Optical constants in the EUV Soft x-ray (5 ÷152 nm) spectral range of B4C thin films deposited by different deposition techniques

B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet region (EUV 160-30 nm). This material is also used in multilayer for soft X-ray applications, such as Si/B4C or W/B4C, or as interlayer in Mo/Si multilayer to avoid interdiffusion also because of its high thermal stability. Our work concerns on B4C thin films deposited on Si [100] substrates by means of three different deposition techniques: RF plasma magnetron sputtering, e-beam evaporation, pulsed laser ablation (PLD). We performed reflectance vs incidence angle measurements from 5 nm to 152 nm on different samples deriving the optical constants with a least-square fitting method. Complete films characterization have been carried out with compositional (XPS), structural (XRD) and morphological (AFM, SEM) analyses.