Circular dichroism in hard X-ray photoelectron diffraction observed by time-of-flight momentum microscopy

Area of Science:

• Surface Science
• Solid-State Physics
• Materials Science

Background:

• X-ray photoelectron diffraction (XPD) provides structural information for solids and thin films.
• Momentum microscopy offers high-resolution k-space imaging of XPD patterns.
• XPD is valuable for identifying dopant sites and tracking phase transitions.

Purpose of the Study:

• To investigate circular dichroism in the angular distribution (CDAD) of core-level XPD patterns.
• To demonstrate the generality of core-level CDAD across different elements.
• To explore the origin and symmetry of CDAD fine structure.

Main Methods:

• High-resolution momentum microscopy with circularly-polarized hard X-rays.
• Experimental measurements for core levels of Si, Ge, Mo, and W.
• Theoretical calculations using Bloch-wave and one-step photoemission models.

Main Results:

• Pronounced CDAD with asymmetries up to 80% observed in XPD patterns.
• Core-level CDAD is independent of atomic number and exhibits fine structure.
• CDAD shows antisymmetry with respect to crystal mirror planes, indicating Kikuchi diffraction.

Conclusions:

• Core-level CDAD is a general and sensitive probe of electronic and structural properties.
• The fine structure in CDAD provides signatures of Kikuchi diffraction.
• Integration of XPD into theoretical packages unifies photoemission and diffraction theories.