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The work contains results of investigations on the phenomena of the electron emission in thin oxide layers (ITO) in which internal electric field has been generated. Two conducting and transparent films of In2O3:Sn were evaporated on both sides of a microscopic cover glass. One film of the thickness 10 divided by 20nm was the emitting surface. The other, of thickness 1 micrometers , was polarized in order to create an internal field. Applying a negative voltage Upol to field electrode created the internal electric field. The investigations were performed in the vacuum of the order 10-6Pa. As a result of applying Upol and illumination, electrons are released and enter electron multiplier. The electrons create voltage pulses in the multiplier, which are recorded in the multichannel pulse amplitude analyzer. The pulses are recorded in channels of the pulse analyzer, creating so-called voltage pulse amplitude spectrum. The amplitude spectra were measured for unilluminated samples and illuminated by a quartz lamp. With increasing Upol and after illumination the count frequency of pulses grows monotonically. At low Upol the increase is linear. At higher Upol this dependence is exponential. This may be evidence that the electric field initiates electron collisions, which proceed according to impact ionization mechanism. Photoinduced optical second harmonic has been also observed in these films. Theoretical calculations have shown that SnO4 tetrehedral interacting with SiO4 clusters of the glass substrate play central role in observed nonlinear photoinduced changes.
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