1. 1. Scanning Electron Microscope IH2652- Methods and Instruments of Analysis Prof. Henry H Radamson Prepared by: Sumit Mohanty Mohamed Atwa Ahmed Al-Askalany KTH Royal Institute of Technology 1
2. 2. Agenda Introduction and Applications Environmental SEM Complementarity of SEM and AFM SEM vs. TEM 3D Imaging with SEM 2
3. 3. Introduction and Applications 3
4. 4. SEM-Structure SEM Introduction 4
5. 5. Interaction volume The generated radiation will not be detected unless it escapes from the SP. Electrons will not backscattered out of SP if they have penetrated more than a fraction of micrometers, Therefore the BS signal come from a much smaller area SEM Introduction 5
6. 6. The affect of accelerating voltage SEM Introduction 6
7. 7. Biology Lung tissue Embryo limbs Nria Cortadellas, Eva Fernndez, and Almudena Garcia;Biomedical and Biological Applications of Scanning Electron Microscopy, Handbook of instrumental techniques. RBCs: Chris Toumey, Nature Nanotechnology 6, 191193 (2011) doi:10.1038/nnano.2011.55 Parasites Red blood cells SEM Applications 7
8. 8. Fig.1 Fig.1: S. Zhou et al. / Biomaterials 24 (2003) 35633570 Fig.2: D.R. Chen et al. / Polymer Degradation and Stability 67 (2000) 455-459 Fig.2 a b SEM Applications 8
9. 9. Environmental SEM 9
10. 10. Gaseous Electron Microscopy Conventional and Auger SEM Require Vacuum (Usually in the range of 10-5 mBar) Sample Charging Sample Bursting http://www.ammrf.org.au/myscope/images/sem/pump-evac.png 10
11. 11. Gaseous SEM (Environmental SEM) Works in: Air Low Vacuum High Pressure Variable Pressure Gases Used Include: N2 O2 Ar, He, H2O... http://www.phy.cam.ac.uk/research/research -groups-images/bss/images/esem.jpg 11
12. 12. GSEM Image Quality Factors Image quality and microanalysis results depend on: The size of the electron beam The accelerating voltage Sample nature Pressure in different parts of the chamber Type of gas 12
13. 13. Use of Gas in Imaging Gas atoms or molecules interact with the primary electron beam and produce positive ions. Positive ions neutralize the negative charge on the surface of the insulating sample Gas atoms can also aid the imaging process through avalanche electron generation http://www.azom.com/work/Environm ental%20Scanning%20Electron%20Micr oscopy%20- %20ESEM_files/image004.gif 13
14. 14. Typical Operation Parameters Wet Mode (Condensed Water) Electron Beam Energy: 20 kV Emission Current: 49 A. SE Detection Method: Gaseous detector Working distance: 19 mm (Compensates for Skirting Beam) V. Kazmiruk -Scanning Electron Microscopy -Intech (2012) 14
15. 15. Gaseous Detector https://en.wikipedia.org/wiki/Gaseous_detection _device#mediaviewer/File:GDD_principle.svg Probe electrons ionize gas atoms/molecules Electric field pulls secondary and backscattered electrons towards plate electrodes Electrons are multiplied in collisions with gas atoms/molecules Location and energy of electrons used to form image 15
16. 16. Skirting Beam Phenomenon PLA1: Final Aperture Z: Distance which electrons scatter : Solid angle of scattering Sf: Scattered fraction of electrons (Skirt) UnSf: Unscattered fraction of electrons rs+dr: Scattering radius V. Kazmiruk -Scanning Electron Microscopy - Intech (2012) 16
17. 17. Skirting Phenomenon (Continued) V. Kazmiruk -Scanning Electron Microscopy -Intech (2012) rs is the skirt radius Z the gas atomic number E the incident beam energy P is the pressure T the temperature GPL the gas path length 17
18. 18. Sample Image Plant material: Insulating Fragile White circles are Stomata, pores for gas-exchange Imaged using the wet mode parameters mentioned before V. Kazmiruk -Scanning Electron Microscopy - Intech (2012) 18
19. 19. Complementary techniques AFM and SEM 1. Surface Structure 2. Composition 3. Environment 19
20. 20. Surface structure Principle difference process vertical changes in topography Atomically smooth surfaces AFM Vertical resolution of