bluuebunny/crossref_metadata_2025 huggingface dataset:
Migration of nitrogen implanted into iron induced by the presence of a buried carbon-rich layer
Authors: Jagielski J. , Moncoffre N. , Marest G. , Fayeulle S.
Published: July 2002

A redistribution of nitrogen atoms towards a buried carbon-rich layer is observed for thin iron films implanted at 250 °C. The effect is attributed to the formation of ε-Fe3−x(C,N) iron carbonitride. Above 300 °C the ε-carbonitride phase becomes unstable and consequently the redistribution effect vanishes leading to well-separated profiles of nitrogen and carbon atoms.
High-efficiency and low-threshold InGaAs/AlGaAs quantum-well lasers
Authors: Hu S. Y. , Young D. B. , Corzine S. W. , Gossard A. C. , Coldren L. A.
Published: July 2002

High-efficiency and low-threshold InGaAs/AlGaAs quantum-well laser structures have been grown by molecular beam epitaxy. Material characterization was performed on polyimide-planarized ridge-waveguide lasers. The measured material gain data are compared to theoretical calculations that include the valence-band mixing effects. Total injection current densities of 84 and 60 A/cm2 have been measured from 50-μm-wide laser diodes with cavity lengths of 2850 μm (from a double-quantum-well sample) and 1770 μm (from a single-well sample), respectively. Moreover, we have also obtained a cw threshold current as low as 2.1 mA from a 1.7-μm-wide and 140-μm-long as-cleaved ridge-waveguide device. In addition, the lateral current leakage for the double-quantum-well sample is found to be twice that of the single-well one.
Differential losses in Bragg fibers
Authors: de Sterke C. Martijn , Bassett I. M. , Street Arthur G.
Published: July 2002

Most dielectric waveguides depend for guidance on total internal reflection within a region of elevated refractive index. A little-explored alternative to this is Bragg reflection. Here we consider a ‘‘Bragg’’ optical fiber in which a cylindrical Bragg grating is used to inhibit radial power flow. We find that such Bragg fibers can be guaranteed to be effectively single-moded, with no polarization degeneracy; the electric field in this fundamental mode is purely azimuthal (transverse electric polarized).
Cathodoluminescence from high-pressure synthetic and chemical-vapor-deposited diamond
Authors: Lawson Simon C. , Kanda Hisao , Kiyota Hideo , Tsutsumi Takahiro , Kawarada Hiroshi
Published: July 2002

The nature of an UV cathodoluminescence band, which can appear in both boron-doped high-pressure high-temperature (HPHT) synthetic diamond and boron-doped diamond grown by chemical-vapor-deposition (CVD) techniques, is investigated. The band has a peak energy at 4.6 eV (270 nm), a full width at half-maximum of ∼0.4 eV and at low temperatures (∼130 K) can represent the overwhelmingly dominant cathodoluminescence (CL) from selected regions of a given sample. The band has been examined from boron-doped HPHT diamond grown from different solvent catalysts and from boron-doped CVD diamond grown under a variety of deposition conditions. Low-temperature spatially resolved CL imaging, using a scanning electron microscope with CL attachment, has revealed a clear growth-sector dependence of the 4.6 eV band in HPHT diamond. Using this technique an investigation of the relationship between this band and other commonly observed CL bands has been carried out. The band has an interesting temperature dependence which is investigated over the temperature range 77–300 K and explained in terms of competition between exciton capture and exciton release at some unidentified trapping center.
Impurity incorporation in vapor phase epitaxy: S in GaAs
Authors: Sandoval H. , Mimila-Arroyo J. , Bourgoin J. C.
Published: July 2002

The dependence of S impurity incorporation into GaAs vs growth rate, and substrate temperature has been investigated during vapor phase epitaxial growth. The specific technique used, close space vapor transport, has been selected to allow the growth rate Vg and the substrate temperature θ to vary independently and in very large ranges. The concentration ND of incorporated impurities has been determined for a variety of values of Vg and θ, using an electrical method. Comparison of the experimental data with a simple model gives the variation of the sticking coefficient versus temperature. The model assumes that the impurities incorporated are those which stick on the surface during the time a monolayer is grown, when desorption can be neglected during this time. This sticking coefficient is thermally activated with an activation energy of 2 eV. The agreement between the experimental data and the variation of ND vs Vg and θ deduced from this model, confirms its validity and demonstrates that high purity GaAs can be grown by this technique under high growth rate conditions.
Spatially resolved atomic hydrogen concentrations and molecular hydrogen temperature profiles in the chemical-vapor deposition of diamond
Authors: Connell L. L. , Fleming J. W. , Chu H.-N. , Vestyck D. J. , Jensen E. , Butler J. E.
Published: July 2002

We report here a direct measurement of the spatially resolved atomic hydrogen concentration profiles during hot-filament-assisted chemical-vapor deposition (HFCVD) of diamond films. The ground-state hydrogen (1s 2S1/2) atoms generated in this process are monitored by an optical four-wave-mixing technique, third-harmonic generation (THG). For THG, a 364.6 nm dye laser beam is focused into the HFCVD reactor and the third-harmonic radiation near resonant with the Lyman-α (2p 2P0j↔1s 2S1/2) transition in atomic hydrogen at 121.6 nm is observed. The resultant THG intensity and THG peak shift with respect to the Lyman-α transition are both dependent on hydrogen atom concentration. Titration experiments based on the reaction NOCl+H→HCl+NO were conducted to obtain absolute hydrogen atom concentrations from the relative concentrations determined in the THG experiment. Spatially resolved molecular hydrogen temperature and concentration profiles obtained by coherent anti-Stokes Raman scattering in a similar HFCVD reactor are reported. The observed H atom concentrations exceed computed equilibrium concentrations based on the measured gas temperatures. Transport of the atomic hydrogen from the hot filament surfaces is discussed and diffusion is shown to be the principal mechanism controlling the H atom distribution.
Structural and electrical studies of radio frequency sputtered hydrogenated amorphous silicon carbide films
Authors: Choi W. K. , Loo F. L. , Ling C. H. , Loh F. C. , Tan K. L.
Published: July 2002

The structural and electrical properties of radio frequency (rf) sputtered hydrogenated amorphous silicon carbide films are presented in this paper. Films were prepared with sputtering pressure Ps varied from 0.8 to 3 Pa, or with substrate temperature Ts varied from 100 to 300 °C. For films deposited with an argon plus hydrogen ambient, the deposition rate was found to increase with increase in Ps and decrease with an increase in Ts. For films prepared with an argon ambient only, the deposition rate increased slightly with an increase in Ps or Ts. The deposition rate was also approximately two to eight times higher when sputtering was carried out in an argon plus hydrogen ambient than in argon only. Infrared (IR), x-ray photoelectron (XPS), and Raman spectroscopies were employed in the structural analysis. The IR results showed that the Si–C bond gave the most prominent absorption peak and was affected by changes in Ps. The Si–H and SiHn stretching modes were observed in all films, and the amount of Si–H bonds NSi–H were found to increase as Ps or Ts was increased. The C–Hn stretching mode was absent in all films, and this was attributed to the low carbon content in these films.

The Si–N stretching mode was suggested to contribute to the extra features between 800 to 1100 cm−1 in the IR spectra for films prepared at a higher Ps (3 Pa) or Ts (300 °C). The stoichiometry of silicon carbide and the film composition were determined by the XPS method. The carbon content of silicon carbide was found to be similar to the target composition and varied only slightly with changes in Ps or Ts. The Raman spectra showed that only the C–C bond can be detected in all of the films. From the electrical measurements, the film’s conductivity was found to reduce from 4.21×10−9 to 4.35×10−11 Ω−1 cm−1 as Ps was increased from 0.8 to 3 Pa; and decreased from 3.81×10−9 to 1.31×10−8 Ω−1 cm−1 when Ts was raised from 150 to 300 °C. The conductivity was found to be related to NSi–H, with higher NSi–H resulting in lower conductivity. A comparison with data published in the literature suggested that rf sputtering technique was not effective in varying the carbon content in amorphous silicon carbide film. This technique, however, can be used to vary NSi–H and thus change the structural and electrical properties of the sputtered films.
The effect of dislocations on the transport properties of III/V-compound semiconductors on Si
Authors: Bartels A. , Peiner E. , Schlachetzki A.
Published: July 2002

The transport properties of InP and GaAs epitaxial layers grown on exactly (001)-oriented Si substrates were investigated by temperature-dependent van der Pauw measurements combined with anodic stripping. Electron concentrations n at T=300 K decreasing from around 1018 cm−3 at the heterointerface to a constant level of 1016 cm−3 toward the surface agree well with the concentration profile of Si donors. Their activation energy is 2.9 and 1.3 meV in InP/Si and GaAs/Si, respectively. At low temperatures a marked decrease of the electron mobility μ at the heterointerface occurred. A quantitative analysis of μ (T) led to the model of charged dislocations as scattering centers. By comparison with the dislocation densities of 2×108 and 1×108 cm−2 in the vicinity of the surface of 2- and 3-μm-thick layers found by wet chemical etching we derived the occupation probability of the charged centers along the dislocation lines as 0.2 and 1.0 for InP and GaAs, respectively. At 300 K μ was almost unaffected by dislocation scattering and values of 3600 cm2/(V s) (InP) and 3800 cm2/(V s) (GaAs) for n of 2×1016 and 8×1016 cm−3 were obtained which are close to the values found with homoepitaxial layers.
Magnetic properties of the SmMn2(Ge1–xSix)2 system
Authors: Saha Shibaji , Ali Naushad
Published: July 2002

Magnetization and thermal expansion measurements have been carried out on the polycrystalline SmMn2(Ge1–xSix)2 system (x=0.00, 0.01, 0.02, 0.03, 0.05, 0.08, 0.10, 0.12, and 0.15) to study its magnetic properties. It is found that the temperature range of stability of the antiferromagnetic region increases with the increase of Si content. This behavior is explained as a decrease in the Mn–Mn intralayer separation. Ferro- to antiferromagnetic (T2) and antiferro- to ferromagnetic (T1) transitions are found to be first order for all the samples up to x=0.10. For x=0.15 sample the antiferro- to ferromagnetic (T1) transition is of first order while the ferro- to antiferromagnetic (T2) transition appears to be second order. A magnetic phase diagram of SmMn2(Ge1–xSix)2 has been determined.
Stress measurements in silicon devices through Raman spectroscopy: Bridging the gap between theory and experiment
Authors: De Wolf Ingrid , Maes H. E. , Jones Stephen K.
Published: July 2002

The different steps that have to be taken in order to derive information about local mechanical stress in silicon using micro-Raman spectroscopy experiments, including theoretical and experimental aspects, are discussed. It is shown that the calculations are in general less complicated when they are done in the axes system of the sample. For that purpose, the secular equation is calculated in the axes system [110], [−110], [001], which is important for microelectronics structures. The theory relating Raman mode shift with stress tensor components is applied using two analytical stress models: uniaxial stress and planar stress. The results of these models are fitted to data from micro-Raman spectroscopy experiments on Si3N4/poly-Si lines on silicon substrate. In this fit procedure, the dimensions of the laser spot and its penetration depth in the substrate are also taken into account.
Thin anodic oxides formed on GaAs in aqueous solutions
Authors: Schmuki P. , Sproule G. I. , Bardwell J. A. , Lu Z. H. , Graham M. J.
Published: July 2002

Thin (0–250 Å) anodic oxides were formed on p-GaAs (100) in aqueous solutions (borate buffer, pH 8.4 and 0.3 M NH4H2PO4, pH 4.4). The thickness, composition, and electrochemical behavior were characterized by x-ray photoelectron spectroscopy, secondary ion mass spectrometry, ellipsometry, and electrochemical impedance spectroscopy. In borate buffer, oxide growth results in a two-layer structure with an outer As2O3-rich layer and ion transfer is mainly diffusion controlled. From the potential dependence of the film thickness a growth rate of 25 Å/V was determined. Due to the formation of a Ga-phosphate precursor layer in NH4H2PO4, films grow under field control which results in a time dependence of oxide thickness and composition. Under pseudosteady state conditions a growth rate of 28 Å/V was obtained. Films formed in NH4H2PO4 have, except for the outer phosphate layer, a fairly uniform composition in depth with a significant enrichment of Ga2O3, and show a 40 times higher specific charge transfer resistance than films formed in borate buffer. The superior quality of the oxide formed in NH4H2PO4 is also reflected in its high stability against H2O etch. In addition, substrate pretreatment and the effects of oxide washing on composition were investigated and the importance of an appropriate preparation of samples for ex situ analysis is demonstrated.
Band theoretical investigation of the Curie temperatures of modified R2Fe17-based intermetallic compounds
Authors: Ching W. Y. , Huang Ming-Zhu
Published: July 2002

The Curie temperatures of several Nd2Fe17-based intermetallic compounds are calculated based on the spin-fluctuation model of Mohn and Wohlfarth and the band structure results calculated using the self-consistent orthogonalized linear combinations of the atomic orbitals method in the local spin density approximation. It is shown that the calculated Tc can qualitatively account for the observed Tc enhancement in this class of modified compounds by interstitial doping of N or C, or by elemental substitution of Fe by Si, Al or Ga. A simple explanation of Tc enhancement based purely on the magnetovolume effect is not justified. It is also shown that neither the Stoner–Curie temperature nor the characteristic spin-fluctuation temperature is adequate to explain the experimentally observed Tc enhancement in these compounds.
Magnetic properties of R(Fe,Mn)11Ti compounds
Authors: Zhao T. , Kou X. C. , Zhang Z. D. , Sun X. K. , Chuang Y. C. , de Boer F. R.
Published: July 2002

High-field magnetization measurements have been performed on both free-powder samples and magnetically aligned samples of R(Fe,Mn)11Ti (R=Y, Nd, Sm, Gd, Er) compounds at 4.2 K in a step field up to 28 T. The temperature dependence of ac susceptibilities of R(Fe,Mn)11Ti has been measured in a temperature range from 4.2 to 800 K. It has been found that both the magnetic moment of the transition-metal sublattice and the Curie temperature of RFe11−xMnxTi compounds decrease with increasing x. Spin reorientations occur in ErFe11−xMnxTi compounds as the result of competition between the uniaxial anisotropy of the transition-metal sublattice and the planar or conical anisotropy of the Er sublattice. The intersublattice exchange constants nRT of ErFe11−xMnxTi compounds have been deduced by the high-field free-powder method. The effect of the substitution of Fe by Mn on the magnetic anisotropies of R(Fe,Mn)11Ti with R=Y, Nd, Sm has been investigated. First-order magnetization processes take place in SmFe11−xMnxTi compounds when the external field is applied perpendicular to the alignment direction.
Study of the cracking of highly porous p+ type silicon during drying
Authors: Belmont O. , Bellet D. , Bréchet Y.
Published: July 2002

The origin of the cracking of highly porous silicon layers during drying is investigated. Optical and scanning electron microscopy observation allow us to observe the cracking occurrence. In situ x-ray diffraction experiments, under controlled vapor pressure of pentane, reveal that large capillary stresses occur at a vapor pressure P* during the controlled drying. These stresses lead to the cracking of the highly porous layer, which occurs for samples thicker than a critical thickness hc. Taking into account the mechanical properties of the material, a model based on energy balance is presented. This model predicts a layer thickness hc of cracking occurrence, showing that hc varies as (1−p)3/γLV2 (where γLV is the surface tension of the drying liquid and p is the porosity). This model is in good agreement with experimental data obtained with two liquids, water, and pentane, which have very different surface tension and also for two different porosities.
Effects of hydrogen and rf power on the structural and electrical properties of rf sputtered hydrogenated amorphous silicon carbide films
Authors: Choi W. K. , Loo F. L. , Loh F. C. , Tan K. L.
Published: July 2002

The effects of the rf power (100 to 600 W) and the hydrogen partial pressure (PH=0.15 to 0.6 Pa.) on the deposition rate and the structural and electrical properties of rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films were investigated. The films were deposited in an argon plus hydrogen ambient. The deposition rate increased with increasing rf power, but decreased with increasing PH. The refractive index increases from 1.85–3.6 as the rf power increases from 100–600 W and from 2.8 to 3.5 as PH increases from 0.15–0.6 Pa. The optical gap increases from 1.5 to 2.15 eV as PH increases from 0.15–0.6 Pa, but decreases from 2.8–1.38 eV as the rf power increases from 100–600 W. The Si–C bond gave the most prominent absorption peak in the infrared spectra, and increased with increasing rf power but not affected by changes in PH. The Si–H bonds increases from 3.06×1021 to 1.64×1022 cm−3 as PH was increased from 0.15–0.6 Pa. The optical gap increases from 1.5–2.15 eV and the conductivity reduces from 7.3×10−9 to 1.9×10−11 Ω−1 cm−1 accordingly. No C–Hn stretching mode was detected in all the films and this was attributed to the low carbon content of the films. We conclude that rf sputtering technique is not effective in varying the carbon content in a-Si1−xCx:H films.
CdTe/MgTe heterostructures: Growth by atomic layer epitaxy and determination of MgTe parameters
Authors: Hartmann J. M. , Cibert J. , Kany F. , Mariette H. , Charleux M. , Alleysson P. , Langer R. , Feuillet G.
Published: July 2002

Atomic layer epitaxy (ALE) is investigated for the binary semiconductor MgTe. Reflection high-energy electron-diffraction studies on MgTe atomic deposition, together with x-ray diffraction, high-resolution transmission electron microscopy, and photoluminescence experiments on ALE-grown CdTe/MgTe superlattices are reported. They reveal that an autoregulated growth at 0.7±0.1 MgTe monolayer/ALE cycle can be achieved in a substrate temperature range between 260 and 300°C. New values of the zinc-blende MgTe lattice parameter, aMgTe=6.420 ±0.005 Å, of the ratio of the elastic coefficients 2c12c11 (MgTe)=1.06, and of the 300 K MgTe band gap, EG=3.5 eV, are obtained by correlating x-ray-diffraction and optical results.
Colossal magnetoresistance in Sm1−xSrxMnO3 films
Authors: Kasai Masahiro , Kuwahara Hideki , Tomioka Yasuhide , Tokura Yoshinori
Published: July 2002

Magnetotransport properties were investigated for Sm1−xSrxMnO3 films that were prepared by the pulsed laser deposition technique. Application of a magnetic field causes a huge change in the resistivity for x=0.45, 0.50, and 0.55, in some cases exceeding five orders of magnitude. Measurement of the magnetization curve at low temperature which is removed after loading of a high magnetic field (5T) suggests the existence of the antiferromagnetic correlations. In accord with this, the magnetoresistance shows an irreversible behavior against the field sweep. The results imply that the colossal isothermal magnetoresistance in the thin films, of which the hole concentration is of a commensurate value of around x=1/2, has the same origin as the magnetic-field-induced first-order transition reported for the single crystals that is the magnetic-field-induced melting of the charge-ordered state.
Effect of surface treatment on an n-CdSe0.6Te0.4 thin-film photoanode/polysulphide electrolyte solar cell
Authors: Das V. Damodara , Damodare Laxmikant
Published: July 2002

Polycrystalline thin films of n-CdSe0.6Te0.4 were deposited in a vacuum of 5×10−5 Torr by thermal flash evaporation with a deposition rate of 20±1 Å/s on indium oxide coated glass plates [σ=1.25×104 (Ω cm)−1] held at 200 °C. Application of surface treatment techniques such as annealing and photoelectrochemical etching on the films revealed that the films exhibit photoelectrochemical behavior with increased conversion efficiency and stability after treatment. Gärtner’s model [Phys. Rev. 116, 84 (1954)] was used in the calculation of the solid state parameters of the films like the carrier concentration ND and minority carrier diffusion length Lp for different surface treatments. Chemical etching improves the efficiency and fill factor from 1.53% and 40% to 2.72% and 50% respectively, whereas photoelectrochemical etching improves further the efficiency to 3.83% and fill factor to 59% and the stability of the photoelectrode in the polysulphide electrolyte.
Empirical bond-order potential description of thermodynamic properties of crystalline silicon
Authors: Porter Lisa J. , Yip Sidney , Yamaguchi Masatake , Kaburaki Hideo , Tang Meijie
Published: July 2002

Thermodynamic properties of silicon (diamond cubic phase) are calculated using an empirical many-body potential developed by Tersoff [Phys. Rev. Lett. 56, 632 (1986)] based on the concept of bond order. It is shown that this model gives predictions in good agreement with experiment for those properties governed by energetics (free energy, entropy, and heat capacity). The thermal expansion coefficient is less well described, which is traced to the fact that the model potential, in its present version, is overly stiff and therefore unable to account properly for the volume dependence of the transverse acoustic modes. Furthermore, sensitivity of the potential to whether each atom remains bonded to only four neighbors indicates that the short-range nature of the potential may necessitate model improvement before it is suitable for studies of thermomechanical properties at elevated temperatures or large deformations.
Interdiffusion in epitaxial Co/Pt multilayers
Authors: McIntyre P. C. , Wu D. T. , Nastasi M.
Published: July 2002

Interdiffusion kinetics were measured using x-ray diffraction methods in epitaxial (001) and (111) Co/Pt multilayers in which the chemical modulation wavelength was in the range 2.5–4.0 nm. Multilayers were prepared by e-beam evaporation and were subsequently annealed in vacuum at temperatures between 275 and 375 °C. The activation enthalpy of the interdiffusion process in this temperature range was estimated using a novel approach for scaling nonlinear diffusion data. Activation enthalpies for interdiffusion in (001) and (111) multilayers were determined to be 1.1±0.2 and 0.8±0.2 eV, respectively. The low values obtained for the activation enthalpies may result from coherency strains or “short-circuit’’ diffusion in the faulted, epitaxial multilayers.
Optical confinement and threshold currents in III–V nitride heterostructures: Simulation
Authors: Bougrov V. E. , Zubrilov A. S.
Published: July 2002

Waveguiding properties of InGaN/GaN/AlGaN double heterostructures were modeled. A comparison between double heterostructures (DHs) and separate confinement heterostructures (SCHs) has been made. This is an attempt to consider influence of material absorption in passive layers of nitride laser structures on a threshold current. This absorption significantly increases the threshold current, and is especially important in the case of quantum well SCHs. The threshold current density in nitride-based lasers has been estimated to be about 10 kA/cm2. Due to high absorption of light in passive layers, no decrease in the threshold current of single quantum well SCH lasers in comparison with DH lasers is expected. The threshold current density can be decreased in multiquantum well lasers. In these lasers, the threshold current density is expected to be about several kA/cm2. The optimal thickness of active and adjacent layers as well as alloy compositions in cladding layers have been estimated, and as our simulation has shown, no more than 8%–10% of AlN in claddings are needed.
Magnetism of Fe thin layers on GaAs (001)
Authors: Filipe A. , Schuhl A.
Published: July 2002

We study the magnetic properties of Fe thin films epitaxially grown on GaAs (001) for a large range of substrate temperature. Magnetization deficiency has been detected and studied. Its dependence with both thickness and temperature clearly show the existence of a nearly half-magnetized phase at the interface, covered by “as-bulk” Fe. In order to inhibit this interdiffusion, we study several methods. Using previous O3 oxidation of GaAs, the Fe layer is fully magnetized even for deposition at 200 °C.
Studies of laminated and single layer high moment soft FeTaN films
Authors: Inturi V. R. , Barnard J. A.
Published: July 2002

Detailed studies on the effect of Ti base layers in high moment soft FeTaN films and the effective utilization of Ti as a seed layer in thick laminated FeTaN films are presented in this article. Because of the reduced eddy current losses in thick films (∼2 μm), laminated films (FeTaN/Si3N4) exhibit better initial permeabilities at higher frequencies than single layer films having the same total thickness. Moreover, if a thin (30–100 Å) layer of Ti is used as a seed layer for the FeTaN layers in the laminate, the soft magnetic properties are significantly improved. X-ray diffraction results show that the laminates with a Ti seed layer have an enhanced (110) growth texture resulting in better soft magnetic properties.
Effects of lamination on soft magnetic properties of FeN films on sloping surfaces
Authors: Sin Kyusik , Wang Chuei-Tang , Wang Shan X. , Clemens Bruce M.
Published: July 2002

We have found that the soft magnetic properties of FeN/AlN laminated films do not degrade on sloping surfaces. The easy axis coercivities of FeN/AlN multilayer films are approximately 1.5 Oe and have little variation with slope angle, α. The anisotropy fields slightly vary from 13 to 17 Oe when the slope angles (α) change from 0° to 60°. In contrast, single layer FeN films show a significant degradation of soft magnetic properties with the slope angle. Residual stress does not have a significant correlation with magnetic properties. The large coercivities and saturation fields in the single layer FeN films can be ascribed to a change in the (110) texture of the films.
Alpha-elastic recoil detection analysis of the energy distribution of oxygen ions implanted into silicon with plasma immersion ion implantation
Authors: Barradas N. P. , Maas A. J. H. , Mändl S. , Günzel R.
Published: July 2002

Plasma immersion ion implantation was used to implant oxygen ions into silicon with applied voltage pulses of −40 kV and 2.5 μs length. Positive ions, O2+ and O+, with a continuous energy distribution between 0 and 40 keV were implanted. Between 3×104 and 3×105 pulses, corresponding to nominal doses from 2×1016 to 2×1017/cm2, were used. The resulting oxygen depth profiles were measured with elastic recoil detection analysis using 13.4 MeV α particles. Rutherford backscattering was used to determine possible co-implanted contaminants. The obtained depth profiles were simulated using a linear superposition of calculated single-energy profiles. The results obtained for the energy distribution of the incident ions are compared with calculations obtained from a theoretical model, and the agreement is very good. The incident flux is found to be composed of 34(5)% O2+ and 66(5)% O+ ions with an Fe contamination of ∼0.5%.
Determination of unknown stress states in silicon wafers using microlaser Raman spectroscopy
Authors: Narayanan S. , Kalidindi Surya R. , Schadler Linda S.
Published: July 2002

A new technique was developed to predict the unknown in-plane stress state and the magnitude of the stress components in (111) silicon wafers using micro-Raman spectroscopy. The approach is based on analyzing the combined signal from the initially degenerate peaks of the F2g mode in silicon as a function of the angle between the incident laser polarization and the polarization selected from the scattered beam using an analyzer. The peak position of the combined signal when plotted as a function of the angle was found to contain the information required to estimate the magnitude of the individual stress components in the plane-stress condition. The development of this technique is described in this paper for (111) silicon wafers.
Fabrication of large scale periodic magnetic nanostructures
Authors: Wassermann E. F. , Thielen M. , Kirsch S. , Pollmann A. , Weinforth H. , Carl A.
Published: July 2002

We report on the fabrication of large scale periodic magnetic nanostructures designed as possible candidates for a future application in magnetic data storage technology. The nanostructures are prepared on glass substrates by electron beam evaporation of Fe or Co onto photoresist masks, which are periodically patterned using optical interference lithography with an Ar+ laser (λ=457.8 nm) in combination with subsequent selective etching. We present our first results on the fabrication of periodic arrays of isolated magnetic dots with an average diameter of 600 nm and periodicity of 900 nm over areas of 5 cm2.
Transmission electron microscopy and cathodoluminescence studies of extended defects in electron-beam-pumped Zn1−xCdxSe/ZnSe blue-green lasers
Authors: Bonard Jean-Marc , Ganière Jean-Daniel , Vanzetti Lia , Paggel Jens J. , Sorba Lucia , Franciosi Alfonso , Hervé Denis , Molva Engin
Published: July 2002

We report on studies of extended defects in electron-beam-pumped Zn1−xCdxSe/ZnSe blue and blue-green laser structures. To establish a direct correlation between the local luminescence properties and the presence of structural defects, the same thin foil samples were sequentially examined by transmission electron microscopy (TEM) and cathodoluminescence (CL) microscopy. The majority of the non-radiative defects were found to have one or more threading dislocations in their vicinity. Stacking faults, as a rule, did not give rise per se to non-radiative recombination centers. In several instances we observed nonradiative defects by CL with no extended defect counterparts in TEM.
Amphoteric behavior of Sn in In0.5Ga0.5P layers grown by liquid phase epitaxy
Authors: Yoon I. T. , Oh S. J. , Park H. L.
Published: July 2002

Sn-doped In0.5Ga0.5P epilayers, grown on semi-insulating (100) GaAs substrates by the liquid phase epitaxy technique, have been investigated using photoluminescence and Hall effect measurements from 15 to 300 K. The Sn dopant in InGaP shows amphoteric behavior with a compensation ratio of ∼0.4–0.6. Transitions involving shallow Sn acceptors have been identified through photoluminescence measurements for the first time and the ionization energy of Sn was determined to be 57 meV, which is in good agreement with the hydrogenic acceptor value. It was also found that the Sn shallow donor has an ionization energy 17–12 meV with increasing carrier concentrations through Hall measurements.
Growth and excitonic properties of single fractional monolayer CdSe/ZnSe structures
Authors: Ivanov S. V. , Toropov A. A. , Shubina T. V. , Sorokin S. V. , Lebedev A. V. , Sedova I. V. , Kop’ev P. S. , Pozina G. R. , Bergman J. P. , Monemar B.
Published: July 2002

Single fractional monolayer (FM) CdSe/ZnSe structures have been grown by molecular beam epitaxy (MBE), employing both conventional MBE and migration-enhanced epitaxy (MEE). A precise calibration of the FM mean thickness in the range of 0.15–3.0 ML has been performed for both techniques, revealing more than a 3.5 times lower Cd incorporation ability for the MEE mode at the same Cd and Se incident fluxes. Steady-state and time-resolved photoluminescence spectroscopy is used to characterize the intrinsic morphology of the CdSe FMs, with a special emphasis on the submonolayer thickness range. Both MBE and MEE grown samples exhibit inhomogeneity of the excitonic system, which can be explained by coexistence of a homogeneous alloylike layer and relatively large CdSe 2D clusters. The MEE samples display smaller fluctuations of the layer thickness and island sizes.
Second harmonic spectroscopy and control of domain size in antiferromagnetic YMnO3
Authors: Fiebig M. , Fröhlich D. , Leute S. , Pisarev R. V.
Published: July 2002

A novel technique for the visualization of antiferromagnetic domains making use of second harmonic generation is used to study the easy-plane antiferromagnet YMnO3. Domain states characterized by small, medium, or large domains are observed. Switching from one state to another can be achieved by a heat treatment above TN and subsequent cooling below TN. Contributions to the mechanism of this unusual behavior of domains are discussed.
Fabrication of a micromotor driven by electromagnetic vibration
Authors: Honda T. , Yamasaki J.
Published: July 2002

A new electromagnetic rotary mechanism utilizing a friction drive is proposed. An electromagnetic vibration excited on a permanent magnet is converted to a rotary movement through a frictional force. A trial motor, composed of a magnet rotor with inclined legs and an excitation coil, was fabricated and successfully operated. A no-load revolution speed up to 400 rpm and a reversible rotation were achieved.
Pulsed plasma polymerization of pentafluorostyrene: Synthesis of low dielectric constant films
Authors: Han Licheng M. , Timmons Richard B. , Lee Wei W. , Chen Yuanye , Hu Zhibing
Published: July 2002

A variable duty cycle pulsed plasma was employed to synthesize polymeric films from pentafluorostyrene monomer. The physical properties of the resultant films are observed to vary in progressive fashion with changes in the plasma duty cycles employed during deposition, all other plasma variables remaining constant. The sequential variations in film compositions with plasma duty cycles were demonstrated spectroscopically (infrared and x-ray photoelectron spectroscopy) as well as by dielectric constant, thermal stability, and surface energy measurements. In the case of pentafluorostyrene, a trade off in dielectric constant and thermal stabilities is observed as the lower dielectric constant films exhibit poorer thermal stability. In particular, this study shows that the variable duty cycle pulsed plasma synthesis approach can be employed to adjust physical properties of films, particularly dielectric constants, in unusually controllable fashion.
Microanalysis by monochromatic microprobe x-ray fluorescence—physical basis, properties, and future prospects
Authors: Chen Z. W. , Wittry D. B.
Published: July 2002

A monochromatic microprobe for x-ray fluorescence is obtained by a doubly-curved crystal diffractor which focuses characteristic radiation from a small laboratory-based x-ray source. Monochromatic microprobe x-ray fluorescence (MMXRF) provides unique advantages over conventional XRF, i.e., smaller analytical volume, higher sensitivity for the detection of impurities, and more accurate quantitation. Possible photon energies, voltage for the x-ray source, and type of diffractor geometry are discussed. Calculations of geometric aberration, collection solid angle, and beam intensity are given for a Johann-based diffractor. Properties of a mica diffractor used to focus Cu Kα1 x rays are predicted by ray tracing and experimentally verified by x-ray topographs and images of the focal spot. With the mica diffractor and a 20 μm x-ray source at 30 kV and 0.1 mA, ∼1.1×108 photons/s were obtained in a probe of 57 μm×43 μm and probes less than 10 μm appear to be theoretically possible. Energy dispersive spectra for bulk specimens of Si, GaAs, Mg, and Muscovite obtained with the Cu Kα1 probe exhibited extremely high signal/background ratios. The sources of background and reasons for low values are discussed. The low background resulted in predicted detection limits as low as 1.6 ppm for a measurement time of 500 s. Detection limits in the ppb range should be possible with higher power for the x-ray source, better detectors for energy dispersive spectrometry, improved diffractor fabrication and appropriate selection of the exciting photon energy.
Electrical properties of extremely low doped GaSb Schottky diodes
Authors: Mason Whitney , Waterman J. R.
Published: July 2002

This article presents capacitance–voltage (C/V), current–voltage (J/V), and deep level spectroscopy (DLTS) measurements on Al/GaSb Schottky diodes; the GaSb was doped n type using a Ga2Te3 source. We found a net doping density of 1.71×1015 cm−3 and a barrier height of 0.436 eV from the C/V measurements. At room temperature, the J/V characteristics gave an ideality factor of 1.2 and an apparent barrier height of 0.48 eV. DLTS measurements showed a single peak in the capacitance at about 80 K, giving an activation energy of 0.219 eV. This value is comparable to the value seen in Te-doped GaSb Schottky diodes doped with other sources and in undoped GaSb.
Systematic errors of locally resolved photothermal radiometric measurements
Authors: Walther H. G. , Kitzing T.
Published: July 2002

Thermal properties and thermal depth profiles can be estimated in principle from laterally resolved radiometric measurements. Care has to be taken to prevent signal distortions due to systematic measurement errors. The effects of scattering of the heating beam from the rough sample surface and of infrared diffraction at the collecting optics have been discussed with respect to the photothermal signal. An experimental evaluation is given.
Effect of radiation transport on the kinetics of phosphor degradation
Authors: Grossman Mark W.
Published: July 2002

The mechanism of phosphor degradation due to ultraviolet (UV) radiation is viewed as a sum of parallel pseudo x-order photochemically induced reactions. The values of the rate constants are assumed proportional to local UV surface intensity, which produces phosphor degradation. Using the Kubelka–Monk [P. Kubelka and F. Munk, Z. Tech. Phys. 12, 593 (1931)] theory for UV propagation through a phosphor layer, it is shown that the UV radiation is exponentially decreasing through the phosphor layer. Surprisingly, the resulting form of the degradation curve is nearly independent of the order of the elementary reaction. For any pseudo x-order UV driven degradation mechanism, the decay of optically active sites takes the following form: M(t)=A+B log(t) provided the observation time is restricted to 1/k0⩽t⩽1/kmin where k0 and kmin are the largest and smallest rate constants, respectively. Here A and B are constants dependent on k0, the equivalent fraction of the phosphor luminescent sites undergoing degradation, and the optical properties of the phosphor layer. A similarity is found between the inverse of the UV attenuation coefficient and the fraction of absorption sites with respect to the maintenance slope. In the limit of a continuous distribution of rate constants, the analytic results of the discrete model are confirmed. Also, in this limit it is found that kmin=k0 exp(−Kkmd), where Kkm is a constant found from the Kubelka–Monk analysis and d is the phosphor layer thickness. Experimental data for fluorescent lamps is discussed in conjunction with this theory. Viewing the decay of light output over time as due to the effective decay of optically active sites in the phosphor and taking into account the distribution of UV radiation good correlation to the theory is obtained.
Growth temperature dependence of the magnetic and structural properties of epitaxial Fe layers on MgO(001)
Authors: Jordan S. M. , Lawler J. F. , Schad R. , van Kempen H.
Published: July 2002

We have studied the growth and magnetic properties of molecular beam epitaxy grown layers of bcc Fe(001) on MgO(001) substrates at a wide range of temperatures. For growth temperatures in the range 80−595 K, the iron forms islands which increase in lateral size with increasing temperature. Completed films in the same temperature range show the magnetic properties expected for a system with biaxial anisotropy, and a coercivity of <10 Oe. The value of the first cubic anisotropy constant divided by the magnetization (K1/M) remained constant. No evidence for uniaxial magnetic anisotropy in the films was found. Above 595 K, the films’ structure and magnetic properties changed dramatically to those characteristic of a particulate system.
Kinetic behavior analysis of porphyrin Langmuir–Blodgett films for conductive gas sensors
Authors: Tepore A. , Serra A. , Manno D. , Valli L. , Micocci G. , Arnold D. P.
Published: July 2002

Meso, meso′-buta-1,3-diyne-bridged Ni (II) octaethylporphyrin dimer thin films have been deposited by the Langmuir–Blodgett method and, for the first time, have been considered as the active layer in resistive gas sensors. In particular, the electrical conductivities of these films undergo a remarkable variation due to exposure to small concentrations of NO in air at an operating temperature of 50 °C. To interpret the behavior of such organic films, a model has been built up and the conductivity variation as a function of test gas concentrations and time has been derived. The fitting of theoretical and experimental behavior allows us to determine the number of adsorbed gas molecules per porphyrin dimer, response and recovery times, adsorption and desorption coefficients. The reliability of the model is proved by obtained results. In particular, the determined adsorption and desorption coefficients depend only on test gas species but are unaffected by other experimental conditions such as gas concentration.
Anomalous Hall resistivities of single-crystal Fe16N2 and Fe–N martensite films epitaxially grown by molecular beam epitaxy
Authors: Takahashi H. , Komuro M. , Hiratani M. , Igarashi M. , Sugita Y.
Published: July 2002

The anomalous and ordinary Hall resistivities for Fe16N2 (saturation magnetization 4πMs: 29 kG at room temperature) and Fe–N martensite (24.8 kG) films have been measured in the temperature range from 30 to 300 K and compared with pure Fe (21 kG) films. All films were epitaxially grown on GaAs(001) substrates by molecular beam epitaxy. The saturation anomalous Hall resistivity ρAS for Fe16N2 at 300 K was 4.0×10−7 V cm/A which was much higher than the values for Fe–N martensite (1.9×10−7 V cm/A) and Fe (1.5×10−7 V cm/A). Also the anomalous Hall constant RA at 300 K for Fe16N2 was 1.5×10−11 V cm/A G, which was much higher than the values for Fe–N martensite (0.8×10−11 V cm/A G) and Fe (0.7×10−11 V cm/A G). Such results are consistent with a much larger magnetic moment for Fe16N2. To investigate the consequences of the giant magnetic moment for Fe16N2 as compared with Fe–N martensite and Fe, the temperature dependences of ρAS and RA were measured. The values of ρAS and RA decreased monotonically with decreasing temperature for Fe16N2, Fe–N martensite and Fe. In the temperature range from 30 to 300 K, the ρAS value for Fe16N2 was much higher than the values for Fe–N martensite and Fe. This originated from the larger thermal fluctuation of the magnetization for Fe16N2. The striking features of Fe16N2 magnetism were its giant magnetic moment and its large thermal fluctuation of the magnetic moment. The electrical resistivity at room temperature for Fe16N2 was around 30 μΩ cm as compared with 10 μΩ cm for Fe. The difference was due mainly to the difference in the residual resistivities. The electrical resistivity for Fe16N2 decreased monotonically with decreasing temperature, which is normal for a metallic material.
Structural and magnetic fourfold symmetry of Co/Cu multilayers electrodeposited on Si(001) substrates
Authors: Shima M. , Salamanca-Riba L. , Moffat T. P. , McMichael R. D. , Swartzendruber L. J.
Published: July 2002

We have observed in-plane fourfold symmetry of the magnetization and magnetoresistance in Co/Cu multilayers electrodeposited on Si(001) substrates covered with a thin evaporated Cu seed layer. The fourfold symmetry correlates with the in-plane crystalline structure of the multilayers. High-angle x-ray diffraction shows that the Co/Cu multilayers have a strong (001) texture. Φ-scan x-ray diffraction reveals that the multilayers have fourfold symmetry in the plane with a 45° rotation with respect to the Si substrates. We estimated an anisotropy field of 98 mT from vector magnetization curves, which is in fairly good agreement with the value obtained from Co/Cu multilayers electrodeposited on (001) Cu single crystal substrates. The giant magnetoresistance appears to depend on the in-plane orientation of the multilayer due to the magnetocrystalline anisotropy.
Field emission energy distribution analysis of cubic-BN-coated Mo emitters: Nonlinear behavior
Authors: McCarson B. L. , Schlesser R. , Sitar Z.
Published: July 2002

Voltage-dependent field emission energy distribution (V-FEED) and current versus voltage measurements were performed on Mo tips coated with intrinsic cubic boron nitride (c-BN) to determine the origin of the field-emitted electrons. Spectra were collected from the Mo emitters under ultrahigh vacuum conditions both before and after being coated. In some instances multiple FEED peaks were observed in the collected spectra. These corresponded to multiple emission sites on the emitter. The energy of the field-emitted electrons from the c-BN-coated emitters usually depended linearly upon the applied voltage and could be explained using a simplified band-bending model. However, at higher voltages the FEED measured from the c-BN-coated emitters departed from this linear behavior. These nonlinearities were attributed to a contact resistance at the Mo/c-BN interface which had a greater influence on the energy distribution of emitted electrons at larger emission currents.
Dielectric properties of fiber-filled composites
Authors: Lagarkov A. N. , Matytsin S. M. , Rozanov K. N. , Sarychev A. K.
Published: July 2002

Results are presented of the comprehensive experimental investigation of the dielectric properties of composites filled with conducting fibers results. The results apply to the percolation threshold values and microwave dielectric dispersion of these materials. The fiber-filled composites exhibit a great variety of dielectric dispersion behavior, and offer wide possibilities of tailoring their dielectric dispersion. The experimental data are in good agreement with the recent theoretical approach [see A. N. Lagarkov and A. K. Sarychev, Phys. Rev. B 53, 6318 (1996)] as regards the values of percolation threshold and the shape of dielectric dispersion dependences. This agreement is a validation of the original assumption that the permittivity of effective medium is a scale dependent function in fiber-filled composites.
In
0.5
Ga
0.5
As
quantum dot intermixing and evaporation in GaAs capping layer growth
Authors: Lee Jeong-Sik , Ren Hong-Wen , Sugou Shigeo , Masumoto Yasuaki
Published: July 2002

Our study of GaAs growth over self-assembled In0.5Ga0.5As quantum dots grown by metalorganic vapor-phase epitaxy showed that GaAs capping layer surface morphology at the onset strongly depended on temperature. Incompletely capped In0.5Ga0.5As islands were elongated toward [110], indicating anisotropy in intermixing. During higher-temperature growth interruption, islands show craters in quantum dot centers. Craters become hexagonal holes whose depth matches GaAs capping layer thickness. Postannealing photoluminescence spectra show no peak corresponding to overly large quantum dot radiation, indicating that growth interruption after capping layer formation at a certain thickness eliminates overly large quantum dots.