In Situ Nano-scale TEM Study On Mechanical Properties And Stress Induced Damage Behavior Of ZnO

As one of the key technologies for high-quality surface manufacturing,nanometric cutting technology has potential to meet the requirements for nano-scale roughness and flatness of high-performance devices,which are crucial for special large equipment in aerospace,clean energy,military equipment,MEMS,etc.However,due to the special nano effects of materials,such as “small size effect” and “surface effect”,the stress-induced damage behavior of nanomaterials is completely different from that of bulk materials,which severely restricts the establishment of the nanometric cutting theory and further development of nanometric cutting technology.As a new generation of semiconductor materials,ZnO nanomaterials have important application prospects in the fields of high-performance semiconductor and photoelectric conversion devices,due to their excellent properties in piezoelectricity and photoelectricity.At present,most of the research of ZnO nanomaterials focuses on their photoelectric and piezoelectric properties,while the research on mechanical properties of ZnO nanomaterials is limited.In this paper,the mechanical properties and stress-induced damage behaviors of ZnO nanomaterials were studied by means of in situ nano-mechanical experiment in TEM.A new sample preparation method for in situ experiment was invented,which avoids the damage to the sample in the preparation process by the traditional method using focused ion beam.Using this new method,the sample preparation difficulty was mainly solved.As a kind of hard and brittle material,at the same time a semiconductor material,the stress-induced damage behavior of ZnO at nano scale is of great significance for exploring the nanometric cutting mechanism.In the present work,the elastic modulus of ZnO nanowires under different tensile strain rates was studied,and the results showed that the same nanowire had different elastic modulus under different tensile strain rates.The elastic modulus increased obviously with the increase of the strain rate.Moreover,the tensile test results of 12 ZnO nanowires with different diameters showed that the elastic modulus has little reliance on sample diameter.The dislocation motion and stacking faults are considered to be the reasons for the change of elastic modulus.In the study of the stress-induced damage behavior of ZnO,we observed the dislocation generation and motion phenomenon of ZnO nanowires under different loading states.It was found that the dislocation movement within the material has great differences under different stress states.In uniaxial tensile state,the dislocation within the ZnO nanowire moves in the opposite direction of stress.While in the buckling state,the dislocation moves from both ends of the nanowire to the middle and converges at the middle.The local plastic deformation of brittle materials was observed in the buckling experiment of ZnO nanowires,which confirmed the idea that brittle materials would undergo elastoplastic transformation under complex stress state.