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. 2022 Sep 1:10:965891.
doi: 10.3389/fchem.2022.965891. eCollection 2022.

Controlling the oxidation and wettability of liquid metal via femtosecond laser for high-resolution flexible electronics

Jingzhou Zhang  1 , Chengjun Zhang  2 , Haoyu Li  1 , Yang Cheng  2 , Qing Yang  2 , Xun Hou  1 , Feng Chen  1
Affiliations

Controlling the oxidation and wettability of liquid metal via femtosecond laser for high-resolution flexible electronics

Jingzhou Zhang et al. Front Chem. .

Abstract

Liquid metal-based electronic devices are attracting increasing attention owing to their excellent flexibility and high conductivity. However, a simple way to realize liquid metal electronics on a microscale without photolithography is still challenging. Herein, the wettability and adhesion of liquid metal are controlled by combining the stirring method, femtosecond laser microfabrication, and sacrificial layer assistant. The adhesive force of liquid metal is dramatically enhanced by adjusting its oxidation. The wetting area is limited to a micro-pattern by a femtosecond laser and sacrificial layer. On this basis, a high-resolution liquid metal printing method is proposed. The printing resolution can be controlled even less than 50 μm. The resultant liquid metal pattern is applied to electronic skin, which shows uniformity, flexibility, and stability. It is anticipated that this liquid metal printing method will hold great promise in the fields of flexible electronics.

Keywords: electronic skin; femtosecond laser; flexible electronics; oxide-EGaIn; wettability.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
(A) Schematic diagram of high-resolution liquid metal printing method on PDMS surface. (B) Optical image of a logo of XJTU on PDMS substrate after fs laser selective ablation. (C) Photograph of the liquid metal logo on the resultant surface with high resolution. (D) Photograph of the liquid metal logo on the resultant surface with higher magnification.
FIGURE 2
FIGURE 2
Comparison between original and magnetic stirred EGaIn droplets. (A) Photographs of the droplets and their surfaces, scale bar: 500 μm. (B) 3D confocal microscopy images of EGaIn and O-EGaIn surfaces. (C) XPS analysis of EGaIn and O-EGaIn surfaces. (D) Surface roughness of EGaIn with different magnetic stirring times. (E) Relationship between oxygen contents of EGaIn and magnetic stirring time. (F) Conductivity of EGaIn with different stirring times. (G) Adhesive force between flat PDMS surface and EGaIn droplet with different stirring times. (H) O-EGaIn as electronic direct ink writing on different surfaces.
FIGURE 3
FIGURE 3
Wettability of O-EGaIn on different PDMS surfaces. (A) SEM image of the untreated PDMS surface. (B) SEM image of the fs laser-scanned PDMS surface. (C) O-EGaIn droplet on the untreated surface. (D) O-EGaIn droplet on the laser-scanned surface. (E) Adhesive force between O-EGaIn droplet and fs laser-scanned surface with different scanning speeds.
FIGURE 4
FIGURE 4
Influence of sacrificial layer on liquid metal printing. (A) Usage of the sacrificial layer to remove the ablation particles on an un-scanned area. (B) SEM image of the untreated square pattern on PDMS surface without sacrificial layer. (C) SEM image of the untreated square pattern using sacrificial layer method. (D) Process of a liquid metal droplet contacting with and then leaving from the untreated square pattern on PDMS surface with different widths. (E,F) Relationship between adhesive force and width of untreated area with (E) different stirring times and (F) different sacrificial layer treatments. (G) Optical images of LM patterns on PDMS surfaces with high resolution, such as spiral, triangular array, diamond array, Chinese knot, and goldfish. Scale bar: 5 mm.
FIGURE 5
FIGURE 5
Conductivity of printed liquid metal lines. (A) Relationship between the resistance of liquid metal lines and their line widths. (B) Influence of the resistance on different twisting angles. (C) Variation of the resistance with stretch rate increasing. (D) Reversible switching of the resistance with repeated stretching and recovering.
FIGURE 6
FIGURE 6
Uniformity of laser-induced flexible microheater via combining O-EGaIn and the sacrificial layer. (A) Schematic of the electronic skin to control the local temperature of the body. (B) Photograph of as-prepared flexible microheater. (C) Uniformity of the liquid metal line. (D) SEM image of the liquid metal spiral line. (E,F) Infrared temperature distribution image of the flexible microheater. (G) Temperature field uniformity test of microheater. (H) Change in temperature of the microheater as a function of time. (I) Relationship between the input voltage and the stable temperature of the microheater.
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