SEM Issue

[Noah212]

I had the incredible opportunity of using a scanning electron microscope today, although I encountered a significant issue and am hoping some of you here can offer some insight. The butterfly scales I imaged were visibly waving back and forth/flexing on the SEM's monitor even though they were in a vacuum chamber and on a vibration isolation table.

Here are the images:

(Besides converting from .tif to .jpg, these are straight from the SEM)








The imaging lab where I worked today is on the fifth floor (though each floor is probably 3 stories) and a subway runs underneath. Could this be the source of the movement even though the SEM is on a vibration isolation table? Other specimens didn't suffer from this strange movement so I don't think that the subway and height actually affected anything.

My theory is that the scales, which are overlapping on each other and are really quite thin, don't have enough support and thus are somewhat free to move around, though I'm not quite sure what forces would cause this movement seeing as the specimen is in a vacuum chamber and the SEM itself is on a vibration isolation table.


Any ideas?

[rjlittlefield]

My theory is that the scales, which are overlapping on each other and are really quite thin, don't have enough support and thus are somewhat free to move around, though I'm not quite sure what forces would cause this movement seeing as the specimen is in a vacuum chamber and the SEM itself is on a vibration isolation table.

Any ideas?

I have no experience in this area. But it occurs to me that the electron beam itself will carry some momentum, and because the beam hits each scale only periodically, there's some opportunity to set up resonances.

Have you tried changing the beam intensity to see if the motion changes?

--Rik

[Pau]

I agree with each Rik's word

[dmillard]

It's been years since I have done any SEM (using Polaroid PN 55!), but perhaps the streaking and distortion may come from a charge build-up, and resulting movement, due to insufficient sputter coating on the non-conductive scales, or failure to adequately ground them on the stub on which they are mounted.

Regards,
David

[g4lab]

I also have not done SEM since the days of P/N 55

But I agree with the charge build up theory. The scales are mostly insulating even though you may have coated them.

There could also be thermal effects in the electron beam since the scales don't have much mass thermal nor otherwise. They are designed and intended to be light and fluffy.

[flyer2o12]

Hi,

I do SEM all the time and I have experienced this in my first few weeks of using it. The result is a charge build up in your sample which then deflects the electron beam. The reason for the charge accumulation is because there is insufficient amount of gold covering applied to your sample. So try to double or treble the sputtering time of your sample or you can experiment.