bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical changes accompanying facet degradation of AlGaAs quantum well lasers
Authors: Houle F. A. , Neiman D. L. , Tang W. C. , Rosen H. J.
Published: July 2002

The temperature of single quantum well semiconductor laser facets increases during operation, eventually reaching a critical temperature, thermal runaway, and catastrophic optical damage. A study of changes in composition of the near-surface region of facets which accompany heating has been carried out for continuously operated, uncoated AlGaAs-GaAs-AlGaAs graded index separately confined heterostructure single quantum well lasers. High resolution depth profiles by scanning Auger microscopy show that the laser facets can be quite variable in initial composition, and undergo pronounced stoichiometry changes even during the first few minutes of operation. At longer times a continuing out-migration of the group III elements is observed. Unlike the double heterojunction lasers, facet oxidation is not pronounced and is not responsible for diffusion of Ga and Al. There are indications, however, that a slow leakage of oxygen into the crystal may occur. Spatially resolved analyses provide evidence that carrier-mediated elemental redistribution is an important factor in facet degradation. The progressive accumulation of defects which may act as non-radiative recombination centers provides a simple means of facet heating. Analyses of lasers which have suffered catastrophic damage indicate that the facets are not always melted, and that there is no typical chemical state which distinguishes them from facets of lasers which are fully operational. These results are compared to studies of facet degradation in double heterojunction lasers. Implications of the data for models of catastrophic optical damage are discussed.
Current-induced displacements and precession of a Bloch wall in Ni-Fe thin films
Authors: Salhi E. , Berger L.
Published: July 2002

Rectangular or exponential current pulses of duration ≂0.1 μs traversing a Bloch wall are found to induce wall displacements Δx≤10 μm/pulse in a Ni81Fe19 film of thickness ≂263 nm. The critical current density for wall displacement is jc≂1.35×106 A/cm2, about 20–200 times lower than for Néel or cross-tie walls investigated earlier. Wall motion arises probably from the precession of wall spins under the influence of the ‘‘s-d exchange torque’’ exerted by conduction electrons crossing the wall. The low jc value and easy precession of spins in a Bloch wall reflect the very small value ≂300 μT of the wall demagnetizing field which opposes spin orientation out of the wall plane in films of this thickness. A dc in-plane hard-axis field causes a linear decrease of jc. A dc easy-axis field smaller than Hc produces only a very slow decrease of jc.
Oscillation of magnetoresistance in [Ni–Fe/Cu]20/Cu/Fe multilayers with thickness of Cu spacer neighboring Fe buffer layer
Authors: Nakatani Ryoichi , Dei Toshiyuki , Sugita Yutaka
Published: July 2002

In [Ni–Fe (1.0 nm)/Cu(1.0 nm)]20/Cu(t nm)/Fe(5.0 nm) multilayers with giant magnetoresistance effects, oscillations of magnetoresistance ratio and preferred orientation depending on Cu spacer thickness t have been observed. Corresponding to the oscillation of the magnetoresistance ratio, the preferred orientation oscillates between <100≳ and <111≳, though the thicknesses of each Ni–Fe and Cu layer in the multilayer are fixed. Both the periods of the oscillations are about 0.6 nm. When the multilayers have stronger <100≳ and weaker <111≳ preferred orientations, they show higher magnetoresistance ratios.
Doping and residual impurities in GaAs layers grown by close-spaced vapor transport
Authors: Le Bel C. , Cossement D. , Dodelet J. P. , Leonelli R. , DePuydt Y. , Bertrand P.
Published: July 2002

The close-spaced vapor transport (CSVT) technique is used to grow GaAs epitaxial layers from various n- or p-type doped GaAs sources. The transport agent is H2O with PH2O = 4.58 Torr. n-type layers can be grown with Te- or Ge-doped GaAs sources. The transport coefficients of both dopants (ratio of the electrically active dopant concentration in the layer to the electrically active dopant concentration in the source) is 100% for Te or Ge, in the substrate temperature range comprised between 750 and 850 °C. p-type layers are obtained with Zn-doped GaAs sources. The transport coefficient of Zn is about 1% and is also independent of the substrate temperature. The transport coefficients and their independence on temperature are in agreement with a mass-transport controlled model based on the hypothesis that the transport reactions of GaAs and the doping impurities are in equilibrium at the source and substrate temperatures. Si-doped GaAs cannot be used as a source to obtain conductive n-type layers. When undoped semi-insulating (SI)-GaAs wafers are used as sources in CSVT, n-type layers are obtained. They are characterized by ND−NA=9×1015–3×1016 cm−3 and μ300K=3000–4000 cm2 V−1 s−1, independent of the temperature, in the temperature range investigated. Glow discharge mass spectroscopy analyses performed on a source and on a layer indicate that C, O, Si, and S are the major residual impurities in the GaAs layer. All these impurities have their origin in the technique (reactor, transport agent). Ge is also present in the layers, as indicated by photoluminescence. It is a minor impurity. Its origin is probably the SI-GaAs source.
Mechanisms of atomic layer epitaxy of GaAs
Authors: Yu Ming L.
Published: July 2002

We have studied the surface chemistry of trimethylgallium and diethylgallium chloride on GaAs(100) surfaces as related to the atomic layer epitaxy (ALE) of GaAs. We have observed that during the Ga deposition, the reaction pathway of trimethylgallium changes such that there is significant CH3Ga emission at high Ga coverages. An examination of the Ga coverage dependence reveals that this stoichiometry dependent CH3Ga desorption can lead to self-limiting Ga deposition which is a prerequisite for ALE. Numerical simulation of the reaction shows reasonable agreement with low-pressure ALE growth data. Diethylgallium chloride was found to deposit GaCl on the GaAs surfaces, but with residence time decreasing rapidly with increasing Ga coverage. Again a numerical examination of this stoichiometry dependent phenomenon indicates that it can significantly contribute to the self-limiting Ga deposition. Both systems showed that stoichiometry dependent reactions can be important mechanisms for the atomic layer epitaxy process.
X-ray diffraction study of surface acoustic wave device under acoustic excitation
Authors: Zolotoyabko E. , Jacobsohn E. , Shechtman D. , Kantor B. , Salzman J.
Published: July 2002

The acoustic field inside a surface acoustic wave device was studied by means of double-crystal x-ray diffraction. Angular satellites in the diffraction pattern were observed due to the coherent scattering on the acoustic superlattice. Satellite dynamics allows determination of the acoustic wave amplitude. Due to the sensitivity of x-ray diffraction to the direction of atomic displacements, the amplitude of different polarization components in the Rayleigh wave can be obtained.
Boron diffusion through thin gate oxides: Influence of nitridation and effect on the Si/SiO2 interface electrical characteristics
Authors: Mathiot D. , Straboni A. , Andre E. , Debenest P.
Published: July 2002

The diffusion of boron in N2 ambient is studied by using p+ polysilicon metal-oxide-silicon structures annealed during times long enough to allow boron diffusion through the gate oxide, up to the underlying substrate. Assuming equilibrium segregation at the interfaces, the boron diffusivity in the oxide is calculated by numerically fitting the resulting profile in the substrate. It is found that B diffuses in SiO2 with an activation energy of about 3 eV. We also quantify the influence of the nitridation of the oxide, and confirm its efficiency as a diffusion barrier. However, this study reveals a strong inconsistency between the extracted diffusivity values of B in SiO2 and the amount of B atoms being able to reach the Si/SiO2 interface to account for the observed interface state density.
Domain configurations in the giant magnetostrictive TbxHo1−xFe1.9 system in different easy axis regimes
Authors: Busbridge S. C. , Piercy A. R.
Published: July 2002

Domains have been observed in TbxHo1−xFe1.9 over the composition range 0<x<0.2 and temperature range −10 to +100 °C, as a function of bias field. In the region where this system is 〈100〉 easy, the movement of {110} 90° domain walls is shown to be responsible for the generation of negative magnetostrain, with increasing bias field. When 〈111〉 is easy, 71° domain walls in {110} have been identified with a bias field applied. For x=0.1, at remanence, 180° domain walls rotate smoothly with increasing temperature, from {100} when 〈100〉 is easy to {110} when 〈111〉 is easy. The presence of a bias field, at any temperature, brings out {110} walls which are 90° walls in the 〈100〉 easy, low temperature, regime and 71° walls in the 〈111〉 easy, high temperature, regime. At intermediate temperatures these walls remain in {110} with the magnetization in directions between 〈100〉 and 〈111〉. These domain observations are shown to be consistent with theoretical magnetomechanical behavior based on a 〈1uu〉, 0<u<1, transition in easy axis.
Isotope effects for mega-electron-volt boron ions in amorphous silicon
Authors: Svensson B. G. , Ridgway M. C. , Petravić M.
Published: July 2002

The depth profiles of 10B and 11B implanted into amorphous silicon have been analyzed by secondary ion mass spectrometry. Implantation energies between 0.4 and 5.0 MeV were used, and each sample was sequentially implanted with both 10B and 11B without changing the acceleration voltage but only the field in the mass analyzing magnet. A shift between the two profiles is clearly resolved and has been carefully studied as a function of ion energy. A maximum shift of 3.5% in mean projected range (Rp) is revealed at 0.6–0.8 MeV [Rp(11B)≥Rp(10B)], and for higher energies the ratio Rp(11B)/Rp(10B) decreases slowly to a value of ∼1.006 at 5.0 MeV. This reverse shift (heavier isotope penetrates deeper) is attributed to a larger electronic stopping cross section (Se) for 10B than for 11B at a given energy E where Se∼Ep and p≥0. The experimental data for Rp(11B)/Rp(10B) and Rp(11B) are compared with calculations, and it is demonstrated that the variation of Rp(11B)/Rp(10B) with ion energy hinges strongly on the Se vs E dependence. A close velocity proportional dependence (p=0.50±0.03) is found to be valid up to ∼300 keV, and then p decreases gradually with a maximum in Se (p=0) at ∼2.0 to 2.5 MeV. A semiempirical expression is presented for Se and shown to yield excellent agreement with both the relative isotope shift and the absolute range values; the deviations are less than 0.2% and 3.0%, respectively.
Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si. I. Phase formation and interface structure
Authors: Liu C. S. , Chen L. J.
Published: July 2002

Interfacial reactions of ultrahigh-vacuum-deposited Cu thin films on atomically cleaned (111)Si have been studied by transmission electron microscopy, x-ray diffractometry, and Auger electron spectroscopy. An interface compound, CuSix with x=11.2–14 at. %, was observed to be present at the Cu/Si interface. η″-Cu3Si was found to form in samples annealed at 200 °C for 1 h. Solid-phase-epitaxial growth of silicon on (111)Si through a transport media (Cu or Cu3Si) was observed to occur at a temperature as low as 200 °C. Preferentially oriented η″-Cu3Si is the only phase present in samples annealed at 200–800 °C. In samples annealed at or higher than 850 °C, a mixture of η′-Cu3Si and η″-Cu3Si was found to be present.
Melt-spun PrCo5 and related magnet materials: Coercivity enhancement by carbon addition
Authors: Fuerst C. D. , Herbst J. F. , Murphy C. B. , Van Wingerden D. J.
Published: July 2002

We have investigated melt-spun Pr-Co alloys with the objective of optimizing their permanent magnet characteristics. Among a variety of elemental additives studied, carbon was found capable of significantly improving the properties, the coercivity in particular. For binary Pr-Co systems optimum values of the remanence, Br=5.7 kG, intrinsic coercivity, Hci=5.8 kOe, and energy product, (BH)max=4.7 MG Oe, were obtained from the Pr16Co84 composition. These values were enhanced to Br=5.8 kG, Hci=16.5 kOe, and (BH)max=7.4 MG Oe for Pr18Co76C6. In both cases the melt-spun ribbons were principally composed of PrCo5. The 16.5 kOe coercivity of the carbon-containing ribbons is the highest ever reported for a PrCo5-based material. Two new rare earth-cobalt phases were tentatively identified during the course of this work: PrCo7 (hexagonal TbCu7 structure) and PrCo2Cx (cubic MgCu2 structure). Survey results for other melt-spun, RCo5-based alloys are also described.
Quantum interference devices and field-effect transistors: A switch energy comparison
Authors: Palm Thomas , Thylén Lars , Nilsson Olle , Svensson Christer
Published: July 2002

We compare quantum interference devices, exemplified by a resonant tunnel transistor, an Aharonov–Bohm interferometer, and a Y-branch switch, to field-effect transistors regarding their capability to reach fundamentally limited switch energies as well as their normalized transconductance. The resonant tunnel transistor is found to behave similarly to the field-effect transistor (FET). The Aharonov–Bohm interferometer is essentially equivalent to a single-mode Y-branch switch, while the Y branch has an advantage in allowing multimode operation. The normalized transconductance of these two devices can be an order of magnitude larger than for a FET.
Linearity and hysteresis in the magnetoresistive response of (NiFe,NiFeCo)/Cu and Co/Cu/NiFe multilayers in patterned stripes
Authors: Noguchi K. , Araki S. , Chou T. , Miyauchi D. , Honda Y. , Kamijima A. , Shinoura O/. , Narumiya Y.
Published: July 2002

The linearity and hysteresis in the magnetoresistive (MR) response of NiFe/Cu and NiFeCo/Cu multilayers prepared by ion beam sputtering, and Cu/Co/Cu/NiFe multilayers prepared by MBE are investigated. These characteristics in the linear regions for the second peak of antiferromagnetically coupled NiFe/Cu multilayers are almost the same as those of NiFeCo/Cu ones at 50-Hz ac applied fields. The MR amplitude at the first peak is inferior to that at the second one, whereas, the linearity and hysteresis are superior. In weakly coupled Cu/Co/Cu/NiFe multilayers, a nonhysteretic MR response is obtained at a NiFe layer thickness of 10 Å. The linearity and symmetry around the zero magnetic field of the MR curve depend on the Cu layer thickness. When the thicknesses of the NiFe and Cu layers are 10 and 45 Å, respectively, good linearity and no hysteresis are observed without biasing techniques. The output levels in the linear regions of three different multilayers are 1.5–2.5 times as large as that of the conventional Permalloy film. These multilayers are promising materials for the fabrication of MR head for ultrahigh density recording.
Current-distribution effects in microstructures for perpendicular magnetoresistance experiments
Authors: Lenczowski S. K. J. , Veerdonk R. J. M. van de , Gijs M. A. M. , Giesbers J. B. , Janssen H. H. J. M.
Published: July 2002

We present a simple Ohmic model to calculate the current distribution in small pillar-like structures for perpendicular magnetoresistance experiments. These calculations are consistent with three-dimensional electrostatic simulations, based on the finite element method, and facilitate the analysis of magnetoresistance data of microstructured multilayers.
Trapping of hydrogen impurities in helium-implanted niobium and tantalum
Authors: Haussalo P. , Keinonen J. , Jäske U.-M. , Sievinen J.
Published: July 2002

Trapping of hydrogen impurities at helium precipitates in helium-implanted niobium and tantalum has been studied. The samples were implanted at room temperature with 100 keV 4He+ ions to doses of (0.6–36)×1016 cm−2. Some of the samples were postirradiated with 60 keV and 4 MeV protons, and annealed at elevated temperatures up to 1070 K. The helium and hydrogen concentration distributions were characterized simultaneously using the elastic-recoil-detection-analysis technique. The hydrogen distributions were also measured by the nuclear resonance reaction 1H(15N,αγ) 12C. The observed hydrogen distributions show that defect-hydrogen complexes at He bubbles are built from the ion-irradiation-induced and pre-existing vacancies and pre-existing hydrogen impurities migrated to the associated internal surfaces and that the hydrogen impurities saturate the surfaces. Recovery energies of about 2.1 eV in Nb and about 2.7 eV in Ta were observed for the hydrogen trapping defects.
Effective internal fields and magnetization buildup for magnetotransport in magnetic multilayered structures
Authors: Levy Peter M. , Camblong Horacio E. , Zhang Shufeng
Published: July 2002

Starting with the Kubo formula for electric conductivity we derive a set of equations that define the spin diffusion that is present when current is driven through inhomogeneous magnetic media. We show the spin accumulation, or nonequilibrium magnetization, attendant to charge transport through regions of inhomogeneous magnetization is governed by the same equations found in a thermodynamic approach to magnetoelectric transport.
Helical anisotropy and Matteucci effect in Co-Si-B amorphous wires with negative magnetostriction (abstract)
Authors: Yamasaki J. , Takajo M. , Humphrey F. B.
Published: July 2002

The Co-Si-B amorphous wires having the negative magnetostriction comprises shell and core domains and exhibits the re-entrant flux reversal as the Fe-Si-B wire with positive magnetostriction. One of the characteristic features of Co based wires is that a sharp pulse voltage generation between two wire ends (Matteucci effect) is accompanied with re-entrant flux reversal, which is useful for sensor application because of no need for sense windings. In this work, we studied the origin of the large Matteucci effect of Co-Si-B wires by domain observation with a Kerr microscope and by Sixtus–Tonks experiments by driving the reverse domain propagation with the circular fields generated by the current through wires. We also tried to measure the hysteresis loop in the circular direction by integrating the Matteucci voltage. It was found that the domain patterns of the Co-Si-B wire surface is not the previously reported bamboo configuration but the helical configuration. Most of the anisotropy of the amorphous materials is magnetostrictive in origin. The helical anisotropy of Co based wire seems consistent, if we assume the same residual stress distribution as in the steel rod quenched into the water. Because of the helical anisotropy, the Co wire has the big circular component of magnetization in the core domain as well as in the shell domain, and both domain can interact near the interface region. It was found that reverse domain propagation along the wire axis can be caused by application of the circular field and that the shell domain moves discontinuously during the re-entrant flux reversal in the core domain. These circular magnetization components in both core and shell domains due to helical anisotropy and their interaction seems responsible for the large Matteucci effect in the Co-Si-B wires.
Perpendicular giant magnetoresistance of microstructures in Fe/Cr and Co/Cu multilayers (invited)
Authors: Gijs M. A. M. , Giesbers J. B. , Johnson M. T. , aan de Stegge J. B. F. , Janssen H. H. J. M. , Lenczowski S. K. J. , van de Veerdonk R. J. M. , de Jonge W. J. M.
Published: July 2002

We discuss the fabrication and microstructuring techniques of pillar structures made of high vacuum sputtered Fe/Cr multilayers and of molecular beam epitaxy evaporated Co/Cu multilayers, for which we measured the giant magnetoresistance effect with the current perpendicular to the multilayer plane from 4 K to 300 K. Using optical lithography and reactive ion etching techniques we obtained structures with a typical height of 0.5 μm and a width ranging between 3 and 10 μm. For both Fe/Cr and Co/Cu multilayers we find an enhanced magnetoresistance with respect to the in-plane case. The perpendicular magnetoresistance of the Fe/Cr pillars strongly decreases with temperature, while for the Co/Cu samples the temperature dependence is weaker, indicating electron-magnon scattering processes of different strength.
Enhanced remanence in isotropic Fe-rich melt-spun Nd-Fe-B ribbons
Authors: Withanawasam L. , Hadjipanayis G. C. , Krause R. F.
Published: July 2002

High isotropic remanences and energy products have been obtained in melt-spun Nd-Fe-B samples with a fine grained mixture of α-Fe and Nd2Fe14B1 containing more than 50 wt % of α-Fe. Reduced remanences as high as 0.78 with high saturation magnetization (190 emu/g) led to (BH)max of 14 MGOe. The coercivities varied from 2–4 kOe for samples with 70–50 wt % α-Fe, respectively. Reversible demagnetization curves were observed consistent with the ‘‘exchange spring’’ mechanism.
Fluorescence associated with Fe3+ ions in nanostructured Al2O3
Authors: Mo Chi-Mei , Zhang Lide , Yao Xiaohui , Fan Xiaojun
Published: July 2002

The fluorescence phenomena of nanostructured Al2O3 without doping and after doping of nano-Fe2O3 (4.61 and 48.01 wt %) were systematically investigated. The results show that a new fluorescence band with a peak position of about 17 500 cm−1 occurs for boehmite, η-Al2O3 and γ-Al2O3 and it disappears for α-Al2O3. This band can be attributed to fluorescence of Fe3+ in the systems with low-order degree (boehmite, η- and γ-Al2O3 and interfaces), which arises from 6A1→4T1 d5 electron transitions of Fe3+.
Suppression of vacuum breakdown using thin-film coatings
Authors: Mayberry C. S. , Wroblewski B. , Schamiloglu E. , Fleddermann C. B.
Published: July 2002

Thin-film metal and metal oxide coatings ion sputter deposited onto the cathode electrode of a parallel-plate high-voltage gap were found to suppress electron emission in high vacuum. Electric fields as high as 60 kV/mm have been sustained across a 1 mm gap for pulse durations of 10 μs. Lesser electric fields were sustained for pulse durations exceeding 10 ms. The behavior of 500 nm thick coatings was independent of the type of coating used, whereas the breakdown voltage for thinner coatings depended upon the material and the deposition conditions. The breakdown properties of various coatings, as well as a discussion of the suppression of electron emission is presented.
Surface roughness effect on surface impedance of superconductors
Authors: Wu Z. , Davis L. E.
Published: July 2002

The measured values of microwave surface resistance and reactance of a superconductor have generally three contributions from (1) the intrinsic properties, (2) the internal defects, and (3) the external surface roughness. In this paper, we formulate the increased factor of surface resistance and reactance of superconductors using Morgan’s square-grooves model and with the consideration that the current flows along the irregular surface. Numerical results obtained using a finite difference method are presented together with fitted closed-form formulas.
Anisotropy in effective conductivities of rectangular arrays of elliptic cylinders
Authors: Lu Shih-Yuan
Published: July 2002

Effective conductivities of inhomogeneous systems with rectangular arrays of elliptic cylinders are accurately evaluated with a boundary collocation scheme. The investigation is conducted from 0 to the close packing in inclusion volume fractions f, and from 0 to ∞ in conductivity ratios of the inclusion to matrix σ. Results of the calculation agree very well with a reciprocal theorem developed by Keller [J. Appl. Phys. 34, 991 (1963); J. Math. Phys. 5, 548 (1964)]. The effect of different array arrangement on effective conductivities is studied by changing the aspect ratio of the inclusion ra, from 2 to 10 and the array edge length ratio re, from 1 to 10. The anisotropy in effective conductivities of the array is also examined. It is found that, with unit ra/re, the enhancement in conductivity in the direction parallel to the major axis of the inclusion increases appreciably when compared to that of the square array of circular cylinders of equal inclusion volume fractions, while the enhancement in the perpendicular direction decreases only slightly.
Polarization currents in zinc oxide varistors from 77 to 450 K
Authors: Major R. W. , Werner A. E. , Wilson C. B. , Modine F. A.
Published: July 2002

The time and temperature dependencies of polarization currents are investigated to higher temperatures and with greater temperature resolution than has been reported previously for zinc oxide varistors. Arrhenius plots of these transient polarization currents yield two thermal activation energies near 140 and 8 meV, which are in reasonable agreement with values reported recently, as well as an additional thermally activated level at 0.66 eV, which becomes evident in the extension of the measurements to T≳300 K. Conductance data in this higher temperature range yield the nearly identical energy of 0.68 eV for the intergranular (Schottky) barrier height. The temperature dependence of the exponent m in the power-law expression for the current-time dependence I=I0t−m was carefully examined and found to change twice from 0.5 to 1.0. The nonmonotonic behavior of m(T) can be interpreted as due to resolution of polarization currents from two different traps, each of which evolves from diffusive to dispersive transport as temperature is lowered rather than, for example, a complicated distribution of relaxation times.
Observation and electronic characterization of ‘‘new’’ E′ center defects in technologically relevant thermal SiO2 on Si: An additional complexity in oxide charge trapping
Authors: Conley John F. , Lenahan P. M. , Evans H. L. , Lowry R. K. , Morthorst T. J.
Published: July 2002

Using electron-spin resonance (ESR), we demonstrate that several E′ variant precursors exist in a variety of technologically significant thermally grown thin SiO2 films on Si. The E′ variants include two varieties with the ubiquitous Eγ′ line shape (zero-crossing g=2.0005, O3≡Si⋅) and a second very narrow line shape (zero-crossing g=2.0019, structure unknown). We tentatively label the g=2.0019 defect EP for provisional E′ and distinguish the Eγ′ variants Eγn′ (neutral) and Eγp′ (positive). We combine ESR, capacitance versus voltage electrical measurements, and charge injection sequences to compare the electronic properties of the defects. We find that paramagnetic EP defects are positively charged while paramagnetic Eγ′ centers can be either positively charged or, under some circumstances, neutral. We find that EP precursors have a very large capture cross section for holes (σ=10−13 cm2) and that paramagnetic EP defects have an even larger capture cross section for electrons (σ=10−12 cm2). Both EP capture cross sections are an order of magnitude greater than those of the Eγp′ defects. We find that EP centers are distributed much more broadly throughout the oxide than either the Eγp′ or Eγn′ defects. We also find a two order of magnitude variation in EP density dependent upon processing variations. In addition, EP centers, unlike the Eγ′ variations, are not stable at room temperature. With their large capture cross section for holes and even larger capture cross section for electrons, EP defects may be relevant to device reliability and charge trapping under conditions of a low, relatively pure hole fluence such as in hot hole injection in short n-channel metal-oxide-semiconductor field-effect transistors.
Distribution of blocking temperature in bilayered Ni81Fe19/NiO films
Authors: Soeya Susumu , Imagawa Takao , Mitsuoka Katsuya , Narishige Shinji
Published: July 2002

Exchange paths were investigated for unidirectional exchange coupled 40 nm Ni81Fe19/50 nm NiO films by performing several field cooling experiments. Our experimental data were very consistent with the assumed existence of a variety of exchange paths. Each exchange path seemed to produce its own local unidirectional anisotropy and different local blocking temperature. The measureable exchange coupling could be described as consisting of the sum of the respective exchange paths, each with its own local blocking temperature. On the other hand, an observed blocking temperature of about 230 °C was determined from the exchange paths having the highest local blocking temperature. The local blocking temperatures were thought to be widely distributed, ranging from room temperature to about 230 °C, and the maximum existence probability was most likely at about 215 °C. This indicated that the exchange paths having the local blocking temperature of 215 °C made the largest contribution to the exchange coupling field at room temperature. According to cross sectional transmission electron microscopy observations, this variety of exchange paths was caused by inhomogeneous Ni81Fe19-NiO interfaces associated with interfacial disorder and fluctuating atomic arrangement.
Mechanism of photocurrent multiplication in amorphous silicon carbide Schottky cells
Authors: Akita Seiji , Ueda Hiro-omi , Nakayama Yoshikazu
Published: July 2002

The mechanism of the photocurrent multiplication for both polarities of an applied voltage (two-way) observed in a simple structure of SnO2/amorphous silicon carbide/Au has been explained by a model based on electron tunneling through the Schottky barriers. Photoholes trapped in the depletion layers at the electrodes of SnO2 and Au induce tunneling by enhancing the electric field applied to the barriers. The model has been in qualitative agreement with electrical properties measured in the steady state and transient state. The dark current at high applied voltages shows Fowler–Nordheim type conduction. The dependence of the steady-state photocurrent on temperature and light intensity indicates that the photocurrent is controlled by electron injection rather than by trap-controlled recombination in the bulk. The rise and decay properties in the transient photocurrent indicate that the trapping and detrapping rates of photoholes in the depletion layers depend on the light intensity and applied voltage but not on temperature.
Dependence of critical current density on microstructure in the SnMo6S8 Chevrel phase superconductor
Authors: Bonney L. A. , Willis T. C. , Larbalestier D. C.
Published: July 2002

Microstructure and superconducting properties of hot isostatic pressed SnMo6S8 were systematically studied. Magnetization was measured in fields up to 30 T at 4.2–14 K. SnMo6S8 exhibits critical current densities limited by flux pinning, not by granularity. Samples exhibited Birr(T)∼Bc2(T), indicative of strong flux pinning. Pinning force curves contained two distinct peaks, indicating that at least two pinning mechanisms are active. The microstructure contained two types of defects which could pin flux: grain boundaries and planar intragranular defects. Lower-field pinning (B/Bc2≤0.3) was directly correlated to the grain boundary density. Higher-field pinning (B/Bc2≥0.5) appeared to be controlled by the intragranular pins. Compared to Nb3Sn, the grain sizes are large and the contribution from grain boundary pinning is small. Inhibiting grain growth through lower-temperature processing and increasing the density of intragranular defects both appear feasible means of further increasing Jc.
rf surface resistance measurements of binary and ternary niobium compounds
Authors: Gemme G. , Fabbricatore P. , Musenich R. , Parodi R. , Rossi T. , Viviani M. , Zhang B.
Published: July 2002

The superconducting properties of binary and ternary niobium compounds for rf applications are investigated. The materials under study are niobium nitride (NbN), niobium-titanium nitride (NbTiN), and niobium tin (Nb3Sn). Preparation techniques of the compounds are discussed. NbN and NbTiN are obtained by thermal reaction of bulk Nb in nitrogen atmosphere. Nb3Sn has been obtained using a technique originally developed for high-field magnet fabrication and modified to be applied to rf cavity production. The experimental apparatus and measurement technique are described. In particular the raw experimental data have been carefully analyzed to obtain important informations on fundamental material parameters. The effect of field penetration in the superconductor and the influence on the experimental results of the normal metallic substrate on which the superconductor is grown is also considered. The measurements show that NbN and Nb3Sn are effectively potentially good materials for rf applications due to their low theoretical BCS surface resistance. So far the results obtained with NbTiN are more difficult to interpret because the quality of the material did not allow sufficiently accurate collection of data.
Compositional separation in Co-Mn magnetic thin films
Authors: Rogers David J. , Maeda Yasushi , Takei Koji
Published: July 2002

The compositional distribution in fcc Co-Mn magnetic thin films was studied in order to examine the possibility of a compositional separation, similar to that observed previously in hcp Co-Cr thin film magnetic recording media, occurring in an fcc alloy system. Spin-echo 59Co NMR study of Co75Mn25 films revealed a change from a homogeneous compositional distribution in a film deposited at a substrate temperature (Ts) of RT to a compositionally separated state in a film deposited at a Ts of 300 °C. Vibrating sample magnetometry revealed an associated three-fold enhancement in saturation magnetization in the films deposited at a Ts of 300 °C.
Heat resistance of Mo/Si, MoSi2/Si, and Mo5Si3/Si multilayer soft x-ray mirrors
Authors: Takenaka Hisataka , Kawamura Tomoaki , Ishii Yoshikazu , Asagiri Satoru
Published: July 2002

The effects of heating on both the reflectivity and layered structures of Mo/Si and Mo-silicide/Si (MoSi2/Si and Mo5Si3/Si) multilayers were evaluated. The Cu-Kα x-ray reflectivity and the periodic length of the Mo/Si multilayer markedly decreased after heating at above 300 °C, while those of the Mo-silicide/Si multilayers changed only slightly even after heating up to 600 °C. Transmission electron microscopy observations revealed markedly less thermally induced deterioration in the Mo-silicide/Si multilayers than in the Mo/Si multilayer, indicating that Mo-silicide/Si multilayers have better heat resistance than Mo/Si multilayers.
An amorphous magnetic bimetallic sensor material
Authors: Kraus L. , Hašlar V. , Závěta K. , Pokorný J. , Duhaj P. , Polak C.
Published: July 2002

An amorphous bimetal ribbon consisting of magnetostrictive (Fe40Ni40B20) and nonmagnetostrictive (Co67Fe4Cr7Si8B12) layers was prepared by planar flow casting from a double-chamber crucible. The effect of applied tensile stress on hysteresis loops and the surface domain structures of the stress-relieved bimetal was investigated at room temperature. The hysteresis loops can be well explained by superpositions of hysteresis loops of the individual layers. Only the magnetostrictive layer is responsible for the influence of applied stress on magnetic behavior. At a certain stress, the magnetic anisotropy of the magnetostrictive layer abruptly changes from a hard-ribbon-axis to an easy-ribbon-axis type. This transition is accompanied by a change of domain structure and a sharp maximum of the coercive field. A simple model taking into account an interplay of the applied tensile stress with the compressive stress produced by thermal contraction after stress relief and/or by bending of the ribbon has been developed. The observed behavior can be well explained by the model.
Evaluation of Cu adhesive energy on barrier metals by means of contact-angle measurement
Authors: Furuya Akira , Hosoi Nobuki , Ohshita Yoshio
Published: July 2002

The adhesive energies at Cu/SiO2, Cu/TiN, and Cu/TiW interfaces were investigated by measuring the contact angles of Cu particles to the substrate. To form the Cu particles, thin Cu films deposited on each substrate were annealed at 500 °C for 50 h. The adhesive energies are determined to be 0.8, 1.8, and 2.2 N/m for the SiO2, TiN, and TiW, respectively. The Cu particle on TiW film shows the highest adhesion. When TiW is used as a barrier metal, fine Cu lines are fabricated by reactive ions etching without peeling. On the other hand, Cu lines on the TiN film are peeled during the etching. This is consistent to the evaluation result that TiW has higher adhesive energy than TiN.
O interstitial generation and diffusion in high temperature annealed Si/SiO2/Si structures
Authors: Devine R. A. B. , Mathiot D. , Warren W. L. , Aspar B.
Published: July 2002

The profile of oxygen atoms diffused from SiO2 films into Si substrates as interstitials during high temperature annealing has been studied by infrared absorption spectroscopy using 18O as a tracer. The measured absorbance profile in the substrates can be explained in terms of a simple diffusion model in which the SiO2 layer acts as a reservoir of O and there is no energy barrier to diffusion across the Si/SiO2 interface. The driving force for diffusion is the temperature-dependent solubility of oxygen interstitials in the Si. We find evidence both for the outdiffusion of oxygen from the SiO2 layer into the Si during extended annealing and retrodiffusion back into the SiO2 layer during temperature ramp down. From etchback profiling data on O interstitials we are able to revise the Arrhenius law for O diffusion in Si and obtain an activation energy of 2.57 eV and a preexponential factor of 0.22 cm2 s−1. It is further suggested that there is evidence for enhancement of the O diffusion coefficient in Si at low temperatures resulting from the presence of foreign species such as H. These observations are important in understanding the structure of a thermally grown SiO2/Si interface and annealing-induced degradation in Si-based devices.
Plasma-assisted electron emission from (Pb,La)(Zr,Ti)O3 ceramic cathodes
Authors: Shur D. , Rosenman G. , Krasik Ya. E. , Kugel V. D.
Published: July 2002

Strong pulsed electron emission has been observed from 12/65/35 lead lanthanum zirconate titanate ceramic composition in two different nonswitched phases at room temperature and at the temperature 100 °C. The electron emission parameters of this composition appear to be independent of phase for the two phases investigated. Fast photography and direct observation show that the strong electron emission occurs from the surface discharge plasma. The new experimental data make it possible to demonstrate the validity of the Child–Langmuir law for this electron emitter. A pulsed plasma lead lanthanum zirconate titanate ceramic cathode with burst frequency up to 100 kHz and collector current density up to 10 A/cm2 is developed.
Cathodoluminescence study on dislocations in silicon
Authors: Sekiguchi T. , Sumino K.
Published: July 2002

A study was made on the characteristics of cathodoluminescence (CL) from Si crystals with various configurations of dislocations. D3 and D4 were observed along slip lines, while D1 and D2 were found to be strong in the region where plural slip lines intersect each other. It was shown that not only Lomer–Cottrell dislocations but also jogs act as recombination centers for D1 and D2 luminescence. The spatial distributions of D1 and D2 luminescence were observed to be similar to each other, this was also true of D3 and D4. The effect of hydrogenation on CL distribution was also investigated. Contrary to the reports of other groups, no evidence was obtained on the enhancement of D line luminescence due to metal contamination.
Phase transitions in disordered systems: Exactly solvable model
Authors: Nicolaides D. , Lisyansky A. A.
Published: July 2002

The critical behavior at phase transitions of random systems is studied within the framework of an exactly solvable model which takes into account interactions of fluctuations with equal and opposite momenta. Using the replica method, the dimensional reduction by 2 for the φ4 model with a quenched random field is explicitly shown. Phase transitions in systems with two interacting order parameters which in addition are coupled to two independent random fields are also studied. In the absence of random fields the model demonstrates fluctuation induced phase transitions of the first order for spacial dimension d<4. In random systems with only one quenched random field present, second order phase transitions are restored. Two random fields suppress any phase transitions for d<4. For interaction of an infinite range, the model demonstrates the mean field critical asymptotics independently of dimensionality or the presence of random fields.
Magnetic properties and imaging of Mn-implanted GaAs semiconductors
Authors: Shi Jing , Kikkawa J. M. , Awschalom D. D. , Medeiros-Ribeiro G. , Petroff P. M. , Babcock K.
Published: July 2002

Submicron ferromagnets have been successfully incorporated into GaAs semiconductors by Mn+ ion implantation and subsequent heat treatment. Transmission electron microscopy, x-ray fluorescence spectrum analysis, and atomic force microscopy are used to structurally characterize the GaMn precipitates which form within the GaAs matrix. These crystallites are room-temperature ferromagnets with controllable magnetic properties. Magnetic force microscopy images reveal that unmagnetized samples contain both magnetic dipoles and quadrupoles, but that after magnetization the single-domain state predominates.
Stability of a circular void in a passivated, current-carrying metal film
Authors: Mahadevan Mohan , Bradley R. Mark
Published: July 2002

We perform a linear stability analysis of a preexisting circular void in a passivated current-carrying metal thin film. We introduce small perturbations to the shape of a circular void and study the time evolution of these perturbations in two cases. In the first case, we take only current crowding and surface electromigration into account and find that the void relaxes to a nontrivial steady state in which there are slitlike projections from an otherwise circular void. The relaxation time needed to approach this steady state is also calculated. We then include the effect of surface self-diffusion in our analysis and find that the steady state is a circular void drifting with constant speed. Our calculations indicate that a circular void whose radius is small compared to the line width is stable with respect to small perturbations of its shape in the presence of current crowding, surface electromigration, and surface self-diffusion.
Preparation of soft magnetic Fe/Ta and Fe:N/Ta:N multilayered films with large magnetization for inductive recording head
Authors: Naoe Masahiko , Nakagawa Shigeki
Published: July 2002

Fe/Ta multilayered films were deposited on Si substrates by ion beam sputtering (IBS) by alternately using separate Fe and Ta targets. Thickness of Fe and Ta layers ℓFe and ℓTa bilayers ℓFe+ℓTa in specimen films and total thickness of multilayers films with 10 bilayers were constant at 100 and 1000 Å, respectively. For as-deposited films, coercivity Hc took minimum value of 0.15 Oe at ℓFe of 88 Å and ℓTa of 12 Å, where saturation magnetization 4πMs was 18.3 kG. Films postannealed at 500 °C exhibited 4πMs of 19.1 kG, Hc of 0.05 Oe and μr of 1820. Fe:N/Ta:N multilayered films with N content of ∼10 at. % were deposited by bombarding N ions extracted from the subgun while the films were being grown. For as-deposited films, Hc took minimum value of 0.07 Oe and μr took maximum value of 1310 at ℓFe:N of 93 Å and ℓTa:N of 7 Å, where 4πMs was 20.5 kG. Films postannealed at 500 °C exhibited 4πMs of 21.2 kG, Hc of 0.03 Oe and μr of 2380. Consequently, Fe/Ta and Fe:N/Ta:N multilayered films may be very suitable for magnetic cores in inductive heads for ultrahigh density recording.
Superexchange interactions in Ni0.5Co0.5Fe2O4
Authors: Lee Choong Sub , Lee Chan Young
Published: July 2002

Slowly cooled Ni0.5Co0.5Fe2O4 has been investigated over a temperature range from 13 to 880 K using the Mössbauer technique. X-ray diffraction shows that it has an inverse spinel structure and a lattice constant of a=8.346±0.005 Å. The Mössbauer spectra that are laid less overlapping at low temperature have been fitted with two sextets in the ferrimagnetic state. The iron ions at both A (tetrahedral) and B (octahedral) sites are found to be in ferric high-spin states. Its Néel temperature TN is found to be 865±3 K. As the temperature increases toward TN a more overlapping effect of the six-line patterns in A and B sites is observed and interpreted to have originated from different temperature dependencies of the magnetic hyperfine fields at A and B iron sites. Assuming that A–B magnetic interactions are stronger than A–A and B–B interactions, we have calculated the hyperfine fields at the A and B iron sites in ionic distribution (Fe)A[Ni0.5Co0.5Fe]BO4 as a function of temperature. The theoretical Mössbauer spectra from the above calculated hyperfine fields are obtained and compared with experimental spectra.
Media for 10 Gb/in.2 hard disk storage: Issues and status (invited)
Authors: Lambeth D. N. , Velu E. M. T. , Bellesis G. H. , Lee L. L. , Laughlin D. E.
Published: July 2002

Future 10 Gb/in.2 recording densities represent submicron trackwidths and sub-100 nm bit lengths. This requires extremely small magnetic switching units and very high coercivities of the media to satisfy the signal-to-noise ratio requirements. At the same time the question of magnetic thermal stability and the lack of transducers capable of performing at these densities makes it difficult to evaluate media. An uncoupled, highly uniform magnetic grain size of about 10 nm is a compromise toward maintaining an adequately low media noise and yet maintaining magnetic stability. Here we discuss current media construction, the detrimental role of substrate roughness, the role of new media structures and alloys on microstructure and magnetic properties as well as techniques for evaluating media performance prior to the availability of the required playback heads.
Magnetic relaxation at high linear densities in thin films with perpendicular magnetic anisotropy
Authors: Lairson B. M. , Liu W. , Payne A. P.
Published: July 2002

We have measured the rate at which recorded signals decay in perpendicular Co78Cr17Ta5 alloys, Co70Cr15Ta5Pt10 alloys, and Pd/Co multilayers. At low write frequencies, the magnetization decay resembles that observed by magnetometry. At high write frequencies, the relative decay rate decreases substantially. This is attributed to a change in the demagnetizing energy associated with high linear densities in perpendicular media. A model for magnetization decay is used to deduce the activation volume, the size distribution, and the barrier to flux reversal which exists for the alloy films. A time scale tε is introduced, over which the decay rate is dominated by the initial condition applied by the write head. The observed decay in the multilayers was much lower (<0.5%/time decade) than in the alloys (3%–4%/time decade) at all of the spatial frequencies tested.
Symmetry of the magneto-optic response of the Sagnac interferometer
Authors: Dodge J. S. , Klein L. , Fejer M. M. , Kapitulnik A.
Published: July 2002

We demonstrate the application of the Sagnac interferometer to magneto-optic measurements at an oblique angle of incidence. With an appropriate choice of polarization states for the two counter-propagating beams, a wide variety of magneto-optic effects may be measured, in the absence of an external perturbing field, with a sensitivity of a few hundred nanoradians. Using simple symmetry analysis of the conventional Kerr rotation measurement geometry, we may distinguish contributions to the non-reciprocal phase shift due to the polar, longitudinal and transverse Kerr effects, and consequently completely determine the magnetization vector direction, averaged over the probed region. Magneto-optic hysteresis loops were taken on a permalloy film to demonstrate the effectiveness of the new technique. We discuss the relevance of the Sagnac interferometer to magnetic microscopy and to the study of magnetic anisotropies in thin films.