Cryogenic Transmission Electron Microscopy (Cryo-TEM)
Cryo-TEM involves performing Transmission Electron Microscopy TEM analysis while keeping the sample at cryogenic temperatures, i.e. -170°C (or 103 K).
Transmission Electron Microscopy (TEM) is a technique that images a sample using an electron beam. High energy electrons (80-200 keV) are transmitted through electron transparent samples (~100 nm thick) and imaged on a plane.
The main reasons for the use of low temperature are
- The study of thin, frozen slices of suspensions, allowing for morphology studies of particles in their dispersed state.
- The reduction of sample heating by the electron beam and thus the reduction of potential beam damage of sensitive materials
- The study of low-temperature phases of crystalline materials
The production of thin (~100 nm) slices of frozen aqueous dispersions (‘vitrified ice layers’) is achieved using a Vitrobot ™ sample preparation tool, a dedicated cryo-sample-transfer unit and a cryo-TEM sample holder.
Ideal Uses of Cryo-TEM
- Colloidal dispersions of liposomes, polymersomes, emulsions
- Studies of particle clustering in the dispersion
- Electron-beam sensitive samples
- Low-temperature crystal phase studies
- Allows for imaging of soft matter in its near natural state in an aqueous dispersion
- Allows for imaging of otherwise too beam sensitive materials
- The sample preparation of aqueous dispersions requires method development for different sample types, as it is very dependent on the particle concentration, particle size and material viscosity
- The sample thickness of vitrified ice layers is determined by the particle size. The transparency of the sample thus sets a limit to the particle size at a few hundred nm
- The analysis time for Energy Dispersive X-ray Spectroscopy (EDS) analysis is limited because of beam-induced sublimation of the frozen water layer, even at cryogenic temperatures
Cryo-TEM Technical Specifications
- Signals Detected: Transmitted electrons
- Elements Detected: B-U (with EDS)
- Detection Limits: 1 at%
- Imaging/Mapping: Yes (with EDS)