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Microscopy Techniques and Principles
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Microscopy Techniques and Principles
Lecture 7
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Question
What are the key operating environment differences among Optical Microscopy (reflected), SEM, SPM, and TEM?
Answer
Optical microscopy operates in ambient, liquid, or vacuum environments; SEM requires vacuum; SPM can operate in ambient, liquid, or vacuum; TEM requires a high vacuum environment.
Question
Primary mode of imaging for amorphous/polymer samples
Answer
Mass-thickness contrast arises from variations in the mass density and thickness of the sample. Heavier or thicker regions scatter electrons more, producing contrast. This mode is primarily used for amorphous or polymer samples.
Question
Polymer samples might need _____ for sufficient contrast
Answer
additional staining with heavy elements (metal oxides) for sufficient contrast.
Question
How does electron acceleration voltage affect electron wavelength and TEM resolution?
Answer
Higher acceleration voltages produce shorter electron wavelengths and improve TEM resolution; e.g., at 40 kV wavelength is 0.00601 nm and resolution is 0.56 nm, while at 500 kV wavelength is 0.00142 nm and resolution improves to 0.13 nm.
Question
Primary mode for crystalline samples
Answer
Diffraction contrast arises when crystalline structures produce diffracted electron beams due to ordered atomic planes. It is primarily used for imaging crystalline samples where contrast highlights crystal defects, inclusions, or variations in orientation.
Question
Why might polymer samples need staining with heavy elements like metal oxides for TEM imaging?
Answer
Because polymers are composed of light elements that produce low contrast, staining with heavy elements (e.g., RuO₄) increases electron scattering to enhance image contrast.
Question
What is the significance of reciprocal lattice space in electron diffraction?
Answer
helps understand and predict the directions and intensities of diffracted beams based on crystal geometry.
Question
How are Miller indices related to diffraction patterns in reciprocal lattice space?
Answer
Miller indices label specific lattice planes and correspond to spots or reflections in diffraction patterns. Each spot in reciprocal space corresponds to a particular set of crystallographic planes identified by Miller indices.
Question
What can be observed in a High Resolution TEM image of a nanomaterial?
Answer
Atomic-scale lattice fringes and fine structural details of the nanomaterial can be observed, revealing crystallinity, defects, and morphology at near-atomic resolution.