Sample preparation
Ultra thin slicing preparation (for block samples): For block samples with silicon nitride insulation layer, ultra-thin slicing technology is required. Firstly, the sample is embedded and fixed with epoxy resin or other embedding agents, and then sliced using an ultra-thin slicer. The slice thickness is usually controlled between tens of nanometers and hundreds of nanometers to meet the requirement that the electron beam can penetrate the sample. This process requires precise operation to ensure that the thickness of the slices is uniform and complete, and to avoid defects such as wrinkles and tears that may affect the observation effect.
Powder sample dispersion (for powdered samples): If the study focuses on insulating layer samples containing silicon nitride powder or powder formed after treatment, an appropriate amount of powder can be dispersed in organic solvents (such as ethanol, acetone, etc.), evenly dispersed by ultrasonic oscillation, and then a small amount of dispersed droplets can be absorbed onto a copper mesh with a supporting film (such as carbon film). After the solvent evaporates, the powder sample will adhere to the supporting film and can be observed by TEM.
TEM observation and analysis
Choose the appropriate imaging mode and electron beam parameters:
Bright field imaging (BF) mode: This is the most commonly used mode that forms images by transmitting electrons, presenting different contrasts for different phases in the sample. Thicker or higher atomic number areas appear darker, while the opposite appears brighter. By using bright field imaging, the phase distribution inside the silicon nitride insulation layer can be clearly observed, such as observing the dispersed nanoscale filler phases in the silicon nitride matrix and their interface characteristics.
Dark field imaging (DF) mode: By collecting only electrons at specific scattering angles for imaging, it can highlight certain weakly scattered phases or structural details. It has unique advantages for studying phase structures with low content or contrast in silicon nitride insulation layers, and can further supplement the information observed by bright field imaging, providing a more comprehensive understanding of phase structure characteristics.
Electron beam parameter adjustment: Reasonably select the acceleration voltage and current of the electron beam based on the thickness of the sample and the required resolution. Generally speaking, an acceleration voltage between 80-200 kV is commonly used. A higher acceleration voltage can help penetrate slightly thicker samples, but it is also necessary to consider the potential damage to the samples and the impact on image contrast, which needs to be optimized and adjusted based on actual observation results.
Observing lattice patterns and diffraction patterns:
Lattice stripe observation: When the electron beam penetrates the sample, if there is a crystalline phase in the sample, clear lattice stripes can be seen in high-resolution TEM images. By measuring the spacing between lattice fringes and comparing it with known crystal structure data, the type of crystalline phase and its crystallographic orientation can be determined. For example, for the crystalline regions that may exist in the silicon nitride insulation layer due to high temperature and other conditions, observe their lattice patterns to determine what crystal structure it is, and then analyze the changes in phase structure under these conditions.
Diffraction pattern analysis: Perform selected area electron diffraction (SAED) operation to select a specific region in the sample, causing the electron beam to produce diffraction patterns in that region. The features such as spots and circles presented by diffraction patterns are closely related to the crystal structure and phase structure in the sample. By analyzing the diffraction patterns, the crystal phases, crystal symmetry, and orientation relationships between different crystal phases in the sample can be determined, providing a strong basis for further research on the phase structure of silicon nitride insulation layers.
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