basic descriptaion of microscopy

1. BY-
PRAVEEN KUMAR LITORIYA
REGISTRATION NO-Y-16273028
DEPARTMENTOF PHYSICS
DR. HARI SINGH GOURUNIVERSITY, SAGAR

2. • INTRODUCTION
• DEFINITION
• HISTORICAL BACKGROUND
• VARIOUSTYPES OF MICROSCOPES
• SCANNING ELECTRON MICROSCOPE (SEM)
• COMMENTS
• REFERENCES

6. Type Probe Technique Best Resolution Penetration Uses and Constraints
Optical
Microscopy
Visible Light Detect reflected light
(opaque samples) or
transmitted light
(transparent samples).
Light focused using lenses.
~200 nm Surface or
volume (can
probe through
transparent
materials)
Scanning Electron
Microscopy (SEM)
Electrons Detect electrons back-
scattered by the sample.
Electrons focused using
electromagnets.
~1 nm Surface Sample must be in a
vacuum.
Transmission
Electron
Microscopy (TEM,
STEM)
Electrons Detect electrons scattered as
they move through the
sample.
Electrons focused using
electromagnets.
~0.05 nm Volume Samples must be <100 nm
thick.
Atomic Force
Microscopy (AFM)
Cantilever
Tip
Detect the electrostatic force
between the sample and the
probe tip.
~0.1 nm Surface Can be used to manipulate
atoms on the sample
surface.

7.  It is a microscope that produces an image by using an
electron beam that scans the surface of a specimen inside a
vacuum chamber.
What can we study in a SEM?
 Topography and morphology
 Chemistry
 Crystallography
 Orientation of grains
 In-situ experiments:
 Reactions with atmosphere
 Effects of temperature
“Easy” sample
preparation!!
“Big” samples!

8. AFM Cantilever Tip Ant Head Blood Cells
Diamond Thin Film
(Numerous Multifaceted Micro-
crystals)
Microstructure of a plain carbon
steel that contains 0.44 wt% of
carbon
Calcium Phosphate
Crystal

9. The instrument in brief
Nicks.ksu.edu/equipment/sem.html

10.  The SEM uses electrons instead of light to form an
image.
 A beam of electrons is produced at the top of the
microscope by heating of a metallic filament.
 The electron beam follows a vertical path through
the column of the microscope. It makes its way through
electromagnetic lenses which focus and direct the
beam down towards the sample.
 Once it hits the sample, other electrons
( backscattered or secondary ) are ejected from the
sample. Detectors collect the secondary or
backscattered electrons, and convert them to a signal
that is sent to a viewing screen similar to the one in an
ordinary television, producing an image.

12.  Best resolution that can be obtained: size of the
electron spot on the sample surface
 The introduction of FEG has dramatically improved the
resolution of SEM’s
 The volume from which the signal electrons are
formed defines the resolution
 SE image has higher resolution than a BSE image
 Scanning speed:
 a weak signal requires slow speed to improve signal-to-
noise ratio
 when doing a slow scan drift in the electron beam can affect
the accuracy of the analysis

13. References
 Fundamentals of materials Science and Engineering – William D. Callister
 Physical Metallurgy – Robert W. Cahn
 Physical Metallurgy and Advanced Materials – R. E. Smallman
 Physical Metallurgy Principles – Robert E. Reedhill
 http://en.wikipedia.org/scanning_electron_microscope

14. Thank You