Cryo Transfer Scanning Electron Microscope (Cryo-SEM) Made Easy

By Marilyn Carey, Gatan UK

Cryo-SEM is now a widely used technique for the observation of many sample types from a host of different academic, R&D and quality control facilities for example, botanical, biological, agricultural, pharmaceutical, petrochemical, food, cosmetic, detergent and construction industries. Cryo-SEM has two main advantages over other sample preparatory techniques; samples remain hydrated and preparation time is extremely short, typically 15 minutes or less. A modern FEG-SEM equipped with Gatan’s Alto 2500 has enabled Cryo-SEM to be regarded as a high resolution technique, with the visualization of structures less than 5nm to be achievable at low accelerating voltage.

Cryo-SEM has three principal operational phases and the basics of the technique are simple.

	Phase one: The sample is mounted onto a suitable sample mount attached to a sample holder. Large selection of sample holders to choose from.
	Step 1 This sample is attached to a stub. Step 2 The stub is inserted into holder. Step 3 The holder is then attached to the transfer rod.
	Step 4 The sample holder is then cooled quickly by plunging into liquid nitrogen slush.
	Step 5 The sample is then transferred under vacuum to the preparation chamber. Sample now held under vacuum in transfer device following plunge cooling ready for phase two.
	Phase two: Step 6 The transfer device is attached to the preparation chamber and the sample holder transferred to the cold stage.
	Step 7 In the preparation chamber the sample may be fractured, to expose internal microstructure.
Sample of chocolate fractured at low temperature. The sample may also now be sublimated to remove superficial water/enhance detail and coated, to make it conductive. Phase three: Step 8 The sample is transferred to the SEM chamber and observed at low temperature. Sample of chocolate fractured at low temperature. The procedure step by step.