| Popis: |
The presence of adsorbed atoms or nonpolar molecules on the surface of a cathode results in an insignificant increase in field-emission current density over that observed for clean metal surfaces. If the adsorbate consists of polar molecules, at fields over 1 MV/cm, the current density can increase by an order of magnitude and more. When the adlayer thickness is several nanometers, the quantum nature of the image forces must be taken into consideration. Calculations show that in this case, owing to the polaron effect, the tunnel emission current is substantially lower than that typical of cathode surfaces free from foreign microinclusions and films. |
