Manuel Schnabel Part II Student Department of Materials University of Oxford Mo 6 S 9-x I x Nanowires

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

We can even think about using chemically treated nanotubes as parts in nano- sized engines……. Nano-Engine

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

Mo 6 S 9-x I x Nanowires Nanowires (NW) with x=6, x=4.5 already known (Mo 6 S 3 I 6, Mo 6 S 4.5 I 4.5 ; 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

Mo 6 S 2 I 8 Nanowires New stoichiometry, 2+8≠9 so different properties conceivable. Before properties can be researched, processing route and structure need to be found. 1.Solvent Study 2.Concentration Study 3.ADF STEM and EDX

Sedimentation process: we monitored the Linear transmission of MoSI dispersion over time Transform into effective local concentration using Lambert-Beer Law:  C=ln(I0/I)/l  C is known as turbidity Solvent Study Laser Detector Cuvette

Sedimentation Maths Concentration follows for n sedimenting phases Equations with different numbers of exponential decay terms (n=1,2,3) fitted – the one that fits best indicated the right number. t1t2 C0 C2 C1

Sedimentation Curves

Sedimentation Parameters Most solvents were found to have 2 sedimenting phases ->in 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.

628 Surface Energy Expect solvent to work well if its surface energy is the same as that of the solute -> plot %solute vs solvent surface energy to find NW surface energy (37mJ/m 2 ) -> It is different to the surface energy of 636 or 644 => arrangement of surface atoms different. TheoryPractice

TEM – Different Phases Sediment 1Sediment 2Sediment 3 As-sonicated Solute 1: Big bundles 2: Small lumps, thin bundles 3: Thin bundles Solute: Thin bundles ->Only 2 phases after all.

ADF STEM Fires a 40pm probe at the sample and records number of incoherently scattered electrons with annulus. Gives atomic number contrast only (I  Z 2 ) Should allow us to distinguish Mo (Z=96), S (Z=32), and I (Z=129) with subatomic resolution Sample not 1 atom flat – we see stacks of atoms, signal averaged and blurred. research.ibm.com

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

Conclusions MoSI 628 NWs are readily dispersed in common solvents (confirmed by TEM) Vastly different solvents to 636 and 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.

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