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Paper-based Printable Electronics Made Possible with Nanowire Inks

Published on 2017-01-17. Author : SpecialChem

By suspending tiny metal nanoparticles in liquids, Duke University scientists have brewed up conductive ink-jet printer “inks” to print inexpensive, customizable circuit patterns on just about any surface.

Printed electronics, which are already being used on a wide scale in devices such as the anti-theft radio frequency identification (RFID) tags on the back of new DVDs, currently have one major drawback: for the circuits to work, they first have to be heated to melt all the nanoparticles together into a single conductive wire, making it impossible to print circuits on inexpensive plastics or paper.

Silver Nanostructures
Duke University chemists have found that silver nanowire films
conduct electricity well enough to form functioning circuits
without applying high heat, enabling printable electronics on
heat-sensitive materials like paper or plastic

Tweaking the Shape of the Nanoparticles in Ink

A new study by Duke researchers shows that tweaking the shape of the nanoparticles in the ink might just eliminate the need for heat.

By comparing the conductivity of films made from different shapes of silver nanostructures, the researchers found that electrons zip through films made of silver nanowires much easier than films made from other shapes, like nanospheres or microflakes. In fact, electrons flowed so easily through the nanowire films that they could function in printed circuits without the need to melt them all together.

Achieving Higher Conductivity with Nanowires


The nanowires had a 4,000 times higher conductivity than the more commonly used silver nanoparticles that you would find in printed antennas for RFID tags,” said Benjamin Wiley, assistant professor of chemistry at Duke. “So if you use nanowires, then you don’t have to heat the printed circuits up to such high temperature and you can use cheaper plastics or paper.

There is really nothing else I can think of besides these silver nanowires that you can just print and it’s simply conductive, without any post-processing,” Wiley added.

Applications of Printed Electronics


These types of printed electronics could have applications far beyond smart packaging; researchers envision using the technology to make:
  • Solar cells
  • Printed displays
  • LEDS, touchscreens
  • Amplifiers
  • Batteries 
  • Implantable bio-electronic devices 

Silver has become a go-to material for making printed electronics, Wiley said, and a number of studies have recently appeared measuring the conductivity of films with different shapes of silver nanostructures. However, experimental variations make direct comparisons between the shapes difficult, and few reports have linked the conductivity of the films to the total mass of silver used, an important factor when working with a costly material.

We wanted to eliminate any extra materials from the inks and simply hone in on the amount of silver in the films and the contacts between the nanostructures as the only source of variability,” said Ian Stewart, a recent graduate student in Wiley’s lab and first author on the ACS paper.

Quick and Easy Way to Make Thin Films

Nanowire

Stewart used known recipes to cook up silver nanostructures with different shapes, including nanoparticles, microflakes, and short and long nanowires, and mixed these nanostructures with distilled water to make simple “inks.” He then invented a quick and easy way to make thin films using equipment available in just about any lab -- glass slides and double-sided tape.

We used a hole punch to cut out wells from double-sided tape and stuck these to glass slides,” Stewart said. By adding a precise volume of ink into each tape “well” and then heating the wells -- either to relatively low temperature to simply evaporate the water or to higher temperatures to begin melting the structures together -- he created a variety of films to test.

The team says they weren’t surprised that the long nanowire films had the highest conductivity. Electrons usually flow easily through individual nanostructures but get stuck when they have to jump from one structure to the next, Wiley explained, and long nanowires greatly reduce the number of times the electrons have to make this “jump”.

But they were surprised at just how drastic the change was. “The resistivity of the long silver nanowire films is several orders of magnitude lower than silver nanoparticles and only 10 times greater than pure silver,” Stewart said.

Aerosol Jets to Print Silver Nanowire Inks


The team is now experimenting with using aerosol jets to print silver nanowire inks in usable circuits. Wiley says they also want to explore whether silver-coated copper nanowires, which are significantly cheaper to produce than pure silver nanowires, will give the same effect.

The research was supported by funding from the National Science Foundation and a GAANN Fellowship through the Duke Chemistry Department.

About The Duke University

Duke University is a private research university located in Durham, North Carolina, United States. Founded by Methodists and Quakers in the present-day town of Trinity in 1838, the school moved to Durham in 1892. In 1924, tobacco and electric power industrialist James Buchanan Duke established The Duke Endowment, at which time the institution changed its name to honor his deceased father, Washington Duke.

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Source: The Duke University
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