Experimental Laboratory Exercises

Electrostatic charging

Nonconducting samples have a problem with charging. If the charge from the electron beam strikes a nonconducting surface and cannot flow away, the charge on the surface deflects the electron beam and it become impossible to form a good image. Typically the screen turns white when there is charging. Working at low resolution and low acceleration voltage (1 kV) helps to reduce the effects of charging. Putting a conducting tip on the surface allows you to focus on a small area around the tip.

Charging distorts an image of a gold pattern on a glass substrate.

By touching a grounded probe tip to the glass, the charge can be drawn away in an are around the tip and it is possible to get a clear image.

A tip contacting a gold structure on a glass substrate.

The backscatter detector has less trouble with charging than the secondary electron detector. Below images taken with the backscatter detector before and after a tip has been contacted to a gold line. The discharge of the charge when the tip came in contact with the gold lines caused the lines to fuse.

An image take with the backscatter detector before contact was made.

After making contact with the tip the thin gold lines are damaged.