Research On The Spatial Distribution, Microstructure And Diffusion Of Germanium Nanocrystals And Nanopores In The Silica Matrix

In this thesis,transmission electron microscopy has been employed to investigate the Ge nanocrystals?Ge-ncs?and nanocavities embedded in Si O₂ matrix.The main content focuses on the influence of annealing time and co-implantation of Er³⁺ions,Si⁺ions and Ge⁺ions on the distribution and microstructure of Ge-ncs and nanocavities.The thesis consists of four chapters.In chapter 1,the basic characteristics,unique properties,and applications of semiconductor nanomaterials are reviewed.In chapter 2,the ion implantation method for preparation of semiconductor nanocrystals and the transmission electron microscopy for characterization of nanocrystals are introduced.In chapter 3,Ge-ncs were synthesized by implantation of Ge⁺ions into the Si O₂matrix,followed by a thermal annealing at 1000 ^oC.High-resolution transmission electron microscopy?HRTEM?was employed to characterize both the morphology of the formed Ge-ncs and the evolution of their depth-distribution as a function of annealing durations.It is evidenced that the formation of nanocavities can release of the compressive stress exerted on Ge-ncs by Si O₂ matrix.Some Ge-ncs are found inside nanocavities,which can move into the implanted layer through a nanocavity-assisted diffusion mechanism.This finding sheds light on a new process that can explain the non-uniformity of spatial distribution for Ge-ncs.In chapter 4,nanocrystals were synthesized by ion implantation of Ge⁺ions,co-implantation of Si⁺and Ge⁺ions and co-implantation Er⁺,Si⁺and Ge⁺ions,respectively.The morphology and microstructure of the nanocrystals are characterized by HRTEM.It is revealed that the extra Si ions in Si O₂ matrix can reduce the out-diffusion of Ge atoms from the Ge-ncs and inhibit the formation of nanocavities.Meanwhile,the implanted Er³⁺ions can inhibit the growth of Ge-ncs through Oswald ripening mechanism,which makes the size of nanocrystals more uniform.