Chapter 7
Using Metal Atoms and Molecular High-Temperature Species in New Materials Synthesis Apparatus and Techniques
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: November 24, 1987 | doi: 10.1021/bk-1987-0357.ch007
Mark P . Andrews A T & T Bell Laboratories, Murray Hill, N J 07974
This article describes recent advances in the area of preparative scale vacuum evaporation technology which have greatly extended the range of application of free transition metal atoms and molecular high tem perature species for chemical synthesis. These advances include (1) the development of liquid nitrogen-cooled electron beam furnaces for chemical compound synthesis in cooled, liquid organic sol vents; (2) the use of large cooling capacity helium gas cryostats for synthesis under quench condensed conditions at temperatures below 20 K; (3) techniques and apparatus for using photoexcited metal atoms and molecular species for preparative scale synthesis of organometallic compounds; (4) and procedures for examining the microscopic events leading to chemical reactivity and stability which are important in designing large-scale reactions. Fundamentals of design, principles of operation, reactant and product manipulation, quantification, and applications for new materials synthesis are elaborated.
Technology e v o l v e s d y n a m i c a l l y through t h e development o f new o r improved m a t e r i a l s , which i n t u r n permit t h e c r e a t i o n o f new t e c h nologies. Successful technology i s u s u a l l y c r u c i a l l y l i n k e d t o l e a d e r s h i p i n m a t e r i a l s s c i e n c e where advances o f t e n a r i s e out o f the c l o s e c o l l a b o r a t i o n o f p h y s i c i s t s , chemists and e n g i n e e r s . The c h e m i s t r y o f substances a v a i l a b l e f o r use as m a t e r i a l s c o n t i n u e s t o d e v e l o p a t t h e c o n f l u e n c e o f assessed p h y s i c a l p r o p e r t i e s , c h e m i c a l
0097-6156/87/0357-015S$09.00/0 © 1987 American Chemical Society
In Experimental Organometallic Chemistry; Wayda, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: November 24, 1987 | doi: 10.1021/bk-1987-0357.ch007
7.
ANDREWS
Using Metal Atoms & Molecular High-Temperature Species 159
r e a c t i v i t y , end use ( i n m a t e r i a l s s c i e n c e and d e v i c e f a b r i c a t i o n ) , and advances i n s y n t h e t i c t e c h n i q u e s . Among these s y n t h e t i c t e c h n i q u e s are those which u t i l i z e atomic or m o l e c u l a r vapors generated i n a vacuum and condensed at a c o l d s u r f a c e where p r o d u c t s may be formed and i s o l a t e d . T h i s i s the p r i n c i p l e o f some o f the t h i n f i l m t e c h n o l o g i e s - i t i s a l s o the elementary p r i n c i p l e behind the p r e sent day use of f r e e atoms of the t r a n s i t i o n m e t a l s , l a n t h a n o i d s , and a c t i n o i d s , and m o l e c u l a r h i g h temperature s p e c i e s (HTS) i n the p r e p a r a t i o n of o r g a n i c , o r g a n o m e t a l l i c , c o - o r d i n a t i o n and m e t a l c l u s t e r compounds and c a t a l y s t m a t e r i a l s . The i n t r o d u c t i o n o f the carbon-vapor r e a c t o r ( l _ ) i n i t i a t e d the use of h i g h temperature s p e c i e s f o r s y n t h e s i s . E x t e n s i o n s to the m e t a l l i c elements f o l l o w e d . ( 2 - 4 ) The r a t h e r e x t e n s i v e l i t e r a t u r e (1-12) t h a t has i s s u e d from but a s m a l l number of l a b o r a t o r i e s , r e c o g n i z e s the k i n e t i c and thermodynamic advantages of t h i s t e c h n i q u e i n p r o v i d i n g more d i r e c t or h i g h e r y i e l d r o u t e s to e x i s t i n g compounds and making a v a i l a b l e new compounds and m a t e r i a l s . The use o f atomic and m o l e c u l a r h i g h temperature s p e c i e s f o r c h e m i c a l compound s y n t h e s i s i s w e l l documented,(2-8,13,14) and t h e r e i s a p r a c t i c a l e x p o s i t i o n of techniques f o r d e a l i n g w i t h low v o l a t i l i t y compounds and r e c o v e r i n g a i r s e n s i t i v e m a t e r i a l s f o l l o w i n g t h i s chapter. A p p l i c a t i o n s of vapor s y n t h e s i s (VS) to m a t e r i a l s are r e a l l y j u s t emerging. A b r i e f overview of the s u b j e c t has been given.(12) Thus, b e s i d e s i t s u t i l i t y i n making o r g a n i c and o r g a n o m e t a l l i c compounds, vapor s y n t h e s i s has seen e x p r e s s i o n i n polymer s c i e n c e , c a t a l y s i s , c o l l o i d s y n t h e s i s , and e l e c t r o - a c t i v e m a t e r i a l s . Some examples are p r o v i d e d at the c o n c l u s i o n o f t h i s c h a p t e r . Recent d e s i g n s o p h i s t i c a t i o n i n the area of p r e p a r a t i v e s c a l e vacuum e v a p o r a t i o n technology has i n t r o d u c e d a d d i t i o n a l s y n t h e t i c f l e x i b i l i t y and g r e a t l y extended the range of a p p l i c a t i o n of vapor synthesis. These advances r e f l e c t changing requirements i n the f i e l d of vapor s y n t h e s i s , p a i r e d w i t h a c o n s c i o u s n e s s of the potent i a l f o r c o n t r i b u t i o n s to new m a t e r i a l s s y n t h e s i s . ( 1 2 ) T h i s chapter s k e t c h e s these advances i n terms of d e s i g n fundamentals, p r i n c i p l e s o f o p e r a t i o n , r e a c t a n t and product m a n i p u l a t i o n , q u a n t i f i c a t i o n and synthetic strategies. E x p e r i m e n t a l Approaches VS techniques can be d i s t i n g u i s h e d on the b a s i s of whether the r e a c t i o n v e s s e l i s s t a t i o n a r y or r o t a t a b l e . ( 2 - 6 ) The procedures are f u r t h e r d i s t i n g u i s h e d a c c o r d i n g to whether a l l vapors are condensed at low temperatures to g i v e a s o l i d , f u s i b l e f i l m ( s t a t i c VS), or whether metal atoms or HTS are d e p o s i t e d d i r e c t l y i n t o d y n a m i c a l l y mixed neat l i q u i d s , s o l u t i o n s or suspensions of s o l i d s ( l i q u i d phase VS). G i v e n the same s t a r t i n g m a t e r i a l s , the p r o d u c t s o b t a i n e d may r e f l e c t the c h o i c e of technique or procedure. Except i n the intended p r e p a r a t i o n of metal aggregates, the f a c i l e selfa s s o c i a t i o n r e a c t i o n s of the condensed vapors must be suppressed t o f a v o r atom c o - r e a c t a n t i n t e r a c t i o n s ; hence, h i g h pumping speeds are r e q u i r e d w i t h s e n s i t i v e s t r a t e g i e s f o r m i x i n g r e a g e n t s , as are e f f i c i e n t furnace and r e f r i g e r a t i o n d e s i g n s . ( 3 - 6 )
In Experimental Organometallic Chemistry; Wayda, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
160
EXPERIMENTAL ORGANOMETALLIC CHEMISTRY
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: November 24, 1987 | doi: 10.1021/bk-1987-0357.ch007
C o c o n d e n s a t i o n Methods U s i n g S t a t i c R e a c t o r s ( 4 - 7 , 1 0 ) , Background. The g l a s s or s t a i n l e s s - s t e e l r e a c t o r i s the cheapest to f a b r i c a t e and e a s i e s t to use.(4-7) A b e l l j a r v e r s i o n of such a r e a c t o r i s d e p i c t e d i n F i g u r e 1, whereas a v e r s i o n which i s s u b m e r s i b l e i n a c r y o g e n such as l i q u i d n i t r o g e n i s r e p r e s e n t e d i n the F i g u r e s i n the short a r t i c l e f o l l o w i n g t h i s chapter. V e s s e l s of 1-50-L c a p a c i t y can be manufactured to accommodate f u r n a c e s of v a r i o u s d e s i g n s , i e , r e s i s t a n c e , e l e c t r o n - b e a m , l a s e r , i n d u c t i o n , or e l e c t r i c a r c h e a t i n g , and cathode or magnetron s p u t t e r i n g . P r o c e d u r a l d e t a i l s pert a i n i n g to the s y n t h e s i s of o r g a n o m e t a l l i c compounds i n s t a t i c g l a s s r e a c t o r s are p r o v i d e d i n r e f e r e n c e s ( 6 , 1 0 and 14). Resistance heati n g i s s u i t a b l e f o r e v a p o r a t i n g Cr, Mn, Fe, Co, N i , Pd, Cu, Ag, Au, Zn, Ge, Sn, Pb, elements of groups 5 and 6, and a m u l t i t u d e of molecular species.(5-10) To reduce the sometimes deleterious e f f e c t s of thermal r a d i a t i o n from c r u c i b l e s , we have found i t advantageous to enclose them i n t a n t a l u m radiation shields. A l t e r n a t i v e l y , r e f r a c t o r y wools can be wrapped about the c r u c i b l e s , however, i n some cases p y r o l y s i s on the l a r g e s u r f a c e a r e a can prevent r e a c t i o n or c a u s e f r e e r a d i c a l p o l y m e r i z a t i o n s of alkenes.(15) In l a r g e r than m i l l i g r a m q u a n t i t i e s , T i , V and the more r e f r a c t o r y m a t e r i a l s are b e s t e v a p o r a t e d by electron beam. (13,14) In any case, f o r metals i t i s u s u a l to degas the element i n a p r e l i m i n a r y step by m e l t i n g or s u b l i m i n g . In a separate step, the metal s u r f a c e i s degassed j u s t below i t s v a p o r i z a t i o n p o i n t u n t i l a s t a b l e base p r e s s u r e i s reached w i t h o u t c o o l i n g the vacuum v e s s e l . H e a t i n g i s reduced and the cryogen i s installed. N o r m a l l y , the r e a c t i o n chamber i s i s o l a b l e from the vacuum s t a t i o n , which i s capable of s u s t a i n i n g a p r e - r e a c t i o n vacuum of
