Atomically flat vs Optically flat

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Discussion Overview

The discussion centers around the differences between atomically flat surfaces and optically flat surfaces, exploring definitions and implications of each term. It includes technical explanations and clarifications regarding the characteristics of these surfaces.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that atomically flat surfaces imply a level of flatness at the atomic scale, which may be nearly impossible to achieve.
  • Others argue that optically flat surfaces are defined by their appearance to the human eye, with examples such as glass or ice, though these may not be atomically flat due to molecular impurities.
  • A participant provides a definition of optical flats, noting they are polished to be extremely flat within a few millionths of an inch, which raises questions about the scale of flatness.
  • Another participant mentions that commercial optics typically specify flatness to within a fraction of a wavelength, suggesting a scale of 30 to 140 nm, and posits that atomic flatness refers to flatness on the scale of approximately 0.1 nm.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of atomically flat versus optically flat surfaces, indicating that multiple competing views remain without a consensus.

Contextual Notes

Definitions of flatness may depend on specific contexts and applications, and the discussion highlights the complexity of achieving true atomic flatness versus the practicalities of optical flatness.

onqun
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Hello,

What is the difference between optically flat surface and atomically flat surface?
 
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Atomically flat surfaces would suggest that the surface is flat on an atomic level which is a nearly if not completely impossible accomplishment. Optically flat suggests that the surface is flat to the human eye such as glass or ice. Note that even though glass and ice looks flat and smooth to the naked eye, they are in fact covered with numerous molecular impurities and are thus not atomically flat.
 
Yuqing said:
Optically flat suggests that the surface is flat to the human eye such as glass or ice.

No. Here is one definition: http://en.wikipedia.org/wiki/Optical_flat

"Optical flats are optical-grade glass structures lapped and polished to be extremely flat on one or both sides, usually within a few millionths of an inch..."
 
Commercial optics have surfaces specified to be flat to within some fraction of a wavelength. Typically this is between 1/4 to 1/20 of some specified (usually visible) wavelength. As such, the flatness is on the scale of 30 to 140 nm.

Since it is impossible to be flatter than the size of an atom, I presume "atomic flatness" means flat on the scale of an atom, or roughly 0.1 nm.
 

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