Hybrid Photoelectron Momentum Microscope at the Soft X-ray Beamline I09 of the Diamond Light Source

TL;DR

This paper introduces a new soft X-ray momentum microscopy endstation at Diamond Light Source, enabling high-resolution 4D mapping of photoelectron distributions in crystalline solids with applications in band mapping and dichroism measurements.

Contribution

The paper presents a novel endstation combining a hemispherical spectrometer and TOF analyzer for comprehensive momentum-resolved photoelectron studies at the Diamond Light Source.

Findings

Achieved energy resolution of 10.2 meV (FWHM)

K-space field of view exceeds 6 Å^-1

Demonstrated applications in band mapping and dichroism

Abstract

Soft X-ray momentum microscopy of crystalline solids is a highly efficient approach to map the photoelectron distribution in four-dimensional (E,k) parameter space over the entire Brillouin zone. The fixed sample geometry eliminates any modulation of the matrix element otherwise caused by changing the angle of incidence. We present a new endstation at the soft X-ray branch of beamline I09 at the Diamond Light Source, UK. The key component is a large single hemispherical spectrometer combined with a time-of-flight analyzer behind the exit slit. The photon energy ranges from hv = 105 eV to 2 keV, with circular polarization available for hv > 150 eV, allowing for circular dichroism measurements in angle-resolved photoemission (CD-ARPES). A focused and monochromatized He lamp is used for offline measurements. Under k-imaging conditions, energy and momentum resolution are 10.2 meV (FWHM) and 0.010 angstroms^-1 (base resolution 4.2 meV with smallest slits and a pass energy of 8 eV). The large angular filling of the entrance lens and hemisphere (225 mm path radius) allows k-field-of-view diameters > 6 angstroms^-1. Energy filtered X-PEEM mode using synchrotron radiation revealed a resolution of 300 nm. As examples we show 2D band mapping of bilayer graphene, 3D mapping of the Fermi surface of Cu, CD-ARPES for intercalated indenene layers and the sp valence bands of Cu and Au, and full-field photoelectron diffraction patterns of Ge.