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Synthesis of Silver Colloids:Synthesis of Silver Colloids:
Experiment and Computational ModelExperiment and Computational Model
Ionel HalaciugaPhD Student
Clarkson University, Potsdam NYwww.clarkson.edu/programs/goia_group
Physics Department Colloquium, November 14th 2008
OutlineMotivation and objectivesPreparation of metallic layers via thick-film technologyTypical approaches for preparation of spherical particlesNew method for synthesis of spherical Ag particles and their characterization
Formation MechanismSize and MorphologyDegree of dispersion (PSD)CompositionSurface modification
Computational modelSolvent effect
Temperature effect
Conclusions
Motivation and ObjectivesDisplay technologies market trends
Motivation and ObjectivesDisplay technologies market trends
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$ U
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2003 2004 2005 2006 2007 2008 2009
CRTFPD FPD advantages over CRT:
•Small volume occupation
•High image quality
•Lightweight
•Low driving voltage
•Low power consumption
Motivation and ObjectivesFlat Panel Displays
TFT - LCDOLEDPDPFEDLEP
Motivation and ObjectivesPhotosensitive paste:
•Organic solvent
•Epoxy resin
•Dispersing agent
•Ag powder
Anisotropic particles cause scattering and/or reflection of the ultraviolet rays resulting in a defective patterning
Spherical particles having “smooth” surface are desired
Tappped density > 2 g/cm3
Particles’ diameter: 1- 2 μmAg powder requirements for FPD:
Preparation of metallic layers via thick-film technology
Wet film
Dry film
Sintered film
Drying
“Burn-out”
Sintering“Clean” film
Industrial Applications:•MLCC
•Resistors
•Solar Cells
•Plastic Electronics
•Radio Frequency I.D. Tags
•Flat Panel Displays
Paste Deposition:•flexography•spin coating
•screen printing•ink-jet printing
Preparation of metallic layers via thick-film technology
Human hair (~ 60 μm)
dielectric layers (~ 6 μm)
metallic layers (<1 μm)
100 μm
Human hair (~ 60 μm)
dielectric layers (~ 6 μm)
metallic layers (<1 μm)
100 μm
MLCC
Typical approaches for preparation of spherical particles
PhotoreductionPhotoinitiator (organic molecule)
Radicals (reducing capabilities)
hν
Thermolysis
Electrochemical methods
-Low concentration of metal -Lack in controlling particle properties (size, shape, dispersity)-Large amount of organics used
Major disadvantages
Chemical Precipitation
CLUSTERS
METAL IONS / COMPLEXES
METAL ATOMS
Reduction
NANOSIZEPRIMARY PARTICLES
Diffusional growthNUCLEI (~8-10Å)
POLYCRYSTALLINEPARTICLES
CRYSTALLINEPARTICLES
Diffusional growth Aggregation
LARGE MONODISPERSE PARTICLES
Me n+ + Red m- ⇔ Me0 + Ox m-n
ΔE0 = E01 - E0
2
ΔG0 = -nFΔE0
STABLENANOSYSTEMS
Chemical Precipitation
2 μm
Formation of Silver Particles
Ascorbic acid solution
Ag – polyamine complex solution
*Simple method
Formation of Silver Particles
Formation of Silver Particles
Crystallite size
~ 18 nm
Degree of Dispersion (PSD)
Tapped density > 3 g/cm3
Histogram Measured by Laser Diffraction
Formation of Silver Particles
Amine molecular weight
Amine molecular weight
Formation of Silver Particles
Formation of Silver Particles
Temperature* different magnifications
20 oC 60 oC
Temperature effect
Formation of Silver Particles
Formation of Silver Particles10
0% H
2O
95% H
2 O
5% Polyol
75%
H2O
25%
Pol
yol 100%
Polyol
~ 80 nm
~ 1 μm
~ 0.2 μm
~ 0.5 μm
Formation of Silver Particles
100% Polyol
Composition
LECO:
C: 3,300 ppm
O: 17,000 ppm
N: 1,700 ppm
T: 60oC
Ag:EDA molar ratio: 1:4
Surface Modification
Coating with 0.5% ceramic and kept at 2200C for 9 hours
Surface Modification
Crystallite size
~ 18 nm ~ 57 nm
Weight loss
~ 2.15 % ~ 0.18 %
Surface Modification
Computational Model
Computational Model
Computational ModelKinetic factor effect
Computational ModelTemperature effect
6991.44753080
97096.796710060
173012530149032040
d(nm)
tsat (s)d(nm)tsat (s)
SimulationExperiment
T ( C)
Computational ModelSolvent effect
2H O 1 mPa sη =DEG 7.64 mPa sη =
ConclusionsA rapid and convenient method for producing micrometer and submicrometer size dispersed silver spheres suitable for most applications in electronics was presented.The particles are formed by rapid aggregation of nanosize silver subunits, substantiated directly by X-ray diffraction and electron microscopy.The size of the primary particles is NOT influenced by the nature of the polyamine nor by the solvent, having effect only on the aggregation dynamics – offers the ability to control the particle size without polymeric dispersing agents. Two stage computational model was used to simulate the formation of silver spheres in various experimental conditions.
The simplicity of the process and the high concentration of silver make the described process an advantageous route to manufacture cost effectively in large scale dispersed silver particles for applications in plasma display panels, low temperature co-fired ceramics, multilayer ceramic capacitors and solar cells.
ReferencesR. Young: Flat Panel Display Market Outlook, NPD Breakfast with the Experts, CES, 2006.T. Itakura, K. Torigoe, and K. Esumi. Langmuir 11, 1995. pp. 4129-4134Y. Kashiwagi, M. Yamamoto, and M. Nakamoto. Journal of Colloid and Interface Science 300, 2006. pp. 169-175.H. Bönnemann and R. M. Richards: European Journal of Inorganic Chemistry, 2001. pp. 2455-2480.L. Suber, I. Sondi, E. Matijević, and D. V. Goia: Journal of Colloid and Interface Science 288, 2005. pp. 489–495.K. P. Velikov, G. E. Zegers, and A. van Blaaderen:Langmuir 19, 2003. pp. 1384-1389.
I. Halaciuga and D.V. Goia. Journal of Materials Research 23, 2008. pp. 1776-1784.I. Halaciuga and D.V. Goia. CARTS USA 2008.D.T. Robb, I. Halaciuga, V. Privman, and D.V. Goia. 2008 APS March Meeting.D.T. Robb, I. Halaciuga, V. Privman, and D.V. Goia. Journal of Chemical Physics 129, 2008.
AcknowledgementsProf. Dan V. GoiaProf. V. PrivmanGoia Research Group (www.clarkson.edu/programs/goia_group)
Dr. Dan Robb (currently Assistant Prof. at Berry College - Georgia)
Mr. Ted Champagne (FE-SEM micrographs)
Sponsors:NSF (grant DMR-0509104)DuPont
Thank you!Thank you!
Questions ?Questions ?
