Controllable factors affecting the epitaxial quality of LaCoO$_3$ films grown by polymer-assisted deposition

摘要

LaCoO$_3$ epitaxial films grown on (100) SrTiO$_3$ substrates were prepared by the simple polymer-assisted deposition successfully. Based on the characteristics by X-ray diffractometer, infrared spectroscopy and thermal analyzer, the influence of molecular weight of polyethyleneimine, heat-treatment condition, spin-coating speed on the crystallinity and epitaxial quality of LaCoO$_3$ films were discussed. It is found that the number of a??NH groups plays a key role in the cationchelation of polyethyleneimine. Comparatively, more a??NH groups existing in polyethyleneimine with larger molecular weight contribute to the improvement of epitaxial quality of LaCoO$_3$ epitaxial film. When polyethyleneimine begins to release the bound metal ions, higher heat-treatment temperature and a relatively rapid rate of heating can effectively preventnucleus from growing in other orientations, thereby improving the epitaxial quality of film. Besides, the choice of spin speed will directly affect the thickness and surface roughness of the film, and may even affect the structure and performance of the film. The results will help to understand the cation-chelation mechanism of polyethyleneimine in the polymer-assisted deposition and extend this simple method for preparation of epitaxial films.