Generating high-resolution self-packaged liquid metal nanopatterns

In a new report now published in Matter, Licong An, and a team of scientists in materials engineering, industrial engineering, and the nanotechnology center at Purdue University, U.S., and Wuhan University, China, described ...

Introducing a new method: Pulsed laser lithography (PLL) The field of high-density electronics is of great significance in materials engineering, and is suited to form high-density patterns for integrated electronics in harsh environments. Materials and industrial scientists have used room-temperature gallium indium (EGaIn) to develop high-density patterns due to their distinct properties including high fluidity, high electrical conductivity and high deformability. Research efforts to develop high-resolution liquid metal patterns are based on lithography patterning, among a diverse range of methods, with broad appeal in electronic applications across liquid metal batteries, microfluidics and energy harvesting devices.

In this work, primary author and research associate Licong An, who is presently at the materials engineering department at Purdue University, described the method as a "practical and scalable technique to fabricate self-packaged, high-resolution liquid metal patterns." The team intend to "practically integrate electric chips for use in harsh environments." The scientists primarily introduced the pulsed laser lithography method in this work to develop 3D liquid metal patterns with sub-micron level resolution, protected via a mechanically stable oxide package shell. Licong An highlighted the significance of this approach: "For the first time, the one-step lithography method can be directly used to pattern liquid metal," he said.

Laser interference lithography is invented for nano-patterning liquid metal (LM). The resolution in LM patterns breaks the optical limit of laser beams. Pulsed-laser-induced compression enables uniform 500-nm LM nanolayers. The robust oxide shell on LM boosts the mechanical properties and reliability. Credit: Matter (2022). DOI: 10.1016/j.matt.2022.01.004 Read more

Schematic of the formation of liquid metal nano-patterns and surface morphologies of laser-treated samples. (A) Schematic of high-resolution liquid metal nano-pattern formation. (B) Schematic of the formation of interference beam and laser lithography-induced liquid metal nano-patterns. (C) Surface morphology and EDX mapping of the sample after laser sintering. Scale bar, 0.5 cm in (C) and 10 mm in (c-1, c-2, c-3, c-4). (D) Surface morphology and EDX mapping of the sample after laser lithography. The white dots in (d-1) indicate the ablation-induced oxide nanoparticle assemblies. Scale bar, 0.5 cm in (D) and 500 nm in (d-1, d-2, d-3, d-4). (E) Surface morphology and EDX mapping of the sample after laser ablation. Scale bar, 0.5 cm in (E) and 500 nm in (e-1, e-2, e-3, e-4). Credit: Matter (2022). DOI: 10.1016/j.matt.2022.01.004 Read more

Characterization of the liquid metal nano-patterns. (A) Cross-section view and EDX mapping of liquid metal nano-patterns. Scale bar, 500 nm. (a-1) is one zoomed-in pattern, (a-2) (a-4) are the EDX mappings of the single pattern. Scale bar from (a-1) to (a-4), 100 nm. (B) Surface morphology of liquid metal nano-patterns. Scale bar, 1 mm. (C and D) Interference electric field from the incident beam and the liquid metal scattered fields in the vertical cross-section view (C) and the top view (D). Scale bar, 1 mm. (E and F) AFM morphology (E) and height profile (F) of liquid metal nano-patterns. Scale bar, 1 mm. (G) An Eiffel Tower pattern in rainbow color induced by pulsed laser lithography. Scale bar, 2 cm. (H) Reflectance curve of pattern area and as-sprayed liquid metal nanoparticles. (I and J) Numeric top view (I) and cross-section view (J) of height profile of the nano-patterns. (K) Relationship between the resolution of liquid metal patterns and the laser spot size.(L) Comparison of minimum line width and line spacing of the present work and other published liquid metal patterning technologies. Credit: Matter (2022). DOI: 10.1016/j.matt.2022.01.004 Read more

Structural analysis of liquid metal nano-patterns. (A) The crystallinity of the surface oxides of as-sprayed LMNPs, as-PLLed, as-peeled, and asannealed oxide package shells and simulated Ga2O3 XRD peaks. (B) Raman spectra of the annealed gallium oxide shell. (C and D) XPS curves of the Ga-O bonding. (C) XPS analysis indicating the energy peak of Ga 3d. (D) XPS analysis indicating the energy peak of Ga 2P. Credit: Matter (2022). DOI: 10.1016/j.matt.2022.01.004 Read more

Mechanical and electrical properties of liquid metal nano-patterns. (A) Force-displacement curve of liquid metal nano-patterns and liquid metal particles. (B) Relative change in resistance (R/R0) as a function of the damage times. (C–E) Ruptured surface morphology after mechanical and thermal damage: (C), mechanical cutting; (D) mechanical scratching; (E), laser damage. Scale bar, 500 nm. (F–I) Schematics of the liquid metal nano-patterns without any damage (F), after mechanical cutting (G), after mechanical scratching (H), and after laser damage (I). (J–M) Schematic of electric response of liquid metal nano-patterns without any damage (J), after mechanical cutting (K), after mechanical scratching (L), and (M) after laser damage. Credit: Matter (2022). DOI: 10.1016/j.matt.2022.01.004 Read more