Making use of x-ray optical effects in photoelectron-, Auger electron-, and x-ray emission spectroscopies: Total reflection, standing-wave excitation, and resonant effects

Abstract

We present a general theoretical methodology and related open-access computer program for carrying out the calculation of photoelectron, Auger electron, and x-ray emission intensities in the presence of several x-ray optical effects, including total reflection at grazing incidence, excitation with standing-waves produced by reflection from synthetic multilayers and at core-level resonance conditions, and the use of variable polarization to produce magnetic circular dichroism. Calculations illustrating all of these effects are presented, including in some cases comparisons to experimental results. Sample types include both semi-infinite flat surfaces and arbitrary multilayer configurations, with interdiffusion/roughness at their interfaces. These x-ray optical effects can significantly alter observed photoelectron, Auger, and x-ray intensities, and in fact lead to several generally useful techniques for enhancing surface and buried-layer sensitivity, including layer-resolved densities of states and depth profiles of element-specific magnetization. The computer program used in this study should thus be useful for a broad range of studies in which x-ray optical effects are involved or are to be exploited in next-generation surface and interface studies of nanoscale systems.

Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission

“…This scan sweeps the SW vertically through the sample over roughly one-half of its period, and generates what is termed a rocking curve (RC) of various individual core-level photoelectron peak intensities. We present below experimental results together with theoretical photoemission calculations that quantitatively incorporate the standing-wave field 19,20 .…”

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

“…Additional resonant effects on the x-ray optical constants below and above the Gd 3d 5/2 (M 5 ) absorption edge were also used to move the scanning depth of the SW in a controlled way and to increase the amplitude of the SW. Moving the SW position in this way over a resonance was demonstrated by Bedzyk and Materlik [34] for Bragg reflections from single-crystal planes and with x-ray fluorescence detection; this paper describes this technique being used with reflection from a multilayer heterostructure and with photoelectron detection. The SW data is compared to simulations using the Yang X-Ray Optics (YXRO) software package [35], which includes detailed x-ray optical and photoemission intensity modeling and implicitly both Bragg and Kiessig interference effects. The expected depth resolution of the SW technique with fitting of experimental RCs to x-ray optical theory while varying geometric parameters is expected to be 1/10th of the SW period, which is comparable to the size of 1 unit cell (u.c.)…”

Functional materials for information and energy technology: Insights by photoelectron spectroscopy

“…Fig. 9 shows the depth profiles obtained from the analysis of different spieces' rocking curves using YXRO simulation package [52]. As the first noteworthy result, we show that the Na + and Cs + ions have distinctly different depth distributions within the liquid layer, more specifically that Cs + ions are on average by 0.4 nm farther away from the hematite surface than Na + ones.…”

“…X-ray optical and photoemission simulations were again carried out using the YXRO software package [52]. A model system equivalent to the one depicted in Fig.…”