Technique Sinters Thin Films at Lower Temps

A revised approach to the process of photonic sintering could advance thin films for solar cells, flexible electronics, sensors and other printed technologies by decreasing the temperature required for fabrication.

Sintering is the fusing of nanoparticles to form a solid, functional thin film. Previous constraints on production temperatures, speed and cost have inhibited adoption at commercial and industrial scales.

Schematic of an experimental photonic sintering setup. Courtesy of Rajiv Malhotra/Oregon State University.

Now engineers at Oregon State University have discovered that previous approaches to photonic sintering were based on a flawed view of the basic physics involved, leading to gross overestimation of product quality and process efficiency. The researchers believe they can create high-quality products at much lower temperatures, at least twice as fast and with 10 times more energy efficiency than other nanoparticle sintering techniques.

In the study, the Oregon team experimentally characterized the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. They showed that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. They used light from a xenon lamp to fuse the nanoparticles into functional thin films, achieving high densification without nanoparticle melting.

Electromagnetic finite element analysis of photonic heating was coupled to an analytical sintering model to examine the role of interparticle neck growth in photonic sintering. Analysis showed that photonic sintering is an inherently self-damping process; that is, the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached.

Addressing production constraints such as temperature, the researchers said, should allow high-tech products to printed onto substrates as cheap as paper or plastic wrap.

“Lower temperature is a real key,” said Rajiv Malhotra, a professor of mechanical engineering. “To lower costs, we want to print these nanotech products on things like paper and plastic, which would burn or melt at higher temperatures. We now know that is possible, and how to do it. We should be able to create production processes that are both fast and cheap, without a loss of quality.”

Products that could benefit from photonic sintering include solar cells, gas sensors, radiofrequency identification tags and flexible electronics, said Malhotra. Wearable biomedical sensors could emerge, along with new sensing devices for environmental applications.

The research, published in Nature Scientific Reports (doi: 10.1038/srep14845 [open access]), was supported by a four-year, $1.5 million National Science Foundation Scalable Nanomanufacturing Grant, which focuses on transcending the scientific barriers to industry-level production of nanomaterials.