Raman scattering in pure and carbon-doped Mg B2 films

We have studied Raman scattering in Mg B2 thin films grown by hybrid physical-chemical vapor deposition on SiC and Al2 O3 substrates. The Cooper-pair-breaking peak corresponding to the larger gap was observed and its position correlates with the value of Tc, which varies with film strain. The temperature dependence of the E2g phonon frequency and linewidth was studied. Carbon doping of Mg B2 films suppresses Tc, and leads to a hardening of the E2g phonon mode, an increased luminescence background in the spectra, and a stronger contribution of disorder-activated phonons to Raman spectra.