bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-temperature interdiffusion in titanium–permalloy thin-film diffusion couples
Authors: Miller R. J. , Gangulee A.
Published: July 2002

Interdiffusion in thin-film Ti–Permalloy (nominally 81 at. % Ni+19 at. % Fe) diffusion couples has been investigated in the temperature range 200°–350°C. These diffusion couples were isothermally annealed in vacuum for times up to 6×105 s, and their magnetic properties such as the coercivity, the anisotropy field, the saturation magnetization, and electrical properties such as the sheet resistance and the sheet magnetoresistance were monitored as functions of time. From the observed changes in these properties and from concurrent x-ray diffraction measurements, it may be concluded that the dominant mechanism in this interdiffusion process is the volume diffusion of Ti in Permalloy; the activation energy for this process is estimated to be 1.9 eV.
Cryosorption pumping of deuterium by MS-5A at temperatures above 4.2 K for fusion reactor applications
Authors: Fisher P. W. , Watson J. S.
Published: July 2002

An excalibur CVR-1106 cryosorption pump was fitted with a special cooling system to permit measurement of deuterium pumping speeds at temperatures between 6 and 20 K. Pumping speeds were found to be a function of feed rate, loading prior to each run, loading during runs, and thermal treatment between runs. At feed rates <3×10−4 Torr l s−1 cm−2, speeds were near 1 l s−1 cm−2 initially and declined monotonically with loading. At high feed rates, speeds reached a higher maximum (∠3 l s−1 cm−2) but also generally declined with loading; however, after 50–100 Torr l had accumulated, the pump underwent a spontaneous transition which effected a return to the original (high) pumping speed. This transition was accompanied by pressure spikes in the test chamber and temperature spikes in the sieve panel. Initial speeds for each consecutive run equaled the final speed for the preceding run if the pump was maintained at operating temperature; however, if it was warmed to 77 K and recooled, a restoration to the maximum speed was observed at the beginning of the next run.
Pressure measurements in a cryogenic environment
Authors: Edwards D. , Limon P.
Published: July 2002

A technique is presented which allows the measurement of He and H2 pressures in a cold system (∠4 K) with instrumentation at room temperature. It is applied to vacuum measurements of a section of a beam tube to be used in a proton accelerator application. The primary result is that with the beam tube at 4.7 K the helium pressure is less than 10−11 Torr and the H2 pressure is negligible.
Thickness dependence of an amorphous overlayer Ge film on the electrical conductivity of ultrathin Pt films
Authors: Ogawa S.
Published: July 2002

The resistance of ultrathin Pt films as influenced by amorphous Ge thin overlayers has been studied. The ratio of change in resistance of the Pt films with overlays of the amorphous Ge is negligibly small for continuous Pt films but is much larger for semicontinuous and discontinuous Pt films, especially for discontinuous ones: As order, these ratio are 10−2, 1, and 102, respectively. The changes in resistance of semicontinuous and discontinuous Pt films markedly depend on the thickness of the overlay. With the thickness of the overlay, at first, the resistance increases slightly for semicontinuous Pt films and decreases rapidly for the discontinuous one, and then decreases for both films to a saturation value (∠60 Å). The decreases in resistance of both Pt films with the thickness of the overlay can be explained by electrical conduction of the localized states in the energy gap of the overlay.
Identification of surface radicals by vibration spectroscopy: Reactions of C2H2, C2H4, and H2 on Pt (111)
Authors: Ibach H. , Lehwald S.
Published: July 2002

High-resolution electron energy loss spectroscopy has been applied to study the adsorption of acetylene and ethylene on Pt (111) and the surface reactions of these adsorbates as a function of temperature and in the presence of chemisorbed hydrogen. Making use of the surface selection rule and the observed frequencies a rather detailed picture is developed about the chemical nature of the adsorption states and reaction intermediates. Below room temperature, acetylene rehybridizes so as to form one strong di/σ-like bond to the surface and an additional bond to the surface with the remaining π orbital. Ethylene is essentially just di/σ bonded. Around room temperature, ethylene converts to a new chemical species which we identify to be ethylidene (CH3–CH=). Ethylidene is also formed from acetylene when the surface is first exposed to hydrogen, then to acetylene at low temperatures, and subsequently annealed to 350 K. The same result was obtained by exposing adsorbed acetylene to atomic hydrogen at 350 K. We further find that the hydrogenation of adsorbed acetylene to ethylidene proceeds via the intermediate –CH2–C≡ (2-ethyl–1-ylidine).
Ion nitriding of steels
Authors: Jindal P. C.
Published: July 2002

This paper deals with the ’’ion-nitriding’’ method of nitriding various grades of steels in a laboratory model furnace. Four different grades of steels such as AISI 4140, Nitralloy 135 Mod., high-speed steel M2 and stainless steel 304 were ion nitrided at different temperatures with cycle times ranging from 1 to 36 h in a gaseous mixture of nitrogen and hydrogen under a total pressure of 7 Torr (9.1×103 Pa). Results obtained with 4140 steel show that ion nitriding at 950°F is much faster than conventional gaseous nitriding. At a given temperature of ion nitriding, case depth versus treatment time follows a parabolic law for all four grades of steels. Current theoretical and experimental evidence has been used to explain different nitriding rates observed for various steels. Finally results of ion nitriding performed at 750°F have been presented to show the versatility of this process.
Graded metal carbide solar selective surfaces coated onto glass tubes by a magnetron sputtering system
Authors: Harding G. L. , Window B.
Published: July 2002

A solar selective absorbing surface consisting of mixed iron, chromium, and nickel carbides on copper has been deposited onto 1.5 m long, 22 mm o.d. glass tubes by reactive and nonreactive dc sputtering. Grading the properties of the metal carbide from metal rich at the copper substrate to dielectric at the surface results in solar absorptances ∠93% and emittances ∠4% at 300 K (both properties averaged along the length of a tube). Aging experiments show that absorptances deteriorate slowly at 300°C in vacuum due to diffusion in the graded film. Emittances at elevated temperature for copper and for the selective surfaces deposited onto tubes have been determined using a calorimetric technique.
AES study of sulfur surface segregation on polycrystalline copper
Authors: Singh B. , Vook R. W. , Knabbe E.-A.
Published: July 2002

The surfaces of four polycrystalline copper samples were examined under UHV conditions by AES: OFHC Cu, 99.99% Cu, 99.9999% Cu, and 0.086 wt. % Ag in OFHC Cu. Surface chemical compositions in the range of 25°–600°C were determined. Sulfur concentrations on the surfaces at various temperatures were also measured as a function of time. In almost all cases the sulfur concentration increased as (time)1/2. This process was interpreted in terms of a model based on diffusion controlled ’’outgassing’’ in which the sulfur segregated to the surface instead of vaporizing. The activation energies for this process for the four samples ranged from 0.18 to 0.31 eV/atom. RHEED data from an OFHC Cu sample indicated that sulfur formed an orthorhombic Cu2S structure on the surface. Around 500°C the Ag–Cu alloy experienced a complex, rapid stage of segregation of sulfur. Above this temperture range the surface sulfur concentration dropped rapidly, reaching zero at 600°C.
Fourier analysis of linear surface kinetics in reactive molecular beam scattering
Authors: Sawin H. H. , Merrill R. P.
Published: July 2002

The surface kinetics of reactive molecular beam scattering have been analyzed by discrete Fourier analysis of the scattered product waveform. In experiment and by calculation, it has been shown that with square wave modulation, harmonics in the scattered waveform as high as 29 can be significant. These harmonics can be used to characterized the transfer function of linear surface kinetics with modulation at four or fewer frequences. Optimum signal-to-noise in the derived rate parameter is obtained using the phase shift of the first harmonic where K/ω is approximately one. Fourier waveform analysis of square wave modulation compares favorably with lock-in amplifier detection, cross correlation modulation, and pulse testing for the analysis of surface kinetics.
A computational and experimental analysis of fifth-order deflection aberrations
Authors: Rao V. R. M. , Nixon W. C.
Published: July 2002

The influence of fifth-order deflection aberrations for purely magnetic post lens single-deflection systems has been investigated. A regrouping of the large numbers of third- and fifth-order aberration coefficients has been performed to reduce the numbers of coefficients to six to the third order and seven to the fifth order. Optimization then consists of minimizing the relevant regrouped coefficients. The third- and fifth-order field curvature coefficients have been measured and agree reasonably well with calculated values. It has also been found possible to obtain a change of sign between the third- and fifth-order astigmatism coefficients leading to a partial cancellation of the total astigmatism. The maximum deflection angle was about 15° from the optic axis in all the deflection systems analyzed.
Monte Carlo modeling of current distribution in shaped electron beams
Authors: Dayan P. S. , Jones G. A. C.
Published: July 2002

A Monte Carlo type simulation of electron interaction in a shaped electron beam lithography system has been developed. The simulation has been used to model a shaped beam system using Köhler illumination, and shows correct imaging when electron interaction is neglected. The loss of resolution due to interaction is demonstrated, and it is proposed that this technique may be used for the quantitive assessment of the effects on interaction in shaped beam systems.
Current distribution in shaped e-beams
Authors: Rao V.R.M. , Jones G.A.C. , Ahmed H.
Published: July 2002

The current distribution in electron beams shaped by using either Köhler or critical illumination of apertures has been determined experimentally. The experimental technique is to scan a square image across sharp edges of a Faraday cage aperture while the first and second differentials of the current are displayed on an oscilloscope. The measurements show that the type of illumination is not an important factor in determining the ultimate edge sharpness. All measurements were made with 20-kV accelerating voltage and it was found that for a square of side 3.5 μm imaged at an angular aperture 3.7 mrad the current density edge deteriorated to about 0.7 μ at 3 μA for both types of illumination. Results of imaging a menu of variable shapes in resist are used to demonstrate uniform current density distribution in the shaped beam.
Electron-beam fabrication of a 1.25 μm, 16-bit I2L microprocessor
Authors: Havemann R. H. , Smith R. L. , Evans S. A. , Arledge L. A. , Love R.L. , Varnell G. L.
Published: July 2002

E-beam direct slice writing has been utilized to fabricate a 55% linear shrink of the SBP9989, a 16-bit I2L microprocessor in the familiar TI SBP9900 series. The scaled device contains approximately 5 K gates and the chip area is 14.4 mm2 as compared with 37.1 mm2 for the full-sized chip. The chip layout is maintained in a database which can be easily manipulated to change design rules, scale selected geometries (pnp base width, collector size, etc.) or vary the overall scaling factor. The design requires minimum geometries of 1.25 μm and an overall process registration of ±0.75 μm. Patterns were delineated in TI-323A positive and TI-309 negative electron resists using EBMIII, a vector-scanned, laser-controlled electron beam exposure machine with a minimum beam diameter of 0.4 μm and level-to-level registration accuracy of <±0.25 μm. The oxide-separated, double-level-metal fabrication process used ion implantation and anisotropic plasma etching to achieve maximum control of junction depths and etch profiles, respectively. Fabricated units were fully functional from −55 °C to +125 °C and showed a speed improvement of 2× at one-half the power of the full-size chip.
A high speed electron beam lithography system
Authors: Eidson J. C. , Scudder R. K.
Published: July 2002

The Hewlett–Packard electron beam lithography system is described. The system is capable of being used either for direct writing on a wafer or for mask generation. It has been designed for high throughput production applications with data rates up to 300 MHz, using a field emitter electron source, a modified raster scan, and electrostatic deflectors. Deflection field aberrations are corrected so that patterns up to 5 in. square may be exposed with layer to layer registration better than 0.13 microns. The system architecture and design constraints will be discussed.
Variably shaped electron beam lithography system, EB55: I. System design
Authors: Fujinami M. , Matsuda T. , Takamoto K. , Yoda H. , Ishiga T. , Saitou N. , Komoda T.
Published: July 2002

The precision electron beam exposure system EB55 has been developed for direct wafer writing of submicron patterns. This paper describes the system architecture, design approach, and system specifications. The system utilizes a variably shaped beam column with a spot size ranging from 0.5 to 5.1 μm square, which is adjustable in 0.02 μm increments. Pattern data, compressed by a pattern data preparation software, is supplied to the high-speed digital control unit, where it is expanded to provide control data at a 320 ns shot rate to an analog unit. The analog unit provides deflection current and voltage to the electrostatic deflection plates and magnetic deflection coils with 0.02 μm resolution. Pattern accuracy is maintained by deflection distortion correction and overlay techniques. The deflection error is measured within 0.02 μm accuracy over a 2.6 mm square field with a mark detector and laser position sensor and corrected by a digital correction unit. Overlay accuracy is assured by registering to fiducial marks on the wafer and measuring wafer deformation to determine field adjustments. The exposure time per wafer is about 41 min with 0.5 μm minimum linewidth and ±0.1 μm overlay accuracy (3σ) using 20 μC/cm2 resist sensitivity and 8×108 shots per wafer. In this case, the writing time, the registration time, and the stage move time are 32, 3, and 6 min, respectively.
Electron-beam array lithography stitching experiments
Authors: Kellogg E. M. , Bono D. C. , Dalterio M. J. , Gibilaro G. R. , Greenstein D. B. , Harte K. J. , Singhal V. K. , Walker D. M.
Published: July 2002

A series of experiments to demonstrate the feasibility of the EBAL (electron-beam array lithography) concept is described, using a system of electron optics that deflects the electron beam in two stages: coarse and fine deflection. The field of view is divided up into a mosaic of smaller fields, called lenslets. It is required to stitch the lenslet fields into a complete, coherent field. A stitching theory is used [Singhal et al. (to be published)], together with a calibration plate. This procedure is demonstrated using two techniques: test patterns on resist are written and developed for examination by microscope; also electronic stitching is done, wherein test fiducial marks at lenslet boundaries are located with the electron beam, and data from adjacent lenslets are compared. This technique gives quantitative results more directly than writing on resist. We present results on 3×3 lenslet resist stitching to an accuracy of 0.2 μm, and 5×5 lenslet electronic stitching to 0.14 μm, which help to demonstrate the feasibility of EBAL for microcircuit lithography.
Discontinuity reduction method in pattern connection
Authors: Idesawa M. , Soma T. , Goto E.
Published: July 2002

A method of reducing the discontinuities which appear in the connecting boundaries of element patterns or in the stitching boundaries of sub-scanning-fields is proposed. Pattern elements are overlapped in the connecting region, and the beam dose in the overlapping area of each pattern element is controlled so that they are compensated by each other. Computer simulations and experiments were performed proving that the proposed method is very effective in reducing these discontinuities. For instance, by selecting an overlapping area which is several times wider than the expected positioning errors or edge definition of element pattern, discontinuities in pattern connection can be reduced remarkably without any special improvement of positioning accuracy.
Advanced pattern data processing technique for a raster scan electron beam exposure system
Authors: Koyama K. , Sasaki S. , Tokita M.
Published: July 2002

With the increasing complexity and integration in recent LSI designs, the amount of data to be processed in EB exposure systems tends to increase steadily. This increase in data may lead to degradation in the systems’ throughputs. An overall technique associated with both software and hardware presents a realistic solution to this problem. Parallel processors combined with a simplified data format have provided efficient data manipulation. A compaction method working on smaller stripe areas is easily realized in hardware, yet can achieve significant data reduction. The data edit function, operating asynchronously with the data preparation procedure, eliminates repeated processing of identical chip patterns or chip element patterns. The feasibility of the technique thus featured has been proven on EB-105, a raster scan electron beam exposure system.
Submicron electron-beam patterning of aluminum by a double-layer pattern transfer technique
Authors: Sato M. , Kawabuchi K. , Yoshimi M. , Yamazaki T.
Published: July 2002

A double-layer pattern transfer technique has been developed for submicron aluminum patterning. The double-layer consists of an electron beam resist and an inorganic material ’’spacer’’ having high resistance to reactive ion etching of aluminum. When plasma-deposited silicon dioxide is used as a spacer, severe side-etch of aluminum occurs. On the other hand, by using plasma-deposited silicon nitride as a spacer, submicron aluminum patterns are formed without any etch bias. On profiled surfaces, aluminum patterns with 0.75 μm lines and 0.75 μm spaces are produced without linewidth variations due to the surface topography, by applying etch-back technique to the silicon nitride spacer before resist coating.
Wavelength dependence of laser-enhanced oxidation of silicon
Authors: Schafer S. A. , Lyon S. A.
Published: July 2002

The thermal oxidation rate of Si in dry oxygen is increased by illumination with low-power visible and ultraviolet laser light and is found to be a function of the wavelength of the laser radiation. Visible laser radiation increases the thermal oxidation rate of Si by approximately 40%, and ultraviolet radiation at 350 nm by 60%, over the temperature range of 770–900 °C. A laser- induced rate increase of 40% is also observed in wet (H2O+O2) thermal oxidation. However, no significant wavelength dependence is seen in this case. It may be concluded from these data that ultraviolet laser light affects some component of the dry oxygen reaction that is not present (or not important) in wet thermal oxidation. There appears to be a threshold energy of 3.0 to 3.5 eV for this observed optical effect. Possible mechanisms for the optical interaction are discussed.
Localized and delocalized charge transfer during adsorption on semiconductors: Experiments and cluster calculations on the prototype surface ZnO(101̄0)
Authors: Göpel W. , Rocker G.
Published: July 2002

We present a combined experimental and theoretical study on chemisorption effects at an ionic semiconductor surface which exhibits negligible concentration of intrinsic surface states in the band gap. Chemisorption may be characterized by localized electronic charge redistribution in the valence-band range and by delocalized charge transfer between the adsorption complex and free electrons in the conduction-band range. Geometries, electronic structures, and total energies of adsorption complexes are discussed on the basis of results from sindo1 cluster calculations.
Investigation of InP surface and metal interfaces by surface photovoltage and Auger electron spectroscopies
Authors: Shapira Y. , Brillson L. J. , Heller A.
Published: July 2002

We have used surface photovoltage spectroscopy (SPS) and Auger electron spectroscopy (AES) to investigate the extrinsic surface states produced within the InP band gap by a variety of wet chemical treatments as well as by UHV metal chemisorption, oxidation, and Ar+ bombardment. UHV-cleaved surfaces display no intrinsic surface states, only extrinsic states associated with an excess of surface P. We have attempted to correlate the various SPS features with the chemical composition of these surfaces, particularly with KAg(CN)−2 -treated surfaces, for which the surface recombination velocity on  p-InP is known to decrease significantly.
New high resolution electron spectrometer for surface vibrational analysis
Authors: Kesmodel L. L.
Published: July 2002

The design and performance of a new electron spectrometer for high resolution electron energy loss (EELS) analysis of surface vibrations is described. Based on the 127° cylindrical deflection analyzer (CDA), the spectrometer incorporates a two-stage monochromator, a new lens system with out-of-plane focusing, relatively large (60 mm) energy-dispersing elements, and stringent magnetic field attenuation. Basic spectrometer geometry is compatible with commercial surface analysis systems employing Auger electron spectroscopy (AES), photoelectron spectroscopy (ESCA), low energy electron diffraction (LEED), etc. Performance of the instrument is shown to equal or exceed that of other spectrometers in terms of monochromatic current for a given energy resolution. An overall system resolution of 3.5 meV (28 cm−1) FWHM is routinely achieved at 1.5×10−10 A incident current and high signal levels (105–107 cps) for elastic beam reflection. A higher resolution of 2.5 meV (20 cm−1) has been obtained but with substantial sacrifice of signal level. Performance of the spectrometer is illustrated for the cases of direct (potential barrier) reflection from a palladium(100) crystal surface and for carbon-monoxide adsorption.
Hard diamondlike carbon films deposited by ionized deposition of methane gas
Authors: Mōri Toshio , Namba Yoshikatsu
Published: July 2002

Very hard diamondlike carbon films have been prepared with the aid of an ionized deposition technique. The growth mechanism of films deposited in the presence of methane gas is discussed. The properties of these carbon films are as follows: The concentration of hydrogen atoms contained in the films is almost negligible. Micro-Vickers hardness changes depended largely on the deposition conditions, but some of the values obtained were larger than that of sapphire. The 111, 220, and 311 reflections can be observed clearly in the electron diffraction patterns. Moreover the crystal structure obtained from these rings is very close to that of diamond.
Nondestructive analysis of Hg1−xCdxTe (x=0.00, 0.20, 0.29, and 1.00) by spectroscopic ellipsometry. II. Substrate, oxide, and interface properties
Authors: Arwin H. , Aspnes D. E.
Published: July 2002

Properties of Hg1−x CdxTe substrates, their electrochemically grown anodic oxides, and their interfaces are studied under as-grown conditions using the nondestructive analytic capabilities of spectroscopic ellipsometry to avoid ambiguities arising from destructive analytic techniques. Pseudodielectric functions that are the most accurate representations of the intrinsic bulk responses that we are able to achieve are given for each of the materials studied. The dielectric functions of the oxides are calculated from (tan ψ, cos Δ) data in a three-phase model. These oxides are uniform with sharp interfaces at both substrate and ambient. Residual Te layers of thicknesses of the order of 6%–8% of the initial oxide thicknesses are found on the Hg-containing substrates after their native oxides are stripped with HCl. Four-phase model calculations show that these Te layers are not present (±2 Å) in the as-grown condition for the Hg-containing materials and therefore cannot be invoked to explain leakage in integrated-circuit devices. However, a small residual amorphous (a-Te) layer ∼1.5 Å thick between the semiconductor and electrochemically grown anodic oxide is seen for CdTe. The optical data show the oxide on CdTe to be predominantly the tellurite CdTeO3. The composition of the oxide on HgTe cannot be identified uniquely, but it probably contains a substantial fraction of TeO2. A residual absorption tail below the fundamental edge on all oxides is consistent with the presence of ∼3%–4% a-Te in the oxides. The oxides on the alloys can be represented as physical mixtures of those of the endpoints, suggesting an oxidation mechanism and a structure consisting of TeO2 and some Hg tellurites captured in a relatively insoluble matrix of CdTeO3. After correcting for residual Te overlayers, all substrate dielectric functions for a given material are found to be identical to within 1% regardless of sample history, placing upper limits of less than 2% for cationic or anionic outdiffusion in these materials. A similar consistency of broadening parameters implies that the actual limits may be much lower. The properties of the Hg1−x CdxTe compounds studied in this work vary smoothly with x and show no chemical or physical anomalies.
Probing valence states with photoemission and inverse photoemission
Authors: Himpsel F. J. , Fauster Th.
Published: July 2002

Photoemission and inverse photoemission (or bremsstrahlung spectroscopy) are shown to be complementary techniques for probing occupied and unoccupied electronic states, respectively. The momentum of delocalized valence states can be measured as well as their energy if low electron (photon) energies in the 10–40 eV range are used. Thus, energy band dispersions are obtained for bulk, surface, and adsorbate states which cannot be determined by other techniques. A status report of inverse photoemission is given and illustrated by results for bulk states in ferromagnets and silicides, for broken bond states on silicon surfaces, and for unoccupied molecular adsorbate orbitals.
Stress modification of WSi2.2 films by concurrent low energy ion bombardment during alloy evaporation
Authors: Yee D. S. , Floro J. , Mikalsen D. J. , Cuomo J. J. , Ahn K. Y. , Smith D. A.
Published: July 2002

The effect of ion bombardment on alloy film stress was studied by coevaporating W and Si in the presence of 100 and 400 eV Ar+ ion bombardment at room temperature, 350 and 500 °C. In the absence of ion bombardment, internal stress increases and becomes more tensile as deposition temperature increases. At room temperature, increasing ion bombardment causes the stress to go from tensile to compressive. At 350 °C tensile stress increases as a function of ion flux and decreases slightly at higher flux value. At 500 °C, the effect on stress due to ion bombardment is less pronounced. The correlation between the effect of ion bombardment on stress, deposition temperature, and the structure of the material is discussed using the concept of enhanced surface diffusion and local atomic rearrangement as a mechanism responsible for ion beam stress modification. By using this mechanism, we explain the diminished effect of ion bombardment on stress in the WSi2 films that contain compound phases compared to the amorphous WSi2 in which ion bombardment is more effective. We also attribute this diminished effect of ion bombardment to the more dominant effect of stress due to phase transformation occurring during deposition. The effect of improving the crystalline order and increasing the grain size due to ion bombardment has also been observed. The modification of stress during deposition has been found to have no consequence on the internal stress obtained after 1000 °C postdeposition annealing.
Elevated-temperature sputtering of Ni–Au alloys: Surface and subsurface composition modifications measured by ion scattering spectroscopy
Authors: Lam N. Q. , Hoff H. A. , Régnier P. G.
Published: July 2002

The effects of 3-keV Ne+ ion sputtering on surface and subsurface compositions of a Ni–6 at. % Au alloy at temperatures between 25 and 600 °C were investigated using ion scattering spectroscopy. The equilibrium composition in the surface atom layer during heating prior to sputtering, the time evolution of the surface composition during sputtering, and subsurface concentration profiles after rapid specimen quenching to room temperature were measured as a function of temperature. The steady-state composition at the alloy surface was found to be temperature dependent during sputtering at temperatures above ∼400 °C, which was attributed to significant contributions of the second atom layer to the sputtered-atom flux. This interpretation was supported by the results of theoretical modeling which was performed using the kinetic model of Lam and Wiedersich. From the steady-state concentration profiles measured, the effective altered-layer thicknesses were determined, and information about radiation-enhanced diffusion in the bombarded alloy was also obtained.
The role of surface forces in metal–metal contacts
Authors: Pashley M. D. , Pethica J. B.
Published: July 2002

A real metal–metal contact involves the interaction between many small asperities on each surface. It is the way that these asperities deform and adhere that determines the more macroscopic properties of friction and wear. It is possible to investigate the interaction of a single asperity with another surface by contact experiments between a sharp metal point (1 μm radius) and a flat surface. This type of experiment also enables the interfacial adhesive energy to be directly measured. This parameter is important in thin film adhesion. In order to achieve true metal–metal contact, the experiments are performed on cleaned specimens in ultrahigh vacuum. The force required to separate the contact after a known load has been applied can be measured together wtih the area of contact (determined from electrical resistance). Results show that at very low applied loads the behavior is dominated by the action of surface forces which may themselves be strong enough to initiate plastic flow. There is also direct as well as independent evidence that these small deformed volumes are considerably harder than the bulk. The presence of oxide layers on the metal surface initially reduces the surface energy, but if sufficiently thick will also change the mechanical behavior of the contact. The latest results will be presented together with a discussion of simple models which include the role of surface forces in the contact between two surfaces. The work clearly shows the surface energy can be an important parameter in the behavior of metal–metal single asperity contacts.
Chemical reactions at Pt/oxide/Si and Ti/oxide/Si interfaces
Authors: Liehr M. , LeGoues F. K. , Rubloff G. W. , Ho P. S.
Published: July 2002

Surface spectroscopies and transmission electron microscopy (TEM) techniques have been used to investigate the influence of interfacial oxide (≤50 Å) on chemical bonding and reaction at Pt/Si(111) and Ti/Si(111) interfaces. In both cases the deposited metal undergoes reaction even at room temperature, but the nature of this reaction is very different for Pt vs Ti. Ti reduces a SiO2 surface layer, producing Ti–O bonds; cross-sectional TEM shows that the as-deposited interface is smooth and continuous, a consequence of the Ti–SiO2 interfacial reaction. In contrast, Pt reacts with Si from the substrate, presumably through pinholes, thereby forming silicide. Aggregation of Pt on the SiO2 is observed, confirming the absence of Pt–SiO2 reaction. The disappearance of Si–O bonding features in photoemission spectra is found to be strongly correlated to the morphology of the metal overlayer.
The Si/GaAs(110) heterojunction
Authors: List R. S. , Mahowald P. H. , Woicik J. , Spicer W. E.
Published: July 2002

Si/n-GaAs(110) interfaces grown at both 20 and 300 °C have been studied by UPS, XPS, and LEED. The valence band discontinuity as well as the growth morphology and crystalline order was found to depend on the growth temperature. Discontinuities of 0.6±0.1 and 0.3±0.1 eV were found for 20 and 300 °C growths, respectively. We believe that this difference can be attributed to dangling bond type defect states associated with the more disordered 20 °C growth. In contrast, the growth temperature does not effect the Fermi level pinning, 0.65 eV below the GaAs conduction band minimum (CBM), or the interfacial chemistry.
I
n s
i
t
u ellipsometry studies of the growth of hydrogenated amorphous silicon by glow discharge
Authors: Collins R. W.
Published: July 2002

I n situ single-wavelength ellipsometry measurements have been used to monitor the growth of thin films of hydrogenated amorphous silicon (a-Si:H) deposited on c-Si substrates using an rf glow discharge. Detailed results are presented for two depositions: one from pure SiH4 and the other from SiH4 diluted in Ar (1:10). Other parameters were fixed to obtain material with optimal photoelectronic properties. At the outset of deposition, for even the highest quality material, a nucleation process is observable in the first 65(±10) Å which causes significant deviations of the in situ ellipsometry data from that calculated using thickness independent optical constants. The deviations are modeled in terms of changes with film thickness in bulk density deficits and surface roughness layers. Spectroscopic ellipsometry analysis of films of different thicknesses prepared under identical conditions are presented to support our models. The oxidation behavior of a-Si:H in an O2 plasma, also presented, provides information on the structure of the surface roughness on the films.
Si(111) cleavage and the (2×1) reconstruction process
Authors: Pearson E. M. , Halicioglu T. , Tiller W. A.
Published: July 2002

Using a computer simulation technique with a semiempirical potential, a Si crystal was cleaved along the (111) plane. The π-bonded chain structural features of the Si(111) cleavage surface are observed and found to be a consequence of the dynamics of this cleavage process and seem not to be influenced by the final energetics.
Effect of baking temperature and air exposure on the outgassing rate of type 316L stainless steel
Authors: Odaka K. , Ishikawa Y. , Furuse M.
Published: July 2002

The outgassing rates of a vacuum remelted type 316L stainless steel were measured as a function of baking temperatures, baking durations, and air exposure/baking cycles. Long-time baking, as was expected, reduced the outgassing rate of the stainless steel. A subsequent air exposure and short-time baking in vacuum was found to reduce the outgassing rate much more than the preceding long-time baking. The outgassing rate after baking qAB was reduced with the repeated air exposure/baking cycles at a constant baking temperature. After a few air exposure/baking cycles, qAB was not reduced and remained constant with a further air exposure/baking cycle. This indicates that the surface of the stainless steel reached the steady state with respect to the outgassing as a result of the repeated air exposure/baking cycles. For this thoroughly degassed state, the effect of baking temperature was evaluated in the range of 150 to 450 °C. Six-hour baking at 150 °C was sufficient to attain the outgassing rate of 1.3×10−10 Pa m3/s m2. The relation between the outgassing rate after baking q*AB and the maximum baking temperature TBmax was approximately expressed by the equation log q*AB =−1.87 log TBmax−4.51. The Auger electron spectroscopy (AES) analysis showed that the Cr enrichment at the surface became more evident as the maximum baking temperature increased. Further for a given baking temperature, little significant difference in AES spectra was observed between the thoroughly degassed state and the intermediately degassed state.
Electronically excited photodissociation and desorption of molecules on surfaces
Authors: Chuang T. J. , Domen K.
Published: July 2002

CH2I2 molecules adsorbed on Al2O3 and Al surfaces are used as a model system for studying the photofragmentation and desorption processes involving electronic excitation of the adsorbate. The molecules are promoted into an antibonding state with a pulsed 308-nm laser and the desorption behavior is monitored by time-of-flight mass spectrometry. The system is characterized by x-ray photoelectron spectroscopy, Auger electron spectroscopy, and thermal desorption spectroscopy. The desorption yields as well as the mass and the kinetic energy distributions are determined as a function of surface coverage and laser fluence. The results reveal the electronic, thermal, and ‘‘explosive’’ desorption characteristics depending on both the gaseous exposure and the laser irradiation conditions.
Dynamical processes at surfaces
Authors: Holloway S.
Published: July 2002

Some of the various fates open to a molecule when it scatters from a surface are presented. The physical origins of representative multidimensional potential-energy (hyper)surfaces are discussed, taking as a specific example the charge-transfer reaction A2(gas)→A−2 (surface). By virtue of the temporarily bound negative molecular ion, such systems exhibit a very strong translation/vibrational energy mixing. Trajectory calculations using model potentials for N2, Cl2, and I2 illustrate both T→V coupling and in the limit of high primary energy, collision induced dissociation. The role of topological features in the potential and their possible experimental ramifications are presented. To obtain information on reactive gas–surface potentials it is proposed that for H2 scattering from metals, diffraction data may be inverted. The viability of the approach is demonstrated by performing wave-packet dynamical calculations on a potential having both reactive and diffractive channels open. It is stressed throughout that in order to develop a conceptual understanding of the gas–surface interaction process, a multidimensional approach to the problem is necessary.
New method to control composition ratio of alloy films by compressed magnetic field–magnetron sputtering technique
Authors: Hata Tomonobu , Kamide Yukihiro
Published: July 2002

We propose a new method to control a composition ratio of Si to refractory metal by a compressed magnetic field–magnetron sputtering source. This magnetron sputtering source has two magnetic coils, one is a conventional magnetron coil behind the target (Bm) and the other is a compressing coil (Bc) to increase magnetic field parallel to the target surface. The Bm and Bc can control the spatial position of intense plasma on the target surface. Experiments were performed using a 98-mm Si target with an additional ring-shaped Ta target, which has 98-mm outer diameter and 5-mm width. The Si/Ta ratio of sputtered films was controlled from 1 to 10 only by changing Bc from 108 to 197 G for constant Bm (=630 G).
Gas density reduction effects in magnetrons
Authors: Rossnagel S. M.
Published: July 2002

The gas density in front of a magnetron cathode has been found to be significantly reduced as a function of magnetron current. The reduction is due to gas heating and rarefaction resulting from collisions with the sputtered atoms ejected from the cathode surface. The density reduction is nonlinear with discharge current, and is sensitive to the sputter yield of the cathode, the average ejection energy of the sputtered atoms, the cross section for sputtered atom–gas atom collisions and the pressure, temperature, and thermal conductivity of the background gas. The process can be treated semiquantitatively in terms of heat conduction from the hot region near the cathode to the cold walls of the chamber. The presence and magnitude of this gas density reduction should have significant impact on the understanding of the plasma impedance, as well as the deposited film properties and the relative arrival rates for reactive depositions.
Radial current distribution at a planar magnetron cathode
Authors: Wendt A. E. , Lieberman M. A. , Meuth H.
Published: July 2002

Experiments and theory are used to investigate the radial distribution of current at the cathode of a cylindrically symmetric, planar magnetron discharge. We have developed a simple model of the distribution of incident ions at the cathode, in the form of an integral equation. Energetic electrons, produced by secondary electron emission when ions strike the cathode, are accelerated into the discharge through a thin sheath. The Hamiltonian motion of the energetic electrons in the magnetic field determines the birthplace of discharge ions, and thus, the distribution of ion current density at the cathode. The radial current distribution has been measured for various magnetic fields using a radially staggered array of sixteen 1-mm-diam current probes imbedded in a 9-in.-diam cathode. In agreement with the model, the current distribution is peaked at the radius at which the magnetic field is tangent to the cathode plate, and the width of the distribution scales as the square root of the energetic electron Larmor radius.
Chemical reactions at the Si/GaAs(110) and Si/InP(110) interfaces: Effects on valence-band discontinuity measurements
Authors: List R. S. , Kendelewicz T. , Williams M. D. , McCants C. E. , Lindau I. , Spicer W. E.
Published: July 2002

Many photoemission measurements of the valence-band discontinuity are based on the relative positions of the centroids of poorly resolved photoemission peaks. While such measurements are in principle accurate for abrupt, nonreactive interfaces, real interfaces are rarely so simple. We present high-resolution soft x-ray photoemission core level spectra which monitor the band bending and chemistry at two representative heterojunctions. The Si/InP(110) interface is highly reactive, has well-resolved chemically shifted In and P components, and has preferential outdiffusion of In while the Si/GaAs(110) heterojunction has very subtle chemical reactions which are confined to the interfacial region. The effects of even such subtle chemical shifts can obscure the determinations of band bending and lead to errors as large as 0.3 eV for the Si/GaAs(110) heterojunction discontinuity. Such results emphasize the importance of obtaining high-resolution photoemission spectra and applying careful analysis for accurate determinations of band bending and valence-band discontinuities.
Theory of the local tunneling spectrum of a vibrating adsorbate
Authors: Baratoff A. , Persson B. N. J.
Published: July 2002

We present a model describing the essentials of tunneling between the tip of a scanning tunneling microscope (STM) and an electronic resonance on an isolated adsorbed molecule. Conditions for observing enhanced inelastic tunneling and its experimental manifestations are identified in terms of the energy and width of the resonance and of its coupling to a particular molecular vibration. For a broad resonance, this occurs if it is partially filled; we then predict a conductance decrease as large as 10% at the inelastic threshold for typical chemisorption systems. For a resonance weakly hybridized with the underlying electrode, strong multiphonon excitation is possible, although as a rule it will not be readily apparent. Relevant systems of interest for local spectroscopy with future STM’s are discussed.
Atomic resolution atomic force microscopy of graphite and the ‘‘native oxide’’ on silicon
Authors: Marti O. , Drake B. , Gould S. , Hansma P. K.
Published: July 2002

An atomic force microscope (AFM) can image surfaces of conductors, insulators, and even organic materials. Images of highly oriented pyrolytic graphite show atomic structure with a corrugation height of 0.03 nm. Images of the ‘‘native oxide’’ layer grown in ambient pressure on a (111) facet on a (100) silicon wafer show steps. Images of the native oxide layer on a (111) silicon wafer show features 0.6 nm apart and aligned with the silicon substrate. The images shown here were obtained with an instrument that can also operate as a scanning tunneling microscope (STM); it is an AFM/STM.
Residual stress anisotropy, stress control, and resistivity in post cathode magnetron sputter deposited molybdenum films
Authors: Cuthrell R. E. , Mattox D. M. , Peeples C. R. , Dreike P. L. , Lamppa K. P.
Published: July 2002

As part of the program to develop a large-area thin-film pulse heater for a lithium ion source, the residual stress in post cathode magnetron sputter deposited molybdenum films has been studied. It was found that in films prepared in the low-pressure sputtering regime, the residual film stress is very sensitive to the gas pressure during sputtering and that the film stresses are highly anisotropic. The transition pressure for changing from compressive to tensile residual stress, as defined by Thornton and Hoffman, depends on the relationship between the measurement direction in the film and the post cathode orientation. In order to deposit a nearly stress-free film a pressure cycling technique was developed which deposited alternate film layers containing tensile and compressive stresses. Film resistivity and thermal coefficient of resistivity measurements were made during the pulse heating of the molybdenum films.
The deposition rate and properties of the deposit in plasma enhanced chemical vapor deposition of TiN
Authors: Jang Dong Hoon , Chun John S. , Kim Jae Gon
Published: July 2002

Titanium nitride (TiN) films were deposited onto tool steels and cemented carbide cutting tools by plasma enhanced chemical vapor deposition (PECVD) using a gaseous mixture of TiCl4, N2, H2, and Ar in order to find out the effects of the deposition temperature and rf power density on the deposition rate and properties of deposited TiN. The deposition rate and crystallinity of the deposited TiN was affected by the deposition temperature as well as the plasma power density. The deposition rate was decreased with an increase in deposition temperature between 270 and 430 °C. The crystallinity of deposited TiN was improved by an increase in deposition temperature as well as rf power density. Crystalline TiN was obtained above 300 °C and showed a strong crystallographic preferred orientation of 〈200〉. TiN layers deposited by PECVD using TiCl4 as a reactant contained chlorine, the content of which was increased with a decrease in deposition temperature. Oxygen at the interface between the TiN deposited layer and the substrate excluded nitrogen and chlorine. The surface morphology of the deposited TiN is a dome-shaped cluster composed of many fine grains.
Review of ion-based coating processes derived from the cathodic arc
Authors: Sanders David M.
Published: July 2002

The cathodic vacuum arc provides a means of producing large currents of positive ions of a wide variety of materials. These ions can be utilized to produce coatings with improved properties such as higher density and adhesion. The processing is particularly useful in reactive deposition of ceramic coatings having excellent stoichiometry. In this review, emerging aspects of the technology are emphasized.
Sputter deposition of gold in rare-gas (Ar,Ne)–O2 discharges
Authors: Klumb Arlene M. , Aita Carolyn Rubin , Tran Ngoc C.
Published: July 2002

In the present study, we investigate the films that result when a gold cathode is sputtered in rare-gas (Ne, Ar)–O2 discharges. Si(111) substrates were used. The results show that a large increase in resistivity, a decrease in reflectivity to one-half the value for metallic gold, and the possible formation of a second phase with no long-range crystallographic order detectable by x-ray diffraction are coincident with the formation of Au–O bonds in the films. Au–O bond formation occurs at a lower gas O2 content when Ne rather than Ar is used as the rare-gas component of the discharge.