bluuebunny/crossref_metadata_2025 huggingface dataset:
Accounting for the Hugoniot elastic limits of polymers by using pressure-dependent yield criterion
Authors: Rosenberg Z. , Partom Y.
Published: July 2002

A factor of over 20 is measured between the Hugoniot elastic limits (HEL) of some polymers and their static shear strengths as measured under 1D stress conditions. This factor is too large to be accounted for by strain rate effects. In the present work we derive a new relation between the HEL and the shear strength which is based on a pressure-dependent yield criterion (like the Mohr–Coulomb criterion). The agreement between the experimental value for HEL of Plexiglas and its compressive yield strength is very good, strongly supporting our approach.
Classical electron trajectory in scanning electron microscope mirror image method
Authors: Chen H. , Gong H. , Ong C. K.
Published: July 2002

A scanning electron microscope (SEM) is employed to study the charging phenomenon of polymethylmethacrylate using the mirror image method. Classical scattering theory is modified to calculate the total trapped charge Q. This theory has also been used to justify the use of a fitting procedure to calculate Q. The fitting procedure is more feasible for a SEM which does not have low accelerating voltage facility. Results from both methods are compared. Details of derivation are given.
Silver doping and its influence on the oxygenation during in situ growth of YBa2Cu3O7−x thin films
Authors: Kumar Dhananjay , Sharon M. , Apte P. R. , Pinto R. , Pai S. P. , Purandare S. C. , D’Souza C. P. , Gupta L. C. , Vijayaraghavan R.
Published: July 2002

The influence of Ag doping on both oxygenation and deoxygenation during growth of YBa2Cu3O7−x films at 700 °C by pulsed laser deposition has been studied. Experiments show that undoped and Ag-doped films grown at 200 mTorr oxygen pressure and quenched immediately after termination of growth have a superconducting transition temperature Tc of 61 and 86 K, respectively. The high Tc of 86 K obtained with quenched Ag-doped films is thought to be due to both enhanced oxygen incorporation and reduced deoxygenation associated with Ag doping. These results show that Ag-doped YBa2Cu3O7−x films could be crucial for realizing devices based on multilayer structures.
Onset of electrical conduction in Pt and Ni films
Authors: Maaroof A. I. , Evans B. L.
Published: July 2002

The resistance Rf of Pt and Ni films has been measured during deposition (by ion-beam sputtering) for different deposition rates r and substrate temperatures TS (300≤TS≤575 K). At the onset of deposition (the nucleation stage) Rf varies only slowly with deposition time T and oscillations occur in Rf vs T which are damped at the larger values of r,TS. Over the second stage, during which the metallic nuclei grow in size, Rf decreases over many orders of magnitude and the Rf versus fractional coverage x behavior is described by percolation-type equations around a critical thickness tc. The film thickness tmin (=rTmin) at which the film becomes continuous (x=1) is identified with the minimum in the Rt2 vs t graph. For t≳tmin the Rf vs t behavior is described by surface and grain-boundary scattering equations, the derived values of grain size are related to TS, r, and compared with transmission electron microscope observations. Postdeposition temperature cycling measurements on films deposited at TS=300 K show predominantly thermally activated conduction for t<t0 (tc<t0<tmin). Rf is decreased by annealing, except in the case of Pt (t<1 nm) and Ni (t≤1.5 nm), due to agglomeration and the formation of conducting links which also change the temperature coefficient of resistance.
Pressure dependencies of magnetostrictive strain and d coefficient in Terfenol-D after thermal or magnetic annealing
Authors: Galloway N. , Greenough R. D. , Jenner A. G. I. , Schulze M. P.
Published: July 2002

The pressure dependence of the magnetostrictive strain coefficient, d33, and maximum strains in applied fields of 120 kA m−1 have been measured in samples of Terfenol-D before and after thermal or magnetic annealing. Application of an annealing field, Ha, parallel to the 〈111〉 axes which are normal to grains oriented along the [112̄] axis, leads to an increase in d33 of as much as 81%, with applied uniaxial prestresses as low as 3 MPa. The variation of optimum d33 values as a function of stress applied along the [112̄] axis shows anomalous oscillations after magnetic annealing. The thermal and magnetic effects of the annealing procedures are discussed and a mechanism to explain magnetic annealing is proposed.
Application of the ratio d/χ to the investigation of magnetization processes in giant-magnetostrictive materials
Authors: Piercy A. R. , Busbridge S. C. , Kendall D.
Published: July 2002

The change in magnetostriction Δλ with change in magnetization ΔM for domain-wall motion is shown to depend only on the wall type, the magnetostriction constants, and the saturation magnetization and not on the field required to effect the change. The quantity Π=Δλ/ΔM (or the dynamic equivalent d/χ) is therefore a valuable parameter for use in investigating magnetization processes. Theoretical values of Π are given for different wall processes in 〈111〉 and 〈100〉 easy materials and used to interpret experimental measurements in different (Tb, Dy, Ho)Fe2 materials. It is shown that Π vs M curves are more sensitive to the detail of the magnetization process than λ vs M curves. In 〈111〉 easy compositions the processes are found to be complex with the combination of wall motion processes changing continuously with increasing magnetization and no region where a single process dominates. In contrast, for 〈100〉 easy materials, there is an extended region in which 90° wall processes dominate. In both cases, quasistatic and dynamic processes are shown to be equivalent, independent of temperature, and independent of the frequency and magnitude of the drive field.
Sputtering pressure effects and temperature-dependent magnetism of Co/Pd multilayers
Authors: Jeong S. Y. , Shan Z. S. , He P. , Shen J. X. , Zhang Y. B. , Woollam J. A. , Sellmyer D. J.
Published: July 2002

The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the coercivity mechanism of Co(2 Å)/Pd(13 Å) multilayers were studied as the sputtering Ar pressure varied from 3–15 mTorr and the temperature from 300 to 35 K. It is found that the roughness of the interfaces or film surface increases with increasing sputtering pressure, the anisotropy increases with decreasing temperature and increasing Ar pressure and shows a maximum at PAr≊12 mTorr, and the coercivity increases with Ar pressure and shows stronger temperature dependence at higher Ar pressure. The coercivity mechanism was analyzed in terms of the coercivity predicted by Kronmüller’s theory [Phys. Status Solidi B 144, 385 (1987)]. Wall pinning is found to be the main mechanism and the size of the pinning site increases slightly as the Ar pressure increases.
Annealing temperature dependence of effective magnetic anisotropy of Fe-Cu-Nb-Si-B nanocrystalline alloys
Authors: Xiong Xiang-Yuan , Ho Kai-Yuan
Published: July 2002

The effective magnetic anisotropy Keff of Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloys annealed at different temperatures was studied by means of magnetization measurements. The results show that the effective magnetic anisotropy Keff of the alloys annealed at Ta=480–550 °C is one order of magnitude smaller than that of individual α-Fe(Si) crystallites with the same Si content. With increasing Ta, the effective magnetic anisotropy Keff increases slightly (from 860 to 910 J/m3), and the initial permeability reaches a maximum value at Ta=550 °C. The improvement of the soft magnetic properties mainly results from the large decrease in saturation magnetostriction λs of the alloy and has nothing to do with the variation of the effective magnetic anisotropy.
Third-order nonlinear spectroscopy in As2S3 chalcogenide glass fibers
Authors: Asobe Masaki , Kanamori Terutoshi , Naganuma Kazunori , Itoh Hiroki , Kaino Toshikuni
Published: July 2002

Third-order nonlinear optical properties of As2S3-based glass fibers are studied at a wavelength of around 1.55 μm. Through time-resolved pump-probe measurements and analysis of spectrum broadening due to self phase modulation, it is confirmed that As2S3-based glass fibers are capable of instantaneous nonlinear refractive response to a subpicosecond pulse. Stimulated Raman scattering (SRS) with a Stokes shift Δk=344 cm−1 is observed using a picosecond pump pulse. The Raman gain coefficient was estimated to be 4.4×10−12 (m/W), which is two orders of magnitude higher than that for silica fiber. The relaxation time of the Raman contribution to nonlinear refraction is estimated to be 97 fs and the influence of the SRS on subpicosecond pulse propagation is observed as a low-frequency Raman gain. The two-photon absorption (TPA) coefficient is estimated to be α2=6.2×10−15 (m/W) through a transmission change measurement. The TPA figure of merit for As2S3 glass at a wavelength of 1.55 μm is estimated to be low enough for all-optical switching applications.
Stability of C54 titanium germanosilicide on a silicon-germanium alloy substrate
Authors: Aldrich D. B. , Chen Y. L. , Sayers D. E. , Nemanich R. J. , Ashburn S. P. , Öztürk M. C.
Published: July 2002

The stability of C54 Ti(Si1−yGey)2 films in contact with Si1−xGex substrates was investigated. The C54 Ti(Si1−yGey)2 films were formed from the Ti-Si1−xGex solid phase metallization reaction. It was determined that initially C54 Ti(Si1−yGey)2 forms with a Ge index y approximately the same as the Ge index x of the Si1−xGex substrate (i.e., y≊x). After the formation of the C54 titanium germanosilicide, Si and Ge from the Si1−xGex substrate continue to diffuse into the C54 layer, presumably via lattice and grain boundary diffusion. Some of the Si diffusing into the C54 lattice replaces Ge on the C54 lattice and the Ge index of the C54 Ti(Si1−yGey)2 decreases (i.e., y<x). We propose that this process is driven by a reduction in C54 crystal energy which accompanies the replacement of Ge with Si on the C54 lattice. The excess Ge diffuses to the C54 grain boundaries where it combines with Si1−xGex from the substrate and precipitates as Si1−zGez which is Ge-rich relative to the substrate (z≳x). This segregation and precipitation enhances the agglomeration of the C54 titanium germanosilicide film (i.e., lower agglomeration temperature). It was observed that rapid thermal annealing techniques could be used to reduce the annealing duration and resulted in a reduction of the Ge segregation.
Transmission electron microscopy study of microstructure and [112̄0]//[001] polycrystalline epitaxy of CoNiCr/Cr bilayer films
Authors: Tang Li , Lu Dong , Thomas Gareth
Published: July 2002

Detailed investigations of the microstructure and polycrystalline epitaxy of CoNiCr/Cr bilayer films have been carried out using various techniques of transmission electron microscopy. The average grain size for both the Cr and CoNiCr layers was about 510 Å although there is a great difference in their morphology. Analysis of the discontinuous ring (arced) diffraction patterns of the layers showed that the Cr underlayer is strongly [001] textured and the CoNiCr layer is weakly [112̄0] textured. The angular distribution of the Cr underlayer [001] texture axis was determined to be 6.7° and the ratio of the number of [001] textured grains to that of the randomly oriented grains was estimated to be 3:7 using dark-field imaging techniques.
Theoretical analysis of birefringence and form-induced polarization mode dispersion in birefringent optical fibers: A full-vectorial approach
Authors: Tzolov Velko P. , Fontaine Marie
Published: July 2002

A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full-vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form-induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.
Donor generation from native defects induced by In+ implantation into tin-doped indium oxide
Authors: Haynes Tony E. , Shigesato Yuzo
Published: July 2002

Low-resistivity tin-doped indium oxide thin films have been implanted with 115In+ ions in order to increase the concentration of electrically active oxygen vacancies. The carrier density, Hall mobility, and optical properties of the as-implanted films have been determined as a function of In+ dose. Three dose ranges are described. For doses up to 2.5×1014/cm, both carrier density and Hall mobility initially decrease to respective saturation values. Then, at doses between 2.5×1014/cm2 and 2.5×1015/cm2, the carrier density increases while the mobility remains constant. At still higher doses, the Hall mobility begins to decrease abruptly. Mechanisms accounting for the implantation-induced changes in each of these three dose ranges are discussed. In particular, it is shown that the rate of increase of the carrier density with In+ dose in the intermediate range agrees quantitatively with the rate of production of oxygen-vacancy donors that is necessary to fully accommodate the implanted In substitutionally on In2O3 lattice sites during implantation.
Stresses in chemical vapor deposited epitaxial 3C-SiC membranes
Authors: Su C. M. , Fekade A. , Spencer M. , Wuttig Manfred
Published: July 2002

The internal stresses in chemical-vapor-deposited 3C-SiC films were studied by a vibrating membrane technique. The differential thermal expansivity of 3C-SiC films was investigated by the change of the internal stress as a function of temperature. It was found that the internal stress of the films is dominated by thermal stresses and its magnitude depends both on doping and the film thickness. While p doping substantially increases the stress, increasing the film thickness reduces the stress of the SiC layer. The thermal expansivity of the SiC layer shows a lower value which is significantly less than that of bulk 3C-SiC and tends to approach the expansivity of the Si substrate. It is proposed that the stress dependence of the SiC films on doping and film thickness is the result of the film morphology which is heavily faulted for very thin films and more perfect as the film thickness increases.
Photoelectric properties of Ag–As–S glasses
Authors: Tanaka K. , Itoh M. , Yoshida N. , Ohto M.
Published: July 2002

Photoconductive and photovoltaic responses in glassy Ag–As–S ion-conducting semiconductors have been studied. The ac conductivity of the glass increases with illumination, while the increase is ascribed to enhanced ionic conduction caused by temperature rise and to interfacial photoeffects. Bulk photocurrent is not detected. By contrast, photovoltages appear in Ag–As–S samples having sandwich and floating electrodes. The photovoltaic characteristics are discussed in terms of classical electrodynamics assuming interaction between electronic carriers and Ag+ ions.
Spectroscopic ellipsometry and thermoreflectance of GaAs
Authors: Ozaki Shunji , Adachi Sadao
Published: July 2002

Spectroscopic-ellipsometry (SE) and thermoreflectance (TR) spectra of GaAs are presented. Measurements are carried out on the same bulk sample in the 1.2–5.6 eV photon-energy range at room temperature. These spectra are analyzed based on a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental SE and TR data over the entire range of photon energies. The fact definitely links the temperature-induced change in the dielectric function (TR) to the first derivative of the pseudodielectric function (SE). It is also concluded that the broadening terms cannot be neglected in the analysis of TR spectra.
Thermophysical effects in laser processing of materials with picosecond and femtosecond pulses
Authors: Pronko P. P. , Dutta S. K. , Du D. , Singh R. K.
Published: July 2002

Application of picosecond and femtosecond laser pulses to the controlled ablation of materials represents a relatively unexplored yet important topic in laser processing. Such ultrashort pulses are of potential value in areas of thin-film deposition, micromachining, and surgical procedures. We report here some early results of systematic studies being done from the femtosecond to the nanosecond regime, as an assessment of the problems and benefits associated with various laser pulse durations and their use in processing optically absorbing media. Experimental data and theoretical results of computer simulations are presented and compared for the threshold energies of ablation in gold as a function of pulse width from 10 ns to 100 fs. This work is then extended to include further numerically computed results for gold and silicon on ablation rates, threshold surface temperatures, liquid thicknesses, and vaporization rates as a function of pulse duration throughout the ultrafast regime from tens of femtoseconds to a few hundred picoseconds.
Structural characterization of epitaxial BaTiO3 thin films grown by sputter deposition on MgO(100)
Authors: Kim Sangsub , Hishita Shunichi , Kang Young Min , Baik Sunggi
Published: July 2002

Epitaxial thin films of BaTiO3 have been prepared using radio-frequency magnetron sputter deposition on MgO(100) substrates. Various x-ray-diffraction techniques were employed to characterize the crystal structure of the films. The films were fully tetragonal and consisted of c domains. Their tetragonality has been shown to be 1.013, which is almost the same as the bulk value of BaTiO3. However, the cross-sectional transmission electron microscopic micrograph showed that a very small amount of a domains coexists forming 90° domain boundaries in the matrix of c domains. In spite of the negligible strain caused by the phase transformation, it seems to be inevitable to form a certain small amount of a domains in the BaTiO3 film on MgO system.
Magnetostatic wave dynamic magnetization response in yttrium iron garnet films
Authors: Tsankov Mincho A. , Chen Ming , Patton Carl E.
Published: July 2002

The dynamic microwave magnetization (DMM) amplitude of magnetostatic waves in yttrium iron garnet films at 5–6 GHz has been measured as a function of input power. The measurement is based on the characteristic frequency shift in the power transmission spectrum. This shift is related to the reduction of the effective static magnetization and, therefore, the increase of the DMM amplitude at high power. The measurements were made on 7.2-μm-thick, single-crystal yttrium iron garnet films. A pulsed frequency-swept microwave signal at 5–6 GHz was used to launch the magnetostatic waves. The signals were excited and detected by planar microstrip transducers. Measurements were made for magnetostatic forward volume waves (MSFVW) and magnetostatic surface waves (MSSW). The duty cycle of the pulsed microwave signal was kept at 0.1% in order to avoid sample heating effects. The shifts for small features in the transmission vs frequency profiles were used to determine the DMM amplitudes. At low power, the DMM amplitude increased with power. Saturation occurred at high power. The results indicate a saturation DMM response at about 10% of the saturation magnetization for input power in the 3–4 W range for MSFVW signals and above 0.5 W for MSSW signals.
Impedance spectroscopy on lithiated Ti oxide and Ti oxyfluoride thin films
Authors: Stro/mme M. , Gutarra A. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Films of Ti oxide and Ti oxyfluoride were produced by reactive magnetron sputtering of Ti in Ar+O2(+CF4). Compositional and structural analyses were accomplished by Rutherford backscattering spectrometry, x-ray diffraction (XRD), infrared absorption spectrometry, and atomic force microscopy (AFM). Electrochemical characterization of films immersed in a Li conducting electrolyte was performed with cyclic voltammetry and coulometric titration. Detailed impedance spectra were recorded for the 2×105–1×10−3 Hz range. The impedance responses of pure and fluorinated Ti oxide films in the lithium containing electrolyte differed significantly even if their structures, according to AFM and XRD, were very similar. One main difference was the size of the charge transfer resistance, presumably connected to the Li ion injection from the electrolyte into the film. A modest fluorination lowered this resistance by about two orders of magnitude. The voltammetric and the impedance responses, as well as the magnitude of the chemical diffusion coefficient, of the fluorinated Ti oxide film were strikingly similar to the response of WO3 films. This similarity does not occur for the pure Ti oxide films, where a process, believed to be the Li ion injection, could be identified with the main features of the frequency-dependent impedance. Underlying this charge transfer mechanism, however, a process represented by a constant phase element seems to be operating. This latter process may have its origin in Li diffusion into the film.
Theoretical study on the strain dependence of the magnetic anisotropy of X/Co(X=Pt, Cu, Ag, and Au) metallic multilayers
Authors: Kyuno K. , Ha J.-G. , Yamamoto R. , Asano S.
Published: July 2002

A first-principles calculation of the magnetic anisotropy energies of X/Co (X=Pt, Cu, Ag and Au) metallic multilayers has been performed to investigate the effect of strain on the magnetic anisotropy. It is successfully predicted that Pt/Co and Au/Co multilayers exhibit perpendicular magnetic anisotropies in accordance with experiments. The strength of the hybridization of electronic states at the interface determines the relative position of the Fermi energy to the local density of states (LDOS) of ‖m‖=2 character of Co d electrons of minority spin. If the LDOS of ‖m‖=2 character is large at the Fermi energy, a system shows a perpendicular anisotropy. The anisotropy energies of all the systems increase as a function of interatomic distance in the in-plane direction. The magneto-elastic constants are more than twice the value of pure Co. The origin of this large value is explained in terms of the change of relative position of the Fermi level to that of the LDOS of ‖m‖=2 character as the value of strain increases.
Comprehensive Rutherford backscattering and channeling study of ion-beam-synthesized ErSi1.7 layers
Authors: Wu M. F. , Vantomme A. , De Wachter J. , Degroote S. , Pattyn H. , Langouche G. , Bender H.
Published: July 2002

Heteroepitaxial ErSi1.7 layers with excellent crystallinity (χmin of Er is 1.5%) have been prepared by high-dose 90 keV Er implantation into a Si(111) substrate using channeled implantation. Such an ErSi1.7/Si system offers a rare opportunity to study comprehensively the structure, orientation, and strain using Rutherford backscattering spectrometry and channeling analysis. We found that the minimum yield and width of the [0001] dip of the Er atoms are quite different from that of the Si atoms in the silicide layer. It is confirmed that the azimuthal orientation of the hexagonal ErSi1.7 layer to the cubic Si substrate is ErSi1.7 [0001] ∥ Si[111] and ErSi1.7 {112̄0} ∥ Si {110}, and that the epilayer is compressively strained. Besides, by using the angular scan and image scan, we reveal that the dips of the {101̄0} family are missing for the Si atoms in the epilayer but do exist for the Er atoms in the same epilayer. The reason for this drastic difference is explained by the separate {101̄0} planes and the different steering potential of the Si and Er atoms in ErSi1.7.
Magnetostriction and thin-film stress in high magnetization magnetically soft FeTaN thin films
Authors: Minor M. K. , Viala B. , Barnard J. A.
Published: July 2002

Domain structures in thin-film heads can be significantly influenced by magnetoelastic anisotropy. In this study we have undertaken systematic measurements of magnetostriction and stress in as-deposited and annealed states in FeN and FeTaN single-layer thin films with varying nitrogen contents. Magnetostriction was positive for FeN films, increased with increasing nitrogen content, and shifted toward negative values after annealing. Stress in as-deposited FeN films was tensile and decreased (became more compressive) with increasing nitrogen content. Annealing the FeN films resulted in significant stress relief. By contrast, magnetostriction was found to be negative for simple FeTa (zero nitrogen) and increased linearly with increasing nitrogen content to positive values. The magnetostriction in FeTaN did not change significantly after annealing at 200 and 250 °C. FeTaN film stresses were compressive in the as-deposited state and increased in magnitude (became more compressive) with increasing nitrogen content. After annealing these stresses were relieved slightly. Ta has been found to be very effective in enhancing the thermal stability of the FeN films.
Neutron diffraction and Mössbauer spectral study of the Nd2Fe16TiCx solid solutions
Authors: Marasinghe G. K. , Ezekwenna Peter C. , James W. J. , Long Gary J. , Pringle O. A. , Hu Z. , Yelon W. B. , Grandjean F.
Published: July 2002

Three samples of Nd2Fe16TiCx, with x equal to 0.0, 0.3, and 2.8, with the Th2Zn17-type rhombohedral structure, have been studied by powder x-ray and neutron diffraction, magnetic measurements, and Mössbauer spectroscopy. Nd2Fe16Ti and Nd2Fe16TiC0.3 were synthesized by induction melting stoichiometric amounts of the constituent elements, whereas Nd2Fe16TiC2.8 was synthesized by methane-derived gas phase insertion of carbon into finely ground Nd2Fe16Ti at 600 K. The neutron diffraction determined titanium site occupancies are similar in both Nd2Fe16Ti and Nd2Fe16TiC2.8 in which titanium preferentially occupies the 6c transition metal site. In contrast, the titanium occupancies in Nd2Fe16TiC0.3 are markedly different in that titanium avoids the 6c transition metal site and randomly occupies the other three transition metal sites. This difference in occupancies most likely occurs because the titanium diffusion rate during the quenching of Nd2Fe16TiC0.3 is affected by the presence of carbon in the melt. Even though the unit cell volume of Nd2Fe16TiC2.8 is larger than that of Nd2Fe17N3, the 615 K Curie temperature of Nd2Fe16TiC2.8 is much lower than the 746 K Curie temperature of Nd2Fe17N3. This is an indication that the volume expansion, which occurs upon nitrogenation of R2Fe17, is not the only factor which contributes to the increase in the Curie temperature. The Mössbauer spectra of Nd2Fe16Ti confirm the high preferential titanium occupancy of the 6c site.

At 85 K the weighted average hyperfine field of Nd2Fe16Ti is approximately 263 kOe, a value which is 33 kOe smaller than that in Nd2Fe17. The 85 K Mössbauer spectrum of Nd2Fe16TiC0.3 is virtually identical to that of Nd2Fe17 and indicates an approximately random titanium occupancy of the four transition metal sites.
High field magnetization isotherms of the Pr2Fe17D5 system
Authors: Isnard O. , Guillot M. , Miraglia S. , Fruchart D.
Published: July 2002

We have investigated the magnetic properties of the ferromagnetic compounds Pr2Fe17 and Pr2Fe17Dx. First, the sample preparation is described and the location of interstitial deuterium atoms is reviewed according to previous neutron diffraction analysis. In this article, we report high field magnetization measurements performed up to 200 kOe in continuous fields, and isothermal magnetization curves measured between 2 and 300 K on oriented powder samples. Below 250 K, an anomaly in the magnetization curves of Pr2Fe17D5 has been detected. We discuss the influence of hydrogen on this field-induced anomaly, which is strongly temperature dependent and possible origins such as crystal field effects or first order magnetization process. A comparison is made with Pr2Fe17Nx in which no anomaly was observed.
Quantum oscillations of properties in magnetic multilayers (invited)
Authors: Bayreuther G. , Bensch F. , Kottler V.
Published: July 2002

An oscillatory interlayer exchange coupling observed in many sandwich and multilayer films can be understood as an interference effect of electron waves partially reflected at each interface with spin dependent reflection coefficients. Consequently, we might expect all magnetic properties in some way related to the density of states to oscillate as a function of the magnetic and nonmagnetic layer thickness. In order to experimentally test this concept we have measured different magnetic properties of Ni/Au multilayer films prepared by magnetron sputtering on glass substrates. The Ni thickness was kept constant at tNi=(7.3±0.5) Å while the Au layer thickness was varied between 4 Å and 80 Å. The films had a coherent fcc structure with (111) texture. The saturation field and the remanence oscillate as a function of tAu with a period which agrees well with a theoretical value calculated from the bulk Fermi surface of Au and proves that indeed an oscillatory exchange coupling is present. The Curie temperature shows oscillations with tAu clearly correlated with the exchange coupling constant, J: TC oscillates like the absolute value of J. This behavior is indeed expected from mean field theory. Similar oscillations are found for the spin wave parameter and the ground state magnetic moments. The variation of the exchange coupling with temperature and the role of inhomogeneities for the interpretation of the experimental data are discussed.
On the low resistance Au/Ge/Pd ohmic contact to n-GaAs
Authors: Hao P. H. , Wang L. C. , Deng Fei , Lau S. S. , Cheng J. Y.
Published: July 2002

We report that a Au/Ge/Pd layered structure can result in low contact resistivities (∼10−6 Ω cm2) to n-GaAs processed in three temperature ranges (175–200, 340–350, and 425–450 °C). The contacts processed below the Au–Ge eutectic temperature (361 °C) show good surface and interface morphology, thermal stability, Au wire bondability, and reproducibility. The ohmic contact formation mechanisms are also presented.
Recording performance of submicron track width thin film heads
Authors: Lam T. T. , Luo Y. , Zhu J.-G. , Tong H.-C. , Rottmayer R.
Published: July 2002

This spin-stand measurement study focuses on recording characteristics at submicron scale track width. The pole tips of a set of identical thin film heads were trimmed from the air-bearing surface by focused ion beam etching. A set of thin film heads with track widths ranging from W=2 μm to W=0.5 μm were produced. Recording experiments were performed on a high precision spin-stand tester using these heads. Both on-track and off-track performances were studied and analyzed. As the track width is scaled down, degrading of recording performance is observed. When the width of a recording head is decreased, the onset of partial erasure occurs at a lower density, and the noise power per unit head track width increases. Further investigation on the track profiles reveals that the extent of partial erasure is higher at the track edge as density increases, and this phenomenon is more pronounced in narrower track width heads.
High-resolution observation of magnetization processes in 2 μm × 2 μm × 0.04 μm permalloy particles
Authors: Runge K. , Nozaki Y. , Otani Y. , Miyajima H. , Pannetier B. , Matsuda T. , Tonomura A.
Published: July 2002

The magnetization process in an array of 2 μm × 2 μm × 0.04 μm permalloy particles fabricated on a 100 nm carbon membrane was investigated by means of high-resolution Lorentz microscopy and electron holography in magnetic fields parallel and perpendicular to the film surface. For perpendicular fields, the magnetization reversal was found to begin with the nucleation of a vortex which gradually transformed into a closure domain configuration. At the remanent state, the flux closure was achieved with the generation of a new type of doubled domain wall.
Spin orientation in an exchange coupled Fe/Cr/Fe trilayer determined by polarized neutron reflection
Authors: Bland J. A. C. , Leung H. T. , Blundell S. J. , Speriosu V. S. , Metin S. , Gurney B. A. , Penfold J.
Published: July 2002

We have used polarized neutron reflection to determine the layer-dependent spin orientations in an antiferromagnetically coupled 100 Å Cr/50 Å Fe/15 Å Cr/50 Å Fe/Si sandwich structure prepared by sputtering. At low field, the net Fe layer magnetic moments align in an asymmetric canted orientation with a near zero total magnetic moment for the sample. At high fields, a canted state, nearly symmetric with respect to the applied field direction is observed and the magnetization in each layer does not reach the bulk saturation value until the layers are ferromagnetically aligned. The behavior is discussed in the context of current theories of exchange coupling.
Electronic and magnetic structure of iron nitride, Fe16N2 (invited)
Authors: Sakuma Akimasa
Published: July 2002

The result of spin-polarized band calculation for Fe16N2 is presented. The most distant Fe atoms from N is found to have the largest magnetic moment. The major role of the N atom is to expand the Fe lattice, leading to the enhancement of the magnetic moments. Quantitatively speaking, the calculated moment of Fe16N2 is about 2.4 μB which is much smaller than the measured value reported. It is also shown that the correction with the orbital magnetic moment and the generalized gradient approximation (GGA) cannot account for this discrepancy. From the point of view of the many body effects, a possibility of the giant moment is also discussed. An important feature of this model is a generation of hopping sites with the N atoms, which likely promotes a ferromagnetic coupling of Fe atoms keeping their large spin-polarization in the atomic limit.
Anisotropic-network-stabilized ferroelectric gels for active matrix addressing
Authors: Hikmet R. A. M. , Boots H. M. J. , Michielsen M.
Published: July 2002

Ferroelectric gels have been produced by polymerization of liquid crystal (LC) diacrylates in mixtures of nonreactive molecules showing the ferroelectric LC (FLC) phase. Within the gels, the orientational, optical, and electrical properties of the nonreactive molecules are to a large extent dominated by the polymer network. For this reason the gels are also referred to as anisotropic-network-stabilized FLC. In this publication gels with homogeneous and hybrid orientations are described. Network molecules of various birefringences are used to show that the effective birefringence within the gels can be reduced. The extinction angle within the gels is also influenced by the anisotropy and the concentration of the network. The gels also show continuous switching over a broad range of voltages. The voltage range becomes broader and shifts to higher voltages with an increasing network concentration. This behavior of FLC gels makes them suitable for the production of grey levels in display applications. Using a transistor as an electronic switch for applying voltages it is shown that gels with homogeneous and hybrid orientations can give smooth transmission–voltage curves.
Ferromagnetic nanocomposite films of cobalt in a ceramic matrix formed by thermal decomposition of cobalt nitride, CoN, precursor
Authors: Maya L. , Paranthaman M. , Thompson J. R. , Thundat T. , Stevenson R. J.
Published: July 2002

Cobalt nitride films, CoN, in a pure form and also as a nanocomposite in boron nitride or silicon nitride were generated by reactive sputtering of cobalt metal, cobalt boride, or cobalt silicide as targets, respectively, in a nitrogen plasma. Cobalt nitride decomposes into the elements by heating under vacuum at 500 °C. The nanostructure of the composites was preserved in the heating treatment thus creating a fine dispersion (<10 nm) of cobalt particles, in a ceramic matrix. The magnetic properties of the nanocomposites were established. The precursor cobalt nitride is paramagnetic while the cobalt dispersions, having dimensions smaller than single magnetic domain, show characteristics typical of those systems such as superparamagnetism and, at temperatures lower than the blocking temperature, marked hysteresis. The coercive fields at 5 K for the BN and Si3N4 nanocomposites are 3250 and 850 Oe, respectively. These films are of interest as data recording media.
Surface relief associated with martensite and bainite in a Cu–Zn–Al alloy measured by atomic force microscopy
Authors: Yang Zhi-Gang , Fang Hong-Sheng , Wang Jia-Jun , Li Chun-Ming , Bao Xiang-Zheng , Zheng Yan-Kang , Huang Yun-Qing
Published: July 2002

Atomic force microscopy was employed to quantitatively study the surface relief accompanying martensite and bainite in a Cu–Zn–Al alloy. It is demonstrated that the surface relief angle associated with martensite is 14.3°, in good agreement with the theoretical result deduced from the phenomenal theory of martensite crystallography (PTMC). However, the surface relief angle associated with bainite is 2.0°–3.2°, which disagrees with the PTMC result. This indicates that the transformation mechanism of bainite is different from that of martensite. The fine structures of the surface relief associated with martensite and bainite are also investigated. The surface relief of martensite is composed of the small parallel relief caused by small martensite plates, and that of bainite is composed of small cells induced by subunits in bainite.
First-principles study of the giant magneto-optical Kerr effect in MnBi and related compounds
Authors: Oppeneer P. M. , Antonov V. N. , Kraft T. , Eschrig H. , Yaresko A. N. , Perlov A. Ya.
Published: July 2002

First-principles band-structure calculations of the magneto-optical Kerr spectra of MnBi and related compounds are reported. We find that band-structure theory, based on density-functional theory in the local spin-density approximation, explains the measured Kerr effect of MnBi very well. A giant Kerr rotation of about −1.75° at 1.8 eV photon energy is given by our ab initio calculations, in accordance with recent experiments. A second peak at 3.4 eV in the Kerr rotation spectrum, however, comes out smaller in our calculations than what was recently measured. It is discussed that this can be due to the Mn–Bi stoichiometry. The microscopic origin of the giant Kerr effect in MnBi is analyzed in detail. We find that the huge Kerr effect in MnBi is caused by the combination of a sizeable magnetic moment of 3.7 μB on manganese, the large spin-orbit coupling of bismuth, and a strong hybridization between the manganese d bands and the bismuth p states. The magneto-optically active states are mainly the p states of Bi. We pay further attention to the experimentally observed unusual temperature dependence of the MnBi Kerr spectra. We show that the observed temperature dependence can be explained by the reduction of the magnetic moment and the average lifetime with increasing temperature. The ab initio calculated Kerr effect in MnBi is furthermore compared to that calculated for the isoelectronic compounds MnAs and MnSb, and that of CrBi, CrTe, and Mn2Bi.
The spectrum of microdisk lasers
Authors: Frateschi N. C. , Levi A. F. J.
Published: July 2002

A model for quantitative analysis of microdisk laser emission spectra is presented. Conformal mapping is used to determine radial and azimuthal eigenvalues, eigenvectors, and cavity Q corresponding to leaky optical resonances in an optically transparent dielectric disk. The effects of gain and loss in a microcavity active medium are also included in the model. Our results compare well with experimental data obtained from an InGaAs/InGaAsP quantum well microdisk laser of radius R=0.8 μm.
High-field fast-risetime pulse failures in 4H- and 6H-SiC pn junction diodes
Authors: Neudeck Philip G. , Fazi Christian
Published: July 2002

We report the observation of anomalous reverse breakdown behavior in moderately doped (2–3×1017 cm−3) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140–150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.
Influence of substrate-boron concentration on the residual end-of-range defects in 450 °C annealed As+-implanted junctions
Authors: Nakada Akira , Massazumi Oka Mauricio , Tamai Yukio , Shibata Tadashi , Ohmi Tadahiro
Published: July 2002

In order to clarify the origin of enhanced leakage currents observed in As+-implanted junctions annealed at a temperature as low as 450 °C [M. M. Oka, A. Nakada, K. Tomita, T. Shibata, T. Ohmi, and T. Nitta, Jpn. J. Appl. Phys. 34, 796 (1995)], two-step implantation/anneal experiments have been conducted and the spatial distribution of end-of-range defects has been investigated. As a result, it has been demonstrated that the residual damage in 450 °C annealed junctions is strongly influenced by the doping level of p-type silicon substrate. The defects were found deeply distributing in the substrate, i.e., about 350 nm below the silicon surface when the doping level was 2.5×1015 cm−3. The defect distribution further extends for higher boron doping levels. Taking these experimental results into account, As +-implanted n+p junctions were formed on substrates having varying doping levels. About two orders of magnitude reduction in the leakage current was observed with decrease in the substrate boron concentration from 1016 to 1014 cm −3. For low boron concentration of 1.6×1014 cm−3, the leakage current level as low as 1.7×10−9 A/cm2 has been achieved by a 450 °C postimplantation annealing.
The birefringence of the optically nonlinear crystal 4-amino benzophenone
Authors: Pan F. , Bailey R. T. , Cruickshank F. R. , Pugh D. , Sherwood J. N. , Simpson G. S. , Wilkie S.
Published: July 2002

A precise method is presented for measuring the refractive index of an anisotropic prism with light polarized orthogonal to the prism axis which is also a dielectric axis. Prisms have been cut from crystals of the optically nonlinear 4-amino benzophenone with exceptionally low defect concentration as identified by synchrotron white light topography. The linear refractive indices of these have been measured and fitted to four-parameter Sellmeier equations to an accuracy of 7×10−6–3×10−3. The values are accurately verified by observation of the external angle of incidence to a (001) plane required to meet the conditions of type-I phase matching with a fundamental wavelength of 1064 nm. The phase matching is of Hobden class six for this wavelength. In common with similar organic molecular materials, the molecular charge transfer axis defines the most polarizable direction in the crystal, with the C=O direction being much less significant.
Depth profiles of vacancy- and interstitial-type defects in MeV implanted Si
Authors: Coffa S. , Privitera V. , Priolo F. , Libertino S. , Mannino G.
Published: July 2002

We demonstrate that the depth distribution of defects in MeV implanted n-type and p-type crystalline Si is severely affected by the impurity content of the material. Silicon samples with different concentrations of dopants (P or B) and intrinsic contaminants (i.e., C and O) were implanted with 1 or 2 MeV He ions to fluences in the range 2.5×108–1×1013/cm2. Using deep-level transient spectroscopy and spreading resistance measurements, we have identified the defects and determined their concentration and depth distribution. It is found that less than 4% of the defects generated by the beam escape recombination and are stored in electrically active, room temperature stable defect clusters, such as divacancies and carbon–oxygen pairs. When the concentration of these defects is much smaller than the doping level, their profile mirrors the initial defect distribution, as calculated by transport of ions in matter (TRIM), a Monte Carlo code. In particular, the profile presents a maximum at the same depth predicted by TRIM and a width which is strongly dependent on the impurity content of the substrate. Indeed this width can be as large as 2 μm when implants are performed on a lightly doped, pure epitaxial substrate and returns to the value predicted by TRIM (∼0.5 μm) upon increasing the concentration of dopants and intrinsic contaminants which act as traps for the diffusing point defects. The broadening of the concentration profiles is however shown to be unavoidable at high implantation fluences when most of the traps are already full and unable to interrupt the free migration of newly generated defects. Finally, by comparing defect distributions in n-type and p-type samples we have detected the spatial separation between vacancy-type and interstitial-type defects, resulting from the ion momentum transfer. The observed phenomena are explained in terms of a trap limited diffusion of the defects generated by the beam. These effects are only observable for a light ion such as He since direct defect clustering within the diluted collision cascades is expected to be significantly inhibited.
Terahertz-field-induced recovery of resonant electron transparency of semiconductor superlattices in electric field
Authors: Tkachenko O. A. , Baksheyev D. G. , Tkachenko V. A.
Published: July 2002

An experiment on detecting the influence of THz irradiation on coherent resonant electron tunneling through a short superlattice in an electric field is proposed. It is numerically shown that transmission via the upper levels of the lowest miniband, being suppressed down to the values T=10−2–10−1 by applied voltage, is restored to T∼1 by the THz field of certain amplitudes and frequencies. This is caused by electron delocalization due to stimulated multi-quantum transitions to the levels close to the center of the miniband. Thus, amplification of incident irradiation and higher-harmonics generation are possible.
Kinetics of transformation with nucleation and growth mechanism: Special consideration of crystallographic relationship and epitaxial growth
Authors: Yu Ge , Lee S. T. , Lai J. K. L. , Ngai L.
Published: July 2002

Based on the calculation of the survival probability, equations describing the kinetics of phase transformation with nucleation and growth mechanism are derived for general cases by including the temporal and spatial dependence both for the nucleation rate and for the growth rate. Particularly in this study, the crystallographic relationship in the growth is taken care of. For the simple case, in which the growth rate in the crystallographically identical directions are the same and the shape of grains remains congruent during the crystal growth, the influence of the shape factor on the kinetics can be determined for grains of different contours. The application to epitaxial growth yields the coverage quotient of a certain plane in the deposited crystals as a function of the reaction time and the position. Also the thickness distribution during the deposition can be determined. The exploration of the relationships between the growth kinetics and the crystallography is helpful to obtain reliable information about the mechanisms of nucleation and growth from the evaluation of the measurements.
Generalized relationship between dark carrier distribution and photocarrier collection in solar cells
Authors: Green Martin A.
Published: July 2002

A recently identified relationship between the probability of collection of a photogenerated carrier in a solar cell and the dark minority-carrier concentration at the point of generation is generalized to three-dimensional geometries with arbitrary doping profile and variable band gap including abrupt compositional changes, grain boundaries, and floating junctions. The proof of the resulting relationship is simpler and more transparent than in earlier work with more restricted geometries.