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Acyl
cyanidepoisoning


Registered: 12/13/05
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The edge of a diamond
#7511502 - 10/12/07 01:40 AM (16 years, 3 months ago) |
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If a diamond consists of an infinite lattice of carbon atoms all bonded to four other carbon atoms, what the hell happens at the edge of the diamond?
I mean, I can rationalize an ionic lattice.. but a covalent bond lattice? The bonds cant bend that way, so what happens? A thin layer of graphite?
This question was asked on another chemistry forum with no real answer given...
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TheCow
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Re: The edge of a diamond [Re: Acyl]
#7511600 - 10/13/07 11:17 AM (16 years, 3 months ago) |
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Edit: Oh I think I misunderstood your question. Do you maybe mean when a diamond gets cut, what happens at the edges?
Edited by TheCow (10/13/07 11:18 AM)
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Chesh
道

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Re: The edge of a diamond [Re: Acyl]
#7512074 - 10/13/07 01:35 PM (16 years, 3 months ago) |
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Non-bonded electron valencies? That seems too reactive to be characteristic of diamond, tho.
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Acyl
cyanidepoisoning


Registered: 12/13/05
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Re: The edge of a diamond [Re: TheCow]
#7512168 - 10/13/07 02:03 PM (16 years, 3 months ago) |
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Yeah, but in any case the structure at the edge would be the same.. no?
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Chesh
道

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Re: The edge of a diamond [Re: Acyl]
#7512246 - 10/13/07 02:32 PM (16 years, 3 months ago) |
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Not necessarily, there could be 'surface effects' similar to structures that give rise to surface tension in liquids. The bulk and surface often have very different characteristics. Not that I'm claiming that this is what's happening in diamonds. It's just a possibility.
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TheCow
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Re: The edge of a diamond [Re: Acyl]
#7512288 - 10/13/07 02:42 PM (16 years, 3 months ago) |
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The structure would theoretically be the same, but if you scanned with a STM it would look all rough and fucked up, as it is not perfect in reality
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Chesh
道

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Re: The edge of a diamond [Re: TheCow]
#7519656 - 10/15/07 02:17 PM (16 years, 3 months ago) |
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Interesting, if you cut a diamond, the lattice undergoes 'reconstruction' to minimize the energy jump that accompanies the broken bonds, thus reforming the four bonds to each carbon lattice we expect, much like a fullerene rearrangement. I also suspect this will result in a slightly lower density and more disordered structure in the surface layers of the lattice compared to the interior portion.
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johnm214



Registered: 05/31/07
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Re: The edge of a diamond [Re: Chesh]
#7526133 - 10/16/07 11:39 PM (16 years, 3 months ago) |
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Quote:
The interatomic distance in such four-member rings is anticipated to be an intermediate between diamond and graphite. This particular atomic configuration is considered as an intermediate hybridization in between single and double bonds. We posit that the oriented growth of the diamond on (0 0 1) silicon generates (0 0 1) twins in the diamond structure. Raman spectra from these materials show non-cubic diamond features. We suggest that this demonstrates their connection to twinning.
I have no idea what the twinning or whatnot they're talking about is, but they do mention an intermediate between graphite and diamond allotropes
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johnm214



Registered: 05/31/07
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Re: The edge of a diamond [Re: johnm214]
#7526168 - 10/16/07 11:54 PM (16 years, 3 months ago) |
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I think what I said above is right, the following description is in the link provied. While it describes carbon atoms as monkies, and is thus a little confusing, I think its saying that at the edge the diamon is sp2. I would imagine, however; like grpahite, that the prevalence of the double bonds would give rise to resonance giving strength in the plane of the surfaces of the diamond. This is both similar in effect, and different in structure to graphite, then; it would appear.
Quote:
In diamond, each carbon atom[monkey] holds hands and feet with four different carbon atoms. These four different atoms are all on different sides. Near the edge of a diamond, a carbon atom faces a real problem. There are carbon atoms on one side of it, but no carbon atoms on the other side. One solution for these on-the-edge carbon atoms find is that while their feet hold hands with two different carbon atoms in the interior of the diamond, the edge carbon atom’s hands are both linked to the same neighboring carbon atom.
We can actually use high power microscopes to see that this is true. There is a nice example of this taken on a real diamond at the National Center for Electron Microscopy and published last year in an article by M. A. O’Keefe et. al. . They published their work in a magazine called Ultramicroscopy (volume 89, page 215). In this picture one sees white short rods. Each of these short rods is a pair of atoms. Each atom in the pair is holding both hands of the other atom in the pair. Quite frankly, it is an amazing microscope. I would like to see it someday.
SEE: http://www.ccmr.cornell.edu/education/ask/index.html?quid=38
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trendal
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Re: The edge of a diamond [Re: johnm214]
#7526935 - 10/17/07 08:44 AM (16 years, 3 months ago) |
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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Acyl
cyanidepoisoning


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Re: The edge of a diamond [Re: trendal]
#7528095 - 10/17/07 02:57 PM (16 years, 3 months ago) |
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Nice, thanks for the link john
and the pic, trendal
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