Image of the month

Electron mirror

May's image illustrates a phenomenon that most SEM users wish to avoid: the electron mirror.  This occurs when an insulating sample is imaged using the high vacuum mode of a scanning electron microscope.  As the electron beam is scanned across the surface of the sample an electrical charge develops.  Typically this results in a very poor SEM image showing a variety of bright spots and streaking.  In an extreme case, such as this, enough electrical charge builds up on the surface to form an electron mirror that deflects the electron beam away from the sample.  If the beam is reflected through 180° it will scan the roof of the microscope chamber; allowing the microscope to effectively take a “self portrait”, as seen here. To the right of the image (coloured yellow) can be seen a much distorted view of the surface of the sample.  To the left and centre of the image (in blue) can be seen a “reflection” of the interior of the SEM chamber.  To avoid this phenomenon, insulating samples must be coated with a thin layer of conductive material, typically gold.  Alternatively, the microscope can be used in either the low vacuum or environmental SEM modes, which prevent electrical charge from developing.  This image was captured by Dr Chris Stain using the Centre’s Quanta 600F SEM.

Page navigation


Search Form

A-Z lists