Graphane is the material of choice for physicists on the cutting edge of materials science, and Rice University researchers are right there with the pack – and perhaps a little ahead.
Researchers mentored by Boris Yakobson, a Rice professor of mechanical engineering and materials science and of chemistry, have discovered the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane naturally opens up spaces of pure graphene that look – and act – like quantum dots.
That opens up a new world of possibilities for an ever-shrinking class of nanoelectronics that depend on the highly controllable semiconducting properties of quantum dots, particularly in the realm of advanced optics.
The theoretical work by Abhishek Singh and Evgeni Penev, both postdoctoral researchers in co-author Yakobson's group, was published online last week in the journal ACS Nano and will be on the cover of the print version in June. Rice was recently named the world's No. 1 institution for materials science research by a United Kingdom publication.
Graphene has become the Flat Stanley of materials. The one-atom-thick, honeycomb-like form of carbon may be two-dimensional, but it seems to be everywhere, touted as a solution to stepping beyond the limits of Moore's Law.
Graphane is simply graphene modified by hydrogen atoms added to both sides of the matrix, which makes it an insulator. While it's still technically only a single atom thick, graphane offers great possibilities for the manipulation of the material's semiconducting properties.
Quantum dots are crystalline molecules from a few to many atoms in size that interact with light and magnetic fields in unique ways. The size of a dot determines its band gap – the amount of energy needed to close the circuit – and makes it tunable to a precise degree. The frequencies of light and energy released by activated dots make them particularly useful for chemical sensors, solar cells, medical imaging and nanoscale circuitry.
Singh and Penev calculated that removing islands of hydrogen from both sides of a graphane matrix leaves a well with all the properties of quantum dots, which may also be useful in creating arrays of dots for many applications.
"We arrived at these ideas from an entirely different study of energy storage in a form of hydrogen adsorption on graphene," Yakobson said. "Abhishek and Evgeni realized that this phase transformation (from graphene to graphane), accompanied by the change from metal to insulator, offers a novel palette for nanoengineering."
Their work revealed several interesting characteristics. They found that when chunks of the hydrogen sublattice are removed, the area left behind is always hexagonal, with a sharp interface between the graphene and graphane. This is important, they said, because it means each dot is highly contained; calculations show very little leakage of charge into the graphane host material. (How, precisely, to remove hydrogen atoms from the lattice remains a question for materials scientists, who are working on it, they said.)
"You have an atom-like spectra embedded within a media, and then you can play with the band gap by changing the size of the dot," Singh said. "You can essentially tune the optical properties."
Along with optical applications, the dots may be useful in single-molecule sensing and could lead to very tiny transistors or semiconductor lasers, he said.
Challenges remain in figuring out how to make arrays of quantum dots in a sheet of graphane, but neither Singh nor Penev sees the obstacles as insurmountable.
"We think the major conclusions in the paper are enough to excite experimentalists," said Singh, who will soon leave Rice to become an assistant professor at the Indian Institute of Science in Bangalore. "Some are already working in the directions we explored."
"Their work is actually supporting what we're suggesting, that you can do this patterning in a controlled way," Penev said.
When might their calculations bear commercial fruit? "That's a tough question," Singh said. "It won't be that far, probably -- but there are challenges. I don't know that we can give it a time frame, but it could happen soon."
Funding from the Office of Naval Research supported the work. Computations were performed at the Department of Defense Supercomputing Resource Center at the Air Force Research Laboratory.
David Ruth | EurekAlert!
Researchers invent process to make sustainable rubber, plastics
25.04.2017 | University of Delaware
Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging
24.04.2017 | Pohang University of Science & Technology (POSTECH)
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
25.04.2017 | Physics and Astronomy
25.04.2017 | Materials Sciences
25.04.2017 | Life Sciences