T. Miller

Band structure of metallic pyrochlore ruthenates Bi2Ru2O7 and Pb2Ru2O6.5

The band structure of Bi2Ru2O7 and Pb2Ru2O6.5 has been computed self‐consistently from first principles for the first time by the pseudofunction method. We discover that the 6s bands of Bi and Pb are very deep and unlikely to contribute to the metallic behavior as previously believed. The unoccupied 6p bands, however, are only several eV above the Fermi energy and are mixed with the Ru 4d band at the Fermi surface via the framework O atoms, leading to band conduction and delocalized magnetic moments. The predicted location of the 6s bands and the location and width of the O 2p band are confirmed by synchrotron radiation and ultraviolet electron spectroscopy of single crystals.

Surface core-level shifts for Ge(100)-(2×1)

Abstract Using surface-sensitive photoemission techniques, Ge 3d core-level binding energies for surface atoms of Ge(100)−(2 × 1) are found to be smaller than the bulk values by 0.41 eV. The surface atoms with shifted core-level binding energies correspond to one full (100) atomic layer. A surface core-exciton resonance is observed in the partial-yield measurements. The empty surface state involved in this excitonic transition, without binding-energy correction, is located at the valence-band maximum.

Ultraviolet/ozone cleaning of carbon-contaminated optics

It is shown that ozone generated by UV light can be used to clean carbon-contaminated synchrotronradiation optics.

Fermi surfaces and energy gaps in Sn/Ge(111)

One third of a monolayer of Sn adsorbed on Ge(111) undergoes a broad phase transition upon cooling from a (×)R30° normal phase at room temperature to a (3×3) phase at low temperatures. Since band-structure calculations for the ideal (×)R30° phase show no Fermi-surface nesting, the underlying mechanism for this transition has been a subject of much debate. Evidently, defects formed by Ge substitution for Sn in the adlayer, at a concentration of just a few percent, play a key role in this complex phase transition. Surface areas near these defects are pinned to form (3×3) patches above the transition temperature. Angle-resolved photoemission is employed to examine the temperature-dependent band structure, and the results show an extended gap forming in k-space as a result of band splitting at low temperatures. On account of the fact that the room temperature phase is actually a mixture of (×)R30° areas and defect-pinned (3×3) areas, the band structure for the pure (×)R30° phase is extracted by a difference-spectrum method. The results are in excellent agreement with band calculations. The mechanism for the (3×3) transition is discussed in terms of a response function and a tight-binding cluster calculation. A narrow bandwidth and a small group velocity near the Fermi surface render the system highly sensitive to surface perturbations, and formation of the (3×3) phase is shown to involve a Peierls-like lattice distortion mediated by defect doping. Included in the discussion, where appropriate, are dynamic effects and many-body effects that have been previously proposed as possible mechanisms for the phase transition.

Direct transitions, indirect transitions, and surface photoemission in the prototypical system Ag(111)

Abstract The sp band of Ag(111) is nearly free-electron like near the Fermi level. Photoemission from this band in the surface-normal direction gives rise to a direct-transition peak which disperses with varying photon energies. Contrary to predictions of the standard three-step model, the line shape is significantly asymmetric. The lower binding-energy side of this peak has a higher intensity, and is joined by a broad indirect-transition plateau extending to a rounded cut-off at the sp band edge. This study is an analysis of the asymmetry of the direct-transition peak and the intensity and line shape of the indirect-transition region. The optical transition-matrix element consists of two terms. One is the usual momentum-matrix element dominated by the direct band-to-band transitions in the bulk, with a small contribution from the surface due to the finite mean-free path. The other is a ∇· A term, which dominates the surface contribution and gives rise to indirect transitions involving all valence states without any restrictions on the crystal momentum. Interference between the bulk and surface contributions results in an asymmetric line shape for the direct-transition peak. The contribution from ∇· A is shown to be well correlated with the difference in dielectric function between Ag and vacuum. The effects discussed in this paper are fairly general in nature, and should be taken into account in high-resolution photoemission work.

Disposition kinetics of cyclohexanone in beagle dogs

Abstract The disposition kinetics of cyclohexanone, a commonly used industrial solvent, was studied in beagle dogs following intravenous administration of a 284 mg/kg dose at various rates for 18 or 21 days. The major metabolite of cyclohexanone was identified as cyclohexanol. Plasma and urine concentrations of the compound and the metabolite were determined using a newly developed gas chromatographic procedure. A two-compartment open model was used to analyze plasma concentration-time data of cyclohexanone. The distribution half-life, biological half-life, and clearance values for cyclohexanone were 6.6 ± 3.6 min, 81.0 ± 22.5 min, and 27.4 ± 4.3 ml/kg/min, respectively. Between 74 and 100% of the administered dose of cyclohexanone was converted to cyclohexanol and approximately 60% of the dose was excreted in the urine as the glucuronide conjugate of cyclohexanol. Peak cyclohexanol concentrations in plasma following intravenous bolus administrations of 284 mg/kg of cyclohexanone ranged from 140 to 220 μg/ml and occurred between 5 and 30 min after cyclohexanone administration. Apparent plasma elimination half-life of the metabolite was 99 min. Urinary excretion data suggested that less than 1% of the dose was excreted as cyclohexanol and cyclohexanone. Under the dosage schedule employed in the present study, there was neither any accumulation of cyclohexanone nor any evidence of enzyme induction on repeated administrations. The data gathered in the present investigation are useftul in calculations of cyclohexanone peak or steady-state levels during comparative toxicological studies involving different dosage regimens.

Angle-resolved photoemission from atomic-layer-resolved quantum well states in Ag/Fe(100)

Abstract Angle-resolved photoemission from thin films of Ag on Fe(100) grown with a low temperature deposition and annealing technique shows clear quantum well peaks for coverages up to 12 monolayers. Pairs of peaks are sometimes observed in the spectra; atomic layer resolution is demonstrated and used to explain these pairs without invoking spin splitting. The peaks are observed only within an energy window defined by the minority spin hybridization gap within the Fe substrate. Large intensity variations of the quantum well states with photon energy are observed.

Engineering Electronic Structure of a Two-Dimensional Topological Insulator Bi(111) Bilayer on Sb Nanofilms by Quantum Confinement Effect

We report on the fabrication of a two-dimensional topological insulator Bi(111) bilayer on Sb nanofilms via a sequential molecular beam epitaxy growth technique. Our angle-resolved photoemission measurements demonstrate the evolution of the electronic band structure of the heterostructure as a function of the film thickness and reveal the existence of a two-dimensional spinful massless electron gas within the top Bi bilayer. Interestingly, our first-principles calculation extrapolating the observed band structure shows that, by tuning down the thickness of the supporting Sb films into the quantum dimension regime, a pair of isolated topological edge states emerges in a partial energy gap at 0.32 eV above the Fermi level as a consequence of quantum confinement effect. Our results and methodology of fabricating nanoscale heterostructures establish the Bi bilayer/Sb heterostructure as a platform of great potential for both ultra-low-energy-cost electronics and surface-based spintronics.

Quantum well photoemission from atomically uniform Ag films : determination of electronic band structure and quasi-particle lifetime in Ag(100)

Photoemission from atomically uniform layers of Ag on a Fe(100) substrate is employed for the determination of the bulk electronic band structure of Ag. The high degree of control of the layer thickness allows the interferometric measurement of the electron momentum normal to the sample surface. This leads to an unprecedented precision in the electronic band structure determined from the experiment. The high quality of the layers also allows the discussion of the line shape of the quantum well peaks for the first time and gives access to the intrinsic and extrinsic broadening parameters of the line shape.

Influence of concentration and rate of intravenous administration on the toxicity of cyclohexanone in beagle dogs

Abstract The importance of concentration and rate of intravenous administration in affecting the toxicity of cyclohexanone was investigated. Four groups (I–IV) comprised of three male dogs each received a dosage of 284 mg/kg/day for 18–21 days as follows: 6% ( v v ) solution at 75 (I) or 5 ml/min (II); or 0.75% solution at 75 (III) or 5 ml/min (IV). Signs of toxicity observed included vocalization, lacrimation, scleral vasodilation, mydriasis, salivation, urination, defecation, restlessness, stupor, ataxia, occasional convulsive movements, hyperpnea, and/or dyspnea. Also, regimen I produced a metabolic acidosis with an apparent respiratory component. The severity of the responses correlated well to the maximal plasma concentrations of cyclohexanone attained, which ranged from 80 to 320 μg/ml, and to the conditions of administration as follows: I > II > III > IV. This distinction became even more apparent with repeated administrations and affected the prognosis for recovery. The concentration of cyclohexanone given was more critical than the rate of injection in producing localized tissue inflammation at injection sites, hemolysis, and secondary responses, e.g., bone marrow hyperplasia and extramedullary hematopoiesis. The rate of administration was also important since, at either concentration of cyclohexanone employed, the group receiving the compound at a faster rate had a greater response. Thus, the influence of iv administration factors on cyclohexanone toxicity was great, showing the importance of taking such factors into account in any safety evaluation study.