4 - Incident ion techniques

Summary

Introduction

At low incident kinetic energies (at most a few tens of eV) the interaction of incident ions with a surface is dominated by charge transfer to neutralise the ion. This produces electron emission characteristic of the electronic structure of the surface, and therefore forms a valence level spectroscopy known as INS. This will be discussed in detail in the next section.

By contrast, a number of techniques in surface studies utilise the kinetic energy transfer of more energetic incident ions to provide information on the surface. Most of these techniques use incident inert gas ions He⁺, Ne⁺ or Ar⁺ in the energy range from a few hundred eV to a few keV although some use is also made of similarly low energy alkali metal ions (Li⁺, Na⁺, K⁺) and oxygen ions, and there are also techniques based on the use of far more energetic (up to 1 MeV or more) incident ions of He⁺ and H⁺. While these incident ions may also suffer charge transfer at the surface, and can produce electronic excitations both in the form of core level ionisation and plasmon excitation, most techniques concentrate on the kinetic energy transfers between the incident ion and the atoms which comprise the surface.