A new aberration correction method has been developed for photoemission electron
microscopy (PEEM). In order to correct the spherical and chromatic aberrations, a moving
focus method was adopted. Several experimental limitations to achieving optimal
resolution have also been overcome. A high brightness Hg lamp system has been
developed to overcome the insufficient brightness of the conventional Hg lamp. An
improvement of brightness by over 100 times as compared with the conventional lamp was
achieved. Image blur was also found due to a weak environmental AC magnetic
field caused by essential microscope components, i.e., the power transformer and
CCD camera. After implementing the high brightness lamp and eliminating stray
magnetic field by proper shielding, preliminary experiments demonstrate that
aberration correction by moving focus can improve the PEEM image resolution.
Anomalous step contrast in low energy electron microscopy (LEEM) images observed during Pb deposition on a W(110) surface is discussed. The steps are dark on the clean surface, and become bright by Pb deposition at about 200 °C. The contrast reversal is related to the presence of a two-dimensional (2D) Pb gas on the surface and its atomic density distribution. Upon further deposition the steps become dark again and show an anomalous intensity profile. This change is attributed to the 2D crystallization process.
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