Combining silicon with a light-producing semiconductor may help develop micrometer-scale lasers, shows Doris Keh-Ting Ng and her colleagues from the A*STAR Data Storage Institute.
Silicon has revolutionized the manufacture of electrical devices. This abundant semiconductor is easily processed into tiny components, such as transistors, using methods that are scalable to industrial levels, thus enabling the production of hundreds of thousands of elements on a single chip. Electronic engineers would like to further expand the functionality of these integrated circuits by enabling them to create, manipulate and detect light.
These optoelectronic devices could speed up processing of digital information, and lead to micrometer-scale lasers, for use in barcode scanners for example. The problem, however, is that silicon is not an efficient light generator.
Ng’s team designed and produced a laser compatible with silicon fabrication techniques by combining silicon and another semiconductor material that can produce light: indium gallium arsenide phosphide (InGaAsP). “Our results demonstrate a promising approach for efficient and compact active optoelectronic devices on silicon using a very thin III-V semiconductor layer,” says Ng.
Agency for Science, Technology and Research (A*STAR) research articles from Innovation Toronto
- Quick-change materials break the silicon speed limit for computers – September 22, 2014
- Dyes help harvest visible and infrared light – July 31, 2014
- Modified anticancer drug gives a ‘green light’ for its own success – July 31, 2014
- Flexible plastics that turn mechanical vibrations into electrical energy could replace batteries | energy harvesting – April 14, 2014
- Scientific breakthrough could operate at tens of thousands times faster than today’s state-of-the-art microprocessors | quantum plasmonic tunnelling – April 10, 2014
- Create Your Own Stem Cell Bank From a Drop of Blood | stem cell banking
- Self-powered wireless light detectors
- Dye-sensitized solar cells that use carbon nanotube thin films as transparent electrodes offer significant cost savings
- A*STAR Scientists Discover “Switch” Critical to Wound Healing
- Lab-on-a-chip realizes potential
- New packaging plastic that protects as well as aluminium foil | prolonging shelf-life
- Smart windows for buildings that change from transparent to colored states at the flick of a switch
- A holistic approach catches eye disease early
- Medical Sensors Improve With Holey Gold Nanostructures
- Patient, Heal Thyself: Solution To Personalised Treatment For Chronic Infections Could Lie In The Patient’s Own Blood
- Promising New Alloy for Resistive Switching Memory
- Microelectronics: Automating cancer detection
- Data storage: Maintaining privacy on the cloud
- Graphene makes a magnetic switch
- Alternative energy: A cooler way to clean hydrogen
- Carbon capture: Making use of minerals
- Nanotechnology: Color Printing Reaches New Highs
- New Singapore plastic film is the future of 3D on-the-go
- Biochemical engineering: Waste not, want not
- Drug manufacture: Going green with iron
- Scientists design, control movements of molecular motor
- Video analysis: Detecting text every which way
- Researchers unravel the secret to making cheap, high-density data storage
- Smallest Antenna Can Increase Wi-Fi Speed 200 Times
- First full colour images at 100,000 dpi resolution
- Robots Will Quickly Recognize and Respond to Human Gestures, With New Algorithms
- Scotty Beam This Up: Bessel beam “tractor beam” concept theoretically demonstrated
- Revolutionary Chipset for High-Speed Wireless Data Transfer
- Dye-Sensitized Solar Cells That Use Carbon Nanotube Thin Films as Transparent Electrodes Offer Significant Cost Savings
- T-Rays technology could help develop Star Trek-style hand-held medical scanners
- Oncoproteins Inside Cancer Cells to Suppress Aggressive Cancer Growth
- How to Combat Hospital-Acquired Infections and Life-Threatening Toxins
- A new spin on silk
- Samsung files patent for liquid zoom lens
The Agency was established in 1991 to foster scientific research and talent for a knowledge-based Singapore.
The Biomedical Research Council (BMRC) oversees 7 research institutes and several other research units that focus on both basic as well as translational and clinical research to support the key industry clusters in Biomedical Sciences, pharmaceuticals, medical technology, biotechnology and healthcare services.
Having established a strong foundation in basic biomedical research capabilities, there is now an added focus on translating new knowledge and technologies created at the “benches” into new clinical applications for diagnosis and treatment that can one day be delivered at the “bedsides” of our hospitals and disease centres.
A*STAR scientists have developed a unique fast-pulsing fiber laser that has the widest wavelength output to date1. This type of laser could replace several fixed-wavelength lasers and form the basis of compact devices useful for a range of medical and military applications.
The team developed an all-fiber laser, constructed similarly to a fiber-optic cable. The key component is a glass tube, whose core is doped with atoms that act as a gain medium — a material from which energy is transferred to boost the output power of the laser — through which light particles, or ‘photons’, travel. The doping atoms are selected according to the specific wavelengths of light that they will absorb, store and then release, creating an efficient, controllable output beam.
“To date, most tunable all-fiber pulsed lasers achieve a maximum tuning range of about 50 nanometers,” says Xia Yu from the A*STAR Singapore Institute of Manufacturing Technology, who worked on the project with her team and her collaborator Qijie Wang from Nanyang Technological University. “We have achieved a widely-tunable laser in the mid-infrared wavelength band, with a range of 136 nanometers (from 1,842 to 1,978 nanometers). We used thulium as the doping atom; this generates a laser that operates in the eye-safe range, meaning it could have medical and military applications.”
The researchers combined two techniques to create their laser and ensure the output was tunable. They used nonlinear polarization evolution, a filtering effect that picks out pulses of light at the desired wavelength and channels them into the output beam. This simultaneously ensures that the output can be adjusted to a specific wavelength while generating ultrafast pulsed light. They also used bidirectional pumping — injecting energy into the gain medium from both ends of the fiber — to ensure a high optical power for as wide a range of wavelengths as possible. The gain occurs when thulium ions are excited to higher-energy states; they then release more photons when they return to lower-energy states.
A decision-making tool helps producers of pharmaceutical and other valuable chemicals make the leap to an entirely new way of manufacturing
Historically, pharmaceutical industries have relied on novel medications to meet profit targets; however in today’s competitive markets, the huge expenditures associated with drug development now challenge this approach. An international team led by A*STAR researchers show how manufacturers can make rapid decisions about switching to alternative drug manufacturing procedures with promising economic prospects1.
High-value chemicals are traditionally made through ‘batch processing’; where inputs such as raw materials and energy are combined in a single reactor until the desired output is obtained. While this approach is simple, it can only be performed in a sequential manner. So if demand for a drug suddenly increases — combating an emerging strain of influenza, for instance — such step-by-step operations cannot cope with the production scale-up required.
Soo Khean Teoh from the Institute of Chemical and Engineering Sciences at A*STAR and her co-workers have developed a methodology to assess the feasibility of switching from batch to ‘continuous’ processing, where all stages of chemical reactions occur simultaneously: flowable reagents are constantly fed into reactor, and likewise, products are extracted nonstop.
With continuous processing, operations are quicker, more energy-efficient, and use smaller installation facilities than batch techniques. Yet most chemical producers are hesitant to implement continuous systems, unless they see clear technical and economic benefits.
“The biggest challenge is that there is no ‘one-size-fits-all’ solution for changing from batch to continuous methods, because of the complex and varied chemistries involved,” explains Teoh. “We had to devise a method which guides users to understand the process in question, brainstorm about potential benefits, and help them come to swift decisions.”
The researchers’ method initially screens chemical processes to uncover key business requirements and potential pitfalls, such as sticky reagents, with simple yes/no/maybe evaluations. Successful candidates are then broken down into a flow chart analysis that identifies factors such as possible equipment, control schemes, and plant configurations. If the analysis makes economic sense, a final stage of process execution is put into place.
Liquid-phase reactions that proceed quickly and emit or absorb large quantities of energy proved to be particularly favorable for continuous processing. For example, the team demonstrated that the Reformatsky reaction — an organozinc-catalyzed reaction that frequently overheats with batch processing — could profit enormously from a continuous approach.
“Our methodology makes understanding the process much clearer, especially to the chemists and engineers dealing with the synthesis,” says Teoh. “It makes it easier to decide to proceed or to kill the idea, minimizing wasted effort.”
A coating that blocks 90 per cent of the heat from sunlight could be used to develop smart windows
By fine-tuning the chemical composition of nanoparticles, A*STAR researchers have developed a coating that is promising for fabricating smart windows suitable for tropical countries. Such windows block almost all the infrared heat from sun rays, while admitting most of the visible light.
The transparency of glass to visible light makes it the most common way to let light into a building. But because glass is also transparent to near-infrared radiation — windows also let in heat, giving rise to the well-known greenhouse effect. While this heating is welcomed in colder climates, it means that air conditioning has to work harder to maintain a comfortable temperature in tropical climes.
Developing smart windows that allow most of the sun’s light in, while blocking near-infrared radiation, would cut energy costs and reduce carbon emissions.
“In tropical Singapore, where air conditioning is the largest component of a building’s energy requirements, even a small reduction in heat intake can translate into significant savings,” notes Hui Huang of the A*STAR Singapore Institute of Manufacturing and Technology.
Huang and his co-workers have developed such windows by coating glass with tin oxide nanoparticles doped with small amounts of the element antimony. By varying the nanoparticles’ antimony concentration, they could optimize their ability to absorb near-infrared radiation.
“Our infrared shielding coating, with 10-nanometer antimony-doped tin oxide nanoparticles, blocks more than 90 per cent of near-infrared radiation, while transmitting more than 80 per cent of visible light,” says Huang. “These figures are much better than those of coatings obtained using commercial antimony-doped tin oxide nanopowders. In particular, the infrared shielding performance of our small antimony-doped tin oxide nanocrystals is twice that of larger commercial antimony-doped tin oxide powders.”
The team produced the tiny nanoparticles using a synthesis technique known as the solvothermal method, in which precursors are heated under pressure in a special vessel, called an autoclave. The solvothermal method permits synthesis at relatively low temperatures. It also enables the nanoparticle size to be tightly controlled, which is important when trying to block some wavelengths of light while allowing others to pass through.
The work has already attracted the interest of industry. “A local glass company supporting this project is interested in licensing this smart window technology with infrared shielding,” says Huang. Potentially, the coating techniques could be applied on-site to existing windows, he adds.
Learn more: Admitting visible light, rejecting infrared heat
Silicon holograms harness the full visible spectrum to bring holographic projections one step closer
We can’t yet send holographic videos to Obi-Wan Kenobi on our droid, but researchers at Agency for Science, Technology and Research (A*STAR), Singapore, have got us a little bit closer by creating holograms from an array of silicon structures that work throughout the visible spectrum.
Many recent advances in hologram technology use reflected light to form an image; however the hologram made by Dong Zhaogang and Joel Yang from the A*STAR Institute of Materials Research and Engineering uses transmitted light. This means the image is not muddled up with the light source.
The team demonstrated the hologram of three flat images at wavelengths ranging from blue (480 nanometers) to red (680 nanometers). The images appeared in planes 50 microns apart for red and higher spacings for shorter wavelengths.
“In principle, it can be tuned to any wavelength,” says Yang.
Holograms can record three-dimensional images, which mean they can store large amounts of information in increasingly thin layers.
Recently, holograms that are mere hundredths of the thickness of a human hair have been made from metal deposited onto materials such as silicon. The holograms are created by nanoscale patterns of metal that generate electromagnetic waves that travel at the metal–silicon interface; a field called plasmonics.
Silicon holograms are slightly thicker than the metal-based ones, but have the advantage of being broadband. Plasmonic holograms only operate in the red wavelengths because they undergo strong absorption at blue wavelengths.
A disadvantage of the silicon holograms is their poor efficiency at only three per cent; however Dong estimates this could easily be tripled.
“The losses can be lowered by optimizing the growth method to grow polycrystalline silicon instead of amorphous silicon,” he says.
The hologram is an array of tiny silicon skyscrapers, 370 nanometers tall with footprints 190 nanometers by 100 nanometers. Unlike a city grid, however, the tiny towers are not laid out in neat squares but at varying angles.
The hologram operates with circularly polarized light, and the information is encoded on to the light beam by the varied angles of the skyscrapers. These alter the phase of the transmitted light through the ‘Pancharatnam–Berry effect’.
“What’s interesting about this hologram is that it controls only the phase of the light by varying the orientation of the silicon nanostructures. The amplitude is the same everywhere; in principle you can get a lot of light transmitted,” says Yang.
The A*STAR researchers focused on nanofabrication and measurements and collaborated with Cheng-Wei Qiu from National University of Singapore, whose team specializes in hologram design.
Learn more: Silicon brings more color to holograms
Mini midbrains provide next generation platforms to investigate human brain biology, diseases and therapeutics
Scientists in Singapore have made a big leap on research on the ‘mini-brain’. These advanced mini versions of the human midbrain will help researchers develop treatments and conduct other studies into Parkinson’s Disease (PD) and ageing-related brain diseases.
These mini midbrain versions are three-dimensional miniature tissues that are grown in the laboratory and they have certain properties of specific parts of the human brains. This is the first time that the black pigment neuromelanin has been detected in an organoid model. The study also revealed functionally active dopaminergic neurons.
The human midbrain, which is the information superhighway, controls auditory, eye movements, vision and body movements. It contains special dopaminergic neurons that produce dopamine – which carries out significant roles in executive functions, motor control, motivation, reinforcement, and reward. High levels of dopamine elevate motor activity and impulsive behaviour, whereas low levels of dopamine lead to slowed reactions and disorders like PD, which is characterised by stiffness and difficulties in initiating movements.
A material whose optical properties can be modified on a small scale by laser light promises a wide range of applications
Properties of small areas of a versatile optical film can be tweaked by applying ultrashort pulses of laser light, A*STAR researchers show1. This tunability makes the material suitable for various light-based applications, from lenses to holograms.
When the shutter button on a camera is depressed, it focuses by electrically adjusting the positions of the constituent parts of the lens. Similarly, the parameters of optical components in many devices and scientific instruments are adjusted by moving their parts, or by stretching or heating them. Being able to use light to adjust optical components would offer many advantages, including fast response and easy integration into small and robust systems.
Now, such an optically adjustable system has been developed by Qian Wang of the A*STAR Institute of Materials Research and Engineering and co-workers, along with collaborators at the University of Southampton, UK, and the Nanyang Technological University, Singapore.
The team studied a material widely used in CD and DVD disks — chalcogenide glass. In rewritable CD and DVD data-storage devices, microsecond or nanosecond (10−9 second) laser pulses are used to switch the medium between two states — crystalline and disordered. In contrast, Wang and her team used a tightly controlled series of much shorter femtosecond (10−15second) optical pulses to set the glass into incremental states between completely crystalline and completely disordered. By scanning the focused laser beam across the glass film, they could modify regions as small as about 0.6 micrometers (see image).
Scientists in Singapore have developed a revolutionary emissions abatement system that removes pollutants from exhaust gas to help the international shipping industry meet ambitious emissions targets.
In 2013, the International Maritime Organization (IMO) introduced new regulations to reduce exhaust emissions attributed to the shipping industry. Shipping is responsible for around 90% of global trade and the effect of reducing emissions such as sulphur oxides (SOx), nitrous oxides (NOx), particulate matter and greenhouse gases such as carbon dioxide (CO2) will have a huge impact on global totals.
Researchers from the Agency for Science, Technology and Research Institute of High Performance Computing (IHPC) together with Sembcorp Marine Ltd and Ecospec Technology Pte Ltd have risen to the challenge of finding ways to meet the IMO’s new emissions targets.
The team from Sembcorp Marine Ltd and Ecospec Technology Pte Ltd has developed an exhaust gas treatment system, called cSOx, which removes SOx and CO2 from ships’ diesel engine and boiler exhaust emissions. It uses ultra-low-frequency electromagnetic waves to treat seawater, thereby optimising the system’s ability to absorb sulphur dioxide and CO2.
Adding genes to bacteria offers sustainable routes to make compounds currently obtained from petrochemicals
The dream of replacing petrochemicals with renewable resources in the manufacture of synthetic fibers and plastics has moved a step closer. A*STAR researchers have genetically modified the bacterium Escherichia coli to produce a compound that can be converted into a base material for manufacturing nylon and other synthetic products1.
“We need to reduce consumption of oil and gas and move toward more sustainable technologies,” explains Sudhakar Jonnalagadda who carried out the work with colleagues at the A*STAR Institute of Chemical and Engineering Sciences.
Production of most synthetic fibers and plastics begins with crude oil; a finite resource whose extraction and processing has significant environmental impact. The alternative sustainable route uses bacteria to make the precious starting materials from simple substances such as glucose. The glucose can be extracted from biomass which includes crops and other biological materials that can be grown to meet demand.
Bacteria do not naturally produce the required products in significant quantities, so the trick is to persuade these microorganisms to become mini manufacturing plants for chemicals required by industry. One such chemical is muconic acid, which can be readily converted into adipic acid, a chemical used in huge quantities to manufacture nylon.
Mass-produced microvalves are the key to scalable production of disposable, plug-and-play microfluidic devices
The elusive ‘lab on a chip’ capable of shrinking and integrating operations normally performed in a chemical or medical laboratory on to a single chip smaller than a credit card, may soon be realized thanks to disposable, plug-and-play microfluidic devices developed by A*STAR researchers1.
Microfluidic systems use networks of channels much narrower than a human hair to control the movement of miniscule amounts of fluids. Recent advances in microfluidics technology have proven invaluable for immediate point-of-care diagnosis of diseases and have greatly improved enzymatic and DNA analysis. High throughput microfluidic systems are also being employed in stem cell studies and for the discovery of new drugs.
A stumbling block for successful miniaturization and commercialization of fully integrated microfluidic systems, however, has been the development of reliable microfluidic components, such as microvalves and micropumps. Zhenfeng Wang and colleagues from the Singapore Institute of Manufacturing Technology (SIMTech), A*STAR have removed that obstacle by developing an efficient and scalable method to fabricate disposable plug-and-play microfluidic devices.
“Integrating valves and pumps into thermoplastic devices is usually challenging and costly because the fabrication process is very complicated,” says Wang. “Mass-producing the microvalve module separately from the main device, however, makes the fabrication of the main device relatively simple and robust.”
Helping computers learn to tackle big-data problems outside their comfort zones
Imagine combing through thousands of mugshots desperately looking for a match. If time is of the essence, the faster you can do this, the better. A*STAR researchers have developed a framework that could help computers learn how to process and identify these images both faster and more accurately1.
Peng Xi of the A*STAR Institute for Infocomm Research notes that the framework can be used for numerous applications, including image segmentation, motion segmentation, data clustering, hybrid system identification and image representation.
A conventional way that computers process data is called representation learning. This involves identifying a feature that allows the program to quickly extract relevant information from the dataset and categorize it — a bit like a shortcut. Supervised and unsupervised learning are two of the main methods used in representation learning. Unlike supervised learning, which relies on costly labeling of data prior to processing, unsupervised learning involves grouping or ‘clustering’ data in a similar manner to our brains, explains Peng.