bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of secondary electron from the substrate in x-ray lithography using harder radiation spectra
Authors: Itoga K. , Marumoto K. , Kitayama T. , Sumitani H. , Amemiya M. , Watanabe Y.
Published: July 2002

Proximity x-ray lithography using harder spectra has been proposed as a next generation lithography technology. The secondary electron from the substrate is one of the issues that should be solved to realize this technology. We investigated the effect of the electron from the silicon substrate on the pattern quality when using the shorter wavelength exposure. As a figure of merit for the effect of the electron from the substrate, we proposed a function R which is defined as the ratio of the energy absorption in the substrate to that in the resist. We confirmed the validity of R by comparing it with a Monte Carlo simulation (SPEED). Several exposure experiments, which corresponded to various R values, were carried out by changing mirror, filter, and mask membrane. We found an adequate range of R where the secondary effect can be ignored from these experiments. Furthermore, we showed that R could effectively be reduced by using an absorption edge of the resist material. Bromine is the best material to suppress the value of R in every wavelength region.
Electron induced chemical nanolithography with self-assembled monolayers
Authors: Geyer W. , Stadler V. , Eck W. , Gölzhäuser A. , Grunze M. , Sauer M. , Weimann T. , Hinze P.
Published: July 2002

We demonstrate a simple scheme to generate chemical surface nanostructures. Electron-beam writing is used to locally modify the terminal nitro functionality in self-assembled monolayers of 4′-nitro-1,1′-biphenyl-4-thiol to amino groups, while the underlying aromatic layer is dehydrogenated and cross linked. Using low energy electron proximity printing and conventional electron-beam lithography with a beam energy of 2.5 keV and doses from 2500 to 50 000 μC/cm2, templates of reactive amino sites with lateral dimensions down to ∼20 nm could be fabricated. The templates were used for the surface immobilization of fluorinated carboxylic acid anhydrides and rhodamine dyes. The molecular structures were then imaged and analyzed by atomic force and scanning confocal fluorescence microscopy.
Progress in the Continuous Observation of Thin-Film Nucleation and Growth Processes by Electron Microscopy
Authors: Poppa Helmut
Published: July 2002

A brief review of past work on the continuous observation of thin-film growth processes through electron microscopy is followed by a discussion of the advantages and limitations of the in-situ technique. Experimental measures of improving the applicability of in-situ observations, specifically the improvement of vacuum conditions at the site of the electron microscope specimen, are described. The heterogenous nucleation of silver from the vapor phase on amorphous carbon is used to illustrate the feasibility of quantitative nucleation experiments inside an electron microscope. Absolute nucleation rates were measured directly and through detailed analysis of the nucleus size distribution function. It was found that the nucleation rate is time-dependent and corresponding activation energies for adsorption and surface diffusion assume reasonable values.
In Situ Transmission Electronmicroscopic Study of Crystal Growth by Chemical Vapor Deposition
Authors: Gabor Thomas , Blocher John M.
Published: July 2002

A gas-reaction chamber has been constructed, which allows the in situ transmission electronmicroscopic study of gas-solid reactions at temperatures up to 900 °–1000 °C. The morphological and crystallographic properties of iron, of iron and wüstite, and of magnetite depositing epitaxially on (111) gold substrates, either by the thermal decomposition of Fe(CO)5 or by decomposition and chemical reaction from Fe(CO)5–H2 or from Fe(CO)5–H2–H2O mixtures, are described. In other examples, the oxidation of the initially depositing iron is illustrated. In some of the experiments, polycrystalline iron foils were substituted for the (111) gold substrates, and a profound effect of iron deposition on the rate of grain growth in the iron foil was found. Coalescence of iron crystallites and high mobility of the deposit were observed. Incidental observations on the decomposition of Ni(CO)4 are described. These permit comparison of the epitaxial relationships in the Ni–Au and NiO–Au systems with those of the corresponding iron systems.
OWL II pulsed-electron-beam generator
Authors: Frazier G. B.
Published: July 2002

OWL is a water-dielectric line-type pulse generator capable of producing ∠100-nsec electron beams with total energies of as much as 150 kJ. In its present form, OWL II consists of an oil-immersed, 1/3-MJ Marx generator charging a 3.9-Ω coaxial pulse-forming line which is series switched into either a two- or three-stage impedance transformer. The output impedance is 1.9 or 1.1 Ω, depending upon which transformer is used, and nominal beam outputs in the two cases are 1.3 MV at 0.8 MA and 0.9 MV at 1.2 MA, respectively. The pulse width can be selected at either 60 or 120 nsec (FWHM of power) by interchanging two available pulse lines. Shot-to-shot reproducibility in output of ±2% with a mean electron energy ∠1.0 MeV is obtained with the 1.9-Ω final transformer. A triggered multichannel water switch minimizes the risetime of pulses injected into the transformer section.
Evaluation of metal-film adhesion to flexible substrates
Authors: Goldstein Lester F. , Bertone Thomas J.
Published: July 2002

Techniques for evaluating the adhesion of thin metal films deposited onto flexible substrates have been reviewed. The use of the scratch test for this application has been examined, and a correlation between scratch-test results and actual failure during simulated usage is presented. It was found that aluminum adheres more strongly to Teflon than does silver for the specimens tested and that the failure modes for these two metal–dielectric interfaces are substantially different. The shearing stresses required to remove the films from their substrates have been calculated and are in close agreement with previously reported data on rigid substrates.
High-pressure characteristics of the quadrupole ion trap
Authors: Dawson P. H. , Lambert C.
Published: July 2002

Quadrupole mass analyzers are able to operate at relatively high pressures, but few detailed measurements of their behavior in this region have been made. The quadrupole ion trap was used to investigate the influence of added gases on the 28-amu peak and to assess the importance of various collision processes.
Abstract: Surface analytical studies using ion scattering spectrometry, Auger electron spectroscopy and secondary ion mass spectrometry
Authors: Heiland W. , Taglauer E.
Published: July 2002

Ion scattering spectrometry (ISS), LEED and Auger electron spectroscopy (AES) are combined in one apparatus. By this means the ISS signal can be calibrated as a function of surface composition. This is done for the case of sorption of O and S on Ni. 1,2 By assuming appropriate cross sections an estimate of relative neutralization yields is possible. For the scattering of Ne+ from sulfur adsorbed on nickel the neutralization seems to be a factor of 7 lower than in the case of Ni so that the surface sensitivity is very good (Fig.1). From this figure a detection limit of 10−4 of a monolayer of S on Ni is estimated.

In the case of oxygen adsorption of Ag (110) no simple relations between oxygen signals detected by AES and ISS and the observed LEED pattern have been established. Both signals increase in proportion to the change of the work function with increasing exposure, whereas the Ag signal from ISS decreases (Fig.2). But in the exposure range where (3×1) to (2×1) LEED patterns are observed the oxygen concentration according to AES and ISS does not change from 0.3 to 0.5 of a monolayer. A naive interpretation of the Ag−ISS signal by shadowing may not be justified in that case, even though the detection of oxygen by ISS is a strong indication that at least part of the oxygen is adsorbed above the silver atoms. 4

For many problems ISS can be improved by using an electrostatic anlyzer and a quadrupole mass filter in series, 5 especially when a high yield of true secondary ions buries the peaks of backscattered ions (Figs.3 and 4). In the case of the Nb−Cu sample the high ion yield is due to oxygen contamination of the Nb as shown by the He+ backscattering spectrum, whereas in the Cu−Be case it is obviously due to BeOH contamination as shown by the secondary mass spectrum. This is recorded by using the electrostatic analyzer as an energy window, the secondary ions being accelerated to the appropriate energy. Figure Captions Fig. 1. Auger electron spectroscopy and ion scattering from a S−covered Ni surface. The S concentration amounts to about 0.02 of monolayer. From the spectrum with low impact angle (Ψ = 10,0°) and low scattering angle the sensitivity is estimated to 10−4 of a monolayer. Fig. 2. Auger electron spectroscopy and ion scattering from a O−covered Ag surface. The work function change Δ φ is reported by Engelhard et al.. 3 Fig. 3. Ion scattering from a Nb−Cu surface contaminated by O. The sputtered ions are suppressed by using a mass filter in series with an electrostatic analyzer. Fig. 4. Same technique as used for Fig. 3 in case of a Cu−Be sample.
Steady-state mass balance approach to substrate biased rf sputtering
Authors: Dove D. B. , Gambino R. J. , Cuomo J. J. , Kobliska R. J.
Published: July 2002

An analysis is given of the net mass flux from target to film during steady-state substrate biased rf sputtering. Expressions are derived for film composition and growth rate in terms of relative sputtering rates of atomic species in the surface region of the target and film, and the geometrical transfer efficiencies between target and film. Calculations have been carried out of predicted film composition as a function of substrate bias voltage for several cases, and a comparison is made with experimental data.
Thin-film deposition using low-energy ion beams (3) Mg+ ion-beam deposition and analysis of deposits
Authors: Amano J. , Lawson R. P. W.
Published: July 2002

The energy dependence of the growth characteristics of Mg thin film s on C substrates deposited by retarding a 4-keV mass-analyzed ion beam of Mg+ ions to a range of energies between 24 and 500 eV has been studied by Rutherford backscattering analysis and scanning electron microscopy. An incident Mg+ beam energy of about 100 eV produced the optimum film−in the shortest time when the space-charge spreading of the beam at low energies is compared with self-sputering of the deposit at the higher energies. This is though to be due to deeper penetration of the Mg+ ions into the C substrates above 100 eV.
Properties of the silicon–SiO2 interface
Authors: Williams Richard
Published: July 2002

The combination of thermally grown oxide on silicon has achieved preeminence in technology because of its remarkable properties. As a result of extensive investigation, many of the properties of the interface are well understood. This article reviews the main lines of evidence for our present understanding. The energy-band relations at the silicon–SiO2 interface have been determined mainly by measurements of internal photoemission. These data can be combined with the results of C–V measurements to give a detailed picture of the behavior of mobile ions in the oxide.
Chemical preparation of GaAs surfaces and their characterization by Auger electron and x-ray photoemission spectroscopies
Authors: Chang C. C. , Citrin P. H. , Schwartz B.
Published: July 2002

Surface regions of GaAs crystals treated by removal of anodically grown oxide layers with aqueous HCl and NH4OH solutions were investigated with Auger electron and x-ray photoemission spectroscopies. After treatment and air exposure, the surfaces were covered with about 10 Å of oxide consisting of Ga2O3 and As2O3. Semiquantitative estimates of the surface compositions revealed that after removal of the anodic oxide with HCl etch, the surfaces contained excess As, up to 10 Å of carbon contamination, and small quantities of S, Cl, Ca, and N. The excess As originates from a pileup of elemental As at the oxide/GaAs interface during oxide growth. The As-rich surface is highly reactive and readsorbs contaminants from the air and/or the etch-rinsing solutions. By contrast, after removal of the anodic oxide with NH4OH etch, the surfaces contained much less excess As, carbon, and contaminants. The most reproducible results were obtained by following a procedure developed in this work which produced surfaces containing only about 0.5 Å carbon and no detectable excess As or contaminants. The procedure involves a thick anodic oxide growth and NH4OH etch to remove contaminants, followed by a light anodic oxidation and NH4OH etch for eliminating the excess As. A charged vacancy model for anodic oxide growth is advanced which accounts for the chemical composition throughout the anodic oxide. The model for the accumulation of excess As at the oxide/GaAs interface indicates that this pileup is difficult to avoid and may contribute to the band bending and stabilization of the GaAs surface potential near midgap.
Almost perfect epitaxial multilayers
Authors: Matthews J. W. , Blakeslee A. E.
Published: July 2002

Multilayers composed of many pairs of GaAs and Ga(As0.5P0.5) layers have been grown epitaxially on substrates whose lattice parameter matched that of the multilayer taken as a whole. The thickness of the individual layers in the multilayer was such that it was not energetically favorable for misfit dislocations to be made. Examination of thinned portions of these samples in a transmission electron microscope operating at 200 kV revealed that they were almost dislocation-free. They contained a few long dislocations that were present to accommodate part of the imperfect matching of the multilayer to its substrate. Images of these long dislocations were used to determine the planarity of interfaces between layers. It was found that the interfaces were flat to within the accuracy of measurement.
Optimization of Al step coverage through computer simulation and scanning electron microscopy
Authors: Blech I. A. , Fraser D. B. , Haszko S. E.
Published: July 2002

Minute cracks in integrated circuit metallization at step edges constitute a very real hazard to device reliability. The computer simulations of metal film deposition reported in this study are in excellent agreement with SEM photographs of actual film step coverage obtained on unheated substrates. The use of the simulation technique to optimize step coverage has led to the modification of the planetary system used to support the wafers in the electron beam metal deposition apparatus. However, even with optimization of the planetary-source configuration, small cracks in metal films at steps occur if the step angles are greater than a maximum value determined by the system geometry. For the deposition system used in this work that maximum angle is 40°. However, steps with angles of 50° have been successfully coated with crack-free films when the substrates are heated above 300°C during deposition. We conclude that good step coverage may be obtained by optimization of the source-planetary configuration in the deposition apparatus, by controlling the substrate step profiles and by the use of elevated substrate temperatures.
Advances in cleaning metal and glass surfaces to micron-level cleanliness
Authors: Stowers Irving F.
Published: July 2002

A high-pressure 6.9-MPa liquid spraying technique has been developed to remove small (≳5 μm) contaminant particles from large (100 m2) surface areas. Chemically polished and etched 304 stainless-steel components are solvent sprayed to achieve cleanliness levels of less than 10 particle/cm2≳5 μm diameter. The high-pressure and high-liquid-velocity cleaning technique can remove 99.9% of ≳5-μm-diam particles in 5–10 s compared to only 20–60%≳5-μm particles by ultrasonic cleaning in 2–10 min. High levels of particulate cleanliness are required for large solid–state laser systems where contaminants may migrate to optical surfaces and cause severe pitting. The pitted glass must be removed and periodically repolished to maintain acceptable beam quality. Special Class 100 clean room procedures and equipment have been developed to determine the degree of cleanliness of laser components and to maintain cleanliness during installation and operation. Development of these cleaning procedures resulted in greatly reduced failure rates for solid-state disk amplifiers. Although developed specifically for cleaning optical components, the basic technique should find wide application in any field requiring particulate-free surfaces.
Surface structure and orbital symmetries of (110) surface states of GaAs
Authors: Chadi D. J.
Published: July 2002

The orbital symmetries of (110) surface electronic states of GaAs for three different surface-relaxation models are analyzed using the tight-binding method. Although the atomic displacements involved in all three relaxations are basically very similar, they give rise to different orderings of some surface states when these states are characterized by their orbital symmetries. Angle-resolved photoemission measurements using polarized radiation therefore provide a useful tool for distinguishing between competing surface structures determined from low-energy electron-diffraction studies. A comparison of the recent, preliminary measurements by Williams and Lapeyre with our theoretical results shows that only the ’’bond-relaxation’’ model for the surface is in agreement with the experimental results. Local densities of surface states and the orbital symmetries of surface states are discussed.
High-current ion source for use on the PR-30 implanter
Authors: Williams N.
Published: July 2002

An ion source of the Freeman type has been extensively reworked and tailored for the routine production of dopant species on the PR-30 ion implantation machine. The modified source is presently used on several such machines within the Bell System, routinely producing intense beams of B+, P+, As+, and Sb+. Typical PR-30 target currents for the above species are 1, 5, 6, and 5 mA, respectively, with peak currents about 20% higher than these figures. With the possible exception of B+, these beam current intensities are the highest presently available for implantation applications. Further studies on improved B+ production are being pursued. BF3 gas is used as a feed for B+ production and solid charges are used for P+, As+, and Sb+, ususally without a carrier gas, so as to maintain maximum beam purity. The source lifetime is typically 30–60 h at the above current levels and is limited by filament sputtering. Operation of the source is relatively facile and good beam stability can be obtained.
An XPS/AES study of films on electroplated Co–Sn alloy
Authors: Thomas J. H. , Sharma S. P.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and AES have been used to study the chemistry of the native oxide film which occurs on electroplated Co–Sn (20% Co, 80% Sn) alloy and the films which form on a sputtered Co–Sn surface exposed to pure oxygen. The native oxide is similar in composition to that which forms on Sn–Ni, that is, the film is primarily stannic hydroxide (or hydrated SnO2). The films on sputtered Co–Sn exposed to pure oxygen vary in chemical composition with the exposure and are different than the native oxide. At low exposures (<10−1 Torr min) the film is primarily SnO with only a trace of cobalt oxide. At higher exposures (∠10 Torr min or higher) the film consists of SnO2 and CoO. Film thicknesses as a function of exposure have been computed from XPS intensity measurements and vary from 6.7 to 10.5 Å.
Plasma stream transport method (2) Use of charge exchange plasma source
Authors: Tsuchimoto Takashi
Published: July 2002

The plasma stream transport method using a single plasma source has limitations for practical film deposition. Using a charge exchange phenomenon, a new plasma source is devised and tested by the plasma stream transport machine. Metals, silicon dioxide, and nitride films are deposited by this system. The mechanism of deposition under relatively high vacuum surrounding a silicon wafer is discussed as is the effect of radical atoms.
Conduction processes and threshold switching in amorphous Si films
Authors: Dey S. K. , Fong W. T. J.
Published: July 2002

Electrical conduction processes in a-Si films prepared by electron-beam evaporation in a Ti–Si–Ti sandwich structure are investigated following a switching sequence. The results show a Poole–Frenkel-type conduction above 104 V cm−1 but the ratio, βPF/βm(βm= measured coefficient), varied from 0.63 to 1.89 within the samples investigated and temperature range. A discrete activation energy of 0.21 eV was obtained in the region −75°C to +25°C. However, at very low temperature a T−1/4 dependence appropriate to the hopping conductance was obtained. Further support to the above was derived from the observed power-law dependence of ac conductivity on frequency and very low activation energy. The σαωs graph gave a value of s=2.28 which was unaffected by temperature. The higher than quadratic frequency dependence together with other few departures from theories prove that although the amorphous nature of the film is retained after ’’forming’’ the structure is significantly disturbed and both material and phase changes are likely. Finally, the observed opposite effects of low and high frequency on delay time is explained in terms of an electrothermal model for switching.
Growth of CuInSe2 films using molecular beam epitaxy
Authors: White F. R. , Clark A. H. , Graf M. C. , Grindle S. P. , Kazmerski L. L.
Published: July 2002

Molecular beam epitaxy has been used to grow single crystals of CuInSe2 epitaxially on CdS (0001) at 300 °C. Film composition, as determined from Auger spectroscopy, is within a few percent of stoichiometry in our best films, but all films show a variation in Cu concentration at the surface. Polycrystalline films deposited on fused quartz have optical absorption spectra with the same general shape as found in earlier films produced by conventional two-source evaporation, although the value of the absorption coefficient is somewhat higher in the MBE-produced films. Composition control is generally not yet adequate to give consistent electrical properties.
Surface cesium concentrations in cesium-ion-bombarded elemental and compound targets
Authors: Chelgren J. E. , Katz W. , Deline V. R. , Evans C. A. , Blattner R. J. , Williams P.
Published: July 2002

Auger electron spectrometry has been used to characterize the atomic cesium concentration [Cs]a at the surface of cesium ion bombarded silicon and various metal silicides. The Si− ion yield was found to be proportional to [Cs]v2.8±0.1. Surface cesium concentration was also found to increase with increasing inverse sputtering yield S−1 of the substrate. Deviations from a linear dependence of [Cs]v on S−1 are ascribed to differential sputtering effects.
UHV technique for intervacuum sample transfer
Authors: Hobson J. P. , Kornelsen E. V.
Published: July 2002

An alternative to the modern UHV multiport surface analytic system is a transfer technique for intervacuum sample transfer which maintains the sample at UHV (<10−9 Torr) at all times. Major advantages are (1) economical use of available facilities by a number of experimentalists (2) instrument and surface standardization (3) complementary experiments by remote specialized laboratories (4) preparation of samples in specialized facilities (e.g., space shuttle or thermonuclear reactor) followed by a transfer to surface analytic facility. Such a transfer system has been built and tested. Transfers currently take three to four hours between nearby stations. Intercontinental transfers are feasible using a battery operated ion pump during transport. For a transfer a UHV system must have a suitable gate valve (35-mm bore, 10−13 l s−1 helium closed conductance) and a platform capable of accepting a standard 22.8–mm-diam ring, which carries the sample itself.
Low profile electron collector system
Authors: Penberth M. J. , Wallman B. A.
Published: July 2002

The design of the exposure region of an Electron-Beam Microfabrication System is usually a compromise between beam formation, deflection, and registration signal collection. In systems where a post final lens deflection assembly is used, this region is inevitably restricted in space and access for signal collection becomes difficult. Annular planar detectors of the silicon semiconductor diode type have been used in these situations but are restricted in their range of electron energy response and noise performance. An attractive alternative is the channel plate electron multiplier which can be configured into a compact annular assembly with low profile (6 mm). Additionally, it is sensitive to low energy secondary, and high energy backscattered electrons and can be made selectively sensitive to the higher energy electrons alone by suitable biasing. In the design implementation described, an annular channel plate is provided with a signal collection plate and electronic drive scheme to decouple the output signal from the relative high bias potential needed on the plate. The system has proved useful in viewing a variety of registration features in the EBMF 2 Microfabricator ranging from high contrast metallic marks used in drift correction to low contrast etch pits in silicon covered with electron resist for direct slice writing.
Methane outgassing from a Ti sublimation pump
Authors: Edwards D.
Published: July 2002

A Ti sublimation pump together with a small 20 l/s ion pump is typically used as the pump for UHV systems. It is well known that the Ti surface will not pump methane and that the ion pump pumping speed for CH4 is only 1 l/s in the low 10−11 Torr range. Thus it is important to identify and if possible reduce the sources of CH4 outgassing. In this study we report the first quantitative measurements of the methane outgassing rate from a 1500 cm2 Ti sublimation chamber both before and after the Ti evaporation. The contrast to the very low CH4 outgassing rate from the chamber before the Ti is flashed (<10−12 Torr l/s) the CH4 outgassing rate after the Ti evaporation is considerable (4×10−11 Torr l/s) with a very slow decrease with repect to time, and has been found to be significant in terms of the ISABELLE requirements. To essentially eliminate the methane outgassing from the Ti getter chamber, it has been determined sufficient to heat the Ti chamber for four hours at 100 C after the Ti evaporation has been completed. Using a similar procedure a reasonably rapid processing of the ISABELLE vacuum system to an ultrahigh vacuum condition should be possible after an atmospheric exposure.
Atom-probe field-ion microscopy of a high intensity gallium ion source
Authors: Culbertson Robert J. , Robertson G. H. , Kuk Y. , Sakurai T.
Published: July 2002

The emission characteristics of a liquid-metal ion source have been investigated with a magnetic-sector atom-probe field-ion microscope. The emission is classified into low, intermediate, and high intensity emission regimes. In the high intensity emission regime the emission is approximately 99% Ga+, but Ga++ and molecular gallium ions are also present. The relative intensities of Ga+, Ga++, Ga2+, and Ga3+ were measured as a function of total current in the high intensity emission regime. Energy distributions of these four species were also measured at various total currents. Spectral analysis of the optical emission from the ion source indicate that the light is due to radiation from neutral atomic gallium. It is concluded that a considerable amount of gas phase neutral gallium is in the vicinity of the emitter. Also, the ionization of atomic gallium takes place at the emitter surface, while the molecular ions are formed far from the surface.
Infrared study of the interaction between delta alumina and 1-butene
Authors: Bianchi D. , Pajonk G. , Teichner S. J.
Published: July 2002

A new type of IR cell has been recently developed in this laboratory in order to register exclusively the spectrum of the adsorbed reacting phase during the isomerization of 1-butene, between 25° and 110°C. The spectra of the adsorbed phases were of three kinds : two of them are of an olefinic structure and are exhibited by a phase adsorbed reversibly; the third one is of an nonolefinic type and belongs to the phase irreversibly adsorbed. This species is involved in the deactivation of the catalyst during isomerization of 1-butene whereas one of the two first ones is intermediate in this reaction.
Calibrated flow reactor to determine reaction rates: CO–oxidation on Pd(110)
Authors: Goschnick J. , Grunze M.
Published: July 2002

We describe the construction and the principles of operation of a flow reactor designed to obtain reaction rates of heterogeneous reactions over a wide pressure range. In this communication we restrict the discussion to the low pressure region and demonstrate the performance of the apparatus with transient reaction studies for the CO-oxidation reaction on Pd(110).
Pumping of corrosive or hazardous gases with turbomolecular and oil-filled rotary vane backing pumps
Authors: Fischer K. , Henning J. , Abbel K. , Lotz H.
Published: July 2002

Since at high-vacuum pressure the gas density is low, no real problems occur while pumping, e.g., corrosive or even explosive media by means of turbomolecular pumps. New problems arise from pumping radioactive gases like tritium. Here the turbomolecular pumps have to be adapted to the fact that the leakage from the pump’s interior to the ambient has to be kept as low as possible. Backing pumps have to pump higher gas densities. Some corrosive or hazardous gases can be pumped with standard pumps using special pump fluids. Many other applications, however, require protective measures to guarantee acceptable lifetimes of the vacuum equipment. The paper describes the necessary pumps and accessories to meet the requirements of safely pumping vapors and gases in the processes of plasma etching, plasma deposition, low pressure CVD, and explosive gas mixtures.
Theoretical studies of Si(111) surface structures
Authors: Chadi D. J.
Published: July 2002

A brief discussion of the 1×1, 2×1, and 7×7 reconstructed surfaces of Si(111) is given. The emphasis is on surface atomic geometry and its effect on electronic and chemical properties of the surface.
Cyclic pressure fluctuations above rotary pumps and their effects on pumping speed measurements
Authors: Kendall B. R. F.
Published: July 2002

The cyclic pressure fluctuations above a positive-displacement rotary vacuum pump are discussed for the case of constant gas flow into a small test volume attached to the pump. It is shown that the average pressure above the pump rises as the test volume is reduced, leading to a corresponding underestimate of the true pumping speed. The effect was apparently discovered almost thirty years ago, but subsequently misinterpreted as a resonance phenomenon. The apparent reduction of pumping speed can range from a few percent or less for medium-sized pumps up to 20–30 percent for certain extreme cases encountered with large pumps.
Performance of mechanical vacuum pumps in the molecular flow range
Authors: Hablanian M. H.
Published: July 2002

An important and remarkable property of oil-sealed rotary vane mechanical vacuum pumps has been demonstrated. Such pumps retain their positive displacement pumping mechanism at partial pressures approaching the ultrahigh vacuum region. Pumping speed measurements for helium, based on partial pressure, have been made at an inlet pressure as low as 10−6 Pa with an ultimate partial pressure of helium near 10−8 Pa. Experiments conducted with a nominal 3 l/s two-stage pump (Varian 200) demonstrate that a constant pumping speed is maintained at very low helium concentrations as long as the presence of helium at the discharge of the pump is minimal, i.e., as long as the maximum compression ratio for helium is not exceeded. Similar results may be expected with other gases except the pump oil vapor or species outgassing from the pump.
Submicroscopic pattern replication with visible light
Authors: Fischer U. Ch. , Zingsheim H. P.
Published: July 2002

Contact imaging with visible light is possible at submicroscopic resolution because the near field of a radiating object contains information of sufficiently high resolution. In this paper we demonstrate this principle by contact imaging of planar submicroscopic metal patterns with blue light (400 nm). Experimental details are described for two experiments: (1) The shadow of an opaque pattern was recorded on a negative photoresist and developed using permanganate staining. (2) An image of a transparent metal pattern was imprinted onto a molecular dye layer, exploiting the fact that photochemical bleaching of the dye is inhibited by contact with the metal due to energy transfer. Development was by silver decoration. The resolution obtained was 100 nm with the photoresist, and 50 to 70 nm with the dye layer.
A miniature scanning electron microscope for investigation of the interior surface of a superconducting Nb radiofrequency accelerating cavity
Authors: Mathewson A. G. , Grillot A.
Published: July 2002

A miniature scanning electron microscope with an electron beam diameter ∠1 μm has been constructed for high resolution examination at room temperature of the interior surface of a superconducting Nb radiofrequency accelerating cavity. Various objects and surface structures were observed, some of which could be correlated with lossy regions or ’’hot spots’’ detected previously on the outside surface during cavity operation at ?4.2 K by a chain of carbon resistors. No internal surface features were observed which could conclusively be correlated with field emitting electron sources.
Pumping chlorinated gases in plasma etching
Authors: Duval Pierre
Published: July 2002

Plasma etching of aluminum, aluminum alloys, and some other materials involves the use of chlorine-based gases which are particularly corrosive to vacuum systems if precautions are not taken. Emphasizing safety concerns, we will demonstrate the proper use of cold traps, activated charcoal sorbent, and/or inert synthetic fluids to lubricate forepumps, enabling the user to deal with this corrosion problem. The sorption capacity of activated charcoal is discussed for the proper design of sorption traps, and methods of regenerating large cold traps saturated with hazardous products are examined. Information on the use of turbomolecular pumps in reactive ion etching is also given.
Particle and energy transport in the plasma scrape-off zone and its impact on limiter design
Authors: Ulrickson M. , Post D. E.
Published: July 2002

The design of limiters for fusion devices depends critically on the transport properties of the plasma edge. Recent data from Langmuir probe experiments and calorimeter probe experiments on the poloidal divertor experiment (PDX) have provided information about the transport of particles and energy in the edge region of a plasma. These data have been used as input to a simple one dimensional model in which the particle and thermal diffusion coefficients are permitted to be functions of the density and temperature. The transport coefficients deduced from the data are then applied to the cases of the TFTR device and a device like FED/INTOR to predict the optimum design for limiters or pump limiters. The results indicate the optimum limiter should have a concave shape when viewed from the plasma. The effect of the uncertainties in the deduced coefficients on the optimum design performance are also discussed.
Characterization of GaAs(111) surfaces by AES and LEED
Authors: Alonso M. , Soria F. , Sacedȯn J. L
Published: July 2002

A quantitative Auger formalism which allows us to predict the composition of GaAs(111) surfaces with any combination of Ga and As atoms in the outermost bilayer is presented, and applied to the study of (111) surfaces prepared by different combinations of ion bombardment and annealing (IBA), as well as by simultaneous ion bombardment and annealing (SIBA). The formalism predicts the coverage of the only structure quantitatively determined, GaAs(111) 2×2-Ga, and of all the structures reported in the literature for the (111) surfaces. By a SIBA (Ar, 0.6–1 kV, 870 K) treatment, we have obtained for the first time a 2×2 superstructure on the (1̄1̄1̄)As face, corresponding to 1/4 of an As monolayer in the first layer. The effect of the different methods of preparation has been studied by the interaction of the corresponding surfaces with oxygen. The (1̄1̄1̄)As surfaces prepared by SIBA present a sticking coefficient smaller than those obtained on any (111) surface prepared by IBA. Consequently, the sticking coefficient seems to depend strongly on the method of surface preparation, but much less on the degree of saturation of the dangling bonds on Ga atoms of the first layer, as suggested before.
The passivation of electrically active sites on the surface of crystalline silicon by fluorination
Authors: Weinberger B. R. , Deckman H. W. , Yablonovitch E. , Gmitter T. , Kobasz W. , Garoff S.
Published: July 2002

A nonoxide surface passivation for crystalline silicon is described. It involves the fluorination of the silicon surface. Characterization by photoconductive lifetime measurements and C–V measurements on MIS structures indicate that the fluorinated silicon surface is extraordinarily electrically passive, ≲1010 traps per cm2. Our technique for producing such high quality surfaces is described as is a novel gate insulator structure employing organic thin films. Potential device advantages of this alternative to oxide technology are also discussed.
The retention of deuterium and tritium in POCO AXF-5Q graphite
Authors: Causey R. A. , Baskes M. I. , Wilson K. L.
Published: July 2002

The retention of 100 eV deuterium and tritium ions in POCO AXF-5Q graphite has been measured for the temperature range 323–1773 K. Both nuclear reaction analysis and dissolution counting were used. Below 1000 K, the retention is thought to be characterized by saturation of the near-surface region and by surface diffusion on internal porosity. Above 1000 K, the retention appears to be controlled by transgranular diffusion with decoration of high energy traps.
Study of interface formation on PbTe
Authors: Lai B. , Wells G. M. , Cerrina F. , Anderson J. R. , Papagno L. , Lapeyre G. J.
Published: July 2002

We have investigated the formation of the Schottky barrier on bulk PbTe single crystals, cleaved along the (100) surface, for several metal overlayers (Al,Au,In,Pb) by means of photoelectron spectroscopy with synchrotron radiation. We find that the Schottky barrier height varies widely with the metal used thus indicating that the Fermi level is not pinned for these interfaces. Pb and Al overlayers form a degenerate n-type interface, while Au and In give nondegenerate interfaces. The height of the barrier follows the correlation with ΔHR, the interfacial heat of reaction, found for other semiconductors. The index of interface behavior S estimated from our data, 0.2, is in disagreement with the results obtained from other semiconductors, correlating S with the heat of formation of the semiconductor. From a morphological point of view, the interface type is in agreement with predictions based on the heat of interface reaction ΔHR. The interfaces are found to be morphologically very different, ranging from the strongly reacted PbTe:Al to the abrupt and uniform PbTe:Au. In, Pb form a nonreacted interface, with a film growth by islands not yet coalesced in a continuous film at 200 Å of coverage.
Properties of Cr–N films produced by reactive sputtering
Authors: Shih K. K. , Dove D. B. , Crowe J. R.
Published: July 2002

Cr–N films have been produced by reactive sputtering of Cr in an argon–nitrogen atmosphere. The dependence of composition and resistivity of the sputtered films on nitrogen partial pressure in the sputtering gas mixture has been determined. The structure of these films was characterized by x-ray diffraction and found to be polycrystalline in nature with a fiber texture. The Knoop hardness of these films has been measured with values of about 1000 kg/mm2. The temperature coefficient of resistivity is negative and quite large in most of the films.
Investigation of the two-dimensional electron gas in HgCdTe by quantum Hall effect measurements
Authors: Kirk W. P. , Kobiela P. S. , Schiebel R. A. , Reed M. A.
Published: July 2002

By means of the first observations of the quantum Hall effect in a type II–VI semiconducting compound, Hg1−xCdxTe, we have studied the two-dimensional electron gas formed by the inversion layer of a MISFET (metal–insulator–semiconductor field effect transistor) device. Extensive details regarding the fabrication and use of the MISFET are described. The data also indicate an abrupt onset of the quantum Hall effect which, when interpreted with a percolation threshold theory, is used to further investigate conditions affecting charge transport mechanisms in the two-dimensional electron gas at a HgCdTe interface.
Magnetoresistance effect of Ni–Fe film formed by ion beam sputtering
Authors: Nagai Yasuhiro , Toshima Tomoyuki
Published: July 2002

This paper reports the result of experimentally investigating the magnetoresistance effect in Ni–Fe films formed by ion beam sputtering (IBS). Although IBS-formed Ni–Fe film has a well-defined uniaxial magnetic anisotropy and high permeability, its magnetoresistance effect is smaller than that of film formed by radio-frequency (rf) sputtering. This small magnetoresistance effect was found to be caused by an increase in film resistivity rather than by a decrease in magnetoresistivity. The increase in resistivity cannot be explained merely by impurity concentration; it is also due to defects produced by Ar+ ion bombardment and the impingement of particles with relatively high energies. When the substrate temperature was higher than 220 °C, the resistivity became smaller as the substrate temperature was increased because of both having larger crystal grains and recovery of defects.
Ion bombardment effect on preferred orientation in Ni–Fe film formed by ion beam sputtering
Authors: Nagai Yasuhiro , Tago Akio , Toshima Tomoyuki
Published: July 2002

This paper reports on the results of experimental investigation into the preferred orientation of Ni–Fe film formed by ion beam sputtering. Through experiments concerning ion bombardment and substrate temperature, argon ion bombardment is found to increase the amount of the (111) crystal texture in addition to contributing to the texture orientation itself. In terms of film morphology, the fracture cross section indicates a more obvious columnar structure with the film surface becoming slightly rougher as the amount of argon ion bombardment increases. Conversely, nitrogen and oxygen-mixed ion bombardment weakens the (111) preferred orientation, and the effect becomes more notable when the ion has a higher energy. On the other hand, although the substrate temperature increase makes the (111) texture better oriented, the amount of the crystal texture becomes smaller due to this temperature increase. Additionally, the observed lattice distortion corresponds well to that estimated by the internal stress.
Effects of carbon and sulfur on the decomposition of hydrocarbons on nickel
Authors: Kikowatz R. , Flad K. , Hörz G.
Published: July 2002

The kinetics and mechanisms of the decomposition of C2H2, C2H4, and n-C4H10 on polycrystalline Ni resulting in the carburization of the metal have been studied at 1300 to 1500 K and 10−4–10−1 Pa. Special attention has been given to the reaction-retarding effect of surface-segregated carbon. Simultaneous investigations of the reaction rates (by measuring partial pressure changes) and of the nonmetal surface coverages (by applying Auger electron spectroscopy) were carried out in an UHV flow reactor. It was found that hydrocarbon decomposition and carburization are blocked at a certain temperature-dependent concentration of dissolved carbon by the formation of a surface graphitic carbon monolayer in which two C atoms are adsorbed per Ni atom. This monolayer formation is accompanied by surface faceting. The influence of adsorbed sulfur on CH4 decomposition was studied in a flow apparatus by carburizing thin Ni foils in CH4–H2 and CH4–H2–H2S mixtures (1060 to 1280 K, 1-atm total pressure) under conditions where surface reactions are rate controlling. The reaction kinetics were monitored by applying the resistance–relaxation method. For pH2S/pH2 ratios between 8×10−9 and 9×10−5 the initial rate of carburization was found to decrease by a factor of up to 100. The kinetic data are interpreted in terms of the poisoning of active surface sites by adsorbed sulfur. This analysis yields information on the adsorption isotherm for sulfur.
Elimination of backstreaming from mechanical vacuum pumps
Authors: Hablanian M. H. , Bez E. , Farrant J. L.
Published: July 2002

Mechanical vacuum pumps used to obtain pressures near or below 0.1 Pa (∼0.75 mTorr) contain oil for sealing, lubrication, and cooling of internal moving parts. The presence of this fluid at the inlet of the pump provides the possibility of backstreaming and contamination of the vacuum system. The degree of backstreaming depends on the nature of the lubricating fluid, its bulk temperature as well as the friction conditions at the sliding surfaces. The usual choice of dimensional tolerances between rotating and stationary parts is made to obtain a low degree of backleakage and assure low ultimate pressure. However, when pumps are used only for initial evacuation and backing of high vacuum pumps the lowest ultimate pressures are not required. Therefore, possible design avenues were explored in order to eliminate the source of backstreaming from mechanical pumps. If the ultimate pressure is limited to 1 or 2 Pa (∼10 mTorr) the sealing fluid between inlet and discharge parts of the pump can be omitted. In this article a mechanical vacuum pump is described which does not use any oil (or other liquids), but produces an adequate pressure ratio of 50 000 to be useful in many high-vacuum applications.
Entropy-driven surface segregation of Pt in PtRh alloys
Authors: van Langeveld A. D. , Niemantsverdriet J. W.
Published: July 2002

Pt segregation to the surface of PtRh alloys, as reported by several authors, cannot be explained by segregation models based on the enthalpy of segregation alone. However, a model, which includes the influence of lattice vibrational entropy, predicts the surface composition of PtRh alloys correctly over the complete concentration range.
Microdischarges on an electron gun under high vacuum
Authors: Watanabe Hisao , Yoshimura Nagamitsu , Katoh Shoji , Kobayashi Nobuyuki
Published: July 2002

Two types of microdischarges on an electron gun operated at 100 kV—one of which occurs between the high-voltage electrodes and the other over the insulator surface—were experimentally examined, by concentrating the greatest interest on gas molecules on the respective surfaces. Microdischarges between the high-voltage electrodes in high vacuum were induced by gas molecules adsorbed on the electrode surfaces. Argon glow cleaning showed a distinct conditioning effect on the electrode surfaces. Microdischarges over the insulator surface were enhanced by the outgassing from the insulator. The reason is that the insulator surface with a high density of gas molecules causes high yield secondary electron emission, leading to positive charge-up over the insulator surface. Thermal degassing for the electrodes and insulator showed a conditioning effect to reduce microdischarges between the electrodes and over the insulator surface.