Supporting Information

ForEffects of Bismuth Oxide Buffer Layer on BiFeO3 Thin Film

1

Ching-Chich Leua,*, Tsung-Ju Linb, Shu-Yu Chenb, and Chen-Ti Hub

aDepartment of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 811, Taiwan, ROCbDepartment of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30043, Taiwan, ROC

*E-mail: ccleu@nuk.edu.tw

Figure S1 The XPS Bi 4f core level spectra of as deposited (a) LT-

Bi2O3 and (b) HT-Bi2O3, and being etched (c) LT-Bi2O3 and (d) HT-

Bi2O3 films, respectively. The films were etched by dilute HF solution

for 20 sec at room temperature. The peaks at 159.2 eV and 157 eV are

attributed to Bi2O3 and metallic Bi, respectively. [1, 2]

2

170 168 166 164 162 160 158 156 154

(d)

(c)

(b)

(a)

BiBi

Bi-O

Bi-O

Bi 4f

Inte

nsi

ty (

arb

. unit)

Binding energy (eV)

Reference

1.C. Ostos, O. Raymond, N. Suarez-Almodovar, D. Bueno-Baqués, L. Mestres, and

J. M. Siqueiros, “Highly textured Sr, Nb co-doped BiFeO3 thin films grown on

SrRuO3/Si substrates by rf- sputtering,” J. Appl. Phys., 110, 024114, 7pp (2011).

2.U. W. Hamm, D. Kramer, R. S. Zhai and D. M. Kolb, “On the valence state of

bismuth adsorbed on a Pt(111) electrode: an electrochemistry, LEED and XPS

study,” Electrochimica Acta, 43, 2969-78 (1998).

3

XPS O 1s core level spectra of the specimens:

Figure S2 shows the XPS O 1s core level spectra of (a) BFO, (b) B*FO,

(c) LT-Bi2O3 /BFO, (d) HT-Bi2O3/BFO, and (e) BFO/LT-Bi2O3,

respectively. The O 1s peak consists of three single subpeaks at ~ 529.6

eV, 531.2 eV, and 533.1 eV.[1, 2] The peak at lower energy is ascribed to

the O2- ions at the lattice sites of BFO, while the peaks at middle and higher

energies are related with the oxygen deficient regions (the loss of oxygen

in the sample) and the relaxed O phases, respectively. The relaxed O

phases may also be attributed to the absorbed oxygen associated with

oxygen vacancies. (some of them created by cation defects) Therefore, the

peaks of both middle and higher energies (peak II + peak III) are associated

with the oxygen-related defective structures. The deconvulated peak

positions and their calculated peak area ratios of the specimens are

summarized in Table S1. In is worth noting that the area ratio of peak II in

the BFO/LT-Bi2O3 is abnormal high, where its position is different from

those in the other samples. There is a high possibility of the existence of

second phase in this specimen.

Reference

1.C. Ostos, O. Raymond, N. Suarez-Almodovar, D. Bueno-Baqués, L.

Mestres, and J. M. Siqueiros, “Highly textured Sr, Nb co-doped BiFeO3

thin films grown on SrRuO3/Si substrates by rf- sputtering,” J. Appl. Phys.,

110, 024114, 7pp (2011).

2.L. Fang, J. Liu, S. Ju, F. Zheng, W. Dong, and M. Shen, “Experimental

and theoretical evidence of enhanced ferromagnetism in sonochemical

synthesized BiFeO3 nanoparticles,” Appl. Phys Lett., 97, 242501, 3pp

(2010).

4

536 534 532 530 528 526

raw data fit line background peak I peak II peak III

(b)

(e)

(d)

(c)

O 1s

Binding energy (eV)

Inte

nsity

(ar

b. u

nit)

(a)

Figure S2 The XPS O 1s core level spectra of (a) BFO, (b) B*FO, (c) LT-

Bi2O3 /BFO, (d) HT-Bi2O3/BFO, and (e) BFO/LT-Bi2O3, respectively.

5

Table S1 Peak positions for the core levels of O 1s.

samples Peak positions in eV (area ratio %)

Peak I Peak II Peak III

BFO 529.66 (59.4) 531.20 (34.6) 533.22 (6.0)

B*FO 529.59 (70.1) 531.25 (24.8) 533.19 (5.1)

LT-Bi2O3/BFO 529.56 (65.6) 531.20 (29.1) 533.26 (5.3)

HT-Bi2O3/BFO 529.55 (69.1) 531.20 (30.9) -

BFO/LT-Bi2O3 529.52 (44.3) 530.89 (51.9) 533.16 (3.8)

6

Calculation of the contributed polarization from polarization axes of

BFO:

To correlate the variations of remanent polarization values to their texture

structure of BFO, calculation of the contributed polarization from various

polarization axes was performed. The polar axes is the [111] for the BFO with

rhombohedral symmetry [1]. The contributed polarization values of each plane

was obtained by multiplying the Pr values with their integrated intensity ratio

(Pr(hkl)×α(hkl)). α(hkl) is the integrated intensity ratio of each peak, which is defined as

, where I(100) represents the peak area of (100) peak, and vice versa. We used

software to deconvolute the overlapped diffraction peaks and integrated their peak

area individually. For example: the tilted angles between (111) and (100) was

55.49°, therefore the Pr values of this plane is Pr(100) ＝ Pr(111)×cos55.49°. Then,

the contributed polarization values normal to the film surface is a summation of

all the calculated polarization values of each plane. The calculated polarization

values as function of the buffer conditions for the BFO are displayed in Figure S3.

Noting that all the calculated polarization values are normalized by those of their

polar axes.

Reference

1.G. Catalan and J. F. Scott, "Physics and Applications of Bismuth Ferrite," Adv.

Mater., 21, 2463-85 (2009).

)111()011()110()100(

)(

)( IIII

I hkl

hkl

7

Figure S3 2Pr values (from fig. 8) and calculated polarization values normal to film surface as functions of buffer conditions of (a) BFO, (b) B*FO, (c) LT-Bi2O3/BFO, (d) HT-Bi2O3/BFO, and (e) BFO/LT-Bi2O3 films. All the calculated polarization values are normalized by those of their polar axes.

2

3

4

5

6 measured 2Pr value

(e)(d)(c)(b)(a)0.6

0.7

0.8

0.9

calculated polraization value

Polarization (norm

alized)2P

r (μ

C/c

m2 )

8

Frequency-depended dielectric behavior of the specimens:

Figure S4 displays the frequency-depended dielectric behavior of

specimens. The variation of dielectric constant at 100k Hz as function of

the buffer condition is shown in the inset. It is reported that the dielectric

constants of ferroelectric films are extensively affected by various material

characteristics: (1) grain size,[1] (2) density of pinholes,[2] (3) leakage

current density,[2] and (4) ferroelectric polarization.[3] . As shown in the

inset, the B*FO possesses nearly twice higher dielectric constant than the

BFO does. Furthermore, the dielectric constants of all the Bi2O3-buffered

BFO are even greater than that of the B*FO, implying their property was

comprehensively improved by the buffer layer.

Reference

1.C.-F. Chung and J.-M. Wu, "Low Leakage BiFeO3 Thin Films Fabricated

by Chemical Solution Deposition," Electrochemical and Solid-State

Letters, 8, F63-6 (2005).

2.J. G. Wu and J. Wang, "Improved ferroelectric behavior in (110) oriented

BiFeO3 thin films," J. Appl. Phys., 107, 034103, 4pp (2010).

3.S. Chopra, S. Sharma, T. C. Goel, and R. G. Mendiratta, "Structural,

dielectric and pyroelectric studies of Pb1−XCaXTiO3 thin films," Solid State

Communications, 127, 299-304 (2003).

9

Figure S4 Variation of dielectric constant with frequency of (a) BFO, (b) B*FO, (c) LT-Bi2O3/BFO, (d) HT-Bi2O3/BFO, and (e) BFO/LT-Bi2O3 films. The inset displays the tendency of dielectric constant at 100k as function of buffer conditions.

80

120

160

200

240

(e)(d)(c)(b)

(a)

80

120

160

200

240

280

320 (a) (d) (b) (e) (c)

Die

lect

ric

const

ant

Frequency (Hz)0 200 k 600 k400 k 800 k 1 M

Die

lectr

ic

con

sta

nt

Figure S5 Hysteresis loops of the in-plane magnetization versus magnetic field for (a) BFO, (b) B*FO, (c) LT-Bi2O3/BFO, (d) HT-Bi2O3/BFO, and (e) BFO/LT-Bi2O3 films. The inset reveals the 2Mr tendency of films as function of buffer conditions.

(a) (b) (c) (d) (e)0.4

0.8

1.2

1.6

2.0

2Mr

(em

u/c

m3 )

-2000 -1000 0 1000 2000-3

-2

-1

0

1

2

Magnetic field (Oe)

(c) (d) (e)

Mag

netiz

atio

n(em

u/cm

3 )

-3

-2

-1

0

1

2

3

(a) (b)M

agne

tizat

ion(

emu/

cm3 )

10

11

XPS Fe 2p core level spectra of the specimens:

Figure S6 displays the XPS Fe 2p core level spectra of (a) BFO, (b) B*FO,

(c) LT-Bi2O3/BFO, and (d) HT-Bi2O3/BFO, respectively. The fitting analysis of

Fe 2p2/3 shows that the peak consists of two subpeaks at ~ 711.1 eV, and 709.6

eV, which are attributed to Fe3+ and Fe2+ ions, respectively.[1-3] The

deconvoluted peak positions and their calculated peak area ratios of the

specimens are summarized in Table S2.

It was reported that the charge defects such as oxygen vacancies come from

the volatile of bismuth [4], leading the transition from Fe3+ to Fe2+.[5, 6] The

calculated Fe2+ ratios here are corresponding well to the tendency of both the

amount of oxygen-related defective structure (from Table S1) and the Bi/Fe

ratio by EDS.

Reference

1.C. Ostos, O. Raymond, N. Suarez-Almodovar, D. Bueno-Baqués, L. Mestres,

and J. M. Siqueiros, “Highly textured Sr, Nb co-doped BiFeO3 thin films

grown on SrRuO3/Si substrates by rf- sputtering,” J. Appl. Phys., 110, 024114,

7pp (2011).

2.L. Fang, J. Liu, S. Ju, F. Zheng, W. Dong, and M. Shen, “Experimental and

theoretical evidence of enhanced ferromagnetism in sonochemical synthesized

BiFeO3 nanoparticles,” Appl. Phys. Lett., 97, 242501, 3pp (2010).

3.J. Wei, D. Xue, “Effect of non-magnetic doping on leakage and magnetic

properties of BiFeO3 thin films,” Appl. Surf. Sci., 258, 1373-6 (2011).

4.A. Lahmar, K. Zhao, S. Habouti, M. Dietze, C. H. Solterbeck, and M. Es-

Souni, "Off-stoichiometry effects on BiFeO3 thin films," Solid State Ionics,

202, 1-5 (2011).

5.J. Wu, G. Kang, and J. Wang, "Electrical behavior and oxygen vacancies in

BiFeO3/[(Bi1/2Na1/2)0.94Ba0.06TiO3 thin film," Appl. Phys. Lett., 95, 192901, 3pp

(2009).

6.J. Prado-Gonjal, D. Ávila, M.E. Villafuerte-Castrejón, F. González-García,

L. Fuentes, R.W. Gómez, J. L. Pérez-Mazariego, V. Marquina, E. Morán,

Structural, microstructural and Mössbauer study of BiFeO3 synthesized at low

temperature by a microwave-hydrothermal method, Solid State Sciences, 13,

2030-2036 (2011).

12

Figure S6 The XPS Fe 2p3/2 core level spectra of (a) BFO, (b)

B*FO, (c) LT-Bi2O3 /BFO, and (d) HT-Bi2O3/BFO, respectively.

The inset displays the whole XPS Fe 2p core level spectra of the

specimens.

718 716 714 712 710 708 706

raw data fit line background

Fe3+

Fe2+ Fe3+ Fe2+

Inte

nsity

(ar

b. u

nit)

Binding energy (eV)

Fe 2P3/2

(b)

(c)

(d)

(a)

730 725 720 715 710 705 700

Inte

nsi

ty (

arb

. unit)

(b)

(c)

(d)

Fe 2P3/2Fe 2P

1/2

Binding energy (eV)

(a)

13

Table S2 Peak positions for the core levels of Fe 2p.

samples

Peak positions in eV (area ratio %) Oxygen-related

defective structure(area ratio %)*

EDS composition(Bi/Fe ratio)Fe2+ Fe3+

BFO709.65 (30.9)

711.12 (69.1)

40.6 0.83

B*FO709.58 (24.8)

711.02 (75.2)

29.9 1.02

LT-Bi2O3/BFO 709.55 (28.5)

711.11 (71.5)

34.4 0.97

HT-Bi2O3/BFO 709.72 (25.1)

711.29 (74.9)

30.9 1.07* From the Table S1