We present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures of multiple bars. The instrument builds around the novel concept of a "virtual cell" in which a gas flow onto the sample surface creates a localized high-pressure pillow. This allows the instrument to be operated with a low pressure of a few millibar in the main chamber, while simultaneously a local pressure exceeding 1 bar can be supplied at the sample surface. Synchrotron based hard x-ray excitation is used to increase the electron mean free path in the gas region between sample and analyzer while grazing incidence <5 ○ close to total external refection conditions enhances surface sensitivity. The aperture separating the high-pressure region from the differential pumping of the electron spectrometer consists of multiple, evenly spaced, micrometer sized holes matching the footprint of the x-ray beam on the sample. The resulting signal is highly dependent on the sample-to-aperture distance because photoemitted electrons are subject to strong scattering in the gas phase. Therefore, high precision control of the sample-to-aperture distance is crucial. A fully integrated manipulator allows for sample movement with step sizes of 10 nm between 0 and −5 mm with very low vibrational amplitude and also for sample heating up to 500 ○ C under reaction conditions. We demonstrate the performance of this novel instrument with bulk 2p spectra of a copper single crystal at He pressures of up to 2.5 bars and C1s spectra measured in gas mixtures of CO + H 2 at pressures of up to 790 mbar. The capability to detect emitted photoelectrons at several bars opens the prospect for studies of catalytic reactions under industrially relevant operando conditions.Published under license by AIP Publishing. https://doi. ARTICLEscitation.org/journal/rsi FIG. 13. Mass spectrometry signal of m/z corresponding to CO (red), O 2 (blue), and CO 2 (black) and left axis. The single crystal temperature (dashed black and right axis) was ramped at a rate of 2.5 ○ C/s.

A new undulator beamline (P22) for hard X-ray photoelectron spectroscopy (HAXPES) was built at PETRA III (DESY, Hamburg) to meet the increasing demand for HAXPES-based techniques. It provides four special instruments for high-resolution studies of the electronic and chemical structure of functional nano-materials and catalytic interfaces, with a focus on measurements under operando and/or ambient conditions: (i) a versatile solid-state spectroscopy setup with optional wide-angle lens and in-situ electrical characterization, (ii) a HAXPEEM instrument for sub-µm spectro-microscopy applications, (iii) an ambient pressure system (> 1 bar) for operando studies of catalytic reactions and (iv) a time-of-flight spectrometer as a full-field k-microscope for measurements of the 4D spectral function ρ(E B ,k). The X-ray optics were designed to deliver high brightness photon flux within the HAXPES energy range 2.4-15 keV. An LN 2-cooled double-crystal monochromator with interchangeable pairs of Si(111) and (311) crystals is optionally combined with a double channel-cut post-monochromator to generate X-rays with variable energy bandpass adapted to the needs of the experiment. Additionally, the beam polarization can be varied using a diamond phase plate integrated into the beamline. Adaptive beam focusing is realized by Be compound refractive lenses and/or horizontally deflecting mirrors down to a spot size of ~20x17 µm 2 with a flux of up to 1.1x10 13 ph/s (for Si(111) at 6 keV).

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For beam collimation and focusing at the new PETRA III undulator beamlines, UHV compatible 1D and 2D compound refractive lens changers have been designed. Since these units are going to be integrated in the upstream part of the beamlines in the optics hutches, the primary design goal was to ensure reliability, failsafe operation and convenient optical alignment combined with high mechanical precision. It was chosen to further develop established concepts and combine it with actuators on the air side rather than active in-vacuum actuators. Precise and reproducible alignment is achieved by pneumatic linear motion actuators that position the lens stacks in a high precision prism. Alignment is facilitated by on-axis pinholes and an integrated diamond beam monitor. Reproducibility and first tests of a 1D lens changer at beamline P22 for intermediate focusing down to <90 µm are shown.