High Resolution Electron Energy Loss Spectrometers (EELS)

High-resolution electron energy loss spectroscopy (EELS) is a powerful surface- analytical technique which provides unique vibrational analysis of metal and semiconductor surfaces in a high-vacuum environment. Increasingly, insulators and polymer films are also being studied by means of charge-neutralization techniques. EELS readily provides important information on:

• adsorbate vibrational frequencies
• molecular structure of adsorbates (decomposition, polymerization)
• bond strengths at surfaces
• adsorption geometry--surface-bonding sites
• surface chemistry (oxide formation, reduction, intermediates, etc.)
• overtone and combination vibrational bands
• surface acoustic and optical phonons

Importantly, EELS affords higher surface sensitivity and wider spectral range than infrared spectroscopy. For example, a spectral range of 200-5000 cm^-1 can be scanned in a few minutes, and less than 10^-3 monolayers of adsorbed CO may be detected. In contrast to IR spectroscopy, EELS is not limited by strict dipole selection rules, which often hinder observation of important modes and adsorbates. In EELS both long-range dipole and short-range "impact" scattering mechanisms are operable and may be effectively studied as a function of scattering angle and impact energy. For example, molecular adsorbates which exhibit weak dipole activity can be detected in the "impact" scattering regime. Information obtained from EELS ideally complements data obtained with Auger, ESCA, LEED, SIMS, STM and other surface probes, and offers ease of interpretation for the experimentalist.