In a study published in Nano Letters, Tokyo Metropolitan University researchers created the first tungsten disulfide nanotubes that point in the same direction upon formation.
They employed chemical vapor deposition to create arrayed tungsten disulfide nanotubes, each made up of rolled nanosheets, on a sapphire surface under precisely regulated conditions. By resolving the long-standing problem of jumbled orientations in collected amounts of nanotubes, the team’s method holds promise for the exotic anisotropy of single nanotubes in real-world device applications.
Nanotubes comprise sheets of atoms folded into a nanoscale tube, converting a two-dimensional sheet into a one-dimensional one. They are known to have various properties that rely on how the ends of the sheet meet. Carbon nanotubes, for example, can be conducting or semiconducting depending on whether a “twist” remains in the tube structure after a nanosheet is rolled up.
On the other hand, tungsten disulfide nanotubes are made of nanosheets that have been repeatedly rolled to produce a nanostructure like a Swiss roll. They are a strong contender for use in semiconducting devices because, interestingly, they are always known to be semiconducting, regardless of how they are rolled. However, to achieve all of the desired characteristics of individual tungsten disulfide nanotubes, devices need many nanotubes in one location.
This is possible, but there is a big catch: they typically point in random directions. This is known to negatively affect characteristics such as carrier mobility, directly impacting the device’s usefulness. Additionally, any special optical qualities are obscured. Since numerous nanotubes are made up of a jumbled pile, their properties will not replicate the direction-dependent characteristics of single nanotubes, no matter how intriguing such characteristics may be.
A Tokyo Metropolitan University group led by Professor Kazuhiro Yanagi has now developed a novel method that could potentially address this persistent issue. To create a template for growing nanotubes, they employed a sapphire substrate with a certain crystalline plane exposed to the surface.
To create multi-walled rolled tungsten disulfide nanotubes on the surface, tungsten and sulfur-containing gases were introduced to the substrate at specific rates and temperatures to enable chemical vapor deposition. They discovered that, in the correct circumstances, each nanotube pointed in a certain crystallographic direction. Arrayed tungsten disulfide nanotubes have never been grown before.
The scientists demonstrated that their arrays of nanotubes retain individual nanotubes’ unique, anisotropic properties, particularly in their interaction with light. They think that their technology will enable tungsten disulfide nanotubes in real-world electronics that fully exploit their unique electric and optoelectronic capabilities.
The study was supported by JSPS KAKENHI Grant Numbers JP17H06124, JP20H02573, JP21H05017, JP22H05469, JP23H00259, JP24H01200, JP23K23179, JP22H05468, JP23H05469, JP22K18986, JP21H05235, JP21H05232, JP20H05664, JP21H01012, JP21H05234 and JP21H05232, the JST CREST Program through Grant Numbers JPMJCR17I5 and JPMJCR24A5, the US-JAPAN PIRE collaboration, Grant Number JPJSJRP20221202, the JST ASPIRE Program through Grant Number JPMJAP2310, a Tokyo Metropolitan Government Advanced Research Grant, Grant Number H31-1, and the JST FOREST Program through Grant Number JPMJFR213K.
Journal Reference:
Ahad, A., et al. (2024) Synthesis of Arrayed Tungsten Disulfide Nanotubes. Nano Letters. doi.org/10.1021/acs.nanolett.4c03895.
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