Atom probe tomography (APT) is a characterisation technique that can provide structural and compositional information at the atomic scale. As a voltage-pulsed technique it was initially only amenable to electrically conductive materials but the more recent advent of laser-assisted APT enabled analysis of non-conductive materials alike, including also near-atomic 3D chemical mapping of soft/non-crystalline biological samples. Whilst a lot of effort is being put into cryogenic specimen preparation protocols, recent attempts of APT analysis of biological material have relied on novel sample preparation techniques, for example the use of conductive coatings [1,2].
The most promising material used for coating of biological samples that has been proven successful is graphene [3]. This study aims to understand the effects of graphene coating on APT data quality metrics such as evaporation field, signal-to-noise ratio, mass-resolution and hit multiplicity, using the well-known standard material, tungsten. Tungsten needles were sharpened into APT specimens via electropolishing, coated with graphene, and then run in voltage-pulsed atom probe mode.
The APT results show that graphene can be identified in the form of distinct carbon peaks in the mass spectrum. Interpretation of the evaporation data reveals a lower electrostatic field on the specimen tip than would be expected for pure tungsten. The field then increases as the graphene and the encapsulated solution (from the coating process) are evaporated through to the tungsten substrate. Although resolving the atomic layer of graphene in the three-dimensional reconstruction remains challenging, the evaporation data helps to better understand the influence of this coating towards application for APT analysis of biological samples.