Tuning the Elasticity of Cross-Linked Gold Nanoparticle Assemblies

Composite materials of organically stabilized or cross-linked metal nanoparticles represent a versatile material class with manifold potential applications. Numerous studies explored their tunable optical and charge transport properties. However, due to challenging experimental requirements, only a few studies addressed their mechanical properties. Here, we report the first investigation on the tunability of the elastic properties of cross-linked gold nanoparticle (GNP) composites. Thin films consisting of GNPs (diameter 3-4 nm) cross-linked with a,o-alkanedithiols of different chain length, as well as 1,4-benzenedithiol, were fabricated by spin-coating and transferred onto circular apertures with diameters of ∼100 mm. The mechanical properties of thus-prepared freestanding membranes with thicknesses between 21 and 51 nm were probed using bulge tests with atomic force microscopy (AFM) based deflection readout. We demonstrate that, along with their optical and charge transport characteristics, the elastic modulus of these GNP composites can be adjusted in a range from ∼3.6 to ∼10 GPa by shortening the a,o-alkanedithiol chain length from 10 to 3 methylene units. These variations in elasticity are attributed to the varying fraction of soft organic matter and to structural differences within the composites. Our results provide a basis for further experimental and theoretical studies, as well as for applications of cross-linked nanoparticle composites in future micro- and nanoelectromechanical (MEMS/NEMS) devices, their design, and modeling.