bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear self-defocusing in doped silica sono-gels
Authors: Ramos Rocío , Petersen Paul Michael , Johansen Per Michael , Lindvold Lars , Ramírez Mila , Blanco Eduardo
Published: July 2002

Experiments with nonlinear self-refraction of Gaussian laser beams in silica sono-gels doped with copper tetrasulfonated phthalocyanine are reported. The propagation of laser beams inside nonlinear sol-gel samples with different Cu-phthalocyanine concentrations has been monitored by measuring the spatial beam profile in the near field and in the far field behind the sample. The experimental results are analyzed by a new simple theoretical approach, in which we assume that the incident Gaussian beam induces a phase shift that varies as a Gaussian function of the beam radius. The beam propagation behind the sample is determined by the Huygens–Fresnel integral formalism. By solving the Huygens–Fresnel integral, analytical expressions for the spatial beam profile in both the near field and the far field after the nonlinear sample are obtained. Experiments are carried out with a diode pumped frequency doubled Nd–YAG laser at 532 nm. We obtain very large third-order nonlinearities in these doped sol-gel samples at temperatures just above room temperature. When we compare the predictions of the theory with the experimental data, we find experimental values of the nonlinear third-order susceptibility up to −2.3×10−4 esu.
Photothermal and electroreflectance images of biased metal-oxide-semiconductor field-effect transistors: Six different kinds of subsurface microscopy
Authors: Batista J. A. , Mansanares A. M. , da Silva E. C. , Fournier D.
Published: July 2002

Six different configurations for metal-oxide-semiconductor field-effect-transistor reflectance microscopy are presented, each one revealing a particular contrast of the operating structure. These different images are obtained by interchanging the modulation of gate-source and drain-source potentials, as well as by varying the probe beam intensity. Three main components were identified in the signal, their relative importance depending on the experimental configuration: the electroreflectance component, the photoinjected carrier (probe-induced) component and the bias current (Joule effect) component. The high ability of the technique to detect defects in these structures is also demonstrated.
Effects of thermal annealing on emission characteristics and surface properties of field emitter arrays
Authors: Ito Fuminori , Konuma Kazuo , Okamoto Akihiko , Yano Akihiro , Miyano Souichiro
Published: July 2002

The effects of thermal annealing below 500 °C on Spindt-type Mo field emitter arrays (FEAs) were studied through emission characteristics and Mo surface analysis. The anode current of the FEAs increases with increasing annealing time and then saturates after a certain period that is shorter for higher-temperature annealing. X-ray photoelectron spectroscopy and temperature programmed desorption show that MoO3 formed on the Mo surface desorbs at around 500 °C. The enhancement of the anode current is caused mainly by MoO3 desorption, since the period required for MoO3 desorption corresponds to that required for current saturation.
High accuracy Raman measurements using the Stokes and anti-Stokes lines
Authors: Trzeciakowski Witold , Martínez-Pastor Juan , Cantarero Andrés
Published: July 2002

We show that by measuring the separation between the Stokes and anti-Stokes peaks excited by two different laser lines we obtain a very precise determination of absolute phonon energies. The method is useful for measuring small changes of these energies with strain, temperature, laser power, etc. It doubles the changes and avoids the necessity of using the reference lines in the Raman spectra. The method can be applied for the determination of phonon deformation potentials, for the characterization of strained heteroepitaxial layers, and for micro-Raman analysis of strain in silicon integrated circuits. We give examples of phonon shifts in Si, Ge, GaAs, InAs, and GaP as a function of applied biaxial strain, laser power, and temperature.
Ferromagnetic resonance modes in coupled layers with cubic magnetocrystalline anisotropy
Authors: Layadi A.
Published: July 2002

The ferromagnetic resonance (FMR) relations of an interfacially coupled two-layer magnetic system have been derived. In the case modeled here, the two films are assumed to be characterized by uniaxial and cubic magnetocrystalline anisotropies. Analytical expressions for the resonance condition have been found for a strong coupling case for both ferromagnetic and antiferromagnetic coupling. The FMR modes have also been studied as a function of the coupling strength. In the strong coupling cases, the system behaves as a single thin film with effective cubic and uniaxial anisotropy fields and effective magnetogyric ratios. When the coupling is antiferromagnetic a “spin-flop” can occur beyond a critical coupling value Kcrit. There will be a discontinuity in mode position. The critical coupling and field have been derived. This analysis could be used to study experimentally the nature and the strength of the magnetic coupling in systems with cubic and/or uniaxial magnetocrystalline anisotropies.
Nanometer scale mixing homogeneity in light emitting polymer blend thin films
Authors: Hsu Jui-Hung , Wei Pei-Kuen , Fann Wunshain , Chuang Kuen-Ru , Chen Show-An
Published: July 2002

Phase separation in polymer blend thin films is directly observed by near-field scanning optical microscopy. Time-resolved fluorescence spectra indicate that the phase domains are composed of different fractions of the two constituent polymers. The mixing homogeneity was found to vary with the blending ratio.
Theoretical study of hyperfine fields at impurity nuclei in GdX (X=Zn,Cd) compounds: A two-center model
Authors: de Oliveira A. L. , Ramunni V. P. , Tovar Costa M. V. , de Oliveira N. A. , Troper A.
Published: July 2002

We theoretically discuss the local moment formation and the hyperfine field behavior of nonmagnetic (s−p and noble) impurities diluted in ferromagnetic rare-earth compounds GdX (X=Zn, Cd). It is experimentally observed in these systems that all impurities enter substitutionally at the “nonmagnetic” X lattice site, creating a strong local charge perturbation. In our simplified model, one calculates the local magnetic moment in the perturbed conduction band at the origin (a charge perturbed X site). The polarization of the conduction band arises from the Gd 4f moments and the conduction electron polarization produced by the host magnetic moment at the origin is treated within the Born approximation. The general trend of the experimental hyperfine field data is well reproduced by our self-consistent calculations.
AlN as an encapsulate for annealing SiC
Authors: Jones K. A. , Xie K. , Eckart D. W. , Wood M. C. , Talyansky V. , Vispute R. D. , Venkatesan T. , Wongchotigul K. , Spencer M.
Published: July 2002

AlN films grown by either organometallic vapor phase epitaxy (OMVPE) or pulsed laser deposition (PLD) can be used to encapsulate SiC when heated in an argon atmosphere at temperatures at least as high as 1600 °C for times at least as long as 30 min. The coverage of the AlN remains complete and the AlN/SiC interface remains abrupt as determined by Auger electron spectroscopy. However, considerable atomic movement occurs in the AlN at 1600 °C, and holes can form in it as the film agglomerates if there are large variations in the film thickness. Also, the SiC polytype near the surface can in some instances be changed possibly by the stress generated by the epitaxial AlN film. Using x-ray diffraction measurements, we also found that, during the 1600 °C anneal, grains with nonbasal plane orientations tended to grow at the expense of those with basal plane orientations in the OMVPE films, whereas grains with only the basal plane orientation tended to grow in the PLD films. However, there is no indication that the type of grain growth that is dominant affects the film’s ability to act as an encapsulate.
Plasma chemistry aspects of a-Si:H deposition using an expanding thermal plasma
Authors: van de Sanden M. C. M. , Severens R. J. , Kessels W. M. M. , Meulenbroeks R. F. G. , Schram D. C.
Published: July 2002

The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl (SiH3) radical whereas the ion-electron induced dissociation mechanism leads to SiHx (x<3) radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals SiHx(x<3) with silane. Almost independent of the plasma conditions used, approximately one H2 is produced per consumed SiH4 molecule. Disilane production is observed which roughly scales with the remaining silane density. Possible production mechanisms for both observations are discussed.
Quantitative analysis of excitonic photoluminescence in nitrogen-doped ZnSe epilayers
Authors: Zhu Z. M. , Li G. H. , Liu N. Z. , Wang S. Z. , Han H. X. , Wang Z. P.
Published: July 2002

We have investigated the photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen radio frequency-plasma source. The PL data shows that the relative intensity of the donor-bound exciton (I2) emission to the acceptor-bound exciton (I1) emission strongly depends on both the excitation power and the temperature. This result is explained by a thermalization model of the bound exciton which involved in the capture and emission between the neutral donor bound exciton, the neutral acceptor bound exciton and the free exciton. Quantitative analysis with the proposed mechanism is in good agreement with the experimental data.
Ga
0.51
In
0.49
P/In
x
Ga
1−x
As/GaAs
lattice-matched and strained doped-channel field-effect transistors grown by gas source molecular beam epitaxy
Authors: Lin Yo-Sheng , Lu Shey-Shi , Chang Pei-Zen
Published: July 2002

Recently, it was demonstrated that doped-channel field-effect-transistor (DCFET) structure has the advantages of high breakdown voltage, high current drivability, and high turn on voltage. Therefore, a series of lattice-matched and strained Ga0.51In0.49P/InxGa1−xAs/GaAs (0⩽x⩽0.22) DCFETs were studied in order to find the optimized structure. Through dc and microwave measurements, we observed that the introduction of a 150-Å-thick strained InxGa1−xAs (0.15⩽x⩽0.22) channel can enhance device performance, compared to the lattice-matched one (x=0). The optimized performance of transconductance (gm), current-gain cutoff frequency (ft) and maximum oscillation frequency (fmax) all occurred when indium content x was between 0.15 and 0.20 for devices with 1-μm-long gate and these optimized results are comparable to those state-of-the-art results of pseudomorphic high electron mobility transistors. We also found that DCFETs are very ideal for single-voltage-supply operation. Degradation of device performance was observed for larger indium content (x=0.22), which is associated with strain relaxation in this highly strained channel. Experimental results showed that Ga0.51In0.49P/InxGa1−xAs/GaAs DCFETs with indium content x between 0.15 and 0.20 were very suitable for microwave high power device applications.
Approximate model for wave propagation in piezoelectric materials. II. Fibrous composites
Authors: Nayfeh Adnan H. , Dong Jennifer J. , Faidi Waseem
Published: July 2002

A continuum mixture theory with microstructure is developed for guided wave propagation in unidirectional fibrous composites of piezoelectric materials exhibiting hexagonal symmetry. The theory leads to the simple system of coupled equations for the actual composites which retain the integrity of the propagation process in each constituent but allow them to coexist under analytically derived interaction parameters. As a consequence of the analysis, effective mixture properties of the composite are obtained in the zero-frequency (static) limit. The utility of the resulting equations is demonstrated by studying the propagation of harmonic waves in the system.
Effects of thermal annealing on photoluminescence and structural properties of (ZnSe)2(CdSe)n short-period-superlattices multiple quantum wells
Authors: Tu R. C. , Su Y. K. , Chou S. T.
Published: July 2002

This work investigates how thermal annealing affects the optical and structural properties of (ZnSe)2(CdSe)n short-period-superlattices multiple quantum wells (SPS MQW) grown by molecular beam epitaxy using photoluminescence (PL) and high-resolution transmission electron microscopy (HRTEM) techniques. A characteristic that differentiates annealed SPS MQW from annealed conventional quantum wells is that much greater blueshifts can be observed in annealed SPS MQW as the annealing temperature rises above 400 °C. We attribute the larger blueshifts to thermally induced interdiffusion of Zn and Cd atoms between alternate ZnSe and CdSe layers. Furthermore, the PL emission in annealed (ZnSe)2(CdSe)n SPS MQW quenches at higher temperatures and yields a larger value for the activation energy than in as-grown SPS MQW. HRTEM images of samples annealed at 450 °C for 30 min clearly indicate that SPS structures remain in the quantum well regions of as-grown SPS MQW, but intermix and disappear in the well regions of annealed (ZnSe)2(CdSe)n SPS MQW.
Oxide confining layer on an InP substrate
Authors: Legay P. , Caillet F. , Decobert J. , Leprince L. , Le Roux G. , Quillec M.
Published: July 2002

Wet thermal oxidation of a strained balanced superlattice structure, epitaxially grown on InP and including high Al content layers, is investigated. The oxidation kinetics are studied as a function of temperature and oxidation duration. The results are interpreted with a simple diffusion model. We propose use of this structure as a confining layer for monolithic long wavelength vertical cavity surface emitting lasers.
Effectiveness of AlN encapsulant in annealing ion-implanted SiC
Authors: Handy Evan M. , Rao Mulpuri V. , Jones K. A. , Derenge M. A. , Chi P. H. , Vispute R. D. , Venkatesan T. , Papanicolaou N. A. , Mittereder J.
Published: July 2002

Aluminum nitride (AlN) has been used as an encapsulant for annealing nitrogen (N), arsenic (As), antimony (Sb), aluminum (Al), and boron (B) ion-implanted 6H-SiC. Atomic force microscopy has revealed that the AlN encapsulant prevents the formation of long grooves on the SiC surface that are observed if the AlN encapsulant is not used, for annealing cycles up to 1600 °C for 15 min. Secondary ion mass spectrometry measurements indicated that the AlN encapsulant is effective in preserving the As and Sb implants, but could not stop the loss of the B implants. Electrical characterization reveals activation of N, As, Sb, and Al implants when annealed with an AlN encapsulant comparable to the best activation achieved without AlN.
Elastic constants of multidomain LiTaO3 crystal
Authors: Takanaga Izumi , Kushibiki Jun-ichi
Published: July 2002

All the independent components of the elastic constant tensor of multidomain LiTaO3 crystal were determined by measuring bulk acoustic wave velocities and density for five multidomain LiTaO3 substrates perfectly depoled by heat treatment. Comparing these determined constants with the elastic constants of single-domain LiTaO3 crystal revealed that the elastic constants of multidomain crystal cij differ from both the elastic constants at constant electric field cijE and those at constant electric displacement cijD for single-domain crystal. The angular dependences of leaky surface acoustic wave velocity were measured on single and multidomain 36°Y-cut LiTaO3 substrates by line-focus-beam acoustic microscopy and compared with the calculated results using the determined constants. The measured results agreed well with the calculated results. The constants will be used to enhance theoretical understanding of the elastic properties of residual multidomains.
Study of phase change in materials under high pressure
Authors: Singh V. P. , Renuka D. V.
Published: July 2002

Propagation of converging shock in metals and radioactive materials is studied. Variation of pressure in different metals and radioactive materials has been calculated numerically as the shock converges to its center.
Solid solubility of As in CoSi2 and redistribution at the CoSi2/Si interface
Authors: Mangelinck D. , Cardenas J. , d’Heurle F. M. , Svensson B. G. , Gas P.
Published: July 2002

The solid solubility of As in CoSi2 and the redistribution of As at the CoSi2/Si interface at temperatures between 650 and 950 °C have been investigated. As was implanted in the cap Si layer of mesotaxy samples (epitaxial CoSi2 layers buried in a Si substrate). The As profiles after annealing were measured by secondary ion mass spectrometry. The solubility of As is lower in the cobalt disilicide than in silicon. A detailed description of thermodynamic equilibrium between the solution of As in CoSi2 and the solution of As in Si shows that the distribution coefficient is dependent on the concentration. Within the experimental accuracy, the enthalpy of solution, deduced from the distribution coefficient, is constant in the temperature range and equal to 0.28 eV. The solution of As in CoSi2 can thus be described by Henry’s law, which is valid for dilute solutions. Accumulation of As at both interfaces of the buried CoSi2 layer has been observed and is discussed in terms of segregation and precipitation. A transient enhancement of the As diffusion in the Si substrate has also been found. Simulation of the redistribution process shows that this enhancement is not due to the diffusion of As in CoSi2 but more likely associated with the excess of point defects resulting from ion implantation or from the silicide film. On the basis of both ternary phase diagram calculations and experimental results, it is shown that there is a ternary equilibrium between Si(As), CoSi2, and SiAs in contrast to the equilibrium between Si(As), CoSi2, and CoAs reported previously by other authors. It is shown that the latter equilibrium should decrease the solubility of As in Si, but such a decrease has never been observed experimentally.
Co silicide formation on epitaxial Si1−yCy/Si (001) layers
Authors: Roichman Y. , Berner A. , Brener R. , Cytermann C. , Shilo D. , Zolotoyabko E. , Eizenberg M. , Osten H. J.
Published: July 2002

We investigated the formation and structure of cobalt silicide (CoSi2) on Si1−yCy (0⩽y⩽0.81%) layers grown by molecular beam epitaxy on Si (001). The incorporation of C in the Si lattice causes the following phenomena during silicidation: (i) the formation of CoSi2 is delayed in temperature scale, as compared to pure Si; (ii) epitaxial CoSi2 grains are formed at T⩾600 °C; (iii) a two sublayer structure of CoSi2 is observed, where the upper sublayer contains a very small amount of C and has a homogeneous microstructure, while the lower sublayer, which has a higher C concentration, contains randomly oriented CoSi2 nanocrystallites; (iv) spatial inhomogeneity results in significant variation (within ±40%) in the CoSi2 layer thickness; (v) no strain relaxation in the Si1−yCy layer during silicidation is detected up to 700 °C; and (vi) the distribution of carbon and boron in the semiconductor during silicidation is not changed significantly. The two latter findings show the potential of CoSi2 on Si1−yCy for device application despite the mentioned inhomogeneity in CoSi2 microstructure.
Electron correlation effects on tunneling through a two-level quantum dot
Authors: Anda E. V. , Chiappe G. , Davidovich Maria A. , Ferrari V.
Published: July 2002

The possibility of detection of the Kondo effect by means of the measurement of Bohm-Aharonov oscillations of the current going through a quantum dot embedded in one of the arms of a mesoscopic ring connected to two leads is demonstrated. The ring is threaded by a magnetic flux and the dot is subjected to a gate voltage V0 which controls its charge content. Whenever the dot has an odd number of electrons and, as a consequence, a net spin the system is in the Kondo regime. Thus, the Kondo effect can be turned on and off as the two dot levels and their associate Coulomb blockade peaks are tuned to the Fermi level by changing V0. Since the Kondo resonance provides a new channel for the electrons to tunnel through the dot it allows the flowing of current along the arm of the ring which contains the dot even though the dot levels are out of resonance. The interference between the waves going along the upper and lower arms of the ring gives rise to the Bohm-Aharonov oscillations of the current and is a clear sign of the Kondo effect.
Scanning photoelectron microscopy study of the laser-induced transformations of polycrystalline CdTe films
Authors: Nelson Art J. , Danailov M. , Gregoratti L. , Marsi M. , Kiskinova M.
Published: July 2002

We have used pulsed-laser treatment to provide highly localized chemical reactions in the near-surface region of polycrystalline CdTe thin films. Using scanning photoelectron microscopy, the lateral changes in the composition and morphology of the films as a function of the irradiation conditions and of the distance from the center of the laser beam were characterized. Results show that the films undergo thermal-induced heterogeneity in the morphology and in the lateral distribution of the elements and chemical phases due to local melting and dissociation of the film. This transformation leads to a local increase of the conductivity and enrichment with elemental Te.
Inhomogeneous broadening of intersubband transitions due to nonscreening roughness of heterointerfaces
Authors: Vasko F. T. , Sun J. P. , Haddad G. I. , Mitin V. V.
Published: July 2002

The shape of the terahertz absorption peak in quantum wells with rough heterointerfaces is studied. Although the long-range variations of the ground level are screened in heavily doped structures, the intersubband in-plane energy remains nonuniform due to the second-level variations. The equation for intersubband polarization is considered in the resonant approximation, taking into account the depolarization shift. The line shape of the intersubband absorption peak is described for the case with long-range variations of heterointerfaces.
Nonlinear optical properties of poly[(4′-acetylphenylaminoformyloxy- 4-styrene)-co-(4-hydroxystyrene)] and guided mode-mode second-harmonic generation in waveguide
Authors: Jung J. H. , Kinoshita T.
Published: July 2002

Linear and nonlinear optical properties of electrically poled films of newly synthesized poly [(4′-acetylphenylaminoformyloxy-4-styrene)-co-(4-hydroxystyrene)] [poly(AS-co-HS)] are investigated. Linear optical properties of a poly(AS-co-HS) film are measured by the prism-coupling method. Ultraviolet (UV) transparency down to 350 nm identifies that this polymer is a promising candidate for second-harmonic generation (SHG) in the UV-visible light region. Corona-poling technique is used to produce a noncentrosymmetric structure. The induced d33 at λ=1064 nm is 2.8 pm/V. High glass-transition temperature (Tg=160 °C) results in very long decay time of the nonlinearity, d33. The decay time at operating temperature of 80 °C is estimated to be more than ten years. Guided-mode blue and green SHGs are demonstrated using the film as a slab waveguide.
Interlayer exchange coupling in Fe/Au multilayers
Authors: Opitz J. , Zahn P. , Binder J. , Mertig I.
Published: July 2002

The aim of this article is to present ab initio calculations of interlayer exchange coupling for Fe/Au (001) multilayers with the same spacer thickness as in recently performed experiments. The structure is characterized by a bcc–fcc transition. The calculations are based on density functional theory using a scalar relativistic screened Korringa–Kohn–Rostoker method. The results show that in case of ideally smooth interfaces the differences of the theoretically and experimentally obtained coupling strengths by one order of magnitude remain. It will be demonstrated that the usual explanation by means of a mesoscopic roughness fails.
Co
59
nuclear magnetic resonance study of molecular-beam epitaxy grown Co/V multilayers
Authors: Thomson T. , Riedi P. C. , Krishnan R.
Published: July 2002

Co 59 nuclear magnetic resonance (NMR) measurements have been undertaken to determine the local atomic environment of Co in Co/V multilayers, previously studied by magnetometry. These NMR measurements provide confirmation, on a local atomic scale, of the results deduced from the earlier magnetization study. Co/V multilayers show considerable interfacial mixing with a magnetically dead, vanadium rich layer penetrating approximately 2 Å into an adjoining Co layer. The presence of this dead layer has the effect of modifying the hyperfine field experienced by the Co nuclei at a distance of several atomic planes from the interface.
Spin valves with antiparallel-pinned flux compensation layer
Authors: Mao Sining , Chen Jian , Murdock Ed
Published: July 2002

The reduction of the demagnetization field in the spin-valve sensor was realized by introducing an antiparallel-pinned flux compensation layer built in a bottom spin-valve structure of substrate/Ta/NiFe/IrMn/NiMn/NiFe/Co/Cu/Co/NiFe/Ta. Two antiferromagnetic layers, NiMn and IrMn, were used to pin the pinned and flux compensation layers separately. The magnetization direction of the flux compensation layer was set through a magnetic anneal at a temperature between the blocking temperatures of IrMn and NiMn. The bias field and sensitivity were improved with a reduction of the demagnetization field at the free layer. Furthermore, the free layer coercivity was reduced and a better magnetic stability was achieved.
Thickness effect on stress-induced exchange anisotropy of NiFe/NiFeMn
Authors: Lai Chih-Huang , Chen Shing-An , Huang J. C. A.
Published: July 2002

Samples with the structure Mo (20 nm)/NiFe (t nm)/NiFeMn (12 nm)/Mo (2 nm) were grown on the Al2O3 (11–20) substrates by a MBE system. Although no magnetic field was applied during depositions, shifted hysteresis loops were observed in as-deposited samples, which were attributable to the stress-induced exchange anisotropy. With increasing thickness of NiFe, the residual stress on NiFe decreased, which resulted in the decrease of NiFe anisotropy. The exchange field decreased with increasing NiFe thickness but with a transition point at t=12nm, at which the residual stress on top of NiFe might be significantly released.
Site occupancy of Sm in (Nd1−xSmx)5(Fe1−yTiy)17
Authors: Chu Z. , Yelon W. B. , Missell F. P. , Murakami R. K.
Published: July 2002

The ferromagnetic compound Nd5Fe17 has a large average Fe moment (2.1 μB), a reasonably high Curie temperature (503 K), but basal plane spin orientation. Partial replacement of Nd by Sm leads to a uniaxial spin arrangement with substantial anisotropy field. Natural Sm has a large neutron absorption cross section (5650 b) which is usually thought to prevent neutron diffraction measurements unless Sm is replaced by a separated isotope with low absorption. However, the unique geometry of the MURR neutron powder diffractometer allows measurements on thin samples and data have been successfully collected on samples with up to about 50% Sm (Nd2.5Sm2.5Fe17). Samples prepared without Ti contain the 2:17 phase as well as the 5:17 phase, while those prepared with Ti have a very high concentration of the 5:17 phase which forms more readily (with minor amounts of TiFe2). The locations of Sm atoms in these compounds have been determined. These results may provide important information about the crystal fields at different sites in the 5:17 phase and suggest improved routes for synthesis of this potentially useful compound.
Substrate effect on the magnetic behavior of manganite films
Authors: Steren L. B. , Sirena M. , Guimpel J.
Published: July 2002

The film thickness (t) dependence of the magnetic properties of La0.6Sr0.4MnO3 (LSMO) films grown on (001) MgO and (001) SrTiO3 substrates has been studied. Hysteresis loops measured at low temperature show a smooth increase of the retentivity accompanied by a decrease of the coercitive field as the film thickness increases. The increase of coercitivity with decreasing t can be interpreted in terms of a change in the domain structure of the films mainly due to an augmentation of domain pinning defects. The magnetic anisotropy has been measured using ferromagnetic resonance (FMR). A volume (VA) and a surface (SA) anisotropy contribution have been deduced from FMR angular dependence studies for both series of samples. In the LSMO films grown on MgO a VA component that corresponds to an easy-axis perpendicular to the plane of the films has been found while in contrast, the LSMO films grown on SrTiO3 present an easy-plane anisotropy. The SA is positive for both series favoring a perpendicular magnetic anisotropy. The measured magnetic anisotropy has been assigned to substrate-induced effects.
Characterization of a pulsed bifilar helical wiggler
Authors: Meurdesoif Y. , Gardelle J. , Lefevre T. , Rullier J. L. , Donohue J. T.
Published: July 2002

An adiabatic entrance, obtained by placing resistive shunts at half-period intervals between the adjacent clockwise and counterclockwise helical current turns of the wiggler winding, is often used to assure good beam injection into the bifilar helical wiggler of a free electron laser (FEL). If the wiggler is pulsed, the time dependence of the magnetic field in the entrance may differ from that of the uniform section of the wiggler, and the magnetic field as a function of position along the axis may not be gradually increasing, in other words adiabatic. In addition, if a waveguide is used to contain the radiation, as in microwave frequency FELs, the tube itself may partially shield and retard the magnetic field in its interior. We investigate the time dependence of the magnetic field in a pulsed wiggler both experimentally and theoretically. Good agreement between measurements and our model is found. By using shunts of varying resistance, and by choosing carefully the time at which the beam enters the wiggler, we obtain an entrance and an exit which are approximately adiabatic. The best result is achieved when the 60-ns-long electron bunch traverses the wiggler about 100 μs after the pulsed wiggler current has reached its maximum.
Strain in wet thermally oxidized square and circular mesas
Authors: Alonzo A. C. , Cheng X.-C. , McGill T. C.
Published: July 2002

In this paper, we report the observation, through optical microscopy, of drumhead-like patterns in square and circular mesas which have been wet thermally oxidized to completion. Micro-Raman spectroscopy measurements are used to show that these patterns roughly correspond to variations in strain induced in surrounding semiconductor layers by the oxidation process. In addition, the patterns have a specific orientation with respect to the crystallographic axes of the semiconductor. A crystallographic dependence of the oxidation process itself is demonstrated and used to explain the orientation of the drumhead patterns.
Magnetic properties of nanostructured wires deposited on the side edge of patterned thin film
Authors: Matsuyama K. , Komatsu S. , Nozaki Y.
Published: July 2002

In the present study, magnetic nanowires with various cross-sectional dimensions have been fabricated by evaporating a magnetic material on the side edges of the patterned nonmagnetic thin film. The method allows the lengths of the two short axes to be defined precisely by controlling the thickness of the oxide (Wx) and magnetic material (Wy). The MFM images of the produced Co wires (2 μm length) with dimensions of Wx=Wy=200 nm and Wx=Wy=50 nm present the single domain configuration. The MFM and magnetoresistance (MR) measurement demonstrate that the longitudinal magnetization switching field increases with the decrease of Wx and Wy, which becomes 1.3 kOe for wires with Wx=Wy=50 nm. The profile of the MR hysteresis suggests that considerable coherent rotation takes place before the irreversible longitudinal switching. Transverse saturation fields larger than 6 kOe were measured in the orthogonal two short axis directions, which confirms the successful fabrication of three-dimensional wires with comparable cross-sectional dimensions.
The effect of temperature on the magnetization reversal mechanism in sintered PrFeB
Authors: Crew D. C. , Lewis L. H. , Welch D. O. , Pourarian F.
Published: July 2002

To understand the effects of nucleation fields and intergranular dipolar interactions on the magnetization reversal mechanism, recoil curves from the major hysteresis loop have been measured on a sample of sintered PrFeB as a function of temperature from 150 to 300 K. At room temperature the reversible magnetization behavior indicates a reversal mechanism of nucleation of domain walls whose motion after nucleation is resisted by dipolar fields. As the temperature is reduced, the coercivity, and hence the nucleation field, is observed to increase while the dipolar fields, dependent on microstructure and saturation magnetization, remain approximately constant. These temperature-dependent changes in the relative magnitudes of the dipolar field and nucleation field cause the reversible magnetization behavior to change from domain wall motion to rotation. This change in behavior is attributed to the supposition that at temperatures where the nucleation field exceeds the dipolar field, once nucleated, domain walls are swept out of the material.
Model for predicting atomic substitutions in intermetallic compounds
Authors: Girt Er. , Altounian Z.
Published: July 2002

A thermodynamic model was developed for calculating the probabilities of atomic substitutions in different sites in intermetallic compounds. The model considers three contributions: chemical, elastic and structural, in calculating the changes that occur in the enthalpy due to the atomic substitutions at different sites in intermetallic compounds. The model was tested for over forty rare-earth containing compounds such as Nd2(Fe,X)17(C), Nd2(Fe,X)14B, R(Fe,X)12, R(Al,X)12, Nd3(Fe,X)29 and Er(Ni,X)5 where X is the substituent atom. Comparison of the model calculations with results obtained from neutron diffraction show that the model precisely determines the sites preferentially occupied by the X atoms.
Magnetovolume effect in Nd5Fe17
Authors: Sabiryanov R. F. , Jaswal S. S.
Published: July 2002

The effect of volume expansion on the magnetic properties of Nd5Fe17 is explored using first-principle electronic structure calculations. A volume expansion of 6% increases the magnetization by ∼6% and the average total exchange parameter by ∼34%. As a result, the Curie temperature (TC) is expected to increase from 509 to 682 K. Therefore, some nonhybridizing interstitial and substitutional impurities should produce a moderate increase in TC of Nd5Fe17. The possible interstitial sites are discussed.
Strong noncollinearity between nonequivalent Nd magnetic moments in Nd2Fe14B at low temperature
Authors: Bartolomé F. , Tonnerre J. M. , Jaouen N. , Raoux D. , Chaboy J. , Garcı́a L. M. , Maruyama H. , Steinmann R.
Published: July 2002

A temperature-dependent x-ray resonant magnetic scattering study through the spin reorientation transition (SRT) that Nd2Fe14B undergoes below TSRT=135 K is presented. The experimental results evidence a strong noncollinearity between the magnetic moments of Nd atoms in 4f and 4g crystallographic sites in the low-temperature phase.
Theoretical study of hyperfine fields at diluted s–p, noble, and nd impurities in ferromagnetic compounds GdX (X=Zn, Cd)
Authors: de Oliveira A. L. , Tovar Costa M. V. , de Oliveira N. A. , Troper A.
Published: July 2002

The hyperfine fields at nd (n=3,4,5) impurities and at noble impurities diluted in ferromagnetic compounds GdX (X=Zn, Cd) are discussed in the framework of a two center model. In these systems it is observed that all impurities enter substitutionally at the “nonmagnetic” X lattice site, thus creating a strong local charge perturbation. In our model, one calculates the local magnetic moment in the charge perturbed conduction band at the origin. The magnetization of the s–p conduction band arises from the Gd 4f moments. Then one obtains the conduction electron polarization contribution to the hyperfine field. The transition (and noble) impurities also create an Anderson–Moriya d resonance in the strongly perturbed Slater–Koster local density of states at the origin, thus originating an additional local moment and thereby a core polarization contribution to the magnetic hyperfine field. The self-consistently calculated hyperfine fields are in quite good agreement with available experimental data.
Co
59
nuclear magnetic resonance in the metamagnetic system Y1−xGdxCo3
Authors: Reis M. S. , Oliveira I. S. , Garcia F. , Dubenko I. S. , Gaidukova I. Yu. , Takeuchi A. Y. , Guimarães A. P.
Published: July 2002

A detailed nuclear magnetic resonance (NMR) study of some intermetallic compounds of the series Y1−xGdxCo3 is presented. These are results where the NMR lines corresponding to the four magnetic sites of these compounds appear clearly resolved in the NMR spectra. We found, however, that the number of lines and their widths are strongly dependent on the radio frequency (rf) power level, which may help to explain some of the discrepancies found in NMR literature on these compounds. From the dependence of the NMR spectra with rf power we concluded that the site labeled 18h presents the largest local magnetic anisotropy. No significant changes are observed in the value of the hyperfine fields at any site as a function of the Gd concentration, x.
Electron density fluctuations at interfaces in Nb/Si bilayer, trilayer, and multilayer films: An x-ray reflectivity study
Authors: Suresh N. , Phase D. M. , Gupta Ajay , Chaudhari S. M.
Published: July 2002

A grazing incidence x-ray reflectivity technique has been used to determine electron density profile (EDP) as a function of depth in Nb-on-Si and Si-on-Nb bilayer, Nb–Si–Nb and Si–Nb–Si trilayer, and Nb/Si multilayer structures. In each case, films having layer thicknesses of 35 Å were deposited on float glass and Si(100) substrates under ultrahigh vacuum conditions using an electron beam evaporation technique. EDP determined in as-deposited bilayer films shows that the widths of Si-on-Nb and Nb-on-Si interfaces are 20 and 40 Å, respectively. The large difference observed in the widths is attributed to the different growth morphology of 35 Å Nb and 35 Å Si single layer films as revealed by atomic force microscopy investigations. In situ dc resistance measurements carried out on 35 Å single layer Nb films during growth show percolation at a thickness much less than the layer thickness. In case of as-deposited Nb–Si–Nb trilayer film, EDP shows a width of 21 Å at both the interfaces viz. Si-on-Nb and Nb-on-Si whereas in the case of as-deposited Si–Nb–Si trilayer films, the widths of Si-on-Nb and Nb-on-Si interfaces are 21 and 42 Å, respectively. The EDPs obtained from bilayer and trilayer films are used to determine layer-by-layer electron density variation in Nb/Si multilayer structures. The results corresponding to the as-deposited multilayer structure indicate that interdiffusion is larger in the bottom layers of the stack. To study the role of kinetic and thermodynamic factors in the interfacial reactions, the bilayer, trilayer, and multilayer samples were isochronally annealed in vacuum up to a temperature of 300 °C in steps of 50 °C for 1 h. EDP of annealed bilayer and trilayer films show an increase in interfacial width due to interdiffusion of Nb and Si and samples annealed at 250 and 300 °C show Nb-rich and Si-rich intermixed regions. In addition to this, plateau regions having an electron density of 1.8 e/Å3 are observed in the EDP of Nb–Si–Nb and Si–Nb–Si trilayer structures annealed at 300 °C which indicates the formation of a Nb3Si phase. Structural parameters obtained from EDP are extended to interpret the results in as-deposited and annealed multilayer structures. The observed contraction in a bilayer period of an annealed multilayer structure is interpreted in terms of formation of a dense Nb3Si phase confirmed by wide angle x-ray diffraction measurements. Consequently, the multilayer structure is fully destroyed between 250–300 °C.
Comment on “Analysis of high-resolution x-ray diffraction in semiconductor strained layers” [J. Appl. Phys. 86, 782 (1999)]
Authors: Fatemi M.
Published: July 2002

The multilinear regression analysis proposed for optimizing the measurements and minimization of errors in the x-ray peak separation method is examined. It is shown that the interpretation of the residuals as the errors of the physical variables leads to paradoxical conclusions, and prevents the definition of a unique numerical value for the probable error. It is also shown that if the method is to yield a permissible set of lattice parameters, the residuals of the best fit must fall within the range of experimental uncertainties estimated in advance. Thus, the residuals are only useful as a measure of the internal consistency among the data, but they cannot be used to quantify or minimize the errors within that set.
Reply to “Comment on ‘Dominant diffusing species during cobalt silicide formation’ ” [J. Appl. Phys. 87, 8216 (2000)]
Authors: Comrie C. M. , Newman R. T.
Published: July 2002

Ideally, when a marker is used to determine the dominant diffusing species during phase formation, the marker should be chemically inert with respect to its surroundings, should not interfere significantly with the overall development of the reaction, and should not selectively couple to the diffusing motion of either element involved in the reaction. Finding a single marker that satisfies all these requirements is unfortunately extremely difficult and, in general, compromises have to be made. d’Heurle and Zang point out certain deficiencies tantalum has when used as a marker during CoSi2 formation. We acknowledge these deficiencies, but contend that the additional experiments carried out using tantalum markers in different systems (Ta marker in NiSi2) and different markers for the same system (Xe marker for CoSi2) suggest that these deficiencies are unlikely to make results of the original investigation completely invalid.
Energy transfer in condensed media. I. Two-level systems
Authors: West Bruce J. , Lindenberg Katja
Published: July 2002

A new method for constructing the dynamical description of energy transfer in condensed media is applied to a two-level system. The method yields a quantum Langevin equation that is thermodynamically consistent and therefore provides temperature dependences of physical observables. We calculate spectral and transport properties for the two-level system weakly coupled to the surrounding medium and discuss their temperature dependences.
Molecular structures and energetics for the lowest triplet states of glyoxal
Authors: Gaw Jeffrey F. , Schaefer Henry F.
Published: July 2002

The equilibrium geometries of the lowest three triplet states of trans glyoxal (HCOHCO) have been predicted at the self-consistent-field (SCF) level of theory using a double zeta plus polarization (DZ+P) basis set, designated C,O(9s5p1d/4s2p1d), H(4s1p/2s1p). Two of the molecular structures thus predicted differ radically from the known 1Ag ground state equilibrium geometry. The predicted relative energies of the three triplet states are notably altered when the effects of electron correlation are treated theoretically. Using configuration interaction (CI) including single and double excitations, the predicted adiabatic excitation energies are 23 000 (ã Au3 n→π*), 31 000 (3Bg n→π*), and 31 000 cm−1 (3Bu π→π*), when corrected for unlinked cluster effects.
The equilibrium properties of charged hard spheres with adhesive interactions between oppositely charged ions
Authors: Rasaiah Jayendran C. , Lee Song Hi
Published: July 2002

The equilibrium properties of charged hard spheres with adhesive interactions between oppositely charged ions are studied in the hypernetted chain/mean spherical (HNC/MS) approximation and in the Percus–Yevick/Mean spherical (PY/MS) approximation which are solved analytically. Numerical solutions to the hypernetted chain (HNC) approximation for this model are also compared with the HNC/MS approximation for a model 2–2 electrolyte in the preparative concentration range. The effect of adhesion on the low density phase transition of the primitive model electrolyte is found to be slight in contrast to the effect of charge on the phase separations at high densities of a two component mixture of hard spheres in which there is adhesion only between molecules of different species.
The photodissociation spectrum of SO+2
Authors: Thomas Timothy F. , Dale Fred , Paulson John F.
Published: July 2002

The photodissociation spectrum of SO+2 corresponding to the process SO+2 +hν→SO++O has been measured on a triple quadrupole system for the wavelength ranges: 3000–3400 and 4400–5120 Å. The spectrum in the visible has been assigned to the C̃ 2B1←Ã 2A2 transition and vibrational structure analyzed to yield λ00=4187 Å, the harmonic vibrational frequencies ν̃′1=953 cm−1, ν̃′′2=499 cm−1, ν̃′1=767 cm−1, and ν̃2 =410 cm−1, and the anharmonicity constants X″11 =−6.3 cm−1, X′′12 =−6.1 cm−1, X″22 =−4.2 cm−1, X12 =−6.3 cm−1, and X′22 =−7.4 cm−1. Apparent photodissociation cross sections ranged from ∼1×10−20–1.6×10−19 cm2 in the visible spectrum. In the UV spectrum the highly congested vibrational structure could not be resolved sufficiently for analysis; photodissociation cross sections ranged from ∼2–4×10−19 cm2 with broad bands roughly corresponding to expected progression in ν1 and ν′2 within the C̃ 2B1←X̃ 2A1 electronic transition. The process SO+2 +hν→S++O2 showed an onset near 3108 Å and the corresponding photodissociation spectrum showed sufficient vibrational structure to yield ν̃′′2∼454 cm−1, ν̃′1 ∼955 cm−1, and ν̃2 ∼411 cm−1. This new process, which had σ≤3×10−20 cm2, was proposed to result from the D̃ 2B2←X̃ 2A1 transition. Several new photodissociation cross section measurements on N2O+ have also been made in the vicinities of 3381 and 4880 Å, taking advantage of the high sensitivity (→10−21 cm2) of the triple quadrupole system.
Precise measurement of the J=2←1 fine structure interval in N(II) by far-infrared laser magnetic resonance
Authors: Cooksy A. L. , Hovde D. C. , Saykally R. J.
Published: July 2002

Far-infrared laser magnetic resonance spectroscopy has been used to measure the J=2←1 fine structure intervals in the 3P ground states of singly ionized 14N and 15N atoms. In 14N(II) this separation is 2459.3703(14) GHz, and in 15N(II) it is 2459.3816(19) GHz. The hyperfine constants and gJ factors have been evaluated for both isotopes. Zero field energies for the hyperfine components of the J=2←1 transition in both isotopes are given in an effort to facilitate their observation in interstellar sources. A complete description of the hyperfine and Zeeman Hamiltonian matrix elements for atomic fine structure transitions is given in an LS coupled basis set.