At the Georgia Institute of Technology, researchers are studying the formation of these metal oxide nanotubes to understand the key factors that drive the emergence of nanotubes with specific diameters and lengths from a “soup” of precursor chemicals dissolved in water. Their goal is to develop general guidelines for controlling nanotube diameter with sub-nanometer precision and nanotube length with precision of a few nanometers.
So far, the researchers have obtained encouraging results with a model system that produces aluminosilicogermanate (AlSiGeO) nanotubes. The research, which will be presented August 23rd at the 234th National Meeting of the American Chemical Society, could open the door for developing a more general set of chemical “rules” for dimensional control of nanotubes that could lead to a range of new applications for inorganic nanotubes and other nanometer-scale materials. The research has been sponsored by the American Chemical Society Petroleum Research Fund.
“We have shown that there is a clearly quantifiable molecular-level structural and thermodynamic basis for tuning the diameter of nanotubes,” said Sankar Nair, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering. “We’re interested in developing the science of these materials to the point that we can manipulate their curvature, length and internal structure in a sophisticated way through inexpensive water-based chemistry under mild conditions.”
Using chemical reactions carried out in water at less than 100 degrees Celsius, Nair’s research team – which included graduate students Suchitra Konduri and Sanjoy Mukherjee – varied the germanium and silicon content during the nanotube synthesis and then quantitatively characterized the resulting nanotubes with a variety of analytical techniques to show a clear link between the nanotube composition and diameter.
Simultaneously, the group’s molecular dynamics calculations showed a strong correlation between the composition, diameter and internal energy of the material.
“There appear to be energy minima that favor or stabilize certain nanotube diameters because they have the lowest energy, and those stable diameters change with the composition of the material,” said Nair. “This shows that the nanotube dimensions are not just a fortuitous coincidence of the many synthesis parameters, but that there is an underlying thermodynamic basis arising from the subtle balance of interatomic forces within the material.”
Specifically, the molecular dynamics simulations – which are corroborated by the experiments – show that the variation of germanium and silicon content causes sheets of aluminum hydroxide to form nanotubes with diameters ranging from 1.5 to 4.8 nanometers and lengths of less than 100 nanometers. If that turns out to be a general principle applicable to other metal oxides, it could be used to dramatically expand the catalog of nanotube structures available.
Once the researchers fully understand the factors affecting the formation of nanotubes from aluminosilicogermanate materials, they hope to apply similar principles to other metal oxides. The ultimate goal will be an ability to predictably vary the dimensions of nanotubes – and potentially other useful nanostructures – employing different chemical process conditions across a broader range of metal oxide materials.
“One can get a large range of useful properties with metal oxide materials,” Nair noted. “Almost all metals form oxides and many of them form layered sheet-like oxides, so if one can coax them into nanotube form with dimensions comparable to single-walled carbon nanotubes, the range of useful properties would be great.”
Controlling the dimensions of nanostructures is critical because properties such as electronic band-gap depend strongly upon the dimensions. Dimension control has proven to be difficult in carbon nanotube fabrication processes, leading to an entire area of research focused on purifying nanotubes of specific dimensions from an initial mixture of different sizes.
“If we are able to produce single-walled nanotubes of specific and controllable diameter with inexpensive water-based chemistry, devices based on them would perform in a consistent and predictable manner,” Nair explained. “If we could synthesize the same nanotube structure with predictably different diameters and lengths, we can tune the properties like the band-gap across a wide range. We could even get a limited toolbox of materials to do many different things.”
Though the chemical reactions that produce the metal oxide nanotubes are complicated, they occur over a period of days at low temperatures and can be carried out with simple laboratory apparatus. That facilitates control over processing conditions and allows the researchers to track many different aspects of the reaction with a variety of characterization tools.
“There is a lot of complex chemistry that can be done in the aqueous phase, which motivated us to understand the processes by which metal ions dissolved in water organize themselves together with oxygen into specific nanotubular arrangements, perhaps aided by water and other species present in the solution,” Nair added.
The metal oxide nanotubes have properties very different from those of carbon nanotubes, which have been studied heavily since they were discovered in the 1990s. “For example, the materials that we are working with are much more hydrophilic than carbon and can load nearly 50 percent of their weight with water,” Nair explained. “There is a whole range of behavior in oxide nanotubes that we cannot explore with carbon-based materials.”
John Toon | EurekAlert!
Cancer diagnosis: no more needles?
25.05.2018 | Christian-Albrechts-Universität zu Kiel
Less is more? Gene switch for healthy aging found
25.05.2018 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences