Proton and light ion nanobeams from field ionization of water

We observe emission of protons and Hn+ (n up to 4) at room temperature from field ionization of thick films of water adsorbed on Pt or Pd, not on W tips. This differs from previous field ionization experiments of water, all of which show hydrated proton emission. Our observations are explained by the ionic dissociation of water on Pt and Pd surfaces. These thick film experiments are made possible by a special local water supply arrangement. An ion point source based on this ionization process is shown to produce nanobeams of light ions suitable for high resolution ion microscopy.