Study On The Electromechanical Coupling Properties Of Piezoelectric Thin Film/Nanobelt Via Nanoindentation Method

Nanoindentation method is commonly used to characterize the mechanical properties of bulk materials, because of its flexibility, high accuracy and requirements of the small sample size. During nanoindentation the substrate will influence the characterization of film/substrate or nanobelt/substrate, so that the indentation results reflect integrated properties but not the intrinsic mechanical properties, generally. Therefore, how to measure mechanical parameters of film/substrate or nanobelt/substrate has become a hot current issue for microelectronic materials.In the dissertation, the relationship between the nanoindentation loading curve of the thin film/nanobelt is modified as exponent function to obtain the loading curve exponent x and the maximum indentation load F_max, so that the substrate effect is considered to measure the mechanical parameters of thin film or nanobelt. The electromechanical coupling coefficients of transversely isotropic PZT thin film and elastic moduli of ZnO nanobelt are evaluated by combining finite element method and nanoindentation test. The content is divided into three parts and they are given as follow.1. Electromechanical coupling coefficients of film PZT are evaluated considering the substrate effect.(1) Evaluation of elastic moduli. In the forward analysis, piezoelectric effect is considered and ignored for PZT thin film, and with the assistance of the substrate effect, the dimensionless equations related the elastic moduli of film/substrate system with the loading curve exponent x and the maximum indentation load F_max are established by extensive FEM simulation. In the reverse analysis, the nanoindentation test was performed on PZT thin film to obtain the experimental indentation loading curves, and they were fitted as the power function. The loading curve exponent x and the maximum indentation load F_max extracted from the experimental indentation curves of the nanoindentation test are substituted into the established dimensionless equations to solve the elastic moduli.(2) Evaluation of piezoelectric coefficients. In the forward analysis, with assistance of the substrate effect, the dimensionless equations related the elastic moduli of film/substrate system with the maximum indentation load F_max and the loading curve exponent x are established by extensive FEM simulation for transversely isotropic piezoelectric thin film. In the reverse analysis, the nanoindentation test was performed on PZT thin film, and the experimental indentation curves are fitted as the power function to extract the maximum indentation load F_max and the loading curve exponent x. The experimental indentation data are substituted into the dimensionless equations to solve piezoelectric coefficients.2. In nanoindentation test, considering the substrate and aspect ratio effects on Young's modulus of nanobelt, Young's modulus of ZnO and ZnS nanobelts are evaluated combining FEM and nanoindentation test. In the forward analysis, with assistance of the substrate effect, the dimensionless equations related the Young's modulus and aspect ratio of nanobelt with the loading curve exponent x and the maximum indentation load F_max are established by extensive FEM simulation. In the reverse analysis, the nanoindentation test was performed on ZnO and ZnS nanobelts, and the experimental indentation loading curves can be fitted as the power function. The loading curve exponent x and the maximum indentation load F_max extracted are substituted into the dimensionless equations to solve Young's moduli.3. ZnO nanobelt is modeled as transversely isotropic materials, and elastic moduli of ZnO nanobelt are evaluated combining FEM and nanoindentation test considering substrate effect and size effect in nanoindentation test. In the forward analysis, the clear relationships between the indentation loading parameters and the elastic properties of nanobelt/substrate system are established through extensive FEM simulation. The numerical loading responses are simulated at the appropriate penetration depth to utilize the substrate effect. The dimensionless equations between the x, F_max and elastic moduli of nanobelt/substrate system are established by extensive FEM. In the reverse analysis, a nanoindentation test was performed on the single ZnO nanobelt, and the experimental indentation curves can be fitted as the power function. The loading curve exponent x and the maximum indentation load F_max are extracted from the loading curve of experimental indentation, and they are substituted into the dimensionless equations to solve the elastic moduli of ZnO nanobelt.