Resolving topography of an electron beam-sensitive oxalate-phosphate-amine metal–organic framework (OPA-MOF)

Scanning electron microscopy (SEM) has, for many years, been the favoured method to gain insights into morphology, micro- and surface structure of new materials, thus development of SEM instruments and modes of use has been rapid. Yet, high-quality, charge artefact-free SEM-representation of highly beam-sensitive non-conductive hybrid metal–organic frameworks (MOF) remains challenging, particularly if access to highly specialised instrumentation is limited—a situation many researchers face. This study details a systematic approach taken to determine the appropriate instrument operating conditions and sample preparation methods for characterisation of a oxalate-phosphate-amine MOF (OPA-MOF) under conventional high-vacuum SEM conditions. We show that a double-coating method adapted from biological sciences, where a carbon coating (≤15 nm) is followed by a thin gold coating (~3–5 nm), enables charge- and damage-free imaging of the electron beam-sensitive OPA-MOF. Details of micro-topography are sufficiently resolved for intended purposes (~100 nm) and are not unduly masked by the coating.