Manuel Schnabel

1
Mo6S9-xIx Nanowires

• Manuel Schnabel
• Part II Student
• Department of Materials
• University of Oxford

2
Nanomaterials

• What advantages do they offer?
• Scaling down of macroscopic effects - steel
  microstructure, microchips, CNT reinforcement
• Quantum size effect - Quantum computing, QD in
  photovoltaics
• Increased surface area/volume ratio- Catalysts,
  sintering
• NEMS

3
Nano-Engine
We can even think about using chemically treated
nanotubes as parts in nano-sized engines.
http//www.nas.nasa.gov/
4
1-D Nanomaterials

• Specific uses of 1-D Nanostructures (vs. 2-D and
  0-D)
• Molecular interconnects (ballisticity)
• Composites- Mechanical reinforcement,
  Percolation
• AFM tips
• Field Emission

5
Mo6S9-xIx Nanowires

• Nanowires (NW) with x6, x4.5 already known
  (Mo6S3I6, Mo6S4.5I4.5 aka 636, 644)
• Monodisperse properties
• Dissolve in common solvents, debundle on dilution
• Can connect to GNPs
• Store loads of Li batteries, superparamagnetism.
  
• Low friction coefficient - lubricant

6
Mo6S2I8 Nanowires

• New stoichiometry, 28?9 so different properties
  conceivable.
• Before properties can be researched, processing
  route and structure need to be found.
• Solvent Study
• Concentration Study
• ADF STEM and EDX

7
Solvent Study

• Sedimentation process
• we monitored the Linear transmission of MoSI
  dispersion over time
• Transform into effective local concentration
  using Lambert-Beer Law
• ?Cln(I0/I)/l
• ?C is known as turbidity

8
Sedimentation Maths

• Concentration follows for n sedimenting phases
• Equations with different numbers of exponential
  decay terms (n1,2,3) fitted the one that fits
  best indicated the right number.

C1
C2
C0
t1
t2
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Sedimentation Curves
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Sedimentation Parameters
Most solvents were found to have 2 sedimenting
phases -gtin line with 636 and 644 data. Acetone
and THF had 3.
A good solvent is one with a large retained and
a low purification time. DMF and DMAc
best. Water, Chloroform and THF are useless.
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628 Surface Energy

• Expect solvent to work well if its surface energy
  is the same as that of the solute
• -gt plot solute vs solvent surface energy to find
  NW surface energy (37mJ/m2)
• -gt It is different to the surface energy of 636
  or 644 gt arrangement of surface atoms different.

Theory Practice
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TEM Different Phases
1 Big bundles 2 Small lumps, thin bundles 3
Thin bundles Solute Thin bundles -gtOnly 2 phases
after all.
Solute
As-sonicated
Sediment 1 Sediment 2 Sediment 3
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ADF STEM

• Fires a 40pm probe at the sample and records
  number of incoherently scattered electrons with
  annulus.
• Gives atomic number contrast only (I ? Z2)
• Should allow us to distinguish Mo (Z96), S
  (Z32), and I (Z129) with subatomic resolution
• Sample not 1 atom flat we see stacks of atoms,
  signal averaged and blurred.

research.ibm.com
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ADF STEM
Can see both interwire spacing (bottom), and
planar spacing at an angle (top). Measurement of
spacings and angles in many such images will give
structure of wires and bundles.
5nm
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Conclusions

• MoSI 628 NWs are readily dispersed in common
  solvents (confirmed by TEM)
• Vastly different solvents to 636 and 644-
  different arrangement of surface atoms
• ADF STEM shows spacings which also differ from
  636 and 644
• We expect 628 to have different properties to 636
  and 644, giving a wider range of properties in
  the MoSI system.

16
Questions?

• Acknowledgements
• Dr. Valeria Nicolosi
• Dr. Peter Nellist
• EM Group
• Mo6 d.o.o