Sheets of carbon nanotubes come with a rainbow of colors

The color map shows the unique colors of 466 carbon nanotubes with unique (n, m) designations based on chiral angles and diameters. Credit: Kauppinen Group / Aalto University

Nanomaterials researchers in Finland, the United States, and China have created color atlases for 466 single-walled carbon nanotubes.

Nanotube Color Atlas Advanced material For a new way to predict the specific color of a thin film made by combining any of the 466 types. The study was conducted by researchers at Aalto University in Finland, Rice University, and Peking University in China.

“Carbons that look black to us can look transparent or have a rainbow color,” said Esko I. Kauppinen, a physicist at Aalto University, the corresponding author of this study. “When the carbon nanotubes in the sheet completely absorb the light, the sheet looks black. When less than about half of the light absorbed by the nanotubes, the sheet looks transparent. The atomic structure of the nanotubes causes a particular color. When only light is generated, or wavelengths that are absorbed or not absorbed, they are reflected as visible colors. “

Carbon nanotubes are long, hollow carbon molecules that resemble garden hoses in shape, but are only one atom thick on the sides and about one-50,000th the diameter of human hair. The outer wall of the nanotube is made of rolled graphene. Also, the graphene wrapping angle can vary in the same way as the angle of a roll of holiday gift wrapping paper. Carefully wrap the gift wrap at zero angles so that the edges of the paper are aligned on both sides of the gift wrap tube. If the paper is inadvertently rolled diagonally, the paper will stick out to one end of the tube.

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

Kaupinen’s research group has been studying carbon nanotubes and nanotube thin films for years, and previously succeeded in mastering the production of color nanotube thin films that appear green, brown, and silver-gray.

In a new study, Kauppinen’s team investigated the relationship between the spectrum of absorbed light and the visual color of dry nanotube films of various thicknesses, clearly identified the tinting mechanism of nanotube films, and identified specific colors in the film. We have developed a quantitative model that can predict. Combine different unique colors and specified tubes (n, m).

Junichiro Kono, a US engineer and physicist who solved the mystery of colorful armchair nanotubes in the laboratory in 2012, used a film made entirely of (6,5) nanotubes to calibrate and verify the Aalto model. Provided. Researchers at Aalto University and Peking University used this model to calculate the absorption of rice film and its visual color. Experiments have shown that the measured color of the film corresponds very closely to the color predicted by the model.

The Aalto model shows that the thickness of the nanotube film and the color of the nanotubes it contains affect the light absorption of the film. Aalto’s Atlas, a 466-color nanotube film, is a combination of different tubes. Studies show that the thinnest and most colorful tubes affect visible light more than larger diameter and faded tubes.

“Esko’s group did a great job of explaining color theoretically and quantitatively, which really distinguishes this study from previous studies on nanotube fluorescence and coloration,” Kono said. Said.

Since 2013, Kono’s lab has pioneered ways to produce highly ordered 2D nanotube films. Kono said he wanted Kaupinen’s team to supply a highly ordered 2D crystal film of single-chirality nanotubes.

“That was the original idea, but unfortunately there wasn’t a movie that was in line with the right single chirality at the time,” Kono said. “In the future, we plan to extend this research to study polarization-dependent colors in highly ordered 2D crystal films.”

The experimental method used by Aalto researchers to grow nanotubes for film was the same as in previous studies. Nanotubes grow from carbon monoxide gas and iron catalysts in reactors heated above 850 ° C. The growth of nanotubes with different colors and designations (n, m) is regulated with the help of carbon dioxide added to the reactor.

“Since my last study, I’ve been thinking about how we can explain the emergence of nanotube colors,” said Professor Nanwei of Peking University, who previously worked as a postdoctoral fellow at Aalto University. “Of the allotropes of carbon, graphite and charcoal are black and pure diamond is colorless to the human eye, but now single-walled carbon nanotubes take all colors, including red, blue, green and brown. I realized that I could do it .. “

According to Kaupinen, the colored thin films of nanotubes are flexible and ductile, which can be useful for colored electronic structures and solar cells.

“The color of the screen can be changed, for example, with the help of mobile phones, other touch screens, or tactile sensors on the windows,” he said.

According to Kaupinen, the study can also provide the basis for new types of environmentally friendly dyes.

Carbon color: Colored thin film of nanotubes created for the first time

For more information:
Nan Wei et al. Color of single-walled carbon nanotubes, Advanced material (2020). DOI: 10.1002 / adma.202006395

Courtesy of Aalto University

Quote: Sheets of carbon nanotubes are the rainbow of colors acquired on December 14, 2020 from https: // (2020, December 14) Will be provided in days)

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Sheets of carbon nanotubes come with a rainbow of colors

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