Arthur T Knackerbracket has found the following story:
A variety of two-dimensional materials that have promising properties for optical, electronic, or optoelectronic applications have been held back by the fact that they quickly degrade when exposed to oxygen and water vapor. The protective coatings developed thus far have proven to be expensive and toxic, and cannot be taken off.
Now, a team of researchers at MIT and elsewhere has developed an ultrathin coating that is inexpensive, simple to apply, and can be removed by applying certain acids.
The new coating could open up a wide variety of potential applications for these "fascinating" 2-D materials, the researchers say. Their findings are reported this week in the journal PNAS, in a paper by MIT graduate student Cong Su; professors Ju Li, Jing Kong, Mircea Dinca, and Juejun Hu; and 13 others at MIT and in Australia, China, Denmark, Japan, and the U.K.
Research on 2-D materials, which form thin sheets just one or a few atoms thick, is "a very active field," Li says. Because of their unusual electronic and black phosphorus and a whole category of materials known as transition metal dichalcogenides (TMDs), corrode when exposed to humid air or to various chemicals. Many of them degrade significantly in just hours, precluding their usefulness for real-world applications.
"It's a key issue" for the development of such materials, Li says. "If you cannot stabilize them in air, their processability and usefulness is limited." One reason silicon has become such a ubiquitous material for electronic devices, he says, is because it naturally forms a protective layer of silicon dioxide on its surface when exposed to air, preventing further degradation of the surface. But that's more difficult with these atomically thin materials, whose total thickness could be even less than the silicon dioxide protective layer.
There have been attempts to coat various 2-D materials with a protective barrier, but so far they have had serious limitations. Most coatings are much thicker than the 2-D materials themselves. Most are also very brittle, easily forming cracks that let through the corroding liquid or vapor, and many are also quite toxic, creating problems with handling and disposal.
The new coating, based on a family of compounds known as linear alkylamines, improves on these drawbacks, the researchers say. The material can be applied in ultrathin layers, as little as 1 nanometer (a billionth of a meter) thick, and further heating of the material after application heals tiny cracks to form a contiguous barrier. The coating is not only impervious to a variety of liquids and solvents but also significantly blocks the penetration of oxygen. And, it can be removed later if needed by certain organic acids.
"This is a unique approach" to protecting thin atomic sheets, Li says, that produces an extra layer just a single molecule thick, known as a monolayer, that provides remarkably durable protection. "This gives the material a factor of 100 longer lifetime," he says, extending the processability and usability of some of these materials from a few hours up to months. And the coating compound is "very cheap and easy to apply," he adds.
More information: Cong Su et al. Waterproof molecular monolayers stabilize 2-D materials, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1909500116
(Score: 2) by sonamchauhan on Sunday October 06 2019, @12:10PM (4 children)
There's been a buzz about "2D materials" like graphene in recent years. In general, what's special about them?
I understand 2D materials only have a single layer of atoms. But, compared to bulk-scale, what properties tend to differ in "2D" and why?
(Score: 5, Informative) by janrinok on Sunday October 06 2019, @12:45PM (1 child)
The most famous 2D material is graphene [wikipedia.org]. As the link indicates, it has numerous interesting chemical, electrical , optical and other properties and is used in quite a few innovative ideas, particularly in electronics. However, graphene is far from being alone, there are many other materials that are of significant interest. [wikipedia.org]
The reason that they have been reported on increasingly in recent years is that we are only just discovering how to manufacture them reliably and thus discovering their useful properties.
(Score: 2) by sonamchauhan on Tuesday October 08 2019, @05:13AM
Thank you sir!
(Score: 0) by Anonymous Coward on Sunday October 06 2019, @02:37PM (1 child)
The thinner the material, the more quantum effects dominate, completely changing the properties.
(Score: 2) by sonamchauhan on Monday October 07 2019, @08:50AM
thank you!