| 摘要 |
PURPOSE:To fix the brightness of a secondary electron image and also reduce any thermal damage of a scintillator by detecting a part of a luminous signal of the scintillator and controlling a voltage impressed on the scintillator in response to its detection output. CONSTITUTION:A scintillator 5 is attached to the tip of a handle type optical fiber 6 of vacuumproof structure. A part of the fiber 6 is connected to an optical detector 12 and its output is inputted in the high-tension control 14 through a logarithmic 13. Further, a collector electrode is connected to a collector voltage control circuit 10 and the scintillator 5 is connected to a high-tension generation circuit 9. When a probe current incident on a sample 11 is increased by means of this constitution, the secondary electrons 2 from the sample 11 increase, while a circuit 14 controls voltage of the circuit 9 to reduce it responding thereto. Accordingly, while keeping the brightness of a secondary electron image almost fixed, thermal damage of the scintillator 5 can be reduced. |
