Novel UV tape developed for easy transfer of 2D materials

Two-dimensional materials could revolutionise future technology in the electronics industry. However, the commercialisation of devices that contain 2D materials is challenging, due to the difficulty of transferring these thin materials from where they are made onto the device. Now, researchers from Kyushu University have developed a tape that can be used to stick 2D materials to different surfaces, in an easy and user-friendly way. Lead author Hiroki Ago said transferring 2D materials can be a complex process, because the material can tear or become contaminated, which significantly degrades its unique properties. “Our tape offers a quick and simple alternative, and reduces damage,” Ago said.

The researchers focused on graphene, as it is tough, flexible and light, with high thermal and electrical conductivity. It also has potential applications in biosensing, anti-cancer drug delivery, aeronautics and electronic devices. Ago said that one of the main methods of making graphene is through chemical vapour deposition, where graphene is grown on copper film. However, in order to perform properly, the graphene must be separated from the copper and transferred onto an insulating substrate like silicon.

“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 said.

The researchers wanted to provide an alternative way of transferring graphene. They achieved this by using AI to develop a specialised polymer tape, dubbed “UV tape”, which changes its attraction to graphene when irradiated with UV light. Before exposure to UV light, the tape has a strong adhesion to graphene that allows it to ‘stick’. After UV exposure, the atom bonding changes and decreases the level of adhesion to graphene by approximately 10%. The tape also becomes stiffer and easier to peel off. These changes allow the tape to be peeled off the device substrate while leaving the graphene behind.

The newly designed UV tape is able to transfer 2D materials, including graphene and transition metal dichalcogenides, onto a range of different substrates, including silicon, ceramic, glass and plastic. Image credit: Ago Lab, Kyushu University

The researchers also developed tapes that can transfer other 2D materials, including white graphene (hBN), an insulator that acts as a protective layer when stacking 2D materials, and transition metal dichalcogenides (TMDs), a promising material for future semiconductors. When the researchers analysed the surface of the 2D materials after transfer, they saw a smoother surface with fewer defects than when transferred using the current conventional technique.

Transfer using UV tape also offers other advantages; because it is bendy, and the transfer process doesn’t require the use of plastic-dissolving solvents, flexible plastics can be used as the substrate of the device, expanding potential applications. “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. It’s very promising for medical imaging or airport security,” Ago said.

The UV tape can also be cut to size, so that an exact amount of 2D material is transferred, minimising waste and reducing cost. 2D layers of different materials can also be laid on top of each other in different orientations, allowing researchers to explore new properties from the stacked materials.

Going forward, the researchers aim to expand the size of the UV tape to the scale needed for manufacturers. Currently, the largest wafer of graphene that can be transferred is 10 cm in diameter. The researchers also want to improve stability, so that the 2D materials can be attached to UV tapes for a longer period of time and distributed to end users, such as other scientists. The research findings were published in the journal Nature Electronics.

Top image credit: iStock.com/BONNINSTUDIO