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Easy-to-make, ultra-low power electronics could charge out of thin air

Posted By Terrance Barkan, Wednesday, October 14, 2020
Researchers have developed a new approach to printed electronics which allows ultra-low power electronic devices that could recharge from ambient light or radiofrequency noise. The approach paves the way for low-cost printed electronics that could be seamlessly embedded in everyday objects and environments.

Electronics that consume tiny amounts of power are key for the development of the Internet of Things, in which everyday objects are connected to the internet. Many emerging technologies, from wearables to healthcare devices to smart homes and smart cities, need cost-effective transistors and electronic circuits that can function with minimal energy use.

Printed electronics are a simple and inexpensive way to manufacture electronics that could pave the way for low-cost electronic devices on unconventional substrates – such as clothes, plastic wrap or paper – and provide everyday objects with ‘intelligence’.

However, these devices need to operate with low energy and power consumption to be useful for real-world applications. Although printing techniques have advanced considerably, power consumption has remained a challenge – the different solutions available were too complex for commercial production.

Now, researchers from the University of Cambridge, working with collaborators from China and Saudi Arabia, have developed an approach for printed electronics that could be used to make low-cost devices that recharge out of thin air. Even the ambient radio signals that surround us would be enough to power them. Their results are published in the journal ACS Nano.

Since the commercial batteries which power many devices have limited lifetimes and negative environmental impacts, researchers are developing electronics that can operate autonomously with ultra-low levels of energy.

The technology developed by the researchers delivers high-performance electronic circuits based on thin-film transistors which are ‘ambipolar’ as they use only one semiconducting material to transport both negative and positive electric charges in their channels, in a region of operation called ‘deep subthreshold’ – a phrase that essentially means that the transistors are operated in a region that is conventionally regarded as their ‘off’ state. The team coined the phrase ‘deep-subthreshold ambipolar’ to refer to unprecedented ultra-low operating voltages and power consumption levels.

If electronic circuits made of these devices were to be powered by a standard AA battery, the researchers say it would be possible that they could run for millions of years uninterrupted.

The team, which included researchers from Soochow University, the Chinese Academy of Sciences, ShanghaiTech University, and King Abdullah University of Science and Technology (KAUST), used printed carbon nanotubes – ultra-thin cylinders of carbon – as an ambipolar semiconductor to achieve the result.

“Thanks to deep-subthreshold ambipolar approach, we created printed electronics that meet the power and voltage requirements of real-world applications, and opened up opportunities for remote sensing and ‘place-and-forget’ devices that can operate without batteries for their entire lifetime,” said co-lead author Luigi Occhipinti from Cambridge’s Department of Engineering. “Crucially, our ultra-low-power printed electronics are simple and cost-effective to manufacture and overcome long-standing hurdles in the field.”

“Our approach to printed electronics could be scaled up to make inexpensive battery-less devices that could harvest energy from the environment, such as sunlight or omnipresent ambient electromagnetic waves, like those created by our mobile phones and wifi stations,” said co-lead author Professor Vincenzo Pecunia from Soochow University. Pecunia is a former PhD student and postdoctoral researcher at Cambridge’s Cavendish Laboratory.

The work paves the way for a new generation of self-powered electronics for biomedical applications, smart homes, infrastructure monitoring, and the exponentially-growing Internet of Things device ecosystem.The research was funded in part by the Engineering and Physical Sciences Research Council (EPSRC).

Tags:  carbon nanotubes  Chinese Academy of Sciences  Energy  Engineering and Physical Sciences Research Council  Graphene  King Abdullah University of Science and Technology  Luigi Occhipinti  Medical  ShanghaiTech University  Soochow University  transistor  University of Cambridge  Vincenzo Pecunia 

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Cardea Bio Inc. Receives Fundamental Patent on “Graphene Transistor and Sensor Mass Production Processes”.

Posted By Terrance Barkan, Thursday, October 8, 2020
Cardea Bio Inc., who is using graphene-based Biology-gated Transistors (Cardean Transistors™) to directly link the live signals that run biology up to electronics and computers, today announced they received an additional fundamental key patent from the United States Patent and Trademark Office’s Notice of Allowance. This is one of several fundamental patents empowering Cardea to be the first and only company to mass produce graphene transistors at commercial scale.

Silicon-based electronics and chipsets have revolutionized our lives by powering computers, smart phones, the Internet; enabling unlimited access to most information and data. However, because silicon is a non-biocompatible material, our currently available electronic systems are not a viable way to access the world’s largest networks of big-data: the molecular data signals that run biology.

Graphene is a nanomaterial that, due to its unique nano-physics properties of being biocompatible and a much faster conductor than silicon, is able to directly connect up to biological signals. In the world of biology, signals are molecular binding interactions of DNA, RNA, and proteins, for example: RNA binding to DNA, and protein-protein binding interactions.

Cardean Transistors operate similarly to silicon semiconductors in that a transistor gate is said to either be open or closed, increasing or decreasing the electrical conductivity of the transistor. This gate change is represented as a 1 or 0 in the digital world. In order to link the two worlds up, there was a need for a solution that could convert the DNA, RNA, and protein binding based signals into electronic 1s and 0s in near real-time.  Cardean Transistors use bits of molecular biology as gates and utilizes binding interactions as the gate change in order to mend this missing link. A Cardean Transistor can for example use an antibody as one side of the gate. If it senses the antigen signal in the biology, they bind and the gate closes, and if not, the gate remains open. With this simple principle, built with very advanced and complex-to-manufacture technology, a molecular signal can become an integrated part of a computer system and allow people to link computers up to biology.

Cardean Transistors are the core of Cardea’s Tech+Bio Infrastructure and can be combined with different kinds of small bits of DNA, RNA, and proteins to build different chipsets (e.g. CRISPR-Chip™, that uses CRISPR as the transistor gate). These chipsets, when combined with modern electronic hardware and cloud-based computational analytical power (such as ML and AI), allow for a new generation of “Powered by Cardea” applications and products with features and capabilities that until now have only been dreamt of. This new type of technology can live-stream biological multi-omics signals to create a bridge between digital and biological networks to provide virtually live insight to life and biology. This can be done at a scale that’s never been possible before and with the potential to change how we do life science, medicine, agriculture and anything else that has an element of biology to it.

Cardea has been developing their Cardean Transistors and Tech+Bio infrastructure since 2013. As the R&D pioneers of graphene transistors and biosensors for detection of biological signals, the company is today the only company in the world with patents, know-how, and capabilities to mass produce gFETs (Graphene Field Effect Transistors) at commercially viable quality. Based on this market leadership and innovator position, Cardea continues to add to its growing IP and international patent pool of approximately 40 patents and patent applications. These patents cover this new Tech+Bio industry, as well as a vast number of technology processes and methods for when mass producing any graphene-based transistor or sensor.

Dr. Brett Goldsmith, Cardea’s CTO, Co-founder, and Co-inventor of most of the Cardea patents and patent applications, says, “It is an honor to get our many years of complex and interdisciplinary efforts in the R&D lab recognized as being novel, non-obvious and  rightfully ours. For example, this last patent on the fabrication process of “Patterning graphene with a hard mask coating” took years of R&D effort to get to work well and then an additional four years of patent application work.” Dr. Goldsmith continues, “It is a long journey with many ups and downs to develop brand new technology. Getting biology and electronics to work together is not easy. We are motivated by the fact that our technologies will help many people via our Innovation Partners.”

All of Cardea’s patented processes for mass production of Cardean Transistors have already been used in the Cardea production department for years. The patented processes are used to produce Cardean Transistors and the chipsets that sit inside “Powered by Cardea” products. One example of such a product is the recently launched CRISPR-BIND, a CRISPR quality control R&D instrument made together with the CRISPR QC group. CRISPR-BIND is used to reduce complexity and resources for researchers performing genome engineering, while ensuring that no errors or mistakes incur.

Cardea CEO and Co-founder Michael Heltzen says: “The same way silicon transistors have allowed knowledge and information to benefit people at a whole new scale over the last couple of decades, we at Cardea are on a mission to let everybody have access to all relevant biological information, data and signals – as live data-streams.” Heltzen continues, “We think of it as the start of the Internet of Biology. Our Tech+Bio Infrastructure will help solve some of the biggest problems humankind is still facing such as severe diseases, lack of food safety and security, limited precision medicine and effective treatment, as well as sustainable ways of producing resources without pollution. With digital insight to how biology works, we will be able to use biology as technology. Think of it as a new and sustainable natural resource becoming available to current and future generations of humankind.”

“I strongly believe that the innovation and inventions happening here at Cardea will change the world for the better. Getting another key patent and being recognized as pioneers in the life science and advanced semiconductor industry is a huge accomplishment for our team and it helps us to stay motivated in our venture to achieving our ambitious goals of giving people easy access to biology as technology” finishes Heltzen.

Tags:  Bioelectronics  Brett Goldsmith  Cardea Bio  Graphene  Michael Heltzen  nanomaterials  Sensors  Transistor 

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Metal wires of carbon complete toolbox for carbon-based computers

Posted By Graphene Council, Friday, September 25, 2020
Transistors based on carbon rather than silicon could potentially boost computers' speed and cut their power consumption more than a thousandfold -- think of a mobile phone that holds its charge for months -- but the set of tools needed to build working carbon circuits has remained incomplete until now.

A team of chemists and physicists at the University of California, Berkeley, has finally created the last tool in the toolbox, a metallic wire made entirely of carbon, setting the stage for a ramp-up in research to build carbon-based transistors and, ultimately, computers.

"Staying within the same material, within the realm of carbon-based materials, is what brings this technology together now," said Felix Fischer, UC Berkeley professor of chemistry, noting that the ability to make all circuit elements from the same material makes fabrication easier. "That has been one of the key things that has been missing in the big picture of an all-carbon-based integrated circuit architecture."

Metal wires -- like the metallic channels used to connect transistors in a computer chip -- carry electricity from device to device and interconnect the semiconducting elements within transistors, the building blocks of computers.

The UC Berkeley group has been working for several years on how to make semiconductors and insulators from graphene nanoribbons, which are narrow, one-dimensional strips of atom-thick graphene, a structure composed entirely of carbon atoms arranged in an interconnected hexagonal pattern resembling chicken wire.

The new carbon-based metal is also a graphene nanoribbon, but designed with an eye toward conducting electrons between semiconducting nanoribbons in all-carbon transistors. The metallic nanoribbons were built by assembling them from smaller identical building blocks: a bottom-up approach, said Fischer's colleague, Michael Crommie, a UC Berkeley professor of physics. Each building block contributes an electron that can flow freely along the nanoribbon.

While other carbon-based materials -- like extended 2D sheets of graphene and carbon nanotubes -- can be metallic, they have their problems. Reshaping a 2D sheet of graphene into nanometer scale strips, for example, spontaneously turns them into semiconductors, or even insulators. Carbon nanotubes, which are excellent conductors, cannot be prepared with the same precision and reproducibility in large quantities as nanoribbons.

"Nanoribbons allow us to chemically access a wide range of structures using bottom-up fabrication, something not yet possible with nanotubes," Crommie said. "This has allowed us to basically stitch electrons together to create a metallic nanoribbon, something not done before. This is one of the grand challenges in the area of graphene nanoribbon technology and why we are so excited about it."

Metallic graphene nanoribbons -- which feature a wide, partially-filled electronic band characteristic of metals -- should be comparable in conductance to 2D graphene itself.

"We think that the metallic wires are really a breakthrough; it is the first time that we can intentionally create an ultra-narrow metallic conductor -- a good, intrinsic conductor -- out of carbon-based materials, without the need for external doping," Fischer added.

Crommie, Fischer and their colleagues at UC Berkeley and Lawrence Berkeley National Laboratory (Berkeley Lab) will publish their findings in the Sept. 25 issue of the journal Science.

Tweaking the topology

Silicon-based integrated circuits have powered computers for decades with ever increasing speed and performance, per Moore's Law, but they are reaching their speed limit -- that is, how fast they can switch between zeros and ones. It's also becoming harder to reduce power consumption; computers already use a substantial fraction of the world's energy production. Carbon-based computers could potentially switch many times times faster than silicon computers and use only fractions of the power, Fischer said.

Graphene, which is pure carbon, is a leading contender for these next-generation, carbon-based computers. Narrow strips of graphene are primarily semiconductors, however, and the challenge has been to make them also work as insulators and metals -- opposite extremes, totally nonconducting and fully conducting, respectively -- so as to construct transistors and processors entirely from carbon.

Several years ago, Fischer and Crommie teamed up with theoretical materials scientist Steven Louie, a UC Berkeley professor of physics, to discover new ways of connecting small lengths of nanoribbon to reliably create the full gamut of conducting properties.

Two years ago, the team demonstrated that by connecting short segments of nanoribbon in the right way, electrons in each segment could be arranged to create a new topological state -- a special quantum wave function -- leading to tunable semiconducting properties.

In the new work, they use a similar technique to stitch together short segments of nanoribbons to create a conducting metal wire tens of nanometers long and barely a nanometer wide.

The nanoribbons were created chemically and imaged on very flat surfaces using a scanning tunneling microscope. Simple heat was used to induce the molecules to chemically react and join together in just the right way. Fischer compares the assembly of daisy-chained building blocks to a set of Legos, but Legos designed to fit at the atomic scale.

"They are all precisely engineered so that there is only one way they can fit together. It's as if you take a bag of Legos, and you shake it, and out comes a fully assembled car," he said. "That is the magic of controlling the self-assembly with chemistry."

Once assembled, the new nanoribbon's electronic state was a metal -- just as Louie predicted -- with each segment contributing a single conducting electron.

The final breakthrough can be attributed to a minute change in the nanoribbon structure.

"Using chemistry, we created a tiny change, a change in just one chemical bond per about every 100 atoms, but which increased the metallicity of the nanoribbon by a factor of 20, and that is important, from a practical point of view, to make this a good metal," Crommie said.

The two researchers are working with electrical engineers at UC Berkeley to assemble their toolbox of semiconducting, insulating and metallic graphene nanoribbons into working transistors.

"I believe this technology will revolutionize how we build integrated circuits in the future," Fischer said. "It should take us a big step up from the best performance that can be expected from silicon right now. We now have a path to access faster switching speeds at much lower power consumption. That is what is driving the push toward a carbon-based electronics semiconductor industry in the future."

Tags:  2D materials  carbon nanotubes  Felix Fischer  Graphene  graphene nanoribbons  Michael Crommie  Steven Louie  transistor  University of California Berkeley 

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Combining graphene and nitrides for high-power, high-frequency electronics

Posted By Graphene Council, Thursday, August 20, 2020
Researchers at Graphene Flagship partners CNR-IMM, Italy, CNRS-CRHEA, France, and STMicroelectronics, Poland, in collaboration with Graphene Flagship Associate Member TopGaN, Poland, collaborated on the Partnering Project GraNitE to produce graphene-enabled hot electron transistor (HET) devices. Thanks to nitride semiconductors, they achieved devices with current densities a million times higher than previous prototypes.

Nitride semiconductors are in the spotlight for their potential to be incorporated into HETs to improve their properties and performance. HETs are a type of vertical transistor that can operate at frequencies in the terahertz (THz) range, making them very valuable for applications in communications, medical diagnostics and security. Graphene is promising for applications in HETs, owing to its thinness and high conductivity. They are typically made from nitrides of gallium, aluminium or indium, or alloys of these metals. Aluminium and gallium nitrides are key ingredients in high-electron mobility transistors (HEMTs) – one of the technological foundations of 5G communications.

Gallium-based technologies do have their limitations, however, and GraNitE seeks to take advantage of graphene and layered materials to overcome them. The GraNitE team incorporated graphene as an active ingredient into high-powered aluminium-gallium nitride (AlGaN) and gallium nitride (GaN) based nitride transistors to better dissipate heat, by taking advantage of graphene's high thermal conductivity. The devices also operate at higher frequency thanks to the incorporation of high-quality graphene.

The team devised two approaches. Their first was to deposit graphene onto the surface of the nitride semiconductor using chemical vapour deposition (CVD). This resulted in highly homogeneous, nanocrystalline graphene films,1 ­­which could lead to uptake by industry. The second was to grow monolayer graphene using CVD on a copper surface, then to transfer and integrate it into thin layers of AlGaN and GaN. This method resulted in a graphene/AlGaN junction with excellent rectifying properties, ideal for applications in switches, with an injection mechanism tuneable by modifying the AlGaN composition and thickness.2

Graphene Flagship partnering project GraNitE used their graphene nitride junction as a key building block to fabricate prototype HET devices. Their devices had a low voltage threshold and an electric current density six orders of magnitude higher than those in previous silicon tests,2 representing an important advance in the development of hybrid graphene/nitride semiconductors, and paving the way for future exploitation of this technology.

"The integration of graphene and nitride semiconductors is one of the most viable approaches to harness the unique properties of these materials for industrial applications," says Filippo Giannazzo, GraNitE Project Leader and Senior Scientist at Graphene Flagship partner CNR-IMM, Italy.

Tags:  chemical vapour deposition  CNR-IMM  Filippo Giannazzo  Graphene  Graphene Flagship  semiconductors  transistor 

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"Simulation microscope" examines transistors of the future

Posted By Graphene Council, Tuesday, August 11, 2020
Since the discovery of graphene, two-dimensional materials have been the focus of materials research. Among other things, they could be used to build tiny, high-performance transistors. Researchers at ETH Zurich and EPF Lausanne have now simulated and evaluated one hundred possible materials for this purpose and discovered 13 promising candidates.

With the increasing miniaturization of electronic components, researchers are struggling with undesirable side effects: In the case of nanometer-scale transistors made of conventional materials such as silicon, quantum effects occur that impair their functionality. One of these quantum effects, for example, is additional leakage currents, i.e. currents that flow "astray" and not via the conductor provided between the source and drain contacts.

It is therefore believed that Moore's scaling law, which states that the number of integrated circuits per unit area doubles every 12-18 months, will reach its limits in the near future because of the increasing challenges associated with the miniaturisation of their active components. This ultimately means that the currently manufactured silicon-based transistors — called FinFETs and equipping almost every supercomputer — can no longer be made arbitrarily smaller due to quantum effects.

Two-dimensional beacons of hope
However, a new study by researchers at ETH Zurich and EPF Lausanne shows that this problem could be overcome with new two-dimensional (2-D) materials — or at least that is what the simulations they have carried out on the "Piz Daint" supercomputer suggest.

The research group, led by Mathieu Luisier from the Institute for Integrated Systems (IIS) at ETH Zurich and Nicola Marzari from EPF Lausanne, used the research results that Marzari and his team had already achieved as the basis for their new simulations: Back in 2018, 14 years after the discovery of graphene first made it clear that two-dimensional materials could be produced, they used complex simulations on "Piz Daint" to sift through a pool of more than 100,000 materials; they extracted 1,825 promising components from which 2-D layers of material could be obtained.

The researchers selected 100 candidates from these more than 1,800 materials, each of which consists of a monolayer of atoms and could be suitable for the construction of ultra-scaled field-effect transistors (FETs). They have now investigated their properties under the "ab initio" microscope. In other words, they used the CSCS supercomputer "Piz Daint" to first determine the atomic structure of these materials using density functional theory (DFT). They then combined these calculations with a so-called Quantum Transport solver to simulate the electron and hole current flows through the virtually generated transistors. The Quantum Transport Simulator used was developed by Luisier together with another ETH research team, and the underlying method was awarded the Gordon Bell Prize in 2019.

Finding the optimal 2-D candidate
The decisive factor for the transistor’s viability is whether the current can be optimally controlled by one or several gate contact(s). Thanks to the ultra-thin nature of 2-D materials — usually thinner than a nanometer — a single gate contact can modulate the flow of electrons and hole currents, thus completely switching a transistor on and off.

"Although all 2-D materials have this property, not all of them lend themselves to logic applications," Luisier emphasizes, "only those that have a large enough band gap between the valence band and conduction band.” Materials with a suitable band gap prevent so-called tunnel effects of the electrons and thus the leakage currents caused by them. It is precisely these materials that the researchers were looking for in their simulations.

Their aim was to find 2-D materials that can supply a current greater than 3 milliamperes per micrometre, both as n-type transistors (electron transport) and as p-type transistors (hole transport), and whose channel length can be as small as 5 nanometres without impairing the switching behaviour. "Only when these conditions are met can transistors based on two-dimensional materials surpass conventional Si FinFETs," says Luisier.

The ball is now in the experimental researchers' court

Taking these aspects into account, the researchers identified 13 possible 2-D materials with which future transistors could be built and which could also enable the continuation of Moore's scaling law. Some of these materials are already known, for example black phosphorus or HfS2, but Luisier emphasizes that others are completely new — compounds such as Ag2N6 or O6Sb4.

"We have created one of the largest databases of transistor materials thanks to our simulations. With these results, we hope to motivate experimentalists working with 2-D materials to exfoliate new crystals and create next-generation logic switches," says the ETH professor. The research groups led by Luisier and Marzari work closely together at the National Centre of Competence in Research (NCCR) MARVEL and have now published their latest joint results in the journal ACS Nano. They are confident that transistors based on these new materials could replace those made of silicon or of the currently popular transition metal dichalcogenides.

Tags:  2D materials  EPF Lausanne  ETH Zurich  Graphene  Mathieu Luisier  transistor 

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Graphene transistors with high on-off switching ratio

Posted By Graphene Council, Thursday, July 16, 2020
Commercial off-the-shelf graphene transistors have been used to achieve high on-off ratios, with potential for integration in digital logic circuits. Researchers have achieved this feat by coating the transistors with a liquid dielectric that induces an electrochemical effect that gates the graphene field effect transistors (GFETs). On-off ratios larger than 104 were achieved, as demonstrated in the recent publication in IEEE Access.

Since the first experimental isolation of graphene, the material has been considered as a potential replacement for silicon, due to its ultrathin form, flexibility, transparency, and high carrier mobility. However, graphene lacks an essential feature that enables semiconductors to be at the heart of digital logic components– an energy bandgap. The lack of a bandgap makes graphene switches impossible to fully turn off, resulting in poor on-off ratios.

Researchers have been exploring different avenues to exploiting the favourable properties of graphene in transistors. It was found that GFETs can be gated (switched) by electrochemical modification with a thin layer of silicon dioxide, which enabled the use of graphene for digital logic. Nevertheless, the switching times of such devices were on the order of 10 seconds, which is far too slow for use in circuitry. The most recent work demonstrates devices that have a high switching ratio while maintaining high speed.

The devices were made with a simple procedure that utilizes off-the-shelf commercial components. A wafer housing an array of graphene transistors was purchased, while the liquid dielectrics, also purchased, were deposited at precise locations using a micromanipulated probe. The scientists demonstrated good operation with liquid gates made of glycerine, honey, and caramelized honey. Caramelized honey has lower water content than pure honey, which results in a higher resistance, favourable for gate dielectrics. Achieved resistance was as high as 10 MOhm at a low operating voltage of 4V. The speed of operation was ranged from 2 to 120 milliseconds, depending on the gate dielectric material.

While the current devices demonstrate limited repeatability, they are still a promising candidate for non-volatile memory or reconfigurable devices. Pending further device optimization, liquid dielectric gated graphene field effect transistors could be incorporated in digital logic devices. Due to the ultrahigh carrier mobility of graphene, these devices may even operate at lower subthreshold levels than what is currently possible with CMOS.

Tags:  Graphene  transistor 

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Graphene transistors enable selective ion sensing

Posted By Graphene Council, Friday, June 26, 2020
New research shows that graphene field effect transistors can be used to selectively detect ions in a liquid solution. The work, just published in Nature Communications, paves the way to applications such as genome sequencing, medical diagnostics, environmental monitoring, and industrial process control.

State of the art technology for detecting and resolving ions in solution relies on ion sensitive field effect transistors (ISFETs). Standard ISFETs are made of silicon, due to the ease of technological processing, however silicon ISFETs have some drawbacks that hinder their performance in real-life scenarios.

To achieve selectivity to different ionic species, ISFETs that are selective to specific ions are assembled into arrays and post-processing is used to estimate ion concentration. Since many ISFETs are packed on small areas to implement selectivity, each ISFET has to be made small, which leads to low-frequency noise that is prominent in silicon. Increasing the size of individual ISFETs leads to loss of resolution, which imposes a tradeoff that limits practical use.

The present research, reported by teams in Canada and Spain, overcomes the tradeoff by using graphene instead of silicon as the ISFET channel. Graphene has high carrier mobility even in large-area devices, which enables construction of a single large sensor for multiple ionic species. Post-processing of the transistor signal enables the measuring of concentration of K+, Na+, NH4+, NO3-, SO42-, and Cl- ions down to concentrations lower than 10-5 M in a multianalyte solution. These ions were chosen due to their prominence in agriculture runoff, hence the importance of their detection in water quality monitoring.

Practical graphene ISFET use was demonstrated by monitoring the uptake of ions by duckweed in an aquarium over a period of three weeks. The researchers tracked, with high precision and selectivity, the concentration of seven different ionic species over time after adding plant nutrients to the aquarium. This novel work demonstrates that large-area graphene ISFETs can be fabricated from wafer scale graphene by a facile method, yielding ISFETs with a high signal-to-noise-ratio and high-resolution sensing. Graphene ISFETs hence overcome poor selectivity typically associated with ISFETs made of other materials and can be applied to real-life scenarios in environmental sensing.

Tags:  Electronics  Graphene  Sensors  transistor 

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Researchers pioneer new production method for heterostructure devices

Posted By Graphene Council, Tuesday, June 23, 2020
Researchers at the University of Exeter have developed a pioneering production method for heterostructure devices, based on 2D materials such as graphene.

The new study, published in Nature Communications, focuses on a production method, based around mechanical abrasion, where multilayer structures are formed through directly abrading different Van der Waals material powders directly on top of one another.

The new technique saw sharp heterointerfaces emerge for certain heterostructure combinations. The results pave the way for a wide range of heterointerface based devices to be opened up.

To demonstrate the applicability of this method, researchers demonstrated a multitude of different functional devices such as resistors, capacitors, transistors, diodes and photovoltaics.

The work also demonstrated the use of these films for energy applications such as in triboelectric nanogenerator devices and as a catalyst in the hydrogen evolution reaction.

Darren Nutting, from the University of Exeter and co-author of the study said: “The production method is really simple, you can go from bare substrate to functional heterostructure device within about 10 minutes.

“This is all without the need for complex growth conditions, 20 hours of ultra-sonication or messy liquid phase production.

“The method is applicable to any 2D material crystal, and can easily be automated to produce heterostructures of arbitrary size and complexity. This allows for the production of a plethora of device possibilities with superior performance to those created using more complex methods.”

Dr Freddie Withers, also from the University of Exeter and lead author added: “The most interesting and surprising aspect of this work is that sharply defined heterointerfaces can be realised through direct abrasion, which we initially expected would lead to an intermixing of materials when directly abrading layer by layer. This observation allows for a large number of different devices to be realised through an extremely simple and low-cost fabrication process.

“We also found that the performance of our materials significantly outperform the performance of competitive scalable 2D materials production technologies. We think this is due to larger crystallite sizes and cleaner crystallite interfaces within our films. Considering the rudimentary development of the abrasive process thus far, it will be interesting to see how far we can push the performance levels.”

Tags:  2D materials  Darren Nutting  Graphene  transistor  University of Exeter 

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HKUST Research Team Successfully Discovers New Material Generation Mechanism for Chip Design, Quantum Computing and Noise Reduction

Posted By Graphene Council, Monday, June 8, 2020
The research team of the Hong Kong University of Science and Technology (HKUST) has recently made important progress in the field of new materials. Combining the characteristics of two-dimensional materials and topological materials, the team has for the first time discovered a universal generation mechanism of new materials with "type-II" Dirac cones. Many extraordinary properties of the material are realized in experiments, which addressed the key issue that the material could only be obtained sporadically under stringent limits. This mechanism can guide the preparation of new two-dimensional materials that have specific directional responses to external signals such as electric fields, magnetic fields, light waves, sound waves, etc., and will provide valuable applications for modern electronic communications, quantum computing, optical communications, and even sound insulation and noise reduction materials. 

As a typical representative of two-dimensional materials, since its discovery in 2004, graphene has been regarded as one of the greatest material discoveries in the 21st century. As the thinnest, strongest and most thermally conductive "super material" in the world today, graphene has been widely used in transistors, biosensors and batteries, and its discovery led to the 2010 Nobel Prize in Physics. On the other hand, topological materials, because of the existence of extraordinary properties such as zero-dissipative edge transport, are considered to be the cornerstones of the development of future electronic devices, and their discovery led to the 2016 Nobel Prize in Physics. In fact, graphene is also a topological material, and its extraordinary properties are mostly derived from its topological "Dirac cones". However, the "Dirac cones" in graphene belong to the "type-I" Dirac cones of the theoretical predictions. The more unique "type-II" Dirac cones in the theoretical predictions, because of their strongly directional responses to external signals that the type-I Dirac cones do not have, will bring many more possibilities to the development and applications of electronic devices. However, so far, the "Dirac cone of the second kind" can only be found sporadically in some materials, lacking a systematic generation mechanism.

To address this critical issue, the research team led by Prof. WEN Weijia and Dr. WU Xiaoxiao, from the Department of Physics, for the first time, discovered and successfully implemented the systematic generation mechanism of new two-dimensional materials with type-II Dirac cones based on the relevant theories of two-dimensional materials and topological materials, using the band-folding mechanism (a material-independent, universal principle for periodic lattices). Due to its unique topological bands, its response to external signals is extremely directional, so the two-dimensional materials with type-II Dirac cones have important academic and application values for the designs of high-precision detecting devices of external signals, such as electric fields, magnetic fields, light waves, and sound waves. The systematic design and material independence of this scheme also help to relax the precision requirements for circuit designs, making the design of corresponding electronic products easier and more flexible. The team used acoustic field scanning techniques to directly observe the type-II Dirac cone in acoustics, as well as many of its properties that were only proposed in theories previously.

The success of this experimental study has opened up a new field of researches and applications of two-dimensional materials and topological materials, and brought many more possibilities for the future applications of the new materials. The findings of this study have been published in the renowned journal Physical Review Letters.

The ventilated sound absorbers developed by Prof. Wen’s group based on acoustic metamaterials. The ventilated sound absorbers can simultaneously achieve high-performance sound absorption and air flow ventilation, which is important for noise reduction applications in the environment with free air flows, such as air conditioners, exhaust hoods, and ducts.

"Our findings of the deterministic scheme for type-II Dirac points could profoundly broaden application prospects on fronts such as 5G communications, optical computing such as quantum computing and noise reduction. Our team plans to apply the experimental results to electronic devices such as dedicated chips, new touch control materials, filter modules, wireless transmission and biosensors.” said Prof. Wen, “Also, type-II DPs observed in acoustic waves suggest viable new materials for sound barriers, providing potential solutions for high-efficiency soundproofing walls. While we improve the performance of acoustic metamaterials, we will seek to continuously expand their applications in aspects ranging from low-frequency sound absorption, noise reduction in ventilation systems, intelligent active noise cancelling, traffic noise abatement to architectural acoustics. We also hope that these materials can be truly industrialized.”

Long engaged in researching the field of advanced materials, Prof. Wen and his team have made a range of key achievements in the basic and applied research of new materials science. In 2014, he was awarded second-class 2014 State Natural Science Award (SNSA) for the project on "Structural and Physical Mechanism Investigation for Giant Electrorheological Fluid".

Tags:  Batteries  biosensors  Graphene  Hong Kong University of Science and Technology  transistor  WEN Weijia  WU Xiaoxiao 

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New study reveals unexpected softness of bilayer graphene

Posted By Graphene Council, Saturday, May 2, 2020
In the study, published in the journal Physical Review B, the researchers showed that bilayer graphene, consisting of two layers of graphene, was noticeably softer than both two-dimensional (2D) graphene and three-dimensional (3D) graphite along the stacking direction.

This surprising result differs from previous research which showed that 2D graphene, a flat single layer of carbon atoms arranged in a honeycomb structure had many of the same mechanical properties as 3D graphite, which is a naturally occurring form of carbon made up from a very weak stack of many layers of graphene.

Measuring stiffness
Graphene is a 2D material, but has 3D properties such as its stiffness in the ‘out-of-plane’ direction, perpendicular to the plane of the graphene sheets.

The behaviour of π electrons within multilayer graphene determine its out-of-plane stiffness. In this study, the researchers found that when bilayer graphene is compressed out-of-plane, some π electrons are ‘squeezed’ through the graphene planes, which are impenetrable to small molecules such as water. This response makes the material softer and much easier to compress.   

Dr Yiwei Sun, lead author of the study from Queen Mary University of London, said: “Our previous study showed that 2D graphene and 3D graphite have many of the same mechanical properties, so we were surprised to see that bilayer graphene is much softer than both of these materials. We think that the softness of bilayer graphene results from the ‘squeezing’ of pi-electronic orbitals through the graphene layers. For example, if the bread on a burger is replaced by a bagel it is even easier to compress because the contents can be squeezed out of the bagel hole.”

Realising potential
Often hailed as a 'wonder material', graphene has the highest known thermal and electrical conductivity and is stronger than steel, as well as being light, flexible and transparent. 

It was discovered in 2004 by peeling off graphene flakes from bulk graphite (used in pencil leads and lubricants) using sticky tape.

Stacking the graphene flakes one on top of the other provides more possibilities as the material’s extraordinary properties are determined by interactions between its stacked layers. Its unique characteristics can also be fine-tuned for various applications by stacking other 2D materials, such as boron nitride and molybdenum disulphide, to graphene.

This study provides insight into the complex interactions between graphene bilayers and enables quantification of its properties, which is critical for exploring future applications of the material in devices such as vertical transistors and pressure sensors.

Tags:  2D materials  boron nitride  Graphene  Queen Mary University of London  transistor  Yiwei Sun 

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