The proposed thesis relates to the growth and characterization of thin and ultra-thin films characterized by a spin-polarized electronic structure. In particular, we will consider materials belonging to the following two classes: (i) magnetic materials, and in particular transition metals such as Fe, Co and Ni; (ii) heavy metals, such as Pt, Au, Pb and Bi, where electronic states are present with a net spin polarization due to spin-orbit effects.
The scientific background is that of spintronics, which traditionally exploits magnetic materials for information storage and the creation of spin polarized currents. However, novel microelectronic devices have been proposed in which spin current generation and manipulation can be controlled also electrically, i.e. without the use of magnetic materials, as in the case (ii) discussed above. The proposed research work will focus on the study of metastable thin films, i.e. with a crystallographic structure different from that of the corresponding bulk material. The purpose will be to highlight the role of low-dimensionality (confinement effects, magnetic anisotropies), the interaction with the substrate (charge transfer, inter-diffusion) and surface effects (the presence of surface states, changes related to the exposure to gases or alkaline metal vapors). Applicants are strongly suggested to read the enclosed bibliography, which presents two studies carried out by the proponents of this activity in recent years.
The thesis activity will involve: (i) the optimization of the growth of the above materials in a controlled environment (ultra-high vacuum conditions, low growth rates) in order to favor the formation of well-ordered and homogeneous films; (ii) the study of the crystallographic structure and morphology while tuning the growth parameters and the thickness of the films by means of electron diffraction techniques; (iii) the study of the electronic structure through spectroscopy techniques. In particular, the valence band structure will be mapped by means of UV photoemission and inverse photoemission spectroscopies, both with spin resolution. The necessary tools to complete the thesis work are present at the surface physics lab "VESI" of the physics department. Familiarity with the basics of surface physics (provided by the master's degree courses in physical engineering - nanotechnologies and physical technologies branch) is desirable. The thesis requires a full-time activity in the lab (Monday to Friday) and will last for a minimum of six months.
 
Bibliography:

• A. Calloni, M. Cozzi, M. S. Jagadeesh, G. Bussetti, F. Ciccacci and L. Duò “Magnetic behavior of metastable Fe films grown on Ir(111)” J. Phys.: Condens. Matter 30 (2018) 015001 (DOI: 10.1088/1361-648X/aa99c3)
• F Bottegoni, A Calloni, G Bussetti, A Camera, C Zucchetti, M Finazzi, L Duò and F Ciccacci “Spin polarized surface resonance bands in single layer Bi on Ge(111)” J. Phys.: Condens. Matter 28 (2016) 195001 (DOI: 10.1088/0953-8984/28/19/195001)
• F. Goto, A. Calloni, G. Albani, A. Picone, A. Brambilla, C. Zucchetti, F. Bottegoni, M. Finazzi, L. Duò, F. Ciccacci, and G. Bussetti, “Mapping the evolution of Bi/Ge(111) empty states: From the wetting layer to pseudo-cubic islands” J. Appl. Phys. 129 (2021) 155310 (DOI: 10.1063/5.0048275)