Variable Pressure SEM

Any increase of pressure in the gun chamber from its normal very low value will cause the electron gun to fail after a very short time. To protect it, the VPSEM contains some limiting apertures that restrict the flow of gas up the optical column from specimen to gun chamber. In the ESEM there may be as many as four apertures. Two are conventionally placed, separating the gun chamber from the column, and the column from the specimen chamber (the final aperture). Two more are placed just above the final aperture, dividing the vacuum system into five separate regions in all. Each of these has its own vacuum pumping system, and the result is a mechanically complex microscope with a sequence of pressures that the electrons 

The detector system just described is analogous to a gas-filled detector used for x-rays. At 

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As a special development in recent years, SEMs have been designed which no longer necessitate high vacuum (enviromnental SEM, ESEM variable pressure SEM, VPSEM). This development is important for the imaging of samples with a residual vapour pressure, such as aqueous biological or medical samples, but also samples in materials science (wet rock) or organic chemistry (polymers). 

Another method is automated serial sectioning of specimens with an ultramicrotome integrated into an environmental scanning electron microscope (ESEM). This method involves imaging the surface of the specimen after removal of each slice. The reason for the choice of an ESEM (or a variable-pressure SEM) is to avoid specimen charging. The experimental setup of such an ultramicrotome operating in situ within an ESEM is described in [16]. 

Experiments involving hydrated polymers have been monitored using variable pressure SEMs (e.g., [214]), although recent evidence has shown extensive radiation damage [215, 216] occurs during these studies (see Section 5.5.2). Because the AFM can be operated in a wide range of environments, many other dynamic experiments are possible. The effect of hydration on polymer blends and membranes [135, 217] and the effect of UV irradiation in various gaseous environments on the friction of polymer films [218] are just a few examples of the himdreds of AFM dynamic studies on polymers. 

In the second case, the deformation method will not be by a standard test, but suitable samples will be designed to fit the microscope. The in situ deformation of polymers is almost always conducted in the SEM at low magnification and is most often used for fibers and fabrics. Variable pressure SEM and AFMs are also... 

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