1. Self-assembled MoSIx Nanowire Networks Jure Strle adviser: prof. dr. Dragan Mihailovič February 2008 University of Ljubljana Faculty of mathematics and physics

2. Contents MoSIx Nanowires Sample Preparation Analysis Conclusion

3. MoSIx Nanowires Structure: Mo 6 S 9-x I x (MoSIx) nanowires are molecular nanowires Mo octahedra are linked by S atoms and coated by six I or S atoms (known stoichiometries Mo 6 S 3 I 6, Mo 6 S 4.5 I 4.5 ) Synthesis: Mo, S and I are mixed in desired molar ratio, sealed into an ampoule and heated nanowires are synthesized in bundles thick 50–1000 nm, single wire diameter is ~0.95 nm A. Meden et al., Nanotechnology 16, 1578 (2005) V. Nicolosi et al., Advanced Matter 19, 543 (2007)

4. MoSIx Nanowires Properties: soluble in water and various organic solvents (isopropanol, ethanol, chloroform...) high young modulus, low shear modulus electrical conductivity measured by nanolithographical contacts > 1 S/m sulfur terminated – form thiol bonds with biomolecules and gold MoSIx nanowires might be used to self-assemble as connections in moletronic circuits

5. AFM Results nanowires are mostly thinner than 3 nm they tend to form networks, often with small nanoparticles

6. Sample Preparation

7. centrifugation is essential to separating phases preparation steps are monitored by UV-Vis

8. Network Analysis analyzed topographic image is part of a much larger network > 400 um 2 most nanowires are under 2.5 nm in height measured data: particle heights (red and blue) number (k), height and angles between nanowires connected to particles (red) number (k), height and angles between nanowires in non-particle junctions (green)

9. Analysis Results height distribution shows two distinct peaks, which implies two types of particles peak at ~1.4 nm consists of free particles peak at ~4 nm consists mostly of particles connected to nanowires size and position of bigger particles suggest they are the Au nanoparticles we added (nominal size 5 nm)

10. Analysis Results angle distributions at 180° suggest bonding between nanowires happens more easily via nanoparticle

11. Degradation particles have been reduced in size in one month considerably – are they gold at all? the thinnest nanowires have disappeared, leaving fragments behind transmission electron microscopy confirms gold nanoparticles by EDS

12. Conclusion we have successfully produced self-assembled networks from MoSIx nanowires and golden nanoparticles method for self-assembly was shown to be reproducible mechanism of network growing is not yet explained, sedimentation time appears to play an important role in bonding between gold nanoparticles and nanowires plans for near future: –more TEM observations to better understand network composition and bonding –optical scattering experiment for monitoring aggregation of material in solution –measuring electrical conductivity of MoSIx networks