Structural study in highly compressed BiFeO3 epitaxial thin films on YAlO3
Heng-Jui Liu, Hsiang-Jung Chen, Wen-I Liang, Chen-Wei Liang, Hsin-Yi Lee, Su-Jien Lin, and Ying-Hao Chu
Citation: Journal of Applied Physics 112, 052002 (2012); doi: 10.1063/1.4746036 View online: http://dx.doi.org/10.1063/1.4746036
View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/112/5?ver=pdfcov Published by the AIP Publishing
Articles you may be interested in
The effects of La substitution on ferroelectric domain structure and multiferroic properties of epitaxially grown BiFeO3 thin films
Appl. Phys. Lett. 103, 132907 (2013); 10.1063/1.4822327
Heteroepitaxial growth and multiferroic properties of Mn-doped BiFeO3 films on SrTiO3 buffered III–V semiconductor GaAs
J. Appl. Phys. 114, 094106 (2013); 10.1063/1.4820579
Epitaxial growth of multiferroic BiFeO3 thin films with (101) and (111) orientations on (100) Si substrates Appl. Phys. Lett. 102, 242906 (2013); 10.1063/1.4811484
Mapping of the epitaxial stabilization of quasi-tetragonal BiFeO3 with deposition temperature Appl. Phys. Lett. 100, 122905 (2012); 10.1063/1.3696048
X-ray nanodiffraction of tilted domains in a poled epitaxial BiFeO3 thin film Appl. Phys. Lett. 99, 232903 (2011); 10.1063/1.3665627
Structural study in highly compressed BiFeO
3epitaxial thin films on YAlO
3Heng-Jui Liu,1,2Hsiang-Jung Chen,3Wen-I Liang,3Chen-Wei Liang,3Hsin-Yi Lee,2 Su-Jien Lin,1and Ying-Hao Chu3,a)
1
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
3
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan (Received 15 December 2011; accepted 30 April 2012; published online 4 September 2012) We report a study on the thermodynamic stability and structure analysis of the epitaxial BiFeO3
(BFO) thin films grown on YAlO3 (YAO) substrate. First, we observe a phase transition of
MC–MA–T occurs in thin sample (<60 nm) with an utter tetragonal-like phase (denoted as MII
here) with a large c/a ratio (1.23). Specifically, MII phase transition process refers to the
structural evolution from a monoclinic MC structure at room temperature to a monoclinic MA at
higher temperature (150C) and eventually to a presence of nearly tetragonal structure above 275C. This phase transition is further confirmed by the piezoforce microscopy measurement, which shows the rotation of polarization axis during the phase transition. A systematic study on structural evolution with thickness to elucidate the impact of strain state is performed. We note that the YAO substrate can serve as a felicitous base for growing T-like BFO because this phase stably exists in very thick film. Thick BFO films grown on YAO substrate exhibit a typical “morphotropic-phase-boundary”-like feature with coexisting multiple phases (MII, MI, and R) and
a periodic stripe-like topography. A discrepancy of arrayed stripe morphology in different direction on YAO substrate due to the anisotropic strain suggests a possibility to tune the MPB-like region. Our study provides more insights to understand the strain mediated phase co-existence in multiferroic BFO system.VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746036]
I. INTRODUCTION
Multiferroics have been widely studied due to their fasci-nating physical properties, such as the coupling between elec-tric and magnetic orders1,2and conduction in domain walls,3 offering an opportunity for novel devices. Among those multi-ferroics, BiFeO3(BFO) is the most promising one because of
its high curie temperature of ferroelectric order (Tc¼ 1103 K)
and antiferromagnetic order (TN¼ 643 K).4–6Recently, it has
been shown a strain-driven conceptual “morphotropic phase boundary”7(MPB) with superior spontaneous polarization in the epitaxial thin film BFO under highly compressive strain (4%).8,9Generally, MPB describes a phase transition from tetragonal (T), monoclinic (M) to rhombohedral (R) symme-tries induced by compositional change, which is usually observed in the lead-based ferroelectrics. These compounds captured significant attention due to the strongly enhanced ferro/piezoelectricity.10–14However, Pb-based compounds are not environmentally friendly, strain-driven MPB suggests a new avenue to design new green ferro-/piezoelectrics.
In the previous studies,7,15–17the MPB-like region in the strained BFO thin films is composed at least two phases, which are usually labeled as MII (or tetragonal-like) and R
(rhombohedral-like) phases.15High-resolution x-ray diffrac-tion (XRD) techniques disclosed the monoclinic nature of MIIphase and defined precisely that the R phase is similar to
rhombohedral structure presented in bulk BFO yet the degree of distortion presents larger. In addition, an extra phase with
monoclinic or triclinic structure is found to accommodate the lattice difference between MII and R BFO, which is
la-beled as MI.15,16These phase stacking sequence of MPB-like
structure could also be connected to the sawtooth-like mor-phology observed from atomic force microscopy (AFM) and transmission electron microscopy (TEM).7,15,17On the other hand, plenty of studies exuberantly focused on the under-standing of those bridge phases, and they further inferred that the MIIphase in fact belongs to the MCstructure (Cm or
Pm symmetry) with a shear angle along [100] direction. When the compressive strain is reduced by environmental change such as thickness or substrates, MIIphase transforms
into R-like phase, which is later confirmed to be MAor
dis-torted rhombohedral structure (Cc or R3c symmetry) with a shear angle rotation from [100] to [110] direction, a process that induces a spontaneous polarization rotation correspond-ingly.17–21 This structural transition has been considered as the main contributor to the piezoelectric anomaly in the BFO/LAO (LaAlO3) system.
While detailed information of phase transition in BFO has been deeply discussed in the system of BFO/LAO, there were not many works about highly strained BFO thin films on YAlO3(YAO) substrates (a¼ c ¼ 3.70 A˚ , b ¼ 3.67 A˚, and
b¼ 88.47 in pseudocubic setting), which the lattice should
be more suitable for the predicted tetragonal structure of BFO (P4mm symmetry with a¼ 3.66 A˚ and c ¼ 4.67 A˚).22,23 In this study, we replace the LAO substrates with YAO sub-strates to scrupulously inspect the variations of MPBs between these two substrates. We observe a MC–MA–T
phase transition via temperature-dependent experiments, which is distinct to the case of BFO on LAO substrates.25,26
a)Author to whom correspondence should be addressed. Electronic mail:
Our study also builds an universal view of polarization rota-tion undergoing the MC–MAphase transition. In latter part of
study, we turn our focus onto the thicker film with MPB-like region and elucidate the existence of in-plane strain anisot-ropy in the BFO/YAO system that provides a new mean to control the MPB-like region. With the aim of understanding the inherent influence of in-plane strain anisotropy offered by YAO substrates, we study and compare the entire evolu-tion of BFO lattice parameters with thickness variaevolu-tion on LAO and YAO substrates.
II. EXPERIMENTAL PROCESS
Epitaxial BFO thin films were prepared by reflection high-energy electron diffraction (RHEED)-assisted pulsed laser deposition from a BFO target with 10% excess bismuth. Growth was carried out at 700C at oxygen pressure of 100 mTorr on single-crystal YAO (110) substrates in orthorhom-bic index. The thickness of the BFO films was controlled by a combination of RHEED monitoring and deposition time. The films were then cooled in oxygen pressures of approxi-mately 760 Torr. The topography of all samples and their polarization domain structures were studied using atomic force microscopy (AFM, Veeco Escope) and piezoelectric force microscopy (PFM). Tips used for PFM imaging were Ti-Pt coated cantilevers with an elastic constant of 4.5 N/m and a resonance frequency of 120190 kHz. When perform-ing the PFM measurements, the scannperform-ing speed was set at 5 lm/s, the ac excitation frequency was 10.5 kHz, and the ac amplitude was 7 Vpp. The PFM images have been recorded with the tip cantilever scanning along [100] and [010] direc-tion. Structural details of the samples were collected by synchrotron-based x-ray diffraction techniques at beamline BL-13 A at the National Synchrotron Radiation Research Center (NSRRC) in Hsinchu, Taiwan. The incident beam was monochromated at 12 KeV with Si (111) double crystal mirror. Two sets of slits were placed before samples to get the beam size about 0.4 mm 0.8 mm, and the other two were placed after the sample (or before scintillation counter) to decrease background noises. The x-ray reciprocal space
map was measured step by step and plotted in the reciprocal lattice unit that is normalized to YAO substrate in pseudocu-bic settings (1 r.l.u.¼ 2p/aYAO,pc).
III. RESULTS AND DISCUSSION
For understanding the structural evolution of the BFO thin films grown on YAO substrates, two relevant phases of BFO reported before should be mentioned first. For instance, the BFO thin films grown on the substrates with larger lattice mismatch (>4%, related to the lattice of bulk BFO) such as LaAlSrO4, LAO, and YAO prefer to form the monoclinic
MCstructure illustrated in Fig.1(a). Those grown on the
sub-strates with smaller lattice mismatch such as SrTiO3(STO)
belong to monoclinic MA structure (Fig.1(b)). For MC, the
monoclinic distortion is along [100] with respect to pseudo-cubic structure; therefore, the corresponding domain struc-tures would result in three-fold splitting and double splitting in the reciprocal space mappings (RSMs) of (H00) and (HH0) planes. By contrast, MAhas a monoclinic distortion
along [110] in the pseudocubic index, which results in the opposite diffraction patterns in RSM analysis. In general, MAis also indicated as the R-like phase due to that the unit
cell volume is close to the bulk BFO.
We first study the structural evolution of 18 nm BFO thin film on YAO as a function of elevated temperature. The h2h x-ray diffraction scans along [001]pc,YAO direction
shown in Fig.2(a)reveals the existence of MIIphase
diffrac-tion peaks from room temperature to 400C. The calculated c-axis lattice parameter of MIIphase displays a temperature
dependent behavior, which is distinct from that of YAO sub-strates (Fig.2(b)). YAO substrate exhibits nearly linear ther-mal expansion along its norther-mal direction [001]pc, whereas
the c-axis parameter of BFO thin film varies: it is elongated and then stabilized in the temperature range of 100250C,
however, it decreases again when temperature mounts higher. This non-linear variation of c-axis lattice parameter of BFO implies that a possible ferroelectric or antiferromag-netic transition occurs due to structural variation.27,28 In order to study this transition, detailed structure of MIIphase
FIG. 1. The schematics of each structure and the corresponding diffraction features:(a) MC, with the shear orientation along [100] direction, (b)MA, with the
shear orientation along [110], and (c)T phase, without shear angle. The shear angle will cause the peak splitting due to the four kinds of domains, and its direc-tion will results in the reverse patterns in the (H0L) and (HHL) scattering zones.
is shown by measuring asymmetry RSMs exhibited in Figs.2(c)–2(h). These RSMs (Figs. 2(c) and 2(d)) demon-strate the typical diffraction patterns at room temperature: Three-fold splitting and two-fold splitting are observed respectively around (103) and (113) reflections, recognized as MC in Fig.1(a). The lattice parameters of this MC
struc-ture obtained from RSMs are a¼ 3.79 A˚ , b ¼ 3.75 A˚, c¼ 4.63 A˚ , and bMC¼ 88.83. We further performed the
same measurements at 150C. One can find that the RSMs of the same sample at 150C (Figs.2(e) and2(f)) display reverse patterns, which present a typical MAstructure feature
(Fig.1(b)): two-fold splitting and three-fold splitting corre-sponding to the (103) and (113) reflections. In order to com-pare with MC, the a-axis and b-axis of MAare redefined into
the MCcoordinate for clarity and the lattice parameters are
calculated as a¼ 3.768 A˚ , b ¼ 3.761 A˚, c ¼ 4.645 A˚, and bMA¼ 87.1. This provides a direct evidence of phase
transi-tion. Besides, this MAphase sustains high c/a ratio (1.23),
which is different from the previous MAcases such as BFO
thin films on STO substrate (c/a 1.04).17–21,24Similar phe-nomena are also observed in the case of LAO substrates.25–27 First principle prediction proposed by I~niguezet al. has indi-cated highly compressive strained BFO thin films show two sets of symmetries for energetically favorable phases.29One is thePm, or Cm symmetry, where the shear direction is along [100],18,29and the other is theCc symmetry, where the shear direction is along [110].30 Both have a large c/a value and
only a little difference in energy, which means these two sets of symmetries for the MII phase can be stably existed on
these substrates. Hence, we suggest that the MCphase would
change its symmetry from Pm or Cm at low temperature to CC (the MA phase) at high temperature. If we further
increase the temperature to 275C, the structure seems to become more tetragonal as shown in Figs. 2(g) and 2(h): there is nearly one diffraction spot, which represents the withdrawal of tilting angle, in the (103) and (113) reflec-tions. Overviewing the heating process, it is apparent to con-clude that MII exhibits MC–MA–T phase transition through
the study of RSMs.
To verify the MC–MA–T phase transition, PFM
mea-surement was carried out. In general, MC and MAhave
dif-ferent in-plane polarization directions due to their difdif-ferent shear directions. Due to the self-poling effect (asymmetric electrostatic boundary conditions), the complicated eight polarization domain states can be limited to only four com-ponents, as shown by the schematics in Figs. 3(a) and
3(b).19,31 For MC phase, the scanning cantilever along with
[100] should result in three levels of piezoresponse signals: the two opposite polarizations perpendicular to the cantilever lead to the darkest (red arrow) and brightest contrast (blue arrow); the other two opposite polarizations parallel to the cantilever almost present the same contrasts in the medium color level (green arrow). For MAphase, only two levels of
piezoresponse signals can be expected because for the four
FIG. 2. (a) X-ray normal scan of a BFO thin film with reference to YAO (001)pcpeaks at various temperatures. Dashed line is used as a guide to visualize the
shifts of the MIIpeaks. (b)c-axis lattice parameters of BFO (001) and YAO (001)pcfrom RT to 400C. (c) and (d) show experimental RSMs of (103) and
(113) of our BFO thin film at RT. (e) and (f) are the RSMs of (103) and (113) of the BFO thin film at 150C. (g) and (h) are the RSMs of (103) and (113) of the BFO thin film at 275C. These RSMs unveiled the phase transition of M
variant polarizations, only the polarizations project onto the perpendicular components can be detected when the cantile-ver scans along in [100] direction.
At room temperature, the surface topography shows a smooth with a little step bunching morphology (Fig. 3(c)). Its in-plane PFM image shows stripe-like feature when scan-ning along [100] direction (Fig.3(d)). The stripes are formed to minimize the electrostatic and elastic energy of the ferro-electric domains, hence the domain walls would intersect the {001} plane in theh110i direction to form four disparate do-main states, such as the colored indicators in Fig.3(c).17,19,32 The PFM results are consistent of Bokov’s prediction for the MCphase.31Repeating the AFM and PFM measurements at
150C (Fig. 3(d)), we find a revolute domain structure occurs while the topography remains the same. A puddle-like feature with dark and bright contrasts and the domain walls that intersect the {001} plane in the h110i indicate a typical MA feature. The fact that the in-plane polarization
direction changes from [100] to [110] at elevated tempera-ture confirms again the strained BFO/YAO system under-goes a phase transition from MC to MA, which is consistent
with the results in RSMs analysis. However, we do not have clear IP-PFM image for the sample at 275C, so the newly unveiled phase transition of MA-T still needs to be
confirmed.
In order to explore the impact of strain state on BFO thin films imposed by YAO substrates, BFO samples with various thicknesses (18 nm to 300 nm) were characterized by RSMs in normal direction shown in Figs. 4(a)–4(d). As thickness increases, multiple phases are coexisted; and when
the thickness is larger than 60 nm, the coexistence of “MI,”
“MII,” “MII,tilt,” and “R” pictures the view of MPB-like
region in BFO. The notations here, except for the MII
struc-ture defined before, three extra notations of MI, MII,tilt, and R
marked in these RSMs are also adapted from previous stud-ies on BFO/LAO system.15,26 More specifically, “R” refers to the distorted rhombohedral phase of BFO bulk; “MI” and
“MII,tilt” are the intermediate phases possessing tilted
mono-clinic structure to accommodate the large lattice mismatch between “MII” and “R.”18In this work, MIIappears in all the
samples and the mixed phase region starts to be formed above 60 nm, which exhibits the similar sawtooth-like mor-phology (Figs.5(b)–5(d)) consisting of MIand MII,tiltphases
that happened in BFO/LAO system.15,26 We further study these BFO phases via the characterizations of rocking curves for each phase. First, we selected the position of MIphase at
L¼ 0.887 (c ¼ 4.18 A˚ ) as shown in Fig.4(e). From the result of the rocking curve, only a broader shoulder around DH¼ 0 is observed in the thin film with 18 nm. As thickness keeps increasing to 60 nm, two extra peaks are located at DH 60.05, indicating that MI phase has a tilting angle
about 63from the surface normal direction. In addition, we also scrutinized the rocking curves of MII phase shown in
Fig.4(f). The MIIphase begins to split into three peaks when
the thickness reaches above 300 nm: one is for normal direc-tion and two outer peaks are MII,tiltphase. It can be
specu-lated that the MIis the main intermediate phase to balance
the lattice mismatches between MIIand R, while the R phase
begins developing. As the proportion of R raises with increasing thickness, only MI phase is not enough to FIG. 3. (a) Schematics of the ferroelectric polarizations in MC, which shows four kinds in-plane polarization variants on the {100} planes. Three contrasts
(blue, green, and red) are expected from PFM measurements when the cantilever is aligned to [100]. (b) Schematics of the ferroelectric polarizations in MA,
which also have four in-plane polarization variants on {110}. However, when conducting PFM measurements with the cantilever aligned to [100], two con-trasts (dark, light) are expected in MA. (c) AFM and PFM phase images of a BFO sample at RT with the cantilever aligned to [100]. (d) AFM and PFM phase
images of the same scanning area and direction as shown in (c) but at 150C. The blue, green, and red arrows in phase images of (c) and (d) indicate the direc-tions of the in-plane polarization variants illustrated in (a) and (b). The combinadirec-tions of these polarization variants would cause the stripe-like and puddle-like domain features in MCand MA, respectively.
compensate increasing height difference from MII to R;
hence, some part of MIIis dragged by adjacent MIto form a
tilting structure (MII,tilt), which results in a sawtooth-like
feature.
In Figs.5(a)–5(d), we examined the morphology evolu-tion via scanning probe microscope. When BFO is thin (18 nm), the topography of pure MII phase is very flat
shown in Fig.5(a). When the film is thick enough, the arrays of the striped regions consisting of periodic arranged stripe-like structure emerges. These stripe-stripe-like structures, or MPB-like regions, have been proven to the presence of intimately mixed MII, R, MI, and MII,tilt phases. Moreover, the AFM
images of these stripes on YAO substrates show a different feature and strain release process compared to those on LAO substrates, especially in the thickest film (300 nm). In the case of BFO/LAO system (Fig.5(e)), we could barely find the difference between the stripe-like feature along [010] and [100] direction of LAO substrate. The stripe-like feature on the YAO substrate (Fig. 5(d)), interestingly, exposes an anisotropy behavior. For clarity, we focus on the thickest sample to speculate the discrepancies from two orthogonal direction of YAO substrate (namely, one is [010]pc and
another is [100]pc). Along [010]pc direction, the stripes
arrangement has a commodious spacing (approximately 6.5 stripes per unit length in average) with more deeper valley
structures (about 2.4 nm, statistically speaking). On the con-trary, those stripes along [100]pc possess a very dense
(almost 10 stripes per unit length), shallow (about 1.6 nm in average) morphology. Through careful measurements on the these features shown in Fig. 5(f), the stripes along [010]pc
direction show that one side inclines about 1.8 from film surface and the other side inclines about 2.9, corresponding to the MII,tilt and MI phases from XRD rocking curves,
respectively. On the contrary, the stripes along [100]pc
direc-tion show that one side inclines about 1.91 and the other side inclines about 2.61. This phenomenon is confirmed by the rocking curves of thickest film presented in Figs. 4(e)
and 4(f). One can find that the peaks of MI phase along
[100]pc direction are located at outer position than those
along [010]pcdirection, implying the MIphase along [100]pc
tilts more than [010]pcdirection. The opposite situation can
be observed in the rocking curves of MII phase. The tilted
angles of MIphase are then extracted from rocking curves,
which are 2.96 and 2.7 along [100]pcand [010]pc,
respec-tively. And those of MII,tiltare 1.27and 1.46 along [100]pc
and [010]pc, respectively. If we gather further statistics of the
valley volume per unit length, one could derive that the vol-ume ratio of [010]pc and [100]pc is about 1.33, which also
implies that the strain energy released in [010]pcdirection is
larger than that of [100]pcdirection. From the understanding FIG. 4. (a)-(d) X-ray normal reciprocal space maps (RSM) of thin films with various thicknesses. MII, MII,tilt, MI, and R phase are marked near the position of
of MIIphase and YAO pseudocubic lattice setting discussed
above, both in-plane lattices of MIIare larger than those of
YAO, and the domains along [010]pcdirection would suffer
larger stress than those along [100]pc, representing that more
elastic energy should be released along [010]pcto sustain the
completeness of MIIstructure everywhere. Therefore, the
in-formation mentioned above serves as a guide for the fact that the arrayed stripe anisotropy should be directly related to the lattice difference of the a-axis and b-axis of the YAO substrate.
The structural development of dominant phase MII is
crucial to understand the progress of the strain state because formation of MPB-like feature functions as the outlet of large compressive strain. In this passage, we discuss about
the entire trend of MII behavior. The a/b ratio of the MII
phase is calculated to be about 1.01 shown in Fig. 6(a), illustrating the effect of biaxial compressive strain. From Fig. 6(b), one also can perceive that the shear angle b decreases with increasing thickness and the c/a ratio keeps almost the same (about 1.235 above 60 nm). These obser-vations suggest that the relaxation of the compressive strain goes through two ways on YAO substrate, which is relaxed by the recovery of lattice constants first and then by the more shear distortion of lattice structure. Second, the in-plane lattice parameters obtained from symmetry and asymmetry reflections are listed in Table I. The reduced in-plane lattice (a- and b-axis) and elongated out-of-plane lattice (c-axis) accompanying with increasing thickness elucidate that the BFO films grown on YAO sub-strate should sustain the compressive stress. Besides, we compare the similar thickness experiment on LAO sub-strates performed by Zeches et al. in the lower part of Table I. The obvious shrinkage of cell volume on LAO substrates indicates that MII would fully relax when
thick-ness exceeds 80 nm and almost converts into R phase above 260 nm, while on YAO substrate, the cell volume sustains nearly constant in samples with thickness larger than 300 nm. Therefore, the critical thickness of the MII
phase on YAO substrate is much larger; and meanwhile, the YAO substrate offers a better environment for MII
phase growth.
IV. CONCLUSION
In conclusion, we have demonstrated that highly com-pressively strained BFO thin films can be successfully grown on YAO substrate with the presence of MII (T-like) phase.
The structural details from symmetry and asymmetry XRD analysis manifest that the MIIphase has a monoclinic
struc-ture MC at room temperature, and then goes through a new
kind of phase transition MC-MA-T when the temperature is
elevated. The PFM results confirm the MII phase indeed
transforms from MCto MAthrough the in-plane polarization
rotation from [100] to [110]. BFO thin films with various thicknesses are investigated to draw out the minute picture. With increasing film thickness, BFO thin films gradually ex-hibit the typical mixed phase feature. The surface
FIG. 5. The topography of (a) 18 nm, (b) 60 nm, (c) 180 nm, and (d) 300 nm BFO thin films grown on YAO substrate. (e) 120 nm BFO grown on LAO substrate. (f) line-trace along the blue line and red line in (d), which shows different periodic arrangement of strips at [100]pc,YAO and [010]pc,YAO.
Unlike the uniform arrayed stripes along both LAO [100] and [010] observed in (e), this arrayed stripe anisotropy should results from the lattice difference of a-axis and b-axis of the YAO substrate.
FIG. 6. (a) The ratio of c/a and a/b are calculated from TableIat different thickness, indicating a stably MII phase can survive at thickness above
300 nm. (b) The variation of shear angle of MIIphase gradually decreases as
thickness increases.
TABLE 1. Lattice parameters of monoclinic BFO phase grown on YAO and LAO substrates with different thickness
Substrate thickness a (A˚ ) b (A˚ ) c (A˚ ) b (˚) V(A˚3)
YAO 18nm 3.78(9) 3.75(1) 4.63(2) 88.83 65.81(9) 66nm 3.76(5) 3.73(2) 4.65(1) 88.54 65.33(0) 180nm 3.76(6) 3.72(7) 4.65(2) 88.24 65.26(4) 300nm 3.76(5) 3.72(4) 4.65(7) 88 65.25(5) LAO* 17nm 3.83(8) 3.77(2) 4.62(7) 88.67 66.69(1) 53nm 3.84(4) 3.75(3) 4.64(4) 88.51 66.79(3) 89nm 3.66(7) 3.58(6) 4.69(1) 88.63 61.58(2) 120nm 3.66(5) 3.59(1) 4.70(1) 88.79 61.85(6) LAO** 260nm 3.95(5) 3.95(5) 3.97(1) 89.4 61.94(1)
*From supporting material of ref.7 **From ref.26
morphology and XRD studies reveal that stripes consisting of sawtooth-like periodic arrays have nearly the same phases (MIand R) with respect to those on LAO substrates. And for
the merits of YAO substrate, the dominated phase MIIshows
almost the same unit cell volume with thickness exceeding 300 nm. This suggests YAO is a suitable environment for T-like BFO growth. Nevertheless, in our work, we have manipulated a substrate-induced anisotropy to serve as a method to tune the morphology of stripe arrays: denser and shallower stripes prefer to arrange along YAO [100]pc, and
broader and deeper stripes prefer to arrange along YAO [100]pc. We can associate the phenomena with the little
dif-ference presented in YAO in-plane lattice parameters.
ACKNOWLEDGMENTS
Financial support of the National Science Council through project NSC 100-2119 -M-009-003 is gratefully acknowledged by the authors.
1
W. Eerenstein, N. D. Mathur, and J. F. Scott,Nature (London)442, 759 (2006).
2H. Bea, M. Gajek, M. Bibes, and A. Barthelemy,J. Phys.: Condens. Matter
20, 434221 (2008).
3
J. Seidel, L. W. Martin, Q. He, Q. Zhan, Y.-H. Chu, A. Rother, M. E. Hawkridge, P. Maksymovych, P. Yu, M. Gajek, N. Balke, S. V. Kalinin, S. Gemming, F. Wang, G. Catalan, J. F. Scott, N. A. Spaldin, J. Orenstein, and R. Ramesh,Nature Mater.8, 229 (2009).
4
G. A. Smolenskii, V. A. Isupov, A. I. Agranovskaya, and N. N. Kranik, Sov. Phys. Solid State 2, 2651 (1961).
5R. Palai, R. S. Katiyar, H. Schmid, P. Tissot, S. J. Clark, J. Robertson, S. A.
T. Redfern, G. Catalan, and J. F. Scott,Phys. Rev. B77, 014110 (2008).
6
P. Fischer, M. Polomska, I. Sosnowska, and M. Szymanski,J. Phys. C: Solid State Phys.13, 1931 (1980).
7R. J. Zeches, M. D. Rossell, J. X. Zhang, A. J. Hatt, Q. He, C.-H. Yang, A.
Kumar, C. H. Wang, A. Melville, C. Adamo, G. Sheng, Y.-H. Chu, J. F. Ihlefeld, R. Erni, C. Ederer, V. Gopalan, L. Q. Chen, D. G. Schlom, N. A. Spaldin, L. W. Martin, and R. Ramesh,Science326, 977 (2009).
8D. Ricinschi, K.-Y. Yun, and M. Okuyama,J. Phys.: Condens. Matter
18, L97 (2006).
9
C. J. M. Daumont, S. Farokhipoor, A. Ferri, J. C. Wojdeł, Jorge I~niguez, B. J. Kooi, and B. Noheda,Phys. Rev. B81, 144115 (2010).
10E. Cross,Nature (London)432, 24 (2004). 11
D. E. Cox, B. Noheda, G. Shirane, Y. Uesu, K. Fujishiro, and Y. Yamada, Appl. Phys. Lett.79, 400 (2001).
12H. Fu and R. E. Cohen,Nature (London)403, 281 (2000). 13
M. Ahart, M. Somayazulu, R. E. Cohen, P. Ganesh, P. Dera1, H.-K. Mao, R. J. Hemley, Y. Ren, P. Liermann, and Z. Wu,Nature (London)451, 545 (2008).
14
Z. Wu and R. E. Cohen,Phys. Rev. Lett.95, 037601 (2005).
15A. R. Damodaran, C.-W. Liang, Q. He, C.-Y. Peng, L. Chang, Y.-H. Chu,
and L. W. Martin,Adv. Mater.23, 3170 (2011).
16
Z.-H. Chen, S. Prosandeev, Z. L. Luo, W. Ren, Y.-J. Qi, C. W. Huang, L. You, C. Gao, I. A. Kornev, T. Wu, J.-L. W. P. Yang, T. Sritharan, L. Bel-laiche, and L. Chen,Phys. Rev. B84, 094116 (2011).
17Z.-H. Chen, Z. Luo, Y. Qi, P. Yang, S. Wu, C. Huang, T. Wu, J. Wang,
C. Gao, T. Sritharan, and L. Chen,Appl. Phys. Lett.97, 242903 (2010).
18
H. M. Christen, J. H. Nam, H. S. Kim, A. J. Hatt, and N. A. Spaldin,Phys. Rev. B.83, 144107 (2011).
19Z.-H. Chen, Z.-L. Luo, C.-W. Huang, Y.-J. Qi, P. Yang, L. You, C.-S. Hu,
T. Wu, J.-L. Wang, C. Gao, T. Sritharan, and L. Chen,Adv. Funct. Mater. 21, 133 (2011).
20G.-Y. Xu, H. Hiraka, G. Shirane, J.-F. Li, J.-L. Wang, and D. Viehland,
Appl. Phys. Lett.86, 182905 (2005).
21
H.-W. Jang, S. H. Baek, D. Ortiz, C. M. Folkman, R. R. Das, Y.-H. Chu, P. Shafer, J.-X. Zhang, S. Choudhury, V. Vaithyanathan, Y.-B. Chen, D. A. Felker, M. D. Biegalski, M. S. Rzchowski, X.-Q. Pan, D. G. Schlom, L.-Q. Chen, R. Ramesh, and C. B. Eom, Phys. Rev. Lett.101, 107602 (2008).
22
C. Ederer and N. A. Spaldin,Phys. Rev. Lett.95, 257601 (2005).
23H. Bea, B. Dupe, S. Fusil, R. Mattana, E. Jacquet, B. Warot-Fonrose, F.
Wilhelm, A. Rogalev, S. Petit, V. Cros, A. Anane, F. Petroff, K. Bouze-houane, G. Geneste, B. Dkhil, S. Lisenkov, I. Ponomareva, L. Bellaiche, M. Bibes, and A. Barthelemy,Phys. Rev. Lett.102, 217603 (2009).
24B. Dupe, I. C. Infante, G. Geneste, P.-E. Janolin, M. Bibes, A. Barthelemy,
S. Lisenkov, L. Bellaiche, and S. Ravy,Phys. Rev. B.81, 144128 (2010).
25
J. Kreisel, P. Jadhav, O. Chaix-Pluchery, M. Varela, N. Dix, F. Sanchez, and J. Fontcuberta,J. Phys.: Condens. Matter23, 342202 (2011).
26H.-J. Liu, C.-W. Liang, W.-I. Liang, H.-J. Chen, J.-C. Yang, C.-Y. Peng,
G.-F. Wang, F.-N. Chu, Y.-C. Chen, H.-Y. Lee, L. Chang, S.-J. Lin, Y.-H. Chu,Phys. Rev. B85, 014104 (2012).
27
K.-T. Ko, M.-H. Jung, Q. He, J.-H. Lee, C.-S. Woo, K. Chu, J. Seidel, B.-G. Jeon, Y. S. Oh, K. H. Kim, W.-I. Liang, H.-J. Chen, Y.-H. Chu, Y.-H. Jeong, R. Ramesh, J.-H. Park, and C.-H. Yang,Nat. Commun.2, 567 (2011).
28
I. C. Infante, J. Juraszek, S. Fusil, B. Dupe, P. Gemeiner, O. Dieguez, F. Pailloux, S. Jouen, E. Jacquet, G. Geneste, J. Pacaud, J. Iniguez, L. Bel-laiche, A. Barthelemy, B. Dkhil, and M. Bibes, Phys. Rev. Lett. 107, 237601 (2011).
29
O. Dieguez, O. E. Gonzalez-Vazquez, J. C. Wojdeł, and J. I~niguez,Phys. Rev. B.83, 094105 (2011).
30
A. J. Hatt, N. A. Spaldin, and C. Ederer,Phys. Rev. B.81, 054109 (2010).
31
A. A. Bokov and Z.-G. Ye,J. Appl. Phys.95, 6347 (2004).
32
N. Balke, S. Choudhury, S. Jesse, M. Huijben, Y.-H. Chu, A. P. Baddorf, L. Q. Chen, R. Ramesh, and S. V. Kalinin, Nat. Nanotechnol. 4, 868 (2009).
![FIG. 1. The schematics of each structure and the corresponding diffraction features:(a) M C , with the shear orientation along [100] direction, (b)M A , with the](https://thumb-ap.123doks.com/thumbv2/9libinfo/7918702.156742/3.918.95.825.840.1095/schematics-structure-corresponding-diffraction-features-shear-orientation-direction.webp)
