Preparation And Physical Properties Of Freestanding SrRuO₃ Films

Transition Metal Oxide(TMO)has attracted more and more attention because of its rich phase structure and novel physical properties.TMO epitaxial films with perovskite structure are restricted by single crystal substrate,which to some extent restricts their wider application.It is expected that the freestanding form of the film will not only obtain richer performance,but also expand the application of the film.In particular,the freestanding single crystal oxide films have shown a wide range of applications in flexible electronic devices and integration with traditional silicon semiconductor devices due to their two-dimensional flexibility and flexible transferability,paving the way for a new generation of multifunctional electronic devices.In this study,ferromagnetic metal Sr Ru O₃(SRO)was used as the research object,and Sr₃Al₂O₆(SAO)sacrificial layer was used to prepare SRO freestanding thin films.In this paper,we systematically studied the effects of the SAO sacrificial layer on the microstructure and physical properties of the top layer SRO films,and studied the changes of the structure and physical properties of the SRO freestanding films after the epitaxial stress release.The main contents and results of the study are as follows:1.Using a pulsed laser deposition technique,a water-soluble SAO film with a perovskite-like structure was deposited on the(001)-oriented Sr Ti O₃(STO)substrate as a buffer layer.Through the analysis of the surface morphology and epitaxial characteristics of SAO thin films prepared under different conditions,we determined the best deposition conditions of SAO thin films:deposition temperature of 800?,oxygen partial pressure of 0.1Pa.It was found that the extracellular cell constant of SAO thin films increased gradually with the increase of oxygen partial pressure,but it was impossible to grow good crystalline SAO thin films at high oxygen pressure(>3Pa).However,the deposition temperature and thickness have little effect on the microstructure of SAO films.These results provide an important experimental basis for the epitaxial growth of the top layer of SRO films.2.The SRO films were grown on the SAO buffer layer and the phase diagram of SRO on SAO had been constructed.According to the X-ray diffraction results,it is found that adjusting the thickness of the SAO buffer layer can achieve the transformation of the top SRO from compression strain to relaxation strain,and then to tensile strain state.After the insertion of 2-5 nm thick SAO,the compressed strain of SRO films changed into a relaxed state,and the Curie temperature of SRO films increased from?120 K to?150 K,which was close to the Curie temperature of bulk(160K).As the thickness of the SAO layer increases to more than 10 nm,the SRO films show tensile strain.The results show that the SRO films subjected to tensile stress exhibit typical stepped surface morphology and strain epitaxy.By fitting the transport characteristics,it is found that at low temperature(<30 K),the tensile strain SRO films exhibit obvious metal-insulator phase transition and positive magnetoresistance,with the disappearance of non-Fermi-liquid transport.The magnetic anisotropy of SRO films under tensile and compressive strain is obvious,while the magnetic properties of the films in relaxation state are isotropic.3.By means of deionized water etching of SAO,we prepared SRO freestanding films and successfully transferred them to silicon substrates or conventional flexible substrates.It is found that the lattice constant of the transferred film is close to that of the bulk material,indicating that the tensile stress from the SAO buffer layer is released.The transport test results show that the freestanding films have lower room temperature resistivity and maintain good ferromagnetic metal properties,and the Curie temperature rises to more than 150 K.These results provide important experimental basis for the preparation and physical properties of perovskite TMO freestanding films,and have important significance for the applications of TMO films in traditional silicon semiconductors and flexible electronic devices.