MMaterialsgateNEWS 2015/02/23

Related MaterialsgateCARDS

New technique for making molybdenum disulfide developed

Extra control over monolayer material with advantages over graphene

Graphene, a single-atom-thick lattice of carbon atoms, is often touted as a replacement for silicon in electronic devices due to its extremely high conductivity and unbeatable thinness. But graphene is not the only two-dimensional material that could play such a role.

University of Pennsylvania researchers have made an advance in manufacturing one such material, molybdenum disulphide. By growing flakes of the material around "seeds" of molybdenum oxide, they have made it easier to control the size, thickness and location of the material.

Unlike graphene, molybdenum disulfide has an energy band gap, meaning its conductivity can be turned on and off. Such a trait is critical for semiconductor devices used in computing. Another difference is that molybdenum disulphide emits light, meaning it could be used in applications like LEDs, self-reporting sensors and optoelectronics.

The study was led by A. T. Charlie Johnson, professor in the Department of Physics & Astronomy in Penn's School of Arts & Sciences, and includes members of his lab, Gang Hee Han, Nicholas Kybert, Carl Naylor and Jinglei Ping. Also contributing to the study was Ritesh Agarwal, professor of materials science and engineering in Penn's School of Engineering and Applied Science; members of his lab, Bumsu Lee and Joohee Park; and Jisoo Kang, a master's student in Penn's nanotechnology program. They collaborated with researchers from South Korea's Sungkyunkwan University, Si Young Lee and Young Hee Lee.

Their study was published in the journal Nature Communications.

"Everything we do with regular electronics we'd like to be able to do with two-dimensional materials," Johnson said. "Graphene has one set of properties that make it very attractive for electronics, but it lacks this critical property, being able to turn on and off. Molybdenum disulphide gives you that."

Graphene's ultra-high conductivity means that it can move electrons more quickly than any known material, but that is not the only quality that matters for electronics. For the transistors that form the basis for modern computing technology, being able to stop the flow of electrons is also critical.

"Molybdenum disulphide is not as conductive as graphene," Naylor said, "but it has a very high on/off ratio. We need 1's and 0's to do computation; graphene can only give us 1's and .5's."

Other research groups have been able to make small flakes of molybdenum disulphide the same way graphene was first made, by exfoliating it, or peeling off atomically thin layers from the bulk material. More recently, other researchers have adopted another technique from graphene manufacture, chemical vapor deposition, where the molybdenum and sulfur are heated into gasses and left to settle and crystalize on a substrate.

The problem with these methods is that the resulting flakes form in a scattershot way.

"Between hunting down the flakes," said Kybert, "and making sure they're the right size and thickness, it would take days to make a single measurement of their properties"

The Penn team's advance was in developing a way to control where the flakes form in the chemical vapor deposition method, by "seeding" the substrate with a precursor.

"We start by placing down a small amount of molybdenum oxide in the locations we want," Naylor said, "then we flow in sulfur gas. Under the right conditions, those seeds react with sulfur and flakes of molybdenum disulphide being to grow."

"There's finesse involved in optimizing the growth conditions," Johnson said, "but we're exerting more control, moving the material in the direction of being able to make complicated systems. Because we grow it where we want it, we can make devices more easily. We have all of the other parts of the transistors in a separate layer that we snap down on top of the flakes, making dozens and potentially even hundreds, of devices at once. Then we were able to observe that we made transistors that turned on and off like they were supposed to and devices that emit light like they are supposed to."

Being able to match up the location of the molybdenum disulphide flakes with corresponding electronics allowed the researchers to skip a step they must take when making graphene-based devices. There, graphene is grown in large sheets and then cut down to size, a process that adds to the risk of damaging contamination.

Future work on these molybdenum disulphide devices will complement the research team's research on graphene-based biosensors; rather than outputting the detection of some molecule to a computer, molybdenum disulfide-based sensors could directly report a binding event through a change in the light they emit.

This research also represents first steps that can be applied toward fabricating a new family of two-dimensional materials.

"We can replace the molybdenum with tungsten and the sulfur with selenium," Naylor said, "and just go down the periodic table from there. We can imagine growing all of these different materials in the places we choose and taking advantages of all of their different properties."

Source: University of Pennsylvania – 19.02.2015.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

First experimental observation of piezoelectricity in an atomically thin material—MoS2—could lead to wearable devices

Researchers from Columbia Engineering and the Georgia Institute of Technology report today that they have made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2), resulting in a unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable. In a paper published online October 15, 2014, in Nature, research groups from the two institutions demonstrate the mechanical generation of electricity from the two-dimensional (2D) MoS2 material. The piezoelectric effect in this material had previously been predicted theoretically. Piezoelectricity... more read more

A new combination of materials can efficiently guide electricity and light along the same tiny wire, a finding that could be a step towards building computer chips capable of transporting digital information at the speed of light.

Reporting today in The Optical Society's (OSA) high-impact journal Optica, optical and material scientists at the University of Rochester and Swiss Federal Institute of Technology in Zurich describe a basic model circuit consisting of a silver nanowire and a single-layer flake of molybdenum disulfide (MoS2). Using a laser to excite electromagnetic waves called plasmons at the surface of the wire, the researchers found that the MoS2 flake at the far end of the wire generated strong light emission. Going in the other direction, as the excited electrons relaxed, they were collected by the wire and converted back into plasmons, which emitted light of the same wavelength. "We have... more read more

Faster electronic device architectures are in the offing with the unveiling of the world’s first fully two-dimensional field-effect transistor (FET) by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab).

Unlike conventional FETs made from silicon, these 2D FETs suffer no performance drop-off under high voltages and provide high electron mobility, even when scaled to a monolayer in thickness. Ali Javey, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of electrical engineering and computer science, led this research in which 2D heterostructures were fabricated from layers of a transition metal dichalcogenide, hexagonal boron nitride and graphene stacked via van der Waals interactions. “Our work represents an important stepping stone towards the realization of a new class of electronic devices in which interfaces based on van der Waals interactions... more read more

Versatility of new technique shows promise as new benchmark in exfoliation chemistry of two-dimensional chalcogenides

A team of scientists from the National University of Singapore (NUS) has successfully developed a method to chemically exfoliate molybdenum disulfide crystals, a class of chalcogenide compounds, into high quality monolayer flakes, with higher yield and larger flake size than current methods. The exfoliated flakes can be made into a printable solution, which can be applied in printable photonics and electronics. This breakthrough, led by Professor Loh Kian Ping, who heads the Department of Chemistry at the NUS Faculty of Science, and is also a principal investigator with the Graphene Research Centre at the Faculty, has generic applicability to other two-dimensional chalcogenides, such as... more read more


Partner of the Week

Search in MaterialsgateNEWS

Books and products