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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Dramatic enhancement of 1.54 μm emission in Er doped GaN quantum well structures

Erbium (Er) doped III-nitride materials have attracted much attention due to their capability to provide highly thermal stable optical emission in the technologically important as well as eye-safer 1540 nm wavelength window. There is a continued need to exploring effective mechanisms to further improve the quantum efficiency (QE) of the 1.54 μm emission in Er-doped III-nitrides. GaN/AlN multiple quantum wells (MQWs:Er) have been synthesized by metal organic chemical vapor deposition and explored as an effective means to improve the QE of the 1.54 μm emission via carrier confinement and strain engineering. The 1.54 μm emission properties from MQWs:Er were probed by photoluminescence (PL) emission spectroscopy. It was found that the emission intensity from MQWs:Er is 9 times higher than that of GaN:Er epilayers with a comparable Er active layer thickness. The influences of the well and barrier width on the PL emission at 1.54 μm were studied. The results revealed that MQWs:Er consisting of well width between 1 and 1.5 nm and the largest possible barrier width before reaching the critical thickness provide the largest boost in QE of the 1.54 μm emission. These results demonstrate that MQWs:Er provide a basis for efficient photonic devices active at 1.54 μm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Nanocrystalline Si/SiO{sub 2} core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

We report the fabrication of a stable Si/SiO{sub 2} core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiO{sub x} matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Flux-driven algebraic damping of diocotron modes

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 and m = 2 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius R{sub m}, where there is a matching of ω{sub m} = mω{sub E} (R{sub m}) for the mode frequency ω{sub m} and E × B-drift rotation frequency ω{sub E}. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This new mechanism of damping is due to transfer of canonical angular momentum from the mode to halo particles, as they are swept around the “cat’s eye” orbits of the resonant wave-particle interaction. This paper provides a simple derivation of the time dependence of the mode amplitudes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Assessment of natural radioactivity concentrations and gamma dose levels around Shorapur, Karnataka

This study assesses the level of background radiation around Shorapur. The study region locates the western part of the Yadgir district of Karnataka. Shorapur and Shahapur talukas are mostly composed of clay, shale sandstone, granite rock and part of study area is black soil. Thirty sample locations were selected along the length and breadth of Shorapur and Shahapur taluka. Natural radionuclide activity concentrations in soil samples were determined using 4'X4' NaI (Tl) gamma spectroscopy. Outdoor gamma dose measurements in air at 1 m above ground level were determined using Rad Eye PRD survey meter. Estimated dose values are compared with the survey meter values and found to be good agreement between them and also with the data obtained from different other areas of Karnataka and India. The average values were found to be slightly higher in the present investigation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Light fidelity (Li-Fi): An effective solution for data transmission

The rapid advancement in the field of science has led to the development of many technologies, gadgets and equipment which in turn has hold pressure on Wi-Fi, modems, board band connections etc., to lessen this stress new revolution in this field has rooted on termed “LI-FI”. Li-Fi stands for light fidelity i.e. light is used for the transmission of data. The concept of Li-Fi is taking the fiber out of fiber optics sending information through an LED that varies in intensity faster than human eye can follow. Li-Fi offers an entirely new paradigm in wireless technology in term of communication, speed, flexibility, usability etc. The idea of data through illumination is similar to radio waves communication difference lies in the use of LED in LI-Fi, which made it superior than Wi-Fi. Hence Li-Fi is linked to the visible light communication network provision transmission which is looked upon as an advancement. Thus a new class of light with high intensity light source of solid state design bringing clean lighting solution to general and specialty lighting. With energy efficiency, long useful lifetime, full spectrum and dimming. Li-Fi is just not only confined to light and LED indeed it is a platform with versatile advantages and facilities. This paper gives a brief idea about the introduction of Li-Fi, its working, advantages, limitations etc.

42 ENGINEERING↗
DOE OSTI2016

Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Observation of low voltage driven green emission from erbium doped Ga{sub 2}O{sub 3} light-emitting devices

Erbium doped Ga{sub 2}O{sub 3} thin films were deposited on Si substrate by pulsed laser deposition method. Bright green emission (∼548 nm) can be observed by naked eye from Ga{sub 2}O{sub 3}:Er/Si light-emitting devices (LEDs). The driven voltage of this LEDs is 6.2 V which is lower than that of ZnO:Er/Si or GaN:Er/Si devices. Since the wide bandgap of Ga{sub 2}O{sub 3} contain more defect-related level which will enhance the effects of recombination between electrons in the defect-related level and the holes in the valence band, resulting in the improvement of the energy transfer to Er ions. We believe that this work paves the way for the development of Si-based green LEDs by using wide bandgap Ga{sub 2}O{sub 3} as the host materials for Er{sup 3+} ions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Self-similarity and scaling transitions during rupture of thin free films of Newtonian fluids

Rupture of thin liquid films is crucial in many industrial applications and nature such as foam stability in oil-gas separation units, coating flows, polymer processing, and tear films in the eye. In some of these situations, a liquid film may have two free surfaces (referred to here as a free film or a sheet) as opposed to a film deposited on a solid substrate that has one free surface. The rupture of such a free film or a sheet of a Newtonian fluid is analyzed under the competing influences of inertia, viscous stress, van der Waals pressure, and capillary pressure by solving a system of spatially one-dimensional evolution equations for film thickness and lateral velocity. The dynamics close to the space-time singularity where the film ruptures is asymptotically self-similar and, therefore, the problem is also analyzed by reducing the transient partial differential evolution equations to a corresponding set of ordinary differential equations in similarity space. Here, for sheets with negligible inertia, it is shown that the dominant balance of forces involves solely viscous and van der Waals forces, with capillary force remaining negligible throughout the thinning process in a viscous regime. On the other hand, for a sheet of an inviscid fluid for which the effect of viscosity is negligible, it is shown that the dominant balance of forces is between inertial, capillary, and van der Waals forces as the film evolves towards rupture in an inertial regime. Real fluids, however, have finite viscosity. Hence, for real fluids, it is further shown that the viscous and the inertial regimes are only transitory and can only describe the initial thinning dynamics of highly viscous and slightly viscous sheets, respectively. Moreover, regardless of the fluid’s viscosity, it is shown that for sheets that initially thin in either of these two regimes, their dynamics transition to a late stage or final inertial-viscous regime in which inertial, viscous, and van der Waals forces balance each other while capillary force remains negligible, in accordance with the results of Vaynblat, Lister, and Witelski.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Probing the remarkable thermal kinetics of visual rhodopsin with E181Q and S186A mutants

We recently reported a very unusual temperature dependence of the rate of thermal reaction of wild type bovine rhodopsin: the Arrhenius plot exhibits a sharp “elbow” at 47 °C and, in the upper temperature range, an unexpectedly large activation energy (114 ± 8 kcal/mol) and an enormous prefactor (10 72±5 s -1 ). In this report, we present new measurements and a theoretical model that establish convincingly that this behavior results from a collective, entropy-driven breakup of the rigid hydrogen bonding networks (HBNs) that hinder the reaction at lower temperatures. For E181Q and S186A, two rhodopsin mutants that disrupt the HBNs near the binding pocket of the 11-cis retinyl chromophore, we observe significant decreases in the activation energy (~90 kcal/mol) and prefactor (~10 60 s -1 ), consistent with the conclusion that the reaction rate is enhanced by breakup of the HBN. Finally, the results provide insights into the molecular mechanism of dim-light vision and eye diseases caused by inherited mutations in the rhodopsin gene that perturb the HBNs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Low-dark current 10 Gbit/s operation of InAs/InGaAs quantum dot p-i-n photodiode grown on on-axis (001) GaP/Si

We demonstrate 10 Gbit/s operation of InAs/InGaAs quantum dot (QD) p-i-n photodiodes (PDs) grown on on-axis (001) GaP/Si substrates. A 3.0 × 50 μm2 QD PD shows a small dark current of 0.2 nA at a bias voltage of −3 V, which corresponds to a dark current density of 0.13 mA/cm2. This low-dark current characteristic obtained from a narrow-stripe device indicates that sidewall and threading dislocations have small effects on the dark current. The 3 dB bandwidth was 5.5 GHz at a bias voltage of −5 V. Large signal measurement with non-return-to-zero signals shows 10 Gbit/s eye opening.

Inoue, D.↗
DOE OSTI2020

Nanosecond carrier lifetimes in solution-processed enargite (Cu 3 AsS 4 ) thin films

Enargite (ENG) Cu 3 AsS 4 is a promising material for photovoltaic applications due to its constituent earth abundant elements of differing ionic radii, ideal predicted optoelectronic properties, and demonstrated use in a working thin-film solar cell. However, little is known about ENG's defect properties; such knowledge is necessary to assess its potential for future use in high-efficiency devices. One indicator of a material's quality is its photogenerated carrier lifetime, which can be related to its bulk defect properties. Here, we use a combination of time-resolved terahertz spectroscopy and time-resolved photoluminescence to assess carrier dynamics in ENG thin films processed from nanoparticle precursors. The Shockley–Read–Hall (SRH) lifetimes are on the multi-nanosecond scale, which exceed those reported in more mature systems and represent promising values for a candidate photovoltaic material. These results suggest that ENG is worthy of further research and development effort with an eye toward future photovoltaic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Synchrotron studies of functional interfaces and the state of the art: A perspective

The dramatic improvements in synchrotron light sources across the world imply tremendous opportunities for interface science. In this work, we describe a variety of current scattering and spectroscopic techniques with an eye toward how these will evolve, particularly with the advent of diffraction-limited sources. We also note the importance of in situ and operando methods for both understanding interface creation and interface evolution in different environments. As interfaces are often where critical processes occur, whether in regard to energy/chemical/materials/quantum information science, understanding the utility of these x-ray techniques will be of considerable importance to the cultivation of next-generation scientists.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Flux-driven algebraic damping of m = 2 diocotron mode

Experiments with pure electron plasmas in a Malmberg–Penning trap have observed linear in time, algebraic damping of m = 2 diocotron modes. Transport due to small field asymmetries produces a low-density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius of the mode. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from spatial Landau damping in which a linear wave–particle resonance produces exponential damping. This paper reports an analytic theory that captures the main signatures reported for this novel damping, namely, that the damping begins when the halo particles reach the resonant radius and that the damping is algebraic in time with nearly constant damping rate. The model also predicts a nonlinear frequency shift. The model provides two ways to think about the damping. It results from a transfer of canonical angular momentum from the mode to halo particles being swept by the mode field through the nonlinear cat's eye orbits of the resonant region. More mechanistically, the electric field produced by the perturbed charge density of the resonant particles acts back on the plasma core causing E × B drift that gives rise to the damping and nonlinear frequency shift.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Specific features of diffuse reflection of human face skin for laser and non-laser sources of visible and near-IR light

The specific features of diffuse reflection from different areas of human face skin for laser and non-laser sources of visible and near-IR light have been investigated to localise the closed-eye (eyelid) region. In the visible spectral range the reflection from the eyelid skin surface can be differentiated by measuring the slope of the spectral dependence of the effective optical density of skin in the wavelength range from 650 to 700nm. In the near-IR spectral range the reflectances of the skin surface at certain wavelengths, normalised to the forehead skin reflectance, can be used as a criterion for differentiating the eyelid skin. In this case, a maximum discrimination is obtained when measuring the skin reflectances at laser wavelengths of 1310 and 1470nm, which correspond to the spectral ranges of maximum and minimum water absorption. (optical technologies in biophysics and medicine)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Scattering of light passing through a statistically rough interface between media with different refractive indices after laser correction of vision

Forward scattering of light passing through large-scale irregularities of the interface between two media having different refractive indices is considered. An analytical expression for the ratio of intensities of directional and diffusion components of scattered light in the far-field zone is derived. It is theoretically shown that the critical depth of possible interface relief irregularities, starting from which the intensity of the diffuse component in the passing light flow becomes comparable with the directional light component, responsible for the image formation on the eye retina, is 3 - 4 {mu}m, with the increase in the refractive index in the postoperational zone taken into account. These profile depth values agree with the experimentally measured ones and may affect the contrast sensitivity of vision.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Nanosensitive optical coherence tomography for the study of changes in static and dynamic structures

We briefly discuss the principle of image formation in Fourier domain optical coherence tomography (OCT). The theory of a new approach to improve dramatically the sensitivity of conventional OCT is described. The approach is based on spectral encoding of spatial frequency. Information about the spatial structure is directly translated from the Fourier domain to the image domain as different wavelengths, without compromising the accuracy. Axial spatial period profiles of the structure are reconstructed for any volume of interest within the 3D OCT image with nanoscale sensitivity. An example of application of the nanoscale OCT to probe the internal structure of medico-biological objects, the anterior chamber of an ex vivo rat eye, is demonstrated. (laser biophotonics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Potentialities of laser systems for remote sensing of the atmosphere at a wide variability of optical and physical characteristics: dimensionless-parametric modelling

Within the framework of generalisation of different approaches to the modelling of atmospheric lidars, the methodology capabilities for dimensionless-parametric analysis are expanded. The developed approach simplifies the analysis of the signal-to-noise ratio and potential capabilities of existing and newly developed monitoring systems with a wide variability of atmospheric and optical conditions and a great variety of modern lidars. Its applicability to the problems of remote atmospheric sensing, environmental monitoring and lidar navigation in providing the eye safety, noise immunity and reliability is discussed. (paper)

42 ENGINEERING↗
DOE OSTI2017

High-power optical parametric oscillator based on a high-pulse repetition rate, master Nd : KGW laser

An optical scheme of an optical parametric oscillator with a master laser based on an Nd : KGW active element excited by two orthogonally oriented diode side pump modules is proposed to form radiation pulses with energies above 30 mJ and a repetition rate of 1 – 20 Hz in the eye-safe spectral range of 1.5 – 1.6 μm. The two-module excitation of the active medium makes the distribution of the master laser radiation intensity in the output beam cross section more uniform and provides a reliable operation of the optical parametric oscillator. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗