科研之友
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摘要
Self-focusing of an atomic-scale high-energy electron wave packet by channeling along a zone axis in crystalline silicon is directly measured by scanning transmission electron microscopy using thin epitaxial SrTiO(3)(100) islands grown on Si(100) as test objects. As the electron probe propagates down a silicon atom column, it is progressively focused onto the column, resulting in a fourfold increase in the scattered signal at the channeling maximum. This results in an enhancement of the visibility of the SrTiO(3) islands, which is lost if the sample is flipped upside down and the channeling occurs only after the probe scatters off the SrTiO(3) layer. The evolution of the probe wave function calculated by the multislice method accurately predicts the trends in the channeling signal on an absolute thickness scale. We find that while electron channeling enhances the visibility of on-column atoms, it suppresses the contribution from off-column atoms. It can therefore be used as a filter to selectively image the atoms that are most aligned with the atomic columns of the substrate. By using this technique, coherent islands can be distinguished from relaxed islands. For SrTiO(3) films formed in a topotactic reaction on Si(100), we show that only similar to 55% of the SrTiO(3) is aligned with the Si atom columns. The fraction of coherent SrTiO(3) islands on Si(100) can be increased by choosing growth conditions away from equilibrium.
- 出版日期2011-8-17
