Study of excimer laser irradiation effects on properties of crystalline YBaCuO thin films

The influence of UV laser irradiation on the physical properties of epitaxial YBa₂Cu₃O_7-δ thin (< 1 μm) films fabricated by laser ablation was studied. The samples were irradiated by pulsed excimer laser beam at different incident energy densities E_ir ≤ 130 mJ/cm², i.e. 2-3 times below the ablation threshold of YBaCuO. The analysis of the sample cross-section using transmission electron microscope shows that such irradiation forms a disordered layer on the top of the crystalline film. Sample surface amorphization was observed also by atomic force microscope. Due to strong UV irradiation absorption in YBaCuO this surface layer acts like a protective cover for the sample interior. Only a small reduction of superconducting critical temperature T_c was observed. Both transport measurements in normal state and magneto-optical studies in superconducting state indicate that between the disordered layer and the bottom non-modified part of the film there exists a wide transitional region with reduced carrier concentration.