5 July 2010

Nanotechnology 21, 295704 (2010)

Nanochannel alignment analysis by scanning transmission ion microscopy

I. Rajta1, G.A.B. Gál1, S.Z. Szilasi1, Z. Juhász1, S. Biri1,
M. Mátéfi-Tempfli2 and S. Mátéfi-Tempfli2

1 Institute of Nuclear Research of the Hungarian Academy of Sciences (HAS-ATOMKI), H-4026, Bem tér 18/c, Debrecen, Hungary
2 Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Place Croix du Sud, 1, bâtiment Boltzmann a1, bte 3, B-1348 Louvain-la-Neuve, Belgium

In this paper a study on the ion transmission ratio of a nanoporous alumina sample is presented. The sample has been 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 µm thickness, had pore diameters of ~215 nm and spacing of ~450 nm. The perfect hexagonal order is valid only inside typical domains of 1-10 µm lateral size. The scanning electron microscope (SEM) images reveal errors in this arrangement along the domain boundaries.

Figure 1. Schematic top view of the sample.

When the proton beam size was limited to a single domain, a peak transmission ratio of 19% has been observed as is expected from the geometry (~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 has been reduced to 5%. The STIM analysis over an area larger than the typical domain size has revealed an overall capillary angular spread of ~2°.

Figure 2. Schematic side view of the sample.

The video below shows the STIM transparency as a function of sample tilt angle to the beam. The lighter pixels indicate higher transparency, i.e. the domains in which the nanocapillaries are aligned to the beam direction.