Molybdenum work function determined by electron emission microscopy
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o b j e c t of this work w a s t o determine the c o r r e l a t i o n b e t w e e n the e f f e c t i v e w o r k f u n c t i o n a n d c r y s t a l l o graphic orientation from polycrystalline molybdenum. A u n i q u e m e t h o d of m e a s u r i n g t h e e m i s s i o n f r o m m e t a l s a t h i g h t e m p e r a t u r e s h a s b e e n d e v e l o p e d by i n t e g r a t i n g a g u a r d e d F a r a d a y cage i n t o a t h e r m i o n i c e m i s s i o n microscope. ~ A n u m b e r of thermionic e m i s s i o n m i c r o s c o p e s h a v e b e e n d e s i g n e d a n d b u i l t i n the p a s t ,~ s o m e w i t h a F a r a d a y c a g e f o r e m i s s i o n m e a s u r e m e n t s .3-~ T h e m i c r o s c o p e h a s a r e s o l u t i o n o f 0.15 a t a m a g n i f i c a t i o n of X 1 4 0 0 . I t a l l o w s one t o e x a m i n e the f i n e g r a i n s t r u c t u r e a n d s t a b i l i t y t h r o u g h b o t h v i s u a l o b s e r v a t i o n s a n d q u a n t i t a t i v e m e a s u r e m e n t of t h e e l e c t r o n e m i s s i o n . L o w c u r r e n t s (5 x 10-1CA) c a n be m e a s u r e d w i t h t h e F a r a d a y c a g e a n d the s a m p l e c a n a c h i e v e t e m p e r a t u r e s up t o 2 3 0 0 ° K . EXPERIMENTAL
APPARATUS
Fig. 1 is an assembly drawing of the emission microscope indicating the location of the basic components which are: the emitter and heater, the X, Y, and Z traverse mechanism, lenses, screen, Faraday cage, and v a c u u m system. The microscope was modified to operate at approximately X80 magnification to accommodate the relatively large grains of the samples investigated. The Faraday cage current can be related to the sample electron current density by the following equation: do-
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w h e r e I i s t h e c u r r e n t f r o m the s a m p l e a s m e a s u r e d i n the F a r a d a y c a g e , M i s the m a g n i f i c a t i o n a t the c u r r e n t c o l l e c t i n g p l a n e , A c is t h e a r e a o f t h e h o l e in t h e c e n t e r of t h e s c r e e n a t the c o l l e c t i n g p l a n e , a n d Jo i s the emitter c u r r e n t density. Secondary effects of e l e c t r o n b e a m d e f l e c t i o n a n g l e s u p o n Jo h a v e b e e n c a l c u l a t e d a n d are negligible. F r o m Jo, t h e e f f e c t i v e w o r k f u n c t i o n ~b i s t h e n c a l c u l a t e d f r o m the w e l l - k n o w n R i c h a r d s o n - D u s h m a n e q u a t i o n , w h i c h is w r i t t e n a s DEAN L. JACOBSON, formerly Section Manager, Electro-Optical Systems, Division of Xerox Corp., Pasadena, Calif., is Member of Faculty, Mechanical Engineering Department, Arizona State University, Tempe, Ariz. ALBERT E. CAMPBELL is Department Manager, Electro-Optical Systems, Division of Xerox Corp. Manuscript submitted March 2 9 , 1971. METALLURGICAL TRANSACTIONS
Jo = A T 2 e x p [ - C p / k T ] w h e r e A h a s t h e v a l u e 120 a m p s / c m 2 K2 a n d T i s t h e e m i t t e r temperature. T h e e r r o r l i m i t for the work functions w a s d
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