Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Penn Researchers Find New Way to Prevent Cracking in Nanoparticle Films

16.10.2012
Making uniform coatings is a common engineering challenge, and, when working at the nanoscale, even the tiniest cracks or defects can be a big problem. New research from University of Pennsylvania engineers has shown a new way of avoiding such cracks when depositing thin films of nanoparticles.

The research was led by graduate student Jacob Prosser and assistant professor Daeyeon Lee, both of the Department of Chemical and Biomolecular Engineering in Penn’s School of Engineering and Applied Science.

Graduate student Teresa Brugarolas and undergraduate student Steven Lee, also of Chemical and Biomolecular Engineering, and professor Adam Nolte of the Rose-Hulman Institute of Technology participated in the research.

Their work was published in the journal Nano Letters.

To generate a nanoparticle film, the desired particles are suspended in a suitable liquid, which is then thinly and evenly spread over the surface through a variety of physical methods. The liquid is then allowed to evaporate, but, as it dries, the film can crack like mud in the sun.

“One method for preventing cracking is modifying the suspension’s chemistry by putting binding additives in there,“ Prosser said. “But that is essentially adding a new material to the film, which may ruin its properties.”

This dilemma is highlighted in the case of electrodes, the contact points in many electrical devices that transfer electricity. High-end devices, like certain types of solar cells, have electrodes composed of nanoparticle films that conduct electrons, but cracks in the films act as insulators. Adding a binder to the films would only compound the problem.

“These binders are usually polymers, which are insulators themselves,” Lee said. “If you use them, you’re not going to get the targeted property, the conductivity, that you want.”

Engineers can prevent cracks with alternative drying methods, but these involve ultra-high temperatures or pressures and thus expensive and complicated equipment. A cheap and efficient method for preventing cracks would be a boon for any number of industrial processes.

The ubiquity of cracking in this context, however, means that researchers know the “critical cracking thickness” for many materials. The breakthrough came when Prosser tried making a film thinner than this threshold, then stacking them together to make a composite of the desired thickness.

“I was thinking about how, in the painting of buildings and homes, multiple coats are used,” Prosser said. “One reason for that is to avoid cracking and peeling. I thought it could work for these films as well, so I gave it a try.”

“This is one of those things where, once you figure it out,” Lee said, “it’s so obvious, but somehow this method has evaded everyone all these years.”

One reason this approach may have remained untried is that it is counterintuitive that it should work at all.

The method the researchers used to make the films is known as “spin-coating.” A precise amount of the nanoparticle suspension — in this case, silica spheres in water — is spread over the target surface. The surface is then rapidly spun, causing centrifugal acceleration to thin the suspension over the surface in a uniform layer. The suspension then dries with continued rotation, causing the water to evaporate and leaving the silica spheres behind in a compacted arrangement.

But to make a second layer over this first, another drop of liquid suspension would need to be placed on the dried nanoparticles, something that would normally wash them away. However, the researchers were surprised when the dried layers remained intact after the process was repeated 13 times; the exact mechanism by which they remained stable is something of a mystery.

“We believe that the nanoparticles are staying on the surface,” Lee said, “because covalent bonds are being formed between them even though we’re not exposing them to high temperatures. The inspiration for that hypothesis came from our colleague Rob Carpick. His recent Nature paper was all about how silica-silica surfaces form bonds at room temperature; we think this will work with other kinds of metal oxides.”

Future research will be necessary to pin down this mechanism and apply it to new types of nanoparticles.

The research was supported by the National Science Foundation and the Penn Materials Research Science and Engineering Center.

Evan Lerner | EurekAlert!
Further information:
http://www.upenn.edu

More articles from Materials Sciences:

nachricht Glass's off-kilter harmonies
18.01.2017 | University of Texas at Austin, Texas Advanced Computing Center

nachricht Explaining how 2-D materials break at the atomic level
18.01.2017 | Institute for Basic Science

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

A big nano boost for solar cells

18.01.2017 | Power and Electrical Engineering

Glass's off-kilter harmonies

18.01.2017 | Materials Sciences

Toward a 'smart' patch that automatically delivers insulin when needed

18.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>