bluuebunny/crossref_metadata_2025 huggingface dataset:
Recommended practice for calibrating vacuum gauges of the thermal conductivity type
Authors: Ellefson R. E. , Miiller A. P.
Published: July 2002

This article describes and recommends various methods for calibration of thermal conductivity vacuum gauges in the pressure range of the order of 10−1 Pa ( 10−3 Torr) to an atmosphere and is one of a series published by the American Vacuum Society. It contains data from many sources and represents the opinions of a number of experts in the field. The text was developed by a sub-committee of the Recommended Practice Committee of the American Vacuum Society. The Thermal Conductivity Gauging Committee is made up of users and manufacturers of vacuum gauges who have a variety of experience in the practical use of thermal conductivity gauges.
Chemical vapor deposition of fluoroalkylsilane monolayer films for adhesion control in microelectromechanical systems
Authors: Mayer T. M. , de Boer M. P. , Shinn N. D. , Clews P. J. , Michalske T. A.
Published: July 2002

We have developed a new process for applying a hydrophobic, low adhesion energy coating to microelectromechanical (MEMS) devices. Monolayer films are synthesized from tridecafluoro-1,1,2,2- tetrahydrooctyltrichlorosilane (FOTS) and water vapor in a low-pressure chemical vapor deposition process at room temperature. Film thickness is self-limiting by virtue of the inability of precursors to stick to the fluorocarbon surface of the film once it has formed. We have measured film densities of ∼3 molecules nm2 and film thickness of ∼1 nm. Films are hydrophobic, with a water contact angle >110°. We have also incorporated an in situ downstream microwave plasma cleaning process, which provides a clean, reproducible oxide surface prior to film deposition. Adhesion tests on coated and uncoated MEMS test structures demonstrate superior performance of the FOTS coatings. Cleaned, uncoated cantilever beam structures exhibit high adhesion energies in a high humidity environment. An adhesion energy of 100 mJ m−2 is observed after exposure to >90% relative humidity. Fluoroalkylsilane coated beams exhibit negligible adhesion at low humidity and ⩽20 μJ m−2 adhesion energy at >90% relative humidity. No obvious film degradation was observed for films exposed to >90% relative humidity at room temperature for ∼24 h.
Self-assembled gold silicide wires on bromine-passivated Si(110) surfaces
Authors: Rout B. , Sundaravel B. , Das Amal K. , Ghose S. K. , Sekar K. , Mahapatra D. P. , Dev B. N.
Published: July 2002

Thin Au films (∼45 nm) deposited by thermal evaporation under high vacuum on bromine-passivated Si(110) substrates, upon annealing showed the formation of long gold silicide wire-like islands on top of a thin uniform layer of gold silicide in a self-assembled Stranski–Krastanov growth process. Optical micrographs showed long, straight and narrow islands with aspect ratios as large as 200:1. Scanning electron microscopy images revealed the presence of facets. The islands are aligned along the [1̄10] direction on the Si(110) surface. Rutherford backscattering spectrometry measurements with an ion microbeam identified the islands to possess varying thickness across a single island as one would expect for islands having facets and also showed the uniform silicide layer over the Si substrate to be very thin (∼1.5 nm). The observed alignment of the gold silicide islands on the Si(110) surface has been explained in terms of the lattice mismatch between gold–silicide and silicon and invoking the theory of shape transition in heteroepitaxial growth. We have observed islands as long as 200 μm and as narrow as 100 nm in this nonultrahigh vacuum growth on chemically passivated Si(110) surfaces. The method, with properly optimized parameters, may provide a way to grow quantum wires.
Ion and substrate effects on surface reactions of CF2 using C2F6, C2F6/H2, and hexafluoropropylene oxide plasmas
Authors: Butoi Carmen I. , Mackie Neil M. , Williams Keri L. , Capps Nathan E. , Fisher Ellen R.
Published: July 2002

The surface reactivity of CF2 radicals has been characterized during plasma processing of a variety of substrates using the imaging of radicals interacting with surfaces technique. The plasma molecular beam sources are 100% C2F6, 50/50 C2F6/H2, and 100% hexafluoropropylene oxide (HFPO) gas mixtures. Simulation of spatially resolved laser-induced fluorescence images in the 100% C2F6 system shows that CF2 has a scatter value, S, >1.0 with SiO2, polyimide and photoresist substrates. A scatter of >1.0 indicates that CF2 molecules are generated at the surface during plasma processing. With the 50/50 C2F6/H2 plasma, CF2 exhibits a lower scatter value (∼0.85) on Si, SiO2, and polyimide substrates. With the HFPO plasma source, S⩾1 for all continuous wave powers and substrates processed. Values of S∼0.8 are obtained for ion-free and pulsed plasmas, however, revealing ion collisions with the substrate play an important role in the surface generation of CF2. The radical-surface interaction data are correlated with data from surface characterization by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy of the substrates. The key finding is that our results suggest the surface reactivity behavior of CF2 radicals correlates well to the overall plasma process (etching or deposition).
Vapor Generation and Deposition of Zinc at High Rates
Authors: Butler J. F.
Published: July 2002

A system for zinc vapor generation and deposition onto a strip substrate at high rates is described. A resistance heated graphite crucible with a special design to suppress uncontrolled boiling is able to produce zinc vapor outputs as high as 150 lb/h for the 300 in.2 hearth area utilized. An efficient system for nozzling the zinc vapor onto the strip substrate from an enclosed hood allows this maximum vaporization rate to be condensed uniformly at a thickness of 0.6 mils across a 12-in. width at a line speed of 100 ft/min. Control of the vaporization rate is obtained through variation in the power input according to a heat flow model and also by means of a barometric liquid-zinc leg which is used to fill and empty the crucible and feed it continuously from outside the vacuum chamber. Other methods used to control the system are also discussed briefly as is the type of coating produced by deposition at these high rates.
Application of Static Metallic Adhesion Data to Friction
Authors: Aldrich R. G. , Keller D. V.
Published: July 2002

The significance of metallic adhesion phenomena are reviewed relative to the sliding friction behavior of metals and alloys. A model is presented for the analysis of sliding friction based upon contact resistance measurements and experimental data presented for the materials combinations ultra-pure iron vs ultra-pure iron, iron 65-ppm carbon vs iron 65-ppm carbon, and 440 C stainless steel vs 440 C stainless steel. It is shown that the behavior observed for these materials combinations under conditions of sliding friction can be predicted from normal force adhesion experiments using a four wire contact resistance bridge circuit. The effects of environment as well as compressive load, sliding frequency, time, and specimen geometry are discussed. It is further shown that significant data are generated by the adhesion technique for the definition of the mechanical properties of the true load bearing area.
Remote plasma enhanced metalorganic chemical vapor deposition of TiN from tetrakis-dimethyl-amido-titanium
Authors: Yun Ju-Young , Rhee Shi-Woo , Park Sanggee , Lee Jae-Gab
Published: July 2002

Effect of H2 and N2 plasma in the remote plasma enhanced metalorganic chemical vapor deposition of TiN (titanium nitride) from tetrakis-dimethyl-amido-titanium was studied in the deposition temperature range of 200–400 °C. The deposition rate with H2 plasma is faster than with N2 plasma and both processes showed similar activation energies, 16.7 and 18.3 kcal/mol, in the deposition temperature range of 200–300 °C. Above this temperature range, the deposition rate was decreased due to the gas phase dissociation of the precursor. H2 plasma was effective in removing hydrocarbon impurities and carbon was incorporated as a form of TiC but with N2 plasma, TiN film was formed with rough surface due to the incorporation of free carbon. The film with H2 plasma showed low resistivity due to the lower incorporation of free carbon.
Backstreaming from Cryogenic Traps
Authors: Hablanian M. H. , Herrick R. F.
Published: July 2002

An unusual mechanism of gross backstreaming has been recently observed in diffusion-pump systems with liquid-nitrogen traps. It occurs during or following the charging of the trap with liquid nitrogen and can be recognized by the appearance of small droplets upstream from the trap and by accompanying pressure fluctuations. The amount of pumping fluid which may reach the baseplate of a typical bell-jar vacuum system due to this mechanism may be few orders of magnitude greater than the normally expected steady-state backstreaming rate. The phenomenon is produced by fracture of the frozen pumping fluid film due to the unequal thermal expansion coefficients between it and the metal surfaces on which it has been previously deposited. The elastic energy stored in the film is sufficient to impart high velocity to the fragments resulting from the fracture. The paper describes the observations and suggests methods of prevention.
A Clean Cryo-Vacuum System with High Pumping Speeds for All Gas Species
Authors: Powers R. J. , Chambers R. M.
Published: July 2002

Calibration of the Harvard College Observatory spectrometers that are to fly aboard the Apollo telescope mount (ATM) required a completely clean vacuum system having the capability for pumping hydrogen, helium, argon, and other inert gases at high speeds between 10−6 and 10−8 Torr. The spectrometer performance would be degraded if contaminated by exposure to hydrocarbons, electromagnetic radiation, or metallic films. For this reason, a cryogenically pumped system was selected. This paper describes the concept, development, and operation of the vacuum system which was both cryo-condensation and cryosorption pumped in the molecular flow range. Molecular sieve, bonded to liquid helium-cooled panels, provided the clean, fast, and economical pumping device. Data presented show pumping speeds measured, adsorbent capacity of molecular sieve, liquid helium consumption rates, and cryogenic performance of the system. This data permits analysis of the cryo-vacuum pumping technique for other applications.
A Radiant Heated Titanium Sublimator
Authors: Harra D. J. , Snouse T. W.
Published: July 2002

A new radiant heated sublimator is described which employs an approximately spherical shell of titanium enclosing a tungsten filament heater. The sublimator is relatively simple in construction and can dispense ∼37 g of titanium at sublimation rates up to 0.5 g/h. The sublimation rate at a given power input remains relatively constant throughout the life of the sublimator, making it very simple and reliable to operate. Comparative experiments are described with both spherical and cylindrical sublimators which illustrate the effect of various designs on the sublimation rate versus power and time characteristics. The operating characteristics of this device are discussed relative to other sublimation sources in common use in the field of titanium sublimation pumping.
Advances in Diffusion Pump Technology
Authors: Hablanian M. H. , Maliakal J. C.
Published: July 2002

A review of major advances in diffusion pump technology in the sixties is presented. The discussion is limited to oil diffusion pumps, their optimum design parameters, performance evaluation, and application experience. Significant improvements have been achieved since the beginning of space-related applications (1957). Modern pumps produce speed efficiency of better than 0.5, the maximum throughout is better than 1 Torr 1/sec per kilowatt of power, forepressure tolerance is better than 0.5 Torr, backstreaming rates at the inlet approach 10−7 g/cm2 min and the ultimate pressure 1×10−9 Torr without traps. The major design trends and effects of baffles are also reviewed. The general emphasis is on enduring, functional design and performance aspects rather than a complete review of technical literature.
A Study of the Effectiveness of the Standard Surface Cleaning Techniques as Applied to Ni(111), Ni(100), and Ni Sheet Using Auger Electron Spectroscopy (AES)
Authors: Horgan A. M. , Dalins I.
Published: July 2002

An investigation of the standard surface cleaning techniques, e.g., oxygen reaction at high temperatures and argon ion bombardment, has been carded out with special reference to Ni(111), Ni(100), and Ni sheet using Auger electron spectroscopy (AES) to monitor surface conditions. Carbon, sulphur, chlorine, nitrogen, and oxygen are observed as impurities on these surfaces. On Ni(111) a heavy carbon deposit (> 10 Å thick) is noted. Argon ion bombardment is not effective in removing this layer. High temperature reaction (> 700°C) with oxygen is required to eliminate the surface carbon. The kinetics of this reaction are recorded by monitoring the rate of production of carbon monoxide dNCO/dt which obeys the relationship dNCO/dt=kPO20.9±0.1 exp−(32±2 kcal mol−1)/RT in the temperature range 663–917°C and oxygen pressure range 1.0×10−8 to 5.9×10−7 Torr. After this carbon removal the sulphur and chlorine impurities are eliminated using argon ion bombardment. Reaction with oxygen at 1100°C and 10−6 Torr is also effective in removing these latter impurities. At this point only a small carbon peak due to slow diffusion from the bulk is present on the surface. However, a short anneal to 700 °C for <1 min caused small amounts of sulphur and chlorine to reappear. This effect is discussed in terms of diffusion and support effects. The minimum attainable coverage (θs) of sulphur on the Ni(111) was θs=0.1. For Ni(100) and Ni sheet a much smaller carbon peak compared to Ni(111) is observed. This may be “removed” by heating alone. Some reaction of surface carbon and oxygen takes place to give gaseous carbon monoxide. Some carbon diffuses into the bulk. On cooling, carbon slowly diffuses to the surface. Sulphur and chlorine impurities may be removed by argon ion bombardment. Removal of these impurities by oxygen reaction at high temperatures is unsatisfactory. Oxidation occurs. Hydrogen reduction is not particularly successful, although this oxygen can be removed by prolonged argon ion bombardment.
Permeation and Outgassing of Vacuum Materials
Authors: Perkins W. G.
Published: July 2002

The recent literature dealing with the gas permeation characteristics of vacuum materials is reviewed. Experimental techniques for the measurement of gas diffusivity, permeability, and solubility in solids are discussed and evaluated, and computational techniques for the analysis of gas–solid permeation data are described. Materials discussed include alloys such as stainless steels and Kovar; pure metals such as copper, nickel, molybdenum, and tungsten; refractory oxides and ceramics; organic materials such as Viton, Teflon, and other elastomers; and laminated metal materials. Application of the results of diffusivity, permeability, and solubility measurements to the observed outgassing characteristics of some vacuum materials is discussed briefly.
Tungsten metallization for LSI applications
Authors: Wagner R. S. , Sinha A. K. , Sheng T. T. , Levinstein H. J. , Alexander F. B.
Published: July 2002

It is shown that MOS–LSI devices can be satisfactorily metallized with tungsten thin films using the rf-diode sputtering technique. The apparatus used consisted of a roots-blower and a Vacion pumped belljar system equipped with an 8-in. diam CVD W-cathode and a W-substrate table (anode) to which a dc bias could be applied. The control substrates were oxidized silicon wafers in which the back-oxide was removed to facilitate proper application of the bias. The effect of sputtering power (200–400 W) and of substrate bias (−200−+250 V) was studied on the deposition rate, substrate temperature, and various properties of the film such as electrical resistivity, stress, impurity concentration, constitution, and microstructure. The present process of W-film depostition has been found to offer several advantages. Low-power and low-voltage operation results in high quality MOS-compatible W-films. Substrate heating during the sputter deposition is kept to a minimum, thereby eliminating any undesirable metallurgical interactions in the W to Si Ohmic contact areas. The deposition rates can be controlled by adjusting the rf power. Use of a dc substrate bias offers further flexibility in control of film properties. Film resistivities are typically in the range 12–20 μΩ/cm upon sputtering at 250-W power with −125-V substrate bias. The film stresses are compressive (<2×1010 dyn cm−2) under negative bias; this has been found to lead to good step coverage. The films possess excellent high-resolution etchability. These factors make the present metallization process very suitable for CCD (single-level metallization) as well as LSI-IGFET (two-level metallization) applications.
New method for imaging atoms
Authors: Dou Juying , Chen Ergang , Zhu Changchun , Yang Deqing
Published: July 2002

We introduce the principle on a new high resolution thermal field emission microscope (HRTFEM). The crystalline structures of W(111), W(100), and W(110) tips have been observed. Both theoretical analyses and experiments show that HRTFEM has high resolving power with which atoms can be distinguished clearly. By using this HRTFEM, the states of atoms on tip surface can be studied easily.
Effects of reactive ion etching on the electrical characteristics of GaN
Authors: Rong B. , Cheung R. , Gao W. , Alkaisi M. M. , Reeves R. J.
Published: July 2002

We present an investigation of the electrical characteristics of plasma exposed GaN. The specific contact resistance of ohmic contacts fabricated on GaN after argon plasma bombardment for 2.5 min at 0.03 W/cm2 are measured to decrease by a factor of 4 compared to the unetched surface. Gold has been found to be the best material for GaN Schottky diode. A study of the electrical performance of diodes fabricated on plasma exposed GaN has been undertaken. To compare the effect of the chemical versus physical factors, as well as the role played by the ion mass of the etchant species during the etching process on diode behavior, GaN surfaces have been exposed to Ar, N2, as well as SF6+N2 plasmas before diode fabrication. Our data indicate that a plasma with low ion mass etchant species or a dominant chemical mechanism of etching with a high etch rate creates less surface damage. The use of a SF6+N2 plasma should be possible for GaN transistor gate recessing.
Observations of the microscopic growth mechanism of pillars and helices formed by glancing-angle thin-film deposition
Authors: Malac Marek , Egerton Ray F.
Published: July 2002

We have studied the mechanisms influencing growth of thin films onto an oblique rotating substrate by cross-sectional transmission electron microscopy and scanning electron microscopy. We have analyzed the growth of pillars and helices in random and regular arrays, and have examined the influence of introducing a line of missing nuclei on the growth of regular array of pillars and helices.
Influence of gas composition on wafer temperature in a tungsten chemical vapor deposition reactor: Experimental measurements, model development, and parameter identification
Authors: Chang Hsiao-Yung , Adomaitis Raymond A. , Kidder John N. , Rubloff Gary W.
Published: July 2002

Experimental measurements of wafer temperature in a single-wafer, lamp-heated chemical vapor deposition system were used to study the wafer temperature response to gas composition. A physically based simulation procedure for the process gas and wafer temperature was developed in which a subset of parameter values were estimated using a nonlinear, iterative parameter identification method, producing a validated model with true predictive capabilities. With process heating lamp power held constant, wafer temperature variations of up to 160 K were observed by varying the feed gas H2/N2 ratio. Heat transfer between the wafer and susceptor was studied by shifting the instrumented wafer off the susceptor axis, exposing a portion of the wafer backside to the chamber floor. Model predictions and experimental observations both demonstrated that the gas velocity field had little influence on the observed wafer and predicted gas temperatures.
Formation of a large-scale Langmuir–Blodgett monolayer of alkanethiol-encapsulated gold particles
Authors: Huang Shujuan , Tsutsui Gen , Sakaue Hiroyuki , Shingubara Shoso , Takahagi Takayuki
Published: July 2002

In this article, we present an experimental study of the formation of a Langmuir–Blodgett (LB) monolayer of alkanethiol-encapsulated gold particles. We developed a procedure for preparing the LB spreading suspension from an aqueous gold colloid, and we fabricated a large-scale densely packed monolayer of alkanethiol-encapsulated particles covering an entire substrate using the LB technique. Scanning electron microscopy observations demonstrated that this LB monolayer is composed of domains of ordered close-packed encapsulated gold particles, some of which extended to about 10 μm in extent. A detailed study of the forming mechanism of the LB monolayer of gold particles indicates that the ordered particle domains were formed by a self-organization process induced by the evaporation of the spreading suspension before LB compression. These domains were then aggregated to a densely packed monolayer by the compression process. The proposed method provides a feasible procedure for fabricating a variety of new nanostructured materials.
Technology and realization of metallic curved waveguide mirrors in polymer film waveguides based on anisotropic plasma etching
Authors: Wolff S. , Grosse A. , Schimper H.-J. , Giehl A. R. , Kuhnke M. , Grote R. , Fouckhardt H.
Published: July 2002

Curved waveguide mirrors acting in the same way as cylindrical lenses are fabricated in a polymer film waveguide. The waveguide material used is Cyclotene 3022™ (bisbenzocyclobutene) developed by the Dow Chemical Company. The waveguide mirror structure is dry etched into the film waveguide employing electron cyclotron resonance reactive ion etching. To enhance their reflectivity the vertical dry-etched sidewalls are metallized. Curved polymer film waveguide mirrors showing a reflectivity of 75% are realized.
High rate sputtering for Ni films by an rf-dc coupled magnetron sputtering system with multipolar magnetic plasma confinement
Authors: Kawabata K. , Tanaka T. , Kitabatake A. , Yamada K. , Mikami Y. , Kajioka H. , Toiyama K.
Published: July 2002

Ni films were prepared by an rf-dc coupled magnetron sputtering with multipolar magnetic plasma confinement (MMPC) at the low pressure of 6.7×10−2 Pa and at the long distance of 120 mm, when permanent magnets were placed around a nickel target (200 mm φ, 5 mm thick) outside the chamber. When rf power and dc bias voltages were applied simultaneously to the target, the deposition rate of the Ni films significantly increased with the target dc bias voltage (VT). The highest value of the deposition rate was about 250 nm/min at VT=−820 V. The high rate sputtering for Ni films was possible at the low Ar gas pressure of 6.7×10−2 Pa. The resistivity for all the films deposited at different dc bias voltages was 7.1–8.2 μΩ cm whose value was close to the bulk value. It is shown that the sputtering system with MMPC has some advantages in comparison with conventional magnetron sputtering, such as high deposition rate, plasma discharge stability, and the preparation of high quality magnetic thin films.
Deposition and properties of tetrahedral amorphous carbon films prepared on magnetic hard disks
Authors: Chan C. Y. , Lai K. H. , Fung M. K. , Wong W. K. , Bello I. , Huang R. F. , Lee C. S. , Lee S. T. , Wong S. P.
Published: July 2002

The areal density of information stored on the hard disk has doubled every two years. This substantial increase in disk storage has resulted from the application of giant magnetoresistance heads, new thin film media, and better electronic recording channels. However, such an increase cannot be easily attained without reducing the separation between the magnetic read-write head and magnetic recording medium surfaces. This can be achieved by using a thinner protective overcoat. In this study, ultrathin tetrahedral amorphous carbon (ta-C) films were deposited on magnetic hard disks (CoCrTa/Cr/NiP/Al–Mg) by a magnetic filtered cathodic arc deposition under different substrate bias voltages. The obtained films exhibited smoother surfaces than the uncoated disks as indicated by the atomic force microscopic measurement. The Raman spectra acquired showed a single asymmetric Lorentzian curve shape. Tetrahedral amorphous carbon coatings were subjected to an accelerated corrosion test in vapors of concentrated hydrochloric acid for 24 h. The corrosion test demonstrated a reduced density of corrosion sites when compared to conventional diamond-like carbon films. Similarly, the scratch resistance of the ta-C coated disks, investigated by a nanoindenter, showed significant improvement in comparison to uncoated disks.
Nonlinear optical and electro-optic properties of InAs/GaAs self-organized quantum dots
Authors: Ghosh S. , Lenihan A. S. , Dutt M. V. G. , Qasaimeh O. , Steel D. G. , Bhattacharya P.
Published: July 2002

The electro-optic and nonlinear optical properties of self-organized InxGa1−xAs/GaAs quantum dots were studied experimentally. The quantum dot heterostructures were grown by molecular beam epitaxy. The measured linear and quadratic electro-optic coefficients for In0.4Ga0.6As quantum dots are 2.58×10−11 m/V and 6.25×10−17 m2/V2, respectively. For InAs quantum dots, the measured linear and quadratic electro-optic coefficients are 2.43×10−10 m/V and 3.37×10−17 m2/V2, respectively. Pump–probe differential transmission spectroscopy measurements were made on the dot samples at cryogenic temperatures with linear and circularly polarized pump and probe beams. The ground and excited state recombination times are 620 and 290 ps, respectively.
Theoretical Investigation of Oil Backstreaming through a Vacuum Trap
Authors: Jones D. W. , Tsonis C. A.
Published: July 2002

An approximate theoretical analysis of the oil backstreaming through an optically tight, liquid-nitrogen-cooled elbow trap is made. Sticking coefficient, oil deflection due to intermolecular collision, and diffusion are considered, and numerical results are presented for the backstreaming through a 36-in.-diam trap. The results are discussed from the standpoints of ultrahigh-vacuum system operation procedures and trap design in general. The advantages of double-bounce traps, dual-dimensional traps, and the use of low-pressure purge gas are pointed out.
Affect on pumping-speed measurements due to variations of test dome design based on Monte Carlo analysis
Authors: Nesterov S. B. , Vassiliev Yuri. K. , Longsworth Ralph. C.
Published: July 2002

Test domes for measuring the pumping speed of cryopumps are defined in Pneurop standard PN5ASRCC/5 and the American Vacuum Society Recommended Practice for Cryopumps published in 1999. The test domes try to provide a measure of the speed of a pump as if the cryopump is mounted in the center of a large flat plate in a large chamber. This is referred to as the intrinsic speed. In this case, the flow distribution into the pump is diffuse while in the test dome the flow pattern has a stronger axial component. The location of the pressure gauge is intended to compensate for the different flow pattern. Certain parameters in the design of the test domes are not rigidly specified. A Monte Carlo analysis (MCA) has been carried out to analyze the differences in speed that will be measured for different allowable configurations of the test dome. The results show that the variations that are allowed in the recommended practice have little impact on differences in the pumping speed that will be measured. The analysis shows that the axial flow is greater and more uniform in the two-gauge dome than the single dome. The different flow patterns have no impact on pumps that have “porous” inlets (uniform capture probability from all angles) and the recommended location of the pressure gauge gives measured speeds that are very close to the intrinsic speed. Pumping speed measurements of a real cryopump are influenced by the flow pattern. The APD Cryogenics M8 cryopump was analyzed using MCA and found to have calculated speeds that are about 9% higher than the intrinsic speed in the single dome and 11% higher in the two-gauge dome. The probability of Ar molecules being captured by an M8 cryopump in either test dome is about 11% greater than in a large chamber.
In situ electron spin resonance observation of Si(111) 7×7 surface during hydrogenation process
Authors: Futako Wataru , Nishizawa Masayasu , Yasuda Tetsuji , Isoya Jun-ichi , Yamasaki Satoshi
Published: July 2002

In situ observation of the hydrogenation processes of Si(111)-7×7 was carried out using an ultrahigh vacuum electron spin resonance (UHV ESR) system. The termination reaction of the surface dangling bond with hydrogen, including the isolating effect of the dangling bond, was observed. The reactivity of hydrogen molecules with the Si(111)-7×7 surface is much less than that of oxygen. The g-value anisotropy showed that the signal originated from adatom dangling bonds of the Si(111)-7×7 structure. Thermal annealing at a temperature higher than 400 °C promoted hydrogen desorption. In both hydrogenation and annealing processes the maximum of the effective spin density observed is approximately 3×1013 cm−2.
Influence of ion stimulated gas desorption from residual gas analyzer on partial pressure measurement
Authors: Kurokouchi Satoshi , Kato Shigeki
Published: July 2002

The influence of ion stimulated gas desorption (ISD) from the ion-extraction plate of a residual gas analyzer (RGA) ion source on partial pressure measurement was evaluated, using a modified RGA. ISD from the extraction plate occurs due to bombardment with ionized gas molecules, and is thought to be closely related to physical sputtering and chemical reactions on the plate surface. Our experimental results indicate that partial pressure detection limits deteriorate due to an ISD signal increase, which in turn is dependent on total pressure, the species and kinetic energy of the ion, and the temperature of the ion-extraction plate. Where the ion-extraction plate is heated to 250 °C and the dominant gas species is massive or reactive, ISD signals account for an amount on the order of 100 ppm of partial pressure signal intensity. This ISD problem can affect the accuracy of partial pressure measurement in all pressure ranges. However, there are several methods to reduce ISD. Among the possible methods, a simple modification of the ion source to restrict the ion-bombarded area would diminish ISD the most effectively.
Molybdenum-doped indium oxide transparent conductive thin films
Authors: Meng Yang , Yang Xi-liang , Chen Hua-xian , Shen Jie , Jiang Yi-ming , Zhang Zhuang-jian , Hua Zhong-yi
Published: July 2002

We developed a novel transparent conductive film, molybdenum-doped indium oxide (IMO). Using normal thermal reactive evaporation without any special treatments, IMO films have been prepared on normal glass microscope slides at about 350 °C with electrical resistivity of 1.7×10−4 Ω cm, mobility over 100 cm2 V−1 s−1, and an average spectral transmittance in the visible region over 80%. From x-ray photoelectron spectroscopy and x-ray diffraction spectra of the IMO films, it is confirmed that the lattice of IMO is the same as that of In2O3 of cubic bixbyite structure, Mo6+ substitutes for In3+ in In2O3, and there are no new compounds in IMO. The valence difference of 3 between Mo6+ and In3+ is of great advantage to the IMO film with high conductivity and high transparency simultaneously.
Investigation of Pt/Ti bilayer on SiNx/Si substrates for thermal sensor applications
Authors: Giani A. , Mailly F. , Pascal-Delannoy F. , Foucaran A. , Boyer A.
Published: July 2002

Pt/Ti thin films on SiNx/Si substrates have been investigated for thermal sensor applications on SiNx membrane. Therefore, Pt/Ti adhesion during KOH etching of silicon and high temperature coefficient of resistance (TCR) are the principal aims of this study. ac sputtering and electron beam evaporation have been investigated for metal deposition. Vacuum annealing is used to improve the Pt/Ti characteristics. Stress characterizations and adhesion strength are evaluated by an x-ray diffraction pattern and adhesive tape test, respectively. TCR and resistivity were finally measured to confirm the compatibility with good thermal sensor sensitivity. Pt/Ti films elaborated by electron beam evaporation and vacuum annealed present the best characteristics for thermal sensor applications: good adhesion is obtained even after 5 h in KOH etching solution, electrical resistivity is about 15 μΩ cm and TCR is 3.3×10−3/°C. Finally, by using these platinum thin films, a thermal accelerometer has been manufactured and tilt measurements have been achieved.
Inductively coupled plasma etching of InP using CH4/H2 and CH4/H2/N2
Authors: Chen Hsin-Yi , Ruda Harry E.
Published: July 2002

Inductively coupled plasma etching of InP in CH4/H2 and CH4/H2/N2 gas mixtures was studied to understand the etching mechanisms and the influence of etching gas composition on etching rate, etching profile, and surface morphology. CH4/H2 plasmas generally had higher etching rates than CH4/H2/N2 plasmas. Deterioration of InP surfaces, following etching, reflected the preferential loss of P over In due to the diffusivity and reactivity of H being higher than CH3 on InP surfaces, and also since PH3 is more volatile than In(CH3)3. In extreme circumstances, this can lead to the formation of In-rich droplets on the surface, with associated surface roughening. This was supported by the opposing trends of surface roughness (measured using atomic force microscopy) and P/In ratio (from x-ray photoelectron spectroscopy) as a function of the CH4 gas concentration for CH4/H2 gas mixtures. The addition of N2 to the CH4/H2 plasmas improved the surface morphology as N radicals reduced the rate of P removal by reacting with H radicals. However, an inevitable increase in the N+ and N2+ concentrations led to erosion of the SiO2 masks and caused sloping sidewalls.
Characterization of gadolinium and lanthanum oxide films on Si (100)
Authors: Wu X. , Landheer D. , Sproule G. I. , Quance T. , Graham M. J. , Botton G. A.
Published: July 2002

High-resolution transmission electron microscopy, electron energy loss spectroscopy, and Auger electron spectroscopy, were used to study gadolinium and lanthanum oxide films deposited on Si (100) substrates using electron-beam evaporation from pressed-powder targets. As-deposited films consist of a crystalline oxide layer and an amorphous interfacial layer. A complicated distinct multilayer structure consisting of oxide layers, silicate layers, and SiO2-rich layers in thick (∼30 nm) annealed films has been observed for both gadolinium and lanthanum films. For thinner annealed films (∼8 nm), there is no longer a crystalline oxide layer but an amorphous gadolinium or lanthanum silicate layer and an interfacial SiO2-rich layer. The formation of the lanthanum silicate by annealing lanthanum oxide is found to be thermodynamically more favorable than the formation of gadolinium silicate.
Fabrication of Gd2O2S:Tb based phosphor films coupled with photodetectors for x-ray imaging applications
Authors: Tao S. , Gu Z. H. , Nathan A.
Published: July 2002

The Gd2O2S:Tb based phosphor coupled with photodetectors has been widely used in digital x-ray imaging applications. The key issues associated with phosphor film are x-ray absorption and conversion efficiency, spatial resolution, deposition uniformity, and integration with the imaging array. In this article we report on experimental studies of the phosphor film synthesis, deposition, and characterization. A composite material, consisting of Gd2O2S:Tb, polyvinyl alcohol, and water coupled with a small amount of additives, is synthesized as a phosphor paste. The parameters controlling film quality include individual component concentrations, grain sizes of phosphor, and viscosity of the solution. A sedimentation technique is used to deposit the phosphor directly on the imaging array. A number of phosphor films have been synthesized with the particle sizes ranging from 2.5 to 25 μm and film thickness ranging from 85 to 1100 μm, and measurement results of x-ray conversion efficiency and spatial resolution in terms of modulation transfer function are presented. A new technology for phosphor patterning is proposed to seamlessly integrate the phosphor with the photodetectors by using negative photoresist SU-8 and preliminary results are presented.
Simulation of hydrogen outgassing in ultrahigh vacuum chamber and fusion device by recombination limited model
Authors: Akaishi K. , Nakasuga M. , Funato Y.
Published: July 2002

To simulate hydrogen outgassing in an ultrahigh vacuum (UHV) chamber and a fusion device, an outgassing theory based on the recombination limited model is presented, where the time evolution of hydrogen concentration in the wall of the vacuum chamber is described by a one-dimensional diffusion equation. The hydrogen outgassing rate is expressed as a boundary condition in the diffusion equation. For the UHV chamber the effect of surface treatment, such as baking and oxidation, and the benefits of a thin-walled chamber for reduction of outgassing rate are examined, and it is shown that the present theory explains well the experimental results which have been reported on these matters. For the fusion device the time evolution of after-shot outgassing observed in the large helical device is simulated. For the simulation, it is essential to know first the initial concentration profile of hydrogen retained in the first wall immediately after the discharge shot. The profile is constructed by referring the calculated depth distribution of hydrogen implanted into Pd using the TRIM code. As a result good agreement between the experimental hydrogen release rate and the calculated one is shown.
New Hot-Filament Ionization Gauge with Low Residual Current
Authors: Redhead P. A.
Published: July 2002

The design and performance of a new type of hot-filament ionization gauge is described. The ions are extracted from the ionization region, focused through an aperture in a shield electrode, and then collected on a short, fine wire. The sensitivity factor of this gauge is about 13 Torr−1 for nitrogen. The ratio of the soft x-ray flux reaching the collector of the new gauge to that of a Bayard-Alpert gauge is calculated, and the x-ray limit of the new gauge estimated to be 3×10−13 Torr. Measurements at low pressures indicate that the x-ray limit cannot be greater than 7×10−13 Torr and may be considerably less. False pressure indications, caused by the electronic desorption of positive ions from chemisorbed gases on the grid (in particular, oxygen), are at least 500 times smaller in the new gauge than in the Bayard–Alpert gauge.
Gas Flow in Vacuum Systems with Local Temperature Variations for the Molecular Flow Range
Authors: Lewin G.
Published: July 2002

It is customary to measure gas flow Q in Torr liter/sec and to calculate the pressure distribution in a system by using the relations Q=CΔP and Q=SP (C conductance, S pumping speed, P pressure). This requires that Q be the same everywhere in the system. If the temperature varies locally, Q varies also but the particle flow (molecules/sec) remains constant throughout. An analogous procedure based on the particle flow is proposed for systems with local temperature variations, and a particle conductance and particle speed are substituted for conductance and pumping speed. Examples are given to illustrate the method.
Measuring Small Gas Flows Into Vacuum Systems
Authors: Hawk Charles E. , Baker William C.
Published: July 2002

A description of a new mass flowmeter for measuring small flow rates into vacuum systems on a continuous, direct reading, and instantaneous basis. The theory, operation, and characteristics are described including typical performance results in practical applications.
Backstreaming Measurements Above Liquid-Nitrogen Traps
Authors: Hablanian M. H.
Published: July 2002

Gravimetric measurements of diffusion-pump backstreaming rates were made above liquid-nitrogen-cooled traps. Experiments were made of over 500-h duration, with 6-in. and 35-in. pumps, with and without a water-cooled baffle and a creep barrier. The surfaces collecting the backstreaming oil were cooled to liquid-nitrogen temperature to prevent errors due to re-evaporation. Design compromises are discussed as related to the requirement of maximum pumping speed and minimum backstreaming. The results indicate that opaque water-cooled baffles have substantial redundancy in the design. A combination of a water-cooled partial baffle, a liquid-nitrogen trap, and a special cold cap over the upper nozzle is described, which permits important improvements in system speed without significant increase in the backstreaming rate.
The Sensitivity of Bayard–Alpert Gauges
Authors: Redhead P. A.
Published: July 2002

The sensitivity of Bayard–Alpert gauges has been measured as a function of the grid-filament spacing and found to vary by as much as a factor of 2.5. It is suggested that the large variation of sensitivity from one gauge to another results from variability of filament positioning. An hypothesis is proposed, and substantiated by test, which relates the sensitivity to the angular momentum, about the axis of the grid, with which electrons are launched into the grid. It is shown that electrons with small initial angular momentum have the longest orbits in the useful ionizing volume. A new type of Bayard–Alpert gauge has been developed, based on this hypothesis, whose sensitivity is independent of filament position and of the potential of the envelope. The sensitivity factor of this new design is about 55 Torr−1 for nitrogen.
Cryosorption Pumping of Air on Molecular Sieves at 77 K—The Ultimate Achievable Vacuum
Authors: Stern S. A. , DiPaolo F. S.
Published: July 2002

The cryosorption pumping of air and some of its components on Molecular Sieve 5A pellets was studied at 77 K and in the pressure range from atmospheric to about 10−6 Torr. The lowest residual pressures attainable in an enclosure by cryosorption pumping of air was calculated by the graphical method of Turner and Feinleib, using the latest adsorption isotherm data available. This method was also used to evaluate the relative efficiency of single-stage and two-stage cryosorption pumping. In the latter case, it is shown that much lower residual pressures can be reached by isolation of the “non-condensable” air components in the first pumping stage under dynamic conditions than by allowing this stage to reach adsorption equilibrium. The calculations were confirmed experimentally by means of a new type of cryosorption pump. This pump was designed to optimize heat transfer between adsorbent pellets and refrigerant fluid, as well as gas flow at transition range pressures.
Vacuum Systems for Sputtering
Authors: Shirn G. A. , Patterson W. L.
Published: July 2002

Oil diffusion pumped vacuum system operation has been examined in the light of sputtering system requirements. It was found that cleanliness is an important problem because of the low deposition rates of the sputtering process. A model for a cleaning action of the throughput of the sputtering gas was derived. The model indicated that certain changes in the operating procedure of the vacuum system would increase the cleaning action of the sputtering gas significantly. The requirement is that the throughput of the sputtering gas be maximum. Measurements of partial pressure of O2 vs Ar throughput show the model to be essentially correct. The action of the high throughput on oil backstreaming was also measured. It was found that high throughput reduces oil vapor backstreaming considerably.
Cryosorption pumping for intersecting storage rings
Authors: Halama H. J. , Aggus J. R.
Published: July 2002

The pumps selected for storage ring vacuum systems must efficiently pump helium and hydrogen at pressures below 10−10 Torr. In addition, they have to work in a background of nuclear radiation. The presence of an ample supply of liquid helium in the proposed Intersecting Storage Accelerator (ISABELLE) makes cryosorption pumping very attractive. We have investigated, therefore, the behavior of Linde Type 5A molecular sieve, bonded to a stainless steel panel, at 4.2 and 5 K in the pressure range from 10−11 to 10−8 Torr. By fitting our experimental data, we obtained the constants K and B in the equation ϑ = K exp(−ε2B) which can be used to calculate the adsorption isotherms for helium and hydrogen on bonded molecular sieve 5A at various temperatures. Furthermore, we have determined the causes of a steeper slope of the isotherms in the 10−11 Torr range. Finally, a pump containing a cryosorption panel was exposed to a flux of 1.7×105 protons and pions per second which resulted in no pressure change. Based on the reults of this investigation, we have designed a cryosorption pump which can be operated at 4.2 K either inside or outside the superconducting magnet dewars.
Improved titanium sublimation pumping techniques for long−term, high−throughput, clean pumping applications
Authors: Harra D. J.
Published: July 2002

Methods for controlling the location and temperature of the titanium compounds formed during pumping and techniques facilitating periodic removal of the accumulated titanium compounds are discussed. A titanium sublimation pumping module is described which results in improved gas handling capability, longer useful operating life, and reduced down time. Data are presented from pumping speed measurements for N2, H2, and H2O, including measurements of hydrogen generation during pumping of H2O. Test data on performance degradation due to peeling effects of the titanium film are also described.
Monte Carlo design of a 3−gauge test dome
Authors: Denison D. R.
Published: July 2002

The preliminary results of the Monte Carlo analysis of the 3−gauge (or conductance tube) test dome reported at the 6th International Vacuum Congress1 have been extended to the noncosine distribution for molecules reflected back into the test dome from a pump being tested. The gauge locations for the measurement of ’’intrinsic pumping speed’’ are presented showing the influence of reflection coefficient on optimum gauge location. The distribution from one actual pump configuration has been obtained from the Monte Carlo calculations and applied to the test dome design. The pumping speed obtained from this design for a 3−gauge test dome is compared with the results obtained with a Fischer−Mommsen test dome.
Lubrication for vacuum applications
Authors: Friebel Virgil R. , Hinricks James T.
Published: July 2002

The selection and use of lubricants for vacuum applications is a critical part of the mechanisms design phase which is often overlooked. Both wet and dry lubricants can be used for mechanical and electrical moving interfaces in vacuum. Deciding on what type of lubrication system to use and the incorporation of the appropriate hardware design considerations are critical to the performance of the mechanisms. The use of design features such as lubricant reservoirs, labyrinth seals, and barrier films can enable wet lubricated systems to function for long periods in vacuum. Dry lubricated hardware has a finite life due to the sacrificial mode of dry lubricants. The use of suitable dry lubricant materials and designs can allow millions of cycles of operation in vacuum. Dry lubricants have a potential particulate contamination problem while wet lubricants can contaminate by both outgassing and migration by creep.