CAT@EMIL

Ambient pressure - High Energy XPS (AP-HE-XPS)

The instrument is part of the Energy Materials in-situ laboratory EMIL, which is a unique infrastructure designed to allow for in-system, in-situ, and operando X-ray analysis of an unprecedented range of materials and devices for energy conversion and storage. The scientific aim at CAT@EMIL is to study the electronic surface/near surface structure of functional materials in the presence of a reactive environment. This includes both gas/solid interfaces (e.g. heterogeneous catalysis) and liquid/solid interfaces (e.g. catalytic water splitting).

The EMIL beamline has two branches – soft (80 eV – 2200 eV) and tender (2200 eV – 10 keV) x-rays – which converge at the CAT instrument.

Selected Applications:

• X-ray photoelectron spectroscopy (XPS) under high vacuum (p=10-10 Pa) and ambient pressure conditions (typically p=100 Pa)
• X-ray aborption spectroscopy (XAS) at pressure up to 1kPa (up to 1MPa with reaction cell) in NAP-HE-XPS endstation.

Fig. 1: Sketch demonstrating the main components of the AP-HE-XPS (left). Photo of the complete AP-HE-XPS endstation (right, courtesy of Specs GmbH, Berlin)

Methods

HAXPES, NAP-XPS, XPS, XPD, Time-resolved PES, XPD, NEXAFS, XRF, Mass Spectrometry

Remote access

not possible

Fig. 2: Photo of the main components of the reaction cell

Table. 1: Gas analytics

Obviously, the understanding of the interaction of a catalyst surface with the reactants plays a key role in a detailed description of catalytic processes. X-ray photoelectron spectroscopy (XPS) is a well-established powerful tool to study in detail the outermost surface of solids but it was traditionally restricted to high vacuum and low pressure conditions. However, recently a methodology based on a differentially pumped electrostatic lens system has gained much interest. Such an instrument is operated by the Max Planck Institute for Chemical Energy Conversion (MPI-CEC) and the Fritz-Haber-Institut der MPG (FHI-MPG) at HZB/BESSY II at the ISISS beamline in the low photon energy range. A further developed set-up is installed at CAT@EMIL. The feasibility to investigate buried layers is added by the extension of the kinetic energy range of photo-electrons to up to 7000eV (typically 5000eV). A very flexible, modular sample environment has been developed that allows to apply AP-XPS to a huge variety of problems.

A sketch of the main components of the AP-HE-XPS instrument and a photo of the complete set-up (courtesy of SPECS GmbH, Berlin) is shown as Fig. 1.

Variable pressure soft X-ray absorption (vP-XAS)

A variable pressure soft X-ray absorption cell has been constructed by FHI that works in the conversion electron yield detection and total fluorescence yield mode. This reaction cell allows to measure surface sensitive X-ray absorption spectra in a pressure range between 10² - 10⁵ Pa, i.e. up to atmospheric pressure at temperatures up to 400ºC. This low volume reaction cell makes it feasible to study heterogeneous catalytic reactions in a broad pressure range and hence allows to link results obtained with AP-XPS and measurments obtained in a catalytic reactor.

A photo of the main components of the reaction cell is shown in Fig. 2.