bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of anisotropy on magnetic interactions: A relativistic electron approach
Authors: Godfree J. A. , Staunton J. B.
Published: July 2002

Using a relativistic multiple-scattering approach to describe the electronic behavior, the interactions between magnetic impurities embedded in a nonmagnetic metallic host are investigated. The addition of a third, heavy nonmagnetic impurity is found to enhance the magnetic anisotropy energy of a magnetic pair in the system such that in some cases it becomes comparable in magnitude to their effective exchange energy. The resulting anisotropic magnetic interaction is found to be more complex than that shown by other model calculations.
Pressure dependence of magnetic ordering temperature for decamethylferrocenium tetracyanoethanide
Authors: Huang Z. J. , Chen Feng , Ren Y. T. , Xue Y. Y. , Chu C. W. , Miller J. S.
Published: July 2002

It has been demonstrated that the linear-chain charge-transfer salt, decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE), is a ferromagnet with a transition temperature of ∼4.8 K. This low-temperature 3D ordering has been attributed to a strong intrachain and a weak interchain interaction. To study these interactions, we have determined the Tc up to 20 kbar by measuring the ac susceptibility χ at low frequency. Our results show that the Tc increases with pressure at a rate of ∼0.22 K/kbar, while the χ peak indicative of the ferromagnetic transition continues to decrease rapidly. A small peak was also detected above the main transition at pressures above 3 kbar. This new peak persists even after the pressure is removed. The result from dc magnetization suggests that this corresponds to a metamagnetic state. For the first time, we have observed pressure-induced phase-transition in this material.
Spin frustration and metamagnetic behavior in a molecular-based quasi-1D ferrimagnetic chain: (MnTPP)(TCNE)
Authors: Zhou P. , Morin B. G. , Epstein A. J. , McLean R. S. , Miller Joel S.
Published: July 2002

We report an experimental observation of spin frustration and metamagnetic behavior in a quasi-1D ferrimagnetic chain, (MnTPP)+(TCNE)−. Metastability, hysteresis effects, and irreversibility of thermal and magnetic histories are observed in magnetization measurements. The ‘‘memory’’ phenomenon is seen in the temperature dependence of the thermoremanent and isothermal remanent magnetization. This system may be relevant to the magnetic behavior of the quantum/classical spin chains. The isothermal M(H) at T=2.25 K supports a first order transition which may be related to effects of local anisotropy.
Angular dependencies of thermal and nonlinear characteristics of spin wave signal processing devices
Authors: Marcelli R. , Slavin A. N.
Published: July 2002

In the development of planar spin wave signal processing devices (delay lines, filters, resonators) based on thin yttrium-iron garnet (YIG) films, it is necessary to improve thermal stability of their characteristics and to enlarge their dynamic range of linearity. This can be done by selecting the orientation of the external bias magnetic field in relation to the film normal. Using the explicit approximate expressions for the spin wave spectrum in YIG films and taking into account the temperature dependencies of both saturation magnetization M0 and external bias magnetic field He we calculate the ‘‘thermostable’’ and the ‘‘linear’’ orientations of the bias magnetic field. It is shown herein that these two orientations coincide when the temperature dependence of the bias magnetic field is negligible. The proper orientation of the bias field improves the thermostability of a tunable YIG-film resonator by one order of magnitude in the whole range of tunability (from 5 to 10 GHz).
The effect of Li3N addition by mechanical alloying on Nd2Fe14B—Formation of NdN2
Authors: Tang J. , Troupe J. E. , O’Connor C. J. , Falster A. U. , Simmons W. B.
Published: July 2002

Curie temperatures of R2Fe17 and RTiFe11 (R=rare earths) can be raised drastically by addition of interstitial nitrogen. Can one see similar effects in Nd2Fe14B? This question is particularly interesting because Nd2Fe14B’s relatively low Curie temperature has limited its applications in high temperature operations. Nitrogen additions by heat treating Nd2Fe14B in flowing N2 at different temperatures have been reported to raise its Curie temperature by 20–50 °C. We report an attempt of nitriding Nd2Fe14B by mechanical alloying it with Li3N. Our attempt resulted in the formation of a rare form of neodymium nitride, NdN2. The original goal to nitride Nd2Fe14B by mechanical alloying it with Li3N seems to be inapplicable.
Simulation of magnetoresistive response in a small Permalloy strip
Authors: Koehler T. R. , Yang Bo , Chen Wenjie , Fredkin D. R.
Published: July 2002

A micromagnetic simulation program has been used to calculate the magnetoresistance of a free-standing 4 μm×1 μm×200 Å Permalloy strip for a variety of numerical hysteresis loops in which a constant bias field is applied along the easy axis and a variable field is applied along the hard, in-plane axis. The main purpose of this study is to correlate noise in the magnetoresistive response with micromagnetic behavior and to show that the noise is considerably reduced by the application of the bias field. Two different methods for evaluating the magnetoresistive response are discussed.
Micromagnetics of imperfect permalloy particles (abstract)
Authors: Chen Wenjie , Fredkin D. R. , Koehler T. R.
Published: July 2002

In previous micromagnetic modeling1,2 of permalloy particles made by nanolithography,3 each individual particle is assumed to be a rectangular plate, but scanning electron micrographs show that the particles are better described by thin plates with round ends. Using our finite element code, we have investigated the effects of corner shapes of the permalloy particles. These particles are all 1.47 mm long, 0.18 mm wide, and 50 nm thick. The particle with semicircular ends has a higher coercivity and shows better agreement with the experiments than the particle with square ends. Qualitatively distinct behaviors are also found among interacting pairs of particles with different shapes at the ends. We have also studied the effects of voids. When the dimension of a void is much less than the exchange length of the material, the micromagnetics of the particle is not affected. For larger voids, particles with one, two, and three voids have been studied. Their easy axis hysteresis loops are all compared to the hysteresis loop of a voidless particle. It has been found that voids near the ends of the particle can serve as pinning sites and tend to increase the coercivity. On the other hand, a void in the middle of the particle reduces the coercivity because of an increase of the self demagnetizing field.
Reevaluation of spin-dependent cross sections of solutes in Fe
Authors: Stearns Mary Beth
Published: July 2002

The resistivity data of Fe-based ternary alloys has been reevaluated taking into account that the conduction electrons in Fe are predominantly highly polarized (∼95%) d-like electrons. This drastically changes the previously derived values of solute cross sections and scattering rate ratios of the majority and minority conduction electrons. It further removes the perplexing result of previous analyses that the spin-up and spin-down cross sections of sp solute atoms were not equal but varied by about a factor of 7. These cross sections should be equal since the nonmagnetic sp electrons cause only a charge perturbation. The vastly different cross-section ratios from those previously obtained cast doubt on the proposed explanation of the giant magnetoresistance effect as being due to spin-dependent scattering from solute or interface atoms. A more plausible explanation of the large magnetoresistance at low fields for both pure Fe and its layered structures is that it is caused by the large scattering at antiparallel magnetic boundaries due to the high polarization of the conduction electrons. Moreover, since past analyses of scattering, transport effects, etc. in 3d ferromagnetics have assumed that the conduction electrons are sp-like, all of these results should also be critically reexamined to determine their validity.
Magnetic properties of Cr and Mn powders (abstract)
Authors: Zhukov A. P. , Ivanov S. A. , Nudelman M. A. , Ponomarev B. K. , Kaloshkin S. D. , Shatov A. A.
Published: July 2002

Mn and Cr powders were produced from electrolytic Mn and Cr by ball milling in a stainless steel container with carbon steel balls. The milling time, t, varied from 5 min to 8 h. Structures were investigated by x-ray and electron microscopy. Chemical compositions of samples were checked by flame atomic absorption spectrometry. The magnetization was measured by induction method in a pulsed magnetic field up to 10 T. The main part of Mn and Cr powder volume was occupied by α-Mn and b.c.c. Cr, respectively. Diffraction peaks became vaster and more asymmetric with increasing t due to the onset of defects of the structure. The presence of MnO was observed in the Mn sample after 8 h of milling. The size of Mn and Cr particles over same critical t (for chromium t=100 min) was no more than 1 mm. A noticeable Fe content, which increases at higher t, was observed. The Mössbauer spectra of Cr and Mn samples showed the lines of α-Fe and γ-Fe. High values of saturation magnetization, σ, up to 5.4 emu/g, and susceptibility and existence of the hysteresis in low fields at temperatures up to 360 K, indicate ferromagnetic ordering of the samples. Within the range of 78–360 K σ only slightly depends on temperature, but noticeably grows with increasing t at fixed temperature in Cr powders, remaining practically constant in Mn powders. No correlation could be observed between Fe content and σ : the latter remained the same in Mn with Fe concentration increasing, but in Cr, as Fe concentration increased sevenfold, it grew by four times. Spontaneous magnetization per mass unit of Fe, σ, was sufficiently lower than that of pure α-Fe (220 emu/g). The obtained values of σ correspond neither to Fe solid solution nor to pure Cr or Mn. Elucidation of the obtained results can be done both by the presence of α-Fe particles and by variation of exchange interactions caused by sample defects. A noticeable difference of σ values from those properties of bulk α-Fe can be explained by γ-Fe availability and grinding of particles being smaller than single domain sizes.
Combined low- and high-angle x-ray structural refinement of a Co/Pt(111) multilayer exhibiting perpendicular magnetic anisotropy
Authors: Ankner J. F. , Borchers J. A. , Farrow R. F. C. , Marks R. F.
Published: July 2002

We have used Cu Kα radiation to measure both specular reflectivity (000) and longitudinal Bragg diffraction (222) from a Co/Pt multilayer grown by molecular-beam epitaxy on a sapphire (0001) substrate. By refining both low- and high-angle profiles, we are able to separate the effects of surface morphology from microstructure. Our results indicate mixing at the interfaces consistent with the existence of alloy or compound formation.
Magnetic and structural characteristics of Fe/Al multilayers deposited by ion beam sputtering with Kr
Authors: Hamaguchi T. , Aida H. , Nakagawa S. , Naoe M.
Published: July 2002

Fe/Al multilayers have been prepared by the ion beam sputtering method with use of Ar and Kr as the working gas. Sputtering by Kr ion beam deposited the multilayer with better crystallinity, smaller interdiffusion between layers, and lower electrical resistivity than sputtering by Ar ion beam. Multilayers with thicknesses of Fe and Al layers of 50–120 Å and 15–20 Å, respectively, possessed excellent soft magnetism. Such soft magnetism seems to be related, in part, to the fine granulation in Fe layers.
High-energy spin-density-wave correlated fluctuations in paramagnetic Cr+5 at.% V
Authors: Werner S. A. , Fawcett E. , Elmiger M. W. , Shirane G.
Published: July 2002

Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr+5 at.% V are extended up in energy to about 80 meV. These fluctuating spin–spin correlations occur at incommensurate positions, corresponding to the SDW wave vector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T=10 and 300 K.
Spin fluctuations of La2−xSrxCu1−yZnyO4−δ (x=0.14, y=0.012) (abstract)
Authors: Matsuda M. , Kuroda K. , Yamada K. , Endoh Y. , Chou H. , Shirane G. , Birgeneau R. J. , Kastner M. A. , Tanaka I. , Kojima H.
Published: July 2002

Magnetism of high-Tc superconductors is still the subject of intensive investigation. Zn substitution for Cu together with removal of oxygen suppresses the superconductivity quickly. We prepared two crystals to perform a neutron scattering study of the spin fluctuations of La2−xSrxCu1−yZnyO4−δ. One is a Zn-doped and deoxygenated crystal La1.86Sr0.14Cu0.988Zn0.012O4−δ (♯1) which does not show superconductivity above 1.5 K. The other is a Zn-doped crystal La1.86Sr0.14Cu0.988Zn0.012O4 (♯2) which shows superconductivity below 16 K. The incommensurate spin excitations observed previously in superconducting samples1,2 containing no Zn remain in both samples. However, there is significant difference in the spectral weight χ″(q,ω) at low temperatures between the non-superconducting and superconducting Zn-doped crystals. In crystal ♯1 the spectral weight at low temperatures is qualitatively similar to that of Zn-undoped non-superconducting samples.3 In crystal ♯2 the spectral weight at low temperatures is qualitatively similar to that of Zn-undoped superconducting samples.1,2 These results demonstrate that there is an intimate relationship between the magnetism and the superconductivity. We are in the process of further measurements.
Crystal field, phase separation, and percolative superconductivity in ErBa2Cu3Ox (6<x<7) (abstract)
Authors: Mesot J. , Allenspach P. , Staub U. , Furrer A. , Mutka H.
Published: July 2002

Inelastic neutron scattering has been employed to study the crystalline-electric-field (CEF) level scheme of Er3+ in ErBa2Cu3Ox (6<x<7). We have been able to resolve all the seven ground-state CEF transitions for a series of samples covering the superconducting as well as the semiconducting phases. All the CEF transitions are characterized by a monotonic behavior of their energies and intensities versus the oxygen content x, with the exception of the lowest-lying CEF state which exhibits a most unusual behavior: when going from x=7 to x=6, we observe a major shift to lower energies and a significant decrease of the intensity: moreover, there is evidence for real substructures associated with this CEF transition as shown in Fig. 1. More specifically, we find the observed energy spectra to be the result of a superposition of three stable states, whose spectral weights distinctly depend on the oxygen content x. We identify the three stable states A1, A2, and A3 by two local regions of metallic (Tc≊90 K, Tc≊60 K) and a local region of semiconducting character, respectively, i.e., there is clear experimental evidence for phase separation. The superconducting phases are shown to result from the formation of a two-dimensional percolative network. A bond percolation model correctly predicts the critical oxygen concentrations associated with the two-plateau structure of Tc. A preliminary account of the present work has recently been published.1
Surface and interface excitations for bilayer Ising-model systems in a transverse field (abstract)
Authors: Salman A. , Cottam M. G.
Published: July 2002

We present some calculations for the surface and interface excitations (spin waves) in layered solid structures which may be represented by the Ising model in a transverse magnetic field. In particular, we consider a two-medium system consisting of a ferromagnetic thin film on a semi-infinite substrate of another ferromagnetic material. By generalizing previous results for a single semi-infinite medium,1,2 we show that there may be excitations localized near the surface and interface of the coupled magnetic system, depending on the parameters of the model. We deduce dispersion relations for these surface and interface spin waves, as well as for the quantized (or ‘‘standing’’) bulk spin waves in the thin film, including the effects of relaxational damping of the modes. For nonzero values of the transverse field, the formalism can be applied at temperatures above and below the critical temperatures in the two media. Although our theory provides a description of some real anisotropic magnetic materials when placed in a transverse magnetic field, it is also of wider applicability within a pseudo-spin formalism for certain order–disorder ferroelectrics and Jahn–Teller systems.
Preparation of NiZn ferrite films by spin-spray ferrite plating on oxygen-plasma-treated substrates
Authors: Zhang Q. , Itoh T. , Abe M. , Tamaura Y.
Published: July 2002

Polycrystalline NixZnyFe3−x−yO4 films were prepared by the spin-spray ferrite plating method on oxygen-plasma-treated and non-plasma-treated glass substrates from an aqueous solution at 96 °C. The oxygen-plasma treatment increased film adhesion to the substrate, and enabled films thicker than 15 μm to be grown. A film with composition of (x+y)=0.75 had a saturation magnetization of 103 emu/g, a coercive force of ∼7 (Oe), ferromagnetic resonance linewidth (perpendicular to the film plane) of 80 (Oe), and resistivity of 106 Ω cm. These results compare favorably with ceramics of NiZn ferrite on the market.
Magnetic force scanning tunneling microscopy of high density recording
Authors: Gomez R. D. , Burke E. R. , Adly A. A. , Mayergoyz I. D. , Gorczyca J. A. , Kryder M. H.
Published: July 2002

The magnetic force scanning tunneling microscope has been used to investigate the characteristics of magnetization patterns on rigid thin-film disk media, having wavelengths in the range from 20 to 1 μm. The images, which directly exhibit magnetic field distributions, compare favorably with a theoretical model that incorporates the ratio of the transition length relative to the bit length. The profiles of the long to intermediate wavelength patterns were analyzed to obtain estimates for the transition length parameter. At high recording densities, our results suggest two major contributing effects responsible for signal loss: (a) reduction in the magnetization and (b) ‘‘bit cluster formation.’’ As the wavelength is decreased, the tracks eventually lose the capability to retain the recorded pattern, and merely appear as a more or less random distribution of localized ‘‘magnetic patches’’ on the surface.
Magnetic moments in Cr thin films on Fe(100)
Authors: Pierce D. T. , Celotta R. J. , Unguris J.
Published: July 2002

The magnetism at the surface of a Cr film grown epitaxially on a Fe(100) whisker is observed as a function of Cr thickness by scanning electron microscopy with polarization analysis. Use of a wedge-shaped film of linearly increasing thickness allows the magnetism to be followed continuously for 75 Cr layers. Over the temperature range measured from just below the Néel temperature of bulk Cr, TN, to 1.8 TN, the surface magnetic moment is seen to persist and change direction with each additional Cr layer, but there are phase slips in this antiferromagnetic ordering. These are consistent with an incommensurate spin density wave (SDW) in the Cr film having a wavelength of 40 layers at TN. An irregularity in the antiferromagnetic stacking order in the first four layers is discussed and the behavior of the moments at the subsequent phase slip is examined. The limitations which prevent the determination of the surface magnetic moment from the spin polarization of secondary electrons are discussed.
Magnetic structure of Cr overlayers on Fe(100) (abstract)
Authors: Walker T. G. , Pang A. W. , Hopster H. , Alvarado S. F.
Published: July 2002

Epitaxial films of Cr were grown at 200 °C on Fe(100). The magnetic order of the Cr overlayers was studied by spin polarized electron energy loss spectroscopy (SPEELS). The exchange scattering asymmetry is large (negative) for the bare Fe surface and rapidly drops with increasing Cr coverage in the submonolayer range changing sign at around one monolayer Cr. This shows directly the antiferromagnetic coupling of the first Cr layer to the Fe substrate. With further increase in the Cr thickness the exchange asymmetry oscillates with a period of about 2 layers, thus proving directly the layer-by-layer antiferromagnetic order in the Cr films. The oscillation amplitude shows variations with thickness resembling features found in the magnetic coupling in Fe/Cr/Fe sandwiches. The SPEELS spectra show a maximum in the spin flip channels around 1.9 eV. This structure broadens with increasing Cr thickness. This large spin flip energy suggests a surface enhanced exchange splitting and an enhanced Cr surface moment.
Micromagnetics of small unshielded MR elements
Authors: Yuan Samuel W. , Bertram H. Neal
Published: July 2002

A two-dimensional micromagnetic simulation is carried out for small unshielded magnetoresistive (MR) elements. The response of the magnetization to uniform cycling of a transverse external field is studied. For an isolated element without any bias field, the magnetic response is hysteretic, resulting in noisy MR output. For longitudinal patterned exchange bias, the pinning width has to exceed a critical value to achieve a noise-free response. Increasing the edge biasing angle beyond 45° induces undesirable multidomain activities. Soft adjacent layer (SAL) biasing is investigated by using a dual-layer model. Various exchange biasing schemes of the end regions of the MR and SAL layers have been numerically implemented, and it is seen that symmetric exchange coupling of the edge regions of both layers yields a desirable MR response.
Magneto-optical Kerr spectroscopy in Pt-Ni multilayers
Authors: Kielar P. , Nyvlt M. , Parizek V. , Prosser V. , Visnovsky S. , Krishnan R. , Tessier M.
Published: July 2002

The magnetic multilayers consisting of ultrathin 3d-transition metal and Pt or Pd layers are considered for the magneto-optical storage media with increased information density. This paper reports on the magneto-optical polar Kerr rotation and ellipticity spectra in Pt-Ni multilayers at photon energies from 1.5 to 5.2 eV prepared by evaporation onto glass substrates. The thickness of individual Pt layers was kept constant at 2 nm in all samples studied while that of Ni layers varied between 0.9 and 3.9 nm. The prominent feature of the Kerr rotation spectra is a broad negative peak the amplitude of which increases with the individual Ni-layer thickness. The multilayer spectra show less structure than that of pure Ni. Nevertheless the trends in multilayer spectra when the thickness of individual Ni layers changes can be reasonably simulated using the electromagnetic wave theory and permittivity spectra in bulk (or thick film) Ni and Pt.
Magneto-optical studies of Sm(Fe,Ti)12 perpendicular textured sputtered films
Authors: Cadieu F. J. , Navarathna A. , Rani R. , Hegde H. , Bojarczuk N. A. , Gambino R. J.
Published: July 2002

Measurements of the polar Kerr rotation and optical coercivity as a function of photon energy have been made on ≊2 μm thick ThMn12-type crystalline sputtered films of Sm(Fe,Ti)12. The optical coercivity for a Ti containing (222) textured film was 3.10 kOe at a photon energy of 1.25 eV, 2.96 kOe at 1.84 eV, and 2.92 kOe at 2.45 eV. The optical coercivity for a similar composition (002) textured Sm(Fe,Ti)12 film was relatively constant at 1.24 kOe. These samples were measured in air at 300 K without any protective overcoating. The polar Kerr rotation observed for these crystalline films versus the photon energy paralleled that observed for pure Fe. The magnetometer and optical coercivities for the (222) textured Sm(Fe,Ti)12 films were 1.5 and 2.5 times as large, respectively, as for similar composition (002) textured films. Differences in grain sizes incorporated during the direct synthesis of the films onto heated substrates are needed to account for the large differences observed in the coercivities for the (222) versus (002) textured films.
High pulsed field magnetostriction in Ho2Fe17 single crystal
Authors: García-Landa B. , Algarabel P. A. , Ibarra M. R. , Kayzel F. E. , Anh T. H. , Franse J. J. M.
Published: July 2002

Magnetostriction measurements were performed on Ho2Fe17 single crystals, using high pulsed magnetic fields up to 15 T and in the temperature range of 5–300 K. Volume deformations in the basal plane have been observed to be one order of magnitude greater than the volume longitudinal deformation along the c axis. The main contribution to the magnetostriction modes arises from the 3d–3d exchange interaction.
Simple evaluation of linewidth-enhancement factor in quantum well laser with strain
Authors: Wartak Marek S. , Makino Toshihiko
Published: July 2002

A simple formula for linewidth-enhancement factor α in quantum well laser with strain was derived and compared with Westbrook and Adams theory [IEE Proc. 135. Pt.J, 223 (1988)]. Strain is incorporated through light and heavy hole effective masses. It has been found that tensile strain results in better improvement of ‖αmat‖ than compressive strain.
Control of the saturation value of planar Si doping in AlInAs layers grown by metalorganic chemical vapor deposition
Authors: Ishikawa Hideto , Nomachi Ichiro , Miwa Shiro , Maruyama Toshiyuki , Kamada Mikio
Published: July 2002

We observed a strong correlation between sheet carrier concentration in Si planar-doped AlInAs layers and the flow rate of AsH3 supplied during the doping. The AlInAs layers were grown by metalorganic chemical vapor deposition and were planar doped by supplying Si2H6 in AsH3 atmosphere. The sheet carrier concentration measured by the van der Pauw method and the sheet Si atom concentration measured by secondary ion mass spectrometry agreed well. Our results can be interpreted on the basic of a previously introduced model taking into account Si incorporation and desorption. We applied this desorption effect to doping control in Si planar-doped AlInAs/GaInAs selectively doped heterostructures. By changing AsH3 flow rate at a given doping time and Si2H6 flow rate, we could control the sheet Si atom concentration and hence the two-dimensional electron gas in the selectively doped heterostructures.
The influence of oxygen on the analysis of a Pt/Si structure with secondary ion mass spectrometry
Authors: Elst K. , Vandervorst W.
Published: July 2002

The introduction of oxygen during analysis with secondary ion mass spectrometry (SIMS) is an important tool to reduce ion beam induced topography, to enhance positive ion yields, and to remove transient effects during shallow and multilayer profiling. Its main drawback, however, is that due to the tendency of some elements to segregate towards the internal SiO2/Si interface (formed by an oxygen primary beam), large profile distortions can occur. In this work, the influence of oxygen pressure on the measurement of the Pt/Si structure is investigated and its relation to the observed SIMS depth profile is established. In the low pressure regime (leading to incomplete oxidation of Si), the profile disturbances occur in the interface region and are totally the result of ionization variations. The depth at which these disturbances are seen, as well as as the magnitude of the variations, are strongly dependent on the oxygen pressure in relation to the primary current density. The latter can be explained by the competition for the Si atoms between the formation of a Pt-Si alloy and an oxide. For high pressures where Si is completely oxidized, two regimes are observed. In the first regime, when the sample still contains a large amount of Pt, a large decay length is observed, representative of the strong segregation toward the SiO2/Si interface. In a later stage, when the amount of Pt has been reduced, the decay length decreases significantly suggesting that the segregation disappears. Internal depth profiling has shown that the two decay lengths can be correlated with two different internal Pt distributions, whereby the longest decay length corresponds to a Pt accumulation in the interface region. This correlation is in agreement with theoretical predictions about the role of the internal distribution on the SIMS decay length. The work also revealed that the polarity of the detected ions has a pronounced influence on the segregation caused by field-induced migration. This segregation depended strongly on the oxidizing conditions, suggesting the formation of higher quality oxides under higher oxygen pressures.
Isothermal capacitance transient spectroscopy of electron and hole emissions from interface states in metal-oxide-semiconductor transistors
Authors: Yoshida Haruhiko , Niu Hirohiko , Kishino Seigô
Published: July 2002

Isothermal capacitance transient spectroscopy has been expansively applied to the study of interface states in metal-oxide-semiconductor (MOS) transistors. We propose a simple technique to precisely measure the emission transient of both majority carriers and minority carriers using the identical Si-MOS transistor. We have improved on a conventional technique to measure the emission transient of minority carriers to solve a few problems. The emission transient of majority carriers is measured after applying the injection pulse to the gate electrode as usual. Similarly, the emission transient of minority carriers is measurable merely by reversing the injection-pulse polarity. The validity of the proposed technique has been demonstrated with the use of Au-diffused Si-MOS transistors. As a result, the density of the interface states has been determined over the energy range from Ev+0.30 eV to Ec−0.24 eV using the very same Si-MOS transistor.
Ballistic transport through a double bend in an electron waveguide
Authors: Ji Zhen-Li
Published: July 2002

The transport properties of a double bend in a two-dimensional electron waveguide are investigated by performing calculations of the transmission and conductance. The bends can introduce significant mode mixing at energies high enough for multimode transport. If the bent regions become fully circular, the bends introduce almost no additional resistance to the current flow except for energies very close to one of the thresholds for propagation in the channel. There are extremely narrow dips in conductance just below the threshold energies for the next channel. Bound states are found in the bent regions. We consider the spatial distribution of currents and show that complicated flow patterns with vortex structures appear at conductance dips. When bend regions are not fully circular, the conductance dips are considerably broadened and a series of superimposed resonant peaks is found. The results are in qualitative agreement with recent measurements.
Determination of two-dimensional electron gas population enhancement within illuminated semiconductor heterostructures by persistent photoconductivity
Authors: Anagnostakis E. A. , Theodorou D. E.
Published: July 2002

The illumination-induced enhancement of the sheet density of the two-dimensional electron gas (2DEG) dwelling within the quantum well of a semiconductor heterostructure is determined as a function of cumulative photon dose through a theoretical interpretation that processes the experimental data of the persistent photoconductivity effect exhibited by the doped, wide-band-gap side of the probed heterojunction (HJ). The interpretation takes into account the photocurrent flowing within the HJ interface along with the subsequent alterations in the persisting charge, ionized donor, and 2DEG populations. Results are given for typical AlxGa1−xAs/GaAs heterodiodes.
The dynamics of amorphous-to-crystalline interface evolution in ion-implanted polycrystalline silicon
Authors: England J. M. C. , Timans P. J. , Hill C. , Augustus P. D. , Ahmed H.
Published: July 2002

Time-resolved reflectivity measurements have been used to investigate the morphology of an evolving amorphous-crystalline interface during solid phase epitaxial regrowth of an ion-implanted polycrystalline silicon film. Isothermal electron beam heating was used to produce partly regrown specimens for cross-sectional transmission electron microscopy analysis, and this has enabled a direct correlation to be established between the interface shape and the observed reflectivity transients. Using a thin-film optical model of an evolving rough interface, this correlation has enabled interface shapes to be inferred from the reflectivity at higher temperatures, where it is difficult to achieve partial regrowth. For undoped material, smaller grain sizes have been found to lead to rougher interfaces, with regrowth rates typically 20 times slower than for single crystal. At 620 °C, the presence of high concentrations of arsenic results in a smoother interface, but as the regrowth temperature is increased, the interface becomes rougher. The complex interplay between doping, temperature, and initial microstructure is investigated at temperatures up to 850 °C.
Novel surface electronic states in finite superlattices
Authors: Glessner William , Yu Roger H.
Published: July 2002

We have numerically investigated the surface states for the case of lower-surface potential barrier and found several low-energy Tamm states [Physik Zeits Sowjetunion 1, 733 (1932)]. Localized above-barrier states are also found in our calculations.
Perimeter recombination in planar solar cells
Authors: Luque A. , Tobías I.
Published: July 2002

The recombination in the perimeter region of a planar solar cell is analyzed. A simple, quasi-analytical model is developed that allows the calculation of perimeter current in a variety of situations. Experimental confirmation of the model is obtained by measuring the current collected by the cell when the perimeter is illuminated. This measurement also informs us of internal cell parameters. Cells with high resistivity bases show the greatest perimeter recombination currents. In small size concentration cells this can cause a significant reduction of open circuit voltage: about 5 mV in our 1.5 cm2 cells at one sun that means 16 mV in 1 mm2 cells of the same technology. However, it is shown that the importance of this recombination component decreases as the concentration increases. Some methods for minimizing it are also discussed.
Weak links and critical current density in Bi2Sr2CaCu2Ox thin films
Authors: Lu H. A. , Chen J. , Wessels B. W. , Schulz D. L. , Marks T. J.
Published: July 2002

Magnetization measurements were performed on epitaxial and textured Bi2Sr2CaCu2Ox thin films deposited on (100) LaAlO3 and MgO substrates. An anomalous dependence of the critical current density derived from magnetization hysteresis measurement on magnetic field is observed. The measured critical current density shows a minimum at a magnetic field (Hm) far below the upper critical field Hc2. The measured Hm in epitaxial films has an exponential dependence on temperature, e−T/T0 (T0∼12.5 K). The anomalous field dependence of critical current density is attributed to the presence of weak links in the films.
Microstructure induced magnetic anisotropy in Fe/Cr (110) superlattices
Authors: Folkerts W. , Hakkens F.
Published: July 2002

A special corrugated microstructure of Fe/Cr(110) superlattices is discovered, which develops spontaneously when grown on Ge(110) substrates. This microstructure was studied using low energy electron diffraction and transmission electron microscopy. Also magnetic and transport properties of these superlattices were measured. We conclude that the microstructure induces a magnetic anisotropy, which has a strong influence on the magnetoresistance curves.
Discontinuity of B-diffusion profiles at the interface of polycrystalline Si and single crystal Si
Authors: Batra S. , Manning M. , Dennison C. , Sultan A. , Bhattacharya S. , Park K. , Banerjee S. , Lobo M. , Lux G. , Kirschbaum C. , Norberg J. , Smith T. , Mulvaney B.
Published: July 2002

Boron diffusion in polycrystalline Si-on-single crystal Si systems has been studied by secondary ion mass spectrometry. The extrapolated B-diffusion profiles in polycrystalline Si and in the single crystal Si substrate reveal a discontinuity at the polycrystalline Si-single crystal Si interface. The discontinuity in the B profiles is believed to occur due to the blockage of B-defect complexes by the interfacial oxide between polycrystalline Si and the single-crystal Si substrate, as well as the immobility of these defect complexes in single crystal Si. The B in the implant peak region above the B solid solubility limit is found to be immobile in single crystal Si during annealing due to the formation of electrically inactive B-defect complexes. In polycrystalline Si, however, our results show that the B in the peak region spreads out more rapidly than in single crystal Si possibly due to the diffusion of B-defect complexes along grain boundaries. The B-defect complexes are electrically inactive as determined by spreading resistance analysis. If the B concentration is lowered below the solid solubility limit, either by decreasing the dose or by raising the anneal temperature, no discontinuity is observed in the B profile across the polycrystalline Si-single crystal Si interface.
High field characteristics of metal-oxide-semiconductor capacitors with the silicon in inversion
Authors: Patrikar R. M. , Lal R. , Vasi J.
Published: July 2002

Degradation of the gate oxide is often studied by stressing of metal-oxide-semiconductor (MOS) capacitors. Usually the MOS capacitor is stressed in accumulation to avoid the complications due to a voltage drop across the depletion layer if stressed in inversion. High field stressing studies for MOS capacitors with the silicon in inversion are presented in this article. Our observations show that in this mode, silicon properties (mainly minority carrier generation lifetime) play an important role.
An improved resistor shunted junction model of superconducting metal-oxide-semiconductor field effect transistors
Authors: Lai H. , Qian G. , Cahay M.
Published: July 2002

Some preliminary experimental realizations of three terminal devices using low and high Tc electrodes and various semiconducting materials for the active channel have been reported recently. However, little progress has been made towards the theoretical modeling of these systems. We develop the resistively shunted junction model proposed by Ivanov and Claeson, but remove some of the unecessarily restrictive (and sometimes unrealistic) assumptions made by these authors. The model is based on the classic metal-oxide-semiconductor field effect transistor theory modified to take into account the superconducting current flowing between source and drain. Contrary to Ivanov and Claeson, (1) we use the Fermi–Dirac distribution of carriers in the active channel, (2) we take into account the field dependent mobility in the channel, and (3) we do not assume full ionization of the dopants. These points are essential in a highly degenerate two-dimensional electron gas at low temperature. We show that by including the effect of Coulomb and surface scattering in the electron mobility dependence on carrier concentration, the critical current expression of Likharev gives a good fit to the critical current in the superconducting metal-oxide-semiconductor field effect transistor reported by Hatano et al. For a source to drain voltage of 0.1 meV, the minimum gate channel transit time and maximum transconductance per unit width for Hatano’s device are calculated to be around 70 ps and 0.5 mS/mm, respectively.
The vibrational modes of silicon acceptors in p-type GaAs grown by molecular beam epitaxy on a (111)A plane
Authors: Ashwin M. J. , Fahy M. R. , Newman R. C.
Published: July 2002

Silicon impurities in p-type GaAs grown by molecular beam epitaxy occupy As lattice sites and give rise to an infrared active localized vibrational mode (LVM) which appears as a Fano profile near 395 cm−1 in samples with p=1019 cm−3 or 1020 cm−3. 2 MeV electron irradiation reduces p, leading to the emergence of the usual LVM absorption line of SiAs at 399 cm−1. The treatment also leads to site switching to produce SiGa donors giving an LVM at 384 cm−1.
Fission-fragment excited xenon/rare gas mixtures. II. Small signal gain of the 2.03 μm xenon transition
Authors: Hebner G. A. , Hays G. N.
Published: July 2002

The results of small signal gain measurements of the 2.03 μm (5d[3/2]1−6p[3/2]1) xenon transition in fission-fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures is presented. Time resolved small signal gain was probed using a cw He/Xe discharge laser as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio, and impurity concentration. Small signal gains of up to 6%/cm were observed for pump rates of 15 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the laser gain and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented.
Measurements of the cathode sheath in a magnetron sputtering discharge using laser induced fluorescence
Authors: Bowden M. D. , Nakamura T. , Muraoka K. , Yamagata Y. , James B. W. , Maeda M.
Published: July 2002

Magnetron discharges are widely used as sputtering sources for thin film deposition. Despite the importance of the sheath region where the electric field can be very high, there have been few experimental investigations of this region in magnetron plasmas. We report values of the sheath thickness deduced from measurements of the electric field distribution using laser spectroscopy. With this technique, a transition which is normally forbidden becomes in the presence of an electric field partially allowed so that laser induced fluorescence on this transition can be used as a measure of the electric field. It was found that the sheath thickness was approximately equal to the maximum displacement, in the absence of collisions, of a secondary electron from the cathode surface.
The influence of hydrogen plasma treatment and proton implantation of electrical properties of AlGaAsSb
Authors: Polyakov A. Y. , Eglash S. J. , Milnes A. G. , Ye M. , Pearton S. J. , Wilson R. G.
Published: July 2002

The effects of hydrogen plasma treatment and 300 keV proton implantation on the electrical properties of AlGaAsSb layers matched to GaSb are studied. It is shown that the hydrogen introduced from a plasma can form electrically neutral complexes with donors and acceptors in this material system. The results can be explained under the assumption that the hydrogen has an acceptor and a donor level in AlGaAsSb and an estimate of the depth of these levels as a function of composition is made. It is also shown that after heavy irradiation of AlGaAsSb with protons the material becomes p type with the hole concentration of about 1016 cm−3, independent of the initial doping level in the starting material.
Comparison between the growth and shrinkage of oxidation stacking faults in silicon and silicon on insulator
Authors: Tsamis C. , Tsoukalas D. , Stoemenos J.
Published: July 2002

We present results on the growth and shrinkage of oxidation stacking faults in silicon implanted with oxygen (SIMOX) structures and compare them with bulk silicon. The growth results show an enhanced length of the faults in SIMOX. Using the silicon direct bonding technique, we determine the critical silicon film thickness for which the length of the faults becomes the same as in bulk silicon. The shrinkage behavior of the faults during annealing in inert ambient was also studied and similar results for both materials were obtained. From these experiments we get insight into the fundamental properties of silicon self-interstitials.
Optical and structural properties of annealed PE:LiNbO3 waveguides formed with pyrophosphoric and benzoic acids
Authors: Ziling C. , Pokrovskii L. , Terpugov N. , Savatinova I. , Kuneva M. , Tonchev S. , Armenise M. N. , Passaro V. M. N.
Published: July 2002

The optical and structural properties of protonated lithium niobate waveguides have been investigated. The proton-exchange process was performed by immersing Z-cut substrates in molten pyrophosphoric and benzoic acids at 240 °C for 8 h. Surface refractive index changes of 0.148 (pyrophosphoric acid) and 0.124 (benzoic acid) were obtained at λ=632.8 nm. The exchanged samples were subjected to annealing for 1 h through each 20° starting from 200 °C. Reflection high-energy electron diffraction, optical measurements, and vibrational (IR and Raman) spectra were used at each stage of annealing in order to study the guiding characteristics. Immediately after the exchange process and at low-temperature annealings a two-step index profile was detected. The dependence of the profile parameters on the annealing temperature up to 360 °C was followed and correlated with the phase transformations in the LiNbO3-HNbO3 system. The hydrogen concentration in the waveguide layers was estimated by using optical measurements and Raman spectra.
Effect of heat treatment on the state of Si impurity in GaAs studied with the photoluminescence technique
Authors: Suezawa M. , Kasuya A. , Nishina Y. , Sumino K.
Published: July 2002

The effect of heat treatment of Si-doped GaAs was investigated with photoluminescence (PL) measurement. The dependence of PL spectra on the carrier concentration due to Si shows that the PL lines in the wavelength range between 950 and 1500 nm are classified into two types depending on whether the carrier concentration is lower or higher than approximately 7×1017 cm−3. There is also a similar behavior for PL spectra in the bound exciton wavelength region between 800 and 950 nm. The characteristic carrier concentration is about 6×1017 cm−3, and is related to the onset of overlap between wavefunctions of excitons bound to Si impurity.
Collection efficiency of photoexcited carriers of electrochemically etched surface
Authors: Nabutovsky V. M. , Eherman K. , Tenne R.
Published: July 2002

The collection efficiency of a photoexcited layered type semiconductor WSe2 exhibits appreciable gain, especially in the near infrared region, following photoetching. A theoretical model, which considers surfaces that are inclined in an oblique angle with respect to the incident light, and that also considers the anisotropic diffusion length in this material, was proposed. The theory explains the large gain in the infrared region (up to 4–5 times after photoetching) and small gain in the shorter wavelengths by ‘‘crossover’’ from carriers diffusion mainly along the layers (⊥c) in the first case to diffusion mainly along the c axes in the second case. From the fit to experimental data, it was found that the diffusion length transverse to the layers (∥c) is 2–2.5 μm whereas the diffusion length in the plane of layers (⊥c) is 9–11 μm.
Superconductivity in rapidly quenched metallic systems with nanoscale structure
Authors: Goswami R. , Banerjee S. , Chattopadhyay K. , Raychaudhuri A. K.
Published: July 2002

Nanocomposites of Al-In, Al-Pb, and Zn-Pb have been prepared and characterized using rapid quenching techniques and the nature of superconducting transitions in them has been studied by resistivity measurements. The precipitated second phases (In and Pb) have particle sizes (d) of a few tens of nanometers such that ξ0≥d≥dmin, where ξ0 is the superconducting zero temperature coherence length and dmin is the minimum particle size that supports superconductivity. The onset of superconductivity generally starts in samples with d∼ξ0 and progressively other grains with d≤ξ0 become superconducting. We suggest that the proximity effect of the matrix plays a significant role. In an Al-In system, even with 40 wt.% In, the zero resistivity state is obtained at T∼1.33 times the Tc of Al. But in Al-Pb and Zn-Pb, the zero resistivity state is obtained at T∼4 and 5 times the Tc of Al and Zn with only 10–15 wt % Pb, respectively.