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Magnetic field-induced spin switching of NdFeO3 crystal was demonstrated with TDS spectroscopy. The critical magnetic field to achieve the magnetic phase transition is modulated by temperature. In particular, a useful one-way spin switching has been found in NdFeO3 crystal.

For complex welding, Petri net (PN) theory is adopted to model a welding flexible manufacturing system (WFMS) in this paper. When the model called the multi timed color Petri net (MTCPN) was designed, a professional simulation software package was used to test it theoretically. Then, a scheduling method was devised to optimize the conflicting information in the model. A welding experiment based on the model is carried out. The results of the welding experiment and the model simulation show that the modeling method is correct and feasible. This research presents a new way to optimize a WFMS and it develops the application area of PN theory.

Because of the complexity of controlling the flexible manufacture system in welding, a theory of Petri net is adopted to model and simulate in this paper. When we model the complex system, a new way named TCPN is used to analyze information. And two kinds of models are built which are STCPN and MTCPN on the two systems, single welding robot system and multi welding robot system, respectively. After building and analyzing the control models, an optimization algorithm named full rank is designed to optimize and consummate the models, which is proved right in theory by simulation software cpntools. The result of the simulation experiment illustrates that the way of the model is rational and feasible.

Three coordination polymers [Co(L) 2 (SCN) 2 ] ( 1 ), [Mn(L) 2 (SCN) 2 ] ( 2 ) and [Cd(H 4 L) 2 Cl 2 ] ( 3 ), were obtained by the reaction of Co II , Mn II , Cd II salts with di-Schiff base ligand N , N ′-bis(3-pyridylmethyl)-4,4′-biphenylenedimethyleneimine (L) and its reduced form (H 4 L), respectively and their structures were determined by X-ray crystallography. In the solid state, complexes 1 and 2 feature 1D hinged chains, while complex 3 has a 2D network structure. Complex 2 was found to show optical limiting property with a 3 ns pulsed laser at 532 nm in DMF solution.

One-dimensional photonic crystals with a defect layer of CdS were fabricated. The observed enhancement of two-photon absorption (TPA) in the CdS layer can be attributed to the intensified optical field confined within the defect layer of the photonic crystal. The results show that the enhancement of TPA coefficient depends basically on the number of periods of the photonic crystal and the defect mode position in the photonic band gap. The observation agrees qualitatively with the expectations of a computation by matrix transfer formulation.

The composite nanoparticles of Au-core capped by CdS shells of different thickness were prepared and assembled into densely packed 3-dimensional films by the layer-by-layer self-assembly (LBL) technique. These films exhibited the 3-dimensional structure of densely packed Au@CdS composite nanoparticles and the shell thickness was tunable by changing the concentration of Cd2+-thiourea complexes. These multilayer films exhibited enhanced third-order optical nonlinear responses and ultrafast response times (several picoseconds). The third-order nonlinear optical susceptibility of the film with the CdS shell thickness of 4.4 nm was estimated to be 1.48 x 10(-9) esu and the value decreases with the increase of the CdS shell thickness. The enhancement of the optical nonlinearity was explained based on the calculation according to the electrostatic approximation by the solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric field effects in the CdS shell region. Additionally, the nonlinearity was optimized by determination of the values of the dielectric constant and thickness of the different shell.

We report the ultrafast and large third-order nonlinear optical properties of CdS nanocrystals (NCs) embedded in a polymeric film. The CdS NCs of 2 nm radius are synthesized by an ion-exchange method and highly concentrated in the two layers near the surfaces of the polymeric film. The two-photon absorption coefficient and the optical Kerr coefficient are measured with laser pulses of 250 fs duration at 800 nm wavelength. The one-photon and two-photon figures of merit are determined to be 3.1 and 1.3, respectively, at irradiance of 2 GW/cm(2). The observed nonlinearities have a recovery time of approximately 1 ps. The two-photon-generated free carrier effects have also been observed and discussed. These results demonstrate that CdS NCs embedded in polymeric film are a promising candidate for optical switching applications.

Prepolymers containing vanadyl phthalocyanines, prepared by the reaction of amino-substituted vanadyl phthalocyanines and diglycidyl ether of biphenol A, can be cured to give transparent network polymeric films, which show absorptions at 780 nm and 820 nm, respectively. The films are stable to organic solvents, inorganic bases and acids. Ultrafast optical responses were observed for both polymers with typical decay time of about 240 fs.

Irradiance dependence of excitonic nonlinear absorption in Cadmium Sulfide (CdS) nanocrystals has been studied by using Z-scan method with nanosecond laser pulses. The wavelength dependence of nonlinear absorption has also been measured near the excitonic transition of 1S(e)-1S3/2(h). We observe the saturable absorption, which can be described by a third-order and a fifth-order nonlinear process for both 3.0-nm-sized and 2.3-nm-sized CdS nanocrystals. The experimental results show that the excitonic nonlinear absorption of CdS nanocrystals is greatly enhanced with decreasing particle size. A two-level model is utilized to explain both irradiance and wavelength dependence of the excitonic nonlinearity., Comment: 24 pages, 6 figures

We present femtosecond optical Kerr effect (OKE) studies of the third-order non-linear optical response of poly (distyrybenzene-co-triethylene glycol) (PDTG) under both resonance and off-resonance conditions. The excited-state enhancement of OKE signal was observed under resonance excitation. The temporal behavior of resonant OKE signal was found to be characterized by a fast component with time constant of about 250 fs and a slow component with lifetime of about 420 ps, which are attributed to delocalized π-electron and intra-chain singlet exciton migration among the backbone of the polymer, respectively. The off-resonance OKE signal only was seen to consist of an ultrafast response due entirely to delocalized electrons contribution.

Carbon nanoparticle colloids were prepared by Nd:YAG laser ablation of a carbon target immersed in water. The nanoparticles were collected on substrates and analyzed with micro-Raman spectroscopy and electron microscopy. Optical limiting properties of the carbon nanoparticle colloids towards 532 nm wavelength were characterized using a nanosecond Nd:YAG laser. A strong optical limiting response was detected for the carbon nanoparticle colloids with C60 as reference at input laser fluence above 0.6 J/cm2. The effects of carbon nanoparticle concentrations upon the optical limiting behavior were also investigated. A convenient method for preparing carbon nanoparticle based optical limiters is proposed in this investigation.

Femtosecond nonlinear optical response of BaTiO 3 and ZrO 2 matrices doped with gold nanoparticle were investigated by off-resonance optical Kerr effect. The experimental results show that the third-order nonlinear optical susceptibility of the composite films strongly depends on metal particle size and matrix refractive index. A calculation based on Lorenz–Mie scattering theory was performed to explain the experimental results. Additionally, optimization of nonlinearity was obtained by considering the particle size and matrices refractive index.

Iron(III) tetracarboxylic phthalocyanine (FePcC) was synthesized and the S1 excited state dynamics of the monomer solution was investigated by femtosecond (fs) pump–probe and picosecond time-resolved photoluminescence (ps-TRPL) measurement. The singlet state S1 relaxation comprises of three components with lifetimes of hundreds of fs, 130 ps and 1.3 ns, respectively. The fs optical Kerr effect (OKE) signals of FePcC show an ultrafast response under both on-resonant and off-resonant excitation. The magnitude of χ(3) in FePcC was determined to be about 10−11 esu (corresponding to 10 −19 m 2 V −2 ) under both on-resonant and off-resonant conditions.

TiO 2 amorphous film doped with gold nanoparticles was fabricated by alternating rf-sputtering method under vacuum condition. The nonlinear optical response was investigated by the optically heterodyne optical Kerr effect (OHD-OKE) and pump-probe methods at a wavelength of 780 nm with a laser pulse of 130 fs. The values of real and imaginary part of χ (3) were determined to be about 10 −8 esu with the wavelength close to the surface plasmon absorption peak. The time-resolved OKE and pump-probe results suggest that the main physical mechanism involved in the large nonlinear birefringence and dichroism of the Au:TiO 2 composite films stems mainly from the hot electron contributions.

CdS nanocrystals of different particle sizes dispersed in ZrO2 films were fabricated by sol–gel and dipping method. The size dependent excited state optical properties were systematically investigated by photoluminescence, time-resolved photoluminescence and Raman spectroscopy. The experimental results show that the relaxation of the excited state is composed of two processes. The fast component that arises from band edge emission shows a weak dependence on particle size, while the slow component, which is attributed to the shallow defect level emission, exhibits strong dependence on particle sizes.

The optical properties of titanylphthalocyanine (TiOPc) thin film fabricated by physical jet deposition technique were investigated by using absorption, femtosecond (fs) optical Kerr effect (OKE) and fs pump–probe techniques. The third-order nonlinear optical susceptibility of TiOPc film was measured to be 3×10 −10 esu. The OKE response of TiOPc films shows a decay process with subpicosecond time constant, demonstrating that the excited state of TiOPc molecule has little contribution to the photo-induced birefringence. From the fs pump–probe experiment, a complicated decay behavior with three decay components was observed, which originates from the contribution of exciton–exciton annihilation process, the enhanced intersystem crossing process and the relaxation of the triplet state.

The optical and non-linear optical properties of peripheral-substituted vanadium oxide phthalocyanine (VOPc) film and substituted VOPc/polymer composite film were investigated using stationary and transient spectroscopy techniques. The absorption Q band of the VOPc/polymer composite film shows a red shift relative to that of the peripheral-substituted VOPc film, revealing the monomeric characteristics of VOPc molecules. Effective quenching of PL emission was observed for the VOPc/polymer composite film and could be assigned to the efficient VOPc–polymer interaction. From pump-probe and optical Kerr effect (OKE) measurements, two decay components were obtained by fitting the transients for both VOPc films. The fast component, in a femtosecond time domain, originates from the electron–phonon interaction, and the difference in their slow decay is an indication of an efficient ISC process in the VOPc/polymer composite film. The third-order non-linear optical susceptibilities of these films were determined to be in the order of 10-11 esu.

We report the broadband terahertz (THz) radiation in the metallic ferromagnetic (FM) heterostructures, upon irradiation of a femtosecond laser pulse at room temperature. The origin of THz generation from FM heterostructures can be interpreted using two terms: the transient demagnetization (a local modification of spin order of the FM metal) and electric-dipole radiation resulting from a non-local spin current pulses. Here, we show that the THz emission is dominated by the photo-excited transient charge current, which is converted from the spin current with inverse spin Hall effect. We tailor the metallic heterostructures with different non-magnetic thin layer (Pd or Ru) and FM materials (CoFeB or CoFe), to shape the THz transients. Moreover, we find that a saturation effect of THz radiation for CoFeB/Pd is less compared to CoFeB/Ru. THz emission spectroscopy can be used to qualitatively visualize the spin accumulation in the heterostructures.

In this work, by using terahertz time-domain spectroscopy (THz-TDS), we investigate the temperature range of the SRT, and the resonant frequency and relaxation time of the THz spin waves in Sm x Dy1−x FeO3 single crystal. We show that the resonant frequency of the FM mode (measured at 40 K) increases linearly with the Sm dopant concentration within the range from x = 0.5 to 0.7. The temperature- and dopant-induced changes of the magnetic anisotropy of Fe3+ ions are accessed by the resonant frequency shifts. Upon cooling, the lifetime of oscillations in the AFM mode increases exponentially and can be subtly tuned by varying the Sm dopant. These results lead to an improved understanding of dopant-tuned spin wave dynamics and magnetoanisotropy parameter in rare-earth orthoferrites.

An interface is constructed based on a bismuth ferrite oxide (BFO) thin film and p-type silicon, and the temperature dependence of the interface properties has been studied systematically using terahertz time-domain spectroscopy. The BFO/Si interface exhibits quasi-two-dimension electron gas (2DEG) transport in the temperature range of 80 to 140 K: the electrons at the interface possess large electron mobility (∼106 cm2/V s) and long scattering time (∼100 ps). As the temperature is higher than 140 K, an abrupt decrease in THz interface conductivity is observed due to the breakdown of the 2DEG induced by the surface phase transition in the BFO thin film. Our result reveals that the interface formed between BFO and Si provides a special platform for designing and fabricating THz photonic devices.

We report the broadband terahertz (THz) radiation in ferromagnetic half-metallic Heusler alloy Co2MnSn thin film upon the irradiation of a femtosecond laser pulse at room temperature. The magnetic-, sample symmetry-, and pump fluence-dependent THz emission reveals that the THz radiation is originated from the magnetic-dipole radiation, i.e., the light-induced subpicosecond demagnetization. In addition, by optical pump-THz probe spectroscopy, we found that the photoexcited increase of the scattering rate of hot carriers thereby leads to the photoinduced negative THz conductivity in Co2MnSn thin film.

A type of ferroelectric oxide films, consisting of three PbZr0.4Ti0.6O3 stacks with different periodic thicknesses, has been designed and fabricated on F-doped transparent conductive tin oxide substrates by using one single precursor solution and spinning-coating process. These films exhibit superior ferroelectric, dielectric, and optical performance. Each PbZr0.4Ti0.6O3 multilayer has a high reflectivity band with ∼110 nm photonic band width and average reflectivity of >80%, a dielectric constant of 530 and dielectric tunability of ∼28% at 1 MHz, a remnant polarization of 36 μC/cm2, and a polarization loss of

Understanding and controlling the transient optical anisotropy of strong correlation systems is of great interest in the quest for information processing and storage. Here, we report on ultrafast optical pump-probe measurements with linearly and circularly polarized laser pulses in the manganite La0.67Ca0.33MnO3 thin film. We show both the time-resolved reflectivity and the polarization state (Kerr rotation and ellipticity) of the probe-pulse at different temperatures, which are analyzed by the ultrafast intersite transition between Mn3+ and Mn4+ sites at photon energies around 1.55 eV. During the temperature-induced dynamical spectral weight transfer, a spin-flip photo-transition between spin up eg states of Mn3+ and spin down eg states of Mn4+ ions occurs and is imprinted on the optical anisotropy of the probe beam.

In this article, a novel metamaterial is designed aimed at generating a single electromagnetic hot spot, in order to realize the localization of the incident electromagnetic field at terahertz band, and this kind of metastructure is an ideal candidate for many research fields such as spintronics, nonlinear magnetic response, near-field optics, and optical antenna, etc. The specially tailored metamaterial takes the shape of diabolo with a metal triangle pair connected by a cubic gallium arsenide (GaAs) gap. We demonstrated by simulation that both electric- and magnetic-field of incident THz pulse can be confined in the small GaAs gap when a synchronized femtosecond laser pulse is illuminated. The numerical simulation results show that 2 orders of magnitude of field enhancement can be obtained for a 1-by-1 μm GaAs gap, and the field enhancement factor can also be further improved by tailoring the GaAs gap down to nanometer scale.

By using optical pump-terahertz (THz) probe spectroscopy, the photoexcited terahertz conductivity dynamics of chemical vapor deposition grown graphene is investigated in different atmospheric environments. It is shown that the Fermi energy of doped graphene is engineered by oxygen adsorption and desorption, which is probed by transient THz conductivity measurement. We show that the ultrafast energy relaxation processes depend on Fermi energy (changed by environmental gas) and the density of excited carriers (changed by photo-excitation fluence). The rise process of the negative conductivity dynamics becomes less efficient upon decreasing the Fermi energy and/or increasing the pump fluence. All findings show that the Fermi energy of graphene engineered by environmental gas allows us to tune the ultrafast energy relaxation pathways in photoexcited graphene.

Magnetic field and temperature dependence of spin wave excitation and manipulation in RFeO 3 (R=Nd) are studied with THz time-domain spectroscopy. Our studies reveal that the spin reorientation transition triggered by external magnetic field is strongly anisotropic: magnetic fields along a-axis is much easier to switch the spin alignment than that along c-axis in NdFeO3 crystal.

We employ a combination of pulsed- and continuous-wave polarized terahertz spectroscopy techniques to probe temperature-dependent spin waves in the antiferromagnet $\mathrm{Nd}\mathrm{Fe}{\mathrm{O}}_{3}$. Our optical data span 1.6--467 K and reveal a conspicuous spin reorientation between 110 and 170 K, during which the lower-energy mode softens completely. Complementary inelastic neutron scattering reveals that the frequencies of the optically excited spin waves are consistent with a temperature-variable spin gap in the low-energy spin-wave dispersion of $\mathrm{Nd}\mathrm{Fe}{\mathrm{O}}_{3}$. The result links the temperature dependence of the spin waves to a dynamic in-plane anisotropy. The magnetic anisotropy is calculated based on the results of the optical measurements. The change observed in the anisotropy energy along the $a$ and $c$ crystal axes suggests that the spin reorientation evident in $\mathrm{Nd}\mathrm{Fe}{\mathrm{O}}_{3}$ is driven by temperature-dependent in-plane anisotropy.

This paper presents dynamical diffraction properties of a femtosecond pulse in a sinusoidal volume holographic grating (VHG). By the modified coupled-wave equations of Kogelnik, we show that the diffraction of a femtosecond pulse on the VHG gives rise to periodical energy oscillation and pulse splitting. In the initial stage of diffraction, one diffracted pulse and one transmitted pulse emerge, and energy of the transmitted pulse periodically transfers to the diffracted pulse and vice versa. In the latter stage, both the diffracted and transmitted pulses split into two spatially separated pulses. One pair of transmitted and diffracted pulses propagates in the same direction and forms the output diffracted dual pulses of the VHG, and the other pair of pulses forms the output transmitted dual pulses. The pulse interval between each pair of dual pulses is in linearly proportional to the refractive index modulation and grating thickness. By the interference effect and group velocity difference we give explanations on the periodical energy oscillation and pulse splitting respectively.

The terahertz paper photonic crystals, including one-dimensional stacks, two-dimensional square and hexagonal lattices as well as three-dimensional body-centered cubic lattice, are designed and fabricated. Femtosecond laser direct writing is employed to process paper layers. The transmission properties of these photonic crystals in THz range are characterized using time-domain THz spectroscopy. The experimental results are in good agreement with the numerical simulations and well explained by the photonic band-structure calculated by the plane wave expansion method. Our results demonstrate that paper photonic crystals have a good performance on molding the flow of THz radiation. From another point of view, the fabrication method proposed in this work can be widely extended to manufacture different micro-structures on various materials.

Based on Kogelnik's coupled-wave theory and matrix optics, generation of femtosecond double pulses by modulating thickness of the buffer layer of two-layer volume holographic grating (TL-VHG) is discussed. Expressions of diffraction field when a femtosecond pulse incidents on the TL-VHG are deduced. Simulation results show when thickness of the buffer layer increases from 6mm to 11 mm or even larger, one incident pulse splits into double femtosecond pulses with the same duration and peak intensity, and pulse interval is linearly proportional to the thickness. The reason of these phenomena is due to the interference of diffraction waves reconstructed from two gratings and phase shift resulting from the buffer layer thickness. Time-delay of diffracted double pulses is explained by group time delay of periodic media. It is shown that the slope of the pulse interval with respect to the thickness of buffer layer is 2 times of that of pulse time-delay. Furthermore, we demonstrate it is possible to control the output double pulses' duration and pulse interval by varying the grating thickness.

Using sheet-by-sheet method, multiwalled carbon nanotubes (MWCNTs)/polyetheretherketone (PEEK) multilayered composites are manufactured. The shielding efficiencies and dielectric constants of the MWCNTs/PEEK composites are investigated in the frequency range of 0.1-1.6 THz using terahertz time domain spectroscopy (THz-TDS). The MWCNTs/PEEK composite with a carbon-nanotubes fraction of 1.2% turns to be metallic. Moreover, compared with multilayered graphite/PEEK and single layered MWCNTs/PEEK composites, the multilayered MWCNTs/PEEK composites present excellent terahertz absorptive with a frequency response consistent with Drude's free-electron model. (C) 2014 Wiley Periodicals, Inc.

In this paper, several experiments were conducted to further clarify the formation mechanism of self organized void array induced by a single laser beam, including energy-related experiments, refractive-index-contrast-related experiments, depth-related experiments and effective-numerical-aperture experiment. These experiments indicate that the interface spherical aberration is indeed responsible for the formation of void arrays.

The temporal physical behavior of multifunctional materials such as multiferroics after the laser irradiation has been very intriguing in recent years. Here, the ultrafast carrier dynamics of the multiferroic BiFeO3 film in a broad temperature range is investigated using optical pump-probe spectroscopy. The photoexcited electrons in BiFeO3 release their energy through coupling with the longitudinal-optical phonons (~ 1 ps) and with the magnetic lattice (several ps). The temperature dependences of the peak value of the optical reflectivity and the time constants of carrier relaxation channels show significantly changes from 137.5 K to around 195 K, which is in accordance to the previously reported hidden phase transition. Our study demonstrates that ultrafast spectroscopy is a sensitive method to look insight into the dynamical interactions among the on-site high-energy electrons accumulated in the p conduction band of Bi, coherent optical phonon, and the magnetic lattice.

By using two-color femtosecond optically heterodyned optical Kerr effect and off-resonant single beam Z-scan methods, we investigated the ultrafast photo-induced birefringence of three poly(p-phenylenevinylene) (PPV) derivatives, MEH-PPV (poly-5-(2-ethylhexoxy)-p-phenylenevinylene)), DO-PPV (poly-(2,5-dioctyloxy-1,4-phenylenevinylene)) and DD-PPV (poly-(2,5-didodecyloxy-1,4-phenylenevinylene)). As the 400 nm laser pulse was near the absorption region of PPV derivatives, an ultrafast rise of optical Kerr signal followed by a slow decay process with lifetime about several hundred picosecond was observed. The magnitudes of the real part of χ (3) for PPV derivatives were calculated to be in the order of 10 −10 esu which was one order of magnitude larger than that in 800 nm OKE case. We assign this enhancement to the populated excited state due to the near-resonant excitation in these PPV derivatives.

The nonlinear optical response of 2,5-dioctyloxy PPV (DO-PPV) solution was measured using two-color femtosecond optically heterodyned optical Kerr effect (OHD-OKE). The OHD-OKE signal showed an ultrafast rise followed by a single exponential decay with lifetime of 310 ps. Combined with the site-select-fluorescence results, the decay process of OHD-OKE response was assigned to the migration of photo-induced exciton among the polymer backbone.

The third-order nonlinear optical properties of copper phthalocyanine (CuPc) and magnesium phthalocyanine (MgPc) films were investigated by femtosecond optical Kerr effect (OKE) and pump-probe techniques. For both CuPc and MgPc, the third-order nonlinear optical susceptibility was enhanced at least by one order of magnitude in comparison with that of the metal-free Pc, and the enhancement effect arises from different mechanisms for both films. From pump-probe measurement, quite different transmittance and decay behavior between CuPc and MgPc films were observed. The CuPc films show an ultrafast decay, while the decay behavior of MgPc film is complicated with several temporal components, which could be explained by the relaxation of singlet excited state.

By using the physical jet deposition technique, we have fabricated thin films of the star-like C 60 (CH 3 ) x (PAN) x copolymer with different PAN chain lengths. Femtosecond optical heterodyned optical Kerr effect of these films was measured. All the copolymer films show a very fast response under ultrafast excitation. From the measurement, third-order nonlinear optical susceptibility of the copolymer film was found improved as compared to that of pure PAN and the fullerene molecule which resulted from a new lower excited state and the charge transfer process in the copolymer.

We have measured the real components of the third-order optical nonlinearity of organometallic compound films of C 60 M 2 (M=Pd, Pt, and Sm) by using the femtosecond optically heterodyned optical Kerr effect at 647.0 nm. The results show that there is an enhancement of the real components of the third-order optical nonlinearity of C 60 M 2 films compared to that of pristine C 60 film. We attribute the origin of this enhancement to the charge transfer from the metal atoms to the C 60 molecules.

Silver nanoparticles were precipitated directly in Ag + doped silicate glass by a 150 fs, 800 nm, 250 kHz femtosecond laser irradiation. The irradiated pattern turned to yellow without heat treatment. The absorption peak about 400 nm, ascribed to the surface plasmon resonance of the formed silver nanoparticles, was observed. We believe that the reduced Ag atoms, via capturing free electrons created by multi-photon process, may aggregate into the Ag nanoparticles due to femtosecond laser inducing heat accumulation effect. This result has promising applications for the fabrication of 3D multi-colored images inside a transparent material.

A dialkyldithiophosphate modified MO& nanoparticle LB film was prepared on copper substrate. The tribological behaviors of the film against steel were evaluated using a one-way reciprocating frictiontester. The structural changes of the film during the rubbing process were investigated with a Fourier transform infrared microscope and by X-ray photoelectron spectroscopy. It was found that the nanoparticle LB films decreased the friction coefficient and increased the vvear resistance of the copper substrate significantly. Analyses indicate that formation of a transferred film on the steel counterface. and the occurrence of the tribochemical changes during friction process. mainly involved disordering and partial decomposition of the surface-modified agent. The nucleus of the MO& nanoparticle plays a role in load carrying and antiwear. especially after partial decomposition of the surface-modified agent with increased friction times. A shearing effect was mainly responsible for exciting the tribochemical change. 0 1999 Elsevier Science S.A. All rights reserved.

The electronic states of TiO{sub 2} ultrafine particles (UFP) are characterized by photoluminescence spectra and diffuse reflection spectra. The results obtained indicate that the surface structure, i.e., TiOH groups, TiOC{sub 2}H{sub 5} groups, and the defect state, plays an important role in the electronic states of the TiO{sub 2} UFP. Moreover, free exciton emission is observed at room temperature. This emission is attributed to the quantum confinement and the dielectric confinement effects on the TiO{sub 2} UFP.

Temperature dependence of FID signal emitted by AFM in NdFeO3 is investigated by employing THz time-domain spectroscopy. Our results reveal that Γ4→Γ24 phase transition occurs around T1=170 K, and both two phases have the same AFM resonant frequency of 0.485 THz. The frequency softening is observed for Γ24→Γ2 occurring around T2=110 K.

In this paper, self-organized microgratings are fabricated in SrTiO(3) crystal just by scanning the focus of a tightly-focused linearly-polarized femtosecond laser beam to form a single line. The polarization direction of the laser beam is rotated by a λ/2 waveplate to check the effect of the polarization azimuth on the micrograting morphology. Fourier analyzing of the microscopic images of the microgratings indicates that the polarization plane azimuth of the laser beam does have influence on the microgratings in the aspects of groove orientation and groove spacing. A possible mechanism of polarization dependence is also proposed.

The coherent longitudinal acoustic (LA) phonons in La and Nb codoped polycrystalline BiFeO3 (BLFNO) films are photo-induced and detected by the ultrafast reflectance spectroscopy. The generation mechanism of LA phonons is attributed to the transient photostriction effect, which is a combination of the optical rectification effect and the electrostriction effect. The strain modulation of sound velocity and out-of-plane elastic properties are demonstrated in BLFNO film on SrTiO3, which gives the insight into the dynamical coupling between electrical polarization and lattice deformation. Our findings are desired for the design of BiFeO3-based photo-driven remote control micro/nano devices.

In insects, chitinases participate in the periodic shedding of old exoskeletons and the turnover of peritrophic membranes. Chitinase family members have been identified in dozens of species, including Tribolium castaneum, Drosophila melanogaster, and Anopheles gambiae. In this study, nine chitinases and three hypothetical chitinases have been identified in Bombyx mori L. (Lepidoptera: Bombycidae) through genome-wide searching. Phylogenetic analyses revealed that seven of them belong to the seven chitinase groups, respectively. BmCht25 and BmCht26 could not be grouped into the known chitinase groups, and might belong to two new groups of the chitinase family. BmCht10, BmCht25, and BmIDGF have glutamate amino acid substitutions in the active catalytic domain. Only BmCht5 and BmCht10 contain CBD domain and PEST sequences (rich in proline, glutamic acid, serine, and threonine). BmCht5 and BmCht26 are located on chromosome 7, and others (BmCht6, BmCht7, BmCht10, BmCht11, BmCht20, BmIDGF) are located on separate chromosomes of Bombyx mori, respectively. The present study provides important background information for future studies using Bombyx mori as a model organism for insect development and virus and host interaction.

We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet, YFeO3, associated with a quasi-ferromagnetic spin resonance at a frequency of 0.3 THz, using a single THz pulse. The intrinsic dielectric anisotropy of YFeO3 in the THz range allows for coherent control of both amplitude and phase of the excited spin wave.

Au:CdS nanocomposite film was investigated using femtosecond pump–probe measurement at 800 nm. Time dependence of transmittance shows a two-photon absorption followed by a saturable absorption and recovery process, which clearly demonstrates that resonant energy transfer between CdS and Au nanocomposite systems occur with excitation at 800 nm. In addition, enhancement of the two-photon absorption coefficient in Au:CdS nanocomposite with a factor of more than 6 was observed compared to that of bulk CdS.

A new terahertz (THz) modulator based on bias-driven carrier conductivity change in a heterojunction was proposed. BiFeOsub3/subfilm and silicon were selected as building blocks for fabricating the THz modulator. THz nonlinear transmission as a function of bias voltage was studied systematically. THz peak transmission as a function of bias shows a similar tendency as the current-voltage response of the heterojunction: the forward bias leads to the exponential enhancement of THz transmission, and in contrast, the reverse bias shows no observable changes in THz transmission. The modulation depth and modulation bandwidth of THz pulse can reach up to 42% and 1.0 THz with forward bias of 4.8 V, respectively. The observed bias dependent THz transmission in the BFO/Si heterojunction is well-interpreted by the proposed model: the diffused carriers across the heterojunction are localized in BFO thin film with applied forward bias. Our finding provides great potential for applications in designing all electrical broadband THz modulators.

Magneto-optical information storage has been a hot research subject for several years. FePt exhibits abundant physical properties and has received much attention as a candidate material. Its alloy film with perpendicular anisotropy and small grain size has important applications in magnetic recordings due to the large intrinsic magnetic anisotropy which ensures long-time thermal stability of nanometer sized bits. However, the large coercive field of FePt is a significant factor that hinders its application. As is well known, the magnetic anisotropy in FePt alloy can be precisely modulated by carbon-doping, and as a result, the coercive field of FePt film can be modified effectively with the carbon dopant. On the other hand, the microscopic mechanism of magnetic storage relies on the motion of spin system. Ultrashort femtosecond laser has been demonstrated to be a very effective tool to investigate the dynamical coupling among different degrees of freedom, such as electron, spin and lattice in a ferromagnetic film. The research on spin dynamics has become a new frontier of condensed matter physics, which is crucial for ultrafast magnetic recording materials. In this work, by using the time-resolved magneto-optical Kerr effect spectroscopy, we study the ultrafast spin dynamics of two FePt alloy films with different carbon dopants under the applied magnetic field along the film surface. The FePt alloy films with different carbon dopants are fabricated on silicon substrates by the sputtering method. The main experimental findings in this work are as follows. (i) The transient Kerr signal is linearly proportional to the magnetization with the magnetic field up to 0.8 T, while the transient reflectivity of the film is independent of the applied magnetic field. (ii) For FePt alloy films with different coercive fields, it is found that the demagnetization time of the film with smaller coercive field is significantly faster than that of the larger counterpart: the former shows 0.8 ps demagnetization time, and the latter has a magnitude of 1.2 ps. The demagnetization times for both soft and hard magnetic films are independent of the applied magnetic field. (iii) With ultrafast laser pulse radiation, we observe the propagation of acoustic phonon with a resonance frequency of ～ 49 GHz, and the frequency of the acoustic phonon is independent of the applied magnetic field. From the above, the spin dynamics of the samples shows strong correlation with carbon-doping. Our experimental findings are desired for basic research as well as for the design and development of novel magneto-optical devices.

Single crystal of Sm0.5Tb0.5FeO3 was grown by an optical floating zone method. The spin reorientation transition behavior (Γ2 → Γ24 → Γ4) is observed in the temperature range from 150 to 250 K. The dynamics of spin reorientation transition is studied by terahertz time-domain spectroscopy (THz-TDS). FM mode was only discovered when temperature is below 55 K. And the FM mode resonant frequency increases from 0.216 THz to 0.268 THz with temperature deceasing from 55 K to 39 K. The AFM mode resonant frequency is fixed at 0.542 THz except in the very low temperature range. Our results demonstrate that THz-TDS is an effective means to study the dynamical iron ions SRT in RFeO3.