X-Ray Photoelectron Spectroscopy (XPS)

Andrey Shchukarev and AXIS Ultra DLD electron spectrometer

ImageMattias Pettersson

The X-ray photoelectron spectroscopy (XPS) platform is an open infrastructure at UMU enabling users both within UMU and outside to obtain analyses of the chemical composition of their sample surface. Knowledge of the elemental composition, oxidation state and spatial distribution of atoms at surfaces, near-surfaces, and interfaces is crucial to our understanding of key reactions in nature and technology. Surfaces are, after all, the immediate interface through which materials - as small as metal nanoparticles and bacteria, to as big as nuclear fuel reactors and spaceships - interact with their environments. XPS, also known as Electron Spectroscopy for Chemical Analysis (ESCA), is now one of the most widely used tools in countless fields of science and engineering where an advanced understanding of surfaces and interfaces is needed.

Starting from 2024, XPS Platform provides new surface analysis techniques: Ultraviolet Photoelectron Spectroscopy (UPS) to investigate valence band and Low Energy Inverse Photoemission Spectroscopy (LEIPS) to define the energy of LUMO (Lowest Unoccupied Molecular Orbital). Both UPS and LEIPS will allow direct experimental determination of band gap and provide electronic structure measurements. Moreover, LEIPS experiments are first routinely available in Sweden.

All experiments are performed with the AXIS Ultra DLD electron spectrometer and the new AXIS SUPRA⁺ spectrometer installed in November 2023, both manufactured by KRATOS Analytical Ltd. (UK).

The main fields of application at our XPS Platform facility are currently:

• Environmental samples, in particular, the composition of mineral-aqueous solution interface
• Biological specimens such as intact bacterial cells, algae, fungi, viruses, etc.
• Control of surface modification of materials for catalysis and sorption
• Energy storage materials
• Antibacterial and medical applications
• Cellulose-based materials
• Materials for organic microelectronics
• Commercial analysis for the external customers (industry, consulting agencies, etc.)

The platform supports a unique field of research, developed at the Department of Chemistry, involving investigations of fast-frozen samples, including mineral-aqueous solution interfaces, interfaces of biomaterials with biologically relevant media, and surface chemistry of microorganisms. The platform also supports a large range of research projects by providing state-of-the-art surface analysis in areas including ecology, chemistry, physics, archaeology, molecular biology, dentistry and engineering.

User fees are based on hourly pay. As almost all samples are unique in their surface composition, users are requested to contact the XPS Platform manager/staff to discuss their analytical requests and time schedule. For each new user, measurements of the first sample are free of charge. During each calendar year, a 10% discount is applied after 10 hours of measurements, 20% after 20 hours, and 30% after 50 hours. Users typically receive results within 1-3 days. PhD students, Postdocs, and industry have a priority using XPS Platform facility.

The UMU XPS platform is the only facility for XPS analyses in Northern Sweden (north of Uppsala). Furthermore, XPS Platform represents the only facility in Sweden, and was the first in the world to provide cryogenic XPS analyses routinely. The Platform has established relations with other XPS facilities in Sweden (e.g., KTH, Chalmers, Linköping University) and plans to consolidate the national XPS network, create a shared vision enabling a future national infrastructure (“Swedish National Platform for X-ray Photoelectron Spectroscopy [SNAxPS]”), where Umeå is one node specializing in cryo-XPS and LEIPS.