bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion implantation with controlled nonuniformity
Authors: Oka Y.
Published: July 2002

A new method of ion implantation can implant two areas of one wafer at once with controllably different doses, given a ratio of the two areas. Surface doses for a particular ratio of the two areas are calculated. A twofold-triangular waveform generator has been designed to deflect the implant beam along the x-axis. The experimental results with respect to ion implantation with controlled nonuniformity agree reasonably well with calculated results. There may be a possibility of accurate production control for ranks or classification of electrical characteristics of semiconductor devices if the doping level can be changed controllably even in one wafer.
Diffuse optical scattering from Cu surfaces with variable roughness
Authors: Jansen Frank , Hoffman R. W.
Published: July 2002

Polarization data from He–Cd laser light scattered from the surfaces of Cu films deposited in UHV and measured in situ, are compared with calculations to investigate if we can conclude directly from the spectra whether first order theory is applicable. The ratio of the pp and ss diffusely scattered radiation differs by as much as 20% from the values predicted for the smoothest surfaces of unannealed films for which the scattering probability per unit solid angle is ∠10−5 for k≳10−3 Å−1. When the size of the majority of the surface undulations is smaller than the wavelength of the incident light, the measured polarization ratio exceeds that calculated from first order theory. The roughness of Cu films and the diffuse scattered intensity increase by annealing to temperatures of 700°C. The discrepancy between the data and calculation increases with the roughness. For a macroscopically rough surface the experimental polarization ratio is smaller than the theoretical value. The cross polarization intensities are nonzero for all surfaces after annealing but this has not been found to be a useful indication of the limit of validity of first order scattering theory. Differences between the measured polarization ratios and those predicted by first-order scattering theory are explained in terms of geometrical and multiple scattering effects.
Local atomic order in native III–V oxides
Authors: Lucovsky G. , Bauer R. S.
Published: July 2002

This paper considers the nature of the local atomic boning in native III–V oxides. On the basis of comparisons with the elemental oxides of the constituent group V atoms, we argue that the key factor in establishing the increased stability of phosphide oxides relative to both arsenide and antimonide oxides is a donor–acceptor pair bond, P=O, that is well-known in phosphorous–oxygen chemistry. The stability of this bond is to a large extent related to its partial π-bonding character. Detection of this group at oxidized surfaces or in the bulk of anodized oxides, should be possible by Raman scattering or low energy electron loss spectroscopy.
Emission spectroscopy of glow-discharge and sputtering plasmas used in amorphous Si:H film deposition
Authors: Paesler M. A. , Okumura T. , Paul W.
Published: July 2002

We analyze the optical emission spectra of glow discharge (g.d.) plasmas and find evidence for Si–H complexes. From a similar analysis of sputtering plasmas, we find that a significant silicon–hydrogen gas phase reaction does not occur. The dissimilarities of the plasmas out of which g.d. and sputtered films are condensed coupled with the similarities of the films themselves, lead us to reason that the properties of amorphous Si:H films are determined by structure that is locked into the growing film surfaces. To study the physics of how the hydrogen enters the Si:H matrix, one must turn to investigations of these surfaces.
Ti getter study
Authors: Edwards D. , Lanni C.
Published: July 2002

It has been shown that significantly lower ultimate pressures in a baked vacuum chamber are obtained if the Ti is flashed onto the getter chamber walls after the bakeout, when the entire system has cooled to room temperature, rather than flashed onto the chamber walls with the system hot as at the end of the bakeout with the system nominally at the bakeout temperature.
A simple method of end-point determination for plasma etching
Authors: Hitchman M. L. , Eichenberger V.
Published: July 2002

It is shown that end-point detection in plasma etching can be accomplished simply and without the use of sophisticated and expensive equipment by using a commercial vacuum gauge to monitor the effluent gas.
Conversion of compression fittings to quick-connects
Authors: Banna M. S. , Slaughter A. R.
Published: July 2002

Two designs are given for converting commercially available compression fittings to quick-connects. In each case, only two easily machinable pieces are needed.
Addendum: Cryopump measurements relating to safety, pumping speed, and radiation outgassing [J. Vac. Sci. Technol. 16, 927 (1979)]
Authors: Ruby L. , Wong N. P.
Published: July 2002

A previously developed theretical model of radiation induced outgassing of a deuterium loaded cryopump has been refined to take into account temperature dependence of the thermal conductivity and heat capacity.(AIP)
Low cost spinner for semiconductor surface preparation prior to MBE growth
Authors: Miller D. L. , Newman P. G.
Published: July 2002

A simple and inexpensive method has been devised for clean and reproducible gallium arsenide surface preparation. Etching during spinning is followed by rinsing and gas drying at high RPM.
Raman spectroscopy as a surface sensitive technique on semiconductors
Authors: Stolz H. J. , Abstreiter G.
Published: July 2002

It is demonstrated that the measurement of a bulk phonon property, i.e., the Raman intensity of the resonantly excited symmetry forbidden LO-phonon via its dependence on the surface electric field, is a sensitive method to measure surface band bending in polar semiconductors. The observation of coupled phonon-plasmon modes shows the existence of flat band conditions on clean, UHV-cleaved (110)GaAs. This condition can also be reached on pinned surfaces by photoexcitation with laser power densities in excess of 500 W/cm2. A curve fitting of the observed L+/L−-spectrum with the Lindhard–Mermin dielectric function yields information on the wave-vector smearing due to strong light absorption and impurity scattering.
Computerized optimization of electron-beam lithography systems
Authors: Chu H. C. , Munro E.
Published: July 2002

An optimization program has been developed for designing combined focusing and dual-channel deflection systems with low aberrations for electron beam lithography. The program can handle any combination of magnetic and electrostatic lenses and deflectors, and uses the damped least squares method for minimizing a weighted sum of squares of aberrations, subject to specified physical constraints. The program has been used to optimize the design of several types of lithography system. The results show that, in many cases, the program can yield designs with extremely low aberrations. For example, a system with one magnetic lens and two deflectors has been found which, at the corners of a 5 mm scan field with 5 mrad aperture, has only 0.19 μm overall aberration before dynamic corrections; by adding an electrostatic retarding field, this can be reduced to 0.12 μm. By adjusting the strengths and positions of the deflectors, several of the aberrations can be individually eliminated, including field curvature. It is also shown that electrostatic subfield deflectors can be added without significantly increasing the aberrations, and a pure electrostatic focusing and deflection system for ion beam lithography has been designed which is limited almost entirely by axial chromatic aberration.
Mean free path of emitted gas from spacecraft
Authors: Walters William P. , Yen Shee-Mang
Published: July 2002

A simple expression may be derived for the ratio of the mean free paths of the ambient gas to the emitted gas from an orbiting spacecraft.
Fabrication process for surface acoustic wave filters having 0.5 μm finger period electrodes
Authors: Itoh M. , Gokan H. , Esho S. , Asakawa K.
Published: July 2002

A new fabrication process using ion milling has been developed for 0.5-μm finger period SAW filters, Electron-resist (PMMA) patterns are transferred to a 200-Å-thick Ti film using liftoff, followed by oxygen ion-beam etching, in order to transfer the Ti patterns to a 1900-Å-thick AZ 1350 film. The two-step mask transfer process yields high-durability masks. Using argon ion-beam etching, 700-Å-thick Al electrodes are delineated. The etching masks are easily removed by oxygen plasma, because the Ti film is etched away during the Al etching. A desirable shape for delineated electrodes is obtained by adjusting the AZ 1350 film thickness. A 0.5-μm finger period SAW filter, fabricated using the process, shows 7dB insertion loss at 1.89 GHz.
Temperature-dependent low-energy electron diffraction from aluminum
Authors: Viljoen P. E. , Wessels B. J. , Berning G. L. P. , Roux J. P.
Published: July 2002

The intensity profiles for near normal specular and normal incident nonspecular LEED beams for the three low-index surfaces (100), (110), and (111) of aluminum have been measured as a function of temperature. From the decrease in the intensities the effective Debye temperature has been found as a function of peak energy. The mean square surface normal atomic displacements relative to the bulk are compared with calculations from the Jones et al. model. The experimentally determined ratios at zero energy are 3.6 for the (100), 4.1 for the (111), and 8.0 for the (110) surface. Theoretical calculations of the Debye temperature as a function of energy from these values agree reasonably well with experimental measurements. Electron attenuation for normal penetration into the surface for the three crystallographic planes has been determined in terms of the incident electron energy. The values are α(100) = 0.16 E0.25, α(110) = 0.12 E0.26, and α(111) = 0.20 E0.22, where α is defined as the ratio of the diffraction amplitudes from successive layers in the crystal. The shift of the peaks towards lower energy is linear over a wide temperature range and has been interpreted in terms of an increase in the surface thermal expansion which amounts to several times the bulk value. This is qualitatively supported by interplanar and interrow determinations at different temperatures.
An Auger electron spectroscopy (AES) study of the initial stages of oxidation of the single crystal Be (0001) surface
Authors: Fowler D. E. , Blakely J. M.
Published: July 2002

The oxidation of Be(0001), in particular the early stages of the reaction, was tracked dynamically by AES using a computer controlled single pass CMA. The reaction was followed by monitoring the three Auger transitions, Be(KVV), BeO(KVV), and O(KVV) in dN/dE mode. Because the Be(KVV) and the BeO(KVV) signals overlap, a multiple linear regression analysis based on a linear combination of the spectra of clean, cleaved Be and a BeO crystal was done to separate them. Results have been obtained for oxygen partial pressures ranging from 4.7×10−7 Pa (3.6×10−9 Torr) to 1.3×10−4 Pa. Considerable structure is seen in the uptake curves suggesting the occurrence of multiple stages of growth. The oxidation process appears to be linearly dependent on pressure for high pressures. Further conclusions are made difficult due to the strong enhancement of the oxidation by the AES incident electron beam. Finally, at all pressures studied, an excess of oxygen signal compared to that expected from stoichiometric BeO exists in the very early stage of the oxidation.
The preparation and characterization of transition metal nitride films
Authors: Dawson P. T. , Stazyk S. A. J.
Published: July 2002

Nitride surface films of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W have been prepared by reaction with NH3 gas at high temperature. The films have been characterized by x-ray diffraction, Auger electron spectroscopy, depth profiling, and scanning electron microscopy.
Behavior of small leaks in the presence of liquid or gaseous helium at 4.2 K
Authors: Sinharoy S. , Lange W. J.
Published: July 2002

Increased present day use of cryogenics necessitates an understanding of the behavior of small leaks at liquid helium temperatures. Little is to be found in the literature except that related to super-fluid effects in the range 1.4 to 2.9 K. We report the results of an investigation on the behavior of two small leaks (leak rates in the vicinity of 2×10−7 atm cc air/s at room temperature) at 4.2 K in contact with gaseous as well as liquid helium. In both cases, a significant increase in the leak rate was found when the leaks were in contact with liquid helium at 4.2 K. The observed behavior is explained using a model based on the changes in the physical properties of helium with temperature.
Pressure pulsations above turbomolecular pumps
Authors: Danziger S. , Kendall B. R. F. , Dormer J.
Published: July 2002

The effect of increasing the temperature of the cooling water for a Leybold Turbovac 350 is studied. (AIP)
MBE evaporation source fitted with shutter and water-cooled jacket
Authors: Bosacchi A. , Franchi S. , Allegri P. , Avanzini V.
Published: July 2002

The design and performance of a MBE growth chamber are reported. The heating element is a 0.5 mm diameter tungsten wire.
Mask fabrication for VLSI using an electron beam exposure system
Authors: Watakabe Y. , Kato T. , Shigetomi A. , Morimoto H.
Published: July 2002

This study describes the results of feature size distribution, pattern location accuracy, and level-to-level registration error on chrome master masks fabricated by an Ee−BES-40 electron beam exposure system. The system has the capability of high speed electron beam blanking at 40 MHz, the capacity for large size masks (with 6 in. mask cassettes), and an automatic cassette handling system. OEBR-100 (PGMA), as the electron beam negative resist, is used for 5 and 6 in. chrome masks. Both wet processing and dry plasma technology are used for chrome etching. Test patterns and 64 K DRAM TEG, as the practical pattern, are used in this study. More than 40 measurements are taken, uniformly distributed over 96 and 112 mm squares, and the feature size distribution is measured by a laser interferometer x–y measuring system. Pattern location accuracy and level-to-level registration error are obtained using the Ee−BES-40 quality assurance programs called market and plotmarket. market operates by scanning over the resist image of the test pattern, utilizing the normal fiducial mark location hardware. The following results are obtained: (1) Feature size distribution within the 6 in. mask: ±0.1 μm, (2) Level-to-level registration error: less than 0.1 μm. High quality masks with about 0.02 defects/cm2, and rapid throughput of ten masks in 6 h using the automatic ten cassette handling system are obtained.
Deposition of thin Mylar films by a vacuum thermal evaporation technique
Authors: Shrinet V. , Chaturvedi U. K. , Agrawal S. K. , Nigam A. K.
Published: July 2002

Mylar films were deposited on ultrasonically cleaned optically flat glass slides and subjected to a ‘‘scotch tape’’ adhesion test.
The effect of the atomic incident angle upon the microstructure of thick beryllium deposits produced by physical vapor deposition
Authors: Nieh T. G. , Karlak R. F. , Vidoz A. E.
Published: July 2002

Thick (1–3 mm) beryllium deposits were produced by physical vapor deposition on a carbon-coated polished 4130 steel substrate at 400 °C and with rates of deposition from 0.1 to 0.3 mm/h. The deposit microstructure was examined by metallographic technique and the characteristics of the growing as well as fracture surfaces by scanning electron microscopy. The texture of the deposits was determined by x-ray diffraction and correlated with the deposition parameters. The deposits have unique grain and crystalline texture characteristics. They consist of columnar grains with their major axis parallel to the direction of incident adatoms. The self-shadowing mechanism was not observed to have a prevalent contribution to the development of the microstructure during the growing process. The deposits were found also to be highly oriented with the major axis of their columnar grains, corresponding to the [001] crystallographic direction and always pointing toward the evaporation source. Within the range of deposition parameters that have been analyzed, the deposition rate was shown to have an insignificant effect upon the microstructure and texture characteristics of the deposits.
Electron-beam lithography three-mark silicon automatic registration and its capabilities for process distortion compensation
Authors: Tobias Eric , Carroll Allen
Published: July 2002

Submicron e-beam lithography requires that successive levels be accurately registered to each previously processed pattern on a wafer. Using a Perkin–Elmer manufacturing electron-beam exposure system (MEBES)R, we estimate the ability of an automated three-mark registration system to correct for distortion created by typical silicon processing. The results show that this registration system is capable of tracking process-induced distortions typically to within 0.15 μm everywhere on 64-mm-diam silicon wafers.
High-resolution study of the influence of gas adsorption on LEED fine structures
Authors: Baribeau J.-M. , Carette J.-D.
Published: July 2002

Fine structures in LEED I–V curves at low energy (≲20 eV) result from the interference between a wave directly diffracted from the crystal and a wave temporarily trapped in a preemergent beam between the substrate and its surface potential barrier. High-resolution study of these singularities is of great interest since a detailed analysis of their line shape leads to the characterization of the surface barrier of metals. Using a high-resolution electron spectrometer, the intensity of the (00) beam from W(110) in the [10] azimuth is measured revealing a LEED fine structure related to the (2̄0) beam threshold. The effect on this feature of hydrogen and oxygen chemisorption is examined. An enhancement of the singularities and a modification of their line shape is observed with increasing hydrogen coverage while oxygen slightly alters the fine structure up to a coverage of half a monolayer. An analysis based on the four-beam approximation shows that these behaviors reflect a change in the bulk scattering properties caused by the adlayer rather than an important change of the surface barrier. The possibility of relating this kind of observation to the structure of the adlayer is discussed.
Vacuum ultraviolet driven chemical vapor deposition of localized aluminum thin films
Authors: Calloway A. R. , Galantowicz T. A. , Fenner W. R.
Published: July 2002

Incoherent vacuum ultraviolet (VUV) light has been used to deposit aluminum from photodissociated trimethylaluminum vapor at room temperature. The depositions of aluminum on quartz, silicon, and sapphire show distinct patterns of the shadow mask that was used to shield areas of the substrate from the VUV light beam. Because of its simplicity and low cost, this new method may provide an attractive alternative to presently used methods for depositing metals, semiconductors, and insulators.
Angle-resolved photoemission studies of the CdS band structure
Authors: Stoffel N. G. , Margaritondo G.
Published: July 2002

We have investigated the valence band structure of wurtzite CdS using synchrotron radiation in the 7–35-eV range. This is the first such study for a II-VI compound. We find that direct transitions largely determine the shape of the experimental spectra. Information from all high-symmetry points in the Brillouin zone is available from normal- and off-normal-emission spectra. Polarization selection rules aid the interpretation of our results. A comparison with our experimentally determined critical-point energies shows that existing theoretical band structure calculations for wurtzite CdS are qualitatively correct, but underestimate the extent of the band dispersion. For instance, we observe an upper valence-band width of 4.5 eV which is significantly larger than the predicted values, 3.0–3.3 eV.
Solar-powered magnetron pump/gage
Authors: Chapman R. , Hobson J. P.
Published: July 2002

An ion pump/gage of the cold cathode magnetron-type has been operated entirely by solar energy. Experiments were carried out continuously for a period of 18 months, at a latitude of 45°, 27′N. The whole apparatus was placed outside the building on the south side and was exposed to the full annual range of climatic conditions and temperatures. The pump was sealed off in a Pyrex 7740 envelope and was self-pumping and self-gaging. Operated only from its solar power source, it maintained the vacuum below 10−5 Torr at all times, even after a week without any sunshine. The experiment was carried out to evaluate pumping and gaging requirements in an evacuated solar energy collector.
Final design and status of the NSLS vacuum system
Authors: Schuchman Joseph C.
Published: July 2002

The National Synchrotron Light Source (NSLS) is a dedicated facility for the production of synchrotron radiation. It consists of a linac booster injector, two electron storage rings, and a total of 44 experimental beam ports. This paper will describe the final vacuum system design and present operating status. It will discuss the philosophy and thoughts behind the design and selection of material and components. Also discussed will be fabrication, test, and installation techniques and problems.
Internal contacts to photovoltaic structures using ion beam milling
Authors: Potter R. R. , Sites J. R.
Published: July 2002

Characterization of individual junctions within a multilayered semiconductor structure is beneficial to understanding overall performance. Ion beam milling with masks to profile selected areas, followed by metallization, is used to make internal contacts to multilayered photovoltaic structures. Junctions deep within the structure may be analyzed using a straightforward model tested previously on the nSi/SnO2/CdSe/electrolyte tandem solar cell. Internal contacts are made to the CdS/CuInSe2/Mo thin film solar cell. In this type of cell, an undesirable Schottky barrier may occur at the CuInSe2/Mo interface; its effects should be separated from those of the primary CdS/CuInSe2 barrier. In addition to specific results, problems and limitations of the technique are discussed.
Inertial fusion target mounting methods: New fabrication procedures reduce the mounting support perturbation
Authors: Brinker B. A. , Cavese J. M. , Miller J. R. , Noyes S. G. , Sheble S. , Whitaker L. T.
Published: July 2002

Ablatively driven inertial fusion targets require a high degree of geometrical perfection to achieve optimum burn conditions. Detailed target fabrication specifications are given by designers to minimize instability growth during the implosion process. Currently, the most significant target imperfection arises from the mass introduced by the target delivery support attachment. Alternate target supporting schemes have been investigated to reduce the target support mass perturbation while reliably permitting target irradition experiments. The new support schemes developed have reduced dimensions, use new materials, and significantly improve target implosion symmetry. A thousand-fold reduction in the effective target support mass is achievable with the developed target delivery support systems. Delivery reliability for the described systems is higher than that of conventional capillary butt mounts.
Surface phonons on clean- and adsorbate-covered nickel disilicide (NiSi2) thin films
Authors: Dubois L. H. , Rowe J. E.
Published: July 2002

The (111) and (100) surfaces of nickel disilicide (NiSi2) thin films were studied by high resolution electron energy loss spectroscopy (EELS) and intrinsic surface phonons were detected at 267 cm−1 [NiSi2(111)] and 232 cm−1 [NiSi2(100)]. These modes were quite weak on the clean surface, but increased in intensity ∼ tenfold in the presence of adsorbed oxygen, carbon, or methanol. The growth of small (<100 Å) silicon crystallites was observed after thinning the silicide films by several sputter/annealing cycles. Similar energy loss spectra were recorded from crystallites formed on either NiSi2(111) or NiSi2(100) and were characterized by two modes at 460±10 and ∼510 cm−1.
Photon- and electron-stimulated desorption from rare earth oxides
Authors: Loubriel G. , Knotek M. L. , Stulen R. H. , Koel B. E. , Parks C. C.
Published: July 2002

Resonance in the photon-stimulated desportion (PSD) spectra of La, Ce, and Er oxides are reported at photon energies near the La(4d), Ce(4d), and Er(3d) edges. These resonances, also seen in soft x-ray absorption (SXA), arise from excitations of d electrons to the 4f shell. Comparisons of SXA and PSD show how PSD can be used to determine surface valency. ESD data from Ce and Er oxides is used to establish the importance of the 5p level in the electronic pathways which lead to desorption.
The segregation of impurities at the (110) surface of an Fe–10 at. % single crystal
Authors: Bezuidenhout F. , du Plessis J. , Viljoen P. E.
Published: July 2002

Measurement of the nonequilibrium surface concentration in a Fe–10 at. % Si (110) sample as an function of temperature reveals specific interrelated segregation behavior. A review of the initial processes in this single crystal shows the existence of certain interactions. In agreement with work on the other ternary systems, evidence has been found that carbon and silicon show a repulsive interaction in the segregation process. At lower temperatures the surface free energy favors the carbon and above a transition temperature, the silicon on the surface. On the other hand, silicon and phosphorus cosegregate, which is indicative of an attractive interaction. This has the effect that much less phosphorus is available for segregation to the surface or grain boundaries than in a pure Fe–P system. The LEED pattern for the silicon covered surface is the same as for a 1% Si sample viz. a c(7×1) superstructure with reference to the c(a×(2a)1/2) surface net, where a is the unit cell parameter in the [001] direction. Elongation of the spot in one direction indicates a change of order in the [001] direction in agreement with the silicon island formation. The pattern of the phosphorus covered surface shows a maximum surface coverage by phosphorus in good agreement with the observed value as determined by AES.
Gain degradation mechanism for channel electron multipliers
Authors: Lichtensteiger M. , Webb C.
Published: July 2002

The gain of channel electron multipliers (CEM) decreases rapidly during experiments which involve exposure of samples to ∼10−8 Torr H2O during electron bombardment—an environment which very effectively oxidizes semiconductors. In subsequent experiments it was found that reoxidation of samples of CEM glass (it is subject to reduction treatment during manufacture) occurs when it is exposed to the same set of conditions. We discuss the possible influence of this on the gain degradation commonly observed as a function of total counts.
Cleaning and conditioning of the walls of plasma devices by glow discharges in hydrogen
Authors: Waelbroeck F. , Winter J. , Wienhold P.
Published: July 2002

Surface conditioning by rf-assisted dc glow (RG) discharges has been studied in a stainless steel vessel in order to optimize the rate of surface deoxidization via water formation. This is the simplest way to decontaminate the almost carbon-free surfaces of plasma devices which have been exposed to air after a prolonged operation in hydrogen. This rate depends strongly on the wall temperature TW, the pump speed Sp, the discharge current IRG, and the hydrogen pressure P2. It is small at ambient temperature; the conditioning should be made at TW>100 °C. Surface oxygen is removed, even at room temperature, when 1% to 2% of methane is added to the hydrogen. Carbon monoxide is formed and evacuated. The addition of He or Ne does not accelerate the oxygen removal from reoxidized surfaces. An equation derived from a simplified model describes the parametric dependences of the water release well. The occurrence of arcs during RG discharges depends on wall conditioning; they are not observed after a prolonged bakeout at 200 °C. The problems which arise when a residual gas analyzer is used to measure the partial pressures of water, carbon oxides, and hydrocarbons in hydrogen are addressed, and a conditioning technique which reduces the resulting errors is described.
Characterization of titanium films in the Tandem Mirror Experiment Upgrade (TMX-U)
Authors: Hsu W. L. , Bastasz R. , Bauer W. , Malinowski M. E. , Mills B. E. , Allen S. L. , Clower C. A.
Published: July 2002

Titanium gettering is used extensively in the Tandem Mirror Experiment Upgrade (TMX-U) to achieve good vacuum conditions for the production of a sustained energetic plasma. The gettering films under different operating conditions were analyzed by thermal desorption spectroscopy and Auger electron spectroscopy. A sputter profile of the films showed a Ti deposition rate of ≂1 nm per evaporation sequence. Large quantities of protium (H/Ti≊0.2), oxygen (O/Ti≊0.3), and carbon (C/Ti≊0.1) were detected in the films regardless of their location and the plasma isotope to which they were exposed. While the Ti films that were exposed to deuterium plasmas showed a substantial increase in deuterium content, deuterium still remained a small fraction of the overall hydrogen concentration (D/H≊0.1). Analyses of the results suggest that getter pumping of H2O from the background gas in the (TMX-U) vacuum system is the primary source for protium and oxygen measured in the films.
Management of vacuum leak-detection processes, calibration, and standards
Authors: Wilson Norman G.
Published: July 2002

Vacuum leak detection requires integrated management action to ensure the successful production of apparatus having required leak tightness. Implementation of properly planned, scheduled, and engineered procedures and test arrangements are an absolute necessity to prevent unexpected, impractical, technically inadequate, or unnecessarily costly incidents in leak-testing operations. The use of standard procedures, leak standards appropriate to the task, and accurate calibration systems or devices is necessary to validate the integrity of any leak-test procedure. In this paper, the need for implementing these practices is discussed using case histories of typical examples of large complex vacuum systems. Aggressive management practices are of primary importance throughout a project’s life cycle to ensure the lowest cost; this includes successful leak testing of components. It should be noted that the opinions and conclusions expressed in this paper are those of the author and are not those of the Los Alamos National Laboratory or the Department of Energy.
TEM investigation of the differences in ion milling induced damage of Hg1−xCdxTe and CdTe heterojunctions
Authors: Carey G. P. , Cole S. , Yamashita T. , Silberman J. A. , Spicer W. E. , Wilson J. A.
Published: July 2002

The lattice defects induced by ion milling at the liquid phase epitaxy (LPE) grown HgCdTe on CdTe heterojunction have been investigated using transmission electron microscopy (TEM). TEM analysis reveals that subjecting both materials to identical milling conditions results in much higher defect densities (2–3 orders of magnitude) in the CdTe than in the HgCdTe (x=0.30). In addition, high resolution lattice images of both regions reveal that the stacking fault widths in the HgCdTe are much narrower than in the CdTe, which implies that the stacking fault energy is much higher in the HgCdTe as compared to the CdTe. These observed phenomena are shown to support the weakness and metallicity of the Hg–Te bond as proposed by theoretical considerations.
Frequency dependence of a quartz oscillator on gas pressure
Authors: Kokubun K. , Hirata M. , Ono M. , Murakami H. , Toda Y.
Published: July 2002

The frequency shifts of a tuning-fork-shaped quartz oscillator with gas pressure were studied experimentally and theoretically. The experimental measurements showed that the frequency shift of the oscillator was very small in the pressure region below 1 Torr and much larger in the higher pressure region above 1 Torr. The experimental results were theoretically analyzed on the basis of a string-of-beads model for a quartz oscillator. The theoretical analysis showed that the resonance frequency shift of the quartz oscillator was small in the molecular flow region. In the viscous flow region the frequency shift was found to be proportional to the pressure. These theoretical results are in good agreement with the experimental data. The frequency shift of the oscillator in the higher pressure region was also found to be proportional to the molecular weight of the gas species in both theory and experiment.
Surface morphologies and flux discontinuities in polycrystalline films
Authors: Huang Huei Li
Published: July 2002

The surface morphological changes at the grain boundary (GB) is characterized by a surface flux discontinuity quantity M′ which is compounded by the capillarity-induced surface diffusion and the electromigration-induced surface and GB diffusion in polycrystalline films. The quantity M′ has to do with the surface diffusivity and the so-called threshold current density across the GB in connection with the pertinent physical parameters in the GB concerned. Qualitative plots of the GB profiles by treating M′ as a parameter show very good conformity with experimental observations. The circumstances surrounding the existence and nonexistence of the threshold current density in relation to the surface diffusivity variation across the GB and the mobile concentration gradient of the diffusion species in the GB are discussed for pure system and light alloy system. Their relation to the GB segregation and the second phase formation is pointed out.
Deuterium permeation properties of beta-irradiated and unirradiated poly(vinyl alcohol) and polystyrene shells
Authors: Scott L. A. , Schneggenburger R. G. , Anderson P. R.
Published: July 2002

We measured the permeability of inertial fusion (IF) fuel shells made of poly(vinyl alcohol) (PVA) and polystyrene (PS) with deuterium. Activation energies of permeation (Ep̄) were determined using permeability coefficients measured over the temperature range 25–100 °C for PVA, and −100 to 25 °C for PS shells. We then exposed this same batch of shells to intense beta irradiation from tritium and repeated the permeation measurements. Comparing permeabilities of the same shells before and after irradiation, we obtained a measure of the effect beta irradiation has on fuel retention characteristics of the polymers. Our results show that irradiation does change the permeability of PVA, while the permeability of irradiated PS is relatively unchanged.
Titanium–silicon and silicon dioxide reactions controlled by low temperature rapid thermal annealing
Authors: Brillson L. J. , Slade M. L. , Richter H. W. , VanderPlas H. , Fulks R. T.
Published: July 2002

Auger electron spectroscopy measurements coupled with sputter depth profiling demonstrate that titanium silicide forms between Ti and SiO2 at conventional annealing temperatures in UHV and that rapid thermal annealing at relatively low temperatures can enhance silicide formation at Ti–Si relative to Ti–SiO2 interfaces within the same thin film structure. Reactions and diffusion at these interfaces occur on a short time scale (seconds) at low temperatures (400–700 °C), yet resemble interactions obtained at multimicron thicknesses. UHV fabrication and analysis reveals that these reactions are sensitive to interface contamination and sputter-induced disorder.
Long-term evaluation of fluoroelastomer O-rings in UF6
Authors: Russell R. G. , Otey M. G. , Dippo G. L.
Published: July 2002

A major component in the gaseous centrifuge enrichment plant (GCEP) was fluoroelastomer O-rings, which were used to seal the uranium hexafluoride (UF6) gas system. A program utilizing accelerated test conditions was used to help identify the best material out of four selected candidates and to predict the service life of these materials at GCEP conditions. The tests included accelerated temperatures, mechanical stress, and UF6 exposure. Data were evaluated using the Newman–Keuls1 ranking system to identify the best material and a zero-order reaction rate equation to help predict service life. This presentation includes a description of the test facility, the materials tested, the types of tests, objectives of the study, service life predictions, and conclusions. The O-rings are predicted to last ∼30 years , and a high-molecular-weight polymer had the best performance ranking.
Space Station technology experiments and uses
Authors: Breckenridge Roger A. , Russell Richard A.
Published: July 2002

With the advent of the Space Station will come significant opportunities to conduct research in the near-Earth space environment. We anticipate that the Space Station will be an in-space facility where long duration missions can be conducted. A great deal of experimentation is expected to be performed in such areas as science and applications, technology, and commercial ventures. NASA is working very actively to establish the experimental requirements from each experiment area. This paper addresses the in-space technology experimental applications and uses of the Space Station as presently envisioned for this next step in space.
Effect of measuring conditions on the accuracy of a spinning rotor gauge
Authors: Hirata M. , Isogai H. , Ono M.
Published: July 2002

The performance of a spinning rotor gauge was measured for nitrogen under various conditions. The effective accommodation coefficient was determined to be 1.05 by comparison with the standard McLeod gauge. The ratio of the reading of the gauge to that of a diaphragm gauge showed a variation ±1% at pressures from 0.1 to 10 Pa. The deviation of the ratio at 0.3 Pa was within ±1% for 7 months. The lower limit of the measuring pressure of the gauge was affected by fluctuations of its offset. The angular deviation of gauge positioning changed the offset up to 10−3 Pa (nitrogen equivalent). Just after starting the operation of the gauge at pressures less than 10−5 Pa, the offset changed by ±3×10−5 Pa from its final value. This was revealed to be due to a temperature variation of the rotor. And the offset depended not only on the amplitude of vibration but also on its frequency.
Characterization of impurities in p-type HgCdTe by photo-Hall techniques
Authors: Bartoli F. J. , Hoffman C. A. , Meyer J. R.
Published: July 2002

Due to mixed conduction effects, conventional temperature-dependent Hall measurements do not yield an accurate characterization of doping levels in high-purity p-type HgCdTe (NA≲5×1015 cm−3). In the present work, we report a new and highly promising technique for determining compensation densities in p-type material by measuring the mobility of photoexcited electrons at low temperatures where most of the holes are frozen out and the total impurity concentration is equal to 2ND. As long as the photoexcitation is sufficiently strong that the electrons dominate the conductivity yet sufficiently weak that scattering by photoexcited holes is negligible, the compensation may be determined directly by fitting a comprehensive theory for transport in a photoexcited narrow gap semiconductor to the measured mobilities. Experimental photo-Hall results are reported for p-type Hg1−xCdxTe samples (0.215<x<0.23) with acceptor densities in the 1015 to 1016 cm−3 range. Photoexcitation is provided by a pulsed CO2 laser. At temperatures between 10 and 30 K, theory and experiment agree well over an extremely large range of photoexcited electron densities (1012–1016 cm−3). Donor and acceptor concentrations and acceptor binding energies have been determined for samples with both single (probably Cu) and double (probably Hg vacancies) acceptors. Since the method has its greatest sensitivity to ND at low excitation levels (n<1013 cm−3), it should be possible to perform routine characterizations using only a blackbody source. The model predicts that donor densities as low as 1014 cm−3 may be measurable.
Mechanism of N2 implantation of Co, WC, and Co–W alloys
Authors: Oblas D. W. , Sarin V. K.
Published: July 2002

Experimental results are presented showing the effects of nitrogen implantation on a series of materials that are related to the WC–Co cemented carbides: pure Co, W, Co–W alloys (10–30 wt. % W), and WC (single crystal and binderless). Implantations were carried out at 180 keV, with a fluence of 2.5×1017 N+2/cm2 at implant temperatures of approximately 400 °C. Results show that nitrogen is not readily retained by pure Co. However, for the Co–W alloys the retained nitrogen increases with the W concentration but the nitrogen profiles are non-Gaussian and indicate diffusion of the implanted nitrogen. For the W and the WC samples, most of the implanted nitrogen is retained and the profiles have a Gaussian-type shape similar to those obtained for nitrogen implanted WC–Co cemented carbides. There is evidence to indicate the formation of nitride bonding in the nitrogen-implanted W and WC samples. Preliminary low-load (10–25 g) indentation measurements, did not show any significant changes in hardness as a result of nitrogen implantation.
Surface oxide chemistry of Hg0.8Cd0.2Te
Authors: Lopes V. C. , Hart T. R.
Published: July 2002

The surface oxide chemistry of Hg0.8Cd0.2Te in aqueous solutions with the pH ranging from 1–11 has been determined from the electrophoresis zeta potential. A four parameter acid dissociation model was developed to fit the experimental data. The dissociation of tellurous acid, which was formed by a surface oxide of TeO2 combining with water, was found to dominate the surface oxide chemistry for pH between 1 and 9. The point of zero zeta potential (PZZP) occurred at pH = 1.8. The tellurous acid dissociated in a two-step pattern with surface charge densities of approximately −2×1012 electrons/cm2 from pH of 4 to 6.5 and −4×1012 electrons/cm2 from pH of 9 to 9.5. As the pH was increased beyond 10, oxidized Cd dominated the surface oxide chemistry.
A simple high-pressure reaction chamber connected to an ultrahigh vacuum system for surface studies
Authors: Bracconi P. , Pörschke E. , Klatt K. H. , Lässer R.
Published: July 2002

An experimental setup for surface investigations of metal films by electron spectroscopy has been equipped with a simple high-pressure reaction chamber. The design and operation of the chamber is described. Results of our investigations on metal hydrides are presented.
Operation of a Bayard–Alpert gauge in a uniform 0–0.16 tesla magnetic field
Authors: Filippelli Albert R.
Published: July 2002

The behavior of one widely used Bayard–Alpert ionization gauge in a magnetic field has been experimentally investigated for two cases: field orthogonal to, and parallel to the grid axis. Emission, grid and collector currents, and current to the wall surrounding the gauge were measured as functions of field magnitude and direction for N2 in the pressure range 5×10−8 to 2×10−4 Pa. In addition to graphical presentation of these data, a qualitative description is given of the oscillatory components observed in the collector and wall currents. The data show that the zero-field gauge sensitivity can lead to large pressure measurement errors when operating the gauge in fields as weak as 0.005 T and that under certain conditions these errors may reasonably be accounted for by first determining gauge response as a function of field.
Neutral density effects in the end cells of the Phaedrus tandem mirror
Authors: Breun R. A. , Brouchous D. A , Conrad J. R. , Peranich L. , Persing H. , Ross S.
Published: July 2002

Cold neutral gas density has important consequences for the energy and particle balances of the hot ion plasma in the end cells of tandem mirrors. Charge exchange loss from cold gas penetration into this plasma detracts from the pressure in the end cells needed for magnetohydrodynamic stability of the mirror. Unfortunately, cold gas can be a by-product of neutral beam injection and of fueling. This report describes measurements of neutral pressure in the rf heated tandem mirror Phaedrus. The emphasis is on the dynamics of gas flow into the end cells, the effects of cold gas on the plasma, and on wall reflux for different wall conditions. The effects of neutral beams and neutral beam generated wall reflux are also studied. A numerical gas flow code is used to model the effects of plasma pumping, charge exchange, and wall reflux on end cell plasma parameters. The titanium sticking coefficient for hydrogen gas was determined to be 0.08±0.08. Wall reflux coefficients in the end cell were determined to be 1.4±0.2 without titanium gettering and 0.75±0.25 with gettering.
Evaluation of charcoal sorbents for helium cryopumping in fusion reactors
Authors: Tobin Albert G. , Sedgley Douglas W. , Batzer Thomas H. , Call Wayne R.
Published: July 2002

Improved methods for cryopumping helium were developed for application to fusion reactors where high helium generation rates are expected. In this study, small coconut charcoal granules were utilized as the sorbent, and braze alloys and low temperature curing cements were used as the bonding agents for attachment to a copper support structure. Problems of scale-up of the bonding agent to a 40 cm diam panel were also investigated. Our results indicate that acceptable helium pumping performance of braze bonded and cement bonded charcoals can be achieved over the range of operating conditions expected in fusion reactors.
X-ray photoelectron spectroscopy study of the Ni/Si oxide/Si interface
Authors: Dillingham T. R. , Chourasia A. R. , Chopra D. R. , Martin S. R. , Peterson K. L. , Hu C. Z. , Gnade B.
Published: July 2002

The electronic structure of the Ni/Si oxide/Si interface has been investigated using x-ray photoelectron spectroscopy. This interface represents a more realistic situation encountered in semiconductor device processing technology. Approximately 35 Å of high-purity Ni was sputter deposited on 〈111〉Si (covered with a thin native oxide layer) at room temperature. A sputter profiling technique was employed to determine the composition and reactivity as a function of depth. The measurements show considerable reactivity at the Ni/Si oxide/Si interface, even at room temperature. The Ni 2p3/2 peak exhibits a gradual shift to higher binding energy which indicates that the overlayer cannot be regarded as a single unique nickel silicide phase. The large positive shift of the Ni 2p3/2 and the small shift of the corresponding Si 2p peak suggest that ionicity plays a nominal role in the Ni–Si chemical bond. The valence-band spectra show a dominant 3d-derived feature which gradually shifts to higher binding energy. The observed shifts in the Ni levels are attributed to the change in the electronic configuration of Ni in going from Ni-rich silicide to Si-rich silicide. A study of the composition as a function of depth shows that the Ni/Si oxide/Si interface is not sharply defined due to the interdiffusion of Ni and Si. Thus, the interface is identified as a graded transition region with composition ranging from Ni-rich to Si-rich silicide.
Theory of the W(100) surface reconstruction and hydrogen adsorption effects
Authors: Sugibayashi T. , Hara M. , Yoshimori A.
Published: July 2002

The reconstruction of the W(100) surface and the H adsorption effects are discussed on the phenomenological model combined with the lattice gas model for the adsorbed H where couplings are assumed between the displacements of the surface W atoms and between the displacements and the adsorbed H. Analyses are made by computer simulation. The present model for the clean surface, which is an extension of the two-dimensional XY model, is found to be also nonuniversal. At low coverages of the adsorbed H, the directional transition of displacements of the surface W atoms is found to be gradual, and a possibility of the adsorbed H condensation is pointed out.