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12 Nov 2007

Volume 91, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 91, 203501 (2007); http://dx.doi.org/10.1063/1.2806922 (3 pages)

Michael N. Feiginov and Dibakar Roy Chowdhury
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Layer-by-layer and pseudo-two-dimensional growth modes for heteroepitaxial BaTiO3 films by exploiting kinetic limitations

Junsoo Shin, S. V. Kalinin, A. Y. Borisevich, E. W. Plummer, and A. P. Baddorf

Appl. Phys. Lett. 91, 202901 (2007); http://dx.doi.org/10.1063/1.2790477 (3 pages) | Cited 14 times

Online Publication Date: 13 November 2007

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Pulsed laser deposition has enabled formation of highly oxidized and strained BaTiO3 films on SrTiO3 substrates in a layer-by-layer growth mode to thicknesses of 125 nm. Balancing thermodynamics and diffusion lengths enables controlled growth at the higher oxygen pressures required. Growth above 800 °C produces an array of uniform pseudo-two-dimensional islands on single-step terraces which are independent of film thickness and correlated with threading dislocations. Control over growth modes is enabled by the manipulation of diffusion lengths and produces films with morphologies with broad applicability for fabrication of high-quality oxide films and self-assembled nanostructures.
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68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
66.30.Lw Diffusion of other defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.16.Dn Self-assembly

Studies on forming gas annealing treated BiFeO3 thin films and capacitors

Chia-Ching Lee, Lin-Jung Wu, and Jenn-Ming Wu

Appl. Phys. Lett. 91, 202902 (2007); http://dx.doi.org/10.1063/1.2806191 (3 pages) | Cited 7 times

Online Publication Date: 13 November 2007

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The structure and electric properties of BiFeO3(BFO)/BaPbO3(BPO) and Pt/BFO/BPO capacitors with forming gas annealing (FGA) treatment were investigated. X-ray diffraction patterns indicated that the annealing did not affect the structure and phase of BFO films. A degraded electric property was obtained in FGA-treated Pt/BFO/BPO films. It can be attributed to the formation of reduction and incomplete reduction of Bi+3 of BFO. Retention and fatigue properties were obtained in FGA-treated BPO/BFO/BPO capacitors. The normalized Pr loss was 22.8% after applying a voltage above 2Vc (coercive voltage) with 1011 cycles. The retention behavior within 30 000 s is governed by the logarithmic time dependence.
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61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Evidence for the existence of a metal-insulator-semiconductor junction at the electrode interfaces of CaCu3Ti4O12 thin film capacitors

Guochu Deng, Tomoaki Yamada, and Paul Muralt

Appl. Phys. Lett. 91, 202903 (2007); http://dx.doi.org/10.1063/1.2814043 (3 pages) | Cited 33 times

Online Publication Date: 14 November 2007

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P-type conductivity has been observed in CaCu3Ti4O12 (CCTO) ceramics and also in thin films deposited by pulsed laser deposition. I-V and C-V relationships of the CCTO thin films showed characteristics typical of a tunnel metal-insulator-semiconductor structure, evidencing its capacitance response as the origin of the high apparent dielectric constant observed in CCTO thin films. The very thin insulating layer on top of the film can be reduced in thickness by treatment in HCl acid, as shown by smaller threshold voltages in the I-V curves. The overall behavior is compatible with a conduction activation energy of ∼ 80 to 100 meV in the bulk of the film, and a diffusion potential at the interface of 500 to 800 meV. The acceptor concentration is of the order of 1019 cm−3.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
81.15.Fg Pulsed laser ablation deposition

Effect of interparticle distance and interfacial area on the properties of insulator-conductor composites

K. S. Deepa, M. T. Sebastian, and J. James

Appl. Phys. Lett. 91, 202904 (2007); http://dx.doi.org/10.1063/1.2807271 (3 pages) | Cited 22 times

Online Publication Date: 15 November 2007

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The influence of conducting phase characteristics on dielectric properties of insulator-conductor composites was demonstrated by studying composites of polytetrafluoroethylene and different volume fractions of La0.5Sr0.5CoO3−y (LSCO). LSCO was prepared as coarse grained powder by solid state reaction and as fine powder by citrate gel method. The composites with fine powder of LSCO showed a rapid increase in dielectric constant and conductivity at 30%, while the corresponding value for coarse powder was 50%. The percolative behavior was found when the interparticle distance reduced to ∼ 250 nm in both cases. The permittivity and conductivity of the composites were found to increase with the interfacial area.
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77.22.Ch Permittivity (dielectric function)
77.84.Lf Composite materials

Antiferroelectric hysteresis loops with two exchange constants using the two dimensional Ising model

I. B. Misirlioglu, L. Pintilie, K. Boldyreva, M. Alexe, and D. Hesse

Appl. Phys. Lett. 91, 202905 (2007); http://dx.doi.org/10.1063/1.2814059 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2007

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Monte-Carlo simulations are carried out to reproduce hysteresis loops of antiferroelectric single crystals using an Ising Hamiltonian in two dimensions where pseudospin interactions are defined by two constants. It is shown that with this approach, hysteresis loops can be obtained in very good qualitative agreement with the experiments. While our approach is similar to that of Milhazes et al. [Phys. Status Solidi B 242, 1141 (2005)] , we also demonstrate that the hysteresis loop shapes heavily depend on the ratio of the electrostaticlike term to the intrinsic Hamiltonian of the system.
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77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point

Nanosecond-range measurements of imprint effect for Pt/IrO2/Pb(Zr0.4Ti0.6)O3/IrO2/Pt thin-film capacitors

A. Q. Jiang, Y. Y. Lin, and T. A. Tang

Appl. Phys. Lett. 91, 202906 (2007); http://dx.doi.org/10.1063/1.2815643 (3 pages) | Cited 13 times

Online Publication Date: 15 November 2007

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The determination of the coercive voltage from the height of domain-switching current plateau in ferroelectric thin films provides the liability to estimate the coercive-voltage shift with imprint time shortly on the order of polarization-reversal time. The voltage shift exhibits a linear time dependence in a logarithmic scale above an initial time ( ∼ 1 μs), below which the voltage is nearly constant. The modeling of imprint on the basis of the interfacial charge injection at different stressing voltages strongly supports Schottky emission as a dominant mechanism, instead of Frenkel-Poole emission and Fowler-Nordheim tunneling.
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77.55.-g Dielectric thin films
84.32.Tt Capacitors
77.80.Fm Switching phenomena

An approach to further improve piezoelectric properties of (K0.5Na0.5)NbO3-based lead-free ceramics

Hongliang Du, Wancheng Zhou, Fa Luo, Dongmei Zhu, Shaobo Qu, and Zhibin Pei

Appl. Phys. Lett. 91, 202907 (2007); http://dx.doi.org/10.1063/1.2815750 (3 pages) | Cited 41 times

Online Publication Date: 15 November 2007

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An approach to further improve piezoelectric properties of (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (KNLN) ceramics, i.e., the optimum poling temperatures (Tp) of KNLN ceramics should be chosen near the polymorphic phase transition temperatures, is proposed. This is contrary to conventional wisdom associated with electrical poling of ceramics. Piezoelectric constant d33 of KNLN (x = 0.07) ceramics increases from 210 to 274 pC/N by selecting optimum Tp. This result indicates that this approach is very effective in improving piezoelectric properties of KNLN ceramics. Moreover, this approach can also be applied to other (K0.5Na0.5)NbO3 based ceramics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point

Morphotropic phase boundary and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3–KNbO3 lead-free piezoelectric ceramics

Guifen Fan, Wenzhong Lu, Xiaohong Wang, and Fei Liang

Appl. Phys. Lett. 91, 202908 (2007); http://dx.doi.org/10.1063/1.2815918 (3 pages) | Cited 31 times

Online Publication Date: 15 November 2007

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The crystal structure and piezoelectric properties of ternary ceramics x(Bi1/2Na1/2)TiO3–y(Bi1/2K1/2)TiO3–zKNbO3 (abbreviated as BNT-BKT-KN100x/100y/100z) system have been investigated. Effects of BKT and KN on the crystalline structure were examined. The morphotropic phase boundary (MPB) phase diagram of BNT-BKT-KN ternary system was determined by x-ray diffraction patterns from sintered specimens. Near the MPB, BNT-BKT-KN82/16/2 ceramics had good performances with piezoelectric constant d33 = 215 pC/N which reached a maximum value in this ternary system and planar electromechanical coupling factor kp = 35%. Besides, BNT-BKT-KN87/10/3 ceramics had good performances with piezoelectric constant d33 = 138 pC/N and electromechanical coupling factor kp = 38% which attained a maximum value in this ternary system.
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77.65.Bn Piezoelectric and electrostrictive constants
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
81.30.Dz Phase diagrams of other materials

Structural and compositional investigation of yttrium-doped HfO2 films epitaxially grown on Si (111)

Z. K. Yang, W. C. Lee, Y. J. Lee, P. Chang, M. L. Huang, M. Hong, K. L. Yu, M.-T. Tang, B.-H. Lin, C.-H. Hsu, and J. Kwo

Appl. Phys. Lett. 91, 202909 (2007); http://dx.doi.org/10.1063/1.2816121 (3 pages) | Cited 9 times

Online Publication Date: 16 November 2007

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Cubic phase yttrium-doped HfO2 (YDH) ultrathin films were grown on Si (111) substrates by molecular beam epitaxy. Thorough structural and morphological investigations by x-ray scattering and transmission electron microscopy reveal that the YDH thin films are epitaxially grown on the Si substrates with (111)YDH‖(111)Si and [10math]YDH‖[1math0]Si. The interface between YDH and Si is atomistic sharp and free of interfacial layer. We have also determined the yttrium content of YDH films to be 19% by using anomalous x-ray diffraction (AXD) across Y k edge and angle resolved x-ray photoelectron spectroscopy (AR-XPS). The agreement between the AXD and AR-XPS results manifests that the incorporated Y atoms homogeneously substitute Hf atoms in the crystalline lattice and form a substitutional solid solution.
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77.55.-g Dielectric thin films
79.60.Dp Adsorbed layers and thin films
78.70.Ck X-ray scattering

Spin-filtering multiferroic-semiconductor heterojunctions

Na Sai, Jaekwang Lee, Craig J. Fennie, and Alexander A. Demkov

Appl. Phys. Lett. 91, 202910 (2007); http://dx.doi.org/10.1063/1.2814961 (3 pages) | Cited 4 times

Online Publication Date: 16 November 2007

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We report on the structural and electronic properties of the interface between the multiferroic oxide YMnO3 and semiconductor GaN studied with the Hubbard-corrected local-spin-density approximation to density-functional theory. We find that the band offsets at the interface between antiferromagnetically ordered YMnO3 and GaN are different for spin-up and spin-down states. This behavior is due to the spin splitting of the valence band induced by the interface. The energy barrier depends on the relative orientation of the electric polarization with respect to the polarization direction of the GaN substrate suggesting an opportunity to create magnetic tunnel junctions in this material system.
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75.50.Ee Antiferromagnetics
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.80.-e Ferroelectricity and antiferroelectricity
73.20.At Surface states, band structure, electron density of states
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