A flaky solution for improving coverage of 2-D materials

There’s a new solution afloat for coating large swaths of substrates with two-dimensional materials—and that solution is ionic. Chemists have previously investigated ways to dissolve 3-D crystals that exist naturally as stacks of atomically thin 2-D sheets. A famous example is 3-D graphite with its 2-D graphene layers. Liquids filled with 2-D flakes could help scientists cover macroscopic areas with these materials, which have attractive optical, electronic, or mechanical properties. But researchers have struggled with using existing solutions to liberate uniform, single sheets from their parent crystals. A team led by Christopher A. Howard of University College London has overcome this problem with help from alkali metals and organic solvents. The researchers soaked 10 different layered materials, including graphite and molybdenum disulfide, in liquid ammonia sprinkled with lithium or potassium. The baths enable metal atoms to work themselves between the sheets of a layered material. Once removed from the ammonia, a metal-loaded material is given a dip in aprotic organic solvents. Here, negatively charged single layers of the stacked material, such as molybdenum disulfide, flake off, leaving alkali-metal cations (Nat. Chem. 2016, DOI: 10.1038/nchem.2650). The 2-D flakes can then be transferred to a substrate by simply letting the liquid dry or by electroplating.