Femtosecond Laser Scanning Tunneling Microscope (fs-STM)
The fs-STM is a combination of a low-temperature STM with a femtosecond laser system. The STM system is operated in UHV and consists of four chambers. The STM chamber is connected to a preparation chamber, in which the samples are cleaned by ion sputtering and annealing. A molecule deposition chamber is attached to the preparation chamber and is used to prepare and deposit sample molecules on the single-crystaline samples. The load-lock chamber is used to transfer samples from atmosphere into the UHV chamber. A manipulator, coolable with liquid helium (LHe), is used to transfer the sample from the preparation chamber to the STM chamber, where the measurements take place. The STM is attached to a bath cryostat, which is also cooled by LHe, enabling a temperature in the STM down to 5 K. The pressure inside the shielding of the STM is as low as 10-14 mbar due to the cryopump effect of the cryostat. Therefore, it is possible to measure for several weeks, once the sample is prepared. The STM has a resolution of 1 pm in vertical and 10 pm in lateral direction. The femtosecond laser is focussed by an optical system to hit the sample surface with pulses of 70 fs (FWHM) and a wavelength of 400 nm. With this setup, it is possible to atomically resolve molecules adsorbed on the surface, while the laser system enables to follow reactions on a femtosecond timescale by variation of the delay time between two pulses.
