Electron Microscopes

We will be discussing The history of the electron microscope Two major difference between the electron microscope and light microscope How the electron microscope works. The difference between the scanning electron and transmission electron microscopes. How specimens are prepared for electrons microscopes.

SEM and TEM History In 1931 Max Knoll and Ernst Ruska built the first electron microscope prototype. (400x) In the 1930’s Manfred von Ardenne pioneered the scanning electron microscope. Siemens produced the first commercial TEM in All modern electron microscopes are based on the Ruska prototype (2 million times)

Find the 2 differences. Light Microscope Transmission Electron

Differences include… Magnification Magnify up to 2000x MaMa up to 2 million x Resolution is the minimum distance between two distinguishable objects in an image. The shorter wavelength of electrons allow them to produce images with higher resolution and magnification

How do they work?

Transmission Electron Microscope 1.Thermionic emission produces electrons. Tungsten metal is heated releasing electrons. 2. Copper coils in a vacuum tube direct the electrons toward the specimen. Electrons are deflected by air molecules. The coils are lenses that accelerate and focus electrons. 3.The electrons travel through the sample onto a fluorescent imaging screen. 4.TEM is used most often in research to examine details of cells and small organisms

How are TEM and SEM’s different?

Scanning Electron Microscope SEM produce images by detecting low energy secondary electrons from the surface of a specimen. The electron beam is rastered across a sample and detectors build an image based on the feedback from secondary electrons. (computer scanner) Purpose- Scientists have been able to examine the surface of specimens in great detail.

Preparing Samples for TEM Samples must be nm thick- (1/200 thickness of a cell) and must be able to withstand a being in a vacuum. 1. Fixed- Gluteraldehyde covalently links proteins to their neighbors. Asmium tetroxide stabilizes lipids and proteins 2. Dehydrated 3. Placed in a resin 4. Cut with a diamond knife (microtomer- machine) 5. Placed on a copper grid and covered with a carbon dust or plastic film

Review of History 1.In the 1930’s who pioneered the scanning electron microscope? 2.Which company produced the first TEM in 1939? 3.All current modern microscopes are based on whose prototype?

Differences in light microscopes and TEM 4.When you are looking at your computer screen, you know that a picture has low resolution because it doesn’t have enough ____________. 5.How many times does an electron microscope magnify specimens? 6.What feature of electrons allow them to produce images of higher resolution and magnification?

How do TEM’s work? 7. What is the name of the process that liberates electrons? 8. Why do electrons need a vacuum tube to move? 9. What is the purpose of the copper coils lenses in the TEM? 10. What is TEM used for in research?

How does a SEM work and specimen preparation 11. How do electrons produce an image in SEM? 12. How do scientists use SEM’s? 13. How thick are samples examined by a TEM? 14. Why do specimens have to be fixed, dehydrated and placed in resin in order to be viewed by TEM? 15. Name the machine that cuts the preserved specimen like a meat slicer.

Answers 1.Manfred von Ardenne 2.Siemens 3.Ruska 4.Pixels 5.2 million times 6.Shorter wavelength 7.Thermionic emission 8.Electrons are deflected by air particles 9.Copper coils focus and accelerate electrons toward the specimen 10.Scientist look at intricate details in small specimens

Answers part 2 11.Electrons raster the surface of a specimen with electrons and record feedback from secondary electrons. 12.Scientist examine the surface of small specimens 13.The specimen is nm 14.The specimen is put into a vacuum. 15. Microtome

Please examine the images at this SEM interactive website and determine what they are. sonplans/interactive/vemwindow.htmlhttp://school.discoveryeducation.com/les sonplans/interactive/vemwindow.html

Are there any questions?