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Neutron phase contrast imaging (NPCI) is a non-destructive analysis tool currently in use with thermal neutrons. It relies on neutron transmission gratings to detect the phase signal. These gratings are typically fabricated from gadolinium (Gd), as this element has the highest neutron absorption cross section at 250,000 barns. There is a wealth of literature documenting the fabrication process of these gratings, including depositing Gd via sputter coating, evaporation and particle settling techniques at dimensions appropriate to absorb thermal neutrons. However tighter packing density, less contamination and thicker Gd films are necessary for neutrons at higher energy levels ( >0.025 eV). With these requirements in mind, we investigated the electrodeposition of Gd on Si substrate gratings for use with higher energy neutrons. Electrodeposition of Gd alloys is well documented in literature. With a very cathodic reduction potential of -2.28 V (acidic solution), depositing pure Gd metal is a tricky endeavor. In addition to excessive hydrogen evolution during plating, Gd undergoes rapid oxidation when exposed to air. This phenomenon is exacerbated with thin films due to their high surface area and can lead to pyrophoric events and brittle films that sluff off the substrate over time. We investigated aqueous solutions and with the use of many oxygen scavengers, we successfully plated gadolinium oxide (Gd2O3) thin films. However, this technique was not viable due to poor adhesion and rapid oxidation. Hoping for less oxygen contamination, we moved to two polar, aprotic organic solvents with promising potential windows: dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The solubility of gadolinium(III) salts was investigated in the two solvents. At elevated temperatures, gadolinium(III) fluoride and gadolinium(III) chloride were soluble compounds, as well as gadolinium toluenesulfonic acid (GdTsOH). To increase conductivity, potassium chloride (KCl) and tetrabutylammonium tetrafluoroborate (TBATFB) were used as conducting salts. Pulsed plating techniques led to repeatable thin film deposition and EDS confirmed the presence of gadolinium uniformly spread over the surface. However, these films also suffered from poor adhesion, likely due to water contamination in the bath. The limitations outlined above led to electroplating Gd in dimethyl sulfone (DMSO2). DMSO2 is used in industry as a high-temperature solvent; its large dielectric constant reflects its high polarity, indicating strong intermolecular interactions in liquid phase. A melting temperature of 109 °C eliminates the concern of water contamination in the bath. Solubility tests are being repeated in this new polar solvent and linear sweeps and EIS continue to indicate favorable plating conditions. Parameters, such as Gd metal loading and substrate pretreatments are being optimized for thick films with good adhesion. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-5179 A

We report on a nanoelectrode array sensor for the detection of gaseous iodine at levels below 20 ppb within short exposure times. The sensor is constructed on a free-standing anodic aluminum oxide wafer with 120 nm diameter, 50 um length nanopores. On each wafer surface, continuous metal films are deposited: on one surface, a gold film is deposited such that it covers the nanopores, and, on the opposite surface, a platinum film is deposited such that the nanopores remain open and their volumes in contact with the environment. The gold film serves as the working electrode and the platinum film serves as the auxiliary and pseudo-reference electrode. The nanopores are filled with a pH 9 buffer aqueous solution to create an array of billions/cm2 electrochemical cells in parallel. Ionic conductivity is maintained for environments with relative humidity levels greater than ~30%. Here we report on sensor performance improvements that allow using this sensor in more arid environments, as well as in the presence of other relevant interferent analytes (e.g. Cl2). The detection mechanism is the electrochemical oxidation of anionic species formed by the dissolution and subsequent hydrolysis of gas phase I2 in pH 9 buffer electrolyte. Gas phase I2 dissolves in the buffer following Henry's Law and then is hydrolyzed to several species, including the anionic species iodide and tri-iodide. The hydrolysis mechanism of I2 in the pH 9 buffer enables it to function as a concentrator for the anionic species. When the sensor is exposed to a gas stream containing iodine, continuous accumulation of the electrochemically detectable anionic species is possible, enabling preconcentration of the incoming flow-stream by several orders of magnitude. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

We report on a nanoelectrode array sensor for the detection of I2 (iodine gas) at levels as low as near 0,02 ppm within tens of seconds of exposure. The sensor is constructed on a free-standing anodic aluminum oxide wafer with nanopores of 120 nm diameter and 50 um length. On each wafer surface, continuous metal films of tens of nm thickness are deposited: on one surface, a gold film is deposited such that it covers the nanopores, and, on the opposite surface, a platinum film is deposited such that the nanopores remain open and their volumes in contact with the environment. The gold film serves as the working electrode and the platinum film serves as the auxiliary and pseudo-reference electrode. The nanopores are filled with a pH 9 buffer aqueous solution to create an array of electrochemical cells in parallel, and ionic conductivity is maintained for environments with relative humidity levels greater than about 30%. The detection mechanism is the electrochemical oxidation of anionic species of I2 that form from the dissolution and subsequent hydrolysis of gas phase I2 in the pH 9 buffer electrolyte: the gas phase I2 dissolves in the buffer in proportion to Henry's Law constant and then the dissolved I2 is hydrolyzed to several species, including the anionic species iodide and tri-iodide. The detection of I2 is achieved by measuring oxidizing current during the cyclic voltammetry technique bounded between -0,2 and 0,5 V vs the Pt pseudoreference electrode. The hydrolysis mechanism of I2 in the pH 9 buffer enables the buffer to function as a concentrator for the anionic species of I2. When the sensor is exposed to a gas stream containing I2, practically continuous accumulation of the electrochemically detectable anionic species of I2 is possible, with a saturation point where the pH 9 buffer contains > 100 ppm iodide anion. For context, the sensor can detect iodide anions in pH 9 buffer at levels as low as 0,01 ppm. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Aluminum deposition is an industrially important process that is often not optimized in an electrochemical sense. One method of growing thin aluminum films is electrodeposition; this process has been gaining traction in ionic liquids over the last two decades, although details of the process are still under debate. These inconsistencies are largely attributed to widely variable results based on electrolyte purity and a strong dependence on a multitude of parameters including composition, temperature and even experimental set up. This work is targeted to elucidate some of these properties with electrochemical and rheological measurements, alongside NMR and microscopy techniques. Some of the most promising aluminum deposition is done in chloroaluminate ionic liquids. These solutions have high aluminum concentration and low vapor pressure but typically higher viscosity then molecular solvents or aqueous chemistries. 1-ethyl-3-methyl imidazolium chloride (EMIC) and AlCl3 in acidic ratios will readily deposit aluminum. This electrolyte deposits aluminum by the reduction of Al2Cl7 - to aluminum and produces AlCl4 - anions in a relatively complex 3 electron transfer mechanism. The composition of the electrolyte is determined by the ratio of AlCl3 to EMIC and is confirmed by NMR. The varying compositions of the ionic liquid influence both the physical and electrochemical properties. The Walden rule applies well to most ionic liquids and states that the conductivity and viscosity are related, and as a corollary the mobility of ions is dependent as well. We systematically investigate the diffusion parameters that lead to insight of reaction kinetics of the chloroaluminate system. There are methods that have been developed for this type of investigation that do not apply to this system because of a few complications. For example, the Cottrell model indicates a diffusion controlled system, while attempting Koutecky-Levich does not apply because the system cannot reach a diffusion limited regime in the window of the electrolyte. We assert that in a quiescent system the ionic interactions of the electrolyte become quite strong and resistant to cleavage, leading to restricted Al2Cl7 - diffusion. The structuring and interaction of the ionic liquid may be shown in the rheological data, indicating that the solutions are thixotropic. Since the conductivity and diffusivity are dependent on the viscosity, we assert that as the solution is allowed to rest and coordinate in a preferred structure the diffusivity would decrease significantly. This implies that the measured diffusion rates in a quiescent experiment are not relevant in a system that implements convection, which is almost any real system. We apply data derived from the quiescent system experiments to dynamic systems by understanding how the macroscale physical properties change as the system goes from static to dynamic. As mentioned above, the Cottrell equation can measure the diffusion rates of an electrochemically active species, which allows measurement of transport for Al2Cl7 -. Proton pulse field gradient spin echo nuclear magnetic resonance spectroscopy (PGSE NMR) can measure the diffusivity of the cationic species in the system (EMIm+), and the bulk conductivity was used to determine the combined mobility of ions in solution. The anions and cations contribute to the bulk conductivity separately, which necessitates the multiple methods of investigation, as well as the redundancy of using solutions of varying compositions. All of these experiments give results based on a static solution. We apply the viscosity dependence to the data gathered in static solutions to predict properties in dynamic conditions. A close approximation of zero shear viscosity was determined through falling ball experiments. The dynamic viscosity was measured by a rheometer at varying shear rates. The diffusion properties and conductivity are related to viscosity. Composition and temperature variation in the viscosity studies gave insight to the mobility of both the anions and cations under all static or dynamic conditions, and point to complex interaction at the electrode interface for deposition from the Al2Cl7 - in this ionic liquid. Using the diffusivity and composition data gathered from this set of experiments allows for investigation of the reaction kinetics, and optimization of the kinetics to diffusion balance. Increasing the plating rate reduces fabrication times but infringing on the precursor diffusion limits leads to dendritic and poor quality deposits. Adjusting the parameters to give similar kinetic and diffusion properties of the Al2Cl7 - in this electrolyte will give the best deposition properties based on both rate and dense, compact and level morphologies. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Thick multi-layer metal stacking offers the potential for fabrication of rectangular waveguide components, including horn antennas, couplers, and bends, for operation at terahertz frequencies, which are too small to machine traditionally. Air-filled, TE10, rectangular waveguides for 3 THz operation were fabricated using two stacked electroplated gold layers on both planar and non-planar substrates. The initial layer of lithography and electroplating defined 37 micrometer tall waveguide walls in both straight and meandering geometries. The second layer, processed on top of the first, defined 33 micrometer thick waveguide lids. Release holes periodically spaced along the center of the lids improved resist clearing from inside of the electroformed rectangular channels. Processing tests of hollow structures on optically clear, lithium disilicate substrates allowed confirmation of resist removal by backside inspection.

The plating characteristics of a commercially available indium plating solution are examined and optimized to help meet the increasing performance demands of integrated circuits requiring substantial numbers of electrical interconnections over large areas. Current fabrication techniques rely on evaporation of soft metals, such as indium, into lift-off resist profiles. This becomes increasingly difficult to accomplish as pitches decrease and aspect ratios increase. To minimize pixel dimensions and maximize the number of pixels per unit area, lithography and electrochemical deposition (ECD) of indium has been investigated. Pulse ECD offers the capability of improving large area uniformity ideal for large area device hybridization. Electrochemical experimentation into lithographically patterned molds allow for large areas of bumps to be fabricated for low temperature indium to indium bonds. The galvanic pulse profile, in conjunction with the bath configuration, determines the uniformity of the plated array. This pulse is manipulated to produce optimal properties for hybridizing arrays of aligned and bonded indium bumps. The physical properties of the indium bump arrays are examined using a white light interferometer, a SEM and tensile pull testing. This paper provides details from the electroplating processes as well as conclusions leading to optimized plating conditions.

The alloying reaction of Nickel and Aluminum is exothermic and the heat output from this process can be utilized for many different applications from local brazing and welding to melting and heat generation as an energy source. One of the challenges associated with this reaction is that the components are in the solid state, thus mixing and reaction rates suffer from diffusion limitations. Structuring the separate elemental phases on the nanoscale is used to minimize diffusion distances and improve reactant mixing, increasing the overall rate. One method of fabricating these films with control over the nickel and aluminum phase structure is the electrochemical codeposition process. This technique allows for nickel particles on the nanoscale to be incorporated into an aluminum matrix, with control over the composition and size. This method has manufacturing cost, speed, and safety advantages over traditional thin film vacuum techniques, if some of the challenges to dispersion plating can be overcome. In the present work, the electrodeposition of Aluminum in 1-butyl 2-methylimidazolium based Ionic liquids was investigated as a means of incorporating disperse Nickel nanoparticles into an aluminum matrix material. While aluminum electrodeposition has been investigated thoroughly, modifications from normal parameters are required to compensate for the codeposition process. Chloroaluminate ionic liquids (ILs) are used for their desirable properties including room temperature operation, high purity and high efficiency aluminum deposition. 1-butyl 2-methylimidazolium cations were chosen specifically for their electrochemical stability. ILs are inherently high viscosity which affects the particulate mobility, the addition of co-solvents to the IL will significantly decrease the viscosity and allow for control of particle motion. This along with control of the convection of the electrolyte will allow for modification and optimization of transport of particles to the electrode surface. Energetic output is influenced by several different properties, the most important being composition. The production of maximum heat is realized when the stoichiometry of the nickel and aluminum are 1 to 1 as this allows the chemical reaction, the production of AlNi, to go to completion without excess of either constituents. The stoichiometry of Ni to Al is optimized to approach the correct ratio by controlling the transport of the particles to the surface as well as the growth rate of the aluminum matrix material. These parameters cannot be decoupled as the matrix material is what secures the particles to the electrode, and therefore they must be optimized together. The aluminum deposition has been investigated in the absence of particles to determine how the surfactants and co solvent dilutions affect the matrix growth characteristics. Migration and agglomeration of the particles in the electrolyte are very important as they determine the dispersion of the Ni phase in the deposited film. These properties are controlled by the surface chemistry of the particles in solution and by the particle-particle interaction in the solution. Pure nickel particles dispersed in the IL and co-solvent show loose agglomeration in the deposited film. Uniform distribution at the nanoscale is needed to ensure consistent burn properties once the reactions are triggered, so surface modification is used to decrease attraction between particles. These modifications include oxide layers as well as surfactants added to the electrolyte and results are shown in this work. Initial attempts of the high quantity incorporation show minor agglomeration of the as received nickel particles as can be seen in the back scattered SEM of a cross section of the deposited film, the lighter grey contrast is the nickel phase (figure 1). Deposits were fabricated and analyzed with various techniques including electrochemical quartz crystal microbalance (EQCM) for particle incorporation and viscosity measurements, zetasizer for particle agglomeration and mobility, rotating disk electrode (RDE) for transport properties, scanning electron microscopy (SEM) for dispersion imaging, Energy-dispersive X-ray spectroscopy (EDS) for elemental analysis, and differential scanning calorimetry (DSC) for exothermic reaction properties. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1

An electroformed, three-dimensional stylus Paul trap was designed to confine a single atomic ion for use as a sensor to probe the electric-field noise of proximate surfaces. The trap was microfabricated with the UV-LIGA technique to reduce the distance of the ion from the surface of interest. We detail the fabrication process used to produce a 150 μm tall stylus trap with feature sizes of 40 μm. We confined single, laser-cooled, (25)Mg(+) ions with lifetimes greater than 2 h above the stylus trap in an ultra-high-vacuum environment. After cooling a motional mode of the ion at 4 MHz close to its ground state (n= 0.34 ± 0.07), the heating rate of the trap was measured with Raman sideband spectroscopy to be 387 ± 15 quanta/s at an ion height of 62 μm above the stylus electrodes.