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Thick sputtered tantalum coatings for high-temperature energy conversion applications
Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications. In these applications, high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain operational temperatures and reduce losses due to waste heat. The reflectance of the coatings (8 and 30 μm) was characterized with a conformal protective hafnia layer as-deposited and after one hour anneals at 700, 900, and 1100 °C. To further understand the high-temperature performance of the coatings, the microstructural evolution was investigated as a function of annealing temperature. X-ray diffraction was used to analyze the texture and residual stress in the coatings at four reflections (220, 310, 222, and 321), as-deposited and after anneal. No significant changes in roughness, reflectance, or stress were observed. No delamination or cracking occurred, even after annealing the coatings at 1100 °C. Overall, the results of this study suggest that the thick Ta coatings are a promising alternative to bulk substrates and pave the way for a relatively low-cost and easily integrated platform for nanostructured devices in high-temperature energy conversion applications.
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.
Nanocrystalline high-entropy alloy (CoCrFeNiAl0.3) thin-film coating by magnetron sputtering
Not Available
The impact of nano-bubbles on the laser performance of hafnia films deposited by oxygen assisted ion beam sputtering method
Abstract not provided
Plasma flares in high power impulse magnetron sputtering
Self-organized ionization zones and associated plasma flares were recorded with fast cameras in side-on view. Flare velocities were estimated to be about 20 000 m/s suggesting that the local tangential field E{sub {xi}} is about 2000 V/m based on a concept where flare-causing electrons are initially ejected by E{sub {xi}} Multiplication-Sign B drift. At distances of 10 mm and greater from the target, where the electric field is very small, plasma flares are guided by the magnetic field B.
Optimizing TaO{sub x} memristor performance and consistency within the reactive sputtering “forbidden region”
Standard deposition processes for depositing ReRAM oxides utilize mass flow of reactive gas to control stoichiometry and have difficulty depositing a precisely defined sub-stoichiometry within a “forbidden region” where film properties are discontinuous with mass flow. We show that by maintaining partial pressure within this discontinuous “forbidden region,” instead of by maintaining mass flow, we can optimize tantalum oxide device properties and reduce or eliminate the electroforming step. We also show that defining the partial pressure set point as a fraction of the “forbidden region” instead of as an absolute value can be used to improve wafer-to-wafer consistency with minimal recalibration efforts.
Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta{sub 2}O{sub 5})
Amorphous tantala (a-Ta{sub 2}O{sub 5}) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta{sub 2}O{sub 5} coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta{sub 2}O{sub 5} and other a-T{sub 2}O{sub 5} studies.
Plasma sputtering robotic device for in-situ thick coatings of long, small diameter vacuum tubes
A novel robotic plasma magnetron mole with a 50 cm long cathode was designed, fabricated, and operated. The reason for this endeavor is to alleviate the problems of unacceptable resistive heating of stainless steel vacuum tubes in the BNL Relativistic Heavy Ion Collider (RHIC). The magnetron mole was successfully operated to copper coat an assembly containing a full-size, stainless steel, cold bore, RHIC magnet tubing connected to two types of RHIC bellows, to which two additional pipes made of RHIC tubing were connected. To increase the cathode lifetime, a movable magnet package was developed, and the thickest possible cathode was made, with a rather challenging target to substrate (de facto anode) distance of less than 1.5 cm. Achieving reliable steady state magnetron discharges at such a short cathode to anode gap was rather challenging, when compared to commercial coating equipment, where the target to substrate distance is 10's cm; 6.3 cm is the lowest experimental target to substrate distance found in the literature. Additionally, the magnetron developed during this project provides unique omni-directional uniform coating. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system is driven by a motorized spool. Excellent coating adhesion was achieved. Measurements indicated that well-scrubbed copper coating reduced secondary electron yield to 1, i.e., the problem of electron clouds can be eliminated. Room temperature RF resistivity measurement indicated that a 10 μm copper coated stainless steel RHIC tube has a conductivity close to that of pure copper tubing. Excellent coating adhesion was achieved. The device details and experimental results are described.
Lithium sputtering from lithium-coated plasma facing components in the NSTX divertor
Not Available
Sputtering of lithiated and oxidated carbon surfaces by low-energy deuterium irradiation
Not provided.
Thin film iron pyrite deposited by hybrid sputtering/co-evaporation as a hole transport layer for sputtered CdS/CdTe solar cells
Not Available
Magnetron sputter deposition of ultrathick boron carbide coatings on spherical substrates for inertial confinement fusion
Not Available
Evaluation of sputtered nickel oxide, cobalt oxide and nickel–cobalt oxide on n-type silicon photoanodes for solar-driven O 2 (g) evolution from water
Thin films of nickel oxide (NiO x ), cobalt oxide (CoO x ) and nickel–cobalt oxide (NiCoO x ) produced integrated, protected Si (111) photoanodes integrated, protected Si photoanodes that did not require deposition of a separate heterogeneous electrocatalyst for water oxidation.