Better Imperfections: Optically Active Defects Improve Carbon Nanotubes

Optical Properties of Carbon Nanotubes

The optical properties of carbon nanotubes, which consist of a rolled-up hexagonal lattice of sp2 carbon atoms, can be improved through defects. A new reaction pathway enables the selective creation of optically active sp3 defects. These can emit single photons in the near-infrared even at room temperature. Credit: Simon Settele (Heidelberg)

Heidelberg scientists achieve defect control with a new reaction pathway.

The properties of carbon-based nanomaterials can be altered and engineered through the deliberate introduction of certain structural “imperfections” or defects. The challenge, however, is to control the number and type of these defects. In the case of carbon nanotubes – microscopically small tubular compounds that emit light in the near-infrared – chemists and materials scientists at Heidelberg University led by Prof. Dr. Jana Zaumseil have now demonstrated a new reaction pathway to enable such defect control. It results in specific optically active defects – so-called sp3 defects – which are more luminescent and can emit single photons, that is, particles of light. The efficient emission of near-infrared light is important for applications in telecommunication and biological imaging.

Usually, defects are considered something “bad” that negatively affects the properties of a material, making it less perfect. However, in certain nanomaterials such as carbon nanotubes these “imperfections” can result in something “good” and enable new functionalities. Here, the precise type of defects is crucial. Carbon nanotubes consist of rolled-up sheets of a hexagonal lattice of sp2 carbon atoms, as they also occur in benzene. These hollow tubes are about one nanometer in diameter and up to several micrometers long.

Through certain chemical reactions, a few sp2 carbon atoms of the lattice can be turned into sp3 carbon, which is also found in methane or diamond. This changes the local electronic structure of the carbon nanotube and results in an optically active defect. These sp3 defects emit light even further in the near-infrared and are overall more luminescent than nanotubes that have not been functionalized. Due to the geometry of carbon nanotubes, the precise position of the introduced sp3 carbon atoms determines the optical properties of the defects. “Unfortunately, so far there has been very little control over what defects are formed,” says Jana Zaumseil, who is a professor at the Institute for Physical Chemistry and a member of the Centre for Advanced Materials at Heidelberg University.

The Heidelberg scientist and her team recently demonstrated a new chemical reaction pathway that enables defect control and the selective creation of only one specific type of sp3 defect. These optically active defects are “better” than any of the previously introduced “imperfections.” Not only are they more luminescent, they also show single-photon emission at room temperature, Prof. Zaumseil explains. In this process, only one photon is emitted at a time, which is a prerequisite for quantum cryptography and highly secure telecommunication.

According to Simon Settele, a doctoral student in Prof. Zaumseilʼs research group and the first author on the paper reporting these results, this new functionalization method – a nucleophilic addition – is very simple and does not require any special equipment. “We are only just starting to explore the potential applications. Many chemical and photophysical aspects are still unknown. However, the goal is to create even better defects.”

This research is part of the project “Trions and sp3-Defects in Single-walled Carbon Nanotubes for Optoelectronics” (TRIFECTs), led by Prof. Zaumseil and funded by an ERC Consolidator Grant of the European Research Council (ERC). Its goal is to understand and engineer the electronic and optical properties of defects in carbon nanotubes.

“The chemical differences between these defects are subtle and the desired binding configuration is usually only formed in a minority of nanotubes. Being able to produce large numbers of nanotubes with a specific defect and with controlled defect densities paves the way for optoelectronic devices as well as electrically pumped single-photon sources, which are needed for future applications in quantum cryptography,” Prof. Zaumseil says.

Also involved in this research were scientists from Ludwig Maximilian University of Munich and the Munich Center for Quantum Science and Technology. The results were published in the journal Nature Communications.

Reference: “Synthetic control over the binding configuration of luminescent sp3-defects in single-walled carbon nanotubes” by Simon Settele, Felix J. Berger, Sebastian Lindenthal, Shen Zhao, Abdurrahman Ali El Yumin, Nicolas F. Zorn, Andika Asyuda, Michael Zharnikov, Alexander Högele and,  Jana Zaumseil, 9 April 2021, Nature Communications.
DOI: 10.1038/s41467-021-22307-9


Recent Posts

Sleeping Too Much Linked to a 69% Increased Risk of Dementia

A new study analyzes how sleep duration and timing impact dementia risk. The time individuals…

December 1, 2022

NASA Artemis I – Flight Day 15: Orion Capsule “Go” for Distant Retrograde Orbit Departure

On Wednesday, November 30, NASA’s Artemis I mission management team met to review the overall…

December 1, 2022

Supermassive Black Hole Violently Rips Star Apart, Launches Relativistic Jet Toward Earth

Rare Sighting of Luminous Jet Spewed by Supermassive Black Hole Astronomers discover a bright optical…

December 1, 2022

NASA’s BioSentinel Mission Underway After Successful Lunar Flyby

NASA’s BioSentinel – a shoebox-sized CubeSat designed to learn what happens to life in deep…

November 30, 2022

Prehistoric Superpredator: Weird Whatcheeria Was the “T. rex of Its Time”

Ancient Iowan superpredator got big by front-loading its growth in its youth. Fossils found only…

November 30, 2022

Depression Risk Increases With Hours Worked in Stressful Jobs

Longer work weeks were strongly associated with a higher increase in depression symptoms in an…

November 30, 2022