bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic nanostructure array in crossed holographic gratings on silica glass by two interfered infrared-femtosecond laser pulses
Authors: Kawamura Ken-ichi , Sarukura Nobuhiko , Hirano Masahiro , Ito Naoko , Hosono Hideo
Published: July 2002

Two cross-superposed holographic gratings were encoded on silica glass by femtosecond laser pulses (wavelength ∼800 nm). A variety of periodic nanostructures from a one-dimensional wire array to two-dimensional arrays of holes or islands were formed by changing the energy density and the incidence angle of the irradiation laser beams. The smallest dimensions were a width of ∼15 nm for wires and a diameter of ∼20 nm for holes. Laser-driven microexplosions occurring within the microcylindrical-lens array created by the first laser pulse are suggested as a mechanism for the formation of these structures. Only two pulses are required to encode these periodic structures, which are applicable to emerging nanostructured devices such as photonic crystals and quantum dot or wire arrays.
High-pressure structures of methane hydrate observed up to 8 GPa at room temperature
Authors: Hirai H. , Uchihara Y. , Fujihisa H. , Sakashita M. , Katoh E. , Aoki K. , Nagashima K. , Yamamoto Y. , Yagi T.
Published: July 2002

Three high-pressure structures of methane hydrate, a hexagonal structure (str.A) and two orthorhombic structures (str.B and str.C), were found by in situ x-ray diffractometry and Raman spectroscopy. The well-known structure I (str.I) decomposed into the str.A and fluid at 0.8 GPa. The str.A transformed into the str.B at 1.6 GPa, and the str.B further transformed into the str.C at 2.1 GPa which survived above 7.8 GPa. The fluid solidified as ice VI at 1.4 GPa, and the ice VI transformed to ice VII at 2.1 GPa. The structural changes occurring with increasing pressure were observed reversibly with decreasing pressure. The symmetric stretching vibration, ν1, of the methane molecule observed in the Raman spectra changed along with the structural changes. The bulk moduli, K0, for the str.I, str.A, and str.C were calculated to be 7.4, 9.8, and 25.0 GPa, respectively. The difference in the bulk moduli implies the difference in fundamental structure of the high-pressure structures.
Spreading of a viscous drop due to gravity and capillarity on a horizontal or an inclined dry wall
Authors: Reznik S. N. , Yarin A. L.
Published: July 2002

Spreading of a drop on a plane dry wall (horizontal or inclined) due to gravity and capillarity is studied in the inertialess approximation for arbitrary Bond numbers. In the case of a horizontal wall it is shown that the initial stage of spreading is fully dominated by gravity, and rolling motion sets in at the contact line (CL). When the rate of the CL motion reaches the order of the characteristic wetting velocity, wetting effects are accounted for. The apparent contact angle at this stage is affected by the bulk flow and only at the end approaches the well-known Hoffman’s law. Deviations from the latter are shown to be important in the region of contact angles close to π and to increase with the Bond number. This follows from the fact that the bulk flow effects driven by gravity are stronger as the Bond number is higher. They affect the apparent contact angle. The latter increases as the Bond number increases which agrees qualitatively with experimental observations. A comparison with the known analytical solutions is proceeded. In the case of an inclined surface it is shown that rolling motion near the leading contact line sets in only when the slope angle exceeds a certain threshold value. On inclined surfaces drops develop bump near the leading contact line, as well as a long tail emerges.
Modifications of magnetic properties of Pt/Co/Pt thin layers by focused gallium ion beam irradiation
Authors: Vieu C. , Gierak J. , Launois H. , Aign T. , Meyer P. , Jamet J. P. , Ferré J. , Chappert C. , Devolder T. , Mathet V. , Bernas H.
Published: July 2002

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20–100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=1014 Ga+/cm2, the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5–10)×1014 Ga+ ions/cm2, the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2×1015 Ga+ ions/cm2. We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co–Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using a focused Ga+ ion beam to pattern magnetic properties of similar samples at a sub-100 nm scale.
State-to-state and total rotational energy transfer rate constants for CN(B 2Σ+,v=0,N)+H2, CN(X 2Σ+,v=2,N)+H2, D2, and CN(X 2Σ+,v=3,N)+NO
Authors: Brunet Sophie M. K. , Guo Jingzhong , Carrington Tucker , Filseth S. V. , Sadowski C. M.
Published: July 2002

State-to-state and total rotational energy transfer (RET) rate constants were measured for collisions of CN(B 2Σ+,v=0,Ni=4,7,8,11) with H2, CN(X 2Σ+,v=2,Ni=4,11) with H2 and D2, and CN(X 2Σ+,v=3,Ni=4) with NO at room temperature and under single, or near-single, collision conditions. Rate constants were also measured for electronic quenching of CN(B 2Σ+,v=0,Ni=4,7,8,and 11) by H2. In general, state-to-state RET rate constants showed very small or no even–odd alternations as the final rotational state varied. Total rate constants for CN(X 2Σ+,v=2,N)/H2, D2 were found to decrease with increasing rotational quantum number, N. By contrast, total rate constants for CN(B 2Σ+,v=0,N)/H2 were found to be relatively independent of N. Exponential energy gap and angular momentum fitting functions were found to represent measured state-to-state RET rate constants very well and were substantially equally effective in this regard.
Amorphization and annealing of LiTaO3 single crystal irradiated with Ar+ ions at 77 K
Authors: Zhang Z. , Rusakova I. A. , Chu W. K.
Published: July 2002

The defect structure of radiation damage due to irradiation of Ar+ ions and the regrowth of LiTaO3 single crystal has been studied using Rutherford backscattering-channeling, cross-sectional transmission electron microscopy, optical transmittance, and surface profilometer. The irradiation were carried out at 77 K with 217 keV Ar+ ions to various doses between 3×1013 and 6×1015 Ar+/cm2. Postannealing was performed in dry O2 ambient at temperatures from 648 to 823 K, which are below Curie temperature (878 K). The optical measurement showed that the as-irradiated samples are as transparent as the unirradiated sample, indicating that the radiation-induced point defects are highly mobile even at 77 K. However, the long-range migration of oxygen interstitials were suppressed at 77 K. Volumetric expansion occurred when irradiation doses exceeded 1.25×1014 Ar+/cm2. Collective lattice distortion was observed in the sample that had received a dose of 1.5×1014 Ar+/cm2. This study shows that both disorder overlapping and the disorder-induced strain energy play important roles in the amorphization process. The regrowth of the amorphized layers depends on the microstructure of the damage. The activation energy for the regrowth of the amorphized layer that received more irradiation (6×1015 Ar+/cm2) is 0.74 eV, lower than the activation energy of the amorphized layer (1.20 eV) that received less irradiation (6×1014 Ar+/cm2).
Perfectly conducting incompressible fluid model of a wire array implosion
Authors: Velikovich Alexander L. , Sokolov Igor V. , Esaulov Andrey A.
Published: July 2002

An incompressible perfectly conducting magnetohydrodynamic model is applied to describe a multiwire array implosion on the (r,θ) plane using the theory of analytic functions. The plasma columns emerging from the electrical explosion of individual wires move and change the shape of their cross section in the magnetic field produced by the currents flowing on the surfaces of the columns and closing through a cylindrical return current can. Geometry of both the “global” and “private” magnetic fields and self-consistent distributions of the electric currents on the conducting surfaces are determined for any wire array configuration including nested wire arrays, wires close to the return current can, etc. The coupled equations of motion and magnetostatics for an essentially two-dimensional problem are reduced to one-dimensional parametric governing equations, written for the boundary of the fluid contours. The implosion dynamics is shown to be driven by a competition between the implosion pressure, making the array converge to the axis as a set of individual plasma columns, and the tidal pressure that makes the wires merge, forming an annular conducting shell. Their relative roles are determined by the gap-to-diameter ratio πRc(t)/NRw(t). If this ratio is large at early time, then the array implodes as a set of individual plasma columns. Otherwise, when the ratio is about π or less, the tidal forces prevail, and the plasma columns tend to form a shell-like configuration before they start converging to the axis of the array. The model does not allow the precursor plasma streams to be ejected from the wires to the axis, indicating that this process is governed by the finite plasma conductivity and could only be described with a proper conductivity model.
Raman spectra of fluorine-doped silica glasses with various fictive temperatures
Authors: Shimodaira N. , Saito K. , Ikushima A. J.
Published: July 2002

We have demonstrated the change of the Raman spectra in F-doped silica glasses with various fictive temperatures, and have also presented a useful peak-deconvolution technique for evaluating the relative concentration of D1 and D2 bands that could be attributed to four- and three-membered ring structures. The intensities of D1 and D2 bands are mainly dominated by the fictive temperature, and they are not almost affected by the F content at the same fictive temperature. It has been made clear that the intensity of D1 band as well as D2 band has a linear relationship with the IR peak position around 2260 cm−1 that is correlated with the average Si–O–Si bond angle, irrespective of the F content. The “activation energies” of D1 and D2, estimated from the Arrhenius plot, are 0.26 and 0.41 eV, respectively.
Structural and electronic properties of electron cyclotron resonance plasma deposited hydrogenated amorphous carbon and carbon nitride films
Authors: Godet C. , Conway N. M. J. , Bourée J. E. , Bouamra K. , Grosman A. , Ortega C.
Published: July 2002

Hydrogenated amorphous carbon and carbon nitride films (a-C1−xNx:H) have been synthesized from methane, acetylene, or acetylene–nitrogen precursor gases using a high density electron cyclotron resonance plasma. The deposition and etching rates, along with the film stoichiometry, density, Raman signature of the sp2 phase, and optical and transport properties, have been studied as a function of plasma parameters (microwave power and negative bias of the substrate). While low-density H-rich carbon films have been grown from methane for ion energies up to 200 eV, films grown using acetylene have been obtained at high deposition rate (1.1 nm s−1) with H content below 25 H at. % and density of 2.0 g cm−3, which makes them interesting as electronic materials. For dense carbon nitride alloys, the maximum (N/N+C)=0.35 is limited by the vanishing growth rate, which results from ion-assisted chemical etching mechanisms. A larger N2 plasma etching rate related with lower film density is observed for (N/N+C) values above 0.20. As a function of the N content, Raman spectra give evidence of a continuous structural ordering of the sp2 phase, which is confirmed by a modeling of the ohmic conductivity σ(T) data based on hopping transport within a bandtail distribution of localized π states. With increasing N content, a better overlap of p orbitals along with an increase in the localization length are expected as a consequence of a less constrained environment. A maximum of the room-temperature conductivity at (N/N+C)=0.28 reveals the onset of a transition towards polymeric alloys with lower mean coordination number.
Layer guided shear horizontally polarized acoustic plate modes
Authors: McHale G. , Newton M. I. , Martin F.
Published: July 2002

The theoretical basis describing Love waves propagating on a finite thickness substrate covered by a finite thickness solid layer having a lower shear acoustic speed is considered. A generalized dispersion equation is derived for shear horizontally polarized acoustic waves in this system. Two types of solutions to the dispersion equation, both satisfying stress free boundary conditions at the free surfaces, are shown to exist. The first type of solution has a displacement that decays with depth into the substrate while the second does not. Analytical approximations to the solutions for a thin solid guiding layer show that these solutions can be considered as generalizations of Love waves and resonant shear horizontally polarized acoustic plate modes (SH-APM), respectively. Numerical solutions to the dispersion equation are developed and the spectrum of modes for thick guiding layers is examined with particular reference to sensor applications. As expected, increasing the thickness of the guiding layer leads to multiple Love wave modes. However, each of these Love wave modes is found to possess a set of shear horizontally polarized acoustic plate modes. As the guiding layer thickness is increased, the Love wave speed decreases until at approximately νl/4f, where νl is the shear acoustic speed of the layer and f is the frequency, a sharp transition occurs in the Love wave speed from a value close to the shear acoustic speed of the substrate, νs, to one close to the shear acoustic speed of the layer, νl. A similar pattern is observed for the layer guided SH-APM’s with an increase in the guiding layer thickness resulting in a sharp transition in the speed of the SH-APM towards a value close to that of the next lower SH-APM. It is shown that the appearance of the second Love wave mode is a result of a continuation of the lowest SH-APM associated with the previous Love wave mode. A physical interpretation is developed for the Love waves on the finite substrate and for the layer guided SH-APM’s and from this interpretation it is suggested that layer guided SH-APM sensors could provide significantly enhanced mass sensitivity.
Operation and performance of a free electron laser oscillator down to 190 nm
Authors: Marsi M. , Trovò M. , Walker R. P. , Giannessi L. , Dattoli G. , Gatto A. , Kaiser N. , Günster S. , Ristau D. , Couprie M. E. , Garzella D. , Clarke J. A. , Poole M. W.
Published: July 2002

We present recent results obtained by the European Free Electron Laser (FEL) project at the ELETTRA storage ring. Coherent and tunable light was produced in the ultraviolet down to below 190 nm, the shortest lasing wavelength obtained so far with a FEL oscillator. The performance of the FEL is described, together with a series of technical solutions that have been adopted on it. These solutions increase its validity as a source for applications, and demonstrate the potential of FEL oscillators to become sources with features in the vacuum ultraviolet.
Electron field emission from boron-nitride nanofilms
Authors: Sugino Takashi , Kimura Chiharu , Yamamoto Tomohide
Published: July 2002

Hexagonal polycrystalline boron-nitride (BN) films are synthesized on Si substrates by plasma-assisted chemical-vapor deposition. In the case of BN films thicker than 20 nm, the turn-on electric field of the electron emission decreases with increasing surface roughness. On the other hand, in the case of BN film as thin as 8–10 nm, it is found that the turn-on electric field is reduced to 8.3 V/μm in spite of the surface of the BN nanofilm being flat, as well as the Si substrate. The Fowler–Nordheim (FN) plot of the field-emission characteristics of the BN nanofilm indicates a straight line, suggesting the presence of FN tunneling. This finding means that introduction of the BN nanofilm leads to a significant reduction in the effective potential barrier height.
1064 nm laser emission of highly doped Nd: Yttrium aluminum garnet under 885 nm diode laser pumping
Authors: Lupei V. , Pavel N. , Taira T.
Published: July 2002

Highly efficient 1064 nm continuous-wave laser emission under 885 nm diode pumping in concentrated Nd: Yttrium aluminum garnet (YAG) crystals (up to 3.5 at. % Nd) and ceramics (up to 3.8 at. % Nd) is reported. A highly doped (2.4 at. %) Nd:YAG laser, passively Q switched by a Cr4+:YAG saturable absorber, is demonstrated.
On the role of interface states in low-voltage leakage currents of metal–oxide–semiconductor structures
Authors: Crupi F. , Ciofi C. , Germanò A. , Iannaccone G. , Stathis J. H. , Lombardo S.
Published: July 2002

This work investigates the additional gate current component with respect to the direct tunneling of electrons between the conduction bands measured in ultrathin oxide metal–oxide–semiconductor field-effect transistors at low voltages, before and after the application of a high field stress. We discuss several possible conduction mechanisms on the basis of the band diagram profiles obtained by means of a one-dimensional self-consistent Poisson–Schrodinger solver and we explain why this additional leakage current is mainly due to electron tunneling involving the native and stress-induced interface states in the silicon band gap either at the cathode or at the anode.
Phase integral theory, coupled wave equations, and mode conversion
Authors: Littlejohn Robert G. , Flynn William G.
Published: July 2002

Phase integral or WKB theory is applied to multicomponent wave equations, i.e., wave equations in which the wave field is a vector, spinor, or tensor of some kind. Specific examples of physical interest often have special features that simplify their analysis, when compared with the general theory. The case of coupled channel equations in atomic or molecular scattering theory in the Born–Oppenheimer approximation is examined in this context. The problem of mode conversion, also called surface jumping or Landau–Zener–Stückelberg transitions, is examined in the multidimensional case, and cast into normal form. The group theoretical principles of the normal form transformation are laid out, and shown to involve both the Lorentz group and the symplectic group.
Transitions and statistical characteristics of vibrations in a bimodular oscillator
Authors: Ostrovsky L. A. , Starobinets I. M.
Published: July 2002

Regular and stochastic oscillations in a simple periodically forced vibroacoustic system with a piecewise-linear (bimodular) elasticity are considered from the viewpoint of their statistical properties: oscillation spectra, the largest Lyapunov exponents, and fractal dimension. It is shown that a strange attractor exists in a limited range of parameters together with a triple-period dynamic cycle being absorbed by the latter at some finite value of the parameter. The corresponding bifurcation process is followed in detail.
An instability of the red blood cell shape
Authors: Peterson Mark A.
Published: July 2002

The infinitesimal stability of fluid vesicle shapes is studied as a function of vesicle volume and spontaneous membrane curvature at fixed area. It is found that the azimuthally symmetric shapes are infinitesimally unstable for some values of these parameters. A possible connection with the sickling of red blood cells is pointed out.
Magnetic domains in sintered Fe-Nd-B magnets
Authors: Livingston J. D.
Published: July 2002

Magnetic domain structures in sintered Fe-Nd-B magnets from several suppliers were studied using the polar Kerr effect. Most grains were multidomain in the thermally demagnetized state. Measurement of average surface domain width in several large grains yielded a domain-wall energy of 25 ergs/cm2 for the Fe14Nd2B primary phase. After saturation and subsequent demagnetization in reverse field, most grains were again multidomain. Consistent with this observation, thermal remagnetization was small. A Fe-Nd-B-based magnet with much higher coercivity showed a much higher percentage of single-domain grains in the field-demagnetized state and a much higher thermal remagnetization, i.e., a behavior more nearly similar to earlier results on sintered Co5Sm magnets.
Dispersion of localized elastic modes in thin supported gold layers measured by Brillouin scattering
Authors: Hillebrands B. , Baumgart P. , Mock R. , Güntherodt G. , Bechthold P. S.
Published: July 2002

The dispersion of higher-order localized elastic modes of gold layers on glass has been measured by Brillouin scattering. For layer thicknesses h≥100 Å the dispersion of the sound velocities is well described by elastic continuum theory, whereas for h<100 Å deviations occur due to island formation. The results yield a reliable, nondestructive method to determine either elastic constants and mass density or the thickness of thin supported metal layers.
Semimetallic Hall properties of PbTe-SnTe superlattice
Authors: Ishida A. , Aoki M. , Fujiyasu H.
Published: July 2002

The PbTe-SnTe superlattice was expected to be a type-II superlattice where the valence band edge of SnTe is higher than the conduction band edge of PbTe. To ascertain the type-II structure, we prepared the PbTe-SnTe superlattice by hot wall epitaxy, and performed its Hall measurement. Magnetic-field-dependent and relatively small Hall coefficients were obtained for the superlattices, which show coexistence of free electrons and holes in the superlattice. Hall coefficients of the superlattices increased with annealing time owing to the gradual disappearance of the coexistence. Diffusion of Sn was studied using x-ray diffraction analysis.
Characterization and entrainment of subboundaries and defect trails in zone-melting-recrystallized Si films
Authors: Geis M. W. , Smith Henry I. , Chen C. K.
Published: July 2002

We have studied the morphology and crystallographic angular discontinuities of subboundaries and defect trails in zone-melting-recrystallized Si films. These subboundaries and defect trails, which originate at the interior corners of the faceted solidification front, are classified into seven types. Evidence is presented that in-plane stress due to temperature gradients plays a major role in causing such defects. Various schemes for entraining subboundaries and defect trails are described.
Electrical characterization of Schottky contacts of Au, Al, Gd, and Pt on n-type and p-type GaAs
Authors: Okumura T. , Tu K. N.
Published: July 2002

The Schottky barrier heights of several metals (Au,Al,Gd, and Pt) fabricated by electron-beam deposition on n- and p-type GaAs were measured with I-V, C-V,and photoresponse techniques. In the as-deposited state, all metals gave very similar I-V characteristics for n-type substrates with a barrier height qφb=0.63−0.65 eV and ideality factor n=1.20-1.45. The poor I-V characteristics in the as-deposited state were consistent with the higher barrier height determined with the C-V characteristics. Moderate annealing at 350 °C for 30 min improved the I-V characteristics of all of them (qφb≂0.74 eV), as well as the photoyield in the internal photoemission process except the Au diode. No variation of the photothreshold energy was observed for n-type GaAs among the annealed contacts, suggesting that the Fermi-level is pinned by the native defects of GaAs. The barrier height was determined to be 0.90 eV for n-type GaAs. On p-type GaAs, the photothreshold energy varied and the barrier heights for Al,Gd,Au, and Pt were determined to be 0.89, 0.81, 0.70, and ohmic, respectively. The sum of the barrier heights for n and p type was therefore not equal to the band gap of GaAs. This implies that the pinning levels for n- and p-type surfaces are different. While there is pinning on a n-type surface, there is no pinning level for a p-type surface, so the barrier height on a p-type surface is dependent on the metal in contact.
A 57Fe Mössbauer study of Nd2(Fe1−xCox)14B
Authors: Deppe P. , Rosenberg M. , Hirosawa S. , Sagawa M.
Published: July 2002

A Mössbauer study of the compositional series Nd2(Fe1−xCox)14B confirmed the preferential occupation of j2 sites by the Fe atoms at least for x>0.6 and the strong dependence on x of the relative amount of Fe distributed on this type of site. The j2-site preference of Fe also influences the hyperfine field of Fe at the j2 site as a consequence of the higher concentration of Co around the j2 sites as compared to that of a statistical distribution.
Properties of Fe-Al-Si-N thin films prepared by N2 reactive sputtering
Authors: Kumura T. , Yamauchi K. , Kobayashi T.
Published: July 2002

We have attempted to prepare Fe-Al-Si-N films by rf magnetron sputtering in an atmosphere of Ar+N2, employing an Fe-Al-Si target, and investigated the influence of nitrogen on the properties of sendust alloys. Some properties, such as Vicker’s hardness and electrical resistivity of the films, were improved in the presence of nitrogen. In addition, the Fe-Al-Si-N films interestingly show superior magnetic properties to those of sendust films. For example, effective permeability at 1 MHz of the film, prepared under the selected conditions, reached a maximum of approximately 4000, exceeding 2200 of our standard sendust film. The microstructure of Fe-Al-Si-N and Fe-Al-Si films has been observed using scanning electron microscopy. As a result, we have found a difference in microstructure between the nitrogen-containing films and the regular films.
Impurity diffusion and layer interdiffusion in AlxGa1−xAs-GaAs heterostructures
Authors: Deppe D. G. , Holonyak N. , Plano W. E. , Robbins V. M. , Dallesasse J. M. , Hsieh K. C. , Baker J. E.
Published: July 2002

Data are presented and a model describing the diffusion of the donor Si in GaAs from grown-in dopant sources. In addition, the effects of background impurities on Si diffusion and layer interdiffusion in AlxGa1−xAs-GaAs superlattices are described. These results are obtained on epitaxial GaAs samples with alternating doped and undoped layers and on AlxGa1−xAs-GaAs superlattices with doped (Si or Mg) layers. The layer-doped GaAs and the AlxGa1−xAs-GaAs superlattices have been grown using metalorganic chemical vapor deposition and are characterized using secondary ion mass spectroscopy and transmission electron microscopy. Different annealing conditions are used to study the interaction between the grown-in impurities and the native defects of the crystal controlling the diffusion processes. The model describing the impurity diffusion and layer (Al-Ga) interdiffusion is based on the behavior of column III vacancies, VIII, and column III interstitials, IIII, and the control of their concentration by the position of the crystal Fermi level and the crystal stoichiometry. Experimental data show that n-type AlxGa1−xAs-GaAs superlattices undergo enhanced layer interdiffusion because of increased solubility of the VIII defect, while enhanced layer interdiffusion in p-type superlattices is caused by an enhanced solubility of IIII. The model employed is consistent with the experimental data and with the data of previous work.
Plasma-enhanced chemical vapor deposition of i
n s
i
t
u doped epitaxial silicon at low temperatures. II. Boron doping
Authors: Comfort James H. , Reif Rafael
Published: July 2002

A comparison of in situ boron doping of epitaxial silicon films deposited from 700 to 800 °C by both very-low-pressure chemical vapor deposition (VLPCVD) and plasma-enhanced chemical vapor deposition (PECVD) is presented. Neither the growth rate nor the morphology of films deposited by silane VLPCVD or PECVD are affected by the addition of up to 500 ppm diborane at a total pressure of 6 mTorr. VLPCVD and PECVD boron incorporation depends linearly on diborane partial pressures, and films doped to 1020 B atoms/cm3 have been prepared. VLPCVD boron incorporation is found to increase with increasing temperature. No significant increase in boron incorporation is observed with increasing power for PECVD. Surface decomposition of diborane under low surface coverage conditions is proposed as the rate-controlling step for boron incorporation during doped epitaxial growth at low temperatures. Doping profiles with uniform concentrations in the range 1016–1020 B atoms/cm3 are readily achieved at low temperatures by VLPCVD from diborane-silane mixtures without the need for plasma enhancement.
Concerning lattice defects and defect levels in CuInSe2 and the I-III-VI2 compounds
Authors: Massé G.
Published: July 2002

This paper relates different points concerning defect levels and lattice defects in CuInSe2 and the I-III-VI2 compounds. First, we review the main levels observed. Second, we propose a hypothesis concerning the electrical compensation processes acting in the I-III-VI2 materials. Third, we discuss the nature of the defects responsible for the levels, and improve interpretations, by carrying out the deformation potential in antisite defects. Especially, these calculations reinforce the idea that the ‘‘hydrogenic-type’’ acceptor observed in the I-III-VI2 materials must rather be attributed to the Cu or Ag vacancy than to an antisite defect.
Study on mechanism of selective chemical vapor deposition of tungsten using in situ infrared spectroscopy and Auger electron spectroscopy
Authors: Kobayashi Nobuyoshi , Goto Hidekazu , Suzuki Masayuki
Published: July 2002

Selective chemical vapor deposition (CVD) of tungsten (W) using tungsten hexafluoride (WF6) and monosilane (SiH4) is investigated by in situ infrared spectroscopy and Auger electron spectroscopy. The infrared spectra show that trifluorosilane (SiHF3) is the main by-product species, and that silicon-tetrafluoride (SiF4) is less than 20%–25% of SiHF3 in partial pressure. The main chemical reaction involved in selective W CVD can be expressed as WF6+2SiH4→W+2SiHF3+3H2. Based on our experimental results, a new mechanism of selective W CVD, which notes hydrogen dissociation having a central role in this process, is proposed. It disproves the widely accepted model, which is based on the assumption that SiF4 is the major reaction product.
Ultrasonic imaging system using a leaky surface acoustic wave transducer composed of piezoelectric ceramic and fused quartz
Authors: Toda Kohji , Sawaguchi Akihiro
Published: July 2002

An ultrasonic imaging system is described by using a leaky surface acoustic wave (SAW) transducer composed of a piezoelectric ceramic thin plate/interdigital transducer/fused quartz. It is shown, both numerically and experimentally, that three operation modes of the transducer at a water-solid interface are available. Each of the three modes has a different operation frequency range, corresponding to the leaky SAW velocity. The bulk wave in water as an acoustical coupler between the transducer and a tested object has a frequency-dependent angle relation; therefore, the acoustic beam steering is easily controlled and flexible in design. The reflection type of C-mode ultrasonic imaging results are demonstrated and are promising for nondestructive testing.
Magnetic properties of Sm2Fe17Cx compounds
Authors: Wang Y. Z. , Hadjipanayis G. C.
Published: July 2002

A systematic investigation of the magnetic and structural properties of as-cast Sm2Fe17Cx compounds with 0≤x≤1.5 has been made with x-ray diffraction, thermomagnetic analysis, and superconducting quantum interference device magnetometry. Crystal structure studies have shown that the ternary carbides form a rhombohedral Th2Zn17-type structure. The lattice constants at room temperature increase with x, indicating that carbon substitutes interstitially. The Curie temperature increases strongly with x from TC = 130 °C for x=0 to 247 °C for x=1.5. The introduction of interstitial carbon atoms into the 2:17 structure leads to a dramatic change in the magnetic anisotropy of Sm2Fe17Cx compounds. The value of K1 increases with increasing x, and a transition from an ‘‘easy-plane’’ to an ‘‘easy-axis’’ anisotropy takes place.
Characterization of silica glasses sintered under Cl2 ambients
Authors: Awazu Koichi , Kawazoe Hiroshi , Muta Ken-ichi , Ibuki Toshio , Tabayashi Kiyohiko , Shobatake Kosuke
Published: July 2002

Chlorine incorporated into silica glasses by sintering porous soot rods under Cl2/He atmosphere or by fabricating with plasma methods were found to be mostly as ≡SiCl, which gives rise to an optical absorption tail above ≂7.5 eV. The cross section of the optical absorption at ≂7.77 eV (160 nm) was found to be 1.14×1020 cm2. This value was almost the same as that of ≡SiCl in SiCl4 molecule in the gas phase. A minor fraction (10−3∼10−1) was found to be present as Cl2 molecule, which gives the absorption band at 3.8 eV.
Enhanced surface sum frequency generation from LB layer covered silver film
Authors: Chen Zhan , Zhang Zhiming
Published: July 2002

We report an experimental study of enhanced optical sum frequency generation (SFG) due to the prism excitation of surface plasmons from a silver film covered with monomolecular layers of arachidic acid. The enhanced transmitted SFG was measured, as two counter-propagating surface plasmon waves were excited by the 1.064 μm output of a pulsed Nd:YAG laser and 6448 Å light from a Nd:YAG laser pumped dye laser. This signal was calculated by using Green’s function considering the adsorbates and the surface currents of the silver. The ratio of measured SFG to the product of the incident light showed good agreement with the calculation. By comparing the experimental curve of one layer of the arachidic acid covered silver sample to that of the bare silver sample, the nonlinear polarizability coefficient for a single arachidic molecule is evaluated.
Application of the transfer function method in calculations of the directivity pattern of ultrasonic transducer
Authors: Kielczynski P. , Pajewski W.
Published: July 2002

In this paper the authors applied an original transfer function method for calculations of radiation patterns in the case of Bessel circular transducers. It is known that the amplitudes of some natural vibration modes of circular plates are Bessel functions of zero order [R. R. Aggarval, JASA 24, 463 (1952)]. In the paper the natural vibrational modes of a circular disk-shaped ultrasonic transducer were employed. As it follows from the numerical calculations, it is possible to obtain for Bessel-like transducers the nondiffracting main lobe. The latter is in accordance with the suggestions of the paper [J. Durnin, J. Opt. Soc. Am. 4, 651 (1987)].
Low-temperature anisotropy of the Faraday rotation in the samarium iron garnet
Authors: Guillot M. , Le Gall H. , Desvignes J. M. , Artinian M.
Published: July 2002

Faraday rotation (FR) measurements performed on single crystals of samarium iron garnet (SmIG) at 1.15-μ wavelength in a magnetic field up to 20 kOe applied along the 〈210〉 cubic direction in the 6–77-K temperature range are reported. Abrupt changes of both spontaneous FR and FR susceptibility are evidenced at 20 and 60 K, temperatures which correspond to the three spin-reorientation transitions 〈210〉■〈110〉■〈111〉; the results are compared to the FR data previously obtained for the 〈111〉 direction.
Excitation mechanisms of oxygen atoms in a low pressure O2 radio-frequency plasma
Authors: Collart E. J. H. , Baggerman J. A. G. , Visser R. J.
Published: July 2002

Using a low-pressure reactive ion etching reactor in a pulsed radio-frequency (rf) power mode the rise time of the plasma induced emission of O at 777 and 844 nm was monitored on a ms time scale. With a two-photon excitation scheme the rise time of the oxygen atom ground state concentration was followed by measuring the laser induced fluorescence (LIF) at 844 nm. An absolute density measurement was performed by comparing the LIF signal in the reactor to the LIF signal of a known concentration of O in a microwave discharge. Using these time resolved measurements the reliability of optical emission actinometry in low pressure O2 rf plasmas for a determination of relative atomic oxygen densities was examined. By comparing the rise times with the ignition time of the plasma it is concluded that both emission lines are caused by dissociative excitation. The consequences for the applicability of actinometry will be discussed. A comparison of experimental emission intensities to calculated ones suggests that highly energetic (e.g., secondary) electrons are responsible for the dissociative excitation of O2.
Thermal and electrical properties of the novel organic nonlinear crystal L-arginine phosphate monohydrate
Authors: Dhanaraj G. , Srinivasan M. R. , Bhat H. L. , Jayanna H. S. , Subramanyam S. V.
Published: July 2002

The thermal expansion, specific heat, dielectric constant, and resistivity of the novel organic nonlinear crystal, L-arginine phosphate monohydrate have been measured as a function of temperature. The thermal expansion is highly anisotropic and has been interpreted on the basis of crystal structure. The dielectric constant and resistivity exhibit a temperature dependence that is similar to that of an ionic crystal. No anomalies are observed in these physical properties from the liquid nitrogen temperature up to its melting point.
Interaction of a dislocation with an elliptic hole or rigid inclusion in an anisotropic material
Authors: Wu Kuang-Chong
Published: July 2002

Two-dimensional problem of a dislocation interacting with an elliptic hole or rigid inclusion in an anisotropic medium is considered. Closed-form solutions of the displacements and stresses are obtained. Explicit expressions for the interaction energy are given. For dislocations very near to the elliptic boundary, it is shown that the level curve of the interaction energy is geometrically similar to the elliptic boundary regardless of the types of the dislocations. For dislocations very far from the elliptic boundary, real-form expressions for interaction energy are obtained. The degenerate case of a crack or a rigid line inclusion is also discussed.
Threshold oscillation of an NF(a1Δ)/BiF visible wavelength chemical laser
Authors: Benard D. J.
Published: July 2002

A novel shock tube reactor was used to pulse heat a gaseous mixture of He, FN3, and Bi(CH3)3 along a 40 cm optical path between two highly reflective mirrors. Production of NF(a1Δ) by dissociation of the azide was found to occur in a ‘‘delayed avalanche’’ approximately 50 μs after shock reflection, and weak lasing at 470 nm was observed that is assignable to electronic transitions in the BiF(A–X, Δv=3) band.
Intra-4f-shell transitions at room temperature of Er3+ ions in Ca1−xErxF2+x thin films grown on Si(100)
Authors: Barrière A. S. , Raoux S. , Garcia A. , L’Haridon H. , Lambert B. , Moutonnet D.
Published: July 2002

Intra-4f-shell transitions of Er3+ ions in Ca1−xErxF2+x thin films were studied by means of photoluminescence (PL) and cathodoluminescence (CL) measurements at room temperature. The samples, with x varying from 0.01 to 0.2, were epitaxially grown on Si(100) substrates by sublimation of solid solution powders. Using the 488-nm line of an Ar+-ion laser as the excitation source, it is shown that the films present strong PL lines corresponding to the internal transitions between the 4S3/2,4F9/2,4I11/2, and 4I13/2 excited levels and the 4I15/2 fundamental state of Er3+ (4f11) ions. Their centers of gravity were pointed out at λ=533, 650, 980, and 1530 nm, respectively. These electronic transitions were also evidenced by means of the CL technique. Moreover, this technique showed that the luminescence is uniform in all points of the layers. The PL intensities vary considerably as a function of the erbium substitution rate. In the visible range the strongest luminescence was found for x less than 0.01, while for the 1530-nm line (which presents evident potential applications for optical communications) the highest luminescence intensity corresponds to x close to 0.16. The refractive index (n) of the layers also varies with the erbium concentration. For a 1.3-μm incident radiation, n continuously increases from 1.425 to 1.466 when x varies from 0.035 to 0.19. This result shows that these structures can lead to the realization of plane optical waveguides.
Surface acoustic wave properties of ZnO films on {001}-cut 〈110〉-propagating GaAs substrates
Authors: Kim Yoonkee , Hunt William D. , Hickernell Frederick S. , Higgins Robert J.
Published: July 2002

GaAs has been employed as a material for acoustic charge transport (ACT) devices principally because it is a piezoelectric semiconductor. However, because GaAs is a weakly piezoelectric material, the surface acoustic wave (SAW) interdigital transducer (IDT) drive power required to achieve charge transport is typically about 27 dBm. An enhancement of the piezoelectric coupling could potentially improve device lifetime, reliability, dynamic range, and decrease device power consumption. To this end the use of a ZnO film on top of an ACT-like substrate to enhance the piezoelectric coupling has been investigated. Moreover, the ZnO film structure would also make it possible to monolithically integrate SAW devices and GaAs electronics. In order to provide a basis for the design of such devices, SAW properties are reported, including velocity, effective piezoelectric coupling constant, and attenuation, measured on ZnO films sputtered on {001}-cut 〈110〉-propagating GaAs substrates. The measurements have been performed for the different film thicknesses over the range of 1.6–4 μm and with films of different grain sizes. IDTs operating between 180 and 360 MHz were fabricated, and a knife-edge laser probe was used to measure the SAW propagation. The measured data for the velocity shows good agreement with theoretical values. The quality of the dc triode-sputtered films was superior to that of the rf magnetron-sputtered ones due to higher K2 and less attenuation. The value of K2 for the 1.6-μm-thick dc triode-sputtered one was measured to be 0.75% which is comparable with 1.07% for bulk crystalline ZnO.
Fracture of metal-polymer line structures. II. Rigid-rodlike polyimide
Authors: Leu J. , Ho P. S. , Chiu S. L.
Published: July 2002

The fracture behavior of the Au/Cr line structures formed on a rigid-rodlike polyimide, biphenylenetetracarboxylic dianhydride-phenylenediamine (BPDA-PDA), film substrate has been investigated using a stretch deformation technique and compared with that of the Au/Cr line structures formed on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline. In general, the effects of metal line dimensions on the deformation behavior can be attributed to the changes in the mechanical environment induced by metal confinement at the line interface. This gives rise to a fracture behavior and geometrical dependence of these two polyimide structures which are qualitatively similar in most aspects. However, the fracture energy and crack propagation rate of these two polyimide line structures are quantitatively different, with values about twice higher for the BPDA-PDA line structures. This cannot be accounted for solely by the different chemical bonding; instead, the high fracture toughness of the BPDA-PDA structure has to be attributed to its superior mechanical properties, particularly its plastic deformation characteristics, which are related to its molecular structure.
Thermogalvanomagnetic properties of Sn-doped Bi95Sb5 and its application for solid state cooling
Authors: Jandl P. , Birkholz U.
Published: July 2002

Measurements of the complete set of thermogalvanomagnetic coefficients of Sn-doped Bi95Sb5 have been carried out from liquid nitrogen up to room temperature as a function of magnetic field strength and crystallographic direction (parallel and perpendicular to the trigonal axes). The dependences of the transport coefficients on temperature, magnetic field strength, and impurity density as well as their complex mutual correlations are explained, qualitatively. These investigations were performed in order to establish the optimum tin concentration that will maximize the thermomagnetic and thermoelectric figures of merit at a given temperature and magnetic field. As calculated theoretically a 2.5-fold enhancement of the thermomagnetic figure of merit was achieved. The crystals were grown by the horizontal zone-leveling technique under a hydrogen atmosphere. To achieve high homogeneity and to avoid constitutional supercooling a traveling double-ellipsoid mirror furnace was built up. This method enables us to produce a small liquid zone and a steep temperature gradient at the solid–liquid interface.
Characteristics of Sm2Fe17Cx compounds prepared from ball-milled blends of Sm2Fe17 and graphite
Authors: Mao O. , Ström-Olsen J. O. , Altounian Z. , Yang J.
Published: July 2002

A series of Sm2Fe17Cx (x=0–6, nominal) interstitial compounds were synthesized by blending Sm2Fe17 and graphite in a ball mill followed by annealing of the sample powders at 450 °C for 10 h. X-ray structural analyses show that the lattice constants and the unit cell volume, v, of the carbides increases with x almost linearly up to x=2.5 and become constant above x=3.0. The Curie temperature, Tc, linearly increases with x up to x=1.7 and saturates for x≳2.0. The saturation values of lattice expansion, Δv/v, and Tc are 6.1% and 403 °C, respectively. Sm2Fe17Cx powders synthesized with this technique are highly anisotropic. Coercivities for powders with x≳2.2 are 0.8 T at room temperature. A coercivity of 1.6 T has been achieved in such powders after nitriding.
Resistivity and LIII-edge absorption studies in valence fluctuation system Ce2Ni3Si5
Authors: Mazumdar Chandan , Nagarajan R. , Godart C. , Gupta L. C. , Padalia B. D. , Vijayaraghavan R.
Published: July 2002

From our x-ray (LIII-edge) absorption (XAS) investigations of Ce2Ni3Si5, we show that Ce-valence is temperature dependent; it is 3.07 and 3.11 at 280 and 8 K, respectively. We also report on our resistivity measurements of two related materials Ce2−xRxNi3Si5 (R=Y, Gd and x=0.1). Absence of any qualitative difference in the resistivities of these two samples suggests that the enhancement of resistivity at low temperature on introduction of impurity atoms is due to Kondo hole scattering implying that Ce2Ni3Si5 is a concentrated Kondo system.
Electronic structure of second harmonic generation crystal Li3VO4
Authors: Sakata S. , Nagoshi Y. , Nii H. , Ueda N. , Kawazoe H.
Published: July 2002

The origin of second harmonic generation (SHG) of Li3VO4 was investigated from the viewpoint of the band structure by using the tight-binding method. The tight-binding parameters were optimized to reproduce the density of states (DOS) obtained from x ray photoelectron spectroscopy and the optical band gap. Although Li3PO4 has the same crystal structure as Li3VO4, it shows no SHG. To explain the difference in optical nonlinearity we compared the electronic structures of Li3VO4 and Li3PO4, in particular at the bottom of conduction band (CB) and the top of valence band (VB), since they are known to play a primary role in SHG. In Li3PO4, the bottom of CB consists of P 3s and O 2p orbitals and the top of VB is composed of O 2p orbitals. These electronic structures result in a relatively low DOS at the bottom of CB and a wide band gap in Li3PO4. On the other hand, in Li3VO4, both bottom of CB and top of VB are composed of V 3d and O 2p. The preferential contribution of V 3d orbitals to the band edge states leads to a high DOS at the bottom of CB, a narrow band gap and delocalization of electrons on V–O bonds. We conclude that these electronic structures are responsible for the high optical-nonlinearity of Li3VO4.