A novel time-of-flight spectrometer for PAES

Positron annihilation induced Auger electron spectroscopy (PAES) uses the annihilation of a positron with an electron of the inner shell of atoms whereas X-rays or high-energy electrons initiate the ionisation in conventional AES. Advantages of PAES are the extremely high surface sensitivity and the higher signal to noise ratio. In order to benefit from PAES one has to use a low-energy positron beam of high intensity, which is available at NEPOMUC at the new Munich research reactor FRM-II. The energy of the Auger electrons is mostly analysed by hemispherical energy analysers. Due to their small solid angle (typically >= 0.1%) and the necessity to scan over certain energy ranges in >= 1eV steps one still needs several hours using an intense positron source like NEPOMUC (at the FRM-II) or even weeks at the lab-beam based on a beta-emitter to obtain an Auger spectrum. For this reason, a novel time-of-flight spectrometer (TOF-PAES) was developed, which efficiently collects the Auger electrons emitted in a solid angle of 2 pi around the sample, and hence reduces the measurement time to less than one hour. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.