Apr 03, 2009

Scanning Electron Microscopy (a) and Transmission Electron Microscopy (b-c) of the assembly of nanocrystals on silicon nanowires Si-DTA-thymine-CdSe.

We developed new bi-functional molecules which can be “anchored” to one side of a surface, and can “recognize” a complementary molecule on the other side. This molecular recognition is achieved by weak interactions that are non-covalent and reversible. After grafting these molecules onto the surface of silicon nanowires, we showed that by using their chemical function for recognition, it is possible to assemble nano-objects on the nanowires.


Let us select a well-known couple of molecules: diaminotriazine (DAT) and thymine. These molecules can recognize themselves and can be assembled by the establishment of three hydrogen bonds. By combining a DAT pattern with a “tripod” molecule, i.e. which has three anchoring functions, we obtain a bi-functional molecule which can be anchored firmly to a surface and can be assembled with thymine. This bi-functional molecule was synthesized and grafted by thermal hydro-silylation to a set of nanowires. In parallel, we developed another molecule having a thymine function that can be grafted to the surface of a semiconducting nanocrystal of CdSe. In possession of this couplet of molecules, we drove the assembly of CdSe nanocrystals on the surface of the nanowires in solution.

By electronic microscopy, one can directly visualize this assembly (fig.1).

Conclusion: chemical recognition between DAT and thymine, by the creation of multiple connections, is effective and can be carried out in solution. We can now imagine grafting these molecules to a substrate in a precise location and using them to direct the assembly of functionalized nanowires or nanoparticles on these specific zones. It is another step towards the positioning of nano-objects in various types of nanometric devices employing chemical means.


Further reading: Kai Huang et al, J. Phys. Chem. C 113 (2009) 21389.


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