The first Cs corrected microscopes became generally available at the beginning of the 21st century. Cs corrected microscopes require very tight environmental conditions, which often means that when purchasing a Cs corrected microscope you also have to build a new building as well. An example of purpose built high resolution microscope laboratory is SuperSTEM in the UK. However, it is possible to meet the environmental conditions by converting existing rooms, removing the need for a new building, and therefore making ownership of a Cs corrected microscope more affordable.
The required environmental conditions fall into four groups; Electromagnetic force (EMF), Temperature, Acoustic and Vibration, where the biggest cause of instabilities can come from outside interferences, such as trains, power cables and general road traffic. In most cases these outside interferences can be mitigated, for example moving power cables; however trains and traffic cannot be relocated. This paper outlines measures that can be made to minimise the environment factors by careful design and choice of equipment.
The environmental targets set by the design team were as follows; EMF AC and DC <0.5mG, mechanical displacement (vertical and horizontal) <0.3µm, acoustic noise for all frequencies with a flat field response microphone <60db, room temperature and air movements targets were set as; temperature 20oC ±0.2 hr-1 fluctuation, air flow within the room was to be vertical with a minimum air flow of 100mm sec-1. These targets were considered as reasonable to obtain while also meeting the requirements of the Cs corrected microscopes, which were under consideration at that time of planning.
The final design of the rooms, equipment, anti-vibrational block and services gave the following results. The EMF measurement gave an AC X and Y of 0.05mG and Z 0.2mG with no significant DC component. The acoustics were compromised by noise coming from the floor above with a maximum of 55db at 120Hz. Room temperature was measured at 20oC ±0.08 over a five hour period with a 2.5kW load. The room remain within specification, even when the door was left open for two hours. The isolation block showed no external vibration being measured from the roads or surrounding buildings above the normal background. Vibration measurements were also taken during the night as wel