bluuebunny/crossref_metadata_2025 huggingface dataset:
The dependence of direct overwrite characteristics on the magnetization of dc-magnetron-sputtered films (abstract)
Authors: Cheng S-C. N. , Kryder M. H.
Published: July 2002

The magnetization of rare-earth transition-metal (RE-TM) films has been found to play an important role in single-layer film direct overwrite characteristics. In this study, the magnetization of films was varied by changing the compensation temperature and the Curie temperature, independently. Direct overwrite characteristics which were investigated included the minimum and maximum pulse width to erase and to write a certain size domain, the pulse-width margins for erase, and the erasable size of domain. A decrease in the compensation temperature, which leads to an increase in the magnetization at high temperatures, causes the minimum erasure pulse width to increase and the largest erasable domain size to decrease. However, a decrease in the compensation temperature causes the writing pulse width to decrease. The effects of magnetization on the direct overwrite characteristics were further investigated by applying external magnetic fields up to 580 Oe. The minimum pulse width to erase domains was found to increase with an increase of the applied field, which was in the direction to assist domain nucleation. The maximum erasure pulse width decreases rapidly with an increase of the magnetic field. The disappearance of the erasure margin when the gap between the compensation temperature and the Curie temperature increases results from the fact that the minimum erasure pulse width becomes equal to the minimum writing pulse width. In order to have a wide range of erasable domain sizes, while still maintaining a short writing pulse width, it is shown that film compositions must be adjusted to have both a low compensation temperature and a low Curie temperature.
The magnetization process in RE-TM alloys studied using the extraordinary Hall effect (abstract)
Authors: Edwards J. , Hintz M. , Callaby R. , Dahlberg E. Dan
Published: July 2002

The extraordinary Hall effect can be used to monitor the magnetization component perpendicular to the plane of a thin film.1 This technique has been used to monitor the time dependence of the magnetization of a series of RE-TM alloys. At room temperature these samples exhibit relatively square hysteresis loop, i.e., the demagnetization effects are minimal. The data are accumulated in the presence of applied magnetic fields approximately equal to the coercive field. The time dependence of the magnetization can be altered by tuning the applied field by only a few percent. Two simple models have been applied to the magnetization process in these films. The first considers the magnetization process in the films if disorder is dominate; then the relaxation of the magnetization would be quasilogrithmic in time. The second is if disorder does not dominate then one might expect an exponential time dependence to be observed. The data have been analyzed in terms of both of these simple models.
B-H loops modified by superposing ac magnetic fields
Authors: Huang Der-Ray , Li James C. M.
Published: July 2002

The B-H loops of ferromagnetic amorphous alloys can be modified with the apparent coercivity reduced by superposing a suitable ac magnetic field. For as-cast Fe78B13Si9 (Allied 2605S2) with the superposed field, the width of the dc B-H loops could be reduced to a third of the dc value without the ac field. For dc or low-frequency B-H loops, it seems that an ac magnetic field of proper frequency and magnitude can vibrate the domain walls sufficiently so that a small additional field can move them. When the frequency for B-H loop measurement was higher than 10 Hz, the effect of superposing an ac magnetic field appeared to be just the superposition of the two applied fields.
The antiferromagnetic form factor of La2NiO4
Authors: Wang X. L. , Stassis C. , Johnston D. C. , Leung T. C. , Ye J. , Harmon B. N. , Lander G. H. , Schultz A. J. , Loong C.-K. , Honig J. M.
Published: July 2002

Neutron-diffraction techniques have been used to study the antiferromagnetic form factor of a La2NiO4 single crystal at 15 K. The antiferromagnetic form factor was obtained by measuring the integrated intensities of 16 magnetic reflections. A plateau is clearly seen at low Q (up to 3 Å−1) in the experimentally determined form factor, similar to those observed for La2CuO4 and Sr2CuO2Cl2. As in the case of these latter compounds, the fit of the experimental data by a Ni2+ ionic form factor is not satisfactory. The experimental data are compared with a recent spin-polarized band calculation and with a covalency model.
Enhancement of T
c of Bi-Sr-Ca-Cu-O superconductor by rapid heating and cooling in a ballistic compressor
Authors: Duan Q. , Dash J. , Takeo M. , Huang J.
Published: July 2002

Exposure of the Bi-Sr-Ca-Cu-O superconductor to hot, dense argon in a ballistic compressor followed by rapid cooling enhances Tc of the superconductor. Similar increases of about 3 K were found for measurements on both pellets and thin films.
Magnetic transitions in UNiGa
Authors: Havela L. , Sechovsky V. , Jirman L. , de Boer F. R. , Brück E.
Published: July 2002

Magnetization, magnetic susceptibility, and electrical resistivity studies of UNiGa in the single-crystalline form revealed a strong uniaxial anisotropy both in the paramagnetic and in magnetically ordered state below Tc = 38 K. At T=35 K the system undergoes an antiferromagnetic transition, but by applying a field of about 1 T ferromagnetic alignment can be achieved.
Magnetic hysteresis model for magnetic recording including spatial fluctuations of interaction fields
Authors: Ribeiro A. L.
Published: July 2002

For materials with a particulate structure, Néel was the first to point out the importance of statistical fluctuations of the magnetic interaction fields. He has shown how they influence the material behavior and how reptation can be generated. These aspects are not taken into account by some classical hysteresis models, e.g., the Preisach model. A recent paper by Della Torre and Kádár [IEEE Trans. Magn. MAG-23, 2820 (1987)] improved the Preisach model in order to consider the influence of fluctuations. Our paper presents an hysteresis model, based on the superposition of the elementary characteristics of single bistable particles. The interaction field is assumed to have a Gaussian statistic distribution, with a mean value and a standard deviation depending on the macroscopic magnetization. The spatial fluctuations of the field acting on the bistable particles are seen to enhance the mean-field components. Being that the fluctuations are stronger when the material is macroscopically demagnetized, it is expected that minor cycles must lose congruency, which is a property of the classical Preisach model, as Mayergoyz [J. Appl. Phys. 61, 3803 (1985)] has pointed out.
Interlayer magnetic coupling in transition-metal multilayered structures
Authors: Fry J. L. , Ethridge E. C. , Levy P. M. , Wang Y.
Published: July 2002

The magnetic coupling of two layers of Fe through an intervening layer of Cr as a function of the Cr layer thickness has been computed. By including both RKKY and superexchangelike interactions between planes of Fe, and accounting for the surface roughness of the interfaces, the experimentally observed oscillations in the coupling between Fe layers as a function of Cr layer width could be reproduced. The predominance of antiferromagnetic coupling reflects the dominance of superexchange over RKKY exchange and is a consequence of the position of the Fermi level of Cr in a minimum between peaks in the density of states. This condition can be used to explain similar behavior in Co/Ru and to identify other possible transition metal systems for which this behavior may be observed.
Optimization of low-noise media for 100-Mb/in.2 recording with a magnetoresistive head
Authors: Miller M. S. , George P. K. , Madsen T. A. , Simpson E. M. , Walber J. P.
Published: July 2002

Single-layer and multilayer longitudinal media were evaluated for 100-Mb/in.2 recording at a 6-μin. flying height with a magnetoresistive head. It was found that the multilayer media produced transition jitter values that were at least 23% below comparable single-layer results. Timing margins, estimated from the measured jitter and asymmetry data, indicate that single-layer media may prove marginal for this application. Multilayer timing margins were projected to be 40%. Signal-to-noise ratio, resolution, and overwrite comparisons are also made for both types of media. The improvements demonstrated with the multilayer media are attributed to the reduced media noise associated with this type of structure. Increased Cr spacer layer thickness in the multilayer media was found to increase jitter and reduce the D70 density response.
On the magnetism of Au4Ti, Au4V, Au4Cr, Au4Mn, Au8TiCr, and Au8VMn
Authors: Yahagi H. , Yano K. , Itoga H. , Chaki A. , Ukai T. , Mori N.
Published: July 2002

It is pointed out that the energy decrease due to the magnetization of the spin is large in the ferromagnetic substances and that the energy decrease due to the formation of the antiferromagnetic disposition is large in the antiferromagnetic substances. The calculation is made for the energy decrease in the ferromagnetic state as a function of the number of d electrons. This calculation explains the paramagnetic Au4Ti, the weak ferromagnetic Au4V, and the ferromagnetic Au4Mn. The energy decrease for Au5 and Au3V2 is also calculated, and it is shown that ferromagnetism appears in the vicinity of Au4V. The calculation is made for the energy decrease in the antiferromagnetic state as a function of the number of d electrons. This calculation suggests that antiferromagnetism appears in Au4Cr. The anisotropy energies for Au4V and Au4Mn are calculated to be in agreement with the experimental result. It is shown that the magnetic moment in Au4Cr should be parallel to [001] direction. Finally, the magnetism of Au8TiCr and Au8VMn is discussed, with results consistent with experiments.
Ferromagnetism under pressure in CePt, CePd, and Ce3Pd5 (abstract)
Authors: Huber J. G.
Published: July 2002

The intermetallic compound CePt orders ferromagnetically at a Curie temperature (θC) of 5.8 K.1 The earliest measurement of CePt to identify its ferromagnetism and to determine its θC was actually that of magnetization under pressure up to 7 kbar. Reference has been made to the results,1,2 but the data are only now being presented. Additionally, we are reporting measurement on CePt of low-field ac susceptibility (χac) under pressure up to 16 kbar. Magnetization and χac data both yield plots of θC versus pressure (p); and while measurement of χac gives only a qualitative indication of the pressure dependence of the saturation moment, it is by far the easier experiment. We find d(ln θC)/dp = 1.3 × 10−2 kbar−1, in accord with other studies.3,4 Kappler et al. have reported that CePd (isostructural with CePt) and Ce3Pd5 also order ferromagnetically at 6.5 and 1.5 K, respectively.5 Our measurements of χac under pressure show that d(ln θC)/dp equals 0.6×10−2 kbar−1 for CePd but that it is essentially zero for Ce3Pd5.
Electrical resistivity of antiferromagnetic and paramagnetic Cr-Mo-Si alloys
Authors: Smit P. , Alberts H. L.
Published: July 2002

Resistivity measurements on antiferromagnetic and paramagnetic Cr-Mo-Si alloys are reported in the temperature range 4–450 K. The magnetic contribution to the resistivity of the antiferromagnetic alloys was obtained by using the results of alloys that remained paramagnetic at all temperatures as a model. These results are consistent with existing theories by McWhan and Rice [Phys. Rev. Lett. 19, 846 (1967)] and Jones [in Encyclopedia of Physics, edited by S. Flügge (Springer, Berlin, 1956), Vol. 19, p. 227].
Prediction of Shapiro steps in the dc voltage across a magnetic domain wall traversed by a dc current and exposed to high-frequency magnetic fields
Authors: Berger L.
Published: July 2002

In metallic ferromagnets, a current of electrons traversing a domain wall exerts a torque on the wall spins through the s-d exchange interaction. This torque may induce a precession of the wall spins around the easy axis. In turn, the wall precession at a rate ω0 generates a dc voltage δV across the wall, given by the formula eδV = ℏω0 similar to the Josephson equation for superconducting junctions. In the present theoretical work, a high-frequency (hf), in-plane, hard-axis magnetic field is also applied. For a certain range of values of the dc current density, the rate of wall precession is synchronous with that of the hf drive field. In other ranges, precession is asynchronous, or there is no precession. As a result, the voltage δV has a stepwise dependence on the current density. This is the analog of the well-known Shapiro steps for the superconducting Josephson voltage.
Anisotropy of the Faraday rotation of CoFe2O4 single crystals
Authors: Ostorero J. , Guillot M. , Leblanc M. , Rouet D.
Published: July 2002

Faraday rotation measurements, performed at 1150 nm wavelength on single-crystal platelets of CoFe2O4 with two different crystallographic orientations [100] and [111], are presented under magnetic fields up to 20 kOe, in the 5–580-K temperature range. A high anisotropy of magnetic origin is observed particularly at low temperatures (T<230 K) where saturation cannot be obtained along the [111] direction in a 20-kOe magnetic field. The high Faraday rotation measured at 1150 nm and 300 K (−5700°/cm) is about twice that of Bi-substituted garnet films at this wavelength. The results are interpreted on the basis of contributions proportional to the magnetization of each magnetic sublattice.
Magnetic and magneto-optic properties of bismuth-substituted thulium iron-garnet films
Authors: Hansen P. , Tolksdorf W.
Published: July 2002

The saturation magnetization Ms, the uniaxial anisotropy constant Ku, and the Faraday rotation θF of epitaxially grown garnet films of composition Tm3−xBixFe5−yGayO12 were investigated for 0≤x≤0.83 and 0≤y≤1.57. The Bi content of the films was controlled by the melt composition and supercooling. The low-temperature saturation magnetization is determined by the antiparallel alignment of the Tm sublattice magnetization, and the increase of the Curie temperature is controlled by the bismuth content. No compensation temperature was observed due to the small Tm moment, in agreement with literature data. The uniaxial behavior of these films is associated with the stress-induced anisotropy increasing linearly with the lattice mismatch. The growth-induced part turned out to be negligible. The strong enhancement of the Faraday rotation compares well with that observed for other Bi-substituted iron garnets, yielding a contribution of θF = −1.9 × 106 deg/m at λ=633 nm and T=295 K. The temperature dependence of Ms and θF (λ=633 nm) was measured in the temperature range 4.2 K≤T≤TC. It agrees well with the calculated temperature variation based on the molecular-field theory.
Some remarks on Preisach modeling
Authors: Pescetti D.
Published: July 2002

Two distinct contributions are given in this paper: (i) The effects of variables’ transformations on the existence of the generalized Preisach model (GPM) are considered. By GPM we mean a generalization of the Preisach model which allows the description of both the irreversible and reversible components of the magnetization. We find that the toroidal transformation preserves the existence of the GPM. Moreover, we find that the transformations x′=y, y′=x, and x′=x+ky, y′=y do not preserve, in general, the existence of the GPM. The proofs are based on the Mayergoyz’s theorem. (ii) The connection between hysteresis and memory in Preisach modeling is investigated, and an algorithm which allows reconstruction of a significant part of the input’s history by a set of measurements made on the actual state of an irreversible Rayleigh hysteresis transducer is given.
Read/write simulation of Ba-ferrite particulate media
Authors: Tsutsumi M. , Kugiya F. , Kodama N. , Suzuki M. , Koizumi M. , Akagi F. , Speliotis D. E.
Published: July 2002

A M-H loop model for Ba-ferrite particulate media is introduced where a modified Stoner–Wohlfarth model is used as a magnetization reversal model. It is confirmed that this model can be applied for read/write simulation of Ba ferrite. Using this model, the read/write performance of Ba-ferrite media is investigated and compared with that of acicular particulate media. The results indicate that: (i) For high-density recording, longitudinally oriented Ba ferrite is superior to acicular particulate media because of its high coercive squareness S*; (ii) to improve read/write performance of the Ba-ferrite in use today, narrowing of anisotropy field distribution is effective; and (iii) perpendicularly oriented Ba ferrite has good read/write performance only at narrow head-medium spacings.
Effect of microstructure on coercivity of c-axis in-plane-oriented Co/Cr multilayered films
Authors: Wang D. , Sellmyer D. J. , Hadjipanayis G. C.
Published: July 2002

The effect of the insertion of nonmagnetic Cr planes on coercivities of thin Co films has been studied in Co/Cr multilayered films. The in-plane coercivity Hc∥ can be as high as 1800 Oe and can be adjusted easily, ranging from 650 to 1800 Oe. The large Hc∥ is related to the Co(110) in-plane orientation which is induced by a Cr(100) in-plane-oriented underlayer. In addition, it appears that a decreasing saturation magnetization Ms, a decreasing average structural coherence length D in the direction perpendicular to the film, and a narrowing distribution of D are correlated to the increasing in Hc∥. The effects of texture, Cr interlayers, D and its distribution, and the Cr underlayer on the magnetic properties are discussed.
Interaction of metal particles for magnetic recording with media formulation components
Authors: Jung C. , Raghavan S. , Mathur M. C. A.
Published: July 2002

The interaction of commercially available, iron-based magnetic particles with certain particulate media formulation components has been investigated using the technique of flow microcalorimetry. The heat of wetting of these particles by solvents has been found to be a function of the solvent dipole moment and particle coercivity and surface area. Di(2-ethyl hexyl) phosphoric acid, a model dispersant, appears to interact chemically with a particle of high coercivity. Solvent basicity influences the heat and extent of interaction of the dispersant.      
Effect of transverse stress on the critical current of bronze-process and internal-tin Nb3Sn
Authors: Ekin J. W. , Bray S. L. , Bahn W. L.
Published: July 2002

The effect of transverse stress on the critical current of two substantially different Nb3Sn superconductors, a bronze-process conductor and an internal-tin conductor, has been measured. Photomicrographs of the two conductors reveal a basic difference in their microstructure. The bronze-process conductor exhibits columnar grains that are radially oriented within the Nb3Sn filaments, while the grains of the internal-tin conductor are more equiaxed and randomly oriented. The radial orientation of the bronze-process grains defines an anisotropy between the axial and transverse directions that might account for the greater sensitivity of the critical current to transverse stress reported previously. The effect of transverse stress measured on the internal-tin conductor, however, is comparable to that of the bronze-process conductor. Thus, these data indicate that the transverse stress effect is not highly dependent on either grain morphology or fabrication process. From an engineering standpoint the similarity of the transverse stress effect for these two types of Nb3Sn superconductors represents an important simplification for setting first-order quantitative limits on the mechanical design of large superconducting magnets.
A simple method of interface-state reduction in metal-nitride-oxide-semiconductor structures
Authors: Sheu Yea-Dean
Published: July 2002

A method for reducing the interface-state density in polysilicon gate metal-nitride-oxide-semiconductor (MNOS) capacitors is reported. The method involves deposition of a sacrificial blanket aluminum layer on top of a chemical-vapor-deposition (CVD) oxide over MNOS capacitors. The entire stack was then annealed at 450 °C in nitrogen and then the metal and CVD oxide were stripped away. The interface state density was reduced from 1011 to 1010 cm−2 eV−1 after this anneal. It is believed that Al reacts with trace water in the CVD oxide and generates active hydrogen. The hydrogen diffuses to the Si/SiO2 interface and passivates the interface states.
InAs quantum-well-base InAs/GaSb hot-electron transistors
Authors: Taira K. , Funato K. , Nakamura F. , Kawai H.
Published: July 2002

Narrow InAs-base GaSb/InAs hot-electron transistors have been grown by low-pressure metalorganic chemical vapor deposition. The InAs bases are 30, 50, and 100 Å thick. The ground-state electron subband energy E0 is determined from values of collector current. For thinner wells, values of E0 are well explained by a simple effective mass calculation. Here, a mixing of InAs conduction-band states with GaSb valence-band states is neglected because of symmetry mismatch. The effect of nonparabolicity of the InAs conduction band is taken into account.
Measurement and detail analysis of gain on balmer-alpha line of hydrogen-like carbon in wall-confined CO2 laser-produced plasmas
Authors: Miura E. , Kitagawa Y. , Daido H. , Sawai K. , Matsuo K. , Nishihara K. , Kato Y. , Nakai S.
Published: July 2002

A 1-cm-long hollow parylene (C8H8) cylinder-type target was irradiated with a long pulse CO2 laser (400 J/50 ns) to produce a confined soft x-ray laser source. The amplification of the Balmer-alpha line (182.2 Å) of the H-like carbon was observed using two different gain determination methods. The time- and space-integrated gain coefficient up to 2.2(+0.6/−1.1)cm−1 was obtained from the ratio of the axial to transverse line intensity. By using the C8H7Cl target, the gain coefficient increased up to 2.8(+0.6/−1.1)cm−1, inferring the radiative cooling effect. The experimental results agreed with the simulation results within a factor of 5. By reducing the cylinder mass by a factor of 20, the simulation result gave the long gain duration up to 20 ns in FWHM and large gain region up to 1.3 mm in radius.
Account of ionization mechanism in low-pressure Ar-Hg discharges
Authors: Lin Tingsheng , Goto Toshio , Arai Toshihiko , Murayama Seiichi
Published: July 2002

An attempt was made to clarify the ionization mechanism and to interpret the characteristics of the measured Hg+ ion density in low-pressure Ar-Hg discharge for the mercury lamp using the measured Hg6p3P0,1,2 population density, electron density, and electron temperature. The stepwise ionization caused by collisions between Hg metastable atoms and electrons and that between Hg excited atoms were concluded to be the most important ionization processes. As the extinction processes of Hg+ ions, the ambipolar diffusion and recombination of Hg atoms, Hg+ ions and electrons were taken into account. The measured dependencies of the Hg+ ion density on bath temperature was interpreted well with the model including the above processes.
The effect of reduced growth area by substrate patterning on misfit accommodation in molecular beam epitaxially grown InxGa1−xAs/GaAs
Authors: Beam III E. A. , Kao Y. C.
Published: July 2002

The effect of reduced growth area on the misfit accommodations of InxGa1−xAs/GaAs grown by molecular beam epitaxy has been studied with cross-sectional transmission electron microscopy (XTEM). Composition grading techniques as well as strained-layer superlattices were used for InxGa1−xAs compositions up to x=0.53 and growth areas which ranged from approximately 10 cm2 (blanket areas) to 4 μm2 squares. Results indicate that the use of step-composition grading and linear-composition grading are particularly effective when combined with reduced growth areas up to 30×30 μm and InxGa1−xAs compositions up to x=0.25. Dislocations which are generated for misfit accommodation during growth are effectively driven to the edges of the patterned growth areas with considerably fewer interactions than dislocations nucleated in blanket areas. XTEM samples prepared from blanket areas were generally found to contain randomly distributed threading dislocation-free regions on the order of 20–30 μm in width bounded by high density dislocation pile-ups. Higher InxGa1−xAs compositions resulted in large densities of threading dislocations with Burgers vectors perpendicular to the growth direction, particularly for step-composition graded layers. We attribute this behavior to roughening of the growth interface.
Characterization of the DX centers in AlGaAs:Si by admittance spectroscopy
Authors: Dueñas S. , Izpura I. , Arias J. , Enríquez L. , Barbolla J.
Published: July 2002

In this work we have applied the admittance spectroscopy technique to characterize the DX centers in AlxGa1−xAs alloys doped with silicon. Our experimental results reveal the existence of two DX centers related to silicon in AlxGa1−xAs alloys, named DX-I and DX-II centers, with thermal activation energies of 0.370 and 0.415 eV, respectively. These values are lower than those obtained by other authors using capacitance techniques. To explain this disagreement it should be noticed that capacitance techniques can be affected by the nonexponential behavior of the thermal emission transients of the DX centers in AlxGa1−xAs alloys.
Study of the ablation threshold of polyimide (Kapton H) utilizing double-pulsed XeCl excimer laser radiation
Authors: Mihailov S. , Duley W.
Published: July 2002

Changes in the ablation threshold of polyimide accompanying two rapid sequential pulses of 308-nm-XeCl excimer less radiation have been studied. Assuming that subthreshold radiation couples into the polymer thermally, the heat conduction equation for the system is solved in order to estimate resulting surface and subsurface temperatures. A ‘‘threshold’’ temperature for etching is suggested below which no surface modification is observed but where thermal degradation of the surface may occur. For pairs of pulses whose combined fluence is near the single pulse fluence threshold for etching, separation of the pulses in time resulted in the initiation, cessation, and reinitiation of soot deposition on the polymer surface. It is suggested that this temporally dependent preferential etching is caused by the formation of an atmosphere above the target that is rich in molecules such as CO, CN, C2H2, and C2. This atmosphere then undergoes dissociation through multiphoton and photopyrolytic processes upon receipt of the second pulse resulting in the deposition of a carbonaceous residue on the surface. The residue then acts as sites for the initiation of conical structures.
Monte Carlo simulation of laser induced chemical vapor deposition
Authors: Zeiri Yehuda , Atzmony Uzi , Bloch Joseph , Lucchese Robert R.
Published: July 2002

We have used a Monte Carlo method to simulate laser induced chemical vapor deposition processes, assuming that the laser beam photodissociates the parent organometallic molecules in the gas phase. Metal containing fragments formed during the organometallic decomposition may diffuse to the substrate and are assumed to be instantly adsorbed on the surface at the point they hit. The effects of the total gas pressure in the system, the nature of the buffer gas, and the intensity of the laser beam on the shape of the deposited layers and on the deposition kinetics were studied. This model is also applicable to the simulation of electron beam chemical vapor deposition when low pressures are considered.
Electromagnetically generated acoustic determination of delamination
Authors: Imaino W.
Published: July 2002

Previous work has demonstrated a technique for acoustically detecting localized delamination of metallized patterns on insulating substrates [W. Imaino, L. Crawforth, A. C. Munce, and A. Julaiana, in Proceedings of the IEEE Ultrasonics Symposium, edited by B. R. McAvoy (IEEE, New York, 1986), p. 1065]. Employing a high-spatial-resolution permeable electromagnetic acoustic transducer to preferentially excite the metallization, the acoustic coupling between the metal foil and substrate may be probed. Scanning, then, provides a map of delaminations. To extend and generalize these results, the detailed generation mechanism and acoustic response of the substrate has been studied. A computer program developed previously [W. Imaino, J. Acoust. Soc. Am. Suppl. 1 80, S7 (1986)] was used to model the acoustic source. In this investigation, a finite-element calculation is used to provide a more detailed description of the acoustic behavior of the delaminated plate. The effects of source size relative to defect dimensions and acoustic properties of the substrate have been studied. The determination of the localized coupling is complicated by structural resonances of the substrate, which make single frequency measurements unfavorable. However, the analysis shows that the spectral acoustic behavior provides an indication of metallization to substrate coupling. A signal-processing algorithm based on this analysis has been formulated and will be described.
Graded band-gap ohmic contacts to n- and p-type InP
Authors: Dutta R. , Shahid M. A. , Sakach P. J.
Published: July 2002

W-Sb and W-In-Sb thin films were deposited by co-sputtering independent targets on n- and p-type InP wafers. The composition of the films was ascertained by monitoring the sputtering rate of each target. Au was sputtered on the back side and the sandwiched wafers were annealed in a quartz furnace to up to 400 °C. The conduction and diffusion characteristics of the films were studied as a function of the annealing temperatures. The Auger depth profile shows an outdiffusion of In to the surface of the WInSb film. P from the substrate out-diffuses into the W matrix while Sb forms an interfacial In-Sb phase. The x ray diffractogram of samples annealed to 400 °C shows the transition of as-deposited amorphous W into the crystalline state and formation of In-Sb related interfacial phase. The electrical characteristics are ohmic for as-deposited films on n-type material, whereas it becomes ohmic below 400 °C for p-type substrate. The 1000-Å-thick WInSb film when annealed to 400 °C showed a sheet resistance of ∼12 ohm/⧠ and a contact resistance in the 10−6 Ω cm2 range.
Effect of substrate temperature on deposition rate of rf plasma-deposited hydrogenated amorphous silicon thin films
Authors: Andújar J. L. , Bertran E. , Canillas A. , Campmany J. , Morenza J. L.
Published: July 2002

We present a study about the influence of substrate temperature on deposition rate of hydrogenated amorphous silicon thin films prepared by rf glow discharge decomposition of pure silane gas in a capacitively coupled plasma reactor. Two different behaviors are observed depending on deposition pressure conditions. At high pressure (30 Pa) the influence of substrate temperature on deposition rate is mainly through a modification of gas density, in such a way that the substrate temperature of deposition rate is similar to pressure dependence at constant temperature. On the contrary, at low pressure (3 Pa), a gas density effect cannot account for the observed increase of deposition rate as substrate temperature rises above 450 K with an activation energy of 1.1 kcal/mole. In accordance with laser-induced fluorescence measurements reported in the literature, this rise has been ascribed to an increase of secondary electron emission from the growing film surface as a result of molecular hydrogen desorption.
Comment on ‘‘Magnetization reversal in nucleation controlled magnets. I. Theory; and II. Effect of grain size and size distribution on intrinsic coercivity of Fe-Nd-B magnets’’
Authors: Weizhong Tang
Published: July 2002

In discussing a previous statistical model for the problem of coercivity of nucleation controlled permanent magnets [J. Appl. Phys. 64, 6406 and 6416 (1988)], its validity to the problem of Fe-Nd-B type magnets is questioned.
Power extraction studies in a gasdynamic laser
Authors: Chakravarty Purandar , Reddy N. M. , Reddy K. P. J.
Published: July 2002

A generalized two-dimensional flow-radiation coupled model to extract power from a gasdynamic laser is proposed. The model is used for the study of power extraction from a 9.4-μm CO2 downstream-mixing gasdynamic laser, where a cold CO2+H2 stream is mixed with a vibrationally excited N2 stream at the nozzle exits. This model is developed by coupling radiation with the two-dimensional, unsteady, laminar and viscous flow modeling needed for such systems. The analysis showed that the steady-state value of 9.4-μm intensity as high as 5×107 W/m2 can be obtained from the system studied. The role of H2 relaxant in the power extraction process has also been investigated.
Characteristics of indium-doped GaAs layers grown by liquid phase epitaxy with indium content in the range (0.3–7)×1019 cm−3
Authors: Dhar S. , Mallik Kanad , Nag B. R.
Published: July 2002

GaAs layers grown by liquid phase epitaxy and doped with indium in the concentration range of (0.3–7)×1019 cm−3 are studied by etch pit density (EPD), Hall, capacitance-voltage and current-voltage measurement techniques. Layers doped with indium in the range (0.5–5)×1019 cm−3 show about 10%–15% increase in mobility and a corresponding decrease in the background impurity concentrations. In the same range, EPD is found to fall below 102 cm−2. Above 5×1019 cm−3 In doping, mobility decreases drastically, and the dislocation density measured by EPD count goes above 103 cm−2. This result, together with a comparison of free carrier concentrations measured by Hall and capacitance-voltage techniques indicate that dislocation-related scatterings are effective in lowering the mobility for high indium content layers. Reverse current-voltage characteristics of gold Schottky diodes fabricated on the layers do not show any dependence of breakdown voltages on In doping. Simple theoretical calculations give evidence to the fact that the reverse breakdown process in the diodes are, in fact, controlled by the normal avalanching mechanisms dependent on the electrically active background impurities.
In-diffusing divacancies as sources of acceptors in thermally annealed GaAs
Authors: Morrow Richard A.
Published: July 2002

We suggest that annealing GaAs samples at high temperatures encourages the relatively rapid in-diffusion of divacancies which either are acceptors themselves or quickly dissociate into acceptors. Rapid quenching to room temperature freezes in these defects and results in altered electrical properties for the samples. A simple model, fit to some sparse existing data, yields a 950 °C estimate of (3–5)×10−7 cm2/s for the diffusivity of the divacancy. When combined with other existing data, obtained at lower temperatures, on the in-diffusion of a defect with a level at Ec-0.23 eV and tentatively identified as the divacancy, we find the diffusivity of the divacancy to be given by (3×10−3)exp(−0.94 eV/kT) cm2/s over the temperature range 250–950 °C.
Epitaxial YBa2Cu3O7−y thin-film growth on NdGaO3 substrate by laser ablation
Authors: Mukaida Masashi , Miyazawa Shintaro , Sasaura Masahiro , Yonezawa Hiroki
Published: July 2002

As-grown superconducting YBa2Cu3O7−y thin films with various thicknesses were successfully grown on lattice-matched NdGaO3 substrates by ArF laser ablation deposition. An as-grown 2000-Å-thick film has a zero-resistance temperature (Tc) at 90 K and a 170-Å-thick film has a Tc at 88 K. The existence of a thin interfacial diffusion layer between a 170-Å-thick film and the substrate was observed by Auger electron spectroscopy. Rutherford backscattering spectroscopy suggest that as-grown YBa2Cu3O7−y films on NdGaO3 substrates are high-quality crystals. It is demonstrated that the NdGaO3 has considerable potential as an electronic substrate material by less interfacial diffusion layer and good crystallinity of grown thin films.
Formation of iodinated nickel phthalocyanine thin films by double-source evaporation of iodine and nickel phthalocyanine
Authors: Yudasaka M. , Hironaga K. , Nakanishi K.
Published: July 2002

Thin films of iodinated nickel phthalocyanine were made by double-source evaporation of nickel phthalocyanine and iodine in vacuum. They were obtained by keeping the substrate temperature at about −90 °C. The c axes of crystallites composing the film were almost perpendicular to the quartz glass substrate. The conductivities of the films were 0.1–1 S/cm at room temperature which decreased slightly as the measuring temperature was lowered to −170 °C.
The operation and characteristics of diphthalocyanine field effect transistors
Authors: Clarisse C. , Riou M.-T.
Published: July 2002

Field effect transistors (FETs) have been fabricated with metal phthalocyanines and rare earth diphthalocyanines. The influence of the metallic ion in mono- and diphthalocyanines and the conditions of FET fabrication on electrical characteristics has been determined for devices tested in ambient atmosphere. Aging under various conditions has identified the role of oxygen on the device behavior. Unlike conventional inorganic FETs, these diphthalocyanine based devices work through the modulation of an accumulation layer formed by majority carriers.
Low-temperature neutron irradiation of magnetron-sputtered NbN films
Authors: Herzog R. , Weber H. W. , Kampwirth R. T. , Gray K. E. , Gerstenberg H.
Published: July 2002

Four types of differently prepared NbN films were irradiated at 4.6 K with fast neutrons to a fluence of 5.3 × 1022 m−2 (E≳0.1 MeV). The critical current densities Jc were measured in magnetic fields up to 23 T prior to irradiation, following low-temperature irradiation, and again after an annealing cycle to room temperature. In all films, Jc was found to be completely unchanged by the radiation and annealing treatments in fields up to 15 T, but to increase at higher magnetic fields. At the same time, the upper critical fields Bc2 increased by about 0.5 T (∼2%). Replotting Jc versus reduced field B/Bc2 leads to identical field dependencies also in the high-field range. Hence, the observed increase of Jc is equantitatively explained as a Bc2 effect.
Thermally stimulated current of Li+ ion-implanted amorphous selenium
Authors: Kang T. W. , Tong C. , Eom G. S. , Leem J. Y. , Kim T. W.
Published: July 2002

A thermally stimulated current (TSC) technique is applied to examine the activation energy, capture cross sections, escape frequency, and trap polarity in amorphous Se (a-Se) implanted with low energy (<20 keV) Li+ ions. TSC glow curves for Li+ -ion-implanted a-Se show two peaks near 230 and 330 K. The value of δ/ω is 0.46 for 230 K, which means that the thermally stimulated currents are due to the first-order kinetics. The trap activation energy levels obtained by peak shape method and various heating rate methods are distributed from 0.22 to 0.33 eV for the 230-K peak and to 1.42 eV for the 330-K peak. The values of the capture cross section and the escape frequencies are 2.75×10−19 cm2 and 5.5×105 s−1 for the 230-K peak, and 5.75×10−20 cm2 and 6.43×105 s−1 for the 330-K peak, respectively. It is found that the trapped charge carriers are mainly holes in Li+ ion-implanted a-Se.
Optoelectronic properties of hydrogenated amorphous silicon films deposited under negative substrate bias
Authors: Roca i Cabarrocas P. , Morin P. , Chu V. , Conde J. P. , Liu J. Z. , Park H. R. , Wagner S.
Published: July 2002

We present a detailed study of the effects of ion bombardment on the optoelectronic properties of a-Si:H films. Two series of samples were deposited from a rf glow discharge at 30 and 100 mTorr of silane pressure, corresponding to two different deposition conditions. The energy of the ions impinging on the substrate was increased by applying a negative dc bias in steps of 25 V to the substrate holder. The increase of the substrate bias from 0 to −100 V had no effect on the deposition rate of a-Si:H at 30 mTorr, whereas a factor of 2 decrease was observed for deposition at 100 mTorr. The density of states of the a-Si:H films, determined by photothermal deflection spectroscopy and by the constant-photocurrent method, decreased as the substrate bias was increased up to −50 V, especially for the series deposited at 100 mTorr. At the same time the valence-band tail became sharper. These observations are consistent with the improvement of the electron drift-mobility deep-trapping-lifetime (μdτd)e product, determined by time-of-flight, and of the hole-mobility recombination-lifetime (μτr)h product determined from the voltage dependence of the photocurrent collection efficiency. For both series of samples, the films with the best electronic properties were obtained at a negative substrate bias of 50 V. No correlation was found between the substrate bias and the light-induced degradation behavior of these films. The saturated density of light-induced defects shows a direct correlation with the optical gap.
Interactions between arsenic and boron implanted in silicon during annealing
Authors: Yokota Katsuhiro , Ochi Masatoshi , Hirao Takashi , Horino Yuuji , Satho Mamoru , Ando Yasuo , Matsuda Kouji
Published: July 2002

Arsenic ions (As+) and Boron ions (B+) were implanted into silicon (Si) at energies such that their respective projected ranges differ. In the implanted Si, the overlapping population of implanted As and B atoms occurred in the region in Si almost midway between their projected ranges near the surfaces after annealing. The only region in Si with As atoms concentration more than three times as large as the B atom concentration became n type.
Escape time from a biased asymmetric double quantum well
Authors: Pandey Lakshmi N. , George Thomas F.
Published: July 2002

The escape time from the quasibound states of an asymmetrical structure consisting of a narrow well and a wide well separated by a relatively thick barrier under bias has been calculated. As expected, a monotonic decrease in the escape time from the ground state of the wide well as a function of applied voltage has been found. However, the variation of the escape times from the ground state of the narrow well and the first-excited state of the wide well versus applied voltage form a minimum at a common point. This is the signature of resonant tunneling when these two states almost coincide.
Efficient pulsed CO2 laser calculations
Authors: Stone David H. , Honey David A.
Published: July 2002

A computationally efficient scheme for generating pumping rates was developed for use with a pulsed CO2 laser model. A steady-state solution of the Boltzmann electron transport equation generates the rates. Vibrational temperatures for the CO2 and N2 populations are determined by iterating the Boltzmann solver with the rate equation model. Rapid convergence and coarse grids allow quick calculations of pulse shape, peak power, and total energy. Results compare well with a fully time-dependent Boltzmann solver.
Novel in situ pattern etching of GaAs by electron-beam-stimulated oxidation and subsequent Cl2 gas etching
Authors: Sugimoto Y. , Taneya M. , Akita K. , Kawanishi H.
Published: July 2002

A new method for in situ pattern etching of GaAs was demonstrated by using an electron-beam (EB)-stimulated-oxidized surface layer as a mask for subsequent Cl2 gas etching. This process is based on the experimental results that GaAs oxide prepared by EB irradiation under an oxygen atmosphere is resistive to Cl2 gas etching, whereas GaAs oxide without an EB can be easily etched. The resistance of the oxide mask against Cl2 gas etching varies depending on the EB dose with which the oxide of GaAs is formed. A fine pattern, such as a 1 μm linewidth in a 5-μm pitch line-and-space, is obtained.
Noncontact minority-carrier lifetime measurement for magnetic field applied Czochralski silicon crystals
Authors: Kirino Y. , Shimura F.
Published: July 2002

Minority-carrier recombination lifetime has been measured with a noncontact laser/microwave method for magnetic field applied Czochralski silicon crystals in the temperature range from 20 to 250 °C. The lifetime behavior in both as-grown and heat treated silicon crystals strongly depends on the thermal history of the samples. It is shown that the lifetime measurement is very sensitive to grown-in and thermally induced defects which cannot be detected by conventional infrared absorption spectroscopy or transmission electron microscopy.
Photogenerated carrier recombination time in bulk ZnSe
Authors: Milward J. R. , Ji W. , Kar A. K. , Pidgeon C. R. , Wherrett B. S.
Published: July 2002

We have measured the free-carrier recombination time in polycrystalline bulk ZnSe to be in the range 7–14 ns at room temperature. We used an excite and probe technique with near-band-edge nanosecond laser pulses to measure the decay of induced free-carrier absorption. We estimate the free-carrier-pair absorption cross section to be in the range (3–6)×10−17 cm2.
Strain effects in InSb p+/n diodes and metal-insulator-semiconductor devices
Authors: Weiguo Sun
Published: July 2002

An InSb metal-insulator-semiconductor device has been used to investigate the influence of external strain on the shift of the I-V characteristics of an InSb diode. Measured flatband voltage change of C-V characteristics and calculated gate voltage increment owing to stresses have been compared. A simple estimate of external strain of the beam deflection was described. The relationships between external strain and short current, dynamic resistance and open circuit voltage have been shown. A brief discussion of effects in InSb I-V characteristics is given.
Anomalous magnetization vibration in Co-based amorphous strip films at high frequency
Authors: Hamakawa Yosihiro , Yuitoo Isamu , Sasaki Shinobu , Shiiki Kazuo
Published: July 2002

Dynamic response behavior of magnetization within the frequency of 1–20 MHz in Co-based amorphous strip films is observed with a scanning Kerr microscope. When an ac current is applied to the conductor under a strip, immovable and movable magnetic regions appear alternately from the 180° walls to the hexagonal domains. The number of these regions increases by one each time the frequency is increased by an integer times the basic frequency. Moreover, when the magnetic anisotropy and strip-width become large, the number of magnetization immovable regions increases. The 180° walls seem to behave like strings. Standing waves occur on them and this affects the magnetization changes in the hexagonal domains.
WNx Schottky diodes on plasma treated GaAs
Authors: Paccagnella A. , Callegari A. , Carnera A. , Gasser M. , Latta E. , Murakami M. , Norcott M.
Published: July 2002

The influence of the GaAs surface condition on the properties and thermal stability of WNx Schottky diodes on GaAs has been studied by performing in situ H2 and N2 plasma treatments just before the WNx sputter deposition. The WNx/GaAs contacts have been investigated by x-ray photoelectron spectroscopy, Rutherford backscattering, nuclear reaction analysis, secondary ion-mass spectroscopy, x-ray diffraction, and transmission electron microscope and correlated to electrical current-voltage and capacitance-voltage measurements. A strong correlation was found between the diode properties and the surface conditions, both for the as-deposited samples and for samples annealed in the range 700–850 °C. Poor rectifying properties were obtained for the plasma-cleaned diodes due to the cumulative effects of plasma cleaning and sputter deposition. After annealing, improved characteristics were generally found. The highest Schottky barrier height values φI-V=0.76 V, which were found for the H2 plasma treated diodes annealed at 800 °C, were almost independent of the WNx composition and sputtering conditions. The H2 treated samples also showed the smoothest WNx/GaAs interface. HCl cleaned and N2 treated surface also showed high-barrier height and small interfacial reactions after high-temperature annealing.