To see the other types of publications on this topic, follow the link: Electrical engineering|Mechanical engineering|Materials science.
Dissertations / Theses on the topic 'Electrical engineering|Mechanical engineering|Materials science'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Electrical engineering|Mechanical engineering|Materials science.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Yu, Hong. "Modeling and Characterization of Electrical Resistivity of Carbon Composite Laminates." Thesis, University of Delaware, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10745689.
Full textAbstract:
<p> In the past few decades, composite materials especially carbon fiber reinforced polymers (CFRP) have been widely used as structural materials for its high strength to weight ratio, tailorable properties, and excellent corrosion properties. Applications that require better understanding of the electrical properties of CFRP laminates include carbon fiber assisted heating during composites manufacturing, self-sensing of damage of composite structures, integrated electromagnetic shielding, and lightning strike protection. Accurate predictive model describing the electrical conduction behavior of CFRP laminates is the key for them to be used for such applications.</p><p> Different approaches have been explored to model the electrical conduction of CFRP under various current conditions. A comprehensive literature review revealed that most methods used to model electrical conduction of CFRP fail to capture the impact of micro-structure of CFRP, especially the fiber-fiber contact, and resin-rich layer between plies, which can drastically change the conduction pattern.</p><p> The aim of this dissertation work is to develop a model that capture key electrical conduction mechanisms of CFRP, which address the impact of the micro-structure and geometrical parameters. The model is constructed in a modular fashion by validating the model with experimental validation after the addition of each key mechanism module. First, the model constructs a resistor network framework for describing electrical conduction behavior of UD laminas and fiber tows subjected to low DC currents. The model is validated with reported experimental results, and by characterization of resistivity of dry carbon fiber tows.</p><p> The next module investigates the specific features of a multi-ply laminate such as: varying ply orientation, existence of resin-rich layer, and dependence on geometric parameters that influence the local resistivity. A meso-scale fiber bundle model is proposed to strike a balance between the level of details modeled and the computational cost. Influence of the resin-rich layer is described with an inter-ply connectivity term. Expressions for estimating contact resistance from multiple sources including direct fiber-fiber contact and tunneling resistance across thin resin layer are introduced. The refined model is compared against experimental results and finite element model. A parametric study is conducted to investigate the impact of geometrical parameters.</p><p> Finally, the dissertation work investigates the impact of high current density both numerically and experimentally. Simplified analytical model examining the impact of localized Joule heating revealed that current concentrations due to microstructure constraints can introduce excessive Joule heating at contact spots. Thus, it is vital not to under-estimate the temperature rise at contact points, even at seemingly small overall applied currents. Based on these analysis, the model is further refined with the implementation of the module that introduces Joule heating. Both reversible change in resistivity such as temperature dependent resistivity and irreversible change such as thermal and electric degradation of resin matrix is considered.</p><p> Electrical characterization under high current density is carried out for dry fiber tows and cured composites experimentally. The contributions of reversible and irreversible resistivity change are identified with carefully designed repetitive current tests. It is found that for dry fiber tows with sizing and for cured composites, thermal breakdown of the thin resin/sizing layer contributes significantly to the nonlinear conduction behavior under high current density. The developed model captures important characteristics of the electrical conduction behavior when compared with experimental results. Possible explanations are offered for cases and regions where the model shows discrepancies with experimental results. This model should prove useful to address and design and fabricate composite components in which electric and thermal conductivity play a key role in defining their functional properties. </p><p>
2
Muzumdar, Manoj D. (Manoj Deepak) 1976. "ICEMENDR : intelligent capture environment for mechanical engineering drawing." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9470.
Full textAbstract:
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.<br>Includes bibliographical references (p. 45-46).<br>I designed and implemented an intelligent environment for recognizing simple mechanical engineering sketches. This involves the analysis of complex mechanical engineering parts and their components and consists of creating a hierarchical recognition system capable of parsing these parts with simpler geometric primitives. The system seeks to provide an intuitive pencil-and-paper-like interface for sketch recognition by allowing incremental recognition of what a user draws on the system. The system's knowledge is arranged in simple Recognizer modules that have very specialized information on a particular aspect of recognizing a part.<br>by Manoj D. Muzumdar.<br>M.Eng.
3
Salary, Roozbeh Ross. "Computational Fluid Dynamics Modeling and in situ Physics-Based Monitoring of Aerosol Jet Printing toward Functional Assurance of Additively-Manufactured, Flexible and Hybrid Electronics." Thesis, State University of New York at Binghamton, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10840384.
Full textAbstract:
<p> Aerosol jet printing (AJP)—a direct-write, additive manufacturing technique—has emerged as the process of choice particularly for the fabrication of flexible and hybrid electronics. AJP has paved the way for high-resolution device fabrication with high placement accuracy, edge definition, and adhesion. In addition, AJP accommodates a broad range of ink viscosity, and allows for printing on non-planer surfaces. Despite the unique advantages and host of strategic applications, AJP is a highly unstable and complex process, prone to gradual drifts in machine behavior and deposited material. Hence, real-time monitoring and control of AJP process is a burgeoning need. In pursuit of this goal, the objectives of the work are, as follows: (i) <i>In situ </i> image acquisition from the traces/lines of printed electronic devices right after deposition. To realize this objective, the AJP experimental setup was instrumented with a high-resolution charge-coupled device (CCD) camera, mounted on a variable-magnification lens (in addition to the standard imaging system, already installed on the AJ printer). (ii) <i>In situ </i> image processing and quantification of the trace morphology. In this regard, several customized image processing algorithms were devised to quantify/extract various aspects of the trace morphology from online images. In addition, based on the concept of shape-from-shading (SfS), several other algorithms were introduced, allowing for not only reconstruction of the 3D profile of the AJ-printed electronic traces, but also quantification of 3D morphology traits, such as thickness, cross-sectional area, and surface roughness, among others. (iii) Development of a supervised multiple-input, single-output (MISO) machine learning model—based on sparse representation for classification (SRC)—with the aim to estimate the device functional properties (e.g., resistance) in near real-time with an accuracy of ≥ 90%. (iv) Forwarding a computational fluid dynamics (CFD) model to explain the underlying aerodynamic phenomena behind aerosol transport and deposition in AJP process, observed experimentally. </p><p> Overall, this doctoral dissertation paves the way for: (i) implementation of physics-based real-time monitoring and control of AJP process toward conformal material deposition and device fabrication; and (ii) optimal design of direct-write components, such as nozzles, deposition heads, virtual impactors, atomizers, etc.</p><p>
4
Herring, Jessica A. "Mechanical and electrical characterization of carbon Black-doped closed-cell Polydimethylsiloxane (PDMS) foam." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98652.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 51-52).<br>Carbon Black-doped Polydimethylsiloxane (CB-PDMS) can be used as a pressure sensing material due to its piezoresistive properties. The sensitivity of such a sensor is in part dependent on the stiffness of the material. A closed-cell CB-PDMS foam is being explored as a possible flexible, lightweight, and waterproof underwater sensing material for use in unmanned underwater vehicles and other hydrodynamic sensing purposes. The percolation threshold for conduction through the CB-PDMS foam is theorized, and a number of different concentrations based on the theorized threshold are explored in order to determine the optimum weight percent of Carbon Black dopant to achieve a high sensitivity, low stiffness sensing CB-PDMS foam. Sinusoidal mechanical pressure patterns were applied and voltage response measured. An optimum dopant weight percent out of the concentrations tested was found at 5.5 wt% CB-PDMS.<br>by Jessica A. Herring.<br>S.B.
5
Anant, Vikas 1980. "Engineering the optical properties of subwavelength devices and materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42233.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.<br>Includes bibliographical references (p. 145-154).<br>Many applications demand materials with seemingly incompatible optical characteristics. For example, immersion photolithography is a resolution enhancing technique used to fabricate the ever-shrinking nanostructures in integrated circuits but requires a material that has-at the same time--a large index of refraction and negligible optical loss. Other applications require devices that have optical properties that seem exorbitant given the constraints posed by the geometry, materials, and desired performance of these devices. The superconducting nanowire single-photon detector (SNSPD) is one such device that, on the one hand, needs to absorb and detect single telecom-wavelength photons (A = 1.55 pm) with near-perfect efficiency, but on the other hand, has an absorber that is subwavelength in its thickness (A/390). For both cases, it is simply not enough to look for alternative materials with the desired optical properties, because the materials may not exist in nature. In fact, it has become necessary to engineer the optical properties of these devices and materials using other means. In this thesis, we have investigated how the optical properties of materials and devices can be engineered for specific applications. In the first half of the thesis, we focused on theoretical schemes that use subwave-length, resonant constituents to realize a material with interesting optical properties. We proposed a scheme that can achieve high index (n > 6) accompanied with optical gain for an implementation involving atomic vapors. We then explored the applicability of this high-index system to immersion lithography and found that optical gain is problematic. We solved the issue of optical gain by proposing a scheme where a mixture of resonant systems is used. We predicted that this system can yield a high refractive index, low refractive index, anomalous dispersion, or normal dispersion, all with optical transparency. In the second half, we studied the optical properties of SNSPDs through theoretical and experimental methods. In the study, we first constructed a numerical model that predicts the absorptance of our devices. We then fabricated SNSPDs with varying geometries and engineered a preprocessing-free proximity-effect correction technique to realize uniform linewidths. We then constructed an optical apparatus to measure the absorptance of our devices and showed that the devices are sensitive to the polarization of single photons.<br>by Vikas Anant.<br>Ph.D.
6
Kneer, Emil Anton 1965. "Electrochemical aspects of chemical mechanical polishing of tungsten and aluminum." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282711.
Full textAbstract:
Chemical mechanical polishing (CMP) of metals has emerged as a critical process step for the fabrication of advanced integrated circuit devices in the semiconductor industry. In a typical metal CMP process, the metal film is blanket deposited to fill recessed features on a patterned dielectric on silicon. Following metal deposition and gap fill, the metal overabundance is polished away by CMP, leaving an inlayed metal pattern or damascene structure on the substrate. Removal of the metal overabundance also planarizes the wafer surface for subsequent processing steps. The material removal process occurring during CMP is thought to involve the combined action of chemical oxidation and dissolution, and mechanical removal of material by abrasives. However, the relative contribution of mechanical and chemical effects during metal CMP is not well understood. The objective of this research was to characterize the fundamental electrochemical behavior of tungsten and aluminum thin films in polishing chemistries of interest to CMP. It was also of interest to determine the extent to which electrochemical oxidation and dissolution, or mechanical removal by abrasive action assists in material removal during CMP. A simultaneous electrochemical tester and polishing tool was developed to characterize the electrochemical behavior of tungsten and aluminum during and after abrasion. Small-scale polishing experiments were also carried out to measure polishing (removal) rates of the metals during CMP. Electrochemical dissolution rates and polishing rates were compared. It was found that the electrochemical dissolution rate of tungsten or aluminum during or after abrasion was very small compared to actual polishing rates. However, the presence of an oxidant enhanced polishing rates dramatically. The findings indicate that the mechanism for removal during CMP is primarily corrosion assisted metal removal, and not electrochemical dissolution and/or removal of the oxidation product of the metal.
7
Gan, Tian S. M. Massachusetts Institute of Technology. "Design and fabrication of granular materials for surface acoustic waves." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100133.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.<br>Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 134-147).<br>Granular materials with structural discreteness and periodicity can lead to novel propagation behaviors of mechanical waves. Acoustic studies of granular media typically involve macroscopic particles whereas contact-based vibrations of microparticles remain largely unexplored. The adhesion which can be neglected on millimeter scale is significant on micron scales and therefore microparticles are expected to yield qualitatively different dynamics. We model the microparticle array as locally resonant metamaterials for surface acoustic waves by using the effective medium approach. In experiment, we employ the convective assembly method to fabricate the centimeter-sized, two-dimensional granular crystal consisting of 1[mu]m silica spheres adhered to the substrate. Laser-induced transient grating technique is used to generate and detect surface acoustic waves in microsphere array samples. We demonstrate, both experimentally and by theoretical analysis, that the Rayleigh wave in the substrate interacts with the contact resonance of microspheres leading to hybridization and "avoided-crossing" at a high frequency regions~10 2 MHz. Furthermore, we fabricate the microsphere waveguide structure by template-assisted-self-assembly. By using the same laser technique, we have observed the waveguide behavior in experimental measurement.<br>by Tian Gan.<br>S.M.
8
Smith, Craig Edward. "Monitoring Damage Accumulation In SiC/SiC Ceramic Matrix Composites Using Electrical Resistance." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1249917100.
Full text
9
Rich, Steven I. "Electrically Activated Stiffness-Switching with Low-Melting-Point Conductive Thermoplastics." Thesis, Carnegie Mellon University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10977483.
Full textAbstract:
<p> As technology becomes more integrated into our daily lives, the need for machines that can safely and comfortably interact with the human body has grown. While the rigidity of traditional robotic materials, such as metals and plastics, can provide mechanical and electrical stability to these devices, it can also reduce safety and comfort when placed in contact with soft human tissue. In recent years, these issues have been addressed by incorporating compliant materials, like liquids or soft polymers, into wearable or biomedical devices. However, these materials, by virtue of their softness, cannot support the high loads required for operations like stabilization or gripping. To address this apparent trade-off between load-bearing stiffness and conformable softness, several groups have constructed stiffness-tuning devices, capable of alternating between a high-stiffness state and a low-stiffness state. Although there exist a wide variety of mechanisms by which we can achieve this switching behavior, thermally activated phase change provides the highest stiffness ratio between the soft and stiff states. In this work, use low-melting point conductive thermoplastics to create electrically activated stiffness-switching devices. When a voltage is applied across this thermoplastic, the resulting electric current causes the polymer to heat and melt. This phase change corresponds to an effective stiffness change. </p><p> In the first study, we introduce a novel stiffness switch layout that employs liquid metal as compliant electrodes oriented across the face of a conductive thermoplastic. This new layout results in an 80% decrease in required voltage, a 60% decrease in activation time, and the ability to switch the stiffness of arbitrary geometries. </p><p> In the second study, we examine the effects of the composition of a conductive thermoplastic composite on its stiffness-switching properties, and use these findings can help guide the design of stiffness-switching composites for a three soft robotic applications.</p><p>
10
Nittala, Aditya Kameshwara. "Electrical and Mechanical Performance of Aluminum Alloys with Graphite Nanoparticles." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1554117521295178.
Full text
11
Burr, Tracey Alexandra 1967. "Electrical properties of silicon surfaces and interfaces." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9689.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.<br>Includes bibliographical references (p. 159-168).<br>This work addresses two scientific challenges associated with diminishing device size. First, alternative surface passivation chemistries are investigated to meet the narrowing process tolerances for high quality silicon surfaces. Second, Si-based light emitting devices are studied to address a longer-term move towards photons instead of electrons for data transfer. A concerted effort is made to engineer environmentally benign solutions to these challenges. Highly effective Si( 100) surface passivation is achieved by immersing wafers in very dilute solutions of methanolic iodine. The electrical quality of Si surfaces is monitored in terms of surface recombination lifetime, employing radio frequency photo conductance decay (rfPCD) measurements. J/methanol treated surfaces are shown to have higher lifetimes and greater air stability than hydrogen terminated surfaces, while retaining comparable planarity and smoothness. Using XPS, UPS, and ATR-FTIR, the identity of the primary passivating surface species is ascertained to be a methoxysilane (Si-OCH3), and the most plausible passivation mechanism is deduced. Our results clearly illustrate the relationship between chemical passivation and electrical passivation. Thin films of visibly emitting silicon nanoparticles are fabricated using a pulsed laser ablation supersonic expansion technique. The electrical and electroluminescence characteristics of devices containing these films are shown to be controlled by carrier transport through the nanoparticulate silicon layer. A conduction mechanism encompassing both geometric and electronic effects most effectively relates the high resistivity with structural properties of the films. The observed temperature dependent PL, EL, and I-V characteristics of the devices are consistent with a model in which carrier transport is controlled by space-charge-limited currents or tunneling through potential barriers on a percolating lattice.<br>by Tracey Alexandra Burr.<br>Ph.D.
12
Smith, Ernest Gregory. "The electrical properties of ruthenium-aluminium alloys." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/18217.
Full textAbstract:
The electrical properties of platinum, gold-palladium and a selection of alloys from the ruthenium-aluminium system have been studied at high temperatures (up to 1000°C). The majority of the ruthenium-aluminium alloy compositions studied lie near or in the ruthenium aluminide phase field. Ruthenium aluminide is a B2 structure intermetallic which is suited to high temperature applications because in addition to a high melting point (2060°C), oxidation resistance to 1200°C and high temperature strength, it is also relatively ductile at room temperature. The possibility of high temperature electrical applications required an investigation of the electrical properties of ruthenium-aluminium alloys as compared to platinum and gold-palladium. Two sets of apparatus, capable of measuring the resistivity and thermo-e.m.f to high temperatures, were constructed and used to obtain the first experimental results for the electrical properties of ruthenium-aluminium alloys. Chemical analysis of these alloys has been performed for the first time, and together with energy dispersive spectroscopy, has revealed a composition at which there is a resistivity minimum and a positive thermo-e.m.f maximum, which appears to be associated with the formation of the ordered ruthenium aluminide phase. The resistivity and the temperature dependence of resistivity of some ruthenium-aluminium alloys are similar to that of platinum, the least resistive of the three materials investigated.
13
Yu, Tae-Hwan. "Electrical properties and structural disorder in stannate pyrochlores." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/40609.
Full text
14
Yoon, Jung Uk 1971. "SIMOX BOX metrology : using physical and electrical characterization." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32682.
Full text
15
Ahn, Sang Hoon 1970. "Electrical studies of silicon and low K dielectric material." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9130.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999.<br>Includes bibliographical references (leaves 108-111).<br>Junction capacitance measurement is a well-established powerful characterization technique that allows one to explore electrical and physical properties of defects in bulk and interface of electronic materials. Capacitance-Voltage (CV) measures the overall net carrier concentration and a built-in voltage for a diode junction. Deep level transient spectroscopy (DLTS) as one of the most sensitive electrical measurement techniques can detect electrically active impurity concentration on the level of 10-1 to 10-5 of substrate doping concentration. The characteristic energy level and capture cross-section of the traps in the semiconductor energy gap can be extracted from DLTS temperature scans. Coupled with CV free carrier concentration profile, isothermal profiling by DLTS can determine the distribution of electrically active defects in the semiconductor. CV can also measure dielectric constant, K, on a metal-oxide-silicon structure. In this thesis, the junction capacitance technique is a primary tool used to study Er, Fe, and Mo in silicon. Si:5r is a candidate system for a light emitter in Si-based microphotonics. Fe is one of the most troublesome elements that degrade integrated circuit performance and solar cell efficiency. Mo is a fairly unknown contaminant typical of integrated circuit processing. Fluorosilicate glass is being used as a dielectric material for inter-metal levels in the current generation microprocessor. By measuring the reaction kinetics of the Er-related donor state, a defect structure for Si:Er light emitter center was deduced. The role of heterogeneous precipitation in Fe internal gettering was observed and modeled by measurement of residual [FeB] associates following [Fe] saturation, quench, and annealing processing. The diffusivity of Mo was determined and models for both the substitutional and the kick out diffusion mechanism were constructed. Finally, a predictive model for the F-content dependent dielectric constant variation of Si02 was established.<br>by Sang Hoon Ahn.<br>Ph.D.
16
Marks, Jordan (Jordan Christine). "Development of sodium silicate adhesives for electrical steel bonding." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89976.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.<br>Cataloged from PDF version of thesis. Vita.<br>Includes bibliographical references (page 46).<br>Inorganic adhesives have several benefits over traditional joining methods for joining electrical steels used in magnetic cores of numerous industrial applications. As insulators with very high melting temperatures, the adhesives offer the possibility of increasing the efficiency of these machines. The aim of this project was to characterize sodium silicates as adhesives for such applications and develop methodology for their processing. The chemical and physical properties of the water-soluble sodium silicates were easily altered by changing the composition of Na₂O, SiO₄, and water, offering a spectrum of properties to investigate. Several aspects of the electrical steel provided by POSCO were also investigated, including surface chemistry and microstructure due to processing of the steel sheets. Coating efficacy was evaluated based on the adhesive's ability to wet the substrate to form a uniform coating, as well as resistance to mechanical loads, including adhesion and flexural strain. Greater degree of alkalinity in the sodium silicates resulted in improved wetting, uniformity, adhesion, and flexural strain for the range of viscosities that supported these behaviors. The microstructure of the electrical steels influenced the interaction of the adhesive with the surface, but properties still improved with higher alkalinity. Firing parameters were used to alter the mechanical properties of the silicates, as well as to determine operability limits. The best mechanical properties occurred for those coupons fired between 600°C and 800°C. The efficacy did not degrade significantly with long exposure to high temperatures, offering promise for sodium orthosilicates as appropriate adhesives for the described applications. Further study of the environmental conditions under which the adhesives will be used, as well as full characterization of the insulating properties will allow the processes developed here to be scaled up for industrial use.<br>by Jordan Marks.<br>S.B.
17
Fruitman, Clinton 1946. "The effects ofpH and electrical bias on abrasion of alumina in aqueous solutions." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/278471.
Full textAbstract:
Various coolant chemicals are known to have enhancing and suppressing effects on wear and the quality of finish, but little has been understood about the nature of these effects. Studies were performed to examine the effects of pH and surface bias on wear, subsurface damage, and the various theories of chemical interaction with the wear process. Results of this examination of wear suggest that chemical adsorbates can play a significant role in wear fracturing. Previous observations of plastic mechanisms in brittle wear have lead tribologists to suggest that chemically induced changes in plasticity are the cause of these effects. Instead, this thesis contends occurrence of plastic effects to be by-product of localized hydrostatic compression and insufficient stress intensity to cause fracture. Crack rates and stress intensities required for fracture to occur are known to vary with adsorption.
18
Jeoung, Jun Sik. "Structural and electrical characterization of low-dose low-energy SIMOX materials." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280614.
Full textAbstract:
The effects of implantation dose, energy, and annealing conditions on the microstructure and the formation and evolution of defects in the low-dose, low-energy SIMOX materials were investigated using transmission electron microscopy (TEM), scanning electron microscopy, scanning electron microscopy (SEM), optical microscopy secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS). The quality of top Si layer and buried oxide layer (BOX) was also characterized with the electrical measurements. From the structural characterization of 100 keV implanted samples, it was found that the optimum dose window to form a continuous BOX layer after annealing was 3.0 to 3.5 x 10¹⁷ O⁺/cm². In addition, the formation mechanisms of dislocations and stacking faults in SIMOX materials were also proposed. The Hg-based pseudo-MOSFET technique was a very effective in-situ technique to evaluate the electrical quality of low-dose low-energy SIMOX. Based on the comparisons of device parameters of low-dose low-energy SIMOX and commercial SIMOX samples, we found that the quality of top Si layer of SIMOX sample prepared at 100 keV with a dose of 3.5 x 10¹⁷ O⁺/cm² was excellent. However, the interface properties (interfacial trap density) needed to be improved. The dielectric quality of low-dose low-energy SIMOX evaluated by breakdown voltage measurements showed a strong dependency on the microstructure of samples.
19
Chen, Jimmy Kuo-Wei. "The electrical and optical properties of doped yttrium aluminum garnets." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32136.
Full text
20
Lavik, Erin Baker. "The electrical properties of pure and doped nanocyrstalline cerium oxide." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/46096.
Full text
21
Russo, Analisa. "Variation of electrical resistance in superelastic NiTi for sensor applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/57875.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 32).<br>Nickel-Titanium (NiTi) is a most commonly known as a heat-activated shape memory alloy. However, the material sometimes displays a constant-temperature property called "superelasticity." A superelastic material is one which can undergo very high reversible strains due to stress-induced change in crystal structure. In the case of Superelastic NiTi, Martensitic transformation occurs. The two crystal structures differ to the extent that the gradual phase transformation is coupled to a gradual change in resistivity. In fact, resistive sensing is a common characterization technique for shape memory alloys. The unique material properties of superelastic NiTi could also be the basis for creating a resistive sensor that is sensitive enough to measure small displacements, and robust enough to measures large displacements. This study focuses on NiTi which displays superelastic behavior above room temperature. To assess the material's potential as a strain sensing medium, the NiTi wire is shape-set into coil springs which amplify the sensor's net deformation. The relationship between strain and resistance is measured. The study shows that various aspects of the strain-resistance response, including non-linear hysteretic behavior and temperature dependence of electrical resistivity, pose challenges to sensor design. Though the accuracy of the spring sensors is still under development, several recommendations are made with regard to effective device design. In addition, the design of a one-axis strain rate sensor, which differentiates between only two modes of behavior, is explored.<br>by Analisa Russo.<br>S.B.
22
Xu, Zhihong 1965. "Electrical behaviour of bismuth and platinum contacts to crystallized selenium." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22684.
Full textAbstract:
Diode structures have been fabricated involving a thin film of bismuth or platinum deposited on a layer of polycrystalline trigonal selenium, itself deposited on a substrate of either bismuth or platinum. Current-voltage and capacitance-voltage measurements on the diodes indicate that the Se-Bi and Se-Pt contacts are basically Schottky junctions with low barrier heights. Despite these barriers, near-ohmic contacts were obtained with bismuth or platinum layers thicker than about one micrometer, due to junction shunting. The barrier height for the Se-Pt contact was estimated to be about 0.3 volt below that of the Se-Bi contact. Negative capacitance, at a frequency of 100 Hz or less, was observed with forward bias on some of the Se-Bi diodes, with electrical characteristics similar to those reported earlier for Se-Tl. It was shown experimentally that the negative capacitance did not come from inductance sources external to the sample. An aging effect was observed whereby a sample, where originally the capacitance was entirely positive, showed negative capacitance after a storage period of about ten months. Negative capacitance was created in Se-Bi diodes by incorporating a thin high resistance layer of CdO into the devices during fabrication. Furthermore, a decrease of negative capacitance was found with increasing the counter electrode area. Negative capacitance was also observed in diodes fabricated using CuInSe$ sb2$. To explain the main electrical characteristics, an equivalent circuit model is proposed, involving a fixed inductive element L, arising from carrier transit delays in the junction during high level injection.
23
Schiefelbein, Susan L. "A new technique to measure the electrical properties of molten oxides." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11244.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.<br>Includes bibliographical references (leaves 191-196).<br>by Susan L. Schiefelbein.<br>Ph.D.
24
Fried, Naomi Anne. "Electrical properties of binary solutions of molten titanium dioxide-barium oxide." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10600.
Full text
25
Stefanik, Todd Stanley 1973. "Electrical properties and defect structures of praseodymium-cerium oxide solid solutions." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16623.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2004.<br>Includes bibliographical references (p. 130-135).<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>A defect chemistry model consistent with observed trends in the pO2 and temperature dependence of electrical conductivity in praseodymium cerium oxide (PCO) was developed. Four point DC conductivity measurements were made from 1 atm to 1018 atm p02 over isotherms ranging from 600-1 000ʻC in materials containing 0-20% Pr. A pO02-dependent ionic conductivity was observed at high pO2 values in compositions containing 0.5% and 1% Pr. This behavior was attributed to oxidation of Pr3+ to Pr4+ under oxidizing conditions, thereby decreasing the concentration of acceptor dopants in the PCO material. In compositions containing 10% and 20% Pr, an electron hopping conductivity was observed at high pO02 values. This contribution was strongest at low temperatures and was attributed to the formation of a praseodymium impurity band within the CeO2 band gap. Defect association significantly altered the predicted pO2 dependence of the impurity band conductivity, especially at low temperatures. The temperature dependences of the thermodynamic parameters governing defect formation and transport in PCO were determined. The reduction enthalpy of cerium was significantly decreased with additions of Pr from approximately 4.7 eV (the value in pure CeO2) to 3.4 eV in 20% PCO. The energy between the Pr impurity band and the CeO2 conduction band was approximately 0.95 eV for 10% and 20% PCO samples. The measured trap depth was significantly higher (approximately 1.6 eV) in 0.5% and 1% PCO. The migration enthalpy for impurity band hopping conductivity was approximately 0.55 eV, slightly higher than the hopping enthalpy for intrinsic carriers in CeO2 (0.4 eV).<br>(cont.) The oxygen ion migration enthalpy measured for most samples was approximately 0.6- 0.7 eV, in agreement with values determined for other rare-earth doped systems. At 20% Pr, the total migration energy increased to approximately 0.9 eV. This increase was attributed to an association energy at high doping levels. Coulometric titration and points to the possible existence of uncharged oxygen vacancies, particularly at low temperatures. During the course of these experiments, it became evident that the mechanical stability of PCO needs to be addressed if the material is to be used in real applications. Oxygen uptake/evolution during reduction/oxidation cycles appears to result in development of significant stresses and cracking. While the material may be useful in powder form, this cracking issue must be addressed if it is to be used in bulk or thin film form.<br>by Todd Stanley Stefanik.<br>Ph.D.
26
Amruthaluri, Sushma. "Synthesis of copper carbon nanotube composite and its electrical conductivity measurement." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/1283.
Full textAbstract:
The matrices in which Multi Walled Carbon Nanotubes (MWCNTs) are incorporated to produce composites with improved electrical properties can be polymer, metal or metal oxide. Most composites containing CNTs are polymer based because of its flexibility in fabrication. Very few investigations have been focused on CNT-metal composites due to fabrication difficulties, such as achievement of homogeneous distribution of MWCNTs and poor interfacial bonding between MWCNTs and the metal matrix. In an effort to overcome poor interfacial bonding for the Cu - MWCNT composite, silver (Ag) and nickel (Ni) resinates have been incorporated in the ball milling stage. Composites of MWCNT (16, 12, and 8 Vol %) - Cu+Ag+Ni were pelleted at 20,000 psi (669.4 Mpa) and sintered at 950 °C. The electrical conductivity results measured by four probe meter showed that the conductivity decreases with increase in the porosity. Moreover from these results it can also be stated that an addition of optimum value of (12 Vol %) MWCNT leads to high electrical conductivity (9.26E+07 s-m"), which is 50% greater than the conductivity of Cu. It is anticipated that the conductivity can be increased substantially with hot isostatic pressing of the pellet.
27
Rice, Philip Zachary. "The Effect of Nanostructure on the Electrical Properties of Metal Oxide Materials." Thesis, State University of New York at Albany, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3568291.
Full textAbstract:
<p> Resistive random access memory (ReRAM) is a potential replacement technology for Flash and other memory implementations. Advantages of ReRAM include increased scalability, low power operation, and compatibility with silicon semiconductor manufacturing. Most of the ReRAM devices described to date have utilized thin film based metal oxide dielectrics as a resistive switching matrix. The goal of this dissertation project has been to investigate the resistive switching behavior of nanoparticulate metal oxides and to develop methods to utilize these materials in ReRAM device fabrication. To this end, nanoparticles of TiO<sub>2</sub> and HfO<sub>2</sub> were synthesized under a variety of conditions resulting in various size, shape, and crystallinity. Electrical measurements of individual nanoparticles, as well as composite films of nanoparticles, were performed with limited success. To improve the stability of nanoparticle films, a spin on glass, hydrogen silsesquioxane (HSQ), was incorporated into the film stack. Addition of HSQ prevented electrical shorting and stabilized the nanoparticle films. In addition to serving as a stabilizer for nanoparticle films, HSQ was also found to have its own resistive switching properties. Composite films consisting of HSQ and nanoparticles yielded modified switching behavior which was tunable based upon nanoparticle composition and the thickness of the nanoparticle film. Our results demonstrate that both V<sub>SET</sub> and V<sub>RESET</sub> of HSQ switching can be increased when nanoparticles are incorporated with HSQ, without any significant changes to the device's high and low resistance states. We conclude that metal oxide nanoparticles can function as the dielectric material for ReRAM and can also be used to modulate the switching properties of composite ReRAM devices.</p>
28
Jutarosaga, Tula. "Formation and Electrical Properties of Buried Oxide Layers in Thin Simox Materials." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193603.
Full textAbstract:
The effects of implantation conditions and annealing conditions on the formation of buried oxide layers in the low-dose low-energy SIMOX materials were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR). The electrical properties of the buried oxide layers were investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements.The distribution of oxygen and defects in the as-implanted materials due to the implantation conditions (oxygen dose and energy) had significant effects on the formation of the buried oxide layer in low-dose low-energy SIMOX substrates. Multiply faulted defects (MFDs) and small oxide precipitates were observed in the projection range (Rp) in as-implanted samples. As increasing the dose, the mixture of silicon and oxide (silicon striations) also formed around Rp. The locations and shapes of the silicon striations control the density and size of silicon islands in the fully-annealed SIMOX at 1350oC.Upon annealing, the buried oxide layers become stoichiometric. Also, different domains including round, square, and pyramid shapes with the step-terrace structure were observed at the top silicon and buried oxide interface. Round domains are observed in the early stage of the annealing process, while the square and pyramid domains are observed after the high temperature annealing. The mean RMS roughness decreases with increasing time and annealing temperature and decreases with either increasing the implantation dose or decreasing implantation energy. Qualitative mechanisms of Si-SiO2 surface flattening are presented in terms of the variations of morphological features with the processing conditions.In the fully-annealed SIMOX wafers, the silicon pipes and silicon islands were observed in the sample implanted with the dose below 3.0×1017 O+/cm2 and above 3.5×1017 O+/cm2, respectively for the samples implanted at 100 keV. The presence of silicon pipes and islands degrades the quality of the buried oxide layer by reducing the breakdown field strength. It was found that proper annealing ambient and ramping rates would allow the formation of the buried oxide layer containing no silicon island. By controlling the oxygen content in the ambient, the growth of the buried oxide can be enhanced.
29
Cagas, Jean (Cagas Quijano Jean Allison) 1977. "Electrical study of molybdenum in silicon and fluorinated SiO₂ for interlayer dielectrics." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9556.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999.<br>Includes bibliographical references (leaves 27-28).<br>Molybdenum is unintentionally introduced into silicon at various points in semiconductor processing. This introduction is a concern because molybdenum introduces a deep level state into the forbidden gap of silicon, degrading minority carrier lifetime. In this project, DLTS was used to measure the concentration of electrically active molybdenum. Temperature dependence was investigated by varying annealing temperature and keeping annealing time constant, and time dependence was studied by performing rapid thermal anneals at 750°C and varying annealing time. DLTS spectra were generated and isothermal depth profiles of trap concentration were found using additional data from C-V measurements. For a rate window of 35 ms, the molybdenum peak occurred at 165K. The energy level of molybdenum was 0.3eV and the capture cross section was 5.5x10·16cm2. At high temperatures, the diffusion behavior of molybdenum exhibited a Gaussian profile. At low temperatures, however, the profiles exhibited an initial kick-out mechanism followed by normal diffusion. Fluorinated SiO2 is becoming an extremely important material for intermetal dielectrics. As integrated circuits are scaling down in size, the RC constant is becoming the bottleneck to faster circuit speeds. The addition of fluorine decreases the dielectric constant of SiO2 by decreasing the ionic and electronic polarizability of the entire structure. The addition of fluorine still has some detrimental effects, however, such as lower hardness and increased water adsorption. For this project, eight oxide films with varying fluorine content were studied. The dielectric constant K of each film was calculated with the saturation capacitance from C-V measurements, oxide thickness, and diameter. While all the observed values of K were lower than known values for pure SiO2, they did not exhibit a decreasing trend. Possibly, processing conditions might have had more of a dominant effect for such small differences in fluorine content. From changing C-V profiles and fluctuating saturation capacitance, it is suggested that there was movement of charge in the oxide layers. However, this was not consistent for all the films.<br>by Jean Cagas.<br>S.B.
30
Freire, Ricardo Satuf 1962. "Short fiber composites with high electrical and thermal conductivity." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278242.
Full textAbstract:
This research describes the preparation of electrically and thermally conductive polymer composites. The filler used is short carbon fibers. These were dispersed in methyl methacrylate (MMA) and settled under different vibrational and gravitational forces, resulting in well packed sediments. To improve further the dispersability of the fiber/MMA system, steric stabilization was attempted by using organic dispersants of increasing chain length. Subsequent polymerization of the dense sediments produced composites with high fiber volume fractions. The electrical and thermal conductivities of these composites were studied. Fiber size, distribution, orientation and volume fraction are shown to have a profound influence on these properties. A general effective media equation, which relates percolation and effective media theories, is shown to describe the electrical conductivity of the composites. The specific thermal conductivity of the high fiber fraction composites is greater than that of stainless steel. Applications include electronic packaging and electromagnetic interference shielding.
31
Spears, Marlene Ann. "Defect chemistry and electrical properties of ruthenium- and bismuth-substituted gadolinium titanate pyrochlore." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11443.
Full text
32
Chen, Kevin M. (Kevin Ming) 1974. "Electrical breakdown and luminescence from erbium oxide and Er-doped silicon thin films." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9816.
Full text
33
Stockton, William B. (William Blake). "Structure and electrical properties of assemblies of polyaniline : from blends to self-assembled multilayers." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32660.
Full text
34
Kumar, Priyank Vijaya. "Enhanced electrical, optical and chemical properties of graphene oxide through a novel phase transformation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98736.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 86-98).<br>Graphene oxide (GO) is a versatile, solution-processable candidate material for next-generation, large-area, ultrathin electronics, optoelectronics, energy conversion and storage technologies. GO is an atom-thick sheet of carbon functionalized with several oxygen-containing groups dominated by the epoxy and hydroxyl functional groups on the basal plane, with carboxyls and lactols at the sheet edges. It is well known that reduction of GO at temperatures > 150°C leads to the removal of oxygen atoms from the carbon plane, leading to the formation of reduced GO (rGO) structures. Although GO has been utilized for multiple applications in the last decade, our understanding of the structure-property relationships at the atomic-level has still been lacking owing to the amorphous nature and chemical inhomogeneity of GO, which has in turn limited our ability to design and tailor GO nanostructures for high-performance applications. In particular, the material's structure and its structural evolution at mild annealing temperatures (< 1000°C) has been largely unexplored. In this thesis, we use a combination of first-principles computations, classical molecular dynamics simulations based on reactive force fields and experiments to model realistic GO structures and develop a detailed understanding of the relationship between the carbon-oxygen framework and the sheet properties, at the atomic level. Based on our understanding, we demonstrate a new phase transformation in GO sheets at mild annealing temperatures (50-80°C), where the oxygen content is preserved and as-synthesized GO structures undergo a phase separation into prominent oxidized and graphitic domains facilitated by oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. We then use this novel phase transformation to improve two sets of applications. 1) We demonstrate that cell capture devices making use of phase transformed-GO substrates have higher capture efficiencies compared to devices making use of as-synthesized GO substrates. 2) We show that the reduction of phase transformed-GO leads to better electrical properties of rGO thin films. Our results fill an important gap and establish a complete theory for structural evolution of GO over the entire range of temperatures, i.e. from room temperature to ~1000°C. Taken together, this structural transition in GO enables us to predict and control the sheet properties in new ways, as opposed to reduction, which is till date the only handle to control the structure of GO. This could potentially open the door for completely new applications or for enhancing the performance of existing applications based on GO.<br>by Priyank Vijaya Kumar.<br>Ph. D.
35
Hwang, Gyuweon. "Surface trap passivation and characterization of lead sulfide quantum dots for optical and electrical applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98741.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 113-119).<br>Quantum dots (QDs) are semiconductor nanocrystals having a size comparable to or smaller than its exciton Bohr radius. The small size of QDs leads to the quantum confinement effects in their electronic structures. Their unique optical properties, including a tunable emission from UV to IR, make QDs attractive in optoelectronic applications. However, further improvements in device performance are required to make them competitive. One well-known factor that presently limits the performance of QD thin film devices is sub-band-gap states, also referred to as trap states. For instance, trap states impair optical properties and device performance by providing alternative pathways for exciton quenching and carrier recombination. Chemical modification of QDs has been commonly used for passivating trap states and thereby improving QD devices. However, the influence of chemical modifications of ligands, QD surfaces, or synthetic routes on electrical properties of QD thin films is not sufficiently characterized. Suppressing the trap states in QD thin films is a key to improve the performance of QDbased optoelectronics. This requires fundamental understanding of trap state source, which is lacking in these materials. In this thesis, I pursue to find a systematic method to control density of trap states by exploring different characterization techniques to investigate trap states in QD thin films. These attempts provide insight to develop a rationale for fabricating better performing QD devices. This thesis focuses on the trap states in IR emitting lead sulfide (PbS) QD thin films, which have great potential for application in photovoltaics, light emitting diodes (LEDs), photodetectors, and bio-imaging. Previously, QD thin films are treated with different ligands to passivate trap states and thereby improve the device performance. Through my work, I pursued to unveil the electrical characteristics and chemical origin of trap states, and develop a strategy to suppress the trap states. First, I hypothesize that surface dangling bonds are a major source of trap states. An inorganic shell layer comprised of cadmium sulfide (CdS) is introduced to PbS QDs to passivate the surface states. Addition of CdS shell layers on PbS QDs yields an enhanced stability and quantum yield (QY), which indicates decreased trap-assisted exciton quenching. These PbS/CdS core/shell QDs have a potential for deep-tissue bio-imaging in shortwavelength IR windows of 1550-1900 nm. However, the shell layer acts as a transport barrier for carriers and results in a significant decrease in conductivity. This hinders the incorporation of the core/shell QDs in electrical applications. An improved reaction condition enables the synthesis of PbS/CdS QDs having a monolayer-thick CdS shell layer. These QDs exhibit QY and stability comparable to thick-shell PbS/CdS QDs. Incorporation of these thin-shell QDs improves external quantum efficiency of IR QD-LEDs by 80 times compared to PbS core-only QDs. In the second phase of my work, I explore capacitance-based measurement techniques for better understanding of the electrical properties of PbS QD thin films. For in-depth analysis, capacitance-based techniques are introduced, which give complementary information to current-based measurements that are widely used for the characterization of QD devices. Nyquist plots are used to determine the dielectric constant of QD films and impedance analyzing models to be used for further analysis. Mott-Schottky measurements are implemented to measure carrier concentration and mobility to compare PbS core-only and PbS/CdS core/shell QD thin films. Drive-level capacitance profiling is employed to characterize the density and energy level of trap states when QD films are oxidized. Lastly, I investigate the chemical origin of trap states and use this knowledge to suppress the trap states of PbS QD thin films. Photoluminescence spectroscopy and X-ray photoelectron spectroscopy show that standard ligand exchange procedures for device fabrication lead to the formation of sub-bandgap emission features and under-charged Pb atoms. Our experimental results are corroborated by density functional theory simulation, which shows that the presence of Pb atoms with a lower charge in QDs contributes to sub-bandgap states. The trap states generated after ligand exchange were significantly reduced by oxidation of under-charged Pb atoms using 1,4-benzoquinone. The density of trap states measured electrically with drive-level capacitance profiling shows that this reduces the electrical trap density by a factor of 40. In this thesis, I characterized trap states and showed that by suppressing the trap states we can modify the electrical properties of QD thin films, which influence the performance of QD devices directly. This work is a starting point to fully analyze the trap states in QD thin devices and thereby provides insight to design a rationale for fabricating better performing QD devices.<br>by Gyuweon Hwang.<br>Ph. D.
36
Clancy, Edward Arthur. "Relating cardiac electrical and mechanical alternans to ventricular stability." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/72252.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1987.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.<br>Bibliography: leaves 187-195.<br>by Edward Arthur Clancy.<br>M.S.
37
Park, Jihong. "Electrical properties of polycrystalline solar cell silicon." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1061389017.
Full text
38
Nakos, James Spiros. "Effects of crystal growth process parameters on the microstructural optical and electrical properties of CdTe and CdMnTe." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14574.
Full text
39
Kim, Sunho Ph D. Massachusetts Institute of Technology. "Defect and electrical properties of high-K̳ dielectric Gd₂O₃ for magneto-ionic and memristive memory devices." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129007.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2020<br>Cataloged from student-submitted PDF of thesis. The "K̳̳" in title on title page appeared as subscript "K."<br>Includes bibliographical references (pages 127-134).<br>While high-[subscript K] dielectrics utilized in CMOS technology are noted for their highly insulating characteristics, they have demonstrated surprising electrolytic behavior as key components in a variety of thin film memory devices, including those based on magneto-ionic and memristive behavior. In this work, we focus on the rare earth sesquioxide, Gd₂O₃, a well-known high-κ dielectric that has exhibited a variety of electrolytic properties during the development and operation of the first magneto-ionic devices developed at MIT. Specifically, we focused our investigation on the defect chemistry and electrical properties of Gd₂O₃ in order to better understand the relationship between the structure, chemistry, processing conditions, and operating environment and the material's low-temperature ionic and electronic transport properties and the means for their optimization vis-à-vis memory device operation.<br>Phase (monoclinic and cubic) and dopant controlled (Ca, Ce, Sr, Zr) polycrystalline pellets of 8 different Gd₂O₃ systems were prepared to investigate various defect regimes in consideration of this material's polymorphism. We considered intrinsic anion-Frenkel disorder and electronic disorder, equilibration with the gas phase, water incorporation, and dopant incorporation in the defect modeling, taking into account the roles of crystallographic structure as well as oxygen ion defect and protonic generation. The primary method utilized to characterize the defect chemistry and transport properties of Gd₂O₃ was the analysis of the dopant, p0₂ and temperature dependencies of the electrical conductivity extracted from complex impedance spectra obtained over the p0₂ range of 1 to 10⁻¹⁵ atm, for 5 isotherms between 700 and 900 °C with 50 °C steps and for a range of acceptor and donor dopants.<br>Based on the p0₂ dependency of conductivities, in light of the defect modeling, the majority point defects in each system were identified. Electronic and ionic migration energies and thermodynamic parameters were extracted via the defect modeling and temperature dependencies of conductivities. In nearly all cases, the predominant charge carrier under oxidizing conditions at elevated temperatures was identified as the p-type electron-hole, largely due to oxygen excess non-stoichiometry in these systems. With decreasing p0₂, transport tended to switch from semiconducting towards ionic. Depending on phase, dopant type & concentration, temperature, and relative humidity, the predominant ionic conductivity was found to be via oxygen interstitials, oxygen vacancies, and/or protons, the latter given by the propensity of Gd₂O₃ to take up water in solid solution from the environment by the formation of OH[superscript .]species.<br>Unexpectedly, the ionic mobilities of defects in the denser and less symmetric monoclinic system exhibited higher ionic mobilities than the more open bixbyite structure. The hole electronic species in the investigated systems were found to migrate via the small polaron hopping mechanism with rather large hopping energies. This resulted in an inversion of hole and proton mobility magnitudes at reduced temperatures in the monoclinic system. Extrapolation of ionic and electronic defect conductivities to near room temperature, based on our derived defect and transport models, was not able to explain, on its own, the observed electrolytic properties of the Gd₂O₃ thin films utilized in magneto-ionic devices.<br>In an attempt to connect the transport properties obtained under equilibrium conditions at elevated temperatures with the behavior of Gd₂O₃ near room temperature, selected thin films Gd₂O₃, prepared by pulsed laser deposition or sputtering, were investigated by complex impedance spectroscopy over the temperature range of 20 - 170°C. While films prepared under dry conditions were indeed found to be highly electrically insulating, films exposed to water vapor exhibited dramatically higher proton conductivities (more than ~10⁸ x) than values extrapolated from high temperature. Parallel thermogravimetric analysis on Gd₂O₃ powder specimens, as a function of temperature, under high humidity conditions, demonstrated a correlation between uptake/loss of incorporated water and conductivity upon cooling and heating, respectively.<br>We can therefore conclude that the large disconnect between the electrical and electrolytic properties observed between high-κ dielectrics used in CMOS devices such as Gd₂O₃, and their much more highly conductive counterparts used in thin film memory devices, depends strategically on the thin film processing conditions. High-κ dielectrics are fabricated in carefully controlled environments with low relative humidity, while research on, for example, Gd₂O₃ - based magneto-ionic memory devices, is performed under ambient laboratory conditions, where significant water uptake becomes possible at surfaces and grain boundaries. The results and insights obtained in this study can be expected to be applied in achieving further progress in the understanding and optimization of magneto-ionic, memristive, and other devices that rely on proton gating.<br>by Sunho Kim.<br>Ph. D.<br>Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
40
Huang, Mantao. "Voltage control of electrical, optical and magnetic properties of materials by solid state ionic transport and electrochemical reactions." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127898.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020<br>Cataloged from the official PDF of thesis.<br>Includes bibliographical references (pages 139-153).<br>Reversible post-fabrication control of material properties enables devices that can adapt to different needs or environmental conditions, and brings additional levels of functionality, paving the way towards applications such as reconfigurable electronics, reconfigurable antennas, active optical devices and energy efficient data storage. One promising way of achieving the controllability is through solid-state ionic transport and electrochemical reactions in thin film structures, where the properties of materials can be electrically controlled by a gate voltage in an addressable way. Here we explore using such ionic gating method to control the electrical, optical and magnetic properties of solid-state thin film layers, and show that large modification can be achieved for a wide range of properties. We demonstrate a new type of three terminal resistive switching device where the resistivity of a thin film conductive channel can be controlled by a gate voltage. We demonstrate solid-state ionic gating of the optical properties of metals and oxides and show the versatility of the approach by implementing voltage-controlled transmission, thin film interference, and switchable plasmonic colors. We also show that the approach allows for voltage control of ferrimagnetic order, demonstrating voltage induced 180-degree switching of the Néel vector, as a new way of magnetic bit writing. These findings extend the scope of voltage programmable materials and provide insights into the mechanisms of voltage controlled material properties by solid-state ionic transport and electrochemical reactions.<br>by Mantao Huang.<br>Ph. D.<br>Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
41
Smith, Jacob A. "Electrical Performance of Copper-Graphene Nano-Alloys." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1550675878730599.
Full text
42
Rong, Ziqin. "Better multivalent battery materials through diffusion high-throughput computations." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/111221.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.<br>Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 45-52).<br>Accelerating the discovery of advanced materials is essential for human beings. However, the traditional trial-and-error way of developing materials is often very empirical and time- consuming. In 2011, the launch of Materials Genome Initiative marked a large-scale collaboration between computer scientists and materials scientists to deploy proven computational methods to predict, screen, and optimize materials at an unparalleled scale and rate. This thesis is based on this idea. Finding a suitable cathode material for Mg batteries has been one of the key challenges to the next-generation multi-valent battery technology. In this thesis, a high-throughput computation system is proposed to solve such problem. I tested the high-throughput structures applying traditional NEB calculations schemes and find out it is very different to scale traditional NEB method to a high-throughput application. Then I proposed a new scheme for estimating migration minimum- energy path (MEP) geometry and energetics (PathFinder and ApproxNEB). By testing our methodology against standard NEB calculations and literature values, we find that the PathFinder algorithm can reliably predict the geometry of cation migration MEP within 0.2 Å at negligible computational cost. Furthermore, we find that the ApproxNEB calculation scheme yields activation barriers for migration within an error bound of 20 meV while using significantly fewer computational resources than NEB. We envision that our methods can be used to accelerate NEB calculations, as well as to provide a robust estimation criterion for migration barriers in ionic materials for highthroughput computational screening of materials. Based upon these two newly developed methods, coupled with EndPointFinder, I developed two functional high-throughput applications (ApproxNEB for estimating migration barriers and PathFinder for calculating migration geometric paths), and have already put PathFinder high-throughput system into production and calculate around 2000 structures.<br>by Ziqin Rong.<br>S.M.
43
Jacobs, Gregory. "Simulation, Control Design, and Experiments on Single and Double Inverted Pendulum Systems." Thesis, Southern Illinois University at Edwardsville, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10010746.
Full textAbstract:
<p> The discipline of control engineering has been applied for thousands of years. As long as humans have needed a system to vary automatically, different devices, electronics and algorithms have been designed to attain system control and stability. This study intends on implementing the theory developed my mathematicians such as Henri Poincaré, Aleksandr Lyapunov, Rudolf E. Kálmán and many others in an attempt to stabilize an unstable system: a cart and inverted pendulum. In order to stabilize the inverted pendulum system, control designs consisting of both classical and modern approaches will be explored to design effective PID and LQR controllers. Furthermore, an adaptive controller will be designed as well for a one-degree-of-freedom unstable system. For accurate control design, linear and non-linear system identification techniques will be used to attain mathematical dynamic system models. Multiple tuning techniques will be utilized to achieve the most stable system possible. A micro-processor (Arduino) will be used in conjunction with a computer for data communication and digital control algorithms. The utilization of an Arduino will require the design and implementation of digital control systems, digital tuning techniques, and digital filtering. If successful, the implemented theory will result in the stabilization of a multiple degree of freedom system with chaotic potential.</p>
44
Weber, Mark 1964. "The processing and properties of electrically conductive fiber composites." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40279.
Full textAbstract:
The electrical and mechanical properties of electrically conductive fiber composites were measured and related to composite microstructure. Samples were manufactured by compression molding, extrusion, and injection molding to determine the effect of processing method on fiber length and orientation. A strong correlation between the processing-induced fiber-phase microstructure and the measured properties is found. The results are highly dependent on the type of conductive fiber. Computer-generated flow-field models are able to illustrate the thermal and flow processes which affect microstructure. A simple orientation model gives good qualitative agreement with experimental observations in injection molded composites.<br>Two models for predicting volume resistivity are proposed. One model assumes that the fibers are aligned end-to-end, and the effect of fiber orientation and concentration is obtained. The results agree qualitatively with experimental data, and give a lower bound or resistivity. More realistic fiber-fiber contacts are considered in the second model. The resistivity is expressed in terms of the area of contact, and orientation, length, and concentration of the fibers. Model predictions are in excellent agreement with experimental results.
45
Yeung, Yan Mui Kitty. "Engineering Plasmonic Waves in Two-Dimensional Electron Systems." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467363.
Full textAbstract:
Plasmonic waves are waves of mobile charge carriers caused by their collective oscillations. They can be excited in solid-state conducting materials and behave distinctively in different numbers of dimensions. With fabrication technologies available for solid-state materials, one can functionalize the dimensional properties by engineering the boundaries and interfaces of the plasmonic wave medium. For instance, plasmonic waves in two-dimensional (2D) conductors, such as semiconductor heterojunction and graphene, exhibit strong subwavelength confinement – with a wavelength about a factor of 100 below the electromagnetic wavelength at the same frequency. Hence, 2D plasmonic devices can be constructed below the diffraction limit of light. To utilize this ultra-subwavelength confinement is the main motivation of this thesis.
This thesis establishes the machinery behind the unique behaviors of 2D plasmons, and compares them to plasmons in higher dimensions, namely plasma oscillations in bulk materials and surface plasmons on conducting-insulating interfaces. The Coulomb restoring force and mobile charge carrier inertia causing the collective oscillations are formulated into a transmission-line model. This formulation is used to engineer ultra-subwavelength plasmonic circuits in gigahertz integrated electronics and terahertz metamaterials.
As one of the demonstration platforms, we use GaAs/AlGaAs 2D electron gas. Amongst a variety of devices, the thesis focuses on an on-chip solid-state 2D plasmonic Mach-Zehnder interferometer operating at microwave frequencies. The gated 2D plasmonic waves achieve a velocity of ~c/300 (c: free-space speed of light). Due to this ultra-subwavelength confinement, the resolution of the 2D plasmonic interferometer is two orders of magnitude higher than that of its electromagnetic counterpart at a given frequency.
Another material we use, which hosts mobile charge carriers in 2D, is graphene. We fabricate metamaterials in the form of graphene plasmonic crystals in a continuous graphene sheet with periodic structural perturbations. Plasmonic bands in the far-infrared are formed and excited via symmetry-based selection rules, in a manner akin to photonic crystals. The plasmonic bands can be engineered by manipulating the charge carrier concentration, the dimensions of the periodic lattice, the shape of the perturbation and the lattice symmetry. These demonstrations may generate new avenues for a wealth of subwavelength graphene plasmonic devices, such as band gap filters, modulators and switches.<br>Engineering and Applied Sciences - Applied Physics
46
Moon, Peter Kenneth. "Electrical conductivity and structural disorder in Gd₂Ti₂O₇-Gd₂Zr₂O₇ and Y₂Ti₂O₇-Y₂Zr₂O₇ solid solutions." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14700.
Full text
47
Kymissis, Ioannis 1977. "Field emission from organic materials." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16947.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.<br>Includes bibliographical references (p. 207-218).<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Field emission displays (FEDs) show great promise as high performance flat panel displays. The light emission process is efficient, long lifetimes are possible with high brightness, and bright passive matrix displays can be built. Because passive matrix displays don't need a transistor backplane, it was once thought that these displays would be cheaper to fabricate than their competitors. It is now clear that this is not the case. Fabricating a transistor backplane has turned out to be less expensive than micromachining an array of uniform field emitter tips with aligned gates. Competing technologies which use an active backplane (such as active matrix liquid crystal panels) have become ubiquitous, and FED technologies developed to date have been too expensive for the consumer market. This thesis presents a new strategy for creating a low-cost field emission display. This strategy begins by creating a field emitter out of organic conductors-a class of materials mostly neglected to date for this application. The organic emitter is made by copying a non-lithographic template. The process takes 5 minutes, occurs at room temperature and at atmospheric pressure, and does not damage the template. We show that organic conductors are easy to pattern into regular patterns and can form structures which exhibit field emission, with field enhancement factors of about 100-600 times. The field emission follows a Fowler-Nordheim characteristic. Also explored are some of the properties of organic conductors in vacuum such as conductivity over time, the interaction of the organic field emitter with background gases, and the conduction mechanism. In particular, we show that oxygen degrades the emission properties of organic field emission tips, and that organic materials retain sufficient conductivity in vacuum to serve as field emitters.<br>(cont.) The second prong of the strategy is to combine the field emitter with an inexpensive transistor. A thin-film transistor made using an organic semiconductor is used to control the emission from the field emitter. We demonstrate a circuit architecture which allows the transistor to control the field emitter without creating a micromachined gate. This architecture uses only one high voltage supply for the panel to extract and accelerate electrons toward the phosphor screen. We show that the field emitter current can be controlled over a range of about 1000:1 using only 30V. This is verified through measurements of spot brightness on a phosphor screen. We then show that using the transistor has additional advantages. The current noise is reduced by a factor of 20, and DC current degradation is eliminated for oxygen partial pressures up to 1 x 10-6 torr. A new linearized analysis is presented which explains the DC current control and noise reduction, and also estimates the work function fluctuation on the emitter tip. The experimental results are examined in the context of this analytical framework. The work in this thesis shows (1) that a field emitter can be made from an organic conductor using a simple process (2) a field emission display can be controlled without making an array of micromachined gates and (3) using a transistor has a number of advantages in addition to controlling the field emitter ...<br>by Ioannis Kymissis.<br>Ph.D.
48
Lovelace, Edward Carl Francis. "A mechanical-state observer for high-speed variable-reluctance motor drives." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/40232.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996.<br>Includes bibliographical references (p. 191-192).<br>by Edward Carl Francis Lovelace.<br>M.S.
49
Teowee, Gimtong. "Electrical and optical characterization of wet chemically derived lead zirconate titanate thin films." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/186081.
Full textAbstract:
The present investigation is concerned with the preparation and characterization of sol-gel derived lead zircon ate titanate (PZT) powders and films. Particular emphasis is placed on the synthesis, processing and characterization of thin films. The chemistry employed involves the use of alkoxides of Ti/Zr and lead acetate trihydrate. PZT gels were prepared and characterized insights gained were used as the basis for the synthesis and characterization of thin films. A model was also proposed to augment further understanding of the PZT capacitors obtained. PZT thin films were successfully prepared on various substrates such as platinized Si wafers and Corning 7059 glass. Numerous electrical and optical characterizations were performed, namely dielectric constant and loss, hysteresis loop, switching, fatigue, aging, leakage currents, refractive index, UV transmission spectroscopy, second harmonic generation (SHG) and waveguide loss. These electrical and optical properties are discussed in conjunction with film microstructure and phase assemblage. Very high quality films were obtained (e.g., dielectric constant as high as 3000 at 1kHz, and fatigue-free beyond 10⁸ cycles and optical loss as low as 1.1 dB/em). Aging of these films can be kept as low as l%/decade. It was found that the domains play an important role in determining the dielectric properties. A model of the Pt-PZT-Pt capacitor was successfully developed based on totally depleted back-to-back Schottky barriers and the model predictions agree extremely well with measured device characteristics. This model also explains the different dielectric behaviours of FE films compared to those of bulk ceramics. By tailoring the chemistry and controlling the post-deposition processing conditions and hence microstructures, the properties (both electrical and optical) of the PZT films can be effectively engineered.
50
Marmon, Jason Kendrick. "Light-matter interactions in semiconductor nanowires| Light-effect transistor and light-induced changes in electron-phonon coupling and electrical characteristics." Thesis, The University of North Carolina at Charlotte, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10243428.
Full textAbstract:
<p> This dissertation explores three related embodiments of light–matter interactions at the micro– and nano–scales, and is focused towards tangible device applications. The first topic provides a fundamentally different transistor or electronic switch mechanism, which is termed a light–effect transistor (LET). The LET, unlike exotic techniques, provides a practical and viable approach using existing fabrication processes. Electronic devices at the nanoscale operate within the ballistic regime, where the dominate source of energy loss comes from impurity scattering. As a LET does not require extrinsic doping, it circumvents this issue. Electron–phonon coupling, however, is the second largest source, and it is a pertinent and important parameter affecting electronic conductivity and energy efficiency, such as in LETs. The third topic is laser writing, or the use of a laser to perform post–growth modifications, to achieve specific optical and electrical characteristics. </p><p> A LET offers electronic–optical hybridization at the component level, which can continue Moore’s law to the quantum region without requiring a FET’s fabrication complexity, e.g., physical gate and doping, by employing optical gating and photoconductivity. Multiple independent gates are therefore readily utilized to achieve unique functionalities without increasing chip space. LET device characteristics and novel digital and analog applications, such as optical logic gates and optical amplification, are explored. Prototype cadmium selenide (CdSe) nanowire–based LETs show output and transfer characteristics resembling advanced FETs, e.g., on/off ratios up to ~1.0x10<sup> 6</sup> with a source-drain voltage of ~1.43 V, gate-power of ~260 nW, and a subthreshold swing of ~0.3 nW/decade (excluding losses). The LET platform offers new electronic–optical integration strategies and high speed and low energy electronic and optical computing approaches.</p><p> Electron–phonon coupling is typically studied as an intrinsic property, which is particularly important for electronic transport properties at the nanoscale, where controversy and even contradictory experimental and theoretical findings still persist. Zinc telluride (ZnTe) has important uses in optical or laser refrigeration, and the existing studies do not consider extrinsic effects, such as laser–forming tellurium–based species. Nanostructures, with their large surface–to–volume ratios, are more susceptible to extrinsic perturbations that ultimately effect coupling. In this dissertation, ZnTe is studied in bulk, thin film, and nanowire forms with primary focus on the latter. Raman spectroscopy under near resonant excitation is used to extract electron–phonon coupling strengths, which is obtained through the ratio of the first and second order Raman peaks, <i>R</i> = <p style="font-variant: small-caps"> I2LO/I1LO</p> (and is proportional to the Huang–Rhys factor). Laser–formation of tellurium–based species on ZnTe nanowires dynamically altered the ratio R from ~6-7 to 2.4 after laser processing, while tuning the (532 nm) laser power from a few microwatts to 150 microwatts (with constant optical exposure time) did not significantly impact the EPC strength. Other explored effects include size dependence, chemical effects (methanol exposure), and interface effects (e.g., at a gold–nanowire junction). The findings suggest that the previously reported size dependence in ZnTe was extrinsic in nature. Tunable coupling strengths also suggest the possibility of novel electronic and optoelectronic devices.</p><p> The electrical characteristic of CdSe nanowire M-S-M devices are shown to be tunable with laser illumination. As with any semiconductor material, sufficiently low optical powers produce stable and reproducible electrical properties, while higher optical powers and exposure times can induce laser modifications of the material. Drastic modification of electrical characteristics were observed, such as from converting an ohmic response (linear slope change) to rectified characteristics, and modification of both forward and reverse currents. Results suggest the potential to laser write wavelength–specific electronic functions that could be used in applications requiring wavelength discrimination, such as with night vision products. Using a combination of laser modification and device fabrication processes provides the ability to offer a menu of electrical behaviors using the same materials and fabrication processes.</p>