Scanning Tunneling Microscopy Determination of Single Nanocrystal Core Sizes via Correlation with Mass Spectrometry

Abstract

We show that single alkanethiol-passivated gold nanocrystals can be identified by core size in scanning tunneling microscopy (STM) experiments, through a comparison of the measured STM heights with a direct determination of the gold core sizes by mass spectrometry. We take advantage of the discrete size distribution to correlate the peaks in a histogram of nanocrystal heights with the distinct abundance peaks in a mass spectrum. The correlation establishes a mapping from STM height to core mass or mean core diameter. This is vitally important for the interpretation of size-dependent "single-molecule" tunneling spectra from nanocrystal compounds.

Effect of Ligand Shell Structure on the Interaction between Monolayer-Protected Gold Nanoparticles

“…24 An analysis of the images shows that the height of these objects is not always equal to their diameter as one would expect for spherical objects. Both literature [34][35][36][37] and our images of ligand-coated nanoparticles of similar size show that isolated nanoparticles appear "flat" in STM, i.e., their height is typically less than 3 nm (Figure S1a, in Supporting Information, SI). Similarly, particles in packed layers have a height that corresponds to their diameter (Figure S1b, in Supporting Information).…”

“…32 In STM metallic nanoparticles appear as circular objects (to a first approximation). 24,[34][35][36][37] The diameter of these objectss for the most partscorresponds to the diameter of the particles measured in TEM plus twice the extended length of the ligand molecules (in the case of DDT ∼1.5 nm). 24 An analysis of the images shows that the height of these objects is not always equal to their diameter as one would expect for spherical objects.…”

Charge Transport in Nanoparticle Assemblies

“…These steps in current are known as “Coulomb staircase”. Coulomb blockade and often Coulomb staircases have been observed in studies involving individual NPs using nanometer-separated electrodes, ,,,,− , STM, − or electrochemical methods. − For example, Figure shows an I − V curve of a single Au NP device at 4.2 K. The device was fabricated by evaporating Au grains on nanometer-separated Au electrodes created by electromigration. The I − V curve exhibits both a Coulomb blockade gap around zero bias and steps at higher voltages.…”

Reactive capture of gold nanoparticles by strongly physisorbed monolayers on graphite

“…The closely packed MUA-AuNP assemble as multiple layers; a section analysis spanning the central dark region reveals multiple plateaus with heights differing by 0.5-1.5 nm 3 (see Section S5 in the electronic Supplementary Material for analyses of the AuNP heights and packing in Fig. 3) [65]. A magnified view (Fig.…”

“…The mixed monolayer of 1 and 2 afforded reduced surface coverage of captured MUA 30 -AuNP, with most still appearing as closely packed, single-or multi-layer clusters. The AuNP single layers exhibit STM heights of 0.6-1.2 nm and widths of 2-4 nm [65]. A few captured AuNP appear separated from their closest neighbors, e.g.…”