Particles! workshop plan 3:30-3:45 Intro to workshop, introductions to each other 3:45-4:30 Introduction to particle technology –Particle technology basics –Air pollution 4:30-5:15 Laboratory tours - flame reactor, metal powder reactor 5:15-5:45 Where are the particles, conductive pastes activity 5:45-6:45 dinner 6:45-7:45 How are the circuit boards printed? Screen printing activity. Important powder properties, flowability activity 7:45-8:45 Details about our process to make the powders, design activities 8:45-9 Wrap up and clean up
Size, composition control Avoid agglomeration Quantity/cost Holy grail Our laboratory’s approach: develop processes for niche applications only one or two of the objectives required make use of aerosol approaches when advantageous Particle processing – general goals
Particles, how to make them Top down –Milling –Refining micron scale patterning techniques Bottom up –From atoms or molecules to clusters to particles to macroscale materials
Methods of making fine particles Starting from molecular level –From precursor Aerosol Combustion synthesis Thermal or plasma synthesis Solution phase synthesis Precipitation Sol gel Emulsion –Evaporation/condensation Starting from cluster level –Spray pyrolysis –Electrospray
Aerosol example: Cu doped ceria Water cooled substrate for particle deposition CH 4 O2O2 N2N2 Burner Nebulizer Compressed Air Rotameters Metal acetate precursors 0.3 mol /l in water R.K. Pati, S. Hou, O. Akhuemonkhan, I.C. Lee, D. Chu, S.H. Ehrman, submitted (2006)
Solution phase example: Fe nanoparticles K.C. Huang and S.H. Ehrman, Langmuir, in press (2006) Precipitation of iron from iron chloride in presence of sodium borohydride and trace amount of palladium ions as seeds Polyacrylic acid added as dispersing agent
Why the emphasis on aerosol processes in our lab? Advantages in some cases: –Rapid –Simple, less steps required –No solvents –Amenable to continuous processing –Potential for scalablity
Disadvantages Poor size control Poor control of aggregation Difficult to make non-oxides –Interesting alternatives - sodium coated metal nanoparticles (Axelbaum, Zachariah) in aerosol process May battle thermodynamics in mixed systems
Particle Synthesis Setup Compressed Nitrogen Atomizer (RETEC) Diffusion Dryer (TSI Model 3062) Reactor Furnace (Lindberg) Temperature: 300 ° C ~ 1000 ° C Powder Collection (X-ray Diffraction) By-Pass (R.T. control) Precursors 0.3 M precursor in water/alcohol solution (10% by volume)
Colors of Copper Powders 300 ° C450 ° C600 ° C1000 ° C Cu·N Cu·N +ETOH Cu·Ac Cu·Ac + ETOH Pure Cu Image J.-H. Kim
Other results with alcohol Can make phase pure copper from copper nitrate Enable formation of copper acetate at lower temperatures Works for nickel nitrate too! ~ 0.1 mol % H 2 estimated, well below flammability limit in air Particle synthesis (polydisperse)
Temperature also important Scanning Electron Microscope Images, JH Kim Polydisperse Copper Powders Cu Cu: 600 °C Cu Cu: 1000 °C From copper nitrate with co-solvent
Spray pyrolysis processes (adapted from Gurav et al., Aerosol Sci. and Tech., 1993)
Composition is a variable What composition will give you a melting point of 1100 K and the highest conductivity possible? What composition will give you a melting point of 1250 K and the highest conductivity possible?
Particle diameter is a variable We want 1 micron diameter particles Equationsd Droplet diameter dpdp Particle diameter CMpMass concentration pp Density of copper nitrate solid d dpdp dropletdry saltend particle
Now we want to make lots of particles Process scale up calculation
Wrap up Particle technology, it’s everywhere! One application, metal powders for conductive pastes, everywhere too, big business! Particle properties are important for patterning the conductive pastes Lots of chemical engineering goes into developing the process to make the metal powders!
So what’s a micro or nanoparticle? Micro: particle < 100 microns in diameter Nano: particle < 100 nanometers in diameter May form larger structures: agglomerates, films These can be 100’s of microns in size 500 nm Size selected Cu nps Top view of film of TiO 2 nps 100 nm CuO/CeO 2 nps Cu microparticles
Particles are everywhere! Pollen? Soot? Viruses? Calicivirus Polio Virus All images Bar = 50 nm Photo Credit: F.P. Williams, U.S. EPA More images for public use at Pollen
Particles (nano) in the past Lampblack (carbon black) produced in quantity by the ancient Chinese Pigments used by other civilizations several hundred years BC in glass and other ceramics Examples of nano in the not so- distant past… Ref. G. Ulrich,Chemical and Engineering News, 1984 Ref: Johnson, P. H., and Eberline, C. R., “Carbon Black, Furnace Black”, Encyclopedia of Chemical Processing and Design, J. J. McKetta, ed., Vol. 6, Marcel Dekker, 1978, pp
Particles in the lab Studies of reactions of halogen compounds in hydrogen flames, late 1960’s, early 1970’s 1970’s application of this towards making optical fibers Bell Laboratories research “Modified Chemical Vapor Deposition” Ref: Simpkins PG, Greenbergkosinki S., MacChesney JB, Journal of Applied Physics, 50 (9) 5676 (1979).
Particles in industry - Vapor-phase axial deposition of optical fiber preforms start with rod (preform) of pure silica, SiO 2 O 2 /H 2 burner produces nanoparticles of silica + Ge, Ti, B, P etc… graphite furnace to consolidate fume consolidated preform is drawn into optical fiber H 2, O 2, SiCl 4 + GeCl 4 + TiCl 4...
Particles in the lab – Optical behavior Size dependent optical properties CdSe nanoparticles, synthesized in solution monodisperse size, different sizes in each vial illuminated with UV light emitting different (size dependent) wavelengths of visible light phenomena result of size-dependent quantum confinement image: Felice Frankel, MIT particles: Moungi Bawendi’s group at MIT, Department of Chemistry Ref: Tobin JG, Colvin VL, Alivasatos AP, Phys. Rev. Let. 66 (21) 2786 (1991) Murray CB, Norris DH, Bawendi MG, J. Am. Chem. Soc., 115 (19) 8706 (1993)
Particles in the market place Commercially available nanoparticles, for example Qdots Can be functionalized to bind to specific targets Used extensively today for diagnostics in biotechnology Here, dual labeled mouse fibroblasts. Actin stained red. Nuclear membrane labeled with red and green probes, appearing yellow.
Nano in the lab – electronic behavior Single electron transistors a single electron excess charge on a particle markedly changes its conductive properties could eventually lead to orders of magnitude decrease in device size huge implications for computing Difficulties: –stability at T >> 0 K ? –manufacturing in quantity? –how to pattern/order them? Doped Si substrate SiO 2 insulating layer gold leads + linker molecules nanoparticles after Klein et al., Nature, 389, 699 (1997)
Nano in the marketplace Still waiting on this one… Meanwhile… top down getting really small, sub 0.2 micron feature size in an integrated circuit Two new nano issues –Polishing at nano level between processing steps –Small features -> contaminants = killer nano particles!!
Nano in the marketplace Killer particles? Rule of thumb: particle > 1/3 of smallest feature size can cause killer defect Defect detection –Performance after production –On-line, light scattering At these size scales, on-line very challenging!
In my lab, what do we do? As chemical engineers we develop processes for making inorganic nanoparticles and nanoparticle based materials It’s a great time for chemical engineers to get involved –Relevance of manufacturing to enabling this technology –Ability to characterize improving rapidly