Optical parameters of In–Se and In–Se–Te thin amorphous films prepared by pulsed laser deposition

The thin films of materials based on In–Se are under study for their applicability in photovoltaic devices, solid-state batteries and phase-change memories.The amorphous thin films of In₂Se_3−xTe_x (x=0–1.5) and InSe were prepared by pulsed laser deposition method (PLD) using a KrF excimer laser beam (λ=248 nm, 0.5 J cm⁻²) from polycrystalline bulk targets. The compositions of films verified by energy-dispersive X-ray analysis (EDX) were close to the compositions of targets. The surfaces of PLD films containing small amount of droplets were viewed by optical and scanning electron microscopy (SEM).The optical properties (transmittance and reflectance spectra, spectral dependence of index of refraction, optical gap, single-oscillator energy, dispersion energy, dielectric constant) of the films were determined.The values of index of refraction increased with increasing substitution of Te for Se in In₂Se₃ films, the values of the optical gap decreased with increasing substitution of Te for Se in In₂Se₃ films.     

Observation of optical properties related to room-temperature ferromagnetism in co-sputtered Zn1−xCoxO thin films

We report on the analysis of optical transmittance spectra and the resulting ferromagnetic characteristics of sputtered Zn_1−xCo_xO films. Zn_1−xCo_xO films were prepared on (0001)-oriented Al₂O₃ substrates by the radio-frequency (rf) magnetron co-sputtering method. The XRD results showed that the crystallinity of films was properly maintained up to x=0.30 and no second phase peaks were detected up to x=0.40. The transmittance spectra showed both the increase of the absorption band intensity and the red shift of the absorption peak as well as the band edge with increasing x. We have proved experimentally that these changes depend on Co concentration. These optical properties suggest that sp-d exchange interactions and typical d-d transitions become activated with increasing x, which leads to the enhancement of ferromagnetic properties in Zn_1−xCo_xO films as shown in the AGM results. Therefore, it is concluded that the ferromagnetism derives from the substitution of Co²⁺ for Zn²⁺ without changing the wurtzite structure.     

The effect of growth ambient on the structural and optical properties of MgxZn1−xO thin films

Mg_xZn_1−xO (x = 0.0-0.20) thin films have been deposited by sol-gel technique on glass substrates and the effect of growth ambient (air and oxygen) on the structural, and optical properties have been investigated. The films synthesized in both ambient have hexagonal wurtzite structure. The c-axis lattice constant decreases linearly with the Mg content (x) up to x = 0.05, and 0.10 respectively for air- and oxygen-treated films, above which up to x = 0.20, the values vary irregularly with x. The change in the optical band gap values and the ultraviolet (UV) peak positions of Mg_xZn_1−xO films show the similar change with x. These results suggest that the formation of solid solution and thus the structural and optical properties of Mg_xZn_1−xO thin films are affected by the growth ambient.     

Effect of Bi additive on structure and optical properties of amorphous BixIn25−xSe75 chalcogenide films

We report the structure and optical properties of thermally evaporated Bi_xIn_25?xSe₇₅ (0 ≤ x ≤ 7) films by using X-ray diffraction and optical spectroscopic techniques. The as-prepared samples were found to be amorphous by X-ray diffraction while the crystallization of Se, In₂Se₃ and Bi₂Se₃ phases has been observed upon annealing the films at 440 K. The enhancement in the main diffraction peak intensity was accepted as the increase in the crystalline character for the devitrified films with Bi content. The addition of 5 at.% of Bi results in the large change in the electrical parameters due to the carrier type reversal in the as-prepared samples. The red shift in the absorption edge along with a decrease in the transmittance has been observed for the as-prepared samples. The inverse relationship between optical gap and the tailing parameter (except x = 1) were observed with the increase in Bi content. The optical gap was found to increase up to x ≤ 1 and thereafter, resulted in the decrease in it for the thermally annealed samples. These results have been discussed in conjunction with the structural relaxation and impurity mediated heterogeneous crystallization of the film network.     

Influence of zirconium doping on structure,microstructure, dielectric and impedance properties of strontium bismuth niobate ceramics

Efforts have been made in this work to enhance the dielectric properties of SrBi₂Nb₂O₉ (SBN) by partial substitution of Zr⁴⁺ for Nb⁵⁺. Systematic investigations on structure, microstructure, dielectric and impedance properties of the SrBi₂(Nb_2−(4/5)xZr_x)O₉ [where, x = 0, 0.1 and 0.2] ceramic samples were carried out to understand the effect of substitution of Zr⁴⁺ for Nb⁵⁺ in SrBi₂Nb₂O₉. The X-ray diffraction (XRD) investigations indicated that the lattice volume of SrBi₂(Nb_{2− (4/5)x}Zr_x)O₉ with x = 0.1 and 0.2 decreases compared to SBN. The SEM investigations revealed an increase in the size of grains and the change on shape of grains to elongated plate shaped structure with the increase of x (x = 0.1 and 0.2) in SrBi₂(Nb_2−(4/5)xZr_x)O₉. Higher Curie temperature and enhanced peak dielectric constant at the Curie temperature were observed for both the SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1 and 0.2 ceramic samples compared to SBN. Among the investigated compositions the higher Curie temperature and enhanced peak dielectric constant at the Curie temperature was observed for SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1.     

Magnetic properties and magnetic entropy changes of perovskite manganese oxide La0.8-xEuxSr0.2MnO3 (x = 0, 0.075)

Magnetocaloric effect and critical exponent analysis of La_0.8-xEu_xSr_0.2MnO_{3 (}x = 0, 0.075) manganites synthesized via a solid state reaction route have been explored. Rietveld analysis indicates that crystal structure of La_0.8-xEu_xSr_0.2MnO_{3 (}for x = 0.0) is in orthorhombic structure with pbnm space group. After the substitution of Eu, the structure changes from orthorhombic (for x = 0.0) to rhombohedral structure for (x = 0.075) with $\mathrm{R}\overline{3}c$ space group. The T_C is 287 K and 271 K for the samples with x = 0.000 and x = 0.075, respectively, and the magnetic entropy change is 2.76J K ^− 1•kg⁻¹ for x = 0.000 and 3.94J K ^− 1•kg⁻¹ for x = 0.075. The real cooling power (RCP) is 447.7 J•kg⁻¹ for the sample with x = 0.000 and 445 J•kg⁻¹ for the samples with x = 0.075. Both samples show a second order phase transition in the vicinity of T_C. The critical exponents were determined using modified Arrott plots and Kouvel-Fisher methods. The critical behavior of these two samples fit best with the mean field model.     

Elucidating NO coupling effects on ignition of toluene reference fuels by chemical functional group analysis

Derived cetane number (DCN), Research and Motor Octane Numbers (RON and MON) have been fundamentally analyzed using Quantitative Structure-Property Relationship (QSPR) regression models with key chemical functional groups. Both RON and MON exhibit strong sensitivities to the abundances of (CH₂)_n and benzyl-type groups but lack sensitivity to the CH₃ group, most dominant in real gasolines. Residual and EGR gases contain NO_x known to synergize with fuel autoignition chemistry. Two TRF mixtures having high and low aromatic content but sharing the same RON and MON values were used to evaluate NO_x coupling effects. DCN measurements with NO addition were found to be strongly correlated with the abundance of the (CH₂)_n group. Similar experiments of 200 ppm NO in a Rapid Compression Machine show promotion (inhibition) of ignition for the high (low) aromatic TRF fuel. Kinetic modeling attributes the promotion to the NONO₂ interconversion reactions, NO + HO₂ = NO₂ + OH, CH₃ + NO₂ = CH₃O + NO and NO₂ + H = NO + OH. The inhibitive effect relates specifically to low temperature kinetics and high NO loading conditions, leading to the formation of meta-stable species (e.g. CH₃ + NO₂ (+M) = CH₃NO₂ (+M)) that decelerate the rate of conversion of HO₂ to more reactive OH radicals. The coupling of NO with real gasolines depends on chemical composition and temperature conditions not only encompassed by RON and MON criteria, but by the chemical functional group characteristics. The relevance of this finding to the significance of preferential vaporization of multi-component gasolines on low-speed pre-ignition (LSPI) is discussed. Within the context of chemical functional group distributions of five distillation cuts of a marketed ethanol-free gasoline determined by NMR spectroscopy, the analyses identify considerable variations of key functionalities with fuel distillation properties, indicating chemical kinetic autoignition behaviors that are dependent on preferential vaporization.     

Surface topographic study of chalcogenide thin films of GexSb(As)40−xS50Te10 glasses

The surface topography and fractal properties of Ge_xSb(As)_40−xS₅₀Te₁₀ (x = 10, 20, 27 at.%) films, evaporated onto glass substrates, have been studied by atomic force microscopic imaging at different scales. The surface of the chalcogenide films is smooth (<5 nm roughness), isotropic and having some particular differences in texture. All films are self-similar with Mean Fractal Dimension in the range of 2.25–2.63. The films with Ge_xSb_40−xS₅₀Te₁₀ composition are more uniform in terms of surface morphology (grains structure) than those with Ge_xAs_40−xS₅₀Te₁₀ composition for which the film surface exhibits a superimposed structure of large particles at x = 10 and 20 at.%.     

Structure and magnetic properties of Co-substituted NiZn ferrite thin films synthesized by the sol-gel process

Co-substituted NiZn ferrite thin films, Ni_0.5Zn_0.5Co_xFe_2−xO₄ (0≤x≤0.2), were synthesized by the sol-gel process. The structure and magnetic properties of Ni_0.5Zn_0.5Co_xFe_2−xO₄ ferrite thin films have been investigated. The diffraction peak shifted towards the lower angle and the lattice parameter increased with Co substitution. There is little influence of Co substitution on the microstructure of NiZn ferrite thin films. The saturation magnetization gradually increases with the increase in Co substitution when x≤0.10, and decreases when x>0.10. Meanwhile, the coercivity initially decreases with the increase in Co substitution when x≤0.10, and increases when x>0.10.     

Experimental and modeling study on the ignition delay times of ammonia/methane mixtures at high dilution and high temperatures

Ammonia is a promising alternative clean fuel due to its carbon-free character and high hydrogen density. However, the low reactivity of ammonia and the potential high NO_x emissions hinder its applications. Blending methane into ammonia can effectively improve the reactivity of pure NH₃. In addition, lean combustion, as a high-efficiency and low-pollution combustion technology, is an effective measure to control the potential increase in NO_x emissions. In the present work, the ignition delay times (IDTs) of NH₃/CH₄ mixtures highly diluted in Ar (98%) with CH₄ mole fractions of 0%, 10%, and 50% were measured in a shock tube at an equivalence ratio of 0.5, pressures of 1.75 and 10 bar and a temperature range of 1421 K - 2149 K. A newly comprehensive kinetic model (named as HUST-NH₃ model) for the NH₃/CH₄ mixtures oxidation was developed based on our previous work. Four kinetic models, the HUST-NH₃ model, Glarborg model [19], Okafor model [7], and CEU model [10], were evaluated against the ignition delay times, laminar flame speeds, and species profiles of pure ammonia and ammonia/methane mixtures from the present work and literature. The simulation results indicated that the HUST-NH₃ model shows the best performance among the above four models. Kinetic analysis results indicated that the absence of NH₃ + M = NH₂ + H + M (R819) and N₂H₂ + M = H + NNH + M (R902) in the CEU model and Okafor model cause the deviations between the experimental and simulation results. The overestimation of the rate constants of NH₂ + NO = NNH + OH (R838) in the Glarborg model is the main reason for the overprediction of the NH₃ laminar flame speeds.     

Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

A WF₆–H₂–N₂ precursor system was used for plasma-enhanced chemical vapor deposition (PECVD) of WN_x films. We examined the microstructural changes of the WN_x films depending on N₂/H₂ flow-rate ratio and post-annealing (600–800 °C for 1 h). As the N₂/H₂ flow rate was increased from 0 to 1.5, as-deposited WN_x films exhibited various different crystalline states, such as nanocrystalline and/or amorphous structure comprising W, WN, and W₂N phases, a fine W₂N granular structure embedded in an amorphous matrix, and a crystalline structure of β-W₂N phase. After post-annealing above 600 °C, crystalline recovery with phase separation to β-W₂N and α-W was observed from the WN_x films deposited at an optimized deposition condition (flow-rate ratio = 0.25). From this PECVD method, an excellent step coverage of ∼90% was obtained from the WN_x films at a contact diameter of 0.4 μm and an aspect ratio of 3.5.     

Third-order optical nonlinearities of lead-free (Na1−xKx)0.5Bi0.5TiO3 thin films

(Na_1−xK_x)_0.5Bi_0.5TiO₃ (NKBT) (x = 0.1, 0.2, and 0.3) thin films with good surface morphology and rhombohedral perovskite structure were fabricated on quartz substrates by a sol-gel process. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties were investigated by Z-scan technique performed at 532 nm with a picosecond laser. A two-photon absorption effect closely related with potassium-doping content was found in thin films, and the nonlinear refractive index n₂ increases evidently with potassium-doping. The real part of the third-order nonlinear susceptibility χ⁽³⁾ is much larger than its imaginary part, indicating that the third-order optical nonlinear response of the NKBT films is dominated by the optical nonlinear refractive behavior. These results show that NKBT thin films have potential applications in nonlinear optics.     

Electronic structure and optical properties of TbNi5−xCux

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_5−xCu_x series. Within the framework of LSDA+U calculations, electronic structure for x=0, 1, 2 is calculated and additionally optical conductivity is obtained. Disorder effects of Cu for Ni substitution on a level of LSDA+U densities of states (DOS) are taken into account via averaging over all possible Cu ion positions in the unit cell for given doping level x. Gradual smoothing of optical conductivity structure at 2 eV together with simultaneous intensity growth at 4 eV corresponds to increase of Cu and decrease of Ni content.     

Optical properties of PMN–PT thin films prepared using pulsed laser deposition

(1 ? x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–PT) thin films have been deposited on quartz substrates using pulsed laser deposition (PLD). Crystalline microstructure of the deposited PMN–PT thin films has been investigated with X-ray diffraction (XRD). Optical transmission spectroscopy and Raman spectroscopy are used to characterize optical properties of the deposited PMN–PT thin films. The results show that the PMN–PT thin films of perovskite structure have been formed, and the crystalline and optical properties of the PMN–PT thin films can be improved as increasing the annealing temperature to 750 °C, but further increasing the annealing temperature to 950 °C may lead to a degradation of the crystallinity and the optical properties of the PMN–PT thin films. In addition, a weak second harmonic intensity (SHG) has been observed for the PMN–PT thin film formed at the optimum annealing temperature of 750 °C according to Maker fringe method. All these suggest that the annealing temperature has significant effect on the structural and optical properties of the PMN–PT thin films.     

Exploring the chemistry behind low temperature auto-ignition of isopropyl nitrate in an RCM: An experimental and kinetic modeling study

The low-temperature auto-ignition chemistry of isopropyl nitrate (iPN) was experimentally and numerically investigated in the present study. The ignition delay times (IDTs) of iPN were measured stoichiometrically over a temperature range of 560–600 K at effective pressures of 5 and 10 bar in a rapid compression machine. A two-stage ignition phenomenon of iPN was observed. Both the first-stage IDTs and total IDTs vary rapidly within the narrow temperature range investigated (∼40 K). A recent iPN kinetic mechanism proposed by Fuller and Goldsmith for pyrolysis studies was extended. The reaction kinetics of CH₃CHO + NO₂ has been theoretically calculated at 500–1500 K and 0.01–100 atm. The rate information of CH₃ + NO₂ was updated based on previous theoretical results. The O₂-addition channel of acetyl radical (CH₃CO), which accounts for the first-stage IDT, was also considered in the present work. The extended iPN kinetic model predicts the two-stage IDTs well. Simulation results suggest that the IDTs are most sensitive to the following two reactions: (1) CH₃ + NO₂ = CH₃O + NO; (2) CH₃ + NO₂ = CH₃NO₂. The former promotes the overall reactivity by yielding the reactive methoxy radical, while the latter forms a relatively stable product (i.e., CH₃NO₂). The reaction of CH₃CHO + NO₂ = CH₃CO + HONO supplements the formation of CH₃CO. The different consumption channels of CH₃CO radicals (the O₂-addition reaction and the decomposition reaction) lead to different chain reactions yielding OH radicals with increasing temperature in the ignition process. The “NONO₂ loop” is the main route for OH formation in the studied conditions, which is mainly responsible for the iPN ignition.     

Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO₃)₂(CH₃OH)](NO₃) and [NdL(NO₃)₂(CH₃OH)](NO₃) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV-vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol⁻¹, ΔS=56.54 J mol⁻¹ K⁻¹ for [PrL(NO₃)₂(CH₃OH)](NO₃) and ΔH=−24.63 kJ mol⁻¹, ΔS=22.07 J mol⁻¹ K⁻¹ for [NdL(NO₃)₂(CH₃OH)](NO₃)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes-BSA system. The binding average distance between complexes and BSA was obtained on the basis of Förster's theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.     

Magnetocaloric properties of DyCo2−xGax alloys

The influence of the substitution of Ga atoms for Co atoms in DyCo₂ compounds on magnetocaloric properties has been investigated. A series of DyCo_2−xGa_x alloys with x=0, 0.03, 0.06, 0.1, 0.15, and 0.2 was prepared by the arc-melting method for this investigation. Experimental results revealed that the Ga substitution for Co in DyCo₂ can form a single phase with the cubic Laves phase structure up to x=0.2. As the Ga content x increases, the lattice parameter and the Curie temperature T_c increases from 143 to 196 K linearly. The maximum magnetic entropy changes in a low field change of 0-1.5 T, increasing from 8.24 to 10.61 J/K kg when the Ga content x increases from 0 to 0.03, but decreasing gradually to 3.51 J/K kg as the Ga content further increases to x=0.2. All the samples show a relatively large magnetic entropy change with very small hysteresis loss.     

Properties of Cu2ZnSn(SxSe1−x)4 thin films prepared by one-step sulfo-selenization of alloyed metal precursors

The pentenary system, Cu₂ZnSn(S_xSe_1−x)₄ (CZTSSe), is a promising alternative for thin film solar cells. In this study, CZTSSe thin films were prepared using a two-stage process involving the thermal diffusion of sulfur (S) and selenium (Se) vapors into sputtered metallic precursors at approximately 450 °C. The effects of the sulfur content on the composition, structure, optical and electrical characteristics of the CZTSSe thin films were investigated. The films showed a kesterite structure with a predominant (112) orientation. X-ray diffraction and Raman spectroscopy confirmed the formation of a single phase CZTSSe compound. The band gap was dependent on the sulfur content and was calculated to be 1.25 eV, 1.33 eV and 1.40 eV for CZTSSe films with a S/(S + Se) ratio of 0.3, 0.5 and 0.7, respectively. All films exhibited p-type semiconductor properties.     

Influence of Co doping content on its valence state in Zn1−xCoxO (0 ≤ x ≤ 0.15) thin films

Zn_1−xCo_xO (0 ≤ x ≤ 0.15) thin films grown on Si (1 0 0) substrates were prepared by a sol-gel technique. The effects of Co doped on the structural, optical properties and surface chemical valence states of the Zn_1−xCo_xO (0 ≤ x ≤ 0.15) films were investigated by X-ray diffraction (XRD), ultraviolet-visible spectrometer and X-ray photoelectron spectroscopy (XPS). XRD results show that the Zn_1−xCo_xO films retained a hexagonal crystal structure of ZnO with better c-axis preferred orientation compared to the undoped ZnO films. The optical absorption spectra suggest that the optical band-gap of the Zn_1−xCo_xO thin films varied from 3.26 to 2.79 eV with increasing Co content from x = 0 to x = 0.15. XPS studies show the possible oxidation states of Co in Zn_1−xCo_xO (0 ≤ x ≤ 0.05), Zn_0.90Co_0.10O and Zn_0.85Co_0.15O are CoO, Co₃O₄ and Co₂O₃, with an increase of Co content, respectively.     

Effect of Sc substitution on the structure,electrical, and magnetic properties of multiferroic BiFeO3 thin films grown by a sol–gel process

Multiferroic BiFeO₃ (BFO), Bi_1−xSc_xFeO₃ (BSF), and BiFe_1−xSc_xO₃ (BFS) (x=0.3 mol%) thin films are prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel technique. The effect of Sc substitution along with the annealing ambient (N₂ and O₂) on the structure, electrical, and magnetic properties of the films are reported. X-ray diffraction (XRD) analysis reveals that the films can be prepared with the single-phase perovskite structure by annealing at 700 °C for 10 min either in O₂ or N₂ ambient. The unit cell volume increases on the substitution of Sc, which are 61.39, 62.50, and 62.57 (Å)³ for BFO, BSF, and BFS, respectively. X-ray photoelectron spectroscopy (XPS) study reveals that the chemical environments of Bi and Fe are different in BFO, BSF, BFS films. Similarly, XPS spectra for Sc2p lines in BSF and BFS also have different peak positions; this indicates Sc doping has certain chemical impact on BSF and BFS films. Systematic studies of Sc substitution along with the effect of annealing ambient on the dielectric constant (ε) and dielectric loss (tan δ), leakage current, remnant polarization (P_r), coercive field (E_c), and magnetic properties of the films are carried out. The room temperature values of ε and tan δ at 1 kHz for BFO and BFS films annealed in N₂ ambient are (∼208; 0.035) and (∼235; 0.023), respectively. The comparative value of leakage current for the BFO and BFS films at an applied field strength of 50 kV/cm are 2.997×10⁻⁴ and 1.87×10⁻⁵ A/cm², respectively. Room temperature value of coercive magnetization for BFS films has one order small compared to that of the BFO films; this indicates BFS films are magnetically soft and more suitable for potential device applications. Finally, among the studied compositions, the BFS films annealed in N₂ ambient show the best property.