bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise analysis and image focusing for magnetic force microscopy
Authors: Che Xiaodong , Lederman M. , Gibson G. A. , Bertram H. N. , Schultz S.
Published: July 2002

Magnetic force microscopy (MFM) has been widely utilized to reveal magnetization distributions by sensing the external magnetic-field distribution very close to the sample. The resolution of MFM is determined by the size of the sensor tip and by the spacing between the tip and the measured sample. A technique is developed to analyze the noise and linearity of a MFM image, and consequently to improve the spatial resolution by reducing the spacing loss. As a demonstration, a series of MFM images of a single permalloy particle is obtained and numerically analyzed. The spacing loss is reduced and a much higher resolution image is obtained.
Magnetic-nonmagnetic transition in CrAs and the related compounds
Authors: Suzuki Takanobu , Ido Hideaki
Published: July 2002

Crystallographic parameters of Cr1−xMxAs (M=Ti, Mn, Fe, Co, and Ni; x≤0.1) and CrAs1−xXx (X=P and Sb; x≤0.1) have been precisely determined as a function of temperature from 77 to 320 K. Discontinuous changes of lattice parameters have been observed at the Néel temperature. By this crystallographic method, the Néel temperatures TN of these systems have been determined. By analyzing the results, it has been found that the magnetic state of the compounds around CrAs is strongly controlled by orthorhombic B-axis length: (i) the compounds with B axis less than a critical length Bc of 3.38 Å do not have magnetic ordering and are Pauli paramagnetic down to 0 K: (ii) the compounds with B axis≥Bc undergo a transition at TN from helical to Pauli paramagnetic states: (iii) the compounds of NiAs type with larger B axis (hexagonal a axis) show a Curie–Weiss paramagnetism at high temperatures.
Magnetic ordering in amorphous Bi2O3-ZnO-Fe2O3 films sputtered at high temperatures
Authors: Srinivasan G. , Uma Maheshwar Rao B.
Published: July 2002

The onset of a long-range magnetic order is reported in amorphous Bi2O3-ZnO-Fe2O3 films sputtered at high substrate temperatures. Samples of 0.1 Bi2O3-0.4 ZnO-0.5 Fe2O3 were deposited in a mixed oxygen-argon atmosphere at substrate temperatures Ts=450–875 K. Films are found to be x-ray amorphous for Ts≤675 K. For higher Ts values, nonmagnetic crystalline phases are precipitated in the sample. The samples are paramagnetic at room temperature for substrate temperatures below 475 K. A spontaneous magnetic moment is observed in films deposited at higher Ts. The saturation-induction 4πM at 77 K is in the range 800–3600 G and 4πM increases with increase in Ts. The Curie temperature is found to decrease with Ts. A uniaxial anisotropy character in the films is evident from ferromagnetic resonance studies. Thus, data on structural and magnetic parameters indicate the possible presence of ordered clusters in films sputtered at high temperatures. The presence of ordered clusters need to be independently confirmed with techniques such as transmission electron microscopy.
Static and dynamic magnetic properties of (CoZr)100−x(RE)x amorphous thin films
Authors: Suran G. , Ouahmane H. , Rivoire M. , Sztern J.
Published: July 2002

The saturation magnetization, uniaxial anisotropy, and the dynamical magnetic properties of amorphous (Co92Zr8)100−x(RE)x thin films have been studied for various magnetic rare earths and for 0≤x≤3. The films were rf sputtered in presence of a dc magnetic field applied parallel to the film plane. For RE=Nd, Pr, Dy, and Tb, the films exhibit an in-plane uniaxial anisotropy Ku, the magnitude of Ku being related to the particular RE. When RE=Gd and Sm a biaxial anisotropy develops constituted by a Ku and a perpendicular anisotropy Kp. The resonance linewidth as a function of x and RE is also reported.
In-plane uniaxial anisotropy, coercivity, and magnetic aftereffect of CoZrDy amorphous films
Authors: Suran G. , Roky K. , Sztern J. , Porte M.
Published: July 2002

Amorphous alloy thin films of (Co95Zr5)100−xDyx with a well-defined in-plane uniaxial anisotropy Ku were prepared by rf sputtering. The saturation magnetization, Ku, and the coercive field were studied as a function of temperature and for the composition range 4≤x≤20. Ms could be fitted by the molecular-field model, Ku interpreted by a single-ion anisotropy process, and Hc by a model of Alben, Becker, and Chi [J. Appl. Phys. 49, 1653 (1978)]. At low temperatures (T≤50 K) and for the whole concentration range a new type of aftereffect is observed, the main characteristic of which is described.
Electronic and magnetic structure of Fe ions in NiCr2S4
Authors: Park Jae Yun , Ko Heung Moon , Lee Woon Hwa , Ji Sang Hee , Kim Chul Sung
Published: July 2002

The magnetic semiconductor NixFe1−xCr2S4 (x=0.985, 0.97, 0.96) has been investigated over the temperature range from 12 to 600 K using a Mössbauer technique. The electronic structure of Fe ions in NiCr2S4 was calculated with the Hamiltonian incorporating free-ion term, axial and rhombic crystal field, spin-orbital couplings, and exchange interactions. The ground orbital state is separated by 9.64 ‖λ‖ from the first excited state, thereby making the quadrupole splitting somewhat insensitive to temperature. Using x-ray crystallographic data, the contribution of direct lattice sum to the electric-field gradient has been considered. In calculating the temperature dependence of quadrupole splitting, the axial field parameter Δ1=−3.0‖λ‖, the rhombic field parameter Δ2=−2.8‖λ‖, and the covalency factor α2=0.73 in Ni0.985Fe0.015Cr2S4 were determined. Magnetic hyperfine and quadrupole interactions in the antiferromagnetic state of Ni0.96Fe0.04Cr2S4 at 12 K have been studied, yielding the following results: H=147.8 kOe, 1/2e2qQ(1+1/3η2)1/2=−1.96 mm/s, θ=66°, φ=90°, and η=1.0. The line broadening which suggests the electron relaxation was observed with decreasing temperature.
Measurements of magnetic circuit characteristics for comprehension of intrinsic magnetic properties of materials from surface inspection
Authors: Chen Z. J. , Devine M. K. , Jiles D. C.
Published: July 2002

A transfer function is presented for calculating magnetic field and flux density inside a test material as a result of surface measurement. By considering flux leakage, we introduce a parameter η, called the leakage coefficient, which can be experimentally determined. It is introduced into the equations to make the transfer function more practical. The distribution of field inside a test material is then discussed in accordance with a surface magnetic charge model.
Neutron scattering from the geometrically frustrated pyrochlore antiferromagnet Tb2Mo2O7 (abstract)
Authors: Gaulin B. D. , Reimers J. N. , Tun Z. , Mason T. E. , Greedan J. E.
Published: July 2002

The magnetic metal ions in the cubic pyrochlore Tb2Mo2O7 form an infinite three-dimensional network of corner-sharing tetrahedra with a very high potential for frustration in the presence of antiferromagnetism. Previous bulk susceptibility measurements show strong irreversibilities below a temperature of Tf∼25 K. We have performed neutron scattering measurements that show short range spatial correlations that develop continuously with decreasing temperature, while the characteristic time scale for the fluctuating moments decreases dramatically below Tf. Further, the results indicate extremely slow spin dynamics are relevant near Tf. The low temperature state of this pure material, which exhibits frustration that is solely geometrical in origin, closely resembles that of a spin glass.
Magnetic specific heat and critical magnetic susceptibility of the diluted antiferromagnet CopMg1−pO
Authors: Seehra Mohindar S. , Kannan R. , Ibrahim Manjula M.
Published: July 2002

For CopMg1−pO, a prototype randomly diluted fcc antiferromagnet, measurements of the specific heat versus temperature show that the size of the λ anomaly at TN decreases as p decreases. These results show that with increasing dilution, a progressively larger fraction of the magnetic entropy is removed by short-range order processes. The critical susceptibility χc at TN increases as p decreases, supporting the idea that near Mg sites, the balance of the two antiferromagnetic sublattices is destroyed. After correcting for single ion contribution, χc(p)/χc(1) is found to vary as (p−pc)−τ for p<0.47 (pc=0.136). The experimental value of τ≊0.7 is in reasonable agreement with the numerical estimate of τ=0.5±0.2 by Harris et al. for cubic systems.
Antiferromagnetic exchange and enhanced magnetoresistance in glass/ Fe50 Å/Co11 Å/CutCu/Co11 Å/ Cu10 Å structures
Authors: Freitas P. P. , Trindade I. G. , Melo L. V. , Leal J. L. , Barradas N. , Soares J. C.
Published: July 2002

Glass/ Fe50 Å/Co11 Å/Cut/Co11 Å/Cu10 Å structures were sputtered in a high-vacuum system with a base pressure of 5×10−8 Torr. The magnetoresistance (MR) reaches 8% at room temperature for tCu=10 Å with a saturation field of 700 Oe. For tCu=22 Å the MR reaches 6.4% for a 200 Oe field. Our results are analyzed in a semiclassical approach by solving the Boltzmann equation for the five-layer structure with λCo=76 Å and λCu=420 Å and using both interfacial and bulk spin-dependent scattering. Interlayer coupling was checked by magneto-optical measurements using the transverse Kerr-effect geometry. For tCu=10 Å we observe zero-remanence magnetization curves with saturation fields around 1 kOe. For tCu=22 Å no evidence for macroscopic antiferromagnetic coupling is observed since the hysteresis cycle is almost square.
The heavy fermion compound YbAgCu4
Authors: Schlottmann P.
Published: July 2002

We re-examine the experimental data for the specific heat, the magnetic susceptibility, magnetization, and inelastic neutron scattering for the moderately heavy-electron compound YbAgCu4 within the framework of the single-ion Anderson model. Such an analysis has previously given excellent agreement between theory and experiment for numerous light heavy-fermion compounds. We extend here previous interpretations for the specific heat and magnetization within the Coqblin–Schrieffer model to a common set of model parameters by incorporating a weak valence admixture. The crystalline field splitting in this compound appears to be small compared to the Kondo temperature. Existing exact solutions of the Anderson model within the framework of Bethe’s ansatz are used for the thermodynamic properties. A simple resonant-level model is introduced to parametrize the Kondo resonance and to qualitatively interpret the inelastic neutron scattering cross section.
Metric dependent aspects of inverse problems and functionals based on helicity
Authors: Kotiuga P. R.
Published: July 2002

The helicity of a vector field is a metric independent density. Functionals with first order elliptic systems for Euler–Lagrange equations have been constructed from the helicity. The metric invariance is preserved for finite element discretizations involving ‘‘Whitney elements.’’ This paper relates differential geometric aspects of inverse problems to helicity based functionals in two contexts. First, the inverse problem of electrical impedance tomography in isotropic media is known to be equivalent to determining a metric within a given conformal class from a given ‘‘Dirichlet to Neumann’’ map. This fact is related to the helicity functional and Wexler’s algorithm for recovering an isotropic conductivity. Second, Maxwell’s equations in ‘‘spinor form’’ are shown to be the Euler–Lagrange equations of some complexified time dependent generalization of the helicity functional. In this case metric dependent aspects yield insight into the ‘‘inverse kinematic problem in seismology.’’ These two examples illustrate the underlying geometric structure in classes of inverse problems and algorithms for their solution. ‘‘Do you know Grassmann’s Ausdehnungslehre? Spottiswood spoke of it in Dublin as something above and beyond quarternions. I have not seen it, but Sir William Hamilton of Edinburgh used to say that the greater the extension the smaller the intention.’’ ‘‘May one plough with an ox and an ass together? The like of you may write everything and prove everything in 4nions, but in the transition period the bilingual method may help to introduce and explain the more perfect.’’ Excerpt of a letter from J. C. Maxwell to P. G. Tait; A. P. Wills, Vector Analysis with an Introduction to Tensor Analysis (Prentice–Hall, Englewood Cliffs, NJ, 1931), pp. XXV–XXVI.
Spin density waves in dilute CuMn alloys
Authors: Cable J. W. , Tsunoda Y.
Published: July 2002

Neutron scattering studies on concentrated CuMn alloys show static spin density waves (SDW) that are incommensurate with the lattice and which become dynamic above the freezing temperature Tf with a dispersion relation that is essentially vertical. The existence of both the static and the dynamic SDW in dilute CuMn alloys where the Mn atoms may be separated beyond the range of SDW stability was examined. There is no such cutoff range in the Overhauser SDW model where the transition temperature is simply linear with concentration, but a recent calculation by Ioffe and Feigel’man gives magnetic order that does depend on an interaction range and the density of spins on the lattice. For CuMn alloys, they obtain spin-glass ordering at low Mn concentration with a crossover to short-range helical order near 10% Mn. Our neutron scattering measurements were made on single crystals of CuMn alloys containing 1.4% and 3.0% Mn. Elastic scans along 〈1ζ0〉 at temperatures well below Tf yield the same type of intensity distribution as that previously observed for the more concentrated alloys and show the existence of static SDW at dilutions down to 1.4% Mn. Inelastic scans in the same Q region for the Cu–3% Mn alloy clearly show the presence of dynamic SDW at temperatures up to T/Tf=7.5. These results favor the SDW model of Overhauser as the best description of the magnetic order in dilute CuMn alloys.
Magnetic susceptibility of bcc sodium (abstract)
Authors: Green M. S. , Fry J. L. , Ethridge E. C. , Fazleev N. G.
Published: July 2002

The random phase approximation has been employed to compute the spin and orbital susceptibilities of bcc sodium. The calculations were based upon a self-consistent local exchange and correlation potential and an orthogonalized plane wave basis set. Assuming no overlap between core orbitals, expressions for the necessary matrix elements were formulated and computed accurately. Convergence of various sums was investigated and the results for bcc sodium were compared with the corresponding electron gas values. While the spin susceptibility agreed well with electron gas estimates, it was 25% lower than measured values. The orbital susceptibility was found to be an order of magnitude smaller than electron gas values because of matrix element effects. Including core contributions, the total susceptibility was found to be 0.477±0.022×10–6 emu/cm3 compared with the experimental value of 0.585±0.015. Recent correlation corrections to the band structure of sodium employing the GW method have been used to account for the discrepancy.
The effects of substitutional impurities on the magnetic, electronic, and hyperfine interactions in ilvaite, CaFe3Si2O7O (OH), a mixed-valence iron silicate (abstract)
Authors: Bluncson Cherie R. , Evans B. J.
Published: July 2002

Ilvaite, a mixed-valence iron silicate, rivals magnetite in the complexity of the phenomena exhibited in connection with the simultaneous occurrence of Fe2+ and Fe3+ on equivalent sites. Inasmuch as the effects of impurities on the several phase transitions and electron delocalization have been explored little, if at all, an investigation of the effect of manganese impurities by means of measurements on a large suite of samples has been undertaken. Significant variations in magnetic properties are observed even for low impurity levels. For a Mn2+ content of 0.5 wt %, the low temperature magnetic phase transition is at ∼40 K, for a Mn2+ content of 1.2%, the transition temperature is less than 20 K and for a Mn2+ content of 4.5%, the transition appears to be well below 10 K. In addition to the quantitative variations, the 1/χ versus T curves are qualitatively different for samples with different concentrations of manganese. The 57Fe Mössbauer spectra are also qualitatively different at 298 K with pronounced differences in the resolution of the two Fe2+ patterns and in their relative intensities. In agreement with earlier reports, no evidence for magnetic ordering at 120 K has been observed in the susceptibility curves; the ordering is, however, exhibited in the 57Fe Mössbauer spectra obtained at 82 K. The exploration of the effect of Mn2+ impurities has permitted rare insights to be gained on the relationship between the bulk and local, site-specific properties of ilvaite. Further progress is expected to result from electrical conductivity and x-ray diffraction measurements.
Magnetic scattering of circularly polarized x rays (abstract)
Authors: Fischer P. , Schütz G. , Kaiser W. , Hunecke J. , Knülle M. , Stähler S.
Published: July 2002

The interference of charge and magnetic scattering from ferromagnetic targets leads in case of circularly polarized x rays to a relative difference (flipping ratio) of the Bragg peak intensity in the order of 10−3, when the magnetization aligned in the scattering plane is reversed (spin-dependent scattering). We have measured the spin-dependent scattering in Fe, Gd, and Tb polycrystalline metallic foils using circularly polarized synchrotron radiation. From the data, magnetic form factors have been deduced. As demonstrated for Gd and Tb, from the flipping ratios the orbital and spin contribution can be directly separated by varying the angle between the scattering vector and the sample magnetization. Spin-dependent resonance scattering has been studied at the K edge of a Ni single crystal. A significant enhancement of the magnetic scattering amplitude compared to the magnetic resonance scattering of linearly polarized light and sample magnetization perpendicular to the scattering plane has been observed. A strongly increased nonresonant magnetic scattering with opposite sign compared to the resonant magnetic effects is observed in the preedge energy region below −10 eV with respect to the K-absorption onset. The applicability of magnetic scattering using circularly polarized synchrotron radiation for the investigation of ferromagnetic media especially in view of its complementarity to neutron studies is discussed.
Magnetic and crystallographic study of Co electrodeposited alumite films
Authors: Daimon Hideo , Kitakami Osamu
Published: July 2002

Magnetic properties and crystallographic structures of alumite films of which pores were filled with Co were investigated. The perpendicular magnetic anisotropy energy of the films was smaller than their shape anisotropy energy, which is due to the magnetocrystalline anisotropy of hcp-Co particles in the pores. The c-axis orientation of hcp-Co particles was found to be influenced by the pH near the cathode and the ac frequency used in the deposition. The c axis rose from the in-plane direction of the film to the normal one when the Co was electrodeposited into the pores at high pH value and low ac frequency, and the perpendicular magnetic anisotropy of the films increased. The deposition of Co at high pH value and low ac frequency was supposed to decrease the current density in the reduction process of Co2+ ions, which caused the preferred c-axis orientation to the normal direction of the film.
Diode laser induced chemical vapor deposition of WSix on TiN from WF6 and SiH4
Authors: Desjardins P. , Izquierdo R. , Meunier M.
Published: July 2002

A compact and inexpensive laser direct writing system, using a continuous wave GaAlAs diode laser array emitting 1 W at λ=796 nm, has been developed for the deposition of WSix on TiN from a gas mixture of WF6 and SiH4. Lines 4 to 15 μm wide and 110–950 nm thick are deposited at 5 μm/s in a static reactor. The W/Si ratio in the bulk of the deposit, as measured by Auger electron spectroscopy, is between 1.1 and 1.4 for the lines deposited from a gas mixture of 1 Torr WF6 and 3 Torr/SiH4. In a dynamic reactor, with a flowing gas mixture of 1 sccm WF6 and 3 sccm SiH4 diluted in 50–150 sccm Ar, lines written at 100 μm/s are typically 4–12 μm wide and 250–800 nm thick. The W/Si ratio in the bulk of the deposit is between 1.5 and 1.8 in this case. Thickness decreases when the argon flow increases suggesting that the growth rate is limited by the transport of the reactive species, at least for a portion of the growth. A tungsten-rich top surface of the deposited layer is also observed, indicating that room temperature reactions, between the gas species and the deposited materials, continue after the deposition.
Spectral widths of a F2 (D′3Π2g→A′3Π2u) laser
Authors: Hill Peter Collin , Herman Peter Robert , Sia Robert
Published: July 2002

Spectral widths are reported for a high-pump power F2 excimer laser operating at 3–10 atm pressure. Single-shot interferograms of 1576 Å radiation were produced by a vacuum ultraviolet Fabry–Perot and recorded on film in an argon atmosphere. The 0.01–0.05 Å widths arise from population accumulation in the lower laser state commensurate with laser action developing on multiple rotational lines.
Giant magnetoresistance in layered magnetic compounds (invited) (abstract)
Authors: van Dover R. B. , Gyorgy E. M. , Cava R. J.
Published: July 2002

Some stable compounds form in layered structures, in which magnetically ordered planes alternate with planes that are essentially nonmagnetic or disordered. SmMn2Ge2, for example, consists of planes of ferromagnetically aligned Mn2 separated by a SmGe2 structure (with the Sm moments disordered). Between 90 and 150 K, alternate Mn2 planes align antiferromagnetically, but can be rotated into overall ferromagnetic alignment by a moderate field (2–15 kOe). This is a classic metamagnetic behavior. A first-order structural phase transition accompanies the magnetic transition; it consists of a dilation of the c-axis lattice parameter and contraction of the a-axis lattice parameter with no discernable change in crystal symmetry. We have found that a 4%–8% change in the resistivity is associated with the magnetic transition, which may be related to band-structure effects as well as the elimination of the interlayer magnetic scattering channel. Since these are well-annealed, equilibrium compounds, they allow the study of this scattering channel in the limit of zero layer roughness (unlike thin film multilayers). The use of arc-grown single crystals allows us to measure the anisotropic response of the compounds: for example, the resistivity anisotropy of SmMn2 Ge2 is ρc/ρa∼25, and the AFM-FM transition is found to decrease ρc while it increases ρa. The study of this and similar layered structures serves as a complement to the study of artificial thin film magnetic multilayers.
Preparation of organic semiconductive thin film by plasma polymerization of 3,4,9,10-perylenetetracarboxylic dianhydride and related compounds
Authors: Tanaka Kazuyoshi , Nishio Satoru , Matsuura Yukihito , Yamabe Tokio
Published: July 2002

Homogeneous semiconductive organic thin films were obtained by the radio-frequency (rf) plasma polymerization of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and related compounds such as 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) and perylene. The highest dc electrical conductivity of 1.0×10−1 S/cm at room temperature was obtained in the PTCDA-polymerized sample film prepared with a rf power of 10 W. The conductivity of the films prepared with a rf power of 60 W was lower by three orders of magnitude than those with a rf power of 10 W. Furthermore, the conductivities of the PTCDA- and the PTCDI-polymerized films decreased by exposure to air. In order to clarify these phenomena, the structure and optical properties of the sample films were examined based on the infrared, the electron spectroscopy for chemical analysis, and the ultraviolet-visible measurements.
Correlation between optical spectroscopy and capacitance-voltage profile simulation applied to interface states in multilayer GaAs/AlGaAs heterostructures
Authors: Rimmer J. S. , Hamilton B. , Dawson P. , Missous M. , Peaker A. R.
Published: July 2002

We have determined the interface state density at each interface in a series of GaAs/AlGaAs multilayer heterostructures using capacitance-voltage profile simulation. We find that the values obtained correlate to the interface recombination velocities determined by time resolved photoluminescence and also to the strength of excitonic transitions observed in steady-state photoluminescence. The optical data therefore support the validity of our results. The results show that the interface state density follows a trend that decreases with the growth of each successive interface thereby supporting the view that the interfaces act as gettering planes for impurities during growth. In addition, the parallel application of electrical and optical techniques has allowed us to estimate the activation energy and minority carrier capture cross section of the dominant recombination centers.
Measurements of x-ray emission from zinc and molybdenum transition radiators
Authors: Piestrup M. A. , Ho A. H. , Li Qiang , Silzer R. M. , Feldman G. , Skopik D. M.
Published: July 2002

This article describes the measurements of x-ray power, spatial and spectral distributions from transition radiators whose spectra are narrowed by the foil material’s K-shell photoabsorption edge. We used two foil stacks, one composed of 15 foils of 3-μm-thick Zn and the other composed of 15 foils of 4-μm-thick Mo. At low average currents, the x-ray spectrum produced by transition radiation was measured by pulse height analysis to be between 5 and 9.7 keV for the Zn radiator and between 10 and 20.0 keV for the Mo radiator. These measurements compared well with calculations. The x-ray spatial distribution from the Zn radiator was measured using a silicon linear diode array. The x rays generated by the Zn radiator were found to be emitted in a forward-directed cone with half angle of ∼1.9 mrad with the center of the expected annulus filled. The power density in the peak of the annulus was found to be 50 mW/(mA cm2). At a high average electron-beam current of 12.5 μA, the x-ray power produced by a stack of ten Zn foils was measured in the spectral range between 5 and 9.66 keV to be 1.54 mW with the peak power in the 1 μs macropulse to be 8.5 W. Electron-beam energies between 249 and 282 MeV were used in these experiments.
Cap and capless annealing of Fe-implanted InGaAs
Authors: Gruska B. , Ullrich H. , Bauer R. K. , Bimberg D. , Wandel K.
Published: July 2002

The distribution of Fe implanted at medium (1–4×1014 cm−2) and low (2×1012 cm−2) doses into InGaAs and annealed with or without a cap is investigated and the degree of compensation of such implanted regions is assessed. Secondary ion mass spectrometry profiles of low dose implanted Fe reveal a substantial role of the capping layer. Fe concentrations below as well as above the estimated metal vacancy concentration produced by implantation are observed. The effect of the cap strongly depends on the wet chemical surface preparation before insulator deposition. A correlation of the magnitude of the Fe accumulation at the InGaAs surface with defect related photoluminescence intensity is established. On the basis of the substitutional-interstitial diffusion model the barrier effects of the various caps for host and dopant atoms are analyzed. The best semi-insulating properties were obtained for plasma enhanced chemical vapor deposition SiO2 caped samples using a H2SO4:H2O2:H2O=1:1:125 surface preparation before deposition resulting in a 53% incorporation of Fe. A high electrical activation is proved directly by capacity-voltage profiles.
Thermoelectric measurements of energy deposition during shock-wave consolidation of metal powders of several sizes
Authors: Mutz Andrew H. , Vreeland Thad
Published: July 2002

The degree of shock energy localization within individual particles and between neighboring particles of different size was explored during shock-wave consolidation of spherical metal powders. The thermoelectric voltage generated by the passage of a shock wave through a copper powder-constantan powder interface was recorded. The sizes of the copper and constantan powders were varied between mean diameters of 40 and 98 μm. Shock-wave pressures of 5 GPa were applied by flyer plate impact, and the resulting voltage versus time signals were collected with a 10 ns time resolution. In order to analyze the signals, a simulation of the thermocouple system was developed to account for the effects of multiple particle interactions and a slightly nonplanar copper-constantan interface. The resulting simulated voltage versus time signals are a good match for the observed signals when the size ratio of the copper and constantan particles is less than a factor of 2, and reveal the preferential deposition of energy in smaller particles at the expense of larger particles within the size range examined. The amount of energy localized near particle surfaces was found to be a majority of all the energy, with a significant minority deposited throughout the particle bulk.
Investigation of ion-implanted GaP layers by Brillouin scattering
Authors: Zuk J. , Kiefte H. , Clouter M. J.
Published: July 2002

Surface-acoustic-wave propagation in 200-keV N+- and 100-keV Ar+-implanted GaP have been studied by means of high-resolution Brillouin spectroscopy. The acoustic-wave velocity variations with dose showed marked softening (−13% for Ar+ implantation) associated with progressive disorder, towards amorphization, of the implanted layers. For Ar+ implantation a dose of 3×1014 cm−2 corresponded to the onset of disorder saturation and amorphization of GaP, while for N+ implantation, even at 1×1016 ions cm−2, the amorphous phase was not reached. Annealing studies indicated a partial recovery of the crystal lattice, the most successful being for nonamorphized samples.
Defect identification in semiconductors by Brewster angle spectroscopy
Authors: Lewerenz H. J. , Dietz N.
Published: July 2002

The sensitivity of the pseudo Brewster angle φB and the reflectivity for p-polarized light at this angle Rp‖φB to small changes in absorption is used for the identification of deep and shallow defects in semiconductors. Brewster angle spectroscopy (BAS) was performed on undoped and n-type GaAs as well as on undoped and p-type InP. Comparison with literature values shows that BAS can be used to identify deep defects at room temperature without electrical contacting. The changes in the spectra of undoped and doped GaAs and InP can be explained by involving the respective donor and acceptor levels in the transition processes. For CuInS2 the defects are analyzed by measuring Rp close to φB as a function of photon energy. The findings can be explained on the basis of existing photoluminescence data, postulating two additional deep levels at hν=Ev+0.350 eV and hν=Ev+0.625 eV. The comparison of model spectra for shallow defects with φB spectra of CuInS2 grown with sulphur excess leads to identification of a level at Ev+0.015 eV in accordance with luminescence data on the energetic position of sulphur interstitials. The applicability of BAS is shown, taking into account the experimental limitation through depolarization and angle divergence.
dc electrical conductivity of tellurite phosphate glasses
Authors: Abdel-Kader A. , El-Mallawany R. , ElKholy M. M.
Published: July 2002

The dc electrical conductivity of the ternary glasses [81 mol, TeO2-19 mol P2O5]0.95 [RnOm]0.05 (R=La, Ce, Pr, Nd, Sm, and Yb) have been measured in the temperature range 50–300 °C. The electrical conductivity data have been examined and discussed on the basis of small polaron hopping conduction theory for the purpose of determining why rare earth containing tellurite glasses show lower electrical conductivity than the undoped glass. The values of the activation energies were in the range 0.84–1.04 eV depending upon the kind of the rare-earth ion. It is concluded that the lower dc electrical conductivity of these rare earth containing tellurite phosphate glasses is predominantly due to a higher activation energy.
High resolution x-ray diffraction analysis of Si/GaAs superlattices
Authors: Gillespie H. J. , Wade J. K. , Crook G. E. , Matyi R. J.
Published: July 2002

High-resolution x-ray diffraction has been used to characterize Si/GaAs superlattices grown on GaAs substrates by molecular beam epitaxy. A typical superlattice structure consisted of ten periods of thin (<5 Å) layers of pseudomorphic silicon alternating with thick GaAs layers; typical GaAs thicknesses range from approximately 100 to 1850 Å. X-ray rocking curves showed sharp and intense satellite peaks (out to 22 orders in one case), indicating a high level of structural quality. Excellent agreement has been obtained between the observed diffraction patterns and those calculated via dynamical simulation. Structural models in which the silicon exists as 2.7 Å bilayers with interfacial Si/GaAs alloy transition layers of either monolayer or bilayer thickness fully describes the observed diffraction patterns.
Laser-induced acoustic phonon gratings in semiconductor thin films
Authors: Wang J. , Hutchings D. C. , Miller A. , Van Stryland E. W. , Welford K. R. , Muirhead I. T. , Lewis K. L.
Published: July 2002

Laser induced ultrasonic standing waves are observed in molecular beam deposited ZnSe thin films using the transient grating technique. This observation is attributed to a very short trapping time for single photon absorption in the band tail. The period of the standing wave is used to determine the acoustic phonon velocity in the ZnSe thin film which indicates that it is longitudinal acoustic phonons which are excited.
Rapid annealing effect in the superconducting 2223 Bi(Pb)SrCaCuO thin films prepared by sputtering
Authors: Hakuraku Y. , Mori Z.
Published: July 2002

Thin films of Bi(Pb) SrCaCuO were prepared on MgO (100) by single-target sputtering. This deposition process yielded c-axis oriented superconducting thin films with a smooth surface. The as-grown films showed a 2223 single phase and zero resistivity at about 83 K. After deposition, the films were rapidly annealed at 830–850 °C within 120 s in air. The superconducting properties of the annealed films were greatly improved by optimizing the temperature and time during rapid annealing. The lead concentration in the as-grown films apparently was almost zero. However, the films annealed while placing a Bi(Pb)SrCaCuO bulk sample directly on the film surface had a clear lead concentration. The relative cationic ratio of the other elements in the annealed films was almost the same as that of the as-grown films. X-ray photoelectron spectroscopy measurement was carried out to study the change of chemical environments of each ion. Films annealed at 840 °C for 30 s in air showed zero resistivity at 105 K and had the critical current density of about 3×106 A/cm2 at 77 K.
Photon-gated persistent spectral hole burning by electron transfer from a doped donor to an acceptor branched to a host polymer matrix
Authors: Suzuki H. , Nishi T. , Shimada T. , Hiratsuka H.
Published: July 2002

Two-color photon-gated persistent spectral hole burning (PSHB) via donor-acceptor electron transfer is reported in systems where the acceptor, 10-chloroanthracene, was intentionally branched to a side chain of the poly(methylmethacrylate) (PMMA) host polymer while the donor, metal-free tetraphenylporphine, was dispersed in the polymer. The systems, which had an acceptor concentration of up to 10−1 M, were prepared without aggregation of the acceptor. Spectral holes were burnt in the Qx(0,0) absorption band of the donor when the systems were simultaneously irradiated with a frequency-selective excitation (duration: 500 ps; energy: 200 nJ/cm2) and a gating excitation (wavelength: 514.5 nm; duration: 33 ms; energy: 14 μJ/cm2). The difference absorption spectrum between the unburned absorption spectrum and one recorded after photon-gated PSHB has confirmed that the hole formation mechanism is donor-acceptor electron transfer from a photoexcited donor to a ground-state branched acceptor. The thermal stability of burnt holes measured with a temperature cycling experiment increased when the acceptor was branched into PMMA. The effect of acceptor branching on the PSHB characteristics is discussed with reference to those for an acceptor-doped system.
The effect of nonlinear gain on the stability of evanescently coupled semiconductor laser arrays
Authors: Nichols D. T. , Winful H. G.
Published: July 2002

We show that nonlinear gain saturation can enhance the stability of evanescently coupled semiconductor laser arrays.
Very high purity InP layer grown by liquid-phase epitaxy using erbium gettering
Authors: Wu Meng-Chyi , Chiu Cheng-Ming
Published: July 2002

Very high purity InP layers have been grown by liquid phase epitaxy using rare-earth erbium as the donor-gettering source. All the Er-doped samples still exhibit n-type conduction, but its carrier concentration decreases with increasing the Er amount into the growth solution. The 300 K electron concentration as low as 7×1013 cm−3 has been achieved on high-purity layers. By low-temperature photoluminescence measurement, the donor impurities of the InP samples have been obviously reduced due to the Er gettering. The free-exciton line with a linewidth of 0.9 meV dominates in the exciton spectra and the intensity ratio of free exciton to exciton-bound-to-neutral-donor lines exceeds 2.6 for the high-purity layers with n=7×1013 cm−3.
Improvement of magneto-optical properties of Co/Pt multilayers prepared by sputtering in Ar
Authors: Nakajima Junsaku , Takahashi Akira , Ohta Kenji , Ishikawa Toshio
Published: July 2002

We investigated methods for increasing the coercive force and the Kerr rotation angle and for reducing the Curie temperature of Co/Pt multilayers to make them suitable as magneto-optical recording media. The multilayers were prepared by magnetron sputtering using Ar gas. It was found that the coercive force increased with the magnetic flux density above the magnetron target and such an increase did not degrade the crystalline quality nor make less rectangular the Kerr hysteresis loops. The Kerr rotation angle increased when the number of layers per unit thickness was increased without changing the total Co content. The Curie temperature increased with Co content but was not affected by the number of layers. Therefore, Co content and number of layers per unit thickness were optimized in order to obtain a large Kerr rotation angle and a low Curie temperature. Moreover, read/write characteristics of a magneto-optical disk using the Co/Pt multilayer were examined: a carrier-to-noise ratio of 45 dB was obtained for a bit length of 0.76 μm.
A method for the determination of the elastic constant ratio K33/K11 in nematic liquid crystals
Authors: Scharkowski A. , Crawford G. P. , Z̆umer S. , Doane J. W.
Published: July 2002

A detailed analysis of the recently proposed [Appl. Phys. Lett. 60, 3226 (1992)] method for the direct determination of the bend-to-splay bulk elastic constant ratio (K33/K11) in nematic liquid crystals is presented. K33/K11 is directly measured from the optical birefringence pattern of an escaped-radial nematic director field using the Frank elastic free-energy approach to determine the stable structure in supramicrometer capillary tubes with strong homeotropic anchoring conditions. No external field or a priori knowledge of the anisotropy in magnetic or electric susceptibility is required. The simple experimental setup used is available in most laboratories, making this an attractive and convenient technique to probe the elastic character of nematic materials. The results for 5CB and PCH-5 are in good agreement with data obtained from conventional electo-optic and magneto-optic techniques.
The effect of void growth on Taylor cylinder impact experiments
Authors: Addessio F. L. , Johnson J. N. , Maudlin P. J.
Published: July 2002

Taylor cylinder impact experiments have provided useful information concerning the dynamic response of materials. In an effort to obtain data at elevated strain rates, Taylor experiments have been conducted at high velocities. Sections of the recovered specimens reveal a region of porosity located near the base of the cylinders. Computational simulations have been performed to explore the effect of porosity growth on the experimentally observable parameters for Taylor impact tests. The constitutive model used to simulate the growth of voids is based on the Gurson yield surface. A robust and efficient numerical algorithm was developed and implemented into an explicit, two-dimensional, finite-element computer code. The calculations provided good qualitative comparison with experimental data.
Reply to ‘‘Comment on ‘Application of low-temperature ions in the nonequilibrium state plasma of a Penning source’ ’’ [J. Appl. Phys. 69, 7933 (1991)]
Authors: Sato Yukio
Published: July 2002

The results of Sato et al. [J. Appl. Phys. 69, 7933 (1991)] are extended based on Hopkins [J. Appl. Phys. 73, 1007 (1993)]. This is a report on a relation between the confinement time of ions and the Larmor radius of ions in a Penning source.
Thermal problem of curvilinear cracks in bonded dissimilar materials
Authors: Chao C. K. , Shen M. H.
Published: July 2002

Boundary problems for a circular insert bonded partially to the interior of an infinite medium of another material under an uniform heat flow are formulated and solved in closed form. The unbonded portions of the interface may be regarded as circular arcs of discontinuities or curved cracks. By application of the complex function theory dealing with sectionally holomorphic functions, the present problem is reduced to the solution of the problem of linear relationship or Hilbert problem. Exact solution is given for an example of a single circular-arc crack. It is found that the temperature gradients or heat flux near the tips of a curved crack possess the characteristic inverse square-root singularity in terms of the radial distance away from the crack tip which is the same as those obtained for a straight crack between dissimilar materials. Due to this singular behavior, the heat flux intensity factor is introduced to measure the thermal energy intensification cumulated in the vicinity of the crack tip. Numerical results for the temperature and heat flux intensity factor are provided in graphic forms. It is shown that the material of a circular insert having a lower heat conductivity would make the heat flux intensity factor smaller. Consequently, the thermal energy intensification is diminished.
A Monte Carlo computer simulation of electromigration
Authors: Smy T. J. , Winterton S. S. , Brett M. J.
Published: July 2002

In this article, a Monte Carlo computer program is used to simulate the motion of atoms during electromigration. In the program, current density is accurately determined in two dimensions and the result of the impressed current is a drift of activated atoms along the grain boundaries in response to an ‘‘electron wind’’ force. The grain structure simultaneously undergoes annealing—atoms are moved so as to minimize the curvature of the grain boundaries. Heat is lost to the back of the substrate and a single temperature of the metal line is used to characterize both thermal conduction and Joule heating. Qualitatively correct predicted results include the dependence of mean lifetime upon current density, temperature and grain size, the distribution of failure times (log normal), and the occurrence of 1/f noise in measured results.
Interband tunneling in nonparabolic semiconductors in the presence of an electric field
Authors: Chakraborty P. K. , Ghatak K. P.
Published: July 2002

An attempt is made to study the interband tunneling rate for small-gap semiconductors having Kane-type energy bands in the presence of an external electric field, taking InSb as an example for the purpose of numerical computations. The experimentally obtained tunneling currents, which may not be limited by the factor 2, can be better explained by this formulation. Thus, the present analysis is applicable for wider ranger of electric fields and are more consistent with the experimental results than that previously proposed.
Cryogenic scanning tunneling microscopy/spectroscopy on the (001) surfaces of YBa2Cu3Oy epitaxial thin films
Authors: Nantoh Masashi , Hasegawa Tetsuya , Yamaguchi Wataru , Takagi Akihiko , Ogino Masahiro , Kitazawa Koichi , Kawasaki Masashi , Gong Jianping , Koinuma Hideomi
Published: July 2002

As-grown surfaces of c-axis-oriented laser-ablated YBa2Cu3Oy (YBCO) films have been investigated by scanning tunneling microscopy and spectroscopy (STM/STS) at 4.2 K. The square atomic arrangement with an average spacing of 0.4 nm was observed on the specimens even after exposure to ambient atmosphere, indicating that the (001) surface of the YBCO thin film was stable and free from severe contamination or chemical reaction. The STS observations revealed the semiconductive nature of the surface with a band gap of 0.1 eV. However, the tunneling spectrum varied its shape depending on the tip-to-sample distance and a clear superconducting gap structure with 2Δ∼40 meV appeared when the STM tip was closer to the surface than the usual position of the scanning mode, suggesting that the semiconductive layer is confined in the surface region of atomic size thickness.
Photothermal microscopy: Thermal contrast at grain interface in sintered metallic materials
Authors: Mansanares A. M. , Velinov T. , Bozoki Z. , Fournier D. , Boccara A. C.
Published: July 2002

A theoretical and experimental study of the influence of planar thermal barriers on photothermal reflectance microscopy signals is presented. An analytical solution is developed for the problem of vertical barriers in a semi-infinite solid and the signal contrast obtained when scanning through the barrier is discussed as a function of the thermal resistance, the thermal diffusion length, and the pump and probe beam dimensions. The shape and the width of the signal perturbation introduced by the barrier is also analyzed. For the case of slanted barriers results of finite-element calculations are presented, and the main feature of the signal when going from vertical to slanted barriers is thus shown. Finally, the theoretical predictions are compared with measurements made on Fe sintered samples. Scanning through grain interfaces revealed different signal shapes and contrast. Good agreement between theory and experiment was found when the optical contrast at the interface is negligible. Examples are shown where the thermal barrier model is no longer valid and an extended model seems to be necessary.
Dislocation generation mechanisms of InxGa1−xAs (0≤x≤1) epilayers grown on (100) InP substrates by molecular beam epitaxy
Authors: Chang Shou-Zen , Lee Si-Chen , Chen C. R. , Chen L. J.
Published: July 2002

The mechanisms of strain relaxation and dislocation generation for the 2-μm-thick InxGa1−xAs epilayers grown on (100) InP substrates with 0≤x≤1 were investigated. It was found that the growth mode and dislocation density of the InxGa1−xAs epilayers are not only dependent on the lattice mismatch with respect to InP substrates, but the abundance of Ga atoms and the degree of cation disorder in the alloy composition also play important roles. In the negative mismatched range even with a medium lattice mismatch (e.g., ε=−1.1%), InGaAs alloys with a high degree of cation disorder and containing more Ga atoms (x=0.32–0.37) trigger island growth and introduce high-density V-shaped dislocations. In the positive mismatched range, island growth occurs at x≊0.82 (ε=2%) and few V-shaped dislocations are generated. The difference between these two ranges is due to their different Ga concentrations which introduce different island nucleation centers in the initial growth stage.