Synthesis of Silver Colloids: Experiment and Computational ... · Outline Motivation and objectives Preparation of metallic layers via thick-film technology Typical approaches for

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

0

20

40

60

80

100

120

$ U

S B

ILLI

ON

S

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 ?