The Model 11-020 LEED Electronics supports all Princeton Research Instruments LEED optics, as well as LEED optics formerly manufactured by Physical Electronics, Inc. The unit includes all of the electronic controls necessary for the operation of these optics in LEED mode. All connections to the electron optics are made through MHV connectors and a set of 21 foot long coaxial cables furnished with the optics. An instruction manual is included.
The electron beam voltage comes from a well regulated low-ripple power supply, which is variable from 0 to 1,600 volts. The beam voltage can be scanned manually, and the gun remains focused when the beam voltage is varied. Terminals are provided for external resistance programming of the electron beam energy. Terminals are also provided for an external source of beam voltage of up to 3 kV for use in Auger mode. The focusing voltage is obtained from the beam voltage power supply, and is controlled by a ten-turn potentiometer for precise adjustment of focus.
The system can be operated in the retarding mode to achieve very low incident electron energies while maintaining useful beam current levels.
A digital voltmeter is used to measure the electron beam energy within ± .1 eV. A low voltage recorder output proportional to the beam energy is also available for use when measuring beam intensity versus electron energy. When setting up the electron gun and when making qualitative measurements, the digital voltmeter is also used to measure primary beam current, corrected for the secondary emission of the target.
The suppressor grid and screen voltage are obtained from separate power supplies. The suppressor grid voltage varies the pattern contrast, and can be adjusted from -15 volts to +100 volts with respect to the electron gun cathode. The display (collector) screen voltage, which determines the pattern brightness, is adjustable from zero to 5 kV.
This option adds a circuit board with an isolated BNC input that allows an external DC control voltage to set the beam voltage in the Model 11-020 electronics. A user-supplied digital to analog converter (DAC) can then be used to program the beam voltage, despite the fact that the beam voltage control circuitry is not referenced to chassis ground.