1 0 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 fibers is key to enabling progress in numerous photonic applications. Most notably, these would improve Internet performance, which heavily relies on optical fibers for data transmission and where current technology is starting to reach its limits. Backscattering in optical fibers is often highly undesirable as it causes attenuation of signals propagating down the optical fiber and limits the performance of many fiber-based devices, such as fiber optic gyroscopes that navigate airliners, submarines, and spacecrafts. However, the ability to measure backscattering reliably and accurately can be beneficial in other instances, such as the characterization of installed fiber cables where the backscatter is used tomonitor the condition of a cable and identify the location of any breaks along its length. The latest generation of hollow-core nested antiresonant nodeless fibers (NANFs) exhibit backscattering that is so low that up until this point it remained unmeasurable. The researchers developed an instrument that enables them to reliably measure the extremely weak signals back-scattered in their latest hollow-core fibers—confirming that scattering is over four orders of magnitude lower than in standard fibers, in line with theoretical expectations. www.southampton.ac.uk, www.ulaval.ca/en. TESTING | CHARACTERIZATION NANOMAPPING WITH ULTRASOUND Researchers at Delft University of Technology and ASML, both in the Netherlands, recently developed a new imaging technique based on ultrasound that can explore materials at the nanoscale. “Existing nondestructive imaging techniques for nanoelectronics, such as optical and electron microscopy, are not accurate enough or applicable to deeper structures,” explains Delft researcher Gerard Verbiest. “A well-known 3D technique on a macroscale is ultrasound. But resolution is typically determined by the wavelength of the sound used. “To improve this, ultrasound has already been integrated into an atomic force microscope (AFM),” Verbiest continues. “The advantage here is that it isn’t the wavelength, but the size of the tip of the AFM, that determines the resolution. But at the initial frequencies, the AFM response was unclear. So the team increased the frequency of the sound used even further. Increasing the frequency is something that has only become possible recently, Verbiest explains. They achieved this through photoacoustics and integrated the technique into an AFM. The new method is particularly interesting for nanoelectronics, but the researchers say there are potential applications outside of electronics as well. It could be used to make detailed images of single living cells and also aid heat transport research in materials science. www.tudelft.nl/en, www.asml. com/en. IMPROVING OPTICAL FIBERS For the first time, researchers from the University of Southampton, U.K., and Université Laval, Canada, successfully measured back reflection in cutting-edge hollow-core fibers that is around 10,000 times lower than conventional optical fibers. This discovery highlights yet another optical property in which hollow-core fibers are capable of outperforming standard optical fibers. Improving optical Triangular holes make this material more likely to crack from left to right. Courtesy of N.R. Brodnik et al./Phys. Rev. Lett. Engineers at Iowa State University, Ames, developed technology capable of recovering precious metals from electronic waste. Using controlled applications of oxygen and relatively low temperatures, the team says they can dealloy a metal by slowly moving the most reactive components to the surface where they form spikes of metal oxides. iastate.edu. BRIEF Researchers Gerard Verbiest, Ruben Guis, and Martin Robin. Courtesy of Delft University of Technology. A new dealloying method brings the most reactive components to the surface, forming stalagmite-like spikes (left), while leaving the least reactive components in the core surrounded by metal-oxide spikes (right).
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