Fig. 1

Stack without and with nanoporous platinum. (a, b): Schematic representation of the stack without (a) and with nanoporous platinum film (graded index Pt layer and constant index Pt layer) (b). (c), (d): Top view SEM of the stack without nanoporous platinum: Si/NiCr/Ti (c) and with nanoporous platinum: Si/NiCr/Ti/Pt constant index/Pt graded index (d); (e)-(f): Lateral view SEM of the stack without (e) and with (f) nanoporous platinum (graded and constant index Pt layer): Si/NiCr/Ti/Pt constant index/Pt graded index. Using spectral ellipsometry the graded index Pt layer is analysed as a graded effective medium consisting of nanocrystalline platinum and void (air). The constant index Pt layer is compact and also consists of nanocrystalline platinum. The graded index Pt layer has a large negative real part of dielectric constant ε1 and a large imaginary part of dielectric constant ε₂. The nanoporous platinum layer causes the strong absorption of light due to the large ε₂ of the graded index layer. Scale bar 100 nm.