Formation of YBa₂Cu₃O_{6 + x} clusters in laser-generated plasma

Abstract

We have studied the influence of YBa₂Cu₃O_{6 + x} clusters formed in the plasma generated by laser ablation of a YBa₂Cu₃O_{7 − δ} target on the optical transmission spectra of amorphous YBaCuO films deposited on glass substrates arranged along the direction of predominant plasma expansion in the laser plume. It is established that intense cluster formation begins in the region of rapid decrease in the film thickness, where the temperature of plasma decreases to a level at which stable atomic complexes characteristic of the target composition can form (under the experimental conditions studied, this was observed at as distance of L > 6 cm from the target). As the amount of clusters in the deposit increases, the magnitude of the interference fringes, which are characteristic of optically homogeneous media, gradually decreases and eventually almost vanishes. At the same time, features typical of the electron structure of YBa₂Cu₃O_{7 − δ} appear and grow in the optical transmission spectra of the YBaCuO films, including the absorption due to free charge carriers at ℏω < 1.2 eV (characteristic of “metallic” clusters) and the minima at ℏω = 1.4 and 1.75 eV (characteristic of a dielectric state).