Nanotip Formation from Liquid Metals for Soft Electronic Junctions

Abstract

Liquid metals and alloys with high-aspect-ratio nanodimensional features are highly sought-after for emerging electronic applications. However, high surface tension, water-like fluidity, and the existence of self-limiting oxides confer specific peculiarities to their characteristics. Here, we introduce a high accuracy nanometric three-dimensional pulling and stretching method to fabricate liquid-metal-based nanotips from room- or near-room-temperature gallium-based alloys. The pulling rate and step size were controlled with a resolution of up to 10 nm and yielded different nanotip morphologies and lengths as a function of the base liquid metal alloy composition and the pulling parameters. The obtained nanotips presented high aspect ratios over lengths of a few microns and apexes between 10 and 100 nm. The liquid metal alloys were found confined within nanotips with about 10 nm apexes when vertically pulled at 100 nm/s. An amorphous gallium oxide skin was shown to cover the surface of the nanotips, while the liquid core was composed of the initial liquid metal alloys. The electrical contact established at the nanotips was characterized under dynamic conditions. The liquid metal nanotips showed an Ohmic resistance when a continuous liquid metal channel was formed, and a controllable semiconductor state corresponding to a heterojunction formed at the junction between the liquid metal phase and the gallium oxide semiconductor skin. The variable threshold voltages of the heterojunction were controlled via stretching of the nanotips with a 10 nm step resolution. The liquid metal nanotips were also used for establishing soft electronic junctions. This novel method of liquid metal nanotip fabrication with Ohmic and semiconducting behaviors will lead to exciting avenues for developing electronic and sensing devices.

Soft Liquid Metal Infused Conductive Sponges

“…In recent decades, Ga has attracted growing research interests due to its fascinating properties including fluidity, metallic electrical and thermal conductivities. [ 1 ] Gallium and its alloys have shown applications in microfluidics, [ 2 ] sensing, [ 3 ] catalysis, [ 4 ] self‐healing materials, [ 5 ] soft composites for biomedical devices, wearable electronics, [ 6 ] and electromagnetic wave shielding materials. [ 7 ]…”

Scalable Strategy to Directly Prepare 2D and 3D Liquid Metal Circuits Based on Laser-Induced Selective Metallization

“…Flexible contacts and flexible circuits are important for flexible electronics. Alliou developed a liquid metal nanotip for flexible electronic contacts . This liquid metal nanotip presented soft and conductive junctions, demonstrating a promising alternative to toxic mercury or often damaged hard metals for probing sliding contacts.…”

“…Alliou developed a liquid metal nanotip for flexible electronic contacts. 9 This liquid metal nanotip presented soft and conductive junctions, demonstrating a promising alternative to toxic mercury or often damaged hard metals for probing sliding contacts. Flexible circuits are also key to ensuring electrical conductivity during stretching and bending.…”

Flexible Tactile Sensing Microfibers Based On Liquid Metals

“… 11 Owing to their excellent electrical conductivity, thermal conductivity, and low toxicity, they have been receiving considerable attention to tackle current challenges. 12 − 21 To the best of our knowledge, the research of LM composite fibers is in the initial stage. 12 , 22 − 26 Furthermore, there has been a steady growth of research papers in this field, 27 − 30 reporting various LM composite fiber sensors, including self-powered sensors, 31 implantable biosensors, 32 selective biosensors, 33 strain sensors, 34 and capacitive sensors.…”

“…To overcome these limitations, there are several emerging strategies for creating flexible fibers, and liquid metals (LMs) may represent one of the candidate materials . Owing to their excellent electrical conductivity, thermal conductivity, and low toxicity, they have been receiving considerable attention to tackle current challenges. − To the best of our knowledge, the research of LM composite fibers is in the initial stage. ,− Furthermore, there has been a steady growth of research papers in this field, − reporting various LM composite fiber sensors, including self-powered sensors, implantable biosensors, selective biosensors, strain sensors, and capacitive sensors . For example, Wu previously reported the LM microfibers as self-powered sensors .…”