Surface molecular reaction studied with the STM
Gérald Dujardin
Laboratoire de Photophysique Moléculaire
Bât. 210, Université Paris-Sud
91405, Orsay, France
The real-space atomic resolution imaging capability of the Scanning Tunneling
Microscope (STM) has greatly modified our understanding of elementary processes in surface
reactions. It has now become possible to observe directly with atomic resolution how
molecules adsorb on a surface. For semiconductors, the influence of the geometrical and
electronic surface structures on molecular adsorption reactions can be monitored at the
atomic-scale. One can also examine how the adsorption of a molecule modify, in return, the
local structural and electronic properties of the surrounding surface atoms.
Perhaps the most promising use of the STM is, not only to probe, but moreover to
induce surface reactions at the atomic scale. Individual atoms and molecules can be
manipulated with the tip of the STM. Such modifications at the atomic level may induce
dynamical processes on the surface whose evolution in time can be traced by imaging with the
STM. This combined use of the STM as an atomic manipulator to create a desired arrangment
of atoms and as an atomic viewer to monitor the dynamics which result provides us with
outstanding insights on energetic and dynamical properties of surface atoms.
Atomic manipulations enable also to create on the surface novel atomic structures
having specific reactivity. Molecular reactions, which cannot occur on the « natural » surface,
can be selectively activated by such « STM made » atomic structures. This ability to encode
the chemical reactivity of individual predetermined atomic sites opens up interesting new
perspectives in the field of surface reactions.