DetailARPES, UPS
Photoelectron spectroscopy (PES) is one of the most powerful and most frequently used spectroscopic techniques in solid state physics, physical chemistry and materials science. Using the photoelectric effect, PES provides a material sensitive and non-destructive probe for modern scientists to examine the chemical composition (XPS or ESCA ) and the electronic structure (UPS and ARPES) of matter. By illuminating a sample with light of a certain photon energy (hν), electrons are released from a solid, using the photon energy to overcome their binding energy (Eb) and work function (Φ). The remaining energy provided by the photons is transferred into the kinetic energy (Ekin) of the photoelectrons. Such a transition can only occur from occupied electronic states of an energy Ei into unoccupied states of energy Ef, when the energy is conserved.
On the other hand, also the wave vector (or momentum) k ( kx, ky, kz) has to be conserved. The surface breaks the geometry, not affecting the energy conservations rule, but affecting the momentum conservation such, that the parallel wave component kӀӀ is conserved after crossing the surface, but the component along the surface normal (k┴) is not conserved. Finally the electrons can be analyzed in an electron analyzer with respect to their Ekin (or recalculated to Eb) and to Θ (or recalculated to the parallel wave vector component (kӀӀ). On this basis, a 2D distribution of the electrons (number of electrons for given Eb and kӀӀ is measured, directly reflecting the electronic (or band) structure of the material.
Such experiments in laboratory environments equire intense, small spot UV light sources of high stability for optimum performance. The intensity of the light source is the key point for fast and efficient measurements, while small spot sizes ensure measurements with highest angle (or momentum) resolution. SPECS offers a series of UV sources fitted to various demands, starting from flexible and robust UV sources for economic application to highly sophisticated UV sources for different gases and photon energies with monochromators for highest performance and energy resolution.
