Self-assembled MoSIx Nanowire Networks

Jure Strle

adviser: prof. dr. Dragan Mihailovič

February 2008

University of LjubljanaFaculty of mathematics and physics

Contents

• MoSIx Nanowires

• Sample Preparation

• Analysis

• Conclusion

MoSIx Nanowires

Structure:

• Mo6S9-xIx (MoSIx) nanowires are molecular nanowires

• Mo octahedra are linked by S atoms and coated by six I or S atoms (known stoichiometries Mo6S3I6, Mo6S4.5I4.5)

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)

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

AFM Results

• nanowires are mostly thinner than 3 nm• they tend to form networks, often with small

nanoparticles

Sample Preparation

Sample Preparation

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

Network Analysis

• analyzed topographic image is part of a much larger network > 400 um2

• 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)

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)

Analysis Results

• angle distributions at 180° suggest bonding between nanowires happens more easily via nanoparticle

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

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