Development of Sub-Å Order Acoustic-Noise-Reduction Specimen Holder for Transmission Electron Microscope

Abstract

This paper addresses countermeasures against the small vibration less than 1 Å excited by the acoustic disturbance for electron microscopes. We investigated about the eigenmodes of the specimen holder and goniometer, and added damping factor or changed the natural frequencies. In small strain region less than 10-6 order, most of all damping metals lose their damping factor. Then we applied the wide range tuned mass damper on the specimen holder to restrict not only its bending mode around 250Hz but also the other mode of the goniometer around 400Hz. Both modes were well restricted and the gains of the allowance sound pressure levels were around 5 dB with 1/3-octave-bandpass-filtered random noise. Vibrations in 2 kHz order were caused by the eigenmodes of the tilting mechanism and its support structure placed on the head of the specimen holder. We increased the stiffness of the support structure to avoid closing of the natural frequencies to those of the tilting mechanism. Vibrations around 2.5 kHz were well restricted and the gain of the allowance sound pressure level was around 5 dB. In higher frequencies where the eigenmodes of the support structure exist, the allowance levels of the sound pressure decreased, however they were larger than ordinary levels of the acoustic disturbance. Therefore, the developed specimen holder is useful as a countermeasure against the vibration less than 1 Å caused by the acoustic disturbance. This specimen holder has already been applied to the products on the market.