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Rajeshuni Ramesham - One of the best experts on this subject based on the ideXlab platform.

  • review of vacuum packaging and maintenance of mems and the use of Getters therein
    Journal of Micro-nanolithography Mems and Moems, 2009
    Co-Authors: Rajeshuni Ramesham, Richard C Kullberg
    Abstract:

    Key types of microelectromechanical systems (MEMS) sensors need vacuum or other controlled ambients in order to operate properly. Examples include MEMS infrared sensors and sensitive MEMS gyros. Steps to attain and maintain the vacuum ambient include: (i) Proper processing to reduce trapped gasses in the package, (ii) hermetically sealing the package, and (iii) providing a means to pump away gasses that outgas into the package. Proper package processing and getter technology are key to success in this endeavor. Although many aspects of package processing and assembly are proprietary, the key items to control include leaks (i.e., obtaining a hermetic package) and outgassing from materials within the vacuum cavity. Once gas loads are minimized as much as possible, the actual service life of a package depends on pumping away any internal gases built up through outgassing, leaks, or permeation. This pumping is done by a class of materials called Getters. Gettering technology is discussed in relation to vacuum-packaged MEMS/MOEMS. With proper materials and processes, controlled ambients to include vacuum can be obtained in MEMS/MOEMS packages. Not only can they be obtained, they can be maintained for the desired system lifetime.

  • Getters for Reliable Hermetic Packages
    Support Program for NASA Products Greenbelt Maryland USA, 2000
    Co-Authors: Rajeshuni Ramesham
    Abstract:

    A variety of sealed-off devices such as cathode ray tubes (CRT's) electron tubes, plasma displays, particle accelarators and colliders vacuum thermal insulation, ultra-high vacuum (UHV), extreme high vacuum (XHV) systems for semiconductor processing, X-ray tubes, lamps, field-emission displays (FEDs) flat panel displays (FPDs), some microelectromechanical systems (MEMS) and science instruments for space applications, nuclear systems require a vacuum for their successful operation.

Nataliya Tsud - One of the best experts on this subject based on the ideXlab platform.

  • activation of binary zr v non evaporable Getters synchrotron radiation photoemission study
    Applied Surface Science, 2005
    Co-Authors: V Matolin, V Dudr, S Fabik, V Chab, K Masek, Iva Matolinova, K C Prince, Tomas Skala, F Sutara, Nataliya Tsud
    Abstract:

    Abstract Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these Getters was investigated by synchrotron radiation photoelectron spectroscopy using photon excitation energies of 600, 250 and 73 eV. Depth resolved results were compared to the results of the SIMS profiling. The measurements confirmed the disappearance of the superficial oxide layer covering the air-exposed Zr–V surfaces via its progressive reduction during the thermal activation. The depth sensitive results showed that the activated getter surface is covered by a residual zirconium sub-oxide.

  • activation of binary zr v non evaporable Getters a soft x ray photoemission study of carbide formation
    Surface Science, 2004
    Co-Authors: S Fabik, V Dudr, V Chab, K Masek, K C Prince, F Sutara, Nataliya Tsud, K Veltruska, M Vondracek, V Matolin
    Abstract:

    Abstract Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these Getters was investigated by photoelectron spectroscopy using two photon excitation energies of 600 eV (synchrotron light) and 1253.6 eV (Mg Kα laboratory source). During the activation by heating from 120 to 320 °C, the adsorbed carbon was transformed to metal carbides and diffused to the subsurface region.

Jeffrey R Serne - One of the best experts on this subject based on the ideXlab platform.

  • Getters for improved technetium containment in cementitious waste forms
    Journal of Hazardous Materials, 2018
    Co-Authors: Matthew R Asmussen, James J Neeway, Amanda R Lawter, Carolyn I Pearce, Brian W Miller, Wayne W Lukens, Mark E Bowden, Micah A Miller, Edgar C Buck, Jeffrey R Serne
    Abstract:

    A cementitious waste form, Cast Stone, is a possible candidate technology for the immobilization of low activity nuclear waste (LAW) at the Hanford site. This work focuses on the addition of getter materials to Cast Stone that can sequester Tc from the LAW, and in turn, lower Tc release from the Cast Stone. Two Getters which produce different products upon sequestering Tc from LAW were tested: Sn(II) apatite (Sn-A) that removes Tc as a Tc(IV)-oxide and potassium metal sulfide (KMS-2) that removes Tc as a Tc(IV)-sulfide species, allowing for a comparison of stability of the form of Tc upon entering the waste form. The Cast Stone with KMS-2 getter had the best performance with addition equivalent to ∼0.08wt% of the total waste form mass. The observed diffusion (Dobs) of Tc decreased from 4.6±0.2×10-12cm2/s for Cast Stone that did not contain a getter to 5.4±0.4×10-13cm2/s for KMS-2 containing Cast Stone. It was found that Tc-sulfide species are more stable against re-oxidation within getter containing Cast Stone compared with Tc-oxide and is the origin of the decrease in Tc Dobs when using the KMS-2.

  • technetium Getters to improve cast stone performance
    MRS Proceedings, 2015
    Co-Authors: James J Neeway, Amanda R Lawter, Jeffrey R Serne, Robert M Asmussen, Nikolla P Qafoku
    Abstract:

    The cementitious material known as Cast Stone has been selected as the preferred waste form for solidification of aqueous secondary liquid effluents from the Hanford Tank Waste Treatment and Immobilization Plant (WTP) process condensates and low-activity waste (LAW) melter off-gas caustic scrubber effluents. Cast Stone is also being evaluated as a supplemental immobilization technology to provide the necessary LAW treatment capacity to complete the Hanford tank waste cleanup mission in a timely and cost effective manner. Two radionuclides of particular concern in these waste streams are technetium-99 (99Tc) and iodine-129 (129I). These radioactive tank waste components contribute the most to the environmental impacts associated with the cleanup of the Hanford site. A recent environmental assessment of Cast Stone performance, which assumes a diffusion controlled release of contaminants from the waste form, calculates groundwater in excess of the allowable maximum permissible concentrations for both contaminants. There is, therefore, a need and an opportunity to improve the retention of both 99Tc and 129I in Cast Stone. One method to improve the performance of Cast Stone is through the addition of “Getters” that selectively sequester Tc and I, therefore reducing their diffusion out of Cast Stone. In this paper, we present results ofmore » Tc and I removal from solution with various Getters with batch sorption experiments conducted in deionized water (DIW) and a highly caustic 7.8 M Na Ave LAW simulant. In general, the data show that the selected Getters are effective in DIW but their performance is comprised when experiments are performed with the 7.8 M Na Ave LAW simulant. Reasons for the mitigated performance in the LAW simulant may be due to competition with Cr present in the 7.8 M Na Ave LAW simulant and to a pH effect.« less

  • technetium and iodine Getters to improve cast stone performance
    2015
    Co-Authors: Nikolla P Qafoku, James J Neeway, Amanda R Lawter, Tatiana G Levitskaia, Jeffrey R Serne, Joseph H Westsik, Michelle M V Snyder
    Abstract:

    To determine the effectiveness of the various getter materials prior to their solidification in Cast Stone, a series of batch sorption experiments was performed at Pacific Northwest National Laboratory. To quantify the effectiveness of the removal of Tc(VII) and I(I) from solution by Getters, the distribution coefficient, Kd (mL/g), was calculated. Testing involved placing getter material in contact with spiked waste solutions at a 1:100 solid-to-solution ratio for periods up to 45 days with periodic solution sampling. One Tc getter was also tested at a 1:10 solid-to-solution ratio. Two different solution media, 18.2 MΩ deionized water (DI H2O) and a 7.8 M Na LAW simulant, were used in the batch sorption tests. Each test was conducted at room temperature in an anoxic chamber containing N2 with a small amount of H2 (0.7%) to maintain anoxic conditions. Each getter-solution combination was run in duplicate. Three Tc- and I-doping concentrations were used separately in aliquots of both the 18.2 MΩ DI H2O and a 7.8 M Na LAW waste simulant. The 1× concentration was developed based on Hanford Tank Waste Operations Simulator (HTWOS) model runs to support the River Protection Project System Plan Revision 6. The other two concentrations were 5× andmore » 10× of the HTWOS values. The Tc and I tests were run separately (i.e., the solutions did not contain both solutes). Sampling of the solid-solution mixtures occurred nominally after 0.2, 1, 3, 6, 9, 12, 15 days and ~35 to 45 days. Seven getter materials were tested for Tc and five materials were tested for I. The seven Tc Getters were blast furnace slag 1 (BFS1) (northwest source), BFS2 (southeast source), Sn(II)-treated apatite, Sn(II) chloride, nano tin phosphate, KMS (a potassium-metal-sulfide), and tin hydroxapatite. The five iodine Getters were layered bismuth hydroxide (LBH), argentite mineral, synthetic argentite, silver-treated carbon, and silver-treated zeolite. The Tc Kd values measured from experiments conducted using the 7.8 M Na LAW simulant (the simulant selected to represent LAW) for the first 15 days for four Tc Getters (BFS1, BFS2, Sn(II)-treated apatite, and Sn(II) chloride) show no, to a very small, capacity to remove Tc from the LAW simulant. For the Tc-getter experiments in the 7.8 M LAW simulant, the majority of the effluent samples show very small drops in Tc concentrations for the 35-day compared to the 15-day samplings. However, the Tc concentration in the simulant blanks also dropped slightly during this period, so the effect of the getter contacting LAW simulant at 35 days compared to 15 days is minimal; except that the BFS1 1:10 test shows a slow but steady decrease in Tc concentration in the LAW simulant supernatant from the beginning to the 35 day contact at which point about 20% of the original Tc has been removed from solution. Lastly, the KMS getter gives the highest Kd value for Tc at 35 days where Kd values have increased to 104 mL/g. When considering the different I Getters reacting with the 7.8 M LAW simulant, two Getters are much more effective than the others: Ag zeolite and Syn Arg. The other Getters have calculated iodide distribution coefficients that show very limited effectiveness in the caustic conditions created by the LAW simulant. These are preliminary results that will need more detailed analyses including both pre- and post-batch sorption getter solid-phase characterization using state-of-the-art instrumentation such as synchrotron X ray absorption spectroscopy, which can delineate the oxidation state of the Tc and likely iodine species as well as some of the Getters key major components, sulfur and iron in the BFS, and tin and sulfur in the tin-bearing and sulfur-bearing Getters. This report also describes future experimental studies to be performed to better elucidate the mechanisms controlling the Tc and I sequestration processes in the various Getters and leach tests of getter-bearing Cast Stone monoliths.« less

Sheng Liu - One of the best experts on this subject based on the ideXlab platform.

  • getter free vacuum packaging for mems
    Sensors and Actuators A-physical, 2009
    Co-Authors: Dexiu Huang, Xuefang Wang, Sheng Liu
    Abstract:

    Abstract Quite a few MEMS devices such as accelerators, gyroscopes, infrared sensors need to work in vacuum environment to enhance their performance. The traditional vacuum packaging methods use Getters to increase vacuum maintaining lifetime. However, the getter's characteristics of high temperature activation, powder pollution, large package size limit its use in MEMS vacuum packaging. This study analyzes the factors that influence the vacuum level, and derived a relationship between the balanced vacuum level, the effective leak rate, and vacuum maintaining lifetime. A novel vacuum package design with vacuum buffer cavity was proposed, the vacuum maintaining lifetime could be increased at least 20 times as compared to the ordinary package with the same volume. Reliability experiments were conducted so as to verify that the new package design can achieve reliable vacuum packaging without Getters to meet the requirements of device applications for vacuum with about 0.1 Pa in pressure level. This unique package design also provided a complementary way to work with Getters to enhance the vacuum package performance and reliability of hermeticity.

P N Vyugov - One of the best experts on this subject based on the ideXlab platform.

  • applications of zr v hydrogen Getters in vacuum plasma devices phase structural and hydrogen sorption characteristics
    Journal of Alloys and Compounds, 2005
    Co-Authors: M V Lototsky, V A Yartys, Ye V Klochko, V N Borisko, R I Starovoitov, V M Azhazha, P N Vyugov
    Abstract:

    Abstract The paper considers materials science aspects of the applications of the reversible hydrogen Getters in vacuum-plasma devices. The selection of hydrogen getter material, which is located in the vacuum chamber of the installation, is based on a convenience of switching of its functions from the “internal” source of hydrogen supply to the mode of control over the hydrogen pressure by chemically “pumping” hydrogen from the volume into the getter. The energy of plasma particles bombarding the surface of the material allows controlling the supply of the plasma-forming gas (hydrogen). The arc-melted ZrV alloy modified by small amounts of oxygen was used as getter material. Hydrogen sorption characteristics of the alloy were studied in the Sieverts-type setup. The hydrides were characterised by vacuum Thermal Desorption Spectroscopy. X-ray diffraction was employed to study phase-structural composition of the getter and its hydride. A technology of the production of the MH elements for vacuum-plasma installations has been developed. The MH elements on the basis of the H-saturated ZrV(O) alloy have shown a resistance against sputtering during their bombardment by high-energy particles in vacuum.