#One Direction: Researchers grow nanocircuitry with semiconducting graphene nanoribbons In a development that could revolutionize electronic circuitry,
a research team from the University of Wisconsin at Madison (UW) and the U s. Department of energy's Argonne National Laboratory has confirmed a new way to control the growth paths of graphene nanoribbons on the surface of a germainum crystal.
Germanium is a semiconductor, and this method provides a straightforward way to make semiconducting nanoscale circuits from graphene, a form of carbon only one atom thick.
The method was discovered by UW scientists and confirmed in tests at Argonne.""Some researchers have wanted to make transistors out of carbon nanotubes,
but the problem is that they grow in all sorts of directions, "said Brian Kiraly of Argonne."
"The innovation here is that you can grow these along circuit paths that works for your tech."
"UW researchers used chemical vapor deposition to grow graphene nanoribbons on germanium crystals. This technique flows a mixture of methane, hydrogen,
and argon gases into a tube furnace. At high temperatures, methane decomposes into carbon atoms that settle onto the germanium's surface to form a uniform graphene sheet.
By adjusting the chamber's settings, the UW team was able to exert very precise control over the material."
"What we've discovered is that when graphene grows on germanium, it naturally forms nanoribbons with these very smooth,
armchair edges,"said Michael Arnold, an associate professor of materials science and engineering at UW-Madison.""The widths can be very, very narrow,
and the lengths of the ribbons can be very long, so all the desirable features we want in graphene nanoribbons are happening automatically with this technique."
"Graphene, a one-atom-thick, two-dimensional sheet of carbon atoms, is known for moving electrons at lightning speed across its surface without interference.
This high mobility makes the material an ideal candidate for faster, more energy-efficient electronics. However, the semiconductor industry wants to make circuits start
and stop electrons at will via bandgaps, as they do in computer chips. As a semimetal, graphene naturally has no bandgaps,
making it a challenge for widespread industry adoption. Until now. To confirm these findings, UW researchers went to Argonne staff scientists Brian Kiraly and Nathan Guisinger at the Center for Nanoscale Materials,
a DOE Office of Science User Facility located at Argonne.""We have some very unique capabilities here at the Center for Nanoscale Materials,
"said Guisinger.""Not only are designed our facilities to work with all different sorts of materials from metals to oxides,
we can also characterize, grow and synthesize materials.""Using scanning tunneling microscopy, a technique using electrons (instead of light
or the eyes) to see the characteristics of a sample, researchers confirmed the presence of graphene nanoribbons growing on the germanium.
Data gathered from the electron signatures allowed the researchers to create images of the material's dimensions and orientation.
In addition, they were able to determine its band structure and extent to which electrons scattered throughout the material."
"We're looking at fundamental physical properties to verify that it is, in fact, graphene and it shows some characteristic electronic properties,
"said Kiraly.""What's even more interesting is that these nanoribbons can be made to grow in certain directions on one side of the germanium crystal,
but not the other two sides.""For use in electronic devices, the semiconductor industry is interested primarily in three faces of a germanium crystal.
Depicting these faces in terms of coordinates (X y z), where single atoms connect to each other in a diamond-like grid structure,
each face of a crystal (1, 1, 1) will have axes that differ from one (1, 1, 0) to the other (1, 0,
0). Previous research shows that graphene sheets can grow on germanium crystal faces (1, 1, 1) and (1, 1,
0). However, this is the first time any study has recorded the growth of graphene nanoribbons on the (1,
which reacts very rapidly to incident light of all different wavelengths and even works at room temperature.
It is the first time that a single detector has been able to monitor the spectral range from visible light to infrared radiation and right through to terahertz radiation.
The HZDR scientists are already using the new graphene detector for the exact synchronization of laser systems.
A tiny flake of graphene on silicon carbide and a futuristic-looking antenna and there it is the new graphene detector.
Like no other single detector system which has gone before, this comparatively simple and inexpensive construct can cover the enormous spectral range from visible light all the way to terahertz radiation."
"In contrast to other semiconductors like silicon or gallium arsenide, graphene can pick up light with a very large range of photon energies and convert it into electric signals.
We only needed a broadband antenna and the right substrate to create the ideal conditions,
"explained Dr. Stephan Winnerl, physicist at the Institute of Ion beam Physics and Materials Research at the HZDR.
Back in 2013 Martin Mittendorff, who was a Phd student at the HZDR at that time, had developed the precursor to the graphene detector.
In his present position as a postdoc at the University of Maryland he has perfected now it with his Dresden colleagues and with scientists from Marburg, Regensburg and Darmstadt.
How it works: the graphene flake and antenna assembly absorbs the rays, thereby transferring the energy of the photons to the electrons in the graphene.
These"hot electrons"increase the electrical resistance of the detector and generate rapid electric signals. The detector can register incident light in just 40 picoseconds these are billionths of a second.
Wide spectral range achieved through silicon carbide substratethe choice of substrate has now proved a pivotal step in improving the little light trap."
"Semiconductor substrates used in the past have absorbed always some wavelengths but silicon carbide remains passive in the spectral range,
"explained Stephan Winnerl. Then there is also an antenna which acts like a funnel and captures long-wave infrared and terahertz radiation.
The scientists have therefore been able to increase the spectral range by a factor of 90 in comparison with the previous model, making the shortest detectable wavelength 1000 times smaller than the longest.
By way of comparison, red light, which has the longest wavelength visible to the human eye,
is only twice as long as violet light which has the shortest wavelength on the visible spectrum. This optical universal detector is already being used at the HZDR for the exact synchronization of the two free-electron lasers at the ELBE Center for High-power Radiation Sources with other lasers.
This alignment is particularly important for"pump probe"experiments, as they are called, where researcher take one laser for the excitation of a material("pump)
"and then use a second laser with a different wavelength for the measurement("probe")."The laser pulses must be synchronized exactly for such experiments.
So the scientists are using the graphene detector like a stopwatch. It tells them when the laser pulses reach their goal,
and the large bandwidth helps to prevent a change of detector from being a potential source of error.
Another advantage is that all the measurements can take place at room temperature, obviating the need for the expensive and time-consuming nitrogen or helium cooling processes with other detectors.
Image: The external antenna on the detector captures long-wave infrared and terahertz radiation and funnels it to a graphene flake
which is located in the center of the structure on a silicon carbide substrate t
#Graphene flakes as an ultra-fast stopwatch Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with colleagues from the USA and Germany, have developed a new optical detector from graphene
which reacts very rapidly to incident light of all different wavelengths and even works at room temperature.
It is the first time that a single detector has been able to monitor the spectral range from visible light to infrared radiation and right through to terahertz radiation.
The HZDR scientists are already using the new graphene detector for the exact synchronization of laser systems.
A tiny flake of graphene on silicon carbide and a futuristic-looking antenna and there it is the new graphene detector.
Like no other single detector system which has gone before, this comparatively simple and inexpensive construct can cover the enormous spectral range from visible light all the way to terahertz radiation."
"In contrast to other semiconductors like silicon or gallium arsenide, graphene can pick up light with a very large range of photon energies and convert it into electric signals.
We only needed a broadband antenna and the right substrate to create the ideal conditions,
"explained Dr. Stephan Winnerl, physicist at the Institute of Ion beam Physics and Materials Research at the HZDR.
Back in 2013 Martin Mittendorff, who was a Phd student at the HZDR at that time, had developed the precursor to the graphene detector.
In his present position as a postdoc at the University of Maryland he has perfected now it with his Dresden colleagues and with scientists from Marburg, Regensburg and Darmstadt.
How it works: the graphene flake and antenna assembly absorbs the rays, thereby transferring the energy of the photons to the electrons in the graphene.
These"hot electrons"increase the electrical resistance of the detector and generate rapid electric signals. The detector can register incident light in just 40 picoseconds these are billionths of a second.
Wide spectral range achieved through silicon carbide substrate The choice of substrate has now proved a pivotal step in improving the little light trap."
"Semiconductor substrates used in the past have absorbed always some wavelengths but silicon carbide remains passive in the spectral range,
"explained Stephan Winnerl. Then there is also an antenna which acts like a funnel and captures long-wave infrared and terahertz radiation.
The scientists have therefore been able to increase the spectral range by a factor of 90 in comparison with the previous model, making the shortest detectable wavelength 1000 times smaller than the longest.
By way of comparison, red light, which has the longest wavelength visible to the human eye,
is only twice as long as violet light which has the shortest wavelength on the visible spectrum. This optical universal detector is already being used at the HZDR for the exact synchronization of the two free-electron lasers at the ELBE Center for High-power Radiation Sources with other lasers.
This alignment is particularly important for"pump probe"experiments, as they are called, where researcher take one laser for the excitation of a material("pump)
"and then use a second laser with a different wavelength for the measurement("probe")."The laser pulses must be synchronized exactly for such experiments.
So the scientists are using the graphene detector like a stopwatch. It tells them when the laser pulses reach their goal,
and the large bandwidth helps to prevent a change of detector from being a potential source of error.
Another advantage is that all the measurements can take place at room temperature, obviating the need for the expensive and time-consuming nitrogen or helium cooling processes with other detectors c
#Engineers reveal record-setting flexible phototransistor Inspired by mammals'eyes, University of Wisconsin-Madison electrical engineers have created the fastest,
most responsive flexible silicon phototransistor ever made. The innovative phototransistor could improve the performance of myriad products-ranging from digital cameras,
night-vision goggles and smoke detectors to surveillance systems and satellites-that rely on electronic light sensors. Integrated into a digital camera lens, for example, it could reduce bulkiness and boost both the acquisition speed and quality of video or still photos.
Developed by UW-Madison collaborators Zhenqiang"Jack"Ma, professor of electrical and computer engineering and research scientist Jung-Hun Seo, the high-performance phototransistor far and away exceeds all previous flexible phototransistor parameters,
including sensitivity and response time. The researchers published details of their advance this week in the journal Advanced Optical Materials.
and 0s that create the digital image. While many phototransistors are fabricated on rigid surfaces and therefore are flat,
At that point, a reflective metal layer is on the bottom.""In this structure-unlike other photodetectors-light absorption in an ultrathin silicon layer can be much more efficient
The researchers also placed electrodes under the phototransistor's ultrathin silicon nanomembrane layer-and the metal layer and electrodes each act as reflectors
and improve light absorption without the need for an external amplifier.""There's a built-in capability to sense weak light,
whose work was supported by the U s. Air force.""It shows the capabilities of high-sensitivity photodetection and stable performance under bending conditions,
University of Wisconsin-Madison electrical engineers have created the fastest, most responsive flexible silicon phototransistor ever made.
night-vision goggles and smoke detectors to surveillance systems and satellites-that rely on electronic light sensors. Integrated into a digital camera lens, for example, it could reduce bulkiness and boost both the acquisition speed and quality of video or still photos.
Developed by UW-Madison electrical engineers, this unique phototransistor is flexible, yet faster and more responsive than any similar phototransistor in the world.
professor of electrical and computer engineering, and research scientist Jung-Hun Seo, the high-performance phototransistor far and away exceeds all previous flexible phototransistor parameters,
and 0s that create the digital image. While many phototransistors are fabricated on rigid surfaces and therefore are flat,
At that point, a reflective metal layer is on the bottom.""In this structure-unlike other photodetectors-light absorption in an ultrathin silicon layer can be much more efficient
The researchers also placed electrodes under the phototransistor's ultrathin silicon nanomembrane layer-and the metal layer and electrodes each act as reflectors
and improve light absorption without the need for an external amplifier.""There's a built-in capability to sense weak light,
whose work was supported by the U s. Air force.""It shows the capabilities of high-sensitivity photodetection and stable performance under bending conditions,
#New protein nanoparticles allow scientists to track cells and interactions within them Engineers have designed magnetic protein nanoparticles that can be used to track cells
or to monitor interactions within cells. The particles, described today in Nature Communications, are enhanced an version of a naturally occurring, weakly magnetic protein called ferritin. erritin,
which is as close as biology has given us to a naturally magnetic protein nanoparticle, is really not that magnetic.
an MIT professor of biological engineering and the paper senior author. e used the tools of protein engineering to try to boost the magnetic characteristics of this protein.
The new ypermagneticprotein nanoparticles can be produced within cells allowing the cells to be imaged or sorted using magnetic techniques.
The paper lead author is former MIT graduate student Yuri Matsumoto. Other authors are graduate student Ritchie Chen and Polina Anikeeva, an assistant professor of materials science and engineering.
Magnetic pull Previous research has yielded synthetic magnetic particles for imaging or tracking cells, but it can be difficult to deliver these particles into the target cells.
prompting them to start producing the protein on their own. ather than actually making a nanoparticle in the lab
After repeated rounds of screening, the researchers used one of the most promising candidates to create a magnetic sensor consisting of enhanced ferritin modified with a protein tag that binds with another protein called streptavidin.
Researchers could track this activity using magnetic resonance imaging (MRI), potentially allowing them to observe communication between neurons, activation of immune cells,
Such sensors could also be used to monitor the effectiveness of stem cell therapies, Jasanoff says. s stem cell therapies are developed,
it going to be necessary to have noninvasive tools that enable you to measure them, he says.
The researchers are now working on adapting the magnetic sensors to work in mammalian cells. They are also trying to make the engineered ferritin even more strongly magnetic e
and accurately and freezing them in place could enable improved nanoscale sensing methods and aid research to manufacture advanced technologies such as quantum computers and ultra-high-resolution displays.
The device, fabricated at Purdue University's Birck Nanotechnology Center, uses a cylindrical gold"nanoantenna"with a diameter of 320 nanometers,
or about 1/300th the width of a human hair. The structures concentrate and absorb light,
"and making it possible to manipulate nanometer scale objects suspended in a fluid.""The proposed approach enables the immediate implementation of a myriad of exciting applications,
"said Alexandra Boltasseva, associate professor of electrical and computer engineering. Findings are detailed in a paper appearing online in Nature Nanotechnology Monday (Nov 2).
) Plasmonic devices harness clouds of electrons called surface plasmons to manipulate and control light. Potential applications for the nanotweezer include improved-sensitivity nanoscale sensors
and the study of synthetic and natural nanoobjects including viruses and proteins; creation of"nanoassemblies"for plasmonic materials that could enable a host of advanced technologies;
ultra-resolution"opto#uidic"displays; and plasmonic circuitry for quantum logic units. The nanotweezer might be used to create devices containing nanodiamond particles
or other nanoscale light-emitting structures that can be used to enhance the production of single photons, workhorses of quantum information processing,
which could bring superior computers, cryptography and communications technologies. Conventional computers use electrons to process information.
However, the performance might be ramped up considerably by employing the unique quantum properties of electrons
and photons, said Vladimir M. Shalaev, co-director of a new Purdue Quantum Center, scientific director of nanophotonics at the Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering."
"The nanotweezer system has been shown to cause convection in fluid on-demand, resulting in micrometer-per-second nanoparticle transport by harnessing a single plasmonic nanoantenna,
which until now has been thought to be said impossible doctoral student Justus C. Ndukaife. Previous research had shown that convection using a single plasmonic nanoantenna was too weak to induce such a strong convection, below 10 nanometers per second,
which cannot result in a net transport of suspended particles. However, the Purdue researchers have overcome this limitation,
increasing the velocity of particle transport by 100 times by applying an alternating current electric field in conjunction with heating the plasmonic nanoantenna using a laser to induce a force far stronger than otherwise possible."
"This work brings the outstanding spatial resolution of plasmonic hotspots to the field of rapid electrokinetic patterning (REP),
said Steve Wereley, a professor of mechanical engineering. Ndukaife said, "The local electromagnetic field intensity is enhanced highly, over 200 times, at the plasmonic hotspot.
The interesting thing about this system is that not only can we trap particles but also do useful tasks
because we have these hotspots. If I bring a particle to the hotspot then I can do measurements,
and sensing is enhanced because it is in a hotspot.""The new hybrid nanotweezer combines a near-infrared laser light
and an electric field, inducing an"electrothermoplasmonic flow.""""Then, once we turn off the electric field the laser holds the particles in place,
so it can operate in two modes. First, the fast transport using alternating current, and then you turn off the electric field
and it goes into the plasmonic tweezing mode, "he said. The Purdue researchers are the first to induce electrothermoplasmonic flow using plasmonic structures.
The system also makes it possible to create patterns to project images, potentially for displays with ultra-fine resolution.
The technique was demonstrated with polystyrene particles i
#An important step in artificial intelligence: Researchers in UCSB's Department of Electrical and Computer engineering are seeking to make computer brains smarter by making them more like our own Abstract:
In what marks a significant step forward for artificial intelligence, researchers at UC Santa barbara have demonstrated the functionality of a simple artificial neural circuit.
For the first time, a circuit of about 100 artificial synapses was proved to perform a simple version of a typical human task:
image classification.""It's a small, but important step,"said Dmitri Strukov, a professor of electrical and computer engineering.
With time and further progress, the circuitry may eventually be expanded and scaled to approach something like the human brain's,
what computers would require far more time and energy to perform. What are these functions? Well, you're performing some of them right now.
As you read this, your brain is making countless split-second decisions about the letters and symbols you see,
Key to this technology is the memristor (a combination of"memory"and"resistor"),an electronic component
Unlike conventional transistors, which rely on the drift and diffusion of electrons and their holes through semiconducting material,
the resulting device would have to be loaded enormous with multitudes of transistors that would require far more energy."
"Classical computers will always find an ineluctable limit to efficient brain-like computation in their very architecture,
"This memristor-based technology relies on a completely different way inspired by biological brain to carry on computation."
however, many more memristors would be required to build more complex neural networks to do the same kinds of things we can do with barely any effort and energy,
Potential applications already exist for this emerging technology, such as medical imaging, the improvement of navigation systems or even for searches based on images rather than on text.
The energy-efficient compact circuitry the researchers are striving to create would also go a long way toward creating the kind of high-performance computers
and memory storage devices users will continue to seek long after the proliferation of digital transistors predicted by Moore's Law becomes too unwieldy for conventional electronics."
and giving a serious boost to future computers,"said Prezioso. In the meantime, the researchers will continue to improve the performance of the memristors,
The very next step would be to integrate a memristor neural network with conventional semiconductor technology,
###Konstantin Likharev from the Department of physics and Astronomy at Stony Brook University also conducted research for this project.
'805-893-4765copyright University of California-Santa Barbaraissuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
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"While lotus leaves repel water and self-clean when it rains, a moth's eyes are antireflective because of naturally covered tapered nanostructures where the refractive index gradually increases as light travels to the moth's cornea,
"said Tolga Aytug, lead author of the paper and a member of ORNL's Materials Chemistry Group."
"This produces a surface consisting of a porous three-dimensional network of high-silica content glass that resembles microscopic coral."
Where solar panels are concerned, the suppression of reflected light translates into a 3-6 percent relative increase in light-to-electricity conversion efficiency and power output of the cells.
Coupled with the superhydrophobic self-cleaning ability, this could also substantially reduce maintenance and operating costs of solar panels.
In addition the coating is highly effective at blocking ultraviolet light. Other potential applications include goggles, periscopes, optical instruments, photodetectors and sensors.
In addition, the superhydrophobic property can be effective at preventing ice and snow buildup on optical elements and can impede biofouling in marine applications.
Aytug emphasized that the impact abrasion resistance of the coating completes the package, making it suitable for untold applications."
"We have shown that our nanostructure glass coatings exhibit superior mechanical resistance to impact abrasion-like sand storms
The work was supported by the Laboratory Directed Technology Innovation Program. STEM research was supported by the DOE Office of Science Basic energy Sciences.
A portion of the research was conducted at the Center for Nanophase Materials sciences, a DOE Office of Science User Facility.
Photovoltaic device measurements were done at the University of Utah h
#Artificial photosynthesis: New, stable photocathode with great potential Many of us are familiar with electrolytic splitting of water from their school days:
if you hold two electrodes into an aqueous electrolyte and apply a sufficient voltage, gas bubbles of hydrogen and oxygen are formed.
If this voltage is generated by sunlight in a solar cell, then you could store solar energy by generating hydrogen gas.
This is because hydrogen is a versatile medium of storing and using"chemical energy"."Research teams all over the world are
therefore working hard to develop compact, robust, and cost-effective systems that can accomplish this challenge.
because an efficient hydrogen generation preferably proceeds in an acidic electrolyte corroding very fast solar cells. Electrodes that so far have been used are made of very expensive elements such as platinum or platinum-iridium alloys.
New photocathode with several advantages Under the"Light2hydrogen"BMBF Cluster project and an ongoing"Solar H2"DFG Priority programme, a team from the HZB Institute for Solar fuels has developed now a novel photoelectrode
it consists of chalcopyrite (a material used in device grade thin film solar cells) that has been coated with a thin, transparent, conductive oxide film of titanium dioxide (Tio2.
and contains a small amount of platinum in the form of nanoparticles. This new composite presents some special talents.
Firstly, it produces under sun light illumination a photovoltage of almost 0. 5 volts and very high photocurrent densities of up to 38 ma/cm2;
almost all sun light reaches the photoactive chalcopyrite, leading to the observed high photocurrent density and photovoltage comparable with those of a conventional device-grade thin-film solar cell.
HZB recipe and technology The recipe for this novel and elegant coating was developed by Anahita Azarpira in the course of her doctoral studies in a team headed by Assoc.
Prof. Thomas Schedel-Niedrig. She uses a chemical vapour coating technique (sprayed ion-layer gas reaction/Spray-ILGAR) that was developed
In this process, the titanium dioxide and platinum precursors are dissolved in ethanol and converted to a fog using an ultrasonic bath.
The produced aerosol is directed over the heated substrate using a stream of nitrogen gas resulting into a polycrystalline thin film grown on the chalcopyrite substrate over time with embedded nanoparticles of platinum.
in order to optimize the properties of the novel composite photoelectrode device. The properties were optimal with a volumetric proportion of about 5%platinum (H2ptcl6) in the precursor solution."
"More than 80%of the incident visible sunlight was converted photoelectrically by this composite system into electric current available for the hydrogen generation,
In addition, it has been reported in the very recently published article that the composite shows high long-term stability over 25 hours
the majority of the required voltage between the composite photocathode and a platinum counter electrode of around 1. 8 volts is still coming from a battery.
i e to chemical energy for storage. As a consequence we have developed successfully and tested a demonstrator device for solar hydrogen production with a company in Schwerin under the Light2hydrogen project, according to Schedel-Niedrig g
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