Microscopy is the set of techniques and methods aimed at visualizing objects of study which, due to their small size, are beyond the resolution range of the human eye. In the case of optical and electron microscopy, the technique in itself involves the diffraction, reflection or refraction of an electromagnetic wave/electron beam that interacts with the sample, and the collection of the scattered radiation or of any other signal to create an image

Optical microscopy: In this type of microscope the area observed is greatly illuminated. They generally reach a magnification of around 1000, although this figure can be doubled with powerful eyepieces. The useful magnification limit is 2000 due to the power of resolution. Generally, optical microscopes consist of a mechanical and an optical part. The latter part consists of three lens systems: i) the condenser that illuminates the object studied, ii) the objective that magnifies the image and enables it to be observed from the eyepiece and iii) the eyepiece that further enhances the image and that makes it visible to the human eye. Depending on the arrangement and type of components, the nature of the light employed, the presence of filters, etc., there can be different types of optical microscopes: stereoscopic, incident light, metallographic, transmitted light, fluorescence, polarized light, etc.

Confocal microscopy: This type of microscope uses a monochromatic laser beam as a light source, characterized by a specific wavelength. The light emitted from the sample passes through a very small opening, called pinhole (pinhole diaphragm), located before the photodetectors. This enables a layered approach and, due to the superimposition of layers, it is possible to reconstruct the surface of the samples, obtaining high-resolution images, thus facilitating the study of roughness, profiles and superficial alterations, among others.

Scanning electron microscopy: This method is based on making a very narrow beam of electrons, accelerated with energies from a few hundred eV to keV, to impact on a sample that is opaque to the electrons. This beam focuses on and scans the surface of the sample.

The deriving radiation can be of low energy, leading to so-called secondary electrons, resulting in the observation of three-dimensional images. By comparison, backscattered electrons are of high energy and their emission intensity will depend on the atomic number of atoms of the sample, which may reveal a different chemical composition of the sample due to contrast differences.

Likewise, the X-ray emission from the sample can be used to perform elemental qualitative and semiquantitative analyses. To this end, different microanalysis techniques can be used such as EDS or WDS.

When working in high vacuum mode, samples should be prepared. To do so, they are made more conductive by coating them with gold or coal and they must be dehydrated. When working under vacuum or environmental mode, the fresh sample can be observed without coating or dehydration, which makes it a non-destructive technique