Transtition Metal Doped ZnO Thin Film Synthesis by Sol-gel Method
Sunil Thapa (BGSU)
Transition metal doped semiconductors, also known as Diluted Magnetic Semiconductors (DMS), are increasingly popular due to their potential application in Spintronic devices. We used the Sol-gel method to deposit transition metal doped zinc oxide on a glass substrate, and dried it at 120 °C for 10 minutes. After coating 16 times, the films were annealed at 500 °C for 1 hr. This method is a cheap way to get uniform thin films. We used SQUID (Superconducting Quantum Interference Device) to measure the extremely subtle magnetic field near the device. Also, SEM (Scanning Electron Microscopy) was done to see the surface structure.
Brightness Changes of the Star KIC 8462852
Wadha Alsubaie (BGSU)
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Aerodynamics of a Hemi-Larynx Model: Calibration Considerations
Josh Mewhinney (BGSU)
Physical understanding of the larynx as a sound source has been of significant interest to medical professionals, speech-language pathologists, and biophysicists for about 70 years. The laryngeal sound source involves air pressures that drive the vocal folds into sustained oscillation. The removal of half the larynx due to cancer creates the hemi-larynx condition. The air pressures that drive the vocal folds in the hemi-larynx case will be studied using the M5 laryngeal model. The asymmetry of the vocal folds in this case will create asymmetric pressures on the two vocal folds, and measuring the asymmetry of pressures for a range of glottal diameters and angles is the goal of this study. By doing so, a more complete picture of how phonation occurs in the hemi-larynx may be suggested. However, before pressure data can be obtained in this research, accurate calibration of equipment is imperative. The study is not yet past the calibration stage, and a discussion of equipment calibration may prove useful to our group. Thus, the techniques we have used to cross calibrate flow meters and calibrate pressure transducers for this research project will be discussed, as well as uncertainty of the measurements and dimensional analysis for the model.
Antara Antu (BGSU)
Core/shell nanoparticles are a class of nanostructured materials that have recently received increased attention due to their long photoluminescence lifetime which makes them promising for photovoltaic or optoelectronics devices. At least two semiconductor materials are needed to obtain core/shell structure. The segregation into two spatially separated phases, core and shell, commonly relies on differences in physical and chemical properties between the two metals. In laboratory, we have used CdS material by the process of cation exchange for shell formation over PbS nanosheets because they have much less lattice mismatch. Cation exchange allows shrinking of core nanosheet in size by replacing the outer layer of Pb ion by Cd ion while maintaining the total thickness of nanosheets. This method not only grows a shell around the core nanosheets but also improves the morphology of core nanosheets to an extent, which cannot be achieved by direct synthesis method. Core/shell structure becomes very popular in the realm of nanotechnology because the shell provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. The shell further delivers a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. By rationally tuning the cores as well as the shells of such materials (mostly semiconductors), a range of core–shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems.Quantum Computing: A Brief Overview
John Waddle (BGSU)
This presentation is a summary of the theory behind and current implementations of quantum computation, which promises to deliver solutions to problems that are unsolvable through the use of classical computational techniques. Instead of using the classical binary system of information encoding, quantum computers can make use of superposition to represent data in a completely different way. These quantum bits (qubits) can be represented by various systems, ranging from photons to quantum dots. The uses of quantum computing range from efficient factoring techniques—which are of considerable importance in cryptography—to simulations of quantum-mechanical systems. Unfortunately, its application has been severely limited in practice. This is due primarily to quantum decoherence, the irreversible loss of quantum information into the computer environment. However, progress has been made toward building fault-tolerant apparatuses, capable of maintaining the coherence of quantum bits and correcting for error. While considerably more research is required before the technology can be used for practical applications, the outlook is promising.
Fundamentals of zinc oxide as a semiconductor
Keshab Bashyal (BGSU)
In recent years, zinc oxide (ZnO) semiconductors have attracted much attention. In spite of recent rapid developments, controlling the electrical conductivity of ZnO has been remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of commonly observed n-type conductivity in as-grown ZnO is still under debate. To discuss these current challenges, I am reviewing a paper “Fundamentals of ZnO as a Semiconductor” by Anderson Janotti and Chris G. Vande Walle. In this review I will discuss some basic crystalline and electronic properties of ZnO. I then discuss the stability and electronic structure of native defects and impurities and their influence on the electronic and optical properties of ZnO. I discuss this topic from the perspective of conduction research on ZnO at BGSU as well. Specifically, we plan to use the Density Functional Theory to model various defects in ZnO.
Saroj Dahal (BGSU)
Fusion has the potential of providing an abundant supply of energy. There are certain criteria and requirements for fusion a reaction to occur. These requirements can be fulfilled by various techniques, one of which is the inertial confinement fusion concept. In this presentation, I will give a brief introduction about the fusion reaction and ways of accomplishing it, along with the concept of inertial confinement fusion.
From Modules to Atoms: Improving the Reliability of Commercially Relevant Photovoltaic Technologies
Dr. Marco Nardone (BGSU/SEES)
Reliability is a major obstacle to the deployment of photovoltaic (PV) energy conversion devices. Improving module reliability will lead to significant reductions in soft costs/financing risks, which is a key pathway to meeting the U.S. Department of Energy SunShot 2020 goals for the cost of solar energy. Despite several decades of R&D, the underlying physics of various electronic degradation issues remains elusive. Working with the National Renewable Energy Laboratory and industry partners, we are developing unique characterization and modeling capabilities that will allow us to study today’s dominant degradation mechanisms and proactively detect new and future failure modes. Issues that we are currently investigating include potential-induced degradation in silicon modules, metastabilities in cadmium telluride (CdTe) thin-film devices, and reverse bias breakdown due to partial shading of copper indium gallium selenium (CIGS) thin-film cells.
There are several possible physical mechanisms behind PV degradation: defect accumulation under light soak or charge injection; ion migration; shunting; and contact delamination, to name a few. Corresponding to these mechanisms are various degradation modalities, such as loss of photovoltage while the current remains relatively unchanged, or vice versa, dramatic decrease in current at constant voltage, as well and significant changes in device resistances. In this talk, we will consider the specific case of CdTe-based PV where voltage and fill factor are most sensitive to light soak and no commonly accepted model of degradation has been established.
To address this challenge, we are developing a numerical simulation tool with the versatility to enable quantitative testing of postulated degradation mechanisms. For example, one possible mechanism is based on the generation of defects due to the presence of non-equilibrium charge carriers. The coupled defect kinetics and semiconductor equations are solved numerically using an implicit time-dependent solver to predict degradation modes for CdTe cells exposed to light, bias, and various temperatures. Simulated current-voltage, quantum efficiency, and capacitance-voltage changes over time are compared to available stress data. In general, this numerical tool can be used to simulate coupled optical, thermal, and semiconductor physics in more than 1D, and with time dependence, for any type of semiconductor device. The simulation tool is based on the customization of COMSOL® Multi-physics and is therefore widely accessible. A brief overview of the COMSOL® package will be given as a tool becoming increasingly popular in industrial physics.
Modeling Instruction in Science: Turning Students From Simple Fact Memorizers to Active Scientific Researchers
David Pepple (BGSU)
Modeling instruction is a dynamic process which involves students constructing models of scientific concepts. Through this type of instruction, students move from simply memorizing scientific facts to an application of scientific principles. By changing from the traditional lecture and testing mindset, this form of teaching helps students develop a deeper understanding of scientific concepts and helps them actually learn how to think like a scientist.
Positron lifetime measurements of transparent ceramic YAG
Paul Husband (BGSU)
Ceramics have been proven to offer advantages over single crystals, and there have been tremendous advances in the area of fabricating yttrium aluminum garnet (YAG) transparent ceramics for laser applications. However, transparency is still less than the value predicted by theory and the development of YAG transparent ceramics for scintillation devices requires understanding and control of trapping defects. In the present work, positron lifetime spectroscopy (PLS) is applied to study porosity and trapping defects in YAG ceramics, and is compared with single crystals. Measurements are carried out using a conventional coincidence lifetime spectrometer with 180 ps resolution. The use of PLS reveals various defect types and concentrations, and greatly enhances transparent ceramic research.
Intraglottal geometry and flow dynamics in a canine larynx model
Dr. Liran Oren (Univ. of Cincinnati)
According to the classic Myoelastic-aerodynamic theory of voice production, vocal folds vibration is fashioned by the interaction between vocal fold elasticity and intraglottal aerodynamics. Recent computational and experimental studies have shown that vortical structures may form between the vibrating folds during the closing phase of the folds' vibrations. The role of these vorticies and their affect on the vibration mechanism is yet to be determined. Dr. Oren will discuss these findings and their clinical applications.
2-Dimensional colloidal PbS/CdS core shell nanosheet heterostructures
Simeen Khan (BGSU)
PbS/CdS core/shell nanosheets were synthesized using the cation exchange method. A strong quantum confinement was observed in the PbS core due to a decrease in its thickness, indicated by a blue shift in photoluminescence. HRTEM revealed a flat atomic interface between PbS and CdS, and also the relationship between the energy-gap and the thickness in an extremely one-dimensionally confined nanostructure. The photoluminescence lifetime of the core/shell nanosheets was significantly longer than the core-only nanosheets, indicating better surface passivation.
Status of Proton Radiation Test Facilities in the U.S.
Dr. Andew Kostic (The Aerospace Corp.)
Proton testing is an established requirement for characterization and qualification of space systems. Earth orbiting satellites can experience Single Event Effects (SEE), total ionizing dose (TID) and displacement damage (DD) effects due to the proton environment. Modern ICs are becoming more susceptible to proton (SEE) due to the use of high-Z materials in the semiconductor manufacturing process and proton direct ionization.
The energy and flux levels of the protons necessary for the testing can only be supplied by a cyclotron or synchrotron. These machines are large and extremely expensive to build and operate. The Indiana University Cyclotron Facility (IUCF) had provided the space community with over 2,000 hours of beam time for microelectronics proton testing. IUCF abruptly closed in October 2014, creating a testing crisis. An industry-wide team was established including experts from NASA, Boeing, Vanderbilt University, The Aerospace Corporation and the Jet Propulsion Laboratory to identify and qualify new sources for proton testing.
This presentation describes:
Development of New Scintillation Detectors
Anthony M. Colosimo (BGSU)
Scintillation detectors have been widely used in a broad range of applications, including medical diagnostics, mining, high energy and nuclear physics, astronomy and national security. The development of new scintillator materials is crucial for the advancement of these fields; for decades there has been an ongoing search for the ideal scintillator. In this talk, I will give a brief introduction about scintillation and describe our methods in search of new materials for scintillator devices, such as Y3Al5O12 and ZnO, tuning their properties and fabricating new detectors. Our recently developed x–ray induced luminescence (XRIL) spectrometer, combined with photoluminescence (PL) and standard scintillation measurements using phototubes, are shown to be effective tools for developing new efficient and fast scintillation detectors and devices with good energy resolution. This work has been funded in part by the CURS award and has resulted in three publications, as well as the 2015 Bowman Undergraduate Research Award.
Exploring Heusler alloys for catalysis
Nishan Senanayake (BGSU)
Catalysts increase the rate of a chemical reaction by decreasing the activation energy. One of the best catalysts is IrO2 or Ru metal. But Ir and Ru are the least abundant elements in the crust of Earth. So scientists strive to find other affordable catalytic materials. One recent theoretical study outlined a new successful concept, which is based on a simple picture of electronic orbitals. It says that if a surface has higher density of states near the Fermi level, that surface can act as a good catalyst. Not many materials exhibit this behavior. But we propose that magnetic materials can be made catalytically active in the presence of external magnetic field. Following this approach, we modeled a surface with the ferromagnetic Heusler alloy, Ni2MnGa. In order to test the catalytic performance, we dissociated a NH3 molecule that was attached to the slab and compared it to the gas phase counterpart. The surface of our alloy drastically lowered the dissociation barrier indicating that Ni2MnGa can be a promising catalyst, but it could not be significantly enhanced by means of an external magnetic field. Analysis of this result showed that Ni2MnGa is not a good candidate for this task. But now we know what the good candidates should be like. In order to do this, we have adopted a powerful computational technique called the “Nudged Elastic Band Method” which allows us to find the optimal energy path for the reaction, and will facilitate our further search for magnetically driven catalysis.
A 6-year study of LPV stars in the metal-rich cluster NGC 6388
Mohammad Al-Jassim (BGSU)
The fundamental mechanisms underlying the behavior of long period variable stars remains a matter of some debate, and more data on their modes of vibration will help constrain the currently proposed models. We present the results of six years of observation of the galactic globular cluster NGC 6388, a metal-rich cluster with many confirmed and suspected variables. Using time series photometry of the relative fluxes of the stars, via the ISIS image subtraction package, we were able to quantitatively and qualitatively characterize the periodic behavior of multiple LPV stars of the Mira, Semiregular, and Irregular varieties, as well as Pop II Cepheids and RR Lyrae. We present the regular and folded light curves of those stars, and discuss how they improved the data currently available on the cluster’s variables.
Colloidal-Atomic Layer Deposition (c-ALD): An Overview
Prakash Adhikari (BGSU)
Atomic layer deposition (ALD) is very well known thin film deposition technique. Usually, this technique is widely used to grow high quality thin films with a very high degree of accurate thickness and uniform surface for a variety of applications. A similar but a new technique is now proposed and developed in the field of colloidal nanoparticles which is very analogous to ALD. This new technique is called colloidal atomic layer deposition (c-ALD). This presentation will be about c-ALD and the ongoing research in this field.
Size and Shape Tuning of PbSe Nanocrystals
Shailendra Chiluwal (BGSU)
Due to tunable and photostable luminescence properties along with broadband absorption and narrow emission, colloidal nanocrystals (NCs) are suitable for optoelectronic and photovoltaic applications. Based on structural morphology and dimensions of quantum confinement, NCs can be divided into three types: quantum dots, nanorods and nanosheets. Systematic adjustment of reaction conditions can be used to control the size and shape of the NCs. Our recent results shows that growth time and growth temperature have important roles for the control of size of the PbSe NCs. The amount of chloroalkane present in the reaction also has effects on growth of the crystal. Also,the effects of chemical ratios will be discussed.
Wide Band Gap Materials: Synthesis, Characterization, and Emerging New Physics
Dr. Farida Selim (BGSU)
Wide band gap materials exhibit a range of novel physical phenomena that make them perfect candidates for fundamental research and applications. Their electronic and photonic properties strongly depend on their size, structure and defects. The possibility of tailoring the properties of thin film wide band gap oxides by epitaxial strain and the induced interesting phenomena at the interfaces has attracted much attention. Our recent work on inducing persistent photoconductivity in SrTiO3 has extended the discussion to tuning the properties of bulk wide band gap materials.
In our laboratory, we grow thin films, nanocrystals, and bulk materials of wide band gap oxides, characterize them and search for new phenomena. We combine advanced positron annihilation spectroscopy and novel luminescence techniques with conventional structural, electrical and optical characterization methods to tune their properties and develop them for optoelectronic and semiconductor devices.
Phonation onset, phonation offset, and relaxation and hysteresis of human vocal fold tissue
Dr. Lewis Fulcher (BGSU)
In a pioneering paper in 1988 Titze showed that the essence of the mechanism that transfers energy from the stream of air flowing through the glottal channel to the kinetic energy of the vocal fold oscillation could be captured in the Surface Wave Model. He and his collaborators carried out a series of experiments with physical models to test the predicted dependence of the phonation (onset) pressure on the viscous properties of biomaterials and the dependence of onset pressure on glottal halfwidth. During these experiments, it was also found that the minimum (offset) pressure required to sustain vocal fold oscillation is considerably lower than the onset pressure required to set the vocal folds in oscillation. Since this phenomenon was clearly a hysteresis effect, that is, the pressure to initiate vocal fold oscillation as the pressure was increasing was higher than the minimum pressure required to sustain oscillation when the pressure was decreasing, some researchers sought an explanation in possible hysteresis properties of the vocal folds and/or their driving forces.
A set of recent measurements of the viscoelastic properties of human vocal fold tissue by Alipour and his colleagues has provided much new information about the forces required to elongate vocal fold tissue and the forces that this tissue exerts as it returns to its original shape. As expected, these two forces are not the same, clear evidence for a hysteresis effect. However, our preliminary investigation of this tissue hysteresis effect has indicated that it behaves much like a damping effect, that is, a certain amount of energy is absorbed during the cycle that is not available for subsequent oscillations. Thus, the tissue hysteresis effect does not seem to explain the difference between the phonation onset and offset pressures. Alipour also observed that the force required to elongate the tissue to a given length decreases over time, and relaxes to a constant value after a number of cycles. Since the effective force constant relaxes to a smaller value, it seems reasonable to expect the effective damping constant to relax to a smaller value. At present we are exploring the prospect that relaxation of the damping constant may provide an explanation of why offset pressures are lower than onset pressures.
From 0D Quantum-Dots to 2D Nanosheets
Dr. Liangfeng Sun (BGSU)
A big obstacle for developing colloidal quantum dots (QDs) based optoelectronic devices is the surface ligands. They are necessary for preventing the QDs from aggregating, but significantly impede charge transport in QD films since they are typically organic insulators. To improve the charge transport in QD films, short organic ligands, inorganic ligands, and atomic ligands have been developed to replace the original long organic ligands. Although they improve the mobility of the charge carriers in the QD films, the existing inter-QD spacing and the boundary of QDs still hinder the charge carrier transport.
Making two-dimensional (2D) nanosheets (NSs) can effectively reduce these hindrances, yet retain the tunable quantum confinement in one dimension. It has been demonstrated recently that the charge carrier mobility of a single layer of PbS NS is about ten times higher than that from PbS QD films. We report a method to synthesize colloidal PbS NSs through oriented attachments of QDs, with tunable thickness from 1.2 nm to 4.6 nm. The thickness-dependent photoluminescence spectra from PbS nanosheets are observed for the first time. The photoluminescence peaks and the corresponding optical absorption edges overlap and are tunable from 1470 nm to 2175 nm by changing the thickness of the NSs. The one-dimensional confinement energy of these quasi-two-dimensional nanosheets is found to be proportional to 1/L instead of 1/L2 (where L is the thickness of the nanosheet), which is consistent with results calculated using density functional theory as well as tight-binding theory.
Quantum mechanical simulations in the search for new chemical spectroscopic capabilities
Dr. Alexey Zayak (BGSU)
Density Functional Theory (DFT) is a powerful tool that is in the core of the supercomputer-based research of materials. DFT-based simulations allow us to "look" inside of atomic structures, understand how chemistry works, and what atoms and electrons do. A big challenge for modern materials science is to study properties of chemical interfaces. In particular, organic-inorganic interfaces play a very significant role in many current and emerging technologies. Integrating such materials into hybrid structures allows for combining the individual materials' strengths while compensating for deficits. In many cases, such combinations lead to new physical phenomena and technological breakthroughs. However, a controlled design of such heterogeneous structures is a major challenge, because their physical and chemical properties vary on the scale of a few chemical bonds, which is extremely difficult to access by existing spectroscopic techniques. Typically, researchers, who work with nano-systems, cannot "see" interfaces they make. In the search for methods of studying chemical properties of surfaces and heterogeneous interfaces, we focus on the Raman scattering, and reveal its novel capabilities for sensing local chemical properties in complex environments.
Andy Layden -- Aug 2015