Graphene quantum dots: The next big small thing


QDOTS imagesCAKXSY1K 8Rice University-led team creates tiny materials in bulk from carbon fiber

 

 

This transmission electron microscope image shows a graphene quantum dot with zigzag edges. The quantum dots can be created in bulk from carbon fiber through a chemical process discovered at Rice University.0113_QUANTUM_HRTEM

A Rice University laboratory has found a way to turn common carbon fiber into graphene quantum dots, tiny specks of matter with properties expected to prove useful in electronic, optical and biomedical applications.

The Rice lab of materials scientist Pulickel Ajayan, in collaboration with colleagues in China, India, Japan and the Texas Medical Center, discovered a one-step chemical process that is markedly simpler than established techniques for making graphene quantum dots. The results were published online this month in the American Chemical Society’s journal Nano Letters.

“There have been several attempts to make graphene-based quantum dots with specific electronic and luminescent properties using chemical breakdown or e-beam lithography of graphene layers,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and of chemistry. “We thought that as these nanodomains of graphitized carbons already exist in carbon fibers, which are cheap and plenty, why not use them as the precursor?”

Quantum dots, discovered in the 1980s, are semiconductors that contain a size- and shape-dependent band gap. These have been promising structures for applications that range from computers, LEDs, solar cells and lasers to medical imaging devices. The sub-5 nanometer carbon-based quantum dots produced in bulk through the wet chemical process discovered at Rice are highly soluble, and their size can be controlled via the temperature at which they’re created.

The Rice researchers were attempting another experiment when they came across the technique. “We tried to selectively oxidize carbon fiber, and we found that was really hard,” said Wei Gao, a Rice graduate student who worked on the project with lead author Juan Peng, a visiting student from

Green-fluorescing graphene quantum dots created at Rice University surround a blue-stained nucleus in a human breast cancer cell. Cells were placed in a solution with the quantum dots for four hours. The dots, each smaller than 5 nanometers, easily passed through the cell membranes, showing their potential value for bio-imaging.

Nanjing University who studied in Ajayan’s lab last year. “We ended up with a solution and decided to look at a few drops with a transmission electron microscope.”

The specks they saw were bits of graphene or, more precisely, oxidized nanodomains of graphene extracted via chemical treatment of carbon fiber. “That was a complete surprise,” Gao said. “We call them quantum dots, but they’re two-dimensional, so what we really have here are graphene quantum discs.”

Gao said other techniques are expensive and take weeks to make small batches of graphene quantum dots. “Our starting material is cheap, commercially available carbon fiber. In a one-step treatment, we get a large amount of quantum dots. I think that’s the biggest advantage of our work,” she said.Further experimentation revealed interesting bits of information: The size of the dots, and thus their photoluminescent properties, could be controlled through processing at relatively low temperatures, from 80 to 120 degrees Celsius. “At 120, 100 and 80 degrees, we got blue, green and yellow luminescing dots,” she said.

They also found the dots’ edges tended to prefer the form known as zigzag. The edge of a sheet of graphene — the single-atom-thick form of carbon — determines its electrical characteristics, and zigzags are semiconducting.

Their luminescent properties give graphene quantum dots potential for imaging, protein analysis, cell tracking and other biomedical applications, Gao said. Tests at Houston’s MD Anderson Cancer Center and Baylor College of Medicine on two human breast cancer lines showed the dots easily found their way into the cytoplasm and did not interfere with the cells’ proliferation.

“The green quantum dots yielded a very good image,” said co-author Rebeca Romero Aburto, a graduate student in the Ajayan lab who also studies at MD Anderson. “The advantage of graphene dots over fluorophores is that their fluorescence is more stable and they don’t photobleach. They don’t lose their fluorescence as easily. They have a depth limit, so they may be good for in vitro and in vivo (small animal) studies, but perhaps not optimal for deep tissues in humans.

Dark spots on a transmission electron microscope grid are graphene quantum dots made through a wet chemical process at Rice University. The inset is a close-up of one dot. Graphene quantum dots may find use in electronic, optical and biomedical applications.

“But everything has to start in the lab, and these could be an interesting approach to further explore for bioimaging,” Romero Alburto said. “In the future, these graphene quantum dots could have high impact because they can be conjugated with other entities for sensing applications, too.”

Co-authors include Angel Martí, a professor of chemistry and bioengineering, postdoctoral research associates Zheng Liu and Liehui Ge, senior research scientist Lawrence Alemany and graduate student Xiaobo Zhan, all of Rice; Rice alumnus Li Song of Shinshu University, Japan; Bipin Kumar Gupta of the National Physical Laboratory, New Delhi, who worked at the Ajayan lab on an Indo-US Science and Technology Forum fellowship; Guanhui Gao of the Ocean University of China; Sajna Antony Vithayathil, a research technician, and Benny Abraham Kaipparettu, a postdoctoral researcher, both at Baylor College of Medicine; Takuya Hayashi, an associate professor of engineering at Shinshu University, Japan; and Jun-Jie Zhu, a professor of chemistry at Nanjing University.

The research was supported by Nanoholdings, the Office of Naval Research MURI program on graphene, the Natural Science Foundation of China, the National Basic Research Program of China, the Indo-US Science and Technology Forum and the Welch Foundation.

Advertisements

QMC receives U.S. patent for synthesis of Group II-VI inorganic tetrapod quantum dots


QDOTS imagesCAKXSY1K 8

*** Note to Readers: In our efforts to provide timely updates in the world of “Nano”, we post the following announcement. We have previously posted about this company and find the premise of the technology to be very promising IOHO. We appreciate your thoughts, comments and responses as to how you think this technology will impact the industry, specifically in Nano-Bio, Nano-Pharma and Nano-Medicine.  Cheers!  BWH

Published on November 21, 2012 at 12:11 AM

quantum material corp logoQuantum Materials Corporation, Inc. (OTCQB: QTMM) proudly announces the USPTO patent grant of a fundamental disruptive technology for synthesis of Group II-VI inorganic tetrapod quantum dots. The patent, “Synthesis of Uniform Nanoparticle Shapes with High Selectivity” and invented by Professor Michael S. Wong’s group at William Marsh Rice University, Houston, TX, for the first time gives precise control of both QD shape and dimension during synthesis and is adaptable to quantum dots production of industrial scale quantities. The new synthesis is a greener method using surfactants as would be found in laundry detergent instead of highly toxic chemicals used during industry standard small batch synthesis.

Quantum Materials Corporation, Inc.(QMC) has acquired the exclusive worldwide license for this patent and its wholly owned renewable energy subsidiary, Solterra Renewable Technologies, has the same rights specific to Quantum Dot Solar Applications.  QMC last week announced a high quantum yield of 80% for a new class of tetrapod QD synthesized with this patented process.

According to a new market research report, “Quantum Dots (QD) Market – Global Forecast & Analysis (2012 – 2022)” published by MarketsandMarkets (http://www.marketsandmarkets.com), the total market for Quantum dots is expected to reach $7.48 Billion by 2022, at a CAGR of 55.2% from 2012 to 2022.

The Rice University QD synthesis remarkably produces same-sized tetrapods, in which more than 92+ percent are full tetrapods, with a similar high degree of process control over QD shape, size, uniformity, and selectivity. The synthesis is applicable to a wide range of mono and hybrid Group II-VI tetrapod QD with/without shell and can optimize specific characteristics by modifying process parameters.

Across the broader QD industry however, other companies have been striving to increase production, but none have predicted scaling quantum dot production remotely close to multiple kilograms per day.

Quantum Materials Corporation’s development of breakthrough software-controlled continuous flow chemistry process allows scaling of tetrapod quantum dot production to 100Kg/Day. Increasing production will transform tetrapod quantum dots from a novelty to a commodity, available across industries and applications where prior limited availability and high prices restricted product development. For example, 100Kg daily QD production can support a QD Solar Cell Plant producing one Gigawatt/year of R2R flexible QD solar cells at an industry competitive .75 cents/Watt at the start.

Tetrapod QD offer inherent advantages over spherical QD including higher brightness, truer and more colors, the use of less active material (QDs) for any application, higher photostability and therefore longer lifetime; which together more than justify their product development. OLEDs, for example, share design architecture similarities and would not require entirely new research to adapt to TQD-LEDs.  Spherical Quantum dots, at the low price of $2000/gm. are 30 times more expensive than gold today.

It simply has not been economically feasible to commercialize QD applications due to their high cost, which stems from the difficulty of small batch manufacture, the inability to produce uniform, same size QD from batch to batch, and to promise a reliable, timely supply. Over the last half dozen years university and corporate quantum dot research has increased dramatically and there are ready QD applications that may now be “business planned” for joint ventures or possible licensing with Quantum Materials Corporation and Solterra Renewable Technologies.

Stephen B. Squires, CEO and President of Quantum Materials Corporation, Inc. and Solterra Renewable Technologies, Inc., said, “With the granting of the US Patent, tetrapod quantum dots are well positioned to revolutionize several industries in offering dramatic performance at cost effective levels. While the technology has been under review, we have continued to execute our vision to establish global manufacturing centers and strategic partnerships for creating dramatic value in our companies.”  Squires continued, “We are excited to continue our business plan with the IP protection offered by the granted allowances. Adoption of quantum dots will result in new classes of products with advanced features, improved performance, energy efficiency, and lower cost.”

Art Lamstein, Director of Marketing for QMC and SRT added, “The timeline is moved forward to present day and market forecasts will need be rewritten for quantum dot based renewable energy, photovoltaics, biotech diagnostic assays, drug delivery platforms, theranostic cancer and other biomedicine treatments, QD-LED and opto-electronic devices, photonics, low power SSL lighting, batteries, fuel cells, thermo-QD  applications, quantum computing, memory, and conductive inks (to name a few).”QDOTS imagesCAKXSY1K 8

Lava dots: Rice makes hollow, soft-shelled quantum dots


Lava dots: Rice makes hollow, soft-shelled quantum dotsHOUSTON — (Nov. 19, 2012) — Serendipity proved to be a key ingredient for the latest nanoparticles discovered at Rice University. The new “lava dot” particles were discovered accidentally when researchers stumbled upon a way of using molten droplets of metal salt to make hollow, coated versions of a nanotech staple called quantum dots.

The results appear online this week in the journal Nanotechnology. The researchers also found that lava dots arrange themselves in evenly spaced patterns on flat surfaces, thanks in part to a soft outer coating that can alter its shape when the particles are tightly packed.

“We’re exploring potential of using these particles as catalysts for hydrogen production, as chemical sensors and as components in solar cells, but the main point of this paper is how we make these materials,” said co-author Michael Wong, professor of chemical and biomolecular engineering at Rice. “We came up with this ‘molten-droplet synthesis’ technique and found we can use the same process to make hollow nano-size particles out of several kinds of elements. The upshot is that this discovery is about a whole family of particles rather than one specific composition.”

Like their quantum dot cousins, Rice’s lava dots can be made of semiconductors like cadmium selenide and zinc sulfide.

Wong’s lab has been working steadily to improve the synthesis of quantum dots for more than five years. In 2007, Wong’s team discovered a cleaner and cheaper way to synthesize four-legged quantum dots — particles smaller than a living cell that look like tiny versions of children’s jacks. These “nanojacks,” which are also called quantum tetrapods, can be used to harvest sunlight in a revolutionary new kind of solar panel.

The key step in the 2007 discovery was the use of a surfactant called CTAB. In 2010 Rice graduate student Sravani Gullapalli was attempting to refine the “nanojack” synthesis even further when she discovered lava dots.

“This new chemistry to make the tetrapods was fairly cheap, but we were looking for an even cheaper way,” Wong said. “Sravani said, ‘Let’s get rid of this expensive phosphorus surfactant and just see what happens.’ So she did, and these little things just popped out on the electron microscope screen.”

Wong recalled the team’s initial surprise. “We said, ‘What is going on here? How do you go from four-legged nanojacks to these little balls?'”

He said it took the team more than a year to decipher the unusual formation mechanism that yielded the hollow, soft-shelled particles.

To make the particles, Gullapalli added three kinds of solid powder — cadmium nitrate, selenium and a tiny amount of CTAB — to an oil solvent. She then slowly heated the mixture while stirring. The cadmium nitrate melted first and formed tiny nanodroplets that cannot be seen with the naked eye.

“Nothing happens until the temperature continues to rise and the selenium melts,” Gullapalli said. “The molten selenium then wraps around the cadmium nitrate droplet, and the cadmium nitrate diffuses out and leaves a hole where the droplet once was.”

She said the cadmium selenide shell surrounding the hole is nanocrystalline and is enveloped in a soft outer shell of pure selenium.

When Gullapalli examined the lava dots with a transmission electron microscope, she found them to be bigger than standard quantum dots, about 15-20 nanometers in diameter. The holes were about 4-5 nanometers in diameter. She also noticed something peculiar: When sitting by themselves they appeared round, and when tightly packed, the shell appeared to become compressed, even though neighboring dots never came into actual contact with one another.

“That’s one of the twists to this weird chemistry,” Wong said. “The solvent forms its own surfactant during this process. The surfactant coats the particles and keeps them from touching each other, even when they are tightly packed together.”

This shows what Rice University scientists discovered.

(Photo Credit: S. Gullapalli/Rice University)

Wong’s team later found it could use the molten droplet method to make lava dots out of zinc sulfide, cadmium sulfide and zinc selenide.

“We found that the hollow particles met and even exceeded some performance metrics of quantum dots in a solar-cell test device, and we’re continuing to examine how these might be useful,” Gullapalli said.

 

When sitting by themselves, lava dots appear round, but their soft outer shells flatten when they are packed near one another.

(Photo Credit: S. Gullapalli/Rice University)