Clem, Paul G.; Nieves, Cesar A.; Yuan, Mengxue Y.; Ogrinc, Andrew L.; Furman, Eugene F.; Kim, Seong H.; Lanagan
, Michael T.
Ionic conduction in silicate glasses is mainly influenced by the nature, concentration, and mobility of the network-modifying (NWM) cations. The electrical conduction in SLS is dominated by the ionic migration of sodium moving from the anode to the cathode. An activation energy for this conduction process was calculated to be 0.82eV and in good agreement with values previously reported. The conduction process associated to the leakage current and relaxation peak in TSDC for HPFS is attributed to conduction between nonbridging oxygen hole centers (NBOHC). It is suggested that ≡Si-OH = ≡Si-O- + H0 under thermo-electric poling, promoting hole or proton injection from the anode and responsible for the 1.5eV relaxation peak. No previous TSDC data have been found to corroborate this mechanism. The higher activation energy and lower current intensity for the coated HPFS might be attributed to a lower concentration of NBOHC after heat treatment (Si-OH + OH-Si = SiO-Si + H2O). This could explain the TSDC signal around room temperature for the coated HPFS. Another possible explanation could be a redox reaction at the anode region dominating the current response.
Structural disorder causes materials’ surface electronic properties, e.g., work function ([Formula: see text]), to vary spatially, yet it is challenging to prove exact causal relationships to underlying ensemble disorder, e.g., roughness or granularity. For polycrystalline Pt, nanoscale resolution photoemission threshold mapping reveals a spatially varying [Formula: see text] eV over a distribution of (111) vicinal grain surfaces prepared by sputter deposition and annealing. With regard to field emission and related phenomena, e.g., vacuum arc initiation, a salient feature of the [Formula: see text] distribution is that it is skewed with a long tail to values down to 5.4 eV, i.e., far below the mean, which is exponentially impactful to field emission via the Fowler–Nordheim relation. We show that the [Formula: see text] spatial variation and distribution can be explained by ensemble variations of granular tilts and surface slopes via a Smoluchowski smoothing model wherein local [Formula: see text] variations result from spatially varying densities of electric dipole moments, intrinsic to atomic steps, that locally modify [Formula: see text]. Atomic step-terrace structure is confirmed with scanning tunneling microscopy (STM) at several locations on our surfaces, and prior works showed STM evidence for atomic step dipoles at various metal surfaces. From our model, we find an atomic step edge dipole [Formula: see text] D/edge atom, which is comparable to values reported in studies that utilized other methods and materials. Our results elucidate a connection between macroscopic [Formula: see text] and the nanostructure that may contribute to the spread of reported [Formula: see text] for Pt and other surfaces and may be useful toward more complete descriptions of polycrystalline metals in the models of field emission and other related vacuum electronics phenomena, e.g., arc initiation.
This report documents an experimental program designed to investigate High Energy Arcing Fault (HEAF) phenomena. The experiments focus on providing data to better characterize the arc to improve the prediction of arc energy emitted during a HEAF event. An open box experiment allow for direct observation of the arc, which allows diagnostic instrumentation to record the phenomenological data needed for better characterization of the arc energy source term. The data collected supports characterization of the arc and arc jet, enclosure breach, material loss, and electrical properties. These results will be used to better characterizing the hazard for improvements in fire probabilistic risk assessment (PRA) realism. The experiments were performed at KEMA Labs located in Chalfont, Pennsylvania. The experimental design, setup, and execution were completed by staff from the NRC, the National Institute of Standards and Technology (NIST), Sandia National Laboratories (SNL) and KEMA Labs. In addition, representatives from the Electric Power Research Institute (EPRI) observed some of the experimental setup and execution. The HEAF experiments were performed between August 22, 2020 and September 18, 2020 on near-identical 51 cm (20 in) cube metal boxes suspended from a Unistrut support structure. The three-phase arcing fault was initiated at the ends of the conductors oriented vertically and located at the center of the box. Either aluminum or copper conductors were used for the conductors. The low-voltage experiments used 1 000 volts AC, while the medium-voltage experiments used 6 900 volts AC consistent with other recently completed experiments. Durations of the experiment ranged from 1 s to 5 s with fault currents ranging from 1 kA to 30 kA. Real-time electrical operating conditions, including voltage, current and frequency, were measured during the experiments. Heat fluxes and incident energies were measured with plate thermometers, radiometers, and slug calorimeters at various locations around the electrical enclosures. The experiments were documented with normal and high-speed videography, infrared imaging and photography.
Understanding the role of physical processes contributing to breakdown is critical for many applications in which breakdown is undesirable, such as capacitors, and applications in which controlled breakdown is intended, such as plasma medicine, lightning protection, and materials processing. The electron emission from the cathode is a critical source of electrons which then undergo impact ionization to produce electrical breakdown. In this study, the role of secondary electron yields due to photons (γ ph) and ions (γ i) in direct current breakdown is investigated using a particle-in-cell direct simulation Monte Carlo model. The plasma studied is a one-dimensional discharge in 50 Torr of pure helium with a platinum cathode, gap size of 1.15 cm, and voltages of 1.2-1.8 kV. The current traces are compared with experimental measurements. Larger values of γ ph generally result in a faster breakdown, while larger values of γ i result in a larger maximum current. The 58.4 nm photons emitted from He(21P) are the primary source of electrons at the cathode before the cathode fall is developed. Of the values of γ ph and γ i investigated, those which provide the best agreement with the experimental current measurements are γ ph = 0.005 and γ i = 0.01. These values are significantly lower than those in the literature for pristine platinum or for a graphitic carbon film which we speculate may cover the platinum. This difference is in part due to the limitations of a one-dimensional model but may also indicate surface conditions and exposure to a plasma can have a significant effect on the secondary electron yields. The effects of applied voltage and the current produced by a UV diode which was used to initiate the discharge, are also discussed.
Helium is frequently used as a working medium for the generation of plasmas and is capable of energetic photon emissions. These energetic photon emissions are often attributed to the formation of helium excimer and subsequent photon emission. When the plasma device is exposed to another gas, such as nitrogen, this energetic photon emission can cause photoionization and further ionization wave penetration into the additional gas. Often ignored are the helium resonance emissions that are assumed to be radiation trapped and therefore not pertinent to photoionization. Here, experimental evidence for the presence of helium atomic emission in a pulsed discharge at ten's of Torr is shown. Simulations of a discharge in similar conditions agree with the experimental measurements. In this context, the role of atomic and molecular helium light emission on photoionization of molecular nitrogen in an ionization wave is studied using a kinetic modeling approach that accounts for radiation dynamics in a developing low-temperature plasma. Three different mixtures of helium at a total pressure of 250 Torr are studied in simulation. Photoionization of the nitrogen molecule by vacuum ultraviolet helium emission is used as the only seed source ahead of the ionization front. It is found that even though radiation trapped, the atomic helium emission lines are the significant source of photoionization of nitrogen. The significant effect of radiation trapped photon emission on ionization wave dynamics demonstrates the need to consider these radiation dynamics in plasma reactors where self-absorbed radiation is ignored.
Electrical conduction in silica-based capacitors under a combined effect of intermediate electric field and temperature (2.5 - 10 kV/mm, 50-300°C) is dominated by localized motion of high mobility ions such as sodium. Thermally stimulated polarization and depolarization current (TSPC/TSDC) characterization was carried out on poled fused silica and AF32 glass samples. Two relaxation mechanisms were found during the depolarization step and an anomalous response for the second TSDC peak was observed. Absorption current measurements were performed on the glass samples and a time-dependent response was observed when subjected to different electro-thermal conditions. It was found that at low temperature (T = 175 °C) and short times, the current follows a linear behavior (I α V) while at high temperature (T = 250 °C), the current follows V0.5. TSPC/TSDC and absorption current measurements results led to the conclusion that (1) Poole-Frenkel dominates conduction at high temperatures and at longer times and that (2) ionic blockage and/or H+/H3O+ injection are responsible for the observed anomalous current response.
For high voltage electrical devices, prevention of high voltage breakdown is critical for device function. Use of polymeric encapsulation such as epoxies is common, but these may include air bubbles or other voids of varying size. The present work aimed to model and experimentally determine the size dependence of breakdown voltage for voids in an epoxy matrix, as a step toward establishing size criteria for void screening. Effects were investigated experimentally for both one-dimensional metal/epoxy/air/epoxy/metal gap sizes from 50 μm to 10 mm, as well as spherical voids of 250 μm, 500 μm, 1 mm and 2 mm sizes. These experimental results were compared to modified Paschen curve and particle-in-cell discharge models; minimum breakdown voltages of 6 - 8.5 kV appeared to be predicted by 1D models and experiments, with minimum breakdown voltage for void sizes of 0.2 - 1 mm. In a limited set of 3D experiments on 250 μm, 500 μm, 1 mm and 2 mm voids within epoxy, the minimum breakdown voltages observed were 18.5 - 20 kV, for 500 μm void sizes. These experiments and models are aimed at providing initial size and voltage criteria for tolerable void sizes and expected discharge voltages to support design of encapsulated high voltage components.
Sandia National Laboratories sponsored a three-year internally funded Laboratory Directed Research and Development (LDRD) effort to investigate the vulnerabilities and mitigations of a high-altitude electromagnetic pulse (HEMP) on the electric power grid. The research was focused on understanding the vulnerabilities and potential mitigations for components and systems at the high voltage transmission level. Results from the research included a broad array of subtopics, covered in twenty-three reports and papers, and which are highlighted in this executive summary report. These subtopics include high altitude electromagnetic pulse (HEMP) characterization, HEMP coupling analysis, system-wide effects, and mitigating technologies.
Modern computational validation efforts rely on comparison of known experimental quantities such as current, voltage, particle densities, and other plasma properties with the same values determined through simulation. A discrete photon approach for radiation transport was recently incorporated into a particle-in-cell/direct simulation Monte Carlo code. As a result, spatially and temporally resolved synthetic spectra may be generated even for non-equilibrium plasmas. The generation of this synthetic spectra lends itself to potentially new validation opportunities. In this work, initial comparisons of synthetic spectra are made with experimentally gathered optical emission spectroscopy. A custom test apparatus was constructed that contains a 0.5 cm gap distance parallel plane discharge in ultra high purity helium gas (99.9999%) at a pressure of 75 Torr. Plasma generation is initiated with the application of a fast rise-time, 100 ns full-width half maximum, 2.0 kV voltage pulse. Transient electrical diagnostics are captured along with time-resolved emission spectra. A one-dimensional simulation is run under the same conditions and compared against the experiment to determine if sufficient physics are included to model the discharge. To sync the current measurements from experiment and simulation, significant effort was undertaken to understand the kinetic scheme required to reproduce the observed features. Additionally, the role of the helium molecule excimer emission and atomic helium resonance emission on photocurrent from the cathode are studied to understand which effect dominates photo-feedback processes. Results indicate that during discharge development, atomic helium resonance emission dominates the photo-flux at the cathode even though it is strongly self-absorbed. A comparison between the experiment and simulation demonstrates that the simulation reproduces observed features in the experimental discharge current waveform. Furthermore, the synthesized spectra from the kinetic method produces more favorable agreement with the experimental data than a simple local thermodynamic equilibrium calculation and is a first step towards using spectra generated from a kinetic method in validation procedures. The results of this study produced a detailed compilation of important helium plasma chemistry reactions for simulating transient helium plasma discharges.
The influence of different quantum yields for photons and secondary emission yields for ions striking a surface is investigated. Using a one-dimensional particle-in-cell simulation, these secondary emission coefficients are varied to observe the impact on discharge current. The discharge is assumed to occur in pure helium gas at a pressure of 75 torr. To handle binary particle interactions, the Direct Simulation Monte Carlo (DSMC) method is utilized. The model includes electron-neutral interactions, neutral-neutral interactions, and photon-neutral interactions. It is observed that the discharge current in the early stages of discharge is heavily dependent upon the quantum yield due to photon impact. In the later stages of discharge, the current depends on both the quantum yield and secondary emission coefficient for ion impact.
In most models of vacuum breakdown, there is some initial emission of electrons from the cathodic surface, usually employing some form of Fowler-Nordheim emission. While this may be correct for 'textbook' surfaces, it is generally unreliable for real surfaces and fitted parameters are often used. For example, the beta employed is generally unphysical based on usual definitions (e.g., it incorporates more, but unexplained, physics than just a geometry-based field concentration effect). In this work, we describe experimental efforts to better characterize which surface structure parameters influence the vacuum field emission current.
We present here a multi-length scale integration of compositionally tailored NaSICON-based Na+ conductors to create a high Na+ conductivity system resistant to chemical attack in strongly alkaline aqueous environments. Using the Pourbaix Atlas as a generalized guide to chemical stability, we identify NaHf2P3O12 (NHP) as a candidate NaSICON material for enhanced chemical stability at pH > 12, and demonstrate the stability of NHP powders under accelerated aging conditions of 80 °C and pH = 13-15 for a variety of alkali metal cations. To compensate for the relatively low ionic conductivity of NHP, we develop a new low temperature (775 °C) alkoxide-based solution deposition chemistry to apply dense NHP thin films onto both platinized silicon wafers and bulk, high Na+ conductivity Na3Zr2Si2PO12 (NZSP) pellets. These NHP films display Na+ conductivities of 1.35 × 10-5 S cm-1 at 200 °C and an activation energy of 0.53 eV, similar to literature reports for bulk NHP pellets. Under aggressive conditions of 10 M KOH at 80 °C, NHP thin films successfully served as an alkaline-resistant barrier, extending the lifetime of NZSP pellets from 4.26 to 36.0 h. This integration of compositionally distinct Na+ conductors across disparate length scales (nm, mm) and processing techniques (chemically-derived, traditional powder) represents a promising new avenue by which Na+ conducting systems may be utilized in alkaline environments previously thought incompatible with ceramic Na+ conductors.
Robust, safe, and reliable grid-scale energy storage continues to be a priority for improved energy surety, expanded integration of renewable energy, and greater system agility required to meet modern dynamic and evolving electrical energy demands. We describe here a new sodium-based battery based on a molten sodium anode, a sodium iodide/aluminum chloride (NaI/AlCl3) cathode, and a high conductivity NaSICON (Na1+xZr2SixP3−xO12) ceramic separator. This NaI battery operates at intermediate temperatures (120–180 °C) and boasts an energy density of >150 Wh kg−1. The energy-dense NaI-AlCl3 ionic liquid catholyte avoids lifetime-limiting plating and intercalation reactions, and the use of earth-abundant elements minimizes materials costs and eliminates economic uncertainties associated with lithium metal. Moreover, the inherent safety of this system under internal mechanical failure is characterized by negligible heat or gas production and benign reaction products (Al, NaCl). Scalability in design is exemplified through evolution from 0.85 to 10 Ah (28 Wh) form factors, displaying lifetime average Coulombic efficiencies of 99.45% and energy efficiencies of 81.96% over dynamic testing lasting >3000 h. This demonstration promises a safe, cost-effective, and long-lifetime technology as an attractive candidate for grid scale storage.
A new multi-step, solution-phase method for the spontaneous deposition of tungsten from a room temperature ethereal solution is reported. This immersion process relies on the deposition of a sacrificial zinc coating which is galvanically displaced by the ethermediated reduction of oxophilic WCl6. Subsequent thermal treatment renders a crystalline, metallic tungsten film. The chemical evolution of the surface and formation of a complex intermediate tungsten species is characterized by X-ray diffraction, infrared spectroscopy, and X-ray photoelectron spectroscopy. Efficient metallic tungsten deposition is first characterized on a graphite substrate and then demonstrated on a functional carbon foam electrode. The resulting electrochemical performance of the modified electrode is interrogated with the canonical aqueous ferricyanide system. A tungsten-coated carbon foam electrode showed that both electrode resistance and overall electrochemical cell resistance were reduced by 50%, resulting in a concomitant decrease in redox peak separation from 1.902 V to 0.783 V. This process promises voltage efficiency gains in electrodes for energy storage technologies and demonstrates the viability of a new route to tungsten coating for technologies and industries where high conductivity and chemical stability are paramount.
Vanadium dioxide (VO2) is an attractive material for a variety of applications due to its metal-to-insulator transition (MIT) observed at modest temperatures. This transition takes VO2 from its low temperature insulating monoclinic phase to a high temperature (above 68°C) metallic rutile phase. This transition gives rise to a change in resistivity up to 5 orders of magnitude and a change in complex refractive index (especially at IR wavelengths), which is of interest for radar circuit protection and tunable control of infrared signature. Recently, collaborations have been initiated between CINT scientists and external university programs. The Enhanced Surveillance funds help fund this work which enabled synthesis of VO2 films for several collaborations with internal and external researchers.
There is a rising interest in developing functional electronics using additively manufactured components. Considerations in materials selection and pathways to forming hybrid circuits and devices must demonstrate useful electronic function; must enable integration; and must complement the complex shape, low cost, high volume, and high functionality of structural but generally electronically passive additively manufactured components. This article reviews several emerging technologies being used in industry and research/development to provide integration advantages of fabricating multilayer hybrid circuits or devices. First, we review a maskless, noncontact, direct write (DW) technology that excels in the deposition of metallic colloid inks for electrical interconnects. Second, we review a complementary technology, aerosol deposition (AD), which excels in the deposition of metallic and ceramic powder as consolidated, thick conformal coatings and is additionally patternable through masking. Finally, we show examples of hybrid circuits/devices integrated beyond 2-D planes, using combinations of DW or AD processes and conventional, established processes.
We have measured the cross-plane thermal conductivity (κ) of (010)-textured, undoped, and lanthanum-doped strontium niobate (Sr2-xLaxNb2O7-δ) thin films via time-domain thermoreflectance. The thin films were deposited on (001)-oriented SrTiO3 substrates via the highly-scalable technique of chemical solution deposition. We find that both film thickness and lanthanum doping have little effect on κ, suggesting that there is a more dominant phonon scattering mechanism present in the system; namely the weak interlayer-bonding along the b-axis in the Sr2Nb2O7 parent structure. Furthermore, we compare our experimental results with two variations of the minimum-limit model for κ and discuss the nature of transport in material systems with weakly-bonded layers. The low cross-plane κ of these scalably-fabricated films is comparable to that of similarly layered niobate structures grown epitaxially.
The reflection of an optical wave from metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieving high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a “magnetic mirror” that does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can be achieved only by using artificially tailored materials. Here, we experimentally demonstrate, for the first time to the best of our knowledge, the magnetic mirror behavior of a low-loss all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse-electric dipoles placed close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.
In recent years, increasing deployment of large wind-turbine farms has become an issue of growing concern for the radar community. The large radar cross section (RCS) presented by wind turbines interferes with radar operation, and the Doppler shift caused by blade rotation causes problems identifying and tracking moving targets. Each new wind-turbine farm installation must be carefully evaluated for potential disruption of radar operation for air defense, air traffic control, weather sensing, and other applications. Several approaches currently exist to minimize conflict between wind-turbine farms and radar installations, including procedural adjustments, radar upgrades, and proper choice of low-impact wind-farm sites, but each has problems with limited effectiveness or prohibitive cost. An alternative approach, heretofore not technically feasible, is to reduce the RCS of wind turbines to the extent that they can be installed near existing radar installations. This report summarizes efforts to reduce wind-turbine RCS, with a particular emphasis on the blades. The report begins with a survey of the wind-turbine RCS-reduction literature to establish a baseline for comparison. The following topics are then addressed: electromagnetic model development and validation, novel material development, integration into wind-turbine fabrication processes, integrated-absorber design, and wind-turbine RCS modeling. Related topics of interest, including alternative mitigation techniques (procedural, at-the-radar, etc.), an introduction to RCS and electromagnetic scattering, and RCS-reduction modeling techniques, can be found in a previous report.
Novel low loss photopatternable matrix materials for IR metamaterial applications were synthesized using the ring opening metathesis polymerization reaction (ROMP) of norbornene followed by a partial hydrogenation to remove most of the IR absorbing olefin groups which absorb in the 8-12 {micro}m range. Photopatterning was achieved via crosslinking of the remaining olefin groups with alpha, omega-dithiols via the thiol-ene coupling reaction. Since ROMP is a living polymerization the molecular weight of the polymer can be controlled simply by varying the ratio of catalyst to monomer. In order to determine the optimum photopattenable IR matrix material we varied the amount of olefin remaining after the partial hydrogenation. Hydrogenation was accomplished using tosyl hydrazide. The degree of hydrogenation can be controlled by altering the reaction time or reaction stoichiometry and the by-products can be easily removed during workup by precipitation into ethanol. Several polymers have been prepared using this reduction scheme including two polymers which had 54% and 68% olefin remaining. Free standing films (approx. 12 {micro}m) were prepared from the 68% olefin material using draw-down technique and subsequently irradiated with a UV lamp (365 nm) for thirty minutes to induce crosslinking via thiol-ene reaction. After crosslinking, the olefin IR-absorption band disappeared and the Tg of the matrix material increased; both desirable properties for IR metamaterial applications. The polymer system has inherent photopatternable behavior primarily because of solubility differences between the pre-polymer and cross-linked matrix. Photopatterned structures using the 54% as well as the 68% olefin material were easily obtained. The synthesis, processing, and IR absorption data and the ramifications to dielectric metamaterials will be discussed.
We will present a study of the structure-property relations in Reststrahlen materials that possess a band of negative permittivities in the infrared. It will be shown that sub-micron defects strongly affect the optical response, resulting in significantly diminished permittivities. This work has implications on the use of ionic materials in IR-metamaterials.
The role of crystal coherence length on the infrared optical response of MgO thin films was investigated with regard to Reststrahlen band photon-phonon coupling. Preferentially (001)-oriented sputtered and evaporated ion-beam assisted deposited thin films were prepared on silicon and annealed to vary film microstructure. Film crystalline coherence was characterized by x-ray diffraction line broadening and transmission electron microscopy. The infrared dielectric response revealed a strong dependence of dielectric resonance magnitude on crystalline coherence. Shifts to lower transverse optical phonon frequencies were observed with increased crystalline coherence. Increased optical phonon damping is attributed to increasing granularity and intergrain misorientation.
We have demonstrated a novel microfluidic technique for aqueous media, which uses super-hydrophobic materials to create microfluidic channels that are open to the atmosphere. We have demonstrated the ability to perform traditional electrokinetic operations such as ionic separations and electrophoresis using these devices. The rate of evaporation was studied and found to increase with decreasing channel size, which places a limitation on the minimum size of channel that could be used for such a device.
Recent advances in nanoparticle inks have enabled inkjet printing of metal traces and interconnects with very low (100-200°C) process temperatures. This has enabled integration of printable electronics such as antennas and radio frequency identification (RFID) tags with polyimide, teflon, PCBs, and other low temperature substrates. We discuss here printing of nanoparticle inks for three dimensional interconnects, and the apparent mechanism of nanoparticle ink conductivity development at these low process temperatures.
Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes negatively impacts in desalination and water treatment. With biofouling there is a decrease in permeate production, degradation of permeate water quality, and an increase in energy expenditure due to increased cross-flow pressure needed. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The overall goal of the work described in this report was to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers - UV-curable epoxy traces printed on the surface of a water-treatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated. Creation of low-cost, efficient water-treatment membranes helps assure the availability of fresh water for human use, a growing need in both the U. S. and the world.
We have successfully developed a nucleic acid extraction system based on a microacoustic lysis array coupled to an integrated nucleic acid extraction system all on a single cartridge. The microacoustic lysing array is based on 36{sup o} Y cut lithium niobate, which couples bulk acoustic waves (BAW) into the microchannels. The microchannels were fabricated using Mylar laminates and fused silica to form acoustic-fluidic interface cartridges. The transducer array consists of four active elements directed for cell lysis and one optional BAW element for mixing on the cartridge. The lysis system was modeled using one dimensional (1D) transmission line and two dimensional (2D) FEM models. For input powers required to lyse cells, the flow rate dictated the temperature change across the lysing region. From the computational models, a flow rate of 10 {micro}L/min produced a temperature rise of 23.2 C and only 6.7 C when flowing at 60 {micro}L/min. The measured temperature changes were 5 C less than the model. The computational models also permitted optimization of the acoustic coupling to the microchannel region and revealed the potential impact of thermal effects if not controlled. Using E. coli, we achieved a lysing efficacy of 49.9 {+-} 29.92 % based on a cell viability assay with a 757.2 % increase in ATP release within 20 seconds of acoustic exposure. A bench-top lysing system required 15-20 minutes operating up to 58 Watts to achieve the same level of cell lysis. We demonstrate that active mixing on the cartridge was critical to maximize binding and release of nucleic acid to the magnetic beads. Using a sol-gel silica bead matrix filled microchannel the extraction efficacy was 40%. The cartridge based magnetic bead system had an extraction efficiency of 19.2%. For an electric field based method that used Nafion films, a nucleic acid extraction efficiency of 66.3 % was achieved at 6 volts DC. For the flow rates we tested (10-50 {micro}L/min), the nucleic acid extraction time was 5-10 minutes for a volume of 50 {micro}L. Moreover, a unique feature of this technology is the ability to replace the cartridges for subsequent nucleic acid extractions.
This report focuses on our recent advances in the fabrication and processing of barium strontium titanate (BST) thin films by chemical solution depositiion for next generation fuctional integrated capacitors. Projected trends for capacitors include increasing capacitance density, decreasing operating voltages, decreasing dielectric thickness and decreased process cost. Key to all these trends is the strong correlation of film phase evolution and resulting microstructure, it becomes possible to tailor the microstructure for specific applications. This interplay will be discussed in relation to the resulting temperature dependent dielectric response of the BST films.
This report focuses on our recent advances in the fabrication and processing of barium strontium titanate (BST) thin films by chemical solution deposition for next generation functional integrated capacitors. Projected trends for capacitors include increasing capacitance density, decreasing operating voltages, decreasing dielectric thickness and decreased process cost. Key to all these trends is the strong correlation of film phase evolution and resulting microstructure, it becomes possible to tailor the microstructure for specific applications. This interplay will be discussed in relation to the resulting temperature dependent dielectric response of the BST films.
Flow cytometry is an indispensable tool in clinical diagnostics, for example in cancer, AIDS, infectious disease outbreaks, microbiology, and others. The cost and size of existing cytometers precludes their entry into field clinics, water monitoring, agriculture/veterinary diagnostics, and rapidly deployable biothreat detection. Much of the cost and footprint of conventional cytometers is dictated by the high speed achieved by cells or beads in a hydrodynamically focused stream. This constraint is removed by using ultrasonic focusing in a parallel microfluidic architecture. In this paper, we describe our progress towards a microfabricated flow cytometer that uses bulk and microfabricated planar piezoelectric transducers in glass microfluidic channels. In addition to experimental data, initial modeling data to predict the performance of our transducers are discussed.
A microflame-based detector suit has been developed for sensing of a broad range of chemical analytes. This detector combines calorimetry, flame ionization detection (FID), nitrogen-phosphorous detection (NPD) and flame photometric detection (FPD) modes into one convenient platform based on a microcombustor. The microcombustor consists in a micromachined microhotplate with a catalyst or low-work function material added to its surface. For the NPD mode a low work function material selectively ionizes chemical analytes; for all other modes a supported catalyst such as platinum/alumina is used. The microcombustor design permits rapid, efficient heating of the deposited film at low power. To perform calorimetric detection of analytes, the change in power required to maintain the resistive microhotplate heater at a constant temperature is measured. For FID and NPD modes, electrodes are placed around the microcombustor flame zone and an electrometer circuit measures the production of ions. For FPD, the flame zone is optically interrogated to search for light emission indicative of deexcitation of flame-produced analyte compounds. The calorimetric and FID modes respond generally to all hydrocarbons, while sulfur compounds only alarm in the calorimetric mode, providing speciation. The NPD mode provides 10,000:1 selectivity of nitrogen and phosphorous compounds over hydrocarbons. The FPD can distinguish between sulfur and phosphorous compounds. Importantly all detection modes can be established on one convenient microcombustor platform, in fact the calorimetric, FID and FPD modes can be achieved simultaneously on only one microcombustor. Therefore, it is possible to make a very universal chemical detector array with as little as two microcombustor elements. A demonstration of the performance of the microcombustor in each of the detection modes is provided herein.
Detailed studies of the properties of ceramic CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) have clarified the physics of this interesting material and revealed several features not reported before. The dielectric relaxational properties of CCTO are explained in terms of a capacitive-layer model, as for an inhomogeneous semiconductor, consisting of semiconducting grains and insulating grain boundaries as also concluded by others. The kinetics of the main [low-temperature (T)] relaxation reveal that two different thermally activated processes in CCTO grains control the dynamics. A likely candidate defect responsible for the two processes is the oxygen vacancy which is a double donor. A higher-T relaxation is determined by grain boundary conduction. Both Nb and Fe doping lowered both the apparent dielectric constant {var_epsilon}{prime} and the dielectric loss, but increased Fe doping led to more dramatic effects. At 3 at.% Fe doping, the anomalous {var_epsilon}{prime}(T) response was removed, making the CCTO an intrinsic, very-low-loss dielectric. The intrinsic {var_epsilon}{prime}({approx}75) and its T dependence are measured and shown to be largely determined by a low-lying soft TO phonon. At low T, cubic CCTO transforms into an antiferromagnetic phase at T{sub N} = 25 K. T{sub N} is essentially independent of Nb doping (up to 4 at.%) and of hydrostatic pressure (up to {approx}7 kbar), but decreases significantly with Fe doping. Analysis of the high-T dependence of the magnetic susceptibility provided insight into the role of Fe as a dopant. Finally, an {var_epsilon}{prime}(T) anomaly associated with the onset of antiferromagnetic order has been discovered, providing evidence for coupling between the polarization and sublattice magnetization. The possible origin of this coupling is discussed.
Solution stamping nanolithography (SSNL) was used to print patterns of metallic copper and high-temperature-superconducting YBa{sub 2}Cu{sub 3}O{sub 7}. SSNL combines soft lithography and chemical-solution deposition to achieve direct printing of inorganic materials. The size of the printed patterns is determined by both the stamp feature size and the wetting properties of the solution.
This report contains the summary of the 'Magnetophoretic Bead Trapping in a High-Flowrate Biological Detection System' LDRD project 74795. The objective of this project is to develop a novel biodetection system for high-throughput sample analysis. The chief application of this system is in detection of very low concentrations of target molecules from a complex liquid solution containing many different constituents--some of which may interfere with identification of the target molecule. The system is also designed to handle air sampling by using an aerosol system (for instance a WESP - Wet Electro-Static Precipitator, or an impact spray system) to get air sample constituents into the liquid volume. The system described herein automatically takes the raw liquid sample, whether air converted or initially liquid matrix, and mixes in magnetic detector beads that capture the targets of interest and then performs the sample cleanup function, allowing increased sensitivity and eliminating most false positives and false negatives at a downstream detector. The surfaces of the beads can be functionalized in a variety of ways in order to maximize the number of targets to be captured and concentrated. Bacteria and viruses are captured using antibodies to surface proteins on bacterial cell walls or viral particle coats. In combination with a cell lysis or PCR (Polymerase Chain Reaction), the beads can be used as a DNA or RNA probe to capture nucleic acid patterns of interest. The sample cleanup capability of this system would allow different raw biological samples, such as blood or saliva to be analyzed for the presence of different infectious agents (e.g. smallpox or SARS). For future studies, we envision functionalizing bead surfaces to bind to chemical weapons agents, radio-isotopes, and explosives. The two main objectives of this project were to explore methods for enhancing the mixing of the capture microspheres in the sample, and to develop a novel high-throughput magnetic microsphere trap. We have developed a novel technique using the magnetic capture microspheres as 'stirrer bars' in a fluid sample to enhance target binding to the microsphere surfaces. We have also made progress in developing a polymer-MEMS electromagnet for trapping magnetic spheres in a high-flowrate fluid format.
A variety of solution deposition routes have been reported for processing complex perovskite-based materials such as ferroelectric oxides and conductive electrode oxides, due to ease of incorporating multiple elements, control of chemical stoichiometry, and feasibility for large area deposition. Here, we report an extension of these methods toward long length, epitaxial film solution deposition routes to enable biaxially oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO)-coated conductors for superconducting transmission wires. Recent results are presented detailing an all-solution deposition approach to YBCO-coated conductors with critical current densities J{sub c} (77 K) > 1 MA/cm{sup 2} on rolling-assisted, biaxially textured, (200)-oriented Ni-W alloy tapes. Solution-deposition methods such as this approach and those of other research groups appear to have promise to compete with vapor phase methods for superconductor electrical properties, with potential advantages for large area deposition and low cost/kA {center_dot} m of wire.
Development of next generation electronics for pulse discharge systems requires miniaturization and integration of high voltage, high value resistors (greater than 100 megohms) with novel substrate materials. These material advances are needed for improved reliability, robustness and performance. In this study, high sheet resistance inks of 1 megohm per square were evaluated to reduce overall electrical system volume. We investigated a deposition process that permits co-sintering of high-sheet-resistance inks with a variety of different material substrates. Our approach combines the direct write process of aerosol jetting with laser sintering and conventional thermal sintering processes. One advantage of aerosol jetting is that high quality, fine line depositions can be achieved on a wide variety of substrates. When combined with laser sintering, the aerosol jetting approach has the capability to deposit resistors at any location on a substrate and to additively trim the resistors to specific values. We have demonstrated a 400 times reduction in overall resistor volume compared to commercial chip resistors using the above process techniques. Resistors that exhibited this volumetric efficiency were fabricated by 850°C thermal processing on alumina substrates and by 0.1W laser sintering on Kapton substrates.
The microcombustor described in this report was developed primarily for thermal management in microsystems and as a platform for micro-scale flame ionization detectors (microFID). The microcombustor consists of a thin-film heater/thermal sensor patterned on a thin insulating membrane that is suspended from its edges over a silicon frame. This micromachined design has very low heat capacity and thermal conductivity and is an ideal platform for heating catalytic materials placed on its surface. Catalysts play an important role in this design since they provide a convenient surface-based method for flame ignition and stabilization. The free-standing platform used in the microcombustor mitigates large heat losses arising from large surface-to-volume ratios typical of the microdomain, and, together with the insulating platform, permit combustion on the microscale. Surface oxidation, flame ignition and flame stabilization have been demonstrated with this design for hydrogen and hydrocarbon fuels premixed with air. Unoptimized heat densities of 38 mW/mm{sup 2} have been achieved for the purpose of heating microsystems. Importantly, the microcombustor design expands the limits of flammability (Low as compared with conventional diffusion flames); an unoptimized LoF of 1-32% for natural gas in air was demonstrated with the microcombustor, whereas conventionally 4-16% observed. The LoF for hydrogen, methane, propane and ethane are likewise expanded. This feature will permit the use of this technology in many portable applications were reduced temperatures, lean fuel/air mixes or low gas flows are required. By coupling miniature electrodes and an electrometer circuit with the microcombustor, the first ever demonstration of a microFID utilizing premixed fuel and a catalytically-stabilized flame has been performed; the detection of -1-3% of ethane in hydrogen/air is shown. This report describes work done to develop the microcombustor for microsystem heating and flame ionization detection and includes a description of modeling and simulation performed to understand the basic operation of this device. Ancillary research on the use of the microcombustor in calorimetric gas sensing is also described where appropriate.
Photonic crystals are of interest for GHz transmission applications, including rapid switching, GHz filters, and phased-array technology. 3D fabrication by Robocasting enables moldless printing of high solid loading slurries into structures such as the ''woodpile'' structures used to fabricate dielectric photonic band gap crystals. In this work, tunable dielectric materials were developed and printed into woodpile structures via solid freeform fabrication (SFF) toward demonstration of tunable photonic crystals. Barium strontium titanate ceramics possess interesting electrical properties including high permittivity, low loss, and high tunability. This paper discusses the processing route and dielectric characterization of (BaxSr1-XTiO3):MgO ceramic composites, toward fabrication of tunable dielectric photonic band gap crystals.
We have conducted surface treatment and alloying experiments with Al, Fe, and Ti-based metals on the RHEPP-1 accelerator (0.8 MV, 20 W, 80 ns FHWM, up to 1 Hz repetition rate) at Sandia National Laboratories. Ions are generated by the MAP gas-breakdown active anode, which can yield a number of different beam species including H, N, and C, depending upon the injected gas. Beams of intense pulsed high-power ion beams have been used to produce surface modification by changes in microstructure caused by rapid heating and cooling of the surface. Increase of beam power leads to ablation of a target surface, and redeposition of ablated material onto a separate substrate. Experiments are described in which ion beams are used in an attempt to increase high-voltage breakdown of a treated surface. Surface alloying of coated Pt and Hf layers is also described. This mixing of a previously deposited thin-film layer into a Ti-alloy substrate leads to significantly enhanced surface wear durability, compared to either untreated Ti-alloy alone, or the Ti alloy alone treated with the ion beam. Thin-film layers have been produced from a number of target materials. Films of fine-grain Pt and Er are described, and are compared to conventionally formed films. First attempts to form high-dielectric constant BaTiO{sub 3} are described.
In this investigation, YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) films were fabricated via a metal acetate, trifluoroacetic acid based sol-gel route, and spin-coat deposited on (100) LaAlO{sub 3} with a focus on maximizing J{sub c}, while minimizing processing time. We demonstrate that the use of a low pO{sub 2} atmosphere during the pyrolysis stage can lead to at least a tetiold reduction in pyrolysis time, compared to a 1 atm. O{sub 2} ambient. High-quality YBCO films on LaAlO{sub 3}, with J{sub c} values up to 3 MA/cm{sup 2} at 77 K, can be routinely crystallized from these rapidly pyrolyzed films.