Definitions

1. Definitions Microscope - A device with a lens or series of lenses that enlarge (magnify) the appearance of an object. Does not apply to SEM. Image- Perception of an object using your eyes (vision). One can sense an object without vision (touch, etc..). Requires visible light.

2. Lens - A lens is an optical component which is used to focus beams of radiation. Lenses for light are usually made of a transparent material, whereas non-uniform electromagnetic fields are used as lens for electrons. Curved glass or mirror for Visible light convex concave Concave surface of metal (e.g. satellite dish) Radio waves

3. Concave mirror or Fresnel lens Heat Solenoid (electromagnetic fields that can be varied) Subatomic particles (electrons, protons, positrons)

4. Magnification - The ratio between image size to the object size. Can be varied by changing the distance between the object and the final lens (of the eye) or by inserting a second lens between the two. Resolution - The point at which two or more objects can be distinguished as separate individual objects.

5. History: First record of using glass lens for magnification was by Al Hazen, an Muslim scientist from what is now known as Iran, in the 10 and 11th century. He performed the bulk of his studies and work in Spain. His treatise on the colors of the sunset were translated to Latin. He contradicted Ptolemy's and Euclid's theory of vision that objects are seen by rays of light emanating from the eyes. According to Al Hazen, the rays originate from the object of vision and not in the eye. Because of his extensive research on vision, he has been considered by many as the father of modern optics. http://home.att.net/~mleary/alhazen.htm

6. Antonie van Leeuwenhoek 15th century on - Studies done with glass magnifiers to study objects in detail mostly as a curiosity by non-scientists - Antonie van Leeuwenhoek (dry goods merchant) described three shapes of bacterial cells using his simple, single lens microscope (glass bead in metal holder). Was probably influenced by Robert Hooke.

7. Instructions on making A Leeuwenhoek microscope http://www.mindspring.com/%7Ealshinn/Leeuwenhoekplans.html

8. Robert Hooke In 1665, Hooke described cork and other microorganisms in a drop of water. First to produce a book on microscopical observations. Made several modifications creating a compound microscope. Few improvements were made to the light microscope until the 19th century.

9. By mid-19th century, became evident that theoretical resolution limits of light were reached. Above a magnification of 1,500 resolution lost. The image can be magnified, but blurred (empty magnification).

10. Wavelength - the distance between peaks of the waveform In 1870, Ernst Abbe derived mathematical expression for resolution of microscope: Resolution is limited to approx. 1/2 the wavelength of illuminating source

11. Shortest visible wavelength - Blue light has a wavelength of 0.47 um. Resolution max = 0.2 um (200 nm) Cannot go beyond this even with better optics. Solution? Use illumination of shorter wavelength Antone de Broglie (1924) Theory of wave nature of electrons Hermann Busch (1924) axial magnetic fields refract electrons Electron optics

12. 1935 - Max Knoll demonstrates the theory of the scanning electron microscope 1938 - First scanning electron microscope produced by von Ardenne Knoll and Ruska 1986 Nobel Prize winners 1939 - Ruska and von Borries, working for Siemens produce the first commercially available EM

13. 1939 - First EM built in North America by James Hillier and Albert Prebus at the University of Toronto Dr. Ladd Dr. Prebus

15. Light vs Electron Microscope