Infrared optical properties of chromium nanoscale films with a phase transition

Thickness-dependent infrared spectra measured during growth of Cr on diamond C(100) under ultrahigh vacuum conditions reveal a structural phase transition from a discontinuous phase to the crystalline bulk one with Drude-type optical properties. The thickness of 2.5 nm of the observed phase transition well agrees with literature data on the theoretically predicted maximum size for stable fcc nanoclusters the formation of which should be supported on C(100) owing to a good lattice match. Below 2.5 nm, the spectral behavior surprisingly well corresponds to a Drude-Smith type dielectric function, which allows one to determine the conductivity for the discontinuous phase and to get quantitative information on the effect of coherent backscattering.