A theoretical study of the oxygen K-edge near-edge X-ray absorption fine structure of N20/Ir（110）

A multiple-scattering chtster method is employed to calculate the oxygen K-edge near-edge X-ray absorption fine structure of N20/Ir（110） and its monolayer. Two peaks and one weak resonance appear in both cases. The self- consistent field DV-Xa calculations of the peaks and resonance show that the physical origin of the pre-edge peak x is different from those of the main peak 1 and the other weak resonance al. This setup is intrinsic to the N20 monolayer, owing to the interaction between the neighbouring molecular chains in the monolayer and partly to the adsorbed atomic oxygen, according to both the theoretical and experimental data.     

A theoretical study of the oxygen K-edge near-edge X-ray absorption ne structure of N2O/Ir(110)

A multiple-scattering cluster method is employed to calculate the oxygen K-edge near-edge X-ray absorption fine structure of N₂O/Ir(110) and its monolayer. Two peaks and one weak resonance appear in both cases. The selfconsistent field DV-X calculations of the peaks and resonance show that the physical origin of the pre-edge peak x is different from those of the main peak 1 and the other weak resonance σ₁. This setup is intrinsic to the N₂O monolayer, owing to the interaction between the neighbouring molecular chains in the monolayer and partly to the adsorbed atomic oxygen, according to both the theoretical and experimental data.     

Influence of intra-cavity loss on transmission characteristics of fiber Bragg grating Fabry–Perot cavity

A theoretical model of the fiber Bragg grating Fabry–Perot(FBG-FP) transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured.The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited.The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1,which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.     

Infrared diode laser spectroscopy of O2–N2O van der Waals complex in the v1 symmetric stretch region of N2O

The rovibrational spectrum of O2–N2O van der Waals complex is measured in the ν1 symmetric stretch region of N2 O monomer using a tunable diode laser spectrometer. The complex is generated by a slit-pulsed supersonic expansion with gas mixtures of O2, N2 O, and He. Both a- and b-type transitions are observed. The effective Hamiltonian for an open-shell complex consisting of a diatomic molecule in a ^3Σ electronic state and a closed-shell partner is used to analyze the observed spectrum. Molecular constants in the vibrationally excited state are determined accurately. The band-origin of the spectrum is determined to be 1284.7504（25） cm^-1, red-shifted from that of the N2 O monomer by ～ 0.1529 cm^-1.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

Structure and Photoluminescence of Polycrystalline MgxZn1-xO Films

Different photoluminescence （PL） spectra are observed for rf magnetron sputtered polycrystalline Mg0.25Zn0.75O and Mg0.37Zn0.63O films on silicon substrates when excited by different wavelengths. When the excitation wavelength is 280nm, a UV emission peak at 370nm and a blue peak at 462nm are generated for the Mg0.25Zn0.75O film, and those two peaks for the Mg0.37Zn0.63O film shift to 366nm and 466nm, respectively. The wavelengths of the PL peaks are related to the excitation wavelength. The stronger peak is obtained in the blue band due to a large number of oxygen vacancies caused by excess Zn and Mg atoms, while the weaker peak is obtained in the ultraviolet band.     

Influence of Ambient Atmosphere on the Plasmon Resonance Absorption of Ag／SiOx（0≤x≤2） Nanocomposite Film

Nanocomposite films consisting of nanosized Ag particles embedded in partially oxidized amorphous Si-containing matrices were prepared by radio frequency magnetron co-sputtering deposition.We studied the influence of ambient atmosphere during the preparation and heat-treatment of Ag/SiOx(0≤x≤2) nanocomposite film on its optical absorption properties.We found that the plasmon resonance absorption peak shifts to shorter wavelengths with the increasing oxygen content in the SiOx matrix.The analysis indicates that the potential barrier between Ag nanoparticles and SiOx matrix increases with the increasing x value,which will induce the surface resonance state to shift to higher energy.The electrons in the vicinity of the Fermi level of Ag nanoparticles must absorb more energy to be transferred to the surface resonance state with the increasing x value.It was also found that the plasmon resonance absorption peaks of the samples annealed in different ambient atmospheres are located at about the same position.This is because the oxidation surface layer is dense enough to prevent the oxygen from peretration into the sample to oxidize the silicon in the inner layer.     

Oxygen vacancy in N-doped Cu₂ O crystals:A density functional theory study

The N-doping effects on the electronic properties of Cu2O crystals are investigated using density functional theory.The calculated results show that N-doped Cu2O with or without oxygen vacancy exhibits different modifications of electronic band structure.In N anion-doped Cu2O,some N 2p states overlap and mix with the O2p valence band,leading to a slight narrowing of band gap compared with the undoped Cu2O.However,it is found that the coexistence of both N impurity and oxygen vacancy contributes to band gap widening which may account for the experimentally observed optical band gap widening by N doping.     

Optical absorption and electromagnetically induced transparency in semiconductor quantum well driven by intense terahertz field

An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented.The formalism relies on the stationary single-photon Schro¨dinger equation in the full quantum mechanical framework.The optical absorption dynamics in both weak and strong couplings are discussed and compared.The excitonic absorption spectra show the Autler-Townes doublets for the resonance terahertz field,a replica peak for the non-resonance terahertz field,and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling.In particular,the electromagnetically induced transparency phenomenon window range is discussed.In the strong coupling region,the multi-order energy level resonance splitting due to the strong optical field is found.There are three(non-resonance terahertz field) or four(resonance terahertz field) peaks in the optical absorption spectra.This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.     

Theoretical calculation of of B-like ions： photoionization cross sections N^2＋, O^3＋ and F^4＋

There can be found some notable discrepancies with regard to the resonance structures when R-matrix calculations from the Opacity Project and other sources are compared with recent absolute experimental measurements of Bizau et al [Astron.Astrophts.439 387(2005)] for B-like ions N2+,O3+ and F4+.We performed close-coupling calculations based on the R-matrix formalism for the photoionizations of ions mentioned above both for the ground states and first excited states in the near threshold regions.The present results are compared with experimental ones given by Bizau et al and earlier theoretical ones.Excellent agreement is obtained between our theoretical results and the experimental photoionization cross sections.The present calculations show a significant improvement over the previous theoretical results.     

Stochastic Resonance in a Bistable System Subject to Non-Gaussian and Gaussian Noises

In this paper, we consider the phenomenon of stochastic resonance （SR） in a quartic bistable system under the simultaneous action of a multiplicative non-Gaussian and an additive Gaussian noises and a weak periodic signal. The expression of the signal-to-noise ratio R is derived by applying the two-state theory in adiabatic limit. We discuss the effects of the parameter q indicating the departure of the non-Gaussian noise from the Gaussian noise, the correlation time r of the non-Gaussian noise, and coupling intensity A between two noise terms on the stochastic resonance. It is found that the signM-to-noise ratio of the system, as a function of the additive noise intensity, undergoes the transition from having one peak to having two peaks, and then to having one peak again when the parameter q or the noise correlation time τ is increased. The parameter q and τ play opposite roles in the SR of the system.     

Excitonic optical absorption in semiconductors under intense terahertz radiation

The excitonic optical absorption of GaAs bulk semiconductors under intense terahertz （THz） radiation is investigated numerically. The method of solving initial-value problems, combined with the perfect matched layer technique, is used to calculate the optical susceptibility. In the presence of a driving THz field, in addition to the usual exciton peaks, 2p replica of the dark 2p exciton and even-THz-photon-sidebands of the main exciton resonance emerge in the continuum above the band edge and below the main exciton resonance. Moreover, to understand the shift of the position of the main exciton peak under intense THz radiation, it is necessary to take into consideration both the dynamical Franz-Keldysh effect and ac Stark effect simultaneously. For moderate frequency fields, the main exciton peak decreases and broadens due to the field-induced ionization of the excitons with THz field increasing. However, for high frequency THz fields, the characteristics of the exciton recur even under very strong THz fields, which accords with the recent experimental results qualitatively.     

Electromagnetic Properties of S11 States in a Light Cone Quark Model

Using relativistic spin-flavor wave functions of a Lorentz-covariant light cone quark model, we calculate the electromagnetic form factors of two S11 resonances, N（1535） and N（1650）, and the helicity amplitudes A1/2 and S1/2 for electroexcitation of the S11 resonances from the nucleon. The electromagnetic form factors of these S11 resonances are found to be similar to those of the nucleon in shape, while the charge form factor of neutral N（1650） is nearly zero. The relative peak height of the S11 charge form factors is controlled by the mixing angle common to both resonance wave functions. As in most quark models, there is a systematic overestimate of A1/2 in both N（1535） and N（1650） cases at the photon point. A sizeable S1/2 for all cases is produced as suggested by experiments.     

Reconsideration of Orth Ⅰ and Orth Ⅱ Phases in Ln-System Superconductors

A block model is used to calculate the combinative energy in LnBa2Cu3O7-x （Ln=Y, Er, Nd） systems, and the energy has no difference for orth-Ⅰ and orth-Ⅱ in the plateau range. Namely, no matter what phase it is, when the oxygen deficiency is in the range of δ-0.35-0.55, the plateau appears in the energy -δ curves, and the combinative energy has close correlation with the Tc value. The result in the present work gives some hints to reconsider the role of the order of oxygen defects or its effect on superconductivity in LnBa2Cu3O7-x. The existence of the orth-Ⅱ seems not to be the reason for the plateau in the Tc curve. This is an important problem for LnBa2Cu3O7-x and some suggestion is given in the discussion.     

Effect of the Coadsorption of CO and O2 on the Phase Diagram of the Ziff—Gulari—Barshad Model

The effect of the coadsorption of CO and O2 on the Ziff-Gulari-Barshad surface catalytic reaction system in studied by Monte Carlo simulation.The coadsorption of both species adds an extra reaction step to the classical Ziff-Gulari-Barshad model.It is shown that the second-order phase transition from the reactive state to the O-passivated state in the Ziff-Gulari-Barshad model is eliminated,and the production rate of CO2 increases linearly along the fraction yco of CO in gas phase when it is low,in agreement with experimental results.We also find that the increase of the probability of the coadsorption leads to the decrease of the critical value of yco of the discontinuous phase transition to the CO-passivated state.     

Effects of O2/Ar ratio and annealing temperature on electrical properties of Ta2O5 film prepared by magnetron sputtering

The effects of the oxygen-argon ratio on electric properties of Ta2O5 film prepared by radio-frequency magnetron sputtering were investigated.The Ta2O5 partially transforms from the amorphous phase into the crystal phase when annealing temperatures are 800℃ or higher.The lattice constant of Ta2O5 decreases with the increase of the O2/Ar ratio,which indicates that oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies during the deposition process.For the films deposited in working gas mixtures with different O2/Ar ratios and subsequently annealed at 700℃,the effective dielectric constant is increased from 14.7 to 18.4 with the increase of the O2/Ar ratio from 0 to 1.Considering the presence of an SiO2 layer between the film and the silicon substrate,the optimal dielectric constant of Ta2O5 film was estimated to be 31.Oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies,and the oxygen vacancy density and leakage current of Ta2O5 film both decrease with the increase of the O2/Ar ratio.The leakage current decreases after annealing treatment and it is minimized at 700℃.However,when the annealing temperature is 800℃ or higher,it increases slightly,which results from the partially crystallized Ta2O5 layer containing defects such as grain boundaries and vacancies.     

Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients

Bi3.25La0.75 Ti3O12 （BLT） ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total l eccm N2/02 mixed gas with various ratio at 750℃ for 30rain. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroeleetric properties. Alter the BLT film is annealed in 20%O2, the largest P~ value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen.     

Defect types and room temperature ferromagnetism in N-doped rutile TiO2single crystals

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device （SQUID）, X-ray photoelectron spectroscopy （XPS）, and positron annihilation analysis （PAS）. Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3＋, arising from titanium vacancies and the replacement of O with N atoms in the futile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism （RTFM）, and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.     

Improved performance of AlGaN/GaN HEMT by N2O plasma pre-treatment

The influence of an N_2O plasma pre-treatment technique on characteristics of AlGaN/GaN high electron mobility transistor(HEMT) prepared by using a plasma-enhanced chemical vapor deposition(PECVD) system is presented.After the plasma treatment,the peak transconductance(g_m) increases from 209 mS/mm to 293 mS/mm.Moreover,it is observed that the reverse gate leakage current is lowered by one order of magnitude and the drain current dispersion is improved in the plasma-treated device.From the analysis of frequency-dependent conductance,it can be seen that the trap state density(D_T) and time constant(τ_T) of the N20-treated device are smaller than those of a non-treated device.The results indicate that the N_2O plasma pre-pretreatment before the gate metal deposition could be a promising approach to enhancing the performance of the device.     

Nonlinear optical properties of Er_2O_3-doped 75Nb_2O_5-20TeO_2-5ZnO glasses

We have performed time-resolved degenerate four-wave mixing (DFWM) experiments in 75Nb2O5-20TeO2-5ZnO glasses doped by Er2O3 at different excitation intensities and lattice temperatures. DFWM signal exhibits three peaks at high excitation intensities, where a main peak appears at zero time delay and two rather weak side peaks locate symmetrically at the negative and positive time delay, respectively. The main peak is attributed to local-field effect and two side peaks are attributed to Coulomb interaction (CI).