Characterization of Carbon Nanostructures Based on Transmission Line Model.

PhDIn the past two decades carbon nanotubes and graphene have attracted a lot of research attention due to their exceptional electronic properties. The research focus on improving the synthesising techniques will eventually lead to their applications in terahertz wave, millimetre wave and microwave frequencies. In this thesis, a modelling technique based on the transmission line theory is proposed to calculate the 2-port S-parameters of vertically aligned CNT arrays with finite sizes and arbitrary cross sections. The process takes into account all the coupling in the array and gives the analytical solution of S-parameters. The simulation results from the proposed technique are compared with results obtained by effective single conductor model and shows a good matching for small arrays and an increasing difference with the increase of array sizes. From the S-parameters, the fundamental properties of CNT arrays such as input impedance and absorption are obtained and compared with measurement results in microwave frequencies. The dependence of these properties on ambient temperature and host medium are also presented to explore the tunability of CNT arrays. From the Fabry-Perot the wave propagating velocity is also calculated for arrays with different sizes and fitted with a power function. The S-parameters allows the extraction of the complex permittivity, permeability and conductivity of the CNT array. The extracted permittivity and absorption are compared with measurement results. The graphene nanoribbons are simulated in the same manner. The graphene sheet on top of a microstrip gap is simulated using transmission line model at microwave frequencies to show the impact of parasitics and contact resistances. Finally, a graphene based microwave absorber is proposed and modelled under both electric and magnetic bias. The absorber shows good broadband absorption rate and a potential for turning transparent and opaque to microwaves under both electric and magnetic bias.China Scholarship Council (CSC

Solid State Circuits Technologies

The evolution of solid-state circuit technology has a long history within a relatively short period of time. This technology has lead to the modern information society that connects us and tools, a large market, and many types of products and applications. The solid-state circuit technology continuously evolves via breakthroughs and improvements every year. This book is devoted to review and present novel approaches for some of the main issues involved in this exciting and vigorous technology. The book is composed of 22 chapters, written by authors coming from 30 different institutions located in 12 different countries throughout the Americas, Asia and Europe. Thus, reflecting the wide international contribution to the book. The broad range of subjects presented in the book offers a general overview of the main issues in modern solid-state circuit technology. Furthermore, the book offers an in depth analysis on specific subjects for specialists. We believe the book is of great scientific and educational value for many readers. I am profoundly indebted to the support provided by all of those involved in the work. First and foremost I would like to acknowledge and thank the authors who worked hard and generously agreed to share their results and knowledge. Second I would like to express my gratitude to the Intech team that invited me to edit the book and give me their full support and a fruitful experience while working together to combine this book

Advanced Characterization and Optical Properties of Single-Walled Carbon Nanotubes and Graphene Oxide

Photophysical, electronic, and compositional properties of single-walled carbon nanotubes (SWCNTs) and bulk nanotube samples were investigated together with graphene oxide photoluminescence. First, we studied the effect of external electric fields on SWCNT photoluminescence. Fields of up to 10 7 V/m caused dramatic, reversible decreases in emission intensity. Quenching efficiency was proportional to the projection of the field on the SWCNT axis, and showed inverse correlation with optical band gap. The magnitude of the effect was experimentally related to exciton binding energy, as consistent with a proposed field-induced exciton dissociation model. Further, the electronic composition of various SWCNT samples was studied. A new method was developed to measure the fraction of semiconducting nanotubes in as- grown or processed samples. SWCNT number densities were compared in images from near-IR photoluminescence (semiconducting species) and AFM (all species) to compute the semiconducting fraction. The results provide important information about SWCNT sample compositions that can guide controlled growth methods and help calibrate bulk characterization techniques. The nature of absorption backgrounds in SWCNT samples was also studied. A number of extrinsic perturbations such as extensive ultrasonication, sidewall functionalization, amorphous carbon impurities, and SWCNT aggregation were applied and their background contributions quantified. Spectral congestion backgrounds from overlapping absorption bands were assessed with spectral modeling. Unlike semiconducting nanotubes, metallic SWCNTs gave broad intrinsic absorption backgrounds. The shape of the metallic background component and its absorptivity coefficient were determined. These results can be used to minimize and evaluate SWCNT absorption backgrounds. Length dependence of SWCNT optical properties was investigated. Samples were dispersed by ultrasonication or shear processing, and then length-fractionated by gel electrophoresis or controlled ultrasonication shortening. Fractions from both methods showed no significant absorbance variations with SWCNT length. The photoluminescence intensity increased linearly with length, and the relative quantum yield gradually increased, approaching a limiting value. Finally, a strong pH dependence of graphene oxide photoluminescence was observed. Sharp and structured excitation/emission features resembling the spectra of molecular fluorophores were obtained in basic conditions. Based on the observed pH-dependence and quantum calculations, these spectral features were assigned to quasi-molecular fluorophores formed by the electronic coupling of oxygen-containing addends with nearby graphene carbon atoms

Suivi immergé de durabilité du béton par nano capteurs sans fil

Making the construction industry more sustainable requires the extension of the life of structures, achievable through the anticipation of structural deficiencies. Structural deficiencies often originate at the core of concrete structures from micro scale defects, whose detection is the key to predict structural ageing. The in-situ, real-time detection of such defects remains a major scientific and technological challenge and no cost effective technique is currently available. In this thesis, we present the design, fabrication and validation of the first wireless nano sensor node for embedded monitoring of concrete structures.The device is composed of 3 main parts: a sensing element, a conditioning circuit and an antenna. The first is a highly reproducible, hysteresis-free, flexible sensor fabricated by inkjet printing carbon nanotubes (CNTs) on polymer. We achieved the batch production of more than 140 sensors and also demonstrated low dispersion in device resistance as well as in its sensitivity to strain and temperature. The sensor also responds to humidity and pH, indicating that this fabrication process is adapted to the creation of a multifunctional nano sensor.The low-cost, low-power conditioning circuit adapts the sensors’ output to the input requirements of a regular analog-to-digital converter (ADC), compensating for temperature sensitivity. The antenna is specifically designed to maximise transmission through concrete for the wireless communication of the measurements. Power is supplied by a battery enabling the operation of the node for over 5 years. The circuitry is housed in a protective casing to insulate it from the harsh concrete environment. The volume of the assembled device is more than 3 times smaller than state of the art embedded nodes for concrete.The devices are tested both in laboratory conditions and in real-size concrete structures. The outputs of the sensors embedded in a mortar slab under 3-point bending tests suggest that the devices are capable of detecting the opening of micro cracks caused by increasing load. Moreover, continuous outdoor deployment since December 2014 demonstrates that this setup may be capable of detecting thermal-induced micrometric deformations and suggests that our technology provides a higher durability for embedded monitoring than commercial metallic strain gauge. In conclusion, the scientific and technological results of this research show the strong applicative potential of wireless nano sensors for embedded monitoring of concrete materials.Mettre en œuvre le développement durable en construction nécessite de prolonger la durée de vie des structures grâce à la détection précoce des fragilités structurales. Celles-ci trouvent très souvent leur origine au cœur même des structures, au niveau de défauts micrométriques. Détecter ces défauts in situ et en temps réel représente un défi scientifique et technologique majeur et aucune solution bas coût n’est actuellement disponible. Cette thèse présente le premier nanocapteur intelligent sans fil pour le suivi noyé des structures en béton. Le système est composé de trois parties : un élément sensible, un circuit de conditionnement du signal, et une antenne. Le premier est un capteur de déformation fabriqué par impression jet d’encre de nanotubes de carbone sur polymère. Ces capteurs sont fabriquées en série, jusqu’à 140 à la fois. Ils ne présentent pas d’hystérésis, résistent aux cyclages mécaniques, et sont très reproductibles en termes de résistance et de sensibilité (en température et en déformation) au sein d’une même série. Les capteurs sont sensibles également au pH et à l’humidité, ce qui suggère que cette technologie pourrait être adaptée à la création de nano capteurs multifonctionnels. Le circuit de conditionnement est à bas coût et faible consommation énergétique. Il met en forme le signal du capteur tout en compensant sa sensibilité à la température. L’antenne a été conçue pour maximiser sa portée à cœur du béton, permettant ainsi la communication sans fil des mesures du capteur vers l’utilisateur. Le système, protégé par un boitier spécialement conçu, est alimenté par une batterie pour une durée de vie estimée à plus de 5 ans. Le volume total du système final est plus de 3 fois inférieur à l’état de l’art des capteurs noyés.De nombreuses expériences en laboratoire ainsi que dans une structure en béton de taille réelle suggèrent que le dispositif est capable d’observer à la fois l’ouverture de micro fractures dues à des charges appliquées et les déformations micrométriques dues à des dilatations thermiques. De plus, nos capteurs à base de nanotubes ont montré une durabilité plus importante au cœur du béton que des capteurs de déformation métalliques commerciaux. En conclusion, les résultats scientifiques et technologiques de ces travaux montrent le fort potentiel applicatif des nano capteurs sans fil pour l’instrumentation noyée des matériaux cimentaires

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

18th Space Photovoltaic Research and Technology Conference

The 18th Space Photovoltaic Research and Technology (SPRAT XVIII) Conference was held September 16 to 18, 2003, at the Ohio Aerospace Institute (OAI) in Brook Park, Ohio. The SPRAT conference, hosted by the Photovoltaic and Space Environments Branch of the NASA Glenn Research Center, brought together representatives of the space photovoltaic community from around the world to share the latest advances in space solar cell technology. This year s conference continued to build on many of the trends shown in SPRAT XVII-the continued advances of thin-film and multijunction solar cell technologies and the new issues required to qualify those types of cells for space applications