Scientists from Princeton University have invented a superconducting two-dimensional ink that can be easily stored, applied and put into practice, writes Physics Today. This technology, developed by graduate student Xiaoyu Song, her supervisor Leslie Schoop and their colleagues, could revolutionize the manufacturing of microchips and flexible electronics, and pave the way for quantum computers.
Two-dimensional ink is called, allowing you to apply a layer with a thickness of one molecule. Creation of two-dimensional objects using such inks does not require complex techniques, and the resulting “drawings” are resistant to the environment and do not require protective coatings. Thanks to these inks, two-dimensional materials that were previously only available in the laboratory can become commercially available. Electrically conductive ink can be used to draw an electrically conductive pattern. They are used to apply chips to flexible surfaces, and can be useful in a variety of applications, from consumer electronics to supercomputers.
The material for the ink, which was synthesized by the Princeton working group, was tungsten disulfide WS2. It is known in the form of several modifications – the same in their chemical composition, but different in the crystal structure of substances. The so-called 1T'-tungsten disulfide was used for the ink. It is quite difficult to obtain it, since conventional methods give a mixture of various crystal structures. Previously, it was predicted that two-dimensional "flakes" of 1T' tungsten disulfide may have the property of superconductivity. However, there was no convenient way to obtain these "flakes" on an industrial scale.
The technology for obtaining "flakes" was previously worked out on a similar substance – tungsten ditelluride. But the two-dimensional ink made from it turned out to be unstable in air and required complex organic stabilizing molecules. And the existing methods did not allow isolating the pure 1T'-phase of two-dimensional tungsten disulfide; it turned out to be contaminated with other crystalline phases.
As a starting material for the synthesis of tungsten disulfide, scientists usually used potassium-tungsten disulfide, but they were unable to create a monomolecular tungsten disulfide with the desired crystal structure. A Princeton graduate student figured out how to cook the starting material at a high temperature, which created the desired crystal structure with ordered layers of WS2. To remove potassium ions, the resulting substance was immersed in acid, and to exfoliate into monomolecular layers, it was irradiated with ultrasound. Thus, monomolecular layers of tungsten disulfide with the desired structure were obtained. The monolayers were then centrifuged and placed in plain water.
The resulting ink, as it turned out, has a number of amazing properties. They were stable at room temperature and did not deteriorate for a month. With such ink, you can create “patterns” that are also resistant to external influences and do not require protective coatings. They can be applied to a variety of substrates: silicon/silica wafers, indium tin oxide, borosilicate glass, polymeric materials.
But the most valuable thing is the superconducting properties of this ink. They have the properties of a conductor at room temperature and pass into the superconducting state at a temperature of 7.3 ° Kelvin, which is higher than all values for transition metal dichalcogenides (chalcogenides are compounds with sulfur and its analogues according to the periodic table). It is important that the resulting tungsten disulfide has the desired crystal structure, otherwise superconductivity will not work.
The resulting tungsten disulfide ink is a good candidate for topological insulators, that is, substances that are arranged as an insulator in the volume, but as a conductor on the surface. Topological insulators are considered a promising material for dissipationless transistors in quantum computers operating on the quantum Hall effect. (The Hall effect is the occurrence in a conductor in a magnetic field of an electromotive force perpendicular to the directions of the current and magnetic field.)
The resistance of the resulting two-dimensional ink to external influences makes it an interesting material for studying the relationship between topological properties and superconductivity. The ease of synthesis and the stability of the resulting inks suggest that they can be applied in a wide variety of areas, such as quantum computing, the manufacture of integrated circuits, and flexible devices.
