Observation of the K2 4Δg state by cw perturbation-facilitated optical-optical double resonance spectroscopy

This paper reports for the first time both, an experimental observation and theoretical calculations of the K₂ 4³Δ_g state. For the experiment we used cw perturbation-facilitated optical-optical double resonance (PFOODR) spectroscopy. A single mode Ti-sapphire laser and a dye laser served as the pump and probe lasers, respectively. A total of 55 PFOODR signals have been assigned to the 4³Δ_g ← b³Π_u transitions. Absolute vibrational numbering was determined by using quantum defect analysis combined with comparing observed intensities with calculated Franck-Condon factors (FCF). For the former we used known parameters from the 2³Δ_g state since the 2³Δ_g and the 4³Δ_g states belong to the same Rydberg series. We report here our experimental and calculated spectroscopic constants, the corresponding RKR potential energy curve, the Franck-Condon table for the 4³Δ_g ↔ b³ Π_u system, as well as a comparison with the theoretical potential energy curve. The T_e value is found to be 28408.938(52) cm⁻¹.     

Low-frequency alternative-current magnetic susceptibility of amorphous and nanocrystalline Co60Fe20B20 films

This investigation experimentally studies the low-frequency alternating-current magnetic susceptibility (χ_ac) of amorphous and nanocrystalline CoFeB films by measuring the magnetic field established by passing currents of various frequencies through such films of various thicknesses (t_f). A CoFeB film is sputtered onto a glass substrate with t_f from 100 Å to 500 Å under the following conditions: (a) As-deposited films were maintained at room temperature (RT) and (b) films were post-annealed at T_A=150 °C for 1 h. The samples thus obtained are analyzed in a magnetic field that was generated by an alternating current (AC) at various frequencies from 10 Hz to 25,000 Hz. The experimental results demonstrate that the χ_ac declines as the thickness of the as-deposited sample and the post-annealed sample (T_A=150 °C) increases because the lower coercivity (H_c) of thinner CoFeB films is similar to a soft magnetic characteristic and is associated with a higher χ_ac value. The best χ_ac value is obtained at a thickness of 100 Å under both conditions. The χ_ac value of the post-annealed sample exceeds that of the RT sample at thicknesses from 100 Å to 500 Å because the magneto crystalline anisotropy of the post-annealed sample yields the highest χ_ac value at the optimal resonance frequency (f_res), at which the spin sensitivity is maximal. The X-ray diffraction patterns (XRD) of as-deposited CoFeB films reveal their amorphous structure. The XRD results for the post-annealed films include a main peak at 2θ=44.7° from the body-centered cubic (BCC) nanocrystalline CoFe that indicated a (110) textured structure. Post-annealing treatment caused that the amorphous structure to become more crystalline by a thermally driven process, such that the χ_ac value of the post-annealed sample exceeded that of the RT sample. This experimental result demonstrates that the χ_ac value decreased as the thickness of the thin film increased. Finally, the CoFeB thin films had the best χ_ac at low frequency (<50 Hz) following post-annealing treatment. The results obtained under the two conditions indicate that the maximum χ_ac value and the optimal f_res of a 100 Å-thick CoFeB thin film were 1.6 and 30 Hz, respectively, following post-annealing at T_A=150 °C for 1 h, suggesting that a 100 Å-thick CoFeB thin film that has been post-annealed at T_A=150 °C can be utilized as a gage sensor and in transformer applications at low frequencies.     

A Theoretical Study of ãA2 CH2

The potential energy surface and dipole moment surfaces of the ã⁴A₂ electronic state of CH₂⁺ are calculated ab initio using an augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set, with the incorporation of dynamical correlation using the coupled cluster method with single and double excitations and perturbatively connected triple excitations [CCSD(T)]. We use these surfaces in the MORBID program system to calculate rotation and rotation-vibration term values for ã-state CH₂⁺, CD⁺₂, and CHD⁺ and to simulate the rotation and rotation-vibration absorption spectrum of CH₂⁺ in the ã⁴A₂ electronic state. Our work is motivated by studies of CH₂⁺ that use the Coulomb explosion imaging technique and by the goal of predicting spectra that may be obtained from discharge sources. Although the ã state is the lowest-lying excited state above the X?/Ã ground state pair, it turns out to be relatively high-lying, and we determine that T_e(ã)=30447.5 cm⁻¹. The equilibrium bond angle for ã-state CH₂⁺ is only 77.1°; as a result the asymmetric top κ value is close to 0, and the molecule is equally far from the oblate and prolate symmetric top limits in this electronic state.     

High-resolution FTIR measurement of the ν4 band of methylene fluoride-d2

A high-resolution (0.002 cm⁻¹) infrared absorption spectrum of methylene fluoride-d₂ (CD₂F₂) of the lowest fundamental mode ν₄ in the region from 460 to 610 cm⁻¹ has been measured on a Bruker IFS 120-HR Fourier transform infrared spectrometer. More than 3500 transitions have been assigned in this B-type band centered at 521.9 cm⁻¹. The data have been combined with upper state pure rotational measurements in a weighted least-squares fit to obtain molecular constants for the upper state resulting in an overall standard deviation of 0.00018 cm⁻¹. Accurate value for the band origin (521.9578036 cm⁻¹) has been obtained and inclusion of transitions with very high J (?60) and K_a (?34) values has resulted in improved precision for sextic centrifugal distortion constants, in particular D_K, H_KJ, and H_K.     

High-resolution infrared analysis of the ν7 band of cis-ethylene-d2 (cis-C2H2D2)

The spectrum of the ν₇ band of cis-ethylene-d₂ (cis-C₂H₂D₂) has been recorded with an unapodized resolution of 0.0063 cm⁻¹ in the 740-950 cm⁻¹ region using a Bruker IFS 125 HR Fourier transform infrared spectrometer. By fitting 2186 infrared transitions of ν₇ with a standard deviation of 0.00060 cm⁻¹ using a Watson’s A-reduced Hamiltonian in the I^r representation, accurate rovibrational constants for ν₇ = 1 state have been derived. The band center of ν₇ has been found to be 842.20957 ± 0.00004 cm⁻¹. In a simultaneous fit of 1331 infrared ground state combination differences from the present ν₇ transitions, together with 22 microwave frequencies, ground state constants have been improved. The rms deviation of the ground state fit was 0.00027 cm⁻¹.     

New spectroscopic studies of the Comet-Tail (AΠi-XΣ) system of the CO molecule

In the electronic emission spectrum of the ¹²C¹⁶O⁺ molecule, 11 bands of the Comet-Tail (A²Π_i-X²Σ⁺) system have been recorded and analyzed. Spin splitting in most of the observed lines of the 0-2, 1-0, 2-0, 2-1, 3-0, 4-0, 4-2, 6-0, 7-0, 7-1, and 8-1 bands, comprising nearly 3400 lines, has been recorded under high resolution by conventional spectroscopy. The rotational analysis of bands has been performed by nonlinear least-squares procedures and by means of effective Hamiltonians of Brown et al. and the rovibronic structure parameters have been obtained. The data of bands of the A-X system and earlier analyzed bands of the B-X and B-A systems have been merged together. As a result of this global fit, the state of information about the energy structure has been significantly enlarged for the A state and enlarged and improved for the X state. Also RKR potential curves for both states and Franck-Condon factors as well as r-centroids of the Comet-Tail system of CO⁺ have been calculated.     

Electronic structure and Fermi surface of new K intercalated iron selenide superconductor KxFe2Se2

Using the ab initio FLAPW-GGA method we examine the electronic band structure, densities of states, and the Fermi surface topology for a very recently synthesized ThCr₂Si₂-type potassium intercalated iron selenide superconductor K_xFe₂Se₂. We found that the electronic state of the stoichiometric KFe₂Se₂ is far from that of the isostructural iron pnictide superconductors. Thus the main factor responsible for experimentally observed superconductivity for this material is the deficiency of potassium, i.e. the hole doping effect. On the other hand, based on the results obtained, we conclude that the tuning of the electronic system of the new K_xFe₂Se₂ superconductor in the presence of K vacancies is achieved by joint effect owing to structural relaxations and hole doping, where the structural factor is responsible for the modification of the band topology, whereas the doping level determines their filling.     

Optoelectronic properties of Cu1−xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite for p-type transparent conducting oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite have been synthesized by solid-state reaction method to investigate their optical and electrical properties. The properties of electrical resistivity and Seebeck coefficient were measured in the high temperature ranging from 300 to 960 K, and the Hall effect and the optical properties were measured at room temperature. The obtained results of Seebeck showed the samples are p-type conductor. The optical properties at room temperature exhibited the samples are transparent visible light material with optical direct gap 3.45 eV. The low electrical resistivity, hole mobility and carrier density at room temperature displayed value ranging from 0.29 to 0.08 Ω cm, 1.8 to 8.6 cm²/V s and 1.56 × 10¹⁸ to 4.04 × 10¹⁹ cm⁻³, respectively. The temperature range for transparent visible light is below 820 K because the direct energy gap contains value above 3.1 eV. Consequently, the Cu_1−xPt_xFeO₂ delafossite enhance performance for materials of p-type transparent conducting oxide (TCO) with low electrical resistivity.     

In situ Raman spectroscopy of phase transformation in CrOx-Y2O3 system at elevated temperatures

A CrO_x-Y₂O₃ sample was prepared by a deposition-precipitation method and phase transformation of the sample under N₂ and air atmospheres was characterized by in situ Raman spectroscopy and X-ray diffraction (XRD) techniques. It was found that when the CrO_x-Y₂O₃ sample was heated, CrO₃ transformed to YCrO₄ and then to YCrO₃ and Cr₂O₃. Also, the transformation started from the surface region of the sample and then extended to the bulk, due to the fact that the phase transformation was detected by Raman spectroscopy at lower temperature compared to that by XRD. In addition, both atmosphere and temperature had influence on the phase transformation in the surface region, while the phase transformation in the bulk was merely dependent on the temperature. It was also found that low oxidation state Cr(III) species on the surface could be re-oxidized to high oxidation state Cr(V) or Cr(VI) species when the thermal treated sample was exposed to ambient air.     

Study of the electron paramagnetic resonance spectra of Zn(antipyrine)2(NO3)2:VO

In this work, a full ligand-field energy matrix (10×10) diagonalization treatment for 3d¹ ions in tetragonal symmetry is developed on the basis of the two-s.o.-coupling-parameter model. Spin Hamiltonian parameters (g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) of the tetragonal V⁴⁺ center in Zn(antipyrine)₂(NO₃)₂ are calculated from the complete energy matrix diagonalization method and the perturbation theory method. The calculated results from both methods are not only close to each other but also in good agreement with the experimental values. Furthermore, the compressed defect structure of V⁴⁺ center is discussed.     

Luminescent properties of nanoparticles YPXV1−XO4:Dy phosphors

Phosphors of nanoparticles YP_XV_1−XO₄:Dy³⁺ (0?X?1) have been prepared by a citrate sol-gel method. X-ray diffraction, transmission electron microscope (TEM), scanning electron microscope (SEM) and photoluminescence excitation and emission spectra were utilized to characterize the phosphors. The results of XRD showed that a solid solution formed in YP_XV_1−XO₄:Dy³⁺ phosphor series from X=0 to X=1 with zircon structure. TEM and SEM studies revealed that the obtained YP_XV_1−XO₄:Dy³⁺ nanocrystals appeared to be spherical with some agglomeration and their sizes ranged from 30 to 80 nm. Upon short ultraviolet excitation, the optical properties of all the powder presented that the characteristic transitions of Dy³⁺ due to ⁴F_9/2-⁶H_15/2 (blue) and ⁴F_9/2-⁶H_13/2 (yellow) were detected. Besides this, in the system of YP_XV_1−XO₄:Dy³⁺, the yellow-to-blue intensity ratio (Y/B) depended on the value of P/V greatly, with the increasing of X value and the decreased Y/B value. The phosphor found to yield white light when the value of X in the range of X=0.775-0.85, the optimum concentration for Dy³⁺ is 1 mol% of Y in the host, and the emission intensity increased with the annealing temperature.     

Effect of nitrogen content on the properties of CrNxOyCz coating prepared by DC reactive magnetron sputtering

The CrN_xO_yC_z coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N₂ content on composition and structure of the CrN_xO_yC_z coatings was investigated. The structure of the CrN_xO_yC_z coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrN_xO_yC_z coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrN_xO_yC_z coatings depended on N₂ content. The evolution of the structure of CrN_xO_yC_z coatings was consistent with CrN_x-based coatings, and the CrN_xO_yC_z coatings contained Cr₂O₃, CrO₂, CrO, Cr₃C₂, CrN_x (Cr, CrN, Cr₂N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing.     

Precision improvements in the geo-fit retrieval of pressure and temperature from MIPAS limb observations by modeling CO2 line-mixing

In this paper, we present an improvement of the retrieval of pressure and temperature from the observations of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board of the environmental satellite (ENVISAT). The improvement has been obtained by integrating a state-of-the-art CO₂ line-mixing model in a two-dimensional inversion system (Geo-fit). We describe the implementation of this model in the Geo-fit system and we show its capability to reproduce the CO₂ spectral features affected by line-mixing. The upgraded analysis algorithm provides a better fit of the set of MIPAS observations analyzed by the European Space Agency (ESA) ground segment although these observations have been selected with criteria that should avoid line-mixing effects. Moreover, we show that this set of observations can be extended improving the precision of the retrieved pressure and temperature fields without increasing the computing demands. Since the CO₂Q branches are very sensitive to pressure and temperature, the capability to model accurately the line-mixing effects opens the possibility to exploit at best these spectral regions to infer pressure and temperature distributions. According to this idea, we propose a new set of spectral intervals, including the most intense CO₂Q branches. It is shown that the analysis of these intervals provides a significant improvement (up to 70%) in the precision of the retrieved pressure and temperature profiles, while using a smaller number of observations with respect to the ESA ground segment analysis. Since the knowledge of pressure and temperature is necessary for the retrieval of the altitude distribution of all the atmospheric constituents, the benefits of more precise pressure and temperature fields obtained in this work propagate into the quality of all the MIPAS products.     

Structure and magnetic properties of melt-spun Tb0.27Dy0.73Fex ribbons

The structure and magnetic properties of the melt-spun ribbons of Tb_0.27Dy_0.73Fe_x alloy are investigated as a function of various wheel speeds during melt-quenching using a single-roll technique. It is found that Tb_0.27Dy_0.73Fe_x alloy is difficult to be fabricated as amorphous state by using the melt-quenching method. X-ray diffractions show that all these ribbons for x=1.7−2.0 are the MgCu₂-type phase at the wheel speed of 45 m s⁻¹. For Tb_0.27Dy_0.73Fe_x alloy, the high wheel speed is beneficial to eliminate the RFe₃ phase and form the perfect MgCu₂-type phase. Compared with the bulk of Tb_0.27Dy_0.73Fe_1.95, these ribbons exhibit higher intrinsic coercivity value and their saturation magnetizations increase as well. The magnetostriction of Tb_0.27Dy_0.73Fe_1.95 composite with 4% epoxy resin is 640×10⁻⁶ at 900 kA m⁻¹.     

Observation of the 5pΠu Rydberg state of Li2

Some weak, collisionally induced transitions in ⁷Li₂ have been recorded by Fourier transform spectrometry in the near infrared, following excitation of the 5d¹Π_g state by optical-optical double resonance. They have been assigned as transitions to the 1 ¹Δ_g state from levels v=0 and 1 of a new ungerade Rydberg state, 5p¹Π_u. Quantum defect considerations indicate that the principal quantum number for this new state is 5, and that the assignment to 5p is compatible with a Rydberg series of which the lowest members would be the B¹Π_u and C¹Π_u states.     

The structural and magnetic properties of Ni2Mn1−xBxGa Heusler alloys

The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni₂Mn_1−xB_xGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L2₁ crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni₂Mn_1−xB_xGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni₂Mn_1−xB_xGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed.     

Effect of annealing temperature on microstructure, hardness and adhesion properties of TiSixNy superhard coatings

A series of TiSi_xN_y superhard coatings with different Si contents were prepared on M42 steel substrates using two Ti and two Si targets by reactive magnetron sputtering at 500 °C. These samples were subsequently vacuum-annealed at 500, 600, 700, 800 and 900 °C, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microindenter, Rockwell hardness tester and scratch tester were applied to investigate the microstructure, phase configuration, hardness and adhesion properties of as-deposited and annealed samples. The results indicated that there were two bonds, TiN and Si₃N₄, in all presently deposited TiSi_xN_y thin films, that structure was nanocomposite of nanocrystalline (nc-) TiN embedded into amorphous Si₃N₄ matrices. Annealing treatment below 900 °C played a little role in microstructure and hardness of the coatings although it greatly affected those of steel substrates. The film-substrate adhesion strength was slightly increased, followed by an abrupt decrease with increasing annealing temperature. Its value got to the maximum at 600 °C. Annealing had little effect on the friction coefficient with its value varying in the range of 0.39-0.40.     

Thermal stability, oxygen non-stoichiometry and transport properties of LaNi0.6Fe0.4O3

Thermal stability, oxygen non-stoichiometry and electrical conductivity of LaNi_0.6Fe_0.4O_3−δ were investigated in the temperature region of 20-1000 °C in Ar/O₂ gas flows at oxygen partial pressures between 0.5 and 21,000 Pa. Diffusion mobility was measured in Ar/O₂ gas flow at pO₂ = 18 Pa. Crystal structure of this compound was found to be stable at the mentioned experimental conditions. LaNi_0.6Fe_0.4O_3−δ is a p-type semiconductor with metallic type conductivity above 150 °C at the investigated pO₂ range. Two different (fast and slow) oxygen exchange areas on the temperature-pO₂ diagram were established, which are due to two different oxygen anion positions in the double B-site mixed perovskite structure. Oxygen non-stoichiometry in the fast oxygen exchange region reaches about 0.005 of oxygen atomic index. Chemical diffusion and oxygen surface exchange coefficients do not vary at 600-800 °C, but show visible increase above 800-850 °C.     

High magnetostriction at low fields of (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds

The structure and magnetostriction of the (Tb_1−xDy_x)_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λ_a (λ_a=λ_‖-λ_⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ_a being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compounds, which could become a kind of promising magnetostrictive material.     

Effect of post-deposition annealing on structural and electrical properties of high-k HoTiO3 gate dielectrics

In this article, the authors developed a high-k HoTiO₃ gate dielectric deposited on Si (1 0 0) through reactive cosputtering. They found that the HoTiO₃ dielectrics annealed at 800 °C exhibited excellent electrical properties such as high capacitance value, small density of interface state, almost no hysteresis voltage, and low leakage current. This phenomenon is attributed to the decrease in intrinsic defect (related to oxygen vacancy) due to a rather well-crystallized HoTiO₃ structure and composition observed by X-ray diffraction, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy, respectively.