Measurement Of Young's Modulus Of Free-standing SrRuO₃ & SrTiO₃ Single Crystal Films By Buckling Method

The free-standing film preparation technology refers to the technology of peeling off the epitaxial film by chemical etching or physical etching.This technology has strongly promoted the development of metal oxide single crystal films.The prepared free-standing metal oxide single crystal films can be freely transferred to different substrates while maintaining stable performance.Therefore,they are well compatible with silicon-based semiconductor technology,or be applied to flexible devices.Young's modulus is an important material parameter and it is also a basic physical quantity required to study the strain regulated of the physical properties of free-standing metal oxide films.However,the traditional macroscopic testing method of Young's modulus is difficult to apply free-standing single crystal thin films,while the microscopic Young's modulus testing method generally has problems such as complicated operation and time-consuming testing.The buckling method is a simple and effective method for measuring Young's modulus,which has been widely used in the measurement of polymers and metal films in the past.In this study,the Young's modulus of free-standing Sr Ru O₃ and Sr Ti O₃ single crystal films was measured by introducing the buckling method and combined with wet etching.The main research contents and results of this article are as follows.(1)Free-standing Sr Ru O₃ and Sr Ti O₃ single crystal films were prepared by combining pulsed laser deposition and wet etching.An experimental method for measuring Young's modulus of free-standing single crystal thin films was constructed by buckling method,and some key conditions such as etching time and pre-strain range were determined.(2)The Young's modulus of the free-standing Sr Ru O₃ single crystal film with a thickness from 5 nm to 30 nm was measured.The results show that the Young's modulus of the free-standing Sr Ru O₃ single crystal film first decreases and then increases with the decrease in thickness,ranging from 34.6±3.9 Gpa to 152.2±6.7 Gpa.Based on the analysis of transmission electron microscope and surface resistance test,it is believed that the competition between defect softening effect and surface hardening effect may be the reason for the nonlinear change of Young's modulus of free-standing Sr Ru O₃single crystal film.When the film is thicker,the softening effect of defects dominates,the thickness decreases,which causes the defects increase,and the Young's modulus decreases.When the film is thinner,the surface hardening effect is dominant,the thickness decreases,which leads the surface effect to enhance,and the Young's modulus increases.(3)The Young's modulus of the free-standing Sr Ti O₃single crystal film with a thickness from 4 nm to 14 nm was measured.The results show that the Young's modulus of the free-standing Sr Ti O₃ single crystal film also shows a trend of first decreasing and then increasing with the decrease in thickness,ranging from 53.7±8.2 Gpa to114.3±14.8 Gpa.The Young's modulus of Sr Ti O₃ and Sr Ru O₃ change in the same trend.Because the direction of surface relaxation of Sr Ti O₃ is opposite to that of Sr Ru O₃,the surface effect of Sr Ti O₃ has a softening effect.Due to the flexural electrical effect,there is a large strain gradient elasticity in Sr Ti O₃,and its competitive relationship with the surface softening effect leads to the nonlinear change trend of Young's modulus.When the film is thicker,the surface softening effect is dominant,the thickness decreases,the surface effect is enhanced,and the Young's modulus is decreased.When the film is thinner,the strain gradient elasticity dominates,the thickness decreases,and the strain gradient increases,then the modulus increases.