Bio Focus: Ionic liquid gels enable wearable bioelectronics sensors
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Hexagonal BN converted directly to cubic BN through a new phase
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ften outshined by diamond, cubic boron nitride (c-BN) is nevertheless an impressive material. In a handful of important ways, c-BN even has an edge: a wider bandgap, more resistance to oxidation due to a passivating layer of durable boron oxide, and acceptance of both p- and n-type dopants, compared with diamond’s acceptance of only p-type. The promise of exploiting these properties in future electronics makes clear the need for robust processing of BN. Researchers at North Carolina State University have developed a method of fabricating phase-pure c-BN at ambient temperature and pressure in air—via a new phase of BN (named Q-BN) with its own exciting properties. Jagdish (Jay) Narayan led a team that extended previous, similar work on carbon into the BN material system. Narayan had a hypothesis that he could tweak the phase-changing behavior of carbon to directly convert graphite to diamond, bypassing the thermodynamic barrier by taking a “scenic route” through kinetics. Then, because carbon and BN are material cousins, he thought he could do the same for converting hexagonal BN (h-BN) to c-BN. This work is published in a recent issue
Bio Focus Ionic liquid gels enable wearable bioelectronics sensors
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he age of wearable electronics is here. With devices that can count our steps and track our heartbeat, scientists and engineers have devised increasingly creative, convenient, and even fashionable ways to monitor human health in real time. Despite their convenience, many of these devices may never be as accurate as the bulky transdermal electrodes and instruments used in medical practice—at least not in their current form. A team of researchers in France have developed a way to fabricate small bioelectronic sensors that are both highly sensitive and comfortable to wear
of the Journal of Applied Physics Diamond/c-BN/c-sapphire (doi:10.1063/1.4948688). 1336 cm–1 –1 With a 20-ns pulsed laser, liq1076 cm uid BN was undercooled by more than 700 K. Upon quenching, Narayan and his team observed 200 nm a new phase, which they named, appropriately, Q-BN. The critical parameter in this process, in order to kinetically drive the transformation, is time: “We do it so 500 1000 1500 2000 2500 3000 3500 rapidly the system is not able to Raman Shift (cm–1) equilibrate,” says Narayan. The team found that an interRaman spectra from diamond/c-BN single-crystal films. mediate undercooling of liquid h-BN resulted in c-BN directly, while a deeper undercooling resulted in the new Q-BN phase. By varying determined that Q-BN’s atomic density process parameters, the team was also able is higher than that of c-BN, which sugto nucleate and grow c-BN nanocrystalgests increased hardness. Because Q-BN lites in Q-BN. Upon further exploration, is isostructural to Q-carbon, Narayan the team found they could grow c-BN thin expects a hardness greater than that of films and nanoscale dots and needles, condiamond—comparable to the 17% greater trol twinning defects in c-BN, grow epiha
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