Mendis B G
Department of Physics, Durham University, South Road, Durham DH1 3LE, UK.
Acta Crystallogr A. 2010 May;66(Pt 3):407-20. doi: 10.1107/S0108767310004770. Epub 2010 Mar 31.
A Bloch wave model based on perturbation theory is used to analyse high-angle annular dark-field (HAADF) imaging of a substitutional and interstitial W atom in [111]-oriented body-centred-cubic Fe. For the substitutional atom the 1s Bloch state is scattered to high angles thereby producing HAADF dopant atom contrast. Intraband scattering of the 1s state is the strongest individual Bloch wave transition but collective interband scattering of the non-1s states to the 1s state leads to variations in the high-angle scattering with depth of the dopant atom. The non-1s states are Coulomb attracted towards the W atom thereby giving rise to an 'atom focusing' effect similar to channelling. For the interstitial atom, which in the [111] orientation does not overlap with an atom column of the host lattice, high-angle scattering and Coulomb attraction takes place through the non-1s states. Scattering of the 1s state is, however, negligible.
基于微扰理论的布洛赫波模型用于分析在[111]取向的体心立方铁中替位和间隙钨原子的高角度环形暗场（HAADF）成像。对于替位原子，1s布洛赫态被散射到高角度，从而产生HAADF掺杂原子对比度。1s态的带内散射是最强的单个布洛赫波跃迁，但非1s态到1s态的集体带间散射导致高角度散射随掺杂原子深度而变化。非1s态被库仑吸引向钨原子，从而产生类似于沟道效应的“原子聚焦”效应。对于间隙原子，在[111]取向下它不与主体晶格的原子列重叠，高角度散射和库仑吸引通过非1s态发生。然而，1s态的散射可以忽略不计。
