Research Team Develops Anticorrosive Coating for 2D Materials

This diagram shows an edge-on view of the molecular structure of the new coating material. The thin layered material being coated is shown in violet at bottom, and the ambient air is shown as the scattered molecules of oxygen and water at the top. The dark layer in between is the protective material, which allows some oxygen (red) through, forming an oxide layer below that provides added protection. Image and caption courtesy of the researchers/MIT News.

A team of researchers culled from various departments at the Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts, USA), along with researchers from several partnering universities and organizations, have developed an ultrathin anticorrosive coating for two-dimensional (2D) materials.

Based on a family of compounds known as linear alkylamines, the new coating can be applied in layers that are 1 nm thick and forms a contiguous barrier once the material is heated after application. This “unique approach” produces a monolayer that is very thin yet remarkably durable, according to Ju Li, a professor in MIT’s Materials Science and Engineering department and a researcher in the protective coating project. As a result of this protective monolayer, adds Li, the life of materials can be extended for periods ranging from a few hours to months.

Applying the coating is a simple process of placing the 2D material in a bath of liquid hexylamine, a form of the linear alkylamine. After approximately 20 minutes, the liquid hexylamine builds a protective coating at a temperature of 266 °F (130 °C). From there, the material is immersed for another 20 minutes in vapor of the same hexylamine for a smooth, crack-free finish. “You just put the wafer into this liquid chemical and let it be heated,” said MIT graduate student Cong Su.

As opposed to previous protective coatings for 2D materials, the new coating is inexpensive and easy to both apply and remove. In addition, the coating cannot be penetrated by many liquids and solvents, and it blocks oxygen to a significant extent. All of these properties make it potentially useful for a variety of 2D materials, such as transition metal dichalcogenides (TMDs) and black phosphorous, as well as in a variety of applications, including optics, electronics, and optoelectronics, according to the researchers. 

While 2D materials have many promising applications, they quickly corrode when exposed to oxygen, water vapor, or various chemicals. This compromises the materials’ utility in real-life scenarios. “If you cannot stabilize them in air, their processability and usefulness is limited,” Li said. Currently, silicon serves as a common protective layer for electronic devices but is less useful for atomically thin materials that are slighter than the silicon layers themselves. In addition to coating thickness issues, other coatings have significant drawbacks, including brittleness and toxicity.

But with the new coating, Su points out, “the first hurdle to using these fascinating 2D materials” can be cleared. “Practically speaking, you need to deal with the degradation during processing before you can use these for any applications,” which is a step that has now been accomplished as a result of the research team’s new coating, Su said.

Several researchers from the project, including Li and Su, collaborated on a paper that appears in the journal Proceedings of the National Academy of Sciences (PNAS)

Source: MIT News,