Solution-Phase Growth of Metal Nanowires

Penta-twinned nanowires have been grown for a number of different face-centered cubic (fcc) metals. These fascinating objects have been beneficial in applications such as electrocatalysis and flexible, transparent electronic devices of various kinds: wearable electronic textiles and sensors, health-monitoring devices, electromagnetic interference shielding, electrochromic and optoelectronic devices, and low-voltage electrical heaters. For many applications, nanowires with high aspect ratios have the best performance. In this work, we review our studies aimed at predicting the aspect ratios of nanowires that grow from a combination of atomic deposition and surface diffusion. These studies are based on characterizing atomic-scale surface diffusion that occurs through atom hopping between binding sites on the metal surfaces. The hopping rates are then input to the theory of absorbing Markov chains, which allows us to predict nanowire aspect ratios. We consider two systems: the growth of bare Ag nanowires and the growth of Cu nanowires in the presence of solution-phase hexadecylamine (HDA) capping agents and chloride. We show using embedded-atom method potentials that bare Ag nanowires can grow from Marks decahedra due to their strained structure. In the case of Cu wires, we use first-principles calculations based on density functional theory to show that Cl adsorption leads to more rapid Cu atom diffusion on nanowire sides than on the ends, which facilitates nanowire growth. Moreover, Cl adsorption affects the adsorption of the HDA capping agent, such that the nanowire ends contain little or no capping agent, while the sides are covered with HDA. These combined factors promote the growth of nanowires with aspect ratios exceeding 1000. Our studies are consistent with multiple experiments.