bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociative pumping of the alkanes using nonevaporable getters
Authors: Emerson L. C. , Knize R. J. , Cecchi J. L. , Auciello O.
Published: July 2002

The pumping speed of a standard Zr–Al getter was measured over a temperature range of 110 to 640 °C for the gaseous members of the alkane series (CnH2n+2) extending from methane through n-butane. For a given member of the series, the pumping speed increases monotonically with temperature. The strength of the temperature dependencies decreases with increasing alkane mass. These data are in qualitative agreement with the predictions of a model which assumes that dissociation is the rate limiting process.
Downstream pressure control: Calculation of the transfer function and optimization of control parameters leading to a new controller design
Authors: Fischer R.
Published: July 2002

The transfer function and the block diagram of the downstream closed loop were calculated. This was based on the differential equation of the controlled system and on the analysis of the sensor, the controller, and the control valve. Since the relationship between the actual pumping speed and the opening angle of the control valve is indeed time variant but not linear, linearization of this transfer element became necessary. Subsequently, the leading and perturbating behavior of the closed loop control defined in this way was investigated. With that, it was possible to optimize the control parameters of the downstream closed loop control. These optimized parameters were confirmed by computer simulation and are the basis of a new optimized downstream pressure controller.
Standardization and temperature correction of calibrated leaks
Authors: Solomon G. M.
Published: July 2002

Calibrated leaks are important tools in the control and measurement of vacuum in research and industry. These devices are best known for their major application as calibration standards for helium leak detectors. Other such devices are used as flow standards for use in gauge calibration, pump speed measurements, and flow calibration. Because of their importance in calibration work and certification of leak detectors, the AVS Standards Committee on Calibrated Leaks targeted areas which need clarification as the initial thrust of their work. This paper will discuss the need for standardizing the units which are used in quoting leak rates of calibrated leak devices. The flow characteristics of permeation-type calibrated leaks will be reviewed with respect to the temperature correction equations which are appropriate for their use. Also, a brief report on the status of the work being performed by the Calibrated Leak Standards Committee will be presented.
Design of plasma etching and deposition systems
Authors: Kumagai H. Y.
Published: July 2002

Plasma etching and plasma deposition are widely used processes in the fabrication of microelectronic devices. The design of equipment used to carry out these processes involves vacuum technology as well as numerous considerations involved in the mechanical and electrical design of such machinery. In this paper, the design concepts will be discussed with reference to commercially available machinery as examples of functional designs.
Fermilab Accumulator Ring ultrahigh vacuum system
Authors: Mills F. E. , Bartelson C. , Gormley M. , Klen J. , Lee G. N. , Marriner J. , Misek J. R. , Rathbun T. D. , Satti J. A. , Sax W.
Published: July 2002

An average pressure of 3×10−10 Torr is required in order to store a beam of antiprotons (for up to 20 h) in the Fermilab Accumulator Ring. The Accumulator Ring has a circumference of 474 m and consists of 114 main magnets which surround a continuous, stainless-steel vacuum chamber with a mean diameter of 12 cm. The Accumulator Ring is located in a below grade tunnel which is inaccessible during normal operation. Consequently, all monitoring and control operations must be done remotely. In this paper we describe: (1) the rationale of the Accumulator Ring’s vacuum system; (2) the specific choice of pumping systems (roughing, ion, and sublimation) that was selected for implementation; (3) the details of the instrumentation, control, and bakeout systems (300 °C) for monitoring the pressure and desorbing the vacuum chamber; and (4) the operating experience and performance of the entire system.
The kinetics of tellurium precipitation in Hg0.8Cd0.2Te
Authors: Schaake H. F. , Tregilgas J. H.
Published: July 2002

The kinetics of tellurium precipitation in Hg0.8Cd0.2Te have been studied at two different precipitation temperatures for two different starting concentrations of excess tellurium. For a starting concentration of 1017 cm−3 excess tellurium, it is found that the fraction of unprecipitated excess tellurium may be described by an equation fXSTe=exp[−(kt)n] where n is between 0.5 and 2. For a starting concentration of 2×1018 cm−3 excess tellurium, it is found that precipitation to a concentration of <1017 cm−3 occurs within the first 15 min of annealing at either temperature. Subsequently the precipitation to the equilibrium excess tellurium concentration is extremely slow, with a time constant the order of hours. The microstructure determined by transmission electron microscopy (TEM) for this latter case consists of a few precipitates ∼2000 Å in diameter. Possible reasons for the observed behavior are discussed.
Influence of layer thickness on the quality of mercury cadmium telluride epilayers grown by the interdiffused multilayer process
Authors: Raccah Paul M. , Zhang Z. , Garland J. W. , Chu Amy H. M. , Bevan M. J. , Thompson J. , Woodhouse K. T.
Published: July 2002

The interdiffused multilayer process (IMP), in which alternate submicron layers of CdTe and HgTe are grown by metal–organic vapor-phase epitaxy (MOVPE) and are allowed to interdiffuse during the deposition of subsequent layers, has been used to grow mercury cadmium telluride epitaxially on CdTe substrates. A thorough investigation by electrolyte electroreflectance (EER) shows that epilayers of 1×1 cm grown by this method have a reasonable lateral homogeneity with lateral fluctuations in the alloy composition being less than ±0.008. The homogeneity in depth of the composition of the layer is of the order of ±0.005, and the interface region is quite abrupt (less than 3000 Å in thickness). These characteristics are quite attractive and compare well with state of the art liquid-phase epitaxy (LPE) materials. In order to understand better the potential of this relatively novel growth method we have investigated the dependence of the quality of the layers on the combined thickness of the CdTe and HgTe layers, each pair of which constitutes a cycle. Materials grown from a small number of thick cycles were found to be highly strained or downright inhomogeneous. Those grown from a high number of very thin cycles also were found to be highly strained and to have relatively large fluctuations in composition with the depth of the layer. However, for intermediate cycle thicknesses of the order of 2500 Å the epilayers were found to be strain-free, and the density of polarizable defects was found to be negligible; i.e., those materials were found not to be impurity doped and to be relatively free of charged extended defects. For this reason, the best IMP materials are at this time superior to LPE materials. On the other hand, they were found to exhibit a significant amount of alloy clustering, which is not surprising given the growth method, and thus still are inferior to bulk or molecular beam epitaxy (MBE) n-type materials.
Theoretical studies of electronic properties of semimagnetic superlattices in a magnetic field
Authors: Wu G. Y. , McGill T. C. , Smith D. L. , Mailhiot C.
Published: July 2002

We present our first theoretical study of the electronic properties of superlattices formed from semimagnetic semiconductors. Both Cd0.8Mn0.2Te/Cd0.7Mn0.3Te and Hg0.95Mn0.05Te/ Cd0.78Mn0.22Te systems are considered explicitly. Magnetic field splittings are calculated with and without the exchange interaction. We find that the exchange interaction dominates the magnetic effects in the wide-gap Cd0.8Mn0.2Te/Cd0.7Mn0.3Te system while the Landau level shift is also important in the Hg0.95Mn0.05Te/ Cd0.78Mn0.22Te system. We present calculations of the superlattice band-gap variation with temperature and its derivative with magnetic field as a function of the superlattice layer thickness. Variation of the band offset in determining the values of the various quantities is examined.
Diamondlike carbon high-temperature diffusion barrier for copper-gasketed stainless-steel flanges
Authors: Nyaiesh A. R. , Garwin E. L. , Hoyt E. W.
Published: July 2002

Diamondlike carbon films of 5−15 nm were deposited on copper gaskets which were sealed in 304−stainless steel flanges. The carbon films acted as a diffusion barrier during high temperature bakeout (550 °C at 1 x 10−5 Torr for up to 200 hours) which prevented carbon diffusion into the copper. (AIP)
Separation of gas phase and electron-stimulated-desorption ions in the modulated-ion-current pressure gauge
Authors: Watanabe F. , Ishimaru H.
Published: July 2002

The behavior of gas phase and electron-stimulated-desorption ions in the modulated-ion-current pressure gauge is described. In order to obtain optimum separation of the two ion peaks, electron energy, shield grid potential, emission current, and various shapes of electron reflectors were examined. In addition, observations were made in the residual gas at 10−11 to 10−10 Torr.
Radioluminescence of individual deuterium–tritium-filled glass microbubble laser targets
Authors: Smith G. H. , Souers P. C. , Fearon E. M. , Tsugawa R. T. , Darling D. H.
Published: July 2002

Visible radioluminescence was observed from single 200-μm-diam deuterium–tritium (D–T)-filled glass microbubble laser targets. Most of the light is caused by tritium beta particles hitting the glass, and no beta particles escape outside the microbubble. At room temperature, white light is created with an efficiency of 0.2 to 0.3 photons/beta particle. This efficiency rises an order of magnitude at 35 K, probably because of freezing of radiation defects into the glass. It decreases when the D–T liquifies and drops even lower upon solidification. This is probably caused by pooling of the D–T at the bottom of the microbubble plus light absorption in small crystallites. Radioluminescence offers a means of certifying the D–T fill of individual microbubble laser targets made of transparent material.
Plasma-enhanced chemical vapor deposition SiN films: Some electrical properties
Authors: Ling C. H. , Kwok C. Y. , Prasad K.
Published: July 2002

Experimental data are presented on the effects of varying deposition parameters of silane/ammonia flow rate ratio, rf power, deposition pressure, and substrate temperature, on the resistivity and breakdown field, static and dynamic dielectric constants, activation energy, and barrier height, of plasma-enhanced chemical vapor deposition SiN films prepared in the temperature range 100–300 °C. Results show a strong dependence of the breakdown field and resistivity on rf power, the former increasing by a factor of 5 and the latter by 11 orders of magnitude, as power varies from 50 to 250 W. Current–voltage measurements favor a Frenkel–Poole conduction process, with a barrier height in the range 0.8–1.2 eV and an activation energy in the range 0.29–0.45 eV. Annealing in nitrogen at 400 °C leads to a decrease in film resistivity. This is attributed to the loss of hydrogen, incorporated as Si–H and N–H bonds in the film. The decrease in positively charged dangling bonds is supported by the resulting shift in the flat-band voltage on a metal–insulator semiconductor structure. Partial recovery of film resistivity has been demonstrated through further annealing in hydrogen. Polarization and trapping instabilities in the capacitance–voltage measurements have also been observed.
Quantitative analysis of He in solids by sputtered neutral mass spectrometry
Authors: Gnaser H. , Bay H. L. , Hofer W. O.
Published: July 2002

Sputtered neutral mass spectrometry is shown to be a very sensitive, depth-differential technique for the analysis of helium in solids. Detection limits in nickel are some 10 ppm for near-surface He distributions and can be lowered to a few ppm if extreme depth resolution is not important. Range parameters of 4He in Ni and Si agree very well with theoretical data. Quantitative evaluation of He concentrations with an accuracy of 4% can be done by producing an internal standard via in situ ion implantation.
Formation of tungsten borides studied by field ion microscopy
Authors: Ohmae N. , Nakamura A. , Koike S. , Umeno M.
Published: July 2002

Metallurgical transformation of a W filament into W2B5 or WB4 was found in our field ion microscope observations of boron fibers. The W–boride formation at the B/W interface is of technological and industrial importance. Processes of the W–boride formation have been studied using field ion microscopy by sputter-depositing B films onto a W tip and by heating the tip at varied temperatures. Stable W2B5 was formed at heating temperatures higher than 1200 K. The formation of W2B5 {0001} was found frequently on the W{011}. This may be caused by the small misfit between the locations of W atoms in bulk W and of those in borides. Characteristics in the He-ion image of W2B5 obtained in this study showed a resemblance to that previously observed at the core of boron fibers.
An experimental study of microarea analysis of insulators by secondary ion mass spectrometry using charge compensation
Authors: Fan Chui-zhen , Chen Xue-kang , Yu Zhen-jiang
Published: July 2002

A method is proposed to acquire secondary ion images of poorly conducting samples with a common scanning Auger microscopy/secondary ion mass spectrometry system. In the region of the primary ion beam spot (which does not move and with ∼2-mm diameter), a fine focused electron beam (∼1-μm diameter) was used for charge compensation. When it was moved inside the spot, the secondary ion signal varied obviously and an image using this signal was formed. The contrast of this image results from charge compensation, and we expect that some relevant information, such as distribution of conductivity in a very small area, can be acquired. The results show that it may be used to find a failure point on an integrated circuit where a short circuit or an open circuit exists. Under proper conditions, element maps including hydrogen were also obtained.
Ion implanted junction formation in Hg1−xCdxTe
Authors: Bubulac L. O. , Tennant W. E. , Lo D. S. , Edwall D. D. , Robinson J. C. , Chen J. S. , Bostrup G.
Published: July 2002

This work reports on two significantly different methods to form junctions in Hg1−xCdxTe by ion implantation: a ‘‘displaced Hg diffusion source’’ for n-on-p junctions and an ‘‘implanted species diffusion source’’ for p-on-n devices. For each one, the role of background impurities, stoichiometric defects, and implanted species of junction formation have been determined. In spite of superficial damage created by the implant, these methods produced implanted junctions of either type with low damage in the near-junction region, resulting in excellent electrical characteristics.
Adsorption of H2O on annealed and damaged iron
Authors: Baer D. R. , Jones R. H.
Published: July 2002

The tips of advancing cracks are highly strained and may adsorb atoms or molecules from gaseous or liquid environments at rates different from unstrained surfaces. The influence of stress and sputter damage has previously been investigated for H2S adsorption on iron, and this paper reports the extension of the work to H2O on iron. Auger electron spectroscopy and x-ray photoelectron spectroscopy examination of water adsorption on polycrystalline and (110) iron show that the saturation coverage of oxygen is not altered by ion beam damage, but that the adsorption rate can be increased by more than a factor of 10. These results are similar to those found for H2S and have been interpreted in terms of a precursor adsorption model.
A generalized approach to vacuum system automation
Authors: McMahon R. W. , Celler Z. , Hanssmann M. G. , Shuen A. K.
Published: July 2002

Computer automation of vacuum equipment has traditionally been dominated by custom hardware and software solutions, requiring long and expensive development periods. On-going modification and support of the installed computer equipment often requires an appreciable portion of a computer specialist’s time. In order to achieve a more cost effective approach, the authors have analyzed a variety of vacuum deposition and etching processes running on equipment supplied by numerous manufacturers. The following observations have led to the development of a generalized vacuum equipment automation system which requires minimal custom engineering time to install and support: (1) In spite of the high marketing profile given to RS-232, IEEE-488, and SECS II interfaces, by far the most common and easy to use interfaces provided by vacuum equipment vendors are simple digital and analog. (2) Most processes involve between 50 and 300 discrete or continuous parameters; however, few of these parameters vary at rates appreciably higher than 1 Hz. (3) The inter-relationships between these many parameters are often complex and/or difficult to specify in a fixed manner. The computer must therefore be capable of operating according to process logic entered and modified in the field by a process engineer, who may not be a computer specialist. (4) The skill level of vacuum operators varies from doctorate to grade school; uses of vacuum equipment vary from pure research to high-volume production. The user interface must therefore be highly adaptable yet easy to use.
Lubricating of mechanisms for vacuum service
Authors: Roller K. G.
Published: July 2002

Seizure of metal parts which occurs during sliding or rolling in a vacuum environment can be prevented by use of appropriate lubricants. Fluid lubricants, having low evaporation rates, dry solid film lubricants, soft, low shear strength metals, and composite materials are customarily used, but ion implanted metals and ceramics are available for extremely harsh environments. Bearings, bushings, gears, cams, guides and slides, solenoids, commutators, motor brushes, and sliprings can be lubricated to yield vacuum service lives comparable to those achieved in normal atmospheric pressure applications, or even longer due to the absence of O2 and H2O. The use of fluid and dry lubricants may require the incorporation of seals to prevent molecular or particulate contamination of test or production hardware within the vacuum system. The most important parameter to be considered in selecting the appropriate lubricant is the operating temperature, which drastically affects the evaporation and contamination rates. Fluid based lubricants are available having evaporation rates of 10−9 to 10−13 g cm−2 s−1 and metals, composites, and dry lubricants having 10−10–10−14 g cm−2 s−1 loss rates at room temperature.
Techniques for testing cryopump capacity
Authors: Porter John R.
Published: July 2002

Pneurop has proposed guidelines for measuring cryopump specifications (Minutes of Pneurop Committee–Vacuum Technology, ‘‘Acceptance Specifications, Part 5: Cryopumps ,’’ 1987). However, conditions used during capacity merasurement are not specific for condensibles. Methods used for this measurement strongly affect the results, and the distinction between useful capacity and gross capacity is important to the end user of equipment affected by this specification. This paper describes various methods for measuring condensible and adsorbable gas capacity and compares their relative merits. Gases which are condensed on the pumping arrays required considerations different from those which are adsorbed. A cyclical test has been developed and standardized for in-house use which provides information on pumping speed stability and condensation characteristics of cryopumps.
Scrubbing characteristics of CCl4 and C2F6 with a titanium sublimation trap
Authors: Hu Yao-Zhi
Published: July 2002

A quadrupole mass spectrometer with a mass range from 1 to 200 amu gives much useful information about scrubbing of contaminated effluent gases with a titanium sublimation trap. The gases investigated are CCl4 and C2 F6, which have been used to etch semiconductor materials in a glow discharge. The total pressure of test gases was measured with a capacitance manometer. The detailed experimental results of CCl4 for both continuous and intermittent titanium evaporation under various conditions are presented. It is shown that the major constituents in the residual atmosphere are always H2, CH4, and C2 H6. The toxic gas, comprised of mostly chlorine rather than the parent CCl4, was of the order of 0.1% of the total pressure. The efficiency of the trap was demonstrated even though the stainless-steel trap was not cleaned over one month. However, the titanium surface was almost inert for C2 F6.
Vacuum vessel heating system for the Advanced Toroidal Facility
Authors: Langley R. A. , Neilson G. H. , Alban A. M. , Slaughter E. , Sumner J. N. , White J. A.
Published: July 2002

An 80-kW system for heating the Advanced Toroidal Facility (ATF) stainless-steel vacuum vessel to 150 °C, the design limit of the vessel, has been designed. The system’s primary purpose is to accelerate the outgassing of the vessel walls during the initial pumpdown following an opening to atmospheric pressure. It will also measure the thermal time constant of the vessel. These measurements are important for assessing the vessel’s power-handling capability. The main body of the vessel is induction heated by applying 440-V, 60-Hz power directly to the main torsatron windings. The eddy currents that this power induces in the vessel produce an estimated 50 kW of joule heating. The vacuum vessel temperature is measured with an array of thermocouples. A programmable logic controller regulates the temperature and provides interlock and overheating protection. A system of 60 heating tapes, each rated at 520 W, is installed on the ports and ducts attached to the vessel. This system, in conjunction with the induction heating system, is planned to provide temperature uniformity. The total heating power and rates of rise and fall of the vessel temperature have been calculated using a model of the vacuum vessel. The results are given.
Photon stimulated gas desorption from pure aluminum
Authors: Iwata T. , Kanazawa K. , Ishimaru H.
Published: July 2002

To investigate photon stimulated gas desorption from a sample inside, it is necessary to separate the gas desorption from the sample surface and the one from inside. When a sample has no inside gas content, does photon stimulated gas desorption soon become very small after surface gas is cleaned away? An experiment using a thin film carefully prepared at an ultrahigh vacuum can give this answer. The gas desorption experiments were carried out in a molecular-beam epitaxy apparatus made of aluminum alloys with special surface treatments. The apparatus is connected with the TRISTAN accumulation ring. Synchrotron light can be applied on samples in the apparatus. Pure aluminum films were prepared by vacuum evaporation (99.999% aluminum) on a silicon wafer in the pressure range from 10−9 to 10−8 Torr. Gas desorption measurements were made at a pressure around 10−10 Torr using ionization gauges and a quadrupole mass analyzer. Photon stimulated gas desorption of a pure aluminum sample was small compared to other materials. Now the experimental apparatus is being improved to measure the very low gas desorption yield more precisely. The final purpose is to make clear the relation between an internal gas content of material and photon stimulated gas desorption.
Electrical and structural characteristics of thin epitaxial dielectric films formed by i
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i
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u rapid isothermal processing
Authors: Radpour F. , Singh R. , Krisa W. L. , Chou P. , Rahmati M. , Chen C. F. , Narayan J.
Published: July 2002

Growth of epitaxial dielectrics of II-A fluorides on Si and compound semiconductors has generated considerable research interest in recent years. In general, molecular-beam epitaxy and vacuum deposition techniques are being employed for the epitaxial growth of II-A fluorides on semiconductor substrate maintained between ∼400 and 900 °C during the deposition of dielectric material. With the typical deposition rate of ∼1 to 2 Å/s, 8–17 min are required to deposit 1000 Å of dielectric material. This type of prolonged heating may not be suitable for future submicron and three-dimensional Si integrated circuits, as well as for compound semiconductor devices. We have developed a new reduced thermal budget (product of processing temperature and time) processing technique for the deposition of epitaxial dielectric films on Si and compound semiconductors. In this process, epitaxial dielectric film is deposited in the electron beam system at room temperature and subsequently subjected to in situ rapid isothermal processing by using incoherent light sources incorporated in the electron beam system. In this paper, electrical and structural characteristics of thin epitaxial dielectric films on Si, GaAs, and InP are described.
Effects of plasma stripping on the oxidation states of aluminum–silicon and tungsten surfaces
Authors: Hackenberg J. , Linn J.
Published: July 2002

Dry removal of photoresist has recently undergone several process developments that allow for rapid removal rates well in excess of 2 μ/min. Several commercially available resist strippers have utilized microwave frequencies and elevated temperatures with oxygen to achieve these rapid strip rates. This reactive oxygen atmosphere has an effect on the oxidation states of metal conductors such as aluminum–silicon and tungsten, by formation of thicker oxide layers than normal air passivation. Exposure to hydrogen/nitrogen plasmas reduces the oxide layer to less than that of normal air passivation.
X-ray photoelectron spectroscopy studies of enameled steels
Authors: Paparazzo E. , Fierro G. , Ingo G. M. , Sturlese S.
Published: July 2002

X-ray photoelectron spectroscopy is used for studying, both qualitatively and quantitatively, the chemistry of steel/enamel interfaces. Experimental evidence is presented that high adherence is achieved when the interface consists of a single, fully reacted iron silicate plase. Conversely, poor adherence is characterized by an iron silicate phase plus some unreacted FeO. The presence of this latter phase derives from the fact that oxide formation by the steel is unbalanced by oxide dissolution through glass attack, whereas there is no evidence for FeO diffusion into enamel. Our results lend experimental support to the chemical theories of adherence at steel/enamel interfaces.
Diffusion of silicon in Pd2Si during growth
Authors: Comrie C. M. , Egan J. M.
Published: July 2002

The diffusion of silicon in Pd2Si during silicide formation has been studied with the aid of radioactive 31Si. Annealing samples with the structure Si〈 〉/31Si/Pd at 350 °C produces Pd2Si in which the 31Si is broadly distributed throughout the silicide, thereby indicating a very high silicon self-diffusion in Pd2Si during silicide formation. Since silicon self-diffusion in Pd2Si in the absence of growth is low at these temperatures, this suggests that silicon diffuses by a vacancy mechanism during polycrystalline Pd2Si growth. If samples with the structures Si〈111〉/epitaxial Pd2Si/31Si/Pd are annealed at the same temperature, the 31Si is found to be broadly distributed throughout the subsequently grown Pd2Si, but very little diffusion of 31Si back into the epitaxial region is observed. It is argued that a silicon vacancy mechanism is the most probable diffusion mechanism to have produced the observed 31Si distribution and it is therefore proposed that silicon diffuses by a vacancy mechanism in both polycrystalline and epitaxial Pd2Si growth.
Space-charge-limited currents in molecular-beam epitaxy grown CdTe
Authors: Graft R. , Dinan J. , Lee U. , Fischer T. , Ramsey J. , Golding T. , Wilson H.
Published: July 2002

Space-charge-limited (SCL) current measurements on molecular-beam epitaxy grown CdTe epilayers are reported. Trapping effects are clearly evident and classic SCL IV curves are obtained for both HgCdTe and InSb substrates. Analysis of an observed Ohmic–SCL crossover for Vbias ≂0.3 V yields the following electrical properties for the thin-film CdTe (at 300 K): electrical resistivity=4×109 Ω cm; EFermi =0.67 eV above the valence-band edge, and free thermal charge=2×107 holes/cm3 . Temperature-dependent measurements show that the Fermi level moves toward midgap with increasing temperature, possibly due to thermal filling of deep donor levels. Quantitative interpretation of the magnitude of the measured SCL current requires the existence of an Ohmic conduction path at or near the growth interface.
Characterization of CdTe polycrystalline films by x-ray photoelectron and Auger spectroscopies
Authors: Zelaya O. , Sánchez-Sinencio F. , González-Hernández J. , Peña J. L. , Farías M. H. , Cota-Araiza L. , Hirata G. A. , Rábago F.
Published: July 2002

Using x-ray photoelectron spectroscopy (XPS) and scanning Auger microprobe (SAM) techniques we have studied the stoichiometry and contamination of CdTe polycrystalline films grown by the hot wall close-spaced vapor transport technique. XPS and SAM analyses show that the density of impurities in the bulk of the films is <1018 cm−3. Cross sections of the CdTe films perpendicular to the surface–glass interface were exposed by cleaving in vacuum. SAM measurements on these surfaces show that small concentrations of C impurities appear on some regions and some others present only Cd and Te. Thus, we intend to show that films produced with this technique are reasonably free of bulk contamination.
Determination of the local electronic structure of atomic-sized defects on Si(001) by tunneling spectroscopy
Authors: Hamers R. J. , Köhler U. K.
Published: July 2002

Tunneling spectroscopy and voltage-dependent scanning tunneling microscopy have been used to study the geometry and electronic properties of atomic-sized defects on the Si(001) surface. Individual dimer vacancies are shown to be semiconducting, consistent with the π-bonded defect model of Pandey. Another type of characteristic defect is found which gives rise to strongly metallic tunneling I–V characteristics, demonstrating that it has a high density of states at the Fermi level and is likely active in Fermi level pinning on Si(001). Spatially dependent I–V measurements and tunneling barrier height measurements also directly reveal the spatial extent of this metallic character and provide direct measures of the ‘‘size’’ of the defects.
Scanning tunneling microscopy studies of structural disorder and steps on Si surfaces
Authors: Swartzentruber B. S. , Mo Y.-W. , Webb M. B. , Lagally M. G.
Published: July 2002

Scanning tunneling microscopy observations of several forms of disorder on Si surfaces are presented. These include dimer vacancies on Si(001), step bunches associated with a morphological phase transition on vicinal Si(111), and step structure on vicinal Si(001). A recipe for cleaning of Si surfaces to produce a minimum amount of disorder is presented.
HgTe/CdTe superlattice band calculation with a transfer matrix method
Authors: Yoo K. H. , Aggarwal R. L. , Ram-Mohan L. R.
Published: July 2002

A transfer matrix method has been applied to study the HgTe/CdTe superlattice system by varying layer thicknesses, valence-band offset, and strain systematically. The energy gap can be understood in terms of a midzone energy separation mainly depending on HgTe layer thickness, and a bandwidth mainly depending on CdTe layer thickness. Strain causes a simple displacement of bands by different amounts for different bands and sometimes causes an interesting band reversal. In the presence of an external magnetic field, optical transition probability and selection rules between Landau levels are obtained.
Measurements of energy and flux of neutrals at the wall in the Tokamak Fusion Test Reactor
Authors: Wampler W. R. , Kilpatrick S. J.
Published: July 2002

The energy and flux of charge-exchange neutral deuterium incident on the wall in the Tokamak Fusion Test Reactor (TFTR) were measured using a carbon resistance probe. This device utilizes the increase in electrical resistance of a thin carbon film produced by the impinging particles. Particle energies and fluxes were determined from the stopping effect of thin layers of silicon over the carbon. Film thicknesses were chosen to give a useful energy range from about 50 to 5000 eV. Time-resolved data were obtained for the first time by using a transient digitizer to record the signals every millisecond during the discharge. The deduced flux and Maxwellian temperature were 0.7×1014/cm2s and kT=350 eV, respectively, during Ohmic heating. Neutral beam heating (10 MW) increased the temperature by a factor of 4 and increased the flux by a factor of 2. The observed flux of neutrals to the wall is large enough for changes in the recycling of these particles to affect plasma fueling significantly.
Surface roughness and fractal nature of thin films of MgF2 and Ag/MgF2
Authors: Varnier F. , Mayani N. , Rasigni G.
Published: July 2002

An extensive study of magnesium fluoride as an underlayer is reported. Its behavior and characteristics are compared to those of the calcium and lithium fluorides previously studied. In addition, the possible fractal nature of the MgF2 films is investigated and compared to that of CaF2 and LiF thin films.
Carbon contaminant in the ion processing of aluminum oxide film
Authors: Chaug Yi-Shung , Roy Nripen
Published: July 2002

Ion processing can induce contamination on the bombarded surface. However, this process is essential for the microelectronics device fabrication. Auger electron spectroscopy has been used to study the simultaneous deposition of carbon impurity during ion bombardment of magnetron rf-sputtering deposited aluminum oxide film. Ion bombardment on aluminum oxide results in a preferential removal of surface oxygen and a formation of a metastable state of aluminum suboxide. Cosputtered implanted carbon contaminant appears to have formed a new state of stoichiometry on the surface of the ion bombarded aluminum oxide and existed as an aluminum carbide. This phase has formed due to the interaction of the implanted carbon and the aluminum suboxide. The Ar+ ion sputter etching rate is reduced for the carbon contaminated oxide. The electrical resistance of the aluminum oxide between two gold strips has been measured. It is found that the electrical resistance is also reduced due to the formation of the new stoichiometry on the surface.
Different response of atomic force microscopy and scanning tunneling microscopy to charge density waves
Authors: Meyer E. , Wiesendanger R. , Anselmetti D. , Hidber H. R. , Güntherodt H.-J. , Lévy F. , Berger H.
Published: July 2002

We have studied the transition metal dichalcogenides 1T–TaS2 and 1T–TaSe2 exhibiting charge density waves (CDW) at room temperature by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with atomic resolution. STM images are dominated by the charge density wave modulation, while the AFM operated with an applied loading in the range of 10−8–10−7 N responds only to the atomic surface structure. Several possible explanations for this experimental result are discussed, including differences in what STM and AFM are sensitive to, as well as a possible local pressure dependence of the CDW state.
The crystallographic and electroluminescent characteristics of ZnS:Mn thin films prepared by radio frequency ion-plating technique
Authors: Kiyota Shigeyuki , Terai Keiko , Kikuchi Norifumi , Kojima Takuma , Takahashi N. Shin-ichi , Kurita Shouichi
Published: July 2002

ZnS:Mn thin films were deposited by a radio frequency (rf) ion-plating technique. The microstructure of the films consisted of a columnar structure and had no dead layer. The grain size was larger than that of films deposited by thermal evaporation. As the dc accelerating voltage increased, the peak intensities of cubic(111) x-ray diffraction became large and the full widths of half-maximum (FWHM) decreased somewhat. It is suggested that energies of the ionized and neutral molecules is increased by the dc field. Electroluminescent (EL) properties of the ZnS:Mn thin films prepared by the rf ion-plating technique have been investigated. As the rf power and the dc accelerating voltage increased, the luminance versus the applied voltage (L–V) curve shifted to lower applied voltage. When the dc accelerating voltage was too large, the L–V curve shifted to higher voltage and the maximum luminance decreased because the substrate insulating layer was degraded. The EL device with the ZnS:Mn layer of 1.0 μm thickness luminesced up to 1500 cd/m2 (1 kHz) without post-deposition annealing.
Test of a visible/near-ultraviolet transmitting, coherent fiber-optic bundle for ultrahigh-vacuum applications
Authors: Klepper C. C. , Simpkins J. E.
Published: July 2002

A visible/near-ultraviolet transmitting, coherent fiber-optic bundle designed for vacuum applications was tested for vacuum compatibility under ultrahigh vacuum conditions at temperatures up to 310 °C. This development was motivated by the need to view the light emitted by neutrals recycling in the throats of large pump limiters, such as the Advanced Limiter Test-II (ALT-II) and the Tore Supra outboard limiter, without access to a direct, unobstructed optical view from an external port at the back end of the limiter. The temperature inside the pump limiter chamber is typically high (∼250 to 300 °C), and the outgassing rate of the fiber-optic bundle must remain low at these temperatures. The fiber bundle that was tested was built as a prototype for a bundle to be eventually used in a pump limiter and is now installed in the pumping duct of the ALT-II pump limiter on TEXTOR. The bundle was designed to be coherent to allow the possibility of imaging a region of the limiter throat onto a spatially resolving instrument.
Characterization of sputter-deposited ZrBxOy films
Authors: Ebisawa J. , Hayashi Y. , Ando E. , Suzuki K. , Matsumoto K.
Published: July 2002

ZrBxOy films for optical durable coating application were deposited by reactive dc magnetron sputtering of Zr–B alloy target on soda-lime-silica glass substrate without intentional heating. Effect of boron content on film properties was investigated. The refractive index of the film was decreased from 2.1 to 1.69 corresponding to the increase of B2O3 content from 0 to 64 mol %. The films containing more than 13 mol % B2O3 fraction were amorphous and showed remarkably improved mechanical durability compared with ZrO2 film. More than 51 mol % B2O3 content resulted in degrading of chemical durability. Measurement of mechanical properties was carried out together with characterization on crystalline structure and chemical binding state.
Electron stimulated desorption effects in secondary ion emission from BF+2 implanted SiO2
Authors: Lanzillotto A-M. , Magee C. W.
Published: July 2002

The effect of electron stimulated desorption (ESD) during secondary ion mass spectrometry (SIMS) from BF+2 implanted SiO2 was investigated. We have quantitatively illustrated that the F+ depth profile is directly related to electron current density while the Si+ and B+ profiles remain nearly constant. We have also determined that ESD produces the same ionic species as does Ar+ bombardment. A mass analysis of ESD species from BF+2 implanted SiO2 has revealed a very extensive ionization from this surface. In addition to F+ , a significant abundance of Si+ , Si+2 , Si+3, and SiO+ ESD was also detected.
Scanning electron microscopy study of surface roughening induced by thermal treatment of Pt under ultrahigh vacuum
Authors: Nishiyama Satoru , Tsuruya Shigeru , Masai Mitsuo
Published: July 2002

The surface roughening of platinum foils thermally treated under ultrahigh vacuum (UHV) has been studied by scanning electron microscopy. Formation of ∼1-μm high roughness was observed on HCl-doped Pt foils which were thermally treated at 1073 K under UHV, whereas no roughening was observed on HCl-doped Pt foil treated at 673 K under UHV. Evacuation under low vacuum (10−2 Pa) at both 673 and 1073 K did not bring about the surface roughening of the HCl-doped Pt foil. In the absence of HCl doping there was never a surface roughening, even though the Pt foil was evacuated at 1073 K under UHV. These results indicate that the surface roughening was attributable to an evolution of HCl from the HCl-doped Pt foil by the thermal treatment. It is clearly indicated that this surface roughening is closely related to the enhanced activity of Pt powder catalysts by UHV treatment.
The spreading resistance technique applied to mercury cadmium telluride heterojunctions
Authors: Boukerche M. , Yoo S. S. , Faurie J. P.
Published: July 2002

The spreading resistance technique has been used to characterize beveled heterojunctions of mercury cadmium telluride grown by molecular beam epitaxy. We show that important information on the growth axis profiles can be recovered when probing both at room temperature and cryogenic temperature. Examples of in situ and ex situ doped structures as well as CdHgTe/CdTe and CdHgTe/HgTe heterojunctions are described. In the latter case the measurements seem to indicate the presence of an inversion layer between the n-type narrow bandgap material and the semimetal.
Scanning tunneling microscopy of the linear chain compounds NbSe3, TaS3, and TaSe3
Authors: Slough C. G. , Giambattista B. , McNairy W. W. , Coleman R. V.
Published: July 2002

Studies of NbSe3, TaS3, and TaSe3 at 77 and 4.2 K with scanning tunneling microscopy (STM) resolve the linear chain structure in all three compounds and detect the superimposed charge-density wave (CDW) modulations present in NbSe3 and orthorhombic TaS3. Two independent CDWs on separate chains are observed in NbSe3 and the STM amplitudes are proportional to the amount of Fermi surface obliteration induced by each CDW. In orthorhombic TaS3 coupled CDW modulations are observed on two of the three surface chains and these are 180° out of phase. In TaSe3 the two surface chains per unit cell are clearly resolved and the surface Se atoms give a STM deflection proportional to the surface atomic heights.
The Wentzel–Kramers–Brillouin method in multidimensional tunneling: Application to scanning tunneling microscopy
Authors: Huang Z. H. , Feuchtwang T. E. , Cutler P. H. , Kazes E.
Published: July 2002

The Wentzel–Kramers–Brillouin method is commonly used for semiclassical approximations to the wave function in both the classically allowed and the forbidden regions of one-dimensional potentials. In a multidimensional space, the method can be adapted to construct wave functions in an ‘‘allowed’’ region from classical trajectories or wave normals. However, in a ‘‘forbidden’’ region, this construction is not very well understood. It has been argued that the approximation can be implemented by constructing a single set of semiclassical paths that satisfy in the forbidden region the same path equations as in the allowed regions. We show that such an approach is generally inapplicable. However, it is correct if the incident wave is normal to the turning surface. In general, the wave function in the forbidden region is specified by two sets of wave fronts, the equiphase and the equiamplitude surfaces. We present a formal scheme for constructing these wave fronts. This reveals that for non-normal incidence the paths are not the solutions of a single set of ordinary differential equations, such as Newton’s equations of motion for the trajectories in the allowed region. The analysis enables us to answer some of the basic questions concerning tunneling in multidimensional nonseparable potentials.
Scanning tunneling microscopy images of carburized nickel alloys
Authors: Harada Shûzi , Goda Masaki
Published: July 2002

Tunneling images of carburized nickel (100), (110), and (111) surfaces were obtained with a scanning tunneling microscope (STM). Atomic images of graphite deposited on a single nickel surface were observed. The atomic distance and alignment of carbon in the above images were, however, different from those of highly ordered pyrolytic graphite. These modifications were discussed from a viewpoint of the effect of the nickel surface.
Organometallic chemical vapor deposition of SnO2 single crystal and polycrystalline films
Authors: Vetrone Jim , Chung Yip-Wah
Published: July 2002

Tin oxide films were deposited by organometallic chemical vapor deposition using tetramethyltin and oxygen as reactants. Possibilities for single crystal growth were investigated by depositing thin films at various growth conditions and on several different orientations of rutile titania and sapphire single crystal substrates. Single crystal films were deposited on titania (110) oriented crystals. The morphology of these films appears practically featureless at 40 kx in a scanning electron microscope. Atomic resolution images of these films were also obtained using atomic force microscopy. Highly textured polycrystalline films were grown on rutile titania (100), (001), and (111) oriented single crystals. X-ray diffraction results show that the orientation of these films follows that of the substrate. Single crystal films having a submicron sized morphology were deposited on sapphire (11̄02) crystals. Films grown on sapphire (0001) substrates are polycrystalline and show strong (200) or (110) texture depending on the growth conditions. Highly (110) textured films were also deposited on fused quartz substrates at growth temperatures below 475 °C and deposition rates lower than 0.3 μm/h. The dependence of film morphology and preferred orientation on substrate and growth conditions is discussed.
Hydrogen wall pumping on electron beam evaporation of graphite during radio-frequency discharge with hydrogen
Authors: Akaishi K. , Asano M. , Kubota Y. , Miyahara A.
Published: July 2002

A model for the mechanism of hydrogen wall pumping in fusion devices has been proposed. In this model the following process is assumed as a trigger for wall pumping: carbon evaporation occurs first under high heat loading of a graphite first wall, and pumping for hydrogen is generated simultaneously due to trapping of energetic hydrogen particles onto the fresh carbon film formed as a result of the carbon evaporation on the wall. The demonstration experiment for the hypothesis has been made in a vacuum coater having physical vapor deposition facilities. It is observed that the wall pumping for hydrogen or deuterium gas occurs in the coater, when carbon vapor is generated with an electron beam evaporator in a hydrogen or deuterium plasma produced with a radio-frequency discharge, and is deposited on surrounding wall surfaces. As a result of the experiment, the typical pumping speed for the hydrogen or deuterium gas is estimated to be as large as 5×10−2 ℓ/s cm2 (2×1015 molecules/s cm2 ) at a carbon deposition rate of about 2×1016 C/s cm2 onto a wall having total surface area of 1000 cm2 and in the presence of hydrogen or deuterium plasma having electron density of about 2×109 cm−3.