Lecture - Surface Science Lab Station - T. Gouder, JRC Karlsruhe

Surface Science Lab Station - lecture

The Surface Science Lab Station integrates surface preparation, analysis and treatment techniques in one single, well controlled environment. It allows carrying out complex surface science studies in-situ and with minimal technical efforts. It was originally designed for corrosion studies on light actinides (U and Th), focussing on

• Single surface-gas interactions, by studying gas adsorption under UHV. While being different from real world corrosion conditions, the reaction parameters can be closely controlled (gas dosage, mixing, temperature…).
• Performing plasma reactions thus reaching high reaction stages (e.g. high oxides) and simulating the effects of heavy corrosion conditions.

We developed a small target sputter deposition source to prepare thin films from minute amounts of starting materials. Co-deposition of several elements, reactive sputtering, post-sputtering treatment (e.g. by plasma), combined sputtering-evaporation etc. are powerful tools for preparing a wide range of surface systems.

Special emphasis is given to the combination of spectroscopy techniques (XPS, UPS, BIS, LEED, TPD, ELS, HREELS, Kelvin probe). The system has a modular setup, where the various techniques are mounted in individual chambers, which can be connected to the station. Separation into independent devices allows maintenance and modifications of the individual chambers while continuing operation of the rest of the system.

The machine was originally acquired for work on light actinide systems (study of corrosion, electronic structure, surface physics) and used for in-situ spectroscopy studies and for preparing thin film samples (e.g. alloys, hydrides) for external studies. Later on, we extended work to non-actinide systems (rare earths and transition metals). We opened the laboratory to external users, profiting from the flexible design to carry of their different experiments.

As an example, we will report on the study of surface oxidation and reduction of uranium by oxygen, hydrogen and water, present either as molecular gases or as atomic gases (generated by ECR plasma). Films are analysed in-situ by X-ray and Ultra-Violet Photoelectron Spectroscopy. Pure U oxidation states of +4,+5 and +6 are observed and they correspond to U5f², U5f¹ and U5f⁰ configuration respectively. The gradual oxidation of U under corrosive conditions can thus be followed in detail.