PERFORMANCE OF TURBOMOLECULAR PUMPS IN AN EXTENDED TEM SPECIMEN CHAMBER EQUIPPED FOR INSITU VAPOR-DEPOSITION EXPERIMENTS

For in-situ TEM investigations of thin film and particle growth as well as catalytic processes, a vacuum chamber was attached to the specimen goniometer stage to allow metal vapour deposition and gas exposure experiments on thin substrates under clean vacuum conditions. The chamber contains evaporation sources, a gas inlet system, a residual gas analyzer, and an ionization gauge. It is differentially pumped by a specially selected turbomolecular pump (tmp) in order to minimize the influence of vibrations or stray fields on the resolution of the microscope. This has been tested by through-focus series of phase-contrast images from thin carbon films, and by Fourier-transformed images thereof. Virtually no influence on the specified point resolution of 0.3 nm of our TEM was found for a tmp with magnetic bearings. Also, a tmp with horizontally oriented rotor axis did not introduce significant vibrations during the first few months of operation. However, a deterioration was detectable after longer periods of time, due to wear of the bearings. In any case, installation of damping bellows between pump and chamber was necessary to eliminate residual vibrations of lower frequencies.