Saturday, August 09, 2014

Nanotubes by design

There is a paper in this week's issue of Nature (with an accompanying news commentary by my colleague Jim Tour) in which the authors appear to have solved a major, two decade+ challenge, growing single-walled carbon nanotubes of a specific type.   For a general audience:  You can imagine rolling up a single graphene sheet and joining the edges to make a cylinder.  There are many different ways to do this.  The issue is, different ways of rolling up the sheet lead to different electronic properties, and the energetic differences between these different tube types are very small.  When people have tried to grow nanotubes by any number of methods, they tend to end up with a bunch of tube types of similar diameters, rather than just the one they want.

The authors of this new paper have taken an approach that has great visual appeal.  They have used synthetic chemistry to make a planar hydrocarbon molecule that looks like they've taken the geodesic hemisphere end-cap of their desired tube and cut it to lay it flat - like making a funky projection to create a flat map of a globe.  When placed on a catalytically active Pt surface at elevated temperatures, this molecular seed can fold up into an endcap and start growing as a nanotube.  The authors show Raman spectroscopic evidence that they only produce the desired tube type (in this case, a metallic nanotube).  The picture is nice, and the authors imply that they could do this for other desired tube types.  It's not clear whether this is scalable for large volumes, but it's certainly encouraging.

This is very cute.  People in the nanotube game have been trying to do selective synthesis for twenty years.  Earlier this summer, a competing group showed progress in this direction using nanoparticle seeds, an approach pursued by many over the years with limited success.  It will be fun to see where this goes.  This is a good example of how long it can take to solve some materials problems.

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