1. Class: Material Science EngineeringStudent : Hoang Van TienHanoi -2012

2. Nanomaterials Top -down approaches Bottom-up approaches Functional approaches Biomimetic approaches Speculative 3. Bottom up synthesis Solgel synthesis Precipitation Physical vapor synthesis Chemical vapor condensation Spray conversion processing 4. Chemical vapor condensation Chemical vapor deposition (CVD) synthesis isachieved by putting a carbon source in the gasphase and using an energy source, such as aplasma or a resistively heated coil, to transferenergy to a gaseous carbon molecule. Types :plasma enhanced CVD, thermalchemical CVD, alcohol catalytic CVD, vapourphase growth, aero gel-supported CVD andlaser-assisted CVD. -Gaseous carbon sources : methane, carbonmonoxide and acetylene 5. Case study: preparation of carbon nano tube by chemical vapor condensation method. -plasma enhanced CVD, -thermal chemical CVD, -alcohol catalytic CVD, -vapour phase growth, -aero gel-supported CVD -laser-assisted CVD. 6. the growth mechanism 7. process The energy source is used to "crack" themolecule into reactive atomic carbon. The carbon diffuses towards the substrate,which is heated and coated with a catalystwhere it will bind. Carbon nanotubes will be formed if theproper parameters are maintained. 8. positional control onnanometre scale CVD carbon nanotube synthesis is essentiallya two-step process :-catalyst preparation-actual synthesis of the nanotube. The catalyst is generally prepared by sputtering atransition metal onto a substrate and then using eitherchemical etching or thermal annealing to induce catalystparticle nucleation. Thermal annealing results in cluster formation on thesubstrate, from which the nanotubes will grow. 9. Thermal chemical vapor depositiona schematic diagram of thermal CVD apparatus in the synthesis of carbon nanotubes. 10. Catalytic growthSchematics of a CVD deposition ovenThis method is based on the decomposition of a hydrocarbon gas over atransition metal to grow nanotubes in a chemical vapor deposition (CVD)reactor 11. Thermal chemical vapor deposition Catalysts : Fe , Ni, Co Substrate : Si,SiO2,glass Gas flow : 40ml/min t = 450-1050 oC The diameter range of the carbon nanotubes depends on the thickness of the catalytic film example : - By using a thickness of 13 nm, the diameter distribution lies between 30 and 40 nm. - By using a thickness of 27 nm is used, the diameter range is between 100 and 200 nm. 12. product Advantages: -Typical yield: 20-100% - Long tubes with diameter ranging from 10-240 nm for MWNT (multi walled nanotubes) and 0.6-4 nm for SWNT( single walled nanotubes). - Easiest to scale up to industrial production; long length, simple process, SWNT diameter controllable, quite pure Disadvantages: - large diameter range=>>>poorly controlled. -often riddled with defects 13. Laser-assisted thermalchemical vapour deposition 14. Sources of laser:a medium power, continuouswave CO 2 laser,perpendicularonto asubstrate, pyrolyses sensitised mixtures of Fe(CO) 5vapour and acetylene in a flow reactor. Catalyst: Fe (very small iron particles) Substrate: sillica.iron pentacarbonylvapour, single- and multi-+ethylenewalled carbon+acetylene nanotubes 15. product The diameters of the SWNTs range from 0.7to 2.5 nm. The diameter range of the MWNTs is 30 to 80nm 43 prefer grow single rather than multi-wallednanotubes . Hight purity High power requirement 16. Purification The main impurities :graphite (wrapped up) sheets,amorphous carbon, metal catalyst and the smallerfullerenes Rules :-separate the SWNTs from the impurities- give a more homogeneous diameter or size distribution. The techniques that will be discussed are oxidation, acidtreatment, annealing, ultrasonication, micro filtration,ferromagnetic separation, cutting, functionalisation andchromatography techniques. 17. applicationsNanotubes are rolled-up graphene sheets, and graphene isone of the stiffest materials when subjected to deformationsparallel to the sheet.nanotubes show exceptional mechanical properties,especially a high strength-to-weight ratio.Applications: Field emission Field emission Nanotube sensors Nanotube transistors Nanotubes as SPM tips. 18. Schematics of a nanotube transistor, with some measurements. 19. Use of a MWNT as AFM tip. VGCF stands for Vapour Grown Carbon Fibre.At the centre of this fibre the MWNT forms the tip 20. sources1. D.A.Bochvar and E.G.Galpern, Dokl.Akad.Nauk.USSR, 209, (610, 1973 )2.http://www.ou.edu/engineering/nanotube, 20033. http://nanotube.msu.edu/4.http://www.pa.msu.edu/cmp/csc/nanotube.htm5 5.http://en.wikipedia.org/wiki/Carbon_nanotube 6. http://students.chem.tue.nl/carbonnanotubes/applica