Category Archives: Applications

Researchers at the University of California, Riverside Bourns College of Engineering and the Russian Academy of Sciences have successfully demonstrated pattern recognition using a magnonic holographic memory device, a development that could greatly improve speech and image recognition hardware.

Pattern recognition focuses on finding patterns and regularities in data. The uniqueness of the demonstrated work is that the input patterns are encoded into the phases of the input spin waves.

Clockwise are: photo of the prototype device; schematic of the eight-terminal magnonic holographic memory prototype; and a collection of experimental data obtained for two magnonic matrixes. Credit: UC Riverside

Clockwise are: photo of the prototype device; schematic of the eight-terminal magnonic holographic memory prototype; and a collection of experimental data obtained for two magnonic matrixes.
Credit: UC Riverside

Spin waves are collective oscillations of spins in magnetic materials. Spin wave devices are advantageous over their optical counterparts because they are more scalable due to a shorter wavelength. Also, spin wave devices are compatible with conventional electronic devices and can be integrated within a chip.

The researchers built a prototype eight-terminal device consisting of a magnetic matrix with micro-antennas to excite and detect the spin waves. Experimental data they collected for several magnonic matrixes show unique output signatures correspond to specific phase patterns. The microantennas allow the researchers to generate and recognize any input phase pattern, a big advantage over existing practices.

Then spin waves propagate through the magnetic matrix and interfere. Some of the input phase patterns produce high output voltage, and other combinations results in a low output voltage, where “high” and “low” are defined regarding the reference voltage (i.e. output is high if the output voltage is higher than 1 millivolt, and low if the voltage is less than 1 millivolt.

It takes about 100 nanoseconds for recognition, which is the time required for spin waves to propagate and to create the interference pattern.

The most appealing property of this approach is that all of the input ports operate in parallel. It takes the same amount of time to recognize patterns (numbers) from 0 to 999, and from 0 to 10,000,000. Potentially, magnonic holographic devices can be fundamentally more efficient than conventional digital circuits.

The work builds upon findings published last year by the researchers, who showed a 2-bit magnonic holographic memory device can recognize the internal magnetic memory states via spin wave superposition. That work was recognized as a top 10 physics breakthrough by Physics World magazine.

“We were excited by that recognition, but the latest research takes this to a new level,” said Alex Khitun, a research professor at UC Riverside, who is the lead researcher on the project. “Now, the device works not only as a memory but also a logic element.”

The latest findings were published in a paper called “Pattern recognition with magnonic holographic memory device” in the journal Applied Physics Letters. In addition to Khitun, authors are Frederick Gertz, a graduate student who works with Khitun at UC Riverside, and A. Kozhevnikov, Y. Filimonov and G. Dudko, all from the Russian Academy of Sciences.

Holography is a technique based on the wave nature of light which allows the use of wave interference between the object beam and the coherent background. It is commonly associated with images being made from light, such as on driver’s licenses or paper currency. However, this is only a narrow field of holography.

Holography has been also recognized as a future data storing technology with unprecedented data storage capacity and ability to write and read a large number of data in a highly parallel manner.

The main challenge associated with magnonic holographic memory is the scaling of the operational wavelength, which requires the development of sub-micrometer scale elements for spin wave generation and detection.

By combining 3D holographic lithography and 2D photolithography, researchers from the University of Illinois at Urbana-Champaign have demonstrated a high-performance 3D microbattery suitable for large-scale on-chip integration with microelectronic devices.

“This 3D microbattery has exceptional performance and scalability, and we think it will be of importance for many applications,” explained Paul Braun, a professor of materials science and engineering at Illinois. “Micro-scale devices typically utilize power supplied off-chip because of difficulties in miniaturizing energy storage technologies. A miniaturized high-energy and high-power on-chip battery would be highly desirable for applications including autonomous microscale actuators, distributed wireless sensors and transmitters, monitors, and portable and implantable medical devices.”

CREDIT: University of Illinois

CREDIT: University of Illinois

“Due to the complexity of 3D electrodes, it is generally difficult to realize such batteries, let alone the possibility of on-chip integration and scaling. In this project, we developed an effective method to make high-performance 3D lithium-ion microbatteries using processes that are highly compatible with the fabrication of microelectronics,” stated Hailong Ning, a graduate student in the Department of Materials Science and Engineering and first author of the article, “Holographic Patterning of High Performance on-chip 3D Lithium-ion Microbatteries,” appearing in Proceedings of the National Academy of Sciences.

“We utilized 3D holographic lithography to define the interior structure of electrodes and 2D photolithography to create the desired electrode shape.” Ning added. “This work merges important concepts in fabrication, characterization, and modeling, showing that the energy and power of the microbattery are strongly related to the structural parameters of the electrodes such as size, shape, surface area, porosity, and tortuosity. A significant strength of this new method is that these parameters can be easily controlled during lithography steps, which offers unique flexibility for designing next-generation on-chip energy storage devices.”

Enabled by a 3D holographic patterning technique–where multiple optical beams interfere inside the photoresist creating a desirable 3D structure–the battery possesses well-defined, periodically structured porous electrodes, that facilitates the fast transports of electrons and ions inside the battery, offering supercapacitor-like power.

“Although accurate control on the interfering optical beams is required to construct 3D holographic lithography, recent advances have significantly simplified the required optics, enabling creation of structures via a single incident beam and standard photoresist processing. This makes it highly scalable and compatible with microfabrication,” stated John Rogers, a professor of materials science and engineering, who has worked with Braun and his team to develop the technology.

“Micro-engineered battery architectures, combined with high energy material such as tin, offer exciting new battery features including high energy capacity and good cycle lives, which provide the ability to power practical devices,” stated William King, a professor of mechanical science and engineering, who is a co-author of this work.

To date, chip-based retinal implants have only permitted a rudimentary restoration of vision. However, modifying the electrical signals emitted by the implants could change that. This is the conclusion of the initial published findings of a project sponsored by the Austrian Science Fund FWF, which showed that two specific retinal cell types respond differently to certain electrical signals – an effect that could improve the perception of light-dark contrasts.

“Making the blind really see – that will take some time,” says Frank Rattay of the Institute of Analysis and Scientific Computing at the Vienna University of Technology – TU Wien. “But in the case of certain diseases of the eyes, it is already possible to restore vision, albeit still highly impaired, by means of retinal implants.”

Pulse emitter

To achieve this, microchips implanted in the eye convert light signals into electrical pulses, which then stimulate the cells of the retina. One major problem with this approach is that the various types of cells that respond differently to light stimuli in a healthy eye are all stimulated to the same degree. This greatly reduces the perception of contrast.

“But it might be possible,” Rattay says, “to stimulate one cell type more than the other by means of special electrical pulses, thus enhancing the perception of contrast.”

Within the framework of an FWF project, he and his team have discovered some promising approaches. Together with colleagues Shelley Fried of Harvard Medical School and Eberhard Zrenner of University Hospital Tübingen, he is now corroborating the simulated results with experimental findings.

Simulated & stimulated

With the help of a sophisticated computer simulation of two retinal cell types, Rattay and his team have discovered something very exciting. They found that by selecting specific electrical pulses, different biophysical processes can actually be activated in the two cell types. For example, monophasic stimulation, where the electrical polarity of the signal from the retinal implant does not change, leads to stronger depolarisation in one cell type than in the other.

“Depolarization means that the negative charge that prevails in cells switches briefly to a positive charge. This is the mechanism by which signals are propagated along nerves,” Rattay explains. This charge reversal was significantly weaker in the other cell type. In their simulation, the team also found as much as a fourfold difference in the response of calcium concentrations in the two cell types to a monophasic signal.

On and off

“Calcium is an important signal molecule in many cells and plays a key role in information processing. For this reason, we specifically considered calcium concentrations in our simulation by considering the activity of membrane proteins involved in calcium transport,” explains Paul Werginz, a colleague of Rattay and lead author of the recently published paper.

Concretely, the team devised models of two retinal cell types that are designated as ON and OFF cells. ON cells react more strongly when the light is brighter at the centre of their location, while OFF cells react more strongly when the light is more intense at the edges. The two cell types are arranged in the retina in such a way as to greatly enhance contrast. The problem is that instead of light pulses, conventional retinal implants emit electrical pulses that elicit the same biochemical reactions in both cell types. Consequently, contrast perception is greatly reduced. However, Rattay’s work shows that this needn’t be the case.

Shape as a factor

Rattay’s research group also found that the shape of the individual ON and OFF cells affect the way in which the signals are processed. For example, the different length of the two cell types is an important factor. This too, Rattay believes, could be an important finding that might help to significantly improve the performance of future retinal implants by modulating the electrical signals they emit. Rattay and his team are in hot pursuit of this goal in order to develop strategies that will allow many blind people to recognise objects visually.

Frank Rattay is a professor at the Institute of Analysis and Scientific Computing of the Vienna University of Technology, where he heads the Computational Neuroscience and Biomedical Engineering group. For decades he has been publishing internationally recognised work on the generation and optimisation of artificial nerve signals.

SEMI has announced that executives from MEMS giants Bosch and STMicroelectronics, MEMS largest fabless Invensense and dominating IC foundry TSMC will be delivering the keynote talks at the European MEMS Summit (Sept 17-18, 2015 – Milan, Italy).

For the first installment of SEMI’s European MEMS Summit, themed “Sensing the Planet, MEMS for Life,” Stefan Finkbeiner, GM and CEO of Bosch Sensortec, Benedetto Vigna, Executive VP and General Manager of the Analog, MEMS & Sensors group of STMicroelectronics, Behrooz Abdi, CEO and President of Invensense, and Maria Marced, President of TSMC Europe will join SEMI to share their vision of the current challenges facing the MEMS industry and their recipes for success. With these headliners, SEMI’s European MEMS Summit promises to be a powerhouse of MEMS experts, both from a technological standpoint and from a business standpoint.

“We are very excited to offer attendees a high-profile collection of international speakers for this first edition of our European MEMS Summit,” commented Yann Guillou, business development manager at SEMI. “Elaborated with the support of industry representatives, we have made an effort to address the most crucial industry issues with the belief that this conference program will be a positive contribution to the MEMS industry and will help MEMS actors collectively shape their industry’s progress. Above all, our hope is that attendees will leave the Summit with a better understanding of the crucial technological and business challenges faced by the MEMS value chain as well as an idea of the solutions that are being proposed today to address those problems.”

The Summit’s conference will bring together a diversity of high caliber MEMS technology experts, including representatives of ARM, ASE Group, CEA-Leti, Freescale, IHS, Infineon, SITRI, Tronics Microsystems, X-FAB, Yole Développement and more. The event will insist on the importance of understanding the dynamics of the marketplace in perpetuating a global comprehension of the evolution of MEMS. Speakers will provide their outlooks on the MEMS market, their expectations for future marketplace trends and their assessment of the changes in business models, the supply chain, and the ecosystem. One full day of the event will be dedicated to “Applications” to give attendees a more global vision of how MEMS are being applied in the automotive, consumer electronics, wearable and industrial sector as well as the importance of MEMS in the growth of the Internet of Things. Despite a strong focus on business-related aspects, technology will not be forgotten; speakers will address topics such as new detection principles, innovation in materials, new packaging solutions, MEMS on 300mm wafers and more.

The Summit will be held at the grandiose Palazzo Lombardia, in Milan, Italy. At the heart of the Palazzo and in complement to the conference, SEMI will organize a MEMS Exhibition, giving companies with MEMS activities a chance to reach out to other participants who are coming from the same sector. The European MEMS Summit will include numerous networking opportunities – a gala dinner, a networking cocktail hour and numerous coffee and lunch breaks.

For any question regarding the event, contact Yann Guillou from SEMI ([email protected]).

Stiff competition in sensors for high-volume design wins and a recovery in actuator growth shuffled the ranking of suppliers in the $9.2 billion market for sensors and actuators in 2014, according to IC Insights’ new 2015 O-S-D Report—A Market Analysis and Forecast for Optoelectronics, Sensors/Actuators, and Discretes. The new O-S-D Report says the overall trend in sensors and actuators is for the largest suppliers to keep getting bigger, gaining marketshare because more high-volume applications—such as smartphones and the huge potential of the Internet of Things (IoT)—and automotive systems require well-established track records for quality, long-term reliability, and on-time delivery of semiconductors.

Sensor leader Robert Bosch in Germany extended its lead in this market with a 16 percent sales increase in 2014 to nearly $1.2 billion. The German company became the first sensor maker to reach $1.0 billion in 2013 when its sales climbed 29 percent, reflecting continued strong growth in its automotive base and expansion into high-volume consumer and mobile applications. Bosch’s marketshare in sensor-only sales grew to 20 percent in 2014 from 18 percent in 2013 and 15 percent in 2012, according to the 10th edition of IC Insights’ annual O-S-D Report.

Meanwhile, STMicroelectronics saw its sensor/actuator sales volume fall 19 percent in 2014 to $630 million, which caused it to drop to fourth place among the market’s top suppliers from second in 2013. ST’s drop was partly caused by marketshare gains by Bosch and U.S.-based InvenSense, which climbed from 14th in 2013 to ninth in the 2014 sensor/actuator ranking with a 33 percent increase in sensor sales to $332 million last year. Bosch and InvenSense sensors—which are made with microelectromechanical systems (MEMS) technology—have knocked ST’s MEMS-based sensors from a number of high-volume smartphones, including Apple’s newest iPhone handsets.

ST’s drop in sensor revenues and modest sales increases in MEMS-based actuators at Texas Instruments (micro-mirror devices for digital projectors and displays) and Hewlett-Packard (mostly inkjet-printer nozzle devices) moved TI and HP up one position in IC Insights’ 2014 ranking to second and third place, respectively (as shown in Figure 1). Infineon remained in fifth place in the sensors/actuator ranking with an 8 percent sales increase to $520 million last year. The 2015 O-S-D Report provides top 10 rankings of suppliers in sensors/actuators, optoelectronics, and discrete semiconductors in addition to a top 30 O-S-D list of companies, based on combined revenue in optoelectronics, sensors/actuators and discretes.

Figure 1

Figure 1

The new O-S-D Report forecasts worldwide sensor sales to increase 7 percent in 2015 to reach a record-high $6.1 billion after growing 5 percent in 2014 to $5.7 billion and rising just 3 percent in 2013.  Total actuator sales are expected to increase 7 percent in 2015 to $3.7 billion, which will tie the record high set in 2011. Actuator sales fell 10 percent in 2012 and dropped another 4 percent in 2013 before recovering in 2014 with a 7 percent increase to $3.5 billion.  MEMS technology was used in about 34 percent of the 11.1 billion sensors shipped in 2014 and essentially all of the 999 million actuators sold last year, based on an analysis in the new O-S-D Report.  Tiny MEMS structures are used in these devices to perform transducer functions (i.e., detecting and measuring changes around sensors for inputs in electronic systems, and initiating physical actions in actuators from electronic signals).

Researchers from the Georgia Institute of Technology have developed a novel cellular sensing platform that promises to expand the use of semiconductor technology in the development of next-generation bioscience and biotech applications.

The research is part of the Semiconductor Synthetic Biology (SSB) program sponsored and managed by Semiconductor Research Corporation (SRC). Launched in 2013, the SSB program concentrates on synergies between synthetic biology and semiconductor technology that can foster exploratory, multi-disciplinary, longer-term university research leading to novel, breakthrough solutions for a wide range of industries.

The Georgia Tech research proposes and demonstrates the world’s first multi-modality cellular sensor arranged in a standard low-cost CMOS process. Each sensor pixel can concurrently monitor multiple different physiological parameters of the same cell and tissue samples to achieve holistic and real-time physiological characterizations.

“Our research is intended to fundamentally revolutionize how biologists and bioengineers can interface with living cells and tissues and obtain useful information,” said Hua Wang, an assistant professor in the School of Electrical and Computer Engineering (ECE) at Georgia Tech. “Fully understanding the physiological behaviors of living cells or tissues is a prerequisite to further advance the frontiers of bioscience and biotechnology.”

Wang explains that the Georgia Tech research can have positive impact on semiconductors being used in the development of healthcare applications including the more cost-effective development of pharmaceuticals and point-of-care devices and low-cost home-based diagnostics and drug testing systems. The research could also benefit defense and environmental monitoring applications for low-cost field-deployable sensors for hazard detections.

Specifically, in the case of the more cost-effective development of pharmaceuticals, the increasing cost of new medicine is largely due to the high risks involved in the drug development. As a major sector of the healthcare market, the global pharmaceutical industry is expected to reach more than $1.2 trillion this year. However, on average, only one out of every ten thousand tested chemical compounds eventually become an approved drug product.

In the early phases of drug development (when thousands of chemical candidates are screened), in vitro cultured cells and tissues are widely used to identify and quantify the efficacy and potency of drug candidates by recording their cellular physiology responses to the tested compounds, according to the research.

Moreover, patient-to-patient variations often exist even under the administration of the same type of drugs at the same dosage. If the cell samples are derived from a particular patient, patient-specific drug responses then can be tested, which opens the door to future personalized medicine.

“Therefore, there is a tremendous need for low-cost sensing platforms to perform fast, efficient and massively parallel screening of in vitro cells and tissues, so that the promising chemical candidates can be selected efficiently,” said Wang, who also holds the Demetrius T. Paris Junior Professorship in the Georgia Tech School of ECE. “This existing need can be addressed directly by our CMOS multi-modality cellular sensor array research.”

Among the benefits enabled by the CMOS sensor array chips are that they provide built-in computation circuits for in-situ signal processing and sensor fusion on multi-modality sensor data. The chips also eliminate the need of external electronic equipment and allow their use in general biology labs without dedicated electronic or optical setups.

Additionally, thousands of sensor array chips can operate in parallel to achieve high-throughput scanning of chemicals or drug candidates and real-time monitoring of their efficacy and toxicity. Compared with sequential scanning through limited fluorescent scanners, this parallel scanning approach can achieve more than 1,000 times throughput enhancement.

The Georgia Tech research team just wrapped its first year of research under the 3-year project, with the sensor array being demonstrated at the close of 2014 and presented at the IEEE International Solid-State Circuits Conference (ISSCC) in February 2015. In the next year, the team plans to further increase the sensor array pixel density while helping improve packaging solutions compatible with existing drug testing solutions. 

“Georgia Tech’s research combines semiconductor integrated circuits and living cells to create an electronics-biology hybrid platform, which has tremendous societal and technological implications that can potentially lead to better and cheaper healthcare solutions,” said Victor Zhirnov, director of Cross-Disciplinary Research and Special Projects at SRC.

Nanoelectronics research center imec, today reported the financial results for fiscal year ended December 31, 2014. Revenue for 2014 totaled 363 million euros, a 9 percent growth from the previous year.

The fiscal year end total includes the revenue generated through R&D contracts from international partners, collaborations with universities worldwide and funds from European research initiatives. The annual revenue figure also covers a yearly grant from the Flemish government totaling 48.8 million euro in 2014, and a 4.1 million euro grant from the Dutch government to support the Holst Centre, a research center setup by imec and TNO.

“I am extremely proud that 2014, our 30th anniversary year, concludes as one of our strongest years ever,” said Luc Van den hove, president and CEO at imec. “We reported strong financial growth, announced new collaborations and inspiring innovations. We filed a record number of patents, achieved notable industry awards and published prominent scientific papers—all a testament to our commitment to innovate. Moreover, we also added significant talent to our already impressive roster of researchers, growing to a total of 2,188 employees by the end of 2014.”

“Looking to the future, together with our partners, we are committed to overcome the next challenges. First, we work to enable the fabrication of sub-10nm technology. With further scaling, new lithography techniques and new materials, and based on CMOS technology, we’ll be busy doing that for another number of years. But we have also started looking for materials and techniques for the post-CMOS era. There are many alternatives, and it is our task to see which of these can be scaled to a technology that can be mass-produced. Next to that, we help our partners with technologies for the sustainable and smart applications of the Internet-of-Things, Internet-of-Energy, and Internet-of-Health. It is expected that 2015 will be an important year for the breakthrough of these systems. A breakthrough that will be positive for the whole semiconductor industry;” continued Luc Van den hove. “This groundbreaking research requires ever more talent. That’s why today we have over 100 vacancies for a variety of profiles. Vacancies for people who have the ambition to contribute to the technologies for a sustainable future.”

2014 Organizational Highlights:

  • As an international scientific hub, 71 nationalities are now represented at imec, a multicultural environment, attracting top global talent
  • 950 peer-reviewed papers and conference presentations were published
  • ·         Imec and the organization’s researchers received 34 awards. Amongst them, imec took home the CS Industry R&D Award 2014, recognizing success and progression along the entire value chain of the semiconductor industry, for its outstanding work on III/V FinFET devices. Imec also received the PRoF Award for Research 2014, acknowledging the application of imec’s nanotechnology research and development in the healthcare domain. In July 2014, imec was awarded by the European Commission with the HR excellence in Research label, a recognition of imec’s human resource policy to create the best possible employment and working conditions for researchers 
  • With a record of 143 filed patents, imec was the leading Belgian applicant of European patents in 2014. In the past years, imec has increased its investment in building a patent portfolio to support its R&D offering and to form a solid base for more application oriented activities. Imec’s patent portfolio also leverages the patent portfolio of Flemish Academia with which the organization collaborates
  • Two new spin-offs were launched in 2014—Luceda Photonics, active in photonics design, and Bloom Technologies, focusing on wearable health monitoring for expectant mothers
  • To house its growing talent base, imec opened a new office building, as it aims to expand further across its R&D focuses. Additionally, the center also started building a new cleanroom that adheres to the very latest standards with a significant footprint for the most advanced semiconductor tools. The new cleanroom will enable the organization to remain at the forefront of nanoelectronics research and development, offering a neutral platform where all the key players from the semiconductor value chain closely collaborate to advance the next generation technology nodes and advancing industrial innovation
  • Imec IC-link is imec’s industrial arm offering SMEs, universities and research institutes access to advanced foundry technologies, assembly, test, and place and route services. With a customer base of more than 300 SMEs and 700 universities and research institutes (through Europractice service), IC-link tapes-out an average of 500 designs per year

SIGFOX and Texas Instruments (TI) announced the two companies are working together to increase IoT deployments using the Sub-1 GHz spectrum. Customers can use the SIGFOX network with TI’s Sub-1 GHz RF transceivers to deploy wireless sensor nodes that are lower cost and lower power than 3G/cellular connected nodes, while providing long-range connectivity to the IoT.

Targeting a wide variety of end-user applications, including environmental sensors, smart meters, agriculture and livestock sensors, asset tracking and smart cities, the SIGFOX and TI collaboration maximizes the many benefits of narrowband radio technology and reduces barriers to entry for manufacturers wanting to connect their products to the cloud. Using the SIGFOX infrastructure reduces the cost and effort to get sensor data to the cloud and TI’s Sub-1 GHz technology provides years of battery life for less maintenance and up to 100 km range.

“TI’s Sub-1 GHz technology is an excellent fit for the SIGFOX network, because it supports long-range and high-capacity connectivity in a system-cost-optimized way that users everywhere require to fully benefit from the potential of the Internet of Things,” said Stuart Lodge, executive vice president of global sales at SIGFOX. “TI technology that leverages our ultra-narrowband technology is a powerful endorsement and will be a key part of our rapid network deployment in key global markets.”

SIGFOX’s two-way network is based on an ultra-narrowband (UNB) radio technology for connecting devices, which is key to providing a scalable, high-capacity network with very low energy consumption and unmatched spectral efficiency. That is essential in a network that will handle billions of messages daily.

“Narrowband technology is the superior option for a global Internet of Things network, because it offers the lowest-cost, most energy-efficient connectivity, along with the data capacity and robust coexistence, that competing technologies just cannot match,” said Oyvind Birkenes, general manager, Wireless Connectivity Solutions, TI. “We are excited to be working with SIGFOX to expand their network deployments and bring the benefits of narrowband Sub-1 GHz technology to users worldwide.”

TI’s CC1120 Sub-1 GHz RF transceiver uses narrowband technology to deliver the longest-range connectivity and superior coexistence to SIGFOX’s network with strong tolerance of interference. Narrowband is the de-facto standard for long-range communication due to the high spectral efficiency, which is critical to support the projected high growth of connected IoT applications. The CC1120 RF transceiver also provides years of battery lifetime for a sensor node, which reduces maintenance and lowers the cost of ownership for end users.

From mobile phones and computers to television, cinema and wearable devices, the display of full color, wide-angle, 3D holographic images is moving ever closer to fruition, thanks to international research featuring Griffith University.

Led by Melbourne’s Swinburne University of Technology and including Dr Qin Li, from the Queensland Micro- and Nanotechnology Center within Griffith’s School of Engineering, scientists have capitalised on the exceptional properties of graphene and are confident of applications in fields such as optical data storage, information processing and imaging.

“While there is still work to be done, the prospect is of 3D images seemingly leaping out of the screens, thus promising a total immersion of real and virtual worlds without the need for cumbersome accessories such as 3D glasses,” says Dr Li.

First isolated in the laboratory about a decade ago, graphene is pure carbon and one of the thinnest, lightest and strongest materials known to humankind. A supreme conductor of electricity and heat, much has been written about its mechanical, electronic, thermal and optical properties.

“Graphene offers unprecedented prospects for developing flat displaying systems based on the intensity imitation within screens,” says Dr Li, who conducted carbon structure analysis for the research.

“Our consortium, which also includes China’s Beijing Institute of Technology and Tsinghua University, has shown that patterns of photo-reduced graphene oxide (rGO) that are directly written by laser beam can produce wide-angle and full-colour 3D images.

“This was achieved through the discovery that a single femtosecond (fs) laser pulse can reduce graphene oxide to rGO with a sub-wavelength-scale feature size and significantly differed refractive index.

“Furthermore, the spectrally flat optical index modulation in rGOs enables wavelength-multiplexed holograms for full colour images.”

Researchers say the sub-wavelength feature is particularly important because it allows for static holographic 3D images with a wide viewing angle up to 52 degrees.

Such laser-direct writing of sub-wavelength rGO featured in dots and lines could revolutionise capabilities across a range of optical and electronic devices, formats and industry sectors.

“The generation of multi-level modulations in the refractive index of GOs, and which do not require any solvents or post-processing, holds the potential for in-situ fabrication of rGO-based electro-optic devices,” says Dr Li.

“The use of graphene also relieves pressure on the world’s dwindling supplies of indium, the metallic element that has been commonly used for electronic devices.

“Other technologies are being developed in this area, but rGO looks by far the most promising and most practical, particularly for wearable devices. The prospects are quite thrilling.”

The ability of materials to conduct heat is a concept that we are all familiar with from everyday life. The modern story of thermal transport dates back to 1822 when the brilliant French physicist Jean-Baptiste Joseph Fourier published his book “Théorie analytique de la chaleur” (The Analytic Theory of Heat), which became a corner stone of heat transport. He pointed out that the thermal conductivity, i.e., ratio of the heat flux to the temperature gradient is an intrinsic property of the material itself.

The advent of nanotechnology, where the rules of classical physics gradually fail as the dimensions shrink, is challenging Fourier’s theory of heat in several ways. A paper published in ACS Nano and led by researchers from the Max Planck Institute for Polymer Research (Germany), the Catalan Institute of Nanoscience and Nanotechnology (ICN2) at the campus of the Universitat Autònoma de Barcelona (UAB) (Spain) and the VTT Technical Research Centre of Finland (Finland) describes how the nanometre-scale topology and the chemical composition of the surface control the thermal conductivity of ultrathin silicon membranes. The work was funded by the European Project Membrane-based phonon engineering for energy harvesting (MERGING).

The results show that the thermal conductivity of silicon membranes thinner than 10 nm is 25 times lower than that of bulk crystalline silicon and is controlled to a large extent by the structure and the chemical composition of their surface. Combining state-of-the-art realistic atomistic modelling, sophisticated fabrication techniques, new measurement approaches and state-of-the-art parameter-free modelling, researchers unravelled the role of surface oxidation in determining the scattering of quantized lattice vibrations (phonons), which are the main heat carriers in silicon.

Both experiments and modelling showed that removing the native oxide improves the thermal conductivity of silicon nanostructures by almost a factor of two, while successive partial re-oxidation lowers it again. Large-scale molecular dynamics simulations with up to 1,000,000 atoms allowed the researchers to quantify the relative contributions to the reduction of the thermal conductivity arising from the presence of native SiO2 and from the dimensionality reduction evaluated for a model with perfectly specular surfaces.

Silicon is the material of choice for almost all electronic-related applications, where characteristic dimensions below 10nm have been reached, e.g. in FinFET transistors, and heat dissipation control becomes essential for their optimum performance. While the lowering of thermal conductivity induced by oxide layers is detrimental to heat spread in nanoelectronic devices, it will turn useful for thermoelectric energy harvesting, where efficiency relies on avoiding heat exchange across the active part of the device.

The chemical nature of surfaces, therefore, emerges as a new key parameter for improving the performance of Si-based electronic and thermoelectric nanodevices, as well as of that of nanomechanical resonators (NEMS). This work opens new possibilities for novel thermal experiments and designs directed to manipulate heat at such scales.