Plasma Polymerization - American Chemical Society

14 Thermal Modification of Plasma-Polymerized Organosilazane T h i n Films

Downloaded by UNIV OF CALIFORNIA SANTA CRUZ on October 24, 2014 | http://pubs.acs.org Publication Date: September 24, 1979 | doi: 10.1021/bk-1979-0108.ch014

A. M. WROBEL and M. KRYSZEWSKI Polish Academy of Sciences, Centre of Molecular Studies, Boczna 5, 90-362 Lodz, Poland

C o n s i d e r a t i o n o f the s t r u c t u r e o f o r g a n o s i l i c o n compounds focussed our a t t e n t i o n on the p o s s i b i l i t y o f producing plasma polymer f i l m s with p a r t i c u l a r y i n t e r e s t i n g thermal p r o p e r t i e s from organosilazanes. The high thermal s t a b i l i t y of these f i l m s [ l , 2 j and t h e i r r e l a t i v e l y low content o f organic s t r u c t u r e [ 3 j , suggested that they may be transformed by an appropriate pyrol y t i c process i n t o new m a t e r i a l s of almost completely i n o r g a n i c s t r u c t u r e and thus, of s u p e r i o r thermal s t a b i l i t y . The present paper r e p o r t s r e s u l t s of thermally produced m o d i f i c a t i o n s i n the s t r u c t u r e and p r o p e r t i e s o f polymer f i l m s formed by plasma p o l y m e r i z a t i o n of h e x a m e t h y l c y c l o t r i s i l a z a n e ( I ) . Me 2

HN Me s'i

NH SiMe

0

2

0

2

W I

Experimental H e x a m e t h y l c y c l o t r i s i l a z a n e (HMCTS) monomer, product o f PCR Research Chemicals Inc., was p u r i f i e d by r e c t i f i c a t i o n i n vacuum. Plasma polymerizations were c a r r i e d out i n an apparatus des c r i b e d p r e v i o u s l y [ 4 ] . T h i s apparatus i n c o r p o r a t e s a vacuum b e l l j a r c o n t a i n i n g two p a r a l l e l c i r c u l a r e l e c t r o d e s spaced 3 cm apart, each having a s u r f a c e area of 40 cm . Polymer f i l m s were depo s i t e d i n a 20 kHz glow discharge on 0 . 1 mm t h i c k s t a i n l e s s s t e e l tape placed on the lower e l e c t r o d e . Polymer d e p o s i t i o n s were performed under the f o l l o w i n g constant c o n d i t i o n s : current den s i t y , j = 1 mA/cm ; monomer vapour pressure, ρ = 0 . 3 Torr; and discharge d u r a t i o n , t = 20 s. _ Polymer f i l m s were modified by vacuum p y r o l y s i s a t 10 Torr and at temperatures o f 600 and 800 C. I n f r a r e d s p e c t r a of polymer f i l m s were obtained on a P e r k i n 2

2

5

0-8412-0510-8/79/47-108-237$05.00/0 © 1979 American C h e m i c a l Society

In Plasma Polymerization; Shen, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


238

PLASMA

POLYMERIZATION

Elmer, Model 457, spectrophotometer using the attenuated t o t a l r e f l e c t i o n (ATR) technique. R e s u l t s and D i s c u s s i o n E f f e c t of P y r o l y s i s on the Chemical S t r u c t u r e of Polymer F i l m s . In order to study the e f f e c t o f thermal m o d i f i c a t i o n on chemical s t r u c t u r e of plasma-polymerized h e x a m e t h y l c y c l o t r i s i l a zane (PP-HMCTS), an i n f r a r e d a n a l y s i s of the polymer f i l m was c a r r i e d out a f t e r d i f f e r e n t durations of g y r o l y s i s . IR s p e c t r a of polymer f i l m s p y r o l y s e d at 600 and 800 C are shown i n F i g s l a and b, r e s p e c t i v e l y . The spectrum of untreated polymer f i l m ( F i g . l a A) shows s t r o n g a b s o r p t i o n bands at 1160 and 890 cm" which o r i g i n a t e from Si-NH-Si bonds, and correspond to 6(NH) and v ( S i N S i ) v i b r a t i o n s , r e s p e c t i v e l y [j>]. The presence of methyl groups attached to s i l i c o n i s demonstrated by a s t r o n g , sharp abs o r p t i o n band at 12^0 cm" , due to ^ ( C H ^ ) v i b r a t i o n s , and by abs o r p t i o n a t 780 cm" corresponding to v ( S i C ) and p(CH ) v i b r a t i o n s . The unmodified polymer spectrum ( F i g . l a A) a l s o e x h i b i t s new bands at 2120 and 1020 cm" , absent i n the monomer spectrum. The former band (at 2120 cm" ) corresponds to v(SiH) v i b r a t i o n s . These groups are formed by the fragmentation of the monomer molecules l e a d i n g to the a b s t r a c t i o n of methyls from s i l i c o m atoms [ 3 ] . The second band (at 1020 cm" ) i s t y p i c a l of methylene groups between two s i l i c o n atoms, and i s assigned to u)(CH ) v i b r a t i o n s [ 5 ] . The presence of these groups i n the polymer i n d i cates c r o s s l i n k i n g through the formation of methylene and ethylene linkages between s i l i c o n atoms. The s p e c t r a i n F i g . l a c l e a r l y show that p y r o l y s i s leads to s i g n i f i c a n t changes i n the s t r u c t u r e of PP-HMCTS. For example, the absorptions at 2120 (SiH), 1250 ( S i C H ) , and 1160 cm" (NH) decay markedly w i t h i n c r e a s i n g p y r o l y s i s time. At h i g h e r temperature ( F i g . l b ) these changes proceed c o n s i d e r a b l y f a s t e r and l e a d to a polymer f i l m of almost i n o r g a n i c s t r u c t u r e . A s t r o n g , broad a b s o r p t i o n band at 1000 - 800 cm" ( F i g . l b E) i s very s i m i l a r to that observed i n the spectrum of s i l i c o n n i t r i d e [ 6 , 7 , £ ] . Hence, one may conclude that thermally modified f i l m i s e n r i c h e d i n s i l i c o n - n i t r o g e n inorganic linkages. Analogous heat treatment was c a r r i e d out a l s o on f i l m s dep o s i t e d from a mixture of monomer and ammonia; equal p a r t i a l pressures of 0.3 T o r r were u t i l i z e d and the same discharge parameters as described p r e v i o u s l y a p p l i e d here a l s o . Our e a r l i e r s t u d i e s [2] had shown that a d d i t i o n of ammonia to HMCTS vapour improves the thermal s t a b i l i t y of r e s u l t i n g polymer f i l m s , and t h e i r adhesion to metal s u b s t r a t e s . I t was found a l s o that pyrol y s i s of these f i l m s induces s i m i l a r changes i n the IR s p e c t r a as those i n F i g . 1. However, these p y r o l y s e d f i l m s were found to have a more i n t e n s e and broader a b s o r p t i o n band w i t h i n the 1000 800 cm" range ( F i g . 2). The i n t e n s i f i c a t i o n of a b s o r p t i o n i n t h i s r e g i o n was f e l t to be due to a more s a t u r a t e d s t r u c t u r e of the p y r o l y s i s product, caused by Si-N bonds, a c c o r d i n g to the p r e v i o u s l y reported [2] h i g h e r c o n c e n t r a t i o n of Si-NH-Si l i n k a g e s i n t h i s l a t t e r type of polymer f i l m s . 1

a g

1

3

1

1

1

2

1

3

1

1



Figure

V j

1.

Infrared

ι 600

durations

1

of pyrolysis

1

in

ι—' » « ' " ' « 2300 2000 1200 1000 800 WAVENUMBER (cm" )

ATR spectra of PP-HMCTS film after different vacuum at: (a) 600°C and (b) 800°C.

• • • 2300 2000 1200 1000 800 WAVENUMBER (cm-)


1

600

240

PLASMA

POLYMERIZATION

K i n e t i c s of Thermal Decomposition. In order to examine the k i n e t i c s of thermal decomposition r e a c t i o n s , r e l a t i v e changes i n IR a b s o r p t i o n i n t e n s i t y at 2120, 1250 and 1160 cm" ( F i g . 1 ) , cor responding to SiH, S i C H and NH groups, r e s p e c t i v e l y , were s t u d i e d as a f u n c t i o n of p y r o l y s i s time. Absorption data were evaluated as the r a t i o of areas under the peaks, A/A ; A being the i n i t i a l peak area, and A the area a f t e r a given time 8 f p y r o l y s i s . The r a t i o A/A f o r SiH, S i C H and NH groups i s shown as a f u n c t i o n of p y r o l y s i s time at 600 and 800°C i n F i g s 3a and b, r e s p e c t i v e l y . The r e l a t i v e c o n c e n t r a t i o n of these groups i s seen to decrease with i n c r e a s i n g p y r o l y s i s time. However, a l a r g e i n c r e a s e i n the concentration o f SiH groups a t the e a r l y stages of p y r o l y s i s i s a l s o noted. This i s presumably due to r a p i d recombination of ato mic hydrogen, e v o l v i n g from NH groups, with s i l i c o n r a d i c a l s formed through the s c i s s i o n of Si-C bonds. The decay of NH groups proceeds very r a p i d l y as a r e s u l t of hydrogen a b s t r a c t i o n ; new S i N bonds with t e r t i a r y n i t r o g e n are subsequently formed according to the f o l l o w i n g s i m p l i f i e d scheme: 1

3


Q

3

Si /

N

-> X

Me

SiMe

+

-Me

(1)

-> \ ·

+

-Η

(2)

x

\-H /

\L' Me

/

+

·Ν'

X

->

X

Me-

+

-H

X

Si—N^ /

->

(3)

CH

(4) h

From r e a c t i o n (4) we might expect to f i n d methane i n the gaseous r e s i d u e f o l l o w i n g p y r o l y s i s . Gas-chromatographic a n a l y s i s of the gaseous p y r o l y s a t e has indeed shown methane to be the main com ponent [ 3 ] . This process g r a d u a l l y e l i m i n a t e s the organic s t r u c ture from the polymer f i l m , and the remaining s o l i d acquires an even i n c r e a s i n g i n o r g a n i c c h a r a c t e r . To e s t a b l i s h the order of thermal decomposition r e a c t i o n s , the k i n e t i c data were v e r i f i e d using the f i r s t order r e a c t i o n equation: - f = k C

(5)

where c o n c e n t r a t i o n may be expressed as C = A/A ; f o l l o w i n g i n t e g r a t i o n , equation (5) becomes - In = kt (6) A P l o t s of £ n ( A / A ) as a f u n c t i o n of p y r o l y s i s time (t) f o r the decomposition of SiH, S i C H and NH groups are l i n e a r at both tem peratures (Figs 4a and b ) , i n d i c a t i n g that the r e a c t i o n s are indeed f i r s t o r d e r . For the case of S i C H ( F i g . 4a), thermal s c i s s i o n of Si-C bonds appears to take p l a c e i n two stages. This may be due to the presence of some S i ( C H ) groups i n the polymer, remnants Q

Q

3

3

3

2



14.

WRÔBEL AND KRYSZEWSKI

0

1600

1400

Thermal

241

Modification

1200 1000 800 WAVENUMBER (cm" )

600

400

1

Figure

2.

Infrared ATR spectrum of PP-HMCTS film deposited in the of ammonia after 45-min pyrolysis in vacuum at 800°C

PYROLYSIS TIME (min.) Figure

S.

Relative

presence

PYROLYSIS TIME (min )

intensity of IR absorption, A/A , as a function time at: (a) 600°C and (b) 800°C. 0

of

pyrolysis



Figure

10

4.

20

0

3

80 90

100

3

0.01 0

10

20

30

40

for: (a)

PYROLYSIS TIME (min.)

Plots of In (A/A ) as a function of pyrolysis time at different temperatures SiH, SiCH and (b) NH groups. (O) SiH, (A) SiCH .

30 40 50 60 70 PYROLYSIS TIME (min.)


50

H > H O 2

S3

Ο F κ! M

>

to to

14.


Thermal

243

Modification

of the o r i g i n a l s t r u c t u r e o f the monomer. The f i r s t r e a c t i o n stage, which proceeds a t a s i g n i f i c a n t l y h i g h e r r a t e than the second, i s presumably due to a b s t r a c t i o n o f one methyl from S i ( C H ) . We note that the p y r o l y s i s time at the break p o i n t s of the S i C H curves i n F i g . 4a agrees w e l l with that determined from the maxima of the SiH curves i n F i g s 3a and b. These r e s u l t s s t r o n g l y suggest that the sharp r i s e i n the SiH curve noted i n F i g s 3a and b i s due to the higher c o n c e n t r a t i o n o f the s i l i c o n r a d i c a l s produced through Si-C bonds s c i s s i o n during the f i r s t stage of t h i s r e a c t i o n . In view o f the experimentally observed l i n e a r r e l a t i o n s h i p between £n(A/A ) and t , an Arrhenius equation has been used to determine the apparent a c t i v a t i o n i n e r g i e s f o r the p a r t i c u l a r decomposition r e a c t i o n s . We f i n d 15 kcal/mole f o r N-H, 23 kcal/mole f o r Si-Η and 31 kcal/mole f o r Si-C bonds s c i s s i o n s . These values are very approximate, s i n c e they were evaluated assuming a l i n e a r r e l a t i o n s h i p £n k = f ( l / T ) f o r the temperatures under study. As p y r o l y s e s were c a r r i e d out a t o n l y two experimental temperatures, the v a l i d i t y o f t h i s assumption could not be v e r i f i e d . The a c t i v a t i o n energy values suggest that s c i s s i o n o f N-H bonds seems to be a predominant r e a c t i o n during the p y r o l y s i s pro cess. This r e a c t i o n , according to the scheme (1-3), leads to the formation o f a h i g h l y c o r s s l i n k e d i n o r g a n i c s t r u c t u r e i n the po lymer f i l m . The k i n e t i c s of thermal decomposition were a l s o examined f o r polymer f i l m deposited from the mixture of monomer and ammonia under the plasma c o n d i t i o n s , as d e s c r i b e d e a r l i e r . The r e l a t i v e i n t e n s i t y o f IR a b s o r p t i o n , A/A , was evaluated f o r SiH, S i C H and NH groups as a f u n c t i o n o f p y r o l y s i s time at 600 C. As shown i n F i g . 5, the shape of the r e s u l t i n g curves i s s i m i l a r to that noted f o r polymer f i l m deposited without ammonia ( F i g . 3a). However, the i n i t i a l i n c r e a s e i n c o n c e n t r a t i o n o f SiH groups i s c o n s i d e r a b l y s m a l l e r and a maximum peak i n the SiH curve i s l e s s sharp than i n the e a r l i e r case ( F i g . 3a). Moreover, the SiCH^ curve r e v e a l s a more r a p i d decay o f m e t h y l - s i l i c o n groups during the i n i t i a l stage of p y r o l y s i s . The order of thermal decomposition r e a c t i o n s was e s t a b l i s h e d as p r e v i o u s l y by p l o t t i n g £n(A/A ) vs t . The r e s u l t i n g l i n e a r p l o t s , shown i n F i g s 6a and b, i n d i c a t e that decomposition of SiH, SiCH and NH groups i n polymer f i l m deposited from the mixture of monomer and ammonia a l s o proceeds by a f i r s t order r e a c t i o n me chanism. In F i g . 6, the k i n e t i c s f o r the two types of f i l m s ( i . e . polymerized w i t h and without ammonia) are compared. The i d e n t i c a l slopes of the SiH curves shown i n F i g . 6a i n d i c a t e that the same r e a c t i o n rate constants apply f o r s c i s s i o n of Si-Η bonds i n both polymers. The shape of the S i C H curves i s very s i m i l a r and d i s t i n c t o v e r l a p i n g of these curves i s observed f o r the l a t e r stages of the r e a c t i o n ( F i g . 6 a ) . This shows that s c i s s i o n of Si-C bonds during the second stage o f the r e a c t i o n proceeds at n e a r l y the same rate f o r both polymers; only i n i n i t i a l p y r o l y s i s times i s 3


3

Q

Q

3

Q

3



244

PLASMA

1.51

1

1

1

I

1

POLYMERIZATION

Γ

PYROLYSIS TIME (min.) Figure 5. Rehtive intensity of IR absorption, A/A , as a function of pyrolysis time at 600°C for PP-HMCTS film deposited in the presence of ammonia 0


In Plasma Polymerization; Shen, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979. 0

3

Figure 6. Plots of In (A/A ) as a function of pyrolysis time at 600°C for: (a) SiH, SiCH and (b) NH groups; open symbols: polymer film deposited without ammonia; full symbols: polymer film deposited in the presence of ammonia.


|g 01


246

PLASMA

POLYMERIZATION

there a d i f f e r e n c e . Here a sharper break i n the SiCHg curve i s observed f o r polymer f i l m deposited w i t h ammonia; t h i s occurs due to more r a p i d decay of SiCH^ groups, as seen from the curve shown i n F i g . 5. A d i s t i n c t break noted i n the NH curve f o r po lymer deposited with ammonia ( F i g . 6b) shows that decomposition of NH groups a l s o takes p l a c e by a two-stage r e a c t i o n . These r e s u l t s are i n a good agreement with our previous s t u d i e s [ 2 ] , which showed that ammonia under glow discharge con d i t i o n s i s a r e a c t i v e comonomer and that the p o l y m e r i z a t i o n of HMCTS i n the presence of t h i s gas produces h i g h e r c r o s s l i n k i n g of the polymer f i l m through methyl a b s t r a c t i o n from s i l i c o n atoms and the formation of Si-NH-Si l i n k a g e s . Hence, c r o s s l i n k i n g s i g n i f i c a n t l y reduces the c o n c e n t r a t i o n of S i ( C H ) groups remaining i n the polymer f i l m . This could e x p l a i n the more r a p i d decay of S i C H groups i n polymer deposited i n the presence of ammonia, as observed during the i n i t i a l p y r o l y s i s stage (Figs 5 and 6a) when an a b s t r a c t i o n of s i n g l e methyls from S i ( C H ) groups takes place. According to our e a r l i e r c o n s i d e r a t i o n s , the s m a l l e r r i s e noted i n the SiH curve ( F i g . 5 ) , i s due presumably to the lower con c e n t r a t i o n of s i l i c o n r a d i c a l s produced through s c i s s i o n of Si-C bonds during the f i r s t stage of t h i s r e a c t i o n . Furthermore, due to the g r e a t e r c o n c e n t r a t i o n o f Si-NH-Si bonds i n the polymer f i l m , c r o s s l i n k i n g v i a formation of new Si-N bonds with t e r t i a r y n i t r o g e n , according to scheme (1-3), seems to take p l a c e more r e a d i l y during p y r o l y s i s than the generation of SiH groups. In g e n e r a l , our data a t t e s t to the complexity of thermal de composition r e a c t i o n s i n the polymer f i l m . A good example of t h i s i s the apparent two-stage decomposition of NH groups i n the polymer deposited i n the presence of ammonia ( F i g . 6b). A d d i t i o n a l experimentation w i l l be r e q u i r e d to f u l l y account f o r the mechanisms i n v o l v e d i n t h i s process. P r o p e r t i e s o f thermally m o d i f i e d f i l m s . Thermally m o d i f i e d f i l m s produced i n t h i s work were found to be c o l o u r l e s s , glassy m a t e r i a l s with extremely s t r o n g adhesion to the metal s u b s t r a t e . P a s s i v a t i o n t e s t s have shown that the coated metals d i s p l a y e d ex c e l l e n t r e s i s t a n c e to c o r r o s i v e chemicals. Exposure of f i l m s to concentrated a c i d s , such as HC£, HN0 , H S0 and Η Ρ 0 f o r s e v e r a l hours had no v i s i b l e e f f e c t upon t h e i r s u r f a c e . In order to examine the e f f e c t of oxygen on the p r o p e r t i e s and chemical s t r u c t u r e of thermally m o d i f i e d f i l m s i n vacuum, these were heated i n oxygen under atmospheric pressure at a tem perature of 600°C. I t was found that even a f t e r such treatment f i l m s s t i l l e x h i b i t e d s t r o n g adhesion to the metal s u b s t r a t e , and good r e s i s t a n c e to a t t a c k by c o r r o s i v e agents. I n f r a r e d ana l y s e s of the p r e v i o u s l y m o d i f i e d f i l m s f o l l o w i n g d i f f e r e n t dura t i o n s of h e a t i n g i n oxygen have shown s i g n i f i c a n t s t r u c t u r a l changes. The s p e c t r a i n F i g . 7 r e v e a l a new a b s o r p t i o n band at 1100 -f 1000 cm" , which i s c h a r a c t e r i s t i c of S i - O - S i bonds, and corresponds to ν (Si-0-Si) vibrations [5]; a s i m i l a r absorption band i s o b s e r v e d f n the s p e c t r a of s i l i c o n oxide f i l m s [ 7 ] . 3

2

3

3

3

2

tf

2

3

4

1

a



14.

WRÔBEL A N D KRYSZEWSKI

Thermal

ι

1400

1200

1

Modification

1

1000

1

r

800

WAVENUMBER (cm-')

600

Figure 7. Infrared ATR spectra of PP-HMCTS film. (A) previously pyrolysed in vacuum; (B, C, and D) following various durations of heating in oxygen atmos phere at600°C.

American Chemical Society Library 1155 16th St. N. w. In Plasma Polymerization; Shen, M., et al.; Washington. D. Society: C. 2003fi ACS Symposium Series; American Chemical Washington, DC, 1979.


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Moreover, as seen from F i g . 7, the i n t e n s i t y of the a b s o r p t i o n i n t h i s r e g i o n i n c r e a s e s markedly with treatment time ( F i g . 7C and D). These r e s u l t s suggest that PP-HMCTS f i l m s p r e v i o u s l y pyrolysed i n vacuum may be transformed, by c o n t r o l l e d o x i d a t i v e heat treatment, i n t o new m a t e r i a l s with a high content of s i l i c o n oxynitride inorganic structure. I t i s i n t e r e s t i n g to note that plasma polymer f i l m s obtained from other organosilazanes, such as hexamethyldisilazane and cy c l i c compounds with four and eight-membered methyl s i l a z a n e rings, were found to form f i l m s of s i m i l a r p r o p e r t i e s when p y r o l y s e d i n vacuum. In c o n t r a s t with present r e s u l t s , however, heat t r e a t ments c a r r i e d out on polymer f i l m s deposited from organosiloxanes, such as hexamethyldisiloxane, h e x a m e t h y l c y c l o t r i s i l o x a n e and octamethylcyclotetrasiloxane, resulted i n s i g n i f i c a n t deterioration i n f i l m adhesion to the metal s u b s t r a t e . In the case of s i l o x a n e polymer f i l m s a s t r o n g p e e l i n g e f f e c t may be observed a f t e r only 1 min. of p y r o l y s i s i n vacuum at 600°C. From these observations i t may be concluded that o r g a n o s i l a zanes are p a r t i c u l a r l y u s e f u l f o r the p r o d u c t i o n of f i l m s with e x c e l l e n t thermal p r o p e r t i e s ; the Si-N s t r u c t u r a l u n i t i n these compounds appears to p l a y a most s i g n i f i c a n t r o l e . Our r e s u l t s show that PP-HMCTS f i l m s , f o l l o w i n g thermal mo d i f i c a t i o n , may be s u i t a b l e as p a s s i v a t i o n coatings f o r metals. T h e i r other p r o p e r t i e s as e l e c t r i c a l , o p t i c a l and mechanical are p r e s e n t l y under study i n our l a b o r a t o r y . Conclusions Based on the r e s u l t s reported i n t h i s paper, the f o l l o w i n g conclusions may be drawn. 1. Thermal m o d i f i c a t i o n of PP-HMCTS f i l m s g r a d u a l l y reduces the organic s t r u c t u r e from the polymer which evolves towards a ma t e r i a l of e s s e n t i a l l y i n o r g a n i c c h a r a c t e r . 2. Formation of Si-N i n o r g a n i c l i n k a g e s through the s c i s s i o n of N-H and Si-C bonds seems to be a predominant process during t h e r mal decomposition of PP-HMCTS. 3. Thermal decomposition of Si-Η, Si-C and N-H bonds i n PP-HMCTS proceeds by a f i r s t order r e a c t i o n mechanism. 4. Thermally m o d i f i e d PP-HMCTS f i l m s due to t h e i r h i g h thermal s t a b i l i t y , s t r o n g adhesion to the metal s u b s t r a t e and h i g h r e s i s tance to c o r r o s i v e agents, appear very promising as a p a s s i v a t i o n coatings f o r metals. Acknowledgments The authors wish to thank P r o f e s s o r s M.R. Wertheimer and H.P. S c h r e i b e r (Ecole Polytechnique of Montreal) f o r v a l u a b l e sug gestions and c r i t i c a l reading of the manuscript.


14.


Thermal Modification

249

Abstract Plasma-polymerized hexamethylcyclotrisilizane thin films were pyrolysed in vacuum at 600 and 800°C. Infrared analysis of the polymer films carried out after different durations of pyro lysis revealed significant changes in their structure. A distinct decay of SiH, SiCH and NH groups in the polymer with increasing pyrolysis time was observed. The appearance and growth of an ab sorption band at 1000 - 800 cm , suggested the formation of si licon-nitrogen inorganic linkages in the polymer film. Study of thermal decomposition processes showed that scission of Si-Η, SiC and N-H bonds proceeds according to a first order reaction me chanism. The apparent activation energies evaluated for the res pective decomposition reactions suggest that scission of N-H bonds dominates during pyrolysis. Thermally modified films were found to be colourless, glassy material with extremely strong adhesion to metal substrates; they displayed excellent resistance to corrosive chemicals. 3


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References 1. A.M. Wróbel and M. Kryszewski, Bull. Acad. Pol. Ser. Sci. Chem. (1974) 22, 471. 2. A.M. Wróbel and M. Kryszewski, IUPAC Symposium, "International Round Table for Plasma Polymerization and Surface Treatment", Limoges, June 1977. 3. A.M. Wróbel, M. Kryszewski and M. Gazicki, Polymer, (1976) 17, 678. 4. A.M. Wróbel, M. Kryszewski and M. Gazicki, Polymer, (1976) 17, 673. 5. A.L. Smith, Spectrochimica Acta, (1960) 16, 87. 6. G. Turban and Y. Catherine, Thin Solid Films, (1976) 35, 179. 7. W.A. Pliskin, J . Vac. Sci. Technol., (1977) 14, 1064. 8. W. Kern and S. Rosler, J . Vac. Sci. Technol., (1977) 14, 1082. Received March 29, 1979.


Plasma Polymerization - American Chemical Society

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