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ROOM TEMPERATURE PHOTOCHEMICAL STABILIZATION OF CATALYST THIN FILMS OF THE METASTABLE β-Bi2O3 PHASE

• M. Lourdes Calzada

lcalzada@icmm.csic.es D.Perez-Mezcua, I.Bretos, R.Jiménez, J.Ricote, R.J.Jiménez-Rioboó, C.Gonçalves da Silva, & D.Chateigner, & L.Fuentes,* R.Sirera $

• Inst. Ciencia de Materiales de Madrid (ICMM-CSIC). Cantoblanco, 28049. Madrid. Spain.

&CRISMAT-ENISCAEN and IUT-Caen, Univ.Caen Normandie, 14050 – Caen. France.

*Centro de Investigación en Materiales Avanzados, 31109 – Chihuahua. México.

$ Departamento de Química, Facultad de Ciencias, Universidad de Navarra, E-31008 Pamplona,

• Navarra. Spain.

Spring Mee*ng 2016 Lille – France

Ins$tuto de Ciencia de Materiales de Madrid

Motivation & Background

Photochemical synthesis (low-temperature processing) and stabilization of non-equilibrium phases

UV-irradiation

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Motivation & Background

Photosensi$ve precursor solu$on

Low-temperature crystallized ferroelectric film

deposi'on, drying photoexcita'on, pyrolysis, ozonolysis pyrolysis, crystalliza'on Gel film Photoac$vated gel film

Reduc$on of the crystalliza$on temperature to integrate ferroelectrics in standard CMOS (<5000C)

IR lamp (250 W) Gas flux thermocouple probe UV excimer lamp

(222 nm, 225 W/m2)

Chemical Solu*on Deposi*on (CSD)

CSD produces films with high degree of composi$onal control and large deposi$on areas at low cost, which have made them the method of prepara$on of a wide range of oxide films for electronic applica$ons

Synthesis of precursor solu*on Deposi*on onto a substrate Removal of

• rganic species

Crystallisa*on (600-8000C)

spinning drop of solu$on Photosensi$ve precursor solu$on

PhotoChemical Solu/on Deposi/on (PCSD)

Chamber for the film

http://www.icmm.csic.es/eosmad/

Ins$tuto de Ciencia de Materiales de Madrid fro rom m 300ºC Photosensitive precursor solution Gel film Photoactivated gel film Low-temperature crystallized PZT ferroelectric film ( ) photoactive species UV irradiation IR heating

• n

enhanced decomposition

• f organics

deposition, drying photoexcitation, pyrolysis, ozonolysis pyrolysis, crystallization Photoactive sol, Ph (from 450ºC) Low-temperature crystallization of ferroelectric films

UV-irradia/on of photosensi/ve compounds

Motivation & Background

Calzada et al., Adv.Mater., 2004, 16, 1620

Ins$tuto de Ciencia de Materiales de Madrid

N-methyldiethanolamine (MDEA) N N-methyldiethanolamine (MDEA) N Chemical structure of metal complexes allows charge transfer bands between MDEA ligands and metallic center (LMCT, MLCT) when the system is UV irradiated

+ Metal-alkoxide

sol Metal complexes in solution with high UV-absorption

UV-absorber molecules formed with metal cations with a d0 or d10 electronic configuration

Martín-Arbella et.al., J.Mater.Chem., 2011, 21, 9051.

d0 d10 d10

Photosensitive solution with photoactive species ( )

Charge transfer metal complexes

Solution synthesis of metal oxide precursors

Martín-Arbella et al., J.Mater.Chem., 2011, 21, 9051

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Na

Mg

H Li Be Ca Sc Ti V Cr

Mn

Fe Co Ni Cu Zn Ga Ge As Se

Br

Kr Rb Sr Y Zr Nb

Mo

Tc Ru Rh Pd Ag Cd In Sn Sb Te

I

Xe Cs Ba La Hf Ta W

Re

Os Ir Pt Au Hg Tl Pb Bi Po

At

Rn Fr Ra Ac Rf Db Sg

Bh

Hs Mt Ce Pr Nd Pm Sm Eu

Gd

Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu

Am Cm

Bk Cf Es Fm

Md

No Lr B C N O F Ne Al Si P

S

Cl Ar He K

General applicability !!! Low temperature deposition challenging for any oxide film

K Rb Cs Ge As Se Br Ag Cd Sn Sb Te I Au Hg Tl Pb Bi Po At Possible solution synthesis of charge transfer metal complexes for most high-k dielectric oxides

Solution synthesis of metal oxide precursors

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Na

Mg

H Li Be Ca Sc Ti V Cr

Mn

Fe Co Ni Cu Zn Ga Ge As Se

Br

Kr Rb Sr Y Zr Nb

Mo

Tc Ru Rh Pd Ag Cd In Sn Sb Te

I

Xe Cs Ba La Hf Ta W

Re

Os Ir Pt Au Hg Tl Pb Po

At

Rn Fr Ra Ac Rf Db Sg

Bh

Hs Mt Ce Pr Nd Pm Sm Eu

Gd

Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu

Am Cm

Bk Cf Es Fm

Md

No Lr B C N O F Ne Al Si P

S

Cl Ar He K K Rb Cs Ge As Se Br Ag Cd Sn Sb Te I Au Hg Tl Pb Po At

Bismuth (III) oxide precursors

Bismuth is one of the less toxic heavy metal, which has increased the interest in bismuth containing materials. They show a wide variety of applications that include metallurgic additives, green catalysts, non-toxic pigments, biomaterials for biomedicine or cosmetics. Their compounds also show thermoelectric, ferroelectric and multiferroic properties.

Func/onal bismuth oxides

Bi

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400º C

500 nm

BiFeO3 film

500 nm (Bi0.5Na0.5)0.945Ba0.055TiO3 film

Bismuth-based perovskite ferroelectric thin films

BiFeO3 and (Bi0.5Na0.5)0.945Ba0.055TiO3 perovskite films at low temperatures

Perovskite oxide thin films deposited from UV-absorber precursor solutions and crystallized at low temperatures by UV-irradiation

Pérez-Mezcua et al., J.Mater.Chem.C, 2014, 2, 8750

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Na

Mg

H Li Be Ca Sc Ti V Cr

Mn

Fe Co Ni Cu Zn Ga Ge As Se

Br

Kr Rb Sr Y Zr Nb

Mo

Tc Ru Rh Pd Ag Cd In Sn Sb Te

I

Xe Cs Ba La Hf Ta W

Re

Os Ir Pt Au Hg Tl Pb Po

At

Rn Fr Ra Ac Rf Db Sg

Bh

Hs Mt Ce Pr Nd Pm Sm Eu

Gd

Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu

Am Cm

Bk Cf Es Fm

Md

No Lr B C N O F Ne Al Si P

S

Cl Ar He K K Rb Cs Ge As Se Br Ag Cd Sn Sb Te I Au Hg Tl Pb Bi Po At Possible solution synthesis of charge transfer metal complexes for most high-k dielectric oxides

Bismuth (III) binary oxide polymorphs

β-Bi

• Bi2O3 is the most active

heterogeneous photocatalyst of these compounds and δ-Bi

• Bi2O3

has the highest oxide-ion conductivity of all of the binary metal oxides

Polymorphic forms of the binary oxides of bismuth (III)

• M. Mehring. Coordination Chemistry Reviews. 2007, 251, 974.

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Bismuth (III) binary oxide polymorphs

Stabiliza/on of δ-BiO3 at room temperature ?

Bismuth oxide thin films deposited from UV-absorber precursor. The crystallization is accelerated by UV- irradiation and is independent from the substrate

20 30 40 50 60 70 Pt111

+

+ + + + ++ ++ ++

Al2O3 Al2O3 Al2O3 Al2O3 Al2O3 Al2O3

2θ (º)

(1 (111) 11) δ−

δ−Bi2O3

Al2O3

++

++ (22 (222) 2) δ−

δ−Bi2O3

ØPt-coated silicon substrate Øborosilicate glass substrate Øsilicon substrate Øaluminium oxide substrate

250ºC-350ºC Switzer et al., Science, 1999, 284, 293. Luca et al., J.Appl.Phys. 2013, 113, 046101

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Bismuth (III) binary oxide polymorphs

Stabiliza/on of δ-BiO3 or β-Bi2O3 thin films at room temperature ?

The conductivity behavior of the Bi2O3 films, measured for the first time close to room temperature, indicates that the high-temperature β-Bi2O3 polymorph is the phase stabilized in these films by the UV-irradiation. The conductivity of these films using planar capacitors shows a chaotic behavior similar to that measured in published works that report the stabilization of the non-equilibrium δ- Bi2O3 phase in films prepared by different methods.

Switzer et al., Science, 1999, 284, 293 Skorodumova et.al., Appl.Phys.Lett. 2005, 86, 241910.. Koza et al., ACS Nano. 2013, 7(11), 9946.

These measurements show an electrical behaviour of the films similar to that measured at high temperature for β-Bi2O3 bulk ceramics

Harwig et al., J.Sol.Stat.Chem. 1978, 26, 265

0.9 1.2 1.5 1.8 2.1

• 8
• 7
• 6
• 5
• 4
• 3
• 2
• 1

1

1.27eV

α δ

heating Ahrrenius fitting cooling Ahrrenius fitting Conductividy data

log(σd.c. Ω-1 cm-1) 1000/T(K)

1.27eV

β

extrapolated β-Bi2O3 conductvity to lower temperature

1 2 3 4 5

• 3 .5
• 3 .0
• 2 .5
• 2 .0
• 1 .5
• 1 .0
• 0 .5

0 .0

Sl ope -2.98

Pt 3 50 K N 2 1 m v a .c. Lin e ar fit

log (σ d . c . (Ω

• 1 cm
• 1))

Log(time elapsed (s))

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2θ (0) l

• g

i n t e n s i t y ( a . u . )

Pt β-Bi2O3

2θ (0) I n t e n s i t y

1 / 2(

a . u . )

glass β-Bi2O3

2θ (0) l

• g

i n t e n s i t y ( a . u . )

β-Bi2O3

a) b) c)

β-Bi2O3 a = 7.78(1) Å c = 5.64(1) Å

film on borosilicate glass substrate film on borosilicate glass substrate film on Pt -coated Si substrate

a = 7.7137(2) Å c = 5.6394(2) Å

crystallite size:

(along a) 88(15) Å (along c) 142(15) Å GoF = 1.08

a = 7.7299(2) Å c = 5.6587(2) Å

crystallite size:

(along a) 104(5) Å (along c) 262(5) Å GoF = 1.45

P t

1 1 1

P t

2

2 2 2 2 1 2 1 2 2 2 2 2 2 2 2 2

2 3 4 2

3 2 1 2 1

2 2 2

4

2 1 3 / 4 2 1 2 3

4 2

2 1 3 / 4 2 1 2 3

4 2 4

2 1 3 / 4 2 1 3 2 2 3 2 2 3 2 2

A u

1 1 1

* * 2 1 1

* substrate

The pure β-Bi2O3 tetragonal polymorph is unequivocally identify in these films by using advanced structural characterization techniques, dispelling any doubt about a possible stabilization of the δ-Bi2O3 phase previously reported. Synchrotron radiation in the beamline MCX of the Elettra- Sincrotrone Trieste

β-Bi2O3 thin films stabilized at room temperature

Room temperature stabiliza/on of the tetragonal β-Bi2O3 polymorph in these films

Diffractometer equipped with a four-circle

• pened Eulerian goniometer (χ, φ).

CRISMAT-ENISCAEN

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β-Bi2O3 thin films stabilized at room temperature

Op/cal and photocataly/c proper/es of the β-Bi2O3 thin films

• 20 -15

100 200 0.0 0.2 0.4 0.6 0.8 1.0 Bi2O3 film Blank

MB degradation (A/A0)

Time (min)

dark light

200 400 600 800 1000 0.0 0.2 0.4 0.6 0.8

Absorbance (A.U.)

Wavelength (nm)

• riginal

60 min 120 min 240 min

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 3000 6000 9000 12000 15000 18000

(αhν)1/2 (eV/m) hν (eV)

Eg = 2.995 eV

300 400 500 600 700 800

• 0.5

0.0 0.5 1.0 1.5 2.0 2.5

Exp Tan Psi Fit Cos Delta Exp Cos Delta Fit Tan Psi

Tan (ψ) and Cos (δ) Wavelength (nm)

Etg= 2.830 eV

The stabilization of β-Bi2O3 thin films allows us to make use at room temperature of their functional

• properties. From optical properties, an indirect and a

Tauc band gap of Eg ~ 2.995 eV and Etg ~ 2.830 eV are

• calculated. This means that these β-Bi2O3 films show a

maximum of light absorption at ∼425 nm, in the visible

• range. A β-Bi2O3 film with an area of only ∼2cm2 and a

thickness of ∼50 nm shows to be very efficient for the degradation of the dye (methylene blue, MB), which is totally degraded for short times of light exposure

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α-Bi2O3 film δ-Bi2O3film tf (nm) RS (m) Rf (m) σ(GPa)* tf (nm) RS (m) Rf (m) σ(MPa)* 48 ± 0.5 32.9 ± 3.3 8.6 ± 0.9 + 13.0 ± 2.6 44 ± 1.0 32.9 ± 3.3 41.7 ±4.2 – 1.0 ± 0.9

Table I. Stresses of the α-Bi2O3 and δ-Bi2O3 films on Pt-coated silicon substrates.

The molecular structure of the bismuth (III)–N- methyldiethanolamine coordination complex has been determined by single crystal X-ray diffraction, indicating that are in the range of those measured for the β-Bi2O3 polymorph, with the bismuth in a pseudo-octahedral geometry. The UV irradiation of the layers containing the bismuth complex produces the rupture of the C –, N – and H – bonds, with decomposition of organic residuals and volatilization of CO, CO2, NO, NO2, H2O species. This leads to an amorphous – Bi – O – Bi – cross-linking network with similar interatomic distances to those of the β-Bi2O3 phase. Therefore, the transition from one to the other seems natural and can

• ccur at very low temperature, as it happens here (250ºC). In addition, the

absence of residual stress in the irradiated film also favors the stabilization of the of β-Bi2O3 polymorph in these films.

β-Bi2O3 thin films stabilized at room temperature

Op/cal and photocataly/c proper/es of the β-Bi2O3 thin films

Le Bris et al., Inorganic Chemistry Communications. 2007, 10, 80.

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The results of this work demonstrate the potential of UV-light to fabricate high-tech materials of non- equilibrium crystalline phases. This processing technology is successfully applied to the fabrication of thin films of the metastable β-Bi2O3 phase at only 250ºC from strong UV-absorbing precursors, when the formation temperature of this polymorph is ∼650ºC. Not only that, the metastable phase is stabilized at room temperature and shows a wide temperature stability range. The use of advanced characterization techniques, X-ray synchrotron radiation and four-circle diffractometry, allows us to unequivocally identify the development in the films of the pure β-Bi2O3 tetragonal polymorph. Electrical measurements carried out close to room temperature in β-Bi2O3 thin films show a conductivity behavior compatible with that reported for bulk β-Bi2O3 materials at the high temperatures where the phase is stable. Additionally, the optical properties

• f these β-Bi2O3 thin films evidence an excellent visible light absorption with a very high efficient

photodegradation of dyes.

Conclusions

Acknowledgments: This work was financed by Spanish Project MAT2013-40489-P. The COST Action IC1208 also contributed to this study. I.B. acknowledges the financial support by Fundación General CSIC (Spanish ComFuturo Programme).

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