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Liquid metals yield large 2-D semiconductor films

Spontaneously forming oxide skin offers route to converting gallium, other metals to sulfides

by Mitch Jacoby
February 27, 2017 | A version of this story appeared in Volume 95, Issue 9

This composite includes a photo of liquid gallium droplets and a TEM image showing the characteristic lattice fringes of GaS.
Credit: Nat. Commun.
The spontaneously forming oxide film that stabilizes millimeter-sized gallium droplets (left) offers a simple way to prepare ultrathin crystalline films of gallium sulfide (micrograph, right).

The curious properties of gallium and related liquid metals, “especially the tendency to spontaneously form thin oxide skins in air,” have led researchers in recent years to use these materials for chemical patterning and for making stretchy and self-healing electronics. Now, a team of researchers in Australia and the U.S. has exploited that property to prepare these materials as large, ultrathin patterned semiconductor films via methods that are compatible with electronics industry manufacturing (Nat. Commun. 2017, DOI: 10.1038/ncomms14482). Due to their potential use in microelectronic devices, metal sulfides and other semiconducting chalcogenide compounds keep grabbing attention—especially when researchers report methods for preparing them as atomically thin films. But many of those methods require high temperatures or yield tiny defective flakes, rendering the methods incompatible with the semiconductor industry. Torben Daeneke and Kourosh Kalantar-Zadeh of RMIT University, Melbourne, and coworkers show that those problems can be avoided by using liquid metals. The team deposited gallium on a wafer-sized substrate that had been patterned with a fluorinated compound and then converted the gallium oxide to a high-quality 1.5-nm-thick film of gallium sulfide. The team used a similar method to make large In2S3 films and showed that the materials can be used to build transistors.


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