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Lecture on Material Characterization: Scanning Electron Ion Prop Microscopy in Material Characterization

Jul 21, 2024

Lecture on Material Characterization: Scanning Electron Ion Prop Microscopy in Material Characterization

Introduction

  • Instructor: Deva Prata Pradhan, Associate Professor at Material Science Center, IIT Kharagpur
  • Course: NPTEL Online Certification on Material Characterization
  • Focus of Lecture:
    • Scanning Electron Microscopy
    • Scanning Ion Microscopy (Helium Ion Microscope)
    • Scanning Prop Microscopy
  • Topics Covered:
    • Basic principles
    • Different parts and functions of microscopes
    • Signal acquisition and image construction
    • Parameter variation and sample preparation
    • History of microscope development
    • Magnification and resolution

Microscopy Basics

Definition

  • Microscope: Device to view objects too small for the naked eye
  • Microscopy: Science of investigating small objects using a microscope
  • Greek Roots: "Micro" (small) + "scopion" (to look at)

Principle of Vision

  • Eyes alone are insufficient without light; light is necessary for visibility
  • Light waves (400-700 nm) may be too large to visualize smaller objects
  • Electron Microscopy: Uses electron beams with adjustable wavelengths to see smaller objects
  • Ion Microscopy: Uses ions, which penetrate less than electrons, providing superior images
  • Probe Microscopy: Uses physical probes to detect objects similar to how a blind person uses a cane

Techniques in Focus

Scanning Electron Microscopy (SEM)

  • Basic principle and parts
  • Function and signal acquisition
  • Image construction

Scanning Ion Microscopy (SIM)

  • Focused on the Helium Ion Microscope
  • Principles and parts
  • Superior images compared to SEM

Scanning Probe Microscopy (SPM)

  • Uses physical probes
  • Principles and applications

Historical Development

Timeline

  • 1590: Hans and Zacharias Janssen develop the first microscope
  • 17th Century: Galileo and Leeuwenhoek contribute to compound microscopes
    • Robert Hooke visualizes microorganisms and publishes Micrographia
  • 18th Century: Improvements in lens and magnification
  • 19th Century: Understanding of maximum resolution
  • 20th & 21st Century: Transition from light microscopes to electron and ion microscopes
    • Ion microscopes commercialized around 2007
    • Coexistence of electron and ion microscopes anticipated

Key Terms: Magnification and Resolution

Magnification

  • Ratio of image size to object size
  • High magnification without good resolution results in blurry images

Resolution

  • Closest spacing between two points seen as separate entities
  • Higher resolution means smaller minimum spacing (d_min)
  • Human Eye Resolution: 0.15 mm

Formulas and Concepts

  • Rayleigh Criterion: 胃_min = 1.22位/D
    • 胃_min: Angular resolution
    • 位: Wavelength of light
    • D: Diameter of light-gathering element
  • Aperture and Focal Length: d_min = 0.61位 / NA
    • NA: Numerical Aperture (渭sin伪)
    • Smaller 位 means better resolution; higher NA improves resolution
  • Diffraction Limit: Even perfect lenses are limited by diffraction
    • Airy disks and rings
    • Rayleigh Criterion for just-resolved points

Modern Microscope Advancements

  • Optical Microscopes: Resolution limit around 150 nm using UV light and oil immersion lenses
  • Electron Microscopes: Offer superior nanometric resolution
  • Ion Microscopes: Provide even better resolution and commercial availability since 2007

Conclusion

  • Overview of major microscopy techniques
  • Historical development and recent advancements
  • Importance of understanding magnification, resolution, and diffraction for improving image quality
  • Introduction to aberrations as a topic for the next lecture

End of Lecture

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