Dissertations / Theses on the topic 'Nanowire'
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1
Pfüller, Carsten. "Optical properties of single semiconductor nanowires and nanowire ensembles." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16360.
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Diese Arbeit beschreibt die optische Charakterisierung mittels Photolumineszenzspektroskopie (PL) von Halbleiter-Nanodrähten (ND) im allgemeinen und einzelnen GaN-ND und GaN-ND-Ensembles im speziellen. ND werden oftmals als vielversprechende Bausteine zukünftiger, kleinster Bauele- mente bezeichnet. Diese Vision beruht insbesondere auf einigen attraktiven Eigenheiten, die ND im allgemeinen zugeschrieben werden. Im ersten Teil dieser Arbeit werden exemplarisch einige dieser Eigenschaften näher untersucht. So wird anhand von temperaturabhängigen PL-Messungen an Au- und selbstinduzierten GaAs/(Al,Ga)As-ND der Einfluss des Keimmaterials auf die PL der ND untersucht. Weiterhin werden die optischen Eigenschaften von ZnO-ND untersucht, die auf Si-, Saphir- und ZnO-Substraten gewachsen wurden. Die optische Charakterisierung von GaN-ND nimmt den Hauptteil dieser Arbeit ein. Die detaillierte Untersuchung einzelner GaN-ND und von GaN-ND-Ensembles zeigt die Relevanz des großen Oberflächen-zu-Volumen-Verhältnisses und dass jeder ND ganz eigene optische Eigenschaften aufweist. Die unerwartet starke Verbreiterung des strahlenden Übergangs donatorgebundener Exzitonen wird durch das vermehrte Auftreten von Oberflächendonatoren erklärt, deren statistische Relevanz durch PL-Messungen an einzelnen ausgestreuten und freistehenden GaN-ND nachgewiesen werden kann. Weiterhin wird der Einfluss elektrischer Felder auf die optischen Eigenschaften von GaN-ND ermittelt. Die Ein- und Auskopplung von Licht mit GaN ND wird mithilfe von Reflektanz- und Ramanmessungen bestimmt. Die zentralen Ergebnisse dieser Arbeit motivieren die Einführung eines Modells, dass die typischerweise nichtexponentielle Rekombinationsdynamik in ND-Ensemblen erklärt. Es basiert auf einer Verteilung der Rekombinationsraten. Vorläufige Ergebnisse dieses Modells beschreiben das nichtexponentielle Rekombinationdynamik in GaN ND-Ensemblen zufriedenstellend und erlauben eine Abschätzung ihrer internen Quanteneffizienz.This thesis presents a detailed investigation of the optical properties of semiconductor nanowires (NWs) in general and single GaN NWs and GaN NW ensembles in particular by photoluminescence (PL) spectroscopy. NWs are often considered as potential building blocks for future nanometer-scaled devices. This vision is based on several attractive features that are generally ascribed to NWs. In the first part of the thesis, some of these features are examined using semiconductor NWs of different materials. On the basis of the temperature-dependent PL of Au- and self-assisted GaAs/(Al,Ga)As core-shell NWs, the influence of foreign catalyst particles on the optical properties of NWs is investigated. The effect of the substrate choice is studied by comparing the PL of ZnO NWs grown on Si, Sapphire, and ZnO substrates. The major part of this thesis discusses the optical properties of GaN NWs. The investigation of the PL of single GaN NWs and GaN NW ensembles reveals the significance of their large surface-to-volume ratio and that each NW exhibits its own individual recombination behavior. An unexpected broadening of the donor-bound exciton transition is explained by the abundant presence of surface donors in NWs. The existence and statistical relevance of these surface donors is confirmed by PL experiments of single GaN NWs which are either dispersed or free-standing. Furthermore, the influence of electric fields on the optical properties of GaN NWs is investigated and the coupling of light with GaN NWs is studied by reflectance and Raman measurements. The central results of this thesis motivate the introduction of a model that explains the typically observed nonexponential recombination dynamics in NW ensembles. It is based on a distribution of recombination rates. Preliminary simulations using this model describe the nonexponential decay of GaN NW ensembles satisfactorily and allow for an estimation of their internal quantum efficiency.
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Zhou, Jing Cao. "Microtubule-templated nanowire and nanowire arrays." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1495961141&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Rudolph, Andreas [Verfasser], and Werner [Akademischer Betreuer] Wegscheider. "MBE growth of GaAs nanowires and nanowire heterostructures / Andreas Rudolph. Betreuer: Werner Wegscheider." Regensburg : Universitätsbibliothek Regensburg, 2012. http://d-nb.info/1025386205/34.
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Woodruff, Jacob Huffman. "Deterministic germanium nanowire growth : controlling the position, diameter, and orientaion of germanium nanowires /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Sivakumar, Kousik. "Nanowire sensor and actuator." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 5.53 Mb., 108 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435931.
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Xu, Fei. "Optical fibre nanowire devices." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65527/.
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The Optical Fibre Nanowire (OFN) is a potential building block in future micro- and nano-photonic device since it offers a number of unique optical and mechanical properties. In this thesis, the background and fundamental features of nanowires are introduced; the theory, design and demonstration of novel nanowire devices are discussed. At first, a short adiabatic taper tip is manufactured, and it is used as optical tweezers for trapping 1μm microspheres. Then, the most important devices - the OFN resonators including the simple Optical Nanowire Loop Resonator (ONLR) and complicated 3D Optical Nanowire Microcoil Resonator (OMNR) - are investigated theoretically and experimentally. A one-turn loop resonator and two-, three-, and four-turn ONMR are demonstrated experimentally; several kinds of methods on optimizing the ONMR profile are presented to make the manufacture of high-Q ONMRs easier. In order to protect and stabilize the ONMR, embedding the device in Teflon is demonstrated. Finally, more applications in refractometric sensing are presented: schemes of sensors based on an embedded ONLR and ONMR are presented. The sensor sensitivities are calculated: 700 nm/RIU (RIU is the Refractive Index Unit) can be achieved at the wavelength of 970 nm for a diameter of 600 nm. Additionally, a refractometric sensor based on an embedded ONMR is demonstrated experimentally; its sensitivity is about 40 nm/RIU.
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Husain, Ali Scherer Axel. "Nanotube and nanowire devices /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-05252004-113507.
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Mrzel, A., A. Kovic, A. Jesih, and M. Vilfan. "Decoration of MoSI Nanowires with Platinum Nanoparticles and Transformation into Molybdenum-nanowire Nased Networks." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35168.
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In this communication, we present solution-based coating procedure of MoSI nanowires (NW) with
platinum nanoparticles. The average particle diameter was found to be around 2.82 nm, showing a narrow
size distribution. This single-step in situ reduction method at room temperature in water solution can
easily be applied for large-scale applications. We also prepared two-dimensional networks of MoSI NW
bundles by deposition via spraying from a purified stable dispersion in acetonitrile onto NaCl crystals and
nonconductive silicon wafer with pre-assembled molybdenum electrodes. The formation of a conductive
molybdenum network was achieved by annealing in hydrogen due to coalescence of the templates MoSI
bundles during transformation. Stable water dispersion of molybdenum NW network was prepared by
simply dissolving the NaCl substrate with molybdenum network on the surface.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35168
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Morioka, Naoya. "Fundamental Study on Carrier Transport in Si Nanowire MOSFETs with Smooth Nanowire Surfaces." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188599.
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Lee, Huyong. "Titanium Oxide Nanowire Growth by Oxidation Under a Limited Supply of Oxygen: Processing and Characterization." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1236191211.
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Alber, Ina [Verfasser], and Reinhard [Akademischer Betreuer] Neumann. "Synthesis and Plasmonic Properties of Metallic Nanowires and Nanowire Dimers / Ina Alber ; Betreuer: Reinhard Neumann." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1177039982/34.
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Xu, Sheng. "Oxide nanowire arrays for energy sciences." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42876.
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Oxide nanowire arrays are playing an important role in energy sciences nowadays, including energy harvesting, energy storage, and power management. By utilizing a wet chemical growth method, we demonstrated the capabilities of synthesizing density controlled vertical ZnO nanowire arrays on a general substrate, optimizing the aspect ratio of the vertical ZnO nanowire arrays guided by a statistical method, epitaxially growing patterned vertical ZnO nanowire arrays on inorganic substrates, epitaxially growing patterned horizontal ZnO nanowire arrays on non-polar ZnO substrates, and the lift-off of the horizontal ZnO nanowire arrays onto general flexible substrates. In addition, single crystalline PbZrxTi1-xO3 (PZT) nanowire arrays were epitaxially grown on conductive and nonconductive substrates by hydrothermal decomposition. Beyond that, based on the as-synthesized ZnO nanowire arrays, we demonstrated multilayered three dimensionally integrated direct current and alternating current nanogenerators. By integrating a ZnO nanowire based nanogenerator with a ZnO nanowire based nanosensor, we demonstrated solely ZnO nanowire based self-powered nanosystems. Also, utilizing a commercial full-wave bridge rectifier, we rectified the alternating output charges of the nanogenerator based on PZT nanowire arrays, and the rectified charges were stored into capacitors, which were later discharged to light up a laser diode (LD). In addition, blue/near-ultraviolet (UV) light emitting diodes (LED) composed of ordered ZnO nanowire arrays on p-GaN wafers were presented.
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Keilbach, Andreas. "Oriented Nanochannels for Nanowire Synthesis." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-117691.
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Guan, Nan. "Nitride nanowire light-emitting diode." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS372/document.
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Les nanofils nitrures présentent des propriétés optoélectroniques extraordinaires et sont considérés comme des matériaux prometteurs pour des diodes électroluminescentes (LEDs), grâce à leur haute qualité cristalline, leurs surfaces non-polaires, leur bonne flexibilité mécanique, leur rapport d’aspect élevé, etc.Cette thèse adresse la croissance, la fabrication, les caractérisations optiques et électriques et la simulation optique des dispositifs à base de nanofils nitrures, avec un accent particulier sur les LEDs à nanofils.Premièrement, cette thèse présente la croissance par épitaxie en phase vapeur aux organométalliques de nanofils nitrures cœur-coquille auto-assemblés contenant des puits quantiques InGaN/GaN sur les facettes plan m avec différentes concentrations d’In. Puis est décrite la fabrication de LEDs utilisant ces nanofils suivant deux différentes stratégies d’intégration (intégrations planaires et verticales).L’intégration planaire est basée sur des nanofils uniques dispersés horizontalement. J’ai proposé une plateforme photonique intégrée composée d’une LED à nanofil, d’un guide d’onde optimisé et d’un photodétecteur à nanofil. J’ai également développé un système d’alignement des nanofils.L’intégration verticale a pour objectif la réalisation de LEDs flexibles reposant sur une assemblée de nanofils verticaux encapsulées dans des polymères. Je montre que ceci permet la fabrication de LEDs flexibles monochromatiques, bi-couleurs ou blanches.Les nanofils épitaxiés sur des matériaux 2D par épitaxie de van de Waals sont faciles à décoller de leur substrat natif. Avec cette motivation, dans la dernière partie de cette thèse, j’ai étudié la croissance organisée des nanofils GaN sur du graphène micro et nano-structuré utilisant l’épitaxie par jets moléculairesNitride nanowires exhibit outstanding opto-electronic and mechanical properties and are considered as promising materials for light-emitting diodes (LEDs), thanks to their high crystalline quality, non-polar facets, good mechanical flexibility, high aspect ratio, etc.This Ph.D. thesis addresses the growth, the device fabrication, the optical and electrical characterizations and the optical simulations of III-nitride NW devices, with a special emphasis on the LED applications.First, this thesis presents the growth of m-plane InGaN/GaN quantum wells with different In concentrations in self-assembled core-shell nanowires by metal-organic chemical vapor deposition. Then, by using these nanowires, LED devices based on two different integration strategies (namely, in-plane and vertical integration) are demonstrated.The in-plane integration is based on the horizontally dispersed single nanowires. I have proposed a basic integrated photonic platform consisting of a nanowire LED, an optimized waveguide and a nanowire photodetector. I have also developed a nanowire alignment system using dielectrophoresis.The vertical integration targets the fabrication of flexible LEDs based on vertical nanowire arrays embedded in polymer membranes. Flexible monochromatic, bi-color, white LEDs have been demonstrated. Their thermal properties have been analyzed.The nanowires grown on 2D materials by van der Waals epitaxy are easy to be lifted-off from their native substrate, which should facilitate the fabrication of flexible nanowire devices. With this motivation, in the last part of this thesis, I have investigated the selective area growth of GaN NWs on micro- and nano- scale graphene by molecular beam epitaxy
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Li, Mingwei Mayer Theresa S. "Hybrid integration of nanowire resonator arrays." [University Park, Pa.] : Pennsylvania State University, 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2212/index.html.
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Saj, Damian, and Izabela Saj. "Nanowire-based InP solar cell materials." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-19455.
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In this project, a new type of InP solar cell was investigated. The main idea is that light is converted to electrical current in p-i-n photodiodes formed in thin InP semiconductor nanowires epitaxially grown on an InP substrate. Two different types of samples were investigated. In the first sample type (series C03), the substrate was used as a common p-type electrode, whereas a short p-segment was included in all nanowires for the second sample type (B07). Current – voltage (I-V) characteristics with and without illumination were measured, as well as spectrally resolved photocurrents with and without bias. The main conclusion is that the p-i-n devices showed good rectifying behavior with an onset in photocurrent that agrees with the corresponding energy band gap of InP. An interesting observation was that in series B07 (with included p-segments) the photocurrent was determined by the band gap of hexagonal Wurtzite crystal structure, whereas series C03 (without p-segments) displayed a photocurrent dominated by the InP substrate which has a Zincblende crystal structure. We found that the overall short-circuit current was ten as large for the latter sample, stressing the importance of the substrate as a source of photocurrent.
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Ramadan, Sami. "Silicon nanowire : fabrication, characterisation and application." Thesis, University of Newcastle upon Tyne, 2015. http://hdl.handle.net/10443/2984.
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This thesis focuses on the fabrication considerations and the characterisation of silicon nanowires and their integration into chemical sensors. One aim is to optimize a top-down fabrication process for silicon nanowires, in particular the methods that use optical lithography, wet etching and thermal oxidation. The main concerns here are to achieve a reproducible and high yield fabrication process and to obtain a controllable structure. Extensive work was carried out to study the parameters that affect the repeatability of the process. The properties of silicon nitride films, the oxidation method and the characteristics of the anisotropic etchant were found to be key parameters affecting the reproducibility of the process. Several silicon nitride films were deposited under various conditions and their optical properties were tested before and after thermal oxidation. It was found that the oxynitride thickness depends on the refractive index of the nitride film: the lower the refractive index, the thinner the oxynitride. Then an etching process was developed to selectively etch the oxidised silicon nitride over silicon dioxide. The etching process included two steps: firstly ion milling to remove the oxynitride film and secondly using boiling phosphoric acid to strip the silicon nitride film. Nitride-rich silicon nitride films exhibited higher etching selectivity over silicon dioxide compared with silicon-rich silicon nitride. Based on the etch selectivity, oxynitride thickness, and silicon dioxide thickness the maximum thickness of silicon nitride film that can be used to act as a mask during the fabrication of silicon nanowires was determined. The impact of oxidation method on the reliability of the process was studied, and SOI and bulk silicon samples were oxidised at the same temperature and time using lamp-based RTP radiation and also a furnace with resistive heating. The results showed that the SOI sample is colder than the bare silicon sample when both were heated using the lamp-based RTP. This effect was considered during the fabrication of silicon nanowires to obtain a reliable process. Comprehensive experimental measurements were carried out to compare the characteristics of Tetra-Methyl Ammonium Hydroxide (TMAH) and Potassium Hydroxide (KOH) etching to optimise the fabrication process. The use of TMAH was found to lead to a more reliable process. ii Another aim of the project was to characterise the fabricated devices, and for this the contact properties and the electrical properties of the silicon nanowires needed to be evaluated. Extensive electrical measurements were carried out to study the thermal stability and ohmic contact formation for the silicon nanowire. Three metallization schemes were studied: Al/Ti, Al/W/Ti and Al/Ti/AlOx. All these exhibited ohmic contact to the nanowires. However, Al/Ti/Si and Al/W/Ti/Si were found to be unstable after 425 °C RTP annealing. Al/Ti/AlOx/Si withstood this level of temperature but the contact resistance was about ten times higher than that of Al/W/Ti. The electrical resistivity of the silicon nanowires was then studied; it was found that the measured electrical resistivity decreases with the nanowire thickness. Several models were then developed to explain the apparent increase in resistivity. It was suggested it can be largely attributed to the reduction of the conductive area of the nanowire due to interface traps. Finally, a silicon nanowire sensor was designed and fabricated, and this sensor was used to detect the changes in pH. The preliminary results showed that the sensor detected the change of pH in the buffer solution. However, reliability and yield were low, which was assumed to be due to the large parasitic current between the source/drain and the buffer solution.
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Nerowski, Alexander. "Electrochemical Metal Nanowire Growth From Solution." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-118937.
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The aim of this work is to make electrochemical metal nanowire growth a competitive method, being up to par with more standardized procedures, like e.g. lithography. This includes on the one hand the production of nanowires as reliable and reproducible parts, potentially suited for nanoelectronic circuit design. Therefore, this work presents a systematic investigation of the causes of nanowire branching, the necessary conditions to achieve straight growth and the parameters affecting the diameter of the wires. The growth of ultrathin (down to 15 nm), straight and unbranched platinum nanowires assembly is demonstrated. On the other hand, it is the objective to go beyond purely electronic applications. An examination of the crystallography of the wires reveals nanoclusters inside the wire with a common crystallographic orientation. The versatility of the wires is illustrated by implementing them into an impedimetric sensor capable of the detection of single nanoscaled objects, such as bacteriaDie Zielstellung der vorliegenden Arbeit ist es, die elektrochemische Herstellung von metallischen Nanodrähten zu einer wettbewerbsfähigen Methode zu machen, die sich mit standardisierten Prozessen, wie z. B. der Lithographie messen kann. Dies beinhält auf der einen Seite die Produktion der Nanodrähte als zuverlässige und reproduzierbare Bauteile, die im nanoelektrischen Schaltungsdesign Verwendung finden können. Daher befasst sich diese Arbeit mit einer systematischen Untersuchung der Ursachen für die Verzweigung von Nanodrähten, den notwendigen Bedingungen um gerades Wachstum zu erlangen und mit den Parametern, die Einfluss auf den Durchmesser der Drähte haben. Der Wuchs von sehr dünnen (bis zu 15 nm), geraden und unverzweigten Nanodrähten aus Platin wird gezeigt. Auf der anderen Seite ist es erklärtes Ziel, über rein elektronische Anwendungen hinaus zu gehen. Eine Untersuchung der Kristallographie der Nanodrähte zeigt, dass die Drähte aus Nanopartikeln bestehen, die eine gemeinsame kristallographische Orientierung aufweisen. Die Vielseitigkeit der Drähte wird anhand einer Sensoranwendung gezeigt, mit der es möglich ist, einzelne nanoskalige Objekte (wie z. B. Bakterien) zu detektieren
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Opoku, Charles. "Solution processable nanowire field-effect transistors." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580355.
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The use of orientated semiconducting nanowires as the active material in solution processable printable transistors is an area of research that can offer enormous potential in the field of high performance electronics. Lightweight, flexible and low cost components that are compatible with plastic substrates can further increase the appeal of this field. Currently, the most commonly used materials for field-effect transistors in large area electronics are polycrystalline, amorphous silicon and organic semiconductors. However, these classes of semiconductors face several limitations with regards to their compatibility in plastic electronics, either due to their high temperature processing (silicon) or low charge carrier mobility (organics). The current work investigates alternative semiconductors based on nanomaterials that can be used as active layers in large area electronics, with performances comparable to or exceeding those of amorphous silicon which can be processed at much lower temperatures. In this thesis, we explore semiconducting inorganic nanowires including silicon, germanium, and zinc oxide nanowires as the channel material in field-effect transistors to realise high performance printed electronics. Several main challenges, such as deposition of nanowire 'inks', ohmic contacts to nanowires, surface states, and the use of organic dielectrics are addressed as follows: (1) Development of two new nanowire deposition methods based on either spray coating or dip-coating has led to alignment control for nanowires and also high density coatings on various substrates. These techniques can offer scalability for large area surfaces at room temperature. (2) Solving problems of making near-ohmic contacts m nanowire transistors fabricated at low temperatures ensured efficient charge injection m devices. Optimised FETs with high work function metal electrodes and treated nanowire surfaces exhibited high output currents reaching 1mA, high on/off current modulation of ~ 107, and high hole mobility in the range of 5-26cm2Ns. (3) Investigation of high Schottky barrier nanowire FETs led to better understanding of source contact barrier lowering by the gate field and the discovery of a new type of nanowire transistor operation that can offer improved power dissipation and near ideal current-voltage saturation. characteristics with drain voltage saturation of less than 2V, even at large gate voltages. (4) The control of nanowire surfaces, especially at the nanowire-insulator interface was achieved using low-k organic dielectrics and self-assembled monolayers. This also resulted in the demonstration of high performance p-type transistors exhibiting 10uA output current, on/off current ratio of ~107 and the high field-effect mobility in the range of 5-20cm2/V-s. (5) Finally, a high performance n-type ZnO nanowire transistor on a flexible plastic substrate with a low-k dielectric was demonstrated with output current of ~1uA, on/off current modulation of ~105, subthreshold voltage swing of ~O.26mV/dec and a field-effect mobility in the range of 49- 65cm2/V-s. In short, this thesis delivers a new realisation of a concept in which solution processable high performance electronic devices may be fabricated using low temperature processing steps on various substrates including plastics. The approach is general to a broad range of nanowire material systems and can be applied to e-paper, flexible displays, chemical and biological sensors, RFID tags, memory elements and ambient intelligence devices.
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Musin, Ildar R. "Rational engineering of semiconductor nanowire superstructures." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50338.
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Semiconductor nanowire synthesis provides a promising route to engineer novel nanoscale materials for applications in energy conversion, electronics, and photonics. The addition of methylgermane (GeH₃CH₃) to standard GeH₄/H₂ chemistry is demonstrated to induce a transition from <111> to <110> oriented growth during the vapor-liquid-solid synthesis of Ge nanowires. This hydride-based chemistry is subsequently leveraged to rationally fabricate kinking superstructures based on combinations of <111> and <110> segments with user defined angles and segment lengths. The addition of GeH₃CH₃ also eliminates sidewall tapering and enables Ge nanowire growth at temperatures exceeding 475 °C, which greatly expands the process window. User-programmable diameter modulation is demonstrated without kinking using tetramethyltin (Sn(CH₃)₄) or trimethylsilane (SiH(CH₃)₃) reacting directly on the sidewalls of growing nanowires to either block or allow conformal deposition. Catalyst modification with tetramethyltin is demonstrated to tune growth kinetics and provides further control over nanowire design. Morphological markers, generated via user-defined changes to diameter along the nanowire axial direction, enable a new approach to rapid, accurate, and facile extraction of growth rate information from electron microscopy images. The ability to engineer nanowire structure by tuning chemistry either at the nucleation point or on the sidewall is demonstrated in this work, thus enabling the rational fabrication of complex superstructures.
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Shougee, Abdurrahman. "High capacitance silicon nanowire array electrodes." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/59137.
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The interest in the development of improved, alternative and application-specific electrical energy storage solutions presents the opportunity for Si-based device with the functionality of electrochemical capacitors (ECs). Metal-assisted chemical etching (MACE) provides a low temperature and low-cost method of obtaining a high-density array of high aspect ratio silicon nanowires. The high surface area of the silicon nanowire arrays (SiNWA) is utilised to develop a high capacitance electrode, in conjunction with an ionic liquid (IL) electrolyte giving low volatility, high thermal stability, and high chemical stability enabling a higher operating voltage. High silicon reactivity necessitates passivation of the Si surface. A low temperature (120 °C) wet oxidation process provides a highly dense, ultra-thin (~1.4 nm) protective layer that extends the operating voltage and yields a high energy and power density, bringing the SiNWA electrode within the range of ECs. An alternative coating of metal oxide (TiO2) provides further performance improvement, and with energy and power densities of 0.9 and Wh·kg-1 and 2228 W·kg-1 respectively, places the developed SiNWA electrode towards the frontier of EC devices, as per the Ragone plot. Intermittent presence of apparent faradaic peaks observable on the cyclic voltammetry (CV) plots of SiNWA electrodes was analysed and attributed to the presence of deep level traps (DLTs) as a result of residual Ag from the MACE process. Multiple post-etch doping steps to degenerately dope the surface – pinning the Fermi level below the Si valence band – were found to mitigate the effect of the DLTs, improving the capacitive character and cycling stability of the electrodes.
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Nedic, Stanko. "Zinc oxide nanowire field effect transistors." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708233.
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Zhu, Xueni. "Silicon nanowire growth and electrical characterisations." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610055.
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Van, den Heever Thomas Stanley. "A zinc oxide nanowire pressure sensor." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5369.
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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.Thesis presented in partial fulfilment of the requirements for the degree Master of Science in Engineering at the University of Stellenbosch
ENGLISH ABSTRACT: Measurement of pressure with zinc oxide (ZnO) nanowires was investigated. ZnO exhibits the piezoelectric effect, generating a voltage when pressure is applied to the material. This relationship between pressure and output voltage was used to make a pressure sensor. A study of the physical and mathematical working of the piezoelectric effect in ZnO nanowires was done. Simulations were conducted by means of specialised software to test the theory. The simulations gave results as the theory had predicted. ZnO nanowires were grown using various methods. Vapour liquid solid (VLS) was found to be the best method to grow uniform and dense arrays of ZnO nanowires. Statistical methods were employed to obtain the optimal parameters for the growth of ZnO nanowires through the VLS method. After the growth of the ZnO nanowires a pressure sensor was built. The manufacturing of the pressure sensor consisted of different steps. The sensors were tested to verify that they worked as described in theory and as shown in the simulations. The output voltage was lower than the simulated value due to imperfections and losses throughout the system. The output voltage versus applied pressure graphs did coincide with the bulk ZnO materials as well as related products, such as force sensing resistors. The output voltage is too low, but there are various methods by which the output voltage can be increased. These methods are discussed. The finished sensor can be used to continuously monitor pressure on a plane.
AFRIKAANSE OPSOMMING: Die meting van druk deur sink oksied (ZnO) nanodrade was ondersoek. ZnO toon die piëzo-elektriese effek - spanning word gegenereer wanneer druk op die materiaal aangewend word. Hierdie verhouding tussen druk en uitsetspanning is gebruik om ’n druksensor te vervaardig. ’n Studie van die fisiese en wiskundige werking van die piëzo-elektriese effek in ZnO nanodrade is gedoen. Simulasies deur middel van gespesialiseerde sagteware is uitgevoer om die teorie te bevestig. Die simulasies het resultate getoon soos deur die teorie beskryf word. ZnO nanodrade is gegroei deur verskillende metodes. Verdamping vloeistof vastestof (VVV) is as die beste metode gevind om uniforme en digte skikkings van ZnO nanodrade te kry. Statistiese metodes is aangewend om die optimale parameters vir die groei van ZnO nanodrade deur middel van die VVV metode te kry. Na afloop van die groei van die ZnO nanodrade is ’n druksensor vervaardig. Die vervaardigingsproses het uit verskillende stappe bestaan, ten einde die bou van ’n werkende druksensor uit die ZnO nanodrade te realiseer. Die sensors is getoets om te bevestig dat dit werk, soos beskryf deur die teorie en gewys in die simulasies. Die uitsetspanning was laer as wat verwag was as gevolg van onvolmaakthede en verliese in die hele stelsel. Die uitsetspanning teenoor druk grafieke van die sensor het ooreengestem met die van die grootmaat materiale, asook verwante produkte soos druk sensitiewe weerstande. Die uitset spanning is baie laag en daar bestaan verskillende maniere waarop die uitsetspanning verhoog kan word. Hierdie metodes word bespreek.
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Pahara, Justin Gerald. "ZnO nanowire electrodes in bioelectronic devices." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/283923.
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Toomey, Emily. "Superconducting nanowire electronics for alternative computing." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127003.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 141-153).
With traditional computing systems struggling to meet the demands of modern technology, new approaches to both hardware and architecture are becoming increasingly critical. In this work, I develop the foundation of a power-efficient alternative computing system using superconducting nanowires. Although traditionally operated as single photon detectors, superconducting nanowires host a suite of attractive characteristics that have recently inspired their use in digital circuit applications for amplification, addressing, and memory. Here, I take advantage of the electrothermal feedback that occurs in resistively shunted nanowires to develop two new technologies: (1) A multilevel memory cell made by incorporating a shunted nanowire into a superconducting loop, allowing flux to be controllably added and stored; and (2) An artificial neuron for use in spiking neural networks, consisting of two nanowire-based relaxation oscillators acting analogously to the two ion channels in a biological neuron. By harnessing the intrinsic dynamics of superconducting nanowires, these devices offer competitive energy performance and a step towards bringing memory and processing closer together on the same platform.
by Emily Toomey.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Clavijo, William. "Nanowire Zinc Oxide MOSFET Pressure Sensor." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/625.
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Fabrication and characterization of a new kind of pressure sensor using self-assembly Zinc Oxide (ZnO) nanowires on top of the gate of a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is presented. Self-assembly ZnO nanowires were fabricated with a diameter of 80 nm and 800 nm height (80:8 aspect ratio) on top of the gate of the MOSFET. The sensor showed a 110% response in the drain current due to pressure, even with the expected piezoresistive response of the silicon device removed from the measurement. The pressure sensor was fabricated through low temperature bottom up ultrahigh aspect ratio ZnO nanowire growth using anodic alumina oxide (AAO) templates. The pressure sensor has two main components: MOSFET and ZnO nanowires. Silicon Dioxide growth, photolithography, dopant diffusion, and aluminum metallization were used to fabricate a basic MOSFET. In the other hand, a combination of aluminum anodization, alumina barrier layer removal, ZnO atomic layer deposition (ALD), and wet etching for nanowire release were optimized to fabricate the sensor on a silicon wafer. The ZnO nanowire fabrication sequence presented is at low temperature making it compatible with CMOS technology.
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Williams, Benjamin Luke. "CdTe nanowire structures for solar cells." Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/14653/.
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This thesis investigates the growth and characterisation of CdTe and core-double shell ITO/CdS/CdTe nanowires (NWs), ITO/ZnO/CdS/CdTe/Mo thin-film solar cells and ITO/ZnO/CdS/CdTe(NW)/CdTe/Mo core-triple shell NW solar cells. First, the generation of Au-catalysed CdTe NWs arrays on Mo foils is reported, with CdTe being deposited by close-space sublimation. NWs were up to 20 μm long, had diameters in the range 5 – 500 nm and densities in the range 106 – 107 cm-2. A vapour-liquid-solid mechanism of NW growth, mediated by a Au-Te liquid catalyst, which accounts for the initial delay to NW nucleation (and the observed film growth) is postulated. By fitting a theoretical model of NW growth to experimental NW radius-time data, values for the sidewall diffusion length (2 μm) and sticking probability (0.61) were obtained. NW growth was also achieved on CdTe/Mo, with higher NW densities (108 cm-2) achieved compared to growth directly on Mo. NW defects were evaluated by TEM and photoluminescence (PL). TEM analysis showed low-energy Σ = 3 grain boundaries present in the NWs, their incidence being dependent on the growth axis, which was either <110>, <111> or <112>. No high energy grain boundaries were observed. Their low-temperature PL spectra were dominated by excitonic emission with rarely observed above-gap emission also being recorded. PL also provided evidence of a deep level due to Au. UV-VIS-IR measurements showed that above-gap reflectance of NW arrays (~ 0.1%) was lower than for films of equivalent material (~ 10%). Methods of coating the NWs with conformal CdS and ITO shells were explored, with RF sputtering proving most suitable. HRTEM imaging demonstrated that the CdS/CdTe interface was epitaxial, the quality of the core-shell interface being thought to be critical for NW solar cells. Low temperature PL spectra of CdS/CdTe NWs showed CdS luminescence typical of single-crystal material and also implied that interdiffusion at the core-shell interface occurred. Above-gap reflectance for core-double shell ITO/CdS/CdTe NWs was ~ 0.1%. The fabrication procedures for thin-film CdTe devices on Mo foils were investigated so that understanding could be transferred to NW device fabrication. For thin-film devices, a peak efficiency of 8.0% was achieved upon incorporation of a double-anneal treatment process and a highly-resistive transparent ZnO layer. The main limitation to performance was the rectifying back contact, having a barrier height of = 0.51 eV. Methods to improve the quality of the contact are suggested based on device modelling. Simulations comparing the operation of thin-film and NW solar cells predict that when minority carrier diffusion lengths are short (< 0.7 μm), JSC enhancements can be achieved by adopting the NW device’s radial junction configuration. For the full NW device, efficiencies of 2.5% were obtained.
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Choe, Hwan Sung. "Modulated Nanowire Structures for Exploring New Nanoprocessor Architectures and Approaches to Biosensing." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10799.
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For the last decade, semiconducting nanowires synthesized by bottom-up methods have opened up new opportunities, stimulated innovative scientific research, and led to applications in materials science, electronics, optics, and biology at the nanoscale. Notably, nanowire building blocks with precise control of size, structure, morphology, and even composition in one, two, and three dimensions can successfully demonstrate high-performance electrical characteristics of field-effect transistors (FETs) and highly sensitive, selective, label-free, real-time biosensors in the fields of nanoelectronics and nano-biosensing, respectively. This thesis has focused on the design, synthesis, assembly, fabrication and electrical characterization of nanowire heterostructures for a proof-of-concept nanoprocessor and morphology-modulated kinked nanowire molecular nanosensor.Physics
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Coen, Tom. "Modeling multiple state electrostatically formed nanowire transistors." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9365/.
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The present thesis work proposes a new physical equivalent circuit model for a recently proposed semiconductor transistor, a 2-drain MSET (Multiple State Electrostatically Formed Nanowire Transistor). It presents a new software-based experimental setup that has been developed for carrying out numerical simulations on the device and on equivalent circuits.
As of 2015, we have already approached the scaling limits of the ubiquitous CMOS technology that has been in the forefront of mainstream technological advancement, so many researchers are exploring different ideas in the realm of electrical devices for logical applications, among them MSET transistors.
The idea that underlies MSETs is that a single multiple-terminal device could replace many traditional transistors. In particular a 2-drain MSET is akin to a silicon multiplexer, consisting in a Junction FET with independent gates, but with a split drain, so that a voltage-controlled conductive path can connect either of the drains to the source.
The first chapter of this work presents the theory of classical JFETs and its common equivalent circuit models. The physical model and its derivation are presented, the current state of equivalent circuits for the JFET is discussed. A physical model of a JFET with two independent gates has been developed, deriving it from previous results, and is presented at the end of the chapter.
A review of the characteristics of MSET device is shown in chapter 2. In this chapter, the proposed physical model and its formulation are presented. A listing for the SPICE model was attached as an appendix at the end of this document.
Chapter 3 concerns the results of the numerical simulations on the device. At first the research for a suitable geometry is discussed and then comparisons between results from finite-elements simulations and equivalent circuit runs are made. Where points of challenging divergence were found between the two numerical results, the relevant physical processes are discussed.
In the fourth chapter the experimental setup is discussed. The GUI-based environments that allow to explore the four-dimensional solution space and to analyze the physical variables inside the device are described. It is shown how this software project has been structured to overcome technical challenges in structuring multiple simulations in sequence, and to provide for a flexible platform for future research in the field.
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Fernández, Regúlez Marta. "Silicon Nanowire growth technologies for nanomechanical devices." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96375.
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Nanohilos de silicio obtenidos mediante el mecanismo de vapor-liquido-solido (VLS) ofrecen extraordinarias propiedades para aplicaciones en dispositivos nanomecánicos. Su calidad estructural (baja densidad de defectos, superficie lisa) y sus propiedades mecánicas únicas (auto-ensamblado robusto, alta rigidez y piezoresistencia gigante) junto con, recientes progresos en el control del crecimiento, prometen permitir un funcionamiento sin precedentes para una gran variedad de sistemas. Sin embargo, la fabricación generalmente está limitada a prototipos y más esfuerzos para conseguir un control simultáneo de las propiedades de los nanohilos y la posición son necesarios.
Esta tesis ha sido centrada en el desarrollo de tecnologías de fabricación con alto rendimiento/ a gran escala de dispositivos basados en nanohilos de silicio que exploten sus propiedades excepcionales. Tecnologías de fabricación para el crecimiento selectivo de matrices de nanohilos de silicio y de nanohilos individuales en dispositivos funcionales han sido desarrolladas y posteriormente adaptadas para la fabricación de diversos dispositivos basados en nanohilos.
En particular, el diseño, la fabricación y la caracterización de un cantilever piezoresistivo en el que el elemento de sensado está compuesto por una matriz de nanohilos ha sido demostrado. Los coeficientes piezoresistivos gigantes característicos de los nanohilos de Silicio se trasladan en un incremento en la sensibilidad mecánica comparada con dispositivos basados en silicio volumétrico. Por otro lado, se ha realizado la fabricación de resonadores nanomecánicos basados en nanohilos individuales. La caracterización de estos dispositivos demostró que los nanhilos individuales son excepcionales plataformas para el desarrollo de sensores de masa ultra sensibles y para el estudio de propiedades fundamentales de estructuras nanomecánicas.Silicon nanowires obtained via vapor-liquid-solid (VLS) mechanism offer many extraordinary properties for applications in nanomechanical devices. Their structural quality (low defect density, surface flatness) and unique mechanical properties (robust self-assembly, high stiffness, giant piezoresistance) together with, recent advances in growth control, promise to allow unprecedented performance of wide variety of systems. However, device fabrication is generally limited to prototype fabrication and more efforts to achieve simultaneous control of nanowire properties and location are needed. This thesis has been focused towards the development of high yield/ large scale fabrication technologies based on catalyst grown Si nanowire to realize devices that exploit their exceptional properties. Fabrication technologies for the selective growth of silicon nanowire arrays and single nanowire on functional devices have been developed and posteriorly adapted for the fabrication of several nanowire based devices. In particular, the design, fabrication and characterization of a piezoresistive cantilever in which the active sensor is composed of an horizontal Si nanowire array has been demonstrated. Giant piezoresistance coefficients characteristics of Si nanowires are translated into an increment in the cantilever mechanical sensitivity compared with similar bulk devices. On the other hand, the fabrication of nanomechanical resonators based on single nanowires for mass sensing applications with different transduction mechanims has been performed. The characterization of these devices proved that single nanowires are exceptional platforms to develop ultra-high sensitive mass sensors and to study fundamental properties of nanomechanical structures.
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Söderstrand, Alexander. "Models of superconducting nanowire single-photon detection." Thesis, KTH, Fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217346.
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Shao, Chenxu. "Fabrication of indium nitride nanowire hybrid devices." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114558.
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Semiconductor nanowires, known for their high quality, large surface-to-volume ratio and coaxial quantum confinement, are a promising material for the next generation nano-electronics and nano-photonics devices. Intensive research on this material has been done over the past decade. In particular, the single nanowire electrical device, which can be fabricated using cleanroom technology and is compatible with the well-developed integrated-circuit processing technique, has significant practical applications. In this work, the complete process of fabricating a single nanowire device, from mask design to pre-patterned chip making, from nanowire transfer to nanowire device fabrication, from substrate preparation and cleaning to dicing, from spin-coating and exposure to developing, from metal deposition and lift-off to packaging, was carefully investigated. In addition, basic measurements and preliminary results such as resistance - temperature (R-T) behavior, resistance - magnetic field (R-B) behavior and current - voltage (I-V) curve, are shown. This thesis thus provides detailed information about compatibility of single semiconductor nanowires with the standard integrated-circuit technique and can serve as a manual for single nanowire electrical device fabrication.Les nanofils semiconducteurs, connus pour leur haute qualité, leur large rapport surface/volume et leur confinement quantique coaxial, sont des matériaux prometteurs pour la prochaine génération de technologies nanoéléctroniqueset nanophotoniques. Une recherche intensive sur ces matériaux a été effectuée au cours de la dernière décennie. En particulier, les nanofils, qui peuvent être fabriqués en salle blanche, sont compatibles avec la technique maîtrisée du traitement en circuit intégré et ils ont des applications pratiques significatives. Dans ce travail, le processus complet de fabrication d'un dispositif à nanofil simple, de la conception du masque à la fabrication de puces, du transfert du nanofil à la fabrication de dispositifs à nanofil, de la préparation et nettoyage du substrat au découpage en dés, du dépôt par centrifugation et de l'exposition au développement, de la déposition et décollage du métal à l'emballage, a été examiné soigneusement. En outre, des mesures de base et des résultats préliminaires sont également présentés. Cette thèse fournit donc des informations détaillées sur la compatibilité des nanofils semiconducteurs avec la technique standard de circuit intégré et peut servir de manuel pour la fabrication de dispositifs à base de nanofilssimples.
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Smith, Ainsley H. "Quantum confined states in cylindrical nanowire heterostructures." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2007. http://digitalcommons.auctr.edu/dissertations/2364.
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We present an investigation of quantum confinement effects in nanowire heterostructures through the use of an effective-mass model with a band-offset induced potential barrier.
The characteristic size of microelectronics is rapidly approaching the nanometer scale and because of this, nanostructure based devices in the field of nanomaterial research is continually being emphasized. The quantum confinement effect exhibited by the nanowire is the most interesting in one-dimensional nanostructures. Potential applications for the nanowire include its use in the fabrication of high performance devices such as the p — n junction diode, the p-channel or n-channel coaxial gated field effect transistor, and the complimentary field effect transistors, to name a few.
In the fabrication of such devices, a doping process is used in order to supply free carriers. This process involves introducing doped impurities which unfortunately causes difficulties. These difficulties are characterized by a marked decrease in the mobility of the aforementioned carriers and include the scattering of the free carriers. To remedy these problems a novel doping mechanism has been proposed. It involves the use of a radial heterojunction in a core-shell nanowire where it has been suggested that one can dope impurities in the shell and inject free carriers to the core or vice versa. This separation of free carriers reduces their scattering rate and improves their mobility, both preferred properties for high-speed devices.
A better understanding of the heterojunction under strong cylindrical confinement is important to guide the future fabrication of nanowire-based high-speed devices. In order to achieve this, the question as to whether the band offset evolves with the size of the nanowire needs to be addressed.
The inquiry into the relationship between band offset evolution and nanowire size led us to employ an effective-mass model with a band-offset induced potential barrier to study the band structure of carriers in cylindrical core-shell and core-multishell nanowires. Quantum confined states and band alignment effects are found to be dependent upon the height of the potential barrier, the core-shell radius ratio, and the diameter of the quantum wire.
The subband charge densities are studied for clarifying the quantum confinement. By numerically solving the effective-mass model we were able to provide an interpretation of experimental observations on carrier accumulation and one-dimensional ballistic transport in Ge-Si core-shell nanowire heterostructures. The model serves as the continuum limit to the first-principles simulation approach.
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Razavieh, Ali. "Rf linearity in low dimensional nanowire mosfets." Thesis, Purdue University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3636500.
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ABSTRACT Razavieh, Ali. Ph.D., Purdue University, May 2014. RF Linearity in Low Dimensional Nanowire MOSFETs. Major Professors: Joerg Appenzeller and David Janes. Ever decreasing cost of electronics due to unique scaling potential of today's VLSI processes such as CMOS technology along with innovations in RF devices, circuits and architectures make wireless communication an un-detachable part of everyday's life. This rapid transition of communication systems toward wireless technologies over last couple of decades resulted in operation of numerous standards within a small frequency window. More traffic in adjacent frequency ranges imposes more constraints on the linearity of RF front-end stages, and increases the need for more effective linearization techniques. Long-established ways to improve linearity in DSM CMOS technology are focused on system level methods which require complex circuit design techniques due to challenges such as nonlinear output conductance, and mobility degradation especially when low supply voltage is a key factor. These constrains have turned more focus toward improvement of linearity at the device level in order to simplify the existing linearization techniques. This dissertation discusses the possibility of employing nanostructures particularly nanowires in order to achieve and improve RF linearity at the device level by making a connection between the electronic transport properties of nanowires and their circuit level RF characteristics (RF linearity). Focus of this work is mainly on transconductance (gm) linearity because of the following reasons: 1) due to good electrostatics, nanowire transistors show fine current saturation at very small supply voltages. Good current saturation minimizes the output conductance nonlinearities. 2) non-linearity due to the gate to source capacitances (Cgs) can also be ignored in today's operating frequencies due to small gate capacitance values. If three criteria: i) operation in the quantum capacitance limit (QCL), ii) one-dimensional (1-D) transport, and iii) operation in the ballistic transport regime are met at the same time, a MOSFET will exhibit an ideal linear Id-Vgs characteristics with a constant gm of which is independent of the choice of channel material when operated under high enough drain voltages. Unique scaling potential of nanowires in terms of body thickness, channel length, and oxide thickness makes nanowire transistors an excellent device structure of choice to operate in 1-D ballistic transport regime in the QCL. A set of guidelines is provided for material parameters and device dimensions for nanowire FETs, which meet the three criteria of i) 1-D transport ii) operation in the QCL iii) ballistic transport, and challenges and limitations of fulfilling any of the above transport conditions from materials point of view are discussed. This work also elaborates how a non-ideal device, one that approaches but does not perfectly fulfill criteria i) through iii), can be analyzed in terms of its linearity performance. In particular the potential of silicon based devices will be discussed in this context, through mixture of experiment and simulation. 1-D transport is successfully achieved in the lab. QCL is simulated through back calculation of the band movement of the transistors in on-state. Quasi-ballistic transport conditions can be achieved by cooling down the samples to 77K. Since, ballistic transport is challenging to achieve for practical channel lengths in today's leading semiconductor device technologies the effect of carrier back-scattering on RF linearity is explored through third order intercept point (IIP3) analysis. These findings show that for the devices which operate in the QCL, while 1-D sub-bands are involved in carrier transport, current linearity is directly related to the nature of the dominant scattering mechanism in the channel, and can be improved by proper choice of channel material in order to enforce a specific scattering mechanism to prevail in the channel. Usually, in semiconductors, the dominant scattering mechanism in the channel is the superposition of different mechanisms. Suitable choice of channel material and bias conditions can magnify the effect of a particular scattering mechanism to achieve higher linearity levels. The closing section of this thesis focuses on InAS due to its potential for high linearity since it has small effective mass and large mean-free-path.
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Smith, Damon Allen. "Mechanical, electromechanical, and optical properties of germanium nanowires." 2009. http://hdl.handle.net/2152/7678.
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In order to completely assess the potential of semiconductor nanowires for multifunctional applications such as flexible electronics, nanoelectromechanical systems (NEMS), and composites, a full characterization of their properties must be obtained. While many of their physical properties have been well studied, explorations of mechanical, electromechanical, and optical properties of semiconductor nanowires remain relatively sparse in the literature. Two major hurdles to the elucidation of these properties are: (1) the development of experimental techniques which are capable of mechanical and electromechanical measurements coupled with detailed structural analysis, and (2) the synthesis of high quality nanowires with the high yields necessary to produce the quantities needed for composite fabrication. These issues are addressed in this dissertation by utilizing the supercritical fluid-liquid-solid (SFLS) synthesis method to produce germanium (Ge) nanowire specimens for mechanical and electromechanical measurements coupled with high-resolution transmission electron microscopy (HRTEM). In addition, excellent dispersibility and large quantities allow for optical measurements of dispersions and composites. Ge cantilever nanoelectromechanical resonators were fabricated and induced into resonance. From the frequency response, the Young's modulus of the nanowires was determined to be insensitive to diameter and on par with the literature values for bulk Ge. The mechanical quality factors of the resonators were found to decrease with decreasing diameter. The data indicate that energy dissipation from the oscillating cantilevers occurs predominantly via surface losses. The mechanical strengths of individual Ge nanowires were measured by in situ nanomanipulation in a scanning electron microscope (SEM). The nanowires were found to tolerate diameter-dependent flexural strains more than two orders of magnitude higher than bulk Ge. Corresponding bending strengths were in agreement with the ideal strength of a perfect Ge crystal, indicative of a reduced presence of extended defects. The nanowires also exhibited plastic deformation at room temperature, becoming amorphous at the point of maximum strain. The optical absorbance spectra of Ge nanowires were measured and found to exhibit spectra markedly different from bulk Ge. Simulations using a discrete dipole approximation (DDA) model suggest that the difference in light absorption results from light trapping within the nanowires.text
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Chang, Ko-Wei, and 張恪維. "Formation and Characterization of Semiconductor Nanowires and Nanowire Heterostructures." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/70453796279100838749.
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博士國立成功大學
化學工程學系碩博士班
93
One-dimensional (1-D) nanostructures, such as nanotubes, nanowires, and nanorods have great potential for improving our understanding of the fundamental concepts of the roles of both dimensionality and size on physical properties, as well as for application in nanodevices and functional materials. In this dissertation, a bottom up approach for synthesis of semiconductor nanowires and nanowire hetorostructures are demonstrated. Many research efforts have been thus devoted to synthesize single crystal Ga2O3 nanowires via the vapor-liquid-solid (VLS) mechanism under high temperatures (800-1240 °C). In the first part of the dissertation, β-Ga2O3 nanowires were synthesized using Ga metal and H2O vapor in the present of Ni catalyst on the substrate at 800 oC. Two kinds of Ga vapor supply systems are employed in this study. Remarkable reduction of the diameter and increase of the length of the β-Ga2O3 nanowires are achieved by the separation of Ga and H2O vapor before they reach the substrate for a sufficient supply of the Ga vapor. An alternative method to synthesize β-Ga2O3 nanowires on Au- pretreated Si (100) and sapphire (0001) substrates at the temperatures ranging from 850 to 450 °C has also been further experimental by using a single precursor of gallium acetylacetonate ((CH3COCHCOCH3)3Ga) that could provide not only sufficient Ga vapor but also O vapor during the nanowires growth. Size control of the nanowire diameters was achieved by varying the growth conditions, i.e., substrate temperatures, pressures, and Ga vapor concentration. In addition, selective growth of vertically well-aligned Ga2O3 nanowires has been successfully grown on Au-coated sapphire (0001) substrates at temperatures of 450~ 650 oC. Structural characterization of the Ga2O3 nanowires by X-ray-diffraction (XRD) and transmission electron microscopy (TEM) reveals that the nanowires are preferentially oriented in the (-2,0,1) direction. Formation of the flower-like nanorod bundles at a temperature of 750 oC via the VS mechanism is also demonstrated. Next, we demonstrated the synthesis of GaN nanowires on Ni-pretreated Si substrates via the VLS mechanism at temperatures lower than those have been reported using ammonia gas and a Ga organometallic compound, i.e. gallium acetylacetonate, with a low decomposition temperature (~196 oC). Structural characterization of the 1D GaN nanostructures by HRTEM shows that straight GaN nanowires, needle-like nanowires (nanoneedles), and bamboo-shoot-like nanoneedles are synthesized at 750, 650, and 550 oC, respectively. In addition to selecting a proper catalyst, providing sufficient precursors has been demonstrated to be a crucial factor for the low-temperature growth of 1D GaN nanostructures via the VLS mechanism. For the synthesis of the Ga2O3/ZnO core-shell nanowires, a two-stage process was used. Well-aligned β-Ga2O3 nanowires were first grown on Au pre-coated sapphire (0001) substrates. The Ga2O3 nanowires were then used as 1D template for the ZnO-shell deposition. Formation of the well-aligned and single-crystalline ZnGa2O4 nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga2O3/ZnO core-shell nanowires. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing the single-crystalline ZnGa2O4 nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitixal relationship between ZnGa2O4 and Ga2O3 phases during the solid state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained from the single-crystalline ZnGa2O4 nanowires, suggesting the existence of the oxygen vacancies within them. With the similar method as just mention above, we also demonstrate the formation of Ga2O3/TiO2 core-shell heterostructure at the temperature of 400 oC~ 600 oC by low pressure chemical vapor deposition. TEM analyses reveal that the amorphous TiO2 layer and TiO2 nanoparticles were formed on the surfaces of the Ga2O3 nanowires at temperatures of 400 oC and 600 oC, respectively. Well- aligned Ga2O3/TiO2 nano-barcodes were formed after further 1000 oC annealing of the core-shell nanowires for 1 hr.
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Tzeng, Jiun-Wei, and 曾俊瑋. "Study on Electromechanical Properties of Silicon Nanowires and Nanowire FETs." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/42357116449026610197.
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碩士正修科技大學
電子工程研究所
100
The thesis is to study the piezoresistive properties of silicon (Si) nanowire (NW) and electromechanical properties of SiNWFETs. Fisrtly, we discuss the piezoresistive properties of SiNWs through a four-point bending technique (4PB). The 4PB can apply an external uniaxial mechanical stress on SiNWs. The magnitude of mechanical stress can be directly obtained by a foil strain gauge mounted on the surface of SiNWs. Then a new current-voltage stress measurement system is carried out for further analysis of piezoresistive properties of SINWs. The piezoresistive coefficient of 41×10-11 Pa-1 and gauge factor of 68 can be obtained. The values appear to be consistent with the piezoresistive properties of Si bulk. The second part is to explore the electromechanical properties of SiNWFETs. We use the back bulk electrode as the gate of SiNWs. This is so-called the silicon nanowire FETs. Similarly, the 4PB can be also used to apply a uniaxial tensile mechanical stress to SiNWFETs. Then we can observe the electromechanical properties of SiNWFETs. From the view of our experiment data, the piezoresistive coefficient and gauge factor have been greatly increased. This results can carry out a novel “electromechanical devices” of SiNWFETs.
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Retamal, José Ramón Durán, and 喬斯. "Nanowire Transistors." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/80537999193220287294.
Full textAbstract:
碩士臺灣大學
電機工程學研究所
98
The electrical and optical properties of the ZnO nanowires (NWs) have been investigated through back gate field effect transistors (FET) fabricated by photolithographic process and e-beam lithography. The electrical behavior has been characterized by the output and transfer characteristics, and the results show good electron mobility (~100 cm2v-1s-1), relative low concentration (~ 1016 cm-3), high Ion/Ioff ratio (~105), large subthreshold swing slope (0.5 V/dec). Enhanced performance has been observed after rapid thermal annealing at 300 C for 3 minutes and under vacuum conditions, ascribed to the improvement of the surface states caused by the oxygen absorbed species in the surface of the NW. Under white light illumination a maximum sensitivity (Iphoto/Idark) of ~106 is measured below the subthreshold swing region. By other side the oxygen absorbed species effect combined with the photogenerated electron-holes upon ultraviolet (UV) illumination has been used to fabricate UV photodetectors and optoelectronic switches. For first time ZnO NWs have been functionalized with NiO nanoparticles using Ni thermally evaporated and oxidized with oxygen flow at 600 C for 30 minutes, as the SEM and XRD results corroborate. Finally the resistive random-access memory (RRAM) effect has been demonstrates with ZnO NWs using the conductive filament model and the concept of back gate effect has been applied successfully to the RRAM in order to create a high resistance state.
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KANJAMPURATH, SIVAN ASWATHI. "Carrier dynamics in semiconductor nanowires." Doctoral thesis, 2021. http://hdl.handle.net/11573/1500622.
Full textAbstract:
This Ph.D. thesis presents results on the ultrafast spectroscopy of semiconductor nanowires with the aim of studying the carrier dynamics in these quasi-one-dimensional nanostructures. Six different semiconductor nanowire systems were studied using optical measurement techniques in the span of the last three (2017-2020) years and their results are discussed here.
Fast transient absorption spectroscopy with a femtosecond laser source was the primary experimental technique used throughout this thesis. With the use of a femtosecond laser system, the time evolution of photoexcited carriers in the nanowire structures was probed, giving insights into several fundamental physical phenomena of the photoexcited carriers. Several other optical measurement techniques such as photoluminescence, cathodoluminescence, Raman spectroscopy and UV-Vis steady state spectroscopy were also used.
The first material investigated for this thesis was Si nanowires grown through plasma-enhanced chemical vapor deposition. These nanowires were grown on a transparent quartz substrate, and the as-grown samples were used for studying the optical response to light excitation using a femtosecond laser with energy less than the direct bandgap (3.3 eV) energy of Si. Even when excited below the direct bandgap energy, an absorption signal was observed at 3.3 eV in the transient absorption measurements. By comparing the results obtained in this thesis with those obtained by the excitation above the direct bandgap energy, this work enabled me to disentangle the electron and hole dynamics with respect to the direct bandgap transition in Si.
The second material under study was InP nanowires. InP nanowires of both zincblende and wurtzite structures were studied using ultrafast transient absorption spectroscopy. The samples were probed both in the visible and in the near infrared (NIR) spectral region. The changes in the band structure due to the changes in the crystal structure were observed in the form of different energy transitions in different crystal structures. The transient absorption response was systematically studied to understand both the spectral and the kinetic properties of these electronic transitions. Carrier temperature of photoexcited carriers as a function of delay times were also extracted for the highest energy transition in the wurtzite InP with the help of these measurements. The energy loss rate by the hot carriers were also calculated as a function of carrier temperature giving insights into the occurrence of a phonon-bottleneck.
The third material under study was GaAs nanowires. This short study investigated the photoinduced changes in the visible spectral region. This study was done with a high pump energy with the aim of observing the two critical points in the band structure of GaAs namely, E1 and E1 + Δ. The most common experimental technique to observe the critical points is ellipsometric studies, however, in this thesis their observation using ultrafast spectroscopic techniques are presented.
The NWs of ternary alloy semiconductor GaAsP, with about 20 % phosphide and 80% arsenide content were studied next. This study was aimed at investigating the rate of hot carrier cooling as a function of the diameter of the nanowires after photoexcitation using an ultrafast laser pulse. Carrier temperatures and energy loss rates were extracted from the analysis of the transient absorption spectra. The experimental data provided direct evidence that nanowires
ii
with smaller diameter sustain higher carrier temperatures compared to nanowires with larger diameter for longer periods of time.
The fifth system under study was ZnSe nanowires decorated with Ag-nanoparticles. This study was aimed at understanding the modifications in the optical properties and carrier dynamics of ZnSe nanowires when Ag plasmonic nanoparticles were deposited on their sidewalls. Ag-nanoparticles were deposited on the sidewalls of ZnSe nanowires through thermal dewetting, creating a physical contact between the metal and the semiconductor. The energy of the local surface plasma resonance of these nanoparticles was very close to the optical bandgap of ZnSe nanowires. Low temperature photoluminescence measurements showed significant changes in the line shape of donor acceptor pair bands of ZnSe, with enhanced phonon replicas in the presence of Ag-nanoparticles. Ultrafast spectroscopic measurements showed changes in the rise time and decay time of transient absorption signal in the presence of Ag-nanoparticles. As a comparison, ZnSe nanowires were also decorated with Au-nanoparticles, in which case there was no overlap between the energy of local surface plasmon resonance of Au-nanoparticles and the optical bandgap of ZnSe nanowires. In this latter case there were no significant changes in the optical properties of ZnSe. This comparison enabled us to understand the importance of resonant interactions between plasmonic nanoparticles and semiconductor nanowires.
The final section of this thesis presents doping induced changes in the optoelectronic properties of ZnO nanorods. ZnO nanorods were synthesized using a cheap, and scalable seed mediated chemical bath deposition method. Doping with cobalt was done simultaneously by introducing Co2+ ions in the growth solution and the doping concentration was determined by the amount of Co2+ introduced in the growth solution. Co-doped ZnO nanorods were prepared in order to study their usability as a photoanode material for photoelectrochemical water splitting. Through cathodoluminescence and ultrafast spectroscopic measurements, the improvements in the optoelectronic properties of Co-doped ZnO nanorods were explored. All the measurements pointed to the formation of more surface defects in the presence of Co-doping and their role in the modification of the optoelectronic properties of the nanorods. These were then characterized using photoelectrochemical measurements such as incident photon to current efficiency and voltammetry measurements to quantify photogenerated current density. This allowed the determination of the ideal value of Co2+ in growth solution for photoelectrochemical applications, which was found to be 1%. These nanorods were further improved by functionalizing their surfaces with a metal organic framework, the zeolitic imidazolate framework – 8 (ZIF-8). Further optical characterization of these ZIF-8 coated Co-doped ZnO nanorods were also discussed, demonstrating further improvement in photoelectrochemical performance.
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Pelatt, Brian D. "A novel method for zinc oxide nanowire sensor fabrication." Thesis, 2009. http://hdl.handle.net/1957/14785.
Full textAbstract:
Interest in nanomaterials is motivated partly by their potential for sensor arrays to detect
different gases. Nanowires in particular are of interest because their high surface-to-volume
ratio promises the possibility of high sensitivity. However, because of their discrete
quasi-one-dimensional geometry, electrical integration of nanowires into photolithographically
defined devices and circuits is challenging and remains one of the obstacles to
their widespread use. In this thesis, a novel method for fabricating electrically integrated
zinc oxide nanobridge devices using carbonized photoresist is investigated. The conductivity
of carbonized photoresist is known and nanowire growth on carbonized photoresist
has recently been reported, suggesting the possibility of simultaneous use as a nucleation
layer and electrode. However, these reports did not characterize the contact between the
ZnO nanowires and carbonized photoresist. In this work, ZnO nanobridges are fabricated
between opposing carbonized photoresist electrodes and characterized both electrically
and with electron microscopy. Operation of nanobridge devices as bottom gate transistors,
UV sensors, and gas sensors is demonstrated.Graduation date: 2010
42
"Full Band Monte Carlo Simulation of Nanowires and Nanowire Field Effect Transistors." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.40344.
Full textAbstract:
abstract: In this work, transport in nanowire materials and nanowire field effect transistors is studied using a full band Monte Carlo simulator within the tight binding basis. Chapter 1 is dedicated to the importance of nanowires and nanoscale devices in present day electronics and the necessity to use a computationally efficient tool to simulate transport in these devices. Chapter 2 discusses the calculation of the full band structure of nanowires based on an atomistic tight binding approach, particularly noting the use of the exact same tight binding parameters for bulk band structures as well as the nanowire band structures. Chapter 3 contains the scattering rate formula for deformation potential, polar optical phonon, ionized impurity and impact ionization scattering in nanowires using Fermi’s golden rule and the tight binding basis to describe the wave functions. A method to calculate the dielectric screening in 1D systems within the tight binding basis is also described. Importantly, the scattering rates of nanowires tends to the bulk scattering rates at high energies, enabling the use of the same parameter set that were fitted to bulk experimental data to be used in the simulation of nanowire transport. A robust and efficient method to model interband tunneling is discussed in chapter 4 and its importance in nanowire transport is highlighted. In chapter 5, energy relaxation of excited electrons is studied for free standing nanowires and cladded nanowires. Finally, in chapter 6, a full band Monte Carlo particle based solver is created which treats confinement in a full quantum way and the current voltage characteristics as well as the subthreshold swing and percentage of ballistic transport is analyzed for an In0.7Ga0.3As junctionless nanowire field effect transistor.Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2016
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Bukovsky, Sayanti. "Nanoscale Material Characterization of Silicon Nanowires for Application in Reconfigurable Nanowire Transistors." 2020. https://tud.qucosa.de/id/qucosa%3A75531.
Full textAbstract:
Silicon Nanowire based Reconfigurable Field Effect Transistor (SiNW RFET) presents a solution to increase the system functionality beyond the limits of classical CMOS scaling in More-than-Moore era of semiconductor technology. They are not only spatially reconfigurable, i.e., the source and the drain can be interchangeable in design, but in such devices one can also control the primary charge carrier by controlling the voltage in the control gate. The two key morphological factors controlling reconfigurability are the structure and composition of the Schottky junctions, which serve as the location for Program and Control gates and radial strain induced by the self-limiting oxidation, which influences the carrier mobility resulting in symmetric p and n characteristic curves of an RFET. Despite its potential, in-depth nanoscale studies on the structural and compositional characterization of the key features controlling the reconfigurability are limited and thereby presents as a novel area of research.
In this study, the composition and morphology of the Schottky junction and the radial strain profile due to self-limiting oxidation were studied using advanced imaging and sample preparation techniques like Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) imaging alongside with precise sample preparation methods like Focused Ion Beam (FIB) liftout techniques.
For analysis of radial strain in nanowires that underwent self-limiting oxidation, a TEM lamella was taken of a cross-section of the NW. The lamella was kept at 200 nm thickness to preserve the strain state of the nanowire cross-section.
It was observed that nanowires undergoing such oxidation have an omega (Ω) shaped oxide shell where the shell was discontinued at the spot where the nanowire was touching the substrate. Fast Fourier transform of the high-resolution image of such a NW crossection was used to calculate the strain profile.
The strain is also found to be not radially uniform for such Ω shaped oxide shells. The strain profile shows a local maxima near the nanowire base where it touches the substrate then a minima approximately at the geometric center followed by the maximum strain at the area adjacent to the oxide shell thereby showing a sinusoidal profile. Theoretical simulations performed by Dr. Tim Baldauf further verified the nature of the sinusoidal strain that was observed experimentally. Similar simulations were done for different omega shell shapes, which yielded strain plots of similar sinusoidal strain plots, with the local maxima depending on the level of encapsulation of the NW by the shell.
In the characterization of the Schottky junction, a TEM lamella was taken along the longitudinal direction of a nanowire, which was silicidized from both ends, similar to ones used in SiNW RFET devices. High resolution TEM micrographs and EDX (Energy dispersive X-Ray Spectroscopy) in the TEM along the Schottky junction showed a Ni rich phase and pure Si on either side of the junction. This participating phase was identified as NiSi2. However, the transition between the phases shows a gradient and in-situ experiments were designed to verify the sharpness of the junction.
In in-situ silicidation experiments, Si nanowires with a thin native oxide shell were distributed on an electron transparent surface and were partially covered with Ni islands by shadow sputtering. The whole setup was then heated in a heating stage of a TEM and the Ni was allowed to disperse within the Si nanowires forming NiSi2. HRTEM (High Resolution TEM), EDX and EELS (Electron Energy Loss Spectroscopy) studies were performed on the silicidized samples for further ex-situ analysis.
During the in-situ experiment, it was observed that Ni-phase interface is atomistically sharp and seldom progresses perpendicularly to the nanowire’s direction but through the closed packed planes of the NW. The interface velocity at different temperatures was used to calculate the activation energy of the silicidation process. The value of the activation energy indicates the Ni undergoing volume diffusion through the Ni-rich phase. The velocity of the interface was observed to be much higher in nanowires with smaller diameters than those with higher diameters, further proving the hypothesis.
During the in-situ experiments, in around 10% of nanowires that underwent complete silicidation and held isothermally, the crystalline silicide phase was observed to partially or fully diffuse out of the nanowire core, leaving only a thin shell of Silicon oxide forming ultra-thin walled SiO2 nanotubes (NT).
The onset and the time required for completion of the process varies in the nanowires depending on size of the nanowire, the distance and contact to the nearest Ni islands and presence of defects such as kinks and twists within the nanowire.
In order to study the dynamics of the process, the velocity of the receding front was calculated for nanowires of two different diameters. They are found to be identical, indicating the volume flow rate of the process is directly proportional to the cross-sectional area. The voids were formed by the reduced diffusivity of Ni in Ni2Si phase in comparison to phases with lower percent of Ni. This indicates that the reason behind the phenomenon is coalition of Kirkendall voids and thus dependent on volume diffusion.
From this study, it can be concluded that the extent of self-limiting oxidation and shape of the shell can influence the radial strain state. This can be used to manipulate the strain to tailor the electron and hole transfer characteristics within the RFET. A variety of factors including temperature, time, orientation and radius of the nanowires has been studied with respect to silicidation of a SiNW. The calculated activation energy can be used for precise process control over the location and morphology of Schottky junction. Although not directly related to SiNW RFET devices, the self-assembly of ultra-thin-walled SiO2 NT is a novel research area in itself, the findings of which can be applied in to design novel electronics and sensors.:TABLE OF CONTENTS
Preface
List of Abbreviations
CHAPTER 1: Introduction and Motivation
1.1 Definition and History
1.2 Synthesis Routes
1.3 Properties and Applications
1.4 Nanoscale Electronics and Role of Si Nws
1.4.1
1.4.2 SiNW Reconfigurable Field Effect Transistor
1.5 Introduction to The Topic of The Thesis
1.6 Outline of The Thesis
CHAPTER 2: Physical Basics and Previous Research: A Short Summary
2.1 Strain Measurement and Effects of Strain on on Nanoelectronics
2.1.1 Strain Analysis in Planar CMOS Structures
2.2 Silicidation and Schottky Junction
2.2.1 In-situ Silicidation
2.2.2 Silicon oxide nanotubes
CHAPTER 3: Background of Instruments and Experimental Set-up
3.1 Scanning Electron Microscope
3.2 Transmission Electron Microscope
3.2.1 Imaging Techniques
3.2.2 TEM sample preparation
3.3 Focused Ion Beam
CHAPTER 4: Strain in Nanowire
4.1 Goal of This Study
4.2 Strain in SiNW RFET Devices
4.3 Strain Analysis in SiNW Cross-section
4.3.1 Sample Preparation
4.3.2 Experimental Process
4.3.3 Results and Discussion
4.4 Conclusions
CHAPTER 5: Schottky Junction
5.1 Crystallographic Data on Nickel Silicides
5.2 Formation of Silicides in 2-D Structures
5.2.1 Sample History
5.2.2 Sample Preparation
5.2.3 Results and Discussion
5.3 Formation of Silicides in 1-D Structures: Schottky Junction in NWs
5.3.1 Sample History
5.3.2 Sample Preparation
5.3.3 Results and Discussion
5.3.4 Shortcomings of The Lift-out Technique
5.4 In-situ Silicidation
5.4.1 Motivation
5.4.2 Sample Preparation
5.4.3 Experimental Procedure
5.4.4 Results and Discussions
5.4.5 Shortcoming of The Experiment
5.5 Self-assembling SiO2 Nanotubes
5.5.1 Sample Preparation
5.5.2 Experimental Process
5.5.3 Results and Discussion .
5.5.4 Post In-situ Experiment TEM Analysis
5.5.5 Conclusions
CHAPTER 6: Conclusions and Outlook
6.1 Strain Analysis
6.2 Schottky Junction Studies
Bibliography
Acknowledgements
44
Lin, Yong-Han, and 林永翰. "Electronic transport in conducting metal oxide nanowires and through their nanowire contacts." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/75782840642276085567.
Full textAbstract:
博士國立交通大學
物理研究所
95
Fair understanding of the intrinsic electronic transport properties of individ- ual nanowires (NWs) is certainly the key step for numerous nanoelectronic applications. Quantitative knowledge about the relevant electronic contacts is also very crucial in correctly interpreting the experimental results. In this work, we have studied the intrinsic electronic transport properties of indi- vidual single-crystalline RuO2 and IrO2 NWs, which belong to the family of transition metal oxides that have advantages of being chemically stable while possessing comparatively high conductivities. With the help of the standard electron-beam lithographic technique, individual NWs are contacted by submi- cron metal electrodes from above. By applying di®erent probe con‾gurations to our measurements, not only the intrinsic electronic transport properties of the individual as-grown NWs but also the temperature behaviours of high- resistance electronic contacts, Rc(T), have been determined down to liquid- helium temperatures. Two main results have been obtained. First, the measured temperature dependent resistivity of the NWs is found to agree well with the current theo- retical understanding of these materials. Although they can be well described by the existing theory, we found that the Debye temperature in RuO2 NWs is signi‾cantly reduced to only one half of its bulk value when the diameter of the NW decreases down to ¼ 40 nm. (Comparable experiments on IrO2 NWs with diameters down to this scale have not been performed.) Possible mechanisms accounting for this observation have been discussed. It is conjec- tured that the chemical binding in the NWs may be gradually weakened as the diameter decreases. Second, for high-resistance electronic contacts, the measured Rc(T) reveals semiconducting or insulating behaviour, i.e., it increases rapidly with decreas- ing temperature. However, di®erent temperature dependence has been found for di®erent kind of NW. For RuO2 NWs, the temperature behavior of Rc can be satisfactorily explained in terms of the thermally °uctuation-induced tunneling through a junction formed at the interface between the electrode and the NW. On the other hand, for IrO2 NWs, a power law of the form logRc / T¡1=2 over a very wide temperature range from ¼ 100 K down to liquid-helium temperatures has been observed. This later conduction process is ascribed to the hopping of electrons through nanoscale metal (Cr) granules incidentally formed at the contact region during the thermal evaporation of the submicron Cr/Au electrodes. Although such a di®erence may arise from the di®erent surface conditions of di®erent kinds of NWs (such as di®erent surface stresses), we believe that either mechanism could occur even for the same kind of NW; they just appear randomly. Unfortunately, direct evidences supporting this viewpoint are not obtained in this work.
45
Wu, Chia-wei, and 吳佳緯. "Fabrication and Study of Germanium Nanowire and Silicon Nanowire Transistors." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/tyxce9.
Full textAbstract:
碩士國立中央大學
電機工程研究所
97
In the past four decades, semiconductor industrials keep downscaling the size of MOSFETs in order to achieve the goals of high operation speed and high device density. However, the reduction of device size won’t last forever. When transistors shrink into or below 30 nm regime, leakage current due to severe short channel effects and thin gate dielectric causes the increase of off-state power consumption, and consequently causes functionality failure. One-dimensional devices based on nanowires or nanotubes are considered the immediate successors to replace the traditional silicon technology with relatively low technological risk. Germanium nanowire transistor, which has higher carrier mobility and can be further enhanced by quantum confinement effect, is one of the most promising devices. In addition, the control of gate to channel can also be improved by using high-k dielectrics. In this thesis, we propose a method of selectively oxidizing silicon-germanium wires to form germanium nanowires. The process is fully compatible to CMOS technology, and nanowires formed by this way can self-align to source/drain electrodes. Besides, we fabricate silicon nanowire transistors with self-aligned electrodes in FinFET-like structure and measure the current-voltage (I-V) characteristics under room-temperature and low-temperature. The results provide a information foundation for fabricating germanium nanowire transistors in the future.
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Sutrakar, Vijay Kumar. "A Computational Study of Structural and Thermo-Mechanical Behavior of Metallic Nanowires." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3370.
Full textAbstract:
This thesis is an attempt to understand ways to improve thermo-mechanical and structural properties of nano-structured materials. A detailed study on computational design and analysis of metallic nanowires is carried out. Molecular dynamic simulation method is applied. In particular, FCC metallic nanowires, NiAl, and CuZr nanowires are studied. Various bottom-up approaches are suggested with improved structural and thermo¬mechanical properties.
In the first part of the thesis, Cu nanowires are considered. Existence of a novel and stable pentagonal multi-shell nanobridge structure of Cu under high strain rate tensile loading is reported. Such a structure shows enhanced mechanical properties. A three-fold pseudo-elastic-plastic shape recovery mechanism in such nanowires is established. This study also shows that the length of the pentagonal nanobridge structures can be characterized by its inelastic strain. It is also reported that an initial FCC structure is transformed into a new HCP structure. The evidence of HCP structure is confirmed with the help of experimental data published in the literature. Subsequent to the above study, a novel mechanism involving coupled temperature-stress dependent reorientation in FCC nanowires is investigated. A detailed map is generated for size dependent stress-temperature induced solid-solid reorientation in Cu nanowires.
In the second part of the thesis, deformation mechanisms in NiAl based intermetallic nanowires are studied. A novel mechanism of temperature and cross-section dependent pseudo-elastic/pseudo-plastic shape and strain recovery by an initial B2 phase of NiAl nanowire is reported. Such a recoverable strain, which is as high as ~ 30%, can potentially be utilized to realize various types of shape memory and strain sensing phenomena in nano-scale devices. An asymmetry in tensile and compressive yield strength behavior is also observed, which is due to the softening and hardening of the nanowires under tensile and compressive loadings, respectively. Two different deformation mechanisms dominated by twinning under tension and slip under compression are found. Most interestingly, a superplastic behavior with a failure strain of up to 700% in the intermetallic NiAl nanowires is found to exist at a temperature of 0.36Tm. Such superplastic behavior is attributed to the transformation of the nanowire from a crystalline phase to an amorphous phase after yielding of the nanowire.
In the last part the work, another type of nanowires having Cu-Zr system is considered. A novel stress induced martensitic phase transformation from an initial B2 phase to BCT phase in a CuZr nanowire under tensile loading is reported. It is further shown that such a stress induced martenistic phase transformation can be achieved under both tensile as well as compressive loadings. Tensile-compressive asymmetry in the stress-strain behavior is observed due to two different phase transformation mechanisms having maximum transformation strains of ~ 5% under compressive loading and ~ 20% under tensile loading. A size and temperature dependent tensile phase transformation in the nanowire is also observed. Small nanowires show a single step tensile phase transformation whereas the nanowires with larger size show a two step deformation mechanism via an intermediate R-phase hardening followed by R-phase yielding. A study of energetic behavior of these nanowires reveals uniform distribution of stress over the nanowire cross-section and such stress distribution can lead to a significant improvement in its thermo-mechanical properties. Similar improvement is demonstrated by designing the nanowires via manipulating the surface configuration of B2-CuZr system. It is found that the CuZr nanowires with Zr atoms at the surface sites are energetically more stable and also give a uniform distribution of stresses across the cross-section. This leads to the improvement in yield strength as well as failure strain. An approach to design energetically stable nano-structured materials via manipulating the surface configurations with improved thermo-mechanical properties is demonstrated which can help in fundamental understanding and development of similar structures with more stability and enhanced structural properties. Further ab-initio and experimental studies on the confirmation of the stability of the nanowires via manipulating the surface site is an open area of research and related future scopes are highlighted in the closure.
47
Sutrakar, Vijay Kumar. "A Computational Study of Structural and Thermo-Mechanical Behavior of Metallic Nanowires." Thesis, 2013. http://etd.iisc.ernet.in/2005/3370.
Full textAbstract:
This thesis is an attempt to understand ways to improve thermo-mechanical and structural properties of nano-structured materials. A detailed study on computational design and analysis of metallic nanowires is carried out. Molecular dynamic simulation method is applied. In particular, FCC metallic nanowires, NiAl, and CuZr nanowires are studied. Various bottom-up approaches are suggested with improved structural and thermo¬mechanical properties.
In the first part of the thesis, Cu nanowires are considered. Existence of a novel and stable pentagonal multi-shell nanobridge structure of Cu under high strain rate tensile loading is reported. Such a structure shows enhanced mechanical properties. A three-fold pseudo-elastic-plastic shape recovery mechanism in such nanowires is established. This study also shows that the length of the pentagonal nanobridge structures can be characterized by its inelastic strain. It is also reported that an initial FCC structure is transformed into a new HCP structure. The evidence of HCP structure is confirmed with the help of experimental data published in the literature. Subsequent to the above study, a novel mechanism involving coupled temperature-stress dependent reorientation in FCC nanowires is investigated. A detailed map is generated for size dependent stress-temperature induced solid-solid reorientation in Cu nanowires.
In the second part of the thesis, deformation mechanisms in NiAl based intermetallic nanowires are studied. A novel mechanism of temperature and cross-section dependent pseudo-elastic/pseudo-plastic shape and strain recovery by an initial B2 phase of NiAl nanowire is reported. Such a recoverable strain, which is as high as ~ 30%, can potentially be utilized to realize various types of shape memory and strain sensing phenomena in nano-scale devices. An asymmetry in tensile and compressive yield strength behavior is also observed, which is due to the softening and hardening of the nanowires under tensile and compressive loadings, respectively. Two different deformation mechanisms dominated by twinning under tension and slip under compression are found. Most interestingly, a superplastic behavior with a failure strain of up to 700% in the intermetallic NiAl nanowires is found to exist at a temperature of 0.36Tm. Such superplastic behavior is attributed to the transformation of the nanowire from a crystalline phase to an amorphous phase after yielding of the nanowire.
In the last part the work, another type of nanowires having Cu-Zr system is considered. A novel stress induced martensitic phase transformation from an initial B2 phase to BCT phase in a CuZr nanowire under tensile loading is reported. It is further shown that such a stress induced martenistic phase transformation can be achieved under both tensile as well as compressive loadings. Tensile-compressive asymmetry in the stress-strain behavior is observed due to two different phase transformation mechanisms having maximum transformation strains of ~ 5% under compressive loading and ~ 20% under tensile loading. A size and temperature dependent tensile phase transformation in the nanowire is also observed. Small nanowires show a single step tensile phase transformation whereas the nanowires with larger size show a two step deformation mechanism via an intermediate R-phase hardening followed by R-phase yielding. A study of energetic behavior of these nanowires reveals uniform distribution of stress over the nanowire cross-section and such stress distribution can lead to a significant improvement in its thermo-mechanical properties. Similar improvement is demonstrated by designing the nanowires via manipulating the surface configuration of B2-CuZr system. It is found that the CuZr nanowires with Zr atoms at the surface sites are energetically more stable and also give a uniform distribution of stresses across the cross-section. This leads to the improvement in yield strength as well as failure strain. An approach to design energetically stable nano-structured materials via manipulating the surface configurations with improved thermo-mechanical properties is demonstrated which can help in fundamental understanding and development of similar structures with more stability and enhanced structural properties. Further ab-initio and experimental studies on the confirmation of the stability of the nanowires via manipulating the surface site is an open area of research and related future scopes are highlighted in the closure.
48
Han-TingHsueh and 薛漢鼎. "Growth of Si, CuO and ZnO nanowires and the fabrication of nanowire sensors." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/62556241166388520343.
Full text
49
Chen, Yi-Hung, and 陳沂宏. "Silicon Nanowire pH Sensors." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/46659145777838772141.
Full textAbstract:
碩士國立中興大學
機械工程學系所
99
This study presents the fabrication of silicon nanowire pH sensors with highly- and instantly-sensitive and repeatedly-used properties. The silicon nanowire pH sensors are composed of two main parts: (1) the silicon nanowires covered by a thin oxide layer using semiconductor process, (2) the micro channel with good transmittance. Three silicon nanowires in parallel and five silicon nanowires in parallel pH sensors are fabricated. The resistance change of the pH sensors are measured under different pH values. The experimental results showed that the resistance of the three nonowires pH sensor changed from 850 to 400 kΩ as the pH varied from 3 to 10, and the percentage of the resistance change to each pH was about 10.4%. The resistance of the five nanowires pH sensor varied from 36.2 to 32.2 kΩ in the pH range of 3-10, and the percentage of the resistance variation to each pH was about 1.51%.
50
Husain, Ali. "Nanotube and Nanowire Devices." Thesis, 2004. https://thesis.library.caltech.edu/2043/6/Title.pdf.
Full textAbstract:
The microelectronic revolution has spawned many fields that take advantage of the incredibly small size devices that can be made. However, the limits of photolithography and even electron beam lithography are fast approaching. Future progress in miniaturization of electronics, mechanical devices and optical structures will require new processes and materials.
The work presented in this thesis is an investigation into the possibilities of using new nanomaterials to fabricate simple devices. It is a challenge to integrate these materials with traditional microfabrication techniques. The processes commonly used to make electronics can damage or destroy some nanomaterials. Also, it is difficult to place and orient these novel substances. Finally, at the nanometer scale, different physical properties emerge due to confinement effects and the large surface-area-to-volume ratio.
We have fabricated devices out of carbon nanotubes and electrodeposited nanowires. The nanowires have been fabricated in gold, platinum, silver and nickel. For all the nanowires except silver we have measured the temperature dependence of the resistance and found that it is consistent with bulk metals. We have created and tested crossed nickel nanowires for magnetoresistive effects and found none.
From the platinum wires we have fabricated and tested the first doubly clamped resonator fabricated out of "bottom-up" materials. This resonator has much lower Q than comparable devices made by traditional techniques. The resonator also exhibits non-linear behavior well described by the Duffing oscillator.
From carbon nanotubes we have created a doubly-clamped beam. In addition, we have created a novel carbon nanotube field emission device with integrated grid. Work is ongoing to achieve experimental results from these devices.
The appendix describes photonic crystal defect cavity lasers, which offers interesting potential for integration with nanotubes and nanowires.