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Full field electron spectromicroscopy applied to ferroelectric materials
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Layout of a LEEM/PEEM instrument (LEEM III, Elmitec GmbH) with magnetic lenses. The sector field separates the incoming electron beam from the reflected or backscattered electrons. The sample bias adjusts the electron start voltage. TL, FL, and IL are the transfer, field, and intermediate lens of the imaging column. In PEEM mode, an energy analyzer is used just before the last projective lenses. (b) Layout of an energy-filtered PEEM with electrostatic lenses (NanoESCA, Omicron Nanotechnology GmbH). The double hemispherical analyzer and the low electron energy in the PEEM column optimize transmission and give a lateral resolution independent of the spectroscopic resolution. (c) and (d) Photographs of typical instruments represented in (a) and (b). In (d), 1, 2, and 3 are the positions for direct PEEM, small area spectroscopy, and spectroscopic imaging, 4 and 5 are the sample position and the double hemispherical analyzer.

Image of FIG. 2.
FIG. 2.

Schematic energy levels in a photoemission experiment. The initial state (left) is excited by a photon hν, giving the final state as measured by the spectrometer (right). The work function, , is the difference between the local vacuum level and the sample Fermi energy, .

Image of FIG. 3.
FIG. 3.

(a) Schematic of a spectromicroscopy experiment. Electron optics conserves the provenance of the electrons in the sample field of view. The energy analyzer filters the kinetic energy, giving a spectroscopic image of the photoemission on the 2D detector. (b) Typical photoemission spectrum. The shaded rectangles highlight the high intensity photoemission threshold at low kinetic energy, the core level region, and the valence band. In PEEM, the kinetic energy is referenced with respect to the Fermi level of the sample holder.

Image of FIG. 4.
FIG. 4.

(a) Energy-filtered, threshold image of a BaTiO (BTO)(001) single crystal showing three main intensity levels, . (b) Threshold spectra as extracted from the (solid) rectangles in (a). (c) Photoemission threshold map obtained using a pixel-by-pixel fit to the threshold spectra.

Image of FIG. 5.
FIG. 5.

(Top) electron reflectivity curves from PFM written P and P domains in as-received PZT. (Bottom) Same after annealing in oxygen. The inset shows the P (inner), P (outer) PFM written squares and the surrounding unwritten “imprint” area. The MEM-LEEM transition is taken as the midpoint in the drop in reflectivity. The FoV is about 15 m. Reprinted with permission from Krug , Appl. Phys. Lett. , 222903 (2010). Copyright 2010 American Institute of Physics.

Image of FIG. 6.
FIG. 6.

Reflectivity curves before (solid symbols) and after (open symbols) exposure of a BTO(001) single crystal to UV light. Insets: MEM image before (upper right) and after (bottom left) exposure to UV light. Reprinted with permission from Wang , Appl. Phys. Lett. , 092902 (2012). Copyright 2012 American Institute of Physics.

Image of FIG. 7.
FIG. 7.

(a) Time dependence of intensity contrast due to screening by UV-generated electron-hole pairs. (b) Time dependence of intensity contrast after UV light is switched off. (c) Schematic showing the drift of photogenerated charge carriers in an out of plane polarized ferroelectric slab. Reprinted with permission from Wang , Appl. Phys. Lett. , 092902 (2012). Copyright 2012 American Institute of Physics.

Image of FIG. 8.
FIG. 8.

(a) MEM-LEEM transition map obtained by a pixel by pixel analysis of the 3D dataset. (b) PEEM threshold spectra from PFM-polarized P and P domains in epitaxial BFO. (c) Thickness dependence of the MEM-LEEM transition (red squares) and the photoemission threshold (black circles) contrasts as measured by MEM-LEEM and PEEM, respectively. (d) calculated from PEEM (red squares) and MEM-LEEM (black circles). Red curve is fit to PEEM/LEEM data with . Blue diamonds are values used for numerical simulations. Reprinted with permission from Rault , Phys. Rev. Lett. , 267601 (2012). Copyright 2012 American Physical Society.

Image of FIG. 9.
FIG. 9.

(a) Schematic of the Brillouin zone for BTO(001). (b) Integrated photoemission intensity measured from a single in-plane domain. The sample holder Fermi level is at 48.75 eV. The wave-vector resolved constant energy cuts were acquired in the shaded region (c) k-resolved constant energy cuts in reciprocal space through the valence band (shaded area in (b)) showing the rich band structure.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Full field electron spectromicroscopy applied to ferroelectric materials