Transmission electron microscopy (TEM) – in-situ techniques

About this technique

---

There are a number of in-situ techniques that can be carried out in a conventional transmission electron microscope (TEM). Most of these rely on special holders rather than on modifications to the TEM. Simplest amongst these are cooling and heating holders.

Cooling to liquid nitrogen temperature has a number of uses. Beam sensitive materials generally damage less when very cold. Some materials undergo low temperature phase transformations and these can be readily studied. Whether heating or cooling, the specimen will undergo very significant drift as the temperature changes. For this reason, most cooling or heating experiments involve dwells at specific temperatures – the drift stops when the temperature stabilises.

Heating enables a number of phase transformation processes to be studied. Most heating stages have an upper limit of 800°C. Higher temperatures may be possible, but the holder life will be reduced. Crystallisation, precipitation, dissolution etc are all readily studied by use of a heating holder. One recurrent problem is oxidation of the specimen, particularly for reactive materials such as Mg-based alloys. Although the vacuum in modern TEMs is very high, the electron transparent region of the specimen may be only 50 nm thick and may quickly disappear.

Other in-situ methods accessible via specialised holders include cooling/strain- and pico-indentation. The latter permits measurement of mechanical properties and correlation of stress/strain curve features with crystallographic features in the specimen. For these dynamic techniques, video imaging capability is useful. Modern TEMs use digital imaging rather than film, and so still or video data can be readily acquired.