By suspending tiny metal nanoparticles in liquids, Duke scientists are developing conductive inks for inkjet printers that can print inexpensive, customizable circuit patterns on any surface virtually .
Printed electronics have been widely used on a number of devices, such as anti-theft radio frequency identification (RFID) tags that are usually found behind new DVDs. It currently has a major drawback: in order for the circuit to work, it must first be heated to fuse all of the nanoparticles into a single conductive filament, which makes it impossible to print circuits on cheap plastic or paper.
A new study by Duke University researchers shows that adjusting the shape of the nanoparticles in ink eliminates the need for heating.
By comparing the conductivity of thin films made from different shapes of silver nanostructures, the researchers found that electrons made of silver nanowires are much easier to fabricate than films made of other shapes such as nanospheres or microdisks. In fact, the flow of electrons through a film made of nanowires is so easy that they can be used in printed circuits without melting them together.
Benjamin Wiley, an assistant professor of chemistry at Duke University, said: “the conductivity of nanowires is 4000 times higher than that of commonly used silver nanoparticles that can be found on printed RFID tags. So if you use nanowires, then you don’t need to heat the printed circui to such a high temperature that you can use cheaper plastic or paper.”
Wiley added: “in addition to these silver nanowires, I really don’t think there is anything else that can be simply printed out like this. Without any post-processing, it can be directly conductive.”
Applications of these types of printed electronics may go far beyond smart packaging. Researchers envision using this technology to make solar cells, printed displays, LEDs, touch screens, amplifiers, batteries, and even some implanted bioelectronic devices.
Wiley said that silver has become a raw material for the manufacture of printed electronic materials, and many recent studies have shown the measurement of the electrical conductivity of silver nanostructure films of different shapes. However, experimental errors make it difficult to make direct comparisons between different shapes, and there are few reports that relate the conductivity of the film to the total mass of silver used, which is an important factor when using expensive materials.
“We want to eliminate any extra materials from ink, just focus on the silver content in the film and the link between the nanostructures as the only source of variation,” said Stewart, another graduate student.
Stewart uses known recipes to make silver nanostructures with different shapes, including nanoparticles, microchips, and short and long nanowires. These nanostructures are then mixed with distilled water to make a simple “ink.” He then invented a quick and easy way to make films using glass slides and double-sided adhesive tapes that can be easily found in any laboratory.
Stewart said: “We used punches to punch wells out of double-sided tape and stick it to the glass.” By adding a precise amount of ink to each well of the tape, the well was then heated to a temperature of The relatively low temperature at which the water evaporates or the relatively high temperature at which the structure begins to melt, he has obtained a variety of films for testing.
The research team said that they are not surprised that the long nanowire film has the highest conductivity. Electrons usually pass easily through a single nanostructure, but they tend to get stuck when they have to jump from one structure to the next, Wiley explained, while long nanowires greatly reduce the number of electronic “jumps.”
However, they were surprised by the intensity of this change. “The resistivity of long silver nanowire films is orders of magnitude lower than that of silver nanoparticles, and only ten times larger than pure silver,” Stewart said.
The team is now experimenting with aerosol inkjet printers to print silver nanowire inks in available circuits. Wiley said that they also want to explore whether silver-plated copper nanowires can produce the same effect, which is much cheaper than pure silver nanowires.