High resolution emission spectroscopy of the E2Π–X2Σ+ transition of SrH and SrD

Emission spectra of SrH and SrD have been studied at high resolution using a Fourier transform spectrometer. The molecules have been produced in a high temperature furnace from the reaction of strontium metal vapor with H₂/D₂ in the presence of a slow flow of Ar gas. The spectra observed in the 18 000–19 500 cm^?1 region consist of the 0–0 and 1–1 bands of the E²Π–X²Σ⁺ transition of the two isotopologues. A rotational analysis of these bands has been obtained by combining the present measurements with previously available pure rotation and vibration–rotation measurements for the ground state, and improved spectroscopic constants have been obtained for the E²Π state. The present analysis provides spectroscopic constants for the E²Π state as ΔG(½) = 1166.1011(15) cm^?1, B_e = 3.805503(32) cm^?1, α_e = 0.098880(47) cm^?1, r_e = 2.1083727(89) Å for SrH, and ΔG(½) = 839.1283(23) cm^?1, B_e = 1.918564(15) cm^?1, α_e = 0.034719(23) cm^?1, r_e = 2.1121943(83) Å for SrD.     

Influence of the orthorhombic distortion on the van Hove singularities in the DOS and ARPES spectra of layered cuprates

Four atom states Cu3d_{x² −  y²}, Cu4s, O_a2p_xare involved in a tight-binding model for the superconducting CuO₂plane. The orthorhombic distortion is taken into account by the differences of Cu–O hopping amplitudes and single-site oxygen energies ε_aand ε_bof two oxygen positions in the elementary cell as well. An effective ‘oxygen’ Hamiltonian including only the electron amplitudes at the oxygen ions is derived. Simple expressions for the constant energy contours and the Fermi surface are obtained and they qualitatively describe the photoemission spectra. Extended saddle points nearp = (π,0) andp = (0,π) are observed in qualitative agreement with the ARPES data. The van Hove singularities of the density of states (DOS) related to the extended saddle points are calculated by a Monte Carlo method. It is found that the splitting of the singularity of the DOS at the bottom of the conduction band is created by the energy difference ε_a −  ε_b = 2δ.     

3 MeV electron irradiation-induced defects in CuInSe2 thin films

3 MeV electron irradiation induced-defects in CuInSe₂ (CIS) thin films have been investigated. Both of the carrier concentration and Hall mobility were decreased as the electron fluence exceeded 1×10¹⁷ cm⁻². The carrier removal rate was estimated to be about 1 cm⁻¹. To evaluate electron irradiation-induced defect, the electrical properties of CIS thin films before and after irradiation were investigated between 80 and 300 K. From the temperature dependence of the carrier concentration in non-irradiated thin films, we obtained N_D=1.8×10¹⁷ cm⁻³, N_A=1.7×10¹⁶ cm⁻³ and E_D=18 meV from the SALS fitting to the experimental data on the basis of the charge balance equation. After irradiation, a new defect level was formed, and N_T0=1.4×10¹⁷ cm⁻³ and E_T=54 meV were also obtained from the same procedure. From the temperature dependence of Hall mobility, the ionized impurity density was discussed before and after the irradiation.     

Thermal and chemical expansion of mixed conducting La0.5Sr0.5Fe1−xCoxO3−δ materials

Oxygen deficiency, thermal and chemical expansion of La_0.5Sr_0.5Fe_1−xCo_xO_3−δ (x = 0, 0.5, 1) have been measured by thermogravimetry, dilatometry and high temperature X-ray diffraction. The rhombohedral perovskite materials transformed to a cubic structure at 350 ± 50 °C. The thermal expansion of the materials up to the onset of thermal reduction was 14–18 × 10^− 6 K^− 1. Above 500 °C in air (400 °C in N₂), chemical expansion contributed to the thermal expansion and the linear thermal expansion coefficients were significantly higher, 16–35 × 10^− 6 K^− 1. The chemical expansion, ε_c, showed a maximum of 0.0045 for x = 0.5 and 0.0041 for x = 1 at 800–900 °C. The normalized chemical expansion, ε_c/Δδ, was 0.036 for x = 0.5 and 0.035 for x = 1 at 800 °C. The chemical expansion can be correlated with an increasing ionic radius of the transition metals with decreasing valence state.     

High room-temperature pyroelectric response of MgO-modified Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ceramics

The dielectric and pyroelectric responses of MgO-modified Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ceramics were investigated near F_R(LT)–F_R(HT) phase transition. It was found that MgO additive reduced the F_R(LT)–F_R(HT) phase transition temperature from 41 °C to room temperature (24 °C). Superior room-temperature pyroelectric properties were obtained in the composition of 0.10 wt% MgO addition without DC bias. The largest pyroelectric coefficient, 65 × 10⁻⁸ C cm⁻² K⁻¹, was detected. Accordingly, the detectivity figures of merit F_d had maximum values of 20 × 10⁻⁵ Pa^−1/2, and especially the voltage responsivity F_v = 0.91 m²C⁻¹ is the highest value reported so far among all pyroelectric materials. It shows promising potential for application in uncooled pyroelectric infrared detector.     

Synthesis of ammonia at atmospheric pressure with Ce0.8M0.2O2−δ (M = La,Y, Gd,Sm) and their proton conduction at intermediate temperature

Ionic conduction in fluorite-type structure oxide ceramics Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) at temperature 400–800 °C was systematically studied under wet hydrogen/dry nitrogen atmosphere. On the sintered complex oxides as solid electrolyte, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in the solid states proton conducting cell reactor by electrochemical methods, which directly evidenced the protonic conduction in those oxides at intermediate temperature. The rate of evolution of ammonia in Ce_0.8M_0.2O_2−δ (M = La, Y, Gd, Sm) is up to 7.2 × 10^− 9, 7.5 × 10^− 9, 7.7 × 10^− 9, 8.2 × 10^− 9 mol s^− 1 cm^− 2, respectively.     

M/Li+(M = Mg2+, Zn2+, and Mn2+) ion-exchange on lithium ion-conducting perovskite-type oxides and their properties

Lithium ions of perovskite-type lithium ion conductor La_0.55Li_0.35TiO₃ were replaced by divalent Mg²⁺, Zn²⁺, and Mn²⁺ ions in an ion-exchange reaction using molten chlorides. The polycrystalline Mg-exchanged and Zn-exchanged samples are solid electrolytes for divalent Mg²⁺ and Zn²⁺ ions, whose dc ionic conductivities (σ = 2.0 × 10^− 6 S cm^− 1 at 558 K for the Mg-exchanged sample, La_0.56(2)Li_0.02(1)Mg_0.16(1)TiO_3.01(2) and σ = 1.7 × 10^− 6 S cm^− 1 at 708 K for the Zn-exchanged samples, La_0.55(1)Li_0.0037(2)Zn_0.15(1)TiO_2.98(2)) were compared to those of the known highest Mg²⁺ and Zn²⁺ inorganic solid electrolytes. The Mn-exchanged sample, then, showed paramagnetic behavior in the temperature range of 2 to 300 K. The Mn ions in the exchanged sample are divalent and the spin configuration is in high spin state (S = 5/2).     

Titanium oxide thin layers deposed by dip-coating method: Their optical and structural properties

TiO₂ thin films were prepared by sol-gel method. The structural investigations performed by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) showed the shape structure at T = 600 °C. The optical constants of the deposited film were obtained from the analysis of the experimentally recorded transmittance spectral data in the wavelength of 200–3000 nm range. The values of some important parameters of the studied films are determined, such as refractive index n and thickness d. In this work, using the transmission spectra, we have calculated the dielectric constant (ε_∞) for four layered TiO₂ films; a simple relation is suggested to estimate the third-order optical nonlinear susceptibility χ⁽³⁾. It has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. The estimations of the corresponding band gap E_g, χ⁽³⁾ and ε_∞ are 2.57 eV, 0.021 · 10⁻¹⁰ esu and 5.20, respectively.     

Infrared spectroscopy of superionic conductor LiNaSO4: Vibrational modes and thermodynamics

Infrared active phonon spectra of lithium sodium sulphate, LiNaSO₄, were studied at temperatures between 20 K and 780 K. Dielectric constant [ε = ε′ + iε″] and energy loss function [− Im(1/ε)] were obtained from Kramers–Kronig analysis. Our IR data show a more complete set of vibrational modes than previous investigations. The IR data of LiNaSO₄ at 20 K are consistent with the P31c symmetry, indicating that LiNaSO₄ shows no structural phase transitions between 20 K and 300 K, in contrast to LiKSO₄. On heating from 20 K, phonon modes related to Li and Na vibrations show a dramatic line broadening and decrease in intensity. An extra mode is recorded near 380 cm^− 1 at 500 K. The absorption shows a systematic increase in intensity on further heating. These changes are attributed to anharmonic effects and Li diffusion or hopping. Dramatic spectral changes in the internal modes occur near 620 K on heating, suggesting the onset of the rotational disorder of SO₄ tetrahedra, but the Li atom spectrum shows weak response to the rotational disorder.     

Ferroelectric phase transition and optical performance of PLZnNZT transparent ceramics

Lead-based Pb_0.97La_0.02(Zn_1/3Nb_2/3)_0.3(Zr_0.53Ti_0.47)_0.7O₃ (PLZnNZT) transparent ceramics with the addition of 2 wt% excess PbO were prepared by hot-pressing sintering method. The hot-pressing sintered PLZnNZT ceramics exhibit dense and large-grained microstructure, and perovskite structure with distorted cubic-like symmetry. The ceramics exhibit normal ferroelectric-like dielectric behavior with slightly diffused ferroelectric phase transition characteristic. The PLZnNZT ceramics exhibit fully developed, symmetric and saturated P–E hysteresis loop and large piezoelectric constant d₃₃, being 468 pC/N. The ceramics with 120 μm thickness exhibit maximum transmittance of 53% at 850 nm when Fresnel losses was not included, almost totally transparent in the mid IR region (2500–5600 nm), and low-lying optical band gap energy E_g of 3.23 eV. Three diffused Raman bands centering around 240 cm⁻¹, 560 cm⁻¹ and 750 cm⁻¹ are observed by micro-Raman spectroscopy, which can be attributed to F2g [BO₆] bending vibration, A1g [BO₆] stretching vibration and “soft mode” mixed by the bending and stretching vibrations, respectively, confirming the normal ferroelectric-like characteristic.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Synthesis and structure determination of a chain-like aluminophosphate obtained with 1,2-diaminopropane as the structure-directing agent

Colorless plate-like crystals (AlPO-1,2DAP) crystallize from a clear ‘AlPO₄-1,2-diaminopropane’ reaction system. The results of elemental, thermal and FTIR analyses give the following chemical formula: (NH₄⁺)(1,2-H₂DAP)²⁺(AlP₂O₈)³⁻, confirmed also by single crystal structure determination. The X-ray diffraction data collected at 150 K reveal the space group Pc2₁n with a=8.2788(2), b=16.7882(3), c=8.6608(2) Å, and V=1203.73(5) Å³. The AlPO-1,2DAP has a chain structure related to the aluminophosphate AlPO-enA structure. Two occluded cations, NH₄⁺ and doubly protonated diamine, balance the negative charge and interact with the chain oxygen atoms via hydrogen bond network.     

Ferromagnetic order and spin-glass behavior in multi-metallic compound Ni1.125Co0.375[Fe(CN)6] · 6.8H2O

Multi-metallic Prussian blue compound Ni_1.125Co_0.375[Fe(CN)₆] · 6.8H₂O has been synthesized. The Mössbauer spectroscopy at room temperature and IR spectra study revealed that the metal ions are bonded through cyanide ligand and the presence of low spin Fe^III(S = 1/2) and high spin Fe^III(S = 5/2) ions, as showed in these structure: Fe^III(S = 1/2)-CN-(Co^II/Ni^II)(96%) and Fe^III(S = 5/2)-NC-(Co^II/Ni^II) (4%). The Curie constant of C = 3.00 cm³ K mol⁻¹ and Weiss paramagnetic Curie temperature of θ = 16.43 K were observed in fitting according to Curie–Weiss law. These results indicate that there existed a ferromagnetic exchange interaction in the complexes. The observed value of coercive field (H_c) and remanent magnetization (M_r) at 4 K for the compound are 497 Oe and 1.03 Nβ. The presence of spin-glass behaviours in the compound is ascribed mainly to domain mobility or domain growth under different cooling conditions.     

Structural,XPS and impedance analysis of LixCoVO4 (x = 0.8, 1.0, 1.2)

Lithium cobalt vanadate Li_xCoVO₄ (x = 0.8; 1.0; 1.2) has been prepared by a solid state reaction method. The XRD analysis confirms the formation of the sample. A new peak has been observed for Li_1.0CoVO₄ and for Li_1.2CoVO₄ indicating the formation of a new phase. The XPS analysis indicates the reduction in the oxidation of vanadium and oxygen with the addition of Li in Li_xCoVO₄ (x = 0.8, 1.0, 1.2). The impedance analysis gives the conductivity value as 2.46 × 10^− 5, 6.16 × 10^− 5, 9 × 10^− 5 Ω^− 1 cm^− 1 for Li_xCoVO₄ (x = 0.8; 1.0; 1.2), all at 623 K. The similarity in the bulk activation energy (E_a) and the activation enthalpy for migration of ions (E_ω) indicate that the conduction in Li_1.2CoVO₄ has been due to hopping mechanism.     

Diffusion of Fe,Co, Nd,and Dy in R2(Fe1−xCox)14B where R=Nd or Dy

Transition metal and rare earth diffusion coefficients at 1323 K in Dy_2−yNd_y(Fe_1−xCo_x)₁₄B were determined by field emission energy dispersive spectroscopy compositional analysis of diffusion couple specimens. Various arrangements of component materials and temperatures were examined in order to understand the mechanisms affecting diffusion of the components and to predict the stability of functionally graded microstructures consisting of a dysprosium-rich (Dy_2−yNd_y(Fe_1−xCo_x)₁₄B) outer layer and a neodymium-rich (Nd₂(Fe_1−xCo_x)₁₄B) interior. Estimates of the mutual interdiffusion coefficients of Dy, Nd, Fe, and Co in this system were obtained from the preparation of arc melted and annealed polycrystalline specimens, assuming that the diffusion coefficients were independent of concentration (Grube solution). Fifteen diffusion couples were prepared and heat treated at 1323 K for various times in order to provide data for calculation of the diffusion coefficients. The results indicate that the diffusion coefficients of Fe and Co (D_Fe=3.28×10⁻¹⁰ cm²/s and D_Co=7.63×10⁻¹⁰ cm²/s) were significantly higher at 1323 K in this system than those for Dy and Nd (D_Nd=2.3×10⁻¹² cm²/s and D_Dy=2.9×10⁻¹² cm²/s).     

First high-resolution analysis of the ν15, ν12, ν5, ν10 and ν2 bands of oxirane

Fourier transform spectra of oxirane (ethylene oxide, c-C₂H₄O) have been recorded in the 730–1560 cm^?1 (6.4–13.7 μm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.0019 cm^?1. A total of six vibration bands, ν₁₅, ν₁₂, ν₅, ν₃, ν₁₀ and ν₂, have been observed and analyzed. The corresponding upper state ro-vibrational levels were fit using Hamiltonian matrices accounting for various interactions. Satisfactory fits were obtained using the following polyads {15¹, 12¹, 5¹} and {10¹, 2¹} of interacting states. As a result, an accurate and extended set of Hamiltonian constants were obtained. The following band centers were derived: ν₀ (ν₁₅) = 808.13518(60) cm^?1, ν₀ (ν₁₂) = 822.27955(37) cm^?1, ν₀ (ν₅) = 876.72592(15), ν₀ (ν₃) = 1270.37032(10) cm^?1, ν₀ (ν₁₀) = 1471.35580(50) cm^?1 and ν₀ (ν₂) = 1497.83309(15) cm^?1 where the uncertainties are one standard deviation.     

Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum cobaltite

Oxygen nonstoichiometry, structure and transport properties of the two compositions (La_0.6Sr_0.4)_0.99CoO_3−δ (LSC40) and La_0.85Sr_0.15CoO_3−δ (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, σ, of the materials is high (σ > 500 S cm^− 1) in the measured temperature range (650–1000 °C) and oxygen partial pressure range (0.209–10^− 4 atm). At 900 °C the electrical conductivity is 1365 and 1491 S cm^− 1 in air for LSC40 and LSC15, respectively. A linear correlation between the electrical conductivity and the oxygen vacancy concentration was found for both samples. The mobility of the electron-holes was inversely proportional with the absolute temperature indicating a metallic type conductivity for LSC40. Using electrical conductivity relaxation the chemical diffusion coefficient of oxygen was determined. It was found that accurate values of the chemical diffusion coefficient could only be obtained using a sample with a porous surface coating. The porous surface coating increased the surface exchange reaction thereby unmasking the chemical diffusion coefficient. The ionic conductivity deduced from electrical conductivity relaxation was determined to be 0.45 S cm^− 1 and 0.01 S cm^− 1 at 1000 and 650 °C, respectively. The activation energy for the ionic conductivity at a constant vacancy concentration (δ = 0.125) was found to be 0.90 eV.     

Patterning of Aluminium thin film on polyethylene terephthalate by multi-beam picosecond laser

High speed patterning of a 30 nm thick Aluminium thin film on a flexible Polyethylene Terephthalate substrate was demonstrated with the aid of Computer Generated Holograms (CGH׳s) applied to a phase only Spatial Light Modulator. Low fluence picosecond laser pulses minimise thermal damage to the sensitive substrate and thus clean, single and multi-beam, front side thin film removal is achieved with good edge quality. Interestingly, rear side ablation shows significant Al film delamination. Measured front and rear side ablation thresholds were F_th=0.20±0.01 J cm⁻² and F_th=0.15±0.01 J cm⁻² respectively. With laser repetition rate of 200 kHz and 8 diffractive spots, a film removal rate of R>0.5 cm² s⁻¹ was demonstrated during patterning with a fixed CGH and 5 W average laser power. The effective laser repetition rate was f_eff~1.3 MHz. The application of 30 stored CGH׳s switching up to 10 Hz was also synchronised with motion control, allowing dynamic large area multi-beam patterning which however, slows micro-fabrication.     

Device linearity improvement and current enhancement utilizing high-to-low doping-channel FETs

We report device linearity improvement and current enhancement in both a heterostructure FET (HFET) and a camel-gate FET (CAMFET) using InGaAs/GaAs high-low and GaAs high-medium-low doped channels, respectively. In an HFET, a low doped GaAs layer was employed to build an excellent Schottky contact. In a GaAs CAMFET, a low doped layer together withn⁺andp⁺layers formed a high-performance majority camel-diode gate. Both exhibit high effective potential barriers of >1.0 V and gate-to-drain breakdown voltages of >20.0 V (atI_g=1.0 mA mm⁻¹). A thin, high doped channel was used to enhance current drivability and to improve the transconductance linearity. A 2×100 μm²HFET had a peak transconductance of 230 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. The device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 200 to 800 mA mm⁻¹. A 1.5×100 μm²CAMFET had a peak transconductance of 220 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. Similarly, the device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 160 to 800 mA mm⁻¹. The improvement of device linearity and the enhancement of current density suggest that high-to-low doped-channel devices for both an HFET and a CAMFET are suitable for high-power large signal circuit applications.     

Transport and phase dynamics of poly(vinyl pyrrolidone) doped plastically crystalline N-methyl-N-propylpyrrolidinium tetrafluoroborate

The plastic crystal phase forming N-methyl-N-propylpyrrolidinium tetrafluoroborate organic salt (P₁₃BF₄) was combined with 2, 5 and 10 wt.% poly(vinyl pyrrolidone) (PVP). The ternary 2 wt.% PVP/2 wt.% LiBF₄/P₁₃BF₄ was also investigated. Thermal analysis, conductivity, optical thermomicroscopy, and Nuclear Magnetic Resonance (¹¹B, ¹⁹F, ¹H, ⁷Li) were used to probe the fundamental transport processes. Both the onset of phase I and the final melting temperature were reduced with increasing additions of PVP. Conductivity in phase I was 2.6 × 10^− 4 S cm^− 1 5.2 × 10^− 4 S cm^− 1 1.1 × 10^− 4 S cm^− 1 and 3.9 × 10^− 5 S cm^− 1 for 0, 2, 5 and 10 wt.%PVP/P₁₃BF₄, respectively. Doping with 2 wt.% LiBF₄ increased the conductivity by up to an order of magnitude in phase II. Further additions of 2 wt.% PVP slightly reduced the conductivity, although it remained higher than for pure P₁₃BF₄.