed needed, and we present plasma current modeling that corroborates our observations

Selective formation of pyridinic-type nitrogen-doped graphene and its application in lithium-ion battery anodes

We report a high-yield single-step method for synthesizing nitrogen-doped graphene nanostripes (N-GNSPs) with an unprecedentedly high percentage of pyridinic-type doping (>86% of the nitrogen sites), and investigate the performance of the resulting N-GNSPs as a lithium-ion battery (LIB) anode material. The as-grown N-GNSPs are compared with undoped GNSPs using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), helium ion-beam microscopy (HIM), and electrochemical methods. As an anode material we find that pyridinic-type N-GNSPs perform similarly to undoped GNSPs, suggesting that pyridinic sites alone are not responsible for the enhanced performance of nitrogen-doped graphene observed in previous studies, which contradicts common conjectures. In addition, post-mortem XPS measurements of nitrogen-doped graphene cycled as a lithium-ion battery anode are conducted for the first time, which reveal direct evidence for irreversible chemical changes at the nitrogen sites during cycling. These findings therefore provide new insights into the mechanistic models of doped graphene as LIB anodes, which are important in improving the anode designs for better LIB performance

Hyponatremia Associated with Bupropion

Bupropion is widely used for the treatment of depressive disorder and smoking cessation. Hyponatremia, including a syndrome of inappropriate secretion of antidiuretic hormone (SIADH), is not rare complication of treatment with antipsychotic drugs. We report a 60-year-old man who experienced severe hyponatremia after a treatment with bupropion for depressive disorder for the first time in the Korea