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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Site specific isolated nanostructure array formation on a large area by broad ion beam without any mask and resist

We report the formation of isolated nanostructure arrays on a large area via broad ion beam implantation without the aid of any mask or resist. Desired ions have been implanted at specific locations of the prefabricated silicon ripple or triangular structures by exploiting the variation of local ion impact angles. We have shown that the implantation of Fe ions on an O{sup +} ions induced pre fabricated triangular shaped patterned Si surface results in a self-organized periodic array of striped magnetic nanostructures having several micron length and about 50 nm width arranged with a spacial separation of ∼200 nm. The morphology, composition, crystalline structure, and magnetic property of these nanopatterns have been analyzed using high-resolution cross-sectional transmission electron microscopy and atomic force microscopy. A geometrical model has been proposed to explain the fundamental features of such ion-induced nanopattern structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2010

Large-Format AlGaN PIN Photodiode Arrays for UV Images

A large-format hybridized AlGaN photodiode array with an adjustable bandwidth features stray-light control, ultralow dark-current noise to reduce cooling requirements, and much higher radiation tolerance than previous technologies. This technology reduces the size, mass, power, and cost of future ultraviolet (UV) detection instruments by using lightweight, low-voltage AlGaN detectors in a hybrid detector/multiplexer configuration. The solar-blind feature eliminates the need for additional visible light rejection and reduces the sensitivity of the system to stray light that can contaminate observations.

Aslam, Shahid↗
NASA NTRS1990

Large-format electrographic and array detectors for a space Schmidt imaging telescope

Possible optical designs of imaging detectors for the spaceborne Schmidt telescope proposed by Carruthers et al. (1990) are discussed, surveying the currently or potentially available technology. Consideration is given to FUV electrographic detectors of large format (e.g., 120 mm with 10-micron resolution) using CsI photocathodes, the possible extension of the same technology to the mid-UV using Cs2Te instead of CsI, large CCD arrays for the visible and NIR, electron-bombarded CCDs for the FUV and mid-UV, and the data handling and processing requirements of these detectors.

Carruthers, George R.↗
DOE OSTI2017

Three-dimensional crossbar arrays of self-rectifying Si/SiO 2 /Si memristors

Memristors are promising building blocks for the next generation memory, unconventional computing systems and beyond. Currently common materials used to build memristors are not necessarily compatible with the silicon dominant complementary metal-oxide-semiconductor (CMOS) technology. Furthermore, external selector devices or circuits are usually required in order for large memristor arrays to function properly, resulting in increased circuit complexity. Here we demonstrate fully CMOS-compatible, all-silicon based and self-rectifying memristors that negate the need for external selectors in large arrays. It consists of p- and n-type doped single crystalline silicon electrodes and a thin chemically produced silicon oxide switching layer. The device exhibits repeatable resistance switching behavior with high rectifying ratio (10 5 ), high ON/OFF conductance ratio (10 4 ) and attractive retention at 300 °C. We further build a 5-layer 3-dimensional (3D) crossbar array of 100 nm memristors by stacking fluid supported silicon membranes. The CMOS compatibility and self-rectifying behavior open up opportunities for mass production of memristor arrays and 3D hybrid circuits on full-wafer scale silicon and flexible substrates without increasing circuit complexity.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Technique for Extension of Small Antenna Array Mutual-Coupling Data to Larger Antenna Arrays

A technique is presented whereby the mutual interaction between a small number of elements in a planar array can be interpolated and extrapolated to accurately predict the combined interactions in a much larger array of many elements. An approximate series expression is developed, based upon knowledge of the analytical characteristic behavior of the mutual admittance between small aperture antenna elements in a conducting ground plane. This expression is utilized to analytically extend known values for a few spacings and orientations to other element configurations, thus eliminating the need to numerically integrate a large number of highly oscillating and slowly converging functions. This paper shows that the technique can predict very accurately the mutual coupling between elements in a very large planar array with a knowledge of the self-admittance of an isolated element and the coupling between only two-elements arranged in eight different pair combinations. These eight pair combinations do not necessarily have to correspond to pairs in the large array, although all of the individual elements must be identical.

Bailey, M. C.↗
DOE OSTI2017

Galaxies into the Dark Ages

We consider the capabilities of current and future large facilities operating at 2–3 mm wavelength to detect and image the [C ii] 158 μm line from galaxies into the cosmic “dark ages” (z ∼ 10–20). The [C ii] line may prove to be a powerful tool in determining spectroscopic redshifts, and galaxy dynamics, for the first galaxies. We emphasize that the nature, and even existence, of such extreme redshift galaxies, remains at the frontier of open questions in galaxy formation. In 40 hr, the Atacama Large Millimeter Array has the sensitivity to detect the integrated [C ii] line emission from a moderate metallicity, active star-forming galaxy [Z{sub A}=0.2 Z{sub ⊙}; star formation rate (SFR)=5 M{sub ⊙} yr{sup −1}], at z = 10 at a significance of 6σ. The next-generation Very Large Array (ngVLA) will detect the integrated [C ii] line emission from a Milky Way–like SFR galaxy (Z{sub A}=0.2 Z{sub ⊙}, SFR=1 M{sub ⊙} yr{sup −1}), at z = 15 at a significance of 6σ. Imaging simulations show that the ngVLA can determine rotation dynamics for active star-forming galaxies at z∼15, if they exist. Based on our very limited knowledge of the extreme redshift universe, we calculate the count rate in blind, volumetric surveys for [C ii] emission at z∼10–20. The detection rates in blind surveys will be slow (of the order of unity per 40 hr pointing). However, the observations are well suited to commensal searches. We compare [C ii] with the [O iii] 88 μm line, and other ancillary information in high z galaxies that would aid these studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Compact, ∼1 kpc Host Galaxy of a Quasar at a Redshift of 7.1

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C ii] fine-structure line and the underlying far-infrared (FIR) dust continuum emission in J1120+0641, the most distant quasar currently known (z=7.1). We also present observations targeting the CO(2–1), CO(7–6), and [C i] 369 μm lines in the same source obtained at the Very Large Array and Plateau de Bure Interferometer. We find a [C ii] line flux of F{sub [CII]}=1.11±0.10 Jy km s{sup −1} and a continuum flux density of S{sub 227GHz}=0.53±0.04 mJy beam{sup −1}, consistent with previous unresolved measurements. No other source is detected in continuum or [C ii] emission in the field covered by ALMA (∼ 25″). At the resolution of our ALMA observations (0.″23, or 1.2 kpc, a factor of ∼70 smaller beam area compared to previous measurements), we find that the majority of the emission is very compact: a high fraction (∼80%) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter. The remaining ∼20% of the emission is distributed over a larger area with radius ≲4 kpc. The [C ii] emission does not exhibit ordered motion on kiloparsec scales: applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of (4.3±0.9)×10{sup 10} M{sub ⊙}, only ∼20 × higher than the central black hole (BH). The other targeted lines (CO(2–1), CO(7–6), and [C i]) are not detected, but the limits of the line ratios with respect to the [C ii] emission imply that the heating in the quasar host is dominated by star formation, and not by the accreting BH. The star formation rate (SFR) implied by the FIR continuum is 105–340 M{sub ⊙} yr{sup −1}, with a resulting SFR surface density of ∼100–350 M{sub ⊙} yr{sup −1} kpc{sup −2}, well below the value for Eddington-accretion-limited star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

An extremely high velocity molecular jet surrounded by an ionized cavity in the protostellar source Serpens SMM1

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of a one-sided, high-velocity (∼80 km s{sup −1}) CO(J = 2→1) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free–free emission detected by the Very Large Array and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free–free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA observations of the Antennae galaxies. I. A new window on a prototypical merger

We present the highest spatial resolution (≈0.''5) CO (3-2) observations to date of the 'overlap' region in the merging Antennae galaxies (NGC 4038/39), taken with the Atacama Large Millimeter/submillimeter Array. We report on the discovery of a long (3 kpc), thin (aspect ratio 30/1), filament of CO gas that breaks up into roughly 10 individual knots. Each individual knot has a low internal velocity dispersion (≈10 km s{sup –1}); the dispersion of the ensemble of knots in the filament is also low (≈10 km s{sup –1}). At the other extreme, we find that the individual clouds in the supergiant molecular cloud 2 region discussed by Wilson and collaborators have a large range of internal velocity dispersions (10 to 80 km s{sup –1}), and a large dispersion among the ensemble (≈80 km s{sup –1}). Other large-scale features observed in CO emission, and their correspondence with historical counterparts using observations in other wavelengths, are also discussed. We compare the locations of small-scale CO features with a variety of multi-wavelength observations, in particular broad- (BVIJH) and narrow-band data (H{sub α} and Pa{sub β}) taken with the Hubble Space Telescope, and radio (3.6 cm) continuum observations taken with the Karl G. Jansky Very Large Array. This comparison leads to the development of an evolutionary classification system that provides a framework for studying the sequence of star cluster formation and evolution—from diffuse supergiant molecular clouds (SGMCs) to proto, embedded, emerging, young, intermediate/old clusters. The relative timescales have been assessed by determining the fractional population of sources at each evolutionary stage. The main uncertainty in this estimate is the identification of four regions as candidate protoclusters (i.e., strong compact CO emission but no clearly associated radio emission). Using the evolutionary framework, we estimate that the maximum age range of clusters in a single GMC is ≈10 Myr, which suggests that the molecular gas is removed over this timescale, resulting in the cessation of star formation and the destruction of the GMC within a radius of about 200 pc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

ALMA observation of the disruption of molecular gas in M87

We present the results from Atacama Large Millimeter Array (ALMA) observations centred 40 arcsec (3 kpc in projection) south-east of the nucleus of M87. Here, we report the detection of extended CO (2–1) line emission with a total flux of (5.5 ± 0.6) × 10 -18 erg s -1 cm -2 and corresponding molecular gas mass M $H{_2}$ =(4.7±0.4)×10 5 M ⊙ , assuming a Galactic CO to H 2 conversion factor. ALMA data indicate a line-of-sight velocity of -129 ± 3 km s -1 , in good agreement with measurements based on the [C II] and H α+[N II] lines, and a velocity dispersion of σ = 27 ± 3 km s -1 . The CO (2–1) emission originates only outside the radio lobe of the active galactic nucleus (AGN) seen in the 6 cm Very Large Array image, while the filament prolongs further inwards at other wavelengths. The molecular gas in M87 appears to be destroyed or excited by AGN activity, either by direct interaction with the radio plasma, or by the shock driven by the lobe into the X-ray emitting atmosphere. This is an important piece of the puzzle in understanding the impact of the central AGN on the amount of the coldest gas from which star formation can proceed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Evidence of Radio Polarization Induced by the Radiative Grain Alignment and Self-scattering of Dust Grains in a Protoplanetary Disk

The mechanisms causing millimeter-wave polarization in protoplanetary disks are under debate. To disentangle the polarization mechanisms, we observe the protoplanetary disk around HL Tau at 3.1 mm with the Atacama Large Millimeter/submillimeter Array (ALMA), which had the polarization detected with CARMA at 1.3 mm. We successfully detect the ring-like azimuthal polarized emission at 3.1 mm. This indicates that dust grains are aligned with the major axis being in the azimuthal direction, which is consistent with the theory of radiative alignment of elongated dust grains, where the major axis of dust grains is perpendicular to the radiation flux. Furthermore, the morphology of the polarization vectors at 3.1 mm is completely different from those at 1.3 mm. We interpret the polarization at 3.1 mm to be dominated by the grain alignment with the radiative flux producing azimuthal polarization vectors, while the self-scattering dominates at 1.3 mm and produces the polarization vectors parallel to the minor axis of the disk. By modeling the total polarization fraction with a single grain population model, the maximum grain size is constrained to be 100 μm, which is smaller than the previous predictions based on the spectral index between ALMA at 3 mm and the Very Large Array at 7 mm.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Fabrication of an Absorber-Coupled MKID Detector

Absorber-coupled microwave kinetic inductance detector (MKID) arrays were developed for submillimeter and far-infrared astronomy. These sensors comprise arrays of lambda/2 stepped microwave impedance resonators patterned on a 1.5-mm-thick silicon membrane, which is optimized for optical coupling. The detector elements are supported on a 380-mm-thick micro-machined silicon wafer. The resonators consist of parallel plate aluminum transmission lines coupled to low-impedance Nb microstrip traces of variable length, which set the resonant frequency of each resonator. This allows for multiplexed microwave readout and, consequently, good spatial discrimination between pixels in the array. The transmission lines simultaneously act to absorb optical power and employ an appropriate surface impedance and effective filling fraction. The fabrication techniques demonstrate high-fabrication yield of MKID arrays on large, single-crystal membranes and sub-micron front-to-back alignment of the micro strip circuit. An MKID is a detector that operates upon the principle that a superconducting material s kinetic inductance and surface resistance will change in response to being exposed to radiation with a power density sufficient to break its Cooper pairs. When integrated as part of a resonant circuit, the change in surface impedance will result in a shift in its resonance frequency and a decrease of its quality factor. In this approach, incident power creates quasiparticles inside a superconducting resonator, which is configured to match the impedance of free space in order to absorb the radiation being detected. For this reason MKIDs are attractive for use in large-format focal plane arrays, because they are easily multiplexed in the frequency domain and their fabrication is straightforward. The fabrication process can be summarized in seven steps: (1) Alignment marks are lithographically patterned and etched all the way through a silicon on insulator (SOI) wafer, which consists of a thin silicon membrane bonded to a thick silicon handle wafer. (2) The metal microwave circuitry on the front of the membrane is patterned and etched. (3) The wafer is then temporarily bonded with wafer wax to a Pyrex wafer, with the SOI side abutting the Pyrex. (4) The silicon handle component of the SOI wafer is subsequently etched away so as to expose the membrane backside. (5) The wafer is flipped over, and metal microwave circuitry is patterned and etched on the membrane backside. Furthermore, cuts in the membrane are made so as to define the individual detector array chips. (6) Silicon frames are micromachined and glued to the silicon membrane. (7) The membranes, which are now attached to the frames, are released from the Pyrex wafer via dissolution of the wafer wax in acetone.

Brown, Ari↗
NASA NTRS2021

Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations

We present the discovery of an extreme flaring event from Proxima Cen by the Australian Square Kilometre Array Pathfinder(ASKAP), Atacama Large Millimeter/submillimeter Array(ALMA), Hubble Space Telescope(HST),Transiting Exoplanet Survey Satellite(TESS), and the du Pont Telescope that occurred on 2019 May 1. In the millimeter and FUV, this flare is the brightest ever detected, brightening by a factor of>1000 and>14,000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Surprisingly, optical emission associated with the event peaks at a much lower level with a time delay. The initial burst has an extremely short duration, lasting for<10 s. Taken together with the growing sample of millimeter M dwarf flares, this event suggests that millimeter emission is actually common during stellar flares and often originates from short burst-like events.

Stellar activity↗
NASA NTRS2026

CH3OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH3OH/HCN Production Rate Ratio

We report the detection of methanol (CH3OH) toward interstellar comet 3I/ATLAS using the At-acama Compact Array of the Atacama Large Millimeter/Submillimeter Array (ALMA) on UT 2025 August 28, September 18 and 22, and October 1, and of hydrogen cyanide (HCN) on September 12 and 15. These observations spanned pre-perihelion heliocentric distances (r H ) of 2.6 – 1.7 au. The molecules showed outgassing patterns distinct from one another, with HCN production being depleted in the sunward hemisphere of the coma, whereas CH3OH was enhanced in that direction. Statistical analysis of molecular scale lengths in 3I/ATLAS indicated that CH3OH included production from coma sources at Lp > 258 km at 99% confidence. However low signal-to-noise on long baselines, which sample emission on small spatial scales closest to the nucleus, prevented definitively ruling out CH3OH as purely a parent species. In contrast, HCN production was indistinguishable from direct nucleus sublimation. The CH3OH production rate increased sharply from August through October, including an uptick near the inner edge of the H2O sublimation zone at rH = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH3OH/HCN ratios in 3I/ATLAS of 124+30−34 and 79+11−14on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS)

Comae↗
DOE OSTI2016

Electromagnetic coupling and array packing induce exchange of dominance on complex modes in 3D periodic arrays of spheres with large permittivity

In this study, we investigate the effect on wave propagation of array packing and electromagnetic coupling between spheres in a three-dimensional (3D) lattice of microspheres with large permittivity that exhibit strong magnetic polarizability. We report on the complex wavenumber of Bloch waves in the lattice when each sphere is assumed to possess both electric and magnetic dipoles and full electromagnetic coupling is accounted for. While for small material-filling fractions we always determine one dominant mode with low attenuation constant, the same does not happen for large filling fractions, when electromagnetic coupling is included. In the latter case we peculiarly observe two dominant modes with low attenuation constant, dominant in different frequency ranges. The filling fraction threshold for which two dominant modes appear varies for different metamaterial constituents, as proven by considering spheres made by either titanium dioxide or lead telluride. As further confirmation of our findings, we retrieve the complex propagation constant of the dominant mode(s) via a field fitting procedure employing two sets of waves (direct and reflected) pertaining to two distinct modes, strengthening the presence of the two distinct dominant modes for increasing filling fractions. However, given that one mode only, with transverse polarization, at any given frequency, is dominant and able to propagate inside the lattice, we are able to accurately treat the metamaterial that is known to exhibit artificial magnetism as a homogeneous material with effective parameters, such as the refractive index. Results clearly show that the account of both electric and magnetic scattering processes in evaluating all electromagnetic intersphere couplings is essential for a proper description of the electromagnetic propagation in lattices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Searches for large-scale anisotropy in the arrival directions of cosmic rays detected above energy of 10{sup 19} eV at the Pierre Auger observatory and the telescope array

Spherical harmonic moments are well-suited for capturing anisotropy at any scale in the flux of cosmic rays. An unambiguous measurement of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data from observatories located in both the northern and southern hemispheres. To this end, a joint analysis using data recorded at the Telescope Array and the Pierre Auger Observatory above 10{sup 19} eV is presented in this work. The resulting multipolar expansion of the flux of cosmic rays allows us to perform a series of anisotropy searches, and in particular to report on the angular power spectrum of cosmic rays above 10{sup 19} eV. No significant deviation from isotropic expectations is found throughout the analyses performed. Upper limits on the amplitudes of the dipole and quadrupole moments are derived as a function of the direction in the sky, varying between 7% and 13% for the dipole and between 7% and 10% for a symmetric quadrupole.

79 ASTRONOMY AND ASTROPHYSICS↗