Low Energy Electron Position Sensor

A surface barrier diode for position determination of low energy electrons was recently fabricated relying heavily on past experience. This diode was fabricated on a 1 "diameter, . 006 " thick 2000 ¿-cm resistivity N type silicon slice with the active sensor area occupying about 1/2" by 1/2" of the area in the middle of the wafer. The sensitive front side of the unit consisted of a gold plated p-type inversion layer while the reverse side had a contact array on it providing position readout. This array was made up of two perpendicular sets of parallel evaporated conductors mutually isolated from each other. A unit having 32 readout lines in each of the X and Y directions was completed and it was shown that a sensor with 64 lines in each of the above directions can also be made with the technique currently in use. The units were tested using an electron gun and an accelerating potential providing up to 50 KV. The motion of the sample behind a fixed baffle with a pinhole in it provided the positioning of the electron beam onto the sample. When testing the units having 32 lines on their backs, it was found that only about 10% of the lines were responding to the electron beam. The internal noise of the rest of the channels masked the increase in counts when the beam was activating them.