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Journal of Applied Physics

Issue 4 • Date Feb 1988

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Displaying Results 1 - 25 of 56
  • 3D transient eddy current fields using the u‐v integral‐eigenvalue formulation

    Page(s): 991 - 996
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    The three‐dimensional eddy current transient field problem is formulated using the u‐v method. This method breaks the vector Helmholtz equation into two scalar Helmholtz equations. Null field integral equations and the appropriate boundary conditions are used to set up an identification matrix which is independent of null field point locations. Embedded in the identification matrix are the unknown eigenvalues of the problem representing its impulse response in time. These eigenvalues are found by equating the determinant of the identification matrix to zero. When the initial transient forcing function is Fourier decomposed into its spatial harmonics, each Fourier component can be associated with a unique eigenvalue by this technique. The true transient solution comes through a convolution of the impulse response, so obtained with the particular external field decay governing the problem at hand. The technique is applied to the FELIX (fusion electromagnetic induction experiments) medium cylinder experiment; computed results are compared with data. A pseudoanalytic confirmation of the eigenvalues so obtained is formulated to validate the procedure. View full abstract»

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  • The effect of accelerating gap geometry on the beam breakup instability in linear induction accelerators

    Page(s): 997 - 1008
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    The electron beam in a linear induction accelerator is generally susceptible to growth of the transverse beam breakup instability. In this paper we analyze a new technique for reducing the transverse coupling between the beam and the accelerating cavities, thereby reducing beam breakup growth. The basic idea is that the most worrisome cavity modes can be cutoff by a short section of coaxial transmission line inserted between the cavity structure and the accelerating gap region. We have used the three‐dimensional simulation code SOS to analyze this problem. In brief, we find that the technique works, provided that the lowest TE mode cutoff frequency in the coaxial line is greater than the frequency of the most worrisome TM mode of the accelerating cavity. View full abstract»

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  • A simplified thermal model for calculating the maximum output power from a 1.3‐μm buried heterostructure laser

    Page(s): 1009 - 1014
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    A one‐dimensional thermal model is presented for calculating the maximum output power from InGaAsP/InP (λ=1.3 μm) buried heterostructure lasers, whose output power is limited by thermal considerations. The effect of Auger recombination and ohmic resistance, which play significant roles in these lasers at high temperatures, is included. We have also incorporated the temperature dependence of efficiency from first principles using experimentally available data for Auger and radiative recombination coefficients. Calculations made on InGaAsP/InP lasers show that a maximum cw power of 57 mW/facet (diamond heat sink) and a maximum operating temperature of up to 132 °C for a geometry similar to the double‐channel buried heterostructure laser can be achieved. In addition, the model has been used to determine the maximum achievable power as a function of device geometry (active layer thickness, width, and length of the device). We find that by increasing the length of the laser from 300 to 700 μm we can increase the output power of the laser by 79%. The results obtained agree reasonably well with experiment. View full abstract»

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  • High‐speed photography of surface geometry effects in liquid/solid impact

    Page(s): 1015 - 1021
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    Recent theoretical studies of liquid/solid impact, in particular the geometric wave theory of Lesser and Field, have emphasized the importance of the detailed geometry in the contact area. In parallel with the theoretical work, we have developed a two‐dimensional technique using gels for impact and shock studies. A combination of high‐speed photography and schlieren optics allows the shocks in the liquid and solid, if it is transparent, to be visualized, as well as important processes, such as jetting, to be recorded. This paper describes the gel technique and gives results for a range of surface geometries for collision velocities of a few hundred meters per second. The relevance to damage initiation in liquid/solid impact problems, such as rain erosion, steam turbine blade erosion, and cavitation, are discussed. View full abstract»

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  • Modeling for rf discharge characteristics

    Page(s): 1022 - 1031
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    A radio‐frequency discharge characteristics model for the dc self‐bias current density Jsb versus the dc self‐bias voltage Vsb and the gas pressure p is developed. The model considers positive ions and electrons only and is consistent with a previously developed model for dc sputtering discharge characteristics. Two different concepts for the cathode fall distance are established: Li, for the ions, which is time independent, and Le, for the electrons, which is a time‐averaged length. A relationship between the cathode fall distance L and the discharge efficiency n is developed. The area ratio power law for the voltage distribution between the electrodes is theoretically analyzed and the resulting quadratic power law is experimentally confirmed. The predicted pressure dependence of Vsb is rather complicated, and its mathematical expression has been left with an adjustable exponential parameter to be determined by the best fit to experimental data. View full abstract»

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  • Analysis of He‐implanted LiNbO3 by elastic recoil detection

    Page(s): 1032 - 1036
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    He‐implanted samples of LiNbO3 have been analyzed by 24‐MeV 28Si elastic recoil detection. For 50‐keV He implants, the Li and H profiles show a depletion of Li from the sample near‐surface region which coincides with a gain of H. The Li loss is seen to increase with increasing ion fluence and implantation temperature. View full abstract»

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  • Interactions between interstitial atoms in silicon: Arsenic‐argon‐boron and boron‐argon‐phosphorus

    Page(s): 1037 - 1040
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    Experiments were performed that examined the behavior of overlapping populations of two triplet combinations of implanted dopants in silicon: arsenic‐argon‐boron and boron‐argon‐phosphorus. It was found that the chemical profile and electrical activity of arsenic could be adjusted practically at will. Anomalous behavior was observed with boron. Similar control was displayed with boron and phosphorus when argon was present. The experimental results are both consistent with and supportive of calculations on a model silicon lattice that predict complex formation; arrangements of these triplets in close proximity are more stable energetically than when they are sufficiently separated that interactions are minimal. View full abstract»

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  • A study of detonation processes in heterogeneous high explosives

    Page(s): 1041 - 1045
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    A model of multiple processes is used to simulate the behavior of reaction in detonation of heterogeneous high explosives. The features of the model are (1) the partition of the explosive medium into hot spots and the region exclusive of hot spots and (2) the separation of the mechanical‐thermal process and chemical process. For each process, a characteristic time is assigned and is defined by a phenomenological relation. With assumptions, some fast processes are ignored in the governing equations. This investigation indicates the necessity of including a slow process near the end of the reaction. Comparisons with experiments using a Fabry–Perot velocimeter are presented for triaminotrinitrobenzene. View full abstract»

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  • Interdiffusion and structural relaxation in Mo/Si multilayer films

    Page(s): 1046 - 1051
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    Interdiffusion and structural change on annealing of sputter‐deposited Mo/Si and Mo(N)/Si(N) multilayer thin films have been investigated over the temperature range from 674 to 1027 K. X‐ray diffractometry shows that in the as‐deposited Mo/Si multilayers the Mo is bcc with the stacking of (110) plane parallel to the substrate, and the Si is amorphous, while in the as‐deposited Mo(N)/Si(N) multilayers, both Mo and Si nitrides are amorphous. The interdiffusivities have been determined from the decay rate of satellite peak intensity around (000). The activation energies for the interdiffusion in Mo/Si and Mo(N)/Si(N) multilayers are 105±5 and 351±88 kJ mol-1, respectively. A drastic decrease in the satellite peak intensity on annealing is observed in the Mo/Si multilayer films, which is interpreted to be due to interdiffusion and structural relaxation. On the other hand, a remarkable increase in the satellite intensity is found for the nitride multilayer films, which is explained by crystallization into β‐Mo2N/α‐Si3N4. The modulation wavelength decreases by 8%–12% after anneal. The decrease in the thickness of annealed Mo/Si multilayer films is also found by a depth profilometer. View full abstract»

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  • Open‐tube Zn diffusion in GaAs using diethylzinc and trimethylarsenic: Experiment and model

    Page(s): 1052 - 1059
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    We have characterized the diffusion of Zn into GaAs from the organometallic sources diethylzinc and trimethylarsenic. This method produces surface hole concentrations in excess of 1020 cm-3 with good control of junction depths as shallow as 0.1 μm. Smooth surface morphology is retained. The profile shape is much more complex than the accepted interstitial‐substitutional Zn‐diffusion model would predict. To explain the observed profiles, a new model for Zn diffusion is proposed and implemented in a computer simulation. View full abstract»

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  • A novel heteroepitaxy method of Ge films on CaF2 by electron beam exposure

    Page(s): 1060 - 1064
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    A novel heteroepitaxy method of Ge films on CaF2/Si(111) structures is presented, in which two successive processes of electron beam (e‐beam) exposure and predeposition of thin Ge layers at room temperature are done prior to the growth of thick Ge films at elevated temperatures. It was found in the e‐beam exposed region that the island growth of the predeposited Ge layer was prevented and the surface morphology and crystalline quality of the Ge overlayer grown at 600  °C were dramatically improved. These results were virtually independent of the sequence of the predeposition and exposure processes. From discussion on the growth mechanism of this method, a most plausible model that e‐beam dissociates the surface composition of CaF2 and improves the wettability between Ge and CaF2 is proposed. View full abstract»

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  • Effect of interfacial oxide on solid‐phase epitaxy of Si films deposited on Si substrates

    Page(s): 1065 - 1069
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    The effect of interfacial oxide on defect generation and regrowth rate in solid‐phase epitaxy of amorphized Si has been investigated. Si‐ion implantation was used to amorphize the chemical‐vapor‐deposited polycrystalline Si (poly‐Si) and to reduce the oxygen concentration at the poly/single‐crystalline Si interface. The crystallinity of the epitaxial layers obtained under different conditions, such as surface treatment, Si‐ion‐implantation dose, and thermal annealing, was examined by high‐resolution electron microscopy and Rutherford backscattering spectroscopy (RBS). Experimental results showed that microtwins were induced by inhomogenious oxygen distribution at the interface and that low defect density (the channeling minimum yield in RBS; χmin=7%) could be achieved for specimens with maximum interfacial oxide thickness of about 4 Å. View full abstract»

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  • Density of ZnS thin films grown by atomic layer epitaxy

    Page(s): 1070 - 1074
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    The density of ZnS thin films is determined as a function of the film thickness. The films were prepared using atomic layer epitaxy. Two experimental techniques are used, namely, (1) spectroscopic ellipsometry combined with He‐ion backscattering spectrometry and (2) spectroscopic ellipsometry alone using an effective medium approximation. Both methods give approximately the same results. In the ZnS thin films having a cubic crystal structure, the mean density increases from about 2.5 to about 4.0 g/cm3 with increasing film thickness in the thickness range of 25–400 nm. In the films thicker than 500 nm the density starts to decrease from the value 4.0 g/cm3. In the thickness range of 1000–2000 nm the density is 3.7–3.8 g/cm3. When the distance from the substrate is between 50 and 300–400 nm the local density of the cubic thin films has a maximum value which is close to the bulk density 4.1 g/cm3. The stoichiometric atomic ratio of sulfur to zinc is found to be between 0.9 and 1.0. The ratio has a tendency to increase with increasing film thickness. View full abstract»

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  • Growth of GaAs on GaAs‐coated Si by liquid‐phase epitaxy

    Page(s): 1075 - 1079
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    The liquid‐phase‐epitaxial growth of GaAs on partially masked GaAs‐coated Si substrates prepared by molecular‐beam epitaxy is described. Uniform layers were obtained in stripe windows narrower than 20 μm at an optimum growth temperatures of 800 °C. Smaller supercooling, however, resulted in smoother surface morphologies. The growth can be explained in terms of the mass transport of the growing species from bulk of the melt to the substrate surface and the subsequent incorporations into the solid. A marked difference between the growth on GaAs‐coated Si and that on GaAs substrates was observed. The growth on GaAs substrates appears to be dominated by surface reaction while transport processes are the limiting factor on GaAs‐coated Si. The migration length of the growing species was estimated to be very short on GaAs substrates and about 15 μm on GaAs‐coated Si. View full abstract»

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  • Structural aspects of superlattices of Fe‐W, Fe‐Mo, and Fe‐Nb metals

    Page(s): 1080 - 1085
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    X‐ray diffraction and Mössbauer absorption results are reported for the layered structures Mo/Fe, Nb/Fe, and W/Fe, with layer periodicities in the range 0.5–50 nm. The films are amorphous for periodicities of 0.5–2 nm, but with composition modulation, and are crystalline with coherency in the growth direction for periodicities of 2–50 nm. The superlattice diffraction patterns are in agreement with a one‐dimensional model, provided the effects of depositing part‐plane layers are taken into account. In the intermediate region near periodicities of 2 nm, mixed crystalline and amorphous phases are observed, with sharp diffraction patterns from the crystalline regions. It is suggested that the lattice mismatch is taken up by deposition defects for periodicities above 3 nm, and by these defects and columnar boundaries with the amorphous phase for periodicities near 2 nm. View full abstract»

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  • Deep‐level analysis in Te‐doped GaAs0.62P0.38

    Page(s): 1086 - 1092
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    Deep‐level transient spectroscopy and photocapacitance techniques have been used to study the features of the main electron trap, with thermal activation energy equal to ΔEB=0.39 eV, present in Te‐doped GaAs0.62P0.38, obtained by vapor‐phase epitaxy. Nonexponential behavior of this trap in thermal emission and capture has been interpreted using a model based on the alloy broadening effect. Good agreement of the deep‐level parameters determined from the emission and capture data has been obtained, and additionally confirmed by results of independent measurements of the transition region width. The influence of this level on the luminous intensity of light emitting diodes suggests that it can be an effective nonradiative recombination center. View full abstract»

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  • The study of charge carrier kinetics in semiconductors by microwave conductivity measurements. II.

    Page(s): 1093 - 1098
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    In previous work [J. Appl. Phys. 60, 3558 (1986)] an introduction was given to the study of charge carrier kinetics in semiconductors by microwave conductivity measurements. This paper compares quantitatively our experimental results to theoretical calculations for single‐crystalline Si wafers, taking into account the dependence on the microwave frequency and the dark conductivity of the sample, which ranged from σ=0.2 to 400 Ω-1 m-1. In particular, difficulties arising from experimental conditions that cannot easily be treated by theory are discussed. It is shown that quantitative measurements of samples with low dark conductivity can be performed even in a very simple configuration, which permits determination of the sum of charge carrier mobilities. View full abstract»

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  • Influence of photoexcitation on hopping conduction in neutron‐transmutation‐doped GaAs

    Page(s): 1099 - 1103
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    The nature of the tunneling‐assisted hopping conduction in neutron‐transmutation‐doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 °C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (AsGa) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, AsGa≤1×1018 cm-3, consists of the coexistence of the hopping and band conductions. View full abstract»

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  • Conduction in n+‐i‐n+ thin‐film polycrystalline/silicon devices in relation to the film deposition conditions

    Page(s): 1104 - 1110
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    The electrical conduction in n+‐i‐n+ thin‐film polycrystalline/silicon devices, in relation to the deposition conditions of the low‐pressure chemically vapor deposited film, is investigated. Transmission electron microscopy study showed the following: (i) By decreasing the growth pressure from 180 to 80 mTorr, the mean grain size increases by a factor of 3. (ii) In the material grown at 180 mTorr, there is a mean dilatation for the d111 lattice plane amounting to 2.7%, while in the material grown at 80 mTorr, the systematic dilatation previously observed is absent. The current‐voltage characteristics show a linear behavior in a voltage region and a nonlinear behavior at higher voltages attributed to Joule heating within the sample. The energy gap of the material grown at 80 mTorr is 1.12 eV, while for the material grown at 180 mTorr, it decreases to 0.96 eV. The shrinkage of the energy gap could be due to the high density of ‘‘tail states’’ close to the conduction or valence band. View full abstract»

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  • Platinum silicide contact to arsenic‐doped polycrystalline silicon

    Page(s): 1111 - 1116
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    PtSi contacts to As‐doped polycrystalline silicon have been studied with respect to dopant redistribution, microstructure, and contact resistance. Arsenic was found to pileup at the PtSi‐polysilicon interface upon silicide formation. Cross‐sectional transmission‐electron microscopy revealed columnar PtSi grains and a relatively flat interface between PtSi and polysilicon. These observations are similar to those reported for the case of PtSi formed on the single‐crystal silicon. The specific contact resistance (ρc) has been investigated as a function of As concentration ranging from 8×1019 to 2×1021 cm-3 and of its dependence on substrate preclean procedures prior to Pt deposition. It was found that ρc decreases with increasing As concentration, as expected from theory. However, the contact resistance to As‐doped polysilicon is about ten times higher than contacts to similarly doped single‐crystal Si. The origin of this difference is attributed to the fact that not all of the implanted As was activated. Hall‐voltage measurements showed that only about 10% of the implanted As was electrically active after an 880 °C, 20 min furnace annealing. Rapid‐thermal annealing was then used to activate a higher fraction of the implanted As. Consequently, a much lower ρc was obtained: e.g., 7.5×10-8 Ω cm2 for samples annealed at 1050 °C for 30 s, in contrast to a value of 8.4×10-7 Ω cm2 for a furnace‐annealed sample. View full abstract»

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  • Annealing effect on the resistivity of polycrystalline silicon films passivated with plasma‐deposited silicon‐nitride films

    Page(s): 1117 - 1120
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    The thermal annealing effect on resistivity is investigated for polycrystalline silicon films passivated with plasma‐enhanced chemically vapor deposited silicon‐nitride (p‐SiN) films. The resistivity in the heavily doped polycrystalline silicon films has a minimum value at an annealing temperature of approximately 500 °C, and the resistivity in the lightly doped films monotonically increases with the increase of annealing temperature. The dependence of the resistivity on annealing temperature is explained in terms of the variations of the density and the energy level of the traps at the grain boundaries, which are caused by the adsorption or the decomposition of hydrogen atoms. These conclusions are obtained by comparing the dependence in the polycrystalline silicon films with  p‐SiN films with that in the plasma‐hydrogenated polycrystalline silicon films without  p‐SiN films. View full abstract»

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  • Back bias effects on two‐dimensional electron gas

    Page(s): 1121 - 1125
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    A new technique is described to study heterostructure field‐effect transistors. This technique is based on the application of an electric field perpendicular to the channel via a p‐doped substrate. The measurements demonstrate that the centroid of the two‐dimensional electron gas resides approximately 10 nm below the heterointerface and that application of a negative substrate potential increases the confinement of these charges towards the interface. A negative substrate voltage decreases the K’ factor of the transistor and also reduces the well capacity. Capacitance voltage measurements confirm that a parasitic channel in the donor layer can be formed and that it is shielded from the substrate by the two‐dimensional electron gas. View full abstract»

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  • Transient transport in bulk Ga0.47ln0.53As and the two‐dimensional electron gas in Ga0.47ln0.53As/Al0.48ln0.52As

    Page(s): 1126 - 1129
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    Transient electronic transport properties of the bulk Ga0.47In0.53As and the two‐dimensional electron gas (2DEG) at the Ga0.47In0.53 As/Al0.48In0.52As heterointerface for various electric fields are investigated by ensemble Monte Carlo simulations. The average electron velocity during transient transport in the 2DEG at the Ga0.47In0.53As/Al0.48In0.52As interface is about 8 times the steady‐state velocity for E=20 kV/cm at room temperature and 30% higher than that in the intrinsic bulk Ga0.47In0.53As because of a higher peak velocity and a shorter transient time. This transient velocity enhancement in conjunction with higher 2DEG densities may significantly improve the performance of submicron‐gate and even near‐micron‐gate Ga0.47In0.53As/Al0.48In0.52As high electron mobility transistors. View full abstract»

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  • Flux‐flow‐type Josephson oscillator for millimeter and submillimeter wave region. IV. Thin‐film coupling

    Page(s): 1130 - 1135
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    Power emission from a flux‐flow‐type Josephson oscillator with a thin‐film coupling method is studied experimentally. The thickness of one electrode of the oscillator is made thin enough to allow electromagnetic fields generated by the oscillator to be emitted through the thin‐film electrode. Radiation power from the oscillator is detected with superconductor‐insulator‐superconductor detectors, which are fabricated on top of the oscillator. Experimental results show that sufficient power can be obtained from the oscillator by using the thin‐film coupling method when the thickness of the electrode is comparable to the London penetration depth. The results obtained are in reasonable agreement with theoretical predictions. The thin‐film coupling method will be useful when the oscillator is connected to external circuits, such as an impedance matching circuit. View full abstract»

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  • Properties of ion‐beam‐sputtered Ni/Fe artificial lattice film

    Page(s): 1136 - 1140
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    This paper reports the results of experimental and analytical investigations into the properties of ion‐beam‐sputtered Ni/Fe artificial lattice films. Through structure analysis, it is known that the Fe layer has poor crystallinity and the Ni layer has a face‐centered‐cubic structure with strong preferred orientation. Additionally, the Ni/Fe lattice film is found to possess good soft‐magnetic properties with lower coercivity less than 1 Oe and uniaxial anisotropy as the lattice period is decreased. The saturation magnetization and magnetostriction are also confirmed to be controlled by changing the lattice period and the thickness of Ni and Fe layers. As a result of the simplest model analysis, the very small magnetostriction obtained in this experiment is thought to be realized by the balance in magnetostriction among Ni, Fe, and Ni‐Fe interdiffusion layers. Furthermore, a good domain structure is observed in the Ni/Fe lattice film with very small magnetostriction. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory