Category Archives: graphene

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

Graphene-based neural probes

I have two news bits (dated almost one month apart) about the use of graphene in neural probes, one from the European Union and the other from Korea.

European Union (EU)

This work is being announced by the European Commission’s (a subset of the EU) Graphene Flagship (one of two mega-funding projects announced in 2013; 1B Euros each over ten years for the Graphene Flagship and the Human Brain Project).

According to a March 27, 2017 news item on ScienceDaily, researchers have developed a graphene-based neural probe that has been tested on rats,

Measuring brain activity with precision is essential to developing further understanding of diseases such as epilepsy and disorders that affect brain function and motor control. Neural probes with high spatial resolution are needed for both recording and stimulating specific functional areas of the brain. Now, researchers from the Graphene Flagship have developed a new device for recording brain activity in high resolution while maintaining excellent signal to noise ratio (SNR). Based on graphene field-effect transistors, the flexible devices open up new possibilities for the development of functional implants and interfaces.

The research, published in 2D Materials, was a collaborative effort involving Flagship partners Technical University of Munich (TU Munich; Germany), Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS; Spain), Spanish National Research Council (CSIC; Spain), The Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN; Spain) and the Catalan Institute of Nanoscience and Nanotechnology (ICN2; Spain).

Caption: Graphene transistors integrated in a flexible neural probe enables electrical signals from neurons to be measured with high accuracy and density. Inset: The tip of the probe contains 16 flexible graphene transistors. Credit: ICN2

A March 27, 2017 Graphene Flagship press release on EurekAlert, which originated the news item, describes the work,  in more detail,

The devices were used to record the large signals generated by pre-epileptic activity in rats, as well as the smaller levels of brain activity during sleep and in response to visual light stimulation. These types of activities lead to much smaller electrical signals, and are at the level of typical brain activity. Neural activity is detected through the highly localised electric fields generated when neurons fire, so densely packed, ultra-small measuring devices is important for accurate brain readings.

The neural probes are placed directly on the surface of the brain, so safety is of paramount importance for the development of graphene-based neural implant devices. Importantly, the researchers determined that the graphene-based probes are non-toxic, and did not induce any significant inflammation.

Devices implanted in the brain as neural prosthesis for therapeutic brain stimulation technologies and interfaces for sensory and motor devices, such as artificial limbs, are an important goal for improving quality of life for patients. This work represents a first step towards the use of graphene in research as well as clinical neural devices, showing that graphene-based technologies can deliver the high resolution and high SNR needed for these applications.

First author Benno Blaschke (TU Munich) said “Graphene is one of the few materials that allows recording in a transistor configuration and simultaneously complies with all other requirements for neural probes such as flexibility, biocompability and chemical stability. Although graphene is ideally suited for flexible electronics, it was a great challenge to transfer our fabrication process from rigid substrates to flexible ones. The next step is to optimize the wafer-scale fabrication process and improve device flexibility and stability.”

Jose Antonio Garrido (ICN2), led the research. He said “Mechanical compliance is an important requirement for safe neural probes and interfaces. Currently, the focus is on ultra-soft materials that can adapt conformally to the brain surface. Graphene neural interfaces have shown already great potential, but we have to improve on the yield and homogeneity of the device production in order to advance towards a real technology. Once we have demonstrated the proof of concept in animal studies, the next goal will be to work towards the first human clinical trial with graphene devices during intraoperative mapping of the brain. This means addressing all regulatory issues associated to medical devices such as safety, biocompatibility, etc.”

Caption: The graphene-based neural probes were used to detect rats’ responses to visual stimulation, as well as neural signals during sleep. Both types of signals are small, and typically difficult to measure. Credit: ICN2

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

Mapping brain activity with flexible graphene micro-transistors by Benno M Blaschke, Núria Tort-Colet, Anton Guimerà-Brunet, Julia Weinert, Lionel Rousseau, Axel Heimann, Simon Drieschner, Oliver Kempski, Rosa Villa, Maria V Sanchez-Vives. 2D Materials, Volume 4, Number 2 DOI https://doi.org/10.1088/2053-1583/aa5eff Published 24 February 2017

© 2017 IOP Publishing Ltd

This paper is behind a paywall.

Korea

While this research from Korea was published more recently, the probe itself has not been subjected to in vivo (animal testing). From an April 19, 2017 news item on ScienceDaily,

Electrodes placed in the brain record neural activity, and can help treat neural diseases like Parkinson’s and epilepsy. Interest is also growing in developing better brain-machine interfaces, in which electrodes can help control prosthetic limbs. Progress in these fields is hindered by limitations in electrodes, which are relatively stiff and can damage soft brain tissue.

Designing smaller, gentler electrodes that still pick up brain signals is a challenge because brain signals are so weak. Typically, the smaller the electrode, the harder it is to detect a signal. However, a team from the Daegu Gyeongbuk Institute of Science & Technology [DGIST} in Korea developed new probes that are small, flexible and read brain signals clearly.

This is a pretty interesting way to illustrate the research,

Caption: Graphene and gold make a better brain probe. Credit: DGIST

An April 19, 2017 DGIST press release (also on EurekAlert), which originated the news item, expands on the theme (Note: A link has been removed),

The probe consists of an electrode, which records the brain signal. The signal travels down an interconnection line to a connector, which transfers the signal to machines measuring and analysing the signals.

The electrode starts with a thin gold base. Attached to the base are tiny zinc oxide nanowires, which are coated in a thin layer of gold, and then a layer of conducting polymer called PEDOT. These combined materials increase the probe’s effective surface area, conducting properties, and strength of the electrode, while still maintaining flexibility and compatibility with soft tissue.

Packing several long, thin nanowires together onto one probe enables the scientists to make a smaller electrode that retains the same effective surface area of a larger, flat electrode. This means the electrode can shrink, but not reduce signal detection. The interconnection line is made of a mix of graphene and gold. Graphene is flexible and gold is an excellent conductor. The researchers tested the probe and found it read rat brain signals very clearly, much better than a standard flat, gold electrode.

“Our graphene and nanowires-based flexible electrode array can be useful for monitoring and recording the functions of the nervous system, or to deliver electrical signals to the brain,” the researchers conclude in their paper recently published in the journal ACS Applied Materials and Interfaces.

The probe requires further clinical tests before widespread commercialization. The researchers are also interested in developing a wireless version to make it more convenient for a variety of applications.

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

Enhancement of Interface Characteristics of Neural Probe Based on Graphene, ZnO Nanowires, and Conducting Polymer PEDOT by Mingyu Ryu, Jae Hoon Yang, Yumi Ahn, Minkyung Sim, Kyung Hwa Lee, Kyungsoo Kim, Taeju Lee, Seung-Jun Yoo, So Yeun Kim, Cheil Moon, Minkyu Je, Ji-Woong Choi, Youngu Lee, and Jae Eun Jang. ACS Appl. Mater. Interfaces, 2017, 9 (12), pp 10577–10586 DOI: 10.1021/acsami.7b02975 Publication Date (Web): March 7, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Making graphene cheaply by using soybeans

One of the issues with new materials is being able to produce them in a commercially viable fashion and it seems that researchers in Australia may have helped  to do that with graphene. From a Feb. 15, 2017 news item on phys.org,

A breakthrough by CSIRO-led [Australia’s Commonwealth Scientific and Industrial Research Organisation] scientists has made the world’s strongest material more commercially viable, thanks to the humble soybean.

From a Feb. 15, (?) 2017 CSIRO press release (also on EurekAlert), which originated the news item, expands on the theme (Note: A link has been removed),

Graphene is a carbon material that is one atom thick.

Its thin composition and high conductivity means it is used in applications ranging from miniaturised electronics to biomedical devices.

These properties also enable thinner wire connections; providing extensive benefits for computers, solar panels, batteries, sensors and other devices.

Until now, the high cost of graphene production has been the major roadblock in its commercialisation.

Previously, graphene was grown in a highly-controlled environment with explosive compressed gases, requiring long hours of operation at high temperatures and extensive vacuum processing.

CSIRO scientists have developed a novel “GraphAir” technology which eliminates the need for such a highly-controlled environment.

The technology grows graphene film in ambient air with a natural precursor, making its production faster and simpler.

“This ambient-air process for graphene fabrication is fast, simple, safe, potentially scalable, and integration-friendly,” CSIRO scientist Dr Zhao Jun Han, co-author of the paper published today in Nature Communications said.

“Our unique technology is expected to reduce the cost of graphene production and improve the uptake in new applications.”

GraphAir transforms soybean oil – a renewable, natural material – into graphene films in a single step.

“Our GraphAir technology results in good and transformable graphene properties, comparable to graphene made by conventional methods,” CSIRO scientist and co-author of the study Dr Dong Han Seo said.

With heat, soybean oil breaks down into a range of carbon building units that are essential for the synthesis of graphene.

The team also transformed other types of renewable and even waste oil, such as those leftover from barbecues or cooking, into graphene films.

“We can now recycle waste oils that would have otherwise been discarded and transform them into something useful,” Dr Seo said.

The potential applications of graphene include water filtration and purification, renewable energy, sensors, personalised healthcare and medicine, to name a few.

Graphene has excellent electronic, mechanical, thermal and optical properties as well.

Its uses range from improving battery performance in energy devices, to cheaper solar panels.

CSIRO are looking to partner with industry to find new uses for graphene.

Researchers from The University of Sydney, University of Technology Sydney and The Queensland University of Technology also contributed to this work.

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

Single-step ambient-air synthesis of graphene from renewable precursors as electrochemical genosensor by Dong Han Seo, Shafique Pineda, Jinghua Fang, Yesim Gozukara, Samuel Yick, Avi Bendavid, Simon Kwai Hung Lam, Adrian T. Murdock, Anthony B. Murphy, Zhao Jun Han, & Kostya (Ken) Ostrikov. Nature Communications 8, Article number: 14217 (2017) doi:10.1038/ncomms14217 Published online: 30 January 2017

This is an open access paper.

A new type of diode from South Korea’s Ulsan National Institute of Science and Technology

A Feb. 8, 2017 news item on phys.org features a ‘dream’ diode from Ulsan National Institute of Science and Technology,

A team of researchers, affiliated with UNIST [Ulsan National Institute of Science and Technology] has created a new technique that greatly enhances the performance of Schottky Diodes (metal-semiconductor junction) used in electronic devices. Their research findings have attracted considerable attention within the scientific community by solving the contact resistance problem of metal-semiconductor, which had remained unsolved for almost 50 years.

As described in the January [2017] issue of Nano Letters, the researchers have created a new type of diode with a graphene insertion layer sandwiched between metal and semiconductor. This new technique blows all previous attemps out the water, as it is expected to significantly contribute to the semiconductor industry’s growth.

A Jan. 27, 2017 UNIST press release, (also on EurekAlert), which originated the news item, describes the research in greater detail,

The Schottky diode is one of the oldest and most representative semiconductor devices, formed by the junction of a semiconductor with a metal.  However, due to the atomic intermixing along the interface between two materials, it has been impossible to produce an ideal diode. (An ideal diode acts like a perfect conductor when voltage is applied forward biased and like a perfect insulator when voltage is applied reverse biased.)

graphene interlayer 2

The schematic view of internal photoemission (IPE) measurements on metal/n-Si(001) junctions with Ni, Pt, and Ti electrodes for with and without a graphene insertion layer.

Professor Kibog Park of Natural Science solved this problem by inserting a graphene layer at the metal-semiconductor interface. In the study, the research team demonstrated that this graphene layer, consisting of a single layer of carbon atoms can not only suppress the material intermixing substantially, but also matches well with the theoretical prediction.

“The sheets of graphene in graphite have a space between each sheet that shows a high electron density of quantum mechanics in that no atoms can pass through,” says Professor Park. “Therefore, with this single-layer graphene sandwiched between metal and semiconductor, it is possible to overcome the inevitable atomic diffusion problem.”

The study also has the physiological meaning of confirming the theoretical prediction that “In the case of silicon semiconductors, the electrical properties of the junction surfaces hardly change regardless of the type of metal they use,” according to Hoon Hahn Yoon (Combined M.S./Ph.D. student of Natural Science), the first author of the study.

The internal photoemission method was used to measure the electronic energy barrier of the newly-fabricated metal/graphene/n-Si(001) junction diodes. The Internal Photoemission (IPE) Measurement System in the image shown above has contributed greatly to these experiments. This system has been developed by four UNIST graduate students (Hoon Han Yoon, Sungchul Jung, Gahyun Choi, and Junhyung Kim), which was carried out as part of an undergraduate research project in 2012 and was supported by the Korea Foundation for the Advancement of Science and Creativity (KOFAC).

This is the internal photoemission (IPE) measurement system, developed by Hoon Hahn Yoon of Physics at UNIST.

Shown above is the Internal Photoemission (IPE) Measurement System, developed by Hoon Hahn Yoon, combined M.S./Ph.D. student of Natural Science at UNIST.

“Students have teamed up and carried out all the necessary steps for the research since they were undergraduates,” Professor Park says. “Therefore, this research is a perfect example of time, persistence, and patience paying off.”

This study has been jointly conducted by Professor Hu Young Jeong of the UNIST Central Research Facilities (UCRF), Professor Kwanpyo Kim of Natural Science, Professor Soon-Yong Kwon of Materials Science and Engineering, and Professor Yong Soo Kim of Ulsan University. It has been also supported by the National Research Foundation of Korea, Nuclear Research Basis Expansion Project, as well as the Global Ph.D Fellowship (GPF).

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

Strong Fermi-Level Pinning at Metal/n-Si(001) Interface Ensured by Forming an Intact Schottky Contact with a Graphene Insertion Layer by Hoon Hahn Yoon, Sungchul Jung, Gahyun Choi, Junhyung Kim, Youngeun Jeon, Yong Soo Kim, Hu Young Jeong, Kwanpyo Kim, Soon-Yong Kwon, and Kibog Park. Nano Lett., 2017, 17 (1), pp 44–49 DOI: 10.1021/acs.nanolett.6b03137 Publication Date (Web): December 14, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Better bioimaging accuracy with direct radiolabeling of nanomaterials

Even I can tell the image is improved when the chelator is omitted,

Courtesy: Wiley

A Feb. 9, 2017 news item on phys.org describes a new, chelator-free technique for increased bioimaging accuracy,

Positron emission tomography (PET) plays a pivotal role for monitoring the distribution and accumulation of radiolabeled nanomaterials in living subjects. The radioactive metals are usually connected to the nanomaterial through an anchor, a so-called chelator, but this chemical binding can be omitted if nanographene is used, as American scientists report in the journal Angewandte Chemie. The replacement of chelator-based labeling by intrinsic labeling significantly enhances the bioimaging accuracy and reduces biases.

A Feb 9, 2017Wiley press release (also on EurekAlert), which originated the news item, provides more detail,

Nanoparticles are very promising substances for biodiagnostics (e.g., detecting cancerous tissue) and biotherapy (e.g., destroying tumors by molecular agents), because they are not as fast [sic] metabolized as normal pharmaceuticals and they particularly enrich [sic] in tumors through an effect called enhanced permeability and retention (EPR). Chelators, which have a macrocyclic structure, are used to anchor the radioactive element (e.g., copper-64) onto the nanoparticles’ surface. The tracers are then detected and localized in the body with the help of a positron emission tomography (PET) scanner. However, the use of a chelator can also be problematic, because it can detach from the nanoparticles or bias the imaging. Therefore, the group of Weibo Cai at University of Wisconsin-Madison, USA, sought for chelator-free solutions—and found it in nanographene, one of the most promising substances in nanotechnology.

Nanographene offers the electronic system to provide special binding electrons for some transition metal ions. “π bonds of nanographene are able to provide the additional electron to stably incorporate the 64Cu2+ acceptor ions onto the surface of graphene,” the authors wrote. Thus, it was possible to directly and stably attach the copper isotope to reduced graphene oxide nanomaterials stabilized by poly(ethylene glycol) (PEG), and this system was used for several bioimaging tests including the detection of tumors in mice.

After injection in the mouse model, the scientists observed long blood circulation and high tumor uptake. “Prolonged blood circulation of 64Cu-RGO-PEG […] induced a prompt and persistent tumor uptake via EPR effect,” they wrote. Moreover, the directly radiolabeled nanographene was readily prepared by simply mixing both components and heating them. This simple chelator-free, intrinsically labeled system may provide an attractive alternative to the chelator-based radiolabeling, which is still the “gold standard” in bioimaging.

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

Chelator-Free Radiolabeling of Nanographene: Breaking the Stereotype of Chelation by Sixiang Shi, Cheng Xu, Dr. Kai Yang, Shreya Goel, Hector F. Valdovinos, Dr. Haiming Luo, Emily B. Ehlerding, Dr. Christopher G. England, Dr. Liang Cheng, Dr. Feng Chen, Prof. Robert J. Nickles, Prof. Zhuang Liu, and Prof. Weibo Cai. Angewandte Chemie International Edition DOI: 10.1002/anie.201610649 Version of Record online: 7 FEB 2017

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

This paper is behind a paywall.

Figuring out how stars are born by watching neutrons ‘quantum tunnelling’ on graphene

A Feb. 3, 2017 news item on Nanowerk announces research that could help us better understand how stars are ‘born’,

Graphene is known as the world’s thinnest material due to its 2D structure, where each sheet is only one carbon atom thick, allowing each atom to engage in a chemical reaction from two sides. Graphene flakes can have a very large proportion of edge atoms, all of which have a particular chemical reactivity.

In addition, chemically active voids created by missing atoms are a surface defect of graphene sheets. These structural defects and edges play a vital role in carbon chemistry and physics, as they alter the chemical reactivity of graphene. In fact, chemical reactions have repeatedly been shown to be favoured at these defect sites.

Interstellar molecular clouds are predominantly composed of hydrogen in molecular form (H2), but also contain a small percentage of dust particles mostly in the form of carbon nanostructures, called polyaromatic hydrocarbons (PAH). These clouds are often referred to as ‘star nurseries’ as their low temperature and high density allows gravity to locally condense matter in such a way that it initiates H fusion, the nuclear reaction at the heart of each star.

Graphene-based materials, prepared from the exfoliation of graphite oxide, are used as a model of interstellar carbon dust as they contain a relatively large amount of atomic defects, either at their edges or on their surface. These defects are thought to sustain the Eley-Rideal chemical reaction, which recombines two H atoms into one H2 molecule. The observation of interstellar clouds in inhospitable regions of space, including in the direct proximity of giant stars, poses the question of the origin of the stability of hydrogen in the molecular form (H2).

This question stands because the clouds are constantly being washed out by intense radiation, hence cracking the hydrogen molecules into atoms. Astrochemists suggest that the chemical mechanism responsible for the recombination of atomic H into molecular H2 is catalysed by carbon flakes in interstellar clouds.

A Feb. 2, 2017 Institut Laue-Langevin press release, which originated the news item, provides more insight into the research,

Their [astrochemists’s] theories are challenged by the need for a very efficient surface chemistry scenario to explain the observed equilibrium between dissociation and recombination. They had to introduce highly reactive sites into their models so that the capture of an atomic H nearby occurs without fail. These sites, in the form of atomic defects at the surface or edge of the carbon flakes, should be such that the C-H bond formed thereafter allows the H atom to be released easily to recombine with another H atom flying nearby.

A collaboration between the Institut Laue-Langevin (ILL), France, the University of Parma, Italy, and the ISIS Neutron and Muon Source, UK, combined neutron spectroscopy with density functional theory (DFT) molecular dynamics simulations in order to characterise the local environment and vibrations of hydrogen atoms chemically bonded at the surface of substantially defected graphene flakes. Additional analyses were carried out using muon spectroscopy (muSR) and nuclear magnetic resonance (NMR). As availability of the samples is very low, these highly specific techniques were necessary to study the samples; neutron spectroscopy is highly sensitive to hydrogen and allowed accurate data to be gathered at small concentrations.

For the first time ever, this study showed ‘quantum tunnelling’ in these systems, allowing the H atoms bound to C atoms to explore relatively long distances at temperatures as low as those in interstitial clouds. The process involves hydrogen ‘quantum hopping’ from one carbon atom to another in its direct vicinity, tunnelling through energy barriers which could not be overcome given the lack of heat in the interstellar cloud environment. This movement is sustained by the fluctuations of the graphene structure, which bring the H atom into unstable regions and catalyse the recombination process by allowing the release of the chemically bonded H atom. Therefore, it is believed that quantum tunnelling facilitates the reaction for the formation of molecular H2.

ILL scientist and carbon nanostructure specialist, Stéphane Rols says: “The question of how molecular hydrogen forms at the low temperatures in interstellar clouds has always been a driver in astrochemistry research. We’re proud to have combined spectroscopy expertise with the sensitivity of neutrons to identify the intriguing quantum tunnelling phenomenon as a possible mechanism behind the formation of H2; these observations are significant in furthering our understanding of the universe.”

Here’s a link to and a citation for the paper (which dates from Aug. 2016),

Hydrogen motions in defective graphene: the role of surface defects by Chiara Cavallari, Daniele Pontiroli, Mónica Jiménez-Ruiz, Mark Johnson, Matteo Aramini, Mattia Gaboardi, Stewart F. Parker, Mauro Riccó, and Stéphane Rols. Phys. Chem. Chem. Phys., 2016, Issue 36, 18, 24820-24824 DOI: 10.1039/C6CP04727K First published online 22 Aug 2016

This paper is behind a paywall.

R.I.P. Mildred Dresselhaus, Queen of Carbon

I’ve been hearing about Mildred Dresselhaus, professor emerita (retired professor) at the Massachusetts Institute of Technology (MIT), just about as long as I’ve been researching and writing about nanotechnology (about 10 years including the work for my master’s project with the almost eight years on this blog).

She died on Monday, Feb. 20, 2017 at the age of 86 having broken through barriers for those of her gender, barriers for her subject area, and barriers for her age.

Mark Anderson in his Feb. 22, 2017 obituary for the IEEE (Institute of Electrical and Electronics Engineers) Spectrum website provides a brief overview of her extraordinary life and accomplishments,

Called the “Queen of Carbon Science,” Dresselhaus pioneered the study of carbon nanostructures at a time when studying physical and material properties of commonplace atoms like carbon was out of favor. Her visionary perspectives on the sixth atom in the periodic table—including exploring individual layers of carbon atoms (precursors to graphene), developing carbon fibers stronger than steel, and revealing new carbon structures that were ultimately developed into buckyballs and nanotubes—invigorated the field.

“Millie Dresselhaus began life as the child of poor Polish immigrants in the Bronx; by the end, she was Institute Professor Emerita, the highest distinction awarded by the MIT faculty. A physicist, materials scientist, and electrical engineer, she was known as the ‘Queen of Carbon’ because her work paved the way for much of today’s carbon-based nanotechnology,” MIT president Rafael Reif said in a prepared statement.

Friends and colleagues describe Dresselhaus as a gifted instructor as well as a tireless and inspired researcher. And her boundless generosity toward colleagues, students, and girls and women pursuing careers in science is legendary.

In 1963, Dresselhaus began her own career studying carbon by publishing a paper on graphite in the IBM Journal for Research and Development, a foundational work in the history of nanotechnology. To this day, her studies of the electronic structure of this material serve as a reference point for explorations of the electronic structure of fullerenes and carbon nanotubes. Coauthor, with her husband Gene Dresselhaus, of a leading book on carbon fibers, she began studying the laser vaporation of carbon and the “carbon clusters” that resulted. Researchers who followed her lead discovered a 60-carbon structure that was soon identified as the icosahedral “soccer ball” molecular configuration known as buckminsterfullerene, or buckyball. In 1991, Dresselhaus further suggested that fullerene could be elongated as a tube, and she outlined these imagined objects’ symmetries. Not long after, researchers announced the discovery of carbon nanotubes.

When she began her nearly half-century career at MIT, as a visiting professor, women consisted of just 4 percent of the undergraduate student population.  So Dresselhaus began working toward the improvement of living conditions for women students at the university. Through her leadership, MIT adopted an equal and joint admission process for women and men. (Previously, MIT had propounded the self-fulfilling prophecy of harboring more stringent requirements for women based on less dormitory space and perceived poorer performance.) And so promoting women in STEM—before it was ever called STEM—became one of her passions. Serving as president of the American Physical Society, she spearheaded and launched initiatives like the Committee on the Status of Women in Physics and the society’s more informal committees of visiting women physicists on campuses around the United States, which have increased the female faculty and student populations on the campuses they visit.

If you have the time, please read Anderson’s piece in its entirety.

One fact that has impressed me greatly is that Dresselhaus kept working into her eighties. I featured a paper she published in an April 27, 2012 posting at the age of 82 and she was described in the MIT write up at the time as a professor, not a professor emerita. I later featured Dresselhaus in a May 31, 2012 posting when she was awarded the Kavli Prize for Nanoscience.

It seems she worked almost to the end. Recently, GE (General Electric) posted a video “What If Scientists Were Celebrities?” starring Mildred Dresselhaus,

H/t Mark Anderson’s obituary Feb. 22, 2017 piece. The video was posted on Feb. 8, 2017.

Goodbye to the Queen of Carbon!

Detonating (exploding) your way to graphene

Physicists at Kansas State University use controlled detonation to make graphene according to a Jan. 25, 2017 news item on Nanowerk (Note: A link has been removed),

Forget chemicals, catalysts and expensive machinery — a Kansas State University team of physicists has discovered a way to mass-produce graphene with three ingredients: hydrocarbon gas, oxygen and a spark plug.

Their method is simple: Fill a chamber with acetylene or ethylene gas and oxygen. Use a vehicle spark plug to create a contained detonation. Collect the graphene that forms afterward.

Chris Sorensen, Cortelyou-Rust university distinguished professor of physics, is the lead inventor of the recently issued patent, “Process for high-yield production of graphene via detonation of carbon-containing material”. Other Kansas State University researchers involved include Arjun Nepal, postdoctoral researcher and instructor of physics, and Gajendra Prasad Singh, former visiting scientist.

For further reading here’s the Jan. 25, 2017 Kansas State University news release, which originated the news item,

“We have discovered a viable process to make graphene,” Sorensen said. “Our process has many positive properties, from the economic feasibility, the possibility for large-scale production and the lack of nasty chemicals. What might be the best property of all is that the energy required to make a gram of graphene through our process is much less than other processes because all it takes is a single spark.”

Graphene is a single atom-thick sheet of hexagonally coordinated carbon atoms, which makes it the world’s thinnest material. Since graphene was isolated in 2004, scientists have found it has valuable physical and electronic properties with many possible applications, such as more efficient rechargeable batteries or better electronics.

For Sorensen’s research team, the serendipitous path to creating graphene started when they were developing and patenting carbon soot aerosol gels. They created the gels by filling a 17-liter aluminum chamber with acetylene gas and oxygen. Using a spark plug, they created a detonation in the chamber. The soot from the detonation formed aerosol gels that looked like “black angel food cake,” Sorensen said.

But after further analysis, the researchers found that the aerosol gel was more than lookalike dark angel food cake — it was graphene.

“We made graphene by serendipity,” Sorensen said. “We didn’t plan on making graphene. We planned on making the aerosol gel and we got lucky.”

But unlike other methods of creating graphene, Sorensen’s method is simple, efficient, low-cost and scalable for industry.

Other methods of creating graphene involve “cooking” the mineral graphite with chemicals — such as sulfuric acid, sodium nitrate, potassium permanganate or hydrazine — for a long time at precisely prescribed temperatures. Additional methods involve heating hydrocarbons to 1,000 degrees Celsius in the presence of catalysts.

Such methods are energy intensive — and even dangerous — and have low yield, while Sorensen and his team’s method makes larger quantities with minimal energy and no dangerous chemicals.

“The real charm of our experiment is that we can produce graphene in the quantity of grams rather than milligrams,” Nepal said.

Now the research team — including Justin Wright, doctoral student in physics, Camp Hill, Pennsylvania — is working to improve the quality of the graphene and scale the laboratory process to an industrial level. They are upgrading some of the equipment to make it easier to get graphene from the chamber seconds — rather than minutes — after the detonation. Accessing the graphene more quickly could improve the quality of the material, Sorensen said.

The patent was issued to the Kansas State University Research Foundation, a nonprofit corporation responsible for managing technology transfer activities at the university.

I wish they’d filmed one of their graphene explosions even if it meant that all we’d get is the sight of a canister and the sound of a boom. Still, they did show a brief spark from the spark plug.