This thesis presents an introduction to the design and simulation of a novel class of integrated photonic phased array switch elements. The main objective is to use nano-electromechanical (NEMS) based phase shifters of cascaded under-etched slot nanowires that are compact in size and require a small amount of power to operate them. The structure of the switch elements is organized such that it brings the phase shifting elements to the exterior sides of the photonic circuits. The transition slot couplers, used to interconnect the phase shifters, are designed to enable biasing one of the silicon beams of each phase shifter from an electrode located at the side of the phase shifter. The other silicon beam of each phase shifter is biased through the rest of the silicon structure of the switch element, which is taken as a ground. Phased array switch elements ranging from 2×2 up to 8×8 multiple-inputs/multiple-outputs (MIMO) are conveniently designed within reasonable footprints native to the current fabrication technologies. Chapter one presents the general layout of the various designs of the switch elements and demonstrates their novel features. This demonstration will show how waveguide disturbances in the interconnecting network from conventional switch elements can be avoided by adopting an innovative design. Some possible applications for the designed switch elements of different sizes and topologies are indicated throughout the chapter. Chapter two presents the design of the multimode interference (MMI) couplers used in the switch elements as splitters, combiners and waveguide crossovers. Simulation data and design methodologies for the multimode couplers of interest are detailed in this chapter. Chapter three presents the design and analysis of the NEMS-operated phase shifters. Both simulations and numerical analysis are utilized in the design of a 0º-180º capable NEMS-operated phase shifter. Additionally, the response of some of the designed photonic phased array switch elements is demonstrated in this chapter. An executive summary and conclusions sections are also included in the thesis.

Οι τεχνικές Μικροσκοπίας Ατομικής Δύναμης που χρησιμοποιούν ακίδες σάρωσης έχουν την ικανότητα όχι μόνο να παρατηρούν επιφάνειες σε ατομικό επίπεδο αλλά και να τις τροποποιούν σε πολύ μικρή κλίμακα. Αυτό αποτελεί και το κίνητρο για τη χρησιμοποίηση των τεχνικών αυτών στη δημιουργία συσκευών αποθήκευσης με πολύ μεγαλύτερη πυκνότητα από τις συμβατικές συσκευές. Σε διάφορα ερευνητικά προγράμματα αποθήκευσης δεδομένων τεχνολογίας MEMS/NEMS με ακίδες, η σχετική τροχιά κίνησης της ακίδας ως προς το αποθηκευτικό μέσο ακολουθεί ένα μοτίβο raster. Παρά την απλή υλοποίησή της, η προαναφερθείσα κίνηση σάρωσης έχει σημαντικά μειονεκτήματα. Στο πλαίσιο της εργασίας αυτής προτείνεται μια εναλλακτική τοπολογία σπειροειδούς κίνησης. Η προτεινόμενη μέθοδος μπορεί να εφαρμοσθεί σε οποιοδήποτε σύστημα που βασίζεται σε διαδικασίες σάρωσης, όπως συστήματα αποθήκευσης και AFM συστήματα απεικόνισης. Στην εργασία αυτή μελετάται η περίπτωση των συσκευών αποθήκευσης με ακίδες, όπου η τροχιά που διαγράφει η ακίδα σε σχέση με το επίπεδο x/y που ορίζεται από το μέσο αποθήκευσης, είναι η σπειροειδής καμπύλη του Αρχιμήδη. Η χρήση μιας τέτοιας σπειροειδούς τροχιάς οδηγεί σε σήμα θέσης αναφοράς με εξαιρετικά στενό συχνοτικό περιεχόμενο, το οποίο ολισθαίνει πολύ αργά στον χρόνο. Για πειραματική επιβεβαίωση, ο προτεινόμενος τρόπος σπειροειδούς κίνησης εφαρμόστηκε σε σύστημα αποθήκευσης πληροφορίας με ακίδες με δυνατότητες θερμομηχανικής εγγραφής και ανάγνωσης δεδομένων σε φιλμ πολυμερούς. Επιπλέον, μελετήθηκε η αξιοποίηση των ιδιοτήτων του νέου τύπου κίνησης από αρχιτεκτονικές ελέγχου ειδικά σχεδιασμένες και βελτιστοποιημένες για τη συγκεκριμένη οικογένεια τροχιών αναφοράς, με στόχο την επίτευξη πολύ υψηλότερων συχνοτήτων σάρωσης για την ίδια ακρίβεια θέσης. Προς επιβεβαίωση των θεωρητικών αναλύσεων, παρουσιάζονται αποτελέσματα εξομοιώσεων καθώς και πειραματικά αποτελέσματα από πειραματική διάταξη. Στο πλαίσιο της διατριβής πραγματοποιήθηκε και η μοντελοποίηση του καναλιού θερμομηχανικής αποθήκευσης με ακίδες σε μεμβράνες πολυμερούς υλικού. Ενώ η θεωρητική μορφή των θερμομηχανικά εγγεγραμμένων κοιλωμάτων είναι κωνική, στην πράξη η μορφή του απέχει πολύ από το θεωρητικό μοντέλο. Για τον λόγο αυτό, αναπτύχθηκε μοντέλο του συμβόλου ως προς την ταχύτητα σάρωσης κατά τη διαδικασία εγγραφής, με βάση πειραματικά δεδομένα. Στο πλαίσιο της διατριβής μελετήθηκε επίσης η δυνατότητα ανάπτυξης συνδυασμένων αρχιτεκτονικών ελέγχου παρακολούθησης και ανάκτησης χρονισμού συμβόλου, όπου η πληροφορία για τη στιγμιαία ταχύτητα του σαρωτή παρέχεται από το μέσο αποθήκευσης μέσω των κυκλωμάτων συγχρονισμού. Τα αποτελέσματα των εξομοιώσεων επιβεβαιώνουν την δυνατότητα αυτή, και επιπλέον δείχνουν ότι υπό προϋποθέσεις η ακρίβεια παρακολούθησης του συστήματος βελτιώνεται. Τέλος, διερευνήθηκε η απόδοση των προτεινόμενων μεθόδων στην περίπτωση φορητών συσκευών, τα οποία υπόκεινται σε εξωτερικές διαταραχές. Στο πλαίσιο της διερεύνησης αυτής, συλλέχθηκαν πειραματικά αποτελέσματα και αναλύθηκαν μετρήσεις τυπικών εξωτερικών διαταραχών. / The AFM techniques using scanning probes have the capacity not only to observe surfaces in atomic level but also to modify them at a very small scale. This feature motivates the use of these techniques to create storage devices capable of storing data in a much higher density than conventional devices. In various MEMS/NEMS-based data storage technology research projects with probes, the relative trajectory follows a raster pattern or similar. Despite its simple implementation, the aforementioned scanning pattern has significant disadvantages. In this work, an alternative spiral motion topology is proposed. The proposed method can be applied to any system based on scanning probes, such as storage systems and AFM imaging systems. In this work, the case of storage devices with probes is studied, in which the trajectory of the probe with respect to the x/y plane of the storage medium, is the spiral curve of Archimedes. The use of such a spiral trajectory leads to a reference position signal with extremely narrowband frequency content, which slides very slowly in time. For experimental verification, the proposed method of spiral motion was applied on a single probe experimental setup, with read and writes data thermomechanical capabilities on very thin polymer films. The aforementioned inherent properties of the proposed approach enable system designs with improved tracking performance and with non-intermittent, high-speed storage capabilities. Thus, the exploitation of these properties by architectures specifically designed and optimized for the particular reference trajectory is studied, in order to achieve much higher scanning frequencies for the same positioning accuracy. To verify the theoretical analysis, simulation results are presented as well as experimental results from the application of the proposed techniques and architectures in experimental AFM systems with a single probe. In this dissertation the modeling of the thermomechanical storage channel with probes in thin polymer films was also carried out. While the theoretical form of thermomechanically engraved indentations is conical, in practice its form is far from this theoretical model. Hence, a symbol model was developed in respect to the scanning speed during the write process, based on experimental data. This model can be used to properly design the equalization circuits depending on the motion speed of operation. Moreover, the possibility of developing combined architectures of tracking control and symbol timing recovery was also investigated, where the information regarding the scanner speed is provided from the storage medium via symbol timing synchronization circuits. The simulation results confirm this approach and, furthermore, show that, under certain conditions, the system’s tracking accuracy is improved. Finally, the performance of the proposed methods in the case of portable storage devices was investigated, where the systems are subjected to external disturbances. As part of this investigation, experimental results were collected and measurements of external disturbances, typical for such devices, were analyzed.

This thesis presents an introduction to the design and simulation of a novel class of integrated photonic phased array switch elements. The main objective is to use nano-electromechanical (NEMS) based phase shifters of cascaded under-etched slot nanowires that are compact in size and require a small amount of power to operate them. The structure of the switch elements is organized such that it brings the phase shifting elements to the exterior sides of the photonic circuits. The transition slot couplers, used to interconnect the phase shifters, are designed to enable biasing one of the silicon beams of each phase shifter from an electrode located at the side of the phase shifter. The other silicon beam of each phase shifter is biased through the rest of the silicon structure of the switch element, which is taken as a ground. Phased array switch elements ranging from 2×2 up to 8×8 multiple-inputs/multiple-outputs (MIMO) are conveniently designed within reasonable footprints native to the current fabrication technologies. Chapter one presents the general layout of the various designs of the switch elements and demonstrates their novel features. This demonstration will show how waveguide disturbances in the interconnecting network from conventional switch elements can be avoided by adopting an innovative design. Some possible applications for the designed switch elements of different sizes and topologies are indicated throughout the chapter. Chapter two presents the design of the multimode interference (MMI) couplers used in the switch elements as splitters, combiners and waveguide crossovers. Simulation data and design methodologies for the multimode couplers of interest are detailed in this chapter. Chapter three presents the design and analysis of the NEMS-operated phase shifters. Both simulations and numerical analysis are utilized in the design of a 0º-180º capable NEMS-operated phase shifter. Additionally, the response of some of the designed photonic phased array switch elements is demonstrated in this chapter. An executive summary and conclusions sections are also included in the thesis.

No description available.

The development of micro and nano-electromechanical systems (MEMS and NEMS) with entirely new or improved functionalities is typically based on novel or improved designs, materials and fabrication methods. However, today’s micro- and nano-fabrication is restrained by manufacturing paradigms that have been established by the integrated circuit (IC) industry over the past few decades. The exclusive use of IC manufacturing technologies leads to limited material choices, limited design flexibility and consequently to sub-optimal MEMS and NEMS devices. The work presented in this thesis breaks new ground with a multitude of novel approaches for the integration of non-standard materials that enable the fabrication of 3D micro and nanoelectromechanical systems. The objective of this thesis is to highlight methods that make use of non-standard materials with superior characteristics or methods that use standard materials and fabrication techniques in a novel context. The overall goal is to propose suitable and cost-efficient fabrication and integration methods, which can easily be made available to the industry. The first part of the thesis deals with the integration of bulk wire materials. A novel approach for the integration of at least partly ferromagnetic bulk wire materials has been implemented for the fabrication of high aspect ratio through silicon vias. Standard wire bonding technology, a very mature back-end technology, has been adapted for yet another through silicon via fabrication method and applications including liquid and vacuum packaging as well as microactuators based on shape memory alloy wires. As this thesis reveals, wire bonding, as a versatile and highly efficient technology, can be utilized for applications far beyond traditional interconnections in electronics packaging. The second part presents two approaches for the 3D heterogeneous integration based on layer transfer. Highly efficient monocrystalline silicon/ germanium is integrated on wafer-level for the fabrication of uncooled thermal image sensors and monolayer-graphene is integrated on chip-level for the use in diaphragm-based pressure sensors. The last part introduces a novel additive fabrication method for layer-bylayer printing of 3D silicon micro- and nano-structures. This method combines existing technologies, including focused ion beam implantation and chemical vapor deposition of silicon, in order to establish a high-resolution fabrication process that is related to popular 3D printing techniques. / <p>QC 20121207</p>

Three-dimensional (3D) integration of micro- and nano-electromechanical systems (MEMS/NEMS) with integrated circuits (ICs) is an emerging technology that offers great advantages over conventional state-of-the-art microelectronics. MEMS and NEMS are most commonly employed as sensor and actuator components that enable a vast array of functionalities typically not attainable by conventional ICs. 3D integration of NEMS and ICs also contributes to more compact device footprints, improves device performance, and lowers the power consumption. Therefore, 3D integration of NEMS and ICs has been proposed as a promising solution to the end of Moore’s law, i.e. the slowing advancement of complementary metal-oxide-semiconductor (CMOS) technology.In this Ph.D. thesis, I propose a comprehensive fabrication methodology for heterogeneous 3D integration of NEM devices directly on top of CMOS circuits. In heterogeneous integration, the NEMS and CMOS components are fully or partially fabricated on separate substrates and subsequently merged into one. This enables process flexibility for the NEMS components while maintaining full compatibility with standard CMOS fabrication. The first part of this thesis presents an adhesive wafer bonding method using ultra-thin intermediate bonding layers which is utilized for merging the NEMS components with the CMOS substrate. In the second part, a novel NEM switch concept is introduced and the performance of CMOS-integrated NEM switch circuits for logic and computation applications is discussed. The third part examines two different packaging approaches for integrated MEMS and NEMS devices with either hermetic vacuum cavities or low-cost glass lids for optical applications. Finally, a novel fabrication approach for through silicon vias (TSVs) by magnetic assembly is presented, which is used to establish an electrical connection from the packaged devices to the outside world. / Tredimensionell (3D) integration av mikro- och nano-elektromekaniska system (MEMS/NEMS) med integrerade kretsar (ICs) är en ny teknik som erbjuder stora fördelar jämfört med konventionell mikroelektronik. MEMS och NEMS används oftast som sensorer och aktuatorer då de möjliggör många funktioner som inte kan uppnås med vanliga ICs.3D-integration av NEMS och ICs bidrar även till mindre dimensioner, ökade prestanda och mindre energiförbrukning av elektriska komponenter. Den nuvarande tekniken för complementary metal-oxide-semicondictor (CMOS) närmar sig de fundamentala gränserna vilket drastiskt begränsar utvecklingsmöjligheten för mikroelektronik och medför slutet på Moores lag. Därför har 3D-integration identifierats som en lovande teknik för att kunna driva vidare utvecklingen för framtidens elektriska komponenter.I denna avhandling framläggs en omfattande fabrikationsmetodik för heterogen 3D-integration av NEMS ovanpå CMOS-kretsar. Heterogen integration betyder att både NEMS- och CMOS-komponenter byggs på separata substrat för att sedan förenas på ett enda substrat. Denna teknik tillåter full processfrihet för tillverkning av NEMS-komponenter och garanterar kompatibilitet med standardiserade CMOS-fabrikationsprocesser.I den första delen av avhandlingen beskrivs en metod för att sammanfoga två halvledarskivor med en extremt tunn adhesiv polymer. Denna metod demonstreras för 3D-integration av NEMS- och CMOS-komponenter. Den andra delen introducerar ett nytt koncept för NEM-switchar och dess användning i NEM-switch-baserade mikrodatorchip. Den tredje delen presenterar två olika inkapslingsmetoder för MEMS och NEMS. Den ena metoden fokuserar på hermetisk vakuuminkapsling medan den andra metoden beskriver en lågkostnadsstrategi för inkapsling av optiska komponenter. Slutligen i den fjärde delen presenteras en ny fabrikationsteknik för så kallade ”through silicon vias” (TSVs) baserad på magnetisk självmontering av nickeltråd på mikrometerskala. / <p>20170519</p>

Optical communications systems operate at the limits of their margins to respond to increasing capacity demands. Some of the signal processing functions required must soon operate at speeds beyond electronic implementation. Optical signal processors are fundamentally analog which requires precise control of the operating state. Programmable optical components are consequently essential. The thesis explores and elucidates the properties of meshes of generalized Mach-Zehnder interferometers (GMZIs) amenable to silicon (Si) photonics integration that are based on multimode interference couplers with programmability achieved via voltage controlled phase-shift elements within the interferometer arms to perform a variety of finite impulse response (FIR) and infinite impulse response (IIR) signal processing functions. The thesis presents a novel class of integrated photonic phased array systems with a single-stage, multistage, and feedback architectures. The designed photonic integrated systems utilize nano-electromechanical-system (NEMS) operated phase shifters of cascaded free suspended slot waveguides that are compact and require a small amount of power to operate. The structure of the integrated photonic phased array switch (IPPAS) elements is organized such that it brings the NEMS-operated phase shifters to the exterior sides of the construction; facilitating electrical connection. The transition slot couplers used to interconnect the phase shifters to the rest of the silicon structure are designed to enable biasing one of the silicon beams of each phase shifter from an electrode located at the side of the phase shifter. The other silicon beam of each phase shifter is biased through the rest of the silicon structure of the fabric, which is taken as a ground. Phased array processors of 2×2 and 4×4 multiple-input-multiple-output (MIMO) ports are conveniently designed within reasonable footprints native to the current fabrication technologies. The response of the single-stage 4×4 broadband IPPAS element is determined, and its phase synthesis states required for single-throw, double-throw and broadcast routing operations are predicted. The transmission responses of the single-stage wavelength division multiplexing (WDM) processors of 2×2 and 4×4 MIMO ports are simulated. The wavelength steering capability of the transmission interferograms by applying progressive phase shifts through the array of NEMS-operated phase shift elements of the single-stage 4×4 WDM (de)multiplexer is demonstrated. The advantages of cascading broadband and WDM phased array sections are articulated through several study cases. Five different cascaded phased array architectures are trialed for the construction of non-blocking 4×4 IPPAS broadband switches that are essential elements in the construction of universal photonic processors. A cascaded 2×2 WDM (de)multiplexer that can set the bandwidth of the (de)multiplexed cyclic channels into a binary number of programmable values is demonstrated. The envelope and wavelength modulations of the transmission responses utilizing a cascaded forward structure of three 2×2 sections that can be utilized for the (de)multiplexing of different bandwidth channels are demonstrated providing individual wavelength steering capability of the narrowband and wideband channels and the individual wavelength steering capability of the slow envelope and wavelength modulating functions. Innovative universal 2×2 and 4×4 cascaded phased array processors of advanced high-order architectures that can function as both non-blocking broadband routers and tunable WDM (de)multiplexers with spectrum steering and bandwidth control of the (de)multiplexed demands are introduced. The multimode interference (MMI) coupler is utilized for the construction of several IIR feedback photonic processors. Tunable photonic feedback processors have the advantage of using less number of MMI couplers compared to their counterparts of FIR forward-path processors saving on the footprint and loss merits. A passive feedback 2×2 (de)multiplexer made of a 4×4 MMI coupler and two loopback paths is proposed. The inclusion of an imbalance in the lengths of the loopback paths of the same symmetrical feedback (de)multiplexer is demonstrated to achieve wavelength modulation of the (de)multiplexed transmission responses that are useful for the (de)multiplexing of different bandwidth channels. Several newly introduced IIR feedback architectures are demonstrated to function similarly as their counterparts of FIR forward-path processors as binary bandwidth variable (de)multiplexers, envelope and wavelength modulation (de)multiplexers, and universal feedback processors. The investigation provided in this thesis is also supported with dynamic zero-pole evolution analysis in the complex plane of analysis of the studied FIR and IIR photonic processors to enhance understanding the principle of operation. This research expands the prospective for constructing innovative silicon-on-insulator (SOI) based optical processors for applications in modern optical communication systems and programmable elastic optical networks (EONs).

L'étude de contacts atomiques ajustables est rendue possible par la réalisation de jonctions à cassure. Ce type de structure est constitué d'un conducteur métallique, tel que l'aluminium ou l'or, déposé sur un substrat, et dans lequel une constriction localement sous-gravée forme un pont suspendu. En déformant le substrat, cette constriction est étirée de façon contrôlée. De cette manière l'étirement de la jonction peut être stabilisé au stade d'un contact de taille atomique. Le travail de recherche présenté ici est scindé en deux parties. D'une part, des jonctions à cassure simples en aluminium sur substrat en bronze ont été étudiées aux très basses températures. A l'aide du phénomène de réflexions d'Andreev nous arrivons à la conclusion que l'aluminium, à l'inverse de l'or, ne forme pas de chaînes monoatomiques plus longues qu'un dimère. Une structure double de type transistor à un électron (SET) a également été mesurée aux très basses températures. D'autre part, un système composé d'une ou de deux jonctions à cassure sur membranes fines en silicium monocrystallin a été développé et caractérisé à température ambiante. Ce système constitue un nanosystème électromécanique, ou NEMS, intégrable en technologie silicium. Des membranes, d'une épaisseur de 340 nm seulement, ont été fabriquées à partir de substrats SOI. Les propriétés mécaniques statiques et dynamiques de ces membranes sont étudiées. Plusieurs actionnements mécaniques stables, constitués d'une pointe déplacée par un piézo, ont été développés. Ils permettent à chaque jonction à cassure sur membrane d'être adressée individuellement, y compris aux très basses températures. L'influence d'une illumination en lumière laser sur la conductance de contacts point en or est étudiée. Une augmentation de la conductance est mesurée. L'influence du substrat peut être exclue grâce à l'utilisation de membranes fines. Cet effet est relié à un phénomène de transmission assistée par photons. Dans ce travail, des jonctions à cassure, initialement développées pour la physique fondamentale, sont intégrées sur des membranes en silicium, permettant ainsi une utilisation en tant que capteurs électromécaniques.

This dissertation deals with the calculation of the mechanical properties, electronic structure, electronic transport, and optical properties of strained carbon nanotubes (CNTs). CNTs are discussed for straintronics as their electronic bands show a strong strain-sensitivity. Further, CNTs are stiff, possess a large rupture strain and they are chemically inert, which make them a suitable material in terms of reliability and functionality for straintronic devices. Therefore, this work aims to explore the potential of strain-dependent CNT devices with regard to their mechanical, electronic, and optical properties from a first-principles point of view. There is no work so far that systematically compares these strain-dependent, physical properties from ab initio calculations, which are suitable for small CNTs only, to tight-binding calculations, which are suitable to model large CNTs. First, the structural and mechanical properties of CNTs are investigated: Structural properties are obtained by geometry optimization of many CNTs using density functional theory (DFT). The mechanical properties of CNTs are calculated in the same way. The resulting stress-strain relations are investigated and their key parameters are systematically displayed with respect to the CNT chirality and radius. The ground state electronic properties are calculated using tight-binding models and DFT. Both methods are compared systematically and it is explored where the tight-binding approximation can be applied in order to obtain meaningful results. On top of the electronic structure, a transport model is used to calculate the current through strained CNTs. The model includes the effect of ballistic conductance, parametrized electron-phonon scattering and the influence of an applied gate voltage. Finally, a computationally efficient model is described, which is able to predict the current through strained CNT transistors and enables to find optimal operation regimes for single-chirality devices and devices containing CNT mixtures. Optical properties of strained CNTs are explored by calculating quasiparticle excitations by the means of the GW approximation and the solution of the Bethe-Salpeter equation for CNT excitons. Due to the numerical effort of these approaches, the data for just one CNT is obtained. Still, it is explored how the above-mentioned many-body properties can be related to the ground state results for this CNT. This finally leads to empirical approaches that approximately describe the many-body results from the ground state properties. It is elucidated how such a model can be generalized to other CNTs in order to describe the strain dependence of their optical transitions. / Diese Dissertation befasst sich mit der Berechnung der mechanischen Eigenschaften, der elektronischen Struktur, der Transport- und der optischen Eigenschaften von verspannten Kohlenstoffnanoröhrchen (engl. carbon nanotubes, CNTs). CNTs werden für die Straintronik diskutiert, da ihre elektronischen Bänder eine starke Dehnungsempfindlichkeit aufweisen. Weiterhin sind CNTs steif, besitzen eine hohe Zugfestigkeit und sind chemisch inert, weshalb sie in Bezug auf Zuverlässigkeit und Funktionalität ein geeignetes Material für straintronische Bauelemente sind. Ziel dieser Arbeit ist es daher, das Potenzial von dehnungsabhängigen CNT-Bauteilen hinsichtlich ihrer mechanischen, elektronischen und optischen Eigenschaften aus der Perspektive von first principles-Methoden zu untersuchen. Es gibt bisher keine Arbeit, in der die Ergebnisse verschiedener Methoden – ab initio-basierte Berechnungen für kleine CNTs und tight-binding Berechnungen, die näherungsweise die elektronische Struktur großer CNTs beschreiben – miteinander systematisch vergleicht. Einführend werden die strukturellen und mechanischen Eigenschaften von CNTs untersucht: Strukturelle Eigenschaften ergeben sich durch Geometrieoptimierung vieler CNTs mittels Dichtefunktionaltheorie (DFT). Die mechanischen Eigenschaften von CNTs werden in gleicher Weise berechnet. Die daraus resultierenden Spannungs-Dehnungs-Beziehungen werden untersucht und deren relevante Parameter systematisch in Abhängigkeit von CNT-Chiralität und CNT-Radius dargestellt. Die Eigenschaften des CNT-Grundzustands werden unter Verwendung von tight-binding-Modellen und DFT berechnet. Beide Methoden werden systematisch verglichen und es wird untersucht, wo die tight-binding-Näherung angewendet werden kann, um aussagekräftige Ergebnisse zu erzielen. Basierend auf der elektronischen Struktur der CNTs wird ein Transportmodell aufgesetzt, durch das der Strom durch verspannte CNTs berechnet werden kann. Dieses Modell beinhaltet den Einfluss der ballistischen Leitfähigkeit, Elektron-Phonon-Streuung in parametrisierter Form und den Einfluss eines Gates. Damit wird ein numerisch effizientes Modell beschrieben, das in der Lage ist, den Strom durch verspannte CNT-Transistoren vorherzusagen. Auf dessen Basis wird es möglich, optimale Arbeitsbereiche für reine CNT-Bauelemente und Bauelemente mit CNT-Mischungen zu berechnen. Die optischen Eigenschaften verspannter CNTs werden durch die Berechnung von Quasiteilchenanregungen mittels der GW-Approximation und der Lösung der Bethe-Salpeter-Gleichung für CNT-Exzitonen untersucht. Aufgrund des numerischen Aufwandes dieser Ansätze werden diese Daten für nur ein CNT erhalten. Daran wird der Zusammenhang zwischen den oben genannten Vielteilchen-Eigenschaften und den Grundzustandseigenschaften für dieses CNT demonstriert. Daraus ergeben sich empirische Ansätze, die es gestatten, die Vielteilchen-Ergebnisse näherungsweise auf die elektronischen Grundzustandseigenschaften zurückzuführen. Es wird dargestellt, wie ein solches Modell für andere CNTs verallgemeinert werden kann, um die Verspannungsabhängigkeit ihrer optischen Übergänge zu beschreiben.

This dissertation deals with the calculation of the mechanical properties, electronic structure, electronic transport, and optical properties of strained carbon nanotubes (CNTs). CNTs are discussed for straintronics as their electronic bands show a strong strain-sensitivity. Further, CNTs are stiff, possess a large rupture strain and they are chemically inert, which make them a suitable material in terms of reliability and functionality for straintronic devices. Therefore, this work aims to explore the potential of strain-dependent CNT devices with regard to their mechanical, electronic, and optical properties from a first-principles point of view. There is no work so far that systematically compares these strain-dependent, physical properties from ab initio calculations, which are suitable for small CNTs only, to tight-binding calculations, which are suitable to model large CNTs. First, the structural and mechanical properties of CNTs are investigated: Structural properties are obtained by geometry optimization of many CNTs using density functional theory (DFT). The mechanical properties of CNTs are calculated in the same way. The resulting stress-strain relations are investigated and their key parameters are systematically displayed with respect to the CNT chirality and radius. The ground state electronic properties are calculated using tight-binding models and DFT. Both methods are compared systematically and it is explored where the tight-binding approximation can be applied in order to obtain meaningful results. On top of the electronic structure, a transport model is used to calculate the current through strained CNTs. The model includes the effect of ballistic conductance, parametrized electron-phonon scattering and the influence of an applied gate voltage. Finally, a computationally efficient model is described, which is able to predict the current through strained CNT transistors and enables to find optimal operation regimes for single-chirality devices and devices containing CNT mixtures. Optical properties of strained CNTs are explored by calculating quasiparticle excitations by the means of the GW approximation and the solution of the Bethe-Salpeter equation for CNT excitons. Due to the numerical effort of these approaches, the data for just one CNT is obtained. Still, it is explored how the above-mentioned many-body properties can be related to the ground state results for this CNT. This finally leads to empirical approaches that approximately describe the many-body results from the ground state properties. It is elucidated how such a model can be generalized to other CNTs in order to describe the strain dependence of their optical transitions. / Diese Dissertation befasst sich mit der Berechnung der mechanischen Eigenschaften, der elektronischen Struktur, der Transport- und der optischen Eigenschaften von verspannten Kohlenstoffnanoröhrchen (engl. carbon nanotubes, CNTs). CNTs werden für die Straintronik diskutiert, da ihre elektronischen Bänder eine starke Dehnungsempfindlichkeit aufweisen. Weiterhin sind CNTs steif, besitzen eine hohe Zugfestigkeit und sind chemisch inert, weshalb sie in Bezug auf Zuverlässigkeit und Funktionalität ein geeignetes Material für straintronische Bauelemente sind. Ziel dieser Arbeit ist es daher, das Potenzial von dehnungsabhängigen CNT-Bauteilen hinsichtlich ihrer mechanischen, elektronischen und optischen Eigenschaften aus der Perspektive von first principles-Methoden zu untersuchen. Es gibt bisher keine Arbeit, in der die Ergebnisse verschiedener Methoden – ab initio-basierte Berechnungen für kleine CNTs und tight-binding Berechnungen, die näherungsweise die elektronische Struktur großer CNTs beschreiben – miteinander systematisch vergleicht. Einführend werden die strukturellen und mechanischen Eigenschaften von CNTs untersucht: Strukturelle Eigenschaften ergeben sich durch Geometrieoptimierung vieler CNTs mittels Dichtefunktionaltheorie (DFT). Die mechanischen Eigenschaften von CNTs werden in gleicher Weise berechnet. Die daraus resultierenden Spannungs-Dehnungs-Beziehungen werden untersucht und deren relevante Parameter systematisch in Abhängigkeit von CNT-Chiralität und CNT-Radius dargestellt. Die Eigenschaften des CNT-Grundzustands werden unter Verwendung von tight-binding-Modellen und DFT berechnet. Beide Methoden werden systematisch verglichen und es wird untersucht, wo die tight-binding-Näherung angewendet werden kann, um aussagekräftige Ergebnisse zu erzielen. Basierend auf der elektronischen Struktur der CNTs wird ein Transportmodell aufgesetzt, durch das der Strom durch verspannte CNTs berechnet werden kann. Dieses Modell beinhaltet den Einfluss der ballistischen Leitfähigkeit, Elektron-Phonon-Streuung in parametrisierter Form und den Einfluss eines Gates. Damit wird ein numerisch effizientes Modell beschrieben, das in der Lage ist, den Strom durch verspannte CNT-Transistoren vorherzusagen. Auf dessen Basis wird es möglich, optimale Arbeitsbereiche für reine CNT-Bauelemente und Bauelemente mit CNT-Mischungen zu berechnen. Die optischen Eigenschaften verspannter CNTs werden durch die Berechnung von Quasiteilchenanregungen mittels der GW-Approximation und der Lösung der Bethe-Salpeter-Gleichung für CNT-Exzitonen untersucht. Aufgrund des numerischen Aufwandes dieser Ansätze werden diese Daten für nur ein CNT erhalten. Daran wird der Zusammenhang zwischen den oben genannten Vielteilchen-Eigenschaften und den Grundzustandseigenschaften für dieses CNT demonstriert. Daraus ergeben sich empirische Ansätze, die es gestatten, die Vielteilchen-Ergebnisse näherungsweise auf die elektronischen Grundzustandseigenschaften zurückzuführen. Es wird dargestellt, wie ein solches Modell für andere CNTs verallgemeinert werden kann, um die Verspannungsabhängigkeit ihrer optischen Übergänge zu beschreiben.