Meng Gao

Fabrication of Nanoscale Circuits on Inkjet‐Printing Patterned Substrates

Nanoscale circuits are fabricated by assembling different conducting materials (e.g., metal nanoparticles, metal nano-wires, graphene, carbon nanotubes, and conducting polymers) on inkjet-printing patterned substrates. This non-litho-graphy strategy opens a new avenue for integrating conducting building blocks into nanoscale devices in a cost-efficient manner.

Inkjet printing wearable electronic devices

In recent years, wearable electronics have experienced tremendous development due to their promising applications in fields such as portable, flexible/stretchable human-interactive sensors, displays, and energy devices. To effectively fabricate wearable electronics, a high-efficient, cost-saving, and eco-friendly manufacture technology is required. Inkjet printing, which rapidly, precisely, and reproducibly deposits a broad variety of functional materials in a non-impact, addictive patterning, and maskless approach, serves as an effective tool for the fabrication of wearable electronics. In this review, the recent advances in inks, strategies, and the applications of inkjet-printed wearable electronics are summarized. Based on uniform and high-resolution patterns, well-compatible functional inks can be deposited to fabricate flexible/stretchable and durable wearable electronics. Perspectives on the remaining challenges and future developments are also proposed.

Flexible Circuits and Soft Actuators by Printing Assembly of Graphene

An effective way to improve the electrical conductivity of printed graphene patterns was demonstrated by realizing the assembly of giant graphene oxide sheets during the printing process. The synergetic effect of printing-induced orientation and evaporation-induced interfacial assembly facilitated the formation of laminar-structured patterns. The resulting patterns after chemical reduction showed excellent electrical conductivity in printed graphene electronics. Because of their high conductivity, mechanical flexibility, and advantage in pattern design, printed graphene electrodes were applied in electrical-driven soft actuators, which can realize controllable deformation with low driving voltage. Such achievements will be of great significance for the development of graphene-based flexible and printed electronics.

Direct-Writing Multifunctional Perovskite Single Crystal Arrays by Inkjet Printing

Perovskite single-crystalline microplate arrays are directly achieved in large scale by inkjet printing, which present high performance lasing property with quality factors up to 863 and RGB (red-green-blue) emission. This facile, nonlithographic method makes its promising applications on multi-integrated coherent light sources and other high-performance integrated optoelectronic applications.

Interface Manipulation for Printing Three‐Dimensional Microstructures Under Magnetic Guiding

Precisely controlled 3D microstructures are printed by 2D interface manipulation. The morphologies of 3D microstructures are deterministically dependent on the receding angles of droplets on the surfaces, and the exact relationship between 3D morphology and interface properties is clarified. Accurate-positioned and oriented-patterned 3D arrays are facilely printed, demonstrating high controllability and large-scale fabrication of uniform 3D microstructures.

Transparent Ag@Au–graphene patterns with conductive stability via inkjet printing

A patterned electrode film with ultrahigh conductive stability and transparency is obtained via inkjet printing based on a kind of high-stability conductive ink and a viscoelastic state substrate. The Ag@Au nanotriangle platelets and graphene oxide hybrid (Ag@Au NTPs–GO) nanomaterial ink was synthesized. Then, it is inkjet-printed on the specific viscoelastic state base to improve the accuracy of patterns, and a flexible and transparent conductive film with Ag@Au nanotriangle platelets and reduced graphene oxide hybrid (Ag@Au NTPs–rGO) patterns was obtained after reduction. The patterns show no undesirable coffee ring effects, and the inkjet-printed rGO-based lines with ∼7 μm width and a film with high transparency (∼98%)are achieved. Meanwhile, the structure models of Ag–rGO and Ag@Au–rGO are built and calculated. It is found that the addition of a thin layer of Au coated on the surface of Ag can effectively reduce the surface energy of the Ag–reduced graphene oxide material and improve the stability of the materials conductivity. These enhancements of the printed film benefit from the core@shell structured nanomaterial, the viscoelastic state substrate and the high resolution patterns. This facile strategy will be significant for highly stable integrated circuit boards and highly transparent devices.

Direct Writing of Patterned, Lead-Free Nanowire Aligned Flexible Piezoelectric Device

A high‐performance flexible piezoelectric nanogenerator (PNG) is fabricated by a direct writing method, which acquires both patterned piezoelectric structure and aligned piezoelectric nanowires simultaneously. The voltage output of the as‐prepared PNG is nearly 400% compared with that of the traditional spin‐coated device due to the effective utilization of stress. This facile printing approach provides an efficient strategy for significant improvement of the piezoresponse.

Sliding three-phase contact line of printed droplets for single-crystal arrays

Controlling the behaviours of printed droplets is an essential requirement for inkjet printing of delicate three-dimensional (3D) structures or high-resolution patterns. In this work, molecular deposition and crystallization are regulated by manipulating the three-phase contact line (TCL) behaviour of the printed droplets. The results show that oriented single-crystal arrays are fabricated based on the continuously sliding TCL. Owing to the sliding of the TCL on the substrate, the outward capillary flow within the evaporating droplet is suppressed and the molecules are brought to the centre of the droplet, resulting in the formation of a single crystal. This work provides a facile strategy for controlling the structures of printed units by manipulating the TCL of printed droplets, which is significant for realizing high-resolution patterns and delicate 3D structures.

Gas/liquid interfacial manipulation by electrostatic inducing for nano-resolution printed circuits

A critical requirement for highly conductive metallic printing circuits is to obtain consecutive and high-resolution printed patterns. However, the aggregation or assembly of metallic nanocrystals in solution is usually random, which perplexes the consecutiveness and resolution of the printed circuits. In this study, we prepared consecutive nano-resolution circuits by gas/liquid interfacial manipulation. Consecutive gas/liquid interfaces were achieved by electrostatic inducing of a cationic metal ink using anionic surfactant onto the gas/liquid interface to form continuous patterns. Gas/liquid interfacial morphology was manipulated by gas/liquid/solid three phase contact line (TCL); Through controlling TCL sliding on different surfaces, submicron or nano-resolution circuits were fabricated, which showed excellent conductivity. This facile strategy showed significant potential for use in wearable electronics and high-resolution electronic circuits.

Printing 1D Assembly Array of Single Particle Resolution for Magnetosensing

Magnetosensing is a ubiquitous ability for many organism species in nature. 1D assembly, especially that arranged in single-particle-resolution regulation, is able to sense the direction of magnetic field depending on the enhanced dipolar interaction in the linear orientation. Inspired by the magnetosome structure in magnetotactic bacteria, a 1D assembly array of single particle resolution with controlled length and well-behaved configuration is prepared via inkjet printing method assisted with magnetic guiding. In the fabrication process, chains in a tip-to-tip regulation with the desired number of particles are prepared in a confined tiny inkjet-printed droplet. By adjusting the receding angle of the substrate, the assembled 1D morphology is kept/deteriorated depending on the pinning/depinning behavior during ink evaporation, which leads to the formation of well-behaved 1D assembly/aggregated dot assembly. Owing to the high-aspect-ratio characteristic of the assembled structure, the as-prepared 1D arrays can be used for magnetic field sensing with anisotropic magnetization M// /M⊥ up to 6.03.