Molybdenum Di-Sulphide (MoS2): A potential challenger to graphene

Sheets of tin sulphide - The diameter of the roll is about 10 times smaller than a human hair.

A team of researchers from the University of Southampton's Optoelectronics Research Centre (ORC) has developed a new way to fabricate a potential challenger to Manchester's Graphene.

Graphene, a single layer of carbon atoms in a honeycomb lattice, is increasingly being used in new electronic and mechanical applications, such as transistors, switches and light sources, thanks to the unprecedented properties it offers: very low electrical resistance, high thermal conductivity and mechanically stretchable yet harder than diamond.

Molybdenum Di-Sulphide (MoS2)

Now, ORC researchers have developed Molybdenum Di-Sulphide (MoS2), a similar material to graphene that shares many of its properties, including extraordinary electronic conduction and mechanical strength, but made from a metal (in this case molybdenum combined with sulphur).

This new class of thin metal/sulphide materials, known as transition metal di-chalcogenides (TMDCs), has become an exciting complimentary material to graphene.

However, unlike graphene, TMDCs can also emit light allowing applications, such as photodetectors and light emitting devices, to be manufactured.

Until recently, fabrication of TMDCs, such as MoS2, has been difficult, as most techniques produce only flakes, typically just a few hundred square microns in area.

Dr Kevin Huang, from ORC who has led the research, explains: "We have been working on the synthesis of chalcogenide materials using a chemical vapour deposition (CVD) process since 2001 and our technology has now achieved the fabrication of large area (>1000 mm2) ultra- thin films only a few atoms thick."

"Being able to manufacture sheets of MoS2 and related materials, rather than just microscopic flakes, as previously was the case, greatly expands their promise for nanoelectronic and optoelectronic applications."

Dr Huang and his team published their findings in the latest issue of the journal Nanoscale.

They are currently working with several UK companies and universities, as well as leading international centres at MIT and Nanyang Technological University (Singapore).

Dr Huang adds: "Our ability to not only synthesise large uniform thin films but also to transfer these films to virtually any substrate has led to increased demand for our materials."

More Information
"Scalable high-mobility MoS2 thin films fabricated by an atmospheric pressure chemical vapor deposition process at ambient temperature" Author: Chung-Che Huang, Feras Al-Saab, Yudong Wang, Jun-Yu Ou, John C. Walker, Shuncai Wang, Behrad Gholipour, Robert E. Simpsond and    Daniel W. Hewaka - Nanoscale, 2014, Advance Article DOI: 10.1039/C4NR04228J - Received 25 Jul 2014

Has Graphene Been Detected in Space?

Artist's impression of the graphenes (C24) and fullerenes found in a planetary nebula. 

The detection of graphenes and fullerenes around old stars as common as our Sun suggests that these molecules and other allotropic forms of carbon may be widespread in space. 

Credit: IAC; original image of the Helix Nebula: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner, STScI and T.A. Rector, NRAO.

A team of astronomers, using the Spitzer Space Telescope, have reported the first extragalactic detection of the C70 fullerene molecule, and the possible detection of planar C24 ("a piece of graphene") in space.

Letizia Stanghellini and Richard Shaw, members of the team at the National Optical Astronomy Observatory in Tucson, Arizona, describe how collisional shocks powered by the winds from old stars in planetary nebulae could be responsible for the formation of fullerenes (C60 and C70) and graphene (planar C24).

The team is led by Domingo Anibal Garcia-Hernandez of the Instituto de Astrofisica de Canarias in Spain and includes international astronomers and biochemists.

Planetary nebulae originate from stars similar to our Sun that have reached the end of their lives and are shedding shells of gas into space. In this case, the planetary nebulae are located in the Magellanic Clouds, two satellite galaxies to our own Milky Way, that are best seen from the Southern Hemisphere. At the distance of the Magellanic Clouds, planetary nebulae appear as small fuzzy blobs.

However, unlike planetaries in our own Milky Way Galaxy whose distances are very uncertain, the distance to planetaries in the Magellanic Clouds can be determined to better than 5%. With such accurate distances, the research team determined the true luminosity of the stars and confirmed that the objects are indeed planetary nebulae and not some other object in the astrophysical zoo.

Fullerenes, or Buckyballs, are known from laboratory work on Earth and have many interesting and important properties. Fullerenes consist of carbon atoms arranged in a three dimensional sphere similar to the geodesic domes popularized by Buckminster Fuller.

The C70 fullerene can be compared with a rugby ball, while C60 is compared to a soccer ball. Both of these molecules have been detected in the sample. Graphene (planar C24) is a flat sheet of carbon atoms, one atom thick, that has extraordinary strength, conductivity, elasticity and thinness.

Cited as the thinnest substance known, graphene was first synthesized in the lab in 2004 by Geim and Novoselov for which they received the 2010 Nobel Prize in physics. "If confirmed with laboratory spectroscopy - something that is almost impossible with the present techniques - this would be the first detection of graphene in space," said team member Garcia-Hernandez.

The team has proposed that fullerenes and graphene are formed from the shock-induced (i.e., grain-grain collisions) destruction of hydrogenated amorphous carbon grains (HACs). Such collisions are expected in the stellar winds emanating from planetary nebulae, and this team sees evidence for strong stellar winds in the ultraviolet spectra of these stars.

"What is particularly surprising is that the existence of these molecules does not depend on the stellar temperature, but on the strength of the wind shocks," says Stanghellini.

The Small Magellanic Cloud is particularly poor in metals (any element besides hydrogen and helium, in astronomers' parlance), but this sort of environment favors the evolution of carbon-rich planetary nebulae, which turns out to be a favorable place for complex carbon molecules.

One box of Girl Scout cookies worth $15 billion - YouTube

In a paper published in the journal ACS Nano, scientists  described how graphene, a single-atom-thick sheet of carbon, can be made from just about any carbon source, including food, insects, and waste.

Read the original study: DOI: 10.1021/nn202625c

“I said we could grow it from any carbon source, for example, a Girl Scout cookie, because Girl Scout cookies were being served at the time,” says James Tour, professor of mechanical engineering and materials science and of computer science at Rice University. “So one of the people in the room said, ‘Yes, please do it. … Let’s see that happen.’”

A sheet of graphene is so thin that one sheet made from one box of shortbread cookies would cover nearly three football fields.

The scientists say the experiment is a whimsical way to make a serious point: that graphene, touted as a miracle material for its toughness and conductivity since its discovery in 2004, can be drawn from many sources.

Tour and graduate students Gedeng Ruan, lead author of the paper, and Zhengzong Sun, also tested other materials, including chocolate, grass, polystyrene plastic, insects (a cockroach leg) and even dog faeces.

In every case, the researchers were able to make high-quality graphene via carbon deposition on copper foil.

In this process, the graphene forms on the opposite side of the foil as solid carbon sources decompose; the other residues are left on the original side. Typically, this happens in about 15 minutes in a furnace flowing with argon and hydrogen gas and turned up to 1,050 degrees Celsius.

Tour expects the cost of graphene to drop quickly as commercial interests develop methods to manufacture it in bulk. In earlier research, Tour  described a long-sought way to make graphene-based transparent electrodes by combining graphene with a fine aluminum mesh.

The material could possibly replace expensive indium tin oxide as a basic element in flat-panel and touch-screen displays, solar cells, and LED lighting.

The new findings have “a lot to do with current research topics in academia and in industry,” Tour says. “Carbon—or any element—in one form can be inexpensive and in another form can be very expensive.”

Diamonds are a good example., he says. “You could probably get a very large diamond out of a box of Girl Scout cookies.”

Sandia National Laboratory, the Air Force Office of Scientific Research, and the Office of Naval Research MURI program funded the research.

More news from Rice University: www.media.rice.edu/media/

Discoverers of graphene bring graphene-based electronics a step closer

The researchers who unveiled graphene in 2004 and who were awarded the Nobel Prize in 2010 for “groundbreaking experiments regarding the two-dimensional material" have led new research that reveals more about the electronic properties of the wonder material.

The team says their findings promise to accelerate research looking at ways to build graphene-based devices such as touch-screens, ultrafast transistors and photodetectors, and will potentially open up countless more electronic opportunities.

Discoverers of graphene bring graphene-based electronics a step closer - Image 1 of 1

Flourescein Dye used to study world's thinnest sheet

The world's thinnest material is being studied with a dye used to stain the Chicago River green on St. Patrick's Day, scientists in Illinois said.

The dye flourescein, also used to find old blood stains at crime scenes, is being used to examine graphene, a one-atom thick sheet, Northwestern University scientists said.

Graphene has the potential to be used to make low-cost carbon-based electronics that are transparent and flexible, researcher Jiaxing Huang said in a release Wednesday.

Using flourescein to examine graphene and its derivatives avoids the use of expensive and time-consuming techniques such as atomic force microscopy and scanning electron microscopy.

"It's a simple and dirt-cheap method that works surprisingly well in many situations," Huang said of the flourescein imaging. Huang and his team have named their technique "fluorescence quenching microscopy."