Variation of relative intensities between surface and bulk plasmon losses due to crystal orientations for aluminium in low energy electron reflection loss spectroscopy

The contrast change of secondary electron images due to the crystal orientations is observed by the ultra high vacuum scanning electron microscope (UHV-SEM) for crystal grains of clean surface of polycrystalline Al in the primary energy E_p of 200 eV to 5 keV. The low energy electron loss spectra are measured by the cylindrical mirror analyzer. The relative intensity ratio between surface and bulk plasmon loss spectra was dependent on the crystal orientations. The SEM images taken by the surface and bulk plasmon signals at E_p = 230 eV show the inverse contrast depending on the grains. The inversion of the relative intensities between the surface and bulk plasmon losses is explained qualitatively by taking into account of variation of the penetration depth of the incident beam caused by the electron channeling.