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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Near-field infrared imaging of polar domain walls in Ni 3 TeO 6

Domain walls are leading platforms for the development of ultra-low power switching and memory devices due to their potential to be moved, created, and erased in real time and to mitigate heat flux. Interface vs wavelength size effects unfortunately preclude the measurement of phonons by traditional spectroscopic techniques, so it has been challenging to unravel the primary excitations of the lattice and the symmetries that they represent across these functional interfaces. In this work, we employ synchrotron-based near-field infrared nanospectroscopy to image polar domain walls in multiferroic Ni 3 TeO 6 . This is a unique platform because, in addition to hosting polar and chiral domains that are interlocked with one another, Ni 3 TeO 6 displays both charged and neutral interfaces depending upon the direction allowing the development of structure–property relations. From a local structure and a strain point of view, we find charged walls that are twice as wide as neutral walls as well as strong frequency shifts of vibrational modes across the charged walls. The near-field amplitude drops across the walls as well. We discuss these trends in terms of polarization and chirality as well as phonon lifetimes at functional interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Properties of V-defect injectors in long wavelength GaN LEDs studied by near-field electro- and photoluminescence

The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermionic emission out of the QWs. In InGaN/GaN QWs, the thermionic hole transport is hindered by the high quantum confinement and polarization barriers. To overcome this drawback, hole injection through semipolar QWs located at sidewalls of V-defects had been proposed. However, in the case of the V-defect injection, strong lateral emission variations take place. In this work, we explore the nature of these variations and the impact of the V-defects on the emission spectra and carrier dynamics. The study was performed by mapping electroluminescence (EL) and photoluminescence (PL) with a scanning near-field optical microscope in LEDs that contain a deeper well that can only be populated by holes through the V-defects. Applying different excitation schemes (electrical injection and optical excitation in the far- and near-field), we have shown that the EL intensity variations are caused by the lateral nonuniformity of the hole injection. We have also found that, in biased structures, the PL intensity and decay time in the V-defect regions are only moderately lower that in the V-defect-free regions thus showing no evidence of an efficient Shockley-–Read–Hall recombination. In the V-defect regions, the emission spectra experience a red shift and increased broadening, which suggests an increase of the In content and well width in the polar QWs close to the V-defects.

Electroluminescence↗
DOE OSTI2020

Symmetry crossover in layered MPS 3 complexes (M=Mn, Fe, Ni) via near-field infrared spectroscopy

In this paper, we employ synchrotron-based near-field infrared spectroscopy to reveal the vibrational properties of bulk, few-sheet, and single-sheet members of the MPS 3 (M=Mn, Fe, Ni) family of materials and compare our findings with complementary lattice dynamics calculations. MnPS 3 and the Fe analog are similar in terms of their symmetry crossovers, from C2/ m to P $\bar{3}$1 m , as the monolayer is approached. These states differ as to the presence of a C 3 rotation around the metal center. On the other hand, NiPS 3 does not show a symmetry crossover, and the lack of a B u symmetry mode near 450 cm -1 suggests that C 3 rotational symmetry is already present, even in the bulk material. We discuss these findings in terms of local symmetry and temperature effects as well as the curious relationship between these symmetry transformations and those that take place under pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Near-field probing of strong light-matter coupling in single IR antennae

Quantum well intersubband polaritons are traditionally studied in large scale ensembles, over many wavelengths in size.In this presentation, we demonstrate that it is possible to detect and investigate intersubband polaritons in a single sub-wavelength nanoantenna in the IR frequency range. We observe polariton formation using a scattering-type near-fieldmicroscope and nano-FTIR spectroscopy. In this work, we will discuss near-field spectroscopic signatures of plasmonic antennae withand without coupling to the intersubband transition in quantum wells located underneath the antenna. Evanescent fieldamplitude spectra recorded on the antenna surface show a mode anti-crossing behavior in the strong coupling case. Wealso observe a corresponding strong-coupling signature in the phase of the detected field. We anticipate that this near-fieldapproach will enable explorations of strong and ultrastrong light-matter coupling in the single nanoantenna regime,including investigations of the elusive effect of ISB polariton condensation.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Near-field antenna testing using the Hewlett Packard 8510 automated network analyzer

Near-field antenna measurements were made using a Hewlett-Packard 8510 automated network analyzer. This system features measurement sensitivity better than -90 dBm, at measurement speeds of one data point per millisecond in the fast data acquisition mode. The system was configured using external, even harmonic mixers and a fiber optic distributed local oscillator signal. Additionally, the time domain capability of the HP8510, made it possible to generate far-field diagnostic results immediately after data acquisition without the use of an external computer.

Kunath, Richard R.↗
NASA NTRS1995

Satellite observations of zonal electric fields near sunrise in the equatorial ionosphere

We report here on a number of examples of anomalous enhancements of eastward electric fields near sunrise in the equatorial ionospheric F-region. These examples were selected from the data base of the equatorial satellite, San Marco D (1988), which measured ionospheric electric fields during a period of solar minimum. The eastward electric fields reported correspond to vertical plasma drifts. The examples studied here are similar in signature and polarity to the pre-reversal electric field enhancements seen near sunset from ground-based radar systems. The morphology of these sunrise events, which are observed on about 14% of the morning-side satellite passes, are studied as a function of local zonal velocity, magnetic activity, geographic longitude and altitude. The nine events studied occur at locations where the zonal plasma flow is generally measured to be eastward, but reducing as a function of local time and at satellite longitudes where the magnetic declination has the opposite polarity as the declination of the sunrise terminator.

Aggson, T. L.↗
NASA NTRS2006

Modeling of the Near Field Coupling Between an External Loop and an Implantable Spiral Chip Antennas in Biosensor Systems

In this paper, the near field coupling between an external hand-held loop antenna and an implantable miniature (1x1 mm) printed square spiral chip antenna used in bio-MEMS sensors for contact-less powering and RF telemetry is investigated. The loop and the spiral are inductively coupled and effectively form a transformer. The numerical results include the quasi-stationary magnetic field pattern of the implanted antenna, near zone wave impedance as a function of the radial distance and the values of the lumped elements in the equivalent circuit model for the transformer.

Simons, Rainee N.↗
NASA NTRS1972

Magnetic dipole moment determination by near-field analysis

A method for determining the magnetic moment of a spacecraft from magnetic field data taken in a limited region of space close to the spacecraft. The spacecraft's magnetic field equations are derived from first principles. With measurements of this field restricted to certain points in space, the near-field equations for the spacecraft are derived. These equations are solved for the dipole moment by a least squares procedure. A method by which one can estimate the magnitude of the error in the calculations is also presented. This technique was thoroughly tested on a computer. The test program is described and evaluated, and partial results are presented.

Eichhorn, W. L.↗
NASA NTRS1990

Analysis of near-field Cassegrain reflector - Plane wave versus element-by-element approach

A near-field Cassegrain reflector (NFCR) is an effective way to magnify a small phased array into a much larger-aperture antenna for limited scan applications. Traditionally the pattern analysis of NFCR is based on a plane wave approach, which simplifies the computation tremendously, but fails to provide design information about the most critical component of the whole antenna system, the feed array. Currently available computers make it possible to calculate the pattern of an NFCR by a more exact element-by-element approach. Each element in the feed array is considered individually, and the diffraction pattern from the subreflector is calculated by the geometrical theory of diffraction (including uniform theories at the shadow boundaries). The field contributions from all elements are superimposed at the curved main reflector surface, and a physical-optics integration is performed to obtain the secondary pattern.

Houshmand, Bijan↗
NASA NTRS1992

Ground signature extrapolation of three-dimensional near-field CFD predictions for several HSCT configurations

A CFD analysis of the near-field sonic boom environment of several low boom High Speed Civilian Transport (HSCT) concepts is presented. The CFD method utilizes a multi-block Euler marching code within the context of an innovative mesh topology that allows for the resolution of shock waves several body lengths from the aircraft. Three-dimensional pressure footprints at one body length below three-different low boom aircraft concepts are presented. Models of two concepts designed by NASA to cruise at Mach 2 and Mach 3 were built and tested in the wind tunnel. The third concept was designed by Boeing to cruise at Mach 1.7. Centerline and sideline samples of these footprints are then extrapolated to the ground using a linear waveform parameter method to estimate the ground signatures or sonic boom ground overpressure levels. The Mach 2 concept achieved its centerline design signature but indicated higher sideline booms due to the outboard wing crank of the configuration. Nacelles are also included on two of NASA's low boom concepts. Computations are carried out for both flow-through nacelles and nacelles with engine exhaust simulation. The flow-through nacelles with the assumption of zero spillage and zero inlet lip radius showed very little effect on the sonic boom signatures. On the other hand, it was shown that the engine exhaust plumes can have an effect on the levels of overpressure reaching the ground depending on the engine operating conditions. The results of this study indicate that engine integration into a low boom design should be given some attention.

Siclari, M. J.↗
NASA NTRS2007

On the Magnitude of the Electric Field Near Thunderstorm-Associated Clouds

Electric field measurements made in and near clouds during two airborne field mill programs are presented. Aircraft equipped with multiple electric field mills and cloud physics sensors were flown near active convection and into thunderstorm anvil and debris clouds. The magnitude of the electric field was measured as a function of position with respect to the cloud edge in order to provide an observational basis for modifications to the lightning launch commit criteria (LLCC) used by the U.S. space program. These LLCC are used to reduce the risk that an ascending launch vehicle will trigger a lightning strike that could cause the loss of the mission or vehicle. The results suggest that even with fields of tens of kV/m inside electrically active convective clouds, the fields external to these clouds decay to less than 3 kV/m within fifteen kilometers of cloud edge. Fields exceeding 3 kV/m were not found external to anvil and debris clouds.

Merceret, Francis J.↗
DOE OSTI2024

Near-Field Nanoimaging of Colloidal Transition Metal Dichalcogenide Waveguides

Bulk transition metal dichalcogenide (TMDC) nanostructures are regarded as promising material candidates for integrated photonics due to their high refractive index at the near-infrared wavelengths. Here in this work, colloidal TMDC waveguides with tailorable dimensions are prepared by a scalable synthetic approach. The optical waveguiding properties of colloidal nanowires are studied by the near-field nanoimaging technique. In addition to dependence on thickness and wavelength, the excitonic responses and resultant waveguide modes in TMDC nanowires can be modulated by the environmental temperature. With the high-throughput production and tunable optical properties, colloidal TMDC nanowires highlight the potential for active optical components and integrated photonic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Scattering-type Scanning Near-Field Optical Microscopy of Polymer-Coated Gold Nanoparticles

Scattering-type scanning near-field optical microscopy (s-SNOM) has emerged over the past years as a powerful characterization tool that can probe important properties of advanced materials and biological samples in a label-free manner, with spatial resolutions lying in the nanoscale realm. In this work, we explore such usefulness in relationship with an interesting class of materials: polymer-coated gold nanoparticles (NPs). As thoroughly discussed in recent works, the interplay between the Au core and the polymeric shell has been found to be important in many applications devoted to biomedicine. We investigate bare Au NPs next to polystyrenesulfonate (PSS) and poly(diallyldimethylammonium chloride) (PDDA) coated ones under 532 nm laser excitation, an wavelength matching the surface plasmon band of the custom-synthesized nanoparticles. We observe consistent s-SNOM phase signals in the case of bare and shallow-coated Au NPs, whereas for thicker shell instances, these signals fade. For all investigated samples, the s-SNOM amplitude signals were found to be very weak, which may be related to reduced scattering efficiency due to absorption of the incident beam. We consider these observations important, as they may facilitate studies and applications in nanomedicine and nanotechnology where the precise positioning of polymer-coated Au NPs with nanoscale resolution is needed besides their dielectric function and related intrinsic optical properties, which are also quantitatively available with s-SNOM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Noise predictions of a high bypass turbofan engine using the Lockheed Near-Field Noise Prediction Program

The prediction of engine noise during cruise using the Near-Field Noise Prediction Program developed by Lockheed is examined. Test conditions were established which simulate the operation of a high bypass turbofan engine under a wide range of operating conditions. These test conditions include variations in altitude, flight Mach number and thrust setting. Based on the results of noise prediction made using the Lockheed program, an evaluation of the impact of these test conditions on the overall sound pressure level(OASPL)and the one-third octave band spectra is made. An evaluation of the sensitivity of flight condition parameters is also made. The primary noise source from a high bypass turbofan was determined to be fan broadband shock noise. This noise source can be expected to be present during normal cruising conditions. When present, fan broadband shock noise usually dominates at all frequencies and all directivity angles. Other noise sources of importance are broadband shock noise from the primary jet, fan noise, fan mixing noise and turbine noise.

Rawls, J. W., Jr.↗