Lecture 5: Microscopy PHYS 430/603 material Laszlo Takacs UMBC Department of Physics
Light microscopy The principle and a commercial scope Useful sites:
Optical microscope (OM) and transmission electron microscope (TEM)
TEM modes: Composite image, bright field image, dark field image, selected area diffraction Transmitted and diffracted beamsDiffraction patternFirst image Bright fieldBright field, transmitted electrons only Dark fieldSelected area diffraction pattern
Comparing imaging and diffraction in a TEM.
Electron diffraction from a monocrystalpolycrystalglass
How do scanning microscopies work? Image = table of numbers Measurement generates a value for every location: Reflectivity of light (scanner) Ejected electrons (SEM) Current between tip and surface (STM) Force between tip and surface (AFM) Any quantity of interest that can produce useful contrast Interpret numbers as intensities for display or printer. Digital image processing.
How do scanning microscopies work? Image = table of numbers Measurement generates a value for every location: Reflectivity of light (scanner) Ejected electrons (SEM) Current between tip and surface (STM) Force between tip and surface (AFM) Any quantity of interest Interpret numbers as intensities for display or printer. Digital image processing.
The principle of the SEM. There is no image formation in the optical sense. This is classical analog system. Modern SEMs record the measured intensities in a computer memory rather then project them directly on a CRT screen. This way image processing is possible before the final image is created. TV does the same.
Measurable effect caused by high-energy electrons
Typical morphological contrast by secondary electrons. It only looks like an illuminated landscape. The contrast comes from how many secondary electrons are generated and how efficiently they are collected by the detector. The illumination comes from above, the detector is n the side.
Magnifications: very different features are seen on different length scales
Depth of field
X-ray analysis
Images of a Lunar rock: (a) Backscattered electrons (depend on Z) (c) Fe X-rays (d) P X-rays (b) Sketch of phases; m = metal tr = trolite, FeS sc = Fe-Ni phosphide wh = phosphate
The principle of STM/AFM