Toronto’s QD (Quantum Dot) Solar sole Canadian among five winners of solar technology challenge


QD Solar untitledFive North American solar start-up companies have been selected to receive further support in developing their technology and moving them closer to market under the SunRISE TechBridge Challenge, which had 56 team entries.

Of the five winners, one is Canadian colloidal quantum dot cell developerQD Solar, which will gain support from Greentown Launch acceleration and DSM Partnership/Investment, as well as desk and lab space at Greentown Labs in Somerville, MA, and networking and coaching to accelerate their business and networking in the cleantech community in the Greater Boston area.

QD Solar uses low-cost, nano-engineered particles to produce solar cells that can capture wasted infrared light, resulting in a 20% increase in efficiency over conventional solar panels, based on research conducted at the Nanomaterials for Energy Laboratory in the University of Toronto’s Department of Electrical and Computer Engineering.

The SunRISE TechBridge Challenge challenged companies to present innovative solutions and new materials that will lower the levelized cost of energy (LCOE) for photovoltaic (PV) systems, including novel materials for existing and emerging high performance PV modules, technologies enabling non-traditional solar deployment, and business models that integrate solar PV with energy storage.

QD Solar started life at the University of Toronto and MaRS Innovation, and in March received $2.55 million from Sustainable Development Technology Canada (SDTC).

QDSolar

Conventional solar panels waste a large portion of available sun energy because their silicon solar cells can’t capture infrared light energy, a problem that QD Solar set out to solve with their proprietary quantum dot-based solar cells using nano-engineered, low-cost materials that can absorb infrared light.

QD Solar CEO Dan Shea is a former executive with Celestica and Blackberry.

In 2009, co-founder Edward Sargent and his team at the University of Toronto received a grant from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia to advance their research into colloidal quantum dots for solar power applications.

The SunRISE TechBridge Challenge was organized by Fraunhofer TechBridge and the SunRISE Partners, which include Royal DSM and Greentown Labs.

The Fraunhofer TechBridge Challenge is an offering of the Fraunhofer Center for Sustainable Energy Systems (CSE), which organizes several industry-sponsored annual challenges to accelerate promising technologies through targeted industry-driven validation projects, including the SunRISE Challenge, Advanced Industrial Surfaces, the Microgrid Challenge, and the Innovation Ecosystem Program.

Fraunhofer Gesellschaft is a German applied R&D organization which has 66 institutes and independent research units throughout Germany and 80 institutes and centers around the world.

Nicola Bettio, a member of QD Solar’s Board of Directors, manages the KAUST Innovation Fund and anticipates the establishment of the company’s presence in a significant development facility in KAUST’s Research & Technology Park in the near future.

KAUST University: Partnering for sustainable fresh water production: Video


cropped-microbots-water.jpg

Published online Jun 7, 2016

Combining methods for water desalination results in low-cost, highly efficient water production.

Innovative solutions to improve the efficiency of water desalination are a major focus in countries such as Saudi Arabia, where fresh water for industrial, agricultural and human use is scarce. A research partnership between KAUST and the National University of Singapore has won global acclaim for its unique and efficient yet low-cost method of conducting desalination called hybrid multi-effect adsorption desalination.

In a world of dwindling freshwater supply, how can we meet the demands of a growing population? This video explains a new hybrid process which can double the freshwater output of traditional thermally-driven desalination without requiring additional energy. Developed by the King Abdullah University of Science and Technology (KAUST) and the National University of Singapore (NUS), this desalination method is now being piloted for wider implementation by MEDAD, a KAUST-supported startup company. For more information on the new hybrid technology.

Video explains the hybrid process of adsorption desalination using animations.

© 2016 KAUST

The collaboration has resulted in two desalination pilot schemes—one at KAUST itself and the other at a second location also in Saudi Arabia—as well as a spin-off company called MEDAD that will help to commercialize the hybrid desalination technology. The project is led by Kim Choon Ng from the University’s Water Desalination and Reuse Center. Ng has devoted his career to finding ways of reducing the cost of desalination through novel technologies.

Traditional desalination techniques use membranes and pressure to separate salt and other minerals from seawater, but these techniques are expensive, energy intensive and inefficient.

“Desalination is particularly complicated in the challenging environment of the Gulf, where high salinity, silt levels and increased water temperatures make working with the seawater quite difficult,” Ng said. “The frequent occurrence of hazardous algal blooms has also contributed to high pre-treatment costs and severe fouling of membranes. These elements combine to considerably increase the overall unit cost of producing desalinated water.”

Ng and his team recognized that the only viable option to overcome these challenges was to base their system on thermal desalination rather than membrane-based techniques.

They investigated a combined technique and utilized an existing industrially-proven method called multi-effect distillation (MED). This involves spraying saline water over the outer surfaces of a series of tubes (or stages) arranged in a tower. At the top of the tower, saline water is fed in and heated by a steam-driven compressor. The resulting water vapor is collected while the salt is left behind. This process is repeated over subsequent stages, and the vapor from each stage is channeled through the tubes to the bottom of the tower, where it condenses to generate fresh water as it cools.

Ng’s team combined MED with a thermally-driven process called adsorption desalination (AD), which uses low-cost silica gel adsorbents with a very high affinity for water vapor. The researchers adapted the last stage of MED so that the vapor uptake is carried out by AD.

The water vapor is attracted to designated adsorption gel beds while the remaining gel beds undergo desorption, removing the water and preparing the silica gel for the next round. Crucially, there are no major moving parts in the AD cycle, meaning it uses far less energy than some other techniques, and it can run on waste heat from other industrial processes.

“The best part about AD is that it can be run at low temperatures and low pressures,” explained Ng. “In fact, we can run cycles at only 7°C and at a pressure of 2 kPa. This presents a unique opportunity to exploit the renewable energy resources that the Kingdom has—namely solar and geothermal energy—to run the system. Also, because we are producing cooling as part of the process, we can link into air-conditioning systems.”

Simulations on the hybrid MEDAD system indicate that it could double or even triple desalinated water production. Experiments conducted at the pilot plant at KAUST have already increased fresh water production by more than 50 percent. This represents the highest water production ever reported for a desalination technique and earned the team a GE-Aramco “Global Innovation Challenge” award in January 2015. The breakthrough also helps extend the lower end of the temperature range at which the system can operate, which has been a major limitation with MED in the past.

“This represents a major leap forward in water production using thermally-driven cycles, and it is attributed to the excellent thermodynamic synergy between MED and AD cycles,” noted Ng. “We believe it can be developed fully to an extent where the energy efficiency of desalination can meet the target needed for sustainability.”

————–

The technology has been licensed by the NUS Industry Liasion Office, part of the NUS Enterprise, and the University’s Innovation and Economic Development Office, to MEDAD.

 

Kim Choon Ng and Muhammad Wakil inspect the MEDAD hybrid desalination pilot at KAUST.

Kim Choon Ng and Muhammad Wakil inspect the MEDAD hybrid desalination pilot at KAUST.

© 2015 KAUST

Kim Choon Ng (left) explains the hybrid cycle to visitors at KAUST, including Ahmad Khowaiter from Saudi Aramco (center), Dr. Abdulrahman from the Saline Water Conversion Commission (SWCC) (right) and Dr. Ahmed Al Arifi from SWCC (far right).

Kim Choon Ng (left) explains the hybrid cycle to visitors at KAUST, including Ahmad Khowaiter from Saudi Aramco (center), Dr. Abdulrahman from the Saline Water Conversion Commission (SWCC) (right) and Dr. Ahmed Al Arifi from SWCC (far right).

© 2015 KAUST

 

Development of safe and durable high-temperature lithium-sulfur batteries: U of Western Ontario, Canada



Scheme of MLD alucone coated C-S electrode and cycle performance of stabilized high temperature Li-S batteries. (click on image to enlarge)

Posted: Jun 22, 2016

Safety has always been a major concern for electric vehicles, especially preventing fire and explosion incidents with the best possible battery technologies.

Lithium-sulfur batteries are considered as the most promising candidate for EVs due to their ultra-high energy density, which is over 5 times the capacity of standard commercial Li-ion batteries. This high density makes it possible for electric vehicles to travel longer distances without stopping for a charge.

However, batteries operating at the high temperatures necessary in electric vehicles presents a safety challenge, as fire and other incidents become more likely.

Prof. Andy Xueliang Sun and his University of Western Ontario research team, in collaboration with Dr. Yongfeng Hu and Dr. Qunfeng Xiao from the Canadian Light Source, have developed safe and durable high-temperature Li-S batteries using by a new coating technique called molecular layer deposition (MLD) technology for the first time. This research has been published in Nano Letters (“Safe and Durable High-Temperature Lithium–Sulfur Batteries via Molecular Layer Deposited Coating”).

TOC EV Battery diagram

Scheme of MLD alucone coated C-S electrode and cycle performance of stabilized high temperature Li-S batteries. (click on image to enlarge)

“Close collaboration with CLS to obtain such detailed information is very important to our understanding,” said Dr. Sun. “We need not only to design novel materials for energy storage, but also deep understanding on the science behind materials.”

“We demonstrated that MLD alucone coating offers a safe and versatile approach toward lithium-sulfer batteries at elevated temperature,” said Dr. Sun.

MLD is an ultrathin-film technique with applications in energy storage systems, providing precise and flexible control over film thickness and chemical composition of the target material at a molecular scale.

The MLD alucone coated carbon-sulfur electrodes demonstrated very stable and improved performance at temperatures as high as 55oC, which will significantly prolong battery life for high-temperature Li-S batteries.

X-ray studies at the CLS revealed the specific mechanism and interaction between sulfur and alucone MLD coating.

“By using synchrotron-based high energy X-ray photoelectron spectroscopy (HEXPS), it demonstrated the coating ends up hindering unwanted side reactions,” said Dr. Hu. This is achieved as the coating passivating the surface of the electrode.

Next up, the team will focus on the safe lithium sulfur batteries with synchrotron X-ray in-situ battery study in future.

Source: Canadian Light Source

Ultra-thin solar cells can easily bend around a pencil


Scientists in South Korea have made ultra-thin photovoltaics flexible enough to wrap around the average pencil. The bendy solar cells could power wearable electronics like fitness trackers and smart glasses. The researchers report the results in the journal Applied Physics Letters (“Ultra-thin Flexible GaAs Photovoltaics in Vertical Forms Printed on Metal Surfaces without Interlayer Adhesives”).

 

Bend solar Cells id43736Ultra-thin solar cells are flexible enough to bend around small objects, such as the 1mm-thick edge of a glass slide, as shown here. (Image: Juho Kim, et al/ APL)

 

Thin materials flex more easily than thick ones – think a piece of paper versus a cardboard shipping box. The reason for the difference: The stress in a material while it’s being bent increases farther out from the central plane. Because thick sheets have more material farther out they are harder to bend.

“Our photovoltaic is about 1 micrometer thick,” said Jongho Lee, an engineer at the Gwangju Institute of Science and Technology in South Korea. One micrometer is much thinner than an average human hair. Standard photovoltaics are usually hundreds of times thicker, and even most other thin photovoltaics are 2 to 4 times thicker.
The researchers made the ultra-thin solar cells from the semiconductor gallium arsenide. They stamped the cells directly onto a flexible substrate without using an adhesive that would add to the material’s thickness. The cells were then “cold welded” to the electrode on the substrate by applying pressure at 170 degrees Celcius and melting a top layer of material called photoresist that acted as a temporary adhesive. The photoresist was later peeled away, leaving the direct metal to metal bond.
The metal bottom layer also served as a reflector to direct stray photons back to the solar cells. The researchers tested the efficiency of the device at converting sunlight to electricity and found that it was comparable to similar thicker photovoltaics. They performed bending tests and found the cells could wrap around a radius as small as 1.4 millimeters.
The team also performed numerical analysis of the cells, finding that they experience one-fourth the amount of strain of similar cells that are 3.5 micrometers thick.
“The thinner cells are less fragile under bending, but perform similarly or even slightly better,” Lee said.
A few other groups have reported solar cells with thicknesses of around 1 micrometer, but have produced the cells in different ways, for example by removing the whole substract by etching.
By transfer printing instead of etching, the new method developed by Lee and his colleagues may be used to make very flexible photovoltaics with a smaller amount of materials.
The thin cells can be integrated onto glasses frames or fabric and might power the next wave of wearable electronics, Lee said.
Source: American Institute of Physics

 

Nanotechnology Education for the Global World: Training the Leaders of Tomorrow


Nano Education 062116 nn-2016-03872b_0004

Nanoscience is one of the fastest growing and most impactful fields in global scientific research. In order to support the continued development of nanoscience and nanotechnology, it is important that nanoscience education be a top priority to accelerate research excellence. In this Nano Focus, we discuss current approaches to nanoscience training and propose a learning design framework to promote the next generation of nanoscientists. Prominent among these are the abilities to communicate and to work across and between conventional disciplines. While the United States has played leading roles in initiating these developments, the global landscape of nanoscience calls for worldwide attention to this educational need. Recent developments in emerging nanoscience nations are also discussed. Photo credit: Jae Hyeon Park.

Education has long been recognized as an important factor for growing the fields of nanoscience and nanotechnology and solidifying and expanding their roles in the global economy. In many countries, there is growing interest in developing educational programs across the full spectrum of educational levels from K-12 to postgraduate studies.

Various formal and informal educational practices are being designed and tested that promote general awareness of nanoscience and nanotechnology as well as provide advanced learning and skills development, including through group learning and peer assessment”In their article, the authors discuss innovative learning models that are being applied at the undergraduate level in order to train future leaders at the interface of engineering and management.

students running nanoscience experiments

Middle and high school students spend time at the California NanoSystems Institute at UCLA running nanoscience experiments. High school teachers from over 100 schools and 30 school districts are trained, networked to one another, and supplied with kits for their classrooms. Graduate students, postdocs, faculty, and staff run, expand, and improve these fully subscribed outreach events on a continuous basis. (© American Chemical Society)

While thee programs are not strictly focused on nanotechnology, many graduates pursue nanotechnology-focused careers and they provide examples of important factors that should be considered in the nanotechnology field.Moreover, they represent the growing trend of holistic learning, which integrates coursework across disciplines, promotes foreign experiences, and encourages industrial internships.

Here is the set of recommendations they make:

Inspire Students To Envision What Is or Could Be Possible

Possibilities include a greater focus on nanotechnology applications in courses or hands-on laboratory experiences that tie in with class concepts. Even before reaching the classroom, students should have positive views of nanoscience and the potential it holds. Successful learning practices start with capturing the imagination of students. Communicating the remarkable features of nanoscience in a simple and clear way to the mainstream public would go a long way toward achieving this goal.

Promote Role Models Who Impact Society

From an educational perspective, the tech world is a particularly good example because successful entrepreneurs such as Steve Jobs, Elon Musk, Sheryl Sandberg, and Mark Zuckerberg have captured the public audience and inspired countless students to think beyond the classroom. In nanotechnology, similar role models can inspire students with the many opportunities available in the field.

Encourage Global Collaboration

Nanotechnology research and development is truly global. Early exposure to these trends will better inform students about career opportunities and give them ideas about how to work together in teams across disciplines and cultures. A growing number of partnerships already provide international experiences for nanoscience and nanotechnology students.

Support Early Exposure Inside and Outside of the Laboratory

For many students, nanoscience and nanotechnology are about working in a lab doing scientific research. While this activity is common, its generalization could not be farther from the truth. There are many possible ways to get involved in nanotechnology, from instructional education and hands-on training to entrepreneurship and manufacturing.Holistic approaches that integrate these different possibilities, while providing targeted career development, would greatly benefit students and the overall goals of nanotechnology education. Developing a strong workforce infrastructure for nanotechnology

Communication Across Fields

Stressing the importance of communication, the authors conclude:

“Finally, one of the great strengths of the nanoscience and nanotechnology communities is that we have taught each other how to communicate across fields, to look at and to leverage each other’s approaches, and to address the key issues of a multitude of fields.

As a field, we are increasingly viewed as problem solvers in science and technology, developing new tools, materials, methods, and opportunities. Bringing this aspect of our field to students (and scientists and engineers at all levels) will have significant impact on the world around us and our ability to make it better.”

By Michael Berger. © Nanowerk

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Transparent, flexible supercapacitors pave the way for a multitude of applications


transparentf Super CapacitorsThe transparent, flexible supercapacitor prototype, based on single-walled carbon nanotube thin films, is shown during charging and discharging. Credit: Kanninen et al. ©2016 IOP Publishing

The standard appearance of today’s electronic devices as solid, black objects could one day change completely as researchers make electronic components that are transparent and flexible. Working toward this goal, researchers in a new study have developed transparent, flexible supercapacitors made of carbon nanotube films. The high-performance devices could one day be used to store energy for everything from wearable electronics to photovoltaics.

The researchers, Kanninen et al., from institutions in Finland and Russia, have published a paper on the new supercapacitors in a recent issue of Nanotechnology.

In general, supercapacitors can store several times more charge in a given volume or mass than traditional capacitors, have faster charge and discharge rates, and are very stable. Over the past few years, researchers have begun working on making supercapacitors that are transparent and flexible due to their potential use in a wide variety of applications.

“Potential applications can be roughly divided into two categories: high-aesthetic-value products, such as activity bands and smart clothes, and inherently transparent end-uses, such as displays and windows,” coauthor Tanja Kallio, an associate professor at Aalto University who is currently a visiting professor at the Skolkovo Institute of Science and Technology, told Phys.org. “The latter include, for example, such future applications as smart windows for automobiles and aerospace vehicles, self-powered rolled-up displays, self-powered wearable optoelectronics, and electronic skin.”

The type of supercapacitor developed here, called an electrochemical double-layer capacitor, is based on high-surface-area carbon. One prime candidate for this material is single-walled carbon nanotubes due to their combination of many appealing properties, including a , high strength, high elasticity, and the ability to withstand extremely high currents, which is essential for fast charging and discharging.

The problem so far, however, has been that the carbon nanotubes must be prepared as in order to be used as electrodes in supercapacitors. Current techniques for preparing thin films have drawbacks, often resulting in defected nanotubes, limited conductivity, and other performance limitations.

In the new study, the researchers demonstrated a new method to fabricate thin films made of single-walled carbon nanotubes using a one-step aerosol synthesis method. When incorporated into a supercapacitor, the thin films exhibit the highest transparency to date (92%), the highest mass specific capacitance (178 F/g), and one of the highest area specific capacitances (552 µF/cm2) compared to other carbon-based, flexible, transparent supercapacitors. The films also have a high stability, as demonstrated by the fact that their capacitance does not degrade after 10,000 charging cycles.

With these advantages, the new device illustrates the continued improvement in the development of transparent, flexible supercapacitors. In the future, the researchers plan to further improve the energy density, flexibility, and durability, and also make the supercapacitors stretchable.

“One more important characteristic to be realized and urgently expected in future electronics is the stretchability of the conductive materials and assembled electronic components,” said coauthor Albert Nasibulin, a professor at the Skolkovo Institute of Science and Technology and an adjunct professor at Aalto University. “Together with Tanja, we are currently working on a new type of stretchable and transparent single-walled carbon nanotube supercapacitor. We are confident that one can create prototypes based on carbon nanotubes that might withstand 100% elongation with no performance degradation.”

Explore further: Researchers develop stretchable wire-shaped supercapacitor

More information: Kanninen et al. “Transparent and flexible high-performance supercapacitors based on single-walled carbon nanotube films.” Nanotechnology. DOI: 10.1088/0957-4484/27/23/235403

 

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New nanoparticle technology developed to treat aggressive thyroid cancer


Thyroid Cancer NanoP 5-newnanoparti
Immunofluorescence images of cells (nuclei shown in blue; actin shown in green; BRAF shown in red). Left: control; right: after treatment with nanoparticles that silence BRAF. Credit: Jinjun Shi, Brigham and Women’s Hospital

Anaplastic thyroid cancer (ATC), the most aggressive form of thyroid cancer, has a mortality rate of nearly 100 percent and a median survival time of three to five months. One promising strategy for the treatment of these solid tumors and others is RNA interference (RNAi) nanotechnology, but delivering RNAi agents to the sites of tumors has proved challenging. Investigators at Brigham and Women’s Hospital, together with collaborators from Massachusetts General Hospital, have developed an innovative nanoplatform that allows them to effectively deliver RNAi agents to the sites of cancer and suppress tumor growth and reduce metastasis in preclinical models of ATC. Their results appear this week in Proceedings of the National Academy of Sciences.

“We call this a ‘theranostic’ platform because it brings a therapy and a diagnostic together in one functional nanoparticle,” said co-senior author Jinjun Shi, PhD, assistant professor of Anesthesia in the Anesthesia Department. “We expect this study to pave the way for the development of theranostic platforms for image-guided RNAi delivery to advanced cancers.”

RNAi, the discovery of which won the Nobel Prize in Physiology or Medicine 10 years ago, allows researchers to silence mutated genes, including those upon which cancers depend to grow and survive and metastasize. Many ATCs depend upon mutations in the commonly mutated cancer gene BRAF. By delivering RNAi agents that specifically target and silence this mutated gene, the investigators hoped to stop both the growth and the spread of ATC, which often metastasizes to the lungs and other organs.

When RNAi is delivered on its own, it is usually broken down by enzymes or filtered out by the kidneys before it reaches tumor cells. Even when RNAi agents make it as far as the tumor, they are often unable to penetrate or are rejected by the cancer cells. To overcome these barriers, the investigators used nanoparticles to deliver the RNAi molecules to ATC tumors. In addition, they coupled the nanoparticles with a near-infrared fluorescent polymer, which allowed them to see where the nanoparticles accumulated in a mouse model of ATC.

By measuring the glow from the near-infrared fluorescent polymer, the team verified that nanoparticles had reached the primary site of ATC in the thyroid. The team found that the nanoparticles circulated for long periods of time in the blood stream and accumulated at high concentrations in the tumors.

In addition, the team reports evidence that BRAF had been successfully silenced at these sites. They found that, for cells grown in a dish and treated with the nanoparticles containing RNAi agents, cell growth was drastically slowed and the number of cancer cells that were able to migrate decreased by as much as 15-fold. In mouse models, tumor growth was also slowed and fewer metastases formed.

In order to translate the new platform into clinical applications, the research team notes the importance of having an imaging diagnostic that will allow them to quickly assess which patients most likely to benefit from RNAi nanotherapeutics.

“Most patients who present to surgeons with anaplastic are out of options and this new research gives these patients some options. Having an approach that allows us to rapidly visualize and simultaneously deliver a targeted therapy could be critical for the efficient treatment of this disease and other lethal cancers with a poor prognosis,” said co-senior author, Sareh Parangi, MD, associate professor in the MGH Department of Surgery.

Explore further: Chemistry trick may herald transformational next-generation RNAi therapeutics aimed at cancer, viral infections

More information: Theranostic near-infrared fluorescent nanoplatform for imaging and systemic siRNA delivery to metastatic anaplastic thyroid cancer, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1605841113

 

MIT: Researchers discover new way to turn electricity into light, using graphene: Could Make Chips “A Million Times Faster”


  • MIT-Glowing-Graph-1This illustration depicts the process of light emission from a sheet of graphene, which is represented as the blue lattice on the top surface of a carrier material. The light-colored arrow moving upwards at the center depicts a fast-moving electron. Because the electron is moving faster than light itself, it generates a shock wave, which spews out plasmons, shown as red squiggly lines, in two directions.

    By slowing down light to a speed slower than flowing electrons, researchers create a kind of optical “sonic boom.”

    When an airplane begins to move faster than the speed of sound, it creates a shockwave that produces a well-known “boom” of sound. Now, researchers at MIT and elsewhere have discovered a similar process in a sheet of graphene, in which a flow of electric current can, under certain circumstances, exceed the speed of slowed-down light and produce a kind of optical “boom”: an intense, focused beam of light.

    This entirely new way of converting electricity into visible radiation is highly controllable, fast, and efficient, the researchers say, and could lead to a wide variety of new applications. The work is reported today in the journalNature Communications, in a paper by two MIT professors — Marin Soljačić, professor of physics; and John Joannopoulos, the Francis Wright Davis Professor of physics — as well as postdoc Ido Kaminer, and six others in Israel, Croatia, and Singapore.

    The new finding started from an intriguing observation. The researchers found that when light strikes a sheet of graphene, which is a two-dimensional form of the element carbon, it can slow down by a factor of a few hundred. That dramatic slowdown, they noticed, presented an interesting coincidence. The reduced speed of photons (particles of light) moving through the sheet of graphene happened to be very close to the speed of electrons as they moved through the same material.

    “Graphene has this ability to trap light, in modes we call surface plasmons,” explains Kaminer, who is the paper’s lead author. Plasmons are a kind of virtual particle that represents the oscillations of electrons on the surface. The speed of these plasmons through the graphene is “a few hundred times slower than light in free space,” he says.

    This effect dovetailed with another of graphene’s exceptional characteristics: Electrons pass through it at very high speeds, up to a million meters per second, or about 1/300 the speed of light in a vacuum. That meant that the two speeds were similar enough that significant interactions might occur between the two kinds of particles, if the material could be tuned to get the velocities to match.

    That combination of properties — slowing down light and allowing electrons to move very fast — is “one of the unusual properties of graphene,” says Soljačić. That suggested the possibility of using graphene to produce the opposite effect: to produce light instead of trapping it. “Our theoretical work shows that this can lead to a new way of generating light,” he says.

    Specifically, he explains, “This conversion is made possible because the electronic speed can approach the light speed in graphene, breaking the ‘light barrier.’” Just as breaking the sound barrier generates a shockwave of sound, he says, “In the case of graphene, this leads to the emission of a shockwave of light, trapped in two dimensions.”

    The phenomenon the team has harnessed is called the Čerenkov effect, first described 80 years ago by Soviet physicist Pavel Čerenkov. Usually associated with astronomical phenomenon and harnessed as a way of detecting ultrafast cosmic particles as they hurtle through the universe, and also to detect particles resulting from high-energy collisions in particle accelerators, the effect had not been considered relevant to Earthbound technology because it only works when objects are moving close to the speed of light. But the slowing of light inside a graphene sheet provided the opportunity to harness this effect in a practical form, the researchers say.

    There are many different ways of converting electricity into light — from the heated tungsten filaments that Thomas Edison perfected more than a century ago, to fluorescent tubes, to the light-emitting diodes (LEDs) that power many display screens and are gaining favor for household lighting. But this new plasmon-based approach might eventually be part of more efficient, more compact, faster, and more tunable alternatives for certain applications, the researchers say.

    Perhaps most significantly, this is a way of efficiently and controllably generating plasmons on a scale that is compatible with current microchip technology. Such graphene-based systems could potentially be key on-chip components for the creation of new, light-based circuits, which are considered a major new direction in the evolution of computing technology toward ever-smaller and more efficient devices.

    “If you want to do all sorts of signal processing problems on a chip, you want to have a very fast signal, and also to be able to work on very small scales,” Kaminer says. Computer chips have already reduced the scale of electronics to the points that the technology is bumping into some fundamental physical limits, so “you need to go into a different regime of electromagnetism,” he says.

    Using light instead of flowing electrons as the basis for moving and storing data has the potential to push the operating speeds “six orders of magnitude higher than what is used in electronics,” Kaminer says — in other words, in principle up to a million times faster.

    One problem faced by researchers trying to develop optically based chips, he says, is that while electricity can be easily confined within wires, light tends to spread out. Inside a layer of graphene, however, under the right conditions, the beams are very well confined.

    “There’s a lot of excitement about graphene,” says Soljačić, “because it could be easily integrated with other electronics” enabling its potential use as an on-chip light source. So far, the work is theoretical, he says, so the next step will be to create working versions of the system to prove the concept. “I have confidence that it should be doable within one to two years,” he says. The next step would then be to optimize the system for the greatest efficiency.

    This finding “is a truly innovative concept that has the potential to be the key toward solving the long-standing problem of achieving highly efficient and ultrafast electrical-to-optical signal conversion at the nanoscale,” says Jorge Bravo-Abad, an assistant professor at the Autonomous University of Madrid, in Spain, who was not involved in this work.

    In addition, Bravo-Abad says, “the novel instance of Čerenkov emission discovered by the authors of this work opens up whole new prospects for the study of the Čerenkov effect in nanoscale systems, without the need of sophisticated experimental set-ups. I look forward to seeing the significant impact and implications that these findings will surely have at the interface between physics and nanotechnology.”

    The research was supported by the U.S. Army Research Laboratory and the U.S. Army Research Office, through the Institute for Soldier Nanotechnologies at MIT. The team included researchers Yichen Shen, Ognjen Ilic, and Josue Lopez at MIT; Yaniv Katan at Technion, in Haifa, Israel; Hrvoje Buljan at the University of Zagreb in Croatia; and Liang Jie Wong at the Singapore Institute of Manufacturing Technology.

World’s most efficient nanowire lasers: Benefit to Fiber Optics Communications


Perovskite Nano wires 160616141636_1_540x360
Perovskite-based nanowire lasers are the most efficient known. A topological image of a nanowire is shown (left insert). Room temperature emission images above the lasing threshold for two nanowires composed of different halides, iodide (red in center) and bromide (green on the right), are shown in top inserts.
Credit: Image courtesy of Xiaoyang Zhu, Columbia University

Known for their low cost, simple processing and high efficiency, perovskites are popular materials in solar panel research. Now, researchers demonstrated that nanowires made from lead halide perovskite are the most efficient nanowire lasers known.

Efficient nanowire lasers could benefit fiber optic communications, pollution characterization, and other applications. The challenge is getting the right material. These ultra-compact wires have a superior ability to emit light, can be tuned to emit different colors, and are relatively easy to synthesize. The development of these perovskite wires parallels the rapid development of the same materials for efficient solar cells.

Semiconductor nanowire lasers, due to their ultra-compact physical sizes, highly localized coherent output, and efficiency, are promising components for use in fully integrated nanoscale photonic and optoelectronic devices. Lasing requires a minimum (threshold) excitation density, below which little light is emitted.

A high “lasing threshold” not only makes critical technical advances difficult, but also imposes fundamental limits on laser performance due to the onset of other losses. In searching for an ideal material for nanowire lasing, researchers at Columbia University and the University of Wisconsin-Madison investigated a new class of hybrid organic-inorganic semiconductors, methyl ammonium lead halide perovskites (CH3NH3PbX3), which is emerging as a leading material for high-efficiency photovoltaic solar cells due to low cost, simple processing and high efficiencies.

The exceptional solar cell performance in these materials can be attributed to the long lifetimes of the carriers that move energy through the systems (electrons and holes) and carrier diffusion lengths.

These properties, along with other attributes such as high fluorescence yield and wavelength tunability, also make them ideal for lasing applications. Room temperature lasing in these nanowires was demonstrated with:

  • The lowest lasing thresholds and the highest quality factors reported to date
  • Near 100% quantum yield (ratio of the number of photons emitted to those absorbed)
  • Broad tunability of emissions covering the near infrared to visible wavelength region.

Specifically, the laser emission shifts from near infrared to blue with decreasing atomic number of the halides (X=I, Br, Cl) in the nanowires. These nanowires could advance applications in nanophotonics and optoelectronic devices. In particular, lasers that operate in the near infrared region could benefit fiber optic communications and advance pollution characterization from space.

This work was supported by the DOE Office of Science (Office of Basic Energy Sciences) and the National Science Foundation.


Story Source:

The above post is reprinted from materials provided byDepartment of Energy, Office of Science. Note: Materials may be edited for content and length.


Journal Reference:

  1. Haiming Zhu, Yongping Fu, Fei Meng, Xiaoxi Wu, Zizhou Gong, Qi Ding, Martin V. Gustafsson, M. Tuan Trinh, Song Jin, X-Y. Zhu. Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors. Nature Materials, 2015; 14 (6): 636 DOI: 10.1038/NMAT4271

Researchers create organic nanowire synaptic transistors that emulate the working principles of biological synapses


Bio Synapsis 5768059a6d266Schematic of biological neuronal network and an ONW ST that emulates a biological synapse. Credit: Science Advances (2016). DOI: 10.1126/sciadv.1501326

A team of researchers with the Pohang University of Science and Technology in Korea has created organic nanowire synaptic transistors that emulate the working principles of biological synapses. As they describe in their paper published in the journal Science Advances, the artificial synapses they have created use much smaller amounts of power than other devices developed thus far and rival that of their biological counterparts.

Scientists are taking multiple paths towards building next generation computers—some are fixated on finding a material to replace silicon, others are working towards building a quantum machine, while still others are busy trying to build something much more like the human mind. A hybrid system of sorts that has organic artificial parts meant to mimic those found in the brain. In this new effort, the team in Korea has reached a new milestone in creating an artificial synapse—one that has very nearly the same power requirements as those inside our skulls.

Up till now, artificial synapses have consumed far more power than human synapses, which researchers have calculated is on the order of 10 femtojoules each time a single one fires. The new synapse created by the team requires just 1.23 femtojoules per event—far lower than anything achieved thus far, and on par with their natural rival. Though it might seem the artificial creations are using less power, they do not perform the same functions just yet, so natural biology is still ahead. Plus there is the issue of transferring information from one neuron to another. The “wires” used by the human body are still much thinner than the metal kind still being used by scientists—still, researchers are gaining.

As part of this latest effort, the team placed 144 of their artificial synapses on a 4 inch wafer and connected them together in a two dimensional mesh with wires that were just 200 to 300 nanometers on average. The idea was to test the possibility of causing the synapses to fire (open or close) based on information coming from a wire, or being sent from other artificial neurons. Each synapse mimicked the natural kind in shape as well—they were long and thin and were made of two types of organic material that allowed for holding or releasing ions.

The new artificial synapses are one more step on the road towards a computer that works in ways very similar to the human brain, and most believe if we ever get there, the machines we create will be far more powerful than anything nature has ever produced.

More information: W. Xu et al. Organic core-sheath nanowire artificial synapses with femtojoule energy consumption, Science Advances (2016). DOI: 10.1126/sciadv.1501326

Abstract
Emulation of biological synapses is an important step toward construction of large-scale brain-inspired electronics. Despite remarkable progress in emulating synaptic functions, current synaptic devices still consume energy that is orders of magnitude greater than do biological synapses (~10 fJ per synaptic event). Reduction of energy consumption of artificial synapses remains a difficult challenge. We report organic nanowire (ONW) synaptic transistors (STs) that emulate the important working principles of a biological synapse. The ONWs emulate the morphology of nerve fibers. With a core-sheath–structured ONW active channel and a well-confined 300-nm channel length obtained using ONW lithography, ~1.23 fJ per synaptic event for individual ONW was attained, which rivals that of biological synapses. The ONW STs provide a significant step toward realizing low-energy–consuming artificial intelligent electronics and open new approaches to assembling soft neuromorphic systems with nanometer feature size.