Its thin metal tip scans the specimen surface like the needle of a record player and registers the atomic irregularies and differences of approximately one nanometre (a billionth of a millimetre) with minuscule electric currents. However, even though the tip of the microscope only has the width of an atom, it has not been able so far to take a look inside molecules.
"In order to increase the sensitivity for organic molecules, we put a sensor and signal transducer on the tip," says Doctor Ruslan Temirov. Both functions are fulfilled by a small molecule made up of two deuterium atoms, also called heavy hydrogen. Since it hangs from the tip and can be moved, it follows the contours of the molecule and influences the current flowing from the tip of the microscope. One of the first molecules studied by Temirov and co-workers was the perylene tetracarboxylic dianhydride compound. It consists of 26 carbon atoms, eight hydrogen atoms and six oxygen atoms forming seven interconnected rings. Earlier images only showed a spot with a diameter of approximately one nanometre and without any contours. Much like an X-ray image, the Jülich scanning tunnelling microscope shows the molecule's honeycombed inner structure, which is formed by the rings.
"It's the remarkable simplicity of the method that makes it so valuable for future research," says Professor Stefan Tautz, Director at the Institute of Bio- and Nanosystems at Forschungszentrum Jülich. "The spatial dimensions inside molecules can now be determined within a few minutes, and the preparation of the specimen is based predominantly on standard techniques," says Tautz. In the next step, the Jülich scientists are planning to calibrate the measured current intensity as well. If they are successful, the measured current intensities may allow the type of atoms to be directly determined.
COMPAMED.de; Source: Forschungszentrum Jülich