Polymer tape's sticky properties change when irradiated with UV light.

The discovery of graphene – a material with an ever-increasing number of uses – came from the humblest of beginnings: a hunk of graphite, and Scotch tape. Now, tape is once again taking center stage as an unlikely hero of science and technology as researchers from Japan have developed an adhesive with stickiness properties that can be programmed by UV light.

Nanomaterials like graphene, which are mere atoms thick and known as two-dimensional (2D) materials, are on their way to revolutionizing technologies across multiple industries. However, their inherent fragility makes the manufacturing of devices that contain 2D materials a challenge due to the difficulty in handling, moving, and attaching their components.

To solve this dilemma, Japanese adhesive manufacturer Nitto Denko and a research team from Kyushu University have collaborated to develop a series of tapes that can be used to easily transfer 2D materials to various surfaces.

"Transferring 2D materials is typically a very technical and complex process; the material can easily tear, or become contaminated, which significantly degrades its unique properties," says lead author Professor Hiroki Ago of Kyushu University's Global Innovation Center. "Our tape offers a quick and simple alternative, and reduces damage."

Unsticking a costly process

Made from an atom-thick sheet of carbon, graphene is flexible, robust, and sports high thermal and electrical conductivity that is tailor-made for tech applications from aeronautics to medicine.

Creating graphene for these cutting-edge applications, however, is difficult and costly.

"One of the main methods of making graphene is through chemical vapor deposition, where graphene is grown on copper film. But to perform properly, the graphene must be separated from the copper and transferred onto an insulating substrate, like silicon," Ago explained. "To do this, a protective polymer is placed over the graphene, and the copper is then removed using etching solution, such as acid. Once attached to the new substrate, the protective polymer layer is then dissolved with a solvent. This process is costly, time-consuming, and can cause defects to the graphene's surface or leave traces of the polymer behind."

Ago's team found that using UV tape to transfer graphene instead of polymer better maintained the material's integrity and reduced defects.

Ago Lab, Kyushu University

The UV Tape changes its attraction to materials of various properties when irradiated with UV light.

The unexposed tape has strong adhesion, while after UV exposure, the atom bonding decreases the level of adhesion by roughly 10% and stiffens the tape. Combined, these property changes allow the tape to be peeled from the substrate easily while leaving the 2D application behind.

The various developed UV tapes can transfer 2D material onto a range of different substrates, including ceramic, glass, plastic, and silicon – all more efficiently while maintaining higher surface integrity of the materials than traditional processes.

The other designs can transfer white graphene, an insulator that can be inserted as a protective layer when stacking 2D materials, and transition metal dichalcogenides, a promising material for the next generation of semiconductors.

Making 2D transfer child's play

The team has succeeded in transferring wafers of graphene up to 10 centimeters in diameter. The process can be done easily by hand or scaled up for mass production using machines. Because the tape is flexible, the transfer process doesn't require the use of solvents, while equally flexible plastics can also be used as the recipient substrate, expanding potential applications even further.

"For example, we made a plastic device that uses graphene as a terahertz sensor. Like X-rays, terahertz radiation can pass through objects that light can't, but doesn't damage the body," Ago said. "It's very promising for medical imaging or airport security."

What's more, the UV tape can be cut so that the exact amount of 2D material needed is transferred, minimizing waste and further reducing cost. 2D layers of different materials can also be layered in different orientations, allowing researchers to explore new emerging properties from the stacked materials.

Professor Ago's team aims to expand the size of the UV tape to the scale needed for commercial manufacturing, as well as resolve the problem of small defects from wrinkles and bubbles that form, and improve stability for distribution so that 2D materials can be attached to UV tapes for longer durations.

"The end users can then transfer the material onto their desired substrate by applying and removing the UV tape like a child's sticker, with no training needed," said Ago. "Such an easy method could fundamentally change the style of research and accelerate the commercial development of 2D materials."