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.
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:
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
Structured light and nanomaterials open new ways to tailor light at the nanoscale
23.04.2018 | Academy of Finland
On the shape of the 'petal' for the dissipation curve
23.04.2018 | Lobachevsky University
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
23.04.2018 | Physics and Astronomy
23.04.2018 | Physics and Astronomy
23.04.2018 | Trade Fair News