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The new semiconductor technique: the door to the applications of the molybdenum sulfide will be opened

According to the overseas media reports, the researchers at North Carolina State University said recently, they have developed a new technique for creating high-quality semiconductor thin films at the atomic scale (The thickness of the film is only the diameter of one atom). Assistant Professor of Materials science and Engineering Cao Linyou said, the new technology can make existing semiconductor technology scaling down to the atomic level, including lasers, diodes and luminous computer chips. 

It is reported, the material researchers studied is molybdenum sulfide, an inexpensive semiconductor material with electronic and optical properties similar to materials already used in the semiconductor industry. However, molybdenum sulfide is different from other semiconductor materials, because it can form the single layer film by one atomic layer-growth without compromising its original properties.

In the new technique, researchers place sulfur and molybdenum chloride powders in a furnace and gradually raise the temperature to 850 degrees Celsius, which vaporizes the powders. The two substances react to form molybdenum sulfide. While still maintain a high temperature, the vapor of molybdenum sulfide is deposited to the substrate, and form molybdenum sulfide thin film.

Cao Linyou said, “the key to success is to find a new growth mechanism of molybdenum sulfide, namely self-limiting growth, and the researchers can accurately control the thickness of the molybdenum sulfide layer by controlling the partial pressure and vapor pressure in the high temperature furnace.” According to introduction, partial pressure is the tendency of atoms or molecules suspended in the air to condense into a solid and settle onto the substrate; Vapor pressure is the tendency of solid atoms or molecules on the substrate to vaporize and rise into the air.

In order to obtain the single layer of molybdenum sulfide on the substrate, the partial pressure must be higher than the vapor pressure. The higher the partial pressure, the more layers of molybdenum sulfide will be deposited to the bottom. If the partial pressure is higher than the vapor pressure of a single layer of atoms on the substrate, but lower than the vapor pressure of two layers, the balance between the partial pressure and the vapor pressure can ensure that thin-film growth automatically stops once the monolayer is formed. This is the "self limiting growth of the film".

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