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Articles 91 - 104 of 104
Full-Text Articles in Engineering
Tunable Multiferroic Properties In Nanocomposite Pbtio3-Cofe2O4 Epitaxial Thin Films, M. Murakami, K.-S. Chang, M. Aronova, C.-L. Lin, Ming Yu, Jason Hattrick-Simpers, M. Wuttig, I. Takeuchi, C. Gao, B. Hu, S. Lofland, L. Knauss, L. Bendersky
Tunable Multiferroic Properties In Nanocomposite Pbtio3-Cofe2O4 Epitaxial Thin Films, M. Murakami, K.-S. Chang, M. Aronova, C.-L. Lin, Ming Yu, Jason Hattrick-Simpers, M. Wuttig, I. Takeuchi, C. Gao, B. Hu, S. Lofland, L. Knauss, L. Bendersky
Jason R. Hattrick-Simpers
We report on the synthesis of PbTiO3–CoFe2O4 multiferroic nanocomposites and continuous tuning of their ferroelectric and magnetic properties as a function of the average composition on thin-film composition spreads. The highest dielectric constant and nonlinear dielectric signal was observed at (PbTiO3)85–(CoFe2O4)15, where robust magnetism was also observed. Transmission electron microscopy revealed a pancake-shaped epitaxial nanostructure of PbTiO3 on the order of 30 nm embedded in the matrix of CoFe2O4 at this composition. Composition dependent ferroics properties observed here indicate that there is considerable interdiffusion of cations into each other.
Effects Of Neutron And Gamma Radiation On Lithium-Ion Batteries, Jie Qiu, Dandan He, Mingzhai Sun, Shimeng Li, Cun Wen, Jason Hattrick-Simpers, Yuan Zheng, Lei Cao
Effects Of Neutron And Gamma Radiation On Lithium-Ion Batteries, Jie Qiu, Dandan He, Mingzhai Sun, Shimeng Li, Cun Wen, Jason Hattrick-Simpers, Yuan Zheng, Lei Cao
Jason R. Hattrick-Simpers
No abstract provided.
Exploration Of Artificial Multiferroic Thin-Film Heterostructures Using Composition Spreads, K.-S. Chang, M. A. Aronova, C.-L. Lin, M. Murakami, M.-H. Yu, Jason R. Hattrick-Simpers, O. O. Famodu, S. Y. Lee, R. Ramesh, M. Wuttig, I. Takeuchi, C. Gao, L. A. Bendersky
Exploration Of Artificial Multiferroic Thin-Film Heterostructures Using Composition Spreads, K.-S. Chang, M. A. Aronova, C.-L. Lin, M. Murakami, M.-H. Yu, Jason R. Hattrick-Simpers, O. O. Famodu, S. Y. Lee, R. Ramesh, M. Wuttig, I. Takeuchi, C. Gao, L. A. Bendersky
Jason R. Hattrick-Simpers
We have fabricated a series of composition spreads consisting of ferroelectric BaTiO3 and piezomagnetic CoFe2O4 layers of varying thicknesses modulated at nanometer level in order to explore artificial magnetoelectricthin-film heterostructures. Scanning microwavemicroscopy and scanning superconducting quantum interference device microscopy were used to map the dielectric and magnetic properties as a function of continuously changing average composition across the spreads, respectively. Compositions in the middle of the spreads were found to exhibit ferromagnetism while displaying a dielectric constant as high as ≈120.
Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. Lofland, Jason Hattrick-Simpers, H. Chang
Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. Lofland, Jason Hattrick-Simpers, H. Chang
Jason R. Hattrick-Simpers
We have performed variable-temperature multimode quantitative microwavemicroscopy of in situepitaxial Ba1−xSrxTiO3 thin-film composition spreads fabricated on (100) LaA1O3 substrates. Dielectric properties were mapped as a function of continuously varying composition from BaTiO3 to SrTiO3. We have demonstrated nondestructive temperature-dependent dielectric characterization of local thin-film regions. Measurements are simultaneously taken at multiple resonant frequencies of the microscope cavity. The multimode measurements allow frequency dispersion studies. We observe strong composition-dependent dielectric relaxation in Ba1−xSrxTiO3 at microwave frequencies.
Joint Map Registration And High Resolution Image Estimation Using A Sequence Of Undersampled Images, Russell C. Hardie, Kenneth J. Barnard, Ernest E. Armstrong
Joint Map Registration And High Resolution Image Estimation Using A Sequence Of Undersampled Images, Russell C. Hardie, Kenneth J. Barnard, Ernest E. Armstrong
Russell C. Hardie
n many imaging systems, the detector array is not sufficiently dense to adequately sample the scene with the desired field of view. This is particularly true for many infrared focal plane arrays. Thus, the resulting images may be severely aliased. This paper examines a technique for estimating a high-resolution image, with reduced aliasing, from a sequence of undersampled frames. Several approaches to this problem have been investigated previously. However, in this paper a maximum a posteriori (MAP) framework for jointly estimating image registration parameters and the high-resolution image is presented. Several previous approaches have relied on knowing the registration parameters …
Optical Bandgap Formation In Alingan Alloys, G. Tamulaitis, K. Kazlauskas, S. Juršėnas, A. Žukauskas, M. A. Khan, J. W. Yang, J. Zhang, Grigory Simin, M. S. Shur, R. Gaska
Optical Bandgap Formation In Alingan Alloys, G. Tamulaitis, K. Kazlauskas, S. Juršėnas, A. Žukauskas, M. A. Khan, J. W. Yang, J. Zhang, Grigory Simin, M. S. Shur, R. Gaska
Grigory Simin
We report on the spectral dynamics of the reflectivity, site-selectively excited photoluminescence,photoluminescence excitation, and time-resolved luminescence in quaternary AlInGaN epitaxial layers grown on GaN templates. The incorporation of a few percents of In into AlGaN causes significant smoothening of the band-bottom potential profile in AlInGaN layers owing to improved crystal quality. An abrupt optical bandgap indicates that a nearly lattice-matched AlInGaN/GaN heterostructure with large energy band offsets can be grown for high-efficiency light-emitting devices.
Enhanced Luminescence In Ingan Multiple Quantum Wells With Quaternary Alingan Barriers, Jianping Zhang, J. Yang, Grigory Simin, M. Shatalov, M. Asif Khan, M. S. Shur, R. Gaska
Enhanced Luminescence In Ingan Multiple Quantum Wells With Quaternary Alingan Barriers, Jianping Zhang, J. Yang, Grigory Simin, M. Shatalov, M. Asif Khan, M. S. Shur, R. Gaska
Grigory Simin
We report on the comparative photoluminescence studies of AlGaN/GaN, GaN/InGaN, and AlInGaN/InGaN multiple quantum well(MQW) structures. The study clearly shows the improvement in materials quality with the introduction of indium. Our results point out the localized state emission mechanism for GaN/InGaN structures and the quantum well emission mechanism for AlInGaN/InGaN structures. The introduction of indium is the dominant factor responsible for the observed differences in the photoluminescence spectra of these MQW structures.
Sio2-Passivated Lateral-Geometry Gan Transparent Schottky-Barrier Detectors, V. Adivarahan, Grigory Simin, J. W. Yang, A. Lunev, M. Asif Khan, M. Pala, M. Shur, R. Gaska
Sio2-Passivated Lateral-Geometry Gan Transparent Schottky-Barrier Detectors, V. Adivarahan, Grigory Simin, J. W. Yang, A. Lunev, M. Asif Khan, M. Pala, M. Shur, R. Gaska
Grigory Simin
We report on a transparent Schottky-barrierultraviolet detector on GaN layers over sapphire substrates. Using SiO2 surface passivation, reverse leakage currents were reduced to a value as low as 1 pA at 5 V reverse bias for 200 μm diameter device. The device exhibits a high internal gain, about 50, at low forward biases. The response time (about 15 ns) is RC limited, even in the internal gain regime. A record low level of the noise spectral density, 5×10−23 A2/Hz, was measured at 10 Hz. We attribute this low noise level to the reduced reverse leakage current.
Selective Area Deposited Blue Gan-Ingan Multiple-Quantum Well Light Emitting Diodes Over Silicon Substrates, J. W. Yang, A. Lunev, Grigory Simin, A. Chitnis, M. Shatalov, M. Asif Khan, Joseph E. Van Nostrand, R. Gaska
Selective Area Deposited Blue Gan-Ingan Multiple-Quantum Well Light Emitting Diodes Over Silicon Substrates, J. W. Yang, A. Lunev, Grigory Simin, A. Chitnis, M. Shatalov, M. Asif Khan, Joseph E. Van Nostrand, R. Gaska
Grigory Simin
We report on fabrication and characterization of blue GaN–InGaN multi-quantum well (MQW)light-emitting diodes(LEDs) over (111) silicon substrates. Device epilayers were fabricated using unique combination of molecular beam epitaxy and low-pressure metalorganic chemical vapor depositiongrowth procedure in selective areas defined by openings in a SiO2mask over the substrates. This selective area deposition procedure in principle can produce multicolor devices using a very simple fabrication procedure. The LEDs had a peak emission wavelength of 465 nm with a full width at half maximum of 40 nm. We also present the spectral emission data with the diodes operating up to 250 …
Indium-Silicon Co-Doping Of High-Aluminum-Content Algan For Solar Blind Photodetectors, V. Adivarahan, Grigory Simin, G. Tamulaitis, R. Srinivasan, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska
Indium-Silicon Co-Doping Of High-Aluminum-Content Algan For Solar Blind Photodetectors, V. Adivarahan, Grigory Simin, G. Tamulaitis, R. Srinivasan, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska
Grigory Simin
We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrierphotodetectors with the cut-off wavelength of 278 nm.
Very-Low-Specific-Resistance Pd/Ag/Au/Ti/Au Alloyed Ohmic Contact To P Gan For High-Current Devices, V. Adivarahan, A. Lunev, M. Asif Khan, J. Yang, Grigory Simin, M. S. Shur, R. Gaska
Very-Low-Specific-Resistance Pd/Ag/Au/Ti/Au Alloyed Ohmic Contact To P Gan For High-Current Devices, V. Adivarahan, A. Lunev, M. Asif Khan, J. Yang, Grigory Simin, M. S. Shur, R. Gaska
Grigory Simin
We report on Pd/Ag/Au/Ti/Au alloyed metallic contact to pGaN. An 800 °C anneal for 1 min in flowing nitrogen ambient produces an excellent ohmic contact with a specific contact resistivity close to 1×10−6 Ω cm2 and with good stability under high current operation conditions. This high-temperature anneal forms an alloy between Ag,Au, and pGaN resulting in a highly p-doped region at the interface. Using x-ray photoelectron spectroscopy and x-ray diffractionanalysis, we confirm that the contact formation mechanism is the metal intermixing and alloying with the semiconductor.
Time-Resolved Electroluminescence Of Algan-Based Light-Emitting Diodes With Emission At 285 Nm, M. Shatalov, A. Chitnis, V. Mandavilli, R. Pachipulusu, J. P. Zhang, V. Adivarahan, S. Wu, Grigory Simin, M. Asif Khan, G. Tamulaitis, A. Sereika, I. Yilmaz, M. S. Shur, R. Gaska
Time-Resolved Electroluminescence Of Algan-Based Light-Emitting Diodes With Emission At 285 Nm, M. Shatalov, A. Chitnis, V. Mandavilli, R. Pachipulusu, J. P. Zhang, V. Adivarahan, S. Wu, Grigory Simin, M. Asif Khan, G. Tamulaitis, A. Sereika, I. Yilmaz, M. S. Shur, R. Gaska
Grigory Simin
We present a study on the time evolution of the electroluminescence(EL)spectra of AlGaN-based deep ultraviolet light-emitting diodes(LEDs) under pulsed current pumping. The ELspectra peaks at 285 nm and 330 nm are found to result from recombination involving band-to-band and free carriers to deep acceptor level transitions. The 330 nm long-wavelength transitions to deep acceptor levels in the p-AlGaN layer as well as the nonradiative processes significantly influence the LED internal quantum efficiency.
Luminescence Mechanisms In Quaternary AlXInYGa1-X-YN Materials, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan
Luminescence Mechanisms In Quaternary AlXInYGa1-X-YN Materials, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan
Grigory Simin
Low-temperature photoluminescence investigations have been carried out in the quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by pulsedmetalorganic chemical-vapor deposition (PMOCVD). With increasing excitation power density, the emission peaks in both AlInGaN epilayers and MQWs show a strong blueshift and theirlinewidths increase. The luminescence of the samples grown by PMOCVD is attributed to recombination of carriers/excitons localized at band-tail states. We also demonstrate theluminescence properties of AlInGaN and AlGaN materials grown by a pulsed atomic-layerepitaxy and conventional MOCVD, respectively.
Plasmonics On The Slope Of Enlightenment: The Role Of Transition Metal Nitrides, U. Guler, A. Kildishev, A. Boltasseva, V. Shalaev
Plasmonics On The Slope Of Enlightenment: The Role Of Transition Metal Nitrides, U. Guler, A. Kildishev, A. Boltasseva, V. Shalaev
U. Guler
The key problem currently faced by plasmonics is related to material limitations. After almost two decades of extreme excitement and research largely based on the use of noble metals, scientists have come to a consensus on the importance of exploring alternative plasmonic materials to address application-specific challenges to enable the development of new functional devices. Such a change in motivation will undoubtedly lead to significant advancements in plasmonics technology transfer and could have a revolutionary impact on nanophotonic technologies in general. Here, we report on one of the approaches that, together with other new material platforms, mark an insightful technology-driven …