b)

The theory of photoemission from metals is still in the state of development. There are relatively few rigorous calculations of photo-emission spectra from metals. Much of the work which is being done currently is addressed to the question of the role of many-body inter-actions in this type of problem, and it is, indeed, a theoretical question on ideal metal surfaces of considerable complexity. The intro-duction of surface roughness requires a model theory, and it requires some model concept. Now, the thing I am going to address myself to in this talk is to the role of surface plasmons in enhancing the photo-emission of metals. As shown in Fig. 1, a surface plasmon is essentially an electro-magnetic wave which can exist on the surface of the metal and which is exponentially damped with distance away from the metal surface. This surface electromagnetic wave is obtained by solving Maxwell • s equations for a metal dielectric interface. When you do that, you obtain the dispersion relation of Fig. 1, which describes how the frequency varies with wave number for the surface plasmon. The electric field accompany-ing the surface plasmon can propagate along the surface with a velocity which is determined by this dispersion curve. The wave is exponentially damped with depth away from the free surface. The upper part of Fig. 1 shows the nature of the electric field lines. If you were to imagine charges distributed along the surface (positive and negative charges along the surface) then the electric field lines would have this type of configuration. The condition for the existence of plasmons which I will be talk-ing about later on is obtained by equating the real part of th