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

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Discussion Overview

The discussion revolves around the feasibility of achieving an "ideal surface" with a peak roughness of approximately 1 nm, particularly in the context of silicon wafers and other materials. Participants explore the implications of surface roughness measurements, the limitations imposed by atomic structures, and the practical challenges of obtaining and maintaining such surfaces in experimental setups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants express skepticism about the accuracy of roughness measurements provided by manufacturers, suggesting that the highest peak could be significantly higher than the average roughness reported.
  • One participant references a paper indicating a high peak-to-average ratio in ZnO thin films, raising concerns about similar discrepancies in silicon wafers.
  • There is a discussion about the theoretical limits of surface roughness based on atomic structures, specifically referencing the ionic radius of silicon.
  • Some participants propose that using materials like mica could provide smoother surfaces compared to silicon wafers, though there are questions about sourcing and cleaning these materials.
  • Technical challenges related to mounting and maintaining large, flat surfaces in vacuum conditions are discussed, with suggestions for using external electronics to control mechanisms within the vacuum.
  • One participant humorously mentions the extreme conditions their project might face, including gamma radiation, while expressing a desire to explore quantum physics through their hobby project.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the maximum peak roughness of silicon wafers or the best materials to achieve the desired surface characteristics. Multiple competing views on the feasibility and methods for obtaining ideal surfaces remain present throughout the discussion.

Contextual Notes

Participants note limitations in the available information regarding maximum surface roughness and the potential impact of coatings on measurements. There are also unresolved questions about the practicalities of achieving and maintaining the desired surface conditions in experimental setups.

Who May Find This Useful

This discussion may be of interest to those involved in materials science, surface engineering, and experimental physics, particularly in contexts where surface properties are critical to performance.

gggnano
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TL;DR
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!
 
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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?
 
gggnano said:
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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Baluncore said:
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...
 
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snorkack said:
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.
 
Baluncore said:
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/
 
"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.

gggnano said:
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.
 
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
^ 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
^ 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
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
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
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.

gggnano said:
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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