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A new method of surface barrier transmissivity determination is proposed. It is based on the elementary mathematical processing of emitted electron energy distributions obtained at slightly di †erent work function values of the same sample. The basic assumptions are the constancy of the electron energy distribution before escape into vacuum, and the dependence of the transmissivity only on the di †erence of electron energy and the work function value. The method was applied to an opaque negative electron affinity GaAs photoemitter, and the energy dependence of the GaAs/Cs/O-vacuum interface barrier transmissivity was obtained. The knowledge of the transmissivity made it possible to determine the energy distribution of electrons before their escape into vacuum. The latter contains a great number of very low energy electrons, which can be explained with multiple reÑections at the GaAs-CsO and CsO-vacuum borders.

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