Angle resolved photoelectron spectroscopy (ARPES) is the overarching name of several photoelectron spectroscopies where the electron’s energies and emission angles relative to the sample surface are measured. With these quantities, it is possible to get information about the electronic band structure of the examined samples, because the emission angle bears a direct connection to the momenta of the electrons prior to photoexcitation. Modern, sophisticated ARPES setups are also equipped with spin detectors.
In nanoARPES measurements, the photons are focused on the nanometer scale so that spectra exclusively emerging from microscopic objects can be recorded. In case of soft X-rays, zone plates are used for photon focusing down to ~100 nm spot dimensions. When the photon spot is scanned across the surface, photoelectron maps of the sample can be created.