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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Holistic comparison of environmental barrier coating material candidates through design of a figure of merit

The first figure of merit for environmental barrier coating (EBC) materials was designed through a ranking system for material properties pertaining to established EBC failure modes in service. Seven past, present, and novel EBC candidate materials were used in the figure of merit design: SiO 2 , Ba 0.75 Sr 0.25 Al 2 Si 2 O 8 (BSAS), HfSiO 4 , Yb 2 Si 2 O 7 , Yb 2 SiO 5 , Yb 2 O 3 , and YbPO 4 . Utilizing compiled data from the literature, the presented figure of merit verified Yb 2 Si 2 O 7 as the state-of-the-art candidate with optimal EBC properties and inferred that YbPO 4 should be considered as a potentially viable EBC material candidate. Further, the figure of merit allows for a holistic comparison of EBC candidates and informs experimental and computational search efforts for next-generation complex EBCs. Clear knowledge gaps found through this work include CaO–MgO–Al 2 O 3 –SiO 2 (CMAS)-resistant coatings, EBC lifetimes before delamination, and oxidant diffusion rates in relevant EBC microstructures. It was shown that while some materials show promise for solving a single key failure mode for EBCs (i.e., CMAS reactivity), a community-wide goal should be placed on materials development to achieve acceptable resistance against all major failure modes, which are interconnected. Novel compositionally complex EBC materials, in addition to layered EBC architectures, show promise for the optimization of material properties for long-lifetime EBCs in combustion environments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An examination of the performance of molecular dynamics force fields: Silicon and silicon dioxide reactive ion etching

Classical molecular dynamics (MD) simulations of plasma-surface interactions were performed of physical sputtering and reactive ion etching (RIE), with predictions based on several force fields. In this paper, we focus mainly on SiO 2 but include some results for Si substrates as well. Here, we compare predictions from these MD simulations to experimental studies of SiO 2 physical sputtering (by Ar + ions), RIE of Si, and RIE of SiO 2 (both using F atoms and Ar + ions). MD results using different published force fields are compared to reported yields from published vacuum beam experiments. The near-surface depth profiles predicted using different force fields are compared. One motivation for the present study is to document the nature and magnitude of differences in the predictions for selected systems and conditions of practical interest.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Hydrosilyation of CO 2 using a silatrane hydride: structural characterization of a silyl formate compound

The silatrane hydride compound, [N(CH 2 CH 2 O) 3 ]SiH, reacts with CO 2 in the presence of the [tris(2-pyridylthio)methyl]zinc hydride complex, [Tptm]ZnH, to afford the silyl formate and methoxide derivatives, [N(CH 2 CH 2 O) 3 ]SiO 2 CH and [N(CH 2 CH 2 O) 3 ]SiOCH 3 . The molecular structure of [N(CH 2 CH 2 O) 3 ]SiO 2 CH has been determined by X-ray diffraction, thereby demonstrating that the formate ligand adopts a distal conformation in which the uncoordinated oxygen atom resides with a trans-like disposition relative to silicon. In conclusion, density functional theory calculations indicate that the atrane motif of [N(CH 2 CH 2 O) 3 ]SiO 2 CH is flexible, such that the energy of the molecule changes relatively little as the Si···N distance varies over the range 2.0–3.0 Å.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Fe(Si2O3)2 by Materials Project

FeSiO3(SiO)3 crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of one FeSiO3 ribbon oriented in the (1, 0, 0) direction and one SiO ribbon oriented in the (1, 0, 0) direction. In the FeSiO3 ribbon, Fe is bonded in a rectangular see-saw-like geometry to four O atoms. There are a spread of Fe–O bond distances ranging from 1.83–2.09 Å. Si is bonded in a trigonal non-coplanar geometry to three O atoms. There is one shorter (1.65 Å) and two longer (1.68 Å) Si–O bond length. There are three inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to two equivalent Fe and one Si atom. In the second O site, O is bonded in a bent 120 degrees geometry to two equivalent Si atoms. In the third O site, O is bonded in a water-like geometry to two equivalent Fe atoms. In the SiO ribbon, there are three inequivalent Si sites. In the first Si site, Si is bonded in a single-bond geometry to one O atom. The Si–O bond length is 1.64 Å. In the second Si site, Si is bonded in a single-bond geometry to one O atom. The Si–O bond length is 1.69 Å. In the third Si site, Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.64–1.66 Å. There are three inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the second O site, O is bonded in a bent 120 degrees geometry to two Si atoms. In the third O site, O is bonded in a bent 120 degrees geometry to two equivalent Si atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Collection of Aerosol Particles in a Single-Stage, High Gradient Magnetic Collector

The collection of aerosol particles that have magnetic components such as actinides, Co/Ni/Fe, brass, and alloys are of interest in the nuclear industry and for regulatory applications. The collection of these particles is important for monitoring and a number of collection approaches have been developed based on separations mechanisms including size, mass, electrical or thermal properties. In this work, we present the performance of a single-stage, high gradient magnetic collector with a nickel foam matrix for removing airborne magnetic particles. The collection efficiencies for two different particle size regimes and compositions (NaCl and Fe 3 O 4 below 200 nm and SiO 2 and Fe 3 O 4 at 1-2 μm) were measured to assess the performance of the magnetic collector. The high gradient magnetic collector did not remove nanosized magnetic Fe 3 O 4 particles any more effectively than non-magnetic NaCl particles. However, in the larger size range, the collector more efficiently removed Fe 3 O 4 particles compared to SiO 2 with a collection efficiency of 99% compared to 84% for SiO 2 . The removal mechanism could be attributed to both filtration and the high gradient magnetic field.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Robust highly durable solid oxide fuel cell cathodes – Improved materials compatibility & self-regulating surface chemistry

Solid oxide fuel cells (SOFCs) are electrochemical conversion devices that directly transform hydrogen or hydrocarbon fuels to electricity, with energy efficiencies as high as 90%, coupled with reduced emissions. Several factors, however, remain to be addressed when considering scale-up of SOFC technology, including the need to overcome decreased performance due to sluggish rates of the oxygen reduction reaction (ORR) at the cathode under reduced temperatures and susceptibility to degradation in performance from surface poisoning e.g. from chromia, while limiting the use of critical raw materials (lanthanides and transition metals) present in high performing mixed ionic electronic conducting electrodes like (La,Sr)CoO 3 (LSC). In this project we explored the key descriptors for determining ORR activity in SOFC electrodes and tried to recover performance degradation by applying them to SOFC electrodes. In order to do this, we first selected a model mixed ionic electronic conducting (MIEC) oxide, Pr-doped CeO 2 (Pr 0.1 Ce 0.9 O 2-δ , PCO), which is a chemically stable fluorite and free of inherent poison sources (e.g. Sr segregation in LSC) that potentially react with external impurities such as Cr-species vaporized from the interconnect. The three approaches originally planned in this project are as follows: 1) evaluation of scavenger exsolution characteristics, 2) study of scavengers gettering efficacy following Cr and Si poisoning and 3) integration of new compositions into porous electrodes. Among them, exceptional progress has been made in 2) and 3), especially understanding the role of surface infiltrants in impacting electrode performance and degradation of PCO materials. We found that the Smith acidity scale for binary oxides serves as a powerful descriptor for tuning and predicting the oxygen exchange kinetics on MIEC PCO surfaces. As a result, with infiltration with binary oxides, ranging from strongly basic (Li 2 O) to strongly acidic (SiO 2 ) onto the surface of porous PCO, it was possible to systematically vary the chemical surface exchange coefficient (k chem ) by 6 orders of magnitude! L i2 O increased k chem by nearly 1,000 times over that of pristine PCO, while SiO 2 decreased k chem by nearly the same factor. Strikingly, although the pre-exponential of k chem scales linearly with the acidity of the infiltrated binary oxide, there is nearly no change in the activation energy. With this insight, we attributed the origin of these dramatic changes in k chem values to the systematic increase and decrease in the surface electron density induced by infiltrated binary oxides. More interestingly, although both Cr 2 O 3 and SiO 2 were determined to be acidic by Smith, suggesting that this feature could likely be the primary reason that these compounds serve to poison the ORR on SOFC cathodes, the effect of poisoning could be subsequently tuned by adding multiple infiltrants and controlling their relative surface acidities. We also systematically examined the effect of serial infiltration of basic and acidic oxides. It turned out that serial infiltration of Li not only recovers approximately 20-fold degraded k chem of PCO by acidic Cr 2 O 3 but its k chem is enhanced even beyond that of the non-infiltrated PCO by more than three orders of magnitude. This was further verified with a screen-printing PCO symmetric cell in terms of the electrode performance (area-specific resistance, ASR) related to approach 3). These observations point to acidity as a key descriptor not only in tuning and predicting the ORR activity of SOFC cathodes that largely determines the overall performance of SOFC, but in mitigating and reactivating poisoned electrode performance. This work provides novel guidelines for making the electrode performance much more active and robust in SOFCs, which can further be applied to all applications requiring oxygen exchange reaction, such as electrolyzers, permeation membranes and gas sensors.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

FWP FEAA149: “Next Generation Environmental Barrier Coatings”

Environmental barrier coatings (EBCs) are required coatings for utilization of SiC/SiC ceramic matrix composite (CMC) components in gas turbines, where the EBC represents the life-limiting factor for such components. EBC/CMC systems have shown success in aero-engine applications with increased turbine inlet temperatures and improved efficiencies, which are achieved through higher temperature stability, lower density, and decreased reliance on cooling air compared to traditional superalloys. While industrial gas turbines (IGTs) do not currently utilize SiC/SiC CMCs, the current shift towards low-carbon or carbon-free fuel sources for power generation could result in a need for EBC/CMC components with higher temperature capabilities. In this work, three tasks were outlined to improve understanding of EBC lifetimes to encourage use in IGTs with carbon-free fuel such as hydrogen: 1. Define the bond coating oxidation kinetics and EBC failure criteria, 2. Measure thermal expansion coefficients of each layered material, and 3. Perform advanced characterization and modeling to assess EBC lifetimes. Cyclic steam oxidation tests were conducted on various EBC/Si/SiC chemistries and EBC/SiC architectures to define substrate oxidation kinetics and EBC failure modes. An open-source code was developed to quantify the undulating thermally grown oxide thickness with thousands of measurements from specimen cross-section images. Bond coating oxidation kinetics were determined and used to develop a kinetic and thermodynamic model for predicting EBC lifetimes. High-temperature Raman spectroscopy was utilized for determining the SiO 2 thermally grown oxide phase transformation as the life-limiting feature for EBCs. Model efforts supported the claim that the SiO 2 phase transformation causes elevated stress during thermal cycling with associated cracking that decreases the adhesion strength of the EBC, eventually resulting in coating spallation. The finite element model subroutine will be made publicly available upon internal review. Further development of an EBC lifetime model for IGTs involves definition of a critical SiO 2 thickness for EBC spallation and must also consider both environmental (gas velocity, pressure, etc.) and specimen (EBC dopants, layer architectures, etc.) effects into predicted bond coating oxidation kinetics for long-lifetime components.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Shape-Selective Mesoscale Nanoarchitectures: Preparation and Photocatalytic Performance

We create ordered arrays of shape-selective gold-titania composite nanomaterials at the mesoscale (100 µm to 5 mm) by a combination of both bottom-up and top-down approaches for exquisite control of the size, shape, and arrangement of nanomaterials. Lithographic techniques along with wet chemical synthetic methods were combined to create these composite nanomaterials. The photocatalytic activity of these TiO 2, TiO 2 -Au and SiO 2 -TiO 2 -Au nano-composite mesoscale materials was monitored by the photodegradation of a model analyte, methyl orange, under UV and visible (Vis) illumination. Bare TiO 2 - and SiO 2 -TiO 2 -coated pillar arrays showed significant activity toward methyl orange in UV light with degradation rates on the order of 10 −4 –10 −3 min −1 . The photocatalytic activity of these arrays was also found to depend on the nanoparticle shape, in which particles with more edges and corners were found to be more reactive than spherical particles (i.e., the photocatalytic activity decreased as follows: diamonds > squares > triangles > spheres). SiO 2 -TiO 2 -Au nano-composite pillar arrays were tested in both UV and Vis light and showed increased activity in Vis light but decreased activity in UV light as compared to the bare semiconductor arrays. Additionally, the Au nanorod-functionalized nanoarrays exhibit a strong shape-dependence in their photocatalytic activity toward methyl orange degradation in Vis light.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Shock-tube studies of silicon-compound vapors

Test gas mixtures containing SiO, SiO2, Si2, and SiH were produced in a shock tube by processing shock waves through a mixture of SiCl4 + N2O + Ar, SiH4 + Ar, or SiH4 + O2 + Ar. Absorption spectra of the test gases were studied photographically in the reflected shock region using a xenon flash lamp as the light source in the range of wavelengths between 250 and 600 nm. SiO was found to be a dominant species in the vapors produced by the SiCl4 + N2O and SiH4 + O2 mixtures. Spontaneous combustion was observed in the SiH4 + O2 + Ar mixture prior to the shock arrival, and the resulting solid SiO2 particles evaporated behind the shock wave. Spectral absorption characteristics of SiO, SiO2, Si2, and SiH were determined by studying the test gases.

Park, C.↗
NASA NTRS1989

Laboratory studies of refractory metal oxide smokes

Studies of the properties of refractory metal oxide smokes condensed from a gas containing various combinations of SiH4, Fe(CO)5, Al(CH3)3, TiCl4, O2 and N2O in a hydrogen carrier stream at 500 K greater than T greater than 1500 K were performed. Ultraviolet, visible and infrared spectra of pure, amorphous SiO(x), FeO(x), AlO(x) and TiO(x) smokes are discussed, as well as the spectra of various co-condensed amorphous oxides, such as FE(x)SiO(y) or Fe(x)AlO(y). Preliminary studies of the changes induced in the infrared spectra of iron-containing oxide smokes by vacuum thermal annealing suggest that such materials become increasingly opaque in the near infrared with increased processing: hydration may have the opposite effect. More work on the processing of these materials is required to confirm such a trend: this work is currently in progress. Preliminary studies of the ultraviolet spectra of amorphous Si2O3 and MgSiO(x) smokes revealed no interesting features in the region from 200 to 300 nm. Studies of the ultraviolet spectra of both amorphous, hydrated and annealed SiO(x), TiO(x), AlO(x) and FeO(x) smokes are currently in progress. Finally, data on the oxygen isotopic composition of the smokes produced in the experiments are presented, which indicate that the oxygen becomes isotopically fractionated during grain condensation. Oxygen in the grains is as much as 3 percent per amu lighter than the oxygen in the original gas stream. The authors are currently conducting experiments to understand the mechanism by which fractionation occurs.

Nuth, Joseph A.↗
NASA NTRS1993

Structure and chemistry of Orion S

We present interferometric observations of the SiO J = 2-1, H13CO(+) J = 1-0, HC3N J = 11-10, CH3OH J(K) = 2(0)-1(0), and SO2 J(KpK0) = 8(17)-8(08) transitions along with the 3.1 mm continuum toward the young stellar object Orion S. The HC3N and H13CO(+) emission trace similar spatial and velocity distributions which are extended and follow the Orion molecular ridge. The SiO emission is more spatially confined, peaking to the west of the 3.1 mm continuum source, while the CH3OH emission peaks to the southwest. Weak SO2 emission was detected southeast of the continuum source position. Column densities and fractional abundances are derived for each species at different positions in the region. In general, the molecular abundances near the continuum source are similar to those in the quiescent material near IRc 2, but the abundances decrease toward the continuum source position indicating localized depletions of at least a factor of three. The presence of strong SiO emission with much weaker SO2 emission is interpreted as resulting from high-velocity shock interactions between the outflow from Orion S and the surrounding cloud.

Mcmullin, Joseph P.↗
NASA NTRS1994

Structure and chemistry in the northwestern condensation of the Serpens molecular cloud core

We present single-dish and interferometric observations of gas and dust in the core of the Serpens molecular cloud, focusing on the northwestern condensation. Single-dish molecular line observations are used to probe the structure and chemistry of the condensation while high-resolution images of CS and CH30H are combined with continuum observations from lambda = 1.3 mm to lambda = 3.5 cm to study the subcondensations and overall distribution of dust. For the northwestern condensation, we derive a characteristic density of 3 x 10(exp 5)/ cu cm and an estimated total mass of approximately 70 solar mass. We find compact molecular emission associated with the far-infrared source S68 FIRS 1, and with a newly detected subcondensation named S68 N. Comparison of the large-and small-scale emission reveals that most of the material in the northwest condensation is not directly associated with these compact sources, suggesting a youthful age for this region. CO J = 1 approaches 0 observations indicate widespread outflow activity. However, no unique association of embedded objects with outflows is possible with our observations. The SiO emission is found to be extended with the overall emission centered about S68 FIRS 1; the offset of the peak emission from all of the known continuum sources and the coincidence between the blueshifted SiO emission and blueshifted high-velocity gas traced by CO and CS is consistent with formation of SiO in shocks. Derived abundances of CO and HCO(+) are consistent with quiescent and other star-forming regions while CS, HCN, and H2CO abundances indicate mild depletions within the condensation. Spectral energy distribution fits to S68 FIRS 1 indicate a modest luminosity (50-60 solar luminosity), implying that it is a low-mass (0.5-3 solar mass) young stellar object. Radio continuum observations of the triple source toward S68 FIRS 1 indicate that the lobe emission is varying on timescales less than or equal to 1 yr while the central component is relatively constant over approximately 14 yr. The nature of a newly detected compact emission region, S68 N, is less certain due to the absence of firm continuum detections; based on its low luminosity (less than 5 solar luminosity) and strong molecular emission, S68 N may be prestellar subcondensation of gas and dust.

Mcmullin, Joseph P.↗
NASA NTRS1994

The circumstellar environment of IRAS 05338-0624

Millimeter continuum and spectral line observations with 10 sec, 30 sec, and 60 sec resolution are used to characterize the structure and chemistry of the gas around the young, embedded star, IRAS 05338-0624. On arcminute scales, emission from dense gas tracers outline an isolated condensation centered on the IRAS source position. The condensation is characterized by a size of approximately 60 sec, a density of 2 x 10(exp 5)/cc, and a virial mass of 40 solar mass. Interferometric CS J = 2-1 observations show two peaks, one toward the continuum peak and the other toward a position 14 sec west and 8 sec south. Single-dish maps of SO, CH3OH, and SiO show pronounced wing emission to the west of the IRAS source, which interferometer observations reveal to be a compact region of outflow activity. CS emission at redshifted and blueshifted velocities reveals a bipolar outflow oriented with a position angle of 45 deg, while SiO emission appears to be tracing a fast shock interaction region at the CS red-lobe peak, 14 sec west and 8 sec south of the IRAS source. Finally, H(13)CO(+) emission traces clumps of quiescent gas toward the IRAS source and adjacent to the blue lobe of the outflow. Column densities and molecular fractional abundances are derived to explore the interaction between the surrounding condensation and the young stellar object. We find evidence for gas phase depletions within the overall condensation in several gas tracers (CO, CS, HCN, SO) but not in the region immediately around the young stellar object. Enhanced abundances of SO, CH3OH, and SiO (by factors of 4, greater than 100, greater than 1000, respectively) are observed in the shocked gas; these enhancements may be explained in terms of a nondissociative shock liberating mantle materials that contain some amount of refractory materials, a moderate velocity dissociative shock in which only minor sputtering of Si occurs, or a shock that impacts surrounding material with a range of speeds.

Mcmullin, Joseph P.↗
NASA NTRS1999

Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud

Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2" = 800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at lambda = 3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0 +/- 0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 Msolar for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within approximately 100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 Msolar assuming Td = 24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 2(2)-1(1) transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5"-10" (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular transitions have been observed with the James Clerk Maxwell and Caltech Submillimeter telescopes in the 230, 345, 490, and 690 GHz atmospheric windows toward all four sources, containing, among others, lines of CO, HCO+, HCN, H2CO, SiO, SO, and their isotopomers. These lines show 20-30 km s-1 wide line wings, deep and narrow (1-2 km s-1) self-absorption, and 2-3 km s-1 FWHM line cores. The presence of highly excited lines like 12CO 4-3 and 6-5, 13CO 6-5, and several H2CO transitions indicates the presence of material with temperatures > or approximately 100 K. Monte Carlo calculations of the molecular excitation and line transfer show that the envelope model derived from the dust emission can successfully reproduce the observed line intensities. The depletion of CO in the cold gas is modest compared to values inferred in objects like NGC 1333 IRAS 4, suggesting that the phase of large depletions through the entire envelope is short lived and may be influenced by the local star formation density. Emission in high-excitation lines of CO and H2CO requires the presence of a small amount of approximately 100 K material, comprising less than 1% of the total envelope mass and probably associated with the outflow or the innermost region of the envelope. The derived molecular abundances in the warm (Tkin > 20 K) envelope are similar to those found toward other class 0 YSOs like IRAS 16293-2422, though some species appear enhanced toward SMM 1. Taken together, the presented observations and analysis provide the first comprehensive view of the physical and chemical structure of the envelopes of deeply embedded young stellar objects in a clustered environment on scales between 1000 and 10,000 AU.

NASA Discipline Exobiology↗
NASA NTRS2005

In Situ Electrochemical Deposition of Microscopic Wires

A method of fabrication of wires having micron and submicron dimensions is built around electrochemical deposition of the wires in their final positions between electrodes in integrated circuits or other devices in which the wires are to be used. Heretofore, nanowires have been fabricated by a variety of techniques characterized by low degrees of controllability and low throughput rates, and it has been necessary to align and electrically connect the wires in their final positions by use of sophisticated equipment in expensive and tedious post-growth assembly processes. The present method is more economical, offers higher yields, enables control of wire widths, and eliminates the need for post-growth assembly. The wires fabricated by this method could be used as simple electrical conductors or as transducers in sensors. Depending upon electrodeposition conditions and the compositions of the electroplating solutions in specific applications, the wires could be made of metals, alloys, metal oxides, semiconductors, or electrically conductive polymers. In this method, one uses fabrication processes that are standard in the semiconductor industry. These include cleaning, dry etching, low-pressure chemical vapor deposition, lithography, dielectric deposition, electron-beam lithography, and metallization processes as well as the electrochemical deposition process used to form the wires. In a typical case of fabrication of a circuit that includes electrodes between which microscopic wires are to be formed on a silicon substrate, the fabrication processes follow a standard sequence until just before the fabrication of the microscopic wires. Then, by use of a thermal SiO-deposition technique, the electrodes and the substrate surface areas in the gaps between them are covered with SiO. Next, the SiO is electron-beam patterned, then reactive-ion etched to form channels having specified widths (typically about 1 m or less) that define the widths of the wires to be formed. Drops of an electroplating solution are placed on the substrate in the regions containing the channels thus formed, then the wires are electrodeposited from the solution onto the exposed portions of the electrodes and into the channels. The electrodeposition is a room-temperature, atmospheric-pressure process. The figure shows an example of palladium wires that were electrodeposited into 1-mm-wide channels between gold electrodes.

Yun, Minhee↗
NASA NTRS2020

High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta

We present high angular resolution (∼80 mas) ALMA continuum images of the SN1987A system, together with CO J = 21, J = 65, and SiO J = 54 to J = 76 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in Hα images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J = 6 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J = 6 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J = 2 1 and SiO J = 5 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared–millimeter spectral energy distribution give ejecta dust temperatures of 18–23 K. We revise the ejecta dust mass to Mdust = 0.2–0.4 Mfor carbon or silicate grains, or a maximum of <0.7 Mfor a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.

Interstellar dust↗
DOE OSTI2020

Ultrathin Amorphous Silica Membrane Enhances Proton Transfer across Solid-to-Solid Interfaces of Stacked Metal Oxide Nanolayers while Blocking Oxygen

A large jump of proton transfer rates across solid-to-solid interfaces by inserting an ultrathin amorphous silica layer into stacked metal oxide nanolayers is discovered using electrochemical impedance spectroscopy and Fourier-transform infrared reflection absorption spectroscopy (FT-IRRAS). The triple stacked nanolayers of Co 3 O 4 , SiO 2 , and TiO 2 prepared by atomic layer deposition (ALD) enable a proton flux of 2400 ± 60 s -1 nm -2 (pH 4, room temperature), while a single TiO 2 (5 nm) layer exhibits a threefold lower flux of 830 s -1 nm -2 . Based on FT-IRRAS measurements, this remarkable enhancement is proposed to originate from the sandwiched silica layer forming interfacial SiOTi and SiOCo linkages to TiO 2 and Co 3 O 4 nanolayers, respectively, with the O bridges providing fast H + hopping pathways across the solid-to-solid interfaces. Finally, together with the complete O 2 impermeability of a 2 nm ALD-grown SiO 2 layer, the high flux for proton transport across multi-stack metal oxide layers opens up the integration of incompatible catalytic environments to form functional nanoscale assemblies such as artificial photosystems for CO 2 reduction by H 2 O.

36 MATERIALS SCIENCE↗