Dis inguishing he Rhombohed al Phase om O ho hombic Phases
in Epi axial Doped H O2Fe oelec ic Films
Ad ian Pe a u,*Ole G onenbe g, Ul ich Schu mann, Lo enz Kienle, Ra i D oopad,
and He mann Kohls ed
Ci e This: ACS Appl. Ma e . In e aces 2024, 16, 42534−42545
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ABSTRACT: Epi axial s ain plays an impo an ole in he
s abiliza ion o e oelec ici y in doped ha nia hin ilms, which
a e eme ging candida es o Si-compa ible nanoscale de ices. He e,
we epo on epi axial e oelec ic hin ilms o doped H O2
deposi ed on La0.7S 0.3MnO3-bu e ed S TiO3subs a es,
La0.7S 0.3MnO3S TiO3-bu e ed Si (100) wa e s, and igonal
Al2O3subs a es. The in es iga ed ilms appea o consis o ou
domains in a hombohed al phase o ilms deposi ed on
La0.7S 0.3MnO3-bu e ed S TiO3subs a es and wo domains o
hose deposi ed on sapphi e. These indings a e suppo ed by
ex ensi e ansmission elec on mic oscopy cha ac e iza ion o he
in es iga ed ilms. The doped ha nia ilms show e oelec ic
beha io wi h a emanen pola iza ion up o 25 μC/cm2and hey
do no equi e wake-up cycling o each he pola iza ion, unlike he epo ed polyc ys alline o ho hombic e oelec ic ha nia ilms.
KEYWORDS: e oelec ic H O2, ul a hin ilm epi axy, ha nia, epi axial H 0.5Z 0.5O2 hin ilms, Y-doped e oelec ic H O2.
1. INTRODUCTION
Fe oelec ic ma e ials a e o inc easing echnological
impo ance ha ing con inuously ex ending applica ions includ-
ing e oelec ic andom-access memo ies
1,2
o s o age,
senso s and ac ua o s,
3,4
op ics,
5,6
and elec onic de ices o
neu o-inspi ed elec onics such as mem is o s, necessa y o
building up elec onic synapses o neu omo phic compu -
ing.
7−9
Recen ly disco e ed e oelec ici y in doped ha nia
ul a hin ilms opens new pe spec i es o he ealiza ion o
special de ices like e oelec ic ield-e ec ansis o s and
e oelec ic unnel junc ions
10,11
due o hei compa ibili y
wi h he Si echnology.
Single-c ys al Y-doped H O2 e oelec ic ilms deposi ed on
y ium-s abilized zi conia ha e al eady been epo ed,
exhibi ing he o ho hombic pola phase wi h he space
g oup Pca21(o-phase) and a pola iza ion o 16 μC/cm2,
gene ally conside ed esponsible o e oelec ici y in hin
doped ha nia ilms.
12
On he o he hand, epi axial H 0.5Z 0.5O2
ilms deposi ed on La0.7S 0.3MnO3/S TiO3(subs a e) by
pulsed lase deposi ion (PLD) ha e ecen ly been e-
po ed.
13,14
These ilms do no c ys allize in he commonly
epo ed o-phase, bu in a pola hombohed al phase ( -phase),
s abilized ia epi axial s ain, and was iden i ied wi h a la ge P
o 34 μC/cm2. Mo eo e , hese hombohed al ilms do no
equi e “wake-up” cycling o es ablishing e oelec ic swi ch-
ing unlike mos o he epo ed polyc ys alline ilms wi h an
o ho hombic pola phase. Recen ly, polyc ys alline H -
(Z )1+xO2c ys allizing in a hombohed al e oelec ic phase
wi h a low coe ci e ield ha e been epo ed.
15
Meanwhile,
epi axial doped ha nia ilms we e epo ed by some au ho s,
being deposi ed on se e al single c ys al subs a es like y ia-
s abilized zi conia (111)YSZ, (100)YSZ,
16
LSMO-bu e ed
LaAlO3,
14,17,18
S TiO3,
13,14,18,19
NdScO3, NdGaO3, MgO,
18
YAlO3, (LaAlO3)0.3−(S 2AlTaO6)0.7 (LSAT), DyScO3,
14,18
S TiO3-bu e ed Si,
20
and GaN-bu e ed Si.
21
An in e es ing
s udy on epi axial doped ha nia ilms deposi ed on a ious
La0.7S 0.3MnO3(LSMO)-bu e ed subs a es e eals ha
TbScO3and GdScO3a e e y good candida es o epi axial
s ess s abiliza ion o he e oelec ic phase.
18
In mos o hese
s udies, he s ess-s abilized me as able pola o ho hombic
phase (Pca21) was epo ed o be esponsible o he
e oelec ici y in doped ha nia ilms,
12,17,19,20,22−26
whe eas
he hombohed al (space g oups R3mo R3) phases a e less
epo ed. The eason migh be he ac ha he o ho hombic
phase is ha d o dis inguish om he hombohed al phase. In
his a icle, we ocus on he challenge o dis inguishing
be ween hese phases.
Recei ed: June 24, 2024
Re ised: July 23, 2024
Accep ed: July 28, 2024
Published: Augus 5, 2024
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Apa om he epi axial ha nia ilms deposi ed on sapphi e,
ITO-bu e ed YSZ, and GaN, only epi axial ilms deposi ed on
LSMO-bu e ed subs a es ha e been epo ed o be e o-
elec ic.
A s udy on o he bu e laye s like LaNiO3, La0.5Ca0.5MnO3,
S RuO3, and Ba0.95La0.05SnO3showed a low o no s abilized
e oelec ic phase, excep o hose wi h mangani e elec o-
des.
27
In addi ion o he epi axial s ain imposed by he subs a e,
ac o s such as deposi ion empe a u e, pa ial gas p essu e,
and ilm composi ion also play an impo an ole in
de e mining he o ma ion o c ys al phases. Fo example,
Kaise e al. epo ed ha ei he a monoclinic o a
hombohed al phase is s able in H O2 hin ilms g own by
molecula beam epi axy on c-cu sapphi e depending on he
oxygen pa ial p essu e. DFT simula ions ha e shown ha he
hombohed al phase is s abilized by oxygen acancies, no due
o he epi axial s ain.
28
Fu he mo e, i was discussed ha a
zi conium subs i u ion may ha e he same e ec .
Supe la ice and laye s uc u es p o ide a u he imp o e-
men o he e oelec ic pe o mance o ha nia-based ilms.
Thus, “wake-up” ee e oelec ic capaci o s based on H O2/
Z O2supe la ices
29
o capaci o s wi h imp o ed e oelec ic
and dielec ic pe o mances ha e been epo ed.
30,31
In his wo k, he ocus will be on e oelec ic epi axial
doped ha nia ilms deposi ed on h ee di e en subs a es o
compa e hei s uc u al p ope ies and o de e mine hei
c ys al s uc u e. Thus, Z /Y:H O2/La0.7S 0.3MnO3/S TiO3
(100), Z /Y:H O2/La0.7S 0.3MnO3/S TiO3/Si (100), and Z /
Y:H O2/Al2O3(0001) sys ems a e in es iga ed he e. The
s uc u al cha ac e iza ion o each o hese h ee sys ems
(comp ising XRD and TEM esul s) is p esen ed in a sepa a e
subsec ion, and he elec ical cha ac e iza ion is shown in he
las sec ion o he esul s.
2. EXPERIMENTAL METHODS
2.1. Ma e ials. H 0.5Z 0.5O2and H 0.93Y0.07O2 hin ilms o
hicknesses a ying om 2.5 o 12 nm we e deposi ed by pulsed
lase deposi ion (PLD) on La0.7S 0.3MnO3-bu e ed S TiO3(001)
(STO) subs a es, La0.7S 0.3MnO3-bu e ed Nb (0.5%)-doped S TiO3
(001), S TiO3-bu e ed Si subs a es, and sapphi e (0001) subs a es.
The doped H O2and he LSMO ilms we e deposi ed in a single
p ocess wi hou b eaking he acuum. The H 0.5Z 0.5O2-and
H 0.93Y0.07O2-sin e ed ce amic a ge s we e pu chased om EVO-
CHEM whe eas he LSMO a ge was pu chased om P axAi . A K F
excime lase o 248 nm in wa eleng h was used o abla ion in a
comme cial PLD sys em om Su ace GmbH. The La0.7S 0.3MnO3
ilms we e deposi ed a a subs a e empe a u e o 780 °C, unde 0.15
mba O2, and a a lase luence and equency o 1.4 J/cm2, and 2 Hz,
espec i ely. The doped H O2 ilms we e deposi ed a a subs a e
empe a u e o 800 °C, unde 1.5 ×10−2mba O2, and a a lase
luence o 1.4 J/cm2and a equency o 5 Hz. A e deposi ion, he
ilms we e cooled a 5 C/min o oom empe a u e unde 3 mba o
oxygen p essu e. Epi axial 20 nm S TiO3bu e laye s we e deposi ed
on Si(100) subs a es by molecula beam epi axy (MBE) a Texas
S a e Uni e si y. The epi axial oxide g ow h on silicon was achie ed
using a codeposi ion p ocess in which bo h he alkaline ea h me al
and he Ti shu e s we e opened in a con olled oxygen en i onmen .
Since, unde hese g ow h condi ions, he s icking coe icien o he
indi idual elemen s is uni y, ca e ul calib a ion o he luxes was
pe o med o s oichiome ic oxide ilms. The g ow h a e used was
app oxima ely 2A/min and was calib a ed using RHEED in ensi y
oscilla ions.
2.2. XRD Cha ac e iza ion. The XRD measu emen s including
wide- ange ecip ocal space maps (RSMs) and pole igu es we e
acqui ed wi h a Sma Lab di ac ome e (Rigaku) equipped wi h a 9
kW Cu anode X- ay ube and a 2D HyPix-3000 X- ay de ec o . A wo-
bounce monoch oma o was used o high- esolu ion XRD scans.
2.3. TEM Sample P epa a ion and Analysis. C oss-sec ional
TEM samples we e p epa ed om he S TiO3and Al2O3subs a es
using ocused ion beam (FIB) milling in an FEI Helios Nanolab
sys em. Be o e Ga-ion e ching, a p o ec i e P coa ing was deposi ed
wi h a gas injec ion sou ce inside he FIB sys em. A plan- iew sample
on a Si subs a e wi h epi axial S TiO3and LSMO laye s was p epa ed
wi h a P ecision Ion Polishing Sys em (PIPS, Model 691 om Ga an
Inc.).
The FIB samples we e analyzed using a JEOL JEM-2100 wi h
elec ons accele a ed o 200 kV ex ac ed om a LaB6 ca hode, while
he PIPS sample was analyzed wi h an FEI Tecnai F30 G2a 300 kV
and a ield emission gun.
2.4. De ice Fab ica ion. Fe oelec ic capaci o s we e ab ica ed
by deposi ing Cu op elec odes by he mal e apo a ion h ough a
s encil mask. The de ice size a ies om 25 o 225 μm2. O he
e oelec ic capaci o s on Si subs a es we e pa e ned by using UV
op ical li hog aphy and A +ion beam e ching.
2.5. Elec ical Cha ac e iza ion. The e oelec ic hys e esis
loops (P−Vloops) o he e oelec ic capaci o s we e measu ed by
using a Radian Technologies P emie II e oelec ic es e . The es
signal used he e consis s o a linea amp wa e o m wi h a pe iod in
he ange o 0.1 o 150 ms. Addi ional e oelec ic hys e esis loops
we e measu ed wi h an aixACCT TF Analyze 3000.
3. RESULTS AND DISCUSSION
3.1. S uc u al Cha ac e iza ion. 3.1.1. H 0.5Z 0.5O2
(HZO) Films Deposi ed on LSMO-Bu e ed (001)-O ien ed
Nb:STO Subs a es. 3.1.1.1. X- ay Di ac ion Analysis. An X-
ay di ac ion (XRD) scan o a H 0.5Z 0.5O2(HZO) ilm on
LSMO-bu e ed (001)-o ien ed Nb:STO subs a es is depic ed
in Figu e 1a. The specula e lec ions 001, 002, and 003 o he
Nb:STO subs a e a e he mos in ense ones, ollowed by he
specula e lec ions o he epi axial LSMO ilm. The 003 and
006 e lec ions o he HZO ilm a e also p esen . Figu e 1b
shows he magni ied 003 HZO egion, whe e he hickness
oscilla ions a e clea ly isible, demons a ing good c ys alline
Figu e 1. (a) The XRD pa e n o he H 0.5Z 0.5O2/La0.7S 0.3MnO3/
S TiO3(subs a e) he e os uc u e; (b) he de ailed H 0.5Z 0.5O2003
egion wi h hickness oscilla ions; he blue line ep esen s he
expe imen al da a, and he ed line is he simula ion o he
di ac og am showing a ilm hickness o 8 nm. (c) Simula ion o
he La0.7S 0.3MnO3001 egion ( ed line), he ilm hickness is ound
o be abou 71 uni cells, i.e., 27 nm. (d) Rocking cu e o he
H 0.5Z 0.5O2003 e lec ion; FWHM = 0.032°.
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quali y and well-de ined in e aces. An a e age HZO ilm
hickness o 8 nm is es ima ed om he i o he 003 e lec ion
egion, using he o mula o he heo e ical di ac og am,
32
adap ed o in e plana spacing:
I n( ) sin( d sin / )/sin( d sin )/ 2
[ ]
, whe e dis he
in e plana spacing o he XRD peak in ol ed ( he planes a e
Figu e 2. (a) Wide ange RSM o he HZO/LSMO/STO (subs a e) he e os uc u e. The spo s belonging o LSMO/STO a e deno ed in da k
blue, whe eas he spo s om he HZO ilm a e deno ed in ed. The angles ma ked nex o he HZO spo s ep esen he in-plane o a ion o he
co esponding HZO domains; he hkl Mille indices a e assigned he e o he R3mphase. (b) Pole igu e o he HZO {201} and HZO {022} spo s;
he black, ed, blue, and g een a ows indica e he ou domains wi h he amilies o spo s associa ed wi h hem. Pole igu e simula ion o he HZO
ilms: (c) phase R3m, conside ing (001) ou -o -plane o ien a ion and p esence o ou domains, wi h an in-plane o a ion o 90°wi h espec o one
ano he ; (d) phase Pca21conside ing (111) ou -o -plane o ien a ion and p esence o ou domains, wi h an in-plane o a ion o 90°wi h espec o
one ano he , and he p esence o {200}, {020}, and {002} spo s.
Figu e 3. HZO/LSMO/STO (subs a e) he e os uc u e. (a) 2θscans o he 12 poles a chi = 71.1°and o he specula spo (chi = 0°in black). 2θ
scans o he 12 poles a (b) chi = 55.7°and (c) a chi = 35°.
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42536
pa allel o he sample su ace), θis i s co esponding
di ac ion angle, λis he X- ay wa eleng h, and nis he ilm
hickness in he numbe o in e plana spacing. The heo e ical
di ac og am is plo ed wi h a ed line as shown in Figu e 1b.
A simila analysis o he LSMO ilm e ealed an LSMO ilm
hickness o 27.4 nm, as illus a ed in Figu e 1c. The ocking
cu e o he H 0.5Z 0.5O2003 e lec ion illus a ed in Figu e 1d
shows a FWHM o 0.032°, indica ing a good c ys alline quali y
o hese ilms.
Nex , wide- ange ecip ocal space maps (RSMs) and pole
igu es we e measu ed o he same s ack o de e mine he
c ys allog aphic phase and he o ien a ion o he HZO ilms.
Thus, in he ecip ocal space map o he H 0.5Z 0.5O2/
La0.7S 0.3MnO3/S TiO3(subs a e) he e os uc u es shown in
Figu e 2a, he subs a e e lec ions 001, 002, and 003 a e
iden i ied and labeled in da k blue colo on he RSM. The
ecip ocal space spo s co esponding o he epi axial LSMO
laye could no be dis inguished om hose o he STO
subs a e, due o lack o esolu ion in he wide ange RSM
measu emen s. He e, we like o speci y ha he sample was on
pu pose in-plane o a ed by an angle φ= 15°(wi h espec o
he in-plane a-di ec ion o he STO subs a e) o a oid he
con ibu ion o nonspecula spo s o he STO/LSMO). Fo
mo e cla i y, a wide- ange RSM o he same sample measu ed
a φ= 45°is shown in Figu e S1, whe e he 111, 112, 113, and
221 spo s o he STO/LSMO a e also p esen . The HZO ilms
g ow epi axially ou -o -plane on he LSMO/STO empla e,
and he ilms appea o consis o ou kinds o domains,
belonging o he same c ys allog aphic R3mphase, i s
epo ed by Wei e al.,
13
ha ing ou kinds o in-plane
o ien a ions, o a ed by 90°wi h espec o one ano he . A
simila domain s uc u e was epo ed by Nukala e al. o such
he e os uc u e.
14
The eason o his domain con igu a ion
could be explained by he 4- old symme y imposed by he
subs a e, as also desc ibed by Es andi
a e al.
18
and obse ed in
he e oepi axy o oxides
33
o semiconduc o s.
34
The esul s a e
illus a ed in Figu e 2a. The angles ma ked nex o he HZO
spo s in he wide- ange RSM ep esen he in-plane o a ion o
he co esponding HZO domains. F om he 022 HZO spo ,
we ex ac ed he la ice pa ame e alues o a= 7.17 and c=
Figu e 4. (a) HRTEM mic og aph showing an LSMO back elec ode
in ZA [
54
2] g owing along (012) planes. An FFT analysis shown
below in (b) and (c) was pe o med on he wo HZO egions ma ked
wi h ci cles. The le g ain is in [100] ZA, and he igh FFT shows a
supe posi ion o a [100] and a [
1
00] ZA which could be explained by
a win wi h a 2- old o a ion a he [003] di ec ion. These domains a e
indica ed by yellow and ed ec angles. The o ange ellipse in he le
FFT in (b) ma ks he addi ional [
2
22] mino i y g owing di ec ions o
he main [003] g owing di ec ion. The SAED pa e n in (d) is simila
o ha o FFT in (c).
Figu e 5. (a) Wide- ange RSM o a 5.6 nm hick HYO ilm deposi ed on La0.7S 0.3MnO3/S TiO3/Si (subs a e); he e, he obse ed spo s om he
HYO ilm a e assigned o (001)-o ien ed ilms o he e oelec ic R3mphase, consis ing o ou ypes o domains wi h 0°, 90°, 180°, and 270°in-
plane o ien a ion. The measu emen was acqui ed a φ= 0°. (b) Pole igu e o he HYO {022}, HYO {201}, STO/LSMO {011}, and Si {111}
e lec ions; he yellow, ed, whi e, and g een a ows indica e he ou domains wi h he amilies o spo s associa ed wi h hem. The measu ed 2θ
ange is 24.9−37.4°. The adial di ec ion ep esen s he χaxis anging om 0° o 90°, whe eas he azimu hal di ec ion ep esen s he φaxis wi h a
ange om 0° o 360°.
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8.82 Å. Mo e p ecise alues will be ex ac ed om he high-
esolu ion in-plane and ou -o -plane scans.
A pole igu e o he HZO/LSMO/STO (subs a e)
he e os uc u e is shown in Figu e 2b. The adial di ec ion
ep esen s χ, which anges be ween 51°and 85°, while he
azimu hal di ec ion ep esen s φ, which anges be ween 0°and
360°. Please no e ha he pole igu e p esen ed he e is no
measu ed o a single e lec ion bu o a wo- he a ange
be ween 23°and 37°. Thus, he HZO {201} and HZO {022}
amilies o e lec ions a e seen he e. The 12 poles o he HZO
{201}, measu ed a a 2θangle o 30.5°and he 12 poles o he
HZO {022} measu ed a a 2θangle o 35.6°a e clea ly isible
in he pole igu e. F om he c ys al symme y o he R3m
phase, one expec s h ee poles o each, spaced by 120°, bu
he p esence o ou kinds o c ys allog aphic domains o a ed
90°wi h espec o one ano he would gi e us he obse ed 12
poles. To ep oduce he measu ed da a, we conside ed ou
domains o he R3mphase ha ing he (001) o ien a ion and an
in-plane o a ion o 90°wi h espec o one ano he and
simula ed he pole igu e using he MTEX
35
simula ion ool.
The simula ed pole igu e is p esen ed in Figu e 2c. As can be
seen, bo h {201} (a chi = 71.15°) and {022} (a chi = 55.7°)
spo amilies could be ep oduced in he simula ion o he R3m
phase. I one conside s he o ho hombic Pca21phase wi h a
single (111)-o ien ed domain, h ee poles o a ed by 120°a e
expec ed o he HZO{
1 1
1}, om he c ys al symme y, as
simula ed wi h MTEX and also expe imen ally epo ed,
18
and
one pole o each o he {020}, {200}, and {002} e lec ions.
The HZO{
1 1
1} o he Pca21phase would be he
co esponding HZO{201} spo s o he R3mphase, and he
HZO{020} o he Pca21phase would be he co esponding
HZO{022} spo s o he R3mphase. Fu he mo e, i one
conside s (111) g own ilms consis ing o ou domains ha ing
ou in-plane o ien a ions o a ed 90°wi h espec o one
ano he and simula es he pole igu e, one can ep oduce he
12 spo s co esponding o HZO {
1 1
1}, as shown in he
simula ed pole igu e om Figu e 2d. To enhance cla i y, he
poles om each domain in he simula ion om Figu es 2c,d
a e indica ed wi h an a ow o a speci ic colo . Thus, we ha e
black, ed, blue, and g een a ows o indica e he ou domains.
Addi ionally, 12 poles a e expec ed a a wo- he a angle o
abou 35.6°, each o he {020}, {200}, and {002} e lec ions
con ibu ing wi h ou spo s in he simula ion, sepa a ed by a
90°angle in phi. The co esponding wo- he a angles o he
nonsymme y equi alen 020, 002, and 200 e lec ions o he
Pca21phase a e close o each o he . Thus, i is di icul o
dis inguish be ween he R3mand Pca21phases based on he
(low esolu ion) wide- ange RSM and pole igu es. One way o
dis inguish he R3mphase om he Pca21phase is o compa e
he in e plana spacing o he 12 spo s measu ed a a chi angle
o 71.15°wi h he in e plana dis ance o he specula 111 spo
o he Pca21phase. In he case o he Pca21phase, all spo s
should ha e he same d-spacing (due o he symme y),
whe eas o he R3mphase, he specula spo ( he 003
e lec ion) should ha e a la ge d-spacing alue.
13,14
Symme ic
wo- he a scans o he 12 poles measu ed a chi = 71.15°a e
plo ed oge he wi h he ou -o -plane e lec ion (chi = 0°) as
shown in Figu e 3a. The 12 spo s sha e nea ly he same 2θ
alues, whe eas he ou -o -plane e lec ion has a smalle 2θ
(la ge d-spacing), which is an indica ion o he R3mphase.
Ano he possibili y o dis inguish be ween he wo
polymo phs is o measu e symme ic 2θscans a a ound 35°
o he 12 spo s a a chi angle o 55.7°. In he case o he R3m
phase, he {022} spo s should ha e he same 2θ alues,
whe eas o he Pca21phase, he {020}, {200}, and {002}, each
con ibu ing wi h ou spo s ( om he ou domains)
sepa a ed by 90°in φwi h espec o one ano he (see Figu e
2d), should ha e sligh ly di e en 2θ alues. Simila ly, one can
analyze he 12 spo s measu ed a chi = 35°a a 2θo abou
50°. Thus, o he R3mphase, he {204} spo s should show he
same 2θ alues whe eas o he Pca21phase, he {022}, {202},
and {220} each con ibu ing wi h ou spo s sepa a ed by 90°
in φwi h espec o one ano he should ha e sligh ly di e en
2θ alues. The symme ic wo- he a scans o he 12 poles
measu ed a chi = 55.7°and a 2θ alue a ound 35°a e
p esen ed in Figu e 3b, and he 12 poles measu ed a chi = 35°
and a 2θ alue o a ound 50°a e shown in Figu e 3c. To
imp o e he ease o unde s anding o he eade , he 2θscans
o each {020}, {200}, and {002} as in Figu e 3b and {022},
{202}, and {220} e lec ions as in Figu e 3c co esponding o
he Pca21phase a e depic ed using dis inc colo s: ed, g een,
and blue. Thus, in he case o he Pca21phase, he e lec ions
o he same colo (sepa a ed in phi by 90°) should sha e he
same 2- he a alue and should be sligh ly di e en o each
colo . When hese 2θ alues a e all equal, assuming he
e oelec ic Pca21phase, would imply a=b=c, which
con adic s he epo ed me ics o his c ys allog aphic phase,
making i unlikely ha he in es iga ed ilms a e in he Pca21
phase. These esul s a e ins ead in good ag eemen wi h he
me ics o he R3mphase. Howe e , he exis ence o a sepa a e
Figu e 6. (a) Plan- iew SAED pa e n o Si/STO/LSMO/HYO. The
subs a e Si is o ien ed in he [100] zone axis as well as he STO
which is o a ed by 45°wi h espec o Si. HYO shows mainly wo
ypes o e lec ions. The ed ci cles depic he HYO [001] zone axis
wi h {220} e lec ions aligned wi h he STO (101) planes ( ed a ow)
while he e lec ions ma ked by he g een ci cles a e aligned wi h he
STO (110) planes (g een a ow). (b) shows a high- esolu ion TEM
mic og aph in he same iewing di ec ion which is con i med by he
FFT in (c) showing he same di ac ion pa e n as in a). In (c), he
g een, ed, and yellow ci cles we e used o il e ing he FFT and
building a colo ed in e se FFT shown in (d). The majo i y o he
domains ha e an [003] ou -o -plane o ien a ion wi h {220} e lec ions
ma ked by ed and g een ci cles. The mino i y (yellow) is o ien ed
wi h STO (200).
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e oelec ic hombohed al phase which is no jus a s uc u al
dis o ion caused by epi axial s ess dis o ion o he Pca21
o ho hombic phase is s ill unde deba e, as sugges ed by Fina
and Sanchez.
36
To gain a clea e unde s anding o how he scans om
Figu e 3c ela e o pa icula e lec ions and domains,
simula ed pole igu es o bo h R3mand Pca21phases o he
12 spo s a chi = 35°and a 2θo abou 50°a e shown in Figu e
S5.
3.1.1.2. T ansmission Elec on Mic oscopy Cha ac e -
iza ion. The same HZO ilm on he LSMO-bu e ed (001)-
o ien ed Nb:STO subs a e analyzed by XRD was used o
TEM cha ac e iza ion. The HRTEM mic og aph in Figu e 4a
shows he LSMO back elec ode g owing along (012) planes
while he HZO hin ilm g ows mainly in he [003] di ec ion o
he R3mphase. Howe e , a mino i y g owing di ec ion along [
2
22] was also obse ed (ma ked wi h an o ange ellipse in he
FFT in Figu e 4b, as also epo ed by Wei e al).
13
This
mino i y g ow h di ec ion is no obse ed in XRD measu e-
men s. Di e en domains o he HZO we e p esen wi h (02
2
)
planes o ien ed o he igh o he le , hese planes a e
indica ed by a black and a ed a ow, espec i ely. F equen ly
bo h o ien a ions supe impose, as can be seen in he FFT in
Figu e 4c. This pa e n can be explained by a 2- old win
o a ion a ound he [003] g owing di ec ion. Acco dingly, we
can see he e a leas wo o he ou domains obse ed in XRD.
The missing wo domains canno be dis inguished in his
o ien a ion because hey ha e he same di ac ion pa e n. Fo
ins ance, he [110] zone axis (ZA) is equi alen o he [100]
ZA in a hombohed al symme y. A clea iew o he bounda y
o he domains, howe e , was no ound in many mic og aphs
examined.
The selec ed a ea elec on di ac ion (SAED) pa e n in
Figu e 4d was aligned pa allel o he [100] ZA o he STO. In
Figu e 7. (a) High- esolu ion 2θ/ωscan o a 4.7 nm hick HZO ilm deposi ed on sapphi e. (b) Wide ange RSM o he same ilm on sapphi e.
The spo s belonging o sapphi e a e deno ed in black, whe eas he spo s om he HZO ilm a e deno ed in ed. The angles deno ed nex o he
HZO spo s ep esen he in-plane o a ion o he co esponding HZO domains assigned o he R3mphase. The sapphi e subs a e was o a ed by
phi = 30°du ing he RSM measu emen . (c) Pole igu e o he HZO {201}, HZO {022}, sapphi e {10
2
} and sapphi e {104} spo s. The adial
di ec ion ep esen s he χaxis anging om 0° o 90°, whe eas he azimu hal di ec ion ep esen s he φaxis wi h a ange om 0° o 360°.
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his o ien a ion, he LSMO is in he [
2
2
1
] ZA and he
epi axial g ow h o all ilms is clea ly isible. The di ac ion
pa e ns o STO and LSMO a e indica ed by black ho izon al
lines. Fo HZO, he (003) e lec ions in he g owing di ec ion
a e mos p ominen , while in-plane no e lec ions can be
e idenced, and also he diagonal planes a e e y ain (ma ked
wi h o ange ci cles).
Fu he mo e, om his SAED pa e n, a di e ence in he d-
alues o (006) and (042) can be obse ed, as illus a ed by he
dashed ing a ound he (006) e lec ions. These e lec ions
would co espond o he {222} planes o he e oelec ic
o ho hombic phase, which canno ha e a d- alue di e ence
(in a elaxed s uc u e) due o he o ho hombic symme y. An
e ec o an ellip ical dis o ion o he di ac ion pa e n by
unp ecise adjus men s o he p ojec o lens sys em can be
Table 1. aand cLa ice Pa ame e s o he S ained Doped
H O2Films Deposi ed on Di e en sys ems in his Wo k
We e Ex ac ed om High-Resolu ion 2θ/ωScans and In-
Plane Scans
a
he e os uc u e a(Å) c(Å)
8 nm HZO/LSMO/STO 7.194 8.899
7.7 nm HYO/LSMO/STO 7.170 8.953
7.6 nm HZO/LSMO/STO/Si 7.236 8.822
5.6 nm HYO/LSMO/STO/Si 7.212 8.883
6.2 nm HYO/Al2O37.207 8.879
2.6 nm HYO/Al2O37.239 8.773
4.7 nm HZO/Al2O37.219 8.805
H O2,R3m(no. 160); a=b;α= 90°;β= 90°;γ= 120°
a om x y z occupancy
H 0.83335 0.16665 0.25089 1
H 0.00000 0.00000 0.58415 1
O 0.14966 0.85034 0.15904 1
O 0.48699 0.51301 0.32788 1
O 0.00000 0.00000 0.85998 1
O 0.00000 0.00000 0.35364 1
a
The c ys allog aphic s uc u e is he one epo ed by Wei e al. in e
13 adap ed o he la ice pa ame e s measu ed in his wo k.
Figu e 8. Pole igu e simula ion o he HZO ilms using MTEX. (a) Phase R3m, conside ing (001) ou -o -plane o ien a ion and p esence o wo
domains (indica ed by he ed and he blue a ows), wi h an in-plane angula o a ion o 180°wi h espec o one ano he . (b) Phase Pca21
conside ing (111) ou -o -plane o ien a ion, and he p esence o wo domains, wi h an in-plane angula o a ion o 180°wi h espec o one ano he .
Figu e 9. In-plane XRD o he HYO(6.2 nm)/Al2O3: (a) in-plane
scan showing he HYO(220) and Al2O3(300) e lec ions; he la ice
pa ame e s and he FWHM a e gi en in he inse . (b) In-plane phi-
scan o he HYO(220) egion showing a 6- old in-plane symme y;
he FWHM is 4.1°.
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uled ou , because he e lec ions o he polyc ys alline P om
he FIB p epa a ion a e no ellip ically dis o ed.
Supe imposed a e he [100] ZA o STO and he [
2
2
1
] ZA
o LSMO which a e illus a ed by black e ical lines. The
e lec ions o HZO in he diagonal a e e y ain . The e o e,
he ec angles om he FFT a e used he e double sized o
illus a e he di ac ion pa e n o HZO. The ings in he
SAED pa e n in (d) o igina e om he p o ec i e P coa ing
used in he FIB.
3.1.2. H 0.93Y0.07O2(HYO) Films Deposi ed on S TiO3-
Bu e ed Si (100)-O ien ed Subs a es. 3.1.2.1. X- ay
Di ac ion Analysis. Y ium-doped Ha nia ilms
H 0.93Y0.07O2(HYO) we e deposi ed on Si (100)-o ien ed
subs a es on which a 10 nm S TiO3(STO) was deposi ed by
molecula beam epi axy (MBE) a Texas S a e Uni e si y.
37,38
The H 0.93Y0.07O2/La0.7S 0.3MnO3epi axial s ack was deposi ed
by PLD, using he same deposi ion pa ame e s as hose
deposi ed on Nb:S TiO3subs a es. The wide- ange RSM o
he doped ha nia ilms deposi ed on La0.7S 0.3MnO3/S TiO3/
Si (subs a e) shows ea u es simila o hose deposi ed on
La0.7S 0.3MnO3/S TiO3(subs a e), an ou -o -plane o ien a-
ion, and he p esence o ou kinds o domains wi h di e en
in-plane o ien a ions, as desc ibed be o e. The wide- ange
RSM was acqui ed a φ= 0°, and besides he specula Si(004),
he Si(022) spo was isible in his di ac ion geome y. The
nonspecula STO/LSMO di ac ion spo s
1
11,
1
12, and
2
21
a e also p esen . The esul s a e shown in Figu e 5a. A pole
igu e o HYO{022}, HYO{201}, STO/LSMO{011}, and
Si{111} measu ed o a 2θ anging om 34.8° o 47.8°is
shown in Figu e 5b. The 12 spo s o he HYO{022} and
HYO{201} a ising om he ou domains a e p esen on he
pole igu e, simila o he esul s om doped ha nia ilms
deposi ed on LSMO-bu e ed STO subs a es.
3.1.2.2. T ansmission Elec on Mic oscopy Cha ac e -
iza ion. The TEM p epa a ion o plan- iew samples g own
on he STO subs a es was no success ul because in 3 ials
he samples b oke apa du ing mechanical polishing be o e
inishing he p epa a ion. As a esul , a Z /Y:H O2sample on
S TiO3-bu e ed Si was p epa ed. This sample should be
Figu e 10. (a) HRTEM mic og aph o Al2O3in [210] ZA and HZO
in [100] ZA. Two di e en domains we e ound ia FFT analysis in
(b) and (c); again, he [100] ZA is mi o ed a he (003) plane. The
SAED pa e n in (d) shows bo h domains, and he Al2O3[210] ZA is
indica ed by e ical black lines. In his sys em, he (003) e lec ions
a e a he weak compa ed o he STO/LSMO sys em, and he (060)
e lec ion is isible in-plane. In FFTs e en he (030) planes. The
di ac ion ings o igina e om he P coa ing which was used o
p o ec du ing FIB p epa a ion.
Figu e 11. Fe oelec ic cha ac e iza ion. Dynamic e oelec ic pola iza ion hys e esis loops o he (a) Cu/H 0.5Z 0.5O2/La0.7S 0.3MnO3/S TiO3,
(b) Cu/H 0.93Y0.07O2/La0.7S 0.3MnO3/S TiO3/Si, and (c) Cu/H 0.93Y0.07O2/La0.7S 0.3MnO3/Nb:S TiO3capaci o s. (d) “Wake-up” e ec
in es iga ion on a p is ine e oelec ic capaci o .
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ep esen a i e, as indica ed by he XRD analysis. A SAED
pa e n o he plan- iew sample wi h Si o ien ed in he [100]
ZA is shown in Figu e 6a. He e, he HYO o ms a simila
di ac ion pa e n as epo ed by Wei e al.
13
wi h 12 {120}
e lec ions which can be explained by HYO ha ing a leas wo
domains o a ed in plane by 90°. The g een and ed ci cles in
Figu e 6a indica e wo domains. The domains ma ked wi h
g een ci cles a e o ien ed wi h he STO (110) planes while he
domains ma ked wi h ed ci cles a e o ien ed wi h he STO
(101) planes. Adding he 2- old win o a ion obse ed in he
c oss-sec ional TEM analysis esul s in he ou domains
obse ed in XRD pole igu es. These ou ypes o domains
may o m du ing he c ys al nuclea ion du ing PLD, whe e
each nucleus can be o ien ed wi h STO (110), (−110), (1−
10), o (−1−10). The same colo code is used in he FFT
shown in Figu e 6c o he HRTEM mic og aph in shown
Figu e 6b. These colo ed ci cles we e used o he il e ed
in e se FFT in Figu e 6d which illus a es he g anula
mic os uc u e o he HYO hin ilm. Howe e , all indi idual
g ains a e epi axial.
A TEM image in a di e en o ien a ion, il ed away om he
[100] zone axis o Si, is shown in Figu e S4. He e, s ong
Moi e inges appea which we e again used o a il e ed
in e se FFT. F om hese alse colo images, he a e age wid h
o 20 domains can be oughly es ima ed o be 10 nm ±3 nm.
The high c ys allini y o he HZO, as indica ed by he ocking
cu e, a gues o cohe en in e aces be ween hese 10 nm-
sized domains as would be he case o wins.
In addi ion o he obse ed majo i y e lec ions in he SAED
pa e n shown in Figu e 6a om HYO wi h he [003] ou -o -
plane o ien a ion, a mino i y is obse ed in he FFTs (see
yellow ci cles in Figu e 6c and blue ci cles in Figu e S4b) ha
is o ien ed wi h he STO (200) planes.
3.1.3. H 0.5Z 0.5O2Films Deposi ed on Al2O3(0001)
Subs a es. 3.1.3.1. X- ay Di ac ion Analysis. Nex , Y- and
Z -doped H O2 ilms we e deposi ed on igonal Al2O3(0001)
single c ys al subs a es. A 5 nm hick H 0.5Z 0.5O2 ilm
deposi ed on Al2O3(0001) is cha ac e ized by XRD
expe imen s, as p esen ed in Figu e 7. The high- esolu ion
ω-2θscan shown in Figu e 7a allowed o he p ecise
measu emen o he cla ice pa ame e , lis ed in Table 1,
and de e mina ion o he ilm hickness based on he hickness-
oscilla ion pe iod, which in his case was 4.7 nm. A wide- ange
RSM shown in Figu e 7b was measu ed a an in-plane o a ion
angle o φ= 30°. Thus, in addi ion o he specula 006 spo ,
he 113, 116, and 119 spo s o he Al2O3subs a e a e obse ed
a his in-plane phi angle. The HZO ilm appea s o consis o
wo kinds o domains, belonging o he same -phase R3mno.
160, o a ed in-plane by 180°wi h espec o one ano he and
by 30°wi h espec o he Al2O3c ys allog aphic cell. The
co esponding angles o hese wo domains, which we e
ob ained om he simula ion o he RSM a e deno ed nex o
indexed HZO spo s in he igu e. The pole igu e o he same
sample is p esen ed in Figu e 7c. The HZO {201}, HZO
{022}, sapphi e {10
2
} and sapphi e {104} spo s om he
la ice planes symme ically equi alen a e ma ked on he pole
igu e. The 2θ anges om 25° o 37.8°.
The sapphi e {10
2
} and {104} spo s e lec he igonal
symme y o he phase, esul ing in h ee spo s on he pole
igu e o each amily. The HZO {201} and HZO {022} spo s
should also show h ee spo s each, acco ding o he
c ys allog aphic symme y o he R3mphase, bu six spo s
a e obse ed expe imen ally. This can be explained by he
p esence o wo kinds o domains, belonging o he same
igonal phase R3m, o a ed in-plane by 180°wi h espec o
one ano he , as deduced o he wide- ange RSM simula ion
discussed abo e. This domain con igu a ion has been epo ed
in p io s udies on HZO ilms deposi ed on GaN and
sapphi e,
14
also being imposed by he symme y o he
subs a e. To e i y ha , a pole igu e o he HZO ilms was
simula ed using MTEX, acco ding o he p oposed assump ion,
and he esul s a e shown in Figu e 8a. The simula ion
co esponds o he indings ob ained om he expe imen s.
The simula ion o he Pca21phase o a (111) o ien ed
monodomain ilm gi es h ee poles om he {1
1
1}, and one
poles om each {020}, {002} and {200} e lec ion amilies. I
one conside s wo (111) domains o a ed in-plane by 180°
wi h espec o one ano he , he simula ions ep oduce he
obse ed six {111} poles, as well as he six poles o he {020},
{002}, and {200} ones, as shown in Figu e 8b. Also, in his
case, i is di icul o dis inguish be ween he R3mand Pca21
c ys allog aphic phases om he pole igu e XRD measu e-
men s.
Conside ing he ela i ely uni o m in ensi y dis ibu ion o
he e lec ions co esponding o a speci ic amily o spo s, one
can s a e ha he olume ac ion o he wo ypes o HZO
domains appea s o be equally dis ibu ed.
The measu ed wide- ange RSM o he HZO deposi ed on
sapphi e could also be assigned o a e oelec ic o ho hombic
phase like, o example, he one epo ed by Xu e al.
39
Wi h
his assump ion, he ilms a e epi axial and ha e an (111) ou -
o -plane o ien a ion. Such an example is illus a ed in Figu e
S2, whe e he obse ed spo s in he RSM om he H O2 ilms
deposi ed on sapphi e a e assigned o he abo e-men ioned
c ys allog aphic phases.
To p ecisely de e mine he in-plane la ice pa ame e s o he
deposi ed ilms, we pe o med in-plane X- ay di ac ion
measu emen s. Thus, in he case o doped ha nia ilms
deposi ed on sapphi e, he HYO (220) and Al2O3(300)
e lec ions we e obse ed, as can be seen in Figu e 9a. This
means ha he (220) c ys allog aphic planes o he epi axially
doped ha nia ilms a e pa allel wi h he (300) planes o he
unde lying sapphi e subs a es and pe pendicula o he HYO
(003) planes which a e pa allel wi h he sample su ace. The
epi axial ela ionship in his case conside ing he R3m
c ys allog aphic phase is [220] HZO(001) //[300]
Al2O3(001). I one would conside he e oelec ic o ho-
hombic phase Pca21ins ead o he igonal phase (R3m), he
(111) c ys allog aphic plane is pa allel wi h he sample su ace,
whe eas he (20
2
) plane o ms an angle o 89.84°wi h he
(111) plane, e y close o 90°. Fo his eason, based on he in-
plane XRD measu emen s, one canno dis inguish be ween he
e oelec ic o ho hombic phase and he hombohed al one.
F om hese high- esolu ion in-plane scans, one can p ecisely
de e mine he in-plane la ice pa ame e o he hombohed al
HYO ilms deposi ed on sapphi e, which is 7.207 Å. Nex , he
2-The aChi/Phi axis was ixed a he HYO(220) peak posi ion,
and a phi-scan was pe o med, wi h a comple e 360°phi-axis
scan ange. The 3- old in-plane symme y expec ed o he
hombohed al ilms combined wi h he p esence o he wo
180°in-plane o a ed domains is consis en wi h he obse ed
six e lec ions spaced by 60° om his scan and wi h he esul s
om he pole igu es o he HZO ilms deposi ed on sapphi e,
discussed abo e. The in-plane phi scan shown in Figu e 9b is
equi alen o an in-plane ocking cu e, and he wid h o he
e lec ions gi es us a measu e o he in-plane mosaici y. In he
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