Cryo‐SEM specimen preparation under controlled temperature and concentration conditions

Abstract

SummaryCryogenic temperature scanning electron microscopy (cryo-SEM) is an excellent technique for imaging liquid and semi-liquid materials of high vapour pressure, which are highly viscous or contain large (>0.5 μm) aggregates, in which nanometric details are to be studied. However, so far there have been no adequate tools for controlled cryospecimen preparation. The specimen preparation stage is critical, because most of those samples are very sensitive to concentration and temperature changes, leading to nanostructural artefacts in the specimens. We designed and built a system for easy and reliable cryo-SEM specimen preparation under controlled conditions of fixed temperature and humidity. We describe this new methodology, and demonstrate its applicability, by showing imaging data of three liquid material systems. We have studied carbon nanotubes (CNTs) dispersions in superacid. We also characterized a number of systems made of water/isooctane/nonionic and cationic surfactant that showed different microemulsion phases as function of the system composition and temperature. In all of the examples given, we demonstrate artefact-and contamination-free specimens, which have preserved their native nanostructure. Our new system paves the way for a new methodology for the newly emerging field of cryo-SEM.

Direct-Imaging Cryo-SEM of Nanostructure Evolution in Didodecyldimethylammonium Bromide-Based Microemulsions

“…Preparation was carried out in a Controlled Environment Vitrification System (CEVS) in a fully controlled saturation and temperature environment. Details of this modified CEVS and the methodology of specimen preparation are given elsewhere [34]. The CEVS chamber was saturated with water and isooctane in equal amounts.…”

“…Cryo-SEM allows us to image nanometric features in relatively large (micrometer and larger) objects, and image concentrated or highly viscous liquids for which cryo-TEM is not practicable. Recently we described a novel cryo-SEM methodology [34] that allows us prepare specimens under conditions of controlled temperature and concentration, rather similarly to what we have practiced in cryo-TEM for a long time [16]. This methodology allows us image, among others, microemulsion systems.…”

Cryogenic‐temperature electron microscopy direct imaging of carbon nanotubes and graphene solutions in superacids

“…Liquid nanostructured systems can now be studied by cryo‐SEM using much‐improved cryogenic specimen holders and transfer systems (Wepf et al ., ). In recent years, we have developed a novel specimen preparation methodology for cryo‐SEM specimens that preserves the original nanostructure of labile complex liquids at specified composition and temperature, quite similarly to what had been done in cryo‐TEM (Issman & Talmon, ).…”

Cryogenic Transmission Electron Microscopy Nanostructural Study of Shed Microparticles

“…While cryo-TEM has become an important direct-imaging method, one must take into account that it cannot be used for highly viscous samples, or those containing large objects, because the specimens must be very thin (100–300 nm thick), and larger objects are excluded from the specimen during preparation [29]. Thicker specimens or those containing large object can be imaged by cryo-electron tomography [39], or by cryo-SEM [40].…”