| RESEARCH HIGHLIGHTS |


circulating in their blood when discharged from hospital. Compared to those who had hastily rid their bodies of the virus, these children had lower cytokine levels and com- plained more of joint pain. The results further supported the conclusion that clinical severity is closely associated with immunological


response and virus elimination. “Children with early viral clearance have milder disease,” says Ng. But more concerning for Ng was the seemingly healthy, yet still infectious, group. “You think they are safe, but they are not.” Ng is keen to compare these results with other infected infant populations. “The virus


is here to stay, so the best thing we can do is to try to understand it.”


1. Simarmata, D., Ng, D. C. E., Kam, Y.-W., Lee, B., Sum, M. S. H. et al. Early clearance of Chikungunya virus in children is associated with a strong innate immune response. Scientific Reports 6, 26097 (2016).


Materials


CRACKING THE CODE FOR FISSURE CONTROL


SCIENTISTS FIND A WAY TO CONTROL THE WAY CRACKS FORM AND SPREAD TO MAKE A COATING FOR ELECTROCHROMIC MATERIALS


A micrograph showing the


highly ordered cracked surface of a metal oxide thin film.


Cracks in a material typically compromise its strength and integrity, so research focus has traditionally been on preventing their occurrence and spread. An A*STAR team has now taken a different approach, prompting and directing the propagation of cracks on thin films to make highly ordered patterned coatings for electrochromic materials1. The transmission of light by electrochromic


materials alters in response to brief bursts of electrical charge. They have optical uses ranging from the windows in Boeing 787-9 Dreamliners which change color at the touch of a button, to privacy glass around hotel bath- rooms which switch between clear and opaque, to auto-dimming rear view car mirrors. To feasibly expand the potential uses


for these materials, scientists must reduce the amount of electrical power needed to modulate their optical property changes, explains team leader Sing Yang Chiam from


www.astar-research.com


the A*STAR Institute of Materials Research and Engineering. To achieve this, “devices will require a greater surface area of contact for enhanced interaction”, he says. “If you use nanoparticles for a large surface area, scattering makes for poor optical properties. Using a film with controlled cracks allows us to increase the surface area for better electrical efficiency, without sacrifice of the optical properties.” Chiam’s team’s first step was to grow a thin film on top of a regular array of


NiO/Ni(OH)2


pillars fixed to a rigid substrate. Such a structure introduced strain at predetermined and regular points on the film. For example, spots with no support from any pillars were mechanically weak. The team found that briefly air-drying the newly formed films was sufficient to trigger the crack formation at these locations. Further dehydration in a furnace caused the material to shrink and cause significant crack propagation. Electron microscopy images showed that the


cracking pattern on the surface was so ordered that it looked “artificially squarish” (see image), Chiam says. An unprecedented level of fragmen- tation control at the submicron and nanometer scale had been achieved. Finally, the team checked the electrochromic


performance of the films using cyclic voltam- metry measurements to measure their switching and optical properties. “The resultant structures yielded excellent electrochromic performance with high-coloration efficiency and stable cycling stability,” Chaim confirms. “While the demonstrated enhancement is


in electrochromics, I think the significance of the work is in the discovery of a method to order and control fragmentation at such a scale,” he adds.


1. Guo, L., Ren, Y., Kong, L. Y., Chim, W. K. & Chiam, S. Y. Ordered fragmentation of oxide thin films at submicron scale. Nature Communications 7, 13148 (2016).


A*STAR RESEARCH 19


© 2017 A*STAR Institute of Materials Research and Engineering


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