Epitaxial growth and optical characterization of compound semiconductor β-FeSi2 prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on FZ n-Si (1 1 1) substrates by pulsed laser deposition (PLD). The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) analysis. This indicates that β-FeSi₂/Si (2 0 2/2 2 0) and the single-crystalline β-FeSi₂ can be prepared using PLD. In photoluminescence (PL) measurements at 8 K detected by Ge detector, the PL spectra of the samples annealed at 900 °C for 1, 5, 8 and 20 h showed that the PL intensity of the A-band peak increased depending on annealing time in comparison with those of as-deposited samples. The intrinsic PL intensity of the A-band peak at 0.808 eV of the β-FeSi₂ from the 20-h-annealed sample was investigated for the first time by the PLD method detected by an InGaAs detector. This result has been confirmed by temperature dependence and excitation power density of the 20-h-annealed sample with the comparison of other defect-related band peaks of the sample. Cross-sectional scanning electron microscopy (SEM) observation was also performed and the thickness of the thin films was found to be at 75 nm for 20-h-annealed. The thermal diffusion for the epitaxial growth of β−FeSi₂/Si was observed when the compositional ratio of Fe to Si was around Fe:Si=1:2 for 20-h-annealed carried out by energy dispersive X-ray spectroscopy (EDX). We discussed high crystal quality of the epitaxial growth and optical characterization of β-FeSi₂ achieved after annealing at 900 °C for 20 h.     

Synthesis of carbon nanotubes and iron oxide nanoparticles in MW plasma torch with Fe(CO)5 in gas feed

The MW plasma torch (2.45 GHz) in the mixture of CH₄/H₂/Ar (42/430/1540 sccm) with added Fe(CO)₅vapors was used for the synthesis of iron oxide nanoparticles and carbon nanotubes. The particles with well-defined facets consisting of Fe₃O₄ and -Fe₂O₃ and self-assembled into long chains were produced at the power of 360 W. At higher power of 440-460 W the deposit contained significant amount of multi-walled carbon nanotubes covered by iron oxide nanoparticles. The diameter of CNTs was 8-20 nm. The particles had Fe₃O₄ and/or -Fe₂O₃ cores of spherical shape covered by a thin layer of carbon.     

Calculation of radiative transition probabilities and radiative recombination rate coefficients for H2, OH, H 2+ and OH+ molecules

A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B → X) and Werner (C → X) band systems of H₂ and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between H₂⁺ (X) and H₂(X), and between OH⁺(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated as a function of temperature in the range 1500–15 000 K.     

The effect of chemical treatment on apatite-forming ability of the macroporous zirconia films formed by micro-arc oxidation

Macroporous and nano-crystalline zirconia film was prepared by micro-arc oxidation (MAO) of zirconium, and the effect of chemical treatment in H₂SO₄ or NaOH aqueous solutions on the microstructure and apatite-forming ability of the film was investigated. Compared with the MAO film, the chemically treated films do not exhibit apparent changes in phase component, morphology and grain size, however, have more abundant basic Zr-OH groups. The films treated with H₂SO₄ and NaOH solutions can induce apatite formation on their surfaces in simulated body fluids (SBF) within 1 day, whereas no apatite was detected on the untreated ZrO₂ surface by 30 days. It is believed that the enhanced apatite-forming ability of the chemically treated ZrO₂ films is related to the abundant basic Zr-OH groups on their surface.     

Hydrolysis and stability of thin pulsed plasma polymerised maleic anhydride coatings

The stability of plasma polymerised layers has become important because of their widespread use. This study explored the hydrolysis and degradation stability of coatings of plasma polymerised maleic anhydride. Coatings made with different plasma parameters were exposed to aqueous media of different pH as a function of time. ATR-FTIR was used for structure analysis and a toluidine blue staining method allowed quantitative analysis of the hydrolysis of anhydride groups to acid groups. Coatings with constant thickness were obtained at different plasma powers and layers with varying thickness were obtained at constant plasma power by adjusting the polymerisation time. The results show that the hydrolysis resistance of the modified layer is determined by the power used in the plasma polymerisation, while changes in the chemistry of the modified layer are insignificant.     

High Energy P+P(P)→P+P(P)+Xj(cc) Process and Two Methods for Calculating Double-Pomeron Exchange Mechanism

Using the X_j(cc) double diffractive production processes in high energy P + P(P) collisions, we have comparatively discussed the D-L phenomenological method of calculating the double-pomeron exchange (DPE) and the method based on the exchange of a pair of nonperturbative color singlet gluons. From the energy dependence of the total cross sections calculated with the two methods we find the two methods fitting well. We conclude that the two methods are consistent.     

Adjustable thermal conductivity in carbon nanotube nanofluids

Homogeneous and stable nanofluids have been produced by suspending well dispersible multi-walled carbon nanotubes (CNTs) into ethylene glycol base fluid. CNT nanofluids have enhanced thermal conductivity and the enhancement ratios increase with the nanotube loading and the temperature. Thermal conductivity enhancement was adjusted by ball milling and cutting the treated CNTs suspended in the nanofluids to relatively straight CNTs with an appropriate length distribution. Our findings indicate that the straightness ratio, aspect ratio, and aggregation have collective influence on the thermal conductivity of CNT nanofluids.     

Production of CN(BΣ) state from dissociative excitation reaction of BrCN with microwave discharge flow of Ar

The mechanism of the dissociative excitation reaction of BrCN with the microwave discharge flow of Ar was investigated based on the CN(B²Σ⁺-X²Σ⁺) emission-spectroscopic and the electrostatic-probe measurements. By passing Ar and BrCN through P₂O₅, the contamination of H₂O molecules into the reaction region was reduced to ≈30%, being confirmed by monitoring the reduction of the OH(A²Σ⁺-X²Π) emission intensity. The variation of the CN(B²Σ⁺-X²Σ⁺) emission intensity on the pressure of Ar, P_Ar, of 0.1-0.3 Torr was compared with that of the density of electrons whose kinetic energy was lower than the ionization energy of BrCN, 11.9 eV. The dissociation of BrCN was found to proceed predominantly via the charge transfer from Ar⁺ followed by the BrCN⁺ − e⁻ recombination. When the contamination of H₂O molecules in the reaction region was not reduced, the dissociation via the energy transfer from metastable Ar atoms became significant. The present study shows that the contamination of H₂O molecules in the reaction system makes significant effect onto the gas-phase plasma process.     

Effects of non-stoichiometry on crystallinity, photoluminescence and afterglow properties of Sr2MgSi2O7:Eu, Dy phosphors

Eu²⁺, Dy³⁺ co-doped Sr₂MgSi₂O₇ phosphors with deficient, stoichiometric or excess amounts of silicon are prepared by solid-state reaction. XRD and SEM results indicate that all the samples studied are found to be free from impurities and samples with SiO₂ excess possess better crystallinity and larger grain size. Photoluminescence reveals that the position of Eu²⁺ emission is not changed with various compositions. However, both photoluminescence intensity and afterglow properties are increased by an incorporation of excess SiO₂ and are decreased by SiO₂ deficiency. The thermoluminescence results show that the corresponding increase or decrease in afterglow is associated with trap density, but no change in trap depth. The underlying reason of photoluminescence and afterglow enhancement is discussed.     

Thermal wave scattering by two overlapping and parallel cylinders

In this paper an analytical solution of the temperature of an opaque material containing two overlapping and parallel subsurface cylinders, illuminated by a modulated light beam, is presented. The method is based on the expansion of plane and cylindrical thermal waves in series of Bessel and Hankel functions. This model is addressed to the study of heat propagation in composite materials with interconnection between inclusions, as is the case of inverse opals and fiber reinforced composites. Measurements on calibrated samples using lock-in infrared thermography confirm the validity of the model.