We demonstrate the use of a novel design of a photoelectron microscope in combination to an imaging energy filter for momentum resolved photoelectron detection. Together with a time resolved imaging detector, it is possible to combine spatial, momentum, energy, and time resolution of photoelectrons within the same instrument. The time resolution of this type of energy analyzer can be reduced to below 100 ps. The complete ARUPS pattern of a Cu(111) sample excited with He I, is imaged in parallel and energy resolved up to the photoelectron emission horizon. Excited with a mercury light source (h nu=4.9 eV), the Shockley surface state at the energy threshold is clearly imaged in k-space. Electron-electron interactions are observed in momentum space as a correlation hole in two-electron photoemission. With the high transmission and the time resolution of this instrument, possible new measurements are discussed: Time and polarization resolved ARUPS measurements, probing change of bandstructure due to chemical reaction, growth of films, or phase transitions, e.g., melting or martensitic transformations.
We report on a compact electron spin analyzer based on exchange scattering from a magnetic surface. The heart of the detector is an Fe(001) thin film grown on W(001) with chemisorbed oxygen in the p(1 x 1) structure. The device is mounted at the exit of an energy dispersive analyzer and works at a scattering energy of about 13.5 eV. Its figure of merit is 2 x 10(-3), combined with an excellent stability of more than 2 weeks in UHV.
Series of CuxO thin-films in the entire range of compositions 1≤x≤2 were obtained by varying the oxygen flux in an rf-sputter deposition process. Growth windows for three crystalline phases, i.e., the thermodynamically stable cuprous oxide Cu2O and cupric oxide CuO as well as the metastable paramelaconite Cu4O3, were observed. The crystalline phases persist non-stoichiometrically over a wide range of compositions. These flux-range windows are separated by ranges where highly disordered, almost amorphous material is obtained. All samples were analysed with respect to their thermoelectric properties, i.e., Seebeck coefficient, electrical, and thermal conductivity. Clear trends of these transport parameters were found and used to determine the thermoelectric figure of merit ZT. The ZT-values at room temperature are highest for the two thermodynamically stable crystalline phases CuO and Cu2O.
Multilayer samples of alternating n-type ZnO and insulating ZnS layers were deposited by radiofrequency (RF) magnetron sputtering on glass substrates. The number of ZnO/ZnS periods was varied throughout the series to increase the number of interfaces, whilst keeping the ratio of total thicknesses of ZnO and ZnS constant. Scanning electron microscopy (SEM) revealed the individual layers, but also a columnar structure. The in-plane Seebeck coefficient S and electric conductivity r were measured between 50 K and 300 K. The dependence of S and r on thickness d of the individual ZnO layers can be modeled by introducing a narrow interface layer of high conductivity for d > 100 nm. At lower d, fluctuations of the interfaces lead to additional effects on S and r which arise due to percolation and can be explained qualitatively in the framework of a network model.
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