bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser drilling into an absorbing liquid
Authors: Mueller R. E. , Bird J. , Duley W. W.
Published: July 2002

The interaction of continuous CO2 laser radiation with water is described. Tightly focused radiation at powers of up to 120 W is used to generate and maintain a conical depression in the water surface similar to the keyhole created during laser penetration welding. The observed penetration depth of up to 7 mm is explained in terms of a hydrodynamic model and observations on the interaction induced liquid flows are described. The momentum reaction to the flow of steam up out of the keyhole generates a downward flow in the liquid around the keyhole with a velocity of ∼20 cm/s under the conditions of these experiments. The experiment has also been performed under variable gravity conditions provided by the NASA KC-135 Microgravity Aircraft to observe effects associated with changes in hydrostatic pressure and buoyancy on the system.
Compositional evolution and magnetic properties of nanocrystalline Fe73.5Cu1Nb3Si13.5B9
Authors: Knobel M. , Turtelli R. Sato , Rechenberg H. R.
Published: July 2002

Melt-spun FeCuNbSiB ribbons were annealed at 540–550 °C for various times (≤1 h). The development of a nanocrystalline structure was investigated by means of Mössbauer spectroscopy. From measured hyperfine fields and intensities the crystalline phase was inferred to be pure Fe1−xSix, with x=0.18 after 1 h annealing. The residual amorphous volume fraction was determined to be ≂50%. With help of these results it has been possible to evaluate the amorphous contribution to magnetostriction in the nanocrystalline state. The development of a nanocrystalline structure was found to play a role in the main mechanisms of magnetic disaccommodation.
Optical properties of epitaxial CoSi2/Si and CoSi2 particles in Si from 0.062 to 2.76 eV
Authors: Wu Z.-C. , Arakawa E. T. , Jimenez J. R. , Schowalter L. J.
Published: July 2002

We have measured the optical properties of epitaxial CoSi2 films on Si from 0.062 to 2.76 eV by ellipsometry and spectrophotometry. The energy dependencies of the dielectric constants show Drude behavior at energies lower than ∼0.2 eV with Drude parameters ℏωp=(5.8±0.2) eV and ℏ/τ=(0.09±0.02) eV. Using the measured optical constants, the CoSi2 film is shown to have maximum absorptance at a thickness of ∼20 nm for λ≳1.4 μm. Finally, we have calculated the absorptance of a composite film of CoSi2 particles embedded in Si and found that the absorptance peak due to a surface plasmon resonance in the CoSi2 particles shifts to higher energy as the ellipsoidal particles become more elongated, in agreement with recent observations by Fathauer et al. [Phys. Rev. B 44, 1345 (1991)].
Formation and electronic state of DO3-type ordered structure in sputtered Fe-Si thin films
Authors: Miyazaki Masahiro , Ichikawa Masashi , Komatsu Takayuki , Matusita Kazumasa
Published: July 2002

Fe100−xSix (0≤x≤41.0) thin films with a thickness of 1 μm were deposited on crystallized-glass substrates by rf planar magnetron sputtering, and the structure of as-sputtered films and the structural changes due to the annealing were examined through x-ray diffraction analyses, electrical resistivity measurements, and conversion electron Mössbauer spectroscopy. The amorphous structure in as-sputtered Fe71.6Si28.4 thin films transformed into the DO3-type ordered structure due to the annealing at 500 °C, and it was found that three kinds of Fe sites having the internal magnetic fields of 314, 203, and 129 kOe existed in its ordered structure because of the excess Si atoms from ideal Fe3Si composition. The electronic state such as electron spin density and electron charge density of Fe atoms in the DO3-type structure in the thin films were almost the same as those in bulk Fe-Si alloys.
Model of gas composition and plasma properties in sealed cw CO2 lasers
Authors: Byron Stanley R. , Apter Henri
Published: July 2002

A comprehensive set of gas-phase reactions is described that accounts for the observed CO2 decomposition in sealed cw CO2 lasers that are free of H2O vapor. The model includes reactions among the species CO2, CO, O, O2, and O3, the electron Boltzmann equation to determine dissociation and ionization rates, and the negative ions O−, O2−, CO3−, and CO4−, which affect the reduced field E/N through their influence on ambipolar diffusion and ion neutralization. The CO2 formation mechanism is O+O2+M→k2O3+M, k2=4.2×10−34 cm6/s at 300 K, e−+O3→k3O−+O2, k3=1×10−8 cm3/s, O−+CO→k4CO2+e−, k4=7×10−10 cm3/s. The value for k3 is about 5 times larger than expected on the basis of electron-beam and drift tube measurements in room-temperature ozone and is attributed to electronic and/or vibrational excitation of ozone.
A computer simulation method for studying the ablation of polymer surfaces by ultraviolet laser radiation
Authors: Gai Huadong , Voth Gregory A.
Published: July 2002

A computer algorithm designed to simulate the ablation of polymer surfaces by ultraviolet laser radiation is presented. The method is based on a synthesis of the dressed state picture of radiation-matter interactions and a semiclassical ‘‘surface hopping’’ technique. A primary feature of the algorithm is that the intrinsically quantum mechanical process of ultraviolet photon absorption can be simulated while classical molecular dynamics techniques are simultaneously employed to integrate the equations of motion for the nuclear positions and momenta of the polymers. Illustrative results obtained from the algorithm are presented for the ablation of a model polymer surface. Quite different energy redistribution behavior is observed for electronic excitations to a repulsive electronic potential energy surface versus excitations to surfaces that have the possibility of bound vibrational motion. These results suggest that the postulated ‘‘direct’’ photochemical (bond-breaking) ablation mechanism for 193 nm lasers may be dynamically distinct from thermal ablation processes that result from intense local heating of the material by longer wavelength lasers.
Formation of a metastable ferromagnetic τ phase during containerless melt processing and rapid quenching in Mn-Al-C alloys
Authors: Kim Y. J. , Perepezko J. H.
Published: July 2002

Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable τ (L10) phase formed directly from the melt. Complete solidification to τ phase was interrupted by the competitive evolution of an equilibrium ε phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic τ phase in a Mn0.55Al0.433C0.017 alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034 alloy), a transition in structure development occurred so that the samples exhibited γ2 phase formation as well as τ and ε phases. Both microstructural observations and x-ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable τ phase from the melt may be facilitated by containerless processing.
Threading dislocations in InxGa1−xAs/GaAs heterostructures
Authors: Tamura M. , Hashimoto A. , Nakatsugawa Y.
Published: July 2002

Threading dislocation morphologies and characteristics, as well as their generation conditions in InxGa1−xAs films grown by molecular beam epitaxy on GaAs (001) substrates have been investigated, mainly using cross-sectional transmission electron microscopy. The 3-μm-thick InxGa1−xAs films are mostly examined for x ranging over x=0.01, 0.05, 0.1, 0.15, 0.2, 0.3, and 0.5. Moreover, for x=0.2, epitaxial layers having film thicknesses of 0.5, 1, and 2 μm are investigated. The formation of a high density of threading dislocations which reach the film surface is detected in epilayers of x≥0.2 at a fixed film thickness of 3 μm and with film thicknesses greater than 2 μm at x=0.2. In layers of x≤0.15, such threading dislocations are rarely detected, although dislocation segments on the {111} planes threading into the upper regions from the interface are frequently observed. Most of the observed threading dislocations are 60° and pure-edge type dislocations along the <211≳ and <110≳, and [001] directions, respectively. The former type dislocations are mainly observed in layers of x≤0.15; the latter predominantly exist in layers of x≥0.3. In epilayers of x=0.2, the two types of threading dislocations mentioned above coexist. It is also discussed that the formation of the above-mentioned threading dislocations is strongly associated with misfit dislocations which are introduced in the InxGa1−xAs layers under the different growth modes, depending on x.
Direct determination of praseodymium valence in Pr2(CoxFe1−x)14B
Authors: Capehart T. W. , Mishra R. K. , Herbst J. F.
Published: July 2002

Using x-ray-absorption near-edge spectroscopy (XANES) the Pr valence in the pseudoternary Pr2(CoxFe1−x)14B compounds has been directly determined. Praseodymium LIII edge XANES structures were obtained for the x=0, 0.3, 0.5, 0.7, and 1 compositions spanning the entire Co concentration range. It is found that the Pr valence is constant through the series and is identical to that in formally trivalent praseodymium acetate. The results demonstrate that the anomalous variation of the magnetocrystalline anisotropy with x in the Pr2(CoxFe1−x)14B compounds vis-à-vis their Nd-based counterparts does not arise from a Pr valence instability, as has been speculated in the literature, but must originate elsewhere. For comparison purposes XANES spectra for some relevant Ce and Nd materials are also reported.
Electromigration in two-level interconnect structures with Al alloy lines and W studs
Authors: Hu C-K. , Ho P. S. , Small M. B.
Published: July 2002

It is demonstrated that electromigration testing needs to be performed in structures that reflect use conditions, such as when there is a flux divergence as provided by the W stud-Al(Cu) interface rather than in a simple planar structure. The Al(Cu)/W interface has been investigated using both drift velocity and resistometric techniques with pure Al, Al(0.5 wt. % Cu) and Al(2 wt. % Cu) lines on W studs for interlevel connections. It is shown that the mass depletion can be correlated to the resistance change and electromigration failure in line/stud chains. A new effect is demonstrated in that a critical length of Al has to be depleted on Cu before the Al can migrate; when such migration starts the Al catches up with the Cu rich region, leading to slower motion and the production of extrusions which will also cause failures by shorting to adjacent lines.
Oxygen dependence of the magnetic order of Nd in NdBa2Cu3O6+x
Authors: Clinton T. W. , Lynn J. W. , Lee B. W. , Buchgeister M. , Maple M. B.
Published: July 2002

Neutron scattering and specific heat measurements have been carried out on a series of NdBa2Cu3O6+x powder samples with varying oxygen concentrations (x=0.94, 0.78, 0.45, 0.3, 0.13) in order to study the effects of oxygen on the magnetic order of Nd. For our highest oxygenated superconducting NdBa2Cu3O6.94 (Tc≂92 K), three-dimensional (3D) long range order develops below TN≂0.53 K, with a spin configuration which is antiferromagnetic along all three crystallographic axes. For a small reduction of oxygen to x=0.78, we observe drastic effects on the Nd order; 3D order is inhibited and only short range 2D correlations are found at low temperature. However, the 2D correlations develop at a much higher temperature, near 1.5 K. At (nonsuperconducting) x=0.45, the 3D magnetic order is better developed at low temperature, yet long range order still does not occur. For x=0.3, 3D long range magnetic order of the Nd ions is reestablished, developing below TN≂1.5 K, three times that of the fully oxygenated material. All of these ordering temperatures are much higher than what is expected based on dipolar interactions alone, and this coupled with our experimental results indicates that exchange interactions play an essential role, and are strongly influenced by the chain layer oxygen.
Leaky Rayleigh waves
Authors: Seshadri S. R.
Published: July 2002

In an elastically isotropic semiinfinite medium having a free surface with a weak harmonic corrugation, the interaction between the Rayleigh wave guided along the free surface and the shear vertical and pressure bulk elastic waves propagating in the substrate is investigated for the propagation directions lying in a plane perpendicular to the average free surface and containing the grating vector. The governing equations of this interaction are deduced and are shown to be consistent with the requirements of reciprocity and power conservation. The theory is applied to determine the characteristics of the output coupler in which the Rayleigh wave guided along the free surface radiates the bulk elastic waves in the substrate as well as those of an input coupler in which the shear and the pressure bulk elastic waves in the substrate incident on the corrugated region of the free surface launches the Rayleigh wave. Techniques for optimizing the performance of the input coupler to achieve maximum excitation efficiency of the Rayleigh wave are examined. The characteristics of these transducers are presented with the help of some illustrative numerical results.
Effects of high-flux low-energy (20–100 eV) ion irradiation during deposition on the microstructure and preferred orientation of Ti0.5Al0.5N alloys grown by ultra-high-vacuum reactive magnetron sputtering
Authors: Adibi F. , Petrov I. , Greene J. E. , Hultman L. , Sundgren J.-E.
Published: July 2002

The effects of incident ion/metal flux ratio Ji/JMe and ion energy Ei on the microstructure, texture, and phase composition of polycrystalline metastable Ti0.5Al0.5N films produced by reactive magnetron sputtering have been investigated using x-ray diffraction (XRD), plan-view and cross-sectional transmission electron microscopy, and Rutherford backscattering spectroscopy. The films, typically ≂1 μm thick, were deposited at a pressure of 20 mTorr (2.67 Pa) in pure N2 on thermally oxidized Si(001) substrates at 250±25 °C. The N2+ ion flux to the substrate was controlled by means of a variable axial magnetic field superimposed on the permanent magnetic field of the magnetron. Films deposited at Ei=20 eV (≂10 eV per incident accelerated N) with Ji/JMe=1 exhibited a complete (111) texture with a porous columnar microstructure and an average column size of ≂30 nm. Increasing Ei from 20 to 85 eV, while maintaining Ji/JMe constant at 1, resulted in a small change in texture as the XRD intensity ratio I002/(I111+I002) increased from ≂0 to 0.14, a decrease in average column size to 25 nm, and a reduction in intracolumn porosity.

The stoichiometric ratio N/(Ti+Al) increased from 1 at Ei=20 eV with Ji/JMe=1 to 1.23 at Ei=85 eV indicating trapping of excess N while the lattice constant a0 increased from 0.4157 to 0.4188 nm due to compressive stress. Ei values ≥100 eV led to alloy phase separation. In contrast, maintaining Ei at ≂20 eV and increasing Ji/JMe from 1 to ≥5.2 resulted in a change from a porous (111) texture to a dense completely (002)-oriented microstructure with an increase in the average column size to 35 nm. N/(Ti+Al) and a0 remained essentially constant and the alloy remained single phase. Mechanistic pathways leading to microstructure and texture changes through variations in Ei at constant Ji/JMe and in Ji/JMe at constant Ei were found to be quite different. The average energy deposited per metal atom, 〈Ed〉=Ei(Ji/JMe), is therefore not a universal parameter, as has been previously proposed, for describing film growth.
Structural evaluation of epitaxially grown organic evaporated films by total reflection x-ray diffractometer
Authors: Ishida Kenji , Hayashi Kouichi , Yoshida Yuji , Horiuchi Toshihisa , Matsushige Kazumi
Published: July 2002

An in-plane-type total reflection x-ray diffractometer was newly constructed, and the epitaxial growth of paraffin molecules (n-C33H68) vacuum-evaporated onto a KCl (001) surface was investigated. The molecular chains in as-evaporated films were shown to arrange themselves parallel to the 〈110〉 direction of the KCl substrate. After the evaporation, moreover, some molecules were revealed to reorient and tend to deviate their c axis by about ±5° from the 〈110〉 direction of the KCl crystal, probably because of the lattice mismatchings between the paraffin and substrate crystals.
A theory of ion beam induced charge collection
Authors: Breese M. B. H.
Published: July 2002

The ion beam induced charge technique can image the depletion regions of microelectronic devices through their thick metallization and passivation layers, and buried dislocation networks in semiconductor material by measuring the number of charge carriers created by a focused MeV light ion beam scanning over the sample surface. In this paper it is shown how the charge pulse height can be calculated in terms of the ion type and energy, and the minority carrier diffusion length. The effect of surface layers, depletion layers, ion induced damage, and ion channeling on the measured charge pulse height are also considered. It is shown how this approach can be used to simulate the charge pulse height reduction due to ion induced damage.
Tip artifacts in atomic force microscope imaging of thin film surfaces
Authors: Westra K. L. , Mitchell A. W. , Thomson D. J.
Published: July 2002

We report a study of tip artifacts in atomic force microscope (AFM) images of thin film surfaces. Specifically, a troublesome artifact that occurs when an AFM tip images surface features with a radius of curvature less than the apex of the tip. These artifacts are not easily detected, since the affected AFM images are similar to those expected for a thin film with a columnar microstructure. In a study of 23 thin films, we found that for a significant fraction, the AFM image was affected by this type of tip artifact. In the worst cases, the AFM images consisted almost entirely of images of the AFM tip. We discuss a simple technique to determine the extent of these tip artifacts.
Radiation induced carrier enhancement and intrinsic defect transformation in n-GaAs
Authors: Jorio Anouar , Rejeb Chedly , Parenteau Martin , Carlone Cosmo , Khanna Shyam M.
Published: July 2002

Gallium arsenide grown by the metallorganic chemical vapor deposition method and n doped with silicon to a concentration of 1015 cm−3 was exposed to reactor neutron irradiation in the 1012 to 3×1014 cm−2 1 MeV equivalent fluence range. Studies of the defects through deep level transient spectroscopy (DLTS), photoluminescence (PL), and transport measurements on this material indicate correlation between the nature and density of defects, and some of the transport parameters. Contrary to the general perception of degradation of electronic properties of semiconductors on nuclear irradiation, we observe enhancement in some of the electrical/optical properties of GaAs on irradiation at lower fluence levels. These properties degrade on irradiation at higher fluences. The PL intensity of irradiated GaAs increases over the 1×1012 to 1×1013 cm−2 fluence range. At 1×1013 cm−2, the increase in the signal from different PL peaks ranges from 25% to 200%. Similarly, the carrier density of irradiated GaAs, as determined by transport measurements, increases by about 25% on irradiation at 3×1012 cm−2, before decreasing at and above 3×1013 cm−2 fluence. The density of the EL2 trap as determined through the DLTS technique, remains constant with fluence and that of the EL12 trap at 780 meV below the conduction band decreases at an injection ratio of −0.5±0.3 cm−1 up to ≂1×1014 cm−2 fluence. The EL6 trap at 0.38 meV below the conduction band is introduced at a rate of 0.30±0.04 cm−1. Thus, neutron irradiation restructures the deep levels, with the consequence that the carrier density goes through a maximum at low fluence levels. Through PL measurements, the maximum in carrier density corresponds to a fluence level of (1.0±0.2)×1013 cm−2. At fluences above 1014 cm−2, we observe the introduction of a deep level at 260±85 meV below the conduction band (EL14) at a rate of 1.7±0.4 cm−1. Above 1014 cm−2, we observe an increase in carrier depletion in GaAs through PL and transport measurements.
Magnetic and electrical studies on Ho0.85Tb0.15Fe2−xNix system
Authors: Kumar M. Senthil , Reddy K. V. , Rama Rao K. V. S.
Published: July 2002

Cubic Laves phase alloys of Ho0.85Tb0.15Fe2−xNix (0≤x≤2) were prepared and the lattice parameters, evaluated as a function of x at room temperature, show deviation from Vegard’s law. This was attributed to the presence of a magnetovolume effect and charge transfer. Magnetization measurements were performed in the temperature range 77–700 K. The results suggest that the system undergoes a gradual transition from ferri- to ferromagnetic with increasing x. This has been explained based on the 3d band model. Furthermore, a monotonic decrease in Curie temperature with x was observed. Electrical resistivity studies were carried out in the temperature range 16–700 K. An anomaly was found in the vicinity of the Curie temperature for x=2 which has been attributed to the existence of the long-range nature of the critical fluctuations due to short-range spin ordering.
Disorder-driven first-order phase transformations: A model for hysteresis
Authors: Dahmen Karin , Kartha Sivan , Krumhansl James A. , Roberts Bruce W. , Sethna James P. , Shore Joel D.
Published: July 2002

Hysteresis loops in some magnetic systems are composed of small avalanches (manifesting themselves as Barkhausen pulses). Hysteresis loops in other first-order phase transitions (including some magnetic systems) often occur via one large avalanche. The transition between these two limiting cases is studied, by varying the disorder in the zero-temperature random-field Ising model. Sweeping the external field through zero at weak disorder, we get one large avalanche with small precursors and aftershocks. At strong disorder, we get a distribution of small avalanches (small Barkhausen effect). At the critical value of disorder where a macroscopic jump in the magnetization first occurs, universal power-law behavior of the magnetization and of the distribution of (Barkhausen) avalanches is found. This transition is studied by mean-field theory, perturbative expansions, and numerical simulation in three dimensions.
Magnetism and spin dynamics of nanoscale FeOOH particles
Authors: Ibrahim M. M. , Edwards G. , Seehra M. S. , Ganguly B. , Huffman G. P.
Published: July 2002

The nature of magnetism and electron paramagnetic resonance (EPR) spin dynamics in 30 Å particles of FeOOH have been investigated in the range 5–350 K. X-ray diffraction shows that the particles are neither α-Fe2O3 nor α-FeOOH based and they convert to Fe3O4 (α-Fe2O3) on heating to 800 K in vacuum (air). Magnetization M vs T data show a blocking temperature TB in the range 40 K<TB<100 K so that for T≥100 K, scaling of M with H/T for H up to 50 kOe verifies superparamagnetism. In EPR, both the linewidth ΔH and the g value decreases upon increasing T so that near 300 K, g≂2.05 (characteristic of Fe3+). A model of motional narrowing is used to explain the ΔH vs T behavior. The dramatic changes in M, ΔH, g value, and the recoilless fraction of Mössbauer spectroscopy observed near 50 K are all related to the thermal motion of the superparamagnetic nanoscale particles.
Compositional heterogeneity and the origins of the multicell cubic state in Sn-doped lead zirconate titanate ceramics
Authors: Viehland Dwight , Forst Donald , Li Jie-Fang
Published: July 2002

A systematic study of Sn-doped lead zirconate titanate ceramics has been carried out as a function of Sn and Ti contents. Dielectric constant and remanent polarization measurements have been performed and compared to our recent transmission electron microscopy study. The dielectric maximum was found to be associated with a multicell cubic state, rather than a macroscopic transformation into an antiferroelectric state. In addition, a strong deviation from Curie–Weiss behavior was observed for temperatures several hundred degrees above the permittivity maximum. Evidence is presented that the dielectric maximum is associated with a metastable locking of the incommensuration, rather than a phase transformation. Under application of an electric field, the metastability is seemingly overridden, and a tripling of the dielectric constant is observed. The strong enhancement of the dielectric softening is believed to arise due to a modulation of the phase on the incommensurate structure by the electric field.
Mechanism of cleaning and etching Si surfaces with low energy chlorine ion bombardment
Authors: Bello Igor , Chang W. H. , Lau W. M.
Published: July 2002

Effects of 35Cl+ bombardment of Si (100) surfaces were studied with a mass-separated low energy ion beam system operated under ultrahigh vacuum and with in situ x-ray photoelectron spectroscopy (XPS). Before ion bombardment, each silicon sample was etched with a hydrofluoric acid solution and rinsed in deionized water. XPS showed that the surface received no ion bombardment was effectively hydrogen passivated and had no silicon with an oxidation number higher than 2. However, oxygen was found which was probably present in the form of Si—OH or adsorbed water. Chlorine ion bombardment at room temperature initially drove the surface oxygen to the formation of silicon oxide which was subsequently etched off by further ion bombardment. The surface oxidation was initiated by the formation of Si—Cl bonds followed by the thermodynamically favorable replacement of Si—Cl with Si—O. The removal of the surface oxygen depended critically on the bombardment energy. At a bombardment energy of 1±0.6 eV, oxygen bonding was still observed even with a dose of 1018/cm2. The critical dose for oxygen depletion was found to be about 1×1018/cm2 for 40 eV bombardment, and about 1×1016/cm2 for 100 eV bombardment. Physical sputtering was the main oxide removal mechanism. Once the surface oxygen atoms were consumed, the silicon surface was etched by the chlorine ions with an enhancement by the chlorine chemistry. However, the absence of Si—Clx (x≳1) was clearly shown by XPS. Hence, bombardment must have promoted the desorption of the surface silicon chlorides.
Coupled finite element/boundary element method for semiconductor quantum devices with exposed surfaces
Authors: Chen Minhan , Porod Wolfgang , Kirkner David J.
Published: July 2002

We present a study of the boundary conditions for the potential at exposed semiconductor surfaces in split-gate structures, which views the exposed surface as the interface between the semiconductor and air. A two-dimensional numerical algorithm is presented for the coupling between the nonlinear Poisson equation in the semiconductor (finite element method) and Laplace’s equation in the dielectric (boundary element method). The utility of the coupling method is demonstrated by simulating the potential distribution in an n-type AlGaAs/GaAs split-gate quantum wire structure within a semiclassical Thomas–Fermi charge model. We also present a comparison of our technique to more conventional Dirichlet and Neumann boundary conditions.
Optical properties of buried cobalt disilicide layers in silicon
Authors: Lu F. , Perry C. H. , Namavar F.
Published: July 2002

The optical reflectivity from highly conducting buried and exposed CoSi2 layers produced by Co ion implantation of Si substrates has been measured over the energy range 0.012–6.2 eV (0.2–100 μm). Both as-implanted and high temperature annealed heteroepitaxial layers were investigated. The frequency dependant optical constants associated with the CoSi2 films were derived from the multicomponent reflectivity spectra; the analysis accounted for the contributions from the Si-CoSi2 interfaces. A Drude term was used to describe the free carriers, and a classical oscillator model was included to simulate interband electronic transitions for the CoSi2. The plasma frequency and relaxation time of the free carriers were measured as a function of anneal conditions. A direct correlation between the effective carrier concentration and the measured channeling data from Rutherford backscattering was observed.
Structural, optical, and electrical properties of epitaxial chalcopyrite CuIn3Se5 films
Authors: Xiao H. Z. , Yang L.-Chung , Rockett A.
Published: July 2002

Single crystal CuIn3Se5 epitaxial films have been synthesized on GaAs(001) by a hybrid sputtering and evaporation technique. The microstructure, microchemistry, and selected electrical and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy, cathodoluminescence, optical absorption and reflection, and four-point probe resistivity measurements. The results showed that the CuIn3Se5 crystals have an ordered point defect structure, a band gap of ≥1.18 eV, an optical absorption coefficient of about 15 000 cm−1 at a photon energy of 1.35 eV, and a film resistivity of ≳105 Ω cm. The results suggest the presence of band tails giving rise to subgap radiative recombination and absorption. Antiphase domain boundaries, stacking faults, and nanotwins were observed in the epitaxial layers and were reduced in number by rapid thermal annealing.
Vibrational infrared-absorption bands related to the thermal donors in silicon
Authors: Lindström J. L. , Hallberg T.
Published: July 2002

Thermal donor formation in silicon at 390, 420, and 450 °C has been investigated and correlated with IR vibrational absorption bands observable at room temperature. It is suggested that oxygen is clustering in different structures giving rise to absorption bands at 975, 988, 1000, 1006, and 1012 cm−1. The bands at 975, 988, and 1000 cm−1 are related to the three first appearing double donors as studied by low-temperature infrared spectroscopy. The 1012 cm−1 band is related to the most frequently appearing type of structure and is suggested to correspond to a different type of donor, possibly the shallow thermal donors or the new thermal donors. The development of the new bands with heat treatment time shows a complex behavior. The early stages of thermal donor formation as studied at 390 °C are not governed by ordinary long-range oxygen diffusion but by a transformation process of pre-existing clusters corresponding to the 1012 cm−1 band. At 450 °C the cluster transformation process appears in parallel with an aggregation of oxygen atoms diffusing to the clusters. Another group of vibrational bands appears in the range 724–745 cm−1. These bands develop simultaneously with the 975–1012 bands and are suggested to be related to a different vibrational mode of the oxygen atoms in the clusters.
Reflection of low energy hydrogen from carbon at oblique incidence
Authors: Mayer M. , Eckstein W. , Scherzer B. M. U.
Published: July 2002

The particle reflection coefficient is determined experimentally and by computer simulation for the bombardment of two different kinds of carbon with deuterium at normal and oblique incidence in the energy range from 1 keV down to 33 eV. Highly oriented pyrolytic graphite (HOPG) and EK98 graphites served as targets, the former as an example with a relatively flat surface, the latter with a rough surface topography. The experimental technique is based on the measurement of the trapped amount by nuclear reaction analysis using the reaction d(3He,p)α; protons are detected with a surface barrier detector. It is found that the usual assumption of complete trapping at low fluences is not fulfilled at low energies (≤100 eV). This is demonstrated by measuring the decrease of the implanted amount of deuterium with further bombardment of protons at the same energy. This loss of implanted atoms can be described by an exponential function which can be used to determine the correct trapping coefficient and from this the correct particle reflection coefficient. The experimentally determined particle reflection coefficients for HOPG agree reasonably well with data calculated with the Monte Carlo program TRIM.SP (version TRVMC); only at the lowest energy of 50 eV the experimental values are somewhat higher at intermediate angles of incidence than the calculated ones. The rough surface of EK98 is investigated with a scanning tunneling microscope. It is found that this surface can be described by a fractal surface of dimension 2.05. For this surface agreement of the experimental values with those calculated with the program VFTRIM (based on TRIM.SP, assuming a fractal surface) is found.
Free volume and ionic conductivity of poly(ether urethane)-LiClO4 polymeric electrolyte studied by positron annihilation
Authors: Peng Z. L. , Wang B. , Li S. Q. , Wang S. J.
Published: July 2002

The positron lifetime spectra and ionic conductivity have been measured for poly(ether urethane)-LiClO4 polymeric electrolyte as a function of temperature. The glass transition temperature Tg, free-volume Vf, and fractional free-volume f were derived from the positron annihilation parameters. A correlation between fractional free-volume f(T) and conductivity σ above Tg, log[σ/σ(Tg)]=C1[f(T)−f(Tg)]/f[T], was first experimentally confirmed using measured positron annihilation results. The comparison of the value of the obtained constant C1 with the universal values for the segmental diffusion of amorphous polymers indicated that the critical free volume required for the ion transport is much smaller than that required for polymer chain segment mobility. Carrier transport and the segmental motion are discussed in terms of the free-volume theory.
Growth of epitaxial AlN(0001) on Si(111) by reactive magnetron sputter deposition
Authors: Ivanov I. , Hultman L. , Järrendahl K. , Mårtensson P. , Sundgren J.-E. , Hjörvarsson B. , Greene J. E.
Published: July 2002

2H–AlN(0001) layers have been grown on Si(111) by reactive magnetron sputtering from an Al target in Ar+N2 gas mixtures at temperatures Ts=400–900 °C. Variations in reactive gas consumption, target voltage, and current–voltage characteristics versus nitrogen partial pressure were used to determine deposition parameters required to yield stoichiometric AlN with growth rates ≥2 μm h−1. High-resolution cross-sectional transmission electron microscopy (XTEM) analyses of films grown at 900 °C showed that the initial 6–8 monolayers were (111)-oriented cubic 3C before transforming to the (0001)-oriented 2H polytype. The epitaxial relationship was found by XTEM and x-ray diffraction (XRD) to be 2H–AlN(0001)//3C–AlN(111)//Si(111) with 2H–AlN[12̄10]//3C–AlN[110]//Si[110]. High-resolution XRD ω−2Θ and ω rocking curve widths for films grown at Ts=900 °C were 70 and 500 arc sec, respectively, the lowest values yet reported.
Study of the oxidation of gold-tin preforms using x-ray photoelectron spectroscopy
Authors: Taylor J. Ashley , Merchant Sailesh M. , Perry D. L.
Published: July 2002

This study uses x-ray photoelectron spectroscopy (XPS) to investigate the nature of the oxide formed on clean Au–Sn binary alloys (ζ and δ phases) and on preforms with the eutectic composition (29 at % Sn) at low O2 pressures (<10−3 Torr) and at high O2 pressures (up to one atmosphere) at temperatures ranging from room temperature to 200 °C. Sn Auger parameters and XPS angular-resolved data were obtained in addition to the core binding energies to identify the oxide layer. The oxidation of the Au–Sn alloys is basically similar to the oxidation of metallic Sn. The Auger parameter indicates that with low-pressure oxidation a layered oxide structure is formed consisting of SnO and a slightly tin-rich oxide at the interface. Probably a thin skin of Sn(IV) oxide exists on the outer surface of the low-pressure oxide. High-temperature and low-pressure promotes the growth of SnO. As the pressure is increased the Sn(IV) oxide grows more noticeably and with high-pressure oxidation the Sn(IV) oxide grows thicker than the Sn(II) oxide at the interface. The Sn(II) oxide at the interface appears similar to the Sn(II) oxide structure formed at low pressure. The Auger parameter indicates that the Sn(IV) oxide possesses a structure different than that of Cassiterite.
Laser-induced surface structures on diamond films
Authors: Tosin P. , Blatter A. , Lüthy W.
Published: July 2002

Periodic ripples are observed to develop at the surface of faceted chemical vapor deposited diamond films during laser irradiation at an angle of incidence beyond a critical value. The grating pattern perpetuates itself across the surface upon irradiation with subsequent, overlapping pulses. The ripples have spacings of typically 10 μm, and are oriented parallel to the plane of incidence, irrespective of the laser wavelength or the polarization. Neither diffraction nor interference effects can therefore be the cause for the rippling. Rather, a shadowing effect appears to initiate the corrugation. The occurrence of permanent ripples poses a limit to the laser polishing of rugged diamond films. However, rippling is avoided and significantly smoother films result (with an average roughness of 33 nm compared to about 100 nm) by rotation of the diamond film during laser processing.
Thermodynamics of latent heat storage in parallel or in series with a heat engine
Authors: Charach Chaim , Conti Massimo
Published: July 2002

The thermodynamics of a latent heat storage element, connected to a heat source, periodically varying in time, and to a heat engine, is addressed. Two typical modes of operation, referred to as the series and the parallel setups, are considered. They differ with regard to the active phase of the heat source. For the series mode the entire amount of heat transfer fluid (HTF), coming from the source, is first passed through the thermal storage element (TSE) before entering the engine. For the parallel setup only a fraction of the HTF, supplied by the heat source, is delivered directly to the engine, whereas the remaining fraction of HTF is pumped into the TSE to facilitate the exergy storage. The optimal selection of the freezing point of the phase-change material (PCM), the stability of operation of the engine, and the entropy production in the TSE during the heat storage-discharge cycle are considered. The parallel and the series modes of operation are compared for some simplified TSE models. For these models the series setup yields a higher efficiency and stability than the parallel scheme.
Phonon mode study of Si nanocrystals using micro-Raman spectroscopy
Authors: Xia Hua , He Y. L. , Wang L. C. , Zhang W. , Liu X. N. , Zhang X. K. , Feng D. , Jackson Howard E.
Published: July 2002

First-order Raman spectra of hydrogenated nanocrystalline silicon (nc:Si:H) films show unexpected features in their optical vibrational modes for crystallites with sizes ranging from 2 to 6 nm. Two size-dependent spectral regions, one with the stronger intensity peaking at 505–509 cm−1 and another a shoulder-like band between 512 and 517 cm−1, are clearly identified using a detailed line-shape analysis and the strong phonon confinement model. The strong size dependence of the relative integrated intensities of the two bands suggests that the modification of the vibrational spectra can be attributed to an effect induced by the atomic vibrations from the near-surface region of the nanocrystals.
Raman and photoluminescence analysis of stress state and impurity distribution in diamond thin films
Authors: Bergman L. , Nemanich R. J.
Published: July 2002

Photoluminescence (PL) and Raman spectroscopy were employed to investigate the nature and sources of stress and the type and distribution of impurities and defects in thin diamond films grown on silicon substrates. The types of impurities and defects which were detected in the diamond films are the nitrogen, silicon, and the sp2-type bonding of the graphitic phase. Our Raman analyses indicate that the diamond films exhibit a net compressive stress. After compensating for the thermal interfacial stress and for the stress due to grain boundaries it was found that the residual internal stress is compressive in nature. From Raman line-shape analysis it was determined that the internal stress is due to the various impurities and defects present in the film. Moreover, the stress magnitude exhibits a strong correlation with the graphitic phase implying that the sp2 bonding produces a dominant compressive stress field. The PL analytical line-shape investigation of the nitrogen band at 2.154 eV indicates that the nitrogen centers are uniformly distributed in the film. The PL line shape exhibited a close fit to the Lorentzian–Gaussian convoluted line known as the Voit profile. The deconvolution of the line resulted in a dominant Gaussian component, corresponding to stress arising from line type defects, and a much smaller Lorentzian component corresponding to point defect stress. The Gaussian component was attributed to the graphitic phase implying that the sp2 bonding is not in the form of a point defect but rather takes the form of a line or extended defect. The line-shape investigation of the silicon band at 1.681 eV showed that the silicon centers are correlated with the silicon/diamond interfacial stress. Finally, the response of the nitrogen and silicon optical centers to the internal stress, which is manifested via the PL linewidth, was also studied. The silicon band exhibits the narrower linewidth which may indicate that the silicon center complies less to the internal stress than the nitrogen center or that the two optical centers are interacting with different types of stress sources.
A virtual interface method for extracting growth rates and high temperature optical constants from thin semiconductor films using in situ normal incidence reflectance
Authors: Breiland W. G. , Killeen K. P.
Published: July 2002

A method is presented in which both optical constants and growth rates may be simultaneously extracted from the in situ normal incidence reflectance of a growing thin film. The method employs a virtual interface model, thus avoiding cumulative errors that are encountered if a standard multiple-layer model is used. No a priori knowledge of underlying film materials, structures, or locations of interfaces is required. A method to accurately estimate all parameters for starting values in the least-squares fitting of the data is also presented. This allows one to use a fully automated procedure for extracting information that requires no prior knowledge other than the starting reflectance of the substrate. Monte Carlo simulations are presented to study the ultimate accuracy of the method under ideal conditions for a film structure typical of compound semiconductor growth. Optical constants of GaAs and AlAs at 634 C have been obtained over a wavelength range of 400–990 nm with this method and agree with values obtained by others using ellipsometry. The method provides a pre-growth calibration tool analogous to the use of reflection high energy electron diffraction in molecular beam epitaxy (MBE) that can be used in chemical vapor deposition applications as well as in MBE. Multiple calibrations can be performed for different materials within a single growth run.
Interfacial transport in porous media: Application to dc electrical conductivity of mortars
Authors: Schwartz Lawrence M. , Garboczi Edward J. , Bentz Dale P.
Published: July 2002

A mortar is a composite of inert sand grains surrounded by a porous cement paste matrix. We investigate the electrical conductivity of model mortars that include enhanced electrical conduction in the matrix–sand grain interfacial region. The electrical conductivity is evaluated by a combination of finite element, finite difference, and random walk methods for periodic and disordered models of mortar. Since the effective conductivity within the interfacial zone is often much higher than the bulk matrix conductivity, the qualitative features of transport in these systems is often controlled by the connectivity of the interfacial zone. Special attention is thus given to the geometrical percolation of this zone. A family of effective medium approximations give a good qualitative description of the disordered model’s electrical properties. A simple four parameter Padé approximant is found to successfully describe the electrical conductivity of the periodic model over the entire range of parameters studied. Finally, we show that our calculations can be used to obtain a reasonable estimate of the permeability to viscous fluid flow.
Simultaneous in situ measurements of properties of particulates in rf silane plasmas using a polarization-sensitive laser-light-scattering method
Authors: Shiratani Masaharu , Kawasaki Hiroharu , Fukuzawa Tsuyoshi , Yoshioka Takashi , Ueda Yoshio , Singh Sanjay , Watanabe Yukio
Published: July 2002

A polarization-sensitive laser-light-scattering method is developed for simultaneous in situ measurements of properties (size, size dispersion, density, and refractive index) of particulates formed in processing plasmas. The developed system is applied to observe the growth processes of particulates in a range of their size larger than about 10 nm in rf silane plasmas. A size, a size dispersion (logarithm of a standard deviation of size), a density, and a refractive index of particulates in the plasmas are found to be 10–200 nm, about 0.1, 107–109 cm−3 and about 3–5i, respectively. The former three of such values agree fairly well with ones deduced from scanning electron microscopic (SEM) observation. These particulates grow through three phases of nucleation and initial growth, rapid growth, and growth saturation. Coexistence of two size groups of particulates with narrow size dispersions during and after the rapid growth phase verified by the SEM observation may be explained by a model taking into account coagulation between oppositely charged particulates.
Determination of local order in the amorphous precursor to Ba-hexaferrite thin-film recording media
Authors: Snyder J. E. , Harris V. G. , Das B. N. , Koon N. C. , Sui X. , Kryder M. H.
Published: July 2002

Ba-hexaferrite thin films for recording media applications are often fabricated by a two-step process: sputter deposition of an amorphous precursor, followed by annealing to crystallize the BaFe12O19 phase. The magnetic anisotropy of the crystalline films can be either in-plane or perpendicular, depending on the sputtering process used in the first step. However, conventional structural characterization techniques have not been able to distinguish between different as-sputtered films. Using polarization-dependent extended x-ray absorption fine structure (PD-EXAFS), we have observed anisotropic local structure around both Ba and Fe atoms in the amorphous precursor films. Comparison of the results suggests that the amorphous films consist of networks of Fe atoms surrounded by their O nearest neighbors, with Ba atoms fitting into in-between spaces as network modifiers (there might also be some minor Fe network modifying contribution). The local structural anisotropy of the amorphous films appears to determine the orientation of the fast-growing basal plane directions during annealing, and thus the directions of the c axes and the magnetic anisotropy.
Magnetization and specific heat studies of Gd2In
Authors: Jee Chan-Soo , Lin C. L. , Mihalisin T. , Wang Xue-Qin
Published: July 2002

We have measured the temperature and magnetic field dependence of the magnetization for Gd2In. The results show that Gd2In exhibits a helical ferromagnetic transition at 190 K and an antiferromagnetic transition at 100 K in zero and low applied fields. Both the helical ferromagnetic state at temperatures between 100 and 190 K and the antiferromagnetic state at low temperatures are transformed to a simple ferromagnetic state by high applied fields. The antiferromagnetic transition temperature decreases with increasing applied field and approaches zero at H=25 kOe. We have also measured the temperature dependence of the specific heat for Gd2In. The data show two distinct specific heat anomalies which are associated with the two magnetic transitions.