James Michael Hochrein

Isothermal mass flow measurements in microfabricated rectangular channels over a very wide Knudsen range

Measurement and modeling of gas flows in microelectromechanical systems (MEMS) scale channels are relevant to the fundamentals of rarefied gas dynamics (RGD) and the practical design of MEMS-based flow systems and micropumps. We describe techniques for building robust, leak-free, rectangular microchannels which are relevant to micro- and nanofluidic devices, while the channels themselves are useful for fundamental RGD studies. For the first time, we report the isothermal steady flow of helium (He) gas through these channels from the continuum to the free-molecular regime in the unprecedented Knudsen range of 0.03–1000. On the high end, our value is 20-fold larger than values previously reported by Ewart et al (2007 J. Fluid Mech. 584 337–56). We accomplished this through a dual-tank accumulation technique which enabled the monitoring of very low flow rates, below 10−14 kg s−1. The devices were prebaked under vacuum for 24 h at 100 °C in order to reduce outgassing and attain high Kn. We devised fabrication methods for controlled-depth micro-gap channels using silicon for both channel ceiling and floor, thereby allowing direct comparisons to models which utilize this simplifying assumption. We evaluated the results against a closed-form expression that accurately reproduces the continuum, slip, transition, and free-molecular regimes developed partly by using the direct simulation Monte Carlo method. The observed data were in good agreement with the expression. For Kn > ~100, we observed minor deviations between modeled and experimental flow values. Our fabrication processes and experimental data are useful to fundamental RGD studies and future MEMS microflow devices with respect to extremely low-flow measurements, model validation, and predicting optimal designs.

Thermal degradation of β‐carotene studied by ion mobility atmospheric solid analysis probe mass spectrometry: full product pattern and selective ionization enhancement

Atmospheric solid analysis probe mass spectrometry has the capability of capturing full product patterns simultaneously including both volatile and semi-volatile compounds produced at elevated temperatures. Real-time low-energy collision-induced fragmentation combined with ion mobility separations enables rapid identification of the chemical structures of products. We present here for the first time the recognition of full product patterns resulting from the thermal degradation of β-carotene at temperatures up to 600 °C. Solvent vapor-induced ionization enhancement is observed, which reveals parallel thermal dissociation processes that lead to even- and odd-numbered mass products. The drift-time distributions of high mass products, along with β-carotene, were monitored with temperature, showing multiple conformations that are associated with the presence of two β-rings. Products of masses 346/347, however, show a single conformation distribution, which indicates the separation of two β-rings resulting from the direct bond scission at the polyene hydrocarbon chain. The thermal degradation pathways are evaluated and discussed.

Effects of Moisture and Hydrogen Exposure on Radiation-Induced MOS Device Degradation and Its Implications for Long-Term Aging

Transistors and ICs built in several different captive and commercial facilities were exposed to moisture, irradiated, and annealed. The moisture exposures were performed using highly accelerated stress test (HAST) at 130degC and 85% relative humidity. Irradiation of n-channel transistors exposed to HAST followed by a long-term anneal resulted in some increase in interface-trap and oxide-trapped charge buildup. However, exposing p-channel transistors to HAST preirradiation resulted in extremely large and unexpected voltage shifts immediately following irradiation. They were observed for devices with either doped oxide or nitride final chip passivation. Because of this, nitride passivation may not be sufficient to prevent H2O from causing enhanced radiation-induced degradation over long time periods in some devices (e.g., commercial devices with nitride final chip passivation packaged in plastic packages). The smaller voltage shifts for the n-channel transistors may be related to the formation of phosphosilicate glass (PSG) overlying the sources and drains of the n-channel transistors impeding the diffusion of moisture to the gate oxides. It is shown that, the large radiation-induced voltage shifts for the p-channel transistors can lead to enhanced IC parametric degradation and functional failure at lower radiation levels. Large increases in radiation-induced field oxide leakage current were also observed for transistors exposed to HAST preirradiation. Transistors were also annealed (prior to irradiation) and irradiated in H2. Approximately the same level of radiation-induced degradation was observed for n- and p-channel transistors suggesting that the diffusion kinetics for H2 diffusion are considerably different than for H2O diffusion. These results raise the concern that exposure of devices to moisture or hydrogen can lead to long-term radiation-induced aging effects.

Composition of the essential oils from Rocky Mountain juniper (Juniperus scopulorum), Big sagebrush (Artemisia tridentata), and White Sage (Salvia apiana).

The essential oils of Juniperus scopulorum, Artemisia tridentata, and Salvia apiana obtained by steam extraction were analyzed by GC-MS and GC-FID. For J. scopulorum, twenty-five compounds were identified which accounts for 92.43% of the oil. The primary constituents were sabinene (49.91%), {alpha}-terpinene (9.95%), and 4-terpineol (6.79%). For A. tridentata, twenty compounds were identified which accounts for 84.32% of the oil. The primary constituents were camphor (28.63%), camphene (16.88%), and 1,8-cineole (13.23%). For S. apiana, fourteen compounds were identified which accounts for 96.76% of the oil. The primary component was 1,8-cineole (60.65%).

Nanoliter MEMS package gas sampling to determine hermeticity

Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-term component reliability because it is within this environment that all internal materials age. As MEMS package sizes decrease with miniaturization, characterization of the internal atmosphere becomes increasingly difficult. Typical transistor metal cans (e.g., TO-5 type) and large MEMS devices have internal volumes of tenths of a milliliter. Last year, gas-sampling methods for smaller-sized MEMS packages were developed and successfully demonstrated on volumes as low as 3 microliters (package outside dimensions: ~1 x 2 x 5 mm). This year, we present gas sampling methods and results for a much smaller MEMS package having an internal volume of 30 nanoliters, two orders of magnitude lower than the previous small package. After entirely redesigning the previous sampling manifold, several of the 30 nanoliter MEMS were gas sampled successfully and results showed the intended internal gas atmosphere of nitrogen was sealed inside the package. The technique is a radical jump from previous methods because not only were these MEMS packages sampled, but also the gas from each package was analyzed dozens of times over the course of about 20 minutes. Additionally, alternate methods for gas analyses not using helium or fluorinert will be presented.

Identification of volatile butyl rubber thermal-oxidative degradation products by cryofocusing gas chromatography/mass spectrometry (cryo-GC/MS).

Chemical structure and physical properties of materials, such as polymers, can be altered as aging progresses, which may result in a material that is ineffective for its envisioned intent. Butyl rubber formulations, starting material, and additives were aged under thermal-oxidative conditions for up to 413 total days at up to 124 °C. Samples included: two formulations developed at Kansas City Plant (KCP) (#6 and #10), one commercially available formulation (#21), Laxness bromobutyl 2030 starting material, and two additives (polyethylene AC-617 and Vanax MBM). The low-molecular weight volatile thermal-oxidative degradation products that collected in the headspace over the samples were preconcentrated, separated, and detected using cryofocusing gas chromatography mass spectrometry (cryo-GC/MS). The majority of identified degradation species were alkanes, alkenes, alcohols, ketones, and aldehydes. Observations for Butyl #10 aged in an oxygen-18 enriched atmosphere ( 18 O2) were used to verify when the source of oxygen in the applicable degradation products was from the gaseous environment rather than the polymeric mixture. For comparison purposes, Butyl #10 was also aged under non-oxidative thermal conditions using an argon atmosphere. UNCLASSIFIED UNLIMITED RELEASE (UUR) UNCLASSIFIED UNLIMITED RELEASE (UUR) 4 ACKNOWLEDGMENTS The authors gratefully acknowledge the contributions of Donald R. Bradley for his assistance in sample preparation and aging. We would also like to thank Mark Wilson for providing the butyl rubber samples as developed by him at Kansas City Plant. Funding was provided by the Enhanced Surveillance Campaign (ESC). 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 DEAC0494AL85000. UNCLASSIFIED UNLIMITED RELEASE (UUR) UNCLASSIFIED UNLIMITED RELEASE (UUR) 5 CONTENTS

Development of a Chemiresistor Sensor for Polypropylene Degradation Products

This paper presents the development of a sensor to detect the oxidative and radiation induced degradation of polypropylene. Recently we have examined the use of crosslinked assemblies of nanoparticles as a chemiresistor-type sensor for the degradation products. We have developed a simple method that uses a siloxane matrix to fabricate a chemiresistor-type sensor that minimizes the swelling transduction mechanism while optimizing the change in dielectric response. These sensors were exposed with the use of a gas chromatography system to three previously identified polypropylene degradation products including 4-methyl-2-pentanone, acetone, and 2-pentanone. The limits of detection 210 ppb for 4-methy-2-pentanone, 575 ppb for 2-pentanone, and the LoD was unable to be determined for acetone due to incomplete separation from the carbon disulfide carrier.

Method for creating gas standards form liquid HFE-7100 and FC-72.

HFE-7100 and FC-72 fluorinert are two fluids used during weapon component manufacturing. HFE-7100 is a solvent used in the cleaning of parts, and FC-72 is the blowing agent of a polymeric removable foam. The presence of either FC-72 or HFE-7100 gas in weapon components can provide valuable information as to the stability of the materials. Therefore, gas standards are needed so HFE-7100 and FC-72 gas concentrations can be accurately measured. There is no current established procedure for generating gas standards of either HFE-7100 or FC-72. This report outlines the development of a method to generate gas standards ranging in concentration from 0.1 ppm to 10% by volume. These standards were then run on a Jeol GC-Mate II mass spectrometer and analyzed to produce calibration curves. We present a manifold design that accurately generates gas standards of HFE-7100 and FC-72 and a procedure that allows the amount of each to be determined.