bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetooptical polar Kerr effect and reflectivity of terbium iron garnet between 2 and 6 eV
Authors: Thuy N. P. , Višňovský Š. , Prosser V. , Krishnan R. , Vien T. K.
Published: February 2003

The complex polar Kerr magnetooptic effect and reflectivity of Tb3Fe5O12 ferrimagnetic garnet between 2 and 6 eV and the corresponding dielectric tensor element spectra are reported. The spectra are similar to those of Y3Fe5O12. The main differences observed in Tb3Fe5O12 consist in the increase of the values of both diagonal and off-diagonal tensor elements above 4eV and in the splitting in the off-diagonal element spectra near 5.3eV. It is suggested that the strong transition near 4.4eV present in both Y3Fe5O12 and Tb3Fe5O12 involves the states which are localized mostly at the tetrahedral iron ion. The low energy Kerr ellipticities are consistent with the observed near infrared Faraday rotation.
High magnetic field study of antiferromagnetic sulfur La2Fe2S5
Authors: Plumier R. , Sougi M. , Lecomte M.
Published: February 2003

Orthorhombic double sulfur La2Fe2S5 (TN = 88 K) contains Fe2+ on both octahedral and tetrahedral sites. Each type of site is aligned on chains parallel to [001]. Previous neutron diffraction work shows both the existence of three distinct magnetic structures in the temperature ranges : TN≳T≳T1 (T1 = 30 K), T1≳T≳T2 (T2 = 17 K), T<T2 and the appearance of a nuclear dimerization along [001] at T1 and along [100] at T2. Detailed magnetization measurements up to 15 Tesla and at various temperatures also show distinct behaviours in these temperature ranges. Whereas at T≳T1 the magnetization increases linearly with H at T1≳T≳T2 and starting at 11.5 Tesla a departure from linearity is observed. At T<T2, this departure which then starts at 8.5 Tesla is more pronounced and ends at 13.5 Tesla. On the other hand, at T<T2 and H<8.5 Tesla, we observe that the magnetization curve is made of two linear parts intersecting at H = 5 Tesla in such a way that the upper part extrapolates to the origin of the (M,H) diagram whereas a weak ferromagnetic moment μo (T) is obtained from the lower part. These observations are related to the progressive erasure of the dimerization respectively along [100] at T<T2 and along [001] at T<T1 through magnetoelastic coupling in an applied magnetic field.
Implantability of small bubble diameter garnet films
Authors: Vella-Coleiro G. P. , Wolfe R. , Blank S. L. , Caruso R. , Nelson T. J. , Rana V. V. S.
Published: February 2003

Measurements of anisotropy in implanted bubble films indicate that in addition to straining the lattice, implantation also has the effect of suppressing the growth-induced anisotropy. After annealing at 1000 °C, most of the as-grown anisotropy is restored, which points to oxygen defects as the most likely mechanism for the effect. The Curie temperature has been found to be lowered by as much as 70 °C by implantation at a typical device dose, and the anisotropy of the implanted layer varies quite rapidly with temperature at elevated temperatures. The results indicate that with proper choice of material parameters and implantation conditions safisfactory bubble propagation can be obtained in high density small bubble diameter devices based on ion-implanted propagation patterns over a wide temperature range.
Application of artificial domain control
Authors: Kuroki K. , Fukawa K. , Wada T.
Published: February 2003

Artificial domain control has been applied to grain oriented Si-Fe. Lines are scribed on the surface of the sheet by a ball with 1.0 mm diameter, on one side of sheet surface. Directions of scribing are cross grain, with grain, and 10 °, 20 °, 30 °, 45 °, 60 ° from the rolling direction. Spacing of lines is 10mm. Scribing produces slight plastic deformation at the surface of the sheet. Scribing in the cross grain direction reduced total loss in the rolling direction, 7% at a flux density of 1.7 Tesla. Scribing in the cross grain direction causes refinement of 180 ° domains which are the primary structure in (110) [001] oriented Si-Fe. Scribing in the with grain direction improves the total loss in the cross grain direction. Scribing 30 ° to 60 ° to the with grain improves the total losses in both the grain and cross grain direction. The improvement in total loss by scribing may be caused by slight local plastic deformation. Heat treatment, which causes recovery, cancels the effect of scribing.
Vibration induced magnetization
Authors: Schneider C. S. , Semcken E. A.
Published: February 2003

Brown’s theory of stress-induced magnetization has been extended using the irreversible differential susceptibility, χirr(H), and Kondorsky’s rule beyond the Rayleigh region with the concepts of macroscopic stress field, Hσ, and reversible stress sensitivity. A graphical representation of the susceptibility integrals is given and simplified results for Rayleigh stresses confirmed experimentally for mild steel along with details of magnetization change throughout the first cycle. The fraction of stress-active or 90 ° domain walls was determined from the fit of the data to the theory to be f = 0.61±.02 in excellent agreement with Brown’s prediction of (√2)/(1+√2) = 0.59. Continued symmetric tension/compression cycling of Rayleigh stresses generates increased magnetization equal to the p-series times the first cycle magnetization, where p is not less than two, its value at the coercive field. Thus vibration-induced magnetization converges rapidly, never exceeds π2/6 times the first cycle magnetization, and does not contribute to significant long term instability.
Magnetostriction of some hexagonal ferrites
Authors: Licci F. , Rinaldi S.
Published: February 2003

With the aim of beginning a systematic characterization of the magnetoelastic properties of the hexagonal ferrites we measured the room temperature magnetostriction in a number of these materials. The analysis of the experimental results allows us to conclude that: a) the saturation magnetostriction in hexaferrites is of the same order of magnitude as in the cubic spinels; b) again in analogy with the spinels λ∥ is always negative, the Fe2+ containing samples being the only exception; c) the ions inducing the larger magnetostriction are cobalt and nickel; d) there are no indications of minima in the magnetostriction associated with compensation of the anisotropy, such compensation being obtained by varying the composition.
Magnetic and structural properties of Rh substituted Co-Cr alloy films with perpendicular magnetic anisotropy
Authors: Kobayashi K. , Ishida G.
Published: February 2003

RF sputtered Co0.78−xCr0.22Rhx (where x is 0–0.06) alloy films for high density perpendicular recording were studied. First, Co-M (M = Cr, Ti, V, Mo, Pd, and Rh) alloy films were studied. They exhibit hcp crystallization and have a high orientation of the c-axis normal to the film plane. However, they have a smaller coercive force (less than 300 Oe), and with the exception of Co-Cr, they do not have a columnar structure or satisfy the relation Hk ≳4πMs. Next, Co-Cr-Rh alloy films were studied. They also exhibit hcp crystallization and their structure is columnar. They show perpendicular magnetic anisotropy similar to that of Co-Cr, and in particular, a higher c-axis orientation was obtained. The ΔΘ50, half the width of a rocking curve of a (002) peak, is about 20–40% smaller than that of Co-Cr. By measuring the recording characteristics of Co-Cr-Rh disks (on an anodized aluminum substrate), a maximum recording density of 23,000FRPI was obtained.
Magnetic behaviour of narrow track thin-film heads
Authors: Druyvesteyn W. F. , Raemaekers E. L. M. , Verhaar R. D. J. , de Wilde J. , Fluitman J. H. J. , Groenland J. P. J.
Published: February 2003

The influence of the trackwidth on the performance of thin film heads has been tested. Results of experiments on the wafer have indicated an increase in the head efficiency with decreasing trackwidth. This was underlined by measurements of the head fringe field and tape recording experiments. A model which takes the domain structure into account has been developed to interpret this behaviour.
Exchange induced unidirectional anisotropy at FeMn-Ni80Fe20 interfaces
Authors: Tsang C. , Heiman N. , Lee Kenneth
Published: February 2003

We have systematically investigated exchange coupled films of sputter deposited Ni80Fe20/FeMn and FeMn/Ni80Fe20 and obtained films with high exchange bias and low coercive forces. The variation of film properties with deposition conditions as well as with the permalloy and FeMn thicknesses have also been studied. The results demonstrated a strong dependence of exchange bias effect (HUA) on the amount of γ-phase FeMn, the amount of impurities, as well as the abruptness of the transition profile at the interface. In addition, our results have also raised a number of new questions concerning the magnetic state of the interface and the origin of the interface coupling phenomena.
Magnetic properties, aging effects and application potential for magnetic heads of Co-Fe-Si-B amorphous alloys
Authors: Shiiki K. , Otomo S. , Kudo M.
Published: February 2003

Zero magnetostrictive alloys (Co0.94Fe0.06)-Si-B about 5mm wide and ∼25 μm thick were prepared by the single roller type quenching method. By choosing proper compositions and by annealing at temperatures higher than the Curie temperature, the alloys with saturation magnetic flux density of 0.95 T in which permeabilities are as high as 500 at 5 MHz, were obtained. The permeabilities at frequenceis below about 100 kHz decrease drastically even by aging at temperatures as low as 100°C. At high frequencies above about 500 kHz, no significant changes occur in the permeabilities by similar aging. Therefore, the alloys are suitable for high frequency applications. Recording and reproducing characteristics of a video head made of the amorphous alloy were measured at frequencies from 1 to 6 MHz, using Co-γ-Fe2O3 magnetic tapes. The output signals for the head are higher than those for both Mn-Zn ferrite heads and Sendust alloy heads.
Increases in magnetic hyperfine field at the surface of ultra-thin epitaxial Fe films (invited)
Authors: Tyson J. , Owens A. H. , Walker J. C. , Bayreuther G.
Published: February 2003

Previous investigations of ultra-thin epitaxial Fe (110) films grown on Ag (111) have indicated that there is a measurable increase at 4.2 K in the magnetic hyperfine field compared with bulk value in iron atoms in the first three surface layers of the films. As these films were produced in ultra-vacuum and then removed for study by transmission Mössbauer spectroscopy it was necessary to provide a protective overcoat to prevent oxidation of the surface. Because of this it was not possible to rule out interaction of the Fe surface with the overcoat layers as a cause of the increased surface hyperfine field. A series of new films have been made of isotopically pure 56Fe. A thin probe layer of 57Fe ranging in thickness from 4–10 Å was then deposited on the film surface and a variety of different overcoat layers subsequently chosen to protect these films. Overcoating materials included Ag, Au, Cu, Ge, MnF2, and NaCl. While there were differences in the hyperfine fields and isomer shifts of the 57Fe probe layer associated with different overcoat materials, the overall results suggest that the increased hyperfine field is related to an increased localization of the 3d electrons for Fe atoms at or near the surface. An observation of a decrease in 4s electron density indicated by the isomer shift data is consistent with this view and is in qualitative agreement with the theoretical work of Wang and Freeman.
Magnetic properties of monodispersed submicromic α-Fe2O3 particles
Authors: Muench George J. , Arajs Sigurds , Matijević Egon
Published: February 2003

Magnetic properties are reported of recently prepared spherical hematite (α-Fe2O3) particles of narrow size distributions with average diameters (d) varying between 20 and 300 nm. Mass magnetization (σ) of these particles has been determined as a function of temperature (T) up to 1000 K and of magnetic field (H) as high as 22 kOe. Specifically, magnetic behavior of α-Fe2O3 particles of d = 300 nm is described in detail. Their Curie (Néel) temperature has been determined to be 960 K. The Bean-Livingston plot indicates a change in magnetic anisotropy from higher symmetry at room temperatures to unidirectional behavior at elevated temperatures. This observation is consistent with the change of saturation and remanent magnetization with T. The measurements of σ on different size particles indicate that below 100 nm the particle magnetic susceptibility increases with decreasing size.
Magnetic structure of small NiFe2O4 particles
Authors: Morr A. H. , Haneda K.
Published: February 2003

The magnetic structure of small NiFe2O4 particles has been investigated. Samples (in the few hundred angstrom size range and up) were prepared by chemical precipitation followed by a heat treatment at relatively low temperatures. Mössbauer spectra of the 57Fe nuclei, obtained with a longitudinal magnetic field applied, unambiguously establish that a non-collinear structure exists. Further, the magnetic moment at low temperatures is appreciably lower than the value reported for bulk material. A model is proposed in which the NiFe2O4 particles consist of a core with the usual spin arrangement and a surface layer with atomic moments inclined to the direction of the net magnetization. The temperature dependence of this structure is also reported.
Magnetic properties of melt-spun Pr-Fe alloys
Authors: Croat J. J.
Published: February 2003

The magnetic properties of a series of amorphous Pr1−xFex alloys (.45⩽x⩽ .90) prepared by spin melting are reported. Use of high purity constituents significantly increases the range over which Roentgen amorphous alloys can be obtained by this technique. The ratio of spontaneous to saturation magnetization (at 95 kOe) indicates that, over the composition interval 0.45⩽x⩽ .75, these alloys have sperimagnetic structures in which the Fe is ferromagnetic while the Pr moments are randomly oriented. At high applied field these alloys form collinear ferromagnetic structures. At reduced temperatures (20K) coercivities of over 4800 kA/m (60 kOe) were observed. Although exhibiting the pronounced temperature dependent behavior characteristic of non S-state rare earth-transition metal alloys, room temperature coercivities were still appreciable; a maximum room temperature value of 224 kA/m (2.8 kOe) was found at composition x = 0.6.
Zn2W: Improvements of magnetic properties by copper substitution
Authors: Licci F. , Pareti L. , Rinaldi S.
Published: February 2003

With the aim of evaluating the possibility of improving the properties of BaZn2Fe16O27 (Zn2-W) as a permanent magnet material, we have measured the effects on its room temperature magnetic properties, of substituting zinc with copper and, for comparison, with nickel. We have found that the substitution of 50 to 70 moles percent of zinc with copper improves the properties of the starting compound, having the following effects: it leaves the high saturation magnetization of the Zn2-W unchanged or even slightly increased; it induces an increase of the anisotropy constant K1 up to 20% and of the Curie temperature Tc up to 20%; it reduces the sintering temperature significantly. Some observed data have also been interpreted on the basis of the magnetic structure typical of this class of materials.
Magnetic fields produced by the human eye (invited)
Authors: Katila T. , Maniewski R. , Poutanen T. , Varpula T. , Karp P. J.
Published: February 2003

The retina and the pigment epithelium of the human eye contain sources of bioelectric currents, which give rise to intra- and extraocular electric current densities. This paper first gives a review on the magnetic fields arising from ocular currents: the magneto-oculogram (MOG) and the magnetoretinogram (MRG). A mathematical model is presented for calculation of the field distributions and a comparison with experimental data is made. Finally results from experiments on motion and light induced changes in ocular magnetic fields are used to determine retinal current densities.
Possible risks to human lungs from magnetometric dust clearance experiments
Authors: Sterling T. D.
Published: February 2003

Cohen, Arai and Brain did a magnetization study on smokers and nonsmokers from which they conclude that the dust clearance ability of the cigarette smoker’s lungs is markedly impaired. Their conclusion may be incorrect because they overlooked that during the magnetization phase of their experiment, iron oxide clusters were preferentially formed in smoker’s bronchi because of their high mucus content and consequent low resistance to redistribution of particles. Prudence dictates avoidance of the Cohen, Arai, Brain type study until health hazards related to this work are investigated.
Stress distributions in silicon crystal substrates with thin films
Authors: Isomae Seiichi
Published: February 2003

The three-dimensional stress distributions in a substrate due to a rectangular film deposited on the substrate are calculated by linear elastic theory on the assumption of a concentrated force at the film edge. Furthermore, on the basis of the results, resolved shear stress distributions in a (001) silicon crystal substrate are calculated to evaluate the character of the dislocations generated at the film edge. These calculated results are compared to experimental ones obtained in a sample of a (001) silicon substrate with a 3×3-mm-square pattern of Si3N4 film. The results show that the glide planes and Burgers vectors of the dislocations generated at the film edge can be determined by a simple rule.
AlGaAs grown by metalorganic chemical vapor deposition for visible laser
Authors: Mori Yoshifumi , Watanabe Naozo
Published: February 2003

Doping efficiency of selenium hydride (for Se donors) to GaAs in metalorganic chemical vapor deposition was shown to be high and near unity, whereas that of sulfur hydride (for S donors) was nearly two orders lower. The difference was even greater with the addition of aluminum to grow AlxGa1−xAs. Doping efficiency of diethyl zinc (for Zn acceptors) was shown to be three to four orders lower than of Se. A higher partial flow ratio of arsenic to column III elements was necessary to grow high-quality layers of AlxGa1−xAs with larger x. Room-temperature cw operation of AlxGa1−xAs/AlyGa1−yAs double heterostructure visible (760–780 nm) lasers grown by MOCVD has been achieved. The planar lasers, with an oxide-insulated stripe structure 10 μm wide and 250 μm long showed a cw threshold current from 150 to 300 mA.
Diffusion marker experiments with rare-earth silicides and germanides: Relative mobilities of the two atom species
Authors: Baglin J. E. E. , d’Heurle F. M. , Petersson C. S.
Published: February 2003

A marker study of the silicides (and germanides) of rare-earth elements obtained from metallic thin films on Si (and Ge) substrates indicates that Si(and Ge) atoms constitute the dominant diffusing species during the formation of these two types of compounds. Rutherford backscattering is used to distinguish between pairs of elements having different atomic weights but very similar with respect to their chemical and metallurgical behavior. An experiment conducted with the diffusion bilayer sample Ge-Tb on Si confirms the results obtained with bilayers of the type Y-Tb on Si (or Ge). Examination of the structure of the silicides which are formed provides clues about the difference in mobility between the Si and the metal atoms.
Molecular-beam epitaxial growth of InP homoepitaxial layers and their electrical and optical properties
Authors: Asahi Hajime , Kawamura Yuichi , Ikeda Mutsuo , Okamoto Hiroshi
Published: February 2003

InP epitaxial layers are grown on (100) surfaces of InP substrates by molecular-beam epitaxy (MBE). Layers grown at a substrate temperature of 450 °C with beam intensity ratio 124P+4/115In+?100 have mirror-smooth surfaces. Undoped epilayers are n type, with a carrier concentration of 1–3×1016 cm−3 and an electron mobility of 3000 cm2/V sec at room temperature. The photoluminescent (PL) intensity is comparable to that of bulk and liquid phase epitaxial InP, while the intensity of deep-level emission is smaller than that of them. PL topographs of MBE epilayers are featureless as compared with those of bulk crystals. Deep-level transient spectroscopy shows three levels of electron trap centers, while hole trap centers cannot be detected.
Temperature and strain dependences of electrical resistance of Ni-Si-B amorphous alloys
Authors: Fukamichi K. , Kimura H. M. , Masumoto T.
Published: February 2003

Ni-Si-B amorphous alloys were prepared from the melt by a rapid quenching method in order to investigate the temperature and strain dependences of electrical resistance. The room-temperature coefficient of electrical resistance becomes very small in a wide temperature range by adjusting the metalloid content, and its sign changes around the total conduction electron CE≊1.5 with the resistivity ρ≊150 μΩ cm. A linear relationship between the strain and the change in the electrical resistance is observed, and the strain gauge factor is estimated to be about 2.0. In addition, the electrical resistivity of these amorphous alloys is much higher than that of conventional strain gauge alloys, and shows no anisotropy in magnetic fields because they are paramagnetic. From these results, it is concluded that Ni-Si-B amorphous alloys are suitable for applications to strain gauge materials.
Electron tunneling at Al-SiO2 interfaces
Authors: Av-Ron M. , Shatzkes M. , DiStefano T. H. , Gdula R. A.
Published: February 2003

The Murphy-Good tunneling theory, modified with a Franz-type two-band dispersion relation, accurately represents emission of electrons from metals into SiO2 using parameters that are invariant with temperature and that agree with independent measurements. Parameters related to properties of the SiO2 do not change when different metal electrodes are used. Deviations of the measured I-V characteristic from the model calculation which occur at low field can be explained in terms of interfacial inhomogeneities in the effective barrier height. For thin dry SiO2 grown on boron-dope silicon, the effective size of the inhomogeneities increases with decreasing oxidation temperature.
The bias-dependent photoelectric barrier height of the Schottky diodes
Authors: Wu Ching-Yuan
Published: February 2003

An interfacial layer model is developed to interpret the bias-dependent photoelectric barrier height of the Schottky barrier diodes fabricated on the low doping substrate. It is shown that the barrier height shift of a reversely biased Schottky diode measured by the photoelectric method is dependent on the magnitude of the applied reverse bias. The origins of the barrier height shift are mainly due to the applied voltage drop across the interfacial layer and the image-force lowering. Comparisons between the developed model and the experimental results of the fabricated Al-nGaAs and Au-nGaAs Schottky barrier diodes are made; these strongly support the present model. Moreover, the interfacial layer properties deduced from the barrier height shift are in quantitative agreement with the ideality factors measured from the forward I-V characteristics of the n-GaAs Schottky diodes.
Electron microscopy study of the ferroelectric domains and domain wall structure in PbZr0.52Ti0.48O3
Authors: Goo E. K. W. , Mishra R. K. , Thomas G.
Published: February 2003

The crystallography of the domains and domain walls in lead zirconate titanate are studied using electron diffraciton and transmission electron microscopy. Both 90 ° and 180 ° domains are observed and the 90° domains are shown to be deformation twins with displacement along 〈110〉 on {110}. The thickness of the 90 ° domain wall is determined to be ≲100 Å.
Electroreflectance of ion-implanted GaAs
Authors: Brown R. L. , Schoonveld L. , Abels L. L. , Sundaram S. , Raccah P. M.
Published: February 2003

A systematic investigation of the electrolyte electroreflectance of GaAs with implanted Be, Se, and Si ions has been made. Topographical maps of carrier concentration and of implant-dependent modifications of the lineshapes have been obtained. The fluences for the implanted samples ranged from ∼1013 to 1015 ions/cm2. Using the E0 and E1 peaks, the lineshape variations have been mapped for the low- as well as high-fluence samples. The evidence suggests that at high fluence the extreme structural damage, resulting from implantation, generates an amorphous layer which upon annealing recrystallizes by a mechanism similar to liquid phase epitaxy. Depending on the fluence of the implant, apparent peak shifts of as much as 80 meV have been observed. These are explained as definitely not due to gross changes in the E1 and E1+Δ1 transitions but rather either due to a modification of the simple parabolic band model or due to a definite folding of one of these structures with a third, probably of excitonic origin and analyzed here for the first time. Moreover, the study of GaAs with Be and Se implants proved that electroreflectance is an unusually sensitive tool for the study and characterization of inversion layers.
Preparation of high-purity InP by the synthesis, solute diffusion technique
Authors: Kubota Eishi , Sugii Kiyomasa
Published: February 2003

High-purity InP crystals were prepared by the synthesis, solute diffusion (SSD) technique. By vacuum baking of raw indium at 900 °C for 6 h, the first-to-freeze part of InP had a carrier concentration of ND−NA = 6.4×1014 cm−3 at 300 K and a mobility of μ = 79 100 cm2/V sec at 77 K. It is concluded that S and/or Si contained in In raw material are dominat donor impurities in the SSD-InP crystal, because their contents can be decreased by the vacuum baking.
Study of electrical and chemical profiles of Si implanted in semi-insulating GaAs substrate annealed under SiO2 and capless
Authors: Feng M. , Kwok S. P. , Eu V. , Henderson B. W.
Published: February 2003

We have studied, compared, and correlated the chemical redistribution of Cr and Si, electrical profiles, mobilities, carrier concentrations, and channel conduction currents in Si-implanted semi-insulating GaAs substrates annealed with and without a SiO2 cap under an As4 and H2 ambient for 20 min at 830 and at 860 °C. Differences observed between capless and SiO2-encapsulated annealing methods include the position and activation of net donor concentration peaks, the gradient of the leading edge of the profiles, and mobilities. An explanation of these differences is provided using a Cr redistribution model and a charge neutrality equation where this complex electrical behavior cannot be explained solely by the implanted impurity atoms and thermal diffusion effects.
Laser spark ignition and extinction of a methane-air diffusion flame
Authors: Schmieder Robert W.
Published: February 2003

Laser sparks have been used to ignite and extinguish a methane/air diffusion flame. Simple shock models of strong explosions and convective transport appear capable of accounting for the probabilities of ignition and extinction as a function of the position of the spark.
Charge-exchange neutral-atom filling of ion diodes: Its effect on diode performance and A-K shorting
Authors: Prono D. S. , Ishizuka H. , Lee E. P. , Stallard B. W. , Turner W. C.
Published: February 2003

We present a model, supported by experimental evidence, showing how high-density charge-exchange neutral atoms (<10 keV) are created in a partially ionized anode plasma and flow into an ion-diode, anode-cathode (A-K) gap. The buildup of the neutral atoms in the A-K gap and their ionization can cause early A-K shorting which limits high-power and/or long-pulse, ion-diode operation. Ways to avoid the charge-exchange phenomena are mentioned. The ability to produce large-pulsed fluxes of energetic neutrals may have unique applications of its own. For example, high rep-rate spark gaps could benefit from the reduced gas load of an injected short pulse of high-density neutral atoms. Also discussed is the possibility of using an ion-diode geometry to fill a spark-gap cavity with neutrals and then initiate total volume breakdown by ion-impact ionization, thereby avoiding inductive electron filaments.
New bistable liquid-crystal twist cell
Authors: Berreman D. W. , Heffner W. R.
Published: February 2003

We have shown experimentally that some cholesteric liquid crystals in cells with parallel or skew director orientations at the two surfaces may be made to have two bistable laminar states that can be switched either way by applying temporary electric potentials between the surfaces. Numerical solutions of the Oseen-Frank equations in the laminar case, augmented with cholesteric twist and electric field terms, confirm the bistability. Numerical solutions of the Leslie-Ericksen hydrodynamic equations in the laminar case, similarly augmented, describe the switching mechanism. We have made and operated several such cells.
Unit sphere description of liquid-crystal configurations
Authors: Thurston R. N.
Published: February 2003

In any one-dimensional liquid-crystal configuration, the unit director n(z) generates a path on the unit sphere. Paths that satisfy the equilibrium equations are characterized by special properties that are independent of the boundary conditions. This paper explores these properties for nematic liquid crystals, and applies them to delimit the kinds of equilibrium states that are possible and to simplify calculations needed in the design of liquid-crystal displays. The applications include simple approximate formulas for (1) the relation between the director angle at the boundary ϑb and at the midplane ϑm for twisted states, (2) the dependence on elastic constants of the critical value of ϑb below which the 180° twisted state disappears, being replaced by its topologically equivalent planar state [G. Porte and J. P. Jadot, J. Phys. 39, 213 (1978)], and (3) the region of elastic constant space for bistability of topologically equivalent planar and 180° twisted states. The unit sphere is also applied to specify the paths of nonequilibrium states that are useful in stability studies.
An x-ray diagnostic for light-ion current measurements
Authors: Bleach R. D. , Nagel D. J. , Mosher D. , Stephanakis S. J.
Published: February 2003

A technique to determine the number and current density of MeV protons in an intense beam was tested on the GAMBLE II generator. Diode current and voltage and an absolute measurement of K-line radiation emitted from a 6-μm-thick aluminum target were used to determine the number and current density of protons incident on the target. Time-dependent x-ray measurements can be used to infer variations in the ion-beam current density.
Plasma Si nitride—A promising dielectric to achieve high-quality silicon MIS/IL solar cells
Authors: Hezel R. , Schörner R.
Published: February 2003

Substantial advantages of plasma Si nitride, for the first time applied to silicon MIS inversion layer (MIS/IL) solar cells, are demonstrated: The highest positive interface charge densities ever used for this type of solar cell (up to 7.2×1012 cm−2), absolute stability of the charges up to the nitride despoition temperature (220 and 300 °C, respectively), excellent passivation of the entire cell, and good AR coating properties. High uv sensitive MIS/IL solar cells were fabricated with these layers on p–Si (100). AM1 efficiencies of 15% (active area) at 25 °C were obtained.
Characteristics of two-step and two-photon-excited emissions in 14NH3
Authors: Pinson P. , Delage A. , Girard G. , Michon M.
Published: February 2003

Stimulated emissions between 12 and 291 μm have been obtained in 14NH3 utilizing two-step and two-photon excitation. Twelve new lines were observed. A discussion of the parameters available to control the emissions is given.
Equilibrium ion content of water vapor in air
Authors: Carlon Hugh R.
Published: February 2003

New data are presented giving equilibrium ion concentrations in moist air as functions of temperature and humidity. The ions are thought to be decomposition products of neutral water clusters which are found whenever cluster generation mechanisms such as evaporation or combustion are active. The temperature dependence of the ion concentration can be modeled closely by the equilibrium ion product of water. The electrical conductivity of moist air is found to have a quadratic humidity dependence, suggesting that presently accepted electrostatic and insulator theories should be reviewed.
Analysis of gain suppression in undoped injection lasers
Authors: Yamada Minoru , Suematsu Yasuharu
Published: February 2003

This paper gives an analysis and discussion of gain suppression in injection lasers which have an undoped active region and an index guiding structure. In previous papers, we used a semiclassical density-matrix analysis to show that an injection laser with an updoped active region has a nearly, but not perfectly, homogeneous (or uniform) gain property under operating conditions due to the mode coupling effects by phase synchronization of electrons to the lasing field. The gain of adjacent modes is well suppressed by the oscillating mode, and single-longitudinal-mode operation is obtained in undoped injection lasers. However, such suppression depends closely on the spacial distribution of the resonating field and injected carrier density. In this paper, the suppression effect is examined theoretically considering electronic intraband relaxation, effects from the standing wave of the lasing field, spatial diffusion of carriers, etc. When the relaxation time is larger than 3×10−13 sec, the gain shows ’’hole burning,’’ namely, strong nonuniformity across the spectral or energy distributions, and, at the same time, the gain of some resonating modes is increased. Single-longitudinal-mode operation is not obtained in such a strongly inhomogeneous laser. When the relaxation time is smaller than 2×10−13 sec, the gain can be seen to be nearly homogeneous, and the gain of nonoscillating modes is sufficiently suppressed, that is, lower than that at threshold, because of the strong-mode-coupling effect. The relaxation time of GaAs is expected to be approximately 1×10−13 sec, implying 0.1% of excess suppression. The spatial distribution of the resonating field and induced ’’spatial hole burning’’ of carriers tends to increase the gain of higher transverse modes, but only weakly affects the fundamental transverse modes when the oscillating mode is the fundamental mode. It is then necessary to design the laser so that such higher transverse modes are cut off. The results of this analysis explain the experimental data of well-designed lasers which have an undoped active region and an index guiding structure. Such a gain suppression effect is crucial for the operation of injection lasers in a single-longitudinal mode.
Plasma dynamics of an arc-driven, electromagnetic, projectile accelerator
Authors: Powell John D. , Batteh Jad H.
Published: February 2003

A model is analyzed to study the electromagnetic acceleration of projectiles using a device known as the rail gun. Current is conducted between the rails by a plasma arc which drives the projectile. The analysis includes determining the electromagnetic fields within the gun and solving the fluid-mechanical equations of the plasma under the assumption that the flow parameters are steady in a frame that accelerates with the arc. Specifically, a set of coupled equations is derived which, when solved, yields the properties of the arc and the acceleration of the projectile. A limiting-case analytic solution to the equations is found, and an iterative technique is employed to solve the equations numerically in the more general case. The results of the calculation are applied to analyze the arc in an experiment recently carried out by Rashleigh and Marshall. Some approximate scaling relations, which indicate how the properties of the arc vary with the dimensions of the rail gun, the mass of the projectile, the mass of the arc, and the accelerating current, are then derived. The results of the calculation are compared with those of others and some suggestions for future investigations are given.
Boundary-layer model of field effects in a bistable liquid-crystal geometry
Authors: Cheng Julian , Thurston R. N. , Berreman D. W.
Published: February 2003

Electric-field-induced switching between equilibrium configurations in certain bistable liquid-crystal geometries is governed by the motion of disclinations, propelled by elastic distortions of the equilibrium states subjected to applied fields. In this paper and the next (paper II), we describe the distortions and energies of bistable planar horizontal and vertical states, and nonplanar twist states in a tilted geometry, using exact numerical solutions of the equilibrium equations as well as a ’’boundary-layer’’ approximation in the high-field limit. The calculations illustrate the manner in which the distortions become concentrated in boundary layers within a coherence length from the surface, and show the convergence of the planar and nonplanar vertical states at relatively low fields. Implications for the switching mechanism are discussed. In paper II, the boundary-layer model is used to describe the forces governing the movement of disclinations in bistable switching, producing a quantitative description of their velocity and justification for a mobility-limited switching time.
The Propagation of disclinations in bistable switching
Authors: Cheng Julian , Thurston R. N.
Published: February 2003

The boundary-layer model is used to calculate the energy density of the forces that govern the movement-of-strength 1/2 disclinations in a bistable tilted liquid-crystal geometry during switching. The distortions of the bistable states and the disclinations separating them are studied. The mobility is calculated for vertical and transverse applied fields and compared with experimental data, showing good agreement especially at high fields. Implications about a switching mechanism are discussed.
Low-temperature thermally stimulated luminescence of high quality quartz
Authors: Malik D. M. , Kohnke E. E. , Sibley W. A.
Published: February 2003

An investigation of the thermally stimulated luminescence (TSL) from quartz irradiated at 95 K has been made below room temperature. The synthetic quartz specimens were of very high quality with a Q of about 106. Such material contains few impurities and the TSL is weak. Nonetheless, it was determined that three regions of TSL glow peak interest exist. Region I (115–145 K) contains a single sharp peak having a maximum in its broad spectral emission at about 450 nm; Region II (145–185 K) is quite complex in structure, and is dependent upon defect content and sample treatment; Region III (185–270 K) can be eliminated by electrodiffusion (sweeping) techniques or by irradiation at temperatures above 250 K prior to the 95-K irradiation. Both Regions II and III show broadband spectral emission with maxima near 380 nm. The intensity of the TSL glow peak in Region III appears to correlate well with the presence of Al-Na+ and/or Al-Li+ centers as determined from other measurements, suggesting it may provide yet another method for quartz crystal quality evaluation.
Low-temperature thermoluminescence studies of Al23
Authors: Cooke D. Wayne , Payne Irvin W. , Santi Ronald S.
Published: February 2003

Thermoluminescence (TL) and emission spectra studies of single-crystal A1203 have been conducted in the temperature interval 10-300 K. Glow curves resulting from either x or UV radiation at 10 K were recorded and analyzed to yield thermal activation energies (E) and frequency factors (s) associated with each glow peak. A typical glow curve exhibits maxima at 60 K (E = 0.17 eV, s = 5×1012 s−1), 100 K (E = 0.22 eV, s = 8×109 s−1), 220 K (E = 0.56 eV, s = 7×1010 s−1), 260 K (E = 0.72 eV, s = 3×1012 s−1), and 290 K (E and s could not be deduced). Spectral emission from these peaks are characterized by predominant bands centered near either 330 or 410 nm. Specifically, the TL peaks at 60, 100, 220 K exhibit the band near 330 nm, whereas the 260- and 290-K peaks display the 410-nm band. Thermal annealing, optical excitation, and photobleaching experiments were also conducted in efforts to deduce the recombination mechanisms responsible for the glow peaks. Experimental results suggest that the 60-, 100-, and 220-K peaks are due to the thermal release of trapped holes which recombine with electrons of the F centers producing F+ centers in an excited state. De-excitation of these centers produces 330-nm radiation. Moreover, the 260- and 290-K peaks are attributed to the thermal release of trapped electrons that recombine with existing F+ centers converting them to excited-state F centers, which relax to the ground state and produce 410-nm radiation.
The reaction of fluorine atoms with silicon
Authors: Flamm Daniel L. , Donnelly Vincent M. , Mucha John A.
Published: February 2003

Fluorine atoms etch silicon with a rate, RF(Si) = 2.91±0.20×10−12T1/2nFe−0.108 eV/kT Å/min, where nF (cm−3) is the atom concentration. This etching is accompanied by a chemiluminescent continuum in the gas phase which exhibits the same activation energy. These phenomena are described by the kinetics: (1) F(g)+Sisurf→SiF2(g), (2) SiF2(g) +F(g) →SiF*3(g), (3) SiF2(g) +F2(g) →SiF*3(g) +F(g), (4) SiF*3(g) →SiF3(g) +hνcontinuum where formation of SiF2 is the rate-limiting step. A detailed model of silicon gasification is presented which accounts for the low atomic fluorine reaction probability (0.00168 at room temperature) and formation of SiF2 as a direct product. Previously reported etch rates of SiO2 by atomic fluorine are high by a constant factor. The etch rate of SiO2 is RF(SiO2) = (6.14±0.49)×10−13nF T1/2e−0.163/kT Å/min and the ratio of Si to SiO2 etching by F atoms is (4.74±0.49)e−0.055/kT.
Temperature dependence of minority carrier lifetime in single-crystal and polycrystalline Si solar cells
Authors: Mathur P. C. , Sharma R. P. , Saxena P. , Arora J. D.
Published: February 2003

Measurements of minority carrier lifetime in the base region of single-crystal and polycrystalline silicon solar cells have been made using the open-circuit voltage decay method in the temperature range 77–500 K. For single-crystal cells, the lifetime is governed by Hall-Shockley-Read theory in the low-temperature region while significant contribution of band to band Auger recombination is found at high temperatures. A temperature dependence ∼T−n was found for the band to band minority carrier lifetime in the high-temperature region with n∼0.3. In polycrystalline cells, the lifetime is found to increase exponentially with temperature, which is interpreted as due to the presence of recombination barriers on the surface.
Effect of annealing on resistivity and photoconductivity of solar-grade polycrystalline silicon and on solar-cell performance
Authors: Jain G. C. , Chakravarty B. C. , Prasad A.
Published: February 2003

The effect of annealing on the restistivity and photoconductivity of solar-grade polycrystalline silicon of grain size 100–1200 μm has been examined in the temperature range 900-1100 °C. Both resistivity and photoconductivity strongly depend on the temperature of annealing and grain size. The atmosphere in which annealing takes place, e.g., air, nitrogen, argon, or vacuum does not seem to have any effect on the results. Heat cycling of the starting material causes a reduction in the short-circuit current of the solar cell.
Conduction polarization in sodium germanate glasses
Authors: Doi Akira , Day Delbert E.
Published: February 2003

Only one thermally stimulated depolarization current (TSDC) peak was found in germanate glasses containing from 0.19 to 32.5 mol% Na20, whereas comparable silicate glasses exhibit two such peaks. Equations are developed showing that the distortion of the equilibrium Na+-ion distribution by an applied electrical field produces a polarization in general agreement with the observed TSDC peak. It is proposed that the TSDC peak is due to dc conduction.
Spatially resolved photoconductivity of polycrystalline silicon
Authors: Scholl F. W.
Published: February 2003

Spatially resolved photoconductivity measurements are used to deduce information describing majority carrier current flow and minority carrier grain boundary recombination in solar grade polycrystalline silicon. Relative to the bulk silicon diffusion velocity, grain boundary recombination velocity of SGB = 0.28 is measured. Measurements using two superposed light sources show intensity dependent nonlinear recombination processes at the grain boundary. Numerical calculations of grain boundary recombination velocity are presented that clarify the microscopic origin of these nonlinearities.
Barrier heights at the polycrystalline silicon-SiO2 interface
Authors: Hickmott T. W. , Isaac R. D.
Published: February 2003

Capacitance-voltage measurements of the dependence of flat-band voltage of polycrystalline-silicon (polysilicon) gate metal-oxide-silicon capacitors on oxide thickness are used to measure the position of the Fermi level in degenerately doped polysilicon as a function of the doping of the polysilicon. For boron-doped polysilicon, the experimental difference between the Fermi level in polysilicon and the intrinsic level in the substrate silicon, φms, is ∼0.54 V. The Fermi level is pinned within 20 meV of the valence band edge. For arsenic-doped and phosphorus-doped polysilicon, evaluation of φms is complicated by the occurrence of positive charge at the polysilicon-SiO2 interface which is generated by reaction of doped polysilicon with SiO2. If such positive charge is close to the polysilicon-SiO2 interface it acts as a dipole layer and lowers the values of φms. If positive charge is slightly deeper in the SiO2 it contributes to negative bias instability due to electron injection into polysilicon capacitors. If electron exchange of positive charge with electrons in polysilicon does not occur, positive charge generated at the polysilicon-SiO2 interface appears as fixed positive charge. For As-doped polysilicon, φms∼−0.46 V; for P-doped polysilicon, φms∼−0.52 V. These experimental values of φms are influenced by positive charge at the polysilicon-SiO2 interface. We conclude that the Fermi level for degenerately doped n-type polysilicon is pinned close to but below the conduction band edge and does not depend on doping for carrier concentrations between 3×1019 and 4×1020 cm−3.
Anisotype multiheterojunction eutectic composites: The CdTe-GaTe system
Authors: van Hoof L. A. H. , Albers W.
Published: February 2003

A general introduction is given to the in situ growth of anisotype multiheterojunctions. Structures based on the CdTe-GaTe system are discussed in some detail. Electrical measurements including I-V characteristics and the photovoltaic effect are reported.
Voltage dependence of the dark and photocurrents in semiconductor-electrolyte junctions
Authors: El Guibaly F. , Colbow K. , Funt B. L.
Published: February 2003

Expressions for the dark and photocurrent of a semiconductor-electrolyte junction are derived. Charge transfer kinetics, surface recombination, recombination in the space-charge region, and series resistance are discussed in our model. A measurement of the I-V characteristics, both in the dark and under illumination, aids in the estimation of the parameters of the device. The model agrees with the general observed quantum efficiency variation with voltage.
Effect of adding HCl to the oxidizing ambient on characteristics of metal-oxide-semiconductor capicitors
Authors: Hamasaki M.
Published: February 2003

Electrical properties of HCl oxide and dry oxide are investigated and compared. Surface state density near midgap is independent of HCl content added in the oxidizing ambient. The excellent performance of metal-oxide-semiconductors using HCl oxide is attributed to the cleaning effect of HCl, and not to the chlorine incorporated in the oxide. Incorporated chlorine causes a positive charge in the oxide and creates a surface state near the conduction-band edge. The amount of positive charge is less than that of incorporated Cl by several orders of magnitude, and the major portion of Cl is in a neutral charge state. A negative charge arises near the metal/SiO2 interface, and for thin oxide, surface state density near midgap is increased.