Energy filtering of reflection electron microscopy, diffraction and holography (REM, RHEED and REH) on clean silicon surfaces has been performed by using an omega-type energy filter built into a high-resolution UHV electron microscope with a field emission gun. Due to the glancing reflection geometry, electrons are travelling near the surface over a long distance, and multiple surface plasmon excitation occurs. By removing plasmon-loss electrons, background intensity in RHEED has been lowered and contrast of REM images and holograms has been improved. Although electrons that lost a small amount of energy due to surface plasmon excitation etc. are found to be still coherent, their coherency deteriorate due to a spread of angular distribution after the inelastic scattering. By making no-plasmon-loss hologram, improvement of spatial and phase resolution is expected.