Cold Cathode Electron Gun Mark I

    Prev Next
    1. P^2 - Paul 24 months ago | reply

      Looks like gas discharge. What's the pressure? (Rather, what's the electron mean free path?)

    2. nebarnix 24 months ago | reply

      Its about 0.1 Torr. The mean free path is longer than you'd expect at this pressure for an electron. I will gather more data tonight. The pressure gauge was disconnected at the time of this experiment. Oops.

    3. P^2 - Paul 24 months ago | reply

      Well, that's just really cool.

      I know that filament temperature is important in EMs, since a hot filament imparts a wide velocity spectrum to the emitted electrons, which makes focusing harder. Is that an issue in a SEM? (lower resolution but also lower energy electrons) Does the cold cathode help?

      Also, I'm guessing you're low enough energy and fluence here that you don't have to worry about X rays, but if you're going above ~10 kV and a microamp then you should consider some kind of dosimetry and radiation protection.

    4. nebarnix 24 months ago | reply

      Correct. I am sure that there are lots of drawbacks to the cold cathode design. However the largest plus is the fact that it can operate at such a low pressure. Its still not quite EnvSEM low, but it could be easily done given a differential pumping scheme.

      The voltage required to sustain arc ignition is about 12kV through a 10 meg current limiting resistor. Of course, the arc has a resistance so I'm sure the electrons are not that high energy. I also need to get a HV probe connected to the cathode to determine this.

      I'm sure I have a huge chromatic context here, that's ok though. At this point, I'm not trying to break any magnification barriers... And filtering can be accomplished using spray apertures to some extent.

    keyboard shortcuts: previous photo next photo L view in light box F favorite < scroll film strip left > scroll film strip right ? show all shortcuts