Dissertations / Theses on the topic 'Au based alloy nanowires'
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Jiao, Mingzhi. "Microfabricated Gas Sensors Based on Hydrothermally Grown 1-D ZnO Nanostructures." Doctoral thesis, Uppsala universitet, Mikrosystemteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-320183.
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In this thesis, gas sensors based on on-chip hydrothermally grown 1-D zinc oxide (ZnO) nanostructures are presented, to improve the sensitivity, selectivity, and stability of the gas sensors. Metal-oxide-semiconductor (MOS) gas sensors are well-established tools for the monitoring of air quality indoors and outdoors. In recent years, the use of 1-D metal oxide nanostructures for sensing toxic gases, such as nitrogen dioxide, ammonia, and hydrogen, has gained significant attention. However, low-dimensional nanorod (NR) gas sensors can be enhanced further. Most works synthesize the NRs first and then transfer them onto electrodes to produce gas sensors, thereby resulting in large batch-to-batch difference. Therefore, in this thesis six studies on 1-D ZnO NR gas sensors were carried out. First, ultrathin secondary ZnO nanowires (NWs) were successfully grown on a silicon substrate. Second, an on-chip hydrothermally grown ZnO NR gas sensor was developed on a glass substrate. Its performance with regard to sensing nitrogen dioxide and three reductive gases, namely, ethanol, hydrogen, and ammonia, was tested. Third, three 1-D ZnO nanostructures, namely, ZnO NRs, dense ZnO NWs, and sparse ZnO NWs, were synthesized and tested toward nitrogen dioxide. Fourth, hydrothermally grown ZnO NRs, chemical vapor deposited ZnO NWs, and thermal deposited ZnO nanoparticles (NPs) were tested toward ethanol. Fifth, the effect of annealing on the sensitivity and stability of ZnO NR gas sensors was examined. Sixth, ZnO NRs were decorated with palladium oxide NPs and tested toward hydrogen at high temperature. The following conclusions can be drawn from the work in this thesis: 1) ZnO NWs can be obtained by using a precursor at low concentration, temperature of 90 °C, and long reaction time. 2) ZnO NR gas sensors have better selectivity to nitrogen dioxide compared with ethanol, ammonia, and hydrogen. 3) Sparse ZnO NWs are highly sensitive to nitrogen dioxide compared with dense ZnO NWs and ZnO NRs. 4) ZnO NPs have the highest sensitivity to ethanol compared with dense ZnO NWs and ZnO NRs. The sensitivity of the NPs is due to their small grain sizes and large surface areas. 5) ZnO NRs annealed at 600 °C have lower sensitivity toward nitrogen dioxide but higher long-term stability compared with those annealed at 400 °C. 6) When decorated with palladium oxide, both materials form alloy at a temperature higher than 350 °C and decrease the amount of ZnO, which is the sensing material toward hydrogen. Thus, controlling the amount of palladium oxide on ZnO NRs is necessary.
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Elbasiony, Amr Mohamed Wahba [Verfasser]. "Electrodeposition of tin and tin based alloys from ionic liquids : nanowires, thin films and macroporous structures / Amr Mohamed Wahba Elbasiony." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2015. http://d-nb.info/107822692X/34.
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Burr, Loïc [Verfasser], Christina [Akademischer Betreuer] Trautmann, Ralph [Akademischer Betreuer] Krupke, Robert [Akademischer Betreuer] Stark, and Friedemann [Akademischer Betreuer] Völklein. "Ion-track technology based synthesis and characterization of gold and gold alloys nanowires and nanocones / Loïc Burr. Betreuer: Christina Trautmann ; Ralph Krupke ; Robert Stark ; Friedemann Völklein." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112269622/34.
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Ji, Chunxin. "Synthesis, characterization and applications for gold-silver alloy and nanoporous gold nanowires." Available to US Hopkins community, 2002. http://wwwlib.umi.com/dissertations/dlnow/3080690.
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Sjöberg, Ted. "Plasticity modelling of nickel based super alloy Alloy 718." Licentiate thesis, Luleå tekniska universitet, Material- och solidmekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16884.
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The ever growing demand on reduced fuel consumption in modern aircrafts puts high requirements on manufacturers to reduce weight in all parts of the aircraft. With a total weight of up to one fifth of an aircraft’s total operating weight, ways to decrease the weight of the engine systems are continuously sought. The containment structure that surrounds the fan and turbine in larger commercial aircrafts is designed to prevent any debris to escape and damage any other systems such as fuel tanks or fuselage in the event that a blade should come off. This structure adds considerable bulk to the engine and because of the importance of the containment structure any redesign needs to be thoroughly tested. The high costs associated with containment testing means industry is looking into the feasibility of substituting parts of the expensive experimental testing with more economical numerical simulations. In this thesis modelling of the plastic behaviour of the nickel based super alloy, called Alloy 718, is investigated in an effort to correctly model the material in numerical simulations. This material is one of the most widely used materials in the parts of an aircraft engine subjected to elevated temperatures due to its retained strength and resistance to corrosion and creep. The material models chosen to model the plastic behaviour were the widely used Johnson-Cook and Zerilli-Armstrong models, because of their proven applicability for wide ranges of strain rates. The models were calibrated using data collected from tensile testing performed in a high speed VHS machine from Instron. Tensile tests were performed at quasi-static conditions and raised strain rates up to 1000 s-1. With an induction coil testing was also performed at temperatures up to 650 oC. Fitting the models to the data gave models valid from quasi-static to high rate conditions. In order to test the accuracy of the models they need to be validated. For this purpose a reverse impact experiment using free flying discs impacting a long slender rod was designed. This design enables the force history to be accurately monitored throughout the impact, while still achieving high strain rates. An investigation into producing additional data for use in validation was also performed. This investigation utilized a series of high speed photographs on which shape measurements were carried out in order to find parameters such as plate velocity and average strain without interfering with the experimental resultsGodkänd; 2014; 20140115 (tedsjo); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Ted Sjöberg Ämne: Hållfasthetslära/Solid Mechanics Uppsats: Plasticity Modelling of Nickel Based Super Alloy Alloy 718 Examinator: Professor Mats Oldenburg, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Forskare Paul Åkerström, Swerea MEFOS Tid: Fredag den 28 februari 2014 kl 09.00 Plats: E246, Luleå tekniska
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Shi, Teng. "Confined States in GaAs-based Semiconducting Nanowires." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1460447182.
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Kockert, Maximilian Emil. "Thermoelectric transport properties of thin metallic films, nanowires and novel Bi-based core/shell nanowires." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23001.
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Thermoelektrische Phänomene können in Nanomaterialien im Vergleich zum Volumenmaterial stark modifiziert werden. Die Bestimmung der elektrischen Leitfähigkeit, des absoluten Seebeck-Koeffizienten (S) und der Wärmeleitfähigkeit ist eine wesentliche Herausforderung für die Messtechnik in Hinblick auf Mikro- und Nanostrukturen aufgrund dessen, dass die Transporteigenschaften vom Volumenmaterial sich durch Oberflächen- und Einschränkungseffekte verändern können.
Im Rahmen dieser Abschlussarbeit wird der Einfluss von Größeneffekten auf die thermoelektrischen Eigenschaften von dünnen Platinschichten untersucht und mit dem Volumenmaterial verglichen. Dafür wurde eine Messplattform als standardisierte Methode entwickelt, um S einer dünnen Schicht zu bestimmen. Strukturelle Eigenschaften wie Schichtdicke und Korngröße werden variiert. Grenz- und Oberflächenstreuung reduzieren S der dünnen Schichten im Vergleich zum Volumenmaterial.
Außerdem wird eine Methode demonstriert um S von einzelnen metallischen Nanodrähten zu bestimmen. Für hochreine und einkristalline Silber-Nanodrähte wird der Einfluss von Nanostrukturierung auf die Temperaturabhängigkeit von S gezeigt.
Ein Modell ermöglicht die eindeutige Zerlegung des temperaturabhängigen S von Platin und Silber in einen Thermodiffusions- und Phononen-Drag-Anteil.
Des Weiteren werden die thermoelektrischen Transporteigenschaften von einzelnen auf Bismut-basierenden Kern/Hülle-Nanodrähten untersucht. Der Einfluss des Hüllenmaterials (Tellur oder Titandioxid) und der räumlichen Dimension des Nanodrahts auf die Transporteigenschaften wird diskutiert. Streuung an Oberflächen, Einkerbungen und Grenzflächen zwischen dem Kern und der Hülle reduzieren die elektrische und thermische Leitfähigkeit. Eine Druckverformung induziert durch die Hülle kann zu einer Bandöffnung bei Bismut führen, sodass S gesteigert werden kann. Das Kern/Hülle-System zeigt in eine Richtung, um die thermoelektrischen Eigenschaften von Bismut erfolgreich anzupassen.Thermoelectric phenomena can be strongly modified in nanomaterials compared to the bulk. The determination of the electrical conductivity, the absolute Seebeck coefficient (S) and the thermal conductivity is a major challenge for metrology with respect to micro- and nanostructures because the transport properties of the bulk may change due to surface and confinement effects. Within the scope of this thesis, the influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. For this reason, a measurement platform was developed as a standardized method to determine S of a thin film. Structural properties, like film thickness and grain size, are varied. Boundary and surface scattering reduce S of the thin films compared to the bulk. In addition, a method is demonstrated to determine S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, the influence of nanopatterning on the temperature dependence of S is shown. A model allows the distinct decomposition of the temperature-dependent S of platinum and silver into a thermodiffusion and phonon drag contribution. Furthermore, the thermoelectric transport properties of individual bismuth-based core/shell nanowires are investigated. The influence of the shell material (tellurium or titanium dioxide) and spatial dimension of the nanowire on the transport properties are discussed. Scattering at surfaces, indentations and interfaces between the core and the shell reduces the electrical and the thermal conductivity. A compressive strain induced by the shell can lead to a band opening of bismuth increasing S. The core/shell system points towards a route to successfully tailor the thermoelectric properties of bismuth.
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Najafi, M., Barmachi N. Rastegar, S. Soltanian, Z. Alemipour, and A. Aftabi. "The Effect of Diameter and Thermal Treatment on Magnetic Properties of Co1-xZnx Alloy Nanowires." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35350.
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Sansa, Perna Marc. "Characterization of nanomechanical resonators based on silicon nanowires." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/125966.
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Els sensors de massa nanomecànics han atret un gran interès darrerament per la seva alta sensibilitat, que ve donada per les petites dimensions del ressonador que actua com a element sensor. Aquesta tesi tracta sobre la fabricació i caracterització de ressonadors nanomecànics per a aplicacions de sensat de massa. Aquest objectiu inclou diferents aspectes: 1) el desenvolupament d’una tecnologia de fabricació per a ressonadors nanomecànics basats en nanofils de silici, 2) la caracterització de la seva resposta freqüencial utilitzant mètodes elèctrics i 3) l’avaluació del seu rendiment com a sensors de massa.
Durant aquest treball hem fabricat ressonadors nanomecànics basats en nanofils de silici doblement fixats, utilitzant dues estratègies de fabricació diferents: els nanofils crescuts amb mètodes bottom-up (“de baix a dalt”), i els definits amb mètodes de litografia top-down (“de dalt a baix”). Aprofitant les característiques d’ambdues tècniques, hem fabricat nanofils amb dimensions laterals de fins a 50 nanòmetres, i amb un alt nombre de dispositius per xip, aconseguint un alt grau de rendiment per a estructures d’aquestes dimensions.
Hem aplicat esquemes avançats de detecció elèctrica basats en la mescla de senyals cap a freqüències baixes per tal de caracteritzar la resposta freqüencial dels ressonadors. Hem demostrat que el mètode de freqüència modulada (FM) proporciona la millor eficiència en la transducció de l’oscil·lació mecànica en una senyal elèctrica. Aquesta tècnica ha permès detectar múltiples modes de ressonància del ressonador, a freqüències de fins a 590 MHz. La detecció de modes de ressonància superiors és important per tal de solucionar una de les principals problemàtiques en el camp dels sensors de massa nanomecànics: desacoblar els efectes de la posició i la massa de la partícula dipositada. També hem combinat la informació obtinguda de la caracterització elèctrica amb simulacions d’elements finits per tal de quantificar l’estrès acumulat als nanofils durant la seva fabricació.
Hem estudiat els sistemes de transducció electromecànica en ressonadors basats en nanofils de silici comparant l’eficiència de tres mètodes de detecció: el mètode FM ja esmentat i els mètodes de dos generadors, 1ω i de dos generadors, 2ω. D’aquesta manera hem demostrat que dos mecanismes de transducció diferents coexisteixen en els nanofils de silici bottom-up: el mecanisme lineal (en què la senyal transduïda és proporcional al moviment del ressonador) i el quadràtic (en què la senyal transduïda és proporcional al quadrat del moviment del ressonador). Per altra banda, en els ressonadors top-down només és present el mecanisme de transducció lineal. Aquest mecanisme lineal és el que permet la gran eficiència del mètode FM per a la caracterització de la resposta freqüencial de ressonadors basats en nanofils de silici.
Per tal d’utilitzar els ressonadors nanomecànics com a sensors de massa, el seguiment de la freqüència de ressonància en temps real és indispensable. Hem dissenyat i implementat una configuració en llaç tancat basada en la caracterització FM i un algorisme de detecció de pendent. Aquest sistema permet el seguiment de canvis en la magnitud i freqüència de la resposta del ressonador, possibilitant la detecció de massa en temps real i la caracterització de l’estabilitat temporal del sistema. D’aquesta manera s’ha pogut avaluar l’eficiència del sistema per a aplicacions de sensat de massa. La sensibilitat en massa dels sensors de dimensions més reduïdes és de l’ordre de 6 Hz/zg (1 zg = 6·10-21 g), i les mesures d’estabilitat en freqüència en llaç tancat mostren una resolució en massa de 6 zg a temperatura ambient.Nanomechanical mass sensors have attracted interest during the last years thanks to their unprecedented sensitivities, which arise from the small dimensions of the resonator which comprises the sensing element. This thesis deals with the fabrication and characterization of nanomechanical resonators for mass sensing applications. This objective comprises three different aspects: 1) the development of a fabrication technology of nanomechanical resonators based on silicon nanowires (SiNW), 2) the characterization of their frequency response by electrical methods and 3) the evaluation of their performance as mass sensors. During this work, we have fabricated nanomechanical resonators based on SiNW clamped-clamped beams, using two different approaches: bottom-up growth of SiNW and top-down definition by lithography methods. By exploiting the advantages of each technique, we have succeeded in fabricating nanowires of small lateral dimensions, in the order of 50 nanometers, and with high number of devices per chip, achieving a high throughput taking into account the dimensions of these structures. We have applied advanced electrical detection schemes based on frequency down-mixing techniques for the characterization of the frequency response of the devices. We have found that the frequency modulation (FM) detection method provides the best efficiency in transducing the mechanical oscillation into an electrical signal. This technique has enabled the detection of multiple resonance modes of the resonator at frequencies up to 590 MHz. The detection of high modes of resonance is important to address one of the issues in nanomechanical mass sensing, decoupling the effects of the position and mass of the deposited species. Moreover, by combining the information obtained from the experimental characterization of the frequency response with FEM simulations, we have quantified the stress accumulated in the SiNWs during the fabrication. We have studied the electromechanical transduction mechanisms in SiNW resonators by the comparative performance of three electrical detection methods: the aforementioned FM and two more detection techniques (namely the two-source, 1ω and the two-source, 2ω). We have proved that two different transduction mechanisms co-exist in bottom-up grown SiNWs: linear (in which the transduced signal is proportional to the motion of the resonator) and quadratic (in which the transduced signal is proportional to the square of the motion of the resonator). On the other hand, in the top-down nanowires only the linear transduction mechanism is present. It is this newly found linear transduction which enables the outstanding performance of the FM detection method when characterizing the frequency response of SiNW resonators. For the use of nanomechanical resonators in mass sensing applications, the real-time tracking of their resonance frequency is needed. We have designed and implemented a novel closed-loop configuration, based on the FM detection technique and a slope detection algorithm. It allows the monitoring of changes in the magnitude and the frequency of the response of the resonator, enabling not only the real time detection of mass, but also the characterization of the temporal stability of the system. In this way, its overall performance for mass sensing applications has been characterized. The mass sensitivity of the system for the smallest resonators stands in the range of 6 Hz/zg (1 zg = 6·10-21 g) and the frequency stability measurements in the closed loop configuration reveal a mass resolution of 6 zg at room temperature.
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Hedley, Joseph Henry. "DNA-based conducting polymer nanowires for biosensor applications." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2566.
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Novel DNA-based conductive polymer nanowires formed from thienyl-pyrrole derivatives have been synthesized and characterised by high-resolution ES-MS, ¹H and ¹³C NMR spectroscopy. Bulk DNA-templating of these materials is demonstrated by FTIR, while relative control over nanowire dimensions and deposition is shown by AFM. The electronic properties of these materials were investigated by Scanned Conductance Microscopy (SCM) and two-point I-V measurements. The resistance of the DNA/polymer nanowires, determined from variable temperature I-V measurements, was found to be in the range of 10¹²-10¹⁴Ω. Nanowire conductivity values were calculated to be in the range of 1.9x10-⁷-3.75x10-⁴S cm-¹ at 303K. FTIR data demonstrates the availability of the alkyne group in bulk DNAtemplated materials for subsequent nanowire functionalisation using ‘click’ chemistry. Efforts to couple 3-azido propanol and ssDNA probe DNA is also presented.
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Liu, Qiong. "Mechanical properties of Ti-o based ceramic nanowires." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/201954/1/Qiong_Liu_Thesis.pdf.
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This thesis thoroughly investigated the mechanical properties of Ti-O based ceramic nanowires. It revealed that elastic bending properties including elastic strain and elastic moduli of different kinds of Ti-O based ceramic nanowires were related to their crystalline structures, defects in the structures, and defect activities during bending deformation. These findings help to provide more opportunities for strain engineering on Ti-O NWs and promote potential applications of Ti-O NW-based devices.
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Tsourdalakis, Emmanuel. "Phase transformations in Ti3Al based alloy." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28449.
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Approved for public release; distribution is unlimitedA 'super a2' Ti3Al based alloy with additions of niobium, chromium and tantalum was studied with respect to phase transformation under different heat treatment and aging times and temperatures. As received samples were heated at temperatures ranging between 1000 degrees C ad 1300 degrees C and quenched to retain the high temperature microstructure. Quenched samples were aged between 500 degrees C and 850 degrees C for various times and transformation were studied using dilatometry, x-ray analysis, transmission electron microscopy and microhardness testing. It was found that at around 650 degrees C the transformation of Beta-a2 occurred after two hours of aging, while below this temperature, aging for up to 100 hours at 500 degrees C produced only the Beta-w transformation with very little a2. Also, an 'w-type' phase was observed at this aging temperature. Microhardness measurements and x-ray diffraction confirmed the above results. Quenching from high temperature showed the presence of lath-like features which were poor in Ta and Cr and had the B2 structure. Finally some regions with an orthorhombic structure were observed in the as quenched samples. Overall, peak hardness was obtained after aging the quenched Beta phase sample at 650 degrees C. This corresponded to a macrostructure of retained beta with a fine acicular structure of a2..
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Mohamed, Hasan Daw Ashtawi. "DNA-based routes to metal, inorganic and polymer nanowires." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2150.
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This thesis describes the preparation and characterization of conductive nanowires. The synthesis of the nanowires was achieved using a DNA-templating strategy. The chemical identity of the nanowires was characterized using FTIR, XPS and XRD, while the structural character, electronic properties and magnetic behavior were probed using AFM, EFM and MFM, respectively. The formation of Fe3O4 nanowires involved initial association of Fe²+ and Fe³+ ions to the DNA, and subsequent co-precipitation of the Fe3O4 material, upon addition of NaOH. Chemical characterization confirmed the formation of Fe3O4 within the product material. AFM data revealed one-dimensional (1-D) nanostructures with diameters up to 30 nm, whilst EFM and MFM showed that the nanowire structures are electrically conducting and exhibit magnetic behaviour. The preparation of Fe and Rh nanowires, respectively, was achieved by DNA-templating approach in conjunction with either chemical or electrochemical reduction. Chemical characterization confirmed a metal/oxide core/shell structure. AFM data showed 1-D nanostructures with granular character, and diameters up to 26 nm for Fe and 31 and 23 nm for Rh, respectively. The structures were confirmed to be electrically conducting and to display magnetic behaviour as indicated by EFM and MFM, respectively. Finally, DNA-templating of 2,6-diaminopurine-propyl-2,5 bis-dithenyl pyrrole and thymine-propyl-pyrrole by chemical oxidation using FeCl3 yielded supramolecular polymers. FTIR and XPS studies confirmed the presence and interaction of the component polymer chains. The DNA/CPs nanowires showed smooth and uniform structures with diameters up to 25 and 35 nm, and they were found to be electrically conducting. The attempted formation of larger structures based on the base pair hydrogen bonding between the two types of nanowires was investigated by AFM studies. However, reliable evidence for larger structures formation based on this specific interaction was not found.
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Tao, Ran. "Piezoelectric generators based on semiconducting nanowires : simulation and experiments." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT094/document.
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L’alimentation en énergie des réseaux de capteurs miniaturisés pose une question fondamentale, dans la mesure où leur autonomie est un critère de qualité de plus en plus important pour l’utilisateur. C’est même une question cruciale lorsque ces réseaux visent à assurer une surveillance d’infrastructure (avionique, machines, bâtiments…) ou une surveillance médicale ou environnementale. Les matériaux piézoélectriques permettent d’exploiter l’énergie mécanique inutilisée présente en abondance dans l’environnement (vibrations, déformations liées à des mouvements ou à des flux d’air…). Ils peuvent ainsi contribuer à rendre ces capteurs autonomes en énergie. Sous la forme de nanofils (NF), les matériaux piézoélectriques offrent une sensibilité qui permet d’exploiter des sollicitations mécaniques très faibles. Ils sont également intégrables, éventuellement sur substrat souple.Dans cette thèse nous nous intéressons au potentiel des nanofils de matériaux semi-conducteurs piézoélectriques, tels que ZnO ou les composés III-V, pour la conversion d’énergie mécanique en énergie électrique. Depuis peu, ceux-ci ont fait l’objet d’études relativement nombreuses, avec la réalisation de nanogénérateurs (NG) prometteurs. De nombreuses questions subsistent toutefois avec, par exemple, des contradictions notables entre prédictions théoriques et observations expérimentales.Notre objectif est d’approfondir la compréhension des mécanismes physiques qui définissent la réponse piézoélectrique des NF semi-conducteurs et des NG associés. Le travail expérimental s’appuie sur la fabrication de générateurs de type VING (Vertical Integrated Nano Generators) et sur leur caractérisation. Pour cela, un système de caractérisation électromécanique a été construit pour évaluer les performances des NG réalisés et les effets thermiques sous une force compressive contrôlée. Le module d’Young et les coefficients piézoélectriques effectifs de NF de GaN; GaAs et ZnO et de NF à structure cœur/coquille à base de ZnO ont été évalués également dans un microscope à force atomique (AFM). Les nanofils de ZnO sont obtenus par croissance chimique en milieu liquide sur des substrats rigides (Si) ou flexibles (inox) puis sont intégrés pour former un générateur. La conception du dispositif VING s’est appuyée sur des simulations négligeant l’influence des porteurs libres, comme dans la plupart des études publiées. Nous avons ensuite approfondi le travail théorique en simulant le couplage complet entre les effets mécaniques, piézoélectriques et semi-conducteurs, et en tenant compte cette fois des porteurs libres. La prise en compte du piégeage du niveau de Fermi en surface nous permet de réconcilier observations théoriques et expérimentales. Nous proposons notamment une explication au fait que des effets de taille apparaissent expérimentalement pour des diamètres au moins 10 fois plus grands que les valeurs prévues par simulation ab-initio ou au fait que la réponse du VING est dissymétrique selon que le substrat sur lequel il est intégré est en flexion convexe ou concaveEnergy autonomy in small sensors networks is one of the key quality parameter for end-users. It’s even critical when addressing applications in structures health monitoring (avionics, machines, building…), or in medical or environmental monitoring applications. Piezoelectric materials make it possible to exploit the otherwise wasted mechanical energy which is abundant in our environment (e. g. from vibrations, deformations related to movements or air fluxes). Thus, they can contribute to the energy autonomy of those small sensors. In the form of nanowires (NWs), piezoelectric materials offer a high sensibility allowing very small mechanical deformations to be exploited. They are also easy to integrate, even on flexible substrates.In this PhD thesis, we studied the potential of semiconducting piezoelectric NWs, of ZnO or III-V compounds, for the conversion from mechanical to electrical energy. An increasing number of publications have recently bloomed about these nanostructures and promising nanogenerators (NGs) have been reported. However, many questions are still open with, for instance, contradictions that remain between theoretical predictions and experimental observations.Our objective is to better understand the physical mechanisms which rule the piezoelectric response of semiconducting NWs and of the associated NGs. The experimental work was based on the fabrication of VING (Vertical Integrated Nano Generators) devices and their characterization. An electromechanical characterization set-up was built to evaluate the performance and thermal effects of the fabricated NGs under controlled compressive forces. Atomic Force Microscopy (AFM) was also used to evaluate the Young modulus and the effective piezoelectric coefficients of GaN, GaAs and ZnO NWs, as well as of ZnO-based core/shell NWs. Among them, ZnO NWs were grown using chemical bath deposition over rigid (Si) or flexible (stainless steel) substrates and further integrated to build VING piezoelectric generators. The VING design was based on simulations which neglected the effect of free carriers, as done in most publications to date. This theoretical work was further improved by considering the complete coupling between mechanical, piezoelectric and semiconducting effects, including free carriers. By taking into account the surface Fermi level pinning, we were able to reconcile theoretical and experimental observations. In particular, we propose an explanation to the fact that size effects are experimentally observed for NWs with diameters 10 times higher than expected from ab-initio simulations, or the fact that VING response is non-symmetrical according to whether the substrate on which it is integrated is actuated with a convex or concave bending
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Ebenhoch, Carola [Verfasser]. "Memristive Systems Based on Metal Oxide Nanowires / Carola Ebenhoch." Konstanz : KOPS Universität Konstanz, 2021. http://d-nb.info/1237222109/34.
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Wang, Lixin. "Ferrocene-based molecular electronics and nanomanufacturing of palladium nanowires." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7757.
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Thesis (Ph. D.)--University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Cano-Castillo, U. "Environment-assisted cracking of spray-formed Al-alloy and Al-alloy-based composite." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260730.
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Kockert, Maximilian Emil [Verfasser]. "Thermoelectric transport properties of thin metallic films, nanowires and novel Bi-based core/shell nanowires / Maximilian Emil Kockert." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/123689698X/34.
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Butt, M. Taqi Zahid. "Study of gold-based alloy phase diagrams." Thesis, Brunel University, 1990. http://bura.brunel.ac.uk/handle/2438/7389.
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The partial constitutions of the Au-Ge-X and Au-Pb-X ternary alloys have been investigated, where X is a metallic element, selected from the sub-groups period 1m and rrm of the periodic table (In, Ga, Zn, or Cd), which forms one or more stable compounds with gold, but which forms no stable compound with Ge and Pb. The Smith Thermal Analysis Method, supplemented by metallographic and X-ray techniques, was used to determine the constitutions of the ternary systems. Eutectiferous, pseudobinary systems were found between Ge and the stable congruent intermediate compounds, AuIn, Auln2' AuGa, AuGa2' AuZn and AuCd. The solubility of Ge in the AuX compounds was not determined directly. However, it was 1.3 at.% Ge for Zn and Cd containing alloys and less than 1.0 at. % Ge for In and Ga containing alloys at the eutectic temperatures, which is in accordance with the Hume-Rothery rule. Ternary eutectic points were also determined in the Auln-AuIn2-Ge, Auln2-In-Ge and AuGa-AuGa2-Ge partial ternary systems. No evidence of liquid immiscibility was found in any of these ternary systems. The experimental results obtained were in good agreement with computed features of the diagrams. However, pseudobinary systems were not found between Pb and the stable congruent melting intermediate compounds, AuGa, AuGa2, AuZn and AuCd (the AuIn-Pb and AuIn2-Pb sections had already been investigated). The evidence of an extensive liquid immiscibility was found in each of these systems. The miscibility in the liquid state was found to decrease progressively down group IV when the elements of this group react with AuX compounds, which can be attributed to the progressive increase of the atomic size and decrease in electronegativities and solubility parameters of the elements, down this group. Two rules were derived to relate the liquid immiscibility/miscibility of ternary systems. One of the rules based upon the atomic sizes and melting points of the constituent elements showed a fair agreement with many systems. However, the other rule based upon the solubility parameter and electronegativities of the constituent elements showed good agreement with immiscible systems, but gave a poor predictability for miscible systems. The lower temperature equilibria of the Au-rich portion of the Au-Sn binary phase diagram are not well defined. So, long term heat treatment of samples at appropriate temperatures and compositions was carried out. Optical microscopy and SEMIEDAX techniques were employed and hence the low temperature equilibria of the Au-Sn binary system have been amended.
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Singhal, Dhruv. "Forêt de nanofils semiconducteurs pour la thermoélectricité." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY016/document.
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La conversion thermoélectrique a suscité un regain d'intérêt en raison des possibilités d'augmenter l'efficacité tout en exploitant les effets de taille. Par exemple, les nanofils montrent théoriquement une augmentation des facteurs de puissance ainsi qu'une réduction du transport des phonons en raison d'effets de confinement et/ou de taille. Dans ce contexte, le diamètre des nanofils devient un paramètre crucial à prendre en compte pour obtenir des rendements thermoélectriques élevés. Une approche habituelle consiste à réduire la conductivité thermique phononique dans les nanofils en améliorant la diffusion sur les surfaces tout en réduisant les diamètres.Dans ce travail, la caractérisation thermique d'une forêt dense de nanofils de silicium, germanium, silicium-germanium et alliage Bi2Te3 est réalisée par une méthode 3-omega très sensible. Ces forêts de nanofils pour le silicium, le germanium et les alliages silicium-germanium ont été fabriqués selon une technique "bottom-up" suivant le mécanisme Vapeur-Liquide-Solide en dépôt chimique en phase vapeur. La croissance assistée par matrice et la croissance par catalyseurs en or des nanofils à diamètres contrôlés ont été réalisés à l'aide d'alumine nanoporeuse comme matrice. Les nanofils sont fabriqués selon la géométrie interne des nanopores, dans ce cas le profil de surface des nanofils peut être modifié en fonction de la géométrie des nanopores. Profitant de ce fait, la croissance à haute densité de nanofils modulés en diamètre a également été démontrée, où l'amplitude et la période de modulation peuvent être facilement contrôlées pendant la fabrication des matrices. Même en modulant les diamètres pendant la croissance, les nanofils ont été structurellement caractérisés comme étant monocristallins par microscopie électronique à transmission et analyse par diffraction des rayons X.La caractérisation thermique de ces nanofils a révélé une forte diminution de la conductivité thermique en fonction du diamètre, dont la réduction était principalement liée à une forte diffusion par les surfaces. La contribution du libre parcours moyen à la conductivité thermique observée dans ces matériaux "bulk" varie beaucoup, Bi2Te3 ayant une distribution en libre parcours moyen (0,1 nm à 15 nm) très faible par rapport aux autres matériaux. Même alors, des conductivités thermiques réduites (~40%) ont été observées dans ces alliages attribuées à la diffusion par les surfaces et par les impuretés. D'autre part, le silicium et le germanium ont une conductivité thermique plus élevée avec une plus grande distribution de libre parcours moyen. Dans ces nanofils, une réduction significative (facteur 10 à 15 ) a été observée avec une forte dépendance avec la taille des nanofils.Alors que les effets de taille réduisent la conductivité thermique par une meilleure diffusion sur les surfaces, le dopage de ces nanofils peut ajouter un mécanisme de diffusion par différence de masse à des échelles de longueur atomique. La dépendance en température de la conductivité thermique a été déterminée pour les nanofils dopés de silicium afin d'observer une réduction de la conductivité thermique à une valeur de 4,6 W.m-1K-1 dans des nanofils de silicium fortement dopés avec un diamètre de 38 nm. En tenant compte de la conductivité électrique et du coefficient Seebeck calculé, on a observé un ZT de 0,5. Avec l'augmentation significative de l'efficacité du silicium en tant que matériau thermoélectrique, une application pratique réelle sur les appareils n'est pas loin de la réalitéThermoelectric conversion has gained renewed interest based on the possibilities of increasing the efficiencies while exploiting the size effects. For instance, nanowires theoretically show increased power factors along with reduced phonon transport owing to confinement and/or size effects. In this context, the diameter of the nanowires becomes a crucial parameter to address in order to obtain high thermoelectric efficiencies. A usual approach is directed towards reducing the phononic thermal conductivity in nanowires by achieving enhanced boundary scattering while reducing diameters.In this work, thermal characterisation of a dense forest of silicon, germanium, silicon-germanium and Bi2Te3 alloy nanowires is done through a sensitive 3ω method. These forest of nanowires for silicon, germanium and silicon-germanium alloy were grown through bottom-up technique following the Vapour-Liquid-Solid mechanism in Chemical vapour deposition. The template-assisted and gold catalyst growth of nanowires with controlled diameters was achieved with the aid of tuneable nanoporous alumina as templates. The nanowires are grown following the internal geometry of the nanopores, in such a case the surface profile of the nanowires can be modified according to the fabricated geometry of nanopores. Benefiting from this fact, high-density growth of diameter-modulated nanowires was also demonstrated, where the amplitude and the period of modulation can be easily tuned during the fabrication of the templates. Even while modulating the diameters during growth, the nanowires were structurally characterised to be monocrystalline through transmission electron microscopy and X-ray diffraction analysis.The thermal characterisation of these nanowires revealed a strong diameter dependent decrease in the thermal conductivity, where the reduction was predominantly linked to strong boundary scattering. The mean free path contribution to the thermal conductivity observed in the bulk of fabricated nanowire materials vary a lot, where Bi2Te3 has strikingly low mean free path distribution (0.1 nm to 15 nm) as compared to the other materials. Even then, reduced thermal conductivities (~40%) were observed in these alloys attributed to boundary and impurity scattering. On the other hand, silicon and germanium have higher thermal conductivity with a larger mean free path distribution. In these nanowires, a significant reduction (10-15 times) was observed with a strong dependence on the size of the nanowires.While size effects reduce the thermal conductivity by enhanced boundary scattering, doping these nanowires can incorporate mass-difference scattering at atomic length scales. The temperature dependence of thermal conductivity was determined for doped nanowires of silicon to observe a reduction in thermal conductivity to a value of 4.6 W.m-1K-1 in highly n-doped silicon nanowires with 38 nm diameter. Taking into account the electrical conductivity and calculated Seebeck coefficient, a ZT of 0.5 was observed. With these significant increase in the efficiency of silicon as a thermoelectric material, a real practical application to devices is not far from reality
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De, luna bugallo Andres. "Fabrication and characterization of nanodevices based on III-V nanowires." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00731763.
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Semiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results.
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Tambe, Michael Joseph. "Controlled growth and doping of core-shell GaAs-based nanowires." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59237.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Includes bibliographical references (p. 151-158).
The use of compound semiconductor heterostructures to create electron confinement has enabled the highest frequency and lowest noise semiconductor electronics in existence. Modem technology uses two-dimensional electron gasses and there is considerable interest to explore one-dimensional electron confinement. This thesis develops the materials science toolkit needed to fabricate, characterize, and control the compositional, structural and electronic properties of core-shell GaAs/AlGaAs nanowires towards studying quasi-one-dimensional confinement and developing high mobility electronics First, nanowire growth kinetics were studied to optimize nanowire morphology. Variations in nanowire diameter were eliminated by understanding the role Ga adatom diffusion on sidewall deposition and vertical growth was enabled by understanding the importance of Ga and As mass-transport to nanowire nucleation. These results demonstrate that arrays of vertically-aligned GaAs nanowires can be produced. Then, the deposition of epitaxial AlGaAs shells on GaAs nanowires was demonstrated. By reducing the nanowire aerial density the stability of the nanowire geometry was maintained. A variety of analytical electron microscopy techniques confirmed the shell deposition to be uniform, epitaxial, defect-free, and nearly atomic sharp. These results demonstrate that core-shell nanowires possess a core-shell interface free of many of the imperfections that lithographically-defined nanowires possess. Finally, the adverse effect of the Au seed nanoparticle during n-type doping was identified and n-type doping was achieved via the removal of the Au nanoparticle prior to doping. A combination of energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force microscopy demonstrated that if the Au seed nanoparticle is present during the shell deposition, Au diffuses from the seed nanoparticle and creates a rectifying IV behavior. A process was presented to remove the Au nanoparticle prior to shell deposition and was shown to produce uniform n-type doping. The conductivity of GaAs/n-GaAs nanowires was calculated as a function of donor concentration and geometric factors taking into account the effects of Fermi level pinning. The control demonstrated over all of these parameters is sufficient enough for core-shell nanowires to be considered candidates for high mobility electronics.
by Michael Joseph Tambe.
Ph.D.
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Luna, bugallo Andrès de. "Fabrication and characterization of nanodevices based on III-V nanowires." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112117/document.
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Les nanofils semiconducteurs sont des nano-objets dont la longueur peut aller jusqu'à quelques microns et dont la section peut être inférieure à la dizaine de nanomètre. En particulier, les nanofils de nitrures d'éléments III (GaN, AlN, InN, leurs alliages ternaires et leurs hétérostructures) sont extrêmement prometteurs en vue du développement d’une nouvelle génération de dispositifs d’électronique et d’optoélectronique tels que photodétecteurs, nanotransistors, biocapteurs, source de lumière, cellules solaires, etc.Dans ce travail, nous présentons la fabrication et la caractérisation de deux types de dispositifs à base de nanofils de nitrures III-V : des photodétecteurs d’une part et des dispositifs émetteurs de lumière d’autre part. Tout d'abord, nous avons réalisé et caractérisé un photodétecteur UV aveugle à la lumière du jour à base de nanofils de GaN verticalement alignés sur un substrat de Si(111) contenant une jonction p-n. Nous avons montré que ces dispositifs présentent une réponse supérieure à celle de leurs homologues en couches minces. Ensuite, nous avons fait la démonstration de photodétecteurs UV à base de nanofils uniques contenant des disques quantiques GaN / AlN multi-axiales insérés dans une région non intentionnellement dopé. Les résultats obtenus par spectroscopie de photoluminescence (PL) et cathodoluminescence (CL) montrent des contributions spectrales en-dessous et au-dessus de la bande interdite du GaN attribuées a la variation de l'épaisseur des disques. Les spectres de photocourant montrent un pic sous la bande interdite lié à l'absorption inter-bande entre les états confinés dans les disques les plus larges. Enfin, nous présentons une étude de photodétecteurs et émetteurs de lumière à base de nanofils de GaN contentant une hétérostructure cœur-coquille InGaN / GaN. Les fils utilisés comme photodétecteurs ont montré une contribution en dessous de la bande interdite de GaN. D’autre part, les mesures OBIC démontrent que ce signal provient exclusivement de la région active. Les fils de type LED basés sur la même structure montrent une forte émission d'électroluminescence et un décalage vers le rouge lorsque le taux d’indium présent dans les disques quantiques augmente, en accord avec les résultats de photoluminescence et de cathodoluminescenceSemiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results
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Lari, Leonardo. "Investigation of growth and structure of gallium nitride based nanowires." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507165.
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Abdullah, Ilyaas. "CdSe based nanowires for the photocatalytic production of hydrogen gas." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29398.
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Photocatalytic production of hydrogen was investigated towards achieving a decarbonized supply of hydrogen gas for clean energy conversion technologies such as the proton exchange membrane fuel cell (PEMFC). This study uses a template-directed electrodeposition technique to synthesize multi-segmented CdSe based nanowires for use as a photocatalyst device for hydrogen production. CdSe, Ni, Au and Pt nanowires were successfully synthesized with dimensions ranging from 100 nm to 350 nm in diameter and up to 10 µm long. The CdSe stoichiometry was not easily controlled despite following literature protocols and requires a more systematic investigation. The electrodeposition of Ni nanowires was found to be most effective with very few problems encountered. Improvements in the morphology of Au and Pt nanowires were made by using a constant current as opposed to constant potential electrodeposition techniques. Multi-segmented nanowire devices were prepared with nanowires left embedded in a porous anodized aluminium oxide (AAO) template. Polymer PEDOT: PSS and noble metal Pt was used as an anode and cathode electrocatalyst materials respectively. A prototype photocatalytic testing system was set-up using a 1600 W xenon arc lamp as a light source, an in-house made photoreactor as the device holder, and a mass spectrometer for online gas detection measuring ionic currents of evolved species. The set-up was able to successfully detect hydrogen evolved during the tests but does require further development if more complete photocatalytic testing is to be conducted in future. Photocatalytic hydrogen production from the irradiated devices was inconclusive, but hydrogen detection from devices was observed in an 80 % MeOH solution with no irradiation. Through these tests it was learned that photocatalytic activity needs to be differentiated from regular catalytic activity. This is particularly the case if testing is conducted in organic media and if the photocatalytic phenomena is to be properly isolated and understood correctly
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Hull, S. "Precipitation in aluminium based and iron based alloys." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370120.
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Squire, Peter James. "Development of multi-component iron-based amorphous alloy." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/462/.
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This present study is concerned with developing a new alloy system which is capable of forming a metallic glass on rapid solidification of the melt, rather than modifying a known glass forming composition, and assessing its glass forming ability. Iron (Fe) was chosen as the solvent element because it is significantly cheaper than the base elements found in some other metallic glasses and does not require the addition of large quantities of expensive alloying elements to enable vitrification. A ternary system using carbon (C) and boron (B) was studied initially as these metalloids are known to aid glass formation in other systems. Manganese and molybdenum were selected as secondary alloying additions in order to determine if they would have an effect on the Fe-C-B alloy with the best glass forming ability. A combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry and secondary ion mass spectroscopy was used to investigate the microstructure of as-cast and rapidly solidified alloys. Differential scanning calorimetry (DSC) was used to investigate the thermal behaviour of the alloys. The ability of the iron-based alloys to form a glass on rapid solidification from the melt could not be predicted by observation of the as-cast microstructure or through computational methods. It was found that vitrification of the ternary system was only possible for compositions which were close to a eutectic point and that stabilisation of the supercooled liquid was caused by competition for nucleation between austenite and metastable phases, rather than between primary equilibrium solidification products. Of the ternary compositions where an amorphous phase was produced it was concluded that Fe₈₀.₉C₅B₁₄.₁ had the best glass forming ability (GFA). It was determined that the addition of manganese and/or molybdenum to the base composition generally had the effect of improving the GFA through the increased complexity of the system making it more difficult for recrystallisation to occur. Of the multi-component alloys it was concluded that Fe₆₀.₉Mn₁₀Mo₁₀C₅B₁₄.₁ had the best GFA as it had the highest values for each of the parameters used to describe GFA. It is believed that this is due to competition between the austenite and alpha stabilisers (manganese and molybdenum respectively) causing enhanced stability of the supercooled liquid.
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Lei, Wang S. "Potential applications of a toughened silicon-based alloy." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45385.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (leaves 21-22).
Silicon has long been used as an alloying element in various metal alloys, in engineered ceramics, and in the semiconductor industry. However, due to its intrinsic low fracture toughness, it is generally perceived as a poor choice of material for mechanical applications. This study explores some potential short and long term applications for a new type of castable silicon-rich alloy with an increased fracture toughness, by utilizing several different material selection indices.
by Wang S. Lei.
M.Eng.
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Ching, Suet Ying. "Plasmonic properties of silver-based alloy thin films." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/194.
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The plasmonic properties of silver-based alloy thin films were studied. Silver-ytterbium (Ag-Yb) and silver-magnesium (Ag-Mg) prepared by thermal co-evaporation were investigated extensively for various thin film properties. The optical properties were intensively analyzed and discussed because the dielectric response of a material is particularly significant in terms of its plasmonic properties. The study of silver-based alloy thin films has been mostly about Ag alloying with other transition metals, but the results of Ag-Yb and Ag-Mg in this work showed that the intensity of plasma resonance is tunable, in which the idea may also apply to other silver-rich binary alloy thin films regardless of the kind of second metal components. In our research, the Ag plasma resonance was weakened with respect to the concentration of Yb and Mg in the alloy thin films. The change in the optical characteristics around Ag plasma resonance frequency was attributed to an increase in “resonance damping. This is confirmed from modeling using classical free-electron theory. The increase in the damping was experimentally corroborated by the concentration dependence of electrical conductivity and estimated average crystallite size of Ag-Yb and Ag-Mg thin films. The reduction in electrical conductivity was not only caused by introducing less conductive Yb or Mg but also through disturbing the Ag lattice structure to promote additional electron scattering at grain boundaries. The Ag-Yb and Ag-Mg alloys carried intermediate properties between their pure components despite the presence of Yb or Mg oxides. Besides optical and electrical properties, changes in the electronic work function were also assessed since it is also important in applications. Plasmonic nanostructures and transparent organic light-emitting diodes (OLEDs) were fabricated to demonstrate their potential applications. Two-dimensional disc-arrays nanostructures composed of pure Ag and Ag-Yb were implemented to evaluate the plasmonic properties. The damping loss in Ag-Yb caused weakened coupling of incident photons and surface plasmons when compared to pure Ag without altering the coupling wavelengths, suggesting potential plasmonic materials for tuning the coupling strength of surface plasmons by controlling the concentration of Yb which may also apply to Ag-Mg. Ultrathin Ag-Yb and Ag-Mg films were used as cathodes in transparent OLEDs for demonstration, which was beneficial by virtue of overall device transmittance though sacrificing electrical conduction leading to poor light emission unless inserting additional ultrathin lithium fluoride to modify the ultrathin cathodes.
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Gorsky, Daniel A. "Niyama Based Taper Optimizations in Steel Alloy Castings." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1316191746.
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Böhnert, Tim [Verfasser], and Kornelius [Akademischer Betreuer] Nielsch. "Magneto-thermopower and Magnetoresistance of Co-Ni Alloy and Co-Ni/Cu Multilayered Nanowires. / Tim Böhnert. Betreuer: Kornelius Nielsch." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1052996698/34.
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Offenberger, Sean Alan. "Investigation of Zinc Oxide Nanowires for Impedance Based Structural Health Monitoring." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/82502.
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The goal of this work is to investigate the piezoelectricity of composite laminates embedded with layers of zinc oxide (ZnO) nanowires. ZnO nanowire embedded composites have the potential to sense and actuate giving the potential for these smart composites to serve the function of being load bearing structures and monitoring the integrity of the structure. This work examines the piezoelectric characteristics of composite beams by investigating their electromechanical coupling in the form of vibration under the presence of electrical excitation. With the help of a mathematical model, piezoelectric constants are estimated for these samples. A layer of ZnO nanowires were grown on plane woven fiberglass fabric that was incorporated into a carbon fiber epoxy composite. The beam deflection velocity was measured as a varying voltage was applied to the composite. Using Hamilton's Principle and Galerkin's method of weighted residuals, a mathematical model was derived to estimate piezoelectric constants for the composites from the experimental data. Piezoelectric properties were determined using vibrational testing and a mathematical model. Piezoelectric constants h31, g31, and d31 were estimated to be 9.138 E7 V/m, 6.092 E-4 Vm/N, and 2.46 E-14 respectively. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M.Master of Science
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Roussey, Arthur. "Preparation of Copper-based catalysts for the synthesis of Silicon nanowires." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10164.
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Les travaux dans cette thèse ont pour objectif la synthèse de catalyseurs (nanoparticules de cuivre) de taille contrôlée pour la synthèse de nanofils de silicium dans des conditions compatibles CMOS, c'est-à-dire en évitant l'utilisation de l'or comme catalyseur et pour des croissances basse température (<450°C). Les résultats obtenus ont permis de montrer que les techniques de chimie de surface classiquement utilisées pour la préparation de catalyseurs sur des supports 3D (silice, nitrure de titane…) sont directement applicables et transférables sur des supports 2D (wafer de silicium recouvert de films fins de SiO2, SiOx et TiN). Nous avons par exemple pu préparer des nanoparticules de cuivre de taille contrôlée (de 3 nm à 40 nm de diamètre moyen suivant les conditions expérimentales et supports). De plus, les mécanismes de formation des nanoparticules en fonction des propriétés de surface des matériaux étudiés ont été démontrés en combinant diverses techniques d'analyses de surface. La croissance de nanofils de silicium à partir de ces catalyseurs sur substrats 2D a également été réalisée avec succès dans des procédés à basse température. Il a notamment été montré l'existence d'un diamètre minimum critique à partir de laquelle la croissance basse température était possibleThe work presented in this PhD thesis aimed at the preparation of copper nanoparticles of controllable size and their utilization as catalysts for the growth of silicon nanowires in a process compatible with standard CMOS technology and at low temperature (< 450°C). The growth of silicon nanowires by Chemical Vapor Deposition (CVD) via the catalytic decomposition of a silicon precursor on metallic nanoparticles at low temperature (Vapor Solid-Solid process) was demonstrated to be possible from an oxidized Cu thin film. However, this process does not allow the control over nanowires diameter, which is controlled by the diameter of the nanoparticle of catalyst. In this PhD is presented a fully bottom-up approach to prepare copper nanoparticles of controllable size directly on a surface without the help of external stabilizer by mean of surface organometallic chemistry. First, the preparation of copper nanoparticles is demonstrated on 3D substrates (silica and titanium nitride nanoparticles), along with the fine comprehension of the formation mechanism of the nanoparticles as a function of the surface properties. Then, this methodology is transferred to planar (2D) substrates typically used in microelectronics (silicon wafers). Surface structure is demonstrated to direct the Cu nanoparticles diameter between 3 to 40 nm. The similarities between the 2D and 3D substrates are discussed. Finally, the activity of the Copper nanoparticles in the growth of Silicon nanowire is presented and it is demonstrated that in our conditions a critical diameter may exist above which the growth occurs
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REZVANI, SEYED JAVAD. "Fabrication and characterization of semiconductor Nanowires based on Silicon and Germanium." Doctoral thesis, Università degli Studi di Camerino, 2014. http://hdl.handle.net/11581/401771.
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Low-Dimensional semiconducting material specially Silicon and Germanium are of the vastly studied systems due to their interesting properties and also their abundance which makes them economically favored. Germanium, in particular, has the advantage of enhanced electrical properties compared to silicon while compatible with conventional silicon technology. In the middle, the 1-D systems due to their unique properties can be tuned for different band gaps because of the quantum confinement which will be applied in the other two dimensions. Hence the electrons in these systems act like they are bounded in a two dimensional quantum well. This tuning happens to be a useful property for fabrication of the advanced devices. For instance, the transport mechanism in these structures can lead to a ballistic regime, i.e. the scattering happens only at the boundaries. This property opens up vast variety of the application of the 1-D semiconductors system. However, this property strongly depends on the surface properties of the synthesized structures. The possibility to control the surface roughness can lead to an enhanced electronic transport in these structures. Furthermore, doping of these structures with a magnetic element can lead to a 1-D diluted magnetic semiconductor system with an enhanced ferromagnetic transition temperature (up to 400 K) due to the confinement as it has been demonstrated for Ge nanodots doped with Mn. This will allow another way of the control over the energy band level tuning as well as ferromagnetic behavior with possibility to be utilized in spintronic applications. The enhanced electrical and optical properties of Si and Ge nanowires make them an interesting subject in a frame of study. Although there has been many studies in last decade on these system, the mechanism behind the fabrication processes and the properties of the fabricated structures are not clearly understood yet. Hence, in this work I have tried to go further in comprehension of the mist that still remains on top of the knowledge of the fabrication and properties of 1-D Si and Ge systems. In this thesis I have considered two approaches, so called ''top down'' and ''bottom up''. The ''top down'' approach includes the self assembly of semiconductor nanowires by vapor liquid solid growth and the ''endotaxial'' growth. The ''bottom up'' approach will be focused on metal assisted etching fabrication of silicon nanowires. Amongst the different mechanism available for the self assembly of nanowires (bottom up), Vapor Liquid Solid (VLS), is the well studied method to grow semiconducting nanowires. This method can be used in a molecular beam epitaxy (MBE) system with few modifications of the original idea. MBE technique, allowing low temperature growth, low deposition rate and fine control over ultra high vacuum level, it is considered one of the most reliable and sensitive deposition techniques in nanostructure fabrication. VLS growth in MBE differs from the chemical deposition methods in the sense that the liquid droplet does not act as a catalyst but as a seed, i.e. nucleation center, and the growth is strongly dependent on the diffusion of the adatom rather than direct impinging on the liquid droplet. This growth mechanism of nanowires is called diffusion induced VLS (DI-VLS). In this framework the growth of the wires are strongly affected by their diffusion. There are models concerning the DI-VLS mechanism including models concerning the diffusion of adatoms or the models based on the mass transfer in the process. However, these models explaining this mechanism do not clarify certain aspects of the growth. Here, I have carried out a systematic experimental work to have a more clear understanding of the above mentioned mechanisms which is reported in the first chapter. I have shown that the geometry of the wire can be affected by the growth condition which has not been considered previously in the models. I have also found that the DI-VLS model is size dependent and discussed the effects that controls the growth at high temperatures. I have studied ''endotaxial'' growth of the Mn-Ge nanowires which can be categorized as a bottom up method (second chapter). Due to the novelty and importance of the work I preferred to report the experimental results in a separate chapter, rather than include them as a section in the first chapter. This work is done based on the idea proposed by Tromp and Tersoff about the possibility of the nanowire growth by strain relaxation of the wetting layers deposited on a substrate. This method can have more control over the dimension of the grown structure, particularly the diameter of the nanowires which is a crucial parameter in the quantum confinement. Since these wires are in the plane of the substrate they are easier to be utilized as a device compared to the VLS grown wires which are in vertical or tilted direction with respect to the substrate. Nonetheless the engineering of the electrical contacts may reveal several problems due to their superposition in the substrate matrix. Regarding the top down approach frame, wires are fabricated rather than synthesized. For silicon nanowire fabrication, metal assisted chemical etching (MAcE) is one of the studied methods which is relatively simple and economically favored. However, the process mechanism is in its infancy and clear understanding of the roles played by the different parameters, involved in the process, is still lacking. In this thesis I have tried to clear out these roles by a deep and systematic study. I propose a model which can explain up to some extent the effect of doping and metal catalyst on the growth and structure of the fabricated wires. For both of the two methods mentioned above the level of control of the different parameters may allow device fabrication. In VLS system, I have engineered the dimension of the droplets to have a very narrow distribution of the diameter which resulted in a narrow distribution of the grown Ge wires. In MAcE, I used two stage polymer and plasma etching lithography which resulted in a sub 100 nm large uniform area of the silicon nanowires. Both single silicon and germanium wires have been contacted in order to characterize their electrical properties. Unique electrical properties of the DI-VLS synthesized germanium nanowire are reported at the end of the first chapter, while the complicated properties of semi porous silicon nanowire, as well as its optical properties are reported at the end of the third chapter. Finally, I desire to thank all the colleagues and technicians of other research groups who helped me to carry on the experimental work. The results presented in this thesis are in collaboration of groups, listed below : Transmission electron microscopy at University of Marseilles, France and IIT Turin Scanning electron microscopy in INRiM, Turin Nanolithography in INRiM, Turin Photoluminescence spectroscopy at Polytechnic of Turin.
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Dong, Zhenning. "Synthesis of GaAs nanowires and nanostructures by HVPE on Si substrate. Application to a microbial fuel cell based on GaAs nanowires." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC091/document.
Full textAbstract:
Nous avons proposé d'étudier le potentiel de l'outil d'épitaxie HVPE (Hydride Vapour Phase Epitaxy) pour la croissance de nanofils de GaAs. La morphologie nanofil permet au matériau épitaxié de libérer les contraintes dans le cas de l’hétéroépitaxie et de mettre en œuvre des procédés de croissance sur des substrats à faible coût comme les substrats de silicium. Dans ce contexte, j’ai effectué la croissance auto-catalysée de nanofils et des nanoobjets de GaAs par HVPE sur substrat silicium. La HVPE utilise des molécules de GaCl synthétisées à l'intérieur du réacteur dans la zone en amont du substrat à haute température (T> 700 °C). La décomposition du GaCl est beaucoup plus difficile entre 600 °C et 700 °C. Dans ce manuscrit des calculs thermodynamiques des constantes d’équilibre de formation du gallium liquide sont donnés et analysés. Les rapports de flux atomiques III/V obtenus sont de 11 à 222, bien plus élevés que les rapports utilisés dans procédés MBE et MOVPE. Ce travail expérimental a été couplé à un travail de modélisation théorique. Une étude de la faisabilité d’utiliser un substrat constitué de nanofils de GaAs comme électrode dans une pile microbienne a également été initiéeIII-V semiconductor nanowires exhibit excellent electrical and optical properties in laterally confined geometry which is very promising for monolithic integration of photonic nanodevices on silicon substrates. Hydride Vapor Phase Epitaxy (HVPE) process growth was therefore developed in this thesis for the growth of GaAs nanowires. This report is organized into two chapters.The first chapter introduces the state-of-the-art of self-catalyzed GaAs nanowires and nano-structures on silicon substrate. We have demonstrated the growth of self - catalyzed GaAs nanowires by HVPE on un-patterned Si (111) substrates at a low temperature of 600 °C with extremely high GaCl/AsH3 flow ratios. A model that explains well the experimental findings was developed. The second part proposes the design of a Microbial Fuel Cell (MFC) prototype based on GaAs nanowire samples. A MFC prototype based on GaAs nanowire and substrate was developed
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Li, Suiqiong. "Development of novel acoustic wave biosensor platforms based on magnetostriction and fabrication of magnetostrictive nanowires." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Dissertations/LI_SUIQIONG_40.pdf.
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Mallampati, Bhargav. "Development of High Gain Ultraviolet Photo Detectors Based on Zinc Oxide Nanowires." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500106/.
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Semiconductor nanowires acts as an emerging class of materials with great potential for applications in future electronic devices. Small size, large surface to volume ratio and high carrier mobility of nanowires make them potentially useful for electronic applications with high integration density. In this thesis, the focus was on the growth of high quality ZnO nanowires, fabrication of field effect transistors and UV- photodetectros based on them. Intrinsic nanowire parameters such as carrier concentration, field effect mobility and resistivity were measured by configuring nanowires as field effect transistors. The main contribution of this thesis is the development of a high gain UV photodetector. A single ZnO nanowire functioning as a UV photodetector showed promising results with an extremely high spectral responsivity of 120 kA/W at wavelength of 370 nm. This corresponds to high photoconductive gain of 2150. To the best of our knowledge, this is the highest responsivity and gain reported so far, the previous values being responsivity=40 kA/W and gain=450. The enhanced photoconductive behavior is attributed to the presence of surface states that acts as hole traps which increase the life time of photogenerated electrons raising the photocurrent. This work provides the evidence of such solid states and preliminary results to modify the surface of ZnO nanowire is also produced.
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Huang, Aijun. "Alloy and process development in cast TiAl-based materials." Thesis, University of Birmingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433490.
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A new quenching and ageing treatment to refine microstructures of a number of cast .TiAI-based alloys has been assessed. This has been done by using Jominy end quenching, to better understand the continuous cooling transformation behaviour of the different alloys, followed by an investigation of the response of the transformed samples to ageing in optimally quenched samples. Ti-46AI-8Ta, Ti-46Al-8Nb, Ti-46AI-5Nb-W, Ti-47AI-2Nb-lMn-lW-O.2Si and Ti-48AI-2Nb-2Cr, have been investigated and the importance of boron content, grain size and oxygen content have been investigated for Ti-46AI-8Nb. It has been found that heavy elements such as Nb and Ta broaden the range of cooling rates over which a fully massively structure can be obtained. The addition of boron leads to the formation of fully lamellar structures over a wide range of cooling rates by suppressing the massive transformation, the feathery and the Widmanstatten transformation. The prior a. grain size also suppresses the massive transformation independent of whether the grain size was achieved by heat treatment or by addition of boron. It has been found that the responses of both high and low oxygen-containing samples are similar at high cooling rates, but are very different at intermediate and low cooling rates. The amount of massive gamma which appears to be nucleated away from the original alpha boundaries is also strongly influenced by cooling rate and oxygen content. It is proposed that the low diffusivity of such heavy elements retards diffusion-controlled phase transformations (feathery and lamellar) so that the partitionless massive transformation can take place at lower cooling rates. In fine-grained samples the dominance of the lamellar microstructure is interpreted in terms of the role of grain boundaries in nucleating lamellae at temperatures above the massive start temperature. The complex role of oxygen is interpreted in terms of the ·stabilisation of a. by oxygen and by the extent of the segregation of oxygen during quenching. The observations made using the Jominy end quenching technique led to the selection of salt bath quenching as the optimum technique to develop crack-free fully massively transformed samples and these have been used to investigate the influence of different ageing schedules (carried out using the HIP (hot isostatic pressing) cycle used for • structural castings) on the microstructure and properties of quenched and aged samples. It has been found that the formation of subgrains during the massive transformation, precipitation of a on the sub grain boundaries and precipitation of a on the four {Ill} planes of the gamma within these sub grains during ageing lead to \:onsiderable refinement of microstructures. The influence of the ageing treatment has been studied by ageing at different temperatures within the two phase field and by two step ageing at low and high temperatures. It has been found that the finest microstructures are obtained by low temperature ageing followed by short, higher temperature ageing. The influence of the ageing sequence on the microstructures is explained in terms of the factors influencing the nucleation and growth, of a precipitates at different ageing temperatures. Room temperature tensile tests have been carried out on salt bath quenched samples aged using either one step or two step ageing. It has been found that one-step ageing brings a more significant improvement in room temperature tensile properties than two-step ageing, where the best properties are found in samples aged at low temperatures, followed by a short excursion into the single a phase field. Two separate appendixes, studying mechanism of Widrnanstiitten transformation and embrittlement of TiAl-based alloys after exposure at service temperatures are given at the end of the thesis.
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Mazwi, Sive. "Hydrogen storage in Ti-based coatings and Ti6Al4V alloy." University of the Western Cape, 2016. http://hdl.handle.net/11394/5319.
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>Magister Scientiae - MScHydrogen has been regarded as an ideal energy carrier for future, it can be stored as a liquid in cryogenic tanks, a gas in high pressure cylinders and as solid in metal hydrides. Hydrogen storage in metal hydrides is of research interest because hydrides often have high energy density than gas or liquid hydrogen and are relatively safe. Ti and Ti alloys are promising hydrogen storage material because they have high affinity for hydrogen, light in weight and react reversibly with hydrogen. This work aims to investigate the hydrogen storage capacity of CP- Ti and Ti6Al4V alloy and Pd/Ti6Al4V alloy, where Pd was deposited on Ti6Al4V alloy. Samples were hydrogenated from room temperature to 650 °C at atmospheric pressure in the vacuum furnace under the 15%H/Ar atmosphere. Hydrogenation was carried out for a period of 3 hours for all samples. Sample composition and layer thickness were determined using Rutherford backscattering spectrometry. The microstructure and phase transformation were investigated using optical microscopy and X-ray diffraction technique. Hydrogen storage capacity was determined using elastic recoil detection analysis and gravimetric method. It was found that hydrogenation temperature has an effect on hydrogen absorption, microstructure and phase transformation. Maximum hydrogen concentration was obtained at hydrogenation temperatures of 550 °C for all materials with 45.57 at.% in CP-Ti, 34.77 at.% in Ti6Al4V alloy and 39 at.% H in Pd/Ti6Al4V coated system. In CP-Ti it was found that hydrogen absorption begins at 550 °C and decreases at hydrogenation temperature of 650 °C and that hydrogenation at both temperatures leads to formation of titanium hydrides and needlelike microstructure. At temperatures below 550 °C no hydrides were formed. For Ti6Al4V alloy ERDA results showed that no significant hydrogen absorption occurred at temperatures below 550 °C and at hydrogenation temperature of 650 °C, hydrogen absorption decreased drastically. The δ- titanium hydride was detected in the sample hydrogenated at 550 °C. Fine needle like microstructure was observed in the sample hydrogenated at 550 °C, and at higher temperature (650 °C ) coarse needles were formed. Pd coatings on Ti6Al4V alloy was found to increase the absorption of hydrogen, and allowing hydrogen to be absorbed at low temperatures.
National Research Foundation (NRF)
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Ahmed, Rizwan, and Shahid Abbas. "Electrical and Optical Characteristics of InP Nanowires based p-i-n Photodetectors." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-13915.
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Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors are classified based on their different structure, fabrication technology, applications and different sensitivity. Infrared photodetectors are widely used in many applications such as night vision, thermal cameras, remote temperature sensing, and medical diagnosis etc. All detectors have material inside that is sensitive to incoming light. It will absorb the photons and, if the incoming photons have enough energy, electrons will be excited to higher energy levels and if these electrons are free to move, under the effect of an external electric field, a photocurrent is generated. In this project Fourier Transform Infrared (FT-IR) Spectroscopy is used to investigate a new kind of photodiodes that are based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied respectively. Polarization effects (at low and high Temperatures) have been investigated. The experiments are conducted for different samples with high concentration of NWs as well as with lower concentration of NWs in the temperature range from 78 K (-195ºC) to 300 (27ºC). These photodiodes are designed to work in near infrared (NIR) spectral range. The results show that the NW photodetectors indeed are promising devices with fairly high break down voltage, change of photocurrent spectra with polarized light, low and constant reverse saturation current (Is). The impact of different polarized light on photocurrent spectra has been investigated and an attempt has been made to clarify the observed double peak of InP photocurrent spectrum. Our investigations also include a comparison to a conventional planar InP p-i-n photodetector.
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Tanaka, Hajime. "Theoretical Study on Carrier Transport in Semiconductor Nanowires Based on Atomistic Modeling." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225606.
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Musolino, Mattia. "Growth, fabrication, and investigation of light-emitting diodes based on GaN nanowires." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17409.
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Diese Arbeit gibt einen tiefgehenden Einblick in verschiedene Aspekte von auf (In,Ga)N/GaN Heterostrukturen basierenden Leuchtdioden (LEDs), mittels Molekularstrahlepitaxie entlang der Achse von Nanodrähten (NWs) auf Si Substraten gewachsen. Insbesondere wurden die Wachstumsparameter angepasst, um eine Koaleszierung der Nanodrähte zu vermindern. Auf diese Weise konnte die durch die NW-LEDs emittierte Intensität der Photolumineszenz (PL) um einen Faktor zehn erhöht werden. Die opto-elektronischen Eigenschaften von NW-LEDs konnten durch die Verwendung von Indiumzinoxid, anstatt von Ni/Au als Frontkontakt, verbessert werden. Zudem wurde demonstriert, dass auch selektives Wachstum (SAG) von GaN NWs auf AlN gepufferten Si Substraten mit einer guten Leistungsfähigkeit von Geräte vereinbar ist und somit als Wegbereiter für eine neue Generation von NW-LEDs auf Si dienen kann. Weiterhin war es möglich, strukturierte Felder von ultradünnen NWs durch SAG und thermische in situ Dekomposition herzustellen. In den durch die NW-LEDs emittierten Elektrolumineszenzspektren (EL) wurde eine Doppellinenstruktur beobachtet, die höchstwahrscheinlich von den kompressiven Verspannungen im benachbarten Quantentopf, durch die Elektronensperrschicht verursachten, herrührt. Die Analyse von temperaturabhängigen PL- und EL-Messungen zeigt, dass Ladungsträgerlokalisierungen nicht ausschlaggebend für die EL-Emission von NW-LEDs sind. Die Strom-Spannungs-Charakteristiken (I-V) von NW-LEDs unter Vorwärtsspannung wurden mittels eines Modells beschrieben, in das die vielkomponentige Natur der LEDs berücksichtigt wird. Die unter Rückwärtsspannung aktiven Transportmechanismen wurden anhand von Kapazitätstransientenmessungen und temperaturabhänigigen I-V-Messungen untersucht. Dann wurde ein physikalisches Modell zur quantitativen Beschreibung der besonderen I-V-T Charakteristik der untersuchten NW-LEDs entwickelt.This PhD thesis provides an in-depth insight on various crucial aspects of light-emitting diodes (LEDs) based on (In,Ga)N/GaN heterostructures grown along the axis of nanowires (NWs) by molecular beam epitaxy on Si substrates. In particular, the growth parameters are adjusted so as to suppress the coalescence of NWs; in this way the photoluminescence (PL) intensity emitted from the NW-LEDs can be increased by about ten times. The opto-electronic properties of the NW-LEDs can be further improved by exclusively employing indium tin oxide instead of Ni/Au as top contact. Furthermore, the compatibility of selective-area growth (SAG) of GaN NWs on AlN-buffered Si substrates with device operation is demonstrated, thus paving the way for a new generation of LEDs based on homogeneous NW ensembles on Si. Ordered arrays of ultrathin NWs are also successfully obtained by combining SAG and in situ post-growth thermal decomposition. A double-line structure is observed in the electroluminescence (EL) spectra emitted by the NW-LEDs; it is likely caused by compressive strain introduced by the (Al,Ga)N electron blocking layer in the neighbouring (In,Ga)N quantum well. An in-depth analysis of temperature dependent PL and EL measurements indicates that carrier localization phenomena do not dominate the EL emission properties of the NW-LEDs. The forward bias current-voltage (I-V) characteristics of different NW-LEDs are analysed by means of an original model that takes into account the multi-element nature of LEDs based on NW ensembles by assuming a linear dependence of the ideality factor on applied bias. The transport mechanisms in reverse bias regime are carefully studied by means of deep level transient spectroscopy (DLTS) and temperature dependent I-V measurements. The physical origin of the detected deep states is discussed. Then, a physical model able to describe quantitatively the peculiar I-V-T characteristics of NW-LEDs is developed.
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Chatterjee, Dipanwita. "Insights into Nucleation, Growth and Shape Control for Designing Anisotropic Nanostructures and Heterostructures." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5357.
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The properties of nanomaterials significantly depend on the size and shape of the nanocrystals. Thus the size and shape control becomes an important and interesting aspect of nanocrystal synthesis. Wet chemical method of synthesis of nanomaterials is an efficient bottom-up approach. It starts at the molecular level and the rate of the reaction can be monitored and regulated at various stages of reaction, thus enabling one to have a better control over the final morphology of the nanocrystal. In order to carry out a morphology controlled synthesis strong understanding of nucleation and growth of a nanocrystal is essential. According to the classical theory of nucleation, the nucleus at its critical radius of nucleation has a shape that is geometrically identical to the equilibrium morphology of the crystal. Into the growth regime the growth of the nucleus happens by attachment of atoms at the growing interfaces of the nucleus. If the rate of attachment is equal at all the growing interfaces the final morphology is called an “equilibrium morphology”. On the other hand, if
the attachment of atoms is not equal at all the growing interfaces it results in the generation of a host of different kinetic shapes or “growth morphologies”. The variation in the rate of growth in different facets can be brought about by selectively attaching capping agents to the different facets, for example. Equilibrium shape is the thermodynamic shape of the crystal and is obtained on minimization of the total surface free energy of the system.
Growth morphologies on the other hand can be subdivided into – (a) symmetry conserving growth morphologies or (b) symmetry breaking / anisotropic growth morphologies depending on whether the point group symmetry of the nucleus has been retained in the
final growth morphology or not. The symmetry will be retained if all the equivalent planes in the nucleus are affected in the same way during the course of the reaction. For example, if the growth of all the 8 {111} planes of a cuboctahedron is stopped and all the 6 {100} planes outgrow the {111} planes, the resulting shape is that of an octahedron. Under some
special circumstances, if the growth of one set of {111} planes is different from the rest of the {111} planes, the resulting shape becomes anisotropic or symmetry breaking. Through this dissertation, a fundamental insight into the heterogeneous nucleation and equilibrium
shapes is obtained and with the help of this understanding, few interesting 1 dimensional
anisotropic nanostructures and heterostructures have been designed by wet chemical synthesis method. Some of these nanostructures have shown excellent activity as electrocatalysts and substrates for surface enhanced Raman spectroscopy. In conclusion, a discussion of the future prospects involving these vast variety of nanostructures has been presented. The knowledge and insights gained from the study in this dissertation can be utilised in predicting and designing growth of similar or related nanostructures and nanoheterostructures
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Lee, Soohwan. "First principles-based atomistic modeling of the structure and nature of amorphous Au-Si alloys and their application to Si nanowire synthesis." 2008. http://hdl.handle.net/2152/18244.
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A great deal of attention has been paid to semiconductor nanowires due to their compatibility of conventional silicon-based technology. Metal-catalytic vapor-liquidsolid (VLS) and various solution-based techniques have widely been used to synthesize silicon/germanium (Si/Ge) nanowires. It is well characterized that the crystallographic orientations, diameter sizes, and surface morphologies of semiconductor nanowires can be controlled by varying process conditions and metal catalysts. Earlier experimental and theoretical studies have identified mechanism underlying metal catalyzed Si/Ge nanowire growth, involving Si/Ge diffusion into a metal catalyst, eutectic Si/Ge-catalyst alloy formation, and Si/Ge precipitation at the catalyst-nanowire interface. However, little is known about the atomic-level details of the structure, energetics and dynamics of amorphous metal alloys such as gold-silicon (Au-Si) and gold-germanium (Au-Ge) despite their importance for well controlled synthesis of Si/Ge nanowires, which is essential for the success of Si/Ge nanowires-based applications. Experiments provide many clues to the fundamental aspects of the behavior and properties of metal alloys, but their interpretations often remain controversial due largely to difficulties in direct characterization. While current experimental techniques are still limited to providing complementary atomic-level, real space information, first principles based atomistic modeling has emerged as a powerful means to address the structure, function and properties of amorphous metallic alloys. This thesis work has focused on developing a detailed understanding of the atomic structure, energetics, and oxidation of Au-Si alloys, as well as molecular mechanisms underlying Au-catalyzed Si nanowire growth. In addition, the surface reconstruction and chemistry of Si nanowires has been examined, with comparisons to planar Si surfaces. In this dissertation, based on first principles atomistic simulations, we present: 1) the atomic structure, energetics, and chemical ordering of amorphous Au-Si alloys with varying Au:Si composition ratios; 2) the behavior of boron (B) in the Au-Si alloy, such as diffusion and agglomeration, and the effect of B addition on the atomic distribution of Si and Au, with implications for in-situ doping of Si nanowires; 3) the origin and structural ordering of Si surface segregation in the Au-Si alloy, providing important insights into the nucleation and early-stage growth of Si nanowires; 4) the interfacial interaction between the Au-Si alloy and various facets of crystalline Si, such as (111), (211), (110), (110), which explains well the underlying reasons for the growth direction of Si nanowires; 5) the oxidation of the Au-Si alloy; and 6) the surface reconstruction and chemistry of Si nanowires with comparisons to planar Si surfaces. Outcomes from the thesis work contribute to: clarifying the atomic structure, energetics and chemical ordering of amorphous bulk Au-Si alloys, as well as their surfaces and interfaces; better understanding molecular mechanisms underlying the Aucatalyzed synthesis of Si nanowires; and identifying the surface reconstruction and chemistry of Si nanowires. The improved understanding can provide invaluable guidance on the rational design and fabrication of Si nanowire-based future electronic, chemical, and biological devices. This thesis work also offers a theoretical platform for studying metal alloy systems with various applications.text
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Burr, Loïc. "Ion-track technology based synthesis and characterization of gold and gold alloys nanowires and nanocones." Phd thesis, 2016. https://tuprints.ulb.tu-darmstadt.de/5541/1/Thesis-Lo%C3%AFc-Burr-e-print.pdf.
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Metallic nanostructures are attracting growing interest because of their potential application in various devices such as batteries, solar cells, or drug delivery systems. This thesis focuses on the synthesis and characterization of three different nanostructures: (1) solid cylindrical AuAg nanowires with controlled composition and size, fabricated by electrodeposition in etched ion-track membranes with cylindrical channels, (2) porous cylindrical Au nanowires attained by selective dealloy-ing of AuAg nanowires, and (3) Au nanocones synthesized by electrodeposition in conical channels.
AuAg nanowires with controlled diameter and composition, namely Au, Au40Ag60, Au60Ag40, and Ag were synthesized and characterized. By dealloying these nanowires were converted into porous Au-based nanowires with diameters above and below 100 nm possessing an enhanced surface area. Surface morphology and com-position of the nanostructures before and after dealloying were studied by means of high spatial resolution energy-dispersive X-ray spectroscopy (EDX) in a high-resolution transmission electron microscope (TEM). The results demonstrate surface segregation effects in solid AuAg nanowires that strongly vary with the initial composition. Surface segregation occurs on a time scale of days (< 3 days) inde-pendently of the wire dimensions. After dealloying of Au40Ag60 nanowires, the porous nanowires have a silver content below 10% and ligament size from 5 to 30 nm. Solid and porous wires are particularly attractive for future applications, e.g., in sensorics. The characterization of such small nanostructures regarding, e.g. electrical transport properties, requires suitable contacts. Special designs to contact nanowires by laser lithography as well as by using pre-patterned templates were developed.
Gold nanocones with sharp tips down to 50 nm diameter and several microns large bases were fabricated. Given by this special geometry, the nanostructures exhibit a high mechanical stability and are freestanding with an aspect ratio of 500 and above. Stable gold nanocone arrays are attractive for a large range of applications including field emission and as coating for hydrophobic surfaces. In this work, the standard wire deposition process from base to tip was inverted in order to improve the electrical and thermal contact of the nanocones to the substrate. After selective removal of the template, 30 µm long gold nanocones with ~ 50 nm sharp tips were freestanding and vertically aligned. Such structures are highly tunable in terms of cone dimensions and number density. The field emission properties of patterned nanocone arrays, investigated in collaboration with the Bergische Universität Wuppertal, exhibit field enhancement factors between 200 and 1000 as well as a maximum emission current ranging from ~ 1 to 100 μA.
The results presented in this thesis emphasize the variety of possibilities that ion-track technology offers in order to tailor dimensions and characteristics of nanostructures.
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Phillips, Francis Randall. "Fabrication and Characterization of Nanowires." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8355.
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The use of nanostructures has become very common throughout high-tech industries.
In order to enhance the applicability of Shape Memory Alloys (SMAs) in
systems such as Nano-Electromechanical Systems, the phase transformation behavior
of SMA nanostructures should be explored. The primary focus of this work is on the
fabrication of metallic nanowires and the characterization of the phase transformation
of SMA nanowires. Various metallic nanowires are fabricated through the use of the
mechanical pressure injection method. The mechanical pressure injection method is a
template assisted nanowire fabrication method in which an anodized aluminum oxide
(AAO) template is impregnated with liquid metal. The fabrication procedure of the
AAO templates is analyzed in order to determine the effect of the various fabrication
steps. Furthermore, metallic nanowires are embedded into polymeric nano bers as a
means to incorporate nanowires within other nanostructures.
The knowledge obtained through the analysis of the AAO template fabrication
guides the fabrication of SMA nanowires of various diameters. The fabrication of
SMA nanowires with di fferent diameters is accomplished through the fabrication of
AAO templates of varying diameters. The phase transformation behavior of the fabricated
SMA nanowires is characterized through transmission electron microscopy.
By analyzing the fabricated SMA nanowires, it is found that none of the fabricated
SMA nanowires exhibit a size eff ect on the phase transformation. The lack of a
size e ffect on the phase transition of SMA nanowires is contrary to the results for
SMA nanograins, nanocrystals, and thin films, which all exhibit a size eff ect on the phase transformation. The lack of a size eff ect is further studied through molecular
dynamic simulations. These simulations show that free-standing metallic nanowires
will exhibit a phase transformation when their diameters are sufficiently small. Furthermore,
the application of a constraint on metallic nanowires will inhibit the phase
transformation shown for unconstrained metallic nanowires. Therefore, it is concluded
that free-standing SMA nanowires will exhibit a phase transformation throughout the
nanoscale, but constrained SMA nanowires will reach a critical size below which the
phase transformation is inhibited.
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Zhen-BangTey and 鄭振邦. "The Preparation and Applications of Magnetic Alloy Nanowires." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/85586135939471703247.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
101
One-dimensional magnetic materials with large magnetic anisotropy have been intensively studied. Its unique high aspect ratio characteristic has been widely used in various fields. Many methods including template-assisted growth, magnetic-field assisted hydrothermal, solvothermal synthesis and electrospinning have been developed to design and fabricate 1D magnetic nanostructures, but these methods usually suffer from tedious procedures, high temperature, high pressure, long reaction and templates. In this study, we demonstrate a magnetic-field induced wet chemical reduction method which is rapid and inexpensive approach to fabricate 1D magnetic materials at room temperature with a fast reaction rate and a high yield. In order to improve the magnetic properties of 1D materials, first, we use nickel chloride and cobalt acetate as the metal salt precursor to fabricate Ni-Co alloy nanowires. The magnetic properties were studied by superconducting quantum interference device (SQUID). The saturation magnetization (Ms) increases by increasing the mole fraction of cobalt. The saturation magnetization of pure Ni nanowires were determined to be about 60.52emu/g, while Ni9Co1, Ni8Co2 and Ni7Co3 alloy nanowire samples were determined to be about 74.47, 90.4, 112.59emu/g, respectively. Ni-Fe alloy nanowires were also fabricated using the similar method. The values of saturation magnetization of Ni9Fe1 and Ni8Fe2 alloy nanowire samples were determined to be about 81.24 and 112.76emu/g, which are higher than the pure Ni nanowires. Since the magnetic properties of cobalt are relatively higher than nickel, we attempt to fabricate the cobalt nanowires. The particle structure can be observed when the ratio of the Ni-Co was up to 6:4 in the system, where water was used as the solvent, and sodium citrate as the dispersant. Cobalt flower-like structure can be also observed when the ratio Ni:Co=0:10. However, changing the solvent to ethylene glycol can prevent the occurrence of the flower-like structure significantly and the Ni, Ni7Co3, Ni5Co5, Ni3Co7 and Co nanowires were fabricated successfully. The saturation magnetization of the 1D cobalt wire were determined to be about 176emu/g which is higher than the 0D cobalt sphere (160emu/g). In this work, we also used the similar method to fabricate Ni-Pt, Ni-Pd nanowires in the different ratios of 9:1, 8:2, 7:3 and 6:4. The degree of alloy becomes more obvious by increasing the composition of Pt or Pd. The diffraction angle also changed approximately with the linear function to the composition of Pt or Pd. Furthermore, Ag dendrites were successfully grown on the chelated copolymer template. The complete dendrites were grown under the PVP concentration of 0.1μM. Moreover, the membrane with Ag dendrites was used as Surface-enhanced Raman Spectroscopy (SERS) substrate and the characteristic peaks of R6G were successfully enhanced in the spectrum.
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Li, Zhong. "Growth and Characterization of ZnSe and ZnTe Alloy Nanowires." Thesis, 2012. http://hdl.handle.net/1807/33854.
Full textAbstract:
The objective of this thesis is to explore the synthesis and characterization of high quality binary ZnTe nanowires with great potential for development of optoelectronic devices including high efficiency photovoltaic cells for energy conversion and high sensitivity photodetectors for green fluorescent protein bioimaging at single molecule level.
To systematically explore the fabrication process for high quality nanowires, a chemical vapour deposition system was built for nanowire growth. Computational fluid dynamics simulations were used to optimize the reactor and growth parameters.
The simulations were validated by experimental measurements. Room temperature photoluminescence measurements showed that high crystal quality with very low defects by single step growth was achieved. This single step growth technique makes a great improvement compared to the reported growth followed by annealing, which achieved equivalent crystal quality. This simplification could be of use in large scale synthesis of nanowires.
The simulation results also showed that reactant species concentration is a key factor influencing the growth. A metal-organic chemical vapour deposition system was thus built to independently control reactant concentrations for ZnTe nanowire growth.
Temperature-dependent photoluminescence measurements of as-grown ZnTe nanowires showed a strong near band-edge emission. In addition, a deep level oxygen-related band was observed for the first time. From the detailed analysis of thermal quenching of the photoluminescence, it was shown that the deep level emission was partially from the intermediate band of the material. This is of great importance due to the theoretical absorption efficiency that is as high as 63% for intermediate band materials, which is more than two times of that of current single junction concentrators, and few materials possessing this property.
Individual ZnTe nanowires, grown after optimization, were patterned and contacted, and their conductivity and photoconductivity were measured at room temperature. A single ZnTe nanowire serving as a photodetector was shown to have the highest reported visible responsivity of 360 A/W (at 530 nm), and a gain of 8,640 (at 3 V bias). The responsivity is roughly 18 times higher than that of silicon avalanche photodiodes. This demonstrates that ZnTe nanowires are strong candidates for single photon detection.
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Hu, Chen-Yu, and 胡宸瑜. "Growth and Analysis of AuMn Alloy-Catalyzed Si Nanowires." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/udt6hp.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
105
Because of the transport property of semiconductors and the ability to control the electron spin, diluted magnetic semiconductor nanowires have good potential in spintronic applications. The confinement effect in the nanowire structure also improves the spin relaxation in the spintronic devices. In addition, manganese can provide large magnetic moment in silicon, Mn-doped Si nanowires is therefore an ideal candidate for spintronic devices. However, the low solubility of manganese in silicon making it very difficult to fabricate manganese-doped silicon nanowires. In this study, the process window of growing Si nanowire using AuMn and pure Mn catalysts via the vapor-liquid-solid mechanism (VLS) in a chemical vapor deposition (CVD) reactor is firstly investigated. Analyses on the resulted structure and composition distribution and the effects from the growth substrates are discussed. The Ge sites in SiGe nanowires helps the incorporation of Mn in the nanowires. Thus, the second part of this study focuses on the incorporation of Mn into SiGe nanowires through oxidizing the as-grown AuMn/SiGe nanowires to form a SiGe section with a higher Ge content. The morphology change of the nanowire due to the oxidation process and the change of chemical distribution is discussed.
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Zhang, Xi Dickey Elizabeth C. "Size effects in alloy and heterostructured Si₁-x[subscript]Gex[subscript] nanowires." 2009. http://etda.libraries.psu.edu/theses/approved/PSUonlyIndex/ETD-4198/index.html.
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