Low energy electron beam processing of YBCO thin films

Effects of low energy 30 keV electron irradiation of superconducting YBa ₂ Cu ₃ O _7−δ thin films have been investigated by means of transport and micro-Raman spectroscopy measurements. The critical temperature and the critical current of 200 nm thick films initially increase with increasing fluency of the electron irradiation, reach the maximum at fluency 3 − 4 × 10 ²⁰ electrons/cm ² , and then decrease with further fluency increase. In much thinner films (75 nm), the critical temperature increases while the critical current decreases after low energy electron irradiation with fluencies below 10 ²⁰ electrons/cm ² . The Raman investigations suggest that critical temperature increase in irradiated films is due to healing of broken Cu[sbnd]O chains that results in increased carrier's concentration in superconducting CuO ₂ planes. Changes in the critical current are controlled by changes in the density of oxygen vacancies acting as effective pinning centers for flux vortices. The effects of low energy electron irradiation of YBCO turned out to result from a subtle balance of many processes involving oxygen removal, both by thermal activation and kick-off processes, and ordering of chains environment by incident electrons.