TEM

Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen to form an image. Because electrons have wavelengths far shorter than visible light, TEM can achieve atomic-scale resolution, enabling visualization of crystal lattices, defects, and nanostructures. Typical TEM operation uses accelerating voltages around 60–300 kilovolts, and samples are prepared to be electron transparent, often requiring thinning to tens of nanometers.

In a TEM, an electron source generates a beam that is shaped by condenser lenses, then directed onto the specimen. Transmitted electrons are collected by an objective lens and projected onto a detector or imaging screen to produce a magnified image. Contrast results from differences in how electrons scatter within the sample, with thicker or denser regions producing more scattering. TEM also supports diffraction modes to study crystal structure and orientation, and can be combined with spectroscopic techniques for composition analysis.

Sample preparation is crucial and varies by material. Biological specimens may be embedded and cryo-preserved or stained to enhance contrast, while materials and nanomaterials are thinned by microtomy, ion milling, or focused ion beam techniques. Imaging modalities include bright-field and dark-field TEM, as well as high-resolution TEM (HRTEM). Scanning TEM (STEM) is a related mode that scans a focused electron probe across the sample, often paired with detectors for energy-dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy (EELS) for elemental analysis.

Applications of TEM span materials science, chemistry, physics, and biology. It enables defect analysis, lattice imaging, nanostructure characterization, and atomic-scale crystallography. Electron diffraction, tomography, and spectroscopy extend TEM’s capabilities to three-dimensional reconstruction and composition mapping. The technique traces its origins to early work by Ernst Ruska and Max Knoll in the 1930s and remains a cornerstone of high-resolution characterization.