Theoretical calculation of the isoelectronic line ratio of Li-like Ti and Cr under different mixture ratios

With the consideration of coronal conditions, a simplified model and the steady-state rate-equation are used to calculate the isoelectronic line ratio for transition in Li-like Ti and Cr from the electron temperature 400 to . The relation between the isoelectronic line ratio and the electron temperature are provided under different mixture ratios of Ti and Cr. Then, the mixture ratio from 2:1 to 3:1 between Ti and Cr are obtained that are suitable for the electron temperature diagnostic by using isoelectronic line ratio of Li-like Ti and Cr. The relative abundance of two close ionization stages, which is from bare nucleus to Be-like ionization stage, are given and show that the He-, Li- and Be-like are the principal ionization stages from 400 to for Ti and from 500 to for Cr. The Li-like charge state will reach the maximum distribution approximately from 400 to for Ti and from 547 to for Cr. The paper also shows that the dielectronic recombination and spontaneous radiative recombination rates only have small effects on the isoelectronic line ratio in the electron temperature 400-.     

Dielectronic Recombination of Sn^10＋ Ions and Related Satellite Spectra

Based on the multi-configuration Dirac-Fock method, theoretical calculations are carried out for the dielectronic recombination （DR） rate coefficients and the collision excitation rate coefficients of Sn^10＋ ions. It is found that the total DR rate coefficient has its maximum value between 10eV and 100eV and is greater than either the radiative recombination or three-body recombination rate coefficients （the number of free electrons per unit is 10^21 cm^3） for the ease of Te 〉 1 eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dieleetronie satellite cannot be ignored at low temperature Te 〈 5 eV.     

The role of Ar III in quantitative spectroscopy on hot argon plasmas

We perform quantitative optical emission spectroscopy on the hot core of the cathode region of a free-burning arc in argon under atmospheric pressure. As the peak temperatures in the centre of the discharge exceed 22 000 K we are able to observe three spectra of argon (Ar I, Ar II and Ar III) and the continuum emission. We report on some inconsistencies concerning the evaluation of Ar III radiation in both line and continuum emission. These are caused by erroneous data in the literature and common misconceptions about the influence of Ar III on the plasma emission. We discuss the impact of this fact on published data.     

Theoretical and Experimental Study of Scattering of a Plane Wave by an Inhomogeneous Plasma Sphere

Scattering of electromagnetic waves by an inhomogeneous plasma sphere has been studied theoretically and experimentally. The offset angles of electromagnetic waves caused by the plasma sphere have been observed experimentally. The effects of the electromagnetic wave frequency and plasma density on the offset angle are discussed. The plasma density is estimated with the offset angle.     

Theoretical study of the KLL dielectronic recombination for highly charged iodine ions

With a developed program for calculation of dielectronic recombination (DR) process, which is based on multi-configuration Dirac-Fock (MCDF) method, the KLL DR processes of the highly charged helium-like to carbon-like iodine ions have been studied systematically. The contributions to doubly excited states from quantum electrodynamic (QED) and Breit effects have been discussed. The KLL DR resonant energies and corresponding resonant strengths have been calculated. The behavior of KLL resonant strengths with increasing Z are analyzed for He-like ions in particular. The theoretical DR spectra for each highly charged ion species are obtained in the KLL region. Comparison has been made between the present calculations and the latest experiments in Tokyo-EBIT.     

Kinetic theory of radiation in non-equilibrium relativistic plasmas

Many-particle QED is applied to kinetic theory of radiative processes in many-component plasmas with relativistic electrons and non-relativistic heavy particles. Within the framework of non-equilibrium Green’s function technique, transport and mass-shell equations for fluctuations of the electromagnetic field are obtained. We show that the transverse field correlation functions can be decomposed into sharply peaked (non-Lorentzian) parts that describe resonant (propagating) photons and off-shell parts corresponding to virtual photons in plasmas. Analogous decompositions are found for the longitudinal field correlation functions and the correlation functions of relativistic electrons. As a novel result a kinetic equation for the resonant photons with a finite spectral width is derived. The off-shell parts of the particle and field correlation functions are shown to be essential to calculate the local radiating power in relativistic plasmas and recover the results of vacuum QED. The influence of plasma effects and collisional broadening of the relativistic quasiparticle spectral function on radiative processes is discussed.     

Surface modification of the nanoparticles by an atmospheric room-temperature plasma fluidized bed

Using hexamethyldisiloxane (HMDSO) monomer, the magnetic nanoparticles (NPs) of nickel oxide (NiO) were modified by using an atmospheric room-temperature plasma fluidized bed (ARPFB). The plasma gas temperature of the ARPFB was not higher than 325 K, which was favorable for organic polymerization. The plasma optical emission spectrum (OES) of the gas mixture consisting of argon (Ar) and HMDSO was recorded by a UV-visible monochromator. The as-treated NPs were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the assembling NPs were isolated greatly after modified by the organosilicon polymer. Moreover, this treatment process changed the wettability of the NPs from super-hydrophilicity to super-hydrophobicity, and the contact angle (CA) of water on the modified NPs surface exceeded 150°. Therefore, the ARPFB is a prospective technology for the NPs surface modification according to the different requirements.     

Characteristic and non-characteristic X-ray yields produced from thick Ti element by sub-relativistic electrons

Measurements are performed to study the electron impact energy dependence of doubly differential bremsstrahlung yields (DDBY) and of characteristic Ti K_α line yields produced from sub-relativistic electrons (10–25 keV) colliding with a thick Ti (Z = 22) target. The emitted radiation is detected by a Si-PIN photo-diode detector with energy resolution (FWHM) of 180 eV at 5.9 keV. The measured data of DDBY are compared with the results predicted by Monte-Carlo (MC) simulations using the general purpose PENELOPE code. A reasonable agreement is found between experimental and simulation results within the experimental uncertainty of measurements of 12%. Characteristic Ti K_α yields are obtained for the considered impact energy range and they are compared with the existing theoretical results. A good agreement is found between the present measurements and the theoretical calculations. Furthermore, data are presented for impact energy dependence of the ratio K_α/(K_α+ K_β) of a thick Ti target under impact of 10–25 keV electrons. The ratio shows a very weak dependence on impact energy in the studied range. The average value of the ratio is found to be 0.881 ± 0.003.     

Simulation of the transport of sputtered atoms and effects of processing conditions

Sputter deposition is a complex process; it is obvious that the energy and direction of the particles arriving at the substrate is in close relation with the transport process from the target to the substrate, it is desirable to model this transport of atoms through the background gas. The transport of sputtered Ag atoms during sputter deposition through the gas phase in the facing targets sputtering system studied by Monte Carlo simulation is presented. The model calculates the flux of the atoms arriving at the substrate, their energy, direction and number of collisions they underwent. The dependence of the deposition rates of Ag atoms on the gas pressure and the distance between the targets and substrate were investigated.     

Bulk periodic structures formation on monocrystalline silicon surface under the action of compression plasma flows

The results of numerical simulation of monocrystalline silicon melting and crystallization under the action of compression plasma flow generated by quasistationary plasma accelerators with regard to phase transformations based on Kolmogorov equation are presented. Temporal and spatial characteristics of melting and crystallization processes for pulses of various forms are discussed. Based on data received and estimates made, the conclusion on substantial role of thermoelectric instability in bulk periodic structures formation was made.     

Theoretical study of local lattice structure of Mn in perovskite fluorides A2MF4 (A=K, Rb; M=Mg, Zn, Cd) series

A theoretical method for investigating the inter-relation between the molecular structure and electronic structure has been established on the basis of the 252×252 complete energy matrices for a 3d⁵ configuration ion in a tetragonal ligand field. By means of this method, which is independent of the X-ray diffraction, the local structure of the paramagnetic Mn²⁺ ion in perovskite fluorides A₂MF₄ (A=K, Rb; M=Zn, Mg, Cd) are determined directly by analyzing the EPR spectrum of octahedral Mn²⁺ center in A₂MF₄ crystals and the optical absorption spectrum of the (MnF₆)⁴⁻ cluster. It is shown that, comparing with the octahedral cubic structure, the local micro-structure in the vicinity of Mn²⁺ displays an elongated distortion when and a compressed distortion when , and ΔR vs. as well as ΔR vs. in the distortion region is, respectively, approximately linear. Simultaneously, the theoretical zero-field-splitting parameters , and are in good agreement with the experimental values.     

Large magnetoresistance in low temperature metallic region of manganite compounds (La0.7−2xEux)(Ca0.3Srx)MnO3 (0.05≤x≤0.15)

Magnetoresistance (MR) and magnetization (dc and ac) measurements have been carried out on the manganites, (La_0.7−2xEu_x)(Ca_0.3Sr_x)MnO₃ (0.05≤x≤0.15), in the temperature range of 5-320 K. At 5 K, an unusually large MR of almost 98% is observed in the x=0.15 sample, nearly up to fields of 4-5 T. This large high-field MR occurs in the metallic region, far below the insulator-metal transition temperature, and does not vary linearly with applied field. The unusual magnetoresistance is explained in the light of various possibilities such as phase segregation, cluster spin-glass behavior, etc.     

Analytically modelling the effects of interaction between two or more rectangular nanomagnets

In a recent paper (Goode and Rowlands J. Magn. Magn. Mater. 295 (2005) 197–218), the micromagnetic equations which govern the magnetization distribution have been studied for rectangular nano-sized magnets where the magnetization is nearly uniform. Analytical solutions to these equations have been obtained in the form of Fourier series in which only the first few terms in the series are necessary to give results accurate to a few percent. In this paper, the above method is extended to include the effects of interaction between two or more rectangular nanomagnets. The near-uniform nature of the magnetization distributions is shown to change depending on the distance the nanomagnets are apart from each other. To estimate at what distance between the nanomagnets this interaction becomes important and therefore must be included in the analysis, the demagnetizing and interaction energies are compared for an array of uniformly magnetized rectangular nanomagnets.     

Discrimination between thermal quenching of the fluorescence and Auger upconversion processes using thermal lens technique

In this work we used the Thermal Lens (TL) technique to discriminate two important processes responsible to reduce the upper-state population and fluorescence quantum efficiency (η) in Cr³⁺ doped colquiriite crystals: the thermal quenching of the fluorescence (TQF) and the Auger upconversion (ETU). We observed a nonlinear increase of the TL signal with laser power due to the decrease of η by ETU and/or TQF. The analysis of these curves allowed the determination of the thermal load, the increase of the crystal temperature as a function of the pump excitation and the discrimination between ETU and TQF processes.     

Hydrothermal synthesis and luminescent properties of LnPO4:Tb,Bi (Ln=La,Gd) phosphors under UV/VUV excitation

Monoclinic LnPO₄:Tb,Bi (Ln=La,Gd) phosphors were prepared by hydrothermal reaction and their luminescent properties under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation were investigated. LaPO₄:Tb,Bi phosphor and GdPO₄:Tb phosphor showed the strongest emission intensity under 254 and 147 nm excitation, respectively, because of the different energy transfer models. In UV region, Bi³⁺ absorbed most energy then transferred to Tb³⁺, but in VUV region it was the host which absorbed most energy and transferred to Tb³⁺.     

The luminescent properties of CaYBO4:Ln(Ln=Eu, Tb) under UV-VUV range

The luminescent properties of CaYBO₄:Ln(Ln=Eu³⁺, Tb³⁺) were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) region. The CT band of Eu³⁺ at about 245 nm blue-shifted to 230 nm in VUV excitation spectrum; the band with the maximum at 183 nm was considered as the host lattice absorption. For the sample of CaYBO₄:0.08Tb³⁺, the bands at about 235 and 263 nm were assigned to the f-d transitions of Tb³⁺ and the CT band of Tb³⁺ was calculated according to Jφrgensen's theory. Under UV and VUV excitation, the main emission of Eu³⁺ corresponding to the ⁵D₀-⁷F₂ transition located at about 610 nm and two intense emission of Tb³⁺ from the ⁵D₄-⁷F₅ transition had been observed at about 542 and 552 nm, respectively. With the incorporation of Gd³⁺ into the host lattice of CaYBO₄, the luminescence of Tb³⁺ was enhanced while that of Eu³⁺ was decreased because of their different excitation mechanism.     

Local structure and magnetic properties of Mn substituted manganites studied by EXAFS and Dc magnetic measurements

We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K edge and magnetic measurements performed on (La_1−xCa_x)(Mn_1−yM_y)O₃ samples (M=Cr or Ni; x=0.37 and 0.75 and y=0.03 or 0.08). The Mn substitution produces important effects on both the sides of the LaMnO₃-CaMnO₃ phase diagram. For x<0.5 the ferromagnetic-metallic phase maintains its main character even after Mn substitution, but both the doping species (Ni or Cr) lower T_C and broaden the magnetic transition, and the EXAFS study evidences two Mn-O distances, suggesting the presence of zones of distorted insulating phase. For x>0.5, after the doping with Cr, the charge ordered phase persists but on a shorter scale, whereas the Jahn-Teller distortion is weakened as indicated by EXAFS measurements, and the formation of ferromagnetic clusters is evidenced by magnetic measurements.EXAFS and magnetic measurements are in mutual agreement, thus confirming the correlation between the local disorder determined by charge localization and magnetic degrees of freedom.     

Temperature dependence of the EPR lines in weakly doped LiNbO3:Yb—possible evidence of Yb ion pairs formation

The electron paramagnetic resonance (EPR) studies of LiNbO₃ single crystal doped with 1 wt% of Yb³⁺ are reported. To put the EPR results in perspective, a brief discussion of optical absorption spectroscopy investigations of LiNbO₃:Yb³⁺ is provided. The temperature behavior of the EPR lines intensity and linewidth for LiNbO₃:Yb³⁺ reveals antiferromagnetic coupling between Yb³⁺ ions. The deconvolution of the EPR lines indicates that EPR signals arise from both the isolated Yb³⁺ ions as well as the Yb³⁺-Yb³⁺ ion pairs; the latter signals dominate. Based on this indication, EPR spectra are interpreted using a spin Hamiltonian for the Yb³⁺ dissimilar ion pairs. The negative sign of the isotropic parameter J confirms the existence of the antiferromagnetic interactions within Yb³⁺-Yb³⁺ pairs. The value of J obtained based on the proposed pair model, assuming the dipole-dipole interactions, is used to identify the positions of the Yb³⁺-Yb³⁺ pairs in the unit cell. Our results suggest the ^evenYb³⁺-^evenYb³⁺ pairs are located at the neighboring Li⁺ and Nb⁵⁺ positions, whereas the pair axis is not parallel to the optical c-axis. Some alternative explanations of the observed EPR spectra are also considered.     

Plasma and surface modeling of the deposition of hydrogenated carbon films from low-pressure methane plasmas

The elementary mechanisms are described which determine the plasma and surface processes during the plasma-enhanced chemical vapour deposition of hydrogenated carbon films from methane. Corresponding model calculations are reviewed and critically discussed in comparison to experimental results. A realistic modeling requires the simultaneous and self-consistent treatment of plasma and surface effects. Several experimental data sets on plasma parameters and the growth and the composition of the films have been reproduced successfully. However, a broader experimental data base is needed for more critical tests of the models. The reliability of the modeling, in particular of the surface effects, is still limited due to the poor availability of elementary data.     

In situ endpoint detection of reactive ion-beam etching of dielectric gratings with an etch-stop layer using downstream mass spectrometry

Downstream mass spectrometry is successfully used in the reactive ion-beam etching of dielectric diffraction gratings of deep grooves with vertical sidewalls to achieve in situ endpoint detection. Silica (SiO₂) gratings with a Sc₂O₃ etch-stop layer are fabricated by reactive ion-beam etching with CHF₃ as etchant, and the mass spectrometric signal of SiF₃⁺ produced by the reactive etching of the SiO₂ grating material is monitored. When the etch-stop layer is reached, a drop of this signal occurs. By comparing the monitoring curves and resulting gratings of different etching methods, we find that the decrease of the monitored signal is strongly influenced by the sidewall steepness of the etched grating grooves. All conditions being equal, the greater sidewall steepness renders the faster decrease of the signal. Consequently, the proposed approach of endpoint detection applies well to the gratings with steep sidewalls. With the help of two previously developed methods, the sidewall steepness of grating grooves is increased, and the optimal endpoint is detected. Employing the proposed technique, we have reproducibly fabricated dielectric gratings with proper groove depth and even groove bottom.