73 research outputs found
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Evaluation of the porous silicon capacitor as a moisture sensor for vacuum applications
A growing demand exists for inexpensive and reliable sensors for moisture detection in reduced pressure processing environments. Sandia`s Porous Silicon Capacitor (PSC) sensor appears to be an ideal candidate for this application. This sensor is a solid state device that detects moisture through changes in dielectric constant with water adsorption. Standard microelectronic fabrication techniques are used in its production affording low cost production and ready integration into complex sensor and electronic arrays. This sensor has previously been investigated for moisture detection in fluid streams, however, little effort has been placed on its behavior in a vacuum environment. Sandia`s Sensors in Vacuum (SIV) test facility has been employed to evaluate the performance characteristics of this sensor in vacuum. In addition, a vacuum-based study allows for a more controlled environment in which the intrinsic lower limit for moisture detection and response times to moisture changes can be easily determined quantitatively. This report describes the performance characteristics of a series of sensors from a single production lot. Calibration of these sensors to moisture levels from part per billion to part per hundred concentrations has been performed. The concentration-dependent sensitivity of these sensors is documented. The response time and drift characteristics of these sensors are also discussed. The investigation of a preliminary method for increasing the recovery time of the sensor after moisture exposure is presented. The role of hydrocarbon contamination, a potential problem in some vacuum schemes, is also evaluated. Specific recommendations are made on how to implement this sensor for vacuum applications
CRISPR-Cas orthologues and variants: optimizing the repertoire, specificity and delivery of genome engineering tools
Robust and cost-effective genome editing in a diverse array of cells and model organisms is now possible thanks to the discovery of the RNA-guided endonucleases of the CRISPR-Cas system. The commonly used Cas9 of Streptococcus pyogenes shows high levels of activity but, depending on the application, has been associated with some shortcomings. Firstly, the enzyme has been shown to cause mutagenesis at genomic sequences resembling the target sequence. Secondly, the stringent requirement for a specific motif adjacent to the selected target site can limit the target range of this enzyme. Lastly, the physical size of Cas9 challenges the efficient delivery of genomic engineering tools based on this enzyme as viral particles for potential therapeutic applications. Related and parallel strategies have been employed to address these issues. Taking advantage of the wealth of structural information that is becoming available for CRISPR-Cas effector proteins, Cas9 has been redesigned by mutagenizing key residues contributing to activity and target recognition. The protein has also been shortened and redesigned into component subunits in an attempt to facilitate its efficient delivery. Furthermore, the CRISPR-Cas toolbox has been expanded by exploring the properties of Cas9 orthologues and other related effector proteins from diverse bacterial species, some of which exhibit different target site specificities and reduced molecular size. It is hoped that the improvements in accuracy, target range and efficiency of delivery will facilitate the therapeutic application of these site-specific nucleases
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Effectiveness of nickel plating in inhibiting atmospheric corrosion of copper alloy contacts
A series of tests was run to determine the effect of Ni plating thickness on connector contact resistance. Copper coupons were plated with an electrolytic nickel strike followed by electroless nickel to produce Ni layers of 10, 20, 55 and 100 {micro}in. The coupons were then exposed to a simulated industrial environment. Pore corrosion was observed after the exposure, which correlated with Ni thickness. In a second series of tests, beryllium-copper four-tine contacts with 50 {micro}in of gold plate over electrolytic nickel strike/electroless-nickel plates of varying thickness were exposed the same corrosive environment. Contact resistance of mated pairs was monitored over a two-month period. The degradation in contact resistance correlated with the Ni thickness used in the connectors
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Final report on LDRD Project: Quantum confinement and light emission in silicon nanostructures
Electrochemically formed porous silicon (PS) was reported in 1991 to exhibit visible photoluminescence. This discovery could lead to the use of integrated silicon-based optoelectronic devices. This LDRD addressed two general goals for optical emission from Si: (1) investigate the mechanisms responsible for light emission, and (2) tailor the microstructure and composition of the Si to obtain photoemission suitable for working devices. PS formation, composition, morphology, and microstructure have been under investigation at Sandia for the past ten years for applications in silicon-on-insulator microelectronics, micromachining, and chemical sensors. The authors used this expertise to form luminescent PS at a variety of wavelengths and have used analytical techniques such as in situ Raman and X-ray reflectivity to investigate the luminescence mechanism and quantify the properties of the porous silicon layer. Further, their experience with ion implantation in Si lead to an investigation into alternate methods of producing Si nanostructures that visibly luminesce
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Enhanced Gas Analysis for Diagnostics and Surveillance (EGADS): Contamination-free sampling and analysis
Providing uncontaminated weapon internal atmosphere samples and measuring their dew points is of paramount importance for enhanced surveillance and accelerated aging. The authors are developing and integrating four types of gas sampling systems for use throughout the weapons complex. They are utilizing tools to extract time/age information from the gas analysis of weapon internal atmospheres
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Porous silicon structural evolution from in-situ luminescence and Raman measurements
The authors performed in-situ photoluminescence and Raman measurements on an anodized silicon surface in the HF/ethanol solution used for anodization. The porous silicon thereby produced, while resident in HF/ethanol, does not immediately exhibit intense photoluminescence. Intense photoluminescence develops spontaneously in HF/ethanol after 18--24 hours or with replacement of the HF/ethanol with water. These results support a quantum confinement mechanism in which exciton migration to traps and nonradiative recombination dominates the de-excitation pathways until silicon nanocrystallites are physically separated and energetically decoupled by hydrofluoric acid etching or surface oxidation. The porous silicon surface, as produced by anodization, shows large differences in photoluminescence intensity and peak wavelength over millimeter distances. Parallel Raman measurements implicate nanometer-size silicon particles in the photoluminescence mechanism
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