The application of photoemission microscopy to the study of heterogeneous reactions over metal single crystal surfaces

The development of UHV instrumentation for photoemission electron microscopy (PEEM) has opened up the possibility of investigating in situ the morphology of metal single crystal surfaces during simple catalytical reactions in the pressure range up to 10^–4 mbar. We have studied the Pt(100) surface during the transition from the high to low rate branches of the CO oxidation reaction. Steps, step bunches and grain boundaries have been identified. They play an important role in the decomposition of CO and the deposition of carbon and probably regulate the reactivity of the Pt surface.     

3s- and 3p-core level excitations in 3d-transition metal oxides from electron-energy-loss spectroscopy

3s- and 3p-core level excitations for a large number of 3d-transition metal oxides, with a formal 3d occupation from 3d⁰ to 3d¹⁰, have been measured by electron energy loss spectroscopy in reflection geometry (REELS) with primary energies 200 eV≤E ₀≤1600 eV. Their intensities decrease systematically with the formal 3d-count, classifying them as transitions to empty 3d-states. The structure of the 3s excitations is analysed in detail and is compared to the 3s-XPS photoemission spectra of the samples. This 3s-REELS structure and its change with the 3d occupation can be explained by the assumption that the excitation arises mainly from a 3s²3dⁿ→3s¹3dⁿ⁺¹ quadrupole transition.     

Optimizing VVT strategies: a decomposition approach

Verification, validation and testing (VVT) of large systems is an important but complex process. The decisions involved have to consider on one hand the controllable variables associated with investments in appraisal and prevention activities and on the other hand the outcomes of these decisions that are associated with risk impacts and systems' failures. Typically, quantitative models of such large systems use simulation to generate distributions of possible costs and risk outcomes. Here, by assuming independence of risk impacts, we decompose the decision process into separate decisions for each VVT activity and supercede the simulation technique by simple analytical models. We explore various optimization objectives of VVT strategies such as minimum total expected cost, minimum uncertainty as well as a generalized optimization objective expressing Taguchi's expected loss function and provide explicit solutions. A numerical example based on simplified data of a case study is used to demonstrate the proposed VVT optimization procedure.     

Low energy excitations in KMnO4 with 1 eV<=ΔE<=10 eV from electron-energy loss spectroscopy

Electron-energy loss spectra of potassium permanganate (KMnO₄) with primary electron energies 25 eV<=E₀<=500 eV show 7 peaks in the energy-loss range 1 eV<=ΔE<=10eV and are successfully analysed with a superposition of 7 independent Gaussians. The intensity of these lines follow roughly a power-law dependence on the primary energy I∝E ₀ ^-α . There are two groups of lines, the first with an exponent α≈0.5, while the lines in the second group decay much stronger with increasingE ₀ corresponding to a value 0.9<=α<=1.3. The 4 lines in the first group are identified as dipole allowed transitions by comparison to recent first principle molecular-orbital calculations for the (MnO₄) molecule by H. Nakai et al. The dipole-allowed excitation spectrum obtained from this analysis agrees very well with these first principle calculations.