September 17, 2012 – In 2009, IBM researchers managed to peer inside the electron cloud of a molecule to capture and sketch its "anatomy." Now they’ve gone one step further: differentiating the chemical bonds within those individual molecules.
The work relies on a noncontact atomic-force microscopy, using a single carbon monoxide (CO) molecule on the AFM tip which oscillates with a tiny amplitude to measure the forces between the tip and the sample, creating the basis for an image. In this newest work the team examined individual carbon-carbon bonds in C60 (aka "buckyball") and two planar polycyclic aromatic hydrocarbons (PAHs), synthesized by Centro de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) at the Universidade de Santiago de Compostela and Centre National de la Recherche Scientifique (CNRS) in Toulouse. They managed to distinguish individual bonds that differ only by 3 pm, about 1/100 of an atom’s diameter.
What they found is that there are two different contrast mechanisms to distinguish bonds: one based on force measured above the bonds, which was a challenge to resolve, according to IBM scientist Leo Gross. The other contrast mechanism "really came as a surprise," he explains: the bonds displayed different length measurements, which was determined to be caused by tilting the CO molecule at the tip apex.
Knowing the variances in individual molecular bonds can increase basic understanding for research in novel electronic devices, organic solar cells, and organic light-emitting diodes (OLEDs). In particular, understanding the relaxation of bonds around defects in graphene, and the changing of bonds in chemical reactions and in excited states could potentially be studied, could be useful.
The research, published in the Sept. 14 issue of the journal Science, is funded within the framework of several European projects (ARTIST, HERODOT, CEMAS), the Spanish Ministry of Economy and Competitiveness, and the Regional Government of Galicia.
A nanographene molecule exhibiting carbon-carbon bonds of different length
and bond order imaged by noncontact atomic force microscopy using a
carbon monoxide functionalized tip. The molecule was synthesized at the
Centre National de la Recherche Scientifique (CNRS) in Toulouse.
(Credit: IBM Research – Zurich)