Is it possible to have "ideal surface" whose highest peak is ~1 nm?

  • #1
gggnano
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3
TL;DR Summary
Not saying that the average roughness is 1 nm because that could mean if million points have 1nm but one is 5 times higher than (1000000+5)/1000001 which is 4-5 times "fake" lower
I mean you could buy a mirror or silicon wafer but they give say 0.5 nm or 5nm 'roughness' which I suspect is the mean average roughness but this doesn't rule out a high "bump" way above the mean average such that for example 1 million bumps of 1 nm and just one of 5 will result in (1000000+5)/1000001 or 4.99... times lower than the highest peak, despite a mean average of ~1. Online stores don't tell you how high is the highest point of 'ideal surface' such as a silicon wafer. Maybe I should use powerful 80w+ laser to flatten the surface? Thanks!
 

Answers and Replies

  • #2
gggnano
43
3
I just discovered this paper which illustrates my concern:

https://www.epj-conferences.org/articles/epjconf/pdf/2017/31/epjconf_incape2017_01055.pdf

"
ZnO thin film
using granular source for deposition of e-beam. The
highest peak is 150nm with average roughness of 28.74
nm"

So from the quote above this is little over 5 times over the mean average, I personally wouldn't mind even 10 times if the average is say 0.5nm because even I am not that picky ("peaky...") but how do I know the difference in say silicon wafers isn't 100 times such that the highest peak is 50nm or higher with 0.5 average?
 
  • #3
Baluncore
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I personally wouldn't mind even 10 times if the average is say 0.5nm because even I am not that picky
There is a limit, based on twice the ionic radius of silicon = 2 * 210 pm = 0.42 nm.
 
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  • #4
snorkack
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There is a limit, based on twice the ionic radius of silicon = 2 * 210 pm = 0.42 nm.
Why twice?
In a sense, the real limit would be perfect single crystal cleavage surface. Of course holes between the atoms, but all atoms in the top layer in the geometrical plane.
The practical limits of that would be the frequency of defects on the surface. Steps, dislocations, vacancies, interstitial or mismatched atoms...
 
  • #5
Baluncore
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Why twice?
If you cut and polish a perfect surface, that is not a cleavage plane, then it will have steps of one atomic diameter, which is twice the ionic radius.

Maybe you should look for a phyllosilicate such as mica.

Surface roughness is usually specified as RMS amplitude.
 
  • #6
gggnano
43
3
There is a limit, based on twice the ionic radius of silicon = 2 * 210 pm = 0.42 nm.

Oh I had no idea, good info! So the claim it's 0.5 average may be true yet again nothing said about maximum, and it turns out it is coated of SIO2 (so it's sand??) with 200 nm of SIO2 which I assume is where the the 0.5 average roughness comes from?

Normally I wouldn't that much since it's not shockingly expensive yet I am puzzled if I can get anything smoother and ideally electro and thermo conductive.

https://www.amazon.de/gp/product/B07ML6FH7V/
 
  • #7
Baluncore
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"Alpha Nanotech Silicone Wafer" "Boron doped". "The silicon substrates are evenly coated with a 200 nm thermally attached SiO2 surface layer"

Silicon is an insulator when pure. It is a semiconductor or resistor when doped.
SiO2, is silicon dioxide, a silicate, an electrical insulator, quartz.
Silicone is a polymer made from siloxane.

Normally I wouldn't that much since it's not shockingly expensive yet I am puzzled if I can get anything smoother and ideally electro and thermo conductive.
You might do better with a thin mica plate, sputtered with gold or silver.
 
  • #9
Baluncore
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How much, and what size mica sheet, do you require?
eBay 'mica insulator'. Avoid opaque composite mica sheet.
https://www.ebay.com.au/itm/304289969301?
Cleave each again, in a vacuum, to make three.
Throw out the contaminated outer layers.
 
  • #10
gggnano
43
3
^ yes but no parameters mentioned I have to guess maybe...5 inches or 10 cm or so for each one will be ok - squared.
 
  • #11
gggnano
43
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^ Yet quick google suggests that they're indeed exceptionally flat even beating the sil. wafers? Yet I'm not too sure about the transparency and it's insulator...it's very cheap too and harmless...
 
  • #12
Baluncore
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Mica can be very thin, which aids thermal conduction.
A gold coating solves the electrical conduction problem.

Why do you need such a large flat slab?

How are you going to mount such a large sheet? Without a thick surface plate to mount things on, you will have problems supporting any large surface, and keeping it flat. You cannot use a vacuum table to hold it in a vacuum chamber, so you will need to rely on gravity or electrostatics, or clamp it onto a defined curved frame, like a cylinder.
 
  • #13
gggnano
43
3
I was planning to use one of my 3d printers + arduino YET it seems as if arduino isn't going to work in a vacuum sooo...
Apparently all of the requirements are super difficult to meet:

1. El. Conductive
2. Absurdly flat area with 5-10nm highest peak
3. In a vaccum
4. Moved by electronics that work in vacuum
5. Somehow able to withstand thousands of newton force and...gamma radiation (ok i'm kidding about this one but since this is just a hobby project which should help me understand quantum physics better: I'm open to any possibility and in fact Gamma rays should be expected to come from nothing if this is done by professionals the way it should be done).

I bet you can even guess by now what the whole idea of the project is...
 
  • #14
Baluncore
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Keep the controller and electronics outside. There are no real problems running rotating shafts through a vacuum wall with an O-ring seal lubricated with vacuum oil.

I bet you can even guess by now what the whole idea of the project is...
If a moderator could guess what the whole idea of the project was, they would probably lock the thread. Why else would you not be open?
 

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