'Native oxide' allows controllable thinning of two-dimensional materials

(Nanowerk News) Two-dimensional (2D) materials today represent one of the most popular research topics in materials science. Being systems with huge surface area (in their monolayer limit, they can be considered as systems with only surface), investigating how they interact with the environment is of crucial importance.
As far as chemical interactions are concerned, even for materials that were previously thought to be quite stable in air, such as transition metal dichalcogenides (TMDs), novel studies revealed degradation (e.g., by oxidation) upon exposure to air.
In a paper published in ACS Nano ("A Scalable Method for Thickness and Lateral Engineering of 2D Materials"), an international team of researchers show how to take advantage of the natural interaction of 2D materials with air to reduce their thickness with (sub-)monolayer precision.
A Scalable Method for Thickness and Lateral Engineering of 2D Materials
(Reprinted with permission by American Chemical Society)
The approach is conceptually simple, and based on a scalable and controllable oxidation/etching process. The top layer(s) of a given layered crystal is first oxidized in air and then selectively etched away upon immersion in a proper reagent. This is very similar to what happens when the native oxide film is etched away from the surface of a silicon substrate, upon immersion into hydrofluoric acid.
The method works for several Ge-based 2D materials just using water as the etching reagent, but it may be extended to other 2D materials, such as black phosphorous and TMDs.
In addition to using this method for reducing the thickness at will, when applied in combination with lithography it can also be used to define precise local patterns in 2D materials.
Because the physical properties of 2D materials depend strongly on the number of layers, this study reporting a facile and low-cost method to engineering them could further promote their integration in functional devices.
Source: University of Rome "Tor Vergata"
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