I. Why do TEM images lack color?

Answer: Color is determined by the frequency of visible light (electromagnetic waves). However, electron microscopes do not use natural light but instead rely on an electron beam as the illumination source, which does not produce color variations.

The Transmission Electron Microscope (TEM) can resolve ultrastructures smaller than 0.2 µm—structures that are beyond the detection limit of optical microscopes.  To observe such fine details, a light source with a shorter wavelength must be used to enhance resolution.  In 1932, Ruska developed the TEM, which utilizes an electron beam instead of visible or ultraviolet light.  The wavelength of an electron beam is much shorter than that of visible or UV light and is inversely proportional to the square root of the accelerating voltage—meaning higher voltages produce shorter wavelengths.  Modern TEMs can achieve resolutions as high as 0.2 nm.However, TEM images are grayscale representations that reflect electron density (i.e., brightness) rather than containing actual color information.

II. The Differences Between TEM and SEM

Answer: When a high-energy incident electron beam bombards the surface of a material, the excited region generates secondary electrons, backscattered electrons, Auger electrons, characteristic X-rays, transmitted electrons, as well as electromagnetic radiation in the visible, ultraviolet, and infrared regions. The scanning electron microscope (SEM) collects information from secondary and backscattered electrons, while the transmission electron microscope (TEM) gathers data from transmitted electrons.

SEM sample preparation does not impose specific requirements on sample thickness. Techniques such as cutting, grinding, polishing, or cleaving can be used to expose specific cross-sections, transforming them into observable surfaces. In contrast, the quality of TEM microscopic images heavily depends on sample thickness. Therefore, the observed portion of the sample must be extremely thin, typically within the range of 10 to 100 nanometers, or even thinner.

III. What are the components of a TEM system?

Answer:

(1) Electron gun: Emits electrons. It consists of a cathode, a grid (Wehnelt cylinder), and an anode. Electrons emitted from the cathode form a beam through a small aperture in the grid and are accelerated by the anode voltage toward the condenser lens, serving to accelerate and focus the electron beam.

(2) Condenser lens: Focuses the electron beam to produce a parallel light source.

(3) Sample holder: Holds the specimen to be observed.

(4) Objective lens: Focuses and forms the initial magnified image (primary magnification).

(5) Intermediate lens: Provides secondary magnification and controls the imaging mode (image mode or electron diffraction mode).

(6) Projector lens: Further magnifies the image (tertiary magnification).

(7) Fluorescent screen: Converts electron signals into visible light for observation by the operator.

(8) CCD camera: A charge-coupled device that converts optical images into digital signals.

IV. What types of TEM samples are there?

Answer:

1. Bulk: Used for general microstructure research;

2. Planar: Used for studying thin films and microstructures near surfaces;

3. Cross-sectional samples: Used for researching the microstructure of uniform thin films and interfaces;

4. Small pieces: Powders, fibers, and nanoscale materials.

V. What are the common applications of TEM?

Answer:

① Morphology observation of samples using mass-thickness contrast (also known as absorption contrast) imaging.

② Phase analysis of samples using techniques such as electron diffraction, micro-area electron diffraction, and convergent-beam electron diffraction to determine the phase, crystal system, and even space group of materials.

③ Determination of crystal structure by utilizing the high-resolution electron microscopy (HREM) method, which allows direct visualization of atomic or atomic cluster arrangements in crystals along specific projection directions.

④ Observation of structural defects in crystals using diffraction contrast imaging and high-resolution electron microscopy techniques to identify defect types and estimate defect density.

⑤ Micro-area chemical composition analysis of samples using energy-dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy (EELS) attached to the TEM.

⑥ In-situ observation of sample deformation and fracture processes using additional TEM accessories such as heating stages or straining stages.

KMD Bioscience boasts a team of professional scientists and advanced imaging laboratories, providing comprehensive Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) services for biological and clinical research, including plant samples, animal tissues, bacterial specimens, and pathological samples. Our experienced experts offer guidance on experimental design for sample collection, preparation, and evaluation. Additionally, we provide professional pathological consultation on imaging results.

Transmission Electron Microscopy (TEM) is a technique that transmits high-energy electrons through an electron-transparent sample (~100 nm thick). These thin samples interact with electrons as they pass through, forming an image. Another method, Scanning Transmission Electron Microscopy (STEM), employs a similar principle but focuses the electron beam into a fine spot, which is then scanned across the sample in a raster pattern.Both TEM and STEM can generate high-resolution images at an atomic scale of approximately 1-2 Å, making them invaluable for cancer research, virology, materials science, and other fundamental research fields.

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