Recent instrumental progress of valence-band photoemission in the X-ray range allows uncovering bulk- and surface-related electronic properties. Four-dimensional recording of energy and momentum-vector gives access to the complete spectral-density function. Systematic measurements for a number of transition metals between 15 eV-6 keV reveal unexpected strong intensity modulations due to photoelectron diffraction. Here, we present a graphical model that illustrates the role of momentum-conservation in Fermi’s Golden-Rule in an intuitive way. Intensity enhancement or reduction by factors >5 are confined to small energy- and momentum-intervals (widths 0.03 Å⁻¹ and 200 meV). Laue-type diffraction involves the photon momentum and is intrinsic in the photoemission process, in accordance with Pendry’s final-state-model. At higher energies, Kikuchi-diffraction imprints additional modulations on valence-band-patterns and quasi-elastic background. The absence of photon-momentum transfer uncovers the extrinsic nature of Kikuchi-diffraction. For Re at 30 K and 3.4 keV the relative weight of the Kikuchi-branch is comparable to the Laue-branch, whereas at 6 keV the Kikuchi-branch prevails.

在X射线范围内价带光发射的最新仪器进展允许揭示与本体和表面相关的电子特性。能量和动量矢量的四维记录使您可以访问完整的光谱密度函数。对15 eV-6 keV之间的多种过渡金属进行的系统测量表明，由于光电子衍射，产生了意想不到的强强度调制。在这里，我们提供了一个图形模型，以直观的方式说明了动量守恒在费米黄金规则中的作用。强度增大或减小> 5的范围仅限于较小的能量和动量间隔（宽度0.03Å ^-1和200 meV）。根据彭德里的最终状态模型，劳厄型衍射涉及光子动量，并且在光发射过程中是固有的。在较高的能量下，菊池衍射在价带模式和准弹性背景上施加附加调制。光子动量转移的缺乏揭示了菊池衍射的外在本质。对于Re在30 K和3.4 keV时，菊苣分支的相对重量与Laue分支相当，而在6 keV时，菊苣分支占主导。