Abstract
Gold nanoparticle monolayers provide convenient templates to study charge transport in organic molecules beyond single junction techniques. Conductance is reported to increase by several orders of magnitude following immersion of alkanethiol-stabilized gold nanoparticle monolayers in a solution containing conjugated thiol-functionalized molecules. Typically, this observation is attributed to molecular exchange. Less attention has been paid to the role of the solvent alone. Here, we report on an increase in conductance of dodecanethiol-stabilized gold nanoparticle monolayers on Si/SiO2 by an average factor of 36 and 22 after immersion in pure ethanol (EtOH) and tetrahydrofuran (THF), respectively. Analysis by scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS) reveals a solvent-induced decrease in lattice constant of close-packed monolayers. We compare the conductance of the monolayer after molecular exchange with two different oligophenylenes to shed light on the respective contribution of the solvent-induced structural change and the molecular exchange itself on the conductance increase.
Highlights
Ordered gold nanoparticle monolayers are increasingly applied as templates for molecular resistor networks [1,2,3,4,5,6,7,8]
Gold nanoparticles with an average diameter of 10.6 nm measured by small-angle X-ray scattering (SAXS) were synthesized [14], functionalized by 1-dodecanethiol [15], assembled to form a monolayer [16], and deposited onto an Si/SiO2 substrate using a patterned poly(dimethylsiloxane) (PDMS) stamp [17]
Considering all aspects we attribute a major role to the solvent in contributing to the observed conductance increase of nanoparticle monolayers undergoing liquid phase molecular exchange protocols
Summary
Ordered gold nanoparticle monolayers are increasingly applied as templates for molecular resistor networks [1,2,3,4,5,6,7,8]. We demonstrate that the solvent alone can induce a structural transition responsible for a large portion of the observed increase in conductivity of micro-contact printed selfassembled gold nanoparticle monolayers. Subsequent measurements of the dried devices (red data points in Figure 1) showed an average increase in conductance by a factor of 36 for EtOH immersion and 22 for THF immersion.
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