The growth of Ag–Au bimetallic nanoparticles on TiO2(1 1 0)

In situ scanning tunneling microscopy (STM) with a tip shadowing technique has been used to follow the growth kinetics of Au on clean TiO2 and a Ag pre-deposited TiO2(1 1 0) surface on a particle-by-particle basis. Results for the clean surface agree well with previous observations in our laboratories using conventional STM that particles initially grow preferentially at the step-sites. However, with the present experimental setup the growth of Au on step-sites can be isolated from that on terrace sites; the rates for the growth rate of particles on step-sites are shown to be much faster. Au growth on Ag pre-covered surfaces suggests that competitive nucleation and growth on empty step-sites and on pre-nucleated Ag particles depends upon the availability of empty step-sites. However, the overall growth closely resembles that of Ag on TiO2(1 1 0) suggesting that the pre-deposited Ag particles are determining the growth mode. Spontaneous formation of Ag–Au particles are evident from the STM images acquired as a function of Au coverage. These binary particles are believed to be of the “alloy” type rather than the “core-shell” type.