Advanced Microscopy for Aqueous and Insulating Materials

Although techniques are available for characterizing morphology and composition of vacuum-compatible materials at high spatial resolution, i.e. Helium Ion Microscopy (HiM) and FESEM/EDX/EBSD, the challenges for imaging/characterizing aqueous and insulating materials are: (1) proper sample preparation without changing their morphology and (2) chemical/composition analysis without coating anti-charging film. The nanoFAB has successfully developed freeze drying process and commissioned variable-pressure (VP) operation mode on SEMs to resolve the above difficulties.

1) Freeze drying of aqueous samples for high resolution imaging.

Without a dedicated cryo-microscopy solution, aqueous/hydrated samples must be dried before being imaged in SEM/HiM. Air drying normally results in fine structure collapsing. Freeze drying process dries samples while they are frozen, and maintains the original morphology of the samples (i.e. without losing its fine structures). Below are HiM images of a zebrafish freeze-dried on the Savant SuperModulyo Freeze Dryer. (Sample courtesy: Prof. Declan W. Ali and MD Ruhul Amin, Department of Biological Sciences, University of Alberta). Fine structures of the fish skins are well preserved.

HiM images of a Zebrafish prepared by freeze drying.

2) VP-SEM/EDX for compositional analysis of insulating materials. 

Although HiM provides the best resolution of direct imaging insulating samples, it is incapable of composition analysis. VP-SEM/EDX offers a solution of characterizing composition of insulating materials when anti-charging film coating is undesirable. VP operation mode is commissioned and available on both Tescan Vega-3 SEM and Zeiss EVO SEM. Below are images and EDX maps of a ceramic sample obtained on the Zeiss EVO SEM at Variable Pressure Mode (Images obtained at the normal High Vacuum mode are included for comparison).

Backscattered (BSD) and Secondary Electron (SE) images of an insulating Ceramic sample without any anti-charging film coating obtained on Zeiss EVO SEM at (A) normal High Vacuum mode, showing serious charging issues and (B) (C) VP mode.


BSD image and EDX map of the Ceramic sample obtained at VP mode showing distribution of different elements.

Please contact Peng Li ( – the Characterization Group Manager, if you have any questions regarding the above techniques.