Real-Time Observation of the Solid-Liquid-Vapor Dissolution of Individual Rutile-Type Nanowires within the Indium-Tin-Oxide Solid Solution

Hudak, Bethany M., Yao-Jen Chang, Lei Yu, Guohua Li, Danielle N. Edwards and Beth S. Guiton, 2014

Image courtesy of ACS Nano

Abstract

The well-known vapor–liquid–solid (VLS) mechanism results in high-purity, single-crystalline wires with few defects and controllable diameters, and is the method of choice for the growth of nanowires for a vast array of nanoelectronic devices. It is of utmost importance, therefore, to understand how such wires interact with metallic interconnects–an understanding which relies on comprehensive knowledge of the initial growth process, in which a crystalline wire is ejected from a metallic particle. Though ubiquitous, even in the case of single elemental nanowires the VLS mechanism is complicated by competing processes at multiple heterogeneous interfaces, and despite decades of study, there are still aspects of the mechanism which are not well understood. Recent breakthroughs in studying the mechanism and kinetics of VLS growth have been strongly aided by the use of in situ techniques, and would have been impossible through other means. As well as several systematic studies of nanowire growth, reports which focus on the role and the nature of the catalyst tip reveal that the stability of the droplet is a crucial factor in determining nanowire morphology and crystallinity. Additionally, a reverse of the VLS process dubbed solid–liquid–vapor (SLV) has been found to result in the formation of cavities, or “negative nanowires”. Here, we present a series of heating studies conducted in situ in the transmission electron microscope (TEM), in which we observe the complete dissolution of metal oxide nanowires into the metal catalyst particles at their tips. We are able to consistently explain our observations using a solid–liquid–vapor (SLV) type mechanism in which both evaporation at the liquid–vapor interface and adhesion of the catalyst droplet to the substrate surface contribute to the overall rate.

Impact Statement

A series of heating studies administered in situ in a TEM. The researchers studied metal oxide nanowires as they dissipated completely into the metal catalyst particles located at their tips. The researchers then used a solid-liquid-vapor type mechanism to demonstrate their observations. The mechanism allowed the catalyst droplet to both evaporate at the liquid-vapor interface and adhere to the substrate surface. These processes factor into the overall rate of dissolution.