Preparation of calcium-doped boron nitride by pulsed laser deposition

Calcium-doped BN thin films Ca_xBN_y (x = 0.05–0.1, y = 0.7–0.9) were grown on α-Al₂O₃(0 0 1) substrates by pulsed laser deposition (PLD) using h-BN and Ca₃N₂ disks as the targets under nitrogen radical irradiation. Infrared ATR spectra demonstrated the formation of short range ordered structure of BN hexagonal sheets, while X-ray diffraction gave no peak indicating the absence of long-range order structure in the films. It was notable that Ca-doped film had 5.45–5.55 eV of optical band gap, while the band gap of Ca-free films was 5.80–5.85 eV. This change in the band gap is ascribed to interaction of Ca with the BN sheets; first principle calculations on h-BN structure indicated that variation of inter-plane distance between the BN layers did not affect the band gap. This study highlights that PLD could prepare BN having short-range structure of h-BN sheets and being doped with electropositive cation which varies the optical band gap of the films.     

Hierarchical hollow microsphere and flower-like indium oxide: Controllable synthesis and application as H2S cataluminescence sensing materials

In the present work, In₂O₃ hierarchical hollow microsphere and flower-like microstructure were achieved controllably by a hydrothermal process in the sodium dodecyl sulfate (SDS)-N,N-dimethyl-formamide (DMF) system. XRD, SEM, HRTEM and N₂ adsorption measurements were used to characterize the as-prepared indium oxide materials and the possible mechanism for the microstructures formation was briefly discussed. The cataluminescence gas sensor based on the as-prepared In₂O₃ was utilized to detect H₂S concentrations in flowing air. Comparative gas sensing results revealed that the sensor based on hierarchical hollow microsphere exhibited much higher sensing sensitivity in detecting H₂S gas than the sensor based on flower-like microstructure. The present gas sensor had a fast response time of 5 s and a recovery time of less than 25 s, furthermore, the cataluminescence intensity vs. H₂S concentration was linear in range of 2–20 μg mL^?1 with a detection limit of 0.5 μg mL^?1. The present highly sensitive, fast-responding, and low-cost In₂O₃-based gas sensor for H₂S would have many practical applications.     

Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R_air/R_alcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R² of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.     

Improvement of dry float–sink separation of smaller sized spheres by reducing the fluidized bed height

In this study, the influence of the fluidized bed height on the float–sink of different sized spheres in a gas–solid fluidized bed was investigated. Fluidized beds with heights h = 200, 150, 100 and 50 mm were prepared using a cylindrical column of inner diameter = 290 mm and a mixture of zircon sand and iron powder as the fluidized medium. Float–sink experiments were carried out using density adjusted spheres of diameter D_sp = 40, 30, 20 and 10 mm. It was found that the float–sink performance at D_sp ?20 mm is not affected by the height of the bed, and the sharpness of separation (the density range where spheres neither float nor sink completely) is less than or equal to 200 kg/m³. In the case of D_sp = 10 mm, the sharpness of separation is a larger value (1100 kg/m³ at h = 200 mm), whereas it decreases with decreasing h and is 400 kg/m³ at h = 50 mm. The fluctuation of the surface height of the fluidized bed was visually recorded. The fluctuation is reduced by reducing h. The fluctuation vs. h correlates with the sharpness of separation at D_sp = 10 mm vs. h. These results indicate that the dry float–sink separation of smaller sized spheres is improved as the fluctuation of fluidized bed surface is decreased by reducing the fluidized bed height.     

Upconversion luminescence of Ba(MoO4)h(WO4)1−h:Yb3+/Er3+ nanocrystals synthesized through hydrothermal method

A series of Yb³⁺/Er³⁺ co-doped Ba(MoO₄)_h(WO₄)_1−h upconversion nanocrystals (UCNCs) were prepared via hydrothermal method. The effects of different concentration ratios of Yb³⁺/Er³⁺ and Mo₄O²⁻/WO₄²⁻ on the upconversion luminescence were investigated, and the optimum doping concentrations of Yb³⁺ and Er³⁺ in the Ba(MoO₄)_0.5(WO₄)_0.5 host were found to be 3 mol% and 1 mol%, respectively. Structure of Ba(MoO₄)_0.5(WO₄)_0.5:0.03Yb³⁺/0.01Er³⁺ was identified as the tetragonal in the X-ray diffraction (XRD) results and the particle size observed in the scanning electron microscope (SEM) was about 40 nm. Under excitation of 980 nm semiconductor laser, three emission bands centered at 528, 550 and 660 nm, originating from ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively, were observed for Ba(MoO₄)_0.5(WO₄)_0.5:0.03Yb³⁺/0.01Er³⁺. The pump power dependence research suggested that these bands arise due to two-photon absorption. The variation of CIE coordinate at different excitation powers was observed.     

Enhanced triethylamine sensing performance of superfine NiO nanoparticles decoration by two-dimensional hexagonal boron nitride

The novel two-dimensional hexagonal boron nitride (h-BN) decorated nickel oxide (NiO) heterojunction was successfully synthesized by a facile solvothermal precipitation method combining with heat treatment. SEM and TEM analysis were used to corroborate the average size (~8 nm) and overall distribution of superfine NiO nanoparticles on h-BN. XRD, FT-IR and XPS characterization confirmed the configuration of highly crystallinity and p-n heterojunction as well as the presence of surface oxygen vacancy defects. Gas sensing test results revealed that the decoration of h-BN could significantly enhanced triethylamine (TEA) sensing property of NiO. The main contribution of such remarkable results lies in NiO nanoparticles that are close to Debye length scale were embedded on vacancy defects of functionalized h-BN nanosheets, which can optimize sensitivity and selectivity by taming two-dimensional (2D) interfacial electronic effects that strongly affect nonmetal-support interaction between grain boundaries. Meanwhile, the formation of p-n Schottky nanoscale heterojunction between NiO and h-BN can significantly enlarge resistance variation and efficiently promoted the adsorbed triethylamine molecules to oxidize into NO₂, H₂O, and CO₂. Our work highlights the important role of coupling functionalized h-BN in gas sensors, which can also provide a valuable avenue in boosting the sensing performance.     

Nanocrystalline spinel Ni0.6Zn0.4Fe2O4: A novel material for H2S sensing

Nanocrystalline powders of Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 0.5) mixed ferrites, with cubic spinel structure and average crystallite size ranging from 28 to 42 nm, were synthesized by the ethylene glycol mediated citrate sol–gel method. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). The response of prepared Ni_1?xZn_xFe₂O₄ mixed ferrites to different reducing gases (liquefied petroleum gas, hydrogen sulfide, ethanol gas and ammonia) was investigated. The sensor response largely depends on the composition, temperature and the test gas species. The Zn content has a significant influence on the gas-sensing properties of Ni_1?xZn_xFe₂O₄. Especially, Ni_0.6Zn_0.4Fe₂O₄ composition exhibited high response with better selectivity to 50 ppm H₂S gas at 225 °C. Incorporation of palladium (Pd) further improved the response, selectivity and response time of Ni_0.6Zn_0.4Fe₂O₄ to H₂S with the shift in the operating temperature towards lower value by 50 °C. The enhanced H₂S sensing properties can mainly be attributed to the selectivity to oxidation of H₂S and noble metal additive sensitization. Furthermore, the sensor exhibited a fast response and a good recovery.     

Facile preparation of heterostructured Bi2O3/Bi2MoO6 hollow microspheres with enhanced visible-light-driven photocatalytic and antimicrobial activity

Hierarchical β-Bi₂O₃/Bi₂MoO₆ heterostructured flower-like microspheres assembled from nanoplates with different β-Bi₂O₃ loadings (0–26.5 mol%) were synthesized through a one-step template-free solvothermal route. Under visible-light illumination (λ > 420 nm), over 99% of rhodamine B was degraded within 90 min on the 21.9 mol% of β-Bi₂O₃ loading Bi₂O₃/Bi₂MoO₆ microspheres. The remarkable enhancement of photocatalytic activity of the hierarchical Bi₂O₃/Bi₂MoO₆ micro/nanostructures can be attributed to the effective separation of the photoinduced charge carriers at the interfaces and in the semiconductors. The electrons (e⁻) are the main active species in aqueous solution under visible-light irradiation. The Bi₂O₃/Bi₂MoO₆ also displays visible-light photocatalytic activity for the destruction of E. coli. In addition, the β-Bi₂O₃ in the hierarchical Bi₂O₃/Bi₂MoO₆ microspheres is very stable and the composite can be easily recycled by a simple filtration step, thus the second pollution can be effectively avoided. A possible photocatalytic mechanism was proposed based on the experimental results.     

Study of the properties of polymers obtained from vegetable oil derivatives by light scattering techniques

Polymers from oleic acid (principal fatty acid of the olive oil) and methyl oleate were studied by static (SLS) and dynamic (DLS) light scattering in acetone solution. The oleic acid (OA) and methyl oleate (MO) were first epoxidized using a performic acid generated in situ. The epoxidized oleic acid (EOA) and methyl oleate (EMO) were reacted with cis-1,2-cyclohexanedicarboxylic anhydride (CH) as cure agent, triethylamine (TEA) as initiator and small amount of 1,4-butanediol diglycidyl ether (BDGE). According to light scattering results the EMO products without BDGE present low M_W, however the EOA ones are characterized by aggregation and M_W approximately 1.98 × 10⁵ g/mol. The aggregation is evidenced by the presence of two modes in DLS experiments. The dimension of the single particle is approximately R_h = 5 nm and for the aggregates R_h increases until 169 nm. The samples with addition of BDGE in the reaction mixtures for both derivatives (EMO and EOA) result to macromolecular products with M_W higher than 1.71 × 10⁵ g/mol, however no aggregation of this macromolecules is observed. Both products present relatively small dimensions and random coil conformation behavior.     

On the sol–gel synthesis and characterization of strontium ferrite ceramic material

A simple oxalate based sol–gel process has been described to produce a highly stable anion deficient strontium ferrite for separation of oxygen from air. The method involves metal nitrates and oxalic acid precursors with ethanol and water as solvents, gel formation, digestion for 4 h, drying at 150 °C for 24 h, and finally decomposition at 800 °C in air. The resulting material (i) exhibits a single perovskite-type cubic (SrFeO_3?ξ; ξ ～ 0.13) phase with a_o = 3.862 ± 0.002 Å, (ii) contains both the Fe⁴⁺ and Fe³⁺ species in 2.8:1 ratio, (iii) undergoes Fe⁴⁺ → Fe³⁺ reduction upon heating at 650 °C in rare gas ambient and transition to an orthorhombic phase with a ～ a_o√2, b ～ 4a_o, c ～ a_o√2, which reverts back to cubic phase with oxygen uptake at elevated temperatures, and (iv) acts as filter for air with excellent oxygen permeation, typical flux density value being 2.45 ml/cm² min at 1000 °C.     

Remarkable oxygen adsorption/desorption capability of Y0.5Tb0.5BaCo4O7+δ under temperature cycles

When the Y_0.5Tb_0.5BaCo₄O_7+δ ceramic powder is heated to 200–380 °C in oxygen atmosphere, it can adsorb oxygen remarkably. The adsorbed oxygen could be released by raising temperature over 420 °C or by switching the atmosphere from oxygen to nitrogen. In a temperature cycle between 360 °C and 440 °C, the relative mass change of the Y_0.5Tb_0.5BaCo₄O_7+δ sample can reach 4.4% of its original mass, and shows high efficiency and stable oxygen adsorption/desorption reproducibility. However, the oxygen adsorption/desorption efficiency in the cycles switched between oxygen and nitrogen atmosphere is poor. The large adsorption capacity, the fast adsorption/desorption speeds, and the easy regeneration of Y_0.5Tb_0.5BaCo₄O_7+δ absorbent under temperature cycles make it to be a highly potential candidate in air separation and oxygen removal.     

Synthesis,crystal structure refinement,electrical and magnetic properties of BaV13O18 and SrV13O18

Polycrystalline samples of BaV₁₃O₁₈ and SrV₁₃O₁₈ were prepared by solid-state reaction of BaCO₃, SrCO₃, V₂O₅ and V at 1773–2073 K in flowing Ar. The crystal structures of BaV₁₃O₁₈ (R-3, a_h=12.6293(10) Å, c_h=7.0121(4) Å) and SrV₁₃O₁₈ (a_h=12.5491(7) Å, c_h=6.9878(3) Å) were refined by the Rietveld method using X-ray diffraction data. BaV₁₃O₁₈ exhibited semiconducting behavior with electrical resistivity from 5.8×10⁻³ to 2.7×10⁻³ Ω cm at 100–300 K. Electrical resistivity of SrV₁₃O₁₈ ranged from 1.5×10⁻³ to 1.8×10⁻³ Ω cm, and it increased slightly up to around 250 K and decreased above 250 K with increasing temperature. Negative Seebeck coefficients of both compounds at 100–300 K indicated that electron was the dominant carrier. BaV₁₃O₁₈ and SrV₁₃O₁₈ showed paramagnetism with the effective magnetic moment of 0.11μ_B and 0.15μ_B, respectively, at 10–100 K.     

Effect of annealing in a various oxygen atmosphere on structural,optical, electrical and gas sensing properties of MoxOy thin films

Molybdenum oxide thin films were thermally evaporated on a glass substrate and monitored by an annealing process in a variable oxygen atmosphere. The effects of post annealing condition on the microstructural, morphological, optical and electrical properties were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscope, spectroscopic ellipsometry and impedance spectroscopy. As-deposited amorphous films crystallized into tetragonal metastable phase of Mo₅O₁₄ on annealing at 500 °C in vacuum and air. This structure transformed to stable orthorhombic of MoO₃ with annealing in oxygen environment. The optical parameters such as the refractive index, extinction coefficient, optical band gap energy and the Urbach energy were calculated from Cauchy formalism. Ellipsometric measurements reveal that the samples present optical gap located between 3.24 and 3.90 eV when the atmosphere becomes rich on oxygen. The variation of the conductivity in terms of the temperature shows an electrical behavior with oxygen environment. Finally, it has been found that MoO₃ thin films had high sensitivity to ethanol, which made them as a good candidate for the ethanol sensor.     

Synthesis of ceramics by sol–gel method in molybdenum,silicon and carbon containing systems. Thermogravimetric studies

The results of investigations on synthesis of ceramics in nanometric systems containing molybdenum compounds, silicon compounds and active carbon have been presented. As precursors ammonium molybdatetetrahydrate ((NH₄)₆Mo₇O₂₄ 4H₂O) and tetraethyl orthosilicate (Si(OC₂H₅)₄) were used. The samples for analysis were obtained by sol–gel method. The course of the process was investigated by thermogravimetric method. The gaseous products were analysed by mass spectrometry. X’ray diffraction (XRD) method was used for identification of solid phases, and morphology of the samples was studied by scanning electron microscopy (SEM). The process proceeded in the following way. At temperature t ⩽ 673 K (NH₄)₆Mo₇O₂₄ 4H₂O decomposes into MoO₃. Then at temperature range of 1046 ⩽ t ⩽ 1065 K MoO₃ is reduced into MoO₂ (or also into Mo). Synthesis of Mo₂C proceeds at temperature in the order of 1273 K. Before the carbothermal reduction of SiO₂ and synthesis of compounds containing molybdenum and silicon we have the Mo₂C–SiO₂-active carbon mixtures. In one stage, at temperature of 1523 K in argon, the synthesis of SiC and the synthesis of compounds containing molybdenum and silicon takes place. In the wide range of initial compositions of the mixtures Mo_4.8Si₃C_0.6 was obtained as the main phase.     

Inverse surface plasmon resonance based effective hydrogen sensing using nanoscale palladium films

We demonstrate a nanoscale palladium (Pd) based inverse surface plasmon resonance (ISPR) setup for sensing highly inflammable hydrogen (H₂) gas. The ISPR setup was employed in Kretschmann configuration to assess the sensitivity of the Pd-films when subjected to H₂ gas exposure. With an adequate broadening of the SPR peak maxima, the SPR angle was found to shift from a value of 46.57° to 50.97°, when the concentration of H₂ was varied between 0% and 0.9%. The shifting can be attributed to the transient development of isolated PdH_x (x < 1) clusters within Pd lattices, resulting in an appreciable change of refractive index locally. The dynamical behaviour of switching on/off states exhibited by a ∼20 nm Pd-film and exposed to 0.1% H₂ gas was monitored over several cycles repetitively. The ISPR based H₂ sensor, as demonstrated in ambient environment, would find scope to detect low level H₂ in industrial and other hazardous areas.     

Defect-impurity complexes with high thermal stability in epi-Si n+-p diodes irradiated with MeV electrons

Defect-impurity complexes with high thermal stability which were generated after high temperature annealing of silicon n⁺-p diodes irradiated with 4 MeV electrons at 300 K have been studied by means of deep level transient spectroscopy (DLTS). Such defects are of interest because of their possible application in controlling the carrier lifetime in silicon power devices. The parameters of four deep level traps have been determined and compared with the results of photoluminescence studies on thermal stability of electron-irradiation-induced defects. A donor like trap with an energy level at E_v + 0.39 eV was assigned to a complex incorporating an interstitial carbon atom and two oxygen atoms (C_iO_2i), which gives rise to the P-line (hν = 0.767 eV) in photoluminescence spectra.     

Fluorine intercalation in the n = 1 and n = 2 layered manganites Sr2MnO3.5+x and Sr3Mn2O6

Fluorine insertion into the oxygen defect superstructure manganite Sr₂MnO_3.5+x has been shown by transmission electron microscopy (TEM) to result in two levels of fluorination. In the higher fluorine content sections, the fluorine anions displace oxygen anions from their apical positions into the equatorial vacancies, thus destroying the superstructure and reverting to a K₂NiF₄-type structure (a = 3.8210(1) Å and c = 12.686(1) Å). Conversely, lower fluorine content sections retain the Sr₂MnO_3.5+x defect superstructure, crystallising in the P2₁/c space group. Fluorine intercalation into the reduced double-layer manganite Sr₃Mn₂O₆ occurs in a step-wise fashion according to the general formula Sr₃Mn₂O₆F_y with y = 1, 2, and 3. It is proposed that the y = 1 phase (a = 3.815(1) Å, c = 20.29(2) Å) is produced by the filling of all the equatorial oxygen vacancies by fluorine atoms whilst the y = 2 phase (a = 3.8222(2) Å, c = 21.2435(3) Å) has a random distribution of fluorine anions throughout both interstitial rocksalt and equatorial sites. Neutron powder diffraction data suggest that the fully fluorinated y = 3 phase (a = 3.8157(6) Å, c = 23.666(4) Å) corresponds to the complete occupation of all the equatorial oxygen vacancies and the interstitial sites by intercalated fluorine.     

High-speed deposition of dense,dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

Dense, dendritic and porous SiO₂ films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (P_L) and total chamber pressure (P_tot) on the microstructure and deposition rate (R_dep) were investigated. Amorphous SiO₂ films were obtained independent of P_L and P_tot. Flame formation was observed between the nozzle and the substrate at P_L > 160 W and P_tot > 15 kPa. At P_L = 206 W, dense, dendritic and porous SiO₂ films were obtained at P_tot < 20 kPa, P_tot = 23 kPa and P_tot > 25 kPa, respectively. The R_dep increased thousands of times under flame formation conditions, the highest R_dep being reached at 1200 μm h^?1, 22,000 μm h^?1 and 28,000 μm h^?1 for the dense, dendritic and porous SiO₂ films, respectively.     

Corrosion inhibition of aluminum in hydrochloric acid solution by alkylimidazolium ionic liquids

The effects of newly synthesized three alkylimidazolium ionic liquids—1-butyl-3-methylimidazolium chlorides (BMIC), 1-hexyl-3-methylimidazolium chlorides (HMIC) and 1-octyl-3-methylimidazolium chlorides (OMIC)—on the corrosion of aluminum in 1.0 M HCl were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss methods. All measurements showed that the inhibition efficiency increased with increase in the concentration of inhibitor and the effectiveness of these inhibitors was in the order of OMIC > HMIC > BMIC. Polarization curves revealed that the studied inhibitors were mixed type inhibitors. The adsorption of the inhibitors on the aluminum surface obeyed Langmuir adsorption isotherm and had a physical mechanism. The effect of temperature on the corrosion behavior in the presence of 5 × 10^?3 M of inhibitors was studied in the temperature range of 303–333 K. The associated activation energy of corrosion and other thermodynamic parameters such as enthalpy of activation (ΔH), entropy of activation (ΔS), adsorption equilibrium constant (K_ads) and free energy of adsorption (ΔG_ads) were calculated to elaborate the mechanism of corrosion inhibition.     

Importance of H2 gas for growth of hot-wire CVD nanocrystalline 3C-SiC from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and the influence of H₂ gas flow rate (F(H₂)) on the film properties was investigated. The SiH₄ gas flow rate was 1 sccm. At the CH₄ gas flow rate (F(CH₄)) of 1 sccm, nanocrystalline cubic SiC (nc-3C-SiC) grew even without H₂. On the other hand, at F(CH₄) = 2 sccm, amorphous SiC grew without H₂ and nc-3C-SiC grew above F(H₂) = 50 sccm. As F(H₂) was increased, the crystallinity improved both at F(CH₄) = 1 and 2 sccm. However, the mean crystallite size decreased at F(CH₄) = 1 sccm and increased at F(CH₄) = 2 sccm. We discuss growth mechanisms of nc-3C-SiC.