The signals used by a scanning electron microscope to produce an image result from interactions of the electron beam with atoms at various depths within the sample. Various types of signals are produced including secondary electrons (SE), reflected or backscattered electrons (BSE), characteristic X-rays and light (cathodoluminescence) (CL), absorbed current (specimen current) and transmitted electrons. SE and BSE detectors are standard equipment in all SEMs, but it is rare for a single machine to have detectors for all other possible signals. The secondary electrons are emitted from very close to the specimen surface, consequently they produce very high-resolution images of a sample surface, revealing details less than 1 nm in size. BSE are beam electrons that are reflected from the sample by elastic scattering from deeper locations within the specimen and, consequently, the resolution of BSE images is less than SE images. However, BSE are often used in analytical SEM, along with the spectra made from the characteristic X-rays, because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen. BSE images can provide information about the distribution, but not the identity, of different elements in the sample. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher-energy electron to fill the shell and release energy. The energy of these characteristic X-rays can be measured by Energy-dispersive X-ray spectroscopy and used to identify and measure the abundance of elements in the sample and map their distribution. Due to the very narrow electron beam, FESEM micrographs have a large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample.
archaeological object and site, architecture, art, decorative arts, manuscript, mosaics, painting, sculpture, textile
animal product, fossil, mineral, shell, skeleton
ceramic (clay/mud brick/terracotta/earthenware/stoneware/porcelain), concrete, glass, stone, metal and metallurgical By-Products, mortar, pigment
animal parts, binding media, glues, wood, paper, textiles, varnishes