Graphene  

Researchers have developed a laser-treatment process that allows them to use printed graphene for electric circuits and electrodes -- even on paper and other fragile surfaces. The technology could lead to many real-world, low-cost applications for printed graphene electronics, including sensors, fuel cells and medical devices.

Researchers at Iowa State University have been looking for ways to use graphene and its amazing properties in their sensors and other technologies. Now, in research published in the journal Nanoscale, they have demonstrated a laser-treatment process that allows them to use printed graphene for electric circuits and electrodes.

Graphene is great at conducting electricity and heat; it’s strong and stable. But researchers have struggled to move beyond tiny lab samples for studying its material properties to larger pieces for real-world applications.

Recent projects that used inkjet printers to print multi-layer graphene circuits and electrodes had the engineers thinking about using it for flexible, wearable and low-cost electronics. For example, “Could we make graphene at scales large enough for glucose sensors?” asked Suprem Das, an Iowa State postdoctoral research associate in mechanical engineering and an associate of the U.S. Department of Energy’s Ames Laboratory.

But there were problems with the existing technology. Once printed, the graphene had to be treated to improve electrical conductivity and device performance. That usually meant high temperatures or chemicals – both could degrade flexible or disposable printing surfaces such as plastic films or even paper.

Das and Jonathan Claussen came up with the idea of using lasers to treat the graphene. Claussen, an Iowa State assistant professor of mechanical engineering and an Ames Laboratory associate, worked with Gary Cheng, an associate professor at Purdue University’s School of Industrial Engineering, to develop and test the idea.

The idea worked: They found treating inkjet-printed, multi-layer graphene electric circuits and electrodes with a pulsed-laser process improves electrical conductivity without damaging paper, polymers or other fragile printing surfaces.

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“This creates a way to commercialize and scale-up the manufacturing of graphene,” Claussen said.

The findings are featured on the front cover of the journal Nanoscale’s issue 35. Claussen and Cheng are lead authors and Das is first author. Additional Iowa State co-authors are Allison Cargill, John Hondred and Shaowei Ding, graduate students in mechanical engineering. Additional Purdue co-authors are Qiong Nian and Mojib Saei, graduate students in industrial engineering.

"This creates a way to commercialize and scale-up the manufacturing of graphene."

Two major grants are supporting the project and related research: a three-year grant from the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 11901762 and a three-year grant from the Roy J. Carver Charitable Trust. Iowa State’s College of Engineering and department of mechanical engineering are also supporting the research.

The Iowa State Research Foundation Inc. has filed for a patent on the technology.

“The breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications,” Claussen said.

Those applications could include sensors with biological applications, energy storage systems, electrical conducting components and even paper-based electronics.

To make all that possible, the engineers developed computer-controlled laser technology that selectively irradiates inkjet-printed graphene oxide. The treatment removes ink binders and reduces graphene oxide to graphene – physically stitching together millions of tiny graphene flakes. The process makes electrical conductivity more than a thousand times better.

“The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate,” Das said. “They heat locally. They bombard locally. They process locally.”

That localized, laser processing also changes the shape and structure of the printed graphene from a flat surface to one with raised, 3D nanostructures. The engineers say the 3D structures are like tiny petals rising from the surface. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.

All of that, according to Claussen’s team of nanoengineers, could move graphene to commercial applications.

“This work paves the way for not only paper-based electronics with graphene circuits,” the researchers wrote in their paper, “it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells and (medical) devices.”

SOURCE  Iowa State University

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Artificial Intelligence  

Scientists have reported the development of a first-of-its-kind synthetic synapse that mimics the plasticity of the human brain, bringing us one step closer to human-like artificial intelligence.

Building a computer that learns and remembers like a human brain is a complex challenge. Our brains contain over 86 billion neurons and trillions of connections—or synapses—that can grow stronger or weaker over time. By studying biological synapses, researchers have applied their findings to the development of neuromorphic engineering.

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Now Chinese scientists report in ACS' journal Nano Letters the development of a first-of-its-kind synthetic synapse that mimics the plasticity of the real thing, bringing us one step closer to human-like artificial intelligence.

While the human brain still holds many secrets, one thing we do know is that the flexibility, or neuroplasticity, of neuronal synapses is a critical feature. In the synapse, many factors, including how many signaling molecules get released and the timing of release, can change. 

"This work would offer a broad new vista for the 2D material electronics and guide the innovation of neuro-electronics fundamentally."

This mutability allows neurons to encode memories, learn and heal themselves. In recent years, researchers have been building artificial neurons and synapses with some success but without the flexibility needed for learning. Tian-Ling Ren and colleagues set out to address that challenge.

The researchers created the artificial synapse out of aluminum oxide and twisted bi-layer graphene. 

By applying different electric voltages to the system, they found they could control the reaction intensity of the receiving "neuron." The team says their novel dynamic system could aid in the development of biology-inspired electronics capable of learning and self-healing.

"This work would offer a broad new vista for the 2D material electronics and guide the innovation of neuro-electronics fundamentally," write the authors of the study.

SOURCE  ACS

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Graphene  

Graphene, impermeable to all gases and liquids, can easily allow protons to pass through it, researchers have found. The discovery could open the door to a whole new type of energy production.

Researchers from the University of Manchester in the United Kingdom have discovered a new way to use graphene to turn air — or hydrogen in the air — into usable energy. Of course, this technology is still years away from being commercially viable, so don't expect to see air-based generators anytime soon.

The team published their report in Nature, an international journal of science, and it describes the process behind the technology. The graphene is worked into a membrane-like structure, which can be used to sieve hydrogen out of the air. In this way, they could use the technology to create generators that are powered by burning hydrogen.

But graphene is not exactly what you'd call a well-known material. Researchers have been working with it for years, and it will take many more to come up with something truly viable. It was first isolated back in 2004 by another team from Manchester University, and since then, they have been continuously working to broaden their understanding of it.

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More recently, researchers from Korea University in Seoul composed a way to grow graphene in bigger quantities. This means we can now create sheets of graphene with more surface area.

However, it still begs the question: What is graphene?

What Is Graphene?

If the term graphene sounds familiar to you, that’s because it probably is. It has an atomic structure identical to graphite, the type of material commonly used in pencils.

Graphene is one atom thick, which means it’s one of the thinnest and lightest materials on the planet. It is a two-dimensional crystal, the first in scientific history actually, and its properties are what make it so promising. Graphene is thin, light and remarkably strong — so strong, in fact, that it is both harder than diamond and about 200 times stronger than steel. It’s impermeable to gasses and liquids, despite its size. In addition, it is transparent, incredibly flexible and works extremely well as a conductor — even better than copper.

Furthermore, silicone has been called the next generation semiconductor because it offers many benefits over other materials. If the recent discoveries about graphene are true, however, it would take the cake, especially considering how conductive it is.

With all of those benefits, it’s impossible to shrug away the incredible potential of this material.

Just imagine what wearable technology, mobile technology and the future of technology as a whole have to gain from a substance like this. It’s so thin and transparent, it could theoretically be used to attach paper-thin interactive displays to pretty much anything, even fabric.

How Can It Be Used to Harvest Hydrogen?

"Graphene can be produced these days in square meter sheets, we hope that it will find its way to commercial fuel cells sooner rather than later."

Modern fuel-cell technology calls for membrane-based cells which trigger a reaction between oxygen and hydrogen as a fuel, and then convert chemical energy into usable electricity. During the process, these membranes separate the protons, and that is essentially what creates the energy. However, with traditional fuel cells, there is a pretty high rate of inefficiency because some of that fuel can leak across the proton membranes, becoming lost or contaminated.

By using graphene to create the membranes, those fuel cells could become extra efficient by stopping that leakage, generating more power. Plus, due to their makeup, they would also be more durable.

During the Manchester University study, researchers found that protons passed through the graphene membranes just fine.

The aforementioned process can be augmented to harvest hydrogen from the air, generating usable electricity.

Co-author of the study, Marcelo Lozada-Hidalgo describes it in more detail:

When you know how it should work, it is a very simple setup. You put a hydrogen-containing gas on one side, apply small electric current and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell. 

We worked with small membranes, and the achieved flow of hydrogen is, of course, tiny so far. But this is the initial stage of discovery, and the paper is to make experts aware of the existing prospects. To build up and test hydrogen harvesters will require much further effort.

Dr Sheng Hu, a postdoctoral researcher and the first author in this work, added: “It looks extremely simple and equally promising. Because graphene can be produced these days in square meter sheets, we hope that it will find its way to commercial fuel cells sooner rather than later”.

More work needs to be done with graphene to understand how protons pass through membranes created out of the material. Even if scientists find a way to create a generator with such technology, in the end, there’s no way to know just how much electricity can be generated from it. This is because there really is not that much hydrogen present in the atmosphere.

Still, it’s a fascinating discovery, and it means we’re just one step closer to the future. We can all agree that efficient and environmentally-friendly energy systems are becoming more and more of a necessity as we push forward.

Source - The University of Manchester

By Kayla Matthews

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Author Bio - Kayla Matthews is a technology journalist and blogger, as well as editor of ProductivityBytes.com. Follow Kayla on Facebook and Twitter to read all of her latest posts.

 Graphene  

Physicists have found a mehtod to induce magnetism in graphene while also preserving graphene’s electronic properties. The finding has the potential to increase graphene’s use in computers, as in computer chips that use electronic spin to store data.

Graphene, the one-atom thick sheet of carbon atoms arranged in a hexagonal lattice, has many desirable properties. Magnetism, however, is not one of them. Magnetism can be induced in graphene by doping it with magnetic impurities, but this doping tends to disrupt graphene’s electronic properties.

Now a team of physicists at the University of California, Riverside has found an ingenious way to induce magnetism in graphene while also preserving graphene’s electronic properties. They have accomplished this by bringing a graphene sheet very close to a magnetic insulator – an electrical insulator with magnetic properties.

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The study results have been published in Physical Review Letters.

"The magnetic graphene acquires new electronic properties so that new quantum phenomena can arise. These properties can lead to new electronic devices that are more robust and multi-functional."

"This is the first time that graphene has been made magnetic this way," said Jing Shi, a professor of physics and astronomy, whose lab led the research. "The magnetic graphene acquires new electronic properties so that new quantum phenomena can arise. These properties can lead to new electronic devices that are more robust and multi-functional."

The finding has the potential to increase graphene’s use in computers, as in computer chips that use electronic spin, or spintronics, to store data.

The magnetic insulator Shi and his team used was yttrium iron garnet grown by laser molecular beam epitaxy in his lab. The researchers placed a single-layer graphene sheet on an atomically smooth layer of yttrium iron garnet. They found that yttrium iron garnet magnetized the graphene sheet. In other words, graphene simply borrows the magnetic properties from yttrium iron garnet.

Magnetic substances like iron tend to interfere with graphene’s electrical conduction. The researchers avoided those substances and chose yttrium iron garnet because they knew it worked as an electric insulator, which meant that it would not disrupt graphene’s electrical transport properties. By not doping the graphene sheet but simply placing it on the layer of yttrium iron garnet, they ensured that graphene’s excellent electrical transport properties remained unchanged.

In their experiments, Shi and his team exposed the graphene to an external magnetic field.  They found that graphene’s Hall voltage – a voltage in the perpendicular direction to the current flow – depended linearly on the magnetization of yttrium iron garnet (a phenomenon known as the anomalous Hall effect, seen in magnetic materials like iron and cobalt).  This confirmed that their graphene sheet had turned magnetic.


SOURCE  University of California, Riverside

By 33rd Square

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 Graphene  

Researchers in Korea have successfully 3D printed graphene nano-structures without the use of any other material. With the entire printed structure being composed of graphene, the strength, as well as full conductivity of the material can be taken advantage of.

There is no question that graphene, has enormous potential, from solar cell technology, to electronics to medicine.  A key factor in developing practical and commercial applications of the one-atom thick carbon sheets is in aligning the material in the desired form depending on the application.

Now 3D printing of graphene is nearing a feasible stage and companies such as Graphene 3D Lab, are at the forefront of the technology.

However, there is a difference between 3D printing pure graphene, and 3D printing a graphene/thermoplastic composites like Graphene 3D has been doing.

While printing with composite materials, using a typical FDM/FFF or powder based laser sintering process, will keep some of graphene’s superior properties intact, most will be lost. The plastic will eventually break down leaving any prints weak, and not much different from a typical object you’d print with a MakerBot Replicator.

Now, researchers, led by Professor Seung Kwon Seol from Korea Electrotechnology Research Institute (KERI), recently published a paper in Advanced Materials where they describe a new process of directly 3D printing pure graphene.

Their techniques mean that graphene nano-structures can be fabricated without the use of any other material. With the entire printed structure being composed of graphene, the strength, as well as full conductivity of the material can be realized.

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"We developed a nanoscale 3D printing approach that exploits a size-controllable liquid meniscus to fabricate 3D reduced graphene oxide (rGO) nanowires," Seol told Nanowerk. "Different from typical 3D printing approaches which use filaments or powders as printing materials, our method uses the stretched liquid meniscus of ink. This enables us to realize finer printed structures than a nozzle aperture, resulting in the manufacturing of nanostructures."

"We are convinced that this approach will present a new paradigm for implementing 3D patterns in printed electronics."

“So far, to the best of our knowledge, nobody has reported 3D printed nanostructures composed entirely of graphene,” says Seol. “Several results reported the 3D printing (millimeter- or centimeter-scale) of graphene or carbon nanotube/plastic composite materials by using a conventional 3D printer. In such composite system, the graphene (or CNT) plays an important role for improving the properties of plastic materials currently used in 3D printers. However, the plastic materials used for producing the composite structures deteriorate the intrinsic properties of graphene (or CNT).”

"We are convinced that this approach will present a new paradigm for implementing 3D patterns in printed electronics," says Seol.

For their technique, the team grew graphene oxide (GO) wires at room temperature using the meniscus formed at the tip of a micropipette filled with a colloidal dispersion of GO sheets, then reduced it by thermal or chemical treatment (with hydrazine).

The deposition of GO was obtained by pulling the micropipette as the solvent rapidly evaporated, thus enabling the growth of GO wires. The researchers were able to accurately control the radius of the rGO wires by tuning the pulling rate of the pipette; they managed to reach a minimum value of ca. 150 nm.

Using this technique, they were able to produce arrays of different freestanding rGO architectures, grown directly at chosen sites and in different directions: straight wires, bridges, suspended junctions, and woven structures.

Seol points out that this 3D nanoprinting approach can be used for manufacturing 2D patterns and 3D geometry in diverse devices such as printed circuit boards, transistors, light emitting devices, solar cells, sensors and so on.

A lot of work remains to reduce the 3D printable size to below 10 nm and increase the production yield. A short video of Seol's process is below:



SOURCE  Nanowerk

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 Graphene  

Continuing research into the material he helped discover, graphene, Andre Geim and a team of researchers have found that protons can pass through the material.  The discovery could be lead to new energy technologies, suggest the researchers.

Scientists in Britain have found that graphene, the world's thinnest, strongest and most impermeable material, can allow protons to pass through it.

The discovery could revolutionize fuel cell technology according to the researchers.

Led by the Nobel prize winner and discoverer of graphene, Andre Geim the team based at Manchester University, said their finding also raised the possibility that, in future, graphene membranes could be used to "sieve" hydrogen gas from the atmosphere to then generate electricity.

"We are very excited about this result because it opens a whole new area of promising applications for graphene in clean energy harvesting and hydrogen-based technologies," said Geim's co-researcher on the study, Marcelo Lozada-Hidalgo.

Graphene is a so-called "wonder material" being 100 times stronger than steel but thinner than any known solid.

The material is renowned for being impermeable to all gases and liquids, giving it the potential for a range of uses like rust-proof coatings, impermeable packaging and transparent solar panels.

"We are very excited about this result because it opens a whole new area of promising applications for graphene in clean energy harvesting and hydrogen-based technologies."

With graphene being impermeable to even hydrogen atoms, Geim's team decided to test how small a particle had to be to pass through the material.  They tried protons, or hydrogen atoms stripped of their electrons, and found they passed through the graphene in ambient conditions.

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Their work has been published in the journal Nature.

Against expectations, they found the protons could pass through the ultra-strong material fairly easily, especially at raised temperatures and if the graphene films were covered with nanoparticles such as platinum, which acted as a catalyst.

Geim and Lozada-Hidalgo, explaining their finding in a telephone briefing for reporters, said this meant graphene could in future be used in proton-conducting membranes, a crucial component of fuel cell technology.

Fuel cells, used in some modern cars, use oxygen and hydrogen as fuel and convert the input chemical energy into electricity. But a major problem is that the fuels leak across the existing proton membranes, "poisoning" the process and reducing the cells' efficiency -- something Geim said could be overcome using graphene.

The team also found that graphene membranes could be used to extract hydrogen from the atmosphere, suggesting the possibility of combining them with fuel cells to make mobile electric generators powered just by the tiny amounts of hydrogen in the air.

"Essentially, you pump your fuel from the atmosphere and get electricity out of it," Geim said. "Our (study) provides proof that this kind of device is possible."


SOURCE  Reuters

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 Graphene  

Researchers have created a supercapacitor film that could replace the need for a battery altogether within the next five years. Consisting of two layers of graphene with an electrolyte layer in the middle the supercapacitor is strong, thin, and is able to release a large amount of energy in a short amount of time.

Cars powered by their own body panels could soon be driving on our roads after a breakthrough in nanotechnology research by a Queensland University of Technology (QUT) team.

The researchers have developed lightweight "supercapacitors" that can be combined with regular batteries to dramatically boost the power of an electric car.

The discovery was made by Postdoctoral Research Fellow Dr Jinzhang Liu, Professor Nunzio Motta and PhD researcher Marco Notarianni, from QUT's Science and Engineering Faculty - Institute for Future Environments, and PhD researcher Francesca Mirri and Professor Matteo Pasquali, from Rice University in Houston, in the United States.

The supercapacitors which are made of a "sandwich" by solution processing and filtering electrochemically-exfoliated graphene sheets mixed with clusters of spontaneously entangled multiwall carbon nanotubes.

The film could be embedded in a car's body panels, roof, doors, hood and floor - storing enough energy to turbocharge an electric car's battery in just a few minutes.

The findings, published in the Journal of Power Sources and the Nanotechnology journal, mean a car partly powered by its own body panels could be a reality within five years, Notarianni said.

"Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but they are able to deliver it very quickly, making them the perfect complement to mass-storage batteries," he said.

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"Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery."

"Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery."

Dr Liu said currently the "energy density" of a supercapacitor is lower than a standard lithium ion (Li-Ion) battery, but its "high power density", or ability to release power in a short time, is "far beyond" a conventional battery. "Supercapacitors are presently combined with standard Li-Ion batteries to power electric cars, with a substantial weight reduction and increase in performance," he said.

"In the future, it is hoped the supercapacitor will be developed to store more energy than a Li-Ion battery while retaining the ability to release its energy up to 10 times faster - meaning the car could be entirely powered by the supercapacitors in its body panels.

"After one full charge this car should be able to run up to 500km - similar to a petrol-powered car and more than double the current limit of an electric car."

Dr Liu said the technology would also potentially be used for rapid charges of other battery-powered devices. "For example, by putting the film on the back of a smart phone to charge it extremely quickly," he said.

The discovery may be a game-changer for the automotive industry, with significant impacts on financial, as well as environmental, factors. "We are using cheap carbon materials to make supercapacitors and the price of industry scale production will be low," Professor Motta said.

"The price of Li-Ion batteries cannot decrease a lot because the price of Lithium remains high. This technique does not rely on metals and other toxic materials either, so it is environmentally friendly if it needs to be disposed of."

The researchers are part of QUT's Battery Interest Group, a cross-faculty group that aims to engage industry with battery-related research.


SOURCE  Queensland University of Technology

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 Graphene  

A graphene, one-atom-thick microelectrode now solves a major problem for investigators looking at brain circuitry. Pinning down the details of how individual neural circuits operate in epilepsy and other brain disorders requires real-time observation of their locations, firing patterns, and other factors.

Researchers from the Perelman School of Medicine and School of Engineering at the University of Pennsylvania and The Children's Hospital of Philadelphia have used graphene -- a two-dimensional form of carbon only one atom thick -- to fabricate a new type of microelectrode that solves a major problem for investigators looking to understand the intricate circuitry of the brain.

Pinning down the details of how individual neural circuits operate in epilepsy and other neurological disorders requires real-time observation of their locations, firing patterns, and other factors, using high-resolution optical imaging and electrophysiological recording. But traditional metallic microelectrodes are opaque and block the clinician's view and create shadows that can obscure important details. In the past, researchers could obtain either high-resolution optical images or electrophysiological data, but not both at the same time.

"We can [] look at other neurological disorders and try to understand the correlation between different neural circuits using this technique."

The Center for NeuroEngineering and Therapeutics (CNT), under the leadership of senior author Brian Litt, PhD, has solved this problem with the development of a completely transparent graphene microelectrode that allows for simultaneous optical imaging and electrophysiological recordings of neural circuits. Their work was published this week in Nature Communications.

"There are technologies that can give very high spatial resolution such as calcium imaging; there are technologies that can give high temporal resolution, such as electrophysiology, but there's no single technology that can provide both," says study co-first-author Duygu Kuzum, PhD. Along with co-author Hajime Takano, PhD, and their colleagues, Kuzum notes that the team developed a neuroelectrode technology based on graphene to achieve high spatial and temporal resolution simultaneously.

Aside from the obvious benefits of its transparency, graphene offers other advantages: "It can act as an anti-corrosive for metal surfaces to eliminate all corrosive electrochemical reactions in tissues," Kuzum says. "It's also inherently a low-noise material, which is important in neural recording because we try to get a high signal-to-noise ratio."

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While previous efforts have been made to construct transparent electrodes using indium tin oxide, they are expensive and highly brittle, making that substance ill-suited for microelectrode arrays. "Another advantage of graphene is that it's flexible, so we can make very thin, flexible electrodes that can hug the neural tissue," Kuzum notes.

In the study, Litt, Kuzum, and their colleagues performed calcium imaging of hippocampal slices in a rat model with both confocal and two-photon microscopy, while also conducting electrophysiological recordings. On an individual cell level, they were able to observe temporal details of seizures and seizure-like activity with very high resolution. The team also notes that the single-electrode techniques used in the Nature Communications study could be easily adapted to study other larger areas of the brain with more expansive arrays.

The graphene microelectrodes developed could have wider application. "They can be used in any application that we need to record electrical signals, such as cardiac pacemakers or peripheral nervous system stimulators," says Kuzum. Because of graphene's nonmagnetic and anti-corrosive properties, these probes "can also be a very promising technology to increase the longevity of neural implants." Graphene's nonmagnetic characteristics also allow for safe, artifact-free MRI reading, unlike metallic implants.

Kuzum emphasizes that the transparent graphene microelectrode technology was achieved through an interdisciplinary effort of CNT and the departments of Neuroscience, Pediatrics, and Materials Science at Penn and the division of Neurology at CHOP.

As the technology is further developed and used, Kuzum and her colleagues expect to gain greater insight into how the physiology of the brain can go awry. "It can provide information on neural circuits, which wasn't available before, because we didn't have the technology to probe them," she says. That information may include the identification of specific marker waveforms of brain electrical activity that can be mapped spatially and temporally to individual neural circuits. "We can also look at other neurological disorders and try to understand the correlation between different neural circuits using this technique," she says.




SOURCE  Penn Medicine

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 Graphene  

Scientists have discovered a way to create a highly sensitive chemical sensor based on the crystalline flaws in graphene sheets. The imperfections have unique electronic properties that the researchers were able to exploit to increase sensitivity to absorbed gas molecules by 300 times.

Researchers have discovered a way to create a highly sensitive chemical sensor based on the crystalline flaws in graphene sheets. The imperfections have unique electronic properties that the researchers were able to exploit to increase sensitivity to absorbed gas molecules by 300 times.

The study is available online in advance of print in Nature Communications.

In many applications, grain boundaries are considered faults because they scatter electrons and may weaken the lattice. But Amin Salehi-Khojin and his colleagues showed that these imperfections are important to the working of graphene-based gas sensors.

The team created a micron-sized, individual graphene grain boundary in order to probe its electronic properties and study its role in gas sensing.

Their first discovery was that gas molecules are attracted to the grain boundary and accumulate there, rather than on the graphene crystal, making it the ideal spot for sensing gas molecules. A grain boundary’s electrical properties attract molecules to its surface.

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A theoretical chemistry group at UIC, led by Petr Kral, was able to explain this attraction and additional electronic properties of the grain boundary. The irregular nature of the grain boundary produces hundreds of electron-transport gaps with different sensitivities.

"We can easily fabricate chip-scale sensor arrays using these grain boundaries for real-world use.”

“It’s as though we have multiple switches in parallel,” said graduate student Poya Yasaei, first author on the paper. “Gas molecules accumulate on the grain boundary; there is a charge transfer; and, because these channels are all paralleled together, all the channels abruptly open or close. We see a very sharp response.”

Researchers have been trying to develop a highly sensitive and robust sensor for decades, said UIC postdoctoral fellow Bijandra Kumar, a co-author on the paper.

“We can synthesize these grain boundaries on a micrometer scale in a controlled way,” Kumar said. “We can easily fabricate chip-scale sensor arrays using these grain boundaries for real-world use.”
Salehi-Khojin said it should be possible to “tune” the electronic properties of graphene grain-boundary arrays using controlled doping to obtain a fingerprint response — thus creating a reliable and stable “electronic nose.”

With the grain boundary’s strong attraction for gas molecules and the extraordinarily sharp response to any charge transfer, such an electronic nose might be able to detect even a single gas molecule, Salehi-Khojin believes, and would make an ideal sensor.


SOURCE  University of Illinois at Chicago

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 Biosensors  

Researchers have demonstrated an atomically thin, ultrasensitive and scalable molybdenum disulfide field-effect transistor based biosensor and established their potential to detect single molecules.

An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations.

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene’s performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.  Research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Molybdenite overcomes these shortcomings.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

"This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time."

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

Related articles Human Brain Project and Graphene Win Billion Euro FET Flagship Funding (33rdsquare.com) Graphene: Where Science Fiction Meets Science Fact (singularityweblog.com) Danish Chemists Use Graphene To Create Molecular Integrated Circuit (33rdsquare.com)

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”



SOURCE  University of California Santa Barbara 

By 33rd Square

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 Nanotechnology  

A team researchers in Korea has synthesized carbon nanosheets similar to graphene, using a plastic. The new material is free of the defects and complexity involved in producing graphene, and can substitute for graphene as transparent electrodes for organic solar cells and in semiconductor chips, they say.

Graphene has been dubbed a “wonder material,” and has potential for numerous applications because of the material's great conductivity, flexibility and durability. However, graphene is hard to come by due to the fact that its manufacturing process is complicated and mass production not yet fully achievable.

Now, a Korean research team has developed a carbon material without artificial defects commonly found during the production process of graphene while maintaining thea material's original characteristics. The newly developed material can be used as a substitute for graphene in solar cells and semiconductor chips. Further, the developed process is based on the continuous and mass-produced process of carbon fiber, making it much easier for full-scale commercialization.

The carbon nanosheet can be mass-produced in a simpler process while having high quality since the new process bypasses the steps that are prone to formation of defects such as elimination of the metal substrate or transfer of graphene to another board. The final product is as effective as graphene.

In recognition of the innovative approach, the research was introduced on the cover of Nanoscale, a high impacting peer-reviewed journal in the field of nano science.

The research team led by Dr. Han-Ik Joh at the Korea Institute of Science and Technolgy (KIST) along with Dr. Seok-In Na at Chonbuk National University and Dr. Byoung Gak Kim at KRICT synthesized carbon nanosheets similar to graphene using polymer, and directly used the transparent electrodes for organic solar cells.

Related articles Inexpensive One-Atom-Thick Graphene Supercapcitors Created  The Amazing Potential of Nanotechnology  Danish Chemists Use Graphene To Create Molecular Integrated Circuit

To manufacture high quality graphene in large volume, the CVD (chemical vapor deposition) method is widely used. The technique for manufacturing graphene on the board of metal film that serves as a catalyst. It manufactures the material by blowing out gas called the source gas onto the board. After it is done the metal has to be removed and graphene has to be transported to another board. However, this method requires intensive post-processing (transfer process) as it has to remove used metal after the manufacturing process and move the manufactured graphene to another board such as a solar cell substrate. In this process the quality quickly degrades as it is prone to wrinkles or cracks.

The research team developed “carbon nanosheet” in a two-step process, which consists of coating the substrate with a polymer solution and heating. Considering that the existing process consists of eight steps to manufacture graphene, the new method makes it much simpler. In addition, the new method can be directly used as solar cell without any additional process.

The research team synthesized a polymer with a rigid ladder structure, namely PIM-1(Polymer of intrinsic microporosity-1) to form the CNS through the simpole process, which is spin-coated on the quarts substrates using PIM-1 solution with light green color and then heat-treated at 1,200 °C, leading to transparent and conductive CNS.

The carbon nanosheet can be mass-produced in a simpler process while having high quality since the new process bypasses the steps that are prone to formation of defects such as elimination of the metal substrate or transfer of graphene to another board. The final product is as effective as graphene.

Dr. Han Ik Joh at KIST said, “It is expected to be applied for commercialization of transparent and conductive 2D carbon materials without difficulty since this process is based on the continuous and mass-produced process of carbon fiber.”

This is a follow-up research from the team that recently released its findings on the carbon nanosheet manufacturing based on polyacrylonitrile. The new findings are even more meaningful as it offers deeper understanding on the growth mechanism of carbon nanosheet and much simpler manufacturing process.


SOURCE  KIST

By 33rd Square

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