Showing papers by "Sandia National Laboratories published in 1978"

Prediction of Flatband Potentials at Semiconductor‐Electrolyte Interfaces from Atomic Electronegativities

Abstract: The electron affinities of several metal oxide semiconductors that have been used as anodes in photoelectrochemical cells are calculated using the atomic electronegativities of the constituent atoms. These electron affinities are quantitatively related to the measured flatband potentials by considering the effects of specific adsorption of potential‐determining ions (for metal oxides used in photoelectrolysis, these are usually OH− and H+). Methods are discussed for determining the pH at which net adsorbed surface charge and thus potential across the Helmholtz layer is zero (point of zero zeta potential, pzzp). This pH value is shown to correlate with the electronegativity of the metal oxides. The application of these ideas to other semiconductor‐electrolyte systems is discussed.

Ion desorption by core-hole Auger decay

Abstract: We present evidence for a fundamentally new mechanism for impact-induced desorption, viz., core-hole Auger decay. We thereby explain why observed thresholds for electron-stimulated desorption (ESD) of positive ions (${\mathrm{O}}^{+}$, O${\mathrm{H}}^{+}$, and ${\mathrm{F}}^{+}$) from certain $d$-band metal oxides (Ti${\mathrm{O}}_{2}$, ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$, and W${\mathrm{O}}_{3}$) correlate in energy with the ionization potential of the highest-lying atomic core levels. We conclude that electron-stimulated desorption is in many interesting cases an atom-specific, valence-sensitive probe of surfaces.

Wind tunnel performance data for two- and three-bucket Savonius rotors

Abstract: Fifteen configurations of a Savonius rotor wind turbine were tested in the Vought Corporation Systems Division 4.9- x 6.1-m Low Speed Wind Tunnel to determine aerodynamic performance. The range of values of the varied parameters was as follows: number of buckets, 2 and 3; nominal freestream velocity, 7 and 14 m/s; Reynolds number per meter, 4.32 x 10/sup 5/ and 8.67 x 10/sup 5/; rotor height, 1 and 1.5 m; rotor diameter (nominal), 1 m; bucket overlap, 0.0 to 0.1 m. The measured test variables were torque, rotational speed, and tunnel conditions. It is concluded that increasing Reynolds number and/or aspect ratio improves performance. The recommended configuration consists of two sets of two-bucket rotors, rotated 90 deg apart, with each rotor having a dimensionless gap width of 0.1 to 0.15.

Controllability/observability analysis of digital circuits

Abstract: The testability of a digital circuit is directly related to the difficulty of controlling and observing the logical values of internal nodes from circuit inputs and outputs, respectively. This paper presents a method for analyzing digital circuits in terms of six functions which characterize combinational and sequential controllability and observability.

Empirical relationships for predicting nonlinear refractive index changes in optical solids

Abstract: The development of high-power glass lasers has stimulated interest in materials with low index nonlinearity. A number of authors have proposed empirical relations between the nonlinear index and linear dispersion parameters. We review these expressions and relate them to both classical and quantum theoretic derivations of the index nonlinearity. We show that the major differences arise in the treatment of local field corrections. We further show that the good agreement obtained between experiment and theory may be fortuitous, due to the fairly large experimental uncertainty and the fact that all the materials investigated to date are really quite similar, being essentially oxide or fluoride materials.

Reinterpretation of electron-stimulated desorption data from chemisorption systems

Abstract: A review of the electron-stimulated-desorption (ESD) literature shows that many of the features of ESD that are difficult to rationalize within the model of Menzel, Gomer, and Redhead can easily be interpreted using the Auger decay model, which has recently been developed to explain ESD from transition-metal oxide surfaces. Specifically, the Auger model helps to explain the charge state of the desorbing species, the high-energy (\ensuremath{\sim} 30-40 eV) onset behavior that is seen, the differences in thresholds for positive and neutral desorbates, ESD cross-section and isotope-effect data, and the high kinetic energies of desorbing particles. The success of the Auger picture for ionically bonded surfaces suggests a number of new applications of ESD, including the deduction of reaction paths in surface chemistry and the study of the evolution of surface oxides.

ISEE-C Solar Wind Plasma Experiment

Abstract: Two 135° spherical section electrostatic analyzers furnish electron and ion measurements of the solar wind on ISEE-C. Each of these instruments utilizes a divided secondary emitter system to intercept the analyzed particles. Secondary electrons selected from all of the emitters simultaneously provide fast two-dimensional measurements of the particle fluxes integrated over polar angle; at a slower rate secondary electrons are successively selected from individual emitters to provide three-dimensional measurements. Speed of the ion measurements is increased by a factor of two by using an active proton peak tracking system to reduce the total range of energy per charge which has to be covered.

Coherent Raman gain spectroscopy using CW laser sources

Abstract: The recent demonstration of stimulated Raman gain (loss) spectroscopy (SRS) using CW laser sources introduces a powerful tool to coherent Raman spectroscopy. In this paper we undertake an experimental and analytical evaluation of several variations of SRS using CW laser sources including (1) direct stimulated Raman gain (loss) measurements, (2) optically heterodyned polarization interferometry, and (3) two-beam nonlinear interferometry. The results show CW SRS to be a convenient and effective means of obtaining direct Raman spectra in applications where background fluorescence precludes the use of conventional Raman techniques. Sensitivities comparable to or exceeding those obtained by coherent anti-Stokes Raman spectroscopy (CARS) are demonstrated. Ultimate sensitivities exceeding those achieved by spontaneous Raman spectroscopy are expected for high-resolution applications in gaseous media.

Adaptive procedure for estimating parameters for the nonsymmetric Tchebychev iteration

Abstract: An iteration based upon the Tchebychev polynomials in the complex plane can be used to solve large sparse nonsymmetric linear systems whose eigenvalues lie in the right half plane. The iteration depends upon two parameters which can be chosen from knowledge of the convex hull of the spectrum of the linear operator. This paper deals with a procedure based upon the power method for dynamically estimating the convex hull of the spectrum. The stability of the procedure is discussed in terms of the field of values of the operator. Results show the adaptive procedure to be an effective method of determining parameters. The Tchebychev iteration compares favorably with several competing iterative methods.

Fault Detection Capabilities of Alternating Logic

Abstract: This paper details the fault detection capability of a design technique named "alternating logic design." The technique achieves its fault detection capability by utilizing a redundancy in time instead of the conventional redundancy in space and is based on the successive execution of a required function and its dual. In combinational networks the method involves the utilization of a self-dual fumction to represent the required function and the realization of the self dual function in a network with structral properties which are sufficient to guarantee the detection of all single faults. One network structure with sufficient structral properties to detect all single stuck-line faults is the standard AND/OR or OR/AND two-level network [1]. However, other more general combinational logic structures also possess sufficient structural properties. Necessary and sufficient structural properties for any alternating network to be capable of detecting all single faults are derived.

An electronically controlled piezoelectric insulin pump and valves

Abstract: A miniature piezoelectric pump and valves with electronic controls for programmed release of insulin is described. The pumping volume and pressure as a function of voltage are calculated and experimentally verified. The volume pumped per stroke is 19 μcc/V and pump pressure is l mm-Hg/V. The pumping rate can be varied from one stroke per second to any slower rate and is controllebdy a quartz crystal oscillator. Pump and valve driver circuits are given.

Automatic Solution of the Sturm-Liouville Problem

Abstract: A general purpose algorithm is described for the automatic computation of eigenvalues and eigenfunctions of Sturm-Llouvllle problems, both singular and nonsmgular The method is based on the solution of initial value problems, using an integrator with a built-in global error estimating capabihty Problems arising in the construction of a satisfactory algorithm for this task are described, as are some of the software engineering aspects The resulting algorithm has performed satisfactorily on a sizable list of test problems

C-V characteristics of metal-titanium dioxide-silicon capacitors

Abstract: Titanium dioxide capacitors were fabricated on silicon wafers using electron-beam evaporation. The TiO2 films varied in thickness from 500 to 2000 A. Post-deposition oxidation at 1000°C in dry O2 was used to promote stoichiometric conversion of the films to the rutile phase. Capacitive densities of greater than 2 pf/sq. mil were obtained (dielectric constants ranged from 4 to 40). For long oxidation times, significant silicon dioxide grows under the TiO2 as a result of oxygen diffusing through the TiO2 film. Titanium was also shown to diffuse into the silicon during the oxidation cycle resulting in an n-type diffusion. Surface state densities ranging from 1011 to 5 × 1011 cm−2 eV−1 at midgap were obtained for good devices. Longer oxidation times result in lower capacitance, leakage current and surface state density.

Flatband Potential of Cadmium Sulfide ( CdS ) Photoanodes and Its Dependence on Surface Ion Effects

Abstract: Results are presented which show that the flatband potential of a semiconducting cadmium sulfide photoanode can be predicted from atomic electronegativity of its constituent atoms. This procedure, previously applied only to metal oxides, now appears generally applicable to any semiconductor‐electrolyte system. The flatband potential was measured in a , OH−/Pt wet photovoltaic cell as a function of S= and OH− concentrations. These measurements showed that the potential‐determining species are HS− and H+. The condition for zero net adsorbed surface charge (PZZP) was also determined by change of solution pS= with added powder and differential potentiometric titration experiments. This is found to occur at a unique S= ion concentration of . The measured flat‐band potential, corrected to the PZZP and for the difference between the Fermi level and the bottom of the conduction band, is in excellent agreement with the value predicted from the atomic electronegativities.

Centers to centroids in graphs

Abstract: For S contained in V(G) the S-center and S-centroid of G are defined as the collection of vertices u an element of V(G) that minimize e/sub s/(u) = max (d(u,v): v an element of S) and d/sub s/(u) = ..sigma../sub v an element of S/d(u,v), respectively. This procedure generalizes the standard definition of center and centroid from the special case of S = V(G). For 1 less than or equal to k less than or equal to absolute value V(G) and u an element of V(G) let r/sub k/(u) = max (..sigma../sub s an element of S/d(u,s): S contained in V(G), absolute value S = k). The k-centrum of G, denoted C(G;k), is defined to be the subset of vertices u in G for which r/sub k/(u) is a minimum. This approach also generalizes the standard definitions of center and centroid since C(G;1) is the center of C(G; absolute value V(G)) is the centroid. The structure of these sets for trees is examined. Generalizations of theorems of Jordan and Zelinka are included. 4 figures, 2 tables.

Imaging Atom Probe Mass Spectroscopy

Abstract: Surface properties of metallic solids are of great technological interest. Their influence is felt in areas as diverse as catalysis, corrosion and the plasma stability in magnetic-confinement fusion reactors. In this paper a new surface analytic capability is reviewed which can provide a unique picture of a metallic surface by directly imaging, in atomic resolution, the spatial distribution of its constituent species and their depth distribution within the near surface region. After thoroughly reviewing the experimental technique and emphasizing design parameters and constraints, the analytic capabilities and limitations of the technique are discussed in detail. Examples are given of surface and near surface compositional analysis and the ability to obtain angstrom resolved depth profiles of implanted species having energies less than 100 eV. Although essentially a research technique requiring special sample preparation, the anticipated practical applications of Imaging Atom-Probe Mass Spectroscopy are numerous, ranging from metallurgical studies of grain boundary segragation and pre-precipitate clustering in alloys, to the direct imaging of constituent atoms within large, biological active molecules.

High field electronic properties of SiO2

Abstract: The effects of very high electric fields on the transport of electrons and holes in SiO2 are discussed. At fields above 5 × 105 V/cm, electrons emit optical phonons, which is a very efficient energy loss mechanism. Holes on the other hand form small polarons in about 10−12 s, and their mobility becomes very low, but is unaffected by field up to 5 × 106 V/cm. The field dependent generation of electron-hole pairs is fit by application of the geminate recombination theory with a distribution of thermalization distances and excitation by X-rays and bandgap radiation is discussed. The first dependent bulk recombination coefficient is discussed in terms of high field mobility of the electrons. The impact ionization of electrons in SiO2 is discussed by comparing recent results for laser-induced breakdown in SiO2 with experiments on thin films involving photocurrents, space charge buildup and prebreakdown currents, and also theoretical predictions. Below 107 V/cm the laser experiments indicate higher impact ionization rates than the thin film experiments or theory.