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DOE OSTI2023

Beam-Impedance Considerations for the EIC HSR Screen

The hadron storage ring (HSR) of the Electron-Ion Collider (EIC) will use the superconducting magnets from the Relativistic Heavy Ion Collider (RHIC). However, the beam pipes of these magnets show too large resistive-wall impedance and secondary electron yield to the HSR beams. The planned solution is to install beam screens that feature a thin film of amorphous carbon with low SEY on top of a high RRR copper layer for reduced impedance. This note discusses beam-impedance considerations that impact the EIC HSR beam screen design.

43 PARTICLE ACCELERATORS↗

DOE OSTI2020

Determination of effective attenuation length of slow electrons in polymer films

Slow electrons (with energy below 10 eV) play an important role in nature and technology. For instance, they are believed to initiate solubility change in extreme ultraviolet resists. Depending on their mobility, such secondary electrons can lead to image blur and degradation of patterning resolution. Hence, it is important to characterize the transport of slow electrons by measuring parameters such as the effective attenuation length (EAL). In this work, we present a technique that allows for prompt characterization of EAL in polymer films. In this experiment, slow electrons are generated in a substrate upon absorption of x-ray photons. The attenuation of electron flux by a polymer film is measured as a function of film thickness, allowing for the determination of EAL for slow electrons. We illustrate this method with poly(hydroxy styrene) and poly(methyl metacrylate) films. Furthermore, we propose an improvement for this technique that would enable the measurement of EAL as a function of electron kinetic energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Field reversal in low pressure, unmagnetized radio frequency capacitively coupled argon plasma discharges

In general, the radio frequency (rf) electric field within a sheath points toward the metal electrode in low pressure, unmagnetized rf electropositive capacitively coupled plasma (CCP) glow discharges. This is due to the large ratio of electron to ion mobility and the formation of an ion sheath. In this work, we studied, using fully kinetic particle-in-cell simulations, a reversed electric field induced by the strong secondary electron emission during the phase of sheath collapse in a high-voltage rf-driven low pressure CCP glow discharge. We explored the transition behavior of the formation of field reversal as a function of driving voltage amplitude and found that field reversal starts to form at around 750 V, for a discharge with an electrode spacing of 4 cm at 10 mTorr argon pressure driven at 13.56 MHz. Accordingly, the energy distribution function of electrons incident on the electrode shows peaks from around 3 to 10 eV while varying the driving voltage from 150 to 2000 V, showing potentially beneficial effects in plasma material processing where relatively directional electrons are preferred to solely thermal diffusion electrons.

Physics↗

DOE OSTI2024

Investigating Gadolinium-Lined Sodium-Iodide Neutron Detectors for Mobile Applications

For enhancing the effectiveness of nonproliferation efforts in neutron detection, most portable instruments rely on 6 Li scintillators, 10 B-based detectors, or gas-filled 3 He proportional counters. Additionally, gamma-ray detectors based on scintillators and semiconductors are often employed for search applications to find radioactive material in the field. These systems typically include dedicated detectors along with separate high voltage supplies and processing electronics for the gamma-ray and neutron detectors. Ideally, a portable radiation detection system should be lightweight, compact, and cost-effective. In the field, scintillators can serve a dual purpose: (1) detecting gamma-rays and (2) detecting neutrons. Gamma-ray detection with scintillators is based on the interaction of gamma-rays within the scintillating material, whereas neutron detection depends indirectly on neutron capture events. These capture events generate conversion electrons and gamma-rays, which can interact with the scintillator. For enhancing neutron capture, the scintillator can be surrounded by neutron absorber materials with a high neutron cross section. The resulting secondary electrons and gamma-rays from neutron interactions, depending on the absorber material used, can then be analyzed to detect the presence of neutron sources. Similarly, semiconductor-based detectors can be employed along with neutron absorbers as liners for neutron detection. 158 Gd has a significantly larger neutron cross section than 3 He, commonly used in gas-filled proportional counters, as shown in Figure 1. For thermal (0.025 eV) neutrons, the absorption cross section of 158 Gd is 10,000 times greater than that of 3 He (refer to Figure 1). This feature makes naturally occurring gadolinium, which consists of 24.8% 158 Gd, a promising neutron absorber material for use in combination with gamma-ray detectors–yielding a hybrid detector–for neutron detection.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗

NASA NTRS1972

The IR emission spectrum of N2 excited under auroral conditions.

Recently determined experimental and theoretical cross sections for electron impact excitation of six triplet states of N2 (A, B, W, C, E, D) have been utilized to predict the absolute IR volume emission rates from N2 under nighttime auroral conditions. Secondary electron fluxes appropriate to an IBC II normal aurora were used in the calculations. The cascade contributions coupling the various electronic states were included as well as the most important quenching processes. The results indicate that the B yields reversibly A and W yields reversibly B cascade processes, which are important in the population of the A, B, and W states, produce appreciable radiation in the 1- to 5-micron wavelength region.

Cartwright, D. C.↗

NASA NTRS1985

Near-conjugate observations of inverted-V electron precipitation using DE 1 and DE 2

A major focus of auroral research has been related to the inverted-V electron precipitation event, distinguished by the 'inverted-V' variation of peak energy flux in an energy-time spectrogram. Thieman and Hoffman (1984), in an examination of plasma data from near-conjugate DE 1/2 passes in the southern hemisphere, have found that some inverted-V events remain reasonably stable over a time span of up to 18 min, while other events change over shorter time periods. The present investigation has the objective to study quantitatively the energization of inverted-V electron fluxes and to compare the results with predictions from adiabatic acceleration by an electrostatic field. The obtained results suggest that the turbulent processes might contirbute minimally to the energy flux of secondary electrons for some events, but significantly for others.

Lin, C. S.↗

DOE OSTI2020

Direct evidence for low-energy electron emission following O LVV Auger transitions at oxide surfaces

Abstract Oxygen, the third most abundant element in the universe, plays a key role in the chemistry of condensed matter and biological systems. Here, we report evidence for a hitherto unexplored Auger transition in oxides, where a valence band electron fills a vacancy in the 2s state of oxygen, transferring sufficient energy to allow electron emission. We used a beam of positrons with kinetic energies of $$\sim 1$$ ∼ 1 eV to create O 2s holes via matter-antimatter annihilation. This made possible the elimination of the large secondary electron background that has precluded definitive measurements of the low-energy electrons emitted through this process. Our experiments indicate that low-energy electron emission following the Auger decay of O 2s holes from adsorbed oxygen and oxide surfaces are very efficient. Specifically, our results indicate that the low energy electron emission following the Auger decay of O 2s hole is nearly as efficient as electron emission following the relaxation of O 1s holes in $$\hbox {TiO}_2$$ TiO 2 . This has important implications for the understanding of Auger-stimulated ion desorption, Coulombic decay, photodynamic cancer therapies, and may yield important insights into the radiation-induced reactive sites for corrosion and catalysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Approaching Angstrom-Scale Resolution in Lithography Using Low-Molecular-Mass Resists (<500 Da)

Resists that enable high-throughput and high-resolution patterning are essential in driving the semiconductor technology forward. The ultimate patterning performance of a resist in lithography is limited because of the trade-off between resolution, line-width roughness, and sensitivity; improving one or two of these parameters typically leads to a loss in the third. As the patterned feature sizes approach angstrom scale, the trade-off between these three metrics becomes increasingly hard to resolve and calls for a fundamental rethinking of the resist chemistry. Low-molecular-mass monodispersed metal-containing resists of high atom economy can provide not only very high resolution but also very low line-width roughness without sacrificing sensitivity. Here we describe a modular metal-containing resist platform (molecular mass <500 Da) where a molecular resist consists of just two components: a metal and a radical initiator bonded to it. This simple system not only is amenable to high-resolution electron beam lithography (EBL) and extreme ultraviolet lithography (EUVL) but also unites them mechanistically, giving a consolidated perspective of molecular and chemical processes happening during exposure. Irradiation of the resist leads to the production of secondary electrons that generate radicals in the initiator bonded to metal. This brings about an intramolecular rearrangement and causes solubility switch in the exposed resist. We demonstrate record 1.9–2.0 nm isolated patterns and 7 nm half-pitch dense line-space features over a large area using EBL. With EUVL, 12 nm half-pitch line-space features are shown at a dose of 68 mJ/cm 2 . In both of these patterning techniques, the line-width roughness was found to be ≤2 nm, a record low value for any resist platform, also leading to a low-performance trade-off metric, Z factor, of 0.6 × 10 –8 mJ·nm 3 . With the ultimate resolution limited by instrumental factors, potential patterning at the level of a unit cell can be envisaged, making low-molecular-mass resists best poised for angstrom-scale lithography.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1986

Carbon and carbon-coated electrodes for multistage depressed collectors for electron-beam devices - A technology review

Various aspects of carbon and carbon-coated multistaged depressed collector (MDC) electrode technology are reviewed. The physical properties of untreated graphite electrodes, ion-textured graphite electrodes, and textured, carbon-coated copper electrodes, and surface treatment procedures for these electrodes are described. The secondary electron emissions of the three electrode types are analyzed. MDC fabrication methods are discussed. The performances of MDCs fabricated with untreated graphite electrodes, ion-textured graphite electrodes, and textured, carbon-coated copper electrodes are evaluated. MDC and TWT efficiency levels for tubes fabricated with the three materials are measured.

Curren, Arthur N.↗

NASA NTRS1978

Research on lunar materials

Abstracts of 14 research reports relating to investigations of lunar samples are presented. The principal topics covered include: (1) optical properties of surface and core samples; (2) chemical composition of the surface layers of lunar grains: Auger electron spectroscopy of lunar soil and ground rock samples; (3) high frequency electrical properties of lunar soil and rock samples and their relevance for the interpretation of lunar radar observations; (4) the electrostatic dust transport process; (5) secondary electron emission characteristics of lunar soil samples and their relevance to the dust transportation process; (6) grain size distribution in surface soil and core samples; and (7) the optical and chemical effects of simulated solar wind (2keV proton and a particle radiation) on lunar material.

Gold, T.↗

NASA NTRS1990

Bremsstrahlung X-rays from Jovian auroral electrons

The spectrum of X-rays from the planet Jupiter is calculated according to an auroral electron beam model. The electrons are assumed to be accelerated by a field-aligned potential drop and penetrate into the atmosphere as a Maxwellian beam of primaries which are scattered, degraded in energy, and merged with a population of ionization secondaries having a power law energy distribution. The soft X-rays observed by the Einstein Observatory satellite are due to bremsstrahlung from the secondary electrons in the H2 atmosphere. The X-ray intensity is best reconciled with a beam of primaries having a characteristic energy 30-100 keV and penetrating the homopause with an auroral energy flux typically of 10-20 ergs/sq cm s but no greater than 50 ergs/sq cm s.

Barbosa, D. D.↗

DOE OSTI2022

Qualitative assessment of uranium ore concentrates and related materials using scanning electron microscopy

Several studies have evaluated the morphology of uranium compounds produced under controlled conditions at the laboratory scale, but it is unclear whether the morphological characteristics of these materials persist in commercially produced uranium ore concentrates (UOCs). To assess the morphology in “real-world” UOCs, we qualitatively evaluated the morphological profile of secondary electron images from over 100 commercial UOCs using a previously published lexicon. We observe differences between samples with differing chemical composition and samples with similar chemical composition and differing provenance. Further, this work contextualizes morphology for commercially produced UOCs and will provide a basis for future machine learning efforts.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2020

Elucidating the Influence of Residual Polymer and Gas Environment on the Electronic Structure of a Graphene Layer Using in Situ APXPS

We use in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and ultraviolet photoelectron spectroscopy (UPS) to develop an effective method for studying changes in the graphene (Gr) electronic structure according to certain circumstance. The amount of polymethyl methacrylate (PMMA) residual polymer (RP), inevitably generated during the Gr transfer process, is significantly reduced from Gr surface by thermal annealing. This processed Gr is then sequentially exposed to specific gas environments (Ar, N 2 , O 2 , and CO 2 ), and APXPS or UPS is carried out to investigate the variations in the Gr electronic structure including the work function. When the amount of PMMA RP on Gr is reduced, the position of the main carbon peak shifts by more than 0.4 eV to a higher binding energy (in XPS spectra), and the secondary electron cutoff moves by about 0.2 eV to a lower binding energy (in UPS spectra). These changes are generally caused by a decrease in the Gr work function. On the other hand, exposure to the gas environments at different temperatures that we investigated did not produce significant changes in the work function and chemical states of Gr. These results confirm that the material in contact with Gr should be considered to achieve the desired Gr performance in electronics.

36 MATERIALS SCIENCE↗

NASA NTRS1992

Gas-exposure enhanced Na* emission from Na-rich surfaces

The optical emission attributed to electronically desorbed excited sodium atoms from NaCl and Na-evaporated surfaces is shown to be enhanced by exposure of the surface to gaseous CO2 and N2. This is the first observation of enhancement of electron-simulated desorption of substrate atoms caused by the exposure of surfaces to gaseous molecules which do not contain the desorbed atoms. The large amount of excited-sodium yield at 60 K provides evidence for nonexistence of the secondary-electron excitation of thermally desorbed ground sodium.

Xu, Jun↗

NASA NTRS2002

Characterization of Corning EPMA Standard Glasses 95IRV, 95IRW, and 95IRX

The preparation, synthesis, and characterization of Corning trace-element glasses 95IRV, 95IRW, and 95IRX by bulk chemical and electron microprobe techniques is discussed. Working values for the doped elements in the 95-series glasses are established. Blank values have been determined by both bulk chemical and electron microprobe analysis, and important x-ray interferences are highlighted. Chemical homogeneity both within a rod cross-section, and along cane length has been documented. These glasses are standard reference materials intended for use as both primary and secondary electron microprobe standards.

Carpenter, Paul K.↗

DOE OSTI2023

Ion-driven destabilization of a toroidal electron plasma—A 3D3V PIC simulation

Ion-driven destabilization of a toroidal electron plasma in a small aspect ratio axisymmetric toroidal device is reported for A r + ions of different initial density values using a high fidelity 3D3V PIC solver. Stability of a recently discovered quiescent quasi-steady state (QQS) of a toroidal electron plasma obtained from “seed” solution as a result of entropy extremization at zero inertia is addressed in the presence of a small ion population. An initial value (f0) of the ion fraction (f = n i / n e) and the corresponding secondary electrons are “preloaded” into the system after the electron plasma attains a QQS state. This procedure is regarded as a proxy to the conventional production of ions in the experimental devices via impact ionization. The resulting electron plasma exhibits destabilized “center of charge motion” (m = 1) along with higher order harmonics with dominant power in the second harmonic. Gradual loss of ions (and also electrons) is observed resulting in time varying f values. Beyond a certain value of f0 (≥ 0.005), growth in wall probe current is observed, which saturates at later simulation time due to the loss of particles. In conclusion, trajectories of ion particles indicate ion trapping in the potential well, which is qualitatively similar to the ion resonance instability in pure electron plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Ultrathin Porous Hydrocarbon Membranes Templated by Nanoparticle Assemblies

Porous polymer membranes are widely desired as catalyst supports, sensors, and active layers for separation membranes. We demonstrate that electron beam irradiation of freely suspended gold or Fe 3 O 4 nanoparticle (NP) monolayer sheets followed by wet chemical etching is a high-fidelity strategy to template two-dimensional (2D) porous crosslinked hydrocarbon membranes. This approach, which relies on secondary electrons generated by the NP cores, can further be used to transform three-dimensional (3D) terraced gold NP supercrystals into 3D porous hydrocarbon membranes. We utilize electron tomography to show how the number of NP layers (monolayer to pentalayer) controls attenuation and scattering of the primary e-beam, which in turn determines ligand crosslink density and 3D pore structure. Furthermore, electron tomography also reveals that many nanopores are vertically continuous due to preferential sintering of NPs. This work demonstrates new routes for the construction of functional nanoporous media.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1989

The nature of the cosmic-ray electron spectrum, and supernova remnant contributions

The observed cosmic-ray (CR) electron spectrum and position fraction e+/(e- + e+) spectrum above 1 GeV are examined, and it is found that a deconvolution of the total spectrum into three components is necessary because of the increase of e+/(e- + e+) above 5 GeV: (1) secondary electrons e+ or e- from the interaction of the CR protons with the interstellar gas provide the total e+ for energies less than 3 GeV, but for energies above 3 GeV these electrons cannot account for the observed positron flux; (2) Electrons (e-) generally thought to derive from supernova remnants (SNRs), probably via shock acceleration, dominate the total spectrum for E of 10 GeV or less but definitely decline relative to total at higher energies; (3) Another (e- + e+) source dominates the total spectrum at E of 40 GeV or greater. The derived spectrum of (2) is consistent in its energy cutoff (though gradual) with that deduced from the observed synchrotron emission of some old SNRs and follows naturally from shock acceleration with synchrotron and inverse Compton scattering losses taken into account. As for (3), nearby pulsars may be important contributors.

Boulares, Ahmed↗