#Ultrafast graphene based photodetectors with data rates up to 50 GBIT/s In cooperation with Alcatel Lucent Bell labs researcher from AMO realized the worldwide fastest Graphene based photodetectors.
In the current work Graphene based photodetectors were integrated in a conventional silicon photonic platform designed for future on-chip applications in the area of ultrafast data communication.
With this step ahead researchers at AMO and Alcatel Lucent Bell labs could not only set a new benchmark for graphene based photodetectors
but also demonstrate for the first time that Graphene based photodetectors surpass comparable detectors based on conventional materials concerning maximal data rates.
The work was supported by the European commission through the Flagship project Graphene and the integrated project Grafol as well as the DPG supported project Gratis.
50 GBIT/s photodetectors based on wafer-scale graphene for integrated silicon photonic communication systems. ACS Photonics Just Accepted Manuscript.
Graphene is hidden inside graphite an ore that has not been particularly sought after in the past. But a few years ago it revealed a secret.
and found a vast room with no walls or ceiling. It is said potentially limitless Professor Dan Li of Monash University's Department of Materials Engineering.
Graphene has usually cautious physicists and chemists itching with excitement mesmerised by the possibilities starting to take shape from flexible electronics embedded into clothing to biomedicine (imagine synthetic nerve cells) vastly superior forms of energy storage (tiny
but immensely powerful batteries) and an array of new materials that could make many of today's common metals and polymers redundant.
But despite the extraordinary potential for graphene's properties the stumbling block has been to get it into a useable form.
Professor Li has invented a cost-effective and scalable way to split graphite into microscopic graphene sheets and dissolve them in water.
One is a graphene gel that works as a supercapacitor electrode and the second is a 3-D porous graphene foam.
The graphene gel provides the same functionality as porous carbon a material currently sourced from coconut husks for use in supercapacitors and other energy conversion and storage technologies but with vastly enhanced performance.
Supercapacitors have an expanding range of applications as their capabilities increase from powering computer memory backup to powering electric vehicles.
Professor Li's team has also been able to give graphene a more functional 3-D form by engineering it into an elastic graphene foam that retains its extraordinary qualities.
Professor Li likened his developments to having invented bricks and said it was time to bring in architects
#Scientists craft atomically seamless thinnest-possible semiconductor junctions Scientists have developed what they believe is the thinnest-possible semiconductor,
a new class of nanoscale materials made in sheets only three atoms thick. The University of Washington researchers have demonstrated that two of these single-layer semiconductor materials can be connected in an atomically seamless fashion known as a heterojunction.
This result could be the basis for next-generation flexible and transparent computing, better light-emitting diodes,
or LEDS, and solar technologies.""Heterojunctions are fundamental elements of electronic and photonic devices, "said senior author Xiaodong Xu, a UW assistant professor of materials science and engineering and of physics."
"Our experimental demonstration of such junctions between two-dimensional materials should enable new kinds of transistors, LEDS, nanolasers,
and solar cells to be developed for highly integrated electronic and optical circuits within a single atomic plane."
"The research was published online this week in Nature Materials. The researchers discovered that two flat semiconductor materials can be connected edge-to-edge with crystalline perfection.
They worked with two single-layer, or monolayer, materials molybdenum diselenide and tungsten diselenide that have very similar structures,
which was key to creating the composite two-dimensional semiconductor. Collaborators from the electron microscopy center at the University of Warwick in England found that all the atoms in both materials formed a single honeycomb lattice structure, without any distortions or discontinuities.
This provides the strongest possible link between two single-layer materials necessary for flexible devices.
Within the same family of materials it is feasible that researchers could bond other pairs together in the same way.
Scientists craft atomically seamless, thinnest-possible semiconductor junctions A high-resolution scanning transmission electron microscopy (STEM) image shows the lattice structure of the heterojunctions in atomic precision.
Credit: University of Warwick The researchers created the junctions in a small furnace at the UW.
First, they inserted a powder mixture of the two materials into a chamber heated to 900 degrees Celsius (1,
652 F). Hydrogen gas was passed then through the chamber and the evaporated atoms from one of the materials were carried toward a cooler region of the tube
and deposited as single-layer crystals in the shape of triangles. After a while, evaporated atoms from the second material then attached to the edges of the triangle to create a seamless semiconducting heterojunction."
"said Sanfeng Wu, a UW doctoral student in physics and one of the lead authors.""Because the materials have different properties,
"Scientists craft atomically seamless, thinnest-possible semiconductor junctions With a larger furnace, it would be possible to mass-produce sheets of these semiconductor heterostructures,
the researchers said. On a small scale, it takes about five minutes to grow the crystals, with up to two hours of heating and cooling time."
"We are excited very about the new science and engineering opportunities provided by these novel structures,
"said senior author David Cobden, a UW professor of physics.""In the future, combinations of two-dimensional materials may be integrated together in this way to form all kinds of interesting electronic structures such as in-plane quantum wells and quantum wires, superlattices, fully functioning transistors,
and even complete electronic circuits.""The researchers have demonstrated already that the junction interacts with light much more strongly than the rest of the monolayer,
which is encouraging for optoelectric and photonic applications like solar cells c
#Competition for graphene: Researchers demonstrate ultrafast charge transfer in new family of 2-D semiconductors A new argument has just been added to the growing case for graphene being bumped off its pedestal as the next big thing in the high-tech world by the two-dimensional semiconductors
known as MX2 materials. An international collaboration of researchers led by a scientist with the U s. Department of energy (DOE)' s Lawrence Berkeley National Laboratory (Berkeley Lab) has reported the first experimental observation of ultrafast charge transfer in photo-excited
MX2 materials. The recorded charge transfer time clocked in at under 50 femtoseconds comparable to the fastest times recorded for organic photovoltaics."
"We've demonstrated, for the first time, efficient charge transfer in MX2 heterostructures through combined photoluminescence mapping and transient absorption measurements,"says Feng Wang, a condensed matter physicist with Berkeley Lab's Materials sciences Division
and the University of California (UC) Berkeley's Physics department.""Having quantitatively determined charge transfer time to be less than 50 femtoseconds,
our study suggests that MX2 heterostructures, with their remarkable electrical and optical properties and the rapid development of large-area synthesis, hold great promise for future photonic and optoelectronic applications."
"Wang is the corresponding author of a paper in Nature Nanotechnology describing this research. The paper is titled"Ultrafast charge transfer in atomically thin Mos2/WS2 heterostructures."
"Co-authors are Xiaoping Hong, Jonghwan Kim, Su-Fei Shi, Yu Zhang, Chenhao Jin, Yinghui Sun, Sefaattin Tongay, Junqiao Wu and Yanfeng Zhang.
MX2 monolayers consist of a single layer of transition metal atoms, such as molybdenum (Mo) or tungsten (W), sandwiched between two layers of chalcogen atoms,
such as sulfur (S). The resulting heterostructure is bound by the relatively weak intermolecular attraction known as the Van der waals force.
These 2d semiconductors feature the same hexagonal"honeycombed"structure as graphene and superfast electrical conductance,
but, unlike graphene, they have natural energy bandgaps. This facilitates their application in transistors and other electronic devices because
unlike graphene, their electrical conductance can be switched off.""Combining different MX2 layers together allows one to control their physical properties,
who is also an investigator with the Kavli Energy Nanosciences Institute (Kavli-ENSI).""For example, the combination of Mos2 and WS2 forms a type-II semiconductor that enables fast charge separation.
The separation of photoexcited electrons and holes is essential for driving an electrical current in a photodetector or solar cell."
"In demonstrating the ultrafast charge separation capabilities of atomically thin samples of Mos2/WS2 heterostructures,
not only for photonics and optoelectronics, but also for photovoltaics.""MX2 semiconductors have extremely strong optical absorption properties
and compared with organic photovoltaic materials, have a crystalline structure and better electrical transport properties,
and MX2 semiconductors provide an ideal way to spatially separate electrons and holes for electrical collection and utilization."
#Conductive nanofiber networks for flexible unbreakable and transparent electrodes Transparent conductors are required as electrodes in optoelectronic devices, such as touch panel screens, liquid crystal displays, and solar cells.
However, ITO-based transparent electrodes are brittle, prone to breakage, and expensive. Therefore, there is strong demand for alternatives to ITO transparent electrodes.
Tokyo Institute of technology researchers report the first development of a facile method for the fabrication of flexible and unbreakable transparent electrodes using nanofibers.
Two-dimensional aluminum (Al) nanofiber networks offering transparent conductors were fabricated by simple wet chemical etching of Al metalized polymer films using an electrospun polystyrene nanofiber mask template.
The resulting Al nanowire networksith a width of 500 nm and an area fraction of 22.0%xhibited 80%optical transmittance and sheet resistance of 45 O sq-1
figures of merit that are comparable to conventional transparent conductors. Notably, the fabrication method developed by the Tokyo Tech group is scalable for mass production and cost effective.
and transparent electrodes are promising for applications in both large-scale and mobile optoelectronic devices including ones that are flexible.
Examples of applications are large displays, large interactive touch screens, photovoltaic solar panels, light-emitting diode panels, smart phones,
and tablets a
#Biomimetic photodetector'sees'in color (Phys. org) Rice university researchers have created a CMOS-compatible biomimetic color photodetector that directly responds to red green
and blue light in much the same way the human eye does. The new device was created by researchers at Rice's Laboratory for Nanophotonics (LANP)
It uses an aluminum grating that can be added to silicon photodetectors with the silicon microchip industry's mainstay technology complementary metal-oxide semiconductor or CMOS.
This color filtering is done commonly using off-chip dielectric or dye color filters which degrade under exposure to sunlight
and can also be difficult to align with imaging sensors. Today's color filtering mechanisms often involve materials that are not CMOS-compatible
but this new approach has advantages beyond on-chip integration said LANP Director Naomi Halas the lead scientist on the study.
Biomimicry was no accident. The color photodetector resulted from a $6 million research program funded by the Office of Naval Research that aimed to mimic cephalopod skin using metamaterials compounds that blur the line between material and machine.
Cephalopods like octopus and squid are masters of camouflage but they are also color-blind. Halas said the squid skin research team which includes marine biologists Roger Hanlon of the Marine Biological Laboratory in Woods Hole Mass
. and Thomas Cronin of the University of Maryland Baltimore County suspect that cephalopods may detect color directly through their skin.
Based on that hypothesis LANP graduate student Bob Zheng the lead author of the new Advanced Materials study set out to design a photonic system that could detect colored light.
Bob has created a biomimetic detector that emulates what we are hypothesizing the squid skin'sees'Halas said.
This is a great example of the serendipity that can occur in the lab. In searching for an answer to a specific research question Bob has created a device that is far more practical and generally applicable.
Zheng's color photodetector uses a combination of band engineering and plasmonic gratings comb-like aluminum structures with rows of parallel slits.
The metallic nanostructures use surface plasmons waves of electrons that flow like a fluid across metal surfaces.
Light of a specific wavelength can excite a plasmon and LANP researchers often create devices where plasmons interact sometimes with dramatic effects.
With plasmonic gratings not only do you get color tunability you can also enhance near fields Zheng said.
Not only are we using the photodetector as an amplifier we're also using the plasmonic color filter as a way to increase the amount of light that goes into the detector he said.
Researchers use aluminum nanostructures for photorealistic printing of plasmonic color palettes More information: Zheng B. Y. Wang Y. Nordlander P. and Halas N. J. 2014) Color-Selective and CMOS-Compatible Photodetection Based on Aluminum Plasmonics.
#Scientists fabricate defect-free graphene set record reversible capacity for Co3o4 anode in Li-ion batteries Graphene has already been demonstrated to be useful in Li-ion batteries,
and size-tunable for battery applications has remained so far elusive. Now in a new study, scientists have developed a method to fabricate defect-free graphene (df-G) without any trace of structural damage.
Wrapping a large sheet of negatively charged df-G around a positively charged Co3o4 creates a very promising anode for high-performance Li-ion batteries.
The research groups of Professor Junk-Ki Park and Professor Hee-Tak Kim from Korea Advanced Institute of Science and Technology (KAIST) and Professor Yong-Min Lee
's research group from Hanbat National University, all in Daejeon, South korea, have published their paper on the new fabrication method in a recent issue of Nano Letters.
First the researchers filled a Pyrex tube with graphite powder, and then placed the open-ended tube inside a slightly larger tube.
The heat causes the molten potassium to move inside the micropores between the graphite powders
so that the potassium molecules become intercalated into the graphite interlayers. The resulting potassium graphite compounds were placed then in a pyridine solution,
which causes the layers to expand away from each other to form graphene nanosheets that could later be cooled
The researchers demonstrated that wrapping a large-sized negatively charged sheet of df-G around a positively charged piece of Co3o4 creates an anode with several impressive characteristics.
To the best of the researchers'knowledge, this reversible capacity is the highest among all Co3o4 electrodes ever reported.
with its perfect crystallinity, improves the anode performance because when a single graphene sheet is wrapped around a bundle of Co3o4 particles,
and then electrically detaching from the anode, which would otherwise occur. Because of this protective effect, the anode's capacity is preserved even after 200 cycles,
whereas anodes with an imperfect graphene layer rapidly decrease with cycling. The large size of the graphene plays a key role in the performance
because a larger size provides a higher cycling stability of the nanosized anode materials by improving their mechanical integrity.
With these advantages, the researchers expect the df-G to bring significant advances of composite electrodes for a variety of electrochemical system,
including batteries, fuel cells, and capacitors r
#Copper shines as flexible conductor Bend them, stretch them, twist them, fold them: modern materials that are light,
flexible and highly conductive have extraordinary technological potential, whether as artificial skin or electronic paper. Making such concepts affordable enough for general use remains a challenge
but a new way of working with copper nanowires and a PVA"nano glue"could be a game-changer.
Previous success in the field of ultra-lightweight"aerogel monoliths"has relied largely on the use of precious gold and silver nanowires.
By turning instead to copper, both abundant and cheap, researchers at Monash University and the Melbourne Centre for Nanofabrication have developed a way of making flexible conductors cost-effective enough for commercial application."
"Aerogel monoliths are like kitchen sponges but ours are made of ultra fine copper nanowires, using a fabrication process called freeze drying,
"said lead researcher Associate professor Wenlong Cheng, from Monash University's Department of Chemical engineering.""The copper aerogel monoliths are conductive
and could be embedded further into polymeric elastomers extremely flexible, stretchable materials to obtain conducting rubbers."
"Despite its conductivity, copper's tendency to oxidation and the poor mechanical stability of copper nanowire aerogel monoliths mean its potential has been unexplored largely.
The researchers found that adding a trace amount of poly (vinyl alcohol)( PVA) to their aerogels substantially improved their mechanical strength
and robustness without impairing their conductivity. What's more, once the PVA was included, the aerogels could be used to make electrically conductive rubber materials without the need for any prewiring.
Reshaping was also easy.""The conducting rubbers could be shaped in arbitrary 1d, 2d and 3d shapes simply by cutting,
while maintaining the conductivities, "Associate professor Cheng said. The versatility extends to the degree of conductivity."
"The conductivity can be tuned simply by adjusting the loading of copper nanowires, "he said.""A low loading of nano wires would be appropriate for a pressure sensor
whereas a high loading is suitable for a stretchable conductor.""Affordable versions of these materials open up the potential for use in a range of new-generation concepts:
from prosthetic skin to electronic paper, for implantable medical devices, and for flexible displays and touch screens. They can be used in rubberlike electronic devices that,
unlike paperlike electronic devices, can stretch as well as bend. They can also be attached to topologically complex curved surfaces,
serving as real skin-like sensing devices, Associate professor Cheng said. In their report, published recently in ACS Nano,
the researchers noted that devices using their copper-based aerogels were not quite as sensitive as those using gold nanowires,
but had many other advantages, most notably their low-cost materials, simpler and more affordable processing,
and great versatility i
#Color hologram uses plasmonic nanoparticles to store large amounts of information In the 4th century, the Romans built a special glass cup,
called the Lycurgus cup, that changes colors depending on which way the light is shining through it.
The glass is made of finely ground silver and gold dust that produces a dichroic, or color-changing, effect.
Although the makers of the Lycurgus cup likely did not know the mechanism responsible for the color-changing glass,
at the University of Cambridge in the UK, have used surface plasmon resonance as a new way to construct holograms.
Similar to the Lycurgus cup, the new holograms can change colors due to light scattering off silver nanoparticles of specific sizes and shapes.
the new holograms could have applications in 3d displays and information storage devices, among others.""This experiment is inspired by the very unique optical properties shown by the Lycurgus cup,
In contrast to other dichroic effects produced by some crystals, such as precious opals, the colorful effects of the Lycurgus cup have little dependence on the position of the observer.
In fact, the dichroism found in the Lycurgus cup has a different origin than crystals and so far this'plasmonic effect'has not been observed in naturally occurring materials."
"Although there are several different ways to construct holograms, almost all traditional holograms are single-color,
The new holograms consist of precisely engineered silver nanoparticles patterned over a substrate. A key difference in the new holograms is the smaller size of the diffraction fringes,
the fringes here are replaced with nanoparticles smaller than half the wavelength of light. The researchers showed that the narrower band diffraction,
is produced by plasmonic-enhanced optical scattering of the nanostructures. The subwavelength distance offers certain advantages.
For instance, two different types of plasmonic nanoparticles can be multiplexed, or combined but not coupled, at subwavelength distances.
By using nanoparticles of silver with different shapes and sizes, the researchers could control the colors.
In addition to providing multiple colors, multiplexing two nanoparticles has the advantage of increasing the bandwidth information limits.
The researchers showed that each nanoparticle carries independent information such as polarization and wavelength, which can be controlled simultaneously.
With twice the number of nanoparticles, the total amount of binary information stored can exceed the traditional limits of diffraction."
"It has been shown that nanoparticles with resonant properties can be uncoupled over subwavelength distances so their electromagnetic fields have minimal interaction,
"The device presented demonstrates that these nanoparticles can store and transfer independent information beyond the diffraction limits,
"Besides the evident application in replacing the typical'rainbow holograms'of credit cards and other security items,
"said coauthor Calum Williams at the University of Cambridge.""Furthermore, this concept can be applied as the basis to produce dynamic three-dimensional color displays.
In the area of informatics, these holographic configurations could store information in subwavelength areas. This means that optical data storage devices such as CDS, DVDS or Blu-ray could potentially expand their storage limits."
"The researchers plan to further investigate these applications and others in the future.""Future research is focused on the study of mechanisms for the tuning the plasmonic effect for display applications,
"Montelongo said.""The main goal is the integration of new modulation schemes to produce ultra-thin displays and dynamic holograms
#Scientists unveil new technology to better understand small clusters of atoms Physicists at the University of York,
working with researchers at the University of Birmingham and Genoa, have developed new technology to study atomic vibration in small particles,
revealing a more accurate picture of the structure of atomic clusters where surface atoms vibrate more intensively than internal atoms.
Using new computer technology based on gaming machines, scientists were able to use a combination of molecular dynamics
"Our work highlights the valuable contribution that computational simulations can have in the field of electron microscopy:
"Professor Jun Yuan, from York's Department of physics, added:""Our work can already explain the numerical discrepancies in the existing experimental data.
We believe that it will also prompt new experiments focusing on the dynamical properties of the atoms at nanostructures,
allowing us to understand the contribution of the previously little probed dynamical structure studies of atomic clusters, towards the physical properties such as catalytic relativities
#Graphene rubber bands could stretch limits of current healthcare New research published today in the journal ACS Nano identifies a new type of sensor that can monitor body movements
Although body motion sensors already exist in different forms they have not been used widely due to their complexity and cost of production.
Now researchers from the University of Surrey and Trinity college Dublin have treated for the first time common elastic bands with graphene to create a flexible sensor that is sensitive enough for medical use
-which imparts an electromechanical response on movement the team discovered that the material can be used as a sensor to measure a patient's breathing heart rate
or movement alerting doctors to any irregularities. Until now no such sensor has been produced that meets needs
and that can be made easily. It sounds like a simple concept but our graphene-infused rubber bands could really help to revolutionise remote healthcare said Dr Alan Dalton from the University of Surrey.
Co-author Professor Jonathan Coleman from Trinity college Dublin commented This stretchy material senses motion such as breathing pulse
and joint movement and could be used to create lightweight sensor suits for vulnerable patients such as premature babies making it possible to remotely monitor their subtle movements and alert a doctor to any worrying behaviours.
These sensors are compared extraordinarily cheap to existing technologies. Each device would probably cost pennies instead of pounds making it ideal technology for use in developing countries where there are not enough medically trained staff to effectively monitor
and treat patients quickly. Explore further: New sensor could light the way forward in low-cost medical imagin g
#Bacterial nanowires: Not what we thought they were For the past 10 years scientists have been fascinated by a type of electric bacteria that shoots out long tendrils like electric wires using them to power themselves
and transfer electricity to a variety of solid surfaces. Today a team led by scientists at USC has turned the study of these bacterial nanowires on its head discovering that the key features in question are not pili as previously believed
but rather are extensions of the bacteria's outer membrane equipped with proteins that transfer electrons called cytochromes.
Scientists had suspected long that bacterial nanowires were pili Latin for hair which are hairlike features common on other bacteria allowing them to adhere to surfaces
and even connect to one another. Given the similarity of shape it was easy to believe that nanowires were pili.
But Moh El-Naggar assistant professor at the USC Dornsife College of Letters Arts and Sciences says he was always careful to avoid saying that he knew for sure that's what they were.
The pili idea was the strongest hypothesis but we were always cautious because the exact composition and structure were very elusive.
Then we solved the experimental challenges and the hard data took us in a completely different direction.
I have never been happier about being wrong. In many ways it turned out to be an even cleverer way for bacteria to power themselves said El-Naggar corresponding author of the study who was named a Popular Science Brilliant 10 researcher in 2012 for his pioneering work
with bacterial nanowires. This latest study will be published online by the Proceedings of the National Academy of Sciences on August 18.
Scientists from USC collaborated with colleagues from Penn State the University of Wisconsin-Milwaukee Pacific Northwest National Laboratory and Rensselaer Polytechnic institute on the research.
The first clue came from tracking the genes of the bacteria. During the formation of nanowires scientists noted an increase in the expression of electron transport genes but no corresponding increase in the expression of pilin genes.
Challenged by this evidence of what nanowires weren't the team next needed to figure out what they actually were.
El-Naggar credits Sahand Pirbadian USC graduate student with devising an ingenious yet simple strategy to make the discovery.
By depriving the bacteria of oxygen the researchers were able to force the bacteria to stretch out their nanowires on command allowing the process to be observed in real time.
And by staining the bacterial membrane periplasm cytoplasm and specific proteins researchers were able to take video of the nanowires reaching out confirming that they were based on membrane and not pili at all.
The process isn't as simple as it sounds. Generating videos of the nanowires stretching out required new methods to simultaneously label multiple features keep a camera focused on the wriggling bacteria and combine the optical techniques with atomic force microscopy to gain higher resolution.
It took us about a year just to develop the experimental setup and figure out the right conditions for the bacteria to produce nanowires Pirbadian said.
We had to go back and reexamine some older experiments and rethink what we knew about the organism.
Once we were able to induce nanowire growth we started analyzing their composition and structure
which took another year of work. But it was well worth the effort because the outcome was very surprising
but in hindsight made a lot of sense. Understanding the way these electric bacteria work has applications well beyond the lab. Such creatures have the potential to address some of the big questions about the nature of life itself including
what types of lifeforms we might find in extreme environments like space. In addition this research has the potential to inform the creation of living microbial circuits forming the foundation of hybrid biological-synthetic electronic devices.
This research was funded at USC by the U s. Department of energy and Air force Office of Scientific research and made possible by facilities at the USC Centers of Excellence in Nanobiophysics and Electron Microsopy and Microanalysis.
Explore further: Researchers use gold substrate to allow for electron cryomicroscopy on difficult proteins More information: Shewanella oneidensis MR-1 nanowires are outer membrane and periplasmic extensions of the extracellular electron transport components PNAS www. pnas. org/cgi/doi/10.1073
/pnas. 141055111 s
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