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 Long-lived storage of a photonic qubit for worldwide teleportation
12.12.2017 | Max-Planck-Institut für Quantenoptik

nachricht Telescopes team up to study giant galaxy
12.12.2017 | International Centre for Radio Astronomy Research

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: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Long-lived storage of a photonic qubit for worldwide teleportation

12.12.2017 | Physics and Astronomy

Multi-year submarine-canyon study challenges textbook theories about turbidity currents

12.12.2017 | Earth Sciences

Electromagnetic water cloak eliminates drag and wake

12.12.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>