bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of plasma sheath expansion, with applications to plasma-source ion implantation
Authors: Emmert G. A. , Henry M. A.
Published: July 2002

In plasma-source ion implantation a target is pulse biased to a high negative voltage, forming an expanding plasma sheath. A numerical simulation model for the evolution of the sheath has been developed and compared successfully with experimental results. The model is one dimensional (planar, cylindrical, or spherical). The time-dependent, self-consistent potential profile is calculated from Poisson’s equation coupled with collisionless fluid equations for the ions and a Boltzmann assumption for the electrons. In addition to the density and potential profile, the simulation yields the ion current to the surface and the energy spectrum of the ions hitting the surface.
Passivation of copper by silicide formation in dilute silane
Authors: Hymes S. , Murarka S. P. , Shepard C. , Lanford W. A.
Published: July 2002

The formation of copper silicide by reaction of silane with sputtered copper films has been observed at temperatures as low as 300 °C. The growth kinetics have been monitored by both sheet resistance and x-ray diffraction techniques. Cu5Si is the first phase to form followed next by Cu3Si, coincident with the loss of the original copper layer. The silicide layer provides significant oxidation protection for the underlying copper up to 550 °C in air.
Porous silicon formation mechanisms
Authors: Smith R. L. , Collins S. D.
Published: July 2002

Recent reports describing photoluminescence in porous silicon have heightened the level of interest in it as a unique electronic material, and have created a need for a more complete understanding of the mechanism of porous silicon formation. The various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon. Because the specific surface dissolution chemistry is critical for a complete understanding of pore formation, some of the more prominent dissolution reactions are also reviewed and their relative importance to pore generation and morphology is discussed. Some aspects of the recently reported quantum effects are also reviewed. Because the mechanism of porous silicon formation involves a wide range of interdisciplinary fields, a considerable number of analogies and examples to related phenomena are also presented throughout the review to aid comprehension.
Double-stream cyclotron maser
Authors: Bekefi G.
Published: July 2002

The double-stream cyclotron maser is a novel source of millimeter wavelength radiation in which two copropagating electron beams are caused to gyrate in a uniform axial magnetic field. The interaction of the slow cyclotron space-charge wave on one beam with the fast cyclotron space-charge wave on the other beam leads to high-frequency bunching. The desired operating frequency is proportional to the electron cyclotron frequency (or a harmonic thereof) and inversely proportional to the difference in beam velocities, and can be achieved at low beam energies and axial magnetic fields. The linear instability growth rate is calculated from the fully relativistic Vlasov equation for the case of cold-electron beams.
High-frequency resonance in acoustic superlattice of barium sodium niobate crystals
Authors: Xu Hui-ping , Jiang Guo-zhong , Mao Lun , Zhu Yong-yuan , Qi Ming , Ming Nai-ben , Yin Jian-hua , Shui Yong-an
Published: July 2002

By using growth striation technique, an acoustic superlattice of barium sodium niobate crystals, the single crystals with the periodic laminar ferroelectric domain structures, has been prepared. High-frequency resonance in the range of 200–400 MHz in such materials has been realized experimentally. The experimental results indicate that the application of acoustic devices with low acoustic loss operating at high frequencies is expected.
Theoretical study of laser heating and dissociation reactions in solids using ultrafast time-resolved x-ray diffraction
Authors: Ma H. , Lin S. H. , Rentzepis P.
Published: July 2002

A theory of ultrafast time-resolved x-ray diffraction is presented. We show that for the case in which vibrational relaxation is fast, the x-ray diffraction intensities in pulse laser heating are determined by the Debye–Waller factor. We also show how the scattering intensities of the diffraction spots change with the position of the dissociating atoms in a time-resolved x-ray diffraction experiment studying dissociation reactions in solids. Our results show that the scattering intensities change in both the fully dissociated and the partially dissociated cases, and that time-resolved x-ray diffraction could be a useful tool in probing dissociation reactions in solids.
Magnetic anisotropy and lattice strain in Co/Pt multilayers
Authors: Zhang B. , Krishnan Kannan M. , Lee C. H. , Farrow R. F. C.
Published: July 2002

The correlation is reported between perpendicular anisotropy and in-plane lattice strain in Co/Pt multilayers. (Cox/Pty)n samples, where x, y are the thickness of the individual Co and Pt layers and n is the number of repeats that were prepared by molecular beam epitaxy and studied by means of polar magneto-optic Kerr effect and transmission electron microscopy. Kerr rotation data and electron diffraction experiments show that the largest perpendicular anisotropy and square hysteresis loop occur when x=3 Å while the Pt layers are subjected to about −2% in-plane strain. As Co thickness increases, Co and Pt layers gradually lose coherency and the magnetic anisotropy goes from perpendicular to planar. This is accompanied by a relaxation of lattice strain in both Co and Pt layers. The close relationship between magnetic anisotropy and lattice strain can be explained as magnetoelastic anisotropy or stress anisotropy effect due to lattice mismatch between the adjacent epitaxial layers.
A numerical study of nonlinear Schrödinger equation solutions for microwave solitons in magnetic thin films
Authors: Chen Ming , Nash Jon M. , Patton Carl E.
Published: July 2002

Dipole-exchange spin wave pulses in magnetic thin films have been numerically modeled with the nonlinear Schrödinger equation. Small input pulse amplitudes yield propagating wave packets which exhibit a linear response. As the amplitude of the input pulse is increased, the propagating spin-wave pulse exhibits soliton and then multisoliton structures. In the soliton regime, three principal characteristics are observed. First, in the zero damping limit, the soliton propagates without changing its shape. Second, the soliton exhibits an inherent velocity in addition to its linear group velocity. Third, the soliton exhibits a damping rate that is approximately twice that in the linear regime.
High-index proton-exchanged MgO:LiNbO3 optical waveguides using adipic acid
Authors: Pun E. Y. B. , Loi K. K. , Mak C. F. , Chung P. S.
Published: July 2002

We report the fabrication and characterization of proton-exchanged optical waveguides in z-cut MgO:LiNbO3 using adipic acid as a new proton source. These waveguides exhibit propagation losses of less than 1 dB/cm, a linear-step index profile, and a surface index increase of 0.149 measured at 0.633 μm wavelength. This is the largest surface index change reported for proton-exchanged MgO:LiNbO3 waveguides. The diffusion parameters were characterized optically, and the diffusion constant D0 and the activation energy Q were found to be 5.40×1010 μm2/h and 103.27 kJ/mol, respectively. The diffusion rate is slower than that of the popular phosphoric acid.
Analysis of ordering in GaInP by means of x-ray diffraction
Authors: Liu Q. , Lakner H. , Scheffer F. , Lindner A. , Prost W.
Published: July 2002

Ga0.51In0.49P layers grown by metal-organic vapor-phase epitaxy in the temperature range from 600 to 730 °C and with various Si-doping concentrations were studied. X-ray diffraction was used to observe the ordering in Ga0.51In0.49P layers. The rocking curves of {115} reflection have shown the existence of ordering in Ga0.51In0.49P even in Si-doped samples with an electron concentration up to 1×1019 cm−3. The samples with ordered structure exhibit an additional {1/2, 1/2, 5/2} reflection. However, no such reflection, which is related to group-III sublattice ordering, was observed in GaAs, AlGaAs, and GaInP layers grown at 730 °C. Photoluminescence (PL) and transmission electron diffraction (TED) results confirm these observations. TED patterns and especially the intensity of the additional ordering spots of Ga0.51In0.49P samples are almost unchanged in the studied doping range up to 1.7×1018 cm−3. An increase of PL peak energy attributed to the ordered structure randomization was not observed. The PL peak shift for highly doped Ga0.51In0.49P was found to be only due to the Burstein–Moss effect.
Effect of radio-frequency power and substrate temperature on properties of hot-plasma-box glow-discharge-deposited hydrogenated amorphous silicon carbon alloys
Authors: Bhusari D. M. , Kshirsagar S. T.
Published: July 2002

The effect of rf power and substrate temperature Ts on the optical, electrical, and structural properties of a-Si1−xCx:H alloy films deposited in the new hot-plasma-box glow-discharge reactor are reported. The rate of deposition as well as the total fraction x of the carbon incorporated in the alloy films were found to vary in a direct proportion with the rf power, whereas the same parameters displayed an inverse proportionality to the changes in Ts. Second, the hydrogen concentration in the alloy films was found to decrease with the increase in substrate temperature while it did not show appreciable variation with the changes in rf power. Next, the structural disorder in the amorphous network was observed to increase rapidly with increase in rf power although a slight improvement was made possible by elevating the Ts. The analysis of Raman scattering and optical band-gap measurements on these alloy films indicates that a large proportion of the Si—C and C—C bond pairs favors the diamondlike (sp3) bonding configuration at low rf power when the Ts is high, whereas the graphitelike (sp2) C—C clusters show up only at high rf power values when the Ts is low. The efficiency of C incorporation in these alloy films prepared by the present technique appears to be better than its best possible magnitude in the conventional open parallel-plate glow-discharge-deposition systems.
Dynamics of a polar electro-optic effect in surface states in nematic liquid crystals
Authors: Lee Sin-Doo , Rhee Bum Ku , Jeon Young Jai
Published: July 2002

We have studied the dynamic properties of a polar electro-optic effect in two surface states in a planar nematic liquid crystal. This polar effect arises from an external symmetry breaking of anisotropic interfacial interactions created by two different aligning layers. The necessary symmetry-breaking is at least comparable to the weak anchorage and the associated relaxation is on the scale of a few hundred microseconds. The relaxation time decreases effectively as the square of the applied field but its asymmetry is a linear function of the field as well as the difference in the surface energies. Some aspects of the dc bias effect is also discussed for practical applications.
Defect studies in oxygen-ion-irradiated silicon-based metal-insulator-semiconductor structures
Authors: Railkar Tarak A. , Bhoraskar S. V. , Dhole S. D. , Bhoraskar V. N.
Published: July 2002

Damages induced by 69 MeV oxygen ions (fluence: 1.3×1014 ions cm−2) in gold–silicon-nitride–silicon metal-insulator-semiconductor (MIS) structures were studied by measuring the pre- and postirradiation junction and interface characteristics. Amount of the space-charge produced at the silicon–silicon-nitride interface was estimated by measuring capacitance-voltage characteristics and the energies of the defects were measured with the technique of deep-level transient spectroscopy. Two new defect levels having energies (Ec−0.34) eV and (Ec−0.63) eV were found in addition to the defects detected in the unirradiated devices. The values of the surface recombination velocities, measured with a variable-energy electron beam, indicate that the radiation-induced defect concentration on the surface was negligible; however, about 7% degradation in the lifetime of minority carriers in the bulk was observed. The results indicate that oxygen ions can be used to modify the junction characteristics of MIS structures while keeping the surface characteristics of the structure almost unaltered.
Ion-beam mixing and solid-state reaction of Fe-Zr multilayers
Authors: Kopcewicz M. , Williamson D. L.
Published: July 2002

The amorphization of an Fe-Zr multilayer film due to ion-beam mixing with protons and due to solid-state reaction is studied in detail using backscatter Mössbauer spectroscopy, x-ray diffraction, and Auger electron spectroscopy. The local structure of the amorphous phase produced by both processes is found to be very similar based on the Mössbauer results. The dose dependence of the ion-beam-mixed phase fraction can be accounted for approximately by a collision cascade mixing model. Incomplete amorphization of the Fe was observed as a result of the proton irradiation with a large enough dose to produce apparent saturation whereas complete amorphization occurred for the identical multilayer structure via solid-state reaction. The latter was characterized by a thermal activation energy of 0.7 eV.
Exciton luminescence in Si1−xGex/Si heterostructures grown by molecular beam epitaxy
Authors: Rowell N. L. , Noël J.-P. , Houghton D. C. , Wang A. , Lenchyshyn L. C. , Thewalt M. L. W. , Perovic D. D.
Published: July 2002

Coherent Si1−xGex alloys and multilayers synthesized by molecular beam epitaxy (MBE) on Si(100) substrates have been characterized by low-temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon-resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. The broad PL band was predominant when the alloy layer thickness was greater than 40–100 Å, depending on x and the strain energy density. The strength of the broad PL band was correlated with the areal density (up to ∼109 cm−2) of strain perturbations (local lattice dilation ∼15 Å in diameter) observed in plan-view TEM. Thinner alloy layers exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. Photoluminescence excitation spectroscopy, external quantum efficiency, time-resolved PL decay, together with the power and temperature dependence of luminescence intensity, have been used to characterize Si1−xGex/Si heterostructures exhibiting both types of PL spectra. The role of MBE growth parameters in determining optical properties was investigated by changing the quantum well thickness and growth temperature. The transition from phonon-resolved, near-band-gap luminescence in thin layers to the broad PL band typical of thick layers is discussed in terms of a strain energy balance model which predicts a ‘‘transition thickness’’ which decreases with increase in x.
Multisite optical spectra and energy levels of trivalent thulium ions in yttrium scandium gallium garnet
Authors: Seltzer Michael D. , Gruber John B. , Hills Marian E. , Quarles Gregory J. , Morrison Clyde A.
Published: July 2002

Intrinsic structural disorder in scandium-substituted garnets, attributed to mixed occupancy of certain sites in the crystal lattice by different cations, has direct consequences for the optical spectra of rare-earth activator ions dispersed over multiple sites. In trivalent thulium-doped yttrium scandium gallium garnet (Tm3+:YSGG), site-selective laser excitation spectra reveal the presence of Tm3+ ions in regular D2 sites, disturbed regular sites, and in octahedral C3i sites. Absorption spectra obtained at 4 K between 0.26 and 1.85 μm are broader than those observed in more-ordered crystal hosts and include structure attributed to Tm3+ ions in sites of other than D2 symmetry. A crystal-field splitting calculation was carried out in which a parametrized Hamiltonian (including Coulombic, spin-orbit, and crystal-field terms for Tm3+ ions in D2 symmetry) was diagonalized for all manifolds of the Tm3+ (4f12) configuration. The rms deviation between 52 experimental and calculated Stark levels of Tm3+ in regular D2 sites was 5 cm−1.
Identification and activation energies of shallow donors in cubic SiC
Authors: Moore W. J.
Published: July 2002

Silicon carbide grown by the chemical vapor deposition process on silicon often contains high concentrations of nitrogen donors with a binding energy of 54 meV as determined from photoluminescence studies. In contrast, the conductivity in the same samples is dominated by a heavily compensated shallow donor with a binding energy below 20 meV. The conventional view is that these two donors are the same. The 54 meV donors usually are assumed to be isolated substitutional nitrogen in regions of low concentration while the <20 meV donors are believed to be nitrogen in regions of high concentration. The most convincing evidence for this identification is the continuum of binding energies from 50 to 15 meV for SiC as a function of donor concentration compiled from published results. Evidence for reassessing the conventional view is given in this article and several experiments supporting the conventional view are reconsidered. As a result of this reconsideration, we propose that the donors below 20 meV which dominate the conductivity are not neutral, substitutional nitrogen in high concentration but some other center. D− centers and donor complexes are possible origins of this donor. The D− center appears to have many of the characteristics required for satisfactory modeling of this material.
Theoretical consideration of misfit dislocation nucleation by partial dislocations in [001] strained-layer heterostructures
Authors: Zou J. , Cockayne D. J. H.
Published: July 2002

The nucleation of misfit dislocations through the extension of dissociated dislocations in the strained interface is considered theoretically. The predicted critical thickness of misfit dislocation nucleation by a dissociated dislocation is compared with that predicted for a perfect dislocation. It is shown that the model of misfit dislocation nucleation by the movement of a dissociated dislocation is more likely.
The effect of growth temperature on the electrical properties of AlInAs/InP grown by molecular beam epitaxy and metal-organic chemical-vapor deposition
Authors: Luo J. K. , Thomas H. , Clark S. A. , Williams R. H.
Published: July 2002

Al0.48In0.52As layers grown on n+-InP substrates by molecular beam epitaxy (MBE) and metal-organic chemical-vapor deposition (MOCVD), as a function of substrate temperature, have been characterized by current-voltage-temperature, capacitance-voltage, deep-level transient spectroscopy, and admittance spectroscopy measurements. It was found that for diodes formed on MOCVD-AlInAs the current in forward bias is dominated by thermionic emission and the reverse current by recombination through the residual midgap states; whereas, for MBE-AlInAs diodes, the respective currents are dominated by defect-assisted tunneling at low forward and reverse biases. Schottky barrier heights were found to decrease with decreasing growth temperature. Three defect levels E1, E2, and E3 were observed in both material systems, and their densities were found to increase rapidly from ∼1012 to ∼1016 cm−3 as the growth temperature decreased from 740 to 500 °C. The decrease of barrier height and the appearance of the defect-assisted tunneling current at low bias were found to correlate with the increase of defect density. The high density of defects may be responsible for the low barrier heights and higher leakage currents previously observed in AlInAs/InGaAs/InP high electron mobility transistors though MOCVD growth provided high quality AlInAs layers.
Reversible transverse susceptibility of particulate recording media
Authors: Lu Jing Ju , Huang Huei Li , Chang Ching-Ray , Klik Ivo
Published: July 2002

The response of a system to an infinitesimal perturbation becomes singular if the system changes its degree of metastability, i.e., if it has an inflection point. This theory is used to calculate the reversible transverse susceptibility χt of a single domain particle executing a major hysteresis loop under the influence of a field H(t) applied at an angle β to the easy axis. Thermal relaxation is taken into account and the response of the nonequilibrium system to the infinitesimal field h(t)=h sin ωt, h⊥H, is found. The resultant χt is studied as a function of β, temperature, and of the frequency Ω of the biasing field H.
Stimulated emission from a (CdMg)Te separate confinement quantum well laser
Authors: Waag A. , Bacher G. , Jakobs A. , Forchel A. , Landwehr G.
Published: July 2002

In this article lasing action of (CdMg)Te quantum well laser structures is reported. The separate confinement quantum well laser structures were grown by molecular beam epitaxy. Stimulated emission has been observed at 77 K and at room temperature. The structures emitted at wavelengths of around 650 nm at room temperature. A (CdMg)Te/CdTe superlattice has been used for the active layer as well as for the electrical confinement layer. Due to this an efficient radiative recombination even at room temperature could be obtained. The distribution of the intensity of the light across the waveguide has been calculated.
Structural and optical properties of CuInS2 bulk crystals
Authors: Angelov M. , Goldhahn R. , Gobsch G. , Kanis M. , Fiechter S.
Published: July 2002

The optical properties of CuInS2 bulk crystals were studied by photoreflectance (PR) and photoluminescence (PL) spectroscopy in comparison with the material structure, verified by energy dispersive x-ray (EDX) microprobe analysis and x-ray diffraction. The samples have been produced by the gradient freeze technique under different sulfur pressures. It was shown by EDX that growth-induced cracking along the ingot is strongly reduced with higher sulfur pressures. The PR spectra at 80 K exhibit two well-resolved transitions. From a comparison with the reflectivity spectra at 80 K, these transitions are explained by the presence of two Wannier excitons. The fit of the spectra yields a broadening parameter of the lower-energy transition which increases approximately linearly with increasing Cu/In ratio. Thus, it is deduced that PR is sensitive to small inhomogeneities in the molecularity of the compound. In agreement with the EDX data photoluminescence indicates the material to be Cu rich. However, a continuous change of the significant PL peaks as a function of the Cu/In ratio could not be observed. According to this, PL is not well suitable to determine small inhomogeneities of the molecularity, in contrast to PR.
Linear electro-optic dispersion in (-)-2-(α-methylbenzylamino)-5-nitropyridine single crystals
Authors: Bailey R. T. , Bourhill G. H. , Cruickshank F. R. , Pugh D. , Sherwood J. N. , Simpson G. S. , Varma K. B. R.
Published: July 2002

The variation of the linear electro-optic effect in (-)-2-(α-methylbenzylamino)-5-nitropyridine with the wavelength of the incident light at room temperature has been measured. The reduced half-wave voltages have been found to have the values 2.1, 2.8, and 6.0 kV at 488, 514.5, and 632.8 nm respectively and the corresponding values of the linear electro-optic coefficient have been evaluated. The interpretation of the results in terms of the structures of the molecule and the crystal is discussed. The thermal variation of the birefringence has also been investigated and the coefficient for the temperature variation of the refractive index difference is found to have the value (dΔn/dT)=9.3×10−5 K−1.
Heat treatment effects on the metal-polymer interface and space-charge formation in thin metallized polyethylene terephthalate films
Authors: Thielen A. , Hendrick E. , Niezette J. , Vanderschueren J. , Feyder G.
Published: July 2002

Space-charge formation in polyethylene terephthalate (PET) ultrathin films has been investigated by means of the thermally stimulated depolarization current (TSDC) method. Important variations of the blocking and injecting properties of the metal-insulator interface have been obtained by using different metals as electrode material and by annealing samples under various conditions, before or after vacuum deposition of electrodes. Depending on the polarization or annealing conditions, conventional and/or anomalous space-charge currents have been observed in the high-temperature region of the TSDC spectrum. Their properties have been explained in terms of modifications of the metal-PET interface.
The improved stability of hydrogenated amorphous silicon films grown by reactive magnetron sputtering at high substrate temperature
Authors: Liang Y. H. , Maley N. , Abelson J. R.
Published: July 2002

We report the electronic properties, stability, and microstructure of a-Si:H films grown at high substrate temperature (320–440 °C) by dc reactive magnetron sputtering. The initial defect state density, determined by the constant photocurrent method, varies from 2–5×1015 cm−3 with H content changing from 15–10 at. % as Ts increases from 320–375 °C. For 100 h of white light exposure at 1 W/cm2, the midgap state density reached an apparent saturation at 2–3×1016 cm−3 over this temperature range. By contrast, films grown at 230–300 °C saturate at 9×1016 cm−3.
Estimate of the ultimate performance of the single-electron transistor
Authors: Lutwyche M. I. , Wada Y.
Published: July 2002

The scaling limit of current semiconductor devices is thought to be about 100 nm. To reduce the size of devices beyond this point will probably require a new device technology. The metal single-electron transistor, using the Coulomb blockade effect, has been proposed as a replacement for semiconductor devices. Recently devices of this kind with potentially useful properties have been fabricated. The scaling of such devices down to atomic dimensions is investigated to see if they can compete with semiconductor logic or analog devices. It concentrates on the operation of a single device and not on the effects of integration. Until now such models for the single-electron transistor have assumed that the capacitance and conductance of the various junctions can be chosen independently, but it is demonstrated that the physical geometry causes restrictions on these choices. A second restriction is that as the device is made smaller the capacitance drops. This means that the temperature of operation rises, but so do the voltages required across the device. A point is reached where these voltages exceed the breakdown voltage of the junctions. For this reason the devices cannot be scaled indefinitely. The model predicts that if the devices are to perform logic functions or analog amplification their maximum speed will be limited to between 1 and 10 ps, which is not a great improvement on semiconductors, especially since for ultimate speed such devices will need to be 100 times smaller. The operation of such high-speed devices will not be possible at room temperature. Operation at 77 K will be possible but very difficult, and with current lithography limits of 10 nm, operation of useful logic even at 4.2 K will be marginal. The model does not rule out the use of the single-electron transistor for other purposes, such as memory and sensitive electrometers, and a process is described for the fabrication of 50 nm devices using a minimum of processing.
Temperature dependence of electronic conduction in thin nitrided oxides
Authors: Yang B. L. , Wong H. , Cheng Y. C. , Liu B. Y.
Published: July 2002

This work reports the temperature dependence of electronic conduction in thin nitrided oxides for temperatures ranging from 298 to 423 K. It was found that the conduction currents in the nitrided oxides have different temperature dependencies from those of conventional thermal oxides. At low electric fields (∼6 MV/cm), the temperature dependencies of the nitrided oxides can be divided into two segments which are attributed to the shallow trap-assisted conduction for temperature less than 400 K and Poole–Frenkel or thermionic emission for temperatures greater than 400 K, whereas the temperature dependence of thermal oxide is governed by exp(−0.143/kT) for the entire temperature range of this study. At high electric fields (∼12 MV/cm), the conduction current of nitrided oxides is mainly governed by Fowler–Nordheim tunneling for temperatures less than 340 K. In studying the temperature dependencies of the electronic trapping in nitrided oxides, we found that the density of trapped charge decreases as large as 27.8% for temperatures rising from 298 to 423 K. It indicates that the density of traps at energy levels less than 0.036 eV (measured from the conduction band of the nitrided oxide) is significantly larger than that of thermal oxides.
Structural analysis of epitaxial films of metal phthalocyanines on hydrogen-terminated Si(111) surfaces
Authors: Kawaguchi Takafumi , Tada Hirokazu , Koma Atsushi
Published: July 2002

Epitaxial growth of vanadyl- and chloro-aluminum-phthalocyanines has been examined on hydrogen-terminated Si(111) surfaces with various surface treatments. Molecular arrangements and orientation were investigated by reflection high-energy electron diffraction (RHEED) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). Sharp RHEED patterns were observed for the films grown on the monohydride-Si(111) surface with a thickness up to 20 monolayers, while epitaxial growth did not occur on a surface terminated with the mixture of polyhydrides. Homogeneity and microscopic flatness of the substrate surface are essential factors for the epitaxial growth. RHEED study revealed that the molecules form commensurate centered rectangular lattices on the monohydride-Si(111) surfaces with an intermolecular distance of 1.38 nm, which was an optimum value for the molecules to stay parallel on the surface. The parallel molecular orientation was confirmed by ARUPS of the epitaxial films.
Comparison and analysis of Pd- and Pt-GaAs Schottky diodes for hydrogen detection
Authors: Kang W. P. , Gürbüz Y.
Published: July 2002

Hydrogen-sensing behaviors of Pd- and Pt-GaAs Schottky diodes, fabricated on the same GaAs substrate, have been systematically compared and analyzed as a function of hydrogen partial pressure and temperature by I-V and ΔI-t methods under steady-state and transient conditions. The effects of hydrogen adsorption on the device parameters such as the barrier height and the ideality factor are investigated. The significant differences in their hydrogen sensing characteristics have been examined in terms of sensitivity limit, linearity of response, response rate, and response time. Adsorption activation energy of hydrogen and the heat of adsorption per hydrogen molecule on the surface of Pd and Pt are investigated and compared in both devices in a low-temperature range (27–100 °C). For the temperature range investigated, Pd-GaAs shows better performance for H2 detection than Pt-GaAs under the same testing conditions. The physical and chemical mechanisms responsible for hydrogen detection are discussed. Analysis of the steady-state reaction kinetics using I-V method confirmed that the atomistic hydrogen adsorption process is responsible for the barrier height change in the diodes.
Study of radiative recombination efficiency in 28–180-Å-wide AlGaAs/GaAs quantum wells grown by molecular beam epitaxy
Authors: Garbuzov D. Z. , Evtikhiev V. P. , Katsavets N. I. , Komissarov A. B. , Kudrik T. E. , Kudryashov I. V. , Khalfin V. B. , Bauer R. K. , Alferov Zh. I. , Bimberg D.
Published: July 2002

The paper reports a theoretical and experimental study of the dependence of the radiative recombination efficiency (ηi) on the GaAs quantum well width (Lz) in AlGaAs/GaAs quantum well structures with binary/binary superlattice confinement. Values of ηi≳60% at room temperature have been obtained for quantum wells with Lz≥40 Å. It is shown that structures with Lz<40 Å exhibit a sharp decrease in ηi associated with nonradiative recombination of the high energy part of nonequilibrium carriers in the confining layers even in the presence of comparatively high potential barriers for Γ electrons.
The effect of surface modification on the luminescence of porous silicon
Authors: Gardelis S. , Hamilton B.
Published: July 2002

The role of the surface in the optical properties of porous silicon remains a key issue. Although the burden of evidence points toward some intrinsic radiative mechanism in small silicon particles, the influence of the surface and ways of controlling surface interactions will always be important. We present here the results of surface modification of porous silicon using annealing and rapid oxidation steps. By comparing new results with existing published data we conclude that hydrogen passivation of the surface is not unique in its ability to saturate dangling bonds and hence promote strong luminescence; oxidation, especially at high temperatures, can play a similar role. Oxidation also produces an additional, low energy band which is linked to residual dangling bond related defects at the Si-SiO2 interface. Furthermore, this band suffers a blue shift with increasing porosity in similar fashion to that observed for the visible emission.
The effects of strain on the threshold current density in InGaAsP/InP strained-layer single-quantum-well lasers
Authors: Seki Shunji , Yokoyama Kiyoyuki
Published: July 2002

Basic design principles are formulated for minimizing the threshold current density in InGaAsP/InP strained-layer single-quantum-well (SL-SQW) lasers. A quaternary InGaAsP active layer is shown to provide more freedom in design than a ternary InGaAs active layer because the amount of strain (both tension and compression) and quantum-well thickness can be independently determined in the InGaAsP system for a given emission wavelength. Strain-induced changes in the valence-band structures are analyzed within the framework of k⋅p theory by taking into account the interaction with spin-orbit split-off bands as well as heavy-hole and light-hole bands. It is clarified that the quantum-well thickness plays a more significant role than the amount of strain when designing compressive-strained wells, while the situation is just the opposite in tensile-strained wells. It is shown that, although the application of biaxial tension reduces the threshold current density in bulk-like SL-SQW lasers more significantly than biaxial compression, the quantum-confinement effect has a pronounced impact on the reduction in the current density in compressive-strained wells. This makes either type of strain attractive for reducing the threshold current density in InP-based SL-SQW lasers.
Al-O interactions in ion-implanted crystalline silicon
Authors: Galvagno G. , La Ferla A. , Spinella C. , Priolo F. , Raineri V. , Torrisi Lucio , Rimini E. , Carnera A. , Gasparotto A.
Published: July 2002

The formation and dissolution of Si-O-Al precipitates have been investigated in Czochralski silicon wafers implanted with 6 MeV Al ions and thermally processed. The data have been compared to the O precipitation in samples implanted with 6 MeV Si or P ions. The amount of precipitated O atoms is about one order of magnitude higher for Al than for Si or P implanted samples. Moreover, a strong gettering of the Al atoms by the silicon dioxide precipitates has been observed. The precipitate evolution has been studied for different annealing times and temperatures. The oxygen precipitation has been simulated by the classical theory of nucleation and growth, with the introduction of new factors that take into account the implant damage distribution, the agglomeration of point defects during the initial stages of the annealing and the oxygen outdiffusion from the sample surface.
Kinetic studies on solid-HDDR processes in Nd-Fe-B-type alloys
Authors: Gutfleisch O. , Verdier M. , Harris I. R.
Published: July 2002

The kinetics of solid-HDDR (hydrogenation, disproportionation, desorption, recombination) processing of Nd-Fe-B-type alloys have been characterized by means of in situ electrical resistivity measurements and hydrogen absorption and desorption studies on nondecrepitated samples. The fundamental differences in reaction rate and mechanism between a Nd16Fe76B8 as-cast and a homogenized stoichiometric Nd2Fe14B alloy at T=800 °C and p(H2)=0.7 bar are reported. The disproportionation and recombination rates were found to be significantly lower in the stoichiometric alloy, particularly in the case of the latter. The onset of the disproportionation and recombination reaction in Nd16Fe76B8 in a temperature range of T=780–880 °C under hydrogen atmosphere was investigated and these reactions were found to depend critically on the pressure. Low-temperature recombination at T=620 °C was studied by the development of the Curie-point resistance anomaly of the Nd2Fe14B matrix phase. It has been shown that the amount of reformed Nd2Fe14B matrix phase during recombination can be monitored by this method.
Magnetoelastic effect in Co/Pd multilayer films
Authors: Kim Young-Suk , Shin Sung-Chul
Published: July 2002

In situ measurements of the stress are reported, and the magnetoelastic contribution to the magnetic anisotropy is clarified, in Co/Pd multilayer films prepared by dc magnetron sputtering. The stress was varied between 2.36×1010 and 4.22×1010 dyn/cm2 in the Co sublayer of the film with an abrupt drop of the stress in the Co sublayer thicker than about 5 Å. This abrupt change seems to be related with a structural transition of a coherent-to-incoherent matching at the interface with thickening the sublayer. The stress-induced anisotropy of the samples having perpendicular magnetic anisotropy is found to be 40%–80%, compared to Néel’s surface anisotropy.
Mechanisms of optical response in superconducting YBa2Cu3O7−δ thin films and grain-boundary weak links
Authors: Bhattacharya S. , Rajeswari M. , Takeuchi I. , Trajanovic Z. , Li Qi , Xi X. X. , Venkatesan T.
Published: July 2002

The optical response of single grain-boundary weak links in superconducting YBCO thin films has been investigated. At temperatures well below the transition temperature, the grain boundary exhibits an optical response which is qualitatively different from transition edge response. Using a resistively shunted-junction model for the grain-boundary weak link, we find that the optical response below the transition temperature can be described by radiation induced thermal modulation of the critical currents of the weak links. The dependence on the bias current and the temperature distinguishes the weak-link optical response from the transition edge optical response. We discuss novel aspects of a potential radiation detector based on grain-boundary weak-link junctions.
Monte Carlo simulation of CuPt-type ordering in off-stoichiometric III-V semiconductor alloys
Authors: Ishimaru Manabu , Matsumura Syo , Kuwano Noriyuki , Oki Kensuke
Published: July 2002

CuPt-type ordering in off-stoichiometric III-V semiconductor alloys has been investigated by a Monte Carlo method based on an Ising-like crystal growth model for the layer-by-layer stacking on a (001) substrate. (110) Fourier power spectra of the atom configurations thus obtained exhibit superlattice spots due to the CuPt ordering. In the (11̄0) spectra, satellite reflections arise, flanking the fundamental lattice spots of the zinc-blende structure and their intensity increases with the progress of ordering. The results are in good agreement with the experimental results previously obtained by transmission electron microscopy. The calculated atomic arrangement confirmed that the compositional modulation is the cause of the satellite reflections along the [110] direction.
Tamm states and donors at InAs/AlSb interfaces
Authors: Shen Jun , Goronkin Herb , Dow John D. , Ren Shang Yuan
Published: July 2002

Localized interface states, viz., generalized Tamm states, can be induced by an interfacial InSb bond in the InAs/AlSb heterojunction system, as confirmed by electronic structure calculations. The calculated energies of the interfacial Tamm states, however, are too low to account for the observed carrier concentrations in InAs quantum wells. Native defects capable of accounting for the observed carrier concentrations are identified, and their electronic structures calculated: AlSb in an AlSb layer is responsible for the semi-insulating character of thin InAs quantum wells and the n-type character of wide wells, and AsAl at an AlAs-like interface is responsible for the high values of electron concentration in the wells. The decrease of electron concentrations with temperature can be attributed to partial freezing of electrons into the shallow levels associated with ionized donors.
Intensity dependence of the third-harmonic-generation efficiency for high-power far-infrared radiation in n-silicon
Authors: Urban M. , Nieswand Ch. , Siegrist M. R. , Keilmann F.
Published: July 2002

The third-harmonic generation of far-infrared (FIR) laser radiation in n-doped silicon was measured with full temporal resolution of the power fluctuations during the FIR laser pulse. Thus, the intensity dependence of the nonlinear coefficient χ(3) could be observed. For 2 MW incident power, corresponding to an intensity of 15 MW/cm2, at a wavelength of 676 μm a power conversion efficiency of 10−3 was reached.
Stress effect on coercivity of γ-Fe2O3 thin films
Authors: Chang W. D. , Chin T. S. , Wu H. S. , Chou S. W. , Jou J. H.
Published: July 2002

Thin Fe3O4 films were deposited in situ on Si(100) substrates by dc-reactive magnetron sputtering method, and then γ-Fe2O3 thin films were obtained by post-oxidation treatment. The effect of residual stress on coercivity of these films was studied by a bending-beam method. In situ stress-temperature curves of the films taken during the whole heat treatment processes revealed the magnitude and state of film stresses. The measured coercivity increments (470 Oe) are very close to the value (460 Oe) calculated based on stress-induced anisotropy for films with pure γ-Fe2O3 phase. For a film with mixed Fe3O4 and γ-Fe2O3 mixed phase, the magnetostriction is calculated to be 17×10−6. In situ stress-temperature data are provided to depict phase transformations and stress effects on the coercivity of such films.
X-ray double crystal characterization of single crystal epitaxial aluminum nitride thin films on sapphire, silicon carbide and silicon substrates
Authors: Chaudhuri J. , Thokala R. , Edgar J. H. , Sywe B. S.
Published: July 2002

A detailed double crystal x-ray diffractometry study of epitaxial AlN thin films grown on sapphire, silicon and silicon carbide substrates was carried out to compare the structure, residual stress and defect concentration in these thin films. The structure of AlN is wurtzite with a small distortion in lattice parameters. This results in a small residual stress of the order of 109 dynes/cm2 in the film and can be accounted for from the difference in thermal expansion coefficients between the film and substrate. Both the x-ray and transmission electron microscopy measurements indicate a low defect density in the AlN thin film grown on 6H-SiC substrate which could be attributed to the small difference in lattice parameters between AlN and 6H-SiC.
Lifetime measurement of the B2∑+u level of N+2 by laser-induced fluorescence
Authors: Fukuchi T. , Wong A. Y. , Wuerker R. F.
Published: July 2002

The optical diagnostic technique of laser-induced fluorescence has been applied to a low pressure nitrogen discharge generated by radio frequency waves. The first negative system of N+2 was investigated with the use of a tunable dye laser. The radiative lifetimes of the B2∑+u(v′=0,1) levels were measured to be 65.1±0.4 and 62.5±0.7 ns, respectively. The obtained lifetimes and transition probabilities agree with the values found in the literature, deduced from electron beam excitation. In addition, rotational constants of the B2∑+u and X2∑+g levels were found from the observed spectra.
X-ray diagnostics of plasma focus DPF-78 discharge with heavy-gas admixtures
Authors: Antsiferov P. S. , Rosmej F. B. , Rosmej O. N. , Schmidt H. , Schulz D. , Schulz A.
Published: July 2002

The x-ray structure (λ<10 Å) of the DPF-78 discharge was investigated with different heavy-gas admixtures to a basic D2 filling. A possible classification of plasma features is proposed. Micropinches with an unusual high aspect ratio of about 10:1 were found. Soft x-ray spectra of single micropinches were registered on film. The use of x-ray spectroscopic methods by means of spectra simulation codes allowed us to estimate the parameters of particular types of pinches with axial size of 0.5 mm and full radial size of 0.05 mm. In the He-like ionization state we obtained ne≊3×1021 cm−3 and Te≊0.8 keV. The electron temperature determined in the H-like ionization stage was considerably higher, Te≊2 keV, indicating a strong ionizing plasma. Possible deviations from the Bennett condition are discussed in connection with the spectroscopic results.
Large Schottky barriers formed on epitaxial InGaP grown on GaAs
Authors: Shiojima Kenji , Nishimura Kazumi , Aoki Tatsuo , Hyuga Fumiaki
Published: July 2002

We report the formation of Schottky contacts, with a barrier height as large as 0.9 eV, on epitaxial InGaP grown on GaAs wafers. The contacts are formed by removing surface oxide layers. Thermal reactions between Ti and InGaP and/or surface treatment with buffered hydrogen fluoride solution are effective for selective removal of surface oxide. These methods do not decrease the InGaP film thickness. They are promising for fabricating GaAs metal-semiconductor field-effect transistors with a thin InGaP film for increased barrier height.
Elastic properties of rigid fiber-reinforced composites
Authors: Chen J. , Thorpe M. F. , Davis L. C.
Published: July 2002

We study the elastic properties of rigid fiber-reinforced composites with perfect bonding between fibers and matrix, and also with sliding boundary conditions. In the dilute region, there exists an exact analytical solution. Around the rigidity threshold we find the elastic moduli and Poisson’s ratio by decomposing the deformation into a compression mode and a rotation mode. For perfect bonding, both modes are important, whereas only the compression mode is operative for sliding boundary conditions. We employ the digital-image-based method and a finite element analysis to perform computer simulations which confirm our analytical predictions.
Growth kinetics of amorphous interlayers by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline V thin films on (001)Si
Authors: Lin J. H. , Chen L. J.
Published: July 2002

The growth kinetics of an amorphous interlayer (a-interlayer) formed by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline V thin films on (001)Si have been investigated by conventional and high-resolution transmission electron microscopy. The growth was found to follow a linear growth law initially in samples annealed at 430–465 °C. The growth then slows down and deviates from a linear growth law as a critical thickness of the a-interlayer is reached. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 1.1±0.3 eV and 4.5 nm, respectively. The correlations among differences in atomic size and electronegativity between metal and Si atoms and activation energy of the linear growth, critical and maximum a-interlayer thickness, the calculated free-energy difference in forming the amorphous phase, as well as atomic mobility in Ti/Si, Zr/Si, Hf/Si, Ta/Si, Nb/Si, and V/Si systems are discussed.