I09: A Two-Color Beamline for Electron Spectroscopies

Schematic of the beamline layout for I09.

The beamline uses one of the four 8 m straight sections in the Diamond storage ring. To allow the hard X-ray undulator to reach a suitably small gap, additional magnets were added to create two minima in the vertical β function (βy) over the straight section. Hard X-rays are delivered by a 2 m in-vacuum undulator with a magnetic period of 27 mm and a minimum gap of 5.2 mm. Its first and third harmonics start at approximately 0.9 and 2.4 keV.

The soft X-ray undulator is a 2.3 m modified APPLE II device, with a magnetic period of 60 mm. The lowest energies accessible for the linear horizontal, circular, and linear vertical lights are about 100, 150, and 200 eV, respectively. The hard and soft undulators are canted by 1.3 mrad and each centered with one of the βy minima. 

The energy of the hard X-rays is selected by an in-house-developed Si(111) double-crystal monochromator (DCM) designed to work between 2.1 and 20+ keV. After the DCM, the beam is reflected horizontally by the first and second hard X-ray mirrors (HM1 and HM2, respectively) in optics hutch 1 (OH1). Two of the HM1 mirror optics focus the hard X-rays vertically to the end-station in EH2 for energies below and above 5 keV. HM2 has a flat mirror that keeps the exit beam of HM2 parallel to the incident beam of HM1. After entering EH2, the hard X-ray beam is focused horizontally to the sample by a third mirror, HM3. For HAXPES experiments, three Si channel-cut crystals, oriented to excite the (004), (333), and (202)/(404) reflections at 5.94, 5.95, and 4.07/8.14 keV, respectively, can be inserted in the beam in EH1 to improve the energy resolution.

The installation of a new HAXPES end-station in EH1 is underway. It is designed to be more versatile than the end-station in EH2 in accommodating HAXPES experiments with different requirements, with a planned pool of exchangeable sample manipulator feedthroughs, optimised for, e.g., high-throughput screening, in-operando HAXPES of device samples, or hard X-ray ARPES. The plan is for this new facility to welcome its first users in 2019. A third end-station, dedicated for soft X-ray ARPES, is being planned for Branch K in the Experimental Cabin. It will feature a momentum microscope being developed in collaboration with the Schöenhense group at University of Mainz and the Claessen group at University of Würzburg. These developments will allow I09 to offer improved capacity and flexibility for HAXPES studies and new opportunities for investigating momentum-resolved electronic structures.