Ionic liquid-based observation technique for nonconductive materials in the scanning electron microscope: Application to the characterization of a rare earth ore

Abstract

A new approach for preparing geological materials is proposed to reduce charging during their characterization in a scanning electron microscope. This technique was applied to a sample of the Nechalacho rare earth deposit, which contains a significant amount of the minerals fergusonite and zircon. Instead of covering the specimen surface with a conductive coating, the sample was immersed in a dilute solution of ionic liquid and then air dried prior to SEM analysis. Imaging at a wide range of accelerating voltages was then possible without evidence of charging when using the in-chamber secondary and backscattered electrons detectors, even at 1 kV. High resolution x-ray and electron backscatter diffraction mapping were successfully obtained at 20 and 5 kV with negligible image drifting and permitted the characterization of the microstructure of the zircon/fergusonite-Y aggregates encased in the matrix minerals. Because of the absence of a conductive layer at the surface of the specimen, the Kikuchi band contrast was improved and the backscatter electron signal increased at both 5 and 20 kV as confirmed by Monte Carlo modeling. These major developments led to an improvement of the spatial resolution and efficiency of the above characterization techniques applied to the rare earth ore and it is expected that they can be applied to other types of ores and minerals.

Chromosome Interior Observation by Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) Using Ionic Liquid Technique

“…5d, 5d′). Brodusch et al (2014) presented ionic liquid treated ore and showed that good contrast was achievable both in SE and BSE modes at various accelerating voltages even at 1 kV. Accelerating voltages used for observation ranged from 1.5 to 5.0 kV.…”

“…Simultaneous detection of SE and BSE signals showed that there were no cavities inside PA chromosomes, as observed in images of both cross (Figs. Brodusch et al (2014) presented ionic liquid treated ore and showed that good contrast was achievable both in SE and BSE modes at various accelerating voltages even at 1 kV. 5d, 5d′).…”

Microscopy Methods for Biofilm Imaging: Focus on SEM and VP-SEM Pros and Cons

“…The sample acquires intrinsic conductive properties into the bulk, not only on the surface (as it happens with sputter coating), but enhanced image contrast without charging phenomena, and 3-D observation of sub-surface structures under higher voltages are allowed [95]. At room temperature, ionic liquids are molten salts, they have high electronic conductivity, and extremely low vapor pressure [96,97]. Recently, they have been used in SEM as a substitute for metal coating [98].…”

Characterization of Scardovia wiggsiae Biofilm by Original Scanning Electron Microscopy Protocol

“…Ionic liquids are, at room temperature, molten salts with high electronic conductivity and irrelevant vapor pressure [46,47]. These properties allow their use in SEM as a substitute for metal coating [48,49]. We covered biofilm samples with IL, to maintain them wet during the SEM investigation.…”