XAS-PEEM
SPELEEM applications , LEEM , energy filtered XPEEM , XAS-PEEM , microprobe-ARPES
X-ray absorption spectroscopyThe PEEM is often used to implement laterally resolved applications of x-ray absorption spectroscopy (XAS) and its related methods. In XAS, the PEEM microscope is used to image the secondary electron emission at fixed kinetic energy, while the photon energy hν is scanned. When the photon energy matches a core level energy, a resonance in the secondary emission intensity is observed, originating from electronic transitions from core levels into unoccupied valence states via excitation processes occurring during the filling of the core holes. Such resonances are unique fingerprints that enable us to get precious information about the emitter chemical state, site location and valence state (x-ray absorption near edge spectroscopy). Due to the very low energy of the secondary electrons (less than 10 eV) and the increase of the inelastic mean free path of electrons at very low energy, XAS and XANES are used to probe buried interfaces or films up to a depth of ~10nm. The resolving power of the monochromator determines the attainable energy resolution so that, in principle, no energy filter is required. Magnetic imaging
Magnetic linear dichroism. XMLD-PEEM is used in the characterization of antiferromagnetic materials, and is sensitive to the alignment of the magnetic axis A. In XMLD the secondary electron intensity depends upon the charge distribution and magnetism. The magnetic contrast is proportional to the cosine of the angle between A and electric field vector E. XMLD-PEEM can thus image the AFM order, e.g. the alignment of the axis A and the domains. Data are acquired using horizontal and vertical linear polarisation of the photons. The XMLD images are usually obtained by subtraction of PEEM images obtained at two energies around the resonances, in order to maximize LMD contrast. |
ReferencesPhotoemission Microscopy;J Feng and Scholl; in Science of Microscopy, pp. 657-695; eds Hawkes P W, Spence J C H Springer, Berlin, 2007. Magnetism; J. Stöhr J and. H.C. Siegmann Springer, Berlin, 2006 Principles of X-Ray Magnetic Dichroism Spectromicroscopy; J. Stöhr, H.A. Padmore, S. Anders, T. Stammler, M.R. Scheinfein; Surf. Rev. Lett. 5, 1297 (1998). doi: 10.1142/S0218625X98001638 Recent advances in chemical and magnetic imaging of surfaces and interfaces by XPEEM; A. Locatelli and E. Bauer; J. Phys.: Condens. Matter 20, 093002 (2008). doi: 10.1088/0953-8984/20/9/093002 X-ray magnetic circular dichroism imaging in a low energy electron microscope; A. Locatelli, S. Cherifi, S. Heun, M. Marsi, K. Ono, A. Pavlovska, and E. Bauer; Surf. Rev. Lett. 9, 171-176 (2002). doi: 10.1142/S0218625X02001896e |