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13 Nov 2006

Volume 89, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages)

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo
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Hot phonons in Si-doped GaN

J. Liberis, M. Ramonas, O. Kiprijanovic, A. Matulionis, N. Goel, J. Simon, K. Wang, H. Xing, and D. Jena

Appl. Phys. Lett. 89, 202117 (2006); http://dx.doi.org/10.1063/1.2388866 (3 pages) | Cited 7 times

Online Publication Date: 17 November 2006

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Microwave noise and electron transport are studied in silicon-doped GaN channels grown by molecular beam epitaxy and subjected to a high electric field. The drift velocity of 2.8×107 cm/s is reached at 290 kV/cm for n ∼ 1×1018 cm−3 channel. No negative differential resistance is observed. The noise temperature exceeds ∼ 5000 K at ∼ 110 kV/cm for n ∼ 3×1017 cm−3 channel. The hot-phonon effect on power dissipation in GaN:Si is 3–4 times weaker as compared with the effect in an undoped AlGaN/GaN two-dimensional channel. Monte Carlo simulation shows a weak effect of hot phonons on hot-electron energy distribution.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.70.+m Noise processes and phenomena
73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects

Critical thickness of heavily boron-doped silicon-germanium alloys

Saurabh Chopra, Mehmet C. Ozturk, Veena Misra, Kris McGuire, and L. E. McNeil

Appl. Phys. Lett. 89, 202118 (2006); http://dx.doi.org/10.1063/1.2374870 (3 pages) | Cited 1 time

Online Publication Date: 17 November 2006

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In this work, the effect of boron concentration on the critical thickness of heavily boron doped Si1−xGex alloys (Si1−x−yGexBy) has been studied using Raman spectroscopy. The experimental results indicate that while boron decreases the stored strain energy, it can substantially increase the critical thickness for a given Ge concentration. The Si1−x−yGexBy critical thickness was calculated using two different models based on energy balance and kinetic considerations. The results show that the kinetic model provides a good estimate for the Si1−x−yGexBy critical thickness.
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78.30.Hv Other nonmetallic inorganics
61.72.up Other materials
61.72.S- Impurities in crystals
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Enhancement of ferromagnetic properties of NiO:Fe thin film by Li doping

Yuan-Hua Lin, Rongjuan Zhao, Ce-Wen Nan, Minghao Ying, M. Kobayashi, Y. Ooki, and A. Fujimori

Appl. Phys. Lett. 89, 202501 (2006); http://dx.doi.org/10.1063/1.2388130 (3 pages) | Cited 11 times

Online Publication Date: 13 November 2006

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Li and Fe codoped NiO thin films (LixNi0.98−xFe0.02O, x = 0–0.05) were obtained by a sol-gel spin-coating method on silicon substrates. Phase composition and microstructure analysis indicated that the film samples contained 20–30 nm sized NiO particles. With increasing Li-doping concentration, the current density of the films increased due to the increase of hole carriers. Magnetization measurements revealed that all the thin films showed room-temperature ferromagnetic properties and could be enhanced by Li doping, which should be due to the fact that hole doping makes ferromagnetic coupling interactions between the hole carriers and localized Fe 3d spins more efficient.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials

Over 70% tunneling magnetoresistance at room temperature for a CoFe and AlOx based magnetic tunnel junction

J. Joshua Yang, Chengxiang Ji, Y. Austin Chang, Xianglin Ke, and M. S. Rzchowski

Appl. Phys. Lett. 89, 202502 (2006); http://dx.doi.org/10.1063/1.2387568 (3 pages) | Cited 19 times

Online Publication Date: 13 November 2006

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More than 70% tunneling magnetoresistance (TMR) ratio has been observed at room temperature for a CoFe and AlOx based magnetic tunnel junction. The annealing of the epitaxial bottom electrode, Si (001)/Ag fcc (200)/Co84Fe16 bcc (200), at 400 °C prior to fabricating the tunnel barrier and the upper electrode is crucial for achieving this high TMR ratio. Moreover a high output voltage could be obtained for this magnetic tunnel junction due to its high V1/2, the bias voltage at which the TMR ratio is reduced to half of that near the zero bias. The rationale for obtaining this high TMR ratio is discussed, and there are reasons to believe that the TMR ratio for this junction could be further improved.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.47.Pq Other materials
75.50.Bb Fe and its alloys

High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys

Y. G. Shi, S. L. Tang, R. L. Wang, H. L. Su, Z. D. Han, L. Y. Lv, and Y. W. Du

Appl. Phys. Lett. 89, 202503 (2006); http://dx.doi.org/10.1063/1.2387865 (3 pages) | Cited 13 times

Online Publication Date: 13 November 2006

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PrxTb1−xFe1.9 (0 ⩽ x ⩽ 1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of PrxTb1−xFe1.9 (0 ⩽ x ⩽ 1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ‖−λ⊥ = 1497 ppm) at 13 kOe at room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate for magnetostriction application.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
61.66.Dk Alloys

Magnetic field processing to enhance critical current densities of MgB2 superconductors

S. X. Dou, W. K. Yeoh, O. Shcherbakova, J. Horvat, J. H. Kim, A. V. Pan, D. Wexler, Y. Li, W. X. Li, Z. M. Ren, P. Munroe, and J. Z. Cui

Appl. Phys. Lett. 89, 202504 (2006); http://dx.doi.org/10.1063/1.2388126 (3 pages) | Cited 11 times

Online Publication Date: 14 November 2006

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A magnetic field of up to 12 T was applied during the sintering process of pure MgB2 and carbon nanotube (CNT) doped MgB2 wires. The authors have demonstrated that magnetic field processing results in grain refinement, homogeneity, and enhancement in Jc(H) and Hirr. The extent of improvement in Jc increases with increasing field. The Jc for a 10 T field processed CNT doped sample increases by a factor of 3 at 10 K and 8 T and at 20 K and 5 T, respectively. Hirr for the 10 T field processed CNT doped sample reached 9 T at 20 K, which exceeded the best value of SiC doped MgB2 at 20 K. Magnetic field processing reduces the resistivity in CNT doped MgB2, straightens the entangled CNTs, and improves the adherence between CNTs and the MgB2 matrix.
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74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.35.Np Adhesion

Domain overlap in antiferromagnetically coupled [Co/Pt]/NiO/[Co/Pt] multilayers

A. Baruth, L. Yuan, J. D. Burton, K. Janicka, E. Y. Tsymbal, S. H. Liou, and S. Adenwalla

Appl. Phys. Lett. 89, 202505 (2006); http://dx.doi.org/10.1063/1.2388892 (3 pages) | Cited 17 times

Online Publication Date: 14 November 2006

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Antiferromagnetically coupled magnetic thin films with perpendicular anisotropy exhibit domain overlap regions originating from magnetostatic stray fields localized in the vicinity of the domain walls. Using high resolution magnetic force microscopy, the authors investigate these overlap regions in [Co/Pt]/NiO/[Co/Pt] multilayers with various strengths of the interlayer exchange coupling. They develop a simple model that provides a quantitative explanation of the formation of these regions and the relationship between the domain overlap width and the coupling strength. Their results are important for application of magnetic layered structures with perpendicular anisotropy in advanced magnetoresistive devices.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics

Swift-heavy-ion-irradiation-induced enhancement in electrical conductivity of chemical solution deposited La0.7Ba0.3MnO3 thin films

R. N. Parmar, J. H. Markna, D. G. Kuberkar, Ravi Kumar, D. S. Rana, Vivas C. Bagve, and S. K. Malik

Appl. Phys. Lett. 89, 202506 (2006); http://dx.doi.org/10.1063/1.2359291 (3 pages) | Cited 2 times

Online Publication Date: 14 November 2006

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Epitaxial thin films of La0.7Ba0.3MnO3 manganite, deposited using chemical solution deposition technique, were irradiated by 200 MeV Ag+15 ions with a maximum ion dose up to 1×1012 ions/cm2. Temperature and magnetic-field-dependent resistivity measurements on all the films (before and after irradiation) reveal a sustained decrease in resistivity with increasing ion dose. A maximum dose of 1×1012 ions/cm2 suppresses resistivity by factors of 3 and 10 at 330 K [insulator-metal (I-M) transition] and at 10 K, respectively. On the other hand, with increasing ion dose, the magnetoresistance enhances in the vicinity of I-M transition but decreases at low temperatures. These results, corroborated by surface morphology of films, suggest that the origin of such properties lies in the irradiation induced improved crystallinity and epitaxial orientation, enhanced connectivity between grains and conglomeration of grains, which result in better conductivity at grain boundaries.
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73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Magnetic properties of hydrogenated Li and Co doped ZnO nanoparticles

O. D. Jayakumar, I. K. Gopalakrishnan, K. Shashikala, S. K. Kulshreshtha, and C. Sudakar

Appl. Phys. Lett. 89, 202507 (2006); http://dx.doi.org/10.1063/1.2387877 (3 pages) | Cited 14 times

Online Publication Date: 15 November 2006

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The effect of hydrogenation on the magnetic properties of Zn0.85Co0.05Li0.10O nanoparticles is presented. It was found that the sample hydrided at room temperature (RT) showed weak ferromagnetism, while that hydrided at 400 °C showed robust ferromagnetism at room temperature. In both cases reheating the sample at 400 °C in air converts it back into the paramagnetic state completely. The characterization of samples by x-ray and electron diffraction showed that room temperature ferromagnetism observed in the samples hydrogenated at RT is intrinsic in nature, whereas that observed in the samples hydrogenated at 400 °C is partly due to the cobalt metal clusters.
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75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
81.40.Gh Other heat and thermomechanical treatments

Magnetoelectric exchange bias systems in spintronics

Xi Chen, Andreas Hochstrat, Pavel Borisov, and Wolfgang Kleemann

Appl. Phys. Lett. 89, 202508 (2006); http://dx.doi.org/10.1063/1.2388149 (3 pages) | Cited 37 times

Online Publication Date: 15 November 2006

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Magnetoelectric switching of perpendicular exchange bias is observed in a Co/Pt multilayer attached to single crystalline magnetoelectric antiferromagnetic Cr2O3(111). The exchange bias field HEB can be set to positive or negative values by applying an electric field Efr either parallel or antiparallel to the magnetic freezing field Hfr while cooling to below the Néel temperature. Based on this result, the antiferromagnetic spin state can be used as a medium for data storage. The authors propose magnetic random access memory cells and magnetic logic devices, which are purely voltage controlled.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Et Exchange and superexchange interactions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Bb Magnetic memory using giant magnetoresistance
84.30.Sk Pulse and digital circuits

Diluted magnetic semiconductors with high Curie temperature based on C1b compounds: CoTi1−xFexSb

Kristian Kroth, Benjamin Balke, Gerhard H. Fecher, Vadim Ksenofontov, Claudia Felser, and Hong-Ji Lin

Appl. Phys. Lett. 89, 202509 (2006); http://dx.doi.org/10.1063/1.2388876 (3 pages) | Cited 14 times

Online Publication Date: 15 November 2006

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Diluted magnetic semiconductors were prepared by substituting titanium in the semiconducting compound CoTiSb with iron. The structural, electronic, and magnetic properties of the pure and doped materials were investigated. It was found that substitution of up to 10% Ti by Fe does not affect the crystalline structure. Self-consistent calculations of the electronic structure predict the material to be a half-metallic ferromagnet. The Curie temperature of the Fe substituted alloy is far above room temperature (>700 K), thus making that material a serious candidate for future electronic applications, in particular, for magnetoelectronics and spintronics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Fn Inorganic compounds
71.20.Nr Semiconductor compounds

Transition metal doping and clustering in Ge

A. Continenza, G. Profeta, and S. Picozzi

Appl. Phys. Lett. 89, 202510 (2006); http://dx.doi.org/10.1063/1.2388894 (3 pages) | Cited 8 times

Online Publication Date: 15 November 2006

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Ab initio calculations of clusters in Ge, up to three-impurity atoms in substitutional and/or interstitial sites, are discussed. Interstitial defects, with usually high formation energies when isolated, are stabilized thanks to the interaction with substitutional sites nearby. Mn impurities show a tendency to cluster and magnetic alignment strongly dependent on the sites; however, the occurrence of some Mn clusters is seen not to degrade magnetism, though reducing the total magnetic moment. Cr codoping leads to large formation energy and antiferromagnetic alignment. Co codoping lowers the energy cost of Mn incorporation without disrupting ferromagnetic ordering, thus representing a possible route to help Mn incorporation in Ge.
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61.72.uf Ge and Si
75.50.Pp Magnetic semiconductors
61.72.J- Point defects and defect clusters
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities

Giant coercivity nanodots and fractals in CoPt films grown on (001) SrTiO3 using pulsed laser deposition

R. K. Rakshit, S. K. Bose, R. Sharma, and R. C. Budhani

Appl. Phys. Lett. 89, 202511 (2006); http://dx.doi.org/10.1063/1.2388859 (3 pages) | Cited 7 times

Online Publication Date: 15 November 2006

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High coercivity nanoscale structures of CoPt are grown on (001) SiTiO3 with pulsed laser ablation. At low growth rate ( ≃ 0.4 Å/s), the film morphology changes from a self-similar fractal to nanodots as the deposition temperature is raised from 700 to 800 °C. While the nanodots are L10 ordered phase with out-of-plane c axis and coercivity Hc⊥ ≃ 30 kOe, the fractals have a nonzero, in-plane c-axis component of the L10 phase. The large lattice mismatch between (001) SrTiO3 and the ac/bc plane of L10 imparts tensile strain to the films whose morphological manifestations can be suppressed at high growth rates.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition

Magneto-optical study of magnetization reversal asymmetry in exchange bias

A. Tillmanns, S. Oertker, B. Beschoten, G. Güntherodt, C. Leighton, Ivan K. Schuller, and J. Nogués

Appl. Phys. Lett. 89, 202512 (2006); http://dx.doi.org/10.1063/1.2392283 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2006

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The asymmetric magnetization reversal in exchange biased Fe/MnF2 involves coherent (Stoner-Wohlfarth) magnetization rotation into an intermediate, stable state perpendicular to the applied field. We provide here the experimentally tested analytical conditions for the unambiguous observation of both longitudinal and transverse magnetization components using the magneto-optical Kerr effect. This provides a fast and powerful probe of coherent magnetization reversal as well as its chirality. Surprisingly, the sign and asymmetry of the transverse magnetization component of exchange biased, low-anisotropy MnF2 and high-anisotropy FeF2 change with the angle between cooling and measurement fields.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics

Degradation-free interfaces in MgB2/insulator/Pb Josephson tunnel junctions

Y. Cui, Ke Chen, Qi Li, X. X. Xi, and J. M. Rowell

Appl. Phys. Lett. 89, 202513 (2006); http://dx.doi.org/10.1063/1.2388891 (3 pages) | Cited 16 times

Online Publication Date: 16 November 2006

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High quality superconductor-barrier interfaces are critical for Josephson tunnel junctions. The authors show that such interfaces can be achieved in MgB2/insulator/Pb trilayer junctions using MgB2 films grown by hybrid physical-chemical vapor deposition and with barriers formed at elevated temperatures. The junctions show clear Josephson tunneling characteristics with high Jc ( ∼ 3 kA/cm2), high IcRN products ( ∼ 1.9 meV), and the expected Ic(B) pattern. The observed π gap is small (2.0 meV) and the σ gap is large (7.4 meV), in agreement with theoretical predictions and indicating that the superconducting property of MgB2 is not degraded at the MgB2-insulator interface.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Enhanced flux pinning properties of YBa2Cu3Oy by dilute impurity doping for CuO chain

Yui Ishii, Jun-ichi Shimoyama, Yoshiaki Tazaki, Takayoshi Nakashima, Shigeru Horii, and Kohji Kishio

Appl. Phys. Lett. 89, 202514 (2006); http://dx.doi.org/10.1063/1.2387979 (3 pages) | Cited 16 times

Online Publication Date: 16 November 2006

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Effects of dilute impurity doping to the CuO chain of Y123 on the flux pinning properties were studied using single crystals and melt-solidified bulks. Cobalt-doped Y123 single crystals and iron-, cobalt- or gallium-doped Y123 melt-solidified bulks exhibited dramatically improved Jc-H characteristics accompanying huge secondary peaks in Jc-H curves. In field Jc of these samples are apparently higher than that of a low level zinc-doped bulk. These results strongly suggest that introduction of local disorders in the CuO chain by dilute impurity doping is a more promising way to improve Jc of RE123 materials than impurity doping to the CuO2 plane.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Dh Effects of crystal defects, doping and substitution

Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency

W. C. Chien, C. K. Lo, L. C. Hsieh, Y. D. Yao, X. F. Han, Z. M. Zeng, T. Y. Peng, and P. Lin

Appl. Phys. Lett. 89, 202515 (2006); http://dx.doi.org/10.1063/1.2374807 (3 pages) | Cited 10 times

Online Publication Date: 17 November 2006

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The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al(1.2 nm)-oxide/CoFeB(4 nm)/Ru(5 nm). A huge change of more than ±17 000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1 MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects

Perfluorocyclobutane containing polymeric gate dielectric for organic thin film transistors with high on/off ratio

Jieun Ghim, Kang-Jun Baeg, Yong-Young Noh, Seok-Ju Kang, Jang Jo, Dong-Yu Kim, Shinuk Cho, Jonathan Yuen, Kwanghee Lee, and Alan J. Heeger

Appl. Phys. Lett. 89, 202516 (2006); http://dx.doi.org/10.1063/1.2390663 (3 pages) | Cited 8 times

Online Publication Date: 17 November 2006

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A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10−3 cm2/V s and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD = −50 V.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
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Improvement on the temperature coefficient of resonant frequency of hexagonal perovskites through intergrowth structures

Fei Zhao, Zhenxing Yue, Jing Pei, Hao Zhuang, Zhilun Gui, and Longtu Li

Appl. Phys. Lett. 89, 202901 (2006); http://dx.doi.org/10.1063/1.2388141 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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Cation-deficient hexagonal perovskites Ba5Nb4O15, Ba6Nb4TiO18, and their intergrowth compounds were prepared by solid-state reaction method. Dielectric measurements showed that the intergrowth compounds had a relatively low temperature coefficient of resonant frequency (τf) compared to that of the simple terms Ba5Nb4O15 and Ba6Nb4TiO18. On the basis of the structure data, the authors proposed a structural parameter d, the degree of atomic displacements, to evaluate the structural dependence of the temperature coefficient of resonant frequency. The reduced τf value of intergrowths was considered to be resulted from the decreased degree of atomic displacements in the hexagonal perovskite structure.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.37.Lp Transmission electron microscopy (TEM)

Enhanced piezoresistive characteristics of Nb2O5 modified La0.8Sr0.2MnO3 ceramics

Vaneet Sharma, Maria R. Hossu, Woo Ho Lee, Ali R. Koymen, and Shashank Priya

Appl. Phys. Lett. 89, 202902 (2006); http://dx.doi.org/10.1063/1.2387567 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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This letter reports the giant piezoresistance phenomenon in Nb2O5 modified La0.8Sr0.2MnO3 (LSMO) polycrystalline ceramics. LSMO modified with 2 mol % Nb exhibited ∼ 2% change in resistivity at 19.2 MPa pressure as compared to 0.5% for the pure LSMO. A dramatic improvement was obtained for 5 mol % Nb-modified LSMO composition, which exhibited a linear change in resistivity with uniaxial stress and the fractional change was of the order of 3% at 19.2 MPa stress. The origin of the giant piezoresistance was found to be related to Nb substitution on the Mn sites which distorts the Mn–O bond, lowering the magnitude of stress required for the manganite lattice transformation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
72.20.Fr Low-field transport and mobility; piezoresistance

Aluminum oxynitride interfacial passivation layer for high-permittivity gate dielectric stack on gallium arsenide

Ming Zhu, Chih-Hang Tung, and Yee-Chia Yeo

Appl. Phys. Lett. 89, 202903 (2006); http://dx.doi.org/10.1063/1.2388246 (3 pages) | Cited 31 times

Online Publication Date: 13 November 2006

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The authors demonstrate a passivation technique for GaAs substrate by employing an aluminum oxynitride (AlON) interfacial passivation layer. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the AlON interfacial passivation layer effectively suppresses the formation of Ga or As oxide during the gate dielectric deposition process. This enabled the fabrication of high quality GaAs n-channel metal-oxide-semiconductor capacitors with HfO2 gate dielectric and TaN metal gate electrode. The metal gate/high-k gate dielectric stack on GaAs demonstrated an equivalent SiO2 thickness of 2.2 nm and low leakage current density of 4.27×10−4 A/cm2 at a gate bias equal to Vfb−1 V. Excellent capacitance-voltage characteristics with low frequency dispersion ( ∼ 4%) were also obtained.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
81.65.Rv Passivation

Effects of O vacancies and C doping on dielectric properties of ZrO2: A first-principles study

Gargi Dutta, K. P. S. S. Hembram, G. Mohan Rao, and Umesh V. Waghmare

Appl. Phys. Lett. 89, 202904 (2006); http://dx.doi.org/10.1063/1.2388146 (3 pages) | Cited 11 times

Online Publication Date: 14 November 2006

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The authors determine electronic properties, structural stability, and dielectric response of zirconia (ZrO2) with oxygen vacancies (O vacancies) and carbon doping (C doping) using first-principles density functional theory calculations based on pseudopotentials and a plane wave basis. They find significantly enhanced static dielectric response in zirconia with oxygen vacancies arising from a softened phonon mode. They also find that effects of carbon doping on the dielectric response are anisotropic.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
61.72.J- Point defects and defect clusters
61.72.up Other materials
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

High performance Aurivillius phase sodium-potassium bismuth titanate lead-free piezoelectric ceramics with lithium and cerium modification

Chun-Ming Wang and Jin-Feng Wang

Appl. Phys. Lett. 89, 202905 (2006); http://dx.doi.org/10.1063/1.2388253 (3 pages) | Cited 30 times

Online Publication Date: 14 November 2006

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The piezoelectric properties of the lithium and cerium modified A-site vacancies sodium-potassium bismuth titanate (NKBT) lead-free piezoceramics are investigated. The piezoelectric activity of NKBT ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature TC, piezoelectric coefficient d33, and mechanical quality factor Qm for the NKBT ceramics modified with 0.10 mol % (LiCe) are found to be 660 °C, 25 pC/N, and 3135, respectively. The Curie temperature gradually decreases from 675 to 650 °C with the increase of (LiCe) modification. The dielectric spectroscopy shows that all the samples possess stable piezoelectric properties, demonstrating that the (LiCe) modified NKBT-based ceramics are the promising candidates for high temperature applications.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
77.80.B- Phase transitions and Curie point

Resistive hystersis effects in perovskite oxide-based heterostructure junctions

M. P. Singh, L. Méchin, W. Prellier, and M. Maglione

Appl. Phys. Lett. 89, 202906 (2006); http://dx.doi.org/10.1063/1.2388145 (3 pages) | Cited 13 times

Online Publication Date: 16 November 2006

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The electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions are reported. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400×200 μm2, have been fabricated upon LCMO/BTO/LCMO heterostructures by photolithography and Ar-ion milling technique. The dc current-voltage (I-V) characteristics of the MFM junctions were carried out. At 300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K, (I-V) curves exhibited some reproducible switching behaviors with well-defined remnant currents. The resulting resistance modulation is very different from what was already reported in ultrathin ferroelectric layers displaying resistive switching. A model is presented to explain the data.
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73.40.Rw Metal-insulator-metal structures

Impact of thin SrTiO3 seed layer to achieve low-temperature crystallization below 300 °C and ferroelectricity of lead zirconate titanate thin film

Ji-Won Moon, Shogo Tazawa, Kazuo Shinozaki, Naoki Wakiya, and Nobuyasu Mizutani

Appl. Phys. Lett. 89, 202907 (2006); http://dx.doi.org/10.1063/1.2390671 (3 pages) | Cited 8 times

Online Publication Date: 16 November 2006

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The authors report low-temperature preparation of Pb(Zr0.6,Ti0.4)O3 (PZT) thin films below 300 °C using SrTiO3 seed layers on (111)Pt/IrO2/SiO2/(001)Si substrates by metal-organic chemical vapor deposition. The critical parameters contributing low-temperature preparation for PZT were crystallinity and orientation of SrTiO3 seeds and deposition rate of PZT films. Using 1–2 nm of SrTiO3 with (h00) and (hh0) mixed orientations, polycrystalline PZT films could be obtained at 290 °C with deposition rate of 0.5–1.0 nm/min. The remanent polarization (2Pr) and coercive field (2Ec) of PZT films on SrTiO3 seeds with deposition rate of 0.5 nm/min were 42.4 μC/cm2 and 256 kV/cm, respectively.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.22.Ej Polarization and depolarization
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