Scientists discover new way to roll atomically thin nanosheets into rolls

Researchers at Tokyo Metropolitan University have developed a new way to roll up atomically thin sheets of atoms to form “nanorolls.” Their unique approach uses sheets of transition metal dichalcogenide with a different composition on each side, achieving a tight roll that results in rolls up to five nanometers in diameter at the center and micrometers in length. Controlling the nanostructure of these volutes promises new developments in the fields of catalysis and photovoltaic devices.

Nanotechnology gives us new tools to control the structure of materials at the nanoscale, promising a comprehensive set of nano tools for engineers to create next-generation materials and devices.

At the forefront of this movement, a team led by Associate Professor Yasumitsu Miyata of Tokyo Metropolitan University is investigating ways to control the structure of transition metal dichalcogenides (TMDCs), a class of compounds with a wide range of interesting properties, such as flexibility. , superconductivity and unique optical absorbance.

In their latest work, published in ACS Nano they set their sights on new ways to make nanoparchments, nanosheets rolled into tight, scroll-like structures. This is an interesting approach to making multi-walled structures: since the structure of each sheet is the same, the orientations of the individual layers are aligned with each other. However, both existing methods of making nanoparchments have significant problems.

In one, the removal of sulfur atoms from the nanosheet surface creates distortions that cause the sheet to curl; but in doing so, they destroy the crystalline structure of the leaf. In the other, a solvent is introduced between the nanosheet and the substrate, peeling the sheet from the base and allowing the formation of defect-free nanorolls. However, the tubular structures thus produced tend to have large diameters.

Instead of approaches like this, the team developed a new way to roll up the leaves. Starting with a single-layer molybdenum selenide nanosheet, they treated the nanosheet with a plasma and replaced the selenium atoms on one side with sulfur; these structures are called Janus nanosheets, named after the ancient two-faced god. Gently adding a solvent then detaches the leaves from the base, which then spontaneously curl into whorls due to the asymmetry between the sides.

These new nanoscrolls are several microns in length, which is significantly longer than previously manufactured single-walled TMDC nanosheets. What’s more, they were found to be tighter than ever, with a center measuring up to five nanometers in diameter, meeting theoretical expectations. The rollers were also found to interact strongly with polarized light and possess hydrogen-producing properties.

With unprecedented control over the nanostructure, the team’s new method provides the basis for investigating new applications of TMDC nanoscrolls to catalysis and photovoltaic devices.