Graphene encapsulation enables vitreous ice sample for APT and near-atomic reconstruction of nanoparticle-liquid interface

Abstract

We report an approach based on graphene encapsulation to investigate the structure and chemical composition of liquid samples with APT. The specimens for probing are prepared by encapsulating the solution with a single graphene membrane on top of a W or Si specimen needle tips, with the final diameter maintained at less than 100 nm. The liquid specimens are then transferred to a laser-pulsed atom probe instrument, and frozen by direct loading and contact onto the cryogenically cooled stage. Field evaporation has been proven to be feasible, and the mass-to-charge-state ratio spectrum acquired from APT determines the ion species. The reconstructed 3D chemical maps further reveal the original position of ions within the frozen hydrated sample [1]. This approach allows exploring domains previously unreachable, such as a single protein in solution [2].