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1 Aug 2011

Volume 99, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 99, 051112 (2011); http://dx.doi.org/10.1063/1.3617421 (3 pages)

Wei Li, Jun Chen, Gerard Nouet, Liang-yao Chen, and Xunya Jiang
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Effects of ferroelectric dead layer on the electron transport in ferroelectric tunneling junctions

Ping Sun, Yin-Zhong Wu, Tian-Yi Cai, and Sheng Ju

Appl. Phys. Lett. 99, 052901 (2011); http://dx.doi.org/10.1063/1.3619841 (3 pages) | Cited 3 times

Online Publication Date: 1 August 2011

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Ferroelectric dead layer is intrinsic and inevitable at the metal-ferroelectrics interface. In general, it is detrimental to the application of nanoscale devices; however, in ferroelectric tunneling junctions with ferroelectric dead layer, an enhanced tunneling electroresistance (TER) can be achieved when the nonswitchable interface polarization at both metal-ferroelectrics interfaces points to the ferroelectric center. The larger the interface polarization, the stronger the TER. In addition, low dielectric constant of dead layer will favor such enhancement. Our results provide an alternative route for achieving larger TER in ferroelectric junctions.
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73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
77.80.-e Ferroelectricity and antiferroelectricity

Elastic relaxation and correlation of local strain gradients with ferroelectric domains in (001) BiFeO3 nanostructures

Jeffrey A. Klug, Martin V. Holt, Ramesh Nath Premnath, Alexandra Joshi-Imre, Seungbum Hong, Ram S. Katiyar, Michael J. Bedzyk, and Orlando Auciello

Appl. Phys. Lett. 99, 052902 (2011); http://dx.doi.org/10.1063/1.3605594 (3 pages)

Online Publication Date: 1 August 2011

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We report an elastic relaxation and increase in local strain variation correlated with ferroelectric domains within epitaxial BiFeO3 thin film nanostructures fabricated by combined electron-beam and focused ion-beam nanolithography. Nano-focused x-ray diffraction microscopy provided new insights into the relationship between film strain and ferroelectric domains in nanostructures, namely: (i) an out-of-plane (C-axis) elastic relaxation of as much as −1.8% Δc/c in a BFO film-based nanostructure relative to the planar film lattice constant; (ii) an out-of-plane rotation trending from the center towards all released edges of the nanostructure; and (iii) an increase of inter-domain strain variation within the nanostructure of approximately 10 times the inter-domain variation found within the planar film, correlated with ferroelectric domain boundaries as confirmed by piezoresponse-force microscopy. These results indicate that the release of in-plane BFO/SRO mismatch strain in a planar film is taken up by the local ferroelectric domain structure after patterning, resulting in greatly increased mechanical strain gradients within the structure.
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77.80.Dj Domain structure; hysteresis
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
68.55.-a Thin film structure and morphology
81.16.Ta Atom manipulation

Phase-field simulation of domain structures in epitaxial BiFeO3 films on vicinal substrates

B. Winchester, P. Wu, and L. Q. Chen

Appl. Phys. Lett. 99, 052903 (2011); http://dx.doi.org/10.1063/1.3605674 (3 pages) | Cited 3 times

Online Publication Date: 1 August 2011

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The ferroelectric domain structures of epitaxial BiFeO3 thin films on miscut substrates were studied using a phase-field model. The effects of substrate vicinality towards (100) are considered by assuming charge-compensated surface and film/substrate interface. The predicted domain structures show remarkable agreement with existing experimental observations, including domain wall orientations and local topological domain configurations. The roles of elastic, electric, and gradient energies on the domain structures were analyzed. It is shown that the substrate strain anisotropy due to the miscut largely determines the domain variant selection and domain configurations.
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77.55.fp Other ferroelectric films
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.Dj Domain structure; hysteresis

Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O3 thin films using second harmonic piezoresponse force microscopy

Nishit M. Murari, Seungbum Hong, Ho Nyung Lee, and Ram. S. Katiyar

Appl. Phys. Lett. 99, 052904 (2011); http://dx.doi.org/10.1063/1.3619839 (3 pages) | Cited 3 times

Online Publication Date: 2 August 2011

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Here, we present a direct observation of fatigue phenomena in epitaxially grown Pb(Zr0.2Ti0.8)O3 (PZT) thin films using second harmonic piezoresponse force microscopy (SH-PFM). We observed strong correlation between the SH-PFM amplitude and phase signals with the remnant piezoresponse at different switching cycles. The SH-PFM results indicate that the average fraction of switchable domains decreases globally and the phase delays of polarization switching differ locally. In addition, we found that the fatigue developed uniformly over the whole area without developing region-by-region suppression of switchable polarization as in polycrystalline PZT thin films.
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77.84.Cg PZT ceramics and other titanates
77.55.Px Epitaxial and superlattice films
77.55.fg Pb(Zr,Ti)O3-based films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena

Inhibition of polydomain formation in PbTiO3/PbZr0.2Ti0.8O3 superlattices by intercalation of ultra-thin SrTiO3 layers

C. Hubault, C. Davoisne, L. Dupont, A. Perrin, A. Boulle, J. Holc, M. Kosec, M. G. Karkut, and N. Lemée

Appl. Phys. Lett. 99, 052905 (2011); http://dx.doi.org/10.1063/1.3619843 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2011

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We used pulsed laser deposition to grow a series of PbTiO3/PbZr0.2Ti0.8O3 superlattices on SrTiO3 and SrRuO3/SrTiO3 substrates. An a/c polydomain structure was evidenced by reciprocal space mapping and by transmission electron microscopy. Insertion of ultra-thin layers of SrTiO3 at the interfaces between PbTiO3 and PbZr0.2Ti0.8O3 layers has inhibited this polydomain formation. A strong decrease in the tetragonality indicates clearly that the polarization state in these superlattices has changed due to the insertion of the SrTiO3 layers. A purely elastic mechanism does not seem to explain the determined structural parameters.
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77.55.Px Epitaxial and superlattice films
68.65.Cd Superlattices
81.15.Fg Pulsed laser ablation deposition
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Effective reduction of fixed charge densities in germanium based metal-oxide-semiconductor devices

Shaoren Deng, Qi Xie, Davy Deduytsche, Marc Schaekers, Dennis Lin, Matty Caymax, Annelies Delabie, Sven Van den Berghe, Xinping Qu, and Christophe Detavernier

Appl. Phys. Lett. 99, 052906 (2011); http://dx.doi.org/10.1063/1.3622649 (3 pages) | Cited 3 times

Online Publication Date: 3 August 2011

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Metal-oxide-semiconductor capacitor was fabricated using in situ O2 plasma passivation and subsequent deposition of a HfO2 high-k gate stack on Ge. By extracting flat band voltages from capacitors with different equivalent oxide thicknesses (EOT), the effect of forming gas annealing (FGA) and O2 ambient annealing on the fixed charge was systematically investigated. The O2 ambient annealing is more effective than FGA as it reduced fixed charge density to 8.3 × 1011 cm−2 compared to 4.5 × 1012 cm−2 for at the same thermal budget and showed no degradation of EOT. Further, the distribution of fixed charges in gate stack was discussed in detail.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Tunable temperature dependence of electrocaloric effect in ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene terpolymer

Xinyu Li, Xiao-shi Qian, S. G. Lu, Jiping Cheng, Zhao Fang, and Q. M. Zhang

Appl. Phys. Lett. 99, 052907 (2011); http://dx.doi.org/10.1063/1.3624533 (3 pages) | Cited 18 times

Online Publication Date: 3 August 2011

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The electrocaloric effect (ECE) was directly measured in a relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer. It was observed that the temperature dependence of ECE of the terpolymer films depends critically on the film preparation conditions. While the uniaxially stretched terpolymer films show pronounced temperature dependence of ECE, the non-stretched films exhibit nearly temperature independent ECE from 5 °C to 45 °C. Such a difference is likely caused by the changes in possible polar states and polar-correlation range by film stretching. Besides, large ECE (T > 15 °C) can be induced in both films at 30 °C and 150 MV/m.
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77.84.Jd Polymers; organic compounds
77.80.Jk Relaxor ferroelectrics
77.55.Kt Pyroelectric films
73.61.Ph Polymers; organic compounds
77.70.+a Pyroelectric and electrocaloric effects

Ferroelectric phase transition in polycrystalline KTaO3 thin film revealed by terahertz spectroscopy

V. Skoromets, S. Glinšek, V. Bovtun, M. Kempa, J. Petzelt, S. Kamba, B. Malič, M. Kosec, and P. Kužel

Appl. Phys. Lett. 99, 052908 (2011); http://dx.doi.org/10.1063/1.3624710 (3 pages) | Cited 4 times

Online Publication Date: 4 August 2011

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KTaO3 single crystal is an archetypal incipient ferroelectric in which a long-range ferroelectric order does not establish at low temperatures owing to quantum fluctuations. We report on a strong evidence of the ferroelectric phase transition near 60 K revealed by terahertz spectroscopy and microwave permittivity measurements of a polycrystalline KTaO3 thin film on (0001) sapphire substrate prepared by chemical solution deposition. The soft mode behavior is clearly observed in the terahertz (THz) spectra with a minimum frequency at 60 K. At the same temperature microwave permittivity maximum appears. The THz spectra strongly resemble that of strained epitaxial SrTiO3/DyScO3 films: the ferroelectric soft mode is linearly coupled to a central peak which is silent in the paraelectric phase and it becomes coupled to the polarization below the ferroelectric transition temperature with a progressively increasing bare strength.
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77.84.Ek Niobates and tantalates
77.55.fj Niobate- and tantalate-based films
72.30.+q High-frequency effects; plasma effects
77.22.Ej Polarization and depolarization
78.70.Gq Microwave and radio-frequency interactions
77.80.B- Phase transitions and Curie point
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