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 (80keV-200keV) are transmitted through electron transparent samples (~100nm 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
  • Colloidal dispersions of liposomes, polymersomes, emulsions
  • Studies of particle clustering in the dispersion
  • Electron-beam sensitive samples
  • Low-temperature crystal phase studies
Technical Specifications

Signals Detected: Transmitted electrons
Elements Detected: B-U (with EDS)
Detection Limits: 1 at%
Imaging/Mapping: Yes (with EDS)

Strengths
  • Allows for imaging of soft matter in its near natural state in an aqueous dispersion
  • Allows for imaging of otherwise too beam sensitive materials
Limitations
  • 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

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