Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Taking Thin Films to the Extreme

01.10.2014

Layering rough surfaces with nanometer-thin optical interference coatings opens new array of possible applications, such as nearly weight-free logos on the sides of spacecraft

Applying a well-known optical phenomenon called thin-film interference, a group of researchers at Harvard University has demonstrated the ability to "paint" ultra-thin coatings onto a rough surface -- work that holds promise for making future, flexible electronic devices, creating advanced solar cells and detailing the sides of next-gen rocket ships and spacecraft with extremely lightweight decorative logos.


M. Kats / Harvard

Gold-coated notebook paper pieces with ultra-thin germanium films of different thickness deposited on top

When light passes through oil in water, it becomes iridescent, revealing a myriad of colors that glisten and shift along with your perspective. This behavior, known as thin-film interference, is well-studied and is implemented in creating all manner of optical devices. Recently, the Harvard team demonstrated that this behavior can persist when patterned on extremely rough and flexible surfaces.

“Normally when you think of thin-film interference, you think of smooth substrates,” said Mikhail Kats, a postdoctoral fellow at Harvard University working in the lab of Federico Capasso. He and Capasso describe their work in the journal Applied Physics Letters, from AIP Publishing. “With increasing roughness the effect is expected to fade and you just don’t get this coherent behavior.”

Optically speaking, notebook paper is at the far end of the roughness spectrum, owing to its fibrous composition. However, after the researchers deposited onto paper an initial layer of gold and a subsequent layer of germanium, the paper began to display interference. The optical trickery lies in the influence of the film’s angle of incidence.

Traditionally, thin films needed to be transparent and no thinner than roughly one-quarter of the wavelength of light – 600 nm – to exhibit interference colors.

This is due to the phase shifts, or changes in optical path length, which occur as a result of changes in the observer’s angle of incidence. The path length directly corresponds to which colors appear to an observer - tilt your head and they change slightly.

At the nanometer scale, however, the amount of phase shift that occurs is greatly diminished due to the significantly smaller thickness of the films, resulting in a decrease in the angle of incidence’s effect. Tilt your head now, and the colors remain unchanged.

“You can use this effect to essentially see atomic monolayers, bilayers or tri-layers with your naked eye,” Kats said.

This would allow for the coloring of metallic objects by use of far less material than with traditional paint – a claim confirmed by the orange, indigo, and violet hues visible from the 7, 10 and 15 nm layered sheets of paper.

“There’s a famous story where, by not painting the space shuttle’s fuel tank, 600 pounds were saved, because that’s how much the paint weighed,” Kats said. “If you wanted to put a logo on something that you’re sending up in space, or you wanted to color it, here you could do it without almost any increase in weight.”

Future applications of the films include making extremely thin, flexible photodetectors and optoelectronic devices, including solar cells.

“I don’t think a solar cell made out of these materials is going to break any efficiency records, but we might demonstrate one that uses 1/10th-1/100th of the material of a conventional cell,” Kats said. “And that’s still an interesting parameter to explore when it comes to cost.”

The article, "Ultra-thin optical interference coatings on rough and flexible substrates" is authored by Mikhail A. Kats and Federico Capasso. It will appear in the journal Applied Physics Letters on September 30, 2014. After that date, it can be accessed at:
http://scitation.aip.org/content/aip/journal/apl/105/13/10.1063/1.4896527

ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org

Jason Bardi | newswise

More articles from Physics and Astronomy:

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

nachricht Magnetic moment of a single antiproton determined with greatest precision ever
19.01.2017 | Johannes Gutenberg-Universität Mainz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

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...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | 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

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>