Search

In order to study a large number of generalized Bell states (GBSs) efficiently, it is important to classify them by local unitary (LU) equivalence. For example, there are C254(=12650) sets of four GBSs in C5⊗C5, which greatly exceed the C164(=1820) sets of four GBSs in C4⊗C4, and it is inconceivable to explore these sets directly without prior classification. In this paper, we consider the classification of GBS sets in C5⊗C5. First, two simple and useful characterizations of LU-equivalence of GBS sets are given. Then, one characterization is used to divide all 12 650 sets of four GBSs into eight equivalence classes including six locally distinguishable classes and two classes that cannot be discriminated by one-way local operations and classical communication. The second characterization is powerful and can be used to write a program, by using which all C255(=53130) sets of five GBSs in C5⊗C5 are divided into 21 equivalence classes including 9 locally distinguishable classes and 12 locally indistinguishable classes.

Tracer diffusion coefficients of camphorquinone in polypropylene glycol (PPG) with molecular weight 400, 1000, 2000, and 4000 have been measured as a function of temperature by using the forced Rayleigh scattering technique. At a fixed temperature, the diffusion coefficient decreases with increasing molecular weight of PPG. A master curve is obtained when the diffusion data are normalized with respect to the viscosity of the PPG liquid. A modified Stokes–Einstein equation for tracer diffusion is used to calculate the effective hydrodynamic radius R*. Below room temperature, R* is found to decrease with decreasing temperature. The decrease of R* is discussed in terms of dynamic heterogeneity and rotation–translation coupling mechanisms. The rotation–translation coupling mechanism has recently been proposed to account for the enhancement of the tracer diffusion coefficient in the molecular liquid in the supercooled state. Comparing R* calculated for CQ in PPG with that for the same tracer in salol in the su...

The frequency dependence of the first molecular hyperpolarizability β of a thiophene based charge-transfer chromophore has been measured by using a number of excitation wavelengths emitted from an optical parametric amplifier pumped by a 1 KHz 130 fs Ti/sapphire laser. The excitation wavelength covers the resonance and nonresonance region of the charge transfer chromophore. β shows a maximum on the red side of the charge transfer electronic absorption band. A comparison of the experimental result with a recent proposed calculation involving the Kramers–Kronig transformation of the charge-transfer absorption spectrum is made. It is found that while the Kramers–Kronig transformation analysis predicts a correct position of the β maximum, it does not yield an agreement in the resonance region of the frequency dependent first molecular hyperpolarizability.

The tracer diffusion coefficient of camphorquinone in salol has been measured by forced Rayleigh scattering technique at temperatures from 266 to 220 K. Over this temperature range, the shear viscosity of salol changes by nearly nine orders of magnitude. The diffusion coefficient is found to be much faster than the value predicted by the Stokes–Einstein equation. The enhancement of the diffusion coefficient is interpreted as due to the rotation–translation coupling mechanism, a mechanism commonly invoked to account for the intensity of the shear wave doublet in the depolarized Rayleigh scattering spectrum of a rotationally anisotropic molecular liquid in the supercooled state. The rotation–translation coupling parameter extracted from the translation diffusion measurement is compared with that obtained from the depolarized Rayleigh scattering spectrum of salol. Qualitative agreement between the two types of experiments is obtained.

The first hyperpolarizability (β) of a strongly charge-transfer (azulenic-barbituric) chromophore is measured by hyper-Rayleigh scattering (HRS) experiment using 11 excitation wavelengths, ranging from 900 nm to 1907 nm. The measured wavelength-dependence of the β value is used to investigate the dispersion relation of the first hyperpolarizability of the charge-transfer chromophore. When excited by the 1064 nm wavelength laser radiation, the experimental HRS spectrum shows a two-photon resonance (TPR) peak, which does not coincide with the maximum of the linear absorption spectrum. The wavelength dependence of the first hyperpolarizability cannot be explained by an undamped or damped two level model. However, incorporating vibrational motion in the damped two-level model results in a good fit between theoretical and experimentally measured β, especially in the vicinity of TPR region.

The first molecular hyperpolarizabilities (β) of a series of charge-transfer nonlinear optical (NLO) chromophores are measured with the hyper-Rayleigh scattering (HRS) technique using two excitation wavelengths at 1064 and 1907 nm. The 1907 nm wavelength is the longest excitation wavelength used for the HRS experiment. For some of these chromophores, β values in excess of 1000×10−30 esu at 1907 nm are obtained, and due to two-photon enhancement, even greater β values are found with the 1064 nm excitation. Chromophores with such large hyperpolarizability are expected to have potential applications in practical electro-optical devices. The dispersion of β is analyzed using a two-vibronic-state model developed previously in our laboratory. The study shows that it is necessary to consider the vibronic structure of the chromophore in the excited state in order to account for the behavior of the first molecular hyperpolarizability of the charge-transfer NLO chromophores.

Solutions of an incompatible polystyrene (PS)–polyisoprene (PIP) blend dissolved in CHCl3 are investigated by light scattering as a function of total polymer concentration at a fixed composition in the semidilute regime. Two diffusive modes are observed in the intensity–intensity time-correlation function. As the total polymer concentration increases, it is found that the rate constant of the fast mode increases and that of the slow mode as well as the relative amplitude of the fast mode decrease. With the help of a theory developed in this laboratory, we deduce from the light scattering data the self-diffusion coefficients and the Flory–Huggins interaction parameter χF of the two polymers. The self-diffusion coefficients of both polymers decrease as the total polymer concentration increase. Meanwhile, the Flory–Huggins interaction parameter χF between PS and PIP in CHCl3 (equal to 0.017) is nearly independent of polymer concentration. After making corrections for the excluded volume effect between unlike polymer using polymer solution theory, we obtain from χF a net segment–segment interaction parameter χF0, which is rather close to that obtained from the solvent free dry blend.

The dispersion of the first molecular hyperpolarizability β of strongly charge-transfer chromophores is investigated. The investigation extends the well-known Oudar–Chemla nonresonant two-level model into the resonant regime. An equation for β that includes the effect of dephasing and vibrational structure of electronic states is derived. It is shown that if only the dephasing mechanism is included in the two-level model, the intrinsic hyperpolarizability β0 calculated using the Oudar–Chemla equation from the hyper-Rayleigh scattering (HRS) experimental data will decrease with decreasing the excitation wavelength. The trend is reversed when the vibrational structure is also incorporated. It is concluded that in order to obtain a consistent β0 in the HRS experiment using an excitation wavelength in the resonance regime, it is inadequate to include only the dephasing mechanism. The vibronic structure also plays an important role and needs to be considered in the data analysis in order to obtain a β0 to agre...

Hyper-Rayleigh scattering (HRS) has been carried out for new azulenic donor–acceptor chromophores using near-infrared laser excitation at wavelengths of 1064 and 1907 nm. Hyperpolarizabilities obtained with the 1064 nm incident excitation are large compared with those obtained using the 1907 nm excitation, due to the effects of two-photon resonance enhancements in the former case. The HRS experiment using the 1907 nm excitation, while challenging to carry it out, gives the hyperpolarizability value closer to the intrinsic molecular hyperpolarizability. The popular two-level model that is used to predict the first hyperpolarizability of donor–acceptor charge transfer chromophores is employed to compare the measurements made on the same chromophores with 1064 and 1907 nm excitations. The model is found not to be able to correlate the results obtained at the two wavelengths. The first hyperpolarizability data obtained by using the 1907 nm excitation are consistent with electric field induced second harmonic generation data obtained by using the same wavelength.

The experimental setup used to perform hyper-Rayleigh scattering at the near infrared wavelength of 1907 nm is described. The setup described is employed to measure the first molecular hyperpolarizabilities, β, of three new thiophene-based nonlinear optical chromophores. Although scattering at this wavelength is weak and the experiment requires great care, use of it allows one to obtain near dispersion-free first hyperpolarizability. Comparing the results with those obtained on the same chromophores using the 1064 nm excitation, we show that the two state model, which is commonly used to relate the β values at different wavelengths, fails to correlate the results at these two excitation wavelengths.

The effects of surface tension, surface dilational modulus, stress relaxation time, and shear stress modulus on the surface laser light scattering (SLLS) spectrum of polymer solutions are investigated. The capillary wave component is significantly affected by both the stress relaxation time and the amplitude of the shear stress modulus. At moderate concentration, before crossing over to the elastic regime, a strong quasielastic component dominates the SLLS spectrum in polymer solution. In the viscoelastic regime, the capillary wave component of the SLLS spectrum is suppressed by the increase of the surface dilational modulus. The decrease of the surface tension gives rise to an effect similar to that caused by increasing the dilational modulus. However, at high polymer concentration in the elastic regime, the dilational modulus has only a negligible effect on the SLLS spectrum, in contrast to the effect of surface tension.

A detailed experimental study of the surface laser light scattering (SLLS) spectrum of the polyisobutylene (PIB)/decane solution over a wide range of polymer concentration is carried out. In the dilute solution, the SLLS spectrum is found to be described adequately by a scattering theory from a capillary wave. As the polymer concentration increases, the solution viscoelasticity is found to play an important role in affecting the dynamics of surface waves. By comparing experiment with theory, a clear-cut capillary wave to elastic wave evolution in the PIB/decane solution is found. The nature of the quasielastic peak that appears in the SLLS spectrum of the viscoelastic polymer solution is delineated.

A theory of light scattering from the polymer solution/air interface that includes the effect of surface adsorption is developed. The polymer solution is assumed to exhibit a linear viscoelastic response. The surface laser light scattering (SLLS) spectrum is calculated from surface hydrodynamic equations appropriate for linear viscoelastic fluids using the method of initial value problems. Numerical calculations are made to investigate the effects of surface tension and dilational modulus on the SLLS spectrum. The results show that the SLLS spectrum from polymer solutions having a high surface tension solvent displays a two-peak structure. The high-frequency peak exhibits more capillary wave character, and diminishes rapidly with decreasing surface tension or increasing dilational modulus as a result of surface adsorption. The two-peak structure is, however, found to be much less pronounced in a solution with a low surface tension solvent.

The temporal dependence of the time correlation function detected by quasielastic light (QEL) scattering in solution consisting of two homopolymers with arbitrary hydrodynamic and thermodynamic properties is investigated. New results appropriate for the ternary polymer solution in various concentrations are obtained. These new results should facilitate the analysis of the QEL scattering data of a ternary solution in any concentrations. Information about tracer diffusion coefficients of the constitutive polymers and their excluded volume interaction parameter is shown to be obtainable from the QEL experiment of the ternary polymer solution. Applications to ternary polymer solutions with one polymer isorefractive with the solvent, solutions with two polymers differing only in molecular weight, and solutions with two polymers having arbitrary refractive index increments are discussed. Clarification in regard to the ternary solution under the zero average contrast (ZAC) condition is also made. It is shown that under the ZAC condition, the autocorrelation function of the composition fluctuation in general decays with two exponentials, even at 1:1 symmetric composition.

The dynamic behavior of the mixture polystyrene (PS)–poly(methyl methacrylate) (PMMA)–dioxane in the semidilute concentration regime has been investigated by quasielastic light scattering. Two types of PS–PMMA–dioxane solution have been studied: One at a fixed composition but with different total polymer concentrations, and the other at a fixed total polymer concentration but with different compositions. For each solution, two distinct modes have been observed in the autocorrelation function of the scattered light; their relaxation times and relative amplitudes are studied as functions of composition and total polymer concentration. The present method differ from the previous one by not requiring one polymer to be isorefractive with solvent. By using the experimental results and with the help of theory, the self-diffusion coefficients of PS and PMMA and the Flory–Huggins interaction parameter χF have been deduced. The χF values obtained in this work are in good agreement with that obtained by other methods.

Dynamic light scattering studies of polystyrene (PS) in tetrahydrofuran (THF) in 1,4-dioxane (DO) and in THF/DO mixed solvent, subject to an external dc field, have been carried out. In THF the rate constant for the decay of the intensity autocorrelation function (IACF) is found to increase with increasing the external applied electric field; in DO, the electric field is found to have only a negligible effect on the IACF; in the mixed solvent it exhibits an intermediate effect, depending on the THF content. A hydrodynamic theory is proposed to account for the observed electric field induced effect in THF.

Linear electroabsorption (LEA) and linear electro‐optic (LEO) measurements are demonstrated using a model guest/host system consisting of disperse red 1 (DR1) doped in poly(methyl)methacrylate (PMMA). The LEA response is measured over a wavelength range of 300–700 nm. Electro‐optic measurements of the real and imaginary parts of the electric field‐induced Pockels coefficient are carried out at wavelengths near and far from the resonant absorption. A shift in the absorption maximum and change in the band shape of the LEA spectrum are related to the linear Stark effect and dipolar orientation. Expressions for the real and imaginary parts of the Pockels coefficient derived from the two experiments are provided. Induced dipolar order as a result of the contact poling process is investigated by the LEA measurement. Information concerning the relaxation of the induced dipolar order, investigated by the LEA measurement, is compared to the relaxation results obtained by using the second‐harmonic generation technique.

A microscopic theory based upon the model of molecular defect volume fluctuations is developed to provide an interpretation of the ultraslow mode and excess static light scattering intensity observed in supercooled glass‐forming liquids. By including the defect volume as a variable in the set of slow variables comprising of the number density and momentum density, it is shown that in an one component viscoelastic fluid, a diffusive mode associated with the fluctuations of defect volume is present, in addition to the usual q independent structural relaxation mode associated with density fluctuations. Fluctuations of defect volume arise from the configurational rearrangement of molecules. A two fluid model previously proposed for interpreting the anomalous quasielastic light scattering results in an one component fluid follows naturally from the present model.

An experimental study of poly(N‐vinyl‐2‐pyrrolidone) (PVP) in water solution has been carried out by using the surface laser light scattering (SLLS) technique. The concentration dependence data of the peak frequency and linewidth are obtained from the SLLS spectra of the PVP/water solutions with two PVP molecular weights over a wide concentration range varying from the dilute to semidilute regime. The equilibrium surface tension of the solution is also measured as a function of polymer concentration and molecular weight. In the dilute solution, the peak frequency and surface tension show only a small decrease with increasing concentration. However, in the semidilute concentration regime, the surface tension and the frequency shift decrease rapidly with increasing concentration, accompanied by the dramatic increase in the spectral linewidth. The surface tension, SLLS spectral peak frequency and linewidth show an important molecular weight dependence. Over the entire concentration range investigated, the SL...

A detailed light scattering study of polystyrene (PS) in diethyl malonate (DEM) semidilute solution has been carried out. DEM is a theta solvent for PS at 32 °C. Dynamic light scattering measurements carried out at temperatures closed to the theta temperature show only a diffusion mode in the intensity autocorrelation function; no slow modes are found in the semidilute PS/DEM solution with concentration up to more than 18 times the overlap concentration. For this system, the mutual diffusion coefficient is found to be mainly determined by the osmotic modulus, with the solution stress modulus making a negligible contribution. A slowing down of the mutual diffusion coefficient as the temperature approaches the critical temperature (at the critical concentration) is observed. These results show that despite considerable chain entanglements existing in the semidilute/concentrated PS/DEM solution, no viscoelastic slow modes are found. These results are not in agreement with the existing literature data for the...

The hyper‐Rayleigh scattering (HRS) intensity of two symmetric carbocyanine dyes (1122 DEDC and 1144 DEDC, full names given in the text) in methanol is measured as a function of dye concentration. These dye molecules at equilibrium show a negligible permanent dipole moment. The low concentration data showing that the HRS intensity is proportional to the dye concentration are used to determine the first hyperpolarizability for each of these dyes. However, above a concentration ρb=0.1×10−3 M, the HRS intensity shows an anomalous concentration dependence. Above ρb, the HRS intensity shows a saturation behavior and it even decreases with increasing concentration at high dye concentration. The depolarization ratio of the HRS intensity is also measured as a function of dye concentration. At lowest concentration, the depolarization ratio is 0.18. As the dye concentration increases, the depolarization ratio also rapidly increases but the increase quickly saturates as the concentration exceeds ρb. The concentratio...

The behavior of surface and trapped charge that originate during contact electric‐field poling of a model guest–host nonlinearly active polymer has been investigated. Charge effects in thin films of para‐nitroaniline doped polymethylmethacrylate were studied during and after the poling process by simultaneous measurement of the current through the poling circuit and the second harmonic generation (SHG) signal from the polymer system. The poling current present in a fresh sample was found to differ in both magnitude and temporal dependence to that observed in the sample during subsequent polings. The magnitude of the steady‐state current eventually reached during the poling process was found to depend on temperature and is related to the mobility of charge. A sharp drop‐off in SHG signal intensity that occurred when the poling electrodes were grounded is shown to result from the removal of surface charge that orients chromophore dipoles near the surface of the film; the decay in the macroscopic polarizatio...

Quadratic electro‐absorption (QEA) and quadratic electro‐optic measurements were performed with a guest/host system consisting of 4(4’‐N,N‐Dimethylaminophenyl)‐1,1‐bis(trifluoromethyl sulfonyl)‐1,3‐butadiene doped in poly(ethyl)methacrylate host polymer. The imaginary part of the QEA response was measured over a wavelength range of 450–600 nm. The real and imaginary parts of the electric field induced optical Kerr coefficient were measured at wavelengths near and far from resonance. Under different polarizations of the optical field in the QEA measurement, the two contributing coefficients of the third order susceptibility (χ(3)) were deduced. A distinctive temperature variation of the third order response was observed. Temperature dependence measurements from ambient to well above the glass transition of the guest‐host system were carried out. The same chromophore in a different polymer host, poly(vinyl)chloride, was also investigated. Correct expressions for the real and imaginary parts of the Kerr coef...

We present a new method to determine the Flory–Huggins polymer–polymer interaction parameter and self‐ (or tracer) diffusion coefficients in a ternary polymer solution made of two monodisperse polymers and a solvent by quasielastic light scattering (QELS). Previously proposed methods based on the random phase approximation (RPA) were restricted to special cases with two polymers having the same molecular weight and identical interaction parameters with the solvent. The present method (also using RPA) has removed these restrictions. It is applicable to an arbitrary ternary solution with polymers having different molecular weight and solvent interaction parameters. To illustrate, we have analyzed the published QELS data of the PDMS/PMMA/toluene ternary system to obtain self diffusion coefficients for each polymer and the Flory–Huggins polymer–polymer interaction parameter as a function of polymer composition in the system.

First order hyperpolarizabilities, β, for donor–acceptor substituted heteroaromatic compounds are measured by the hyper‐Rayleigh scattering technique. Hyper‐Rayleigh scattering utilizes the mechanism of number density fluctuations and enables the second harmonic generation signal of nonlinear optical chromophores to be generated as scattered light. Effects of substituting different electron donating groups to the parent heteroaromatic compounds and different solvents on the hyperpolarizability is investigated using this technique.

Dynamics and coupling of concentration fluctuations to longitudinal stress relaxation in a viscoelastic binary polymer solution have been analyzed using nonequilibrium thermodynamics. The calculation supplements the result previously obtained by this author using the Bearman–Kirkwood hydrodynamic equation for a multicomponent system. We have shown that the dynamics of concentration fluctuations is affected by the stress modulus of the solution only when there is a difference in the specific volume between polymer and solvent components. The present work also extends Bearman–Kirkwood’s result by further relating the partial longitudinal stress modulus of the polymer to the total longitudinal stress modulus of the polymer solution.

A detailed study of the decay of the second‐harmonic generation (SHG) signals of several guest–host nonlinear optical polymer systems has been carried out. The decay of the SHG signal is found to be affected by surface and trapped space charges. A fast component is observed at a low poling field and is found to be mainly due to surface charges which orient the chromophores near the surface. A second component, associated with macroscopic polarization, is induced at high field. The intensity of the second component, which decays considerably slower than the fast component, rapidly increases when the poling field is greater than a threshold voltage. Above the temperature of glass transition Tg, a single exponential function gives a good fit to the shape of the second component of the SHG intensity decay curve. The time constant of the slow component is found to increase with successive poling‐decay cycles and reaches a steady‐state value after several cycles have been performed. This lengthening effect is f...

The dependence of the second harmonic generation (SHG) signal of an amorphous polymer system containing nonlinear optical (NLO) chromophores on the polarizing electric field is investigated. It is shown that under a weak poling field condition, the SHG intensity is proportional to Ep2, provided that the polarizing electric field Ep is greater than a threshold field Es. Above Es, the macroscopic polar orientational order is established. The lengthening of the relaxation time for polar orientational order with increasing Ep is also observed. Theoretical analysis shows that the relaxation time is proportional to the polar order initially induced by the polarizing field. Experiments have been carried out to confirm the theoretical prediction.

Measurements of the second order nonlinear susceptibility by second harmonic generation (SHG) signal were made on the 2‐methyl 4‐nitroaniline/poly(methyl methacrylate) guest/host system as a function of the nonlinear optical (NLO) chromophore concentration and the poling field strength. The polar orientational order parameters (POP) L33 and L31 (defined in the text) were calculated from the SHG signals. The POPs were found to depend on the NLO chromophore concentration. The concentration dependence of POP is described in terms of Kirkwood’s g factor that describes the orientational pair correlation. The ratio of polar order parameters (L33/L31), measured in the weak poling field condition, is 3, independent of the NLO chromophore concentration; this result is in agreement with the result of a recent calculation. The usual Onsager local field factor, derived without considering orientational pair correlations, was shown to be inadequate. The static dielectric constant of the guest/host system is extracted ...

The orientational order parameter associated with the second order nonlinear optical (NLO) coefficient is calculated by using a statistical mechanics method that includes the angular dependent intermolecular interaction potential. It is shown that in addition to the alignment of dipoles due to the poling field, the orientational pair correlation (OPC) factor is also important in determining the orientational order parameter. When OPC is included, the order parameter becomes a function of the NLO chromophore concentration. The concentration dependent part of the order parameter is shown to be proportional to the Kirkwood g factor associated with the orientational correlation of the electric dipoles. In the weak field limit, it is shown that the ratio of two nonlinear optical coefficients, χ33/χ31, remains equal to 3, independent of the specific nature of the anisotropic intermolecular potential.

Efforts are made to relate the depolarized light scattering spectral power density to the dynamic shear compliance spectrum of a viscoelastic liquid. Generalized Langevin equations are used to describe the dynamics and coupling of reorientation and translational motions. It is shown that in the presence of the coupling, the depolarized scattering spectrum consists of two components; one is associated with the reorientational motion, and the other with the viscoelastic relaxation of the solution. Methods to obtain the dynamic shear compliance from the depolarized light scattering spectrum are described. It is also shown that in the limit of very slow reorientational motion, the depolarized light scattering spectrum is proportional to the imaginary part of the dynamic compliance spectrum, a result predicted by the Pockels photoelastic law.

Photon correlation spectroscopic studies of the mutual diffusion of poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blends are carried out. The experimental investigation deals with the measurement of the mutual diffusion coefficient of the PEO/PMMA blend by varying the molecular weight of PEO but keeping the molecular weight of PMMA fixed. At 20% volume fraction of PEO, and high PMMA molecular weight, the mutual diffusion coefficient linearly decreases with M−1PEO. The temperature dependence of the mutual diffusion coefficient is non‐Arrhenius. The Onsager coefficient of mutual diffusion is obtained as a function of temperature.

Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(α‐methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self‐diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self‐diffusion coefficient follows the Williams–Landel–Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self‐d...

We report the characteristics of graphene-based terahertz (THz) photodetector based on noise thermometry technique by measuring its noise power at frequency from 4 to 6 GHz. Hot electron system in graphene microbridge is generated after THz photon pumping and creates extra noise power. The equivalent noise temperature and electron temperature increase rapidly in low THz pumping regime and saturate gradually in high THz power regime which is attributed to a faster energy relaxation process involved by stronger electron-phonon interaction. Based on this detector, a conversion efficiency around 0.15 from THz power to noise power in 4–6 GHz span has been achieved.

[Fe1−δ(FeO)δ]x(TiO2)1−x (0≤δ≤0.91, 0.34≤x≤0.54) granular films were fabricated by magnetron sputtering. Large coercivity (HC = 10.5 kOe) and exchange-bias-field (HE = 6.5 kOe) at 5 K were found in the film with δ=0.84 and x = 0.48. AC susceptibility measurements exhibit a frequency (f) dependent peak Tf in the in-phase susceptibility curve. The fitting of the relation of Tf vs f with both the Vogel-Fulcher law and critical slowing down theory indicate that the evident enhancement of the HC and HE can be qualitatively ascribed to the existence of cluster-spin glass state. The results may help to deeply understand the origin of exchange bias and related effects.

The lifetimes of K(+)..Cl(-), K(+)..CN(-), and K(+)..SF(6)(-) heavy-Rydberg ion-pair states produced through Rydberg electron transfer reactions are measured directly as a function of binding energy using electric field induced detachment and the ion-pair decay channels discussed. The data are interpreted using a Monte Carlo collision code that models the detailed kinematics of electron transfer reactions. The lifetimes of K(+)..Cl(-) ion-pair states are observed to be very long,100 micros, and independent of binding energy. The lifetimes of strongly bound (30 meV) K(+)..CN(-) ion pairs are found to be similarly long but begin to decrease markedly as the binding energy is reduced below this value. This behavior is attributed to conversion of rotational energy in the CN(-) ion into translational energy of the ion pair. No long-lived K(+)..SF(6)(-) ion pairs are observed, their lifetimes decreasing with increasing binding energy. This behavior suggests that ion-pair loss is associated with mutual neutralization as a result of charge transfer.

Molecular dynamics was used to simulate the tensile behavior of monoclinic ZrO2 bicrystals constructed by fusing two symmetrically tilted single crystals at several temperatures ranging from 300 to 1200 K and then annealing them to 300 K. The average amorphous grain boundary (GB) is about 11 A thick (approximately twice the average unit-cell dimension). Axial elongation of the typical bicrystal at constant (boundary) velocity leads to failure at a global strain of about 4%, at which the maximum stress (i.e., the tensile strength) is approximately 6 GPa. The failure process is ductile, driven by growth and coalescence of voids in the GB, in contrast with that of the monoclinic single crystal, which undergoes essentially brittle fracture at a tensile stress of around 10 GPa. The tensile strength of the bicrystal is approximately inversely proportional to the thickness of the GB. Decreasing the fusion temperature increases the thickness of the GB and lowers the tensile strength accordingly. The dependence of...

Fluorescence resonant energy transfer (FRET) has been investigated between donor-acceptor pairs of type I CdSe/ZnS and type II CdSe/ZnTe quantum dots (QDs). An Au nanoparticles assisted FRET enhancement was clearly demonstrated. It is found that the efficiency of the energy transfer depends on the excitation wavelength and is largest when in resonance with the Au surface plasmon mode. With the large tunability of the emission intensity in near infrared region, our finding paves an excellent route for creating highly efficient optoelectronic devices and bioimaging labels derived from type II QDs.

The device performances of pentacene-based organic thin film transistors (OTFTs) were greatly improved by irradiation of infrared light. The field effect mobility and maximum drain current increase from 0.20±0.01 to 0.57±0.02 cm2/V s and 1.14×10−5 to 4.91×10−5 A, respectively. The (001) peak of the pentacene “thin film” phase increases in intensity by 4.5 times after infrared irradiation at 50 W for 2 h. Two types of crystal orientations, i.e., “crystal I” (2θ=5.91°) and “crystal II” (2θ=5.84°), coexist in the pentacene. The improvement of the characteristics of OTFTs is attributed to crystallization and crystal reorientation induced by infrared light.

We report that a far field magneto-optical system designed for detecting the off-plane magnetization in polar configuration can also detect the in-plane magnetization, while preserving the high sensitivity by using symmetric illumination and photoelastic modulation, even though the optical axis of the system is vertical to the sample surface. The spatial resolution can reach 500 nm at 514 nm in wavelength. The in-plane sensitivity can be eliminated by using an aperture to remove the off-axis obliquely incident light generated by the high numerical aperture objective lens that focuses the laser beam onto the sample surface.

A self-assembled benzimidazole-copper complex (SABCC) is utilized as the gate insulating material for pentacene organic thin film transistors (OTFTs) fabricated on a flexible polyethylene terephthalate plastic substrate. The fabrication features of SABCC are self-assembling, water-based processing, and selectivity of deposition. The pentacene OTFTs exhibit reasonable device characteristics. Threshold voltage, carrier mobility, on/off current ratio, and subthreshold swing are determined to be ∼−4.2 V, ∼0.08 cm2 V−1 s−1, ∼4×103, and ∼4.4 V/decade, respectively. The water-based fabrication process of the SABCC gate insulator on copper electrodes may provide an opportunity for low cost OTFTs on flexible plastic substrates.

Based on the high surface sensitivity of piezoelectric polarization of strained nitride semiconductors, surface functionalized nitride light emitting devices (LEDs) provide an excellent opportunity for the development of biological sensors. To demonstrate our working principle, a probe chip based on In0.22Ga0.78N∕GaN multiple quantum wells has been constructed and exposed to target DNA solutions, matched and/or mismatched, with different concentrations. The pronounced changes of photoluminescence spectra as well as Raman scattering A1(LO) spectra in matched target DNA clearly illustrate the feasibility of our proposed mechanism. The results shown here open up a new possibility for the application of nitride LEDs in biosensor engineering.

Substantial improvements in the nanofabrication and characteristics of gold Fresnel zone plates yielded unprecedented resolution levels in hard-x-ray microscopy. Tests performed on a variety of specimens with 8-10keV photons demonstrated a first-order lateral resolution below 40nm based on the Rayleigh criterion. Combined with the use of a phase contrast technique, this makes it possible to view features in the 30nm range; good-quality images can be obtained at video rate, down to 50ms/frame. The important repercussions on materials science, nanotechnology, and the life sciences are discussed.

A series of Ni(1−x)FexO (x=0, 0.015, 0.03, 0.05, and 0.1) bulk samples was synthesized by the chemical concentration-precipitation method. Phase composition analysis was carried out, which showed that trace amounts of ferromagnetic phase NiFe2O4 could not be detected by x-ray diffraction in these bulk samples with x≤0.03. When x>0.03, NiFe2O4 ferrite is detected easily. The magnetic properties of all the bulk samples were investigated by measuring their magnetization as a function of temperature and magnetic field. The results indicated that all the bulk samples sintered in air exhibited large room-temperature ferromagnetic behavior ascribed to a ferromagnetic impurity phase. Simultaneously, an exchange bias and training effect were also observed in all the bulk samples, suggesting the possibility of the existence of a strong ferromagnetic/antiferromagnetic exchange coupling in this kind of compound. Specifically, the exchange bias field could be tuned by changing the concentration of the Fe dopant.

Highly conductive PrBaCo2O5.5+δ thin films were grown on (001) SrTiO3 by pulsed laser deposition. Microstructural studies from synchrotron x-ray diffraction and transmission electron microscopy reveal that the as-grown PrBaCo2O5.5+δ films are a-axis oriented with excellent single crystallinity. Two domain structures with c axes in the plane directions parallel to the substrate surface were found with an atomic sharp interface. Transport property and isothermal magnetoresistance measurements for both as-grown and post-annealing were done to understand the physical properties of the films. An abnormal positive magnetoresistance effect was observed in the postannealed films, which suggests that the spins in the system are polarized easier.

We report investigations on the optical properties of type-II CdTe∕CdSe core-shell quantum dots. By varying the core size, we provide an elegant way to verify that the detected emission signal indeed arises from type-II band alignment. The photoluminescence (PL) peak energy increases with a third root of the excitation power. Both of the PL peak energy and linewidth exhibit unique temperature dependence. All these observations can be rationalized by the band bending effect resulting from the spatially separated photoexcited carriers in a type-II band alignment.

The writing process in the formation of χ(2) gratings for disperse red 1 (DR1)∕polymethylmethacrylate film at room temperature is investigated. The writing laser power and film thickness dependence for the growth of the second harmonic generation (SHG) intensity in optically poled films is delineated. The effective growth rate of the SHG intensity is shown to be proportional to the fourth power of the fundamental laser intensity. This result is not in agreement with the existing theory. A model to account for the experimental result associated with the writing process is proposed. The dependence of the induced SHG intensity on the film thickness dependence is also studied. An equation that can adequately describe the dependence on the fundamental laser intensity and the film thickness for the effective growth rate of the SHG intensity is provided.

The power dependence of the optical poling process of a new azo chromophore in the polymethylmethacrylate matrix at room temperature has been investigated. The existing theory is found to be inconsistent with the experiment. A simple model based on the rate equation is proposed to describe the writing process of the chromophore/polymer system. The measured growth rate and the plateau second-harmonic generation intensity as induced by all optical poling are found to be in good agreement with the prediction of the simple model.

We have provided a model to interpret the non-quadratic-intensity dependence behavior commonly observed in the two-photon fluorescence (TPF) experiment excited with high laser intensity. The model also provides one with a different technique to measure the two-photon absorption cross section of an organic chromophore in solution. In contrast to the commonly used low intensity technique that depends on the quadratic-intensity law, the present technique is based on the non-quadratic-intensity dependence of two-photon fluorescence. Auxiliary data such as two-photon quantum efficiency and fluorescence collection efficiency, essential in the low intensity method, are not required in the present technique. TPF measurements of Rhodamine B in methanol are carried out to demonstrate the validity of the present method. The method is used to determine the two-photon absorption cross section of a new chromophore attached with tricyano-derivatized furan as the electron acceptor. The two-photon absorption cross section measured using this method is also compared with that using a conventional transmission technique.

One-, two-, and three-photon absorption induced fluorescence intensities of a novel nonlinear optical chromophore have been measured by using a tunable femtosecond pulsed laser as the excitation. Four resonance peaks are observed as the excitation wavelength is tuned from 600 to 2000 nm. These peaks correspond to the one-, two- and three-photon fluorescence resonance. Except for intensity difference, the lifetime and the fluorescence spectrum are found to be the same for the one-, two-, or three-photon resonance, hence suggesting that the same excited energy level is involved in emitting the fluorescence intensity. A three-level model is developed to account for the incident excitation laser intensity dependence of the one-photon and multiphoton fluorescence intensity. The model allows the multiphoton absorption cross sections to be extracted; it can also account for the deviation observed in the linear, square, and cubic intensity dependence of the one-, two-, and three-photon fluorescence intensity, respectively. To determine the absorption cross sections, the present method does not require the fluorescence quantum efficiency data, needed in the low intensity technique.