Enhancement of the Conductivity and Uniformity of Silver Nanowire Flexible Transparent Conductive Films by Femtosecond Laser-Induced Nanowelding

Subwavelength Quasi-Periodic Array for Infrared Antireflection

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm² area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system.

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

Continuous Wave Laser Nanowelding Process of Ag Nanowires on Flexible Polymer Substrates

In this paper we present the laser nanowelding process of silver nanowires (AgNWs) deposited on flexible polymer substrates by continuous wave (CW) lasers. CW lasers are cost-effective and can provide moderate power density, somewhere between nanosecond pulsed lasers and flash lamps, which is just enough to perform the nanowelding process efficiently and does not damage the nanowires on the polymer substrates. Here, an Nd:YAG CW laser (wavelength 532 nm) was used to perform the nanowelding of AgNWs on polyethylene terephthalate (PET) substrates. Key process parameters such as laser power, scan speed, and number of scans were studied and optimized, and mechanisms of observed phenomena are discussed. Our best result demonstrates a sheet resistance of 12 ohm/squ with a transmittance at λ = 550 nm of 92% for AgNW films on PET substrates. A transparent resistive heater was made, and IR pictures were taken to show the high uniformity of the CW laser nanowelded AgNW film. Our findings show that highly effective and efficient nanowelding can be achieved without the need of expensive pulse lasers or light sources, which may contribute to lower the cost of mass producing AgNWs on flexible substrates.

High-Performance Flexible Transparent Electrodes Fabricated via Laser Nano-Welding of Silver Nanowires

Silver nanowires (Ag-NWs), which possess a high aspect ratio with superior electrical conductivity and transmittance, show great promise as flexible transparent electrodes (FTEs) for future electronics. Unfortunately, the fabrication of Ag-NW conductive networks with low conductivity and high transmittance is a major challenge due to the ohmic contact resistance between Ag-NWs. Here we report a facile method of fabricating high-performance Ag-NW electrodes on flexible substrates. A 532 nm nanosecond pulsed laser is employed to nano-weld the Ag-NW junctions through the energy confinement caused by localized surface plasmon resonance, reducing the sheet resistance and connecting the junctions with the substrate. Additionally, the thermal effect of the pulsed laser on organic substrates can be ignored due to the low energy input and high transparency of the substrate. The fabricated FTEs demonstrate a high transmittance (up to 85.9%) in the visible band, a low sheet resistance of 11.3 Ω/sq, high flexibility and strong durability. The applications of FTEs to 2D materials and LEDs are also explored. The present work points toward a promising new method for fabricating high-performance FTEs for future wearable electronic and optoelectronic devices.

Radio Frequency Induction Welding of Silver Nanowire Networks for Transparent Heat Films

Transparent heat films (THFs) are attracting increasing attention for their usefulness in various applications, such as vehicle windows, outdoor displays, and biosensors. In this study, the effects of induction power and radio frequency on the welding characteristics of silver nanowires (Ag NWs) and Ag NW-based THFs were investigated. The results showed that higher induction frequency and higher power increased the welding of the Ag NWs through the nano-welding at the junctions of the Ag NWs, which produced lower sheet resistance, and improved the adhesion of the Ag NWs. Using the inductive welding condition of 800 kHz and 6 kW for 60 s, 100 ohm/sq of Ag NW thin film with 95% transmittance at 550 nm after induction heating could be decreased to 56.13 ohm/sq, without decreasing the optical transmittance. In addition, induction welding of the Ag NW-based THFs improved haziness, increased bending resistance, enabled higher operating temperature at a given voltage, and improved stability.

Invisible Silver Nanomesh Skin Electrode via Mechanical Press Welding

Silver nanowire (AgNW) has been studied as an important material for next-generation wearable devices due to its high flexibility, high electrical conductivity and high optical transmittance. However, the inherently high surface roughness of AgNWs and low adhesion to the substrate still need to be resolved for various device applications. In this study, an embedded two-dimensional (2D) Ag nanomesh was fabricated by mechanical press welding of AgNW networks with a three-dimensional (3D) fabric shape into a nanomesh shape, and by embedding the Ag nanomesh in a flexible substrate. The effect of the embedded AgNWs on the physical and electrical properties of a flexible transparent electrode was investigated. By forming embedded nanomesh-type AgNWs from AgNW networks, improvements in physical and electrical properties, such as a 43% decrease in haziness, 63% decrease in sheet resistance, and 26% increase in flexibility, as well as improved adhesion to the substrate and low surface roughness, were observed.