Nanoclast iconNanoclast

Microwave Oven Is Key to Safer Quantum Dot Manufacturing

As we noted earlier this month, quantum dots have finally made a broad commercial impact on LED technology. So now it’s time to refine the processes for making them and to increase profit margins.

Now researchers at Oregon State University (OSU) have thrown their hat into the ring, presenting a manufacturing method for quantum dots that promises a new era in LED lighting.

In research published in the Journal of Nanoparticle Research, the OSU researchers employed a so-called “continuous flow” chemical reactor. Chemicals were continuously put into the reactor and came out as a continuous stream of product. This continuous flow setup makes the process cheaper, faster, and highly scalable. Meanwhile, using microwaves to heat the reagents—with a machine that operates on more or less the same principle as your microwave oven at home—addresses the issue of how to maintain precise temperature control during the chemical process.

The researchers claim that this method leads to precisely sized and shaped quantum dots that are consistent in their composition. They believe that this development will mark a big change in LED lighting.

“We may finally be able to produce low-cost, energy-efficient LED lighting with the soft quality of white light that people really want,” said Greg Herman, an associate professor of chemical engineering at OSU, in a press release. “At the same time, this technology will use nontoxic materials and dramatically reduce the waste of the materials that are used, which translates to lower cost and environmental protection.”

The environmental benefit of the quantum dots stems from the use of copper indium diselenide, which is a more environmentally benign material than the cadmium that is typically used in LED lighting systems.

Because the process will give manufacturers the ability to fine-tune the size and shape of the quantum dots, that flexibility should make them able to produce dots for a variety of applications. Smaller dots emit green light, while the larger dots emit light in the orange to red range.

The OSU researchers believe that their precision manufacturing method will yield better color control than other quantum-dot-making techniques. So much so that they foresee quantum dots produced via this method providing a cheaper alternative in an array of applications including optics, electronics, and biomedicine.

Carbon Fiber Cloth Can Generate Hydrogen

Splitting water can yield clean-burning hydrogen fuel, but catalysts that generate hydrogen are often expensive, and unstable in water. Now a team from Singapore and Taiwan have shown that carbon fiber cloths coated in inexpensive catalysts can generate hydrogen, and perform not only in water but in seawater as well. The researchers detailed their findings online August 21 in the journal Science Advances.

The most effective catalyst for generating hydrogen is platinum. However, this metal is scarce and expensive, limiting its use in large-scale hydrogen generation. Instead, the researchers investigated molybdenum sulfide as a catalyst. Molybdenum and sulfur are respectively about 300 and more than 100,000 times more abundant than platinum.

"One hundred grams of pure molybdenum metal costs $44, while the same amount of platinum costs $3,211.86 today," says study co-author Bin Liu, a materials scientist at Nanyang Technological University in Singapore.

Normally, molybdenum disulfide is bad at generating hydrogen. However, prior studies found that while its flat surfaces are not catalytically active, its edges are. The researchers incorporated nickel into the catalyst, which essentially punched holes into the molybdenum sulfide, increasing the amount of its exposed edges.

Read More

Can Big Data Shed Light on Nanotech Research?

It can take days for a supercomputer to unravel all the data contained in a single human genome. So it wasn’t long after mapping the first human genome that researchers coined the umbrella term “bioinformatics” in which a variety of methods and computer technologies are used for organizing and analyzing all that data.

Now teams of researchers led by scientists at Duke University believe that the field of nanotechnology has reached a critical mass of data and that a new field needs to be established, dubbed “nanoinformatics.”

If you’re not convinced that there’s as much data being produced in nanotechnology research as there is genetic research, you can choose to use the other buzz word of our time “big data,” which seems to be used interchangeably in the research, which was published in the journal Beilstein Journal of Nanotechnology.

Read More

New Method for Layering 2-D Materials Offers Breakthrough in Energy Storage

For the past couple of years, researchers have been excited at the prospect of what they can make from all the possible instantiations of transition metal dichalcogenides (TMDs). TMDs are combinations of one of 15 transition metals such as molybdenum or tungsten, with one of the three members of the chalcogen family, which includes sulfur, selenium and tellurium. To date, only a small number of combinations have been tested, raising hope that there may be some as yet unidentified combination out there that will prove to be a viable alternative for silicon.

Now researchers at Drexel University have multiplied the number of potential silicon replacements by demonstrating that they can combine two transition metals—in this case molybdenum and titanium—using carbon atoms as the glue bonding the two together. With the method they have developed for combining the two-dimensional (2-D) versions of these materials, the researchers are testing various combinations to see what combinations might be applicable to energy storage, electronics, or wear-resistant materials.

“By sandwiching one or two atomic layers of a transition metal like titanium between monoatomic layers of another metal, such as molybdenum, with carbon atoms holding them together, we discovered that a stable material can be produced,” said Babak Anasori, the post-doctoral researcher who led the research, in a press release. “It was impossible to produce a 2-D material having just three or four molybdenum layers in such structures, but because we added the extra layer of titanium as a connector, we were able to synthesize them.”

The researchers believe that their work, which was published in the journal ACS Nano, will prove to be significant in the future because it provides a way to combine elemental materials in a stable compound. The Drexel team claims that each new combination should exhibit new properties. Eventually, they say, a combination will be discovered that could revolutionize a variety of different technologies, including thermoelectrics, batteries, catalysis, solar cells, electronic devices, and structural composites.

“While it’s hard to say, at this point, exactly what will become of these new families of 2-D materials we’ve discovered, it is safe to say that this discovery enables the field of materials science and nanotechnology to move into an uncharted territory,” Anasori said in the release.

The combining of 2-D versions of elements that resist being joined on the atomic scale has proven difficult and has required over a decade of research at Drexel.

“Due to their structure and electric charge, certain elements just don’t ‘like’ to be combined,” Anasori said. “It’s like trying to stack magnets with the poles facing the same direction—you’re not going to be very successful and you’re going to be picking up a lot of flying magnets.”

The key to making this all work was the discovery of a material called MAX phase by a Drexel researcher over two decades ago. MAX phase (the M is for transition metal, the A for "A group" metal, and the X for carbon and/or nitrogen) is described as a kind of primordial goo from which all things came—it contains all the elements but needs to be organized by the researcher.

The first order placed with MAX phase as the source material was a material developed in 2011 called “MXene.” It derived its name from the process of etching and exfoliating atomically thin layers of aluminum from MAX phases.

Two years ago, this blog covered research that showed MXenes were effective in energy storage applications.

The Drexel researchers were continuing their research into the use of MXenes in energy storage applications, working their way through the periodic table. When they reached the transition metals, they were stymied by molybdenum.

“We had reached a bit of an impasse, when trying to produce a molybdenum containing MXenes,” Anasori said in the release. “By adding titanium to the mix we managed to make an ordered molybdenum MAX phase, where the titanium atoms are in center and the molybdenum on the outside.”

Michel W. Barsoum, one of the Drexel researchers who first synthesized MXene over four years ago, added in the release: “This new layering method gives researchers an unimaginable number of possibilities for tuning materials’ properties for a variety of high-tech applications.”

Black Phosphorus Takes a Step Toward CMOS

Researchers working at the Institute for Basic Science Center for Integrated Nanostructure Physics at Sungkyunkwan University (SKKU) in South Korea have discovered that they can manipulate black phosphorus to behave as an n-type (excess electrons) semiconductor, a p-type (excess holes), or as if it were ambipolar (both n- or p-type) simply by changing its thickness and its bandgap or by using a different metal to contact it with. (Today’s digital logic, CMOS, requires both n-type and p-type transistors.)

With this knowledge, the Korean researchers were able to fabricate a transistor from the material that can operate at lower voltages than a silicon-based transistor. (Though it wasn’t the first black phosphorus transistor ever made.)

Read More

Scalable Production for Graphene Nanoribbons Boosts Potential in Electronics

The form of graphene that holds possibly the most promise for use in electronics is the graphene nanoribbon. The narrowness of these ribbons is the key. At widths ranging from a few nanometers to no more than few hundred nanometers the edge of the graphene determines its properties: Very narrow nanoribbons act as a semiconductors and wider ones behave as conductors.

There are a number of methods for producing graphene nanoribbons that can be categorized as either “top down” approaches, like lithographic techniques, or “bottom up” methods where the graphene nanoribbons self assemble into a desired form.

Researchers at the University of Wisconsin-Madison recently developed a technique based on a bottom-up approach and managed to do it without the limitation of previous methods. The result looks to be a production technique that is compatible with semiconductor manufacturing methods and can be scaled up to bulk production.

In research published in the journal Nature Communications, the Wisconsin team were able to grow graphene on a conventional germanium semiconductor wafer.

"Graphene nanoribbons that can be grown directly on the surface of a semiconductor like germanium are more compatible with planar processing that's used in the semiconductor industry, and so there would be less of a barrier to integrating these really excellent materials into electronics in the future," said Michael Arnold, an associate professor UW-Madison, in a press release.

Previous bottom-up approaches only worked on metal substrates, and, to date, have not been able to produce nanoribbons with the necessary length to be useful for electronics.

The UW-Madison researchers overcame this limitation by putting a bit of a twist on chemical vapor deposition (CVD)—a technique that has served as a kind of bridge of late between scalability and purity in graphene production. In CVD techniques, the graphene is grown from a vaporous precursor on a metal substrate like copper or nickel in a furnace. What the UW-Madison team did was to start the process with methane, which attaches to the germanium surface and breaks down into various hydrocarbons. These different hydrocarbons then begin to react with each other to form graphene.

The key to the technique is its tenability. The researchers can slow the growth rate of the graphene and thereby both lengthen the nanoribbons and make them narrower by decreasing the amount of methane in the CVD furnace chamber.

"What we've discovered is that when graphene grows on germanium, it naturally forms nanoribbons with these very smooth, armchair edges," Arnold said in the release. "The widths can be very, very narrow and the lengths of the ribbons can be very long, so all the desirable features we want in graphene nanoribbons are happening automatically with this technique."

Novel Process Cuts Costs and Improves Performance of Quantum Dots

While the long road to commercial success for quantum dots seemed to reach its end when Samsung’s first quantum dot televisions shipped this spring, the material still is relatively expensive to make, limiting its commercial impact.

Now researchers at the University of Illinois Urbana Champaign (UIUC) have attempted to address the expensive production costs of quantum dots, and at the same time, improve their performance and efficiency.

In research published in the journal Applied Physics Letters, the UIUC team developed a method to pull out more efficient and polarized light from quantum dots over a large-scale area. The technique involves combining quantum dots with photonic crystal technology.

Read More

Molybdenum Ditelluride: Like 2-D Silicon, But Better

A team of researchers from Korea and Japan have had a breakthrough with a semiconductor material that they claim could be a candidate to replace silicon in future electronics. In the 7 August issue of Science they report the creation of a transistor where the channel consists of layers of a two-dimensional material molybdenum ditelluride (MoTe2). 

Read More

Graphene Offers Promise of Thermoelectric Material for Next-Generation Vehicles

Thermoelectric materials have been a tantalizingly promising technology for producing electricity from heat that would otherwise just be wasted. The basic premise of thermoelectric materials is that an electrical current is generated as a result of a difference in temperature between one side of the material and the other.

This would seem to be an obvious way to generate an electrical current from your computer or your car just based on the heat they produce. But heretofore, the available materials had poor thermoelectric conversion efficiency or were prohibitively expensive for commercial uses—they just didn’t produce that much current for the buck.

But when traditional materials fail, in come the nanomaterials. We’ve covered multi-walled carbon nanotubes for this use, along with nanowires and nanopillars.

Now, researchers at the University of Manchester in the U.K.,in collaboration with the company European Thermodynamics Ltd., have called upon graphene to make thermoelectric materials more useful.

In research published in the journal Applied Materials and Interfaces, the joint academic-industrial team added a small amount of graphene to strontium titanium dioxide (STO), a thermoelectric material that, by itself, generates a current only at extremely high temperatures. The graphene made a big difference: STO’s operating temperature was expanded to room temperature.

“Current oxide thermoelectric materials are limited by their operating temperatures which can be around 700 degrees Celsius,” said Robert Freer, one of the lead University of Manchester researchers, in a press release. “This has been a problem which has hampered efforts to improve efficiency by utilizing heat energy waste for some time.

Another handicap limiting the usefulness of thermoelectric materials is that their energy conversion efficiencies hover around 1 percent. But the Manchester team reports that their new hybrid material will convert 3 to 5 percent of heat into electricity. They reason that because a vehicle loses 70 percent of the energy in fuel via waste heat and friction, applying this material for improved thermal energy recovery will lead to a substantial boost in energy efficiency.

Ampliflying Light 10,000 Times

A new type of device could amplify the light emitted by a nanometer-scale object as much as 10,000 times, improving low-light photography and bringing previously hard-to-see items into view.

Read More


IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

Dexter Johnson
Madrid, Spain
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
Load More