Exploring charge transport properties and functionality of molecule-nanoparticle ensembles

For more than 65 years, scientists have been fascinated by the idea to miniaturize electrical circuits toward the smallest length scales. One particular way is inspired by nature itself, specifically to assemble electrical components and switches from atoms and molecules. The molecules typically used have dimensions of the scale of a few nanometers (1 nanometer = 0,000000001 meter). The scientific research area that represents the study of electrical currents through molecules is called "molecular charge transport" or "molecular electronics". In this thesis, I have performed fundamental research on charge transport through various molecules. Specifically, I have investigated a special type of molecule that has the ability to change its spin state. To test these functional molecules, I have used a more robust type of molecular device that enables me to bridge the size gap mentioned above. This thesis has led to two important new insights. First, the properties of a switchable molecular device can be strongly enhanced artificially by making use of a charge transport mechanism called multiple inelastic cotunneling. Second, we show that the spin transition phenomenon can take place in a molecular-nanoparticle ensemble.Quantum Matter and Optic

Graphene Quantum Strain Transistors and Two-in-One Carbon Nanotube Quantum Transistors

Graphene and carbon nanotubes are ideal for strain engineering in quantum nanoelectromechanical systems due to their long coherence lengths, mechanical strength, and sensitivity to deformations. Mechanical strain induces scalar ($\Delta \mu_{\varepsilon}$) and vector ($\bm{A}$) potentials, which directly tune the Hamiltonian, providing precise control of the energy, momentum, and quantum state of electrons in these materials. This strain-tunability could be used to completely suppress ballistic transmission in graphene quantum strain transistors (GQSTs), generate large pseudomagnetic fields ($\nabla \times \bm{A}$), or carry quantum information (valleytronics). Thus far, experimental challenges have prevented thorough exploration of quantum transport strain engineering (QTSE). To this end, we have constructed low temperature ($T\sim 1$~K) QTSE instrumentation. Incorporating fabrication methods for ultra-short ($\sim 10$~nm), suspended carbon nanotube and graphene devices, we predict tunable uniaxial strains up to $\approx \text{1--10}\%$ using this instrumentation. We first determined the impact of ultra-short channel lengths on transport by measuring unstrained nanotube devices. These formed ``two-in-one" quantum transistors with drastically different behaviour for electrons and holes. In a small bandgap nanotube ($\approx 50$~meV) we observed ballistic transport for electrons, and quantum dot (QD) behaviour for holes, while in larger bandgap nanotubes($\approx 300$~meV), we measured asymmetric QD behaviour between electrons and holes. We showed that this transport asymmetry is caused by electron doping in the nanotube contacts, and is greatly enhanced in ultra-short devices. With these contact effects in mind, we developed a realistic applied theoretical model for transport in uniaxially strained ballistic GQSTs. We calculated conductivity for strained ballistic graphene, and found four transport signatures: gate-shifting of the data from the scalar potential, and strong suppression of conductivity, modification of electron-hole conductivity asymmetry, and a rich resonance spectrum from the vector potential. We calculated high on/off ratios $>10^4$ in realistically achievable GQSTs at sufficient strains. Using our strain instrumentation, we measured transport in strained graphene, observing unambiguously the effects of strain-induced vector and scalar potentials. In graphene QDs, we observed gate-shifting of the charge states with strain, consistent with strong, strain-tunable pseudomagnetic fields. In a strained ballistic graphene device, we observed the four expected transport signatures discussed above, and using our model, we found good semi-quantitative agreement between theory and experiment

Modeling, Characterizing and Reconstructing Mesoscale Microstructural Evolution in Particulate Processing and Solid-State Sintering

abstract: In material science, microstructure plays a key role in determining properties, which further determine utility of the material. However, effectively measuring microstructure evolution in real time remains an challenge. To date, a wide range of advanced experimental techniques have been developed and applied to characterize material microstructure and structural evolution on different length and time scales. Most of these methods can only resolve 2D structural features within a narrow range of length scale and for a single or a series of snapshots. The currently available 3D microstructure characterization techniques are usually destructive and require slicing and polishing the samples each time a picture is taken. Simulation methods, on the other hand, are cheap, sample-free and versatile without the special necessity of taking care of the physical limitations, such as extreme temperature or pressure, which are prominent issues for experimental methods. Yet the majority of simulation methods are limited to specific circumstances, for example, first principle computation can only handle several thousands of atoms, molecular dynamics can only efficiently simulate a few seconds of evolution of a system with several millions particles, and finite element method can only be used in continuous medium, etc. Such limitations make these individual methods far from satisfaction to simulate macroscopic processes that a material sample undergoes up to experimental level accuracy. Therefore, it is highly desirable to develop a framework that integrate different simulation schemes from various scales to model complicated microstructure evolution and corresponding properties. Guided by such an objective, we have made our efforts towards incorporating a collection of simulation methods, including finite element method (FEM), cellular automata (CA), kinetic Monte Carlo (kMC), stochastic reconstruction method, Discrete Element Method (DEM), etc, to generate an integrated computational material engineering platform (ICMEP), which could enable us to effectively model microstructure evolution and use the simulated microstructure to do subsequent performance analysis. In this thesis, we will introduce some cases of building coupled modeling schemes and present the preliminary results in solid-state sintering. For example, we use coupled DEM and kinetic Monte Carlo method to simulate solid state sintering, and use coupled FEM and cellular automata method to model microstrucutre evolution during selective laser sintering of titanium alloy. Current results indicate that joining models from different length and time scales is fruitful in terms of understanding and describing microstructure evolution of a macroscopic physical process from various perspectives.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201

The fabrication and application of carbon nanotube-based hybrid nanomaterials

The evolution of technology has reached a stage where the performances and dimension needed are outpacing what conventional materials can deliver. This has been made more acute with the further necessity of miniaturisation. Therefore, new materials which can overcome this bottleneck are required. Over the past few decades, it was found that when a material is reduced to the nanoscale, they can exhibit properties unparallel by their bulk counterparts. Therefore these nanomaterials poise as a promising candidate for future applications. Of the many nanomaterials, carbon nanotube (CNT) is among the most emblematic. CNT is a hollow one-dimensional structure comprising solely of carbon atoms. They are fascinating as they exhibit physical attributes which surpass many conventional materials and their nanoscale dimension allows greater flexibility in their deployments. However, the utilisation of CNTs is currently frustrated by a host of intrinsic and extrinsic factors. As a result, there are usually significant disparity between their predicted capability and real-world performance. Therefore, the practical application of CNTs remains unfeasible. The premise of this thesis is that by employing CNTs in conjunction with other materials, the hurdles which plague their utilisation may be overcome. Here, the concept of CNT-based hybrid nanomaterials is presented. This thesis demonstrates that by engineering complementary interaction between two materials, many challenges which hamper the utilisations of CNTs and other nanomaterials can indeed be negated. Furthermore, their synergistic interaction allows the performance of the CNT-based hybrid nanomaterials to be superior to their uncoupled precursors. Therefore, this could be a viable strategy to incorporating nanomaterials in a range of applications

Dependable Embedded Systems

This Open Access book introduces readers to many new techniques for enhancing and optimizing reliability in embedded systems, which have emerged particularly within the last five years. This book introduces the most prominent reliability concerns from today’s points of view and roughly recapitulates the progress in the community so far. Unlike other books that focus on a single abstraction level such circuit level or system level alone, the focus of this book is to deal with the different reliability challenges across different levels starting from the physical level all the way to the system level (cross-layer approaches). The book aims at demonstrating how new hardware/software co-design solution can be proposed to ef-fectively mitigate reliability degradation such as transistor aging, processor variation, temperature effects, soft errors, etc. Provides readers with latest insights into novel, cross-layer methods and models with respect to dependability of embedded systems; Describes cross-layer approaches that can leverage reliability through techniques that are pro-actively designed with respect to techniques at other layers; Explains run-time adaptation and concepts/means of self-organization, in order to achieve error resiliency in complex, future many core systems

Asymptotic analysis of extreme electrochemical transport

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2005.Includes bibliographical references (p. 237-244).In the study of electrochemical transport processes, experimental exploration currently outpaces theoretical understanding of new phenomena. Classical electrochemical transport theory is not equipped to explain the behavior of electrochemical systems in the extreme operating conditions required by modern devices. In this thesis, we extend the classical theory to examine the response of two electrochemical systems that form the basis for novel electrochemical devices. We first examine the DC response of an electrochemical thin film, such as the separator in a micro-battery, driven by current applied through reactive electrodes. The model system consists of a binary electrolyte between parallel-plate electrodes, each possessing a compact Stern layer which mediates Faradaic reactions with Butler-Volmer kinetics. Our analysis differs from previous studies in two significant ways. First, we impose the full nonlinear, reactive boundary conditions appropriate for electrolytic/galvanic cells.(cont.) Since surface effects become important for physically small systems, the use of reactive boundary conditions is critical in order to gain insight into the behavior of actual electrochemical thin films that are sandwiched between reactive electrodes, especially at high current densities. For instance, our analysis shows that reaction rate constants and the Stern-layer capacitance have a strong influence on the response of the thin film. Second, we analyze the system at high current densities (far beyond the classical diffusion-limited current) which may be important for high power-density applications. At high currents, we obtain previously unknown characterizations of two interesting features at the cathode end of the cell: (i) a nested boundary layer structure and (ii) an extended space charge region. Next, we study the response of a metal (i.e., polarizable) colloid sphere in an electrolyte solution over a range of applied electric fields.(cont.) This problem, which underlies novel electrokinetically driven microfluidic devices, has traditionally been analyzed using circuit models which neglect bulk concentration variations that arise due to double layer charging. Our analysis, in contrast, is based on the Nernst-Planck equations which explicitly allow for bulk concentration gradients. A key feature of our analysis is the use of surface conservation laws to provide effective boundary conditions that couple the double layer charging dynamics, surface transport processes, and bulk transport processes. The formulation and derivation of these surface conservation laws via boundary layer analysis is one of the main contributions of this thesis. For steady applied fields, our analysis shows that bulk concentrations gradients become significant at high applied fields and affect both bulk and double layer transport processes. We also find that surface transport becomes important for strong applied fields as a result of enhanced absorption of ions by the double layer.(cont.) Unlike existing theoretical studies which focus on weak applied fields (so that both of these effects remain weak), we explore the response of the system to strong applied fields where both bulk concentration gradients and surface transport contribute at leading order. For the unsteady problem at applied fields that are not too strong, we find that diffusion processes, which are necessary for the system to relax to steady-state, are suppressed at leading-order but appear as higher-order corrections. This result is derived in a novel way using time-dependent matched asymptotic analysis. Unfortunately, the dynamic response of the system to large applied fields seems to introduce several complications that make the analysis (both mathematical and numerical) quite challenging; the resolution of these challenges is left for future work. Both of these problems require the use of novel techniques of asymptotic analysis (e.g., multiple parameter asymptotic expansions, surface conservation laws, and time-dependent asymptotic matching) and advanced numerical methods (e.g., pseudospectral methods, Newton-Kantorovich method, and direct matrix calculation of Jacobians) which may be applicable elsewhere.by Kevin Taylor Chu.Ph.D

Performance evaluation of the photovoltaic system

The various renewable energy source technologies, Photovoltaics (PV) transforming sunlight directly into electricity, have become standard practice worldwide, especially in countries with high solar radiation levels. PV systems have been developed rapidly over recent years, and many new technologies have emerged from different producers. For each type of PV module, manufacturers provide specific information on rated performance parameters, including power at maximum power point (MPP), efficiency and temperature factors, all under standard solar test conditions (STC) 1000 W/m2. Air. In addition, the mass (AM) of 1.5 and the cell's temperature was 25 ̊C. Unfortunately, this grouping of environmental conditions is infrequently found in outdoor conditions. Also, the data provided by the manufacturers are not sufficient to accurately predict the performance of photovoltaic systems in various climatic conditions. Therefore, monitoring and evaluating the performance of the off-site systems is necessary. This thesis aims to overview various photovoltaic technologies, ranging from crystalline silicon (c-SI) to thin-film CdTe and GiCs. The following are the main parameters for evaluating the external units' performance to describe the PV systems' operation and implementation. In addition, a review of the impacts of various environmental and operational factors, such as solar radiation, temperature, spectrum, and degradation

The impact of design techniques in the reduction of power consumption of SoCs Multimedia

Orientador: Guido Costa Souza de AraújoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: A indústria de semicondutores sempre enfrentou fortes demandas em resolver problema de dissipação de calor e reduzir o consumo de energia em dispositivos. Esta tendência tem sido intensificada nos últimos anos com o movimento de sustentabilidade ambiental. A concepção correta de um sistema eletrônico de baixo consumo de energia é um problema de vários níveis de complexidade e exige estratégias sistemáticas na sua construção. Fora disso, a adoção de qualquer técnica de redução de energia sempre está vinculada com objetivos especiais e provoca alguns impactos no projeto. Apesar dos projetistas conheçam bem os impactos de forma qualitativa, as detalhes quantitativas ainda são incógnitas ou apenas mantidas dentro do 'know-how' das empresas. Neste trabalho, de acordo com resultados experimentais baseado num plataforma de SoC1 industrial, tentamos quantificar os impactos derivados do uso de técnicas de redução de consumo de energia. Nos concentramos em relacionar o fator de redução de energia de cada técnica aos impactos em termo de área, desempenho, esforço de implementação e verificação. Na ausência desse tipo de dados, que relacionam o esforço de engenharia com as metas de consumo de energia, incertezas e atrasos serão frequentes no cronograma de projeto. Esperamos que este tipo de orientações possam ajudar/guiar os arquitetos de projeto em selecionar as técnicas adequadas para reduzir o consumo de energia dentro do alcance de orçamento e cronograma de projetoAbstract: The semiconductor industry has always faced strong demands to solve the problem of heat dissipation and reduce the power consumption in electronic devices. This trend has been increased in recent years with the action of environmental sustainability. The correct conception of an electronic system for low power consumption is an issue with multiple levels of complexities and requires systematic approaches in its construction. However, the adoption of any technique for reducing the power consumption is always linked with some specific goals and causes some impacts on the project. Although the designers know well that these impacts can affect the design in a quality aspect, the quantitative details are still unkown or just be kept inside the company's know-how. In this work, according to the experimental results based on an industrial SoC2 platform, we try to quantify the impacts of the use of low power techniques. We will relate the power reduction factor of each technique to the impact in terms of area, performance, implementation and verification effort. In the absence of such data, which relates the engineering effort to the goals of power consumption, uncertainties and delays are frequent. We hope that such guidelines can help/guide the project architects in selecting the appropriate techniques to reduce the power consumption within the limit of budget and project scheduleMestradoCiência da ComputaçãoMestre em Ciência da Computaçã

Ultrafast Spin Dynamics of Next-Generation Nanomagnetic Technologies

Over the past 50 years, our society has experienced a technological revolution that has fundamentally changed the way our world operates. At the heart of this revolution are the computational building blocks that work together to perform mathematical operations and save the results. For many years, the size of the computing elements (e.g. transistors) has been consistently shrunk so that more devices could fit on a chip in order to increase computational power. To provide adequate data storage for the ever-increasing number of computations, the hard-disk drive (HDD) was developed in the 1980s and would forever revolutionize the landscape of memory storage. Today, HDDs still account for a vast majority of the data stored worldwide. These devices store information using the magnetization of nanoscopic domains in a granular magnetic film, however, in recent years it has become increasingly challenging to reduce the size of the domains further without fundamentally changing the HDD. Indeed, the latest iteration of this technology has incorporated lasers into the devices to leverage multiple degrees of freedom in order to achieve higher bit densities. This example highlights a common trend for all next-generation computational technologies – the strong coupling between distinct physical systems must be utilized to sustain the improvements our society has become accustomed to. In order to realize this lofty goal, the physics of nanoscale systems must be well understood to predict their behavior. As our collective understanding of this field continues to flourish, novel effects are found that open doors to previously unimaginable technologies that may usher in a revolution of their own. Indeed, there are both technological and fundamental interests to study nanostructured devices.In this thesis, the time-resolved magneto-optic Kerr effect (TR-MOKE) will be utilized to probe the ultrafast spin dynamics of magnetic films, multilayer heterostructures, and nanostructures. Our experimental observations of these systems are evaluated by combining various field of science and technology, including (but not limited to) condensed matter theory, signal processing, and optics. In doing so, we seek to fully explain the data and to enrich the understanding of these underexplored systems to inform the rational design of next-generation technologies. Specifically, a great deal of attention will be paid to emergent nanotechnologies that leverage the coupling between the magnetic system and either the electronic or mechanical properties of the device to tailor the performance. In this work, a novel method to restore the intrinsic magnetization dynamics and simultaneously improve the magneto-optical response of dense nanomagnet arrays will be presented. Then, our work on the spin dynamics of isolated nanomagnets resonantly excited by microwave-frequency acoustic waves will be reviewed, wherein we show for the first time that the coupling efficiency is ultimately limited by the damping of the magnetic system. In addition, the role of the nanomagnet geometry and the acoustic wavelength will be fully explored to determine critical parameters that govern the dynamic magneto-elastic resonance. Lastly, the development of an optical system to study the interplay between ultrafast all-optical switching and surface acoustic waves will be reviewed

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