In order to increase the sensitivity of a scanning tunneling microscope for use with organic molecules, researchers led by Ruslan Temirov, Forschungszentrum Jülich, Germany, have put a sensor and signal transducer on the tip.

Both functions are fulfilled by a D₂ molecule which can follow the contours of the molecule under study and influence the current flowing from the tip of the microscope. The short-range Pauli repulsion between the deuterium and the molecule modulates the conductivity and allows measurement of the fine structures with high sensitivity.

The technique can be used to determine spatial dimensions inside molecules within a few minutes, and the preparation of the specimen is based predominantly on standard techniques. Now, the Jülich scientists plan to calibrate the measured current intensity to allow the type of atoms to be directly determined.

• Imaging Pauli repulsion in scanning tunneling microscopy
  C. Weiss, C. Wagner, C. Kleimann, M. Rohlfing, F. S. Tautz, R. Temirov,
  Phys. Rev. Lett. 2010, 105, 086103.
  DOI: 10.1103/PhysRevLett.105.086103