Graphene in 2017: The Story So Far ~ An Update


Graphene 2017 ImageForArticle_4454(1)

In October 2004, University of Manchester’s Andre Geim, along with his colleague Kostya Novoselov, discovered published their discovery that when a block of graphite is broken down to just 10 or 100 layers thick, a material known as graphene emerges1.

With substantial material properties involving its superior strength as well as both heat and electricity conductibility, while remaining such a thin material, graphene has become one of the most studied materials to date.

While graphene is most often employed in disciplines such as bioengineering, composite materials, energy technology and nanotechnology, its ability to be interjected with other elements allows for its applications to be limitless.directa-plus-colmar-graphene-ski-jacket

One of the most pressing challenges that the graphene industry faces is a lack of pure production of the material. A recent research report conducted by the Centre for Advanced 2 D Materials (CA2DM) at the National University of Singapore has found that most graphene production companies generate a material that is comprised of a graphene content of only 2-10%2.

Canadian based company Elcora Advanced Materials Corporation has become one of the leading graphene producers in the world, while also maintaining products comprised of 55% graphene content. As its unique designed processing technology not only works towards achieving the purest form of graphene possible, Elcora ensures the cost effective production of graphene from natural graphite in a green and efficient manner.

Learn more about Elcora Advanced Materials

By minimizing the need for using harsh chemicals, while also eliminating the environmentally damaging byproducts or waste that often follow graphene production, Elcora is one of the most environmentally safe graphene plants available today3.

After acquiring control of the Ragedera graphite mine located in Colombo, Sri Lanka, Elcora Advanced Material has been able to successfully produce an estimated 18,000 tonnes of high quality graphite per year.

 

With production bases located in both South Wales and Seoul, Korea, Haydale Graphene Industries is one of the numerous companies working towards enhancing the carbon fiber composites for specific aerospace and automotive needs. In doing so, research conducted by both Haydale and scientists from the School of Engineering at Cardiff University have investigated how the addition of graphene nanoplaatelets (GP) and carbon nanotubes (CNT) into the composites can allow for reinforcing benefits of the technology.

These benefits include an increased resistance and tolerance to damage of the vehicle, while also showing a 13% increase in the compression strength following impact performance studies. By positively influencing composites such as aircraft wings and automobile parts, Haydale has improved these important properties that are required for maintaining such high performance structures4.

Learn more about Haydale

In addition to achieving such impressive material improvements, the techniques employed during this process were performed in a much more cost effective, green and efficient manner. The process employed in the development of this composite involved treating the surface of the nanomaterials with Haydale’s low temperature and low energy HDPlas ® plasma process4.

This plasma functionalization process not only produces high integrity materials, but also avoids the typical waste production associated with functionalization processes while simultaneously promoting homogenous dispersion and chemical bonding. Haydale researchers are hopeful that this newly developed material can allow for lighter and stronger wings to be implemented into aircraft deisgns that can simultaneously reduce the amount of carbon dioxide emissions released by these aircrafts.

Rahul Nair from the University of Manchester in the United Kingdom has recently developed a method involving the use of graphene oxide in order to effectively desalinate water. Considered to be the oxidized form of graphene, graphene oxide membranes have recently emerged as an excellent membrane material that is capable of separating multiple different types of molecules and ions present in an aqueous solution5.

The sieving potential of graphene oxide membranes has been successful in removing small nanoparticles, organic molecules and large salts from solution; however, their ability to filter out common salts has not been documented until now. Previous attempts at employing graphene oxide membranes in the filtration of smaller salts in water have caused the membranes to expand and prevent the flow of water from entering the pores of the membrane.Graphene Mem 050815 3-anewapproach

By placing walls composed of a substance known as epoxy resin that is typically used in glues and coatings on either side of the graphene oxide membrane, the team of researchers led by Dr. Nair was able to successfully prevent the swelling of the membranes upon its immersion in water6.

With a uniform pore size within the membrane of only 0.9 nm in width, this highly selective graphene oxide membrane has several advantages as compared to its bulk counterpart, graphene7. As a much more inexpensive option coupled with a long operational lifetime, graphene oxide membranes have a spectacular separation potential that could have a significant impact in a wide variety of energy reduction and environmental conservation industries around the world.

Outside of its potential for water purification purposes, researchers believe that this technology could also provide a useful addition in the dehydration and purification of biofuels. In most biofuel processes, water is formed as a byproduct, and its presence in the biofuel can affect the final product in a detrimental way. Therefore, the hope is that the application of graphene oxide membranes in this industrial process could have an advantageous use.

Request more information about Graphene

Similarly, graphene oxide membranes have a well-documented gas separation ability that prevents any vapor molecules from passing through the membrane. In one of the first studies illustrating this property, researchers measured the loss of weight within a containing initially filled with alcohol before and after it was sealed with a graphene oxide membrane8.

Following the membrane sealing, researchers found that no noticeable variation in the weight of or the pressure within the container was detected. As a result of this remarkable gas separation property, researchers are hopeful the use of graphene oxide membranes can be applied to the controlling of greenhouse gas emissions, as well as the purification of hydrogen-related clean energy gases, in future real world applications.

The University of Cambridge has recently developed a highly conductive ink known as ‘Graphene – IPA Ink.” Composed of powdered graphite dissolved in alcohol, this ink has the potential to be used in inkjet printers that print electrical circuits onto paper.

By forcing the ink through a micrometer-scale capillary at an extremely high pressure, the resulting product is a smooth and conductive material9. Researchers are hopeful that devices such as Radio Frequency Identification (RFID) antennas, passports, electronic tags, and similar everyday items can be printed at a much cheaper rate with the application of electronic circuits printed using this graphene ink.Graphene defectsarepe

While graphene may appear to be a single product, it has developed into several different types of applications in its short 13-year live span since its first entrance into the scientific world. Its wide range of uses allow for this material to have a promising future, in which its varying and impressive properties of transparency, strength and conductivity can improve almost every industry of the world.

The world of two-dimensional materials, like graphene, have allowed for researchers to manipulate different geometries and combinations of these compounds to create wonderful new products of the future. As research and development projects continue to work on graphene and its numerous applied products, new two-dimensional materials continue to be discovered each day in continuance of this revolutionary pathway that has set by graphene.

References

  1. “This Month in Physics History.” American Physical Society. 22 Oct. 2014. Web. https://www.aps.org/publications/apsnews/200910/physicshistory.cfm.
  2. “Graphene R&D.” Elcora Advanced Materials. Web. https://www.elcoracorp.com/graphene-rd/.
  3. Ecclestone, Christopher. “Analyst on How Elcora Has Positioned Themselves as a Leader in the Graphite Space.” InvestorIntel. 06 Apr. 2017. Web. https://investorintel.com/sectors/technology-metals/technology-metals-intel/elcora-pulling-ahead-leadership-graphite-space/.
  4. “Carbon Fibre Composites.” Haydale. 11 Nov. 2014. Web. http://www.haydale.com/news/graphene-toughened-composites-a-milestone-for-next-generation-aerospace-structures/.
  5. An, Di, Ling Yang, Ting-Jie Wang, and Boyang Liu. “Separation Performance of Graphene Oxide Membrane in Aqueous Solution.” Industrial & Engineering Chemistry Research 55.17 (2016): 4803-810. Web.
  6. Rincon, Paul. “Graphene-based Sieve Turns Seawater into Drinking Water.” BBC News. BBC, 03 Apr. 2017. Web. http://www.bbc.com/news/science-environment-39482342.
  7. Wilkinson, Jake. “Developing Graphene Oxide Membranes for the Purification of Water and Green Fuels.” AZoNano.com. 22 Sept. 2016. Web. http://www.azonano.com/article.aspx?ArticleID=4275.
  8. Joshi, R.k., S. Alwarappan, M. Yoshimura, V. Sahajwalla, and Y. Nishina. “Graphene Oxide: The New Membrane Material.” Applied Materials Today 1.1 (2015): 1-12. Web.
  9. “Conductive Graphene Ink Wins Science Photography Competition’s Top Prize.” Phys.org. Web. https://phys.org/news/2017-04-graphene-ink-science-photography-competition.html.
  10. Image Credit: Shutterstock.com/OliveTree

 

Link to Original Article from AzNano

Advertisements

Leaf vein structure could hold key to extending battery life



Close-up of a leaf showing its veins. Credit: Christoph Rupprecht/Flickr
The natural structure found within leaves could improve the performance of everything from rechargeable batteries to high-performance gas sensors, according to an international team of scientists. 

The researchers have designed a porous, such as the veins of a leaf, and could make energy transfers more efficient. The material could improve the performance of rechargeable batteries, optimizing the charge and discharge process and relieving stresses within the battery electrodes, which, at the moment, limit their life span. The same material could be used for high performance gas sensing or for catalysis to break down organic pollutants in water.

To design this bio-inspired material, an international team comprising scientists from China, the United Kingdom, United States and Belgium is mimicking the rule known as ‘Murray’s Law’ which helps natural organisms survive and grow. 

According to this Law, the entire network of pores existing on different scales in such biological systems is interconnected in a way to facilitate the transfer of liquids and minimize resistance throughout the network. The plant stems of a tree, or leaf veins, for example, optimize the flow of nutrients for photosynthesis with both high efficiency and minimum energy consumption by regularly branching out to smaller scales. 

In the same way, the surface area of the tracheal pores of insects remains constant along the diffusion pathway to maximize the delivery of carbon dioxide and oxygen in gaseous forms.

The team, led by Prof Bao-Lian Su, a life member of Clare Hall, University of Cambridge and who is also based at Wuhan University of Technology in China and at the University of Namur in Belgium, adapted 
Murray’s Law for the fabrication of the first ever synthetic ‘Murray material’ and applied it to three processes: photocatalysis, gas sensing and lithium ion battery electrodes. 
In each, they found that the multi-scale porous networks of their synthetic material significantly enhanced the performance of these processes.

Prof Su says:

“This study demonstrates that by adapting Murray’s Law from biology and applying it to chemistry, the performance of materials can be improved significantly. The adaptation could benefit a wide range of porous materials and improve functional ceramics and nano-metals used for energy and environmental applications.” “The introduction of the concept of Murray’s Law to industrial processes could revolutionize the design of reactors with highly enhanced efficiency, minimum energy, time, and raw material consumption for a sustainable future.”

Writing in Nature Communications this week, the team describes how it used zinc oxide (ZnO) nanoparticles as the primary building block of their Murray material. These nanoparticles, containing small pores within them, form the lowest level of the porous network. The team arranged the ZnO particles through a layer-by layer evaporation-driven self-assembly process. 

This creates a second level of porous networks between the particles. During the evaporation process, the particles also form larger pores due to solvent evaporation, which represents the top level of pores, resulting in a three level Murray material. The team successfully fabricated these porous structures with the precise diameter ratios required to obey Murray’s law, enabling the efficient transfer of materials across the multilevel pore network.

Co-author, Dr Tawfique Hasan, of the Cambridge Graphene Centre, part of the University’s Department of Engineering, adds:

“This very first demonstration of a Murray material fabrication process is incredibly simple and is entirely driven by the nanoparticle self-assembly. Large scale manufacturability of this porous material is possible, making it an exciting, enabling technology, with potential impact across many applications.”

With its synthetic Murray material, with precise diameter ratios between the pore levels, the team demonstrated an efficient breakdown of an organic dye in water by using photocatalysis. This showed it was easy for the dye to enter the porous network leading to efficient and repeated reaction cycles. 
The team also used the same Murray material with a structure similar to the breathing networks of insects, for fast and sensitive gas detection with high repeatability.

The team proved that its Murray material can significantly improve the long term stability and fast charge/discharge capability for lithium ion storage, with a capacity improvement of up to 25 times compared to state of the art graphite material currently used in lithium ion battery electrodes. 

The hierarchical nature of the pores also reduces the stresses in these electrodes during the charge/discharge processes, improving their structural stability and resulting in a longer life time for energy storage devices.

The team envisions that the strategy could be used effectively in materials designs for energy and environmental applications.

 Explore further: Researchers optimize the assembly of micro-/meso-/macroporous carbon for Li-S batteries

More information: Xianfeng Zheng et al, Bio-inspired Murray materials for mass transfer and activity, Nature Communications (2017). DOI: 10.1038/ncomms14921 

Journal reference: Nature Communications  

Provided by: University of Cambridge  

Environmentally-friendly graphene textiles could enable wearable electronics


graphene-textiles-19-environmenta

Credit: Jiesheng Ren

A new method for producing conductive cotton fabrics using graphene-based inks opens up new possibilities for flexible and wearable electronics, without the use of expensive and toxic processing steps.

Wearable, textiles-based electronics present new possibilities for flexible circuits, healthcare and environment monitoring, energy conversion, and many others. Now, researchers at the Cambridge Graphene Centre (CGC) at the University of Cambridge, working in collaboration with scientists at Jiangnan University, China, have devised a method for depositing graphene-based inks onto cotton to produce a conductive textile. The work, published in the journal Carbon, demonstrates a wearable motion sensor based on the conductive cotton.

Cotton fabric is among the most widespread for use in clothing and textiles, as it is breathable and comfortable to wear, as well as being durable to washing. These properties also make it an excellent choice for textile electronics. A new process, developed by Dr Felice Torrisi at the CGC, and his collaborators, is a low-cost, sustainable and environmentally-friendly method for making conductive cotton textiles by impregnating them with a graphene-based conductive ink.

Based on Dr Torrisi’s work on the formulation of printable graphene inks for flexible electronics, the team created inks of chemically modified graphene flakes that are more adhesive to cotton fibres than unmodified graphene. Heat treatment after depositing the ink on the fabric improves the conductivity of the modified graphene. The adhesion of the modified graphene to the cotton fibre is similar to the way cotton holds coloured dyes, and allows the fabric to remain conductive after several washes.

Although numerous researchers around the world have developed wearable sensors, most of the current wearable technologies rely on rigid electronic components mounted on flexible materials such as plastic films or textiles. These offer limited compatibility with the skin in many circumstances, are damaged when washed and are uncomfortable to wear because they are not breathable. img_0801

“Other conductive inks are made from precious metals such as silver, which makes them very expensive to produce and not sustainable, whereas graphene is both cheap, environmentally-friendly, and chemically compatible with cotton,” explains Dr Torrisi.

 

Co-author Professor Chaoxia Wang of Jiangnan University adds: “This method will allow us to put electronic systems directly into clothes. It’s an incredible enabling technology for smart textiles.”

The work done by Dr Torrisi and Prof Wang, together with students Tian Carey and Jiesheng Ren, opens a number of commercial opportunities for graphene-based inks, ranging from personal health technology, high-performance sportswear, military garments, wearable technology/computing and fashion.
Electron microscopy image of a conductive graphene/cotton fabric. Credit: Jiesheng Ren
Environmentally-friendly graphene textiles could enable wearable electronics

 

“Turning cotton fibres into functional electronic components can open to an entirely new set of applications from healthcare and wellbeing to the Internet of Things,” says Dr Torrisi “Thanks to nanotechnology, in the future our clothes could incorporate these textile-based electronics and become interactive.”

Graphene is carbon in the form of single-atom-thick membranes, and is highly conductive. The group’s work is based on the dispersion of tiny , each less than one nanometre thick, in a water-based dispersion. The individual graphene sheets in suspension are chemically modified to adhere well to the cotton fibres during printing and deposition on the fabric, leading to a thin and uniform conducting network of many graphene sheets. This network of nanometre flakes is the secret to the high sensitivity to strain induced by motion. A simple graphene-coated smart cotton textile used as a wearable strain sensor has been shown to reliably detect up to 500 motion cycles, even after more than 10 washing cycles in normal washing machine.

The use of graphene and other related 2D materials (GRMs) inks to create and devices integrated into fabrics and innovative textiles is at the centre of new technical advances in the smart textiles industry. Dr Torrisi and colleagues at the CGC are also involved in the Graphene Flagship, an EC-funded, pan-European project dedicated to bringing graphene and GRM technologies to commercial applications.

Graphene and GRMs are changing the science and technology landscape with attractive physical properties for electronics, photonics, sensing, catalysis and energy storage. Graphene’s atomic thickness and excellent electrical and mechanical properties give excellent advantages, allowing deposition of extremely thin, flexible and conductive films on surfaces and – with this new method – also on textiles. This combined with the environmental compatibility of graphene and its strong adhesion to cotton make the graphene- strain sensor ideal for wearable applications.

The research was supported by grants from the European Research Council’s Synergy Grant, the International Research Fellowship of the National Natural Science Foundation of China and the Ministry of Science and Technology of China. The technology is being commercialised by Cambridge Enterprise, the University’s commercialisation arm.

Explore further: New study shows nickel graphene can be tuned for optimal fracture strength

More information: Jiesheng Ren et al. Environmentally-friendly conductive cotton fabric as flexible strain sensor based on hot press reduced graphene oxide, Carbon (2017). DOI: 10.1016/j.carbon.2016.10.045

 

Next-generation Lithium-Sulphur smart battery inspired by Our Stomachs: Proof of Principle for Now


new-lithium-battery-102616-id44921A new prototype of a lithium-sulphur battery – which could have five times the energy density of a typical lithium-ion battery – overcomes one of the key hurdles preventing their commercial development by mimicking the structure of the cells which allow us to absorb nutrients.

Researchers have developed a prototype of a next-generation lithium-sulphur battery which takes its inspiration in part from the cells lining the human intestine. The batteries, if commercially developed, would have five times the energy density of the lithium-ion batteries used in smartphones and other electronics.

 

 

The new design, by researchers from the University of Cambridge, overcomes one of the key technical problems hindering the commercial development of lithium-sulphur batteries, by preventing the degradation of the battery caused by the loss of material within it. The results are reported in the journal Advanced Functional Materials (“Advanced Lithium-Sulfur Batteries Enabled by a Bio-Inspired Polysulfide Adsorptive Brush”).

 

Computer visualisation of villi-like battery material
Computer visualisation of villi-like battery material. (Image: Teng Zhao)
 

 

Working with collaborators at the Beijing Institute of Technology, the Cambridge researchers based in Dr Vasant Kumar’s team in the Department of Materials Science and Metallurgy developed and tested a lightweight nanostructured material which resembles villi, the finger-like protrusions which line the small intestine. In the human body, villi are used to absorb the products of digestion and increase the surface area over which this process can take place.
In the new lithium-sulphur battery, a layer of material with a villi-like structure, made from tiny zinc oxide wires, is placed on the surface of one of the battery’s electrodes. This can trap fragments of the active material when they break off, keeping them electrochemically accessible and allowing the material to be reused.
“It’s a tiny thing, this layer, but it’s important,” said study co-author Dr Paul Coxon from Cambridge’s Department of Materials Science and Metallurgy. “This gets us a long way through the bottleneck which is preventing the development of better batteries.”
A typical lithium-ion battery is made of three separate components: an anode (negative electrode), a cathode (positive electrode) and an electrolyte in the middle. The most common materials for the anode and cathode are graphite and lithium cobalt oxide respectively, which both have layered structures. Positively-charged lithium ions move back and forth from the cathode, through the electrolyte and into the anode.
The crystal structure of the electrode materials determines how much energy can be squeezed into the battery. For example, due to the atomic structure of carbon, each carbon atom can take on six lithium ions, limiting the maximum capacity of the battery.
Sulphur and lithium react differently, via a multi-electron transfer mechanism meaning that elemental sulphur can offer a much higher theoretical capacity, resulting in a lithium-sulphur battery with much higher energy density. However, when the battery discharges, the lithium and sulphur interact and the ring-like sulphur molecules transform into chain-like structures, known as a poly-sulphides. As the battery undergoes several charge-discharge cycles, bits of the poly-sulphide can go into the electrolyte, so that over time the battery gradually loses active material.
The Cambridge researchers have created a functional layer which lies on top of the cathode and fixes the active material to a conductive framework so the active material can be reused. The layer is made up of tiny, one-dimensional zinc oxide nanowires grown on a scaffold. The concept was trialled using commercially-available nickel foam for support. After successful results, the foam was replaced by a lightweight carbon fibre mat to reduce the battery’s overall weight.
“Changing from stiff nickel foam to flexible carbon fibre mat makes the layer mimic the way small intestine works even further,” said study co-author Dr Yingjun Liu.
This functional layer, like the intestinal villi it resembles, has a very high surface area. The material has a very strong chemical bond with the poly-sulphides, allowing the active material to be used for longer, greatly increasing the lifespan of the battery.
“This is the first time a chemically functional layer with a well-organised nano-architecture has been proposed to trap and reuse the dissolved active materials during battery charging and discharging,” said the study’s lead author Teng Zhao, a PhD student from the Department of Materials Science & Metallurgy. “By taking our inspiration from the natural world, we were able to come up with a solution that we hope will accelerate the development of next-generation batteries.”
For the time being, the device is a proof of principle, so commercially-available lithium-sulphur batteries are still some years away. Additionally, while the number of times the battery can be charged and discharged has been improved, it is still not able to go through as many charge cycles as a lithium-ion battery. However, since a lithium-sulphur battery does not need to be charged as often as a lithium-ion battery, it may be the case that the increase in energy density cancels out the lower total number of charge-discharge cycles.
“This is a way of getting around one of those awkward little problems that affects all of us,” said Coxon. “We’re all tied in to our electronic devices – ultimately, we’re just trying to make those devices work better, hopefully making our lives a little bit nicer.”
Source: University of Cambridge

 

University of Cambridge: “Nano-Marbles” Create Intriguing New Materials – Opening Up Applications for Smart Clothing – Buildings – Banknote Security.


Nano-Squezze 060616 160603071657_1_540x360

Researchers have devised a new method for stacking microscopic marbles into regular layers, producing intriguing materials which scatter light into intense colors, and which change color when twisted or stretched.

The team, led by the University of Cambridge, have invented a way to make such sheets on industrial scales, opening up applications ranging from smart clothing for people or buildings, to banknote security.

Using a new method called Bend-Induced-Oscillatory-Shearing (BIOS), the researchers are now able to produce hundreds of metres of these materials, known as ‘polymer opals’, on a roll-to-roll process. The results are reported in the journal Nature Communications.

Some of the brightest colours in nature can be found in opal gemstones, butterfly wings and beetles. These materials get their colour not from dyes or pigments, but from the systematically-ordered microstructures they contain.

The team behind the current research, based at Cambridge’s Cavendish Laboratory, have been working on methods of artificially recreating this ‘structural colour’ for several years, but to date, it has been difficult to make these materials using techniques that are cheap enough to allow their widespread use.

Nano-Squezze 060616 160603071657_1_540x360

Researchers at the University of Cambridge have devised a method to produce “Polymer Opals” on an industrial scale.
Credit: Nick Saffell/University of Cambridge

 

In order to make the polymer opals, the team starts by growing vats of transparent plastic nano-spheres. Each tiny sphere is solid in the middle but sticky on the outside. The spheres are then dried out into a congealed mass. By bending sheets containing a sandwich of these spheres around successive rollers the balls are magically forced into perfectly arranged stacks, by which stage they have intense colour.

By changing the sizes of the starting nano-spheres, different colours (or wavelengths) of light are reflected. And since the material has a rubber-like consistency, when it is twisted and stretched, the spacing between the spheres changes, causing the material to change colour. When stretched, the material shifts into the blue range of the spectrum, and when compressed, the colour shifts towards red. When released, the material returns to its original colour. Such chameleon materials could find their way into colour-changing wallpapers, or building coatings that reflect away infrared thermal radiation.

“Finding a way to coax objects a billionth of a metre across into perfect formation over kilometre scales is a miracle,” said Professor Jeremy Baumberg, the paper’s senior author. “But spheres are only the first step, as it should be applicable to more complex architectures on tiny scales.”

In order to make polymer opals in large quantities, the team first needed to understand their internal structure so that it could be replicated. Using a variety of techniques, including electron microscopy, x-ray scattering, rheology and optical spectroscopy, the researchers were able to see the three-dimensional position of the spheres within the material, measure how the spheres slide past each other, and how the colours change.

“It’s wonderful to finally understand the secrets of these attractive films,” said PhD student Qibin Zhao, the paper’s lead author.

Cambridge Enterprise, the University’s commercialisation arm which is helping to commercialise the material, has been contacted by more than 100 companies interested in using polymer opals, and a new spin-out Phomera Technologies has been founded. Phomera will look at ways of scaling up production of polymer opals, as well as selling the material to potential buyers. Possible applications the company is considering include coatings for buildings to reflect heat, smart clothing and footwear, or for banknote security and packaging applications.

The research is funded as part of a UK Engineering and Physical Sciences Research Council (EPSRC) investment in the Cambridge NanoPhotonics Centre, as well as the European Research Council (ERC).


Story Source:

The above post is reprinted from materials provided byUniversity of Cambridge. The original story is licensed under aCreative Commons Attribution 4.0 International License. Note: Materials may be edited for content and length.


Journal Reference:

  1. Qibin Zhao, Chris E. Finlayson, David R. E. Snoswell, Andrew Haines, Christian Schäfer, Peter Spahn, Goetz P. Hellmann, Andrei V. Petukhov, Lars Herrmann, Pierre Burdet, Paul A. Midgley, Simon Butler, Malcolm Mackley, Qixin Guo, Jeremy J. Baumberg. Large-scale ordering of nanoparticles using viscoelastic shear processing.Nature Communications, 2016; 7: 11661 DOI:10.1038/ncomms11661

Graphene-based flat lenses


graphene flat lenses image

Researchers from the University of Birmingham (which lead the research), University of Cambridge and National Centre for Nanoscience & Technology in Beijing designed the world’s thinnest, tunable, lightweight graphene-based lenses.

The project focused on designing Fresnel lenses, which are flat lenses consisting of concentric rings. The rings diffract light to create constructive interference. The other advantage of these lenses is that their optical performance can be tuned by changing the electrical properties of graphene.

The lenses are one atom layer thick, with focusing properties that can be tuned by applying an electric field and by changing the number of graphene layers. The lenses act like microscopic versions of the ones used in lighthouses and could help focus light onto small pixels (for example, in cell phone cameras or a route laser light in computer chips that move data with photons instead of electron).

The researchers built the 50-µm-wide lenses by depositing 0.335-nm-thick layers of graphene on glass (using CVD) and then carved out the concentric circles with photolithography. The graphene rings diffract light as it passes through the lens. The team found that the intensity of the focused light doubled when they went from five-layer to 10-layer versions of the lenses.

The lenses focused 850-nm light, in the near-infrared range; however, the teams are now looking at designing lenses that work at terahertz frequencies, which have promising applications in security, spectroscopy, and biological imaging.

Source: birmingham.ac.uk

University of Cambridge: A New Class of Biosensors Basis for New Drug Delivery Systems.


Nano Sensing id38606Researchers from the University of Cambridge have developed a new self-assembled material, which, by changing its shape, can amplify small variations in temperature and concentration of biomolecules, making them easier to detect. The material, which consists of synthetic spheres ‘glued’ together with short strands of DNA, could be used to underpin a new class of biosensors, or form the basis for new drug delivery systems.

The interplay between the lipid spheres, called giant vesicles, and the strands of DNA produces a unique response when the material is exposed to changes in temperature. Instead of expanding when heated – as is normally the case – the material contracts, a phenomenon known as negative thermal expansion. Details are published today (7 January) in the journal Nature Communications (“Thermal regulation of volume and porosity in lipid mesophases by coupling mobile ligands to soft membranes”).

Nano Sensing id38606

A lipid membrane functionalised with DNA-linkers. (Image: Lorenzo Di Michele)

In addition to its role as a carrier of genetic information, DNA is also useful for building advanced materials. Short strands of DNA, dubbed ‘sticky ends’, can be customised so that they will only bind to specific complementary sequences. This flexibility allows researchers to use DNA to drive the self-assembly of materials into specific shapes.

Basing self-assembled materials around vesicles – synthetic versions of the soft sacs which envelop living cells – allows for even more flexibility, since the vesicles are so easily deformable. Using short DNA tethers with a cholesterol ‘anchor’ at one end and an exposed sticky DNA sequence at the other, the vesicles can be stuck together. When assembled into a hybrid DNA-lipid network, the DNA tethers can diffuse and rearrange, resulting in massive vesicle shape changes.
Besides negative thermal expansion, the researchers also found that changes in temperature lead to a significant variation in the porosity of the material, which is therefore highly controllable. A similar response is expected by changing the concentration of the DNA tethers, which could also be replaced by other types of ligand-receptor pairs, such as antibodies.
“The characteristics of this material make it suitable for several different applications, ranging from filtration, to the encapsulation and triggered release of drugs, to biosensors,” said Dr Lorenzo Di Michele of the University’s Cavendish Laboratory, who led the research. “Having this kind of control over a material is like a ‘golden ticket’ of sensing.”
This research is part of the CAPITALS, a UK-wide programme funded by the Engineering and Physical Sciences Research Council (EPSRC). Cambridge Enterprise, the University’s commercialisation arm, is currently looking for commercial partners to help develop this material.
Source: Science China Press

Super Effective Camera Chips And Solar Cells Possible With Graphene


QDOTS imagesCAKXSY1K 8Theoretically expected, it was now experimentally proven by scientists for the first time that the fascinating new material graphene is also highly efficient at converting light into electricity–which makes it an ideal candidate to boost the sensitivity of imaging sensors and also to increase the maximum conversion efficiency of photovoltaic cells.

piezoelectric-graphene

 

 

 

 

 

 

 

 

 

(Photo : Mitchell Ong, Stanford School )
This illustration shows lithium atoms (in red) adsorbed to a layer of graphene to create electricity when the graphene is bent, squeezed or twisted.

Current materials used for these applications include silicon and gallium arsenide, but they just generate a single electron for each photon absorbed. Since a photon contains more energy than one electron can carry, much of the energy contained in the incoming light is lost as heat. Graphene on the other hand can generate multiple electrons from absorbing one photon, according to theoretical research that was now confirmed in the lab as described this week in Nature Physics.

Previous work had inspired hope that graphene had this property, says Frank Koppens, a group leader at the Institute of Photonic Sciences in Spain, who led the research. To conduct the experiment, the researchers used two ultrafast light pulses. The first sent a known amount of energy into a single layer of graphene. The second served as a probe that counted the electrons the first one generated.

Koppens said he is “reasonably confident” that the group can enhance the performance of light sensors like those used in cameras, night vision goggles, and certain medical sensors quite soon–after all, his lab is already working on a prototype device to demonstrate the new found capability of graphene.

A second but more difficult application would be solar cells. The material could help to increase the theoretical efficiency limit to about 60%, about twice as much as the 30% limit possible with today’s silicon cells, which currently reach about 20% in the field and 25% in the lab. But Koppens cautions that key engineering challenges stand in the way of that, which includes figuring out how to extract power from a system at all.

The new paper illustrates a “very important concept,” since future devices will depend on an understanding of the physical processes that occur when graphene absorbs light, says says he and colleagues have a still-unpublished paper that describes a similar result. Demonstrating this property in graphene opens a promising new field of research, he says.

Graphene was already exciting as a photovoltaic material because of its unique optical properties, says Andrea Ferrari, a professor of nanotechnology at the University of  Cambridge in the U.K. who was not involved in this research. The material “can work with every possible wavelength you can think of,” he says. “There is no other material in the world with this behavior.” It is also flexible, robust, relatively cheap, and easily integrated with other materials. The new research “adds a third layer of interest to graphene for optics,” he says.

Among Koppens’s collaborators were MIT physics professor Leonid Levitov  and Justin Chien Wen Song, a graduate student in Levitov’s lab, who  helped Koppens interpret the data through theoretical modeling.