The design of an electrostatic variable energy positron beam for studies of defects in ceramic coatings and polymer films

An electrostatic variable energy positron beam for studying defects in ceramic coatings, polymer films and MOS-devices is developed for operation in Doppler-broadening (DB) and positron annihilation lifetime (PAL) modes. In DB mode the implantation energy can be varied between 3 and 30 keV with a beam diameter on the target ranging from 0.4 to 0.5 mm FWHM. In PAL mode the start-signal is given by secondary electron emission from a 25 nm thin carbon foil placed in front of the target. After passing the foil the positron beam is focused on the target with a spot size of 2 mm FWHM at 1 keV down to 0.6 mm FWHM at 30 keV. The target chamber is equipped with an in situ four-point bending device for studying defects introduced by tensile and compressive stresses.