bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstract: Segregation at Cu−Au alloy surfaces
Authors: McDavid J. M. , Fain S. C.
Published: July 2002

Theoretical considerations indicate that surface segregation in alloys should be confined to the outer few atomic layers. A model in which the compositions of only the first two atomic layers can differ from the bulk composition was used to interpret in situ Auger measurements on clean Cu−Au(111) evaporated alloy films. Exponential attenuation lengths independent of alloy composition were assumed to be 4, 8, and 30 Å for Au peaks at 72, 239, and 2024 eV. After normalization of alloy Au Auger intensities to those from pure Au, the data were analyzed to determine the compositions of the first two layers and the bulk, including a correction for the change in lattice parameter with bulk composition. The results indicate that segregation in Cu−Au is confined essentially to the top layer, which is gold rich for the large range of compositions studied. Uncertainties associated with backscattering effects, limitations in knowledge of escape depths, and possible lattice parameter changes near the surface are discussed. The observed gold enrichment agrees qualitatively with predictions based on the lower surface energy of gold.
Abstract: Backscattering spectrometry
Authors: Mayer J. W. , Nicolet M−A. , Chu W. K.
Published: July 2002

Backscattering spectrometry is the microanalysis of the surface and near−surface regions of materials utilizing energetic (typically 1−2 MeV) He and H ions as the analytical probe. 1−4 The ions in the collimated beam provided by a particle accelerator penetrate into the target and are scattered at various depths. Analysis of the energy spectrum of the particles backscattered from the target provides information in three areas: identification of atomic mass of the target constituents, the target composition, and depth profiles. Mass identification is provided by the kinematics of the energy transfer between the projectiles and target atom in the collision process. For MeV He ions, the mass resolution is ±1 atomic mass unit (amu) up to about mass 40, and deteriorates to about ±10 amu for the heaviest elements. Quantitative analysis of the number of target atoms per cm2 is provided by the scattering cross section which connects the measured yield of backscattered particles to target composition. In compositional analysis, backscattering only provides atomic ratios, for information on the chemical nature of the material, x−ray diffraction or other tools with chemical sensitivity must be used. Backscattering techniques are most useful to examine heavy elements in a light−element matrix as the sensitivity is rather poor for light elements unless proton resonance techniques are used.

Depth information is provided by the energy loss of the projectiles on their inward and outward paths through the sample. The energy loss of the projectiles per unit path length depends on the energy of the particle as well as on the projectile and target. Compilations (5) and reviews of stopping cross sections are available. For MeV 4He ions, the depth resolution is about 200−300 Å for depths up to 0.5 μ. At greater depths, energy straggling causes a degradation in depth resolution.

Surveys of the applications of backscattering spectrometry are provided in Ref. 1−4. The technique has been used to analyze ion−implanted samples, thin−deposited films, metal−metal thin film interdiffusion, metal film−bulk silicon reactions, solubility of impurities in bulk samples, oxidation processes and other phenomena occurring in the near−surface region of materials.

A typical beam spot is 1 mm2 in area, but for convenient handling, samples should preferably have a size of 1/2−1 cm2. The uniformity of the sample over the area of the beam spot is critical. Since backscattering analysis has no laterial resolution, the samples have to be checked with scanning electron microscopes or with optical microscpoes to verify this assumption.

The primary strength of backscattering analysis is the ability to provide quantitative information on atomic composition ratios and on absolute thicknesses of films in the range of several thousand Angstroms without resorting to standards. Routine accuracies for this information are of the order of ±5%.
Relationship of heat of chemisorption to π- and σ-level shifts as measured by photoemission
Authors: Yu K. Y. , Spicer W. E. , Lindau I. , Pianetta P. , Lin S. F.
Published: July 2002

Ultraviolet photoemission spectroscopy (UPS) has been used to study the π- and σ-level shifts of chemisorbed CO, C2H2, and C2H4 on Fe and Cu. There appears to be no correlation between these shifts and measured heats of adsorption, indicating breakdown of chemisorption theory which does not properly treat the role of the substrate in the bonding. UPS illustrates the importance of the substrate for the understanding of the bonding mechanism.
Abstract: Metal interfaces: Adhesive energies and electronic barriers
Authors: Ferrante John , Smith John R.
Published: July 2002

We report a fully self-consistent calculation of the electron number density, barrier height, and adhesive energy as a function of separation in an Al–Al contact. The electron number density and barrier heights are strong functions of the separation. The range of strong chemical bonding is about 0.4 nm. The results for the interaction energy minimum are discussed in terms of the numerous surface energy calculations appearing in the recent literature.
Windowed discharge lamp for 16–70 eV
Authors: Russo Carl J. , Kaplow Roy
Published: July 2002

An UHV-compatible, windowed, microwave discharge lamp for deep uv photoemission studies is described. The window used has high optical transmission from 16 to 70 eV. A windowed lamp has several advantages over a differentially pumped lamp. These advantages include higher useful light output because of shorter source-to-sample distance, no contamination of the main vacuum system, preferential filtering of various spectral lines, and simpler main- and lamp-vacuum systems. The electrodeless microwave discharge largely eliminates contamination lines found in dc discharges. Windows of 1000–1500-Å Al–Si alloy are made by evaporating the alloy onto Cu electron-microscope grids.
Abstract: Surface depletion in two-component alloys during evaporation
Authors: Arita M.
Published: July 2002

Fractionation is a well known phenomenon which is observed when evaporation takes place from alloys. If liquid alloys are always homogeneous with respect to concentration during evaporation, the degree of fractionation can simply be calculated from the evaporation rate of each component. However, if liquid alloys are poorly mixed, transport processes such as convection and diffusion cannot completely compensate the evaporation loss of the most volatile component, thereby producing a concentration gradient in the alloy phase. This phenomenon, which is called surface depletion of the most volatile component or surface enrichment of the least volatile component, is also seen in the course of evaporation from solid alloys. Surface depletion may be appreciable in such areas as vacuum vapor deposition of alloys,1,2 thermodynamic study of alloys by vapor transport methods,3–5 and preferential evaporation in fast breeder fuel materials (carbides and oxides of uranium and plutonium).6–8

When diffusion is the only transport process in two-component alloys, the boundary condition at the evaporation surface can be expressed as5 (math) where C1 is the concentration of component i in moles per unit volume, r is the distance in the alloy phase, ki is the evaporation rate constant in length per unit time, D is the interdiffusivity, and Vi is the partial molar volume of component i. Not only the second-order property with respect to the concentrations of the boundary equation, but also the fact that the evaporation surface is moving due to evaporation loss, makes it difficult to analytically solve the diffusion equation. However, if the diffusion profile is approximated by some suitable equation and if all the coefficients in Eq. (1) are virtually constant, it is possible to obtain an approximate solution of the surface concentration as a function of time. For the case of a semi-infinite medium with a planar surface, an exponential approximation of diffusion profile gives the following equation for the surface concentration of component 2: (math) where t is the time and yis and yis are the initial and the subsequent values of CiVi. For the case of a planar sheet of initial thickness 2r0, the surface concentration of component 2 is given as (math) The existing theory of surface depletion,9–11 surface movement due to evaporation loss, has been proven5 to be an extremely limiting case of the present theory, i.e., the former theory may be applied when one component is much more volatile and of much less amount than the other component. When this condition is met, k2≫k1 and V1C1?1; hence, Eq. (1) approximately becomes dC2/dr= −(k2/D) C2, which is the boundary condition at the evaporation surface in the existing theory. Applications of the present theory to available experimental works on evaporation from alloys have been made elsewhere.5
Operating experience with an UHV system in the vicinity of a fission-reactor core
Authors: Dobrozemsky R.
Published: July 2002

For an experiment on neutron decay, an UHV system has been developed for a tangential beam-tube insert of the ASTRA reactor (peak dose and flux density in the beam tube at 8 MW reactor power: 44 Mrad/h and 4×1012 nth/cm2 s, respectively). The central section of the beam-tube insert is evacuated mainly by means of a Zr–Al getter pump, giving an effective pumping speed of 40 l/s (N2 equivalent) for the irradiated section. The main vacuum system is situated outside the reactor shielding and is evacuated by a pump combination (orbitron pump, titanium-sublimation pump, and sputter-ion pump); preevacuation is achieved by cryosorption pumps. During reactor operation the pressure can be kept <10−5 Pa in the irradiated section of the beam-tube insert (<10−7 Pa for the reactor switched off). The radiation-induced desorption (RID) yields mainly CO2 and CO for the residual gas atmosphere. Experience from a three-year operation of this vacuum system is discussed in detail.
Schottky-barrier height of Au/p-InGaAsP alloys lattice-matched to InP
Authors: Escher J. S. , James L. W. , Sankaran R. , Antypas G. A. , Moon R. L. , Bell R. L.
Published: July 2002

The barrier heights of Au/p-InGaAsP alloys lattice-matched to InP substrates are measured by the photoelectric technique. The composition dependence of the barrier height varies smoothly from 0.77 eV for p-InP to 0.50 eV for p-InGaAs. The data are consistent with a barrier height dependence on the As/P anion ratio only.
Surface contraction of the clean W(001) face
Authors: Lee B. W. , Ignatiev A. , Tong S. Y. , VanHove M.
Published: July 2002

Extensive comparison of efficient dynamical LEED calculations with new, more complete experimental data has shown the clean state of the W(001) surface as compressed by about 11% such that the top layer spacing is reduced by 0.18±0.03 Å. This is a greater contraction than had originally been proposed and is more in line with the magnitude of contraction observed in other bcc (001) surfaces.
Secondary-electron energy distribution in high-energy photoemission
Authors: Penn David R.
Published: July 2002

We have calculated the energy distribution of secondary electrons observed in core-level XPS or core-level synchrotron photoemission experiments on Al. The secondary electrons are produced when the photoexcited primary electrons scatter inelastically from the valence electrons via the mechanisms of bulk and surface plasmon production and electron–hole production. The scattering cross sections for these events are determined from the Lindhard dielectric function, although the plasmon dispersion and broadening are taken from experimental measurements. Multiple scattering is taken into account by means of the Wolff–Spencer-Fano integral equation for the electron-energy distribution. The calculated results are compared to experiment.
Isotope effects in ion-scattering double spectroscopy curves for He+→Zn, In, Sn, and Pb
Authors: Helbig H. F. , Adelmann P. J.
Published: July 2002

An ion-scattering double spectroscopy (ISDS) method which traces the dependence of the height of an ISS mass peak on the ion-incident energy has been described. The resulting curves show marked differences for different ion–atom collision pairs and thus can be used for surface atom identification once standard ISDS curves are available. Here ISDS curves for He+→Zn, In, Sn, and Pd are presented for a larger energy range than formerly available. Furthermore, these data are presented for both isotopes of He. It is shown that there are significant differences in the magnitudes and positions of the extrema of ISDS curves when data from 3He and 4He→X are plotted and compared. These differences further distinguish the ISDS signatures of various surface atoms. An explanation for these differences is offered, and a method, exploiting the isotope effects, is described by which information regarding ion–atom interaction potentials might be obtained.
Correlation between the defect structure and electrical properties of deformed Si surfaces
Authors: Murty K. , Suga H. , Lalevic B. , Weissmann S.
Published: July 2002

Deformation by bending of Si wafers with [112], [111], and [100] surface orientation was produced by sputtering tantalum films on clean Si and on Si surface with a thermally grown oxide. Deposition of 0.5–1-μm Ta films produced radii of curvature in the Si wafers of from 350 to 50 m, respectively, as measured by the ABAC method. Stress on the Si surface as a function of annealing temperature exhibited a maximum of 400°C of 500 g/mm2 and 650 g/mm2 with and without oxide layer. Stress on tantalum films at 400°C was found to be 276.3 kg/mm2. At 300°C, stress on Ta film increased with Ta film thickness from 70 to 150 kg/mm2. Transverse and sectional x-ray topographs have revealed small dislocation loops at the deformed Si surface. Defect structure produced by bending was correlated with the electrical measurements on the Si MOS configuration with thin and thick oxide, using conductance and capacitance methods. The effects of induced defects were studied by measuring the density and energy distribution of the surface states, surface potential, and flat band voltage. I–V characteristics of the oxide film indicated Ta diffusion through SiO2 to the Si surface.
Oxygen interaction with Ni/Fe surfaces (1) LEED and XPS studies of Ni 76%/Fe 24% (100)
Authors: Brundle C. R. , Silverman E. , Madix R. J.
Published: July 2002

The interaction of oxygen with a Ni 76%/Fe 24% (100) surface has been studied at 293 K. XPS measurements were made as a function of emission angle to obtain depth distributions. Slight Fe segregation is observed for a clean annealed surface. It is enhanced by oxygen adsorption. By 0.7 monolayers oxidized Fe species are detected, but the Ni remains metallic until well above one monolayer. The Fe concentration in the outer 4 Å has then increased twofold. At about ∠2.7 monolayers (passivation) the surface Fe concentration is nearly three times the original and entirely oxidized. Heating causes further Fe segregation which reduces the Ni2+ to yield Ni0. LEED shows a c (2×2) pattern which persists above one monolayer. Correlations of the XPS and LEED data and comparison with XPS/LEED studies of oxygen on Fe(100) and Ni(100) show that between 0.7–2 monolayers, the surface must be heavily patched with Fe oxide and metallic Ni aggregations, the Ni being covered with a c (2×2) oxygen superstructure.
Raman scattering studies of surface space charge layers and Schottky barrier formation in InP
Authors: Pinczuk A. , Ballman A. A. , Nahory R. E. , Pollack M. A. , Worlock J. M.
Published: July 2002

We show that Raman scattering by LO phonons and their coupled modes can be used to obtain quantitative information on the band bending at surfaces or interfaces of doped III–V semiconductors. We have studied Schottky barrier formation and effects related to surface photovoltage at etched <111≳B surfaces of InP. These experiments yield information similar to that obtained from photoemission and photovoltage measurements, but they can also be carried out on surfaces which are contaminated or even covered with partially transparent layers such as metallic films.
Short channel n-MOS devices via combined e-beam and photolithographic processing
Authors: Henderson R. C. , Nash J. G.
Published: July 2002

A new silicon device processing sequence has been developed to permit fabricating n–MOS circuits with silicon gate lengths 1 μm or less. The processing sequence permits using photolithography to define the larger structures, while using e-beam direct writing to define the critical size features. The compatible process sequence uses positive resists for all pattern definition steps. A low turn-on voltage is achieved by a phosphorus ion implantation step which counter dopes the p-type substrate and provides a self-aligned channel. The e-beam patterns are registered to the optical patterns using tantalum alignment marks protected with a capping layer of CVD oxide plus polysilicon. Diagnostic devices have been fabricated which demonstrate the capability of the new approach.
New e-beam-defined memory structures
Authors: Oliver M. R. , Mercer H. D. , Havemann R. H. , Stein R. J. , Hester R. K. , Blocker T. G. , Easley R. L.
Published: July 2002

High density CCD memory structures often employ a SPS (serial–parallel–serial) structure. However, for two-phase CCD’s a standard SPS array does not optimize storage well size for a given area per bit. Two structures that have an optimized well size have been conceived. Both take advantage of the fact that the optimum two-phase CCD cell (two barriers, two wells, and associated channel stop) is not square but rectangular. The exact aspect ratio is a function of the specific process design rules. Test structures of both concepts, called the SSPS (serpentine SPS) and the CSA (common serial array), have been fabricated using e-beam lithography. The initial test structures area per cell are 28 and 32 μm2. The fabrication process, which has eight e-beam lithography levels, is discussed. The CCD structure is built with an n-type buried channel using two polysilicon levels. Ion implants define the barriers, wells, and channel stops in the array. Barriers and wells are self-aligned to electrode edges, as are diode regions to gate edges. Polysilicon and aluminum levels are etched by plasma. The preparation of e-beam alignment marks prior to device processing is discussed, and the extra steps required to maintain alignment mark integrity are described. The operation of the fabricated arrays is given and specific characteristics of clocking in the common serial array are presented. The advantages of these arrays for memory applications are summarized.
High resolution bubble patterns obtained by electron image projection
Authors: Bril T. W. , Snijders J. T.
Published: July 2002

The packing density in magnetic bubble circuits is increasing very rapidly. When the smallest dimensions in these circuits are 1 μm or less a successor for the optical lithography becomes necessary. For this purpose an electron image projector is a proper candidate. To study the reliability of the technique for making bubble patterns with this projector a single mask 8 kbit shift register has been realized. The NiFe elements are structured via a Ti lift-off procedure and subsequent reactive sputter etching of the NiFe. The lift-off technology is, among other things favorable owing to the slightly negative slope in the PMMA-resist. A high sputter etch rate ratio between NiFe and Ti during the reactive sputter etching process makes a very thin Ti masking layer feasible. It is shown that bubble devices with smallest features of 1 μm can be made. Uniformity over 2 in. slices is good. Proximity effects are of minor importance.
Triple slit scheme for high current variable-shaped beam forming
Authors: Idesawa Masanori , Goto Eiichi , Soma Takashi , Sasaki Tateaki
Published: July 2002

Variable-shaped beam schemes are very promising for advanced VLSI pattern generation. Some of them are made up of two beam shaping apertures, beam shaping deflectors, and projection lenses. In such devices, exposure speed is proportional to the total beam current finally projected onto the target. When the beam current is increased in this scheme, beam blurring caused by space charge effect becomes greater as the beam current increases. The observed beam blurring becomes much greater on the edges corresponding to the sides of the first beam shaping aperture than on those of the second one. A new beam shaping scheme is proposed for reducing this blurring. In this scheme, auxiliary beam shaping means are provided in the upper stream of the previously developed beam shaping system. The beam is preshaped by the new scheme so as to reduce the beam current between the first and the second beam shaping apertures by an amount which is the sum of the finally required and marginal portions, and a clearer beam shape can be formed on the target. Furthermore, to shorten the path length of electrons for reducing the above blurring, a construction method for an octupole electrostatic deflector is developed. In this method, newly designed isolating and supporting mechanisms for electrodes are adopted so as to minimize the size of the deflectors, which are sufficiently minute to be placed in the electron lens and to shorten the path length of electorn beam.
Boersch effect in electron-optical instruments
Authors: Knauer W.
Published: July 2002

This paper analyzes energy broadening in electron and ion beam. Unlike earlier treatments, the present theory takes into consideration thermal and crossover motions jointly, and it includes changes in relative transverse motion where beams converge or diverge. Expressions are presented for energy broadening in cylindrical beams, diverging beams, and beam crossovers. Calculated broadening levels are compared with experimental values given in the literature. Application of the analysis to electron-beam configurations in which chromatic aberrations predominate leads to relations for the maximum current density as a function of spot size. It is shown that, for field-emitting sources, which are imaged into the target, the peak current density is independent of spot size, while, for aperture imaging columns, the maximum current density varies inversely with spot edge resolution.
Resolution test specimen for evaluating the performance of electron deflection systems
Authors: Owen G.
Published: July 2002

A resolution test pattern is described which was developed to evaluate the performance of a large field deflection system incorporating dynamic astigmatism correction. The spot diameters of interest ranged from 1 to 10 μm and a convenient, rapid, repeatable measurement method was required. A further requirement was that the test specimen should respond to an astigmatic spot, and give a clear indication of the magnitude and direction of the astigmatism, so that stigmator corrections could be quickly determined. Because of these requirements conventional test specimens such as metallic grids could not be used, and so a special test specimen was designed. This consists of a series of concentric octagonal gold rings, fabricated on a silicon substrate. The width of the rings varies uniformly from 0.9 to 7.0 μm, and the diameter of the complete test specimen is 140 μm. Three principal applications have been investigated. Firstly, the magnitude and direction of deflection astigmatism have been measured by raster scanning the tangential and saggital line foci over the test specimen. Secondly, spot diameters habe been estimated by raster scanning over the test specimen, and noting the radius of the octagon at which contrast reversal occurs: this is dependent on the spot diameter. Thirdly, to make quantitative spot diameter measurements, the test specimen has been scanned in a line and the resulting video signal displayed as an ’’A’’ trace on an oscilloscope: modulation of the waveform is a measure of the diameter of the spot in the direction of scanned line.
High speed electron optics for direct slice writing
Authors: Pearce-Percy H.T. , Spicer D.F. , Abbot M. , Winborn C. , Varnell G.L.
Published: July 2002

A high throughput vector-scan direct slice writing electron beam lithography machine has been developed. This paper describes the electron optical and the deflection amplifier designs. A double deflection system was chosen because it had high deflection sensitivity, possessed a true pivot point, and the beam remained close to the axis. The design of the deflection and lens system was accomplished using specially developed computer programs. The deflection amplifier and coil system was optimized to give a flat frequency response to 10 MHz. Careful choice of materials eliminated eddy current effects. The system can draw 1.25 μm lines across a 6.35 mm square field. Distortion after correction is typically ±3 μm over the same field.
Multifunction computer configuration for microlithography
Authors: Potosky J.C. , Reekstin J.P.
Published: July 2002

A multiple function, multiple processor computer system has been implemented as the basis for the electron beam microfabrication facility at Rockwell International’s Electronics Research Center. The configuration of a master mini-mainframe interfaced to several satellite miniprocessors provides for the simultaneous operation of two Electron-Beam Microfabricators, pattern data format conversion, graphical pattern editing, and conntinued software development. Expansion of the facility with additional microfabricators requires only a buss interface and a low level 16 bit processor. At present, the system consists of a Digital Equipment Corporation PDP 11/35 CPU which acts as the master processor. PDP 11/34’s act as satellites controlling the microfabricators. An RSX–11M operating system is used with DECNET in the foreground. Microfabricator control programs and pattern data are loaded down to the satellite processors from disk storage on the master computer. Pattern data is manipulated via programs residing in the background. Software development also takes place in the background and is accessed from a remote terminal. Additional peripherals include nine track magnetic tape, paper tape, and large screen graphic display CRT’s.
Measurement of the sputtering yield of Fe from an oxidized stainless steel target using a pulsed dye laser
Authors: Elbern Alwin , Mioduszewski Peter
Published: July 2002

The relative change of the sputtering yield of neutral iron from an oxidized 321 stainless steel target was measured by atomic fluorescence spectroscopy (AFS) using a pulsed dye laser. Simultaneously the relative sputtering yields of Fe+ and Cr+ and also the total sputtering yield of the oxidized target was determined respectively with a quadrupole mass filter and a piezoelectric microbalance. After first cleaning the target by sputtering, it was oxidized under the conditions of: 10−5 Torr O2, 120 min, 500°C in a UHV chamber. These yields were measured as a function of the applied dose, and compared to the depth profiles measured by Auger electron spectroscopy (AES).
Sensitivity to various gases of Granville-Phillips vacuum gauge, series 275, Convectron—A reply
Authors: Bills D. G.
Published: July 2002

An explanation of unexpected results obtained in a comparison of the Granville–Phillips vacuum gauge 275-102 with two other gauges is offered based upon the gas species dependence of the G–P gauge.
Sealing of knife-edge flanges after a high temperature vacuum firing
Authors: Edwards D. , McCafferty D. , Rios L.
Published: July 2002

A 2 3/4-in. Varian flange has been vacuum fired at 900°C for four hours and found to seal without leakage through each of 40 separate closures. This indicates that such a flange may in fact be sufficient for the ISABELLE ultrahigh vacuum system without knife-edge modification.
Improvement in the sensibility of a Cahn RG-2000 vacuum microbalance
Authors: Rothenberg S. J. , Barr F. , Dziurzynski C. T.
Published: July 2002

Improvements in the sensibility of the Cahn RG-2000 vacuum microbalance are described. These result from the use of antivibration pads, light source replacement, power supply improvement and, finally, change in gas admission procedures.
HEED and TEM study of epitaxial CdS/InP thin films on NaCl
Authors: Dhere Neelkanth G. , Parikh Nalin R.
Published: July 2002

Basal planes of hexagonal cadmium sulphide high vacuum deposited on the (111) faces of NaCl single crystals by the hot wall technique have been used for epitaxial deposition of indium phosphide by evaporation of the constituent elements. Two 2-d {111} orientations, of InP films, 180° to one another were found to develop. Two new hexagonal structures with respective c0 values corresponding to ∠3a0 of CdS and ∠√2a0 of InP and also a cubic superstructure having a0 equal to 8 a0/√3 of InP have been encountered in some instances. The new phases have been attributed to intermixing in the heteroepitaxial films.
Improved step coverage by ion beam resputtering
Authors: Harper J. M. E. , Proto G. R. , Hoh P. D.
Published: July 2002

Coverage of steps by ion beam sputtered SiO2 films is greatly improved by bombarding the growing film with an ion beam. Cracks are eliminated at step edges, and step coverage profiles can be controlled by varying the degree of resputtering, as has been observed in rf bias sputtering. Using an ion beam of well-defined energy, flux, and angle, the resputtering process is under direct control. In a dual ion beam system, we examined the step coverage profiles of SiO2 films deposited under 500 eV argon ion bombardment to produce resputtering fractions of 0%, 17%, and 42%. Films deposited with no resputtering show overhanging step profiles, while those deposited with 17% resputtering give smooth sloping profiles with good coverage even with film thicknesses less than the step height. Successful lift-off patterning is also achieved with 17% resputtering. Films deposited with 42% resputtering have sloping profiles but do not fully cover step edges. We conclude that step coverage can be greatly improved using resputtering fractions of less than 20%. This level of resputtering does not degrade other film properties, and is compatible with lift-off processing.
Sputtered iron oxide/silicon heterostructures
Authors: Kardauskas M. J. , Fonash S. J. , Ashok S. , Krishnaswamy S. V. , Messier R. F.
Published: July 2002

Sputtered Fe3O4 films have been demonstrated to form rectifying junctions to p-type silicon but ohmic contacts to n-type Si. Ohmic contacts to this Fe3O4 can be provided by Au, Al, or spray-deposited ITO. The redox couple Fe (CN)3−6/Fe(CN)4−6 also appears to make an effective ohmic contact to this iron oxide. The photovoltaic and electrical characteristics of the Fe3O4/p–Si heterojunction are found to depend strongly on the Fe3O4 film thickness.
Steam corrosion of glass under polymer thin films
Authors: Ali-Zaidi S. R. , Smith M. A. , Levenson L. L.
Published: July 2002

Polymer films averaging 600 Å in thickness were deposited on the outer surfaces of glass bottles to increase the lubricity and scratch resistance of the glass. The bottles were autoclaved in steam at 3 atm absolute pressure. Direct pull tests and in-depth XPS profiles were made to learn how adhesion and the polymer–glass interface changed with autoclaving time. It was found that sodium was depleted from the surface region under the polymer coating. The sodium depletion zone increased linearly with autoclaving time. Sodium was also leached from the uncoated surface, but after 30 min of leaching the sodium depletion depth remained essentially constant. The organic film continued to adhere well independently of autoclaving time.
Pumped oil feed systems for rotary vacuum pumps
Authors: Wycliffe H. , Power B. D.
Published: July 2002

Pumped oil feed systems developed by the authors and their colleagues provide positive lubrication under all inlet pressure conditions, tolerance of wide variations of oil level in the reservoir, and easy incorporation of filtration systems. The wide tolerance to oil charge allows lengthy operation between recharging and permits a smaller charge of expensive fluids to be used. The oil pressure generated can be used to operate safety devices within the vacuum pump and to circulate oil through external coolers or purification systems.
Microradiographic characterization of metal and polymer coated microspheres
Authors: Singleton R. M. , Weir J. T.
Published: July 2002

X-ray microradiography is used to make measurements of opaque metal and polymer coatings on hollow glass microspheres which are used as laser fusion targets at the Lawrence Livermore National Laboratory. Metal coatings include platinum, tantalum, gold, copper, and beryllium where thicknesses range from 1 to 10 μm on 70 to 200 μm diameter mandrels. Contact film images are made with x-ray energies from 1 to 50 keV, depending on the material and geometry. The recorded x-ray images show the internal structure of the coatings which is not observable with optical and SEM techniques. The film images are digitized and directly measured using a small computer-based image analysis system. Wall thicknesses and nonconcentricity can be measured to within 0.3 μm, and diameters to within 1.5 μm.
Chemical durability improvement of glass shells
Authors: Anderson P. R. , Scott L. A. , Rolen J. J.
Published: July 2002

High temperature chemical surface treatments have been used to improve the chemical durability and weatherability of spherical glass shells. The surface treatment consists of exposing heated glass shells to a mixture of sulfur dioxide, air and water vapor. A thin layer of the glass shell is dealkalized as a result of this treatment. The weatherability of treated alkali-silicate and alkali-calcia-silicate shells was improved, as determined qualitatively with the aid of a SEM. The chemical durability of silicate shells containing over 10 wt.% alkali but no calcia was improved by as much as a factor of thirty by the treatment. The chemical durability of glass shells was determined by analyzing the aqueous solutions used for extracting the constituents of the shells. Treated glass shells containing calcia showed greater resistance to dissolution in water than untreated glass shells of the same composition, even though the untreated shells were relatively durable.
Core threshold photoemission spectroscopy from the As 3d core level of GaAs (110) and effects of Ge chemisorption
Authors: Zurcher P. , Lapeyre G. J. , Avci R. , Anderson J.
Published: July 2002

We have investigated the excitation of the As 3d core level of clean and Ge covered GaAs (110) surfaces into low lying conduction band states by observing core-hole decay emission. The investigation was carried out by using synchrotron radiation to record photoemission spectra in the CIS and EDC modes. In contrast to the Ga 3d core excitation, the As 3d core excitation was found to be nonexcitonic in character. The CIS shows three structures at hυ = 43.0, 46.1, and 49.5 eV, which were strongly influenced by Ge-chemisorption. With about a monolayer of Ge, the structures are reduced to a considerably larger degree than the photoemission structure associated with the Ga 3d exciton. The As 3d core level is excited into surface related p-like states lying 2.6, 5.7, and 9.1 eV above the valence band maximum, ’’followed’’ by the radiationless Auger decay of the core holes. The inferred conduction band states are compared to recent band calculations and the state at 2.6 eV is assigned to the Ga-dangling-bond surface state. With the assumption that the As 3d core excitation is to the same surface state as the Ga 3d core excitation, we estimate the exciton binding energy for the latter excitations to be ∠1.8 eV.
Materials options for field-effect transistors
Authors: Wieder H. H.
Published: July 2002

The evolution of monolithic high-speed digital and analog microwave field-effect transistor (FET) technologies is linked inextricably to synthesis, control, and understanding of the properties of the semiconducting binary, ternary, and quaternary III–V compounds. It is also linked to the application and use of ion implantation as a pivotal corollary process. Selection of a Schottky barrier, insulated-gated or heterojunction gate technology defines, in part, the options available in terms of the fundamental surface and interfacial properties of these compounds. Others concern electron transport processes under surface depletion, inversion and accumulation regimes, and the solution of metallurgical problems involved in the formation of ohmic and blocking contacts, the free carrier concentration and mobility profiles, and their stability as a function of process variables used to make such FET.
LEED investigation of extended defects at the surface of Ge films grown epitaxially on GaAs(110)
Authors: Clearfield H. M. , Welkie D. G. , Lu T.-M. , Lagally M. G.
Published: July 2002

Some aspects of the defect structure at surfaces of Ge films grown epitaxially on cleaved GaAs(110) substrates at different growth conditions are investigated by LEED beam angular profile analysis. In particular, steps, domain size, and domain misorientation are considered. The average ordered domain size in the Ge films depends on growth conditions, but appears always to be smaller than that of the substrate with the growth conditions used here. There is no evidence of monatomic steps in either the substrates or the Ge films. The effect of possible multiatomic steps on the LEED profile is considered.
Oxygen induced dissolution and segregation of silicon in platinum single crystals
Authors: Salmerón M. , Somorjai G. A.
Published: July 2002

The segregation of silicon in platinum flat (111), stepped (553) and (332) surfaces is studied as a function of crystal temperature. Silicon segregates below 1000°C with a segregation energy between 17 and 20 kcal/mol. In the retarding field mode, the maximum amount of segregated Si corresponds to a Si (93 eV)/Pt (242 eV) Auger peak ratio of about 5. In the presence of O2, Si dissolves into the bulk at T≳600°C. The rate of Si dissolution increases with O2 pressure and crystal temperatures. At an O2 pressure of 5×10−7 Torr, the activation energy for the dissolution process is 16±2 kcal/mol. Continued exposure to O2 results in the reappearance of Si at the Pt surface as a new phase, SiOx, characterized by Auger peaks of Si (84 eV) and O (515 eV).
Deep-UV photoresists: Poly(methyl methacrylate-co-indenone)
Authors: Hartless R. L. , Chandross E. A.
Published: July 2002

Copolymers of indenone and methyl methacrylate have been evaluated as deep-UV (200–300 nm) positive photoresists. Sensitivities of 0.02 and 0.1 J/cm2 at 248 and 280 nm were found for polymers containing 7% and 18% indenone, respectively. Exposure of a 3 in. resist-coated silicon wafer on a Perkin Elmer 111 Projection Printer (modified for short wavelength) for 40 s resolved equal 0.75 μm lines and spaces. The materials have chemical and physical properties compatible with microfabrication processes. The resists have approximately the same plasma resistance and e-beam sensitivity as poly(methyl methacrylate).
Elastic low-energy electron diffraction from GaAs(110)-p(1×1)-Sb(1 ML)
Authors: Kahn A. , Carelli J. , Duke C. B. , Paton A. , Ford W. K.
Published: July 2002

Auger electron spectroscopy and low-energy electron diffraction are used to study the interface formed by the evaporation of Sb on room temperature GaAs(110). In contrast to Al, the Sb overlayer is ordered and produces a (1×1) diffraction pattern with intensity profiles very different from those measured from the clean substrate surface. The interface is sharp and stable under heat treatment, the Sb film is continuous and thermal desorption experiments reveal the strong bonding that exists between the first Sb monolayer and the substrate.The atomic structure of the GaAs(110)-p(1×1)-Sb(1 ML) system is analyzed with multiple scattering computations. Three types of structures have been examined: chains of Sb atoms parallel and antiparallel to the top layer Ga–As chains, Sb2 dimers attached to the surface Ga species, and a ’’jellium’’ type structure in which one Sb is bonded to the surface Ga atom and the other Sb is randomly distributed above the surface. Only single scattering computation, however, has been used for the later model. Qualitative description of the measured intensities are achieved by structures of the first (antiparallel chains) and third models.
The effects of Fe on the reactivity of Ni(100)
Authors: Semancik S. , Kelley R. D.
Published: July 2002

High pressure reaction methods have been combined with ultrahigh vacuum techniques to investigate the influence of low level Fe on the catalytic activity of the Ni(100) surface. CO dissociation and hydrocarbon formation from H2/CO mixtures are the specific reactions which have been considered. Reactivity changes observed in the presence of surface Fe can be attributed to the different local chemistry involved in CO–Fe and CO–Ni interactions.
Theory of hydrogen chemisorption on ferromagnets
Authors: Morán-López J. L. , Falicov L. M.
Published: July 2002

A theory for hydrogen chemisorption on ferromagnetic 3-d metals is presented. The calculation is a cluster Bethe-lattice approximation based on an Anderson–Hubbard Hamiltonian. Results are given for the change in the substrate magnetization due to chemisorption.
Interpretation of M
V
V and L2,3 V
V Auger spectra of Co
Authors: Zehner D. M. , Noonan J. R. , Madden H. H.
Published: July 2002

The MVV and L2,3 VV Auger spectra of Co have been acquired from a clean polycrystalline foil and the intrinsic line shapes determined using standard deconvolution procedures. The line shapes are observed to be broad and band-like and do not exhibit any narrow atomic-like features as previously observed for Cu. The energies of the peak positions of the Co Auger lines might be interpreted as indicating hole–hole interaction energies (Ueff ) of ∠4.5 eV for the MVV and ∠2 eV for the L2,3 VV transitions, respectively. These values are inconsistent with the expected trend of decreasing Ueff in going from Cu to Co and with the fact that Ueff , a final state property, should be the same for all core–valence–valence decays. An alternative explanation is that the energy shifts are related to initial state screening and/or matrix element effects. These effects, as well as the differing lifetimes of each initial core hole, may also contribute to the larger FWHM of the measured spectra as compared to that obtained by self-folding a calculated DOS. The interpretation of these spectra and a comparison with similar data for Cu are discussed.
Vacuum instrumentation on the Daresbury synchrotron radiation source
Authors: Reid R. J.
Published: July 2002

The vacuum instrumentation for the ultrahigh vacuum system of the electron storage ring of the SRS is part of a complex, interlinked system under the control and supervision of a hierarchy of computers. The vacuum system has been in operation for over one year and has attained average base pressures of better than 5×10−8 Pa. The main pressure measurement devices are Bayard–Alpert ionization gauges and the operational precautions required in using such devices will be discussed. Quadrupole residual gas analyzers are used for partial pressure measurements and their use, particularly in the areas of leak detection and in the monitoring of the progress of bakeout of the ring, will be described. Projected data analysis facilities for residual gas analysis will also be discussed.
Implementation of adaptive process control to a dry etching process
Authors: Bresnock F. J. , Stumpf Th.
Published: July 2002

The implementation of a minicomputer for adaptive process control in a reactive ion etching tool is described. Improved process control was demonstrated including the ability to adapt to nonlinear, time-varying processes. The system provides an extremely flexible process development environment.
Vacuum deposition of high quality metal films on porous substrates
Authors: Barthell Barry L. , Duchane David V.
Published: July 2002

A composite mandrel has been developed consisting of a core of low density polymethylpentene foam overcoated with a thin layer of film-forming polymer. The surface tension and viscosity of the coating solution are important parameters in obtaining a polymer film which forms a continuous, smooth skin over the core without penetrating into the foam matrix. Water soluble film formers with surface tensions in the range of 45 dyn/cm and minimum viscosities of a few hundred centipoises have been found most satisfactory for coating polymethylpentene foam. By means of this technique, continuous polymer fims with thicknesses of 10–20 μm have been formed on the surface of machined polymethylpentene foam blanks. Aluminum has been vacuum deposited onto these composite mandrels to produce metal films which appear smooth and generally defect free even at 10 000 times magnification.
Giant replicate cell approach to the electronic structure calculation of graded interface regions
Authors: Ching W. Y.
Published: July 2002

The usual approach to the theory of interfacial electron states is to assume that the interfaces join abruptly. A multilayer slab geometry is then elected for the calculation of electronic states using methods of varying degree of sophistication. In many cases, the interfaces between semiconductors or dielectric insulators may involve a transition region of several atomic layers. The electron states at one side of the transition region may be quite different from those of the other side. The artificial abrupt connection of the two faces in this case will result in a great strain of bonds at the interface and could lead to the identification of unrealistic interfacial states. An alternate approach to this problem is proposed. We construct a series of giant periodic cells with atomic coordination commensurate with the bonding configurations of the interfacial region. A microscopic first-principles electronic structure calculation is then applied to each giant cell which replicates the bulk interfacial region. Information such as density of states, partial density of states, gap states, and electron localization can be obtained and correlated to the atomic structures. Results for density of states are presented for SiOx with x = 1.5, 1.0, and 0.5 as would be appropriate for the Si–SiO2 interfacial region. States at the upper region of the valence band are found to consist of mainly Si orbitals and their degree of localization is proportional to x. Application of this method to other compound semiconductor interfaces is also discussed.
Hydrogen-induced disruption of oxygen-doped platinum coatings on glass microspheres
Authors: Ping W. L. , Meyer S. F.
Published: July 2002

Sputter-deposited platinum coatings on glass microspheres were severely disrupted after a deuterium–tritium (DT) mix was permeated into the hollow spheres under elevated temperature and pressure conditions. Optical, scanning electron microscope, and x-ray diffraction techniques were used to study the disrupted structure. This characterization, combined with results of separate sputtering experiments and literature information, suggested that hydrogen gas was occluded in the platinum rift structure during the high-pressure fill process. Subsequent release of the hydrogen pressure resulted in an expansion of the occluded gas; because diffusion rates were too low to relieve the stress concentrations thereby produced, the platinum coating delaminated along weakly bound interfaces. Neither oxygen present within the platinum structure nor water (as a Pt-catalyzed H2+O2 reaction product) appeared to contribute significantly to this disruption.