Scale of Structure Organization X-Ray Diffraction (XRD) is used to study crystal structures. X-rays have wavelengths on the order of interatomic spacings (2-3 Angstroms), allowing them to diffract off of crystal planes. The diffraction patterns produced by crystals like quartz and cristobalite are different due to their differing atomic arrangements, despite being chemically identical. Amorphous materials like glass do not have long-range order and thus produce only broad scattering features in XRD.

1. Scale of Structure Organization

2. X-Ray Diffraction (XRD)

3. Basics of Diffraction
For electromagnetic radiation to be diffracted the spacing in the grating
should be of the same order as the wavelength
 In crystals the typical interatomic spacing ~ 2-3 Å so the suitable radiation
is X-rays
 Hence, X-rays can be used for the study of crystal structures
 Neutrons and Electrons are also used for diffraction studies from materials.
 Neutron diffraction is especially useful for studying the magnetic ordering
in materials

6.  The three X-ray scattering patterns above were produced by three chemically
identical forms SiO2
 Crystalline materials like quartz and Cristobalite produce X-ray diffraction patterns
– Quartz and Cristobalite have two different crystal structures
–The Si and O atoms are arranged differently, but both have long-range atomic
order
–The difference in their crystal structure is reflected in their different diffraction
patterns
 The amorphous glass does not have long-range atomic order and therefore
produces only broad scattering features

9. Optical Microscope
Optical microscope is a type of microscope which
uses visible light and a system of lenses to magnify
images of small samples.
There are two basic configurations of the conventional
optical microscope in use, the simple (one lens) and
the compound (many lenses).

10. Assumptions in Light Theory
1.Light travels in a straight line.
2.Portions of light beams can be treated as
individual rays.
3.Law of reflection.
4.Law of refraction.

11. Simple Lens
Kirkpatrick/Francis – “Physics; A World View
SPHERICAL SURFACE

12. Optics of a Microscope
Slide with the letter “F”
The letter “F” as it
appears when
viewed through the
eyepiece
F
Images viewed through the
eyepiece of compound
microscopes will appear
upside-down and
backwards.

13. How it Works?
Light
source or
Mirror
Optical
Condenser
Light
passes
through the
specimen
Objective
Lenses
(X100)
First Image
Eyepiece
or Ocular
(X10)
Image
(X1000)
Retina

14. Basic Components
 Eyepiece Lens: the lens at the
top that you look through.
 Tube: Connects the eyepiece to
the objective lenses
 Objective Lenses: Usually you
will find 3 or 4 objective lenses
on a microscope. They almost
always consist of 5X, 10X, 20X ,
50X and 100X powers.
 Rack Stop: This is an
adjustment that determines how
close the objective lens can get
to the slide.
 Condenser Lens: The purpose
of the condenser lens is to focus
the light onto the specimen.

15. Basic Components
 Stage: The flat platform where you
place your slides. Stage clips hold
the slides in place.
 Revolving Nosepiece or Turret:
This is the part that holds two or
more objective lenses and can be
rotated to easily change power.
 Illuminator: A steady light source
(110 volts) used in place of a mirror.
If your microscope has a mirror, it is
used to reflect light from an external
light source.
 Arm: Supports the tube and
connects it to the base
 Base: The bottom of the
microscope, used for support

16. Total Magnification
• The total magnification of
the specimen being viewed
is calculated using the
ocular lens multiplied by
the objective lens.
• For example, if the ocular
lens is 10x and the ocular
lens is 50x then the total
magnification would be
500x.

17. Focusing a Microscope

18. Focusing a Microscope
• Course-adjustment knob- is the
larger of the two knobs. It is used
in bringing the object into quick
focus.
• Fine-adjustment knob- is used for
improving the clarity of the image,
especially when viewing under
high power.

19. Quality of an Image
• Focal Length
• Size of sample
• Type of sample
• Quality of Microscope and lenses
• Amount of light on the sample
• Quality of sample

20. Numerical Aperture (NA)
The objective collects as much light as possible coming from any
point on the specimen and combines this light to form the image.
The numerical aperture (NA) is a measure of the light collection
capability of the objective and is defined as 𝑵𝑨 = 𝒏. 𝐬𝐢𝐧 𝜶
Objectives with a shorter focal length have a wider angular aperture and therefore
deliver a higher NA and resolution.

21. Numerical Aperture (NA)
The objective with the higher numerical aperture is
clearly able to give us more detail with separation
between the wavelets.
https://microscopeclarity.com/what-is-microscope-resolution/

22. Depth of Field
• The depth of field is the
distance along the optical
axis over which details of
the object can be observed
with adequate sharpness
• "Depth of field" refers to the
thickness of the plane of
focus.
• It is the vertical distance
(from above to below the
focal plane) that yields a
useful image.

23. The series of images show
how the depth of field can
influence the appearance
of an image.
With narrow
depth of
field, only
part of the
image is in
focus at the
same time.
With a large
depth of field,
the entire
image is in
focus at the
same time.
Depth of Field: Example

24. Resolution
• Resolution or resolving power is the closest spacing
of two points which can clearly be seen through the
microscope to be separate entities.
• It is not necessarily the same as the smallest point
which can be seen with the microscope, which will
often be smaller than the resolution limit.
• Resolving power, 𝑑 =
0.61𝜆
𝑛.sin 𝛼
=
0.61𝜆
𝑁𝐴

25. Resolution: Examples
https://microscopeclarity.com/what-is-microscope-resolution/
https://www.cherrybiotech.com/scientific-
note/microscopy/beyond-the-limits-of-light
diffraction-super-resolution-microscopy
https://www.microscope
world.com/t-
camera_resolution.aspx

26. • Inexpensive
• Easy to learn and operate
• Very sharp plane of focus
• Small and portable
Advantages
• Magnification is limited
• Specimen may be disfigured during preparation to be
viewed under the microscope.
• Only has a resolution of 0.2 μm - which is relatively poor
in comparison to other microscopes.
• Poor surface view
Disadvantages

27. Allotriomorphic ferrite in a Fe-0.4C
steel which is slowly cooled; the
remaining dark-etching microstructure
is fine pearlite
Optical micrograph showing colonies of
pearlite (courtesy S. S. Babu)
https://www.phase-trans.msm.cam.ac.uk/2008/Steel_Microstructure/SM.html
Microstructure: Examples

28. Left, as-cast cadmium etched with 2% nital, 30 x ; right, as-cast alloy of Cd and 10% Bi etched
with 2% nital, 60 x .
Microstructure: Examples

29. Microstructure: Examples
Superpure aluminum anodized using the method of Hone and Pearson (Ref. 56),
polarized light, 32 x . Left, held 6 min at 375°C, partly recrystallized. Right, held 2 h at
375°C, fully recrystallized. (Courtesy of E. C. Pearson, Alcan International Ltd.)

30. Color etching of various grain or mixed-crystal areas and sulphate layers
of different thicknesses
Ferrite-perlite microstructure, the ferrite
is tinted while Fe3C is kept white
Klemm (K) etch
This contrasting visualizes the quality
of a soft annealing (K)
https://www.leica-microsystems.com/science-lab/metallography-with-color-and-contrast/
Microstructure: Examples

31. Brightfield image of a cast austenite
structure caused by a laser melting
process
Improved contrast using interference
Microstructure: Examples
The same sample in interference contrast
showing clear contrasting of the
dendrites (B)
Klemm (K) etchant: 50 mL saturated aqueous sodium thiosulfate, 1 g potassium metabisulfites
Beraha (B) etchant: (a) Stock solution: 1:2, 1:1, or 1:0.5 HCI-water
(b) 100 mL stock solution plus 0.6-1.0 g potassium metabisulfite
https://www.leica-microsystems.com/science-lab/metallography-with-color-and-contrast/

32. Scanning Electron Microscopy – (SEM)

33. Construction of SEM
SEM
Magnification range
15x to 200,000x
Resolution of 50 Å
Excellent depth of
focus
Relatively easy
sample preparation

34. A brief description of each system follows:
1. Vacuum system. A vacuum is required when using an electron beam because
electrons will quickly disperse or scatter due to collisions with other molecules.
2. Electron beam generation system. This system is found at the top of the
microscope column. This system generates the "illuminating" beam of electrons known
as the primary electron beam.
3. Electron beam manipulation system. This system consists of electromagnetic
lenses and coils located in the microscope column and control the size, shape, and
position of the electron beam on the specimen surface.
4. Beam specimen interaction system. This system involves the interaction of the
electron beam with the specimen and the types of signals that can be detected.
5. Detection system. This system can consist of several different detectors, each
sensitive to different energy / particle emissions that occur on the sample.
6. Signal processing system. This system is an electronic system that processes the
signal generated by the detection system and allows additional electronic manipulation
of the image.
7. Display and recording system. This system allows visualization of an electronic
signal using a cathode ray tube and permits recording of the results using photographic
or magnetic media.
Components of SEM

35. Principle of SEM image formation
When an electron beam is incident
on the sample then many different
types of signals are generated which
are eventually used to observe or
analyze morphology/ topology of the
sample. SEM is also used for
elemental and state analysis. These
signals includes – Secondary
electrons, Backscattered electrons,
Auger electrons,
Cathodoluminescence and X-rays.
Interaction of Electrons with Specimen: Electrons entering specimen gets
scattered within it and lose their energy gradually upon getting absorbed
within the sample. Scattering range within specimen depends upon-
Energy of electrons – More Energy More Scattering.
Element’s atomic number (Z) making the sample - More Z Less
Scattering.
Density of constituent atoms – More Density less scattering.

36. SEM Sample-
Conducting samples provide a path to ground for the beam electrons, and therefore
require no special preparation. Insulating materials, however, require a thin coating
of a conductor (often carbon or gold) in order to prevent charging.
Sample Preparation-
It is done in order to eliminate the sample charging few steps are followed:
1. Charging: A thin metal coating of about 10nm is done on the sample because
metal film is highly stable and its secondary electron yield is higher. Too thin coating
is not preferred because continuity is lost.
2. Low accelerating voltage: Low KV value of about 1KV can be used to scan
insulating samples because the number of incident electrons becomes equal to the
number of emitted secondary electrons, implying that the sample is not charged.
3. Tilt Observation: In this case secondary electrons yield is higher as electron
beam is entering at an angle.
4. Low Vacuum SEM observation: Ondecreasing the vacuum, the gas molecules
within the sample chamberincreases, which get ionized due to electrons and thus,
on reaching the specimen as positive ions neutralize the charging.
SEM sample Preparation

38. Transmission Electron Microscopy – (TEM)

39. Construction of TEM Instrument components
 Electron gun (described
previously)
 Condenser system (lenses &
apertures for controlling
illumination on specimen)
 Specimen chamber
assembly
 Objective lens system
(image-forming lens - limits
resolution; aperture -
controls imaging conditions)
 Projector lens system
(magnifies image or
diffraction pattern onto final
screen)

40. dislocations
in superalloy
SiO2 precipitate
particle in Si
Examples

41. Sample Preparation for TEM