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Microscale Polymeric Helical Structures Produced By Electrospinning, Royal Kessick, Gary C. Tepper
Microscale Polymeric Helical Structures Produced By Electrospinning, Royal Kessick, Gary C. Tepper
Mechanical and Nuclear Engineering Publications
Microscale helical coils consisting of a composite of one conducting and one nonconducting polymer were produced using electrospinning. The nonconducting polymer was poly(ethylene oxide) and the conducting polymer was poly(aniline sulfonic acid). The coil structures were studied over a range of processing conditions and fiber composition. The data suggest that the helical structures are formed due to viscoelastic contraction upon partial neutralization of the charged fibers. Polymeric microcoils may find applications in microelectromechanical systems, advanced optical components, and drug delivery systems.
Transient Photovoltage In Gan As Measured By Atomic Force Microscope Tip, M. A. Reshchikov, S. Sabuktagin, D. K. Johnstone, H. Morkoç
Transient Photovoltage In Gan As Measured By Atomic Force Microscope Tip, M. A. Reshchikov, S. Sabuktagin, D. K. Johnstone, H. Morkoç
Electrical and Computer Engineering Publications
We studied restoration of the band bending at the surface of undoped GaN layers after illumination with above-bandgap light. The photovoltage saturated with illumination at about 0.2–0.3 eV at room temperature, although the upward band bending for GaN in the dark is of the order of 1 eV. We attribute the photovoltage effect to charging of the surface states, the density of which is estimated at about 10^12 cm^−2. Restoration of the barrier after a light pulse is simulated by a phenomenological model whereby the acceptorlike surface states are emptied of electrons under illumination and filled back in dark due …
The Effect Of Loading On Disturbance Sounds Of The Atlantic Croaker Micropogonius Undulatus: Air Versus Water, Michael L. Fine, Justin Schrinel, Timothy M. Cameron
The Effect Of Loading On Disturbance Sounds Of The Atlantic Croaker Micropogonius Undulatus: Air Versus Water, Michael L. Fine, Justin Schrinel, Timothy M. Cameron
Biology Publications
Physiological work on fish sound production may require exposure of the swimbladder to air, which will change its loading (radiation mass and resistance) and could affect parameters of emitted sounds. This issue was examined in Atlantic croaker Micropogonius chromis by recording sounds from the same individuals in air and water. Although sonograms appear relatively similar in both cases, pulse duration is longer because of decreased damping, and sharpness of tuning (Q factor) is higher in water. However, pulse repetition rate and dominant frequency are unaffected. With appropriate caution it is suggested that sounds recorded in air can provide a useful …
High Quality Zno Epitaxial Grown By Plasma Assisted Molecular Beam Epitaxy, Yun Zhang
High Quality Zno Epitaxial Grown By Plasma Assisted Molecular Beam Epitaxy, Yun Zhang
Theses and Dissertations
Described in this thesis are the growth and characterization of high quality ZnO epitaxy layers.Zinc oxide (ZnO) epitaxy layers were grown on sapphire and epi-GaN substrates respectively, using plasma assisted molecular beam epitaxy (MBE) . Various growth conditions, such as growth temperature, II/VI ratio, and buffer layers, were employed to optimize the quality of the ZnO film. The subsequent characterization of the films was carried out to evaluate the surface, optical and crystalline properties of the film, using AFM, SEM, PL and XRD techniques. It was found out that the high quality of the ZnO film was grown on epi-GaN …
Determination Of The Carrier Concentration In Ingaasn∕Gaas Single Quantum Wells Using Raman Scattering, Patrick A. Grandt, Aureus E. Griffith, M. O. Manasreh, D. J. Friedman, S. Doğan, D. Johnstone
Determination Of The Carrier Concentration In Ingaasn∕Gaas Single Quantum Wells Using Raman Scattering, Patrick A. Grandt, Aureus E. Griffith, M. O. Manasreh, D. J. Friedman, S. Doğan, D. Johnstone
Electrical and Computer Engineering Publications
Raman scattering from longitudinal optical phonon-plasmon coupled mode was observed in a series of InGaAsN∕GaAs single quantum well samples grown by metalorganic vapor phase epitaxy. The phonon-plasmon mode spectra were fitted with the dielectric constant function based on Drude model that contains contributions from both lattice vibrations and conduction electrons. The carrier concentration is calculated directly from the plasmon frequency, which is obtained from the fitting procedure. An empirical expression for the electron concentration, [n], in InGaAsN∕GaAs samples is determined as [n]≈{2.35×1016(ωm−502)}cm−3, where ωm is the peak of the upper frequency branch, L+, of the phonon-plasmon mode measured in unit …
Alternate Spintronic Analog Of The Electro-Optic Modulator, S. Bandyopadhyay, M. Cahay
Alternate Spintronic Analog Of The Electro-Optic Modulator, S. Bandyopadhyay, M. Cahay
Electrical and Computer Engineering Publications
There is significant current interest in spintronic devices fashioned after a spin analog of the electro-opticmodulator proposed by Datta and Das [Appl. Phys. Lett.56, 665 (1990)]. In their modulator, the “modulation” of the spin-polarized current is carried out by tuning the Rashba spin-orbit interaction with a gate voltage. Here, we propose an analogous modulator where the modulation is carried out by tuning the Dresselhaus spin-orbit interaction instead, using a split gate. Additionally, the magnetization of the source and drain contacts in our device is transverseto the channel, whereas in the Datta-Dasdevice, it is along the channel. Therefore, in the …
Thermal Stability Of Electron Traps In Gan Grown By Metalorganic Chemical Vapor Deposition, D. Johnstone, S. Doğan, J. Leach, Y.-T. Moon, Y. Fu, Y. Hu, Hadis Morkoç
Thermal Stability Of Electron Traps In Gan Grown By Metalorganic Chemical Vapor Deposition, D. Johnstone, S. Doğan, J. Leach, Y.-T. Moon, Y. Fu, Y. Hu, Hadis Morkoç
Electrical and Computer Engineering Publications
Deep level transient spectroscopy was used to investigate the thermal stability of electron traps in n-type GaN grown by metalorganic chemical vapor deposition. The concentration of traps at 160 and at 500K increased more than fivefold over the course of several 700Kanneal cycles, while a peak at 320K increased by a factor of only 1.19. The increase in the trap concentration with repeated annealing might be due to a mobile trap or loss of passivant. Hydrogen is very likely present in high concentration in the epilayer, and its passivating effects may be lost with annealing.
Studies Of Ingan∕Gan Multiquantum-Well Green-Light-Emitting Diodes Grown By Metalorganic Chemical Vapor Deposition, K. S. Ramaiah, Y. K. Su, S. J. Chang, C. H. Chen, F. S. Juang, H. P. Liu, I. G. Chen
Studies Of Ingan∕Gan Multiquantum-Well Green-Light-Emitting Diodes Grown By Metalorganic Chemical Vapor Deposition, K. S. Ramaiah, Y. K. Su, S. J. Chang, C. H. Chen, F. S. Juang, H. P. Liu, I. G. Chen
Electrical and Computer Engineering Publications
InGaN(3nm)∕GaN(5nm) three period multiquantum green-light-emitting diodes(LEDs) grown by the metalorganic chemical vapor deposition technique have been studied using high-resolution transmission electron microscopy (HRTEM), double crystal high resolution x-ray diffraction (HRXRD) and low temperature photoluminescence. HRTEM analysis showed that the defect density gradually decreased in the growth direction with increasing thickness. Self-assembled quantum dot-likestructures in the wells and black lumps between the well and barrier due to In segregation and strain contrast were observed, respectively. The HRXRD spectrum of the green LEDstructure was simulated using the kinematical theory method to obtain the composition and thickness of the well and barrier. The …
Reexamination Of Some Spintronic Field-Effect Device Concepts, S. Bandyopadhyay, M. Cahay
Reexamination Of Some Spintronic Field-Effect Device Concepts, S. Bandyopadhyay, M. Cahay
Electrical and Computer Engineering Publications
Current interest in spintronics is largely motivated by a belief that spin-based devices (e.g., spin field-effect transistors) will be faster and consume less power than their electronic counterparts. Here we show that this is generally untrue. Unless materials with extremely strong spin-orbit interaction can be developed, the spintronic devices will not measure up to their electronic cousins. We also show that some recently proposed modifications of the original spin field-effect transistor concept of Datta and Das [Appl. Phys. Lett.56, 665 (1990)] actually lead to worse performance than the original construct.
The Effect Of Hydrogen Etching On 6h-Sic Studied By Temperature-Dependent Current-Voltage And Atomic Force Microscopy, S. Doğan, D. Johnstone, F. Yun, S. Sabuktagin, J. Leach, A. A. Baski, Hadis Morkoç, G. Li, B. Ganguly
The Effect Of Hydrogen Etching On 6h-Sic Studied By Temperature-Dependent Current-Voltage And Atomic Force Microscopy, S. Doğan, D. Johnstone, F. Yun, S. Sabuktagin, J. Leach, A. A. Baski, Hadis Morkoç, G. Li, B. Ganguly
Electrical and Computer Engineering Publications
6H–SiC was etched with hydrogen at temperatures between 1000 and 1450°C. The etchedSi-terminated face for the 6H‐SiC wafer was investigated by atomic force microscopy and temperature-dependent current–voltage (I–V–T)measurements. Mechanical polishing damage was effectively removed by hydrogen etching at temperatures above 1250°C. Atomic force microscopy images revealed that very good surface morphology, atomic layer flatness, and large and large step width were achieved. Schottky diode characteristics were investigated in detail by current–voltage and temperature-dependent current–voltage measurements, and the results showed a transition from defect assisted tunneling to thermionic emission as the annealingtemperature was increased from 1250 to 1450°C.
Stimulated Emission And Time-Resolved Photoluminescence In Rf-Sputtered Zno Thin Films, Ü. Özgür, A. Teke, C. Liu, S.-J. Cho, Hadis Morkoç, H. O. Everitt
Stimulated Emission And Time-Resolved Photoluminescence In Rf-Sputtered Zno Thin Films, Ü. Özgür, A. Teke, C. Liu, S.-J. Cho, Hadis Morkoç, H. O. Everitt
Electrical and Computer Engineering Publications
Stimulated emission (SE) was measured from ZnOthin filmsgrown on c-plane sapphire by rf sputtering. Free exciton transitions were clearly observed at 10 K in the photoluminescence(PL), transmission, and reflection spectra of the sample annealed at 950 °C. SE resulting from both exciton-exciton scattering and electron hole plasma formation was observed in the annealed samples at moderate excitation energy densities. The SE threshold energy density decreased with increasing annealing temperature up to ∼950 °C. The observation of low threshold exciton-exciton scattering-induced SE showed that excitonic laser action could be obtained in rf-sputtered ZnOthin films. At excitation densities below the SE threshold, …
Investigation Of Forward And Reverse Current Conduction In Gan Films By Conductive Atomic Force Microscopy, J. Spradlin, S. Doǧan, J. Xie, R. Molnar, A. A. Baski, Hadis Morkoç
Investigation Of Forward And Reverse Current Conduction In Gan Films By Conductive Atomic Force Microscopy, J. Spradlin, S. Doǧan, J. Xie, R. Molnar, A. A. Baski, Hadis Morkoç
Electrical and Computer Engineering Publications
We have used conductive atomic force microscopy (C–AFM) to investigate the forward and reverse bias current conduction of homo- and heteroepitaxial GaN-based films grown by molecular beam epitaxy. In the case of homoepitaxy, C–AFM shows enhanced current conduction at the centers of ∼30% of spiral hillocks, which are associated with screw dislocations. Local current–voltage spectra taken by C–AFM on and off such hillocks indicate Frenkel–Poole and field emission mechanisms, respectively, for low current levels in forward conduction. In the case of heteroepitaxialGaN films grown on sapphire, the correlation between conduction pathways and topography is more complex. We do observe, however, …
Effects Of Hydrostatic And Uniaxial Stress On The Schottky Barrier Heights Of Ga-Polarity And N-Polarity N-Gan, Y. Liu, M. Z. Kauser, M. I. Nathan, P. P. Ruden, S. Dogan, Hadis Morkoç, S. S. Park, K. Y. Lee
Effects Of Hydrostatic And Uniaxial Stress On The Schottky Barrier Heights Of Ga-Polarity And N-Polarity N-Gan, Y. Liu, M. Z. Kauser, M. I. Nathan, P. P. Ruden, S. Dogan, Hadis Morkoç, S. S. Park, K. Y. Lee
Electrical and Computer Engineering Publications
We report measurements of the Schottky barrier heights of Ni/Au contacts on Ga-polarity and N-polarity n-GaN under hydrostatic pressure and applied in-plane uniaxial stress. Under hydrostatic pressure the two different polarities of GaN yield significantly different rates of Schottky barrier height increase with increasing pressure. Uniaxial stress parallel to the surface affects the Schottky barrier height only minimally. The observed changes in barrier height under stress are attributed to a combination of band structure and piezoelectric effects.
Surface Band Bending In As-Grown And Plasma-Treated N-Type Gan Films Using Surface Potential Electric Force Microscopy, Sang-Jun Cho, Seydi Doğan, Shahriar Sabuktagin, Michael A. Reshchikov, D. Johnstone, Hadis Morkoç
Surface Band Bending In As-Grown And Plasma-Treated N-Type Gan Films Using Surface Potential Electric Force Microscopy, Sang-Jun Cho, Seydi Doğan, Shahriar Sabuktagin, Michael A. Reshchikov, D. Johnstone, Hadis Morkoç
Electrical and Computer Engineering Publications
The surface band bending, as well as the effect of plasma-induced damage on band bending, on GaN surfaces, was investigated. The upward band bending, measured by surface potentialelectric force microscopy (a variant of atomic force microscopy), for the as-grown n -type GaNwas about 1.0 eV which increased to ∼1.4 eV after reactive ion etching (RIE). UV illuminationdecreased the band bending by 0.3 eV with time constants on the order of seconds and hundreds of seconds for the as-grown and RIE treated GaN, respectively. This implies that there is a higher density of the surface states in the samples subjected to …
Characterization Of Ingan/Gan Multi-Quantum-Well Blue-Light-Emitting Diodes Grown By Metal Organic Chemical Vapor Deposition, K. S. Ramaiah, Y. K. Su, S. J. Cheng, B. Kerr, H. P. Liu, I. G. Chen
Characterization Of Ingan/Gan Multi-Quantum-Well Blue-Light-Emitting Diodes Grown By Metal Organic Chemical Vapor Deposition, K. S. Ramaiah, Y. K. Su, S. J. Cheng, B. Kerr, H. P. Liu, I. G. Chen
Electrical and Computer Engineering Publications
The structural,surface morphology, and the temperature dependence photoluminescence of InGaN(3 nm)/GaN(7 nm) 5 period multi-quantum-well blue-light-emitting diode (LED)structures grown by metal organic chemical vapor deposition(MOCVD) have been studied. Quantum dot-likestructures and strain contrast evident by black lumps were observed in the quantum wells using high-resolution transmission electron microscopy(HRTEM) analysis. Double-crystal high-resolution x-ray diffraction (HRXRD) spectra of blue LED were simulated using kinematical theory method, to obtain composition, and period thickness of well and barrier. The “S” shape character shift as red–blue–redshift of the quantum-well emission line, i.e., blue emission peak 2.667 eV at 10 K, was observed with variation of …
Decay Of Spin-Polarized Hot Carrier Current In A Quasi-One-Dimensional Spin-Valve Structure, S. Pramanik, Supriyo Bandyopadhyay, M. Cahay
Decay Of Spin-Polarized Hot Carrier Current In A Quasi-One-Dimensional Spin-Valve Structure, S. Pramanik, Supriyo Bandyopadhyay, M. Cahay
Electrical and Computer Engineering Publications
We study the spatial decay of spin-polarized hot carriercurrent in a spin-valve structure consisting of a semiconductorquantum wire flanked by half-metallic ferromagnetic contacts. The current decays because of D’yakonov-Perel’ spin relaxation in the semiconductor caused by Rashba and Dresselhaus spin–orbit interactions in multi-channeled transport. The associated relaxation length is found to decrease with increasing lattice temperature (in the range from 30 to 77 K) and exhibit a nonmonotonic dependence on the electric field driving the current. The relaxation lengths are several tens of microns which are at least an order of magnitude larger than what has been theoretically calculated for …
Gan Epitaxy On Thermally Treated C-Plane Bulk Zno Substrates With O And Zn Faces, Xing Gu, Michael A. Reshchikov, Ali Teke, D. Johnstone, Hadis Morkoç, Bill Nemeth, Jeff Nause
Gan Epitaxy On Thermally Treated C-Plane Bulk Zno Substrates With O And Zn Faces, Xing Gu, Michael A. Reshchikov, Ali Teke, D. Johnstone, Hadis Morkoç, Bill Nemeth, Jeff Nause
Electrical and Computer Engineering Publications
ZnO is considered as a promising substrate for GaNepitaxy because of stacking match and close lattice match to GaN. Traditionally, however, it suffered from poor surface preparation which hampered epitaxialgrowth in general and GaN in particular. In this work, ZnO substrates with atomically flat and terrace-like features were attained by annealing at high temperature in air. GaNepitaxial layers on such thermally treated basal plane ZnO with Zn and O polarity have been grown by molecular beam epitaxy, and two-dimensional growth mode was achieved as indicated by reflection high-energy electron diffraction. We observed well-resolved ZnO and GaN peaks in the high-resolution …
Phase-Coherent Quantum Mechanical Spin Transport In A Weakly Disordered Quasi-One-Dimensional Channel, M. Cahay, S. Bandyopadhyay
Phase-Coherent Quantum Mechanical Spin Transport In A Weakly Disordered Quasi-One-Dimensional Channel, M. Cahay, S. Bandyopadhyay
Electrical and Computer Engineering Publications
A transfer matrix technique is used to model phase-coherent spin transport in the weakly disordered quasi-one-dimensional channel of a gate-controlled electron spin interferometer [S. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990)]. The model includes the effects of an axial magnetic field in the channel of the interferometer (caused by the ferromagnetic contacts), a Rashba spin-orbit interaction, and elastic (nonmagnetic) impurity scattering. We show that in the presence of an axial magnetic field, nonmagnetic impurities can cause spin relaxation in a manner similar to the Elliott-Yafet mechanism. The amplitudes and phases of the conductance oscillations of the interferometer …
Excitonic Fine Structure And Recombination Dynamics In Single-Crystalline Zno, A. Teke, Ü. Özgür, S. Doğan, X. Gu, Hadis Morkoç, B. Nemeth, J. Nause, H. O. Everitt
Excitonic Fine Structure And Recombination Dynamics In Single-Crystalline Zno, A. Teke, Ü. Özgür, S. Doğan, X. Gu, Hadis Morkoç, B. Nemeth, J. Nause, H. O. Everitt
Electrical and Computer Engineering Publications
The optical properties of a high quality bulk ZnO, thermally post treated in a forming gas environment are investigated by temperature dependent continuous wave and time-resolved photoluminescence (PL) measurements. Several bound and free exciton transitions along with their first excited states have been observed at low temperatures, with the main neutral-donor-bound exciton peak at 3.3605 eV having a linewidth of 0.7 meV and dominating the PL spectrum at 10 K. This bound exciton transition was visible only below 150 K, whereas the A-free exciton transition at 3.3771 eV persisted up to room temperature. A-free exciton binding energy of 60 meV …
Gan Epitaxy On Melt Grown Thermally Prepared Bulk Zno Substrates, Xing Gu
Gan Epitaxy On Melt Grown Thermally Prepared Bulk Zno Substrates, Xing Gu
Theses and Dissertations
Different methods were developed for the preparation of bulk ZnO substrates. Remarkable improvement on the surface, optical and crystalline quality of the bulk ZnO substrate was achieved. ZnO substrates with an atomically flat surface exhibiting terrace-like features were used as a substrate for GaN grown by MBE. High-resolution x-ray diffraction and low temperature PL results show that similar high quality GaN layers can be achieved on both annealed O-face and Zn-face ZnO substrates. The prospect of the device applications of GaN epitaxy on ZnO, including AlGaN/GaN MODFET structure on ZnO and GAN/ZnO based p-n junction were discussed.
Luminescence In Zno, Jin Xu
Luminescence In Zno, Jin Xu
Theses and Dissertations
As a wide band semiconductor with a large binding energy (about 60meV), ZnO is a promising candidate semiconductor material for the next generation of optoelectronic , light emission or high power and high frequency devices. In order to make electrical device from ZnO, it is necessary to investigate optical properties of ZnO.In this thesis, PL setup and the properties of ZnO are introduced briefly and the optical properties of ZnO are investigated in detail. Temperature dependence of PL spectra of ZnO are measured and analyzed. Sharp emission line of PL spectra of rare earth (RE) doped ZnO are also investigated.
Incorporation Of Tetracycline Hydrochloride Into Electrospun Fibrinogen: A Study Of Mechanical Properties And Time Release, Charles Dudley Anderson Jr.
Incorporation Of Tetracycline Hydrochloride Into Electrospun Fibrinogen: A Study Of Mechanical Properties And Time Release, Charles Dudley Anderson Jr.
Theses and Dissertations
Electrospinning has the capacity to create fibers of natural or synthetic polymers with dimensions that are similar to analogous fibers in native tissue. Mats consisting of fibers of these sub-micron dimensions have shown promise in provoking little immune response and in offering a habitable environment for cell proliferation. Fibrinogen is a natural protein capable of being electrospun and offers the benefit of existing as part of the natural coagulation cascade. Mats of fibrinogen could be utilized as possible hemostatic dressings or as an early scaffold for cell migration for either wound repair or tissue engineering. The addition of antibiotic into …
Iii-Nitride Semiconductors Grown By Plasma Assisted Molecular Beam Epitaxy, Lei He
Iii-Nitride Semiconductors Grown By Plasma Assisted Molecular Beam Epitaxy, Lei He
Theses and Dissertations
III-nitride semiconductors are of great interest owing to their commercial and military applications due to their optoelectronic and mechanical properties. They have been synthesized successfully by many growth methods. Among them, molecular beam epitaxy (MBE) is a promising epitaxial growth method owing to precise control of growth parameters, which significantly affect the film properties, composition, and thickness. However, the understanding of growth mechanism of III-nitride materials grown in this growth regime is far from being complete.In this dissertation, GaN and AIGaN growth mechanism under metal-rich conditions were investigated. The Ga surface desorption behavior during the growth was investigated systematically using …
Electrospinning As A Processing Method For Electroactive Polymers And Composites, Kristin Joy Pawlowski
Electrospinning As A Processing Method For Electroactive Polymers And Composites, Kristin Joy Pawlowski
Theses and Dissertations
Electrospinning was examined for its potential to create functional materials. Three distinct electroactive materials were electrospun into fibers and fiber mats and then characterized with the intent of determining their utility in aerospace and biomedical applications such as micro-air vehicles and the cardiovascular system. Electrospun Graft Elastomers demonstrated potential as actuators, as electromechanical strain testing showed comparable response to the film form of this material. Further improvement of electroactive response was realized with high dielectric inclusions and fiber orientation. Electrospin processing imparted piezoelectric properties to the fibers of poly(vinylidene fluoride). Differential scanning calorimetry and infrared spectroscopy indicated a degree of …
Characterization Of Aligned Carbon Nanotube/Polymer Composites, Sumanth Banda
Characterization Of Aligned Carbon Nanotube/Polymer Composites, Sumanth Banda
Theses and Dissertations
The main objective of this thesis is to efficiently disperse and align SWNTs in two different polymer matrices to obtain an orthotropic composite whose strength, stiffness and electrical properties depend on the orientation of the SWNTs. The SWNTs are successfully dispersed and aligned in a polyimide matrix and a polymer blend of UDMA/HDDMA. In-situ polymerization under sonication is used to disperse the SWNTs in polyimide matrix and sonication is used to disperse SWNTs in the UDMA/HDDMA matrix. In both cases, an electric field is used to align the SWNTs in the polymer matrices. In the polyimide, the SWNTs are aligned …
Novel Apparatus To Control Electrospinning Fiber Orientation For The Production Of Tissue Engineering Scaffolds, Eugene David Boland
Novel Apparatus To Control Electrospinning Fiber Orientation For The Production Of Tissue Engineering Scaffolds, Eugene David Boland
Theses and Dissertations
The conception of electrospinning can trace its roots back more than 400 years, when it was observed that rubbed amber can deform a droplet of water on a smooth surface, and is based upon simple concepts of charge separation and surface tension. Since that time, considerable effort has been directed at both the cause and utility of this phenomenon. The specific aim of this dissertation project was to develop an automated electrostatic processing apparatus that was capable of controlling the three-dimensional architecture of an electrospun scaffold to further improve its utility in tissue engineering. The efficacy of using this technique …