PROPERTIES OF AN ELECTRON BUBBLE APPROACHING THE SURFACE OF LIQUID-HELIUM

We have studied the properties of an electron bubble close to the surface of liquid He-4, by using a Density Functional approach. We find that up to an electron-surface distance d(0) similar to 23 Angstrom the bubble is stable, while at smaller distances it becomes unstable and bursts. A potential energy barrier Phi/K-B similar to 38 degrees K for the thermal emission of electrons is obtained from our results, in agreement with experiments. Even when the electron-surface distance is larger than do, however, tunneling through the surface layer dominates the electron escape probability. Large deviations of the electron potential energy from its ideal value are found close to the surface. These deviations have a profound effect on the calculated decay rates of the tunneling curent, which are much smaller than those obtained previously and in semi-quantitative agreement with experiments.