Abstract
This chapter describes the principle, the construction, and the characteristics of an experimental Evoscope tube that has small size, high current-gain, and good resolution. The electron bombardment effect is used in this device which has a high current gain and fast response. The Evoscope is basically a small cathode-ray tube. It has a current amplifying target made of a solid-state diode in a single vacuum envelope, and a unipotential electrostatically focused electron gun which generates a high velocity electron beam and bombards the target. As per study, a reverse biased Au (thin film) Si (n-type) diode bombarded by an electron beam with an energy of several tens of keV. The Evoscope generates a video signal from the target by an electron bombardment (voltaic) effect. The video signal appearing across the load resistor is amplified and used to modulate a conventional television monitor. The polarity of the video signal is positive, but it can be reversed by connecting the load resistor to the gold film instead of the silicon bulk. Moreover, the resolution of the Evoscope depends on the diameter of the scanning spot and on the frequency response which is a function of the depletion layer capacitance and the load resistance. Some figures given in this chapter show the current-gain characteristics obtained from experimental Au-Si diodes of 20 mm diameter.
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