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23 Jul 2001

Volume 79, Issue 4, pp. 449-553

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Highly efficient electroluminescent materials based on fluorinated organometallic iridium compounds

Y. Wang, N. Herron, V. V. Grushin, D. LeCloux, and V. Petrov

Appl. Phys. Lett. 79, 449 (2001); http://dx.doi.org/10.1063/1.1384903 (3 pages) | Cited 109 times

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We report a class of highly efficient electroluminescent materials based on fluorinated iridium compounds. Using aluminum as the cathode, a device, using fac-tris[5-fluoro-2(5-trifluoromethyl-2-pyridinyl)phenyl-C,N]iridium (Ir-2h) as the luminescent layer, displayed intense electroluminescence at 525 nm with an efficiency of 20 cd/A and a maximum radiance of 4800 cd/m2. Differing from the previously reported Ir(ppy)3, Ir-2h can be used in the undiluted form without the use of a charge-transporting host. This indicates that Ir-2h by itself has good enough charge-transporting properties. Photoluminescence studies at room temperature and 77 K revealed that electroluminescence originates from the metal-to-ligand charge transfer state with a quantum yield of 0.56 for Ir-2h and 0.5 for Ir(ppy)3 in toluene at room temperature. In the thin-film form, photoluminescence quantum yield of Ir-2h is a factor of 10 greater than that of Ir(ppy)3 due to the larger self-quenching effect of Ir(ppy)3. © 2001 American Institute of Physics.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds

High-repetition-rate polymeric solid-state dye lasers pumped by a copper-vapor laser

A. Costela, I. García-Moreno, R. Sastre, D. W. Coutts, and C. E. Webb

Appl. Phys. Lett. 79, 452 (2001); http://dx.doi.org/10.1063/1.1385585 (3 pages) | Cited 11 times

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We report on the laser action of pyrromethene 567 incorporated into polymeric matrices and pumped longitudinally with the green line of a copper-vapor laser. When the dye was dissolved in a copolymer of methyl methacrylate and pentaerythritol triacrylate, 290 mW average power at 1 kHz (37% lasing efficiency) was obtained. The laser output decreased to 150 mW after 30 min irradiation time (1.8×106 shots) and to 32 mW after 70 min of operation (4.2×106 shots). Output power of up to 1 W at 6.2 kHz was obtained for short periods of time. Polymeric matrices incorporating rhodamine 6G were also studied. © 2001 American Institute of Physics.
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42.55.Mv Dye lasers

Infrared absorption of an In0.2Ga0.8As/GaAs quantum-well infrared photodetector employing a p–n–p camel diode structure

Heesoo Son, Jinsung Park, Songcheol Hong, Sung-June Jo, and Jong-In Song

Appl. Phys. Lett. 79, 455 (2001); http://dx.doi.org/10.1063/1.1388874 (3 pages)

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Far-infrared absorption of an In0.2Ga0.8As/GaAs multiple-quantum-well infrared photodetector employing a p–n–p camel diode structure is studied. The detector showed a photocurrent response to normal incident light at approximately 3 μm due to the intersubband hole transition, which is attributed to the strong hole–band mixing of the strained multiple quantum well. Application of the camel diode structure to the photodetector substantially reduced the dark hole current, resulting in an improved detectivity. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells

Ultraviolet single-frequency pulses with high average power using frequency-converted passively Q-switched quasimonolithic Nd:yttrium–aluminum–garnet ring lasers

S. Spiekermann, M. Bode, I. Freitag, and F. Laurell

Appl. Phys. Lett. 79, 458 (2001); http://dx.doi.org/10.1063/1.1388028 (3 pages) | Cited 2 times

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We demonstrate a compact ultraviolet light source based on frequency-converted diode-pumped passively Q-switched miniature Nd:yttrium–aluminum–garnet (YAG) ring lasers. A unique pulse-to-pulse stability in single-frequency operation is obtained by diffusion-bonding the Nd:YAG crystal with the Cr4+:YAG saturable absorber crystal to form an all-solid-state quasimonolithic ring laser cavity. Amplified in a longitudinally pumped Nd:vanadate (YVO4) crystal and single-pass frequency quadrupled in periodically poled potassium titanyl phosphate and barium borate crystals, an average output power of 485 mW at 266 nm with 25 μJ pulse energy is achieved with an overall efficiency of 3.3% with respect to the diode pump power. © 2001 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.72.Bj Visible and ultraviolet sources

Optical control of an integrated interferometer using a photochromic polymer

A. Rodríguez, G. Vitrant, P. A. Chollet, and F. Kajzar

Appl. Phys. Lett. 79, 461 (2001); http://dx.doi.org/10.1063/1.1384002 (3 pages) | Cited 10 times

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An integrated optical interferometer has been fabricated using ion exchange technology in glass. Using a photochromic polymer, we show that it is possible to reversibly modulate the phase of the guided wave with an optical control beam. This constitutes a demonstrator of an optically controlled integrated optical device. © 2001 American Institute of Physics.
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42.82.Gw Other integrated-optical elements and systems
07.60.Ly Interferometers
42.70.Jk Polymers and organics
42.79.Hp Optical processors, correlators, and modulators
42.70.Gi Light-sensitive materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.66.Qn Polymers; organic compounds

Zero-point oscillations in the vicinity of atoms

Alexander S. Shumovsky

Appl. Phys. Lett. 79, 464 (2001); http://dx.doi.org/10.1063/1.1384006 (3 pages) | Cited 2 times

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It is shown that the vacuum fluctuations of an electromagnetic field are concentrated near atoms. This effect worsens the quantum limit of precision of the measurements in atomic systems. © 2001 American Institute of Physics.
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03.65.Ta Foundations of quantum mechanics; measurement theory
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
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Ion-irradiation-induced mixing, interface broadening and period dilation in Pt/C multilayers

S. K. Ghose, D. K. Goswami, B. Rout, B. N. Dev, G. Kuri, and G. Materlik

Appl. Phys. Lett. 79, 467 (2001); http://dx.doi.org/10.1063/1.1384901 (3 pages) | Cited 9 times

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Pt/C multilayers of nanometric dimension have been irradiated with 2-MeV-Au ions to a fluence of 1×1014 ions/cm2 and analyzed by x-ray reflectivity and x-ray standing wave measurements. The multilayer period has expanded by ∼9%, the expansion of the Pt layers being larger than that of the C layers. Ion-induced displacement of atoms across the interfaces led to an increased interface roughness and an increase of 2 at. % Pt in C layers. Monte Carlo simulations for ion-induced atomic displacement have been used to explain the observed effects. © 2001 American Institute of Physics.
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68.65.Ac Multilayers
61.80.Jh Ion radiation effects
64.75.-g Phase equilibria
68.35.Ct Interface structure and roughness
68.49.Uv X-ray standing waves
61.82.Rx Nanocrystalline materials

Single-crystalline rocksalt CdO layers grown on GaAs (001) substrates by metalorganic molecular-beam epitaxy

A. B. M. A. Ashrafi, H. Kumano, I. Suemune, Y.-W. Ok, and T.-Y. Seong

Appl. Phys. Lett. 79, 470 (2001); http://dx.doi.org/10.1063/1.1387258 (3 pages) | Cited 11 times

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In this letter, we report the growth of single-crystalline rocksalt CdO layers on (001) GaAs substrates using ZnS buffer layers. The growth processes of CdO layers were studied by reflection high-energy electron diffraction (RHEED), and the grown CdO layers were evaluated with atomic force microscopy (AFM), and x-ray diffraction (XRD) measurements. After an initial growth delay, the formation of polycrystalline CdO was observed in RHEED measurements during the initial growth of very thin CdO layers. With the increase of the CdO layer thicknesses, streaky RHEED patterns were observed, which indicate the formation of single-crystalline cubic-phase CdO layers. Surface morphology of the CdO layers observed by AFM was atomically flat with root-mean-square roughness of ∼ 1 nm. The crystalline structures were elucidated from XRD measurements by the determination of the lattice constant to be 4.686±0.001 Å, indicating the single-phase rocksalt CdO structure. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Gh Oxide surfaces

Determination of the dispersion of the index of refraction and the elastic moduli for molecular-beam-epitaxy-grown Zn1−xBexSe alloys

F. C. Peiris, U. Bindley, J. K. Furdyna, Hyunjung Kim, A. K. Ramdas, and M. Grimsditch

Appl. Phys. Lett. 79, 473 (2001); http://dx.doi.org/10.1063/1.1379356 (3 pages) | Cited 7 times

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The prism coupler technique, together with reflectivity channeled spectra, were used to determine the dispersion of the indices of refraction for a series of ternary alloys of Zn1−xBexSe grown by molecular-beam epitaxy on GaAs substrates. The measurements covered the wavelength range of 400–1300 nm, and the entire Be concentration range, from x = 0 to 1.00. The availability of accurate values of the index-of-refraction then enabled us to determine the elastic moduli c11 for the Zn1−xBexSe and its dependence on the Be concentration x from frequency shifts in Brillouin scattering spectra observed on the epilayers of these ternary alloys. The c11 results clearly indicate that the bonding in Zn1−xBexSe becomes more robust as the Be concentration increases. © 2001 American Institute of Physics.
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78.66.Hf II-VI semiconductors
62.20.D- Elasticity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Fabrication of strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors on Si substrates

K. Kawaguchi, S. Koh, Y. Shiraki, and J. Zhang

Appl. Phys. Lett. 79, 476 (2001); http://dx.doi.org/10.1063/1.1385196 (3 pages) | Cited 4 times

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Strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors (DBRs) which were designed to overcome the limitation of the number of pairs originating from the strain accumulation were fabricated. Raman spectra of Si0.73Ge0.27/Si DBRs with 11 and 25 mirror pairs showed that SiGe and Si layers were under compressive and tensile strain on SiGe virtual substrates as designed. A record reflectivity of 80% was achieved at 1.44 μm in SiGe/Si DBRs with 25 pairs. The surface roughness of the 25 pair sample, however, was increased to about 46 nm compared with 6.3 nm of the 11 pair sample. © 2001 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.67.De Quantum wells
68.65.Ac Multilayers
42.79.Wc Optical coatings
42.15.Eq Optical system design
78.30.Hv Other nonmetallic inorganics

Ti3SiC2 and ice

M. W. Barsoum, M. Radovic, P. Finkel, and T. El-Raghy

Appl. Phys. Lett. 79, 479 (2001); http://dx.doi.org/10.1063/1.1384479 (3 pages) | Cited 25 times

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Despite vast differences in their other properties, the responses of Ti3SiC2 and ice to stress are quite similar in that they are quite strain-rate sensitive; if loaded rapidly, both are brittle, but if loaded slowly they are quite plastic. This stems from the fact that both are plastically very anisotropic; deformation occurs overwhelmingly, if not exclusively, by slip along basal planes. In both cases, stress concentrations and the rate at which they are relaxed dictate the nature of the mechanical response. In the brittle regime, microcracks and their linkage play a dominant role in both cases. © 2001 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Mm Grain and twin boundaries

Direct correlation between microstructure and mechanical tensile properties in Pb-free solders and eutectic SnPb solder for flip chip technology

J. W. Jang, A. P. De Silva, T. Y. Lee, J. K. Lin, and D. R. Frear

Appl. Phys. Lett. 79, 482 (2001); http://dx.doi.org/10.1063/1.1388160 (3 pages) | Cited 11 times

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The relationship between the microstructure and the mechanical tensile properties of lead-free solders and eutectic SnPb solders is presented for flip chip scale interconnects. Eutectic Sn–37Pb and Sn–0.7Cu solder (in wt %) exhibited a ductile fracture after tensile testing. Eutectic Sn–3.5Ag solder (in wt %) had greater strength and exhibited a brittle fracture at the interface. The different fracture behavior of the lead-free solders was attributed to the grain size and configuration of the intermetallics. Minor additions of alloying elements to the high Sn lead-free solder dramatically affected the microstructure and mechanical properties. © 2001 American Institute of Physics.
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81.20.Vj Joining; welding
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.-y Defects and impurities in crystals; microstructure
81.30.Bx Phase diagrams of metals, alloys, and oxides
62.20.M- Structural failure of materials

Local structure of amorphous Zr70Pd30 alloy studied by electron diffraction

T. Takagi, T. Ohkubo, Y. Hirotsu, B. S. Murty, K. Hono, and D. Shindo

Appl. Phys. Lett. 79, 485 (2001); http://dx.doi.org/10.1063/1.1383055 (3 pages) | Cited 55 times

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The structures of melt-spun, and subsequently annealed, Zr70Pd30 alloys, which form a nanosized icosahedral quasicrystalline phase during the primary crystallization of the amorphous phase, have been investigated by means of electron-diffraction pair-distribution-function (PDF) analysis. The PDF analysis for this alloy was performed by precise measurements of elastic halo-electron-diffraction intensities. Possible structure models for as-quenched and annealed amorphous structures were constructed with the help of reverse Monte Carlo simulations. In order to obtain the local atomic structures, the Voronoi-polyhedra analysis was performed. A considerable number of icosahedral clusters with Zr atoms in the center are present in the simulated structure of the as-quenched state, and the number of the clusters increases by annealing. © 2001 American Institute of Physics.
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61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.44.Br Quasicrystals

Visible luminescence from a-SiN films doped with Er and Sm

A. R. Zanatta, C. T. M. Ribeiro, and U. Jahn

Appl. Phys. Lett. 79, 488 (2001); http://dx.doi.org/10.1063/1.1389069 (3 pages) | Cited 18 times

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Relatively strong and narrow red and green light emission has been achieved from amorphous (a-) SiN films independently doped with Er3+ and Sm3+ ions. The films were deposited by cosputtering a Si target partially covered with small pieces of metallic Er (and Sm) in an atmosphere of pure nitrogen. As a consequence of the deposition method and conditions, the films have an amorphous structure, and contents of Er (and Sm) in the low 0.5 at. %. All characterizations were accomplished on as-deposited samples and at room temperature and included: ion-beam analysis (Rutherford backscattering spectrometry and nuclear reaction analysis) and optical techniques (light absorption, Raman scattering, and photoluminescence and cathodoluminescence). A detailed examination of the experimental results allowed the identification of all luminescence features existing in the films. © 2001 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
61.43.Er Other amorphous solids
68.55.-a Thin film structure and morphology
71.55.Jv Disordered structures; amorphous and glassy solids

Optical constants of ice Ih crystal at terahertz frequencies

Chun Zhang, Kwang-Su Lee, X.-C. Zhang, Xing Wei, and Y. R. Shen

Appl. Phys. Lett. 79, 491 (2001); http://dx.doi.org/10.1063/1.1386401 (3 pages) | Cited 9 times

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Terahertz time-domain spectroscopy was used to measure the refractive indices of Ih crystalline ice in the frequency range of 0.25–1.0 THz. With increasing frequency, the real part, n′, of the refractive index increases from 1.787 to 1.793 at 243 K, and the imaginary part, n″, increases from 0.005 to 0.020. The temperature dependence of n′ is less than 0.01%/K and that of n″ is ∼1%/K. Our results connect smoothly to the data of Matsuoka and co-workers [T. Matsuoka, S. Fujita, and S. Mae, J. Appl. Phys. 80, 5884 (1996)] in the microwave range and the data in the far IR range, and can be well described by the existing theoretical models. © 2001 American Institute of Physics.
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78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Low-temperature selective deposition of silicon on silicon nitride by time-modulated disilane flow and formation of silicon narrow wires

Shin Yokoyama, Kenji Ohba, Kensaku Kawamura, Toshiro Kidera, and Anri Nakajima

Appl. Phys. Lett. 79, 494 (2001); http://dx.doi.org/10.1063/1.1387260 (3 pages)

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The low-temperature (410 °C) selective deposition of Si on silicon nitride has been achieved by means of the time-modulated flow of disilane while a very small amount of Si is deposited on SiO2. Very narrow (21 nm width and 28 nm thick) Si wires have been fabricated using the selective deposition. The resistivity of the Si wires fabricated by the selective deposition is much smaller (∼1/5) than that fabricated by the conventional reactive ion etching followed by annealing. This technique will be applicable to the formation of a polycrystalline silicon gate with small resistivity for the high-performance ultrasmall metal–oxide–semiconductor transistors and quantum effect devices. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
73.63.-b Electronic transport in nanoscale materials and structures
73.61.Cw Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization

Greatly enhanced detection sensitivity for carbon, nitrogen, and oxygen in silicon by secondary-ion-mass spectrometry

Hubert Gnaser

Appl. Phys. Lett. 79, 497 (2001); http://dx.doi.org/10.1063/1.1388876 (3 pages) | Cited 1 time

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The detection limits of secondary-ion-mass spectrometry for carbon, nitrogen, and oxygen in silicon are determined and are shown to be as low as about 1×1014 atoms/cm3 for nitrogen and 2×1015 atoms/cm3 for carbon and oxygen. This very high sensitivity is achieved by an analytical approach: to suppress the interference from residual-gas adsorption onto the sputtered surface, the elemental concentrations are extrapolated to a zero contribution from these adsorbed species by an incremental increase of the applied ion-beam erosion rate. © 2001 American Institute of Physics.
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61.72.S- Impurities in crystals
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Dynamical behaviors of GaCl on the GaAs(001) 4×6 surface by pulsed molecular beam scattering

Masafumi Ohashi and Masashi Ozeki

Appl. Phys. Lett. 79, 500 (2001); http://dx.doi.org/10.1063/1.1380394 (3 pages) | Cited 2 times

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We studied dynamical behaviors of gallium chloride (GaCl) on a GaAs(001) 4×6 surface using pulsed molecular beam scattering. The angular distribution of reflected GaCl consists of two parts; inelastic direct scattering contribution and thermal desorption of trapped molecules on the GaAs(001) 4×6 surface. We divided the time of flight spectra of thermally desorbed GaCl into two components with activation energies of 22.0 and 10.5 kcal/mol corresponding to GaCl trapping wells. These wells were associated with two comparatively large domains on the GaAs(001) 4×6 surface. The relatively large activation energy is responsible for the strong dipole-electrostatic interaction between GaCl, which has a large dipole moment, and the ionic GaAs crystal. © 2001 American Institute of Physics.
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68.49.Df Molecule scattering from surfaces (energy transfer, resonances, trapping)
81.05.Ea III-V semiconductors
68.43.Vx Thermal desorption
34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.43.Mn Adsorption kinetics
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Atomic scale investigations of the Co/Pt(111) interface structure and magnetic properties

D. W. Moon, Y. H. Ha, Y. Park, J.-W. Lee, J. Kim, and S.-C. Shin

Appl. Phys. Lett. 79, 503 (2001); http://dx.doi.org/10.1063/1.1388156 (3 pages) | Cited 5 times

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The interface structure of an ultrathin Co overlayer on a Pt(111) crystal was investigated with atomic-layer resolution medium-energy ion scattering spectroscopy and surface magneto-optical Kerr effect (SMOKE). For a 7 ML Co, interdiffusion begins at 673 K to form a heavily distorted Co–Pt surface alloy layer with little change in SMOKE intensity. However, annealing at 773 K formed a 30 atomic-layer-thick Co–Pt substitutional alloy with 3.7% maximum tensile strain, at which the SMOKE intensity increased more than 200%. The enhancement of the Kerr intensity is discussed with the interface alloy formation. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
78.66.Bz Metals and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Colossal magnetoresistance in doped manganites: A consequence of percolation and phase separation

A. K. Pradhan, Y. Feng, B. K. Roul, and D. R. Sahu

Appl. Phys. Lett. 79, 506 (2001); http://dx.doi.org/10.1063/1.1388158 (3 pages) | Cited 15 times

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We report measurements of the resistivity and magnetization of high-quality melt-processed La0.67Ca0.33MnO3 (LCM) and Sr-doped LCM materials that exhibit a sharp and enhanced metal–insulator transition (TMI) with significant colossal magnetoresistance (CMR) and two competing magnetic phases in the vicinity of TMI. Our results can well be explained using percolation in combination with the phase-separation scenario proposed for CMR. We propose that the spin polarization through grain boundaries and the enhanced grain connectivity between the ferromagnetic domains facilitate better percolation through a junction and filament-like resistor network. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
71.30.+h Metal-insulator transitions and other electronic transitions
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials

Scaling behavior of higher harmonic responses in textured (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tapes

Y. J. Zhang and C. K. Ong

Appl. Phys. Lett. 79, 509 (2001); http://dx.doi.org/10.1063/1.1388155 (3 pages)

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A silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Oy tape was studied in terms of harmonic responses χn = χn′−iχn″ (n = 3, 5, 7) to reveal the angular dependence of its physical properties. In the screening method higher harmonic responses are directly related to the nonlinear voltage–current [E(J)] relation of the sample. Therefore, the effect of the silver sheath on the harmonic measurements can be neglected. We performed measurements of the harmonic responses as a function of applied magnetic field or angle between the magnetic field and the tape plane at various temperatures. The measured data could be scaled onto a single curve by using the three-dimensional scaling relation. The derived anisotropic parameter γ ranged from 5.1 to 5.6 at the measured temperature region. Such a small γ value was attributed to the misalignment of the grains in the tape. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Correlation of power handling capability and intermodulation distortion in YBa2Cu3O7−δ thin films

P. Lahl, R. Wördenweber, and M. Hein

Appl. Phys. Lett. 79, 512 (2001); http://dx.doi.org/10.1063/1.1383272 (3 pages) | Cited 13 times

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The nonlinearity of the microwave properties of coplanar thin-film YBa2Cu3O7−δ resonators are examined by measurements of the degradation of the quality factor QL and the increase of the two-tone third-order intermodulation distortion signal with increasing microwave power. A linear correlation between the data of the characteristic microwave powers, which are obtained for the degradation of QL and the intermodulation signal, is experimentally observed and explained in terms of a theoretical model based solely on well-known expressions for the nonlinear surface resistance. Due to these experimental observations and the theoretical model, we conclude, that the degradation of the resonator Q factor and the generation of intermodulation distortion are determined by the same physical mechanism and that thermal effects can most likely be excluded. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines
72.30.+q High-frequency effects; plasma effects
73.25.+i Surface conductivity and carrier phenomena
74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
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Atomic-scale observation of polarization switching in epitaxial ferroelectric thin films

D. L. Marasco, A. Kazimirov, M. J. Bedzyk, T.-L. Lee, S. K. Streiffer, O. Auciello, and G.-R. Bai

Appl. Phys. Lett. 79, 515 (2001); http://dx.doi.org/10.1063/1.1385349 (3 pages) | Cited 4 times

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The thin-film x-ray standing wave (XSW) technique is used for an atomic-scale study of polarization switching in ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT)/electrode heterostructures grown on SrTiO3(001). The XSW is selectively generated in the PZT by the interference between the incident x-ray wave and the weak (001) Bragg diffracted wave from the film. The XSW excites a fluorescence signal from the Pb ions in the PZT film, that is used to determine their subangström displacements after polarization switching has occurred. This experimental method yields unique information on the underlying atomic configurations for different polarization domain states. © 2001 American Institute of Physics.
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77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.49.Uv X-ray standing waves
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization

Temperature dependence of the ohmic conductivity and activation energy of Pb1+y(Zr0.3Ti0.7)O3 thin films

D. P. Chu, B. M. McGregor, P. Migliorato, C. Durkan, M. E. Welland, K. Hasegawa, and T. Shimoda

Appl. Phys. Lett. 79, 518 (2001); http://dx.doi.org/10.1063/1.1387264 (3 pages) | Cited 3 times

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The ohmic conductivity of the sol–gel derived Pb1+y(Zr0.3Ti0.7)O3 thin films (with the excess lead y = 0.0 to 0.4) are investigated using low frequency small signal ac and dc methods. Its temperature dependence shows two activation energies of 0.26 and 0.12 eV depending on temperature range and excess Pb levels. The former is associated with Pb3+ acceptor centers, while the latter could be due to a different defect level yet to be identified. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
73.50.Fq High-field and nonlinear effects
73.61.Le Other inorganic semiconductors
71.55.Ht Other nonmetals
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Optical transitions and radiative lifetime in GaN/AlN self-organized quantum dots

Aleksey D. Andreev and Eoin P. O’Reilly

Appl. Phys. Lett. 79, 521 (2001); http://dx.doi.org/10.1063/1.1386405 (3 pages) | Cited 49 times

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We present a theoretical study of the optical matrix elements and radiative lifetime for the ground state optical transitions in GaN/AlN quantum dots (QD). An efficient plane-wave expansion method is used to calculate the energy levels, wave functions, and optical matrix elements in the framework of a multiband k⋅p model taking account of the three-dimensional strain and built-in electric field distributions for QDs with a hexagonal truncated-pyramid shape. We demonstrate that the built-in electric field determines the energy spectrum of GaN/AlN QDs and leads to a dramatic decrease in the optical matrix element with increasing QD size. As a result, the radiative lifetime for the ground state optical transition increases strongly with QD size. The theoretical results obtained are in good agreement with available experimental data. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
71.15.-m Methods of electronic structure calculations
78.55.Cr III-V semiconductors
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