bluuebunny/crossref_metadata_2025 huggingface dataset:
Field quenching effects in polycrystalline SrS:Pb and SrS:Ce,Pb thin films for electroluminescence devices
Authors: Oberacker T. A. , Schlotterbeck G. , Bilger G. , Braunger D. , Schock H.-W.
Published: July 2002

The luminescence properties of lead ions and their sensitizing effect on cerium activators in strontium sulfide thin-film electroluminescence (TFEL) devices have been investigated. Polycrystalline SrS:Pb and SrS:Ce,Pb thin active layers for such TFEL devices have been prepared by multi-source deposition. Emission spectroscopy under application of a high electric field (EL), under e-beam excitation [cathodoluminescence (CL)], and under CL conditions with additional EL drive has been carried out. It has been found that the luminescence of SrS:Pb under EL drive is very weak, while the CL signal is considerably higher. This CL signal has shown strong quenching effects upon application of an additional ac voltage. The Pb2+ emission dropped to some 5% at an applied voltage of 100 V0p, being roughly 40 V below EL threshold. More than half of this drop occurred between 0 and 30 V0p. A remarkably lower quenching effect on the Ce3+ activator luminescence has been observed. Such luminescence quenching is attributed to the field induced ionization of the luminescent ions. From the obtained results it is concluded that the optical energy transfer from Pb2+ sensitizers to Ce2+ activators in SrS TFEL devices is low.
Kinetic theory of phase separation induced by nonuniform photopolymerization
Authors: Wang X. Y. , Yu Yi-Kuo , Taylor P. L.
Published: July 2002

A kinetic model is developed to study the process of phase separation that occurs when a polymer-dispersed liquid-crystal diffraction grating is produced by a process of photopolymerization. We find that the type of system produced depends sensitively on the rate of polymerization and on whether the spatially periodic illumination used to produce the grating is followed by a period of uniform illumination. While the average liquid-crystal concentration is always increased in the region of least irradiation, in some cases small inclusions of liquid-crystal form by spinodal decomposition at the minima in the irradiating intensity, while in others they form at the maxima. The simplest version of the theory combines the Flory-Huggins and Hillert models of phase separation. In some circumstances it must be augmented by including the effects of interdiffusion of polymer molecules having different degrees of polymerization.
Ion beam syntheses and microstructure studies of a new FeSi2 phase
Authors: Jin S. , Li X. N. , Zhang Z. , Dong C. , Gong Z. X. , Bender H. , Ma T. C.
Published: July 2002

Iron-silicide has been formed by ion implantation of iron into silicon (111). In the as-implanted sample, a new type of orthorhombic FeSi2 phase was found. Although the lattice parameters of the new phase are the same as those of the known semiconductor β-FeSi2, its point group and space group were different and determined to be mmm and Pbca, respectively.
Structural defects and epitaxial rotation of C60 and C70(111) films on GeS(001)
Authors: Bernaerts D. , Tendeloo G. Van , Amelinckx S. , Hevesi K. , Gensterblum G. , Yu L. M. , Pireaux J.-J. , Grey F. , Bohr J.
Published: July 2002

A transmission electron microscopy study of epitaxial C60 and C70 films grown on a GeS (001) surface is presented. The relationship between the orientation of the substrate and the films and structural defects in the films, such as grain boundaries, unknown in bulk C60 and C70 crystals, are studied. Small misalignments of the overlayers with respect to the orientation of the substrate, so-called epitaxial rotations, exist mainly in C70 films, but also sporadically in the C60 overlayers. A simple symmetry model, previously used to predict the rotation of hexagonal overlayers on hexagonal substrates, is numerically tested and applied to the present situation. Some qualitative conclusions concerning the substrate-film interaction are deduced.
Calculation of Lindgård and Mouritsen’s free energy using recently measured moduli of elasticity for hydrogen in zirconium
Authors: Ashida Yuh , Yamamoto Masahiro , Naito Shizuo , Mabuchi Mahito , Hashino Tomoyasu
Published: July 2002

The Young’s modulus E and the modulus of rigidity G of ZrHx (0≤x<0.9) were measured as functions of temperature between 300 and 1300 K for Zr and of hydrogen concentration at 941 and 1001 K in the previous paper. The abrupt change of the observed G for Zr at a critical temperature determines all the unknown coefficients of the free energy (LM free energy) derived by Lindgård and Mouritsen, who discussed the structural phase transition between the α (a hexagonal closed-packed structure) and β (a body centered cubic structure) phases in a Landau theory [Phys. Rev. Lett. 57, 2458 (1986)]. LM free energy is modified so as to include effects of interstitial hydrogen atoms at low hydrogen concentration. A modified LM free energy which represents the transition from the α to β phase through the α+β phase is obtained by introducing an order parameter proportional to hydrogen concentration. The order parameter multiplied by a lattice constant is the displacement between the position of Zr atom in the α phase and its position in the β phase.
Mass, charge, and energy separation by selective acceleration with a traveling potential hill
Authors: Tung L. Schwager , Barr W. L. , Lowder R. S. , Post R. F.
Published: July 2002

A traveling electric potential hill has been used to generate an ion beam with an energy distribution that is mass dependent from a monoenergetic ion beam of mixed masses. This effect can be utilized as a novel method for mass separation applied to identification or enrichment of ions (e.g., of elements, isotopes, or molecules). This theory for mass-selective acceleration is presented here and is shown to be confirmed by experiment and by a time-dependent particle-in-cell computer simulation. Results show that monoenergetic ions with the particular mass of choice are accelerated by controlling the hill potential and the hill velocity. The hill velocity is typically 20%–30% faster than the ions to be accelerated. The ability of the hill to pickup a particular mass uses the fact that small kinetic energy differences in the lab frame appear much larger in the moving hill frame. Ions will gain energy from the approaching hill if their relative energy in the moving hill frame is less than the peak potential of the hill. The final energy of these accelerated ions can be several times the source energy, which facilitates energy filtering for mass purification or identification. If the hill potential is chosen to accelerate multiple masses, the heaviest mass will have the greatest final energy. Hence, choosing the appropriate hill potential and collector retarding voltage will isolate ions with the lightest, heaviest, or intermediate mass. In the experimental device, called a Solitron, purified 20Ne and 22Ne are extracted from a ribbon beam of neon that is originally composed of 20Ne:22Ne in the natural ratio of 91:9. The isotopic content of the processed beam is determined by measuring the energy distribution of the detected current. These results agree with the theory. In addition to mass selectivity, our theory can also be applied to the filtration of an ion beam according to charge state or energy. Because of this variety of properties, the Solitron is envisioned to have broad applications. The primary application is for the enrichment of stable isotopes for medical and industrial tracers. Other applications include mass analysis of unknown gases (atomic and molecular) and metals, extracting single charge states from a multiply charged beam, accelerating the high energy tail in a beam or plasma with a velocity distribution, and beam bunching.
Structural characterization of ordered SiGe films grown on Ge(100) and Si(100) substrates
Authors: Araki T. , Fujimura N. , Ito T. , Wakahara A. , Sasaki A.
Published: July 2002

We observe the formation of an ordered structure in Si1−xGex films grown on Ge(100) substrates, as well as on Si(100) substrates, by molecular beam epitaxy. The structural characterization of these ordered films is performed. The degree of order in the films is quantitatively measured using x-ray diffraction. The dependence of the degree of order on Ge composition is similar between films on Ge(100) and Si(100) substrates. By careful x-ray diffraction analysis, we find that the degree of order is not equivalent in variants.
Magneto-optics in coupled quantum dots
Authors: Ugajin Ryuichi
Published: July 2002

We calculate the optical transition coefficient of two electrons confined in a pair of coupled quantum dots under a magnetic field. When the distance between quantum dots is small, the applied magnetic field causes considerable change in the optical-transition coefficients and induces new types of optical transition. On the other hand, when the distance is large, the Mott insulating states of a pair of electrons are less sensitive to an external magnetic field because of the small size of each quantum dot.
Lattice instability at a fast moving crack tip
Authors: Zhang Y. W. , Wang T. C.
Published: July 2002

A molecular dynamics method is used to analyze the dynamic propagation of an atomistic crack tip. The simulation shows that the crack propagates at a relatively constant global velocity which is well below the Rayleigh wave velocity. However the local propagation velocity oscillates violently, and it is limited by the longitudinal wave velocity. The crack velocity oscillation is caused by a repeated process of crack tip blunting and sharpening. When the crack tip opening displacement exceeds a certain critical value, a lattice instability takes place and results in dislocation emissions from the crack tip. Based on this concept, a criterion for dislocation emission from a moving crack tip is proposed. The simulation also identifies the emitted dislocation as a source for microcrack nucleation. A simple method is used to examine this nucleation process.
Metastable states of Si donors in AlxGa1−xAs
Authors: Jia Y. B. , Grimmeiss H. G.
Published: July 2002

Donor related states in Si-doped AlGaAs with Al compositions ranging from 0.30 to 0.59 were investigated by capacitance measurements. In addition to the stable Si-DX state, two metastable states of the silicon donor were observed. Of the two metastable states, the shallower one is attributed to the X-conduction band related effective mass state arising from substitutional silicon on the group III site. The deeper one is proposed to be related to a donor configuration different from both the substitutional configuration and that of the DX state.
DX-like center generated by uniaxial strains of screw dislocations in CdS
Authors: Istratov A. A. , Vyvenko O. F.
Published: July 2002

A center in plastically deformed CdS, labeled herein as the SDX center, was investigated by means of deep level transient spectroscopy, thermally stimulated capacitance, photocapacitance, and Hall effect measurements. The essential features of the center are: thermally activated electron capture with an activation energy (0.30 eV), comparable with the electron emission activation energy (0.40 eV); an optical ionization energy of the SDX center (1.47 eV) significantly exceeding the equilibrium electron binding energy (0.1 eV); a persistent photoconductivity at low temperatures; dependence of electron emission from SDX centers in an electric field is significantly weaker than expected from the Pool–Frenkel effect. The concentration of SDX centers, as measured by methods of capacitance spectroscopy and conductivity, increases with increasing density of screw dislocations. Exponential electron thermo-emission from the SDX center is accompanied by nonexponentiality of the electron capture. The capture kinetics is fitted using several models. The best agreement with the data is obtained for the model of randomly distributed barrier heights. A model of the origin of SDX centers is proposed and discussed. According to the model, SDX center is a noneffective-mass state (DX level) of a shallow substitutional donor (possibly Al). In as-grown samples, it cannot be occupied because it lies significantly above the Fermi level. In plastically deformed samples the DX level moves down to the Fermi level under the elastic lattice distortions around dislocations and becomes detectable.
Ultrafast dynamics of excited-state absorption in V3+:YAG crystal
Authors: Yumashev K. V. , Kuleshov N. V. , Malyarevich A. M. , Prokoshin P. V. , Shcherbitsky V. G. , Posnov N. N. , Mikhailov V. P. , Sandulenko V. A.
Published: July 2002

Picosecond differential absorption spectra measurements for V3+:YAG were performed and a schematic energy-level diagram for tetrahedrally coordinated V3+ in YAG was deduced. The excited-state absorption transitions from the 1E(1D) level were observed with peaks at 870 and 740 nm. The lifetime of the 1E(1D) excited state of the tetrahedral V3+ was found to be ∼130 ps. The ground-state absorption band of the 3T1(3P) state was found to be at 590 nm.
Effect of an alternating current field on charge trapped in biased double barrier heterostructures
Authors: Davidson William W. , Puri Ashok
Published: July 2002

Charge buildup in a closed double barrier heterostructure is investigated in the presence of an external field. A small ac field is applied to the quantum structure in superposition of a dc field. The motion of the electron cloud is represented by a mean field approximation using a Hartree-like equation. A nonlinear time dependent Schrödinger equation is solved for the amount of charge trapped in the biased heterostructure. We examine the effect of applying ac fields of varying frequencies and amplitudes. Our results indicate that application of the ac field leads to an increase in the mean charge developed in the structure and an increase in the chaotic behavior, as indicated by the autocorrelation and power spectrum calculations.
Transition in (001) AlGaAs/AlAs/GaAs double-barrier quantum structure for infrared photodetection
Authors: Osotchan T. , Chin V. W. L. , Tansley T. L.
Published: July 2002

Optical transitions for the (001) Al0.3Ga0.7As/AlAs/GaAs double-barrier superlattices are evaluated by a semiempirical, tight-binding calculation. The oscillator strength between the hole and electron states confined in either Γ- or X-like well are investigated as a function of AlAs slab thickness. Intersub-band transition within the conduction band, including Γ- and X-like superlattice (SL) states, is described for a quantum well infrared photodetector (QWIP). We found that for a specific design structure, it is possible to achieve the dual wavelength QWIP with comparable oscillator strength for the 3–5 μm and 8–14 μm atmospheric windows. In addition, by varying the AlAs barrier thickness, the characteristics of bound-to-continuous and bound-to-quasibound QWIPs are related to the stationary discrete SL states. As the AlAs thickness increases, the bound-to-continuous state transition becomes weak while the bound-to-quasibound state transition becomes more significant. Optical coupling between X-like state is relatively weak and the transition between the different characteristic states is even weaker.
Rapid collapse of Wannier–Stark localization caused by space charge electric field screening in short-period superlattices
Authors: Hosoda M. , Tominaga K. , Vaccaro P. O. , Watanabe T. , Inomata H. , Fujiwara K.
Published: July 2002

A rapid optical absorption change is observed in a GaAs/AlAs short-period superlattice having Wannier–Stark localization. This phenomenon is clearly explained by a rapid collapse of Wannier–Stark localization due to electric field screening by photogenerated space charges. The screening causes a positive feedback loop between restoration of the blue-shifted wavelength of the absorption band-edge towards the red and an increase in optical absorption, which causes an additional field screening. The experimental bias voltage dependence of the intensity of photoluminescence and photocurrent under high optical excitation, agree well with a model applying Fowler–Nordheim tunneling at the heterointerface cladding layer. It is concluded that the space charges are stopped near the cladding layer and that the superlattice region is almost fully screened to near the flat-band bias condition.
Saturation of electron phase breaking time in GaAs/AlGaAs quantum wires
Authors: Noguchi Mitsuhiro , Ikoma Toshiaki , Odagiri Takahide , Sakakibara Hideki , Wang Shi Nan
Published: July 2002

We have systematically studied an electron phase breaking time in AlGaAs/GaAs quantum wires by measuring the weak-localization effect. The phase breaking time does not saturate down to 0.5 K for quantum wires whose undoped AlGaAs spacers are not thinner than 30 nm, while it saturates below 1 K for quantum wires whose spacers are not thicker than 15 nm. The saturated magnetoconductance shows no antilocalization features characteristic of a spin–orbit interaction. A spin–flip scattering by paramagnetic electron-trapped donors is discussed as one of the possible origins of the saturation.
The frequency spectrum of a phase-modulated interferometer illuminated by a Gaussian source
Authors: McGarrity C. , Jackson D. A.
Published: July 2002

A detailed theoretical analysis with numerical calculations was conducted to study the frequency spectrum resulting from the application of a sinusoidal phase modulation to a two-beam interferometer illuminated by a low-coherence source with a Gaussian spectral profile. Results of these calculations show behavior of the frequency components which was unexpected from earlier derivations of the frequency spectrum. The results of the calculations have been experimentally confirmed using an all-fiber interferometer illuminated by a source with a Gaussian spectral profile. The results will be useful for the signal processing of tandem interferometers for ‘‘white light’’ interferometry in the field of optical sensing.
Applications of the second-order Bragg interaction in a thin-film optical waveguide for the transverse electric mode
Authors: So Daniel W. C. , Seshadri S. R.
Published: July 2002

The operation of output coupler, input coupler, surface emitting amplifier, and surface emitting distributed feedback laser formed on a thin-film dielectric waveguide depends on guided–guided and guided–radiated wave couplings. The characteristics of these devices are treated for the transverse electric mode for wave interactions caused by a suitable relief grating formed on the film–cover interface. Design criteria are deduced and optimization procedures are indicated with illustrative numerical examples. The device characteristics are insensitive to small changes in the physical parameters. Surface emitting amplifier with a uniform near-field pattern and surface emitting distributed feedback laser operating in a single mode are investigated.
Non-linear resistance behavior in the early stages and after electromigration in Al-Si lines
Authors: Scorzoni A. , De Munari I. , Stulens H. , D’Haeger V.
Published: July 2002

A common result obtained in electromigration experiments carried out on Al-Si lines using different high resolution resistometric methods, is a monotonous non-linear resistance increase at the very beginning of the high current electromigration test, and a decrease after the high stressing current is switched off. These effects have often been attributed to the attainment of a steady state of vacancy concentration during and after electromigration. This paper shows how even small abrupt temperature steps, always present at the beginning and after electromigration tests, are the triggering events for different, often reversible, physical phenomena contributing to non-linear resistance changes. Precipitation–dissolution of alloyed elements appears to be the most significant one. Abrupt temperature changes also induce a change of the hydrostatic stress of passivated lines. The relaxation of the hydrostatic stress could be coupled with a void volume change, and the total resistance is a function of both the hydrostatic stress (through resistivity) and of void volume. However, we demonstrate that in our experiments the effect of hydrostatic stress relaxation on resistance variations is negligible with respect to the action of precipitation–dissolution. These non-linear, thermally induced effects, however, do not exclude possible simultaneous resistance changes due to the accumulation/relaxation of the electromigration damage. Experimental results are collected by means of different, complementary techniques.
Excimer laser-induced surface fixation of polymer and its patterning
Authors: Nakayama Yasuhide , Matsuda Takehisa
Published: July 2002

When ArF excimer laser pulses irradiated an UV-absorbing polymer film, such as poly(N,N-dimethylacrylamide) or polystyrene, in close contact with an optically transparent substrate, such as polyethylene or poly(vinyl alcohol), the target was selectively photolyzed, resulting in the formation of a crosslinked polymer which was covalently bonded onto the substrate surface. The formed polymer exhibited IR spectral features very similar to those of the target. Fine surface patterning of the formed polymer layer was attained by pulsed irradiation through a projection mask.
n-type ion implantation doping of AlxGa1−xAs (0⩽x⩽0.7)
Authors: Zolper J. C. , Klem J. F. , Baca A. G. , Sherwin M. E. , Hafich M. J. , Drummond T. J.
Published: July 2002

Si-implant activation characteristics in AlxGa1−xAs for Al compositions of 0%–70% AlAs are presented for doses of 5.6×1012 and 2.8×1013 cm−2 at 100 keV. For both doses, the effective activation efficiency (ηeff) is relatively constant from 0% to 20% AlAs (ηeff=64% for 5.6×1012 cm−2 and 37% for 2.8×1013 cm−2 for 20% AlAs), goes through a minimum at 35% AlAs (ηeff=6.6% for 5.6×1012 cm−2 and 2.5% for 2.8×1013 cm−2), and then increases towards 70% AlAs (ηeff=52.8% for 5.6×1012 cm−2 and 31.1% for 2.8×1013 cm−2). The results are explained based on the compositional dependence of the ionization energy and conduction band density-of-states of AlGaAs. The effects of P coimplantation is also studied but demonstrates no significant enhancement of the activation efficiency of Si implantation for 0%–70% AlAs. Finally, data are presented for Se implantation in Al0.2Ga0.8As with a maximum effective activation efficiency of 5.6% achieved.
Suppression and enhancement of elastodynamic radiation from a point source load in elastic wave band structures
Authors: Suzuki Toshio , Yu Paul K. L.
Published: July 2002

We show that propagation of elastic waves can be completely inhibited, irrespective of propagation directions, if oscillation frequencies of elastic waves fall inside elastic wave band gaps—three-dimensional frequency stop bands of elastic waves generated in three-dimensional periodic elastic materials. We also develop a classical theory for the calculation of radiated fields and energy from a point source load located in three-dimensional periodic elastic media by incorporating the plane wave method, dyadic Green’s function, Poynting theorem, and tetrahedron k-space integration. The fcc structure of tungsten spheres in polyethylene background is studied as an example. The resulting frequency spectra indicate the total inhibition of energy transmission in the elastic wave band gaps and unusual enhancement near the band edges. In addition, the computed data suggest the strong dependency of radiation spectra on the source position in the periodic elastic materials.
Modeling of electron backscattering from topographic marks
Authors: Mkrtchyan M. M. , Farrow R. C.
Published: July 2002

The generation of the backscattered electron (BSE) contrast from topographic marks is investigated applying single-scattering and diffusion theories of electron backscattering. It is found that a combined model, which accounts for both single-scattering and diffusion fractions of electron backscattering, has the potential to explain our recent experimental results. The combined model predicts that the BSE contrast from an isolated topographic mark (e.g., V groove, trench) is a universal function of a dimensionless parameter, the ratio of the mark depth to the full electron range. This is also confirmed by our experimental results. Our model reveals the basic trends for the BSE contrast improvement and is capable of predicting the optimal conditions for any topographic mark detection.
Evolution of coercivity during the early stages of Fe80B20 crystallization
Authors: Vavassori P. , Ronconi F. , Puppin E.
Published: July 2002

We report a study of the evolution of coercivity (Hc) in partially crystallized Fe80B20 samples with an increasing number of crystallites obtained in a controlled way into ferromagnetic amorphous matrix. These samples allow to test existing models for interaction of domain walls with defects since it is possible to change only the number density of crystallites without modifying their dimensions. We observe that the evolution of Hc is mainly related to the nucleation frequency of grains and quite independent from their internal structure. The observed behavior of Hc can be accounted for by considering the dependence of coercivity on the number density of pinning sites and by assuming a two-dimensional bending of the domain walls during their motion. Moreover our results indicate that the changes occurring to the intergranular phase during annealing do not appreciably affect coercivity in the partially crystallized samples.
Intensity fluctuation of a pulsed planar microcavity laser
Authors: Enomoto Takayuki , Sasaki Takuto , Sekiguchi Katsumi , Okada Yoshiko , Ujihara Kikuo
Published: July 2002

Probability distributions of the peak output power from planar microcavity dye lasers with pulsed excitation have been studied experimentally. Two microcavities were used, one operating possibly with a single mode and the other possibly with a number of modes. These expectations are based on the relative magnitude of the mode radius and the pump beam radius. In the former cavity an exponential-like distribution was observed below threshold, which indicates single-mode operation. In the latter cavity a single-peaked distribution appeared even below threshold indicating multiple-mode operation. These results are, respectively, in qualitative agreement with theoretical distributions for steady state. That the observed pulse width is large enough to apply steady state distribution equation is shown by calculating the characteristic transient time for the intensity distribution.
An envelope function description of the quantum well formed in AlxGa1−xAsySb1−y/InAs/AlxGa1−xAsySb1−y heterostructures
Authors: Anwar A. F. M. , Webster Richard T.
Published: July 2002

Schrödinger and Poisson equations are solved self-consistently to calculate the quantum mechanical properties of AlGaAsSb/InAs/AlGaAsSb single quantum wells formed in high electron mobility transistors. The two dimensional electron gas (2DEG) distribution is calculated and shows excellent confinement both at room temperature and at 77 K. The variation of the average distance of the electron cloud, from the first heterointerface, with the 2DEG concentration is a strong function of the quantum well (QW) width. A minimum 2DEG concentration threshold, dictated by the QW width and the unintentional doping level of the substrate, exists at room temperature. This effect may prohibit the pinching-off of the channel at room temperature, especially for wide QWs.
Comparison of isotropic and anisotropic sensor effects in polymer lightguides
Authors: Biebricher M. , Kleckers T. , Franke H.
Published: July 2002

A method for measuring the effective birefringence of polymer lightguides is shown to be a useful tool for chemical sensors. It is demonstrated that the method can be either the nonlinear response of an initially anisotropic lightguide on a linear effect of an in-diffusing compound or a stress induced birefringence in an initially isotropic polymer film. The samples used were polyimide for the anisotropic case and the allyl polymer poly(diallylic terephtalic acid) for the isotropic material.
Depth measurement of doped semiconductors using the Hall technique
Authors: DeSalvo Gregory C. , Look David C. , Bozada Christopher A. , Ebel John L.
Published: July 2002

A new method using the Hall technique to determine the change in surface layer thickness of doped semiconductors is presented. An equation to calculate the semiconductor thickness change has been determined by comparing the difference in Hall measured sheet carrier concentration and mobility before and after a change in surface layer thickness. Experiments were conducted using a wet chemical digital etch to remove n-type GaAs surface layers having an incremental etch depth control of approximately 15 Å in thickness, and the resulting thickness changes were calculated by the Hall technique and measured with a mechanical profilometer. This Hall measurement technique was able to measure changes in surface layer thickness of less than 100 Å, and the accuracy of this new technique compared favorably with mechanical profilometer measurements. The new Hall technique method provides accurate measurements of minute thickness changes, and is more accurate than mechanical profilometers for thickness changes less than 150 Å.
The analysis of piezoelectric/piezomagnetic composite materials containing ellipsoidal inclusions
Authors: Huang Jin H. , Kuo Wen-Shyong
Published: July 2002

A unified method based on the inclusion formulation is proposed to determine the magnetic, electric, and elastic fields in a composite with piezoelectric and piezomagnetic phases. The composite reinforcements are treated as ellipsoidal inclusions that enable the reinforcement geometries ranging from thin flakes to continuous fibers. Utilizing the proposed method, the magneto-electro-elastic tensors analogous to Eshelby tensors for elastic ellipsoidal inclusions are obtained. With these tensors, the magnetic, electric, and elastic fields around the inclusion as well as concentration factors are determined. Furthermore, based upon the Mori–Tanaka mean-field theory [Acta Metall. 21, 571 (1973)] to account for the interaction between inclusions and matrix, the effective magneto-electro-elastic constants (elastic moduli, piezoelectric coefficients, dielectric constants, piezomagnetic coefficients, magnetoelectric, and magnetic permeability) of the composites are expressed explicitly in terms of phase properties, volume fraction, and inhomogeneity shape. The numerical examinations have been conducted for the three-dimensional BaTiO3–CoFe2O4 composite, and the overall composite behavior has been examined numerically. It is found that the composite reveals interesting magnetoelectric coupling which is absent in each constituent.
Three wave mixing using a fiber ring resonator
Authors: Xu C. Q. , Shinozaki K. , Okayama H. , Kamijoh T.
Published: July 2002

Three wave mixing using a fiber ring resonator scheme is discussed, and experimental results are presented. In this scheme, an optical nonlinear medium is placed into the fiber ring laser cavity, and a semiconductor optical amplifier and a tunable optical band pass filter (TOBPF) are used as the gain medium and lasing wavelength selector. The phase-matching condition, which is necessary for efficient wave mixing, can easily be satisfied by tuning the TOBPF. Second-harmonic generation (SHG) and sum-frequency generation (SFG) were demonstrated using a LiNbO3 waveguide with a periodically domain inverted structure. Enhancements of SHG and SFG were achieved.
The role of H2O in enhancing hot filament assisted diamond growth at low temperatures
Authors: Li Tolt Z. , Heatherly L. , Clausing R. E. , Feigerle C. S.
Published: July 2002

The addition of a small amount of oxygen to a hot filament assisted chemical vapor deposition reactor allows diamond to be deposited at significantly lower filament and substrate temperatures. Scanning electron microscopy and Raman spectroscopy are used to compare films grown with and without oxygen addition as a function of substrate temperature at high and low filament temperatures. Oxygen addition is found to favor growth of high quality diamond at low substrate temperatures (<600 °C). The amount of nondiamond carbon is reduced and the clarity and smoothness of facets improves dramatically under these conditions. Equilibrium calculations and residual gas analysis indicate there is H2O in the gas above the substrate during these depositions. The correlation between the dramatic reduction in the nondiamond carbon content of the films and the increased H2O levels near the substrate at low temperatures leads to the conclusion that H2O plays an important role in facilitating deposition at lower temperatures. Potential roles for H2O include terminating carbon dangling bonds by dissociative adsorption and enhancing selective etching of nondiamond carbon by O2. The gas and surface chemistry of diamond deposition at low temperatures with oxygen addition is also discussed.
Dependence on channel potential structures of I–V characteristics in InAlAs/InGaAs pseudomorphic high electron mobility transistors
Authors: Maeda Narihiko , Ito Hiroshi , Enoki Takatomo , Ishii Yasunobu
Published: July 2002

We have systematically examined the relationship between channel potential structures and dc device performances in the InP-based pseudomorphic high electron mobility transistors, in order to obtain a guideline for improving the channel potential structures. Based on the self-consistent calculation of the quantum states in the channel, we have designed and fabricated several pseudomorphic devices with different channel potential structures where the quantum states were systematically changed. By comparing the I–V characteristics in terms of the transconductance, the drain conductance, and the shape of the I–V curve, we have successfully extracted information on the states of channel electrons under actual device operation. Not only the design for the ground state but also that for the excited states has been shown to be important for improving the transconductance. The drain conductance was shown to improve by reducing the total channel thickness, probably due to the enhanced recombination of electrons and holes. One of the channel designs, 20 Å In0.53Ga0.47As/30 Å InAs/70 Å In0.7Ga0.3As, was shown to yield a high transconductance of 1240 mS/mm and a low drain conductance of 40 mS/mm simultaneously, for a 0.7 μm gate length device.
Temperature dependence of electromigration threshold in Cu
Authors: Frankovic R. , Bernstein G. H.
Published: July 2002

Electromigration threshold, the product of current density, j, and the threshold length, lth, was measured for unencapsulated thin-film Cu conductors using edge-displacement techniques. jlth was measured between 175 and 275 °C, and was found to be temperature dependent above 200 °C where jlth decreased with increasing temperature. It is suggested that the temperature dependence of the electromigration threshold may be obtained by considering the effects of the changing deformation mechanisms with changing temperature.
Threshold behavior of nanometer scale fabrication process using scanning tunneling microscopy
Authors: Wang Chen , Li Xiaodong , Shang Guangyi , Qiu Xiaohui , Bai Chunli
Published: July 2002

The fabrication process on a graphite surface is investigated using scanning tunneling microscopy, with emphasis on the effects of high electric field associated with voltage pulse. We have demonstrated that two distinct types of features can be repeatedly produced and are found to be correlated with tip–sample separation, displaying a threshold behavior. By correlating the observation with the general trend of tunneling barrier height versus tip–sample separation, it is suggested that field emission and electrical breakdown are the driving mechanisms for generating craters and mounds, respectively.
Interface-mediated amorphization of coesite by 200 keV electron irradiation
Authors: Gong W. L. , Wang L. M. , Ewing R. C. , Xie H. S.
Published: July 2002

Electron-induced amorphization of coesite was studied as a function of irradiation temperature by in situ transmission electron microscopy at an incident energy of 200 keV. Electron-induced amorphization of coesite is induced by an ionization mechanism and is mainly dominated by an interface-mediated, heterogeneous nucleation-and-growth controlled process. Amorphous domains nucleate at surfaces, crystalline-amorphous (c-a) interfaces, and grain boundaries. This is the same process as the interface-mediated vitrification of coesite by isothermal annealing above the thermodynamic melting temperature (875 K), but below the glass transition temperature (1480 K). The interface-mediated amorphization of coesite by electron irradiation is morphologically similar to interface-mediated thermodynamic melting.
Analysis of four wave mixing in slab waveguide under the undepleted pump approximation
Authors: Yokota Mitsuhiro
Published: July 2002

The four-wave mixing in a slab waveguide is investigated theoretically by using the singular perturbation technique with multiple space scales. In order to apply the perturbation technique, we first introduce the perturbation parameter concerned with the nonlinear coefficients and the multiple space scales in the propagation direction. Substituting the expansion of the field and the multiple space scales into the Maxwell’s equation, we can get the governing equations to each order of the perturbation. From the solvability conditions to have nontrivial solutions for each perturbation solutions, it can be shown that the coupled-mode equations for four waves that are asymptotically correct in the limit of weak nonlinearity are obtained. The dependence of the coupling coefficient on the waveguide width and the field distribution of the phase conjugate wave are discussed numerically. We show that the coupling coefficients have the maximum for the optimum waveguide width.
Positron annihilation in electron-irradiated SixGe1−x bulk crystals
Authors: Kawasuso Atsuo , Okada Sohei , Suezawa Masashi , Honda Tatsuya , Yonenaga Ichiro
Published: July 2002

Position lifetime measurement for SixGe1−x bulk crystals has been performed. The bulk lifetime of positron in the crystals varied between those for Ge and Si. The dependence of the lifetime on the alloy composition showed an abrupt change at x=0.17–0.20 which seems to be correlated with that of the band gap energy. After 3 MeV electron-irradiation, vacancy-type defects giving rise to the lifetimes of ∼280 and ∼330 ps were detected for 0.63⩽x⩽0.82 and 0.20⩽x⩽0.40, respectively, but not for x⩽0.17. The composition-dependent vacancy production was interpreted in terms of the thermal stability of vacancies with the composition.
Thermomechanical study of AlCu based interconnect under pulsed thermoelectric excitation
Authors: Phan T. , Dilhaire S. , Quintard V. , Lewis D. , Claeys W.
Published: July 2002

The thermomechanical behavior of microelectronic interconnect lines under pulsed electric excitation is studied by laser interferometry and reflectometry. An original data processing method and an analytical stationary thermoelastic model are proposed to derive data of interest. The experimental techniques allow one to measure the local transient temperature change at surface and the normal surface displacement produced by Joule heating in the interconnects under normal operating conditions. The proposed data processing method exploits the temporal behavior of the surface temperature change of the interconnects as an “identifying characteristic’’ to analyze the surface displacement. It separates the thermal dilatation which follows “instantaneously’’ the temperature change from the one related to the heat diffusion in the resultant normal surface displacement. After the separation operation, a stationary thermoelastic model for a metallic line bonded to a thick and rigid substrate subject to a uniform temperature change is used to interpret the transient surface displacement measurement. Consequently, the operating temperature, one of the major factors limiting the quality and reliability of the interconnects and other related parameters can be estimated in a simple way.
SiGeC alloy layer formation by high-dose C+ implantations into pseudomorphic metastable Ge0.08Si0.92 on Si(100)
Authors: Im S. , Song J. H. , Lie D. Y. C. , Eisen F. , Atwater H. , Nicolet M.-A.
Published: July 2002

Dual-energy carbon implantation (1×1016/cm2 at 150 and at 220 keV) was performed on 260-nm-thick undoped metastable pseudomorphic Si(100)/ Ge0.08Si0.92 with a 450-nm-thick SiO2 capping layer, at either room temperature or at 100 °C. After removal of the SiO2 the samples were measured using backscattering/channeling spectrometry and double-crystal x-ray diffractometry. A 150-nm-thick amorphous layer was observed in the room temperature implanted samples. This layer was found to have regrown epitaxially after sequential annealing at 550 °C for 2 h plus at 700 °C for 30 min. Following this anneal, tensile strain, believed to result from a large fraction of substitutional carbon in the regrown layer, was observed. Compressive strain, that presumably arises from the damaged but nonamorphized portion of the GeSi layer, was also observed. This strain was not significantly affected by the annealing treatment. For the samples implanted at 100 °C, in which case no amorphous layer was produced, only compressive strain was observed. For samples implanted at both room temperature and 100 °C, the channelled backscattering yield from the Si substrate was the same as that of the virgin sample.
The effect of the surface Fermi level pinning on the properties of δ-doped systems
Authors: Sampaio J. F. , Freire S. L. S. , Alves E. S.
Published: July 2002

Electronic potential profile, energy levels, and their respective occupations are self-consistently calculated for δ-doped semiconductor films, taking into account the charge depleted by the surface. This effect is considered by requiring the Fermi level at the surfaces to be at some fixed value relative to the band gap edges. The electron concentration in the potential well is calculated for different values of the film thickness and of the surface chemical potential. The results show that these calculations can be helpful in determining the Fermi level pinning at the surface by fitting Hall concentrations of δ-doped samples.
Modeling of the microwave surface impedance of current biased YBa2Cu3O7−δ thin films
Authors: Löfgren Martin
Published: July 2002

A theoretical and experimental investigation is made of the surface impedance of dc current biased high-quality epitaxial YBa2Cu3O7−δ thin films using a coplanar resonator technique. The isotropic Ginzburg-Landau theory and a current-dependent coupled-grain model are used to model the resonant frequency shift and the change in unloaded quality factor Q0 due to the bias current. Good quantitative agreement is obtained between the two models and the measured resonant frequency shift. The change in Q0, determined from measurements, can be explained by the coupled-grain model. The Ginzburg-Landau theory predicts a change in Q0 which is several times less than given by measurements.
The influence of texture on power losses in nonoriented electrical steels
Authors: Birsan M. , Szpunar J. A.
Published: July 2002

The power losses in nonoriented electrical steels are affected by both the crystallographic orientation of the grains (texture) and grain size, a parameter not related to texture. In this article, a model is proposed which allows the separation of the textural and nontextural contributions to power losses in these materials. The influence of texture on power losses is associated with the appearance of the perpendicular component of magnetization which is a consequence of the presence of magnetic domain structure.
Piezoelectric interfacial waves in lithium niobate and other crystals
Authors: Laprus W. , Danicki E.
Published: July 2002

Waves propagating along a perfectly conducting plane embedded in a piezoelectric medium are investigated. The theory of such waves is given, and numerical calculations are described. The conditions of existence and the properties of the waves are presented for trigonal lithium niobate, langasite, and cubic dilithium tetraborate. The numerical analysis shows that the waves exist for many orientations of the conducting plane with respect to the crystallographic axes, and for many directions of propagation. The wave velocity is close to that of the slowest bulk wave for the same direction, and the piezoelectric coupling coefficient can be as high as 3.60% for lithium niobate, 0.25% for langasite, and 1.60% for dilithium tetraborate.
Centimeter-wave reflection in the nitrates and nitrites of sodium and potassium: Experiment and theory
Authors: Cornelison Steven G. , Gauss Arthur , Krane J. , Hardy J. R.
Published: July 2002

Temperature-dependent centimeter-wave reflection is studied in powdered samples of potassium nitrate (KNO3), potassium nitrite (KNO2), sodium nitrate (NaNO3), and sodium nitrite (NaNO2). Temperature-dependent reflection measurements at centimeter-wave frequencies were performed on an HP8510B Network analyzer based reflectometer. These measurements are compared to calculations utilizing a Debye relaxation model. Reflection losses seen in KNO2 and NaNO2 are expected to be due to the presence of permanent dipoles that are excited to “hopping’’ modes as the temperature is raised. Although NaNO3 shows little reflection losses, KNO3 shows significant losses as the temperature is raised toward the order/disorder transition temperature of 128 °C. This is believed to be due to the development of “induced’’ dipole moments as the lattice becomes increasingly disordered.
Effects of low-energy (1–1.5 kV) nitrogen-ion bombardment on sharply pointed tips: Sputtering, implantation, and metal-nitride formation
Authors: Kim Y.-C. , Yu C.-J. , Seidman D. N.
Published: July 2002

Low-energy (1–1.5 kV) nitrogen-ion bombardment of sharply pointed Fe-3 at. % Mo tips is performed, at room temperature and 473 K, by applying a negative voltage to the tip in the presence of nitrogen gas (10−3–10−5 Torr) in an ultrahigh vacuum atom-probe field-ion microscope (APFIM). Tip sharpening, as a consequence of sputtering, is observed directly in situ via APFIM. This sharpening phenomenon can be explained by the inertia effect on the trajectories of the field-emitted electrons and nitrogen ions that results in sputtering of the shank of the tip. We also observe that the implanted low-energy (1–1.5 kV) nitrogen ions react with the molybdenum atoms in solid solution in this Fe(Mo) alloy to produce immobile molecular diameter nitrides at room temperature and 473 K. The measured range profile of the implanted 1.5 kV nitrogen species is compared with results calculated using the TRIM.SP Monte Carlo code. This comparison implies that the ionized nitrogen molecules (N21+), generated by the field-emitted electrons, obtain the full potential energy of the tip before bombarding the tip’s surface and then dissociating into nitrogen ions (N1+) at or near the surface. The experimental nitrogen range profile is quantitatively fitted to the Edgeworth expansion of the normal distribution function.
Photoluminescence decay dynamics in an InGaN/GaN/AlGaN single quantum well
Authors: Li Wei , Bergman Peder , Monemar Bo , Amano H. , Akasaki I.
Published: July 2002

The dynamics of photoluminescence lines of a Si-doped InGaN/GaN/AlGaN quantum well (QW) grown by metalorganic chemical vapor deposition have been studied by time-resolved photoluminescence emission spectroscopy. A dominant broad emission band from the InGaN QW has been observed, and attributed to radiative recombination of electrons in the InGaN well with the photoexcited holes. The transient behavior of the observed emissions have been measured at different temperatures and found to be dependent on both emission and excitation probe energy.