Ruotsalainen Kari O, Honkanen Ari-Pekka, Collins Stephen P, Monaco Giulio, Moretti Sala Marco, Krisch Michael, Hämäläinen Keijo, Hakala Mikko, Huotari Simo
Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.
Diamond Light Source, Didcot, Oxfordshire, OX11 0DE, UK.
Sci Rep. 2016 Mar 3;6:22648. doi: 10.1038/srep22648.
The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Dipolar absorption of x-rays is thus diminished, which makes the crystal nearly transparent for certain x-ray wave vectors. Indeed, a relative enhancement of electric quadrupole absorption via the Borrmann effect has been demonstrated recently. Here we show that the Borrmann effect has a significantly larger impact on resonant x-ray emission than is observable in x-ray absorption. Emission from a dipole forbidden intermediate state may even dominate the corresponding x-ray spectra. Our work extends the domain of x-ray standing wave methods to resonant x-ray emission spectroscopy and provides means for novel spectroscopic experiments in d- and f-electron systems.
博尔曼效应是指在衍射条件下完美晶体中X射线的异常透射。它源于入射波和衍射波的干涉，这种干涉在强吸收原子处产生具有节点的驻波。因此，X射线的偶极吸收减弱，这使得晶体对某些X射线波矢几乎透明。事实上，最近已经证明了通过博尔曼效应电四极吸收的相对增强。在这里，我们表明博尔曼效应在共振X射线发射中产生的影响比在X射线吸收中观察到的要大得多。来自偶极禁戒中间态的发射甚至可能主导相应的X射线光谱。我们的工作将X射线驻波方法的领域扩展到共振X射线发射光谱，并为d电子和f电子系统中的新型光谱实验提供了手段。
