bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion mobility measurements in a positive corona discharge
Authors: Stearns Richard G.
Published: July 2002

Two methods are examined for the measurement of the positive-ion mobility in a positive cylindrical corona discharge. The first method employs the novel technique of monitoring the temporal decay of the cathode current following the cessation of the corona near threshold. A detailed analysis of the current decay is offered, and comparison with experimental results on coronas in nitrogen and dry air yield values of positive-ion mobility that agree well with those found in the literature. The second technique for the measurement of the positive-ion mobility is based upon the current-voltage relationship of the discharge near threshold. The classical interpretation of the current-voltage data is found to yield mobility values that are anomalously large. It is suggested that this classical interpretation is incomplete, as it does not consider the dependence of the anode electric field on corona current. One possible cause of such a current dependence is considered in detail: Joule heating of the gas near the anode may increase electron impact ionization, through a reduction in the gas density, in turn lowering the anode electric field. Analysis indicates that such a thermal feedback mechanism is of the correct magnitude to explain the overestimation of positive-ion mobility from the classical interpretation of the current-voltage relationships in the nitrogen and air coronas.
Polystyrene thin film formed by synchrotron radiation chemical vapor deposition
Authors: Yamada Hitomi , Nakamura Makoto , Katoh Hisato , Hayakawa Tetsuo , Morita Shinzo , Hattori Shuzo , Ohashi Haruhiko , Shobatake Kosuke
Published: July 2002

Formation of polystyrene thin film by the synchrotron radiation chemical vapor-deposition method was investigated using a styrene monomer. Polystyrene film was deposited at the irradiated area and vicinity along the irradiated area on a Si substrate. The deposition rate depended on the monomer gas pressure, substrate temperature, and x-ray wavelength. Polystyrene film at the irradiated area was insoluble in benzene solvent, while that at the unirradiated area was easily dissolved. A patterned film deposition could be successfully performed under an irradiation of synchrotron radiation through a Ni mesh mask. The pattern profile was influenced by the gap length between the Si substrate and mask and a clear pattern was obtained after benzene treatment.
The effect of heat-treatment environment on the superconducting properties of plasma-sprayed YBa2Cu3Oy deposits
Authors: Gudmundsson B. , Wang H. , Neiser R. A. , Katz B. , Herman H. , Suenaga M.
Published: July 2002

Plasma-sprayed YBa2CU3Oy coatings consist of a nonsuperconducting tetragonal phase with an a/c ratio of 1/3 (c=11.61) in the as-sprayed condition. This phase is tentatively assigned to the solid solution Y1(Ba2−xYx) Cu3O7+δ. Heat treatment of this phase at 930 °C/24 h in oxygen results in orthorhombic symmetry, an expansion of the c axis (11.66 Å), and the appearance of superconductivity. In this study it is shown that heat treatment in argon at 850 °C prior to the oxygen heat-treatment leads to a crystal structure which closely matches the desired YBa2Cu3Oy (c=11.68), raises Tc, and narrows the transition width.
Nucleation and defect generation in lattice matched and mismatched heteroepitaxial layers in the GaAs/AlxGa1−xP/Si system
Authors: George T. , Weber E. R. , Nozaki S. , Wu A. T. , Noto N. , Umeno M.
Published: July 2002

The heteroepitaxial growth of GaAs on Si substrates at 700 °C using AlxGa1−xP buffer layers grown at 900 °C by metalorganic chemical vapor deposition is studied using transmission electron microscopy. This GaAs/AlxGa1−xP/Si system is unique in that it allows one to study separately the influence of lattice-mismatch (GaAs/AlxGa1−xP) and polar/nonpolar (AlxGa1−xP/Si) effects on the heteroepitaxial growth of compound semiconductors. Island-type nucleation is observed for both effects acting independently, though three-dimensional growth due to the polar/nonpolar effect (AlxGa1−xP/Si) can be suppressed by increasing the Al content (x>0.2) of the AlxGa1−xP layers. The nucleation of the GaAs appears to be modified by the nature of the AlxGa1−xP buffer layers, i.e., whether they are in the form of islands or planar layers. Single-crystal, 3-μm-thick layers of GaAs can be grown directly at 700 °C on the AlxGa1−xP buffer layers without resorting to a two-step technique. This result demonstrates that purely lattice-mismatch or polar/nonpolar effects cannot disrupt the crystallinity of the compound semiconductor layer. The surface morphology as well as the nature of defects generated in the 3-μm-thick GaAs films can be correlated to the nucleation mode of the GaAs.
Excimer-laser doping into Si thin films
Authors: Sera K. , Okumura F. , Kaneko S. , Itoh S. , Hotta K. , Hoshino H.
Published: July 2002

The fabrication of n+ and p+ silicon thin film by using a combination of ‘‘spin-on-glass’’ and XeCl excimer-laser doping is described. The doping can be achieved by rapid dopant atom diffusion into molten silicon from a spin-coated film containing the dopant. This technology offers the advantages of process simplicity, low processing temperature, and ultrashallow high-concentration doping. The obtained sheet resistances (2 kΩ/⧠ for n+ and 9 kΩ/⧠ for p+) are acceptable for thin-film transistors (TFTs). The energy required for doping into a thin film was less than half of that for a silicon wafer. This is mainly due to the absorption rate difference between noncrystalline and crystalline silicon. This process appears extremely promising for TFT fabrication.
Influence of high-level injection on the impedance characteristics of GaAs-AlxGa1−xAs double-heterostructure laser diodes
Authors: Al-Alusi Mazin R. , Darling Robert B.
Published: July 2002

Existing analytical descriptions of the small-signal impedance characteristics of double-heterostructure laser diodes have been based upon the dynamics of a single carrier population (electrons) coupled to the photon density of the cavity. However, the high level of injection necessary to produce the carrier population inversion is more accurately described by a bipolar approach involving both the injected electrons and holes. A bipolar model is presented which includes high-level injection boundary conditions appropriate to the heterojunctions of a buried-channel laser diode. The inclusion of high-level injection conditions is shown to increase the threshold voltage for lasing and the small-signal impedance particularly for the case of thick active layers.
Y-Ba-Cu-O superconducting fibers and wires by spray pyrolysis on carbon fibers
Authors: Wang J. G. , Yang R. T.
Published: July 2002

Superconducting YBa2 Cu3 O7−x fibers and wires have been prepared by spray pyrolysis of metal nitrate precursors on a commercial carbon fiber substrate, followed by heating in air and annealing in O2. The fibers were characterized by x-ray diffraction, scanning electron microscope, and Tc and Jc measurements. The fibers consisted of well-aligned crystals and no carbon, with a Tc (zero) of 82 K and a Jc of 2150 A/cm2 in zero field. Ag-doped fibers were fabricated by adding AgNO3 in the precursor solution, and the Jc value nearly doubled with the addition of 4 wt. % Ag.
On the improvement of DyBa2Cu3O7−δ properties through better sintering
Authors: Seuntjens J. M. , Larbalestier D. C.
Published: July 2002

The sintering of DyBa2Cu3O7−δ has been improved by controlling powder size, sintering temperature, and sintering atmosphere. Sintering below the eutectic temperature has been explored for different temperatures and oxygen partial pressures. Sintering kinetics have been enhanced, yielding high density (up to 95%) and small grain size (down to 1.5 μm) with shorter sintering times and lower temperatures. Two sets of samples, one set containing 10-wt. % Ag2O in the precursor powder and one undoped set, were studied. The sintering rate decreased with decreasing temperature, even in samples sintered in low partial pressures of oxygen (which increase the oxygen vacancy concentration). The addition of Ag2O yielded a dispersion of Ag particles about one-half the DyBa2Cu3O7−δ grain size at grain boundary triple points. Ag tended to enhance grain growth slightly and did not improve the superconducting properties. Resistivity was as low as 220 μΩ-cm at 100 K. Transport critical current densities (Jct) were up to five times higher than in previous larger grain size samples that were sintered above the eutectic temperature. The best of the new samples achieved ∼100 A/cm2 at 4.2 K in fields of 1–7 T. This improvement occurred in spite of there being more than twice as much grain boundary surface area per unit volume. We conclude that the grain boundaries in sintered 123 compounds are not always barriers to current flow, and that increasing the proportion of nonbasal plane faced grain boundaries is important in raising Jct.
Analysis of thermal stress, fracture strength, and the effect of ion exchange on high average power phosphate glass slab lasers
Authors: Lambropoulos John C.
Published: July 2002

It has been recently demonstrated that it is possible to significantly alter the maximum power input required for mechanical failure of glass used for high average power laser applications by employing an ion exchange process that does not alter the optical properties of the strengthened glass. We present the analysis of the thermal stresses, fracture, and strengthening for the experimental geometry used. From this analysis the fracture strength of the untreated and treated glass can be estimated. Some suggestions for the control of thermal stresses during the operation of solid-state lasers using glass slab geometries are presented. The second part of this report presents a micromechanical analysis of the strengthening effect due to the ion exchange process in which the enhancement in fracture strength is correlated to the depth of the zone in which ion exchange has occurred, to the length of microscopic flaws present on the surface of the glass, and to the magnitude of the microscopic volume expansion due to the ion exchange process. In particular, we consider the cases where the depth of the treated zone is much smaller or much greater than the depth of surface flaws. The magnitude of the enhancement in fracture strength is calculated in terms of these microscopic quantities for some material properties typical of phosphate glasses.
Photo-induced electrical defects in low-temperature photochemical vapor-deposited silicon nitride films
Authors: Iborra E. , Lopez-Rubio J. A. , Esquivias I. , Sanz-Maudes J. , Rodríguez T.
Published: July 2002

The electrical properties of the photochemical vapor-deposited silicon nitride/silicon interface are presented as a function of deposition temperature (70 to 200 °C). High values of interface state density Nss (about 3×1012 cm−2 eV−1), an equivalent charge at the interface Qss (about 5×1011 cm−2), and an important injection-type hysteresis of the capacitance voltage C-V curves are observed in the as-grown material. Most defects are found to be generated during the deposition process by the ultraviolet illumination used to activate the chemical reaction of the gases. Low-temperature (250 °C) and short-time (30 min) annealings eliminate part of the defects, resulting in lower values of Nss (about 1×1012 cm−2 eV−1), Qss (about 5×1010 cm−2), and reduced injection-type hysteresis.
Measurement of atomic indium during metalorganic chemical vapor deposition
Authors: Hebner G. A. , Killeen K. P.
Published: July 2002

Atomic indium, produced by the pyrolysis of trimethylindium (TMIn) during metalorganic chemical vapor deposition, has been directly observed using resonant fluorescence spectroscopy. The indium fluorescence signal is linear with TMIn flow rate at a susceptor temperature of 500 °C above a small background threshold level. The threshold for the observation of an indium signal is 325 °C. Addition of trimethylantimony (TMSb) at concentrations less than those required for normal InSb epitaxial growth results in quenching of the indium signal.
Electron-beam plasma enhancement of oxidation in thin aluminum samples
Authors: Schneider Todd , Baron Miles , Edwards Dave , Gandy Rex , Fukai J.
Published: July 2002

In order to gain an insight into the effects of a space environment on materials, thin aluminum samples were exposed to an oxygen plasma produced by an electron beam. Using Rutherford backscattering spectrometry the samples exposed to the oxygen plasma were compared to samples exposed to ordinary oxygen gas. The comparison revealed a considerable increase in oxygen diffusion in the samples exposed to the charged particle environment. The amount of oxygen diffusion depends on the duration of the plasma exposure.
Zinc diffusion in III-V semiconductors using a cubic-zirconia protection layer
Authors: Bisberg J. E. , Chin A. K. , Dabkowski F. P.
Published: July 2002

Zinc was diffused into GaAs, Al0.38Ga0.62As, and GaAs0.6P0.4 using a 2000–3000-Å-thick yttria-stabilized cubic-zirconia (YSZ) protection layer to produce planar p-n junctions. The YSZ layer greatly reduced thermal decomposition of the semiconductor while allowing zinc to diffuse into the III-V semiconductors. The diffusion depth showed a square-root-of-time dependence for all samples protected with YSZ. Characterization of the GaAs diffused with the YSZ protection process indicates that the YSZ layer has virtually no effect on either the carrier concentration profile or activation energy. No thermal decomposition was observed by visual inspection following a diffusion using only elemental Zn on the GaAs, Al0.38Ga0.62As, or GaAs0.6P0.4 samples protected with a YSZ layer. Photoluminescence analysis shows that the YSZ-protected GaAs samples have higher luminescence efficiency relative to unprotected samples. Device fabrication has been demonstrated by combining the YSZ passivation process with selective area diffusion. Our results indicate that the YSZ diffusion procedure has greater tolerance to process variations than previously reported diffusion procedures for zinc in III-V semiconductors.
The effect of deposition rate on the growth of epitaxial Ge on GaAs (100)
Authors: Eres Djula , Lowndes D. H. , Tischler J. Z. , Sharp J. W. , Haynes T. E. , Chisholm M. F.
Published: July 2002

The role of deposition rate in the growth of Ge films on GaAs (100) was investigated using a new supersonic free-jet growth technique capable of achieving epitaxial growth rates several orders of magnitude higher than were previously available. The high growth rates are due to two factors: (1) the high arrival rate of digermane source molecules at a heated GaAs surface, and (2) the high thermal decomposition rate of digermane. Dramatic improvements in surface smoothness were observed with increasing deposition rate, while keeping all other deposition parameters fixed. When the arrival rate of digermane molecules was too high, amorphous films were deposited, in agreement with kinetic considerations. The supersonic free-jet growth technique and the microstructural and electrical properties of the resulting Ge films are described.
The dependence of Schottky barrier potential on substrate orientation in PtSi infrared diodes
Authors: Pellegrini P. W. , Ludington C. E. , Weeks M. M.
Published: July 2002

Platinum silicide Schottky barrier infrared diodes have been formed on p-type silicon substrates having both 〈100〉 and 〈111〉 orientations. The potential barrier to optically generated hot carriers has been measured and found to be 0.219 eV for 〈100〉 substrates and 0.313 eV for 〈111〉. Platinum-layer thickness was varied from 1 to 10 nm. The nearly 0.1 eV difference in Schottky barrier potential appears to depend only on the orientation of the silicon substrates.
The role of hydrogen dilution in deposition of a-SiC:H from silane/ethylene mixtures
Authors: Meikle Scott , Suzuki Yoshiko , Hatanaka Yoshinori
Published: July 2002

The effect of hydrogen dilution on deposition of a-SiC:H from silane/ethylene mixtures has been investigated by analyzing deposited films using optical absorption and x-ray photoelectron spectroscopy (XPS) measurements. Film deposition rate and stoichiometry are found to be sensitive to the hydrogen dilution rate and it is proposed that ethylene decomposes through a two stage reaction with atomic hydrogen. Films with similar stoichiometries deposited using different combinations of ethylene, silane, and hydrogen and are found to have the steepest optical absorption edge when the ethylene/silane ratio is low and when the hydrogen partial pressure fraction is at 80%–85% of the total pressure. XPS measurements show that the density of SiC bonds increases as the slope of the optical edge becomes steeper.
Suppression of an ordered fluid phase by admixture of small particles
Authors: Marcus M. A. , Andrews M. P.
Published: July 2002

Suspensions of fine particles of cobalt in a surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), were prepared by metal-atom synthesis. The particles were rods about 110 Å long by 30–40 Å wide. AOT in pure form shows a hexagonal columnar phase. The addition of only 2 vol % of Co particles suppresses this phase, as shown by optical microscopy and x-ray scattering. At lower Co contents, where the hexagonal phase still exists, segregation of Co particles to isotropic regions could be observed as the temperature was raised to the (H+I) two-phase region.
High-power, broad-band InGaAsP superluminescent diode emitting at 1.5 μm
Authors: Noguchi Yoshio , Yasaka Hiroshi , Mikami Osamu , Nagai Haruo
Published: July 2002

An InGaAsP superluminescent diode operating at 1.5 μm wavelength is successfully developed using a buried bent absorbing waveguide structure and antireflection coating to suppress lasing mode. Optical characteristics such as high output power (5 mW at 200 mA), broad-band spectral width (60–70 nm), short coherence length (about 30 μm), and low spectral modulation depth (less than 10%) are achieved. Injection current dependence of emitting wavelength and spectral width are also investigated.
Electron-beam-enhanced oxidation processes in II-VI compound semiconductors observed by high-resolution electron microscopy
Authors: Thangaraj N. , Wessels B. W.
Published: July 2002

Enhanced oxidation of ZnS and ZnSe semiconductor surfaces has been observed in situ during electron irradiation in a high-resolution electron microscope. The phase present at the surface region has been identified as ZnO by optical diffractogram and selected area electron diffraction techniques. For ZnS oxidation, both hexagonal ZnO having a random orientation and cubic ZnO in perfect epitaxial relationship with the bulk ZnS were observed. Enhanced oxidation of ZnSe to ZnO has also been observed under electron beam irradiation. However, only the hexagonal form was observed. The oxidation rates for both ZnS and ZnSe depended on electron flux but was independent of orientation. A model in which the oxidation process is limited by diffusion through the oxide film is proposed. By electron irradiation the diffusion rate is enhanced presumably by a nonthermal process.
Electron-optical-phonon interaction in binary/ternary heterostructures
Authors: Kim K. W. , Stroscio M. A.
Published: July 2002

The macroscopic dielectric continuum model is used to derive electron-optical-phonon interaction Hamiltonians for binary/ternary heterostructures containing both single and double heterointerfaces. The formulation presented in this work leads to a general prescription for the calculation of mode-strength coefficients in ternary-containing heterostructures. An illustration of these results is provided by exhibiting the mode strengths of the interaction Hamiltonians for the interface and the half-space longitudinal optical modes in a GaAs/AlyGa1−yAs single heterostructure.
Multiphoton ionization spectroscopy measurements of silicon atoms during vapor-phase synthesis of ceramic particles
Authors: Zachariah Michael R. , Joklik Richard G.
Published: July 2002

Resonance-enhanced multiphoton ionization spectroscopy has been applied to the problem of detection of gas-phase species in a dense particle-forming flow. Relative silicon atom profiles in an atmospheric pressure flame reactor producing silica particles have been made using a 2+1 ionization scheme. The results have shown that silicon atoms are confined to a very narrow time window in the reactor (<15 ms). In addition, the nonresonant background indicated the presence of ionizable clusters and could be a valuable tool for observing the presence and location of small clusters. The effect of varying silane loading changed both the location and magnitude of the silicon concentration observed. The results suggest that chain branching chemistry is important in the production of silicon and that enhancement of pyrolytic relative to oxidative processes occurs as the silane loading is increased. Finally, the role of charged particles on electron capture was investigated. It was found that significant attenuation of the electron current can lead to highly erroneous results.
As-cast magnets based on Fe-Nd-C
Authors: Grieb B. , Fritz K. , Henig E.-Th.
Published: July 2002

Fe14Nd2C (Φ) shows structural and intrinsic magnetic properties comparable to Fe14Nd2B. The phase Fe14Nd2C is found in long-time-annealed samples only (≳20 d at 850 °C) because of nucleation difficulties and slow growth kinetics. Compared to the Fe-Nd-B system the phase relations in the Fe-Nd-C system are unfavorable to produce sintered or even as-cast magnet materials, as manifested in the phase diagram presented. Fe14Nd2C is in equilibrium with either ferromagnetic and/or very corrosive phases, therefore the pure Fe-Nd-C material is useless. This situation can be changed by the addition of several elements to the Fe-Nd-C material: boron (even in small amounts of ≊0.05 mass %) accelerates the formation of Φ and reduces annealing times from weeks to hours; Cu added in the correct amount leads to new phase relations between Φ and NdxCuy intermetallic compounds. These intermetallics are nonmagnetic and low melting. Starting from as-cast material using the knowledge about the influences of substituants on phase relations and kinetics, a heat treatment can be chosen that leads directly to an isotropic, magnetically hard material with a rather small grain size (≲20 μm) and coercivities up to 1 T. The magnetization is comparable to isotropic Fe-Nd-B materials.
The influence of a new magnon-electron coupling on the temperature dependence of resistivity in disordered magnetic metals (abstract)
Authors: Lutovinov V. S.
Published: July 2002

It is well known that the anharmonic interaction between quasiparticles controls both the dynamic and transport properties of solids. Recently it was shown that paramagnetic impurities induce indirect magnon-magnon and magnon-phonon interactions in dielectric magnetic materials.1 These anharmonic couplings of an ‘‘impure’’ origin explain the unusual (peaklike) temperature dependence of magnon and phonon relaxation rates in magnetic dielectrics. Later, this idea was applied to disordered ferromagnetic metals and it was shown that in metals magnetic impurities induce effective coherent magnon-electron coupling2 which changes radically the picture of the conduction electron behavior in a weak localization regime. The aim of the present paper is to show that the novel coupling between magnons and conduction electrons results in a maximum in temperature dependent resistivity and is responsible for the nonmonotonous behavior of R(T), observed recently. The mechanism for coupling between magnons and conduction electrons due to impurity degrees of freedom is as follows. The RKKY interaction couples the host spins with the impurity ones, which in turn are coupled to the conduction electrons. In concentrated disordered magnetic metals this indirect coupling between magnons and electrons is stronger than the starting one (for the pure system) at low temperatures. The amplitude of effective magnon-electron coupling is proportional to the impurity subsystem magnetic moment and, hence, to the impurity concentration and to the impurity spin polarization <σ≳=tanh (E/2T), where E is the impurity local mode energy. In the range T≪E this mechanism gives R(T)∼T2, while in the range T≫E it gives R(T) ∼ T−1, with an obvious maximum in the intermediate range T≂E. The interplay of the mechanism under consideration with the weak localization mechanism (and/or Coulomb interaction) gives a minimum in resistivity in the low-temperature range.

An additional minimum at higher temperature is inevitable because of the interplay between the effective magnon-electron interaction of an ‘‘impure’’ origin and the usual (starting) magnon-electron interaction. Namely this temperature dependence was observed experimentally in Fe80−xCrxB20.3
Resonant electromagnetic excitation and detection of ultrasonic waves in thin sheets
Authors: Kawashima K. , Wright O. B.
Published: July 2002

A unified theory of the simultaneous electromagnetic excitation and detection of ultrasonic waves travelling in the through-thickness direction in conducting sheets in the presence of a static magnetic field is presented. What to our knowledge are the highest-frequency room-temperature measurements of this type are described for aluminium sheets of thickness as low as 20 μm for frequencies up to 120 MHz. Maxwell’s equations are solved for the geometry of a planar current sheet above a conducting sheet with sinusoidal time variation. It is shown how, from the solution of a single fourth-order differential equation for the magnetic vector potential, the coupled electromagnetic and elastic wave problem can be solved analytically. The effective transfer impedance is evaluated, a measure of the ultimate efficiency of the combined excitation and detection process. At acoustic resonance its amplitude is inversely proportional to the sum of the ultrasonic attenuation of the sample and the attenuation arising from the electromagnetic-elastic coupling. This high-frequency resonant method should open up a wide range of new applications for the nondestructive evaluation of thickness, ultrasonic attenuation, bonding, and delamination of thin sheets and coatings in the sub-10 μm to 1 mm thickness range.
Nearly diffraction-free CO2 laser beam
Authors: Onae A. , Kurosawa T. , Miki Y. , Sakuma E.
Published: July 2002

Nearly diffraction-free beams have been generated by a CO2 laser with a new type of cavity composed of a concave mirror and an output mirror with high reflectivity (99.4%) in the marginal part and low reflectivity (94.5%) in the central part. The beam propagation behavior is reproduced fairly well by the Fresnel–Kirchhoff integral of the Bessel–Gauss beam.
Characterization by Raman scattering, x-ray diffraction, and transmission electron microscopy of (AlAs)m(InAs)m short period superlattices grown by migration enhanced epitaxy
Authors: Bradshaw J. , Song X. J. , Shealy J. R. , Zhu J. G. , O/stergaard H.
Published: July 2002

We report growth of (InAs)1(AlAs)1 and (InAs)2(AlAs)2 strained layer superlattices by migration enhanced epitaxy. The samples were grown on InP (001) substrates and characterized by Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Satellite peaks in the x-ray data confirm the intended periodicity and indicate the presence of some disorder in the monolayer sample. The energies of the zone folded and quantum confined optic phonons are in reasonable agreement with calculations based on one-dimensional elastic continuum and linear chain models.
Plastic hollow fibers as a selective infrared radiation transmitting medium
Authors: Alaluf M. , Dror J. , Dahan R. , Croitoru N.
Published: July 2002

Plastic hollow waveguides (used as fibers) for infrared (IR) transmission were made from plastic tubes covered, on the internal wall, with a metal layer (Ag) and growing a dielectric thin (AgI) overlayer by direct iodination on it. The existence of several absorption lines at given wavelengths in the middle infrared (mid-IR) region is predicted theoretically and measured experimentally. From the wavelengths of absorption lines the thickness of the AgI film has been computed. The average thickness of the AgI in the hollow waveguide increased with the iodination time and with the concentration of the iodine solution. The crystal size of the AgI was increased with the increase of the AgI thickness. By controlling the iodination process it was possible to make waveguides which can be employed as filters for various wavelengths of the transmitted mid-IR radiation.
Magnetic properties of Ni/Pt multilayers
Authors: Krishnan R. , Lassri H. , Prasad Shiva , Porte M. , Tessier M.
Published: July 2002

We have grown Ni/Pt multilayers (ML) with and without Pt buffer layer, by evaporation under UHV conditions on glass and Si substrates maintained at 30 and 200 °C. The magnetization decreases with t(Ni) and no induced moment is found on Pt from polarization effects even at 5 K. The perpendicular magnetization loops for samples with t(Ni)≤17 Å are rectangular and coercivities as high as 4.7 kOe is obtained for t(Ni)=9 Å at 5 K. For the samples deposited at 20 °C, due to dispersion in the results, KS could not be calculated with accuracy though it is positive. But for the samples deposited on a Pt buffer layer at 200 °C, KS is found to be +0.17 erg cm−2 at 5 K and the volume anisotropy is also higher with respect to those deposited at 30 °C.
Strong-field effect in nanofabrication on chemically prepared silicon
Authors: Hetrick J. M. , Zheng X. , Nayfeh M. H.
Published: July 2002

We investigate the uniformity of scanning tunneling microscope nanofabrication on as-prepared chemically etched silicon. Our results show that continuous fabrication produces isolated nanoscale dots along the motion of the tip rather than uniform lines. These results are discussed with the aid of a self-limiting strong-field effect.
Band diagram of a HgTe-CdTe semimetal-semiconductor abrupt heterostructure
Authors: Djaloshinski L. , Goren D. , Nemirovsky Y.
Published: July 2002

The energy-band diagram and interface potentials at a HgTe-CdTe abrupt heterostructure are presented. An analytic approximation is formulated and compared to an exact (numeric) calculation of the interface potentials. The error introduced by the analytic approximation is negligible for a wide range of doping levels of the CdTe. The analysis predicts that HgTe forms ohmic contacts to p-type CdTe and rectifying junctions to n-type CdTe. Interface charges above 1012 cm−2 modify the interface potentials. Positive interface charge imposes depletion in p-type CdTe resulting in potential barriers that may degrade the ohmic properties of the contacts. The methodology presented in this study may be extended to additional semimetal-semiconductor heterostructures.
Effect of additional elements on the thermal relaxation of magnetic anisotropy in amorphous TbCo films
Authors: Suzuki Yoshio
Published: July 2002

The effect of additional elements on the thermal relaxation of magnetic anisotropy in amorphous TbCo films was studied. Tb-Co amorphous films with various additional elements were prepared, and their perpendicular anisotropy was measured after annealing. It was found that the addition of B or C is effective in suppressing thermal relaxation. By the addition of these elements the relaxation time for the magnetic anisotropy could be extended by a factor of 10. A simple model is proposed in which these light element atoms fill holes in an amorphous structure, thus suppressing changes in the atomic arrangement.
Study of alpha-radiation-induced deep levels in p-type silicon
Authors: Asghar M. , Iqbal M. Zafar , Zafar N.
Published: July 2002

Deep levels introduced by 5.48 MeV alpha particles in p-type silicon have been studied using deep-level transient spectroscopy. The generation rates of these defects have been obtained up to a dose of 1.2×1011 α particles/cm2. Detailed data have been obtained on the electrical characteristics of the two deep levels in the lower-half band gap at Ev+0.21 eV and Ev+0.35 eV and one level in the upper-half gap of silicon at Ec−0.25 eV introduced by irradiation. These characteristics include emission rate signatures, carrier capture cross sections, and their temperature dependence and deep-level concentrations. Detailed isochronal annealing measurements have been performed to obtain data on the annealing behavior of the deep-level defects and also to help identify these centers. Some interesting phenomena relating to temporal changes in our deep level spectra stimulated by minority carrier injection have been observed and discussed in the light of the available literature on radiation-induced defects in silicon.
Photocarrier spreading at a p-n junction
Authors: Gallant M. , Zemel A.
Published: July 2002

Continuous wave and pulsed optical beam induced current measurements were carried out on n-InP/n-InGaAs/n-InP double heterostructures which contain large areas of diffused InGaAs p-n junctions. The flat cw photocurrent and illumination-position independence of the transient photocurrent response, observed when the optical source spot illuminates a floating diode, demonstrates the effect of photocarrier spreading in a p-n junction. The very long photocarrier spreading length observed at low optical power may be an important parasitic coupling mechanism which should be considered in the isolation-design of integrated optoelectronic devices.
Electroluminescence in ZnS1−xTex:CeF3 thin-film devices
Authors: Sohn S. H. , Hyun D. G. , Deguchi K. , Hamakawa Y.
Published: July 2002

The effects of Te codoping in ZnS:CeF3 thin-film electroluminescent devices are reported. ZnS1−xTex:CeF3 thin films are prepared at several Te concentrations and substrate temperatures. The emissive peak position and intensity depend on Te concentrations, substrate temperatures, the annealing, and drive voltages.
Quasi-steady-state heat transfer/thermal stress model for dislocation generation in the vertical gradient freeze growth of GaAs
Authors: Jordan A. S. , Monberg E. M.
Published: July 2002

We have formulated a tractable model of the vertical gradient freeze (VGF) process for GaAs, providing dislocation density contour lines in terms of geometrical and physical parameters. First, the temperature distribution in a cylindrical boule has been determined in closed form involving modified Bessel functions of the first kind, order zero (I0) by solving the quasi-steady-state partial differential equation for heat conduction. Subsequently, the principal thermoelastic stress components have been evaluated and then resolved in the {111}, <11̄0≳ slip system which in excess of the critical resolved shear stress (CRSS) introduce dislocations by slip. We present dislocation density contour maps for 2- and 3-in.-diam undoped (100) GaAs grown by VGF under a variety of linear thermal gradients (v) imposed on the periphery of the boule. We show that for large v the dislocation distribution is similar to that observed in liquid-encapsulated Czochralski (LEC) material but lowering v effectively suppresses dislocation generation even in boules larger than 2 in. in diameter. A comparison of dislocation generation in VGF and standard LEC growth using very recent CRSS data is also given.
Textures of Ta/Al multilayer films
Authors: Yuan X. Y. , Wu Z. Q. , Hu A. , Jiang S. S. , Qiu Y. , Khatanova N. A. , Ilyushin R. S.
Published: July 2002

Ta/Al multilayer films with a modulation wavelength of 7.0 nm were grown using magnetron sputtering. The Bragg θ-2θ scan pattern and the plate film photograph of x-ray diffraction reveal that the sample has Ta(110) and A1(111) axial textures with a mosaic spread of about ±5° and coherency strains. The structure change of the multilayer sample after annealing at 550 °C for 2 h is determined by the plate film photography of x-ray diffraction to study the thermal stability. It is found that after annealing a large amount of Ta and Al atoms at the interfaces are combined into TaAl3 with [(202)+(002)] textures.
Grating coupled liquid crystal waveguides using nematics and smectics
Authors: Bryan-Brown G. P. , Sambles J. R. , Welford K. R.
Published: July 2002

The optical properties of grating coupled waveguides are theoretically modeled and practically demonstrated using nematic and smectic liquid crystals as thin (0.7 μm) waveguide layers. Voltage induced reorientation of the liquid crystal is shown to lead to large changes in reflectivity and transmissivity when the angle of incidence initially corresponds to a guided mode resonance. Time resolved measurements using these thin cells show that the switching time for the nematic phase can be faster than the smectic phase.
A single-site theory of magnetism in amorphous Fe-Ni alloys
Authors: Yu M. , Kakehashi Y.
Published: July 2002

Magnetic properties of amorphous FecNi1−c alloys are investigated on the basis of a single-site theory which combines the geometrical-mean model for the electronic structure calculations of amorphous alloys with the finite-temperature theory of metallic magnetism. Numerical results for magnetization versus concentration curves show strong ferromagnetism in the region 0.1≲c≲0.8. This explains the recent experimental finding of large hyperfine fields for amorphous FecNi1−c alloys in the Invar concentration region. The calculated Curie temperatures for amorphous structure show a shift of the maximum Curie temperature toward higher Fe concentration, which is in qualitative agreement with the experimental data of amorphous (Fe-Ni)90Zr10 alloys. It is demonstrated that such behavior is caused by a change of electronic structure due to structural disorder rather than by simple volume expansion; at around 60 at. % Fe, the main peak of the nonmagnetic density of states of the amorphous alloy shifts to an energy lower than that of the crystalline fcc counterpart so that the Fermi level is at the main peak, leading to a large magnetic energy gain. The agreement between calculated concentration dependence of effective Bohr magneton numbers and the experimental data for liquid alloys also supports this theory.
Generalized self-consistency test of wall computations
Authors: Aharoni Amikam , Jakubovics J. P.
Published: July 2002

The criterion for checking the self-consistency of magnetic domain wall computations, which has been used before for several particular cases, is generalized for walls with a non-zero applied field. Other criteria are established for one-dimensional domain walls, and many examples are given for the usefulness of these criteria.
Quasistatic optical response of pairs of touching spheres with arbitrary dielectric permeability
Authors: Paley A. V. , Radchik A. V. , Smith G. B.
Published: July 2002

The problem of polarization of two touching spherical particles, of any complex dielectric constant, immersed in a uniform external electric field is solved exactly in the tangent-sphere frame. A straightforward integral over the continuum of eigenstates yields the dipole moment for fields parallel and perpendicular to the line joining the centers. Predictions are compared to those from a recent approximate model based on the method of images. A modified Clausius–Mossotti formalism is used to assess the impact on absorption and refraction at optical frequencies (in the quasistatic limit). Actual composite materials containing small touching sphere pairs are considered.
Density measurements of a neon Z-pinch plasma
Authors: Welch B. L. , Griem H. R. , Young F. C.
Published: July 2002

The absolute intensity of near-ultraviolet emission from a neon Z-pinch plasma is measured with a time-gated, two-dimensional optical multichannel analyzer (OMA). The OMA provides spatial and spectral resolution with a 100 ns gate duration. Spatially resolved continuum emission, Ne viii line emission, and Ne viii line-profile measurements are used to determine the pinch diameter, the density of the neon plasma, and the Ne viii 3p level population.
Initiation of traveling normal domains in large composite superconductors
Authors: Kovner V. S. , Kupferman Raz , Mints R. G.
Published: July 2002

We consider the initiating energy for traveling normal domains in large composite superconductors. We perform numerical simulations of normal zone initiation using the effective circuit model. The initiating energy is obtained as a function of transport current and four dimensionless parameters characterizing the composite and cooling conditions. We suggest an analytical expression determining the initiating energy for the traveling normal domains in the region of parameters of practical interest.
Low rf-loss, bondable ohmic contacts on Tl2Ba2CaCu2O8−δ for microwave devices
Authors: Scharen M. J. , Skoglund D. L. , Forse R. J. , Nilsson B. J. L. , Hammond R. B. , Olson W. L.
Published: July 2002

We present two processes for the fabrication of bondable, low-loss ohmic contacts to high-temperature superconductor thin-film devices. Contact resistances at both high and low frequencies are comparable—between 5.0×10−7 and 2.0×10−5 Ω cm2 at 77 K. We demonstrate that losses at low frequency correlate with losses up to 10 GHz. Destructive bond pull strengths for 25-μm-diam, thermosonically attached gold wire average between 5.0 and 8.0 g force, exceeding the industry standard of 3.0 g force. Preliminary results also show that contact resistance as low as 1.7×10−8 Ω cm2 are attainable with annealing. These processes satisfy a pressing need for fabrication of reliable, low-loss ohmic contacts required for the development and production of high-performance passive microwave devices based on high-Tc superconducting thin-film materials.
Modeling of proton-exchanged and annealed channel waveguides and directional couplers
Authors: Charczenko W. , Januar I. , Mickelson A. R.
Published: July 2002

The cosh−2 profile is used to model the hydrogen concentrations of proton-exchanged and annealed LiNbO3 waveguides. These hydrogen concentrations are experimentally determined using a secondary-ion-mass spectrometry. A two-dimensional extraordinary refractive index profile is obtained from a model for the hydrogen concentration profile, assuming a linear relationship between the index change and concentration. A matrix effective refractive index technique with a two-dimensional index profile is then used to analyze proton-exchanged and annealed channel waveguides. Calculated near-field intensities and propagation constants are compared to measured values for various channel waveguides and fabrication conditions. The matrix effective refractive index method, along with coupled-mode equations, are used to simulate the performance of proton-exchanged and annealed directional couplers as a function of various device geometries and thermal annealing conditions. Comparisons of computer simulations to actual device measurements indicate that these analytical techniques are sufficiently fast and accurate enough to be used in computer-aided design of integrated optical components.
Nonexponential fluorescence decay and multiphonon relaxation of the 4F3/2 level of Nd3+ in sodium β″-alumina
Authors: Dai H.
Published: July 2002

We report a temperature-dependent nonexponential decay behavior observed from the 4F3/2 level fluorescence of Nd3+ in sodium β″-alumina (SBA) single crystals. By applying a double-exponential fit to the measured decay data, we find that the decay curve can be approximately decomposed into two single-exponential components with different multiphonon relaxation properties. Multiphonon relaxation rates obtained by the fluorescence-decay measurements and Judd–Ofelt intensity analysis are fitted to the phenomenological multiphonon model for both components. It is shown that the phonons responsible for the trailing decay component are mainly vibrational modes of the spinel blocks of SBA while phonons responsible for the leading component are both spinel modes and phonon modes of Na+ ions in the conduction plane.
Raman scattering and x-ray diffractometry studies of epitaxial TiO2 and VO2 thin films and multilayers on α-Al2O3(112̄0)
Authors: Foster C. M. , Chiarello R. P. , Chang H. L. M. , You H. , Zhang T. J. , Frase H. , Parker J. C. , Lam D. J.
Published: July 2002

Epitaxial thin films of TiO2 and VO2 single layers and TiO2/VO2 multilayers were grown on (112̄0) sapphire (α-Al2O3) substrates using the metalorganic chemical vapor deposition technique and were characterized using Raman scattering and four-circle x-ray diffractometry. X-ray diffraction results indicate that the films are high quality single crystal material with well defined growth plane and small in-plane and out-of-plane mosaic. Single-layer films are shown to obey the Raman selection rules of TiO2 and VO2 single crystals. The close adherence to the Raman selection rules indicates the high degree of orientation of the films, both parallel and perpendicular to the growth plane. Selection rule spectra of two and three layer TiO2/VO2 multilayers are dominated by the VO2 layers with only minimal signature of the TiO2 layers. Due to the low band gap of semiconducting vanadium dioxide, we attribute the strong signature of the VO2 layers to resonant enhancement of the VO2 Raman component accompanied with absorption of the both the incident and scattered laser light from the TiO2 layers.
New cryoelectronic detector concept based on two-dimensional heat diffusion
Authors: Lemke S. , Hebrank F. , Gross R. , Huebener R. P. , Weimann Th. , Pöpel R. , Niemeyer J. , Schnakenberg U. , Benecke W.
Published: July 2002

Superconducting Nb/AlOx/Nb tunnel junctions have been fabricated on Si membrane windows of only 1.2 μm thickness acting as substrates. The membrane windows with areas between (600 μm)2 and (1200 μm)2 remained undamaged after the different fabrications steps. The tunnel junctions positioned on the membranes and the bulk silicon substrate have very similar current-voltage characteristics. Using low-temperature scanning electron microscopy the two-dimensional heat diffusion process has been imaged in the detector geometry. This two-dimensional heat diffusion leads to a new cryoelectronic radiation detector concept combining high energy and spatial resolution with a large effective detector area. Applications of this detector concept include soft-x-ray spectroscopy and the nuclear β decay.
Excimer laser-induced nonlinear photoelectric emission of electrons from silicon
Authors: Krechetov A. I. , Zlobin A. Yu. , Zastavenko A. V. , Ageev V. P. , Konov V. I.
Published: July 2002

Photoelectric emission from silicon has been studied under the action of uv laser radiation. It has been established that photocurrent nonlinearly depends on laser radiation intensity when the quantum value is less than the photoelectric threshold. Photoemission, originating from photoexcited nonequilibrium conductivity electrons, is considered as a process causing such an effect. Photocurrent treatment is suggested as a possible method of nonequilibrium carriers formation kinetics observation. It is essential that the basic mechanisms of photoemission production involve electrons from the most interesting region (≤30 Å) lying just beneath the semiconductor surface.
Relationship between growth processes and strain relaxation in Si1−xGex films grown on (100)Si-(2×1) surfaces by gas source molecular beam epitaxy
Authors: Yasuda Y. , Koide Y. , Furukawa A. , Ohshima N. , Zaima S.
Published: July 2002

The relationship between growth processes and strain relaxation has been investigated on Si1−xGex (0≤x≤1) films grown on (100)Si-(2×1) surfaces by gas source molecular beam epitaxy using Si2H6 and GeH4. It has been found that the critical film thicknesses for the formation of an (8×2) superstructure, {811}-faceted islands, and {311}-faceted islands in the growth process have been found to obey power laws of xn with exponents (n) of approximately −2, −3, and −3 in the range of 0.25≤x≤1.0, respectively. This result indicates that the relaxation of the film strain energy brings about a change into faceted structures and occurs at two steps of {811} and {311} faceting with the film growth. It has been also clarified that the incorporation ratio of Si and Ge atoms into the films is determined by the rate constant ratio of the dissociative adsorption of the hydride compounds, the value of which is six for the Si2H6/GeH4 system.