bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition of silicon alloys in an integrated distributed electron cyclotron resonance reactor: Oxide, nitride, oxinitrides, and multilayer structures
Authors: Bulkin P. , Hofrichter A. , Heitz T. , Huc J. , Drévillon B. , Benattar J. J.
Published: July 2002

The films of SiOxNy were deposited in an integrated distributed electron cyclotron resonance reactor. Due to planar geometry, such deposition processes can be scaled-up for processing of large areas. Deposition kinetics and material properties were studied in order to find the common principles for obtaining faster growth rates and more uniform deposition of high quality films. Films were grown without bias at room temperature from mixtures of SiH4, O2, and N2 at high deposition rates (more than 4.5 nm/s for silica). Optical properties of the films were analyzed using ultraviolet (UV)-visible and infrared spectroscopic ellipsometry. The influence of gas flows, temperature, pressure, microwave power, and rf bias was investigated. A multilayer optical filter was grown on a polycarbonate substrate using a UV-visible ellipsometer to control the deposition process. The success of this test confirms the accuracy of the experimental results and shows high promise for the technology.
Orbitron Pump of 30-cm Diameter
Authors: Maliakal Joseph C. , Limon Peter J. , Arden Eldon E. , Herb R. G.
Published: July 2002

An Orbitron pump of 30-cm diameter was constructed and performance was studied as parameters were varied. The pump arrangement chosen gave pumping speed values of 105 liters/sec for argon, 4500 liters/sec for air, 6000 liters/sec for nitrogen, and 9000 liters/sec for hydrogen.
Comparison of Static and Dynamic Calibration Methods for Ionization Gauges
Authors: Meinke C. , Reich G.
Published: July 2002

Ionization gauges have been calibrated by a static expansion method in the pressure range of 10−2–10−6 Torr with a absolute accuracy of ± 3%. The repeatability of the linear calibration curve is 1%. The sensitivity of the gauges thus calibrated has been checked by a dynamic method, comprising a flow measurement through a porous plug and a calculated circular orifice. The accuracy of this method is ± 7%. Evaluation of the measurements of flow and sensitivity is done by an electronic computer. The results agree within the limits of error with those obtained by the static method. The dynamic method can be used for calibrations down to pressures of 10−10 Torr while the static method has its lower limit at 10−6 Torr because of sorption phenomena.
Alternating Current Electrical Properties of Evaporated Molybdenum Oxide Films
Authors: Simmons J. G. , Nadkarni G. S.
Published: July 2002

The limitations of dc measurements on doped thin film metal-insulator-metal structures are discussed, particularly in regard to the identification of the band structure of such systems. It is shown that the use of ac techniques provides a much wider scope of measurements which can be used to determine information about the energy diagram of thin film insulators. Furthermore such measurements have prominent characteristics which may be related to the band structure of the sample. The technique has been applied to evaporated Au–MoO3–Au samples, the capacitance of which are found to be extremely temperature sensitive; capacitance changes of 50:1 over 100 °C temperature range are reported. At low temperature the capacitance corresponds to the geometric capacitance, but at high temperatures is independent of the film thickness. The results are explained in terms of Schottky barriers at the Au–MoO3 interfaces, and the energy diagram of the system clarified. The doping density in the MoO6 is estimated to be about 1018 cm−3.
Some Causes of Poor Peak Shapes in Quadrupole Field Mass Analyzers
Authors: Whetten N. R. , Dawson P. H.
Published: July 2002

The performance of quadrupole field mass analyzers can be degraded by imperfections in the field. The imperfections may be the result of geometrical errors in the electrode structure or time errors in the applied waveforms. von Busch and Paul considered the nonlinear resonances resulting from these errors for the quadrupole mass filter using an analytical treatment of the ion motion. The authors extended this work to the three-dimensional quadrupole mass spectrometer, and using numerical computation of ion trajectories calculated the extent as well as the position of the resonances. In this paper, new experimental data are presented showing the occurrence of nonlinear resonances and the agreement between theory and experiment. The effect of adjustments in electrodes spacing on peak shapes was investigated. The results demonstrate that an analysis of the nonlinear resonances can provide an indication of the errors that are present. A new type of instability was found in the three-dimensional quadrupole, and a tentative explanation is presented.
Some Calculations of the Thickness Distribution of Films Deposited from Large Area Sputtering Sources
Authors: Gnaedinger Robert J.
Published: July 2002

The distributions of intensity incident upon parallel and perpendicular receiver elements are derived for a uniform, cosine-emitting, circular plane source. The exact expressions representing these distributions have been computer-evaluated and machine-plotted using normalized parameters; these plots are presented. In addition plots are given of the contributions to the total incident intensity on centered receiver elements from circular ring and linear strip elements of the source. The derivation proceeds with the point of view that the source is a sputtering or evaporation surface; it assumes that no molecular scattering occurs during transit and that the sticking coefficient on the receiver is unity. It is found that, for adjacent perpendicular and parallel receiver elements located within the projection of the disk source, the intensity incident upon the perpendicular element is significantly less than that incident upon the parallel element.
The use of yttrium and scandium for fabrication of radioactive electron emitters
Authors: Singleton J. H. , Yannopoulos L. N.
Published: July 2002

Thin films of titanium tritide are widely used as a radioactive source of electrons of average energy ∠5.7 keV. Because of the limited thermal stability of this tritide, such films can only be exposed to temperatures above 200°C for very short time intervals during processing or operation. The production of emitters which can be used at temperatures 100−150°C higher than those using titanium is described. The films of yttrium and scandium, of thickness 5000−12000 Å, on stainless steel substrates, contain in excess of one tritium per metal atom and yield stable electron densities of 1−2×10−10 A/cm2. The films have good adhesion and resist abrasion; they can be sheared to a desired size either before or after loading with tritium. The thermal stability of the electron emitters in vacuum, hydrogen, and a hydrogen−nitrogen mixture has been determined. The data illustrate the profound influence of surface contamination on both the loading and loss of tritium in the films.
Molecular shield: An orbiting low density materials laboratory
Authors: Melfi Leonard T. , Outlaw R. A. , Hueser J. E. , Brock F. J.
Published: July 2002

A molecular shield model in terrestrial orbit above 200 km is analyzed using the kinetic theory of a drifting Maxwellian gas. Data are presented for the components of the gas density within the shield due to the free stream atmosphere, the outgassing from the shield and enclosed experiments, and the atmospheric gas scattered off a shield–orbiter system. The disturbance caused by the orbiter for a 100-m separation produces a negligible effect on the shield density. From the analysis presented, the atmospheric component of the gas density within the shield is less than 103 cm−3, principally atomic hydrogen. (An equilibrium gas density of 103 cm−3 corresponds to a pressure of ?4.0×10−12 Pa at 300 K.)
Investigation of plasmon sidebands by synchrotron radiation tuning of electron escape depths
Authors: Flodstrom S. A. , Bachrach R. Z. , Bauer R. S. , McMenamin J. C. , Hagström S. B. M.
Published: July 2002

Photoelectron spectra of Al and Si have been excited by monochromatized synchrotron radiation at different photon energies. The plasmon loss structures produced by the elastic electrons from the Si 2p and Al 2p core levels have been investigated for different kinetic energies at the elastic electrons. Variation of the plasmon loss intensities for electron kinetic energies of 30–330 eV explains earlier reported absence of plasmon structure in uv photoelectron spectroscopy. The results also indicate that a model of extrinsic bulk plasmon excitation developed by Mahan and modified to account for surface effects could explain the observed threshold behavior of bulk plasmon intensity at low electron kinetic energies.
Discharge cleaning experiment in the JFT-2 tokamak with surface observation by AES
Authors: Gomay Y. , Tazima T. , Fujisawa N.
Published: July 2002

The effects of wall conditioning by tokamak discharges with low toroidal magnetic field have been studied by observing the concomitant changes in discharge characteristics, wall conditions, and residual gases. After 2500 shots of discharge cleaning, stable reproducible plasmas with Zeff=4.5 were obtained with the equilibrium surface composition of vacuum wall samples which consists of the limiter and wall materials (molybdenum and 304 stainless steel, respectively), carbon, and oxygen. Depth profiling by Auger/sputter techniques shows that the mixed layers composed of the same elements as the surfaces were formed on the samples. The layers are thicker by 5–10 times on the sample located at the minimum inner radius of vacuum chamber than on the one located 3.4 cm further away from the plasma. The results indicate that the wall condition is determined by deposition of the metallic particles during the discharge and adsorption of the residual gases during the interval between discharges.
Analysis of the imaging accuracy in reactive ion etching
Authors: Ukai Katsumi , Hanazawa Kunio
Published: July 2002

In reactive ion etching the factors which have influence on imaging accuracy consist of the swell of the resist mask, the reduction of the mask, and the undercutting. We investigated these factors about polycrystalline Si, Al, and Mo films on Si wafer. The undercutting depends on the overetching time and the ion current. In the case of etching poly-Si film, it corresponds with the change of the impedence of CF4 discharge. Also it was made clear by comparing the experimental results with the calculated field model that the size of undercutting depends on not only the random motion of the ions but the lack of uniformity of the cathode fall caused from the ruggedness of the pattern on the substrate surface. This fact is consistent with the phenomenon that the dimensional change by etching within the substrate depends on the pattern size.
Double-aperture method of producing variably shaped writing spots for electron lithography
Authors: Thomson M. G. R. , Collier R. J. , Herriott D. R.
Published: July 2002

Edge definition in an electron-beam lithography instrument may be improved by imaging an illuminated aperture instead of a Gaussian electron source, but such a system suffers from either slow throughput or large minimum feature size. A system has been constructed here in which an image of one aperture is projected onto a second, and both are imaged onto the writing surface. By changing the relative positions with an electrostatic deflection system, the size and shape of the writing spot may be changed within a few nanoseconds. Two square apertures can be used to give a writing spot of rectangular cross section with variable dimensions. Such an arrangement can be used directly in vector scan, and an example of a scheme for raster scan is described. Alternatively, an aperture of complicated shape is used so that the writing spot resembles four independent spots adjacent to each other. By using suitable electrostatic deflection, any combination of the four can be blanked off at any one time. A system employing this technique has been constructed, and simple patterns written on silicon wafers demonstrate a factor of four increase in speed over the Bell Laboratories EBES lithography instrument.
Energy distributions of sputtered copper neutrals and ions
Authors: Lundquist Theodore R.
Published: July 2002

Direct quantitative analysis of surfaces by secondary ion mass spectrometry (SIMS) will depend on an understanding of the yield ratio of ions to neutrals. This ratio as a function of the energy of the sputteredd particles has been obtained for a clean polycrystalline copper surface sputtered by 1000–3000 eV Ar+. The energy distributions of both neutral and ionized copper were measured with a retarding potential analyzer (RPA) using potential modulation differentiation and signal averaging. The maximum for both distributions is identical and occurs near 2.5 eV. The energy distributions of neutrals is more sharply peaked than that of the ions, presumably as a consequence of more efficient neutralization of slow escaping ions by the mobile electrons of copper. The ion–neutral ratio, which is found to be proportional to En/2 with 0.6<n<1.4, is compared with various ionization models.
An AES study of the surface composition of ion-etched iron–chromium alloys: effect of adsorbed CO
Authors: Frankenthal R. P. , Thompson D. E.
Published: July 2002

The surface composition of a series of iron–chromium alloys was analyzed by Auger electron spectroscopy as a function of Ar and Ne ion etching conditions. The relative sensitivity factor was determined from iron and chromium and from an Fe–25%Cr alloy and was found to be independent of composition. No preferential sputtering of either alloy component was observed as long as the surface was free from any impurities. When small quantities of CO are adsorbed onto the alloys’ surfaces, the Cr content appeared to decrease markedly, much more than when H2O adsorbed. It is suggested that the preferential adsorption of CO onto Cr atoms of the alloy surface can account for this effect. Similar effects are likely during ion etching of other alloy systems.
Pseudopotential surface and interface calculations
Authors: Schlüter M.
Published: July 2002

A large body of surface and interface calculations using pseudopotentials has appeared in recent years. Their apparent success in explaining numerous experimental observations has to be contrasted with their inherent limitations and disadvantages. In an attempt to assess pros and cons, I shall first discuss some basic approximations underlying the definition of effective one-electron potentials. Next, I shall describe the use of pseudopotentials in lieu of core plus valence electron crystal potentials. While the neglect of core states brings about computational advantages, new problems arise related to transferability, nonlocality and pseudopotential charge self-consistency. Finally, I shall discuss some surface and interface models, commonly used in connection with pseudopotential calculations.
Surface texturing of copper by sputter etching with applications for solar selective absorbing surfaces
Authors: Curmi P. M. , Harding G. L.
Published: July 2002

Solar selective absorbing surfaces have been produced by texturing copper specimens in a novel magnetron cosputtering system which allows high rate sputter etching of a moving metal plate seeded with low sputter rate material. Unusual topographical features have been produced on copper in this apparatus using titanium seed. The variation of optical properties and surface morphology of the copper as a function of sputter etching conditions has been studied. Typical selective surfaces produced have absorptances α∠0.90 and emittances ε∠0.10 at 300 K.
Plasma etching characteristics of chromium film and its novel etching mode
Authors: Nakata H. , Nishioka K. , Abe H.
Published: July 2002

The influences of chromium and chromium oxide films and gas compositions on plasma etching characteristics were investigated. Oxygen as well as chlorine is found to be responsible for etching. One possible etching reaction is proposed, in which a basic reaction product is assumed to be CrO2Cl2 which will be volatile in gas plasma. The impurities such as W, Fe, and Cu contained in the film become nonvolatile compounds which accumulate on the surface of the film and form a masking layer resulting in a suppression of the reaction. Anomalous etching modes called the contour and reverse etches were found with the chromium oxide films containing tungsten impurities. The mechanism of these anomalous etching modes is discussed, in which the accumulation of the tungsten compounds on the surface of the film is a basic mechanism. The reverse etch mode was applied to the fabrication of photomasks for MOS LSI.
Light scattering spectroscopy of electrons in GaAs–(AlGa)As heterostructures: Correlation with transport properties
Authors: Pinczuk A. , Worlock J. M. , Störmer H. L. , Gossard A. C. , Wiegmann W.
Published: July 2002

We used the resonant inelastic light scattering method to study high mobility electrons confined in modulation-doped GaAs–(AlGa)As multiple quantum-well heterostructures. In spectra of intersubband transitions we observe a correlation between FWHM and electron mobility. In the lower mobility cases (μ≲30 000 cm2/Vs) we find an unusual dependence of FWHM on incident photon energy. The results are interpreted in terms of wave vector conservation broken by intermediate-state relaxation processes similar to those that limit the electron mobility.
Novel plasma developable resist compositions and performance of total dry microfabrications in submicron lithography
Authors: Tsuda M. , Oikawa S. , Kanai W. , Hashimoto K. , Yokota A. , Nuino K. , Hijikata I. , Uehara A. , Nakane H.
Published: July 2002

A principle for the formulation of plasma developable resists and an example of new resist compositions are described. Resist patterns with submicron resolution and excellent profile have been produced readily using new resist compositions and the dry development process which is inherently free from swelling, from which the low resolution of resist images arises. The importance of the dry developable resist in submicron fabrication technology, the characteristics of the new resist compositions in the dry development process, and the dry development mechanism are discussed. The total dry microfabrication including the development of resist, the etching of Si and SiO2 and the removal of resist, was performed in the process using the new resist compositions.
Initial stages of anodic oxidation of GaAs
Authors: Makky W. H. , Cabrera F. , Geib K. M. , Wilmsen C. W.
Published: July 2002

The island stage of the anodic oxidation of GaAs was investigated with transmission electron microscopy (TEM). Many island details are seen in the high-resolution photomicrographs of platinum–carbon secondary replicas of the GaAs surface. The nucleation and coalescence processes are seen to take place continuously during the passivation time. The islands are normally circular in shape except when altered by coalescence. The height of the islands increase with island size up to an area of ≊0.1 μ2 after which the island height increases only slowly or not at all.
Correlation between the ion bombardment during film growth of Pd films and their structural and electrical properties
Authors: Ziemann P. , Kay E.
Published: July 2002

Pd films were produced in a long mean free path dc triode system using Kr as sputter gas ( pKr=1 mTorr) and with simultaneous ion bombardment of the growing Pd film. The resulting film properties are related to the energy En delivered by the bombarding Kr ions to the growing film per arriving sputtered Pd atom. Systematic changes of the Kr concentration, the lattice parameter, strain, grain size, preferential orientation, and residual resistivity are observed as a function of En. Analysis of the data suggests that, in addition to a possible direct influence of the incorporated Kr, defects produced by the ion bombardment are causing these property changes. This is confirmed by preliminary TEM results revealing a high density of dislocations.
Reliability of high vacuum measurements
Authors: Tilford Charles R.
Published: July 2002

In order to allow the users of vacuum measurements to assess the reliability of their measurements, the current state of high-vacuum standards and gauging is reviewed. The discussion includes several types of high-vacuum primary standards currently in use, an assessment of probable errors for several types of hot filament ion gauges, user-controlled factors that may serve to increase the errors, and the information available to date on the performance of a commercially available molecular drag gauge. Examples are given of the introduction of additional errors by the improper application of vacuum gauges.
Current image diffraction (CID) of single crystal metal surfaces
Authors: Bargeron C. B. , Nall B. H. , Jette A. N.
Published: July 2002

Images of single crystal metal surfaces made with a low energy (<400 eV) scanning electron beam exhibit diffraction patterns in the absorbed current. Dynamical theoretical calculations of the total reflectivity of the surface as a function of incident polar and azimuthal angles at a specified energy indicate that these patterns are primarily due to the elastically backscattered electrons. In this paper, several patterns on aluminum (100), (110), and (111) surfaces and the copper(100) surface are presented, some of which have features quite similar to those of electron channeling patterns that have been observed at much higher energies (several keV). That is, patterns containing dark and light lines corresponding to high and low reflectivities from Bragg planes are observed. The energy dependence of these lines correspond to simple Bragg theory. Thus, the inner potential and layer displacement can immediately be extracted from the images.
Plasmons and intersubband plasmons of a superlattice
Authors: Bloss W. L.
Published: July 2002

The collective plasmon modes of a doped or modulated doped semiconductor superlattice are investigated via a calculation of the wave-vector frequency-dependent dielectric constant. Explicit account is taken of the quantum well subband structure; including finite wave functions and intersubband transitions. Superlattice plasmons with dispersion quite different from bulk plasmons are found. Results for the interaction of light with these superlattice plasmons will also be presented. A new intersubband plasmon mode involving the coupling of the charge depolarization response into modes propagating along the superlattice axis is predicted. These collective excitations are also investigated in the classical regime where the electron deBroglie wavelength is much less than the well size. Here, we consider a superlattice of metal slabs, each capable of supporting symmetric and antisymmetric surface plasmon modes which couple into corresponding plasmon bands along the superlattice axis. The relationship between these modes and the ground superlattice plasmon and intersubband plasmon is derived.
Surface magnetism: Recent progress and opportunities
Authors: Campagna M.
Published: July 2002

Analytical and numerical progresses (i.e., Monte Carlo simulations) in the theory of phase transitions as well as experimental advances in the tools for surface magnetism are opening new horizons for this old field of solid state physics. Examples we shall describe involve 10 yr old predictions of magnetic surface reconstruction, their relation to the understanding of different phenomena like wetting or prewetting. Spin-resolved photoemission spectroscopy using synchrotron radiation, inverse photoemission, and electron scattering using polarized electrons from AlGaAs or GaAsP photocathodes are the primary new tools, which take advantage of the simultaneous availability of conventional preparation (e.g., UHV-epitaxy) and characterization techniques used in surface science studies. These experiments are expected to lead also to new insights in the microscopic origin of second order phase transitions in the special case of 3d metals.
Deposition of cesium iodide on Parylene-N pellicles
Authors: Tassano P. L.
Published: July 2002

During the development of a photocathode for a streak camera, Cesium Iodide was vacuum coated onto Parylene−N pellicles. This paper outlines the handling and vacuum evaporation coating techniques which were used to deposit CsI upon Parylene−N and presents a comparison of results between Lawrence Livermore National Laboratory produced foils and those which were commercially available. (AIP)
A scanned microfocused neutral beam for use in secondary ion mass spectrometry
Authors: Eccles A. J. , van den Berg J. A. , Brown A. , Vickerman J. C.
Published: July 2002

The construction of a gun capable of producing a microfocused (FWHM=5 μm) beam of Ar atoms at 10 keV for use in secondary electron and SIMS imaging of insulating samples is described. The design is based on the principle of neutralizing an ion beam by charge transfer subsequent to rastering and microfocusing, and therefore utilizes a final focusing lens with long working distance (60 mm). Neutral beam intensities of up to 20% of the focused ion beam can be produced. The performance of the gun is illustrated by secondary-electron and secondary-ion images of insulators.
Room-temperature formation and oxidation properties of the Cr/Si(111) interface
Authors: Wetzel P. , Pirri C. , Peruchetti J. C. , Bolmont D. , Gewinner G.
Published: July 2002

The structural and electronic properties of the Cr/Si(111) interface formed at room temperature (RT) are investigated by low-energy electron diffraction, x-ray photoelectron spectroscopy and angle resolved ultraviolet photoemission spectroscopy, and work function measurements. The data indicate strong reactive behavior in agreement with a previous study by Franciosi et al. The data show intermixing up to ∼25 monolayer (ML) Cr coverage with an overlayer stoichiometry evolving gradually from Si rich to Cr rich phases with increasing Cr coverage. The reacted phases are metastable and definitely different from any known bulk silicide. Above ∼30-ML Cr coverage, polycrystalline bulk Cr metal is formed. Further insight into the nature of the intermixed layer comes from oxidation studies of the interface as a function of Cr coverage. A progressive shift of the oxidized Cr 3d, Cr 2p3/2, and Si 2p lines with Cr coverage in the 0–25 ML range implies different oxidation states for Si and Cr species at various steps of the interface formation, and in turn, indicates a composition gradient normal to the surface. The data also demonstrate that above ∼2-ML Cr coverage the oxygen uptake of the interface is up to 10 times faster than for definite silicides such as CrSi or CrSi2. The enhanced interface reactivity of the metallic RT grown Si–Cr phases apparently originates in their unique metastable bulk and surface composition and structure.
Structural characterization of surfaces by extended energy-loss fine-structure spectroscopy
Authors: De Crescenzi Maurizio
Published: July 2002

We present recent structural investigations by extended energy-loss fine-structure (EELFS) measurements. The EELFS technique relies on the detection of the fine-structure losses above a core edge in the reflection mode. We demonstrate the possibility of extracting the radial distribution F(R) around each investigated atom. This is obtained by applying to the experimental EELFS data the Fourier transformation and the theoretical analysis used for extended x-ray absorption fine structure (EXAFS) spectroscopy. The aim of this paper is to answer the principal questions addressed by the EELFS technique in the last few years (dipole approximation, phase shift, backscattering amplitude transferability, and quantitative structural parameters, etc.). This is obtained by a systematic investigation on different elements around different core levels and by comparing our experimental spectra with EXAFS spectra. Technological application of the surface-EELFS technique for interface formation studies and clusters lattice parameter determination will be presented and discussed.
Photoelectronic properties of a-Si:H and a-Ge:H thin films in surface cell structures
Authors: Parsons G. N. , Kusano C. , Lucovsky G.
Published: July 2002

We have grown thin films of a-Si:H and a-Ge:H by reactive magnetron sputtering and have studied their photoelectronic properties in surface cell structures. The dark and photocurrents do not obey the expected scaling laws with respect to changes in the sample thickness. This is explained in terms of a model which assumes depletion regions at both surfaces of the thin-film structure. We have analyzed the properties of such structures and have used the thickness dependence of the dark current and activation energy to estimate: (1) the defect concentrations near the Fermi level and (2) the amount of surface band bending. Defect densities so obtained are in agreement with those determined from space-charge limited currents (SCLC’s) and photodeflection spectroscopy (PDS).
Characterization of ultrathin SiO2 films formed by direct low-energy ion-beam oxidation
Authors: Yu C. F. , Todorov S. S. , Fossum E. R.
Published: July 2002

Bombardment of silicon (100) surfaces at room temperature by an oxygen-containing low-energy ion beam is studied as an alternative to thermal oxidation to produce ultrathin oxide films. A self-limiting oxide thickness of about 50 Å is obtained by using ions with energy 100 eV or lower. Auger electron spectroscopy depth profiles of an ion-beam grown oxide and a thermally grown oxide show very similar composition. Grazing angle x-ray photoelectron spectroscopy indicates the presence of lower oxides of silicon near the surface. The capacitance–voltage characteristics of ion-beam grown oxides compare favorably with those of thermally grown oxides.
The growth and stability of Ag layers on Cu(110)
Authors: Taylor T. N. , Hoffbauer M. A. , Maggiore C. J. , Beery J. G.
Published: July 2002

Combined surface science and high-energy ion beam techniques have been used to characterize the composition, structure, and thermal stability of Ag layers <900 Å thick on Cu(110). A uniform Ag/Cu surface composite is formed for one-monolayer coverage. Analysis of its growth with low-energy electron diffraction shows that the Ag is initially confined to the [11̄0] troughs and that further deposition results in a Ag(111) layer exhibiting c(2×4) symmetry. This determination of Ag coverage is consistent with absolute coverages measured with Rutherford backscattering. Beyond one-monolayer coverage, the deposition of Ag at 300 K produces clustering (Stranski–Krastanov mechanism) in contrast to a poorly ordered but more uniform layering mode when deposited at 130 K. Following nucleation for a deposition between one and two monolayers at 300 K, Ag clusters ∼20 Å thick grow laterally across the surface up to five- or six-monolayers deposition. Continuous films grown cold at thicknesses ≤115 Å are found to agglomerate above 500 K exposing a tenacious Ag–Cu interface like that formed by one-monolayer Ag deposition.
Calibration of secondary neutral and secondary ion mass spectrometry: A comparative study
Authors: Tümpner J. , Wilsch R. , Benninghoven A.
Published: July 2002

The sensitivity and the dynamic range of a quadrupole based mass spectrometer for the quasisimultaneous analysis of secondary ions and electron beam postionized sputtered neutrals has been improved. Counting rates larger than 106 counts/s of postionized neutrals with a dynamic range of six orders of magnitude have been obtained for iron samples bombarded by 10-μA, Ar+, 5 keV. A comparison of secondary ion mass spectrometry (SIMS) and secondary neutral mass spectroscopy (SNMS) results considering target preparation, sensitivity, reproducibility, accuracy of quantification, and total time of analysis will be presented for 13 steel targets alloyed with up to 15 different elements. Concentration ranges between 8 ppm and 1% have been covered. From the experimental results we found that the detection limit is in the range of 10−4 (oxygen) of a monolayer on a target area of 4 mm2, when the spectrometer is tuned to a distinct mass. This allows quantitative surface and interface analysis in a concentration range below Auger electron spectroscopy.
Superposition of Auger electron spectroscopy depth profiles obtained on Cr/Ni multilayer samples with different roughnesses
Authors: Zalar A. , Hofmann S.
Published: July 2002

Practical depth profiling by ion sputtering is strongly influenced by sample roughness. Auger electron spectroscopy (AES) depth profiling studies for multilayer Cr/Ni thin-film structures on rough substrates could be explained by assuming a superposition of depth profiles of many microplanes with widely different angles with respect to the ion beam direction. To test the validity of this assumption, the AES depth profiles of samples consisting of two parts with different roughnesses, Ra=0.012 μm and Ra=0.920 μm, were measured. In five subsequent experiments, the analyzed area was changed from 100% to 0% of the part with Ra=0.012 μm. The results were evaluated for the depth resolution Δz as a function of the sputtered depth z between 25 and 375 nm. Good agreement was obtained between experimental results and calculations of the total Δz as a function of the area fractions of the different roughnesses according to a linear superposition of Δz for different microplanes.
Oxygen induced surface segregation of Fe in Fe–18Cr–3Mo(100)
Authors: Polak M. , Schiffmann B.
Published: July 2002

Variations in the composition of the outermost few atomic layers in Fe–18Cr–3Mo (100), caused by exposure to O2 (up to 100 L) at ambient temperature, were studied by monitoring the low-energy Auger (MVV) and autoionization emissions of Fe and Cr, and the MNV emission of Mo. Under these conditions neither Cr–oxide nor Mo–oxide were formed. At∼5-L O2, the Cr0 line disappeared completely, and at ∼10-L O2 enhancement of the Fe autoionization emission at ∼51 eV indicated the onset of Fe–oxide formation. The low-energy region of the spectrum recorded after 100-L O2 exposure exhibited striking resemblance to the spectrum recorded for an oxidized elemental iron sample. Severe relative attenuation of the Mo lines indicated that this constituent, too, does not participate in the initial surface segregation and oxidation, but remains in the subsurface region. The observed O chemisorption induced surface segregation of iron and the formation of surface Fe–oxide rather than the more stable Cr–oxide (or Mo–oxide) is attributed to kinetic effects.
Thermally induced behavior of liquid mixtures of hydrogen isotopes inside a spherical inertial confinement fusion target
Authors: Varadarajan V. , Kim K. , Bernat T. P.
Published: July 2002

A theory is presented which is intended to explain thermally induced formation of uniform liquid layers of ternary mixtures of hydrogen isotopes inside a spherical inertial confinement fusion (ICF) target. The governing equations are the equations of stream function, modified vorticity, and energy, and the equations of conservation of the individual isotopic species. The equations for the diffusion fluxes of the species include both ordinary and thermal diffusions. These coupled equations are solved by a finite-difference method using upwind schemes and variable mesh. The results demonstrate the influence of the concentration- and temperature-induced surface tension gradients in creating the uniform liquid fuel layer inside an ICF target. Comparison of the present theory with the experimental data is made for targets filled, respectively, with D2 and mixtures of H2 and D2, producing good agreement in both cases.
X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy study on the CO chemisorbed over amorphous FeNiB alloys
Authors: Guczi L. , Zsoldos Z. , Schay Z.
Published: July 2002

A surface study has been conducted to determine CO interaction with Fe80B20 and Fe40Ni40B20 samples in amorphous and crystalline forms in the presence and absence of H2. At 300 K molecular CO exists only on Ar+ etched surface of partially and fully crystallized FeNiB indicated by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy peaks at 8.3, 11.6, and 285.5 eV (C 1s), respectively, as well as by CO thermal desorption spectroscopy. CO dissociation revealed by UPS peaks at 5.6 eV also occurs. Oxide species of B, Fe, and Ni cannot be observed at all. On the other hand, at 570 K a C 1s peak appears representing a carbidic and graphitic species in the binding energy (B.E.) range of 283.2 and 284.6 eV, respectively. Regardless of the presence of H2, B is always oxidized on the surface, while Fe and Ni are maintained in metallic form. Since practically no difference exists between carbidic C 1s measured here and on polycrystalline Fe film, the unique high catalytic activity of partially crystallized FeNiB can be interpreted by a hindered transformation of the reactive carbon into its inactive form due to the optimum particle size distribution.
Quantitative analysis of chemical vapor deposition refractory metal silicides
Authors: Streit Lori A. , Williams Peter
Published: July 2002

Chemical vapor deposition films of titanium and tungsten silicides have been characterized using secondary ion mass spectrometry (SIMS) and sputtered neutral analysis (SNA). SIMS data for bulk impurities and interfacial contaminants was quantified by reference to ion implant standards generated in situ in the ion microanalyzer. SNA analyses for film stoichiometry were also performed in the same instrument, ionization of the sputtered neutral flux being achieved by gas phase impact of primary ions. The films were found to contain significant levels of H, O, F, and Cl impurities, which largely migrated on annealing either out of the film or to a subsurface interface.
The signature of point defects in layered materials
Authors: Mizes H. A. , Harrison W. A.
Published: July 2002

Graphite and various transition-metal dichalcogenides have been found to be ideal scanning tunneling microscope (STM) substrates. In this paper we discuss the effects of point defects on the STM images of these materials. We find that the height of the protrusion in a STM image caused by a localized perturbation in the potential is dependent on the tip–sample separation. With a tight-binding approximation we can predict for graphite how the magnitude of the protrusion depends on the scanning height, and how this dependence may be used to predict the type of impurity.
Specific contact resistivity measurements of reactive ion etched contacts
Authors: Schreyer Tim A. , Bariya Anand J. , McVittie James P. , Saraswat Krishna C.
Published: July 2002

Specific contact resistivity measurements have been performed on Ohmic contacts formed by etching in a CHF3/O2 reactive ion etching plasma, to determine the extent to which this process affects contact resistance. Contacts between n+ (Ns≊1020 cm−3) silicon and Ti were used. The low intrinsic specific contact resistivity of this system assures that the experimentally measured resistivity will depend on the contact etch process. Also, deep junction depths (xj≊1.0 μm) were used to minimize the sensitivity of the measurements to possible changes in sheet resistance due to overetching. The resistivity data, which was extracted via a two-dimensional analytical technique, show a strong dependence on the use of a postetch NF3/Ar clean-up plasma, as well as on a forming-gas anneal. However, it also shows little dependence on the amount of O2 flowing in the plasma. Resistivity measurements range from (9±5)×10−9 up to (2.4±0.6)×10−5 Ω cm2, depending on whether the contacts received a NF3 clean-up treatment and a forming-gas anneal. Surface analysis (x-ray photoelectron spectroscopy) of the Si surface shows a layer of fluorocarbon polymer, and a layer of silicon containing atomic F, C, and O.
High-sensitivity plasma-based sputtered neutral mass spectrometry depth profiling of zinc-implanted GaAs
Authors: MacLaren S. W. , Loxton C. M. , Sammann E. , Kiely C. J.
Published: July 2002

A commercial sputtered neutral mass spectrometer, using a rf-generated plasma for both sputtering and postionization of sputtered particles, has been modified to improve sensitivity for trace analysis. The modified instrument has been used to depth profile zinc-implanted gallium arsenide. A detection limit of 20 ppma was attained for zinc under conditions of maximum depth resolution from an analyzed sample area of 0.2 cm2 with a useful yield of 5 to 7×10−10 . The results have been compared with those of secondary ion mass spectrometry. Sputtered neutral mass spectrometry (SNMS) depth profiles revealed zinc redistribution in one heavily implanted sample, leading to the discovery of unusual structural damage through transmission electron microscopy. This investigation is discussed as an example of the usefulness of the SNMS technique in practical applications.
Interface states and Schottky barrier formation at metal/GaAs junctions
Authors: Viturro R. E. , Mailhiot C. , Shaw J. L. , Brillson L. J. , LaGraffe D. , Margaritondo G. , Pettit G. D. , Woodall J. M.
Published: July 2002

We report results of x-ray photoemission and cathodoluminescence spectroscopies studies of interface formation at metal–GaAs junctions. The results are interpreted by using a microscopic model of metal–semiconductor interfaces. Our low-temperature measurements and analyses show the validity of Schottky’s phenomenological description, thereby suggesting that metal-induced gap states and native defect mechanisms are not major factors in determining the Fermi-level energy at the low-temperature formed interface. Our room-temperature results show that a broad range of Fermi-level stabilization and the formation of two reaction-induced interface states are obtained upon metallization of GaAs(100) surfaces. These results strongly imply that the insensitivity of rectifying barrier height on metal work function results from metallization-induced atomic relaxations at the interface.
Surface emitting semiconductor laser array: Its advantage and future
Authors: Iga K. , Koyama F. , Kinoshita S.
Published: July 2002

In this paper we review the research progress of surface emitting lasers. A two-dimensional arrayed configuration of surface emitting lasers will open up a new era of the semiconductor laser, since it provides high power capability, parallel optical processing, and vertical optical interconnection of circuit boards. We present experimental results on vertical cavity surface emitting semiconductor lasers. In order to reduce the threshold current, some improvements have been made on the laser reflector and a circular buried heterostructure has been introduced to confine injection current more effectively. The microcavity structure, which is 7 μm long and 6 μm in diameter, yields a threshold of 6 mA. A possibility of realizing an extremely low threshold current surface emitting laser device and a densely packed two-dimensional array are suggested.
Effects of defects on metal-insulator semiconductor properties of molecular-beam epitaxy grown HgCdTe
Authors: Goodwin M. W. , Kinch M. A. , Koestner R. J.
Published: July 2002

We present results which show that physical defects in molecular-beam expitaxy grown HgCdTe strongly affect its metal-insulator semiconductor properties. In particular, two types of defects, dislocations and pyramidal hillocks, affect the dark and tunnel currents. However, when the dislocation densities are reduced to the same level (105 cm−2) found in material grown by other growth methods, the dark currents and hence storage times are comparable. For cutoff wavelengths of 9.8 μm we observe a storage time of 150 μs in one film. For films with high dislocation densities (107 cm−2) the predominate dark currents at high temperatures (T≥100 K) are generation–recombination dark currents, while for films with low dislocation densities near diffusionlike dark currents dominate.
Phase-selective chemical vapor deposition of boron carbide by nucleation control on patterned substrates
Authors: Jansson U. , Carlsson J.-O. , Markert L. C. , Greene J. E.
Published: July 2002

During film growth by chemical vapor deposition (CVD), the phase deposited can sometimes be controlled by the choice of substrate material. This concept can be employed to obtain phase-selective CVD, i.e., the simultaneous selective deposition of different phases on different regions of a patterned substrate. In this paper, differential nucleation behavior is used to obtain phase-selective deposition of metastable tetragonal boron carbide and rhombohedral B13 C2 on a patterned substrate consisting of adjacent regions of amorphous boron carbide and Mo, respectively.
Thermal noise in vacuum scanning tunneling microscopy at zero bias voltage
Authors: Möller R. , Esslinger A. , Koslowski B.
Published: July 2002

At typical operating conditions of scanning tunneling microscopy (STM) the current noise is dominated by 1/f noise the nature of which is still unclear. However at zero bias and zero average current thermal noise corresponding to the equivalent tunneling conductivity σ is found. Within the experimental limits it agrees well with the Nyquist formula d/dω〈I2 〉=4kTσ, where I is the tunneling current, ω is the angular frequency, k is Boltzmann’s constant and T is the absolute temperature. Since the thermal current noise scales linearly with σ it has the same exponential distance dependence as the tunneling current and can be used to adjust the distance between tip and sample. The performance of such a ‘‘scanning noise microscope’’ based on that principle is compared to the conventional STM technique for the example of a polycrystalline silver surface in UHV. It is shown that this method can also be applied at ambient pressure. This novel technique might be advantageous whenever the effect of the tunneling current on the sample should be avoided, i.e., very delicate samples, electrolytic environment, etc.
Scanning tunneling microscopy studies of semiconductor electrochemistry
Authors: Thundat T. , Nagahara L. A. , Lindsay S. M.
Published: July 2002

We have used scanning tunneling microscopy to investigate topographical changes on potentiostatically controlled semiconductor surfaces due to electrochemical reactions. The electrochemical processes reported here include Ni deposition on Ge(111), localized photoelectrodeposition of gold on GaAs(100) surfaces, and photocorrosion of GaAs. We have also carried out x-ray photoelectron spectroscopy and secondary electron microscopy studies on samples that have been imaged with scanning tunneling microscopy.
Local modification of organic dye materials by dielectric breakdown
Authors: Kaneko R. , Hamada E.
Published: July 2002

Local modifications by dielectric breakdown of organic dye film are made with nanoseconds pulses. Organic dye films (5.8 and 10 nm thicknesses) are spin coated on silicon substrates. A very light load (less than 300 nN) contact profile meter with a diamond tip (100 nm radius) made conductive by ion implantation are used. There are two types of modifications: the depression type and the projection type. It is thought that a modification of the depression type occurs as a result of film destruction, and a modification of projection type is caused by the adhesion of contaminants.
Fabrication of nucleation sites for nanometer size selective deposition by scanning tunneling microscope
Authors: Terashima Kazuo , Kondoh Minoru , Yoshida Toyonobu
Published: July 2002

We report the fabrication in air of nucleation sites for nanometer size selective deposition with a scanning tunneling microscope (STM) for the first time. Nanometer structures between 0.8 and 50 nm for preferential nucleation sites could be produced on a graphite substrate with STM in air. We observed the migration of Au atoms deposited on the graphite with such artificial nanometer structures. It could be observed that the Au clusters reached around there stopped moving and were trapped at these sites. This finding proves the possibility of fabricating artificial nucleation sites in air by STM.