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28 Feb 2005

Volume 86, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 093101 (2005); http://dx.doi.org/10.1063/1.1870108 (3 pages)

G. S. Paraoanu and A. M. Halvari
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Reconciliation of luminescence and Hall measurements on the ternary semiconductor CuGaSe2

Susanne Siebentritt, Inge Beckers, Till Riemann, Jürgen Christen, Axel Hoffmann, and Matthias Dworzak

Appl. Phys. Lett. 86, 091909 (2005); http://dx.doi.org/10.1063/1.1872215 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2005

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Previous Hall and photoluminescence investigations on CuGaSe2 yielded conflicting results: defect depths determined by luminescence are lower than the ionization energy found in electrical measurements. In this contribution, we present time and spatially resolved cathodoluminescence measurements that necessitate a new interpretation of the luminescence data, leading to a consistent model for luminescence and Hall data with three acceptors with ionization energies of 60, 100, and 150 meV. Luminescence decay times are long, in the range of 100 ns, indicating strong capture. Luminescence is spatially inhomogeneous, indicating inhomogeneous distribution of defects.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Ht Other nonmetals
84.60.Jt Photoelectric conversion

Achieving fast oxygen diffusion in perovskites by cation ordering

A. A. Taskin, A. N. Lavrov, and Yoichi Ando

Appl. Phys. Lett. 86, 091910 (2005); http://dx.doi.org/10.1063/1.1864244 (3 pages) | Cited 89 times

Online Publication Date: 25 February 2005

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The oxygen-exchange behavior has been studied in half-doped manganese and cobalt perovskite oxides. We have found that the oxygen diffusivity in Gd0.5Ba0.5MnO3−δ can be enhanced by orders of magnitude by inducing crystallographic ordering among lanthanide and alkali-earth ions in the A-site sublattice. Transformation of a simple cubic perovskite, with randomly occupied A sites, into a layered crystal GdBaMn2O5+x (or isostructural GdBaCo2O5+x for cobalt oxide) with alternating lanthanide and alkali-earth planes reduces the oxygen bonding strength and provides disorder-free channels for ion motion, pointing to an efficient way to design new ionic conductors.
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66.30.J- Diffusion of impurities
66.30.H- Self-diffusion and ionic conduction in nonmetals
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.50.Lt Crystal binding; cohesive energy

Growth of single quantum dots on preprocessed structures: Single photon emitters on a tip

V. Zwiller, T. Aichele, F. Hatami, W. T. Masselink, and O. Benson

Appl. Phys. Lett. 86, 091911 (2005); http://dx.doi.org/10.1063/1.1869544 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2005

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We have grown InP quantum dots in GaInP by gas-source molecular-beam epitaxy on sharp tips etched out of a GaAs substrate. The growth parameters were optimized to produce single quantum dots on the tips, predominantly at the edges. Intensity correlation measurements of the fluorescence from single dots on these tips reveal antibunched photon emision. We propose to use these tip structures with stable single photon emitters at their apex as active probes for further controlled experiments in quantum and nano-optics.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Correlation between the crystalline environment and optical property of Mn2+ ions in ZnGa2O4: Mn2+ phosphor

Jong Su Kim, Jin Su Kim, Tae Wan Kim, Sun Myung Kim, and Hong Lee Park

Appl. Phys. Lett. 86, 091912 (2005); http://dx.doi.org/10.1063/1.1869550 (3 pages) | Cited 22 times

Online Publication Date: 25 February 2005

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Sol-gel-driven ZnGa2O4:Mn2+ phosphors are annealed at various temperatures. As an increase of the annealing temperature of as-grown ZnGa2O4:Mn2+ phosphors, their lattice constants and crystallinities are increased. The resonance signal intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased as the annealing temperature is increased. The decay curves are well fitted with two simple exponential decay functions indicating the existence of two origins. Liquid nitrogen-temperature emission spectra show two emission peaks suggesting that they originate from Mn2+ ions on Td and on Oh sites. The emission intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased. The variation of the optical characteristics agrees with the concentration of Mn2+ ions at Td site and its site environment.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
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)
78.55.Hx Other solid inorganic materials
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
81.40.Gh Other heat and thermomechanical treatments
61.66.Fn Inorganic compounds
61.72.S- Impurities in crystals
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Photoinduced generation of electron anions in H-doped nanoporous oxide 12CaO∙7Al2O3: Toward an optically controlled formation of electrides

Peter V. Sushko, Alexander L. Shluger, Katsuro Hayashi, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 86, 092101 (2005); http://dx.doi.org/10.1063/1.1871359 (3 pages) | Cited 12 times

Online Publication Date: 23 February 2005

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We suggest, on the basis of detailed ab initio calculations of both ground and photoexcited states of H-doped 12CaO∙7Al2O3 (C12A7:H), that stable high-conductivity regions can be optically generated in this insulating system. Each H− ion in C12A7:H can, under photoirradiation at 3.8–4.5 eV, produce up to two electrons and a proton that binds to the lattice network and forms OH−. Mobile electrons play a role of anions in this system. They move over subnanosized cages of the C12A7 lattice via polaron hopping. The insulating state is reversibly restored upon heating to 300 °C.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.38.-k Polarons and electron-phonon interactions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Strongly localized exciton luminescence in Cr-doped GaN

S. Shanthi, M. Hashimoto, Y. K. Zhou, S. Kimura, S. Emura, S. Hasegawa, N. Hasuike, H. Harima, and H. Asahi

Appl. Phys. Lett. 86, 092102 (2005); http://dx.doi.org/10.1063/1.1871365 (3 pages) | Cited 6 times

Online Publication Date: 23 February 2005

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Low-temperature photoluminescence spectrum of the transition metal Cr-doped GaN (GaCrN) shows unusual high-intensity emission lines at 3.365 and 3.311 eV. The spectrum also contains a weak neutral donor bound excitonic transition of wurtzite GaN at 3.47 eV, free excitonic transition of GaCrN at 3.29 eV, and two low-intensity lines at 3.24 and 3.17 eV. From our investigations, we attribute these high-intensity lines to the stacking faults which can bind excitons and are due to the coexistence of wurtzite and zinc blende phases of GaN. The 3.24 and 3.17 eV lines are interpreted as phonon replica lines of the 3.31 eV emission line.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.66.Fd III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
78.55.Cr III-V semiconductors
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
61.72.Nn Stacking faults and other planar or extended defects
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Effect of electrical bias on metastability in hydrogenated nanocrystalline silicon solar cells

Guozhen Yue, Baojie Yan, Jeffrey Yang, and Subhendu Guha

Appl. Phys. Lett. 86, 092103 (2005); http://dx.doi.org/10.1063/1.1872212 (3 pages) | Cited 11 times

Online Publication Date: 23 February 2005

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The effect of electrical bias on metastability in hydrogenated nanocrystalline silicon (nc-Si:H) solar cells is studied. We find that forward bias current injection in the dark does not cause any degradation in nc-Si:H solar cells, while light soaking under reverse bias enhances the light-induced degradation in the cell performance. These phenomena are contrary to those found in hydrogenated amorphous silicon solar cells. We argue that the forward injected carriers mainly transport through the nanocrystallites where carrier recombination does not create metastable defects. The increased degradation under reverse bias is explained in terms of the heterogeneity of the material structure.
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84.60.Jt Photoelectric conversion
85.30.-z Semiconductor devices

Magnetocapacitance probing of the many-particle states in InAs dots

Oliver S. Wibbelhoff, Axel Lorke, Dirk Reuter, and Andreas D. Wieck

Appl. Phys. Lett. 86, 092104 (2005); http://dx.doi.org/10.1063/1.1872219 (3 pages) | Cited 17 times

Online Publication Date: 23 February 2005

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We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasiparticle wave functions in momentum space for one to two electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high-energy orbitals exhibit signatures of anisotropic confinement and correlation effects.
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81.16.Dn Self-assembly
75.75.-c Magnetic properties of nanostructures
73.21.La Quantum dots
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Thickness scaling of the space-charge-limited current in poly(p-phenylene vinylene)

P. W. M. Blom, C. Tanase, D. M. de Leeuw, and R. Coehoorn

Appl. Phys. Lett. 86, 092105 (2005); http://dx.doi.org/10.1063/1.1868865 (3 pages) | Cited 38 times

Online Publication Date: 23 February 2005

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Charge transport in light-emitting diodes (LEDs) based on a poly(p-phenylene vinylene) (PPV) derivative is investigated as a function of sample thickness. Via the thickness dependence, the contributions from the electric field and charge carrier density to the mobility in space-charge-limited (SCL) diodes can be disentangled. It is demonstrated that a field-dependent mobility weakens the thickness dependence of the SCL current, whereas a carrier-density-dependent mobility gives rise to an enhanced thickness dependence. The enhanced thickness dependence of the experimental SCL current in PPV is in agreement with the predictions using a density-dependent mobility only. This observation confirms that in PPV-based LEDs, the hole transport is dominated by filling of the localized states.
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85.60.Jb Light-emitting devices
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
72.20.Fr Low-field transport and mobility; piezoresistance

Spectroscopic characterization of 1.3 μm GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy

H. D. Sun, A. H. Clark, S. Calvez, M. D. Dawson, Y. N. Qiu, J. M. Rorison, K. S. Kim, T. Kim, and Y. J. Park

Appl. Phys. Lett. 86, 092106 (2005); http://dx.doi.org/10.1063/1.1868866 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2005

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We report optical studies of high-quality 1.3 μm strain-compensated GaInNAs/GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum.
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78.67.De Quantum wells
73.21.Fg Quantum wells
68.65.Fg Quantum wells
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.20.Fz Weak or Anderson localization

Ti gate compatible with atomic-layer-deposited HfO2 for n-type metal-oxide-semiconductor devices

Hyundoek Yang, Yunik Son, Sungkwon Baek, Hyunsang Hwang, Hajin Lim, and Hyung-Seok Jung

Appl. Phys. Lett. 86, 092107 (2005); http://dx.doi.org/10.1063/1.1871362 (3 pages) | Cited 18 times

Online Publication Date: 24 February 2005

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The electrical characteristics were evaluated for the metal-oxide-semiconductor (MOS) devices with Ti and Pt gates on the atomic-layer-deposited (ALD) HfO2. The equivalent oxide thickness (EOT) of the Ti gate is shown to be nearly the same as that of the Pt gate, which means that a negligible chemical reaction occurs between the gate and dielectric. The values of the effective metal work function (Φm,eff), extracted from the conventional relations of flatband voltage versus EOT, were ∼ 4.2 eV for Ti and ∼ 5.4 eV for Pt, respectively. However, somewhat higher values of Φm,eff were extracted by considering the existence of an interfacial layer and the high negative charge at an interface between HfO2 and interfacial layer. The exact values of Φm,eff were ∼ 4.37 eV for Ti and ∼ 5.51 eV for Pt, respectively. Therefore, the Ti gate is compatible with ALD-HfO2 and can be a candidate for n-type MOS devices.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions

Electrical and optical properties of Mg-doped Al0.7Ga0.3N alloys

M. L. Nakarmi, K. H. Kim, M. Khizar, Z. Y. Fan, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 86, 092108 (2005); http://dx.doi.org/10.1063/1.1879098 (3 pages) | Cited 24 times

Online Publication Date: 25 February 2005

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Mg-doped Al0.7Ga0.3N epilayers ( ∼ 1 μm) were grown on an AlN/sapphire template by metalorganic chemical vapor deposition and the electrical and optical properties of these epilayers were studied. For optimized Mg-doped Al0.7Ga0.3N epilayers, we have obtained a resistivity around 105 Ω cm at room temperature and confirmed p-type conduction at elevated temperatures(>700 K) with a resistivity of about 40 Ω cm at 800 K. From the temperature dependent Hall effect measurement, the activation energy of Mg acceptor is found to be around 400 meV for Al0.7Ga0.3N alloy. The optimized Mg-doped Al0.7Ga0.3N epilayers have been incorporated into the deep-ultraviolet (UV) (λ<300 nm) light-emitting diode (LED) structures as an electron blocking layer. An enhancement in the performance of the UV LEDs was obtained. LEDs with peak emission wavelengths at 280 nm were fabricated with a circular geometry (300 μm disk diameter). Output power reached 0.35 mW at 20 mA and 1.1 mW at 150 mA dc current. The importance of Mg-doped Al0.7Ga0.3N alloys to suppress the long-wavelength emission components in deep-UV LEDs and the fundamental limit for achieving p-type Al-rich AlGaN alloys are also discussed.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Fi Electroluminescence
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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Nucleation and growth processes of α-Fe nanocrystals in amorphous NdFeBCoDy: In situ x-ray diffraction studies

W. Li, X. H. Li, H. Y. Sun, J. W. Zhang, and X. Y. Zhang

Appl. Phys. Lett. 86, 092501 (2005); http://dx.doi.org/10.1063/1.1871338 (3 pages) | Cited 6 times

Online Publication Date: 23 February 2005

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For a detailed understanding of formation processes of nanocrystals in an amorphous matrix, the study of crystal nucleation and growth processes is of basic interest. In the present study, these processes of α-Fe nanocrystals in amorphous NdFeCoDyB have been studied separately by employing in situ high-temperature x-ray diffraction measurements. A small growth activation energy Eg = (1.8±0.2)eV was determined from the isothermal time dependence of the grain size of α-Fe crystals. By these data together with the nucleation activation energy En = (3.0±0.1)eV, a coarse grain size for the α-Fe phase in the α-Fe/Nd2Fe14B nanocomposites developed from amorphous NdFeBCoDy can be understood.
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75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
64.70.K- Solid-solid transitions
75.50.Kj Amorphous and quasicrystalline magnetic materials
64.60.Q- Nucleation
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

230% room-temperature magnetoresistance in CoFeB/MgO/CoFeB magnetic tunnel junctions

David D. Djayaprawira, Koji Tsunekawa, Motonobu Nagai, Hiroki Maehara, Shinji Yamagata, Naoki Watanabe, Shinji Yuasa, Yoshishige Suzuki, and Koji Ando

Appl. Phys. Lett. 86, 092502 (2005); http://dx.doi.org/10.1063/1.1871344 (3 pages) | Cited 286 times

Online Publication Date: 23 February 2005

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Magnetoresistance (MR) ratio up to 230% at room temperature (294% at 20 K) has been observed in spin-valve-type magnetic tunnel junctions (MTJs) using MgO tunnel barrier layer fabricated on thermally oxidized Si substrates. We found that such a high MR ratio can be obtained when the MgO barrier layer was sandwiched with amorphous CoFeB ferromagnetic electrodes. Microstructure analysis revealed that the MgO layer with (001) fiber texture was realized when the MgO layer was grown on amorphous CoFeB rather than on polycrystalline CoFe. Since there have been no theoretical studies on the MTJs with a crystalline tunnel barrier and amorphous electrodes, the detailed mechanism of the huge tunneling MR effect observed in this study is not clear at the present stage. Nevertheless, the present work is of paramount importance in realizing high-density magnetoresistive random access memory and read head for ultra high-density hard-disk drives into practical use.
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.65.Ac Multilayers
75.47.Np Metals and alloys
75.75.-c Magnetic properties of nanostructures

Flux pinning enhancement in melt-processed YBa2Cu3O7 with extended nanodefects

L. Shlyk, G. Krabbes, G. Fuchs, and K. Nenkov

Appl. Phys. Lett. 86, 092503 (2005); http://dx.doi.org/10.1063/1.1874307 (3 pages) | Cited 9 times

Online Publication Date: 23 February 2005

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Melt-processed YBa2Cu3O7 (YBCO), containing a random array of Y–Ba–Cu–Ir–O nanostructures (about 20–150 nm in diameter and several μm in length) has been grown. The pinning efficiency of the resulting YBCO nanocomposite is superior to Li-doped or undoped melt-processed YBCO at higher magnetic fields. At 77 K, the irreversibility field increases more than 8 T in the presence of the extended nanodefects. The increase of the effective activation energy of the YBCO nanocomposite is nearly twice that of the Li-doped material.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.10.Fq Growth from melts; zone melting and refining
74.62.Dh Effects of crystal defects, doping and substitution

Current-induced metastable resistive state in epitaxial thin films of La1−xCaxMnO3 (x = 0.2, 0.3)

J. Gao and F. X. Hu

Appl. Phys. Lett. 86, 092504 (2005); http://dx.doi.org/10.1063/1.1870128 (3 pages) | Cited 34 times

Online Publication Date: 24 February 2005

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The influence of a transport dc current on electric resistivity has been investigated in epitaxial thin films of La1−xCaxMnO3 (x = 0.2, 0.3). A most prominent finding is the appearance of a remarkable resistive peak at temperatures well below the Curie temperature Tc. Such a resistive peak is developed when the dc current over a critical value was applied in a temperature cycling from 300 to 10 K. The resistance peak turns out to be extremely sensitive to a weak current. Even a very small current could greatly depress the height of the peak. Such a current-induced state with high resistivity is metastable compared to the pristine state. The stability of the induced state has been also studied.
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75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Nanoscopic netted structure of compositional modulation in (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors

A. Hu, I. Hirabayashi, M. Winter, M. R. Koblischka, U. Hartmann, and H. Zhou

Appl. Phys. Lett. 86, 092505 (2005); http://dx.doi.org/10.1063/1.1871348 (3 pages) | Cited 21 times

Online Publication Date: 24 February 2005

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We report a nanoscaled crisscross network in high-quality melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors investigated with atomic force microscopy (AFM) and transmission electron microscopy. In the ten-micrometer scale, such a net was unveiled as a consequence of crossing annular stripes originating from ordering compositional modulation. The AFM topographic images further displayed that this compositional stripe result in a surface modulation with a few-nanometer wavelength and roughness. The forming mechanism of this compositional stripe and its role as strong δTc-type pinning defects were discussed in the context of rare earth∕Ba oscillation around the stoichiometric ratio and the spatial fluctuation of local Tc values.
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74.72.-h Cuprate superconductors
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.62.Dh Effects of crystal defects, doping and substitution
74.78.Na Mesoscopic and nanoscale systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
74.40.-n Fluctuation phenomena
61.66.Bi Elemental solids
61.66.Dk Alloys

Failure analysis of high temperature superconducting films at high microwave power using microsecond time domain measurements

A. J. Purnell, L. F. Cohen, L. Hao, and J. C. Gallop

Appl. Phys. Lett. 86, 092506 (2005); http://dx.doi.org/10.1063/1.1868076 (3 pages)

Online Publication Date: 24 February 2005

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A generic characteristic of resonators can be exploited to determine whether thermal or magnetic mechanisms dominate the failure of high quality, high temperature superconducting thin films at high microwave power. We demonstrate that a transient response can be superimposed on a pulse wave form with a frequency equal to the difference between the driving frequency and the resonant frequency of the resonator. When a thermal failure mechanism dominates, the resonant frequency depends on the temporal separation between pulses. This is in marked contrast to a magnetic failure mechanism, which is insensitive to the pulse separation. For poor quality films the technique cannot differentiate between vortices in weak links and local heating at weak links that happen on a short time scale. We discuss the application of the technique to noncontact microwave bolometry.
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85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Large upper critical field and irreversibility field in MgB2 wires with SiC additions

M. D. Sumption, M. Bhatia, M. Rindfleisch, M. Tomsic, S. Soltanian, S. X. Dou, and E. W. Collings

Appl. Phys. Lett. 86, 092507 (2005); http://dx.doi.org/10.1063/1.1872210 (3 pages) | Cited 77 times

Online Publication Date: 25 February 2005

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Resistive transition measurements are reported for MgB2 strands with SiC dopants. The starting Mg powders were 325 mesh 99.9% pure, and the B powders were amorphous, 99.9% pure, and at a typical size of 1–2 μm. The SiC was added as 10 mol % of SiC to 90 mol % of binary MgB2 [(MgB2)0.9(SiC)0.1]. Three different SiC powders were used; the average particle sizes were 200 nm, 30 nm, and 15 nm. The strands were heat treated for times ranging from 5 to 30 min at temperatures from 675 °C to 900 °C. Strands with 200 nm size SiC additions had μ0Hirr and Bc2 which maximized at 25.4 T and 29.7 T after heating at 800 °C for 30 min. The highest values were seen for a strand with 15 nm SiC heated at 725 °C for 30 min which had a μ0Hirr of 29 T and a Bc2 higher than 33 T.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.71.Mn Superconducting wires, fibers, and tapes
74.25.F- Transport properties
74.25.Op Mixed states, critical fields, and surface sheaths
81.40.Gh Other heat and thermomechanical treatments
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Effects of WO3 dopant on the structure and electrical properties of Pb0.97La0.03(Zr0.52Ti0.48)O3 thin films

Santiranjan Shannigrahi and Kui Yao

Appl. Phys. Lett. 86, 092901 (2005); http://dx.doi.org/10.1063/1.1870125 (3 pages) | Cited 16 times

Online Publication Date: 23 February 2005

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Pb0.97La0.03(Zr0.52Ti0.48)O3+xWO3 at % (x = 0, 0.2, 0.5, 1, and 2) (PLWZT) thin films are deposited on Pt–Ti–SiO2–Si substrates using a sol-gel process. We demonstrate that WO3 dopant plays a significant role on the structure and electrical properties of the PLWZT films. X-ray diffraction (XRD) analyses show that the PLWZT films undergo a dramatic tetragonal–to–cubic crystalline phase transformation with a small amount of WO3 additives. X-ray photoelectron spectroscopy (XPS) study shows that the chemical state of W changes with varying concentration of WO3 in the films. Moreover, PLWZT films with a small amount of WO3 doping (0.2 at %) show a decreased conductivity with an improved remnant polarization value of 30 μC/cm2. In addition, compared to the base (PLZT) film, such doping concentration also leads to significantly improved fatigue characteristics. A defect chemistry mechanism indicating the reduction of oxygen vacancies by the substitution of W for Ti at different doping concentrations has been proposed to explain the observed experimental results.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
64.70.K- Solid-solid transitions
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification

Enhanced tunability and phase transition studies in compositionally varying lead magnesium niobate–lead titanate multilayered thin films

R. Ranjith, Apurba Laha, and S. B. Krupanidhi

Appl. Phys. Lett. 86, 092902 (2005); http://dx.doi.org/10.1063/1.1851611 (3 pages) | Cited 11 times

Online Publication Date: 23 February 2005

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Multilayers of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 thin films were prepared with a compositional variation of PbTiO3 on each layer across the film by pulsed laser ablation technique. The fabricated films were found to possess an enhanced diffusiveness in the dielectric phase transition, which actually seemed to be an envelope of the phase transition of the individual layer relaxor ferroelectrics of a particular composition. They also showed a very high nonlinear dielectric response and hence a high tunability about 70%, an increase of about 40% than that observed for single layer composition. This increase in tunability has been attributed to the lattice strain and the artificially enhanced chemical heterogeneity of the system. These multilayer films also showed a slim hysteresis loop characteristic with a saturation and remnant polarization of 20 and 6 μC/cm2, respectively.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.65.Ac Multilayers
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Effective pyroelectric response of compositionally graded ferroelectric materials

S. Zhong, S. P. Alpay, Z.-G. Ban, and J. V. Mantese

Appl. Phys. Lett. 86, 092903 (2005); http://dx.doi.org/10.1063/1.1866505 (3 pages) | Cited 18 times

Online Publication Date: 23 February 2005

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A thermodynamic theory is used to determine the effective pyroelectric coefficients of polarization graded ferroelectrics, with values in excess of 0.1 μC/cm2 °C are predicted for various barium strontium titanate thin films. Maximum values closer to 0.4 μC/cm2 °C are obtained for a 1 μm thick material—compositionally graded between pure barium titanate and one that has barium to strontium in the ratio of 75:25.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.Nq Composition and phase identification
77.70.+a Pyroelectric and electrocaloric effects
65.40.G- Other thermodynamical quantities
77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
65.40.De Thermal expansion; thermomechanical effects

Stress effects on ferroelectric and fatigue properties of Nd- and La-doped Bi4Ti3O12 thin films

Xiumei Wu, Xiaomei Lu, Aiping Chen, Yuan Yin, Jun Ma, Wei Li, Yi Kan, Dong Qian, and Jinsong Zhu

Appl. Phys. Lett. 86, 092904 (2005); http://dx.doi.org/10.1063/1.1873063 (3 pages) | Cited 9 times

Online Publication Date: 24 February 2005

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The ferroelectric properties of Bi3.15Nd0.85Ti3O12 and Bi3.25La0.75Ti3O12 thin films under applied uniaxial stress were investigated. It was observed in both films that the remnant polarization (Pr) increased with tensile stress, while it decreased with compressive stress. On the contrary, the coercive field (Ec) decreased with the stress changing from maximum compression to maximum tension. Fatigue behavior of the films was improved under either compressive or tensile stress compared with zero stress (free state). These results can be well explained in the scenario of domain reorientation under stress; however, the polarization-strain coupling mechanism could not be simply ruled out.
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77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films

Polarization switching kinetics of epitaxial Pb(Zr0.4Ti0.6)O3 thin films

Y. W. So, D. J. Kim, T. W. Noh, Jong-Gul Yoon, and T. K. Song

Appl. Phys. Lett. 86, 092905 (2005); http://dx.doi.org/10.1063/1.1870126 (3 pages) | Cited 52 times

Online Publication Date: 25 February 2005

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The polarization switching kinetics of epitaxial Pb(Zr0.4Ti0.6)O3 thin films were investigated by measuring write pulse-width dependences of switched polarization ΔP(t) under various applied electric fields. It was found that ΔP(t) follows the predictions of the Kolmogorov–Avrami–Ishibashi model quite well. However, the detailed behaviors of ΔP(t) were different for low and high electric field regions, which separated out around 220 kV/cm. The coercive field also showed different frequency dependences depending on the region. These differences were attributed to changes in the polarization switching kinetics. A possible origin of the switching kinetics changes is also discussed.
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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.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis

Variations of differential capacitance in SrBi2Ta2O9 ferroelectric films induced by photoperturbation

Ching-Chich Leu, Chao-Hsin Chien, Chih-Yuan Chen, Mao-Nan Chang, Fan-Yi Hsu, Chen-Ti Hu, and Yung-Fu Chen

Appl. Phys. Lett. 86, 092906 (2005); http://dx.doi.org/10.1063/1.1879089 (3 pages) | Cited 5 times

Online Publication Date: 25 February 2005

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In this letter, we demonstrated the impact of illumination on the differential capacitance variation of a strontium bismuth tantalite (SBT) capacitor during scanning capacitance microscopy measurements. It was found that illumination with a stray light of laser in an atomic force microscope could perturb the dC/dV signals of the samples. We attribute this phenomenon to the generation of free carriers by the photon absorptions via defect traps in the SBT thin film. Therefore, this present work suggests that the effect of laser illumination must be carefully taken into consideration whenever a field-sensitive technique is employed to analyze the properties of a ferroelectric material.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
73.61.Ng Insulators
77.55.-g Dielectric thin films
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.37.Ps Atomic force microscopy (AFM)
68.55.-a Thin film structure and morphology
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