Paper Written ByWenfeng Shen, Xianpeng Zhang, Qijin Huang, Qingsong Xu, Weijie Song

Preparation of Solid Silver Nanoparticles for Inkjet Printed Flexible Electronics with High

Conductivity

Presented ByGabe Shindnes, Liza Ross, Bill Shi

Purpose

Utilize Ag nanoparticles to develop a method to print

flexible electrical circuits.

Flexible printed LED array

Inkjet Printing Applications Inkjet printing technology has been used for

LED’s, photovoltaic cells, and sensors. Smart Clothing

Possible Conductors

Conductive Polymers, Graphene, Carbon Organo-metallic compounds Metal precursors Metal nanoparticlesWhy they are not suitable for application: Polymers, graphene and carbon have too low conductivity Organo-metallic compounds and metal precursors require too high

temperatures

Remaining solution: Nanoparticles

Silver Nanoparticles

Chosen for their good conductivity, low resistivity, reasonable cost and resistance to oxidation.

TEM Image of Ag Nanoparticles

Synthesis of Poly(acrylic acid) (PAA)-coated AgNP

Silver source: silver nitrate (AgNO3)Reducing agent: Monoethanolamine (MEA)Capping molecule: Poly(acrylic acid)Medium: deionized water

AgNO3 --->PAA coated, charged nanoparticles dispersed in aqueous solution1. Undergo vigorous magnetic stirring for an hour2. Heated up to 65 degrees Celsius3. Colors vary in the sequence of yellowish, brown, orange, and dark red.4. A black precipitate of PAA coated AgNP is collected after adding ethanol5. Collected through funnel and washed with ethanol to remove residual MEA and PAA

Silver ink lines were printed using a common color printer AgNP inks printed on Kodak photo paper, and polyethylene terephthalate

(PET)o PET substrate was precoated with Poly(diallyldimethylammonium)

chloride (PDAC) so the ink would sinter at room temperatureo Kodak paper already had PDAC-like molecules

After printing, samples are heat-treated at temperatures ranging from 50-280 .

Then:The structural and electric properties of silver patterns are investigated

Inkjet Printing and Heat Treatment of Silver Patterns

Dependent Variables and Measurement Methods:

Structural characterizations (electron density, atom positions) - X ray diffraction

Particle size distribution and morphology- Transmission electron microscope

Viscosity of AgNP- Viscometer Surface tension- Drop weight method Electrical resistivity- 4 point probe

system

Results and Discussion

Properties of Poly Acrylic Acid The powder obtained from grinding solid silver NPs was observed

with an X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM- results not shown with SEM), Thermogravimetric/Differential Thermal Analysis (TG/DTA)o XRD: results demonstrate that the powder was composed of

well-crystallized silver NPs, and that the PAA-coated silver particles did not change after being held in the room for 3 months

o Scherrer Formula ( ; formula that determines the size of particles in the form of powder) Showed that all particles were approximately 30nm

Poly Acrylic Acid

Results and Discussion TG/DTA: data showed a miniscule weight loss from room temperature to 300 of

0.7%o caused by the release of organic molecules from the surface of the silver NPso 0.1% weight loss from 955 to 1000 ; caused by temperature disturbance

99.2 % of weight was pure silver

Benefit of using silver NPs is that they can be stored at room temperatureo can also be prepared as printing material by

dispersing NPs with water

Silver NPs ranged from 20nm to 230nm, with mean being somewhere between 30 to 50 nm

Results and Discussion

TEM (Transmission Electron Microscope) Data Data obtained from TEM on Silver

NPs:o Particle size ranged from 10 -

100nmo The majority of the particles

were less than 40nmo Data agrees with the data

obtained from the X-Ray Diffraction (XRD) analysis

Transmission Electron Microscope

Results and Discussion

Silver NP Ink Properties Purpose: Produce small liquid silver droplets and to deposit them in a specific

location on a substrateo Most important properties of droplets for this : Viscosity and Surface Tensiono Increasing the density of Silver NPs in the liquid showed a positive correlation

in both Viscosity and Surface Tension

Other important properties to consider when working with non- Newtonian fluids:

Jet Velocity, Characteristic radius (radius of the orifice), and Density

Dimensionless numbers that describe these properties

Reynolds, Weber (measures spreading behavior)

Results and Discussion

Properties of Silver NPs The Ohnesorge number describes the physical properties of the ink and

the size of the scaleo Oh ranges from 0.1 to 1.0 since Z ranges from 1 to 10o A high Z (larger than 10) will create a large number of viscous satellite

dropletso A low Z (smaller than 1) will prevent the separation of the droplets due

to the viscous forces The Z value of the silver droplets that were created (varying in weight from

10 to 25 percent) ranged from 9.94 to 7.00 which made these inks printable

Results and Discussion The printed line width was set at 1pt, equating to approximately 530μm. If the silver nanoparticles were heated at higher temperatures, the more

conductive the lines became

At higher temperature, there were less cracks, helping induce electrical conductivity

Lines were printed 14 times, with each print decreasing the resistance at an exponential rate

a) Room Temperature b) 50oC c) 80oC d) 140oC

Results and Discussion Greatest resistivity difference between temperatures with only one print

cycle, but decreases significantly with additional print cycles

8μΩ cm when sintered at room temperature compared to 3.7μΩ cm at 180oC

Allows high conductivity at low temperatures

This is important because it allows for inkjet printing for paper and plastic products

Conclusion:

Synthesis of PAA coated AgNPs kept at room temp. without degeneration

Low cost reaction and environmentally friendly No centrifugation—Ideal for low cost and mass

production Lowest electrical resistivity measured was 8.0 µΩ cm → high conductivity