[Image above] Nanoplatelets standing on edge resemble a tiny graveyard. Credit: Koski lab; Brown University
Researchers at Brown University have pioneered a new technique that allows them to produce multilayered and multistructured 2-D semiconductor materials, which are particularly promising for the future of electronics, optical devices, and more.
“What makes silicon telluride very attractive as a 2-D material is that it can be exfoliated or reduced to a monolayer material—just like graphene—but that it mixes the best of all the 2-D worlds: silicon, graphene-like layers, and chalcogenide-like molybdenum disulfide, which has garnered much interest lately,” lead researcher and Brown chemistry professor Kristie Koski writes in an email.
Koski and a team of Brown researchers produced nanoribbons and nanoplatelets of silicon telluride through vapor deposition in a tube furnace. “When heated in the tube, silicon and tellurium vaporize and react to make a precursor compound that is deposited on a substrate by an argon carrier gas. The silicon telluride then grows from the precursor compound,” states a Brown University press release.
Varying furnace temperature and surface treatment generated different shaped structures, each with different crystalline orientations. The team generated nanoribbons (50–1,000 nm wide by 10 μm long) and nanoplatelets that stood straight up on end.
“We see the standing plates a lot,” Koski says in the release. “They’re half hexagons sitting upright on the substrate. They look a little like a graveyard.”
Further, growing the structures on different substrates allowed the researchers to dope the materials, allowing for an even wider variety of potential materials and applications. Growing on sapphire substrates, for example, doped the silicon telluride with aluminum.
Koski says that opto-electronic devices, such as photodetectors and LEDs, are promising applications of the new technology.
“Silicon telluride is completely transparent but brilliant red. It’s a native p-type semiconductor—in the world of 2-D materials, very few are natively p-type,” Koski says in the email. “Phosphorene (2-D phosphorus) is one of the only examples that comes to mind. Silicon telluride has a photoluminescence peak in the red, which is potentially attractive for LEDs or for use as a photodetector.”
Another potential application is batteries. Koski writes, “Silicon right now—especially silicon nanowires—is a key material for lithium-ion batteries. We found that silicon telluride also uptakes fairly sizable amounts of lithium and magnesium and could potentially be used for energy storage.”
Although the nanostructures aren’t stable, Koski says the team has different processing methods to make them stable. “We can add a silicon oxide layer that caps the silicon telluride just by dropping the layers into water, followed by a bake-off of the excess tellurium. Silicon telluride with a silicon oxide capping layer remains stable in air for long periods of time.”
The paper, published in Nano Letters, is “A silicon-based two-dimensional chalcogenide: Growth of Si2Te3 nanoribbons and nanoplates” (DOI: 10.1021/nl504330g).