Researchers Make Inkjet Printable 2D Semiconductors

Method for producing biocompatible water-based inks could bring 2D crystal heterostructures from the lab to real-world products.

Above: Fully inkjet-printed heterostructures on Si/SiO₂. a, Schematic of an all-printed Gr_B/WS₂/GrT heterostructure on Si/SiO₂. b, Left: Optical picture of an array of 4 x 4 Gr_B/WS₂/Gr_T heterostructures printed on Si/SiO₂. Right: Optical picture of one of the heterostructures, showing the two graphene electrodes and the square of photoactive material.

Researchers at the University of Manchester, led by Cinzia Casiraghi, have developed a method of producing water-based and inkjet printable 2D material inks, which could bring 2D crystal heterostructures from the lab into real-world products such as smart packaging applications and identification tags. Notably these inks are biocompatible, which extends their use to biomedical applications.

As well as graphene, the team has successfully exfoliated and printed a range of 2D semiconductors including MoS₂, WS₂ and hexagonal boron nitride (h-BN). Using this approach, it has developed efficient light detectors, and programmable logic memory devices able to store information encoded in binary form. The work was done in collaboration with the University of Pisa and the results reported in Nature Nanotechnology.

2D materials show great promise for use in flexible electronics, because their atomic thickness allows for maximum electrostatic control, optical transparency, sensitivity and mechanical flexibility. In addition, because 2D crystals are characterised by out-of-plane van der Waals interactions, they can be combined easily in one multilayer stack, offering unprecedented control of the properties and functions of the resulting heterostructure-based device.

In this framework, inkjet printing can provide an attractive route to low-cost and large-scale fabrication of heterostructures on any substrate. Furthermore, inkjet printing allows the fabrication of very complex heterostructures, which can provide multiple functions and improved performance. In contrast, methods such as vacuum filtration and spin/spray coating, which have been used previously, offer poor control of the thickness and roughness of the layers and have limited design flexibility, according to the researchers.

Current ink formulations, which would allow heterostructures to be made by simple and low-cost methods, are far from ideal – either containing toxic solvents or requiring time-consuming and expensive processes. In addition, none are optimised for heterostructure fabrication.

Casiraghi said: “Due to the simplicity, flexibility and low cost of device fabrication and integration, we envisage this technology to find potential in smart packaging applications and labels, for example for food, pharmaceuticals and consumer goods, where thinner, lighter and cheaper and easy to integrate components are needed”.

Daryl McManus, PhD student said: “These inks provide a perfect platform to fully exploit the range of properties of 2D materials by allowing for the first time a precise and scalable method for fabrication of devices of arbitrary complexity utilising 2D materials.”

‘Water-based and biocompatible 2D crystal inks for all-inkjet printed heterostructures’ by Daryl McManus et al; Nature Nanotechnology (2017) doi:10.1038/nnano.2016.281