FIELD EMISSION MICROSCOPY 



5. Bartz, G., Weissenberg, G., and Wiskott, 



D., "Radex Rundschau," Heft %, p. 163 

 (1956). 



6. Bartz, G., AND Weissenberg, G., .Va^wrmss., 



44, 229 (1957). 



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(1958). 



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252S (1959). 



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(1959). 

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(1958). 



12. "Encyclopedia of Physics" (Springer Verlag, 



Berlin, 1956), Vol. 34, pp. 565 and 585; H. 

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13. Wiskott, Det.mar, Optik, 13, 403 (1956); 13, 



481 (1956). 



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A. Recknagel, Z. Physik., 104, 381 (1937) 

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 R. Orthuber, Z. angew. Phys., 1, 79 (1948). 



Ludwig Mayer 



Field emission microscopy 



The basic purpose of microscopy is to pro- 

 duce a detailed enlarged image of the speci- 

 men. The final objective must be to reveal 

 the arrangement of the individual atoms as 

 the finest building stones of matter. Of all 

 presently known microscopic devices the 

 field emission microscope has come nearest 

 to that goal. In the form of the field electron 

 microscope it is able to show the presence 

 and behavior of monoatomic layers on speci- 

 men surfaces, and in the form of the recent 

 field ion microscope it has made visible the 

 individual atoms that constitute the surface 

 of a solid. 



The field electron microscope was invented 

 by Miiller (1) in 1936. He had observed that 

 at high temperatures surface migration on a 

 clean metal point tends to produce a per- 

 fectly rounded nearly hemispherical tip 

 which is smooth almost down to the lattice 

 steps of atomic dimensions. Such a tip is 

 placed as a cathode opposite a fluorescent 

 screen on anode potential. If the apphed 

 voltage is high enough to produce a field of 

 about 40 million volts per centimeter at the 

 cathode, electrons are emitted which travel 

 on essentially radial trajectories toward the 

 screen. There they display an electron image 

 of the emitter tip at a magnification approxi- 



EVAPORATOR 



ANODE 



\ Oy SCREEN 



TO PUMP 



Fig. 1. Schematic diagram of field electron mi- 

 croscope, and of highly enlarged electron emitting 

 tip section at upper left. 



mately equal to the ratio of tip-screen dis- 

 tance and tip radius. Tj^pical data are 2000 

 A for the tip radius, 10 cm for the tip screen 

 distance, a voltage of 4000 volts, the image 

 current in the microampere range, and the 

 magnification 500,000 X. The observation is 

 done visually or by photography of the 

 screen. The image brightness is sufficient for 

 taking motion pictures. 



Theory of Field Emission 



The mechanism of field emission is under- 

 stood by using the concepts of quantum me- 



325 



