  We demonstrated on Ag(111) and Ag(100) surfaces that the reciprocal of the
field emission resonance (FER) linewidth, which is proportional to the mean
lifetime of resonant electrons in FER, may vary with the electric field. The
variation on Ag(111) was nearly smooth, whereas that on Ag(100) was sporadic
and fluctuated remarkably. This drastic difference can be explained through
their dissimilar projected bulk band structures and the ensemble interpretation
of quantum mechanics, according to which all resonant electrons are governed by
a single wave function. Ag(100) has an energy gap above its vacuum level,
whereas Ag(111) does not. Consequently, the dissipation rate of the wave
function, which is relevant to the FER linewidth, on Ag(111) was almost stable,
whereas that on Ag(100) fluctuated. The fluctuation revealed that the quantum
trapping effect and surface dipole layer on Ag(100) surface can be investigated
through FER.
