A flood gun is an electromechanical device that provides a steady flow of low-energy electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s to a desired target or "flood area."

Typically, the target is an area on an insulator or semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 where another "writing gun" has just left a net positive charge.

If the energy of a flood gun's electrons is properly balanced, each impinging flood gun electron knocks out one secondary electron from the target, thus preserving the net charge in the target area. This is called "charge neutralization."

Flood guns are typically used in photoelectron spectroscopy, oscilloscopes and ion beam implanters

Ion implantation

Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into another solid. This process is used to change the physical, chemical, or electrical properties of the solid...

 as their secondary electron gun

Electron gun

An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...

.