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15 Nov 2003

Volume 94, Issue 10, pp. 6243-7001

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Electromechanical coupling in free-standing AlGaN/GaN planar structures

B. Jogai, J. D. Albrecht, and E. Pan

J. Appl. Phys. 94, 6566 (2003); http://dx.doi.org/10.1063/1.1620378 (8 pages) | Cited 13 times

Online Publication Date: 31 October 2003

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The strain and electric fields present in free-standing AlGaN/GaN slabs are examined theoretically within the framework of fully coupled continuum elastic and dielectric models. Simultaneous solutions for the electric field and strain components are obtained by minimizing the electric enthalpy. We apply constraints appropriate to pseudomorphic semiconductor epitaxial layers and obtain closed-form analytic expressions that take into account the wurtzite crystal anisotropy. It is shown that in the absence of free charges, the calculated strain and electric fields are substantially different from those obtained using the standard model without electromechanical coupling. It is also shown, however, that when a two-dimensional electron gas is present at the AlGaN/GaN interface, a condition that is the basis for heterojunction field-effect transistors, the electromechanical coupling is screened and the decoupled model is once again a good approximation. Specific cases of these calculations corresponding to transistor and superlattice structures are discussed. © 2003 American Institute of Physics.
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77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.21.Cd Superlattices

Influence of oxygen plasma on electrical and physical parameters of Au–oxide–n-InP structures

R. Touhami, S. Ravelet, M. C. E. Yagoub, and H. Baudrand

J. Appl. Phys. 94, 6574 (2003); http://dx.doi.org/10.1063/1.1615305 (5 pages) | Cited 3 times

Online Publication Date: 31 October 2003

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This article reports on the electrical properties of Au–oxide–n-InP structures obtained by oxygen plasma oxidation and its influence on the conduction mechanism. A discussion on the evolution of the electrical and physical parameters according to the oxidation conditions is presented. We observed that the treatment time and the plasma power strongly influence the parameters, namely, the tuning coefficient, the barrier height at 0 K, the barrier lowering at zero bias, the correct value of the Richardson constant, the dielectric constant, the oxide capacitance, and the oxide thickness. Moreover, in accordance with the current–voltage–temperature measurements, the electrical and physical parameters describing the Au–oxide–n-InP structures depend significantly on the treatment parameters characterizing the oxygen plasma. The results obtained establish the relationships between the parameters of the conduction mechanism and oxidation conditions. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
52.77.-j Plasma applications
81.65.Mq Oxidation
77.22.Ch Permittivity (dielectric function)

High-temperature thermoelectric properties of single-crystal Ca3Co2O6

M. Mikami, R. Funahashi, M. Yoshimura, Y. Mori, and T. Sasaki

J. Appl. Phys. 94, 6579 (2003); http://dx.doi.org/10.1063/1.1622115 (4 pages) | Cited 37 times

Online Publication Date: 31 October 2003

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We measured the high-temperature thermoelectric properties of single-crystal Ca3Co2O6, which consists of parallel one-dimensional Co2O66− chains separated by Ca2+ ions. The resistivity (ρ) along the c-axis decreases rapidly upon increasing temperature from 2×104 to 8 mΩ cm in a temperature region of 300 to 1073 K. The Seebeck coefficient (S) is positive and is 230 and 160 μV/K at 373 and 1073 K, respectively. The thermal conductivity (κ) is as low as 8 W/mK at room temperature and decreases linearly with the increase of temperature to 4.6 W/mK at 773 K. Thus, the estimated dimensionless figure-of-merit [ZT=(S2/ρκ)T (T: absolute temperature)], is about 0.15 at 1073 K. As the thermoelectric figure-of-merit (Z), shows a sharp rise in the measured temperature range, Ca3Co2O6 is expected to possess high thermoelectric efficiency at higher temperatures, and is considered to be a potential candidate for use as a thermoelectric material at high temperatures by virtue of being chemically stable up to 1300 K. © 2003 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Application of Bryan’s algorithm to the mobility spectrum analysis of semiconductor devices

D. Chrastina, J. P. Hague, and D. R. Leadley

J. Appl. Phys. 94, 6583 (2003); http://dx.doi.org/10.1063/1.1621719 (8 pages) | Cited 13 times

Online Publication Date: 31 October 2003

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A powerful method for mobility spectrum analysis is presented, based on Bryan’s maximum entropy algorithm. The Bayesian analysis central to Bryan’s algorithm ensures that we avoid overfitting of data, resulting in a physically reasonable solution. The algorithm is fast, and allows the analysis of large quantities of data, removing the bias of data selection inherent in all previous techniques. Existing mobility spectrum analysis systems are reviewed, and the performance of the Bryan’s algorithm mobility spectrum (BAMS) approach is demonstrated using synthetic data sets. Analysis of experimental data is briefly discussed. We find that BAMS performs well compared to existing mobility spectrum methods.© 2003 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
02.50.-r Probability theory, stochastic processes, and statistics

Strong-contrast expansions and approximations for the effective conductivity of isotropic multiphase composites

D. C. Pham and S. Torquato

J. Appl. Phys. 94, 6591 (2003); http://dx.doi.org/10.1063/1.1619573 (12 pages) | Cited 31 times

Online Publication Date: 31 October 2003

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We extend the previous approach of one of the authors on exact strong-contrast expansions for the effective conductivity σe of d-dimensional two-phase composites to case of macroscopically isotropic composites consisting of N phases. The series consists of a principal reference part and a fluctuation part (a perturbation about a homogeneous reference or comparison material), which contains multipoint correlation functions that characterize the microstructure of the composite. The fluctuation term may be estimated exactly or approximately in particular cases. We show that appropriate choices of the reference phase conductivity, such that the fluctuation term vanishes, results in simple expressions for σe that coincide with the well-known effective-medium and Maxwell approximations for two-phase composites. We propose a simple three-point approximation for the fluctuation part, which agrees well with a number of analytical and numerical results, even when the contrast between the phases is infinite near percolation thresholds. Analytical expressions for the relevant three-point microstructural parameters for certain mixed coated and multicoated spheres assemblages (extensions of the Hashin–Shtrikman coated-spheres assemblage) are given. It is shown that the effective conductivity of the multicoated spheres model can be determined exactly. © 2003 American Institute of Physics.
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72.10.Bg General formulation of transport theory
72.80.Tm Composite materials
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)

Manipulation of the structural and optical properties of InAs quantum dots by using various InGaAs structures

Jin Soo Kim, Jin Hong Lee, Sung Ui Hong, Won Seok Han, Ho-Sang Kwack, Chul Wook Lee, and Dae Kon Oh

J. Appl. Phys. 94, 6603 (2003); http://dx.doi.org/10.1063/1.1621714 (4 pages) | Cited 15 times

Online Publication Date: 31 October 2003

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The structural and optical properties of self-assembled InAs quantum dots (QDs) with various InGaAs structures were investigated by transmission electron microscopy (TEM) and photoluminescence (PL). The emission peak position of InAs QDs covered by a 6 nm In0.15Ga0.85As layer was 1.26 μm with PL linewidth of 31 meV, which is narrower than that of QDs in a GaAs matrix. By inserting a 1 nm In0.15Ga0.85As layer below the InAs QD layer with a 6 nm In0.15Ga0.85As overgrowth layer, the emission peak position was redshifted with larger energy-level spacing between the ground states and the first excited states compared to that of QDs with an In0.15Ga0.85As overgrowth layer only. By covering the InAs QDs on a 1 nm In0.15Ga0.85As layer with an 8 nm InxGa1−xAs layer having graded In composition, the emission peak position was 1.32 μm with relatively larger energy-level spacing and narrower PL linewidth compared to QDs covered by an In0.15Ga0.85As layer. The longer emission wavelength with relatively larger energy-level spacing was largely related to the change in the QD shape and size, especially the aspect ratio (height/width), which was confirmed by cross-sectional TEM images. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.16.Dn Self-assembly
78.55.Cr III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Charging effects on the carrier mobility in silicon-on-insulator wafers covered with a high-k layer

D. Halley, G. Norga, A. Guiller, J. Fompeyrine, J. P. Locquet, U. Drechsler, H. Siegwart, and C. Rossel

J. Appl. Phys. 94, 6607 (2003); http://dx.doi.org/10.1063/1.1621721 (4 pages) | Cited 1 time

Online Publication Date: 31 October 2003

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The carrier mobility μ in low-doped silicon-on-insulator wafers is found to be strongly modified by the deposition of a thin ZrO2 or SrZrO3 top layer grown by molecular-beam epitaxy. Pseudo-metal–oxide–semiconductor field-effect-transistor measurements performed on several samples clearly show a correlation between μ and the density of interface traps (Dit) at the Si/buried-oxide interface. The reduction of Dit by a forming gas anneal leads to a corresponding increase in mobility. Moreover, the high-k/Si interface can contribute to the total drain current via the creation of an inversion channel induced by trapped charges in the high-k layer. Using Hall-effect measurements, we took advantage of this additional current to evaluate the carrier mobility at the high-k/Si interface, without the need of a top gate electrode. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.30.Tv Field effect devices
73.20.-r Electron states at surfaces and interfaces
61.72.Cc Kinetics of defect formation and annealing

On the difference in valence electron plasmon energy and density of states between beta- and cubic-Si3N4

R. G. Egdell, V. E. Henrich, R. Bowdler, and T. Sekine

J. Appl. Phys. 94, 6611 (2003); http://dx.doi.org/10.1063/1.1619568 (5 pages) | Cited 4 times

Online Publication Date: 31 October 2003

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Core and valence level photoemission spectra of β- and cubic-Si3N4 have been measured under monochromatic Al Kα excitation. Strong satellites to high binding energy of the core lines are shown to arise from excitation of valence electron plasmons during the photoemission process. An increase in the plasmon energy from 23.45 eV for β-Si3N4 to 26.10 eV for cubic-Si3N4 is of the magnitude expected from the 26% increase in the valence electron density associated with the shock-induced β-to-cubic phase transition. The measured valence band density of states for cubic-Si3N4 is in agreement with theoretical calculations. © 2003 American Institute of Physics.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Electrical isolation of n- and p-In0.53Ga0.47As epilayers using ion irradiation

C. Carmody, H. H. Tan, and C. Jagadish

J. Appl. Phys. 94, 6616 (2003); http://dx.doi.org/10.1063/1.1619567 (5 pages) | Cited 5 times

Online Publication Date: 31 October 2003

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A study of the evolution of sheet resistance of p- and n-type In0.53Ga0.47As epilayers during O, C, Li, and H irradiation was conducted. The threshold dose at which the material becomes highly resistive increased upon decreasing the mass of the implanted ion, was higher for n-InGaAs as compared to p-InGaAs and was greater for samples with a higher initial free carrier concentration. Implantation with H+ yielded isolation behavior that was different from that for implantation with the three medium-mass ions. The thermal stability of defects induced by implantation was also investigated by cumulative annealing, and was found to be slightly higher in n-InGaAs as compared to p-InGaAs. Shallow donor production in the InGaAs epilayer during implantation played a crucial role in determining the electrical characteristics of the samples. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Dv Thermal stability; thermal effects
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing

Microstructures and thermoelectric properties of Fe0.92Mn0.08Six alloys prepared by rapid solidification and hot pressing

H. Y. Chen, X. B. Zhao, Y. F. Lu, E. Mueller, and A. Mrotzek

J. Appl. Phys. 94, 6621 (2003); http://dx.doi.org/10.1063/1.1622773 (6 pages) | Cited 8 times

Online Publication Date: 31 October 2003

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Iron disilicide based thermoelectric materials Fe0.92Mn0.08Six (1.9⩽x⩽2.5) were prepared by rapid solidification (melt spinning) and hot uniaxial pressing at 1248 K with 50 MPa for 30 min, followed by annealing at 1073 K for 20 h. X-ray diffraction and scanning electron microscopy showed excess silicon phase for samples with x⩾2.1, and both the configurations and the amounts of secondary silicon particles varied with an increase in x. Hall measurements carried out at room temperature showed that the carrier concentrations for Fe0.92Mn0.08Six (1.9⩽x⩽2.5) were between 2.6×1018 and 5.6×1018 cm−3. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured from room temperature to 973 K. It was found that a little excess silicon in the sample, x=2.1, enhanced the Seebeck coefficient weakly, but was effective for decreasing the thermal conductivity. A maximum figure of merit, ZT=0.17, was obtained for Fe0.92Mn0.08Si2.0 at 973 K. © 2003 American Institute of Physics.
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72.80.Jc Other crystalline inorganic semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
72.20.Fr Low-field transport and mobility; piezoresistance
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Stress induced charge trapping effects in SiO2/Al2O3 gate stacks with TiN electrodes

A. Kerber, E. Cartier, G. Groeseneken, H. E. Maes, and U. Schwalke

J. Appl. Phys. 94, 6627 (2003); http://dx.doi.org/10.1063/1.1621718 (4 pages) | Cited 9 times

Online Publication Date: 31 October 2003

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Strong polarity dependent charge trapping effects have been observed in as-deposited SiO2/Al2O3 gate stacks with TiN gate electrodes on n- and p-type Si substrates using current–voltage (I–V) and capacitance–voltage (C–V) sensing techniques. For substrate injection, electron trapping occurs mainly in the bulk of the Al2O3, resulting in positive voltage shifts for both I–V and C–V measurements. In the case of gate injection, positive charge trapping near the SiO2/Al2O3 interface leads to negative voltage shifts for C–V and positive shifts for I–V measurements. The polarity dependent charging effects are explained in terms of the difference in barrier height for substrate and gate injection and of the inherent asymmetry of the dual layer gate dielectric. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.55.-g Dielectric thin films
77.65.Ly Strain-induced piezoelectric fields
73.20.At Surface states, band structure, electron density of states
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Ferromagnetic resonance experiments in an obliquely deposited FeCo–Al2O3 film system

N. A. Lesnik, C. J. Oates, G. M. Smith, P. C. Riedi, G. N. Kakazei, A. F. Kravets, and P. E. Wigen

J. Appl. Phys. 94, 6631 (2003); http://dx.doi.org/10.1063/1.1615295 (8 pages) | Cited 5 times

Online Publication Date: 31 October 2003

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Granular cermet films (Fe50Co50)x–(Al2O3)1−x fabricated using the electron-beam coevaporation technique at oblique incidence of FeCo and alumina atom fluxes have been found to exhibit both oblique and in-plane uniaxial magnetic anisotropy. This anisotropy first appears just below the percolation threshold due to a magnetic coupling of particles taking place at a certain stage of their growth and coalescence. The FeCo content x varied from 0.07 to 0.49. A simple model of the film microstructure is presented based on the results of magnetization measurements and ferromagnetic resonance at intermediate (9.4 GHz) and high (94 GHz) frequencies. At 94 GHz the concentration dependence of the effective anisotropy field follows the solid solution law, since then the magnetic field is sufficient to magnetize the films close to saturation. The 9.4 GHz data points deviate from the solid solution line below the percolation threshold due to both modification of the resonance fields by intergranular interactions in nonsaturated films and the reduction of the average magnetization of granules, comparing to the saturation magnetization, at room temperature. Different mechanisms of line broadening observed at frequencies used in experiments are also discussed. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.30.Gw Magnetic anisotropy
81.05.Mh Cermets, ceramic and refractory composites
81.05.Rm Porous materials; granular materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology

Investigations of chemical and electronic inhomogeneities in BaPb1−xBixO3 via highly spatially resolved electron energy loss spectroscopy

A. Gutiérrez-Sosa, U. Bangert, and W. R. Flavell

J. Appl. Phys. 94, 6639 (2003); http://dx.doi.org/10.1063/1.1620374 (5 pages) | Cited 2 times

Online Publication Date: 31 October 2003

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BaPb1−xBixO3 crystals, doped to various nominal x, were investigated in a scanning transmission electron microscope equipped with energy dispersive x-ray and electron energy loss spectroscopy facilities. Large compositional variations on the nm scale were found in single crystalline regions of any nominal x value. These were accompanied by changes in the core-loss and low-loss energy loss spectra. The low-loss energy loss spectra, furthermore, demonstrate the evolution of electronic structure with doping (i.e., transitions from semiconductor to semimetal) and fluctuations with variations in the local composition. © 2003 American Institute of Physics.
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79.20.Uv Electron energy loss spectroscopy
68.49.Jk Electron scattering from surfaces
71.20.Ps Other inorganic compounds

Magnetic properties of asymmetric antirectangular Ni80Fe20 arrays

C. C. Wang, A. O. Adeyeye, and Y. H. Wu

J. Appl. Phys. 94, 6644 (2003); http://dx.doi.org/10.1063/1.1620682 (5 pages) | Cited 17 times

Online Publication Date: 31 October 2003

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The magnetic properties of antirectangular arrays (2×10 μm2) embedded into 800 Å thick continuous Ni80Fe20 films with interhole spacing(s) in the range of 2–6 μm have been investigated. We observed that the presence of the rectangular holes strongly modifies the shape of the magnetic hysteresis loop compared with continuous film of the same thickness. Specifically, we observed that the coercivity increases dramatically with the reduction of interhole spacing due to magnetic domain wall pinning, in agreement with our magnetic force microscopy images. Complex magnetotransport curves were obtained, which is not readily explained using the conventional anisotropic magnetoresistance effect. We attribute our results to the contribution by magnetic domains to overall resistivity of the antirectangular structures. From field angle dependent magnetotransport measurements, we are able to deduce the pinning strength for different interhole spacing. © 2003 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.47.Np Metals and alloys
75.30.Gw Magnetic anisotropy

Thickness dependence of magnetization reversal in a soft cylindrical particle

Yu. B. Grebenshchikov, N. A. Usov, and K. S. Pestchanyi

J. Appl. Phys. 94, 6649 (2003); http://dx.doi.org/10.1063/1.1619572 (6 pages) | Cited 2 times

Online Publication Date: 31 October 2003

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The hysteresis loops of a soft cylindrical particle with radius R=40–100 nm have been studied by means of numerical simulation in the range of thickness Lz=10–40 nm, close to the exchange length R0. Qualitatively, three different scenarios of magnetization reversal have been obtained depending on the particle thickness and aspect ratio. For a “thick” particle (Lz≫R0) with aspect ratio Lz/R∼1, the magnetization reversal begins via the nucleation of magnetization curling similar to the case of spherical or ellipsoidal particles of a soft magnetic type. On the contrary, for a particle with a small aspect ratio (Lz/R≪1) the magnetization reversal begins via the nucleation of a bending state, whose magnetization is constrained within the particle plane. For a particle with thickness Lz>R0, the bending state can lose its stability at certain value of applied magnetic field, at which one or two vortices nucleate within the particle. The evolution of the vortex pattern in an applied magnetic field determines the shape of the hysteresis loop. On the other hand, for a thin particle (Lz<R0), the bending state tends to rotate as a whole with a decrease in the applied magnetic field. The total particle magnetization is close to the saturation magnetization, the hysteresis loop being practically rectangular. Thus, the behavior of the particle resembles that of a single-domain one, although the actual particle size exceeds the effective single-domain radius considerably. © 2003 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies

Effect of magnetic field on the magnetic properties of electroplated NiFe/Cu composite wires

X. P. Li, Z. J. Zhao, H. L. Seet, W. M. Heng, T. B. Oh, and J. Y. Lee

J. Appl. Phys. 94, 6655 (2003); http://dx.doi.org/10.1063/1.1621084 (4 pages) | Cited 21 times

Online Publication Date: 31 October 2003

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The effect of the magnetic field on the magnetic properties of NiFe/Cu composite wires electroplated under a longitudinal magnetic controlling field is presented. Composite wire samples of 20-μm-diameter Cu electroplated with a layer of Permalloy™ (Ni80Fe20) under the influence of a longitudinal magnetic field of intensities ranging from 0 to 400 Oe were produced, and the microstructure and magnetic properties were measured. The results showed that the longitudinal magnetic field in the composite wire plating makes the packing of the crystals in the plated layer more orderly, and thus increases the uniformity and magnetic softness of the plated material. It also shifts the magnetic anisotropy of the plated layer from circumferential to longitudinal, and increases the critical frequency of the plated composite wire in magnetoimpedance effect testing, at which the magnetoimpedance ratio reaches the maximum. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Pq Electrodeposition, electroplating
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.47.De Giant magnetoresistance

Magnetostrictive bending of cantilever beams and plates

Victor H. Guerrero and Robert C. Wetherhold

J. Appl. Phys. 94, 6659 (2003); http://dx.doi.org/10.1063/1.1621710 (8 pages) | Cited 10 times

Online Publication Date: 31 October 2003

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The models currently used to determine strains, stresses, and deflections in beams and plates made of magnetostrictive films deposited on nonmagnetic substrates are based on the assumption that the film is relatively thin compared to the substrate. Despite the lack of self-consistency and the limitations of these models, they can be used to calculate approximate strains and deflections when the ratio of the thickness of the film to the thickness of the substrate is smaller than about 0.001; even then they do not consistently predict stresses or energies. Unfortunately, the large deflections required in modern applications are only achievable with films that do not satisfy this assumption of relative film thinness, and the results obtained with the traditional models show large errors. In these circumstances it is necessary to introduce robust methods that can be applied regardless of the relative magnitude of the thickness of the film. In this article, one such method is presented. The method represents a self-consistent approach based on the minimization of the total internal energy of a film-substrate system, performed based on the assumption that the magnetostrictive strains can be modeled as anisotropic expansional strains. The expressions obtained using this approach can be used to calculate strains, stresses, deflections, and energies in an accurate way. The method is suitable for generalization to the cases in which the deformation of beams and plates is produced not only due to magnetostriction in the films, but may also include thermal, piezoelectric, or hygroscopic strains. © 2003 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
46.32.+x Static buckling and instability
46.35.+z Viscoelasticity, plasticity, viscoplasticity
62.20.F- Deformation and plasticity

Current amplification in high-temperature superconductor current injection three-terminal devices

O. Morán, R. Hott, R. Schneider, H. Wühl, and J. Halbritter

J. Appl. Phys. 94, 6667 (2003); http://dx.doi.org/10.1063/1.1623922 (6 pages) | Cited 2 times

Online Publication Date: 31 October 2003

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Current injection into superconducting microbridges has been studied for state-of-the-art YBa2Cu3O7−x/SrTiO3/Au (YBCO/STO/Au) planar heterostructures based on c-axis oriented YBCO layers. By injecting a gate current Ig into the YBCO channel of these three-terminal devices the critical current Ic could be reduced up to a gain factor G≡−dIc/dIg∼5 at 77 K. G is found to be roughly proportional to the superconducting quality of the samples as expressed by the critical current density Jc of the YBCO channel. At least for our high-quality samples, this Ic suppression is shown to be mainly due to the perturbation of the electronic superconductive equilibrium state by quasiparticles associated with the injection of the gate current. However, this basic mechanism for the current-injection-based transistor principle was in our experiments always accompanied by substantial parasitic effects, such as current summation and Joule heating due to electric power dissipation in the ultrathin STO barrier. This reduces the efficiency of the transistor mechanism and thus the hopes for THz operation of such devices. © 2003 American Institute of Physics.
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85.25.Cp Josephson devices
74.25.Sv Critical currents

Effect of coupling strength on magnetic properties of exchange spring magnets

Vamsi M. Chakka, Z. S. Shan, and J. P. Liu

J. Appl. Phys. 94, 6673 (2003); http://dx.doi.org/10.1063/1.1621712 (5 pages) | Cited 2 times

Online Publication Date: 31 October 2003

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The main feature of an exchange spring magnet can be characterized by ferromagnetic exchange coupling between a magnetically soft phase and a magnetically hard phase. The coupling constant J, a measure of the coupling strength between the two phases, is a key parameter in controlling the spring magnet properties. A ferromagnetically coupled hard–soft bilayer (FCB) has been used in this article to develop analytical expressions for a spring magnet that correlate the magnetic properties of a FCB and its layer parameters. These analytical expressions have been developed by solving a modified Stoner–Wohlfarth model. A set of analytical solutions describing the magnetic properties of the FCB at the different stages of J have been derived. The evolution of the magnetization reversal in a FCB, as a function of the coupling constant J, and an applied field H, is analyzed in detail. As a result, the approach to enhance the maximum energy product (BH)max is revealed. © 2003 American Institute of Physics.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.50.Ww Permanent magnets

Increase in ferromagnetic/antiferromagnetic exchange bias due to a reduction of the interfacial exchange interaction

F. Ernult, B. Dieny, L. Billard, F. Lançon, and J. R. Regnard

J. Appl. Phys. 94, 6678 (2003); http://dx.doi.org/10.1063/1.1614867 (5 pages) | Cited 10 times

Online Publication Date: 31 October 2003

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We experimentally investigated the influence of the location of nonmagnetic impurities (Au) inserted in the NiO layer of NiO/Co bilayers on the exchange bias. The inserted Au layer actually consists of a discontinuous plane of Au islands leading to local disruption of the exchange interactions within the NiO layer or at the Co/NiO interface. When the Au layer is introduced at the Co/NiO interface, this results in a significant initial increase in the exchange bias field. If the Au layer is moved deeper within the NiO layer, the exchange bias progressively decreases towards its value without Au. Our experiments are interpreted in terms of a reduced dragging of the NiO magnetization during Co magnetization reversal due to the reduced interfacial interaction. This interpretation is supported by numerical simulations which also predict the formation and annihilation of bubble-like domain walls. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Hx Magnetic impurity interactions
75.30.Et Exchange and superexchange interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Study of the electronic properties of some ytterbium filled skutterudites by magnetic susceptibility and x-ray absorption and tin-119 Mössbauer spectroscopy

Fernande Grandjean, Gary J. Long, Bernard Mahieu, J. Yang, G. P. Meisner, and D. T. Morelli

J. Appl. Phys. 94, 6683 (2003); http://dx.doi.org/10.1063/1.1623609 (9 pages) | Cited 3 times

Online Publication Date: 31 October 2003

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Magnetic susceptibility, ytterbium LIII-edge x-ray absorption and tin-119 Mössbauer spectral measurements have been carried out to probe the electronic structure of ytterbium and tin in the filled or partially filled skutterudite compounds, YbyCo4Sb12−xSnx, over a range of x and y values. The ytterbium valence obtained from the magnetic susceptibility and ytterbium LIII-edge x-ray absorption measurements is in excellent agreement and clearly reveals an evolution from intermediate valence ytterbium for x=0 to nearly divalent ytterbium for x=0.8. This evolution parallels an increase in the unit cell volume and hence in the ytterbium site volume available as the tin content increases. The tin-119 Mössbauer spectral hyperfine parameters indicate, without question, that tin substitutes on the antimony sublattice of the skutterudite structure. Further, the tin electronic configuration is both very similar to that of the antimony in the structure and insensitive to the ytterbium content, y. © 2003 American Institute of Physics.
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71.20.Lp Intermetallic compounds
75.50.Cc Other ferromagnetic metals and alloys
78.70.Dm X-ray absorption spectra
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Cr Saturation moments and magnetic susceptibilities
71.70.Jp Nuclear states and interactions
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X-ray Bragg diffraction from langasite crystal modulated by surface acoustic wave

D. V. Roshchupkin, D. V. Irzhak, R. Tucoulou, and O. A. Buzanov

J. Appl. Phys. 94, 6692 (2003); http://dx.doi.org/10.1063/1.1619199 (5 pages) | Cited 11 times

Online Publication Date: 31 October 2003

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X-ray diffraction on the X cut of a langasite crystal (La3Ga5SiO14) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) has been studied at the ESRF synchrotron radiation source. Due to the sinusoidal modulation of the crystal lattice involved by the SAW diffraction satellites appear on the rocking curve, with their number, angular positions, and intensities depending on the amplitude and wavelength of the ultrasonic superlattice. Full extinction of a specific satellite could be performed by adjusting the acoustic amplitude. It is shown that x-ray diffraction can be used to study surface acoustic wave field distributions in crystals. © 2003 American Institute of Physics.
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61.05.cp X-ray diffraction
68.49.Uv X-ray standing waves
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
43.35.Pt Surface waves in solids and liquids
68.35.Iv Acoustical properties
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

Structure of low dielectric constant to extreme low dielectric constant SiCOH films: Fourier transform infrared spectroscopy characterization

Alfred Grill and Deborah A. Neumayer

J. Appl. Phys. 94, 6697 (2003); http://dx.doi.org/10.1063/1.1618358 (11 pages) | Cited 175 times

Online Publication Date: 31 October 2003

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Carbon doped oxide dielectrics comprised of Si, C, O, and H (SiCOH) have been prepared by plasma enhanced chemical vapor deposition (PECVD) from mixtures of tetramethylcyclotetrasiloxane (TMCTS) and an organic precursor. The films have been analyzed by determining their elemental composition and by Fourier transform infrared spectroscopy with deconvolution of the absorption peaks. The analysis has shown that PECVD of TMCTS produces a highly crosslinked networked SiCOH film. Dissociation of TMCTS appears to dominate the deposition chemistry as evidenced by the multitude of bonding environments and formation of linear chains and branches. Extensive crosslinking of TMCTS rings occurs through Si–Si, Si–CH2–Si, Si–O–Si, and Si–CH2–O–Si moieties. The films deposited from mixtures of TMCTS and organic precursor incorporate hydrocarbon fragments into the films. This incorporation occurs most probably through the reaction of the organic precursor and the Si–H bonds of TMCTS. Annealing the SiCOH films deposited from TMCTS and organic precursor results in a large loss of carbon and hydrogen from the films resulting from the fragmentation and loss of the incorporated organic component. The deconvolution of the Si–O–Si asymmetric stretching band of the annealed films shows the existence of a larger fraction of a cage structure and a correspondingly smaller fraction of a networked (highly crosslinked) structure in the SiCOH films deposited from mixtures of TMCTS with organic precursor relative to the films deposited from TMCTS only. The evolution of the volatile hydrocarbon fragments during annealing results in the formation of nanopores and subsequent reduction of the dielectric constants of the films to extreme low-k values. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
78.30.Hv Other nonmetallic inorganics
52.77.Dq Plasma-based ion implantation and deposition
78.66.Nk Insulators
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
61.50.Lt Crystal binding; cohesive energy

Time-resolved x-ray diffraction study of the relaxation process of electric-field-induced strain in KD2PO4

S. J. van Reeuwijk, A. Puig-Molina, O. Mathon, R. Tucoulou, and H. Graafsma

J. Appl. Phys. 94, 6708 (2003); http://dx.doi.org/10.1063/1.1616634 (9 pages) | Cited 3 times

Online Publication Date: 31 October 2003

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In this article, we report on measurements of the strain relaxation process in KD2PO4. The application of a static electric field to a piezoelectric crystal generates stresses, which are released by the introduction of strain. Time-resolved x-ray diffraction experiments on square platelike samples indicated that the strain relaxation process strongly depends on the rise time of the electric field. In the case of an instantaneously applied electric field (rise time 30 ns, i.e., much shorter than the response time of the crystal), the induced strain waves were only weakly damped and still present 400 μs after activating the external electric field (which corresponds to roughly 50 round trips of the strain wave). The strain waves can be suppressed completely by employing a rise time equivalent to the intrinsic response time of the crystal. Measurements on a bar-shaped crystal indicated that the strain waves are generated at the edges of the crystal and propagate along the length of the crystal at the speed of sound. This was concluded from the time of arrival of the strain waves, as well as from the measured vibration frequency. © 2003 American Institute of Physics.
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77.65.Ly Strain-induced piezoelectric fields
77.84.Fa KDP- and TGS-type crystals
61.05.cp X-ray diffraction

Transport properties of ultrathin SrTiO3 barriers for high-temperature superconductor electronics applications

O. Morán, R. Hott, R. Schneider, and J. Halbritter

J. Appl. Phys. 94, 6717 (2003); http://dx.doi.org/10.1063/1.1620375 (7 pages) | Cited 12 times

Online Publication Date: 31 October 2003

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Current transport through ultrathin SrTiO3 (STO) barriers has been studied systematically with respect to its dependence on barrier thickness d=2–30 nm, temperature T, and voltage V in state-of-the-art planar YBa2Cu3O7−x/SrTiO3/Au (YBCO/STO/Au) heterojunctions with c-axis oriented YBCO layer. We identified different transport regimes: Elastic tunneling was observed for samples with a nominal barrier thickness of 2 nm, which represents our experimental minimum for obtaining insulating transport characteristics. Already for slightly thicker STO barriers, resonant tunneling and hopping via a small number of localized states begins to dominate the transport behavior. For d>20 nm, a crossover to variable range hopping behavior is observed in the high-bias voltage regime as well as in the high temperature regime. A localization length of ∼0.46 nm indicating the spread of the localized states can be derived from these experiments. This value is close to the STO lattice constant and corresponds to a high density of localized states of nL∼6×1019(eV)−1 cm−3. In a free electron tunneling model, this corresponds to an average tunnel barrier height of ∼0.4 eV. © 2003 American Institute of Physics.
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73.61.Ng Insulators
73.20.Fz Weak or Anderson localization
74.50.+r Tunneling phenomena; Josephson effects
73.50.Dn Low-field transport and mobility; piezoresistance
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