Atomic Manipulation
Three main parameters can be adjusted to control the manipulation of atoms/molecules on surfaces with the STM:
- the electric field between tip and sample,
- the tunneling current of the electrons, and
- van der Waals or chemical forces, which take effect between tip and sample and which can be
adjusted by variation of the tip sample separation.
While working with single atoms or molecules one distinguishes between lateral and vertical manipulation.
Lateral manipulation means, the particle is moved with the tip along the surface to the desired position,
without loosing contact with the surface. In the case of vertical manipulation the particle is picked up
by the tip and moved to the desired position on the tip. There it is dropped back to the surface.
While only the forces between tip and sample are important for reliable lateral manipulation, the electric
field and the tunneling current play an important role for vertical manipulation. This technique
made it possible to build up artificial nanostructures in the atomic scale. The technical
demands for a STM are even increased due to the manipulation technique: it must be possible to control
the tip position in the range of fractions of an atoms size. The drift stability must be so high, that
it is possible to work with a build up artificial structure for days. Because of the thermal
mobility of most adsorbates the STM has to work at low temperatures (down to 4K).