samples and sample preparation for scanning electron microscopy

There is a lot of objects that can be explored by a scanning electron microscope (SEM) without any preparation at all. In the other cases though a large varity of sample preparation methodes is in use. It demandes a lot of experience and sometimes even the determination to experiment to find a suitable methode for every special specimen. The possibility to produce preparation artefacts has allways to be taken into consideration. At EMTEC we have the most popular methodes of specimen preparation at hand. If we need other more special methodes, we cooperate with laboratories that have vast experience with the requested methode.

  What are prerequissitions for specimens, that shall be explored by a scanning electron microscope ?
The classic desciption of suitable specimens has been:
silicium, etched silicium, etched
77,8 kB
* solid state, conducting current, stable under the electron beam and vacuum.
Today these limitations can be overcome by the use of special preparation and electron microscopical methodes in most cases. Naturally this extends the work that is required in the examination of the sample. Because of this we will try to give you some hints on what you can do in order to simplify the examination.
* Chamber and stage of the scanning electron microscope limit the size and weight of the samples. Our instruments can handle about a maximum of 15x15x5cm and 1 kg. Larger samples have to be reduced, moulded or to be examined using very special types of SEM.
* Smaller samples can be handled much easier. On the low side there is practically no limit for weight and size.
* The samples should be solid and should lack residues of any liquids, oils, greases. Such contributions would normaly have to be removed before the examination of the sample.

SEM sketch

surface of a leaf
surface of a leaf
42,1 kB
A selection of sample preparation methodes for scanning electron microscopy:
* Gross preparation of the samples by means of taking suitable sized and yet representative parts of them.  
* Exposing of internal structures of the sample by means of breaking, cutting, sawing, etching. The production of slides by means of grinding and polishing stations or an ultramiller is also sometimes very helpful.
* Exposing of structures on surfaces by certain cleaning methodes.
* Yielding of portions of the samples by filtration and other mechanical dividing methodes.
* Production of moulds of sample surfaces that can not directly be viewed within the microscope, like f.i. moulds of skin or moulds of surface areas at very large pieces.
* Special methodes of structural preserving drying of biolgical materials.
* Evaporating oder sputtering of coatings in order to achieve conducting surfaces on non conducting samples. The vast amount of non conducting samples can be easily investigated by this methode. In many cases this also improves image contrast and resolution even with conducting samples. If non conducting samples may not be changed by such a coating, it is recently possible to investigate those samples using special scanning electron microscopic methodes.
* Fixation of the samples on suitable substrates, sampleholders, by means of glueing or clamping.

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