The science of flatness, optical or otherwise, and a phenomenon you've probably never heard of at 9:21

[Ben the Ignorant]

The last two seconds of audio are lost, the author apologizes for it on YouTube, but a flawless video nonetheless.

 

[Ben the Ignorant]

About that strange stiction between finely polished surfaces at 9:21, I think I remember feeling the glass microscope plates sticking to each other in biology class. But maybe it was just because they had a near-vacuum between them and atmospheric pressure pushed them together? The video says the surfaces have to be flat to around 1/10µ for the effect to occur, which is the diffraction-limited surface accuracy for lenses; are those tiny glass plates polished like lenses so they won't distort the image?

[andrew s]

28 minutes ago, Ben the Ignorant said:

About that strange stiction between finely polished surfaces at 9:21, I think I remember feeling the glass microscope plates sticking to each other in biology class. But maybe it was just because they had a near-vacuum between them and atmospheric pressure pushed them together? The video says the surfaces have to be flat to around 1/10µ for the effect to occur, which is the diffraction-limited surface accuracy for lenses; are those tiny glass plates polished like lenses so they won't distort the image?

If you biology microscope plates were wet it is likely that it was surface tension holding them together. While good  microscope slides are not normally optically polished. 

Regards Andrew 

PS Nice video thanks for posting.

[Gfamily]

In Asimov's Foundation stories, one of the future technologies was the 'atomic knife' that would cut an between the atoms of a block of metal and allow you to 'weld' two pieces together by letting the 'flat' surfaces form atomic bonds between them. 

Even at age 15 I knew that there would be immediate reactions with oxygen in the air that would prevent the surfaces from binding, no matter how flat.  

[Ben the Ignorant]

51 minutes ago, andrew s said:

If you biology microscope plates were wet it is likely that it was surface tension holding them together.

I can't remember if they were wet or dry, it was too long ago.

[andrew s]

5 minutes ago, Ben the Ignorant said:

I can't remember if they were wet or dry, it was too long ago.

My ex biology teacher still wife assures me most Biology slides would have been wet with water or alcohol !

Regards Andrew

[niallk]

Great vid - thanks for posting!  Another cool effect of surfaces in close proximity is the casimir effect - important in the real world design of MEMS devices (the company I work for is involved in this).

[Mognet]

Thanks for the video. Seems that there's flat, and there's really flat! Some of this makes the surface table I worked with in QA years ago look really bumpy

[Gfamily]

On 06/07/2019 at 11:56, Mognet said:

Thanks for the video. Seems that there's flat, and there's really flat! Some of this makes the surface table I worked with in QA years ago look really bumpy

There's an interesting episode of the Syzygy podcast that talks about the manufacture of the Giant Magellan Telescope - which requires the 8.4 metre surface of the individual mirror elements to be figured to less than 20 nanometres - about the size of individual glass molecules. 

https://player.fm/series/syzygy/ep-39-ridiculously-large-telescopes - NB will start playing when you open the link. 

[wimvb]

Interesting video. It reminded me of measurements I did in a previous lifetime (it seems). At my workplace we used to measure surface roughness with a Dektak stylus profiler, untill we found out that the stylus damaged tiny structures on the surface. We then looked into optical profilers, which use interference of a laser beam to profile a surface without contacting it.

Another technique we used was x-ray diffraction on semiconductor crystals. We measured both the distance between atoms, as well as the thickness of very thin layers on a substrate.

The technique used in the video where a flat disk is placed on a sample to be measured, would have been too crude, since the weight of the disk compresses and deforms the material underneath it. Measurement on this level can be a bit tricky.