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A scanning electron microscope (SEM) is one which can produce very fine images (greater than 1nm resolution) of a sample through the use of focussed electron beams, giving information regarding the topography and composition of a sample. The use of SEMs in material science is vital as it overcomes the wavelength limit of visible light that is associated with light optical microscopy. SEMs can be used in number of scanning modes. For the purpose of these investigations, the modes that were used were:

 

• Secondary Electron Detection

• Energy Dispersive X-Ray (EDX) Spectroscopy

 

 

Secondary Electron Detection

 

The detection of secondary electrons is used to generate very high (up to 500 000 times magnification) resolution of the topography of a material. The images can only provide information down to a depth of approximately 100nm from the surface due to the low kinetic energy of the secondary electrons released after ionisation.

 

 

1Energy Dispersive X-Ray (EDX) Spectroscopy

 

The x-rays detected through the use of energy dispersive X-ray (EDX) spectroscopy are generated by the “electrons decaying to their fundamental state after ionisation” and is used to determine the elemental composition of a sample.

 

It works on a similar, but opposite principle to that of the XPS, where each element has a unique atomic structure, therefore the peaks created in the produced emission spectrum can be matched to the characteristic peaks of known elements. The difference being; that whereas XPS involves exciting atoms within the sample with an X-ray beam and measuring the kinetic (binding) energy of the emitted photoelectrons, EDX involves stimulating the atoms with high energy electron beam and measuring the energy from the emitted x-rays. However XPS is more surface sensitive, collecting information at a depth of approximately 10-12nm. EDX gives information within an average volume of several µm3.