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Graphene speaker

Graphene Enables Flat Speakers for Mobile Audio Systems

Nanomaterials have been responsible for all sorts of innovation of audio speaker designs. We’ve seen magnetic nanoparticles used to eliminate the need for a magnet in speakers.  Carbon nanotubes have also been demonstrated to produce sound with heat. While these designs have been innovative, they were developed to demonstrate the capabilities of nanomaterials rather than to produce a piece of audio equipment.

Now, researchers at Korea Advanced Institute of Science and Technology (KAIST) have developed a new speaker design specifically targeted for the mobile audio market that draws its capabilities from nanomaterials. The KAIST researchers have used graphene to produce a speaker that does not require an acoustic box to produce sound.

In research described in the journal ACS Applied Materials & Interfaces, the researchers used graphene in a relatively simple process that yielded the long-elusive thermoacoustic speaker. Thermoacoustics is based on the century-old idea that sound can be produced by the rapid heating and cooling of a material instead of through vibrations.

While graphene has previously been shown to enable thermoacoustics (and carbon nanotubes have even been used previously to create thermoacoustic speakers), what sets the KAIST researchers’ work apart is the ease with which the graphene-based speakers are fabricated. The simple, two-step process, they say, will make commercial applications more likely. 

They started by first freeze-drying a solution of graphene oxide flakes. They then reduced and doped the oxidized graphene to improve its electrical properties. (The process does not require any templates to complete the fabrication.) The end result: an N-doped, three-dimensional, reduced graphene oxide aerogel (N-rGOA) that is freestanding.

The final aerogel sound element has a porous macroscopic structure can be easily modulated. The speaker the KAIST researchers produced consists of an array of 16 of the aerogels; it operates on 40 watts of power and produce a sound quality comparable to that of other graphene-based sound systems.

The researchers believe that because of the simplicity of their fabrication method, speakers can be mass-produced for use in mobile devices and other applications. As you can see in the video below, the fact that speakers are flat and don’t vibrate means that can be placed against walls and even curved surfaces.

Transmission electron micrographs of brain thin sections, identifying two distinct types of magnetite nanoparticles within frontal brain cells

Nanoparticles Found in Brains Come From External Sources

An international team of researchers, led by Barbara Maher, a professor at Lancaster University, in England, has found evidence that suggests that the nanoparticles that were first detected in the human brain over 20 years ago may have an external rather an internal source.

In research described in the Proceedings of the National Academy of Sciences, the scientists leveraged electron microscopy and magnetic analyses to not only discover the abundant presence of magnetite nanoparticles in the brain, but also determine that these nanoparticles are consistent with high-temperature formation, which means that they were likely not produced inside the body but were manufactured outside of it.

These magnetite nanoparticles are an airborne particulate that are abundant in urban environments and formed by combustion or friction-derived heating. In other words, they have been part of the pollution in the air of our cities since the dawn of the Industrial Revolution.

However, according to Andrew Maynard, a professor at Arizona State University, and a noted expert on the risks associated with nanomaterials,  the research indicates that this finding extends beyond magnetite to any airborne nanoscale particles—including those deliberately manufactured .

“The findings further support the possibility of these particles entering the brain via the olfactory nerve if inhaled.  In this respect, they are certainly relevant to our understanding of the possible risks presented by engineered nanomaterials—especially those that are iron-based and have magnetic properties,” said Maynard in an e-mail interview with IEEE Spectrum. “However, ambient exposures to airborne nanoparticles will typically be much higher than those associated with engineered nanoparticles, simply because engineered nanoparticles will usually be manufactured and handled under conditions designed to avoid release and exposure.”

While the results do seem to confirm previous research that indicates that airborne nanoparticles can reach our brains if inhaled, Maynard cautions that we should be careful not to extrapolate the data too far. He says that the paper had insufficient evidence to establish a causal link between the nanoparticles and neurodegenerative disease.

“What is lacking is any indication of how much exposure is needed to lead to harmful effects, and how the severity and probability of possible effects increases with increased exposure,” explains Maynard.

The formula for determining the risk of any substance is Hazard x Exposure = Risk. In this formula you can see that a highly hazardous substance like an acid may have restricted access, limiting its exposure and in so doing reducing its risk. When this formula is applied to the difference between engineered nanoparticles and those found in the air because of air pollution, we can begin to put the risks into perspective.

“In most workplaces, exposure to intentionally made nanoparticles is likely be small compared to ambient nanoparticles, and so it’s reasonable to assume—at least without further data—that this isn’t a priority concern for engineered nanomaterial production,” said Maynard. 

While deliberate nanoscale manufacturing may not carry much risk, Maynard does believe that the research raises serious questions about other manufacturing processes where exposure to high concentrations of airborne nanoscale iron particles is common—such as welding, gouging, or working with molten ore and steel.

UW–Madison engineers coated the entire surface of this substrate with aligned carbon nanotubes in less than 5 minutes. The breakthrough could pave the way for carbon nanotube transistors to replace silicon transistors,

Carbon Nanotube Transistors Finally Outperform Silicon

Back in the 1990s, observers predicted that the single-walled carbon nanotube (SWCNT) would be the nanomaterial that pushed silicon aside and created a post-CMOS world where Moore’s Law could continue its march towards ever=smaller chip dimensions. All of that hope was swallowed up by inconsistencies between semiconducting and metallic SWCNTs and the vexing issue of trying to get them all to align on a wafer.

The introduction of graphene seemed to take the final bit of luster off of carbon nanotubes’ shine, but the material, which researchers have been using to make transistors for over 20 years, has experienced a renaissance of late.

Now, researchers at the University of Wisconsin-Madison (UW-Madison) have given SWCNTs a new boost in their resurgence by using them to make a transistor that outperforms state-of-the-art silicon transistors.

“This achievement has been a dream of nanotechnology for the last 20 years,” said Michael Arnold, a professor at UW-Madison, in a press release. “Making carbon nanotube transistors that are better than silicon transistors is a big milestone,” Arnold added.  “[It’s] a critical advance toward exploiting carbon nanotubes in logic, high-speed communications, and other semiconductor electronics technologies.”

In research described in the journal Science Advances, the UW-Madison researchers were able to achieve a current that is 1.9 times as fast as that seen in silicon transistors. The measure of how rapidly the current that can travel through the channel between a transistor’s source and drain determines how fast the circuit is. The more current there is, the more quickly the gate of the next device in the circuit can be charged .

The key to getting the nanotubes to create such a fast transistor was a new process that employs polymers to sort between the metallic and semiconducting SWCNTs to create an ultra-high purity of solution.

“We’ve identified specific conditions in which you can get rid of nearly all metallic nanotubes, [leaving] less than 0.01 percent metallic nanotubes [in a sample],” said Arnold.

The researchers had already tackled the problem of aligning and placing the nanotubes on a wafer two years ago when they developed a process they dubbed “floating evaporative self-assembly.” That technique uses a hydrophobic substrate and partially submerges it in water. Then the SWCNTs are deposited on its surface and the substrate removed vertically from the water.

“In our research, we’ve shown that we can simultaneously overcome all of these challenges of working with nanotubes, and that has allowed us to create these groundbreaking carbon nanotube transistors that surpass silicon and gallium arsenide transistors,” said Arnold.

In the video below, Arnold provides a little primer on SWCNTs and what his group’s research with them could mean to the future of electronics. 

In continuing research, the UW-Madison team will be aiming to replicate the manufacturability of silicon transistors. To date, they have managed to scale their alignment and deposition process to 1-inch-by-1-inch wafers; the longer-term goal is to bring this up to commercial scales.

Arnold added: “There has been a lot of hype about carbon nanotubes that hasn’t been realized, and that has kind of soured many people’s outlook. But we think the hype is deserved. It has just taken decades of work for the materials science to catch up and allow us to effectively harness these materials.”

Nanopores in a plastic membrane will make it the first material to block visible light and let our body heat pass through.

Nanomaterial Offers First Fabric That Can Keep Us Cool

The use of nanomaterials in textiles is one of the earliest commercial applications of nanotechnology. Nanomaterials have given us stain-resistant fabrics and enabled a range of wearable electronics. But they’ve yet to solve what has been the most vexing problem in clothing: keeping us cool in hot weather.

Now researchers at Stanford University have taken a nanomaterial called nanoporous polyethylene, or nanoPE (which has been mass produced for use in batteries), and tested it to see how it would tackle the challenge of creating a fabric that can keep us cool.  The results reveal that it may be far more effective at keeping us cool than any other synthetic or natural fabrics.

The reason that clothing has heretofore failed to offer any relief from the heat is because our bodies give off heat in the form of mid-infrared radiation (IR), and our garments block that wavelength from escaping. While this makes clothing a clear benefit when it’s cold, in warm weather it’s a distinct disadvantage.

In research described in the journal Science, the researchers found that the interconnected pores of the nanoPE material allowed 96 percent of the infrared heat to pass through it; cotton allowed only 1.6 percent of the IR to escape.

The Stanford researchers—led by Yi Cui, who has compiled an extensive body of work in getting nanomaterials to improve the performance of batteries—claim that this ability to let IR to pass through would make the person wearing the material feel four degrees Fahrenheit cooler than if they were wearing cotton.

The nanoPE material is able to achieve this release of the IR heat because of the size of the interconnected pores. The pores can range in size from 50 to 1000 nanometers. They’re therefore comparable in size to wavelengths of visible light, which allows the material to scatter that light. However, because the pores are much smaller than the wavelength of infrared light, the nanoPE is transparent to the IR.

It is this combination of blocking visible light and allowing IR to pass through that distinguishes the nanoPE material from regular polyethylene, which allows similar amounts of IR to pass through, but can only block 20 percent of the visible light compared to nanoPE’s 99 percent opacity.

The Stanford researchers were also able to improve on the water wicking capability of the nanoPE material by using a microneedle punching technique and coating the material with a water-repelling agent. The result is that perspiration can evaporate through the material unlike with regular polyethylene.

In the video below, you can see an illustration of how the nanoPE allows both moisture and IR heat to escape through the material.

This material would seem to be a boon for us as global temperatures continue to rise. But it may also help prevent those temperatures from continuing to rise because it will make it possible to work in office buildings without as much energy being used for air conditioning.

“If you can cool the person rather than the building where they work or live, that will save energy,” said Cui in a press release.

Though the nanoPE would—by offering at least an indirect way for securing big energy savings—be one of the biggest advances in clothing since we first started wrapping ourselves in animal hides and furs, it might be good to see if anyone would want to wear the material.

The experiments with the material were conducted on a device that mimics the heat output of human skin, which sounds conspicuously non-human. Anyone that has examined the use of nanomaterials in the textile industry will tell you that the issue raised by textile manufacturers about any new material is the “hand of a fabric”—in other words, how does it feel to our touch.

In continuing research, the Stanford team will be giving the material improved textures and cloth-like characteristics. If they can overcome that hurdle, the next will be producing the material cheaply in mass production.

Nanostructures on a crystal after ion bombardment: Trenches with nanohillocks on either side are created.

Meteorites Offer Insight Into Ion Bombardment on Nanoscale

It turns out if you want to know what happens to semiconductors under ion bombardment, you might do well to look at the effects of meteorites when they impact Earth. At least that’s what a team of researchers at Technische Universität Wien (Technical University of Vienna, TU Wien) discovered when they peered into the crystal surface of a semiconductor with an atomic force microscope (AFM).

In experiments described in the Journal of Physics: Condensed Matter, the researchers bombarded the surface of calcium fluoride with both xenon and lead ions. The AFM revealed the tracks left behind by ions hitting the calcium fluoride surface. Each ion strike creates an initial impact site and a trench several hundred nanometers long that is bordered by a series of nanohillocks on both sides. At the end of trench is a large single hillock created as the ion penetrates into deeper layers of the crystal.

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Surface plasmons allow superfast optical on-chip communications

Nanoscale Wireless Communication Operates at Visible Wavelengths for the First Time

Currently, wireless optical communication on computer chips occurs at near-infrared wavelengths. But if visible light could be used in these on-chip optical communications, the chips could be miniaturized significantly because the wavelengths in that portion of the spectrum are much smaller.

Now researchers at Boston College have developed a nanoscale wireless communication system that does just that. The key to the technology, as described in the journal Nature Scientific Reports, are antennas that can collect photons and reversibly convert them into surface plasmons with a high degree of control.

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Carbon nanotubes wrapped in a polymer offer a powerful sensing platform for many chemicals.

Carbon Nanotube-Based Sensor Detects Toxins With a Mobile Phone

A little over four years ago, researchers at the University of California, Riverside, developed a sensor made from carbon nantoubes for detecting toxic chemicals. So enthusiastic were the researchers with the prospects of their technology that they launched a company, Nano Engineered Applications, that intends to add this sensor to people’s mobile phones.

While the commercial prospects of a smartphone toxin detector are still uncertain, another team of researchers has recently demonstrated a sensing device that also relies on carbon nanotubes (CNTs) to detect different chemicals. Researchers from Japan’s International Center for Materials Nanoarchitectonics and the National Institute for Materials Science, working with collaborators from MIT, combined CNTs with a polymer and discovered that this resulting material offers a powerful sensing platform for toxic chemicals. Their results look to be the first viable demonstration of the power of sensors known as chemresistors.

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Florian Libisch, explaining the structure of graphene

Graphene Doubles Up on Quantum Dots' Promise in Quantum Computing

Quantum dots made from semiconductor materials, like silicon, are beginning to transform the display market. While it is their optoelectronic properties that are being leveraged in displays, the peculiar property of quantum dots that allows their electrons to be forced into discrete quantum states has long held out the promise of enabling quantum computing.

As it turns out, if you really want to exploit quantum dots for quantum computing, you’d have better luck setting aside the semiconductor variety and turning to a pure conductor, like graphene, to do the trick.

Researchers at Technische Universität Wien (TU Wein, or the Vienna University of Technology), along with colleagues from the University of Manchester in the United Kingdom and Rheinisch-Westfälische Technische Hochschule Aachen (RWTH Aachen University), in Germany, have managed to produce quantum dots out of graphene. And according to the multinational team, these dots offer a bold new promise for quantum computing.

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Optical image of the electrodes fabricated by nano-imprint lithography. Nanoscale electrodes (50nm width with separation of 50nm) fan out to microscale patterns and eventually to the contact pads.

Genetically Modified Bacteria Conduct Electricity, Ushering in New Era of Green Electronics

Researchers at the University of Massachusetts at Amherst have genetically modified common soil bacteria to produce nanowires capable of conducting electricity at a level that surprised even the scientists themselves. After years of skepticism that this was even theoretically possible, the practical demonstration could lead to a new generation of “green” electronics in which nanowires could be produced in plant waste, without the need for toxic chemicals.

The research, which was supported by the Office of Naval Research (ONR), goes back to a series of papers that Derek Lovley, a professor at UM Amherst, published back in 2011. Lovely overcame skeptics who claimed it was impossible for soil bacteria to conduct electricity. Brushing aside computer models indicating that it was impossible to make the bacteria into electrically conductive nanowires, Lovley demonstrated through experiments that it was indeed possible.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

Dexter Johnson
Madrid, Spain
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