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.This work was supported by the Office of Basic Energy
Sciences (BES) of the U.S. Department of Energy (DOE)
under contract DE-AC02-05CH11231 through the Structure
and Dynamics of Materials Interfaces Program (FWP
KC31SM) and the Molecular Foundry. M.L. acknowledges
funds from Comunidad de Madrid (P2018/EMT-4308), a
Fulbright grant PRX16/00564, and the MCIU-AEI-FEDERUE
(RTI2018-096937-B-C22 and MAT2014-59772-C2-1-P).
J.C. acknowledges financial support from Ministerio de Ciencia
e Innovación (MICINN) and the European Union through the
project PID2019-104272RB-C52. Also, Y.H. acknowledges
financial support from MCIU through MAT2014-59772-C2-2-
P and L.M. from EC through ERC-2013-SYG-610256.
V.A.P.O. and M.B. acknowledge the financial support from
EC through ERC CoG HyMAP 648319, MINECO PID2019-
106315RB-I00 and ENE2017-89170-R, ″Comunidad de
Madrid″ and European Structural Funds (FotoArt-CM project S2018/NMT-4367) and Fundación Ramón Areces (Art-Leaf
project). M.B. also thanks the Juan de la Cierva Incorporación
contract (IJC2019042430-I). X.Z. was supported by the
NSF-BSF 359 grant number 1906014. The authors thank Prof.
Eran Edri, María Ujué González Sagardoy, and Judit Meseguer-
Oliver for fruitful discussions and Asylum customer support for
help with modifications of the AFM
