A synchrotron is a particle accelerator in which electrons travel in a closed loop, within the so called storage ring. A synchronous electric field accelerates the electrons to nearly the speed of light, while magnetic fields are applied to bend the trajectory to a desired shape. At the bending points, the electrons emit part of their energy in the form of intense, directional, and polarized light of a broad energy spectrum, from infrared to hard X-rays. The generated light (called the synchrotron radiation) can then be monochromatized and used as a primary beam for various photon-involving analytical methods (microscopies, spectroscopies, and diffractions). The radiation path and the apparatus utilizing the radiation are called a beamline.
The Materials Science Beamline (MSB) is a spectroscopy-dedicated beamline operated by the Charles University at the Elettra synchrotron in Trieste, Italy, since 2001. The beamline is versatile, suitable for experiments in materials science and surface physics, with catalysts or organic molecules on various surfaces (provided they are compatible with the ultra-high vacuum). The tuning range of the photon energy is 22–1000 eV, and the light is mainly linearly polarized. The photon beam can be used for "classical" ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS), which probe occupied energy states in the surface of a material. Compared to conventional UV and X-ray sources, monochromatized synchrotron radiation provides a higher energy resolution and through the tunability allows to reach the optimal photoionization cross section and to regulate the level of surface sensitivity. Moreover, fine tuning of the photon energy makes more advanced spectroscopies possible: the resonant photoemission (ResPES) for fine analysis of valence states, the X-ray absorption (XAS) for studying unoccupied energy states, and the near-edge X-ray absorption fine structure (NEXAFS) for revealing the orientation of adsorbed organic molecules in self-assembled layers.
The main instrument at the experimental chamber is the hemispherical energy analyzer (SPECS Phoibos 150), inclined 60° from the beamline axis. Samples are mounted in a holder on a manipulator with x, y, and z linear axes and with the azimuthal and polar rotations. The manipulator also allows heating and cooling of the sample, together with Ar+ sputtering, and has gas lines with precision leak valves and a set of evaporators, thus allowing preparation of well-defined surfaces of various materials in situ.
The chamber is pumped by a combination of a turbomolecular pump and a Ti sublimation pump. The residual atmosphere, as well as gases desorbed from the sample, can be measured by a quadrupole mass spectrometer. The base pressure in the main chamber is in the low 10-10 mbar range.