scanning electron microscope
TRANSCRIPT
SCANNING ELECTRON MICROSCOPE
BYGAJENDRA KUMARID- 2011uit1721
WHAT IS SEM
It is a microscope that uses a focused electron probe to extract structural and chemical information point-by-point from a region of interest in the sample.
WHAT IS SEM
SEM is a powerful magnification tool .The high-resolution, three-dimensional images produced by SEMs provide topographical, morphological and compositional information makes them invaluable in a variety of science and industry applications.
PRINCIPLE
SEM DIAGRAM
Components of sem
• electron gun (filament)• Electron beam generation.
• electromagnetic optics• Controlling diameter of e beam.
• scan coils• Gives parralel e beam.
• sample stage• Hold sample
• detectors• Detects electronic signals
• vacuum system• computer hardware
Electromagnetic lens
A coil of wire through which current flows. Because the current flow produces a magnetic field at right angles, the field pushes inwards into the hole in the centre. This acts to shape a beam of electrons travelling in their natural spiral path down the central hole.
The condenser lens is at the top and the objective lens at the bottom. Each does a different job. The condenser lens converges the cone of the electron beam to a spot below it, before the cone flares out again and is converged back again by the objective lens and down onto the sample.
Interaction of Electron with sample
Elastic interactions- No electron collision so no energy loss.
Inelastic interactionsCollision of electrons and energy
loss.
Interaction of Electron with sample
E collision scatteringAuger effect
SEM SIGNALS
Detectors
Secondary electrons: Everhart-Thornley Detector
Backscattered electrons: Solid State Detector
X-rays: Energy dispersive spectrometer (EDS)
SEM WORKING
http://www.youtube.com/watch?v=bfSp8r-YRw0
APPLICATIONS
Topography and morphology Chemistry Crystallography Orientation of grains In-situ experiments:
Reactions with atmosphere Effects of temperature
Topography and morphology
Chemistry
Fe Ce
Sr
In-situ imaging
oxidation of steel at high temperatures
800 °C, pH2O = 667 Pa
Formation of Cr2O3
2 min 10 min 90 min
Results
SEM Results: 30 nm crystalline
g
Element
Weight%
Atomic%
Ti 45.08 50.15Ni 54.92 49.85
Totals 100.00
The compositions are of 50.15 at.% Ti–49.85 at.% Ni.
A few particles of different sizes have been observed in this sample.
Limitations
Big samplesLiquid samplesInsulators (Usage after
experiment)Very high vacuumVibration freeLarge spaceMorphology Modification