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Direct measurement of electron channeling in a crystal using scanning transmission electron microscopy

机译:使用扫描透射电子显微镜直接测量晶体中的电子通道

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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 SrTiCh 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 ~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.
机译:通过使用在Si(100)上生长的薄外延SrTiO_3(100)岛作为测试对象,通过扫描透射电子显微镜直接测量了原子级高能电子波包在晶体硅中沿带区通道的自聚焦。当电子探针沿硅原子柱向下传播时,它逐渐聚焦到该柱上,从而导致在通道最大值处的散射信号增加了四倍。这导致SrTiCh岛的可见性增强,如果将样品上下颠倒,并且仅在探针从SrTiO_3层散射后才发生通道,这会丢失。通过多层方法计算出的探测波函数的演变可以在绝对厚度尺度上准确预测通道信号的趋势。我们发现,尽管电子通道增强了柱上原子的可见度,但它抑制了柱外原子的贡献。因此,它可以用作过滤器,以选择性地使与基板原子列最对准的原子成像。通过使用此技术,可以将相干岛与松弛岛区分开。对于在Si(100)上进行定势反应形成的SrTiO_3膜,我们表明只有〜55%的SrTiO_3与Si原子柱对齐。通过选择远离平衡的生长条件,可以增加Si(100)上相干SrTiO_3岛的比例。

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