bluuebunny/crossref_metadata_2025 huggingface dataset:
Soft x-ray photoemission study of downstream plasma enhanced chemical vapor deposited SiO2
Authors: Robinson Bennett , McFeely F. R.
Published: July 2002

The distribution of Si oxidation states in 1.7-, 2.0-, and 3.0-nm-thick downstream plasma enhanced chemical vapor deposited SiO2 film upon Si has been studied by soft x-ray photoemission, using synchrotron radiation. The spectra from the as-deposited 3.0-nm-thick oxide show two prominent Si oxidation states, the Si4+ and the Si3+, with the Si3+ oxidation state preferentially located at the oxide vacuum interface. The Si3+ state is considerably larger than that observed in thermal SiO2 and is radiation and thermally sensitive, partially converting to the Si4+ state during annealing and extended irradiation. The analysis of the photoinduced conversion from the Si3+ to the Si4+ oxidation state suggests that the paramagnetic component of the Si3+ structure matrix can be correlated with the structure of the E′ defect center, as measured by electron spin resonance. A model is proposed for the SiO2 deposition mechanism whereby a temperature activated surface oxidation of the Si3+ structure is taking place.
Hydrogen as the cause of pit formation during laser recrystallization of silicon-on-insulator films
Authors: Willems G. J. , Maes H. E.
Published: July 2002

The formation of pits during laser recrystallization of silicon-on-insulator films has been studied in detail. Hydrogen originating from the decomposition of hydrogen bonds in the capping material or in the insulating layer is identified as being the cause of the formation of pits in the recrystallized silicon. These pits are the result of the formation of hydrogen gas bubbles in the molten zone near the solidification interface. A mechanism for the formation of the pits is presented. The dependence of the pit formation on capping layer material composition, annealing conditions, layer thickness, preheating temperature, scan velocity, and silicon film thickness is studied. Also hydrogen-containing insulating layers are discussed. Some recommendations are made to prevent pit formation.
On numerical problems in analytical calculations of extracellular fields in bounded cylindrical volume conductors
Authors: Gootzen T. H. J. M. , Stegeman D. F. , Heringa A.
Published: July 2002

A method is presented for dealing with numerical problems in calculations of potential fields using expansions in modified Bessel functions. Using this method, problems in mathematical physics with cylindrical symmetry, e.g., volume conductor problems, can be solved with high accuracy.
Ultrasonic phase conjugation
Authors: Nikoonahad M. , Pusateri T. L.
Published: July 2002

A real-time ultrasonic phase conjugator is reported. The scheme is based on sampling the wave front in space by means of a transducer array and mixing the signal from each array element with a second harmonic signal using nonlinear circuit components. The same array then retransmits the phase conjugated wave front into the medium. The technique is demonstrated at 300 kHz using a 20-element transducer array, and it is shown that efficient phase conjugation is possible up to spatial frequencies of ±80°.
Analysis of the shallow and deep center occupancies in Si-doped AlxGa1−xAs using a multilevel donor model
Authors: Blom P. W. M. , Koenraad P. M. , Blom F. A. P. , Wolter J. H.
Published: July 2002

The concentration of occupied deep centers in Si-doped AlxGa1−xAs for x≥0.2 has been calculated from a three-level donor model, in which the shallow levels are treated as excited states of the deep (DX) ground state. The deep level is assumed to be tied to the L valley, and the shallow levels to the Γ and X valleys. The behavior of the free-electron density and the thermal activation energy as function of composition is in good agreement with experimental results reported in the literature. In this model of dependent donor levels the deep-level occupancy can be directly calculated without needing deep-level transient spectroscopy measurements. A two-level donor model is used to calculate the pressure dependence of the deep level from a hydrostatic pressure experiment on a GaAs/Al0.3Ga0.7As heterostructure reported in the literature. We assume a shallow level tied to the Γ valley and an arbitrary deep level which is not coupled to any of the conduction bands. The calculation of the position of the deep level relative to the Γ valley as a function of pressure confirms the coupling of the deep level to the L valley. In this dependent donor model no large compensation is needed to fit the experimental data.
Capacitance-voltage studies of InP metal-oxide-semiconductor devices irradiated with 4He+ ions
Authors: Tin C. C. , Barnes P. A. , Williams J. R. , Patuwathavithane C. S. , Van Staagen P. K.
Published: July 2002

Capacitance-voltage (C-V) measurements have been made on n-InP metal-oxide-semiconductor (MOS) devices damaged by 2-MeV 4 He+ ion bombardment. The C-V curves for samples with thin oxide layer (∼100 Å) show the presence of a depletion layer during both forward and reverse bias. This behavior is significantly different from those of normal, undamaged MOS devices. Measurements made on n-InP MOS samples with different oxide thicknesses show that the C-V curves gradually approach that of a MOS device on a p-type substrate. The anomalous behavior of the C-V curves for the irradiated samples can be explained by the presence of an n-p-n structure under the oxide layer.
Effects of energy transfer on quantum efficiency of YAG:Nd
Authors: Lupei V. , Lupei A. , Georgescu S. , Yen W. M.
Published: July 2002

Using the energy transfer parameters deduced from the study on nonexponential luminescence decay of the 4F3/2 level of Nd3+ in YAG at room temperature, it is shown that up to 1.5 at. % Nd, the relative quantum efficiency is reduced by an amount of 18.2C, C being the relative (to Y3+) Nd concentration. It is pointed out that about 20% of this reduction is due to a very effective quenching mechanism inside the nearest-neighbor Nd-ion pairs.
On the self-magnetostatic energy of jagged domain walls
Authors: Mansuripur M.
Published: July 2002

The demagnetizing energy of thin magnetic films can be written in terms of the Fourier components of the magnetization distribution. This formalism is used to investigate the structure of jagged domain walls in both perpendicular and in-plane media. Also introduced is a set of correlation functions and their relationship to demagnetizing energy density in media with random magnetization distribution.
Thermally and ion-induced phase formation in a Pd/Ge bilayer
Authors: Li Jian , Hong Q. Z. , Mayer J. W.
Published: July 2002

Pd/Ge bilayer samples with three different overall compositions centered around Pd2Ge have been thermally annealed or irradiated with 300 keV Kr ions at room temperature. We observed that the first phase formed with ion irradiation, as in thermal annealing is Pd2Ge. In the Pd75Ge25 sample, the formation of an amorphous phase as well as the Pd2Ge phase has been observed after 3×1015 Kr+/cm2 irradiation. Successive irradiations up to the 5×1015 Kr+/cm2 led to the demixing of this amorphous phase to Pd2Ge and Pd.
Transport through InGaAs-InP superlattices grown by chemical beam epitaxy
Authors: Vuong T. H. H. , Tsui D. C. , Tsang W. T.
Published: July 2002

We have studied the tunneling transport of several In0.53Ga0.47As-InP superlattices which were grown by the chemical beam epitaxy technique. When a high electric field is applied perpendicularly to the superlattice layers, the current-voltage characteristics show large negative differential resistances (NDRs) which are periodic in the applied field. The NDRs are caused by the regular expansion of a high-field domain within the superlattice. The regularity and large number of the NDRs observed demonstrate the high quality of the superlattices grown. They also point to their possible application in multiple-logic circuits. The temperature and magnetic-field dependence of the tunneling transport are also reported. In the high-field regime, the magnetic-field dependence is most remarkable for the large effect of the Lorentz force on the tunneling probability, while the temperature dependence of the different series of NDRs may be explained by the varying effectiveness of the phonon scattering on the width of different subbands.
Theoretical investigation of multiline emission from a hybrid CO2 laser
Authors: Sinha Sucharita , Mehendale S. C.
Published: July 2002

A theoretical study of multiline emission from a hybrid CO2 laser for subthreshold operation of the low-pressure cw section is reported. A rate equation model has been used to determine the optimum operating conditions for the hybrid laser system which would yield the most uniform intensity distribution on the various lines. Our calculations indicate that the choice of a proper resonator cavity length is very critical for achieving optimum multiline operation of the hybrid CO2 laser.
A cyclotron resonance mechanism for very-low-frequency whistler-mode sideband wave radiation. II. Description of internal (‘‘trapped’’) resonances
Authors: Sá L. A. D.
Published: July 2002

The second part of the paper presents an analytical and numerical treatment of cyclotron resonances formed inside the potential wells of a set of monochromatic carriers propagating in a duct in the magnetosphere. It is found that those resonances produce oscillatory disturbances in the potential well charge distribution that frequency modulate the carriers to produce sidebands. The frequency spectrum is the same as the one generated by the external resonances defined in part I. The carrier trapping frequencies do not affect the sideband wave frequencies and do not impose sharp constraints on the spectrum bandwidth, on the sideband line separation, or on the maximum interacting carrier frequency separation. When not highly distorted by wave growth, a two-carrier sideband spectrum should have an approximately exponential profile.
Mössbauer analysis of spin directions in magnetic recording media: The problem of line area measurements
Authors: Pollard R. J.
Published: July 2002

Interpretations of Mössbauer measurements of the orientation of magnetic moments in magnetic recording particles have recently been critized. It has been alleged that a serious overestimation of spin-canting angles resulted in part from neglecting thick absorber effects. I show that effects are insignificant. The asymmetric and broadened line shapes which occur in Mössbauer spectra of γ-Fe2O3 at room temperature have the consequence that analyses based on line intensities are erroneous, and that line area measurements are inaccurate unless the analysis is performed upon high-quality data and properly accounts for the asymmetry. Cooling γ-Fe2O3 to 4.2 K reduces the line asymmetry and width.
The phenomenology of dielectric breakdown in thin silicon dioxide films: Al cathodes and p-type Si anodes
Authors: Falster Robert
Published: July 2002

Various aspects of the phenomenology of dielectric breakdown in Al-SiO2-p-Si metal-oxide-semiconductor planar capacitor structures have been investigated.The different types of breakdown events and their distributions are discussed in light of breakdown data from constant current stress tests and linearly ramped voltage tests with variable ramp rates. Many tests were performed on a wide variety of samples using Weibull-type distribution functions in analyzing the data. Of special interest was the influence of substrate parameters, such as oxygen concentration, surface transition-metal contamination, surface roughness, and the relatively simple surface defects which can form during a single oxidation treatment. Using very careful methods, three general types or ‘‘modes’’ of breakdown distribution are observed, a mode being defined as a subset of the complete distribution exhibiting the same or similar time and field parameters in the Weibull distribution. Two of the distinct modes are related to distributed ‘‘weak spots.’’ The third is apparently ‘‘intrinsic.’’ Implications for device reliability are considered. The origin and elimination of the distributed weak spot modes is discussed as are details of the intrinsic mode.
Gain excitation spectrum and acceptor density in CdIn2S4
Authors: Charlebois A. , Fortin E.
Published: July 2002

Optical gain measurements on the donor-acceptor (D-A) photoluminescence band of CdIn2S4 revealed maximum gain coefficients varying from 1.5 to 3.5 cm−1 at 300 K, in an optical excitation energy range of 2.016–2.101 eV. The threshold pumping intensity required for the onset of gain was found to be dependent on the excitation energy. Such characteristics were used to calculate the energy distribution of the acceptor levels in that energy range, which turned out to be exponential.
Intermolecular charge transfer in 1,4-dithioketo-3,6-diphenyl-pyrrolo- [3,4-c]-pyrrole
Authors: Mizuguchi Jin , Homma Seiji
Published: July 2002

Certain organic vapors induce a morphological transformation in 1,4-dithioketo-3,6-dipheyl-pyrrolo-[3,4-c]-pyrrole (DTPP) which is accompanied by enhanced absorption and photoconduction in the near infrared. In order to gain more insight into this phenomenon, intermolecular charge transfer caused by the vapor treatment has been investigated by Fourier transform-infrared-reflection absorption spectrometry (FT-IR-RAS) and x-ray photoelectron spectroscopy (XPS). Spectral shifts have been observed in FT-IR-RAS spectra at wave numbers of about 3125 cm−1 (NH stretching), 1500 and 1600 cm−1 (CC stretching of the aromatic ring), 1180 cm−1 (C■S stretching), and 750 cm−1 (CH ‘‘out-of-plane’’ deformation of the aromatic ring). The N 1s and S 2p in XPS spectra have also been shifted towards lower binding energies by 0.1–0.2 eV, and this is fully consistent with the above results. These shifts are most likely attributed to the charge transfer interaction of C, N, and S atoms between the molecular planes along the b-crystal axis. The electrostatic field induced by the charge transfer transition is responsible for the enhanced efficiency of the exciton dissociation into free-charge carriers.
Anomalous mobility and photo-Hall effect in ZnSe-GaAs heterostructures
Authors: van Houten H. , Colak S. , Marshall T. , Cammack D. A.
Published: July 2002

The Hall and photo-Hall effect are studied experimentally in pure, unintentionally doped n-ZnSe epilayers grown by molecular-beam epitaxy on semi-insulating GaAs substrates. An anomalous depression of the dark values of the room-temperature and peak mobility in the n-ZnSe layer is observed in a substantial fraction of the samples studied, while normal values for the mobility are recovered under illumination with above-band-gap light. This is accompanied by an increase in the effective areal electron density. These results point to space-charge scattering causing the dark mobility reduction. The photo-Hall effect in ZnSe-GaAs heterostructures is discussed in terms of simple models considering both misfit dislocations at the heterostructure interface and extended defects in the bulk of the ZnSe epilayer. Additional photo-Hall experiments have been performed for longer-wavelength laser lines. In this case, the areal electron concentration decreases strongly under intense illumination, while a large room-temperature mobility enhancement is found. This net negative photoconductivity effect suggests a depletion of mobile electrons from the ZnSe epilayer, accompanied by the creation of a low-density but highly mobile conducting layer in the GaAs near the semiconductor heterointerface.
Anomalous distribution of As during implantation in silicon under self-annealing conditions
Authors: Lulli G. , Merli P. G. , Rizzoli R. , Berti M. , Drigo A. V.
Published: July 2002

Anomalous distribution of As implanted in silicon under self-annealing conditions (i.e., with simultaneous damage recovery activated by beam heating) has been investigated and discussed. Rutherford backscattering/channeling, transmission electron microscopy, and carrier profiling techniques have been used to analyze the dopant profiles and the microstructure of samples irradiated with 150-keV As+ ions at a current density of ≂207 μA/cm2, for times of 2, 3, 4, 5, and 6 s. Two relevant effects are observed. The first one consists in the formation of two dopant peaks, electrically inactive, separated by a depletion region at the position of the ion projected range. While the deeper peak disappears with increasing irradiation time, the one located at the maximum of nuclear energy loss grows. Microstructural analysis suggests that both peaks occur as a result of As segregation at lattice defects; in particular, the one located the position of the maximum of nuclear energy loss is the consequence of segregation of As atoms at voids, which are formed during irradiation at elevated temperature. The second relevant effect is the formation of a deep penetrating tail in the As profile, which cannot be explained by a simple thermal diffusion mechanism. Although the contribution of channeling effects cannot be ruled out, the effect seems to be mainly related to a diffusivity enhancement, weakly temperature dependent, due to the interaction of the dopant with radiation-induced defects.
Formation of epitaxial yttrium silicide on (111) silicon
Authors: Siegal Michael P. , Kaatz Forrest H. , Graham William R. , Santiago Jorge J. , Van der Spiegel Jan
Published: July 2002

The growth of epitaxial yttrium silicide on Si(111) in ultrahigh vacuum is studied. Resistivity, epitaxial quality, and pinhole coverages are studied as a function of annealing temperature for each growth method used. The best films result from the growth of a thin, 30–40-Å template layer which is annealed to 700 °C, followed by a thicker film growth by depositing additional Y onto the substrate heated high enough to induce silicide formation (∼300 °C). Annealing to 900 °C results in a Rutherford backscattering minimum channeling yield χmin ∼3%, which is the same order of epitaxial quality previously achieved by only Ni- and Co-silicide films on silicon. Films grown without templates have larger pinhole sizes with pronounced features indicative of the hexagonal nature of these structures. The deposition of Y metal onto a substrate held at room temperature, followed by annealing to 900 °C results in the lowest resistivities (48 μΩ cm for 425-Å films), but with a highly dislocated film structure featuring 1-μm triangular pits which severely limit epitaxial quality.
Thermal stability of Be-, Mg-, and Zn-implanted layers in GaAs for high-temperature device-processing technology
Authors: Tang A. C. T. , Sealy B. J. , Rezazadeh A. A.
Published: July 2002

Results on the thermal stability of active acceptor layers in GaAs formed by Be, Mg, and Zn implantation are reported. Following rapid thermal annealing at 635 °C/35 s and 800 °C/15 s, the sheet carrier concentration is observed to remain constant after subsequent heat treatment below 600 °C for times up to 6 h. At and above this temperature, however, various changes are observed for different implants. These changes in the sheet electrical properties are observed to be reversible in the case of the Zn-implanted samples, where almost complete carrier recovery is observed after the samples were rapid thermal annealed at 800 °C/15 s after a long thermal anneal at 600 °C for 6 h.
Steady-state and transient eddy current predictions using surface impedances in shell structures
Authors: Davey Kent , Turner Larry
Published: July 2002

Surface impedance techniques are useful means of predicting fields in eddy current problems since they circumvent the need to model the conducting regions themselves. Thus, with their use, two-and three-dimensional field predictions can be made using only scalar potentials. Their use is normally confined to (1) problems where the skin depth is small relative to the other dimensions of the problem and (2) steady-state problems where the skin depth itself is well defined. In this regard, the technique is approximate at best. Presented here is a formulation which can realize an exact prediction of the field, both in steady-state and transient problems. The technique is exact for those problems where knowledge is known as to the nature of the field variation tangential to the conductor shell interface; otherwise, an iterative numerical scheme must be employed to converge on the correct tangential variation. Surface impedances are determined generically and expressed in terms of transfer functions for shell-type structures in three different geometries. The surface impedances happen to be trigometric functions, Bessel functions, and spherical Bessel functions in planar, cylindrical, and spherical shell structures, respectively. Their use is easily implemented in finite difference, finite element, and boundary integral formulations; in this paper, the surface impedances are coupled into a boundary integral approach to verify their use in both two-dimensional cylindrical and a three-dimensional spherical problem. The results are compared to analytical expressions and are shown to disagree by no more than 0.01%.
Submicron bubble garnets with nearly isotropic magnetostriction
Authors: Ramesh M. , Jo Soonchul , Campbell R. O. , Kryder M. H.
Published: July 2002

Magnetic garnet films with large, negative and nearly equal magnetostriction coefficients along [111] and [100], supporting submicrometer diameter bubbles were grown using the liquid-phase epitaxy technique. Such isotropic magnetostriction was achieved by incorporating dysprosium ions in the dodecahedral sites. Bismuth was also included in these films to provide the essential uniaxial anisotropy and fine tuning of the magnetostriction coefficients. The effect of growth conditions such as the growth temperature and the melt composition on the magnetostriction coefficients is discussed. Ion-implanted contiguous disk devices fabricated using such films are shown to exhibit similar margins for the ‘‘good’’ and ‘‘bad’’ propagation directions.
Diffusant-immobilization and medium-degradation effects in the diffusion of chemically reactive gas through layered polymers
Authors: Bretzlaff R. S. , Sugihara R. Y.
Published: July 2002

Thin polymeric barrier layers are often interposed between sensitive surfaces and other polymeric layers in which corrosive species slowly evolve as by-products of curing or decomposition. The corrosive species considered here are chemically reactive gases. Reducing the number of reactive species that can diffuse to sensitive surfaces ameliorates problems with corrosion, debonding, and the loss of mechanical strength or dielectric breakdown resistance. As some of the diffusing, reactive species are chemically immobilized in the barrier, the polymer’s diffusion coefficient is reduced. We write the resulting nonlinear diffusion equation in a form having special cases which are linear, facilitating the required analysis of multilayered systems. In the case of high doses of reactive gas impinging on one face of a thick slab of polymer, we calculate concentration profiles that agree well with the available experimental data, supporting the validity of the linearization procedure. In the case of low doses of corrosive species evolving over long periods of time in one layer of a two-layer system, we calculate typical concentration profiles and compute the barrier effectiveness of the second layer in protecting an adjacent surface. The barrier effectiveness is seen to increase faster with a decreasing barrier diffusion coefficient than with an increasing diffusant-immobilization rate in the barrier. Graphical results for the barrier effectiveness are given as a function of the barrier thickness and diffusion coefficient.
Laser initiated electron avalanches observed in a laser microprobe mass spectrometer
Authors: Hutt K. W. , Wallach E. R.
Published: July 2002

Laser triggered electron avalanches have been observed in a laser microprobe mass spectrometer (LAMMS) at an initial pressure of better than 10−7 mbar. The avalanches appear to be space-charge driven. Oscillatory avalanche behavior has been observed, and is discussed as a space-charge dependent feature. The conditions required to inhibit this abnormal behavior in a LAMMS instrument are also discussed.
New negative differential resistance effects in the negative resistance field-effect transistor
Authors: Kastalsky A. , Milshtein M. , Shantharama L. G. , Harbison J. , Florez L.
Published: July 2002

We report two new effects of negative differential resistance in the modulation-doped AlGaAs/GaAs negative resistance field-effect transistor. Both effects are well controlled by a third electrode. Presence of a top n+ AlGaAs layer causes a hot-electron real-space transfer to this layer, and prevents the electron transfer to the collector. Creation of the high-field domain in the source-drain channel is needed to activate the hot-electron injection to the collector. The real-space transfer to the top n+AlGaAs layer, combined with the quenching of the high-field domain by the collector bias, are responsible for the appearance of the observed new negative differential resistance effects.
A comparison of the thermal redistribution of arsenic, ion implanted into titanium disilicide films formed on single and polycrystalline silicon
Authors: Cao D. X. , Reeves G. K. , Harrison H. B.
Published: July 2002

The diffusion behavior of arsenic implanted into silicides of titanium formed on single and polycrystalline silicon has been investigated. The redistribution of arsenic in the films is significant, and physical and electrical data show that the implanted arsenic moves through the silicide layer, particularly towards the silicide-silicon interface at the 900 °C temperature under study. In the case of single-crystal silicon, accumulation of the mobile arsenic at the TiSi2-Si interface leads to a buildup within the silicide and the silicon. By sharp contrast, however, the TiSi2-polysilicon interface appears relatively transparent with no significant accumulation. The resultant dopant profiles outside the silicide show that significantly enhanced diffusion occurs in the single-crystal silicon and is comparable to that of the polycrystalline silicon.
Pressure-induced changes in the crystal structure and electrical properties of bulk InP
Authors: Patel D. , Menoni C. S. , Spain I. L.
Published: July 2002

X-ray diffraction spectra and the electrical properties of bulk InP and InGaAs have been obtained in quenched samples after compressing them into metallic phases above 14 GPa. The x-ray diffraction spectrum of InP was similar to that of the zinc-blende phase, although the [200] reflection was missing and an extra line was observed near the [220] reflection. Transport measurements showed about three orders of magnitude decrease in carrier concentration from 1016 cm−3 before pressurization to 1013 cm−3 after pressurization. The electron mobility was similar to that found for X-conduction-band minima, and the resistivity was increased by about four orders of magnitude. The photoconductivity edge of the band-to-band absorption was quenched.
Optical quality of a channel cleared in a water cloud by a high-energy CO2 laser: Turbulent mixing and recondensation
Authors: Chitanvis Shirish M.
Published: July 2002

Calculations of typical time scales suggest that recondensation (which causes a growth of water droplets within a channel cleared in water clouds by a high-energy CO2 laser beam) and turbulent mixing (which brings in a fresh set of unvaporized particles into the channel from the surrounding cloud) both occur on the time scale of a second. We have therefore constructed a unified model which describes the process of recondensation as well as turbulent mixing. For typical parameters of water clouds, it is argued on the basis of detailed numerical calculation that turbulent mixing clogs up the channel faster than recondensation can.
Noncontact minority-carrier lifetime measurement at elevated temperatures for metal-doped Czochralski silicon crystals
Authors: Shimura F. , Okui T. , Kusama T.
Published: July 2002

Minority-carrier recombination lifetimes have been extensively measured with a noncontact laser/microwave method for metal-doped p-type Czochralski silicon crystals in the temperature range from room temperature to 250 °C. The contrasting behavior of the lifetime as a function of temperature is shown for Fe- and Cr-doped silicon crystals. Iron doping greatly shortens the lifetime in the entire temperature range. Although Cr doping also greatly shortens at room temperature, the degradation effect completely disappears at elevated temperatures. Doping the Na, Ni, Cu, and W shows little effect on lifetime; Na doping results in a rather higher lifetime compared with that of undoped silicon. Moreover, lifetime measurement as a function of holding time at an elevated temperature clearly distinguishes uncontaminated silicon from metal-doped silicon.
ac-bias recording and Preisach diagrams
Authors: Ribeiro A. L.
Published: July 2002

Preisach diagrams can be useful for modeling the magnetic properties of particulate media. On such diagrams, magnetic applied fields are supposed to have a well-determined direction. However, in magnetic recording processes, the applied magnetic fields change both in magnitude and direction. We report an extension of the well-known coherent switching mode for fine particles that makes possible the definition of an effective longitudinal applied field which depends on both longitudinal and transverse components of the externally applied field. The possibilities of Preisach diagrams are explored in the case of reasonably well-aligned particulate media, and a model of ac-biased magnetic recording for such media is presented. It is shown that, knowing the longitudinal and transversal profiles of magnetic head fields and the magnitude of the writing current, it is possible to determine the zones of Preisach diagrams, which correspond to dipoles switched + or −, and the zone corresponding to the unaffected dipoles, which remain in the initial state. The effect of angular dependence of particle switching fields is naturally included, and magnetic remanence in the direction perpendicular to alignment may be obtained whenever the Preisach diagram is also available for that direction.
Atomistic study of magneto-optical amorphous thin films using synchrotron radiation
Authors: Hirscher M. , Egami T. , Marinero E. E.
Published: July 2002

The x-ray scattering intensity from sputter-deposited amorphous Tb24.3Fe75.7 films was measured using synchrotron radiation. The measurements show for the first time that the atomic structure in the film is anisotropic, and that the anisotropy is greatly reduced by annealing. The results can be explained in terms of elastic and anelastic stresses in the film, indicating that the growth-induced bond-orientational anisotropy is present in the film. It is suggested that the magnetic anisotropy due to such anelastic strain may be the origin of the observed magnetic anisotropy in the film.
Microscopic studies of the magnetization-reversal process in Co-alloy thin films (abstract)
Authors: Nguyen T. A. , McFadyen I. R. , Alexopoulos P. S.
Published: July 2002

A quantitative study of the microscopic magnetization-reversal process in 250-Å thick Co, Co90Pt10, and Co88Cr12 films deposited on top of a 250-Å-thick Cr layer has been carried out. The entire structure was on a SiN membrane to allow ease of observation in the transmission electron microscope (TEM). The magnetization-reversal process was studied by using an electromagnet to saturate the film in one direction; the applied field was then reversed until the sample reached a magnetization state between +Mr and −Mr; the field was then reduced to zero and the sample taken to the TEM for observation of the resulting magnetic structure using Fresnel and DPC Lorentz microscopy.1 This process was repeated for a number of reversal fields ranging from zero to the loop closure field. This study shows that as the reversal field was increased from zero towards the coercivity, the magnetization dispersion, i.e., the range of angles between the local magnetization and the original saturation direction, increased. The local magnetization direction varied markedly from one region of the film to the next, indicating that it is strongly tied to the local anisotropy of the film. Once the steep part of the B-H loop is reached, small reversed regions are nucleated. These reversed regions consume the entire film by continued growth and nucleation as the reverse field is increased. The nucleation occurs at the same site when the magnetization is cycled around the B-H loop. This indicates that the local anisotropy determines the sites in which critical nuclei are formed in a given applied field. The boundary between the switched and unswitched regions consists of a complex magnetization vortex structure. Once the entire film has been switched, the local magnetization dispersion decreases as the reverse field is increased. Comparison of the results among the Co-alloy films will be discussed.
Electronic structure of face-centered tetragonal iron
Authors: Peng Songshi , Jansen Henri J. F.
Published: July 2002

Thin films of iron can be grown in either the bcc or fcc structure when using an appropriate substrate. Since the two lattices never match perfectly, it is to be expected that tetragonal distortions are present. Therefore, we have performed total energy calculations for face-centered tetragonal iron in both the ferromagnetic and paramagnetic states. The standard bcc and fcc structures are two special cases of the face-centered tetragonal space group. There are two minima in the total energy, one near the bcc line and one near the fcc line. The fcc minimum has the lowest total energy. Near the fcc minimum we find a region in the c-vs-a plane where our calculations have trouble converging. We associate this with the existence of a low-spin metastable state in this region. We also study the values of the magnetic moments as a function of crystal structure.
Mean field analysis of the magneto-optical properties of TbFeCo
Authors: Challener W. A.
Published: July 2002

TbFeCo alloys have important applications in rewritable optical recording media. In order to determine the contributions to the magneto-optic activity from the rare-earth and transition-metal constituents, we have measured the temperature dependence of the magnetization, Kerr rotation, and Kerr ellipticity. The standard mean field method is shown to be inadequate for this analysis. We introduce a ratio method which provides quick, rough measurements of the contributions to the magneto-optic activity from the alloy constituents.
Formation of 0.1-μm n+p junction by As+ implantation through Pt or PtSi film
Authors: Tsui Bing-Yue , Chen Mao-Chieh
Published: July 2002

Shallow silicided n+p junctions have been formed by implanting arsenic ions into Pt or PtSi films followed by low-temperature furnace annealing in the N2 ambient. Shallow junction diodes with a junction depth of about 0.1 μm, a forward ideality factor lower than 1.02, and a reverse leakage current density less than 5 nA/cm2 at −5 V was achieved with 750 °C, 90-min annealing. Annealing at higher temperatures results in junction degradation due to Pt diffusion from PtSi into the Si substrate. This may be significantly improved by F+ implantation following the As+ implantation. The shallow junction processed with the As+/F+ dual implantation and a subsequent anneal at 800 °C shows even slightly better characteristics than those annealed at 750 °C without F+ implantation.
Investigation of the mixed state of YBa2Cu3O7−δ superconductors
Authors: Forkl A. , Dragon T. , Kronmüller H.
Published: July 2002

The magneto-optical Faraday effect has been used to observe the penetration of magnetic flux into sintered YBa2 Cu3 O7−δ. In addition, measurements of the magnetic polarization are performed with a SQUID magnetometer. The magneto-optical Faraday effect shows an inhomogeneous penetration of the magnetic flux into the sample. In a first step the flux penetrates into the intergranular regions and in a second step into single grains separately. A spatial gradient of the flux density within each grain is built up, indicating pinning forces. In the remanent state in each grain trapped flux is observed. The measured magnetization curves show good agreement with the magneto-optical investigations of the flux penetration.
Drift mobility relaxation in a-Se
Authors: Kasap S. O. , Polischuk B. , Aiyah Viswanath , Yannacopoulos S.
Published: July 2002

Time-of-flight (TOF) hole drift mobility (μd) measurements have been carried out on vacuum deposited and identically aged a-Se photoreceptor type films over a temperature range encompassing the glass transformation region to study the nature of mobility controlling shallow traps in this elemental chalcogenide semiconductor. Differential scanning calorimetry (DSC) experiments using both heating and cooling scans have also been carried out on the same films to correlate the enthalpy relaxation phenomenon with the TOF drift mobility dependence on temperature. By considering the heating rate dependence of the minimum peak in the μd vs T behavior and the heating and cooling rate dependence of the DSC glass transition temperature, it is shown that the mean retardation times, τμ and τH, associated with the relaxation of the shallow traps and the enthalpy, respectively, have similar temperature dependencies, essentially Vogel–Tammann–Fulcher type, with negligible structural contribution. Correlation is also established with the relaxation of the mechanical properties of a-Se, viz., microhardness. Moreover, the rate of equilibration of shallow traps in a-Se is found to be inversely proportional to the viscosity, η, i.e., (∂Nt/∂t)T ∼1/η, or τμ∼η. The present work provides further experimental evidence that the shallow traps in a-Se are structural defects which are thermodynamic in origin and it also shows that their equilibration involves atomic motions similar to those which control the viscosity.
Phase locking in Heisenberg helimagnets
Authors: Harris A. B. , Rastelli E. , Tassi A.
Published: July 2002

We consider a Heisenberg model with ferromagnetic nearest-neighbor and competing further-neighbor exchange interactions in a small applied magnetic field at low temperature T. As a function of the exchange constants, the modulation vector is shown to have devil’s staircase behavior. We consider the effects of nonzero temperature and quantum effects. We find a special modulation wave vector at which the incommensurability energy vanishes for the classical system at T=0.
High moment soft amorphous CoFeZrRe thin-film materials
Authors: Wang S. , Guzman J. I. , Kryder M. H.
Published: July 2002

CoFeZrRe thin films have been deposited and studied systematically for suitability as a material for thin-film recording heads. The addition of Fe and Re results in a higher degree of crystallinity, thus increasing the coercivity. The addition of Fe increases the magnetostriction of the films while the addition of Re decreases the magnetostriction. The large magnetostriction of films with a large Fe content results in high coercivity. Rotating field annealing is very effective in lowering the coercivity of the magnetostrictive films because of the relaxation of internal stresses. By properly choosing the composition of Fe and Re, we have deposited very soft magnetic thin films with a saturation magnetization of 14 kG, coercivity of 0.3 Oe, and near-zero magnetostriction. The input power dependence of the magnetostriction of this series of films is observed, although x-ray fluorescence analysis does not show any apparent compositional variations. Finally, the anisotropy field of the these films can be decreased by rotating field annealing from 25 to 5 Oe.
ZnSe-ZnS multiple-quantum-well optical bistable device
Authors: Wang Hailong , Xu Liang , Shen Aidong , Chen Yunliang , Cui Jie , Qiu Peihua , Li Qun , Zhuang Dakui , Zhang Cheng , Yang Shaochen , Wang Wenyao
Published: July 2002

The characteristics of a Fabry–Perot cavity-type ZnSe-ZnS multiple-quantum-well optical bistable device were measured by using the third harmonic beam of a yttrium aluminum garnet laser as the exciting source. We have obtained an apparent pulse compression effect and a drawn hysteresis loop according to the relation between the incident pulse power and the transmitted power.
The microstructure of Fe and Ag thin films grown by molecular-beam epitaxy on GaAs (001)
Authors: Chien C. J. , Bravman J. C. , Farrow R. F. C.
Published: July 2002

The interfaces and microstructures in molecular-beam epitaxy grown iron and silver films on GaAs(001) have been investigated using high-resolution transmission electron microscopy. Stacking faults were observed in silver films deposited directly on the GaAs (type A films: Ag(500 Å)/GaAs), but not in those which included a six monolayer Fe prelayer between the Ag and the GaAs (type B films: Ag(500 Å)/Fe(6 ml)/GaAs). The introduction of this prelayer reduces the misalignment between the Ag film and GaAs substrate lattices and leads to improved epitaxial quality. In a third structure, which retained the prelayer but to which was added an overlayer of iron (type C films: Fe(500 Å)/Ag(500 Å)/Fe(6 ml)/GaAs), stacking faults were once again found. With the Fe layer between the Ag film and GaAs substrate (type B and C films) the (001) plane of Ag was parallel to the (001) plane of the Fe film and the (001) plane of GaAs substrate but with the Ag lattice rotated 45° about the [001] axis relative to the substrate. Without the Fe prelayer (type A film), the (11̄0) plane of Ag was parallel to the (001) plane of the GaAs substrate. The orientation relationships were [001]Ag parallel to [110]GaAs and [110]Ag parallel to [11̄0] GaAs.
An all-acoustic parametric amplifier in superfluid helium
Authors: Wright D. R. , Foster J. S. , Hadimioglu B. , Quate C. F.
Published: July 2002

Studies of nonlinear acoustic interactions in superfluid helium at temperatures below 0.2 K have culminated in the construction of an all-acoustic parametric amplifier at gigahertz frequencies. This device represents the shortest wavelength parametric amplifier ever made, with signal wavelengths shorter than 1000 Å and pump wavelengths shorter than 600 Å. In the experiment, plane waves are mixed at a predefined angle in the superfluid helium. Two gain regimes are observed. The first regime is a noncollinear phase-matched process, in which the signal phonon stimulates decay of the pump phonon to create gain at the signal frequency. The second regime is a four-phonon collinear process, in which gain on the signal is created by the second harmonic of the pump. This four-phonon process is unusual and is shown to be a combination of three-phonon processes wherein the lack of conservation of energy and momentum in one process is mostly compensated by the other.
Photoluminescence study of HgZnTe alloys
Authors: Ravid A. , Sher A. , Zussman A.
Published: July 2002

Photoluminescence spectra of Hg1−xZnxTe layers with compositions of x=0.226 and 0.248 grown by liquid phase epitaxy on CdZnTe substrates were studied between 12 and 250 K. The annealed x=0.248 sample exhibits two unresolved lines, 15 meV apart, attributed to band-to-band and band to-acceptor transitions. The temperature dependence of the photoluminescence peak energy and of the energy gap, based on infrared transmission measurements, are similar. The linewidth varies with temperature with a slope of 1.6–1.7 kB suggesting transitions obeying the k conservation rule. The measured carrier concentration versus temperature curve reveals a carrier freezeout at low temperatures. The carrier lifetime measured by the photoconductive recovery technique indicates the recombination by the Shockley–Read recombination mechanism. The observed total luminescence intensity exhibits a maximum in this temperature range. The temperature dependence of the quantum efficiency, evaluated from the calculated radiative and the observed total lifetime, was found to agree with that of the total luminescence intensity.
A dangling-silicon-bond defect in topaz
Authors: Priest Vann , Cowan David L. , Reichel Daniel G. , Ross Fred K.
Published: July 2002

Fast neutron bombardment of natural topaz crystals creates an optically active point defect with an absorption peak near 2 eV, coloring the crystal blue. This blue color anneals near 500 °C. The optical absorption is strongly dichroic, with a maximum when E is along the a direction in the orthorhombic lattice. We identify the defect as an oxygen vacancy in an isolated SiO4 tetrahedron, in the form of a doubly occupied dangling silicon bond. The defect is nonmagnetic, but electron spin resonance of its Frenkel partner implies an average oscillator strength f=0.012. A natural blue topaz is colored by this same defect, and electron and gamma irradiations produce a similar blue, but with strikingly different polarization dependences.
Fringe-locked running hologram and multiple photoactive species in Bi12TiO20
Authors: Frejlich Jaime
Published: July 2002

Fringe-locking techniques ar used for the recording of stable 90 ° phase-shifted running holograms in photorefractive crystals. The use of this technique permits the characterization of a fast and a slow photoactive species in Bi12TiO20. We compare our results with those obtained from other methods and discuss the practical interest of this technique.
A helium discharge with neutral gas flow: Comparison of theory with experiments
Authors: Karditsas Panayiotis J.
Published: July 2002

The radio-frequency excited helium discharge is modeled as an equivalent circuit in order to account for the electrode-sheath coupling, which includes an electrode and a sheath capacitance. The results obtained from the solution for the sheath thickness and reactance are used in conjunction with the known uniform plasma column characteristics to obtain the required voltage needed to sustain the current flow through the discharge. The calculations give that the value of the electron density at the sheath edge ns varies between 12%–16% of the centerline electron density ne0, whereas the root mean square of the sheath thickness ŝ assumes values between 6% and 11% of the pipe radius a. Both curves are increasing with increasing current flow through the discharge. The order of magnitude of the electrical conductivity achieved by the 11-MHz radio frequency for the pressure range of 405.33–506.67 Torr, temperature range of 483–510 K, velocity range of 449–485 m/s, in a pipe of radius 0.011 m, is varying from 0.01 to 0.07 mho/m, which is comparable to the lower limits of the ionization achieved under thermal equilibrium for a gas seeded with a few percent of a low ionization potential substance. The comparison of the theoretical estimates for the applied voltage-current curve with the experimental measurements show general agreement and are within±10%, and support the theory that the major loss of the applied voltage occurs in the electrode-sheath region, especially at the higher values of the current flow through the discharge.
Formation of continuous CoSi2 layers by high Co dose implantation into Si(100)
Authors: Hull R. , White A. E. , Short K. T. , Bonar J. M.
Published: July 2002

We have studied the mechanisms for formation of continuous CoSi2 layers by high dose (∼1017 cm−2) Co implantation into Si(100). For single dose implantations, a critical dose exists above which coalescence into a single layer occurs after a vacuum anneal at 1000 °C for 30 min, but below which disconnected, strongly {111} faceted precipitates form. Transmission electron microscopy and Rutherford backscattering suggest that the key condition for continuous layer coalescence to occur is the formation of a connected array of small silicide precipitates either as-implanted or during an intermediate 600 °C anneal. This postulate is supported by the observation that super-critical doses which are builtup by successive subcritical doses and 1000 °C anneals do not coalesce into single layers.