Tag Archives: Nan Wei

Carbon nanotubes (CNTs) in 466 colours

Caption: A color map illustrates the inherent colors of 466 types of carbon nanotubes with unique (n,m) designations based their chiral angle and diameter. Credit: Image courtesy of Kauppinen Group/Aalto University

This is, so to speak, a new angle on carbon nanotubes (CNTs). It’s also the first time I’ve seen two universities place identical news releases on EurekAlert under their individual names.

From the Dec. 14, 2020 Rice University (US) news release or the Dec. 14, 2020 Aalto University (Finland) press release on EurekAlert,

Nanomaterials researchers in Finland, the United States and China have created a color atlas for 466 unique varieties of single-walled carbon nanotubes.

The nanotube color atlas is detailed in a study in Advanced Materials about a new method to predict the specific colors of thin films made by combining any of the 466 varieties. The research was conducted by researchers from Aalto University in Finland, Rice University and Peking University in China.

“Carbon, which we see as black, can appear transparent or take on any color of the rainbow,” said Aalto physicist Esko Kauppinen, the corresponding author of the study. “The sheet appears black if light is completely absorbed by carbon nanotubes in the sheet. If less than about half of the light is absorbed in the nanotubes, the sheet looks transparent. When the atomic structure of the nanotubes causes only certain colors of light, or wavelengths, to be absorbed, the wavelengths that are not absorbed are reflected as visible colors.”

Carbon nanotubes are long, hollow carbon molecules, similar in shape to a garden hose but with sides just one atom thick and diameters about 50,000 times smaller than a human hair. The outer walls of nanotubes are made of rolled graphene. And the wrapping angle of the graphene can vary, much like the angle of a roll of holiday gift wrap paper. If the gift wrap is rolled carefully, at zero angle, the ends of the paper will align with each side of the gift wrap tube. If the paper is wound carelessly, at an angle, the paper will overhang on one end of the tube.

The atomic structure and electronic behavior of each carbon nanotube is dictated by its wrapping angle, or chirality, and its diameter. The two traits are represented in a “(n,m)” numbering system that catalogs 466 varieties of nanotubes, each with a characteristic combination of chirality and diameter. Each (n,m) type of nanotube has a characteristic color.

Kauppinen’s research group has studied carbon nanotubes and nanotube thin films for years, and it previously succeeded in mastering the fabrication of colored nanotube thin films that appeared green, brown and silver-grey.

In the new study, Kauppinen’s team examined the relationship between the spectrum of absorbed light and the visual color of various thicknesses of dry nanotube films and developed a quantitative model that can unambiguously identify the coloration mechanism for nanotube films and predict the specific colors of films that combine tubes with different inherent colors and (n,m) designations.

Rice engineer and physicist Junichiro Kono, whose lab solved the mystery of colorful armchair nanotubes in 2012, provided films made solely of (6,5) nanotubes that were used to calibrate and verify the Aalto model. Researchers from Aalto and Peking universities used the model to calculate the absorption of the Rice film and its visual color. Experiments showed that the measured color of the film corresponded quite closely to the color forecast by the model.

The Aalto model shows that the thickness of a nanotube film, as well as the color of nanotubes it contains, affects the film’s absorption of light. Aalto’s atlas of 466 colors of nanotube films comes from combining different tubes. The research showed that the thinnest and most colorful tubes affect visible light more than those with larger diameters and faded colors.

“Esko’s group did an excellent job in theoretically explaining the colors, quantitatively, which really differentiates this work from previous studies on nanotube fluorescence and coloration,” Kono said.

Since 2013, Kono’s lab has pioneered a method for making highly ordered 2D nanotube films. Kono said he had hoped to supply Kauppinen’s team with highly ordered 2D crystalline films of nanotubes of a single chirality.

“That was the original idea, but unfortunately, we did not have appropriate single-chirality aligned films at that time,” Kono said. “In the future, our collaboration plans to extend this work to study polarization-dependent colors in highly ordered 2D crystalline films.”

The experimental method the Aalto researchers used to grow nanotubes for their films was the same as in their previous studies: Nanotubes grow from carbon monoxide gas and iron catalysts in a reactor that is heated to more than 850 degrees Celsius. The growth of nanotubes with different colors and (n,m) designations is regulated with the help of carbon dioxide that is added to the reactor.

“Since the previous study, we have pondered how we might explain the emergence of the colors of the nanotubes,” said Nan Wei, an assistant research professor at Peking University who previously worked as a postdoctoral researcher at Aalto. “Of the allotropes of carbon, graphite and charcoal are black, and pure diamonds are colorless to the human eye. However, now we noticed that single-walled carbon nanotubes can take on any color: for example, red, blue, green or brown.”

Kauppinen said colored thin films of nanotubes are pliable and ductile and could be useful in colored electronics structures and in solar cells.

“The color of a screen could be modified with the help of a tactile sensor in mobile phones, other touch screens or on top of window glass, for example,” he said.

Kauppinen said the research can also provide a foundation for new kinds of environmentally friendly dyes.

Here’s a link to and a citation for the paper,

Colors of Single‐Wall Carbon Nanotubes by Nan Wei, Ying Tian, Yongping Liao, Natsumi Komatsu, Weilu Gao, Alina Lyuleeva‐Husemann, Qiang Zhang, Aqeel Hussain, Er‐Xiong Ding, Fengrui Yao, Janne Halme. Kaihui Liu, Junichiro Kono, Hua Jiang, Esko I. Kauppinen. Advanced Materials DOI: https://doi.org/10.1002/adma.202006395 First published: 14 December 2020

Thi8s paper is open access.

Colo(u)ring your carbon nanotubes

Finnish research is highlighted in an August 28, 2018 news item on phys.org,

A method developed at Aalto University, Finland, can produce large quantities of pristine single-walled carbon nanotubes in select shades of the rainbow. The secret is a fine-tuned fabrication process—and a small dose of carbon dioxide. The films could find applications in touch screen technologies or as coating agents for new types of solar cells.

An August 28, 2018 Aalto University press release (also on EurekAlert), which originated the news item, provides more detail,

Samples of the colourful carbon nanotube thin films, as produced in the fabrication reactor. Image: Aalto University.
 

Single-walled carbon nanotubes, or sheets of one atom-thick layers of graphene rolled up into different sizes and shapes, have found many uses in electronics and new touch screen devices. By nature, carbon nanotubes are typically black or a dark grey.

In their new study published in the Journal of the American Chemical Society (JACS), Aalto University researchers present a way to control the fabrication of carbon nanotube thin films so that they display a variety of different colours—for instance, green, brown, or a silvery grey.

The researchers believe this is the first time that coloured carbon nanotubes have been produced by direct synthesis. Using their invention, the colour is induced straight away in the fabrication process, not by employing a range of purifying techniques on finished, synthesized tubes.

With direct synthesis, large quantities of clean sample materials can be produced while also avoiding damage to the product in the purifying process—which makes it the most attractive approach for applications.

‘In theory, these coloured thin films could be used to make touch screens with many different colours, or solar cells that display completely new types of optical properties,’ says Esko Kauppinen, Professor at Aalto University.

To get carbon structures to display colours is a feat in itself. The underlying techniques needed to enable the colouration also imply finely detailed control of the structure of the nanotube structures. Kauppinen and his team’s unique method, which uses aerosols of metal and carbon, allows them to carefully manipulate and control the nanotube structure directly from the fabrication process.

‘Growing carbon nanotubes is, in a way, like planting trees: we need seeds, feeds, and solar heat. For us, aerosol nanoparticles of iron work as a catalyst or seed, carbon monoxide as the source for carbon, so feed, and a reactor gives heat at a temperature more than 850 degrees Celsius,’ says Dr. Hua Jiang, Senior Scientist at Aalto University.

Professor Kauppinen’s group has a long history of using these very resources in their singular production method. To add to their repertoire, they have recently experimented with administering small doses of carbon dioxide into the fabrication process.

‘Carbon dioxide acts as a kind of graft material that we can use to tune the growth of carbon nanotubes of various colors,’ explains Jiang.

With an advanced electron diffraction technique, the researchers were able to find out the precise atomic scale structure of their thin films. They found that they have very narrow chirality distributions, meaning that the orientation of the honeycomb-lattice of the tubes’ walls is almost uniform throughout the sample. The chirality more or less dictates the electrical properties carbon nanotubes can have, as well as their colour.

The method developed at Aalto University promises a simple and highly scalable way to fabricate carbon nanotube thin films in high yields.

‘Usually you have to choose between mass production or having good control over the structure of carbon nanotubes. With our breakthrough, we can do both,’ trusts Dr. Qiang Zhang, a postdoctoral researcher in the group.

Follow-up work is already underway.

‘We want to understand the science of how the addition of carbon dioxide tunes the structure of the nanotubes and creates colours. Our aim is to achieve full control of the growing process so that single-walled carbon nanotubes could be used as building blocks for the next generation of nanoelectronics devices,’ says professor Kauppinen.

Here’s a link to and a citation for the paper,

Direct Synthesis of Colorful Single-Walled Carbon Nanotube Thin Films by Yongping Liao, Hua Jiang, Nan Wei, Patrik Laiho, Qiang Zhang, Sabbir A. Khan, and Esko I. Kauppinen. J. Am. Chem. Soc., 2018, 140 (31), pp 9797–9800 DOI: 10.1021/jacs.8b05151 Publication Date (Web): July 26, 2018

Copyright © 2018 American Chemical Society

This paper appears to be open access.

For the curious, here’s a peek at the coloured carbon nanotube films,

 

Caption: Samples of the colorful carbon nanotube thin films, as produced in the fabrication reactor. Credit: Authors / Aalto University