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article imageEssential Science: First circular pure carbon molecule created

By Tim Sandle     Aug 26, 2019 in Science
Carbon atoms are of great importance for science, being able to form a variety of three-dimensional configurations. These allotropes are structurally different and have several key industrial uses.
In new research, scientists have created cyclocarbon – or a ring-like structure comprising only carbon. This has taken decades of research. The synthesis of the spherical carbon is the created of IBM Research–Zürich and Oxford University.
The new molecules are called cyclo[18]carbon, which is a reference to the creation of a circular molecule formed from 18 carbon atoms. The spherical nature of the shape has been confirmed using an atomic force microscope.
A new allotrope of carbon
The cyclo[18]carbon represents a new allotrope of carbon - elementally identical to other forms of carbon but structurally very different, as Nature reports. As an example, with diamonds carbon atoms are tetrahedrally bonded; whereas with graphite, this is formed of hexagonal atomic sheets of carbon. Another form is fullerene, composed of 60 carbon forming an icosahedral structure.
The cyclocarbon has been challenging to create because most attempts have created something highly reactive and therefore unstable. This arises because atoms are typically double-bonded with each other.
In recent decades, many more allotropes, or forms of carbon, have been discovered and researched including ball shapes such as buckminsterfullerene (a sixty-carbon atom form that has high electronic affinity) and sheets such as graphene. Graphene is the carbon-form of the moment. The material is flexible, transparent and conducts heat and electricity ten times better than copper, and it has good optical properties (making it suitable for flexible display screens).
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Ultra-high vacuum scanning tunneling microscopy image of a point defect in graphene that has been epitaxially grown on 6H-SiC(0001)
Argonne National Laboratory
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Synthesis process
With the new research, Laboratory Roots reports, Profesor Przemyslaw Gawel and his team took a different approach to the carbon synthesis route – they adopted a "subtraction" approach; that is they took atoms away rather than attempting to add atoms to a smaller structure. This involved using oxygen–carbon molecules positioned on a layer of sodium chloride, and placed inside a high-vacuum chamber.
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For this process the researchers began with a larger molecule C24O6 and then proceeded to remove a pair of carbon and oxygen atoms (C=O) at a time, by deploying a high-vacuum chamber (a process called induced atom manipulation). Following the removal of six carbon monoxide molecules, a cyclo[18]carbon was created. The new molecule has been assessed as thermodynamically stable.
The synthesis process is described in the following video:
The analysis of the high-powered microscopic image reveals that each of the atoms in the C-18 ring are both triple- and single-bonded (the image analysis showed there were defined positions of alternating triple and single bonds). This is key to what this spherical form of carbon might be used for – as a semiconductor. In this way the cyclocarbon would have some similar properties to graphene.
Further research is required to assess the stability of this novel molecule and to determine the extent that it can be transformed into something practically useful, such as a molecular-sized transistor (this could be anew generation of molecular-scale electronic components).
The research could open up a path for the synthesis of other carbon allotropes and carbon-rich materials, each formed from the coalescence of cyclocarbon molecules.
Research paper
The new study has been published in the journal Science. The research paper is titled “An sp-hybridized molecular carbon allotrope, cyclo[18]carbon.”
Essential Science
CRISPR -  revolutionary new tool to cut and splice DNA.
CRISPR - revolutionary new tool to cut and splice DNA.
Illustration courtesy of Jennifer Doudna/UC Berkeley
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we discussed how scientists working on Switzerland have refined the CRISPR-Cas gene editing method. Through this modification it is now possible for researchers to modify dozens of genes within a cell simultaneously, thereby speeding up the process.
The week before we learned how scientists have fitted a wireless device to the brains of mice and can control the brain neurons via smartphone. It may have an ominous, dystopian sci-fi feel to it but there is a serious side too, with potential for healthcare.
More about carboon, molecules, Electronics
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