Growth And Interface Engineering Of High-quality Ultrathin YBCO Films

YBa2Cu3O7-?(YBCO),as the first discovered superconductor whose critical temperature is higher than the temperature of liquid nitrogen,has received much attention since its discovery.High quality ultrathin YBCO films are of great significance for studing the mechanism of high-temperature superconductivity and developing YBCO-based electric-field-effect superconductor transistors.However,up to now,ultrathin YBCO films that can satisfy electric-field-effect superconductor transistors still require further research.In view of this situation,this paper mainly focuses on how to grow high quality YBCO thin films on SrTi03 substrates and how to improve the superconductivity properties by interface/surface modulation.1.Exploring the use of pulsed laser deposition technology to grow high quality ultrathin YBCO films.By systematically studying the effect of growth temperature,oxidizing atmosphere,post-annealing and other conditions on the YBCO films,we found that high-quality YBCO films can be grown under the mixed gases of oxygen and nitrous oxide.The ultrathin YBCO films obtained under this condition have a flat surface with a roughness within one nanometer.2.The interface/surface modulation of ultrathin YBCO films was investigated.Firstly,we studied the influence of different terminations of the SrTiO3 substrates and found that the different terminations of substrates did not change the properties of YBCO films.Secondly,we studied the properties of YBCO film with different capping materials.These capping materials are La2CuO4,La1.56Sr0.44CuO4,La1.85Sr0.15CuO4,LaMnO3,La0.67Ca0.33MnO3,LaAlO3,SrTiO3 and PrBa2Cu3O7-?(PBCO).It is found that all capping layers have a positive influence on YBCO films,which makes the superconducting performance of YBCO film better.YBCO films with PBCO capping layer has the best performance and YBCO films with La0.67Ca0.33MnO3 capping layer has the worst performance.These results laid good foundation for the development of YBCO-based electric-field-effect superconductor transistors.