Researchers are looking to a material that they once gave up on as a way to make smaller, faster, more energy efficient transistors.

Molybdenite, a mixture of molybdenum and sulfur also called molybdenum disulfide (MoS2), has been shown to have better properties than Silicon It's a relatively common material that is sometimes used as a specialty lubricant and as an ingredient in Teflon.

Transistors have been made of silicon since the beginnings of the industry. But after 50 years the limits of the material are being reached. Molybdenite can be made into smaller transistors than Silicon, down to 0.65 nanometers thick and 4-5 nanometers long. Silicon's minimum thickness is twice or three times that, and that also means its minimum length is in the 10 nanometer range.

Andras Kis, a professor of electrical engineering at Switzerland's École Polytechnique Fédérale de Lausanne, and one of the lead authors on a paper recently published in Nature Nanotechnology, said he got interested in molybdenite because everyone else was already working on graphene. I had to think of something more original, he said.

A lot of research was and is being done on making sheets of graphene, which is a lattice of a single sheet of carbon atoms, and looking at the possibilities for electronic components. There was some work done with molybdenite, Kis said, but at that time the scientists working on it were unsuccessful in creating a functioning transistor.

Kis decided to try again. What he found was that molybdenite can do some things even better than silicon. As important, it has properties that graphene doesn't have.

First, it is a semiconductor. A semiconductor is a material that can conduct electricity when a certain threshold voltage is applied, but is an insulator below that point. This is because of what are called band gaps in the material. The band gap is the barrier that an electron has to hop over to complete the circuit. Silicon has such band gaps, as do germanium and molybdenite. Graphene does not. To get the electronic behavior you want from graphene, it has to be laid out in perfectly straight lines at very small scales. This is not easy to do.

Second, the molybdenite turns off more efficiently than silicon does. Molybdenite has a higher band gap than silicon. In ordinary silicon circuits, there are a few electrons that can jump over the band gap at higher temperatures, for example. But the higher band gap in molybdenite means that happens less often. It also means that an integrated circuit made of molybdenite will use a lot less power than its conventional silicon counterpart.

Molybdenite also has better mobility than silicon -- that is, it takes less energy to get electrons moving through the material of the same thickness. A thick piece of silicon, Kis says, has high mobility. The smaller it is, the harder it is to get electrons to go through it and the more power is necessary. Molybdenite uses much less energy to do the same electronic work.

It will be some years before electronic circuits are made of molybdenite, as silicon technology is probably good for at least another few years. Kis plans on experiments with making actual circuits next, as this demonstrates that there are other materials that can work when silicon reaches its limits.

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