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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Improving the laser performance of ion beam sputtered dielectric thin films through the suppression of nanoscale defects by employing a xenon sputtering gas

Laser damage-prone precursors in high index materials such as hafnia are believed to be the primary limiter in the performance of dielectric multilayer films to advance ultra-high power and energy laser applications. Removing or suppressing these precursors is the key to fabricating laser damage resistant thin films for the enabling technologies. Early work has revealed that nanobubbles formed by entrapped argon (Ar) working gas in ion beam sputtering (IBS) produced hafnia films are primarily responsible for the onset of laser damage upon exposure to UV, ns-laser pulses. In this study, we demonstrate that the UV ns-laser damage onset of IBS produced hafnia films can be improved to 3.1 +/- 0.2 J/cm 2 by substituting the conventional Ar working gas with xenon (Xe), a nearly 1 J/cm 2 increase from that of the Ar produced hafnia films. In addition to the suppression of the overall point-defect density of the hafnia films, the reduction of the Xe entrapment eliminates the nanobubbles and the generation of plasmas that initiates the laser damage. The defect suppression and its correlation to the increase in laser damage threshold is revealed by the combined analysis of Rutherford backscattering spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, and laser damage testing. Monte Carlo simulations suggest a much smaller entrapment of Xe gas by comparison to Ar, which is attributed to the significant difference in the energy of the reflected neutrals (3X) which are likely to be implanted. These results provide an effective process route with a fundamental understanding for producing high laser damage resistant dielectric films for high power and high energy laser applications.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Ion beam sputter etching of orthopedic implanted alloy MP35N and resulting effects on fatigue

The effects of two types of argon ion sputter etched surface structures on the tensile stress fatigue properties of orthopedic implant alloy MP35N were investigated. One surface structure was a natural texture resulting from direct bombardment by 1 keV argon ions. The other structure was a pattern of square holes milled into the surface by a 1 keV argon ion beam through a Ni screen mask. The etched surfaces were subjected to tensile stress only in fatigue tests designed to simulate the cyclic load conditions experienced by the stems of artificial hip joint implants. Both types of sputter etched surface structures were found to reduce the fatigue strength below that of smooth surface MP35N.

Wintucky, E. G.↗
NASA NTRS1994

Optical Scattering and Microstructure of Ion Beam Deposited Metal Coatings

Thin films of gold and platinum have been deposited onto super-polished fused silica substrates using thermal evaporation, ion assisted deposition (IAD), sputtering and ion assisted sputtering. The influence of ion beam flux, coating material and deposition rate on the films microroughness have been investigated. Coatings of gold and platinum have been bombarded with low energy (10-20 eV) Ar ions from an electron cyclotron resonance (ECR) ion source during deposition. Short range surface microroughness of coated surfaces has been examined using scanning tunneling microscopy (STM) and atomic force microscopy (AFM), while long range surface microroughness has been characterized using an angle resolved optical scatterometer. Results indicate that bombardment with low energy ions causes significant reduction in microroughness of metal coatings.

metal↗
DOE OSTI2022

Excitation of long electrostatic solitary waves in ion beam neutralization process

Unusually long electrostatic solitary waves (ESWs) are discovered in a particle-in-cell simulation study of the process of ion beam neutralization by electron emission from a filament. These ESWs are long because the density perturbation responses to the potential wells created by the ESWs are very small. Notably, the density perturbation is small because the trapped (positive) and untrapped (negative) electron density perturbations nearly compensate each other because of a non-Maxwellian electron velocity distribution in the beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Metal DiSulfide thin films synthesized by pulsed ion beam ablation: Self-assembled structures with improved mechanical properties in humid conditions

Thin films composed of transition metal dichalcogenides such as molybdenum disulfide (MoS 2 ) or tungsten disulfide (WS 2 ) are well known for their solid lubricating behavior in dry environments such as space, but deteriorate rapidly in environments where oxygen is present. There have been many attempts over recent decades to improve MoS 2 lubricating performance in humid environments by addition of metals such as titanium to the film. The additions have come in the form of co-sputtering with the MoS 2 , or formation of nano multilayer coatings. We have previously reported on the synthesis of MoS 2 films by high-power ion beam ablation [Prasad et al, Matls. Lett. 65 (2010) 4–6]. The resulting films are observed to contain spheres of pure Mo of 10–100 nm size evenly dispersed throughout the ~1 μm-thick film, a form of self-assembly not before seen in films produced by sputtering or by pulsed laser deposition (PLD). The remaining Mosingle bondS matrix was observed to crystalize in situ under frictional contact into MoS 2 with the basal planes orienting themselves in the direction of sliding underneath the wear surface. The present study concerns metal additions in the form of alternating layers with MoS 2 deposited in between from an ablation target. The addition of Ti resulted in the extension of good tribological performance to humid air conditions, but the path to good performance appears to be relatively narrow. The same distributed Mo spheres were present in the new film, and similar self-assembled morphologies when V was substituted for the Ti, and when multilayers were formed of WS 2 with Zr additions. Furthermore, it appears that addition of Ti resulted in improvements in mechanical film strength that contributed to the wear ability in humid conditions.

Intense ion beams↗
NASA NTRS1983

Interfacial electrical properties of ion-beam sputter deposited amorphous carbon on silicon

Amorphous, 'diamond-like' carbon films have been deposited on Si substrates, using ion-beam sputtering. The interfacial properties are studied using capacitance and conductance measurements. Data are analyzed using existing theories for interfacial electrical properties. The density of electronic states at the interface, along with corresponding time constants are determined.

Khan, A. A.↗
NASA NTRS1974

Calorimetric detection of neutral-atom content of ion beam

Energy deposition technique deduces neutral-beam flux or dose from measured values of incremental resistance increases in platinum wire passed through beam. Steady-state heat balance analysis led to equivalent neutral-beam current. Method was used to detect neutral-atom content of 60-keV argon ion beam.

Roberts, A. S., Jr.↗
NASA NTRS1998

Fluoropolymer Films Deposited by Argon Ion-Beam Sputtering of Polytetrafluoroethylene

The FT-IR, XPS and UV spectra of fluoropolymer films (SPTFE-I) deposited by argon ion-beam sputtering of polytetrafluoroethylene (PTFE) were obtained and compared with prior corresponding spectra of fluoropolymer films (SPTFE-P) deposited by argon rf plasma sputtering of PTFE. Although the F/C ratios for SPTFE-I and -P (1.63 and 1.51) were similar, their structures were quite different in that there was a much higher concentration of CF2 groups in SPTFE-I than in SPTFE-P, ca. 61 and 33% of the total carbon contents, respectively. The FT-IR spectra reflect that difference, that for SPTFE-I showing a distinct doublet at 1210 and 1150 per centimeter while that for SPTFE-P presents a broad, featureless band at ca. 1250 per centimeter. The absorbance of the 1210-per centimeter band in SPTFE-I was proportional to the thickness of the film, in the range of 50-400 nanometers. The SPTFE-I was more transparent in the UV than SPTFE-P at comparable thickness. The mechanism for SPTFE-I formation likely involves "chopping off" of oligomeric segments of PTFE as an accompaniment to "plasma" polymerization of TFE monomer or other fluorocarbon fragments generated in situ from PTFE on impact with energetic Ar ions. Data are presented for SPTFE-I deposits and the associated Ar(+) bombarded PTFE targets where a fresh target was used for each run or a single target was used for a sequence of runs.

Golub, Morton A.↗
DOE OSTI2023

Kinetic modeling of solitary wave dynamics in a neutralizing ion beam

In this work, we characterize the formation and evolution of electrostatic solitary waves (ESWs) in the space-charge neutralization of ion beams using particle-in-cell simulations. These waves become excited when the electrons emitted from an external filament source initiate a two-stream instability in the beam. We show that such electrostatic waves become excited in both two-dimensional (2D) and three-dimensional (3D) beams with different shapes and sizes. Through a 1D Bernstein–Greene–Kruskal (BGK) analysis of the 2D beam, we find that the non-Maxwellian nature of the beam electrons gives rise to large-sized ESWs that are not predicted by BGK theory since it assumes a Maxwellian electron velocity distribution in the beam. Finally, we show that a 1D BGK theory is inadequate to describe ESWs in 3D beams because of complex electron trajectories.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

A guided ion beam investigation of UO 2 + thermodynamics and f orbital participation: Reactions of U + + CO 2 , UO + + O 2 , and UO + + CO

A guided ion beam tandem mass spectrometer was employed to study the reactions of U + + CO 2 , UO + + O 2 , and the reverse of the former, UO + + CO. Reaction cross sections as a function of kinetic energy over about a three order of magnitude range were studied for all systems. The reaction of U + + CO 2 proceeds to form UO + + CO with an efficiency of 118% ± 24% as well as generating UO 2 + + C and UCO + + O. The reaction of UO + + O 2 forms UO 2 + in an exothermic, barrierless process and also results in the collision-induced dissociation of UO + to yield U + . In the UO + + CO reaction, the formation of UO 2 + in an endothermic process is the dominant reaction, but minor products of UCO + + O and U + + (O + CO) are also observed. Analysis of the kinetic energy dependences observed provides the bond energies, D 0 (U + –O) = 7.98 ± 0.22 and 8.05 ± 0.14 eV, D 0 (U + –CO) = 0.73 ± 0.13 eV, and D 0 (OU + –O) = 7.56 ± 0.12 eV. The values obtained for D 0 (U + –O) and D 0 (OU + –O) agree well with the previously reported literature values. To our knowledge, this is the first experimental measurement of D 0 (U + –CO). Furthermore, an analysis of the oxide bond energies shows that participation of 5f orbitals leads to a substantial increase in the thermodynamic stability of UO 2 + relative to ThO 2 + and especially transition metal dioxide cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1983

Field-aligned ion beams upstream of the earth's bow shock Evidence for a magnetosheath source

High time resolution ISEE-1 and -2 observations of upstream field-aligned ion beams at several crossings of the earth's bow shock indicate that some beams are due to high energy magnetosheath particles leaking through the shock into the upstream region. The distribution immediately downstream of these oblique shocks consists of a 'core' of directly transmitted, slightly heated ions, plus a crescent-shaped, high-velocity distribution, centered roughly on the magnetic field in the direction toward the upstream region, with a fairly well defined low velocity cutoff.

Thomsen, M. F.↗
NASA NTRS1982

Ion beam deposition of amorphous carbon films with diamond like properties

Carbon films were deposited on silicon, quartz, and potassium bromide substrates from an ion beam. Growth rates were approximately 0.3 micron/hour. The films were featureless and amorphous and contained only carbon and hydrogen in significant amounts. The density and carbon/hydrogen ratio indicate the film is a hydrogen deficient polymer. One possible structure, consistent with the data, is a random network of methylene linkages and tetrahedrally coordinated carbon atoms.

Angus, John C.↗
NASA NTRS1989

Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves

A two-dimensional quasi-linear numerical code was developed for studying ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves. The model assumes that the central plasma sheet is the particle source, and that the last magnetic field lines on which kinetic Alfven waves exist and diffusion occurs can be either open or closed. As the possible source for the excitement of the kinetic Alfven waves responsible for ion diffusion, the resonant mode conversion of the surface waves to kinetic Alfven waves is considered. It is shown that, depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., on whether field lines are open or closed, the ion distribution function may or may not reach a steady state.

Moghaddam-Taaheri, E.↗
NASA NTRS1981

Ion beam texturing of heat transfer surfaces

Nucleate boiling heat transfer is examined as a means of energy conservation. Nucleate boiling curves were obtained for ion beam textured copper surfaces, untreated cooper surfaces, copper surfaces which had been polished and surfaces which had been coated with a plasma deposited polymer. Results show that texturing aids heat transfer while polishing has the opposite effect. The polymer coatings did not change nucleate boiling behavior. Aging effects were observed for untreated and for polished surfaces, while no such effects were noticed for textured surfaces. These data suggest that aging may be dependent on surface microgeometry, which is important in nucleate boiling heat transfer.

Agarwal, P. K.↗
NASA NTRS1981

Method of cold welding using ion beam technology

A method for cold welding metal joints is described. In order to remove the contamination layer on the surface of the metal, an ion beam generator is used in a vacuum environment. A gas, such as xenon or argon, is ionized and accelerated toward the metal surface. The beam of gas effectively sputters away the surface oxides and contamination layer so that clean underlying metal is exposed in the area to be welded. The use of this method allows cold welding with minimal deformation. Both similar and dissimilar metals can be cold welded with this method.

Sater, B. L.↗