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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Enhancement of critical current density in YBa{sub 2}Cu{sub 3}O{sub 7} films using a semiconductor ion implanter

An up-to-11-fold enhancement was observed in the in-magnetic-field critical current density (J{sub c}) in epitaxial YBa{sub 2}Cu{sub 3}O{sub 7} films on CeO{sub 2}-buffered SrTiO{sub 3} substrates by irradiation with 200- to 750-keV Si and 200-keV B ions. This enhancement indicates that ion beams in the range of 100 to 1000 keV, which are widely used for modifying the conductive properties of semiconducting materials, can significantly improve the vortex-pinning properties in second-generation superconducting wires. Also observed was a scaling relation between J{sub c} and the density of the vacancies (i.e., of Frenkel pairs) produced by the nuclear collisions between incident ions and target atoms, suggesting that this density is a key parameter in determining the magnitude of the J{sub c} enhancement. Also observed was an additional J{sub c} enhancement by a modification of the depth distribution of the vacancies, thus demonstrating the flexibility in controlling artificial pinning center (APC) properties in physical APC introduction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Induced Quasi-Dynamic Disorder in a Structure of Rhenium Ion-Implanted Quartz Glass

The ultraviolet (UV) absorption spectra were studied in UV–Vis–IR quartz glasses exposed to the rhenium ion irradiation at the energy of 30 keV. An increase in ion fluence (5 × 10{sup 15}–5 × 10{sup 17} cm{sup 2}) is found to result in a characteristic fan-shaped broadening of the optical absorption edge of glasses. The results were interpreted in the context of the generalized Urbach rule (the approximation of ion radiation induced quasi-dynamic disorder). The effective radiation disorder cross section of a glass matrix was evaluated from the dose dependence of characteristic Urbach energy. This parameter was found to vary between 1.07 × 10{sup –17}–1.2 × 10{sup –18} cm{sup 2} with increasing fluence. The optical gap width of implanted samples was estimated via the Tautz method for allowed direct interband transitions. The relationship between the second-order deformation potential constants, revealing the correlation between the Urbach energy and the optical gap width in a SiO{sub 2} quartz glass matrix was established using the equivalence principle of static and dynamic structural disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Terrestrial atmospheric ion implantation occurred in the nearside lunar regolith during the history of Earth’s dynamo

Light volatile elements in lunar regolith are thought to be a mixture of the solar wind and Earth’s atmosphere, the latter sourced in the absence of geomagnetic field. However, the extent to which both the current and primitive geodynamo influence the transport of terres trial ions still remains unclear, and this uncertainty is further complicated by the enigmatic composition and poorly constrained location of the Eoarchean exosphere. Here we use 3-D MHD numerical simulations with contemporary magnetized and Archean unmagnetized atmospheres to investigate how Earth’s intrinsic magnetic field affects this transfer, aiming to constrain how and when the lunar isotopic signature provides a record of Earth’s pale-oatmosphere. We find that atmospheric transfer is efficient only when the Moon is within Earth’s magnetotail. The non-solar contribution to the lunar soil is best explained by implantation during the long history of the geodynamo with present-day solar wind conditions, rather than any short, putatively unmagnetized epoch of early Archean Earth. This further suggests the history of the terrestrial atmosphere, spanning billions of years, could be preserved in buried lunar soils. Our results indicate that the elemental abundances of Apollo samples are very sensitive to Earth’s hydrodynamic exobase altitude, which, at the time of ion implantation, was never smaller than 190 km.

Atmospheric dynamics↗
DOE OSTI2015

Change in equilibrium position of misfit dislocations at the GaN/sapphire interface by Si-ion implantation into sapphire. II. Electron energy loss spectroscopic study

In Part I, we have shown that the addition of Si into sapphire by ion implantationmakes the sapphire substrate elastically softer than for the undoped sapphire. The more compliant layer of the Si-implanted sapphire substrate can absorb the misfit stress at the GaN/sapphire interface, which produces a lower threading-dislocation density in the GaN overlayer. Here in Part II, based on experimental results by electron energy loss spectroscopy and a first-principle molecular orbital calculation in the literature, we suggest that the softening effect of Si results from a reduction of ionic bonding strength in sapphire (α-Al{sub 2}O{sub 3}) with the substitution of Si for Al.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Gallium ion implantation greatly reduces thermal conductivity and enhances electronic one of ZnO nanowires

The electrical and thermal conductivities are measured for individual zinc oxide (ZnO) nanowires with and without gallium ion (Ga{sup +}) implantation at room temperature. Our results show that Ga{sup +} implantation enhances electrical conductivity by one order of magnitude from 1.01 × 10{sup 3} Ω{sup −1}m{sup −1} to 1.46 × 10{sup 4} Ω{sup −1}m{sup −1} and reduces its thermal conductivity by one order of magnitude from 12.7 Wm{sup −1}K{sup −1} to 1.22 Wm{sup −1}K{sup −1} for ZnO nanowires of 100 nm in diameter. The measured thermal conductivities are in good agreement with those in theoretical simulation. The increase of electrical conductivity origins in electron donor doping by Ga{sup +} implantation and the decrease of thermal conductivity is due to the longitudinal and transverse acoustic phonons scattering by Ga{sup +} point scattering. For pristine ZnO nanowires, the thermal conductivity decreases only two times when its diameter reduces from 100 nm to 46 nm. Therefore, Ga{sup +}-implantation may be a more effective method than diameter reduction in improving thermoelectric performance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

1.2-kV Vertical GaN PIN Rectifier With Ion-Implanted Floating Guard Rings

Here, this work reports on the fabrication and properties of a homojunction gallium nitride (GaN) p-i-n (PIN) rectifier fabricated on a free-standing GaN substrate. Uniform device performance is achieved with breakdown voltage (BV) >1.2 kV and low ON-resistance × area ( R ON A ). The statistics of the BV measurements show 58.5% of devices achieve BV >1.3 kV, and 71.1% of devices achieve BV >1.2 kV, as attributed to high quality and control in both epitaxial growth and device process. At room temperature, R ON A is 0.23 mΩ∙ cm 2 at a current density ( J ) of 6.9 kA/cm2. The corresponding Baliga’s figure of merit is >5.97 GW/cm 2 . Temperature-dependent reverse I – V measurements were performed and show a positive temperature coefficient of 0.42 V/K, indicating the avalanche capability of reverse breakdown. Further analysis with the Poole-Frenkel model on the temperature-dependent measurement suggested that a trap-assisted tunneling process contributed to the reverse leakage current. Floating guard rings (FGRs) formed by nitrogen implantation serve as an effective edge termination technique in these GaN PIN rectifiers, resulting in uniform performance in both forward and reverse bias.

42 ENGINEERING↗
DOE OSTI2015

Photothermal Superheating of Water with Ion-Implanted Silicon Nanowires

Nanoparticle-mediated photothermal (PT) cancer therapy has been a major focus in nanomedicine due to its potential as an effective, non-invasive, and targeted alternative to traditional cancer therapy based on small-molecule pharmaceuticals[1,2]. Gold nanocrystals have been a primary focus of PT research[3], which can be attributed to their size tunability[4], well understood conjugation chemistry[5], and efficient absorption of NIR radiation in the tissue transparency window (800 nm – 1 μm) due to their size-dependent localized surface plasmon resonances[6].

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

The influence of vacancy generation at the initial stage of ion implantation

The paper presents a coupled isothermal model at the initial stage of a solid surface treatment with particle beams. Mechanical stresses arising due to the interaction of particles with the surface affect the redistribution of the implanted impurity. Vacancies in the metal surface and their generation under stress are also taken into account. The kinetic law is formulated on the basis of thermodynamics of irreversible processes. The authors used numerical investigation methods. As a result, they have obtained the distributions of impurity concentration and deformations for various time moments. The authors also compare the concentration and deformation profiles with and without vacancies and study the influences of some model parameters. The effect of vacancy generation on the diffusion has been established to lead to an increase in the depth of penetration, as well as in the concentration of impurities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Characterization of Ion Implantation and Irradiation Effects in Interface-Dominated Metallic Composites

The candidate structural and fuel cladding materials for the next-generation nuclear power reactors must possess excellent irradiation damage tolerance, and high mechanical and thermal stability that present a challenge for materials design. Here we report an approach to engineer interphase boundaries in metallic composites to achieve superior resistance to void swelling and prevent loss of plastic deformability after irradiation. Model composite systems of face-centered-cubic (Cu) and body-centered-cubic (Nb, Mo or V) metals are used to elucidate the effects of boundary structure and spacing on the damage accumulation and mechanical properties after irradiation. Transmission electron microscopy (TEM) and nano-mechanical testing are used to characterize the irradiation response. A recent development in in situ straining in high-resolution TEM to measure lattice strains and thereby estimate local stresses corresponding to dislocation nucleation and migration is discussed as a capability that in future can enable quantitative characterization of defect interactions in irradiated materials. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2024

Precise Fermi level engineering in a topological Weyl semimetal via fast ion implantation

The precise controllability of the Fermi level is a critical aspect of quantum materials. For topological Weyl semimetals, there is a pressing need to fine-tune the Fermi level to the Weyl nodes and unlock exotic electronic and optoelectronic effects associated with the divergent Berry curvature. However, in contrast to two-dimensional materials, where the Fermi level can be controlled through various techniques, the situation for bulk crystals beyond laborious chemical doping poses significant challenges. Here, we report the milli-electron-volt (meV) level ultra-fine-tuning of the Fermi level of bulk topological Weyl semimetal tantalum phosphide using accelerator-based high-energy hydrogen implantation and theory-driven planning. By calculating the desired carrier density and controlling the accelerator profiles, the Fermi level can be experimentally fine-tuned from 5 meV below, to 3.8 meV below, to 3.2 meV above the Weyl nodes. High-resolution transmission electron microscopy reveals the crystalline structure is largely maintained under irradiation, while electrical transport indicates that Weyl nodes are preserved and carrier mobility is also largely retained. Our work demonstrates the viability of this generic approach to tune the Fermi level in semimetal systems and could serve to achieve property fine-tuning for other bulk quantum materials with ultrahigh precision.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Beam energy tracking system on Optima XEx high energy ion implanter

The Axcelis Optima XEx high energy implanter is an RF linac-based implanter with 12 RF resonators for beam acceleration. Even though each acceleration field is an alternating, sinusoidal RF field, the well known phase-focusing principle produces a beam with a sharp quasi-monoenergetic energy spectrum. A magnetic energy filter after the linac further attenuates the low energy continuum in the energy spectrum often associated with RF acceleration. The final beam energy is a function of the phase and amplitude of the 12 resonators in the linac. When tuning a beam, the magnetic energy filter is set to the desired energy, and each linac parameter is tuned to maximize the transmission through the filter. Once a beam is set up, all the parameters are stored in a recipe, which can be easily tuned and has proven to be quite repeatable. The magnetic field setting of the energy filter selects the beam energy from the RF Linac accelerator, and in-situ verification of beam energy in addition to the magnetic energy filter setting has long been desired. An independent energy tracking system was developed for this purpose, using the existing electrostatic beam scanner as a deflector to construct an in-situ electrostatic energy analyzer. This paper will describe the system and performance of the beam energy tracking system.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Effect of argon ion implantation on the electrical and dielectric properties of CR-39

The objective of the present work is to study the effect of 130 keV Ar{sup +} ions on the electrical and dielectric properties of CR-39 samples at various doses 5×10{sup 14}, 1×10{sup 15} and 1×10{sup 16} Ar{sup +} cm{sup −2}. Current-Voltage (I-V characteristics) measurements have been used to study the electrical properties of virgin and Ar{sup +} implanted CR-39 specimens. The current has been found to be increased with increasing voltage as well as with increasing ion dose. The dielectric spectroscopy of these specimens has been done in the frequency range of 100 kHz-100 MHz. The dielectric constant has been found to be decreasing whereas dielectric loss factor increases with increasing ion fluence. These kind of behavior observed in the implanted specimens indicate towards the formation of carbonaceous clusters due to the cross linking, chemical bond cleavage, formation of free radicals. The changes observed in the dielectric behavior have been further correlated with the structural changes observed through I-V characteristics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ion beam modification of topological insulator bismuth selenide

In this study, we demonstrate chemical doping of a topological insulator Bi 2 Se 3 using ion implantation. Ion beam-induced structural damage was characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Ion damage was reversed using a simple thermal annealing step. Carrier-type conversion was achieved using ion implantation followed by an activation anneal in Bi 2 Se 3 thin films. These two sets of experiments establish the feasibility of ion implantation for chemical modification of Bi 2 Se 3 , a prototypical topological insulator. Ion implantation can, in principle, be used for any topological insulator. The direct implantation of dopants should allow better control over carrier concentrations for the purposes of achieving low bulk conductivity. Ion implantation also enables the fabrication of inhomogeneously doped structures, which in turn should make possible new types of device designs.

36 MATERIALS SCIENCE↗
NASA NTRS1980

More-reliable SOS ion implantations

Conducting layer prevents static charges from accumulating during implantation of silicon-on-sapphire MOS structures. Either thick conducting film or thinner film transparent to ions is deposited prior to implantation, and gaps are etched in regions to be doped. Grounding path eliminates charge flow that damages film or cracks sapphire wafer. Prevention of charge buildup by simultaneously exposing structure to opposite charges requires equipment modifications less practical and more expensive than deposition of conducting layer.

Woo, D. S.↗
NASA NTRS1974

Ion implantation effects in 'cosmic' dust grains

Cosmic dust grains, whatever their origin may be, have probably suffered a complex sequence of events including exposure to high doses of low-energy nuclear particles and cycles of turbulent motions. High-voltage electron microscope observations of micron-sized grains either naturally exposed to space environmental parameters on the lunar surface or artificially subjected to space simulated conditions strongly suggest that such events could drastically modify the mineralogical composition of the grains and considerably ease their aggregation during collisions at low speeds. Furthermore, combined mass spectrometer and ionic analyzer studies show that small carbon compounds can be both synthesized during the implantation of a mixture of low-energy D, C, N ions in various solids and released in space by ion sputtering.

Bibring, J. P.↗