Study of combined electroreflectance and double layer effects at lead electrodes

Reflectance changes at lead electrodes have been measured as a function of surface charge at 45° and 70° angles of incidence using solutions of sodium fluoride and quaternary ammonium salts. These solutions were chosen so as to provide quite different composition for the inner layer at the metal/solution interface, and hence different optical contributions there from. Linear reflectance-surface charge relation has been observed for NaF solutions only at a number of wavelengths. The optical effects from the inner layer has been recognized but could not be separated out from the main er effect by comparative measurements at two angles of incidence. This has been rationalized on the basis of similar variation of the er effect and the optical effect from the double-layer as a function of angle of incidence of light.     

Raman and IR spectra of crystalline phosphine in the γ phase

The γ phase of crystalline phosphine has been studied using IR and Raman spectroscopy. The observations include both pure phases, PH₃ and PD₃, and many of the modes of PH₃, PH₂D and PHD₂ dilute in PD₃ as well as of PD₃, PD₂H and PDH₃ dilute in PH₃. The phase transition β → γ is very slow for PH₃, but much more rapid for PD₃.Evidence is adduced pointing to the existence of inequivalent sites in this crystal, but none of a number of suggested models for the unit cell is entirely consistent with the numbers of multiplet components of the internal modes, nor with the numbers of external (lattice) modes observed in the IR and Raman.     

Molecule formation and energy transfer processes in a vapor with high density of 3P-excited sodium atoms

A rich fluorescence spectrum extending between 4000 and 8200 Å has been observed whenever sodium vapor is excited by dye laser light tuned to the 3²S → 3²P transition. Molecule formation due to collisions between excited and unexcited atoms is manifested by the presence of an emission band of sodium in the spectral range 4160–4570 Å.     

A case for large Auger recombination cross sections associated with deep centers in semiconductors

It is argued that the recent quantitative results concerning localized defects in semiconductors (e.g. GaAs) are consistent with the possibility of large Auger-type cross sections associated with recombination at these centers.It is proposed that many of the capture cross sections reported to be in the range 10^?13–10^?16cm², which exhibit only weak temperature dependence, and which do not depend on carrier concentration, might be explained by this mechanism.     

Disappearance of the heat capacity peak of Sc3In around the curie temperature in high magnetic fields

The low temperature (1.3–20.0 K) heat capacity of the weak itinerant electron ferromagnet Sc₃In was measured in magnetic fields up to ～ 10 T. The heat capacity peak observed around T_c = 6.0 K in zero field becomes smaller with increasing fields and at 9.98 T its magnetic entropy is ≈ 18% of the zero field value. Above T_c, the spin fluctuation contribution to the heat capacity, which is enhanced by the magnetic field at lower fields (?5 T), is quenched at higher fields (?5 T). This depression of the spin fluctuation contibution to the heat capacity by the high magnetic fields occurs at lower magnetic fields than had been considered possible heretofore. Our results suggest that the itinerant ferromagnetism is Sc₃In is completely quenched at 12 T.     

A method to obtain kinematic intensities from low-energy electron diffraction data

In order to use low-energy electron diffraction as a tool for surface crystallography, it would be useful to extract the single scattering, or kinematic part, from the intensity data. Details of a method to do this by taking data with different diffraction geometry but at fixed momentum transfer are presented. The method is illustrated by data from Ni and Ag. The temperature dependence of the averaged intensity is presented. The multiple scattering contributions to the averaged intensity can be accounted for by an effective atomic scattering factor. Conditions for the applicability of the method are discussed. From the resulting kinematic intensities, the surface atomic arrangements can be determined by simple modifications of conventional crystallographic analysis.     

On the electronic structure of cleaved GaAs(110) surfaces exposed to formic acid

GaAs(110) surfaces cleaved in UHV and exposed to HCOOH have been studied by work function measurements (Kelvin method), electron energy loss spectroscopy (ELS) and by low energy electron diffraction (LEED). From the different changes of the work function on n- and p-type material information about intrinsic and extrinsic surface states is derived. In the loss spectra the adsorbed formate species causes a loss near 9 eV. The intensity of the loss near 20 eV generally ascribed to an excitonic transition from the Ga 3d core level into surface states is reduced only by a factor of two after saturation with HCOOH. This might be related to the c(2 × 2) superstructure observed in LEED, which suggests a saturation coverage of half a monolayer.     

Xenon monolayer structures on copper and silver

LEED studies of xenon monolayers at 77K on (111), (100) and (110) faces of copper and (111), (110) and (211) faces of silver show that the xenon atoms are hexagonally close-packed (or nearly so) on each surface, and that the surface area per adatom is about 17Ų. The adsorbate layer is epitaxially related to the substrate but is in full registry only on Cu (111). Surface potential values are consistent with those already reported for annealed polycrystalline films of copper and silver indicating that the latter are not specifically related to surface roughness.     

X-Ray photoelectron spectrum of methylisocyanide gas

The C and N 1s spectra of methylisocyanide gas have been recorded. Two resolvable peaks of equal intensity are observed in the C 1s spectrum. Using the equivalent-cores approximation and thermochemical data, together with MNDO MO calculations and the point-charge potential model, the lower-binding-energy C 1s line is assigned to photo-emission from the isocyano carbon. The strong satellites which have been observed in the spectra of coordination complexes of alkyl and aryl isocyanides are not observed in the spectra of the free molecule. Comparisons of the point-charge-potential-corrected binding energies for C 1s and N 1s photoemissions from CH₃NC and its isomer CH₃CN with those for a host of other molecules show that photoemissions from the internal atoms in these molecules are accompanied by substantially less than average relaxation energies. These smaller relaxation energies can be understood using valence-bond theory.     

Complete integrability in statistical mechanics and the Yang-Baxter equations

In this paper we give a differential formulation of the Yang-Baxter equations. The concept of “exactly solvable” for lattice models is related to the Frobenius concept of complete integrability. These ideas are illustrated in the context of the Baxter model.     

Study of the trapping states in ZnS single crystals grown from gallium melt

The trapping levels in zinc sulphide single crystals grown from gallium melt have been investigated using thermoluminescence techniques. The observed peak at 175° K consists of two overlapping components at 173 and 200° K respectively. Thermal activation energies and frequency factors were calculated for both traps. The dependence of glow curve shape on excitation conditions is caused by the retrapping by non-filled 200° K traps of electrons freed from 173° K traps in the course of the glow curve run. In addition to the results on “pure” crystals, measurements were made on samples grown with chlorine, oxygen and copper impurities, as well. Although no positive identification of the chemical nature of the 173 and 200° K trapping centers has been possible, we find that our results are not inconsistent with a previously suggested model in which the traps are identified as complex defects. Comparison is also made with trap spectra observed earlier in gallium-doped zinc sulphide samples prepared by the usual methods.     

A moiré system for producing numerical data of the profile of a turbine blade using a computer and video store

A new technique has been devised for coding and analysing moiré contours. It uses a video frame store in place of the more usual photographic reference grid, and a small microcomputer to automate fringe detection. The system is based on using a television camera to view a sample, the complete technique being developed primarily as an industrial tool for quality control, or as feedback sensor in flexible manufacturing.     

Geometrical formulation of equilibrium phenomenological thermodynamics

An abstract geometric formulation of equilibrium phenomenological thermodynamics which generalizes and unifies that of Gibbs, Carathéodory, and others is given. As done by Hermann, one adapts here a contact manifold as the basic mathematical structure. Such a manifold for a thermodynamic system is constructed. The empirical laws of thermodynamics have been reformulated in terms of this manifold and by means of exterior differential forms. Such concepts as Gibbs phase rule, Gibbs-Duhem equation and thermodynamic potentials have been reexamined within such a general scheme.     

Preparation and Mössbauer spectra of CoV2O4 spinel doped with Fe2+ on tetrahedral sites

Co²⁺_0.98Fe²⁺_0.02Fe³⁺_?V³⁺_2-? 04 (?? 0.001) was obtained from a sample containing the iron dope mainly in the trivalent state, by reducing it at 910°C in a CO₂/CO atmosphere. Mössbauer spectra of ⁵⁷Fe at the tetrahedral site were taken between 5 and 300 K. Below the Curie temperature (143 K) there is a magnetically induced electric field gradient eQV_zz and a reduction of the hyperfine field H_hf. Values at 5 K are H_hf=141 kG and eQV_zz=5.74 mm/s. The effective splitting of the Fe²⁺⁵E ground-state doublet, as estimated from the temperature dependence of eQV_zz and H_hf, is $\text{2q}\text{δ}\text{/k = 28 K}$. It is derived that in these oxides the coupling of the electronic ⁵E states to local Jahn-Teller active E-modes of vibration is stronger than in comparable sulphides.     

Small polaron electron transport in reduced CeO2 single crystals

An investigation of the electrical properties of reduced ceria, CeO_2?x, carried out on single crystals, shows that CeO_2?x provides one of the clearest examples of hopping conduction and the small polaron mechanism. Included are conductivity and Seebeck coefficient measurements at constant x, obtained by sealing off the specimen chamber after reduction. The Seebeck coefficient is independent of temperature, suggesting that the number of carriers is constant. On the other hand, the mobility is activated, with activation energy E_h = 0.40 eV at small x and increasing to 0.52 eV at x = 0.25. The results for the mobility preexponential are consistent with the adiabatic theory of small polaron behavior. A puzzling feature of the Seebeck data as a function of x is that, for low x, the data fit the well-known Heikes formula, without a degeneracy factor of 2 for spin. Nevertheless, these data are interpreted to show that the proportion of mobile carriers decreases as x increases, presumably because of the presence of short-range ordered configurations which immobilize some carriers.     

Perturbation theory for projected states in the pairing force model: (III). The problem of spurious states

We discuss the possible types of behaviour of spurious states within the framework of the perturbation theory for projected states. The two-level nuclear pairing force model is used to test them.     

Photoelectron asymmetries and two-electron satellites near the 3p → 3d giant-resonance region in atomic Mn

The partial cross-sections and photoelectron angular distributions for several lines in atomic Mn have been measured at photon energies between 50 and 72eV. The intensities of the 3d correlation satellites at 24–26 eV binding energy behave similarly to the mainline intensity near the 3p → 3d giant resonance, but show an enhancement near the 3p threshold which is not present for the main line. A configuration-interaction analysis is applied to help identify the origins of the satellites. The 3p/3d branching ratio from 55–72eV and the shape of the 3d cross section in the resonance region are in good agreement with many-body perturbation-theory calculations.