SFB 1073 Atomic scale control of energy conversion

C04 Study and control of surface photochemistry using a local excitation microscope (Ropers, Wenderoth, Wodtke)

Surface chemistry is highly site specific. Even on single-crystal surfaces, steps, kinks, edges and defects can have a profound influence on the outcome of a chemical reaction. Hence control of surface defect structure and local environment represents an important potential control tactic for photochemical energy conversion. We propose to take an important step towards local (site-specific) surface photochemistry. We will develop an innovative experimental technique combining state-of-the-art scanning tunneling and near-field optical microscopy. This new tool will allow us to study the spatial influences of surface photochemistry by confining the optical excitation region to a defined position underneath the scanning probe tip. Our efforts will be devoted to the integration of nano-optical excitation with atomically resolving low-temperature scanning tunneling microscopy of photochemically active molecules on specially prepared surfaces. This will enable the investigation of structure function relationships in surface photochemistry.

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Fig. 1: The combination of pulsed optical excitation in Scanning Tunneling Microscopy opens a new and promising access to trigger and study surface dynamics on the atomic scale.

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Fig. 2: Carrier dynamics at the GaAs surface. (A) Constant current topography recorded with a Scanning Tunneling Microscope shows the signature of a buried doping atom. (B) Corresponding map of the carrier relaxation time in the presence of the surface near donor.

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Fig. 3: Electron energy loss maps of a gold nanotip for different energy loss. Swift electrons polarize the electron gas in the metal resulting in the excitation of surface plasmon polaritons (SPPs). The observed standing wave patterns are formed due to reflection of SPPs at the tip apex.