This Project concludes in a folio of drawings. The object of study is a renewal of Blacksburg’s old Town Hall on Church Street. The proposed new program for the existing structure is a studio theatre, addition and working areas. The fundamental purpose of this project is to renew Blacksburg’s vision of "Theatre" through the building and use of a small theatre house. Suggesting to completely change what is now thought of, but rarely considered, as a local cultural icon almost automatically brings high level of local conservative scrutiny. The wonderful instance about this project is that by merely suggesting a renewal of this magnitude could spur an incredible debate from the word, "Action." The point is not that the entire production be reduced to a marketing stunt. The point is this: Building is, in part, a public spectacle which is charged by local levels of involvement. This spectacle component to building can be highlighted or subdued through several mediums, but the overarching message is the same. A projected future for the existing icon is a series of four theatres. The first, and foremost, theatre is the town itself. By covering the building, scaffolding and construction staging area with a veil, the existing structure is reduced to a larger-than-life object within the townscape. The new object rests on the platform of Blacksburg during its own construction stage. While not within the scope of this project, it is entirely legitimate that the veil itself could be designed through a local competition. The purpose is to gather curiosity by wrapping the building. The remaining three theatres are more explicit. The centerlined façade may be removed, revealing a covered entry similar to a typical stage set. The articulation of the walls, ceiling and floor resemble a much larger room with an acute perspectival illusion. This is the main street level entrance to the building. The new façade-room may also be used as a stage. The intersection in front of the building could be blocked off from vehicular traffic to provide house seating for a public performance. The Studio theatre is the main "stage" which could be used to facilitate a majority of productions. This abstract cubic space may be manipulated as the house manager and production director see fit. This space is surrounded by occupiable marginalized mechanical volumes. These volumes are for any equipment, or individuals, necessary to maintain the illusion of the theatre. The finished surfaces of the studio should be completely assembled from panels and modular. Every surface, at every moment, in the Studio may be changed. An addition lies directly adjacent to the Studio through a roll-up garage door. This two-story area provides work areas, and rehearsal space in addition to storage. This area may also be manipulated as the house manager and production director see fit. The finished floor of the addition is shared with the large public parking lot behind the existing building. This back lot is also shared with a number of local businesses, and one of Blacksburg’s underground streams. This bowl-like space is the lowest elevation near the town’s original sixteen squares. The back doors of the Shop are oversized to receive any large shipments or materials and/or equipment. When completely open, these two sixteen foot high doors double as a proscenium stage. The pair of doors, in cooperation with an overhead canopy, resembles a typical theatre stage opening. This stage could be used for less formal occasions. It has been worthwhile to remember that a studio theatre type depends on maintaining a high level of abstract qualities, tremendous versatility and the ability to have the performance an the audience on the same level. The inherent difficulty is that a useful theatre space tends to find values and orientations that carry it away from total abstractness and versatility. / Master of Architecture

A Aproximação de Massa Efetiva para a função evnvelope multi-componente, na presença de uma interface, desenvolvida por Marques e Sham, será utilizada aqui, para materiais de gap estreito do grupo II-VI, da seguinte maneira: A) A forte interação entre bandas de condução e valência, nestes materiais, é justificada em um Hamiltoniano de Kane (6x6) modificado, contendo todas as ondas de Bloch propagantes e evanescentes. Na presença de uma interface, a função de onda eletrônica, &#936, é composta de uma onda de Bloch incidente, uma refletida e duas evanescentes, com a mesma energia E e momento paralelo k. Já que a estrutura da maioria dos isolantes utilizados são desconhecidos, a interface semicondutor-isolante por ser considerada como uma barreira infinita, de modo que, &#936, se anule na interface. Existe uma fina região de espessura &#945 na interface, onde o decaimento das ondas evanescentes é indispensável. Distante desta região, as ondas evanescentes possuem um papel insignificante e eventualmente anulam-se. O limite de &#945 &#8594 0 determina as condições de contorno para cada componente da função de onda envelope na interface. B) As condições de contorno são usadas para computar a estrutura de subbandas e o potencial auto-consistente para o Hg1-xCdxTe. A mais interessante característica é o afastamento dos estados de spin duplamente degenerados. Estes resultados serão utilizados para encontrarmos a dependência da energia das subbandas com um campo magnético perpendicular à interface. C) A magneto-condutividade longitudinal é calculada como função do campo magnético B &#8869. Efeitos das interações elétron-elétron e elétrons-impureza são levadas em conta nas aproximações de Hartee-Foch e auto-consistente de Born, respectivamente. Para uma interação elétron-impureza finita, encontram-se fatores de preenchimentos críticos dos níveis de Landau, onde transições de fase são observadas. Estes resultados explicam as descontinuidades presentes, em medidas experimentais, na magneto-resistividade longitudinal e transversal (Hall), em MISFET de Hg (Cd)Te. / The Effective Mass Approximation for multi-component envelope wave function in the presence of an interface in the MOSFET system, developed by Marques and Sham, will be used here, for II-VI narrow-gap semiconductors, in the following way: A) The strong interaction between conduction and valence bands, in these materials, is justified. The (6x6) Kane type modified Hamiltonian is used and the total wave function contains every propagating and evanescent waves. For an interface, the total function, &#936, is composed of one incident and one reflected and two evanescent Bloch waves, with energy E and parallel wave-vector k. Since the band structure of the most used insulators is usually not well known, the insulator-semiconductor interface can be assumed as an infinite barrier; therefore, the total wave-function there can set to zero. The semiconductor evanescent Bloch waves are indispensable in a thin layer, of thickness &#945, close to this region. Far away from the interface their role are insignificant and can be neglected. In the limit &#945 &#8594 0, the boundary condition for each the limit the total Bloch wave function, are derived. B) These boundary conditions are used to calculate the self-consistent electric subband and potential for MISFET of Hg1-xCdxTe. The subbands present a very important spin splitting, due to the internal electric field. C) The effect of a perpendicular magnetic field is also studied and the longitudinal magneto-conductivity are calculated. The effect of electron-electron and electron-impurity interactions are respectively accounted for in the Hartee-Fock and self-consistent Born approximations. For critical electron-impurity interaction, the Landau level filling shows a phase transition at a given fractional occupation (or magnetic field). These results are experimentally observed in both longitudinal and transverse (Hall) magneto-resistance for Hg(Cd)Te.

L’effet Hall quantique (EHQ), observé par exemple dans des gaz bidimensionnels d’électrons (2DEGS) à basse température et sous fort champ magnétique, a révolutionné la métrologie des résistances car il permet d’obtenir un étalon quantique de résistance qui ne dépend que de e et h (respectivement la charge de l’électron et la constante de Planck). Une des missions des métrologues est de développer les étalons en améliorant leurs performances ou en les rendant plus facile à mettre en oeuvre (travaillant à plus haute température ou plus faible champ magnétique). Dans ce contexte, la physique du graphène suscite l’intérêt pour une application en métrologie. Une monocouche de graphène est une feuille d’un seul atome d’épaisseur constituée d’atomes de carbone disposés en nid d’abeille. Une bicouche de graphène est formée par empilement de deux monocouches. Les écarts en énergie entre les premiers niveaux de Landau dans la monocouche et dans la bicouche sont supérieurs par rapport à ceux dans GaAs ce qui rend l’EHQ dans le graphène plus robuste et laisse envisager le développement d’un étalon plus pratique. Durant ma thèse, nous avons mis en place un protocole de fabrication de barres de Hall en graphène exfolié comprenant un repérage optique, des lithographies électroniques, la métallisation, la gravure plasma… L’utilisation de substrat de silicium oxydé en surface rend possible l’utilisation d’une grille en face arrière. En outre la géométrie des échantillons répond au mieux aux critères métrologiques (canal central large, prises de tension bien définies, …). A basse température, le dopage résiduel obtenu après le recuit in situ est de l’ordre de 3-4x1011 cm-2. Les mobilités sont proches de 3000 cm2/(V.s) et 4000 cm2/(V.s) respectivement pour les échantillons monocouche et bicouche à la fois pour les électrons et les trous. Le transport mésoscopique a été caractérisé à basse température par des mesures de localisation faible et de fluctuations universelles de conductance. La longueur de cohérence que nous avons extraite est de l’ordre de 0.5 µm à 1.5 K. La résistance des contacts mesurée en régime d’EHQ est plutôt faible (typiquement quelques ohms). L’EHQ a été étudié en détail à basse température (300 mK < T <1.5 K) et sous fort champ magnétique (jusqu’à 18.5T) à la fois dans la monocouche et la bicouche en mesurant de manière précise la résistance de Hall (RH) et la résistance longitudinale (Rxx). Les mesures fines de RH sont réalisées à l’aide d’un pont de comparaison basé sur un Comparateur Cryogénique de Courant ; elles consistent à comparer indirectement l’EHQ dans l’échantillon de graphène à l’EHQ obtenu dans une barre de Hall en GaAs/AlGaAs qui est supposée fournir la valeur exacte RH/2. Nos mesures révèlent un accord entre la résistance de Hall dans le graphène et la valeur attendue avec une incertitude de quelques 10-7. Au plus faible courant et dans l’état de dissipation minimale (Rxx→0), nous avons obtenu un accord avec une incertitude relative de 3.10-7. Ce niveau de précision est principalement limité par la petite taille de nos échantillons et par les inhomogénéités de la densité qui y sont présents, ces deux caractéristiques amenant de faibles courants de rupture de l’EHQ (1-2 µA). Toutefois, nos résultats sont à ce jour les tests les plus précis concernant l’EHQ dans du graphène exfolié et les premiers tests sur une bicouche. Ils confirment le potentiel de l’EHQ dans le graphène pour une application en métrologie. / The quantum Hall effect (QHE) observed in two dimensional electron gases (2DEGs) at low temperature and under high magnetic induction, has revolutionized the resistance metrology because it leads to a universal and very reproducible quantum resistance standard only dependent on e and h (respectively the electron charge and Planck's constant). One of the metrologists' missions is to develop standards with improved performances and to notably make them more practical, working for example at higher temperature or lower magnetic induction. In this context, graphene physics could be very interesting for metrological applications. Monolayer graphene is a one atom thick layer of carbon atoms condensed in a honeycomb lattice. A bilayer graphene consists in two stacked monolayers. Larger energy spacings between the first Landau Levels in monolayer and in bilayer than in GaAs make the QHE in graphene more robust and give hope that more practical standards could be developed. During the PhD, we have set a protocol up in order to fabricate exfoliated graphene based Hall bars, including location with an optical microscope, e-beam lithography, metallization, plasma etching… Backgated using oxidized silicon wafers the devices were designed to fulfill at best the metrological requirements (large conduction channel, well defined voltage probes…). At low temperature, the typical charge carrier residual doping obtained after the annealing process was 3-4x1011 cm-2. Mobilities were close to 3000 cm2/(V.s) and 4000 cm2/(V.s) respectively for the monolayer and the bilayer based device both for holes and electrons. Mesoscopic transport was characterized at low temperature by weak localization and universal conductance fluctuations (UCF) measurements. The phase coherence length deduced was about 0.5 µm below 1.5 K. The resistance of the contacts, measured in the QHE regime, appeared to be rather low (typically few ohms). The QHE was investigated in details at low temperature (300 mK < T <1.5 K) and high magnetic field (up to 18.5 T) in both monolayer and bilayer graphene by refined measurements of the Hall resistance (RH) and also of the longitudinal resistance (Rxx). The accurate measurements of RH were performed using a Cryogenic Current Comparator based resistance bridge. They consist in an indirect comparison between the QHE in graphene and the QHE obtained in a GaAs based Hall bar, supposed to deliver the expected value RH/2. Our measurements showed an agreement of the Hall resistance in graphene with the expected value within some parts in 107. At the lowest biasing current and in the lowest dissipation state (where Rxx→0) it is possible to demonstrate an agreement within an uncertainty of 3 parts in 107. That accuracy is essentially limited by the small size, and the poor homogeneity of the carrier density of the graphene electronic systems, both acting for a very reduced breakdown current of the QHE (1-2 µA). Nevertheless these results are the most accurate tests of the QHE performed in exfoliated graphene and the first universality test of the QHE with bilayer graphene. They confirm the potential of the QHE in graphene for the metrological application.

Thèse (DEng.) -- Université du Québec à Chicoutimi, 2002. / Bibliogr.: f. 209-220. Document électronique également accessible en format PDF. CaQCU

Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2006. / La p. de t. porte en outre: Thèse présentée à l'Université du Québec à Chicoutimi pour l'obtention du doctorat en ingénierie. CaQCU Comprend des réf. bibliogr. Document électronique également accessible en format PDF. CaQCU

Stuttgart, Univ., Diss., 2003.

Thesis (M. Eng.)(Electronic)--University of Pretoria, 2003. / Summaries in Afrikaans and English. Includes bibliographical references.

A Aproximação de Massa Efetiva para a função evnvelope multi-componente, na presença de uma interface, desenvolvida por Marques e Sham, será utilizada aqui, para materiais de gap estreito do grupo II-VI, da seguinte maneira: A) A forte interação entre bandas de condução e valência, nestes materiais, é justificada em um Hamiltoniano de Kane (6x6) modificado, contendo todas as ondas de Bloch propagantes e evanescentes. Na presença de uma interface, a função de onda eletrônica, &#936, é composta de uma onda de Bloch incidente, uma refletida e duas evanescentes, com a mesma energia E e momento paralelo k. Já que a estrutura da maioria dos isolantes utilizados são desconhecidos, a interface semicondutor-isolante por ser considerada como uma barreira infinita, de modo que, &#936, se anule na interface. Existe uma fina região de espessura &#945 na interface, onde o decaimento das ondas evanescentes é indispensável. Distante desta região, as ondas evanescentes possuem um papel insignificante e eventualmente anulam-se. O limite de &#945 &#8594 0 determina as condições de contorno para cada componente da função de onda envelope na interface. B) As condições de contorno são usadas para computar a estrutura de subbandas e o potencial auto-consistente para o Hg1-xCdxTe. A mais interessante característica é o afastamento dos estados de spin duplamente degenerados. Estes resultados serão utilizados para encontrarmos a dependência da energia das subbandas com um campo magnético perpendicular à interface. C) A magneto-condutividade longitudinal é calculada como função do campo magnético B &#8869. Efeitos das interações elétron-elétron e elétrons-impureza são levadas em conta nas aproximações de Hartee-Foch e auto-consistente de Born, respectivamente. Para uma interação elétron-impureza finita, encontram-se fatores de preenchimentos críticos dos níveis de Landau, onde transições de fase são observadas. Estes resultados explicam as descontinuidades presentes, em medidas experimentais, na magneto-resistividade longitudinal e transversal (Hall), em MISFET de Hg (Cd)Te. / The Effective Mass Approximation for multi-component envelope wave function in the presence of an interface in the MOSFET system, developed by Marques and Sham, will be used here, for II-VI narrow-gap semiconductors, in the following way: A) The strong interaction between conduction and valence bands, in these materials, is justified. The (6x6) Kane type modified Hamiltonian is used and the total wave function contains every propagating and evanescent waves. For an interface, the total function, &#936, is composed of one incident and one reflected and two evanescent Bloch waves, with energy E and parallel wave-vector k. Since the band structure of the most used insulators is usually not well known, the insulator-semiconductor interface can be assumed as an infinite barrier; therefore, the total wave-function there can set to zero. The semiconductor evanescent Bloch waves are indispensable in a thin layer, of thickness &#945, close to this region. Far away from the interface their role are insignificant and can be neglected. In the limit &#945 &#8594 0, the boundary condition for each the limit the total Bloch wave function, are derived. B) These boundary conditions are used to calculate the self-consistent electric subband and potential for MISFET of Hg1-xCdxTe. The subbands present a very important spin splitting, due to the internal electric field. C) The effect of a perpendicular magnetic field is also studied and the longitudinal magneto-conductivity are calculated. The effect of electron-electron and electron-impurity interactions are respectively accounted for in the Hartee-Fock and self-consistent Born approximations. For critical electron-impurity interaction, the Landau level filling shows a phase transition at a given fractional occupation (or magnetic field). These results are experimentally observed in both longitudinal and transverse (Hall) magneto-resistance for Hg(Cd)Te.

Hall Effect integrated circuits are used in a wide range of applications to measure the strength and/or direction of magnetic fields. These sensors play an increasingly significant role in the fields of automation, medical treatment and detection thanks largely to the enormous development of information technologies and electronic industries. Commercial Hall Effect ICs available in the market are all based on silicon technology. These ICs have the advantages of low cost and compatibility with CMOS technology, but suffer from poor sensitivity and detectability, high power consumption and low operating frequency bandwidths. The objective of this work was to develop and fabricate the first fully monolithic GaAs-InGaAs-AlGaAs 2-Dimensional Electron Gas (2DEG) Hall Effect integrated circuits whose performance enhances pre-existing technologies. To fulfil this objective, initially 2 µm gate length pHEMTs and 60/20 µm (L/W) Greek cross Hall Effect sensors were fabricated on optimised GaAs-In.18Ga.82As-Al.35Ga.65As 2DEG structures (XMBE303) suitable for both sensor and integrated circuit designs. The pseudomorphic high electron mobility transistors (pHEMTs) produced state-of-the-art output conductance, providing high intrinsic gain of 405, current cut-off frequency of 4.8 GHz and a low negative threshold voltage of -0.4 V which assisted in designing single supply ICs with high sensitivity and wide dynamic range. These pHEMTs were then accurately modelled for use in the design and simulation of integrated circuits. The corresponding Hall sensor showed a current sensitivity of 0.4 mV/mA.mT and a maximum magnetic DC offset of 0.35 mT at 1 V. DC digital (unipolar) and DC linear Hall Effect integrated circuits were then designed, simulated, fabricated and fully characterised. The DC linear Hall Effect IC provided an overall sensitivity of 8 mV/mT and a power consumption as low as 6.35 mW which, in comparison with commercial Si DC linear Hall ICs, is at least a factor of 2 more power efficient. The DC digital (unipolar) Hall Effect IC demonstrated a switching sensitivity of 6 mT which was at least ~50% more sensitive compared to existing commercial unipolar Si Hall ICs. In addition, a novel low-power GaAs-InGaAs-AlGaAs 2DEG AC linear Hall Effect integrated circuit with unprecedented sensitivity and wide dynamic range was designed, simulated, fabricated and characterised. This IC provided a sensitivity of 533 nV/nT, minimum field detectability of 177 nT (in a 10 Hz bandwidth) at frequencies from 500 Hz up to 200 kHz, consuming only 10.4 mW of power from a single 5 V of supply. In comparison to commercial Si linear Hall ICs, this IC provides an order of magnitude larger sensitivity, a factor of 4 higher detectability, 20 times wider bandwidth and over 20% lower power consumption (10.4 mW vs. 12.5 mW). These represent the first reported monolithic integrated circuits using a CMOS-like technology but in GaAs 2DEG technology and are extremely promising as complements, if not alternatives, to CMOS Si devices in high performance applications (such as high temperatures operations (>150 °C) and radiation hardened environment in the nuclear industry).

Le futur Système International d'unités, fondé sur des constantes fondamentales, va permettre de profiter pleinement des étalons quantiques de résistance, de courant et de tension qui sont reliés à la constante de planck et à la charge élémentaire. Dans cette thèse, nous avons développé et étudié un étalon de résistance fondé sur l'effet Hall quantique (EHQ) dans du graphène obtenu par dépôt chimique en phase vapeur (propane/hydrogène) sur substrat de carbure de silicium. Nous avons réussi à montrer, pour la première fois, qu'un étalon de résistance en graphène pouvait fonctionner à des conditions expérimentales plus pratiques que son homologue en GaAs/AlGaAs, c'est-à-dire à des températures plus élevées (T⋍10 K), des champs magnétiques plus faibles (B ⋍ 3,5 T) et des courants de mesures plus importants (I⋍500 μA). Dans une optique de compréhension et d'amélioration, nous avons analysé la reproductibilité du processus de fabrication de barres de Hall, testé une méthode de modification de la densité électronique et étudié les mécanismes de dissipation en régime d'EHQ.Dans une seconde partie, nous avons démontré qu'il était possible de réaliser une source de courant quantique programmable et versatile, directement reliée à la charge élémentaire, en combinant les deux étalons quantiques de tension et de résistance dans un circuit quantique intégrant un comparateur cryogénique de courant. Des courants ont ainsi pu être générés dans une gamme allant de 1 μA jusqu'à 5 mA avec une incertitude relative jamais atteinte de 10⁻⁸. Nous avons également prouvé que cet étalon de courant, réalisant la nouvelle définition de l'ampère, pouvait être utilisé pour étalonner un ampèremètre. / The future International System of Units, based on fundamental constants, will allow to take full advantage of the quantum standards of resistance, current and voltage that are linked to the planck constant and the elementary charge only.In this thesis, we have developed and studied a resistance standard based on the quantum Hall effect in graphene obtained by chemical vapor deposition (propane/hydrogen) on silicon carbide substrate. For the first time we were able to show that a graphene resistance standard could operate at more practical experimental conditions than its counterpart in GaAs/AlGaAs, ie at higher temperatures (T⋍10 K), weaker magnetics fields (B ⋍ 3,5 T) and larger measurement currents (I⋍500 μA). From an understanding and improvement perspective, we have analyzed the fabrication process of the Hall bar and its reproducibility, tested a method to modify the electronic density, and investigated the quantum Hall effect dissipation mechanisms.In a second part, we have demonstrated that it was possible torealize a programmable and versatile quantum current source from the elementary charge, by combining the two quantum standards of voltage and resistance in a quantum circuit integrating a cryogenic current comparator. Currents were generated in the range from 1 μA to 5 mA, with a relative uncertainty never achieved before of 10⁻⁸. We have also showed that this current standard, realizing the new definition of the ampere, could be used to calibrate an ammeter.