Any of us who have done some do-it-yourself home improvements know that there’s a big difference between measuring “by eye” versus taking out a tape measure to get an exact measurement.
This difference in measurement approaches more or less represents what an international team of researchers from China and the United States have done in measuring the different band gaps that can be created when black phosphorous, also known as phosphorene, is layered.
Previous measurements of the band gaps in layered phosphorene employed fluorescence spectroscopy, which involves using a beam of light to excite electrons in molecules in the test sample, causing them to emit a measurable light. The new, more precise method leveraged in this latest research was optical absorption spectroscopy, in which the absorption of radiation is measured due to its interaction with a sample.
“This is the first measurement based on optical absorption of encapsulated phosphorene,” explained Steven G. Louie, professor of at the University of California Berkeley, in an e-mail interview with IEEE Spectrum. “The optical absorption data are not susceptible to defects and impurities, [unlike] the fluorescence spectroscopy used previously. The encapsulation helps to keep phosphorene from degradation.”
The optical, electrical, and magnetic properties of one-dimensional nanomaterials such as nanorods,nanocrystals, and nanotubesdepend on their size and shape. A number of manufacturing techniques like chemical vapor deposition have been used to try and control these dimensions. However, these manufacturing techniques require tailor-made, multi-step reactions and purification procedures that are difficult to generalize.
Now, researchers at the Georgia Institute of Technology have developed a far more generalized approach that allows the production of many different kinds of one-dimensional nanorods from a wide range of precursor materials. The key to the technique is the use of block copolymer “arms” to create nanometer-scale compartments that serve as chemical reactors. The outer blocks of the arms prevent the aggregation of the nanorods.
The use of DNA in nanodevices has in large part been aimed at manipulating DNA to act like a semiconductor. But what if we could create an inorganic semiconductor that had some of the properties, including flexibility, of DNA?
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.
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.
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.
“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.
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.
“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.”
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.
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: CondensedMatter, 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.