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The overall aim of the programme is to show some of the results which may be obtained with an electron microscope and to guide the student in the interpretation of such results.
Metadata describing this Open University video programme
Module code and title: TS251, An introduction to materials
Item code: TS251; 02
First transmission date: 10-02-1973
Published: 1973
Rights Statement:
Restrictions on use:
Duration: 00:23:21
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Producer: Jim Stevenson
Contributors: Peter Chapman; Peter Swann
Publisher: BBC Open University
Keyword(s): Diffraction pattern; Dislocations; Microstructure of materials; One million volt electron microscope; Optical analogue; Stainless steel
Footage description: Peter Chapman with laser light diffraction apparatus used in Unit 1 with the addition of 2 lenses. He explains why results from X-ray diffraction are different from those achieved with the electron microscope. Sequence of shots of a piece of stainless steel being prepared as a specimen for electron microscopical inspection. Shots of the prepared specimen being placed into the electron microscope (1 million volt electron microscope at Imperial College, London). Commentary explains how the instrument works. Peter Chapman uses the laser apparatus in the studio to demonstrate the principles of electron microscopy. He places a mask into the apparatus and projects a diffraction pattern on the screen. Then, by moving the lenses, an image of the mask is projected. Chapman explains the principle involved. Shots of electron microscope at Imperial College. A diffraction pattern for the steel specimen is shown on the monitoring screen. As the focus of the lenses on the electron microscope is changed, an image of the specimen appears on the screen. P. Chapman places a more complex mask into his laser diffraction unit. The mask attempts to model a polycrystaline material. Shot of the image of the mask. Chapman moves the lens to change the image to a diffraction pattern. He then moves the specimen and observes changes in the pattern. Local changes in orientation are observed. Shots of the same technique being used with the electron microscope. Shot of a specimen image on the monitoring. screen. The specimen is moved on a horizontal plane. Shot of the diffraction pattern for the specimen. The movement is duplicated and changes in the pattern are observed. Shots of Peter Chapman with his laser electron microscope analogue. He uses it to explain how contrast arises in the electron microscope image. Chapman modifies the apparatus so that only one spot of light from the diffraction pattern can reach the screen. For each beam chosen, a different area of the specimen appears brighter on the final viewing screen. Shots of the same technique being used to achieve contrast in the image of the electron microscope. A good quality image is built up by selecting beams from the diffraction pattern. The effect on the image is shown. P. Chapman uses a ray diagram to show how crystal plane orientation and crystal dislocation effect the image in the electron microscope. The effect on the image of tilting a specimen in the electron microscope is discussed. Shots of the image of metal foil under the electron microscope. A dislocation is seen which disappears as the specimen is tilted. P. Chapman discusses the effect of tilting in electron microscopy and emphasises the difficulties in obtaining good results because of this factor. Chapman then explains what useful information can be gained from electron micrographs. He shows a micrograph of a copper specimen to aid his discussion. The specimen shows several dislocations (silicate impurities). Chapman points out that dislocations tend to aggregate around silicate particles. This has implications for the strength of the material.
Master spool number: 6HT/70740
Production number: 00525_5029
Videofinder number: 1552
Available to public: no