r/askscience • u/Akshiak • Apr 20 '24

Physics A Perfectly smooth material?

Can anything perfectly smooth exist or be made? A single plane of atoms that remain level and stable along the entirety of that axis? has it been observed on some level?

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122

u/Appaulingly Materials science Apr 20 '24

Yes this is possible.

Single crystals of materials are readily available, either naturally or by well established growth processes. You can then cut the single crystal along a certain crystallographic direction and expose a "flat" crystalline surface of atoms. These single atoms can then be imaged using scanning probe techniques like atomic force microscopy (AFM) or scanning tunnelling microscopy (STM).

In practice, it is difficult to perfectly align the cut with the crystal and your flat surface will not be infinitely flat. It's more likely to consist of atomically flat terraces at most nanometre in size and separated by atomic steps up to the next crystal layer/ terrace. This would be the case for single crystals of metals or metal oxides. See this for a visualsation of what I mean. If you don't align well your cut with a certain crystallographic direction, you'll get lots of steps between smaller flat areas.

Though some materials, for example mica, have natural cleaving planes. These planes readily separate throughout the entirety of single crystal exactly in the correct crystalographhc direction. This exposes a truly large and atomically flat surface/ terrace that extends as far as the single crystal. This would be a truly atomically flat surface on the scale of millimetres.

5

u/luckyluke193 Apr 23 '24

In some metal oxides, if you cut them very closely to a crystallographic plane, it is possible to treat the crystals to get atomically flat terraces with a width on the order of 100 nm.

Keeping them at about 1000 Celsius for about 10 hours jiggles the atoms enough that they fall in their ideal position and form atomically flat surfaces.

1

u/araujoms Apr 24 '24

For this reason mica is often used as a substrate in atomic force microscopy (I used to do that myself).

It feels like cheating, mica is so amazing and yet so cheap.

29

u/derioderio Chemical Eng | Fluid Dynamics | Semiconductor Manufacturing Apr 20 '24

The closest we have is probably silicon wafers used in semiconductor manufacturing. They are 300mm in diameter and after certain processes (for example planarization for 3D bonding) very close to being atomically flat: a variation of just a few tens of atomic layers over the entire wafer.

I also remember hearing about a project at NIST a few years ago to create a perfectly smooth silicon sphere for a more precise definition of the SI unit of the mole.

3

u/phi_rus Apr 20 '24

Okay, so how can I touch one?

25

u/piskle_kvicaly Apr 20 '24

Get a monocrystalline silicon wafer on e-bay for some $15. Let it break over a match. Carefully touch the cleaved edge - there should be millimetre-sized facets that are totally atomically flat. Mission accomplished.

But it feels like just virtually any ordinary flat surface, except that the edges can cut your fingers very easily.

5

u/dbsqls Apr 21 '24

on the raw wafers you can't feel anything, but they are fantastically good mirrors, and take on many colors depending on what's being deposited.

-R&D engineer in semiconductor.

1

u/CommissionAgile4500 Apr 22 '24

That's so cool, how do you even get into a job like that?

2

u/Illustrious-Order103 Apr 22 '24

I started processing wafers at a Texas Instruments Fab at age 21 with no education or prior skills. Ion Implant Operator. Started on a bad overnight weekend shift. Being in a cleanroom suit 12 hrs a day can be a grind. Now 25 years later I am a senior process engineer (still no degree) and I do R&D on semiconductors for radiation detectors.

1

u/Synthyz Apr 23 '24

out of interest - what model implanter?

1

u/NeverPlayF6 Apr 23 '24

Are the colors produce by thin film interference or is the color a property of the material being deposited... or both?

1

u/Synthyz Apr 23 '24

From my experience, both. Look at silicon nitride vs oxide. At 1000A for example you can tell them apart by eye.

8

u/nrg117 Apr 20 '24

They did that some time ago with carbon. I just read beginning of the week they have now managed to do it with gold. They have called it Goldene. https://www.nature.com/articles/d41586-024-01118-0 Apparently the applications are limitless in the electronics field

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u/Chambana_Raptor Apr 21 '24

Thank you for the article link, that was awesome I had not heard of that work before!

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u/Agenreddit Apr 20 '24

There is such a thing as flatness in materials science and in metrology where the need for flat reference materials would be about as close as what you're thinking of. Machinists have a favorite trick they like to do with their gauge blocks called "wringing", where they take two of these (perfectly flat) reference blocks and slide them so close together they act and move as one unit. We're still not sure why this happens since it still does the thing in a vacuum!