0000000000030842
AUTHOR
J. Kirschner
Element-Selective Magnetic Imaging in Exchange-Coupled Systems by Magnetic Photoemission Microscopy
We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in…
Recent progress in photoemission microscopy with emphasis on chemical and magnetic sensitivity
Abstract With the improved access to synchrotron radiation sources photoemission electron microscopy is developing into a versatile analytical tool in surface and materials science. The broad spectral range and the well-defined polarization characteristics of synchrotron light permit a unique combination of topographic, chemical, and even magnetic investigations down to a mesoscopic scale. The potentiality of photoemission electron microscopy is demonstrated by several experiments on surfaces and microstructured thin film systems, which have been carried out with a newly designed instrument. We discuss its different modes of operation with respect to both microscopy and spectroscopy. A comb…
Imaging spin filter for electrons based on specular reflection from iridium (001)
Abstract As Stern–Gerlach type spin filters do not work with electrons, spin analysis of electron beams is accomplished by spin-dependent scattering processes based on spin–orbit or exchange interaction. Existing polarimeters are single-channel devices characterized by an inherently low figure of merit (FoM) of typically 10 −4 –10 −3 . This single-channel approach is not compatible with parallel imaging microscopes and also not with modern electron spectrometers that acquire a certain energy and angular interval simultaneously. We present a novel type of polarimeter that can transport a full image by making use of k -parallel conservation in low-energy electron diffraction. We studied specul…
Orbital mapping of carbon thin films by XANES-spectromicroscopy
Abstract A laterally resolved micro-XANES study (X-ray absorption near edge structure) of amorphous carbon, hydrogen terminated CVD-diamond (100) and highly oriented pyrolytic graphite (HOPG) is presented. The results were obtained by means of a photoemission electron microscope. Using this technique the well-known spectral features of carbon in its different chemical states (sp 2 , sp 3 ) could be recorded. The sp 2 /sp 3 content of the films was extracted from the spectra. Images, taken at X-ray energies corresponding to maxima (π*, C–H*) of the unoccupied density of states in these spectra, map the lateral distribution of the different orbitals at the sample surface. This study revealed …
Fast elemental mapping and magnetic imaging with high lateral resolution using a novel photoemission microscope
Abstract Using tunable soft X-ray synchrotron radiation and a new-generation photoemission electron microscope with integral sample stage and microarea selector, elemental images and local XANES spectra have been measured. Given the present conditions (PM3 at BESSY), the lateral resolution was in the range of 130 nm with the potential of considerable improvement with high-brilliance sources (a base resolution of 25 nm was obtained in threshold photoemission). Measurements at the oxygen K-edge demonstrate that differences in the local chemical environment of the emitter atom are clearly revealed and can thus be used as a fingerprint technique for its chemical state and geometrical surroundin…
Magnetic Domain Imaging with a Photoemission Microscope
ABSTRACTPhotoelectron emission microscopy (PEEM) has proven to be a versatile analytical technique in surface science. When operated with circularly polarized light in the soft x-ray regime, however, photoemission microscopy offers a unique combination of magnetic and chemical information. Exploiting the high brilliance and circular polarization available at a helical undulator beamline, the lateral resolution in the imaging of magnetic domain structures may be pushed well into the sub-micrometer range. Using a newly designed photoemission microscope we show that under these circumstances not only domains, but also domain walls can be selectively investigated. The high sensitivity of the te…
Anomalous d-like surface resonances on Mo(110) analyzed by time-of-flight momentum microscopy.
The electronic surface states on Mo(110) have been investigated using time-of-flight momentum microscopy with synchrotron radiation (hν=35 eV). This novel angle-resolved photoemission approach yields a simultaneous acquisition of the E-vs-k spectral function in the full surface Brillouin zone and several eV energy interval. (kx,ky,EB)-maps with 3.4 A(-1) diameter reveal a rich structure of d-like surface resonances in the spin-orbit induced partial band gap. Calculations using the one-step model in its density matrix formulation predict an anomalous state with Dirac-like signature and Rashba spin texture crossing the bandgap at Γ¯ and EB=1.2 eV. The experiment shows that the linear dispersi…
Highly efficient multichannel spin-polarization detection.
Since the original work by Mott, the low efficiency of electron spin polarimeters, remaining orders of magnitude behind optical polarimeters, has prohibited many fundamental experiments. Here we report a solution to this problem using a novel concept of multichannel spin-polarization analysis that provides a stunning increase in efficiency by 4 orders of magnitude. This improvement was demonstrated in a setup using a hemispherical electron energy analyzer. An imaging setup proved the principal capability of resolving more than ${10}^{5}$ data points in parallel.