New high resolution electron spectrometer for surface vibrational analysis

Abstract

The design and performance of a new electron spectrometer for high resolution electron energy loss (EELS) analysis of surface vibrations is described. Based on the 127° cylindrical deflection analyzer (CDA), the spectrometer incorporates a two-stage monochromator, a new lens system with out-of-plane focusing, relatively large (60 mm) energy-dispersing elements, and stringent magnetic field attenuation. Basic spectrometer geometry is compatible with commercial surface analysis systems employing Auger electron spectroscopy (AES), photoelectron spectroscopy (ESCA), low energy electron diffraction (LEED), etc. Performance of the instrument is shown to equal or exceed that of other spectrometers in terms of monochromatic current for a given energy resolution. An overall system resolution of 3.5 meV (28 cm−1) FWHM is routinely achieved at 1.5×10−10 A incident current and high signal levels (105–107 cps) for elastic beam reflection. A higher resolution of 2.5 meV (20 cm−1) has been obtained but with substantial sacrifice of signal level. Performance of the spectrometer is illustrated for the cases of direct (potential barrier) reflection from a palladium(100) crystal surface and for carbon-monoxide adsorption.