• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 817
  • 202
  • 133
  • 102
  • 42
  • 12
  • 12
  • 8
  • 8
  • 7
  • 5
  • 4
  • 4
  • 3
  • 2
  • Tagged with
  • 1713
  • 292
  • 285
  • 277
  • 224
  • 207
  • 202
  • 186
  • 173
  • 143
  • 139
  • 125
  • 120
  • 114
  • 112
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Processing and properties of multifunctional polylactide/graphene composites

Gao, Yuqing January 2017 (has links)
This thesis aims to utilize graphene nanoplatelets (GNPs) in biobased and biodegradable thermoplastic polylactide (PLA) matrix for improved properties and multifunctionalities. A comprehensive comparative study was carried out on the effect of the addition of GNPs with different sizes. The mechanical, electrical, thermal and barrier properties of resulting PLA/GNP nanocomposites and their inter-relationship with the microstructure of the composites is revealed. The effect of annealing on dynamic percolation and conductive network formation of PLA/GNP composites including the effect of hybrid GNP fillers of different size is reported, indicating the underlying mechanisms for different behaviours of GNP fillers of different size. Multifunctional engineering biopolymers with improved performances (mechanical and electrical) and added functionalities (barrier properties) were successfully developed through controlled filler distribution and orientation using multilayer co-extrusion technology. Changes in mechanical properties of the PLA/GNP multilayer nanocomposites were successfully correlated with GNP orientation in the filled layers. Multilayer PLA/GNP nanocomposites demonstrated excellent mechanical and barrier properties with low filler loadings compared to traditional mono-extruded films.
32

Cove-Edge Graphene Nanoribbon Semiconductors: from Molecules to Devices

Etkin, Grisha January 2018 (has links)
This dissertation presents research conducted on the structure-property relationships of cove-edge graphene nanoribbon (GNR) semiconductors from the scale of molecular conformation to device performance. The ribbons described here are made derived from perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) and adopt a helical conformation so we call them helical PDI (hPDI). They are n-type semiconductors with exceptional performance in field-effect transistors (FETs), organic photovoltaics (OPVs), narrowband photodetectors, and electron transporting materials in perovskite solar cells. In this work, reaction chemistry is used to design and synthesize new derivatives of hPDI to shine light on their molecular, bulk, and device properties. The first chapter concerns the incorporation of hPDI into alternating donor- acceptor (D-A) macromolecules to create materials with internal charge transfer (CT). Computational and spectroscopic techniques, including femtosecond transient absorption spectroscopy (fsTA), are used to probe the CT character of these materials. A large dihedral angle between donor and acceptor portions limits orbital overlap, leading to lowest energy excited state with HOMO localized on the donor and LUMO localized on the acceptor. Notably, internal CT improves the OPV performance of these oligomers over their parent hPDI, while analogous macromolecules without internal CT exhibit reduced OPV performance. Chapter 2 details a method for side chain engineering of hPDI by installing the side chain in the final step of the synthesis, rather than the first. The aromatic core of hPDI is built up with esters, rather than imides, appending the edges of the ribbons. The ester-appended ribbons are readily transformed into a late-stage intermediate for divergent installation of any desired side chains, including those that pose synthetic challenges when they are introduced into the parent PDI from the beginning. These side chains have a profound effect on the optical, thermal, and charge transport properties of hPDI in the solid state. This strategy of introducing imide side-chains into PDI-based materials in the final step can be generalized to other systems. Chapter 3 demonstrates a method for controlling the conformation of cove-edge GNRs by changing the chemical substitution pattern at their edges. All-sp2 substituents that lock adjacent edge positions into a ring rigidify the aromatic core of these ribbons. When substituents at adjacent edge positions are no longer locked into a ring, the aromatic core becomes flexible. Modulating this flexibility dictates how these ribbons contort to accommodate their cove-edges, with rigid cores contorting into chiral helixes, and flexible cores contorting into a butterfly conformation. This may point the way forward for the use of GNRs in applications that rely on precise control of molecular conformation
33

Charge-writing induced quantum devices in graphene

Herbschleb, Ernst David January 2014 (has links)
No description available.
34

Spin transport in few-layer graphene

Yan, Wenjing January 2014 (has links)
No description available.
35

Synthesis and characterisation of graphene-based membranes

Shin, Yu Young January 2017 (has links)
Graphene, often known as a wonder material due to its remarkable properties, is the thinnest membrane available to us. In this project we have synthesised and characterised different types of graphene membranes and graphene-based membranes. Firstly, we have developed a simple fabrication technique to produce pressurised single-layer graphene membranes that can hold up to reversible strain of ~2%. The graphene balloons were investigated by Raman Spectroscopy: red shift of Raman peaks was observed with increasing strain, in good agreement with theoretical calculation. [2] Also, a characteristic broadening of the Raman peaks is observed beyond 1% strain, which has been attributed to nanoscale strain variations in the membranes. Another type of graphene-based membrane is prepared by assembling millions of tiny graphene flakes together into a laminate. Liquid-phase exfoliation is used to disperse graphene nanoflakes in a solution [3]; the dispersion is then deposited as a laminate by simple fabrication techniques such as drop casting. Because the properties of a graphene laminate strongly depend on the flake size and thickness distribution in the dispersion, it is important to be able to characterise LPE graphene. Here, we have developed a simple qualitative protocol based on Raman spectroscopy to characterise this materials. This protocol was first validated in two works, aimed at studying the enhancement of the yield of LPE graphene using two different stabilisers, n-octylbenzene and perchlorocoronene. We then applied our method to graphene/PIM-1 composite membrane. PIMs are a new class of polymers showing great potential in separation applications. An improvement in the performance of the membrane (e.g. permeability) is expected by adding graphene as a nanofiller. However, little is experimentally known about how the material disperses in PIM. Our results show that Raman spectroscopy is able to identify the presence of re-aggregated graphene-based materials in the composite. This is expected to produce strong changes in the mechanical properties and the physical ageing of the membrane. Lastly, we demonstrated fabrication of self-catalytic reactor membrane composed of graphitic carbon nitride (g-C3N4). Simple LPE and vacuum filtration techniques are employed, maximising the surface area and exposure of the active sites. The g-C3N4 membrane showed significantly enhanced catalytic performance compared to the bulk g-C3N4, achieving ~100% conversion efficiency for photo-degradation of several organic dyes. In conclusion, we investigated different types of graphene-based membranes, showing that LPE is simple technique with high versatility for different applications and Raman spectroscopy is a powerful technique for characterisation of graphene in all cases.
36

High-mobility graphene nano-rectifiers and transistors for high frequency applications

Auton, Gregory January 2016 (has links)
Graphene has the highest mobility of any material at room temperature; this property has attracted a great deal of interest for applications in high frequency electronics, specifically transistors and diodes. To date, there has been little success using graphene for these purposes because it lacks the bandgap necessary to create an efficient device. This work aims to approach this problem from a different angle; using device architecture that potentially does not need a bandgap. This could allow graphene's excellent electrical properties to be exploited fully. The first example of this is the ballistic rectifier; a device that exploits the long mean free path of two dimensional electron gasses so that carriers can be treated like "billiard balls". Here we demonstrate two different four-terminal ballistic rectifiers that redirect carriers from the two input leads to one of the two output leads; the effect of this is to rectify an AC signal into a DC signal. An extremely high voltage responsivity of 23,000 V/W and a very low noise equivalent power of 0.64 pW/Hz1/2 are achieved from a low-frequency AC signal at room temperature. This same device has been tested at 220GHz and showed no signs of a cut-off frequency. Another rectifier tested here is the self-switching diode, a device that uses two side gates attached to its own source to locally gate its own conducting channel. This architecture demonstrates a modest peak responsivity of 690 V/W, a result of graphene's missing bandgap. A side-gated transistor with a modest on/off ratio of ~2.33 is also fabricated in order to better understand the limited capabilities of the graphene self-switching diode. Part of the novelty of this work is the introduction of a modified stamp transfer technique that allowed more flexibility creating hetero-structures. A dry etching recipe for hetero-structures is introduced that does not damage soft masks allowing for a new type of ultra-clean 1D contact. This new contact demonstrates considerably better contact resistance and reliability than previous generations; important for any high frequency application.
37

Fabrication and applications of suspended graphene membranes

Clark, Nicholas January 2016 (has links)
This thesis reports research activity on suspended graphene membranes. Scientific results in the form of peer-reviewed publications are presented, along with supporting information to provide context, detailed experimental procedures, and recommendations of future work. The four papers cover a wide variety of topics, but are linked by common experimental sample fabrication techniques. Understanding the mechanical properties of suspended graphene membranes is crucial to the development of graphene nano-electromechanical devices. In the first presented paper, PeakForce QNM (quantitative nanomechanical mapping) atomic force microscopy imaging was used to rapidly map the nanomechanical properties of a range of suspended graphene membranes. The force-displacement behaviour of monolayer graphene extracted from the peak force imaging map was found to be comparable to that taken using standard nanoindentation. By fitting to a simple elastic model, the two-dimensional elastic modulus was measured at around 350Nm-1, corresponding to a Young's modulus of around 1 TPa. The second paper examines the near-IR light-matter interaction for graphene integrated cavity ring resonators based on silicon-on-insulator (SOI) racetrack waveguides. Fitting of the cavity resonances from the predicted transmission spectra reveal the real part of the effective refractive index for graphene, neff = 2.23 ± 0.02 and linear absorption coefficient, alphagTE = 0.11 ±0.01dB micro metre-1. The evanescent nature of the guided mode coupling to graphene at resonance depends strongly on the height of the graphene above the cavity, which places limits on the cavity length for optical sensing applications. Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle θ. In the third paper, θ-defined tBLG was produced and characterized using optical reflectivity and resonance Raman scattering. This represents the first reported fabrication of a rationally designed (twist engineered) tBLG structure. The θ-engineered optical response is shown to be consistent with persistent saddlepoint excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon. Nano-patterned and suspended graphene membranes find applications in electronic devices, filtration and nano-pore DNA sequencing. However, the fabrication of suspended graphene structures with nanoscale features is challenging. In the fourth and final paper, the direct patterning of suspended membranes consisting of a graphene layer on top of a thin layer of hexagonal boron nitride which acts as a mechanical support is demonstrated for the first time, using a highly focused electron beam to fabricate structures with extremely high resolution within the scanning transmission electron microscope. The boron nitride support enables the fabrication of stable graphene geometries which would otherwise be unachievable, by preventing intrinsic strain in graphene membranes from distorting the patterned features after areas are mechanically separated. Line cuts with widths below 2 nm are reported. It is also demonstrated that the cutting can be monitored in-situ utilising electron energy loss spectroscopy (EELS).
38

Gate-tunable superconductivity in thin films and layered crystals

Shajari, Hasti January 2018 (has links)
Theoretical and experimental work on superconductivity has won a number of Nobel prizes in Physics, beginning with the prize to Kamerlingh Onnes in 1913 that included the initial discovery of superconductivity in mercury. Superconductivity has since been at the forefront of research in condensed matter physics. Furthermore, since the first isolation of graphene by Geim and Novoselov in 2004, there has been growing interest in other monolayer and few-layer crystals. Like graphene, other materials can be exfoliated due to the weak van der Waals interactions between layers, primarily the transition metal dichalcogenides (TMDs). Atomically flat and chemically stable thin two dimensional (2D) layers of TMDs have opened up new opportunities for discovering exciting new physics and ultimately developing thin flexible devices. Defect-free exfoliated TMDs are regarded to be ideal materials for use as channels for field effect transistors (FET), which have been shown to possess remarkable electronic properties. Recent advances in field effect-based TMD devices have been achieved using ionic liquid gating and the formation of electrical double layers. Using the techniques previously developed for isolating graphene, few-layer crystals of 1T- and 2H-TaS2 have been obtained in this project to be used as channel materials for FET and ionic field effect transistor (iFET) devices that incorporate DEME-TFSI ionic liquids as a top gate to control the carrier density. In the first experimental chapter (chapter 5) iFETs using a 1 μm thin film of a highly boron-doped diamond (BDD) as the channel material are introduced and the influence of top gating on the transition temperature using a DEME-TFSI ionic liquid is studied. An enhancement in the Tc of the BDD sample under positive top gate potentials is shown as a result of electron doping at the grain boundaries leading to stronger coupling between the grains. The following chapter (Chapter 6) describes low temperature measurements of graphene FET (GFET) devices. These devices were fabricated to enable a reliable and effective calibration for the DEME-TFSI top gate specific capacitance against the known back gate capacitance. This represents a valuable reference for ionic liquid gating studies of TMD materials. The last experimental chapter describes the electrical properties of few-layer 1T-TaS2 (initial section) and 2H-TaS2 (final section) samples used as channels in FET devices. Charge density wave (CDW) transitions in 1T- and 2H-TaS2 are investigated and gating measurements using ionic liquids on these samples are described and summarised. Although no gate influence was seen on the CDW in 2H-TaS2 , a suppression of the CDW transition in cooling cycles of a 1T-TaS2-based FET sample was observed. This suppression demonstrates that accumulation of additional charge carriers in the sample drives it into a metallic state. In a ∼15 nm 2H-TaS2 FET device, strong enhancement of the superconducting critical temperature from 0.8 to 4.7 K is observed with DEME-TFSI top gating. The influence of an additional back gate potential on the device enhances the transition temperature still further up to 5 K. This indicates a co-operative effect between the top and back gates of the sample. It was also demonstrated that 2H-TaS2 crystals are susceptible to intercalation by DEME+ cations in the ionic liquid; a clear enhancement of Tc was observed after simply placing a drop of ionic liquid on a 2H-TaS2 flake without application of a top gate bias. This research project has studied superconductivity in 2D materials and illustrates the capability of ionic liquid gating as a versatile tool to modify the carrier concentration and enhance the critical temperature of a wide range of different materials.
39

Graphene interface engineering: surface/substrate modifications cum metal contact exploration.

January 2012 (has links)
石墨烯具有獨特的電學,熱力學及機械性能,在科學研究和技術領域受到廣泛的關注。特別是,以石墨烯為基礎的石墨烯場效應電晶體近年來得到了快速發展,使其成為後矽基時代的可選用材料之一。不同于傳統的體半導體材料,石墨烯具有獨特的二維結構;它與周圍環境的介面相互作用對石墨烯器件有決定性的影響。研究石墨烯的介面特性在石墨烯應用中具有重要的意義。因此研究者對於發掘在納米尺度上的石墨烯介面規律及由此獨特的介面特性所導致的電子結構、載流子輸運性質和其他相關現象具有濃厚的興趣。在本論文中,我們從實驗和理論兩個方面對石墨烯與不同基底的介面耦合機制,由金屬電極到石墨烯的電荷注入以及其表面的吸附物對石墨烯的摻雜作用進行了深入细致的研究。 / 首先,通過對薄層石墨烯的表面功能化,可以對其電子結構進行有效的控制和調整。在石墨烯薄片表面吸附不同的自組裝有機分子,可以實現對石墨烯的電子和空穴摻雜。另外,我們對由電子束放射產生的摻雜效應也進行了研究。我們發現當利用電子束處理包含不同層數的石墨烯薄片時,可以形成石墨烯pn結。 其次,我們對石墨烯基底對於石墨烯的重要作用進行了深入的探究。由於商用矽片中存在的帶電雜質及石墨烯褶皺對放置於其上的石墨烯樣品產生了極大的影響,使得石墨烯的遷移率遠小於其理論值。為消弱由基底產生的不利影響,我們利用自組裝單分子膜對二氧化矽/矽襯底的表面進行鈍化處理,從而減少不必要的散射。通過鈍化處理,載流子遷移率上升了近一個數量級(達到 47,000 cm²/Vs)。 / 此外,我們對石墨烯與不同金屬電極接觸的介面電學性質也進行了系統研究。我們發現較低的電阻及線性的電流電壓關係對於石墨烯場效應電晶體並非始終成立。對於本征石墨烯,我們發現石墨烯和金屬電極的接觸具有‘空間電荷區限制’和‘歐姆接觸’兩種接觸模式。並且在偏置電壓控制下,接觸電阻可以可逆的在兩種接觸模式中切換。我們發現該現象可以歸結于石墨烯獨特的錐型能帶色散關係。該現象提供了新的製備高密度非易失性石墨烯記憶體的方法。 / Graphene is an appealing material in both science and technology. Its distinct electronic, thermal and mechanical properties have stimulated enormous scientific interest. In particular, graphene-based field-effect transistors (GFET) have been developed rapidly and are now considered an option for post-silicon electronics. In contrast to traditional semiconductors, the unique two dimensional structure of graphene offers the possibility of studying the interface characteristics for its proximity to the top surface and interface between graphene and the outside environment. We are thus interested in understanding graphene surface and interfacial issues associated with electronic structure, carrier transport and related phenomena on a nano-scale. In this thesis, we investigate both experimentally and theoretically the mechanisms of graphene interfacial couplings to different substrates, charge injection from metal electrodes and its interplay with inert adsorbates. / At first, few layer graphene’s (FLG) electronic properties are adjusted efficiently and controllably through functionalizing its top surface. Both n-type and p-type doped exfoliated graphene sheets are present by virtue of adsorbing organic molecules. Additionally, the doping effects induced by electron beam (EB) irradiation are also studied. We find that by irradiating graphene with EB, graphene p-n junctions can be formed if EB irradiation is applied across a single graphene sheet containing regions with different layers. / Secondly, the crucial roles played by the supported substrate in graphene applications are meticulously interrogated. The existence of charge impurities and ripples adversely affects the mobility of high quality mechanically exfoliated graphene on commercially available SiO₂/Si wafers inferior to its theoretical limit. To suppress the deleterious substrate effect, we utilize self-assembled monolayers to passivate the SiO₂/Si substrate surface. After diminishing the unwanted scattering origins by this method, an increase in carrier mobility by nearly one order of magnitude (up to 47,000 cm²/Vs) is obtained. / Furthermore, the electronic properties of the interfaces between graphene and various metal electrodes are systematically investigated. Our study unambiguously reveals that a low electrical resistance as well as a linear current-voltage relation is not always granted for GFETs. Interestingly, for graphene on SiO₂/Si passivated with highly-ordered OTMS, both ‘space charge region limited’ and ‘ohmic’ contacts can be obtained with a single metal electrode. We also find that by utilizing voltage bias, the contact can be reversibly altered between high resistance and low resistance. We ascribe the phenomenon to graphene’s cone energy dispersion relationship as well as the vanishing density of states at the Dirac points. Our results herald a new avenue for achieving high density non-volatile graphene memory devices. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Xiaomu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstract also in Chinese. / Abstracts in English and Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Electronic Properties of Graphene --- p.1 / Chapter 1.1.1 --- Graphene Band Structure --- p.1 / Chapter 1.1.2 --- Physical Properties of Graphene --- p.4 / Chapter 1.1.3 --- Carrier Transport in Graphene --- p.7 / Chapter 1.1.4 --- Optical Properties of Graphene --- p.9 / Chapter 1.2 --- Motivation and Outline of the Thesis --- p.10 / Chapter 1.2.1 --- Graphene Field-Effect Transistors --- p.10 / Chapter 1.2.2 --- Interface Engineering --- p.15 / Chapter Chapter 2 --- Sample Preparation Details and Characterization Techniques --- p.26 / Chapter 2.1 --- Graphene Preparation --- p.26 / Chapter 2.1.1 --- Mechanical Exfoliation --- p.26 / Chapter 2.1.2 --- Reduced Graphite Oxide --- p.28 / Chapter 2.1.3 --- Graphene Synthesis by CVD on Copper Substrates --- p.28 / Chapter 2.2 --- Characterization of Graphene --- p.29 / Chapter 2.2.1 --- Optical Microscopy --- p.30 / Chapter 2.2.2 --- Raman Spectroscopy --- p.30 / Chapter 2.2.3 --- Scanning Probe Microscopic Techniques --- p.32 / Chapter 2.3 --- GFET Fabrication --- p.33 / Chapter 2.3.1 --- Photolithography Process --- p.34 / Chapter 2.3.2 --- Shadow Mask Method Process --- p.34 / Chapter 2.3.3 --- Lithography-Free Process --- p.35 / Chapter Chapter 3 --- Top Surface Modification of Graphene --- p.37 / Chapter 3.1 --- Charge Transfer by Organic Molecules in Doping of Graphene --- p.37 / Chapter 3.1.1 --- Overview --- p.37 / Chapter 3.1.2 --- Kelvin Probe Force Microscopy --- p.41 / Chapter 3.1.3 --- Experimental Details --- p.45 / Chapter 3.1.4 --- P-type Doping of Graphene by F4-TCNQ --- p.47 / Chapter 3.1.5 --- N-tpye Doping of Graphene by VOPc --- p.48 / Chapter 3.1.6 --- Mechanism of Charge Transfer: A Quantitative Analysis --- p.55 / Chapter 3.2 --- Asymmetric Doping of Graphene by Electron Beam Irradiation --- p.66 / Chapter 3.2.1 --- Overview --- p.66 / Chapter 3.2.2 --- Experimental Details --- p.67 / Chapter 3.2.3 --- Transport Measurements --- p.70 / Chapter 3.3 --- Summary --- p.73 / Chapter Chapter 4 --- Substrate Modification for Graphene --- p.81 / Chapter 4.1 --- Substrate Effects Adjusted by Thermal Annealing --- p.81 / Chapter 4.1.1 --- Overview --- p.81 / Chapter 4.1.2 --- Experimental Details --- p.82 / Chapter 4.1.3 --- Mechanism of Graphene/Substrate Interaction --- p.84 / Chapter 4.2 --- Modified Substrate by Highly Ordered OTMS SAMs --- p.85 / Chapter 4.2.1 --- Overview --- p.85 / Chapter 4.2.2 --- Experimental Details --- p.87 / Chapter 4.2.3 --- Transport Measurements --- p.94 / Chapter 4.2.4 --- Summary --- p.111 / Chapter Chapter 5 --- Graphene/Metal Contacts --- p.116 / Chapter 5.1 --- Graphene/Metal Contacts --- p.116 / Chapter 5.1.1 --- Overview --- p.116 / Chapter 5.1.2 --- Experimental Details --- p.118 / Chapter 5.2 --- Contact Modes and Related Memory Devices --- p.125 / Chapter 5.2.1 --- Bistable Contact Modes --- p.125 / Chapter 5.2.2 --- Related Memory Devices --- p.132 / Chapter 5.2.3 --- Contact Mechanism --- p.136 / Chapter 5.3 --- Transport Mechanism for OFF States --- p.147 / Chapter 5.3.1 --- Temperature-Dependent Transport Measurements --- p.148 / Chapter 5.3.2 --- WKB Approximations --- p.151 / Chapter 5.3.3 --- Tunneling between Fermi Liquid and Luttinger Liquid --- p.154 / Chapter 5.4 --- Summary --- p.156 / Chapter Chapter 6 --- Conclusions and Outlook --- p.161 / Chapter 6.1 --- Major Findings and Summary --- p.161 / Chapter 6.2 --- Outlook for Future Research --- p.165 / Chapter Appendix A --- Transport Model of GFET --- p.169 / Chapter A.1 --- Transport Models --- p.169 / Chapter A.2 --- Drift Current Model --- p.171 / Chapter A.3 --- Quantum Transport Theory of GFET --- p.175 / Chapter A.4 --- Brief Outline of NEGF --- p.177
40

A study of carbon based materials for energy applications

Goher, Qammar Sultan January 2012 (has links)
Carbon based materials such as CNTs and graphene have been widely studied over the last few years. The outstanding electrical and mechanical properties of these materials attracted researchers to find ways to grow and use them in nano-devices. Among the different techniques, PECVD is a relatively simple and low temperature process. It facilitates the growth of CNTs and graphene on particular sites of the substrate. The objective of this research project was to study the growth of CNTs and graphene using PECVD system and to employ them in renewable energy devices. Excimer laser processed materials were also the focus for flexible material for fuel cells and other applications to show the way to a one step manufacturing process that lends itself to large area and low cost processing using standard tools.In the growth of CNTs, the roll of a buffer layer and catalyst materials were studied in depth. Different metals were tested for best results in optimising nanotube growth for the selected applications. The role of the buffer layer in the formation of nanoparticles and their surface adhesion was studied. Different materials were used as a catalyst and analysed for best performance in the PECVD system. Growth parameters such as temperature, pressure, gas flow rate and plasma power were studied during the growth of CNTs in the PECVD system. The growth of graphene has been conducted in two ways: firstly, by the traditional mechanical exfoliation technique (with the help of Manchester University) and second by PECVD techniques.Polymer materials are promising flexible substrates for electronic and energy devices. An excimer laser was used to transform thin metallic films into nanoparticles which could play the role of the catalyst in proton exchange membrane fuel cells. In this study experiments have been conducted into a single step process to convert the poly ethylene naphthalate (PEN) surface to a robust mesoporous carbon material that conducts electrons, whilst depositing the catalyst. Such a technique has been developed for the first time in this work. Laser modification here produced a conical carbon structure and dense arrays of well defined catalysts.A prototype fuel cell was designed and crafted to employ the laser processed PEN as a proton exchange membrane. Some experiments were conducted regarding the transport of protons through laser processed PEN and the conventionally used fuel cell electrolyte, Nafion. It has been observed that the hydrophilic property of Nafion allowed proton transport across this material. It was also observed that PEN is not a good membrane for protonic transport. This material does not have free sites for vehicle transport. The catalytic activity of laser ablated Ni nanoparticles on PEN substrate was studied in temperature programme reaction (TPR) and it was observed that the metallic nanoparticles had some activity at higher temperature. Both Ni and Pt nanoparticles were tested as catalysts on the standard Nafion electrolyte. It was observed that Pt is active for the hydrogen combustion reaction and Ni has less activity for this purpose.It was not expected in this work that efficient hydrogen transport through the polymer would occur, but that future modification of the internal chemistry of PEN can be developed.

Page generated in 0.0307 seconds