What is a Scanning electron microscope?

Scanning Electron Microscopy (SEM) is a device that obtains images by irradiating the surface of a sample with an electron beam and detecting secondary electrons and backscattered electrons emitted from the sample. The principles and features of SEM are explained below.

principle
Generation and focusing of electron beam: Electrons generated from the electron gun are focused into a narrow beam by an electromagnetic lens. This beam is directed toward the sample surface. Electron beam scanning: The sample surface is scanned point by point with an electron beam. During scanning, the electron beam moves finely across the sample surface in a fixed pattern.

Detection of secondary electrons and backscattered electrons:
When the electron beam collides with the sample, secondary electrons and backscattered electrons are emitted from the sample surface. Secondary electrons are electrons generated near the surface of the sample, and reflected electrons are electrons that collide with atoms in the sample and are bounced back.
Image formation: A detector measures the intensity of emitted secondary electrons and reflected electrons, and generates an image of the sample surface based on the signals.

Features
Detailed observation of surface structure: SEM uses secondary electrons to observe the surface structure of a sample with high resolution. You can see minute irregularities and surface textures in detail.

Obtaining composition information:
Since the backscattered electron signal depends on the sample composition, it is possible to evaluate the composition distribution and atomic number contrast on the sample surface.
Large depth of focus: SEM has a large depth of focus, which enables three-dimensional observation, allowing detailed observation of the uneven surface of the sample.

Various detection modes:
In addition to secondary electron detection, SEM allows observation in various modes such as backscattered electron detection and characteristic X-ray detection. This enables multifaceted analysis of sample structure, composition, and physical property information.

SEM is used in a wide variety of fields including materials science, nanotechnology, bioscience, and the semiconductor industry. Specific examples include:
Materials science: Observation of microstructures and defects on material surfaces
Semiconductor: Quality control and failure analysis in the manufacturing process of semiconductor devices
Nanotechnology: Morphological observation of nanomaterials and nanostructures
Bioscience: Observation of surface structures of cells and tissues
Forensic medicine: Microstructural analysis of evidence

SEM's high resolution and diverse detection modes make it an extremely powerful tool in a wide range of research fields.

Application of Scanning electron microscope

The magnification of the scanning electron microscope can be increased to several hundred thousand times. In addition, the resolution can be increased to several nm. It also has the feature that the depth of focus is deep and it is easy to observe the unevenness of the sample. Since the magnification limit of the optical microscope is about 1000 times and the resolution limit is about 150 nm, it is possible to observe at higher magnification and higher resolution. For example, it is used for observing the surface state of various materials such as semiconductor materials and ceramic materials, observing microorganisms such as bacteria and viruses, and observing biological samples such as cells.

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