Dissertations / Theses on the topic 'Nanoscale characterisation'
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Chang, Zhuo. "Nanoscale characterisation of arterial stiffening." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3025854/.
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Arterial stiffening as part of the natural ageing process is strongly linked to cardiovascular risk. Although arterial stiffening is routinely measured in vivo, little is known about how localised changes in artery structure and biomechanics contribute to in vivo arterial stiffening. This is mainly due to the limitation of the conventional mechanical testing methods. To circumvent this challenge, a novel nano-scale structural and mechanical characterisation technique, known as PeakForce Quantitative Nanomechanical Mapping (QNM) technique, was developed in a zebrafish model. Using the zebrafish vertebral column, the utility of the PeakForce QNM for probing small-scale biological samples and structures was validated, which paved the way to probe human artery and investigate the localised alterations in artery structure in vitro with arterial stiffening. Human internal mammary artery (IMA) was used as a model vessel for understanding the development of arterial stiffening in this thesis. This thesis focuses on the role of the tunica media and the outmost layer, the tunica adventitia, in arterial stiffening. Using the PeakFoce QNM, the hydrated and dehydrated arterial sections were tested that provided data on nano-scale changes in collagen fibril structure and mechanical properties in the hydrated media, dehydrated media and adventitia and showed how they related to in vivo stiffness measurements in the vascular system. The indentation depth for AFM measurement on the IMA tissues of 5 μm thickness were controlled at 20 nm and 5 nm in liquid and ambient conditions respectively and thus the indentation depth/tissue thickness ratio was 0.4% and 0.1% for the hydrated and dehydrated samples respectively. Furthermore, integrating the findings in this thesis with the proteome analysis data, the localised alterations in the collagen and ultrastructure were explained, and the in vivo arterial stiffening, nanomechanical and structural changes in artery biopsy samples were linked. This approach could be used to develop new diagnostic methods for vascular disease.
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Choi, Fung Sing. "Nanoscale electrical characterisation of nitride structures." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283496.
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To fully exploit the potential of gallium nitride (GaN) devices for optoelectronics and power electronic applications, the structures of device need to be investigated and optimized. In particular carrier densities, conductivities and localised charges can have a significant impact to device performances. Electrical scanning probe microscopy techniques, including scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM) and kelvin probe force microscopy (KPFM), were utilized to study the structures of nitride devices such as high electron mobility transistors (HEMTs), light emitting diodes (LEDs) and junction diodes. These results combine with other characterisation techniques to give an enhanced understanding about the nitride structures. Leakage currents are one of the major challenges in HEMTs, especially leakages in buffer layers which deteriorate the breakdown voltage of the devices. To achieve an insulating buffer layer, carbon doping is usually used to compensate the unintentional n-type doping of nitride materials. Here, I show that vertical leakage can originate from the formation of inverted hexagonal pyramidal defects during the low temperature growth of an AlGaN:C strain relief layer. The semi-polar facets of the defects enhanced the oxygen incorporation and led to the formation of leakage pathways which were observed using SCM. Leakage occurring at HEMT surfaces will lead to current collapses of devices. In this work, I discovered nano-cracks on a HEMT surface. C-AFM showed enhanced conductivity along these nano-cracks. A model based on stress relaxation analysis was proposed to explain the drop of surface potential along the nano-cracks. Advances in the quality of epitaxial GaN grown by MOVPE have been facilitated by understanding the formation of defects within the materials and structures. However, hillocks as a specific type of defects have not been intensively studied yet. In this work, three types of hillocks were discovered on GaN p-i-n diodes and a GaN film grown on patterned sapphire substrates. It was found that pits were always present around the centres of hillocks. Multi-microscopy results showed these pits were developed from either an inversion domain or a nano-pipe or a void under the sample surface. Formation of hillocks was usually associated with a change of growth condition, such as an increase in Mg doping or a decrease in growth temperature and gas flows, despite the formation mechanism is still unclear. GaN$_{1-x}$As$_x$ is a highly mismatched alloy semiconductor whose band-gap can be engineered across the whole visible spectrum. For this reason and the potential to achieve high p-type doping, GaN$_{1-x}$As$_x$ is a promising material for optoelectronic applications. However, the growth of GaN$_{1-x}$As$_{x}$ at intermediate As fraction while maintaining a high conductivity and uniformity of the material is still challenging. Two n-GaN/p-GaN$_{1-x}$As$_x$ diodes with different Ga flows were investigated. Both samples demonstrated that highly Mg-doped GaN$_{1-x}$As$_x$ with high As fraction is achievable. However, the samples contained both amorphous and polycrystalline regions. The electrical scanning probe microscopy results suggested the amorphous structure has a lower hole concentration and hence conductivity than the polycrystalline structure. Nevertheless, there is still a lack of understanding about the electrical properties and conduction mechanisms of the GaN$_{1-x}$As$_x$ alloy.
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Sanderson, Lisa. "Nanoscale strain characterisation of modern microelectronic devices." Thesis, University of Newcastle upon Tyne, 2012. http://hdl.handle.net/10443/1541.
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Sources of stress and strain in modern microelectronics can be either beneficial to the electrical performance or detrimental to the mechanical integrity and ultimately lifetime of the device. Strain engineering is commonplace in state-of-the-art device fabrication as a means to boost performance in the face of device scaling limitation. The strain present in the device is directly related to the improvement factor and as such precise measurements and good understanding are of utmost importance due to the many thermal processing steps that can induce or cause relaxation of the strain. Front-end-of-line (FEOL) strain characterisation is becoming increasingly challenging due to the small volumes of material and nanoscale feature sizes being analysed. In this work, an extensive survey of strain characterisation techniques was undertaken. Narrow sSOI stripes were profiled using conventional Raman spectroscopy. Unlike with previous studies, it was shown that it is possible to achieve nanoscale measurements using current techniques. This study was supported by ANSYS FE simulation. The review of the literature briefly investigates the possibility of EBSD as a strain measurement tool. It is possible to calculate not just an absolute strain value as achievable with Raman spectroscopy, but the strain tensor. However, this is a difficult and complex process and not necessary for use in industry. This study proposes the possibility of a more simple method that would provide a good calibration technique to confirm Raman measurements. SERS and TERS are explored in detail as the most promising techniques when dealing with device scaling. Currently, SERS is a destructive technique not suitable for use in a highly cost driven industry such as semiconductor manufacturing. While it theoretically gives improved surface selectivity over conventional Raman spectroscopy, there is no improvement to the xy spatial resolution. With Si and SiGe samples, this study concludes there is also often no surface selectivity with either technique and the mechanisms behind the enhancement are not understood to the point of being able to implement the techniques in a process line. However, where a non-destructive technique is desired, outlined in this study is a method of achieving the SERS effect without sacrificing the sample. Aggressive scaling has forced the dimensions of the interconnecting wires that give the devices functionality to the deep submicron range. Copper, Cu has been introduced as a replacement to the traditionally used aluminium, Al because of its superior electrical and mechanical properties and scalability. However, as these wires begin to approach the dimensions of thin foils, the microtexture of the wires becomes significantly different from their bulk counterparts. This can affect the mechanical integrity of the interconnects and this has an impact on the reliability of the device. Failure mechanisms such as blistering, cracking and peeling caused by stress and strain are not uncommon and traditional methods of characterising residual stress in the thin films is no longer applicable to these narrow wires. The mechanical properties and microtexture of thin copper films annealed at temperatures comparative to those found in device manufacturing were characterised in some detail. EBSD was used to determine the grain size and structure of the films before nanoindentation confirmed properties such as hardness and elastic modulus. These results pave the way for investigation of strain applied along deep-submicron interconnects to lead to further understanding of what causes failure mechanisms from interconnecting wires.
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Tinker-Mill, Claire. "Nanoscale imaging and characterisation of Amyloid-β." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/76451/.
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In this work several novel Scanning Probe Microscopy (SPM) methods have been applied to the study of the amyloid peptide implicated in the pathogenesis of Alzheimer’s disease (AD). Amyloid-β (Aβ) undergoes a hierarchy of aggregation following a structural transition making it an ideal subject of studying with SPM. The application of SPM based techniques to biological samples has become increasingly common place. However, these techniques are not always immediately suitable for imaging delicate samples of proteins and adaptions must be made before imaging can be considered successful. AD is the most common form of dementia worldwide, and a growing concern for health authorities. As a result it has attracted the attention of a wide range of disciplines. There has been much work conducted which combines the main pathogenic peptide, Aβ , with Atomic Force Microscopy (AFM) in order to elucidate more about its aggregation behaviour, however these techniques offer little more than structural comments, with only the most advanced forms of cryo-Electron Microscopy (EM) providing more details on the nanoscale. Presented here is a method for reliably and robustly producing samples of Aβ by capturing them at various stages of aggregation, as well as the results of subsequent imaging by various methods of AFM. Each of the AFM techniques studied provides additional “added value” to the data which can typically be collected by AFM; either nanomechanical, elastic, thermal or spectroscopical. By imaging samples of Aβ with Ultrasonic Force Microscopy, a detailed substructure to the morphology could be seen, which correlates well with the most advanced cryo-EM work. In addition this technique was ideal for detecting the most toxic from of Aβ, early aggregates, in a sensitive and non-destructive fashion robustly differentiating them from the underlying layer of another peptide (poly-L-Lysine) that was designed to reliably capture the Aβ aggregates. Early work investigating the potential for combining an established method of thermal AFM with a mid-IR laser system also shows promise for detecting the response of the protein. It was also the focus of this work to study the aggregation of Aβ using Dynamic Light Scattering (DLS), in order to confirm whether the technique could identify differences between populations throughout the aggregation process. This was applied in conjunction with potential therapeutics which target the early aggregates to prevent their accumulation, as well as block formation of fibrils. Ultimately this work aims to shows with care to the initial protocols used, physical techniques such as AFM and DLS can be added to the existing methods of monitoring aggregation. Synergistic use of these techniques can generate a clearer overall picture of the effect of metal ions/developing therapeutics on Aβ aggregation and provide more detail than classical biological techniques alone.
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Bunker, Matthew. "The nanoscale characterisation of particle interactions and tribology." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438350.
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Shaw, Joseph. "Nanopatterning and nanoscale characterisation of solution-processible electronics." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24861.
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Solution-processible electronics represent an emerging technology that will revolutionise the field of inexpensive large-area/volume electronics. In this thesis two scanning probe-based methods; scanning thermal lithography (SThL) and conductive atomic force microscopy (CAFM), are used to firstly enhance the patterning resolution of organic semiconductors and secondly improve the electrical characterisation techniques used to study charge transport in solution-processed systems. By combining SThL with suitable organic precursors, on-demand patterning of semiconducting pentacene nanoribbons ~73 nm in width, is demonstrated. By using pentacene nanoribbons as the transistor semiconductor, the first fully functional nanostructured organic transistors via SThL were produced. Using finite element simulations and experimental data, the effects of simultaneously heating the substrate during SThL patterning were assessed. Substrate heating was found to be an economical and simple way to increase SThL 'writing' speed, and hence patterning throughput by ~2,000%. To demonstrate the applicability of SThL beyond direct patterning of electro-active compounds, an organic precursor was used as a positive etch mask for the patterning of various metal films. This approach enabled the patterning of metal electrodes with sub-500 nm resolution highlighting the potential of SThL as a rapid prototyping tool for nanoscale electronics. Finally, the origin of the enhanced electrical conductivity observed in solution-processed transparent electrodes composed of silver nanowires (AgNWs) and a conductive binder was studied using CAFM. Two different solution-processible binder materials; reduced graphene oxide and zinc oxide (ZnO), were employed. By analysing the lateral charge transport in these composite electrode systems, the impact of the binder material on the macroscopic conductivity was assessed. The formation of binder-composed conductive bridges between AgNWs was identified as a key feature responsible for the enhanced conductivity in the composite electrodes. The ZnO-AgNW hybrid had sheet resistance comparable to conventional indium tin oxide electrodes, with the added benefit of low temperature (~200 °C) solution-processing.
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Meli, Maria-Victoria. "The fabrication and characterisation of nanoscale patterns on surfaces /." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85938.
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Nanopatterning is the fabrication of topologically and chemically patterned surfaces, with structural parameters < 100 nm. It is a topic of great interest given the demand in applying nanoscience and nanotechnology in the next generation of electronic and optical devices, and catalysts. To this end, novel bottom-up strategies hold the most promise to this end for creating a great variety of morphologies in a parallel manner.This Thesis is centered on the development of new methodologies for creating nanopatterned surfaces, and their characterization in light of possible applications. A symmetric, amphiphilic diblock copolymer, polystyrene-b-poly(2-vinylpyridine) was self-assembled at the air-water interface to create an array of surface micelles. The Langmuir-Blodgett technique was used to transfer continuous films of ordered surface micelles to different substrates to be used as a sacrificial mask. Argon ion-milling of the block copolymer-coated substrates resulted in the high-fidelity pattern transfer of the topological features in the case of Au, Si/SiOx, and SiO2 substrates, and the generation of Au island arrays in the case of Si/SiOx, mica and quartz substrates coated with thin (10-20 nm) Au films. The wetting of water on the resulting nanopatterned surfaces was determined to be conformal (Wenzel-type) and the transition to non-conformal (Cassie-type) wetting is described. The extinction of light by the gold island arrays was measured and compared to calculations made using the quasistatic approximation to Mie theory. The response of the localized surface plasmon resonance of these arrays to alkylthiol adsorption and changes in the surrounding medium refractive index was measured and discussed with respect to creating a sensing scheme.
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Davies, A. Michael. "The nanoscale characterisation and modelling of drug particulate interactions." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430511.
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Roberts, Joseph. "Synthesis and characterisation of nanoscale oxides for energy applications." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2005979/.
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The motivation for this research is the synthesis and characterisation of nanostructured oxide materials for potential applications in renewable energy generation or storage. In particular, the research in this thesis addresses the development of nanostructured oxide materials which could be exploited as photovoltaics and transparent conductive oxides. The exploitation of anodised aluminium oxide (AAO) to fabricate nanostructured semiconductor pn-junctions as the basis photovoltaic devices is investigated. Various microstructures are modelled with the aim of identifying ones with high interface area and consequently high energy conversion efficiencies. Experiments reveal that AAO prepared using an oxalic acid electrolyte could be achieved with a growth rate of 5.7μm/h. The uniformity and size of the hexagonal cross-section pores is influenced by the first-step anodisation time. Atomic layer deposition (ALD) was used to coat commercially available AAO, to synthesise conformal nanotubes or wires. It was observed that the uniformity of the nanostructures breaks down towards the bulk of the AAO, without high exposures, due to the lack of precursor penetration. However, the proposed geometric mass-gain model to understand the process is supported by experimental mass gain measurements and how deposition occurs within the templates. A second materials system based on copper / copper oxide is also explored as a method of synthesising and controlling the formation of nanostructured oxide materials. The surface preparation of the starting copper sheet material was investigated and it was found to be pivotal in the nanoscale morphology achievable with subsequent heat treatment to grow nanowires and porous layers. Thermal growth of CuO and Cu2O on pre- treated copper foils at 500°C exhibited growth of high aspect ratio CuO nanowires. Further studies on the growth process disproved the vapour-liquid-solid and vapour-solid growth mechanisms for the nanowires and showed that tensile strain within the Cu substrate was the driving force behind the nanowire growth. The use of nanometre-scale ALD alumina barrier layers was employed to suppress spallation and preserve the nanowire surfaces. It was found that for samples with alumina layers between ~3 and 15nm the oxide spallation was significantly reduced and that for samples with ~20nm of alumina the diffusion of Cu atoms to the surface was hindered. Photovoltaic measurements were made on electrolytically synthesised Cu2O surfaces coated with ALD TiO2, ZnO and Ga-doped ZnO to form pn-junctions. The samples showed only weakly rectifying behaviour which was attributed to short-circuits between the n-type layers and the back contact. Several of the samples did show some difference in electrical response when under illumination indicating that, at least in some parts of the device, the pn-junction had formed. Lastly the growth and characterisation of ALD Ga-doped ZnO was investigated to determine the optimal doping levels for the growth of highly conductive and transparent oxides, to be used as a front contact for photovoltaic devices. It was found that Ga doping at around 1at% in ZnO produced film with the lowest resistivity. CdTe films were then grown onto substrates coated in 1at% Ga-doped ZnO and subjected to AM1.5 photovoltaic IV testing, yielding photovoltaic cells with conversion efficiencies ~10.8% and fill-factors of ~65%.
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Janko, Marek. "Structure and stability of biological materials – characterisation at the nanoscale." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-143453.
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Kapoor, Raman. "Nanoscale characterisation of dielectrics for advanced materials and electronic devices." Thesis, University of Newcastle Upon Tyne, 2013. http://hdl.handle.net/10443/1812.
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Strained silicon (Si) and silicon-germanium (SiGe) devices have long been recognised for their enhanced mobility and higher on-state current compared with bulk-Si transistors. However, the performance and reliability of dielectrics on strained Si/strained SiGe is usually not same as for bulk-Si. Epitaxial growth of strained Si/SiGe can induce surface roughness. The typical scale of surface roughness is generally higher than bulk-Si and can exceed the device size. Surface roughness has previously been shown to impact the electrical properties of the gate dielectric. Conventional macroscopic characterisation techniques are not capable of studying localised electrical behaviour, and thus prevent an understanding of the influence of large scale surface roughness. However scanning probe microscopy (SPM) techniques are capable of simultaneously imaging material and electrical properties. This thesis focuses on understanding the relationship between substrate induced surface roughness and the electrical performance of the overlying dielectric in high mobility strained Si/SiGe devices. SPM techniques including conductive atomic force microscopy (C-AFM) and scanning capacitance microscopy (SCM) have been applied to tensile strained Si and compressively strained SiGe materials and devices, suitable for enhancing electron and hole mobility, respectively. Gate leakage current, interface trap density, breakdown behaviour and dielectric thickness uniformity have been studied at the nanoscale. Data obtained by SPM has been compared with macroscopic electrical data from the same devices and found to be in good agreement. For strained Si devices exhibiting the typical crosshatch morphology, the electrical performance and reliability of the dielectric is strongly influenced by the roughness. Troughs and slopes of the crosshatch morphology lead to degraded gate leakage and trapped charge at the interface compared with peaks on the crosshatch undulations. Tensile strained Si material which does not exhibit the crosshatch undulation exhibits improved uniformity in dielectric properties. Quantitative agreement has been found for leakage at a device-level and nanoscale, when accounting for the tip area. The techniques developed can be used to study individual defects or regions on dielectrics whether grown or deposited (including high-κ) and on different substrates including strained Si on insulator (SSOI), strained Ge on insulator (SGOI), strained Ge, silicon carbide (SiC) and graphene. Strained SiGe samples with Ge content varying from 0 to 65% have also been studied. The increase in leakage and trapped charge density with increasing Ge extracted from SPM data is in good agreement with theory and macroscopic data. The techniques appear to be very sensitive, with SCM analysis detecting other dielectric related defects on a 20% Ge sample and the effects of the 65% Ge later exceeding the critical thickness (increased defects and variability in characteristics). Further applications and work to advance the use of electrical SPM techniques are also discussed. These include anti-reflective coatings, synthetic chrysotile nanotubes and sensitivity studies.
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Freeman, Helen Mary. "Characterisation of radiation damage in nuclear graphite at the nanoscale." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/13659/.
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Graphite is a key component in many of the UK's civil nuclear reactors whose lifetime is heavily dependent on the physical and chemical performance of the graphite. Exposure to neutron radiation at high temperatures (350C) induces complex structural changes over many length scales. This thesis focuses on the nanoscale, an area where a lack of understanding leaves a variety of contentious issues. Transmission electron microscopy (TEM), electron diffraction, and electron energy loss spectroscopy (EELS) were the three main experimental techniques used to study a range of virgin, electron irradiated, and neutron irradiated graphites. Information gained from energy filtered TEM, X-ray diffraction, and Raman was also used to compliment these techniques. In situ electron irradiation experiments were conducted at a range of temperatures to better understand the collective effect of thermal annealing and radiation damage. TEM lattice images were quantified using software provided by the PyroMaN research group to extract information about fringe length and tortuosity as a function of radiation damage. A 3D atomistic modelling technique was also applied to micrographs to produce 3D models of electron irradiated graphite. Electron irradiation resulted in the breaking and bending of basal planes and the fragmentation of crystallites. Analysis of electron diffraction patterns showed a 10% increase in d-spacing and polycrystallisation following electron irradiation. Low and core loss EEL spectra were collected during in situ electron irradiation which were fitted to extract information about specimen density, planar and non-planar sp2 content, and bond length. Irradiated specimens exhibited a reduced planar sp2 content which was thought to be attributed to the introduction of non-hexagonal rings and inter-planar defects. The reduction in planar sp2 bonded carbon was replaced by non-planar sp2 bonded carbon. Bond lengths were also seen to increase due to an increase in peripheral dangling bonds at crystallite boundaries. This quantitative analysis methodology was then applied to neutron irradiated specimens to analyse the bulk material and also material found within microcracks, the latter which could have a significant effect on irradiation-induced dimensional change.
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Beardmore, Joshua Paul. "Production and Characterisation of Nanoscale Structures using Atom Lithographic Techniques." Thesis, Griffith University, 2012. http://hdl.handle.net/10072/365326.
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A metastable neon (Ne) beam generated by a liquid nitrogen cooled, DC discharge source was puried to an atomic beam consisting of a single metastable state. The atomic beam was cooled in the transverse direction by a two dimensional optical collimator, slowed in the longitudinal direction by a novel dual beam Zeeman slower, and then guided through a 30 arc by a hexapole magnetic guide. This resulted in a pure, UV free metastable
atomic beam with a ux of (4.41.1)109 atoms s1.
The metastable neon atomic beam was used to investigate the patterns formed in resist based atom lithography experiments utilising alkanethiol self-assembled monolayer resists. It was observed that very short chain alkanethiols, such as ethanethiol, do not form viable resist layers. They are likely desorbed from the surface during exposure to the metastable beam and replaced by background mechanical pump oil molecules. Above the critical
dosage (71014 atoms cm2) these samples react in a manner similar to bare gold samples and form a carbonaceous resist layer. This dosage was found to be signifcantly aected by the vacuum infrastructure, highlighting the role contamination plays in the formation of negative contrast patterns in resist based atom lithography.
Using ellipsometry the growth of a carbonaceous lm during exposure to a metastable atomic beam was characterised. The desorption cross-section of carbonaceous material from a silicon surface via Ne impact was determined to be many times larger than the polymerisation cross-section. The values determined, along with simple estimates for the mean residence time, volume, and cross-section of the contaminants involved provide insight for the application of the theory to other metastable atom experimental apparatus.
Direct deposition lithography without laser cooling of the atomic beam was achieved and patterning observed for iron atoms with a local average transverse velocity of up to 4 ms1. A broadening of the experimentally deposited samples, from a full width half maximum of 35 nm predicted by simulations to >80 nm on SiOx substrates, was observed. The broadening is
attributed to a substrate dependent diusion mechanism and the scattering and interference of the standing wave light mask near the substrate. An initial characterisation of the magnetic properties of co-deposited iron-nickel (Fe-Ni) structures has been conducted using the longitudinal magneto-optic Kerr eect. Variations in the Fe-Ni concentrations infuence the coercivity of the deposited structures. A reduction in the coercive field in regions with line structures was observed when applying a magnetic field parallel to the co-deposited lines. This has been attributed to the nucleation of magnetic domains in regions were the Fe-Ni alloy possesses a lower magnetic moment per atom. A magnetic anisotropy induced by the
incident angle of the Ni atomic beam was also observed in regions without nanostructuring.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
Science, Environment, Engineering and Technology
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Elfwing, Mattias. "Nanoscale Characterisation of Barriers to Electron Conduction in ZnO Varistor Materials." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2002. http://publications.uu.se/theses/91-554-5236-1/.
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Toal, Brian. "Fabrication and characterisation of nanowire arrays : magnetic and plasmonic interactions at the nanoscale." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676613.
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In this thesis the fabrication and characterisation of nanostructured arrays are discussed. Nanowires, nanotubes and core-shell nanostructures are produced through electrodeposition into the pores of anodised aluminium oxide templates. The electrochemical process is optimised for all materials used. Using nickel, it is demonstrated that the dimensions of the nanowires within the template alter the wavelength position of a reflectivity minima associated with a sub-wavelength optical resonance, corresponding to enhancement of Kerr rotation. The magnetic properties are largely dictated by magnetostatic interactions resulting in an easy axis of magnetisation perpendicular to the nanowire long axis Cobalt nanowires produce a larger Kerr rotation than analogous nickel samples. The magnetic properties are altered by the uniaxial magnetocrystalline anisotropy, confirmed by x-ray diffraction to lie along the long axis of the nanowires. It is therefore possible to rotate the easy axis of magnetisation from the plane of the substrate to the nanowire long axis by increasing the aspect ratio and inter-wire separation. Cobalt nanotubes create a highly complex magneto-optical response with multiple resonances. Nickel-iron alloy nanowires were also made, and the results are compared for changing geometry as well as varying concentration levels. It is revealed through transmission electron microscopy that the grain structure is richly textured with nanocrystalline grains and high volume fraction of grain boundaries. The magnetoplasmonic properties of gold-core cobalt-shell nanowire arrays conclude the thesis. It is found that a nanometric cobalt layer is sufficient to demonstrate magnetic control over optical properties. The optical properties of the array are characteristic of the plasmonic resonances associated with the gold nanowires and the magnetic properties are similar to those of cobalt nanotubes. Combined, however, the wavelength and magnitude of the relative phase shift between P and S polarised components of incident light can be altered with the application of a magnetic field.
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Rocks, Conor Joseph. "Engineering and characterisation of silicon-based nanoscale interfaces and their impact in solar devices." Thesis, Ulster University, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.728644.
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The main objective of this work was to investigate silicon based nanoscale interfaces with other exciting materials and to investigate their applicability to photovoltaics. In this context, quantum confined silicon nanocrystals (Si NCs) were synthesised and methods used to manipulate surface properties in order to maintain desirable opto-electronic properties. Additionally, a spray deposition technique was developed in order to integrate Si NCs more effectively with organic-inorganic halide perovskite, for opto-electronic conversion and photovoltaic applications. One of the most important findings of this work is the control and understanding of Si NC oxidation that presented ideal conditions for the non-metallic growth of carbon nanotubes (CNTs), and the production of a Si NC-CNT nanocomposite. It was experimentally determined that the growth of CNTs was reliant on small nanocrystal assemblies (< 100 nm) coupled with an oxide shell thickness of at least 1 nm, before acting a suitable catalyst. Secondly, practicality of spray technique was demonstrated for perovskite solar devices where surface chemistry and subsequent change in electronic structure affected performance. Through optimizing the absorber thickness the short-circuit current density was increased from 4.9 mA/cm2 to 22.3 mA/cm2, increasing overall power conversion efficiency from 0.83% to 5.22%. Sprayed thin films however showed increased surface degradation that affected the stability under continued illumination, highlighting potential limitations existing for deposition technique. Following, third generation solar cells based on perovskite-quantum dot architectures with p-doped and n-doped Si NCs were fabricated for the first time. The Si NCs embedded within perovskite film absorbed diffusing moisture and became oxidized due to their hydrophilic nature which consequently slowed the chemical decomposition of the perovskite. The slowed degradation allowed composite perovskite-quantum dot devices to perform better under continued illumination with short- circuit current density reaching around 20 mA/cm2 and efficiencies above 6 %. Efforts were made towards an all Si NC heterojunction devices where mixing with perovskite in the solution phase allowed for more compact films that showed rectifying behaviour and demonstrated working devices.
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Janko, Marek [Verfasser], and Robert [Akademischer Betreuer] Stark. "Structure and stability of biological materials – characterisation at the nanoscale / Marek Janko. Betreuer: Robert Stark." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1022791176/34.
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Johnson, N. J. "Developing scanning ion conductance microscopy (SICM) for nanoscale force and topographic characterisation of live cells." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605629.
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Scanning Ion Conductance Microscopy (SICM) uses a scanning nanopipette to obtain high resolution, non-contact images of soft surfaces such as live cells under physiologically relevant conditions. Ion current flowing through the tip aperture is used as a feedback control signal to maintain a constant tip-sample separation. This thesis details recent efforts to improve the mechanical stability of the instrument, develop new software algorithms for scanning control, and create new techniques for mechanical characterization. These advances have led to reduced imaging time, improved spatial resolution, and the ability to image increasingly challenging samples. In addition to improved imaging, SICM was extended to controllably apply and release pressure near a surface. A known hydrostatic pressure can be generated at the pipette tip and the sample’s response followed using SICM distance feedback control. In this fashion the cells were deformed, the pressure released, and their response to zero applied pressure monitored. This new pressure application method was first automated and calibrated on oil droplets. It was then used to investigate the mechanical properties of live osteoblasts and the contribution of the underlying cell cytoskeleton to the measured response. A second pressure application technique was developed to improve the lateral resolution. At very small pipette-sample separations (less than the typical SICM control distance) the micropipette exerts a force due to the high electric field at the pipette tip. This force can be used to deform cells with >100 nm lateral resolution and can rapidly map the mechanical characteristics. In fact, it was possible to observe the cytoskeleton beneath the osteoblast cell membrane. To conclude, cellular topography and dynamics studies were conducted on live T-cells, sperm cells, and viral entry events. These experiments further demonstrated the capabilities of the improved SICM and the new pressure application techniques.
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Eakins, Emily. "Nanoscale characterisation of effect of SiC on microstructure and oxidation behaviour of ZrB2-based ceramics." Thesis, Imperial College London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539288.
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Aleeva, Yana. "Fabrication and characterisation of ZnO nanostructures: from nanoscale building blocks to hybrid nanomaterials - towards emerging technologies in sensing applications." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/977.
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Metal oxide nanostructures characterized by multiple morphologies and structures are at the forefront of applications driven nanotechnology research. In particular, they represent a versatile solution for performance enhancement and applications in multifunctional devices and offer distinct advantages over their bulk counterparts.
The current state in ZnO nanomaterials research and its impact in nanotechnology and modern engineering are discussed through the lens of con-tinuing technological advances in synthetic techniques allowing to obtain the material with predefined specific set of criteria including size, functionality, and uniqueness.
Aim of this research activity is fabrication and study of the potential ap-plications as biomolecular nanoplatforms of ZnO nanostructures obtained using different synthetic techniques ranging from vapor phase deposition (Metal-Organic Chemical Vapor Deposition) to solution growth (Chemical Bath Depo-sition). Moreover, hybrid synthetic approaches are used to obtain complex hier-archical ZnO structures having dual or multiple morphologies. The non-covalent interaction of these inorganic nanosystems with organic molecules, having spe-cific chemical behavior, represents a strategy to obtain hybrid organic-inorganic nanomaterials, thus offering interesting potentiality for the design of high per-formance devices. In particular, it is demonstrated that integration of Metal-Organic Chemical Vapor Deposition and Chemical Bath Deposition strategies with Nanosphere Colloidal Lithography allows to define two-dimensional hybrid ZnO-SiO2 nanoarrays having great potential as innovative fluorescence sensing substrates with individual addressability and tuning of the biomolecular detec-tion capability.
Combination of Metal-Organic Chemical Vapor Deposition with Electro-spinning leads to fabrication of core shell Zn-doped TiO2 ZnO nanofibers char-acterised by hierarchical growth of ZnO nanoneedles onto the TiO2 nanofiber surface. XRD measurements revealed that after ZnO deposition at T > 500 °C, the TiO2 nanofibers were composed of the anatase rutile mixed phases with dif-ferent fractions of rutile, modulated by the Zn dopant concentration. These com-posite nanomaterials may be intriguing to the future study of nanofiber photo-catalysts and sensors, and functional properties based on titanium dioxide.
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Keßler, Michael [Verfasser], Martin H. G. [Akademischer Betreuer] Prechtl, and Annette [Akademischer Betreuer] Schmidt. "Nanocatalysis in Ionic Liquids - Syntheses, Characterisation and Application of Nanoscale Catalysts / Michael Keßler. Gutachter: Martin H. G. Prechtl ; Annette Schmidt." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1069374296/34.
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Garduno, Nolasco Edson. "Nano-scale approaches for the development and optimization of state-of-the-art semiconductor photovoltaic devices." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/nanoscale-approaches-for-the-development-and-optimization-of-stateoftheart-semiconductor-photovoltaic-devices(927e70db-03ff-43e0-8b27-5472bc4a293f).html.
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This project is concerned with both the study of different Multiple Quantum Wells (MQWs) structures using the In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP and a systematic investigation of the properties of InAs QD systems within GaAs with the aim of achieving enhancements of solar cell performance. The key challenge is the growth of QDs solar cell structures which exhibit sufficient absorption (enhanced infrared absorption) to increase short circuit current density (Jsc) but which can still maintains a high open circuit voltage (Voc). The research consists of epitaxial growth using state-of–the-art MBE, optical absorption, photoluminescence and high resolution x-ray diffraction measurements as well as device fabrication and characterization of novel solar cell structures. Optimization was performed on these novel cells to further improve their efficiency by inserting stacks of QD into different regions of the device. The effect of localized doping of such structures was used in an attempt to maintain and enhance the open-circuit voltage which in turn increases the device efficiency. The fabricated devices were characterized using measurements of the dark/light current-voltage (I-V) characteristics and spectral response (50-480 K). Solar cell external quantum efficiencies under standard air mass (AM) 1.5 spectrum were determined and the suitability of these new cells under solar concentration were assessed. Full physical simulations are performed using SILVACO semiconductors modelling software to generate models of multi-junction solar cells that were crucial in informing iterations to growth and fabrication and help to reconcile theory with experiment. One of the key findings, of this thesis, is the fact that Intermediate band photovoltaic devices using material based on InAs/GaAs vertically stacked quantum dot arrays, can be used in applications according to specific configuration criteria such as high temperature operation conditions. The intermediate band cell, including an inter-dot doped configuration, has been found to be a potential candidate as the inter dot doping profile reduces the efficiency degradation below the GaAs values including an enhancement in the open circuit voltage. It has been proved that these devices not only have a good performance at high temperatures but also by changing the vertical stacking QD layer periodicity can enhance the short circuit current density while keeping a large open circuit voltage. It was confirmed in practical device operation that thermal energy is required to enable the intermediate band in InAs/GaAs QD materials. The impact of this works can help in the future improvements of the intermediate band solar cells based on InAs on GaAs QD. The best overall efficiency of 11.6 % obtained in this work is an excellent value for so simple devices configuration. The Si3N4, tested for the first time on InAs/GaAs QD materials, reduces the reflectance on the device surface to a value of 2% and the operational wavelength can be tuned by controlling the layer thickness. A 100 nm Si3N4 antireflective coating proved to be an excellent coating from 700 to 1000 nm. In terms of short circuit current density a 37% enhancement was achieved.
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Almoric, Jean. "Développement d'un nouvel instrument couplant FIB/SEM UHV et OTOF-SIMS à haute résolution spatiale pour la microélectronique et ses applications." Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0368.
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La spectrométrie de masse d’ion secondaire (SIMS) est probablement la technique d'analyse chimique la plus largement utilisée en science des semi-conducteurs et en métallurgie en raison de sa sensibilité ultime à tous les éléments notamment au plus légers. Avec la réduction de la taille des systèmes, l'imagerie chimique 3D haute résolution devient une condition préalable au développement de nouveaux matériaux. Dans cette thèse, nous rapportons le développement et l’optimisation d'un SIMS innovant implémenté dans un microscope électronique à balayage. L'équipement permet d’obtenir une cartographie chimique élémentaire à très haute résolution (~25nm). La capacité de la technique est démontrée avec la caractérisation à l'échelle nanométrique d’une part de superalliages métalliques nécessaire à la fabrication de pièces moteurs pour l’aviation et d’autre part d’alliages chalcogénures utilisés dans les mémoires à changement de phase de dernière génération développées en microélectroniqueSecondary Ion Mass Spectrometry (SIMS) is probably the most widely used chemical analysis technique in semiconductor science and metallurgy because of its ultimate sensitivity to all elements, especially the lighter ones. With systems downsizing, high-resolution 3D chemical imaging is becoming a prerequisite for the development of new materials. In this thesis, we report the development and optimization of an innovative SIMS implemented in a scanning electron microscope. The equipment makes it possible to obtain elementary chemical mapping at very high resolution (~25nm). The capacity of the technique is demonstrated with the characterization at the nanometric scale on the one hand of metallic superalloys necessary for the manufacture of aircraft engine parts and on the other hand of chalcogenide alloys used in the latest generation phase change memories developed in microelectronics
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Chang, Zhuo, and 暢茁. "Nanoscale Characterisation of Arterial Stiffening." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7h5p9w.
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博士國立清華大學
跨院國際博士班學位學程
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Arterial stiffening as part of the natural ageing process is strongly linked to cardiovascular risk. Although arterial stiffening is routinely measured in vivo, little is known about how localised changes in artery structure and biomechanics contribute to in vivo arterial stiffening. This is mainly due to the limitation of the conventional mechanical testing methods. To circumvent this challenge, a novel nano-scale structural and mechanical characterisation technique, known as PeakForce Quantitative Nanomechanical Mapping (QNM) technique, was developed in a zebrafish model. Using the zebrafish vertebral column, the utility of the PeakForce QNM for probing small-scale biological samples and structures was validated, which paved the way to probe human artery and investigate the localised alterations in artery structure in vitro with arterial stiffening. Human internal mammary artery (IMA) was used as a model vessel for understanding the development of arterial stiffening in this thesis. This thesis focuses on the role of the tunica media and the outmost layer, the tunica adventitia, in arterial stiffening. Using the PeakFoce QNM, the hydrated and dehydrated arterial sections were tested that provided data on nano-scale changes in collagen fibril structure and mechanical properties in the hydrated media, dehydrated media and adventitia and showed how they related to in vivo stiffness measurements in the vascular system. The indentation depth for AFM measurement on the IMA tissues of 5 µm thickness were controlled at 20 nm and 5 nm in liquid and ambient conditions respectively and thus the indentation depth/tissue thickness ratio was 0.4% and 0.1% for the hydrated and dehydrated samples respectively. Furthermore, integrating the findings in this thesis with the proteome analysis data, the localised alterations in the collagen and ultrastructure were explained, and the in vivo arterial stiffening, nanomechanical and structural changes in artery biopsy samples were linked. This approach could be used to develop new diagnostic methods for vascular disease.
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ALEEVA, Yana. "Fabrication and characterisation of ZnO nanostructures from nanoscale building blocks to hybrid nanomaterials - towards emerging technologies in sensing applications." Doctoral thesis, 2012. http://hdl.handle.net/10447/98845.
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