Electron Microscopy
Electron microscopy is a powerful imaging technique that enables the capture of ultra-high resolution images of individual atoms in materials and the internal structures of cells. These images, which can provide detailed atomic-level, micro- and meso-structural information, are essential for studying the properties and behavior of various samples. Widely utilized in fields such as materials science, biomedical research, quality control, and failure analysis, electron microscopy offers superior spatial resolution—on the scale of tens of picometers—compared to the resolution achievable with photon-based optical microscopy (~200 nanometers). Beyond surface topography, it provides valuable insights into crystalline structures, chemical compositions, and electrical properties. Electron microscopy is primarily divided into two types: scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Overview
Scanning Electron Microscopy (SEM)
Scanning Electron Microscopy (SEM) is a powerful imaging technique that utilizes a relatively low-power electron beam to interact with a sample's surface, providing high-resolution images. The electron beam induces two types of signals: secondary electrons, which are emitted from the surface of the sample due to inelastic interactions between the electron beam and the atoms in the sample, and backscattered electrons, which are generated through elastic interactions. These signals are detected by electron detectors to produce detailed images of the sample’s surface and internal structure. One of the key advantages of SEM is that it requires little to no sample preparation, making it a faster and less restrictive technique compared to other types of electron microscopy. Large samples, often up to 200 millimeters in size, can be directly imaged after being mounted on a holder or stub. In addition to imaging, SEM commonly incorporates energy-dispersive X-ray spectroscopy (EDS or EDX), which maps the distribution of elements within the sample. Other methods, such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL), are also employed to analyze the high-quality images and optoelectronic properties of the samples, further enhancing the versatility of SEM in materials science and other research fields.
Transmission Electron Microscopy (TEM)
Transmission Electron Microscopy (TEM) is an advanced imaging technique that uses a high-energy beam of electrons to pass through a sample, generating a two-dimensional image at the highest resolution possible. TEM allows for the detailed analysis of nanomaterials, revealing their structure and composition at the atomic level. One critical aspect of TEM is the selection of the appropriate sample holder, or TEM grid, which is essential for obtaining the most precise and informative images. Because TEM requires the electrons to pass through the sample, samples must often be thinned to a thickness of approximately 100 nanometers or less. Once appropriately prepared, the samples are mounted on a TEM grid and examined under ultra-high vacuum conditions with a focused, intense electron beam. In addition to imaging, TEM provides crystallographic information through selected area diffraction (SAD), which analyzes the electron diffraction patterns produced as electrons pass through the sample. To further characterize the sample’s properties, techniques such as Electron Energy Loss Spectroscopy (EELS) and Energy-Dispersive X-ray Spectroscopy (EDX) are used to analyze the atomic composition, chemical bonding, electronic properties, and local material thickness of the sample.
Scanning Transmission Electron Microscopy (STEM)
Scanning Transmission Electron Microscopy (STEM) is a sophisticated technique that combines the features of both scanning and transmission electron microscopy. In STEM, a highly focused electron beam, typically with a spot size ranging from 0.05 to 0.2 nanometers, is scanned across the sample. This technique allows for the simultaneous collection of imaging and spectroscopic data, enabling researchers to correlate spatial information with spectroscopic analysis directly. STEM provides unparalleled resolution and sensitivity, making it ideal for studying the structure, composition, and other properties of materials at the atomic scale. The ability to acquire both high-resolution images and spectroscopic maps in real-time adds a valuable dimension to the characterization of advanced materials, especially in the study of nanomaterials and complex structures.