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28 Jan 2008

Volume 92, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 041901 (2008); http://dx.doi.org/10.1063/1.2831926 (3 pages)

M. A. Avila, K. Suekuni, K. Umeo, H. Fukuoka, S. Yamanaka, and T. Takabatake
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Electrical properties of GaN (Fe) buffers for AlGaN/GaN high electron mobility transistor structures

A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, T. G. Yugova, A. V. Markov, A. M. Dabiran, A. M. Wowchak, B. Cui, J. Xie, A. V. Osinsky, P. P. Chow, and S. J. Pearton

Appl. Phys. Lett. 92, 042110 (2008); http://dx.doi.org/10.1063/1.2838734 (3 pages) | Cited 6 times

Online Publication Date: 30 January 2008

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The electrical properties of AlGaN/GaN high electron mobility transistor structures grown on composite GaN(Fe)/GaN buffers by molecular beam epitaxy were reported. The concentration of Fe in the GaN(Fe) layer ranged from 8×1016 to 3×1017 cm−3 as established by secondary ion mass spectrometry. The thickness of the undoped GaN layer of the buffer was varied from 2.2 to 4.1 μm. For thinner buffers and higher Fe concentration, the buffer was semi-insulating, with the Fermi level pinned near Ec-0.57 eV. For thicker buffers and lower Fe concentration, the top part of the buffer was conducting. Admittance spectra measured in conducting buffers also showed a prominent contribution from Ec-(055–0.6) eV electron traps. Despite the universal prominence of these traps in all our films, the behavior of their concentration with Fe doping and with increased distance from the GaN (Fe)/GaN boundary is not compatible with the assumption that they are due to substitutional Fe acceptors. Possible compensation mechanisms in the studied structures were discussed.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
85.40.Ry Impurity doping, diffusion and ion implantation technology

Electron concentration dependent magnetization and magnetic anisotropy in ZnO:Mn thin films

Z. Yang, J. L. Liu, M. Biasini, and W. P. Beyermann

Appl. Phys. Lett. 92, 042111 (2008); http://dx.doi.org/10.1063/1.2838753 (3 pages) | Cited 18 times

Online Publication Date: 30 January 2008

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Well-above room temperature and electron concentration dependent ferromagnetism was observed in n-type ZnO:Mn films, indicating long-range ferromagnetic order. Magnetic anisotropy was also observed in these ZnO:Mn films, which is another indication for intrinsic ferromagnetism. The electron-mediated ferromagnetism in n-type ZnO:Mn contradicts the existing theory that the magnetic exchange in ZnO:Mn materials is mediated by holes.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thermoelectric properties of InxGa1−xN alloys

B. N. Pantha, R. Dahal, J. Li, J. Y. Lin, H. X. Jiang, and G. Pomrenke

Appl. Phys. Lett. 92, 042112 (2008); http://dx.doi.org/10.1063/1.2839309 (3 pages) | Cited 41 times

Online Publication Date: 30 January 2008

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Thermoelectric (TE) properties of InxGa1−xN alloys grown by metal organic chemical vapor deposition have been investigated. It was found that as indium concentration increases, the thermal conductivity decreases and power factor increases, which leads to an increase in the TE figure of merit (ZT). The value of ZT was found to be 0.08 at 300 K and reached 0.23 at 450 K for In0.36Ga0.64N alloy, which is comparable to those of SiGe based alloys. The results indicate that InGaN alloys could be potentially important TE materials for many applications, especially for prolonged TE device operation at high temperatures, such as for recovery of waste heat from automobile, aircrafts, and power plants due to their superior physical properties, including the ability of operating at high temperature/high power conditions, high mechanical strength and stability, and radiation hardness.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.05.Ea III-V semiconductors

Monte Carlo investigation of terahertz plasma oscillations in ultrathin layers of n-type In0.53Ga0.47As

J.-F. Millithaler, L. Reggiani, J. Pousset, L. Varani, C. Palermo, W. Knap, J. Mateos, T. González, S. Perez, and D. Pardo

Appl. Phys. Lett. 92, 042113 (2008); http://dx.doi.org/10.1063/1.2837183 (3 pages) | Cited 9 times

Online Publication Date: 30 January 2008

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By numerical simulations we investigate the dispersion of the plasma frequency in a n-type In0.53Ga0.47As layer of thickness W and submicron length at T = 300 K. For W = 100 nm and carrier concentrations of 1016–1018 cm−3 the results are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W ⩽ 10 nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a ballistic regime within the in-plane approximation for the electric field. A region of cross over between the 2D and 3D behaviors of the plasma frequency is evidenced for W>10 nm.
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72.30.+q High-frequency effects; plasma effects
72.20.-i Conductivity phenomena in semiconductors and insulators

Effect of edge roughness on electronic transport in graphene nanoribbon channel metal-oxide-semiconductor field-effect transistors

D. Basu, M. J. Gilbert, L. F. Register, S. K. Banerjee, and A. H. MacDonald

Appl. Phys. Lett. 92, 042114 (2008); http://dx.doi.org/10.1063/1.2839330 (3 pages) | Cited 36 times

Online Publication Date: 30 January 2008

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Results of quantum mechanical simulations of the influence of edge disorder on transport in graphene nanoribbon metal-oxide-semiconductor field-effect transistors (MOSFETs) are reported. The addition of edge disorder significantly reduces ON-state currents and increases OFF-state currents, and introduces wide variability across devices. These effects decrease as ribbon widths increase and as edges become smoother. However, the band gap decreases with increasing width, thereby increasing the band-to-band tunneling mediated subthreshold leakage current even with perfect nanoribbons. These results suggest that without atomically precise edge control during fabrication, MOSFET performance gains through use of graphene will be difficult to achieve in complementary MOS applications.
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85.30.Tv Field effect devices

Transport properties of branched graphene nanoribbons

Antonis N. Andriotis and Madhu Menon

Appl. Phys. Lett. 92, 042115 (2008); http://dx.doi.org/10.1063/1.2839373 (3 pages) | Cited 9 times

Online Publication Date: 30 January 2008

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The electronic transport properties of three-terminal graphene nanoribbon T-junctions are investigated using a quantum tight binding molecular dynamics scheme. The transport properties are found to depend very sensitively on the geometric features of the branches of the junctions. This dependence is even more pronounced than the corresponding dependence in the case of T-shaped single wall carbon nanotubes. This is attributed to the strong dependence of the conductivity of the nanoribbons on their chirality, width, and length. An additional factor that influences the conductivity of the T-junction nanoribbons is associated with the junction itself, i.e., the way the branches are interconnected.
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71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
73.63.Bd Nanocrystalline materials
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Measurement of ultrafast carrier dynamics in epitaxial graphene

Jahan M. Dawlaty, Shriram Shivaraman, Mvs Chandrashekhar, Farhan Rana, and Michael G. Spencer

Appl. Phys. Lett. 92, 042116 (2008); http://dx.doi.org/10.1063/1.2837539 (3 pages) | Cited 116 times

Online Publication Date: 30 January 2008

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Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An initial fast relaxation transient in the 70–120 fs range is followed by a slower relaxation process in the 0.4–1.7 ps range. The slower relaxation time is found to be inversely proportional to the degree of crystalline disorder in the graphene layers as measured by Raman spectroscopy. We relate the measured fast and slow time constants to carrier-carrier and carrier-phonon intraband and interband scattering processes in graphene.
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78.66.Tr Fullerenes and related materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.30.Na Fullerenes and related materials
63.22.Dc Free films
78.47.D- Time resolved spectroscopy (>1 psec)

Evaluation of minority-carrier diffusion length in n-type β-FeSi2 single crystals by electron-beam-induced current

Teruhisa Ootsuka, Takashi Suemasu, Jun Chen, and Takashi Sekiguchi

Appl. Phys. Lett. 92, 042117 (2008); http://dx.doi.org/10.1063/1.2835904 (3 pages) | Cited 11 times

Online Publication Date: 31 January 2008

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We have evaluated the diffusion length of minority carriers (holes) in single-crystalline n-type β-FeSi2 bulk grown by chemical vapor transport by means of electron-beam-induced current (EBIC) technique in the edge-scan configuration. The EBIC line-scan data showed a clear exponential dependence of distance from the Al electrode. The diffusion length was estimated to be 20 μm at room temperature, and increased upon high-temperature annealing, reaching approximately 30 μm after annealing at 800 °C for 8 h. This result explained the improvement of photoresponsivity in the Al/n-β-FeSi2 Schottky diodes by high-temperature annealing.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
85.30.Kk Junction diodes

Donor nonuniformity in undoped and Si doped n-GaN prepared by epitaxial lateral overgrowth

E. B. Yakimov, P. S. Vergeles, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, In-Hwan Lee, Cheul Ro Lee, and S. J. Pearton

Appl. Phys. Lett. 92, 042118 (2008); http://dx.doi.org/10.1063/1.2840190 (3 pages) | Cited 13 times

Online Publication Date: 31 January 2008

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Local donor concentrations were measured in the regions of lateral overgrowth and in the normal vertical growth regions of n-GaN films prepared by epitaxial lateral overgrowth (ELOG). The films were doped with Si to various concentrations. The local donor densities were determined from measurements of the collection efficiency dependence of the electron beam induced current (EBIC) on the energy of the probing electron beam. This dependence was compared with the results of theoretical modeling using the local donor density and diffusion length of charge carriers as fitting parameters. The results show that the donor concentration in the ELOG regions is systematically more than two times lower than the concentration in the vertical growth regions in the gaps of the SiO2 mask used for selective growth. The observed difference is ascribed to the anisotropy of the Si incorporation efficiency. Comparison of these EBIC results with the results of capacitance-voltage profiling obtained on large area Schottky diodes shows that the latter yield the donor concentration close to the concentration in the laterally overgrown regions.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.J- Morphology of films

Polariton relaxation bottleneck and its thermal suppression in bulk GaN microcavities

F. Stokker-Cheregi, A. Vinattieri, F. Semond, M. Leroux, I. R. Sellers, J. Massies, D. Solnyshkov, G. Malpuech, M. Colocci, and M. Gurioli

Appl. Phys. Lett. 92, 042119 (2008); http://dx.doi.org/10.1063/1.2839380 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2008

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We discuss the presence of a polariton bottleneck in bulk GaN microcavities. Angle resolved photoluminescence measurements were performed using low excitation power densities for several negative detunings between the exciton and photon modes. At low temperatures, we observe an enhancement in the emission intensity at angles corresponding to the anticrossing of the lower and upper polariton modes, a clear demonstration of the polariton relaxation bottleneck. This feature becomes less prominent with increasing temperature, eventually disappearing at room temperature. We conclude that polariton-acoustic phonon scattering is the dominant polariton relaxation mechanism in bulk GaN microcavities, as supported by theoretical simulations.
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78.55.Cr III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Energy-band alignments of HfO2 on p-GaAs substrates

Goutam Kumar Dalapati, Hoon-Jung Oh, Sung Joo Lee, Aaditya Sridhara, Andrew See Weng Wong, and Dongzhi Chi

Appl. Phys. Lett. 92, 042120 (2008); http://dx.doi.org/10.1063/1.2839406 (3 pages) | Cited 8 times

Online Publication Date: 31 January 2008

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Interfacial reaction and the energy-band alignments of HfO2 films on p-GaAs substrate were investigated by using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been demonstrated that the alloying of HfO2 with Al2O3 (HfAlO) can significantly reduce native oxides formation and increases the valence-band offsets (VBOs) at HfO2/p-GaAs interface. In addition, the effects of Si interfacial passivation layer on band alignments have also been studied. VBO at HfO2/p-GaAs, HfAlO/p-GaAs, and HfO2/Si/p-GaAs interfaces were 2.85, 2.98, and 3.07 eV, respectively.
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77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Rv Passivation
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Conversion from transparent antiferromagnet KNiF3 to transparent ferrimagnets

H. Manaka, Y. Watanabe, K. Kikunaga, T. Yamamoto, N. Terada, and K. Obara

Appl. Phys. Lett. 92, 042501 (2008); http://dx.doi.org/10.1063/1.2837540 (3 pages)

Online Publication Date: 28 January 2008

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We succeeded in performing a magnetic conversion from transparent antiferromagnet KNiF3 to transparent ferrimagnets, with a spontaneous ferromagnetic moment by a percolation method. Considering Coulomb repulsion, the origin of the spontaneous ferromagnetic moment is explained by an inhomogeneous antiferromagnetic spin arrangement, even if nonmagnetic ions are dispersed homogenously over KNiF3. The ferromagnetic transition temperature was obtained to be 24–26 K. The transmittance at 600–1000 nm was excellent. This compound shows an alternative that can be used for an optical isolator that uses commercial semiconductor lasers, and can widely be used in next generation optical information networks.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics

Effect of donor localization on the magnetic properties of Zn–Co–O system

Xue-Chao Liu, Er-Wei Shi, Zhi-Zhan Chen, Tao Zhang, Yong Zhang, Bo-Yuan Chen, Wei Huang, Xi Liu, Li-Xin Song, Ke-Jin Zhou, and Ming-Qi Cui

Appl. Phys. Lett. 92, 042502 (2008); http://dx.doi.org/10.1063/1.2838292 (3 pages) | Cited 10 times

Online Publication Date: 28 January 2008

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The effect of donor localization on the magnetic properties of Zn–Co–O system was investigated by resonant inelastic x-ray scattering and first principle calculations. It was found that the ferromagnetic coupling was induced through charge transfer between Co 3d and donor defect. The charge transfer was dependent on the electron localization of donor defect. The electron localization of oxygen vacancy defect was much stronger than that of donor defect formed by the substitution of Al3+ for Zn2+. In order to elucidate the magnetic mechanism, a series of Zn0.95Co0.05O and Zn0.94Co0.05Al0.01O films were prepared under different oxygen partial pressure (PO2). The magnetic properties of Zn0.95Co0.05O films were dependent on PO2, while Zn0.94Co0.05Al0.01O films showed stable ferromagnetism.
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75.50.Pp Magnetic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials

Heteroepitaxial growth of ferromagnetic rutile CoxTi1−xO2−δ on GaN (0001)

Yasushi Hirose, Taro Hitosugi, Junpei Kasai, Yutaka Furubayashi, Kiyomi Nakajima, Toyohiro Chikyow, Seiji Konuma, Toshihiro Shimada, and Tetsuya Hasegawa

Appl. Phys. Lett. 92, 042503 (2008); http://dx.doi.org/10.1063/1.2838297 (3 pages) | Cited 1 time

Online Publication Date: 28 January 2008

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A rutile CoxTi1−xO2−δ (100) film was heteroepitaxially grown on GaN (0001) by pulsed laser deposition. Magneto-optical Kerr effect and cross-sectional transmission electron microscope (TEM) measurements revealed that Co0.03Ti0.97O2−δ films prepared at an oxygen partial pressure of 10−6–10−5 Torr with a carrier density ne ≥ 3×1018 cm−3 exhibit room-temperature ferromagnetism without any precipitates or secondary phase. High-resolution TEM observations confirmed that the interface between CoxTi1−xO2−δ and GaN is atomically smooth without intermixing. These results lead us to conclude that CoxTi1−xO2−δ is promising as a spin injector in GaN-based spin-electronic devices.
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81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.20.Ls Magneto-optical effects

Thermal and magnetic field-induced martensite-austenite transition in Ni50.3Mn35.3Sn14.4 ribbons

B. Hernando, J. L. Sánchez Llamazares, J. D. Santos, Ll. Escoda, J. J. Suñol, R. Varga, D. Baldomir, and D. Serantes

Appl. Phys. Lett. 92, 042504 (2008); http://dx.doi.org/10.1063/1.2838356 (3 pages) | Cited 16 times

Online Publication Date: 29 January 2008

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Thermal and field-induced martensite-austenite transition was studied in melt spun Ni50.3Mn35.3Sn14.4 ribbons. Its distinct highly ordered columnarlike microstructure normal to ribbon plane allows the direct observation of critical fields at which field-induced and highly hysteretic reverse transformation starts (H = 17 kOe at 240 K), and easy magnetization direction for austenite and martensite phases with respect to the rolling direction. Single phase L21 bcc austenite with TC of 313 K transforms into a 7M orthorhombic martensite with thermal hysteresis of 21 K and transformation temperatures of MS = 226 K, Mf = 218 K, AS = 237 K, and Af = 244 K.
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81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
81.40.Gh Other heat and thermomechanical treatments

Lateral-displacement influence on the levitation force in a superconducting system with translational symmetry

Nuria Del–Valle, Alvaro Sanchez, Carles Navau, and Du-Xing Chen

Appl. Phys. Lett. 92, 042505 (2008); http://dx.doi.org/10.1063/1.2838311 (3 pages) | Cited 12 times

Online Publication Date: 30 January 2008

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The unique properties of superconductors make the design of levitation devices possible. In some of them, lateral displacements of the superconducting levitating part often result in a decrease in the levitation force, which can cause a critical malfunction of the system. In this work, the authors theoretically analyze the levitation force of a system consisting of an infinitely long superconductor over an infinitely long permanent-magnet guideway using a realistic model based on a magnetic-energy minimization procedure, from which they give the physical keys for understanding the levitation force reduction after lateral displacements and how to minimize these effects.
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84.71.Ba Superconducting magnets; magnetic levitation devices
85.70.Rp Magnetic levitation, propulsion and control devices
75.50.Ww Permanent magnets
74.25.Ha Magnetic properties including vortex structures and related phenomena

Influence of disorder on the in-field Jc of MgB2 wires using highly active pyrene

J. H. Kim, X. Xu, M. S. A. Hossain, D. Q. Shi, Y. Zhao, X. L. Wang, S. X. Dou, S. Choi, and T. Kiyoshi

Appl. Phys. Lett. 92, 042506 (2008); http://dx.doi.org/10.1063/1.2838756 (3 pages) | Cited 10 times

Online Publication Date: 31 January 2008

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In this work, we report on significantly enhanced critical current density (Jc) in MgB2 superconductor that was easily obtained by doping with a hydrocarbon, highly active pyrene (C16H10), and using a sintering temperature as low as ∼ 600 °C. The processing advantages of the C16H10 additive include production of a highly active carbon (C) source, an increased level of disorder, and the introduction of small grain size, resulting in enhancement of Jc.
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74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Analyses on double resonance behavior in microwave magnetic permeability of multiwalled carbon nanotube composites containing Ni catalyst

Fusheng Wen, Haibo Yi, Liang Qiao, Hong Zheng, Dong Zhou, and Fashen Li

Appl. Phys. Lett. 92, 042507 (2008); http://dx.doi.org/10.1063/1.2839382 (3 pages) | Cited 24 times

Online Publication Date: 31 January 2008

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The double resonance behavior of microwave magnetic permeability has been observed for multiwalled carbon nanotube composites containing Ni catalyst. One of them is due to the natural resonance at 6.00 GHz and another is due to the exchange resonance at 10.11 GHz. The natural resonance is dependent on magnetocrystalline anisotropy and shape anisotropy of Ni nanostick catalyst and the calculated result of exchange resonance mode with a few modifications was close to the experiment. It is believed that the coexistence of natural resonance and exchange resonance is benefial to large bandwidth as a microwave absorber.
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78.70.Gq Microwave and radio-frequency interactions
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
81.07.De Nanotubes
75.75.-c Magnetic properties of nanostructures

Magnetoelectric effects in composite of nanogranular Fe/TiO2−δ films

S. D. Yoon, C. Vittoria, Y. N. Srivastava, A. Widom, and V. G. Harris

Appl. Phys. Lett. 92, 042508 (2008); http://dx.doi.org/10.1063/1.2838757 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2008

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Employing a new experimental technique to measure magnetoelectric response functions, we have measured the magnetoelectric effect in composite films of nanogranular metallic iron in anatase titanium dioxide at temperatures below 50 K. A magnetoelectric resistance is defined as the ratio of a transverse voltage to bias current as a function of magnetic field. In contrast to the anomalous Hall resistance measured above 50 K, the magnetoelectric resistance below 50 K is significantly larger and exhibits an even symmetry with respect to magnetic field reversal H→−H. The composite films are unique in terms of showing magnetoelectric effects at low temperatures, <50 K, and anomalous Hall effects at high temperatures, >50 K.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
75.47.Pq Other materials
75.50.Bb Fe and its alloys
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Effects of LaNiO3 bottom electrode on structural and dielectric properties of CaCu3Ti4O12 films fabricated by sol-gel method

Y. W. Li, Z. G. Hu, J. L. Sun, X. J. Meng, and J. H. Chu

Appl. Phys. Lett. 92, 042901 (2008); http://dx.doi.org/10.1063/1.2837534 (3 pages) | Cited 6 times

Online Publication Date: 28 January 2008

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CaCu3Ti4O12 (CCTO) thin films are prepared by a sol-gel method on LaNiO3-coated silicon and Pt/TiO2/SiO2/Si substrate. Compared with the films on Pt, the CCTO on LaNiO3 exhibits a (400) orientation. Dielectric loss of CCTO on LaNiO3 is lower than 0.25 within 100 Hz–10 kHz, lower than the reported value of CCTO grown on Pt/TiO2/SiO2/Si by pulse laser deposition. Possible reason is that LaNiO3 acts as seed layer for the growth of CCTO. The crystallinity of CCTO is improved and the dielectric properties are enhanced. Complex impedance spectrum of CCTO on LaNiO3 is discussed according to grain boundary barrier layer capacitance model.
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77.22.Gm Dielectric loss and relaxation
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.Mm Grain and twin boundaries

Low-losses, highly tunable Ba0.6Sr0.4TiO3/MgO composite

U.-Chan Chung, C. Elissalde, M. Maglione, C. Estournès, M. Paté, and J. P. Ganne

Appl. Phys. Lett. 92, 042902 (2008); http://dx.doi.org/10.1063/1.2837621 (3 pages) | Cited 48 times

Online Publication Date: 29 January 2008

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Spark plasma sintering (SPS) is an efficient tool to obtain highly densified ferroelectric-dielectric ceramic composites with clean interfaces and tunable properties. Dielectric MgO and ferroelectric Ba0.6Sr0.4TiO3 (BST) were combined in two-dimensional multilayer and three-dimensional random powders design. Their unmodified BST Curie temperature proves the suppression of interdiffusion while dielectric losses are below 0.5% and the tunability is 40% at room temperature. The composites and pure BST with similar densities (>95%) were obtained, owing reliable comparison of their dielectric properties. Such SPS ceramics can be used as experimental input for simulation and are potential candidates for high frequency applications.
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77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Mh Cermets, ceramic and refractory composites
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
77.80.-e Ferroelectricity and antiferroelectricity

A type of poly(vinylidene fluoride-trifluoroethylene) copolymer exhibiting ferroelectric relaxor behavior at high temperature ( ∼ 100 °C)

Hui-Min Bao, Cheng-Liang Jia, Chang-Chun Wang, Qun-Dong Shen, Chang-Zheng Yang, and Q. M. Zhang

Appl. Phys. Lett. 92, 042903 (2008); http://dx.doi.org/10.1063/1.2838309 (3 pages) | Cited 6 times

Online Publication Date: 29 January 2008

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We report a class of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers synthesized via reductive dechlorination from P(VDF-CTFE) [termed as the reduced P(VDF-TrFE) copolymer], which exhibit ferroelectric relaxor behavior at high temperature ( ∼ 100 °C). It was found that the reduced P(VDF-TrFE) 66/34 mol % copolymer has very high content of head-to-head and tail-to-tail defects, which may act as random defects, leading to the observed ferroelectric relaxor at high temperature. Furthermore, the reduced copolymer also exhibits a high melting point ( ∼ 200 °C), which also makes it attractive for high-temperature dielectric applications.
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77.84.Jd Polymers; organic compounds
77.80.-e Ferroelectricity and antiferroelectricity

Energy-band alignment of HfO2/SiO2/SiC gate dielectric stack

R. Mahapatra, Amit K. Chakraborty, A. B. Horsfall, N. G. Wright, G. Beamson, and Karl S. Coleman

Appl. Phys. Lett. 92, 042904 (2008); http://dx.doi.org/10.1063/1.2839314 (3 pages) | Cited 7 times

Online Publication Date: 30 January 2008

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The band alignment of HfO2/SiO2/SiC gate dielectric stack has been investigated by x-ray photoelectron spectroscopy and electrical characterization. Two types of valence band offsets are observed in the stack layer; the smaller value of 1.5 eV corresponds to the HfO2/SiC band offset while the larger one of 2.2 eV is due to the interfacial SiO2/SiC. The barrier height is extracted to be 1.5 eV from the Schottky emission characteristics and is higher than the reported value for HfO2 on SiC without interfacial SiO2. Thus, presence of an interfacial SiO2 layer increases band offsets to reduce the leakage current characteristics.
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73.20.At Surface states, band structure, electron density of states
79.60.-i Photoemission and photoelectron spectra
73.30.+y Surface double layers, Schottky barriers, and work functions
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

The chemical and electronic structures of YOxNy on Si(100)

X. J. Wang, L. D. Zhang, G. He, J. P. Zhang, M. Liu, and L. Q. Zhu

Appl. Phys. Lett. 92, 042905 (2008); http://dx.doi.org/10.1063/1.2839377 (3 pages) | Cited 5 times

Online Publication Date: 30 January 2008

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Effects of nitrogen incorporation on interfacial property, band gap, and band alignments of high-k Y2O3 gate dielectrics have been investigated. It was found that the incorporation of nitrogen into Y2O3 films can effectively suppress the growth of the interfacial layer between Y2O3 and Si substrate. The incorporation of nitrogen into Y2O3 films leads to the reduction of band gap and valence band offset, but not the conduction offset of Y2O3 films. High temperature annealing will help to increase the band gap and valence band offset of YOxNy film due to the release of the interstitial N atoms.
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77.55.-g Dielectric thin films
71.20.Ps Other inorganic compounds
81.40.Gh Other heat and thermomechanical treatments
61.72.jj Interstitials

Valence band offset of MgO/InN heterojunction measured by x-ray photoelectron spectroscopy

P. F. Zhang, X. L. Liu, R. Q. Zhang, H. B. Fan, H. P. Song, H. Y. Wei, C. M. Jiao, S. Y. Yang, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 92, 042906 (2008); http://dx.doi.org/10.1063/1.2839611 (3 pages) | Cited 13 times

Online Publication Date: 31 January 2008

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MgO may be a promising gate dielectric and surface passivation film for InN based devices and the valence band offset of MgO/InN heterojunction has been measured by x-ray photoelectron spectroscopy. The valence band offset is determined to be 1.59±0.23 eV. Given the experimental band gap of 7.83 for the MgO, a type-I heterojunction with a conduction band offset of 5.54±0.23 eV is found. The accurate determination of the valence and conduction band offsets is important for use of MgO/InN electronic devices.
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79.60.Jv Interfaces; heterostructures; nanostructures
71.20.-b Electron density of states and band structure of crystalline solids
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