MODIFICATION OF A COMMERCIAL SEM WITH A COMPUTER-CONTROLLED CATHODE STABILIZED POWER-SUPPLY

Modification of the high-voltage circuitry of the thermionic electron gun of a commercial scanning electron microscope (SEM) to a fully computer-controlled, cathode-stabilized system is described. The modification permits automatic filament saturation and monitoring. Using this system, variations and drifts in the emission current over time can be adjusted and compensated automatically with a feedback loop in the computer-controlled system. This change also enables the accurate determination and setting of the primary electron beam energy. Therefore, the accelerating voltage is known for comparison to Monte Carlo computer modeling of the electron beam specimen interaction.