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An important step towards next-generation ultra-compact photonic and optoelectronic devices has been taken with the realization of a two-dimensional excitonic laser. Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) embedded a monolayer of tungsten disulfide into a special microdisk resonator to achieve bright excitonic lasing at visible light wavelengths.

“Our observation of high-quality excitonic lasing from a single molecular layer of tungsten disulfide marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications,” says Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and the leader of this study.

Zhang, who also holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in the journal Nature Photonics. The paper is titled “Monolayer excitonic laser“. The lead authors are Yu Ye and Zi Jing Wong, members of Zhang’s research group, plus Xiufang Lu, Xingjie Ni, Hanyu Zhu, Xianhui Chen and Yuan Wang.

A single molecular layer of tungsten (W) and sulfide (S) is widely regarded as one of the most promising 2D semiconductors for photonic and optoelectronic applications. (Credit: Xiang Zhang, Berkeley Lab)

A single molecular layer of tungsten (W) and sulfide (S) is widely regarded as one of the most promising 2D semiconductors for photonic and optoelectronic applications. (Credit: Xiang Zhang, Berkeley Lab)

Among the most talked about class of materials in the world of nanotechnology today are two-dimensional (2D) transition metal dichalcogenides (TMDCs). These 2D semiconductors offer superior energy efficiency and conduct electrons much faster than silicon. Furthermore, unlike graphene, the other highly touted 2D semiconductor, TMDCs have natural bandgaps that allow their electrical conductance to be switched “on and off,” making them more device-ready than graphene. Tungsten disulfide in a single molecular layer is widely regarded as one of the most promising TMDCs for photonic and optoelectronic applications. However, until now, coherent light emission, or lasing, considered essential for “on-chip” applications, had not been realized in this material.

“TMDCs have shown exceptionally strong light-matter interactions that result in extraordinary excitonic properties,” Zhang says. “These properties arise from the quantum confinement and crystal symmetry effect on the electronic band structure as the material is thinned down to a monolayer. However, for 2D lasing, the design and fabrication of microcavities that provide a high optical mode confinement factor and high quality, or Q, factor is required.”

In a previous study, Zhang and his research group had developed a “whispering gallery microcavity” for plasmons, electromagnetic waves that roll across the surfaces of metals. Based on the principle behind whispering galleries – where words spoken softly beneath a domed ceiling can be clearly heard on the opposite side of the chamber – this micro-sized metallic cavity for plasmons strengthened and greatly enhanced the Q factor of light emissions. In this new study, Zhang and his group were able to adapt this microcavity technology from plasmons to excitons – photoexcited electrons/hole pairs within a single layer of molecules.

In this 2D excitonic laser, the sandwiching of a monolayer of tungsten disulfide between the two dielectric layers of a microdisk resonator creates the potential for ultralow-threshold lasing. (Credit: Xiang Zhang, Berkeley Lab)

In this 2D excitonic laser, the sandwiching of a monolayer of tungsten disulfide between the two dielectric layers of a microdisk resonator creates the potential for ultralow-threshold lasing. (Credit: Xiang Zhang, Berkeley Lab)

“For our excitonic laser, we dropped the metal coating and designed a microdisk resonator that supports a dielectric whispering gallery mode rather than a plasmonic mode, and gives us a high Q factor with low power consumption,” says co-lead author Ye. “When a monolayer of tungsten disulfide – serving as the gain medium – is sandwiched between the two dielectric layers of the resonator, we create the potential for ultralow-threshold lasing.”

In addition to its photonic and optoelectronic applications, this 2D excitonic laser technology also has potential for valleytronic applications, in which digital information is encoded in the spin and momentum of an electron moving through a crystal lattice as a wave with energy peaks and valleys. Valleytronics is seen as an alternative to spintronics for quantum computing.

“TMDCs such as tungsten disulfide provide unique access to spin and valley degrees of freedom,” says co-lead author Wong. “Selective excitation of the carrier population in one set of two distinct valleys can further lead to lasing in the confined valley, paving the way for easily-tunable circularly polarized lasers. The demand for circularly polarized coherent light sources is high, ranging from three-dimensional displays to effective spin sources in spintronics, and information carriers in quantum computation.”

This research was supported by the United States Air Force Office of Scientific Research and by the DOE Office of Science through the Light-Material Interaction in Energy Conversion Energy Frontier Research Center.

Caen, Oct. 22, 2015 – Two years after the launch of the PICS project (funded by the FP7 funding instrument dedicated to research for the benefit of SMEs), three European SMEs, IPDiA, Picosun, and SENTECH Instruments along with CEA-Leti and Fraunhofer IPMS-CNT announce the major technological results achieved during this program.

Started in September 2013, the PICS project was focused on developing innovative dielectric materials deposited by atomic layer deposition (ALD) and related tools (ALD batch tool and etching tool) to bring to mass production a new technology of high- density and high-voltage 3D trench capacitors targeting high-end markets like medical or aeronautics. Capacitors are key components presented in every electronic module. The integrated silicon capacitors technology offered by the SME IPDiA outperforms current technologies (using ceramic or tantalum substrates) in stability in temperature, voltage, aging and reliability and enables to build highly integrated and high-performance electronic modules.

The consortium’s three major technological results are:

  • A novel ALD batch tool was developed by Picosun and Fraunhofer IPMS-CNT. It enables to reduce cost-of-ownership and deliver better uniformity and step coverage for high-K dielectrics into 3D structures. With its demonstrated, optimized, and production-proven ALD processes, Picosun is solidifying its position as a technological leader in the IC, Semiconductor, MEMS markets, from R&D to production systems.
  • A new process for accurately etching high-K dielectrics, which are very specific materials, was demonstrated by SENTECH with the help of Fraunhofer IPMS-CNT. As a result, SENTECH has the potential to gain market share in the field of high-k materials, which have high interest for different applications, e.g. LED, MEMS, magnetic data storage.
  • Two new dielectric stacks were developed and integrated into the IPDiA 3D trench capacitors by IPDiA, CEA-Leti and Fraunhofer IPMS-CNT. The initial specifications were fulfilled and proven by electrical measurements. A new record on capacitance density (>500nF/mm² at 3.3V) and an extended operation voltage (10V with 150nF/mm²) were obtained, which expands IPDiA’s ability to meet current market requirements particularly in the field of medical or aeronautics. Qualification procedure was initiated during the project by launching preliminary reliability studies and it will continue in the coming months.

On top of these R&D results, the other main objective of PICS was the industrialization of this new integrated capacitors technology. Thanks to the partnerships set up, the manufacturability and financial viabilities were ensured by developing adequate industrial tools targeting mass production.

The PICS project is a success for all three SMEs and a good example of the benefits brought by the EU funding instrument “Research for the benefit of SMEs”. The SMEs were able to outsource a part of their research to get from RTD performers innovative know-how and cutting-edge technological processes. The project was built to answer the SMEs’ specific needs and a common goal was set up around the new IPDiA capacitors technology and the specific tools (ALD batch tool and etching) required for its commercial exploitation.

 

A team of scientists from the University of Chicago and Penn State University has accidentally discovered a new way of using light to draw and erase quantum-mechanical circuits in a unique class of materials called topological insulators.

In contrast to using advanced nanofabrication facilities based on chemical processing of materials, this flexible technique allows for rewritable “optical fabrication” of devices. This finding is likely to spawn new developments in emerging technologies such as low-power electronics based on the spin of electrons or ultrafast quantum computers. The research was published Oct. 9 in the American Association for the Advancement of Science’s new online journal Science Advances.

“This observation came as a complete surprise,” said David D. Awschalom, the Liew Family Professor and deputy director in the Institute of Molecular Engineering at UChicago, who was one of two lead researchers on the project. “It’s one of those rare moments in experimental science where a seemingly random event — turning on the room lights — generated unexpected effects with potentially important impacts in science and technology.”

The electrons in topological insulators have unique quantum properties that many scientists believe will be useful for developing spin-based electronics and quantum computers. However, making even the simplest experimental circuits with these materials has proved difficult because traditional semiconductor engineering techniques tend to destroy their fragile quantum properties. Even a brief exposure to air can reduce their quality.

In Science Advances, the researchers report the discovery of an optical effect that allows them to “tune” the energy of electrons in these materials using light, and without ever having to touch the material itself. They have used it to draw and erase p-n junctions — one of the central components of a transistor — in a topological insulator for the first time.

Like many advances in science, the path to this discovery had an unexpected twist.

“To be honest, we were trying to study something completely different,” said Andrew Yeats, a graduate student in Awschalom’s laboratory and the paper’s lead author. “There was a slow drift in our measurements that we traced to a particular type of fluorescent lights in our lab. At first we were glad to be rid of it, and then it struck us—our room lights were doing something that people work very hard to do in these materials.”

The researchers went back to Bulley & Andrews Construction, the contractor that renovated the lab space, for more information about the lights. “I’ve never had a client so obsessed with the overhead lighting,” said Frank Floss, superintendent for Bulley & Andrews. “I could have never imagined how important it would turn out to be.”

The researchers found that the surface of strontium titanate, the substrate material on which they had grown their samples, becomes electrically polarized when exposed to ultraviolet light, and their room lights happened to emit at just the right wavelength. The electric field from the polarized strontium titanate was leaking into the topological insulator layer, changing its electronic properties.

Awschalom and his colleagues found that by intentionally focusing beams of light on their samples, they could draw electronic structures that persisted long after the light was removed.

“It’s like having a sort of quantum Etch A Sketch in our lab,” he said. They also found that bright red light counteracted the effect of the ultraviolet light, allowing them to both write and erase. “Instead of spending weeks in the cleanroom and potentially contaminating our materials,” said Awschalom, “now we can sketch and measure devices for our experiments in real time. When we’re done, we just erase it and make something else. We can do this in less than a second.”

To test whether the new technique might interfere with the unique properties of topological insulators, the team measured their samples in high magnetic fields. They found promising signatures of an effect called weak anti-localization, which arises from quantum interference between the different simultaneous paths that electrons can take through a material when they behave as waves.

“One exciting aspect of this work is that it’s noninvasive,” said Prof. Nitin Samarth, the George A. and Margaret M. Downsbrough Department Head of Physics at Penn State, and a lead researcher on the project. “Since the electrical polarization occurs in an adjacent material, and the effect persists in the dark, the topological insulator remains relatively undisturbed. With these fragile quantum materials, sometimes you have to use a light touch.”

To better understand the physics behind the effect, the researchers conducted a number of control measurements. They showed that the optical effect is not unique to topological insulators, but that it can act on other materials grown on strontium titanate as well.

“In a way, the most exciting aspect of this work is that it should be applicable to a wide range of nanoscale materials such as complex oxides, graphene and transition metal dichalcogenides,” said Awschalom. “It’s not just that it’s faster and easier. This effect could allow electrical tuning of materials in a wide range of optical, magnetic and spectroscopic experiments where electrical contacts are extremely difficult or simply impossible.”

The tiny transistor is the heart of the electronics revolution, and Penn State materials scientists have just discovered a way to give the workhorse transistor a big boost, using a new technique to incorporate vanadium oxide, one of a family of materials called functional oxides, into the device.

The researchers knew that vanadium dioxide, which is just a specific combination of the elements vanadium and oxygen, had an unusual property called the metal-to-insulator transition. In the metal state, electrons move freely, while in the insulator state, electrons cannot flow. This on/off transition, inherent to vanadium dioxide, is also the basis of computer logic and memory.

The researchers had the idea that if they could add vanadium oxide close to the transistor it could boost the transistor’s performance. Likewise, by adding it to the memory cell, it could improve the stability and energy efficiency to read, write and maintain the information state. The major challenge they faced was that vanadium dioxide of sufficiently high quality had never been grown in a thin film form on the scale required to be of use to industry, the so-called wafer scale. Although vanadium dioxide, the targeted compound, looks simple, it is very difficult to synthesize. In order to create a sharp metal-to-insulator transition, the ratio of vanadium to oxygen needs to be precisely controlled. When the ratio is exactly right, the material will show a more than four-order-of-magnitude change in resistance, enough for a sufficiently strong on/off response.

In a paper in the online journal Nature Communications, the Penn State team reports for the first time the growth of thin films of vanadium dioxide on 3-inch sapphire wafers with a perfect 1:2 ratio of vanadium to oxygen across the entire wafer. The material can be used to make hybrid field effect transistors, called hyper-FETs, which could lead to more energy efficient transistors. In a paper published earlier this year, also in Nature Communications, the research group led by Prof. Suman Datta at Penn State showed that the addition of vanadium dioxide provided steep and reversible switching at room temperature, reducing the effects of self-heating and lowering the energy requirements of the transistor.

The implementation of vanadium dioxide can also benefit existing memory technologies, a quest that Penn State researchers are actively pursuing.

DCG Systems (R) today announced the release of the Meridian M (TM) system for isolation of routine and challenging electrical faults at the wafer level. Offering photon emission for transistor-level defects and leakage, and a complete portfolio of static laser stimulation techniques for metallization defects, the Meridian M system is a critical tool to support production use cases in memory and foundry failure analysis (FA) labs. Its high sensitivity, extended-wavelength DBX (TM) optics capture even the most challenging faults, including:

  • Large-area process variation in advanced memory devices that can lead to anomalous leakage;
  • High resistivity wordline to wordline or bitline to bitline shorts within memory cells;
  • Resistive faults in low voltage GPUs and other low-voltage logic circuits;
  • Any weakly emitting faults requiring long integration time.

The Meridian M system also captures electrical faults that emit photons primarily in the thermal range (>1850nm), such as partial opens, high-ohmic shorts and electromigration.

“Static optical fault isolation (OFI) is in a renaissance,” said Praveen Vedagarbha, Ph.D., business unit manager of the Meridian product group at DCG Systems. “While dynamic OFI is important for localizing parametric faults, static OFI is faster and easier to use than its dynamic counterpart because it does not require docking to a tester or having the device and tester knowledge necessary to edit the test program. The speed and ease of use of the Meridian M system are particularly valuable in early yield ramp, when rapid feedback to the process engineering team is critical. ”

Among static-only optical fault isolation systems, Meridian M has demonstrated superior performance in localizing faults with the weakest photon emission. Custom-designed optics, a set of user-selectable wavelength ranges, and the lowest background noise in the industry allow Meridian M to be optimized for a variety of fault types, from conventional “optical” emitters such as excessive leakage, saturation and latch-up faults to longer-wavelength “thermal” emitters, such as high-resistance shorts and dopant displacement errors. Because it accommodates full wafers in addition to packaged die, the Meridian M system allows comparison of good die to bad die, aiding interpretation of complex thermal and photon emission images.

Entegris, Inc., a producer of yield-enhancing materials and solutions for highly advanced manufacturing environments, has expanded its wafer shipper family of products with the SmartStack (R) 300 mm Contactless Horizontal Wafer Shipper (HWS). The SmartStack 300 mm is the industry’s first contactless horizontal wafer shipper capable of holding a full lot of 25 wafers, almost twice the capacity of competitive wafer shippers. Entegris’ design departs from traditional interleaf inserts and foam cushions by using a perimeter support ring to contain wafers inside. The wafers are positioned so that they move in unison, preventing wafer-to-wafer contact and potential damage from impact.

“We designed an ideal solution for shipping and storing 25-lens bumped or thin wafers that offers improved safety over conventional wafer shippers,” said Entegris Product Marketing Manager, Doug Moser. “By placing the wafers on rings and removing the interleaf inserts and foam cushions, the wafers are protected from stains, imprints and scratches typically caused by these inserts. Additionally, the new design accommodates 25 wafers in one shipper, thereby increasing shipping density and lowering shipping cost 50% or more, compared with a conventional FOSB.”

The SmartStack 300 mm is designed to accommodate wafers of varied thickness (150 µm to 1100 µm), for a variety of applications including 3D, 2.5D, SoC, MEMS, LED and power semiconductors. The new design is also available in the 150 mm and 200 mm size. The automation-compatible features of the 300 mm HWS enable ease-of-use and limit manual intervention.

Altatech, a specialty equipment manufacturer for mature and advanced materials deposition and defect inspection, announced today the expansion of its Eclipse series with a new, high-speed inspection system dedicated to ultra-thin, transparent and bonded substrates inspection for 3D applications in power, MEMS, and mobile technologies. The Eclipse TS represents a unique high-reliability and easy-to-implement inspection system solution ready for mass production, in response to the demand for these advanced substrates being driven by the rapidly growing markets in automotive, industrial power and mobile electronics. The Eclipse TS has been qualified for volume manufacturing at a leading-edge semiconductor manufacturer.

“We have built a tool based on a strong IP portfolio with a unique capability to inspect the front side, back side and edge of very thin wafers. This is a cost-effective solution with very good throughput. It places Altatech in a leading position within a very large market opportunity,” said Jean-Luc Delcarri, general manager of Soitec’s Altatech Division.

The Eclipse TS is a high-speed inspection system for measuring very thin and stacked wafers down to 50 microns, Taiko rings, stacked substrates, and silicon-on-glass wafers. The system can conduct front-side, back-side and edge inspection in one pass with no back-side contact and accommodate very high bow and wrap wafers up to 6 mm. In today’s 3D technologies, substrates undergo grinding, stacking and gluing. The Eclipse system is able to monitor these processes. Inspection occurs without any contact on the active surface with a throughout of more than 90 wafers per hour for 300-mm substrates.

Compliant with the latest automation standards, the Eclipse TS offers comprehensive reporting for defects classification and yield maps.

The full Altatech Eclipse series of advanced metrology and holistic inspection systems ensure wafer-surface and edge quality by detecting, counting, and binning defects during the wafer manufacturing process as well as performing continuous outgoing wafer-quality inspection. Proprietary Eclipse sub-modules are designed to detect particles and defects of interest on the front surface and wafer edge of patterned or unpatterned wafers.

Showa Denko (SDK) has developed a new grade of silicon carbide (SiC) epitaxial wafers for power devices with very low defect density. SDK will this month start commercial shipments of the new grade, in two different sizes of four inches (100mm) and six inches (150mm) in diameter, under the trade name of “High-Grade Epi (“HGE”)”.

When compared with the mainstream silicon-based semiconductors, SiC-based power devices can operate under high-temperature, high-voltage, and high-current conditions, while substantially reducing energy loss. These features enable the production of smaller, lighter, and more energy-efficient next-generation power control modules. SiC power devices are already used as power sources of servers for data centers, distributed power supply systems for new energies, and in subway railcars. Demand is expected to grow further as plans have been announced to use SiC power devices in vehicles. Furthermore, efforts are under way to develop SiC-based ultra-high-voltage (10KV class) devices for use in power generation/transmission systems.

Power modules for high-voltage, high-current applications mainly contain devices with the structure of SBD (Schottky barrier diode) and transistors with the structure of MOSFET (metal-oxide-semiconductor field-effect transistor). While SiC is increasingly used in SBD, it is difficult to use SiC in MOSFET. As MOSFET’s oxide film, formed on the surface of an epitaxial wafer, is used in device operations, finer surface defect (SD) and various types of crystal defects, including basal plane dislocation (BPD), considerably affect the yield and product quality.

For automotive applications, meanwhile, large chips measuring around 10mm square are made out of epitaxial wafers. This is because one device needs to handle a current as high as 100A. To prevent deterioration in the production yield of such large chips, the defect density of epitaxial wafers should be controlled within 0.1/cm2.

In the new product, HGE, SDK has succeeded in controlling the number of SD within 0.1/cm2 (one-third the current level of SDK’s conventional product) and of BPD within 0.1/cm2 (one-hundredth or less compared with conventional product). As a result, it is now possible to almost eliminate device defects attributable to BPD (assuming the use of a 10mm square chip). SDK believes that the new product will greatly contribute to the commercialization and market expansion of “full SiC” power modules that combine SiC-SBD and SiC-MOSFET.

Using the HGE technology, SDK has also succeeded in producing SiC epitaxial wafers with film thickness of 100um or more, having low levels of defect density and good uniformity. SDK will start commercial shipments of these SiC epitaxial wafers for use in power generation/transmission systems. The size of the market for SiC epitaxial wafers for power devices is expected to reach 100 billion yen in 2025. SDK will continue its efforts to meet requirements for higher quality, contributing toward expansion of the market.

Yamaichi Electronics presents Test Contactors for lab and reliability applications and ultra fine pitch semiconductor devices.

New semiconductor devices, like wafer level CSPs for mobile applications, have ball pitches of 0.35mm. And there is a trend to shrink towards lower pitches.

For testing such devices, Yamaichi Electronics in Europe (European headquarters in Munich, Bavaria) develops test contactors (TC) within the YED254 and YED274 series. The TC is individually modified and designed for different outline dimensions of the package. Very important is a homogeneous force distribution on the device surface to avoid device cracking.

Through Yamaichi Electronics’ experience in developing test and burn-in sockets, the opening and closing mechanism is released for easy handling. The test contactor is designed with compression mount technology, therefore no soldering is needed. Selected materials like air craft aluminum, PEEK, and ceramic PEEK make the socket robust.

This offers the customer a variety of TCs which can be used in any custom application:

  • Evaluation: the first silicon has been received to verify the functionality
  • HAST/HTOL/ELFR: reliability and stress tests for pre-qualification and during silicon production
  • ESD/Latch-Up Test: performed as part of product qualification
  • Failure Analysis: finding device malfunctions during development, production and field

To fulfill these requirements, Yamaichi Electronics has a portfolio of probe pins. The low inductance probe pin for the 0.35mm pitch has a length in working position of only 1.7mm. All pins have been electrical qualified and the standard data are available on request. This helps to select the best performing pin for our customers’ individual needs.

Invention of the first integrated circularly polarized light detector on a silicon chip opens the door for development of small, portable sensors that could expand the use of polarized light for drug screening, surveillance, optical communications and quantum computing, among other potential applications.

The new detector was developed by a team of Vanderbilt University engineers directed by Assistant Professor of Mechanical Engineering Jason Valentine working with researchers at Ohio University. The work is described in an article published on Sept. 22 in the online journal Nature Communications.

Wei Li, left, and Jason Valentine in the lab. (Anne Rayner / Vanderbilt)

Wei Li, left, and Jason Valentine in the lab. (Anne Rayner / Vanderbilt)

“Although it is largely invisible to human vision, the polarization state of light can provide a lot of valuable information,” said Valentine. “However, the traditional way of detecting it requires several optical elements that are quite bulky and difficult to miniaturize. We have managed to get around this limitation by the use of ‘metamaterials’ — materials engineered to have properties that are not found in nature.”

Polarized light comes in two basic forms: linear and circular. In a ray of unpolarized light, the electrical fields of individual photons are oriented in random directions. In linearly polarized light the fields of all the photons lie in the same plane. In circularly polarized light (CPL), the fields lie in a plane that continuously rotates through 360 degrees. As a result there are two types of circularly polarized light, right-handed and left-handed.

Humans cannot readily distinguish the polarization state of light, but there are a number of other species that possess “p-vision.” These include cuttlefish, mantis shrimp, bees, ants and crickets.

Cuttlefish also produce varying patterns of polarized light on their skin, which has led scientists to hypothesize that they use this as a secret communication channel that neither their predators or prey can detect. This has led to the suggestion that CPL could be used to increase the security of optical communications by including polarized channels that would be invisible to those who don’t have the proper detectors.

Unlike unpolarized light, CPL can detect the difference between right-handed and left-handed versions of molecules. Just like hands and gloves, most biological molecules come in mirror-image pairs. This property is called chirality. For example, cells contain only left-handed amino acids but they metabolize only right-handed sugars (a fact utilized by some artificial sweeteners which use left-hand forms of sugar which taste just as sweet as the right-hand version but which the body cannot convert into fat).

Illustration of how circularly polarized light passes through the silicon chip and is absorbed by the metamaterial. (Valentine Lab / Vanderbilt)

Illustration of how circularly polarized light passes through the silicon chip and is absorbed by the metamaterial. (Valentine Lab / Vanderbilt)

Chirality can be dramatically important in drugs because their biological activity is often related to their handedness. For example, one form of dopamine is effective in the management of Parkinson’s disease while the other form reduces the number of white blood cells. One form of thalidomide alleviates morning sickness while the other causes birth defects. The number of chiral drugs in use today is estimated to be 2,500 and most new drugs under development are chiral.

“Inexpensive CPL detectors could be integrated into the drug production process to provide real time sensing of drugs,” said Vanderbilt University doctoral student Wei Li, who played a key role in designing and testing the device. “Portable detectors could be used to determine drug chirality in hospitals and in the field.”

The metamaterial that the researchers developed to detect polarized light consists of silver nanowires laid down in a sub-microscopic zig-zag pattern on an extremely thin sheet of acrylic fixed to an optically thick silver plate. This metamaterial is attached to the bottom of a silicon wafer with the nanowire side up.

The nanowires generate a cloud of free-flowing electrons that produce “plasmon” density waves that efficiently absorb energy from photons that pass through the silicon wafer. The absorption process creates “hot” or energetic electrons that shoot up into the wafer where they generate a detectable electrical current.

The zig-zag pattern can be made either right-handed or left-handed. When it is right-handed, the surface absorbs right circularly polarized light and reflects left circularly polarized light. When it is left-handed it absorbs left circularly polarized light and reflects right circularly polarized light. By including both right-handed and left-handed surface patterns, the sensor can differentiate between right and left circularly polarized light.

Three images of the same surface demonstrate the new detector's capability. The researchers coated the surface with right- and -left-handed metamaterial in the form of the Vanderbilt logo. The image on the left was taken in plain polarized light. The one in the center was taken with left-handed circularly polarized light. And the image on the right was taken with right-handed circularly polarized light. (Valentine Lab / Vanderbilt)

Three images of the same surface demonstrate the new detector’s capability. The researchers coated the surface with right- and -left-handed metamaterial in the form of the Vanderbilt logo. The image on the left was taken in plain polarized light. The one in the center was taken with left-handed circularly polarized light. And the image on the right was taken with right-handed circularly polarized light. (Valentine Lab / Vanderbilt)

There have been two previous efforts to make solid-state polarized light detectors. According to Li, one used chiral organic materials that are unstable in air, worked only in a narrow range of wavelengths and had a limited power range. Another was based on a more complicated multilayer design that only worked at low temperatures.

“That is the beauty of metamaterials: You can design them to work in the fashion you desire,” said Li.

The efficiency of their prototype is 0.2 percent — too low to be commercially viable. Now that they have proven the viability of their approach, however, they have a number of ideas for how they can boost the efficiency to a level comparable to conventional photodetectors.

The research was supported by National Science Foundation grant CBET-1336455, Office of Naval Research grant N00014-14-1-0475, U.S. Army Research Office grant W911NF-12-1-0407 and the Volkswagen Foundation.