The VESI (Versatile Electron Spectroscopy Instrumentation) laboratory houses three ultra-high vacuum chambers (pressure in the order of 10-10 mbar), all interconnected. The first chamber (a), dedicated to samples preparation, houses evaporators for the growth of thin films by molecular beam epitaxy (MBE), either in vacuum or in a controlled O2 atmosphere. The thickness of the films is calibrated, with the precision of the single atomic layer, through a quartz microbalance. The preparation chamber is equipped with an Ar+ ion bombardment system used for the elimination of surface contaminants, a high temperature heating stage (TMAX~2000 K) and a low energy electron diffractometer (LEED). The preparation chamber can be connected with an ancillary vacuum system (b) devoted to the growth of molecular films through organic MBE (OMBE).

The analysis chamber (c) houses a hemispherical electron analyzer (HEA) equipped with a Mott polarimeter for spin-resolved measurements. Electrons are photoemitted by X-rays, produced by a twin anode (Mg and Al) source (photon energies equal to 1253.6 eV and 1486.6 eV, respectively) and by UV photons (He discharge, with photon energies equal to 21.2 and 40.8 eV). The chamber is also equipped with a spin-resolved inverse photoemission spectroscopy system (consisting of a source of spin-polarized electrons and a bandpass photon detector. Polarized electrons are emitted from GaAs photocathodes prepared in an interconnected chamber. The sample is placed on a four-axes manipulator that can be cooled by means a cryostat down to ~30 K. Sample magnetization is achieved by applying a pulsed magnetic field (BMAX~3 kG) through a coil.

This apparatus allows to perform X-ray photoemission spectroscopy (XPS) to characterize the surface chemical composition and core levels, ultraviolet photoemission spectroscopy (UPS) for the valence electronic structure and inverse photoemission spectroscopy (IPES) for empty electronic states, all with spin resolution.

Bibliography:

• G. Berti, A. Calloni, A. Brambilla, G. Bussetti, L. Duò, and F. Ciccacci, Review of Scientific Instruments 85 (2014) 073901 (DOI: 10.1063/1.4885447)
• M. S. Jagadeesh, A. Calloni, A. Brambilla, A. Picone, A. Lodesani, L. Duò, F. Ciccacci, M. Finazzi, and G. Bussetti, Applied Physics Letters 115 (2019) 082404 (DOI: 10.1063/1.5109750)
• A. Calloni, M. Cozzi, M. S. Jagadeesh, G. Bussetti, F. Ciccacci and L. Duò, Journal of Physics: Condensed Matter 30 (2018) 015001 (DOI: 10.1088/1361-648X/aa99c3)
• A. Orbelli Biroli, A. Calloni, A. Bossi, M. S. Jagadeesh, G. Albani, L. Duò, F. Ciccacci, A. Goldoni, A. Verdini, L. Schio, L. Floreano, and G. Bussetti, Advanced Functional Materials 31 (2021) 2011008 (DOI: 10.1002/adfm.202011008)