Cool nanotech image — graphene transistors

The article connected to the image is pretty good, too.

Triple transistor: Single graphene transistors like this one can be made to operate in three modes and perform functions that usually require multiple transistors in a circuit. Credit: Alexander Balandin

Also from the link:

Researchers have already made blisteringly fast graphene transistors. Now they’ve used graphene to make a transistor that can be switched between three different modes of operation, which in conventional circuits must be performed by three separate transistors. These configurable transistors could lead to more compact chips for sending and receiving wireless signals.

Chips that use fewer transistors while maintaining all the same functions could be less expensive, use less energy, and free up room inside portable electronics like smart phones, where space is tight. The new graphene transistor is an analog device, of the type that’s used for wireless communications in Bluetooth headsets and radio-frequency identification (RFID) tags.

 

Update on the rare earth mineral/China issue

I blogged about this topic a couple of times last month, and now it looks like the issue is already coming to North American shores. Not exactly sure what China is up to here, but it is very serious economic saber-rattling, and in a media world full of manufactured bogeymen, this is an issue to actually be concerned about.

From the third (and final) link:

Last month, the New York Times reported that the Chinese government clamped down on its exports of rare earth metals, which are used in the manufacture of all kinds of electronics, to Japan. Now, it appears that a similar thing is happening with Western countries like the United States, the Times reports, though Chinese officials deny it.

The Chinese action, involving rare earth minerals that are crucial to manufacturing many advanced products, seems certain to further intensify already rising trade and currency tensions with the West. Until recently, China typically sought quick and quiet accommodations on trade issues.

But the interruption in rare earth supplies is the latest sign from Beijing that Chinese leaders are willing to use their growing economic muscle. “The embargo is expanding” beyond Japan, said one of the three rare earth industry officials, all of whom insisted on anonymity for fear of business retaliation by Chinese authorities.

They said Chinese customs officials imposed the broader restrictions on Monday morning, hours after a top Chinese official summoned international news media Sunday night to denounce United States trade actions.

As we said last time, the mechanics of any rare earth metal embargo is important to manufacturers and suppliers, but hard to pin down. What’s important, policy-wise, is that we could have a domestic rare earth metal industry in the United States, but we have refused to support it in the belief that the market would always deliver what we needed from low-cost Chinese suppliers.

 

Graphene research may lead to electronics improvement

A fairly radical improvement. Try highly efficient, very-low-heat producing and smaller electronics devices. I enjoy blogging about nanotech research with real promise for market applications.

From the link:

NIST recently constructed the world’s most powerful and stable scanning-probe microscope, with an unprecedented combination of low temperature (as low as 10 millikelvin, or 10 thousandths of a degree above absolute zero), ultra-high vacuum and high magnetic field. In the first measurements made with this instrument, the team has used its power to resolve the finest differences in the electron energies in graphene, atom-by-atom.

“Going to this resolution allows you to see new physics,” said Young Jae Song, a postdoctoral researcher who helped develop the instrument at NIST and make these first measurements.

And the new physics the team saw raises a few more questions about how the electrons behave in graphene than it answers.

Because of the geometry and electromagnetic properties of graphene’s structure, an electron in any given energy level populates four possible sublevels, called a “quartet.” Theorists have predicted that this quartet of levels would split into different energies when immersed in a magnetic field, but until recently there had not been an instrument sensitive enough to resolve these differences.

“When we increased the magnetic field at extreme low temperatures, we observed unexpectedly complex quantum behavior of the electrons,” said NIST Fellow Joseph Stroscio.

What is happening, according to Stroscio, appears to be a “many-body effect” in which electrons interact strongly with one another in ways that affect their energy levels.

Memristor storage coming in 2013

Of course, we’ll have to see if this tech is still state-of-the-art three years down the road.

From the link:

An electronic component that offers a new way to squeeze more data into computers and portable gadgets is set to go into production in just a couple of years. Hewlett-Packard announced today that it has entered an agreement with the Korean electronics manufacturer Hynix Semiconductor to make the components, called “memristors,” starting in 2013. Storage devices made of memristors will allow PCs, cellphones, and servers to store more and switch on instantly.

Making memories: This colorized atomic-force microscopy image shows 17 memristors. The circuit elements, shown in green, are formed at the crossroads of metal nanowires. Credit: StanWilliams, HP Labs

Memristors are nanoscale electronic switches that have a variable resistance, and can retain their resistance even when the power is switched off. This makes them similar to the transistors used to store data in flash memory. But memristors are considerably smaller–as small as three nanometers. In contrast, manufacturers are experimenting with flash memory components that are 20 nanometers in size.

“The goal is to be at least double whatever flash memory is in three years–we know we’ll beat flash in speed, power, and endurance, and we want to beat it in density, too,” says Stanley Williams, a senior fellow at HP who has been developing memristors in his lab for about five years.

Making graphene electronics friendly

Electronics is a very attractive application for both carbon nanotubes and graphene, but graphene is proving fairly stubborn to working out in real world deployment. This news out of the Oak Ridge National Laboratory sounds very promising.

From the link:

Structural loops that sometimes form during a graphene cleaning process can render the material unsuitable for electronic applications. Overcoming these types of problems is of great interest to the electronics industry.

“Graphene is a rising star in the materials world, given its potential for use in precise electronic components like transistors or other semiconductors,” said Bobby Sumpter, a staff scientist at ORNL.

The team used quantum molecular dynamics to simulate an experimental graphene cleaning process, as discussed in a paper published in Physical Review Letters. Calculations performed on ORNL supercomputers pointed the researchers to an overlooked intermediate step during processing.

Imaging with a transmission electron microscope, or TEM, subjected the graphene to electron irradiation, which ultimately prevented loop formation. The ORNL simulations showed that by injecting electrons to collect an image, the electrons were simultaneously changing the material’s structure.

ORNL simulations demonstrate how loops (seen above in blue) between graphene layers can be minimized using electron irradiation (bottom).

Graphene nanomesh may be the semiconductor solution

I’ve done tons of blogging on graphene and this news seems to be direct competition with this graphene news I covered about a week ago. The issue is turning graphene into a semiconductor to allow the material to eventually replace silicon in electronic devices. The last link up there goes to a post outlining the concept of using nanoribbons of graphene, the middle link goes to research claiming a “nanomesh” is a superior method of turning the carbon nanomaterial into a semiconductor.

The release:

New graphene ‘nanomesh’ could change the future of electronics

Graphene, a one-atom-thick layer of a carbon lattice with a honeycomb structure, has great potential for use in radios, computers, phones and other electronic devices. But applications have been stymied because the semi-metallic graphene, which has a zero band gap, does not function effectively as a semiconductor to amplify or switch electronic signals.

While cutting graphene sheets into nanoscale ribbons can open up a larger band gap and improve function, ‘nanoribbon’ devices often have limited driving currents, and practical devices would require the production of dense arrays of ordered nanoribbons — a process that so far has not been achieved or clearly conceptualized.

But Yu Huang, a professor of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science, and her research team, in collaboration with UCLA chemistry professor Xiangfeng Duan, may have found a new solution to the challenges of graphene.

In research to be published in the March issue of Nature Nanotechnology (currently available online), Huang’s team reveals the creation of a new graphene nanostructure called graphene nanomesh, or GNM. The new structure is able to open up a band gap in a large sheet of graphene to create a highly uniform, continuous semiconducting thin film that may be processed using standard planar semiconductor processing methods.

“The nanomeshes are prepared by punching a high-density array of nanoscale holes into a single or a few layers of graphene using a self-assembled block copolymer thin film as the mask template,” said Huang.

The nanomesh can have variable periodicities, defined as the distance between the centers of two neighboring nanoholes. Neck widths, the shortest distance between the edges of two neighboring holes, can be as low as 5 nanometers.

This ability to control nanomesh periodicity and neck width is very important for controlling electronic properties because charge transport properties are highly dependent on the width and the number of critical current pathways.

Using such nanomesh as the semiconducting channel, Huang and her team have demonstrated room-temperature transistors that can support currents nearly 100 times greater than individual graphene nanoribbon devices, but with a comparable on-off ratio. The on-off ratio is the ratio between the currents when a device is switched on or switched off. This usually reveals how effectively a transistor can be switched off and on.

The researchers have also shown that the on-off ratio can be tuned by varying the neck width.

“GNMs can address many of the critical challenges facing graphene, as well as bypass the most challenging assembly problems,” Huang said. “In conjunction with recent advances in the growth of graphene over a large-area substrate, this concept has the potential to enable a uniform, continuous semiconducting nanomesh thin film that can be used to fabricate integrated devices and circuits with desired device size and driving current.

“The concept of the GNM therefore points to a clear pathway towards practical application of graphene as a semiconductor material for future electronics. The unique structural and electronic characteristics of the GNMs may also open up exciting opportunities in highly sensitive biosensors and a new generation of spintronics, from magnetic sensing to storage,” she said.

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The study was funded in part by Huang’s UCLA Henry Samueli School of Engineering and Applied Science Fellowship.

The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional degree programs, including an interdepartmental graduate degree program in biomedical engineering. Ranked among the top 10 engineering schools at public universities nationwide, the school is home to seven multimillion-dollar interdisciplinary research centers in wireless sensor systems, nanotechnology, nanomanufacturing and nanoelectronics, all funded by federal and private agencies.

For more news, visit the UCLA Newsroom and follow us on Twitter.

Graphene replacing silicon — is it “when” and not “if?”

Not quite yet, but headway is being made in making graphene the successor to silicon as the semiconductor for electronics. I first blogged about graphene replacing silicon back in late March 2008 (this blog wasn’t even three months old at the time — hit the link and dig the crazy layout I was using for KurzweilAI posts).

From the first link, the latest news — both good and bad — in making graphene the semiconductor of choice:

“Graphene has been the subject of intense focus and research for a few years now,” Philip Kim tells PhysOrg.com. “There are researchers that feel that it is possible that graphene could replace silicon as a semiconductor in electronics.”

Kim is a scientist at Columbia University in New York City. He has been working with Melinda Han and Juliana Brant to try and come up with a way to make graphene a feasible replacement for silicon. Toward that end, they have been looking at ways to overcome some of the problems associated with using graphene as a semiconductor in electronic devices. They set forth some ideas for electron transport for graphene in Physical Review Letters: “Electron Transport in Disordered Graphene Nanoribbons.”

“Graphene has high mobility, and less scattering than silicon. Theoretically, it is possible to make smaller structures that are more stable at the nanolevel than those made from silicon,” Kim says. He points out that as electronics continue to shrink in size, the interest in finding viable alternatives to silicon is likely to increase. Graphene is a good candidate because of the high electron mobility it offers, its stability on such a small scale, and the possibility that one could come up with different device concepts for electronics.

And here’s a bonus fun graphene graphic from the link:

Graphene is an atomic-scale honeycomb lattice made of carbon atoms. By Dr. Thomas Szkopek, via Wikipedia

Antenna evolution

These aren’t your grandad’s — or dad’s for that matter — antennae.

The release:

The antenna consists of liquid metal injected into elastomeric microchannels. The antennas can be deformed (twisted and bent) since the mechanical properties are dictated by the elastomer and not the metal.

Antennas aren’t just for listening to the radio anymore. They’re used in everything from cell phones to GPS devices. Research from North Carolina State University is revolutionizing the field of antenna design – creating shape-shifting antennas that open the door to a host of new uses in fields ranging from public safety to military deployment.

Modern antennas are made from copper or other metals, but there are limitations to how far they can be bent – and how often – before they break completely. NC State scientists have created antennas using an alloy that “can be bent, stretched, cut and twisted – and will return to its original shape,” says Dr. Michael Dickey, assistant professor of chemical and biomolecular engineering at NC State and co-author of the research.

The researchers make the new antennas by injecting an alloy made up of the metals gallium and indium, which remains in liquid form at room temperature, into very small channels the width of a human hair. The channels are hollow, like a straw, with openings at either end – but can be any shape. Once the alloy has filled the channel, the surface of the alloy oxidizes, creating a “skin” that holds the alloy in place while allowing it to retain its liquid properties.

“Because the alloy remains a liquid,” Dickey says, “it takes on the mechanical properties of the material encasing it.” For example, the researchers injected the alloy into elastic silicone channels, creating wirelike antennas that are incredibly resilient and that can be manipulated into a variety of shapes. “This flexibility is particularly attractive for antennas because the frequency of an antenna is determined by its shape,” says Dickey. “So you can tune these antennas by stretching them.”

While the alloy makes an effective antenna that could be used in a variety of existing electronic devices, its durability and flexibility also open the door to a host of new applications. For example, an antenna in a flexible silicone shell could be used to monitor civil construction, such as bridges. As the bridge expands and contracts, it would stretch the antenna – changing the frequency of the antenna, and providing civil engineers information wirelessly about the condition of the bridge.

Flexibility and durability are also ideal characteristics for military equipment, since the antenna could be folded or rolled up into a small package for deployment and then unfolded again without any impact on its function. Dickey thinks these new applications are the most likely uses for the new antennas, since the alloy is more expensive than the copper typically used in most consumer electronics that contain antennas.

Dickey’s lab is performing further research under a National Science Foundation grant to better understand the alloy’s properties and means of utilizing it to create useful devices.

The research is co-authored by Dickey, NC State doctoral students Ju-Hee So, Amit Qusba and Gerard Hayes, NC State undergraduate student Jacob Thelen, and University of Utah professor Dr. Gianluca Lazzi, who participated in the research while a professor at NC State. The research, “Reversibly Deformable and Mechanically Tunable Fluidic Antennas,” is published in Advanced Functional Materials.

-shipman-

“Reversibly Deformable and Mechanically Tunable Fluidic Antennas”

Authors: Ju-Hee So, Jacob Thelen, Amit Qusba, Gerard J. Hayes and Michael D. Dickey, North Carolina State University; Gianluca Lazzi, University of Utah

Published: November 2009, Advanced Functional Materials

Abstract: This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ~90% efficiency over a broad frequency range (1910–1990 MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (+/- 0.1–0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna.

Carbon nanotubes and electronics

Via KurzweilAI — This post is a two–fer on nanotech and carbon nanotubes.

From the “two” link:

Using Nanotubes in Computer Chips

PhysOrg.com, Sep. 10, 2009 A simple enough manufacturing process developed by MITresearchers could enable carbon nanotubes to replace the vertical wires in chips, permitting denser packing ofcircuits. Read Original Article>>

And from the “fer” link:

Capsules for Self-Healing Circuits

Technology Review, Sept. 11, 2009 Nanotube-filled capsules could restore conductivity to damaged electronics, University of Illinois at Urbana-Champaign researchers have found. Read Original Article>>

Testing graphene for potential applications

Graphene is proving to be one of the most, if not the most, exciting nanotech discovery of the last few years. The material has a lot of promise in terms of applications in medicine, electronics and who know what else.

Here’s some measurement and testing on putting the nanomaterial to actual use in the market.

The release:

Material world: graphene’s versatility promises new applications

July 09, 2009

Since its discovery just a few years ago, graphene has climbed to the top of the heap of new super-materials poised to transform the electronics and nanotechnology landscape. As N.J. Tao, a researcher at the Biodesign Institute of Arizona State University explains, this two-dimensional honeycomb structure of carbon atoms is exceptionally strong and versatile. Its unusual properties make it ideal for applications that are pushing the existing limits of microchips, chemical sensing instruments, biosensors, ultracapacitance devices, flexible displays and other innovations.

In the latest issue of Nature Nanotechnology Letters, Tao describes the first direct measurement of a fundamental property of graphene, known as quantum capacitance, using an electrochemical gate method. A better understanding of this crucial variable should prove invaluable to other investigators participating in what amounts to a gold rush of graphene research.

Although theoretical work on single atomic layer graphene-like structures has been going on for decades, the discovery of real graphene came as a shock.  “When they found it was a stable material at room temperature,” Tao says,  “everyone was surprised.” As it happens, minute traces of graphene are shed whenever a pencil line is drawn, though producing a 2-D sheet of the material has proven trickier.  Graphene is remarkable in terms of thinness and resiliency. A one-atom thick graphene sheet sufficient in size to cover a football field, would weigh less than a gram. It is also the strongest material in nature—roughly 200 times the strength of steel. Most of the excitement however, has to do with the unusual electronic properties of the material.

Graphene displays outstanding electron transport, permitting electricity to flow rapidly and more or less unimpeded through the material. In fact, electrons have been shown to behave as massless particles similar to photons, zipping across a graphene layer without scattering. This property is critical for many device applications and has prompted speculation that graphene could eventually supplant silicon as the substance of choice for computer chips, offering the prospect of ultrafast computers operating at terahertz speeds, rocketing past current gigahertz chip technology. Yet, despite encouraging progress, a thorough understanding of graphene’s electronic properties has remained elusive. Tao stresses that quantum capacitance measurements are an essential part of this understanding.

Capacitance is a material’s ability to store energy. In classical physics, capacitance is limited by the repulsion of like electrical charges, for example, electrons. The more charge you put into a device, the more energy you have to expend to contain it, in order to overcome charge repulsion. However, another kind of capacitance exists, and dominates overall capacitance in a two-dimensional material like graphene. This quantum capacitance is the result of the Pauli exclusion principle, which states that two fermions—a class of common particles including protons, neutrons and electrons—cannot occupy the same location at the same time. Once a quantum state is filled, subsequent fermions are forced to occupy successively higher energy states. As Tao explains, “it’s just like in a building, where people are forced to go to the second floor once the first level is occupied.”

In the current study, two electrodes were attached to graphene, and a voltage applied across the material’s two-dimensional surface by means of a third, gate electrode. Plots of voltage vs. capacitance can be seen in fig1. In Tao’s experiments, graphene’s ability to store charge according to the laws of quantum capacitance, were subjected to detailed measurement. The results show that graphene’s capacitance is very small. Further, the quantum capacitance of graphene did not precisely duplicate theoretical predictions for the behavior of ideal graphene. This is due to the fact that charged impurities occur in experimental samples of graphene, which alter the behavior relative to what is expected according to theory.

Tao stresses the importance of these charged impurities and what they may mean for the development of graphene devices. Such impurities were already known to affect electron mobility in graphene, though their effect on quantum capacitance has only now been revealed. Low capacitance is particularly desirable for chemical sensing devices and biosensors as it produces a lower signal-to-noise ratio, providing for extremely fine-tuned resolution of chemical or biological agents. Improvements to graphene will allow its electrical behavior to more closely approximate theory. This can be accomplished by adding counter ions to balance the charges resulting from impurities, thereby further lowering capacitance.  

The sensitivity of graphene’s single atomic layer geometry and low capacitance promise a significant boost for biosensor applications. Such applications are a central topic of interest for Tao, who directs the Biodesign Institute’s Center for Bioelectronics and Biosensors. As Tao explains, any biological substance that interacts with graphene’s single atom surface layer can be detected, causing a huge change in the properties of the electrons.

One possible biosensor application under consideration would involve functionalizing graphene’s surface with antibodies, in order to precisely study their interaction with specific antigens. Such graphene-based biosensors could detect individual binding events, given a suitable sample.  For other applications, adding impurities to graphene could raise overall interfacial capacitance. Ultracapacitors made of graphene composites would be capable of storing much larger amounts of renewable energy from solar, wind or wave energy than current technologies permit.

Because of graphene’s planar geometry, it may be more compatible with conventional electronic devices than other materials, including the much-vaunted carbon nanotubes. “You can imagine an atomic sheet, cut into different shapes to create different device properties,” Tao says.

Since the discovery of graphene, the hunt has been on for similar two-dimensional crystal lattices, though so far, graphene remains a precious oddity.

 Advanced Online Publication: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2009.177.html

 -Written by Richard Harth
Science Writer
Biodesign Institute

Nanotube devices closer to market

I can blog all day about nanotechnology breakthroughs and we can get excited about the theoretical improvements nanotech promises, but the proof in the pudding is getting nanotech to the market. Particularly some of the more dramatic applications. Improving existing items through nanotech is great, but I want the game-changers to get out there in the real world.

It look like electronic application for nanotube devices are getting close to that point. Couldn’t happen too fast for me.

From the link:

Circuits made from carbon nanotubes are intrinsically faster than those made from silicon. But while products from tennis rackets to bike frames take advantage of nanotubes’ light weight and strength, no commercial devices have yet exploited their remarkable electrical properties.

That’s partly because researchers have had difficulty creating films or other assemblies of nanotubes that preserve those properties: nanotube arrays, for example, proved nowhere near as electrically conductive as tubes taken singly. But a number of groups have found ways around that ­obstacle, and the result has been a flurry of prototype electronic devices that use nanotubes. Here is a sampling.

Stretchy speakers: A transparent, stretchable film of carbon nanotubes made by Shoushan Fan at Tsinghua University in China can act as a loudspeaker even when mounted on a waving flag. Credit: American Chemical Society

Twisting electronics

One step closer to wearables.

The release:

Researchers make new electronics — with a twist

They’ve made electronics that can bend. They’ve made electronics that can stretch.

And now, they’ve reached the ultimate goal — electronics that can be subjected to any complex deformation, including twisting.

Yonggang Huang, Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern University’s McCormick School of Engineering and Applied Science, and John Rogers, the Flory-Founder Chair Professor of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, have improved their so-called “pop-up” technology to create circuits that can be twisted. Such electronics could be used in places where flat, unbending electronics would fail, like on the human body.

Their research is published online by the Proceedings of the National Academy of Sciences (PNAS).

Electronic components historically have been flat and unbendable because silicon, the principal component of all electronics, is brittle and inflexible. Any significant bending or stretching renders an electronic device useless.

Huang and Rogers developed a method to fabricate stretchable electronics that increases the stretching range (as much as 140 percent) and allows the user to subject circuits to extreme twisting. This emerging technology promises new flexible sensors, transmitters, new photovoltaic and microfluidic devices, and other applications for medical and athletic use.

The partnership — where Huang focuses on theory, and Rogers focuses on experiments — has been fruitful for the past several years. Back in 2005, the pair developed a one-dimensional, stretchable form of single-crystal silicon that could be stretched in one direction without altering its electrical properties; the results were published by the journal Science in 2006. Earlier this year they made stretchable integrated circuits, work also published in Science.

Next, the researchers developed a new kind of technology that allowed circuits to be placed on a curved surface. That technology used an array of circuit elements approximately 100 micrometers square that were connected by metal “pop-up bridges.”

The circuit elements were so small that when placed on a curved surface, they didn’t bend — similar to how buildings don’t bend on the curved Earth. The system worked because these elements were connected by metal wires that popped up when bent or stretched. The research was the cover article in Nature in early August.

In the research reported in PNAS, Huang and Rogers took their pop-up bridges and made them into an “S” shape, which, in addition to bending and stretching, have enough give that they can be twisted as well.

“For a lot of applications related to the human body — like placing a sensor on the body — an electronic device needs not only to bend and stretch but also to twist,” said Huang. “So we improved our pop-up technology to accommodate this. Now it can accommodate any deformation.”

Huang and Rogers now are focusing their research on another important application of this technology: solar panels. The pair published a cover article in Nature Materials this month describing a new process of creating very thin silicon solar cells that can be combined in flexible and transparent arrays.

 

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