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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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Machin, Sophie Elizabeth. "Metal oxide nanowires." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648214.
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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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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
6
Evans, G. J. "Transport in silicon nanowires." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598915.
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This thesis models the electrical breakup of geometrically uniform heavily doped silicon nanowires under the action of the random dopant potential. A self-consistent Thomas-Fermi model is used to show the natural formation of islands and structured characteristics of the system are presented. The island's electrical exhibits Coulomb blockade which is a single electronic effect by which the transport of electrons is strongly affected by the discrete nature of the current and where electron-electron repulsion can prevent current flowing. The system is modelled by calculation of the full capacitance matrix, an approximation to the tunnel resistance matrix and a single electron transport simulator, from which the I-V characteristics of a particular nanowire can be simulated. An electrical characteristic of the wire is the threshold voltage and is the point at which it first starts to conduct. However, extraneous charge in the environment (so-called offset charge) can change the device's characteristics and hence the threshold voltage. The numerical evaluation of the threshold voltage distribution for the nanowires is performed for a few examples before developing an analytical approximation to the distribution under offset charge disorder. The approximation is a geometrical interpretation of the phase space describing the device and the limits of applicability are discussed and in particular a two-island system is investigated. Negative differential conductance is shown to be present even in a two-island system and is explained in geometrical terms.
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Siddiqui, Saima Afroz. "Magnetostatic interaction in nanowires." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93838.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-65).
Nonvolatile memory and logic devices rely on the manipulation of domain walls in magnetic nanowires, and scaling of these devices requires an understanding of domain wall behavior as a function of the wire width. Due to the increased importance of edge roughness and microstructure in narrow lines, domain wall pinning increases dramatically as the wire dimensions decrease and stochastic behavior is expected depending on the distribution of pinning sites. This work reports on the field driven domain wall statistics in sub-100 nm wide nanowires made from Co films of 8 nm thickness made by an electron beam lithography and etching process that minimizes edge roughness.
by Saima Afroz Siddiqui.
S.M.
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Kulmala, Tero Samuli. "Nanowires and graphene nanoelectronics." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608195.
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Fasoli, Andrea. "Nanowires and nanoribbons nanoelectronics." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608660.
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Lin, Yu-Ming 1974. "Thermoelectric properties of Bi₁âx̳Sbx̳ nanowires and lead salt superlattice nanowires." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17593.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.In title on t.p., double-underscored "x" appears as subscript.
Includes bibliographical references (p. 138-147).
This thesis involves an extensive experimental and theoretical study of the thermoelectric-related transport properties of BilxSbx nanowires, and presents a theoretical framework for predicting the electrical properties of superlattice nanowires. A template-assisted fabrication scheme is employed to synthesize Bi-based nanowires by pressure injecting liquid metal alloys into the hexagonally packed cylindrical pores of anodic alumina. These nanowires possess a very high crystalline quality with a diameter-dependent crystallographic orientation along the wire axis. A theoretical model for Bil-Sbx nanowires is developed, taking into consideration the effects of cylindrical wire boundary, multiple and anisotropic carrier pockets, and non-parabolic dispersion relations. A unique semimetal-semiconductor (SM-SC) transition is predicted for these nanowires as the wire diameter decreases or as the Sb concentration increases. Also, an unusual physical phenomenon involving a very high hole density of states due to the coalescence of 10 hole carrier pockets, which is especially advantageous for improving the thermoelectric performance of p-type materials, is uncovered for BilxSbx nanowires. Various transport measurements are reported for Bi-related nanowire arrays as a function of temperature, wire diameter, Sb content, and magnetic field. R(T) measurements show distinct T dependences for semimetallic and semiconducting nanowires, as predicted by the theory, and the condition for the SM-SC transition can be clearly identified. Enhanced thermopower is observed for BilxSbx nanowires as the diameter decreases or as the Sb content increases, indicating that both quantum confinement effects and Sb alloying effects are important for improving the thermo-electric performance.
(cont.) The theoretical model is further extended to study transport properties of Te-doped Bi nanowires and Sb nanowires, and good agreement between theoretical predictions and experimental results is obtained. A model for superlattice nanowires is presented to evaluate their potential for thermoelectric applications. Thermoelectric properties of superlattice nanowires made of various lead salts (PbS, PbSe, and PbTe) are investigated as a function of segment length, wire diameter, crystal orientation along the wire axis, and length ratio of the constituent nanodots. An interesting inversion of the potential barrier and well induced by quantum confinement is predicted in superlattice nanowires as the wire diameter decreases. ZT values higher than 4 and 6 are predicted for 5 nm-diameter PbSe/PbS and PbTe/PbSe superlattice nanowires, respectively, at 77K, and these ZT values are significantly larger than those of their corresponding alloy nanowires. For a given superlattice period, the ZT value can be further improved by adopting different segment lengths for the two constituent materials. The model developed here not only can determine the optimal superlattice nanowire parameters (segment length, diameter, materials, and doping level) for thermoelectric applications, but also can be extended to other superlattice systems, such as 3D quantum dot arrays ...
by Yu-Ming Lin.
Ph.D.
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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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Yang, Li. "First-principles Calculations on the Electronic, Vibrational, and Optical Properties of Semiconductor Nanowires." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14133.
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The first part of my PhD work is about the lattice vibrations in silicon nanowires. First-principles calculations based on the linear response are performed to investigate the quantum confinement effect in lattice vibrations of silicon nanowires (SiNW). The radial breathing modes (RBM) are found in our calculations, which have a different size-dependent frequency shift compared with the optical modes. They are well explained by the elastic model. Finally, the relative activity of the Raman scattering in the smallest SiNW is calculated. The RBM can be clearly identified in the Raman spectrum, which can be used to estimate the size of nanowires in experiment.
In the second part of my PhD work, we focus on the electron-hole pair (exciton) in semiconductor nanowires and its influence on the optical absorption spectra. First-principles calculations are performed for a hydrogen-passivated silicon nanowire with a diameter of 1.2 nm. Using plane wave and pseudopotentials, the quasiparticle states are calculated within the so-called GW approximation, and the electron-hole interaction is evaluated with the Bethe-Salpeter Equation (BSE). The enhanced excitonic effect is found in the absorption spectrum.
The third part of my work is about the electronic structure in Si/Ge core-shell nanowires. The electronic band structure is studied with first-principles methods. Individual conduction and valence bands are found in the core part and the shell part, respectively. The band offsets are determined, which give rise to the spatial separation of electron and hole charge carriers in different regions of the nanowires. This allows for a novel-doping scheme that supplies the carriers into a separate region in order to avoid the scattering problem. This is the key factor to create high-speed devices. With the confinement effect, our results show important correction in the band offset compared with the bulk heterostructure. Finally, an optimum doping strategy is proposed based on our band-offset data.
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Au, Frederick Chi Kan. "Electronic properties of silicon nanowires /." access full-text access abstract and table of contents, 2005. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ap-b19887759a.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2005."Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.
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Pfund, Andreas. "Spin states in InAs nanowires /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17861.
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Elfström, Niklas. "Silicon Nanowires for Biomolecule Detection." Doctoral thesis, KTH, Materialfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4695.
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Starting from silicon on insulator (SOI) material, with a top silicon layer thickness of 100 nm, silicon nanowires were fabricated in a top down approach using electron beam (e-beam) lithography and subsequent eactive ion etching (RIE) and oxidation. Nanowires as narrow as 30 nm could be achieved. Further size reduction was done using electrochemical etching and/or oxidation. The nanowires were contacted creating drain, source and back gate contacts and characterized showing similar behavior as Schottky Barrier Metal Oxide Semiconductor Field Effect Transistors (SB-MOSFETs). As an alternative, by thinning the top silicon layer down nanoribbons, ~ 1 μm wide, with a thickness down to 45 nm could be produced using standard optical lithography showing similar behavior as the nanowires. The conduction mechanism for these devices is through electrons in an inversion current layer for positive back gate voltages and through holes in accumulation mode for negative back gate voltages. When the threshold voltage is extrapolated for the nanowires and the nanoribbons it scales with inverse width and thickness respectively, attributed to charged surface and/or interface states affecting more narrow/thinner devices essentially due to increased surface to volume ratio. Nanowires were functionalized with 3-aminopropyl triethoxysilane (APTES) molecules creating amino groups on the surface reactive to pH buffer solutions. By exposing the nanowires to buffer solutions of different pH value the conduction mechanism changed due to the surface becoming more or less negative. Threshold voltage shifts from pH = 3 to pH = 9 were seen to scale with inverse width again attributed to the larger surface to volume ratio for more narrow devices. Simulations confirm this behavior and further show that a charge change of a few elementary charges on the nanowire surface can alter the conductance significantly. Upon addition of the buffer solutions the channel is seen to be quenched for small drain bias attributed to negative surface charges screening the electron current. However, as the drain bias is increased the channel is restored. Computer simulations confirmed this behavior and further showed that the restoration of the channel was due to an avalanche process. A biomolecule detection experiment was set up using the specific binding of biotin to streptavidin. By functionalizing the nanoribbon with biotin molecules the current can be logged and as streptavidin molecules are added the current decreases (increases) if the nanoribbon is run in inversion (accumulation) mode due to the negative charge of the streptavidin molecule, delivered upon binding to biotin. A sensitivity significantly below the picomolar range was observed, corresponding to less than 20 streptavidin molecules attaching to the nanoribbon surface, assuming a homogeneous binding to the biotinylated surface. By decreasing the nanoribbon thickness the response was increased, a behavior attributed to the larger surface to volume ratio of these devices. The response was seen to be larger in the accumulation mode whereas close to the lower oxide in inversion mode. Computer simulations showed that this was due to the hole current running closer to the functionalized surface in accumulation mode and opposite in inversion mode. This was further investigated for different nanoribbon thicknesses and the response was shown to increase with inverse nanoribbon thickness again attributed to the larger surface to volume ratio. The nanoribbon has the advantage of simpler fabrication using standard optical lithography in comparison with e-beam lithography and it may provide a useful scheme for a practical biomolecule sensor.QC 20100719
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Ghita, Marius Mugurel. "Frequency Multiplication in Silicon Nanowires." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/3082.
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Frequency multiplication is an effect that arises in electronic components that exhibit a non-linear response to electromagnetic stimuli. Barriers to achieving very high frequency response from electronic devices are the device capacitance and other parasitic effects such as resistances that arise from the device geometry and are in general a function of the size of the device. In general, smaller device geometries and features lead to a faster response to electromagnetic stimuli. It was posited that the small size of the silicon nanowires (SiNWs) would lead to small device capacitance and spreading resistance, thus making the silicon nanowires useful in generating microwave and terahertz radiation by frequency multiplication. To verify this hypothesis, silicon nanowires based devices were fabricated and investigated using two experimental setups. The setups were designed to allow the investigation of the nanowire based devices at low frequencies and at high frequencies. Both setups consisted of an RF/microwave source, filters, waveguide, and a spectrum analyzer. They also allowed the characterization of the samples with a semiconductor parameter analyzer. The first step in the investigation of the SiNW devices was to install them in the waveguides and perform Current-Voltage (I-V) sweeps using the semiconductor parameter analyzer. The devices that exhibited the non-linear I-V characteristics typical of diodes were further investigated by first exposing them to 70MHz and 500MHz frequencies in the low frequency setup and then to 50GHz microwaves in the high frequency setup. The response of the devices was captured with a spectrum analyzer. The results demonstrate that the non-linear effect of frequency multiplication is present in nanowire devices from DC to 100GHz. The HF setup provides a platform that with an appropriate detector can be used to detect harmonics of the SiNWs in sub-millimeter/THz region of the electromagnetic spectrum.
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Zörgiebel, Felix. "Silicon Nanowires for Biosensor Applications." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-230675.
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Nanostrukturen haben in den letzten Jahrzehnten durch konsequente Förderung wie der im Jahr 2000 gestarteten National Nanotechnology Initiative der USA oder des deutschen Pendants Aktionsplan Nanotechnologie erhebliches Aufsehen, nicht nur in der Wissenschaft, sondern auch in der technischen und wirtschaftlichen Umsetzung erfahren. In Kombination mit biologischen Systemen, deren Funktionalität sich auf der Größenordnung von Nanometern abspielt, finden nanotechnologische Entwicklungen auf dem Gebiet der Medizin ein großes technisches Anwendungsgebiet. Diese Arbeit widmet sich der Untersuchung und technischen Entwicklung von Siliziumnanodrähten als Sensoren für zukünftige medizinische Anwendungen. Im Gegensatz zu Sensoren die auf dotierten Nanodrähten basieren, wurden hier undotierte Nanodrähte untersucht, die mit geringerem Produktionsaufwand auskommen und mittels Schottky-Barrieren als Feldeffekttransistoren nutzbar sind. Deren Eigenschaften wurden im Hinblick auf pH und Biosensorik theoretisch und experimentell untersucht, sowie technisch in ein lab-on-chip sowie ein kompaktes Multiplexer-Messgerät integriert. In einem zweiten, separaten Teil wurden die Eigenschaften undotierter Nanodrähte für die optische Spektroskopie theoretisch modelliert. Die Inhalte beider Teile werden im folgenden kurz zusammengefasst. Um die elektrischen Sensoreigenschaften der Siliziumnanodrähte zu untersuchen, wurden zunächst Computermodelle der Drähte erstellt, mit deren Hilfe der Elektronentransport in flüssiger Umgebung quantenmechanisch modelliert wurde. Die dafür erstellten Modellvorstellungen waren für die sich daran anschließenden experimentellen Untersuchungen des Rauschverhaltens, der pH-Sensitivität sowie der Biosensoreigenschaften sehr vorteilhaft. Mit Hilfe einer neu entwickelten Messmethode konnte der optimale Arbeitspunkt der Sensoren ermittelt werden, sowie die hohe Sensorqualität mittels einer empirischen mathematischen Beschreibung des zu erwartenden Sensorsignals eingeordnet werden. Weiterhin wurden für die Medizintechnik relevante Messungen von Thrombin durchgeführt. Damit ist für den hier beschriebenen Sensortyp ein proof-of-concept für neuartige medizinische Messelemente gelungen. Um die kleinen Abmessungen der Sensoren darüber hinaus technisch nutzbar zu machen, wurden sie in ein lab-on-chip System integriert, in welchem sie als Sensoren für den pH-Wert sowie die ionische Konzentration in Nanoliter-Tropfen verwendet wurden. Desweiteren wurde in Kooperation mit dem Institut für Aufbau- und Verbindungstechnik ein portables Messgerät entwickelt, welches die parallele Messung mehrerer Nanodrahtsensoren ermöglicht. Im zweiten Teil der Arbeit wird eine theoretische Untersuchung zur Eignung von Silizium-Nanodrähten als Messsonden (Probes) für die optische Spektroskopie vorgestellt. Dazu wurde eine Methode entwickelt mittels derer es möglich ist, Raman und Infrarotspektren von Nanostrukturen mittels Molekulardynamik zu berechnen. Die Methode wurde auf undotierte Silizium-Nanodrähte augewendet und zeigt, dass die Oberflächenbeschaffenheit der Drähte die optischen Spektren entscheidend beeinflusst. Damit konnte die Relevanz von Halbeiter-Nanostrukturen auch für Anwendungen in der optischen Spektroskopie gezeigt werdenNanostructures have attracted great attention not only in scientific research, but also in engineering applications during the last decades. Especially in combination with biological systems, whose complex function is controlled from nanoscale building blocks, nanotechnological developments find a huge field of applications in the medical sector. This work is dedicated to the functional understanding and technical implementation of silicon nanowires for future medical sensor applications. In contrast to doped silicon nanowire based sensors, this work is focussed on pure, undoped silicon nanowires, which have lower demands on production techniques and use Schottky-barriers as electric field detectors. The pH and biosensing capabilities of such undoped silicon nanowire field effect transistors were investigated theoretically and experimentally and further integrated in a lab-on-a-chip device as well as a small-scale multiplexer measurement device. In a second separate part, the optical sensing properties of undoped silicon nanowires were theoretically modeled. The main contents of both parts are shortly described in the following paragraphs. A multiscale model of silicon nanowire FETs to describe the charge transport in liquid surrounding in a quantum mechanical framework was developed to investigate the sensing properties of the nanowire sensors in general. The model set the basis for the understanding of the subsequent experimental investigations of noise characterization, pH sensitivity and biosensing properties. With the help of a novel gate sweeping measurement method the optimal working point of the sensors was determined and the high sensor quality could be quantified in terms of an empirical mathematical model. The sensor was then used for measurements of medically relevant concentrations of the Thrombin protein, providing a proof-of-concept for medical applications for our newly developed sensor. In order to exploit the small size of our sensors for technical applications we integrated the devices in lab-on-a-chip system with a microfluidic droplet generation module. There they were used to measure the pH and ionic concentration of droplets. Finally a portable multiplex measurement device for silicon nanowire sensors as well as other ion sensitive FETs was developed in cooperation with the IAVT at TU Dresden (Institut für Aufbau- und Verbindungstechnik). The second part of this thesis investigates the usability of silicon nanowires for optical sensor applications from a theoretical point of view. Therefore a method for the extraction of Raman and Infrared spectra from molecular dynamics simulations was developed. The method was applied to undoped silicon nanowires and shows that the surface properties of the nanowires has a significant effect on optical spectra. These results demonstrate the relevance of semiconductor nanostructures for applications in optical spectroscopy
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au, D. Parlevliet@murdoch edu, and David Parlevliet. "Silicon Nanowires for Photvoltaic Applications." Murdoch University, 2008. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20090930.140302.
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Silicon nanowires are a nanostructure consisting of elongated crystals of silicon. Like many nanostructures, silicon nanowires have properties that change with size. In particular, silicon nanowires have a band-gap that is tuneable with the diameter of the nanowire. They tend to absorb a large portion of the light incident upon them and they form a highly textured surface when grown on an otherwise flat substrate. These properties indicate silicon nanowires are good candidates for use in solar cells.
Nanostructured silicon, in the form of nanocrystalline silicon, has been used to produce thin film solar cells. Solar cells produced using silicon nanowires could combine the properties of the silicon nanowires with the low material costs and good stability of nanocrystalline based solar cells.
This thesis describes the process of optimisation of silicon nanowire growth on a plasma enhanced chemical vapour deposition system. This optimised growth of silicon nanowires is then used to demonstrate a prototype solar cell using silicon nanowires and amorphous silicon. Several steps had to be accomplished to reach this goal.
The growth of silicon nanowires was optimised through a number of steps to produce a high density film covering a substrate. Developments were made to the standard deposition technique and it was found that by using pulsed plasma enhanced chemical vapour deposition the density of nanowire growth could be improved. Of a range of catalysts trialled, gold and tin were found to be the most effective catalysts for the growth of silicon nanowires. A range of substrates was investigated and the nanowires were found to grow with high density on transparent conductive oxide coated glass substrates, which would allow light to reach the nanowires when they were used as part of a solar cell. The silicon nanowires were combined with doped and intrinsic amorphous silicon layers with the aim to create thin film photovoltaic devices. Several device designs using silicon nanowires were investigated. The variant that showed the highest efficiency used doped silicon nanowires as a p-layer which was coated with intrinsic and n-type amorphous silicon.
By the characterisation and optimisation of the silicon nanowires, a prototype silicon nanowire solar cell was produced. The analysis of these prototype thin film devices, and the nanowires themselves, indicated that silicon nanowires are a promising material for photovoltaic applications.
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Hill, Graeme. "Fabrication and characterization of nanowires." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427296.
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Marks, Samuel R. "Characterisation of encapsulation grown nanowires." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/104205/.
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The push to decrease the size of electronic components has been pioneered over the last decade. This has led to electrodeposition being a primary nanoscale fabrication method. However, this technique is beginning to reach its physical limits with respect to the size of media that can be deposited. Therefore, alternative methods of sub 10 nm fabrication are being investigated. This thesis aims to explore: supercritical fluid electrodeposition as an encapsulated nanowire fabrication method, the phase transitions involved when heating said nanowires in situ and the encapsulation of materials within carbon nanotubes to form truly one-dimensional nanowires. All of this is undertaken using electron microscopy as the primary analysis technique. First, the supercritical fluid electrodeposition process is investigated as a nanowire fabrication technique. Initially, Ge planar films are deposited and shown to form electron beam sensitive crystallites embedded within an amorphous Ge matrix. This is expanded upon, with the deposition of Ge into 13 nm anodic alumina pores, also resulting in the formation of amorphous Ge nanowires. More advanced systems are explored, with crystalline CuTe nanowires forming in the P4/nmm space group. Further to this, the CuTeS system, the first supercritical fluid electrodeposited tertiary system, is proved to form in the Cu6Te3S structure. Sn is deposited into hierarchical alumina in attempts to decrease the encapsulated media size. This shows the ability for sub 10 nm nanowire formation from supercritical fluid electrodeposition. Next, the effects of in situ heating for both Te and Bi nanowires are presented. Here the Te system underwent a sublimation phase transition. The experimental rate of sublimation is imperfect and generates an evaporation coefficient of 2 x 10-3 as a multiplying factor. The effects of elemental contamination manifests in two forms during sublimation. The first as unmoving large masses that slow the rate of sublimation. The second, as a small atomic percentage that flows along the nanowire, at the sublimation front, before condensing in the end of the nanowire. Sublimation is not the only observed phase transition with Bi proven to melt in situ becoming an encapsulated liquid. Selected area diffraction, with radial distribution analysis, results in the first liquid Bi radial peak measured at 3.47 Å. This is akin to bulk neutron diffraction and XRD measurements, however, this is believed to be the first nanoscale measurement. Examination of the suspected pressure drop arising from the remnant alumina proves that the alumina coatings are non-continuous, as no experimental pressure drop is observed. Finally, the encapsulation of materials within carbon nanotubes is presented. It is demonstrated that the melt filling, from Ge and SbTe, will form crystalline bulk-like nanowires during encapsulation. The effects of electron beam interaction are visible, with energetic encapsulated crystallites. A study of the encapsulated SbTe indicates that for an 80kV electron beam, the threshold for amorphisation, due to electron beam heating, lies between a beam energy of 0.8 and 1.5 pA cm-2. Striving for higher filling percentages the sublimation filling technique is examined. For the case of Te, both a bulk-like helix and one-dimensional chain structure is observed across a range of nanowire diameters. Additionally, SnTe is formed generating a one-dimensional chain, for low dimension carbon nanotubes, and a zigzag structure within higher diameters. The chemical composition of both systems is examined using EELS. This proves the Te and zigzag SnTe chemical compositions, but suggests that the SnTe one-dimensional chain is SnI. In order to characterise the crystal structures ab initio random structure searches are performed for the first time. These result in a new level of structural understanding arising from this first order simulation process.
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Phillips, Thomas William. "Flow synthesis of silver nanowires." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/64907.
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This thesis reports the development of a droplet-based flow synthesis of silver nanowires. Using traditional batch methods of production it can be difficult to achieve the consistent reaction conditions needed to obtain nanocrystals with the desired properties. Microfluidic reactors offer superior control over reaction conditions and enable the scalable and continuous production of consistent and monodisperse nanoparticles. Silver nanowires are typically synthesised using the polyol reaction, where silver nitrate is reduced in hot ethylene glycol. Previous reports describing the synthesis of silver nanowires have come to contradictory conclusions about the conditions needed for growth. In this thesis a hot-injection polyol synthesis was adapted to a straightforward heat-up procedure for the production of silver nanowires. The success of the reaction was found to be dependent on the batch of ethylene glycol used. The modified synthesis enabled the development of a flow process using a polytetrafluoroethylene tubing-based droplet-based flow reactor. The reactor produced consistent silver nanowires over an eight hour period with no sign of reactor fouling. The reactor was used to investigate the effect of varying the reaction temperature, residence time, and concentration of iron nitrate and sodium chloride additives on the length of the silver nanowires produced. This thesis finishes with the development of an inline liquid-liquid separator based on the selective wetting and permeation of a porous capillary by one of the liquids. Efficient separation of aqueous-organic, aqueous-fluorous, and organic-fluorous flows was achieved over a wide range of flow rates. The separator was successfully applied to the inline aqueous-organic extraction of the pH indicator 2,6-dichloroindophenol. The organic extract and aqueous raffinate were separated using a porous capillary. UV-visible absorption spectroscopy showed the concentration of indicator in the aqueous raffinate to be less than one percent of its original value, confirming the efficacy of the extraction and separation process.
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Krali, Emiljana. "Thermoelectric effects in silicon nanowires." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18084.
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The increasing demand for fossil fuels, and the need to reduce greenhouse gases, requires ‘clean’ energy sources and more efficient utilisation of energy. Thermoelectric (TE) materials provide a means towards achieving these objectives, as they convert a temperature difference [Delta]T directly into an electric potential difference [Delta]V. For practical applications, a TE material is chosen only if the dimensionless figure-of-merit ZT=S^2σT/κ ≥ 1. Where S = [Delta]V/[Delta]T, σ and κ are the Seebeck coefficient, electrical and thermal conductivity, respectively, at temperature T. Conventional bulk TE materials, such as Bi2[subscript]Te3[subscript], require a compromise between S, σ and κ. In nano-structured materials, these parameters may be varied quasi-independently, suggesting a new approach to obtain high values of ZT. In this thesis, silicon nanowire (SiNW) arrays were fabricated using a metal-assisted chemical etching process, creating SiNWs from 30 to 400 nm in diameter, a maximum length of 350 μm and aspect ratio up to 3000. A novel transient measurement method was used to characterise the temperature dependence of S in two different n-type doped SiNW arrays, ≈10^{15} cm^{-3} and ≈10^{18} cm^{-3}. In the lightly doped 35 μm long SiNWs, S=1850 μV/K at 300 K, an increase by a factor of 2.5 compared to its parent bulk Si (S_{Bulk}). Furthermore, the phonon drag component, a manifestation of electron-phonon scattering in the sample, is heavily suppressed due to surface scattering. In the moderately doped 30 μm long SiNW array, S=1480 μV/K = 2.5S_{Bulk} at 300 K. An increase in S was also observed in the n- and p-SiNWs measurements in ambient conditions. A transient method was used to characterise the temperature dependence of κ in the range 300 – 30 K. At 300 K, κ=23 W/mK = 0.19\κ_{Bulk}. Finally, the I-V characteristics of the SiNW arrays were measured and only a limited change was observed from bulk Si. Assuming σ is unchanged, in the 30 μm long SiNWs, 0.0255 ≤ ZT_{NW} ≤ 0.34. This corresponds to an increase in ZT from 32 to 55 times than the bulk Si value.
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Barnett, Christopher Jonathan. "Surface characterisation of ZnO nanowires." Thesis, Swansea University, 2015. https://cronfa.swan.ac.uk/Record/cronfa43027.
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Zagorskiy, D. L., V. V. Korotkov, V. N. Kudryavtsev, S. A. Bedin, S. N. Sulyanov, K. V. Frolov, V. V. Berezkin, and B. V. Mchedlishvili. "Matrix Synthesis of Magnetic Nanowires." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35260.
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In this work nanowires of magnetic metals (Co,Ni and Fe) were obtained via matrix synthesis, using etched track polymer template. The new data on electrodeposition of Ni was obtained. Two effects- the growth rate decrease (while the growing metal nanowires are filling the pores) and current density in-crease were investigated and discussed.
The results of X-rays analysis obtained using synchrotrone source demonstrated the dependence of structure and composition of nanowires on the deposition voltage. Mossbauer spectroscopy was used for in-vestigation of Fe samples. The obtained data are in good agreement with X-rays results.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35260
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Fawzy, Mirette. "Electrochemical synthesis of functional nanowires." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20972.
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Semiconducting, metal, and multi-segmented nanowires of 200 nm diameters with lengths up to 10_m were synthesized through electrochemical deposition in the pores of anodic aluminium oxide (AAO) and polycarbonate track-etched (PCTE) templates. With the work focusing on CdSe nanowires, results from the cyclic electrodeposition/stripping method was reported with different deposition conditions(potential range, solution, and scan rate). The stoichiometric deposition of CdSe nanowires was confirmed by energy dispersive spectroscopy (EDS) analysis, with an average Cd:Se atomic percentage of0.92. Structural characterizations were done on the synthesized nanowires via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. Devices with a single CdSe nanowire were made by standard electron beam lithography techniques. Electrical transport measurements were performed on the nanowire arrays as well as single contacted CdSe nanowires. Photo response measurements were also carried out on the samples in the dark and under illumination. The nanowire arrays showed pronounced visible light photoconductivity. As a direct application, a preliminary proof-of-concept photoelectrochemical activity test for water splitting using the synthesized CdSe nanowires was performed in a water/methanol mixture.
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Bosisio, Riccardo. "Thermoelectric conversion in disordered nanowires." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066212/document.
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Cette thèse porte sur la conversion thermoélectrique de nanofils semi-conducteurs désordonnés en configuration de transistor à effet de champ.On considère d’abord le régime de transport élastique à basse température. En utilisant un modèle d'Anderson 1D, on dérive des expressions analytiques pour le coefficient Seebeck typique d’un nanofil en fonction de la tension de grille, et on montre que celui-ci augmente fortement en bord de bande. Ces résultats sont confirmés par un calcul numérique du Seebeck, basé sur un algorithme de fonctions de Green récursif.On considère ensuite le régime inélastique où les électrons, assistés par les phonons, sautent entre états localisés. En résolvant numériquement le réseau de résistances aléatoires de Miller-Abrahams, on montre que le coefficient Seebeck peut atteindre des valeurs très élevées au voisinage des bords de bande du nanofil. La théorie de percolation de Zvyagin étendue au cas unidimensionnel nous permet de décrire qualitativement nos résultats. Par ailleurs, les échanges de chaleur entre électrons et phonons en bord de bande entraînent la formation de points chauds et froids à la surface du substrat, qui pourraient être utilisés pour le refroidissement de circuits électroniques. Cet effet est étudié pour un ensemble de fils en parallèle. Le facteur de puissance et la figure de mérite de ces systèmes sont aussi estimés.Enfin, on étudie un système général à trois terminaux en réponse linéaire. On calcule les coefficients de transport locaux et non-locaux, et les figures de mérite généralisées, puis l'on discute à l'aide de deux exemples la possibilité d’améliorer la performance d’une machine thermique quantique génériqueThis thesis is focused on thermoelectric conversion in disordered semiconductor nanowires in the field effect transistor configuration. We first consider a low temperature regime, when electronic transport is elastic. For a 1D Anderson model, we derive analytical expressions describing the typical thermopower of a single nanowire as a function of the applied gate voltage, and we show that it is largely enhanced at the nanowire band edges. Our results are confirmed by numerical simulations based on a Recursive Green Function calculation of the thermopower. We then consider the case of inelastic transport, achieved by phonon-assisted hopping among localized states (Variable Range Hopping). By solving numerically the Miller Abrahams random resistor network, we show that the thermopower can attain huge values when the nanowire band edges are probed. A percolation theory by Zvyagin extended to nanowires allows to qualitatively describe our results. Also, the mechanism of heat exchange between electrons and phonons at the band edges lead to the generation of hot and cold spots near the boundaries of a substrate. This effect, of interest for cooling issues in microelectronics, is showed for a set of parallel nanowires, a scalable and hence promising system for practical applications. The power factor and figure of merit of the device are also estimated.Finally, we characterize a general three-terminal system within the linear response (Onsager) formalism: we derive local and non-local transport coefficients, as well as generalized figures of merit. The possibility of improving the performance of a generic quantum machine is discussed with the help of two simple examples
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Elfström, Niklas. "Silicon nanowires for biomolecule detection /." Stockholm : Material Physics, School of Information and Communication Technology, Royal Institute of Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4695.
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Parlevliet, David Adam. "Silicon nanowires for photovoltaic applications /." Murdoch University Digital Theses Program, 2008. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20090930.140302.
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Parlevliet, David. "Silicon Nanowires for Photvoltaic Applications." Thesis, Parlevliet, David (2008) Silicon Nanowires for Photvoltaic Applications. PhD thesis, Murdoch University, 2008. https://researchrepository.murdoch.edu.au/id/eprint/1308/.
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Silicon nanowires are a nanostructure consisting of elongated crystals of silicon. Like many nanostructures, silicon nanowires have properties that change with size. In particular, silicon nanowires have a band-gap that is tuneable with the diameter of the nanowire. They tend to absorb a large portion of the light incident upon them and they form a highly textured surface when grown on an otherwise flat substrate. These properties indicate silicon nanowires are good candidates for use in solar cells.
Nanostructured silicon, in the form of nanocrystalline silicon, has been used to produce thin film solar cells. Solar cells produced using silicon nanowires could combine the properties of the silicon nanowires with the low material costs and good stability of nanocrystalline based solar cells.
This thesis describes the process of optimisation of silicon nanowire growth on a plasma enhanced chemical vapour deposition system. This optimised growth of silicon nanowires is then used to demonstrate a prototype solar cell using silicon nanowires and amorphous silicon. Several steps had to be accomplished to reach this goal.
The growth of silicon nanowires was optimised through a number of steps to produce a high density film covering a substrate. Developments were made to the standard deposition technique and it was found that by using pulsed plasma enhanced chemical vapour deposition the density of nanowire growth could be improved. Of a range of catalysts trialled, gold and tin were found to be the most effective catalysts for the growth of silicon nanowires. A range of substrates was investigated and the nanowires were found to grow with high density on transparent conductive oxide coated glass substrates, which would allow light to reach the nanowires when they were used as part of a solar cell. The silicon nanowires were combined with doped and intrinsic amorphous silicon layers with the aim to create thin film photovoltaic devices. Several device designs using silicon nanowires were investigated. The variant that showed the highest efficiency used doped silicon nanowires as a p-layer which was coated with intrinsic and n-type amorphous silicon.
By the characterisation and optimisation of the silicon nanowires, a prototype silicon nanowire solar cell was produced. The analysis of these prototype thin film devices, and the nanowires themselves, indicated that silicon nanowires are a promising material for photovoltaic applications.
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Parlevliet, David. "Silicon Nanowires for Photvoltaic Applications." Parlevliet, David (2008) Silicon Nanowires for Photvoltaic Applications. PhD thesis, Murdoch University, 2008. http://researchrepository.murdoch.edu.au/1308/.
Full textAbstract:
Silicon nanowires are a nanostructure consisting of elongated crystals of silicon. Like many nanostructures, silicon nanowires have properties that change with size. In particular, silicon nanowires have a band-gap that is tuneable with the diameter of the nanowire. They tend to absorb a large portion of the light incident upon them and they form a highly textured surface when grown on an otherwise flat substrate. These properties indicate silicon nanowires are good candidates for use in solar cells.
Nanostructured silicon, in the form of nanocrystalline silicon, has been used to produce thin film solar cells. Solar cells produced using silicon nanowires could combine the properties of the silicon nanowires with the low material costs and good stability of nanocrystalline based solar cells.
This thesis describes the process of optimisation of silicon nanowire growth on a plasma enhanced chemical vapour deposition system. This optimised growth of silicon nanowires is then used to demonstrate a prototype solar cell using silicon nanowires and amorphous silicon. Several steps had to be accomplished to reach this goal.
The growth of silicon nanowires was optimised through a number of steps to produce a high density film covering a substrate. Developments were made to the standard deposition technique and it was found that by using pulsed plasma enhanced chemical vapour deposition the density of nanowire growth could be improved. Of a range of catalysts trialled, gold and tin were found to be the most effective catalysts for the growth of silicon nanowires. A range of substrates was investigated and the nanowires were found to grow with high density on transparent conductive oxide coated glass substrates, which would allow light to reach the nanowires when they were used as part of a solar cell. The silicon nanowires were combined with doped and intrinsic amorphous silicon layers with the aim to create thin film photovoltaic devices. Several device designs using silicon nanowires were investigated. The variant that showed the highest efficiency used doped silicon nanowires as a p-layer which was coated with intrinsic and n-type amorphous silicon.
By the characterisation and optimisation of the silicon nanowires, a prototype silicon nanowire solar cell was produced. The analysis of these prototype thin film devices, and the nanowires themselves, indicated that silicon nanowires are a promising material for photovoltaic applications.
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Herder, Charles H. (Charles Henry) III. "Study of ultranarrow superconducting NbN nanowires and nanowires under strong magnetic field for photon detection." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/51603.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Includes bibliographical references (leaves 32-34).
Photon detection is an integral part of experimental physics, high-speed communication, as well as many other high-tech disciplines. In the realm of communication, unmanned spacecraft are travelling extreme distances, and ground stations need more and more sensitive and selective detectors to maintain a reasonable data rate. In the realm of computing, some of the most promising new forms of quantum computing require consistent and efficient optical detection of single entangled photons. Due to projects like these, demands are increasing for ever more efficient detectors with higher count rates. The Superconducting Nanowire Single-Photon Detector (SNSPD) is one of the most promising new technologies in this field, being capable of counting photons as faster than 100MHz and with efficiencies around 50%. Currently, the leading competition is from the geiger-mode avalanche photodiode, which is capable of ~20 ~70% efficiency at a ~5MHz count rate depending on photon energy. In spite of this, the SNSPD is still a brand-new technology with many potential avenues unexplored. Therefore, it is still possible that we can achieve even better efficiencies and count rates to keep up with the requirements of burgeoning technologies. This photon detector consists of a meandering superconducting nanowire biased close to its critical current. In this regime, a single incident photon can cause a section of the detector to switch to normal conduction, producing a voltage pulse due to its now-finite resistance. An electron micrograph is given in figure 1. The intrinsic limitations of the detector (disregarding the optical coupling mechanism and the support electronics) are dominated by two primary points. First is the efficiency with which the detector converts an absorbed photon into a voltage pulse. This is controlled by the behavior of the excited electrons at the point of incidence. I will discuss this in greater detail in the next section. The second is the electrothermal time constant of the detector. This limits the relaxation time of the detector and therefore limits the maximum rate at which the detector can count photons. As we will see, detection efficiency increases as the number of Cooper pairs that need to be excited into the normal state to switch conduction modes decreases. One way to decrease the bandgap is to decrease the cross-section of the wire. This has already been shown to increase detection efficiency, but this cannot be done to arbitrarily narrow wires. Not only is there a limitation to fabrication, but there are also interesting quantum effects that occur at very narrow wire widths. Note that much of the research that has been done to understand these quantum effects has been undertaken on wires much wider than those we will be using. Simultaneously, most of the materials used previously have coherence lengths much longer than NbN. Therefore, even though our wires are narrower by a substantial factor, they are still wider than the coherence length of NbN. As such the validity of the one-dimensional approximation to be presented in in 2.2 is debatable for our wires. However, it should be apparent that regardless of behavior, thermal and quantum phase slips will be one of the limiting factors in producing ultra-narrow nanowire photon detectors. Until now, photon detectors have only used current biasing techniques. However, it is well known that both magnetic field and current have the effect of reducing the energy required to excite superconducting charge carriers. Therefore, it may be possible to detect photons using magnetic field close to H, instead of current close to Ic. It is important to note, however, that the readout of the detector in its current configuration depends on some bias current to produce a voltage pulse. Therefore, with the current detector architecture, one still needs a significant bias current. For my thesis, I have first investigated the theory of supercurrents in ultranarrow wires and confirmed the behavior of this theory with our materials and fabrication techniques in order to establish a lower bound for wire width where photon detection is still possible. In addition, I have constructed and executed an initial experiment to test how photon detectors behave under magnetic field bias conditions. I have measured how these different bias conditions affect the efficiency of the detector as well as the dark count rate.
by Charles H. Herder, III.
S.B.
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Kockert, Maximilian Emil. "Thermoelectric transport properties of thin metallic films, nanowires and novel Bi-based core/shell nanowires." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23001.
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Thermoelektrische Phänomene können in Nanomaterialien im Vergleich zum Volumenmaterial stark modifiziert werden. Die Bestimmung der elektrischen Leitfähigkeit, des absoluten Seebeck-Koeffizienten (S) und der Wärmeleitfähigkeit ist eine wesentliche Herausforderung für die Messtechnik in Hinblick auf Mikro- und Nanostrukturen aufgrund dessen, dass die Transporteigenschaften vom Volumenmaterial sich durch Oberflächen- und Einschränkungseffekte verändern können.
Im Rahmen dieser Abschlussarbeit wird der Einfluss von Größeneffekten auf die thermoelektrischen Eigenschaften von dünnen Platinschichten untersucht und mit dem Volumenmaterial verglichen. Dafür wurde eine Messplattform als standardisierte Methode entwickelt, um S einer dünnen Schicht zu bestimmen. Strukturelle Eigenschaften wie Schichtdicke und Korngröße werden variiert. Grenz- und Oberflächenstreuung reduzieren S der dünnen Schichten im Vergleich zum Volumenmaterial.
Außerdem wird eine Methode demonstriert um S von einzelnen metallischen Nanodrähten zu bestimmen. Für hochreine und einkristalline Silber-Nanodrähte wird der Einfluss von Nanostrukturierung auf die Temperaturabhängigkeit von S gezeigt.
Ein Modell ermöglicht die eindeutige Zerlegung des temperaturabhängigen S von Platin und Silber in einen Thermodiffusions- und Phononen-Drag-Anteil.
Des Weiteren werden die thermoelektrischen Transporteigenschaften von einzelnen auf Bismut-basierenden Kern/Hülle-Nanodrähten untersucht. Der Einfluss des Hüllenmaterials (Tellur oder Titandioxid) und der räumlichen Dimension des Nanodrahts auf die Transporteigenschaften wird diskutiert. Streuung an Oberflächen, Einkerbungen und Grenzflächen zwischen dem Kern und der Hülle reduzieren die elektrische und thermische Leitfähigkeit. Eine Druckverformung induziert durch die Hülle kann zu einer Bandöffnung bei Bismut führen, sodass S gesteigert werden kann. Das Kern/Hülle-System zeigt in eine Richtung, um die thermoelektrischen Eigenschaften von Bismut erfolgreich anzupassen.Thermoelectric phenomena can be strongly modified in nanomaterials compared to the bulk. The determination of the electrical conductivity, the absolute Seebeck coefficient (S) and the thermal conductivity is a major challenge for metrology with respect to micro- and nanostructures because the transport properties of the bulk may change due to surface and confinement effects. Within the scope of this thesis, the influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. For this reason, a measurement platform was developed as a standardized method to determine S of a thin film. Structural properties, like film thickness and grain size, are varied. Boundary and surface scattering reduce S of the thin films compared to the bulk. In addition, a method is demonstrated to determine S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, the influence of nanopatterning on the temperature dependence of S is shown. A model allows the distinct decomposition of the temperature-dependent S of platinum and silver into a thermodiffusion and phonon drag contribution. Furthermore, the thermoelectric transport properties of individual bismuth-based core/shell nanowires are investigated. The influence of the shell material (tellurium or titanium dioxide) and spatial dimension of the nanowire on the transport properties are discussed. Scattering at surfaces, indentations and interfaces between the core and the shell reduces the electrical and the thermal conductivity. A compressive strain induced by the shell can lead to a band opening of bismuth increasing S. The core/shell system points towards a route to successfully tailor the thermoelectric properties of bismuth.
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Kim, Dong Sik. "Growth and characterization of ZnO nanowires." kostenfrei, 2009. http://nbn-resolving.de/urn:nbn:de:gbv:3:4-455.
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Ranjan, Nitesh. "Dielectrophoretic formation of nanowires and devices." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1234886392156-77111.
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We report the self assembly of nanostructures via. the bottom-up approach by dielectrophoresis. Dielectrophoresis deals with the force on an electric dipole placed in an external in-homogenous field. The force depends on the geometry and volume of the dielectric material and on the frequency and gradient of the electric field. We report the self-assembly of metallic palladium nanowires from the aqueous solution by dielectrophoresis. The metal cations with the surrounding hydration shell and counter-ion cloud results in the formation of a dipole which responds to the local dielectrophoretic forces. Structural properties and morphology of the palladium nanowires are listed. Depending on the experimental conditions two different types of nanowires were grown. Some of them were extremely thin (5 nm diameter) and branched while the others were thick (25 nm diameter) and dendritic. The wire formation can be divided into the nucleation and growth process. For the particle assembly, a minimum threshold force is needed to overcome the random Brownian motion. The nucleation depends on the asperities on the electrode surface and the growth depends on the tip of the growing wires where exists extremely high field magnitude and in-homogeneties and so the force overcomes the threshold at these locations. We showed that wire growth depends a lot on the formation of the double layer at the electrode/solution interface and potential drop within the double layer. Carbon nanotubes (CNT) were also deposited between the electrodes leading to the formation of field-effect transistors (FETs). We produced CNTFETs having extremely high on/off ratio, in a single step without the requirement of any intermediate burning process of the metallic tubes. Besides these inorganic systems, we also investigated the dielectrophoretic experimental conditions required for self assembly of bio-molecules like microtubules between the electrodes. Hybrid structures were also formed by mixing these materials in combination of two. In conclusion, we report in this work the possibility to assemble a large variety of particles (ions, neutral particles and bio-molecules) between the electrodes leading to the device formation. The thesis was mainly devoted to the task for the synthesis and assembly of the nanostructures via. the bottom-up approach.
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Müller, Torsten. "Ion Beam Synthesis of Ge Nanowires." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29801.
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The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves. Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations. In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation. The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.
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Slinger, Jane Bronwyn. "Post-deposition doping of silicon nanowires." University of the Western Cape, 2018. http://hdl.handle.net/11394/5695.
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Magister Scientiae - MScSilicon nanowires (Si NWs) continue to demonstrate superior properties to their bulk counterparts, with respect to their morphological and electrical transport properties for the use in photovoltaic (PV) applications. The two most common and simplest approaches for Si NW fabrication are the bottom-up approach, namely, vapour-liquidsolid (VLS) growth and the top-down approach, namely, the metal-assisted chemical etching (MaCE) fabrication technique. Thermal diffusion of phosphorus (P) in Si is at present the primary method for emitter formation in Si solar cell processing. Most work done in the literature that is based on the diffusion doping of Si NWs has been carried out by means of VLS-grown Si NWs. Therefore, there is a lack of the understanding of the particular diffusion mechanism of applying the phosphorus dopant source to the MaCE-grown Si NWs.
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KANJAMPURATH, SIVAN ASWATHI. "Carrier dynamics in semiconductor nanowires." Doctoral thesis, 2021. http://hdl.handle.net/11573/1500622.
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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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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.
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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.
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Bid, Aveek. "Resistance Fluctuations And Instability In Metal Nanowires." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/429.
Full textAbstract:
The principal aim of this thesis is to study the electrical transport properties of metal nanowires. Specifically, we have focussed on investigating the resistance fluctuations of Ag and Cu nanowires of diameters ranging from 15nm to 200nm and studied the instabilities that set in when the diameter is reduced below a certain range.
The nanowires were grown electrochemically inside polycarbonate and alumina templates. X-ray diffraction studies on the samples showed the presence of a HCP 4H phase in the Ag nanowires in addition to the usual FCC phase, which is seen in bulk Ag. The relative ratios of these two phases were a maximum for nanowires of diameter 30nm. The X-ray diffraction studies also showed that the samples were of high chemical purity. TEM studies revealed that the wires are single crystalline in nature. Once the wires are released from the template, the wires of diameter 15nm were seen to break down spontaneously into globules due to Rayleigh instability. Wires of larger diameter tended to neck down to smaller radius but did not break down completely into globules.
Both the Ag and Cu nanowire arrays had a fairly linear temperature dependence of resistance down to about 100K and reached a residual resistance below 40-50K. The temperature dependence of resistance could be fitted to a Bloch-Grüneisen formula over the entire temperature range. We found that n = 5 gave the best fit for the wires of all diameters showing that the dominant contribution to the temperature dependence of the resistivity in theses nanowires come from electron-acoustic phonon interactions. The resistivities of the wires were seen to increase as the wire diameter was decreased. This increase in the resistivity of the wires could be attributed to surface scattering of conduction electrons.
In nanowires of diameter 15nm of both Ag and Cu, the relative variance of resistance fluctuations <(ΔR)2>/R2 showed a prominent peak at around ~ 220K for the Ag nanowire and ~ 260K for the Cu wire. Ag wires of diameter 20nm showed a much-reduced peak in noise at a somewhat higher temperature while this feature was completely absent in wires of larger diameter as also for the reference Ag film. The noise in wires of diameter larger than 20nm was similar to that of the reference film. For wires of diameter 15nm as we approach T*, the power spectral density showed a severe deviation from 1/f nature. We could establish that the extra fluctuation seen in the nanowires of the narrowest diameters could originate from the Rayleigh instability. The measured resistance fluctuation was found to have a magnitude similar to that estimated from a simple model of a wire showing volume preserving fluctuation.
In the temperature range T ≤ 100K we observed very large non-Gaussian resistance fluctuations in a narrow temperature range for Ag and Cu wires of diameter 30nm with the fluctuations becoming much smaller as the diameter of the wires deviated from 30nm. In wires of diameter larger than 50nm the noise was almost independent of temperature in this range. The power spectrum of the resistance fluctuations also developed a large additional low frequency component near TP. We could establish that the appearance of this noise at a certain temperature (~30 – 50K) is due to the onset of martensite strain accommodation in these nanowires.
To summarize, we measured the resistance and resistance fluctuations of Ag and Cu nanowires of diameters ranging from 15nm to 200nm in the temperature range 4.2-300K. The temperature dependence of resistance could be fitted to a Bloch-Grüneisen formula over the entire temperature range of measurement (4.2K-300K). The contribution of electron-phonon scattering to the resistivity was found to be similar to that of bulk. The defect free nature of our samples allowed us to identify two novel sources of noise in these nanowires. At high temperatures Rayleigh instability causes the noise levels in wires of diameter around 15nm to increase. At lower temperatures the formation of martensite state leads to an increase in noise in wires of small diameters.
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Bid, Aveek. "Resistance Fluctuations And Instability In Metal Nanowires." Thesis, 2006. http://hdl.handle.net/2005/429.
Full textAbstract:
The principal aim of this thesis is to study the electrical transport properties of metal nanowires. Specifically, we have focussed on investigating the resistance fluctuations of Ag and Cu nanowires of diameters ranging from 15nm to 200nm and studied the instabilities that set in when the diameter is reduced below a certain range.
The nanowires were grown electrochemically inside polycarbonate and alumina templates. X-ray diffraction studies on the samples showed the presence of a HCP 4H phase in the Ag nanowires in addition to the usual FCC phase, which is seen in bulk Ag. The relative ratios of these two phases were a maximum for nanowires of diameter 30nm. The X-ray diffraction studies also showed that the samples were of high chemical purity. TEM studies revealed that the wires are single crystalline in nature. Once the wires are released from the template, the wires of diameter 15nm were seen to break down spontaneously into globules due to Rayleigh instability. Wires of larger diameter tended to neck down to smaller radius but did not break down completely into globules.
Both the Ag and Cu nanowire arrays had a fairly linear temperature dependence of resistance down to about 100K and reached a residual resistance below 40-50K. The temperature dependence of resistance could be fitted to a Bloch-Grüneisen formula over the entire temperature range. We found that n = 5 gave the best fit for the wires of all diameters showing that the dominant contribution to the temperature dependence of the resistivity in theses nanowires come from electron-acoustic phonon interactions. The resistivities of the wires were seen to increase as the wire diameter was decreased. This increase in the resistivity of the wires could be attributed to surface scattering of conduction electrons.
In nanowires of diameter 15nm of both Ag and Cu, the relative variance of resistance fluctuations <(ΔR)2>/R2 showed a prominent peak at around ~ 220K for the Ag nanowire and ~ 260K for the Cu wire. Ag wires of diameter 20nm showed a much-reduced peak in noise at a somewhat higher temperature while this feature was completely absent in wires of larger diameter as also for the reference Ag film. The noise in wires of diameter larger than 20nm was similar to that of the reference film. For wires of diameter 15nm as we approach T*, the power spectral density showed a severe deviation from 1/f nature. We could establish that the extra fluctuation seen in the nanowires of the narrowest diameters could originate from the Rayleigh instability. The measured resistance fluctuation was found to have a magnitude similar to that estimated from a simple model of a wire showing volume preserving fluctuation.
In the temperature range T ≤ 100K we observed very large non-Gaussian resistance fluctuations in a narrow temperature range for Ag and Cu wires of diameter 30nm with the fluctuations becoming much smaller as the diameter of the wires deviated from 30nm. In wires of diameter larger than 50nm the noise was almost independent of temperature in this range. The power spectrum of the resistance fluctuations also developed a large additional low frequency component near TP. We could establish that the appearance of this noise at a certain temperature (~30 – 50K) is due to the onset of martensite strain accommodation in these nanowires.
To summarize, we measured the resistance and resistance fluctuations of Ag and Cu nanowires of diameters ranging from 15nm to 200nm in the temperature range 4.2-300K. The temperature dependence of resistance could be fitted to a Bloch-Grüneisen formula over the entire temperature range of measurement (4.2K-300K). The contribution of electron-phonon scattering to the resistivity was found to be similar to that of bulk. The defect free nature of our samples allowed us to identify two novel sources of noise in these nanowires. At high temperatures Rayleigh instability causes the noise levels in wires of diameter around 15nm to increase. At lower temperatures the formation of martensite state leads to an increase in noise in wires of small diameters.
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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.
Full textAbstract:
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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Smith, Damon Allen. "Mechanical, electromechanical, and optical properties of germanium nanowires." 2009. http://hdl.handle.net/2152/7678.
Full textAbstract:
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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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.
Full textAbstract:
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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Tsai, Wei-Chih, and 蔡維志. "Characterization and Applications of Tungsten Oxide Nanowires, Nickel Nanowires, and Zinc Oxide Nanowires." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/28337297150514241409.
Full textAbstract:
博士國立成功大學
微電子工程研究所碩博士班
97
In this thesis, the growth and physical/chemical properties of one-dimensional tungsten oxide nanowires (TONWs), nickel nanowires (NiNWs), zinc oxide nanowires (ZnO-NWs) were investigated. This study also proposes the use of a these NWs structures for potential in applications of nano electronic and optoelectronic devices. In the first study, for the growth of TONWs, pure tungsten films with a thickness of 60 nm on n-type Si wafers were subjected to thermal annealing in a quartz tube furnace at 700oC in nitrogen ambient for 30 min. After thermal annealing, straight TONWs with a density of around 250 贡m-2 and length/diameter of around 0.2 贡m/20 nm were obtained. However, oxygen adsorption might arise from the oxygen contamination of source material during wire growth, the residual oxygen in sputtered films or intentionally doped oxygen gas during sputtering deposition, and oxygen/humidity adsorption of the grown TONWs. In this study, H-plasma treatment is used to reduce the amount of oxygen adsorption and to tailor the density and morphologies of TONWs. Improved field emission (FE) characteristics are demonstrated and the related reduction in the effective emission barrier height is analyzed and discussed. In general, FE current is a complex function of the work function, tip shape, diameter, length, and density of the emitter array. All of these factors affect the local field around the tip of nanowires and hence the FE current. In the previous study, the as-grown TONWs with a typical work function of 6.2 eV and their FE characteristics have been studied. Nanowires with a lower work function are expected to give better FE characteristics. So NiNWs with a lower work function of 5.15 eV are used as new electron field emitters. Well-ordered and vertically-aligned NiNWs with a controllable length in the range of 2.7~22 mm and high density of 1.5-2.1 109 cm-2 were grown inside the nanopores of anodic alumina oxide templates (AAOTs) using a simple electrochemical deposition (ECD) method. To measure electron FE characteristics of the prepared NiNWs, 60-mm-thick AAOTs were served as an insulating spacer. The relatively better FE characteristics with a turn-on field and the enhancement factor of 8.5-贡m-long NiNWs prepared within 100 pore diameter AAOTs were about 3.46 V/mm and 17621, respectively. It is expected that NiNWs prepared inside the nanopores of AAOTs with controllable diameters and lengths could offer an additional choice of material for electron field emitter applications. In addition, in order to obtain the pristine vertically-aligned NiNWs for FE characteristics measurements, the AAOTs were removed and the electron FE characteristics of the prepared NiNWs before and after removing the AAOTs were measured and discussed. After removing the AAOT, NiNWs showed better electron FE characteristics than the others within the AAOT. The effect of the aluminum oxide pillars on the FE characteristics of NiNWs has been examined, and their removal might make possible the immunity of FE electrons collision and accumulation on the vertical surface of the pillars, leading to a significant improvement in the FE performance. Recently, nano heterostructured materials have attracted lots of attention because of the quantum confinement effects of nano heterojunctions (NHJs) and for their potential applications on quantum optoelectronic devices. In this study, well-ordered and vertically-aligned NiO/ZnO NHJs were grown inside the nanopores of AAOTs using ECD and thermal oxidization. This synthesis method presents a simple and novel method for the self-synthesis of NHJs NWs without using catalysts, easily growing and the length of NWs can be controlled accurately. The electrical characteristics of NiO/ZnO NHJs show a rectifying behavior of a p-n junction, while the Ni/Zn NHJs show an ohmic behavior. The optoelectronic characteristics of NiO/ZnO NHJs show a well rectifying behavior and strong photo response to the ultraviolet (UV) lights (254 and 366 nm). Possible carrier transport of the NiO/ZnO NHJs under UV light irradiation is analyzed and discussed. Because of less dimension of the NiO/ZnO NHJs show profound quantum confinement effect, these devices are expected to exhibit much better optoelectronic performance than conventional planar devices. In order to improve the optoelectronic properties of the NHJs and to overcome the processing expensive and time consuming, a novel technology using hydrothermal growth (HTG) associated with deposition techniques for the fabrication of nano hetero structure based on ZnO nanowires (ZnO-NWs) is reported in this study. The HTG method is the most commonly used for commercial applications because of their low cost of equipment, large-area and uniform fabrication, and low processing temperature. NiO/ZnO-NWs NHJs were formed via e-beam deposition of p-type NiO onto the vertical-aligned ZnO-NWs grown by HTG method. Furthermore, the use of a ZnO-NW-based heterojunction structure for applications of nano optoelectronic sensors and photovoltaic devices was proposed. The optoelectronic properties of the NiO/ZnO-NWs NHJs with different NiO thicknesses under UV light (366 nm, 6 mW/cm2) illumination, with good UV sensitivity were analyzed and discussed. Under simulated AM 1.5G solar light illumination, the fabrication of NiO/Zn-NWs NHJs solar cell and its photovoltaic characteristics were also presented. Finally, ZnO with a wide direct bandgap (3.37 eV) and a large excitation biding energy (60 meV) is a promising n-type semiconductor material for applications of light emitting diodes, sensors, and solar cells. In addition, ZnO-NWs are widely used to yield better efficiency for sensor and solar energy than thin films because of their nanosized structures, high integration, high surface active area, attractive optoelectronic properties, and the profound quantum confinement effect. For the application of photovoltaic and solar cell devices, the growth of ZnO-NWs with controllable diameter/length/density and fabrication of n-ZnO-NWs-based NHJs with p-type GaN are studied. A number of ZnO-NWs/p-GaN NHJs have been studied as a strong candidate for optoelectronic device applications, since these materials (ZnO and GaN) have similar fundamental bandgap energy, the relatively close physical properties, and a low lattice constant mismatch. Under AM 1.5G solar light illumination, the fabrication of n-ZnO-NW/p-GaN solar cells and their photovoltaic characteristics with different lengths of ZnO-NW were analyzed. Effects of the length of ZnO-NWs on the photovoltaic performance of the ZnO-NWs/p-GaN NHJs were also investigated and discussed.
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Shakthivel, Dhayalan. "Thermodynamics and Kinetics of Nucleation and Growth of Silicon Nanowires." Thesis, 2014. http://etd.iisc.ernet.in/handle/2005/2896.
Full textAbstract:
Si nanowires have potential applications in a variety of technologies such as micro and nanoelectronics, sensors, electrodes and photovoltaic applications due to their size and specific surface area. Au particle-assisted vapour-liquid-solid or VLS growth method remains the dominant process for Si nanowire growth. A comprehensive kinetic model that addresses all experimental observations and provides a physico-chemical model of the VLS growth method is thus essential. The work done as part of this research is divided into two sections.
A steady state kinetic model was first developed for the steady state growth rate of Si nanowires using SiCl4 and SiH4 as precursors. The steady state refers to a balance between the rates of injection and ejection of Si into the Au droplet. This balance results in a steady state supersaturation under which wire growth proceeds. In particular evaporation and reverse reaction of Si from the Au droplet and modes of crystal growth for wire growth have been considered in detail for the first time. The model is able to account for both, the radius independent and radius dependent growth rates reported in the literature. It also shows that the radius dependence previously attributed to purely thermodynamic considerations could also as well be explained just by steady state kinetics alone. Expressions have been derived for the steady state growth rate that require the desolvation energy, activation energy for precursor dissociation and supersaturation prevalent in the particle as inputs for calculation.
In order to evaluate this model the incubation and growth of Si nanowires were studied on sapphire substrates in an indigenously built automated MOCVD reactor. Sapphire was chosen as the substrate, as opposed to Si which is commonly used, so as to ensure that the vapour phase is the only source of Si. A classical incubation period for nucleation, of the order of 4-8 minutes, was experimentally observed for the first time.
Using the change in this incubation period with temperature a value of 15kT was determined to be the desolvation energy for growth using SiH4. The steady state growth rate of Si nanowires were measured and compared with the predictions of the model using the values of activation energies so determined.
The thesis based on the current research work is organized as follows:
Chapter 1 introduces the research area followed by a brief outline of the overall work
Chapter 2 provides a summary of current literature, and puts the research described in this thesis in perspective. The diameter dependent growth rate of NWs which was initially solely attributed to the Gibbs-Thomson effect is first summarized. Experimental observations to the contrary are then highlighted. These contradictions provided the incentive for the research described in this thesis. Following a summary of the growth rate theories, the experimental observations on incubation available in the literature are summarized. All the other variants of the VLS method are also discussed.
Chapter 3 describes the design, construction and working of an indigenously built semi- automated CVD reactor. This CVD reactor was used to conduct the Si NW growth experiments over sapphire substrates.
Chapter 4 develops the physical chemistry model for Au catalyzed Si nanowire growth using SiCl4 and SiH4 precursors. The model originated from the contradictions present in the literature over the rate limiting step of the VLS growth mechanism and the steady state growth rate dependence on wire diameter. The development starts with explaining the thermodynamics of the steady state VLS process. The significance of the model lies in the detailed analysis of the all the atomistic process occurring during the VLS growth. In particular the evaporation and reverse reaction of Si from Au-Si droplet is explained in detail and possibly for the first time. Expressions for steady state growth rate by various modes, such as layer by layer growth (LL), by multilayer growth (ML) and growth by movement of a rough interface at the L-S growth interface are derived and presented.
Chapter 5 discusses the results which emerge out the kinetic model from the previous chapter. Under a single framework of equations, the model is successful in explaining both the diameter independent and diameter dependent growth of NWs. As one of the major outcomes of the model, the growth rates of Si NWs are predicted and trends in growth rate are found to agree with those experimentally observed. Growth rate dependencies on pressure and temperature are implicitly included in the equations derived. An estimate of supersaturation has been extracted for the first time using the framework of equations.
Chapter 6 contains the experimental results of the Si NW growth over sapphire substrates. An incubation period in the order of 3-8 minutes has been observed for Si NW growth on sapphire. The data has been compared with existing literature data and interpreted using classical transient nucleation theory. The incubation period data has been utilized to extract the kinetic parameter, QD, which is the desolvation enegy. These parameters and the measured steady state growth rates have been used to estimate the supersaturation existing in the droplet using the framework developed in chapters 4 and 5.
Chapter 7 summarizes the outcome of the current research and highlights the future directions for the research problem addressed in this thesis.
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Roy, Ahin. "Investigation of Structural and Electronic Aspects of Ultrathin Metal Nanowires." Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3091.
Full textAbstract:
The constant trend of device miniaturization along with ever-growing list of unusual behaviour of nanoscale materials has fuelled the recent research in fabrication and applications of ultrathin (~2 nm diameter) nanowires. Although semiconductor nanowires of this dimension is well-researched, molecular-scale single-crystalline metal nanowires have not been addressed in details. Such single crystalline Au nanowires are formed by oriented attachment of Au nanoparticles along [111] direction. A very low concentration of extended defects in these wires result in a high electrical conductivity, making them ideal for nanoscale interconnects. Other metal nanowires, e.g. Ag and Cu, have very low absorption co-efficient useful for fabrication of transparent conducting films. On the other hand, because of the reduced dimensions, there exists a tantalizing possibility of dominating quantum effects leading to their application in sensing and actuation. Also, speaking in terms of atomic structure, these systems suffer from intense surface stress, and the atomistic picture can be drastically different from bulk. Thus, although a myriad of applications are possible with ultrathin metal nanowires, a rigorous systematic knowledge of their atomic and electronic structure is not yet available. This thesis is the first one to model such computationally demanding systems with emphasis on their possible applications.
In this thesis, we have explored various structural and electronic aspects of one-dimensional ultrathin nanowires with ab initio density functional theory coupled with experiments. The merit of Au nanowires has been tested as nanoscale interconnects. From atomistic point of view, these FCC Au nanowires exhibit an intriguing relaxation mechanism, which has been explored by both theory and experiment. The primary factor governing the relaxation mechanism was found to be the anisotropic surface stress of the bounding facets, and it is extended to explain the relaxation of other metallic nanowires. Our studies suggest that AuNWs of this dimension show semiconductor-like sensitivity towards small chemical analytes and can be used as nanoscale sensors. Also, we have found that further reducing the diameter of the Au-nanowires leads to opening of a band gap.
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Roy, Ahin. "Investigation of Structural and Electronic Aspects of Ultrathin Metal Nanowires." Thesis, 2015. http://hdl.handle.net/2005/3091.
Full textAbstract:
The constant trend of device miniaturization along with ever-growing list of unusual behaviour of nanoscale materials has fuelled the recent research in fabrication and applications of ultrathin (~2 nm diameter) nanowires. Although semiconductor nanowires of this dimension is well-researched, molecular-scale single-crystalline metal nanowires have not been addressed in details. Such single crystalline Au nanowires are formed by oriented attachment of Au nanoparticles along [111] direction. A very low concentration of extended defects in these wires result in a high electrical conductivity, making them ideal for nanoscale interconnects. Other metal nanowires, e.g. Ag and Cu, have very low absorption co-efficient useful for fabrication of transparent conducting films. On the other hand, because of the reduced dimensions, there exists a tantalizing possibility of dominating quantum effects leading to their application in sensing and actuation. Also, speaking in terms of atomic structure, these systems suffer from intense surface stress, and the atomistic picture can be drastically different from bulk. Thus, although a myriad of applications are possible with ultrathin metal nanowires, a rigorous systematic knowledge of their atomic and electronic structure is not yet available. This thesis is the first one to model such computationally demanding systems with emphasis on their possible applications.
In this thesis, we have explored various structural and electronic aspects of one-dimensional ultrathin nanowires with ab initio density functional theory coupled with experiments. The merit of Au nanowires has been tested as nanoscale interconnects. From atomistic point of view, these FCC Au nanowires exhibit an intriguing relaxation mechanism, which has been explored by both theory and experiment. The primary factor governing the relaxation mechanism was found to be the anisotropic surface stress of the bounding facets, and it is extended to explain the relaxation of other metallic nanowires. Our studies suggest that AuNWs of this dimension show semiconductor-like sensitivity towards small chemical analytes and can be used as nanoscale sensors. Also, we have found that further reducing the diameter of the Au-nanowires leads to opening of a band gap.
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"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