IBM Fellows Gerd Binnig and Heinrich Rohrer, who shared the 1986 Nobel Prize in Physics with German physicist Ernst Ruska, demonstrated the technique for the first time as part of their work at IBM Research in Zurich, Switzerland. IBM said the research will aid in the development of new organic materials for solar cells, OLEDs) and graphene semiconductors. IBM is also using the technique to help unravel the structure of unknown carbon compounds.
"IBM now for the first time can differentiate individual bonds in molecules," said IBM scientist Leo Gross. "Brighter bonds are shorter and have higher bond order. We can also see that bonds appear at different lengths and can differentiate which are longer and which are shorter in molecules."
The new technique uses an atomic force microscope with a carbon monoxide molecule on its tip along with two contrast-enhancing techniques. The first measures small differences in the force measured above the bonds, with stronger bonds appearing being brighter. The second technique involves tilting carbon monoxide molecules on the microscope’s tip, allowing the measurement of the bond length.
"This is the first time you can measure these properties on individual bonds on individual molecules, whereas previously it was only possible to make such measurements on large ensembles of molecules," Gross claimed.
Many important chemical and electronic properties of semiconductor materials are believed to be related to differences in bond structures between their constituent atoms, especially where crystalline lattice defects act as dopants in organic compounds. IBM said the new technique can distinguish bond lengths differences down to 3 picometers, or about one-hundredth of an atom’s diameter.
Individual molecular bonds between fullerene atoms (buckyballs, left) precisely follow the graphical representation of polygons (right) with atoms at vertices connected by bonds shown as lines.
Next, IBM plans to use its technique to study the structure of organic solar cells in hopes of understanding how bonds between atoms affect their efficiency. The technique also will be used to study future electronic devices made from graphene to understand how the relaxation of bonds around defects enhances performance.
The IBM researchers also plan to explore different tip-termination techniques that could further enhance contrast.
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