Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!dimacs.rutgers.edu!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: neufeld@aurora.physics.utoronto.ca (Christopher Neufeld) Newsgroups: sci.nanotech Subject: Re: Diamonds? Keywords: diamonds, bones Message-ID: Date: 20 Apr 91 00:45:19 GMT Sender: nanotech@athos.rutgers.edu Organization: University of Toronto Physics/Astronomy/CITA Lines: 60 Approved: nanotech@aramis.rutgers.edu In article Howard.Landman@eng.sun.com (Howard A. Landman) writes: > >In article neufeld@aurora.physics.utoronto.ca (Christopher Neufeld) writes: >>I'd design my diamond-building machines to be dominantly atomic step >>extenders. They would come in with a methyl group on a long stick, and >>would insert it at the edge of a step from one crystal plane to the >>other. In doing so they would trade the methyl for the hydrogen on the >>surface of the crystal, ie. the surface of the crystal would always be >>fully hydrogenated, with the crystal being built by substituting a >>methyl group for one or more hydrogens on the surface. > ^^ ^^^^ >The two words "or more" are critical here. Without their presence, >I can prove mathematically that the above process doesn't work, i.e. >is incapable of producing a diamond lattice. There are at least two >approaches, one graph-theoretical, one combinatorial. Before you >look at my proofs, you should pause to try to think this through. >It's actually pretty obvious. > Of course it is. A methyl is carbon and three hydrogens, so on average you have to discard three hydrogens for every carbon laid down. I'm surprised that you critisize me on the basis of something which I might have left out to make my statement incorrect, but didn't. I said what I did because I thought that it might make more sense for the device to be designed to grow planes normal to the (-1,1,1) direction than the (0,0,1) direction. In that geometry half the methyl additions yield one hydrogen, and the other half yield five hydrogens. This is not likely to be something which a single machine can do, so the principle axis growth is more likely, I just thought I'd cover all possibilities. >OR that >the step which adds a methyl carbon removes ON AVERAGE about three >hydrogen atoms. Not so simple sounding anymore, is it? > It's not simple in the first place. I'm just mentioning a way which might, I think, make it easier. You don't want your nanomachines to crawl over the surface of a diamond crystal with hanging carbon bonds or you'll stick tight. Hydrogenating the surface bonds serves two functions, one to make the crystal less sticky and the add-on units more manageable, and two to set it up with the correct electron orbital geometry. There's still the problem of how to fling those hydrogens out of there in the first place, perhaps with a highly electronegative bonding site which could be tucked in between the carbons to grab out the hydrogen. Candidates are nitrogen and oxygen. Flourine won't work unless you can make it polyvalent. You then pull out the arm with the hydrogens attached, leaving the carbon bonds essentially unchanged but unbonded. "Essentially unchanged" could mean a deflection of a few degrees, with the bond angle of water being a good example. I'm not a chemist, so this might all be nonsense. > Howard A. Landman > landman@eng.sun.com -or- sun!landman -- Christopher Neufeld....Just a graduate student | Flash: morning star seen neufeld@aurora.physics.utoronto.ca Ad astra! | in evening! Baffled cneufeld@{pnet91,pro-cco}.cts.com | astronomers: "could mean "Don't edit reality for the sake of simplicity" | second coming of Elvis!"