Where are all the electrons from?

Headnote

Imaging the distribution of triboemitted electrons in vacuum enables the sources of the electron-emission to be identified.

IN A PREVIOUS TLT COLUMN, we discussed the intriguing observation that X-rays were emitted when Scotch tape was rapidly peeled.1 However, elementary particles such as electrons also have been detected when surfaces are rubbed. One model for electron emission suggests that they form due to surface fracture during which a charge imbalance between the faces of the cracks produces large electric field gradients, causing electrons to be emitted from the negatively charged crack face. Testing this idea would require knowledge of where the electrons originate.

Drs. Tom Reddyhoff and Julian Le Rouzic from Imperial College in London have solved this problem by incorporating a microchannel plate electron detector in their tribometer. MicroChannel plates form the basis of image intensifies and consist of an insulating plate containing thousands of small holes, much like a sieve. A high voltage is placed across the faces of the plate so that when an electron enters one...