bluuebunny/crossref_metadata_2025 huggingface dataset:
Multicomponent proton spin–spin relaxation of fibrin gels with magnetically oriented and randomly oriented fibrin fiber structures
Authors: Takeuchi Michihiro , Sekino Masaki , Yamaguchi Kikuo , Iriguchi Norio , Ueno Shoogo
Published: May 2003

We investigated the effect of structural differences in fibrin fibers on the T2 relaxation time. Fibrin fibers have the characteristic of orienting parallel to high magnetic fields during polymerization. Two fibrin gels were polymerized from a fibrinogen solution with and without a 7.05 T magnetic field. Water molecules in the fibrin gel that were polymerized in the high magnetic field exhibited only one relaxation time T2=0.35 s, whereas, water molecules in the fibrin gel that were not exposed to a magnetic field during polymerization had at least two exponential components in the T2 relaxation. The long component, T2=0.35 s, was the same order as the T2 of the fibrinogen solution (=0.41 s) and the fibrin gel polymerized in the high magnetic field. The short component was T2=0.07 s. This difference is attributed to a change in the magnetic dipole–dipole interactions between water molecules and fibrin fibers.
Partial thermoremanent magnetization: Louis Néel’s legacy in rock magnetism (invited)
Authors: Dunlop David J.
Published: May 2003

Louis Neel’s theories of thermoremanent magnetization (TRM) underlie all of rock magnetism. Neel’s relaxation time equation for thermal activation of single-domain (SD) moments has been verified over geological time and temperature scales by laboratory thermal demagnetization of TRM overprints acquired in nature. For multidomain (MD) grains, disagreement with Neel’s predictions is explained by re-equilibration of domain walls by the changing internal demagnetizing field during heating. Much effort has been devoted to testing the laws of additivity, reciprocity, and independence of partial TRMs, which partition the blocking temperature range and appear in nature as successive overprints of the original TRM. For SD grains, the laws are explained by Neel’s theories and are verified experimentally. For MD grains, additivity holds but partial TRMs do not demagnetize over exactly the original blocking temperature interval (nonreciprocity) and are not entirely independent of one another when acquired in different directions. The current frontier in rock magnetism is to overcome this nonideal partial TRM behavior in order to extract precise and trustworthy records of ancient Earth’s magnetic field directions and intensities.
Current distribution image of the rat brain using diffusion weighted magnetic resonance imaging
Authors: Yamaguchi K. , Sekino M. , Ueno S. , Iriguchi N.
Published: May 2003

In this article, we report that the apparent diffusion coefficient (ADC) of rat brain tissue increased by applied external electrical currents. A subtraction magnetic resonance imaging (MRI) map of ADCs with and without applied currents was obtained to quantitatively evaluate the effect of the electrical currents on ADC. The ADC in tissue was directly estimated by the mean diffusivity (MD), or the sum of the diagonal elements of the diffusion tensor Trace(D)/2. Anisotropic diffusion was estimated by fractional anisotropy FA(D). The experimental results show that the MD with applied currents of 4, 6, 8, and 10 mA increased by 6%, 8%, 16%, and 40%, respectively. The mechanism is partially explained by the movement of ions through extracellular space in tissue.
Exchange bias in the Fe/KCoF3 system: A comprehensive magnetometry study
Authors: Malkinski L. , O’Keevan T. , Camley R. E. , Celinski Z. , Wee L. , Stamps R. L. , Skrzypek D.
Published: May 2003

Exchange bias was studied in the Fe/KCoF3 ferromagnet/antiferromagnet system. KCoF3 can be deposited onto single crystal of Fe, either in the polycrystalline or single crystal form, depending on growth conditions. The samples were grown by molecular beam epitaxy on Ga-terminated GaAs (100) wafers. We study effects of the crystal state of the fluoride, thickness of the Fe film, crystallographic orientation of the Fe, and temperature on exchange bias. The structures with single crystal KCoF3 show that the exchange bias is well correlated with the coercivity at low temperatures and vanishes at a temperature close to the Néel temperature. Both the magnitude of the exchange bias and the blocking temperature of the samples with the polycrystalline fluoride were significantly reduced compared to the single crystal structures. As the Fe film thickness was increased, the exchange bias decreased for all samples. In contrast, the blocking temperature remained unchanged for the samples with the single-crystal fluoride. The exchange bias measured along the easy anisotropy axis of the Fe was slightly larger than that measured along the hard axis. In addition, all samples exhibited a weak training effect.
Anomaly of local structure of La0.7Ca0.3−xBaxMnO3 manganites at Curie temperature
Authors: Ulyanov A. N. , Yang Dong-Seok , Yu Seong-Cho
Published: May 2003

The local structure of La0.7Ca0.3−xBaxMnO3 (x=0; 0.03; 0.06;…; and 0.3) lanthanum manganites were studied by extended x-ray absorption fine structure analysis. Dispersion, σMn–O2, and asymmetry, σMn–O3, of the pair distribution function for the Mn–O bond distances of MnO6 octahedron showed a maximum on x dependence. The maximum of σMn–O2 is caused by an increase of dynamic displacements of the Mn–O bond distances near the Curie temperature, TC. The observed x dependence of σMn–O3 is caused by a reduction in mobility of the charge carriers approaching TC from low as well as high temperatures.
Resonant tunneling in magnetoresistive Ni/NiO/Co nanowire junctions
Authors: Sokolov A. , Sabirianov I. F. , Tsymbal E. Y. , Doudin B. , Li X. Z. , Redepenning J.
Published: May 2003

Magnetotransport studies performed on electrodeposited Ni/NiO/Co nanojunctions show a broad distribution of magnetoresistance values spanning from +40% to −25%, with an average of about 2%, corresponding to observations on large-area junctions. The dispersion in the results can be understood in terms of tunneling via localized states in the barrier. Calculations based on Landauer–Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of the inversion of tunnel magnetoresistance sign due to resonant tunneling.
Effects of carbon on magnetic properties and magnetic entropy change of the LaFe11.5Si1.5 compound
Authors: Chen Yuan-fu , Wang Fang , Shen Bao-gen , Sun Ji-rong , Wang Guang-jun , Hu Feng-xia , Cheng Zhao-hua , Zhu Tao
Published: May 2003

Effects of the interstitial carbon atoms on the magnetic properties, especially on the magnetic entropy change, of the LaFe11.5Si1.5 compound, have been studied. X-ray diffraction patterns reveal a monotonous increase of the lattice constant with the concentration of carbon, while the cubic NaZn13-type structure remains unchanged. The Curie temperatures TC of LaFe11.5Si1.5Cy are ∼195, 225, and 241 K for y=0, 0.2, and 0.5, respectively, increasing with the increase of carbon concentration. The maximal magnetic entropy changes |ΔS| of LaFe11.5Si1.5Cy at the respective TC under a magnetic field change of 0–5 T are ∼24.6, ∼22.8, and ∼12.7 J/kg K for y=0, 0.2, and 0.5, respectively, notably exceeding that of Gd (|ΔS| ∼9.8 J/kg K at TC=293 K). The |ΔS| of LaFe11.5Si1.5C0.2 is nearly as giant as that of the parent alloy LaFe11.5Si1.5 due to the first-order field-induced itinerant-electron metamagnetic transition that occurs in both compounds clearly observed for the LaFe11.5Si1.5C0.5 compound. With the increase of carbon concentration, the nature of magnetic transition has been changed from first order to second order, which results in the significant decrease of the magnetic entropy change. The large |ΔS|, convenient adjustment of TC and relatively low cost make the LaFe11.5Si1.5Cy interstitial compounds promising candidates for magnetic refrigerants in the corresponding temperature range.
Ion-beam deposited low resistance magnetic tunnel junctions prepared by a two-step oxidation process
Authors: Zhang Z. G. , Zhang Z. Z. , Freitas P. P.
Published: May 2003

Spin tunnel junctions with ultrathin (<1 nm) AlOx tunnel barriers were fabricated by ion-beam deposition. The tunnel barrier was formed by natural oxidation of an ultrathin Al layer (4–8.5 Å thick) by either a single-step or a two-step oxidation process. The magnetic and transport properties of these tunnel junctions indicate the barrier to be pinhole free for tAl⩾6.5 Å. The minimum Al thickness at which pinholes form depends on ion acceleration voltage used for Al deposition. Single-step oxidation of an 8 Å Al layer leads to a magnetic tunnel junction with a 25% tunnel magnetoresistance (TMR) and R×A of 14 Ω μm2. The two-step oxidation procedure was used for thinner Al layers. TMR ranges from 18%–23% at 8–10 Ω μm2 resistance values, for a total Al thickness of 6.5 Å. Junction resistance has been further decreased down to 4.35 Ω μm2 with a TMR of 10.6% by two-step oxidizing a 6 Å Al layer.
Investigation of magnetic and magnetomechanical hysteresis properties of Fe–Si alloys with classical and mechanical Barkhausen effects and magnetoacoustic emission
Authors: Augustyniak B. , Piotrowski L. , Radczuk M. , Chmielewski M. , Hauser H.
Published: May 2003

Grain oriented Fe 3.5% Si sheet samples with a Goss (GO) microstructure and Fe 3.5% samples with nonoriented (NO) grains were tested using two Barkhausen effects, the classical Barkhausen effect (HBE) and the mechanical Barkhausen effect (MBE), as well as the magnetoacoustic emission (MAE). The aim of the work was to present further evidence that the B(H) hysteresis with effects like HBE and MAE, and magnetomechanical hysteresis with MBE are correlated via internal stress barriers pinning domain walls (DWs). In the case of a GO alloy, the long axis of the sample was parallel to the [100], [110], and [111] directions with respect to the rolling direction. The HBE and MAE were measured using a C-core electromagnet supplied with a triangular wave form of current intensity. The MBE intensity was recorded during a monotonous increase of shear stress using a torque machine. The maxima of MBE intensity for the “first load” mode for a NO sample and for three GO samples indicate an internal stress distribution pinning 90° DWs. The MAE plots reveal at least two maxima which are well correlated with H strength values where creation and annihilation of magnetic domains appears. Since the MBE and MAE are associated with abrupt jumps of 90° DW, the existence of MBE and MAE reinforces the fact that such DWs are present in the tested samples. These walls belong mainly to the secondary closure domains at GO alloys and to closure domains at NO alloy.
Observation of inverse magnetoresistance in epitaxial magnetite/manganite junctions
Authors: Hu Guohan , Chopdekar Rajesh , Suzuki Y.
Published: May 2003

We have fabricated and characterized epitaxial Fe3O4/CoCr2O4/La0.7Sr0.3MnO3 magnetic trilayer junctions (MTJs) grown on (110) and (100) SrTiO3 substrates. Large inverse junction magnetoresistance (JMR) as high as −25% has been observed at a field of 4 kOe in (110) oriented MTJs. The improvement of the JMR over that observed in previous epitaxial magnetite junctions is attributed to the choice of the spinel structure CoCr2O4 barrier, which minimizes structural disorder at the barrier/Fe3O4 interface. As a comparison, studies on (100) MTJs elucidate the effect of the magnetic domain state of the ferromagnetic electrodes on the JMR.
Structure and magnetic properties of sputtered hard/soft multilayer magnets
Authors: Liu W. , Zhang Z. D. , Liu J. P. , Cui B. Z. , Sun X. K. , Zhou J. , Sellmyer D. J.
Published: May 2003

The films with HM=(Pr,Dy)(Fe,Co,Nb,B)5.5 and SM=Fe, FeCo were prepared by sputtering and subsequent heat treatment. The coercivity of Ti-buffered (Pr,Dy)(Fe,Co,Nb,B)5.5 single-layer film with 320 nm thickness is as large as 18.8 kOe at room temperature. X-ray diffraction results reveal that the Pr2Fe14B-type phase is randomly oriented in almost all the multilayer films. For the multilayers of Ti(30 nm)/[HM(16 nm)Fe(x nm)]×20/Ti(30 nm)/Si(substrate), the remanence increases and the coercivity decreases with the addition of Fe content, in comparison with the results of the single-layer film and the maximum energy product of 14.8 MGOe is obtained at x=3.0. A noticeable shoulder on the demagnetization curve is observed at low temperatures. When Fe65Co35 is used as the SM component rather than Fe, similar results are found. The enhancement of the magnetic properties in the nanocomposite multilayer films is explained by means of the exchange coupling between the SM and/or HM nanograins of the intra- and interlayers.
Spin structure at nanojunctions and constrictions
Authors: Skomski R. , Sellmyer D. J.
Published: May 2003

A micromagnetic Green-function approach is used to investigate the effect of nanojunctions, constraints, and other obstacles on spin-dependent conduction. Depending on geometry, the determination of the spin structure involves several types of Bessel functions. A common feature of the Green functions is the involvement of the domain-wall width of the main phase, which can be interpreted as the decay length of the magnetization perturbation away from the junction. This length is typically on the order of 10 nm and independent of the strength of the perturbation. Only the magnitude of the magnetization perturbation depends on the strength of the inhomogenity. A particular feature of the considered structures is that the total spin-dependent scattering cross section, as estimated from the squared magnetization gradient, exhibits a characteristic real-structure dependent maximum as a function of the boundary phase or junction dimensions.
Magnetoresistance and magnetic force microscopy studies in Ni80Fe20 disk- and ring-patterned wires
Authors: Tsai J. L. , Yao Y. D. , Han B. S. , Lee S. F. , Yu C. , Chen T. Y. , Huang E. W. , Zheng D. J.
Published: May 2003

We have investigated the magnetization reversal process of the disk-, ring-, and center dot ring-patterned Ni80Fe20 wires. For the fields applied perpendicular to the wire direction, interesting shape dependent magnetoresistance (MR) ratios were found. The MR ratios were varied from 0.8%, 0.65%, and 0.4% at room temperature and 1.7%, 1.5%, and 1.1% at 10 K for the disk-, ring-, and center dot ring-patterned wires. For the same wires, the switching field is reduced from −170, −110, and −90 Oe at room temperature to −140, −70, and −20 Oe at 10 K. These results were due to the shape anisotropy and domain-wall motion. The anisotropy MR (AMR) ratios measured at 10 K of the disk-, ring-, and center dot ring-patterned wires were 1.9±0.1%, 1.7±0.1%, and 1.3±0.1%, respectively, it is almost even the same (1.1±0.1%) at room temperature. We have observed that the center dot reduces the MR ratio and increases magnetic saturation field of the nanosize Ni80Fe20 wires.
Model of ground state in electron-doped Ca1−xSmxMnO3 (0<x⩽0.20) manganites and ferromagnetic resonance probing of “spontaneous ferromagnetism” in Ca0.8Sm0.2MnO3
Authors: Auslender M. , Shames A. I. , Rozenberg E. , Gorodetsky G. , Martin C. , Maignan A.
Published: May 2003

The model of magnetoimpurity states in an antiferromagnet (AF) by De Gennes is suggested to explain magnetic properties and mixed ground state in the electron-doped manganites Ca1−xSmxMnO3 (0<x⩽0.2). The model predicts that an AF phase of Ca1−xSmxMnO3 is a nonhomogeneous one with strong spatial fluctuations of the magnetic order parameters at a given temperature. The experimental electron paramagnetic and ferromagnetic resonance study performed for the x=0.2 compound reasonably accords with this model. In particular, two new temperature scales revealed in the experiment are naturally explained.
Neural network-based inversion algorithms in magnetic flux leakage nondestructive evaluation
Authors: Ramuhalli Pradeep , Udpa Lalita , Udpa Satish S.
Published: May 2003

Magnetic flux leakage (MFL) methods are commonly used in the nondestructive evaluation (NDE) of ferromagnetic materials. An important problem in MFL NDE is the determination of flaw parameters such as the flaw length, depth, and shape (profile) from the measured values of the flux density B. Commonly used methods use a forward model in a loop to determine B for a given set of flaw parameters. This approach iteratively adjusts the flaw parameters to minimize the error between the measured and predicted values of B. This article proposes the use of neural networks as forward models. The proposed approach uses two neural networks in feedback configuration—a forward network and an inverse network. The second network is used to predict the profile given the measured value of B, and acts to constrain the solution space. Results of applying these methods to MFL data obtained from a two-dimensional finite-element model, with rectangular flaws of various dimensions, are presented.
Magnetic domain structure and lattice distortions in manganite films under tensile strain
Authors: Soh Yeong-Ah , Aeppli G. , Kim C.-Y. , Mathur N. D. , Blamire M. G.
Published: May 2003

We performed detailed studies of the magnetic domain structure and strain effects in epitaxial La1−xSrxMnO3(001) films grown on SrTiO3(001) bicrystal substrates by combining magnetic force microscopy, x-ray diffraction, and classical magnetometry. We show that, in addition to magnetic domain walls which nucleate at grain boundaries, 180° magnetic domain walls not associated with structural defects form along the 〈100〉 direction. The size of the magnetic domains are of the order of tens of microns with the magnetic easy axes along the 〈100〉 direction in the plane of the film. Spin reorientation occurs at the grain boundaries, which we attribute to the different strain state compared to the grain interior.
Understanding of amplitude symmetry and its variation of synthetic spin valve heads for high density recording
Authors: Han Dehua , Stokes Scott , Liu Dacheng , Liu Yanzhang , Jia Lixin , Ding Juren , Wang Hong
Published: May 2003

In synthetic antiferromagnetic spin valve (SAF–SV) recording heads, as SV sensor dimensions approach the nanometer scale and individual layer thickness shrinks to only a few angstroms, it becomes more challenging to achieve a unity amplitude symmetry (LFA–SYM) and a small variation of LFA–SYM. A better understanding of LFA–SYM, good control of its variation, and an effective measurement of SAF–SV canting angles has become more important. In this study, high field transfer curve (HF–Xfer) was measured to determine head magnetic polarity, bias point, and output linearity. Rotational field transfer curve (RF–Xfer) was measured to determine the canting angles of reference layer and pinned layer. Free layer canting angle, its dependence on magnetic field, and the angle between the reference layer and free layer were consequently determined based on HF–Xfer and RF–Xfer data. A good linear correlation between LFA–SYM and free layer canting angle was observed, indicating that the large variation of LFA–SYM was mainly due to a wide range of free layer canting.
Thiophene thiol on the Au(111) surface: Size-dependent adsorption study
Authors: Majumder Chiranjib , Mizuseki Hiroshi , Kawazoe Yoshiyuki
Published: May 2003

The adsorption of the thiophene-2-thiolate and thiophen-2-yl-methanethiolate radicals has been investigated on the Au(111) surface using density functional theory under the framework of the generalized gradient approximation for the exchange-correlation functionals. In order to underscore the quantum size effects on the adsorption geometry, the Au(111) surface was modeled using a finite-sized cluster (Au3 and Au24) truncated from the surface as well as a periodic slab consisting of 100 atoms. The results reveal that the preferential adsorption site differs for the cluster models and slab approaches. The directional nature of the Au–S bond and the influence of the back bond of the terminal sulfur atom are found to play key roles in the adsorption geometry. The adsorption energies suggest that the binding energies for the cluster models are stronger than the slab. Inclusion of an alkyl group in between the thiophene ring and the thiol group enhances the interaction energies of the gold–sulfur bonds.
Influence of domain wall structure on pinning characteristics with self-induced anisotropy
Authors: Asada H. , Wasada Y. , Yamasaki J. , Takezawa M. , Koyanagi T.
Published: May 2003

Wall pinning effects with self-induced spatially varying uniaxial anisotropy in various thick films have been studied using micromagnetic simulation based on the Landau–Lifshitz–Gilbert equation. In the simulation, the discretization region is in the cross section normal to the film plane. It is clarified that the wall structure is strongly related to pinning characteristics. Depinning fields of the wall having a flux-closure asymmetric vortex (C-shaped wall) are different in the wall movement directions due to the asymmetric wall structure. On the other hand, depinning fields of the wall with two vortices (S-shaped wall) which have a symmetric structure do not depend on the wall movement direction. Depinning fields for the S-shaped wall are different from both depinning fields for the C-shaped wall.
Design of multisurface single pole head for high-density recording
Authors: Takahashi S. , Yamakawa K. , Ouchi K.
Published: May 2003

Design of multisurface single pole heads was studied for obtaining a proper recording field profile to meet medium magnetic properties. By locating the bump core at the trailing edge of the base core, field gradient could be much improved compared with the bump core located at the center of the base core. Fields from both the bump and base cores could be individually adjusted by changing their dimensions. A large bump height with a large magnetomotive force could provide both the highest field. The multisurface single pole head which could be adapted to a wide range of medium magnetic properties, such as, a saturation field of 12 kOe and a negative nucleation field of 7 kOe for 200 Gb/in.2 recording. The bump height of 100 nm can provide the maximum field larger than 12 kOe along with the base core field less than 7 kOe and the field gradient larger than 180 Oe/nm.
High rate deposition of diamond like carbon films by very high frequency plasma enhanced chemical vapor deposition at 100 MHz
Authors: Kumar Sushil , Dixit P. N. , Sarangi D. , Bhattacharyya R.
Published: May 2003

Diamond like carbon (DLC) films were grown using 13.56 and 100 MHz plasma as excitation frequencies in the same plasma enhanced chemical vapor deposition (PECVD) system. Deposition rate, stress, hardness, optical band gap, refractive index, Urbach energy, electrical conductivity, and hydrogen content of these films have been measured. It was found that just by changing the excitation frequency from 13.56 to 100 MHz, deposition rates of DLC films were enhanced about five times. Thus, very high frequency (100 MHz) PECVD process, with imposed dc bias, is capable of producing reasonably hard DLC films at high growth rates.
Second-order Møller–Plesset calculations with dual basis sets
Authors: Wolinski Krzysztof , Pulay Peter
Published: May 2003

Following the pioneering work of Jurgens-Lutovsky and Almlöf [Chem. Phys. Lett. 178, 451 (1991)], a second-order Møller–Plesset program was developed which allows the use of a large basis set for the pair correlation functions and a more modest one for the self-consistent field (SCF) orbitals. For several test systems, correlation energies closely approximate the results of a large basis set calculation, at substantial savings. The SCF energy of the large basis set calculation can also be estimated using perturbation theory.
Mixing of interface dipole and band bending at organic/metal interfaces in the case of exponentially distributed transport states
Authors: Paasch G. , Peisert H. , Knupfer M. , Fink J. , Scheinert S.
Published: May 2003

The interface dipole for organic adlayers on metal substrates, as determined by photoemission spectroscopy, is often almost as large (>80%) as the built-in potential determined from the ionization potential and the transport gap. Based on our experimental data and the formal description of the band bending in the thin layer, it is shown that the generally accepted view on the interface of thin organic adlayers with a metal substrate must be refined. First, besides band bending one has in the layer also floating of the potential expressed by the finite value of the potential at the outer surface of the layer. Second, for the usually observed large interface dipole, band bending is negligible as long as the electronic states are well defined in energy. It is demonstrated that an exponential distribution of the transport states, with a width of the distribution that is large compared to the thermal energy, leads to a drastic modification of this picture. For CuPc and two fluorinated CuPc’s a band bending of the magnitude of the measured interface dipole is caused within the first 2 nm of the organic adlayer by a width of the distribution of εa≈300 meV. Even for a much narrower distribution (εa=100 meV) a considerable part of the interface dipole arises from the band bending for cases with a large built-in potential. Consequently, one has to expect that the measured interface dipole within a layer of about 2 nm from the interface has a considerable contribution from the normal band bending mechanism in a system with exponentially distributed tails of the transport states. Beyond this layer of some atomic distances the band bending will be small.
Fabrication of two-dimensional electron systems by focused ion beam doping of III/V semiconductor heterostructures
Authors: Meier Cedrik , Reuter Dirk , Riedesel Christof , Wieck Andreas D.
Published: May 2003

Two-dimensional electron systems have been fabricated by focused ion beam implantation of Si dopant ions in undoped III/V heterostructures grown by molecular beam epitaxy. With this method, lateral patterning of two-dimensional electron gases is possible while the planarity of the sample surface is conserved. In this paper, we present a systematic study of this technique and discuss its potential for applications. In detail, different base material systems are experimentally investigated and compared. The electronic properties of the samples are characterized by low-field Hall measurements, capacitance–voltage spectroscopy, and measurements of the longitudinal magnetoresistance at low temperatures. The dependence of the electronic properties on the implantation parameters is discussed.
Elastic scattering in the iodine–carbon system near the Coulomb barrier
Authors: Pusa P. , Rauhala E. , Alanko T. , Räisn̈en J.
Published: May 2003

Elastic scattering cross sections for the I127+C system at non-Rutherford scattering energies have been investigated. Recoil elastic scattering for the reaction C(127I,C)127I was measured at I127 beam energies of 470, 500, and 530 MeV in the laboratory frame of reference. Angular distributions of recoiling carbon were determined at laboratory scattering angles covering a region from 20° to 75°. The cross sections are presented for the recoil C(127I,C)127I and I127(12C, 12C)127I scattering geometries and were modeled by using the optical model (OM) theory. The OM enables interpolation between data points in the energy-angular plane. Non-Rutherford scattering cross section angular and energy limits are examined for practical elastic recoil detection analysis and Rutherford backscattering.
Electronic noise due to multiple trap levels in homogeneous solids and in space-charge layers
Authors: Van Vliet Carolyne M.
Published: May 2003

A near-exact expression is derived for carrier-density fluctuations associated with multiple trap levels, interacting with one band only (say, the conduction band), using the many-variate Master Equation. The canonical constraint is handled with the Darwin–Fowler method. For a homogeneous solid with a discrete number of traps the spectrum consists of a sum of Lorentzians, as expected. For the case of a continuously distributed energy range, the results do not support a Bernamont–Surdin–McWhorter 1/f-like envelope spectrum; on the contrary, no more than two decades of 1/f noise can be expected. The situation is different, however, when band-bending occurs. Employing a Green’s function approach, developed by us previously, we give a formal complete result, which can be evaluated when Ec(r) is known.
Amorphous-crystalline transition at the Ir/Si(100) interface
Authors: Ouyang C.-P. , Chang J.-J. , Wen J.-F. , Tien L.-C. , Hwang J. , Pi Tun-Wen
Published: May 2003

The amorphous-crystalline transition at the Ir/Si(100) interface has been characterized by using both low-energy electron diffraction (LEED) and synchrotron-based photoemission. Solid-state amorphization occurred at the Ir/Si(100)-2×1 interface deposited at 600 °C. The double domain Si(100)-2×1 LEED pattern disappeared when 1 ML Ir was deposited onto Si(100). Three types of Ir–Si bonding formed on Si(100) at 1 ML Ir coverage and gradually evolved to be amorphous IrSi, Ir3Si5, and IrxSiy (unidentified) bonding environments at Ir coverage less than ∼3 ML. The amorphous Ir–Si reacted layer was grown layer–by–layer-like. An Ir3Si5 crystalline phase, accompanying with amorphous IrSi and IrxSiy alloys, started to form on top of the amorphous Ir–Si reacted layer at Ir coverage near ∼3 ML. The Ir3Si5 crystalline phase was evolved from its corresponding Ir3Si5 amorphous bonding environment in the Ir–Si reacted layer.
Demonstration of a reflective coupling diode in a coupled waveguide structure
Authors: Gilbert M. J. , Akis R. , Ferry D. K.
Published: May 2003

Despite the difficulty in fabrication, resonant tunneling diodes (RTD) have found a great deal of usage in the analog, digital, and mixed signal realms as a means of increasing the speed of signal processing circuitry or in reducing the static power dissipation in the circuitry. Nevertheless, RTDs suffer from their nonplanar structure. In this paper, we present a planar diode which operates via coupling of injected electron modes or a reflective coupling diode from an input waveguide to a corresponding output waveguide in a semiconductor hetrostructure. We demonstrate that the I–V characteristics of this structure exhibit the characteristic negative differential conductance of RTD current–voltage characteristics. The resultant behavior of this planar device shows great promise for eventual implementation in ultrasmall high-speed circuitry.
Nonlithographic epitaxial SnxGe1−x dense nanowire arrays grown on Ge(001)
Authors: Ragan Regina , Ahn Channing C. , Atwater Harry A.
Published: May 2003

We have grown 1-μm-thick SnxGe1−x/Ge(001) epitaxial films with 0<x<0.085 by molecular-beam epitaxy. These films evolve during growth into a dense array of SnxGe1−x nanowires oriented along [001], as confirmed by composition contrast observed in scanning transmission electron microscopy in planar view. The Sn-rich regions in these films dominate optical absorption at low energy; phase-separated SnxGe1−x alloys have a lower-energy band gap than homogeneous alloys with the same average Sn composition.
Interfacial properties of ZrO2 on silicon
Authors: Lin Y.-S. , Puthenkovilakam R. , Chang J. P. , Bouldin C. , Levin I. , Nguyen N. V. , Ehrstein J. , Sun Y. , Pianetta P. , Conard T. , Vandervorst W. , Venturo V. , Selbrede S.
Published: May 2003

The interface of zirconium oxide thin films on silicon is analyzed in detail for their potential applications in the microelectronics. The formation of an interfacial layer of ZrSixOy with graded Zr concentration is observed by the x-ray photoelectron spectroscopy and secondary ion mass spectrometry analysis. The as-deposited ZrO2/ZrSixOy/Si sample is thermally stable up to 880 °C, but is less stable compared to the ZrO2/SiO2/Si samples. Post-deposition annealing in oxygen or ammonia improved the thermal stability of as-deposited ZrO2/ZrSixOy/Si to 925 °C, likely due to the oxidation/nitridation of the interface. The as-deposited film had an equivalent oxide thickness of ∼1.3 nm with a dielectric constant of ∼21 and a leakage current of 3.2×10−3 A/cm2 at −1.5 V. Upon oxygen or ammonia annealing, the formation of SiOx and SiHxNyOz at the interface reduced the overall dielectric constants.
Ultraviolet-emitting ZnO nanowhiskers prepared by a vapor transport process on prestructured surfaces with self-assembled polymers
Authors: Haupt M. , Ladenburger A. , Sauer R. , Thonke K. , Glass R. , Roos W. , Spatz J. P. , Rauscher H. , Riethmüller S. , Möller M.
Published: May 2003

ZnO wires were grown by a vapor–liquid–solid phase transport process. Self-assembled Au nano-clusters act as a catalyst or seed for the highly oriented growth of so-called ZnO whiskers on sapphire substrates by a vapor–liquid–solid phase transport process. The ZnO nanowires were more than 500 nm high and smaller than 30 nm in diameter. Low-temperature photoluminescence measurements reveal intense and detailed ultraviolet light emission near the opitical band gap of ZnO at 3.37 eV. The ZnO nanowires show almost no broad green photoluminescence emission band related to oxygen defects and only a weak signal due to donor–acceptor pair recombination. X-ray diffraction proves that the ZnO wires were grown c-plane oriented on an a-plane sapphire substrate with high crystal quality most likely because of a kind of self-purification during the growth process.
Topology dependence of domain wall depinning in magnetic hard–soft composites
Authors: Lin Z. F. , Chui S. T. , Hu L. B.
Published: May 2003

We study the depinning field Hd in magnetic hard–soft nanocomposite by finite-temperature Monte Carlo simulation for two different topologies of the composites: (1) a hard phase in a soft matrix and (2) a soft phase in a hard matrix. We find that the depinning field and maximum energy product is higher in the first case. The temperature and composition dependence of the switching field and maximum energy product is reported.
Domain orientation in ultrathin (Ba,Sr)TiO3 films measured by optical second harmonic generation
Authors: Mishina E. D. , Sherstyuk N. E. , Barskiy D. R. , Sigov A. S. , Golovko Yu. I. , Mukhorotov V. M. , De Santo M. , Rasing Th.
Published: May 2003

The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG) was used for the structural characterization of submicron domain structures of thin (Ba,Sr)TiO3 (BST) films. It is shown that the lack of separation of these two contributions may lead to completely wrong conclusions about the domain orientation in these films. SHG studies of the thickness dependence of domain fractions (including 180° domains) reveal the presence of ferroelectric domains in ultrathin BST films (6 nm), although no domain structure was observed by atomic force microscopy. Thus the presence of ferroelectric ordering was demonstrated in perovskite films with a thickness down to 6 nm.
Spectral relaxation in pump–probe transients
Authors: Farrow Darcie A. , Yu Anchi , Jonas David M.
Published: May 2003

The relationship between pump–probe transients and the transition frequency correlation function, M(t), is examined. Calculations of pump–probe transients are carried out with a full-quantum expression for a displaced harmonic oscillator coupled to a heat bath. Pump–probe transients for a slowly decaying, overdamped, Brownian oscillator are shown to resemble a power series in M(t), where the slowest time scale is always equal to the slowest decay in M(t). This equality is consistent with a semiclassical model of pump–probe and valid over the full range of temperature, pulse duration, and detuning explored. The contribution of time scales faster than M(t) to the pump–probe transient increases with increasing temperature, pulse duration, and detuning of the pulse center frequency below resonance. Pump–probe transients for a critically damped oscillator that decays on a femtosecond time scale also have faster early time decay at higher temperatures. Based on these calculations a bootstrap method is suggested for extracting M(t) from pump–probe data starting with the slowest decay. Comparisons are made between simulations of pump–probe and three pulse echo peak shift (3PEPS) transients for a single oscillator and for multiple oscillator systems. Additional fast relaxations similar to those in pump–probe are also present in the 3PEPS transients. For the models investigated, pump–probe is comparable to 3PEPS for the extraction of M(t).
Effects of ion implantation on electron centers in hydrogenated amorphous carbon films
Authors: Konchits A. A. , Valakh M. Ya. , Shanina B. D. , Kolesnik S. P. , Yanchuk I. B. , Carey J. D. , Silva S. R. P.
Published: May 2003

Electron spin resonance (ESR) and Raman spectra measurements are carried out on a-C:H and a-C:H:N films both as grown and implanted with W and Ni ions with doses ranged from 0.5×1015 to 1.2×1016 cm−2. The as-grown films have small concentration of paramagnetic centers with a spin density Ns of 1017 cm−3. Upon implantation a significant increase in Ns of (0.5–22)×1019 cm−3 centers with g(Si)=2.0055 and g(C)=2.0025 was observed. These defects are ascribed to dangling bonds in the silicon substrate and in the carbon film, respectively. The correlation between variation of Ns value with implantation dose and behavior of D and G band position and their intensity ratio in the visible Raman spectra is observed. The effects are attributed to changes in the sp2–sp3 systems and hydrogen loss due to ion induced annealing of the carbon films at high ion doses. The temperature and concentration dependencies of the ESR line shape and linewidth are explained using the mechanism of motional narrowing over the temperature range 4.2–300 K. Low temperature anisotropy of the g value is found in the ESR spectra and is explained as arising from the dipole–dipole interaction in the infinitely thin films.
Electrical activation of the ion-implanted phosphorus in 4H-SiC by excimer laser annealing
Authors: Tanaka Yasunori , Tanoue Hisao , Arai Kazuo
Published: May 2003

We developed the annealing method for the activation of the ion-implanted dopants in silicon carbide using excimer laser irradiation. The electrical activation efficiency of the dopants drastically improved while the substrate temperature was kept in the range of 500–700 °C during laser irradiation. A “multiple energy irradiation method” realized the annealing of the implanted layer without ablation of the surface atoms and without redistribution of the dopants that were usually observed in the case of furnace annealing above 1500 °C. We have obtained a very low sheet resistance Rs, namely, 164.7 Ω/□, of the phosphorus ion-implanted layer in 4H-SiC by excimer laser annealing. This value is comparable to that of the furnace-annealed substrate at 1500 °C.
Characterization of isolated hydrogen traps by hydrogen permeation experiments
Authors: Zhang Tong-Yi , Wat Iva
Published: May 2003

The present work analyzes hydrogen permeation through a slab sample containing isolated hydrogen traps. The analysis is based on a flux continuity model that considers both the absorption and desorption processes. An analytical solution in series is derived for a dilute system with a low trap coverage fraction. According to this solution, we are able to characterize isolated hydrogen traps using only hydrogen permeation tests on two groups of samples with each group having different thicknesses. One group of samples, serving as a reference, is made of a pure matrix material without any hydrogen traps, while the other group of samples is made of the same matrix material with traps. The proposed multisample method is demonstrated by numerical calculations and plots, from which we determine the hydrogen diffusion coefficient, the desorption rate, the absorption parameter, the trap density, and the trap enthalpy from the permeation data of the steady flux and the time lag. The maximum error caused by the numerical calculations is less than 7%.
Field-dependent effective temperature and variable range hopping: Application to dark dc conductivity in doped a-Si:H
Authors: Arkhipov V. I. , Emelianova E. V. , Adriaenssens G. J.
Published: May 2003

Field and temperature dependencies of the dark dc hopping conductivity are calculated for an algebraic energy distribution of localized states near the Fermi level. These dependencies are shown to merge in a universal dependence on a field-dependent effective temperature Teff. An analytical expression for Teff is derived. The analytic results agree quantitatively with experimental data obtained by Nebel et al. [Phys. Rev. B 46, 6803 (1992)] for boron- and phosphorous-doped a-Si:H. Although the effective temperature does depend upon a particular choice of the density-of-states (DOS) distribution this dependence is not very strong for DOS functions that are not too steep near the Fermi level.
Predictive Monte Carlo ion implantation simulator from sub-keV to above 10 MeV
Authors: Tian Shiyang
Published: May 2003

In this paper is reported a general and accurate binary-collision-approximation- (BCA-)based Monte Carlo ion implantation model for implants into crystalline silicon. The combination of an improved semiempirical electronic stopping power model and Ziegler-Biersack-Littmark universal potential enables us to simulate a wide variety of implant species with only two different electronic stopping parameters for different implant species. With the model parameters fixed for a given implant species, excellent agreement is found with experimental secondary ion mass spectroscopy data for the energy range from sub-keV to above 10 MeV, and for different implant directions including random equivalent orientation, 〈100〉, 〈111〉, and 〈110〉 channeling directions. When compared with other BCA-based Monte Carlo simulators, it is demonstrated that more accurate results can be obtained for ultralow energy and very high energy implants. Furthermore, it is shown that, while the existing ion implantation simulators with the electronic stopping power based on the effective charge theory fail to predict the long tails of the deeply channeled implant species (such as Al), our model can predict these long tails successfully. Finally, an efficient damage model is also presented, which requires only one additional free parameter to accurately account for the damage accumulation and dechanneling effect. For high dose implants, substantial speed improvement over MARLOWE-based Monte Carlo simulators is observed.
Magnetic coupling and magnetoresistance in La0.55Sr0.45MnO3/ La0.67Ca0.33 MnO3 multilayers
Authors: Sirena M. , Haberkorn N. , Steren L. B. , Guimpel J.
Published: May 2003

We have studied the interlayer coupling and the magnetoresistant effect of La0.55Sr0.45MnO3/ La0.67Ca0.33MnO3 structures. Magnetization loops, measured in La0.55Sr0.45MnO3/La0.67Ca0.33MnO3/La0.55Sr0.45MnO3 trilayers, indicate that there is a ferromagnetic coupling of the La0.55Sr0.45MnO3 layers across the La0.67Ca0.33MnO3 spacer up to room temperature, even above the Curie temperature of the La0.67Ca0.33MnO3 layers. However, magnetization versus temperature curves present signatures of the magnetic ordering of both compounds. No extrinsic magnetoresistance associated with the multilayered structure was observed in the whole temperature range due to the presence of the interlayer ferromagnetic coupling.
Low-temperature magnetic properties and the crystallization behavior of FINEMET alloy
Authors: Ponpandian N. , Narayanasamy A. , Chattopadhyay K. , Raja M. Manivel , Ganesan K. , Chinnasamy C. N. , Jeyadevan B.
Published: May 2003

We have synthesized FINEMET alloy by a melt spinning technique and studied in detail its crystallization behavior and low-temperature magnetic properties. The crystallization behavior is characterized by transmission electron microscopy and Mössbauer spectroscopy. At early stages bcc solid solution precipitates from the amorphous matrix. At later stages, they order to yield DO3 ordered Fe3Si coexisting with a small amount of Fe2B. The analysis of Mössbauer spectra supports this observation. The temperature dependence of the magnetization in the temperature range 10–300 K of the FINEMET alloy in its as-quenched state follows the relation M(T)=M0(T) (1−B T3/2−C T5/2−⋅⋅⋅), which is indicative of the presence of spin wave excitations in the alloy. The value of the C/B ratio and the mean-square value of the range of exchange interaction 〈r2〉 are found to be characteristic of the noncrystalline ferromagnets. The small value obtained for the exchange stiffness constant D is an indication of the softening of the exchange interaction.
Recombination kinetics in wide gap electroluminescent conjugated polymers with on-chain emissive defects
Authors: Nikitenko V. R. , Lupton J. M.
Published: May 2003

We analyze the experimental dependence of temporally and spectrally resolved electroluminescence (EL) from polyfluorene-based light-emitting diodes on electric field and temperature. The blue band in the EL spectrum is caused by emission from the polymer backbone, while the low-energy green emission results from on-chain keto defects, which act as traps for electrons. Although the time and temperature dependencies of the blue and green emission could be explained by the kinetics of redistribution of trapped holes and electrons in energy and space, the increase of the blue-to-green delayed emission ratio with increasing field strength appears to result from a difference in the nature of recombination. We propose that the formation of blue-emitting singlet excitons from close electron–hole pairs after turn-off is impeded by an energy barrier, in contrast to the formation of green-emitting excitons.
Vibrational spectroscopy of HOD in liquid D2O. IV. Infrared two-pulse photon echoes
Authors: Piryatinski A. , Lawrence C. P. , Skinner J. L.
Published: May 2003

Using molecular dynamics simulation and the self-consistent renormalization scheme for liquid-state vibrational spectroscopy developed earlier by us, we have calculated the infrared integrated two-pulse photon echo signal for the OH stretch of dilute HOD in D2O at 300 K. Our echo decay time of 37 fs is in good agreement with the experimental value of 33 fs. The experiment was originally analyzed in terms of a model with both homogeneous and inhomogeneous broadening. The parameters from this analysis are in reasonable agreement with those from our theory. Nonetheless, a critical assessment of this analysis raises some questions about its quantitative accuracy.
Sequence of Mg segregation, grain growth, and interfacial MgO formation in Cu–Mg alloy films on SiO2 during vacuum annealing
Authors: Frederick M. J. , Goswami R. , Ramanath G.
Published: May 2003

Cu-alloy films are being explored for integrated circuits, for creating low-resistivity interconnects with stabilized metal/dielectric interfaces via solute segregation, and for interfacial reactions. Here, we describe the pathways of microstructure evolution in supersaturated Cu– 5–12 at. % Mg films, and phase formation at the film/SiO2 interface during annealing. The as-deposited films consist primarily of a Cu–Mg solid solution with trace amounts of orthorhombic CuMg2. Upon annealing to 400 °C, Mg segregates to the surface and the Cu–Mg grains grow from an average size of 20 to 60 nm, resulting in a ∼25%–40% decrease in film resistivity. In the same temperature regime, CuMg2 phase dissolves and fcc Cu2Mg forms. Upon annealing to higher temperatures, Mg segregates to the film/silica interface, reduces SiO2, and forms fcc MgO on the silica side of the interface. The Si released by this interfacial reaction diffuses into the metal film resulting in a ∼40%–190% increase in resistivity, for films with 8–12 at. % Mg, respectively. These results are of relevance for understanding microstructure evolution in alloy films and exploring the use of Cu alloys as interconnects in integrated circuits.