bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopants effects on the interfacial reaction between Co and strained Si0.8Ge0.2 layers
Authors: Cytermann C. , Holzman E. , Brener R. , Fastow M. , Eizenberg M. , Glück M. , Kibbel H. , König U.
Published: July 2002

Interfacial reactions of cobalt with differently doped Si0.8Ge0.2 layers epitaxially grown on silicon, during furnace annealing up to 600 °C, were compared. Undoped and highly boron- or antimony-doped Si0.8Ge0.2 strained layers were used for this study. The analytical tools employed were Auger electron spectroscopy, secondary ion mass spectroscopy, x-ray diffraction, and transmission electron microscopy. Both dopants accumulate at the surface as a result of the interfacial reaction with Co but boron also remains trapped between the reacted Co monosilicide region and a thin Co-rich near-surface layer. In addition, the boron-doped sample exhibits a large accumulation of Ge at the interface between the unreacted SiGe and the reacted monosilicide. The latter effect is related to the loss of Ge from the unreacted SiGe layers observed after high-temperature annealing, the B-doped SiGe epilayer undergoing the largest loss at 600 °C, while the Sb-doped epilayer was only slightly affected.
Optical properties of the ZnSe1−xTex epilayers grown by molecular beam epitaxy
Authors: Yang C. S. , Hong D. Y. , Lin C. Y. , Chou W. C. , Ro C. S. , Uen W. Y. , Lan W. H. , Tu S. L.
Published: July 2002

ZnSe 1− x Te x epilayers were grown on a GaAs (001) substrate with 0°, 3°, 10°, and 15° tilts toward [110] by molecular beam epitaxy. The energy gap was found to increase with the substrate tilt angle. In addition, a Te-bound exciton and an exciton bound to the Te cluster in the photoluminescence spectra have been identified. The threshold temperature for the observation of the Te-bound exciton in the photoluminescence spectrum of ZnSe1−xTex epilayers was found to increase with the Te concentration.
High performance Sm2+δ Fe15Ga2C2 permanent magnets made by melt spinning and hot pressing
Authors: van Lier J. , Kubis M. , Grünberger W. , Schultz L. , Kronmüller H.
Published: July 2002

Hot pressing was applied to produce high performance permanent magnets from melt-spun Sm2+δ Fe15Ga2C2 ribbons. The isotropic magnets show densities up to 7.8 g/cm3, coercivities μ0JHC up to 2.01 T (15.9 kA/cm) and energy products (BH)max up to 60.3 kJ/m3 (7.58 MGOe). No texture could be observed after hot deformation at 800 °C.
Investigation of the properties of plasma-enhanced chemical vapor deposited silicon nitride and its effect on silicon surface passivation
Authors: Cai L. , Rohatgi A. , Han S. , May G. , Zou M.
Published: July 2002

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are used for a variety of applications in integrated circuit and solar cell industries, such as surface passivation and insulation. The objective of this article is to investigate and understand the impact of the PECVD deposition parameters on the silicon surface passivation and establish the correlation between the properties of the silicon nitride and the ensuing silicon surface recombination velocity. All the films were annealed at 350 °C for 20 min in a rapid thermal annealer after the deposition. It is shown that bonded hydrogen and positive charge in the annealed PECVD silicon nitride films have the opposite effect on the surface passivation. The surface recombination velocity decreases with the increase in the positive charge density and the decrease in the bonded hydrogen content. It is found that the deposition temperature has the most influence on achieving low surface recombination velocity. Higher deposition temperature in the range of 200–300 °C produces lower surface recombination velocity. Optimal silicon nitride deposition conditions resulted in a surface recombination velocity of 119 cm/s on 2 Ω cm p-type silicon.
Enhanced ultrasonic detection of fatigue cracks by laser-induced crack closure
Authors: Xiao Hui , Nagy Peter B.
Published: July 2002

Fatigue cracks are usually initiated by small geometrical irregularities or material inhomogeneities that give rise to sharp local stress concentrations. In the early stages of fatigue, small cracks often remain hidden from conventional ultrasonic detection by stronger scattering from the very same structural imperfection that produced them in the first place. A new experimental method was developed to selectively increase the sensitivity of ultrasonic echographic techniques for such hidden fatigue cracks by exploiting one of their most characteristic features, their susceptibility for closure under compressive stress. Thermo-optical modulation by pulsed infrared laser irradiation was introduced to produce a temporary compressive thermal stress on the surface of the specimen. The resulting dynamic closure of microcracks was detected by a high-frequency ultrasonic surface wave technique. It is demonstrated that this method can be used to effectively distinguish fatigue cracks from other structural imperfections present in the material.
Collisional radiative models with loss and recycling
Authors: Greenland P. T. , Reiter D.
Published: July 2002

We describe how the collisional–radiative model, which is usually used to simplify the treatment of excited states in the description of atomic processes in plasmas, must be extended if transport of the excited states is significant. We identify recycling of neutrals near the plasma edge as a circumstance where this is indeed the case. We show how the effective ionization and recombination rates appropriate to a correct ‘nonlocal’ collisional–radiative model depend on the recycling rate, as well as electron temperature and density. We are able to identify the specific shortcomings of the conventional collisional–radiative model, and show that its use leads to a spurious source of neutral particles. We compare results obtained for the atomic dynamics using both the conventional and extended collisional–radiative models with the exact solution of the appropriate nonlinear equations in which all the excited states are explicitly included, and demonstrate that whereas the conventional model fails to reproduce the exact result, the extended model does so.
Ion composition of expanding microdischarges in dielectric barrier discharges
Authors: Xu Xudong Peter , Kushner Mark J.
Published: July 2002

The properties of the filamentary microdischarges found in dielectric barrier discharges depend on the manner of charging of the dielectric. The charging of the dielectric removes voltage from the gap thereby reducing E/N and producing a transition from an avalanching discharge to a recombination or attachment dominated discharge. In this article, we report on a computational investigation of these processes using a one-dimensional plasma chemistry model. We find that the expansion and ultimate stalling of the microdischarge is largely determined by charging of the dielectric at larger radii than the core of the microdischarge. The lowering of E/N in the core of the microdischarge in attaching gases can quickly consume electrons. This transition produces a discharge consisting of an expanding shell having a high electron density and an inner core dominated by negative ions. In extreme cases where the gas mixture contains thermal electron attaching gases, the core of the microdischarge is essentially a negative ion-positive ion plasma. Using square wave voltage pulses, the residual charge on the dielectric after the microdischarge, which contributes to the gap voltage on the next voltage pulse, is largely determined by the attachment rate in the core of the microdischarge. Rapid attachment reduces the plasma conductivity and leaves residual charge on the dielectric.
Effect of Pt in TbFeCo on magnetic and magneto-optical properties
Authors: Itoh Y. , Van Drent W. P. , Suzuki T.
Published: July 2002

The effect of Pt additives in TbFeCo(Pt)/Pt multilayers on magnetic properties and magneto-optical Kerr effect is investigated. The perpendicular magnetic anisotropy Ku of the multilayer becomes larger (∼2×106 erg/cm3) than that of the TbFeCo(Pt) single layer. Pt layers are found to contribute significantly to the polar Kerr spectra at ultraviolet photon energies beyond 4 eV. The largest enhancement in the Kerr rotation θK is found at about 5 eV. The Kerr rotation θK and ellipticity ηK are enhanced with increasing Pt layer-thickness tPt, and become saturated at tPt=12 Å. This result implies that Pt atoms up to about 6 Å from the interfaces are contributing to the Kerr activity.
Crystallization and Mössbauer studies of melt-spun NdFe10.7TiB0.3Nδ alloys
Authors: Kim Chul Sung , An Sung Yong , Uhm Young Rang , Lee Seung Wha , Kim Y. B. , Kim C. S.
Published: July 2002

Magnetic properties of melt-spun NdFe10.7TiB0.3Nδ ribbons have been investigated as functions of quenching rate and nitriding period. NdFe10.7TiB0.3 were prepared with substrate velocity vs⩽18 m/s and were nitrogenated at 500 °C for 15 min. The NdFe10.7TiB0.3Nδ retains the ThMn12-type tetragonal structure with lattice constants a0=8.640 Å and c0=4.811 Å, but with an increase in the unit cell volume. The NdFe10.7TiB0.3Nδ was confirmed to have uniaxial anisotropy by x-ray diffraction. Mössbauer spectra were taken at various temperatures ranging from 13 to 855 K. The Curie and Debye temperatures are determined to be Tc=833 K and Θ=390 K, respectively. Each spectrum below Tc was fitted with six subspectra of Fe sites (8i1, 8i2, 8j2, 8j1, 8f, and α-Fe). The area fraction of the subspectra at 13 K are 10.2%, 8.2%, 16.5%, 17.5%, 44.3%, and 3.3%, respectively. The magnetic hyperfine fields for the Fe sites decrease in the order, Hhf(8i)>Hhf(8j)>Hhf(8f).
Faraday rotation and magnetic properties of erbium gallium gallate under high magnetic field
Authors: Guillot M. , Schmiedel T. , Xu You
Published: July 2002

Magnetization (M) and Faraday rotation (FR) have been measured in Er3Ga5O12 single crystals in the 4.2–300 K temperature range under high dc magnetic field up to 300 kOe. Experimental data are reported for H applied parallel to the [111] and [100] directions at 633 and 550 nm wavelength. A strong anisotropy of both magneto-optical and magnetic properties is observed. At low temperature, FR and M are proportional only when the magnetization is weak (small magnetic field). In medium and high magnetic field, complex relationships between M and FR are found. The magnetization cannot account for the whole Faraday rotation anisotropy. These data are discussed taking into account the magnetic and magneto-optical properties of the isomorphous erbium iron garnet ferrite.
Magnetic properties and microstructure of giant magnetostrictive TbFe/FeCo multilayers
Authors: Quandt E. , Ludwig A. , Lord D. G. , Faunce C. A.
Published: July 2002

Magnetostrictive multilayer films which combine exchange coupled giant magnetostrictive materials (amorphous Tb0.4Fe0.6) and soft magnetic materials with large polarizations and considerable magnetostriction (crystalline Fe0.5Co0.5) were prepared by magnetron sputtering. The microstructure and the magnetic properties of these multilayers were investigated as a function of the annealing temperatures and the corresponding film stresses. Giant magnetoelastic coupling coefficients (or magnetostrictions) are achieved at low fields, due to the magnetic polarization enhancement in such multilayers, the optimized stress state, and a suitable microstructure. For these optimized Tb0.4Fe0.6(7 nm)/Fe0.5Co0.5(9 nm) multilayers a saturation magnetoelastic coupling coefficient of 27.5 MPa at 20 mT and a coercive field of 2 mT has been achieved.
Physical and chemical properties of the chromium/polyphenylquinoxaline interface
Authors: Bellard L. , Fauquet-Ben Ammar C. , Themlin J.-M. , Cros A.
Published: July 2002

The very first stages of the chromium/polyphenylquinoxaline interface formation are investigated. X-ray photoelectron spectroscopy data evidence that new carbon and nitrogen electron-rich species are formed, necessarily implying cycle opening and bond breaking, associated with polymer disruption. Complementary experiments performed on chromium nitride and on chromium deposited on amorphous carbon films show that mostly chromium carbides and nitrides are formed during chromium interaction with the polymer. The outermost topography is studied by ex situ near-field microscopies. Chromium, with its high reactivity towards the polymer, essentially grows in a layer-by-layer mode. However, for chromium coverages higher than 60 Å, a dense network of cracks spontaneously forms, indicating a mixed-mode failure (cohesive in the chromium film and adhesive at the interface).
Electrode interdependence and hole capacitance in capacitance–voltage characteristics of hydrogenated amorphous silicon thin-film transistor
Authors: Park Hyuk-Ryeol , Kwon Daewon , Cohen J. David
Published: July 2002

The interelectrode capacitance–voltage (C–V) characteristics of back-channel-etched inverted-staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were investigated. It is demonstrated that this simple measurement can be used to diagnose TFT parameters such as the fabricated channel length, the channel resistance, and the error in the mask alignment of the source and drain overlap lengths. The C–V characteristics associated with the hole accumulation in a-Si:H TFTs with n+-type source/drain contacts were also examined. We observed that the ac capacitance increases for low frequencies and/or moderately high measurement temperatures provided the gate voltage is sufficiently negative. One possible mechanism for this hole capacitance is proposed that accounts for the observed frequency and temperature dependence.
Effect on thermal stability of a Cu/Ta/Si heterostructure of the incorporation of cerium oxide into the Ta barrier
Authors: Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man
Published: July 2002

The effects of CeO2 addition on the microstructural change of a Ta diffusion barrier film and thermal stability of the Cu/Ta/Si system were investigated. When a Ta layer was prepared with CeO2 addition, the silicide formation was retarded up to 800 °C. The Cu/Ta+CeO2/Si system retained its structure up to 800 °C without an increase in stack resistivity, while the Cu/Ta/Si structure degraded after annealing at 550 °C. The Ta+CeO2 diffusion barrier showed an amorphous microstructure and chemically strong bonds with Ta–Ce–O. It appeared that the thermal stability of the Cu/Ta+CeO2 interface as well as the Ta+CeO2/Si interface was higher than that of both Cu/Ta and Ta/Si interfaces. Therefore, the Ta film prepared by CeO2 addition effectively prevented the interdiffusion of Cu and Si through the diffusion barrier up to 800 °C.
High perpendicular anisotropy and magneto-optical activities in ordered Co3Pt alloy films
Authors: Yamada Y. , Van Drent W. P. , Abarra E. N. , Suzuki T.
Published: July 2002

The origin of the large perpendicular magnetic anisotropy constant Ku of Co3Pt alloy thin films is discussed. The films deposited onto Al2O3(0001), Al2O3(112̄0), and MgO(111) substrates held at 230–450 °C during deposition exhibit Ku of the order of 107 erg/cm3 at room temperature. While the one dimensional long range order parameter S estimated by x-ray diffraction is very consistent with the development of the perpendicular magnetic anisotropy in the films deposited at 380–450 °C, very little evidence is found to suggest the correlation between S and Ku for the lower deposition temperature range (230–380 °C). To explain this, a short range ordering is suggested to be responsible for the origin of Ku, similar to the cases in Pt72Co28 alloys. The magneto-optical polar Kerr activity of ordered Co3Pt film is found to be enhanced for both θK and ηK in the photon energy range from 2 to 4 eV.
Cd
0.88
Zn
0.12
Te
group index measurements near the exciton energy at low temperature
Authors: Sermage B. , Petiot S. , Tanguy C. , Dang Le Si , André R.
Published: July 2002

The group index of Cd0.88Zn0.12Te has been measured by a time-of-flight technique near the exciton energy at 10 K, in the energy range between 1.61 and 1.65 eV. Even at low temperatures, the standard model relying on a single excitonic contribution to the dielectric constant leads to erroneous optical constants for CdZnTe. By contrast, the experimental results are well fitted with a model taking all excitonic states into account. The parameters obtained by this fit are in excellent agreement with other experimental results and give the refractive index of Cd0.88Zn0.12Te at 10 K in the transparency region and close to the absorption threshold.
Luminescence improvement of SrS:Ce thin films by rapid thermal annealing: Evidence of energy-transfer model for SrS:Ce electroluminescent devices
Authors: Wang C. W. , Horng R. H. , Wuu D. S. , Huang B. C.
Published: July 2002

SrS:Ce thin films and electroluminescent (EL) devices have been deposited on Si substrate using the rf magnetron reactive sputtering method and subsequently submitted to various thermal treatments. The effects of rapid thermal annealing (RTA) on the properties of SrS:Ce thin films and EL devices have been investigated and compared with results obtained using a conventional furnace. Subsequently, the higher temperature of RTA treatment not only remarkably improves the crystallization of SrS phosphor film in the (200) plane but also reduces oxygen interdiffusion problems and enhances both the interface states (Eit) as well as bulk trap (Ebt) densities. These effects all are important factors in yielding brighter electroluminescence. Furthermore, a physical band model based on energy-transfer concept is proposed to elucidate the electroluminescent mechanism of SrS:Ce EL devices. All evidence reveals that the efficient luminous center formed by the Ce atom associated with the Ebt bulk trap is the basis of this energy-transfer model in SrS:Ce EL devices.
Pulsed laser ablation of a single crystal cadmium tungstate (010) surface studied by time-of-flight mass spectrometry
Authors: Tanaka Katsumi , Shirai Natsuki , Chen Tsun-Ming
Published: July 2002

Pulsed laser ablation of a cadmium tungstate (CdWO4)(010) surface was studied by time-of-flight mass spectrometric analysis at 532 and 266 nm. Single crystal CdWO4(010) surfaces with fewer defects than in previous work [J. Appl. Phys. 77. 6581 (1995)] are used, from which the kinetic energy (KE) of O2+ increased linearly with laser fluence. The KE observed at 266 nm was four times larger than that at 532 nm. This result can be explained by the difference between absorption coefficients of the plasma formed at the two laser wavelengths. This fact suggests an inverse bremsstrahlung process in which the desorbed species are accelerated in the flight path by the remaining part of the laser pulse. The desorption process was studied by changing the temperature of the CdWO4 target from 100 to 900 K at a constant laser fluence. As the temperature of the CdWO4 target increased, intensities of desorbed species increased while their KEs were almost constant. These results can be explained well in terms of a temperature dependence of the thermal desorption process of the photochemically formed desorption precursory state. The activation energy (0.3 eV) implies that the desorption precursory species are physisorbed on the surface. The data were analyzed with shifted Maxwell–Boltzmann velocity distributions, in which Maxwell–Boltzmann temperatures and Mach numbers were elucidated as functions of both laser fluence and CdWO4 target temperature.
An analytical model of an emission-gated Twystrode using a field emitter array
Authors: Jensen K. L.
Published: July 2002

An analytical model of a unit cell and of an array of field emitters with a distribution of tip radii is used to estimate the total current and current characteristics on the basis of geometry and materials. Based on the unit cell modeling, analytical estimates of ring cathode inductance, resistance, and capacitance are made to estimate the drive power required to sinusoidally modulate the array in order to produce a bunched electron beam. For a configuration of parameters indicative of a next generation field emitter array (FEA) ring cathode, the characteristics of the array are used to estimate the gain, efficiency, power output, and optimized length of an emission-gated Twystrode (TWT) using a simple model of the beam-wave interaction. The integrated analytical approach and its numerical implementation (“Cassandra”) are validated by comparison to a 1D TWT code (CHRISTINE) which estimates the output power and the optimized length of a TWT. Using “Cassandra,” it is shown that with next generation FEA parameters, interesting and significant levels of performance may be anticipated for a compact, broadband rf inductive output amplifier; in particular, an electronic efficiency of 32% with 15 dB gain may be possible from an array producing 260 mA peak and 71 mA average current at 10 GHz modulation using a helix 1.51 cm long.
Measurements and analysis of radiation effects in polycapillary x-ray optics
Authors: Rath B. K. , Wang Lei , Homan B. E. , Hofmann F. , Gibson W. M. , MacDonald C. A.
Published: July 2002

Polycapillary x-ray optics are arrays of large numbers of small hollow glass tubes which deflect x rays by successive total external reflection. These optics have growing numbers of applications in areas ranging from medical imaging to microanalysis. An accelerated radiation effects study has been performed to understand the performance limitation of these optics for medium to high intensity radiation applications, to study x-radiation damage mechanisms, and to investigate possible ways to mitigate the radiation effects on x-ray transmission efficiency. Exposures have been done in white beam bending magnet radiation with peak energies at 5 and 11 keV and focused broad band radiation centered at 1.4 keV. In situ and ex situ measurements of loss of x-ray transport efficiency have been executed at doses up to 1.8 MJ/cm2. Thin polycapillary fibers displayed noticeable bending and experienced substantial degradation of x-ray transmission. Thicker polycapillary fibers showed a linear but much slower transmission loss as a function of total dose. Annealing effectively restored the low energy (∼8 keV) transmission efficiency of the fibers. Exposure of these fibers at slightly elevated temperatures prevented any measurable loss in the low energy transmission efficiency. A variety of analytical techniques has been used to understand these results. No significant change was observed in the chemical composition of the capillary surface. Profile measurements and high energy transmission efficiency spectra, along with computer simulation studies, suggest that radiation induced bending is the primary cause of transmission efficiency degradation of the fibers.
Effects of rapidly decaying plasmas on Langmuir probe measurements
Authors: Ding Guowen , Scharer John E. , Kelly Kurt L.
Published: July 2002

Sheath motion, displacement current, and probe edge effects on temporal Langmuir probe (LP) ion saturation current measurements are investigated for a pulsed laser produced plasma during the period 100 ns→1000 ns after the turn on of the laser pulse. The plasma has a large volume (hundreds of cm3) and a high initial plasma density (ne>1013 cm−3). The sheath motion and edge effects are found to be very important, but the displacement current is found to be very small. We present both a quantitative correction for the effects of rapidly decaying plasmas on LP ion saturation current measurements and a validity condition for this method. The results are compared with the densities predicted from electron saturation currents, and the former are ⩽30% lower than the latter. The corrected probe measurements are utilized to determine the plasma recombination coefficient. It is found to be in good agreement with the results obtained by Stalder and Eckstrom [J. Appl. Phys. 72, 3917 (1992)] who utilized a microwave method.
Mechanism of donor–acceptor pair recombination in Mg-doped GaN epilayers grown on sapphire substrates
Authors: Kang T. W. , Park S. H. , Song H. , Kim T. W. , Yoon G. S. , Kim C. O.
Published: July 2002

Temperature-dependent photoluminescence (PL) measurements in Mg-doped GaN epitaxial layers grown on sapphire substrates by plasma-assisted molecular beam epitaxy have been performed in order to investigate the process of donor–acceptor pair (DAP) recombination. The PL intensity of the DAP peak decreases below 35 K, and then it increases as the temperature increases in the temperature range between 35 and 100 K. This behavior originates from the interaction between two different Mg-related traps, one shallow and the other deep level. The ionization energies of the shallow trap and the deep level trap determined from the calculations and the PL experiments are 126 and 160 meV, respectively. The DAP recombination process suggests that holes are caught in the shallow trap and that they subsequently transfer, via a tunneling process, from the shallow trap to the deep trap, where recombination with electrons takes place.
Doping-induced band edge displacements and band gap narrowing in 3C–, 4H–, 6H–SiC, and Si
Authors: Lindefelt U.
Published: July 2002

Models for doping-induced band edge displacements and band gap narrowing in both n-type and p-type 3C–, 4H–, and 6H–SiC are presented for the first time. For comparison, Si has also been considered. The models constitute an extension of the theory of Jain and Roulston [Solid State Electron. 34, 453 (1991)] and take into account the three different electron effective mass components associated with hexagonal lattices. Furthermore, a more careful treatment of minority carrier correlation energy has been made, applying a two-band model for the dielectric function of a hole gas in the plasmon-pole approximation. The results for the band edge displacements are expressed in simple analytical form as functions of doping concentration.
Processing factor dependence of resistivity parameters of ruthenate-based thick film resistors with low temperature coefficients
Authors: Crosbie Gary M. , Johnson F. , Trela W.
Published: July 2002

Many analog sensor and control circuits take advantage of the low (<100ppm/°C) temperature coefficient of resistance (TCR) of thick film resistors which are based on fired ruthenate-glass nanocomposites. To manufacture resistors with even smaller TCRs, a knowledge of the effects of processing on conduction mechanism parameters is of particular importance, because TCR is fixed in firing and cannot be trimmed later to a target value, as resistance can be. The peak firing temperature and time were varied, and a special four-probe dc design was used to minimize contact and printing nonuniformities. Corresponding to a greater energy level degeneracy in larger particles, the electrostatic charging energy decreased with the observed coarsening of the resistor microstructure. For the primary data set, the charging energy decreased (at >95% confidence) from 1.56 to 1.15 meV with increasing firing temperature (from 845 to 855 °C) and time (from 8 to 11 min). Model-based estimation of parameters is a means to provide quantitative understanding of how TCR and underlying conduction are controlled by process factors.
Room-temperature photoluminescence from Tb ions implanted in SiO2 on Si
Authors: Amekura H. , Eckau A. , Carius R. , Buchal Ch.
Published: July 2002

The room-temperature photoluminescence (PL) of Tb3+ ions has been studied. The Tb ions were implanted into 200 nm thick SiO2 on Si wafers. To achieve a uniform Tb distribution, the implantations were performed at 50, 100, and 190 keV to a total dose of 8.8×1014–1.3×1016 ions/cm2, resulting in Tb concentrations of 0.18–2.7 at. %. The PL spectrum consists of sharp lines due to the Tb3+ intra-4f transitions and a broadband due to SiO2 defects. The samples were annealed at temperatures ranging from 600 to 1050 °C. Up to 900 °C, the annealing procedure improves the PL yield; at temperatures higher than 1000 °C, the PL yield drops again at high dose. The PL spectra show noticeable influence of Tb–Tb crossrelaxation, which favors the green PL over the blue PL.
The curling nucleation mode in a ferromagnetic cube
Authors: Newell Andrew J. , Merrill Ronald T.
Published: July 2002

A ferromagnetic sphere is uniformly magnetized in a large field. As the field decreases, there is a critical field (the nucleation field) at which the magnetization becomes nonuniform. The initial deviation from uniform magnetization (the nucleation mode) is either coherent rotation or curling. By contrast, a ferromagnetic cube is never uniformly magnetized, and theorists have disagreed on whether nucleation theory for a sphere can be generalized to a cube. A three-dimensional numerical model of a cube is used to show there is a bifurcation at which a curl appears in the magnetization. This bifurcation is a generalized curling-mode nucleation. The nucleation field for a small cube fits the equation for a sphere of the same volume with a reduced demagnetizing factor. The nucleation mode is well approximated by the curling mode for the sphere. The magnetization changes continuously, so the nucleation field is not equal to the switching field or coercivity. When the cube size is twice the single-domain critical size, the nucleation field starts to increase faster than the inverse square of the size. This offers a possible resolution of Brown’s paradox. It has been suggested that nucleation in large particles may begin at the corners, but it is shown here that the greatest deviations are in the center of two opposing faces.
An analysis of the role of high energy neutral bombardment in longthrow/collimated sputtering of refractory metal barrier layers
Authors: Smy T. , Joshi R. V. , Tait N. , Dew S. K. , Brett M. J.
Published: July 2002

The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investigated using a Monte Carlo growth simulator and it was found that the model most consistent with the experimental films was an assumption of resputtering due to reflected neutrals. A significant result is a dramatic increase in the resputtering rate when a collimator was present due to a relative increase in the reflected neutral flux. Finally, the paper presents an analysis of the effect of pressure on bottom and step coverage in high aspect topography.
Study of magneto-optical properties of Ni:SiO2 granular films
Authors: Zhang Rong-Jun , Chen Liang-Yao , Wang Song-You , Qian Dong-Liang , Zheng Yu-Xiang , Zhou Shi-Ming , Yang Yue-Mei , Dai Ning , Wang Yu , Zhang Xi-Xiang , Yan Xiao
Published: July 2002

A series of NixSiO2(1−x) granular films was prepared by ion sputtering, and some of them were annealed. Both the complex dielectric function and magneto-optical polar Kerr spectra of the samples were measured in the 1.5–4.5 eV photon energy range at room temperature. There are broad peaks in the 2.5–3.5 and 3.2–4.5 eV range in the Kerr rotation and ellipticity spectra, respectively. The Kerr intensities increase with increasing Ni composition. For sample x=0.65, the Kerr peaks are redshifted, with reduced intensities after annealing. Both the off-diagonal terms of the dielectric tensor and the optical constants are attributed to enhancement of the Kerr effect in a particular spectral range for the metal–insulator granular films.
The ultrahigh flux polarized cold neutron spectrometer PANDA of the FRM-II reactor
Authors: Loewenhaupt M. , Pyka N. M.
Published: July 2002

At present the high flux research reactor FRM-II is under construction in Garching, Germany. As part of the first set of instruments, a triple axis spectrometer is under construction at the cold source in the reactor hall. This instrument will be mainly used to study inelastic magnetic phenomena in condensed matter physics. Besides an unpolarized beam setup, PANDA is equipped with devices allowing full polarization analysis. This instrument largely profits from its vicinity to the reactor, and uses state of the art neutron optics. Thanks to the large focusing Heusler monochromator and analyzer the neutron flux of the polarization setup will be of the same magnitude as that of an unpolarized beam at a high flux reactor. The accessible energy and Q ranges will be extremely large due to an advantageous flux distribution of the cold source and a particular construction of the beam tube and the biological shielding which contain supermirror neutron guides. A resonant spin echo device, used to perform line shape analysis of dispersive excitations, will complete the extensive array of equipment, available on PANDA.
Higher crystallinity superparamagnetic ferrites: Controlled synthesis in lecithin gels and magnetic properties
Authors: Li Sichu , John Vijay T. , Rachakonda Suguna H. , Irvin Glen C. , McPherson Gary L. , O’Connor Charles J.
Published: July 2002

The synthesis of γ-Fe2O3 nanoparticles in a novel organohydrogel medium is reported. The hydrogel consists of the phospholipid species, lecithin together with the anionic surfactant AOT, water and a hydrocarbon, isoocatane. Transmission electron microscopy observations indicate that the particles are spherical and range in size from 15 to 25 nm. Superconducting quantum interference device characterizations show that the particles exhibit superparamagnetic behavior with a blocking temperature of 24 K (at an applied field of 50 G) and a coercivity of 1600 G at 2 K. The results are compared to the magnetic properties of the γ-Fe2O3 particles of the same size and shape synthesized in water-in-oil microemulsions (reverse micelles). It was found that both blocking temperature and the coercivity of the ferrites synthesized in the lecithin gel media was higher than those synthesized in the reverse micelles. Similar results can be found for cobalt ferrites. These findings reveal the sizes of the domains are the same for these two kinds of particles, while the crystallinity may be higher for the particles synthesized in the lecithin gel media. It is proposed that slow ionic species diffusion through the channels of the gel may lead to such increases in crystallinity during particle growth.
Stochastic dynamic micromagnetic study of fine particles
Authors: Zhang Kezhao , Fredkin Donald R.
Published: July 2002

We have developed a stochastic dynamic micromagnetics code using the Langevin–Gilbert equation and the finite element method to study the thermal switching of fine particles. In this article, results for an ellipsoidal particle with aspect ratio 4.62 are presented. The physical parameters of the particle have been chosen so that the magnetization switches incoherently. The first passage time for the magnetization to switch is calculated repeatedly to obtain statistics. The probability that the magnetization has not switched, Pn(t), can be described well by a delayed stretched exponential Pn(t)=exp[−(t−t0/τ)β], where t0, τ, and β are parameters obtained by maximum likelihood estimation.
In situ observation of hydrogenated amorphous silicon surfaces in electron cyclotron resonance hydrogen plasma annealing
Authors: Nozawa Ryoichi , Takeda Hirohisa , Ito Masafumi , Hori Masaru , Goto Toshio
Published: July 2002

The surface reactions of hydrogenated amorphous silicon (a-Si:H) films exposed to electron cyclotron resonance (ECR) H2 plasma, which is called ECR H2 plasma annealing, has been investigated by in situ polarization modulation infrared reflection absorption spectroscopy (PM-IR-RAS). The surfaces of a-Si:H films were exposed to ECR H2 plasmas at various substrate temperatures. To distinguish the roles of ionic species and atomic hydrogens, permanent magnets were employed to shut out charged species incident on the substrate. The surface reactions of a-Si:H films exposed to only atomic hydrogens were observed by in situ PM-IR-RAS and the results were compared with those exposed to ECR H2 plasmas. It was found that atomic hydrogens reacted with the Si–H2 and (SiH2)n bonds in the vicinity of the surfaces and did not etch the bulk of the films at room temperature. Moreover, it was suggested that atomic hydrogens penetrated into the bulk of a-Si:H film and promoted the Si-network modification as the substrate temperature increased. On the other hand, it was found that ionic hydrogens with the energy of 50 eV had energy enough to etch a-Si:H films.
X-ray reflectivity from ZnSe/GaAs heterostructures
Authors: Ulyanenkov A. , Takase A. , Kuribayashi M. , Ishida K. , Ohtake A. , Arai K. , Hanada T. , Yasuda T. , Yao T. , Tomita H. , Komiya S.
Published: July 2002

ZnSe/GaAs heterostructures have been studied using x-ray reflectivity. Two samples grown by molecular beam epitaxy (MBE) differed in initial growing conditions; the first was prepared by Se treatment of a GaAs substrate, and the second one was exposed to Zn before growth of the ZnSe film. The structure and morphology of the interface between the ZnSe film and GaAs substrate were investigated. The experimental x-ray reflectivity curves, measured at different wavelengths, were simulated using a distorted-wave Born approximation method. Fitting the experimental data indicated the presence of a Ga2Se3 transition layer between the ZnSe film and GaAs substrate for the Se-treated sample, confirming that Zn treatment during the MBE growing process improves the interface quality. Furthermore, the simulations indicated that the concentration of the Ga2Se3 was less than unity. From this, we propose that the transition layer is discontinuous, e.g., possesses an island-like morphology.
Carrier trapping in iron-doped GaInP
Authors: Čėsna A. , Söderström D. , Marcinkevičius S. , Lourdudoss S.
Published: July 2002

Time-resolved photoluminescence decay caused by carrier trapping to the deep Fe level has been studied in epitaxial GaInP. Carrier trapping time is found to be strongly dependent on the Fe concentration up to 1×1018 cm−3. The electron capture cross section for the neutral iron level Fe3+, evaluated from the luminescence transients, is in the range from 6×10−16 to 1×10−15 cm2 for the temperature interval 70–250 K.
Role of a paramagnetic amorphous CoZr seed layer in CoCrPt/Ti perpendicular recording media
Authors: Lee I. S. , Ryu H. , Lee H. J. , Lee T. D.
Published: July 2002

A fresh CoZr45 paramagnetic amorphous layer of 20 nm thickness is introduced as a seed layer prior to the Ti underlayer deposition on glass substrate in CoCrPt/Ti perpendicular recording media. By the fresh layer introduction, the thickness of Ti underlayer could be reduced to 100 Å to obtain good perpendicular magnetic properties. The cause of this reduction of the critical Ti underlayer thickness is the formation of a more smooth and absorbed impurity free surface by the CoZr layer deposition. This ensures better aligned and finer Ti grain formation at an early stage. Details of the improvements of magnetic properties are discussed. In the second half, we are reporting high Ku behaviors of the CoCrPt/Ti films when the magnetic layers are thinner than 200 Å. The high Ku behavior was associated with the (10.0) lattice expansion of the Co alloy to maintain coherency with (10.0) lattice of the Ti film at the interfaces. These will be discussed.
Spin-wave Brillouin scattering in quasimonatomic Co films
Authors: Murayama Akihiro , Hyomi Kyoko , Eickmann James , Falco Charles M.
Published: July 2002

We have observed spin-wave Brillouin scattering in ultrathin Co/Au/Cu/Si(111) films with the Co thicknesses tCo down to one monolayer (ML). A graded Co-wedge sample with tCo=0–7 ML was prepared on 1 ML of Au interlayer by molecular beam epitaxy, where the thickness was calibrated by determining the number of deposited atoms using Rutherford backscattering spectroscopy. Observations of the spin-wave Brillouin excitation show directly collective and ferromagnetic ordering at room temperature. The tCo dependence of uniaxial perpendicular anisotropy is obtained from the field dependence of the spin-wave frequency. In addition, we quantify magnetic inhomogeneities from the field dependence of the spectrum width. With tCo⩽2 ML, the perpendicular anisotropy shows a steep decrease with decreasing tCo, as well the structure-related magnetic inhomogeneity significantly increasing.
Observation of mixed-mode oscillations in spin-wave experiments
Authors: de Aguiar F. M. , Rosenblatt S. , Azevedo A. , Rezende S. M.
Published: July 2002

High-power ferromagnetic resonance experiments in a 1-mm-diam yttrium iron garnet sphere, driven at 8.9 GHz at room temperature, reveal evidence for a universal scenario not yet observed in this system, namely, the periodic–chaotic sequence. Well above the first-order Suhl instability threshold (P/PC∼6 dB), low-frequency (f∼200 kHz) auto-oscillations consisting of large-amplitude peaks followed by n small undulations (mixed-mode oscillations) have been observed. Both periodic and aperiodic trajectories were detected with n=1, 2, 3, and 4, which are reminiscent of the so-called homoclinic chaos. A discussion is made on the basis of a standard two-mode model.
In-plane magnetic anisotropy in CoCrPt and CoCrTa films deposited onto patterned silicon substrates
Authors: Twisselmann D. J. , Farhoud M. , Smith Henry I. , Ross C. A.
Published: July 2002

Topographically induced in-plane magnetic anisotropy has been observed in CoCrTa and CoCrPt films deposited onto oxidized silicon substrates which are lithographically patterned with fine grooves of period 200–320 nm and amplitude 20–50 nm. The coercivity and remanence are higher parallel to the grooves. Anisotropy has been observed in both rf- and dc-magnetron sputtered films with a (112̄0) preferred orientation, which is achieved by growth at elevated temperature on a (200)-oriented Cr underlayer at low base pressures. Anisotropy increases with the amplitude of the grooves in the silica substrate.
Resonance radiation transport in inhomogeneous media: Cylindrical glow discharges
Authors: Curry J. J. , Lawler J. E. , Lister G. G.
Published: July 2002

Numerical simulations of radiation transport in cylindrical geometry are used to determine the effect of radially symmetric inhomogeneities. The focus of this study are inhomogeneities such as may be produced by radial cataphoresis or temperature gradients in cylindrical glow discharges, i.e., a quadratic profile of absorbing atoms which has a minimum on the axis of the cylinder. A propogator function analysis of the Holstein–Biberman equation and a Monte Carlo simulation of resonance photon scattering are simultaneously used to examine three limiting cases of interest: (i) a pure Doppler broadened atomic lineshape, (ii) a pure Lorentz atomic lineshape produced by foreign gas broadening, and (iii) a pure Lorentz atomic lineshape produced by resonance collision broadening. The fundamental mode distribution of excited atoms, the fundamental mode trapped decay rate, and the volume-averaged escape rate for a homogeneous production rate per unit volume are calculated for each of these cases. The trapped decay rates are found to change modestly (depending upon lineshape) as the degree of inhomogeneity is increased, if the volume integral of the absorbing atom density remains fixed. Correction factors for the fundamental mode trapped decay rate are reported.
Strain in GaAs layers grown by liquid phase epitaxial lateral overgrowth
Authors: Zytkiewicz Z. R. , Domagala J. , Dobosz D. , Bak-Misiuk J.
Published: July 2002

High resolution x-ray diffraction has been used to study strain in GaAs layers grown on GaAs substrates by the liquid phase epitaxial lateral overgrowth (ELO) technique. We show that the lattice and thermal expansion coefficient mismatch between the subsequent layers and the substrate, as well as the built-in strain in the SiO2 masking film, lead to long-range deformations (macroscopic bending) extending over the whole area of the sample. Moreover, we show evidences that microscopic bending of individual ELO stripes takes place due to adhesion of their laterally overgrown parts to the masking film.
Connectivity, ionic interactions, and migration in a fast-ion-conducting polymer-in-salt electrolyte based on poly(acrylonitrile) and LiCF3SO3
Authors: Ferry Anders , Edman Ludvig , Forsyth Maria , MacFarlane Douglas R. , Sun Jianzeng
Published: July 2002

The ionic conductivity of a polymeric fast-ion-conductor based on LiCF3SO3 salt and poly(acrylonitrile), [CH2CH(CN)]n), is enhanced by ∼5 orders of magnitude when the composition approaches the “polymer-in-salt” regime; i.e., when the salt content increases from N:Li=12:1 to 1.2:1 (or ∼70 wt % of salt). This is in contrast to common salt-in-polymer electrolytes where a conductivity maximum typically is encountered at intermediate compositions. We suggest that connectivity effects in a microscopically phase segregated material may influence the long-range migration of charge carriers. Conductivity data are augmented with Raman spectroscopic investigations, thus probing microscopic details regarding the state of the dissolved salt.
Low field electron mobility in GaN
Authors: Dhar Subhabrata , Ghosh Subhasis
Published: July 2002

Temperature and doping dependencies of electron mobility in GaN have been calculated using an iterative technique. The following scattering mechanisms, i.e., impurity, polar optical phonon, acoustic phonon, piezoelectric, and electron plasmon are included in the calculation. Ionized impurity scattering has been treated beyond the Born approximation using a phase-shift analysis. The compensation ratio is used as a parameter with a realistic charge neutrality condition. Comparisons with experimental data confirm the present calculation over a wide range of temperatures and electron concentrations. Mobility and electron concentration data from Hall measurements reveal a degenerate layer at the GaN-substrate interface. This degenerate layer affects the bulk mobility and electron concentration and needs to be accounted for in order to extract reliable experimental values of the bulk electron mobility.