In cooperation with SPECS GmbH we developed a new time-of-flight spectrometer allowing to measure both energy and angle in one shot. The electrostatic lens system of the hemispherical analyzer PHOIBOS is used to achive a high acceptance angle of up to ±15°. By calculating the trajectories of the particles with a computer simulation the fligth time and the position on the detector is mapped to the kinetic energy and the angle of the particles at emission

Fig. 1: Custom made UHV chamber for the Themis 1000. The drift tube of the spectrometer is to the right of the main chamber.

In a normal ballistic time-of-flight spectrometer the energy can be calculated very easily. In this newly developed spectrometer the trajectories of the particles are not straight. Therefore we need a computer simulation. This programm simulates the trajectories of the particles for different emission angles and -energies. This allows us to deduce these parameters by measuring the time of flight and the position on the detector relative to the spectrometeraxis.

	Fig. 3:upper: Distribution of the electrostatic field in the drift tube and the resulting electron trajectories for a fixed emission energy and different emission angles. center: Distance to axis vs. time-of-flight map for fixed spectrometer settings (wide angle mode 10V; Ekin=1.5V, Epass=15V). The energy-isolines are horizontal, while the angle-isolines are vertical. The measured electron densities are plotted in false colors (blue for low, red for high densities). lower: Energy vs. angle map resulting from numerically inverting the electron trajectories.

Fig. 1: The first data taken with the Themis 1000. The parabolas are the shockley surface state (upper) and the first image potential state (lower) on Cu(111).

under construction

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