1008 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



Becker, J. A.,^ and C. D. Hartman^ 

 Field Emission Microscope and Flash Filament Techniques for the 

 Study of Structure and Adsorption on Metal Surfaces, J. Phys. 

 Chem., 57, pp. 153-159, Feb., 1953 (Monograph 2073). 



With field emission electron microscopes one can see the structure of the 

 surface of a single crystal at the tip of a metal "point." The magnification is 

 about 10« and the resolution about 20 X lO-^ cm. At 2800°K, the surface of 

 W point is hemispherical. Only the 110, HI and 100 regions consist of small 

 flat planes. In fields of 50 million volts /cm. and 1200°K. these planes enlarge. 

 The edges of the planes are seen to be in violent agitation. Hence surface atoms 

 are mobile at temperatures above one-third of the melting point. Ba atoms 

 show surface mobihty at 400°K. on the 110 and at 800°K. on the 100 planes. 

 With the flash filament technique one can measure the rate at which A'2 is 

 adsorbed on & W ribbon at low pressures. After A^2 has been absorbed for 

 minutes at a low temperature, the ribbon is flashed at 2300°K. The sudden 

 rise of pressure is recorded with an ion gage and measures 6, the layers ad- 

 sorbed. From a family of 6 versus time curves one calculates s, the sticking 

 probability. For T = 300°K., s = 0.55 from ^ = to 1.0. Then s decreases 

 from 0.55 to about 4 X 10""* for d = 2.0. These data yield an activation energy 

 for the conversion of a molecule to two adatoms of about 100 cal./g. mole for 

 d = to 1.0 and 5000 cal./g. mole at = 2.0. Other experiments yield 100,000 

 cal./g. mole for the heat of adsorption of 2 adatoms. The heat of adsorption 

 of molecules is much smaller. 



BOZORTH, R. M.,^ AND R. W. HAMMING^ 



Measurement of Magnetostriction in Single Crystals, Phys. Rev., 

 89, pp. 865-869, Feb. 15, 1953 (Monograph 2074). 



A simplified procedure is given for determing the five magnetostriction con- 

 stants of a single crystal of a ferromagnetic cubic crystal. The crystal is cut 

 as a disk parallel to a (HO) plane, and strain gauges are cemented to the sur- 

 faces to measure strains in (001) and (HI) directions. A magnetic field suffi- 

 cient for saturation is oriented in 10° steps at various angles to the (001) 

 direction, and magnetostriction is measured over a 90° range for each gauge. 

 Each of the 18 data is then multiplied by suitable numbers, obtained by in- 

 version of the strain matrix, to give the constants hi . . . h^ . The method is 

 applied to a crystal of a 78 per cent nickel-iron alloy to determine the magne- 

 tostriction a.ssociated with spontaneous magnetization in the (111) direction: 

 Xlll = 2hi/3 -h 2/15/9, a quantity important in the "Permalloy problem." 

 The constants are also determined for a single crystal of nickel. 



BozoRTH, R. M.,^ AND J. G. Walker^ 



Magnetic Crystal Anisotropy and Magnetostriction of Iron-Nickel 

 AUoys, Phys. Rev., 89, pp. 624-628, Feb. 1, 1953 (Monograph 2076). 



* Bell Telephone Laboratories, Inc. 



