Nanochannel alignment analysis by scanning transmission ion microscopy

In this paper a study on the ion transmission ratio of a nanoporous alumina sample is presented. The sample was investigated by scanning transmission ion microscopy (STIM) with different beam sizes. The hexagonally close-packed Al2O3 nanocapillary array, realized as a suspended membrane of 15 mu m thickness, had pore diameters of similar to 215 nm and spacing of similar to 450 nm. When the proton beam size was limited to a single domain, a peak transmission ratio of 19% was observed as is expected from the geometry (similar to 19-20%). This result points out an almost perfectly parallel alignment of the capillaries within one domain. However, for larger beam scanning areas (sampling multiple domains) the transmission ratio was reduced to 5%. The STIM analysis over an area larger than the typical domain size revealed an overall capillary angular spread of similar to 2 degrees.