  The Vavilov-Cerenkov phenomenon - light emission during the motion of a fast
electron in a dense medium is observable in homogeneous media as well as in
inhomogeneous media like photonic crystals. So long as a space (homogeneous or
inhomogeneous) contains natural waves with phase velocities that are lower than
the velocity of a flying through electron then a Cerenkov emission of light
would appear. In nanofilms and nanowires made of silver, gold, copper there are
so called surface plasmon polaritons, namely natural waves with a low phase
velocity. These waves velocity could be by tens and hundreds times lower than
the light velocity in vacuum. An electron with a velocity that is comparatively
lower than a velocity of an electron that is able to emit in a uniform medium
could emit Cerenkov light. Dispersion relations are calculated for the
corresponding plasmons as well as the angles of emission of the plasmons of
corresponding frequencies.
