Design and Implementation of a Site for a One-Ångstrom TEM

Abstract

The National Center for Electron Microscopy has recently acquired a field-emission TEM to form thebasis of a project to achieve a resolution of one Ångstrom. To reach this resolution, both instrumental and environmental factors need to be considered. We have designed and constructed a new building to provide a suitable environment for this instrument, with emphasis on providing isolation from external influences detrimental to the achievement of ultra-high resolution. Such influences include mechanical vibration, temperature fluctuations, acoustic noise, and stray electromagnetic fields.The microscope chosen for the one-Ångstrom project is a Philips CM300 Ultra-Twin equipped with a field-emission gun. Pre-installation specifications provided by Philips for this 1.7Å-resolution TEM specify maximum-allowable values for vibration levels in three mutually-perpendicular directions. In the most critical direction (console left to right), vibration is required to remain below 0.8)μm/sec in the frequency range from 1Hz to 5Hz, although allowed to rise to 6μm/sec above 10Hz (Region I in fig. 1). Even when resolution is not a critical requirement, vibration must be minimized at 2.5Hz (Region II in fig.1).