bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic and specific heat studies of the effect of sulfur nonstochiometry in CuIr2S4+x (x=−0.1, 0.0, and 0.1)
Authors: Somasundaram P. , Kim D. , Honig J. M. , Pekarek T. M.
Published: July 2002

The magnetic properties and the specific heat of sulfur nonstochiometric CuIr2S4+x (x=−0.1, 0.0, and 0.1) were investigated. The transition temperatures on cooling (Tcool) were 209.6, 206.7, and 218 K, whereas on warming (Twarm) they were 218, 218.3, and 226.7 K, respectively. The change in entropy at the transition temperatures (Twarm) of the x=0.1 and x=0.0 samples were 0.90 and 0.54 J/mol K, respectively.
Optical deep level transient spectroscopy of minority carrier traps in n-type high-purity germanium
Authors: Blondeel A. , Clauws P. , Vyncke D.
Published: July 2002

Deep levels in n-type high-purity (HP) detector grade germanium are studied using optical deep level transient spectroscopy (ODLTS). In this technique, optical injection (using light of above band gap energy) from the back ohmic contact together with a suitable sample configuration results in the detection of centers in the minority half of the band gap. Six deep minority carrier traps are detected in typical n-type HP germanium which turn out to be the same defects as found earlier in typical p-type HP germanium as majority carrier traps. These deep defects are mainly copper related. A formula is deduced to calculate concentrations from the ODLTS spectra. It is shown that in n- and p-type HP germanium not only the same defects are present but that their concentrations are also comparable.
X-ray diffraction study of solid-state formation of metastable MoSi2 and TiSi2 during mechanical alloying
Authors: Yen Bing K.
Published: July 2002

The formation of metastable C40–MoSi2 and C49–TiSi2 during the mechanical alloying of metal/silicon powder mixtures has been investigated by x-ray diffraction. The mechanical alloying of a Si-rich Mo/Si powder mixture results in the formation of both C11b–MoSi2 and C40–MoSi2. The C40–MoSi2 phase is metastable and transforms to C11b–MoSi2 after annealing at 850 °C. The mechanical alloying of a stoichiometric Ti/Si powder mixture leads to the incipient formation of C49–TiSi2 and the subsequent polymorphic transformation to C54–TiSi2. The lattice parameters of C49–TiSi2, as determined from a mechanically alloyed Ti/Si powder sample that has been annealed at 700 °C, are as follows: a0=3.56 Å, b0=13.57 Å, and c0=3.55 Å.
Mechanisms of photosensitivity in germanosilica films
Authors: Bazylenko M. V. , Gross M. , Moss D.
Published: July 2002

Mechanisms underlying the refractive index changes in germanosilica films deposited by hollow cathode plasma enhanced chemical vapor deposition and subjected to UV irradiation are proposed based on observed changes in film thickness, stress, and structure. An increase in refractive index after UV exposure is observed in films deposited under low ion bombardment conditions. This increase in refractive index is accompanied by a reduction in film thickness which is an order of magnitude larger than that expected from the Lorentz–Lorentz relation. This behavior is shown to result from: (i) a significant degree of porosity in the as-deposited material; (ii) oxygen deficiency of the as-deposited material. Upon UV irradiation, the porous structure is compacted, thus accounting for the large decrease in thickness, while the oxygen deficiency is reduced causing a decrease in the material polarizability and counteracting the effect of the thickness reduction. On the other hand, germanosilica deposited under high ion-bombardment conditions is of normal optical quality and exhibits a decrease in refractive index after exposure to UV. This refractive index reduction is shown to be the result of three processes: structural dilation and stress relief on one side; and an increase in material polarizability on the other, with structural dilation having the largest effect. Annealing of the exposed samples has shown that most of the polarizability increase is likely to be annealed out at 500 °C, while the refractive index change caused by structural dilation is stable up to 800 °C. Finally, it is shown that during plasma enhanced chemical vapor deposition, germanosilica is more prone to nucleation and columnar growth than pure silica and therefore a higher level of ion bombardment is required in the former case in order to obtain a high quality homogeneous material.
Effects of nanoscale trenches and mesas patterned in a substrate on domain structures of magnetic films and ion applications in magnetic disk tracking (abstract)
Authors: Chou Stephen Y. , Shi Rick C. , Kong Linshu
Published: July 2002

We patterned nanoscale trenches and mesas with different depths and heights in a SiO2 substrate and then deposited a cobalt film on the substrate. We investigated the effect of the trenches and mesas on the magnetic domain structures of the film. The trenches and mesas, fabricated using electron-beam lithography and a reactive ion etch process, have, respectively, a 100 nm width, a 500 nm length, and a depth and height varying from 10 to 50 nm. The cobalt film deposited is 30 nm thick. The topological images and magnetic images were taken at the same time using a commercial magnetic force microscope with an ultrahigh resolution tip made in-house. For the trenches 50 nm deep and mesas 50 nm tall, distinct magnetic poles were observed at each end of the trenches and mesas, indicating formation of the single domain, even though the trenches and mesas were surrounded by a Co film. As the trench depth or the mesa height is reduced by 30 nm, the magnetic poles gradually disappear with reduction of the thickness. This is not surprising because the exchange interaction of the Co film in trenches or the Co film on the mesa with the surrounding Co film becomes stronger as the depth or the height is reduced. However, it is expected that with a Co alloy film such as CoCrTa, single domain can be formed in the trenches and mesas with much smaller depth and height. The formation of single domain in nanoscale trenches and mesas may be utilized as tracking marks for a hard disk. The track marks, unlike conventional discrete tracks,1 do not require direct etching of the ferromagnetic film, are single magnetic domain with magnetization direction in the long axis of the trenches and mesas, and are suitable for miniaturization. These nanoscale trenches and mesas can be fabricated at low cost using nanoimprint lithography.2 They also might be useful for landing zones.
Raman scattering and photoluminescence of Mg-doped GaN films grown by molecular beam epitaxy
Authors: Popovici G. , Xu G. Y. , Botchkarev A. , Kim W. , Tang H. , Salvador A. , Morkoç H. , Strange R. , White J. O.
Published: July 2002

Photoluminescence, Raman, and Hall measurements are reported for Mg doped GaN films grown by molecular beam epitaxy. The compressive and tensile stress determined by the Raman shift of the phonon lines is due to the growth conditions rather than the presence of Mg in the film. The photoluminescence peak of near band-to-band transitions is also shifted to larger (smaller) energies by the compressive (tensile) stress. The study of the longitudinal optical phonon of the A1 branch shows that its Raman line shape is affected mostly by the crystalline quality of the film.
Irradiation-induced alloying in immiscible Mo–Cu system through multilayer technique
Authors: Chen Y. G. , Liu B. X.
Published: July 2002

Room temperature 200 keV xenon-ion irradiation of multilayers, designed under interfacial free energy concern, did result in the formation of Mo–Cu metallic glasses only within a narrow Mo-enriched composition range. In addition, some Cu-based alloys of metastable fcc solid solutions were also formed at different irradiation stages. To obtain a possible thermodynamic interpretation, a Gibbs-free-energy diagram was calculated based on the semiquantitative Miedema’s model and the related methods proposed by Alonso. The free energy of the Mo–Cu multilayers including excess interfacial free energy was also estimated and was compared to that of the amorphous state. It turned out that the interfacial free energy stored in the multilayered films could raise the energy level of the multilayers to a state higher than that of the metastable phases and thus played an important part, in comparison to the energy deposited by irradiation, in inducing alloying in this immiscible system.
Rotational-disordering phase transition of C60(111) epitaxial films grown on GeS(001)
Authors: Glebov Alexei , Senz Volkmar , Toennies J. Peter , Gensterblum Georg
Published: July 2002

The surface structures of C60 films, epitaxially grown on the GeS(001) surface, were investigated from 90 to 350 K by helium atom scattering (HAS) diffraction. The present HAS results indicate a step-flow growth mode that is consistent with the results of previous x-ray scattering studies. By monitoring the diffraction intensities, the orientational-disordering phase transition is found to be completed at Tc=235 K, which is about 25 K lower than the bulk transition temperature. This surface phase transition appears to be preempted by rotational disordering of C60 molecules at defect sites, already initiated at Ts=130 K.
Cross relaxation and upconversion coefficients of the mid-infrared transitions of Pr3+:LaCl3
Authors: Kirkpatrick Sean M. , Bowman S. R. , Shaw L. B. , Ganem Joseph
Published: July 2002

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ<10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.
Molecular dynamics simulation of single and repeated indentation
Authors: Komvopoulos K. , Yan W.
Published: July 2002

Atomic-scale material responses of dynamic metal-like substrates due to single and repeated indentation by metal-like or covalent rigid tips are interpreted in light of three-dimensional molecular dynamics simulation results. Single-indentation results for a face-centered-cubic metal substrate indented by a relatively blunt tip of the same material and a sharper pyramidal tip of a covalent material are compared to elucidate the effects of interfacial atomic potential and tip shape on the deformation behavior. Force hysteresis occurs due to inelastic deformation and heating of the substrate. The abrupt decrease of the repulsive force during penetration is attributed to permanent deformation. The formation of a connective neck during unloading observed only in the indentations involving the metal tip is associated with the stronger interatomic forces and larger tip surface area in these simulations. The rapid decrease of the attractive force during retraction of the tip is associated with the reconstruction of the elongated neck. Results for different metallic substrates repeatedly indented by a rigid covalent tip up to a fixed maximum depth or maximum normal force are presented in order to reveal the evolution of deformation and heating in the substrate with indentation cycles. Repeated indentation gives rise to behaviors resembling cyclic hardening and softening observed at the macroscale.
Magneto-optical and optical properties of ordered and disordered Fe–Al alloy films
Authors: Kudryavtsev Yu. V. , Nemoshkalenko V. V. , Lee Y. P. , Kim K. W.
Published: July 2002

The influence of order–disorder structural transition on the magnetic, magneto-optical, and optical properties of nearly equiatomic FeAl alloy films was investigated. The disordered state in FeAl alloy films was obtained by means of vapor quenching deposition onto glass substrates cooled by liquid nitrogen. The experimental study of the magneto-optical and optical properties of ordered and disordered FeAl alloy films was carried out in the 0.5–5.0 eV energy range at room temperature. The influence of the order–disorder structural transition on magnetic, magneto-optical, optical properties is discussed by using the results of first-principle calculations of the electronic structure and by the structural defect approach.
The bounds of saturation magnetostriction in polycrystalline materials
Authors: Birsan M.
Published: July 2002

The universally used approximation for the magnetostriction constant of a polycrystalline material is based on the assumption of uniform stress through the aggregate. In this article we calculate the alternative approximation of uniform strain. The calculation is performed in terms of the grains orientation distribution (texture) function, and single crystal constants describing the elastic and magnetostrictive anisotropy. These bounds represent the optimum solution of the incompletely specified problem of crystallites shape distribution in a polycrystalline aggregate. The available experimental data are compared with the two approximations.
Backscattering of slow positrons from semi-infinite aluminum
Authors: Bouarissa N. , Walker A. B. , Aourag H.
Published: July 2002

Monte Carlo simulation for 1–10 keV positron backscattering from semi-infinite aluminum with normal angle of incidence is reported. The elastic scattering cross sections have been obtained from the modified Rutherford differential cross section where the numerical coefficient in the atomic screening parameter is taken to be variable. To model inelastic scattering, we have investigated for the first time the effects of continuous slowing down through collisions with conduction electrons. Attention has also been paid to effects of changing the angle of incidence. Our simulated results and the available experimental data are found to be in reasonable agreement, and show that the energy dependence of the backscattered fractions can be fitted with a simple function: B(E)=0.0187997 ln E+0.102644. This suggests that both the transport model and the scattering cross sections used in the present work are reliable.
A comparative study on the electrical conduction mechanisms of (Ba0.5Sr0.5)TiO3 thin films on Pt and IrO2 electrodes
Authors: Hwang Cheol Seong , Lee Byoung Taek , Kang Chang Seok , Kim Jin Won , Lee Ki Hoon , Cho Hag-Ju , Horii Hideki , Kim Wan Don , Lee Sang In , Roh Young Bum , Lee Moon Yong
Published: July 2002

Electrical conduction mechanisms for Pt/(Ba0.5Sr0.5)TiO3 (BST)/Pt, IrO2/BST/IrO2, and Pt/BST/IrO2 capacitors were studied. The Pt/BST/Pt capacitor shows a Schottky emission behavior with interface potential barrier heights of about 1.5–1.6 eV. The barrier height is largely determined by the surface electron trap states of the BST. The IrO2/BST interface shows an ohmic contact nature due to the elimination of the surface trap states as the result of the formation of strong chemical bonds between the IrO2 and BST which results in the Poole–Frenkel emission conduction mechanism. Pt/BST/IrO2 capacitor shows Schottky emission behavior and a positive temperature coefficient of resistivity (PTCR) effect depending on the bias polarity. The electron trap states at the Pt/BST interface and the positive space charges within the carrier depletion layer result in the PTCR effect.
Influence of misfit dislocation interactions on photoluminescence spectra of SiGe on patterned Si
Authors: Watson G. P. , Benton J. L. , Xie Y. H. , Fitzgerald E. A.
Published: July 2002

The Si substrates were patterned and etched to create arrays of squares separated by 10 μm trenches. Some edges of these squares were ion implanted with a large dose of Ge to create damaged regions that act as misfit dislocation nucleation centers during molecular beam epitaxy of a 700 nm Si0.90Ge0.10 lattice mismatched layer. Low temperature photoluminescence spectra of the material were obtained with an illuminated area selected so that only one type of edge implant was studied at a time. Sub-band gap luminescence peaks associated with dislocations, D lines, were found only in the squares with implants, consistent with electron microscopy results that showed that the control squares had few misfit dislocations. A large D1 luminescence peak was observed in samples that consisted of intersecting arrays of misfit dislocations, while only a small peak was present in specimens implanted such that dislocations lay in only one in-plane direction. These results are interpreted to mean that the D1 peak is intrinsic to the dislocations themselves and not to impurity gettering. These observations further infer that D1 luminescence is related to dislocation kinks.
An approach to the energy gap determination from reflectance measurements
Authors: Dı́az R. , Merino J. M. , Martı́n T. , Rueda F. , León M.
Published: July 2002

A method to obtain the band gap energy value from reflectance measurements has been developed for bulk materials with direct and indirect gaps. In an energy region around the gap value, the experimental reflectivity is fitted by two functions of the type R=A0+A1′(1/hν)2−A1′Eg×(1/hν)3 and R=A0+B[(hν−Eg)/(hν)]4, for direct and indirect transitions, respectively, in an energy range around the gap value. This implies that the absorption coefficient, α, shows a dependence with the energy α=(A/hν)(hν−Eg)m with m=1/2, 2 for direct and indirect gaps, respectively. The method has been checked in several materials of known energy gaps including Si and Ge.
Surface potential of phthalocyanine Langmuir-Blodgett films on metal electrodes
Authors: Itoh Eiji , Kokubo Haruo , Shouriki Shigeto , Iwamoto Mitsumasa
Published: July 2002

Surface potential of Cu-tetra-tert-butyl-phthalocyanine (CuttbPc) Langmuir-Blodgett (LB) films on metal electrodes were measured in a dark vacuum vessel at various temperatures as a function of the number of deposited layers. It was found that the potential built across CuttbPc LB film is a result of the displacement of electronic charges between metal electrodes and film. The spatial charge distribution in CuttbPc LB films was determined on the order of nanometer scale, and the distribution of the electronic density of states was also determined. Finally, we concluded that electrostatic phenomena occurring at the CuttbPc/metal interface is explained by assuming the presence of both electron donating and accepting states in CuttbPc LB films at the film/metal interface.
Texture and microstructural evolution of thin silver films in Ag/Ti bilayers
Authors: Zeng Yuxiao , Alford T. L. , Zou Y. L. , Amali Adam , Ullrich B. Manfred , Deng F. , Lau S. S.
Published: July 2002

The texture and microstructure of thin silver films in Ag/Ti bilayer structures have been characterized as a function of vacuum annealing temperature and time with the use of x-ray diffraction and transmission electron microscopy. A strong preexisting (111) texture in Ag films was further improved upon annealing as evidenced by an increased intensity and narrower distribution of the texture along the film normal. A new (200) texture component was generated after 600 °C annealing; it however had a relatively low intensity when compared to the dominant (111) texture. No abnormal grain growth was observed in annealed Ag films. The texture evolution in all films appeared to complete within the first 15 min annealing, while the microstructure continued to change with additional annealing time. The roles of both surface energy and strain energy in the grain growth were evaluated. A model of the grain growth and texture evolution has been proposed to explain these observations.
Size dependence of the quantum yield of photoluminescence from silicon nanocolloids
Authors: Kimura Keisaku , Iwasaki Shingo
Published: July 2002

We have prepared several nanometer-sized silicon colloids in the range from 3.7 to 9.8 nm with a constant weight density 1 mg/ml. The blue-green emission is found to be independent of size contrast to its intensity. The absolute quantum yield as a function of size is determined. From the proposed model that combines surface as well as volume effects, the emission is proved to be from a surface trapped site. The energy transfer efficiency from volume to the site is almost 100% for the 3.7 nm particle.
Evaluation of imprint in fully integrated (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 ferroelectric capacitors
Authors: Sadashivan S. , Aggarwal S. , Song T. K. , Ramesh R. , Evans J. T. , Tuttle B. A. , Warren W. L. , Dimos D.
Published: July 2002

We have investigated the imprint characteristics of fully integrated ferroelectric lead zirconate titanate based capacitors. These capacitors were fabricated using conducting perovskite La–Sr–Co–O electrodes. We have specifically focused on the effect of several test and capacitor variables, including temperature, unipolar stress amplitude, number of cycles, and device area. Two different figures of merit, one based on coercive voltage changes and the other based on differences in polarization values were used to quantify imprint. The imprint in our capacitors showed a small temperature dependence over the range that we have studied. The unidirectional pulse voltage amplitude had a larger influence on the imprint.
Structural and electronic properties of Ga2Se3
Authors: Peressi M. , Baldereschi A.
Published: July 2002

We study the defect tetrahedral semiconductor Ga2Se3 with ordered vacant sites using state-of-the-art density-functional calculations. The calculated main structural properties (the average cubic lattice parameter, a0=10.20 a.u., and the average Ga–Se bond length, r=4.52 a.u.) and electronic properties (the forbidden energy gap, direct, which amounts to about 2.4 eV) are in good agreement with the experimental data. The role of the coordination defects is analyzed in detail, and the contribution of the different atoms to the electronic density of states is also discussed. No significant differences are found if the vacant sites are ordered according to a monoclinic structure rather than orthorhombic, both previously proposed in literature, since the peculiar features of the structural and electronic properties are strongly related to the vacancies and their local environment rather than to their particular ordering. We also discuss the results obtained for the orthorhombic phase pseudomorphically grown on GaAs or ZnSe(001) substrates.
Effect of poling temperature on optical second harmonic intensity of sodium zinc tellurite glasses
Authors: Narazaki Aiko , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

Poling temperature dependence of optical second harmonic intensity has been examined for Na2O–ZnO–TeO2 glasses. All the glasses exhibit such a tendency that the second harmonic intensity increases, experiences a maximum, and decreases as the poling temperature increases. The poling temperature giving rise to the maximum second harmonic intensity, which we call an optimum poling temperature, correlates with glass transition temperature; there exists a linear relation between them. This phenomenon indicates that the structural change of glass network near the glass transition temperature affects the orientation of electric dipoles with a long range order which induces the second harmonic generation. We suggest that some electrochemical reactions take place on the anode-side surface of glass at around the glass transition temperature where viscous flow is allowed and disturb the orientation of electric dipoles.
GaN (0001)-(1×1) surfaces: Composition and electronic properties
Authors: Wu C. I. , Kahn A. , Taskar N. , Dorman D. , Gallagher D.
Published: July 2002

We use low energy electron diffraction, Auger electron spectroscopy, and ultraviolet and x-ray photoemission spectroscopy to study the surface structure, stoichiometry, and electronic properties of n- and p-type GaN (0001) grown by metal-organic chemical vapor deposition. Ordered (1×1) surfaces with nearly stoichiometric composition are prepared by nitrogen sputtering and annealing. The band bending is found to be 0.75±0.1 eV up and 0.75±0.1 eV down for n- and p-type samples, respectively. The work function, electron affinity, and Ga 3d core level binding energy are also determined.
Theory of magnetoelastic dissipation due to domain wall width oscillation
Authors: Liu Y. , Grütter P.
Published: July 2002

This article presents a general treatment of magnetic dissipation due to domain wall width oscillation via magnetostriction in magnetic samples. The domain wall width is modeled as a harmonic oscillator. The parameters governing this oscillator (effective mass, stiffness, damping coefficient and driving force) are derived and expressed in terms of intrinsic magnetic parameters of magnetic materials. The magnetostriction induced damping of wall width oscillations is frictional in nature. An external ac magnetic field serves as a driving force of the oscillator. It is found that the response to the driving force depends very much on the micromagnetic structures of the magnetic domain wall. Different micromagnetic structures lead to different magnetic dissipation for a given external field. Besides giving a quantitative microscopic explanation to magnetic dissipation data measured by magnetic dissipation force microscopy, this theory predicts two new phenomena: one is that there is a minimum driving force for the wall width to oscillate and the other is a new resonance phenomenon, domain wall width resonance.
The Re-doped high Tc superconductor HgBa2Ca2Cu3Ox: Magnetic irreversibility versus anisotropy
Authors: Fàbrega L. , Martı́nez B. , Fontcuberta J. , Sin A. , Piñol S. , Obradors X.
Published: July 2002

We report on magnetization measurements on grain-aligned Re-doped Hg-1223 superconductor (Tc≈133 K). We analyze the anisotropic magnetic hysteresis Mirr as a function of temperature and magnetic field, and determine the irreversibility line Hirr(T) for magnetic fields applied parallel and perpendicular to the c axis of the structure. The similar values of both Mirr and Hirr(T) along the two main crystallographic directions reveal a marked decrease of the superconducting anisotropy, due to the Re substitution. This anisotropy reduction might be at the origin of the rise of the magnetic irreversibility already reported in these compounds, as compared to those without Re.
Microstructure and soft magnetic properties of FeSiAl(Ti/Ta)(O)N
Authors: Hiramoto M. , Matsukawa N. , Sakakima H. , Ichikawa Y. , Ijima K.
Published: July 2002

The microstructure and magnetic properties of FeSiAl(Ti/Ta)(O)N films prepared by rf magnetron reactive sputtering were studied. The microstructure was controlled by changing the N2 gas flow rate ratio [η=N2/(Ar+N2)] in the sputtering gas. The soft magnetic properties were observed after thermal treatment at around η of 2% and η of 20%, where the saturation magnetostrictions and the intrinsic stresses took small values. The film with η of 20% had a granular structure as mostly observed on nanocrystalline materials. On the other hand, the film prepared with η of 2% had the structure which consisted of needle shaped grains or dendritic grains. The composition of the granular grains and needle shaped grains were mainly Fe and FeSi, respectively. The film with η of 2% exhibited Bs of 1.3 T, permeability of 3000–8000 at 1 MHz, respectively, and realized a high corrosion resistance. The soft magnetic properties of the films with needle shaped grains are explained by two-dimensional random anisotropy effect.
The influence of field- and stress-induced magnetic anisotropy on the magnetoimpedance in nanocrystalline FeCuNbSiB alloys
Authors: Kurlyandskaya G. V. , Garcı́a-Beneytez J. M. , Vázquez M. , Sinnecker J. P. , Lukshina V. A. , Potapov A. P.
Published: July 2002

The correlation between magnetic anisotropy and magnetoimpedance has been studied in field- and stress-annealed Fe73.5Cu1Nb3Si13.5B9 ribbons. As-cast and previously nanocrystallized samples were submitted to different annealing conditions (T=500, 530, and 560 °C and tensile stress σ=150 MPa) in order to induce different magnetic anisotropy. The magnetoimpedance ratio [ΔZ/Z] was measured at 3 MHz using a driving current Irms=10 mA. An hysteretic behavior of the magnetoimpedance ratio is observed. This hysteretic behavior is interpreted considering the magnetization process for samples exhibiting different magnetic anisotropies.
Microstructure and magnetic properties of FeCoN thin films
Authors: Kuo P. C. , Chang S. S. , Kuo C. M. , Yao Y. D. , Huang H. L.
Published: July 2002

Effects of nitrogen contents and substrate temperatures to the microstructure and magnetic properties of the FeCoN films have been investigated. According to the TEM and x-ray Scherrer’s equation analyses, we found that the grain size of films with substrate temperature below 200 °C is roughly about 13 nm, however, it increases very fast for films with substrate temperature above 300 °C. N content in the films is saturated to 30 at. %, as N2 flow ratio N2/(Ar+N2) is higher than 5 vol. %. From the magnetization studies, we have found that the saturation magnetization 4πMs of the optimum samples (with the substrate temperature near 200 °C) is 23.9 kG. The improvement of the magnetic properties is attributed to the combination of α-Fe with N to form the high magnetic moment FeN phases.
High temperature stability of SmTM magnets
Authors: Kim A. S.
Published: July 2002

To meet the demand for permanent magnet materials usable up to 450–500 °C, we investigated and reported that a SmTM magnet with a low temperature coefficient of coercivity and a moderately high coercivity has substantially lower irreversible losses at elevated temperatures than conventional Sm2TM17 magnets. We have continued our studies on the high temperature magnetic behavior of these magnets. The magnetic properties, particularly coercivity, of the SmTM7 alloy magnets are reduced much more slowly than the Sm2TM17 alloy magnets as temperature increases. As a result, the Hci of SmTM7 remains greater than 5 kOe at 500 °C and thus maintains its high-energy product, while the Sm2TM17 magnet has only about 1.7 kOe at the same temperature and has a low energy product. SmTM7 alloy magnets undergoing a long-term stability test at 500 °C exhibit irreversible flux losses of less than 5% after 1240 h. These results indicate that SmTM7 alloy magnets can be usable up to 500 °C for an extended period of time. This will expand the application temperature range of high performance permanent magnets.
Infrared OH− absorptions in Sr0.61Ba0.39Nb2O6 crystals
Authors: Lee Myeongkyu , Lee Howard S. , Feigelson Robert S.
Published: July 2002

The infrared OH− absorptions in Bridgman grown Sr0.61Ba0.39Nb2O6 crystals have been investigated by Fourier transform infrared spectroscopy. Crystals exhibited typical O–H stretching vibrations near ν=3500 cm−1 (λ≈2.87 μm). The polarization dependent absorption measurements revealed that a greater density of O–H bonds are polarized in the a−b plane with a smaller amount of bonds along the c axis. Protons (H+), which prefer a specific site at room temperature, tended to occupy different sites as the temperature increased. As-grown crystals contained protons on the order of 1017 cm−3, and the proton concentration increased by approximately 1 order of magnitude after heat treatment in a humid atmosphere.
Infrared studies of defects formed during postirradiation anneals of Czochralski silicon
Authors: Londos C. A. , Sarlis N. V. , Fytros L. G.
Published: July 2002

This article reports on defect studies of neutron-irradiated Czochralski-grown silicon (Cz-Si) material by means of infrared spectroscopy. In particular, the investigation was focused on the evolution of the 828 cm−1 well-known band of A-center, due to isochronal anneals from room temperature (RT) up to ≈700 °C. The strength of the VO band begins to increase above ≈200 gradually up to 300 °C (stage I); then, it begins to decrease up to ≈400 °C (stage II), where upon it stabilizes up to ≈550 °C (stage III). Upon re-irradiation under exactly the same conditions and repeating the annealing process, the increase of the VO signal in stage I disappears. The phenomenon is ascribed to the existence of defect aggregates labeled as Xi centers which are correlated with (impurity-defect) clusters that compete with Oi in capturing vacancies. The presence of Xi centers is related to the thermal annealings performed. Comparison of the evolution of VO (828 cm−1) and VO2 (887 cm−1) bands between irradiated and re-irradiated materials, during stage II, is made and the results are discussed in the framework of established reaction patterns. The stabilization of the amplitude of the 828 cm−1 line in stage III is examined. The prevailing aspect is that a portion of A-centers in neutron-irradiated Si acquires larger thermal stability by relaxing in the vicinity of larger defects.
Kinetics of Si1−xGex(001) growth on Si(001)2×1 by gas-source molecular-beam epitaxy from Si2H6 and Ge2H6
Authors: Kim H. , Taylor N. , Bramblett T. R. , Greene J. E.
Published: July 2002

Si 1−x Ge x layers with x ranging from 0 to 0.30 were grown on Si(001)2×1 substrates at temperatures ranging from 450 to 950 °C by gas-source molecular-beam epitaxy (GS-MBE) from Si2H6 and Ge2H6. In the low-temperature surface-reaction-limited growth regime, the deposition rate RSiGe increases with increasing Ge concentration due to an enhancement in the hydrogen desorption rate resulting in a correspondingly higher steady-state dangling bond density. In the high-temperature impingement-flux-limited regime, where the steady-state hydrogen coverage approaches zero, RSiGe is controlled by the Si2H6 and Ge2H6 reactive sticking probabilities S which decrease with increasing Ge2H6 flux but are not strongly temperature dependent. SSi2H6 and SGe2H6 range from 0.036 and 0.28 on Si(001) to 0.012 and 0.094 during growth of Si0.82Ge0.18 at Ts=800 °C. In both growth regimes, large changes in RSiGe require only modest increases in incident Ge2H6 to Si2H6 flux ratios, JGe2H6/JSi2H6, due to Ge segregation which is strongly coupled to the steady state hydrogen coverage. The Ge to Si ratio in as-deposited films increases linearly, while SGe2H6/SSi2H6 remains constant, with increasing JGe2H6/JSi2H6. Hydrogen desorption and Ge segregation rates, together with Si2H6 and Ge2H6 reactive sticking probabilities, were quantitatively determined from D2 temperature-programmed desorption (TPD) measurements. The combined results from film growth kinetics and TPD studies, together with the assumption of linear superposition, were then used to develop a predictive model, with no fitting parameters, for RSiGe(Ts,JSi2H6,JGe2H6) during Si1−xGex GS-MBE.
Photorefractive polymer composite trapping properties and a link with chromophore structure
Authors: West K. S. , West D. P. , Rahn M. D. , Shakos J. D. , Wade F. A. , Khand K. , King T. A.
Published: July 2002

The photorefractive properties and the phase stability of polymer composites are dependent on the detail of the alkyl chain substituent attached to the electro-optic dye within the composite. Photorefractive composites based on poly (N-vinylcarbazole) (PVK), sensitized with trinitrofluorenone (TNF) and mixed with a concentration of 47.5 wt. % of electro-optic dye have been tested for photorefractive performance. Two alternative azo dyes of identical molecular weight have been used to produce alternative composites; both dyes were modified to suppress spatial isomerism and incorporated an eight carbon alkyl chain at the electropositive end of the chromophore: either a straight octyl chain or a branched ethylhexyl chain was substituted. The reorientational enhancement of photorefractive performance is similar in the composites resulting from these dyes. The dye with a straight octyl chain led to a composite with improved holographic performance. The dye with a branched ethylhexyl chain led to a composite exhibiting lower diffraction efficiency, but with superior phase stability. A tentative explanation is offered for these differences based on the shape of the alkyl substituent and its effect on a trapping mechanism involving the dye molecules and the sensitisor anions in PVK:TNF-based photorefractive composites.
Direct observation of the Cu2−xSe phase of Cu-rich epitaxial CuInSe2 grown on GaAs (001)
Authors: Fons P. , Niki S. , Yamada A. , Oyanagi H.
Published: July 2002

Cu 2−x Se is an important impurity phase of the ternary chalcopyrite semiconductor CuInSe2 associated with Cu/In composition ratios greater than unity. We have observed directly in a prototypical epitaxial system the formation of Cu2−xSe on Cu-rich CuInSe2 thin films epitaxially grown on GaAs (001). Atomic force microscopy measurements of the surface topology of as-grown films clearly show faceted rectangular crystallites with dimensions on the order of 100 nm. Cross-sectional transmission electron microscopy measurements of the Cu-rich CuInSe2 showed rectangular protrusions on the surface as well as wedge shaped facets in the CuInSe2 film. Two-dimensional reciprocal space x-ray mapping of the as-grown Cu-rich CuInSe2 showed the in-plane lattice constant of the Cu2−xSe phase to be partially strained to the CuInSe2 layer. The presence of the β phase of Cu2−xSe is also presented as an alternative explanation for Cu–Pt ordering reports in CuInSe2 that have appeared in the literature. Strain-related surface undulations observed only in Cu-rich CuInSe2 are also linked to the presence of this strained Cu2−xSe layer.
Theoretical study of a diode with dielectric-gridded cathode
Authors: Schächter L. , Fletchner D. , Golkowski C. , Ivers J. D. , Nation J. A.
Published: July 2002

We investigate the I–V characteristics of a vacuum diode with a gridded cathode. The grid is located on top of a dielectric material that on its back side is covered by a uniform electrode. Ignoring space-charge effects, the current density extracted from the grid is proportional to the dielectric coefficient and it is quadratic with the back electrode voltage. Considering only space-charge associated with the back electrode voltage, it is found that the anode current is proportional to the anode voltage. When all space-charge effects are considered, it is shown that the electrostatic energy coupled into the diode gap through the grid is responsible to the excess of current beyond the Child–Langmuir limit.
Nickel distribution in crystalline and amorphous silicon during solid phase epitaxy of amorphous silicon
Authors: Kuznetsov A. Yu. , Svensson B. G. , Nur O. , Hultman L.
Published: July 2002

Solid phase epitaxy of nickel-doped amorphous silicon (a-Si) films on crystalline silicon (c-Si) substrates has been investigated. The crystallization mode of the a-Si films depends strongly on the nickel concentration. Below ∼5×1018 Ni/cm3, redistribution of nickel into the c-Si substrate occurs and the regrowth process is controlled by an “ordinary” thermally activated solid phase epitaxial crystallization (SPEC) process. In contrast, above 5×1018 Ni/cm3 segregation of Ni in the a-Si films is observed and the silicon crystallization is driven by impurity enhanced SPEC and/or silicide mediated crystallization in the bulk of the amorphous film. The redistribution of Ni during crystallization can be described in terms of an effective distribution coefficient accounting for the actual crystallization rate of a-Si and the Ni diffusivity in a-Si. Further, dissolution of implantation-induced (311) defects is observed in the samples exhibiting Ni diffusion into the crystalline phase during ordinary SPEC. This indicates annealing and /or suppression of the (311) defects due to nickel accumulating in the region of end-of-range defects.
Induction and relaxation of optical second-order nonlinearity in tellurite glasses
Authors: Narazaki Aiko , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

Second harmonic generation has been examined for 30ZnO⋅70TeO2 glass with a two-step poling procedure in order to understand the poling temperature dependence of second harmonic intensity. When the poling temperature increases, the second harmonic intensity increases, manifests a maximum at the temperature which we call an optimum poling temperature, and decreases drastically just below the glass transition temperature. The glass treated with two-step poling, which includes poling at 300 °C and subsequent poling at the optimum poling temperature, i.e., 280 °C, exhibits much smaller second harmonic intensity and more unambiguous Maker fringe pattern than that poled only at 280 °C. This fact suggests that the decrease in second harmonic intensity with an increase in poling temperature cannot be attributed to a reversible process like a thermal fluctuation of dipoles, but is governed by an irreversible one. Based on a linear relation between the optimum poling temperature and glass transition temperature, the irreversible process is deduced to consist of some oxidation reactions such as a migration of nonbridging oxide ions to and subsequent evaporation of oxygen gas at the anode side. Decay of the second harmonic intensity for 30NaO1/2⋅70TeO2 glass as well as 30ZnO⋅70TeO2 glass has also been examined at room temperature. Whereas the 30ZnO⋅70TeO2 glass does not show a decay, the second harmonic intensity of the 30NaO1/2⋅70TeO2 glass decays rapidly with an average relaxation time of 10 h. This relaxation behavior is explainable in terms of the difference in mobility between Zn2+ and Na+ ions.
Processing and optical properties of patternable inorganic–organic hybrid films
Authors: Yamada Noriko , Yoshinaga Ikuko , Katayama Shingo
Published: July 2002

Patternable inorganic–organic hybrid films were synthesized from diethoxydimethlysilane and Ti(OC2H5)4 modified with ethyl acetoacetate (EAcAc). Optical properties and patterning of the hybrid film were studied. The films showed the refractive index of 1.62–1.67 and small in-plane scattering. The hybrid films were patterned by the irradiation of ultraviolet (UV) light at 254 nm. Fourier-transform infrared study revealed that the chelate complex of Ti(OC2H5)4 and EAcAc in the hybrid films was decomposed by UV light. The decomposition of the chelate complex caused the structure change of the hybrid film, leading to the solubility difference between UV irradiated and unirradiated regions. The change of solubility by the UV irradiation makes it possible to fabricate patterned hybrid films.
Mechanism of low temperature nitridation of silicon oxide layers by nitrogen plasma generated by low energy electron impact
Authors: Mizokuro Toshiko , Yoneda Kenji , Todokoro Yoshihiro , Kobayashi Hikaru
Published: July 2002

Thermal silicon oxide layers formed on the Si substrate can be nitrided at low temperatures ranging between 25 and 700 °C by nitrogen plasma generated by low energy electron impact. The nitrogen concentration is high near the oxide surface, and the nitrogen atomic concentration ratio [N/(Si+O+N)] at the surface ranges between ∼10% and ∼25%, depending on the nitridation conditions. For nitridation above 450 °C, only N≡Si3 (i.e., a nitrogen atom bound to three Si atoms) is observed in the nitrided oxide films by x-ray photoelectron spectroscopy measurements, while both N+=Si2 (i.e., an N+ ion bound to two Si atoms) and N≡Si3 are present with nitridation below 400 °C. When a negative bias voltage is applied to the Si with respect to the grid used for the generation of nitrogen plasma, the nitrogen concentration in the film increases, indicating that nitrogen cations play a dominant role in the nitridation. It is concluded that, first, N+ ions react with SiO2 to form N+=Si2, after which inward movement of N+ ions occurs with the assistance of an electrical field induced in the nitrided oxide layers by nitrogen ions at the surface. Ultimately, N+=Si2 is transformed to N≡Si3.
Effect of preamorphization implantation on C54–TiSi2 formation in salicided narrow lines
Authors: Tai Kaori , Okihara Masao , Kageyama Makiko , Harada Yusuke , Onoda Hiroshi
Published: July 2002

The effect of the preamorphization implantation (PAI) process on TiSi2 phase transformation has been investigated by using arrays of submicron TiSi2 lines. The C49–C54 transformation of TiSi2 during annealing is promoted by the PAI process. The promotion of phase transformation cannot be explained only by the difference in grain size of the C49–TiSi2; hence, the nucleation site density for the phase transformation was estimated. The epitaxial relation with the Si substrate also retards the C49–C54 phase transformation. The epitaxial growth of C49–TiSi2 on the Si substrate is observed in a large portion of C49–TiSi2 grains in the sample without PAI, whereas orientation of C49–TiSi2 in the sample with PAI has no relation to that of the Si substrate. Epitaxial C49–TiSi2 is more stable and is difficult to phase transform. After phase transformation, the C54–TiSi2 oriented to the 〈004〉 direction is predominant in the samples without PAI. The strong orientation of C54〈004〉 resulted from one-dimensional growth along submicron lines enhanced by the low density of the nucleation site. On the other hand, in the sample with PAI, an increase in the nucleation site leads to two-dimensional growth, and C54–TiSi2 films exhibit a random orientation with a weak dominant C54〈311〉 orientation.
Gold cluster formation at the interface of a gold/Langmuir-Blodgett film/gold microsandwich resulting in Coulomb charging phenomena
Authors: Philipp G. , Müller-Schwanneke C. , Burghard M. , Roth S. , Klitzing K. v.
Published: July 2002

Structural analysis of the cross section of gold/Langmuir-Blodgett (LB) polymer film/gold sandwich structures was performed using transmission electron microscopy (TEM), and the obtained results were complemented by electron transport investigations of the sandwich structures. The polymer film consisted of four to ten LB monolayers of a nonconducting polymer. TEM analysis of the sandwich cross section revealed a number of gold particles, 2–5 nm in size, formed during the fabrication process within the LB film close to the top electrode. Low temperature dc-transport measurements showed current-voltage (I-V) characteristics with equidistant steps that are not expected if the polymer film is thought to form a single laterally extended tunneling barrier between the metal electrodes. This feature can be understood, however, on the basis of the Coulomb blockade model applied to cluster-like metallic inclusions acting as an island separated from both Au electrodes by tunneling barriers.
Models for the pinning of domain walls in Sm(Co,Fe,Cu,Zr)z type magnets at finite temperatures
Authors: Chui S. T.
Published: July 2002

We discuss simulation results of three different models for the pinning of the domain walls in permanent magnets as a function of temperature. They correspond to pinning of the wall by periodic arrays of planes, faces of cubes and pyramids. The pinning potential can repel or attract the domain walls. The simulation results are compared with recent experimental data for the 2:17 magnets.