Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on<br> charge generation and trapping during illumination with photons of energy larger than the<br> substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe<br> force microscopy, to study the process at the single Au NP level. We found that the<br> photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light<br> intensity due to the combined contribution of electron−hole pair generation in the space<br> charge region in the TiO2−air interface and in the metal−semiconductor junction. Our<br> measurements on single particles provide direct evidence for electron trapping that hinders<br> electron−hole recombination, a key factor in the enhancement of photo(electro)catalytic<br> activity.