Preparation Of Bi-based Oxide Films By Molecular Beam Epitaxy And Optimization Of Its Conditions

In this paper,Bi-based oxide thin films were prepared by molecular beam epitaxy.By using a self-made ozone concentration device to concentrate ozone,a high-concentration ozone that can meet the MBE method for preparing Bi-based films was obtained.The factors affecting the ozone concentration were discussed in detail,and the source furnaces Bi,Sr,Ca,Cu metal.The element was smelted,and the relationship between the temperature T of each beam source furnace and the evaporation rate R was measured.The effects of substrate temperature and ozone partial pressure on the Bi2Sr2CaCu2O8+?(Bi-2212)thin film were analyzed in detail.To improve the epitaxial quality of the film,methods such as making different thickness transition layers between the substrate and the film.Finally,the structure,surface morphology,crystallinity,and electrical properties of Bi-based films were analyzed and studied by detection means.The results of this study are as follows:Improvement the experimental equipment and optimization the ozone concentration conditions.The result is that at a current of 2.0A,a voltage of 235V,an oxygen pressure of 0.03MPa,and an oxygen flow rate of 25L/h,ozone can be obtained for more than 90mol%after 8 hours of concentration and maintained for more than 2 hours.The smaller oxygen flow rate and shorter concentration time will prevent the silica molecules in the silica bottle from fully adsorbing the ozone molecules and the resulting ozone concentration will be reduced.The larger oxygen flow rate and longer concentration time will cause the silica molecules in the silica gel bottle to have exceeded the saturated adsorption,and the phenomenon of "washing bottle" will occur,and the saturated adsorption of ozone molecules cannot be achieved,and the resulting ozone concentration will decrease.The logarithm logR and 1000/T of the evaporation rates of Bi,Sr,Ca and Cu beam source furnaces show a good linear relationship,which is consistent with the derivation of Clausius-Clapeyron equation:logR=a/T+b.For the Bi2Sr2CaCu2O8+? film,the Bi-2212 film was epitaxially grown on a MgO(100)single crystal substrate.When the substrate temperature was 780? and the ozone partial pressure was 1.3 ×10-3 Pa,the film phase had the highest purity and crystal quality Excellent,good surface morphology.Under the same preparation conditions,the crystallinity of the Bi-2212 film grown on the SrTiO3(100)substrate is better than that of the Bi-2212 film grown on the MgO(100)substrate.A certain thickness of the transition layer can reduce the mismatch between the MgO substrate and the Bi-2212 film,reduce the stress caused by the mismatch relationship,improve the crystallinity and surface morphology of the film,and increase the superconducting transition temperature of the film.