Determination of the optical constants of amorphous carbon in the EUV spectral region 40-450 eV

The extreme ultraviolet (EUV) optical constants δ ( ω ) and β ( ω ) of amorphous carbon were determined on the basis of transmission measurements at hω =18-450 eV, the first-principles calculation of the dielectric tensor at hω <25 eV, and the Kramers-Kronig calculation of δ ( ω ). Our optical constants generally agree with the CXRO data, excluding the vicinity of the K-edge. First-principles analysis shows that two thresholds of absorption (at 284 eV and 291 eV) found in the present study are caused, respectively, by the π - and σ - bonds. Their weights are controlled by an orientation of graphene sheets in a-carbon.