selfassembled Mo6S9xIx networks

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Title: selfassembled Mo6S9xIx networks

1
self-assembled Mo6S9-xIx networks

2
motivation

Mo6S9-xIx (MoSIx) nanowires are molecular
nanowires
are synthesized in bundles 2001000 nm, single
wire diameter is 0.95 nm
they are sulfur terminated form thiol bonds
with biomolecules and gold
best measured result of conductivity s 850 000
S/m
MoSIx nanowires might be used to self-assemble as
connections in moletronic circuits

A. Meden et al., Nanotechnology 16, 1578
(2005) V. Nicolosi et al., Advanced Matter 19,
543 (2007)
3
sample preparation

nanowires are put in solvent (water, IPA,...)
ultrasound bath is used to disperse bundles
larger structures and small nanoparticles are
removed by centrifugation (at 2000, 13000 rpm)
solution is left to sediment
Au nanoparticles (nominal size 5 nm) are added to
nanowires
solution is deposited on substrate (mica,
SiO2,...)
preparation steps are monitored by UV-Vis

4
AFM results

5
network analysis

analyzed topographic image is part of a much
larger network gt 400 um2
most wires are under 2.5 nm in height
measured data
particle heights (red and blue)
number (k), height and angles between of
nanowires connected to particles (red)
number (k), height and angles between nanowires
in non-particle junctions (green)
no free particles in immediate vicinity of
nanowires

6
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
from size and position of bigger particles we
conclude they are the Au nanoparticles

7
analysis results

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

8
degradation

particles have been reduced in size in one month
considerably are they gold at all?
the thinnest nanowires have disappeared, leaving
fragments behind
height of larger nanowires has decreased at
first, now it is increasing slowly

9
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, but analysis suggests it happens
during the deposition of solution onto substrate
unanswered question why are some nanowires much
thinner than 1 nm?
plans for near future
more TEM observations to better understand
network composition and bonding
optical scattering experiment for monitoring
aggregation of material in solution
mass spectrometry for determining the structure
of nanoparticles