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A series of discontinuous and semi-continuous silver island films were prepared with sputtering technique and vaporizing method, respectively. The plasmon resonance absorption in visible region, critical percolation infrared transmittance and the fractal dimension of two types of samples were investigated. Only discontinuous vaporized Ag films show resonant plasmon absorption. For sputtered samples, both discontinuous and semi-continuous films show plasmon absorption in visible region. The value of fractal dimension, critical exponent and critical percolation infrared transmittance (Df, ν, Tc) are measured to be (1.56, 1.26, 60%) for sputtered Ag films and (1.60, 1.14, 15%) for vaporized samples.

Effects of well number on temperature characteristics in 1.3-μm InGaAsP–InP multi-quantum-well lasers have been investigated. A smaller well number is suitable for lower threshold current and higher differential quantum efficiency at 25 °C, while larger well number produces better performances at 85 °C. Furthermore, lasers with a larger well number can achieve a less output power penalty at high temperature. For the first time, a theoretical model has been established to precisely explain the relationship between the characteristic temperature of threshold current and that of external differential efficiency.

A systematic investigation has been undertaken on the growth, characterization and performance of tensile-strained multiple-quantum-well (MQW) lasers emitting at 1.34 mum. Two photoluminescence peaks corresponding to n = 1 electron-light hole (E1-LH1) and n = 1 electron-heavy hole (E1-HH1) transitions are clearly observed in MQW structures. The improvements of tensile strained MQW lasers such as the internal quantum efficiency, internal loss and threshold current are attributed to the increased energy separation between LH1 and HH1 when the tensile strain and well width are larger. The relatively thick barrier layer is required to mitigate the strain relaxation between the quantum wells. The degradation of device performance by the excessive barrier height could be attributed to the exacerbated spatial non-uniformity of the carrier distribution in the valence band. The optimized tensile strained MQW lasers with 300 mum cavity length and ridge waveguide (RWG) structure exhibit a lower threshold current of 13 mA and a higher external differential efficiency per facet of 0.29 mWmA(-1) at 25 degreesC.

Polarization insensitive 13 10 nm InGaAsP-InP multi-quantum-well (MQW) semiconductor optical amplifiers (SOAs), with 7degrees tilted ridge waveguide and buried-window end facets, have been fabricated and fully characterized on chip and module level. SOAs chips with an optimized complex strained MQW active region exhibited less than 1 dB polarization dependence of amplified spontaneous power in the drive current range of 50-200 mA. The amplifier module, having a residual facet reflectivity of 2.8 x 10(-5), achieved 25 dB fibre-to-fibre unsaturated gain, for both transverse electric and transverse magnetic polarization states, 11.2 dBm saturation output power, and 7.6 dB noise figure at 1310 nm. The polarization dependence of gain was less than 0.6 dB in the 3 dB gain bandwidth of 56 nm. Coupling efficiency played a significant role in the gain, saturation output power and noise figure of a SOA module. Spot-size-converter integrated SOAs with buried heterostructures are expected to exhibit further improved performances.

We have fabricated 1.3 µm InGaAsP–InP strained-layer multi-quantum-well (MQW) lasers with an AlInAs electron stopper layer (ESL). The ESL was inserted between the MQW active layer and the p-side separate confinement heterostructure (SCH) layer to suppress electron leakage in the conduction band from the active region to the p-cladding layer. Lasers with an ESL exhibited much improved temperature characteristics of threshold current and external slope efficiency. As a result, a lower power penalty of 2.2 dB from 25 °C to 85 °C was achieved at an injected current of 60 mA. The insertion of an AlInAs ESL into the SCH layer is a successful way to realize the uncooled operation of 1.3 µm InGaAsP–InP lasers at high temperatures.

We investigate the effect of geometric anisotropy on the optical nonlinearity enhancement for a periodic composite with a rectangular array of elliptic semiconducting cylinders in an insulating host. By using a series expression of the space-dependent electric field obtained by a simple Fourier method in a periodic composite, we calculate the frequency dependence of the effective third-order nonlinear susceptibility as a function of anisotropy. The results show that the height of the nonlinearity enhancement peak may be increased by several orders of magnitude as the aspect ratio of the ellises is decreased or the lattice edge length ratio is increased. At resonance frequency, there exists a strong anomalous dispersion. We also investigate the effect of the volume fraction of the semiconductor phase for composites with a square array of circular semiconducting cylinders.

Ag–Si nano-composite films were prepared with a co-sputtering technique and step-sputtering method, respectively. The step-sputtered sandwich Ag–Si samples with Ag islands of area fraction approximately 0.43 showed strong resonance absorption near 610 nm. In contrast, the resonance absorption was widened and weakened in the co-sputtered Ag–Si films with the Ag volume fraction at approximately 0.26. The effective dielectric function of the composite materials consisting of multi-stage nanosized metal particles (or clusters) was deduced based on the theory of Sheng. The calculated absorptive coefficients from this modified model coincides very well with the measured spectra of co-sputtered Ag–Si composite films.

The nano-composite films consisting of (Au,Ag) alloy particles embedded in the fused quartz were prepared by the RF co-sputtering technique, and the optical properties of the samples heated in Ar atmosphere and in air atmosphere were investigated. The effective dielectric function for the three-component alloy-dielectric composite system was deduced from the Clausius-Mosotti equation. The calculations from this theory gave a proper explanation for the measured optical absorptive spectra of (Au,Ag)/SiO2 nano-composite films. (C) 2000 Elsevier Science B.V. All rights reserved.

The effect of anisotropic microstructure of a two-dimensional periodic composite on the optical nonlinearity enhancement of the bulk material is investigated. The calculations are based on Stroud–Hui expression for effective third-order nonlinear susceptibility χe and the series expressions of space dependent electric field and/or electric displacement in periodic composite obtained by a simple Fourier approach. The frequency dependences of χe and effective dielectric function ee for the anisotropic composites with metallic elliptic inclusions in an insulating host have been evaluated. The results indicate that for geometric anisotropic composites, the positions of the absorption and nonlinearity enhancement are very close, not separate. When the morphology of inclusions varies, the variation tendencies of strengths of the absorption and nonlinearity enhancement are opposite. With the shape variation of elliptic inclusions from prolate to oblate, the nonlinearity enhancement increases while the absorption decreases.

In three-component metal-dielectric composite materials, there are three kinds of metallic particles. Clausius-Mosotti equation is applied to a collection of the three kinds of metallic particles. A simple formula of effective dielectric function for the three-component composite system is derived. The optical absorptive coefficient of Au-Ag-SiO2 composite material is calculated with the derived formula. The calculation predicts the existence of double resonance absorptive peaks, which gives a satisfied explanation of the measured optical absorptive spectra of Au-Ag-SiO2 composite films. (C) 2000 Elsevier Science B.V. All rights reserved.

Temperature dependence of Ohmic resistance, and nonlinear current–voltage (I–V) characteristics at 77 K were systematically studied in pure potassium blue bronze K 0.3 MoO 3 and Na-doped alloy bronzes K 0.3-x Na x MoO 3(x = 0.02, 0.05, 0.10). No considerable influence of Na ions doping in K 0.3 MoO 3 was found on the Peierls transition temperature, while obvious enchancement on semiconductor gap and remarkable influence on the first threshold field were observed. We attribute the first phenomenon to two opposite effects of Na ions, and the depinning model is proposed to account for the latter. The analytical form of nonlinear charge-density wave current I CDW in a moderate field range fits the power-law relation, i.e. I CDW ∝ (V/V T -1)α, where the exponent α is about 3/2 and slightly enhanced by Na ions doping.

Stripe-width and cavity length dependencies of high-temperature performances of 1.3-/spl mu/m InGaAsP-InP well-designed buried-heterostructure strained multiquantum-well (MQW) lasers were investigated. The threshold currents as low as 4.5/10.5 mA and slope efficiencies as high as 0.48/0.42 mW/mA at 25/spl deg/C/85/spl deg/C were obtained in the MQW lasers with 1.5-/spl mu/m width, 250-/spl mu/m length, and 0.3/0.85 facet reflectivity. With temperature increasing from 25/spl deg/C to 85/spl deg/C, the MQW lasers exhibited lower output power degradation, the minimum value was 1.78 dB at an operation current of 45 mA. The MQW lasers were suitable for application in optical access networks.

Nonlinear transport behavior, which shows a sudden breakdown transition to zero- or negative-differential resistance in the high field, is observed in the quenched thallium- or tungsten-doped blue bronzes K0.15Tl0.15MoO3 and Tl0.3Mo1-xWxO3 at 77 K. It is found that the critical breakdown transition threshold is unstable for the induced field and decreases with increasing cycling times of the conducting current and, finally, reaches a definite value. When the current increases from 30 to 100 mA, the voltage between the two ends of the sample does not show a clear increase, i.e., a similar phenomenon with zero-differential resistance. On the downward cycle of the current, the voltage-current curve exhibits a large electronic hysteresis over the nonlinear region. On the other hand, in the critical region, the breakdown transition is usually accompanied by a voltage pulse with a large amplitude and exhibits a negative-differential resistance. These effects of an electric field on a pinned charge-density wave are phenomenologically interpreted in analogy with the mechanical deformations of the crystal solid.

We report the vibrational density of states (VDOS) for the C70 molecule calculated using the recursion method. The Born potential is adopted for calculating the dynamic matrix. The results show that the peak positions of the VDOS for the C70 molecule are in reasonable qualitative agreement with those of Raman and infrared measurements.

The vibrational densities of states for a deterministic self-affine aggregate and the two-dimensional Eden hulls are computed numerically by the continued-fraction recursion method. It is shown that in contrast with the geometrical complexity the density of states for the diagonally self-affine fractals exhibits a simple power-law scaling. Motivated by these suggestive results, we extend the work done by Alexander and Orbach in 1982 and conclude that the concept of fractons is still valid in characterizing the vibrational spectra of all diagonally self-affine fractals. We also relate the fracton dimensionality to other exponents.

The vibrational densities of states for an octagonal quasiperiodic lattice are calculated. Crossovers from phonon excitations to fracton-like excitations are found in the low-frequency parts of the spectra (this part is referred to as the continuous spectrum); meanwhile, localized vibrational modes are observed in the high-frequency parts (this part is referred to as the characteristic spectrum). The spectral features are governed by alpha and beta, the central and non-central force constants of the Born model. For the low-frequency continuous spectrum, when alpha/beta equals unity (isotropic model) and when alpha/beta is not very large, a power law is satisfied in the fracton-like excitation frequency regime but, when alpha/beta approaches infinity, the spectrum deviates from the original power law. For the high-frequency characteristic spectrum, in an isotropic situation, i.e. in the case when alpha/beta = 1, the localized mode is isolated and a gap separates it from other modes but, when there is no longer isotropy, the gap disappears.

We calculate the vibrational density of states (VDOS) for the C60 molecule using the recursion method. The Born potential is adopted for calculating the dynamic matrix. The results show that the peak positions of VDOS for C60 are in qualitative agreement with those of the Raman and infrared measurements.

The vibrational densities of states for the diffusion-limited aggregate with varying elastic force consstants are calculated by the recursion method of Haydock, Heine and Kelly. It is found that the spectrum with central forces is very different from that with isotropic forces which is characterized by a power-law behaviour in the fraction frequency regime. An interesting crossover is also observed when the ratio of the central to the non-central force constants of the Born model varies from alpha/beta = 1 to alpha/beta = inifity.

A kinetic model is presented which simulates the propagation of cracks in solids composed of discrete atoms. The resulting fracture surface is found to be a fractal, the dimension of which depends on the elastic constants of the material.

Using the57Fe Mossbauer effect the influence of the Ga content in amorphous (Fe1−x Ga x )84B16 on the average hyperfine fields $$\bar H$$ and isomer shift has been studied. For the sample (Fe0.98Ga0.02)84B16 the $$\bar H$$ , as well as the recoilless fraction,f a were measured as functions of temperature ranging from 12 K to 300 K. The experimental results show a linear correlation between Inf a and δ, and well as between δ andx. In the temperature range $$\bar H(T)$$ can be described by the Brillouin function and the second-order Doppler shift is appreciable. The characteristic temperature for such an amorphous alloy is 372 K. the effective vibrating massM eff=79 a.u.

The effect of geometric anisotropy on the optical nonlinearity enhancement for the composites with metal or semiconductor spheriodal-shaped particles periodically in an insulating host is investigated. The frequency dependences of effective nonlinear susceptibility are calculated with the Stroud-Hui relation and a series expression of space-dependent electric field in periodic composites. The results show that for both metal-insulator (MI) and semiconductor-insulator (SI) composites, nonlinearity enhancement increases almost to its maximum when the percolation networks of the inclusion phase form. The nonlinearity enhancement increases to its maximum when the composites are transformed into the Boyd-Sipe layered composites. The behavior of the nonlinearity enhancement near the percolation threshold is also investigated. A local minimum appears in the nonlinear optical responses at the percolation threshold for the MI composites. For the SI composites the local minimum appears when the ratio of the bound-electron number density to the effective mass of the electron is large.

The vibrational densities of states for a series of field-biased diffusion-limited aggregation clusters with varying fractal dimensions in two Euclidean dimensions are computed numerically by the continued-fraction recursion method. It is confirmed that the density of states is characterized by a power-law behavior in the fracton-frequency regime. The fraction dimensionalities are found to favor the Aharony-Stauffer conjecture in the present case. Numerical results also show that the fraction mode is strongly localized in the diffusion-limited aggregation systems.

Magnetoresistance (MR) of a nanostructured material, monodisperse Fe3O4 nanospheres of about 200nm coated with thin SiO2 and compactly cold pressed and sintered, has been investigated. A high MR, up to 10.8% at 1T and 17% at 8T, has been observed at 100K. This enhanced MR is likely arising from the spin-polarized tunneling of conducting electrons through the insulating SiO2 boundaries. The decrease of the MR with the temperature increasing was attributed to the existence of the local spins in the grain boundaries. In addition, the MR ratio decreases with the SiO2 thickness increasing and sintering temperature decreasing. It suggests that the magnetic property of the insulating barrier is crucial for enhancing the low-field MR at a high temperature.

We investigate the effect of geometric anisotropy on optical nonlinearity enhancement for composites with semiconductor elliptical cylinders in an insulating host in a square lattice. The frequency dependences of the effective nonlinear susceptibility are calculated, and the optical nonlinearity of the composites near the percolation threshold are studied. The calculations are based on the Stroud–Hui relation and a series expression of the space-dependent electric field in periodic composites. The results show that, analogous to metal–insulator composites, a local minimum appears in the nonlinear optical responses near the percolation threshold for two-dimensional percolating semiconductor–insulator composites with geometric anisotropy when the ratio of the bound-electron number density to the effective mass of the electron is large. The results also show that the nonlinearity enhancement increases almost to its maximum when a structure with layers of fluctuating thicknesses forms, and there are no further obvious increases of the enhancement when the thickness fluctuation of the layers decreases. We compare the results of our calculation with those calculated by use of the Boyd–Sipe relation in layered composites, and we conclude that the nonlinearity enhancement reaches its maximum when composites with elliptic cylinders are transformed into Boyd–Sipe-type layered composites.

The lattice trapping effect of a crack in solids with layered structure has been studied with a double‐chain model. It is shown that the difference in physicomechanical properties between different atomic planes has significant influence upon this effect, and the stress range for stability of a crack can be enhanced by increasing the difference. This perhaps, provides a way for the lattice trapping effect to be made observable by appropriately synthesizing solids with superlattices of special design.

The authors have calculated the vibrational densities of states for v-SiO2 and the binary v-SiO2-GeO2 glasses. The results for v-SiO2 are in agreement with the neutron scattering spectrum and previous theoretical calculation of Bell et al. (1972). The spectra of v-SiO2-GeO2 glasses which contain only a small fraction of GeO2 are found to have the general features of v-SiO2, except for a new peak characteristic of Ge doping and a split To-like band which agrees with Raman scattering and can be understood simply by the superposition of the local densities of states of SiO4 and GeO4 tetrahedral with different weights.

Structural relaxation is investigated for (Fe1−xCex)84B16 (x = 0.04, 0.06) amorphous alloys by magnetic aftereffect (MAE) and Mossbauer techniques in the temperature range from RT to 420 °C, and electrical resistivity is measured to observe crystallization up to 730 °C. The Hopkinson maximum appears at temperatures higher than 400 °C, and a relaxation spectrum of the Richter type due to diffusion of B atoms with three characteristic peaks below 400 °C is observed. Hyperfine field distribution P(H) in specimens after different thermal cyclings up to 320 °C yields three different types of short range order in the amorphous alloys. The mechanism of the effect of cerium atoms and the evolution of structural defects in the process of annealing are discussed. Im Temperaturbereich zwischen RT und 450 °C werden mittels magnetischem Nachwirkungs-effekt (MAE) und Mosbauertechnik Strukturrelaxationen fur amorphe (Fe1−xCex)84B16 (x = 0,04; 0,06)-Legierungen untersucht und um Kristallisation bis zu 730 °C zu beobachten, der elektrische Widerstand gemessen. Das Hopkinson-Maximum tritt bei Temperaturen hoher als 400 °C auf, und es wird ein Relaxationsspektrum vom Richtertyp infolge von Diffusion von B-Atomen mit drei charakteristischen Maxima unterhalb 400 °C beobachtet. Hyperfeinfeldverteilung P(H) in Proben nach unterschiedlicher zyklischer thermischer Behandlung bis zu 320 °C ergeben drei verschiedene Typen von Nahordnung in den amorphen Legierungen. Der Mechanismus des Einflusses der Ceriumatome und die Entwicklung von Strukturdefekten wahrend des Temperungsprozesses werden diskutiert.

Magnetic after-effects (MAEs) are investigated for (Fe1−xGax)84B16 (x ≦ 0.06) amorphous alloys between RT and 450 °C with a minicomputer controlled automatic disaccommodation apparatus. Hopkinson maximum is found at temperatures higher than 380 °C and the Curie temperature increasing with increasing content of Ga. A relaxation spectrum of Richter type due to diffusion of B atoms is observed in temperature range below 300 °C. The spectrum for Ga-containing alloys initially presents two peaks. Thermal cyclings and anncaling procedures affect the spectrum form and reduce the effect of Ga. Curve fitting of the relaxation spectrum results in a distribution of the activation energy characterized by two maximal values, 1.45 and 1.67 eV. MAEs with low activation energies gradually diminish with heating at low temperatures. The mechanism of effects of gallium and evolution of structural defects are discussed. Magnetische Nachwirkungen (MAE) werden fur amorphe (Fe1−xGax)84B16 (x ≦ 0.06) Legierungen zwischen RT und 450 °C mit einer rechnergesteuerten automatischen Fehlanpassungsapparatur untersucht. Bei Temperaturen hoher als 380 °C wird das Hopkinsonmaximum gefunden und Curietemperaturen, die mit steigendem Gehalt an Ga zunehmen. Im Temperaturbereich unterhalb 300 °C wird ein Relaxationsspektrum vom Richter-Typ beobachtet, das auf die Diffusion Von B-Atomen zuruckzufuhren ist. Das Spektrum fur Ga-enthaltende Legierungen zeigt anfanglich zwei Maxima. Zyklische thermische Belastung und Ausheilverfahren beeinflussen die Form des Spektrums und reduzieren den Einflus des Ga. Kurvenanpassung des Relaxationsspektrums fuhrt zu einer Verteilung der Aktivierungsenergie, die durch zwei Maximalwerte, 1,45 und 1,67 eV, ge-kennzeichnet ist. MAE mit niedriger Aktivierungsenergie verschwinden graduell mit Aufheizung bei niedrigen Temperature. Der Mechanismus der Einflusse des Gallium und die Bildung der Struk-turdefekte werden diskutiert.

The behavior of internal friction (IF) of an Al–0.69 wt% Mg–0.63 wt% Si–0.11 wt% RE (mixed) alloy is investigated. The results show that only one IF peak is obtained near 200 °C between RT and 400 °C, independent of whether the alloy is in the quenched, aged, or annealed state. The ageing behavior of the peak is studied in detail, it is believed that the IF peak near 200 °C is a grain boundary peak associated with precipitation on grain boundaries, and the characteristics of the peak rising during ageing displays the dynamic process of the alloy precipitation. Es wird das Verhalten der inneren Reibung (IF) einer Al–0,69 Gew% Mg–0,63 Gew% Si–0,11 Gew% RE (Misch)-Legierung untersucht. Die Ergebnisse zeigen, das nur ein IF-Maximum bei etwa 200 °C zwischen RT und 400 °C erhalten wird, unabhangig davon, ob sie im abgeschreckten, gealterten oder getemperten Zustand ist. Das Alterungsverhalten des Maximums wird ausfuhrlich untersucht, es wird angenommen, das das IF-Maximum bei 200 °C ein Korngrenzenmaximum darstellt, verknupft mit Prazipitaten an Korngrenzen, und die Charakteristik des Maximums, das wahrend der Alterung zunimmt, den dynamischen Prozes der Legierungsausfallung zeigt.

Using the57Fe Mossbauer effect the influence of the Ga content in amorphous (Fe1−xGax)84B16 on the average hyperfine fields\(\bar H\) and isomer shift has been studied. For the sample (Fe0.98Ga0.02)84B16 the\(\bar H\), as well as the recoilless fraction,fa were measured as functions of temperature ranging from 12 K to 300 K. The experimental results show a linear correlation between Infa and δ, and well as between δ andx. In the temperature range\(\bar H(T)\) can be described by the Brillouin function and the second-order Doppler shift is appreciable. The characteristic temperature for such an amorphous alloy is 372 K. the effective vibrating massMeff=79 a.u.