Master of Science (MS), Bowling Green State University, 2014, Physics

Third generation quantum dot solar cells are one of the promising sources of clean energy. However, poor eciency is a major issue; they are in a positive direction of optimization. To optimize their performance, we should select the materials which can absorb more light radiation in visible and infrared regions. To this regard, the gold plasmonic enhancement shows a promise to improve the eciency of photovoltaics. Here, we report a solution process of depleted heterojunction PbS solar cells in the presence of gold nanoparticles. In our experiment, the solar cells show a better absorption and eciency in the presence of the Au nanoparticles. The fabricated solar cell in the addition of Au nanoparticles has the average efficiency of 4.15%, where as the solar cell without plasmons has the average effieciency of 4.00%.

Committee: Mikhail Zamkov (Advisor); Haowen Xi (Committee Member); Alexey Zayak (Committee Member) Subjects: Physics

Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)

Semiconductor nanostructures such as quantum dots, quantum wires and quantum wells have gained significant attention in the scientific community due to their peculiar properties, which arise from the quantum confinement of charge carriers. In such systems, confinement plays key role and governs the emission spectra. With the advancements in growth techniques, which enable the fabrication of these nanostructured devices with great precision down to the atomic scale, it is intriguing to study and observe quantum mechanical effects through light-matter interactions and new physics governed by the confinement, size, shape and alloy composition. The goal is to reduce the size of semiconductor bulk material to few nanometers, which in turn localizes the charge carriers inside these structures such that the spin associated with them is used to carry and process information within ultra-short time scales. The main focus of this dissertation is the optical studies of quantum dot molecule (QDM) systems. A system where the electrons can tunnel between the two dots leading to observable tunneling effects. The emission spectra of such system has been demonstrated to have both intradot transitions (electron-hole pair residing in the same dot) and interdot transitions (electron-hole pair participating in the recombination origin from different dots). In such a system, it is possible to apply electric field such that the wavefunction associated with the charge carriers can be tuned to an extent of delocalizing between the two dots. This forms the first project of this dissertation, which addresses the origin of the fine structure splitting in the exciton-biexciton cascade. Moreover, we also show how this fine structure can be tuned in the quantum dot molecule system with the application of electric field along the growth direction. This is demonstrated through high resolution polarization dependent photoluminescence spectroscopy on a single QDM, which was described in great det (open full item for complete abstract)

Committee: Eric A. Stinaff Prof. (Advisor); Sergio E. Ulloa Prof. (Committee Member); Arthur R. Smith Prof. (Committee Member); Wojciech M. Jadwisienczak Prof. (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Nanoscience; Nanotechnology; Optics; Physics; Quantum Physics; Solid State Physics

Doctor of Philosophy (PhD), Ohio University, 2013, Physics and Astronomy (Arts and Sciences)

In this document we present a study of the thermodynamic and transport properties of two kinds of quantum impurity systems in the Kondo regime. The first system consists of a spin-1 molecule in which mechanical stretching along the transport axis produces a magnetic anisotropy. We find that a generic coupling between a vibrational mode along this axis and the molecular spin induces a correction to the magnetic anisotropy, driving the ground state of the system into a non-Fermi-liquid phase. A transition into a Fermi-liquid ground state can then be induced by means of stretching, going through an underscreened spin-1 Kondo ground state at zero effective anisotropy. In the second system we study the effects of a charge detector, implemented by a quantum point-contact (QPC), on the Kondo state of a nearby spin-1/2 quantum dot (QD). While making the charge detection possible, the Coulomb interaction between the electrons traversing the QPC and those within the QD contribute to decoherence of the Kondo state. By modeling the QPC as two metallic terminals connected to an intermediate localized level, we can explore three transport regimes of the detector: a zero-conductance regime, a finite-conductance regime in mixed valence, and unitary conductance in a Kondo ground state that has been suggested as an explanation to the "0.7 anomaly" in QPCs. Transitions between these different ground states can be achieved by tuning the strength of a capacitive coupling that parameterizes the electrostatic interaction.

Committee: Sergio Ulloa Prof. (Advisor); Wojciech Jadwisienczak Ph.D (Committee Member); Saw Hla Prof. (Committee Member); Horacio Castillo Ph.D. (Committee Member); Nancy Sandler Ph.D. (Committee Member) Subjects: Condensed Matter Physics; Low Temperature Physics; Nanoscience; Nanotechnology; Physics; Quantum Physics; Solid State Physics

Master of Science (MS), Bowling Green State University, 2013, Physics

I report the design, fabrication, and characterization of colloidal PbS nanocrystals (NC's semiconductors for there use as photo voltaic structures and thin films. I also explain the design and method for film deposition of the NC's for use of the Hall effect experiment. Using a layer by layer deposition technique via dip coating a controlled layer of PbS NC'S can be grown on top of an amorphous substrate. These films were electrically conductive with thickness from .365 (μ m) to .571(μ m) having a roughness on the average of Ra = 0.017(μ m). Conductivity of these films vaired by the size of the quantum dots and the ligands used to spatially separate adjacent quantum dots. PbS QD films were fabricated using 1,2-ethanedithiol (EDT), 3-mercatopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 8-mercaptaoctanaic acid (MOA) to spatially separate quantum dots from one another. The EDT separated 7.2 nm QD film .365 (μ m) had a conductivity of (1.85 X 10-4Ω-1cm-1) and the .571 μm had a conductivity of (2.61 X 10-4Ω-1cm-1 ). The EDT separated 5.1 nm QD film .311 μm had a conductivity of (1.98 X 10-3Ω-1cm-1). Films using EDT ligands had the highest conductivity due to the main means of charge transport being tunneling through hopping conduction. These films using (MOA, MHA) produced photo-luminescent films with higher intensity and more distinguished absorption peaks. Hall mobilities couldn't be accurately determined due to low carrier concentration limiting the magnitude of the Hall voltage.

Committee: LiangFeng Sun (Advisor); Haowen Xi (Committee Member); Mikhail Zamkov (Committee Member) Subjects: Nanotechnology; Optics; Physics

PhD, University of Cincinnati, 2009, Engineering : Electrical Engineering

Due to the three dimensional confinement for the carriers, quantum dot lasers are promised to have superior characteristics than quantum well lasers. The direct modulation is playing one of the key roles in ever increasing optical communications, so the characteristics of the semiconductor lasers are of great importance.In this dissertation, the chirp characteristics of the quantum dot lasers are under investigated in details. The spectrum characteristics of the quantum dot lasers are interpreted to understand the reduced thermal conductivity in InGaAs/GaAs quantum dot active region. A thermal conductive model is employed to quantitatively analyze the thermal conductivity in the quantum dots, which is about one order of magnitude less than that in the quantum well lasers. A gain model is built to analyze the dependence of linewidth enhancement factor on duty cycle in quantum dot lasers. Because of the unusual thermal sensitivity of quantum dot active regions, a range of linewidth enhancement factors, from positive, near-zero to negative, could be expected on different duty cycles. A symmetric gain distribution should be approached to achieve near-zero linewidth enhancement factor. 1.3 micron In(Ga)As/GaAs quantum dot DFB lasers fabricated by holography is demonstrated. Lloyd´s mirror exposure system is used for the interference lithography. The laser structure is designed, the laser mode distribution is simulated, and the Bragg grating is analyzed. A single mode operation around 1.3 micron is realized in the DFB quantum dot lasers. In DFB lasers, on the shorter wavelength side of the peak gain, the spontaneous emission becomes significant and plays an important role in affecting the spectral linewidth, so care should be taken in using linewidth enhancement factor alone as figure-of-merit to describe the linewidth across the whole spectrum. Finally, the correlation of linewidth to distributed coefficient is discussed and effective facet reflectivity is modeled.

Committee: Jason Heikenfeld PhD (Committee Chair); Leigh Smith PhD (Committee Member); David Klotzkin PhD (Committee Member); Kenneth Roenker PhD (Committee Member); Joseph Thomas Boyd PhD (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (PhD), Ohio University, 2012, Physics and Astronomy (Arts and Sciences)

Device miniaturization with advanced fabrication techniques has revolutionized the semiconductor industry along with innovative concepts of carrier spin, potentially important at the fundamental physical limits of scalability. For spin-based information processing, semiconductor coupled quantum dots (CQDs) provide excellent control in spin dynamics due to 3-D confinement, discrete energy levels, and optical orientation and coupling. The research presented in this dissertation investigates spin interactions and exciton relaxation channels in semiconductor CQDs measured through optical control and time-resolved experimental techniques. Our experiments involving photoluminescence (PL) and photoluminescence excitation (PLE) methods revealed effects arising from the structural properties of semiconductor nanostructures, including quantum rings and CQDs. High resolution PL measurements on positively charged exciton states demonstrated experimental evidence of isotropic exchange interaction. Controlling exchange interaction in different spin configurations is fundamental to quantum logic operations. Hence, polarization dependent PL experiments were executed and electric field tunable exchange interaction effects were reported on the neutral exciton states. Next, time-resolved measurements were performed while pumping above the InAs wetting layer (WL) energy and probing below the WL to determine the dynamics of the optically generated electric field in CQDs. The observed, rapid onset of the optically generated electric field may provide the use of CQDs for optical switching applications. Finally, carrier relaxations in the CQDs were identified through the dynamics of the spatially indirect exciton state using a mode-locked laser excitation source and standard time-resolved single photon counting technique. Wave function distribution, carrier tunneling, and phonon scattering led to the observed lifetime and intensity modulations. With time-resolved PLE, bi-exponential lifet (open full item for complete abstract)

Committee: Dr. Eric A. Stinaff (Advisor); Dr. Alexander Govorov (Committee Member); Dr. Jeffrey Rack (Committee Member); Dr. Saw-Wai Hla (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Molecular Chemistry; Molecular Physics; Nanoscience; Nanotechnology; Optics; Physics; Quantum Physics; Solid State Physics

Doctor of Philosophy (PhD), Ohio University, 2011, Physics and Astronomy (Arts and Sciences)

We investigate different aspects of the coherent dynamics of excitons in quantum dot molecules. A theoretical model is developed in order to extract the Forster energy transfer signatures in tunnel coupled quantum dot molecules in the presence of strong interdot tunneling. It is found that Forster coupling can induce spectral doublets in the excitonic dressed spectrum, which is suitable for detection in level anticrossing spectroscopy. The coherent exciton dynamics is investigated both in the closed and open quantum system approach by means of the Lindblad master equation. An adiabatic elimination procedure using the projection operator formalism allows us to extract effective Hamiltonians to describe analytically all relevant anticrossing gaps of the dressed spectrum. It is found that a pair of two indirect excitons can be used as the computational basis of a qubit. An adiabatic control pulse is constructed in order to manipulate the indirect exciton qubit and characterize its coherent dynamics, as well as its decoherence due to spontaneous recombination. On the other hand, recent experiments have shown that indirect excitons in hole tunnel coupled quantum dot molecules exhibit indirect exciton oscillatory relaxation rates, as function of an applied electric field. To this end we developed a model for the experimental results, in which we incorporate relaxation due to exciton-acoustic phonon coupling. We characterize the scattering structure factor and found that it contains an electrically tunable phase relationship between the phonon wave and the hole wave function, which leads to interference effects and oscillatory relaxation rates.

Committee: Sergio Ulloa Dr (Advisor); Alexander Govorov Dr. (Committee Member); Eric Stinaff Dr. (Committee Member); P. Gregory Van Patten Dr. (Committee Member) Subjects: Materials Science; Molecular Chemistry; Molecular Physics; Nanoscience; Optics; Physics; Quantum Physics; Solid State Physics; Theoretical Physics

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

The objective of this thesis is to create highly efective light emitters for LiDAR technology by utilizing gain materials that are based on semiconductor quantum dots (QDs). The primary component of LiDAR technology is the light source, which is typically a laser. In order to function efectively under various conditions and with optimal efciency, the laser must meet specifc criteria: it should be safe for the eyes, provide high output power, exhibit thermal stability, and be insensitive to back-refections. QD materials possess advantageous properties such as three-dimensional carrier confnement and atom-like gain, resulting in discrete density of states. These properties contribute to an ultralow linewidth enhancement factor ‘α', leading to improved thermal stability, reduced sensitivity to back-refection, narrow spectral linewidth, and low-chirp characteristics under modulation. This study focuses on the development of a light source using diode lasers for two specific LiDAR wavelengths: 905 nm and 1.55 μm. The choice of these wavelengths is based on their respective advantages. The 905 nm wavelength has the lowest absorption in the atmosphere, making it an excellent option for topographic LiDARs used in navigation and environmental sensing. On the other hand, the 1.55 μm wavelength is considered eye-safe because it is blocked by retinal water and protects the cornea from potential damage. The 905 nm emitting QDs are based on the GaAs material platform, while the 1.55 μm wavelength utilizes InP-based materials. The work conducted in this thesis starts with material design and progresses to optimizing growth conditions to achieve high-density and uniform QD ensembles. Subsequently, these QDs are implemented into the epitaxial structure of diode lasers, which are then fabricated and characterized to ensure thermal stability and insensitivity to back-refection. The wavelength regime commonly referred to as the ‘Telecom band' is centered at 1.55 μm has well-establi (open full item for complete abstract)

Committee: Shamsul Arafin (Advisor); Joshua Goldberger (Committee Member); Ronald M Reano (Committee Co-Chair); Sanjay Krishna (Committee Chair) Subjects: Electrical Engineering; Engineering; Nanoscience; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2016, Physics

In this thesis we studied the signature of quantum confined electronic structure of CdSe nanocrystal quantum dots (NCQDs) in the electron spin behavior via time resolved Faraday rotation (TRFR) measurement at room temperature. We found that there is a distinction between the optical spin pumping efficiency(SPE) spectrum and the optical absorbance. Although the first peak in the SPE coincides with the band edge absorption peak, the rest of the two spectra show significant distinctions. There is a second peak in the signal from the larger NCQDs 200~meV higher in energy. The SPE diminishes afterwards. In smaller NCQDs there is only one peak in the signal. We model this behavior following a 6-band effective mass approximation spin dependent absorbance calculation. We also investigated the dynamics of the spin signal and the presence of two precessing components in the TRFR signal. We find that the inhomogeneous dephasing is not sufficient to explain the dynamics of both components. We associate one of the components to the spin signal from neutral excitons and the other one to positively charged trions. We describe the data using a magnetic field dependent spin decoherence mechanism that occurs via fluctuation of the exciton energy levels in between the available fine structure states. This model captures the TRFR experiment data on both short and long timescales. Additionally, we developed a NCQD-polymer composite optical waveguide and investigated the optical spin measurement on these structures.

Committee: Berezovsky Jesse (Advisor) Subjects: Optics; Physics

Doctor of Philosophy, University of Toledo, 2015, Physics

The use of single wall carbon nanotubes (SW-CNTs) in solar photovoltaic (PV) devices is a relatively new, but quickly growing field. SW-CNTs have found application as transparent front contacts, and high work function back contacts in thin film solar PV. For the utility of SW-CNTs to be fully realized, however, controllable and stable doping as well as long term protection from doping must be achieved. Spectroscopic techniques facilitate detailed investigations of the intrinsic and variable properties of semiconductor materials without the issues of contact deposition and the possibility of sample contamination. Detailed spectroscopic analysis of the doping induced changes in the optical properties of SW-CNTs has revealed normally hidden excited state transitions in large diameter single walled carbon nanotubes for the first time. Spectroscopic monitoring of the degree of doping in SW-CNTs made possible studies of the dopant complex desorption and readsorption energies and kinetics. The long term protection from doping of SW-CNTs exposed to ambient laboratory conditions was achieved as a result of the more detailed understanding of the doping processes and mechanisms yielded by these spectroscopic studies. The application of SW-CNTs to other roles in solar PV devices was another goal of this research. Efficient collection of photogenerated charge carriers in semiconductor quantum dot (QD) based solar photovoltaic devices has been limited primarily by the poor transport properties and high density of recombination sites in the QD films. Coupling semiconductor QDs to nanomaterials with better transport properties is one potential solution to the poor transport within the QD films. This portion of the work investigated the possibility of charge transfer occurring in nano-heterostructures (NHSs) of PbS QDs and SW-CNTs produced through spontaneous self-assembly in solution. Electronic coupling in the form of charge transfer from the QDs to the SW-CNTs is unambiguously (open full item for complete abstract)

Committee: Randy Ellingson (Committee Chair); Michael Heben (Committee Member); Lawrence Anderson-Huang (Committee Member); Nikolas Podraza (Committee Member); Mikhail Zamkov (Committee Member) Subjects: Materials Science; Optics; Physics; Solid State Physics

Master of Science (MS), Bowling Green State University, 2014, Physics

When quantum dots are removed from solution the quantum yield decreases by 10 times. Forster Resonance Energy Transfer can increase the quantum yield of a film. Forster Resonance Energy Transfer films made through dip-coating with 3-mercaptopropionic acid ligands resulted in a 2 to10 times increase in photoluminescence intensity after absorption adjustment. When 8-mercaptooctanoic acid ligands were used the photoluminescence intensity overall increased significantly but there was only a 2 times increase in absorption adjusted photoluminescence.

Committee: Liangfeng Sun (Advisor); Lewis Fulcher (Committee Member); Mikail Zamkov (Committee Member) Subjects: Physics

Master of Science (MS), Bowling Green State University, 2014, Physics

The charge carrier dynamics in several Au/semiconductor core/shell heterostructures were examined. Firstly, Au/CdS core/shell nanocomposites were synthesized in a four step procedure culminating in a cation exchange performed on the shell. Previous studies of the ultrafast carrier dynamics in Au/CdS nanocomposites with epitaxial boundary regions reported the suppression of plasmon character in transient absorption spectra accompanied by broadband photoinduced absorption. The coupling of electron wavefunctions with lattice defects at the boundary of the two domains has been blamed for these phenomena. In the current study, transmission electron micrographs of Au/CdS synthesized using cation exchange showed no evidence of strain on the lattice of either component, while femtosecond transient absorption data show the retention of bleach regions attributed to CdS's 1S(e)-1S3/2(h) transition and Au's plasmon resonance. Accelerated rates of bleach recovery for both excitations ( τexiton ~ 300 ps, τ plasmon ~ .7 ps) indicated that the interaction of Au and CdS domains leads to faster relaxation to their respective photoexcitations when compared to relaxation times in isolated Au and CdS nanoparticles. It was believed that the Au/CdS boundary was non-epitaxial in the presented core/shell nanocomposites. Secondly, these non-epitaxial Au/CdS core/shells were subsequently used to demonstrate near-field energy transfer from 5 nm diameter Au cores to CdS-encapsulated CdSe quantum dots. To this end, Au/CdS and CdSe/CdS nanocrystals were embedded in semiconductor-matrix-encapsulated-nanocrystal-arrays (SMENA) together. The encapsulation of both domains in the high band-gap semiconductor CdS was a means to suppress charge transfer between the two nanoparticles. The fluorescence intensity in these films was enhanced 6-fold in some cases as a result of the presence of Au domains. It was also demonstrated that the fluorescence enhancement was independent of the potential barrier (open full item for complete abstract)

Committee: Mikhail Zamkov PhD (Advisor); Lewis Fulcher PhD (Committee Member); Liangfeng Sun PhD (Committee Member) Subjects: Chemistry; Nanoscience; Nanotechnology; Physics

Doctor of Philosophy, University of Akron, 2013, Polymer Engineering

Photodetectors are light responsive devices that convert optical signals into electric signals. Photodetectors have wide applications in image sensing, environmental monitoring, day- and night-surveillance, chemical and biological detection, industrial process control, communication, planetary probing and so on. Currently, photodetectors based on GaN, ZnO, Si, InGaAs and bulk PbS cover different sub-bands from UV to infrared region. These photodetectors are expensive and some of them require to be operated at low temperature, which certainly limits their applications. Polymer photodetectors made with conjugated polymers possess the unique features, including room-temperature operation, high sensitivity, low working voltage, low cost, thin profile, large area and flexibility. Ultrasensitive polymer photodetectors with high response speed and spectral response ranging from UV to near infrared have been demonstrated. However, new device structure, high responsivity and stable polymer photodetectors needs to be developed. In my dissertation, we reported various methods to enhance the performance of polymer photodetectors. By solvent annealing and post-production thermal annealing, we were able to demonstrate that polymer photodetectors possess comparable responsivity to inorganic counterparts. We have, for the first time, developed the inverted device structure for polymer photodetectors. By utilizing inorganic nanowires and quantum dots as either cathode or anode buffer layer, we were able to demonstrate robust polymer photodetectors. We also investigate the device performance versus energy offset between the workfunction of anode electrode and the valance band of conjugated polymers, band offset at the heterojunction and purity of conjugated polymers.

Committee: Xiong Gong Dr. (Advisor); Alamgir Karim Dr. (Committee Chair); Stephen Cheng Dr. (Committee Member); Matthew Becker Dr. (Committee Member); Yi Pang Dr. (Committee Member) Subjects: Electrical Engineering; Materials Science; Polymers

PhD, University of Cincinnati, 2006, Arts and Sciences : Physics

We study the magnetic and optical properties of diluted magnetic semiconductor CdMnTe quantum dots (QDs) using various photoluminescence (PL) techniques. We use spatially resolved photoluminescence imaging to study single magnetic QDs. A solid immersion lens is combined with the confocal microscopy to achieve a high spatial resolution (~ 200nm) for PL imaging. We observe formation of exciton magnetic polarons (EMPs) in magnetic QDs for non-resonant excitation at B = 0T and T = 7K. However, the spin alignments of individual EMPs are distributed randomly resulting in zero global magnetization. Moreover, the spin alignment in the magnetic QD persists as long as the excitation is continued. This persistent magnetization is because of a long spin relaxation time of Mn ions. We estimate the relaxation time to be of the order of 1ms in CdMnTe QDs. For resonant excitations, CdMnTe QDs exhibit a strong PL polarization (40%) at B = 0T and T = 7K. The measurements show predominant &sigma +(&sigma -) –polarized PL emission for &sigma +(&sigma -) –polarized excitations that create spin polarized excitons. This suggests that one can control the spin alignment of magnetic impurities in magnetic CdMnTe QDs optically by using selectively polarized excitations. The magnetization created by such spin polarized excitons persists up to 170K. We attribute this robust persistent magnetization to strong three dimensional confinements of excitons in smaller CdMnTe QDs. In a low Manganese density QD sample, we observe a mixture of PL emission lines of magnetic and non-magnetic QDs. The results demonstrate that the Zeeman splitting of such non-magnetic QDs depends on the polarization of excitation. We believe that this excitation dependent Zeeman splitting is due to coupling between magnetic and non-magnetic QDs through the exchange interaction.

Committee: Dr. Leigh Smith (Advisor) Subjects: Physics, Condensed Matter

Master of Science in Electrical Engineering, University of Toledo, 2012, College of Engineering

In 1965, Gordon Moore proposed a law which stated that the number of transistors on a chip approximately doubles every 24 months. In accordance with this law, over the decades, CMOS technology has been providing the required dimensions for implementing high speed, high density, and low power VLSI systems. Current studies project that the miniaturization of these devices will lead to negative outcomes such as power dissipation and electro-migration failures. This will result in diminishing returns in switching performance, diffusion barriers, gate depletion, stray capacitances and off-state leakage. In the past, researchers have focused on investigating alternative technologies at the nano scale to potentially replace CMOS technology in the future. As such, many emerging technologies including Single Electron Transistors (SETs), Spin Transistors, Resonant Tunneling Diodes (RTDs), and Carbon Nano Tubes (CNTs), and Quantum-dot Cellular Automata (QCA) are being investigated as potential candidates to replace conventional CMOS technology.This research deals with the design, implementation and simulation of novel QCA based Field Programmable Gate Arrays (FPGAs). The research is divided into two phases. In the first phase, Multiplexers, Configurable Logic Blocks, and the Programmable Switch Matrices are designed and simulated. A complete FPGA layout is subsequently presented. In the second phase of the research, the proposed designs are tested for possible QCA faults such as cell displacement, cell misalignment, cell omission, cell rotation and stuck at polarization faults.The proposed QCA designs are compared with earlier research in terms of number of QCA cells, area, and latency. Our proposed CLB design shows an improvement of 24% fewer QCA cells, occupies 62% lesser overall area, and has 53% less latency compared to previous works.The circuits in this research are designed, implemented and simulated using the QCA Designer software tool.

Committee: Mohammed Niamat (Committee Chair); Mansoor Alam (Committee Member); Junghwan Kim (Committee Member) Subjects: Electrical Engineering; Nanotechnology; Technology

Master of Science in Electrical Engineering, University of Toledo, 2011, College of Engineering

According to Moore's law, the number of transistors that can be placed on an integrated circuit doubles approximately every 18 months. Recent advancements in CMOS technology have led to the implementation of new computational designs with extremely small size and high device density. However, CMOS technology is reaching its limits. Currently, scientists and researchers are exploring various new technologies that may replace CMOS when its limit is reached in the future. Quantum-dot Cellular Automata (QCA) is one of the novel nanotechnologies that is being considered as a possible replacement for CMOS. It has great potential for very dense memory and low power logic based on single electron effects in quantum dots and molecules. QCA relies on novel design concepts to exploit new physical phenomena such as coulombic interactions and implement unique paradigms such as memory-in-motion and processing-by-wire. This thesis presents a first Altera implementation of Stratix Logic Array Block (LAB) architecture using QCA technology along with simulation results. The design is modeled and simulated using QCADesigner software. A novel Logic Array Block in QCA is developed by implementing Look-Up Tables (LUTs). In the design of the LUT, QCADesigner software is utilized to design and simulate a four-to-sixteen decoder, 16-bit memory, and an output circuit to implement a LUT. The LUT design comprises of QCA memory cells with low read latency. The proposed LAB includes Look-up Tables, D flip-flops, multiplexers and various logic gates that are designed and tested using QCADesigner. The LAB designed in this work comprises of 25,000 QCA cells approximately and has a latency of 17 clock cycles. The LAB design is compared with the previous designs of Configurable Logic Blocks. The results show that the proposed LAB provides high degree of performance, simplicity, and optimization of design area compared to the other designs. This thesis also presents an implementation of a novel Progra (open full item for complete abstract)

Committee: Mohammed Niamat PhD (Committee Chair); Junghwan Kim PhD (Committee Member); Hong Wang PhD (Committee Member) Subjects: Computer Science; Electrical Engineering; Nanoscience

Master of Science in Electrical Engineering, University of Toledo, 2011, College of Engineering

Moore's Law states that the number of transistors on a unit area doubles every 18 months. Till date, CMOS technology has been successfully keeping pace with Moore‟s Law. However, it faces serious fundamental challenges in the future, and will soon reach a limit where the quantum effects will begin to dominate the device performance that make further scaling difficult. The International Technology Roadmap for Semiconductors (ITRS) predicts the size limit for CMOS technology to be limited in the range of 5 nm to 10 nm and believes this limit will be reached by 2017[1]. As the devices are exponentially scaled down various factors including power dissipation, gate leakage current, interconnection noise (introduction of crosstalk and hot electron effect) and stray capacitances will become potential bottlenecks to circuit performance. Thus, there is a pressing need for new technologies which can overcome these limitations more effectively. Researchers are investigating alternative technologies at the nano scale to replace CMOS technology in the future. Amongst the many technologies being investigated, Quantum-Dot Cellular Automata (QCA) is one promising transistor-less technology. This research investigates the design, implementation, and simulation of a nano Field Programmable Gate Array (FPGA) using the Quantum-Dot Cellular Automata. The first phase of the research focuses on modeling, implementation, and simulation of a Configurable Logic Block (CLB) slice for a nano quantum FPGA. The proposed design is compared with various nano FPGA based architectures and optimized with respect to area and latency. The second phase of the research focuses on implementing a novel Built-In Self Test model at the quantum level for testing the CLB. New fabrication faults in the QCA components of the CLB are modeled and tested. Finally, the configurable logic block slices are tested by incorporating BIST in its design. The design is modeled using standard QCA cells with multiple layers (open full item for complete abstract)

Committee: Mohammed Y. Niamat Dr. (Committee Chair); Mansoor Alam Dr. (Committee Member); Ezzatollah Salari Dr. (Committee Member) Subjects: Design; Electrical Engineering; Nanoscience; Nanotechnology

Doctor of Philosophy, The Ohio State University, 2010, Integrated Biomedical Science Graduate Program

Nanoparticles are particles with at least 1 dimension less than 100 nm in size. The risks and consequences of acute and chronic nanoparticle exposure have not yet been adequately evaluated. Additionally, nanoparticle manufacturing plants are becoming more prevalent around the world. Therfore, there is cause for concern regarding the effects of nanoparticle related occupational hazards and also incidental nanoparticle exposure to the general public. This communication sought to further investigate nanoparticle/cell interactions, ensuing toxicity and cellular responses within biological systems. Three model nanoparticles were synthesized: quantum dots (QDs), modified carbon nanoparticles (CNPs) and a zeolite substrate containing silver nanoparticles. QDs were chosen to model mechanisms of nanoparticle internalization and compartmentalization. It was found that QDs interact with scavenger receptors, and enter cells via a clathrin coated pit mediated pathway. The kinetics of QD internalization was established; QDs were found to associate with macrophage cell membranes within 2.5 minutes, and are confined to lysosomes 9 minutes after exposure. QDs were found to be approximately 9 nm in size and aggregated when subjected to acidic conditions. Cadmium ions were found to leach from the core at low pH. Macrophages exposed to quantities 20 times greater than needed for imaging were found to induce TNF-α secretion and cytotoxicity, via apoptosis. To understand how the surface functional groups on nanoparticles drives inflammation and cytotoxicity, CNPs were modified with iron species, benzo(a)pyrene or ozone. Experiments utilizing primary human monocyte-derived macrophages revealed large variability in individual cell responses, ranging from increases in cytokines including TNF-α, to upregulation of complement factors. Carbon nanoparticles were added to cultures of murine macrophages and those modified with iron or B(a)P had little proinflammatory response. However, treating (open full item for complete abstract)

Committee: W. James Waldman Ph.D. (Advisor); Prabir Dutta Ph.D. (Committee Member); Susheela Tridandapani Ph.D. (Committee Member); Marshall Williams Ph.D. (Committee Member) Subjects: Nanoscience

Master of Science, The Ohio State University, 2007, Mechanical Engineering

The three transport properties that make up the thermoelectric figure of merit can be decoupled by the use of certain techniques. In this work, we investigate the effect of two such methods on the thermoelectric properties: (1) Use of rare earth dopants with f-orbitals situated close to the Fermi level, thus resulting in a high thermopower, and (2) use of nanostructured bulk materials with size quantization effects that would affect transport properties of the material. In the first part, we examine the effect of rare-earth dopant in PbSe by using a sequence of samples of pure PbSe (for reference), and PbSe doped with Ce, Pr, Nd, Eu, Gd and Yb. We report the magnetic susceptibility data, as well as a full set of galvanomagnetic and thermomagnetic measurements, from which we deduce the carrier's transport properties, specifically density, mobility, density-of-states effective mass and scattering exponent. In short, the trivalent rare earth atoms act as donors; the mobility of the rare-earth alloys is decreased by mechanisms that we will discuss, while the scattering exponent is not affected. The effective mass is increased, but not sufficiently to overcome the mobility decrease and increase the weighted mobility or improve the thermoelectric performance of the material, except potentially Pb 1-xNd xSe. In the second part, we developed a nanocomposite of PbTe and PbSe, made from core-shell structured nanoparticles sintered together. At a core size of ~20 nm, the core is expected to show size-quantization effects, and confine energy levels at discrete values. Such a confinement would lead to an enhancement in the Seebeck coefficient through the interaction of the discrete energy levels with the host density of states. Moreover, the nanostructures in the matrix should lead to a reduction in the lattice thermal conductivity. In the nanocomposite samples, we did not find the expected Seebeck enhancement, presumably due to the wide size distribution of the cores leading to (open full item for complete abstract)

Committee: Joseph Heremans (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2006, Physics (Arts and Sciences)

We study the dynamics of excitonic states in one dimensional, dimer and trimer, and two dimensional arrangements of colloidal quantum dots using a Density-matrix approach. The dots are coupled via a dipole-dipole interaction akin to the F O mechanism. Coherent oscillations of tuned donor dots are shown to appear as plateaus in the acceptor dots, and therefore in their optical response. This behavior provides one with an interesting and unique handle to monitor the quantum state of clusters in an eavesdropping arrangement. A trimer cluster in a symmetrical loop shows steady states in a shorter characteristic time than the typical radiative lifetime of the dots. Breaking the symmetry of the loop results again in damping oscillatory states in the donor dots and plateaus in the eavesdropping/acceptor dot. The use of realistic parameters allows direct comparison with recent experiments and indicates that coherent state monitoring is possible in real experiments. Estimates of the FO coupling V Fare obtained from a microscopic description of the exciton levels in the quantum dot. We present results for different materials CdS, CdSe, GaAs, and InP as function of dot features. V Fshows a nonmonotonic variation with dot sizes and a maximum value that depends on the specific dot sizes, material parameters, and dot separation. We also study the effect of the orientation factor on coherent energy transfer from a donor quantum dot to an acceptor quantum dot by calculating the polarization of the acceptor dot. We study how the measurement of the acceptor polarization can be used to determine the relative orientation between the donor-acceptor pair. We also find that F O coupling between dots results in a polarization memory transfer.

Committee: Sergio Ulloa (Advisor) Subjects: Physics, Condensed Matter