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Eighty years after the theoretical prediction of the force required to overcome the van der Waals’ bonding between layers in a crystal, engineering researchers at Tohoku University have measured it directly. They report their results this week in the Journal of Applied Physics, from AIP Publishing.

In its proof-of-concept, the team also created more durable gallium selenide crystals. The accomplishment could advance the development of terahertz and spintronics technologies, used in a range of applications from medical imaging to quantum computers.

“This is the first time anyone has directly measured the van der Waals bonding force in the layers of a crystal,” Tadao Tanabe, one of the authors, said. “Even high school students know of this force, but in crystals it was very difficult to measure directly.”

Though considered promising for many technologies, the use of gallium selenide crystals has been hampered by the fact that they’re notoriously fragile. To make them stronger, Tanabe’s team, including Department of Materials Science colleague Yutaka Oyama, imagined growing crystals with small amounts of the selenium replaced with the rare element tellurium.

The researchers surmised that tellurium’s larger electron cloud would produce greater van der Waals’ forces between the crystal layers, strengthening the overall structure. Van der Waals’ are weak electric forces that attract atoms to one another through subtle shifts in the atom’s electron configurations.

The team grew and compared three different types of crystals: one pure gallium selenide, one with 0.6 percent tellurium and one with 10.6 percent tellurium. To test the effect on the tellurium on interlayer bonding, the team invented the equivalent of a crystal sandwich opener. Their system is able to measure with exquisite detail the tensile strength, the force required to pull the crystal until it breaks.

“The tensile testing system is very simple in some ways,” Tanabe said. “But it was very difficult to develop a way to identify the exact point at which the crystal broke.”

The crystals tested were about 3 millimeters in width, and only 1/5 of a millimeter thick, about half the thickness of a piece of standard printer paper. Each crystal is comprised of hundreds of individual layers.

The team used special double-sided tape on either side of a crystal to hold it between an anchored stage and a moveable one that could be pulled away slowly, at a rate of 50 millionths of a meter per second. “This enabled us to very precisely measure the interlayer force at which the crystal broke,” Tanabe said.

The researchers found that the interlayer van der Waals bonding in the tellurium-doped crystals was seven times stronger than in pure gallium selenide ones.

With the addition of tellurium, the soft and cleavable gallium selenide crystal becomes rigid by enhancement of the van der Waals’ bonding force, the authors report, paving the way for using this system to improve crystal-based technologies.

Researchers at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) established a new world efficiency record for quantum dot solar cells, at 13.4 percent.

Colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties. Quantum dot solar cells emerged in 2010 as the newest technology on an NREL chart that tracks research efforts to convert sunlight to electricity with increasing efficiency. The initial lead sulfide quantum dot solar cells had an efficiency of 2.9 percent. Since then, improvements have pushed that number into double digits for lead sulfide reaching a record of 12 percent set last year by the University of Toronto. The improvement from the initial efficiency to the previous record came from better understanding of the connectivity between individual quantum dots, better overall device structures and reducing defects in quantum dots.

The latest development in quantum dot solar cells comes from a completely different quantum dot material. The new quantum dot leader is cesium lead triiodide (CsPbI3), and is within the recently emerging family of halide perovskite materials. In quantum dot form, CsPbI3 produces an exceptionally large voltage (about 1.2 volts) at open circuit.

“This voltage, coupled with the material’s bandgap, makes them an ideal candidate for the top layer in a multijunction solar cell,” said Joseph Luther, a senior scientist and project leader in the Chemical Materials and Nanoscience team at NREL. The top cell must be highly efficient but transparent at longer wavelengths to allow that portion of sunlight to reach lower layers. Tandem cells can deliver a higher efficiency than conventional silicon solar panels that dominate today’s solar market.

This latest advance, titled “Enhanced mobility CsPbI3 quantum dot arrays for record-efficiency, high-voltage photovoltaic cells,” is published in Science Advances. The paper was co-authored by Erin Sanehira, Ashley Marshall, Jeffrey Christians, Steven Harvey, Peter Ciesielski, Lance Wheeler, Philip Schulz, and Matthew Beard, all from NREL; and Lih Lin from the University of Washington.

The multijunction approach is often used for space applications where high efficiency is more critical than the cost to make a solar module. The quantum dot perovskite materials developed by Luther and the NREL/University of Washington team could be paired with cheap thin-film perovskite materials to achieve similar high efficiency as demonstrated for space solar cells, but built at even lower costs than silicon technology–making them an ideal technology for both terrestrial and space applications.

“Often, the materials used in space and rooftop applications are totally different. It is exciting to see possible configurations that could be used for both situations,” said Erin Sanehira a doctoral student at the University of Washington who conducted research at NREL.

For the first time, researchers have used a single-step, laser-based method to produce small, precise hybrid microstructures of silver and flexible silicone. This innovative laser processing technology could one day enable smart factories that use one production line to mass-produce customized devices combining soft materials such as engineered tissue with hard materials that add functions such as glucose sensing.

Using a one-step laser fabrication process, researchers created flexible hybrid microwires that conduct electricity. (a) An optical microscope image of the silver (black) and silicone (clear) microwires. (b) Scanning electron microscopy image of the same fabricated structure. Both scale bars are equal to 25 microns. Credit: Mitsuhiro Terakawa, Keio University

Using a one-step laser fabrication process, researchers created flexible hybrid microwires that conduct electricity. (a) An optical microscope image of the silver (black) and silicone (clear) microwires. (b) Scanning electron microscopy image of the same fabricated structure. Both scale bars are equal to 25 microns. Credit: Mitsuhiro Terakawa, Keio University

The metal component of the microstructures renders them electrically conductive while the elastic silicone contributes flexibility. This unique combination of properties makes the structures sensitive to mechanical force and could be useful for making new types of optical and electrical devices.

“These types of microstructures could possibly be used to measure very small movements or changes, such as a slight movement from an insect’s body or the subtle expression produced by a human facial muscle,” said research team leader Mitsuhiro Terakawa from Keio University, Japan. “This information could be used to create perfect computer-generated versions of these movements.”

As detailed in the journal Optical Materials Express, from The Optical Society (OSA), the researchers produced wire-like structures of silver surrounded by a type of silicone known as polydimethylsiloxane (PDMS). The researchers used PDMS because it is flexible and biocompatible, meaning that it is safer to use on or in the body.

They fabricated the structures, which measure as little as 25 microns wide, by irradiating a mixture of PDMS and silver ions with extremely short laser pulses that last just femtoseconds. In one femtosecond, light travels only 300 nanometers, which is just slightly larger than the smallest bacteria.

“We believe we are the first group to use femtosecond laser pulses to create a hybrid material containing PDMS, which is very useful because of its elasticity,” said Terakawa. “The work represents a step towards using a single, precision laser processing technology to fabricate biocompatible devices that combine hard and soft materials.”

Turning two laser processes into one

The one-step fabrication method used to make the hybrid microstructures combines the light-based chemical reactions known as photopolymerization and photoreduction, both of which were induced using femtosecond laser pulses. Photopolymerization uses light to harden a polymer, and photoreduction uses light to form microstructures and nanostructures from metal ions.

The fabrication technique resulted from a collaboration between Terakawa’s research group, which been studying two-photon photoreduction using soft materials, and a group at the German research organization Laser Zentrum Hannover, that has been advancing single-photon photopolymerization of PDMS.

To create the wire microstructures, the researchers irradiated the PDMS-silver mixture with light from femtosecond laser emitting at 522-nm, a wavelength that interacts efficiently with the material mixture. They also carefully selected silver ions that would combine well with PDMS.

The researchers found that just one laser scan formed wires that exhibit both the electrical conductivity of metal and the elasticity of a polymer. Additional scans could be used to produce thicker and more uniform structures. They also showed that the wire structures responded to mechanical force by blowing air over the structures to create a pressure of 3 kilopascal.

The researchers say that, in addition to making wires structures, the approach could be used to make tiny 3D metal-silicone structures. As a next step, they plan to study whether the fabricated wires maintain their structure and properties over time.

“Our work demonstrates that simultaneously inducing photoreduction and photopolymerization is a promising method for fabricating elastic and electrically conductive microstructures,” said Terakawa. “This is one step toward our long-term goal of developing a smart factory for fabricating many human-compatible devices in one production line, whether the materials are soft or hard.”

Veeco Instruments Inc. (Nasdaq: VECO) announced today the completion of a strategic initiative with ALLOS Semiconductors (ALLOS) to demonstrate 200mm GaN-on-Si wafers for Blue/Green micro-LED production. Veeco teamed up with ALLOS to transfer their proprietary epitaxy technology onto the Propel Single-Wafer MOCVD System to enable micro-LED production on existing silicon production lines.

“With the Propel reactor, we have an MOCVD technology that is capable of high yielding GaN Epitaxy that meets all the requirements for processing micro-LED devices in 200 millimeter silicon production lines,” said Burkhard Slischka, CEO of ALLOS Semiconductors. “Within one month we established our technology on Propel and have achieved crack-free, meltback-free wafers with less than 30 micrometers bow, high crystal quality, superior thickness uniformity and wavelength uniformity of less than one nanometer.  Together with Veeco, ALLOS is looking forward to making this technology more widely available to the micro-LED ecosystem.”

Micro-LED display technology consists of <30×30 square micron red, green, blue (RGB) inorganic LEDs that are transferred to the display backplane to form sub-pixels. Direct emission from these high efficiency LEDs offers lower power consumption compared with OLED and LCD while providing superior brightness and contrast for mobile displays, TV and wearables. The manufacturing of micro-LEDs requires high quality, uniform epitaxial wafers to meet the display yield and cost targets.

“In contrast to competing MOCVD platforms, Propel offers leading-edge uniformity and simultaneously achieves excellent film quality as a result of the wide process window afforded by Veeco’s TurboDisc® technology,” said Peo Hansson, Ph.D., Senior Vice President and General Manager of Veeco MOCVD Operations. “Combining Veeco’s leading MOCVD expertise with ALLOS’ GaN-on-Silicon epi-wafer technology enables our customers to develop micro-LEDs cost effectively for new applications in new markets.”

In the late 18th century, Ernst Chladni, a scientist and musician, discovered that the vibrations of a rigid plate could be visualized by covering it with a thin layer of sand and drawing a bow across its edge. With the bow movement, the sand bounces and shifts, collecting along the nodal lines of the vibration. Chladni’s discovery of these patterns earned him the nickname, “father of acoustics.” His discovery is still used in the design and construction of acoustic instruments, such as guitars and violins.

Recently, investigators have discovered a similar effect with much smaller vibrating objects excited by light waves. When laser light is used to drive the motion of a thin, rigid membrane, it plays the role of the bow in Chladni’s original experiment and the membrane vibrates in resonance with the light. The resulting patterns can be visualized through an array of quantum dots (QDs), where these tiny structures emit light at a frequency that responds to movement. The advance is reported this week in a cover article of Applied Physics Letters, by AIP Publishing.

Background: Image of a Chladni plate's mode of vibration visualized by grains of sand collected at the nodes. Left-top: Cross-sectional scanning tunneling microscopy image of an indium arsenide quantum dot. Left-bottom: Variation of quantum dot emission line frequencies as a function of time due to vibrations of the photonic crystal membrane. Right: Scanning electron micrograph of a photonic crystal membrane, displaced according to one of the vibrational modes, with red and blue representing positive and negative displacement, respectively. Credit: Sam Carter and co-authors

Background: Image of a Chladni plate’s mode of vibration visualized by grains of sand collected at the nodes. Left-top: Cross-sectional scanning tunneling microscopy image of an indium arsenide quantum dot. Left-bottom: Variation of quantum dot emission line frequencies as a function of time due to vibrations of the photonic crystal membrane. Right: Scanning electron micrograph of a photonic crystal membrane, displaced according to one of the vibrational modes, with red and blue representing positive and negative displacement, respectively. Credit: Sam Carter and co-authors

In addition to being a modern take on an old phenomenon, the new discovery could lead to the development of sensing devices as well as methods for controlling the emission characteristics of QDs. Since the light frequency emitted by the QDs is correlated with the movement of the underlying membrane, new devices for sensing motion, such as accelerometers, can be envisioned. A reverse application is also possible since the motion of the underlying membrane can be used to control the frequency of light emitted by the QDs.

The tiny devices in the work reported here consist of a 180-nanometer thick slice of semiconductor, suspended like a trampoline above a solid substrate. An array of QDs, analogous to the sand in the acoustic example, are embedded in the slice, whose thickness is less than one-tenth of one percent that of a human hair.

A second probe laser is used to visualize the resulting resonances. The QDs absorb the probe light and emit a second light pulse in response, which is picked up by a detector and routed to a display. The resulting patterns are remarkably like those visualized in Chladni’s original acoustic experiment, even though the new device is driven entirely by light.

One possible application of this discovery, according to Sam Carter of the Naval Research Lab who is one of the paper’s authors, is to sense subtle forces produced by nearby dense objects. “Concealed nuclear materials could be detectable,” he said, “since dense materials like lead are used to shield the devices.”

The highly dense shielding needed for nuclear materials causes small gravitational anomalies and tiny movements that might be detectable by a device based on the principle discovered here. The investigators plan to continue their work by looking at electronic spin. It is hoped that techniques to measure the effect on spin will increase the sensitivity of the devices.

FlexTech, a SEMI Strategic Association Partner announced a new development project with PARC, a Xerox company, to develop a hybrid, highly bendable, paper-like smart tag, incorporating a thin audio speaker. The product is aimed at applications in packaging, wearables prosthetics, soft robotics, smart tags, and smart cities and homes.

PARC will use ink jet printing to build prototypes of the paper-like smart tags capable of producing audio signals, on a silver-printed polyethylene naphthalene (PEN) or polyimide (PI) substrate. They will develop and demonstrate a process for bonding chips, and printing active and passive components, as well as interconnects on the flexible substrate, essential in meeting the project goals for ruggedness and form factor. PARC will also focus on printing actuators to create thin film audio speakers. The technology will enable custom systems to be built on demand.

“Over the last 15 years PARC has been a pioneer in the exciting field of printed electronics.  We are pleased to continue our collaboration with SEMI-FlexTech in a project which takes advantage of the wide range of expertise on the PARC staff,” said Bob Street, project technical lead at PARC. “This new project is technically challenging because it combines a number of novel technologies needed to achieve stringent requirements, including the capability for a thin, paper-like film to produce clear speech audio.  We are looking forward to the challenge and implications for commercial products.”

In 2014, FlexTech awarded PARC with a project grant to develop printed sensors. Partly because of this work, it is now possible to print transistor circuits in a fully additive fashion, and to combine these with sensors, actuators and other electronic components.

“We have had a long, fruitful relationship with PARC and look forward to excellent results from this project which clearly advances innovation in flexible, printable electronics, enabling solutions that lead to safer, healthier lives,” said Melissa Grupen-Shemansky, CTO at SEMI-FlexTech. “In addition to pushing the boundaries in electronics, PARC pays attention to manufacturability and affordability, ensuring developments are scalable from R&D to production.”

PARC and SEMI-FlexTech staff envisage additive manufacturing delivering intelligence into electronics fabricated on demand, including smart packaging and wearable devices in conformal shapes. At the heart of this development are material science, novel printing technologies as well as process driven design that will deliver libraries of smart components and systems. The constituent “inks” of this technology are nanomaterials, molecular semiconductors, inorganic composites and silicon chiplets that together form circuits, sensors, light emitters, batteries, and more, integrated directly into products of all shapes, sizes and textures.

FlexTech’s R&D program is supported by the U.S. Army Research Laboratory (ARL), based in Adelphi, MD.

NXP Semiconductors N.V. (NASDAQ:NXPI) today debuted two significant technology breakthroughs at the largest fintech innovation event, Money 20/20, October 22-25, 2017, in Las Vegas. The company will showcase its new contactless fingerprint-on-card solution while also demonstrating a new world benchmark for payment card transactions speeds.

Fingerprint sensors on payment cards

The fingerprint-on-card solution gives payment network operators and banks a secure, convenient and fast payment card option to consumers. Coupling dual interface cards with an integrated fingerprint sensor enables faster transactions without the need for end-users to enter a PIN number.

“The result provides a secure and dramatically more convenient way for consumers to make payments. The convenience provided by mobile payment in today’s NFC-based mobile wallets can now be replicated with cards. It is also ideal for use in other form factors and applications such as electronic passports,” said Rafael Sotomayor, senior vice president and general manager of secure transactions and identification business. “The breakthrough reinforces NXP’s commitment to the payment and secure identification space by helping our customers deliver next-generation applications and solutions to the market.”

To ensure a lower barrier of entry for card makers, the company’s secure fingerprint authentication solution on cards does not require a battery and easily fits into standard card maker equipment as part of the broader payment ecosystem. Cards with fingerprint authentication are fully compliant with existing EMVCo point-of-sales (POS) systems.

New Benchmark for Blazing Transaction Speeds

Demonstrating seamless, fast, and smart card transaction experiences, the NXP high-performance platform makes it possible to achieve M/Chip transactions speeds of <200 ms, surpassing the industry requirement of 300 ms.

“This increased level of performance offers flexibility to add new features or higher crypto countermeasures and still meet current industry transaction requirement,” said Sotomayor. “The requirement for faster payment transaction will continue, and NXP is committed to providing the performance to meet these needs and make contactless transactions faster and flawless.”

NXP Demonstrations at Money 20/20 Las Vegas 2017

NXP will demonstrate these technology breakthroughs at its exclusive reception on October 24, 2017, in The Venetian.

The phenomenon that forms interference patterns on television displays when a camera focuses on a pattern like a person wearing stripes has inspired a new way to conceptualize electronic devices. Researchers at the University of Illinois are showing how the atomic-scale version of this phenomenon may hold the secrets to help advance electronics design to the limits of size and speed.

In their new study, mechanical science and engineering professor Harley Johnson his co-authors recast a detail previously seen as a defect in nanomaterial design to a concept that could reshape the way engineers design electronics. The team, which also includes mechanical science and engineering graduate student Brian McGuigan and French collaborators Pascal Pochet and Johann Coraux, published its findings in the journal Applied Materials Today.

On display screens, moire patterns occur when the pixelation is at almost the same scale as a photographed pattern, Johnson said, or when two thin layers of a material with a periodic structure, like sheer fabrics and window screens, are placed on top of each other slightly askew.

At the macro scale, moires are optical phenomena that do not form tangible objects. However, when these patterns occur at the atomic level, arrangements of electrons are locked into place by atomic forces to form nanoscale wires capable of transmitting electricity, the researchers said.

“Two-dimensional materials – thin films engineered to be of single-atom thickness – create moire patterns when stacked on top of each other and are skewed, stretched, compressed or twisted,” Johnson said. “The moire emerges as atoms form linear areas of high electron density. The resulting lines create what is essentially an extremely thin wire.”

For decades, physicists observed microscope images of atomic arrangements of 2-D thin films and recognized them as periodic arrays of small defects known as dislocations, but Johnson’s group is the first to note that these are also common moire patterns.

“A moire pattern is simply an array of dislocations, and an array of dislocations is a moire pattern – it goes both ways,” Johnson said. This realization opened the door to what Johnson’s group refers to as moire engineering – what could lead to a new way to manufacture the smallest, lightest and fastest electronics.

By manipulating the orientation of stacked layers of 2-D thin films like graphene, wires of single-atom thickness can be assembled, building the foundation to write nanocircuitry. A wire of single-atom thickness is the limit of thinness. The thinner the wire, the faster electrons can travel, meaning this technology has the potential to produce the quickest transmitting wires and circuits possible, the researchers said.

“There is always the question of how to connect to a circuit that small,” Johnson said. “There is still a lot of work to be done in finding ways to stitch together 2-D materials in a way that could produce a device.”

In the meantime, Johnson’s group is focusing on types of devices that can be made using moire engineering.

“Being able to engineer the moire pattern itself is a path to new lightweight and less-intrusive devices that could have applications in the biomedical and space industries,” he said. “The possibilities are limited only by the imagination of engineers.”

Research by scientists at Swansea University has shown that improvements in nanowire structures will allow for the manufacture of more stable and durable nanotechnology for use in semiconductor devices in the future.

Dr. Alex Lord and Professor Steve Wilks from the Centre for NanoHealth led the collaborative research published in Nano Letters. The research team defined the limits of electrical contact technology to nanowires at atomic scales with world-leading instrumentation and global collaborations that can be used to develop enhanced devices based on the nanomaterials. Well-defined, stable and predictable electrical contacts are essential for any electrical circuit and electronic device because they control the flow of electricity that is fundamental to the operational capability.

Their experiments found for the first time, that atomic changes to the metal catalyst particle edge can entirely alter electrical conduction and most importantly reveal physical evidence of the effects of a long standing problem for electrical contacts known as barrier inhomogeneity. The study revealed the electrical and physical limits of the materials that will allow nanoengineers to select the properties of manufacturable nanowire devices.

One-of-a-kind multi-probe LT Nanoprobe at Swansea University used to obtain the electrical measurements of nanowires that were correlated to atomic resolution imaging. Credit: Swansea University

One-of-a-kind multi-probe LT Nanoprobe at Swansea University used to obtain the electrical measurements of nanowires that were correlated to atomic resolution imaging. Credit: Swansea University

Dr Lord, recently appointed as a Senior Sêr Cymru II Fellow part-funded by the European Regional Development Fund through the Welsh Government, said: “The experiments had a simple premise but were challenging to optimise and allow atomic-scale imaging of the interfaces. However, it was essential to this study and will allow many more materials to be investigated in a similar way.

“This research now gives us an understanding of these new effects and will allow engineers in the future to reliably produce electrical contacts to these nanomaterials which is essential for the materials to be used in the technologies of tomorrow.

“The new concepts shown here provide interesting possibilities for bridged nanowire devices such as transient electronics and reactive circuit breakers that respond to changes in electrical signals or environmental factors and provide instantaneous reactions to electrical overload.”

The Swansea research team used specialist experimental equipment at the Centre for NanoHealth and collaborated with Professor Quentin Ramasse of the SuperSTEM Laboratory, Science and Facilities Technology Council1-3 and Dr Frances Ross of the IBM Thomas J. Watson Research Center, USA.3 The scientists were able to physically interact with the nanostructures and measure how atomic changes in the materials affected the electrical performance.

Dr. Frances Ross, IBM, USA, added: “”This research shows the importance of global collaboration, particularly in allowing unique instrumentation to be used to obtain fundamental results that allow nanoscience to deliver the next generation of technologies.”

Nanotechnology is the scaling down of everyday materials by scientists to the size of nanometres (one million times smaller than a millimetre on a standard ruler) and is seen as the future of electronic devices. Progressions in scientific and engineering advances are resulting in new technologies such as computer components for smart devices and sensors to monitor our health and the surrounding environment.

Nanotechnology is having a major influence on the Internet of Things which connects everything from our homes to our cars into a web of communication. All of these new technologies require similar advances in electrical circuits and especially electrical contacts that allow the devices to work correctly with electricity.

The process of extracting natural gas from the earth or transporting it through pipelines can release methane into the atmosphere. Methane, the primary component of natural gas, is a greenhouse gas with a warming potential approximately 25 times larger than carbon dioxide, making it very efficient at trapping atmospheric heat energy. A new chip-based methane spectrometer, that is smaller than a dime, could one day make it easier to monitor for efficiency and leaks over large areas.

Scientists from IBM Thomas J. Watson Research Center in Yorktown Heights, NY, developed the new methane spectrometer, which is smaller than today’s standard spectrometers and more economical to manufacture. In Optica, The Optical Society’s journal for high impact research, the researchers detail the new spectrometer and show that it can detect methane in concentrations as low as 100 parts-per-million.

Low maintenance, high impact

The spectrometer is based on silicon photonics technology, which means it is an optical device made of silicon, the material used to make computer chips. Because the same high-volume manufacturing methods used for computer chips can be applied to make the chip-based methane spectrometer, the spectrometer along with a housing and a battery or solar power source might cost as little as a few hundred dollars if produced in large quantities.

“Compared with a cost of tens of thousands of dollars for today’s commercially available methane-detecting optical sensors, volume-manufacturing would translate to a significant value proposition for the chip spectrometer,” said William Green, leader of the IBM Research team. “Moreover, with no moving parts and no fundamental requirement for precise temperature control, this type of sensor could operate for years with almost no maintenance.”

Such low-cost, robust spectrometers could lead to exciting new applications. For example, the IBM team is working with partners in the oil and gas industry on a project that would use the spectrometers to detect methane leaks, saving companies the time and money involved in trying to find and fix leaks using in-person inspection of thousands of sites.

“During natural gas extraction and distribution, methane can leak into the air when equipment on the well malfunctions, valves get stuck, or there’s a crack in the pipeline,” said Green. “We’re developing a way to use this spectrometer-on-a-chip to create a network of sensors that could be distributed over a well pad, for example. Data from these sensors would be processed with IBM’s physical analytics software to automatically pinpoint the location of a leak as well as quantify the leak magnitude.”

Methane is a trace gas, the classification given to gases that make up less than 1 percent of the volume of Earth’s atmosphere. Although the researchers demonstrated methane detection, the same approach could be used for sensing the presence of other individual trace gases. It could also be used to detect multiple gases simultaneously.

“Our long-term vision is to incorporate these types of sensors into the home and things people use every day such as their cell phones or vehicles. They could be useful for detecting pollution, dangerous carbon monoxide levels or other molecules of interest,” said Eric Zhang, a member of the research team. “Because this spectrometer offers a platform for multispecies detection, it could also one day be used for health monitoring through breath analysis.”

Shrinking the spectrometer

The new device uses an approach known as absorption spectroscopy, which requires laser light at the wavelength uniquely absorbed by the molecule being measured. In a traditional absorption spectroscopy setup, the laser travels through the air, or free-space, until it reaches a detector. Measuring the light that reaches the detector reveals how much light was absorbed by the molecules of interest in the air and can be used to calculate the concentration of them present.

The new system uses a similar approach, but instead of a free-space setup, the laser travels through a narrow silicon waveguide that follows a 10-centimeter-long serpentine pattern on top of a chip measuring 16 square millimeters. Some of the light is trapped inside the waveguide while about 25 percent of the light extends outside of the silicon into the ambient air, where it can interact with trace gas molecules passing nearby the sensor waveguide. The researchers used near infrared laser light (1650 nanometer wavelength) for methane detection.

To increase the sensitivity of the device, the investigators carefully measured and controlled factors that contribute to noise and false absorption signals, fine-tuned the spectrometer’s design and determined the waveguide geometrical parameters that would produce favorable results.

Side-by-side comparison

To compare the new spectrometer’s performance with that of a standard free-space spectrometer, they placed the devices into an environmental chamber and released controlled concentrations of methane. The researchers found that the chip-based spectrometer provided accuracy on-par with the free-space sensor despite having 75 percent less light interacting with the air compared to the free-space design. Furthermore, the fundamental sensitivity of the chip sensor was quantified by measuring the smallest discernable change in methane concentration, showing performance comparable to free-space spectrometers developed in other laboratories.

“Although silicon photonics systems — especially those that use refractive index changes for sensing — have been explored previously, the innovative part of our work was to use this type of system to detect very weak absorption signals from small concentrations of methane, and our comprehensive analysis of the noise and minimum detection limits of our sensor chip,” said Zhang.

The current version of the spectrometer requires light to enter and exit the chip via optical fibers. However, the researchers are working to incorporate the light source and detectors onto the chip, which would create an essentially electrical device with no fiber connections required. Unlike current free-space sensors, the chip then does not require special sample or optical preparation. Next year, they plan to start field testing the spectrometers by placing them into a larger network that includes other off-the-shelf sensors.

“Our work shows that all of the knowledge behind silicon photonics manufacturing, packaging, and component design can be brought into the optical sensor space, to build high-volume manufactured and, in principle, low cost sensors, ultimately enabling an entirely new set of applications for this technology,” said Green.