saugnac_all characterization c-b-n solid solution deposited from gaseous phase

8/2/2019 Saugnac_all Characterization C-B-N Solid Solution Deposited From Gaseous Phase

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~ b 0Characterization of C-B-N Solid Solutions Deposited from a

Gaseous Phase between 900 and 10S0CFrederic Saugnac. Francis Teyssandicr.' an d Andre Marchand:

A e r o ~ r a t ; a l L .-\quitaine. 3516'5 S:.t;m Medard-en-Jalles Cedex. France ~ ' O r

e composition. the structure. an d some physical properof boron-carbon-nitrogen solid solutions prepared by

\apor deposition (CVOl have been investigated.Both crystalline films and amorphous granular materialsresulting respectively from heterogeneous an d homogeneous

....er e charanerized by X-ray diffraction, XPS.RBS, an d TE:\1. Th e compositions of these single-phase ma

ar e gathered in two main domains located in th eGIN> I part of the C-B-N composition diagram. It is.t:lled that the carbon-rich domain results from structuralisorder of an ideal C!B 2 N composiltion. The thermal beha"

or of these films indicates that no mass loss can be detectedfter I h at 1700C bu t a graphitization and a formation of

amounts of BuC, ar e observed. Density and preliminary electrical conductivity measurements were also performed. [hey' ....ords: chemical vapor deposition, solidsolutions. carbon. boron, nitrogrn.]

l. IntroductionTHE simii"ritv of the crystalline structures of graphite andhexagon:!1 boron nitride immediately suggests the possibil:ty of obtaining solici solutions of these materials. GraphiteJeing a blaCK ,emimetal and boron nitride a white insulatOr.meresting adjustable , e ~ i c o n d u c t i n g properties could be e . ~ -:,ectcd for their " o l f s v r i n ~ . '

Very lillie work h ~ p ~ e v i o u s l y concerned such materials'.nd most syntheses v. ere carned out by chemical vapor depoition (CYDI. Th e first results on these compounds were pubIshcd in 19"72 bv B:!dzi:!n et uf.' From the reaction of a'C l , -CCL-H: -N: mixture with a carbon rod heatcd at~ 5 0 ' C . ~ 5 - n m - s i z e d a g g r e g ~ t e s with graphite-like structure

\ ~ r e obtained. Th e composition was not mentioned. C-B-Nlaterials were deoosited in 191:>0 bv Diefendorf I! t af. Th enitial gas-phase aO.,-NI-I .-C,H: at high temperature~ 7 0 0 0 C ) and under 101' rrcssure led to C-B-N comroundsI'hich were ("O-rha.-.,: BN-C mixtures as revealed by lRpectroscopy.

It was only in 1987 lhat Bartlett an d co-workers rublished alapo:r'\ showing evidence of the e.xistencc of C-B-N solid soulions. which were studied from the point of view of theirIcel; ical conduct ivit y some time later in a second rub[ ica:on_- Th e same rrecursors as Diefendorf were used withvdrogeo as carrier gas ru t th e t..:mr..:rature rang..: of liJolI 1\rril:.n.1n


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)( lur l l l l i o f Ihl! .-tmeriuJtI Ceramic 50 11:1.1' - Sallg'lG .:t al. VoL 75,162llf materials wcrc obtaincd' verv mouth rhln f i l m ~ (


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Januarv I l ) l ) ~ ( "llil Til C1C!"I 21.J( ion oj C-IJ -N Solid .'.,,1/1 I ions Dl 'pml lcJ (mm a Cas('()us Phase 163

BORON

BINITROGEN N8" 'B

En.rgl (,.,,)f ig. S. X PS spectrum of pure BN. Flood gun = 9 eV.

The "normal" peaks of Band N in pure pyrolytic boroilnitride arc shown in Fig. 5. Each consists of a single wellshaped line which can be used as a reference for the spectraof the C-B-N deposits. When the environment of the centralatom (B or N) becomes more electropositive. the peak shiftsto lower energies, and it shifts [ 0 higher energies if the atomis bound to ~ o r e electrone!!ative ~ e i 2 h b o r s ~ Similarlv. th eC line in graphite can be used as a refe(ence for th e C spectrain C-B-N materials.Figure 6 shows the C. B, an d N spectra of a typical C dep o s i t ~ an d Fig. 7 the spectra of a typical- A film. It is immediJtdv obvious that these are not the spectra of two-phasemixiures of carbon and boron nitride, which would consistonlv of the BN peaks for the Band N atoms and of the C peakof the C atom. The observed spectra are clearly compositepeaks for each type of atom. and they arc evidence of the

CARBONuu1 \7 ,/ I .

u:' I ' . U. '- - C ~ ~ ~ ~ : 284 4 EMrgl (,V)

U


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JO/lrnal of rhe American Ceramic Sociery - 511/1gnac ct 01. Vol.on c N. with thc following grouping:

C" " B -N C/

A similar r e a ~ ( ) n i n g led us to conclude that the nitrogenpeak on th e high-energy side of the reference NB. peak corresponds to a N C B ~ or a NBC, group ~ i n c e ir i located between the NB, an d NC , (+2.5 eV) positions.(0$) Suggested Structures

The above results enable us to suggest structures for th evarious films of domains C an d A, more specifically for thetwo-dimensional graphitic-type layers which constitute theirturbostratic stacking.It is interesting to note first that, following a synthesis o f BC,N by Bartlett an d co-workcf1i. a theoretical study'h ofpossible structures concluded that B- B and N- N bonds havean inhibitory effect on th e stabIlity of graphite-like layef1i. Onthe contrary, a C ~ B N arrangement, as represented at the endof Section Il(3), would not induce internal constraints in th elaver an d would be quite stable. We accordingly looked for ano;ganization of the C, B, an d N atoms centered around suchC;BN groupings, with a BIN ratio close to 2 an d a maximllmnumber of stabilizing graphitic C -C bonds. Th e result of thissearch is th e following elementary ~ e e l l " :

cIC ...... C /B ...... N 'C

I IC BC../ ...... C / ...... CIC

which is built from twO C ~ B N groups with one common atom. This arrangement is compatible with all th e types of

bonding which were identified by X PS. and the corresponding BIN ratio is exactly 2.

Figure 8 shows how this cell ca n be used for generating awhole graphitic plane. In th e upper pan of the figure th e oricntatio-n of the BNB group is kept constant. while it is random in the lower part. Both arrangements correspond to thesame overall chemical composition, C ~ B ~ N . which was foundto be th c "focal point" of th e C domain in Fig. 1. But changes

ca n easily be introduced in t h e ~ e CIBzN-generaled struc.,tures, which lead to slightly different compositions, eitherwith an excess of carbon or with BIN ratios higher than 2:Examples of such changes ar c shown in Fig. 9. :

They may be called "defects" if th e pure CsBzN a r r a n . g e . : ~ ment of Fig. 8 is considered to be the "perfect" lattice. O n e ; ~ . such ~ d e f e c t " ("primary defect"). illustrated in Fig. 9, consists'f:of a nitrogen atom shared b three C,BN groupings. It i:J.volves a local BIN ratio of 3. Another one ("ternary defect") ,is actually a boron nitride microdomain (two N and seven '.B atoms) included in an otherwise "normal" CjBzN lattice.. .Its local BIN ratio is 2:33.

Many others can be imagined, an d it is clear that all com.p G ~ j t i o n s of the C domain can thus be obtained. All of thesestruclUres, which do not involve a lowering of th e carbon COn-lent, should be reasonably stable, and account for the extended domain of existence of solid solutions in the upperpart of the diagram in Fig. l.

It is more doubtful that such regular arrangements exist i;jthe A domain, where the carbon content is much smaller. Butth e relative intensity of the boron XPS peak shifted at-1.8 eV remains q u i t ~ large (Fig. 6. Table I) an d it is quitelikelv that the A films consist ohery small carbon and boronnitride domains linked by numerous C,BN groups. In anvcase. Table I shows that there are no boron atoms with eithera pure carbon or a pure boron environment (no pure borondomain and no boron-substituted carbon domain).

High-resolution transmission electron microscope observations of th e C domain samples confirm the stability ofC ~ B 2 N , as shown by the presence of large-scale (70 nm\groups of parallel C-B-N layers, illustrated, for instance. enFig. 10. Such structures may be expected to "graphitize""rather easily.(5) Thermal Stability a"d "Graphitizatio""

Th e films from domain A arc strongly adherent and diU:-cult to split from their amorphous silica substrate. We were.however able to detach and submit some of them to treatments at'higher temperatures. No mass loss was detected after1 h at 1700c C, an d a typical diffractogram of the resuillngmaterials is shown in Fig. 11. It can be compared wilh lhat of

e

e

... _ ~ - - ~ - - - - - - - ~ - - - - - _ . ~ - - - - - . Fi/:. 9: . S - " ! ! ~ ~ , t t l r d c f ~ l ' h In " I t ,I r ' " i : l u r ~ s , , I It " giapfliiii.: I.,v",'

"

-.

jJ

j. Cullan alom,. 0 Huron .. l l ) m ~ o i\ilroc.C'n a t t J m ~

- ~ ~ ~ - . - X ~ ~ I ~ ~ ~ ~ ~ " 1 - - c - ~ f ~ 0 ~ . c r ; ; r h l l l C : 1 : 1 ~ ' ~ r : - - _.- - .


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Ill5January }l)'I2

Fig. 10. Lattice fringe image of a film from ; ~ ) ' C . From :WOO'C upwmpleted hy a more system.liic c.\;lmil1;lll11n of thc g:d\anumagnelic rrorcrtlcs of these",lid ,,,lUI ions, Hll\\'cvcr. ou r conductl\ 'ity resull' In alre;luy

6E 4C 2

:Jomoll''l d0 0 .....J

-2- 0 20 30 40 5(] 60 !O

C.rban content (%)r i ~ . IJ_, 1',ln:I,;,',,1 l'\,"dlll'1;\lIrl,r:c.-n ~ 1 i r l l ' ; ; ; ' : , " ' : ' . , Itll1l'tllln " Itlh.."l r t . I I " l l f l t"t\llll"/ll

'.

. ---- j


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1M }ournul of Ihe Americanbe compared wi t h ot her.; pub Iished by Moore and coworkers. Will se C-B-N materials were deposited netwcen 15000 and19DOC. The observed room-temperature values an: about th esame order of magnilUde an d increase in th e same way Withthe carbon content. Similarly, their samples usually presenteda slight increase of conductivity with temperature.

Ill. Characterization of Granular Materials(1) Composition

Several types of materials were obtained frum the nucleation process in the gas phase" at9Q() to l000C. Bu t only th cwith the higher carbun content (> 7OC!C') , which show eviden eof being truc solid solutions of carbon, boron, and nitro' en,.are examin d here. The compositions nc the correspondlf1gexperimental parameters are Ii te d in Tables II an d [I!.

Though the oxygen content is not always negligible. it ISsometimes convenient to exclude it in the determination ofth e carbon. boron. an d nitrogen percentages. The values computed in this way are also listed in the table (% %BO, an d.%N). All these CO-Bo-N compositions are located in th e so called "domain C" of Fig. I, although these granular matcrlalsare not always as well ordered (sec below) as the corresponding films, an d they all show a noticeably higher carbon contentthan most films. Th e "idea'" C < B ~ N romposition is conspicuously missing. .

The oxygen content probably originate s rom the exposureof th e materials to ai r after their deposition, and themost likely cause is the absorpti n of W:1tCL ' incc poorlvcrystallized boron nitride is known to react stron.ly withwater vapor. II.::(2) X-ray Diffraction

(A) As-Dcposiled Samples: As already pointcd out in th ecase of th e films, th e diffractograms of the gr:lnular depositsar e not a superposition of carbon and B diffraction speclra.These materials are inde d solid solutions. We observed tw otypes of X-ray diffractograms, depending on th e temperatureof d .position (Td ) of th e samples.At Td = IOOODC: The typical diffractogr m presentedin Fig. 14(a) shows that th e deposit is fairly well twodimensionally ardercct. Wilh a sharp (002) line, a dIU: distanceof 0 . 3 ~ 1 nm , and a coherence length L< ot about 4.5 nm. Butit i' still a turbostratic material since there is no indication ofa srructure in th e (!O) peak.It is quite interesting to compare these results with t h e a r -responding values of an acetylene black (Td about 13004 C):d,m = 0 . 3 4 ~ nm and L, = 2 nm. Simil::!r1y a pyrolvtic carbon

erumic Societv - 5uugnac el ul. Vol. 75.depositcd at lOOO"C shows the same order of magnitude

which'

of to'bu t a sli!:\htly s m a l k ~ d,,,, (0.346 nm). It must be oncludthat the granular C-B-N materials :'Irc better ordered thanth e "pure carbons" deposited in th e same temperature ranl!e.Thcy bear some resemblance 10 t he films f domainar c also deposited near WOO (see Fig. 3).AI T, = 900C: Th e depo its a n: very poorly crystallized'

and can re:!lIy be said to be "amorphous," as shown by tbe,.typic::!1 diffractO ra m of Fig. 14(b): very broad bands an d v iIlarge d'Jf2 distance (u p to 0.37 nm). -.:...(i l) Heal Trt!atmenl 10 1700C Th e diffra to g ms o ( Fig. 14 ar e those of dcp sits with very similar omposilionst(see Table Il) but differ nt Td After heat treatment for 90 mID )at 1700C, their diffractograms ar e those presented in Fig. 15. -.The material deposited at ICOODC is practically unchanged, but ''':the 900C-deposited sample shows a striking structural im- ;provement and an obvious two- imensional development of--:.its rystallinity: the d"'J2 dist nee dropped to 0.343 nm and t h L c value grew to 3 to 4 nm_ The effects of a lower depositiontemperature :Ire almost rubbed out. .;

Figure 15(b) also shows very weak di (f.-act ion lines Jt 0._56an d 0.237 nm which a r c ' sstgned to boron c3rbide. T h ~ s e - lines are particularly visible for samples of high BI, r a t i ~ ; , an d I w Td IIt is also interesting th::!t heat treatment to 1700D C d r i v ~ tOut most of the a sorbed oxygen, with a o r ~ e s p o n d i n g weight10. s of 2% to 6%.(C) Heal Trealmenl above 1700C: Th e I. suits presentedabove show that the graphitic C-B-N solid solution struclUreremains S'table up to 1700C. But above that temperature theformation of boron c:lrbide an d th e drivlf1g Out of nitr gen areIikelv to occur, and a mixture of graphite an d boron carbidemight be th e en d product of th e heat treatmenlS. Figure !6shows the evolution of tw o identical deposirs (46 P3 and-l P4) when heated t :2000C an d a ave. The X-ray diffra .lOgrams ar e indeed those of mixtures of carbon an d bor ncarbide at 2000C. The carbon graphitization is nearly complete at 2500 DC, with a well-developed three-dimension' orde r an d a dim distance of 0.335 or 0.336 nm . The e smallvalues indicate th e presence of boron as Ire dy observed tv\100re ct al.: J It is also interesting that. afrer hear treatment at 2500C, th e more amorphous as-deposited material (-l8 PJI !jiclds better graphitized carbon while th e more crystalline as- fdeposited 46 P3 shows no trace of bo r n ca r bid . In bOlh cases th e weight losses at 2500C are quite considcrnblc. on ith e order of 50%.

Ali of these results show that heattre:lImenr effects on the Jstabilitv an d behavior of granular C-B-N solid solutions 3re 4.

Table II.S.mpl< D..:p h::mp (fiC) r;r2J loon 90 724 \)00 Kl I: '25 900 So 1237 P3 900 01 1737 P4


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ClruTactt:'ri z(J/ioll o f C- f ! -,111 Solid 5o{/ltion " Dt'{)(}rtt -d (mil l 11 (;l/sr'O/lS I 'I/l lscTable 111. Experimental Paramel it iun of Samp,,"s able II '

S"mplc LJ I,Flow rale (Uhf

"H , C,H, TOI J I p r c ~ c ; , u (I..'tP,,) T .... mper;Jlurl."(C ) IdI l 'm )-".J24_537.1/\-1860

1.351.351.601.351.352..()U1.35

1.21.:2U1.21.2I. 1.2

1.2121212I: '1.21.2

26(X)~ 0 ( J ( J _60026()()260u260026UO

1000(J()n':100':IO(}

IOO(}'-J(}O1000

10j(1i l l

IIII6163 1.35135 1.21.2 1212 2fiOO2600 1000l(X)() !

'G ' I' In c d l s ~ J . n c c (0 (he hOl lone: cntrOlnce of (he {(, ... xl ...1 p'pe C':Jfl'yin!! NH 1. S.J.mc dflut l l ln In nlll'OCCn lo r "iamplc:l'Io 2J . 2.-1.. 25. 1, -Lh. Jn J .1S. [ ) \ ' i ~ " ~ 31 a c o n ~ t a n t rt'."tldcncc: t ime fo r s ~ m p ! c . s 6 H h l - t > ~ r c ! r c l : l l v t ! l ~ a I 1 o ~ 5 Q (0 .::: f ll)"" 1';11 '" ii i" wi ('.i" - 00 (Al(a)

Td : 900C48 P d

l2 le '"; 0 " ,' ",. ci'" 0 {! j(b)

peak i s ~ o b s e r v c d , and these spectra obviously belong to solidso!U{ ions. 'Since X-ray pholoek.ctron spcctrosc py is mainly a tcchnique f r nal. sis of the sample surfacc. and since oxygenabsorplion by the granular deposits is fJr from negligiblc.promlncnt 8 -0 and C-O peaks might be expecled in thespectra. It can be seen [hat the peak. shi tcd ab Ul+ I eV from thc rdcrcncc graphitc pcak. is r lher weak. whilethe 8 -0 peak is very conspicuous. This is a confirmation thatmost of the absorbed oxy_cn corresponds I lhe f rmarlon iboric xidc or acid.

T h N- C component, on the highcnergy side of the ref'rcne NB peak. w a alrca y observ'd In the fjlm spectra.It acCOunts tor approxlmatcly one third () the [01 I N intensily, and agrecs well with the previou.ly suggested ( B ~ ,~ l r u c t u r e . Th e small. -N Il l] C-8 shoulder.; on bOl h sides of I he carbon pe k show th t :Iloms are mostly linked to [her , butthat some of them arc 31so bound to eit her B or N.Th e (-J eV) component of the B spectrum is quite inIcnse and confirms the ~ l r u c l u r a l similarity of these gr2nul.:n

Td : l000'C'" 46 p)a

c;:0Tr ! 9 0

\0 5 4 2 \.5 1 o ( ! )(a)

'",..; Td : 900C;;;0


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Ill!) JOIlTnal 0 / Ihe Amaican

4G P 3Td : 1000"CI

~ ; " C O ' \ , 1O 5 2 I 0 ( ~

(a)

~ ;1 3HT l : 25OO"C

II10 5 2 o (AI

(b).

~ P 4Td : 900 'CHTT : 2000 'C

(c)

48 P4HTT : 25OO"C

\0 5 2(d)

Fig. 16. X-ray L1iffraction palterns of luonulor m;lt rials heatHealed succes" velv ot 2IlUO and 250()QC.

, ~ m p l c ~ with thc films. Our previous inlcrpretation rcmainsv;did an d wc assign it to a C!N cnvironmem of th e B :Ilom_

An interesting difference with the films is the mther st n nglow-energy componenl (ncar -4 eV) of the 8 spcctrum. Itcorre:;ponds 10 B-13 bonds and is an inJic:ltion of a nonnegligible proportion of boron-surrounded B ;Homs. that is. ofhomn isl,lnds on the m;ltcrial.

We ma y cl1l1clutle from these XPS rcsults that thc ~ r J n U I M d c p o : i t ~ ar c solid C-l3-N solutions. " i lh some s u r e r r i c i ~ 1 horon oxides. dnd that (I ) boron is mostlv hound (0 C;lrOI1l1an d nitrogen in C,3N groups. similar 10 those which constitute th e film structures. (2) nitrogen :ltoms ar c u ~ u a l l y hound10 on e C and two l3 ncighbors. an d (3) some horon islcts exiSIin th e hulk of th e solid solution.

Thc st rueturc of these matcri,t1s is p r u h ~ h l y 4ualilallvclysimtl,H 10 that of the C films. with the aJdition


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C/lllrtlCI O : ~ 1 . ''i. P. ,\r\';J antJ, O : ) m l l : ~ ' "Prq);Jrul IOl1 P f O r ~ r t l c . : l o dnLl A O " l l C ~ I t I ( ) l l ~

II ! l )orun. IIrIJc: r/':tn F i l m ~ , - r"lfl .XsI/d F,t/n.,. IS7. :2(17-.::, ! t j ~ ~ I . '. r . \ f .J l 'uda. "SI3hdllv In M 0 1 ~ ( U r t . : (o r Cht:mt :Ill\ ' :JpolJr D ~ p o ~ l t c d (31lf"t111 r" r I r IU-, : . ) \ tura ,kl., : . : ~ (7J 2 - , 5 J - 5 ~ (J'tXl, ll.

: ~ J. C L h h ~ r J I . "CVD Boron ' rtndt:: Inll!tr:Jlion or f-lhrou' ::l Structure.Pr"r-.:rLl":' 01 L I J t . I - J ( . m p ~ r ; l l U f c n ~ p \ l s i h . . pp . "&00 ... 7: in Prnct:cdl ' ~ I,) 'he.~ u l J r l h Irll..:rn,t1 I(..'n;,tl C , \ n ( c r c n c ~ ~ l C VD, nn"don. MA , 11.1-; ElIl l rd h ..C F. \\'.skcfh.:/J :Ino 1 \1 . l : : H ~ ) C h . . : r .

. \ \ \ ~ l o t l r t . : . ) . L SIron!!. G. L. Doll, "o J M . Dressclh:Jus. -Therm:;&!St:lhrlltv ul C ( ' l J t . : r ( l ~ l l c = t 1 CU.' Cdmpchllt . :s"- rr . : , tJ- l in E ~ ( t : n d c d b"Ir.n:b_ 1"1lh Rlc::nn..ll CtJnlcrcncc on C.Lrhnn. Pl..:(lil:'-\il\.IIH;,t Stale l i n l ... c r " ( ~ . J u n ~ .:':.'- iO, ItJ;'1J E J I ( ~ u h P \ . Thro ..... ~ : r . \ r n ~ r I I . : J n C:Jrhl\n : O C I ( ' t ~ ')1. \ 1 . 1 ""_ 1.1,\ ]1.1 .... 1J [)

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saugnac_all characterization c-b-n solid solution deposited from gaseous phase

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