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18 Oct 2010

Volume 97, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 97, 162901 (2010); http://dx.doi.org/10.1063/1.3501139 (3 pages)

Wei-Feng Rao, Ke-Wei Xiao, Tian-Le Cheng, Jie E. Zhou, and Yu U. Wang
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Control of domain configurations and sizes in crystallographically engineered ferroelectric single crystals: Phase field modeling

Wei-Feng Rao, Ke-Wei Xiao, Tian-Le Cheng, Jie E. Zhou, and Yu U. Wang

Appl. Phys. Lett. 97, 162901 (2010); http://dx.doi.org/10.1063/1.3501139 (3 pages) | Cited 2 times

Online Publication Date: 18 October 2010

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Computer simulation is performed to study the mechanisms for controlling domain configurations and sizes in crystallographically engineered ferroelectric crystals. It is found that minimal domain sizes and highest domain wall densities are obtained with intermediate electric field applied along nonpolar axis of ferroelectric crystals, while lower and higher fields produce coarser domains, and temperature also plays important role in domain size control. The simulation shows that selection of polar domain variants by external electric field during nucleation stage of ferroelectric phase transition significantly affects subsequent domain growth and evolution kinetics, controlling the formation and sizes of lamellar domains.
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77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point

Path-related unexpected injection charges in BaTiO3 ferroelectric thin films studied by Kelvin force microscopy

Huifen Guo, Gang Cheng, Shujie Wang, Shuxi Dai, Sixin Wu, Shaomin Zhou, Yuncai Li, and Zuliang Du

Appl. Phys. Lett. 97, 162902 (2010); http://dx.doi.org/10.1063/1.3499749 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2010

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The collective effect of injection charges constructed in a dot array using scanning probe microscopy (SPM) in BaTiO3 ferroelectric thin films was investigated with Kelvin force microscopy (KFM). Unexpected charges were observed in the SPM tip paths where poling bias was zero. The analysis of the array with different poling biases shows that the collective effect of the injection charges in the dot array induced a potential difference between film and tip, which in turn injected unexpected charges. The calculated potential difference distribution along the tip’s paths correlates well with KFM images of the unexpected charges.
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77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
73.61.Ng Insulators
77.80.-e Ferroelectricity and antiferroelectricity

Suppression of substrate oxidation during ozone based atomic layer deposition of Al2O3: Effect of ozone flow rate

Jinhee Kwon, Min Dai, Mathew D. Halls, and Yves. J. Chabal

Appl. Phys. Lett. 97, 162903 (2010); http://dx.doi.org/10.1063/1.3500821 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2010

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We demonstrate that interfacial SiO2, usually formed during high-κ oxide growth on silicon using ozone (O3), is suppressed during Al2O3 atomic layer deposition (ALD) by decreasing the O3 flow rate. First-principles calculations indicate that oxygen introduced by the first low-dose O3 exposure is inserted into the surface nucleation layer rather than the Si lattice. Subsequent Al2O3 deposition further passivates the surface against substrate oxidation. Aluminum methoxy [–Al(OCH3)2] and surface Al–O–Al linkages formed after O3 pulses are suggested as the reaction sites for trimethylaluminum during ALD of Al2O3.
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81.65.Mq Oxidation
68.55.A- Nucleation and growth
81.65.Rv Passivation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Organic and inorganic relaxor ferroelectrics with giant electrocaloric effect

S. G. Lu, B. Rožič, Q. M. Zhang, Z. Kutnjak, Xinyu Li, E. Furman, Lee J. Gorny, Minren Lin, B. Malič, M. Kosec, R. Blinc, and R. Pirc

Appl. Phys. Lett. 97, 162904 (2010); http://dx.doi.org/10.1063/1.3501975 (3 pages) | Cited 17 times

Online Publication Date: 19 October 2010

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The electrocaloric effect (ECE) in inorganic thin film and organic relaxor ferroelectrics is investigated by directly measuring the ECE around room temperature. The results reveal that giant ECEs can be obtained in the high energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) relaxor copolymer and in the La-doped Pb(ZrTi)O3 relaxor ceramic thin films, which are much larger than that from the normal ferroelectric counterparts. The large ECE observed, compared with normal ferroelectrics, is likely caused by the large number of disordered fluctuating polarization entities in relaxor ferroelectrics which can lead to extra entropy contributions and larger ECE.
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77.80.Jk Relaxor ferroelectrics
77.84.Cg PZT ceramics and other titanates
77.70.+a Pyroelectric and electrocaloric effects
77.55.Kt Pyroelectric films

Structural and resistance switching properties of ZnO/SrTiO3/GaAs heterostructure grown by laser molecular beam epitaxy

W. Huang, J. Y. Dai, and J. H. Hao

Appl. Phys. Lett. 97, 162905 (2010); http://dx.doi.org/10.1063/1.3505136 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2010

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ZnO thin films were epitaxially grown on (001) GaAs substrate by laser molecular beam epitaxy with SrTiO3 (STO) as a buffer layer. The interface properties of ZnO/GaAs heterostructure are greatly improved by inserting STO buffer layer. The interfacial effects on the transport and dielectric characteristics of the heterostructure have been investigated. The current-voltage characteristic of the heterostructure reveals an asymmetric and resistance switching behavior, exhibiting a temperature-dependent resistance hysteresis in the temperature range of 50–300 K. These measured properties could be attributed to the charge effect at the interface of the heterostructure.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Impact of crystallization behavior of SrxTiyOz films on electrical properties of metal-insulator-metal capacitors with TiN electrodes

M. A. Pawlak, B. Kaczer, M.-S. Kim, M. Popovici, K. Tomida, J. Swerts, K. Opsomer, W. Polspoel, P. Favia, C. Vrancken, C. Demeurisse, W.-C. Wang, V. V. Afanas’ev, W. Vandervorst, H. Bender, et al.

Appl. Phys. Lett. 97, 162906 (2010); http://dx.doi.org/10.1063/1.3505323 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2010

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Metastable perovskite SrxTiyOz (STO) films were formed over a wide composition range by crystallization of layers grown by atomic layer deposition. An expansion of the lattice, decrease in permittivity and mild increase in band gap are observed with increasing Sr content. Sr-rich films [Sr/(Sr+Ti) ∼ 62 at. %] show significant improvement in leakage current at low equivalent oxide thicknesses (EOT) as compared to stoichiometric films (Sr/(Sr+Ti) ∼ 50 at. %). TiN/STO/TiN capacitors with leakage ∼ 10−6 A/cm2 at 1 V were obtained at 0.6 nm EOT for crystalline Sr-rich STO. The difference in leakage behavior was found to correlate with different microstructures developed during crystallization.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
64.70.K- Solid-solid transitions
68.55.aj Insulators
84.32.Tt Capacitors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

A first-principles scheme to phonons of high temperature phase: No imaginary modes for cubic SrTiO3

Yi Wang, James E. Saal, Zhigang Mei, Pingping Wu, Jianjun Wang, Shunli Shang, Zi-Kui Liu, and Long-Qing Chen

Appl. Phys. Lett. 97, 162907 (2010); http://dx.doi.org/10.1063/1.3505338 (3 pages)

Online Publication Date: 20 October 2010

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The issue of imaginary phonon modes predicted by first-principles calculations for high-temperature structures of most materials has been a longstanding problem for decades. We propose that the observed high-temperature structures are actually dynamic averages of related low-temperature structures. This theory is used to predict the phonon dispersions of cubic SrTiO3. The calculated phonon dispersions for the cubic phase, using the force constants calculated from the tetragonal phases, are found to be in remarkably good agreement with existing neutron data, without exhibiting any imaginary phonon modes.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

On electromechanical stability analysis of dielectric elastomer actuators

Bai-Xiang Xu, Ralf Mueller, Markus Klassen, and Dietmar Gross

Appl. Phys. Lett. 97, 162908 (2010); http://dx.doi.org/10.1063/1.3504702 (3 pages) | Cited 7 times

Online Publication Date: 21 October 2010

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Based on the total stress concept, explicit results of the equilibrium state and the critical electric field are obtained for dielectric elastomer actuators. Criticality is discussed in the frame of structure stability and electric breakdown. Specific results are given for four commonly used material models.
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07.07.Tw Servo and control equipment; robots
77.22.Jp Dielectric breakdown and space-charge effects
52.80.-s Electric discharges
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Microwave properties of epitaxial (111)-oriented Ba0.6Sr0.4TiO3 thin films on Al2O3(0001) up to 40 GHz

Lihui Yang, Freddy Ponchel, Genshui Wang, Denis Rémiens, Jean-Fançois Légier, Daniel Chateigner, and Xianlin Dong

Appl. Phys. Lett. 97, 162909 (2010); http://dx.doi.org/10.1063/1.3478015 (3 pages) | Cited 1 time

Online Publication Date: 21 October 2010

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Perovskite Ba0.6Sr0.4TiO3 (BST) thin films have been grown on Al2O3(0001) substrates without/with inserting an ultrathin TiOx seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiOx layer (12-Å-thick) is highly oriented along the (111) direction and exhibits a good in-plane relationship of BST(111)∥Al2O3(0001). The high frequency dielectric measurements demonstrate that the complex permittivity (ε = ε′−jε″) is well described by a Curie–von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity ( ∼ 428) and tunability ( ∼ 41%, at 300 kV/cm and 40 GHz) and their microwave properties (1–40 GHz) potentially could be made suitable for tunable devices.
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68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
77.22.Ch Permittivity (dielectric function)

Heteroepitaxy of single-crystal LaLuO3 on GaAs(111)A by atomic layer deposition

Yiqun Liu, Min Xu, Jaeyeong Heo, Peide D. Ye, and Roy G. Gordon

Appl. Phys. Lett. 97, 162910 (2010); http://dx.doi.org/10.1063/1.3504254 (3 pages) | Cited 4 times

Online Publication Date: 21 October 2010

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We demonstrate that LaLuO3 films can be grown epitaxially on sulfur-passivated GaAs(111)A substrates by atomic layer deposition (ALD). Transmission electron microscopy and x-ray diffraction analyses reveal that the oxide film exhibits a cubic structure with a lattice mismatch of −3.8% relative to GaAs. The epitaxial layer has a high degree of crystalline perfection and is relaxed. Electrical characterizations performed on this structure show interfaces with a low interface state density of ∼ 7×1011 cm−2 eV−1. The measured dielectric constant is around 30, which is close to its bulk crystalline value. In contrast, ALD LaLuO3 is polycrystalline on GaAs(100) and amorphous on Si(111).
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
68.55.aj Insulators

Ferroelectric property improvement of poly(vinylidene fluoride/trifluoroethylene) polymer exposed to a plasma ambient

C. H. Park, Kwang H. Lee, Taewoo Ha, Jae Hoon Kim, Seongil Im, Jungheum Yun, and Gun Hwan Lee

Appl. Phys. Lett. 97, 162911 (2010); http://dx.doi.org/10.1063/1.3505336 (3 pages)

Online Publication Date: 22 October 2010

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We report a dramatic property improvement of ferroelectric polymer poly(vinylidene fluoride/trifluoroethylene) [P(VDF-TrFE)] upon exposure to a plasma ambient. The P(VDF-TrFE) layer for typical nonvolatile memory devices shows only ∼ 6.5 μC/cm2 and 0.55 MV/cm for its remnant polarization and coercive field, respectively, but the values increase to ∼ 13 μC/cm2 and ∼ 1 MV/cm after an optimum period of plasma exposure. Our infrared measurement confirms that the plasma energy creates many C=C double bonds in the polymer chain while removing some of C–F bonds, which are responsible for ferroelectric polarization. Nevertheless, the strengthened polymer can incorporate higher applied field, thereby aligning electric dipoles much better.
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77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
78.30.Jw Organic compounds, polymers
85.50.Gk Non-volatile ferroelectric memories
77.84.Jd Polymers; organic compounds

Understanding structure-property relationship of resistive switching oxide thin films using a conical filament model

Kyung Min Kim, Min Hwan Lee, Gun Hwan Kim, Seul Ji Song, Jun Yeong Seok, Jung Ho Yoon, and Cheol Seong Hwang

Appl. Phys. Lett. 97, 162912 (2010); http://dx.doi.org/10.1063/1.3505354 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2010

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The relations between the reset current IR, room temperature filament resistance R0, and third harmonic coefficient B0 were evaluated by a conical filament model. It was found that IR ∼ 1/R0 when the filament is either very weak, where the filament is more conical, or quite strong, where the filament is more cylindrical. The physical implication of the B0 was also understood from the materials properties. The coherence between the model expectations for the bulkier conical filaments, typically found in TiO2, and the more random-network like filaments, typically found in NiO, suggests a common switching mechanism works in both materials.
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73.61.Le Other inorganic semiconductors
68.55.ag Semiconductors

Extrinsic effects on dielectric response of ultrafine grain BaTiO3 ceramics

Haitao Zhang, Xiangyun Deng, Ting Li, Wen Zhang, Rike Chen, Wenwei Tian, Jianbao Li, Xiaohui Wang, and Longtu Li

Appl. Phys. Lett. 97, 162913 (2010); http://dx.doi.org/10.1063/1.3505924 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2010

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The complex dielectric response of ultrafine grain barium titanate ceramics is investigated using broadband dielectric spectrometer. Extrinsic effects like conduction, space charge associating with grain boundaries are discussed. One dielectric relaxation ascribes to the interaction of defects with grain boundaries, for which the activation energy fitted by Arrhenius equation is equivalent to 0.26 eV and the value shifts to 0.41 eV after annealing treatment. Another relaxation phenomenon locating at elevated temperature can be attributed to interfacial polarization due to space charge accumulation effect. The study of complex impedance spectra suggests that grain boundary effects support extrinsic mechanism.
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77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
61.72.Mm Grain and twin boundaries
61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect

Anomaly in the conductivity relaxation parameters at the phase transition of ferroelectric materials: A time domain study

Y. Leyet, F. Guerrero, H. Amorín, J. de Los S. Guerra, and J. A. Eiras

Appl. Phys. Lett. 97, 162914 (2010); http://dx.doi.org/10.1063/1.3505932 (3 pages)

Online Publication Date: 22 October 2010

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The influence of the ferroelectric to paraelectric transition on the relaxation parameters of conductive processes in ferroelectric materials is studied in the time domain. Three well-known ferroelectric systems were chosen with transition temperatures in different regions, these are, high-temperature PbNb2O6-based ceramics; nanostructured Pb(Zr0.6Ti0.4)O3 ceramics; and submicron BaTiO3. The thermal evolution of relaxation parameters shows clear anomalies in their typical behavior when conductivity processes arise in the temperature range where the ferroelectric transition takes place. The method here described allows obtaining information about the correlation between charge transport and the motion of the off-center ions at the phase transition.
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77.80.B- Phase transitions and Curie point
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
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