Characterization On The Oxidation Of Silver And Copper And Related Structures-Properties

The research on metal oxides(MOs)has long been a prominent branch of modern applied science,due to their peculiar physical,chemical and biological properties,which their metallic counterparts don't have,and thus showing lots of potential industrial applications such as laser diode,field emission gun,gas sensor,etc.A deep understanding on the oxidation of metals,as well as the microstructures and properties of their oxide counterparts,is of great significance for the future design and eventually realization of the new functions of MOs based devices.This dissertation is focused on the investigation into the oxidation of Ag and Cu,and properties of the products,Ag2O and CuO,from an electron microscopy based characterization perspective.The main findings regarding the oxidation of Ag are summarized as follows:1.Applying electron beam(e-beam)irradiation,nanoscale oxidation of Ag was directly realized and in-situ visualized inside transmission electron microscopes(TEMs).The oxidation behavior was proved reversible as the e-beam dose rate varies,indicating an achievable equilibrium between the oxidation product Ag2O and the metallic Ag.The competition between the ionization induced oxidation of Ag and electron-stimulated-desorption(ESD)induced reduction of Ag2O was discussed to account for this dependence on the e-beam dose rate.Preliminary results on patterned oxidation of Ag by configuring the e-beam suggested that the oxidation can be precisely localized within desired area,which can be scaled down to 3 nm.These findings open up a new pathway toward the fabrication of Ag-Ag2O based quantum devices through local oxidation method.2.Atomic-level details of the Ag-Ag2O interface were obtained utilizing aberration corrected high resolution electron microscopy(Cs-corrected HREM)imaging technique.A prevailing orientation relationship(OR)of<110>Ag//<110>AgzO,{111}Ag//{002}Ag2O has been found between Ag and Ag2O.Further study unveiled a twice or three times modulation of original Ag lattice along{111} plane,indicating a plane-preferred O diffusion mechanism of the oxidation process:Initially,small amount of O ions diffused and orderly distributed into the Ag lattice,causing a twice or three times modulation;with the increase of O ion density in the Ag lattice,the rearrangements of atoms led to the nucleation of Ag2O crystals.The main findings regarding the oxidation of Cu are summarized as follows:1.The mechanical behavior of CuO nanowires(NWs)fabricated by heating pure Cu in ambient air was investigated by in situ transmission electron microscopy combined with the Nanofactory EP1000 TEM-STM platform.Anelasticity was consistently observed after stress release for strained NWs.Further investigations indicated that the anelasticity was intrinsic to CuO NWs,although e-beam irradiation was proved capable of accelerating the shape recovery.A mechanism based on the cooperative motion of twin-associated atoms was proposed to account for this phenomenon.The results provide insight into the mechanical properties of CuO NWs,which are promising materials for nanoscale damping systems.2.The structural characteristics of monoclinic CuO NWs were investigated by electron microscopy(EM).Besides the single-crystalline NW,four different twinned NWs with twinning planes of(111),(002),(110)and(202)have been found.The twin boundaries were generally in parallel with the NW axial direction.Moreover,the prevailing existence of(111)and(002)twinned NWs could be closely related to the NW growth as well as the oxidation processes of Cu.Our results provide a systematic investigation on the twin structures of CuO NWs,which could be used as important experimental clues to the underlying oxidation mechanism of Cu and the abnormal properties of Cu NWs.