bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion exchange of Rb, Ba, and Sr in KTiOPO4
Authors: Roelofs M. G. , Morris P. A. , Bierlein J. D.
Published: July 2002

The potassium ions of potassium titanyl phosphate (KTiOPO4, or KTP) are relatively mobile and may be exchanged with other ions from molten salts. Distribution coefficients for potassium, rubidium, barium, and strontium between nitrate melts and titanyl phosphate were measured between 350 and 425 °C. At 425 °C, using melts containing K and a dopant chosen from Rb, Ba, Sr, and with dopant cation mole fractions in the melt of 0.1, Rb is incorporated in the crystal at a site fraction of 0.014, Ba at 0.007, and Sr at 0.002. Introducing 0.008 fraction of Ba increases the low-frequency dielectric constant and loss of KTP several orders of magnitude, giving conductivities (ωε0ε″) of 4×10−5 Ω−1 cm−1 at 200 kHz. The results support a potassium vacancy mechanism for ionic conductivity in KTP. Using low concentrations of divalent ions in the melt, flux-grown KTP has a lower uptake of divalent ions than does hydrothermally grown KTP, an effect attributed to the presence of potassium vacancies created in the high-temperature flux growth process. Ba or Sr incorporation results in a contraction of the lattice constants of the KTP structure.
Permanent magnets by mechanical alloying (invited)
Authors: Schultz L. , Schnitzke K. , Wecker J. , Katter M. , Kuhrt C.
Published: July 2002

Mechanical alloying is applied to prepare Nd-Fe-B, Sm-Fe-TM type (TM: V, Ti, Zr), and interstitial nitride and carbide permanent magnets. Starting from elemental powders, the hard magnetic phases are formed by milling in a planetary ball mill and a following solid-state reaction at relatively low temperatures. For Nd-Fe-B, the magnetically isotropic particles are microcrystalline, show a high coercivity (up to 16 kA/cm for ternary alloys and above for Dy-substituted samples), and can be either used for making bonded magnets or compacted to dense isotropic magnets by hot uniaxial pressing. Magnetically anisotropic samples with a remanence up to 1.31 T and an energy product up to 326 kJ/m3 are formed by die upsetting. The mechanical alloying process has also been applied to prepare magnetic material of three new Sm-Fe-TM phases: Sm-Fe-V with the ThMn12 structure, Sm-Fe-Zr with the PuNi3 structure, and Sm-Fe-Ti with the A2 structure. They all show high or ultrahigh coercivities (up to 51.6 kA/cm for Sm-Fe-Ti), but their saturation magnetization is comparably low. More promising are the interstitial nitrides or carbides of the 2:17 or the 1:12 phases. Magnetically isotropic microcrystalline Sm2Fe17Nx samples with coercivities up to 24 kA/cm were prepared by mechanical alloying and a two-step heat treatment. Their remanence and energy product are equivalent to similarly prepared Nd-Fe-B samples, but their properties at elevated temperatures are superior because of the high Curie temperature of 470 °C and the large anisotropy field of 22 T. Also for Sm2Fe17Cy and 1:12-type Nd-Fe-V-N, coercivities of 18.5 or 6 kA/cm, respectively, were achieved.
Influence of excess N on FeZrN soft magnetic film
Authors: Shimizu O. , Nakanishi K. , Yoshida S.
Published: July 2002

The soft magnetic properties of the FeZrN ternary system were studied in association with excess nitrogen (N) in films. The proportion of excess N (EN) is defined (z−y)/[x+(z−y)]×100 for the film composition expressed FexZryNz. This is because the advent of soft magnetism, in this system, is assumed to be due to suppression of grain growth of α-Fe by ZrN precipitated in grain boundaries, thus causing a ‘‘nanocrystalline effect.’’ This means that N exceeding the amount of Zr is considered ‘‘excess.’’ This paper presents the influence of excess N on soft magnetic properties, and the following conclusion was obtained. Excess N first formed a supersaturated solid solution with Fe, and acted as the origin of induced magnetic anisotropy. Supersaturated N easily moved in Fe and the orientation of easy axis was reversibly changed by re-annealing at 150 °C in a magnetic field perpendicular to the easy axis. When N was in excess, some part of excess N formed Fe4N. Fe4N caused a dispersion of the microscopic anisotropy, and lowered the permeability of the macroscopic hard axis. Both supersaturated N and Fe4N increased magnetostriction constants.
Relation between critical current densities and epitaxy of YBa2Cu3O7 thin films on MgO(100) and SrTiO3(100)
Authors: Kromann R. , Bilde-So/rensen J. B. , de Reus R. , Andersen N. H. , Vase P. , Freltoft T.
Published: July 2002

The preferred orientation of YBa2Cu3O7 thin films grown on single-crystal MgO(100) and SrTiO3(100) substrates has been investigated using x-ray diffraction and transmission electron microscopy. Various types of microstructural defects were identified in the films and correlated with a lowering of the critical current density Jc. On MgO substrates it was found that a film with 5% of its grains rotated 45° with respect to the dominant orientation and a high density of small-angle grain boundaries had Jc reduced by 75% compared to a film with no 45° grain boundaries and a low density of small-angle grain boundaries. On SrTiO3 substrates it was found that an increase in the amount of a-axis oriented material from 0.6% to 8.3% lead to a reduction in Jc by 70% . In general, higher critical current densities were found on SrTiO3 than on MgO substrates. This fact is attributed to the closer lattice match of YBa2Cu3O7 with SrTiO3, resulting in an in-plane mosaic spread of only 0.38° for the best film on SrTiO3 compared to 0.86° for the best film on MgO.
Effect of growth conditions on the properties and morphology of chemically derived epitaxial thin films of Ba2YCu3O7−x on (001) LaAlO3
Authors: McIntyre Paul C. , Cima Michael J. , Smith John A. , Hallock Robert B. , Siegal Michael P. , Phillips Julia M.
Published: July 2002

Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high-temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low-oxygen partial pressures. Superconducting films of 70 nm thickness with zero-field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c-axis normal BYC near the film/substrate interface with the overlying material dominated by grains with c-axis in-plane crystallographic orientation. The transport Jc fell to 2–3×106 A/cm2 for films of 200–250-nm thickness annealed at 780 °C in 1 × 10−3 atm oxygen. As the P(O2) was raised to 0.032 atm at 780 °C, for films of the same thickness, the Jc at 77 K decreased to 0.7 × 106–1 × 106 A/cm2 and the Tc(R = 0) dropped to 89 K. Increasing the furnace P(O2) was also found to degrade the crystalline quality of the films, as characterized by ion channeling Rutherford backscattering spectroscopy.
Ultrasonic inspection of very thin adhesive layers
Authors: Fraisse P. , Schmit F. , Zarembowitch A.
Published: July 2002

It is shown here that ultrasonic measurements can provide accurate information on an adhesive layer whose thickness is negligible compared with the wavelength. In this case, the adhesive layer can be considered as a simple interface between two elastic solids. This kind of contact enables small discontinuities of stresses or displacements between both substrates. A simple formulation is introduced to take into account these discontinuities expressed in terms of imperfect boundary conditions. It is shown that this formulation is consistent with exact calculation in layered media. The range of applications of this model and its limits is also investigated. This model is used to infer quantitative data on the changes in mechanical properties of a thin bonding layer (about 5 μm) from reflection coefficient measurements during its hardening process. The results obtained are in excellent agreement with ultrasonic measurement in bulk.
Microcircuit imaging using an ion-beam-induced charge
Authors: Breese M. B. H. , King P. J. C. , Grime G. W. , Watt F.
Published: July 2002

Ionizing radiation such as photons, keV electrons, or MeV ions can generate electron-hole pairs in semiconducting material. The high penetrating power of MeV light ions allows them to generate electron-hole pairs from deep within intact microelectronic devices, so images can be formed of the device active areas with very little degradation of the spatial resolution of the focused MeV ion beam. Furthermore, the ion-beam-induced charge (IBIC) image contrast is not strongly affected by the energy loss through the overlying device layers. This article is the first to demonstrate the capability of a nuclear microprobe to generate IBIC images of the active regions of devices through the passivation and metallization layers. The effect of the carrier generation volume on IBIC resolution is assessed. The ability of IBIC to align the major crystal axes of semiconductor samples is shown, and the effect of ion-induced damage on IBIC image contrast is considered.
Generation of Maxwell displacement current from spread monolayers containing azobenzene
Authors: Iwamoto Mitsumasa , Majima Yutaka , Naruse Haruhiko , Iriyama Keiji
Published: July 2002

The Maxwell displacement current generated from single fatty acid monolayers containing azobenzene by photoisomerization was investigated in the context of the phase diagram of monolayers on a water surface. Transient displacement-current pulses were found to be produced when successive isomerizations were induced in monolayers by irradiation with ultraviolet and visible light. In contrast, the displacement current was never generated in the so-called solid phase by the application of surface pressure or photoirradiation, probably because of the lack of free volume for the isomerizing chromophore in single monolayers and as well as the aggregation of molecules in the monolayer. The displacement current generated during monolayer compression was also investigated in connection with phase transitions.
An experimental study of the source/drain parasitic resistance effects in amorphous silicon thin film transistors
Authors: Luan Shengwen , Neudeck Gerold W.
Published: July 2002

The effect of source/drain (S/D) parasitic resistance has been experimentally investigated for amorphous silicon (a-Si:H) thin film transistors (TFTs). In general, the apparent field effect mobility decreases with decreasing channel length. However, the apparent threshold voltage is relatively constant. This may be attributed to an ohmic parasitic resistance due to the use of ion-implanted n+ S/D regions. Self-consistent results were obtained from both TFTs and from independent test structures for the TFT parasitic resistance, contact resistance, and sheet resistance. The results showed that the current spreading under the S/D regions is most critical in determining the magnitude of the total parasitic resistance. In this regard, both the S/D ion implantation and the S/D to gate overlap reduce the total parasitic resistance. Finally, the parasitic resistance is modeled as a gate voltage-modulated channel resistance, under the gate overlap, in series with a constant minimum contact resistance.
Barrier voltage deformation of ZnO varistors by current pulse
Authors: Leite E. R. , Varela J. A. , Longo E.
Published: July 2002

The phenomenon of electrical degradation in ZnO varistors was studied by application of high-intensity current pulses. A wave shape of 8×20 μs and rectangular waves of 1 and 2 ms were used. The degradation was estimated by reference electric-field variation and by Schottky voltage barrier deformation. The results showed that current pulses reduce both the height and the width of the barrier voltage. It was also observed that the donor density Nd did not change but the surface states density Ns decreased with degradation.
The origin of hard magnetic properties in rapidly quenched Nd4Fe77.5B18.5 alloy
Authors: Mao M. X. , Cheng Z. H. , Yang C. L. , Li F. S. , Zhang C. L. , Zhang Y. D. , Shen B. G. , Yang L. Y.
Published: July 2002

Until now, the origin of hard magnetic properties of rapidly quenched Nd-Fe-B alloys with lower Nd concentration is not clear. In this paper, the phase compositions of rapidly quenched Nd4Fe77.5B18.5 alloys annealed under different conditions have been studied by using zero-field spin-echo nuclear magnetic resonance (NMR) and Mössbauer effect (ME) techniques. It is found that there exists a certain amount of Nd2Fe14B phase in the samples annealed at 960 °C and ingot alloy, which have poor hard magnetic properties; while, the sample annealed under optimal condition consists only of bct-Fe3B as the main phase and a small amount of a-Fe. However, the ME result indicates that about 5 at. % Fe atoms in FeIII (8 g) site of bct-Fe3B have been replaced by Nd atoms; the NMR result demonstrates that 11B NMR spectrum is the characteristic peak of bct-Fe3B, but it broadens asymmetrically to the high frequency side, which is due to the bct-Fe3B influenced by Nd atoms. The amplitude of radio frequency (rf) excitation field required to get the maximum 11B spin-echo signal from bct-Fe3B in the sample annealed at 839 °C is only about one third as much as that required to excite the 11B in the bct-Fe3B influenced by Nd atoms in the sample annealed at 670 °C for a short time, which implies the latter has a larger coercivity field than the former. It is concluded that the origin of hard magnetic properties of Nd4Fe77.5B18.5 alloy is not related to the 2:14:1 phase, but to the change of bct-Fe3B itself.
Field dependence of the magnetic ordering of Cu in R2CuO4 (R=Nd,Sm)
Authors: Skanthakumar S. , Lynn J. W. , Peng J. L. , Li Z. Y.
Published: July 2002

We have used neutron diffraction techniques to study the field dependence of the magnetic ordering of Cu spins in R2CuO4 (R=Nd,Sm) in order to distinguish between the proposed collinear and noncollinear spin structures. In the proposed collinear spin structure, there are two separate domains with the spins either along the (110) or along the (11̄0) directions, while in the noncollinear model there is a single domain with the alternate-layer spins along the (100) and (010) directions, respectively. If a magnetic field is applied along the (11̄0), strong hysteresis effects are anticipated for the collinear spin structure due to domain repopulation, while such effects are not expected for the noncollinear spin structure. Our field dependent data do not show any hysteresis effects associated with the pure Cu ordering, which strongly suggest that the noncollinear spin structure is correct for the magnetic spin configuration of the Cu spins in both compounds. Hysteresis effects in a field are observed in Sm2CuO4 near and below the Sm ordering temperature, and these are most likely caused by the interaction between Sm and Cu sublattices.
Characterization of copper iodide thin films fabricated via laser-assisted molecular-beam deposition
Authors: Wijekoon W. M. K. P. , Lyktey M. Y. M. , Prasad P. N. , Garvey J. F.
Published: July 2002

The technique of laser-assisted molecular-beam deposition (LAMBD) has been used to fabricate a molecular film by reaction in a molecular beam. Molecular iodine vapor entrained into a stream of helium carrier gas was introduced via a supersonic expansion into the plasma plume of laser-evaporated copper to produce copper iodide. Films were deposited on substrates that were situated about 3 cm downstream on the path of the molecular beam. The surface morphology of films depends greatly on the fluence of the incident laser beam and expansion conditions. Films grown at low laser powers show small surface inhomogeneities in their electron micrographs compared to the films that were grown at higher laser powers. Copper in the LAMBD films is found to be mainly in the Cu+1 state as characterized by electron spectroscopy for chemical analysis. A comparison of the surface and structural properties of LAMBD films with that of a vacuum-evaporated film suggests that both films have similar lattice structures and compositions. It seems that LAMBD can be a powerful technique to deposit novel molecular and composite films for electronics and photonics.
Structure and adhesion of ZrN films formed by reactive magnetron sputtering ion plating and dynamic ion mixing
Authors: Jin S. , Wen X. Y. , Gong Z. X. , Zhu Y. C.
Published: July 2002

Ceramic coatings of zirconium nitride have been fabricated on nickel, silicon, and M2 high-speed steel by methods of reactive magnetron sputtering ion plating (RMSP) and the dynamic ion mixing (DIM). The microhardness values of ZrN film prepared by RMSP with different nitrogen partial pressure have been discussed. The scratch tests provide that the adhesion of ZrN film produced by dynamic ion mixing is better than that by reactive magnetron sputtering ion plating. Auger electron spectroscopy analysis is used to analyze the composition distribution of ZrN film prepared by DIM and indicates that there is a transitional layer between the ZrN film and substrate. Meanwhile, by cross-sectional and the plan-view transmission electron microscopy, it is observed that the interlayer of amorphous structure exists in the interface zone between ZrN film and substrate. According to the analysis of energy-dispersive x-ray analysis patterns, the composition of this amorphous region fabricated by RMSP is Ni51Zr49 (≊NiZr), as is that fabricated by DIM. (Up to now it has not been reported that the amorphous transitional layer occurs in reactive magnetron sputtering ion plating). The reason why the adhesion of coating by DIM is better than that by RMSP is not the formation of the transitional layer in ion-beam-assisted deposition but the particle bombardment effects on the bulk of the thin film.
Effect of high-energy ion irradiation and electron irradiation on textured Bi2Sr2CaCu2Ox—180-MeV Cu11+ and Br11+ irradiations and 3-MeV electron irradiation
Authors: Kumakura H. , Kitaguchi H. , Togano K. , Maeda H. , Shimoyama J. , Okayasu S. , Kazumata Y.
Published: July 2002

180-MeV Cu11+ and Br11+ irradiations and 3-MeV electron irradiation were carried out on textured Bi-2212 tapes and the effects of irradiation on the microstructure and superconducting properties were investigated. Ion irradiation, which creates linear tracks, is very effective in increasing both intragrain Jc and irreversibility field at temperatures below 60 K when field is parallel to the tracks. At 60 K, an order of magnitude higher Birr is obtained for both Cu11+ and Br11+ irradiations. Electron irradiation which creates point defects, on the other hand, is not as effective as ion irradiation except for low temperatures of ∼4.2 K. Apparent pinning potential energy U0 was increased by ion irradiation from ∼15 to ∼40 meV at 41.8 K, while U0 was unchanged by the electron irradiation. However, even U0 of the ion-irradiated sample is still small. This small U0 increases flux creep at temperatures above 60 K and makes ion irradiation less effective. A small increase of transport Jc was obtained by both ion and electron irradiation for small fluences. However, a significant decrease of transport Jc occurred at fluences which optimize intragrain Jc.
Effects of HDDR treatment conditions on magnetic properties of Nd-Fe-B anisotropic powders
Authors: Nakamura H. , Suefuji R. , Sugimoto S. , Okada M. , Homma M.
Published: July 2002

It is reported that Nd-Fe-B magnetic powders prepared by utilizing the HDDR (hydrogenation, disproportionation, desorption, and recombination) phenomena exhibit high coercivity, and the addition of Co, Ga, and Zr induces magnetic anisotropy in these powders. HDDR phenomena are caused by the heat treatment in hydrogen (H treatment) and subsequently in vacuum (V treatment). Present works describe the effects of V-treatment conditions on magnetic properties of Nd12.6Febal.CoxB6.0 (x=0–17.4) alloys. The powders V-treated at lower temperature show lower remanence and no noticeable magnetic anisotropy. V treatment at higher temperature enhances remanence and increases the differences of remanence between the powders aligned with and without magnetic field. Higher values are obtained in Co added alloys. This result suggests that a selective grain growth of Nd2Fe14B grains during V treatment plays an important role for the inducement of magnetic anisotropy in HDDR-treated powders. The temperature for complete recombination reaction under evacuating condition decreases with increasing Co content. It can be said that Co addition enhances recombination reaction and results in acceleration of grain growth.
High-resolution transmission electron microscopy study of solid phase crystallized silicon thin films on SiO2: Crystal growth and defects formation
Authors: Kim J. H. , Lee J. Y. , Nam K. S.
Published: July 2002

A high-resolution transmission electron microscopy study of the solid phase crystallization of amorphous silicon thin films deposited on SiO2 at 520 °C by low pressure chemical vapor deposition and annealed at 550 °C in a dry N2 ambient was carried out so that the grain growth mechanism, various types of defects, and the origins of defect formation could be understood on an atomic level. Silicon crystallites formed at the initial stage of the crystallization had a circular shape and grains had a branched elliptical or a dendritic shape. Many twins, of which {111} coherent boundaries were parallel to the long axis of a grain, were observed in the interior of all the elongated grains. In addition to twins, the following defects were observed in the grain: intrinsic stacking faults, extrinsic stacking faults, perfect dislocations, extended screw dislocations, and Shockley partial dislocations. These defects were formed by the following reasons: errors in the stacking sequence at the amorphous/crystalline interface; jumps of a twin plane; the intersecting of two crystal growth fronts slightly misoriented; and the intersecting of two twin planes at the amorphous/crystalline interface. Among those defects, twins and stacking faults provided a preferable nucleation site for an atomic step of a {111} plane. As a result, it was concluded that grain growth in the 〈112〉 direction along the {111} plane parallel to the long axis of a grain was accelerated by twins and stacking faults.
Beam waist changes in lithium niobate during Z-scan measurement
Authors: Henari Fryad. Z. , Cazzini Karl , El Akkari Fathi , Blau Werner J.
Published: July 2002

The nonlinear propagation of Gaussian beams in LiNbO3 has been investigated using the Z-scan technique. Experimental results shown that the minimum beam waist has been broadened. The third-order optical nonlinearity χ(3) of LiNbO3 has been measured at 514 nm and found for the real and imaginary parts of the nonlinearity to be −1.7×10−5 and −4.3×10−6 esu, respectively.
Novel amino acid crystals for phase-matched second-harmonic generation: L-pyrrolidone-2-carboxylic acid
Authors: Kitazawa Manabu , Higuchi Ryoichi , Takahashi Mitsuo , Wada Tatsuo , Sasabe Hiroyuki
Published: July 2002

A novel nonlinear optical amino acid derivative, L-pyrrolidone-2-carboxylic acid (L-PCA), has been studied for the application of UV generation by frequency upconversion of laser radiation. L-PCA is relatively easy to grow from solution to a large size, typically ∼40×20×20 mm3, by a slow cooling method. This crystal is chemically stable because the crystal lattice is composed of a network of hydrogen-bonded molecules. L-PCA has a wide transparency extending to the UV region (the cutoff wavelength is 260 nm) and is therefore a good candidate for the second-harmonic generation (SHG) of Nd:YAG laser radiation (1064 nm). The nonlinear-optical coefficient d14 was measured to be 0.22 pm/V, and the measured phase-matching angles agreed with values calculated using refractive index data. The effective nonlinear optical coefficient deff of the type-I phase-matched SHG has also been measured to be 0.20 pm/V. UV generation down to 266 nm was achieved by phase-matched SHG in L-PCA crystals.
Substrate temperature and target composition effects on PbTiO3 thin films produced in situ by sputtering
Authors: Jaber B. , Remiens D. , Thierry B.
Published: July 2002

The growth kinetics of PbTiO3 thin films, deposited by radio-frequency magnetron sputtering, have been studied as a function of the substrate temperature and the lead oxide content in the target. An equilibrium zone exists where the composition of the films corresponds to stoichiometric PbTiO3, independent of the lead oxide target composition. This zone appears at relatively low temperature when the film contains little excess of lead. This behavior can be explained by a mechanism involving the competition between the reevaporation of PbO from the film during the growth and the formation of PbTiO3 by the reaction of PbO with TiO2. Under optimal growth conditions we have obtained in situ PbTiO3 thin films at 550 °C.
Arrays of multilayered nanowires (invited)
Authors: Doudin B. , Blondel A. , Ansermet J.-Ph.
Published: July 2002

Multilayered Co/Cu wires with a diameter of 80 nm and a length of 6 μm were produced by electrodeposition in nanoporous polycarbonate membranes. Their magnetoresistance has been measured in a geometry where the current was perpendicular to the layer plane. The anisotropic part of the magnetoresistance was limited to 1.5%. The study, for layer thicknesses ranging from 3 to 100 nm interpreted in terms of the Valet and Fert model, gave estimates of the spin dependent bulk and interface resistivities and their change with temperature. The large Co bulk resistivity value, caused by a large amount of Cu impurities, limited the magnetoresistance in our samples to 20% at room temperature and 30% at 20 K. The Cu spin flip mean free path was found to be temperature independent and determined by scattering at Co impurities in the Cu layer. It was measured for two sets of samples with different amounts of Co impurities.
Effects of doping dyes on the electroluminescent characteristics of multilayer organic light-emitting diodes
Authors: Suzuki Hiroyuki , Hoshino Satoshi
Published: July 2002

We report the effects of dyes doped in the emitting layer on the electroluminescent characteristics of multilayer organic light-emitting diodes (LEDs) using a polysilane polymer, poly(methylphenylsilane) (PMPS), as the hole transporting material. We formed the emitting layer by dispersing in poly(styrene) (PS), one of four dyes whose fluorescence ranged from blue to orange. Two- or three-layer LEDs were prepared by combining PMPS and dye doped PS layers with the indium tin oxide and aluminum used for the hole and electron injecting electrodes, respectively. The three-layer LEDs had an additional vacuum-deposited tris-(8-hydroxyquinoline) aluminum layer. The electroluminescent (EL) characteristics of these multilayer organic LEDs, such as the current-voltage–EL intensity curve, the relative EL efficiency, and the EL emitting species, exhibit a marked dependence on the emitting dye. The observed dependence can be described consistently in terms of the dependence of the charge carrier trapping efficiency on the emitting dyes.
Photovoltaic properties of an AlxGa1−xAs solar cell (x=0–0.22) grown on Si substrate by metalorganic chemical vapor deposition and thermal cycle annealing
Authors: Soga T. , Kato T. , Umeno M. , Jimbo T.
Published: July 2002

The effects of a thermal cycle annealing (TCA) process on the defects in GaAs and AlxGa1−xAs solar cells on Si substrates are described in this paper. The defect density is reduced and the solar cell efficiency is improved by TCA. The defect density and the solar cell efficiency are evaluated in detail with respect to TCA temperature and Al composition. The problems involved in the fabrication of a high efficiency AlGaAs solar cell on a Si substrate are discussed.
Critical radius, size effects and inverse problems for composites with imperfect interface
Authors: Lipton Robert , Vernescu Bogdan
Published: July 2002

We provide new bounds on the interfacial barrier conductivity for isotropic particulate composites based on measured values of effective properties, known values of component volume fractions, and the formation factor for the matrix phase. These bounds are found to be sharp. Our tool is a new set of variational principles and bounds on the effective properties of composites with imperfect interface obtained by us [see R. Lipton and B. Vernescu, Proc. R. Soc. London Ser. A 452, 329 (1996)]. We apply the bounds to solve inverse problems. For isotropic polydisperse suspensions of spheres we are able to characterize the size distribution of the spherical inclusions based on measured values of the effective conductivity.
Adhesive contact of cylindrical lens and a flat sheet
Authors: Chaudhury Manoj K. , Weaver Timothy , Hui C. Y. , Kramer E. J.
Published: July 2002

Methods are developed to estimate the adhesion and surface free energies of compliant materials from the contact deformations of cylindrical lenses with flat sheets. Some important differences are found between the cylindrical contact studied here and the widely studied geometry of spherical contact. For example, while the pull-off force is completely independent of the elastic constants (K) of the materials for spherical contacts, the pull-off force for cylindrical contact is proportional to K1/3. Furthermore, for cylindrical contacts the contact width at separation reaches to a value of 39% of the width (a0) at zero load, whereas the corresponding value is 0.63a0 for spherical contact. The feasibility of using cylindrical contacts to estimate the surface and adhesive energies of polymers was investigated using elastomeric polydimethylsiloxane (PDMS) as a model system. PDMS was used in two ways: (1) unmodified and (2) with its surface hydrolyzed with dilute hydrochloric acid. Significant hysteresis of adhesion was observed with the hydrolyzed PDMS surfaces due to H-bonding interactions, which appeared to depend on normal stress.
Thermally induced structural changes in amorphous carbon films observed with ultraviolet photoelectron spectroscopy
Authors: Reinke P. , Oelhafen P.
Published: July 2002

We used the characteristic changes in the electronic structure of the valence band of amorphous carbon films upon the formation of graphitic clusters to monitor the temperature induced graphitization of a variety of hydrogen-containing (a-C:H) as well as hydrogen-free (a-C) films. The valence band spectra of the films, which were prepared in situ by ion-beam deposition and electron beam evaporation, were determined using photoelectron spectroscopy with excitation energies in the ultraviolet regime (ultraviolet photoemission spectroscopy, HeI, hν=21.22 eV and HeII, hν=40.82 eV). By choosing a variety of deposition parameters we are able to illustrate that the extent of temperature induced structural changes is on one hand determined by the bulk and surface diffusion coefficients of carbon atoms, and on the other hand by the ion irradiation which inhibits the graphitization process.
Longitudinal resonance in ferromagnets with random anisotropy: A formal experimental demonstration
Authors: Suran G. , Boumaiz E. , Frait Z.
Published: July 2002

Several properties of a new resonance mode are reported. It was detected in Co93−xZr7(RE)x (RE=Pr, Nd, Dy, Tb) amorphous thin films possessing an in-plane uniaxial anisotropy Hk. A study as a function of the working frequency shows, that when the external magnetic field H is applied in the plane defined by the film normal and Hk the new mode can be identified as a longitudinal resonance, which should occur in ferromagnets with random anisotropy, and observed even for H∥hrf∥Hk. The mode is localized and this localization is “stronger” for higher working frequencies.
Thickness and grain-size dependence of the coercivity in permalloy thin films
Authors: Akhter M. A. , Mapps D. J. , Ma Tan Y. Q. , Petford-Long Amanda , Doole R.
Published: July 2002

This paper reports the effect of thickness and grain size on the coercivity of Ni81Fe19 permalloy thin films (2.5–30 nm) sputtered on glass substrates for their application in magnetoresistive sensors. Coercivity was systematically investigated as a function of underlayer materials, thickness, and substrate temperature. Lateral grain size of the sputtered films was investigated. The grain size reduced very quickly in the thinner films. It was also found that the coercivity of the films with very small lateral grain size is much lower than those with a normal grain size. The lowest coercivity (Hc=0.8 Oe) was observed in 7.5 nm thick film and having a grain size of 4 nm. When an underlayer is used, its crystallinity affects the lateral grain size in the permalloy and correlates with the observed coercivity variation [P. Galtier, R. Jerome, and T. Valet, Mater. Res. Soc. Symp. Proc. 313, 417 (1993).] It was also observed that the coercivity of the permalloy is dependent on the nature of the underlayer. It was established that the coercivity of Ni81Fe19 films increases when the thickness increased from a critical film thickness and grain size. The variation of the coercivity in thin Ni81Fe19 films with lateral grain size and relationship with domain-wall width is discussed and compared with other theories for magnetization reversal.
Structural and magnetic properties of Nd2Fe17−δCrδ (δ=0, 0.5, 1, 1.9)
Authors: Girt Er. , Altounian Z. , Yang Jun
Published: July 2002

In Nd2Fe17−δCrδ (δ=0, 0.5, 1, 1.9), Cr substitutes for Fe atoms without changing the crystal structure. Neutron diffraction measurements show that for all values of δ, Cr preferentially substitutes for Fe in the 6 c site and randomly substitutes for Fe in the 18 f site. Cr substitution can be explained by considering the enthalphy of mixing using Miedema’s model. The Nd–Cr enthalphy of mixing is positive and this causes preferential substitution of Cr in those sites that have the lowest number of Nd nearest neighbors, i.e., the 6c site. Upon Cr substitution the Curie temperature increases from 327 K up to 374 K for δ=1 and then decreases to a value of 356 K for δ=1.9. This anomalous behavior can be qualitatively explained by two competing mechanisms arising from the decrease in the number of 6c-6c Fe pairs with increasing Cr concentration and from the decrease in volume of Nd2Fe17−δCrδ with increasing δ which affects the 6c-6c interatomic Fe distances.
The effects of the catalytic nature of capacitor electrodes on the degradation of ferroelectric Pb(Zr,Ti)O3 thin films during reductive ambient annealing
Authors: Fujisaki Yoshihisa , Kushida-Abdelghafar Keiko , Shimamoto Yasuhiro , Miki Hiroshi
Published: July 2002

The disappearance of ferroelectricity in Pb(Zr0.52,Ti0.48)O3 (PZT) thin-film capacitors, which is caused by heat treatment in a reductive ambience, is investigated. Bare PZT films are not damaged by annealing in a hydrogen-containing atmosphere (H2 annealing) up to 400 °C, whereas a PZT capacitor with Pt electrodes loses its ferroelectricity during annealing at less than 300 °C. We have found that the degradation of ferroelectricity depends upon the metal used for the top electrode of the PZT capacitor. The increased degradation in the case of a PZT capacitor with Pt electrodes can be explained by a catalytic reaction on the Pt surface. We have made the ferroelectricity of a Pt/PZT/Pt capacitor retained even after the H2 annealing at 300 °C, or above, simply by oxidizing it before the H2 annealing.
Experimental study of copper–alkali ion exchange in glass
Authors: Gonella F. , Caccavale F. , Bogomolova L. D. , D’Acapito F. , Quaranta A.
Published: July 2002

Copper–alkali ion exchange was performed by immersing different silicate glasses (soda-lime and BK7) in different molten eutectic salt baths (CuSO4:Na2SO4 and CuSO4:K2SO4). The obtained optical waveguides were characterized by m-lines spectroscopy for the determination of refractive index profiles, and by secondary ion mass spectrometry for the concentration profiles of the ion species involved in the exchange process. The different oxidation states of copper inside the glass structure were studied by electron paramagnetic resonance and x-ray absorption techniques. Interdiffusion copper coefficients were also determined. The Cu–alkali exchange was observed to give rise to local structural rearrangement of the atoms in the glass matrix. The Cu+ ion was found to mainly govern the exchange process, while competition between Cu–Na and K–Na exchanges occurred when a potassium sulfate bath was used. In this case, significant waveguide modal birefringence was observed.
High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics
Authors: Sarukura Nobuhiko , Ohtake Hideyuki , Izumida Shinji , Liu Zhenlin
Published: July 2002

The THz-radiation power from bulk InAs irradiated with femtosecond optical pulses is significantly enhanced and reaches 650 μW in a 1.7-T magnetic field with 1.5-W excitation power. The THz-radiation power is related almost quadratically both to the magnetic field and excitation laser power. We have also found that the power of the THz-radiation from an InAs sample in a magnetic field is over one order of magnitude higher than that from GaAs. Additionally, a dramatic change of ellipticity is observed, and the spectra of the horizontal and vertical polarization components are found to differ.
Growth of lamellar eutectic dendrites in undercooled melts
Authors: Goetzinger R. , Barth M. , Herlach D. M.
Published: July 2002

Electromagnetic levitation is used to undercool bulk samples of eutectic Ni 21.4 at % Si alloys. Large undercoolings ΔT up to ΔT=220 K are achieved by containerless processing of the melts. Crystal growth velocities are measured as a function of undercooling. The growth kinetics during solidification of the eutectic alloys is controlled by atomic diffusion. A maximum in the relation of the growth velocity on undercooling is observed which is due to the progressively decreasing diffusion coefficient counteracting the enhancement of the driving force of crystallization with increasing undercooling. Microstructure analysis of as-solidified samples reveals colonies of eutectic lamellae enveloped by a nonplanar growth front of a dendritelike morphology. The experimental data are analyzed within current models of crystal growth taking into account a negative temperature gradient in front of the solidification front. While the thermal undercooling causes a dendriticlike morphology of the solidification front, constitutional and curvature undercooling control the formation of the eutectic colonies behind it.
Raman spectroscopic studies on well-defined carbonaceous materials of strong two-dimensional character
Authors: Wilhelm H. , Lelaurain M. , McRae E. , Humbert B.
Published: July 2002

Using 514 nm radiation and a careful experimental protocol allowing us to make quantitative intensity analyses, we have examined the first- and second-order Raman spectra of five varieties of graphite. These include single-crystal graphite and highly oriented pyrolytic graphite as references, then two with a significant content of c-axis translation faults introduced through grinding and exfoliation, and a last sample which is purely turbostratic. We show that full c-axis stacking disorder results in a strong increase of the scattered E2g-mode intensity. We have further shown that even in those strongly disordered stacking sequences, but in which the AB sequence persists over only a few layers, the doublet around 2700 cm−1 is resolved. We argue against assigning the peak around 1355 cm−1 to “disorder,” as is so often done, but to the finite in-plane domain size as proposed a number of years ago; moreover, we suggest that this peak is a more sensitive probe of such small domains than is x-ray diffraction.
Effect of iron on the high temperature magnetic properties and microstructure of Sm(Co, Fe, Cu, Zr)z permanent magnets
Authors: Liu J. F. , Ding Y. , Hadjipanayis G. C.
Published: July 2002

We have fabricated a new magnet with nominal composition of Sm(CobalFe0.1Cu0.078Zr0.033)8.3, which has a room temperature intrinsic coercivity Hci of 40 kOe and a saturation magnetization Ms of 92 emu/g. The new magnet has a temperature coefficient of intrinsic coercivity β(RT−773 K)=−0.15%/K and a high intrinsic coercivity of 10.7 kOe at 773 K.
Variations of the leakage current density and the dielectric constant of Pt/(Ba,Sr)TiO3/Pt capacitors by annealing under a N2 atmosphere
Authors: Hwang Cheol Seong , Joo Suk Ho
Published: July 2002

This article reports variations of the leakage current density of Pt/40 nm-(Ba,Sr)TiO3/Pt capacitors after annealing under a N2 atmosphere containing oxygen of about 0.01 ppm. Annealing a capacitor under a N2 atmosphere at 750 °C for 30 min results in an increase of the leakage current density at 1.5 V by more than six orders of magnitude compared to that of a capacitor annealed under the optimum oxygen concentration (about 5% in O2) at the same temperature. The dielectric constant was decreased after annealing under the N2 atmosphere. The composition of (Ba,Sr)TiO3 (BST) films, measured by Auger electron spectroscopy, did not show any difference between the two samples. The major reason for the huge increase in the leakage current density is due to the roughening of top Pt electrodes by the annealing under N2 atmosphere. Such roughening imposes a strong stress to the BST film surface and generates surface trap states. The stress-induced trap states reduce the interfacial potential barrier height for Schottky emission and result in increased leakage current densities. Capping of the top Pt electrode with a very thin BST layer (about 10 nm) before the annealing eliminates surface roughening, preserves a low leakage current level, and increases dielectric constants.
Interacting amorphous ferromagnetic wires: A complex system
Authors: Velázquez J. , Garcı́a C. , Vázquez M. , Hernando A.
Published: July 2002

Magnetization reversal of high and positive magnetostriction amorphous wires gives rise to a square hysteresis loop owing to their particular domain structure. When two quasi-identical wires are placed close together, the lack of simultaneous magnetization reversal produces a temporal instability in the hysteresis loop as a consequence of the magnetostatic interaction between them. This instability, having chaotic properties, is controlled by the amplitude and frequency of the applied magnetic field and depends on the length of the wires and distance between them. A theoretical model, based on an iterative algorithm, has been developed in order to understand the properties of the whole magnetization. The instability seems to originate in an irreversible rearrangement of the closure domain structure at the ends of the wires after each magnetization reversal. The magnetization of the set of wires follows a potential law that can be explained in the framework of the self-organized criticality, a theory of the complexity.
Excimer laser-induced temperature field in melting and resolidification of silicon thin films
Authors: Hatano Mutsuko , Moon Seungjae , Lee Minghong , Suzuki Kenkichi , Grigoropoulos Costas P.
Published: July 2002

The liquid/solid interface motion and temperature history during excimer laser annealing of 50-nm-thick Si films on fused quartz substrates are investigated by in situ nanosecond time-resolved electrical conductance, optical reflectance, and transmittance at visible and near-IR wavelengths, combined with thermal emission measurements. The temperature response, melt propagation and evolution of the recrystallization process are fundamentally different in the partial-melting and the complete-melting regimes. Because it is necessary to balance the latent heat across the propagating phase-change interface, the maximum induced temperature in the partial-melting regime remains close to the melting point of amorphous Si. The peak temperature rises in the complete-melting regime, but the nonparticipating nature of the liquid Si/fused quartz interface allows substantial supercooling (>200 K), followed by spontaneous nucleation into fine-grained material. These phase transformations are consistent with the recrystallized polycrystalline Si morphologies that indicate grain enhancement in the near-complete-melting regime. It is also found that melting of polycrystalline Si occurs close to the melting point of crystalline Si. This temperature is by approximately 140 K higher than the melting point of amorphous Si.
Raman spectroscopy of phenylcarbyne polymer films under pulsed green laser irradiation
Authors: Lu Y. F. , Huang S. M. , Sun Z.
Published: July 2002

The polycarbyne polymer films were coated on silicon substrates and then irradiated by a pulsed Nd:yttrium–aluminum–garnet laser (λ=532 nm) with various fluences in argon gas atmosphere. Significant changes in microstructures and chemical bonding (sp3/sp2) during laser treatment were investigated by Raman spectroscopy. At a laser fluence below 50 mJ/cm2, the Raman spectrum of the film was similar to that of the original polymer film. In a fluence range from 100 to 650 mJ/cm2, the thermal decomposition of the polymer occurred, resulting in upshift of G peak and downshift of the D peak both with narrower peak width. With increasing laser fluence from 650 to 950 mJ/cm2, both the G and D peaks downshifted simultaneously due to the thermal decomposition. The simultaneous downshift of both peaks indicated the increased sp3/sp2 ratio in the carbon film converted from the polymer. With increasing laser fluence in this range, the thermal decomposition also induced the narrowing of both peaks. The narrowing of both peaks indicated the increased ordering of sp3 and sp2 bonding components in the converted carbon film. The scanning electron microscopy studies provided the further evidence. The carbon films converted from the polymer films may contain the highest sp3 carbon bonding at laser fluences in the range from 850 to 1000 mJ/cm2.
Dissociation of dilute immiscible copper alloy thin films
Authors: Barmak K. , Lucadamo G. A. , Cabral C. , Lavoie C. , Harper J. M. E.
Published: July 2002

The dissociation behavior of dilute, immiscible Cu-alloy thin films is found to fall into three broad categories that correlate most closely with the form of the Cu-rich end of the binary alloy phase diagrams. Available thermodynamic and tracer diffusion data shed further light on alloy behavior. Eight alloying elements were selected for these studies, with five elements from groups 5 and 6, two from group 8, and one from group 11 of the periodic table. They are respectively V, Nb, Ta, Cr, Mo, Fe, Ru, and Ag. The progress of precipitation in approximately 500-nm-thick alloy films, containing 2.5–3.8 at. % solute, was followed with in situ resistance and stress measurements as well as with in situ synchrotron x-ray diffraction. In addition, texture analysis and transmission electron microscopy were used to investigate the evolution of microstructure and texture of Cu(Ta) and Cu(Ag). For all eight alloys, dissociation occurred upon heating, with the rejection of solute and evolution of microstructure often occurring in multiple steps that range over several hundred degrees between approximately 100 and 900 °C. However, in most cases, substantial reductions in resistivity of the films took place below 400 °C, at temperatures of interest to copper metallization schemes for silicon chip technology.