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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Large Area Picosecond Photodetector (LAPPD TM ) - Pilot production and development status

Here, we discuss performance results achieved for fully functional sealed Large Area Picosecond Photodetectors (LAPPD (TM)) in tests performed at Incom Inc., as well as independent test results reported by our early adopters. The LAPPD is a microchannel plate (MCP) based large area picosecond photodetector, capable of imaging with single-photon sensitivity at high spatial and temporal resolutions in a hermetic package. The LAPPD has an active area of 350 square centimeters in an all-glass hermetic package with a fused silica window and bottom plate and sidewalls made of borosilicate float glass. Signals are generated by a bi-alkali Na 2 KSb photocathode and amplified with a stacked chevron pair of MCPs produced by applying resistive and emissive atomic layer deposition coatings to glass capillary array (GCA) substrates. Signals are collected on RF stripline anodes applied to the bottom plates which exit the detector via pin-free hermetic seals under the side walls. LAPPD test and performance results for product produced and delivered to early adopter customers during the first half of 2018 are reviewed. These results include electron gains ≥ 7.5 x 10 6 @ 850/950 V (entry/exit MCP), low dark noise rates (22 Cts/s/cm 2 ), single photoelectron (PE) timing resolution of 64 picoseconds RMS, and single photoelectron spatial resolution along and across strips of 2.8 mm and 1.3 mm RMS respectively. Many of these devices also had very high QE photocathodes that were uniform over the full 195 mm x 195 mm window active area (LAPPD #15 QE% @ 365 nm Max/Avg/Min = 25.8/22.3 ± 3/15.7). An update is additionally provided of developments that enable capacitive signal coupling from the detector to application specific pads or stripline readout patterns deployed on printed circuit boards positioned beneath the file, outside of the vacuum package. We conclude with examples of how sensors offering picosecond timing, in diverse applications can bring transformative change to detector technology and applications in future experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Scaling Properties of the Mean Multiplicity and Pseudorapidity Density in e – +e + , e ± +p, p( p ¯ )+p, p+A and A+A(B) Collisions

The charged-particle pseudorapidity density ( d N ch /dη ) for p( p¯ )+p, p+A and A+A(B) collisions and the mean multiplicity < N ch > for e – +e + , e ± +p , and p( p¯ )+p collisions are studied for a wide range of beam energies ( √s ). Characteristic scaling patterns are observed for both d N ch /dη and < N ch > , consistent with a thermal particle production mechanism for the bulk of the soft particles created in all of these systems. The scaling patterns found also validate an essential role for quark participants in these collisions. The measured values for d N ch /dη and < N ch > are observed to factorize into contributions that depend on log(√s) and the number of nucleon or quark participant pairs N pp . Here the quantification of these contributions gives expressions that serve to systematize d N ch /dη and < N ch > measurements spanning nearly 4 orders of magnitude in s√ and to predict their values as a function of √s and N pp .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Localization of electrons due to orbitally ordered bi-stripes in the bi-layer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} (x {approximately} 0.59).

Electronic phases with stripe patterns have been intensively investigated for their vital roles in unique properties of correlated electronic materials. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. By studying the electronic structure of La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} (x {approx} 0.59) and in combination with earlier scattering measurements, we demonstrate the variation of electronic properties accompanying the melting of so-called bi-stripes in this material. The static bi-stripes can strongly localize the electrons in the insulating phase above T{sub c} {approx} 160 K, while the fraction of mobile electrons grows, coexisting with a significant portion of localized electrons when the static bi-stripes melt below T{sub c}. The presence of localized electrons below T{sub c} suggests that the melting bi-stripes exist as a disordered or fluctuating counterpart. From static to melting, the bi-stripes act as an atomic-scale electronic valve, leading to a 'colossal' metal-insulator transition in this material.

36 MATERIALS SCIENCE↗
DOE OSTI2011

A very promising piezoelectric property of Ta{sub 2}O{sub 5} thin films. I: Monoclinic-trigonal phase transition

Ceramic thin films of tantalum oxide of a new trigonal structure (a=12.713(7) A, {alpha}=28.201(0){sup o}, space-group R3) were produced by thermal treatments of amorphous deposits on (001)Si wafers, either by electrostatic spray deposition or by injection metal-organic chemical vapor decomposition. This trigonal phase comes from the transformation of a monoclinic phase 11L- or 25L-Ta{sub 2}O{sub 5}. The transformation is reversible under oxygen atmosphere and, from results of TEM investigations, occurs mainly via atomic motions along the z unique axis of the monoclinic structure parallel to the polar three-fold axis of the trigonal structure. The non-centrosymmetry and direction of polar axis of the trigonal phase, identified by high resolution TEM imaging, indicate a possibility of very high electric dipole moments linked to a strong piezoelectricity. From results of XPS analyses of both monoclinic and trigonal structures, the binding energies remain similar to those of Ta{sub 2}O{sub 5}. As the formation of the trigonal structure gives rise to an important volume expansion, stresses induced in ceramic thin films are likely influencing both properties of birefringence and piezoelectricity which are presented in a separated article (part II). It is mentioned that the formation of trigonal phase does not occur in bulk Ta{sub 2}O{sub 5} samples, for which an incommensurate phase transition has been observed in a previous work. - Graphical abstract: (a) {theta}/2{theta} X-ray pattern of the tantalum oxide layer prepared by i-MOCVD, cooled down at 5 deg. C min{sup -1} after a thermal treatment at 850 deg. C under N{sub 2} for 1 h. (b) Rhombohedral cell of the Ta{sub 2}O{sub 5} trigonal structure of R3 space-group decorated with its 10 Ta sites. Highlights: > We examine crystallographic properties of a new Ta{sub 2}O{sub 5} trigonal phase. > Its formation occurs only in thin films. > It comes from a reversible transition with a monoclinic phase. > A possibility of strong piezoelectricity is deduced from the present study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Advanced FIB-based Preparation of Cryogenically-prepared Specimens for APT Analysis

The utilization of the focused ion beam scanning electron microscope (FIB-SEM) has aided the application of Atom Probe Tomography (APT) to a continually-growing variety of materials, including soft biological materials. However, the regular application of APT to hydrated interfaces such as those found in biological and environmental materials is lacking in large part due to difficulties in specimen preparation under high and ultra-high vacuum conditions. Although a FIB-SEM based cryogenic specimen preparation approach offers a rational route to the preparation of such specimens for APT analysis, many practical aspects such as welding and limitations in the cryo stage manipulation makes it challenging for routine liftout of site-targeted specimens. In this work, we describe our recent efforts in the development of a site-specific liftout and attachment scheme for cryogenically cooled specimens involving a combination of redeposition and overcoating of organic and organometallic molecules, as shown in Fig. 1a-d for a cryogenically-frozen corroded glass sample containing a hydrated porous gel surface layer. Application of an annular milling pattern to the frozen specimens leads to a needle-shaped morphology necessary for APT analysis with the targeted water-ice filled porous corroded silicate glass region of interest near the apex. Using a custom shuttle device and environmental transfer hub at PNNL to facilitate environmentally-protected specimen transfer, APT analysis was applied to directly map, for the first time, a water/solid interface in 3D to reveal the complex nanoscale water-filled porous network of corroded glass. Application of this unique specimen preparation approach to biological specimens will also be discussed, as well as the application of a unique cryo nanomaniupulator with integrated gas injection system to enable controlled FIB-based welding under cryogenic temperatures.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Design Rules for Self-Assembly of 2D Nanocrystal/Metal–Organic Framework Superstructures

Here, we demonstrate the guiding principles behind simple two dimensional self-assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe 3 O 4 ) NCs into a uniform two-dimensional bi-layered superstructure. This self-assembly process can be controlled by the energy of ligand–ligand interactions between surface ligands on Fe 3 O 4 NCs and Zr 6 O 4 (OH) 4 (fumarate) 6 MOF NPs. Scanning transmission electron microscopy (TEM)/energy-dispersive X-ray spectroscopy and TEM tomography confirm the hierarchical co-assembly of Fe 3 O 4 NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs. First-principles calculations and event-driven molecular dynamics simulations indicate that the observed patterns are dictated by combination of ligand–surface and ligand–ligand interactions. This study opens a new avenue for design and self-assembly of MOFs and NCs into high surface area assemblies, mimicking the structure of supported catalyst architectures, and provides a thorough fundamental understanding of the self-assembly process, which could be a guide for designing functional materials with desired structure.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

An investigation of {sup 60}Co gamma radiation-induced effects on the properties of nanostructured α-MoO{sub 3} for the application in optoelectronic and photonic devices

Gamma ray has sufficient energy to ionize and displace of atoms when interacts with optoelectronic and photonic devices that are placed at γ-radiation exposure environment, can be exposed to gamma radiation, resulting the alteration of the physical properties and hence the performances of devices. A comprehensive investigation of physical properties of the semiconductor materials under the influence of gamma radiation is essential for the effective design of devices for the application in the radiation exposure environment. In this article, a potential candidate for optoelectronic and photonic devices, orthorhombic MoO{sub 3} nanoparticles with average crystallite size of 135.31 nm successfully synthesized by hydrothermal method. Then, the properties of nanoparticles exposed to low (10 kGy) and high (120 kGy) absorbed dose of γ-rays from {sup 60}Co source were characterized by XRD, FESEM, FTIR and UV–Vis–NIR spectrophotometer and effects of absorbed doses was investigated for the first time. A significant change is observed in different physical properties of α-MoO{sub 3} nanoparticles after gamma exposure. The XRD patterns reveal the average crystallite size, intensity and the degree of crystallinity decrease for low dose (10 kGy) and increases for high dose (120 kGy). The calculated average crystallite size exposed to low and high doses are 127.79 nm and 136 nm, respectively. The lattice strain and dislocation density, however, shows the opposite trend of crystallite size with absorbed doses. This result is good evidence for the deterioration of crystallinity for low dose and improvement for high dose. The FESEM results reveal the significant effects of gamma doses on the micrographs of layered structure and on grain size. The optical studies disclose that band gap increases gradually from 2.78 to 2.90 eV, this behavior is associated with the reduction of electronic localized states. These results suggest that α-MoO{sub 3} nanoparticles could tolerate high doses of gamma radiation, making it a promising candidate for optoelectronic and photonic devices for γ-ray exposure environment applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Direct-write liquid phase transformations with a scanning transmission electron microscope

The highly energetic electron beam from a scanning transmission electron microscope (STEM) can induce local changes in the state of matter, ranging from local knock-out and atomic movement, to amorphization/crystallization, and chemical/electrochemical reactions occuring at localized liquid-solid and gas-solid interfaces. To date, fundamental studies of e-beam induced phenomena and practical applications have been limited by conventional e-beam rastering modes that allow only for uniform e-beam exposures. Here we develop an automated liquid phase nanolithography method that is capable of directly writing nanometer scaled features within silicon nitride encapsulated liquid cells. An external beam control system, connected to the scan coils of an aberration-corrected STEM, is used to precisely control the position, dwell time, and scan velocity of a sub-nanometer STEM probe. Site-specific locations in a sealed liquid cell containing an aqueous solution of H 2 PdCl 4 are irradiated to controllably deposit palladium onto silicon nitride membranes. We determine the threshold electron dose required for the radiolytic deposition of metallic palladium, explore the influence of electron dose on the feature size and morphology of nanolithographically patterned nanostructures, and propose a feedback-controlled monitoring method for active control of the nanofabricated structures through STEM detector signal monitoring. As a result, this approach enables both fundamental studies of electron beam induced interactions with matter, as well as opens a pathway to fabricate nanostructures with tailored architectures and chemistries via shape-controlled nanolithographic patterning from liquid phase precursors.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Low-temperature atomic layer deposition of TiO{sub 2} thin layers for the processing of memristive devices

Atomic layer deposition (ALD) represents one of the most fundamental techniques capable of satisfying the strict technological requirements imposed by the rapidly evolving electronic components industry. The actual scaling trend is rapidly leading to the fabrication of nanoscaled devices able to overcome limits of the present microelectronic technology, of which the memristor is one of the principal candidates. Since their development in 2008, TiO{sub 2} thin film memristors have been identified as the future technology for resistive random access memories because of their numerous advantages in producing dense, low power-consuming, three-dimensional memory stacks. The typical features of ALD, such as self-limiting and conformal deposition without line-of-sight requirements, are strong assets for fabricating these nanosized devices. This work focuses on the realization of memristors based on low-temperature ALD TiO{sub 2} thin films. In this process, the oxide layer was directly grown on a polymeric photoresist, thus simplifying the fabrication procedure with a direct liftoff patterning instead of a complex dry etching process. The TiO{sub 2} thin films deposited in a temperature range of 120–230 °C were characterized via Raman spectroscopy and x-ray photoelectron spectroscopy, and electrical current–voltage measurements taken in voltage sweep mode were employed to confirm the existence of resistive switching behaviors typical of memristors. These measurements showed that these low-temperature devices exhibit an ON/OFF ratio comparable to that of a high-temperature memristor, thus exhibiting similar performances with respect to memory applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Double-slit vacuum polarization effects in ultraintense laser fields

The influence of the strong laser-driven vacuum on a propagating electromagnetic probe wave has been studied in detail. We investigate two scenarios, which comprise a focused probe laser beam that passes through a region of vacuum polarized by an ultraintense laser field. By splitting this strong field into two separated monochromatic Gaussian pulses that counterpropagate in a plane perpendicular to the probe-field axis, we demonstrate a leading-order light-by-light diffraction effect that generates an interference pattern reminiscent of the classic double-slit experiment. We calculate the total number of probe photons diffracted as well as the number diffracted into regions where the vacuum polarization signal is higher than the probe background. In addition, we calculate the induced ellipticity and polarization rotation in the probe beam and show how, in the realistic situation in which the centers of the two strong fields are not exactly aligned, certain ranges of beam separation and observation distance may actually lead to an increase over the idealized case of a single strong laser beam.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Millimeter/submillimeter spectroscopy of Tio (X{sup 3}Δ{sub r}): the rare titanium isotopologues

Pure rotational spectra of the rare isotopologues of titanium oxide, {sup 46}TiO, {sup 47}TiO, {sup 49}TiO, and {sup 50}TiO, have been recorded using a combination of Fourier transform millimeter-wave (FTmmW) and millimeter/submillimeter direct absorption techniques in the frequency range 62–538 GHz. This study is the first complete spectroscopic characterization of these species in their X {sup 3}Δ{sub r} ground electronic states. The isotopologues were created by the reaction of N{sub 2}O or O{sub 2} and titanium vapor, produced either by laser ablation or in a Broida-type oven, and observed in the natural Ti isotopic abundances. Between 10 and 11 rotational transitions J + 1 ↔ J were measured for each species, typically in all 3 spin–orbit ladders Ω = 1, 2, and 3. For {sup 47}TiO and {sup 49}TiO, hyperfine structure was resolved, originating from the titanium-47 and titanium-49 nuclear spins of I = 5/2 and 7/2, respectively. For the Ω = 1 and 3 components, the hyperfine structure was found to follow a classic Landé pattern, while that for Ω = 2 appeared to be perturbed, likely a result of mixing with the nearby isoconfigurational a {sup 1}Δ state. The spectra were analyzed with a case (a) Hamiltonian, and rotational, spin–orbit, and spin–spin parameters were determined for each species, as well as magnetic hyperfine and electric quadrupole constants for the two molecules with nuclear spins. The most abundant species, {sup 48}TiO, has been detected in circumstellar envelopes. These measurements will enable other titanium isotopologues to be studied at millimeter wavelengths, providing Ti isotope ratios that can test models of nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Proof of Concept Simulations of the Multi-Isotope Process Monitor: An Online, Nondestructive, Near-Real-Time Safeguards Monitor for Nuclear Fuel Reprocessing Facilities

The International Atomic Energy Agency (IAEA) will require the development of advanced technologies to effectively safeguard nuclear material at increasingly large-scale nuclear recycling facilities. Ideally, the envisioned technologies would be capable of nondestructive, near-real-time, autonomous process monitoring. This paper describes recent results from model simulations designed to test the Multi-Isotope Process (MIP) monitor, a novel approach to safeguarding reprocessing plants. The MIP monitor combines the detection of intrinsic gamma ray signatures emitted from process solutions with multivariate analysis to detect off-normal conditions in process streams nondestructively and in near-real-time. Three computer models including ORIGEN-ARP, AMUSE, and SYNTH were used in series to predict spent nuclear fuel composition, estimate element partitioning during separation, and simulate spectra from product and raffinate streams using a variety of gamma detectors, respectively. Simulations were generated for fuel with various irradiation histories and under a variety of plant operating conditions. Principal component analysis (PCA) was applied to the simulated gamma spectra to investigate pattern variations as a function of acid concentration, burnup, and cooling time. Hierarchical cluster analysis (HCA) and partial least squares (PLS) were also used in the analysis. The MIP monitor was found to be sensitive to induced variations of several operating parameters including distinguishing ±2.5% variation from normal process acid concentrations. The ability of PLS to predict burnup levels from simulated spectra was also demonstrated to be within 3.5% of measured values.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Generation of localized strain in a thin film piezoelectric to control individual magnetoelectric heterostructures

Experimental results demonstrate the ability of a surface electrode pattern to produce sufficient in-plane strain in a PbZr0.52Ti0.48O3 (PZT) thin film clamped by a Si substrate to control magnetism in a 1000 nm diameter Ni ring. The electrode pattern and the Ni ring/PZT thin film heterostructure were designed using a finite element based micromagnetics code. The magnetoelectric heterostructures were fabricated on the PZT film using e-beam lithography and characterized using magnetic force microscopy. Application of voltage to the electrodes moved one of the “onion” state domain walls. This method enables the development of complex architectures incorporating strain-mediated multiferroic devices.

Cui, Jizhai↗
DOE OSTI2011

Critical review: Plasma-surface reactions and the spinning wall method

This article reviews methods for studying reactions of atoms and small molecules on substrates and chamber walls that are immersed in a plasma, a relatively unexplored, yet very important area of plasma science and technology. Emphasis is placed on the ''spinning wall'' technique. With this method, a cylindrical section of the wall of the plasma reactor is rotated, and the surface is periodically exposed to the plasma and then to a differentially pumped mass spectrometer, to an Auger electron spectrometer, and, optionally, to a beam of additional reactants or surface coatings. Reactants impinging on the surface can stick and react over time scales that are comparable to the substrate rotation period, which can be varied from {approx}0.5 to 40 ms. Langmuir-Hinshelwood reaction probabilities can be derived from a measurement of the absolute desorption product yields as a function of the substrate rotation frequency. Auger electron spectroscopy allows the plasma-immersed surface to be monitored during plasma operation. This measurement is critical, since wall ''conditioning'' in the plasma changes the reaction probabilities. Mass spectrometer cracking patterns are used to identify simple desorption products such as Cl{sub 2}, O{sub 2}, ClO, and ClO{sub 2}. Desorption products also produce a measurable pressure rise in the second differentially pumped chamber that can be used to obtain absolute desorption yields. The surface can also be coated with films that can be deposited by sputtering a target in the plasma or by evaporating material from a Knudsen cell in the differentially pumped wall chamber. Here, the authors review this new spinning wall technique in detail, describing both experimental issues and data analysis methods and interpretations. The authors have used the spinning wall method to study the recombination of Cl and O on plasma-conditioned anodized aluminum and stainless steel surfaces. In oxygen or chlorine plasmas, these surfaces become coated with a layer containing Si, Al, and O, due to slow erosion of the reactor materials, in addition to Cl in chlorine plasmas. Similar, low recombination probabilities were found for Cl and O on anodized Al versus stainless steel surfaces, consistent with the similar chemical composition of the layer that forms on these surfaces after long exposure to the plasma. In chlorine plasmas, weakly adsorbed Cl{sub 2} was found to inhibit Cl recombination, hence the Cl recombination probability decreases with increasing Cl{sub 2}-to-Cl number density ratios in the plasma. In mixed Cl{sub 2}/O{sub 2} plasmas, Cl and O recombine to form Cl{sub 2} and O{sub 2} with probabilities that are similar to those in pure chlorine or oxygen plasmas, but in addition, ClO and ClO{sub 2} form on the surface and desorb from the wall. These and other results, including the catalytic enhancement of O recombination by monolayer amounts of Cu, are reviewed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Milky Way kinematics. II. A uniform inner galaxy H I terminal velocity curve

Using atomic hydrogen (H i) data from the VLA Galactic Plane Survey, we measure the H i terminal velocity as a function of longitude for the first quadrant of the Milky Way. We use these data, together with our previous work on the fourth Galactic quadrant, to produce a densely sampled, uniformly measured, rotation curve of the northern and southern Milky Way between 3 kpc<R<8 kpc. We determine a new joint rotation curve fit for the first and fourth quadrants, which is consistent with the fit we published in McClure-Griffiths and Dickey and can be used for estimating kinematic distances interior to the solar circle. Structure in the rotation curves is now exquisitely well defined, showing significant velocity structure on lengths of ∼200 pc, which is much greater than the spatial resolution of the rotation curve. Furthermore, the shape of the rotation curves for the first and fourth quadrants, even after subtraction of a circular rotation fit shows a surprising degree of correlation with a roughly sinusoidal pattern between 4.2<R<7 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗