Laser irradiation effects in YBa 2Cu 3O 7−δ thin films on metallic and single crystal substrates: a micro-Raman study

Abstract

In-depth micro-Raman study of YBa 2Cu 3O 7−δ thin films deposited on metallic substrates (hastelloy-C, inconel-600 and stainless steel-304) with a TiN buffer layer (YBCOM) and single crystal LaAlO 3 (YBCOL) substrate has been carried out in order to investigate the relative phenomenological differences between the behavior of these films on different substrates. A comparative study of films on these substrates revealed that the bandwidths of the prominent oxygen vibrations in YBCOM are significantly larger than those in the case of YBCOL and a defect induced, strong and broad feature around 570 cm −1 is always present in the Raman spectra of YBCOM. The broadening of bands and the presence of the 570 cm −1 band have been attributed to the disorder induced by buffer layer in YBCOM. Variation of the incident laser power ( P L) from 1 to 10 mW, or a continuous irradiation were found to induce unusual, irreversible but, dissimilar changes in the Raman spectra of YBCOM and YBCOL. A significant change in the intensity distribution of oxygen vibrations and a decrease in the bandwidth of the out-of-phase mode in YBCOM films have been attributed to an improvement in the crystallinity of YBCOM films due to oxygen ordering in the CuO 2 planes. Whereas, in YBCOL, the laser irradiation causes oxygen removal from the CuO chains and formation of impurity phase BaCuO 2. Distinct laser induced changes in the Raman spectra of YBCOM and YBCOL have been explained in terms of photoinduced ordering and local heating effects respectively.