Tag Archives: vanadium dioxide

‘Smart’ windows from Australia

My obsession with smart windows has been lying dormant until now. This February 25, 2018 RMIT University (Australia) press release on EurekAlert has reawkened it,

Researchers from RMIT University in Melbourne Australia have developed a new ultra-thin coating that responds to heat and cold, opening the door to “smart windows”.

The self-modifying coating, which is a thousand times thinner than a human hair, works by automatically letting in more heat when it’s cold and blocking the sun’s rays when it’s hot.

Smart windows have the ability to naturally regulate temperatures inside a building, leading to major environmental benefits and significant financial savings.

Lead investigator Associate Professor Madhu Bhaskaran said the breakthrough will help meet future energy needs and create temperature-responsive buildings.

“We are making it possible to manufacture smart windows that block heat during summer and retain heat inside when the weather cools,” Bhaskaran said.

“We lose most of our energy in buildings through windows. This makes maintaining buildings at a certain temperature a very wasteful and unavoidable process.

“Our technology will potentially cut the rising costs of air-conditioning and heating, as well as dramatically reduce the carbon footprint of buildings of all sizes.

“Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital.”

Smart glass windows are about 70 per cent more energy efficient during summer and 45 per cent more efficient in the winter compared to standard dual-pane glass.

New York’s Empire State Building reported energy savings of US$2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows. This was using a less effective form of technology.

“The Empire State Building used glass that still required some energy to operate,” Bhaskaran said. “Our coating doesn’t require energy and responds directly to changes in temperature.”

Co-researcher and PhD student Mohammad Taha said that while the coating reacts to temperature it can also be overridden with a simple switch.

“This switch is similar to a dimmer and can be used to control the level of transparency on the window and therefore the intensity of lighting in a room,” Taha said. “This means users have total freedom to operate the smart windows on-demand.”

Windows aren’t the only clear winners when it comes to the new coating. The technology can also be used to control non-harmful radiation that can penetrate plastics and fabrics. This could be applied to medical imaging and security scans.

Bhaskaran said that the team was looking to roll the technology out as soon as possible.

“The materials and technology are readily scalable to large area surfaces, with the underlying technology filed as a patent in Australia and the US,” she said.

The research has been carried out at RMIT University’s state-of-the-art Micro Nano Research Facility with colleagues at the University of Adelaide and supported by the Australian Research Council.

How the coating works

The self-regulating coating is created using a material called vanadium dioxide. The coating is 50-150 nanometres in thickness.

At 67 degrees Celsius, vanadium dioxide transforms from being an insulator into a metal, allowing the coating to turn into a versatile optoelectronic material controlled by and sensitive to light.

The coating stays transparent and clear to the human eye but goes opaque to infra-red solar radiation, which humans cannot see and is what causes sun-induced heating.

Until now, it has been impossible to use vanadium dioxide on surfaces of various sizes because the placement of the coating requires the creation of specialised layers, or platforms.

The RMIT researchers have developed a way to create and deposit the ultra-thin coating without the need for these special platforms – meaning it can be directly applied to surfaces like glass windows.

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

Insulator–metal transition in substrate-independent VO2 thin film for phase-change device by Mohammad Taha, Sumeet Walia, Taimur Ahmed, Daniel Headland, Withawat Withayachumnankul, Sharath Sriram, & Madhu Bhaskaran. Scientific Reportsvolume 7, Article number: 17899 (2017) doi:10.1038/s41598-017-17937-3 Published online: 20 December 2017

This paper is open access.

For anyone interested in more ‘smart’ windows, you can try that search term or ‘electrochromic’, ‘photochromic’, and ‘thermochromic’ , as well.

Wacky oxide. biological synchronicity, and human brainlike computing

Research out of Pennsylvania State University (Penn State, US) has uncovered another approach  to creating artificial brains (more about the other approaches later in this post), from a May 14, 2014 news item on Science Daily,

Current computing is based on binary logic — zeroes and ones — also called Boolean computing. A new type of computing architecture that stores information in the frequencies and phases of periodic signals could work more like the human brain to do computing using a fraction of the energy of today’s computers.

A May 14, 2014 Pennsylvania State University news release, which originated the news item, describes the research in more detail,

Vanadium dioxide (VO2) is called a “wacky oxide” because it transitions from a conducting metal to an insulating semiconductor and vice versa with the addition of a small amount of heat or electrical current. A device created by electrical engineers at Penn State uses a thin film of VO2 on a titanium dioxide substrate to create an oscillating switch. Using a standard electrical engineering trick, Nikhil Shukla, a Ph.D. student in the group of Professor Suman Datta and co-advised by Professor Roman Engel-Herbert at Penn State, added a series resistor to the oxide device to stabilize their oscillations over billions of cycles. When Shukla added a second similar oscillating system, he discovered that over time the two devices would begin to oscillate in unison. This coupled system could provide the basis for non-Boolean computing. The results are reported in the May 14 [2014] online issue of Nature Publishing Group’s Scientific Reports.

“It’s called a small-world network,” explained Shukla. “You see it in lots of biological systems, such as certain species of fireflies. The males will flash randomly, but then for some unknown reason the flashes synchronize over time.” The brain is also a small-world network of closely clustered nodes that evolved for more efficient information processing.

“Biological synchronization is everywhere,” added Datta, professor of electrical engineering at Penn State and formerly a Principal Engineer in the Advanced Transistor and Nanotechnology Group at Intel Corporation. “We wanted to use it for a different kind of computing called associative processing, which is an analog rather than digital way to compute.” An array of oscillators can store patterns, for instance, the color of someone’s hair, their height and skin texture. If a second area of oscillators has the same pattern, they will begin to synchronize, and the degree of match can be read out. “They are doing this sort of thing already digitally, but it consumes tons of energy and lots of transistors,” Datta said. Datta is collaborating with co-author and Professor of Computer Science and Engineering, Vijay Narayanan, in exploring the use of these coupled oscillations in solving visual recognition problems more efficiently than existing embedded vision processors as part of a National Science Foundation Expedition in Computing program.

Shukla and Datta called on the expertise of Cornell University materials scientist Darrell Schlom to make the VO2 thin film, which has extremely high quality similar to single crystal silicon. Georgia Tech computer engineer Arijit Raychowdhury and graduate student Abhinav Parihar mathematically simulated the nonlinear dynamics of coupled phase transitions in the VO2 devices. Parihar created a short video* simulation of the transitions, which occur at a rate close to a million times per second, to show the way the oscillations synchronize. Penn State professor of materials science and engineering Venkatraman Gopalan used the Advanced Photon Source at Argonne National laboratory to visually characterize the structural changes occurring in the oxide thin film in the midst of the oscillations.

Datta believes it will take seven to ten years to scale up from their current network of two-three coupled oscillators to the 100 million or so closely packed oscillators required to make a neuromorphic computer chip. One of the benefits of the novel device is that it will use only about one percent of the energy of digital computing, allowing for new ways to design computers. Much work remains to determine if VO2 can be integrated into current silicon wafer technology. “It’s a fundamental building block for a different computing paradigm that is analog rather than digital,” Shukla concluded.

There are two papers being published about this work,

Synchronizing a single-electron shuttle to an external drive by Michael J Moeckel, Darren R Southworth, Eva M Weig, and Florian Marquardt. New J. Phys. 16 043009 doi:10.1088/1367-2630/16/4/043009

Synchronized charge oscillations in correlated electron systems by Nikhil Shukla, Abhinav Parihar, Eugene Freeman, Hanjong Paik, Greg Stone, Vijaykrishnan Narayanan, Haidan Wen, Zhonghou Cai, Venkatraman Gopalan, Roman Engel-Herbert, Darrell G. Schlom, Arijit Raychowdhury & Suman Datta. Scientific Reports 4, Article number: 4964 doi:10.1038/srep04964 Published 14 May 2014

Both articles are open access.

Finally, the researchers have provided a video animation illustrating their vanadium dioxide switches in action,

As noted earlier, there are other approaches to creating an artificial brain, i.e., neuromorphic engineering. My April 7, 2014 posting is the most recent synopsis posted here; it includes excerpts from a Nanowerk Spotlight article overview along with a mention of the ‘brain jelly’ approach and a discussion of my somewhat extensive coverage of memristors and a mention of work on nanoionic devices. There is also a published roadmap to neuromorphic engineering featuring both analog and digital devices, mentioned in my April 18, 2014 posting.

Chameleon materials

Harvard’s School of Engineering and Applied Sciences researchers discovered some unexpected properties when testing a new coating according to an Oct. 22, 2013 news item on Azonano,

Active camouflage has taken a step forward at the Harvard School of Engineering and Applied Sciences (SEAS), with a new coating that intrinsically conceals its own temperature to thermal cameras.

In a laboratory test, a team of applied physicists placed the device on a hot plate and watched it through an infrared camera as the temperature rose. Initially, it behaved as expected, giving off more infrared light as the sample was heated: at 60 degrees Celsius it appeared blue-green to the camera; by 70 degrees it was red and yellow. At 74 degrees it turned a deep red—and then something strange happened. The thermal radiation plummeted. At 80 degrees it looked blue, as if it could be 60 degrees, and at 85 it looked even colder. Moreover, the effect was reversible and repeatable, many times over.

The Oct. 21, 2013 Harvard University news release (also on EurekAlert), which originated the news item, discusses the potential for this discovery and describes the process of discovery in more detail (Note: A link has been removed),

Principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS, predicts that with only small adjustments the coating could be used as a new type of thermal camouflage or as a kind of encrypted beacon to allow soldiers to covertly communicate their locations in the field.

The secret to the technology lies within a very thin film of vanadium oxide, an unusual material that undergoes dramatic electronic changes when it reaches a particular temperature. At room temperature, for example, pure vanadium oxide is electrically insulating, but at slightly higher temperatures it transitions to a metallic, electrically conductive state. During that transition, the optical properties change, too, which means special temperature-dependent effects—like infrared camouflage—can also be achieved.

The insulator-metal transition has been recognized in vanadium oxide since 1959. However, it is a difficult material to work with: in bulk crystals, the stress of the transition often causes cracks to develop and can shatter the sample. Recent advances in materials synthesis and characterization—especially those by coauthor Shriram Ramanathan, Associate Professor of Materials Science at Harvard SEAS—have allowed the creation of extremely pure samples of thin-film vanadium oxide, enabling a burst of new science and engineering to take off in just the last few years.

“Thanks to these very stable samples that we’re getting from Prof. Ramanathan’s lab, we now know that if we introduce small changes to the material, we can dramatically change the optical phenomena we observe,” explains lead author Mikhail Kats, a graduate student in Capasso’s group at Harvard SEAS. “By introducing impurities or defects in a controlled way via processes known as doping, modifying, or straining the material, it is possible to create a wide range of interesting, important, and predictable behaviors.”

By doping vanadium oxide with tungsten, for example, the transition temperature can be brought down to room temperature, and the range of temperatures over which the strange thermal radiation effect occurs can be widened. Tailoring the material properties like this, with specific outcomes in mind, may enable engineering to advance in new directions.

The researchers say a vehicle coated in vanadium oxide tiles could potentially mimic its environment like a chameleon, appearing invisible to an infrared camera with only very slight adjustments to the tiles’ actual temperature—a far more efficient system than the approaches in use today.

Tuned differently, the material could become a component of a secret beacon, displaying a particular thermal signature on cue to an infrared surveillance camera. Capasso’s team suggests that the material could be engineered to operate at specific wavelengths, enabling simultaneous use by many individually identifiable soldiers.

And, because thermal radiation carries heat, the researchers believe a similar effect could be employed to deliberately speed up or slow down the cooling of structures ranging from houses to satellites.

The Harvard team’s most significant contribution is the discovery that nanoscale structures that appear naturally in the transition region of vanadium oxide can be used to provide a special level of tunability, which can be used to suppress thermal radiation as the temperature rises. The researchers refer to such a spontaneously structured material as a “natural, disordered metamaterial.”

“To artificially create such a useful three-dimensional structure within a material is extremely difficult,” says Capasso. “Here, nature is giving us what we want for free. By taking these natural metamaterials and manipulating them to have all the properties we want, we are opening up a new area of research, a completely new direction of work. We can engineer new devices from the bottom up.”

Here’s an image, from the scientists, illustrating the material’s thermal camouflage (or chameleon) properties,

A new coating intrinsically conceals its own temperature to thermal cameras. (Image courtesy of Mikhail Kats.)

A new coating intrinsically conceals its own temperature to thermal cameras. (Image courtesy of Mikhail Kats.)

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

Vanadium Dioxide as a Natural Disordered Metamaterial: Perfect Thermal Emission and Large Broadband Negative Differential Thermal Emittance by Mikhail A. Kats, Romain Blanchard, Shuyan Zhang, Patrice Genevet, Changhyun Ko, Shriram Ramanathan, and Federico Capasso. Phys. Rev. X » Volume 3 » Issue 4  or Phys. Rev. X 3, 041004 (2013) DOI:10.1103/PhysRevX.3.041004

This paper is published in an open access journal according to the Harvard news release,

About Physical Review X

Launched in August 2011, PRX (http://prx.aps.org) is an open-access, peer-reviewed publication of the American Physical Society (www.aps.org), a non-profit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy and international activities. APS represents 50,000 members, including physicists in academia, national laboratories and industry in the United States and throughout the world.