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