Category Archives: graphene

Manipulating graphene’s conductivity with honey

Honey can be used for many things, to heal wounds, for advice (You catch more flies with honey), to clean your hair (see suggestion no. 19 here) and, even, scientific inspiration according to a Sept. 22, 2017 news item on phys.org,

Dr. Richard Ordonez, a nanomaterials scientist at the Space and Naval Warfare Systems Center Pacific (SSC Pacific), was having stomach pains last year. So begins the story of the accidental discovery that honey—yes, the bee byproduct—is an effective, non-toxic substitute for the manipulation of the current and voltage characteristics of graphene.

The news item was originated by a Sept. 22, 2017 article by Katherine Connor (who works for  the US Space and Naval warfare Center) and placed in cemag.us,

Ordonez’ lab mate and friend Cody Hayashi gave him some store-bought honey as a Christmas gift and anti-inflammatory for his stomach, and Ordonez kept it near his work station for daily use. One day in the lab, the duo was investigating various dielectric materials they could use to fabricate a graphene transistor. First, the team tried to utilize water as a top-gate dielectric to manipulate graphene’s electrical conductivity. This approach was unsuccessful, so they proceeded with various compositions of sugar and deionized water, another electrolyte, which still resulted in negligible performance. That’s when the honey caught Ordonez’ eye, and an accidental scientific breakthrough was realized.

The finding is detailed in a paper in Nature Scientific Reports, in which the team describes how honey produces a nanometer-sized electric double layer at the interface with graphene that can be used to gate the ambipolar transport of graphene.

“As a top-gate dielectric, water is much too conductive, so we moved to sugar and de-ionized water to control the ionic composition in hopes we could reduce conductivity,” Ordonez explains. “However, sugar water didn’t work for us either because, as a gate-dielectric, there was still too much leakage current. Out of frustration, literally inches away from me was the honey Cody had bought, so we decided to drop-cast the honey on graphene to act as top-gate dielectric — I thought maybe the honey would mimic dielectric gels I read about in literature. To our surprise — everyone said it’s not going to work — we tried and it did.”

Image of the liquid-metal graphene field-effect transistor (LM-GFET) and representation of charge distribution in electrolytic gate dielectrics comprised of honey. Image: Space and Naval Warfare Systems Center

 

Ordonez, Hayashi, and a team of researchers from SSC Pacific, in collaboration with the University of Hawai′i at Mānoa, have been developing novel graphene devices as part of a Navy Innovative Science and Engineering (NISE)-funded effort to imbue the Navy with inexpensive, lightweight, flexible graphene-based devices that can be used as next-generation sensors and wearable devices.

“Traditionally, electrolytic gate transistors are made with ionic gel materials,” Hayashi says. “But you must be proficient with the processes to synthesize them, and it can take several months to figure out the correct recipe that is required for these gels to function in the environment. Some of the liquids are toxic, so experimentation must be conducted in an atmospheric-controlled environment. Honey is completely different — it performs similarly to these much more sophisticated materials, but is safe, inexpensive, and easier to use. The honey was an intermediate step towards using ionic gels, and possibly a replacement for certain applications.”

Ordonez and Hayashi envision the honey-based version of graphene products being used for rapid prototyping of devices, since the devices can be created quickly and easily redesigned based on results. Instead of having to spend months developing the materials before even beginning to incorporate it into devices, using honey allows the team to get initial tests underway without waiting for costly fabrication equipment.

Ordonez also sees a use for such products in science, technology, engineering, and math (STEM) outreach efforts, since the honey is non-toxic and could be used to teach students about graphene.

This latest innovation and publication was a follow-on from the group’s discovery last year that liquid metals can be used in place of rigid electrodes such as gold and silver to electrically contact graphene. This, coupled with research on graphene and multi-spectral detection, earned them the Federal Laboratory Consortium Far West Regional Award in the category of Outstanding Technology Development.

SSC Pacific is the naval research and development lab responsible for ensuring Information Warfare superiority for warfighters, including the areas of cyber, command and control, intelligence, surveillance and reconnaissance, and space systems.

Here’s a link to and a citation for the paper,

Rapid Fabrication of Graphene Field-Effect Transistors with Liquid-metal Interconnects and Electrolytic Gate Dielectric Made of Honey by Richard C. Ordonez, Cody K. Hayashi, Carlos M. Torres, Jordan L. Melcher, Nackieb Kamin, Godwin Severa, & David Garmire. Scientific Reports 7, Article number: 10171 (2017) doi:10.1038/s41598-017-10043-4 Published online: 31 August 2017

This paper is open access.

Liquid circuitry, shape-shifting fluids and more

I’d have to see it to believe it but researchers at the US Dept. of Energy (DOE) Lawrence Berkeley National Laboratory (LBNL) have developed a new kind of ‘bijel’ which would allow for some pretty nifty robotics. From a Sept. 25, 2017 news item on ScienceDaily,

A new two-dimensional film, made of polymers and nanoparticles and developed by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), can direct two different non-mixing liquids into a variety of exotic architectures. This finding could lead to soft robotics, liquid circuitry, shape-shifting fluids, and a host of new materials that use soft, rather than solid, substances.

The study, reported today in the journal Nature Nanotechnology, presents the newest entry in a class of substances known as bicontinuous jammed emulsion gels, or bijels, which hold promise as a malleable liquid that can support catalytic reactions, electrical conductivity, and energy conversion.

A Sept. 25, 2017 LBNL news release (also on EurekAlert), which originated the news item, expands on the theme,

Bijels are typically made of immiscible, or non-mixing, liquids. People who shake their bottle of vinaigrette before pouring the dressing on their salad are familiar with such liquids. As soon as the shaking stops, the liquids start to separate again, with the lower density liquid – often oil – rising to the top.

Trapping, or jamming, particles where these immiscible liquids meet can prevent the liquids from completely separating, stabilizing the substance into a bijel. What makes bijels remarkable is that, rather than just making the spherical droplets that we normally see when we try to mix oil and water, the particles at the interface shape the liquids into complex networks of interconnected fluid channels.

Bijels are notoriously difficult to make, however, involving exact temperatures at precisely timed stages. In addition, the liquid channels are normally more than 5 micrometers across, making them too large to be useful in energy conversion and catalysis.

“Bijels have long been of interest as next-generation materials for energy applications and chemical synthesis,” said study lead author Caili Huang. “The problem has been making enough of them, and with features of the right size. In this work, we crack that problem.”

Huang started the work as a graduate student with Thomas Russell, the study’s principal investigator, at Berkeley Lab’s Materials Sciences Division, and he continued the project as a postdoctoral researcher at DOE’s Oak Ridge National Laboratory.

Creating a new bijel recipe

The method described in this new study simplifies the bijel process by first using specially coated particles about 10-20 nanometers in diameter. The smaller-sized particles line the liquid interfaces much more quickly than the ones used in traditional bijels, making the smaller channels that are highly valued for applications.

Illustration shows key stages of bijel formation. Clockwise from top left, two non-mixing liquids are shown. Ligands (shown in yellow) with amine groups are dispersed throughout the oil or solvent, and nanoparticles coated with carboxylic acids (shown as blue dots) are scattered in the water. With vigorous shaking, the nanoparticles and ligands form a “supersoap” that gets trapped at the interface of the two liquids. The bottom panel is a magnified view of the jammed nanoparticle supersoap. (Credit: Caili Huang/ORNL)

“We’ve basically taken liquids like oil and water and given them a structure, and it’s a structure that can be changed,” said Russell, a visiting faculty scientist at Berkeley Lab. “If the nanoparticles are responsive to electrical, magnetic, or mechanical stimuli, the bijels can become reconfigurable and re-shaped on demand by an external field.”

The researchers were able to prepare new bijels from a variety of common organic, water-insoluble solvents, such as toluene, that had ligands dissolved in it, and deionized water, which contained the nanoparticles. To ensure thorough mixing of the liquids, they subjected the emulsion to a vortex spinning at 3,200 revolutions per minute.

“This extreme shaking creates a whole bunch of new places where these particles and polymers can meet each other,” said study co-author Joe Forth, a postdoctoral fellow at Berkeley Lab’s Materials Sciences Division. “You’re synthesizing a lot of this material, which is in effect a thin, 2-D coating of the liquid surfaces in the system.”

The liquids remained a bijel even after one week, a sign of the system’s stability.

Russell, who is also a professor of polymer science and engineering at the University of Massachusetts-Amherst, added that these shape-shifting characteristics would be valuable in microreactors, microfluidic devices, and soft actuators.

Nanoparticle supersoap

Nanoparticles had not been seriously considered in bijels before because their small size made them hard to trap in the liquid interface. To resolve that problem, the researchers coated nano-sized particles with carboxylic acids and put them in water. They then took polymers with an added amine group – a derivative of ammonia – and dissolved them in the toluene.

At left is a vial of bijel stabilized with nanoparticle surfactants. On the right is the same vial after a week of inversion, showing that the nanoparticle kept the liquids from moving. (Credit: Caili Huang/ORNL)

This configuration took advantage of the amine group’s affinity to water, a characteristic that is comparable to surfactants, like soap. Their nanoparticle “supersoap” was designed so that the nanoparticles join ligands, forming an octopus-like shape with a polar head and nonpolar legs that get jammed at the interface, the researchers said.

“Bijels are really a new material, and also excitingly weird in that they are kinetically arrested in these unusual configurations,” said study co-author Brett Helms, a staff scientist at Berkeley Lab’s Molecular Foundry. “The discovery that you can make these bijels with simple ingredients is a surprise. We all have access to oils and water and nanocrystals, allowing broad tunability in bijel properties. This platform also allows us to experiment with new ways to control their shape and function since they are both responsive and reconfigurable.”

The nanoparticles were made of silica, but the researchers noted that in previous studies they used graphene and carbon nanotubes to form nanoparticle surfactants.

“The key is that the nanoparticles can be made of many materials,” said Russell.  “The most important thing is what’s on the surface.”

This is an animation of the bijel

3-D rendering of the nanoparticle bijel taken by confocal microscope. (Credit: Caili Huang/ORNL [Oak Ridge National Laboratory] and Joe Forth/Berkeley Lab)

Here’s a link to and a citation for the paper,

Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants by Caili Huang, Joe Forth, Weiyu Wang, Kunlun Hong, Gregory S. Smith, Brett A. Helms & Thomas P. Russell. Nature Nanotechnology (2017) doi:10.1038/nnano.2017.182 25 September 2017

This paper is behind a paywall.

Substituting graphene and other carbon materials for scarce metals

A Sept. 19, 2017 news item on Nanowerk announces a new paper from the Chalmers University of Technology (Sweden), the lead institution for the Graphene Flagship (a 1B Euro 10 year European Commission programme), Note: A link has been removed,

Scarce metals are found in a wide range of everyday objects around us. They are complicated to extract, difficult to recycle and so rare that several of them have become “conflict minerals” which can promote conflicts and oppression. A survey at Chalmers University of Technology now shows that there are potential technology-based solutions that can replace many of the metals with carbon nanomaterials, such as graphene (Journal of Cleaner Production, “Carbon nanomaterials as potential substitutes for scarce metals”).

They can be found in your computer, in your mobile phone, in almost all other electronic equipment and in many of the plastics around you. Society is highly dependent on scarce metals, and this dependence has many disadvantages.

A Sept. 19, 2017 Chalmers University of Technology press release by Ulrika Ernstrom,, which originated the news item, provides more detail about the possibilities,

They can be found in your computer, in your mobile phone, in many of the plastics around you and in almost all electronic equipment. Society is highly dependent on scarce metals, and this dependence has many disadvantages.
Scarce metals such as tin, silver, tungsten and indium are both rare and difficult to extract since the workable concentrations are very small. This ensures the metals are highly sought after – and their extraction is a breeding ground for conflicts, such as in the Democratic Republic of the Congo where they fund armed conflicts.
In addition, they are difficult to recycle profitably since they are often present in small quantities in various components such as electronics.
Rickard Arvidsson and Björn Sandén, researchers in environmental systems analysis at Chalmers University of Technology, have now examined an alternative solution: substituting carbon nanomaterials for the scarce metals. These substances – the best known of which is graphene – are strong materials with good conductivity, like scarce metals.
“Now technology development has allowed us to make greater use of the common element carbon,” says Sandén. “Today there are many new carbon nanomaterials with similar properties to metals. It’s a welcome new track, and it’s important to invest in both the recycling and substitution of scarce metalsfrom now on.”
The Chalmers researchers have studied  the main applications of 14 different metals, and by reviewing patents and scientific literature have investigated the potential for replacing them by carbon nanomaterials. The results provide a unique overview of research and technology development in the field.
According to Arvidsson and Sandén the summary shows that a shift away from the use of scarce metals to carbon nanomaterials is already taking place.
….
“There are potential technology-based solutions for replacing 13 out of the 14 metals by carbon nanomaterials in their most common applications. The technology development is at different stages for different metals and applications, but in some cases such as indium and gallium, the results are very promising,” Arvidsson says.
“This offers hope,” says Sandén. “In the debate on resource constraints, circular economy and society’s handling of materials, the focus has long been on recycling and reuse. Substitution is a potential alternative that has not been explored to the same extent and as the resource issues become more pressing, we now have more tools to work with.”
The research findings were recently published in the Journal of Cleaner Production. Arvidsson and Sandén stress that there are significant potential benefits from reducing the use of scarce metals, and they hope to be able to strengthen the case for more research and development in the field.
“Imagine being able to replace scarce metals with carbon,” Sandén says. “Extracting the carbon from biomass would create a natural cycle.”
“Since carbon is such a common and readily available material, it would also be possible to reduce the conflicts and geopolitical problems associated with these metals,” Arvidsson says.
At the same time they point out that more research is needed in the field in order to deal with any new problems that may arise if the scarce metals are replaced.
“Carbon nanomaterials are only a relatively recent discovery, and so far knowledge is limited about their environmental impact from a life-cycle perspective. But generally there seems to be a potential for a low environmental impact,” Arvidsson says.

FACTS AND MORE INFORMATION

Carbon nanomaterials consist solely or mainly of carbon, and are strong materials with good conductivity. Several scarce metals have similar properties. The metals are found, for example, in cables, thin screens, flame-retardants, corrosion protection and capacitors.
Rickard Arvidsson and Björn Sandén at Chalmers University of Technology have investigated whether the carbon nanomaterials graphene, fullerenes and carbon nanotubes have the potential to replace 14 scarce metals in their main areas of application (see table). They found potential technology-based solutions to replace the metals with carbon nanomaterials for all applications except for gold in jewellery. The metals which we are closest to being able to substitute are indium, gallium, beryllium and silver.

Here’s a link to and a citation for the paper,

Carbon nanomaterials as potential substitutes for scarce metals by Rickard Arvidsson, Björn A. Sandén. Journal of Cleaner Production (0959-6526). Vol. 156 (2017), p. 253-261. DOI: https://doi.org/10.1016/j.jclepro.2017.04.048

This paper appears to be open access.

A new wave of physics: electrons flow like liquid in graphene

Unfortunately I couldn’t find a credit for the artist for the graphic (I really like it) which accompanies the news about a new physics and graphene,

Courtesy: University of Manchester

From an Aug. 22, 2017 news item on phys.org (Note: A link has been removed),

A new understanding of the physics of conductive materials has been uncovered by scientists observing the unusual movement of electrons in graphene.

Graphene is many times more conductive than copper thanks, in part, to its two-dimensional structure. In most metals, conductivity is limited by crystal imperfections which cause electrons to frequently scatter like billiard balls when they move through the material.

Now, observations in experiments at the National Graphene Institute have provided essential understanding as to the peculiar behaviour of electron flows in graphene, which need to be considered in the design of future Nano-electronic circuits.

An Aug. 22, 2017 University of Manchester press release, which originated the news item, delves further into the research (Note: Links have been removed),

Appearing today in Nature Physics, researchers at The University of Manchester, in collaboration with theoretical physicists led by Professor Marco Polini and Professor Leonid Levitov, show that Landauer’s fundamental limit can be breached in graphene. Even more fascinating is the mechanism responsible for this.

Last year, a new field in solid-state physics termed ‘electron hydrodynamics’ generated huge scientific interest. Three different experiments, including one performed by The University of Manchester, demonstrated that at certain temperatures, electrons collide with each other so frequently they start to flow collectively like a viscous fluid.

The new research demonstrates that this viscous fluid is even more conductive than ballistic electrons. The result is rather counter-intuitive, since typically scattering events act to lower the conductivity of a material, because they inhibit movement within the crystal. However, when electrons collide with each other, they start working together and ease current flow.

This happens because some electrons remain near the crystal edges, where momentum dissipation is highest, and move rather slowly. At the same time, they protect neighbouring electrons from colliding with those regions. Consequently, some electrons become super-ballistic as they are guided through the channel by their friends.

Sir Andre Geim said: “We know from school that additional disorder always creates extra electrical resistance. In our case, disorder induced by electron scattering actually reduces rather than increase resistance. This is unique and quite counterintuitive: Electrons when make up a liquid start propagating faster than if they were free, like in vacuum”.

The researchers measured the resistance of graphene constrictions, and found it decreases upon increasing temperature, in contrast to the usual metallic behaviour expected for doped graphene.

By studying how the resistance across the constrictions changes with temperature, the scientists revealed a new physical quantity which they called the viscous conductance. The measurements allowed them to determine electron viscosity to such a high precision that the extracted values showed remarkable quantitative agreement with theory.

Here’s a link to and a citation for the paper,

Superballistic flow of viscous electron fluid through graphene constrictions by R. Krishna Kumar, D. A. Bandurin, F. M. D. Pellegrino, Y. Cao, A. Principi, H. Guo, G. H. Auton, M. Ben Shalom, L. A. Ponomarenko, G. Falkovich, K. Watanabe, T. Taniguchi, I. V. Grigorieva, L. S. Levitov, M. Polini, & A. K. Geim. Nature Physics (2017) doi:10.1038/nphys4240 Published online 21 August 2017

This paper is behind a paywall.

The security of the Internet of Nano-Things with NanoMalaysia’s CEO Dr Rezal Khairi Ahmad

I’ve not come across the Internet of Nano-Things before and I’m always glad to be introduced to something new. In this case, I’m doubly happy as I get to catch up (a little) with the Malaysian nano scene. From an April 19, 2017 article by Avanti Kumar for mis.asia.com (Note: Links have been removed),

After being certified in 2011 as a nanocentre, national applied research agency MIMOS continued to make regular moves to boost Malaysia’s nanotechnology ambitions. This included helping to develop the national graphene action plan (NGAP 2020).

Much of the task of driving and commercialising the NGAP ecosystem is in the hands of NanoMalaysia, which was incorporated in 2011 as a company limited by guarantee (CLG) under Malaysia’s Ministry of Science, Technology and Innovation (MOSTI) to act as a business entity.

During another event in March 2016 where I saw that 360 new products were to be commercialised under NGAP, NanoMalaysia’s chief executive officer Dr. Rezal Khairi Ahmad said that benefits would include a US$5 billion impact on GNI (gross net income) and 9,000 related new jobs by the year 2020.

In his capacity as a keynote speaker at this year’s Computerworld Security Summit in Kuala Lumpur (20 April 2017), Dr Rezal agreed to a security-themed interview on this relatively new industry sector.  This is also part of a series of special security features.

To start, I asked Dr Rezal for a brief run-through of his role.

[RKA]  I’m the founding Chief Executive Officer and also Board Member of NanoMalaysia, Nano Commerce Sdn. Bhd, representing NanoMalaysia’s business interests, the Chairman of NanoVerify Sdn. Bhd, a nanotechnology certification entity and a Director of Nanovation Ventures Sdn. Bhd., an investment arm of NanoMalaysia.

Prior to this, I served as Acting Under-Secretary of National Nanotechnology Directorate, Ministry of Science, Technology and Innovation on the policy aspect of nanotechnology and vice president of [national investment body] Khazanah Nasional touching on human capital and investment research.

NanoMalaysia’s primary role in the development of Malaysia’s National Graphene Action Plan 2020 together with Agensi Inovasi Malaysia and PEMANDU [Performance Management & Delivery Unit attached to Prime Minister’s Office] is a major landmark in our journey to ensure Malaysia stays competitive in the global innovation landscape particularly in nanotechnology, which cuts across all industries including ICT [information and communications technologies].

Can you talk about graphene and its significance to local industry?

Graphene is touted as one of the game-changing advanced materials made of one atom-thick carbon and acknowledged by World Economic Forum [WEF] as no. 4 emerging technology in 2016.

Beyond being a fancy nano material, graphene plays a central role in the development of endogenous hardware aspects of Malaysia’s Internet of Things aspirations or the now evolved Internet of Nano-Things (IoNT). Some of these are:
-·Super small, lightweight and hyper-sensitive low-cost Graphene-based sensors and Radio Frequency ID (RFID)
– Higher speed, Low loss and power consumption graphene based optical transmitter and receiver for 5G systems
– Making IoNT a low-cost and practical industrial and domestic solutions in Malaysia.

Let’s move to the security aspects of nanotechnology: what’s your take on IoNT?

In the context of IoNT, which WEF acknowledged to be the top emerging technology in 2016, the current work-in-progress,  ‘ubiquitous’ deployment of sensors in Malaysia and worldwide, I certainly see increasing data security risks at the sensor, transmission, collection, processing and even analytics levels.

The initial industry approaches to IoNT data security will probably be polarised between cascaded and centralised system approaches.

I think some hacking attacks will obviously focus on data theft. I therefore foresee a trend favouring cascaded security – with both hardware, software and more advanced data encryption technologies in place.

What security steps do you currently advise?

The priority is to tackle potential data theft at every stage of IoNT systems.  The best-available preventive measures should include some versions of cascaded and embedded security in the form of hardware tags and advanced encryption.

To end, what’s your main message for business and IT leaders?

The digital era has removed the clear line that once separated State and Business as well as People. Everything and everyone is more interconnected. We are now an ecosystem both by chance and design. Cyber-attacks can be made to afflict either one and be used to hold any one at ransom thus creating a local or even global systemic chain reaction effect.

The connected world presents endless commercial, social and environmental development opportunities…and threats. The development and deployment of emerging cyber-related technologies, in particular IoNT – which promises a market size of US$9.69 billion by 2020 – should be done responsibly in the form of infused data security technologies to ensure prolific market acceptance and profitable returns.

For our part, NanoMalaysia is working with various parties locally and abroad push Malaysia’s strategic industry sectors to be relevant to the Fourth Industrial Revolution supported by cyber-physical systems manifesting into full automation, robots, artificial intelligence, de-centralised power generation, energy storage, water and food supplies, remote assets and logistics management and custom manufacturing requiring secured data sensing, traffic and analytics systems in place.

If you have the time, I advise reading the article in its entirety.

2D printed transistors in Ireland

2D transistors seem to be a hot area for research these days. In Ireland, the AMBER Centre has announced a transistor consisting entirely of 2D nanomaterials in an April 6, 2017 news item on Nanowerk,

Researchers in AMBER, the Science Foundation Ireland-funded materials science research centre hosted in Trinity College Dublin, have fabricated printed transistors consisting entirely of 2-dimensional nanomaterials for the first time. These 2D materials combine exciting electronic properties with the potential for low-cost production.

This breakthrough could unlock the potential for applications such as food packaging that displays a digital countdown to warn you of spoiling, wine labels that alert you when your white wine is at its optimum temperature, or even a window pane that shows the day’s forecast. …

An April 7, 2017 AMBER Centre press release (also on EurekAlert), which originated the news item, expands on the theme,

Prof Jonathan Coleman, who is an investigator in AMBER and Trinity’s School of Physics, said, “In the future, printed devices will be incorporated into even the most mundane objects such as labels, posters and packaging.

Printed electronic circuitry (constructed from the devices we have created) will allow consumer products to gather, process, display and transmit information: for example, milk cartons could send messages to your phone warning that the milk is about to go out-of-date.

We believe that 2D nanomaterials can compete with the materials currently used for printed electronics. Compared to other materials employed in this field, our 2D nanomaterials have the capability to yield more cost effective and higher performance printed devices. However, while the last decade has underlined the potential of 2D materials for a range of electronic applications, only the first steps have been taken to demonstrate their worth in printed electronics. This publication is important because it shows that conducting, semiconducting and insulating 2D nanomaterials can be combined together in complex devices. We felt that it was critically important to focus on printing transistors as they are the electric switches at the heart of modern computing. We believe this work opens the way to print a whole host of devices solely from 2D nanosheets.”

Led by Prof Coleman, in collaboration with the groups of Prof Georg Duesberg (AMBER) and Prof. Laurens Siebbeles (TU Delft,Netherlands), the team used standard printing techniques to combine graphene nanosheets as the electrodes with two other nanomaterials, tungsten diselenide and boron nitride as the channel and separator (two important parts of a transistor) to form an all-printed, all-nanosheet, working transistor.

Printable electronics have developed over the last thirty years based mainly on printable carbon-based molecules. While these molecules can easily be turned into printable inks, such materials are somewhat unstable and have well-known performance limitations. There have been many attempts to surpass these obstacles using alternative materials, such as carbon nanotubes or inorganic nanoparticles, but these materials have also shown limitations in either performance or in manufacturability. While the performance of printed 2D devices cannot yet compare with advanced transistors, the team believe there is a wide scope to improve performance beyond the current state-of-the-art for printed transistors.

The ability to print 2D nanomaterials is based on Prof. Coleman’s scalable method of producing 2D nanomaterials, including graphene, boron nitride, and tungsten diselenide nanosheets, in liquids, a method he has licensed to Samsung and Thomas Swan. These nanosheets are flat nanoparticles that are a few nanometres thick but hundreds of nanometres wide. Critically, nanosheets made from different materials have electronic properties that can be conducting, insulating or semiconducting and so include all the building blocks of electronics. Liquid processing is especially advantageous in that it yields large quantities of high quality 2D materials in a form that is easy to process into inks. Prof. Coleman’s publication provides the potential to print circuitry at extremely low cost which will facilitate a range of applications from animated posters to smart labels.

Prof Coleman is a partner in Graphene flagship, a €1 billion EU initiative to boost new technologies and innovation during the next 10 years.

Here’s a link to and a citation for the paper,

All-printed thin-film transistors from networks of liquid-exfoliated nanosheets by Adam G. Kelly, Toby Hallam, Claudia Backes, Andrew Harvey, Amir Sajad Esmaeily, Ian Godwin, João Coelho, Valeria Nicolosi, Jannika Lauth, Aditya Kulkarni, Sachin Kinge, Laurens D. A. Siebbeles, Georg S. Duesberg, Jonathan N. Coleman. Science  07 Apr 2017: Vol. 356, Issue 6333, pp. 69-73 DOI: 10.1126/science.aal4062

This paper is behind a paywall.

Solar-powered graphene skin for more feeling in your prosthetics

A March 23, 2017 news item on Nanowerk highlights research that could put feeling into a prosthetic limb,

A new way of harnessing the sun’s rays to power ‘synthetic skin’ could help to create advanced prosthetic limbs capable of returning the sense of touch to amputees.

Engineers from the University of Glasgow, who have previously developed an ‘electronic skin’ covering for prosthetic hands made from graphene, have found a way to use some of graphene’s remarkable physical properties to use energy from the sun to power the skin.

Graphene is a highly flexible form of graphite which, despite being just a single atom thick, is stronger than steel, electrically conductive, and transparent. It is graphene’s optical transparency, which allows around 98% of the light which strikes its surface to pass directly through it, which makes it ideal for gathering energy from the sun to generate power.

A March 23, 2017 University of Glasgow press release, which originated the news item, details more about the research,

Ravinder Dahiya

Dr Ravinder Dahiya

A new research paper, published today in the journal Advanced Functional Materials, describes how Dr Dahiya and colleagues from his Bendable Electronics and Sensing Technologies (BEST) group have integrated power-generating photovoltaic cells into their electronic skin for the first time.

Dr Dahiya, from the University of Glasgow’s School of Engineering, said: “Human skin is an incredibly complex system capable of detecting pressure, temperature and texture through an array of neural sensors which carry signals from the skin to the brain.

“My colleagues and I have already made significant steps in creating prosthetic prototypes which integrate synthetic skin and are capable of making very sensitive pressure measurements. Those measurements mean the prosthetic hand is capable of performing challenging tasks like properly gripping soft materials, which other prosthetics can struggle with. We are also using innovative 3D printing strategies to build more affordable sensitive prosthetic limbs, including the formation of a very active student club called ‘Helping Hands’.

“Skin capable of touch sensitivity also opens the possibility of creating robots capable of making better decisions about human safety. A robot working on a construction line, for example, is much less likely to accidentally injure a human if it can feel that a person has unexpectedly entered their area of movement and stop before an injury can occur.”

The new skin requires just 20 nanowatts of power per square centimetre, which is easily met even by the poorest-quality photovoltaic cells currently available on the market. And although currently energy generated by the skin’s photovoltaic cells cannot be stored, the team are already looking into ways to divert unused energy into batteries, allowing the energy to be used as and when it is required.

Dr Dahiya added: “The other next step for us is to further develop the power-generation technology which underpins this research and use it to power the motors which drive the prosthetic hand itself. This could allow the creation of an entirely energy-autonomous prosthetic limb.

“We’ve already made some encouraging progress in this direction and we’re looking forward to presenting those results soon. We are also exploring the possibility of building on these exciting results to develop wearable systems for affordable healthcare. In this direction, recently we also got small funds from Scottish Funding Council.”

For more information about this advance and others in the field of prosthetics you may want to check out Megan Scudellari’s March 30, 2017 article for the IEEE’s (Institute of Electrical and Electronics Engineers) Spectrum (Note: Links have been removed),

Cochlear implants can restore hearing to individuals with some types of hearing loss. Retinal implants are now on the market to restore sight to the blind. But there are no commercially available prosthetics that restore a sense of touch to those who have lost a limb.

Several products are in development, including this haptic system at Case Western Reserve University, which would enable upper-limb prosthetic users to, say, pluck a grape off a stem or pull a potato chip out of a bag. It sounds simple, but such tasks are virtually impossible without a sense of touch and pressure.

Now, a team at the University of Glasgow that previously developed a flexible ‘electronic skin’ capable of making sensitive pressure measurements, has figured out how to power their skin with sunlight. …

Here’s a link to and a citation for the paper,

Energy-Autonomous, Flexible, and Transparent Tactile Skin by Carlos García Núñez, William Taube Navaraj, Emre O. Polat and Ravinder Dahiya. Advanced Functional Materials DOI: 10.1002/adfm.201606287 Version of Record online: 22 MAR 2017

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Gamechanging electronics with new ultrafast, flexible, and transparent electronics

There are two news bits about game-changing electronics, one from the UK and the other from the US.

United Kingdom (UK)

An April 3, 2017 news item on Azonano announces the possibility of a future golden age of electronics courtesy of the University of Exeter,

Engineering experts from the University of Exeter have come up with a breakthrough way to create the smallest, quickest, highest-capacity memories for transparent and flexible applications that could lead to a future golden age of electronics.

A March 31, 2017 University of Exeter press release (also on EurekAlert), which originated the news item, expands on the theme (Note: Links have been removed),

Engineering experts from the University of Exeter have developed innovative new memory using a hybrid of graphene oxide and titanium oxide. Their devices are low cost and eco-friendly to produce, are also perfectly suited for use in flexible electronic devices such as ‘bendable’ mobile phone, computer and television screens, and even ‘intelligent’ clothing.

Crucially, these devices may also have the potential to offer a cheaper and more adaptable alternative to ‘flash memory’, which is currently used in many common devices such as memory cards, graphics cards and USB computer drives.

The research team insist that these innovative new devices have the potential to revolutionise not only how data is stored, but also take flexible electronics to a new age in terms of speed, efficiency and power.

Professor David Wright, an Electronic Engineering expert from the University of Exeter and lead author of the paper said: “Using graphene oxide to produce memory devices has been reported before, but they were typically very large, slow, and aimed at the ‘cheap and cheerful’ end of the electronics goods market.

“Our hybrid graphene oxide-titanium oxide memory is, in contrast, just 50 nanometres long and 8 nanometres thick and can be written to and read from in less than five nanoseconds – with one nanometre being one billionth of a metre and one nanosecond a billionth of a second.”

Professor Craciun, a co-author of the work, added: “Being able to improve data storage is the backbone of tomorrow’s knowledge economy, as well as industry on a global scale. Our work offers the opportunity to completely transform graphene-oxide memory technology, and the potential and possibilities it offers.”

Here’s a link to and a citation for the paper,

Multilevel Ultrafast Flexible Nanoscale Nonvolatile Hybrid Graphene Oxide–Titanium Oxide Memories by V. Karthik Nagareddy, Matthew D. Barnes, Federico Zipoli, Khue T. Lai, Arseny M. Alexeev, Monica Felicia Craciun, and C. David Wright. ACS Nano, 2017, 11 (3), pp 3010–3021 DOI: 10.1021/acsnano.6b08668 Publication Date (Web): February 21, 2017

Copyright © 2017 American Chemical Society

This paper appears to be open access.

United States (US)

Researchers from Stanford University have developed flexible, biodegradable electronics.

A newly developed flexible, biodegradable semiconductor developed by Stanford engineers shown on a human hair. (Image credit: Bao lab)

A human hair? That’s amazing and this May 3, 2017 news item on Nanowerk reveals more,

As electronics become increasingly pervasive in our lives – from smart phones to wearable sensors – so too does the ever rising amount of electronic waste they create. A United Nations Environment Program report found that almost 50 million tons of electronic waste were thrown out in 2017–more than 20 percent higher than waste in 2015.

Troubled by this mounting waste, Stanford engineer Zhenan Bao and her team are rethinking electronics. “In my group, we have been trying to mimic the function of human skin to think about how to develop future electronic devices,” Bao said. She described how skin is stretchable, self-healable and also biodegradable – an attractive list of characteristics for electronics. “We have achieved the first two [flexible and self-healing], so the biodegradability was something we wanted to tackle.”

The team created a flexible electronic device that can easily degrade just by adding a weak acid like vinegar. The results were published in the Proceedings of the National Academy of Sciences (“Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics”).

“This is the first example of a semiconductive polymer that can decompose,” said lead author Ting Lei, a postdoctoral fellow working with Bao.

A May 1, 2017 Stanford University news release by Sarah Derouin, which originated the news item, provides more detail,

In addition to the polymer – essentially a flexible, conductive plastic – the team developed a degradable electronic circuit and a new biodegradable substrate material for mounting the electrical components. This substrate supports the electrical components, flexing and molding to rough and smooth surfaces alike. When the electronic device is no longer needed, the whole thing can biodegrade into nontoxic components.

Biodegradable bits

Bao, a professor of chemical engineering and materials science and engineering, had previously created a stretchable electrode modeled on human skin. That material could bend and twist in a way that could allow it to interface with the skin or brain, but it couldn’t degrade. That limited its application for implantable devices and – important to Bao – contributed to waste.

Flexible, biodegradable semiconductor on an avacado

The flexible semiconductor can adhere to smooth or rough surfaces and biodegrade to nontoxic products. (Image credit: Bao lab)

Bao said that creating a robust material that is both a good electrical conductor and biodegradable was a challenge, considering traditional polymer chemistry. “We have been trying to think how we can achieve both great electronic property but also have the biodegradability,” Bao said.

Eventually, the team found that by tweaking the chemical structure of the flexible material it would break apart under mild stressors. “We came up with an idea of making these molecules using a special type of chemical linkage that can retain the ability for the electron to smoothly transport along the molecule,” Bao said. “But also this chemical bond is sensitive to weak acid – even weaker than pure vinegar.” The result was a material that could carry an electronic signal but break down without requiring extreme measures.

In addition to the biodegradable polymer, the team developed a new type of electrical component and a substrate material that attaches to the entire electronic component. Electronic components are usually made of gold. But for this device, the researchers crafted components from iron. Bao noted that iron is a very environmentally friendly product and is nontoxic to humans.

The researchers created the substrate, which carries the electronic circuit and the polymer, from cellulose. Cellulose is the same substance that makes up paper. But unlike paper, the team altered cellulose fibers so the “paper” is transparent and flexible, while still breaking down easily. The thin film substrate allows the electronics to be worn on the skin or even implanted inside the body.

From implants to plants

The combination of a biodegradable conductive polymer and substrate makes the electronic device useful in a plethora of settings – from wearable electronics to large-scale environmental surveys with sensor dusts.

“We envision these soft patches that are very thin and conformable to the skin that can measure blood pressure, glucose value, sweat content,” Bao said. A person could wear a specifically designed patch for a day or week, then download the data. According to Bao, this short-term use of disposable electronics seems a perfect fit for a degradable, flexible design.

And it’s not just for skin surveys: the biodegradable substrate, polymers and iron electrodes make the entire component compatible with insertion into the human body. The polymer breaks down to product concentrations much lower than the published acceptable levels found in drinking water. Although the polymer was found to be biocompatible, Bao said that more studies would need to be done before implants are a regular occurrence.

Biodegradable electronics have the potential to go far beyond collecting heart disease and glucose data. These components could be used in places where surveys cover large areas in remote locations. Lei described a research scenario where biodegradable electronics are dropped by airplane over a forest to survey the landscape. “It’s a very large area and very hard for people to spread the sensors,” he said. “Also, if you spread the sensors, it’s very hard to gather them back. You don’t want to contaminate the environment so we need something that can be decomposed.” Instead of plastic littering the forest floor, the sensors would biodegrade away.

As the number of electronics increase, biodegradability will become more important. Lei is excited by their advancements and wants to keep improving performance of biodegradable electronics. “We currently have computers and cell phones and we generate millions and billions of cell phones, and it’s hard to decompose,” he said. “We hope we can develop some materials that can be decomposed so there is less waste.”

Other authors on the study include Ming Guan, Jia Liu, Hung-Cheng Lin, Raphael Pfattner, Leo Shaw, Allister McGuire, and Jeffrey Tok of Stanford University; Tsung-Ching Huang of Hewlett Packard Enterprise; and Lei-Lai Shao and Kwang-Ting Cheng of University of California, Santa Barbara.

The research was funded by the Air Force Office for Scientific Research; BASF; Marie Curie Cofund; Beatriu de Pinós fellowship; and the Kodak Graduate Fellowship.

Here’s a link to and a citation for the team’s latest paper,

Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics by Ting Lei, Ming Guan, Jia Liu, Hung-Cheng Lin, Raphael Pfattner, Leo Shaw, Allister F. McGuire, Tsung-Ching Huang, Leilai Shao, Kwang-Ting Cheng, Jeffrey B.-H. Tok, and Zhenan Bao. PNAS 2017 doi: 10.1073/pnas.1701478114 published ahead of print May 1, 2017

This paper is behind a paywall.

The mention of cellulose in the second item piqued my interest so I checked to see if they’d used nanocellulose. No, they did not. Microcrystalline cellulose powder was used to constitute a cellulose film but they found a way to render this film at the nanoscale. From the Stanford paper (Note: Links have been removed),

… Moreover, cellulose films have been previously used as biodegradable substrates in electronics (28⇓–30). However, these cellulose films are typically made with thicknesses well over 10 μm and thus cannot be used to fabricate ultrathin electronics with substrate thicknesses below 1–2 μm (7, 18, 19). To the best of our knowledge, there have been no reports on ultrathin (1–2 μm) biodegradable substrates for electronics. Thus, to realize them, we subsequently developed a method described herein to obtain ultrathin (800 nm) cellulose films (Fig. 1B and SI Appendix, Fig. S8). First, microcrystalline cellulose powders were dissolved in LiCl/N,N-dimethylacetamide (DMAc) and reacted with hexamethyldisilazane (HMDS) (31, 32), providing trimethylsilyl-functionalized cellulose (TMSC) (Fig. 1B). To fabricate films or devices, TMSC in chlorobenzene (CB) (70 mg/mL) was spin-coated on a thin dextran sacrificial layer. The TMSC film was measured to be 1.2 μm. After hydrolyzing the film in 95% acetic acid vapor for 2 h, the trimethylsilyl groups were removed, giving a 400-nm-thick cellulose film. The film thickness significantly decreased to one-third of the original film thickness, largely due to the removal of the bulky trimethylsilyl groups. The hydrolyzed cellulose film is insoluble in most organic solvents, for example, toluene, THF, chloroform, CB, and water. Thus, we can sequentially repeat the above steps to obtain an 800-nm-thick film, which is robust enough for further device fabrication and peel-off. By soaking the device in water, the dextran layer is dissolved, starting from the edges of the device to the center. This process ultimately releases the ultrathin substrate and leaves it floating on water surface (Fig. 3A, Inset).

Finally, I don’t have any grand thoughts; it’s just interesting to see different approaches to flexible electronics.

Graphene ink image wins top prize in UK national science photography competition

Credit: James Macleod, University of Cambridge

That prizewinning image in the above reminded me of the manhole covers in Vancouver, Canada.

Credit: Daderot 20 June 2015 [downloaded from https://commons.wikimedia.org/wiki/File:Manhole_cover_-_Vancouver,_Canada_-_DSC07640.JPG]

An April 3, 2017 news item on phys.org announces about the prize winner,

An image of spectacular swirling graphene ink in alcohol, which can be used to print electrical circuits onto paper, has won the overall prize in a national science photography competition, organised by the Engineering and Physical Sciences Research Council (EPSRC)

An April 3, 2017 EPSRC press release, which originated the news item, provides more detail about the winning entry and the competition,

‘Graphene – IPA Ink’, by James Macleod, from the University of Cambridge, shows powdered graphite in alcohol which produces a conductive ink. The ink is forced at high pressure through micrometre-scale capillaries made of diamond. This rips the layers apart resulting in a smooth, conductive material in solution.

The image, came first in two categories, Innovation, and Equipment and Facilities, as well as winning overall against many other stunning pictures, featuring research in action, in the EPSRC‘s competition – now in its fourth year.

James Macleod, explained how the photograph came about: We are working to create conductive inks for printing flexible electronics and are currently focused on optimising our recipe for use in different printing methods and for printing onto different surfaces. This was the first time we had used alcohol to create our ink and I was struck by how mesmerising it looked while mixing.

The competition’s five categories were: Eureka and Discovery, Equipment and Facilities, People and Skills, Innovation, and Weird and Wonderful. Other winning images feature:

  • A 3D printed gripper which was programmed to lift delicate, geometrical complex objects like a lightbulb, pneumatically rather than using sensors.
  • A scanning electron microscope image showing the surface of a silicon chip, patterned to create a one metre ultra-thin optical wire, just one millionth of a metre wide made into a spiral and wrapped into an area the size of a square millimetre.
  • Researcher Michael Coto with a local student in Vingunguti, Dar es Salaam, Tanzania, testing and purifying polluted water using new solar active catalysts.
  • An image captured on an iPhone 4s through an optical microscope that shows the variety of textures appearing on the surface of a silicon solar cell, not dissimilar to pyramids surrounded by a sea of dunes in a desert, but with the size of a human hair.
  • Tiny biodegradable polymer particles resembling golf balls being developed to target infectious diseases and cancers. Only 0.04mm across, they form part of scaffolds which are being studied to see if they can support the growth of healthy new cells.

One of the judges was physicist, oceanographer and broadcaster, Dr Helen Czerski, Lecturer at UCL, she said: Scientists and engineers are often so busy focusing on the technical details of their research that they can be blind to what everyone else sees first: the aesthetics of their work. Science is a part of our culture, and it can contribute in many different ways. This competition is a wonderful reminder of the emotional and artistic aspects of science, and it’s great that EPSRC researchers have found this richness in their own work.

Congratulating the winners and entrants, Professor Tom Rodden, EPSRC‘s Deputy Chief Executive, said: The quality of entries into our competition demonstrates that EPSRC-funded researchers are keen to show the world how beautiful and interesting science and engineering can be. I’d like to thank everyone who entered; judging was really difficult.

These stunning images are a great way to engage the public with the research they fund, and inspire everyone to take an interest in science and engineering.

The competition received over 100 entries which were drawn from researchers in receipt of EPSRC funding.

The judges were:

  • Martin Keene – Group Picture Editor – Press Association
  • Dr Helen Czerski – Lecturer at the Department of Mechanical Engineering, University College London
  • Professor Tom Rodden – EPSRC‘s Deputy Chief Executive