Analysis of vibration-isolating systems for scanning tunneling microscopes

Abstract

For high-resolution and nanotechnology devices, such as the STM, the effective isolation of environmental vibrations plays a key role. Different types of vibration-reducing systems are analyzed by means of mechanical four-pole theory. A comparison of one- and two-stage spring-suspended systems with magnetic eddy-current damping shows that one-stage systems suffer from poor isolation at high frequencies, which can be improved by additional elastomer elements. Contrary to common belief, two-stage spring systems with eddy-current damping for the upper stage only are superior to similar systems with eddy-current damping of both stages. Plate stacks with elastomer elements yield good amplitude reduction at high frequencies, while vibrations in the 10–100 Hz range may be even enhanced. Several stacks with different arrangements of masses and spring constants are compared, and it is shown that stacks should have only few (2 or 3) plates. For optimum performance it is necessary to combine the plate stack inside the vacuum chamber with soft (pneumatic or spring) suspension of the whole chamber.