High Vacuum Level Research Articles

Operation of a Sealed-Tube-Vircator High-Power-Microwave Source

The high-power-microwave (HPM) sources currently under development typically require constant pumping to maintain the high vacuum levels required for operation. This pumping is often done with either a cryo- or turbopumping system, either of which would be difficult to deploy in a compact portable system. A compact sealed-tube virtual cathode oscillator (vircator) source has been developed at Texas Tech University (TTU) that does not require a bulky external vacuum pump for operation. This device has a base vacuum pressure in the low range compared to the majority of laboratory HPM sources having vacuum levels in the - range. The reduced amount of trapped gasses in the sealed-tube ultrahigh-vacuum environment has the potential to greatly impact device performance. The TTU sealed-tube vircator is useful as a testbed for studying HPM source optimization under UHV conditions. Measured operational characteristics of the tube utilizing a carbon fiber cathode and a nickel anode are presented, along with radiated microwave measurements.

Improved atom number with a dual color magneto—optical trap

We demonstrate a novel dual color magneto—optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose—Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.

Outgassing of Water Molecules During Silicon Fusion Bonding

Wafer bonding is a key technology for wafer level packaging in MEMS applications. By bonding a cap wafer to a MEMS device wafer, the mechanical structure can be sealed in a package and protected against the outside environment. Fusion bonding is a simple direct wafer bonding technique resulting in high bond strength compared to many other bonding methods. In this study, we present a method to bond a cap wafer to a MEMS device wafer which has released moving mass on it. Wafer surfaces are brought into a contact (pre-bonded) in vacuum conditions followed with high temperature annealing to strengthen the bond. Outgassing of water molecules remaining in the MEMS wafer before wafer bonding was found to be the main reason for bonding failures. Scanning acoustic microscopy was used to compare the bonding results between different pre-bonding vacuum levels. Good bonding results were achieved at higher vacuum level. This packaging method appears to be a suitable technique for encapsulating mechanical sensors with moving mass or other micro structures.

Thin Film Packaging for Vacuum MEMS Encapsulation: A Study on Outgassing Phenomenon

Most of the time, MEMS devices require hermetic encapsulation for protection against atmosphere, moisture, particles and standard back-end manufacturing technologies. In the last few years, Wafer Level Packaging (WLP) is moving toward developments on Thin Film Packaging (TFP) in order to save footprint, to reduce chip thickness and packaging costs. In the specific case of high-vacuum MEMS encapsulation (gyro, compass), long term pressure stability is required. As the final performances of these kinds of devices are strongly dependent on the working pressure, using TFP for MEMS encapsulation with controlled vacuum becomes more challenging due to very small cavity volumes. It is then necessary to understand the outgassing phenomenon that take place during TFP encapsulation in order to reduce it. In this paper, our latest developments on thin film packaging technology are presented. Outgassing from materials used in TFP and MEMS devices become key parameters to decrease the pressure inside the package and to improve the reliability. In a first part, pressure and Residual Gas Analysis (RGA) of typical TFP and typical MEMS materials are measured under different time / temperature baking processes. Measurements show that material outgassing mainly comes from H2 and maximum pick appears in the beginning of the thermal process. Thanks to these characterizations, an optimized outgassing baking process in term of time and thermal budget is presented. By minimizing the internal outgassing, materials deposited by PVD sputtering can now be implemented as sealing materials for low pressure MEMS devices. In a second part, specific low temperature Al based materials which has been developed on equipment fully compatible with front-end fab is presented. Multi-layer materials like Ti / Al based materials are compared to our single Al based material to decrease the microstructure size and to improve the sealing performances. Scanning Electronic Microscopy (SEM) and Focused Ion Beam (FIB) cross section characterizations confirm that the grain sizes are highly impacted by sputtering process parameters and a compromise has to be done with MEMS outgassing. Finally, the most suitable outgassing baking process for the inside cavity materials and various Al-based sealing materials and stacks are performed for a MEMS compass device on 200 mm wafers. Pressure inside the cavity less than 10 mbar is obtained and the TFP yield is presented on each process conditions. These results are very promising and showed the capabilities of TFP for vacuum MEMS encapsulation applications despite very small volume cavity. Development of such technology is still under way in order to reach high vacuum level in the range of 10-1 to 10-3 mbar.

Virus electron microscopy

Since the introduction of the first electron microscope in 1939, the development of the field of ultra-structure, in both the physical and biological sciences, has been dramatic in its elucidation of problems in both fields. Although the theoretical limit of the resolving power of the instrument 2 o A was achieved early in its development, further refinements followed rapidly. Modern instruments are capable of reaching high vacuum levels in relatively short time periods and computerisation has made these instruments remarkably user friendly. The development of oil diffusion pump technology led to the ability to attain extremely high vacuum levels, an essential feature in allowing a beam of electrons to travel in a focused stream, through the use of condenser, objective and projector lenses striking a fluorescent screen, thus producing an image of the specimen to be examined.

Autoresonant Trap Mass Spectrometry (ART MS) for remote sensing applications

A novel mass spectrometer is described that uses purely electrostatic fields to store ionized gases within a cylindrical ion trap. Ions are generated directly inside the trap by electron ionization of gas molecules. An anharmonic trapping potential well confines the ion trajectories of all ion masses, and of a wide range of initial energies, to stable oscillatory motions along the axis of the trap. Mass selective ejection is achieved through a novel autoresonant energy pumping process. The new mass spectrometer has unlimited mass range, good sensitivity at high and ultrahigh vacuum levels, very fast scan rates, compact construction, and extremely low power requirements as it uses only static bias potentials and very small RF signal levels (in the 100 mV range). Small size, low power consumption, rugged construction and reliable operation make ART MS technology an ideal candidate for in situ mass spectrometry in a wide variety of remote sampling applications including harsh sampling environments. Fast mass spectra acquisition rates particularly attractive for sampling applications from fast moving platforms such as airplanes, rockets and boats.

Thermographic study of the ovine mammary gland during different working vacuum levels

Thermography is a non-contact, non-invasive technique that detects surface heat emitted as infrared radiation. Because skin temperature reflects the status of underlying tissue metabolism and blood circulation, abnormal thermal patterns can signify areas of superficial inflammation or circulatory impairments (i.e. congestion). In sheep different methods have been adopted to measure udder blood circulation and the effect of cold exposure and lactation on the distribution of blood flow. The effect of milking procedures on udder and teat skin temperature was investigated in cows through thermographic scanning. Thermography results in a very useful tool to evaluate, estimate and differentiate short and longer-term tissue reactions to machine milking. The objective of this study was to evaluate the influence of working vacuum level on udder and teat temperature changes during milking procedures and the recovery by indirect monitoring of the circulatory impairments of teat tissue via infrared thermography. Two groups of six lactating Sarda ewes were milked experimentally at two vacuum levels (28 and 42 kPa) and same pulsation parameters (120 cycles/min and 60% ratio). Thermographic images (Flir System, ThermaCam P25, sensitivity of 0.08 °C) of posterior udder area (PUA) and teats (teat base – TB; mid teat – MT and teat tip – TT) were taken pre-milking (PM), during milking (M) (only for PUA), and immediately after milking (IAM) up to 2 minutes after milking (AM+). Temperatures were recovered by processing the thermographic images in ThermaCam Researcher Basic 2.8 SR-1 Software (Flir System). The PUA showed a drop of 1°C in both treatments between PM and M. After milking, values did not show remarkable changes. The vacuum level effect on teats temperature results to be different between treatments. Results during IAM indicate a general drop of the teats temperatures and specifically for high vacuum level (from 39.82 to 37.92°C and from 39.71 to 37.75°C for low and high vacuum level respectively). During AM+ (monitored up to 60 sec - AM +30; up to 90 sec - AM+60 and up to 120 sec – AM+90) the increase of teat temperatures were different (P vs 37.96°C and AM+90: 39.02 vs 38.58°C for low and high vacuum level respectively). Differences among TB, MT and TT were evident also at AM+90 only for the high vacuum level while in low one, at the same time, it was persistent only the difference between TT and TB. The higher teat temperature for the low vacuum level could be attributable to a faster return to a normal condition of the blood flow in all teat locations. Teat circulation impairments due to milking procedures need further surveys.

Solution derived 12CaO·7Al2O3 thin films on MgO(100) substrate

Abstract 12CaO·7Al 2 O 3 (C12A7) is known as a component of alumina cement and shows various remarkable properties: generation of high oxidizing power using oxygen radical O − , high electric conductivity (∼1500 S cm −1 ) for the electron clathrated one, etc. Most of the C12A7 thin film fabrication processes reported have been based on PLD method so far, which require high vacuum level and high energy consumption. In order to fabricate the C12A7 films with low energy consumption process, we prepared C12A7 films on MgO(1 0 0) substrate by chemical solution deposition (CSD) method from alkoxide solution. Aluminum sec.-butoxide and calcium metal were used as raw materials, and 2-methoxy ethanol was used as a solvent. Crystallization behavior, crystal structure, and morphology of the prepared film, were investigated by XRD, SEM, and TG-DTA. The C12A7 film prepared by the CSD method was mostly polycrystalline, but it showed high peak intensity at (2 1 1) and (4 2 2) reflection compared to the powder C12A7 peaks. This implied the C12A7 film includes slightly (2 1 1) oriented grains among the polycrystalline on the MgO(1 0 0) substrate.

Torsional ultrasound efficiency under different vacuum levels in different degrees of nuclear cataract

To evaluate the efficiency of torsional ultrasound (US) under different vacuum levels in eyes with cataract with different degrees of nuclear density. Cataract Service, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. In this prospective randomized series, eyes with age-related cataract were divided into 3 groups based on nuclear density. Eyes in each group were randomly assigned to 1 of 3 subgroups and treated with phacoemulsification under vacuum of 250 mm Hg (subgroup 1), 450 mm Hg (subgroup 2), or 600 mm Hg (subgroup 3). Data included preoperative and postoperative corrected distance visual acuity (CDVA), endothelial cell density, and central corneal thickness (CCT) and intraoperative US time and cumulative dissipated energy (CDE). The study evaluated 998 patients (1073 eyes). In each group, there was a statistically significant decrease in US time, CDE, and postoperative endothelial cell loss with increased vacuum (P<.05). At 1 day and 7 days, the CDVA was statistically significantly better in subgroups 2 and 3 (P<.05) and the CCT was thinner when vacuum was higher. There was no statistically significant difference in CDVA and CCT between subgroups 30 days postoperatively (P>.05). Torsional US with a high vacuum level was safe for cataract extraction. With less US energy and endothelial cell loss, torsional US was more efficient than with higher vacuum levels with lower levels.

Thermoelastic coupled modeling for a thermal bimorph actuator

This paper presents a theoretical thermoelastic coupled model for a thermal bimorph actuator driven by a harmonically varying thermal load in micro-electro-mechanical systems. The thermoelastic coupling, which arises from the coupling of the strain rate to the temperature field of the heat transport, is considered in this model. The frequency responses are simulated using the theorem of eigenmode expansion. The effects of thermoelastic coupling on the resonant frequency and the quality factor Q for each eigenmode resonance of the deflection are calculated and compared with the same effects resulted from air damping. It shows that for the example of an aluminum–polysilicon thermal bimorph actuator, the resonant frequencies are generally shifted downward with the order larger than that of air damping, whereas the influence of thermoelastic coupling on the Q is more significant than that of air damping under high vacuum level.

Time-Resolved Observation of Carbon Nanotube Growth by Using an Environmental TEM

We report in-situ observations of the growth of carbon nanotubes (CNTs) by using an environmental transmission electron microscope (E-TEM). E-TEM is a specially designed transmission electron microscope (TEM) with a dierential pumping system where gas can be flowed into the specimen whilst keeping a high vacuum level in the remainder of the TEM column. In order to grow CNTs, Ni nanoparticles as a catalyst were deposited on holey SiOx-TEM mesh grids by using a solution phase catalyst deposition method. Chemical vapor deposition (CVD) was carried out inside the TEM column by flowing acetylene gas ( 10 mTorr) over the Ni catalyst heated to 600 C. At a given growth condition, the CNTs grew with a serpentine morphology with the growing apex frequently returning to the substrate to become anchored at both ends. The growth durations were observed to be quite short, and the growth rate was estimated to be 0.2 mm/sec, which is relatively fast, at low C2H2 pressures of <10 mTorr. Growth was confirmed to occur at the tip where the nickel catalyst particle is located, rather than at the base of the tube, as suggested in the tip growth model. Both multi-walled CNT and single-walled CNT were synthesized simultaneously under the same reaction conditions. This suggests that the nature of the catalyst still plays an important role in determining the characteristics of the CNT even though these characteristics can be controlled by altering either the reaction temperature or pressure.

A modified pump-out technique used for fabrication of low temperature metal sealed vacuum glazing

A modified pump-out technique, incorporating a novel pump-out hole sealing process, has been developed that enables a high level of vacuum to be achieved between the panes of a vacuum glazing. The modified pump-out method provides several potential opportunities for the fabrication of a vacuum glazing with improved thermal performance. In particular, improved flexibility for production of a wide range of glazing sizes may allow a lower cost of manufacture to be achieved by avoiding the expense of a high vacuum oven which would otherwise be required for commercial production of high performance, large-scale vacuum glazings. The thermal performance of the vacuum glazing fabricated using the pump-out technique was characterized using a guarded hotbox calorimeter and theoretically analyzed using a finite volume model. The excellent experimentally determined thermal performance of the fabricated vacuum glazing was in good agreement with that predicted theoretically.

43.3: Discharge Characteristics of 42‐in. AC Plasma Display Panel Fabricated by Vacuum Sealing Method

AbstractThe base vacuum level before filling a discharge gas is an important parameter to affect both the address and sustain discharge characteristics in an AC‐PDP. for the improvement in discharge characteristics, the vacuum sealing method is adapted. In this paper, the vacuum sealing method to enhance a base vacuum level is adopted to minimize the residual impurity gas, and the resultant changes in the address and sustain discharge characteristics, such as a dynamic voltage margin, firing voltage, statistical address delay time, and secondary electron coefficient, were examined in comparison with the conventional sealing method in the 42‐in. AC‐PDP with a high Xe (11 %) content. The high base vacuum level in the 42‐in. panel fabricated by the vacuum sealing method can enhance the discharge characteristics, such as a dynamic voltage margin, a firing voltage, and a statistical address delay time, which are caused by a decrease in the residual impurity gases and an increase in the secondary electron coefficient. In particular, in the vacuum sealing method, the sustain voltage was decreased by about 30 V, and the address voltage was also decreased by about 7V in the Xe (11 %) condition.

Environmental chamber for an atomic force microscope

A commercial atomic force microscope (AFM), originally designed for operation in ambient conditions, was placed inside a compact aluminum chamber, which can be pumped down to high vacuum levels or filled with a desired gaseous atmosphere, including humidity, up to normal pressure. The design of this environmental AFM is such that minimal intrusion is made to the original setup, which can be restored easily. The performance inside the environmental chamber is similar to the original version.

Thermographic study of the ovine mammary gland during different working vacuum levels

Thermography is a non-contact, non-invasive technique that detects surface heat emitted as infrared radiation. Because skin temperature reflects the status of underlying tissue metabolism and blood circulation, abnormal thermal patterns can signify areas of superficial inflammation or circulatory impairments (i.e. congestion). In sheep different methods have been adopted to measure udder blood circulation and the effect of cold exposure and lactation on the distribution of blood flow. The effect of milking procedures on udder and teat skin temperature was investigated in cows through thermographic scanning. Thermography results in a very useful tool to evaluate, estimate and differentiate short and longer-term tissue reactions to machine milking. The objective of this study was to evaluate the influence of working vacuum level on udder and teat temperature changes during milking procedures and the recovery by indirect monitoring of the circulatory impairments of teat tissue via infrared thermography. Two groups of six lactating Sarda ewes were milked experimentally at two vacuum levels (28 and 42 kPa) and same pulsation parameters (120 cycles/min and 60% ratio). Thermographic images (Flir System, ThermaCam P25, sensitivity of 0.08 °C) of posterior udder area (PUA) and teats (teat base – TB; mid teat – MT and teat tip – TT) were taken pre-milking (PM), during milking (M) (only for PUA), and immediately after milking (IAM) up to 2 minutes after milking (AM+). Temperatures were recovered by processing the thermographic images in ThermaCam Researcher Basic 2.8 SR-1 Software (Flir System). The PUA showed a drop of 1°C in both treatments between PM and M. After milking, values did not show remarkable changes. The vacuum level effect on teats temperature results to be different between treatments. Results during IAM indicate a general drop of the teats temperatures and specifically for high vacuum level (from 39.82 to 37.92 °C and from 39.71 to 37.75 °C for low and high vacuum level respectively). During AM+ (monitored up to 60 sec - AM +30; up to 90 sec - AM+60 and up to 120 sec – AM+90) the increase of teat temperatures were different (P<0.05) between vacuum levels (AM+30: 38.12 vs 37.54 °C; AM+60: 38.19 vs 37.96 °C and AM+90: 39.02 vs 38.58 °C for low and high vacuum level respectively). Differences among TB, MT and TT were evident also at AM+90 only for the high vacuum level while in low one, at the same time, it was persistent only the difference between TT and TB. The higher teat temperature for the low vacuum level could be attributable to a faster return to a normal condition of the blood flow in all teat locations. Teat circulation impairments due to milking procedures need further surveys.

The ZEPLIN-III dark matter detector: Instrument design, manufacture and commissioning

We present details of the technical design, manufacture and testing of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase xenon detector which measures both the scintillation light and the ionisation charge generated in the liquid by interacting particles and radiation. The instrument design is driven by both the physics requirements and by the technology requirements surrounding the use of liquid xenon. These include considerations of key performance parameters, such as the efficiency of scintillation light collection, restrictions placed on the use of materials to control the inherent radioactivity levels, attainment of high vacuum levels and chemical contamination control. The successful solution has involved a number of novel design and manufacturing features which will be of specific use to future generations of direct dark matter search experiments as they struggle with similar and progressively more demanding requirements.

IN-VACUUM PHOTOGRAMMETRY OF A TEN-METER SQUARE SOLAR SAIL

Solar sailing is a promising, future in-space propulsion method that uses the small force of reflecting sunlight to accelerate a large, reflective membrane without expendable propellants. One of two solar sail configurations under development by NASA is a striped net approach by L'Garde, Inc. This design uses four inflatably deployed, lightweight booms supporting a network of thin strings onto which four quadrants of ultrathin aluminized membranes are attached. The NASA Langley Research Center (LaRC) provided both experimental and analytical support to L'Garde for validating the structural characteristics of this unique, ultralightweight spacecraft concept. One of LaRC's responsibilities was to develop and apply photogrammetric methods to measure sail shape. The deployed shape provides important information for validating the accuracy of finite-element modeling techniques. Photogrammetry is the science and art of calculating 3D coordinates of targets or other distinguishing features on structures using images. A minimum of two camera views of each target is required for 3D determination, but having four or more camera views is preferable for improved reliability and accuracy. Using retroreflective circular targets typically provides the highest measurement accuracy and automation. References 3 and 4 provide details of photogrammetry technology, and reference 5 discusses previous experiences with photogrammetry for measuring gossamer spacecraft structures such as solar sails. This paper discusses the experimental techniques used to measure a L Garde 10-m solar sail test in vacuum with photogrammetry. The test was conducted at the NASA-Glenn Space Power Facility (SPF) located at Plum Brook Station in Sandusky, Ohio. The SPF is the largest vacuum chamber in the United States, measuring 30 m in diameter by 37 m in height. High vacuum levels (10(exp -6) torr) can be maintained inside the chamber, and cold environments (-195 C) are possible using variable-geometry cryogenic cold walls. This test used a vacuum level of approximately 1 torr (sufficient for structural static/dynamic characterization) and instead of using the cryogenic cold walls, used local LN2 cold plates underneath each of the four cold-rigidizable solar sail booms instead.

Cataract Surgery Techniques and Innovations

Cataract surgery and phacoemulsification techniques have advanced dramatically over the past 10 years.The concept was first introduced by Dr Charles Kelman, heralding the era of modern cataract extraction and paving the way for small incision surgery. Since then, the trend has been toward smaller incision surgery with less induced astigmatism and less traumatic surgery by using ultrasound assisted phacoaspiration instead of vacuum-assisted phacoemulsification. Recent refinements in power modulations have led most surgeons to use techniques that utilize less phacoemulsification energy and thus reduce thermal energy delivery and injury to the eye. This is carried out either by using mechanical forces to disassemble the nucleus or by using higher vacuum levels to aspirate the nucleus or a combination of both. This paper will describe QuickChop phacoemulsification and bimanual microincisional phacoemulsication techniques, which attempt to simplify each stage of the operation, in order to minimize trauma and achieve the optimal outcome.

Effect of light on colour stability of sliced smoked rainbow trout Oncorhynchus mykiss fed astaxanthin

Colour stability of sliced smoked fillets of trout fed astaxanthin exposed to light during chilled storage was monitored by instrumental colour measurements and analyses of flesh astaxanthin content. When exposed to light changes in colour parameters at the surface of sliced smoked rainbow trout fillets occurred. The slices became paler. The level of astaxanthin was not affected by either light or storage conditions. Slices exposed to light had higher TBARS values than those stored in the dark. In our experimental conditions the use of a high initial vacuum level and packaging film with a low oxygen transmission rate maintained the astaxanthin content. However these optimal packaging conditions were not able to prevent significant oxidation of lipids after the initial 2–3 days of display.

진공 인라인 실장에 의해 제작된 플라즈마 디스플레이 패널의 전기적ㆍ광학적 특성

The optical and electrical characteristics of plasma display panel(PDP) using the vacuum in-line sealing technology compared with the conventional sealing process in this research. This PDP consisted of MgO protecting layer by e-beam evaporation and battier rib, transparent dielectric layer, dielectric layer, and electrodes by screen printer and then sealed off on Ne-Xe(4 ％) 400 Torr and 430。C. The brightness and luminous efficiency were good as the base vacuum level was higher, and it was to check the advantage of high vacuum level sealing, one of the strong points of the vacuum in-line sealing process. However, the brightness and luminous efficiency was dropped sharply because of a crack on MgO protecting layer by the difference of the expansion and contraction stress on high temperature in the vacuum states between MgO and substrate. Fortunately, the crack was prevented by MgO was deposited on higher temperature than 300。C. Finally, the PDP, was fabricated by the vacuum in-line sealing process, resulted the lower brightness than processing only the thermal annealing treatment in the vacuum chamber, but the luminous efficiency was increased by the reducing power consumption with the decreasing luminous current. The vacuum in-line sealing technology was not to need the additional thermal annealing process and could reduce the fabrication process and bring the excellent optical and electrical properties without the crack of MgO protecting layer than the conventional sealing process.