E L S E V I E R Thin Solid l:ilm.~ 312 (t()(18) lOf l -110

Growth of 8H polytype of diamond using cyclic growth/etch oxy-acetylene flame setup

R. Kapil. B.R. Mehta. V.D. Vankar +'

Thin i"ihn lxd~or+tt+o3", l)~7~ortm<'m ,tf Phy.+'i<'s. hull+in Iostintte ~1" Te<'hmd,.~,y. New Delhi. I I0 016. h+dia

Received I()June 19q7: ~¢¢cpted b Augusl I~1t)7

Abstract

Diamnnd thin films were deposited using n cyclic growth/etch oxy-:tcetylene pr~ces,~ un tungslen subslrates, Growth of 8H p~lytype ol + diamond wax observed in the diamond thin films. Dcpusilion t~l" 8H polylypc of tlimnol~d wa,~ I'tmnd to be .~trongly dcpendcn! tm Ihe process parameters. Twt~ different phuses tff lungslen carbide which were I]~rmed ~tl the sttbslrale/l'ilm interface were alsn idenlified by X-ray diffraction. Rat'nan spectrum of these samples confirmed the presence of 8H p~tytype. <i-.~ 1998 Elsevier Science S,A.

K~,vword.~: Carhtm: Diamond: Rztlllan ~catlcring: X-ray diffraction

1. Introduction

Diamond ix one of the most thscinating and technologi- cally important polymorph of carbon [I,2]. It exists in cubic, hexagonal as well as rhombohedral forms, Analo- gous to silicon carbide, various polytypes of diamond (2H. 4H. 6H, 8H. 10tt, 15R nnd 21R) have theoretically bccn proposed [3-6]. Phelps et al. [3] and Spear et al. [4] have giver, the space groups and theoretically calculated vibra- tion spectra for these diamond polytypes. Theorcticaliy calculated X-ray diffraction data lot different diamond polytypes have been reported by Hoicombe [5] ~md Ownby et al. [6]. Calculations of Ownby et al. [6] were based on improved space groups for different diamond polytypes. Out of these proposed diamond polytypes, Bundy and Kasper [7] have synthesized 2H polytype (Ionsdaleite) at hi~zh pressure and high temperature. Frenklach et al. [8] and Howard et al. [O] have observed 2H ~md 6H polytypes in the htlmogenous nucleation of diamond powder by microwave assisted combustion of chlorinated hydrocar- bons and acetylene-oxygen. Hexagonal 6H polytype uf diamond has also been reported in hot filament chemical vttpor deposition (HFCVD) grown diamond thin films [ I()]. Rossi ct al. [I I] have reported the growth of so-called

(+t+rlc,,l+l+llttJng uultlt~r, hltlJall Ill,diltllC ~+1 "l'cchn~fl+. Thin I:ihu I.nt+o- riltt+l'.X. I')cl+l. Phys+ & ( 'MST, Ilmt] Khas. Nc~v l)clhi+ I t(l()l(~. Intli~l. Tel: + t~ l+l 1 - 6 8 t ' + + l t ; 7 7 : f a x : + t J l - I I - f l 8 6 2 < 1 3 7 : c - m a i l : ~. t['~ illlk~.ll(¢; physic,,.iitd.crnct.itl.

(lt)41)-f+llt.lll/~,~b;/$1~Ll~tl ~ ItJt)S lil~c~icr S~.'icnc¢ S.A All righl.~ rc,,cr~,cd. i ' l l ,',;11[141)- t'~(It,~<l( t.~7 )4r)1|6'+')5-Jl

x-diamond polytype on polycrystulline Ta substrate using CH 4 + H, mixture in HFCVD process. The same polytype wax also observed during deposititm of diamond films on ~ulassy carbon substrate [12]. Growth of 15R polytype of diamond on polycrystalline molybdenum substrates using oxy-acetylene flame process has recently been reported by the present authors [13]. Detailed study of the ,growth of 15R polytytpe with deposition parameters in discussed in a subsequent paper [14]. Non-cubic diamond polytypcs fro.. marion is thought to be enlmnced by rapid quench rates associated with chemical vapor deposition (CVD) and rapid load rates in shock compaction method [6].

In the present paper, growth of 8t-t polytype of diamond using a cyclic growth/etch oxy-acctylene I'hmlc setup in being reported Ibr the first time to the best of our knowl- edge,

2. Experimental

Dimnond thin l'ihus were deposited usinL4 a ~pecially designed oxy-acetylene Ilame setup described elsewhere [I 5]. Sub.~trales used Ibr deposition of diamond thin fihns were polycryslalline IL I l l~Sle l l sheets. Prior to deposition. the stlbslriltes were initially polished wilh fine grade emery paper imd I'~dlowcd by scratching with 2--5 /.tin dinmond paste. Alter polishing, stibsti'~ttes were vapt~r dcgie~lsed in isupropyt aicohtd lind subsetlucntly cletmcd with trichh~roetllylenc attd acetone, Altcr clcmlilig, the ~ub-

R. Kapil ~'l , t . / 7 7 z i , Solid I"ilm~ 312 ¢/99.~. ~ 106- I I0 1(17

_z

11 12 ,,,~

I ' i~0 ~3 .~

20 40 60 80 90 20 2 e ( d e g . )

Fig. I, X-ra~ tlifl'rau'li~ll i~allt-'l'n {~t" sample I.

I'10 42 at,, %" &6 4,7 1 tll I/ ',~, 2.. ~z I

40 60 BO 90 2 0 ( d e g . )

Fig. 2. X-ray dil'fr:l~'tion p;.|ltct'll narnplc 2.

striltes were mot|nice 011 H water cooled rotating stihstl'atc holder made o1" copper. At tile time of tlepl~siti~m, sub- strates were rotated ulotlg an axis normal to its surface and Ills ftamc was kept off ille center. The oxy-acelylenc Ilanle is known to have three clearly defined regions: inner cone, feather and OLtlCr flaillc [2, t6] when operated under fucl ricll (C,H_,/O.~ > I) conditions. The feather has the car- bon radicals and hydrogen required for diamond dcpmi- ties. The outer lhlnle provides etching title to the presence of O and O H radicals. Due to the substrate rotation, different portions of the tlepositi~m area of the .'~ubstratc alternatively pass throuuh the dcpmiiion antt etching re- gion. An the substrate in exposed to the feather, deposition takes place and the stlbStl'atc icitliDcr~lltlre also rises. An the deposition .'u'ea comes out of tile feather and enters into the OlitCl" i1aille, etching of the non-dialuond C O l l l p O l l e l l t lakes place and substrate temperature also tlecreasen. Therefore, ',lie subslratc rotation provides cyclic growth/etch deposi- tion and periodic variation in tile substratc temperature.

Usin,,. ~, tile above nlenti~ned setup, films were tlcposited at dirfercnt C~ H _,/O, flow ratios ( I.I)6 to 1.2) and speeds of rotation (35 to I()0 rpm). The substratc temperature m~n nl;.lintaitled tit ~-725"(" by controlling tile coolant Iqmv. The films WClC characterized using ghlilcillg angle X-ray diffractonaelcr (XRI)) (Rigaku I ) /MAX-RB) ttxing CuK ~e radiation. The substrafcs wcrc rotated along the tlxis per- i~cndict, lar to the surl'ttcc ill the time ~1" data acquisition. The XRI) results given in Ihis paper were recorded at a glancing angle (o') of 3". 111o rot~m temperature Ratuan spectra were excited with a 514.5 utu line from atl At"

laser. The backscattered radiation passing through a Spex Triplcmate in detected by liquid nitrogen cooled CCD. Growth rates of the deposited thin films were 4-5 #m h i

3, Results and discussion

Figs. 1 and 2 show tile XRD patterns of samples , ,nd 2 exhibiting the growth of 8H polytype of diamond. Growth conditions for samples I and 2 tire given in Table I. lriterph.mar spacing (d (,,~)) and imensity ( i / I . ) of differ- ent XRD peaks observed for sample I and sample 2 are listed in Table 2. XRD data of 8H and 4H polytypes. roW,C, WC ;.Illd lUllgslen iu'e also given in Table 2 ibr the identification of observed XRD peaks.

For sample I, peaks (Nos. I0, II, and 12) Imvin,g ,I _.088. 2.065 ar|d 2./,)34 ,,~ and I /I , , 12, 15 and 15. respectively, are tile most promirlertt peaks con'espor|ding to 8I-! polytype, In die calct, lated diffraction data for 8t l polytype, the it, tensity rail,t> of these peaks are If){), 80 and 96 according to ReI'. [5] (.ICPDS 26-1075)and I(X), 76.81 itlld t)4.t)4 as per ReI'. [6]. Tile XRD peaks (Nos. 8. 9, 13, 15. 17. It). 22. 24. 27 and 29)also match very well with Ih5 calculated XRI) data fur 8H pt~lvlvpe. The peaks (Nos,

o v •

I I and 27) d = 2,065 and 1.2(~1 A. arc characteristic peaks o1" CLlbic dianlond and are collision to all tile polytypes of dialllontl. The calculated XRD dala given in Table 2 also nhmvs that man 3 XRI) peaks are common for 8H and 4H polytypes of diamond. But ihc presence ~1" peaks (Non. 12, 15. 22 and 2t, ~) in the oh,,erved XRD data conclusively

" f 'a lqc I [ )¢ l '~ t tn i l iL t t l r~IH';.tlll¢l.t.'l 's I',.',1" :.,i'trill'dt',,, I l i l l e

Sanq',lu" I1~. ( ' , t I ,., " ( ) . Spt. 'cd ~,1 ~ l,41ali.tql ' ] ' i l l lu' e l d¢f ' ,o , . i l ion .~ut',,,Irat,,." I,.'1111",,..'r,111.|1",,,." .~L|l",ql,| l t ' r;,;| j,tl ( I ] l l l ' l ) 'l, I |HI1 ) ( ( "~

I I. i (i 5[1 h(l "725 l'P, lll~4',,l,,,.'n

log R. Kal)il et , I . / T h i n Solid Films 312 t 19q,~) Itt6 I It;

Table 2 d-Spacing and I / I , values of lhc peaks in the ohserved (samples I and 2), calculalcd and slandard d;.ll~l

Peak .u)s+ Sample I Sample 2 W" 8tt polylypc )' 8H polylype ~ 41t polylyl'~e 'j I)iumond 3( '~' tr. .W,(') WC "~

t 4,227/6 4.227/5 . . . . . . . 2 3.~ t ( J / 3 3.1 ) ( } / 3 . . . . . . . 3 2,873/15 2.873/20 . . . . . . . 2.~13/7() 4 2.5g()/3 . . . . . . 2.60/50 - 5 2.52(I/8 ....... ", ,vm/',',~_. . . . . . . . 2 . 5 1 / ~ 0

6 2.357/2 2.3fi0/2 . . . . . 2.3¢)/4(1 - . . . . . . . . . 2 . 2 7 / t t ) O -

7 2 . 2 4 1 / l ( X ) 2.241 / i()() 2 , 2 3 ~ , / l ( x ) . . . . . . 14 2.179/4 - - 2. I ~42/9.32/(()1()) 2.1~/1() 2,1N4/29 . . . . 9 2.154/4 2.t5o/2 - 2.1653/1~.4t, /(()11) 2.t7/9 . . . .

I0 2.0gg/12 2.097/7 - 2 , 1 1 1 2 / l ( X ) / ( ( ) i 2 ) 2 , (1FI I ' l l X ) 2 . 1 1 I / I ( I ( ) - - -

II 2 . 0 6 5 / 1 5 2,()t)I/4 - 2.()5()3/'16,1¢I/((X)~) 2.()6/8() 2.05t}/57 2.()()/I0() - - 12 2.034/15 2.034/12 - 2.02()6/04.94/(013) 2 . 0 3 / t } ( ) . . . .

13 1.951/4 I.(}51/3 - 1.9296/14.16/(014) 1.93/14 1.930/43 . . . . . 14 l .~g6 /g l .gg3/13 . . . . . . I . ~7 / I ( ) ) 15 I.~30/2 I .g23/2 - I ,g205 / I ,31¢ / (015) . . . . . I~) 1,748/2 1.748/2 . . . . . 1.74/40 - 17 1.625/2 1.6_5/_ - 1.70()3 / 2,0(.)/(() I (')) - 1.71F)/2 . . . . . . . . t.6(116/0.51/(017) . . . . . . 18 1.584/29 t.584/22 1.582/15 . . . . . . . . lq 1.502/2 - - 1.4984/1.62 I(()t FI ) 1.50/2 1.4t)N/5 -- 1.49/6(I - 20 1.45(,/2 1 . 4 5 6 / 2 . . . . . . 1.452,/()() 21 1.434/2 1.434/3 . . . . . . . . . 1.421/50 22 1.412/2 1.409/I - 1 . 4 ( ) 2 ( ) / 0 . ~ ) 5 / ( 0 1 9 ) . . . . . .

23 1.303/2 1.363/I - - ) . . . . . 1.34/50 24 1.338/I - - 1 . 3 1 5 3 / 1 5 . 3 5 / ( 0 1 1 ( ) 1 1.32/15 1.315/15 - - -

25 1.2¢)3/41 1,2t)3/14 1._ . / _ . - . . . . 1.29/4(1 1,2(.)3/70 26 1.261'I/2 1.268/i . . . . . 1.26/50 - 27 t.261/4 1.260/I - 1.2t ' ,1(}/46.35/(I I()) 1.26/44 1.201/33 1 .261 /25 - - 28 t.250/3 1.248/I . . . . . . 1.25/50 t . 25g /6( )

S'~ -~-~ ~ _ _ 1 " ) 4 / " ~ 29 1.237/2 - - I,_3. _/__,8 )/((11 I I ) . . . . - - - 1.233/70 . . . . . . . . . I , l g /5 ( ) - . . . . . 1 . 1 f l 2 3 / 7 . 8 ~ ; / ( ( ) 1 1 2 ) I, 16/~ 1. It~2/23 . . . . .

30 1.148/1 1.148/I . . . . . . 1,149/7() 31 1.131/2 1.131/I . . . . . . . 1.13/2(I - 32 1.120/23 I. i 19/10 I.I 19/X . . . . . . .

"A S'I'M 4-0806. " R e I ' . [6]. JCPDS 26-1075.

dJCPDS 26- t078. eASTM 6-1)675. )ASTM 2- I t 34. :" ASTM 5-072t'I.

shows that the 81-1 po ly type of d i amond is the predomirumt

phase in sample I . In the inse! o f F i g . I . X R D pattern o f

sample I. for 2e l = 42 to 46 ° is given. Tilts X R D pattern was recorded tit a scan speed of I ° rnin ~ and step

sampl ing of O.(X)6 and tit ghmcing angle of 3 °. T i l e post-

lion of the most p rominent peaks (Nos. 10, II and 12) of

8H poly type can be clear ly resolved in this f igure at

2 0 ) = 4 3 . 2 9 4 , 43.930 and 44 .530 ° ( d = 2.08, 2,059 and

2.033 A). The peaks (Nos. 4, 6, 16, 19, 23, 25. 26, 28 and

31) match with diffract ion peaks of tz-W2C ( A S T M 2-

i l 34), Tile ditTntctior) peaks (Nos. 3, 5, 14, 20, 21, 25, 28.

29 and 30) match with X R D data of W C ( A S T M 5-(;728).

T h e o t h e r peaks ( N o s . 7, 18, 25 and 32 ) are due Io Ihe

t u n g s t e n suhs t ra te . T h e peaks Nos . I and 2 are u n i d e n t i -

f ied.

I d e n t i f i c a t i o r l o f d i f f r a c t i t m peaks o b s e r v e d fo r s a m p l e 2

are a lso m e n t i o n e d in T a b l e 2. T h e X R D pa t te rn f o r th is

sample shows strong peaks at d = 2.097 and 2.034 ,~,,

showing tile domina l ing presence oV 8t-! polytype o f dia-

nlOlld, in this sample, diffract ion peak at d = 2,061 A,

which is COl l ln lon tO cubic d iamol ld and 8H poly lype o f diarnond, is very weak , These results cor respond Io the

inilial stages or i.he g rowlh of the fillns. The results sugges!

Ihat 8H poly lype is p redoln inanl ly pl'esenl at tile initial

s lages o f f i l l n g r o w t h . A s lhe f l l i c k lwsS increases, 8 t l and

3 ( ' p o l y t y p e s g r o w s i m u l t a n e o u s l y ,

R. Kupil et al. /17t i , SolM I"ilmx 312 f 1998~ It',Y)- 110 109

,4

z ttJ I.- Z ,tie

1100

~:_~ ,

' I ' I ' 1300 7500 1700

RAHAN SHIFT [cm-1)

Fig, 3. Rmnan spectrum of sample I.

Ramarl spectra of sarnples I and 2 are given in Figs. 3 and 4, respectively, in the Raman spectnt of sample I, four Raman peaks centered around 1208, 1336, 14811 and 1565 c r n t were observed. Identification of these peaks ure given irl Table 3. The possibility of nori-dian'lond carbon deposition is very strong in this sample, as it was deposited at C 2 H J O 2 gas flow ratio of I. 16 which is very hlrge in comparison to generally used C2H.,/O.~ gas ratio used ('-- I,I)4) tbr diarnond deposition in oxy-acetylerle t lamc process [2,16], The non-diamond carbon phase is present in the amorphous form as no XRD peaks corresponding to graphite is observed in the XRD pattern for the samples I and 2. It is well known that Raman scattering efficiency of graphitic carbon is 50 times greater than cubic diamond. This explains why sharp Rarnan peaks of diamond poly- types are not observed in the Raman spectra of sample I, Ran la l i spectruln observed for sample 2 along with the deconvoluted peaks is shown in Fig. 4 and as well as in Table 4 along with the theoretically calculated data from Rcf. [4]. Deconvolution shows feature at 1337 cm i and some features at 1199, 1258. 1294 and 13114 cm i which are close to calculated Raman peak positions for 8H polytype [4]. Features at the 1565. 14811 and 1388 cm L are due to the non diamond amorphous carbon [ 10,12.17.18]. The intensities of tllc vibrational modes

¢1

.=

1100 1.~00 lS00 1700

RAHAN SHIFT (cm "1)

Fig, 4. R;.Lm;.uI nlltTclrtllll of sainl+lc 2.

Table 3

Observed Raman peaks for sanlple I Fig. 3 and their a,,,,,iignnl..2rds

Peak Ix|+. Ob.,,erved peakx Assignments ReFerence ti~r .~ainple I

I 12118 cm " I 81t polylype [41 of dialntmd i | 2112 cm " ; )

2 1336 cm i ttialmmd and [ I . 2 .4 ]

i1,~ polylypes ( 1332 era- ' )

3 1481) cm i anlorpht+tts carbon [ t 7,18] 4 I565 c m i amorplltms carbon 11,2.111,18]

,'esuhing from non-cubic polytypes is suggested to be srnall ill comparison It) the rnain vibration band [4], In SiC, the intensities of the Raman peaks of the polytypes are fnund to be lOf~ or less than the main vibration mode [19,20].

The growth of a large number o.f samples at different speeds of rotation and C2H. , /O 2 IJ!.w ratio was carried out. It was observed that with the decrease in the speed of rotation from I00 to 35 rpm there is an increase in the growth of the cubic diamond phase. An u:ihancement in the growth o1" 8H phase was observed with the increase in the C2H_,/O_~ flow ratio (from I,06 to 1.2). Growth of cubic dl:m~ond was also observed at 35 rpm and !.06 C, H 2/O,. g,+:; flow ratio. Periodic variation in the temper- ature, intermittent deposition and growth/etch cyclic pro- tess due to the subs|rate rotation seems to result in the growth of unusual polytypes of diamond+ The variation in the speed of rotation at a constant C2Hz/O_+ flow ratio changes the magnitude and frequency of the above men- tioned changes in the growth environment. Etching ot" non-diamond component in outer flame due to the pres-

Table 4 Observed Ramal l pcak~ for sample 2 Fig. 4 and |heir ;.Ixsiglltl'lelltS

Peak no. Ob,~erxcd l~ak,,, A,,,,,,igimlent,,, Reference i b r sample 2

1 1 1 9 9 cm 141

2 1258 cm

3 1294 cm

4 13114 cm

5 1337 cm

6 1388 c ln 7 1481t c , I 8 15175 cm

8H polylypc O|" d ian lo l ld

t l -+1 )Scm ' )

8It polyLxpC t4] o f dial l lol ld t 1 2 5 8 cm ~ )

8H pol)t) pc [4] o f diat t iol ld 11787 i - , . . ~lll )

8tt l~+Ix'l.x pc I41 n f d iamond

dhm+toild aild 11,2,41 its polyLvl~en

1 3 3 2 c m ~ ) atuoq+hou,', carbon [ 171 anlolphtms t'ad+oll [ 17,181 amoq'4lt'lu.~ carl~.m [ 1.2,17', 181

III) R. Kupil el ul. / 77U, Solid t"ih,s 312 t 199,'0 106 i i0

ence of oxygen radicals is much Ii~sler then hydrogen in feather. With increase in the C ~ H 2 / O ., flow ratio :~t a particular speed o f rotation, super" saturation o1" cilrhl.)ll species increases. This increase in supersaturation of car- bon species is supposed to lead to the growth of graphitic phases. But presence of oxygen radicals in Ihe oulcr flame suppress deposition of graphilic carbot~. This drives Ilw ~mwth kinetics towards the deposition of polytypic phase.,,, which have stacking faults, lower symmetry and lower s u r f a c e free energy than cubic ~lianlond. To investigate the growth mechanism ,ff the non cubic polytype of diamond in the c y c l i c , g r o w t h / e t c h oxy-acctylcne f larne process detailed study of the glowlh or diarntmd tlllder dil'lL'rent deposition conditions and on different substratc materials is in progress,

4. Conclusions

It has been .,,hewn th~:t the growth of 8H polytypc of diamond which was predicted theoretically in possible on tungsten substrates under ,g.rowlh conditions pr(wided by the cyclic growlh/ctch oxy-acetytcnc flame process. The growth of tile 8H polytype and cubic diamond tire found to bc dependent i111.|inly 011 spccd of rotation and C, H 2/02 gas lqow ratio. Raman spectra (}1' these sanlplc.s also shows features resembling those prediclcd for 8H r)olytype.

Acknowledgements

The authors are thankfttl to l)r. A. Pradhan and Ms. C. Roy for their help in R~.llll;.lll measurements. ()lie of the authors (R. Kapil) is grateful to Unixcl-sity Grants Coin-

mission (india) fo r providing a r e s e a r c h fellowship. A u I

tllor.s are ills(! I l la l lk l ' td It) D e p a r t m e n t o f S c i e n c e ;.tlld

Technology for providing ;.i research gl'~.IIlt.

References

Ill K.I'L ,~peaI', J. AII|. ('l,'I;.IIll. ~iIl.'. 72 ( l~,~X~, ~) 171. [21 W.A. Yafl~,~I'qalgh, J. AIn. ('cr~ml. Soc. 75 ( It~)2~ 317(L 13] A.W. I~hclp.,,. W. thermal'd, I).K, Smilh, J. Mawr. rcs. x (i093)21,135. [4] K.E. Sl'wal'. A.W. I~hclf'~s, w . IL While, j, M:lier. I¢,e',, 5 (l~)t.~O) 2277. 15] ('.I '. Ih~tcombc. Calt:ulaled X-t'ay I)ifl'raction Data fir" Pt~lytuorl'~hic

Forms t~l" ('arbon. I.q',l. No. Y-1XI,,,17. ():lk Ridge Y- I2 Plum, Oak Ridge. TN. July 23, I LJ73.

[fi] P.I). ()wni~y, X, Y:m~. J. l,iu, J. Am. ('¢rum. Soc. 75 (It#~,b2) II,IT(~. 171 F.I'. llundy, .I.S, Kasper. ,I, ('hem. Phys, 4(, (I()(~7) 3437. [,~] M. Frcnklach. R. Kcqmlick, I). lhmng, W. I-Io~vard. K.I~. Spear,

A.W. PhcIl~,',. R. Kob;L J, Appl. Phy.~. fi(~ I It)1"l~J) 3~)5. [t)] W. Ilow~rd. I). IIuatlg..I, Yuan, IVl. Frenklach, K.I':. Spc:m R. Koha,

A.W. I~llclps..I. Apffl. i~ll).',. 6t'I I I0',11)) 1247. [ I l l ] S. I';ha:'uava. t1.1). Iti.',l, S. Solwil. M. Anl~l;tl. tI.B. Trir)alhi. AI}I)I.

f'hys, i..'ll. 67 (I()t;5) 17lift. I I I] M. R~':,.q, t;. VilaIi. M.I. Tu'rnmt,~a, V, ,gcs~,v, Appl. Phys. I,cu, (~,~

• ' I',),)3) 2765. I12] M.I.. Tcrranov:L M. Roo~i. V. ,~c~,,a, (i. Vilali. Solid Slate ('om-

mun. ~Jl ( 19~)41 55. I I3j r. Kapil, B.R. MehI~., V.I). Vank~m Appl. I'hy.~. l,cu. 68 (lqt)6)

2520. !14] I,I. Kapil, B.I~,. Mcht;I. V.D. Varikar, l ' l l in Solid Film,, (i~cccpto.l). ll51 r . K:lpil. I].R. ML'hta, V.I). Vankar, Bull. Mater. Sci. 11~',1 Y. Malsui. A. Ytmki, M. S:d~ara, Y. I lir~.,,t'. Jt m, .I. Ar~r~l. F'hy.s, 28

(19xt)) 1718. 117] I). I']c¢lllal;. J. Silvt.,rman. R. I..,,utb,, M.R. Aiitlern~ul. Phys. Roy. B

30 (ItJ84) XT(I. [18] R.J. Ncmanich..I.T. (;lass. (;. l.ucovnk). R.I-. Shmder. J. Vac. gel.

Technol. A6 (19~,~) 1783. [it)] I).W. Fctdman. J.tl. Parker Jr.. W..I. ('h~Lvk¢, I.. P~,lric. I~h),~. Rev.

171) (Itlfl8) flgl~. [211] I).W. I:~,Ithl~:UL J.It. I)aI'kcr Jl'.. W..I. ('ho.~l,c. I.. Pall'it. I~hyn. Roy.

173 (ItJfiS) 787.