The chamber and sample stage
The electron column is positioned directly above the stage. This is where you will mount your samples for analysis, and the stage enables you to move the sample around in multiple directions. The entire system is then enclosed by the vacuum chamber. This seals everything in and allows the vacuum pumps to reduce the pressure inside the SEM.
The need for vacuum
An SEM cannot operate at atmospheric pressure. The electron source will burn out almost immediately, and even if it could operate for long enough, the electrons that are emitted simply would not make it down to the sample without colliding with gas molecules in the atmosphere. So an SEM must operate under a low pressure, called vacuum, so that the source can maintain stable operation over a long period of time, and both the electron beam and the electron signal from the sample can travel through the chamber unimpeded.
Some systems can operate in intermediate modes, called variable pressure (VP-SEM) or environmental (E-SEM) SEMs, but they still require some level of vacuum to be maintained.
Vacuum is most commonly achieved by a combination of a backing pump and a turbo pump. This will usually be the noise you hear when the SEM is powered on.
The sample stage
Your samples will be mounted to a special holder that attaches to the stage inside the SEM. The stage will allow you to navigate around on your sample surface and change between samples. The stage also ensures that you have a good electrical connection to the instrument ground, allowing accumulated charge from the electron beam to flow out of the sample and minimise surface charging. An SEM stage will commonly have 5 axes of motion:
This allows you to navigate around on your sample, or between samples, to find your regions of interest.
This allows you to vary the working distance, to increase your field of view, or to optimise for a different detector, like an EDS detector.
This allows you to tilt the sample relative to the viewing angle, giving a different perspective. It will usually be used to look at the sides or edges of samples.
Not so commonly needed, but the rotation axis can help to align features to the field of view, or to better position a region in the view of a specific detector.
Detectors
The detectors for the SEM are positioned around and above the sample stage, all generally directed towards the same point in space where the electron beam will be focussed onto the sample. The FlexSEM has the following detectors available for different signals:
SE - secondary electron detector, for topography imaging
BSE - back-scattered electron detector, for material contrast
EDS - energy-dispersive X-ray detector, for elemental identification and quantification
UVD - ultra-variable detector, for use in VP-SEM, and also for cathodoluminescence (CL) imaging
Note how the BSE detector sits directly above the sample, and the electron beam passes through the centre of the four quadrants of this detector.