bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface anisotropy in giant magnetic coercivity effect of cubic granular FeCo/SiO2 and NiCo/SiO2 films: A comparison with Néel’s theory
Authors: Chen Chen , Kitakami Osamu , Okamoto Satoshi , Shimada Yutaka
Published: July 2002

The structure and magnetic properties of a series of granular Fe1−xCox/SiO2 and Ni1−xCox/SiO2 films have been studied. Both Fe1−xCox and Ni1−xCox alloy fine grains posses cubic structure within the cobalt composition x<0.7. The grains grow to about 150–200 Å in diameter when the annealing temperature is between 570 and 600 °C, where the samples show a giant magnetic coercivity effect. The experimental results can be successfully accounted for by the thermal relaxation theory, assuming the surface anisotropy dominates in the giant magnetic coercivity effect. By fitting the theory into the experimental results, the surface anisotropy constants of Fe1−xCox and Ni1−xCox fine grains can be obtained in the range x<0.7. The surface anisotropy from Néel’s theory, on the other hand, manifests qualitative similarity to the fitting results as a function of Co contents.
Infrared optical properties of Mn1.56Co0.96Ni0.48O4 spinel films sputter deposited in an oxygen partial pressure series
Authors: Dannenberg Rand , Baliga S. , Gambino R. J. , King A. H. , Doctor A. P.
Published: July 2002

Mn 1.56 Co 0.96 Ni 0.48 O 4 spinel films were sputter deposited onto silicon substrates using a series of oxygen partial pressures. Fourier transform infrared transmission and reflectance, and Raman scattering measurements were made. The 1–25 μm wavelength range was examined using these optical techniques. The complex index of refraction was calculated for this entire wavelength range. Infrared active vibrations were analyzed using multiple oscillator analysis, Kramers–Kronig analysis, and derivative reflectance spectroscopy. The Raman and infrared active lattice vibrations were observed to shift with increasing oxygen partial pressure during film deposition, and were consistent with the earlier published shift in Debye frequency calculated from resistivity data. The films were shown to have an optically transparent window from 6 to 14 μm wavelength, with the multiphonon cutoff occurring at 14 μm. The frequency of the multiphonon cutoff was also observed to shift to higher frequency with the oxygen partial pressure during sputtering. These studies, and the earlier work on the variation of the thermopower and resistivity with oxygen partial pressure and film temperature, are consistent with a change in the ratio of Mn3+ to Mn4+ cations with oxygen, with small polaron hopping as the charge transport mechanism.
Magnetic properties of chromium doped rare earth manganites Ln0.5Ca0.5Mn1−xCrxO3 (Ln=Pr, Nd, Sm and 0.05⩽x⩽0.10) by soft x-ray magnetic circular dichroism
Authors: Toulemonde O. , Studer F. , Barnabé A. , Raveau B. , Goedkoop J. B.
Published: July 2002

Soft-x-ray magnetic circular dichroism (SXMCD) at Mn, Cr L2,3 and Ln M4,5 edges of Ln0.5Ca0.5Mn1−xCrxO3 (Ln=Pr, Nd, Sm and 0.05⩽x⩽0.10) bulk polycrystalline samples have been performed at T=20 K below the ferromagnetic Curie temperature. We show the existence of magnetic sublattice on each of the probed cations. Chromium cations order at low temperature antiparallel to the manganese subnetwork and rare earth cations likely exhibit a sperimagnetic ordering. These results are compared with magnetization measurements and a tentative correlation with magnetoresistance properties is discussed. This work also demonstrates that SXMCD can probe element and site specific magnetic properties of multicomponent systems.
Effective-medium model dependence of the radar reflectivity of conducting particle films
Authors: Stoyanov Aleksandr J. , Howell Barbara F. , Fischer Eugene C. , Überall Herbert , Chouffani Khalid
Published: July 2002

We present a numerical study of the frequency dependent, complex effective permittivity ε for a composite material which consists of lossy graphite-type microsphere inclusions randomly imbedded in a dielectric matrix, with a view towards assessing the suitability of such a composite for its use as a radar absorbing material (RAM). This suitability is determined by the material possessing a large effective absorptivity while at the same time not giving rise to an overly large reflectivity. In this vein we here evaluate, as a function of frequency up to 20 GHz, the effective magnitudes of Re ε and Im ε for particulate composites and their dependence on the volume fraction φ of the particles, while independently varying conductivities. Our calculations are carried out using both the effective-medium theory (mixture theory, valid for small φ), and the multiple-scattering theory of Tsang and Kong valid for general φ but for small particle sizes. Multiple-scattering effects lead to increased effective absorptivities by adding scattering losses to the intrinsic losses of the media. We comment on the optimal values of the medium parameters and packing fractions for composite RAM materials. Percolation effects (transition from matrix dominance to particle dominance) are studied, both for the effective-medium theory and for the multiple-scattering theory, and compared for the two cases.
Electron mobility and drift velocity calculations for bulk GaSb material
Authors: Damayanthi P. , Joshi R. P. , McAdoo J. A.
Published: July 2002

Electron mobility and drift velocity simulation results are presented for bulk GaSb based on a many-valley, anisotropic Monte Carlo model. Our mobility results at 300 K are in good agreement with available experimental data. Values close to the room temperature GaAs mobility have been predicted. Transient drift velocities are demonstrated to be higher than for GaAs and the negative differential velocity regime is shown to occur at much lower electric fields of about 1 kV/cm. The material could be useful as a low voltage oscillator or in high speed photodetection.
Neutral depletion and transport mechanisms in large-area high density plasma sources
Authors: Tynan G. R.
Published: July 2002

Plasma uniformity has been recognized as a significant parameter in large-sized high density plasma processing tools, but neutral uniformity issues have received less attention. In this article we show experimental and modeling results which indicate that significant neutral uniformity variations can occur in high density plasma processing tools. The experiments are carried out in both inductively coupled plasma and helicon plasma sources. A movable static pressure gauge is used to obtain the static radial neutral pressure distribution both with and without a discharge present. Without a wafer present in the reactor, significant (∼20%–40%) reductions in neutral pressure are observed in these sources during steady-state plasma operations. This spatially averaged neutral depletion is accompanied by hollow neutral pressure profiles. The degree of on-axis neutral depletion depends upon both plasma density and neutral fill pressure. We show that the “plasma pumping” effect, wherein electron impact ionization of neutral particles is followed by their rapid removal from the plasma by the pre-sheath electric field, can reproduce the experimental results. This effect has the potential to result in large (∼50%) neutral density variation across 300 mm wafers in high density plasma sources.
Tunneling properties of holes across abrupt heterostructures using Burt’s envelope function theory
Authors: Ekbote S. , Cahay M. , Roenker K.
Published: July 2002

We use the envelope function formalism [M. G. Burt, J. Phys. Condens. Matter 4, 6651 (1992)] with the rigorous boundary conditions [B. A. Foreman, Phys. Rev. B 48, 4964 (1993)] to analyze the tunneling properties of holes across an abrupt InP/In0.53Ga0.47As heterojunction. We compare our results to those derived with boundary conditions obtained from an ad hoc “symmetrized” form of Burt’s Hamiltonian. Our analysis includes the coupling between heavy, light, and spin-orbit bands. The percentage difference between the tunneling coefficients of heavy and light holes calculated in the two approaches increases (up to a maximum value of 30%) with the magnitude of the hole wave vector component parallel to the heterointerface. In addition, the tunneling coefficients of holes are found to be quite sensitive to the orientation of the hole wave vector parallel to the heterointerface. This sensitivity is particularly noticeable for large values of the hole transverse wave vector.
Micro-Raman spectroscopic analysis of tetrahedral amorphous carbon films deposited under varying conditions
Authors: Liu E. , Shi X. , Tay B. K. , Cheah L. K. , Tan H. S. , Shi J. R. , Sun Z.
Published: July 2002

The structure of tetrahedral amorphous carbon (ta-C) films deposited by a filtered cathodic vacuum arc has been studied using micro-Raman spectroscopy in terms of substrate bias, nitrogen gas partial pressure (ta-C:N films) or aluminum content in a mixed aluminum/carbon target (ta-C:Al films) during deposition. The first-order Raman spectra generally show a broad feature overlaid by a disordered (D) peak and a graphitic (G) peak. The contribution of sp3 bonding to the Raman spectrum is not explicit, since the Raman phonon line is more sensitive to the sp2 carbon bonding due to its larger Raman scattering cross section. However by comparing the ratios of the intensities, the full widths at half maximum (FWHM), and the peak areas between the D and G peaks, the sp3 contribution may indirectly be reflected by the complex Raman features. The G peak position for the ta-C and ta-C:N films appears to not change significantly with the change of substrate bias voltage or N2 partial pressure, whereas the shift of the D peak is more appreciable. On the contrary, the G peak position for the ta-C:Al films shows a continuous decrease with increasing Al content. For the undoped ta-C films, the minimum intensity, area, and FWHM ratios between the D peak and the G peak are obtained at a bias around −100 V, which corresponds to the maximum sp3 content in the ta-C films. These ratios for the ta-C:N and ta-C:Al films, however, generally increase with increased N or Al content, which indicates the increase of sp2 bonded clusters.
High pressure effect on magnetic properties and volume anomalies of Ce2Fe17
Authors: Medvedeva I. , Arnold Z. , Kuchin A. , Kamarád J.
Published: July 2002

We present the results of high pressure studies of magnetization, magnetic phase transitions, and related volume anomalies for the intermetallic compound Ce2Fe17 under hydrostatic pressures up to 10 kbar. The giant negative pressure effect on the ferromagnetic ordering temperature ΘT=94 K was determined: dΘT/dP=−(38±2) K/kbar. This extraordinary decrease of ΘT under pressure is not accompanied by the related pronounced decrease of the saturated magnetization under pressure below 2.5 kbar. The effect of pressure on the Néel temperature TN=206 K is less pronounced: dTN/dP=−(1.7±0.2) K/kbar. A large positive spontaneous volume magnetostriction that is observed below TN is suppressed by the application of high pressure and it disappears above 2.5 kbar. A competition of positive and negative exchange interactions between iron atoms is discussed and is thought to be the main reason for the volume anomalies observed. The role of the f electrons of Ce, their possible hybridization with d states of Fe, and their role in magnetic properties of the Ce2Fe17 compound is not yet clear.
Demonstration of a solid-state optical cooler: An approach to cryogenic refrigeration
Authors: Edwards Bradley C. , Anderson Johnny E. , Epstein Richard I. , Mills Gary L. , Mord Allan J.
Published: July 2002

We report the successful operation of an optical cooler system. This device achieved 48 °C of cooling from room temperature and a heat lift of 25 mW when it was pumped with 1.6 W of laser light. Its performance as a function of pump laser wavelength and chamber temperature agrees well with theoretical models. This device validates the physics needed for exploiting the laser cooling of solids to develop practical optical refrigerators.
Correlation between microstructure and optical properties of Ge2Sb2Te5 thin films
Authors: Kim Jin-Hong
Published: July 2002

The microstructure and optical properties of amorphous and crystalline Ge2Sb2Te5 thin films prepared under different sputtering conditions were investigated. The microstructure of amorphous films was modified by changing the sputtering Ar gas pressure during the deposition. The optical properties and the microstructure of the sample prepared at high Ar gas pressure were remarkably different from the samples prepared at low pressures. A strong correlation between the microstructure and optical properties of Ge2Sb2Te5 thin films was found.
Evidence for the effect of carbon on oxygen precipitation in Czochralski silicon crystal
Authors: Liu Peidong , Ma Xiangyang , Zhang Jinxin , Li Liben , Que Duanlin
Published: July 2002

This article reports some new experimental evidence for the effect of carbon on oxygen precipitation in a high carbon content Czochralski silicon (H[C] Cz-Si) crystal. The oxygen precipitation occurring at an intermediate temperature of 950 °C has been especially investigated. In such case, the carbon atoms slightly participate in oxygen precipitation with 1200 °C preannealing, while the carbon atoms actively participate in oxygen precipitation with low temperature preannealing. The experiments show that the 1230 cm−1 absorption band in the Fourier transmission infrared spectrum definitely originates from the oxygen precipitates involving insignificant carbon reduction; on the other hand, the oxygen precipitates involving significant carbon reduction are surely irrelevant to the 1230 cm−1 absorption band. According to the correlation of the change in oxygen and carbon concentrations during oxygen precipitation, it is plausible that there is a critical precipitate size which distinguishes the carbon behavior in oxygen precipitation, that is, the carbon atoms actively participate in oxygen precipitation when the precipitates are smaller than the critical size; whereas, the carbon atoms are only slightly involved in oxygen precipitation when the precipitates are larger than the critical size.
Field inhomogeneity effects on photoreflectance spectra of ZnSe/GaAs
Authors: Song J. H. , Sim E. D. , Baek K. S. , Chang S. K.
Published: July 2002

Photoreflectance measurements from ZnSe epilayers of different thicknesses were carried out. In photoreflectance spectra, the exciton line shape “rotation” is observed to be much slower than that in the reflectance spectra by increasing the epilayer thicknesses. To analyze the exciton line shape rotation quantitatively, the photoreflectance spectra were calculated considering the built-in electric field inhomogeneity effects near the interface as well as the interference effects. Calculated line shapes of the photoreflectance spectra show a good agreement with the observations. Our results imply that inhomogeneity effects of the interface built-in electric field plays an important role in the spectral rotation in photoreflectance.
Electrical conduction in annealed semi-insulating InP
Authors: Fung S. , Zhao Y. W. , Luo Y. L. , Beling C. D.
Published: July 2002

Variable-temperature current–voltage has been used to study the conduction properties of Fe-doped semi-insulating (SI) InP in the as-grown and annealed states. It is found that the trap-filling (TF) process disappears gradually with lengthening of annealing time. This phenomenon is explained by the decrease of the concentration of the empty Fe deep level (Fe3+) that is caused by the thermally induced donor defect formation. The TF process cannot be observed in annealed undoped and long-time annealed Fe-doped SI InP material. The breakdown field of annealed undoped and Fe-doped SI InP is much lower than that of as-grown Fe-doped InP material. The breakdown field decreases with decreasing of temperature indicating an impact ionization process. This breakdown behavior is also in agreement with the fact that the concentration of the empty deep level in annealed InP is lowered.
Impact of plasma etching on the noise performance of Ti/p-Si and Ti/p-Si1−xGex Schottky contacts
Authors: Ouacha H. , Mamor M. , Willander M. , Ouacha A. , Auret F. D.
Published: July 2002

The effect of plasma etching on the noise properties of Ti/p-Si and Ti/p-Si1−xGex (with x=0.05) Schottky junctions has been investigated. The noise measurements were performed over a temperature range of 77–300 K at frequencies of 10–100 kHz. The main noise source observed in these diodes during argon plasma sputter etching was attributed to the generation–recombination noise. From the analysis of the noise data, we have determined the interface state density and evaluated the introduced damage. The results indicate two optimum operating temperatures where low-noise level can be achieved. Furthermore, the activation energies of trap levels have been extracted by using noise spectroscopy (NS) and compared with those measured by deep-level transient spectroscopy (DLTS). We found two additional trap states using NS not detected by DLTS measurements. Finally, a noise comparison between Ti/p-Si and Ir/p-Si fabricated on an unetched substrate has been made.
Monte Carlo calculation of hole initiated impact ionization in 4H phase SiC
Authors: Bellotti Enrico , Nilsson Hans-Erik , Brennan Kevin F. , Ruden P. Paul , Trew Robert
Published: July 2002

In this article, we present a comprehensive, full band theoretical study of the high field, hole transport properties of the 4H phase of silicon carbide (4H-SiC). The calculations are performed using a full band ensemble Monte Carlo simulation that includes numerically tabulated impact ionization rates, and phonon and ionized impurity scattering rates. In addition, the simulation includes a mechanism, interband tunneling, by which the holes can move between bands in the proximity of band intersection points. It is found that there exists a significant anisotropy in the calculated steady-state hole drift velocity for fields applied parallel and perpendicular to the c-axis direction. Good agreement with experimental measurements of the hole initiated impact ionization coefficient for fields applied along the c axis is obtained, provided that interband tunneling in the proximity of band intersections is included in the model. If interband tunneling is not included, the calculated ionization coefficients are orders of magnitude lower than the experimental measurements.
Effect of phase transition on the surface potential of the BaTiO3 (100) surface by variable temperature scanning surface potential microscopy
Authors: Kalinin Sergei V. , Bonnell Dawn A.
Published: July 2002

Variable temperature atomic force microscopy and scanning surface potential microscopy are used to characterize the ferroelectric BaTiO3 (100) surface. The influence of domain structure on surface topography and surface potential distribution is discussed. Domain induced surface corrugations were found to disappear above the Curie temperature confirming the local phase transition. Associated variations of surface potential are quantified. Relaxation of surface potential after the transition to paraelectric state on heating and during the transition to the ferroelectric state on cooling was observed. Differences in kinetics of the topographic structure and surface potential variations are used to distinguish polarization compensation mechanisms.
Photoemission from metals covered with a nanostructured carbon film
Authors: Boscolo I. , Milani P. , Parisotto M. , Benedek G. , Tazzioli F.
Published: July 2002

Though present photoemitting cathodes have attained quantum yields, lifetimes, dark currents, and response times as required by high-luminosity accelerators, their use is hampered by their high reactivity to residual gases even in ultra-high-vacuum conditions. Ultrathin (20–200 nm) films of nanostructured sp2 carbon, directly grown on photocathodes by supersonic cluster-beam deposition, besides providing a strongly bound, inert protective coating, are shown to maintain the photoemission efficiency of clean metallic substrate cathodes. Moreover, nanostructured carbon coating is shown to induce strong nonlinearities in photoemission at high intensities, which can be explained as due to the Auger effect.
Phenomenological magnetic modeling of Au:Fe:Au nano-onions
Authors: Wiggins J. , Carpenter Everett E. , O’Connor Charles J.
Published: July 2002

A new type of materials, the nano-onions, has been shown to exhibit GMR. These nanostructured composites consist of a nonmagnetic core coated with a thin layer of a bulk ferromagnet with a passivating nonmagnetic surface layer. The nano-onion investigated had a 3 nm Au core, a 1 nm Fe layer, and a 2 nm Au coating; all values correspond to the radius. The materials were manufactured using a sequential reverse micelle technique, detailed elsewhere. The sample preparation method produces a powder sample was cold pressed into a pellet. Magnetic investigation of the sample indicated that the material was superparamagnetic with a blocking temperature of 52 K for particles approximately 8 nm in diameter. At 10 K, the coercivity was 420 Oe, indicating a large degree of order. The GMR was measured over the entire temperature range available. At 10 K, in 5 T, a 1% MR was observed. The GMR was modeled using a simple phenomenological magnetic model initially used to study GMR granular thin films. To more accurately match the physical parameters of reverse micelles, the conventional log-normal particle size distribution was replaced with a normal distribution. The model suggested that the system consisted of an ensemble of 1.3 nm particles with a standard deviation of 0.07. The model does not detect the entire 8 nm diam, rather it detects the individual walls of the shell. In this context, it has shown that a simple phenomenological model can accurately predict the magnetic and electronic behavior of nano-onions.
Reflection high-energy electron diffraction based texture determination: Magnetic thin films for perpendicular media
Authors: Litvinov Dmitri , Howard J. Kent , Khizroev Sakhrat , Gong Heng , Lambeth David
Published: July 2002

Application of reflection high-energy electron diffraction (RHEED) to texture determination is demonstrated for magnetic thin film applications. Diffraction pattern analysis based on kinematic theory of RHEED is outlined. Application of the technique is demonstrated for texture characterization of hexagonal-close-packed CoCr alloys that are used as recording layers in perpendicular recording media. It is shown that both texture orientation and texture angular dispersion extracted from RHEED patterns are in agreement with the data obtained using x-ray diffraction.
Growth and magnetic properties of thin epitaxial NixPd1−x alloy films on Cu3Au(100)
Authors: Seider M. , Kaltofen R. , Muschiol U. , Lin M.-T. , Schneider C. M.
Published: July 2002

We investigated the magnetic properties of NixPd1−x films epitaxially grown on Cu3Au(100) surfaces. The films grow nicely layer-by-layer at higher Pd concentrations and exhibit a composition dependent inverse spin reorientation transition. Growth and magnetic properties are found to be strongly affected by the film strain.
Barium ferrite thin film media with perpendicular c-axis orientation and small grain size
Authors: Zhuang Zailong , Rao Maithri , White Robert M. , Laughlin David E. , Kryder Mark H.
Published: July 2002

Barium ferrite thin films with perpendicular c-axis orientation and small grain size (about 300 Å) were successfully fabricated with careful control of sputtering conditions. The c-axis orientation of barium ferrite thin films is most sensitive to the oxygen partial pressure during deposition. All samples with oxygen gas during deposition have a random c-axis texture, as indicated by existence of both weak (00l) peaks and (106) peaks. All the samples without oxygen gas during deposition show only strong (00l) peaks, which indicate excellent perpendicular c-axis orientation. Transmission electron microscopy results show that oxygen gas promotes the growth of in-plane and/or randomly oriented grains. The effect of the Pt interlayer on the barium-rich films was also studied. The Pt interlayer was found to be very effective in improving c-axis orientation of barium-rich films. A relative increase in perpendicular nucleation sites over in-plane and/or random nucleation sites contributes to the improvement in perpendicular c-axis orientation.
Transient behavior of the excitonic magnetic polarons in Cd1−xMnxTe epilayers
Authors: Pittini R. , Shen J. X. , Debnath M. C. , Souma I. , Takahashi M. , Oka Y.
Published: July 2002

We present a study of the dynamics of the excitonic magnetic polarons in Cd1−xMnxTe epilayers. The transient photoluminescence measured by a streak camera under resonant excitation is analyzed with a special attention devoted to line shape of the emission signal. A nonradiative spectral region is observed in zero field and is strongly suppressed in a field of 6 T. This observation is understood to be directly related to the alignment of the Mn2+ spins and is therefore closely related to the formation of magnetic polarons. A few Mn spins are found to be aligned already within 10 ps, but the total Mn spin polarization in the sample is found to increase exponentially with a rise time of 37 ps in Cd0.73Mn0.27Te epilayers. Furthermore, the values of 19.2 and 12.4 meV were determined for the energies of the excitonic magnetic polarons in Cd0.73Mn0.27Te and Cd0.79Mn0.21Te epilayers, respectively.
Comparing theoretical demagnetizing factors with the observed saturation process in rectangular shields
Authors: Aharoni Amikam , Pust Ladislav , Kief Mark
Published: July 2002

An analytic expression is given for the ballistic demagnetizing factors, D′, of the general rectangular prism, in which the field is averaged over the middle cross section of the prism, and for the “side” demagnetizing factor, D″, in which the averaging is over the edges of the prism. The demagnetizing fields are compared with the applied field values when a 250×95×2.35 μm magnetic shield transfers into the saturated state. This shield was made of a Ni80 Fe20 film, with a small uniaxial magnetic anisotropy induced during the electroplating process. Domain structure and the process of magnetic saturation were imaged using wide-field Kerr microscopy in fields up to 400 Oe, both along the easy and the hard axes. The ballistic demagnetizing field is found to be close to the external field necessary to align magnetically the central part of the shield, while the full shield saturation takes place at a field above the recently published magnetometric demagnetizing field. Saturation fields along the hard uniaxial anisotropy axis are larger, due to effective anisotropy fields.
Local hysteresis variation of Co/Pd nanomultilayers
Authors: Choe Sug-Bong , Jang Hyuk-Jae , Shin Sung-Chul
Published: July 2002

Local coercivity variation of Co/Pd nanomultilayers has been investigated by measuring the polar Kerr hysteresis loops of the local areas of submicron size using a magneto-optic Kerr microscope system. Interestingly, the local coercivity distribution was very sensitive to an increase in the number of repeats: the (2 Å Co/11 Å Pd)10 sample showed a smooth variation of the local coercivity, while (2 Å Co/11 Å Pd)18 showed a large fluctuation. Based on the thermally activated relaxation model, we have found that this local coercivity variation had a crucial effect on the contrasting magnetization reversal behavior observed in those samples, wall-motion dominant for the former sample and nucleation dominant for the latter one.
Electrical and optical characteristics of deep levels in vanadium-doped Cd0.96Zn0.04Te materials by photoinduced current, capacitance, and photocapacitance transient spectroscopies
Authors: Zerrai A. , Marrakchi G. , Bremond G.
Published: July 2002

A complete quantitative analysis of electrical and optical properties is carried out on the vanadium transition metal in semi-insulating and n type conductor Cd0.96Zn0.04Te crystals using deep level transient spectroscopy, deep level optical spectroscopy, and photoinduced current transient spectroscopy. Four deep levels are mainly detected, with activation energies at Ec−0.95 eV, Ec−0.78 eV, Ev+0.68 eV, and Ev+0.2 eV. Their electrical and optical characteristics (thermal and optical cross sections, concentrations, and apparent activation energies) are determined. The 0.68 eV hole level and the 0.95 eV electron trap are related to the vanadium doping. These two levels are proposed to be originated from the same defect that interacts with the valence and conduction band, respectively. We have demonstrated that the 0.95 and 0.78 eV electron traps present capture barrier energies with values of 0.2 and 0.15 eV, respectively. The observed resonance bands on the optical cross sections σno and σpo of the 0.95 eV level are attributed to d→d* internal transitions of the V2+(3d3) and V3+(3d2) ions on Cd sites, respectively. Based on the above result, the 0.95 eV level is formally identified to the V2+/V3+ single donor and its real thermal ionization energy locates it near the midgap at 0.75 eV below the conduction band. This level is shown to be the donor trap that explain the semi-insulating character of the V doped CdZnTe materials. It is shown also that the 0.78 and 0.95 eV play a key role in the photorefractive properties of the V doped CdZnTe crystals.
Line-focus-beam acoustic microscopy characterization of optical-grade LiTaO3 single crystals
Authors: Kushibiki J. , Okuzawa T. , Hirohashi J. , Ohashi Y.
Published: July 2002

Basic data for evaluating homogeneities of LiTaO3 single crystals for optical use are investigated by line-focus-beam acoustic microscopy. First, the relationships among leaky surface acoustic-wave (LSAW) velocities, chemical compositions, Curie temperatures, densities, and lattice constants are experimentally investigated as the calibration lines for crystal evaluation using X-, Y-, and Z-cut substrates prepared from three LiTaO3 single crystals grown along the crystallographic Y axis with different Li2O contents ranging from 48 to 49 mol %. It is shown that as the Li2O content increases around the congruent composition, the LSAW velocities linearly increase for all specimen surfaces and all propagation directions, and the increase rate is maximum for Z-cut, Y-axis propagating (ZY) LiTaO3. Next, homogeneities of the above three crystals and a commercially available optical-grade crystal are evaluated using ZY-LiTaO3 specimens and the obtained calibration lines. The chemical composition variations along both the pulling direction and the diameter direction are successfully detected as LSAW velocity variations, due to the changes of crystal-growth conditions. In the commercial crystal, the LSAW velocity variations for the whole examined region (80 mm×60 mm) exhibit a maximum difference of 0.82 m/s, corresponding to the composition change of 0.026 Li2O mol %. It is demonstrated that this ultrasonic method has the unique and useful capabilities of detecting changes of the growth conditions and of evaluating local densities and the crystal-melt interface shape.
Magnetic field dependence of spin reversal behavior in Co/Pd nanomultilayers
Authors: Choe Sug-Bong , Shin Sung-Chul
Published: July 2002

Spin reversal of Co/Pd multilayers under various strengths of an applied field has been quantitatively investigated. The reversal behavior was found to be essentially the same irrespective of the magnitude of the applied field, but the rate of domain evolution was considerably accelerated by increasing the applied field. Quantitative analysis revealed that both the wall-motion speed and the nucleation rate were exponentially proportional to the applied field. The proportional coefficients of the wall-motion speed and the nucleation rate for the samples were found to be same. The reversal ratio of the wall-motion speed to the nucleation rate was found to be nearly independent of an applied field strength.
Quantized spin wave modes in micron size magnetic disks
Authors: Jorzick J. , Demokritov S. O. , Hillebrands B. , Bartenlian B. , Chappert C. , Decanini D. , Rousseaux F. , Cambril E.
Published: July 2002

We report on the observation of spin wave quantization in tangentially magnetized Ni80Fe20 disks by means of Brillouin light scattering spectroscopy. For a large wave vector interval, several discrete, dispersionless modes with a frequency splitting up to 2.5 GHz were observed. The modes are identified as being magnetostatic surface spin wave modes quantized by their lateral confinement in the disk. For the lowest modes, dynamic magnetic dipolar coupling between the disks is found for a disk spacing of 0.1 μm.
Dynamic relaxation in thin films
Authors: Boerner Eric D. , Bertram H. Neal , Suhl Harry
Published: July 2002

The dynamic magnetization process in thin film platelets is studied by numerical micromagnetics. Simulations are conducted without the addition of the phenomenological damping term in the Landau–Lifshitz equation. Excess Zeeman energy is transferred to magnetostatic-exchange coupled spin waves. This allows the average magnetization to relax towards the equilibrium configuration. The strength of the applied field and the size of the platelet both affect how much energy can be transferred to the spin wave modes. For large enough platelets and fields that are not too large, nearly complete reversal can be obtained without a mechanism to dissipate magnetic energy.
Modelling the percolation-type transition in radiation damage
Authors: Trachenko Kostya , Dove Martin T. , Salje Ekhard
Published: July 2002

Following the concept of percolation-type transition in zircon under radiation damage suggested previously, the general simulation model of irradiated material is proposed. The model naturally gives rise to swelling of the undamaged crystalline part of irradiated material. X-ray scattering profiles are calculated and show broadening that increases with radiation damage, in good agreement with published experimental x-ray diffraction data on zircon. The effect of percolation on material bulk properties is studied.
Trapping and detrapping of electrons photoinjected from silicon to ultrathin SiO2 overlayers. II. In He, Ar, H2, N2, CO, and N2O
Authors: Shamir N. , van Driel H. M.
Published: July 2002

Photon-induced gas-assisted charging (PIGAC) of 1.5 nm thick SiO2 overlayers by photoemission from the Si substrate is demonstrated to be a universal feature for all gases. In our case (multi)photoemission is induced by high-intensity 800 nm, 150 fs pulses in samples at 295 K. O2 is more effective than other gases, probably due to the accumulation of surface charge following the formation of O2− on the surface. For the other gases, the efficiency decreases with increasing molecular (or atomic) size, pointing to a mechanism that is dependent on the proximity of the gas molecules to charge traps. Combined measurements of photoemission current and the contact-potential-difference detected charge spillover from the irradiated spot to the rest of the surface. Transfer of PIGAC electrons to long-lifetime charge traps was also detected for all gases. Its efficiency is the highest for He, probably due to the larger effective surface (and thus larger PIGAC) created by He penetration into the oxide layer. Detrapping of trapped electrons also occurs with PIGAC, and is particularly effective for CO and H2. Its mechanism and gas specificity are not understood as yet, but the strong increase of detrapping with decreasing temperature suggests a dependence on longer proximity of the gas molecules to the traps due to an increased surface residence time.
Possibility of multiple tunnelling current peaks in a coupled quantum well system
Authors: Luis D. , Dı́az J. P. , Capuj N. E. , Cruz H.
Published: July 2002

In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a bilayer electron system. Considering both Hartree and exchange-correlation potentials, we have calculated the tunnelling rates between the two quantum wells when an external bias is applied in the double quantum well system. Due to the nonlinear effective-mass equation, it is found that the charge dynamically trapped in both wells produces a reaction field which modifies the system resonant condition. At different electronic sheet densities, we have shown the possibility of having multiple resonant tunnelling peaks in a bilayer electron system.
Depleted semi-insulating silicon/silicon material formed by wafer bonding
Authors: Johansson Mikael , Bengtsson Stefan
Published: July 2002

Wafer bonding has been used to manufacture a silicon material intended as substrate for high-frequency applications. The space charge regions surrounding the bonded silicon/silicon interface deplete the silicon, thereby causing semi-insulating behavior at high frequencies. The material has been characterized electrically for frequencies up to 40 GHz using metal transmission lines on its surface. The results show that transmission lines made on these materials show low losses when signals are transmitted along them. These results have been compared to measurements using similar transmission lines on bulk silicon wafers of different resistivities, on SIMOX wafers, and on quartz.
Near threshold excitation of K
V
V Auger spectra in carbon monoxide using electron–electron coincidence spectroscopy
Authors: Ungier L. , Thomas T. D.
Published: July 2002

Electron–electron coincidence spectroscopy has been used to separate KVV Auger spectra in CO into several component spectra, each arising from different core-excited initial states. Results are presented for the Auger decay of ions in which either a carbon 1s or oxygen 1s electron has been ionized and for the decay of neutral molecules in which either a carbon 1s or oxygen 1s electron has been excited to the vacant 2π orbital. The spectra from the neutral molecules have been studied and analyzed in some detail. These autoionization spectra can be broken into two parts. The highest kinetic energy part where the 2π electron participates in the decay is easily understood; in this case, the Auger transitions lead to well-known one-hole states of CO+. The lower-energy part arises from deexcitation with the 2π electron remaining as a spectator. This part of the spectrum is similar to the ‘‘normal’’ Auger spectrum shifted approximately 10 eV by the Coulomb interaction with the spectator electron. The similarity is greatest for the Auger spectra of CO but is less apparent for the spectrum of N2.
A low energy crossed beam study of the proton transfer reactions of H3O+ with CH3OH and C2H5OH
Authors: Moryl J. E. , Creasy W. R. , Farrar J. M.
Published: July 2002

We present a study of the title reactions over the range from 0.76 to 2.75 eV for proton transfer to methanol and at 0.99 and 1.84 eV for the ethanol system. The dynamics of proton transfer are direct at all collision energies, with the ionic products scattered in the backward direction relative to the incoming ion. The average fraction of the available energy appearing in product translation increases from 0.25 for CH3OH2+ production at 0.76 eV to 0.44 at 2.75 eV. At 0.99 eV, the corresponding fraction for protonation of ethanol is 0.26 and increases to 0.49 at 1.84 eV. The translational energy distributions show depletion of intensity at low values of ET′, suggestive of unimolecular decay of the protonated alcohols via C–O bond cleavage and elimination of H2 across the C–O bond. Isotope effect measurements for protonation of CH3OD and subsequent elimination of H2 vs HD indicate the importance of a large hydride transfer contribution to the isotope effect. These results, along with statistical calculations, are employed to estimate the exit channel barrier with elimination process. Anomalously large elimination isotope effects (kH2/kHD=7) arise because of the near confluence of the CO bond cleavage and HD elimination thresholds. We find that the H2 elimination barrier lies between 2.8 and 2.9 eV, within experimental error equal to the endothermicity of the C–O bond cleavage reaction. This result is in agreement with recent calculations of Nobes and Radom and explains the nonoccurrence of the condensation reaction between CH3+ and H2O.
Collisional dynamics of the IF B 3Π(0+) state. I. Pulsed excitation studies of v′=3 and 4 at high pressure
Authors: Wolf Paul J. , Glover Janice H. , Hanko Leonard , Shea Robert F. , Davis Steven J.
Published: July 2002

Collisional processes in the B 3Π(0+) state of IF were studied using temporally and spectrally resolved laser induced fluorescence. Extremely small electronic quenching rate constants (kq≤1×10−14 cm3 molecule−1 s−1) were measured for He, N2, and SF6. For F2, the measured quenching rate constant was (4±1)×10−12 cm3 molecule−1 s−1. Vibrational energy transfer rate coefficients were measured for He and N2. The v′=4 → v′=3 rate constants for He and N2 were (6.9±0.7) ×10−12 and (3.5±0.3)×10−12 cm3 molecule−1 s−1, respectively. For v′=3 → v′=2, the respective rate constants for He and N2 were (5.4±0.5)×10−12 and (2.5±0.2)×10−12 cm3 molecule−1 s−1.
Rates and pathways of vibrational self-relaxation of HF(v=2) between 300 and 700 K
Authors: Robinson J. M. , Pearson D. J. , Copeland R. A. , Crim F. F.
Published: July 2002

The temperature dependencies of the total self-relaxation rate constants for the vibrational deactivation of HF(v=2) and HF(v=1) and the state-to-state vibration-to-vibration (V–V) and vibration-to-translation-and-rotation (V-T,R) energy transfer components of the HF(v=2) self-relaxation process are measured using the overtone vibration excitation-laser double resonance technique. The total self-relaxation rate constants vary inversely with temperature. The much weaker temperature dependence of HF(v=2) self-relaxation compared to that of HF(v=1) arises from the significant role of the V–V energy transfer route. Competition between energetics and collision duration results in a weaker inverse variation with temperature for the slightly endothermic V–V route than for the exothermic V-T,R route for HF(v=2). The branching ratio for V–V energy transfer increases slightly with temperature and the data suggest that two quantum relaxation processes constitute no more than 10% of the total self-relaxation of HF(v=2). The available temperature dependence data on self-relaxation of HF(v=1–5) form a consistent picture in which the energetics of the V–V and V-T,R relaxation pathways control their relative contributions to the total energy transfer.
Optical spectra and crystal field analysis of Nd3+ in the cubic Cs2NaYCl6 host
Authors: Foster David R. , Richardson F. S. , Schwartz R. W.
Published: July 2002

Optical absorption and emission measurements are reported for the Cs2NaYCl6:Nd3+ (∼5 mol %) system under variable-temperature (4.2–296 K) conditions. The absorption measurements span the 12 000–24 000 cm−1 spectral region, and emission spectra are presented throughout the 13 300–18 860 cm−1 region. All the spectra are consistent with the retention of octahedral (Oh) site symmetry for the Nd3+ ions down to 4.2 K. Thirty-four crystal-field levels spanning 14 multiplets of the Nd3+ 4f3 electronic configuration are located and assigned on the basis of the experimental data. The most intense lines observed in each of the multiplet-to-multiplet transition regions are assigned to one-phonon (electric-dipole) vibronic transitions associated with the three odd-parity moiety modes of the NdCl3−6 cluster, ν3(tlu), ν4(tlu), and ν6(t2u). The ν3 lines generally appear as doublets (split by ∼10–15 cm−1) and are displaced from magnetic-dipole origins by ∼245–260 cm−1; the ν4 lines are displaced from origins by ∼100 cm−1, and are generally sharp and symmetric; and the ν6 lines are generally asymmetric in shape (or appear as doublets split by ∼2–6 cm−1), and are displaced from origins by 70–75 cm−1. Additional vibronic lines are observed persistently at displacement energies of ∼40–45 and ∼55–60 cm−1, but these lines are considerably less intense than those assigned to the ν3, ν4, and ν6 moiety-mode vibrations. The energy level data obtained from experiment is rationalized in terms of a 9-parameter model which includes the radial spin-orbit interaction parameter (ζso), the Slater–Condon one-particle electrostatic interaction parameters (F2, F4, and F6), the two-particle electrostatic configuration-interaction parameters (α, β, and γ), and the octahedral (Oh) crystal-field interaction parameters (B(4)0 and B(6)0). The values deduced for the crystal-field parameters are B(4)0 =2400 cm−1 and B(6)0 =−330 cm−1 (expressed with unit-tensor normalization).
The coupling between intramolecular and intermolecular motion in large van der Waals complexes
Authors: Sage Martin L. , Jortner Joshua
Published: July 2002

In this paper we present a theoretical study of the coupling between intermolecular and intramolecular vibrational motion in large van der Waals complexes, which rest on the expansion of the total vibrational wave function in terms of the ‘‘free’’ molecule wave function, resulting in a set of coupled differential equations for the expansion coefficients. The application of Van Vleck perturbation theory results in explicit first-order and second-order kinetic energy and potential energy corrections. These corrections lead to a shift of the intramolecular vibrational frequencies and to intermolecular vibrational energies which depend on the vibrational quantum numbers for the intramolecular modes. Consideration of the intermode coupling in a model system consisting of one harmonic, intramolecular mode, and one intermolecular mode, predicts a linear dependence of the intermolecular vibrational energy on the vibrational quantum number for the intramolecular motion. This prediction is in accord with the recent experimental results for the S0→S1 transition of the trans-stilbene ⋅ Ar complex.
Energy distribution in the nitric oxide fragments from the ν7 vibrational predissociation of NO–C2H4
Authors: King David S. , Stephenson John C.
Published: July 2002

The rotational level distribution of the NO fragments formed as a result of the predissociation of the vibrationally excited NO–C2H4 (ν7) van der Waals molecule was measured by laser excited fluorescence techniques. The distribution was found to be Boltzmann in character, described by the rotational temperature 75±15 K. An average kinetic energy release of ≊105 cm−1 per fragment, in an isotropic flux distribution, was determined from Doppler profiles of the NO fragments in selected rotational levels.
A theoretical study of the (BeH)+ molecule in the A 1Σ+ state
Authors: Ornellas Fernando R.
Published: July 2002

A theoretical study of the (BeH)+ molecule ion in the A 1Σ+ state is performed using a potential energy curve and a dipole moment function calculated with a configuration interaction wave function. Averaged dipole moments, radiative transition probabilities, and radiative lifetimes are presented for the lower vibrational levels. Spectroscopic constants are obtained by standard fitting procedures.
Surfactant interactions in oil continuous microemulsions
Authors: Huang John S.
Published: July 2002

We have used light scattering to determine the interaction potential between the surfactant coated water droplets in an oil continuous microemulsion system. The forward extrapolated zero angle scattering intensities at various water volume fractions were analyzed in terms of the Carnahan–Starling hard-sphere model modified for two-body attractive interactions. It was found that interparticle attractive interaction due to the overlapping of the surfactant tails could explain the observed phase behavior with respect to changes in the carbon chain length of the oil phase, as well as the existence of the lower critical point. It is further found that the optically determined potential is consistent with the microscopic results obtained with small angle neutron scattering experiments.