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.

Direct Measurement of Electronic Band Structure in Single Quantum Dots of Metal Chalcogenide Composites

“…Figure a shows different slopes for different QD type, indicating that the variation of the CPD is mainly dependent, as expected, on the electronic proprieties of the different materials, rather than on geometrical features. The small fluctuation of the CPD for QDs with the same size and composition can be attributed to variations in particle shape and orientation as well as to the presence of steps on the substrate …”

WSe 2 -contact metal interface chemistry and band alignment under high vacuum and ultra high vacuum deposition conditions

“…Less severe band bending induced by Au deposition under either UHV or HV conditions is consistent with VW-type Au growth on WSe 2 results in Au clusters with significantly smaller Φ than expected of bulk, polycrystalline Au. Au nanoparticles on the order of 5 nm in diameter suspended on a Si(1 1 1) substrate can exhibit a Φ as small as 3.4 eV, with Φ approaching Φ Au,bulk as particle size increases [49]. It is also possible that orbital hybridization near the interface accompanied by charge redistribution results in FLP and therefore an anomalously low Φ Au .…”

Effect of nanoscale size and medium on metal work function in oleylamine-capped gold nanocrystals

“…In gold nanoparticles the environment can affect the work function, which some researchers thought to be a consequence of electrostatic charging in the confined nano-particles volume, among other reasons 17 . In this work we addressed this issue by investigating oleylamine-capped gold nanocrystals (AuNCs) deposited onto a gold substrate by means of self-assembly.…”