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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Multidimensional images and aberrations in STEM

Recent advances in scanning transmission electron microscopy (STEM) have led to increased development of multi-dimensional STEM imaging modalities and novel image reconstruction methods. This interest arises because the main electron lens in a modern transmission electron microscope usually has a diffraction-space information limit that is significantly better than the real-space resolution of the same lens. This state-of-affairs is sometimes shared by other scattering methods in modern physics and contributes to a broader excitement surrounding multidimensional techniques that scan a probe while recording diffraction-space images, such as ptychography and scanning nano-beam diffraction. However, the contrasting resolution in the two spaces raises the question as to what is limiting their effective performance. Here, we examine this paradox by considering the effects of aberrations in both image and diffraction planes, and likewise separate the contributions of pre- and post-sample aberrations. In conclusion, this consideration provides insight into aberration-measurement techniques and might also indicate improvements for super-resolution techniques.

Hoglund, Eric R.↗
DOE OSTI2014

Test of the GEM Front Tracker for the SBS Spectrometer at Jefferson Lab

A new Large-Acceptance Forward Angle Spectrometer (Super BigBite) is under development at JLab/Hall A to optimally exploit the exciting opportunities o?ered by the 12 GeV upgrade of the electron beam. The tracker of this new apparatus is based on the Gas Electron Multiplier (GEM) technology, which has been chosen to optimize cost/performance, position resolution and to meet the high hit rate (>1 MHz/cm2). The first GEM detector modules, designed and built by the INFN Collaboration JLAB12, were tested at the DESY test beam facility in Hamburg, by using an electron beam with energy ranging from 2.0 to 6.0 GeV. In particular, two 40x50 cm2 and one 10x10 cm2 GEM chambers were equipped with a new implementation of the APV25 readout chip. Measurements were performed at di?erent impact points and angles between the electron beam and the plane of the GEM chambers, with one large chamber in a solenoid magnetic field up to 500 Gauss. In this report we present the technical characteristics of the detector and comment on the presently achieved performance.

Mammoliti, F.↗
DOE OSTI2012

Quick-scanning x-ray absorption spectroscopy system with a servo-motor-driven channel-cut monochromator with a temporal resolution of 10 ms

We have developed a quick-scanning x-ray absorption fine structure (QXAFS) system and installed it at the recently constructed synchrotron radiation beamline BL33XU at the SPring-8. Rapid acquisition of high-quality QXAFS data was realized by combining a servo-motor-driven Si channel-cut monochromator with a tapered undulator. Two tandemly aligned monochromators with channel-cut Si(111) and Si(220) crystals covered energy ranges of 4.0-28.2 keV and 6.6-46.0 keV, respectively. The system allows the users to adjust instantly the energy ranges of scans, the starting angles of oscillations, and the frequencies. The channel-cut crystals are cooled with liquid nitrogen to enable them to withstand the high heat load from the undulator radiation. Deformation of the reflecting planes is reduced by clamping each crystal with two cooling blocks. Performance tests at the Cu K-edge demonstrated sufficiently high data quality for x-ray absorption near-edge structure and extended x-ray absorption fine-structure analyses with temporal resolutions of up to 10 and 25 ms, respectively.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

STRESS AND FAILURE ANALYSIS OF RAPIDLY ROTATING ASTEROID (29075) 1950 DA

Rozitis et al. recently reported that near-Earth asteroid (29075) 1950 DA, whose bulk density ranges from 1.0 g cm{sup –3} to 2.4 g cm{sup –3}, is a rubble pile and requires a cohesive strength of at least 44-76 Pa to keep from failing due to its fast spin period. Since their technique for giving failure conditions required the averaged stress over the whole volume, it discarded information about the asteroid's failure mode and internal stress condition. This paper develops a finite element model and revisits the stress and failure analysis of 1950 DA. For the modeling, we do not consider material hardening and softening. Under the assumption of an associated flow rule and uniform material distribution, we identify the deformation process of 1950 DA when its constant cohesion reaches the lowest value that keeps its current shape. The results show that to avoid structural failure the internal core requires a cohesive strength of at least 75-85 Pa. It suggests that for the failure mode of this body, the internal core first fails structurally, followed by the surface region. This implies that if cohesion is constant over the whole volume, the equatorial ridge of 1950 DA results from a material flow going outward along the equatorial plane in the internal core, but not from a landslide as has been hypothesized. This has additional implications for the likely density of the interior of the body.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Final Project Report: Imaging Fault Zones Using a Novel Elastic Reverse-Time Migration Imaging Technique

Imaging fault zones and fractures is crucial for geothermal operators, providing important information for reservoir evaluation and management strategies. However, there are no existing techniques available for directly and clearly imaging fault zones, particularly for steeply dipping faults and fracture zones. In this project, we developed novel acoustic- and elastic-waveform inversion methods for high-resolution velocity model building. In addition, we developed acoustic and elastic reverse-time migration methods for high-resolution subsurface imaging of complex subsurface structures and steeply-dipping fault/fracture zones. We first evaluated and verified the improved capabilities of our newly developed seismic inversion and migration imaging methods using synthetic seismic data. Our numerical tests verified that our new methods directly image subsurface fracture/fault zones using surface seismic reflection data. We then applied our novel seismic inversion and migration imaging methods to a field 3D surface seismic dataset acquired at the Soda Lake geothermal field using Vibroseis sources. Our migration images of the Soda Lake geothermal field obtained using our seismic inversion and migration imaging algorithms revealed several possible fault/fracture zones. AltaRock Energy, Inc. is working with Cyrq Energy, Inc. to refine the geologic interpretation at the Soda Lake geothermal field. Trenton Cladouhos, Senior Vice President R&D of AltaRock, was very interested in our imaging results of 3D surface seismic data from the Soda Lake geothermal field. He planed to perform detailed interpretation of our images in collaboration with James Faulds and Holly McLachlan of University of Nevada at Reno. Using our high-resolution seismic inversion and migration imaging results can help determine the optimal locations to drill wells for geothermal energy production and reduce the risk of geothermal exploration.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Highlights: • Recovery processes in precipitate free zones differ from those in grain interiors. • Most precipitate free zones contain few dislocations, after deformation. • Deformation can induce large misorientations in precipitate free zones. • Some deformed precipitate free zones contain nanoscale grains. - Abstract: Scanning precession electron diffraction and automated crystal orientation mapping in a transmission electron microscope (TEM) have been applied to quantitatively study the crystal orientation of precipitate free zones (PFZs) of four GB regions in an AA6060 alloy in peak aged condition (temper T6) after uniaxial compression to 20% engineering strain. The PFZ width in the alloy was found to be w = 170 ± 40 nm. The results show that some PFZs develop significant misorientations relative to their parent grain, and represent, to the best knowledge of the authors, the first quantitative evidence of this. This misorientation may either be constant inside a particular PFZ, making it appear like a band or a very elongated subgrain, or be partitioned in discrete regions with a diameter comparable to the PFZ width, making the former PFZ into a collection of small grains. The band-like PFZ observed in this work had a misorientation relative to its parent grain of ≈ 7°, while the grain-like PFZ had grains with misorientations between ≈ 12° and ≈ 20° relative to its parent grain. The other PFZs that were observed had only limited misorientations relative to their parent grains, and had either dislocations perpendicular to the GB plane or a dislocation wall at the transition region. A general TEM study of the material at various engineering strains was also conducted and suggests that grain-like PFZs are more frequent for larger strains, indicating that the different PFZ features are likely due to different strain localisation in individual PFZs. This localisation is expected to be influenced by the orientation of the loading axis relative to crystal orientations and GB planes. It is also suggested that the different PFZ features engender different work hardening rates and possibly affect nucleation of intergranular fracture. The results support previous studies on the microstructure evolution of PFZs in age-hardenable aluminium alloys during deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Implementation of density functional embedding theory within the projector-augmented-wave method and applications to semiconductor defect states

We report a new implementation of the density functional embedding theory (DFET) in the VASP code, using the projector-augmented-wave (PAW) formalism. Newly developed algorithms allow us to efficiently perform optimized effective potential optimizations within PAW. The new algorithm generates robust and physically correct embedding potentials, as we verified using several test systems including a covalently bound molecule, a metal surface, and bulk semiconductors. We show that with the resulting embedding potential, embedded cluster models can reproduce the electronic structure of point defects in bulk semiconductors, thereby demonstrating the validity of DFET in semiconductors for the first time. Compared to our previous version, the new implementation of DFET within VASP affords use of all features of VASP (e.g., a systematic PAW library, a wide selection of functionals, a more flexible choice of U correction formalisms, and faster computational speed) with DFET. Furthermore, our results are fairly robust with respect to both plane-wave and Gaussian type orbital basis sets in the embedded cluster calculations. This suggests that the density functional embedding method is potentially an accurate and efficient way to study properties of isolated defects in semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A quality assurance framework for the fully automated and objective evaluation of image quality in cone-beam computed tomography

Purpose: Thousands of cone-beam computed tomography (CBCT) scanners for vascular, maxillofacial, neurological, and body imaging are in clinical use today, but there is no consensus on uniform acceptance and constancy testing for image quality (IQ) and dose yet. The authors developed a quality assurance (QA) framework for fully automated and time-efficient performance evaluation of these systems. In addition, the dependence of objective Fourier-based IQ metrics on direction and position in 3D volumes was investigated for CBCT. Methods: The authors designed a dedicated QA phantom 10 cm in length consisting of five compartments, each with a diameter of 10 cm, and an optional extension ring 16 cm in diameter. A homogeneous section of water-equivalent material allows measuring CT value accuracy, image noise and uniformity, and multidimensional global and local noise power spectra (NPS). For the quantitative determination of 3D high-contrast spatial resolution, the modulation transfer function (MTF) of centrally and peripherally positioned aluminum spheres was computed from edge profiles. Additional in-plane and axial resolution patterns were used to assess resolution qualitatively. The characterization of low-contrast detectability as well as CT value linearity and artifact behavior was tested by utilizing sections with soft-tissue-equivalent and metallic inserts. For an automated QA procedure, a phantom detection algorithm was implemented. All tests used in the dedicated QA program were initially verified in simulation studies and experimentally confirmed on a clinical dental CBCT system. Results: The automated IQ evaluation of volume data sets of the dental CBCT system was achieved with the proposed phantom requiring only one scan for the determination of all desired parameters. Typically, less than 5 min were needed for phantom set-up, scanning, and data analysis. Quantitative evaluation of system performance over time by comparison to previous examinations was also verified. The maximum percentage interscan variation of repeated measurements was less than 4% and 1.7% on average for all investigated quality criteria. The NPS-based image noise differed by less than 5% from the conventional standard deviation approach and spatially selective 10% MTF values were well comparable to subjective results obtained with 3D resolution pattern. Determining only transverse spatial resolution and global noise behavior in the central field of measurement turned out to be insufficient. Conclusions: The proposed framework transfers QA routines employed in conventional CT in an advanced version to CBCT for fully automated and time-efficient evaluation of technical equipment. With the modular phantom design, a routine as well as an expert version for assessing IQ is provided. The QA program can be used for arbitrary CT units to evaluate 3D imaging characteristics automatically.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-J-41: Experimental Validation of a Cascaded Linear System Model for MVCBCT with a Multi-Layer EPID

Purpose: The purpose of this study was to validate the use of a cascaded linear system model for MV cone-beam CT (CBCT) using a multi-layer (MLI) electronic portal imaging device (EPID) and provide experimental insight into image formation. A validated 3D model provides insight into salient factors affecting reconstructed image quality, allowing potential for optimizing detector design for CBCT applications. Methods: A cascaded linear system model was developed to investigate the potential improvement in reconstructed image quality for MV CBCT using an MLI EPID. Inputs to the three-dimensional (3D) model include projection space MTF and NPS. Experimental validation was performed on a prototype MLI detector installed on the portal imaging arm of a Varian TrueBeam radiotherapy system. CBCT scans of up to 898 projections over 360 degrees were acquired at exposures of 16 and 64 MU. Image volumes were reconstructed using a Feldkamp-type (FDK) filtered backprojection (FBP) algorithm. Flat field images and scans of a Catphan model 604 phantom were acquired. The effect of 2×2 and 4×4 detector binning was also examined. Results: Using projection flat fields as an input, examination of the modeled and measured NPS in the axial plane exhibits good agreement. Binning projection images was shown to improve axial slice SDNR by a factor of approximately 1.4. This improvement is largely driven by a decrease in image noise of roughly 20%. However, this effect is accompanied by a subsequent loss in image resolution. Conclusion: The measured axial NPS shows good agreement with the theoretical calculation using a linear system model. Binning of projection images improves SNR of large objects on the Catphan phantom by decreasing noise. Specific imaging tasks will dictate the implementation image binning to two-dimensional projection images. The project was partially supported by a grant from Varian Medical Systems, Inc. and grant No. R01CA188446-01 from the National Cancer Institute.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Beam Stability R&D for the APS MBA Upgrade

Beam diagnostics required for the APS Multi-bend acromat (MBA) are driven by ambitious beam stability requirements. The major AC stability challenge is to correct rms beam motion to 10% the rms beam size at the insertion device source points from0.01 to 1000 Hz. The vertical plane represents the biggest challenge forAC stability, which is required to be 400 nm rms for a 4-micron vertical beam size. In addition to AC stability, long-term drift over a period of seven days is required to be 1 micron or less. Major diagnostics R&D components include improved rf beam position processing using commercially available FPGA-based BPM processors, new X-ray beam position monitors based on hard X-ray fluorescence from copper and Compton scattering off diamond, mechanical motion sensing to detect and correct long-term vacuum chamber drift, a new feedback system featuring a tenfold increase in sampling rate, and a several-fold increase in the number of fast correctors and BPMs in the feedback algorithm. Feedback system development represents a major effort, and we are pursuing development of a novel algorithm that integrates orbit correction for both slow and fast correctors down to DC simultaneously. Finally, a new data acquisition system (DAQ) is being developed to simultaneously acquire streaming data from all diagnostics as well as the feedback processors for commissioning and fault diagnosis. Results of studies and the design effort are reported.

APS MBA Upgrade↗
DOE OSTI2014

Electrodynamic model of the field effect transistor application for THz/subTHz radiation detection: Subthreshold and above threshold operation

Developed in this work is an electrodynamic model of field effect transistor (FET) application for THz/subTHz radiation detection. It is based on solution of the Maxwell equations in the gate dielectric, expression for current in the channel, which takes into account both the drift and diffusion current components, and the equation of current continuity. For the regimes under and above threshold at the strong inversion the response voltage, responsivity, wave impedance, power of ohmic loss in the gate and channel have been found, and the electrical noise equivalent power (ENEP) has been estimated. The responsivity is orders of magnitude higher and ENEP under threshold is orders of magnitude less than these values above threshold. Under the threshold, the electromagnetic field in the gate oxide is identical to field of the plane waves in free-space. At the same time, for strong inversion the charging of the gate capacitance through the resistance of channel determines the electric field in oxide.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Object Detection and Recognition with PointPillars in LiDAR Point Clouds – Comparisions

In the field of autonomous systems, neural networks have been leveraged for object detection and recognition in 2-dimensional images captured by cameras. Other types of sensors are available for sensing surroundings, including LiDAR sensors, and corresponding networks have been developed to perform detection and recognition in the point clouds generated by these sensors. The approaches are similar, both perform convolutions, but have distinct characteristics and challenges. In designing and configuring autonomous systems, a variety of LiDAR sensors are available, along with configurable deep neural networks to leverage their data. This work presents a review of the PointPillars network, an evolution of the seminal PointNet, comparing accuracy and training time relative to different LiDAR sensors, network and training parameters, CPU and GPU hardware, and the criticality of the use of reflective intensity as a feature. The value of using reflectivity as a predictive feature is explored and quantified to determine if it makes a significant difference in accuracy of the PointPillars network. Two separate LiDAR sensors are utilized, a 16-plane and a 32-plane, and corresponding accuracies and training times with the PointPillars network are evaluated.

LiDAR, machine learning, neural network, object re↗
DOE OSTI2020

Quantifying patterns in optical micrographs of one- and two-dimensional ellipsoidal particle assemblies

Current developments in colloidal science include the assembly of anisotropic colloids with broad geometric diversity. As the complexity of particle assemblies increases, the need for ubiquitous algorithms that quantitatively analyze images of the assemblies to deliver key information such as quantification of crystal structures becomes more urgent. This contribution describes algorithms capable of image analysis for classifying colloidal structures based on abstracted interparticle relationship information and quantitatively analyzing the abundance of each structure in mixed pattern assemblies. The algorithm parameters can be adjusted, allowing for the algorithms to be adapted for different image analyses. Three different ellipsoidal particle assembly images are presented to demonstrate the effectiveness of the algorithms: a one-dimensional (1D) particle chain assembly and two two-dimensional (2D) polymorphic crystals each consisting of assemblies of two distinct plane symmetry groups. Angle relationships between neighbouring particles are calculated and neighbour counts of each particle are determined. Combining these two parameters as rules for classification criteria allows for the labeling and quantification of each particle into a defined symmetry class within an assembly. The algorithms provide a labelled image comprising classification results and particle counts of each defined class. For multiple images or individual frames from a video, the script can be looped to achieve automatic processing. The yielded classification data allow for more in-depth image analysis of mixed pattern particle assemblies. Finally, we envision that these algorithms will have utility in quantitative analysis of images comprising ellipsoidal colloidal materials, nanoparticles, or biological matter.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Two-step growth of two-dimensional WSe 2 /MoSe 2 heterostructures

Two dimensional (2D) materials have attracted great attention due to their unique properties and atomic thickness. Although various 2D materials have been successfully synthesized with different optical and electrical properties, a strategy for fabricating 2D heterostructures must be developed in order to construct more complicated devices for practical applications. Here we demonstrate for the first time a two-step chemical vapor deposition (CVD) method for growing transition-metal dichalcogenide (TMD) heterostructures, where MoSe 2 was synthesized first and followed by an epitaxial growth of WSe 2 on the edge and on the top surface of MoSe 2 . Compared to previously reported one-step growth methods, this two-step growth has the capability of spatial and size control of each 2D component, leading to much larger (up to 169 μm) heterostructure size, and cross-contamination can be effectively minimized. Furthermore, this two-step growth produces well-defined 2H and 3R stacking in the WSe 2 /MoSe 2 bilayer regions and much sharper in-plane interfaces than the previously reported MoSe 2 /WSe 2 heterojunctions obtained from one-step growth methods. The resultant heterostructures with WSe 2 /MoSe 2 bilayer and the exposed MoSe 2 monolayer display rectification characteristics of a p-n junction, as revealed by optoelectronic tests, and an internal quantum efficiency of 91% when functioning as a photodetector. As a result, a photovoltaic effect without any external gates was observed, showing incident photon to converted electron (IPCE) efficiencies of approximately 0.12%, providing application potential in electronics and energy harvesting.

2D heterostructures↗
DOE OSTI2022

Rotational Dynamics and Transition Mechanisms of Surface-Adsorbed Proteins

Assembly of biomolecules at solid-water interfaces requires molecules to traverse complex orientation-dependent energy landscapes through processes that are poorly understood, largely due to the dearth of in-situ single molecule measurements and statistical analyses of the rotational dynamics that define directional selection. Emerging capabilities in high-speed atomic force microscopy and machine learning have allowed us to directly determine the orientational energy landscape and observe and quantify the rotational dynamics for protein nanorods on the surface of muscovite mica under a variety of conditions. Comparisons with kinetic Monte Carlo simulations show that the transition rates between adjacent orientation-specific energetic minima can largely be understood through traditional models of in-plane Brownian rotation across a biased energy landscape, with resulting transition rates that are exponential in the energy-barriers between states. However, transitions between more distant angular states are decoupled from barrier height, with jump-size distributions showing a power-law decay that is characteristic of a non-classical Levy-flight random walk, indicating that large jumps are enabled by alternative modes of motion via activated states. The findings provide new insights into the dynamics of biomolecules at solid-liquid interfaces that lead to self-assembly, epitaxial matching and other orientationally anisotropic outcomes and define a general procedure for exploring such dynamics with implications for hybrid biomolecular-inorganic materials design.

Orientational energy landscapes, Rotational dynami↗
DOE OSTI2013

AN AB INITIO MODEL FOR COSMIC-RAY MODULATION

A proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays (CRs) is of vital importance for a better understanding of CR modulation in the heliosphere. This study presents an ab initio model for CR modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. This model is solved for solar minimum heliospheric conditions, utilizing boundary values chosen so that model results are in reasonable agreement with spacecraft observations of turbulence quantities in the solar ecliptic plane and along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modeled slab and two-dimensional (2D) turbulence energy spectra. The modeled 2D spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers. There currently exist no models or observations for the wavenumber where this drop-off occurs, and it is considered to be the only free parameter in this study. The modeled spectra are used as inputs for parallel mean free path expressions based on those derived from quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore, the effects of turbulence on CR drifts are modeled in a self-consistent way, also employing a recently developed model for wavy current sheet drift. The resulting diffusion and drift coefficients are applied to the study of galactic CR protons and antiprotons using a 3D, steady-state CR modulation code, and sample solutions in fair to good agreement with multiple spacecraft observations are presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Magnetization of Materials in Pulsed Magnetic Fields

Magnetism has proven pivotal in the development of many technologies. From navigation compasses, imaging devices in medicine and electric motors, exploitation of the magnetic field on both the macroscopic and atomic scale has played an important role in human development. There is particular interest in the magnetic properties of materials, especially due to the incomplete understanding of why some materials behave magnetically in a specific manner. This has been motivated in some cases by the desire to engineer compounds to fulfil specific roles. One group of compounds being investigated for this purpose are known as molecular magnets, so-called as they are formed of discrete molecule-based units with metal ions providing a magnetic moment while organic or inorganic molecules bridge these metal centres. They can be large, discrete molecular clusters (referred to as 0-D molecular magnets) or long coordination networks in 1-D, 2-D or 3-D. The dimensionality here refers to the number of directions in which spins communicate: all directions (3-D), only in planes (2-D), only in chains (1-D) or no long range communication (0-D). These organometallic compounds, they are sometimes referred to as metal organic frameworks (MOFs) though there is some discrepancy in conventions in regards to whether MOFs should be different from molecular magnets. Molecular magnets offer flexible synthesis routes towards magnetic materials. Being transition complexes, ligands can be substituted to refine the magnetic properties of the final product or the metallic centre can be changed. This can be accomplished through as simple a method as different reactant ratios Materials with novel properties are also being sought such as magnetoelectric multiferroic compounds which display simultaneous ferromagnetism and ferroelectricity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗