Author Topic: Carbon coat issue?  (Read 125 times)

Andrew Mott

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Carbon coat issue?
« on: October 30, 2019, 02:50:18 pm »
Every few months I end up working on a sample that exhibits some uncommon surface features when the sample is exposed to the beam. My assumption is that it is an issue with the carbon coating, but I'm not 100% sure since I coat all samples with the same coater/method and I only run into this issue infrequently. I've attached an optical picture of two different features. When I started working on this sample it exhibited no features and appeared like a clean surface. Feature 1 - marked by the arrow looks like a sort of bubble like feature and Feature 2 (circled) - it essentially looks like something black/gray has just exploded on the surface - in BSE it shows up as a bright spot once it forms.

Has anyone seen anything like this? Any ideas/suggestions on what might be causing this? I appreciate any insight anyone might have. Thanks.

Andrew

Probeman

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    • John Donovan
Re: Carbon coat issue?
« Reply #1 on: October 30, 2019, 03:01:15 pm »
Every few months I end up working on a sample that exhibits some uncommon surface features when the sample is exposed to the beam. My assumption is that it is an issue with the carbon coating, but I'm not 100% sure since I coat all samples with the same coater/method and I only run into this issue infrequently. I've attached an optical picture of two different features. When I started working on this sample it exhibited no features and appeared like a clean surface. Feature 1 - marked by the arrow looks like a sort of bubble like feature and Feature 2 (circled) - it essentially looks like something black/gray has just exploded on the surface - in BSE it shows up as a bright spot once it forms.

Has anyone seen anything like this? Any ideas/suggestions on what might be causing this? I appreciate any insight anyone might have. Thanks.

Andrew

Hi Andrew,
This looks exactly like where the carbon coat has "blown off".   Sometimes it tears like that.   

To my knowledge, the bubble features you mention occurs in two situations. First when the sample has not been pre-heated in a warming oven (60C) prior to carbon coating. This means that adsorbed water vapor on the surface gets trapped underneath the carbon coating. And when the electron beam is applied and the surface heats up, the adsorbed water is released and forms a bubble. Sometimes the water vapor leaks out and the bubble disappears, but if there's a lot of adsorbed water, it can "blow off" the carbon coat in that area as you saw.

Secondly when the sample can volatilize various gases, for example apatites.  I often see carbon bubbles forming on my synthetic chlor-apatite.
john
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