  We derive a generic formalism for studying the energy conversion processes in
bounded metals. Using this formalism we show that in the collision-less limit
the Fermi sea of metals should experience an instability against surface plasma
oscillations, which opens for the latter an intrinsic self-ampli cation
channel. The origin of the instability is clari ed as arising from novel
effects resulting from the translation symetry breaking due to the very
presence of surface. The ampli cation rate of this channel is analytically
evaluated on the basis of energy conservation and the effects of losses are
discussed. In particular, the unique role played by the surface in energy
conversion is unveiled. In contrast with common wisdom and in line with
observations, Landau damping is shown as always overcompensated and therefore
poses no serious issues in sub-wavelength plasmonics.
