Layers of molybdenum disulfide, with an ultra small thickness of three mere atoms were made in the lab of Jiwoong Park, associate professor of chemistry and chemical biology and member of the Kalvi Institute at Cornell for Nanoscale Science. The films were made and grown by PD associate Kibum Kang and grad student Saien Xie. Their work is published online in the journal Nature on 30th April.
“The electrical performance of our materials was comparable to that of reported results from single crystals of molybdenum disulfide, but instead of a tiny crystal, here we have a 4-inch wafer,” Park said.
Molybdenum disulfide, which has gained a lot of attention over the globe for its outstanding chemical properties, has previously been grown only in disjointed, “archipelago”-style single crystal formations, said Park. However, the ultimate goal is to convert it into making smooth, flat, super-thin sheets, making it the bridge to actual devices.
The researchers were able to achieve this extraordinary feat by customizing the growth conditions of their films through a technique called MOCVD or metal organic chemical vapor deposition which is already practiced in industry but through the use of different materials.
Systematically, Park’s team optimized the manner to make the films, tweaking conditions and temperatures similar to experimenting in kitchen. They discovered that their crystals grew perfectly stitched together, with only a tiny bit of hydrogen and in completely dry conditions.
Demonstration of the film’s efficacy was also done when they were put on one another making more layers alternating with silicon dioxide and emplyoing standard photolithography. This effectively proved that these three-atom-thick thick semiconducting films can be created into multi-level devices of unsurpassed thickness.
The method of MOCVD for thin film generation is seemingly quite common. The researchers displayed the ability to simply tune the precursor to make other films such as a tungsten disulfide film with different electrical properties and color. They envision perfecting the process for making the atomically thin films of all varieties, such as a packet of colored paper from which exciting electronic and optoelectronic devices can be derived.
“These were only the first two materials, but we want to make a whole palette of materials,” Park said.