1. BY GAJENDRA KUMAR ID- 2011uit1721

2. 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.

3. 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.

4. PRINCIPLE

5. SEM DIAGRAM

6. 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

7. 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.

9. Interaction of Electron with sample  Elastic interactions- No electron collision so no energy loss.  Inelastic interactions Collision of electrons and energy loss.

10. Interaction of Electron with sample E collisionscatteringAuger effect

11. SEM SIGNALS

12. Detectors Secondary electrons: Everhart-Thornley Detector Backscattered electrons: Solid State Detector X-rays: Energy dispersive spectrometer (EDS)

13. SEM WORKING  http://www.youtube.com/watch?v=bfSp8r- YRw0 http://www.youtube.com/watch?v=bfSp8r- YRw0

14. APPLICATIONS  Topography and morphology  Chemistry  Crystallography  Orientation of grains  In-situ experiments:  Reactions with atmosphere  Effects of temperature

15. Topography and morphology

16. Chemistry Fe Ce Sr

17. In-situ imaging  oxidation of steel at high temperatures 800 °C, pH 2 O = 667 Pa Formation of Cr 2 O 3 2 min 10 min 90 min

18. Results

19. SEM Results: 30 nm crystalline gg Eleme nt Weight % Atomic % Ti45.0850.15 Ni54.9249.85 Totals100.00  The compositions are of 50.15 at.% Ti– 49.85 at.% Ni. A few particles of different sizes have been observed in this sample.

20. Limitations Big samples Liquid samples Insulators (Usage after experiment) Very high vacuum Vibration free Large space Morphology Modification