ArticlePDF Available

Reversible plasma switching in epitaxial BiFeO3 thin films

May 2010
Applied Physics Letters 96(20):2902-202902

May 2010
96(20):2902-202902

DOI:10.1063/1.3431585

Authors:

Yunseok Kim

Sungkyunkwan University

Ionela Vrejoiu

University of Cologne

Marin Alexe

The University of Warwick

Reversible plasma switching in epitaxial multiferroic BiFeO3 thin films was directly observed and analyzed using piezoresponse force microscopy. The polarization could be reversibly switched using oxygen plasma and a subsequent thermal annealing treatment in vacuum, respectively. The domain wall velocity during plasma switching, estimated to about 10-8 m/s, is much slower compared to the normal electrical switching, however a large area of square centimeter scale could be stably switched. The results demonstrate that reversible plasma switching can be achieved by oxygen plasma treatment and it can be a useful tool for an electrode-less control of ferroelectric switching on large area.

Color online PFM phase images of a as-deposited and b-d oxygen plasma treated states for b 1 min, c 4 min, and d 10 min, respectively, in 30-nm-thick BFO thin films. The scale bar corresponds to 400 nm.

…

PFM phase images of different states: [(a) and (d)] as-deposited, [(b) and (e)] oxygen plasma treated for 10 min, and [(c) and (f)] after subsequent annealing at 350 ° C for 30 min, for BFO thin films of [(a)–(c)] 30 nm and [(d)–(f)] 60 nm thickness. The scale bars of (c) and (f) correspond to 400 nm and 300 nm, respectively.

…

Figures - uploaded by Yunseok Kim

Content may be subject to copyright.

Content uploaded by Yunseok Kim

Content may be subject to copyright.

Reversible plasma switching in epitaxial BiFeO

thin ﬁlms

Yunseok Kim,

a兲

Ionela Vrejoiu, Dietrich Hesse, and Marin Alexe

Max Planck Institute of Microstructure Physics, D-06120 Halle (Saale), Germany

共Received 16 April 2010; accepted 27 April 2010; published online 17 May 2010兲

Reversible plasma switching in epitaxial multiferroic BiFeO

thin ﬁlms was directly observed and

analyzed using piezoresponse force microscopy. The polarization could be reversibly switched using

oxygen plasma and a subsequent thermal annealing treatment in vacuum, respectively. The domain

wall velocity during plasma switching, estimated to about 10

−8

m/ s, is much slower compared to

the normal electrical switching, however a large area of square centimeter scale could be stably

switched. The results demonstrate that reversible plasma switching can be achieved by oxygen

plasma treatment and it can be a useful tool for an electrode-less control of ferroelectric switching

Ferroelectric/multiferroic materials are attractive due to

their unique physical properties and wide applications.

1,2

Es-

pecially, magnetoelectric multiferroic materials have recently

been under focus due to possible coupling of ferroelectric

and magnetic properties. Ferroelectric materials have a spon-

taneous polarization with at least two stable orientations,

which usually can be switched by an external electric ﬁeld.

The polarization bound charges on the as-deposited surfaces

are screened by external and/or internal charges to reduce the

energy of the depolarizing ﬁeld.

When there are insufﬁcient

charges to compensate the polarization bound charges, the

energy of the depolarizing ﬁeld can be minimized by domain

formation.

4–6

The particular as-deposited domain structure

depends strongly on the screening of the polarization bound

charges and thus on the particular details of the fabrication

process. However, a monodomain state is preferable to opti-

mize the functional performance of ferroelectric thin ﬁlms in

applications such as data storage, pyroelectric detectors, or

piezoelectric transducers and actuators. Therefore, tech-

niques to manipulate domain states are important for such

applications. By using conventional switching by an external

electric ﬁeld it is difﬁcult to switch the ﬁlms on a centimeter

scale since temporary electrodes are required.

Recently, there have been several reports on ferroelectric

domain states manipulated by external environment.

6–10

Fong et al.

reported that the equilibrium structure of an

epitaxial PbTiO

共PTO兲 ﬁlm in an oxidizing environment is a

monodomain state with upward polarization. On the basis of

these results, they also showed that an oxygen partial pres-

sure allows to control the reversible polarization switching in

the PTO thin ﬁlms.

On the other hand, Takahashi et al.

reported that photochemical treatment induces switching into

a monodomain state, which could be reversed upon subse-

quent heat-treatment, in PTO thin ﬁlms. Alternatively, corona

switching can be effectively applied to the polarization

switching of Pb共Zr , Ti兲O

and poly共vinylidene ﬂuoride-co-

triﬂuoroethylene兲 thin ﬁlms.

9,10

However, there are still no

studies on environmental switching in multiferroic thin ﬁlms,

in particular no direct observations of environmental switch-

ing in ferroelectric/multiferroic thin ﬁlms.

Here we show direct observations of a reversible switch-

ing process assisted by oxygen plasma treatment in epitaxial

multiferroic BiFeO

共BFO兲 thin ﬁlms, using piezoresponse

force microscopy 共PFM兲. Oxygen plasma treatment is com-

monly applied to ferroelectric materials for the surface modi-

ﬁcation or the improvement of surface properties.

11,12

In the

present work, the oxygen plasma was used as a tool to in-

duce the polarization switching of multiferroic BFO thin

ﬁlms at room temperature.

Epitaxial BFO thin ﬁlms with thicknesses of 30 to 170

nm were deposited by pulsed laser deposition 共PLD兲 on a

PLD-grown SrRuO

bottom electrode on top of DyScO

共110兲 substrates. The BFO ﬁlms were deposited at a substrate

temperature of 650 °C, in 0.14 mbar O

. PFM measurements

were performed with an ac voltage of 0.4–1.0 V

rms

at 25

kHz under ambient conditions using a commercial atomic

force microscope 共XE-100, Park Systems兲, combined with a

lock-in ampliﬁer 共SR830, Stanford Research Systems兲. PtIr

coated silicon cantilevers 共ATEC-EFM, Nanosensors兲 with a

spring constant of 2.8 N/m and a resonance frequency of

75 kHz and Pt/Ti coated silicon cantilevers 共NSC14/Ti-Pt,

MikroMasch兲 with a spring constant of 5.0 N/m and a reso-

nance frequency of 160 kHz were used for the switching

processes as well as the local PFM measurements. Oxygen

plasma treatments were performed using a commercial

plasma system 共100-E, Technics Plasma GmbH兲 at a pressure

of 1 Torr and a rf power of 100 W, for different treatment

durations. To obtain the fraction of the area with upward

polarization, PFM phase images were analyzed over areas of

5⫻ 5

␮

. For the box patterns, background poling was

performed over areas of 6 ⫻ 6

␮

under a bias of ⫺5V

applied to the conductive probe, followed by poling a small

box pattern over an area of 2⫻ 2

␮

under a bias of +5 V

applied to the conductive probe.

Figure 1 shows PFM phase images as a function of oxy-

gen plasma treatment time for the 30-nm-thick BFO thin

ﬁlm. The as-deposited domain structure of Fig. 1共a兲 is char-

acterized by a needle shape of upward polarized domains,

which might originate in insufﬁciently screened positive

charges on the multiferroic surface.

4–6

After plasma treat-

ment for 1 min, the domain structure starts to change into

more granular shaped domains of upward polarization, and

the portion of upward polarization also increases with re-

spect to the pristine state. Further increasing the plasma treat-

a兲

Author to whom correspondence should be addressed. Electronic mail:

ykim@mpi-halle.mpg.de.

APPLIED PHYSICS LETTERS 96, 202902 共2010兲

Downloaded 17 May 2010 to 192.108.69.177. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp

ment time, the portion of upward polarization increases and

then saturates as shown in Figs. 1 and 2. After treatment for

10 min, about 80% of the measured area was switched into

the upward polarization. A large area up to 1 cm

could be

switched using plasma treatment, and this switched region

was stable even after several days under ambient conditions.

This indicates the strong inﬂuence of the oxygen plasma

treatment on the BFO thin ﬁlms. As previously reported,

oxygen atmosphere induces a chemical switching inside

ferroelectric thin ﬁlms because its chemical potential pro-

duces an electric ﬁeld across the ﬁlm. The chemical potential

of the oxygen atmosphere or the oxidation of the ferroelec-

tric may switch the polarization direction. In the present

case, the oxygen plasma treatment might generate an atmo-

sphere similar to the oxygen atmosphere of Ref. 8. In addi-

tion to the chemical switching, an electric ﬁeld perpendicular

to the sample surface can be generated during the oxygen

plasma treatment that can be similar to the corona

switching.

9,10

These two reasons might be responsible for the

plasma switching of our BFO epitaxial ﬁlms.

From the PFM phase images of Fig. 1, we could analyze

the domain growth process during the plasma switching as

schematically presented in Fig. 2共b兲. The switching behavior

is similar to a normal electrical switching in ferroelectric/

multiferroic thin ﬁlms. Pre-existing upward polarized do-

mains of the as-deposited state can act as nuclei for the elec-

trical switching process. When the sample is oxygen plasma

treated on the as-deposited BFO ﬁlm surface, the domain

growth starts from these pre-existing upward polarized do-

mains as shown in Fig. 1共b兲 and diagram 2 of Fig. 2共b兲.

Afterwards domains grow laterally and coalesce with each

other as shown in Figs. 1共c兲 and 1共d兲 and diagrams 3 and 4

of Fig. 2共b兲.

The average domain wall velocity could be obtained

from the domain growth behavior before the coalescence

of all domains. At the beginning of domain growth the

domain wall velocity has a maximum value and then de-

creases gradually during the growth process. This behavior is

similar to the domain wall velocity of normal electrical

switching.

13,14

The average domain wall velocity was 1.16

⫻ 10

−8

m/ s, which is three orders of magnitude slower than

the electrical domain wall velocity of the BFO thin ﬁlms.

Although the domain wall movement was very slow, the

oxygen plasma treatment offers easy switching for a large

area of the materials, which can be larger than several square

centimeters.

The polarization can be switched back to its original

downward state by thermal annealing.

6,8

According to Wang

et al.

this is achieved by surface reconstruction during the

annealing procedure, which can occur by ordering of oxygen

vacancies, ﬁnally inducing polarization switching to the

downward polarization. A similar situation of the oxygen va-

cancies can be achieved by vacuum annealing, which re-

leases oxygen from the sample surface.

To conﬁrm that this

is valid also for epitaxial BFO ﬁlms, and that the plasma

switching is reversible, the oxygen plasma-treated BFO ﬁlms

were thermally annealed in vacuum 共 10

−5

mbar兲 at 350 ° C

for 30 min. After this treatment the domain structure was

recovered to the original state, as presented in Fig. 3共c兲. The

reduction condition of the thermal treatment in vacuum most

likely generates oxygen vacancies in the vicinity of the ﬁlm

surface, which can induce the back-switching of the polar-

ization. Interestingly, after the thermal treatment, the upward

polarized domains have a needle shape, which indicates that

the pristine upward polarized regions prefer to be back to the

original upward polarized state. This reversible plasma

switching can also be observed for much thicker BFO ﬁlms

of 60 nm thickness as shown in Figs. 3共d兲–3共f兲. This means

that the electric ﬁeld, generated by oxygen plasma treatment

across the ﬁlm, is sufﬁcient to switch BFO thin ﬁlms of at

least several tens of nanometer thickness. However, when the

oxygen plasma treatment and the subsequent thermal treat-

ment in vacuum were repeated, the domain wall velocity

became slower than before, for the same duration of the oxy-

gen plasma process. In the present work, we could not pre-

cisely control the surface oxidation and the density of surface

oxygen vacancies. Repeated runs might lead to changes in

the surface state, which can affect the domain wall motion.

FIG. 1. 共Color online兲 PFM phase images of 共a兲 as-deposited and 关共b兲–共d兲兴

oxygen plasma treated states for 共b兲 1 min, 共c兲 4 min, and 共d兲 10 min,

respectively, in 30-nm-thick BFO thin ﬁlms. The scale bar corresponds to

400 nm.

FIG. 2. 共Color online兲共a兲 Dependence of the area of upward polarized

domains on the duration of treatment by the oxygen plasma. 共b兲 Schematics

of cross-sectional domain structures in 共1兲 as-deposited and 关共2兲–共4兲兴 oxygen

plasma treated states for 共2兲 1 min, 共3兲 4 min, and 共4兲 10 min.

202902-2 Kim et al. Appl. Phys. Lett. 96, 202902 共2010兲

Downloaded 17 May 2010 to 192.108.69.177. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp

Therefore, further investigations are needed to optimize the

treatment by oxygen plasma and the subsequent thermal

treatment in vacuum.

The oxygen plasma effect was also examined on the box

patterned 共prepoled兲 area as shown in Fig. 4. The plasma

switching could be observed even at 170-nm-thick BFO

ﬁlms. After 1 min oxygen plasma treatment, the polarization

reversal started immediately at the pristine upward polarized

regions 共inside of the box pattern兲, incompletely switched

regions 共lower part of the box pattern兲, and/or the domain

boundaries. The pristine upward polarized regions might be

related to different local defect states or different distribu-

tions of the screening charges, which render the upward po-

larization more stable than the downward polarization, and

the nonpenetrating domains of incomplete switching are un-

stable compared to the fully switched domains.

After the

polarization reversal at these areas, the domain wall laterally

moved from the switched regions, which is similar to the

previous case.

In summary, reversible plasma switching in epitaxial

BFO ﬁlms was directly observed and investigated using

PFM. 30 to 170-nm-thick BFO ﬁlms could be switched to

upward polarization using oxygen plasma treatment. The do-

main wall velocity was much slower compared to the normal

electrical switching, however a large area of centimeter scale

could be stably switched. The switched regions could be re-

covered to the original state of the downward polarization

using a thermal treatment in vacuum. The results show that

reversible plasma switching can be achieved by oxygen

plasma treatment. This method can be a useful tool to control

the switching behavior for a large area of multiferroic

samples.

The ﬁrst author 共Y.K.兲 acknowledges the ﬁnancial sup-

port of the Alexander von Humboldt Foundation.

J. F. Scott and C. A. Araujo, Science 246 , 1400 共1989兲.

J. Wang, J. B. Neaton, H. Zheng, V. Nagarajan, S. B. Ogale, B. Liu, D.

Viehland, V. Vaithyanathan, D. G. Scholm, U. V. Waghmare, N. A.

Spaldin, K. M. Rabe, M. Wuttig, and R. Ramesh, Science 299, 1719

共2003兲.

S. V. Kalinin and D. A. Bonnell, Phys. Rev. B 63, 125411 共2001兲.

S. K. Streiffer, J. A. Eastman, D. D. Fong, C. Thompson, A. Munkholm,

M. V. R. Murty, O. Auciello, G. R. Bai, and G. B. Stephenson, Phys. Rev.

Lett. 89, 067601 共2002兲.

B.-K. Lai, I. Ponomareva, I. I. Naumov, I. Kornev, H. Fu, L. Bellaiche,

and G. J. Salamo, Phys. Rev. Lett. 96, 137602 共2006兲.

R. Takahashi, J. K. Grepstad, T. Tybell, and Y. Matsumoto, Appl. Phys.

Lett. 92, 112901 共2008兲.

D. D. Fong, A. M. Kolpak, J. A. Eastman, S. K. Streiffer, P. H. Fuoss, G.

B. Stephenson, C. Thompson, D. M. Kim, K. J. Choi, C. B. Eom, I.

Grinberg, and A. M. Rappe, Phys. Rev. Lett. 96, 127601 共2006兲.

R. V. Wang, D. D. Fong, F. Jiang, M. J. Highland, P. H. Fuoss, C. Thomp-

son, A. M. Kolpak, J. A. Eastman, S. K. Streiffer, A. M. Rappe, and G. B.

Stephenson, Phys. Rev. Lett. 102, 047601 共2009兲.

C. A. Nguyen, P. S. Lee, W. A. Yee, X. Lu, M. Srinivasan, and S. G.

Mhaisalkar, J. Electrochem. Soc. 154, G224 共2007兲.

J. M. Marshall, Q. Zhang, and R. W. Whatmore, Thin Solid Films 516,

4679 共2008兲.

Y. Park, Y. K. Lee, I. Chung, and J.-Y. Lee, Jpn. J. Appl. Phys. 38, L577

共1999兲.

H. K. Jang, S. K. Lee, C. E. Lee, S. J. Noh, and W. I. Lee, Appl. Phys.

Lett. 76, 882 共2000兲.

B. J. Rodriguez, R. J. Nemanich, A. Kingon, A. Gruverman, S. V. Kalinin,

K. Terabe, X. Y. Lia, and K. Kitamura, Appl. Phys. Lett. 86, 012906

共2005兲.

A. Gruverman, D. Wu, and J. F. Scott, Phys. Rev. Lett. 100, 097601

共2008兲.

Y. C. Chen, Q. R. Lin, and Y. H. Chu, Appl. Phys. Lett. 94, 122908

共2009兲.

Y. Kim, M. Alexe, and E. K. H. Salje, Appl. Phys. Lett. 96, 032904

共2010兲.

J. Woo, S. Hong, D. K. Kim, H. Shin, and K. No, Appl. Phys. Lett. 80,

4000 共2002兲.

FIG. 3. 共Color online兲 PFM phase images of different states: 关共a兲 and 共d兲兴

as-deposited, 关共b兲 and 共e兲兴 oxygen plasma treated for 10 min, and 关共c兲 and

共f兲兴 after subsequent annealing at 350 °C for 30 min, for BFO thin ﬁlms of

关共a兲–共c兲兴 30 nm and 关共d兲–共f兲兴 60 nm thickness. The scale bars of 共c兲 and 共f兲

correspond to 400 nm and 300 nm, respectively.

FIG. 4. 共Color online兲 PFM phase images of the box patterns on the 共a兲

pristine and 关共b兲 and 共c兲兴 oxygen plasma treated states for 共b兲 1 min and 共c兲

12 min, in 170-nm-thick BFO thin ﬁlm. The blue dashed lines indicate the

location of the downward polarized box pattern. The scale bar corresponds

to 600 nm.

202902-3 Kim et al. Appl. Phys. Lett. 96, 202902 共2010兲

Downloaded 17 May 2010 to 192.108.69.177. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp

Nanoscale Probing of Ferroelectric Domain Switching Using Piezoresponse Force Microscopy

Article

Jul 2019

Surface Screening Mechanisms in Ferroelectric Thin Films and its Effect on Polarization Dynamics and Domain Structures

Article

Full-text available

Dec 2016

For over 70 years, ferroelectric materials have been remaining one of the central research topics for condensed matter physics and material science, the interest driven both by fundamental science and applications. However, ferroelectric surfaces, the key component of ferroelectric films and nanostructures, still present a significant theoretical and even conceptual challenge. Indeed, stability of ferroelectric phase per se necessitates screening of polarization charge. At surfaces, this can lead to coupling between ferroelectric and semiconducting properties of material, or with surface (electro) chemistry, going well beyond classical models applicable for ferroelectric interfaces. In this review, we summarize recent studies of surface screening phenomena in ferroelectrics. We provide a brief overview of the historical understanding of physics of ferroelectric surfaces, and existing theoretical models that both introduce screening mechanisms and explore the relationship between screening and relevant aspects of ferroelectric functionalities starting from phase stability itself. Given that majority of ferroelectrics exist in multiple-domain states, we focus on local studies of screening phenomena using scanning probe microscopy techniques. We discuss recent studies of static and dynamic phenomena on ferroelectric surfaces, as well as phenomena observed under lateral transport, light, chemical, and pressure stimuli. We also note that the need for ionic screening renders polarization switching a coupled physical-electrochemical process, and discuss the non-trivial phenomena such as chaotic behavior during domain switching that stem from this.

High-contrast imaging of 180° ferroelectric domains by optical microscopy using ferroelectric liquid crystals

Article

Full-text available

May 2020
APPL PHYS LETT

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an electric field gives rise to an immediate and lasting optical response when an appropriately aligned FLC is observed between crossed polarizers, with one field direction yielding a dark image and the opposite direction yielding a bright image. Here, this peculiar electro-optic response is used to image, with high optical contrast, 180° ferroelectric domains in a crystalline substrate of magnesium-doped lithium niobate. The lithium niobate substrate contains a few domains with upward electric polarization surrounded by regions with downward electric polarization. In contrast to a reference non-chiral liquid crystal that is unable to show ferroelectric behavior due to its high symmetry, the FLC, which is used as a thin film confined between the lithium niobate substrate and an inert aligning substrate, reveals ferroelectric domains as well as their boundaries, with strong black and white contrast. The results show that FLCs can be used for non-destructive readout of domains in underlying ferroelectrics, with potential applications in, e.g., photonic devices and non-volatile ferroelectric memories.

Mechanically Induced Ferroelectric Switching in BaTiO3 Thin Films

Article

May 2020
ACTA MATER

The ability to reverse or switching the polarization of a ferroelectric thin film through a mechanical force under an atomic force microscopy (AFM) tip offers the exciting possibility of a voltage-free control of ferroelectricity. One of the important metrics for characterizing such a switching process is the critical force Fc required to reverse a polarization. However, the experimentally measured values of Fc display a large uncertainty and vary significantly even for the same ferroelectric film. Here, using BaTiO3 thin films as a model system, we systematically evaluate Fc using a combination of AFM-based experiments and phase-field simulations. In particular, we study the influence of the AFM tip radius, misfit strain, and film thickness on Fc as well as the interplay between the flexoelectric and piezoelectric effects. This work provides a deeper understanding on the mechanism and control of mechanically induced ferroelectric switching and thus guidance for exploring potential ferroelectric-based nanodevices based on mechanical switching.

The Effect of Chemical Environment and Temperature on the Domain Structure of Free‐Standing BaTiO3 via In Situ STEM

Article

Full-text available

Aug 2023

Ferroelectrics, due to their polar nature and reversible switching, can be used to dynamically control surface chemistry for catalysis, chemical switching, and other applications such as water splitting. However, this is a complex phenomenon where ferroelectric domain orientation and switching are intimately linked to surface charges. In this work, the temperature‐induced domain behavior of ferroelectric‐ferroelastic domains in free‐standing BaTiO3 films under different gas environments, including vacuum and oxygen‐rich, is studied by in situ scanning transmission electron microscopy (STEM). An automated pathway to statistically disentangle and detect domain structure transformations using deep autoencoders, providing a pathway towards real‐time analysis is also established. These results show a clear difference in the temperature at which phase transition occurs and the domain behavior between various environments, with a peculiar domain reconfiguration at low temperatures, from a‐c to a‐a at ≈60 °C. The vacuum environment exhibits a rich domain structure, while under the oxidizing environment, the domain structure is largely suppressed. The direct visualization provided by in situ gas and heating STEM allows to investigate the influence of external variables such as gas, pressure, and temperature, on oxide surfaces in a dynamic manner, providing invaluable insights into the intricate surface‐screening mechanisms in ferroelectrics.

Large controllability of domain evolution in ferroelectric nanodot via isotropic surface charge screening

Article

Full-text available

Aug 2016
APPL PHYS A-MATER

This work reports a large controllability of domain evolution in BaTiO3 ferroelectric nanodot by isotropic surface charge screening (SCS). The phase field simulations show that the nanodot can exhibit fruitful domain patterns and evolution paths as functions of temperature and screening factor and changing direction of these two variables. Four typical types of experimental processes have been simulated, including the cooling-down and heating-up processes under fixed SCS conditions, and the processes of increasing and decreasing SCS under fixed temperatures. During these processes, the nanodot exhibits up to 13 different kinds of domain patterns, among which some are either polar or toroidal and some are both polar and toroidal. We summarized the phase diagrams as functions of temperature and charge screening factor, and also analyzed the typical domain evolution paths.

Size dependent and distinguishing degenerated vortex states in ferroelectric nanodots under a controllable surface charge condition

Article

Mar 2016

Here we propose a method to detect the degenerated tetragonal vortex states (i.e., the toroidal axis is along x-, y- or z-axis) in ferroelectric nanodots by applying a controllable surface charge (CSC) condition. Electrodes are placed at two parallel surfaces of the nanodot to form a short circuit. Surface charges with a controllable density are then applied to another two parallel surfaces of the nanodot. Under this CSC condition, a characteristic short-circuit current vs. time (I-t) curve related with the evolution of domain structure in a nanodot can be detected. The evolution paths and the characteristic short-circuit I-t curves of the degenerated vortex states in ferroelectric nanodots have been systematically revealed by our phase field simulations with solving the time-dependent Ginzburg-Landau (TDGL) equations. It is found that the degenerated vortex states exhibit distinct evolution features under the CSC condition. In the stages of placing electrodes and increasing surface charges, one, two, and zero short-circuit I-t peak(s) are observed in the nanodots with <100>, <010> and <001> vortex states, respectively. Therefore, the unknown vortex states of a nanodot can be distinguished. We further investigate the effects of temperature and nanodot size on the characteristic I-t curves of the vortex states. The results show that the vortex states can be nondestructively distinguished by applying the CSC condition if the nanodot size is in-between a moderate range (i.e., 8nm-12nm). Our study provides an alternative way of detecting the degenerated tetragonal vortex states in ferroelectric nanodots without the use of scanning probe microscope, and also sheds light on the application of ferroelectric vortex domain structure in novel devices such as memories, sensors and actuators.

Frontiers in Electronic Materials: A Collection of Extended Abstracts of the Nature Conference Frontiers in Electronic Materials, June 17 to 20 2012, Aachen, Germany

Chapter

Apr 2013

High Speed scanning probe microscopy (SPM) imaging is employed here,in which the local device state is simultaneously detected and manipulated in situ by biasing through a conducting atomic force microscopy (AFM) tip. This chapter shows that sufficient ionic compensation of bare (unelectroded) ferroelectric (FE) surfaces can occur such that ultrathin films remain polar.The interest in ultra-short period PbTiO3/SrTiO3 (PTO/STO) superlattices has been fueled during the last years, mostly due to the appearance of an improper FE polarization from the coupling of two rotational antiferrodistortive (AFD) modes of the oxygen octahedra cages. The chapter demonstrates the ability to deterministically control a bulk property, namely the FE polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. FE thin films are attractive candidates for capacitors in random access memory (FeRAM) devices, in which a reversible spontaneous polarization is utilized to store information.Controlled Vocabulary Termsatomic force microscopy; ferroelectric materials; scanning probe microscopy

Origins of domain wall pinning in ferroelectric nanocapacitors

Article

Full-text available

May 2014

We have investigated domain wall pinning and its origins in ferroelectric nanocapacitors using piezoresponse force microscopy. Domain wall pinning of two different types was observed in the nanocapacitors. The first type of pinning originates from local point defects similar to previous reports. The second one originates from immobile local defects in the place of pristine domains. In both cases, pinning and de-pinning processes were observed without significant domain wall bowing. The results can be helpful to understand domain wall motion and improve the reliability of nanoscale ferroelectric memory devices.

Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr0.4Ti0.6)O3 nanotubes

Article

Sep 2012
CURR APPL PHYS

We report the effects of adsorbates on the Raman spectra of Pb(Zr0.4Ti0.6)O3 nanotubes (PZT-NTs). PZT-NTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. This background can be suppressed by adjusting the Raman excitation wavelength from 514.5 nm to 414.6 nm. It can also be removed by post-annealing the PZT-NTs at 500 °C, but it returns readily after re-exposure to air. X-ray photoelectron and Fourier transform infrared spectroscopies show that hydroxyl and carbonate groups are adsorbed onto the surfaces of the PZT-NTs during exposure to air. Moreover, dispersive Raman spectra reveal that the background is a tail of a very broad band from 1000 to 4000 cm−1, which corresponds to hydroxyl groups. These results suggest that the main contribution to the Raman background of the PZT-NTs is that of surface hydroxyl groups rather than carbonate groups.

Corona poling of highly (001)/(100)-oriented lead zirconate titanate thin films

Article

Full-text available

Jun 2008
THIN SOLID FILMS

Corona poling is an interesting non-contact poling process for ferroelectric materials which, has in the past, been extensively applied to ferroelectric polymers, but not to other types of ferroelectric materials. Here, it has been investigated as an alternative technique to the conventional direct-contact poling of ferroelectric thin films. Contact-poling and corona poling techniques were applied to highly (001)/(100) oriented lead zirconate titanate thin films of composition 52% Zr, 48% Ti (PZT52/48). Different poling voltages and durations were used to pole the samples, and the effects on the piezoelectric coefficients e(31,,f) and d(33,f) were explored. From the magnitudes of piezoelectric coefficients and suppression of e(33,f) relative to d(33,f), it was concluded that corona poling is a more suitable technique for poling PZT52/48 thin films than direct poling, since piezoelectric coefficients were higher and sample damage was less for corona poling when compared with contact-poling. (C) 2007 Elsevier B.V. All rights reserved.

Oxygen Plasma Effects on Sol-Gel-Derived Lead-Zirconate-Titanate Thin Films

Article

Full-text available

Feb 2000
APPL PHYS LETT

We studied effects of oxygen plasma treatment on the ferroelectric Pb(Zrx,Ti1−x)O3 (PZT) films prepared by a sol-gel method. Electrical characteristics of the films were found to be improved considerably by exposure to the O2 plasma, with enhanced remanent polarization and decreased leakage current densities. Chemical bonding analysis by means of x-ray photoelectron spectroscopy in the Pb 4f region indicated that the intensity from the perovskite PZT phase increased considerably after the O2 plasma treatment, giving rise to the improved performances of the PZT films. © 2000 American Institute of Physics.

Photochemical switching of ultrathin PbTiO3 films

Article

Full-text available

Mar 2008
APPL PHYS LETT

The ferroelectric domain ground state of PbTiO3 thin films on Nb:SrTiO3 substrates has been studied as a function of film thickness. High resolution linear Qx x-ray diffraction profiles were recorded in order to probe the presence of stripe domains, which were invariably observed for as-grown samples. After photochemical treatment, films thinner than 50 unit cells were switched to a monodomain state that could be reversed upon subsequent annealing. The stripe-domain state is linked to a Qx modulation of the Qz parameter in the reciprocal space, which disappears upon switching.

Effect of domain structure on thermal stability of nanoscale ferroelectric domains

Article

Full-text available

May 2002
APPL PHYS LETT

We performed piezoelectric force microscopy (PFM) measurements on arrays of poled nanosize domains in 150 nm thick 〈111〉 preferentially oriented Pb(Zr0.4Ti0.6)O3 films grown by chemical solution deposition. Each domain of arrays was characterized by dot, egg, and ring structures depending on the pulse width ranging from 1 to 5 ms. The PFM measurements were followed by heat treatments at successively higher temperatures of 100 °C, 130 °C, and 160 °C for 30 min with rapid cooling down to room temperature before each measurement. The retention loss phenomena of the bits were characterized by measuring the number and dimension change of the remaining data bits. It was concluded that the ring-structured bit arrays, which represent fully penetrating domains through the film thickness, were the most stable form in terms of retention loss characteristics. © 2002 American Institute of Physics.

Domain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy

Article

Full-text available

Jan 2005

The kinetics of sidewise domain growth in an inhomogeneous electric field has been investigated in stoichiometric LiNbO3 single crystals by measuring the lateral domain size as a function of the voltage pulse magnitude and duration using piezoresponse force microscopy. The domain size increases linearly with the voltage magnitude suggesting that the domain size is kinetically limited in a wide range of pulse magnitudes and durations. In spite of that, the written domains exhibit strong retention behavior. It is suggested that the switching behavior can be described by the universal scaling curve. Domain kinetics can be described as an activation process by calculating the field distribution using the charged sphere model under the assumption of an exponential field dependence of the wall velocity. The activation energy is found to be a function of the external field.

Nanoscale properties of thin twin walls and surface layers in piezoelectric WO3-x

Article

Full-text available

Feb 2010
APPL PHYS LETT

Reduced WO <sub>3</sub> single crystals have been investigated by conductive and piezoresponse force microscopy. The reduced crystals show a piezoelectric active surface layer with a noncentrosymmetric tetragonal structure which is different from the bulk of the crystal. The domain walls carry a high current while the bulk remains insulating. Twin-related interfaces are atomically thin, the upper bound being less than 10 nm. The reduced surface layer remained in the piezoelectric state even after several weeks, while the current in the twin boundaries was reduced by re-oxidization. This layer shows a significant piezoelectric activity with a piezoelectric coefficient of about 7.9 pm/V.

Effect of Oxygen Plasma Treatment on Hydrogen-Damaged Pt/Pb(ZrxTi1-x)O3/Pt Ferroelectric Thin-Film Capacitor

Article

May 1999

Electron cyclotron resonance (ECR) oxygen plasma treatment of the Pt/Pb(ZrxTi1-x)O3/Pt capacitor was attempted to reduce the property degradation due to hydrogen. It was found that oxygen plasma treatment using ECR modifies the surface of Pt electrodes. Surface modification deteriorates catalytic activity of Pt electrodes, thereby significantly improving ferroelectric properties such as remnant polarization and leakage current. It seems that highly reactive oxygen radicals in ECR plasma play an important role in deteriorating the catalytic activity of Pt electrodes.

Local potential and polarization screening on ferroelectric surfaces

Article

Mar 2001

Sergei V. Kalinin

Electrostatic force microscopy and scanning surface potential microscopy are applied to study force gradient and surface potential on BaTiO3(100) surface. Surface potential evolution during a ferroelectric/paraelectric phase transition and the potential distribution near moving domain walls allow the relationship between potential polarity and polarization orientation. Results indicate that polarization bound charge is completely screened on this surface and domain potential is reverse to that expected from domain polarity. Surface potential is attributed to the formation of double layer due to the complete screening of polarization charge. The absolute value of the measured potential difference between domains of opposite polarity suggests that surface adsorbates play a governing role in potential formation mechanism, though intrinsic screening by free carriers is not completely excluded.

Domain growth dynamics in single-domain-like BiFeO3 thin films

Article

Mar 2009
APPL PHYS LETT

We present a quantitative study of 180° domain wall motion in epitaxial BiFeO3 (111) films, which can be treated as a nearly ideal single-domain environment. The domains were dynamically written by applying voltage pulses and examined by the piezoresponse force microscope technique. A transition of domain growth behaviors from the activated type to the nonactivated type was observed when increasing the pulse voltages. The obtained activation field was close to the ideally thermodynamic switching field of BiFeO3. The asymmetry of activated fields showed the preference of the downward polarization in the BiFeO3/SrRuO3 films.

Enhanced Functional and Structural Characteristics of Poly(vinylidene-trifluoroethylene) Copolymer Thin Films by Corona Poling

Article

Jan 2007

Electrical poling is of much interest for the enhancement of polarization properties of ferroelectric materials such as polyvinylidene-trifluoroethylene PVDF-TrFE in applications ranging from memory devices to piezoelectric actuation. Here, we report the changes in dielectric and optical properties correlated with structural modification of PVDF-TrFE thin films less than 1 um thickness subjected to corona poling at low voltages 6 kV under various thermal conditions. Enhanced crystallinity of hot-poled samples was observed independent of thermal history and crystalline structure, indicating the absence of recrystallization during poling. Absorption measurements confirmed the ordered structure in hot-poled samples due to the permanent orientation of the dipoles and higher crystallinity, thus resulting in increased and long-retained capacitance of the ferroelectric PVDF-TrFE capacitor device from high frequency C-V characterization. X-ray photoelectron spectroscopy further confirmed the shifting of C and F core orbitals to higher binding energy is related to formation of more ferroelectric phases by corona poling.

Reversible plasma switching in epitaxial BiFeO3 thin films

Abstract and Figures

Recommended publications

Visualization and manipulation of meta-stable polarization variants in multiferroic materials

Room temperature magnetic-field manipulation of electrical polarization in multiferroic thin film co...

Large-scale multiferroic complex oxide epitaxy with magnetically switched polarization enabled by so...

Solution Processed Large-scale Multiferroic Complex Oxide Epitaxy with Magnetically Switched Polariz...