Low-energy electrons escape from some materials via distinct “doorway” states, according to a study done by physicists at Austria’s Vienna Institute of Technology. The team studied graphene-based materials and found that the nature of the doorway states depended on the number of graphene layers in the sample.
Low-energy electron (LEE) emission from solids is used across a range of materials analysis and processing applications including scanning electron microscopy and electron-beam induced deposition. However, the precise physics of the emission process is not well understood.
Electrons are ejected from a material when a beam of electrons is fired at its surface. Some of these incident electrons will impart energy to electrons residing in the material, causing some resident electrons to be emitted from the surface. In the simplest model, the minimum energy needed for this LEE emission is the electron binding energy of the material.
Frog in a box
In this new study, however, researchers have shown that exceeding the binding energy is not enough for LEE emission from graphene-based materials. Not only does the electron need this minimum energy, it must also be in a specific doorway state or it is unlikely to escape. The team compare this phenomenon to the predicament of a frog in a cardboard box with a window. Not only must the frog hop a certain height to escape the box, it must also begin its hop from a position that will result in it travelling through the hole (see figure).
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