Search results for "photoemission"
showing 10 items of 174 documents
Application of the open-shell size-consistent self-consistent singles and doubles configuration interaction method to multielectronic transitions in …
2000
The size-consistent self-consistent matrix dressing method has been applied on an open-shell single-configuration reference state. Once the reference state is converged, several low-lying roots can be obtained for the dressed configuration interaction (CI) matrices of appropriate symmetry. The CI matrices were built with a complete-active-space singles and doubles CI method in order to deal properly with multiconfiguration excited states. The vertical ionization and ionization–excitation transitions are obtained from the difference to the closed shell ground-state energy of the neutral molecule. The method has been applied to NH+3 and N+2 using atomic natural orbital basis sets and state-av…
Real-space observation of xenon adsorption and desorption kinetics on graphite (0001) by photoemission electron microscopy
2003
Abstract The growth and desorption of Xe monolayers on the basal plane of graphite has been investigated by real-space imaging using photoemission electron microscopy. Adsorption kinetics was studied at different substrate temperatures (39–65 K), corresponding to different growth modes. Coexisting phases showed up as different grey values in the image. Typical domain sizes of the 2D solid phases around 60 K are of the order of one to several μm. The domains exhibit an elongated shape with their long axis oriented preferentially parallel to step edges of the substrate. With increasing coverage the brightness of the domains increases, the 2D gas-phase regions shrink and finally disappear at h…
Time-of-flight photoemission electron microscopy – a new way to chemical surface analysis
2001
Abstract The time structure of synchrotron radiation at BESSY I (Berlin) was utilised to operate a photoemission electron microscope in the time-of-flight mode. The electrons that are emitted from the sample surface with different energies are dispersed in a drift tube subsequent to the imaging optics. Two ways of fast image detection have been explored, a fast gated intensified CCD camera (800 ps gate time) and a special counting electronics in combination with a 3D (x,y,t)-resolving delay line detector ( time resolution ps). The latter device has a lateral resolution of about 50 μm in the image plane being equivalent to 1000 pixels along the image diagonal. An energy resolution of 400 meV…
Quantitative microscopy of magnetic domains in Fe(100) by core-level x-ray photoelectron spectroscopy
2005
We present an experimental technique for imaging of magnetic domain patterns based on element-specific core-level photoemission using polarized soft-x-ray radiation. It is applied to the measurement of domain patterns at the Fe(100) surface and at the surface of polycrystalline Fe. Different from well established imaging techniques that use a photoemission electron microscope to measure the secondary electron intensity at the Fe absorption threshold, we have investigated the photoemission intensity contrast on the the Fe $2{p}_{3∕2}$ core level using circularly polarized x-ray light. The linear and circular dichroism characteristics of the identical domain pattern are extracted by linear co…
Exchange coupling in the correlated electronic states of amorphous GdFe films
2013
The bulk sensitivity of hard x-ray photoelectron spectroscopy in combination with circularly polarized radiation of the P09 beamline at PETRA III enables the investigation of the magnetic properties of capped films. We have determined the temperature dependence of the magnetic circular dichroism in the Fe 2$p$ and in the Gd 3$d$ states in amorphous GdFe films. The magnetic dichroism reflects the stronger temperature dependence of Gd moments compared to Fe moments in agreement with mean-field models. We resolved the exchange split Gd 3${d}_{5/2}$ substates and found a significant temperature dependence of the splitting which is attributed to a temperature dependent part of the exchange energ…
Magnetic Circular Dichroism in Two-Photon Photoemission
2009
We report the observation of magnetic circular dichroism (MCD) in two-photon photoemission (2PPE). The Heusler alloys Ni2MnGa and Co2FeSi were investigated by excitation with femtosecond laser light, showing MCD asymmetries of A=(3.5+/-0.5)x10;{-3} for Ni2MnGa and of A=(2.1+/-1.0)x10;{-3} for Co2FeSi, respectively. A theoretical explanation is provided based on local spin-density calculations for the magnetic dichroic response; the computed 2PPE MCD agrees well with the experiment. The observed 2PPE magnetic contrast represents an interesting alternative for future time-resolved photoemission studies on surface magnetism practicable in the laboratory.
Circular dichroism in angular resolved photoemission from pure and Rb-doped C60 and C22H14 layers on platinum and tungsten
1997
Abstract Polycrystalline C60 and Pentacene films grown on W(110) and Pt(111) have been studied in valence band photoemission using circularly polarised synchrotron radiation from BESSY with special emphasis on circular dichroism in photoemission. For thin films of C60, dichroic asymmetries of about 10% occur independent of the temperature and the substrate hinting that the rotation of the topmost layer is hindered even at room temperature. For Pentacene we found asymmetries up to 50% in the region of the σ-electrons. Moreover, we found for this molecule a dichroic asymmetry in normal emission, that is a forbidden geometry. This hints on adsorption with the molecules perpendicularly oriented…
Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces
2002
Ag(111) films were deposited at room temperature onto H-passivated Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111) films of 6-12 monolayers have been grown. Angle resolved photoemission spectroscopy has been used to study the valence band electronic properties of these films. Well-defined Ag sp quantum-well states (QWS) have been observed at discrete energies between 0.5-2eV below the Fermi level, and their dispersions have been measured along the GammaK, GammaMM'and GammaL symmetry directions. QWS show a parabolic bidimensional dispersion, with in-plane effective mass of 0.38-0.50mo, along…
Temperature-induced martensite in magnetic shape memory Fe2MnGa observed by photoemission electron microscopy
2012
The magnetic domain structure in single crystals of a Heusler shape memory compound near the composition Fe2MnGa was observed during phase transition by photoelectron emission microscopy at Beamline 11.0.1.1 of the Advanced Light Source. The behavior is comparable with recent observations of an adaptive martensite phase in prototype Ni2MnGa, although the pinning in the recent work is an epitaxial interface and in this work the effective pinning plane is a boundary between martensitic variants that transform in a self-accommodating way from the single crystal austenite phase present at high temperatures. Temperature dependent observations of the twinning structure give information as to the …
The effect of magnetic anisotropy on the spin configurations of patterned La(0.7)Sr(0.3)MnO3 elements.
2013
We study the effect of magnetocrystalline anisotropy on the magnetic configurations of La0.7Sr0.3MnO3 bar and triangle elements using photoemission electron microscopy imaging. The dominant remanent state is a low energy flux-closure state for both thin (15 nm) and thick (50 nm) elements. The magnetocrystalline anisotropy, which competes with the dipolar energy, causes a strong modification of the spin configuration in the thin elements, depending on the shape, size and orientation of the structures. We investigate the magnetic switching processes and observe in triangular shaped elements a displacement of the vortex core along the easy axis for an external magnetic field applied close to t…