Tag Archives: photonics

A multiferroic material for more powerful solar cells

A Nov. 12, 2014 INRS (Institut national de la recherche scientifique; Université du Québec) news release (also on EurekAlert), describes new work on solar cells from Federico Rosei’s laboratory (Note: Links have been removed; A French language version of the news release can be found here),

Applying a thin film of metallic oxide significantly boosts the performance of solar panel cells—as recentlydemonstrated by Professor Federico Rosei and his team at the Énergie Matériaux Télécommunications Research Centre at Institut national de la recherche scientifique (INRS). The researchers have developed a new class of materials comprising elements such as bismuth, iron, chromium, and oxygen. These“multiferroic” materials absorb solar radiation and possess unique electrical and magnetic properties. This makes them highly promising for solar technology, and also potentially useful in devices like electronic sensors and flash memory drives. …

The INRS research team discovered that by changing the conditions under which a thin film of these materials is applied, the wavelengths of light that are absorbed can be controlled. A triple-layer coating of these materials—barely 200 nanometres thick—captures different wavelengths of light. This coating converts much more light into electricity than previous trials conducted with a single layer of the same material. With a conversion efficiency of 8.1% reported by [Riad] Nechache and his coauthors, this is a major breakthrough in the field.

The team currently envisions adding this coating to traditional single-crystal silicon solar cells (currently available on the market). They believe it could increase maximum solar efficiency by 18% to 24% while also boosting cell longevity. As this technology draws on a simplified structure and processes, as well as abundant and stable materials, new photovoltaic (PV) cells will be more powerful and cost less. This means that the INRS team’s breakthrough may make it possible to reposition silicon PV cells at the forefront of the highly competitive solar energy market.

Here’s a link to and a citation for the paper,

Bandgap tuning of multiferroic oxide solar cells by R. Nechache, C. Harnagea, S. Li, L. Cardenas, W. Huang,  J. Chakrabartty, & F. Rosei. Nature Photonics (2014) doi:10.1038/nphoton.2014.255 Published online
10 November 2014

This paper is behind a paywall although there is a free preview via ReadCube Access.

I last mentioned Federico Rose in a March 4, 2014 post about a talk (The exploration of the role of nanoscience in tomorrow’s energy solutions) he was giving in Vancouver (Canada).

University of Cambridge makes waves with graphene piano

The news about the graphene piano (and anti-fraud lasers, etc.) is contained in a report from the University of Cambridge’s Cambridge Innovation and Knowledge Centre (CIKC), according to a Nov. 5, 2013 news item on phys.org (Note: A link has been removed),

Two prototypes – a detection device which users lasers to fight fraud, and a piano which demonstrates the potential of printed electronics – have been unveiled by Cambridge researchers.

A detection device which uses printed lasers to identify counterfeit goods has been developed by researchers, who say that it could help to make products more resistant to fraud.

The detector is one of a number of innovations covered in a new report by the Cambridge Innovation and Knowledge Centre (CIKC), which has been developing advanced manufacturing technologies for photonics and electronics.

The same document also outlines a new method for printing graphene, showing how the one atom-thick material could be used to make cheap, printed electronics. Using a graphene-based ink, researchers have demonstrated this by creating a transparent, flexible piano.

Here’s a video about the transparent piano produced at Cambridge,

The Nov. 5, 2013 University of Cambridge news release, which originated the news item, offers details about the piano and the graphene inks used to produce it,

The printed piano meanwhile demonstrates the potential of using graphene in real applications where printed electronics might be needed – such as heart monitors and other sensors.

The research team behind it, Drs Tawfique Hasan, Felice Torrisi and Prof Andrea Ferrari, at the Cambridge Graphene Centre, have developed a graphene-based ink. Like the material itself, this has a number of interesting properties, including flexibility, optical transparency, and electrical conductivity.

Other conductive inks are made from precious metals such as silver, which makes them very expensive to produce and process, whereas graphene is both cheap, environmentally stable, and does not require much processing after printing. Graphene ink is also superior to conductive polymers in terms of cost, stability and performance.

The piano, designed in collaboration with Novalia Limited, shows off the graphene ink’s potential. The keys of the transparent piano are made from graphene-based inks, which have been printed on to a plastic film. These keys, working as electrodes, are connected to a simple electronic circuit-board, a battery and speaker. When a person touches a graphene electrode, the amount of electrical charge held in the key changes. This is then detected and redirected by the circuit to the speaker, creating the musical note.

The same research team, in collaboration with Printed Electronics Limited, has developed a flexible prototype digital display. This display uses conventional printable materials, but with a transparent, electrically conductive graphene layer on top. The graphene layer is not only a flexible but also more conductive and transparent than the conventional polymer it replaces. These simple displays can be used in a wide range of smart packaging applications such as toys, labelling and board games.

“Both of these devices show how graphene could be printed on to a whole range of surfaces, which makes it ideal for printed electronics,” Dr Hasan, the lead researcher behind the prototypes, said. For example, it might eventually be possible to print electronics on to clothing and to make wearable patches to monitor people with health conditions, such as a heart problem.”

Another potential application is cheap, printable sensors, which could be used to track luggage around an airport to ensure it is loaded on to the correct plane, or to follow products across a production and supply chain.

For anyone who’d like to see the report and get information on the other projects discussed in it just click on the title: Advanced Manufacturing Technologies for Photonics and Electronics – Exploiting Molecular and Macromolecular Materials: Final Report.

*’Unviersity in headline changed to University 11:11 am PDT Nov. 7, 2013.

Solar cells made even more leaflike with inclusion of nanocellulose fibers

Researchers at the US Georgia  Institute of Technology (Georgia Tech)  and Purdue University (Indiana) have used cellulose nanocrystals (CNC), which is also known as nanocrystalline cellulose (NCC), to create solar cells that have greater efficiency and can be recycled. From the Mar. 26, 2013 news item on Nanowerk,

Georgia Institute of Technology and Purdue University researchers have developed efficient solar cells using natural substrates derived from plants such as trees. Just as importantly, by fabricating them on cellulose nanocrystal (CNC) substrates, the solar cells can be quickly recycled in water at the end of their lifecycle.

The Georgia Tech Mar. 25, 2013 news release, which originated the news item,

The researchers report that the organic solar cells reach a power conversion efficiency of 2.7 percent, an unprecedented figure for cells on substrates derived from renewable raw materials. The CNC substrates on which the solar cells are fabricated are optically transparent, enabling light to pass through them before being absorbed by a very thin layer of an organic semiconductor. During the recycling process, the solar cells are simply immersed in water at room temperature. Within only minutes, the CNC substrate dissolves and the solar cell can be separated easily into its major components.

Georgia Tech College of Engineering Professor Bernard Kippelen led the study and says his team’s project opens the door for a truly recyclable, sustainable and renewable solar cell technology.

“The development and performance of organic substrates in solar technology continues to improve, providing engineers with a good indication of future applications,” said Kippelen, who is also the director of Georgia Tech’s Center for Organic Photonics and Electronics (COPE). “But organic solar cells must be recyclable. Otherwise we are simply solving one problem, less dependence on fossil fuels, while creating another, a technology that produces energy from renewable sources but is not disposable at the end of its lifecycle.”

To date, organic solar cells have been typically fabricated on glass or plastic. Neither is easily recyclable, and petroleum-based substrates are not very eco-friendly. For instance, if cells fabricated on glass were to break during manufacturing or installation, the useless materials would be difficult to dispose of. Paper substrates are better for the environment, but have shown limited performance because of high surface roughness or porosity. However, cellulose nanomaterials made from wood are green, renewable and sustainable. The substrates have a low surface roughness of only about two nanometers.

“Our next steps will be to work toward improving the power conversion efficiency over 10 percent, levels similar to solar cells fabricated on glass or petroleum-based substrates,” said Kippelen. The group plans to achieve this by optimizing the optical properties of the solar cell’s electrode.

The news release also notes the impact that using cellulose nanomaterials could have economically,

There’s also another positive impact of using natural products to create cellulose nanomaterials. The nation’s forest product industry projects that tens of millions of tons of them could be produced once large-scale production begins, potentially in the next five years.

One might almost  suspect that the forest products industry is experiencing financial difficulty.

The researchers’ paper was published by Scientific Reports, an open access journal from the Nature Publishing Group,

Recyclable organic solar cells on cellulose nanocrystal substrates by Yinhua Zhou, Canek Fuentes-Hernandez, Talha M. Khan, Jen-Chieh Liu, James Hsu, Jae Won Shim, Amir Dindar, Jeffrey P. Youngblood, Robert J. Moon, & Bernard Kippelen. Scientific Reports  3, Article number: 1536  doi:10.1038/srep01536 Published 25 March 2013

In closing, the news release notes that a provisional patent has been filed at the US Patent Office.And one final note, I have previously commented on how confusing the reported power conversion rates are. You’ll find a recent comment in my Mar. 8, 2013 posting about Ted Sargent’s work with colloidal quantum dots and solar cells.

Fireflies and their jagged scales lead to brighter LEDs (light emitting diodes)

According to the Jan. 8, 2013 news item on ScienceDaily, scientists have used an observation about fireflies to make brighter LEDs (light emitting diodes),

The nighttime twinkling of fireflies has inspired scientists to modify a light-emitting diode (LED) so it is more than one and a half times as efficient as the original.

Researchers from Belgium, France, and Canada studied the internal structure of firefly lanterns, the organs on the bioluminescent insects’ abdomens that flash to attract mates. The scientists identified an unexpected pattern of jagged scales that enhanced the lanterns’ glow, and applied that knowledge to LED design to create an LED overlayer that mimicked the natural structure. The overlayer, which increased LED light extraction by up to 55 percent, could be easily tailored to existing diode designs to help humans light up the night while using less energy.

The Optical Society of America’s Jan. 8, 2013 news release, which originated the news item, describes how the scientists came to make their observations,

“The most important aspect of this work is that it shows how much we can learn by carefully observing nature,” says Annick Bay, a Ph.D. student at the University of Namur in Belgium who studies natural photonic structures, including beetle scales and butterfly wings.  When her advisor, Jean Pol Vigneron, visited Central America to conduct field work on the Panamanian tortoise beetle (Charidotella egregia), he also noticed clouds of twinkling fireflies and brought some specimens back to the lab to examine in more detail.

Fireflies create light through a chemical reaction that takes place in specialized cells called photocytes. The light is emitted through a part of the insect’s exoskeleton called the cuticle.  Light travels through the cuticle more slowly than it travels through air, and the mismatch means a proportion of the light is reflected back into the lantern, dimming the glow. The unique surface geometry of some fireflies’ cuticles, however, can help minimize internal reflections, meaning more light escapes to reach the eyes of potential firefly suitors.

In Optics Express papers, Bay, Vigneron, and colleagues first describe the intricate structures they saw when they examined firefly lanterns and then present how the same features could enhance LED design. Using scanning electron microscopes, the researchers identified structures such as nanoscale ribs and larger, misfit scales, on the fireflies’ cuticles. When the researchers used computer simulations to model how the structures affected light transmission they found that the sharp edges of the jagged, misfit scales let out the most light. The finding was confirmed experimentally when the researchers observed the edges glowing the brightest when the cuticle was illuminated from below.

“We refer to the edge structures as having a factory roof shape,” says Bay.  “The tips of the scales protrude and have a tilted slope, like a factory roof.” The protrusions repeat approximately every 10 micrometers, with a height of approximately 3 micrometers. “In the beginning we thought smaller nanoscale structures would be most important, but surprisingly in the end we found the structure that was the most effective in improving light extraction was this big-scale structure,” says Bay.

Here’s how the scientists applied their observations to LEDs (from the news release),

Human-made light-emitting devices like LEDs face the same internal reflection problems as fireflies’ lanterns and Bay and her colleagues thought a factory roof-shaped coating could make LEDs brighter. In the second Optics Express paper published today, which is included in the Energy Express  section of the journal, the researchers describe the method they used to create a jagged overlayer on top of a standard gallium nitride LED. Nicolas André, a postdoctoral researcher at the University of Sherbrooke in Canada, deposited a layer of light-sensitive material on top of the LEDs and then exposed sections with a laser to create the triangular factory-roof profile. Since the LEDs were made from a material that slowed light even more than the fireflies’ cuticle, the scientists adjusted the dimensions of the protrusions to a height and width of 5 micrometers to maximize the light extraction.

“What’s nice about our technique is that it’s an easy process and we don’t have to create new LEDs,” says Bay.  “With a few more steps we can coat and laser pattern an existing LED.”

Other research groups have studied the photonic structures in firefly lanterns as well, and have even mimicked some of the structures to enhance light extraction in LEDs, but their work focused on nanoscale features. The Belgium-led team is the first to identify micrometer-scale photonic features, which are larger than the wavelength of visible light, but which surprisingly improved light extraction better than the smaller nanoscale features. The factory roof coating that the researchers tested increased light extraction by more than 50 percent, a significantly higher percentage than other biomimicry approaches have achieved to date. The researchers speculate that, with achievable modifications to current manufacturing techniques, it should be possible to apply these novel design enhancements to current LED production within the next few years.

For those who care to investigate further,

Both articles (HTML version) are open access; PDF versions were not checked.

Quantum dots and graphene; a mini roundup

I’ve done very little writing about quantum dots (so much nano, so little time) but there’s been a fair amount of activity lately which has piqued my interest. In the last few days researchers at Kansas State University have been getting noticed for being able to control the size and shape of the graphene quantum dots they produce.  This one has gotten extensive coverage online including this May 17, 2012 news item on physorg.com,

Vikas Berry, William H. Honstead professor of chemical engineering, has developed a novel process that uses a diamond knife to cleave graphite into graphite nanoblocks, which are precursors for graphene quantum dots. These nanoblocks are then exfoliated to produce ultrasmall sheets of carbon atoms of controlled shape and size.

By controlling the size and shape, the researchers can control graphene’s properties over a wide range for varied applications, such as solar cells, electronics, optical dyes, biomarkers, composites and particulate systems. Their work has been published in Nature Communications and supports the university’s vision to become a top 50 public research university by 2025. The article is available online.

Here’s an image of graphene being cut by a diamond knife from the May 16, 2012 posting by jtorline on the K-State News blog,

Molecular dynamics snapshot of stretched graphene being nanotomed via a diamond knife.

Here’s why standardizing the size is so important,

While other researchers have been able to make quantum dots, Berry’s research team can make quantum dots with a controlled structure in large quantities, which may allow these optically active quantum dots to be used in solar cell and other optoelectronic applications. [emphasis mine]

While all this is happening in Kansas, the Econ0mist magazine published a May 12, 2012 article about some important quantum dot optoelectronic developments in Spain (an excellent description for relative beginners is given and, if this area interests you, I’d suggest reading it in full),

Actually converting the wonders of graphene into products has been tough. But Frank Koppens and his colleagues at the Institute of Photonic Sciences in Barcelona think they have found a way to do so. As they describe in Nature Nanotechnology, they believe graphene can be used to make ultra-sensitive, low-cost photodetectors.

A typical photodetector is made of a silicon chip a few millimetres across onto which light is focused by a small lens. Light striking the chip knocks electrons free from some of the silicon atoms, producing a signal that the chip’s electronics convert into a picture or other useful information. …

Silicon photodetectors suffer, though, from a handicap: they are inflexible. Nor are they particularly cheap. And they are not that sensitive. They absorb only 10-20% of the light that falls on to them. For years, therefore, engineers have been on the lookout for a cheap, bendable, sensitive photodetector. …

By itself, graphene is worse than silicon at absorbing light. According to Dr Koppens only 2.7% of the photons falling on it are captured. But he and his colleague Gerasimos Konstantatos have managed to increase this to more than 50% by spraying tiny crystals of lead sulphide onto the surface of the material.

So combining the ability to size quantum dots uniformly with this discovery on how to make graphene more sensitive (and more useful in potential products) with quantum dots suggests some very exciting possibilities including this one mentioned by Dexter Johnson (who’s living in Spain these days) in his May 16, 2012 posting on Nanoclast (on the Institute of Electrical and Electronics Engineers [IEEE] website),

The researchers offer a range of applications for the graphene-and-quantum-dot combination, including digital cameras and sensors.  [emphasis mine] But it seems the researchers seem particularly excited about one application in particular. They expect the material will be used for night-vision technologies in automobiles—an application I have never heard trotted out before in relation to nanotech.

You can get more insights, more precise descriptions if you want to follow up from the Econ0mist article,  and Dexter’s links to more information about the research in his posting.

In my final roundup piece, I received a news release (dated April 24, 2012) about a quantum dot commercialization project at the University of Utah,

One of the biggest challenges for advancing quantum dots is the manufacturing process. Conventional processes are expensive, require high temperatures and produce low yields. However, researchers at the University of Utah believe they have a solution. They recently formed a startup company called Navillum Nanotechnologies, and their efforts are gaining national attention with help from a team of M.B.A. students from the David Eccles School of Business.
The students recently won first place and $100,000 at the regional CU Cleantech New Venture Challenge. The student competition concluded at the University of Colorado in Boulder on Friday, April 20. The student team advances to the national championship, which will be held in June in Washington, D.C. Student teams from six regions will compete for additional prizes and recognition at the prestigious event. Other regional competitions were held at MIT, Cal Tech, the University of Maryland, Clean Energy Trust (Chicago) and Rice University. All the competitions are financed by the U.S. Department of Energy.

The students will be competing in the national Clean Energy Business Plan Competition taking place June 12-13, 2012 in Washington, D.C.  Here are a few more details from the national competition webpage,

Winners of the six regional competitions will represent their home universities and regions as they vie for the honor of presenting the best clean energy business plan before a distinguished panel of expert judges and invited guests from federal agencies, industry, national labs and the venture capital community.

Confirmed Attendees include:

The Honorable Steven Chu
Energy Secretary [US federal government]

Dr. David Danielson
Assistant Secretary, EERE  [US Dept. of Energy, energy efficiency and renewable energy technologies)

Dr. Karina Edmonds
Technology Transfer Coordinator [US Dept. of Energy]

Mr. Todd Park
Chief Technology Officer, White House

Good luck to the students!

Morpho butterflies detect heat for GE

One wonders if Morpho butterflies are going to decide that they need to protect their intellectual property. Yet another scientific group has found a way to exploit the nanostructures on the Morpho butterfly’s wing.  From the Feb. 13, 2012 news item on Nanowerk,

GE [General Electric] scientists are exploring many potential thermal imaging and sensing applications with their new detection concept such as medical diagnostics, surveillance, non-destructive inspection and others, where visual heat maps of imaged areas serve as a valuable condition indicator. Some examples include:

  • Thermal Imaging for advanced medical diagnosis – to better visualize inflammation in the body and understand changes in a patient’s health earlier.
  • Advanced thermal vision – to see things at night and during the day in much greater detail than what is possible today.
  • Fire thermal Imaging – to aid firefighters with new handheld devices to enhance firefighter safety in operational situations
  • Thermal security surveillance – to improve public safety and homeland protection
  • Thermal characterization of wound infections – to facilitate early diagnosis.

“The iridescence of Morpho butterflies has inspired our team for yet another technological opportunity. This time we see the potential to develop the next generation of thermal imaging sensors that deliver higher sensitivity and faster response times in a more simplified, cost-effective design,” said Dr. Radislav Potyrailo, Principal Scientist at GE Global Research who leads GE’s bio-inspired photonics programs. “This new class of thermal imaging sensors promises significant improvements over existing detectors in their image quality, speed, sensitivity, size, power requirements, and cost.”

GE has provided a video and description that illustrates this newest biomimicry work. First the description then the video (from http://www.youtube.com/watch?v=UoaILSCzlTo&feature=youtu.be)

This is a thermographic video of a Morpho butterfly structure in response to heat pulses produced by breathing onto the whole butterfly structure (video part 1) and onto its localized areas (video part 2). Nanostructures on Morpho butterfly wings coated with carbon nanotubes can sense temperature chances down to .02 degrees Celsius, at a response rate of 1/40 of a second. This is a demonstration of how new bio-inspired designs by GE scientists could enable more advanced applications for industrial inspection, medical diagnostics and military. This video was filmed by Bryan Whalen in the Electronics Cooling Lab at GE Global Research.

This newest work seems to have its origins in a DARPA-funded (US Defense Advanced Research Projects Agency) GE project. From the Aug. 12, 2010 GE news release,

Scientists at GE Global Research, GE’s technology development arm, in collaboration with Air Force Research Laboratory, State University at Albany, and University of Exeter, have received a four-year, $6.3 million award from the Defense Advanced Research Projects Agency (DARPA) to develop new bio-inspired nanostructured sensors that would enable faster, more selective detection of dangerous warfare agents and explosives.

Three years ago, GE scientists discovered that nanostructures from wing scales of butterflies exhibited acute chemical sensing properties. [emphasis bold] Since then, GE scientists have been developing a dynamic, new sensing platform that replicates these unique properties.  Recognizing the potential of GE’s sensing technologies for improving homeland protection, DARPA is supporting further research. [emphasis mine]

For anyone who’s particularly interested in the technical details, Dexter Johnson offers more in his Feb. 13, 2012 posting about this research on the Nanoclast blog for the IEEE (Institute of Electrical and Electronics Engineers).

A*STAR and University of Washington joint optoelectronics project

At the University of Washington located in Seattle, a joint project with A*STAR, Singapore’s Agency for Science, Technology and Research is about to get underway. From the Sept. 16, 2011 news item on Nanowerk,

A*STAR Institute of Microelectronics (IME) and the University of Washington announce that they will join forces to provide shared Silicon Photonics processes as part of the Optoelectronics Systems Integration in Silicon programme (OpSIS). This will help the research and development (R&D) community significantly reduce the fabrication cost of silicon photonics integrated circuits.

The silicon photonics integrated circuits to be created under this programme will be immediately available to the photonic research community worldwide, and in the process, facilitate technological advancements and proliferate creative ideas for the development of the next generation devices. As the platform will be offered through multi-project wafer (MPW) runs, which allow users from multiple projects to share the costs of a single fabrication run, research costs are lowered significantly for individual projects.

More information at A*STAR’s Institute of Microeletronics (IME) can be found here and about the University of Washington’s OpSIS programme here.

Nano kerfuffle in Germany; NRC on impact of photonics research in Canada

Thanks to Dexter Johnson who on his IEEE blog, Nanoclast, recently commented on the publication of a German government paper and the resulting international kerfuffle. Apparently a government agency placed a background paper about nanotechnology and its potential risks on their website which was picked up in newspapers that which used alarming headlines (likely to garner readership).  From Johnson’s comments,

The only thing that the UBA [a German government department] has in their favor for covering up their naïve and ill-conceived decision to catalogue a bunch of research that is not even their own on the risk of nanoparticles is that to a large extent the public doesn’t care.

I’m not sure why Johnson is so harsh about the fact that they did not present original research. I expect a background paper to present information that has been previously published and that represents a broad spectrum of opinions and ideas. I would find it disconcerting if original research were to be included.

The whole incident is an interesting example of how anything can take on its own life (something I discussed in my Monday, Oct. 28, 2009 posting discussion of some recent comments by Eric Drexler). You can read one of the English language versions of a ‘kerfuffle’ article here and a ‘damage control’ article here.

According to a news item on Azonano, Canada’s National Research Council (NRC) Canadian Photonics Fabrication Centre has released a report suggesting that over the next five years their client firms will generate about $500M.  You can read more about it all here.