# Can a strong electric field ionize an atom?

Metals have a work function which is the minimum energy needed to ionize an electron. I assume that the energy need is simply the energy difference of the two highest energy levels of a particular metal. This is all well and good and can be accomplished by absorbing a photon of that specific energy.

However, can this same ionization effect be achieved by exposing a metal to a very strong electric field? To gain the energy needed to escape, the electron would have to travel through the field a certain distance, depending on how strong the field is. However, the electron is bound to the atom, so would it be able to do this?

If this effect is possible, how would you quantify it mathematically with some kind of relationship between the work function and the electric field necessary?

ZapperZ
Staff Emeritus
Metals have a work function which is the minimum energy needed to ionize an electron. I assume that the energy need is simply the energy difference of the two highest energy levels of a particular metal. This is all well and good and can be accomplished by absorbing a photon of that specific energy.

However, can this same ionization effect be achieved by exposing a metal to a very strong electric field? To gain the energy needed to escape, the electron would have to travel through the field a certain distance, depending on how strong the field is. However, the electron is bound to the atom, so would it be able to do this?

If this effect is possible, how would you quantify it mathematically with some kind of relationship between the work function and the electric field necessary?

First of all, you are mixing two different "worlds" here.

You first brought up "metal", which is a solid, and invoking the concept of work function. But later on, you switched gears and talked about "atoms" and electron being bound to atoms. Please note that solid state physics is distinctly different than atomic physics. "Work function" is typically concept of solids, not of atoms (where are there binding energies, etc.). The electron in a metal are not bound to any particular atoms. In fact, they form a continuous band, with the highest energy being the Fermi energy. This is not present in atoms.

Now, going back to your original question. In high fields, there is something called "field emission" phenomenon. This is where electrons in metal, for example, can tunnel through the potential barrier of the work function, and emerge outside the metal. This is the basis for why sharp, pointy objects can initial a spark. These sharp regions have very high field enhancement effects, causing a larger amount of field emission current.

The theory of field emission has been formulated and called the Fowler-Nordheim theory. It has been the foundation of many applications and devices involving field emitters.

So yes, if you have an isolated, non-grounded metal, and you put it into a high-enough field, you can ionize it to a certain extent.

Zz.