bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-induced etching of organic polymers in argon and oxygen radio-frequency plasmas
Authors: Baggerman J. A. G. , Visser R. J. , Collart E. J. H.
Published: July 2002

The authors have studied the etching of novolac-based photoresist, polyimide, and polymethylmethacrylate in oxygen and argon rf plasmas at pressures between 0.3 and 10 Pa in a reactive-ion-etching (RIE) reactor. Energy-flux density measurements on the powered electrode were performed under experimental conditions identical to those used during the etch experiments. In both plasmas the etch rate of these polymers depends proportionally on the energy-flux density of the impinging energetic particles, which are the ions and the energetic neutrals formed by elastic and charge-exchange collisions between ions and neutral gas particles in the sheath. In oxygen and argon plasmas under RIE conditions the etch mechanism of these polymers is ion induced. Average values of the overall carbon yield were determined as a function of the average energy of the impinging energetic particles between 50 and 650 eV and as a function of the angle of incidence. The results obtained in oxygen plasmas were compared with those obtained in argon plasmas and the chemical enhancement in the presence of oxygen is determined. By monitoring changes in gas pressure and energy-flux density on the substrate due to polymer etching, details about the oxidation reaction and the identity of the oxidizing particles in the plasma have been obtained. It is shown that the oxidation reaction occurs mainly with molecular oxygen and for the larger part on the polymer surface.
Measurements of alloy composition and strain in thin GexSi1−x layers
Authors: Tsang J. C. , Mooney P. M. , Dacol F. , Chu J. O.
Published: July 2002

The utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1−x layers has been investigated. Using data from the literature and new data for the strain shift of the Si-Si phonon mode presented here, we show how Raman spectra provide several different means of measuring composition and strain in samples as thin as 200 Å. We demonstrate that for largely relaxed layers with compositions near x=0.30, Raman scattering can measure the composition, x, with an accuracy of ±0.015 and the strain, ε, with an accuracy ±0.0025. The accuracy of the alloy composition obtained from Raman spectra is comparable or, in the case of very thin layers, superior to that measured by other techniques such as x-ray diffraction, electron microprobe, and Auger electron spectroscopy.
Giant magnetoresistance in melt-spun Cu87Co13
Authors: Howson M. A. , Musa S. O. , Walker M. J. , Hickey B. J. , Cochrane R. , Stevens R.
Published: July 2002

Results for the temperature and magnetic-field dependence of melt-spun Cu87Co13 are presented and discussed. The magnetoresistance of the as-spun sample exhibits superparamagnetic behavior with a magnetoresistance of 18% at 0.4 K and in a field of 80 kOe. The magnetic-field dependence of the magnetoresistance is approximately proportional to the Langevin function. The microstructure of the sample was investigated by transmission electron microscopy and it appears that the giant magnetoresistance is due to the presence of small Co precipitates with an approximate mean diameter of 12 Å and a mean separation of 35 Å.
Effect of implant temperature on dopant diffusion and defect morphology for Si implanted GaAs
Authors: Robinson H. G. , Haynes T. E. , Allen E. L. , Lee C. C. , Deal M. D. , Jones K. S.
Published: July 2002

Experimental observations of dopant diffusion and defect formation are reported as a function of implant temperature in Si implanted GaAs. The diffusion of Si during post-implant annealing decreases by a factor of 2.5 as the implant temperature increases from −2 to 40 °C. In this same temperature range, the maximum depth and density of extrinsic dislocation loops increase by factors of 3 and 4, respectively. Rutherford backscattering channeling measurements indicate that Si implanted GaAs undergoes an amorphous to crystalline transition at Si implant temperatures between −51 and 40 °C. A unified explanation of the effects of implant temperature on both diffusion and dislocation formation is proposed based on the known differences in sputter yields between crystalline and amorphous semiconductors. The model assumes that the sputter yield is enhanced by amorphization in the lower temperatures, thus increasing the excess vacancy concentration. Estimates of excess vacancy concentration are obtained by simulations of the diffusion profiles and are quantitatively consistent with a realistic sputter yield enhancement.
Diffusive void bifurcation in stressed solid
Authors: Suo Z. , Wang W.
Published: July 2002

Interconnects are susceptible to solid diffusion under residual stress, electric current, and elevated temperature. As atoms diffuse, voids nucleate, drift, and enlarge. At some point, the voids of rounded shape can collapse to narrow slits and sever the interconnects. The fatal slits are often found to be transgranular, i.e., each slit cuts across a single grain. They have raised many concerns, but the underlying mechanism has remained unclear. It is proposed that a void changes shape due to surface diffusion under the combined action of surface energy, elastic energy, and electric current. The void will be rounded if surface energy prevails, but will collapse to a slit if the elastic energy or the electric current prevails. A cylindrical void in an infinite crystal under biaxial stresses, but under no electric current, is analyzed. Four things are done, as follows: (1) A suitable thermodynamic potential is minimized and maximized to select, among a family of ellipses, equilibrium void shapes. The bifurcation diagram consists of a subcritical pitchfork and two Griffith cracks. (2) A void under biased stresses is analyzed to illustrate the effect of imperfections. (3) Exact initial bifurcation modes are determined. The critical loads for the successive modes are closely separated, indicating that the shape evolution will be sensitive to initial imperfections. (4) A variational principle for shape evolution under stress, current and surface energy is identified. Stress-induced evolution time is estimated by using this variational principle.
Compton scattering tomography
Authors: Norton Stephen J.
Published: July 2002

When a fan beam of monoenergetic γ rays is emitted from a point source into a plane and the scattered photons are recorded by a point detector, the locus of points over which singly Compton-scattered photons suffer the same energy loss is a circle passing through the source and detector points. Thus, the number of scattered photons recorded at a particular detector and energy can be expressed as a weighted line integral of the electron density over a circular path uniquely determined by the energy and the detector location. This defines a novel tomographic reconstruction problem in which, by recording the number of scattered photons as a function of energy and detector position, an image of electron density can be reconstructed from measurements of its line integrals over many overlapping circular paths. It is shown here that this image reconstruction problem has an analytical solution which bears some resemblance to the filtered-backprojection algorithm used in conventional (transmission) computed tomography (CT). A tomographic imaging scheme based on this idea would have several potential advantages over conventional CT systems in the field of industrial nondestructive evaluation, e.g., the ability to image from one side of the object, and the absence of moving parts.
Collective excitations in n-i-p-i superlattices: Finite-size effects
Authors: Kushwaha Manvir S.
Published: July 2002

A theoretical investigation has been made of the collective (bulk and surface) excitations in a finite superlattice system consisting of n- and p-doped semiconductors separated by an intrinsic i semiconductor (n-i-p-i superstructure). An implicit dispersion relation is derived employing the fully retarded theory in the framework of a transfer-matrix method. The plasmon-polariton modes are defined by the electromagnetic fields localized at and decaying exponentially away from each interface and from the ends of the superlattice system. Numerical examples are presented for two illustrative cases: (i) all the four layers of a unit cell being of equal thicknesses; and (ii) the thicknesses of n- and p- doped layers being half of the intrinsic layers. The numerical results correspond to an ideal system in which the damping effects are ignored and the semiconducting layers are modeled by real, local dielectric functions. The propagation characteristics of plasmon polaritons and their inverse penetration depths have been studied. The consequences of reducing the size of the superstructure to a single unit cell have also been explored. The major attention has been focused on the comparison of theoretical results for the finite superstructure with those for the semi-infinite and/or infinite superstructure.
Plastically deformed region around indentations on Si single crystal
Authors: Yoshioka M.
Published: July 2002

Expansion of a hemispherical shell by inner pressure has been widely applied for the model of the deformation by an indentation on a flat surface; however, the deformed region is not necessarily spherically symmetric, especially in anisotropic materials such as single crystals. Therefore, whether the spherical model is applicable in an indentation process for objective materials must always be kept in mind. Indentations have been made on the (111) surface of silicon single crystal at various temperatures. The three-dimensional shape of the plastically deformed region was experimentally measured by means of an etching technique and its difference from the hemisphere was observed. It was never spherical but much more complicated, similar to a bottle gourd. The slip mechanism, which resulted in the observed shape of the plastic region, is discussed further. The plastic region was analytically obtained also on the assumption that the stress distribution was spherically symmetrical. The result is approximately in accordance with the observed shape. It is therefore concluded that the stress distribution is nearly spherical although the plastic region is far from it. The yield strength of silicon crystals and their temperature dependence were obtained based on the spherical model.
Exchange anisotropy in films, and the problem of inverted hysteresis loops
Authors: Aharoni Amikam
Published: July 2002

The inverted hysteresis loop is claimed to be possible, in an exchange-coupled bilayer, when a magnetically soft material is affected by the demagnetizing field of the hard material. These demagnetizing fields are caused by the charge on the surfaces, neglected in all the theories that assume a strictly one-dimensional structure, in an infinite material. For these one-dimensional models, an analytic solution is presented, which reduces the computation from a numerical integration of a set of differential equations to the solution of an algebraic, transcendental equation (which contains elliptic functions) for fitting only the boundary conditions. It may then be feasible to introduce at least an approximation for the demagnetizing effect of the surfaces in a finite sample.
Evidence for quantum mesoscopic tunneling in rare-earth layers
Authors: O’Shea M. J. , Perera P.
Published: July 2002

We report on finite size effects and evidence for quantum mesoscopic tunneling (QMT) in thin isolated rare-earth layers prepared in the form of R/Mo multilayers where R represents Tb, Dy, or Dy50Co50. The magnetic transition temperature Tc decreases with decreasing magnetic layer thickness and is discussed within a finite size scaling theory. Evidence for QMT is found in magnetic relaxation measurements in these systems with a sharp crossover to a temperature-independent magnetic relaxation regime at low temperatures. The Tb system has a crossover temperature T0 of 20 K, the largest value reported so far for this crossover.
Si/SiO2 interface states and neutral oxide traps induced by surface microroughness
Authors: Kimura Mikihiro , Mitsuhashi Junichi , Koyama Hiroshi
Published: July 2002

Silicon-surface microroughness was formed by cleaning cycles of an NH4OH-H2O2-H2O solution. Not only the roughness of the silicon surface, but also the roughness of the thermally oxidized surface and that of the surface after the removal of the thermal oxide (corresponding to the Si/SiO2 interface roughness) were observed by means of atomic-force microscopy. By using metal-oxide-semiconductor structured samples, investigations were conducted of the electrical properties induced by surface microroughness, such as the oxide-trapped charges, Si/SiO2 interface states, neutral oxide-trap centers, and oxide-breakdown characteristics. As a result, it was clarified that the neutral oxide traps, as well as the Si/SiO2-interface states, apparently increase in spite of only a small change in roughness. It was also verified, however, that the oxide-trapped charges and the oxide breakdown do not change over the scale of roughness change in the present experiments, if contaminants were carefully eliminated from the Si surface.
Nature of photoluminescence involving transitions from the ground to 4f n−1 5d1 states in rare-earth-doped glasses
Authors: Yokokawa T. , Inokuma H. , Ohki Y. , Nishikawa H. , Hama Y.
Published: July 2002

Photoluminescence from Er3+ or Pr3+ ion-doped silica or ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass, excited by high-energy photos such as excimer laser photons, was investigated mainly through the temperature dependence. When there are two emission states whose energy difference is small, as in the case of 2H11/2 and 4S3/2 in Er3+ or the 1I6/3P1 mixing state and 3P0 in Pr3+, the luminescence from the upper state and that from the lower state are found to depend inversely on temperature. This indicates that the thermalization or thermal equilibrium of electrons between the two emission states occurs.
Effects of surface recombination on carrier distributions and device characteristics
Authors: Mui David S. L. , Coldren L. A.
Published: July 2002

We calculate the effects of surface recombination on carrier distributions and device characteristics. The conventional approach assumes a constant surface recombination velocity in the calculation of the surface recombination current and carrier distributions. In this paper, we use the Shockley–Reed–Hall recombination mechanism to calculate the surface recombination rate without resorting to the use of a surface recombination velocity. The current continuity equation and Poisson’s equation are solved simultaneously for the carrier distributions, current density, and electric field in the bulk. The effects of surface recombination and surface charged states are included explicitly in the boundary conditions and charge neutrality equation. As a result of the inclusion of the surface charged states in the calculation, acceptor, donor, and compensating surface trap states can easily be included in our model. We calculate the influence of surface recombination on the performance of ridge-type devices and show that appropriate surface delta doping can be used to effectively reduce the surface recombination current for an uncompensated surface. We also compare our results to those obtained from a simple model which is based on a constant surface recombination velocity.
Polar distribution of ablated atomic material during the pulsed laser deposition of Cu in vacuum: Dependence on focused laser spot size and power density
Authors: Weaver I. , Lewis C. L. S.
Published: July 2002

Experiments have been carried out to investigate the polar distribution of atomic material ablated during the pulsed laser deposition of Cu in vacuum. Data were obtained as functions of focused laser spot size and power density. Thin films were deposited onto flat glass substrates and thickness profiles were transformed into polar atomic flux distributions of the form f(θ)=cosn θ. At constant focused laser power density on target, I=4.7±0.3×108 W/cm2, polar distributions were found to broaden with a reduction in the focused laser spot size. The polar distribution exponent n varied from 15±2 to 7±1 for focused laser spot diameter variation from 2.5 to 1.4 mm, respectively, with the laser beam exhibiting a circular aspect on target. With the focused laser spot size held constant at φ=1.8 mm, polar distributions were observed to broaden with a reduction in the focused laser power density on target, with the associated polar distribution exponent n varying from 13±1.5 to 8±1 for focused laser power density variation from 8.3±0.3×108 to 2.2±0.1×108 W/cm2, respectively. Data were compared with an analytical model available within the literature, which correctly predicts broadening of the polar distribution with a reduction in focused laser spot size and with a reduction in focused laser power density, although the experimentally observed magnitude was greater than that predicted in both cases.
Surface morphology and electric conductivity of epitaxial Cu(100) films grown on H-terminated Si(100)
Authors: Krastev E. T. , Voice L. D. , Tobin R. G.
Published: July 2002

We have investigated the crystal structure, surface morphology, and electrical conductance of Cu films grown on H-terminated Si(100). The films were grown by thermal evaporation at 10−8 Torr, at deposition rates from 0.1 to 3.5 nm/s and at substrate temperatures from room temperature up to 200 °C. Typical film thicknesses were ∼100 nm. Epitaxial growth was verified by x-ray diffraction for films grown near room temperature at rates up to 2 nm/s. The root-mean-square surface roughness was measured to be 1–2 nm using atomic force microscopy (AFM). Higher growth rates or deposition temperatures above 100 °C produced poor quality, nonepitaxial films. Postdeposition annealing at temperatures up to 175 °C did not improve the surface roughness, and at higher annealing temperatures rapid silicide formation destroyed the Cu film. In situ electrical resistance measurements and AFM images suggest that for about the first 6 nm of growth the film consists of disconnected islands. X-ray-diffraction data show that the islands consist of crystalline Cu; there is no evidence for a silicide layer. At higher thicknesses the film consists of Cu with an impurity concentration of a few tenths atomic percent. The thickness dependence of the electrical conductance implies a high level of surface, interface, or grain-boundary scattering, characterized by a near-zero apparent specularity parameter p.
Simulation of three-dimensional nonperiodic structures of π-vertical Bloch line and 2π-vertical Bloch line in magnetic garnet
Authors: Redjdal M. , Humphrey F. B.
Published: July 2002

The dynamics of three-dimensional nonperiodic structures in magnetic garnet have been investigated using large scale numerical simulations. The width of a single π-vertical Bloch line (πVBL) at equilibrium has been measured to be twice the analytical Bloch line width π(A/2πM2s)1/2, where A is the exchange energy constant and MS the spontaneous magnetization. A 2πVBL has been shown to be 1.5× wider than a πVBL. A comoving technique is used to track a single domain wall with a single πVBL when a 5 Oe field is applied perpendicularly to the surface of the film. At dynamic equilibrium, the VBL to wall velocity ratio is equal to ten, smaller than the value found for a simulated loosely spaced chain of πVBLs. A 2πVBL is split into two single πVBLs when an in-plane field is applied in the same direction as that of the center spin of the 2πVBL. No motion of the surface spins is observed for the first 10 ns when a 30 Oe field is applied although considerable spin distortion occurs in the wall center. When the field is turned off after 8 ns, the relaxing distortion drives the surface spins apart. The containment due to 2π horizontal Bloch line formation during the process is demonstrated.
A study of the magneto-optical Kerr spectra of bulk and ultrathin Fe3O4
Authors: van der Zaag P. J. , Fontijn W. F. J. , Gaspard P. , Wolf R. M. , Brabers V. A. M. , van de Veerdonk R. J. M. , van der Heijden P. A. A.
Published: July 2002

An analysis of the complete dielectric tensor of bulk magnetite, Fe3O4, and of Fe3O4 substituted with a variable degree of Mg2+ or Al3+ allowed the assignment of the main magneto-optical (MO) transitions in Fe3O4 between 0.5 and 4.0 eV. This assignment is consistent with our reinterpretation of the MgFe2O4 and Li0.5Fe2.5O4 MO-Kerr spectra. An analysis of the stoichiometry of a thin Fe3O4 layer is made, based on the Kerr spectrum, which is compared to an analysis based on the Verwey transition. The Kerr spectrum is also used to compare wavelengths for MO-Kerr effect studies of wedge-shaped samples.
Effects of mobile donors on potential distribution in grain contacts of sintered ceramic semiconductors
Authors: Rantala Tuomo S. , Lantto Vilho , Rantala Tapio T.
Published: July 2002

Sintered ceramic semiconductors can be used to monitor the surrounding gas atmosphere. It is based on the conductivity response of the semiconductor to the surface reactions on the grains of porous material. Some nonstoichiometry defect donors, like oxygen vacancies in n-type semiconductors, may be mobile at relatively low temperatures, where semiconductor gas sensors operate. In such case, the donor concentration may considerably decrease in the space charge layer at the semiconductor surface, which may be reflected in the transport properties of electrons through the neck contacts between grains. We model here various neck contacts between spherical grains and compute the electrical potential at the conductive region from the Poisson–Boltzmann equation in cases of mobile single and double donors. The solutions are evaluated numerically with a finite difference method. According to the Schottky-defect model for oxygen vacancies, the surface concentration of donors is kept a fixed parameter in the calculations. The chosen material parameters are those of tin dioxide, which is the key material of semiconductor gas sensors. It is found that mobile donors may strongly modulate the distribution of electrical potential around the neck contacts, and thus, modify the transducing properties of the microstructure of ceramic semiconductor gas sensors.
Studies of grain size effects in rf sputtered CdS thin films
Authors: Tsai C. T. , Chuu D. S. , Chen G. L. , Yang S. L.
Published: July 2002

CdS thin films with various grain sizes were produced by rf sputtering and in situ postannealing processes. For a series of annealing time intervals, the average grain sizes of an as-deposited thin film with thickness ∼4000 Å were found to vary from ∼280 to ∼1500 Å. Three bands located in the green, yellow, and red regions were observed in photoluminescence (PL) spectra of these as-deposited films. The temperature dependence of (PL) spectra of CdS microcrystals was investigated. The variations of the (PL) spectra with average grain size and thickness of CdS thin films were also studied. It was found that the intensity of the yellow band was increased as increasing the film thickness while the intensity of the red band was decreased as the grain size of the film became larger. The peak positions of the yellow and red bands were found to be blue-shifted as the films became thinner.
Application of the principle of minimum entropy production to shock wave reflections. I. Steady flows
Authors: Li H. , Ben-Dor G.
Published: July 2002

Based on new experimental results of Chpoun, Passerel, Li, and Ben-Dor [J. Fluid Mech. 301, 19 (1995)] and numerical results of Vuillon, Zeitoun, and Ben-Dor [J. Fluid Mech. 301, 37 (1995)] regarding the shock wave reflection transitions from regular to Mach reflection and from Mach to regular reflection in steady flows of perfect gases which contradicted the present understanding regarding these processes [Hornung and Robinson, J. Fluid Mech. 123, 155 (1982)], we present a new approach for better understanding the supersonic flow deflection over straight wedges and the transition of steady shock wave reflections over straight wedges. The new approach is based on the principle of minimum entropy production which enables one to choose the physical (stable) solutions out of a variety of possible mathematical ones. To the best of our knowledge the new transition criteria which are proposed in this study agree with all the available experimental results.
Electronic effects of ion mobility in semiconductors: Mixed electronic–ionic behavior and device creation in Si:Li
Authors: Chernyak Leonid , Lyakhovitskaya Vera , Richter Shachar , Jakubowicz Abram , Manassen Yishay , Cohen Sidney R. , Cahen David
Published: July 2002

Micrometer-sized homojunction structures can be formed by applying strong electric pulses, at ambient temperatures, to Li-doped, floating zone n-Si. Two such junctions, arranged back to back, act as a transistor, as evidenced by electron-beam-induced current and current–voltage measurements. The structures are created during a time ranging from ∼100 ms to a few seconds, depending on the size of the structure. The phenomenon is similar to what was observed earlier in CuInSe2 and was explained there by thermally assisted electromigration of Cu. In the case of Si doped with Li we can use secondary-ion-mass spectrometry to detect the redistribution of Li after electric-field application. Such a redistribution is indeed found and corresponds to an n+-p-n structure with the p region extending at least ∼20 μm into the bulk of Si. Structures created in Si doped with Li in this way are stable for at least 13 months after their creation. We ascribe this to the large difference between Li diffusivity at the local temperature that is reached during structure formation (∼400 °C; 10−8 cm2/s) and at room temperature (∼10−15 cm2/s).
Efficient dye-sensitized charge separation in a wide-band-gap p-n heterojunction
Authors: O’Regan Brian , Schwartz Daniel T.
Published: July 2002

We report the fabrication and performance of a dye-sensitized p-n heterojunction formed from a planar interface between two wide-band-gap semiconductors, n-TiO2 and p-CuSCN, which contains an intervening monolayer of a sulforhodamine B dye. When exposed to visible light, the photoexcited dye molecules transfer electrons to the n-TiO2 and holes to the p-CuSCN. The absorbed-photon-to-current efficiency (APCE) is ≳70% and the open circuit voltage is ≊500 mV. This heterojunction is the solid-state analog of the dye-sensitized photoelectrochemical interfaces used in photography and photovoltaics. The high quantum efficiency and voltage show that it is possible to simultaneously optimize both the dye/n-type and dye/p-type interface for efficient forward charge injection and slow charge combination in a solid-state device.
Magnetoelastic and pressure effects at the antiferro–ferromagnetic transition in Hf1−xTaxFe2−y alloys
Authors: Morellon L. , Algarabel P. A. , Ibarra M. R. , Arnold Z. , Kamarád J.
Published: July 2002

Magnetostriction measurements using high-pulsed magnetic fields up to 14 T and thermal expansion measurements under hydrostatic pressure up to 12 kbar have been performed in Hf1−xTaxFe2−y alloys with x=0.17 and 0.15 and y=0.02. These compounds have a first-order magnetic phase transition from an antiferromagnetic (AF) high-temperature state to a ferromagnetic (F) low-temperature state at TAF–F=246 and 290 K, respectively. This transition is accompanied by a volume expansion from the low-volume AF state to the high-volume F state of ΔV/V≊0.56% and 0.38% for x=0.17 and 0.15, respectively. Hydrostatic pressure decreases significantly the AF–F transition temperature, whereas the thermal expansion anomaly becomes more pronounced. The dependence of TAF–F on pressure follows a quadratic behavior and TAF–F reaches a value of 106 K at 10.5 kbar for x=0.17. In search of high magnetostrictive materials, we have found a giant volume magnetostriction value (e.g., ω≊0.7% for the x=0.17 compound) in these alloys at a moderate applied magnetic field within the AF phase near room temperature, making these alloys potential candidates for magnetostrictive transducers.
FeAl underlayers for CoCrPt thin film longitudinal media
Authors: Lee Li-Lien , Laughlin D. E. , Lambeth D. N.
Published: July 2002

B2 ordered FeAl films with a small, uniform grain size have been produced by rf diode sputter deposition on glass substrates. CoCrPt films grown on FeAl underlayers were found to have the (101̄0) lamellar texture. The in-plane coercivities (Hc) of the CoCrPt/FeAl films are comparable to those of the CoCrPt/Cr films and they can be further improved by inserting a thin Cr intermediate layer between the CoCrPt and the FeAl layers. By employing a MgO seed layer or a (002) textured Cr seed layer, (001) textured FeAl can be obtained. However, the (001) FeAl underlayer only induces a weak (112̄0) textured CoCrPt. Thus no improvement in Hc over those produced on unseeded FeAl underlayers was observed.
Noncontact measurement of ultrasonic attenuation during rotating fatigue test of steel
Authors: Ogi Hirotsugu , Hirao Masahiko , Minoura Kiyoshi
Published: July 2002

Acoustic resonance technique has been applied to monitor the fatigue damage process of steel pipes exposed to rotating bending fatigue. The technique incorporates a superheterodyne spectrometer and an electromagnetic acoustic transducer (EMAT). The EMAT was newly developed for this purpose, and uses the magnetostrictive mechanism of ferromagnetic metals and excites and detects axial shear waves traveling around the sample pipe with axial polarization. Noncontact ultrasonic spectroscopy permits the accurate determination of the resonant frequency and the attenuation coefficient throughout the fatigue life. The attenuation coefficient shows a sharp peak around 80%–90% of the life. The evolution is interpreted as reflecting dislocation multiplication, depinning, and formation of cell structures, which is supported by transmission electron microscopy observations.
Effects of H, OH, and CH3 radicals on diamond film formation in parallel-plate radio frequency plasma reactor
Authors: Ikeda M. , Ito H. , Hiramatsu M. , Hori M. , Goto T.
Published: July 2002

Diamond films were successfully synthesized in both parallel-plate radio frequency (rf: 13.56 MHz) CH4 and CH3OH plasmas with injection of H and OH radicals generated in the remote microwave (2.45 GHz) H2/H2O plasma. Effects of H, OH, and CH3 radicals on the diamond film formation in the rf plasma reactor were investigated by the formation of diamond films employing radical injection technique and the measurement of density in the plasma. Under the condition of diamond film formation, CH3 density was measured by infrared diode laser absorption spectroscopy (IRLAS). The kinetics of CH3 in rf CH4 and CH3OH plasmas with injection of H and OH radicals were evaluated from the results of optical emission spectroscopy and lifetime of CH3 radicals estimated by IRLAS.
Study of the nanocrystalline Fe73.5Nb4.5Cr5Cu1B16 alloy by the radio-frequency-Mössbauer technique
Authors: Kopcewicz M. , Grabias A. , Škorvánek I.
Published: July 2002

The influence of Cr on the structural and magnetic properties of iron based amorphous and nanocrystalline alloys is studied for the Fe73.5Nb4.5Cr5Cu1B16 alloy by an unconventional technique which combines the Mössbauer spectroscopy with the effects induced by the radio-frequency (rf) magnetic fields (rf collapse and rf sideband effects). The nanocrystalline bcc-Fe phase, formed by annealing the amorphous precursor for 1 h at temperatures 490 °C–550 °C, was embedded in the retained amorphous matrix. The conventional Mössbauer measurements allowed the identification of three types of phases in the nanocrystalline alloy: (i) the retained amorphous matrix, (ii) the nanocrystalline bcc-Fe phase, whose abundance increased with increasing annealing temperature, and (iii) the interfacial phase formed at the bcc-Fe grain boundaries. The rf collapse effect observed in the Mössbauer spectra of the samples exposed to the rf field of 60.9 MHz permits the study of the magnetic anisotropy in all phases present. The rf collapse effect occurs only in the amorphous phase, thus revealing that the magnetic anisotropy of the amorphous matrix is significantly smaller than that encountered in the nanocrystalline phase. The rf-Mössbauer experiments performed as a function of the rf field intensity allowed the determination of the distributions of the anisotropy fields in the nanocrystalline-amorphous composite alloy. The rf sidebands effect reveals a strong reduction of magnetostriction related to the formation of the nanocrystalline phase.
Nitrogenation of the magnetic compound R(Fe,M)12
Authors: Yang Jinbo , Mao Weihua , Yang Yingchang , Ge Senlin , Zhao Zhenjie , Li Fashen
Published: July 2002

The diffusion mechanism of nitrogen atoms in ThMn12-type crystal structure compounds was investigated by using x-ray diffraction, Mössbauer spectroscopy measurements, thermopiezic analysis, and differential thermal analysis. The studies indicate that the distribution of nitrogen atoms in a R(Fe,M)12 particles with intermediate N content is characterized by a nitrided region and an unnitrided region. The results confirmed that this two-phase region is stable, and the nitrogen atoms do not diffuse further into the particle. Based on the characteristics of the nitrogenation, a trapping diffusion model is applied to the R(Fe,M)12 system. On the basis of this study high performance magnetic powders of NdFe10.5Mo1.5Nx were successfully prepared.
Whiskers in indium tin oxide films obtained by electron beam evaporation
Authors: Castañeda S. I. , Rueda F. , Dı́az R. , Ripalda J. M. , Montero I.
Published: July 2002

Indium tin oxide thin films consisting mainly of whiskers have been deposited on glass by electron beam evaporation. Low deposition rates (35 Å/min) and substrate temperatures in the 120–400 °C range were used. Morphology by scanning electron microscopy, crystal structure, energy dispersive analysis of x-rays, and x-ray photoelectron spectroscopy compositions, optical and conducting properties of films have been studied as a function of temperature of growth and further annealing in air. Whiskers associate and produce flatter surfaces, the grain size increases from ≈390 Å to ≈790 Å, keeping however its fibrous structure after 400 °C-30 min annealing. In films deposited at temperatures below 200 °C, next to cubic In2O3, tetragonal Sn and cubic In2Sn2O(7−x) appear. During growth and after air annealing Sn4+ segregates to the surface, attaining Sn/In concentration ratios of 4.6. On air annealing the optical transmittance and electrical resistance increase, in some cases from 2% to 90% and by a factor of about 4, respectively.
Effect of sample preparation on the magnetic and magnetocaloric properties of amorphous Gd70Ni30
Authors: Foldeaki M. , Chahine R. , Gopal B. R. , Bose T. K. , Liu X. Y. , Barclay J. A.
Published: July 2002

Certain applications of magnetic materials require the knowledge of the magnetocaloric effects, i.e., the adiabatic change of temperature or the isothermal change of the entropy upon application or removal of magnetic field. While the isothermal magnetic entropy change can be calculated from magnetic data only, the calculation of the adiabatic temperature change requires the knowledge of the field-dependent specific heat as well. To compare magnetocaloric effect results obtained from magnetic-only, thermal-only, or combined methods requires the evaluation of the mutual reliability of all methods. In crystalline materials it usually does not present a problem to perform thermal and magnetic measurements on the same sample or at least on samples of identical state. For amorphous materials, unfortunately, thermal measurements are extremely difficult to perform on the ribbons themselves so usually pellets pressed from powdered ribbons, with silver as a binder, are applied. After the magnetic entropy change calculated from thermal measurements performed on such a composite did not agree with the data obtained from magnetic measurements performed on the original ribbon, magnetic measurements were carried out on the pellet and its predecessor powders. Comparison of the results revealed that the pellet’s properties do not reflect the properties of the original ribbon. However, comparison of magnetic and thermal measurements carried out on the pellet itself show good agreement if proper numerical methods are used for evaluation. The study concludes that amorphous ribbons are far more competitive for certain applications than the thermal measurements, performed on the pellet only, would indicate.
Full magnetization process of 3d−4f hard magnetic materials in ultrahigh magnetic fields (an example: RFe11Ti)
Authors: Kuz’min M. D. , Zvezdin A. K.
Published: July 2002

The prospects of using the free-powder high-field magnetization method for a quantitative study of inter-sublattice exchange interaction in 3d−4f hard magnetic materials are analyzed. Such analysis is stimulated by the availability of pulsed magnetic fields ∼103 T generated by implosion. Particular attention is paid to effects due to magnetic anisotropy, essential for these materials. The 3d−4f ferrimagnets where both sublattices contribute positively to the easy-axis anisotropy are shown to be suitable objects of study by the free-powder method, because (i) anomalies in their low-temperature magnetizatization curves are sharp and (ii) anisotropic effects can be allowed for without quantitative knowledge of the anisotropy constants. Moreover, these “good” hard magnetic materials can be brought into metamagnetic regime by diluting the rare earth sublattice with nonmagnetic yttrium; then, regardless of the anisotropy constants, the magnetization curve at low temperatures has just one steplike anomaly, the threshold field being equal exactly to the molecular field acting on the rare earth.
Material transport during excimer-laser nitriding of iron
Authors: Illgner C. , Schaaf P. , Lieb K.-P. , Queitsch R. , Barnikel J.
Published: July 2002

The surface topology and nitrogen concentration profiles of iron irradiated with pulses of an excimer laser in a nitrogen atmosphere were studied by means of optical and scanning electron microscopy, surface profilometry, energy-dispersive x-ray spectroscopy, and resonant nuclear reaction analysis. The observations are combined to distinguish several mechanisms contributing to the material transport: ablation, redeposition of nitride from the plasma and pressure-induced lateral flow of the molten iron towards the edges of the laser spot (piston mechanism). Numerical estimates of the time and spatial evolution of temperature and pressure at the surface led to average rates of the material transport in good agreement with the experiment.
Kinetics and characterization of plasma grown aluminium oxide
Authors: Four S. , Devine R. A. B. , Vallier L.
Published: July 2002

The anodization of aluminium in a microwave excited O2 plasma has been studied at temperatures less than 100 °C. Thirty nanometers of oxide were grown in times substantially less than one hour. The growth kinetics follow those expected using the constant current growth mode. X-ray diffraction, Fourier transform infrared absorption, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electrical studies were carried out. The oxide is amorphous and stoichiometric, the as-grown films have high electrical conductivity. The method may be well suited for the formation of protective coatings.
A comparative analysis of permanent magnet-type bearingless synchronous motors for fully magnetically levitated rotors
Authors: Charpentier J. F. , Lemarquand G.
Published: July 2002

Radial instability of synchronous motors is important data to design magnetic bearings. Moreover, original motor structures must be proposed to decrease the instability. In this article, four structures with a permanent magnet rotor, six poles, and the same main mechanical dimensions are analyzed and compared. The first concerns a rotor with six tiles of permanent magnets radially magnetized and adhered to an iron core. The second is a rotor with six axial permanent magnets tangentially magnetized and separated by iron pole pieces, where the shaft is amagnetic. The third design proposes a rotor with six contiguous tiles of permanent magnets tangentially magnetized and an amagnetic shaft. In the fourth structure each north pole is made up of two contiguous tiles of permanent magnets tangentially magnetized in opposite direction and each south pole is made up of an iron pole piece. The shaft of this structure is amagnetic. The stator structure and the currents in stator windings produce a six poles flux distribution. A finite element method program is employed to study the forces and the torques. The four structures are designed to provide the same motor performance (torque). The radial instability is modeled by outcentering the rotor. The relationships between the radial force and the type of structure are analyzed. The result is that the third structure is the best solution for fully magnetically levitated rotors. It has a small instability and does not generate any disturbing force whose frequency is the double of the rotation frequency. This structure also has good properties to be used as a radial magnetic bearing.
Metal–insulator transition induced by O16−O18 oxygen isotope exchange in colossal negative magnetoresistance manganites
Authors: Babushkina N. A. , Belova L. M. , Ozhogin V. I. , Gorbenko O. Yu. , Kaul A. R. , Bosak A. A. , Khomskii D. I. , Kugel K. I.
Published: July 2002

The effect of O16→O18 isotope exchange on the electric resistivity was studied for (La1−yPry)0.7Ca0.3MnO3 ceramic samples. It was found that at y=0.75, the substitution of O16 by O18 results in the reversible transition from a ferromagnetic metal (FM) to charge ordered (CO) insulator at zero magnetic field. The applied magnetic field (H⩾2 T) transformed the sample with O18 again to the metallic state and caused the increase in the FM transition temperature TC of the O16 sample. As a result, the isotope shift of TC at H=2 T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope exchange, giving rise even to the metal–insulator transition, is discussed in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the CO and FM phases.
Design and construction of a sensitive nuclear magnetic resonance force microscope
Authors: Barrett T. A. , Miers C. R. , Sommer H. A. , Mochizuki K. , Markert J. T.
Published: July 2002

We report our progress in the design and construction of a sensitive and versatile nuclear magnetic resonance force microscope. Improvements over previous designs include the use of higher Q(Q≈105–107), single-crystal double-torsional mechanical oscillators for force detection and the development of extremely convenient positioning and approach capabilities. We describe both a demonstration experiment using large (∼1 cm) torsional oscillators and the micromachining of the small (∼100 μm) torsional oscillators.
Control of double diffusion front unintentionally penetrated from a Zn doped InP layer during metalorganic vapor phase epitaxy
Authors: Otsuka N. , Kito M. , Ishino M. , Matsui Y. , Toujou F.
Published: July 2002

Unintentional Zn diffusion during metalorganic vapor phase epitaxy causes serious damages in semiconductor devices. In this work, profiles of unintentionally diffused Zn atoms from a p-InP layer to the adjoining InP substrate during growth of the p-InP layer are measured by secondary ion mass spectrometry. Zn diffusion profiles with a double diffusion front, which is composed of a shallow front with high Zn concentration and a deep front with low Zn concentration, are investigated as an approach to controlling unintentional diffusion. Diffusion depth of each front is controlled in proportion to Zn dosage, which is proposed as a value calculated as Zn concentration without regard to saturation limit. The diffusion depth for the growth time of 60 min increases in proportion to the Zn dosage as the slope of 0.16 μm/1018 cm−3 for the shallow front and that of 0.32 μm/1018 cm−3 for the deep front at a growth temperature of 600 °C. The deep front expands two times faster than the shallow front, which is normally observed as a p-n junction. Zn concentration at which unintentional Zn diffusion occurs is determined to be more than 2×1017 cm−3. Therefore, the penetration of Zn atoms into the active region of semiconductor devices should be observed when unintentional diffusion takes place. Furthermore, even at low Zn concentration, the introduction of a kick-out mechanism is proposed to explain the diffusion coefficient of the unintentional diffusion.
Optical second-harmonic generation in sputter-deposited AlN films
Authors: Kiehne G. T. , Wong G. K. L. , Ketterson J. B.
Published: July 2002

Results of a study of optical second-harmonic (SH) generation in AlN films deposited on borosilicate glass by reactive direct current magnetron sputtering are reported. As determined by x-ray diffraction (XRD), the films were highly c-axis oriented. The transmitted SH signal for film thickness ranging from 340 to 7800 Å was measured. The signal was consistent with the existence of a dead layer (in which no SH was generated) on the film surface with an effective thickness of ∼300 Å. A set of 7800-Å-thick films were deposited at substrate temperatures from ambient to Ts=400 °C. For films deposited at 100 °C or higher, minimal variation in the SH signal with Ts was found. Values of |d33|=4 pm/V and |d31|=0.04 pm/V, with d33 and d31 having the same sign, were obtained for Ts=400 °C. The approximate tilt angle of the optic axis of the films with respect to the substrate surface normal was determined. XRD results showed that the tilt was due to a tilt of the crystallographic texture axis.
Lateral overgrowth mechanisms and microstructural characteristics of bulk-like GaN layers grown by sublimation method
Authors: Wang Jie , Fareed R. S. Qhalid , Hao M. , Mahanty S. , Tottori S. , Ishikawa Y. , Sugahara T. , Morishima Y. , Nishino K. , Osinski M. , Sakai S.
Published: July 2002

The selective overgrowth method has been used to grow bulk-like GaN layers by sublimation method. Si and SiO2, which have a different evaporation rate, thermal conductivity, and thermal expansion coefficient, have been chosen as mask materials. The effect due to the reduction of dislocation density with different mask materials has been discussed. The lateral growth rates strongly depend on the direction of the mask stripe. For the stripe windows aligned in GaN〈11̄00〉 direction, the lateral growth rate is approximately four times higher than with stripe direction in GaN〈112̄0〉. The microstructure of selectively regrown GaN has been investigated by transmission electron microscopy, scanning electron microscopy, and cathodoluminescence to understand the lateral growth mechanisms in sublimation. The threading dislocations in the region of laterally regrown GaN are extended in two different ways. First, the threading dislocations are perpendicularly propagated into the top surface in the window region. In this case, the density of the threading dislocation is about 109 cm−2 within the window regions of the mask and is reduced to 106 cm−2 in the lateral overgrowth region of the mask due to termination of further propagation of dislocation by the mask. Second, the direction of propagation of dislocations is changed parallel to the c plane in laterally overgrown GaN, and finally, it changes in the direction perpendicular to the c plane in the middle region of the mask.