Lowering Fusion Temperatures Costs for Nano-Based Manufacturing

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NEW BRUNSWICK, N.J., Feb. 15, 2018 — A new method of processing materials for nano-based manufacturing allows intense pulsed light sintering (IPL) to be used at a lower temperature, enabling low-cost, temperature-sensitive plastic substrates to be used in the manufacture of flexible thin-film devices such as touch screens and window coatings.

IPL uses pulsed, large-area, broad-spectrum visible light from a xenon lamp for rapid fusion of nanomaterials into films or patterns used in flexible sensors, solar cells, displays and other applications. The existing method of pulsed light fusion uses temperatures of around 250 °C (482 °F) to fuse silver nanospheres into structures that conduct electricity. Past work on the IPL of silver nanoparticles has shown that a self-damping coupling between densification and optical absorption governs the evolution of the deposited nanomaterial temperature.

Spherical silver nanoparticles and nanowires after being fused by intense pulses of light. Rutgers University-New Brunswick.
Fusing, or sintering, nanoparticles by exposing them to pulses of intense light from a xenon lamp. Courtesy of Rajiv Malhotra/Rutgers University-New Brunswick.

Researchers at Rutgers University-New Brunswick and Oregon State University studied the influence of the nanomaterial shape distribution on this coupling and on the temperature evolution in IPL of silver nanowire–nanoparticle composite films.

Researchers compared film thickness, resistivity, micromorphology, crystallinity and optical properties for varying ratios of nanowire to nanoparticle content in the film. They found that by increasing the nanowire content, they could reduce the maximum film temperature during IPL from 240 °C to 150 °C. At the same time, they were able to alter the temperature evolution trends over consecutive pulses, while enabling film resistivity within four to five times that of bulk silver. Researchers were able to obtain these properties within 2.5 seconds of processing time.

Spherical silver nanoparticles and nanowires after being fused by intense pulses of light. Rutgers University-New Brunswick.
Spherical silver nanoparticles and nanowires after being fused by intense pulses of light. Courtesy of Rajiv Malhotra/Rutgers University-New Brunswick.

These findings could be applied to reducing substrate distortion and damage when thermally sensitive substrates like polymers and paper are used, without compromising process throughput.

“Pulsed light sintering of nanomaterials enables really fast manufacturing of flexible devices for economies of scale,” said professor Rajiv Malhotra. “Our innovation extends this capability by allowing cheaper temperature-sensitive substrates to be used.

“The next step is to see whether other nanomaterial shapes, including flat flakes and triangles, will drive fusion temperatures even lower,” Malhotra said.

Fused silver nanomaterials are used to conduct electricity in devices such as radio-frequency identification (RFID) tags, display devices and solar cells. Flexible forms of these products rely on fusion of conductive nanomaterials on flexible substrates such as plastics and other polymers.

The research was published in RSC Advances (doi: 10.1039/c7ra11013h).

In a separate study, published in Scientific Reports (doi:10.1038/s41598-018-20621-9), researchers demonstrated pulsed light sintering of copper sulfide nanoparticles to make films less than 100 nm thick.

Published: February 2018
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Research & TechnologyAmericaseducationMaterialsnanomaterialsDisplaysflexible displaysindustrialnanothin filmsintense pulsed light sinteringIPLmaterials processingTechnology News

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