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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Reversibility, pattern formation, and edge transport in active chiral and passive disk mixtures

In this study, we numerically examine mixtures of circularly moving and passive disks as a function of density and active orbit radius. For low or intermediate densities and/or small orbit radii, the system can organize into a reversible partially phase separated labyrinth state in which there are no collisions between disks, with the degree of phase separation increasing as the orbit radius increases. As a function of orbit radius, we find a divergence in the number of cycles required to reach a collision-free steady state at a critical radius, while above this radius, the system remains in a fluctuating liquid state. For high densities, the system can organize into a fully phase separated state that is mostly reversible, but collisions at the boundaries between the phases lead to a net transport of disks along the boundary edges in a direction determined by the chirality of the active disk orbits. We map the dynamic phases as a function of density and orbit radii and discuss the results in terms of the reversible-irreversible transition found in other periodically driven non-thermal systems. Finally, we also consider mixtures of circularly driven disks and ac driven disks where the ac drive is either in or out of phase with the circular motion and find a rich variety of pattern forming and reentrant disordered phases.

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

Thermal conductance of aluminum oxy-fluoride passivation layers

Here, the thermal properties of plasma-generated aluminum oxyfluoride passivation layers at the surface of aluminum thin films are measured. The oxyfluoride layers are generated using plasmas produced in mixtures of NH 3 and SF 6 to simultaneously remove oxygen and add fluorine to the aluminum surface, an alternative approach to the more conventional two-step methods that utilize HF treatments to remove the native oxide followed by metal-fluoride (e.g., MgF 2 , LiF, and AlF 3 ) thin film deposition that serves to protect the aluminum surface from further oxidation. Here, the change in thermal properties of the layers as a function of plasma processing time is determined. A significant reduction in thermal boundary conductance is measured with the increasing treatment time, which can be related to the increasing fluorine content in the layers. Acoustic reflection measurements suggest this reduced thermal boundary conductance is related to lower bonding strength to aluminum with increasing fluorine.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Origins of hydrogen that passivates bulk defects in silicon heterojunction solar cells

Silicon heterojunction solar cell fabrication incorporates a significant amount of hydrogen into the silicon wafer bulk, and the amount of injected hydrogen is comparable to that introduced by silicon nitride films during a high-temperature firing step. In this work, the origins of the hydrogen injected during heterojunction cell processing have been identified. We demonstrate that the hydrogen plasma treatment that is routinely included to improve surface passivation considerably increases the hydrogen concentration in the wafers. We also show that the hydrogenated amorphous silicon i/p+ stack is more effective than the i/n+ stack for bulk hydrogen incorporation, and both are more effective than intrinsic films alone.

Sun, Chang (ORCID:0000000282140458)↗
DOE OSTI2021

The inductively driven transmission line: A passively coupled device for diagnostic applications on the Z pulsed power facility

The inductively driven transmission line (IDTL) is a miniature current-carrying device that passively couples to fringe magnetic fields in the final power feed on the Z Pulsed Power Facility. The IDTL redirects a small amount of Z’s magnetic energy along a secondary path to ground, thereby enabling pulsed power diagnostics to be driven in parallel with the primary load for the first time. IDTL experiments and modeling presented here indicate that IDTLs operate non-perturbatively on Z and that they can draw in excess of 150 kA of secondary current, which is enough to drive an X-pinch backlighter. Further experiments show that IDTLs are also capable of making cleaner, higher-fidelity measurements of the current flowing in the final feed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Nitrogen plasma passivated niobium resonators for superconducting quantum circuits

Microwave loss in niobium metallic structures used for superconducting quantum circuits is limited by a native surface oxide layer formed over a timescale of minutes when exposed to an ambient environment. Here, in this work, we show that nitrogen plasma treatment forms a niobium nitride layer at the metal–air interface, which prevents such oxidation. X-ray photoelectron spectroscopy confirms the doping of nitrogen more than 5 nm into the surface and a suppressed oxygen presence. This passivation remains stable after aging for 15 days in an ambient environment. Cryogenic microwave characterization shows an average filling-factor-adjusted two-level-system loss tangent Fδ TLS of (2.9±0.5)·10 –7 for resonators with a 3 μm center strip and (1.0±0.3)·10 –7 for a 20 μm center strip, exceeding the performance of unpassivated samples by a factor of four.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Dopant Compensation within the Intrinsic Poly-Si Isolation Region in Poly-Si/SiOx Passivated IBC Si Solar Cells

We report on the effect of dopant compensation within intrinsic poly-Si regions between p- and n-type fingers of poly-Si/SiOx passivated interdigitated back contact (IBC) solar cells using intrinsic poly-Si as the isolation region between the doped poly-Si fingers. First, we show that dopants from the doped fingers contaminate the intrinsic gap, resulting in doping of the entire intrinsic gap and overlap of the dopant tails from each finger. Next, we show that despite this doping across the gap, shunting between the doped fingers does not occur. We show that this is a result of trap-assisted compensation creating a highly resistive intrinsic region, preventing shunt. We simulate shunt resistance across the gap based on local carrier concentration and deep trap density. We show that trap defects within the poly-Si enhance compensation between the dopant tails. We experimentally confirm these predictions by scanning spreading resistance microscopy of the gap showing ~20 um domain with resistivity ~10^7 ..omega.. cm. Additionally, Kelvin probe force microscopy are compared to finite element simulations which result in the same approximate shape for potential profile, indicating diode behavior across the isolation region. These results demonstrate the powerful effect that trap defects have within the poly-Si isolation region and suggest that precision patterning is not as essential as once thought.

dopant compensation↗
DOE OSTI2023

Electrical Analysis of Pulsed Laser Annealed Poly-Si: Ga/SiOx Passivating Contacts

In this contribution, we examine Ga hyper-doped poly-Si/SiOx contacts realized by pulsed laser melting (PLM). Here, we use Ga as a novel p-type dopant and B as a conventional dopant to induce non-equilibrium doping using an excimer laser. We perform simulations to visualize the maximum melt depth profiles within the poly-Si, with a goal of distributing dopants close to the tunneling oxide, but at the same time preserving the passivation. Hall measurements show that sheet resistance for B is lower than Ga due to its higher solid solubility limit in Si. After comparing the Hall active dopant concentration with the chemical concentration obtained by SIMS measurement, we show nearly 100% activation B activation reaching 10^21 cm-3, while only ~20% activation for Ga. Nevertheless, we achieve active doping concentrations of Ga in poly-Si six times higher than its solid solubility limit in Si (~10^19 cm-3). We compare our Hall mobilities with values in the literature for c-Si and show that B mobilities in laser-treated poly-Si are close to that of the literature value for B, while Ga mobilities are lower, possibly due to additional scattering channels within grain boundaries and deformed lattice. We also compare our results on PLM samples with conventional furnace annealed samples, and we show much higher percent activation and mobilities. Previously, we showed a low contact resistivity of 35.5 +/- 2.4 m..omega..cm2. Here, we further confirm this result by scanning spreading resistance microscopy and Kelvin force nanoprobe microscopy. We demonstrate that our poly-Si: Ga/nCz contact exhibits large drift and diffusion currents under normal cell operating voltage, which widens the laser processing window for a good metal/poly-Si/c-Si contact.

high-efficiency solar cells↗
DOE OSTI2024

Enhanced minority carrier lifetime in bulk hydrogen-passivated InAsSbBi

We investigate the bulk passivation of the dilute bismide alloy InAsSbBi by plasma-assisted hydrogenation. InAsSbBi is of significant interest for mid- to long-wave infrared photodetection due to its bandgap flexibility and potential integration with heterostructured photodetector architectures. Epitaxially grown InAsSbBi samples are characterized by photoluminescence and time-resolved photoluminescence measurements for a range of hydrogenation conditions. Increases in the minority carrier lifetime of over 3× are reported, with no degradation over a period of months following the treatment. Photoluminescence measurements confirm that the hydrogenation process improves the InAsSbBi optical properties. These results offer a path toward the improved performance of InAsSbBi-based photodetectors and potentially other narrow bandgap semiconductor materials and material systems.

Physics↗
DOE OSTI2013

Control over the performance characteristics of a passively mode-locked erbium-doped fibre ring laser

We report an all-fibre ultrashort pulse erbium-doped ring laser passively mode-locked by single-wall carbon nanotubes dispersed in carboxymethylcellulose-based polymer films. Owing to intracavity dispersion management and controlled absorption in the polymer films, the laser is capable of generating both femto- and picosecond pulses of various shapes in the spectral range 1.53 – 1.56 μm. We have demonstrated and investigated the generation of almost transform- limited, inversely modified solitons at a high normal cavity dispersion. (control of laser radiation parameters)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Saturable absorber based on silver nanoparticles for passively mode-locked lasers

A saturable absorber based on plane (tabular) stabilised silver nanocrystals, which is promising for picoseconds laser systems operating in the range 650–900 nm, is studied. This material has a plasmon decay time of about 2 ps, while its absorption at a pump intensity of 10 MW cm{sup -2} decreases by 1.6%, which is sufficient for using this crystal for passive mode locking. (control of laser radiation parameters)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Efficient operation of a room-temperature Fe{sup 2+}:ZnSe laser pumped by a passively Q -switched Er:YAG laser

Efficient generation of a train of laser pulses is obtained at room temperature in a Fe{sup 2+}: ZnSe polycrystal pumped by a passively Q -switched Er:YAG laser. The Fe{sup 2+}:ZnSe laser energy reaches 130 mJ at a slope efficiency with respect to the absorbed pump power of 47%. The average pulse repetition rate in the train is ∼100 kHz. (lasers)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Spectral and power characteristics of a 5% Tm : KLu(WO{sub 4}){sub 2}N{sub m}-cut minislab laser passively Q-switched by a Cr{sup 2+} : ZnSe crystal

Laser characteristics of a 5%Tm : KLu(WO{sub 4}){sub 2} N{sub m}-cut minislab laser passively Q-switched by a Cr{sup 2+} : ZnSe saturable absorber are presented. At a pump power of 21 W, the average laser power at a wavelength of 1.91 μm was 3.2 W (pulse duration 35 ns, pulse energy 0.3 mJ). The maximum slope efficiency of the laser in the Q-switched regime was 31%; the loss in power with respect to the cw regime did not exceed 17%. At pump powers above 15 W, the dependence of the output power in the Q-switched regime on the pump power considerably differed from linear, which was explained by the formation of a thermal lens in the saturable absorber volume. The experimental energies and durations of laser pulses well agree with the values calculated from rate equations. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Dual-wavelength Q-switched laser based on a lens-shaped Nd : YAG active element and a Cr{sup 4+}: YAG passive Q-switch

Dual-wavelength Q-switched lasing at wavelengths of 1047 and 1053 nm is achieved in a longitudinally diode-pumped laser with a lens-shaped Nd:YLF active element and a Cr{sup 4+} : YAG passive Q-switch. Dual-wavelength lasing is achieved as a result of transverse mode locking due to the choice of a cavity length corresponding to the close-to-semiconfocal configuration, which provides identical gains for the two laser wavelengths. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Passive harmonic mode-locking in an erbium-doped fibre laser

We report an all-fibre erbium laser operating in the regime of passive harmonic mode-locking based on the effect of nonlinear polarisation rotation. The generation of the 67th harmonic with a pulse repetition rate of 5.62 GHz and a duration of 1.8 ps is demonstrated. It is shown that as the harmonic number increases, both the frequency modulation parameters and the pulse duration change. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Generation of controllable Ince – Gaussian modes in a passively Q-switched microchip laser under truncated decentred Gaussian beam pumping

We report a passively Q-switched (PQS) Nd : YAG/Cr{sup 4+}: YAG microchip laser pumped by a truncated decentred Gaussian beam for controllable Ince – Gaussian (IG) mode generation. IG{sup e}(n, n) modes (n = 0, …, 4) are obtained experimentally by choosing the appropriate truncation parameter, which is defined as a ratio of the radius of the aperture to the beam waist. The IG{sup e}(4, 4) mode is produced in the PQS Nd : YAG/Cr{sup 4+}: YAG microchip laser under decentred Gaussian beam pumping at a pump power of 2.6 W, the mode selection being achieved by reducing the truncation parameter. The threshold pump powers for different IG{sup e}(n, n) modes are theoretically calculated to illustrate the mode selection process. The pulsed IG{sup e}(n, n) (n ≥ 1) mode generation with a peak power exceeding 1 kW and a nanosecond pulse width is obtained in the PQS microchip laser, which is a potential laser source for forming flexible vortex arrays for optical tweezers. (control of laser radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Control over pulsed operation modes of an erbium-doped fibre laser passively mode-locked via nonlinear polarisation rotation

We have experimentally demonstrated the possibility of controlling pulse generation modes of an erbium-doped fibre ring laser operating in the anomalous dispersion regime and passively mode-locked via nonlinear polarisation rotation. It has been shown that individual adjustment of the pump power and intracavity polarisation controllers leads to changes in pulse generation mode, without changing the cavity. We have evaluated the key spectral, temporal and energetic characteristics of the observed pulse generation modes. (control of laser radiation parameters. active media)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Lasing dynamics of diode-pumped Yb – Er laser with a passive Q switch exposed to high-power external light

The temporal dynamics of diode-side-pumped Yb – Er laser, with a passive Co{sup 2+} : MgAl{sub 2}O{sub 4} Q switch illuminated by a light beam (total fluence of 0.15 – 0.16 J cm{sup −2}) from a semiconductor pulsed module, is investigated. It is shown that, using this external illumination, one can change the lasing onset delay and the time jitter ΔT{sub gi}. The dependence of ΔT{sub gi} on the interval between the instant of switching the illumination module on and the lasing peak position t{sub i} has a minimum at |t{sub i}| ≈ 10 μs. The decrease in ΔT{sub gi} with a change in |t{sub i}| from 90 to 10 μs indicates that instant of lasing peak occurrence for the Yb – Er laser is partially controlled by the pulse from the highly stable semiconductor module. If |t{sub i}| < 10 μs, the enhanced luminescence fluence in the cavity of Yb – Er laser exceeds 0.16 J cm{sup −2}; the light beam from the module does not affect much the lasing process in the ytterbium – erbium laser; and, as a consequence, the time jitter recovers the initial value. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Evolution of the stellar-to-dark matter relation: Separating star-forming and passive galaxies from z = 1 to 0

We use measurements of the stellar mass function, galaxy clustering, and galaxy-galaxy lensing within the COSMOS survey to constrain the stellar-to-halo mass relation (SHMR) of star forming and quiescent galaxies over the redshift range z = [0.2, 1.0]. For massive galaxies, M {sub *} ≳ 10{sup 10.6} M {sub ☉}, our results indicate that star-forming galaxies grow proportionately as fast as their dark matter halos while quiescent galaxies are outpaced by dark matter growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their star formation. Our analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z = 1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M {sub *} ∼ 10{sup 10} M {sub ☉}, the fraction of central galaxies on the red sequence increases by a factor of 10 over our redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. We define a 'migration rate' to the red sequence as the time derivative of the passive galaxy abundances. We find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z = 1 to z = 0. These results imply that the efficiency of quenching star formation for centrals is increasing with cosmic time, while the mechanisms that quench the star formation of satellite galaxies in groups and clusters is losing efficiency.

79 ASTRONOMY AND ASTROPHYSICS↗