The use of molybdenum disulfide as a lubricant has been known since the 17th century, when settlers used it to lubricate carriage axles. Since the 1940s, the substance has been widely used as a component of lubricants. In nature, molybdenum disulfide occurs in the form of a mineral called molybdenite (pictured)
Moore's Law is an empirical assumption that the number of transistors in integrated circuits doubles every few years. However, this law has begun to malfunction as transistors are now so small that current silicon-based technologies cannot offer further opportunities to reduce their physical size.
A group of scientists from the University of New South Wales (Australia) and the University of California at Los Angeles (UCLA) have published description of the technology for the production of two-dimensional semiconductors, which theoretically can solve the problem.
Two-dimensional semiconductors allow the propagation of electrons along the plane, which has a number of advantages: 1) very convenient switching of the transistor from open to closed state and vice versa; 2) directional movement of electrons without scattering, that is, on two-dimensional materials, you can make transistors with zero electrical resistance, which do not waste energy at all when turned on / off. Such materials are called superconductors.
If the resistance is zero, then what happens, superconducting processors will not heat up at all?
However, about everything in order.
Yes, in theory we can actually get zero resistance transistors. But in fact, there are many technological barriers that need to be overcome to create such advanced ultra-thin semiconductors. One of the obstacles is that the deposited ultra-thin films are too heterogeneous, that is, with grain boundaries. These boundaries represent the interface between two crystallites in a polycrystalline material, a defect in the crystal structure. The charge carriers seem to bounce off them and, therefore, resistance losses increase.
One of the most promising ultra-thin semiconductors is molybdenum disulfide (MoS 2 ), the electronic properties of which have been studied over the past two decades.
However, the production of two-dimensional MoS 2 on an industrial scale has proven to be a real challenge. No industrial MoS 2 deposition technology has yet demonstrated the possibility of obtaining a film without grain boundaries, which is critically important for the semiconductor industry. And this is where we come to the scientific paper that was published by researchers from the School of Chemical Engineering at the University of New South Wales and UCLA. They developed a new approach to self-precipitation of MoS 2 , which eliminates the grain boundaries mentioned above.
The unique ability to eliminate graininess is achieved by using gallium metal in a liquid state. Gallium is an amazing metal with a low melting point of only 29.8 ° C. This means that at room temperature it is solid, but if you take it in the palm of your hand, it immediately melts. It becomes liquid, so its surface is atomically smooth. In doing so, the liquid remains a metal, so that the surface provides a large number of free electrons to facilitate chemical reactions.
By bringing the sources of molybdenum and sulfur closer to the surface of liquid gallium, more precisely, a eutectic alloy of indium with gallium, scientists were able to implement chemical reactions that form molybdenum-sulfur bonds in order to obtain the necessary film of MoS 2... The formed two-dimensional material is deposited on an atomically smooth gallium surface, so it naturally forms a perfectly flat shape without graininess. Self-deposition of MoS x on the surface of an indium-gallium eutectic alloy (EGaIn). At further steps of the technological process, a two-dimensional semiconductor film with an ideal structure without graininess is obtained. The process can be carried out on an industrial scale. The illustration above shows how MoS 2 self-precipitates . The illustration below shows the sheets themselves. High-resolution X-ray photoelectron spectroscopy of MoS 2 crystalline sheets . Illustrated G and F: crystal diagram and real octagonal crystal structure
This is a very important step for the industrial production of super-smooth planar semiconductors.
UNSW researchers plan to improve the technology to create other two-dimensional semiconductors and dielectric materials that are used in microelectronics. The scientists emphasize that this method represents a versatile deposition procedure for any large two-dimensional transition metal dichalcogenide (2D TMD or TMD) that can be adapted for large-scale production, replacing traditional 2D TMD methods.
The scientific article was published on October 2, 2020 in the journal Advanced Functional Materials ( doi: 10.1002 / adfm.202005866 ).
