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10 Jul 2006

Volume 89, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 023901 (2006); http://dx.doi.org/10.1063/1.2219984 (3 pages)

Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham
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Investigation of field emission properties of carbon nanotube arrays defined using nanoimprint lithography

Sara M. C. Vieira, Kenneth B. K. Teo, William I. Milne, Oliver Gröning, Laurent Gangloff, Eric Minoux, and Pierre Legagneux

Appl. Phys. Lett. 89, 022111 (2006); http://dx.doi.org/10.1063/1.2219124 (3 pages) | Cited 21 times

Online Publication Date: 12 July 2006

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We demonstrate the use of nanoimprint lithography as an alternative low-cost fabrication route for the production of ordered arrays of individual carbon nanotube field emitters. A high emission site density of 4×105 cm−2 was observed and is well within the specification of the cathode for a field emission display. The measured field enhancement values from the geometry of the nanotubes were in reasonable agreement with the values obtained through electrical measurements. We also show that the distribution of the field enhancement factor is Gaussian, indicative of the presence of well ordered arrays of carbon nanotube field emitters.
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85.35.Kt Nanotube devices
85.45.Db Field emitters and arrays, cold electron emitters
85.45.Fd Field emission displays (FEDs)
85.40.Hp Lithography, masks and pattern transfer

Nonvolatile memory cell effect in multilayered Ni1−xFex self-assembled nanoparticle arrays in polyimide

Jae Hun Jung, Jae Ho Kim, Tae Whan Kim, Chong Seung Yoon, Young-Ho Kim, and Sungho Jin

Appl. Phys. Lett. 89, 022112 (2006); http://dx.doi.org/10.1063/1.2220548 (3 pages) | Cited 21 times

Online Publication Date: 12 July 2006

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Transmission electron microscopy images showed that self-assembled Ni1−xFex nanoparticle arrays were periodically inserted in the polyimide (PI) layers. Capacitance-voltage (C-V) measurements on Al/PI/multiple-stacked Ni1−xFex nanoparticle arrays/PI/p-Si (100) structures at 300 K showed a metal-insulator-semiconductor capacitor behavior with different flatband voltage shifts, which depended on the value of the sweep voltage, due to the variations of the charged electron density in the multiple-stacked Ni1−xFex nanoparticle arrays. Conductance-voltage (G-V) measurements showed that the conductance peak related to the interface trap disappeared, and that the positions of the C-V and the G-V hystereses at the sweep voltage were different.
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73.63.Bd Nanocrystalline materials
84.30.Sk Pulse and digital circuits
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Lp Transmission electron microscopy (TEM)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors

Semiconducting phase of amorphous carbon-nickel composite films

Somnath Bhattacharyya, S. J. Henley, D. Lock, N. P. Blanchard, and S. R. P. Silva

Appl. Phys. Lett. 89, 022113 (2006); http://dx.doi.org/10.1063/1.2216030 (3 pages) | Cited 8 times

Online Publication Date: 12 July 2006

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Amorphous carbon-nickel composite films, which constitute a homogeneously mixed phase of carbon and 10% nickel, are prepared by UV pulsed laser ablation. From the low temperature conductivity study of these films, a nearly activated conduction followed by conductivity saturation below a temperature of 25 K has been identified. This is very different from undoped diamond-like carbon (DLC) films. The presence of additional density of states at the Fermi level observed in these samples when compared with DLC films, is directly confirmed using valence band spectroscopy.
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73.61.Jc Amorphous semiconductors; glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Investigation of multilayer electronic vertically coupled InAs/GaAs quantum dot structures using surface photovoltage spectroscopy

C. H. Chan, H. S. Chen, C. W. Kao, H. P. Hsu, Y. S. Huang, and J. S. Wang

Appl. Phys. Lett. 89, 022114 (2006); http://dx.doi.org/10.1063/1.2221402 (3 pages) | Cited 9 times

Online Publication Date: 12 July 2006

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Using room-temperature surface photovoltage spectroscopy, we have characterized several 30-layer stacked self-assembled InAs/GaAs quantum dot (QD) structures with different spacer layer (SL) thicknesses. Signals from every relevant portion of the samples, including QDs, wetting layer, and GaAs barrier have been observed. The strain-induced field for thinner SL is responsible for a significant modification of the band structure, possibly resulting in the appearance of an additional excited state lying higher than the second excited QD state. A peculiar feature below the fundamental transition is tentatively attributed to the optical absorption from uncoupled dots of which the density is significantly lower than that of vertically coupled ones. The spectra show blueshifted features with a decrease of the SL thickness, indicating that the materials intermixing between InAs QDs and GaAs SL are strongly driven by strain.
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81.07.Ta Quantum dots
73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots
73.50.Pz Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena

Electrical transport through individual nanowires with transverse grain boundaries

X. Y. Xue, P. Feng, C. Wang, Y. J. Chen, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 89, 022115 (2006); http://dx.doi.org/10.1063/1.2221408 (3 pages) | Cited 3 times

Online Publication Date: 12 July 2006

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V2O4∙0.25H2O nanowires are synthesized via hydrothermal route. The nanowires are of metastable phase, and transverse grain boundaries are observed in their microstructures. Transport through individual V2O4∙0.25H2O nanowires shows nonlinear current-voltage (I-V) characteristics in the bias range of −3 to 3 V. The resistance rapidly decreases from 2.54 to 0.5 MΩ as the bias is raised from 0 to 1 V. Such behaviors can be attributed to the presence of the barrier at the transverse grain boundary. By analyzing the I-V curves at various temperatures, the effective barrier height is estimated to be about 0.13 eV. Our results provide important information about how the microstructure mismatch affects the electrical properties.
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81.07.Vb Quantum wires
81.16.-c Methods of micro- and nanofabrication and processing
73.63.Nm Quantum wires
61.72.Mm Grain and twin boundaries
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)

Magnetoresistance in silicon-based semiconductor-metal hybrid structures

A. S. Troup, D. G. Hasko, J. Wunderlich, and D. A. Williams

Appl. Phys. Lett. 89, 022116 (2006); http://dx.doi.org/10.1063/1.2221409 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2006

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Recent experimental and theoretical studies have shown that nonmagnetic semiconductor-metal hybrid (SMH) structures can exhibit a very large geometrical magnetoresistance response. We report the realization of silicon-based SMH structures where the metal is replaced by metallic silicide, and we identify key process and material requirements. The devices exhibit larger magnetoresistance responses than homogeneous silicon systems, and a finite element model correctly predicts these responses. In particular, it is experimentally verified that the response is further increased by alternating the current leads/voltage probes. Such scalable systems may be used to study the geometrical magnetoresistance in generic SMH structures as carrier transport moves from the diffusive to the ballistic regime.
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73.40.Ns Metal-nonmetal contacts
72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Cg Contact resistance, contact potential
73.23.Ad Ballistic transport

Effect of three-dimensional current and temperature distributions on void formation and propagation in flip-chip solder joints during electromigration

S. W. Liang, Y. W. Chang, T. L. Shao, Chih Chen, and K. N. Tu

Appl. Phys. Lett. 89, 022117 (2006); http://dx.doi.org/10.1063/1.2220550 (3 pages) | Cited 14 times

Online Publication Date: 13 July 2006

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Effect of three-dimensional current distribution on void formation in flip-chip solder joints during electromigration was investigated using thermoelectrical coupled modeling, in which the current and temperature redistributions were coupled and simulated at different stages of void growth. Simulation results show that a thin underbump metallization of low resistance in the periphery of the solder joint can serve as a conducting path, leading to void propagation in the periphery of the low current density region. In addition, the temperature of the solder did not rise significantly until 95% of the contact opening was eclipsed by the propagating void.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration

Impedance of nanometer sized silicon structures

G. Conte, M. C. Feliciangeli, and M. C. Rossi

Appl. Phys. Lett. 89, 022118 (2006); http://dx.doi.org/10.1063/1.2221397 (3 pages) | Cited 1 time

Online Publication Date: 13 July 2006

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Laser treatment of amorphous silicon oxide films resulted in the formation of nanocrystalline silicon grains connected along the laser treated trace. The ac response has been analyzed at different temperatures in a wide frequency range. The real admittance probed along the laser trace showed decreasing values after an initial constant conductance when the frequency is increased; this trend is reminiscent of an inductive behavior. Therefore, the whole impedance figure addressed the probed material as a Debye-like single time constant homogeneous system with the full width at half maximum corresponding to the expected 1.14 decades with evidence of resistive losses only.
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73.63.Bd Nanocrystalline materials
81.05.Cy Elemental semiconductors

Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon

A. Klaver, V. Nádaždy, M. Zeman, and R. A. C. M. M. van Swaaij

Appl. Phys. Lett. 89, 022119 (2006); http://dx.doi.org/10.1063/1.2221876 (3 pages) | Cited 1 time

Online Publication Date: 14 July 2006

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We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the defect-state density increased. A similar trend is observed for a-Si:H which has been subjected to light soaking, but in that case the majority of defect states are created around midgap, whereas with electron-beam degradation more defect states are created near the valence-band tail.
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71.55.Cn Elemental semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
61.80.Fe Electron and positron radiation effects

Structural, optical, and magnetic properties of As-doped (Zn0.93Mn0.07)O thin films

Sejoon Lee, Deuk Young Kim, Yoon Shon, and Chong S. Yoon

Appl. Phys. Lett. 89, 022120 (2006); http://dx.doi.org/10.1063/1.2221901 (3 pages) | Cited 13 times

Online Publication Date: 14 July 2006

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The As-doped (Zn0.93Mn0.07)O thin film prepared by As+ ion implantation showed a clear peak of (A0,X) having acceptor binding energy of 181 meV. The sample showed high TC ferromagnetism persisting up to 285 K. The contribution of magnetization from Mn ion at 280 K was determined to be 0.13μB/Mn. The improved ferromagnetism is expected to be originated from hole-induced ferromagnetism and enhanced magnetic anisotropy because crystallographically improved sample showed p-type conductivity with hole concentration of 4.8×1018 cm−3 and hole mobility of 11.8 cm2 V−1 s−1. These results suggest that high TC ferromagnetism can be realized by codoping the acceptor dopant and improving the magnetic anisotropy.
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75.50.Pp Magnetic semiconductors
68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
78.55.Et II-VI semiconductors
73.61.Ga II-VI semiconductors
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High temperature ferromagnetism in Ni-doped In2O3 and indium-tin oxide

Germanas Peleckis, Xiaolin Wang, and Shi Xue Dou

Appl. Phys. Lett. 89, 022501 (2006); http://dx.doi.org/10.1063/1.2220529 (3 pages) | Cited 33 times

Online Publication Date: 10 July 2006

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Observation of high temperature ferromagnetism in Ni-doped In2O3 and indium-tin-oxide (ITO) samples prepared by a solid state synthesis route is reported. Both Ni-doped compounds showed a clear ferromagnetism above 300 K with the magnetic moments of 0.03–0.06μB/Ni and 0.1μB/Ni at 300 and 10 K, respectively. Ni-doped In2O3 samples showed a typical semiconducting behavior with a room temperature resistivity of ρ ∼ 2 Ω cm, while Ni-doped ITO samples were metallic with ρ ∼ 2×10−2 Ω cm. Analysis of different conduction mechanisms suggested that variable range hopping model explains our ρ-T data for the Ni-doped In2O3 sample the best.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.up Other materials
75.30.Cr Saturation moments and magnetic susceptibilities
72.20.Ee Mobility edges; hopping transport
72.80.Jc Other crystalline inorganic semiconductors

Interface electronic structure in MnAs on GaAs (001) studied by in situ photoemission spectroscopy

J. Okabayashi, K. Kanai, K. Kubo, S. Toyoda, M. Oshima, K. Ono, and J. Yoshino

Appl. Phys. Lett. 89, 022502 (2006); http://dx.doi.org/10.1063/1.2217256 (3 pages) | Cited 4 times

Online Publication Date: 10 July 2006

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We have investigated the relationship between surface morphology and electronic structure of MnAs on GaAs (001) depending on the MnAs layer thickness using in situ photoemission spectroscopy. For less than 4 ML (monolayer) growth of MnAs, metallic and ferromagnetic properties were not observed due to the island growth. Valence-band photoemission spectra revealed that the localized Mn 3d states for less than 4 ML growth gradually change to the itinerant characteristics with increasing MnAs layer thickness. Core-level photoemission spectra have revealed that the Ga atoms are not segregated onto the surface and an abrupt interface is identified.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Mn3Sn2: A promising material for magnetic refrigeration

T. Mazet, H. Ihou-Mouko, and B. Malaman

Appl. Phys. Lett. 89, 022503 (2006); http://dx.doi.org/10.1063/1.2220541 (3 pages) | Cited 17 times

Online Publication Date: 10 July 2006

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Mn3Sn2 presents two second-order magnetic transitions of ferromagnetic origin at TC1 ∼ 262 K and TC2 ∼ 227 K. Both transitions give peaks of similar magnitude (ΔSMmax ∼ 27 mJ cm−3 K−1 for ΔH = 5 T) in the temperature dependence of the magnetic entropy change yielding an anomalous magnetocaloric response approaching that of a two-component hybrid material. Its refrigerant capacity of ∼ 1.1 J cm−3 (ΔH = 5 T) for an optimal reversible cycle with cold and hot ends at ∼ 220 and ∼ 280 K is about half that of the best known magnetic refrigerants working around room temperature. However, Mn3Sn2 possess several advantages making it a promising candidate for magnetic refrigeration applications: (i) it has a large temperature span with a roughly constant ΔSM, (ii) it is not subjected to hysteresis losses, and (iii) it is made from low-cost and nontoxic elements.
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75.50.Dd Nonmetallic ferromagnetic materials
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Giant magnetoresistance in an all-oxide spacerless junction

M. P. Singh, B. Carvello, and L. Ranno

Appl. Phys. Lett. 89, 022504 (2006); http://dx.doi.org/10.1063/1.2219413 (3 pages) | Cited 10 times

Online Publication Date: 10 July 2006

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We report the fabrication of an oxide-specific type of magnetoresistive junction, which is a ferromagnetic bilayer. Both electrodes are high spin-polarization oxides: magnetite (Fe3O4) and manganite (La0.7Sr0.3MnO3). Negligible magnetic coupling between both ferromagnetic electrodes is realized, which allows us to obtain parallel and antiparallel magnetic configurations of the electrodes when sweeping the applied magnetic field. The structure exhibits negative giant magnetoresistance (GMR) at low temperatures. This negative MR shows that both electrodes stay spin polarized at the interface and have opposite spin polarizations, i.e., the Fe3O4 layer has a negative spin polarization at low temperature. Maximum GMR (−5%) is obtained at 55 K.
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75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Huge nonequilibrium magnetoresistance in hybrid superconducting spin valves

Francesco Giazotto, Fabio Taddei, Rosario Fazio, and Fabio Beltram

Appl. Phys. Lett. 89, 022505 (2006); http://dx.doi.org/10.1063/1.2220001 (3 pages) | Cited 4 times

Online Publication Date: 11 July 2006

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A hybrid ferromagnet-superconductor spin valve is proposed. Its operation relies on the interplay between nonequilibrium transport and proximity-induced exchange coupling in superconductors. Huge tunnel magnetoresistance values as large as ∼ 106% can be achieved in suitable ferromagnet-superconductor combinations under proper voltage biasing. The controllable spin-filter nature of the structure combined with its intrinsic simplicity makes this setup attractive for low-temperature spintronic applications where reduced power dissipation is an additional requirement.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.25.-j Superconducting devices

L10 FePt films deposited on pyramid-type Si substrate for perpendicular magnetic recording media

C. L. Zha, B. Ma, Z. Z. Zhang, T. R. Gao, F. X. Gan, and Q. Y. Jin

Appl. Phys. Lett. 89, 022506 (2006); http://dx.doi.org/10.1063/1.2221389 (3 pages) | Cited 7 times

Online Publication Date: 11 July 2006

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Tetragonal L10 FePt films are deposited on the pyramid-type Si substrates fabricated by chemical etching process from (100) Si wafers. The films are composed of different easy-axis orientation FePt grains, most of which with the easy axis along substrate normal, the others with the easy axis tilted from the normal direction. When the magnetic field is applied along the perpendicular direction, the easy-axis tilted grains reverse first, and then the magnetization reversal of the whole film is promoted. Small coercivity, suitable α, and high squareness are obtained. And the coercivity increases when the applied field is tilted from the normal direction.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
81.65.Cf Surface cleaning, etching, patterning

Improved oxygen diffusion model to explain the effect of low-temperature baking on high field losses in niobium superconducting cavities

Gianluigi Ciovati

Appl. Phys. Lett. 89, 022507 (2006); http://dx.doi.org/10.1063/1.2220059 (3 pages) | Cited 10 times

Online Publication Date: 13 July 2006

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Radio-frequency (rf) superconducting cavities made of high purity niobium are widely used to accelerate charged particle beams in particle accelerators. The major limitation to achieve rf field values approaching the theoretical limit for niobium is represented by “anomalous” losses which degrade the quality factor of the cavities starting at peak surface magnetic fields of about 100 mT, in the absence of field emission. These high field losses are often referred to as Q drop. It has been observed that the Q drop is drastically reduced by baking the cavities at 120 °C for about 48 h under ultrahigh vacuum. An improved oxygen diffusion model for the niobium-oxide system is proposed to explain the benefit of the low-temperature baking on the Q drop in niobium superconducting rf cavities. The model shows that baking at 120 °C for 48 h allows oxygen to diffuse away from the surface, and therefore increasing the lower critical field towards the value for pure niobium.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Op Mixed states, critical fields, and surface sheaths

Room temperature ferromagnetism in two-step-prepared Co-doped ZnO bulks

T. Zhu, W. S. Zhan, W. G. Wang, and John Q. Xiao

Appl. Phys. Lett. 89, 022508 (2006); http://dx.doi.org/10.1063/1.2221881 (3 pages) | Cited 20 times

Online Publication Date: 14 July 2006

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We have prepared Co-doped ZnO bulks with a two-step method. The bulk samples are sintered at the temperature above 1000 °C to get pure single phase and then treated by Zn vapor in a vacuum. Based on such two-step preparation, clear carrier induced ferromagnetism is found in Zn treated Co-doped ZnO bulks, which suggests that the magnetism mechanism can be of codoping effect. The onset of ferromagnetism is associated with the further increase of the hybridization of the impurity band with 3d states near the Fermi level when additional carrier induced to let the Stoner criterion for ferromagnetism to be satisfied.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
71.55.Gs II-VI semiconductors
71.20.Nr Semiconductor compounds

Growth of epitaxial thin films of the ordered double perovskite La2NiMnO6 on different substrates

H. Guo, J. Burgess, S. Street, A. Gupta, T. G. Calvarese, and M. A. Subramanian

Appl. Phys. Lett. 89, 022509 (2006); http://dx.doi.org/10.1063/1.2221894 (3 pages) | Cited 39 times

Online Publication Date: 14 July 2006

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Epitaxial thin films of La2NiMnO6, a ferromagnetic semiconductor, have been fabricated on different substrates by pulsed laser deposition. The x-ray diffraction and Raman scattering observations reveal that the films are single crystalline and have an orthorhombic structure. The magnetic properties of the films, including the coercive field, remanent magnetization, and Curie temperature, are strongly dependent on the choice of the substrate. The optimized films exhibit a magnetic moment of 4.63μB/f.u. at 5 K, with a Curie temperature close to 280 K. The film characteristics are promising for potential device applications in information storage, spintronics, and sensors.
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81.05.Hd Other semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.50.Pp Magnetic semiconductors

Low-frequency vortex dynamic susceptibility and relaxation in mesoscopic ferromagnetic dots

K. Yu. Guslienko

Appl. Phys. Lett. 89, 022510 (2006); http://dx.doi.org/10.1063/1.2221904 (3 pages) | Cited 31 times

Online Publication Date: 14 July 2006

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Vortex dynamics in a restricted geometry is considered for a magnetic system consisting of ferromagnetic cylindrical dots. To describe the vortex dynamic susceptibility and relaxation the equation of motion for the vortex center position is applied. The dependencies of the vortex dynamic susceptibility and resonance linewidth on geometrical parameters are calculated. A method of extracting damping parameter from the vortex low-frequency resonance peaks is proposed and applied for interpretation of resonance data on FeNi circular dots.
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75.50.Bb Fe and its alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Magnetic tunnel junctions based on CrO2/SnO2 epitaxial bilayers

G. X. Miao, P. LeClair, A. Gupta, G. Xiao, M. Varela, and S. Pennycook

Appl. Phys. Lett. 89, 022511 (2006); http://dx.doi.org/10.1063/1.2216109 (3 pages) | Cited 12 times

Online Publication Date: 14 July 2006

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Magnetic tunnel junctions were fabricated using thin films of the half-metallic ferromagnet CrO2, employing SnO2 tunnel barriers. Heteroepitaxial CrO2/SnO2 bilayers were grown on (100)-TiO2 substrates via chemical vapor deposition. X-ray diffraction and transmission electron microscopy confirmed heteroepitaxy. A polycrystalline cobalt film forms the top magnetic electrode, yielding CrO2(001)/SnO2(001)/Co structures after patterning. Tunneling magnetoresistances (TMR) up to +14% at 10 K were observed. The sign of the TMR reverses for barrier thicknesses <1 nm, attributed to tunneling being dominated by Co-3d states at low thicknesses and Co-4s states at larger thicknesses.
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75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Lp Transmission electron microscopy (TEM)
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Enhanced tunability of magnetron sputtered Ba0.5Sr0.5TiO3 thin films on c-plane sapphire substrates

E. A. Fardin, A. S. Holland, K. Ghorbani, and P. Reichart

Appl. Phys. Lett. 89, 022901 (2006); http://dx.doi.org/10.1063/1.2220530 (3 pages) | Cited 12 times

Online Publication Date: 10 July 2006

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Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1 to 20 GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200 kV/cm and total device Q of more than 15 (up to 20 GHz) were achieved following postdeposition annealing at 900 °C.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Misfit strain relaxation in (Ba0.60Sr0.40)TiO3 epitaxial thin films on orthorhombic NdGaO3 substrates

W. K. Simon, E. K. Akdogan, and A. Safari

Appl. Phys. Lett. 89, 022902 (2006); http://dx.doi.org/10.1063/1.2214216 (3 pages) | Cited 16 times

Online Publication Date: 10 July 2006

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Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on 〈110〉 orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010]BST∥[math10]NGO and [001]BST∥[001]NGO in-plane and [100]BST∥[100]NGO out-of-plane epitaxial relationship. The residual strains are relaxed at h ∼ 200 nm, and for h>600 nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15 nm, respectively. Stress analysis indicates deviation from linear elasticity for h<200. The films with 10<h<25 nm are of monoclinic symmetry due to a finite principal shear stress along [110] of the initial orthorhombic cell.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Dynamical slowing down of polar nanoregion in relaxor-based ferroelctric 0.89Pb(Zn2/3Nb1/3)O3–0.11PbTiO3

Yohei Nakata, Yuhji Tsujimi, Kohei Katsuraya, Makoto Iwata, and Toshirou Yagi

Appl. Phys. Lett. 89, 022903 (2006); http://dx.doi.org/10.1063/1.2221387 (3 pages) | Cited 9 times

Online Publication Date: 10 July 2006

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Light scattering experiment has been performed in a single crystal of 0.89Pb(Zn1/3Nb2/3)O3–0.11PbTiO3. The central peak (CP) spectra have been well detected with high resolution over the wide frequency region up to 150 GHz. The distribution is discovered in the relaxation time associated with the CP. Moreover, it is found that the maximum relaxation time indicates the dynamical slowing down near the temperature Tm at which the low-frequency dielectric constant has a maximum. This finding strongly suggests that the physical origin of the CP is “polar nanoregions.”
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)

In situ transmission electron microscopy study of the nanodomain growth in a Sc-doped lead magnesium niobate ceramic

W. Qu, X. Zhao, and X. Tan

Appl. Phys. Lett. 89, 022904 (2006); http://dx.doi.org/10.1063/1.2219416 (3 pages) | Cited 5 times

Online Publication Date: 10 July 2006

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Sc doping enhances the B-site 1:1 cation ordering in the Pb(Mg1/3Nb2/3)O3 ceramic. At low doping levels, the electrical polar domains remain at the nanometer scale and the relaxor ferroelectric behavior persists. The electric field-induced relaxor to normal ferroelectric phase transition process was directly observed with an in situ transmission electron microscopy technique in a Sc-doped Pb(Mg1/3Nb2/3)O3 polycrystalline sample. It was found that the phase transition started at the grain boundary and took two steps to complete: the gradual coalescence of the polar nanodomains and the abrupt formation of the large wedge-shaped ferroelectric domains.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
68.37.Lp Transmission electron microscopy (TEM)
77.80.Dj Domain structure; hysteresis
61.72.Mm Grain and twin boundaries
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