High quality epitaxial thin films of high
TC superconducting (HTSC) cuprates are grown in situ from stoichiometric targets
using a home-made on-axis plasma sputtering setup. This installation enables
making films of all types of HTSC layered cuprates (including YBa2Cu3Oy
Instantly, it is used to grow La2-xSrxCuO4
thin films with various Sr concentration covering both under- and overdoped
regimes. DC oxygen plasma is mostly used for sputtering, however RF power
source and Ar active gas are also available.
The target is placed on a plasma gun cathode to which positively charged oxygen molecules, after ionization by colliding electrons, are accelerated. Positive ions hit the target and knock off neutral atoms from its surface. These atoms are deposited on a heated substrate situated in front of the target. The planar plasma gun design was optimized to handle relatively high reactive gas pressures (~2 hPa) resulting in a deposition rate of approximately 1.4 nm/min and very smooth surface morphology of the films with a maximum roughness of about 30-40 Å as demonstrated by AFM measurements. The substrate heater was made of kanthal alloy wire, which tolerates heating up to 840 oC in 1 atm O2 to fill remaining oxygen vacancies in the LSCO lattice in-situ. The main growth parameters such as the substrate type and temperature, reactive gas pressure and flow, sputtering and annealing duration, target-film distance, discharge power, etc. can be tuned to make high quality epitaxial films.