Growth manners of c-axis oriented YBa_2Cu_3O_x thin films

摘要

We have directly observed an early growth manner of c-axis oriented YBa_2Cu_3O_x films by a pulsed laser deposition technique grown on off-cut substrates. YBa_2Cu_3O_x thin films grown by ArF pulsed laser deposition on 1.7 deg off cut NdGaO_3 (110) substrates are observed by a field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM) and cross sectional view transmission electron microscope (TEM). From the FE-SEM observation, rugged step edges are clearly observed. YBa_2Cu_3O_x grows along the direction perpendicular to the c-axis of YBa_2Cu_3O_x. XRD measurements have revealed the films are c-axis preferred oriented normal to the (110)-plane of the NdGaO_3 substrates. SEM, AFM and TEM measurements show the film surface to have terraces and steps. The steps are bunched and estimated to be multi(2-5-unit-cell height)-steps. Step edges provide nucleation site for YBa_2Cu_3O_x thin films and weaken the generation of spiral growth and enhance step flow growth. This step flow growth of c-axis oriented YBa_2Cu_3O_x films may reduce grain boundaries, which increase surface resistance (R_s) for microwave devices.