bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation electrical properties and interface studies of plasma nitride layers on n-type InP
Authors: Astito A. , Foucaran A. , Bastide G. , Rouzeyre M. , Leclercq J. L. , Durand J.
Published: July 2002

The growing conditions and the basic electronic and interface properties of InP-nitride-metal structures formed by indirect plasma-enhanced nitridation are reported. The deposited nitride layer PxNyClz is a NP polymer with a chemical composition close to P3N5 but with weak inclusions of H atoms. These nitride films are deposited at temperatures as low as 220–250 °C with growing rates of 50 Å/min and stabilized by a post annealing at 300 °C in a reducing gaseous atmosphere. The optimized composition corresponds to Eg=5.5 eV, εr=6.2, n=1.95, a room-temperature resistivity ρ≳1013 Ω cm and a breakdown voltage Er≳5×107 V cm−1. The capacitance-voltage characteristics of Au-NP-InP diodes reveal that quasi-flat band and strong depletion regimes are reached, i.e., that the Fermi level in InP is swept through the entire upper half part of the electronic gap. These C-V characteristics are hysteresis free, and this allows a meaningful calculation of the interface states density Nis and of their energy distribution Dis(E). This interface states energy distribution Dis(E) is in the 1011 cm−2 eV−1 range and is very similar in magnitude to the ones observed at the InP-oxide or InP-sulfide interfaces despite the large differences in the growing atmospheres. The thermal stability of the InP-NP interface, as checked by inspection of the I-V and C-V curves, is good till 500 °C, this is at least 300 ° higher than with sulfides.
Properties of micrometer-thick plasma-polymerized tetrafluoroethylene films
Authors: Butler M. A. , Buss R. J. , Galuska A.
Published: July 2002

Several physical properties of thin plasma-polymerized films have been measured using a new fiber-optic-based technique. Films of plasma-polymerized tetrafluoroethylene (PPTFE) deposited on the end of an optical fiber form an optical cavity, the reflectivity of which is very sensitive to the film thickness. The fiber is used as an in situ monitor of the deposition rate in the plasma and, after removal from the plasma, the mechanical properties of the film can be measured. With this measurement technique the thermal expansion of the film normal to its surface as well as the swelling of the film when exposed to an array of organic solvents have been determined. A significantly smaller thermal-expansion coefficient and larger degree of swelling are observed relative to bulk PTFE. X-ray photoelectron spectroscopy measurements show that the fluorocarbon chains are highly branched and have a fluorine-to-carbon ratio of 1.45. These results suggest that the plasma-polymerized films are not crystalline and are heavily cross linked.
Mixing of GaAs/(Ga,Al)As interfaces by Ga+ implantation
Authors: Vieu C. , Schneider M. , Planel R. , Launois H. , Descouts B. , Gao Y.
Published: July 2002

The intermixing of GaAs/(Ga,Al)As heterointerfaces by Ga+ implantation and annealing has been investigated. The damage accumulation in a GaAs/AlAs superlattice turned out to be less rapid than in a GaAs/GaAlAs quantum-well structure. Low-temperature photoluminescence (PL) spectroscopy of a GaAs/AlAs superlattice could be performed for doses as high as 1 × 1016 ions/cm2. The photoluminescence spectra exhibited several emission bands on the high energy side. The number and energy of these blue shifted peaks were found to depend on the implanted dose and as confirmed by secondary ion mass spectrometry, they could be interpreted as the emission of several quantum wells of the superlattice, disordered with different mixing rates. Two regimes were evidenced; while the depth extension of the disordering has been directly related to the post-implantation defects distribution in the high dose regime, some diffusion of these defects during annealing has been pointed out in the low dose regime. Cross-sectional transmission electron microscopy observations have confirmed the influence of the structure of the implanted sample on damage accumulation. Moreover, the decrease of the PL intensity after annealing could be related to the presence of extended residual defects in the implanted layers. The study of the influence of annealing time at 760 °C, has shown that the photoluminescence intensity can be progressively recovered, while the intermixing saturates rapidly.
Fracture toughness of YBa2Cu3O6+δ single crystals: Anisotropy and twinning effects
Authors: Raynes A. S. , Freiman S. W. , Gayle F. W. , Kaiser D. L.
Published: July 2002

Indentation/crack length measurements were used to determine hardness and fracture toughness in twinned and detwinned single crystals of YBa2Cu3O6+δ (YBCO). Hardness was found to be isotropic and unaffected by twin boundaries or moisture; the average hardness value was 9.5 GPa. Fracture toughness (Kc) was determined to be anisotropic with the average value for cracks running perpendicular to the basal plane being approximately twice that of cracks parallel to the basal plane; thus, cleavage is easier along basal planes. In addition, the results suggest a small but measurable anisotropy in Kc between the a and b directions. Twin boundaries were found to toughen YBCO, enhancing Kc by about 25%. Moisture promoted crack growth, degrading Kc by about 35%.
Diamond deposition in an argon–methane–oxygen plasma
Authors: Joeris P. , Benndorf C. , Bohr S.
Published: July 2002

The deposition of diamond films by an argon–methane–oxygen mixture in a microwave plasma system is described. Our results demonstrate that it is possible to grow diamond without the addition of hydrogen. The oxygen content is a critical parameter for the phase purity of the deposited films. Mass spectroscopic measurements show that oxygen is suppressing the formation of acetylene in the plasma. These measurements are correlated with Raman spectroscopic data.
Interfacial properties of very thin GaInAs/InP quantum well structures grown by metalorganic vapor phase epitaxy
Authors: Streubel K. , Härle V. , Scholz F. , Bode M. , Grundmann M.
Published: July 2002

GaInAs/InP single quantum well structures with thicknesses below 5 nm were grown by metalorganic vapor phase epitaxy at reduced pressure. The sharpness of the heterojunctions in this III/V system is found to be strongly dependent on the applied gas switching sequence between the growth of the two materials caused by As carry over after GaInAs and by group V atom exchange at the surface during a hydride stabilized growth interruption. The photoluminescence properties can be improved by adding intermediate monolayers of InAsP between InP and GaInAs and GaInAsP between GaInAs and InP. The photoluminescence of very thin quantum wells is split into multiplets due to the formation of growth islands at the interface. Size and lateral distribution of these islands have been observed directly by cathodoluminescence analysis. On the other hand, transmission electron microscopy measurements show that the interfaces within the growth island regions are not atomically smooth but of a certain roughness. Small microislands with diameters of a few lattice constants form the ‘‘internal’’ interface structure.
Direct monitoring of CH3 in a filament-assisted diamond chemical vapor deposition reactor
Authors: Celii F. G. , Butler J. E.
Published: July 2002

The technique of resonance-enhanced multiphoton ionization (REMPI) was used to determine relative density distributions of gas-phase methyl radical (CH3) in a filament-assisted diamond chemical vapor deposition reactor. The dependences of CH3 concentration on input CH4/H2 ratio, filament temperature, and distance from the filament were determined. We also report similar REMPI data for excited-state C(1D) atoms, which were produced photolytically from an unknown gas-phase parent. Arrhenius parameters show that the CH3 is not the parent of the C( 1D) atoms. The CH3 density saturates at high filament temperature. We compare the REMPI measurements with other determinations and models of CH3 concentrations.
Properties of amorphous silicon thin films grown in square wave modulated silane rf discharges
Authors: Andújar J. L. , Bertran E. , Canillas A. , Campmany J. , Serra J. , Roch C. , Lloret A.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) thin films have been obtained from pure SiH4 rf discharges by using the square wave modulation (SQWM) method. Film properties have been studied by means of spectroellipsometry, thermal desorption spectrometry, photothermal deflection spectroscopy and electrical conductivity measurements, as a function of the modulation frequency of the rf power amplitude (0.2–4000 Hz). The films deposited at frequencies about 1 kHz show the best structural and optoelectronic characteristics. Based upon the experimental results, a qualitative model is presented, which points up the importance of plasma negative ions in the deposition of a-Si:H from SQWM rf discharges through their influence on powder particle formation.
Characterization of vertical-cavity semiconductor structures
Authors: Christensen D. H. , Pellegrino J. G. , Hickernell R. K. , Crochiere S. M. , Parsons C. A. , Rai R. S.
Published: July 2002

Several analytical tools are applied to characterize vertical-cavity surface-emitting laser structures grown on GaAs wafers. These epitaxial structures are amenable to x-ray, electron-beam, and optical metrologies. Cross-sectional scanning electron microscopy and transmission electron microscopy were used to measure layer thicknesses and uniformity. Photoluminescence wafer mapping was used to determine alloy composition uniformity across the wafer. Photoreflectance was also used to determine alloy composition. Cross-sectional microphotoluminescence was used to measure average alloy compositions in the top and bottom mirrors. Reflectance spectroscopy was used to characterize the cavity resonances and mirror layers. Double-crystal x-ray diffractometry (DCXRD) was used to characterize mirror layer dimensions, uniformity, and average alloy composition. Excellent agreement was found among these measurement techniques and between simulations and measurements. The results demonstrate the accuracy of the device simulation tools and the applicability of DCXRD in analyzing these structures.
Spatially resolved Raman measurements at electroluminescent porous n-silicon
Authors: Kozlowski F. , Lang W.
Published: July 2002

The cross section of electroluminescent (EL) porous silicon layers (LEPOS) made from n- and p-doped silicon has been investigated by means of micro-Raman and photoluminescence (PL) spectroscopy to find the luminescence active zone in LEPOS. Special care has been taken to avoid the heating of the sample. Additionally an energy dispersive spectroscopy scan over the sample cross section has been performed for n-LEPOS to detect the distribution of oxygen. Since the n samples display much better EL properties than the p samples, the investigations concentrate on the n samples. For n-LEPOS, a layered structure has been found with SiOx/Si at the top followed by a PL active layer. There are two types of samples showing different forms of Raman spectra. Type-I spectra are narrow and shifted by small values as compared with the Raman spectra of bulk silicon. They have a shoulder at about 510 cm−1 only in the PL active layer. Type-II spectra are broad and shifted by about 7–10 cm−1. All the electroluminescent samples show Raman spectra of type I.
Zero-order and first-order theory of the formation of space-charge gratings in photoconductive polymers
Authors: Schildkraut Jay S. , Cui Yiping
Published: July 2002

When a photoconducting polymer is illuminated by light with an intensity that varies sinusoidally with position, the space-charge electric field, hole density, ionized photosensitizer density, hole trap density, and other properties, will also vary with position. We derive an expression for the zero-order Fourier component of the hole density and a linear system of equations for the first-order Fourier component of a number of variables. The system of equations is solved for the steady-state first-order Fourier component of the electric field for the case in which hole untrapping is negligible or no hole traps are present. Next, the equations are simplified for the case in which the initial trap density is far greater than the density of holes, and for the case of no hole traps. Finally, we compare the zero-order hole density and first-order electric field calculated from our equations to values obtained by Fourier transforming the results of numerical calculations.
Magnetic properties and crystal structure of high moment FeTaN materials for thin-film recording heads
Authors: Qiu G. , Haftek E. , Barnard J. A.
Published: July 2002

High-power density, high growth rate dc magnetron reactive sputtering has been used to grow single-layer FeTaN films. Ta has been found effective in improving the soft magnetic properties as well as the thermal stability of FeN films. For films containing ∼1.6 a/o Ta prepared under sputtering conditions of pN2/pAr=0.06, a power density of 2.5 or 3.9 W/cm2 and vacuum post-annealed at 350 °C for 1 h, the following properties are observed: saturation magnetization (Ms) values of ∼1550 emu/cc, coercivity (Hc) of ∼1 Oe, permeability of 1700–2300 at 20 MHz, and anisotropy field of ∼7 Oe. XRD scans yielded peaks characteristic of a random polycrystalline single phase bcc structure.
Monte Carlo simulation of magnetobirefringence in magnetic fluids
Authors: Pan Y. T. , Du C. W. , Liu X. D. , Li Z. G. , Birngruber R.
Published: July 2002

On the basis of the consideration that the magnetic-field-induced optical anisotropy is caused by the combined effects of field-induced orientation of shape-anisotropic scatterers and the chain-like aggregation of magnetic particles in external magnetic field, a unified mathematical expression is established and Monte Carlo technique is implemented to simulate the field dependence of magnetobirefringence. Compared with the previous models, this method is more effective in exposing the micro-origin of the phenomena and can be easily extended to calculate other aspects of the effects.
Photoluminescence assessment of B, P, and Al in Si wafers: The problem of sample heating by a laser beam
Authors: Pelant I. , Dian J. , Matoušková J. , Valenta J. , Hála J. , Ambrož M. , Vácha M. , Kohlová V. , Vojtěchovský K. , Kašlík K.
Published: July 2002

A line shape analysis of free-exciton low-temperature (4.2 K) photoluminescence spectra is applied to monitor the heating of Si samples due to an exciting Ar+-ion laser beam. The heating is studied in dependence on the laser beam intensity. The temperature as a line shape fitting parameter can be established within ±0.15 K. Continuous minor increase of the sample temperature is observed up to an intensity of ∼200 W cm−2, followed by an abrupt temperature jump up to tens of K. Possible inaccuracies, resulting from the heating, in photoluminescent quantitative determination of boron, phosphorus, and aluminum are discussed.
Penetration profiles for fast grain-boundary diffusion by the dissociative mechanism
Authors: Mishin Yu. M. , Herzig Chr.
Published: July 2002

A modified variant of Fisher’s model is proposed to describe the recently discovered phenomenon of fast impurity diffusion along grain boundaries (GBs) in metals as follows, (i) The fast diffusion is assumed to occur by the dissociative mechanism. Depending on the lattice dislocation density ρ the bulk diffusion of the impurity around GBs is either vacancy controlled [if (Dt)1/2≪ρ−1/2] or interstitial controlled [if (DT)1/2≫ρ−1/2]. In the first case the effective bulk diffusivity D depends on the GB concentration whereas in the second case D=const. (ii) Fast diffusers strongly segregate to GBs. The GB saturation effect is taken into account by introducing McLean’s isotherm of GB segregation. The GB penetration profiles calculated from approximate analytical solutions of the model exhibit two parts: a near-surface part caused by the GB saturation effect and a more deeply penetrating linear segregation part with a much smaller slope. The second part of the profile either shows strong downward curvature (vacancy-controlled D) or demonstrates normal Fisher-like behavior (interstitial-controlled D). Methods of profile treatment for the determination of GB diffusion parameters are presented. Based on the present model the available experimental data are critically considered and ideas of future experiments are discussed.
Magnetoelastic thin films of amorphous alloys, sputtered onto silicon wafers
Authors: Wallace John L.
Published: July 2002

Thin films of magnetoelastic alloys with chemical composition similar to ‘‘METGLAS■’’ 2605-S2 and 2605-SC have been deposited by dc magnetron sputtering onto various substrates including micromachined cantilevers of single crystal Si, with or without a polyimide precoat. The complex impedance (R+jX) of in situ pickup coils was measured vs cantilever deflection at various frequencies. Depending on the deposition conditions, many of the films had good magnetoelastic properties. M-H loops and rf permeabilities were measured; and the effects of annealing in both static and rotating magnetic fields were studied.
An investigation on the fine defect structure of CoCrTa/Cr magnetic thin films
Authors: Wong Bunsen Y. , Shen Yong , Laughlin David E.
Published: July 2002

The fine defect structure inside the CoCrTa grains in a CoCrTa/Cr bilayer film has been investigated by high-resolution transmission electron microscopy. A high density of stacking faults bound by partial dislocations has been observed. The origin of these stacking faults and the nucleation and growth of CoCrTa on Cr columns have been discussed. It is suggested the surface morphology of the Cr column could play an important role in determining the number of CoCrTa nuclei and consequently the size of the individual CoCrTa crystallographic variants. In addition, plates of face-centered cubic CoCrTa separating the hexagonal-close-packed regions have been found and we believe that the existence of these plates could lead to coercivity enhancement.
Investigation of the heteroepitaxial interfaces in the GaInP/GaAs superlattices by high-resolution x-ray diffractions and dynamical simulations
Authors: He Xiaoguang , Razeghi Manijeh
Published: July 2002

Two GaAs/GaInP superlattices grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition have been studied using high resolution x-ray diffraction measurements and simulations by solving Tagaki–Taupin equations. The strained layers at both interfaces of the GaAs well are identified from the simulations of the measured diffraction patterns. The purging of indium at the interface of GaInP/GaAs accounts for the strained layer at the GaInP/GaAs interface while the pressure difference in the gas lines, which results in the different traveling time to the sample surface, is attributed to the indium-poor strained layer at the GaAs/GaInP interface. It is shown that high-resolution x-ray diffraction measurements combined with a dynamical simulation, are sensitive tools to study the heteroepitaxial interfaces on an atomic layer scale. In addition, the influence of a miscut of the substrate on the measurement is discussed in the article. It is shown that even though the miscut is small, the diffraction geometry is already an asymmetric one. More than 10% error in the superlattice period for a 2° miscut substrate can result when the miscut substrate is considered a symmetric geometry.
Theory for lateral stability and magnetic stiffness in a high-T
c superconductor-magnet levitation system
Authors: Johansen T. H. , Bratsberg H.
Published: July 2002

A quantitative first-order theory for the lateral force between a permanent magnet and a type-II superconductor is presented. The levitation configuration discussed is that of a long rectangular bar magnet placed above a finite-sized rectangular superconductor. The central issues of stability and stiffness (elastic spring constant) associated with lateral vibrations are discussed. Closed-form expressions for both the force and stiffness are derived, thus bringing out clearly the significance of both geometrical dimensions and the magnetic response of the superconductor. It is assumed that the superconductor is either a sintered granular or consists of grains embedded in a nonactive matrix (composite) so that only intragranular shielding currents are important. The predicted behavior as a function of levitation height agrees very well with existing experimental results.
Effect of structural changes in complex perovskites on the temperature coefficient of the relative permittivity
Authors: Colla E. L. , Reaney I. M. , Setter N.
Published: July 2002

The dielectric behavior and structure of the Sr(Zn1/3Nb2/3)O3-Ba(Zn1/3Nb2/3)O3 solid solution have been investigated with the intention of understanding the relationship between the structural changes and the temperature coefficient of the relative permittivity τε. A correlation between the value of τε and the occurrence of O-octahedra tilts has been established. The occurrence of ferroelastic domains and their influence on τε has also been investigated. It is proposed that the results obtained can be used to generalize about the structure-property relationships in compounds of the same class.
Optical properties of semiconductor lasers with hydrostatic pressure
Authors: Patel D. , Menoni C. S. , Temkin H. , Tome C. , Logan R. A. , Coblentz D.
Published: July 2002

The pressure dependence of the stimulated emission of a 1.3 μm In1−xGaxAsyP1−y (y=0.6) buried heterostructure laser has been measured up to 2.5 GPa. In this pressure range the laser output was tuned over 200 nm. The laser output energy varied linearly with pressure at a rate of (80±3) meV/GPa, corresponding to variation of the direct band gap of the InGaAsP active layer with pressure. From the measured energy shift and from calculations of the fractional volume change in the active layer for the strain conditions of the epilayer, a hydrostatic deformation potential of (−5.7±0.1) eV was obtained.
Defect-related generation-recombination region in heterojunction diodes
Authors: Schmeits M. , Sakhaf M. , Munnix S.
Published: July 2002

A numerical analysis is presented of semiconductor heterojunctions containing deep defect levels, in order to study the mechanism of generation or recombination of electron-hole pairs induced by thermal or optical transitions involving deep defect energy levels. The final aim is to determine the width of the effective generation or recombination region Wgr and compare to the width of the space-charge region W. Numerical solution of Poisson’s equation and the current-transport equations yield the electrical potential and the quasi-Fermi levels for electrons, holes, and occupied deep defects. The resulting transition rates yield the net generation rate of electron-hole pairs as function of position x. An application is made to an InGaAs/InP heterojunction with a midgap level on the InGaAs side. Results for a Si homojunction with a deep acceptor level at Ec−0.54 eV are given for comparison. The applications show that in all cases of reverse bias Wgr is smaller than W, reaching for some parameters describing the heterojunction system a value of 1/3 for the ratio Wgr/W. Usually the two widths are assumed to be equal. The physical origin of this reduction is the existence of competing recombination processes due to free-carrier tails extending from the neutral regions into the space-charge region. In heterojunction structures, this effect is even enhanced in case of accumulation of free carriers due to conduction- or valence-band discontinuities at the junction plane. It is shown that if one considers defects states only in a finite region close to the junction, this may yield marked differences in the value of the resulting current as compared to the homojunction case.
Interpretation of hysteresis curves and Henkel plots by the Preisach model (invited)
Authors: Basso V. , Bue M. Lo , Bertotti G.
Published: July 2002

We discuss some properties of the scalar moving Preisach model (MPM) in relation to the description of magnetic interactions. MPM predictions for the behavior of Henkel plots are worked out. The role of the factorization properties of the Preisach distribution and the consequences of the joint presence of mean-field effects and local random interactions are discussed. Literature data are analyzed in the frame of this description, with particular attention to thin-film media with perpendicular magnetization, where mean-field effects are particularly strong. Some of the theoretical predictions are directly tested by hysteresis and Henkel plot measurements performed on SiFe soft alloys. A good agreement, in some cases involving no adjustable parameters, is found.
Focused injection of vacuum arc plasmas into curved magnetic filters
Authors: Anders Simone , Anders André , Brown Ian
Published: July 2002

Thin films of high quality can be deposited using vacuum arc plasmas when the macroparticles which are produced along with the plasma in the cathode spots are removed by curved magnetic filters (‘‘ducts’’). In order to improve the deposition efficiency of a vacuum arc plasma source coupled to a magnetic filter, the effect of a magnetically focused plasma injection into such a filter has been investigated. Maximum plasma output was found at an optimum focusing field strength of 20–40 mT with an optimum duct bias of +20 V with respect to the anode potential (ground potential). The maximum output is by a factor of 20–30 greater than without focusing field and the duct at ground potential. This significant effect at relatively low injection field strength indicates that not only the magnetic field distribution but also the plasma current distribution is essential for an efficient plasma transport.
Photocurrent transients in semi-insulating GaAs, effects of EL2 and other defects
Authors: Mitchel W. C. , Jiménez J.
Published: July 2002

Photocurrent transient effects in undoped semi-insulating gallium arsenide have elicited conflicting explanations. The photocurrent quenching, enhanced photocurrent, and persistent photocurrent effects are reviewed and new results on these effects are reported. A comparison of the photocurrent transients with optical absorption quenching along with other experiments shows that photocurrent quenching is due to the metastable transformation of the deep donor EL2 and that the enhanced and persistent photocurrent effects are due to a seperate effect that is most likely a metastable transformation of another defect. Thermal recovery experiments show that the activated state responsible for the enhanced photocurrent recovers prior to the recovery of the metastable state of EL2. Furnace annealing experiments are presented showing that the enhanced and persistent photocurrent effects are significantly reduced after anneals at 500 °C, well below the annealing temperature of quenchable EL2. After reviewing existing models we suggest that the absence of a persistent photocurrent immediately after quenching is due to compensation of residual impurities by the second level of EL2. A complex defect, perhaps including EL6 as an intermediary, is proposed for the defect responsible for the charge transfer resulting in the enhanced and persistent photocurrent effects.
Optical constants of ZnSxSe1−x ternary alloys
Authors: Ozaki Shunji , Adachi Sadao
Published: July 2002

The methods for calculation of the various optical constants in ZnSxSe1−x ternary alloys are presented. The model used is based on an interpolation scheme, and the effects of alloy composition are properly taken into account in the calculation. The present model reveals distinct structures in the optical spectra at energies of the E0, E0+Δ0, E1, and E1+Δ1 gaps. The optical constants and properties considered here are the complex dielectric constant ε=ε1+iε2, complex refractive index n*=n+ik, absorption coefficient α, and normal-incidence reflectivity R. The refractive indices in the transparent region are also presented for a variety of waveguiding device applications.
Monitoring neutron embrittlement in nuclear pressure vessel steels using micromagnetic Barkhausen emissions
Authors: Sipahi L. B. , Govindaraju M. R. , Jiles D. C.
Published: July 2002

In nuclear power plants, neutron embrittlement of pressure vessel steels has been one of the main concerns. The use of micromagnetic Barkhausen emissions is a promising method to monitor the variations in microstructural and subsurface stress states due to their influence on these emissions. Measurements of these emissions can reveal neutron irradiation degradation in nuclear power plant components. Samples which were irradiated at different neutron fluences and annealed at different temperatures were obtained from three reactor surveillance programs. The results of different neutron fluences and annealing procedures showed noticeable fractional changes in the magnetic Barkhausen effect signal parameter, ΔMBE/MBE, and in the mechanical properties of these specimens. For example, increased intensity of neutron fluence decreased the ΔMBE/MBE as well as impact energy and upper-shelf energy, but increased Rockwell hardness and yield strength. Typical changes in this parameter were in the range from −20% to −45% for fluences of up to 25×1018 n cm−2.
Metamagnetism and spin arrangement in Nd6Fe13Sn
Authors: Rosenberg M. , Zhou R. J. , Velicescu M. , Schrey P. , Filoti G.
Published: July 2002

A magnetic and Mössbauer spectroscopy study of nonoriented and magnetically oriented samples of Nd6Fe13Sn was performed. At 4.2 K a metamagnetic transition takes place in a field of 7.1 T. Strong evidence for antiferromagnetic spin arrangements in the iron magnetic sublattice and antiferromagnetism of the Nd moments with only a small contribution to the net magnetization in fields up to 14 T was found.
Ion beam induced luminescence in natural diamond
Authors: Sullivan P. A. , Baragiola R. A.
Published: July 2002

We used ion beam induced luminescence (IBIL) to study the evolution of damage during ion implantation of natural type-IIa diamond with 30 keV carbon ions, for different sample temperatures in the range 35–300 K. Blue band-A luminescence decays with irradiation dose from an initial value of ∼10−3 photons/e-h pair. This decay was modeled to obtain an effective damage cross section of ∼40 Å2, which is roughly independent of temperature. We explored the use of IBIL as a tool to characterize the processing of p-n junctions in natural type-IIb diamond and apply it to find conditions that determine the ultraviolet response of light-emitting diodes.
Photoacoustic investigation of thermal and transport properties of amorphous GeSe thin films
Authors: Todorović D. M. , Nikolić P. M. , Vasiljević D. G. , Dramićanin M. D.
Published: July 2002

In this work the possibility of simultaneous determination of thermal and transport properties of thin films using a photoacoustic method was investigated. The properties of amorphous GeSe thin films, which were evaporated on quartz substrata, were examined by measuring their amplitude and phase photoacoustic spectra as a function of the modulated optical laser beam frequency. The measurements were performed in a specially constructed photoacoustic cell which enabled excitation of the sample on one side and detection of the acoustic response on the other. Thermal diffusivity and transport properties (diffusivity coefficient, recombination time, and the surface recombination velocity) of the GeSe thin films were determined by comparing of the experimental results and the calculated theoretical photoacoustic spectra.
Magnetic properties of Sm2Fe14−xCoxSi2-based quasiternary compounds
Authors: Yang F.-M. , Gong W. , Hadjipanayis G. C.
Published: July 2002

The structural and magnetic properties of the off-stoichiometric R2Fe17-type Sm2Fe14−xCoxSi2 compounds with 0≤x≤7 have been investigated by x-ray diffraction, thermomagnetic analysis, and magnetic measurements. Substitution of Co for Fe leads to an increase in Curie temperature, ΔTc=303 K for samples with x from 0 to 7. The saturation magnetization Ms increased with increasing Co content at first and then decreased. A maximum saturation magnetization Ms=124 emu/g was obtained at x about 4. The anisotropy changes from planar x<4 to uniaxial x≥4 with Ha=23 kOe for x=7. Introduction of N leads to an increase in lattice constants causing a further enhancement in the Curie temperature and anisotropy field. The best properties were obtained for the Sm2Fe10Co4Si2N2.3 compound with Tc=742 K, Ha (300 K)=175 kOe.
Experimental and numerical study of laser induced spallation in glass
Authors: de Resśguier T. , Cottet F.
Published: July 2002

The study of dynamic failure under shock loading in very brittle materials such as glass is usually limited by the severe destruction of the tested specimens. In this article, an original approach toward studying this phenomenon, based on the post-shock examination of damaged targets, is presented. A high-power pulsed laser has been used to generate very short compressive pulses in glass targets, and this loading has produced limited damage in the samples. Spallation has been shown to result in the formation of a fractured layer near the rear free surface of the targets, and the influences of the main experimental parameters upon the finite thickness of this layer have been determined. The data obtained have been used to work out a simple macroscopic description of brittle spallation in glass, then this description has been coupled to a constitutive model implemented in a one-dimensional simulation code. The resulting model is able to predict the extent of the damage induced in a soda-lime glass target by a laser-driven shock.
Optical measurements of electronic bandstructure in AlGaInP alloys grown by gas source molecular beam epitaxy
Authors: Najda Stephen P. , Kean Alistair H. , Dawson Martin D. , Duggan Geoffrey
Published: July 2002

A series of bulk (AlyGa1−y)0.52In0.48P epilayers, covering the full range of compositions from y=0 to y=1, have been grown lattice matched on GaAs substrates by gas source molecular beam epitaxy. Double crystal x-ray diffraction, and low temperature photoluminescence (PL) and photoluminescence excitation (PLE) optical spectroscopy have been used to characterize the structures. PL and PLE data indicate the direct-to-indirect energy gap crossover composition to be near y∼0.55 for this alloy system. From PLE, the y dependence of the (5 K) lowest energy direct gap, EΓ–Γ, has been found to be 2.014+0.499y+0.16y2 eV. EΓ–Γ (5 K) for the indirect-gap ternary end-member Al0.52In0.48P is directly determined to be 2.685 eV.
In-plane effective mass of electrons in InGaAs/InP quantum wells
Authors: Schneider D. , Elbrecht L. , Creutzburg J. , Schlachetzki A. , Zwinge G.
Published: July 2002

We measured the in-plane effective mass for electrons in multiquantum wells in InGaAs/InP by the Shubnikov–de Haas effect. We varied the well width from 8.6 down to 2.3 nm where the enhancement of the effective mass is predicted to be very pronounced. The electron concentration was in the range of 3×1011 cm−2, so that band filling can be neglected. The variation of the effective mass from 0.045 to 0.067m0 is in accordance with current theories. We discuss the effect of the interface roughness and ionized impurities on the scattering times as found from our experiments.
Raman study of band bending at ZnSe/GaAs interfaces
Authors: Pagès O. , Renucci M. A. , Briot O. , Aulombard R. L.
Published: July 2002

Apparent p-type conductivity in nonintentionally doped ZnSe layers, grown at high temperature on semi-insulating GaAs substrates, is investigated by Raman spectroscopy. The microprobe technique provides direct evidence for carrier location on the GaAs side of the structures, close to the interface. Line-shape analysis of the coupled LO phonon-plasmon mode for different exciting wavelengths can be achieved, within the model of Hon and Faust [Appl. Phys. 1, 241 (1973)], only when incorporating plasma inhomogeneity. Electronic band bending at the junction in GaAs is deduced from the inferred carrier-density profile. Changes in Raman spectra under strong illumination are shown to proceed from the flattening of the bands through selective carrier photoinjection.
Determination of silicon point defect parameters and reaction barrier energies from gold diffusion experiments
Authors: Ghaderi K. , Hobler G. , Budil M. , Mader L. , Schulze H. J.
Published: July 2002

New experiments on short-time diffusion of gold in silicon are presented. By means of both our experiments and experiments published elsewhere, diffusion of gold in silicon is investigated in the temperature range of 900 °C to 1100 °C. A complete set of parameters is determined from these experiments using Arrhenius’ law. It is found that the short-time diffusion experiments cannot be simulated without barrier energies for both the gold-point defect reactions and the Frenkel pair reaction. Their values have been determined as EAu/I=0.482 eV, EAuI/V=0.971 eV, and EI/V=0.30 eV.
Influence of exciton diffusion and localization on cathodoluminescence imaging of quantum well structures
Authors: Jahn U. , Fujiwara K. , Menniger J. , Hey R. , Grahn H. T.
Published: July 2002

The effect of exciton diffusion and localization on the cathodoluminescence (CL) intensity distribution using a scanning electron microscope has been investigated in a single quantum well and a multiple quantum well structure prepared by growth interrupted molecular beam epitaxy. Although of different origin, lateral variations of the exciton confinement energy occur in both samples on a length scale much larger than the exciton Bohr radius. The spectral and spatial CL intensity distribution is substantially influenced by diffusion of excitons to quantum well regions with low exciton confinement energy. The CL micrographs from both quantum well structures exhibit a similar bright/dark pattern with a typical length scale, which is determined by the exciton diffusion length in this material.
Critical interfacial characteristics for effective conductivities of isotropic composites containing spherical inclusions
Authors: Lu Shih-Yuan
Published: July 2002

A study of the critical behavior of effective thermal conductivities of isotropic composites containing spherical inclusions is presented. Three types of problems are investigated: the debonded inclusion, coated inclusion, and contact resistance problems. For the first two problems, a critical relative interfacial layer thickness, (δ/a)c, is shown to exist and is derived to be a simple function of the reduced thermal conductivities of the inclusion, σ2, and of the interfacial layer, σ3. It depends much more strongly on σ3 than on σ2. As to the third problem, a critical Biot number, (Bi)c, is found to exist and can be simply expressed as 1/(σ2−1). Finally, the critical condition for the contact resistance problem is shown to be a special case of that of the debonded inclusion problem.
Enhancement of the nonreciprocal magneto-optic effect of TM modes using iron garnet double layers with opposite Faraday rotation
Authors: Wallenhorst M. , Niemöller M. , Dötsch H. , Hertel P. , Gerhardt R. , Gather B.
Published: July 2002

Garnet films of composition Lu3−xBixFe5−yGayO12 are grown by liquid-phase epitaxy on [111]-oriented substrates of gadolinium gallium garnet. Faraday rotation and saturation magnetization are measured as a function of substitution levels, which range up to x=1.4 and y=1.8, respectively. Nonreciprocal propagation of the TM0 is studied at a wavelength of 1.3 μm. It is shown that the difference between forward and backward propagation constants can be optimized using double layers with opposite sign of the Faraday rotation. Agreement between experiments and calculations is excellent.
Conventional and photothermally modulated ferromagnetic resonance investigations of anisotropy fields in an epitaxial Fe(001) film
Authors: Meckenstock R. , von Geisau O. , Pelzl J. , Wolf J. A.
Published: July 2002

Conventional angle-dependent ferromagnetic resonance (FMR) measurements on an epitaxial (001) Fe film grown on a GaAs substrate were performed as a function of the orientation of the external magnetic field Bext for three configurations: One with Bext in the film plane and two with Bext out of plane starting in plane in different crystallographic orientations. From these measurements the magnetization M, the crystalline anisotropy constants K1 and K2, the surface anisotropy Ks and an additional uniaxial anisotropy Ku were deduced self-consistently. The temperature dependence of K1 and M was investigated for the in-plane [110] orientation in the range from 100 to 570 K. In addition, locally resolved photothermally modulated FMR measurements were carried out to study the homogeneity of the magnetization and of the crystalline anisotropy across the film. Disturbances of both magnetic parameters as a function of position were observed which are related to local inhomogeneities in the semiconducting substrate.
Imaging of the optical mode of waveguiding devices by scanning near-field optical microscopy
Authors: Cella R. , Mersali B. , Bruno A. , Davy S. , Brückner H. , Licoppe C.
Published: July 2002

Scanning optical microscopy with uncoated dielectric silica probe is used in the near field to investigate the propagation of optical modes along tapered integrated semiconductor optical amplifier devices and at larger working distances to study the electromagnetic intensity profile in the focal plane of various microlensed fibers. We show how this technique provides images of the mode structure of optoelectronic devices and profiled optical fibers with typical sizes in the range 2–10 μm, with an accuracy of 0.2 μm in beamwaist measurements.
Characterization of thermally annealed thin silicon films on insulators by Raman image measurement
Authors: Mizoguchi Kohji , Yamauchi Yuji , Harima Hiroshi , Nakashima Shin-ichi , Ipposhi Takashi , Inoue Yasuo
Published: July 2002

The characterization of the crystallinity by Raman image measurements has been made on thin silicon films on insulators, which are deposited by low pressure chemical vapor deposition using silane (SiH4) and disilane (Si2H6) as gas sources and are subsequently thermally annealed. The degree of crystallization by thermal annealing has been quantitatively evaluated by comparing the integrated Raman scattering intensity of the polycrystalline band and the amorphous band. The volume fraction of the crystalline component in samples grown with silane is larger than that grown with disilane for the same annealing time. Raman images of these thin silicon films reveal that the grain size in samples grown with disilane is a few microns, being bigger than that grown with silane. The affect of the source gas on the grain size of crystallites and on the volume fraction of the crystalline component in the films is attributed to the difference in nucleation rate for two kinds of the films during annealing.
Efficient combination of surface and bulk passivation schemes of high-efficiency multicrystalline silicon solar cells
Authors: Elgamel H. E. , Barnett Allen M. , Rohatgi A. , Chen Z. , Vinckier C. , Nijs J. , Mertens R.
Published: July 2002

Conventional and electromagnetically casted multicrystalline silicon solar cells are fabricated following different passivation schemes. Thin layers (∼100 Å) of thermal dry and plasma-enhanced chemical-vapor-deposition (PECVD) SiO2 are implemented for surface oxide passivation of multicrystalline silicon solar cells and compared. It is found that growing thin layers of thermal dry oxide results in efficient surface passivation. However, for thin PECVD SiO2 layers it is necessary to perform low-temperature forming gas anneal, postdeposition, in order to observe the surface passivation effect. In addition, hydrogen plasma passivation has been optimized for achieving deep penetration of atomic hydrogen in the material (≳30 μm) and as a consequence very effective bulk passivation of multicrystalline silicon solar cells. By combining front and back thermal dry SiO2 passivation with hydrogen remote plasma treatment, a cell efficiency of 17% (independently confirmed) on 4 cm2 area and 180 μm thickness is realized without any Al gettering. On the other hand, the cell efficiencies obtained using thin layers of PECVD SiO2 are found to be very comparable to the efficiency of the cells fabricated with thermal dry SiO2 layers provided that PECVD Si3N4/SiO2 are used as a double-layer antireflection coating.
Paramagnetism and scaling behavior of volume flux pinning force density in a GdBa2Cu3O6+x thin film
Authors: Qin M. J. , Shi Z. X. , Ji H. L. , Jin X. , Yao X. X. , Li H. C. , Rong X. S.
Published: July 2002

Magnetic measurements have been performed on a GdBa2Cu3O6+x superconducting thin film. The paramagnetism carried by rare earth Gd3+ ions in the film tilts the magnetic hysteresis loop and broadens the width of the magnetic hysteresis ΔM, then the magnetization critical current density and the volume flux pinning force density based on the Bean critical state model deviate from intrinsic values. Therefore, in order to get useful information on the pinning mechanism, correction for the paramagnetism is essential. And after correction for the paramagnetism, a scaling law of the volume flux pinning force density is obtained as f(b)=(b/4)0.5(1−b/4)1.5, based on which the possible pinning mechanism in the film is discussed. In the end, deviation from the scaling law at high fields is interpreted by the collective pinning theory.
Field-induced phase switching and electrically driven strains in sol-gel derived antiferroelectric (Pb,Nb)(Zr,Sn,Ti)O3 thin layers
Authors: Sengupta S. S. , Roberts D. , Li J.-F. , Kim M. C. , Payne D. A.
Published: July 2002

Tin-modified lead zirconate titanate thin layers were prepared by a sol-gel method. A room- temperature antiferroelectric (AFE) phase composition Pb0.99Nb0.02[(Zr0.58Sn0.42)0.96Ti0.04] 0.98O3 was prepared and examined for weak- and high-field dielectric properties as a function of temperature, with emphasis on field-induced AFE-ferroelectric (FE) switching characteristics. Thin layers processed with a lead oxide cover coat were found to be free of any secondary phases and showed improved properties. Room-temperature values of dielectric constant K′=390 and saturation polarization Ps=20 μC/cm2 were obtained with field-induced strains up to 0.15% in submicron grain structures.
Kinetics of transformation with nucleation and growth mechanism: Fundamentals of derivation and one-dimensional model
Authors: Yu Ge , Lai J. K. L.
Published: July 2002

New derivation of the kinetics of isothermal phase transformation by using probability calculation has been introduced and demonstrated for the simple one-dimensional case, which yields conclusions for transformation with preferred nucleation at line defects. In contrast to the classical treatments, the present derivation starts from a finite discrete system and follows direct logic. With this method it is possible to determine the distribution function of nuclei and to investigate problems such as the many-nuclei correlation, superposition of more than one process, and various boundary conditions. Further analysis yields formulation for the rate of impingement and other details about the transformation. Combined with the analytical treatment, the specialized algorithm for Monte Carlo simulation of nucleation and growth has been developed. From the results of simulation the limitation of the continuous approach has been detected.