Experimental studies of the elastic properties of gold nanoparticle arrays

This thesis reports on the fabrication and elastic properties of freely suspended two-dimensional arrays consisting of 6 nm gold nanocrystals coated with dodecanethiol ligands. The ordered monolayer arrays form stable membranes that extend over holes with diameters up to 2 mum. An atomic force microscope is used to exert a point force at the center of the nanomembranes and to measure the vertical displacement. From the resulting nonlinear force-displacement curves, an effective Young's modulus, E, of the nanoparticle membranes is obtained. Measurements on 19 arrays with radii ranging from 250 nm to 1100 nm gave values for E in the range of 2.6 GPa to 39 GPa. These values are larger than the elastic modulus of typical polymers, a surprising result given that the ligands are short molecules that do not entangle in the way much longer polymers do. Further surprising is the robustness of the membranes. As the temperature is increased, no clear melting transition is found and the arrays do not weaken before eventually tearing at temperatures in excess of 100°C. Up to the point of tearing, the arrays are fully elastic and exhibit no plastic behavior. Due to their stability, these membranes could find possible applications as pressure sensors.