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A Tour of the SEM

The three major parts of the system are: (1) the column and specimen chamber, resiliently mounted on top of (2) the electronics enclosure, that houses almost all the electronics and control systems, along with a turbo vacuum pump, and (3) the Windows® XP computer which provides the user interface, and also contains a bespoke board for controlling the SEM.

The small screen to the right of the VDU provides a picture of the inside of the chamber, and is useful for ensuring stage movements do not cause specimens to collide with the objective lens.

Scarcely visible between the electronics enclosure and the computer desk is a rotary vacuum pump, which is brought into use during the initial evacuation of the column from the vented state, and periodically thereafter.

The cylindrical structure is the column, containing the tungsten filament, the cathode, anode and electromagnetic lenses and scanning coils. This sits on the specimen chamber, which is the square shape directly below it. The cylindrical housing projecting forward contains the control mechanisms for the stage (see later), and the four knobs on its front face permit manual control of the stage. The lever at approximately “10 o’clock” is for tilting the stage (which can only be carried out manually).

The tilted enclosure on the left houses the electronics for the Secondary Electron detector. The mechanism protruding from the right of the chamber is  the advance/retract mechanism for the backscattered electron detector.

The specimen chamber is accessed by pulling the entire front forward, with the chamber in the vented (no vacuum) state.

This shows the inside of the chamber door, viewed from the right, with the specimen stage. Depending on the size of the specimen mount (or “stub”) the stage can accommodate up to seven separate stubs. The stage can be moved in the X, Y and Z (vertical) directions, and also rotate about its central axis, all under control of the Windows® interface, or alternatively using the knobs on the chamber door. In addition, the stage can be tilted manually.

This provides a closer view of the stage, which is shown holding standard half inch and one inch stubs, along with two custom made stubs providing the facility manually to rotate specimens held in a small horizontal aluminium rod.

This picture shows the Everhart-Thornley secondary electron detector with its Faraday cage, alongside the conical final electro-magnetic lens. The detector works by attracting the secondary electrons dislodged by the electron beam, which then strike a scintillator which emits photons. These, in turn, are amplified using a photo-multiplier which provides an electric signal at its output.

Below the final lens is the retractable Backscattered Electron Detector, and at the rear of the chamber the “Chamberscope”, which is a camera to provide a view of the interior of the chamber when under vacuum, can also be seen.