February AMP_Digital

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 | F E B R U A R Y / M A R C H 2 0 1 9 1 5 BUILDING BETTER GRAPHENE A research team from RMIT Univer- sity, Australia, discovered how to pro- duce higher performing pure graphene than varieties currently available. Af- ter the initial graphene research won the Nobel Prize for Physics in 2010, it was hailed as a transformative material for flexible electronics, more powerful computer chips, as well as solar panels, water filters, and biosensors. But per- formance has been mixed so far. Now, the RMIT team has identi- fied silicon contamination as the root cause of disappointing results and de- tailed how to produce more efficient graphene, launching it into the cat- egory of being a supermaterial. The team inspected commercially available graphene samples—atom by atom— with a state-of-the-art scanning trans- mission electron microscope. The lev- els of silicon contamination discov- ered proved to have massive impacts on the material’s performance, say re- searchers. The 2D property of graphene sheeting, which is only one atom thick, makes it ideal for electricity storage and new sensor technologies that rely on high surface area. The researchers revealed how that 2D property is also graphene’s downfall by making it so vulnerable to surface contamination. Using pure graphene, researchers demonstrated how the material per- formed extraordinarily well when build- ing a supercapacitator. When tested, the device’s capacity to hold electrical charge was massive. In fact, it was the biggest ever recorded for graphene and within sight of the material’s predict- ed theoretical capacity. The team then used pure graphene to build a versatile humidity sensor with the highest sensi- tivity and the lowest limit of detection ever reported. These findings represent a milestone in understanding atomical- ly thin 2D materials and their success- ful integration within high-performance commercial devices. www.rmit.edu.au . RESEARCHERS ANALYZE NANOCRYSTAL LAYOUT Scientists at Lawrence Livermore National Laboratory, Calif., are re- searching the arrangement of nano- crystals in order to make better elec- tronic devices. Nanocrystals are prom- ising building blocks for new and improved devices due to their size-tun- able properties and ability to integrate at low cost. Much of the previous research used solution evaporation methods to generate nanocrystal superlattices and probe the assembly process as the sol- vent is being gradually removed. It is difficult to obtain quantitative infor- mation on the assembly process, how- ever, because the volume and shape of the nanocrystal solution is continually changing in an uncontrollable manner and the capillary forces can drive nano- crystal motion during drying. Electric field-driven growth of- fers a solution to this problem. As an- ticipated, the team found that the elec- tric field drives nanocrystals toward the surface, creating a concentration gradient that leads to nucleation and growth of superlattices. Surprisingly, the field also sorts the particles ac- cording to size. In essence, the electric field both concentrates and purifies the nanocrystal solution during growth. Due to the size-sorting effect, the su- perlattice crystals are better ordered and the size of the nanocrystals in the lattice can be tuned during growth. This discovery may be a useful tool for developing optoelectronic devices, like infrared detectors and color im- provement in monitors, according to researchers. llnl.gov. NANOTECHNOLOGY BRIEF In a new venture between Northwestern University, Evanston, Ill., and Tel Aviv University, Israel, two researchers from each school will receive post-doctoral fellowships supporting two years of work at the partner institution. The fellowships, which cover approximately 75% of the total cost of the research, are funded by philanthropist Roman Abramovich. Both laboratories will pay the remaining expenses. northwestern.edu , aftau.org . Electric fields assemble silver nanocrys- tals into a superlattice. Courtesy of Jacob Long/LLNL. Drs. Esrafilzadeh and Jalili of RMIT work on 3D-printed graphene mesh in the lab.