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Showing papers by "Lawrence Berkeley National Laboratory published in 1976"


Journal ArticleDOI
TL;DR: In this paper, an empirical nonlocal pseudopotential scheme was employed to calculate the electronic structure of eleven semiconductors: Si, Ge, $\ensuremath{\alpha}\ensure Math{-}\mathrm{Sn}$, GaP, GaAs, GaSb, InP, InAs, InSb and CdTe.
Abstract: An empirical nonlocal pseudopotential scheme is employed to calculate the electronic structure of eleven semiconductors: Si, Ge, $\ensuremath{\alpha}\ensuremath{-}\mathrm{Sn}$, GaP, GaAs, GaSb, InP, InAs, InSb, ZnSe, and CdTe. Band structures, reflectivity spectra, electronic densities of states, and valence charge densities are presented and compared to experimental results. Improved optical gaps, optical critical-point topologies, valence-band widths, and valence charge distributions are obtained as compared to previous local pseudopotential results.

1,446 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the voltage noise in continuous metal films and showed that the noise arises from equilibrium temperature fluctuations modulating the resistance to give a power spectrum proportional to the mean voltage across the sample.
Abstract: We have measured the $\frac{1}{f}$ voltage noise in continuous metal films. At room temperature, samples of pure metals and bismuth (with a carrier density smaller by ${10}^{5}$) of similar volume had comparable noise. The power spectrum ${S}_{V}(f)$ was proportional to $\frac{{\overline{V}}^{2}}{\ensuremath{\Omega}{f}^{\ensuremath{\gamma}}}$, where $\overline{V}$ is the mean voltage across the sample, $\ensuremath{\Omega}$ is the sample volume, and $1.0\ensuremath{\lesssim}\ensuremath{\gamma}\ensuremath{\lesssim}1.4$. $\frac{{S}_{V}(f)}{{\overline{V}}^{2}}$ was reduced as the temperature was lowered. Manganin, with a temperature coefficient of resistance ($\ensuremath{\beta}$) close to zero, had no discernible noise. These results suggest that the noise arises from equilibrium temperature fluctuations modulating the resistance to give ${S}_{V}(f)\ensuremath{\propto}\frac{{\overline{V}}^{2}{\ensuremath{\beta}}^{2}{k}_{B}{T}^{2}}{{C}_{V}}$, where ${C}_{V}$ is the total heat capacity of the sample. The noise was spatially correlated over a length $\ensuremath{\lambda}(f)\ensuremath{\approx}{(\frac{D}{f})}^{\frac{1}{2}}$, where $D$ is the thermal diffusivity, implying that the fluctuations obey a diffusion equation. The usual theoretical treatment of spatially uncorrelated temperature fluctuations gives a spectrum that flattens at low frequencies in contradiction to the observed spectrum. However, the empirical inclusion of an explicit $\frac{1}{f}$ region and appropriate normalization lead to $\frac{{S}_{V}(f)}{{\overline{V}}^{2}}\ensuremath{\propto}\frac{{\ensuremath{\beta}}^{2}{k}_{B}{T}^{2}}{{C}_{V}}[3+2\mathrm{ln}(\frac{l}{w})]f$, where $l$ is the length and $w$ is the width of the film, in excellent agreement with the measured noise. If the fluctuations are assumed to be spatially correlated, the diffusion equation can yield an extended $\frac{1}{f}$ region in the power spectrum. We show that the temperature response of a sample to $\ensuremath{\delta}$- and step-function power inputs has the same shape as the autocorrelation function for uncorrelated and correlated temperature fluctuations, respectively. The spectrum obtained from the cosine transform of the measured step-function response is in excellent agreement with the measured $\frac{1}{f}$ voltage noise spectrum. Spatially correlated equilibrium temperature fluctuations are not the dominant source of $\frac{1}{f}$ noise in semiconductors and discontinuous metal films. However, the agreement between the low-frequency spectrum of fluctuations in the mean-square Johnson-noise voltage and the resistance fluctuation spectrum measured in the presence of a current demonstrates that in these systems the $\frac{1}{f}$ noise is also due to equilibrium resistance fluctuations.

360 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model for the emission of nucleons with velocities intermediate between those of the target and the projectile is proposed, where the nucleons which are mutually swept out from the targets and the projectiles form a hot quasiequilibrated fireball which decays as an ideal gas.
Abstract: A simple model is proposed for the emission of nucleons with velocities intermediate between those of the target and projectile. In this model, the nucleons which are mutually swept out from the target and projectile form a hot quasiequilibrated fireball which decays as an ideal gas. The overall features of the proton-inclusive spectra from 250- and 400-MeV/nucleon $^{20}\mathrm{Ne}$ ions and 400-MeV/nucleon $^{4}\mathrm{He}$ ions interacting with uranium are fitted without any adjustable parameters.

335 citations


Journal ArticleDOI
TL;DR: In this paper, the electronic structure of a jellium-Si interface was calculated using a Jellium density corresponding to Al and self-consistent Si pseudopotentials.
Abstract: The electronic structure of a jellium-Si interface is calculated using a jellium density corresponding to Al and self-consistent Si pseudopotentials. Local densities of states and charge densities are used to study states near the interface. At the Si surface, a high density of extra states is found in the energy range of the Si fundamental gap. These states are bulklike in jellium and decay into Si with a high concentration of charge in the dangling-bond free-surface-like Si state. Truly localized interface states are also found but at lower energies. The calculated barrier height is in excellent agreement with recent experimental results.

314 citations


Journal ArticleDOI
TL;DR: In this article, a study of multihadronic final states produced in e/sup +/e/sup -/ annihilation at center-of-mass energies between 3.90 and 4.60 GeV is presented.
Abstract: Evidence is presented, from a study of multihadronic final states produced in e/sup +/e/sup -/ annihilation at center-of-mass energies between 3.90 and 4.60 GeV, for the production of a new neutral state with mass 1865 +- 15 MeV/c/sup 2/ and decay width less than 40 MeV/c/sup 2/ that decays to K/sup plus-or-minus/..pi../sup plus-or-minus/ and K/sup plus-or-minus/..pi../sup plus-or-minus/..pi../sup plus-or-minus/..pi../sup plus-or-minus/. The recoil-mass spectrum for this state suggests that it is produced only in association with systems of comparable or larger mass. (AIP)

279 citations


Journal ArticleDOI
TL;DR: In this article, it is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness.
Abstract: It has been reported for as-quenched AISI 4340 steel that high temperature austenitizing treatments at 1200°C, instead of conventional heat-treatment at 870°C, result in a two-foldincrease in fracture toughness,KIc, but adecrease in Charpy impact energy. This paper seeks to find an explanation for this discrepancy in Charpy and fracture toughness data in terms of the difference betweenKIc and impact tests. It is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness. The microstructural factors which affect this behavior are discussed. Based on these and other observations, it is considered that the use of high temperature austenitizing be questioned as a practical heat-treatment procedure for ultrahigh strength, low alloy steels. Finally, it is suggested that evaluation of material toughness should not be based solely onKIc or Charpy impact energy values alone; both sharp crack fracture toughness and rounded notch impact energy tests are required.

256 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the theory, fabrication, operation, and performance of a cylindrical dc SQUID made with shunted Nb-NbOx-Pb Josephson tunnel junctions.
Abstract: We describe the theory, fabrication, operation, and performance of a cylindrical dc SQUID made with shunted Nb-NbOx-Pb Josephson tunnel junctions. The SQUID is current-biased at a nonzero voltage, and modulated with a 100 kHz flux. The 100 kHz voltage developed across the SQUID is amplified by a cooled, resonantLC circuit that optimally couples the SQUID impedance to the input of a room-temperature FET preamplifier. The SQUID is operated in a flux-locked loop with a dynamic range in a 1-Hz bandwidth of ±3×106. The 3-dB rolloff frequency for the loop response is typicalty 2 kHz, and the slewing rate is generally 2×104 φ0 sec−1. A typical flux noise power spectrum for a SQUID at 4.2 K in a superconducting shield is presented. Above 2×10−2 Hz the spectrum is white and has an rms value of 3.5×10−5 φ0 Hz−1/2. The white noise is intrinsic to the sensor and is close to the theoretical limit set by Johnson noise in the shunts. At lower frequencies, the power spectrum is approximately 10−10 (1 Hz/f) φ 0 2 Hz−1, wheref is the frequency. This value is approximately two orders of magnitude greater than the calculated 1/f noise in the tunnel junctions. The factors contributing to the long-term drift of the SQUID are discussed. By regulating the temperature of the helium bath we have achieved a drift rate of 2×10−5 φ0 h−1 over a 20-h period. A detailed description is given of the coupling efficiency of various input coils wound on the SQUID. The effects of coupling between the input coil, the SQUID, and the feedback (modulation) coil are described, and measurements of the coupling parameters reported. The energy resolution of the SQUID with respect to a current in a 24-turn input coil is 7×10−30 J Hz−1 for frequencies at which the flux noise has a white power spectrum. In terms of energy resolution, the SQUID has a better performance in the 1/f noise region that that of any SQUID previously reported in the literature. The long-term drift over an extended period also represents the lowest value yet reported.

249 citations


Journal ArticleDOI
TL;DR: In this article, double-differential cross sections have been measured for high-energy particles emitted from uranium targets irradiated with $^{20}\mathrm{Ne}$ ions at energies of 250, 400, and 2100 MeV/nucleon and $^{4} ions at 400 MeV /nucleons.
Abstract: Double-differential cross sections have been measured for high-energy $p$, $d$, $t$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ particles emitted from uranium targets irradiated with $^{20}\mathrm{Ne}$ ions at energies of 250, 400, and 2100 MeV/nucleon and $^{4}\mathrm{He}$ ions at 400 MeV/nucleon By using the shape and yield of the proton energy spectra, the shape and yield of the $d$, $t$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ energy spectra can be deduced at all measured angles for all incident projectile energies by assuming that they are formed by a coalescence of cascade nucleons, using a model analogous to that of Butler and Pearson, and Schwarzschild and Zupan\ifmmode \check{c}\else \v{c}\fi{}i\ifmmode \check{c}\else \v{c}\fi{}

244 citations


Journal ArticleDOI
TL;DR: In this article, the authors report evidence for the production of a new narrow charged state in e/sup +/e/sup -/ annihilation at a center-of-mass energy of 4.03 GeV.
Abstract: We report evidence for the production of a new narrow charged state in e/sup +/e/sup -/ annihilation at a center-of-mass energy of 4.03 GeV. This state, which has a mass of 1876 +- 15 MeV/c/sup 2/, is observed in the exotic channel Kminus-or-plus..pi../sup plus-or-minus/..pi.. +- , but not in the nonexotic channel Kminus-or-plus..pi../sup +/..pi../sup -/. It is produced primarily in association with a system of mass 2.01 +- 0.02 GeV/c/sup 2/. These characteristics are just those expected of a charged charmed meson. (AIP)

186 citations



Journal ArticleDOI
TL;DR: In this article, the thermodynamic properties of strong electrolytes are extended to solutions involving a dissociation equilibrium, and the parameters of the strong electrolyte components of the buffer solutions are taken from other work.
Abstract: Equations previously developed and widely applied to the thermodynamic properties of strong electrolytes are extended to solutions involving a dissociation equilibrium. Excellent agreement is obtained with the data for pure phosphoric acid to 6M and for phosphate buffer solutions. The parameters of the strong electrolyte components of the buffer solutions are taken from other work, and the remaining parameters for H+, H2PO 4 − , and H3PO4 are evaluated, including a pK of 2.146. The present method avoids ambiguities which formerly arose in treating weak acids with as small pK as this.

Journal ArticleDOI
TL;DR: In this paper, the spectral structures of GaSe are identified in terms of location in the stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space and atomic character of the states involved in the transitions.
Abstract: Reflectivity and wavelength-modulated reflectivity measurements on GaSe and $\mathrm{Ga}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ mixed crystals are presented for energies ranging from 3 to 6 eV. Additional electroreflectance measurements are used to investigate the excitonic character of the structure at 3.4 eV in GaSe. The results are discussed on the basis of a new pseudopotential band-structure calculation for GaSe. The prominent spectral structures of GaSe are identified in terms of location in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space and atomic character of the states involved in the transitions. The main structures in the optical-response function of GaSe are found to result from excitations of the Ga-Ga bond and from atomiclike transitions between nonbonding Se $p$ and $s$ states. These main transitions are located in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space close to symmetry determined "special $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ points." The observed mixed-crystal spectra can be decomposed into three classes of transitions which exhibit zero, intermediate, and strong energy shifts with anion substitution. Theoretically, the three classes of transitions are found to take place between states with zero or little, intermediate, and large charge concentrations on the anion sites. Thus, the characteristic energy shifts, observed experimentally can directly be related to atomic spectral properties of sulphur and selenium.

Journal ArticleDOI
TL;DR: Preexponential factors for surface reactions have been estimated by use of transition state and hard sphere reaction models, and calculated values can be used to determine rate limiting steps in various surface reactions as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the refractive indices and linear birefringence of seven homologous compounds of p, [pacute]-di-n-alkoxy-azoxybenzenes in the nematic phase.
Abstract: We have measured as functions of temperature the refractive indices and linear birefringence of seven homologous compounds of p, [pacute]-di-n-alkoxy-azoxybenzenes in the nematic phase. Using the Vuks' model of local-field correction, we have deduced from our results both the microscopic and the macroscopic order parameters. The former agree well with those determined by Pines et al from the NMR results. The variations of the various microscopic parameters with the increase of the alkyl chain length are discussed. It is shown that addition of CH2 groups to the alkyl chain increases the average polarizability much faster than the polarizability anisotropy. Contributions to the polarizability anisotropy from the core and from the alkyl chains respectively are found.

Journal ArticleDOI
TL;DR: Vacancy states in Si were investigated using a recently developed self-consistent pseudopotential technique as discussed by the authors, and three different structural models (ideal and two reconstructions) for a neutral vacancy were considered.
Abstract: Vacancy states in Si are investigated using a recently developed self-consistent pseudopotential technique Three different structural models (ideal and two reconstructions) for a neutral vacancy are considered Vacancy states are found to exist in the Si thermal gap for each structure The character of these states is predominantly dangling-bond $p$-like localized on the four atoms surrounding the vacancy The ideal (unreconstructed) vacancy yields an electronic spectrum, which is unstable with respect to Jahn-Teller type distortions The two different reconstruction models considered yield Jahn-Teller stable situations

Journal ArticleDOI
TL;DR: In this article, it was shown that the anomalous [$uuw$]- and [$uv0$]-type axes of easy magnetization have been observed in some cubic rare-earth-iron Laves compounds.
Abstract: Unusual [$uuw$]- and [$uv0$]-type axes of easy magnetization have been observed in some cubic rare-earth-iron Laves compounds. The presence of these directions of spontaneous magnetization can be accounted for, within the phenomenological treatment of the magnetic anisotropy, by including eighth-power direction-cosine terms in the power expansion of the magnetic anisotropy energy. It will also be shown that the single-ion model predicts the existence of these directions. The conditions imposed on the bulk magnetic anisotropy constants are derived. Typical values of these constants in rare-earth-iron Laves phases are calculated using the single-ion model.

Journal ArticleDOI
TL;DR: In this paper, a possible way to remove the discrepancy between calculated and measured α-widths is discussed, and the decay rates of 212 Po and 210 Po are computed with the help of shell-model wave functions for parent and daughter nucleus.

Journal ArticleDOI
TL;DR: The enriched experience benefits brain injured rats even though their learning ability is impaired, and is found to be affected by lesions and, to a lesser extent, by environmental treatment.

Journal ArticleDOI
TL;DR: In this article, a resonance-like structure was observed in the total cross section for hadron production by e$sup +$e$sup -$ colliding beams at a mass of 4414 +- 7 MeV having a total width GAMMA = 33 +- 10 MeV.
Abstract: We observe a resonancelike structure in the total cross section for hadron production by e$sup +$e$sup -$ colliding beams at a mass of 4414 +- 7 MeV having a total width GAMMA = 33 +- 10 MeV. From the area under this resonance, we deduce the partial width to electron pairs to be GAMMA/sub ee/ = 440 +- 140 eV. Further structure of comparable width is present near 4.1 GeV. (AIP)

Journal ArticleDOI
TL;DR: In this paper, the chemisorption-site geometries for chlorine on cleaved Si(111) 2\ifmmode\times\else\texttimes\fi{}1 and Ge( 111) 2
Abstract: The chemisorption-site geometries for chlorine on cleaved Si(111) 2\ifmmode\times\else\texttimes\fi{}1 and Ge(111) 2\ifmmode\times\else\texttimes\fi{}1 surfaces have been determined by comparing detailed pseudopotential calculations with energy distribution spectra and polarization selection rules of photoemission spectroscopy. Strong $p$-symmetry polarization effects observed in photoemission allow us to determine that on Si(111) the correct geometry is a onefold covalent site while on Ge(111) the Cl is in a threefold coordinated ionic site.

Journal ArticleDOI
01 Apr 1976
TL;DR: In this paper, a method was described to solve constrained HFB-equations without the introduction of a Lagrangian multiplier, and rotational bands in164Er and168Yb were calculated.
Abstract: A method is described to solve constrained HFB-equations without introduction of a Lagrangian multiplier. To demonstrate the versatility of the method rotational bands in164Er and168Yb are calculated.

Journal ArticleDOI
TL;DR: In this article, a theoretical description of the valence band structure and chemical bonding for a series of non-transition-metal layer compounds is developed which is consistent with calculated charge densities, densities of states, and with the experimental crystal-structure data and photoemission measurements.
Abstract: A theoretical description of the valence-band structure and chemical bonding for a series of non-transition-metal layer compounds is developed which is consistent with calculated charge densities, densities of states, and with the experimental crystal-structure data and photoemission measurements.

Journal ArticleDOI
TL;DR: In this paper, a nonempirical localized-orbital approach is used to calculate the electronic structure of random networks, and the fundamental absorption edges are found to correspond to indirect gaps, but with several other indirect and direct transitions within a few tenths of an eV of the indirect edge.
Abstract: A nonempirical localized-orbital approach is used to calculate the electronic structure of ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, ${\mathrm{As}}_{4}$${\mathrm{S}}_{4}$, ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$, ${\mathrm{As}}_{4}$${\mathrm{Se}}_{4}$, and ${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$ crystals. Contributions of $s$, $p\ensuremath{\sigma}$, and $p$ lone-pair orbitals to the various molecular levels are illustrated. Densities of occupied states agree closely with experimental photoemission data. The fundamental absorption edges in ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ and ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$ are found to correspond to indirect gaps, but with several other indirect and direct transitions within a few tenths of an eV of the indirect edge, consistent with most of the optical-absorption studies. The method is readily applicable to the electronic structure of fully coordinated random networks but because of the severe self-consistency problems we are unable to tackle problems associated with thermal relaxation at wrongly coordinated atoms.

Journal ArticleDOI
TL;DR: Optical mixing is a process in which two or more optical waves interact and generate new frequency components as mentioned in this paper, and it is used as a spectroscopic technique for far-infrared generation.

Journal ArticleDOI
TL;DR: In this article, the dispersion characteristics of surface polaritons in GaP are measured and compared with theoretical calculations using optical four-wave mixing, and they demonstrate experimentally that optical fourwave mixing can be used to study surface polariton in solids.
Abstract: We demonstrate experimentally that optical four-wave mixing can be used to study surface polaritons in solids. The dispersion characteristics of surface polaritons in GaP are measured and compared with theoretical calculations.

Journal ArticleDOI
TL;DR: In this article, the authors measured large transverse momentum (p/sub perpendicular) with pion beam at c.m. angles centered near 90/sup 0/ for π/π + -/p and pp interactions at 100 and 200 GeV/c.
Abstract: We have measured large-transverse-momentum (p/sub perpendicular/) inclusive ..pi../sup 0/ production at c.m. angles centered near 90/sup 0/ for ..pi../sup + -/p and pp interactions at 100 and 200 GeV/c. This is the first such measurement using a pion beam. The ratio sigma(pp..--> pi../sup 0/X)/sigma (..pi..p..--> pi../sup 0/X) decreases with increasing p/sub perpendicular/ and is independent of energy when expressed as a function of x/sub perpendicular/ = p/sub perpendicular//p/sub max/. We compare the data with predictions of various models. (AIP)

Journal ArticleDOI
TL;DR: In this article, a commonly assumed model for the relaxed GaAs (110) surface is considered, which can account for the insensitivity of the empty cation-derived surface states to metal overlayers, and the lack of evidence for occupied anion surface states.
Abstract: A commonly assumed model for the relaxed GaAs (110) surface is considered. This model can account for the insensitivity of the empty cation-derived surface states to metal overlayers, and the lack of evidence for occupied anion surface states in recent photoemission measurements. With relaxation of the surface, we find that the empty cation-derived surface band becomes more dispersive. The center of mass lies above the conduction-band minimum; however, the threshold of the surface band remains within the bulk band gap.

Journal ArticleDOI
TL;DR: In this article, a self-consistent cranking (SCC) model is improved for high-spin states by the addition of random-phase approximation (RPA) correlations along the yrast line.

Journal ArticleDOI

Journal ArticleDOI
TL;DR: In this article, the power spectrum of the voltage fluctuations in shunted Josephson junctions biased at a constant current greater than the critical current was measured, and it was shown that the voltage noise arises from equilibrium fluctuations in the temperature of the junction, which in turn modulates the voltage across the junction.
Abstract: We have measured the power spectrum of the voltage fluctuations in shunted Josephson junctions biased at a constant current $I$ greater than the critical current ${I}_{c}$. Over the frequency range ${5\ifmmode\times\else\texttimes\fi{}10}^{\ensuremath{-}2}$-50 Hz the power spectra vary approximately as $\frac{1}{f}$, where $f$ is the frequency. At any single frequency, the noise decreases as $I$ is increased. Experimental evidence is presented to show that the voltage noise arises from equilibrium fluctuations in the temperature $T$ of the junction, which in turn modulate ${I}_{c}$ and hence the voltage $V$ across the junction. The magnitude of the power spectra is consistently predicted to within a factor of 5 by an extension of the semiempirical formula of Clarke and Voss: ${S}_{V}(f)=\frac{{(\frac{d{I}_{c}}{\mathrm{dT}})}^{2}{(\frac{\ensuremath{\partial}V}{\ensuremath{\partial}{I}_{c}})}_{I}^{2}{k}_{B}{T}^{2}}{3{C}_{V}f}$. In this formula, we postulate that ${C}_{V}$ is the heat capacity of an "effective" junction volume given by the product of the junction area and the sum of the coherence lengths of the two superconductors. The dependence of ${S}_{V}(f)$ on ${(\frac{\ensuremath{\partial}V}{\ensuremath{\partial}{I}_{c}})}_{I}^{2}$ and ${(\frac{d{I}_{c}}{\mathrm{dT}})}^{2}$ is experimentally established.