Neutron flux measurements with a Li2B4O7 crystal

The effect of neutron irradiation on a lithium tetraborate (Li₂B₄O₇, LBO) single crystal has been investigated. The crystals of high optical quality are found to be quite stable under high neutron fluence. This study shows that LBO crystals can be used as a proportional counter for neutron fluxes of the order 10⁹ cm⁻² s⁻¹ and higher. The detectors fabricated were found to have a sensitivity of ∼3×10⁻¹⁸ A (nv)⁻¹.     

Optical and thermal properties of crystalline Tb: KLu(WO4)2

A single crystal of Tb: KLu(WO₄)₂ with dimensions of 40 mm × 40 mm × 18 mm has been grown by the top-seeded solution growth (TSSG) method. The color of the crystal is brown. Absorption and fluorescence spectra were measured at room temperature. The measured specific heat is a little lower than that of Yb: KLW (0.365 J/g K) at 90 °C. The measured mean linear coefficients of thermal expansion are α_a = 17.1643 × 10^− 6 K^− 1_, α_a^⁎ = 14.0896 × 10^− 6 K^− 1, α_b = 8.7938 × 10^− 6 K^− 1, α_c = 23.1745 × 10^− 6 K^− 1, α_c^⁎ = 20.2866 × 10^− 6 K^− 1. The results indicate that the crystal has a large anisotropy. The refractive index was measured.     

Negative thermal expansion in silicalite-1 and zirconium silicalite-1 having MFI structure

In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming α-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298–1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, α_V = −6.75 × 10⁻⁶ and −17.92 × 10⁻⁶ K⁻¹ in the temperature range 298–1023 K⁻¹ for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298–1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with α_V = 2.647 × 10⁻⁶ and 4.24 × 10⁻⁶ K⁻¹, the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient α_V = −7.602 × 10⁻⁶ and −15.04 × 10⁻⁶ K⁻¹, respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with α_V = −12.08 × 10⁻⁶ and −45.622 × 10⁻⁶ K⁻¹ for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298–1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si–O distances.     

Third-order nonlinear optical properties of bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper

Bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper (BCDT) was synthesized and its third-order optical nonlinearity was characterized using picosecond Z-scan at 1064 nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n₂ as high as 4.0 × 10⁻¹⁸ m²/W and a slight two-photon absorption β, which is determined to be 3.4 × 10⁻¹² m/W. The molecular second-order hyperpolarizability γ was calculated to be 6.5 × 10⁻³² esu. All these results suggest that this material has potential for the application of all-optical switching.     

Study of natural diamond detector spectrometric properties under neutron irradiation

Natural diamond detector (NDD) performance was studied up to a neutron fluence of 10¹⁵ neutron/cm². The variations of the NDD spectrometric response to incident α-particles from ²⁴¹Am source after exposure to fast neutron fluences up to 3×10¹⁶ n/cm² were examined. No significant variations up to the level of 10¹⁴ n/cm² were observed. Degradation of charge collection efficiency at higher fluences is reported. No remarkable increase of the NDD leakage current and count rate change had been observed up to a neutron fluence of 3×10¹⁶ n/cm². The charge collection efficiency variations of neutron irradiated diamond spectrometer were studied ex situ under γ-rays, β-radiation and visible light excitation. Charge collection efficiency restoration up to 75% level and the NDD performance stabilization by extrinsic low-intensity visible light (550 nm<λ<800 nm) or intrinsic excitations have been demonstrated.     

Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO₂ in the range 1.33×10⁻² to 0.133 Pa at a substrate temperature of 160 °C. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO₂ value of 4.00×10⁻² Pa were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fcc structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (1 1 1) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO₂) indicated that the maximum preferred orientation of the films occurred along the (1 1 1) plane at an oxygen partial pressure of 4.00×10⁻² Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655–4.686 Å. The average lattice parameter a₀ found by extrapolation using the Nelson–Riley function was 4.696 Å. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance at λ=600 nm and minimum in the electrical resistivity (9.1×10⁻⁴ Ω cm) of the films occurred at an optimum partial pressure of oxygen of 4.00×10⁻² Pa. The results are discussed.     

Investigation of traps in AlGaN/GaN HEMTs by current transient spectroscopy

Deep levels in AlGaN/GaN HEMTs on Si substrate are known to be responsible for trapping processes like: threshold voltage shift, leakage current, degradation in saturation current and hysteresis effect. The related deep levels are directly characterized by Conductance Deep Level Transient Spectroscopy (CDLTS) method. Hereby we have detected four carrier traps with activation energy of 0.83, 0.50, 0.20 and 0.07 eV and capture cross-section respectively of σ = 3.14 × 10^− 14 cm², σ = 2.57 × 10^− 15 cm², σ = 3.03 × 10^− 17 cm² and σ = 2.65 × 10^− 15 cm². All these traps are located between the substrate and the two-dimensional electron gas (2DEG) channel.     

Carbon fiber polymer–matrix structural composites exhibiting greatly enhanced through-thickness thermoelectric figure of merit

The through-thickness thermoelectric behavior of continuous carbon fiber epoxy-matrix composites is greatly improved by adding tellurium particles (13 vol.%), bismuth telluride particles (2 vol.%) and carbon black (2 vol.%). The thermoelectric power is increased from 8 to 163 μV/K, the electrical resistivity is decreased from 0.17 to 0.02.Ω.cm, the thermal conductivity is decreased from 1.31 to 0.51 W/m.K, and the dimensionless thermoelectric figure of merit ZT at 70 °C is increased from 9 × 10⁻⁶ to 9 × 10⁻². Tellurium increases the thermoelectric power greatly. Bismuth telluride decreases the electrical resistivity and thermal conductivity. Carbon black decreases the electrical resistivity.     

Compression behaviour and micro-structure evaluation of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass under high pressure

Compression behaviour and micro-structure evaluation of Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ bulk metallic glass is investigated at room temperature up to 32.8 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The equation of state of the bulk metallic glass is − ΔV / V = 0.012P − 2.49 × 10^− 4P² − 9.5 × 10^− 7P³ + 5.02 × 10^− 8P⁴. The result shows that the nearest atom pair of the as-quenched bulk metallic glass corresponds to Zr–Zr correlations. And with pressure increasing, the nearest atom pair changes to a new one at 32.8 GPa.     

Tritium digital autoradiography with a Medipix2 hybrid silicon pixel detector

We report on the first measurements of ³H beta autoradiography obtained using a room temperature hybrid pixel detector, consisting of the Medipix2 single particle counting read-out chip bump-bonded to a 300 μm thick silicon pixel detector. This system has 256×256 square pixels of 55 μm pitch for a total sensitive area of 14×14 mm². Each pixel contains a double threshold discriminator and a 13-bit counter. Using a detection threshold equivalent to less than 6 keV and a background count rate of 5×10⁻³ counts mm⁻² s⁻¹, with exposures up to several hours, real-time images have been obtained of tritium-labeled solution drops spotted on a thin mylar foil placed in contact with the continuous top electrode of the silicon detector, in open air condition.     

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.     

High-temperature electrical resistivity and heat capacity studies on nano-crystalline geikielite

We report here for the first time the temperature dependence of the electrical resistivity and heat capacity of nano-crystalline MgTiO₃ geikielite of up to 1000 K. The temperature dependence of heat capacity of nano-crystalline geikielite expressed as C_p = 46.44(5) + 0.0502(2)T − 4.56 × 10⁶T² + 1.423 × 10³T^− 0.5 − 8.672 × 10^− 6T^− 2, where C_p = is specific heat expressed in J/mol. K and T is the temperature in K. Both the electrical resistivity and heat capacity behaviour show that the geikielite (both the natural and synthetic nano-crystalline samples) are stable and remains electrically insulating up to 1000 K.     

The effect of polymeric wall on the permeability of drug-loaded nanocapsules

The aim of this work was to establish a quantitative correlation between the drug permeability and the polymer concentration in the nanocapsules. Indomethacin ethyl ester-loaded nanoemulsion and nanocapsules containing poly(epsilon-caprolactone) at different concentrations (0, 2, 4, 6, 8 and 10 mg/mL) presented drug loading between 0.981 and 1.005 mg/mL, pH values from 5.0 to 5.4, particle sizes between 232 and 261 nm, polydispersity lower than 0.24 and zeta potentials from − 8.54 mV to − 11.86 mV. An alkaline hydrolysis of indomethacin ethyl ester carried out at the particle/water interface was used to simulate a sink condition of release. The number of particles in each suspension was estimated. The calculated values ranged from 5.84 × 10¹² to 6.60 × 10¹² particles cm^− 3, showing similar concentration of particles in the formulations. The diffusion was proposed as the main mechanism of the indomethacin ester release after fitting the data to the Higuchi model. Applying the Fick's first law, the calculated indomethacin ester fluxes (J) decreased from 2.20 × 10^− 7 to 1.43 × 10^− 7 mg cm^− 2 min^− 1. Then, the drug relative permeability decreased according to the increase in the polymer concentration fitting a power law.     

Strain rate dependent plastic mutation in a bulk metallic glass under compression

This paper reported a strain rate dependent plasticity in a Zr-based bulk metallic glass (BMG) under axial compression over a strain rate range (1.6 × 10⁻⁵–1.6 × 10⁻¹ s⁻¹). The fracture strain decreased with increasing strain rate up to 1.6 × 10⁻³ s⁻¹. A “brittle-to-malleable” mutation occurred at strain rate of 1.6 × 10⁻² s⁻¹, subsequently, the macro plasticity vanished at 1.6 × 10⁻¹ s⁻¹. It is proposed that the result is strongly related to the combined action of the applied strain rate, the compression speed, and the propagating speed of the shear band. When the three factors coordinated in the optimal condition, multiple mature shear bands were initiated simultaneously to accommodate the applied strain, which propagated through the specimen and distributed homogeneously in space, dominating the overall plastic deformation by consuming the entire specimen effectively.     

Investigation on third order nonlinear optical,electrical and surface properties of organic stilbazolium crystal of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate

The third order nonlinear optical, electric and dielectric properties of an organic stilbazolium derivative of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate (DSMOS) crystal are reported. The nonlinear refractive index (n₂), two photon absorption coefficient (β) and third order optical susceptibility χ⁽³⁾ have been measured by Z-scan technique using Gaussian beam from the Nd:YAG laser at 1064 nm. The results show a large negative nonlinear refractive index (n₂ = −1.122 × 10−9 cm²/W) with a molecular two photon absorption coefficient β value of 3.625 × 10⁻⁶ cm/W. The low dielectric constant observed in the high frequency region indicates the suitability of the sample for electro-optic applications. The surface features are also investigated by atomic force microscopy (AFM).     

Determination of terbium(III) ions in phosphate rock samples by a Tb3+–PVC membrane sensor based on N,N-Dimethyl-N′, N″-bis(4-methoxyphenyl)phosphoramidate

A poly (vinyl chloride)-based membrane of N, N-Dimethyl-N′, N″-bis(4-methoxyphenyl)phosphoramidate (DMP) as a neutral carrier was prepared and investigated as a Tb³⁺-selective electrode. This electrode constructed with sodium tetraphenylborate (NaTPB) as the anion excluder and 2-nitrophenyl octyl ether (NPOE) as the plasticizer. Its performance was found to be the following: a Nernstian slope of 19.7 ± 0.4 mV per decade across a broad range (1.0 × 10^− 6 to 1.0 × 10^− 1 M); a detection limit of 8.0 × 10^− 7 M between the pH values of 3.5 and 8.0; additionally, the response time was about 10 s; usage of more than 2 months without any potential divergence; good Tb³⁺ selectivity over a wide variety of other metal ions. The membrane sensor was applied to the Tb³⁺ recovery from different water samples, determination of fluoride ions in mouth wash samples and the determination of Tb³⁺ in phosphate rock samples. It was also used as an indicator electrode in the potentiometric titration of Tb³⁺ ions with EDTA.     

Nonlinear optical properties of the PbS nanorods synthesized via surfactant-assisted hydrolysis

PbS nanorods were synthesized by surfactant-assisted homogenous hydrolysis. The products were characterized by UV–vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). PbS nanorods were measured by the Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of the NLO measurements shows that the PbS nanorods have the third-order nonlinear optical properties of both NLO absorption and NLO refraction with self-focusing effects. The nonlinear absorption coefficient and refractive index of the PbS nanorods are 2.16 × 10^− 9 m/W and 3.52 × 10^− 16 m²/W respectively.     

Multi-walled carbon nanotubes-based glucose biosensor prepared by a layer-by-layer technique

The loading of multi-walled carbon nanotubes (MWNTs) and glucose oxidase (GOx) in the alternate layers of a glucose biosensor was first optimized based on a layer-by-layer construction on the surface of a graphite disk electrode. With the increasing of MWNTs/GOx layers, the response current to glucose was changed regularly and the response current reached a maximum value when the number of MWNTs/GOx layers was 6. Owing to a good electrical conductivity, strong adsorption and excellent bioconsistency of MWNTs, the (MWNTs/GOx)₆ films-coated glucose biosensor had an excellent electrochemical properties. The response current of the (MWNTs/GOx)₆ films-coated biosensor to 3 × 10^− 2 M glucose was 1.63 μA while the response time was only 6.7 s. The linear range and the lowest detectable concentration of this biosensor was 5 × 10^− 4∼1.5 × 10^− 2 M and 0.9 × 10^− 4 M, respectively.     

Temperature influence on the voltage-controlled diffractive property of Mn-doped potassium sodium tantalate niobate crystal

We report the temperature influence on the voltage-controlled diffractive property of Mn-doped potassium sodium tantalate niobate crystal. The crystal was grown by the top seeded solution growth method. Its quadratic electro-optic coefficients achieved as high as R₁₁ = 3.50 × 10⁻¹⁵ m²/V² and R₁₂ = −0.44 × 10⁻¹⁵ m²/V² near the Curie temperature, while they declined with the increasing temperature. The external electric field which correspond to the maximum diffraction efficiency of photorefractive grating moved from 166 V/mm to 512 V/mm as the temperature increased from 25 °C to 32.5 °C. The maximum diffraction efficiencies all reached the maximum value of 60% at different temperatures. The results were discussed and compared with the theoretical equations.