Radio age research, manufacturing, communications, broadcasting, television (1941)

Electron Microscope Aduances ( rout iinif il ffiini jiiiili- 17 ) a very thin positive of the original surface. This positive was mounted on the normal specimen screen and placed in the microscope for study. This procedure was lengthy and com))licated but produced excellent results. It was considerably im- proved by the so called Formvar replica method wherein the surface to be studied was merely dipped into a very dilute Formvar solution, stripped from the specimen and placed in the microscope for study. This simplified the process and gave good results. One of the decided ad- vantages was the extreme strength of the film. Of recent date, a new method has been developed wherein polystyrene and silica have been utilized to form a silica replica of the surface to be studied. This process, which is as complicated as the former silver collodion method, has shown great advantage in con- trast. This latter process, when photographed stereoscopically, has given remarkably good results in surface structures of all types and may well result in great new devel- opments relating to surface studies. It will definitely permit the inves- tigator to carry his work into realms far beyond that of the ordi- nai\v microscope not only in metals, but other bulk materials as glass, ceramics, etc. The most interesting application of the replica process has been the u.se of the Formvar process for copying diflfraction grating, the copy in turn being accurately cal- ibrated by light of known wave length and then placed in the elec- tron microscope. The i-esulting micrographs are then used as a standard for calibration of the magnification of the instrument. Such calibrations are easily obtain- able within 2 per cent, which is far beyond accuracy ever before ob- tained in microscope calibration. By far the most difficult study with the electron microscope has been that of the thin sections. Even though the instrument has a depth of focus of ten or more microns, its Microscope Users Users of the RCA Electron Microscope follow, in the or- der in which the instruments have been delivered: 1. American Cyanamid Com- pany. 2. University of Michi- gan. '■!. Institute of Paper Chemistry. 4. University of Il- linois. ."). United States Bureau of Standards, (i. Massachusetts Institute of Technology. 7. A large Eastern Corporation. 8. Inter-Chemical Corporation. 9. Aluminum Corporation of Amer- ica. 10. A Midwestern Chemi- cal Corporation. 11. General Electric Company. 12. Eli Lilly & Company. 1.'5. Duke Univer- sity Hospital. 14. University of Pennsylvania, Johnson Founda- tion. 15. Celanese Corporation. 16. University of Pittsburgh. 17. Export to England. 18. RCA Laboratories, Princeton. 19. Ex- port to England. 20. Monsanto Chemical Company. 21. Export to England. 22. Mt. Sinai Hos- pital. New York. 23. A Chemi- cal Corporation. 24. Export to England. 25. Export to Eng- land. 26. B. F. Goodrich Com- pany. 27. Carnegie Institute of Technology. 28. Export to England. " 29. Export to Eng- land. 30. Republic of Guatemala 31. University of California. ."2. Standard Oil Company of New Jersey. 33. United States Rubber Company. 34. A large Eastern University. 3."). West- inghouse Electric and Manufac- turing Company. 36. Illinois Institute of Technology. 37. Hercules Powder Company. 38. University of Missouri. 39. Ex- port. 40. National Naval Medi- cal Center. 41. United States Naval Research Laboratories. 42. A large Eastern University. 43. Export. 44. United States iJepartment of Agriculture. 45. Goodyear Tire and Rubber Com- pany. 46. New Jersey Zinc Company. penetrating power operating at 60 kv. is less than one micron (1/25,- 000 inches). This imposes a severe restriction upon the thickness of the specimen to be studied, at the same time adding considerable com- |)lications in its preparation. Pres- ent methods of slicing thin sections, such as the microtome have been limited to a minimum thickness of one micron or more, which is be- yond the maximum thickness which the instrument is able to penetrate at normal voltages of 60,000 volts or less. This has been increased by building an electron microscope that has been adapted for use with high voltages up to 300,000 volts. The penetration of matter by the electrons increases rapidly with their kinetic energy, consequently the higher voltage permits resolv- ing details in larger objects. The high voltage instrument is not prac- tical for the smaller laboratories so that other means had to be found for the study of thin sections. The only answer, therefore, was to find methods of producing thinner sec- tions. This has been accomplished by mechanical improvement of the microtome. Further improvement has resulted by advances in the method of supporting the specimen to be cut, such as the latest method of using a special resin. Other methods are being improved rapidly to the point where the electron microscope will soon be as busily engaged in the field of thin sections as in other work. The microscope was designed to fulfill all of the needs of microscopy where depth of focus and higher resolving power were the prerequis- ites. These factors gave us size, shape and distribution of materials under observation. With the avail- able power supply and lenses built into the machine, it was only a small step further to designing an attachment known as the electron diffraction unit permitting the study of the crystal structure and chemistry of the surface of par- ticles which increased the useful- ness of the instrument many times. Recently, there was formed a so- ciety called The National Confer- ence on Electron Microscopy for the purpose of discussing and exchang- ing ideas on application and tech- niques along with the accomplish- ments of the electron microscope, to further this new science and art which is now growing at an amaz- ing rate. The Blue Network finished its first year "in the black," being the first network to make a profit in its first year of operation. 3 0 RADIO AGE