News

Nanocomposite Protects Against Intense Light, Holds Promise for Securing the Safety and Performance of Photonic Assets and Expanding High-Speed Optical Networking Capacity

An international team of researchers has reported a new way to safeguard drones, surveillance cameras and other equipment against laser attacks, which can disable or destroy the equipment. The capability is known as optical limiting.

The work, published in the journal Nature Communication, also describes a superior manner of telecom switching without the use of electronics; instead, they use an all-optical method that could improve the speed and capacity of internet communications. That could remove a roadblock in moving from 4GLTE to 5G networks.

The team reported that a material created using tellurium nanorods – produced by naturally occurring bacteria – is an effective nonlinear optical material, capable of protecting electronic devices against high-intensity bursts of light, including those emitted by inexpensive household lasers targeted at aircraft, drones or other critical systems. The researchers describe the material and its performance as a material of choice for next-generation optoelectronic and photonic devices.

Seamus Curran, a physics professor at the University of Houston and one of the paper’s authors, said while most optical materials are chemically synthesized, using a biologically-based nanomaterial proved less expensive and less toxic. “We found a cheaper, easier, simpler way to manufacture the material,” he said. “We let Mother Nature do it.”

The new findings grew out of earlier work by Curran and his team, working in collaboration with Werner J. Blau of Trinity College Dublin and Ron Oremland with the U.S. Geological Survey. Curran synthesized the nanocomposite used in the work. Collaboration with Prof Wener Blau, School of Physics, Trinity College Dublin and Prof. Hongzhou Zhang, Funded Investigator with AMBER, the SFI Research Centre for Advanced Material and BioEngineering Research, the research made use of unique facilities available at the Advanced Microscopy Laboratory.

The researchers noted that using bacteria to create the nanocrystals suggests an environmentally friendly route of synthesis, while generating impressive results. “Nonlinear optical measurements of this material reveal the strong saturable absorption and nonlinear optical extinctions induced by Mie scattering overbroad temporal and wavelength ranges,” they wrote. “In both cases, Te [tellurium] particles exhibit superior optical nonlinearity compared to graphene.”

Light at very high intensity, such as that emitted by a laser, can have unpredictable polarizing effects on certain materials, Curran said, and physicists have been searching for suitable nonlinear materials that can withstand the effects. One goal, he said, is a material that can effectively reduce the light intensity, allowing for a device to be developed that could prevent damage by that light.

The researchers used the nanocomposite, made up of biologically generated elemental tellurium nanocrystals and a polymer to build an electro-optic switch – an electrical device used to modulate beams of light – that is immune to damage from a laser, he said.

Blau said the biologically generated tellurium nanorods are especially suitable for photonic device applications in the mid-infrared range. “This wavelength region is becoming a hot technological topic as it is useful for biomedical, environmental and security-related sensing, as well as laser processing and for opening up new windows for fiber optical and free-space communications.”

Oremland noted that the current work grew out of 30 years of basic research, stemming from their initial discovery of selenite-respiring bacteria and the fact that the bacteria form discrete packets of elemental selenium. “From there, it was a step down the Periodic Table to learn that the same could be done with tellurium oxyanions,” he said. “The fact that tellurium had potential application in the realm of nanophotonics came as a serendipitous surprise.”

Work will continue to expand the material’s potential for use in all-optical telecom switches, which Curran said is critical in expanding broadband capacity. “We need a massive investment in optical fiber,” he said. “We need greater bandwidth and switching speeds. We need all-optical switches to do that.”

In addition to Curran, Oremland and Blau, researchers involved with the project include Kang-Shyang Liao and Surendra Maharjan, both of UH; Kangpeng Wang, Xiaoyan Zhang, Ivan M. Kislyakov, Ningning Dong, Saifeng Zhang, Gaozhong Wang, Jintai Fan, Long Zhang, Jun Wang, Xiao Zou, Hongzhou Zhang, Juan Du, Yuxin Leng and Quanzhong Zhao, all with the Shanghai Institute of Optics and Fine Mechanics at the Chinese Academy of Sciences; Kan Wu and Jianping Chen, both with Shanghai Jiao Tong University; and Shaun M. Baesman with the U.S. Geological Survey.

Kangpeng Wang has an additional affiliation with the Technion-Israel Institute of Technology and Gaozhong Wang is also affiliated with Trinity College.

Discovery could enable longer lasting and better functioning of devices—including pacemakers, breast implants, biosensors, and drug delivery devices

Researchers with from the National University of Ireland Galway (NUI Galway), Massachusetts Institute of Technology and AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research have today announced a significant breakthrough in soft robotics which could help patients requiring in-situ (implanted) medical devices such as breast implants, pacemakers, neural probes, glucose biosensors and drug and cell delivery devices.

The implantable medical devices market is currently estimated at approximately US$100 billion (2019) with significant growth potential into the future as new technologies for drug delivery and health monitoring are developed. These devices are not without problems, caused in part by the body’s own protection responses. These complex and unpredictable foreign body responses impair device function and drastically limit the long-term performance and therapeutic efficacy of these devices.

One such foreign body response is fibrosis, a process whereby a dense fibrous capsule surrounds the implanted device which can cause device failure or impede its function. Implantable medical devices have various failure rates that can be attributed to fibrosis ranging from 30% to 50% for implantable pacemakers or 30% for mammoplasty prosthetics. In the case of biosensors or drug/ cell delivery devices the dense fibrous capsule which can build up around the implanted device can seriously impede its function, with consequences for the patient and costs to the health care system.

A radical new vision for medical devices to address this problem was published today in the internationally respected journal, Science Robotics. The study was led by researchers from NUI Galway, MIT and the SFI research centre AMBER, among others. The research describes the use of soft robotics to modify the body’s response to implanted devices. Soft robots are flexible devices that can be implanted into the body.

The transatlantic partnership of scientists have created a tiny mechanically actuated soft robotic device known as a dynamic soft reservoir (DSR) that has been shown to significantly reduce the build-up of the fibrous capsule by manipulating the environment at the interface between the device and the body. The device uses mechanical oscillation to modulate how cells respond around the implant. In a bio-inspired design, the DSR can change its shape at a microscope scale through an actuating membrane.

Professor Ellen Roche, senior co-author of the study and Assistant Professor at MIT, and a former researcher at NUI Galway who won international acclaim in 2017 for her work in creating a soft robotic sleeve to help patients with heart failure, said: “This study demonstrates how mechanical perturbations of an implant can modulate the host foreign body response. This has vast potential for a range of clinical applications and will hopefully lead to many future collaborative studies between our teams.”

Professor Garry Duffy, Professor in Anatomy at NUI Galway and AMBER Principal Investigator, and a senior co-author of the study, added: “We feel the ideas described in this paper could transform future medical devices and how they interact with the body. We are very excited to develop this technology further and to partner with people interested in the potential of soft robotics to better integrate devices for longer use and superior patient outcomes. It’s fantastic to build and continue the collaboration with the Dolan and Roche labs, and to develop a trans-Atlantic network of soft roboticists.”

The first author of the study Dr Eimear Dolan, Lecturer of Biomedical Engineering at
NUI Galway and former researcher in the Roche and Duffy labs at MIT and NUI Galway, said: “We are very excited to publish this study as it describes an innovative approach to modulate the foreign body response using soft robotics. I recently received a Science Foundation Ireland Royal Society University Research Fellowship to bring this technology forward with a focus on Type 1 diabetes. It is a privilege to work with such a talented multi-disciplinary team and I look forward to continuing working together.”

To read the full study in Science Robotics, visit: http://robotics.sciencemag.org/lookup/doi/10.1126/scirobotics.aax7043

Dr Jian-Yao Zheng

Peroskovites are a growing family of photovoltaic materials that have created a vast amount of research since their recent discovery. Due to their tunable electronic and optical properties, they are considered state-of-the art materials for solar cell and laser devices. Up to now most work has focused on polycrystalline thin films. A holy grail in this field is the development of ultrathin large-size single crystalline nanosheets which have low defect density and superior properties than their polycrystalline counterparts.

“Looking at silicon as the exemplar material, it is clear that the availability of large single crystals with low point defect and dislocation densities is the key enabler for most of our ICT technologies. For perovskites, we need to have a source of large-area ultrathin materials that are compatible with standard lithography for optoelectronic device production”, says Prof. John Donegan, School of Physics and AMBER principal investigator at the CRANN Institute, Trinity College Dublin, the leader of the semiconductor photonics group and this project.

In spite of prior reports on the fabrication of perovskite nanosheets, the synthetic control over this material is still quite limited compared with other semiconductors. Several methods have been explored to synthesize bulk perovskite single crystals but the thickness is also large, which need further processing for practical device applications. Ultrathin single crystals are also reported but the sizes are less than 1 mm. In this project we have tackled this challenge. The work was carried out under the AMBER industry research programme in the CRANN Institute in Trinity College Dublin in collaboration with the Thermal Management Research Group, of Nokia Bell Labs.

“In an attempt to make PbBr2 nanowires, we unintentionally obtained these shiny crystals in solution at room temperature. When we drop-cast these nanosheets and measured the thickness of them, to our surprise, they are only 100 nm or less in thickness, however, the lateral size can go up to millimeter in the first try”, says Jian-Yao Zheng, the first author of the paper and former postdoctoral researcher at AMBER and the CRANN Institute. “In order to get centimeter-size nanosheets, we carefully controlled the concentration and the temperature of the system, then you can see the growth of large colorful nanosheets. The growth occurred at very low temperature (about 40 ℃), the solution can be heated up in an oven or by an infrared lamp. Therefore, we can observe the in-situ growth of crystals in real time under an optical microscope”.

The growth of nanosheets is highly anisotropic, with an aspect ratio reaching 100,000. In collaborating with Prof. Stefano Sanvito, the director of CRANN as well as the expert in molecular dynamics theory, we find very different formation energy of different crystal facets can lead to the preferential two dimensional growth, resulting in the formation of nanosheets. It is noteworthy that (1) the preparation is low-cost, fast, with environment friendly with simple solvents (ethanol and acetone) and all the chemicals can be recycled, we don’t need bulky equipment such as chemical vapor deposition (CVD) system; (2) The as-prepared crystals are free-standing and are found floating in the solvent, you can scoop them up easily onto any substrate. These lead halide nanosheets are much more stable than perovskite materials which are sensitive to heat, moisture, and oxygen. Lead halide is immune to these environmental factors and can be stored for a long time without degradation. They can be converted to perovskite whenever necessary to incorporate into optoelectronic devices.

These PbBr2 nanosheets are single crystalline. However, following the conversion to perovskite, we cannot be sure about the crystalline nature of the converted material. We do not have convincing evidence that the materials remain as a single crystal. This still needs much more rigorous experimental work. X-ray diffraction (XRD) results show clear and sharp peaks with both lead halide and perovskite nanosheets. We did transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) characterization on these converted nanosheets. The perovskite nanosheets are not stable on exposure to the electron beam, they suffer from the degradation, therefore, we are still not quite sure if our nanosheets are single-crystalline before exposing them to the intense electron beam. Further effort can be made on either improving the conversion process or the extensive study of the crystal nature of these samples after conversion.

Once fabricated, we are very interested in the nanolasers and photodetectors made from these nanoscale perovskite materials. By utilizing focused ion beam (FIB) milling in our Advanced Microscopy Laboratory (AML), we are able to make nice patterns and arrays out from these large nanosheets. Dr. Hugh G. Manning and Prof. John J. Boland of AMBER and the CRANN Institute, assisted with the characterization of photoconducting behavior of these samples. All of these devices are working with 100% device yield, indicating the high quality of the perovskite materials.

Last but not least, can we make even larger nanosheets? The answer is yes. Firstly, the precursors should be continuously supplied during the growth. Secondly, the solvent (acetone and ethanol) is volatile and suffer from the loss during the synthesis, resulting in the change of concentration of precursor, which is very important to control the growth equilibrium. An improved apparatus will facilitate the growth of nanosheets up to wafer-scale while the thickness remains at nanoscale, which should be extremely interesting both in fundamental and practical sense and offer a novel, facile and scalable strategy to make perovskite optoelectronic devices, this is our ambitious hypothesis and we hope it will be realized in the near future.


Figure: The PbBr2 nanosheets form easily in solution and grow over time to be 1 cm or more in diameter and less than 100 nm in thickness. Both photodiode and laser devices were fabricated once the PbBr2 was converted to perovskite materials.

Research presents a predictive model which can enable a material-by-design approach for nanowire networks

Researchers at AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research hosted at Trinity College Dublin, in collaboration with University of Calgary, have developed the first fully predictive model of both the electrical and optical performances of any metal nanowire network. The model, which has been experimentally verified, will enable researchers to quickly benchmark the performance of their materials facilitating a much sought after material-by-design approach. This important breakthrough pushes forward the potential for metallic nanowire networks to meet the needs of next-generation device technologies that require flexible transparent conductors – such as touch screen, display, lighting and solar cells.

The research presents a model which opens new avenues to develop materials for applications requiring transparent conductive (TC) properties beyond the current market leading material ITO (indium tin oxide). ITO, which is found in most touch screen devices, has drawbacks in terms of flexibility, being brittle, coupled with the scarcity of indium and the high cost of the ITO film deposition. In addition to smart phones and other touch screens, transparent conductors are used in modern photovoltaics, light-emitting devices and thin-film heaters. Nanowire networks are well suited as replacements for ITO in a wide variety of current and emerging flexible TC applications. Silver nanowire networks (Ag NWNs), for example, offer a promising alternative as it matches the electro-optical performance of ITO, and can also fulfil the demands for the emerging flexible electronics market, next-generation flexible solar cells, touch screens, displays, thin-film heaters, wearables and anti-static coatings that require flexible electro-optical components.

The development of a predictive model for NWNs is an important step towards a materials-by-design approach for TC applications. The results of this work show that simulation of NWNs can be used as a tool in benchmarking the effectiveness of post-deposition processing methods to be evaluated, potentially improving the efficacies of post-processing methods, and offers a strategic approach to exploring the potential applications of NWN materials guiding the synthesis of systems for specific needs.

The research, published in Scientific Reports*, was a collaboration between Professors John Boland and Mauro Ferreira, AMBER researchers in Trinity’s Schools of Chemistry and Physics, Dr Hugh Manning (lead author) and Dr Claudia Gomes da Rocha at University of Calgary, Canada. This research builds upon previously published work in ACS Nano Nanoscale and Physical Chemistry Chemical Physics.

Lead author of the paper, Dr. Hugh Manning, AMBER and Trinity’s School of Chemistry, said, “There is enormous interest in the development of high performing transparent conductors for a wide variety of applications. Nanowire networks are amongst the leading competitors to the currently used material ITO (indium tin oxide), and also meet the growing industry needs for mechanical flexibility. The key bottleneck in mainstreaming nanowire technologies lies in the need for high optical transparency in balance with low sheet resistance – or essentially maintaining the highly conductive and transparent nature of current transparent conductors, such as ITO, which is found in smart phones for example. The model we have developed can help researchers optimise nanowire networks for various applications by assessing the effectiveness of processing steps taken to improve network performance. Different technologies such as touch screens, lighting, or solar cells require different levels of performance, through material selection and carefully chosen processing steps you can tune the electrical performance of the nanowires to suit the application; this model can help guide that fine tuning.

Prof John Boland, AMBER and Trinity’s School of Chemistry, said, “Nanowire networks offer promising architectures for next generation flexible, transparent devices due to their electrical and optical properties. The model our team has developed has the potential to reduce the lag time from bench to finalised device for specific applications utilising nanowire networks. We envisage the next phase of our research is to expand the model to work with different type of metal nanowires, providing opportunities to further refine the model and its effectiveness, and enhance our understanding of these networks

This publication has emanated from research supported by Science Foundation Ireland (SFI) AMBER Centre under Grant Number SFI/12/RC/2278 and PI grant 16/IA/4462 and the European Research Council under Advanced Grant 321160.