Answer :
Final Answer:
Ray diagrams help visualize how electrons travel through an electron microscope. Here are two key properties demonstrated using ray diagrams:
Single Lens System: Electrons scattered at the same Bragg angle converge to the same point in the back focal plane, regardless of their origin within the sample.
Two Lens System: Electrons originating from the same point in the sample will be focused to the same point in the image plane, even if they initially veer off the optic axis.
Explanation:
Understanding how electrons travel through an electron microscope is crucial for image formation. Ray diagrams provide a simplified illustration of this process. This presentation will explore two key concepts using ray diagrams:
Behavior in a Single Lens System: We will see how electrons scattered at the same Bragg angle converge to a specific point, regardless of their origin within the sample.
Behavior in a Two Lens System: We will demonstrate how electrons originating from the same point in the sample are focused to the same point in the image plane, even if they initially deviate from the straight path.
Speaker Notes
In electron microscopy, understanding how electrons travel through the instrument is crucial for image formation. This presentation will use ray diagrams to illustrate two key properties of electron microscopes:
Single Lens System: In a one-lens system, electrons scattered at the same Bragg angle converge to the same point in the back focal plane, regardless of their origin within the sample.
Two Lens System: In a two-lens system, electrons originating from the same point in the sample will be focused to the same point in the image plane, even if they initially veer off the optic axis.
Slide 2
Single Lens System
Parallel electron beams are incident on a sample.
Electrons interact with the sample and scatter at various angles.
Electrons scattered at the same Bragg angle (θ) travel in specific directions.
A single convex lens focuses these diffracted electrons.
Electrons scattered with the same Bragg angle converge to a single point in the back focal plane, regardless of their origin within the sample.
Speaker Notes
This ray diagram depicts a one-lens system. Parallel electron beams strike the sample. Some electrons scatter elastically at the same Bragg angle (θ). These diffracted electrons travel in specific directions and are then focused by a convex lens. The key takeaway is that electrons scattered at the same Bragg angle converge to the same point in the back focal plane, irrespective of their initial location within the sample. This property allows the microscope to collect information about the sample's crystal structure from various regions.
Slide 3
Two Lens System
Parallel electron beams are incident on a sample.
Electrons from a specific point (P) in the sample scatter in various directions.
Some scattered electrons initially deviate from the optic axis.
A condenser lens collimates the electrons, bringing them closer to parallelism.
An objective lens focuses the electrons onto the image plane.
Electrons originating from the same point (P) converge to a single point in the image plane, even if they initially deviated from the optic axis.
Speaker Notes
This ray diagram shows a two-lens system, which is more common in electron microscopes. Here, parallel electron beams strike a sample point (P). Electrons scatter in various directions, and some might initially veer off the optic axis. The condenser lens collimates these scattered electrons, bringing them closer to parallel paths. Finally, the objective lens focuses the electrons onto the image plane. The important concept here is that electrons originating from the same point (P) in the sample will be focused to the same point in the image plane on the detector, even if they initially deviated from the straight path. This principle allows the microscope to build a high-resolution image by combining information from electrons originating from various points in the sample.
