| The surface and interface of materials, other than the interior, follow different physics and chemistry laws, endowing materials with unexpected properties. With the development of nanoscale materials and size shrinkage of microelectronic devices, effects of surface/interface structure on the properties of materials and performances of devices become a notable issue. Therefore,insight into microcosmic mechanism of surface/interface of materials that is directly associated with unexpected properties will be scientifically significant. In this thesis, using in situ transmission electron microscopy and taking the silver and other metals which play important role in practice for examples, the structural evolvement of surface/interface under different external fields and the effects to the properties of materials and candidate devices structure have been investigated. The main results are summarized as follows:1. In situ study of surface structural evolution of sub-10-nm silver particles under force field.(1) An experimental methodology has been developed to in situ fabricate silver particles with clean surface inside a transmission electron microscope.(2) Liquid-like deformation behavior of sub-10-nm silver particles at room temperature has been observed and reported for the first time. No matter what kind of initial stress (compressing,stretching or shearing) had been applied, the silver nanoparticle would return to its initial shape roughly, when the external load has been retracted.(3) Development of a Coble pseudoelasticity theory based on surface diffusion. The sub-10-nm silver particle relieves stress through surface atoms diffusing, migration and reconstruction, which resembles Coble creep. Therefore the deformation is defined as Coble pseudoelasticity deformation.Meanwhile, molecular dynamics further demonstrated that Coble pseudoelasticity is accomplished by single atom diffusion on surface, and the needed time depends on diffusive events of non-(111)facets with large activation energy barrier.(4) The above results indicated that the Hall-Petch-like "smaller is stronger" trend,i. e.,??R-? (0.5 ? ?? 1), changed to Coble pseudoelasticity regime, i. e., "smaller is very much weaker"??Rn , when entering sub-10-nm range.2. In situ study of the structural evolution of interface between Ag/Cu/Ni and ZrO2 under electric field.(1) The Cu (Ag)/ZrO2/Pt structure evolvement under electric field is investigated. The growth direction of conductive filaments (CFs) of Cu (Ag)/ZrO2/Pt is from the active electrode to the inert one, which contradicts to conventionally theoretical prediction of electrochemical metallization(ECM). When a negative voltage is applied, the dissolution direction of CFs is from inert electrode,which again contradicts to conventional ECM theory. Energy dispersive X-ray spectrometry (EDX)analysis and resistance-temperature characteristics of CFs demonstrated that the CFs is in a metallic phase, so the resistance switching of Cu (Ag)/ZrO2/Pt is the ECM type. First-principle calculations show that,doping ZrO2 system with Cuz+ (Ag+) ions is difficult. Even if doping occurs,ions prefer to present in the interstitial position, which cannot introduce additional oxygen vacancies. The possibility of electronically conductive ternary phase with Cuz+ (Ag+) doped ZrO2 has been ruled out. It is believed that conventional ECM theory failed to differenciate solubility and diffusion coefficients of metal ions in solid-state electrolytes, leading to the aforementioned abnormal phenomenon.(2) The Ni/ZrO2/Pt structure evolvement under electric field has been investigated,which exhibit similar results as in Cu (Ag)/ZrO2/Pt structures. Several conductive filaments are formed across the ZrO2 layer between Ni and Pt electrodes after electric field had been applied. EDX analysis and resistance-temperature characteristics tests have confirmed that CFs is composed of metallic Ni. Due to the compatibility with the current complementary metal oxide semiconductor(CMOS) technology, Ni/ZrO2/Pt interface may provide possibility for future application of resistance switching memory. |
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