title: Sensing the charge state of single gold nanoparticles via work function measurements.
abstract: Electrostatic interactions at the nanoscale can lead to novel properties and functionalities that bulk materials and devices do not have. Here we used Kelvin probe force microscopy (KPFM) to study the work function (WF) of gold nanoparticles (NPs) deposited on a Si wafer covered by a monolayer of alkyl chains, which provide a tunnel junction. We find that the WF of Au NPs is size-dependent and deviates strongly from that of the bulk Au. We attribute the WF change to the charging of the NPs, which is a consequence of the difference in WF between Au and the substrate. For an NP with 10 nm diameter charged with ∼ 5 electrons, the WF is found to be only ∼ 3.6 eV. A classical electrostatic model is derived that explains the observations in a quantitative way. We also demonstrate that the WF and charge state of Au NPs are influenced by chemical changes of the underlying substrate. Therefore, Au NPs could be used for chemical and biological sensing, whose environmentally sensitive charge state can be read out by work function measurements.
authors.affiliation: Applied Science and Technology Graduate Program, University of California at Berkeley , Berkeley, California 94720, United States.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Zhang
authors.forename: Olivier
authors.initials: O
authors.lastname: Pluchery
authors.forename: Louis
authors.initials: L
authors.lastname: Caillard
authors.forename: Anne-Félicie
authors.initials: AF
authors.lastname: Lamic-Humblot
authors.forename: Sandra
authors.initials: S
authors.lastname: Casale
authors.forename: Yves J
authors.initials: YJ
authors.lastname: Chabal
authors.forename: Miquel
authors.initials: M
authors.lastname: Salmeron
keywords: Charge state; Kelvin probe force microscopy; chemical sensing; gold nanoparticle; work function