Study of Micro and Nano Scale Transport of Liquid Metal on Thin Solid Films

Abstract

In recent times, researchers have found potential in using liquid metals in broad-spectrum applications such as processing ceramics, stretchable electronics, 3D printing, coolant technology, energy storage, and many others. Gallium and its alloys are preferred over conventional mercury in all these applications because of its low melting point, high boiling point, and non-toxicity. Given these exciting applications, there is a need to understand the flow behavior of low melting metals in the liquid state, especially at small length scales. The wetting of gallium on metal thin solid films is not well understood. Wetting of liquid metals on thin metal films is complex due to the nature of the interaction between the liquid and the substrate. This interaction involves solidification and chemical reactions, including oxidation of the liquid metal itself. The central theme of this thesis is to understand the liquid metal flow on thin solid films due to various driving forces, such as wetting, chemical reaction, and electromigration. This quest was pursued because of the versatile nature of the phenomenon, which produces patterns ranging from distinct islands to periodic patterns at microscale and nanoscale .Given its interesting and technologically important features, we pursued our research to understand the fundamentals of this phenomenon. In the first part of the work, we investigate the formation of patterns of liquid metals with the rippled surfaces on the metal thin solid films. Flow is observed in situ using a scanning electron microscope (SEM) at high magnifications to gain fundamental insights into the phenomenon of the spontaneous flow of the liquid metal and the formation of the unique surface features . SEM characterization indicates that the liquid-solid reaction and wetting front drives the entire flow and thereby pattern formation...