Researchers have developed an innovative technique for rapidly and efficiently depositing two-dimensional (2D) materials over large areas. This chance discovery could transform the manufacturing of nanosheets, which are crucial for both current and future electronic applications.
A team from Japan, led by Professor Minoru Osada at the Institute for Materials and Systems for Sustainability (IMaSS) at Nagoya University, has made a significant breakthrough in the fast, large-scale deposition of various 2D materials, such as oxides, graphene oxide, and boron nitride. This novel approach, called the ‘spontaneous integrated transfer method’, emerged unexpectedly and has the potential to significantly enhance the fabrication of nanosheets. The results of their research were published in the journal Small.
Nanosheets are remarkably thin, just a few atoms thick, and boast a high surface area relative to their volume, which enables outstanding electronic, optical, mechanical, and chemical characteristics. These properties suggest that nanosheets could lead to breakthroughs in electronics and materials science.
Previously, techniques like chemical vapor deposition (CVD) and the Langmuir-Blodgett (LB) method were commonly used for producing nanosheets. However, these techniques face significant limitations, such as challenges in achieving uniform deposition over large areas and issues with transferring substrates.
While searching for a more effective deposition method, Osada’s team stumbled upon a surprising phenomenon: when nanosheets were introduced to water, they naturally aligned themselves on the water’s surface, forming compact films within just 15 seconds. This occurrence, named the ‘spontaneous spreading phenomenon’, hinted at a more efficient deposition approach.
To test this technique, the researchers placed a mixture containing nanosheets onto the water’s surface. Since ethanol evaporates faster than water, it creates a concentration gradient. Areas where ethanol evaporates more quickly have greater surface tension compared to areas with more ethanol. This difference causes fluid movement from lower to higher tension zones, resulting in convection currents that direct the nanosheets in the solution, leading them to organize into a well-ordered, dense layer on the water.
“The nanosheets effortlessly align and pack tightly, similar to how ice floes come together on water,” explained Osada. “This organized alignment is crucial for achieving uniform and high-quality nanosheet films. We can then easily transfer the completed nanosheet film onto a substrate in just about a minute.”
This technique not only streamlines the production process but also allows for the creation of multilayer films containing 100 to 200 layers—something traditional methods like CVD and LB struggle to achieve. Using atomic force microscopy and confocal laser microscopy, the team confirmed that the nanosheets produced were highly uniform, arranged like pieces in a jigsaw puzzle.
The researchers were impressed by the versatility of this method, successfully applying it to various nanosheet types and structures, thereby enabling the creation of large-area films on substrates of different shapes and materials. “The multilayer films created using this technique demonstrate excellent properties as functional thin films, making them suitable for applications including transparent conductive films, dielectric films, photocatalytic films, corrosion-resistant films, and thermal shielding films,” stated Osada.
In addition to the technological advancements, Osada highlighted the environmental benefits of this method: “This technique is anticipated to be an important eco-friendly process, as it facilitates thin film production on diverse substrates at room temperature using an aqueous solution, without the requirement for vacuum-based film-forming equipment or costly tools, which are typical in traditional thin film techniques.”
