| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 103 === Owing to a high surface area /volume ratio and a unique quantum effect nano sized materials present different optical, electrical, magnetic, mechanical and chemical properties from bulk materials. In recent years, many researches reported that the mechanical properties of material change with their sizes. However, there are still many phenomena not yet clarified or confirmed by direct observations, in particular the effect of bonding types on mechanical properties. Therefore in this study, the influences of various bonding types on the deformation behavior of nanomaterials is emphasized. Metallic Cu, ionic MgO, and covalent GaAs single-crystalline nano pillars with a diameter of 70 nm were cut by using a focused ion beam, and the physical behavior of dislocations was observed by in-situ compression in transmission electron microscopy (TEM). It was found that the gliding velocity of dislocation clusters in metallic Cu single-crystaline nano pillars was the fastest, while the strain rate was the slowest, compared with ionic MgO and covalent GaAs. In the loading direction of <111> for covalent MgO nano pillars, the traditional charge balance {110} <110> slip system with a resolved shear stress of zero was observed to be replaced by non-charge balance {111} <112> partial-dislocation and {100} <110> full- dislocation slip systems.
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