Village: Surfaces and Interfaces
Main Research Techniques: Angle-resolved photoemission
I07: Surface and Interface Diffraction
Beamline I05 is a facility dedicated to the study of electronic structures by angle-resolved photoemission spectroscopy (ARPES). It provides an intense and highly monochromatic beam of vacuum ultraviolet radiation. Photoelectrons emitted from the sample are analysed by a high resolution angle-multiplexing electron analyser. A cryogenic sample manipulator is used to rotate the sample to cover different emission angles above the surface and thus different electron momenta. The spectrometer is housed in an ultrahigh vacuum to allow for optimum sample lifetime of the highly surface sensitive experiment. The resulting energy versus momentum maps are analysed to yield the band dispersions and Fermi surfaces and, owing to the high resolution, the spectral function of electrons near the Fermi level.
ARPES is applied to materials with exotic electronic ground states, such as unconventional superconductors (including high Tc materials), solids exhibiting charge and spin density waves, excitonic insulators and non Fermi liquids. Due to its intrinsically high surface sensitivity and accurate mapping of momentum parallel to the surface, VUV ARPES is particularly suitable for samples with layered structures and preferential cleavage planes.
The high-resolution branch
The high resolution branch (HR-ARPES) will deliver a high flux of photons in a spot size of less than 50 x 50 (h x v) μm2. The energy resolution will allow efficient data taking at 5 – 10 meV energy resolution in the core operation range of 18 – 80 eV. Higher photon energies, up to 240 eV, can be used for band mapping. The end station will be equipped with a cryogenic six-degrees-of-freedom sample manipulator covering all emission angles in the temperature range 10 K < T < 300 K, and housed in an ultrahigh vacuum of 5x10-11 mbar. Sample load-lock, storage and a versatile preparation chamber are used for efficient sample change, in-situ preparation and characterisation.
Full operation is planned for summer 2013.
The nano-focussing branch (nano-ARPES) will concentrate the radiation in a diffraction limited spot of 200 nm or smaller in the energy range 50 – 100 eV. The electron analyser is combined with a sample scanning stage for spatial maps of photoelectrons in the highly sensitive angle-resolved measurement. At selected spots ARPES data can be taken within a single micro-domain, small grain or illuminating a single artificial nano-structure. The energy resolution of 20 – 50 meV is used for efficient band mapping.
Delivery of the beam is expected in 2013; full operation of the nano-ARPES microscope is planned for 2015.