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Transmission Electron Microscopy (TEM) Sample preparation

Sample preparation in Electron Microscopy is one of the most important factors in obtaining high quality data.

A key phrase to remember is if you put “rubbish in” you’ll get “rubbish out”.

Therefore, how can high quality TEM samples actually be produced? This short article will try and answer this question by covering the basic steps of sample preparation for TEM.

The main characteristic of high quality specimens, is that they are thin, very thin. Ideally, a thickness that is close to the mean free path of the electrons that travel through the samples. For instance, High Resolution Imaging will need samples with a thickness of 100 angstrom. For electron Energy Loss Spectroscopy (EELS) between 100 to 500 angstrom and for diffraction contrast around 300 to 500 nanometres.

But how do you achieve the appropriate specimen thickness? 

A sample will normally start as a Bulk material. Using the Fischione Model 130 specimen punch a 3mm disk can be sectioned from the bulk material. This disk will be in the region of 500 microns or thicker. Thus, the size needs to be reduced further. This can be achieved with the use of the Fischione Model 160 specimen grinder. The grinder can reduce the thickness to roughly 20 microns. Then by utilising a high precision Fischione Model 200 dimple grinder the thickness can be reduced to a few microns.

 

The final step to prepare an ideal sample for TEM analysis is Ion Milling. Once the sample thickness is approximately 5 microns or less, the Fischione 1051 TEM Ion Mill can be used to reduce the thickness of the specimen further, potentially until it perforates.

During this procedure the user needs to observe the specimen closely and wait for the coloured fringes to appear. For example, when silicon is very thin (< 1 µm), changes in the colour of its fringes will directly correlate with changes in the specimen thickness. By milling at higher kV until coloured fringes are first observed and then milling at lower kV until perforation, one can accurately endpoint the milling process.

After then being plasma cleaned, ideally using the Fischione 1070, the specimen will be ready for analysis within the microscope.

This article covers the basic principles required to achieve electron transparency, but not all samples are considered equal. Please visit our website or contact us for more in-depth preparation steps on 01582 764334 or click here to email.

Lambda Photometrics is a leading UK Distributor of Characterisation, Measurement and Analysis solutions with particular expertise in Electronic/Scientific and Analytical Instrumentation, Laser and Light based products, Optics, Electro-optic Testing, Spectroscopy, Machine Vision, Optical Metrology, Fibre Optics and Microscopy.