HOUSTON, TEXAS-Rice scientists from Rice University demonstrate how a strict 'diet' may yield single-chirality carbon nanotubes. Having carbon nanotubes search for food as they develop, like a giraffe reaching for foliage on a lofty tree, may lead to a long-awaited breakthrough. Ksenia Bets and Boris Yakobson from Rice University's George R. Brown School of Engineering demonstrate how constraining the growth of nanotubes might help achieve the "holy grail" of generating batches with a single chosen chirality.
The scientists' work in Science Advances presents an approach for controlling the "kite" development of nanotubes by restricting the carbon fuel in a furnace. In this process, the nanotube grows at a metal precursor on a substrate but removes the enzyme as it expands, similar to a kite on a thread.
Carbon nanotube layers are graphene's hexagonal atom lattices wrapped into a tube. Chirality describes how the hexagons are tilted within the lattice, ranging from 0 to 30 degrees. If the nanotubes are metallic or semiconductor is determined by this. For example, the capacity to produce long nanotubes in a singular chirality might allow for the fabrication of highly conductor nanotube threads or semiconductor channels in transistors.
Multiple Barriers in Single Chirality
Nanotubes often form randomly with only one or multiple walls and varying chiralities. That's great for certain uses, but many require "purified" batches, which necessitate centrifugation or other expensive methods of separating the nanotubes.
The researchers stated that the heated carbon feedstock gas supplied through moving nozzles might successfully lead to nanotube growth as much as the catalyst is present. In a release from Science Daily, since the tubes containing various chiralities develop at different rates, they could be segregated by duration, and slower-growing kinds could be removed.
The scientists discovered that specific chiralities could be obtained by etching away portions of the nanotubes. The lab's attempt to describe the mechanics of nanotube development prompted them to consider if the pace of growth as a result of each tube's chirality may be valuable. The angle of "kinks" in the developing nanotubes' edges influences how energetically receptive they are to attaching additional carbon atoms. The catalyst particles move as the nanotubes develop, which is critical, according to the main researcher, Bets, a scientist in Yakobson's lab.
There are dozens of varieties of nanotubes, each with a characteristic diameter and structural twist or chiral angle. Carbon nanotubes are grown on catalytic particles using batch production methods that produce the entire gamut of chiral varieties, but Rice scientists have come up with a new strategy for making batches with a single, desired chirality. Their theory shows chiral varieties can be selected for production when catalytic particles are drawn away at specific speeds by localized feedstock supply. The illustration depicts this, and an analogous process 19th-century scientists used to describe the evolution of giraffes’ long necks due to the gradual selection of abilities to reach progressively higher for food.
Lamarck Giraffes as a Metaphorical Form
Bets believe the paper's mention of Lamarck giraffes - a 19th-century idea of how they got such long necks - isn't completely out of the left field, as mentioned in a report from Helix. It serves as a metaphor since as one moves its leaf,' the pipes that can access it continue to grow rapidly, even though those that are unable to die out, she explained. All the nanotubes that are a little bit sluggish will eventually 'die.'
Speed is merely one component of the plan. They recommend that a bit slower nanotubes be targeted to ensure a collection of single chiralities. Because nanotubes of various chiralities grow at different speeds, a batch is likely to have tiers. Chemical etching would damage the longest nanotubes while maintaining the following level of tubes.
According to Bets, recovering the feedstock might very well allow the 2nd nanotubes to grow significantly until they are sufficiently mature to be harvested. The Yakobson lab will not produce them since it is concerned with theory rather than experimentation. Other laboratories, however, have transformed old Rice hypotheses into products such as boron buckyballs.
She hopes that at least a few institutions will take up the task. According to Bets, it is typically more advantageous in science to present ideas to the audience. Those interested can then try 100 different versions to discover which one works. Based on the university's press release, it may take 100 years for one person to attempt.
Yakobson has been the Karl F. Hasselmann Professor of Engineering and a lecturer of materials science, nanoengineering, and chemistry.
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