Scattering and recoiling imaging spectrometer (SARIS)

Abstract

An ultrahigh vacuum spectrometer system has been designed and constructed for obtaining spatial- and time-resolved, element-specific images of atoms that are scattered and recoiled from surfaces. A pulsed noble gas ion beam in the 1–5 keV range is used to scatter and recoil atoms from a surface. A large, position-sensitive microchannel plate detector with resistive anode encoder, that is sensitive both to ions and fast neutrals records the spatial distribution patterns of the emitted atoms. The use of time-of-flight methods allows capture of these patterns in time windows as short as 10 ns. The sensitivity of these patterns to the details of surface structure provides the basis for a scattering and recoiling imaging spectrometry (SARIS). The primary ion beam current is ∼0.1 nA/cm2, supplied in 20 ns pulses at a rate of 30 kHz, resulting in ∼5×102 ions/pulse; images with adequate statistics can be obtained in several seconds with a total ion dose of <1010 ions/cm2. The SARIS technique can provide unique, element-specific, real-space, surface structural information at a resolution of <0.1 Å on a time scale of seconds for analysis of surface composition, structure, and dynamics. Examples provided for demonstrating the capabilities of the system are 4 keV He+ and Ar+ scattering and recoiling from Pt{111} and 4 keV Kr+ scattering and recoiling from CdS{0001}.