Materials that are only atoms thick, known as two-dimensional (2D) materials, will revolutionize future technologies, including the electronics industry. However, the commercialization of devices containing 2D materials has been challenged by the difficulty of transferring these extremely thin materials from the manufacturing site to the device. Researchers have created UV-sensitive tape that allows for easier, cheaper, and less damaging transfers of two-dimensional materials like graphene.

Researchers at Kyushu University and Nitto Denko have developed a tape that changes its "stickiness" to two-dimensional materials under UV irradiation. Source: Kyushu University Argo Laboratory

Now, a research team at Kyushu University, in collaboration with Japan's Nitto Denko, has developed a tape that can be used to stick 2D materials to many different surfaces, and is simple and easy to use. Their research results were published in the journal "Nature Electronics" on February 9, 2024.

"Transferring 2D materials is usually a very technical and complex process; the materials can easily tear or become contaminated, greatly reducing their unique properties," said lead author Professor Hiroki Ago of Kyushu University's Global Innovation Center. "Our tape provides a quick, easy alternative and reduces damage."

Researchers at Kyushu University have found that using UV tape instead of polymers to transfer graphene better maintains the integrity of the material and reduces defects. Source: Kyushu University Argo Laboratory

The researchers first focused on graphene. Graphene is made from thin sheets of carbon atoms and is tough, flexible, lightweight, and has high thermal and electrical conductivity. Graphene has been hailed as a "miracle material" since its discovery and can be used in fields such as biosensing, anti-cancer drug delivery, aviation and electronic equipment.

"One of the main methods of making graphene is chemical vapor deposition, which involves growing graphene on a copper film. But to function properly, graphene must be separated from the copper and transferred to an insulating substrate such as silicon," Professor Ago explained. "To do this, the graphene needs to be covered with a protective polymer, and then an etching solution such as acid is used to remove the copper. Once attached to the new substrate, a solvent is used to dissolve the protective polymer layer. This process is expensive, time-consuming, and can cause defects on the graphene surface or leave traces of the polymer."

Professor Argo and his colleagues therefore aimed to provide an alternative method of transferring graphene. They used artificial intelligence technology to develop a special polymer tape called "UV tape" that changes its attraction to graphene when exposed to ultraviolet light.

The newly designed UV tape is capable of transferring 2D materials, including graphene and transition metal dichalcogenides, onto a range of different substrates, including silicon, ceramics, glass and plastics. Source: Kyushu University Argo Laboratory

Before UV irradiation, the tape has strong adhesion to graphene and can "stick" it. However, after ultraviolet irradiation, the atomic bonds changed and the adhesion to graphene decreased by about 10%. UV tape also becomes slightly harder and easier to peel off. Taken together, these changes allow the tape to be peeled off the device substrate while leaving the graphene behind.

The researchers also developed tapes that can transfer two other two-dimensional materials: white graphene (hBN), an insulator that can act as a protective layer when two-dimensional materials are stacked, and transition metal dichalcogenides (TMDs), ideal for next-generation semiconductors.

Importantly, when the researchers looked closely at the surface after the 2D material was transferred, they found that the 2D material surface was smoother and had fewer defects than when it is currently transferred using traditional techniques. When testing the properties of these materials, they also found that they were more efficient.

So far, researchers at Kyushu University and Nitto Denko have successfully transferred graphene wafers up to 10 centimeters in diameter using UV tape. For smaller UV tapes, sticking and peeling can be done by hand. However, machines are very useful when it comes to mass production. Source: Nakatani et al., Nature Electronics,

Using UV tape for transfers offers many other advantages over current transfer technologies. Because UV tapes can bend and the transfer process does not require the use of plastic-dissolving solvents, flexible plastics can be used as the substrate for the device, expanding the range of 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 cannot pass through, but it will not cause harm to the human body," Professor Ago said. "It has great potential in medical imaging or airport security."

What's more, UV tape can be cut to size, so only the exact amount of 2D material needs to be transferred, minimizing waste and reducing costs. Two-dimensional layers of different materials can also be easily stacked on top of each other in different orientations, allowing researchers to explore new properties of superimposed materials.

Next, the researchers aim to scale up the UV tape to the scale required by manufacturers. Currently, the largest graphene wafer that can be transferred is 10 centimeters in diameter. Professor Argo and his colleagues are also working on solving the problem of wrinkles and bubbles forming in the tape, which can cause small defects.

The team also hopes to improve the stability of the 2D material so that it can be attached to the UV tape for longer and distributed to end users, such as other scientists.

"The end-user simply applies and removes the UV tape like a child's sticker and transfers the material to the desired substrate without any training," Professor Ago said. "This facile approach could fundamentally change the style of research and accelerate the commercial development of 2D materials."

Compiled source: ScitechDaily