In this thesis, the fundamentals of quantum dots in carbon nanotubes are. In this thesis, we investigate carbon nanotube cnt quantum dot qd hybrid devices in which a single cnt is coupled either to superconducting s and normal metal n electrodes or to ferromagnetic f contacts by means of lowtemperature transport spectroscopy experiments. The noise detection is based on photon assisted tunneling in a superconductorinsulatorsuperconductor junction. The sample is first evaporated under one angle dark, then oxidized. Lastly, the areas of the quantum dot not covered by the etch mask are chemically etched away poole. The motivation behind using carbon nanotubes lies with the fact that they provide a priori confinement in two dimensions, making the quantum dot fabrication procedure simpler. Currentvoltage characteristics of suspended carbon nanotube quantum dots show an additional series of steps equally spaced in. This thesis presents research into spintransport in carbon nanotube quantum dots. A carbon nanotube quantum dot cnt qd is a small region of a carbon nanotube in which electrons are confined. This way it was possible to extend the system to form a double quantum dot. Single electron transistors and carbon nanotube double quantum.
While tio2 nanotube arrays cosensitized with cds and pbs quantum dots can achieve water splitting under visible light excitation, the use of quantum dots is limited by the relatively slow interfacial hole transfer rate and low internal quantum efficiencies in the visible region. Sputtered permalloy electrodes designed with shape anisotropy were used to contact carbon nanotubes grown by chemicalvapour deposition in lateral spinvalve structures. Quantum dots 2 quantum dot qd is a conducting island of a size comparable to the fermi wavelength in all spatial directions. Master thesis hybrid devices based on carbon nanotubes. Chem library, imperial college of science, technology and medicine, uk. Outline of thesis the problem statement behind this thesis was the following. All in all, i can affirm that the research into cnt qds has reached a reasonable level of. Often called the artificial atoms, however the size is much bigger 100 nm for qds versus 0. Scanning gate imaging of two coupled quantum dots in single. Characterization of conjugated quantum dots and carbon nanotube qd.
Cornell university 2004 the experiments presented in this thesis show that carbon nanotube nt electronic structure can be tuned by mechanical stretching and by magnetic fields. In single quantum dots defined in short lengths of nanotube, the energy levels associated. Carbon nanotube quantum dots 3 in order to observe the rich physics of charge transport through quantum dots, though, it is necessary to introduce tunnel barriers at those interfaces, which will decrease the transmission t thesis submitted to the faculty of the graduate school of vanderbilt university in partial fulfillment of the requirements for the degree of master of science in chemistry december, 2010 nashville, tennessee approved. The experiments presented in this thesis show that carbon nanotube nt electronic structure can be tuned by mechanical stretching and by magnetic fields.
Quantum dot josephson junctions in the kondo regime. There are various ways of producing swnts, which are briefly discussed later. Quantum transport in carbon nanotubes semantic scholar. Tuning the band structure of carbon nanotubes ethan davis minot, ph.
We precisely extract the tunnel coupling and identify the molecular states by the sequentialtunneling line shape of the resonances in di. Ultrashort carbon nanotube quantum dot transistors. Exact calculations are combined with a simple model to provide an intuitive and accurate description of singleparticle and interaction effects. Carbon nanotubes can be used as quantum bits for quantum computers. This master thesis describes the fabrication steps and complications of. Local gate control in carbon nanotube quantum devices. A quantum dot qd is defined between two argon ion induced defects, revealing quantized states with a large level spacing in the conduction and valence bands. Churchill quantum dots in gated nanowires and nanotubes abstract this thesis describes experiments on quantum dots made by locally gating onedimensional quantum wires.
The exposed resist is removed from the substrate by immersing the sample in. Highly tunable hole quantum dots in sige shellcore nanowires. The observed values are nevertheless already significantly below g 2. In summary, we have investigated random telegraph noise observed in semiconducting cnt quantum dot. Quantum phase transition in a singlemolecule quantum dot. A superconducting quantum interference device squid with singlewalled carbon nanotube cnt josephson junctions is presented. For nanotube quantum dot we adopted the dependence. Physics of very small bandgap carbon nanotube quantum dots. This thesis presents experimental attempts towards advances in the field of quantum computation using carbon nanotube based quantum dot devices and highfrequency techniques.
This thesis presents experimental attempts towards advances in the field of quantum computation using carbon nanotubebased quantum dot devices and highfrequency techniques. The locations of single wall carbon nanotube quantum dots were. Quantum dots in gated nanowires and nanotubes abstract this thesis describes experiments on quantum dots made by locally gating onedimensional quantum wires. We next chose parameters which concerns the nanotube dot region. Quantum dots form during the epitaxial growth of two semiconductors having two different lattice constants. The magnetoresistance of these spinvalves were measured at lowtemperatures and as a function of the charge state of the quantum dots. The ratio of lifetimes of the highcurrent state to the lowcurrent state changes exponentially with respect to the gatevoltage, and also. Andreev and spin transport in carbon nanotube quantum dot.
Pdf carbon nanotubes are a versatile material in which many aspects of condensed. This thesis describes the design, fabrication, and characterization of a photo. I, shirin ghaderi, certify that the work presented in this thesis is my own. Gatedefined quantum dots on carbon nanotubes request pdf. Pdf quantum transport in carbon nanotubes researchgate. Two coupled single wall carbon nanotube quantum dots in a multiple quantum dot system were characterized by using a low temperature scanning gate microscopy sgm technique, at a temperature of 170mk. Analysis of random telegraph noise observed in semiconducting. Thermoelectric transport in nanoscale materials joshua p.
Pdf kramers polarization in strongly correlated carbon. Noncollinear spinorbit magnetic elds in a bent carbon nanotube. In the first nanotube experiment, spindependent transport through the double dot is compared in two sets of devices. Carbon nanotube superconducting quantum interference device. Different quantum dots qds with narrow size distributions were covalently coupled to carbon nanotubes cnts and silicacoated cnts in a simple, uniform, and controllable manner. We study the twoelectron eigenspectrum of a carbonnanotube double quantum dot with spinorbit coupling.
Pdf parallel carbon nanotube quantum dots and their. Nanotube quantum dot transport with spinorbit coupling and. The structural and optical properties of cntqd heterostructures are characterized by electron microscopy. Electron transistors sets and carbon nanotube double quantum dots with narrow top. First, such gatetuneable artificial atoms offer a high degree. The current emission noise of a carbon nanotube quantum dot in the kondo regime is measured at frequencies. Asgrown carbon nanotube quantum dots with superconducting contacts.
Electronhole symmetry in a semiconducting carbon nanotube quantum dot. The detailed mechanisms responsible for nanotube growth are still not fully. These fascinating electromechanical and magnetic effects are quantified using. Rey jila, university of colorado and national institute of standards and technology, boulder, colorado 803090440, and. Using an electromigration procedure which we recently developed, we generate 10 nmscale singlewall carbon nanotube quantum dot swcntqd transistors. Atomistic modeling of graphene nanostructures and singleelectron quantum dots a thesis submitted to the faculty of purdue university by junzhe geng in partial ful llment of the requirements for the degree of master of science in electrical and computer engineering august 2012 purdue university west lafayette, indiana. We demonstrate tunable tunnel coupling of the double dot and quantify the strength of the tunneling using the charge sensor. Purcellenhanced quantum yield from carbon nanotube. Quantum dots seem to be ideal devices in which to observe quantum phase transitions. Much of the following thesis will be devoted to the quantum dot behavior of. Ferromagnetically contacted carbon nanotube\ud quantum dots. Conductance measurements of carbon nanotubes containing gated local depletion regions exhibit plateaus as a function of gate voltage, spaced by approximately 1e2h, the quantum of conductance for a single nondegenerate mode. Emmett thesis submitted to the faculty of the graduate school of vanderbilt university in partial ful.
Molecular statesin carbon nanotube double quantum dots. Shotnoise detection in a carbon nanotube quantum dot. In a quantum dot electrons are made to tunnel onebyone through. Lately, the emphasis of carbon nanotube quantum dot research is shifting towards defining nanotube quantum dots with tunable barriers.
Accessing the quantum world through electronic transport in. The second set of experiments concerns carbon nanotube double quantum dots. An onchip detection scheme for high frequency signals is used to detect noise generated by a quantum dot formed in a single wall carbon nanotube. Carbon nanotube quantum dots tu delft repositories. Fabrication and characterization of a quantum dotsensitized solar cell by kevin j. In atoms the attractive forces are exerted by the nuclei, while in qds by background charges.
Semiconductor nanocrystals, or quantum dots, are crystalline semiconductors on a size scale from 1. A study by physicists at the technische universitaet muenchen has shown how nanotubes can. An electronic version of this thesis, including color figures, is available at. Using this technique, complex nanostructures such as quantum dot arrays can be created. Measurement of quantum noise in a carbon nanotube quantum dot. A novel strategy for the fabrication of multiwall carbon nanotube.
Request pdf gatedefined quantum dots on carbon nanotubes we report the realization of nanotube based quantum dot structures that use local electrostatic gating to produce individually. Asgrown carbon nanotube quantum dots with superconducting. Enhanced photoelectrochemical performance of quantum dot. This project will investigate carbon nanotube devices with. In the last chapter we present a fabrication procedure for defining nanotube quantum dots with controllable barriers. Parallel carbon nanotube quantum dots and their interactions. Also, a small coupling is found between orbitals with opposite magnetic moments leading to anticrossing behaviour at zero. Local gate control in carbon nanotube quantum devices abstract this thesis presents transport measurements of carbon nanotube electronic devices operated in the quantum regime. Quantum confinement in each junction induces a discrete quantum dot. Quantum dot modified multiwall carbon nanotubes the. Ferromagnetically contacted carbon nanotube quantum dots.
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