Thursday August 08, 2013

A bit of string appears to bend space. This phenomenon is called “charging”, and can cause strange effects in scanning electron beam microscope images.

What’s going on? To make a scanning electron microscope image, we literally scan a beam of electrons across our sample and detect the electrons that are reflected back. If our sample is a poor electrical conductor (like this piece of string), the electrons start to build up, making the sample more and more negatively charged. Eventually, the sample’s negative charge grows so large that it starts to slightly repel the beam of negatively-charged electrons that we’re hitting it with. The result is that the beam gets deflected away from the string as it scans, so it no longer follows its back-and-forth scanning path. The result? Crazy distortion of the image.