bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarimetric determination of the ratio between the constituent phase conjugate signals in degenerate four-wave mixing
Authors: Kim Sok Won , Lee Sang Soo
Published: July 2002

We have derived the polarization dependent coupling constants for transmission and reflection gratings in degenerate four-wave mixing, measured phase-conjugate signals for various polarization conditions, and determined the relative contribution of the two gratings to the signal. The results obtained with cryptocyanine dissolved in methanol as the nonlinear medium show that the signal from transmission grating is 1.53–2.14 times larger than that from a reflection grating depending on the angle between the wave vectors of the forward pump beam and the probe beam.
Fine-particle magnetism in the devitrified metallic glass Fe43Cr25Ni2B12
Authors: Hara Y. , Ando T. , O’Handley R. C. , Grant N. J.
Published: July 2002

A metallic glass, Fe43Cr25Ni20B12, which is paramagnetic at room temperature, becomes ferromagnetic under annealing near the crystallization temperature, then loses its magnetization with further annealing. This unique behavior is closely related to the precipitation of a very fine metastable body-centered-cubic phase in a nonmagnetic matrix. Since the magnetism of the annealed samples arises from very small magnetic particles, superparamagnetic behavior is observed. From the characteristic magnetization curves of superparamagnetism, the average moment and the density of the magnetic particles were estimated and found to be in good agreement with observations made by transmission electron microscopy. The tentative analyses for the sample annealed at 666 K indicate that both nucleation and growth take place in the early stage (3.5–20 h) and that nucleation ceases in the later stage (20–145 h) of the crystallization process.
Growth and characterization of InAs/In1−xAlxAs strained-layer superlattices on GaAs
Authors: Kato H. , Iguchi N. , Kamigaki K. , Chika S. , Nakayama M. , Sano N. , Terauchi H.
Published: July 2002

InAs/In1−xAlxAs strained-layer superlattices (SLSs) have been grown by molecular-beam epitaxy on highly mismatched (001) GaAs substrates. High-quality strained thin films were obtained by growing AlSb and In1−yAlyAs buffer layers between substrates and SLSs. X-ray diffraction analysis and photoluminescence (PL) measurements were used to evaluate the internal strain and strain-induced effects on band structures of SLSs. Comparison between observed and calculated results of x-ray analysis shows that free-standing (unsupported) SLSs are grown on a GaAs substrate. The emission peak energies in PL measurements are interpreted by taking into account the internal strain of individual layers in SLSs.
Rapid thermal annealing-induced epitaxy of ion-implanted amorphous layers on 〈100〉 silicon
Authors: Grob J. J. , Grob A.
Published: July 2002

A high-resolution Rutherford backscattering-channeling experiment was used to investigate the regrowth kinetics of Ge+- and As+-implanted amorphous layers on 〈100〉 silicon during a rapid thermal (lamp) annealing (RTA). Our results are compared to the well-known recrystallization behavior obtained in a standard furnace. A substantial enhancement of the growth rate with no variation of activation energy is shown. The accuracy of the temperature reading is first discussed. It is also shown that incident radiations (light) play no significant role in this enhancement. It is further concluded that there is actually no difference between RTA and furnace annealing, the epitaxy velocity increase being time limited to a few minutes. This transient effect is explained similarly to the increased diffusivity observed at higher temperature.
1/f noise in ion-implanted resistors between 77 and 300 K
Authors: Clevers R. H. M.
Published: July 2002

The conductivity, the Hall effect, and the noise of ion-implanted resistors is measured between 77 and 300 K. The temperature dependence of the carrier concentration in these boron-doped layers cannot be explained by the freeze-out of the boron acceptor level. Possible explanations are a temperature-dependent Hall factor r and a distribution of trap levels 0.1–0.2 eV above the valence-band edge. The mobility μ can be determined from the conductivity and the Hall-effect data. The mobility shows the highest value after annealing at 750 °C. The value of the 1/f noise parameter α shows a weak temperature dependence after annealing at 450, 550, 650, and 900 °C. After annealing at 750 °C the α value decreases from 10−5 at 300 K to lower than 2×10−7 at 77 K. The highest mobility μ gives the lowest 1/f noise parameter α. This indicates that more defects and lattice damage give more 1/f noise. Additional scattering mechanisms have much more influence on the 1/f noise parameter α than on the mobility μ.
Comment on ‘‘Numerical calculation of the temperature distribution and evolution of the field-ion emitter under pulsed and continuous-wave laser irradiation’’ [J. Appl. Phys. 5
9, 1334 (1986)]
Authors: Gipson G. Steven
Published: July 2002

A recent paper having to do with numerical calculations of the temperature distribution in field emitters is criticized for an error in the governing heat-conduction equation used to formulate the finite difference algorithm. The correct form of the equation is derived retaining a possibly significant nonlinear term in the final formula.
Electronic properties of symmetric and asymmetric quantum-well electron barrier diodes
Authors: Newman H. S. , Kirchoefer S. W.
Published: July 2002

The quantum-well electron barrier diode is a device whose current-voltage characteristic originates in the symmetry of the ground-state energies present in a sequence of quantum wells. In this paper, current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the quantum-well electron barrier diode are presented for a number of symmetric and asymmetric configurations fabricated from samples grown by molecular-beam epitaxy. The data demonstrate that the symmetry of the quantum wells determines the symmetry of the I-V characteristic. The effect of doping on the C-V characteristic is also examined. It is shown how the effect of doping can be understood via a solution of Poisson’s equation at zero bias.
Laser-beam heating and high-temperature luminescence of CdTe
Authors: As D. J. , Palmetshofer L.
Published: July 2002

High-temperature luminescence excited by a cw Kr-ion laser beam was used as a probe to measure the temperature of CdTe inside of the laser spot. The luminescence was first studied with low-power laser excitation on externally oven-heated CdTe. The results were then used as a standard for the temperature determination during laser-beam heating. It was found that the lattice temperature can be determined very accurately from the slope on the high-energy side of the luminescence spectrum. The maximum temperature inside the laser spot was measured as a function of the laser power. The results are in good agreement with theoretical calculations of cw laser heating in CdTe.
Electron microdiffraction studies of new SiO2 precipitates in silicon
Authors: Kim Y. , Spence J. C. H. , Long N. , Bergholz W. , O’Keeffe M.
Published: July 2002

Coherent electron microdiffraction patterns have been obtained from a new crystalline precipitate found in silicon wafers annealed at 635 °C for 256 h. On the basis of the experimental evidence presented, the most likely structure is that of keatite (SiO2, tetragonal). The implications for the study of oxygen precipitation in silicon are discussed.
1.3-μm integrated external cavity distributed Bragg reflector laser
Authors: Piccirilli A. B. , Dutta N. K. , Napholtz S. G. , Cella T. , Brown R. L.
Published: July 2002

The fabrication and performance characteristics of single-wavelength integrated external cavity distributed Bragg reflector lasers are described. The active cavity section of these devices utilize the double-channel planar-buried heterostructure scheme for current confinement. The 4-mm-long lasers have threshold current ∼70 mA and emit near 1.3 μm. The lasers exhibit lower dc chirp than distributed feedback lasers.
Correlations between plasma parameters and the deposition of microcrystalline silicon films by plasma of argon and hydrogen
Authors: Avni R. , Carmi U. , Manory R. , Grill A. , Grossman E.
Published: July 2002

The dissociation of chlorosilanes to microcrystalline silicon and its deposition on a solid substrate in a rf plasma of mixtures of argon and hydrogen was investigated as a function of the macrovariables of the plasma. The dissociation mechanism of chlorosilanes and HCl as well as the formation of silicon in the plasma state were studied by sampling the plasma with a quadrupole mass spectrometer. Macrovariables such as pressure, net rf power input, and location in the plasma reactor were found to strongly influence the kinetics of dissociation. The deposition process of microcrystalline silicon films and its chlorine contamination were correlated to the dissociation mechanism of chlorosilanes and to the role of hydrogen chloride.
Random-anisotropy ferromagnetism in amorphous U27Fe73 films
Authors: Freitas P. P. , Plaskett T. S. , McGuire T. R.
Published: July 2002

We measured magnetic and transport properties of amorphous U27Fe73 films deposited by magnetron sputtering. The films show a magnetic ordering temperature Tf =32 K, and a spin-glass regime below a temperature Tirr(H). The Arrott plot shows a characteristic change in concavity at the transition, as predicted by Aharony and Pytte (A-P) for random-anisotropy systems with D≪J. Although we find a finite susceptibility below Tf, with χ0=0.66 in units of the inverse of the demagnetizing factor, the critical exponents δ1 and δ2 are close to the values predicted by the A-P model. The electrical resistivity has a minimum at 31 K, resulting from the competition between exchange scattering and inelastic spin-flip processes. For T>200 K a linear regime with negative dρ/dT is found, characteristic of phonon scattering in amorphous materials. The isotropic magnetoresistance is positive and levels off below Tf reflecting freezing of spin correlations at this temperature. This behavior can be explained by the existence of small Imry and Ma domains and partial local magnetic order below Tf.
Magnetization depth profiling with low-energy electron spectroscopy and MOKE
Authors: Woods J. , Ushioda A. , Donovan M.M. , Sun S. W. , Tobise M. , O’Handley R. C.
Published: July 2002

Low-energy electron spectroscopy with (spin) polarization analysis (LEESPA) is described. The power of this new technique, especially in combination with magneto-optic Kerr effect (MOKE), for studying the important effects of surface magnetism are illustrated with the first results on low magnetostriction amorphous Co-Fe-B ribbons.
Al-Fe-Nd-B magnets: Where does the Al go? (abstract)
Authors: Ramesh R. , Chen J. K. , Thomas G. , Ma B. M.
Published: July 2002

One successful additive to Fe-Nd-B magnets has been Al, which enhances the iHc significantly, even for a 2 at. % (0.8 wt. %) addition. However, in these magnets it is not clear whether Al partitions into the Re2Fe14B phase, the grain boundary phase, or to the interphase interfaces. The main problem, in this case, is the detection of such small quantities in the microstructure. To overcome this ‘‘detectability’’ problem, magnets with 3.9 wt. % of Al have been prepared by the standard sintering route. These magnets exhibit higher iHc compared to the 0.8 wt. % magnet. The results of magnetic, structural, microstructural and microanalytical examination will be reported in this paper. It is hoped that this will clarify unambiguously the question of Al partitioning.
Reordering of polycrystalline Pd2Si on epitaxial Pd2Si
Authors: Comrie C. M. , Liu J. C. , Hung L. S. , Mayer J. W.
Published: July 2002

Polycrystalline Pd2Si is found to reorder on top of epitaxial Pd2Si during silicide growth. The interface between polycrystalline Pd2Si and epitaxial Pd2Si is, thus, not immobile with respect to the silicide lattice during silicide formation and it is, therefore, not possible to use this interface as a structural marker in order to monitor diffusion in epitaxial Pd2Si. The use of Ti as an inert marker has shown that Si is the dominant diffusing species in epitaxial Pd2Si during silicide formation.
X rays from z-pinches on relativistic electron-beam generators
Authors: Pereira N. R. , Davis J.
Published: July 2002

This review summarizes recent experimental data on imploding z-pinches and their radiation output, and gives an overview of theoretical issues concerning radiation production in the pinch plasma. A z-pinch plasma is created when the current from a fast, powerful electrical generator compresses and heats a small amount of material between the electrodes. The hot, dense plasma emits copious amounts of radiation extending from the visible to the x-ray region. With a 10-TW electrical discharge the radiative power may be a few TW, with an energy per pulse of up to tens of kilojoules. Our interest is mainly in the photons with energy around 1 keV, which are useful in x-ray lithography, microscopy, surface studies, and other applications.
Infrared spectra in nonstoichiometric yttria-stabilized zirconia mixed crystals at elevated temperatures
Authors: Liu D. W. , Perry C. H. , Ingel R. P.
Published: July 2002

Infrared (IR) reflectivity measurements were undertaken on pure ZrO2 and stabilized ZrO2⋅Y2O3 solid solutions containing 3-, 4-, 7-, 12-, and 20-wt.% Y2O3 over 10–900 cm−1 region as a function of temperature up to 1400 °C. The observed IR active phonons are related to the phase transitions that depend on composition and temperature. Good agreement was achieved among IR, Raman scattering, and neutron scattering investigations. An IR reflectivity enhancement from 42% to 60% in the low-frequency region (10–110 cm−1) was found as the monoclinic(M)-tetragonal(T) martensitic transition was completed in pure ZrO2 and ZrO2⋅3-wt.% Y2O3.
Silicon surface passivation by hydrogen termination: A comparative study of preparation methods
Authors: Fenner D. B. , Biegelsen D. K. , Bringans R. D.
Published: July 2002

Clean silicon surfaces having low carbon and oxygen contamination are necessary for good epitaxial overgrowth. Methods for low-temperature preparation of clean surfaces are needed to fully enable low-temperature fabrication processes on silicon. In this paper silicon surfaces are compared for residue and chemical passivation after (i) hydrogen termination by various low-temperature, wet-chemical techniques, (ii) cleaving in ultrahigh vacuum (UHV), and (iii) ion sputtering. Surface residue was characterized with x-ray photoelectron spectroscopy (XPS) and small-spot Auger electron spectroscopy (AES). Low-energy electron diffraction (LEED) was also used. Evaluations of passivation were done by exposing the cleaned surfaces to various environments, e.g., UHV, N2 gas, and room air. We have obtained especially promising results with a technique whereby the wafer surface oxide is etched using an HF-alcohol reagent in a flowing nitrogen atmosphere at room temperature while the wafer is spinning, i.e., a spin etch. We have evaluated the tolerances for this process and have found quite practical requirements, which we discuss in detail. Typically, after spin etching the XPS of Si(100) surfaces indicated 0.03 ML (monolayer) of total carbon residue (from C 1s core-level emission) and about 0.005 ML each of oxygen and fluorine, while all such residue was below our AES detection limits. The Si 2p core level at shallow emission angles was free of any chemically shifted components within the noise and linewidth resolution limits. Brief exposure of these passivated surfaces to room air increased the total C and O residue slightly, while LEED patterns remained unreconstructed. By comparison, samples etched by dipping in HF or sputtered by Ar+ ions showed tenfold more surface residue, while cleaved sample surfaces were vastly more reactive.
Near-band-gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon
Authors: Robbins D. J. , Canham L. T. , Barnett S. J. , Pitt A. D. , Calcott P.
Published: July 2002

The systematic study of band-edge luminescence in pseudomorphic Si/Si1−xGex/Si double-heterostructure layers is reported for a wide composition range, 0.12<x<0.24, for the first time. An analytical expression for the exciton energy gap at 4.2 K valid for x<0.24 is derived from the no-phonon line energies: ESX(x) = 1.155−0.874x+0.376x2 eV. Addition of an expression for the exciton binding energy provides an approximation for the energy difference between the alloy valence band and the lowest conduction-band edge at low temperature. An exciton upshift of 16.9 meV due to quantum confinement is observed in a 6.3-nm Si0.83Ge0.17 alloy well. This is consistent with either type-I or type-II band alignment for which the conduction-band offset has a magnitude ‖ΔEc‖ ≤ 10 meV. The excitonic hole is closely confined in the alloy but the spectra suggest that the electron density in the silicon barriers is increased for the thin layer.
Phase-locked flux-flow Josephson oscillator
Authors: Ustinov A. V. , Mygind J. , Oboznov V. A.
Published: July 2002

We report on the observation of large rf induced steps due to phase-locking of unidirectional flux-flow motion in long quasi-one-dimensional Josephson junctions. The external microwave irradiation in the frequency range 62–77 GHz was applied from the edge of the junction at which the fluxons enter. The dependence of the amplitude of the phase-locked step on external magnetic field and microwave power has been measured. The observed zero-crossing steps have potential application in Josephson voltage standards. A simple model for the flux-flow as determined by the microwave driven boundary gate at the edge of the junction is presented.
Fabrication of sol-gel derived ferroelectric Pb0.865La0.09Zr0.65Ti0.35O3 optical waveguides
Authors: Baude P. F. , Ye C. , Tamagawa T. , Polla D. L.
Published: July 2002

Crack-free transparent ferroelectric Pb0.865La0.09Zr0.65Ti0.35O3 [PLZT (9/65/35)] thin films have been deposited on silicon substrates using the sol-gel deposition technique. An intermediate layer of Pb0.90La0.10Ti0.975O3 (PLT) was used to improve the PLZT’s optical quality and to reduce the amount of film cracking. Wet chemical etching, plasma etching, and reactive ion etching were investigated as means of realizing the necessary waveguide structures. Waveguiding was observed in 2–4 mm long by 20 μm wide PLZT (9/65/35) ridge waveguides fabricated by reactive ion beam etching.
Dielectric properties of tetragonal lanthanum modified lead zirconate titanate ceramics
Authors: Dai Xunhu , DiGiovanni A. , Viehland Dwight
Published: July 2002

Tetragonal La-modified lead zirconate titanate ceramics with a Zr/Ti ratio of 40/60 (x/40/60) with La contents (x) between 0 and 21 at. % were prepared by the mixed oxide method and were subsequently characterized using dielectric spectroscopy. Small La contents tended to diffuse the dielectric response in the temperature region around the phase transition, however, no distinct changes were observed in the paraelectric region. Compositions with intermediate La contents showed a thermally driven (spontaneous) transformation from a relaxor to a normal ferroelectric, i.e., micro-macro domain switching. Materials with a high La content exhibited typical relaxor ferroelectric behavior. The relative thermodynamic stability of the ensemble of micropolar regions is then discussed in reference to that of the long-range ferroelectric state.
Absorption losses in MgO-doped and undoped potassium niobate
Authors: Busse L. E. , Goldberg L. , Surette M. R. , Mizell G.
Published: July 2002

Measurements of absorption losses in KNbO3 and MgO-doped KNbO3 were made in the blue and near-infrared wavelength regions using laser calorimetry. In the doped samples, the absorption loss for blue light was found to be 40% lower than that of the undoped samples. An enhancement in the infrared loss, caused by the presence of blue light, was observed in doped and undoped samples, but found to be much greater in the MgO-doped crystals. The blue-enhanced infrared absorption was characterized using two-wavelength laser calorimetry. Temporal variations in the second-harmonic power, caused by nonuniform heating of the active volume by the absorbed infrared and second-harmonic power, are described.
Excess current in shunted Josephson weak links
Authors: Seed R. G. , Vittoria C. , Widom A.
Published: July 2002

In a variety of Josephson weak links the resistively shunted junction model does not properly describe observed excess currents in the voltage current characteristics. A modification of the model is proposed which more adequately describes experimental data.
Overview of applications of micromagnetic Barkhausen emissions as noninvasive material characterization technique
Authors: Sipahi L. B.
Published: July 2002

In this concise overview, the physical principles of magnetic Barkhausen effect will be briefly discussed and its recent applications in material characterization will be considered. There are new trends in micromagnetic Barkhausen effect emissions and its applications in the material characterization area. These emissions take place in magnetic materials subjected to changing applied magnetic field, and can be used, for instance, to study noninvasively surface characterization of materials. Since these emissions are quite sensitive to changes in the microstructure and subsurface stress states in magnetic materials, various applications of these of micromagnetic emissions have been found in areas such as nuclear, aerospace, and automotive technologies which use magnetic materials.
Optical functions of silicon at elevated temperatures
Authors: Jellison G. E. , Modine F. A.
Published: July 2002

The optical functions of silicon have been measured accurately at elevated temperatures using the two-channel spectroscopic polarization modulation ellipsometer. The wavelength region covered is 240–840 nm (5.16–1.47 eV), and the temperature region covered is room temperature to 490 °C. Using this data, the refractive index n and the extinction coefficient k are both parameterized as functions of temperature T and photon energy E for photon energies below the direct band edge of silicon (∼3.36 eV or 370 nm). In this range, n(E,T) can be fit with five parameters, and k(E,T) can be fit with six parameters.
Coherent Raman measurements of polymer thin-film pressure and temperature during picosecond laser ablation
Authors: Hare David E. , Franken Jens , Dlott Dana D.
Published: July 2002

Picosecond time-resolved coherent Raman spectroscopy (ps CARS) is used to study photothermal ablation, induced by 150 ps duration near-infrared optical pulses, of poly-(methyl methacrylate) (PMMA) thin films doped with a small amount of near-infrared absorbing dye. The pressure and temperature shifts of a PMMA transition at ≊808 cm−1 were calibrated in static P and T experiments. Dynamic frequency shifting of the PMMA transition is used to determine temperature and pressure in the ablating thin film, and to investigate the dynamics of fast thin-film volume expansion. When the ablation pulse intensity is varied, ps CARS measurements of T and P are shown to be consistent with the results of conventional measurements below threshold, but near and above threshold picosecond time scale data show noticeable differences. Picosecond time scale ablation involves solid-state shock waves, which are not produced by longer duration ablation pulses. A pressure jump, often several kbar, is produced when the film is heated faster than a characteristic hydrodynamic volume relaxation time τh. Pressure release occurs by shock rarefaction wave propagation. When the rarefaction wave reaches the substrate, a tensile force is exerted on the thin film, causing it to break away from the substrate. The pressure in the thin film at ablation threshold, Pabl≊0.5 GPa, is found to be generated by roughly equal contributions from shock and thermochemical polymer decomposition processes. Therefore the picosecond time scale ablation process is termed shock-assisted photothermal ablation. The value of Pabl is interpreted to be the nanosecond time scale dynamic tensile strength of the thin film under conditions of ultrafast heating. It is found to be about one order of magnitude greater than the static strength of PMMA.
Optical and photoelectrical properties of β-FeSi2 thin films
Authors: Shen W. Z. , Shen S. C. , Tang W. G. , Wang L. W.
Published: July 2002

Absorption, photocurrent, and infrared reflectivity spectra of the polycrystalline β-FeSi2 thin films in relation to the Si substrate temperature are presented. The photocurrent spectra involving both the fundamental interband, extrinsic defect transitions of β-FeSi2 and the intrinsic transitions of Si substrates are observed. Both the absorption and photocurrent measurements show the direct gap nature. A simple recombination model is proposed to account for the photocurrent results. We show that better quality β-FeSi2 films can be achieved at higher substrate temperature. The simplicity, sensitivity, and reliability of the photocurrent measurements for studying β-FeSi2 are well demonstrated.
Switching dynamics of Nb/AlOx/Nb Josephson junctions: Measurements for an experiment of macroscopic quantum coherence
Authors: Castellano M. G. , Leoni R. , Torrioli G. , Chiarello F. , Cosmelli C. , Costantini A. , Diambrini-Palazzi G. , Carelli P. , Cristiano R. , Frunzio L.
Published: July 2002

Josephson junctions based on Nb/AlOx/Nb trilayer technology have demonstrated excellent quality, exhibiting very low dissipation in the subgap region. This property is very important for all those experiments which have to deal with the quantum behavior of macroscopic variables in Josephson devices. In view of performing an experiment of macroscopic quantum coherence with a Josephson device, we measured the escape temperature and the return current of several junctions fabricated with different processes and having different characteristics, by cooling them from 4.2 to 0.3 K. We show that, for what concerns the process of escape from the zero-voltage state, no difference can be found among different junctions. On the other hand, the dissipation properties are strongly influenced by the current density, with lower current density resulting in lower intrinsic dissipation.
Thermoelastic waves in a laminated composite with a second sound effect
Authors: Hawwa Muhammad A. , Nayfeh Adnan H.
Published: July 2002

The propagation of thermoelastic harmonic waves in bilaminated periodic waveguide is studied in the context of the generalized theory of thermoelasticity. A continuum mixture theory is developed for waves traveling in the direction parallel to the layering. As a result, the problem is transformed into a quasi-one-dimensional one. The resulting approximate expressions are found useful in obtaining a qualitative description of the response. The symmetric mode of an exact solution is used to check the validity of the mixture theory. Quasi-elastic and quasi-thermal modes are investigated for the cases when the thermal relaxation time is either included or neglected.
Effects of current spreading under oxide current aperture in vertical-cavity surface-emitting lasers
Authors: Yang Gye Mo , MacDougal Michael H. , Dapkus P. Daniel
Published: July 2002

We discuss a buried oxide layer forming a current aperture in a vertical-cavity surface-emitting laser. The current spreading under the oxide current aperture leads to high threshold and dual-longitudinal-wavelength characteristics. One is the as-grown cavity resonance and the other is the resonance wavelength under the oxide layer. This structure exhibits ≳30 dB side-mode suppression throughout its operating range. Meanwhile, a single-longitudinal-wavelength laser with a minimized current spreading has a low threshold current of 85 μA and several nonlasing modes.
Laser-induced heating of nanocrystals embedded in glass matrices
Authors: Rodrigues P. A. M. , Yu P. Y. , Tamulaitis G. , Risbud S. H.
Published: July 2002

Laser-induced heating of nanocrystals embedded in silicate glass matrices has been studied by photoluminescence and Raman scattering. No nonequilibrium optical phonons were found both for cw and 150-ps-long laser pulses in contrast to bulk samples. The measured laser-induced temperature rise in one sample where the nanocrystal radii are ∼5 nm was found to be in quantitative agreement with a nonlinear theory proposed by Lax for bulk semiconductors. However, in another sample where the nanocrystal radii are only 3 nm, the observed temperature rise at high laser powers was significantly higher than the theoretical prediction.
Fluorescence spectroscopy of silicate glasses codoped with Sm2+ and Al3+ ions
Authors: Nogami Masayuki , Abe Yoshihiro
Published: July 2002

The fluorescence properties of Sm3+ and Sm2+ ions incorporated in silicate glasses were measured using steady-state and laser-induced line narrowing techniques and the effect of Al3+ ions to the local structure around the Sm2+ ion was investigated. Sm3+ ion-containing glasses prepared by a sol–gel method were reacted with H2 gas to form the Sm2+ ions. The energies of the three Stark levels of the D05→7F1 transition were analyzed using C2v symmetry. The addition of Al3+ ions facilitates dispersion of the Sm2+ ions and increases the coordination number of the Sm2+ ion due to the long distance between the Sm2+ and O2− ions, resulting in the increased fluorescence intensity. The fluorescence intensity of the Sm2+ and Sm3+ ions considerably increases in glasses containing more than 5 mol % Al2O3.
Growth mechanism and electrical properties of metallic films deposited on silicone oil surfaces
Authors: Ge Hongliang , Feng Chunmu , Ye Gaoxiang , Ren Yuhang , Jiao Zhengkuan
Published: July 2002

The microstructure and the growth mechanism of the films, which were deposited on silicone oil surfaces by the rf-magnetron sputtering method, were studied systematically. It is found that, at the fixed incident rf capacity, the growth rate is not a constant and it depends on both the nominal film thickness and the substrate temperature. The film structure at the micrometer scale is highly sensitive to the substrate temperature. The dc resistance of the film increases with the increase of time, indicating that the behavior of the defects in the film is much different from that of the film deposited on a solid substrate. The effects of the liquid substrate are also discussed.
Texture control of PbTiO3 and Pb(Zr,Ti)O3 thin films with TiO2 seeding
Authors: Muralt P. , Maeder T. , Sagalowicz L. , Hiboux S. , Scalese S. , Naumovic D. , Agostino R. G. , Xanthopoulos N. , Mathieu H. J. , Patthey L. , Bullock E. L.
Published: July 2002

The nature and the role of 1 to 5 nm thick TiO2 seed layers for the growth of textured PbTiO3 and Pb(Zr,Ti)O3 thin films on textured Pt(111) thin film substrates have been studied. Under otherwise identical in situ sputter deposition process conditions, the PbTiO3 texture could be turned from (100) to (111) orientation by adding the seed layer. This is demonstrated by patterning the TiO2 film. Auger electron spectroscopy and x-ray photoemission spectroscopy showed that the seed layer was a continuous TiO2 film. X-ray photoelectron diffraction measurements revealed epitaxial ordering in the seed layer. As there is no azimutal order among the Pt grains, the reduced information of azimutally averaged polar cuts is obtained. These give strong evidence for a strained rutile (110) structure. Various deposition experiments indicated that the TiO2 is effective only when it is ordered before the PbTiO3 nucleation starts. The epitaxial relationship between PbTiO3(111) and Pt(111) is thus mediated by the intermediate, epitaxial TiO2 film, which is dissolved or transformed to PbTiO3 afterwards. The observed growth behavior is discussed in terms of surface and interface energies.
Numerical modeling of materials processing applications of a pulsed cold cathode electron gun
Authors: Etcheverry J. I. , Martı́nez O. E. , Mingolo N.
Published: July 2002

A numerical study of the application of a pulsed cold cathode electron gun to materials processing is performed. A simple semiempirical model of the discharge is used, together with backscattering and energy deposition profiles obtained by a Monte Carlo technique, in order to evaluate the energy source term inside the material. The numerical computation of the heat equation with the calculated source term is performed in order to obtain useful information on melting and vaporization thresholds, melted radius and depth, and on the dependence of these variables on processing parameters such as operating pressure, initial voltage of the discharge and cathode–sample distance. Numerical results for stainless steel are presented, which demonstrate the need for several modifications of the experimental design in order to achieve a better efficiency.
Reliability of metal–oxide–semiconductor capacitors on nitrogen implanted 4H-silicon carbide
Authors: Treu M. , Burte E. P. , Schörner R. , Friedrichs P. , Stephani D. , Ryssel H.
Published: July 2002

4H- SiC epitaxial layers were implanted with nitrogen up to doses of 1×1015 cm−2 and annealed at different temperatures. Atomic force microscopy revealed that the roughness of the SiC surface increased with the annealing temperature. It was shown that the oxide grows thicker on substrates with doping levels exceeding 1×1018 cm−3. The barrier height at the SiC/SiO2 interface, determined by voltage ramping on metal–oxide–semiconductor capacitors, decreased with increasing implantation dose. This decrease was attributed to residual implantation damage. Constant current injection experiments revealed an opposite charge buildup at the SiC/SiO2 interface for the highest implantation dose compared to samples with no implantation. It was shown that the breakdown behavior can be improved by annealing at 1700 °C compared to 1450 °C despite a higher surface roughness.
Kramers–Kronig analysis of polymer acoustic data
Authors: Wintle H. J.
Published: July 2002

We briefly present the relationships between the acoustic velocity v and attenuation α in their exact form, while retaining the ambiguity in the magnitude of the response function. We show that some recent experimental measurements of v and α in polymers satisfy the Kramers–Kronig relations very well, while others are not as satisfactory. We demonstrate that the nearly local approximation obtained by dropping terms in (αv/ω)2 is quite inappropriate for these materials, and we point out the importance of these measurements for the experimental analysis of space charge in insulators.
Analysis and modeling of Nd:Ti:LiNbO3 Fabry-Pérot channel waveguide lasers
Authors: Lee Ching-Ting , Sheu Lih-Gen , Hwang Fu-Tsai
Published: July 2002

Based on the bidirectional fast Fourier transform beam propagation method (FFT-BPM), a self-consistent Nd:Ti:LiNbO3 Fabry-Pérot waveguide laser model has been developed. By using the bidirectional FFT-BPM and the attenuation effect of pumping and resultant lasers within the waveguide cavity, the interference effect and physical behaviors of the population inversion longitudinal and transversal spatial effects were observed. The resultant laser power is saturated if the waveguide is longer than a critical length, which is a function of the pumping power. Moreover, the resultant laser power density is a nonuniform function along the longitudinal dimension within the waveguide cavity.
Liquid-assisted pulsed laser cleaning using near-infrared and ultraviolet radiation
Authors: She Min , Kim Dongsik , Grigoropoulos Costas P.
Published: July 2002

Nanosecond pulsed laser irradiation is shown to be effective for cleaning contaminant particles as small as 0.3 μm in diameter from NiP magnetic hard disk substrates. A micron-thick liquid film is deposited on the disk surface just before the laser irradiation. The cleaning threshold and efficiency are investigated for the fundamental and frequency-tripled Nd:YAG laser harmonics (wavelengths λ=1064 and 355 nm). The rapid phase-change and thin liquid film ablation processes are examined in order to elucidate the cleaning mechanism. Optical reflectance and photoacoustic beam deflection probes are employed for monitoring the vaporization threshold and the acoustic transients generated. The plume evolution and acoustic wave propagation into the ambient air are visualized by laser flash photography. A jet composed of vapor and liquid columns/droplets is expelled from the laser-irradiated area. The pressure enhancement accompanying the explosive-vaporization process and the momentum supplied by the ablation plume are the main sources of the augmented cleaning efficiency at moderate laser energy densities.
Effects of nitridation by nitric oxide on the leakage current of thin SiO2 gate oxides
Authors: Gerardi C. , Melanotte M. , Lombardo S. , Alessandri M. , Crivelli B. , Zonca R.
Published: July 2002

We have studied the effects of nitridation with nitric oxide on the leakage current of thin (<8 nm) gate oxides. Under gate injection of electrons the oxide leakage current behavior reflects the trend of the electrical thickness and flatband voltage and it can be modeled by the Fowler–Nordheim relation. Conversely, a different behavior is observed for electron injection from the substrate. The leakage current during substrate injection is strictly related to the nitrogen that, as observed by secondary ion mass spectrometry, is located at the SiO2/Si substrate interface.
Impedance spectroscopy of single- and double-layer polymer light-emitting diode
Authors: Kim Seong Hyun , Choi Kang-Hoon , Lee Hyang-Mok , Hwang Do-Hoon , Do Lee-Mi , Chu Hye Yong , Zyung Taehyoung
Published: July 2002

ac electrical properties of the heterostructured polymer light-emitting diode consisting of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH–PPV) and sodium sulfonated polystyrene (SSPS) ionomer are studied. It is found that the carrier in SSPS is not the ion but the electron, and the conduction mechanism seems to be a space-charge limited current with exponential trap distribution. Based on the results of the impedance analysis, we propose a microscopic model to explain the enhancement of the electroluminescence efficiency of the indium tin oxide/MEH–PPV/SSPS/Al structure.
Optical absorption and light scattering in microcrystalline silicon thin films and solar cells
Authors: Poruba A. , Fejfar A. , Remeš Z. , Špringer J. , Vaněček M. , Kočka J. , Meier J. , Torres P. , Shah A.
Published: July 2002

Optical characterization methods were applied to a series of microcrystalline silicon thin films and solar cells deposited by the very high frequency glow discharge technique. Bulk and surface light scattering effects were analyzed. A detailed theory for evaluation of the optical absorption coefficient α from transmittance, reflectance and absorptance (with the help of constant photocurrent method) measurements in a broad spectral region is presented for the case of surface and bulk light scattering. The spectral dependence of α is interpreted in terms of defect density, disorder, crystalline/amorphous fraction and material morphology. The enhanced light absorption in microcrystalline silicon films and solar cells is mainly due to a longer optical path as the result of an efficient diffuse light scattering at the textured film surface. This light scattering effect is a key characteristic of efficient thin-film-silicon solar cells.
Molecular x-ray spectra: S-Kβ emission and K absorption spectra of thiophene
Authors: Perera Rupert C. C. , LaVilla Robert E.
Published: July 2002

The high resolution sulfur Kβ emission in fluorescence and sulfur K absorption of thiophene (C4H4S) were measured with a double crystal spectrometer. The sulfur Kβ emission spectrum was analyzed by comparison with complementary spectral data and with MNDO and ab initio (STO-3G) MO calculations. A tentative assignment of the prominent features in the absorption spectrum was made using MO calculations as a guide. In addition the sulfur LII,III emission spectrum was reinterpreted. The sulfur 1s binding energy of thiophene was estimated as 2477.6 eV.
Equation of state for chain molecules: Continuous-space analog of Flory theory
Authors: Dickman Ronald , Hall Carol K.
Published: July 2002

New, accurate equations of state for fluids of chain molecules are derived as generalizations of the well-known Flory and Flory–Huggins lattice theories to continuous space. Comparison with the results of new Monte Carlo simulations of athermal chains (freely jointed hard disks and spheres), extending over a wide range of densities, reveals that the generalized Flory–Huggins equation of state provides an accurate prediction for the pressure.
Ru L edge x-ray absorption studies of the electronic structure of Ru3(CO)12 adsorption and the formation of Ru–Cu bimetallics on Cu(111)
Authors: Sham T. K. , Ohta T. , Yokoyama T. , Kitajima Y. , Funabashi M. , Kosugi N. , Kuroda H.
Published: July 2002

Ru L2,3 edge XANES (x-ray absorption near edge structure) together with AES (Auger electron spectroscopy) and LEED (low energy electron diffraction) studies of Ru3(CO)12 adsorbed on Cu(111) reveal the following: (a) Ru3(CO)12 adsorbs molecularly on Cu(111) at low temperature (≲−50°). (b) Upon electron bombardment, Ru3(CO)12 dissociates to form bare Ru aggregates which exhibit very broad Ru L2,3 white lines and featureless absorption in the XANES spectrum indicating that the Ru atoms are not well ordered on the Cu(111) surface. (c) Annealing of the bare Ru aggregates on Cu(111) at 450 °C results in the formation of Cu/Ru bimetallic clusters in which the Ru atoms are in the core and exhibit bulk-like Ru L2,3 XANES while the surface is covered with Cu atoms. Analysis of the Ru L3 white line intensity indicates that charge redistribution in the Ru d band occurs upon the transformation from the bare Ru aggregates to the bimetallic Cu/Ru clusters on Cu(111).
A systematic study of polarizability and microscopic third-order optical nonlinearity in thiophene oligomers
Authors: Zhao Ming-Tang , Singh Bhanu P. , Prasad Paras N.
Published: July 2002

A systematic study of the dependence of the band gap, the linear optical susceptibility, the polarizability α, and the second hyperpolarizability γ, on the number of repeat unit is conducted for the thiophene series from monomer to hexamer. The linear optical susceptibilities for oligomers have been determined from the refractive index measurements on vacuum deposited films using the m lines technique. The orientationally averaged polarizabilities 〈α〉 have been measured from refractive index measurements of THF solutions. The orientationally averaged second hyperpolarizabilities 〈γ〉 have been measured by degenerate four-wave mixing studies of THF solutions. The validity of the Lorentz–Lorenz approximation is tested and found to be satisfactory. The experimental values of 〈α〉 and 〈γ〉 for thiophene and 〈α〉 for bithiophene are found to be in qualitative agreement with those obtained by a recent ab initio calculation which used the finite field method and included diffuse polarization functions. The experimentally observed dependence of 〈α〉 and 〈γ〉 on the number N of the thiophene repeat unit is compared with that predicted by a free electron model, PPP methods, and the ab initio calculations. For the case of polarizability, the repeat unit dependence is in good agreement with that predicted by the ab initio calculations but for the case of second hyperpolarizability, the agreement is not as good.
Spherically inhomogeneous fluids. II. Hard-sphere solute in a hard-sphere solvent
Authors: Attard Phil
Published: July 2002

The inhomogeneous Ornstein–Zernike equation and the Triezenberg–Zwanzwig expression for the density profile are solved using the Percus–Yevick closure for the inhomogeneous pair correlations of a hard-sphere fluid in the vicinity of an isolated hard-sphere particle. Results are presented for the solvent density profiles (solute–solvent radial distribution function) around solutes of diameter 0.01–50 times the diameter of the solvent hard spheres. At larger solute diameters, values obtained for the contact density are comparable in accuracy to those given by the scaled-particle theory, and significantly more accurate than those given by the Percus–Yevick analytic results for a bulk asymmetric mixture. A superposition approximation is introduced and this gives the effective solvent-mediated solute-solute interaction. The approximation is expected to be accurate for an asymmetric mixture at low concentrations. Two lower order approximations, the Asakura–Oosawa depletion attraction, and the Derjaguin curvature correction, are tested and found to be qualitatively correct.
Binary nucleation of water–sulfuric acid system: Comparison of classical theories with different H2SO4 saturation vapor pressures
Authors: Kulmala Markku , Laaksonen Ari
Published: July 2002

The classical hydrates interaction model and the classical condensation model have been compared in the temperature range 153.15–363.15 K. Various expressions for the kinetic part of nucleation rate have been examined. In the present study the saturation vapor pressure values of sulfuric acid given by Ayers et al. are extrapolated to lower (stratospheric) temperatures taking into account the temperature dependence of the enthalpy of vaporization. In our model calculations we have compared the effect of three different expressions for saturation vapor pressures. The nucleation rate will differ by several orders of magnitude (depending on temperature, water and acid activity) when using different theories and/or saturation vapor pressures.
An ab initio study on Penning ionization of a polyatomic target: H2O–He* (2 3S)
Authors: Ishida Toshimasa
Published: July 2002

An ab initio calculation is carried out for the system H2O–He* (2 3S) →H2O+(2B1,2A1,2B2)+He+e−. Not only the potential for the resonance H2O–He* (2 3S) state and for the ionized H2O+–He, but also the widths into three different ionized states are calculated with the Feshbach projection operator method. The resonance potential has an attractive well in the direction of lone pairs of the O atom of H2O. The well depth is estimated to be about 450 meV. The potential is compared with those for the same or similar system. The widths obtained reflect distributions of the molecular orbital of the target molecule concerned with the relevant ionization and that ionization into totally symmetric states is favored. The analyses of partial waves of emitted electrons leads to the conclusion that the σ electrons are mainly emitted in regard to the H2O–He pseudoaxis. The obtained results are consistent with results of Penning ionization electron spectroscopy.
Ab initio investigation of the N2–HF complex: Accurate structure and energetics
Authors: Woon David E. , Dunning Thom H. , Peterson Kirk A.
Published: July 2002

Augmented correlation consistent basis sets of double (aug-cc-pVDZ), triple (aug-cc-pVTZ), and modified quadruple zeta (aug-cc-pVQZ′) quality have been employed to describe the N2–HF potential energy surface at the Hartree–Fock level and with single reference correlated wave functions including Mo/ller–Plesset perturbation theory (MP2, MP3, MP4) and coupled cluster methods [CCSD, CCSD(T)]. The most accurate computed equilibrium binding energies De are (with counterpoise correction) 810 cm−1 (MP4/aug-cc-pVQZ′) and 788 cm−1 [CCSD(T)/aug-cc-pVQZ′]. Estimated complete basis set limits of 814 cm−1 (MP4) and 793 cm−1 [CCSD(T)] indicate that the large basis set results are essentially converged. Harmonic frequencies and zero-point energies were determined through the aug-cc-pVTZ level. Combining the zero point energies computed at the aug-cc-pVTZ level with the equilibrium binding energies computed at the aug-cc-pVQZ′ level, we predict D0 values of 322 and 296 cm−1, respectively, at the MP4 and CCSD(T) levels of theory. Using experimental anharmonic frequencies, on the other hand, the CCSD(T) value of D0 is increased to 415 cm−1, in good agreement with the experimental value recently reported by Miller and co-workers, 398±2 cm−1.