SELF

INFORMATION FOR DAVID SMITH

EXTERNAL PHOTOELECTRIC EFFECT IN METALS

1. << Typical curves of quantum output of external photoelectric effect J with respect to photon energy (spectral characteristic) are shown in Fig. 1 and 2. In the range of frequencies adjacent to ₀ , J 10 ^{- 4} and grows proportionally to ( - ₀ )². At h 10 eV, J sharply grows and achieves 0,1—0,15 at h 18 eV, then it slightly decreases. The frequency ₀' at which J begins fast growing is called THE SECOND RED BOUNDARY. It is important that J begins its fast growth at such energies of photon when metal stops to reflect light well (see Fig. 1) ...

At present, most researchers are inclined to think that practically in all the range of spectrum where we can observe the external photoeffect, it is caused by solid absorption of radiation. This is corroborated by the results of direct measuring of the depth of photoelectrons emission from metal that achieves several hundreds . And small value of J between ₀ and ₀'   can be probably explained by the fact that because of large reflection only a small part of light from this band of frequencies penetrates into the metal and is absorbed there. Furthermore, the absorption in this band is small, and the layer of metal in which this occurs (skin-layer) exceeds the depth of electrons emission. At > ₀', simultaneously with decreasing reflection, the absorption of emission abruptly increases, and due to it J grows fast [1, 2]. In a small band of frequency near ₀ (1,5 ₀)  the spectral characteristic of external photoeffect and the temperature dependence of photo-emission from metals can be well described by Fowler Theory [3] >> [4, p. 364].

Additionally to this brief description of diagrams, please pay your attention to the fact that in Fig. 2 the maximums for each metal are different. This evidences that the extremum is individual for each metal. The thickness of skin-layer to which the author of cited article refers exerts a small effect at the band where we study the external photoeffect, since in the entire range of frequencies it means only one layer of metal atoms.

2. In this item I would like to show also the standard representation of photon theory as to the possibility for photons to interact with free electrons of metal.

<< The conservation laws for the energy E and pulse p exclude the possibility, photon to be absorbed by a free electron. We can see it already from the fact that the conservation laws for the energy and pulse for optical transition from the state E₁ , p₁ into the state  E₂ , p₂

(where is the frequency, and k is the wave vector of photon) are incompatible with any velocity of electron < c. Thus, the light absorption by conduction electrons and external photoeffect in metals can occur either in the near-surface layer, where the potential jumps and the exponential fall of wave function of electron out of metal make the conduction electrons bound, or within the volume on the account of conduction electrons interacting with the periodic field of lattice >> [ibidem, p. 363—364].

References:

1. Pines Z.D. The elementary excitations in solid bodies. Moscow, 1965.

2. Walker W.C., Rustig O.P. and Weissler G.L. J. Opt. Soc. of America. 1959, 49, 5, p. 471.

3. Sokolov A.V. Optical properties of metals. Moscow, 1961.

4. Lifshitz T.M. Photoeffect external. In: Physical encyclopaedia, vol. 5, pp. 363—365. Moscow, Sovetskaya encyclopedia, 1966.