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Results for “ABERRATION”

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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways

Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i.e. image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. “Archimedean” spirals, with a constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Planck 2013 results. XXVII. Doppler boosting of the CMB: Eppur si muove

Our velocity relative to the rest frame of the cosmic microwave background (CMB) generates a dipole temperature anisotropy on the sky which has been well measured for more than 30 years, and has an accepted amplitude of v/c = 1.23 × 10 -3 , or v = 369 s -1 . In addition to this signal generated by Doppler boosting of the CMB monopole, our motion also modulates and aberrates the CMB temperature fluctuations (as well as every other source of radiation at cosmological distances). This is an order 10 -3 effect applied to fluctuations which are already one part in roughly 10 5 , so it is quite small. Nevertheless, it becomes detectable with the all-sky coverage, high angular resolution, and low noise levels of the Planck satellite. Here we report a first measurement of this velocity signature using the aberration and modulation effects on the CMB temperature anisotropies, finding a component in the known dipole direction, ( l,b ) = (264°,48°), of 384 km s -1 ± 78 km s -1 (stat.) ± 115 km s -1 (syst.). This is a significant confirmation of the expected velocity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Using the Gerchberg-Saxton algorithm to reconstruct nonmodulated pyramid wavefront sensor measurements

Adaptive optics (AO) is a technique to improve the resolution of ground-based telescopes by correcting, in real-time, optical aberrations due to atmospheric turbulence and the telescope itself. With the rise of Giant Segmented Mirror Telescopes (GSMT), AO is needed more than ever to reach the full potential of these future observatories. One of the main performance drivers of an AO system is the wavefront sensing operation, consisting of measuring the shape of the above mentioned optical aberrations. Aims. The non-modulated pyramid wavefront sensor (nPWFS) is a wavefront sensor with high sensitivity, allowing the limits of AO systems to be pushed. The high sensitivity comes at the expense of its dynamic range, which makes it a highly non-linear sensor. We propose here a novel way to invert nPWFS signals by using the principle of reciprocity of light propagation and the Gerchberg-Saxton (GS) algorithm. We test the performance of this reconstructor in two steps: the technique is first implemented in simulations, where some of its basic properties are studied. Then, the GS reconstructor is tested on the Santa Cruz Extreme Adaptive optics Laboratory (SEAL) testbed located at the University of California Santa Cruz. This new way to invert the nPWFS measurements allows us to drastically increase the dynamic range of the reconstruction for the nPWFS, pushing the dynamics close to a modulated PWFS. The reconstructor is an iterative algorithm requiring heavy computational burden, which could be an issue for real-time purposes in its current implementation. However, this new reconstructor could still be helpful in the case of many wavefront control operations. In conclusion, this reconstruction technique has also been successfully tested on the Santa Cruz Extreme AO Laboratory (SEAL) bench where it is now used as the standard way to invert nPWFS signal.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al{sub 2}O{sub 3}), as well as the Co:ZnO/Al{sub 2}O{sub 3} interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3–4 Co:ZnO layers next to the Al{sub 2}O{sub 3} substrate. The stacking fault density is in the range of 10{sup 17} cm{sup −3}. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Non-descanned multifocal multiphoton microscopy with a multianode photomultiplier tube

Multifocal multiphoton microscopy (MMM) improves imaging speed over a point scanning approach by parallelizing the excitation process. Early versions of MMM relied on imaging detectors to record emission signals from multiple foci simultaneously. For many turbid biological specimens, the scattering of emission photons results in blurred images and degrades the signal-to-noise ratio (SNR). We have recently demonstrated that a multianode photomultiplier tube (MAPMT) placed in a descanned configuration can effectively collect scattered emission photons from each focus into their corresponding anodes significantly improving image SNR for highly scattering specimens. Unfortunately, a descanned MMM has a longer detection path resulting in substantial emission photon loss. Optical design constraints in a descanned geometry further results in significant optical aberrations especially for large field-of-view (FOV), high NA objectives. Here, we introduce a non-descanned MMM based on MAPMT that substantially overcomes most of these drawbacks. We show that we improve signal efficiency up to fourfold with limited image SNR degradation due to scattered emission photons. The excitation foci can also be spaced wider to cover the full FOV of the objective with minimal aberrations. The performance of this system is demonstrated by imaging interneuron morphological structures deep in the brains of living mice.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Amphoteric doping of praseodymium Pr{sup 3+} in SrTiO{sub 3} grain boundaries

Charge compensation in rare-earth Praseodymium (Pr{sup 3+}) doped SrTiO{sub 3} plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr{sup 3+} doping behavior in SrTiO{sub 3} grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy. The presence of Pr{sup 3+} induces structural variations and changes the statistical prevalence of the GB structures. In contrast to the assumption that Pr{sup 3+} substitutes on the Sr site in the bulk, Pr{sup 3+} is found to substitute on both Sr and Ti sites inside the GBs, with the highest concentration at the Ti sites. This amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Design and fabrication of a duoplasmatron extraction geometry and LEBT for the LANSCE H{sup +} RFQ project

The 750-keV H{sup +} Cockcroft-Walton at LANSCE will be replaced with a recently fabricated 4-rod Radio Frequency Quadrupole (RFQ) with injection energy of 35 keV. The existing duoplasmatron source extraction optics need to be modified to produce up to 35 mA of H{sup +} current with an emittance <0.02 π-cm-mrad (rms, norm) for injection into the RFQ. Parts for the new source have been fabricated and assembly is in process. We will use the existing duoplasmatron source with a newly designed extraction system and low energy beam transport (LEBT) for beam injection into the RFQ. In addition to source modifications, we need a new LEBT for transport and matching into the RFQ. The LEBT uses two magnetic solenoids with enough drift space between them to accommodate diagnostics and a beam deflector. The LEBT is designed to work over a range of space-charge neutralized currents and emittances. The LEBT is optimized in the sense that it minimizes the beam size in both solenoids for a point design of a given neutralized current and emittance. Special attention has been given to estimating emittance growth due to source extraction optics and solenoid aberrations. Examples of source-to-RFQ matching and emittance growth (due to both non-linear space charge and solenoid aberrations) are presented over a range of currents and emittances about the design point. A mechanical layout drawing will be presented along with the status of the source and LEBT, design, and fabrication.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO{sub 3}-buffered ferroelectric BaTiO{sub 3} film on GaAs

The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO{sub 3} thin films grown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO{sub 3} grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. Here, we use a combination of aberration-corrected scanning transmission electron microscopy and first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectric polarization of a BaTiO{sub 3} thin film grown on GaAs. We demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO{sub 3}), and propose that the presence of surface charge screening allows the formation of switchable domains.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The role of chemical structure on the magnetic and electronic properties of Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/Si(111) interface

We show that Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} film deposited on Si(111) has a single crystal structure and twin related epitaxial relationship with the substrate. Sub-nanometer electron energy loss spectroscopy shows that in a narrow interface region there is a mutual inter-diffusion dominated by Si and Co. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that the film has B2 ordering. The film lattice structure is unaltered even at the interface due to the substitutional nature of the intermixing. First-principles calculations performed using structural models based on the aberration corrected electron microscopy show that the increased Si incorporation in the film leads to a gradual decrease of the magnetic moment as well as significant spin-polarization reduction. These effects can have significant detrimental role on the spin injection from the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} film into the Si substrate, besides the structural integrity of this junction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Implementing an Accurate and Rapid Sparse Sampling Approach for Low-Dose Atomic Resolution STEM Imaging

Aberration correction for scanning transmission electron microscopes (STEM) has dramatically increased spatial image resolution for beam-stable materials, but it is the sample stability rather than the microscope that often limits the practical resolution of STEM images. To extract physical information from images of beam sensitive materials it is becoming clear that there is a critical dose/dose-rate below which the images can be interpreted as representative of the pristine material, while above it the observation is dominated by beam effects. Here we describe an experimental approach for sparse sampling in the STEM and in-painting image reconstruction in order to reduce the electron dose/dose-rate to the sample during imaging. By characterizing the induction limited rise-time and hysteresis in scan coils, we show that sparse line-hopping approach to scan randomization can be implemented that optimizes both the speed of the scan and the amount of the sample that needs to be illuminated by the beam. The dose and acquisition time for the sparse sampling is shown to be effectively decreased by factor of 5x relative to conventional acquisition, permitting imaging of beam sensitive materials to be obtained without changing the microscope operating parameters. As a result, the use of sparse line-hopping scan to acquire STEM images is demonstrated with atomic resolution aberration corrected Z-contrast images of CaCO 3 , a material that is traditionally difficult to image by TEM/STEM because of dose issues.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Atomic scale study of surface orientations and energies of Ti 2 O 3 crystals

For nanostructured particles, the faceting planes and their terminating chemical species are two critical factors that govern their chemical behavior. In this paper, the surface atomistic structure and termination of Ti 2 O 3 crystals were analyzed using atomic-scale aberration-corrected scanning transmission electron microscopy (STEM) combined with density functional theory (DFT) calculations. STEM imaging reveals that the Ti 2 O 3 crystals are most often faceted along (001), (012), (-114), and (1–20) planes. The DFT calculation indicates that the (012) surface with TiO-termination has the lowest cleavage energy and correspondingly the lowest surface energy, indicating that (012) will be the most stable and prevalent surfaces in Ti 2 O 3 nanocrystals. Finally, these observations provide insights for exploring the interfacial process involving Ti 2 O 3 nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Short spatial filters with spherical lenses for high-power pulsed lasers

We report possible employment of short spatial filters based on spherical lenses in a pulsed laser source (neodymium glass, 300 J, 1 ns). The influence of the spherical aberration on the quality of output radiation and coefficient of conversion to the second harmonics is studied. The ultra-short aberration spatial filter of length 1.9 m with an aperture of 122 mm is experimentally tested. A considerable shortening of multi-cascade pump lasers for modern petawatt laser systems is demonstrated by the employment of short spatial filters without expensive aspherical optics. (elements of laser systems)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Wavefront analysis of the laser beam propagating through a turbid medium

Laser beam propagation through a scattering suspension of polystyrene microspheres in distilled water is studied theoretically and experimentally. The dependence of wavefront aberrations on the particle concentration is investigated. The existence of symmetric wavefront aberrations of the laser beam passed through a turbid medium is shown. (light scattering)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Measurement and correction of the wavefront of the laser light in a turbid medium

We report a numerical and experimental study of the laser beam propagation through a suspension of polystyrene microspheres in distilled water, showing the presence of higher-order centrally symmetric aberrations for the scatterer concentrations in the range from 1.3 × 10{sup 5} to 10{sup 6} mm{sup −3} and analysing the dependence of the scattered light wavefront distortion on the concentration of particles in a turbid medium. The study has also shown the effectiveness of the compensation of the wavefront aberrations of a scattered laser beam using a bimorph adaptive mirror. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Features of correlation measurements of the parameters of pulsed hyperspectral optical fields using an asymmetric interferometer

Differences in correlation measurements of the parameters of pulsed hyperspectral optical fields using symmetric and asymmetric interferometers are considered. It is shown analytically that the resulting cross-correlation function is sensitive to phase perturbations in the original wave field. The considered setup, which contains a telescopic reflective 4f system of parabolic mirrors in one arm, demonstrates that in the case of an asymmetric interferometer, the presence of aberrations leads to degradation of the reconstructed image, whereas in the case of symmetric interferometers these aberrations do not affect the result. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Impact of sunitinib resistance on clear cell renal cell carcinoma therapeutic sensitivity in vitro

Sunitinib resistance creates a major clinical challenge for the treatment of advanced clear cell renal cell carcinoma (ccRCC) and functional and metabolic changes linked to sunitinib resistance are not fully understood. We sought to characterize the molecular and metabolic changes induced by the development of sunitinib resistance in ccRCC by developing and characterizing two human ccRCC cell lines resistant to sunitinib. Consistent with the literature, sunitinib-resistant ccRCC cell lines presented an aberrant overexpression of Axl and PD-L1, as well as a metabolic rewiring characterized by enhanced OXPHOS and glutamine metabolism. Therapeutic challenges of sunitinib-resistant ccRCC cell lines in vitro using small molecule inhibitors targeting Axl, AMPK and p38, as well as using PD-L1 blocking therapeutic antibodies, showed limited CTL-mediated cytotoxicity in a co-culture model. However, the AMPK activator metformin appears to sensitize the effect of PD-L1 blocking therapeutic antibodies and to enhance CTLs’ cytotoxic effects on ccRCC cells. These effects were not broadly observed with the Axl and the p38 inhibitors. Taken together, these data suggest that targeting certain pathways aberrantly activated by sunitinib resistance such as the AMPK/PDL1 axis might sensitize ccRCC to immunotherapies as a second-line therapeutic approach.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

On the significance of power asymmetries in Planck CMB data at all scales

We perform an analysis of the CMB temperature data taken by the Planck satellite investigating if there is any significant deviation from cosmological isotropy. We look for differences in the spectrum between two opposite hemispheres and also for dipolar modulations. We propose a new way to avoid biases due to partial-sky coverage by producing a mask symmetrized in antipodal directions, in addition to the standard smoothing procedure. We also properly take into account both Doppler and aberration effects due to our peculiar velocity and the anisotropy of the noise, since these effects induce a significant hemispherical asymmetry. We are thus able to probe scales all the way to ℓ = 2000. After such treatment we find no evidence for significant hemispherical anomalies along any of the analyzed directions (i.e. deviations are less than 1.5σ when summing over all scales). Although among the larger scales there are sometimes higher discrepancies, these are always less than 3σ. We also find results on a dipolar modulation of the power spectrum. Along the hemispheres aligned with the most asymmetric direction for 2 ≤ ℓ ≤ 2000 we find a 3.3σ discrepancy when comparing to simulations. However, if we do not restrict ourselves to Planck's maximal asymmetry axis, which can only be known a posteriori, and compare Planck data with the modulation of simulations along their respective maximal asymmetry directions, the discrepancy goes down to less than 1σ (with, again, almost 3σ discrepancies in some low-ℓ modes). We thus conclude that no significant power asymmetries seem to be present in the full data set. Interestingly, without proper removal of Doppler and aberration effects one would find spurious anomalies at high ℓ, between 3σ and 5σ. Even when considering only ℓ < 600 we find that the boost is non-negligible and alleviates the discrepancy by roughly half-σ.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Unsupported single-atom-thick copper oxide monolayers

Oxide monolayers may present unique opportunities because of the great diversity of properties of these materials in bulk form. However, reports on oxide monolayers are still limited. Here we report the formation of single-atom-thick copper oxide layers with a square lattice both in graphene pores and on graphene substrates using aberration-corrected scanning transmission electron microscopy. First-principles calculations find that CuO is energetically stable and its calculated lattice spacing matches well with the measured value. Furthermore, free-standing copper oxide monolayers are predicted to be semiconductors with band gaps ~3 eV. The new wide-bandgap single-atom-thick copper oxide monolayers usher a new frontier to study the highly diverse family of two-dimensional oxides and explore their properties and their potential for new applications.

2D materials↗