Nav: Home

Growing carbon nanotubes with the right twist

December 13, 2019

In a recently published paper in Science Advances, Feng Ding of the Center for Multidimensional Carbon Materials, within the Institute of Basic Science (IBS, South Korea) and colleagues, have achieved the creation of a specific type of carbon nanotubes (CNTs) with a selectivity of 90%, and expanded the current theory that explains the synthesis of these promising nano-cylinders.

CNTs are incredibly strong and light nanomaterials made of carbon with superior current carrying capacity and very high thermal conductivity, making them ideal for electronic applications. Although CNTs are considered as some of the most interesting materials for the future, scientists are still struggling for their controllable synthesis.

The CNTs' shape can be compared to paper tubes: in the same way as a cylinder can be created by rolling a sheet of paper, so CNTs can be imagined as a single layer of graphite rolled up on itself. Similarly, as different tubes can be produced by rolling a paper around its long side, its short side, or diagonally at different angles. Depending on the rolling direction, a graphite layer can produce different CNT structures, some are conducting and others are semiconducting, thus selectively creating a specific type of CNT will be key for their future use, such as building energy efficient computer chips. However, CNTs are not produced by rolling, but are grown nanometer after nanometer, adding carbon at the rim of nano-cylinders, one atom at a time. Despite various studies during the last three decades, the understanding on CNT growth remains very limited and rational experimental design for the growth of specific types of CNTs is challenging.

One of the most promising manufacturing methods for CNT is the chemical vapor deposition (CVD). In this process, metal nanoparticles combined with carbon-containing gases form CNTs inside a high-temperature furnace. On the tip of the tubes, the metal nanoparticles play a critical role as catalysts: they dissociate the carbon source from the gases, and assist the attachment of these carbon atoms to the CNT wall, making the tubes longer and longer. The growth of the CNT terminates once the catalyst particle is encapsulated by graphitic or amorphous carbon.

Carbon atoms are inserted onto the interface between a growing CNT and a catalyst nanoparticle, in active sites of the rim, and are available to incorporate new atoms. A previous model of CNT's growth rate showed that the latter is proportional to the density of these active sites at the interface between CNT and the catalyst, or the specific structure of the CNT.

In this study, the researchers monitored the steady growth of CNTs on a magnesium oxide (MgO) support with carbon monoxide (CO) as the carbon feedstock and cobalt nanoparticles as catalysts at 700oC. The direct experimental measurements of 16 CNTs showed how to expand the previous theory. "It was surprising that the growth rate of a carbon nanotubes only depends on the size of the catalyst particle. This implies that our previous understanding on carbon nanotubes growth was not complete," says Maoshuai He, the first author of the paper.

More specifically, carbon atoms that are deposited on the catalyst particle surface can be either incorporated on the active side of the CNT or removed by etching agents, such as H2, H2O, O2, or CO2. To explain the new experimental observations, the team included the effects of carbon insertion and removal during CNT growth and discovered that the growth rate depends on the catalyst's surface area and tube diameter ratio.

"Compared to the previous model, we added three more factors: the rate of precursor deposition, the rate of carbon removal by etching agents, and the rate of carbon insertion into a carbon nanotube wall. When feedstock dissociation cannot be balanced by carbon etching, the rate of carbon nanotube growth will no longer depend on the structure of the carbon nanotube. On the other hand, the previous theory is still valid if the etching is dominating," explains Ding, a group leader of the Center for Multidimensional Carbon Materials.

Interestingly, the new theory of CNT growth leads to a new mechanism to selectively grow a specific type of CNTs, denoted as (2n, n) CNTs, which is characterized by the maximum number of active sites at the interface between the CNT and the catalyst. This CNT structure would correspond to rolling a sheet of graphite diagonally at an angle of around 19 degrees.

"If there is no carbon etching and the carbon nanotubes growth is slow, carbon atoms on the catalyst surface will accumulate," says Jin Zhang, co-author of the study and professor of Peking University, China. "This may lead to the formation of graphitic or amorphous carbon, which are established mechanisms of carbon nanotube growth termination. In this case, only carbon nanotubes which are able to add carbon atoms on their walls, that is with the highest number of active sites, can survive."

Guided by the new theoretical understanding, the researchers were able to design experiments that produced (2n, n) CNTs with a selectivity of up to 90%: the highest selective growth of this type of CNT was achieved in the absence of any etching agent and with a high feedstock concentration.
-end-


Institute for Basic Science

Related Carbon Nanotubes Articles:

New production method for carbon nanotubes gets green light
A new method of producing carbon nanotubes -- tiny molecules with incredible physical properties used in touchscreen displays, 5G networks and flexible electronics -- has been given the green light by researchers, meaning work in this crucial field can continue.
Growing carbon nanotubes with the right twist
Researchers synthetize nanotubes with a specific structure expanding previous theories on carbon nanotube growth.
Research shows old newspapers can be used to grow carbon nanotubes
New research has found that old newspaper provide a cheap and green solution for the bulk production of single walled carbon nanotubes.
Clean carbon nanotubes with superb properties
Scientists at Aalto University, Finland, and Nagoya University, Japan, have found a new way to make ultra-clean carbon nanotube transistors with superior semiconducting properties.
Dietary fiber effectively purifies carbon nanotubes
A dietary fiber can help separate out semiconducting carbon nanotubes used for making transistors for flexible electronics.
Why modified carbon nanotubes can help the reproducibility problem
Scientists at Tokyo Institute of Technology (Tokyo Tech) conducted an in-depth study on how carbon nanotubes with oxygen-containing groups can be used to greatly enhance the performance of perovskite solar cells.
Tensile strength of carbon nanotubes depends on their chiral structures
Single-walled carbon nanotubes should theoretically be extremely strong, but it remains unclear why their experimental tensile strengths are lower and vary among nanotubes.
New study reveals carbon nanotubes measurement possible for the first time
Swansea University scientists report an entirely new approach to manipulation of carbon nanotubes that allows physical measurements to be made on carbon nanotubes that have previously only been possible by theoretical computation.
Neural networks will help manufacture carbon nanotubes
A team of scientists from Skoltech's Laboratory of Nanomaterials proposed a neural-network-based method for monitoring the growth of carbon nanotubes, preparing the ground for a new generation of sophisticated electronic devices.
Efficient, interconnected, stable: New carbon nanotubes to grow neurons
Carbon nanotubes able to take on the desired shapes thanks to a special chemical treatment, called crosslinking and, at the same time, able to function as substrata for the growth of nerve cells, finely tuning their growth and activity.
More Carbon Nanotubes News and Carbon Nanotubes Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.