ELSEVIER Thin S~litt I:ilms 312 (Itlt98) 4(I-45

Preparation of epitaxial PbTiO 3 thin films by pulsed laser deposition

Young Min Kang "~. Sung Chul Bae h, Ja Kang Ku h Sunggi Balk "" " l ) ,7~artn. ' . t ~f,~lal<'ri++ls Sci,'t~{'c ~+t.I I".k,i.c~'rittk,, l~dqm~, , I ".iv<'r~ilv +q,~'cu'm'c +.td Tc<'tm~d~.~,v(l~OSl'l;'~ 'Hi. t~lt~tt~+ 7Uf/-7,~.1, St.~th K+.c<t

h Dt,lt+lrlm+.ll I +~j ( .hemAtrv , t'o/t<ttl k' I/llit cr~Jlv ot .~(</~'/t< c +ttld 7"<'< '/lllolt~,k, v t I ' ( )S1E(71) , / S d . m ~ , 7qO-7,~'4..~+~lllh A',~/'+'~/

I~.¢ccixctl 5 I : c b r u a r ) I t , 'u7: ;.LC¢¢r~lctl 2 9 M:i~ 1997

Ahstract

f-pilaxial Pb'l ' i(), thin Iihns v,ei'u' I'wel+ared m .,,ilu I',~ ptll~,ed laser dept+silion tm M~()((){)I ) and Sr*l'i()~U't)l ) .,,ingle cry.sIal .,,uhntrale.,,. The u'l'l'u'u'ln o1" (~.x)'~z¢l+ prc.,,.sur¢ and s, LII'~MI'III¢ I ¢ l l l pC fa l t l l ' ¢ O11 thu' ,.,rowlh t~t" filnls x,,¢1'¢ jnx'¢.,,ligalcd. The t'ax~'+'d'~lu col|tlilionn for Ihe fabrication t~l' cpitaxial fihns v, el+e identified+ Aplwolwialu" conlrol t~l' t+xygel; pre.,,sure in the range of 2()()-- 251) mTorr was necessary for +pilaxiat PbTi()~ thin fi lms and higher .,,tlbstralc lu~ntr~crtlltlrc up It~ 7<)(VC was rwcfu.t-rcd. The cpil+txi:tl ru'lalitm I+~t, txv~.,+,ll f i lm ar~+.t stll++.~tl+.ltu • is PbTi()~{II{ll}//M~{)({)OI). 1)bTiI}~(lll{l)//M~z()ll()()]. The chemical ¢ompunili~m of the lilm was ~,"v .,,imilar tO Ihe ideal stoichiomctrv of PbTi()t. :e 1998 F.Iscvicr ScJ¢IlU'¢ ,~.A.

Kc~u~,rdw l ipi l ; . t \ .~: P t ~ T i ( ) ; : I : ¢ r r o ¢ l e c t r i c lh i l l f ih l l ' , : P t i l , ¢ d lily, el ' d¢l:,~,,Jli~,ll

I. Introduction

Ferroelectric materialn ',vhiCh hm, e superior dielectric. pyroeleclric, piezoelectric, and electro-optic r>roperlies have been I+eceivin~ gl'eal interests in thin f i lm I~l'nln b¢catls¢ of ll'i¢ diverse applicability It+ Inemorv devices, pyroeleclric detector.,,, surlit¢c actmstic wav¢ (SAW)dev ices . and ¢l¢c- tro-oplic devices. PbTi()t {PT) based perov.',kilt: materials such as (Pb.l.a)TiO~ (PI+T). I-~b(Zr.Ti}()~ <PZT). and (Pb.LaJ(Zr,Ti)()~ t PI.ZT) represent a class o1" fcrro¢l¢¢trJ¢ materials which have been studied for thin film apf~lica- tions [t 21.

Becau,,¢ Ihe I ) r toe lec l l i ¢ I~t~r+el-tiCs ori~i lntt¢ l rom the sti'uctural +.~nisotl'opy of such imttcrials, in order It+ take full ttth'antage of the proportion, it i.s often i'¢quircd to prepare highl,v textured or single Crystal epi taxial thin film.,,. A number of el'fiwt,, have been rnad¢ to prClml'e ¢lfimxial H base Ii'~in t'illr~s u.~ing 'various deposilinn Incthodn incltLdin,g sputtering [3-51+ ,,~1-~01 16]. melalorganic chemical vapor dcposi l i~n ( M ( ) ( ' V I ) ) lTl. ~llld pulsed laser deposition (Pl, i)) [8- 13]. Ainon~ ~ arioun tlcp~v, ilion techniqucn. H . I )

( '~ llilu',~l',.llldili~ .ll itht)l '. ' N~+~x i~t M e m u ~ R & I ) l+i~.l',it+lh l h u n d m l . Ic¢Ir , mk, , hldtl ' , l l i¢',+

h1¢lloi+, 4<+7-7(II. K~uca.

{X)4()+f+()tj(I/ ' tg,~/~,,ItJ()(i , IOt.~X l . . l - ,¢xicr Ncicru+'c S A. Al l l i~ll l", l~+',,,..'Fxt'd.

I'II S ~ ) < J 4 ( ) r b < ) (j < ) < t}7 ) t ) ( )3 2 5 - ,"l

Js parlicularly advantageous because it has the capability oF reproducing Ihe target cnmpt~shioll al case. freedoln of usin,,~, ox,,~een. ,. atlnOnl~heru', high, deposition rate. and so on. 11ence PI+I) has been successfully used For tile IWeparalion of cpilaxial thin films of YBC() high tCml~erattlre super- conductor [ 14,15]. fu'rrt;el¢clri¢ oxide.,, such as BaTiO ~ [ 16] and Bi~Ti~() I. [17], conductive oxide (l.a.Sr)( 'o()~ [18]. Tile Iabrication of hetcrostructure of conductive oxide :rod fcrl'ocl¢clric oxitl¢ has heel1 also possible t l .~Jli ,g PI+I) [19- 2tl.

The pl't)ce.,,sing lXmLincLcr. ', for i~rcparalion of cpilaxial f i tmn by PI+I) urc xvavclcn,..z,|h o f la,,er, lancr enerpy dell- .,,Jly. ambiel l t oxygen pi'c.ssttr¢, substrate lgll l l lOraltlr~, alld M) Or1, / \ ( l l t H l ~ lhcln apl]roprJalu' L'Ol)tl'Ol o[' oxyg¢l l t ] I '¢SSLiI '¢

and ntll+Mi'atu tctlir~cratt]r~ durJll~ del+x+nJtit>n are tit+ most jlrtl')ortanl growth ¢'ondithms for the I~ru'lxu'atioi+ of crfitax- ial H ' -bancd fcrrt+clcclric Ihin f i lms 18-1 I]. In t+rder to uclt icve c l f i taxy, a few hundred I f f l 'orr o1" ,~xy~¢n I'wessure and Il l¢ stlb.',tl'ate lcl l lrpclattt lg hi~her lll+.lll "-55()"(' i.tl'c tcqtfil'¢d, i towexcr, there has been +it+ .,,eriou.,, study tm the ¢flcct,, o1 these Imrainclcrn on when and how lh¢ ¢ifitaxy could I+¢ acllJevetl. In IhJn study, we .,,elected a simple l¢rlt)¢l¢ctric Inatcrial, PI+FI'i()~. and inxostigalcd it+ tlctttil the effect or ox~ggll l+l.CnStil+~. • +.tilt] +',,tll'1.sll';+il¢ tci+]peralttrc on the deposition rate. crystal quality+ tlcpice or <+-axis oriel+-

}', Alht K,,.k' ul al. / 77tin 3",lid l"ih,.~ 312 t i~,~),~'~ 4# 45 41

l~.iliOI1, ,'111(I sm't'ace lu~)rl~hology. The epilaxial rela[ion he- IWeell PT t'ilm and M~() suh.slrat¢ and the chelnical com- po,~itior~ are also claril'ied.

2. Experimental

PlYl"iO.~ Ihin films have been prepared tlnill~ ill1 h! sill.I PLD leclmigue. The .schematic diagram o1" d~e deposiliol~ Chamber ix shown in I:i,g. I. Delails of the apparatus in thin ,',;ttldy were repot'led previously [15]. l..aser s),slerrl em- ployed in Ihis work wa~ an exeimer laser (Queslek 2460) operated in KrF mode. The angle between large[ and sub,slrate ,,¢tlrl'ac¢ is 3(V ;|nd the laser-induced i)lurrle is directed to the sul'~sti;lt¢ surface ,,,,,ill} i|11 approxirnat¢ly 6()" gl'azin~ angle.

Targets were rwel);~red hy a conven~tiol~al ceramic pro- u'e.s.,.;in,,~ procedure. H~() and Ti() , powder.,, were mixed and calcined for Pl¢l'i()~ r~hase rol'n]ation. Excess 3 mole ~/ of Ph() was added Io compensate PI~O I~ss during the p~wder I'q'eparalion and ,,,ul~,sequent thin Ii im deposition. Coll~pacled PhTiO, pellels were sinlered Iw healing up !o 900°C and co~fling slowly at a rale or I"C/mil~ in tl~e i¢lllr~Cl-;,llt.lre i'all~C, .sg()-~9(j"( ' , whicll includes the Curie lelnp~ralure (49()%'). "l"he density o1" Ihe iargel.s was al~(}til 7.4 ~ /cn ] ~ which corresponded Io appl'oximatelv 93g' ~1' the Iheorclical value (7.97 ~ . / c m : ) .

Suhslrales were l~olished MgO(()()l) and SrTiO~({){)l) single crystals. The ]atlice u'()nslanls Or M ~ O and Sr'l"i()~ are 4.21 and 3.9() ;~, r~'specliveIy, which are L'lose Io those or PhTiO~ ( , = 3.90 A, c = 4.1fl ,&). The suh,,lrales ~vere cleaned ultrasonically in Irichloroet, hylel~e, acetone, and methyl alcohol I'or I()rain each .,,ucces.,,ively rollowed t~y I~oiling in InedD, I ah:oh~l I'or I()rain.

After h)atlin.~ tl~e target : |t ld sLfl'lsli'til¢. ~i I'ew hundred reTort or ,)xygen lwe.,,,,,ure was I]laimait~ed in the C11;,1111t'~C1" while i'aisill,~ the '~ul'~slrale leml'~erature I-w resistive healin,, The lemperalul'e was monil(~red I~y a u'hl'ol~el-aluluel ther- moCotlple in ~.'onl[lu'l ~,~,ilh Ihe suhslrale. When Ihe suhslrale lellq~eralUle rcau'hed io a preset value in the range 501)-. 7()(VC', tile Krl" excii11er laser (24~ nrn, 3() ri,~ l~ttl.',,e v,,'idth) Ol'~ei'alin ~ al I() H/ v,a.,, line-f~cu.sed on lllu' l)bri()~ l;.|l'~el

0!

" IW Lens ~ Targel in(~ow

ISubstrale ~.~f::

i ""Zo,I,

V[|CllLIrl~

Exc~mer Laser

]"i,-'. I, S~.'l],~.'I1i~ili~.' di,L,.21aln ~fl 111,." l~Iil~,t'd l,i,,,.'r du'l',O',,ilion ,.,~ ,,Itenl.

Table I l)eponili~l~ condili~q~ and PI~Ti(), lhin l'ihu~

',mtahlen Ior the lwcPal'a|ion *~1 CPila\ial

'l'argel:

S iil'~,,ll~lt~.';

I . il',l." r;

l:lu~:nc,,.': ( )\%'~¢11 l'q'Cs',,,llt'e: ~ U l'r'.,[ r;.ilc' K, IIII~CI ill llr,u':

,~lntCl¢(I Pb'l'i()~ Cel~mli~', ] ' r e\¢u"., ~, PI',(). 7 rpin

.kl~[)((ll)l ). Sr'l'i(),(O~ll ) "- 2.~ ~.'II~

K,']: ex,.:imer. ?,I)~,, r, uls,... ,,,, Mlh. I() | l/ I , I / rm ~

Vmial'de ( i I H) - 3~0 lll'l'~wI') Variable (5~ HI- 7(i(i (')

whicri wan n)laled al about ~ I 'pl l l . The suhslrale was p~).,,itiorted ---3 cm away rrom the largel and --. I u'm of l from the center of Ihe ldUme Io avoid direct expontu'c, The dep~silion u'ondilionn are summarized in Table I. After lhe l'ilm dept)sition, the healer was turned off and IIle f i lm was allo;',ed to cool down lo I'O,'~lll temperalure. The approxi- male cooling l';.lh; WaS l()O"C/min.

('ryslal slru¢lure.n of Ihe thin I'iill-iS were irh'e.sli~aled bv X-ray dil'frac~ion (XRI) ) technique,s, All XRI) mca,sure- nlellln were carried oul with CtIK ~ radiation. The 0 -20 scan nleaSL.'emenls were cal'ried oul u.sing Rigaku D / M a x - 3 B dil'i'ra¢l~m~eter, equipl~ed with a ~raphile monocllrorru.ltor. ~ach specimen was loaded to a ~oniome- lCr ,so lllal the M~()[IO0] is in IIIe plane of incidence of X-ray beam. The sl'~ecimen angle (0 ) was calihraled by inaximizing the intensity of MgO ()02 rellectioll. In order I(~ establish in-plane epitaxial relations. (1~ scan measure- mer0ls ~vere ¢ondt~,,.'led hv rotalirl,g the sample around ihe .suhslrate normal direction arler tillin~,_ the sample to ~*,el PbTiO~ 103 and M~() 2(14 reflections, We used Em'al' 590 generator equil~ped with the Huller rive-circle ~oniometer For d'~e (1~ scan. The lhickness ~)1" file rilm was e,slimaled b\ measul'in~ the mass dirrerenu'e hel'ore and arler the deposi- lion. Surrace m~rpholo~y of lhe I'ilm was ohserved with a s¢; l l l l l i l l~ eleclron micro.,,copy (SEM, Hilachi $570). hs

chemi¢,d COml'~o.sition was determined hy lhe Rttlherford hack,,catterin~ nl~ectrornetry (RBS). The fi lm lhicknes,s was al,,o o . m l ' i r m e d ~.,,iI11 RBS. RBS and charmelir,g experi- Illelil.~ ~:,ere carried out u.,,ing a Van de Graff accelerator (NF.(" 3SI)11). The samples ~,,,ere mourned in a ~oniometric chamber ',,,hich ~llov, ed ad.iu.,,m'~er~! of PhTiO, [001] direc- li~m l'~arall,..'l IO lhe iltcidenl ~' parli¢le,, rot channeling.

3. r e s u l l s ; | l |d discussions

\Ve could ob,,¢r~e tile chan~e hi color and ~hape of ablated l~l~,ltll~ b\ o \ ~ ¢ n pre.,,nure. The o~lor ol" i~lume h~ ~acuum i,, ~hhe blue. and it I~ecome,, ~ello~v ;liltl i'eJ I~\ I'l~\vin~ o \ ~ e n o~er I()l) m'rorr. The ¢llan~e ill color nCu"l|l~ |0 he a r~."nt.Ill o f chemical reaCtiv, n of ahlalo.I I~articlen ~,~itll arnhielll o\)~en ['~'~]. hi ~,a, cl,|um, the l'~h.lnle

4 2 }' . ,~.tio Kant,, <'t t d . / 17mt Solid I"itm.~ 312 ¢ t~)t).~ 40- 45

t t

# PbTlO+/lllj i PbTiO i I IP. l l

o MgO ¢tll. ' ? Unll3enlihed Phase

I';

it + I O 20 30 40 .50 '00 70 P,D

Two Thela ('+)

Fig. 2. X-r i l ) ' d i f f r i l c t i on I~;itlerli~ c,f i~hTi()~ l ' ihn~ dcpt~xitcd at h S l ) C oi l

M~OI (X) I 1 ~,l',i'~,ll';ifl2 al ~-ilriOtl,, o%)'~12n rll.t,x.,,ilrt ,,

spreads out. The plume is confined Io target surface nor- nlal direction hy f lowing oxygen and the size of plulnc becomes sm,'iller by inc'reasing (i×ygerl presstlre,

Figs. 2 and 3 are XRD spectra oi PbTiO~ films de- posiled at wirious oxygen pressure in the range 100-35() rrlTorr on MgO at 650°C arid on SrTiOa +.it 600°C, respec- tively, in the whole range of oxygen pressure, pcmvskite phase was obtained, except sorrle unidentified phases ob- served in tt'le film deposited at 151) mTorr ori MgO. The PbTiO~ Iilrris on MgO show only 001 and hO() rellection peaks, which means that only (001) (for c-domain) or (100) (l'or a-domain) pianos of PbTiO, arc placed parallel to MgO(00t). However, the h00 reflection peaks fronl the PbTiO; fihns ori SrTiO: are overlapped will+ substt'ate peaks.

Fig. 4 sumnmrizes the effects of oxygeri pressure on deposition rale, 001 XRD intensity divided by fihn thick- heSS. and degree of c-axis orientution (only for filrns g r o w n on MgO). Its effect on deposition rate seems to be rather complex. At low oxygen pressure ( i00- i 50 mTorr), because the abhited particles in plume have less chance to collide with ambient oxygen molecules, number of parti- cles reaching the substrate is very large, but thcir kinetic energies arc high enough to respt, tter the adatoms sitting on the film surface. It may explain why low deposition rates were observed at low oxygen pressure. ,'ks the oxygel-

i a PDIiC) Illlf I i l ° S r l ' O I' . . . . .

! ! ! I t,i

" :C" "1 I N ~i~ " L/ t . . . . . . . . . A J . . . . . + ' [~ " 1 ~ ' '

m-,,. ,r <+, il ,t~

I cl 20 30 413 5l:, ,fill. 7 f) 80

Two Thela('G.

Fig .I. X-r;l% diffraction r~ltll¢lil~, ill" Plq'i(), IJlni~ dcpt,~itcd ill hl}()(' ~lil SrritiJ(tlll ) ktlh,,trlt le ;11 X;lriou', II',t.V~2121l ili'c~,,tlr¢.

(A)

(B)

(c)

100 - i ...... "E ' ! ~ on MgO

"E BO E3 on srmio 3 ,g m 60

r r '= c 40 !

, i

~ 2o

0 ' i

1 O0 150 200 ~" ; ° ° F , ,

£ 8o

~ 60 w ! X

~, ~ ~ , J Z 0 t

1 O0 150 200 I O0

t , - ~ 0 0 ' ~ m m 60

~._~ o ~ 40

u) X m 2O 6

0

r i I

I I I 1 250 300 350

i i ! i !

250 300 350

1 O0 150 200 250 300 35 0

O x y g e n Pressure (mTorr)

I:ig. 4. The efl'cci.~ of ox}~¢n I~l¢X~till. • till (A) dep~141ion i'alc'. (It) ihieknc~.~ nornialitcd X-r~l) illlell~Jl) o1' II}111 ) rcl]¢clittii. ;.iiltt ((') d¢Tr¢¢ ill" + -aXi~ orJel l l l i lJ l / l i O1' Plqr i ( )< i ihn~,

pressure increases, the ntlnlber of pro'titles arriving tit the substrat¢ becomes smaller while their kinetic energy be- colnes lower. So Illerc is the optimunl ranoe o1" ox),g711 pressure (2( i l i -25()n lTorr ) which ,,,ires the inaxJlllUin de- position ral¢. 11" oxygen pre.~stlre increases further, Ihe i l t i n l h e r o f particlc.~ arriving a l the .~ult.~ti'ate t i r e r e d u c e d h' l

show the decrease in deposition rale. In order to conlpal'e the crystal quality of the fi lms with

Val')'ill~2 thickness, we slllli.ild ilOrltllilile the XRI ) peak inlcn.~ily b b, dividin 7 with fil iu ihickue~s beeau.~¢ the a n i o i i l l l o r . ~ . ' a l l e l i i l ~ .~pccic.,, I'~)r 7ire,1 e x p o . ~ t i r o ; l re:. i t l l '

X-l'ay jlli.'i't2;.i.~e.~ with f i lm thickne.~.~. PbTi()< I'ilin.~ with .,,uperJor epitaxia[ properlie.,i were ol}lahled in ;i narrow oxygen pt'eS~ill't~ wiudow llt211r 2(1(I tnTorr till Sr'l'i()<. (llltl 250 i11Torr #,ill Mg().

The l>bTi()~ fihu.,, dcposilcd on Sr'l'i()~ ~til}.~li'alt?.,, .,dlow .~tlpel'ior ¢l'),,~lal Cltlalily Ihall lllo.~e oil MT() .,iuh~lralcs. The lalliee l.'t)ll.~ltilll~ of Mg(), SrTi(); , aud Pi'ITi()~ i.lr¢ al~otit 4.24 A. 3.93 A, and 3.till /~ ill tler~tixilitin l¢lnperaltll'O, i'e.~pecliv¢ly. The lallic'e nlist'it helween Si:l'i()~ and l~bTi()~, (oi+ill-Ol,iql)/Oi,lC I, ix ai~Otll - I ) .TG, while ihc

Y, Min K.n,t,, ct al+ / 77+in Solid I"ilms 312 ( 199,~¢~ 40+.45 43

misfit between MLaO and PbTiO.~, (¢I~I~()-~Ii,.i.())//111,.i.(), iS

about 6.8r~. The small lattice rnisl'il seems to be the rnain reason Ibr the superior crystal quality of the tilms de- posited on SrTiO 3 substrates.

Thc degree of ¢'-axis orientation of PbTiO~ films on MgO is evaluated from the XRD spectra by defining a = i~,~l/[l~,, I +/im~]. where lm~ I and /+, m are the XRD intensities of 00t and 100 reflection, respectively. Even though this definition underestimates the amount of a-do- main because of domain tilting [13]. it provides us with a rough estimation of domain abundance. The dependence of

, . , : ' , . + . ,

,'+! 'i : :". +

Fig. 5. SI 'M microglal+hn of PbTi(), fihun del+L~nitcd at {+5()(' un Mg()((XII ) stllistI'ales al xai'Jt+us ~+x).~Cll prcsst(re. (.&) 1511 ll l] 'orr. ( l l l 25() mTolr, and (( ' ) 35()nfl 'orr.

i i * o• t

I) • Pbt,O, ,~, it • PbTIO~ JllJll , o MgO (~J2

• + ~ 20 30 4o so 60 70 ao

T w o TMeta("}

Fi~ 6. X-ray dil'fraclitm pallo'n.~ of PhTiO~ films deposil,,:d on MgO(t]OI) suhMrate ullder 250 l l lTorr ol + ( ' I 'X)r~I,)I | ] ;'(,),~surli~ el| ~,'tlrit+tlS dc21"x.'msjtion temperatures.

<~ on oxygen pressure shows the same characteristics as those of deposition rate and crystal quality+ For the case of the films deposited on SrTiO~ substrates, we could not estimate ~+ because of the peak overlapping.

Fig. 5 shows the change in surface morphology of PbTiO+ films grown on MgO as a function o f oxygen pressure. Surface of the film deposited at 150 rr(l'orr shows high density of particulates. The fihn deposited at 250 mTorr shows very smooth and dense surfi~ce with some square shaped protrusions. However, the film deposited at 350 re tor t consists of very fine grains with smooth sur- face. The change in surface morphology ot' PbTiO~ films by oxygen pressure also seems to be caused by the inter- play between particle energy and resputtering of adatoms. At tow oxygen pressure, the high energy particles resputter the surface of the film producing w'ry rough surface morphology. As oxygen pressure increases, resputtering of adsorbed particles does not occur, and the particles have sufficient energy tier migration to stable mite to show very smooth surface morphology, At high oxygen pressure, the adsorbed particles migrate at the surfitce in a restricted area because of the lack of energy aqd fore1 fine grains.

3.2. l:.'l]b<'Is ++l'.~'uhslrate teml;e,,'atm'e

Fig. 6 is 11+20 XRD scan spectra of PbTiO~ films on MgO(001) deposited at various subslraie temperatu~ in the range 550-7(XFC with 250 reTort of oxygell p~ssin~. All the films exhibit Ibrmalion of perovskite phase. Con- tinuous increase in XRD peak intensities corresponding to the pei~wskite phase is Miown due Io the increase in stibstl'ate telnperalure. Fig. 7 shows the simihlr results Ibr SrTiO~((X)I) substrate at 2IX) nfl'mT of oxygen pressure, For the ca,,,e of sputler deposited PbTiO; [4], the perovskite phase has been reported to Ibrm in a nmTow tenll'~ratul'P window around 6(XFC. Amorphous phase, pb,Ti ,O, type pyrochlore phase, and PbTi ,(): phase have been also observed as lhe substrate temperature increases. However. we coukl not obs,'rxe such phase ill tile ralt,~e o f our eXl~eriment.

44 )'. Mii~ k'+m.k, el a/ . / l ' l t i , S+,Ii<I t"ilm.~ 312 ~ I()q,~i 411-45

l ta PDTIO, ftllt

g . . . . . . . . . . - t Z -

:5__+.++.,'K_ . . . . . . +_.2_. __.A]L . . . . . . . . . . . . . . JL~t: c ,1to • a * {:,

l0 ~0 30 4(" 511 li0 70 BI)

Tw~ Thela( ' )

l:i~. 7. Xira) difir;.iclioll p:,tt,_'rn+. .lt.i r l)b'['i()~ l+illll~, ,.Iu'I~t~'.,ih.'d ¢~ll ,';rTi()d(l()l) stll~slr;ll~.' trader 2li(i inTurr of u~..vp..'n l'm.',,,,tm., al ,,aiiuu~, tleposili~m 1 ¢ I llllu'l'~,l[ I.II'e s.

Fig. 8 shows the efl'ect,~ of subslrl.+le temperature t)n deposition rate, OOl XRD intei+~sity divided hy l'ilm lhi,,:k- less . and degree o1' c-axis orientation. Fig. gA shows thl.it deposit ion rl.lle increased a,s t11¢ subMl+l.tle tClllpel'aturc Ji+- (.,'reascs. Lee el al. [15] explained that the dependence of

(A) "I~O -E- - - - . . i =

der)oKitiOll i,Lit¢ o11 .stLhstrato lerl)[ler;,LlLire j.,,,i due IA) re.,,,il)Lillel'- ing ¢~1 weakly adsorhcd I')artic'les. The icason thal higher lernl~¢ralLIrC is I'avoral)le for higher depositiol~ tale is pre- surnahly due Io Ihe increased migrat iol ! rate o f adsorbed particles to thu' most stable site for cryst: l l l izat ion,

Fi,g. 8B also inq+ties thai tile ¢l'yslal qual i ty has he~n enhanced hy increasing stll~sli'Lile Icnl[}er;.|ture. The I'eLl.~Oll iS Ihat hi~l]er tellq~eralur¢ seems to be bel~¢l'ician for ~211Ill.iileellleill itl crystal l izat ion kinetics,

~l' ;.it,'4,o JllEr~l.l,,;et.;, by Jllet'~3;.i,'.,;Jtl~ ,slib.~li'ate Ik:l11[)el';.Ittli'~ 1.1~ sl'~own in Fig, 8C. Above the Curie terrlr~m'alure of PbTi()~, 492'+C. there is no distil~U'tion between (001) and (!(}0) beeatl,'.ie il has cubic slructure. XRD relle¢ticms fl'onl (0011 arid (100) planes in the films arc a result or ll'ai:sl'on'nlatiort to tetraL2Otl;.ll stru¢ltlre as lernperaltlrc tleerel.lscs during cool ing from the deposit ion tcmperaluu'e [23.24]. Because the lattice conslanl of tell'age, hal PhTiO~ alcmg c-axi.,.; increases wilh respect to ih;+it tfl" cubic i~bTiO~, while ihat l.ll()ilg a-axi.",; decreases, eonlpuvssive .Ml'eSs is favorable for ('-donmins, 13eCtlLiSe the thernial expansion coefl ' icienls of M~O (t4 x i() " / K I25]) are Im+ger titan thai of PI'~TiO~ (8 X i() ~ ' /K [26]). compressive stress is accumulated il'~ the f i lm, t-lcnee the increase in the deposit ion temperature indl.lces tile iilcu'el.lse ill tile compressive slress ;.it tile CI.il'ie

¢,. .~ E l on MgO t C m l ~ c r a t u r c , whid~ racil i tales higher n,. The ,a, bservation is E l on SrTiO 3 " con.si.slenL with PT filun.~ deposiled ILl Slmtlcu'ing [27].

80

F~ ~ ¢ ~ ':'l,it,.vial /'e/alifm (,/Id ,'Oml,osi/i~,t i~ 6o I . . . . . . .

2 I'elalioI|. "FIle 1113 refle¢ti~n (~1" ('-d,)rrll.tirl o f PbTi()~ and . 204 rel ]e¢l jol l or ME() stll~,stl'atC were used Io gel the

120 500 , 550 1 0 1 0 1 0 si, ectra. Bolh peaks appea,, at the same posilion, whM, (B) ~" . ~ suggests that the Pleri()~ f i lm is aligned in plane epitaxi-

<~ 1 " al ly w i lh M ~ O .~tib.~lrl+ltes. Thai is, the in-platle ¢rystatl- E graphic ur ientat ion relatior~ship belweell f i lm anLl .suh.slrale

is I]'bTi()~[ll)()]//Mg()[li)l)]. By u'omhiuling the I'u'sutl o1" x " orientation t'elationsl'fir+ along sul+.stn'ale normal dia'e¢lion

(C) ~oo soo , sso

°~ 80

" ~ 60 ( D E ~._~ ,:. ~ 40

=o -+ J/lttl !1 L ' + ' " : ' J/ltiJll 0

500 550 600 650 700 I,, ,] ~(~ ,'LI .IH 41: flu f,q /:~ ~,1~ ~+13 1Ll~}

Deposition Temperature ( °C) i% ()

Fig, X. The effect,, q+l .~,tlh...lrill~.' tempenalurc on (A) del'~u',itiou+ 1J:LIL'. (1¢) l l l j L ' k n c ~ , ~ na~ l l l l ~ . l l j / u 'd X - n l ~ , i r l l L ' l l ' ~ j h ' , l l ( ( X ) I ) I 'UI ' IL'L' I i~Hi, ; . l l ld ( ( ' ) du '~ lu 'k ' ] : i ~ . t j . t I ) '~L'dll ~.l~k'k"ll]l I ' d lll¢l'i()~ I h i l l I j l l l l i t l l~l M ~ ( ) NII['~MI'i.|IL' n l l t ~ ' & i l l ~

el ~ r-axJ.', Oli¢,ll;liit~ll {)1 PbTi()~ fitm,,. Ih~.' ill-plall¢ el+fil;t\M lel;.|lP.t.ll.

)'. M i , K ,n . t : {'t . I . / 77m~ S , l i d l"ih,.~ 3 1 2 t I*I~AYI .#1 .. 4 5 45

(Fig, 2) we could ctm¢ludc that the PI~Ti()~ films on MgO have Ihc cuhe-ol~-cuhe cpitaxial relation.

Fig. 10 shows the RBS spectra of PhTiO~ I'ilm on Mg() substratc at 650°C of sub,str;.llc tcmpcnltur¢ with 250 n i T o r r

o f oxygen i)l'essure. One o f lilt .spectra was ol'~tairled with tile beam at a rantl(}ln il)cidcncc und the other with tile beam aligned with the [(1()t] crystal axi,s. The composition of Ihc film is consi.slcrtl with Ihosc of stoichi(m~elric Pb'l'iO~ ~is wctl as of tal'gel. The minimuln channeling yield, X,,,,, was calctlluted to I~c --- 7()¢;~, hascd (m the Pb peak. This rather poor cllunneling is c(m~idered due to the doillair~ tilting [13] and periodic tlomuin structure [28]. For in,~lall¢¢, the tilt ;.lllglc of a-domuins in the film, -,-_ . 6 r [13,23], is larger than the crilical angle for toll he;.lln chunneling, ---- I {' [29]. which implies that chatmclirlg h;is been pr()hibitcd in the a-domuins,

4, Conch'sion

Ei)itaxial Pbr r iO~ films were prcl')m'ed using pulsed laser depositiorl on Mg()(()()l ) and SrTiO~(()()I ) substratc.s. T h e f i l m s s h o w an c p i l a x i a l r e l a t i o n ¢~f PbTiO :(001 ) / / M gO{()() I } and Pb'ri() ~[ !()()1//MgO(I(1(1) ;.Llltl a stoichioil~elric ctmq~o.silion. The cl'fcct.s of .'-;ul~sll';.lle tenrIpeualurc and oxygen pucs,surc on the characteristics of epitaxial growth of PbTiO~ thin films were studied. In- creasing substrutc tcnnpcruturc up to 70(VC has enhanced the deposition rate, the cu'y.stal quality, ;.uld the dcgl'cc of ~'-axi.s orielltatit)n. However, in order to , ,,iain ~ood epi- taxial I'i1111s, Ihel"e is u n¢U'l"OW \vind<~w of uxygen l)l"CS.sure i l l the range (~1" 2()1)-25() ii'(rorr. The I ' i lm deposited tllldt:l" this range ol oxygen ]~l'eSSUl'e showed a .,,moolh .,,urrace morplltflogy v,,ilh ~.l good cry.st:llliuc quality.

....... [ t

( "h3 rlt'~olod ~ ' 3 i

>7.

. . . . . . IL i +,1oo~ ,!

t

Chal;r~t)ts

Fig. II,. Ri l ] i t lot l l ;.tlld u'll~lllllu'lt'tl R I IS nl~t.'u'll~| o1 [~br i ( )~ th in I i ] t l l ~lO~AIi ttn ( ( ) ( ) I ) Mg() ill (!,5II (" 'q, i l l l ;.Itl I~\.%gell III'L'4~.III~L ', 2.¢'1)II!.'i'l~,I'l'.

Acknowledgements

This work was supported by th,: Korea Science and Erlgincering Foundalitm tl'lr~augh the Engineering Rese;arch Ccrltcr for Interface of Maleriais,

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