Poll

What method does your lab utilize to determine the carbon coat thickness on your samples?

Quartz thickness monitor
Color on polished brass
Other method (please specify below)

Author Topic: Determining carbon coating thickness  (Read 478 times)

Probeman

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Re: Determining carbon coating thickness
« Reply #15 on: October 14, 2019, 02:35:55 pm »
OK, I have to admit that I'm a little surprised that more people are using the color on brass method than a quartz monitor.  I would have guessed the other way around.



But the data is still quite sparse (only 11 votes so far), so please, if you haven't already, log in and vote on what method your lab utilizes for monitoring the carbon coating thickness during deposition.
The only stupid question is the one not asked!

Jarrod Crum

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Re: Determining carbon coating thickness
« Reply #16 on: November 07, 2019, 12:22:55 pm »
I use the quartz thickness monitor to control thickness of my coatings.  The thickness monitor was calibrated by making coatings on a glass slide partially masked with Kapton tape. Then the tap was removed and the thickness was measured with an optical profilometer with a wide field of view to see the step height change from glass to coating.

I am curious.  How much impact does surface finish of the brass have on the color of the carbon coating?

Probeman

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Re: Determining carbon coating thickness
« Reply #17 on: November 11, 2019, 03:23:36 pm »
I use the quartz thickness monitor to control thickness of my coatings.  The thickness monitor was calibrated by making coatings on a glass slide partially masked with Kapton tape. Then the tap was removed and the thickness was measured with an optical profilometer with a wide field of view to see the step height change from glass to coating.

I am curious.  How much impact does surface finish of the brass have on the color of the carbon coating?

Hi Jarrod,
Do you mean the smoothness of the surface or how oxidized it might be?

We normally re-polish our brass disks using colliodial alumina (0.5 um), so they are very smooth and bright after a minute on the soft lap, but they tend to get a bit "wavy" after repeated polishings.  It doesn't seem to affect our ability to see Newton's colors. 
john
The only stupid question is the one not asked!

Karsten Goemann

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Re: Determining carbon coating thickness
« Reply #18 on: November 11, 2019, 05:16:50 pm »
Hi Jarrod,

We have a quartz thickness monitor on our new coater as well and an optical profiler in the building that we may be able to use for thickness calibration. So it would be good for us to establish this as an additional/alternate method of determining thickness.

Can I ask a few more questions regarding your setup and procedure? What type of coater do you use and do you see an effect of heat and/or light during evaporation on the quartz monitor thickness reading like we do? This seems to be one of the reasons for Leica to use pulsed deposition in their carbon thread coaters, although I haven't used a Leica coater myself, so I don't really know.

Have you got the quartz sensor mounted at the same distance to the carbon source as the samples? We use 100 mm as source-sample distance and there the amount of mass deposited on the sensor seems a bit low for our normal coatings (8-20 nm depending on application) to get a precise enough thickness reading, so I'm considering mounting it closer than the samples and using a tooling factor. That will probably affect heat/light sensitivity more...

Cheers,
Karsten

BenjaminWade

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Re: Determining carbon coating thickness
« Reply #19 on: November 12, 2019, 10:09:20 pm »
Hi all
Here are some measurements I did with our Quorum coater. There is no crystal, the carbon rods are shaped to what we hope is the same size every time then evaporate it under a specific current. Sometimes the whole rod evaporates...sometimes it leaves a little bit left...
We were assuming that each coat was nominally 10nm, so blank slides were masked with Kapton and coated up to 4 times. The stage only holds 4 slides and I should have made a note about which slides were on the outside vs the inside, but i didnt...so will probably have to repeat this again with perhaps moving them around after each coat to get some kind of average.




Of note is the thickness measurements were done on a laser profilometer and to measure the 1 and 2 coat thicknesses its probably getting to its resolution limit. I am going to analyse the same samples on the AFM in a couple of weeks to hopefully either confirm or change the thickness measurements of the 1 and 2 coat samples. If you just took the thickness of the 4x sample you do get nominally 10nm a coat.

Also when you pull the Kapton off it does lift the edge of the carbon coat, so you have to do your step height measurements a ways from the edge of the coat, at least 100um or more. Will repeat it trying a different masking technique using 4xTEM grids on a single slide in the centre of the chamber and report back.

Cheers
« Last Edit: November 13, 2019, 01:31:40 am by BenjaminWade »

BenjaminWade

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Re: Determining carbon coating thickness
« Reply #20 on: November 14, 2019, 10:36:33 pm »
Hi all
Here are the results from the same measurements but using TEM grids as a mask. This time up to 5 repeat coats, all grids mounted on the same single thin section in the middle of the chamber.






So the average coat thickness is ~9nm +/-1nm, matching what I was told the nominal coat thickness of 10nm. I am surprised its so tight clustered really given that a different rod was used for every coat, and the errors in involved in measuring it all.
Here is the combined Resistance vs Thickness of all measurements. Might be able to use it as a very rough estimate for our users samples to determine an average thickness on their samples.



Cheers