bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Ga ion implantation damage and annealing effect in Sn-doped InP using Raman scattering
Authors: Yu Soon Jae , Asahi Hajime , Emura Shuichi , Sumida Hitoshi , Gonda Shun-ichi , Tanoue Hisao
Published: July 2002

The damage of Sn-doped InP by Ga ion implantation with fluences ranging from 1×1013 to 5×1014 cm−2 and annealing effects (150–650 °C) are investigated by means of Raman scattering. The shift and asymmetrical broadening of a longitudinal optical phonon peak and the appearance of transverse optical mode and disorder-activated acoustic modes show that the damage effect by Ga ion implantation is very large, and the crystalline structure becomes amorphouslike at a fluence as low as 1×1014 cm−2. The damaged state is investigated in terms of the spatial correlation model and quantitatively estimated by comparing the Raman peaks for longitudinal optical and transverse acoustic phonon modes with the theoretical calculations. It is shown that the correlation lengths at 1×1013 cm−2 are 36 and 29 Å, respectively. This largely damaged structure is found to be recovered by annealing at as low as 250 °C.
‘‘Critical thickness’’ of amorphous phase formation in binary diffusion couples
Authors: Gösele U. , Tu K. N.
Published: July 2002

In thin-film diffusion couples the sequential growth of equilibrium intermetallic compound phases and the missing of certain of them shown in the equilibrium phase diagram are well-known phenomena. It has been proposed that the first growing equilibrium phase has to exceed a critical thickness before a second equilibrium phase can start to grow. We investigate whether this concept can also be applied to the first growing phase which is a metastable amorphous alloy. We consider two different cases depending on the specific form of Gibbs’ free energy-versus-composition diagrams. In the first case an analogous concept can be applied and the amorphous phase continues to grow after reaching its critical thickness. In the second case the amorphous phase starts to shrink after it has reached its critical thickness. For calculating the critical thickness in the second case a new procedure is suggested which is based on the maximum rate of decrease in Gibbs’ free energy.
Magnetotransport study of Fe-Cr-Fe sandwiches grown on ZnSe(100)
Authors: Chaiken A. , Prinz G. A. , Krebs J. J.
Published: July 2002

Magnetoresistance measurements have been performed on a set of molecular-beam epitaxy-grown Fe-Cr-Fe sandwiches with different chromium thicknesses, 12 Å<tCr<28 Å. For 13 Å<tCr<24 Å, magnetization measurements show that the Fe moments are antialigned at zero field. For samples exhibiting zero-field antialignment, negative magnetoresistance steps are observed at applied fields where discontinuities occur in the magnetization curve. The size of the magnetoresistance steps increases with increasing antiferromagnetic coupling between the Fe layers. The magnetoresistance [ρ(H)−ρ(0)]/ρ(0) is approximately proportional to cos2(Δφ/2), where Δφ≡(φ1−φ2), and φ1(H) and φ2(H) are the angles that the individual moments of the two Fe films make with the in-plane easy 〈100〉 axis.
Polish-induced damage in 〈100〉 GaAs: A comparison of transmission electron microscopy and Raman spectroscopy
Authors: George T. , Weber Z. L. , Weber E. R. , Pollak Fred H.
Published: July 2002

This communication presents a comparative study of polish-induced effects in 〈100〉 GaAs by Raman spectroscopy (strain) and cross-sectional transmission electron microscopy (dislocation density). It is found that the depth and polish-time dependence of both the strain and dislocation density obey the same relationship. However, the skin depth evaluated by Raman scattering is a factor of 10 smaller than that determined from transmission electron microscopy.
Organometallic chemical vapor deposition of strontium titanate
Authors: Feil W. A. , Wessels B. W. , Tonge L. M. , Marks T. J.
Published: July 2002

SrTiO3 thin films were deposited by low-pressure organometallic chemical vapor deposition. Titanium isopropoxide, Sr(dipivaloylmethanate)2, oxygen, and water vapor were used as reactants, and argon was used as a carrier gas. Growth rates ranging from 0.3 to 4.5 μm/h were obtained on (0001) sapphire substrates at 600–850 °C. Highly textured SrTiO3 films with a [111] orientation were obtained at a growth temperature of 800 °C. The growth parameters which influenced the composition, phase stability, morphology, and texture of the thin films were examined.
The effective microwave surface impedance of high T
c thin films
Authors: Klein N. , Chaloupka H. , Müller G. , Orbach S. , Piel H. , Roas B. , Schultz L. , Klein U. , Peiniger M.
Published: July 2002

The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films, Reff (77 K) values of 21 mΩ and RS (77 K) values of 8 mΩ were achieved. The temperature dependence of λ was found to be in good agreement to both weak-coupling BCS theory in the clean limit and the empirical two-fluid model relation with λ (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.
Dislocation energy bands in GaAs: An optical absorption study
Authors: Vignaud D. , Farvacque J. L.
Published: July 2002

Numerical expressions of the piezoelectric and deformation electric fields associated with dislocations in zinc-blende semiconductors are presented. They are used to calculate the optical absorption which they induce. These results are compared with the previously calculated charged-line field absorption. For GaAs, we find that the latter one is prevailing and that the deformation electric field can be always neglected. Application of this model to experimental results in GaAs lead us to propose a two dislocation energy band scheme. One dislocation energy band D1 is located above the valence band and the other D2 is near midgap.
Effects of indium and tin overlayers on the photoluminescence spectrum of mercuric iodide
Authors: James R. B. , Bao X. J. , Schlesinger T. E. , Ortale C. , Cheng A. Y.
Published: July 2002

Mercuric iodide (HgI2 ) crystals with semitransparent metal overlayers of indium and tin were characterized using low-temperature photoluminescence (PL) spectroscopy. The PL spectra were found to differ for points beneath the thin metal overlayers and points that were masked off during each deposition. The photoluminescence data were compared with PL measurements taken on HgI2 photodetectors with indium-tin-oxide (ITO) entrance electrodes. The similarities of the spectra for the HgI2 samples with In, Sn, and ITO conducting overlayers indicate that the regions in the ITO-contacted photodetectors with relatively poor photoresponses are associated with the interaction of indium or tin with the mercuric iodide substrate.
Electron-beam propagation through a magnetic wiggler with random field errors
Authors: Esarey E. , Tang C.-M. , Marable W.
Published: July 2002

The effects of random field errors on the propagation of a relativistic electron beam through a wiggler magnet are analyzed both theoretically and numerically. Both helical and planar wiggler configurations are studied, with and without the effects of transverse focusing forces. Theoretical expressions are derived for the random electron motion for (i) individual realizations of field errors and for (ii) ensembles of statistically identical wigglers. These results are then confirmed through three-dimensional particle simulations of electron-beam transport including the effects of finite emittance. In addition to producing a random walk of the beam centroid, the field errors lead to significant variations in the parallel beam energy. Asymptotically, the variance of the parallel beam energy scales as z1/2, where z is the axial propagation distance. Although transverse beam focusing reduces the asymptotic scaling of the rms centroid displacement from z3/2 to z1/2, transverse focusing is not effective in reducing the parallel energy variation (the variance of the parallel beam energy is only reduced by a factor of √2). Statistically, the variance of the parallel beam energy may be interpreted as an effective parallel energy spread due to field errors. In order to maintain the wave–particle resonance in small-signal free-electron lasers, it is desirable for this effective energy spread to be small compared to the intrinsic efficiency. As an example, in the low-gain regime (assuming a helical wiggler in the strong-wiggler limit), this requirement implies that the normalized rms field error must satisfy δB̂rms<1/(2πN3/2), where N is the number of wiggler periods.
Frequency dependence of the ferromagnetic resonance linewidth of barium ferrite
Authors: El Rayess M. , Sokoloff J. B. , Vittoria C. , Spurgeon W.
Published: July 2002

Ferromagnetic resonance was measured in both a swept frequency mode of operation, in which the magnetic field was fixed, and a field swept mode, using field modulation techniques. Single-crystal spheres of 0.381, 0.305, and 0.483 mm in diameter were inserted in the waveguide and transmission was observed in the measurement. The g values for all the spheres averaged to 2.052±0.011 and the uniaxial anisotropy field was 16.4 kOe.Our measurements show that the linewidth of barium ferrite is nearly independent of resonant frequency from 48 to 105 GHz. This is in disagreement with the Kasuya–LeCraw two-magnon–one-phonon mechanism, which would predict a linewidth linear with the resonant frequency. Previous measurements [J. Magn. Magn. Mater. 54-57, 1141 (1986); IEEE Trans. Magn. MAG-22, 984 (1986)], however, show a strong temperature dependence, which rules out magnon scattering from static defects as the primary contributor to the intrinsic linewidth. These results are consistent with a single scattering process in which the uniform precession magnon is scattered into the continuum of magnons by time-dependent fluctuations of the trigonal symmetry ion between two equilibrium sites on either side of the mirror plane [J. Appl. Phys. 63, 3350 (1988)]. This process differs from the usual two-magnon scattering in that the scattering mechanism is time dependent, and, therefore, the magnon frequency need not be conserved in the process.
Intense surface photoemission: Space charge effects and self-acceleration
Authors: Gilton Terry L. , Cowin James P. , Kubiak Glenn D. , Hamza Alex V.
Published: July 2002

Ultraviolet laser irradiation of surfaces, in the course of photoemission or surface photochemical studies, often produce copious electron emission, up to 1000’s of A/cm2. The time-dependent fields produced by these electrons accelerate some of the electrons up to 5.4 times their initial energies. The steady-state fields return most of the emitted electrons to the surface. We discuss and illustrate both phenomena with theoretical simulations and experiment, and discuss possible implications.
van der Waals epitaxial growth and characterization of MoSe2 thin films on SnS2
Authors: Ohuchi F. S. , Parkinson B. A. , Ueno K. , Koma A.
Published: July 2002

A variation on molecular beam epitaxy (MBE), called van der Waals epitaxy, is described where a material with primarily two-dimensional (2D) bonding is grown on a substrate which also has a 2D structure. Lattice matching difficulties, which limit the choice of materials in MBE of 3D systems, are circumvented since the interlayer bonding is from weak van der Waals interactions. The title system shows a lattice mismatch of 10% yet high quality epitaxial films can be grown. The films were characterized in situ with reflection high energy electron diffraction, Auger electron spectroscopy, and low energy electron loss spectroscopy. Additional characterization after exposure to ambient by x-ray photoelectron spectroscopy, low energy electron diffraction, transmission electron microscopy confirmed the highly ordered nature of the films. Scanning tunneling microscopy provided real space images of the morphology of the epitaxial layer and showed unusual structures attributed to lattice mismatch.
Vacancy formation and extraction energies in semiconductor compounds and alloys
Authors: Berding M. A. , Sher A. , Chen A.-B.
Published: July 2002

Extraction energies for diamond and zinc-blende semiconductor compounds and pseudobinary alloys are calculated using a tight-binding cluster method, where the final state of the removed atom is in a free-atom state. The extraction energies provide a convenient reference from which other final states of the removed atoms can be calculated. In the elemental and compound semiconductors, the convergence of the cluster calculation was verified using a Green’s function calculation with the same Hamiltonian. For the elemental semiconductors, vacancy (or Schottky defect) formation energies, in which the final state of the removed atom is on the surface, have been calculated. For pseudobinary alloys of the form A1−xBxC, we find extraction energies to be very sensitive to the local environment, exhibiting a nonlinear variation between the A- and B-rich local environments; the nonlinearity is especially pronounced for the removal of a C atom. Nonlinearities are found to arise primarily from the occupation of localized vacancy states. The impact that these alloy variations will have on measurable properties are discussed.
Polarized UV spectroscopy of conjugated liquid crystals
Authors: Wu Shin-Tson , Ramos Elena , Finkenzeller Ulrich
Published: July 2002

Polarized absorption spectra of 13 nematic liquid crystals (LCs) with various conjugations and structures were measured in the spectral range from 185 to 400 nm. These absorption bands represent all the π→π* electronic transitions of these LCs. Resonance wavelength, absorption coefficient, and dichroic ratio of each band were characterized. The contribution of each band to LC birefringence is briefly discussed. Some structural effects on the LC absorption are illustrated. These absorption spectra will also serve as valuable data bases for further theoretical calculations on the band structure of LC molecules.
Incorporation of defects during processing of mercuric iodide detectors
Authors: Bao X. J. , Schlesinger T. E. , James R. B. , Stulen R. H. , Ortale C. , Cheng A. Y.
Published: July 2002

The effects of chemical etching in KI solution, heating, and vacuum exposures of HgI2 were individually studied by low-temperature photoluminescence (PL) spectroscopy. Each of these processing steps is important in the manufacturing of mercuric iodide detectors and may be responsible for the incorporation of carrier traps both in the near-surface region and in the bulk. The results of etching experiments showed that the near-surface region has a different defect structure than the bulk, which appears to result from iodine deficiency. Bulk heating at 100 °C also modifies the defect structure of the crystal. Vacuum exposure has an effect similar to chemical etching, but it does not cause significant degradation of the stoichiometry for recently KI-etched specimens. These studies suggest that some features in the PL spectra of HgI2 are associated with stoichiometry of the specimens.
High-voltage millimeter-wave gyro-traveling-wave amplifier
Authors: Gold S. H. , Kirkpatrick D. A. , Fliflet A. W. , McCowan R. B. , Kinkead A. K. , Hardesty D. L. , Sucy M.
Published: July 2002

An intense-beam gyro-traveling-wave amplifier experiment has demonstrated an apparent growth rate of 2.2 dB/cm at 35 GHz, with total gain exceeding 30 dB, and an output power of ∼20 MW (±3 dB), corresponding to an efficiency of ∼11%.
Domain observation and magnetostriction in Tb0.3Dy0.7Fe2 twinned single crystals
Authors: Teter J. P. , Mahoney K. , Al-Jiboory M. , Lord D. G. , McMasters O. D.
Published: July 2002

The ternary alloy Tb0.3Dy0.7Fe2 (Terfenol-D) exhibits the largest known magnetostriction to anisotropy ratio near room temperature. To better determine the interaction between the elastic and magnetic properties of this material, a stoichiometric twinned single crystal was grown by a free-standing float-zone technique. Observations using Scanning electron microscopy and energy dispersive spectroscopy confirmed that the sample was free of the normally present rare-earth (RE) eutectic phase and simultaneously free of Widmanstatten precipitate (RE Fe3). A bar with (111) and (11̄0) faces perpendicular to the [112̄] growth direction was examined. Also, a [111̄] slab was cut from the boule. This slab was studied along the [111̄] and [11̄0] directions with prestress applied along the [111̄]. This is the first report of the effects of applying prestress and magnetic fields in a direction not collinear with the [112̄] growth direction. From magnetization (M) and magnetostriction (λ) measurements as a function of field, prestress, and temperature, we determined the hysteresis and saturation parameters. These measurements do not indicate the [11̄0] λ and M behaviors found previously for RE-rich Terfenol-D. Domain observations with differential phase contrast and x-ray topography have shown different orientations in the twin and parent sections of the [111̄] specimen. The observed structures can be interpreted as arising from domains with magnetization components normal to the surface. The domain observations on the (111) and (11̄0) bar faces and on the [111̄] slab correlate with each other with respect to orientations and domain interpretations.
Cross sections for the vibrational excitation of the H2 X 1Σ+g(v) levels generated by electron collisional excitation of the higher singlet states
Authors: Hiskes J. R.
Published: July 2002

The excitation cross sections, σ(v,v″), for an H2 molecule initially in any one of the 15 vibrational levels, v belonging to the ground electronic state and excited to a final vibrational level, v″ are evaluated for direct excitations via all members of the excited electronic singlet spectrum. Account is taken of predissociation, autoionization, and radiative decay of the excited electronic spectrum that leads to a final population distribution for the ground electronic state, X 1Σ+g(v″). For v=0, account is taken explicitly of transitions via the B, C, B′, and D electronic states in evaluating the cross sections. The additional contribution of excitations via all Rydberg states lying above the D state enhances these cross sections by approximately 10%. For v≳0, cross sections are evaluated taking explicit account of transitions through the B and C states; higher singlet excitations enhance these values by 25%. The choice of the reference total cross sections remains a subjective one, causing the values calculated here to have a possible uncertainty of +20%−30%. For excitations occurring within a hydrogen discharge, collisional excitation-ionization events among the intermediate singlet states will effectively quench the v, v″ excitation process for discharge densities in excess of the range 1015–1016 electrons/cm−3.
Observation of continuous D→X and B→X XeCl excimer fluorescence in a binary-gas microwave discharge
Authors: Hassal Scott B. , Ballik Edward A.
Published: July 2002

A method of exciting a gas discharge with 2.45-GHz microwave radiation has been developed. Using this method, truly continuous-wave discharges have been produced in mixtures of Xe and Cl2. Spectra were recorded over the range 200–320 nm. An examination of 308-nm fluorescence (B→X) as a function of gas ratios and total pressure has been completed. This has indicated that a Xe:Cl2 mixture in the ratio 40:60 at 40-Torr pressure is near optimum. In addition to the 308-nm XeCl transition, the 236-nm XeCl transition (D→X), and the 258-nm molecular chlorine transition were observed in all cases.
Use of voltage contrast to locate defects in patterned high-T
c films
Authors: Jenkins Keith A. , Oh Byungdu
Published: July 2002

Voltage contrast in a scanning electron microscope equipped with a liquid nitrogen temperature stage can be used for inspecting patterned lines of high-Tc films. The observation of voltage on lines of superconducting materials is helpful in rapidly locating material defects, or regions in which the critical current density is exceeded. Voltage can be induced either by forcing current through the lines or by the deposition of charge by the electron beam. Both methods make possible quick voltage observations on lines of a few microns or less.
Parametric constitutive equations for electroelastic crystals upon electrical or mechanical bias
Authors: Gafka Dariusz , Tani Junji
Published: July 2002

Based on general rotationally invariant nonlinear electroelastic equations (energy balance equation and Gibbs function expansion), a complete and deductive derivation of constitutive equations for an electroelastic media upon mechanical or electrical bias has been presented. Bilinear constitutive relations for large quantities have been given and linear, but parametric constitutive formulas for small-field variables have been derived in the reference or intermediate frame. Equations of motion and boundary conditions in the respective configurations, required to solve dynamical problems, are also reported shortly for completeness. Presented reformulation of constitutive equations may be useful in solving nonlinear problems of electromechanical interactions in crystals, for example in analyzing sensors of nonelectric quantities with electric output or modulators.
Transmission electron microscope characterization of cast and hot-worked R-Fe-B:Cu(R=Nd,Pr) permanent magnets
Authors: Fidler Josef , Bernardi Johannes
Published: July 2002

The hard magnetic properties of hot-worked R-Fe-B permanent magnets are improved by the addition of a minor amount of Cu (up to 2 at. %). Transmission electron microscope investigations show that the reason for the increase of the coercivity is the fact that Cu is mainly dissolved in the intergranular region separating the hard magnetic 2:14:1 grains. The results obtained are similar in Nd-Fe-B:Cu and Pr-Fe-B:Cu magnets. The intergranular region has been observed to consist of a eutectic consisting of two phases: the Nd-or Pr-rich phase and the orthorhombic NdCu- or PrCu-phase. This corresponds to the eutectic decomposition of the liquid intergranular phase during cooling. It is suggested that the decrease of the melting temperature of the intergranular phase leads to a better wetting behavior and separation of the hard magnetic grains, and therefore to an enhancement of the coercivity.
Dielectric properties of cement mortar as a function of water content
Authors: Berg A. , Niklasson G. A. , Brantervik K. , Hedberg B. , Nilsson L. O.
Published: July 2002

We have studied the dielectric properties of cement mortars, with water/cement ratios between 0.5 and 0.78, in the frequency range 10−3≤f≤107 Hz. The dielectric response can be modeled by an equivalent circuit incorporating electrode polarization and bulk conduction. The bulk dc conductance and the amplitude of a constant phase element describing the dispersive part of the bulk response display characteristic dependencies on the water content of the samples. The power-law exponent of the constant phase element is independent of water content and can be related to the fractal dimension of the pore surfaces.
Gas flow dynamics in laser ablation deposition
Authors: Kools J. C. S. , Baller T. S. , De Zwart S. T. , Dieleman J.
Published: July 2002

The gas flow dynamics of laser ablation plumes is investigated experimentally and theoretically. Experimentally, angular-resolved time-of-flight (ARTOF) measurements are performed on a model system (laser etching of copper in a chlorine environment). The TOF spectra obtained can be fitted by elliptical Maxwell–Boltzmann distributions on a stream velocity. Theoretically, an analytical model is constructed, based on the hydrodynamical problem of an expanding elliptical gas cloud. The model allows semiquantitative prediction of ARTOF distributions and angular intensity distributions. Observed trends in laser ablation deposition such as independence of the angular intensity distribution on mass of the atom and laser fluence, and dependence of the angular distribution on spot dimensions are explained.
Origin of n-type conduction at the interface between epitaxial-grown layer and InP substrate and its suppression by heating in phosphine atmosphere
Authors: Ishikawa Hideto , Miwa Shiro , Maruyama Toshiyuki , Kamada Mikio
Published: July 2002

The origin of unintentionally introduced n-type conduction at the interface of epitaxially grown layer-InP substrate is identified. From the relation between the sheet carrier concentration and the etching depth, an n-type conducting layer was found at the epitaxial layer-substrate interface. The sheet carrier concentration and the sheet Si concentration at the surface of the InP substrate, which was obtained by secondary ion mass spectrometry analysis, agreed well. As a result, we determined that the Si atoms caused n-type conduction. To make clear that origin of the Si atoms, the following possibilities were investigated. One possibility was the vessel made from silicon dioxide (SiO2), which was used for etching the substrates, but it was determined not to be the cause because no significant difference was observed between a teflon or polypropylene vessel. To investigate the contamination from the air, we used metalorganic chemical vapor deposition to prepare a sample composed of a InP capping layer regrown on another InP layer after exposure to air. Because the Si atom sheet concentration was proportional to the time of exposure to ambient air, we conclude that the Si atoms come from air and are adsorbed on the InP substrate. We also found that the Si atoms adsorbed on InP could be removed by heating the substrate in phosphine (PH3) atmosphere just before growth. Heating makes it possible to suppress n-type conduction.
Interfacial roughness correlation in multilayer films: Influence of total film and individual layer thicknesses
Authors: Savage D. E. , Schimke N. , Phang Y.-H. , Lagally M. G.
Published: July 2002

A series of W/C multilayer films sputter deposited on Si(100) substrates with total thickness ranging from 400 to 6400 Å and bilayer period from 20 to 160 Å were examined to explore the variation of interfacial roughness and interfacial roughness correlation with film thickness and period. The films were characterized with x-ray diffractometry. Average interfacial roughness is obtained from conventional (θ,2θ) scans, while information on roughness correlation is extracted from rocking-curve (transverse-profile) analysis. The magnitude of the roughness is found to depend more on bilayer period than on total film thickness. The observations suggest that interfaces retard the evolution of surface roughness and that thin ‘‘restarting’’ layers may be used to control the growth morphology of thin films.
Optical determinations of the direct energy gap in α-mercuric iodide at elevated temperatures
Authors: Burger A. , Nason D.
Published: July 2002

The band-gap energy of single crystals of α-mercuric iodide has been obtained for temperatures from ambient to the limit of stability of the phase, 400 K. The method is based on measuring the spectral shifts of the excitonic reflection and absorption peaks with changing temperature, and utilizes results for low temperatures from other investigations. The temperature coefficient of the band gap is −3.9×10−4 eV/K from 285 to 400 K, and the direct band gap at 300 K is 2.292 eV.
Elastic and viscoelastic analysis of stress in thin films
Authors: Liu H. C. , Murarka S. P.
Published: July 2002

The occurrence of stress in thin films has led to serious considerations of stability problems in the semiconductor industry. It may cause mechanical failure of films, such as adhesion reduction or contact peel-off, or variations in electrical properties. The existence of stress will also alter electromigration behavior for thin metal lines. The elastic stress in a multilayered structure due to thermal processing is calculated by use of the principle of mechanics balance. It is found that the variation of thickness in one film will not affect the magnitude of stress in another film. The shearing and peeling stress at the edge of a patterned structure, which is responsible for the peeling of a film at the edge, is then modeled and discussed in detail. Finally, the relaxation of stress by viscous motion of SiO2 is analyzed based on Maxwell’s viscoelastic model.
Dependence of intrinsic stress in hydrogenated amorphous silicon on excitation frequency in a plasma-enhanced chemical vapor deposition process
Authors: Dutta Joydeep , Kroll Ulrich , Chabloz Patrick , Shah Arvind , Howling A. A. , Dorier J.-L. , Hollenstein Ch.
Published: July 2002

Intrinsic stress measurements were carried out on hydrogenated amorphous silicon (a-Si:H) films deposited with different excitation frequencies (13.56–70 MHz), by plasma-enhanced chemical vapor deposition. It was observed that films deposited at 70 MHz have one order of magnitude smaller intrinsic stress than those deposited at 13.56 MHz. These results have been linked to the estimated variation of the ion impact energy as a function of excitation frequency, deduced from the measured variation of the peak-to-peak voltage between the electrodes. The observation of diminished ion energy at higher excitation frequencies has been interpreted as the cause, both of the decrease in intrinsic stress as well as of the measured increase in surface roughness, of films prepared at higher frequencies.
A comparison of ferroelectric aging in bulk and thin-film materials
Authors: Pugh Robert D. , Sabochick Michael J. , Luke Theodore E.
Published: July 2002

Thin-film ferroelectric device researchers have reported that hysteresis loop translation−a characteristic of bulk ferroelectric aging−does not occur in thin-film devices. This work examines ferroelectric aging in thin-film materials using a novel measurement procedure that combines the techniques used in bulk and thin-film testing. The results show that the aging characteristics of thin-film ferroelectric materials are the same as those exhibited by bulk materials. In addition, the primary and secondary waiting time effects are shown to be directly related to aging.
Electro-optical and nonlinear optical coefficients of ordered group IV semiconductor alloys
Authors: Soref R. A.
Published: July 2002

Miller’s delta δ14(2ω) of 0.0172 m2/C is found for β-SiC at 1.1 μm from the measured Pockels coefficient r41 [Appl. Phys. Lett. 59, 1938 (1991)]. Assuming δ is constant, we estimate that r41 for zincblende SiC, GeC, SiGe, SiSn, GeSn, and SnC is in the range 2.7 to 11.3 pm/V. For these binary materials, the optical second-harmonic coefficient d14(2ω) is estimated to be 30 to 1160 pm/V. Similar coefficients are expected for the ordered alloys GeSiC, SnSiC, SiGeSn, SnGeC, and SiGeCSn.
Valence bands of poly(methylmethacrylate) and photoion emission in vacuum ultraviolet region
Authors: Ueno N. , Kobayashi Y. , Sekiguchi T. , Ikeura H. , Sugita K. , Honma K. , Tanaka K. , Ortí E. , Viruela R.
Published: July 2002

Photoion and photoelectron yields were measured for poly(methylmethacrylate) in the photon energy region of 8–40 eV using synchrotron radiation. Further, the valence-band structure was investigated with ultraviolet photoelectron spectra and valence effective Hamiltonian calculations. A significant difference was observed between the photon energy dependencies of photoion and photoelectron yields. The threshold energy for photoion emission was found to be 10.5 eV, while that for photoelectron emission was 8.5 eV, indicating holes created near the valence-band top do not contribute to the ion emission. At the higher-energy region, the ion emission efficiency was found to be enhanced in the photon energy region of 17–28 eV. The difference between the threshold energies of photoion and photoelectron emission and the enhancement of the photoion emission are discussed in conjunction with the valence-band structure.
Strain compensation by Ge in B-doped silicon epitaxial films
Authors: Maszara W. P. , Thompson T.
Published: July 2002

A compensation of stress induced in silicon epitaxial films heavily doped with boron was investigated. Addition of a controlled amount of germanium during the film growth allows one to attain a desired compressive or tensile stress in the film, or its complete elimination. The data shows very good correlation with a theoretical model adapted from Herzog et al. [J. Electrochem. Soc. 131, 2969 (1984)]. A 6.45 : 1 ratio of atomic concentrations of Ge and B completely eliminates stress in these films. We determined a critical amount of strain in the films, ≂2–4 μm thick, beyond which misfit dislocations are generated.
A field-free dense plasma produced by electron cyclotron resonance in a linear multipole field
Authors: Fukao Masayuki , Harada Yasuo
Published: July 2002

A description is given of characteristics of a plasma produced by electron cyclotron resonance (ECR) in a linear hexadecapole device. The field configuration generated by eight straight current rods circumferentially located in a glass chamber has a wide magnetic field-free region inside the rods and a strong peripheral field region between the rods and the chamber wall. Plasma was produced by ECR in the strong peripheral field using 2.45 GHz of radio frequency (rf) power and was effectively transferred into the field-free central region along radial field lines. Radial distribution of the ion saturation current Is was measured by a Langmuir probe, being remarkably flat in the field-free region and showing extremely low fluctuations of Is. The electron density at the chamber center increased in proportion to the rf power and significantly exceeded the cutoff density determined by the rf frequency. The production mechanism for the overdense plasma, the influence of the rf electric field direction upon the electron density profile, and the effect of ion drift motion due to the field line curvature are also discussed.
Introduction of extrinsic defects into mercuric iodide during processing
Authors: Hung C.-Y. , Bao X. J. , Schlesinger T. E. , James R. B. , Cheng A. Y. , Ortale C. , van den Berg L.
Published: July 2002

Low temperature (4.2 K) photoluminescence spectroscopy (PL) measurements were performed on mercuric iodide (HgI2) crystals which were intentionally doped with copper or silver during KI etching. PL spectra obtained after these doping experiments show specific Cu and Ag features similar to those previously observed after deposition of Cu or Ag contacts on mercuric iodide crystals. The in-diffusion of Cu or Ag into bulk HgI2 has also been confirmed a few days after doping. This diffusion introduces new recombination centers in the material. This work suggests that the processing steps used to fabricate mercuric iodide nuclear detectors can lead to the introduction of new defects which are detrimental to detector performance.
Avalanche injection model for the lock-on effect in III-V power photoconductive switches
Authors: Zhao Hanmin , Hadizad P. , Hur Jung H. , Gundersen Martin A.
Published: July 2002

The lock-on effect—observed in high-power GaAs and InP photoconductive switches—is characterized by a high on-state conduction current resulting from a high gain switching mechanism. In our study, an analytical model has been developed to determine the fundamental limitations to device performance imposed by this effect on high-power switching devices. In this model, a regional approximation is used to calculate the field distribution in the device and to obtain the device’s current density-voltage (J-V) characteristics. It is shown that negative resistance gives rise to high-field avalanche injection at the anode boundary. Moreover, the analytical results indicate the importance of electron velocity saturation for the onset of negative resistance, as well as the effect of hole injection from the high-field anode region on voltage lowering across the switch. It is determined that lock-on is associated with the transferred-electron effect, and will therefore constrain the use of GaAs and InP as materials for high-power switching devices.
The processes of formation and epitaxial alignment of SrTiO3 thin films prepared by metallo-organic decomposition
Authors: Braunstein G. , Paz-Pujalt G. R. , Mason M. G. , Blanton T. , Barnes C. L. , Margevich D.
Published: July 2002

The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo-organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo-organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single-crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450–500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo-organic (primarily metal-carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indicating the formation of grains that can serve as seeds for the nucleation and growth of randomly oriented SrTiO3 crystallites, thereby leading to a polycrystalline film. Deposition on silicon substrates indeed results in the formation of polycrystalline SrTiO3. However, when the precursor solution is deposited on single-crystalline SrTiO3 substrates, the crystallization process involves a competition between two mechanisms: the random nucleation and growth of crystallites just described, and layer-by-layer solid phase epitaxy. Epitaxial alignment on SrTiO3 substrates can be achieved when the samples are heat treated at temperatures of 1100–1200 °C or at temperatures as low as 600–650 °C when the substrate is heated to about 1100 °C before spin coating.
Langevin approach to hysteresis and Barkhausen jump modeling in steel
Authors: McMichael R. D. , Swartzendruber L. J. , Bennett L. H.
Published: July 2002

To represent the multiplicity of metastable states in a bulk ferromagnetic material with domain-wall pinning effects, fluctuations in the domain-wall energies are described in terms of an ensemble of stochastic Langevin functions. The model parameters used are a correlation length, a rms value for the amplitude of the fluctuations in the domain-wall energy gradient, and a ‘‘demagnetizing factor.’’ The model generates both hysteresis loops and Barkhausen effect (BE) jump size distributions. Jump size distributions were determined experimentally for low-carbon rolled sheet steel with the field applied both parallel and perpendicular to the rolling direction. Both the model and the experimental BE jump size distributions show a power-law behavior for small jumps and a rapid cutoff at large jump sizes.
Emerging magnetic technologies for consumer audio/video (invited)
Authors: Fujiwara Hideo
Published: July 2002

In the field of consumer audio/video, digital technology is the natural path for advancement. In audio systems, it has just been introduced in the form of digital compact cassette tape recorder and mini disk system in which magneto-optical recording is used. Therefore, the digital video instruments, such as small cassette digital video tape recorders (VTR) for high-definition television and static or short moving image devices will be the next attractive goals to be achieved. Technology analysis shows that the basic techniques of signal processing for small cassette VTR, in which the recording density of 1 μm2/bit and the data rate of 130–160 Mb/s are required, are almost at hand. For the media, improved metal-evaporated tape including oblique incident Co-CoO will be the most favorable candidate, although particulate media of metal powder tape (including Co or N modified forms) or Ba-ferrite tape coated by using the newly developed ultrathin coating techniques may take its position with the help of enhanced head sensitivity, because of their better durability. The basic demand for increasing saturation induction Bs of the head materials will be fulfilled by fine grain Fe-based materials, the available Bs being as high as 2 T. A dramatic increase in magnetoresistive (MR) head sensitivity is expected by using the giant MR effect, although a breakthrough is required to extract its full potential. On the other hand, varieties of static (including short moving) image devices will be developed by use of rapidly progressing magneto-optical recording technology. Preliminary techniques are now ready to meet the demand for the required increase in bit rate and recording density. A bit rate of 64 Mbits/s (8 Mbytes/s) has already been attained. A bit density of 107 bits/mm2 (6.5 Gb/in.2) is likely to be realized, and a factor of 2 or 3 more enhancement can be counted on. Rigid disk and perpendicular recording will have a chance to participate in the field if their techniques are applied to removable media.
Morphological instability in epitaxially strained dislocation-free solid films: Linear stability theory
Authors: Spencer B. J. , Voorhees P. W. , Davis S. H.
Published: July 2002

The morphological instability of a growing epitaxially strained dislocation-free solid film is analyzed. An evolution equation for the film surface is derived in the dilute limit of vacancies based on surface diffusion driven by a stress-dependent chemical potential. From the time-dependent linear stability problem the conditions for which a growing film is unstable are determined. It is found that the instability is driven by the lattice mismatch between the film and the substrate; however, low temperatures as well as elastically stiff substrates are stabilizing influences. The results also reveal that the critical film thickness for instability depends on the growth rate of the film itself. Detailed comparison with experimental observations indicates that the instability described exhibits many of the observed features of the onset of the ‘‘island instability.’’
Growth of intermediate phases in Co/Si diffusion couples: Bulk versus thin-film studies
Authors: Jan Chia-Hong , Chen Chia-Ping , Chang Y. Austin
Published: July 2002

Bulk diffusion couples of Co/Si were annealed at 800, 900, 1000, and 1050 °C for times ranging from 24 h to 1 month. The growth rates of the three intermediate phases Co2Si, CoSi, and CoSi2 and the concentration profiles across the couples were determined by optical microscopy and electron probe microanalysis, respectively. Using these data and the data reported in the literature at lower temperatures, the interdiffusion coefficients of Co2Si, CoSi, and CoSi2 were obtained as a function of temperature. The activation energies obtained were 140, 160, and 190 kJ/mol (or 1.45, 1.66, and 1.97 eV) for Co2Si, CoSi, and CoSi2, respectively. The generally small interdiffusion coefficient of CoSi2 and its high activation energy cause the growth rate of CoSi2 to be extremely small at low temperatures. Using the interdiffusion coefficients of Co2Si, CoSi, and CoSi2 extrapolated to low temperatures, the growth rates of Co2Si, CoSi, and CoSi2 in thin-film Co/Si couples were predicted. The predictions were made by numerically solving the diffusion equations with boundary conditions appropriate for thin-film couples. Good agreement was obtained between the calculated values and nearly all the experimental data reported in the literature using different configurations of thin-film couples. Although the methodology was applied successfully to predict the growth of Co2Si, CoSi, and CoSi2 sequentially in thin-film Co/Si couples, it is equally applicable to any binary thin-film diffusion couple.
Dielectric and ferroelectric properties of BaTiO3 thin films grown by the sol-gel process
Authors: Kamalasanan M. N. , Kumar N. Deepak , Chandra Subhas
Published: July 2002

Transparent smooth and crack-free BaTiO3 thin films were deposited on stainless steel, fused silica, platinum plates, and platinized silicon wafers (100) using the sol-gel process. Barium 2-ethyl hexanoate and titanium isopropoxide were used as precursors. Annealing of the films at 750 °C for 2 h was necessary to get polycrystalline films. The electrical properties of the films prepared on stainless-steel substrates showed an electrode barrier effect whereas those prepared on platinum substrates were susceptible to ambient atmospheric humidity. However, films grown on platinum substrates and measured under dry conditions showed very good electrical properties. Ferroelectric hysteresis and C-V characteristics were also studied on these films.
Electron paramagnetic resonance investigation of charge trapping centers in amorphous silicon nitride films
Authors: Warren W. L. , Kanicki J. , Robertson J. , Poindexter E. H. , McWhorter P. J.
Published: July 2002

We have explored the nature of the silicon dangling-bond center in amorphous hydrogenated silicon nitride (a-SiNx:H) thin films, and its relationship to the charge trapping centers using electron paramagnetic resonance (EPR) and capacitance-voltage (C-V) measurements. We have investigated the quantitative relationship between the concentration of silicon dangling bonds using EPR and the concentration of charge traps, measured by C-V measurements, for both UV-illuminated and unilluminated a-SiNx:H thin films subjected to both electron and hole injection sequences. A theoretical framework for our results is also discussed. These results continue to support a model in which the Si dangling bond is a negative-U defect in silicon nitride, and that a change in charge state of preexisting positively and negatively charged Si sites is responsible for the trapping phenomena observed in these thin film dielectrics.
Freezing transition in the Z3 gauge glass
Authors: Fisch Ronald
Published: July 2002

A Monte Carlo algorithm has been used to study the Z3 gauge glass model on simple cubic lattices. The glass transition temperature, Tg, for this model is 0.760±0.010J. There is an anomaly in the temperature derivative of the specific heat at Tg. The freezing transition appears to be describable by a picture in which localized ‘‘nuggets’’ organize themselves into a state of long-range order, leading to an extended state of the inverse susceptibility matrix with eigenvalue zero. The spatial decay of the spin-glass-type gauge-invariant correlation function at Tg seems to be a power law, whose exponent, η, is estimated to be 0.5±0.2.