Pyyhkäisyelektronimikroskopia

Pyyhkäisyelektronimikroskopia, often abbreviated as SEM, is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. As the electron beam interacts with the atoms on the surface of the sample, it generates various signals that can be detected and mapped to form an image. These signals include secondary electrons, backscattered electrons, and X-rays.

Secondary electrons are low-energy electrons that are emitted from the sample's surface due to inelastic collisions with the incident electron beam. They are very sensitive to surface topography and are commonly used to create images with high resolution and excellent depth of field, revealing intricate details of the sample's surface structure.

Backscattered electrons are high-energy electrons from the incident beam that are scattered back out of the sample due to elastic collisions with atomic nuclei. The yield of backscattered electrons is dependent on the atomic number of the elements in the sample. Therefore, backscattered electron imaging is useful for distinguishing different elemental compositions within a sample, with heavier elements appearing brighter.

X-rays are also produced when the electron beam interacts with the sample. These X-rays are characteristic of the elements present in the sample, and their energy can be analyzed using energy-dispersive X-ray spectroscopy (EDX or EDS) to determine the elemental composition and distribution.

SEM is widely used in various fields, including materials science, biology, geology, and nanotechnology, for analyzing the morphology, topography, and elemental composition of samples. It requires samples to be conductive or coated with a thin conductive layer, and it operates under vacuum conditions.