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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Development of New Magnetron Sputter Deposition Processes for Laser Target Fabrication

Magnetron sputter deposition is an enabling technology for laser target fabrication. Solutions are readily available for the deposition of most sub-micron-thick elemental films on planar substrates. However, major challenges still remain for the development of robust deposition processes in regimes of ultrathick (over ~10 μm) coatings and nonplanar substrates. These challenging deposition regimes are directly relevant to laser target applications, including both sphero-cylindrical hohlraums and spherical ablators for inertial confinement fusion (ICF) targets. Understanding underlying physical mechanisms for a specific material system is crucial for process development, given the overall complexity of the deposition process, its nonlinear dependence on deposition parameters, and a very large process space, often precluding conventional process optimization approaches. Here, we describe our approach to developing new deposition processes and give practical advice with examples of new results from our ongoing studies of glassy boron carbide ceramics for next-generation ICF ablators and nonequilibrium gold-tantalum alloys for hohlraums for magnetized ICF schemes. Emphasis is given to two major challenges of ultrathick coatings related to achieving process stability and reducing residual stress.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High-Power Impulse Magnetron Sputter Deposition of Ultrathick Amorphous Carbon

Diamond-like carbon (DLC) is a material of interest for inertial confinement fusion (ICF) ablators. However, the deposition of ultrathick DLC coatings, as required for ICF ablator fabrication, remains a challenge. Here, in this study, we use high-power impulse magnetron sputtering to deposit DLC and demonstrate a set of process parameters leading to high-purity, amorphous DLC coatings with a low compressive residual stress of <400 MPa. Coatings with thicknesses of up to 80 μm are demonstrated.

amorphous carbon↗
DOE OSTI2025

Combinatorial Deposition of Ultrathick Ta-W-Au-Bi High-Entropy Alloys for Next-Generation Hohlraums by Direct-Current Magnetron Sputtering

Hohlraum temperature calculations with the model by J. H. Hammer and M. D. Rosen predict a higher X-ray drive from Ta-W-Au-Bi high-entropy alloys compared to pure Au and recently developed Ta 4 Au and Au-Bi hohlraums. Here, we study the microstructure and properties of 25-75−µm-thick Ta-W-Au-Bi alloy films deposited via combinatorial direct-current magnetron sputtering. All of the films have promising physical properties, including high electrical resistivity, that satisfy the requirements for magnetically assisted inertial confinement fusion experiments. While porosity tends to increase with increasing Bi content, we also found that films with Bi content > 44 at. % exhibited densification close to the substrate/film interface and formed a single-phase alloy. In conclusion, these findings provide a potential path forward for the development of Ta-W-Au-Bi alloys for next-generation hohlraum materials.

Magnetron sputtering↗
DOE OSTI2023

Rotating spokes, potential hump and modulated ionization in radio frequency magnetron discharges

Here, in this work, the transition from the gradient drift instability (GDI) into an m = 1 rotating spoke in the radio frequency magnetron discharge was studied by means of the two-dimensional axial-azimuthal (z–y) particle-in-cell/Monte Carlo collision method. The kinetic model combined with the linear analysis of the perturbation revealed that the cathode sheath (axial) electric field E z triggers the GDI, deforming the local potential until the instability condition is not fulfilled and the fluctuation growth stops in which moment the instability becomes saturated. The potential deformation consequently leads to the formation of the potential hump, surrounding which the azimuthal electric field E y is present. The saturation level of E y was found to be synchronized with and proportional to the time-changing voltage applied at the cathode, resulting in the RF-modulation of the electron heating in the E y due to $\nabla B$ drift. In the saturated stage of the instability, it was shown that the rotation velocity and direction of the spoke present in the simulations agree well with the experimental observation (Panjan 2019 J. Appl. Phys.125 203303). In the instability linear stage, the instability mode wavelength and the growth rate were also found to be in good agreement with the prediction of the GDI linear fluid theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Coherent High-Frequency Axial Oscillations in a Partially Magnetized Direct Current Magnetron Discharge

High-frequency oscillations are observed in a neon plasma of a direct current magnetron discharge. At low discharge currents, we see highly coherent 60 MHz fluctuations. Above a distinct current threshold, secondary 5–10 MHz fluctuations emerge in addition to turbulent fluctuations in the 60–100 MHz range. The oscillations in the total discharge current suggest axial wave propagation. A lower-hybrid wave theory is invoked to model the high-frequency oscillations. Here, we attribute the low-frequency modes to a turbulence-driven inverse cascade process, as suggested by recent simulations.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2023

Characterizing the composition, structure, and mechanical properties of magnetron sputtering physical vapor deposition TiN and TiSiN coatings

Ti(Si)N coatings were deposited on Si wafers via magnetron sputtering physical vapor deposition technique. Scanning electron microscopy and atomic force microscopy were used to study the morphologies, grain size, and thicknesses of the different films. X-ray diffraction confirmed the formation of the titanium nitride cubic phase. X-ray photoelectron spectroscopy (XPS) was used to study the silicon and oxygen levels in the films, and high resolution XPS was used to determine the surface oxide to nitride ratios as well as the silicon–nitrogen environment. The hardness of these films was then determined with nanoindentation. It was shown that grain size and film density could be controlled by the Si level and the ion bombardment to eliminate the oxygen level in the nitride coatings, which led to the harder films. It was suggested that due to the miscibility of Si, a ternary TiSiN solid solution was formed. Stronger (200) orientation of the TiN B1-NaCl crystals was associated with increased hardness of the coatings. In conclusion, this crystalline structure was preserved after incorporating Si.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO 2 films is investigated. HfO 2 films were sputtered from a hafnium metal target in an Ar/O 2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μ s stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. In conclusion, these results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Parameters of ZnO films with p-type conductivity deposited by high-frequency magnetron sputtering

It is demonstrated that a reduction in the defect concentration in ZnO films formed by high-frequency magnetron sputtering allows effective doping with acceptor impurities both in the cation (Li) and anion (N{sup +}) sublattices and p-type conductivity with reproducible charge-carrier parameters (concentration and mobility) to be obtained. ZnO films are doped with nitrogen by annealing in a high-frequency gas discharge atmosphere. Hall measurements by the Van der Pauw technique show that the deposition of thin Eu layers on the ZnO film surface increases the concentration and mobility of majority charge carriers. The embedding of metal impurities with different ionic radii (Ag and Au) in the cation sublattice of the ZnO films to compensate misfit stresses makes it possible to enhance the concentration of radiative-recombination centers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation of Cu{sub 2}O and ZnO Crystal Layers by Magnetron Assisted Sputtering and Their Optical Characterization

Copper (I) oxide and zinc oxide films are formed on silicon and glassy quartz substrates by magnetron assisted sputtering. The thickness of the films is tens and hundreds of nanometers. The films are grown at different substrate temperatures and different oxygen pressures in the working chamber. The film samples are studied by the X-ray diffraction technique, scanning electron microscopy, and optical methods. It is established that an increase in the substrate temperature yields a change in the surface morphology of copper (I) oxide films towards the formation of well-pronounced crystallites. The reflectance and Raman spectra suggest that the quality of such films is close to that of bulk Cu{sub 2}O crystals produced by the oxidation of copper. As concerns ZnO films, an increase in the substrate temperature and an increase in the partial oxygen pressure make it possible to produce films, for which a sharp exciton structure is observed in the reflectance spectra and the emission of excitons bound at donors is observed in the luminescence spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation of Luminescence Spectra and Emission Intensity in the UV and Visible Spectral Regions for n-ZnO/p-GaN and n-ZnO/p-ZnO Structures when Depositing ZnO Films by High-Frequency Magnetron Sputtering

The emission spectra of structures based on ZnO films deposited by high-frequency magnetron sputtering are studied. Clearly pronounced emission lines associated with the recombination of free (λ = 363 nm) and bound excitons (λ = 377, 390, 410 nm) are observed in the PL (photoluminescence) spectra (T = 300 K) of n-ZnO/p-GaN:Mg structures, and no substantial emission is observed in the impurity PL region λ = 450–600 nm. Only emission lines characteristic of n-ZnO (λ = 374 nm) are observed in the EL (electroluminescence) spectra of n-ZnO/p-ZnO structures (T = 300 K).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Luminescence and Stimulated Emission of Polycrystalline Cu(In,Ga)Se{sub 2} Films Deposited by Magnetron-Assisted Sputtering

The stimulated emission of Cu(In,Ga)Se{sub 2} alloy thin films formed by magnetron-assisted sputtering onto a sodium-fluoride layer deposited onto a molybdenum layer on a glass substrate is observed. The structural and optical parameters of the films are determined by scanning electron microscopy, local X-ray spectral microanalysis, X-ray structural analysis, and low-temperature luminescence (T = 10 K) measurements in the range of excitation levels of 1.6–75 kW cm{sup –2} provided by nanosecond nitrogen-laser pulses. The stimulated emission threshold corresponds to ~25 kW cm{sup –2}. Comparative analysis of the emission of Cu(In,Ga)Se{sub 2} thin films suggests that the introduction of sodium results in significant improvement of the structural quality, specifically, in a decrease in the density of energy states in the band tails and in a decrease in the concentration of nonradiative-recombination centers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of the Temperature of Photonic Annealing on the Structural and Optical Properties of ZnO Films Synthesized by Dual Magnetron-Assisted Sputtering

Zinc-oxide films 1.4 μm in thickness are deposited onto glassy substrates by the dual magnetron-assisted sputtering of zinc targets in an argon and oxygen gas atmosphere. The dependences of the structural and optical characteristics of the ZnO films on the temperature of postdeposition photonic annealing are studied. It is established that an increase in the annealing temperature yields an increase in the degree of crystallinity of the films. Electron microscopy shows that the deposited ZnO coatings are columnar in structure and the microstructure density and crystallite size increase upon annealing. It is found that, at an annealing temperature of 450–650°C, the optical transmittance increases to >90% in the spectral range 400–1100 nm. The experimental results show that the temperature of vacuum photonic annealing has the most profound effect on the final properties of ZnO coatings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structure and Properties of Gallium-Oxide Films Produced by High-Frequency Magnetron-Assisted Deposition

The properties of gallium-oxide films produced by the radio-frequency magnetron-assisted sputtering of a β-Ga{sub 2}O{sub 3} target with deposition onto sapphire substrates are studied. The as-deposited gallium-oxide films are polycrystalline and contain crystallites of the α and β phases. Exposure to oxygen plasma does not bring about the appearance of new crystallites but makes crystallites several times larger in average dimensions in the substrate plane. After annealing at 900°C, the crystallite size becomes twice as large as that in the unannealed film. The films not subjected to thermal annealing exhibit a high resistance at 20°C. In the range of 50–500°C, the conductivity of the samples (G) only slightly depends on temperature (T) and, as T is elevated further, exponentially increases with the activation energy 0.7–1.0 eV. After annealing of the films in argon at 900°C (30 min), the conductivity G starts to sharply increase at T ≈ 350°C. In the dependence of lnG on T {sup –1}, a maximum in the range of 470–520°C and a portion of decreasing conductivity at higher temperatures are observed. The unusual temperature dependence of the conductivity after annealing is attributed to a change in the structure and phase composition of polycrystalline gallium-oxide films and, possibly, to some effects at the surface. The structures produced on insulating substrates are solar blind in the visible wavelength region and sensitive to radiation in the ultraviolet region (222 nm).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Oxygen Flow Rate on Structural, Electrical and Optical Properties of Zinc Aluminum Oxide Thin Films Deposited by DC Magnetron Sputtering

Zinc Aluminum Oxide thin films were deposited on glass substrates by reactive DC magnetron sputtering method by varying oxygen flow rates from 1 to 4 sccm. Glancing angle X-ray diffraction patterns ofzinc aluminum oxide thin films exhibits (0 0 2) peak with c-plane preferentially oriented parallel to the substrate. The surface morphology and elemental analysis of the films was observed by field emission scanning electron microscopy attached with energy dispersive X-ray analysis spectroscopy. An average optical transmittance of 83–90% is obtained for the films deposited at various oxygen flow rates. The optical band gap of the films increases from 3.41 to 3.53 eV with the increase of oxygen flow rate due to Burstein–Moss effect. The optical dispersion parameters such as dispersion energy (E{sub d}), oscillator energy (E{sub o}) and static refractive index (n{sub o}) were determined using the Wemple-DiDomenico (W-D) single oscillator model. The nonlinear optical parameters such as optical susceptibility (χ{sup (1)}), third order nonlinear optical susceptibility (χ{sup (3)}) and nonlinear refractive index (n{sub 2}) were also determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Ion-Beam Processing during RF Magnetron Sputtering on the properties of ZnO Films

The effect of ion-beam processing alternating with magnetron sputtering on the properties of zinc-oxide thin films is investigated. It is shown that ion-beam processing reduces the growth rate, coherent-scattering-region sizes, and the resistivity. The stoichiometric index, band gap, and refractive index increase. The transparency of the films in the weak absorption region remains unchanged.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Dynamics of pulsed magnetron discharge in high-current electron guns

High-speed video filming is applied to investigate low-pressure (argon 0.053–0.133 Pa) pulsed gas discharge dynamics in a planar magnetron built-in the explosive emission cathode of a high-current electron gun. It has been found that, in the beginning, the discharge starts at the side surface of the cathode and then spreads to its face. The stability of the discharge ignition instant at the cathode face as a function of the working pressure of the gas and the cathode design has been studied. It has been found that the pulsed longitudinal magnetic field results in the discharge switching over in the axial direction onto the electron gun collector. A qualitative explanation of the observed discharge behavior has been given.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Cobalt Modification of Thin Rutile Films Magnetron-Sputtered in Vacuum

Using X-ray phase analysis, atomic force microscopy, and secondary ion mass-spectrometry, the phase formation and component distribution in a Co–TiO{sub 2} film system have been investigated during magnetron sputtering of the metal on the oxide and subsequent vacuum annealing. It has been found that cobalt diffuses deep into titanium oxide to form complex oxides CoTi{sub 2}O{sub 5} and CoTiO{sub 3}. A mechanism behind their formation at grain boundaries throughout the thickness of the TiO{sub 2} film is suggested. It assumes the reactive diffusion of cobalt along grain boundaries in the oxide. A quantitative model of reactive interdiffusion in a bilayer polycrystalline metal–oxide film system with limited solubility of components has been developed. The individual diffusion coefficients of cobalt and titanium have been determined in the temperature interval 923–1073 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Annealing Temperature on the Microstructure and Morphology of TiN Films Synthesized by Dual Magnetron Sputtering

TiN films synthesized on leucosapphire substrates by dual magnetron sputtering have been annealed in vacuum at 600, 700, 800, and 900°C for 2 min. The microstructure and morphology of the films have been studied by X-ray diffraction and scanning electron microscopy at different temperatures. It has been found that annealing changes the microstructure, texture, grain size, and surface roughness of the TiN films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗