Ch 7 – The Microscope

1
Ch 7 The Microscope

• Compound microscope.
• Magnification, field of view, working distance,
  and depth of focus.
• Comparison microscope.
• Advantages of stereoscopic microscope.
• Plane-polarized light and polarizing microscope.
• Advantages of linking a microscope to a
  spectrophotometer.

2

• Utilizing a microspectrophotometer for examining
  trace physical evidence.
• Mechanism of image formation for light microscope
  Vs scanning electron microscope (SEM).
• Advantages and applications of SEM in forensic
  science.

3

• Virtual image an image cannot be seen directly.
  It can only be seen by a viewer looking through
  a lens.
•  
• Real image an image formed by the actual
  convergence of light rays upon a screen
•  Objective lens the lower lens of a microscope
  that is positioned directly over the specimen
•  Eyepiece lens the lens of a microscope into
  which the viewer looks same as the ocular lens

4

• Transmitted illumination light that passes up
  from the condenser and though the specimen
•  
• Vertical or reflected illumination illumination
  of a specimen from above in microscopy it is
  used to examine opaque specimens
•  Condenser lens system located under the
  microscope stage that focuses light onto the
  specimen

5

• Parfocal construction of a microscope such that
  when an image is focused with one objective in
  position, the other objective can be rotated into
  place and the field will remain in focus
•  Monocular a microscope with one eyepiece
•  Binocular a microscope with two eyepieces
•  Field of view the area of the specimen that
  can be seen after it is magnified

6

• Depth of Focus the thickness of a specimen
  entirely in focus under a microscope
•  
• Plane-Polarized light light confined to a
  single place of vibration
•  Polarizer a device that permits the passage of
  light waves vibrating in only one plane
•  Microspectrophotometer an instrument that
  links a microscope to a spectrometer

7
Compound Microscope
8
Comparison Microscope
9
Polarizing Microscope
10
Stereoscopic Microscope
Cell division in a frog's egg.
11
Microspectrophotometer
12
Scanning Electron Microscope (SEM)
13
SEM Data
Nanoscaled polyimide structures
Side-wall morphology of solar cell gridline
14
Ch. 7 - Microscopy

• Viewing small Specimens

15
The Microscope

• Provides a direct image of a small object of
  interest
• spectroscopy gives an abstract representation
  which must be interpreted on the basis of a model
  or some assumptions
• A typical animal cell is 10-20 nm in diameter
• 5x smaller than the smallest object that can be
  seen directly by the naked eye

16
The Microscope

• Produce a magnified image of a specimen
• Separate the details in the image
• Render the details visible to the human eye or
  camera

17
Lenses

• Refraction of a light ray as it passes through a
  prism

18
Lenses

• Light passing through two identical prisms
  stacked base to base would intersect at point I
• produce a real image
• converging lens

19
Focal Point Focal Length

• The point at which parallel rays are converged to
  an image is the focal point of the lens
• The distance of this point from the lens is the
  focal length

20
Simple Magnifier

• Object O is placed close to the lens
• rays converge but do not intersect
• real image not formed
• The observers eye follows rays back to the point
  of apparent origin (I)
• I bigger than object

21
The Compound Microscope

• Rays pass first through the objective lens
  forming a real, slightly enlarged, inverted image
• The second lens (eyepiece) acts as a simple
  magnifier

22
Compound Microscope

• Both lenses produce magnification
• Overall magnification is found by multiplying the
  two magnifications
• Magnification determined mainly by objective

23
(No Transcript)
24
The Comparison Microscope

• Two compound microscopes combined into one unit
• When viewer looks through the eyepiece, a field
  divided into two equal parts is observed
• specimen on left scope on left side of field
• specimen on right scope on right side of field

25
The Comparison Microscope

• Bullet comparisons
• Hair Fiber comparisons
• Questioned documents

26
Test Fire Reference Gun
27
Use A Comparison Microscope
28
(No Transcript)
29
Striations match
30
Stereoscopic Microscope

• Two separate monocular microscopes
• Each has its own set of lenses

31
Stereoscopic Microscope
Using the Stereo Microscope
Using the Compound Microscope
32
FT-IR Microspectrophotometer
33
Photocopier Toner Analysis

• important for establishing corroborative evidence
  linking documents to specific locations in
  forensic investigations of corporate crime
• Must be performed non-destructively
• cant remove toner from paper
• physical size of specimen is very small
• microscope to find sample
• FT-IR to analyze the sample

34
Photocopier Toner Analysis
35
Limitations of Light Microscope

• Radiation of a given wavelength cant be used to
  probe structural details much smaller than its
  own wavelength
• Light Microscope
• limited to range of visible light
• 0.4 mm (violet) to 0.7 mm (deep red)
• bacteria nitochondria (0.5mm wide) smallest
  objects that can be seen clearly

36
Range of Readily Resolvable Objects
37
Scanning Electron Microscope

• This scanning electron microscope has a
  magnification range from 15x to 200,000x and a
  resolution of 5 nanometers

38
How the SEM Works
39
Conventional light microscopes use a series of
glass lenses to bend light waves and create a
magnified image.
40

• The Scanning Electron Microscope creates the
  magnified images by using electrons instead of
  light waves

41
The SEM shows very detailed 3-dimensional images
at much higher magnifications than is possible
with a light microscope. The images created
without light waves are rendered black and white
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
Samples have to be prepared carefully to
withstand the vacuum inside the microscope
48

• Biological specimens are dried in a special
  manner that prevents them from shriveling.
• Because the SEM illuminates them with electrons,
  they also have to be made to conduct electricity

49

• How do you make a mosquito conductive?
• SEM samples are coated with a very thin layer of
  gold by a machine called a sputter coater
  

50
The specimen is now prepared
51
The sample is placed inside the microscope's
vacuum column through an air-tight door
52

• Air is pumped out of the column
• An electron gun at the top emits a beam of high
  energy electrons.
• travels downward through a series of magnetic
  lenses designed to focus the electrons to a very
  fine spot

53

• Near the bottom, a set of scanning coils moves
  the focused beam back and forth across the
  specimen, row by row

54

• As the electron beam hits each spot on the
  sample, secondary electrons are knocked loose
  from its surface.
• A detector counts these electrons and sends the
  signals to an amplifier

55

• The final image is built up from the number of
  electrons emitted from each spot on the sample

56
(No Transcript)
57
(No Transcript)
58
Fiber Analysis
59
Energy-Dispersive X-Ray Analysis (EDX)

• Electron beam 5,000-20,000eV
• Atomic electrons are dislodged ionizing the
  sample
• Resulting electron vacancy filled by an electron
  from a ghigher shell
• X-ray is produced
• x-ray energy characteristic of the parent atom

60
Gunshot Residue by EDX

• Residue particle from the hand of a person who
  fired a .380 Browning automatic
• The peaks of lead, barium antimony together
  with the shape of the particle are quite specific
  show that the subject had fired a weapon

61
Who am I?

• Im a louse fly of a wallglider (an alpine bird)