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Scientific first - differentiating chemical bonds in individual molecules

EU funding has helped realise a scientific first; using a technique known as non-contact atomic force microscopy (AFM), scientists have successfully been able to differentiate the chemical bonds in individual molecules. The outcome of this result is that scientists around the ...

EU funding has helped realise a scientific first; using a technique known as non-contact atomic force microscopy (AFM), scientists have successfully been able to differentiate the chemical bonds in individual molecules. The outcome of this result is that scientists around the world will now be able to push the exploration of molecules and atoms to the smallest scale. This could also be important for studying graphene devices, which are currently being explored by both industry and academia for their numerous applications including high-bandwidth wireless communication and electronic displays. This research was funded within the framework of several European projects including ARTIST, HERODOT, CEMAS, the Spanish Ministry of Economy and Competitiveness, and the Regional Government of Galicia. The research team's results were published in a recent issue of Science magazine. IBM scientist, Leo Gross explains their discovery: 'We found two different contrast mechanisms to distinguish bonds. The first one is based on small differences in the force measured above the bonds. We expected this kind of contrast but it was a challenge to resolve,' he said. 'The second contrast mechanism really came as a surprise: Bonds appeared with different lengths in AFM measurements. With the help of ab initio calculations we found that the tilting of the carbon monoxide molecule at the tip apex is the cause of this contrast.' The research scientists imaged the bond order and length of individual carbon-carbon bonds in C60, also known as a buckyball for its resemblance to a soccer ball and two planar polycyclic aromatic hydrocarbons (PAHs), which resemble small flakes of graphene. The first fullerene to be discovered was in 1985 and the Buckminsterfullerene (C60) was so named in honour of Buckminster Fuller whose geodesic domes they resembled. PAHs were synthesised by Centro de Investigacion en Quimica Bioloxica e Materiais Moleculares (CIQUS) at the Universidade de Santiago de Compostela, Spain and Centre national de la recherche scientifique (CNRS) in Toulouse, France. However, not all bonds are equal. The individual bonds between carbon atoms in these molecules differ subtly in their length and strength. All the important chemical, electronic and optical properties of such molecules are related to the differences of bonds in the polyaromatic systems. However, now for the first time, these differences have been detected for both individual molecules and bonds. What this ability means is that it can increase basic understanding at the level of individual molecules, important for research on novel electronic devices, organic solar cells and organic light-emitting diodes (OLEDs). In particular, the relaxation of bonds around defects in graphene as well as the changing of bonds in chemical reactions and in excited states could potentially be studied. Previously, the research team was successful in imaging the chemical structure of a molecule but not the subtle differences of the bonds. Discriminating bond order is close to the current resolution limit of the technique and often other effects obscure the contrast related to bond order. Therefore, the scientists had to select and synthesise molecules in which perturbing background effects could be ruled out. To corroborate the experimental findings and gain further insight into the exact nature of the contrast mechanisms, the team performed first-principles density functional theory calculations. Thereby they calculated the tilting of the CO molecule at the tip apex that occurs during imaging. They found how this tilting yields a magnification and the very sharp images of the bonds.For more information, please visit:Science magazine:http://www.sciencemag.orgCEMAS:http://www.zurich.ibm.com/

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Switzerland, Spain, France

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