Au-assisted Growth Of SrTiO₃ Substrates

Gold-oxide nanostructures have attracted extensive attention because of their widespread applications in biomedicine,catalysis and electronic devices.A recent investigation,regarding Au-MgAl2O4,from our group has reported that oxide bases grow underneath dewetted gold nanoparticles high temperatures from nominally stable oxide substrate.The growth of oxide bases has discoveried with the formation of the reconstructed gold-spinel(MgAl2O4)interfaces with low interface energy,while the underlying reason for the growth,such as the adaptability and thermodynamics,remains largely unclear.Accordingly,my thesis focuses on a similar lattice-matched system,Au-SrTiO3.In order to facilitate the following structural characterization,we prepared Au dewetted nanoparticles on the surface of single-crystal SrTiO3 substrates.The morphology and the size distributions of nanoparticles depend on the initial thickness of gold film,the heat-treatment temperature,and the crystallography orientation of SrTi03 substrates.We also discussed the preferential crystallography orientation between Au and SrTi03.Finally,based on the above characterization results,we established a thermodynamic model to reveal the underlying growth mechanism from the energetic point of view.The clarification of the above questions is valuable to understand the morphology evolution of gold-oxide nanostrucutres at high temperature,but also imply new opportunities of synthesizing novel gold-oxide nanostructures.Our results indicate that the dewetted gold nanoparticles have a similar morphology to what have been reported in the literature.The radius of gold nanoparticle increases with the initial film thicknesses and the heat-treatment temperatures.Furthermore,the growth of oxide bases underneath dewetted gold nanoparticles have been replicated in Au-SrTi03 with a height of about 10-30nm.Different to the previous studies,in corresponding to the growth of bases,a large number of particles with small size has been noticed,thus to appear to be a bimodal size distribution.The preferential orientation relationship,according to the XRD result,characterization,is {111{Au//{111}SrTiO3&<110>Au//<110>SrTiO3 for the {111} srTriO3 substrate.On the other hand,for the {100} srTiO3 substrate,the preferential orientation relationships change from {100}Au//{100}SrTiO3&<001>Au//<010>SrTiO3,{100}Au//{100}SrTiO3&<001>Au//<011>SrTiO3,{100}Au//{100}SrTio3&<013>Au//<010>SrTio3 and {110}Au///{100}SrTiO3&{001}Au//<001>SrTiO3 to {111}Au,//{100}SrTiO3&<011>Au//<010>SrTiO3,and{111}Au//{100}SrTiO3&<011>Au//<011>SrTiO3 as the heat-treated temperatures increase.Based on the gold nanoparticle morphology and the preferential crystallographic orientations,a thermodynamic modelis established to analyse the changement of the total surface and interfacial energy during the bases growth.These results reveal that the decrease in the total surface and interfacial energy of gold-oxide nanostructures cannot be compensate the energy need for growing bases.Consequently,other factors,such as the surface energy decrease due to gold evaporation,are partially responsible for the base growth.