Electrostatic charge build up in environmental electron microscopy

[Alex_F]

TL;DR Summary

Mechanism of discharging electrostatic charge in environmental scanning electron microscopy.

Hello,

If I understand it correctly, the samples are grounded inside a scanning electron microscope (SEM) to avoid charge build up through the electron beam. Also the non-conductive are coated with a conductive layer, so they can be grounded as well.

However, I do not know how the charge build up is suppressed inside an environmental electron microscope (ESEM). I have seen articles in which the have studied surface surface morphology of samples made of insulating material without conductive coating (if I am not mistaken).

Could someone please explain the electrostatic charge build up is avoided in ESEM? Do the samples have to be grounded also in ESEM as with SEM?

 

[sophiecentaur]

Summary:: Mechanism of discharging electrostatic charge in environmental scanning electron microscopy.

Could someone please explain the electrostatic charge build up is avoided in ESEM?

Your logic is impeccable. I have no idea of the full answer but I would imagine that it could be to do with the "wet" samples that are mentioned in the Wiki article on ESEM. The system may have limitations?

 

[Alex_F]

Your logic is impeccable. I have no idea of the full answer but I would imagine that it could be to do with the "wet" samples that are mentioned in the Wiki article on ESEM. The system may have limitations?

Thanks for your answer. I suppose that it might be the case that the discharge process relies solely on the presence of humid air inside ESEM to wash off and carry the charges away from the sample, but I am not sure.

 

[sophiecentaur]

What would the electron beam current be? I saw values less than 1μA mentioned and a 20kV accelerating voltage. Perhaps there is a limit to the time that the scan can be run.
If the sample is wet, the discharge could be through the sample itself, though, to the holder. It's got to involve the wetness. I can't think of any other reason to have it wet than to give a path to ground.
Water could affect samples with soluble bits in them so I guess the technique would have limited application.

You don't half learn a lot on PF! Environmental Electron Microscopes - fantastic.

 

[Baluncore]

You don't half learn a lot on PF!

Like the meaning of the term " litote ".

 

[sophiecentaur]

Last time I used the word “litotes” was in O Level Latin. But not the last time I used the grammatical form without realizing it explicitly.

 

[gentzen]

The explanation of discharging given in section Specimen charging (wikipedia on ESEM) is

Instead of this coating, the gas in the ESEM being electrically conductive prevents negative charge accumulation. The good conductivity of the gas is due to the ionization it undergoes by the incident electron beam and the ionizing SE and BSE signals.

This ionization of the gas is the generally accepted explanation. There is no need for humidity or for the sample being grounded.

 

[Alex_F]

The explanation of discharging given in section Specimen charging (wikipedia on ESEM) is

This ionization of the gas is the generally accepted explanation. There is no need for humidity or for the sample being grounded.

That is correct. This is explained very well in this article https://www.nature.com/articles/nmat898.