研究目的
To evaluate the capabilities and potential applications of a commercial EELS detector attached to a cold-field emission SEM in transmission mode for materials characterization at low accelerating voltages, focusing on advantages like reduced Cherenkov radiation and delocalization, and demonstrating its use in bandgap measurements, plasmon imaging, and core-loss spectroscopy.
研究成果
The EELS detector on a cold-field emission SEM at low accelerating voltage (30 kV) offers significant advantages, including absence of Cherenkov radiation, reduced delocalization, and improved detector performance, enabling high-quality bandgap measurements, plasmon spectroscopy, and core-loss analysis. Despite limitations in specimen thickness and radiolysis damage, it is a promising tool for nanomaterials characterization, with demonstrated applications in alloys and plasmonic materials, and potential for further development in low-voltage EELS.
研究不足
Specimen thickness is a major limitation, as t/λ ratios must be kept low (preferably <1) for practical EELS, requiring very thin samples, especially for heavy materials. Radiolysis damage is increased at low voltages, particularly for sensitive compounds like lithium-based materials, leading to phase transformations and limiting analysis. The small collection aperture (5 mrad) reduces signal intensity for high atomic number elements, and energy resolution is affected by instrumental settings like emission current and dispersion.
1：Experimental Design and Method Selection:
The study uses a Hitachi SU-9000 cold-field emission SEM with an attached EELS detector. Experiments are conducted at 30 kV accelerating voltage to avoid Cherenkov radiation and reduce beam damage. Methods include spectrum imaging, energy-filtered STEM using the 'three-windows' method, and zero-loss peak fitting for energy resolution assessment.
2：Sample Selection and Data Sources:
Samples include lithium titanate (LTO), lithium oxide (Li2O), lithiophilite (LiMnPO4), anatase (TiO2), boron nitride nanotubes (BNNT), ZnO, synthetic diamond, AA2099 Al-Li-Cu alloy, silver nanocubes, and silver platelets. Samples are prepared by sonication in ethanol and deposition on TEM grids or specific synthesis methods.
3：List of Experimental Equipment and Materials:
Hitachi SU-9000 cold-field emission SEM, EELS detector with CCD and YAG scintillator, TEM grids, ethanol, ion milling system (UniMill from Technoorg-Linda), and various chemicals for synthesis (e.g., silver nitrate, ethylene glycol).
4：Experimental Procedures and Operational Workflow:
The SEM is operated at 30 kV with specific probe sizes and apertures. EELS spectra are acquired with different dispersions (0.055 to 0.45 eV/channel). Procedures include zero-loss peak fitting, bandgap measurement with background subtraction, spectrum imaging, and energy-filtered imaging. Beam conditions are varied (emission current, condenser lens modes) to assess effects on energy resolution.
5：055 to 45 eV/channel). Procedures include zero-loss peak fitting, bandgap measurement with background subtraction, spectrum imaging, and energy-filtered imaging. Beam conditions are varied (emission current, condenser lens modes) to assess effects on energy resolution.
Data Analysis Methods:
5. Data Analysis Methods: Zero-loss peaks are fitted using pseudo-Voight functions with Python's 'lmfit' package. Bandgaps are determined by linear fitting of low-loss spectra after background removal. Spectrum images are processed to extract chemical and electronic information. Monte Carlo simulations are used for electron trajectory analysis in YAG.
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