Tag Archives: Hua Jiang

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

“Control my chirality, please,” said the carbon nanotube to the researchers

A combined Finnish, Russian, and Danish team have found a way to control the chirality of single-walled carbon nanotubes according to an Apr. 30, 2013 news item on Azonano,

An ultimate goal in the field of carbon nanotube research is to synthesise single-walled carbon nanotubes (SWNTs) with controlled chiralities. Twenty years after the discovery of SWNTs, scientists from Aalto University in Finland, A.M. Prokhorov General Physics Institute RAS in Russia and the Center for Electron Nanoscopy of Technical University of Denmark (DTU) have managed to control chirality in carbon nanotubes during their chemical vapor deposition synthesis.

The Aalto University Apr. 29, 2013 news release, which originated the news item, goes on to explain,

 Over the years, substantial progress has been made to develop various structure-controlled synthesis methods. However, precise control over the chiral structure of SWNTs has been largely hindered by a lack of practical means to direct the formation of the metal nanoparticle catalysts and their catalytic dynamics during tube growth.

– We achieved an epitaxial formation of Co nanoparticles by reducing a well-developed solid solution in CO, reveals Maoshuai He, a postdoctoral researcher at Aalto University School of Chemical Technology.

– For the first time, the new catalyst was employed for selective growth of SWNTs, adds senior staff scientist Hua Jiang from Aalto University School of Science.

By introducing the new catalysts into a conventional CVD reactor, the research team demonstrated preferential growth of semiconducting SWNTs (~90%) with an exceptionally high population of (6,5) tubes (53%) at 500 °C. Furthermore, they also showed a shift of the chiral preference from (6,5) tubes at 500 °C  to (7, 6) and (9, 4) nanotubes at 400 °C.

– These findings open new perspectives both for structural control of SWNTs and for elucidating their growth mechanisms, thus are important for the fundamental understanding of science behind nanotube growth, comments Professor Juha Lehtonen from Aalto University.

For anyone like me who needs a description of chirality, there’s this from Wikipedia,

Chirality (pron.: /kaɪˈrælɪtiː/) is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek, χειρ (kheir), “hand”, a familiar chiral object.

An object or a system is chiral if it is not identical to its mirror image, that is, it cannot be superposed onto it. A chiral object and its mirror image are called enantiomorphs (Greek opposite forms) or, when referring to molecules, enantiomers. A non-chiral object is called achiral (sometimes also amphichiral) and can be superposed on its mirror image.

Human hands are perhaps the most universally recognized example of chirality: The left hand is a non-superimposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide.[2] This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using his left hand, or if a left-handed glove is placed on a right hand. In mathematics chirality is the property of a figure that is not identical to its mirror image.

One of the researchers notes why they, or anyone else, would want to control the chirality of carbon nanotubes, from the news release,

– Chirality defines the optical and electronic properties of carbon nanotubes, so controlling it is a key to exploiting their practical applications, says Professor Esko I. Kauppinen, the leader of the Nanomaterials Group in Aalto University School of Science.

ETA Apr. 30, 2013 at 4:20 pm PDT: Here’s a link to and a citation for the team’s published paper,

Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles by Maoshuai He, Hua Jiang, Bilu Liu, Pavel V. Fedotov, Alexander I. Chernov, Elena D. Obraztsova, Filippo Cavalca, Jakob B. Wagner, Thomas W. Hansen, Ilya V. Anoshkin, Ekaterina A. Obraztsova, Alexey V. Belkin, Emma Sairanen, Albert G. Nasibulin,  Juha Lehtonen, & Esko I. Kauppinen. Scientific Reports 3, Article number 1460  doi:10.1038/srep01460 Published15 March 2013

This article is open access.