From smartphones to the operating interfaces of ticket machines and cash dispensers, touchscreens require transparent electrodes in order to recognize finger pressure. The glass surfaces of these devices are coated with a grid of barely visible gold or silver, the walls of which are so thin they’re barely visible. Called nanowalls or nanowires, these new type of transparent electrodes offer great potential as transparent electrodes in display and solar cell applications.
For the first time, scientists have created nanowalls using 3D printing technology. The new electrodes have a higher conductivity and are more transparent than those made of indium tin oxide, the standard material used in smartphones and tablets today, according to Patrik Rohner, a PhD student and member of the team that developed the electrode at ETH Zurich, a university for technology and the natural sciences in Switzerland.
The greater transparency offered by nanowires or nanowalls improves screen quality. Their improved conductivity also improves accuracy and response, a technology boon that’s sure to drive market growth in this niche market.
WHAT IS NANOTECHNOLOGY?
Nanotechnology is the branch of technology that deals with dimensions and tolerances of less than 100 nanometers, especially the manipulation of individual atoms and molecules. On the measurement scale 1 nanometer is a billionth of a meter, or 10-9 meters,
according to BCC Research analyst Anand Gijare.
NANOWIRES
Gijare says that nanowires are also known as quantum wires as at these scales, effects of quantum mechanics are important. There are many different types of existing nanowires such as metallic (e.g., Ni, Pt, Au), semiconducting (e.g., InP, Si, GaN, etc.), and insulating (e.g., SiO2, TiO2). Repeating molecular units, either organic (e.g., DNA) or inorganic (e.g., Mo6S9–xIx), compose molecular nanowires, he explains.
“Nanowires have great potential in printing applications such as flexible electronics and displays and in sensor technology,” says Gijare. “There are various ongoing research projects and developments for improving the characteristics of nanowires, which will bring a better alternative to silicon–based printing applications that will enable paper–quality displays. Nanotechnology can be used across various science fields, such as chemistry, biology, physics, materials science, and engineering.”
THE DEVELOPMENT OF ‘THE NANODRIP’
Dimos Poulikakos, professor of thermodynamic at ETH, says the team of researchers opted for gold and silver, which conduct electricity much better. But because these metals are not transparent, the scientists had to make use of the third dimension. As he explains to
Fabio Bergamin: “If you want to achieve both high conductivity and transparency in wires made from these metals, you have a conflict of objectives. As the cross-sectional area of gold and silver wires grows, the conductivity increases, but the grid’s transparency decreases.”
Poulikakos says these tiny metal walls use a printing process known as Nanodrip, which he and his colleagues developed three years ago. Bergman writes the basic principle is a process called electrohydrodynamic ink-jet printing: “In this process scientists use inks made from metal nanoparticles in a solvent; an electrical field draws ultra-small droplets of the metallic ink out of a glass capillary. The solvent evaporates quickly, allowing a three-dimensional structure to be built up drop by drop.”
The printing process is called "Nanodrip" because the metallic ink was accumulated drop by drop unto the grid. Bermagin continues: “What is special about the Nanodrip process is that the droplets that come out of the glass capillary are about ten times smaller than the aperture itself. This allows for much smaller structures to be printed.”
ROLE OF NANOTECHNOLOGY IN PRINTING INDUSTRY
The role of nanotechnology in the printing industry is primarily due to printed electronics and the fabrication of semiconductors. Nanotechnology provides advancement to existing printing technologies and their applications, as with ETH Zurich’s discovery of the Nanodrip process, says Gijare.
“Use of nanotechnology in the printing industry is one of the promising areas for researchers and developers of modern fabrication technology. There are several experiments underway for developing nanotechnology based printing applications, inks, pigments and coatings,” he explains. “Nanotechnology is also studied to develop novel printing technologiesand has generated fabulous results in 3D printing, printing electronics, substrates and battery applications.
The printing industry uses nanotechnology to produce inks such as conductive inks, pigments for specialized inks, and security inks using semiconducting organic compounds, metal nanoparticles, carbon nanotubes and other nanomaterials. Nanomaterials show distinct characteristics such as optical properties and produce quantum effects at nanoscale that has helped in developing various new generation electronic components and semiconductors.
DEVELOPMENT TRENDS IN NANOWIRES FOR PRINTING
Nanowires as Transparent Electrodes. Transparent electrodes are gaining popularity in displays, OLEDs and solar panels, according to Gijare. In addition to carbon nanotubes, nanowires play a major role in developing transparent electrodes for various applications. Transparent electrodes will replace tin–doped indium oxide (ITO) electrodes.
“There are ongoing studies on incorporating nanowires of silver, copper and other materials to develop transparent electrodes,” he says, citing a research team at Windsor University that worked on an annealed silver nanowire network embedded in a polyurethane optical adhesive to develop transparent and conductive coatings. The coatings will be applied to rigid glass substrates as well as to flexible polyethylene terephthalate (PET) plastic and elastomeric poly–dimethylsiloxane (PDMS) substrates to produce transparent electrodes.
These electrodes are flexible, possess high bending strains, and are more durable to marring and scratching compared to indium tin oxide (ITO), says Gijare.
Use of nanotechnology in the printing industry is one of the promising areas for researchers and developers of modern printing technology. There are several experiments undertaken for developing nanotechnology–based printing technologies and has generated fabulous results such as next generation lithographies, 3D printing, and nanography.
The global market for nanotechnology-enabled printing technology was estimated to total $14 billion in 2013. The market is expected to grow at a projected compound annual growth rate (CAGR) of 17.7% over the next five years to total $31.8 billion by 2018, according to Gijare.
