Surface-dependent scenarios for dissolution-driven motion of growing droplets

Abstract

Nano-droplets on a foreign substrate have received increasing attention because of their technological possible applications, for instance to catalyse the growth of nanowires. In some cases the droplets can move as a result of a reaction with the substrate. In this work we show that the substrate orientation, the surface morphology and the shape of the pits etched in the substrate by the droplets affect the droplet motion, so that a single mechanism (droplet-induced substrate dissolution) may lead to several unexpected droplet dynamics. The experiments are carried out by low energy electron microscopy on Au-Si and Au-Ge, which are model systems for studying liquid droplet alloys. Studying in-situ the behaviour of Au droplets on various Si and Ge surfaces, we describe a subtle interplay between the substrate orientation, the surface defects, and the droplet motion. Our observations allow a deep understanding of the interfacial mechanisms at the origin of the alloy formation and the associated droplet motion. These mechanisms are based on events of substrate dissolution/recrystallization. The outcomes of this work highlight the importance of the etching anisotropy on the droplet-substrate behaviours, and are essential in the perspective of positioning liquid alloy droplets used for instance as nanowire catalysts.

Detailed characterization of supported eutectic droplets using photoemission electron microscopy

“…Droplet 1 is at the local hot spot and is, thus, fully in equilibrium, whereas the other droplets are on their way to the hot spot. Such motion in the direction of the highest temperature has also been observed for the similar eutectic systems [4][5][6][7][8][9][10]. In the following sections we discuss important characteristics of the morphology of the eutectic PtGe droplets as revealed by PEEM.…”

“…Applications involve the growth of the two-dimensional material germanene [2] or standing-up Si nanowires [3] from the eutectic dropletx. Several of these eutectic systems have been studied by surface electron microscopy [4][5][6][7][8][9][10]. Information on the three-dimensional (3D) details of these liquid droplets, however, is rarely obtained from electron microscopy [11,12].…”

Towards the understanding of the gold interaction with AIII-BV semiconductors at the atomic level

“…Such hierarchy in the surface etching by Au atoms and facets formation is also observed for singlecomponent semiconductors such as Si or Ge 48,49 .…”

Mechanism of droplet motion and in-plane nanowire formation with and without electromigration

“…Horizontal nanowires can also be grown on Si(110). We have shown that during Au deposition on Si(110) at temperatures higher than the eutectic temperature (633 K) elongated liquid droplets form, move on the substrate along a unique axis but in both directions ( [1][2][3][4][5][6][7][8][9][10] and [-110]) and leave in-plane Si nanowires at their back [12,13]. The randomness of the motion direction of the droplet limits the degrees of control and thus the perspectives of possible applications.…”