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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

High-efficiency selective boron emitter formed by wet chemical etch-back for n -type screen-printed Si solar cells

Front metal contact induced recombination and resistance are major efficiency limiting factors of large-area screen-printed n-type front junction Si solar cells with homogeneous emitter and tunnel oxide passivated back contact (TOPCON). Here, this paper shows the development of a selective boron emitter (p + /p ++ ) formed by a screen-printed resist masking and wet chemical etch-back process, which first grows a porous Si layer and subsequently removes it. Various wet-chemical solutions for forming porous Si layer are investigated. An industrial compatible process with sodium nitrite (NaNO 2 ) catalyst is developed to uniformly etch-back the ~47 Ω/ atmospheric pressure chemical vapor deposited heavily doped boron emitter to ~135 Ω/ by growing a 320 nm porous Si layer within 3 min and subsequently removing it. After etching back, the boron emitter was subjected to a thermal oxidation to lower the surface concentration and the emitter saturation current density J 0e . Various etched-back emitters were evaluated by measuring J 0e on symmetric test structures with atomic layer deposited aluminum oxide (Al 2 O 3 ) passivation. Very low J 0e of 21, 14, and 9 fA/cm 2 were obtained for the 120, 150, and 180 Ω/ etched-back emitters, respectively. A solar cell with a selective emitter (65/180 Ω/ ) formed by this etch-back technology and with an Al/Ag contact on the front and TOPCON on the back gave an open-circuit voltage (V oc ) of 682.8 mV and efficiency of 21.04% on n-type Czochralski Si wafer. Finally, this demonstrates the potential of this technology for next generation high-efficiency industrial n-type Si solar cells.

14 SOLAR ENERGY↗
DOE OSTI2017

Time-resolved, dual heterodyne phase collection transient grating spectroscopy

The application of optical heterodyne detection for transient grating spectroscopy (TGS) using a fixed, binary phase mask often relies on taking the difference between signals captured at multiple heterodyne phases. To date, this has been accomplished by manually controlling the heterodyne phase between measurements with an optical flat. In this letter, an optical configuration is presented which allows for collection of TGS measurements at two heterodyne phases concurrently through the use of two independently phase controlled interrogation paths. This arrangement allows for complete, heterodyne amplified TGS measurements to be made in a manner not constrained by a mechanical actuation time. Measurements are instead constrained only by the desired signal-to-noise ratio. A temporal resolution of between 1 and 10 s, demonstrated here on single crystal metallic samples, will allow TGS experiments to be used as an in-situ, time-resolved monitoring technique for many material processing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Comparison of single-ion molecular dynamics in common solvents

Laying a basis for molecularly specific theory for the mobilities of ions in solutions of practical interest, we report a broad survey of velocity autocorrelation functions (VACFs) of Li + and PF 6 - ions in water, ethylene carbonate, propylene carbonate, and acetonitrile solutions. We extract the memory function, γ(t), which characterizes the random forces governing the mobilities of ions. Here, we provide comparisons controlling for the effects of electrolyte concentration and ion-pairing, van der Waals attractive interactions, and solvent molecular characteristics. For the heavier ion (PF 6 - ), velocity relaxations are all similar: negative tail relaxations for the VACF and a clear second relaxation for γ(t), observed previously also for other molecular ions and with n-pentanol as the solvent. For the light Li + ion, short time-scale oscillatory behavior masks simple, longer time-scale relaxation of γ(t). But the corresponding analysis of the solventberg Li + (H 2 O) 4 does conform to the standard picture set by all the PF 6 - results.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Scanning microwave imaging of optically patterned Ge 2 Sb 2 Te 5

The measurement of inhomogeneous conductivity in optically crystallized, amorphous Ge 2 Sb 2 Te 5 (GST) films is demonstrated via scanning microwave impedance microscopy (MIM). Qualitative consistency with expectations is demonstrated in spots crystallized by focused coherent light at various intensities, exposure times, and film thicknesses. The characterization of process imperfections is demonstrated when a mask is used to optically pattern the nanoscale features of crystalline GST in the amorphous film. In conclusion, these measurements show the ability of MIM to resolve partial crystallization, patterning faults, and other details in optically patterned GST.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A low cost and large-scale synthesis of 3D photonic crystal with SP2 lattice symmetry

In this work, a novel lithographic method is proposed to prepare three-dimensional (3D) photonic crystal (PC) that is different from conventional top-down and bottom-up approaches. The method combines a 2D optical mask and off-the-axis double optical exposures to create a desirable 3D PC structure. Since the method uses only two optical exposures of a photo-resist layer, it is inherently a low-cost, high throughput and wafer-scale lithographic method. The method is implemented to make a slanted post 3D PC having the SP2 lattice symmetry. Three types of SP2 3D PC structures were successfully fabricated with a minimum feature size of d=1.5 μm over a large scale of 8x10 mm 2 , without any observable fabrication defects. The SP2 PCs are: (i) SU8 posts in air background, (ii) air pores in CdS background and (iii) Pt coated on SU8 SP2 templates. A spectroscopic study of the SP2 PCs shows select spectral regions of high reflectance, indicating the existence of a photonic stop band. This low-cost and large-scale method could enable broader technological impacts of 3D PC materials in areas such as thermo-photovoltaics and above room-temperature Bose-Einstein Condensation. Furthermore, this off-axis method could lead to the creation of an entirely new class of slanted-rod based photonic crystals, such as topological photonic crystal in 3D.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Real frequency tearing layers with parallel dynamics and the effect on error field locking and resistive wall modes

The response to tearing perturbations of a resonant layer within a toroidal plasma often includes real frequencies. These real frequencies are of importance not only for the stability of the tearing mode but also for determining the response to an error field, including locking torques, and the stability properties when interacting with a resistive wall. Unfortunately, including the physics which drives these frequencies can make the model highly complicated and mask the root physics mechanisms driving the response, making it difficult to draw connections between the physics mechanisms occurring in different regimes. Here, we present a simple and intuitive method to derive the tearing mode layer properties in various regimes of resistive MHD with the key physics effects of pressure gradient, toroidal field line curvature and parallel dynamics, focusing on two important regimes: The resistive-inertial (RI) and the viscoresistive (VR) regimes. The usual Glasser effect, a toroidal effect which involves real frequencies, has been discussed only in the context of the RI regime. We find that it occurs in the VR regime as well. Based on these results and the presence of real frequencies in many other tearing regimes, we reach the conclusion that real frequencies in tearing modes are the rule rather than the exception. We also find that the existence of tearing modes with real frequencies in the VR and RI regimes is related to nearby electrostatic resistive interchange modes, themselves with real frequencies. Another important effect we find is that the threshold for the destabilization of resistive wall tearing modes is significantly lowered by plasma rotation in the presence of real frequency layers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Modifications produced on a large magnetized plasma column by a floating end-plate that is partially emissive: Experiment and theory

An experiment is performed on a large plasma device operated by the Basic Plasma Science Facility at the University of California, Los Angeles, in which an electrically floating structure is placed near the end of the 18-m magnetized plasma column. The structure consists of a flat carbon plate that acts as a mask for a smaller, ring-shaped LaB6 emissive surface whose temperature can be externally controlled. This configuration has been previously used to study electron heat transport and pressure-driven avalanches [B. Van Compernolle and G. J. Morales, Phys. Plasmas 24, 112302 (2017)] by biasing the LaB6 ring-cathode with respect to a distant anode in a cold afterglow plasma. In contrast, the present study is performed during the active portion of the steady-state discharge in which the nominal plasma parameters are determined by the injection of an electron beam from a BaO cathode at the opposite end. It is found that, even without an applied bias on the LaB6 cathode, the self-consistent potential and current profiles are modified near the end plate as the LaB6 temperature is increased, resulting in density increases on the field lines in contact with the ring-cathode. In the absence of enhanced ionization, at the largest cathode temperatures, the ambient density can be doubled. A theoretical model is presented that provides a quantitative explanation for the experimental observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Current loss analysis in photoelectrochemical devices

Ongoing efforts to stabilize the operation of photoelectrochemical (PEC) devices remain critical for achieving economically viable solar fuel production, as devices with lifetimes on the order of 10 to 30 years are projected requirements for utility-scale, PEC device implementation. However, insight into the causes of device degradation and activity losses is generally provided by monitoring the device current, a quantity which masks the relative contributions of photovoltaic component degradation and electrocatalyst activity drops to overall performance losses. In this study, an approach for deconvoluting the various contributors to PEC device losses is described. In particular, the causes for observed fluctuations in device performance are determined through the collection of real-time, current–voltage data, paired with an analytical method that enables the decomposition of drops in device current into its constituent photovoltaic- and catalyst-driven performance losses. We test the validity of this approach by applying it to the data collected for a PEC hydrogen evolution test-bed.

14 SOLAR ENERGY↗
DOE OSTI2021

Signatures of electronic and nuclear coherences in ultrafast molecular x-ray and electron diffraction

Femtosecond x-ray and electron diffraction hold promise to image the evolving structures of single molecules. We present a unified quantum-electrodynamical formulation of diffraction signals, based on the exact many-body nuclear + electronic wavefunction that can be extracted from quantum chemistry simulations. This gives a framework for analyzing various approximate molecular dynamics simulations. We show that the complete description of ultrafast diffraction signals contains interesting contributions involving mixed elastic and inelastic scattered photons that are usually masked by other larger contributions and are neglected. These terms include overlaps of nuclear wavepackets between different electronic states that provide an electronic decoherence mechanism and are important for the time-resolved imaging of conical intersections.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Microscopic model of the doping dependence of linewidths in monolayer transition metal dichalcogenides

A fully microscopic model of the doping-dependent exciton and trion linewidths in the absorption spectra of monolayer transition metal dichalcogenides in the low temperature and low-doping regime is explored. The approach is based on perturbation theory and avoids the use of phenomenological parameters. In the low-doping regime, we find that the trion linewidth is relatively insensitive to doping levels, while the exciton linewidth increases monotonically with doping. On the other hand, we argue that the trion linewidth shows a somewhat stronger temperature dependence. The magnitudes of the linewidths are likely to be masked by phonon scattering for T ≥ 20 K in encapsulated samples in the low-doping regime. We discuss the breakdown of perturbation theory, which should occur at relatively low-doping levels and low temperatures. Our work also paves the way toward understanding a variety of related scattering processes, including impact ionization and Auger scattering in clean 2D samples

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Dynamically morphing microchannels in liquid crystal elastomer coatings containing disclinations

Liquid crystal elastomers (LCEs) hold a major promise as a versatile material platform for smart soft coatings, since their orientational order can be predesigned to program a desired dynamic profile. In this work, we introduce temperature-responsive dynamic coatings based on LCEs with arrays of singular defects-disclinations that run parallel to the surface. The disclinations form in response to antagonistic patterns of the molecular orientation at the top and bottom surfaces, imposed by the plasmonic mask photoalignment. Upon heating, an initially flat LCE coating develops linear microchannels located above each disclination. The stimulus that causes a non-flat profile of LCE coatings upon heating is the activation force induced by the gradients of molecular orientation around disclinations. To describe the formation of microchannels and their thermal response, we adopt a Frank-Oseen model of disclinations in patterned director field and propose a linear elasticity theory to connect the complex spatially-varying molecular orientation to the displacements of the LCE. The thermo-responsive surface profiles predicted by the theory and by the finite element modeling are in good agreement with the experimental data; in particular, higher gradients of molecular orientation produce a stronger modulation of the coating profile. The elastic theory and the finite element simulations allow us to estimate the material parameter that characterizes the elastomer coating’s response to the thermal activation. The disclinations containing LCEs show potential as soft dynamic coatings with a predesigned responsive surface profile.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ion-temperature determination with a baffled Langmuir probe

An electrostatic Langmuir probe for real-time measurements of parameters in magnetized plasma is tested in fully ionized, barium, Q-machine plasma. The small-diameter, long-length, tungsten wire sensor, i.e., the probe tip, oriented with its cylindrical axis perpendicular to the magnetic field (B), is partially shielded by ceramic baffles, or masks, that form sensor-access slots between the baffles. Adjusting the azimuthal orientation of the slots, by rotating the probe about its cylindrical axis, changes the fraction of proximity gyro-orbiting electrons, relative to the fraction of proximity gyro-orbiting ions, that can access the recessed sensor along the magnetic field. Thus, the ratio between the electron and ion saturation currents, $I^{sat}_e$ and $I^{sat}_i$, can be adjusted without having affected the probe bias voltage V b . When optimally shielded ($I^{sat}_e/I^{sat}_i$=1), accurate, real-time measurements of space potential Vs can be acquired. When maximally shielded ($I^{sat}_e/I^{sat}_i$ << 1), accurate, real-time measurements of ion temperature T i can be acquired. Subtracting the floating potential V f of an optimally shielded baffled probe from V f of a maximally shielded baffled probe yields T i (and its fluctuation phase) in real time.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Selective area epitaxy of GaAs films using patterned graphene on Ge

We demonstrate selective area epitaxy of GaAs films using patterned graphene masks on a Ge (001) substrate. GaAs selectively grows on exposed regions of the Ge substrate for graphene stripe widths of 10 μm. The selectivity is highly dependent on the growth temperature and annealing time, which we explain in terms of temperature dependent sticking coefficients and surface diffusion. The high nucleation selectivity over several micrometers sets constraints on experimental realizations of remote epitaxy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Design study of an edge current density diagnostic using new high-performance single-channel beam emission spectrometers at DIII-D

A novel Motional Stark Effect spectroscopy system has been designed for application at the DIII-D tokamak. The system is optimized for studies of the poloidal and toroidal magnetic field in the plasma pedestal region with frame rates of up to 10 kHz. Further, light from an existing high-photon-throughput collection lens is analyzed using four single-channel f/2.8 Czerny–Turner spectrometers that use custom-made lens systems instead of mirrors. Each spectrometer has two separate outgoing legs and is operated in a positive grating order, which allows for simultaneous observations of D-alpha and D-beta spectra. Forward modeling using the code FIDASIM shows a radial resolution of the system close to 0.6 cm and sufficiently good spectral resolution when masking the high throughput light collection lens in the horizontal direction to avoid overly strong Doppler broadening of beam emission lines. Moreover, a detailed sensitivity study considering realistic levels of readout and photon noise shows that the poloidal and toroidal magnetic field strengths can be inferred with an uncertainty of less than 1%, which will allow the inference of changes of the plasma current during transient events.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Foreword to special issue: Papers from the 63rd annual meeting of the APS Division of Plasma Physics, November 8–12, 2021

The 63rd annual meeting of the APS Division of Plasma Physics (DPP) was held on November 8–12, 2021 in Pittsburgh at the David Lawrence Convention Center with both a live (in person) component and a virtual component. Following guidance from an APS COVID task force, all in-person attendees were fully vaccinated and masked. More than 800 physicists attended, safely, in-person. With both virtual and on-site participants, discussions were lively, and the research presentations showed unmatched mastery in the modern observation, theory, simulation, and manipulation of plasma. The presentations included four invited review talks, 97 invited talks, four tutorials, and four presentations from this year's prize and award recipients. There were more than 1200 contributed poster presentations and 725 contributed oral presentations. Including both in-person and remote attendees, DPP 2021 had a record of 2232 participants. As a hybrid meeting, in-person presentations of all invited presentations were broadcast live and were accompanied by a Q&A discussion. Contributed oral and poster presentations were prerecorded along with options to schedule in-person discussions on demand. Five mini-conferences were held: “Gatekeeper Workshop: Creating a Diverse, Equitable, and Inclusive Pipeline,” “Collisionless Shocks in Laboratory and Space Plasmas,” “The High Repetition Rate Frontier in High-Energy-Density Physics,” “Measuring and Modeling Plasma Surface Interactions,” and “The Second Mini-Conference on Machine Learning, Data Science and Artificial Intelligence in Plasma Research.” Finally, on the day before the official start of the meeting, an afternoon “for students, by students” included lightning talks, plasma trivia, and an informal occasion to connect with other students, learn how to get the most from the DPP Annual Meeting, and share successful ways to connect with colleagues and advance their professional careers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Effect of material composition of diamond field emission array cathodes on quality of transversely shaped beams

Diamond field emitter array field emission cathodes (DFEA FECs) are attractive for the next generation of injectors due to their ability to produce transversely shaped beams without the need for complex masking or laser schemes. However, reliability of this cathode technology remains a challenging issue as principal mechanisms guiding and allowing for output beam shaping remained poorly understood. Here, this paper reports the results of testing two DFEA FECs with the same pattern and emitter tip geometry. Although both cathodes were able to sustain gradients of 44 MV/m and produce maximum output integral charge of 0.5 nC per radio frequency pulse, their emission patterns were different. One cathode did not produce a shaped beam, while the other one did. This difference was explained by the extent of the local variations of the diamond material across the arrays as discovered by spatially resolved Raman spectroscopy. The main practical takeaways were (i) tip sharpness was not a prerequisite for producing a shaped beam and instead (ii) material characteristics resulting in different cathode ballast resistance affected emission spatial uniformity across the array and hence the beam shaping.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Simulated impact of fill tube geometry on recent high-yield implosions at the National Ignition Facility

Inertial confinement fusion capsules fielded at the National Ignition Facility are filled with deuterium and tritium fuel by means of a fill tube. The fill tube introduces a low-density pathway into the fuel region of the capsule that allows high Z contaminant to invade the hot spot during the course of the implosion. A recent series of nominally identical high-yield implosions on the NIF has exhibited significant variability in performance. We evaluate the impact of the fill tube in these implosions computationally to determine whether variations in fill tube geometry could have contributed to this variability. The main contrast between the fill tube geometry in the six shots was the outer diameter of the capsule bore hole, a conical hole into which the fill tube is inserted. In our simulations, the geometry of the bore hole can play a significant role in the development of nonlinear flows seeded by the fill tube. Additionally, we find that the amount of space between the bore hole and the fill tube is the primary factor that determines the amount of contaminant jetted into the hot spot by the fill tube and, in turn, the level of yield reduction due to the fill tube in our simulations. As a consequence, some capsules with 5 μm fill tubes are predicted to outperform capsules with 2 μm fill tubes. We also find that micrometer-scale changes to bore hole size can impact fusion yields by up to four times near the ignition threshold. Nevertheless, simulation trends do not reproduce experimental yield trends, suggesting that the fill tube geometry was not the primary factor contributing to the observed variability in performance and that the fill tube could be masking sensitivity to other asymmetries such as other micrometer-scale capsule defects like voids that were not included in our simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Measurement of Stark-split beam and carbon charge exchange emissions for simultaneous B-field and temperature/rotation analysis at DIII-D

A set of two newly designed, single-channel Czerny–Turner spectrometers has been deployed at the DIII-D tokamak for measurements of the motional Stark effect (MSE) split beam emission and the C6+ (CVI) carbon charge exchange recombination (CER) emission at high spectral (δλ = 0.13 nm) and temporal (1–5 kHz) resolution. High throughput optics (f/# = 2.8) allow for good signal-to-noise at high time resolution using fast EMCCD detectors. The MSE emission allows for spectral fitting of the magnitude and direction of the local B-field, while the carbon emission yields local ion temperature and toroidal rotation information. To reduce so-called Doppler broadening of the MSE emission, a new channel-specific variable lens-masking approach has been developed. Experimental data collected from the 2023 DIII-D experimental campaign demonstrate the signal quality and instrument fidelity for both diagnostic measurements. Moreover, initial CER data analysis shows a clear evolution of the toroidal rotation during edge localized modes. Initial progress on the advanced MSE model, including a new validated ray-trace model of the DIII-D collection optics, is shown via sensitivity analysis.

Instruments & Instrumentation↗