bluuebunny/crossref_metadata_2025 huggingface dataset:
High sensitivity magnetic head for a shaft torque sensor
Authors: Sasada I. , Akinaga M.
Published: July 2002

The structure of a magnetic head used for torque sensing is investigated to seek higher sensitivity with low power consumption. The magnetic head investigated consists of two figure-eight coils embedded in a ferrite core. Torque applied to a magnetostrictive steel shaft makes the magnetic coupling between two coils in the head change positively or negatively depending on the sign and the strength of torque. Two structures, the square shape and the diagonal shape, are analyzed in terms of sensitivity and compared to our previous structure, the circle shape, which is an intermediate of the two in shape. It was found that the diagonal structure is the best choice. With this structure using a 14.6 mm square ferrite core, the applied torque is stably detected with 0.1 W power consumption (excitation condition: 60 kHz, 0.1 A) from a case-hardened steel shaft with an air gap 0.5 mm between head and shaft.
Magnetic behavior of yttrium–iron–garnet nanoparticles dispersed in glass composites
Authors: Taketomi Susamu , Shull Robert D.
Published: July 2002

By absorbing amorphous yttrium–iron–garnet (YIG) nanoparticles into nanosized pores of a controlled pore glass (CPG) followed by heat treatment, we synthesized YIG nanocrystal-dispersed glass composites. In a sample which was prepared with a 300 nm pore size CPG and heat treated at 800 °C for 2 h, almost all the amorphous YIG nanoparticles transformed to YIG nanocrystals. The mass fraction of YIG was estimated to be 4.7% from the measured saturation magnetization. In a sample which was prepared from a 49 nm pore size CPG with the same heat treatment, the amount of YIG was estimated to be only 0.54%. Magnetization measurements of different samples revealed that heat treatment at higher temperatures or for longer times resulted in reactions of the YIG particles with the SiO2 of the CPG, and the composites became paramagnetic. However, even in those samples, large initial magnetic susceptibilities were measured, implying the presence of a small amount of unreacted YIG nanocrystals.
Temperature dependence of soft magnetic properties in amorphous Co69Fe4.5Cu1.5Si10B15 alloy
Authors: Jiang Bingzhi , Ulyanov A. N. , Yu Seong-Cho , Lee Heebok , Park Sang-Tae
Published: July 2002

The temperature dependence of soft magnetic properties in amorphous Co69Fe4.5Cu1.5Si10B15 alloy was investigated by the changes of incremental permeability ratio (PR) and magnetoimpedance ratio (MIR) as a function of temperature from 10 to 300 K. The temperature dependence of PR and MIR is directly related to the temperature dependence of soft magnetic properties. The soft magnetic properties in Co69Fe4.5Cu1.5Si10B15 alloy annealed at 400 °C are very stable for temperature variation at low temperature. The spin wave stiffness constant, D, was estimated from the temperature dependence of the magnetization at low temperature.
Intermixing effects in ultrathin barrier magnetic tunneling junctions
Authors: Li Yun , Wang Shan X.
Published: July 2002

Ultrathin tunneling barrier magnetic tunneling junctions were fabricated to study the intermixing effects of ferromagnetic layer, NiFe, and barrier precursor aluminum. Both bottom ferromagnetic layer (NiFe) and aluminum were grown epitaxially on a Pt buffered sapphire (0001) substrate. Grazing incidence x-ray reflectometry indicated an intermixing layer of 0.6 nm (∼3 atomic layers) between the NiFe and Al. Junction barrier height and width were extracted from both R(T) curve and zero-bias conductance. Nonideal oxidation of the intermixing region degrades the device performance, and poses a fundamental limit to the optimization of ultrathin barrier tunnel junctions.
Temperature dependence of magnetoresistance for tunnel junctions with high-power plasma-oxidized barriers: Effects of annealing
Authors: Lee K. I. , Lee J. H. , Lee W. L. , Shin K. H. , Sung Y. B. , Ha J. G. , Rhie K. , Lee B. C.
Published: July 2002

Magnetic tunnel junctions (MTJ) were fabricated with high oxygen-plasma power and the effects of annealing on the temperature dependence of tunneling magnetoresistance (TMR) were investigated experimentally. As grown, TMR increases, peaks around 160 K, and decreases with increasing temperature from 80 K to 300 K. When MTJs are annealed, Tmax, the temperature at which maximum TMR is obtained, decreases as annealing temperature increases to the optimal point. In order to explain the temperature dependence of TMR, the difference of conductance between parallel and antiparallel alignments of magnetizations as a function of temperature is also analyzed. The shifts of Tmax due to annealing are described phenomenologically with spin-dependent transfer rates of electrons through the barrier.
FePt–Ag nanocomposite film with perpendicular magnetic anisotropy
Authors: Yang T. , Ahmad E. , Suzuki T.
Published: July 2002

Magnetic properties of FePt–Ag nanocomposite films synthesized by annealing (FePt/Ag)n multilayers deposited on a MgO(100) substrate by laser ablation are discussed in conjunction with the structure. After annealing over a temperature range from 540 to 650 °C, a large perpendicular magnetic anisotropy constant Ku of the order of 107 erg/cc developed. The so-called δM curve measurements imply that grains are magnetically decoupled. Increasing the Ag layer thickness is found to be useful for the improvement of the (001) orientation of FePt grains. The remanence ratio and coercivity increase with a rise in the annealing temperature. Magnetic grains of less than 10 nm and a small activation volume of the order of 10−19 cm3 are observed.
Study on increasing the coercivity of CoCrPtB media with high Pt content
Authors: Mikami M. , Djayaprawira D. D. , Domon H. , Yoshimura S. , Takahashi Migaku , Komiyama K.
Published: July 2002

The dependence of magnetic properties and microstructure on the composition of CrMox (x=0–40 at. %) underlayer and CoCr-based nonmagnetic interlayer has been examined for CoCr18Pt20B4 longitudinal media. In the media using a single CrMo (10 nm) underlayer, the highest coercivity that can be obtained is only 1.9 kOe. The coercivity is drastically increased up to 5.0 and 6.4 kOe by using substrate/Cr (5 nm)/CrMo (5 nm) dual underlayer and substrate/CrMo (10 nm)/CoCr38Mo2 (1.3 nm), respectively. It is clarified that the improvement of the coercivity is mainly due to the enhancement of the quality of the crystal growth of the magnetic layer, which results in the improvement of magnetocrystalline anisotropy field and in-plane crystallographic orientation.
Evaluation of thickness of initial growth layer in CoCr-based perpendicular media by perpendicular torquemetry
Authors: Saito Shin , Hoshi Fumikazu , Takahashi Migaku
Published: July 2002

Quantitative evaluation of the initial growth layer thickness was performed by using perpendicular torquemetry. It was clarified that: (1) The thickness of the initial growth layer becomes thicker by the increment of the content of Cr, Ta, or B additional element for CoCrPt(B, Ta) media. In the case of CoCr16Pt8Bx media, with increasing x from 0 to 8 at. %, the initial growth layer thickness was increased from 1.5 to 2.2 nm. In the case of CoCr16Pt8Tay media, with increasing y from 0 to 4 at. %, the initial growth layer thickness was increased from 1.5 to 4.8 nm. In the case of CoCrzPt8B4 media, with increasing z from 16 to 24 at. %, the initial growth layer thickness was increased from 1.6 to 2.6 nm; (2) In the CoCrPtB medium, the initial growth region is relatively thin, and c-plane oriented fine grains with homogeneous columnar structure are realized. On the other hand for the CoCrPtTa medium, the initial growth region is relatively thick, and the grain size distribution and surface roughness is large due to selective grain growth; (3) The CoCrPtB magnetic film grew epitaxially on the CoCr/C/Ti underlayer. The perpendicular squareness of CoCrPtB/CoCr/C/Ti epitaxial medium was improved up to 0.88 and was maintained even for the dmag=30 nm.
High saturation magnetization films of FeCoCr
Authors: Vas’ko V. A. , Inturi V. R. , Riemer S. C. , Morrone A. , Schouweiler D. , Knox R. D. , Kief M. T.
Published: July 2002

Thin (∼1000 Å) films of (Fe54Co46)1−xCrx have been prepared by magnetron sputtering on Si/SiO2 substrates. The films were shown to be body-centered-cubic and (110) textured. It was found that the Fe54Co46 films possess a saturation magnetization of 24.5 kG at room temperature. Doping the Fe54Co46 films with Cr in the range of 0–13 at. % increased corrosion resistance, electrical resistivity, and reduced the saturation magnetization as a function of the amount of added Cr. The coercivity of both doped and undoped as-deposited films (80–120 Oe) decreased substantially after a 220 °C magnetic anneal. Electrochemical corrosion testing was done in two chloride salt solutions. Potentiodynamic scans performed on films in a 0.47 M chloride bath solution at pH=2.9 showed a substantial increase in corrosion resistance of the films between 6.6 and 8.2 a/o Cr. Similar scans performed in a 0.01 M chloride solution at pH=5.8 showed good corrosion resistance for all the films.
Effect of noise and localization error of magnetic field sensors on the characterization of complex sources
Authors: Kamondetdacha Rungkiet , Nyenhuis John A , Kildishev Alexander V.
Published: July 2002

Magnetic multipole images are used for characterization of complex magnetic sources. We simulate the multipole imaging of the source by application of selective functions to measured magnetic fields. The objective of this work is to determine the effect of sensor nonidealities on the accuracy of the source characterization. The source is assumed to be within a spherical boundary. The sensor array is arranged in a plane below the boundary, with the axis of the boundary coincident with the symmetry axis of the array. Sensors are radially directed away from the axis of symmetry and are characterized by their noise, offset between the real and ideal position and the deviation of the axis from the radial direction. Several sample sources, consisting of one or two dipoles, were evaluated. The radial component of magnetic field was measured with the planar array of 208 sensors a distance of 15 m below the source. The magnetic field was restored from the spherical expansion coefficients up to eight degree.
Effect of Ge addition on postannealed CoCrGePt thin film media
Authors: Domon H. , Djayaprawira D. D. , Takahashi M. , Endo T. , Furukawa S.
Published: July 2002

The effect of Ge addition to postannealed CoCrGe and CoCrGePt thin film media with CrMn overlayer is discussed. It is found that the postannealing at about 410 °C drastically reduces intergranular exchange interaction and increases coercivity of the media, which is probably due to the diffusion of nonmagnetic elements to the grain boundary in the magnetic layer. It is clarified that Ge addition increases the anisotropy field of postannealed CoCrGe or CoCrGePt media, which agrees well with the previous results obtained in CoCrGe bulk polycrystalline alloy. In particular, the anisotropy field of postannealed CoCr5 media is increased by 70% with 10 at. % Ge addition. The increase of coercivity is mainly due to the increase of anisotropy field. It is confirmed that Ge addition to CoCr-based media can increase Hc and Hkgrain significantly, in case where the grains of the magnetic layer can be magnetically isolated.
Effect of stress on stripe domain onset in sputtered FeAlN and CoFe films
Authors: Zou Pei , Yu Winnie , Bain James A.
Published: July 2002

Stripe domains caused by perpendicular anisotropy degrade soft magnetic properties of thin films used in recording heads. In this work, the relationship between stress and the susceptibility to stripe domains in soft magnetic thin films is studied theoretically and experimentally. The critical stripe domain onset thickness of a polycrystalline film with cubic unit cell under a planar, isotropic stress is calculated as a function stress and texture for sputtered FeAlN and CoFe films. In good agreement with experimental data, the results show that the stripe domain onset thickness depends on stress and texture. In the sputtered Co65Fe35 film, a residual stress close to zero helps eliminate the possibility of stripe domains, while in the sputtered FeAlN film, the role played by stress depends on texture. For the most frequently seen (110)-textured FeAlN film, large compressive stresses help reduce the possibility of stripe domains for low and moderate N concentrations.
Local mapping of strain at grain boundaries in colossal magnetoresistive films using x-ray microdiffraction
Authors: Soh Yeong-Ah , Evans P. G. , Cai Z. , Lai B. , Kim C.-Y. , Aeppli G. , Mathur N. D. , Blamire M. G. , Isaacs E. D.
Published: July 2002

Using x-ray submicrobeam, we spatially mapped the strain in epitaxial La1−xSrxMnO3 films grown on SrTiO3(001) bicrystal substrates. Our results show that there is an elastic strain gradient at the artificial grain boundary, which decays over a length scale of ∼1 μm. The tensile strain at the interior of the grain—due to the lattice mismatch between La1−xSrxMnO3 and SrTiO3—relaxes as the film nears the grain boundary, yielding a grain boundary lattice constant which approaches the value of that in bulk La1−xSrxMnO3.
Physical properties of spin-valve films grown on naturally oxidized metal nano-oxide surfaces
Authors: Mao Ming , Cerjan Charlie , Kools Jacques
Published: July 2002

The physical properties of spin-valve films NiFe 25 Å/CoFe 10 Å/Cu(tCu)/CoFe 30 Å/IrMn 70 Å/Ta 20 Å with graded Cu layer thickness (tCu=18–45 Å) grown on the surface of metal nano-oxide layers (NOLs) were studied. The NOLs were formed from ultrathin Al, Cr, Cu, Nb, Ta, CoFe, NiFe, and NiFeCr layers by natural oxidation. The growth of the spin-valve films on NOLs has led to an enhancement in giant magnetoresistance value by up to 48%. A corresponding reduction in minimum film resistance by over 10% confirms that this enhancement originates from an increase in the mean free path of spin-polarized electrons due to the resultant specular reflection at the nano-oxide surfaces. A wide spectrum of oscillatory interlayer exchange coupling dependence on tCu for these NOL-bearing films suggests that a specular nano-oxide surface does not necessarily result in a smoother multilayer structure. The observation of an enhanced exchange biasing among these spin-valve films appears in contradiction to the observed deterioration of their crystallographic quality. As an important application, TaOx, CrOx, and NbOx could be employed as an alternative to AlOx as the barrier layer for magnetic tunnel junctions.
Linear electro–optic tensor ratio determination and quadratic electro–optic modulation of electrostatically self-assembled CdSe quantum dot films
Authors: Zhang Liangmin , Zhang Fajian , Wang Yongqiang , Claus Richard O.
Published: July 2002

A new class of CdSe quantum dot-doped polymer films are synthesized using electrostatic layer-by-layer self-assembly processing technique. Transmission electron spectroscopy and electron beam diffraction results show that the diameter of the CdSe quantum dots is 2–3 nm and that the CdSe clusters possess a hexagonal structure. X-ray photoelectron spectroscopy allows determination of the concentration of the CdSe quantum dots within the resulting films. Linear electro–optic (Pockels) and quadratic electro–optic (Kerr) effect behavior of the films are investigated by using Mach–Zenhder interferometric and ellipsometric techniques, respectively. Linear electro–optic tensor ratios r333/r113 of 4.3±0.2 were determined. Theoretical calculations of the quadratic electro–optic coefficients are proposed for the conventional ellipsometric technique. The orientational enhancement effect originating from the permanent dipole moment and induced dipole moment of the CdSe clusters is also discussed. From the analysis of experimental data, we determine that the typical reorientational time for a CdSe dot in these films to respond to a sinusoidal electric field is 17.5 ms.
Strain and composition in self-assembled SiGe islands by Raman spectroscopy
Authors: Cazayous M. , Groenen J. , Demangeot F. , Sirvin R. , Caumont M. , Remmele T. , Albrecht M. , Christiansen S. , Becker M. , Strunk H. P. , Wawra H.
Published: July 2002

We have investigated self-assembled Si1−xGex islands grown on Si (001). We show that the average composition and both the εxx and εzz average strain components can be derived from Raman scattering spectra. Both nm-sized and μm-sized islands are investigated. The experimental results are compared successfully with finite-element strain simulations. Raman scattering is shown to be a versatile and reliable tool for investigating capped and uncapped islands. It is shown that strain profiles in μm-sized islands can be obtained by means of micro-Raman.
Observation of discrete energy states of weakly confined vibron in solid parahydrogen
Authors: Katsuki Hiroyuki , Nakamura Toshihiro , Momose Takamasa
Published: July 2002

The first overtone pure vibrational Q2(0) [v=2←0, J=0←0] transition of solid parahydrogen was studied using high-resolution laser spectroscopy. The absorption spectrum exhibits extremely narrow linewidths (20 MHz full-width-at-half-maximum), which allowed us to observe rich spectral structure in the transition. Part of the structure is attributed to the M sublevel splitting of orthohydrogen that induces dipole moments on surrounding parahydrogen molecules, but the finer spectral structure is due to vibron hopping of the v=2 excited state of parahydrogen molecules. The Stark field of the orthohydrogen localizes the vibron on a finite number of parahydrogen molecules, which results in the discrete vibron states. From the analysis of the spectral structure, the vibron hopping frequency of the v=2 state is determined to be −114 MHz. It is also found that the spectral structure cannot be explained completely unless the quantum nature of solid hydrogen is taken into account for the analysis.
Quantitative analysis of one-dimensional dopant profile by electron holography
Authors: McCartney M. R. , Gribelyuk M. A. , Li Jing , Ronsheim P. , McMurray J. S. , Smith David J.
Published: July 2002

The one-dimensional dopant profile of a silicon p–n junction was characterized using off-axis electron holography in a transmission electron microscope (TEM). Quantitative comparisons were made with simulated voltage profiles based on data obtained from secondary-ion mass spectroscopy. Close agreement was obtained over a range of sample thicknesses, and a spatial resolution of 5 nm and sensitivity of 0.1 V were established. By using a sample that had been wedge polished and briefly ion milled, depleted surface layers did not need to be taken into account, and beam-induced charging was removed by carbon coating one exposed surface of the TEM specimen.
Interferential coupling effect on the whispering-gallery mode lasing in a double-layered microcylinder
Authors: Moon Hee-Jong , An Kyungwon
Published: July 2002

Enhanced mode selection through a strong interferential coupling effect was observed in a double-layered cylindrical microcavity laser. The coupling was induced by partial reflection and recombination with refracted light on the internal circular boundary of the fused silica capillary tube, filled with a dye-doped liquid having lower reflective index than that of fused silica. The observed interference period agreed well with the prediction by a ray-optic model.
Large low-field magnetoresistance of phase-separated single-crystalline Pr0.7Pb0.3MnO3
Authors: Li Run-Wei , Wang Zhi-Hong , Wang Wei-Ning , Sun Ji-Rong , Li Qing-An , Zhang Shao-Ying , Cheng Zhao-Hua , Shen Bao-Gen , Gu Ben-Xi
Published: July 2002

A large low-field magnetoresistance (MR) slightly above the metal–insulator transition temperature (234 K) was observed in single-crystalline Pr0.7Pb0.3MnO3. Combining the temperature dependence of magnetization, resistance, and electron spin resonance spectra, it was suggested that phase separation occurs above the Curie temperature; ferromagnetic metallic clusters imbedding in the insulating paramagnetic matrix, and spin-polarized electron tunneling between isolated ferromagnetic clusters should be responsible for the large low-field MR observed. Undoubtedly, this observation opens a window to explore large low-field MR at high temperature, which is very important for the practical application of colossal MR effect.
Local thermal equilibrium plasma modeling for analyses of gas-phase reactions during reactive-laser ablation
Authors: Hermann J. , Dutouquet C.
Published: July 2002

Number densities of atoms, ions, and molecules in plasmas composed of two-element vapor-gas mixtures have been computed assuming local thermal equilibrium. The calculations include the formation of diatomic molecules by chemical reactions between both elements. Temperature range and total number densities of elements have been set to values characteristic for plasmas generated by pulsed-laser ablation of solid targets under low-pressure atmospheres. Mixtures of aluminum, carbon, and titanium vapors with either oxygen or nitrogen have been considered. The model predicts strong oxidation for all materials in O2. Contrarily, only very small quantities of nitride radicals are formed when mixing metal vapor with N2 whereas carbon nitridation leads to CN formation of a few percent. The results contribute to a better understanding of gas-phase reactions during thin film deposition by reactive laser ablation.
New photoluminescence effects of carrier confinement at an AlGaAs/GaAs heterojunction interface
Authors: Yuan Y. R. , Pudensi M. A. A. , Vawter G. A. , Merz J. L.
Published: July 2002

An unusual new line has been observed in the low-temperature photoluminescence spectrum of GaAs/AlGaAs epilayers grown by liquid-phase epitaxy, which represents a unique probe of the heterointerface. A very strong, broad and asymmetric line is seen, with peak energy ranging from that of the bound exciton to that of the shallowest acceptor, increasing roughly linearly with the logarithm of the excitation power. The intensity is seen to exhibit a very strong temperature dependence as the temperature is varied from 1.4 K up to about 20 K where the line falls below the background luminescence intensity. Intensity and energy dependence of the luminescence as a function of the Al mole fraction on one side of the junction is also investigated. By employing a novel step-etching technique, this transition is shown to originate from the GaAs/AlGaAs heterojunction. A qualitative model is proposed to explain the observed data.
Generalized reciprocity theorem for semiconductor devices
Authors: Misiakos K. , Lindholm F. A.
Published: July 2002

A reciprocity theorem is presented that relates the short-circuit current of a device, induced by a carrier generation source, to the minority-carrier Fermi level in the dark. The basic relation is general under low injection. It holds for three-dimensional devices with position dependent parameters (energy gap, electron affinity, mobility, etc.), and for transient or steady-state conditions. This theorem allows calculation of the internal quantum efficiency of a solar cell by using the analysis of the device in the dark. Other applications could involve measurements of various device parameters, interfacial surface recombination velocity at a polycrystalline silicon emitter contact, for example, by using steady-state or transient photon or mass-particle radiation.
Axial structure of a plasma column produced by a large-amplitude electromagnetic surface wave
Authors: Zhelyazkov I. , Benova E. , Atanassov V.
Published: July 2002

Electromagnetic surface waves in the rf and microwave frequency range can be used to produce long large/small-diameter plasma columns. We propose a theory of surface-wave-produced plasmas at two different low-pressure gas-discharge regimes, diffusion and recombination, respectively. For a given regime the axial plasma density profile is specified by two quantities: a numerical parameter σ=ωR/c (ω being the wave frequency, R the tube radius, and c denoting the speed of light) and the collision frequency ν (ν≪ω). Our theory predicts the magnitude of the axial electron number density gradient. The very good agreement between the experimentally measured plasma density gradients and the theoretically calculated ones for diffusion-controlled surface-wave-produced plasma columns confirms the adequacy of the proposed model.
Angular dispersion of ‘‘backward’’ Raman scattering: Absorbing cubic materials (Ge)
Authors: Anastassiadou A. , Raptis Y. S. , Anastassakis E.
Published: July 2002

A previously developed model for the angular dispersion of Raman-scattering power from the surface of cubic materials with negligible extinction coefficient is extended to cubic materials with any value for the extinction coefficient κ. In general, the results show that incorporating extinction coefficient corrections does not change drastically existing results in the limit of κ=0. However, there are situations where such corrections cannot be ignored. Experimental results obtained from Ge are found in good agreement with the predictions of the model.
Curvature of laser-machined grooves in Si3N4
Authors: Wallace Russell J. , Bass Michael , Copley Stephen M.
Published: July 2002

In laser machining, the article to be machined is moved with respect to the laser beam resulting in the formation of a groove in its surface by vaporization. Grooves formed in hot-pressed Si3N4 with a CO2 laser beam at normal incidence are observed to have cross sections that curve out of the plane defined by the velocity direction of the article and the direction of the laser beam. The curved cross sections change from one side of this plane to the other if the velocity direction is reversed. The effect is most pronounced at the lowest velocities and highest incident powers. The cross-section shape is shown to vary systematically with the angle between the velocity direction and the direction of the electric vector of the incident beam, which was found to be partially polarized. A mechanism for the curved cross-section effect is proposed based on the existence of a significant difference in reflectance between the transverse electric (TE) and transverse magnetic (TM) reflections from groove walls in Si3N4 for large angles of incidence. Calculations of values of reflectance for the TM and TE reflections as a function of the angle of incidence show the existence of a large difference for the CO2 wavelength of 10.6 × 10−4 cm.
Thermal expansion of hydrogenated amorphous germanium thin films
Authors: Persans P. D. , Ruppert A. F.
Published: July 2002

We report the first measurements of the linear thermal expansion coefficient αt of hydrogenated amorphous Ge thin films. We have utilized optical reflection interference fringes to measure the gap between the film and a fused quartz substrate in a segment of the film which lifted from the substrate due to intrinsic compressive strain. The linear thermal expansion coefficient of αt=1.7×10−5 K−1 for 300 K <T< 420 K is ∼3 times larger than that of crystalline Ge.
New high field-effect mobility regimes of amorphous silicon alloy thin-film transistor operation
Authors: Shur Michael , Hyun Choong , Hack Michael
Published: July 2002

A new theory of a-Si thin-film transistor (TFT) operation is presented. In addition to the below- and above-threshold regimes described previously, it predicts two new regimes of operation which occur at very high densities of the induced charge in the a-Si TFT channel. In a crystallinelike regime the free-electron concentration exceeds the localized charge concentration at the a-Si-insulator interface. In a transitional regime (at lower densities of the induced charge) almost all localized states in the energy gap of amorphous silicon near the interface are filled. In the crystallinelike regime, the field-effect mobility is close to the band mobility and the operation of an a-Si TFT is truly similar to the operation of a crystalline field-effect transistor. Our estimates show that the gate voltage necessary to achieve the crystallinelike regime is about 50 V for an a-Si TFT with an insulator 1000 Å thick and a relative permittivity of approximately 3.9.
Random and channeled implantation profiles and range parameters for P and Al in crystalline and amorphized Si
Authors: Wilson R. G.
Published: July 2002

We have measured implanted and annealed depth distributions for the two elements adjacent to Si, Al, an acceptor in Si, and P, a donor in Si, using secondary ion mass spectrometry for the atom depth distributions and differential capacitance-voltage profiling for the acceptor or donor depth distributions. Ions of Al or P were implanted into Si amorphized by Si implantation, into crystalline Si in a random orientation, and channeled into the three principal low index directions of the Si lattice, 〈100〉, 〈110〉, and 〈111〉. The ion energies were 25, 50, 75, 100, 150, 200, 300, 400, or 600 keV and the ion influences were 3×1013, 3×1014, and 3×1015 cm−2 for the atom depth distributions, and 1.5×1012 cm−2 for the acceptor and donor profiles. Pearson IV fitting was used to obtain the values of the first four moments of the random depth distributions, the projected range Rp or μ, the range straggle ΔRp or standard deviation σ, the skewness γ1, and the kurtosis β2. For the channeling orientations, the maximum channeling range or the depth of the channeled peak are plotted versus ion energy, and values of the energy exponent p are determined. The random ranges Rp and profiles are compared for amorphized and crystalline Si and compared with range calculations; the profiles in amorphized Si are modified Gaussians as predicted by theory, with no channeling tails, and the profiles in crystalline Si have significant channeling tails that are not easily fit to a modified Gaussian. The different channeling profiles for Al and P are illustrated and explained in terms of their different electronic stopping and ion size. The effects of 30-min furnace annealing at 550 and 800 °C are shown for implanted Al profiles; significant redistribution occurred, and in a manner that depends on Al atom density and whether the Si is amorphous or crystalline. Furnace annealing at 875 and 925 °C or rapid radiant annealing at 900 °C caused no redistribution of P profiles implanted at room temperature.
Growth of GaxIn1−xAs by low-pressure metalorganic vapor-phase epitaxy
Authors: Roth A. P. , Sacilotti M. A. , Masut R. A. , Machado A. , D’Arcy P. J.
Published: July 2002

GaxIn1−xAs layers have been grown on GaAs by low-pressure metalorganic vapor-phase epitaxy using trimethylgallium, trimethylindium, and arsine. The effects of varying the substrate temperature and gas composition on the growth rate and layer composition have been studied. It is found that very uniform ternary layers containing up to more than 20% In can be routinely grown over areas of ∼2×2 cm2. Stable growth is achieved at all indium concentrations, at various substrate temperatures, and gas flow rates. The growth rate and the layer composition are controlled by the organometallic-compound partial pressures in the reactor. The samples have a mirrorlike surface which shows a uniform crosshatched pattern under an optical microscope, typical of lattice mismatched epitaxial layers. The residual concentration is low (n≲6×1014 cm−4) but the low-temperature mobility decreases with increasing indium content in the layers. This mobility reduction is accompanied by a change in the photoluminescence spectra. At large indium concentrations, the spectra are dominated by a narrow line at 50–70 meV below the excitonic emission.
Real-time pulsed nuclear magnetic resonance measurement system for the study of nonequilibrium phenomena in polymers
Authors: Tanaka Hajime , Nishi Toshio
Published: July 2002

A real-time pulsed nuclear magnetic resonance measurement system controlled by a microcomputer has been constructed. The real-time measurements of the spin-spin relaxation time T2, the spin-lattice relaxation time in the rotating frame T1ρ, and the spin-lattice relaxation time T1 become possible by the use of this system. It is applicable to the studies of nonequilibrium phenomena in polymers such as crystallization, phase separation, gelation, polymerization, etc. It is also applicable to wider fields such as biological reaction and chemical reaction. The application of this system to polymer crystallization is presented as an example.
Modeling of titanium diffusion into LiNbO3 using a depth-dependent diffusion coefficient
Authors: Fontaine M. , Delâge A. , Landheer D.
Published: July 2002

A theoretical description of the diffusion of a thin film of titanium (Ti) into a lithium niobate (LiNbO3) crystal is reported. A variable depth diffusion coefficient is used to explain the prominent lateral surface diffusion generally observed in the fabrication of Ti-diffused optical waveguides on non-Z-cut LiNbO3. A finite integral transform technique is used to solve the diffusion equation described by Fick’s law. Since the enhanced lateral diffusion is usually ascribed to anisotropic diffusion, we compare our calculations with those obtained using different diffusion coefficients for each diffusion direction. The approach with a variable depth diffusion coefficient can explain the enhancement of lateral diffusion and the peak of Ti concentration close to the surface observed experimentally.
Determination of the (100) InAs/GaSb heterojunction valence-band discontinuity by x-ray photoemission core level spectroscopy
Authors: Gualtieri G. J. , Schwartz G. P. , Nuzzo R. G. , Malik R. J. , Walker J. F.
Published: July 2002

The valence-band discontinuity ΔEv has been determined for the (100) InAs/GaSb system by x-ray photoemission core level spectroscopy. For 20 Å of InAs on GaSb we find that ΔEv=0.53 eV. The reverse structure, consisting of a 20-Å layer of GaSb on InAs, gave a measured value of ΔEv=0.48 eV. Since the difference in these two values lies within our experimental uncertainty, we report an average offset of 0.51±0.1 eV. The large value of the valence-band discontinuity in this system shows the band lineup to be of the broken gap variety with the InAs conduction-band energy lying below that of the GaSb valence band. This result is in good agreement with theoretical predictions.
Complex refractive indices of AlGaAs at high temperatures measured by i
n s
i
t
u reflectometry during growth by metalorganic chemical vapor deposition
Authors: Kawai Hiroji , Imanaga Shunji , Kaneko Kunio , Watanabe Naozo
Published: July 2002

I n situ reflectometry with a 6328-Å laser beam was used to monitor the AlxGa1−x As growth by metalorganic chemical vapor deposition. The reflection intensity oscillated and was damped with increasing layer thickness. The refractive indices and absorption coefficients were obtained at temperatures of 600, 700, and 800 °C, and these data fall on the line extrapolated linearly from the data obtained up to room temperature. The temperature coefficient of the X-indirect band gap was found to be smaller than that of the Γ-direct band gap. A method for obtaining the growth parameters during deposition is proposed.
Micromagnetic predictions for magnetization reversal in CoNi films
Authors: Victora R. H.
Published: July 2002

A dynamic, micromagnetic theory which includes domain nucleation, incoherent rotation of magnetization within grains, and complete magnetostatic interactions is described in detail. All significant input is derived from experimental data; the precise values of several other input variables, such as exchange constant and damping parameter, are found to be largely irrelevant. Preliminary calculations, which may be compared to measured hysteresis loops, are used to establish the considerable quantitative accuracy of the theory. The remaining calculations make predictions for unmeasured properties such as crystalline anisotropy and domain-wall motion. A substantial prediction of the paper is that it is possible for obliquely deposited CoNi films to have no zig-zag domain walls; however, a finite transition width owing to the incline of the CoNi grains is predicted to occur.
Heteroepitaxial growth of InP on GaAs by low-pressure metalorganic chemical vapor deposition
Authors: Lee M. K. , Wuu D. S. , Tung H. H.
Published: July 2002

Heteroepitaxial growth of InP on GaAs by low-pressure metalorganic chemical vapor deposition is reported. Trimethylindium-trimethylphosphine adduct was used as the indium source and PH3 as the phosphorus source. From x-ray and scanning electron microscopy examination, excellent crystallinity InP epilayers with specular surface morphology can be grown on (100) GaAs substrates. The composition of this heterostructure was identified by the Auger depth profiles. The electron mobility of the undoped InP epilayer can reach 4700 cm2/V s at room temperature. An evident effect of growth temperature on electron mobility is also demonstrated. Carrier concentration profile shows that the carrier distribution in the epilayer is very uniform. The efficient photoluminescence compared with that of InP homoepitaxy shows that high-quality InP/GaAs heteroepitaxial layers can be obtained.
High-temperature heat contents, thermal diffusivities, densities, and thermal conductivities of n-type SiGe(GaP), p-type SiGe(GaP), and p-type SiGe alloys
Authors: Amano T. , Beaudry B. J. , Gschneidner K. A. , Hartman R. , Vining C. B. , Alexander C. A.
Published: July 2002

The high-temperature heat contents of n-type SiGe(GaP), p-type SiGe(GaP), and p-type SiGe alloys were measured from 400 to 1400 K by using a copper block drop calorimeter. The heat capacity and related thermodynamic functions were calculated. Smoothed values of H0T−H0298.15, Cp, S0T−S0298.15, and −(F0T−H0298.15)T−1 were tabulated at 100-K intervals. Thermal diffusivities were measured by using a laser technique. Thermal conductivities were calculated from the heat capacity, thermal diffusivity, and density.
Transient enhanced diffusion of ion-implanted boron in Si during rapid thermal annealing
Authors: Miyake Masayasu , Aoyama Shinji
Published: July 2002

Transient enhanced diffusion of ion-implanted boron at a dose of 1014 cm−2 during rapid thermal annealing has been studied. The boron diffusion coefficient of the enhanced diffusion arising from implantation damage decreases with time t in the form of D0 exp(−t/τ), where D0 is the diffusion coefficient at t=0 and τ is the lifetime of the point defect causing the enhanced diffusion. The temperature dependence of D0 and τ is revealed, and the point defect causing the transient enhanced diffusion is shown to be a vacancy. It is shown that final profile broadening due to the enhanced diffusion is smaller for higher temperatures. Furthermore, it is found that both D0 and τ increase with an increase in implantation energy.
Transient boron diffusion in ion-implanted crystalline and amorphous silicon
Authors: Sedgwick T. O. , Michel A. E. , Deline V. R. , Cohen S. A. , Lasky J. B.
Published: July 2002

Boron diffusion in ion-implanted and annealed single-crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1×1015 and 3×1015cm−2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distance. The samples were annealed by furnace or rapid thermal annealing to 900–1100 °C with or without a preanneal at 600 °C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single-crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profiles of the amorphized samples could be fit with a computational model that did not include anomalous transient effects. It is proposed that excess interstitials cause the transient diffusion in the case of the crystalline samples. The source of interstitials is believed to be provided by the thermal dissolution of small clusters that are formed by the implantation process. They exist for only a short time, during which they enhance the boron diffusion. Since there is no enhanced diffusion in the amorphous region that regrows to single crystal, apparently interstitial clusters are neither produced by nor do they survive the regrowth process in that region. In addition, the interstitials generated by the damage beyond the amorphous-crystalline boundary are prevented from entering the regrown region by the dislocation loops formed at that boundary which act as a sink consuming the interstitials diffusing toward the surface.
CoZrMo amorphous films as a soft adjacent layer for biasing magnetoresistive elements with a current shunt layer
Authors: Yamada K. , Maruyama T. , Ohmukai M. , Tatsumi T. , Urai H.
Published: July 2002

Sputtered Co94−xZr6Mox (4.4≤x≤17 at. %) films have been investigated as a soft-adjacent-layer (SAL) material for trilayered magnetoresistive (MR) sensors with a MR element layer, a current shunt layer, and a SAL for biasing layer. The saturation magnetization 4πMs linearly decreases from 14 to 3 kG with an increase in Mo content. The magnetic anisotropy field Hk decreases to a low value, equivalent to that for NiFe MR films, as the Mo content is increased. The magnetoresistance ratio Δρ/ρ is negative, but sufficiently small, namely one-hundredth of that for NiFe films, while the electrical resistivity ρ, about 140 μΩ cm, is 5.6 times greater than that for NiFe films. The films also have a small magnetostriction coefficient λs on the order of 10−7. A 500-Å-thick CoZrMo film with 12 at. % Mo content is selected as the SAL, because a lesser thickness causes an extreme increase in Hk. Higher Mo content degrades the temperature characteristics of the magnetic properties, due to the lower Curie temperature. Trilayered MR-sensors, 100 μm in length and 10 μm in width, are fabricated with a 400-Å-thick NiFe MR layer, a 400-Å-thick Ti layer, and a SAL using this CoZrMo film. An excellent biasing level is achieved with a 15-mA sense current on the MR sensors. CoZrMo amorphous films have a superior capability as a SAL material, especially for the trilayered MR sensors.
Effect of oxygen on compositionally modulated Gd-Co thin films
Authors: Choe G. , Becker M. F. , Walser R. M.
Published: July 2002

We report on a study of the effect of oxygen on the chemical and structural stability of compositionally modulated Gd-Co multilayer films. Films with bilayer periods (BP) from 10 to 300 Å were prepared by alternate deposition in a multitarget RF diode sputtering system. Oxygen incorporation in the films was controlled during deposition by the application of rf substrate bias, and after deposition by annealing. Oxygen preferentially accumulated in the Gd layer and blocked its diffusion. Co columnar grain growth in samples with large BP appears to be associated with the asymmetric diffusion between the Gd and Co layers. TEM of samples with small BP showed a void network structure in the samples sputtered with 0 V substrate bias, but showed a phase separated amorphous structure in the samples sputtered with 65 V substrate bias. Annealing suppressed the growth of crystalline Gd and Co in samples with oxygen but enhanced the nucleation of GdCo2. A strong growth of Co and Gd grains occurred in annealed samples with low oxygen content but GdCo2 was not observed. Cross-section TEM showed that the growth of these grains was limited by the layer boundaries.
CO2-laser-enhanced electron attachment in externally sustained diffuse gas discharges containing vinyl chloride
Authors: Schaefer G. , Giesselmann M. , Pashaie B. , Kristiansen M.
Published: July 2002

Photon-enhanced attachment can be used as a conduction-control mechanism for diffuse discharge opening switches. This paper presents experimental results on photon-enhanced attachment based on vibrational excitation of vinyl chloride using a line-tunable CO2 laser. Strong resistance increases and discharge turnoff have been observed in low-current, externally sustained dc discharges. The influence of experimental parameters such as discharge pressure, attacher concentration, discharge voltage, and laser wavelength are presented.
Fabrication and properties of high-T
c superconducting wires
Authors: Tiefel T. H. , Jin S. , Sherwood R. C. , van Dover R. B. , Fastnacht R. A. , Davis M. E. , Johnson D. W. , Rhodes W. W.
Published: July 2002

The discovery of high-temperature superconductivity in perovskite-related oxides has generated an enormous amount of research activity and development effort toward applications. Commercially useful bulk superconductors typically require stabilization using a normal metal cladding for reasons of electrical, thermal, and mechanical protection, and in general need to be fabricated into fine fibers and wound into a solenoid configuration. The YBa2Cu3O7−δ type compound is a ceramic material which is mechanically hard and brittle, and is difficult to fabricate into fine wires. However, this difficulty has been overcome by several fabrication methods such as powder-in-tube method (metal-clad composite), powder-coating method (metal-core composite), and molten oxide processing method. The effect of various processing steps on the structure and superconducting properties such as transition temperature and critical current density will be discussed. Some experiments to raise the high field critical current through chemistry and microstructural control will also be described.
Hot phonon effects in silicon field-effect transistors
Authors: Artaki Michael , Price Peter J.
Published: July 2002

An electron temperature model is used to estimate conditions for the onset of hot phonon effects in the n channel of a silicon field-effect transistor. The required power density for an appreciable hot phonon effect on the drift velocity increases with electron temperature in the range of interest. At an electron temperature of 7200 K, with 300-K lattice temperature, it is found to be in the range 3×1030–3×1031 eV/s cm3.
Formation of ferromagnetic iron nitrides in iron thin films by high-dose nitrogen ion implantation
Authors: Nakajima Kensuke , Okamoto Shoichi , Okada Takuya
Published: July 2002

Synthesis of thin films of Fe16N2 has been investigated by use of a high-dose nitrogen ion implantation into thin iron films. Nitrogen molecular ions of N+2 were accelerated to 150 keV and implanted into α-iron films with a thickness of 200 nm. As a result of an implantation with the dose of 4.0×1016 (N2/cm2), 35% of the α-Fe was transformed into an iron nitride with a body-centered-tetragonal (bct) structure. The c axis of the bct lattices was oriented perpendicularly to the film plane. It was found that nitrogen implantation into iron films gives rise to both an increase in the spontaneous magnetization and a perpendicular anisotropy. These facts are explained on the basis of the bct nitride formation and the c-axis orientation. Conversion electron Mössbauer spectroscopy was used to study hyperfine structures and magnetic properties of the implanted films. Three different Fe sites corresponding to the bct nitride were recognized in a spectrum of the implanted film. The maximum hyperfine field was 372.8 kOe at room temperature which is ascribed to the second-nearest-neighbor Fe sites for the nitrogen atoms. It was deduced that the bct iron nitride has an ordered structure analogous to Fe16N2.