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?