7.2 Notes
The Microscope continued
Objectives
Appreciate how a polarizing microscope is designed to characterize polarized light
Appreciate how a microspectrophotometer can be used to examine trace physical evidence
Compare and contrast the image formation mechanism of a light microscope to that of a scanning electron microscope
Outline some forensic applications of the scanning electron microscope
Microspectrophotometer
Combination of computerized spectrophotometer and microscope
Allows for viewing a small particle under the microscope
Allows for the a beam of light directed at the particle to obtain an absorption spectrum
Microspectro. cont.
Visual inspection of color is essential in examining paint, fiber, ink evidenceUsed to distinguish counterfeit and authentic currency by comparing spectral patterns of inked lines on currencyUseful in determining fiber and paint chip chemicals
Scanning Electron Microscope (SEM)
A beam of electrons on the specimen from a tungsten filamentElectrons are focused by electromagnetsThe upper layers of the specimen rebound electrons Rebounded electrons collected by a cathode ray tube or the TV
SEM cont.Emitted electrons are converted into an imageHigh magnification, high resolution, great depth of focus10x to 100,000 x
Can be used to determine elemental composition of a specimen by coupling with an X-rayCan be used to tell if a suspect has recently fired a gun
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