280 research outputs found
Electronic Resonances in Rare-Gas Adsorbates Observed by Spin-Resolved Electron Spectroscopy
Schönhense G, Kessler B, Müller N, Schmiedeskamp B, Heinzmann U. Electronic Resonances in Rare-Gas Adsorbates Observed by Spin-Resolved Electron Spectroscopy. Physica Scripta. 1987;35(4):541-546
Spin-resolved photoemission from Pd(111)
Schmiedeskamp B, Kessler B, Müller N, Schönhense G, Heinzmann U. Spin-resolved photoemission from Pd(111). Solid State Communications. 1988;65(7):665-670
Photoemission Electron Microscopy as a tool for the investigation of optical near fields
Photoemission electron microscopy was used to image the electrons
photoemitted from specially tailored Ag nanoparticles deposited on a Si
substrate (with its native oxide SiO). Photoemission was induced by
illumination with a Hg UV-lamp (photon energy cutoff eV,
wavelength nm) and with a Ti:Sapphire femtosecond laser
( eV, nm, pulse width below 200 fs),
respectively. While homogeneous photoelectron emission from the metal is
observed upon illumination at energies above the silver plasmon frequency, at
lower photon energies the emission is localized at tips of the structure. This
is interpreted as a signature of the local electrical field therefore providing
a tool to map the optical near field with the resolution of emission electron
microscopy.Comment: 10 pages, 4 figures; submitted to Physical Review Letter
Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy
The magnitude of the spin polarization at the Fermi level of ferromagnetic
materials at room temperature is a key property for spintronics. Investigating
the Heusler compound CoMnSi a value of 93 for the spin polarization has
been observed at room temperature, where the high spin polarization is related
to a stable surface resonance in the majority band extending deep into the
bulk. In particular, we identified in our spectroscopical analysis that this
surface resonance is embedded in the bulk continuum with a strong coupling to
the majority bulk states. The resonance behaves very bulk-like, as it extends
over the first six atomic layers of the corresponding (001)-surface. Our study
includes experimental investigations, where the bulk electronic structure as
well as surface-related features have been investigated using spin-resolved
photoelectron spectroscopy (SR-UPS) and for a larger probing depth
spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The
results are interpreted in comparison with first-principles band structure and
photoemission calculations which consider all relativistic, surface and
high-energy effects properly.Comment: 9 pages, 8 figures, Heusler alloy, electronic structure and
photoemissio
Orientation and substrate interaction of adsorbed CO and NO molecules probed by circular dichroism in the angular distribution of photoelectrons
The sensitivity and utility of circular dichroism in the angular distribution of photoelectrons (CDAD) as a probe of molecular orientation is demonstrated for adsorbed CO and NO molecules. A comparison between measured CDAD spectra and calculated values for spatially oriented CO and NiCO clearly confirms the well-known perpendicular adsorption for CO on Ni(100), whereas for CO adsorbed on Fe(100) a tilted adsorption geometry was found. For NO/Ni(100) and for NO on the oxygen-preadsorbed Ni(100) surface, an average tilt angle of α=40±10° was observed. In the case of the oxygen-preadsorbed Ni(100) surface, a higher fraction of NO molecules was found to be in a tilted orientation than on the clean surface
Asymmetric Electrostatic Dodecapole: Compact Bandpass Filter with Low Aberrations for Momentum Microscopy
Imaging energy filters in photoelectron microscopes and momentum microscopes
employ spherical fields with deflection angles of 90{\deg}, 180{\deg} and even
2 x 180{\deg}. These instruments are optimized for high energy resolution, yet
they come along with image aberrations when they are operated in high
transmission mode with medium energy resolution. Here we present a new approach
for bandpass-filtered imaging in real or reciprocal space, using an asymmetric
electrostatic dodecapole. This multipole enables energy-dispersive beam
deflection and correction of image aberrations up to the 3rd order. Owing to a
deflection angle of only 4{\deg}, the total beam displacement in the filter is
just ~10 mm. Hence, the entire instrument is compact and just requires a
straight vacuum tube. The multipole is framed by transfer lenses in the
entrance and exit branch. Two sets of 16 entrance and exit apertures with
different sizes on piezomotor-driven holders allow selecting the desired
resolution. The combination of apertures and dodecapole acts as a bandpass
pre-selector in a high-energy time-of-flight momentum microscope at the hard
X-ray beamline P22 at PETRA-III (DESY, Hamburg). At pass energies between 400
and 600 eV it transmits electrons with kinetic energies in the range of 20-40
eV and thus effectively eliminates unwanted intensity from higher-energy
electrons in the ToF analyzer. At low pass energies, the instrument allows
energy-filtered imaging without subsequent ToF analysis. In a laboratory
experiment the 4{\deg} prototype reached < 500 meV resolution, which is
sufficient for fast survey studies in the X-ray range.Comment: 16 pages, 6 figures, 26 reference
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