APPES at ALS
Ambient pressure photoemission spectroscopy (APPES) with synchrotron light at Advanced Light Source (ALS)
1st Generation Instrument (Currently used at the ALS beamline 9.3.2.): M. Salmeron, D. F. Ogletree, H. Bluhm, F.G. Requejo 2nd Generation Instrument (Currently at ALS beamline 11.0.2 and BESSY beamline U49/2-PGM1) |
Why ambient pressure photoemission spectroscopy?
The use of the original for UHV restricted surface sensitive technique -Study of surface chemistry under thermodynamic equilibrium with various gases (including water vapor!) -Study of catalytic reactions in realistic conditions of pressure and temperature -Study of free liquids -Study of biological surfaces in humid environments Problem that have to be solved for HPPES: -Electrons are scattered by gas molecules -Analyzer needs UHV -X-ray source needs UHV |
Solutions: -Modification of electrostatic lens system of analyzer to implement 3 differential pumping sections (Pressure drop between hemisphere and high pressure chamber around 10E8) -Light from X-ray source passes window for protection of source (e.g. Al e.g. Al, Si, Be) |
The Endstation System at the ALS / LBNL: The endstation consists of two UHV-chambers for sample preparation/characterization and the actual high pressure measurements. *Preparation Chamber: *High Pressure Chamber: *Sample holder and Transfer system: |
Sample – Beam – Analyzer – Geometry: Beam – sample geometry for solids or liquids: |
Analyzer angles: Angle in xy-plane: 45º, Elevation angle: 35º = (111) direction |
Analyzer modifications: Commercial Phoibos 150 Analyzer from Specs: 2/3 of lens section replaced |
High Pressure Photoemission Spectroscopy (HPPES) at ALS |
High Pressure Photoemission Spectroscopy at ALS |
Guido |
Water droplet at the sample stage |