Novel method for fabrication of room temperature polypyrrole–ZnO nanocomposite NO2 sensor

Nanocomposites of polypyrrole (PPy) and zinc oxide (ZnO) nanoparticles (NPs) were prepared by spin coating method. These nanocomposites were characterized by Fourier transform infrared (FTIR), Field emission scanning electron microscope (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis techniques, which proved the polymerization of pyrrole monomer and the strong interaction between polypyrrole and ZnO NPs. The nanocomposites were used for gas sensing to CH₃OH, C₂H₅OH, NH₃, H₂S and NO₂ at room temperature. It was revealed that PPy–ZnO nanocomposites with different ZnO weight ratios (10%, 20%, 30%, 40% and 50%) could detect NO₂ at low concentration with very higher selectivity and sensitivity at room temperature than the reported PPy. The PPy–ZnO nanocomposites responded to NO₂ at concentration as low as 10 ppm. PPy–ZnO nanocomposite containing ZnO (50%) showed the maximum sensitivity 38% with 92.10% stability to 100 ppm NO₂ gas at room temperature. The sensing mechanism of PPy–ZnO nanocomposites to NO₂ was presumed to be the effects of p–n junction between PPy and ZnO.     

FEA calculation of pressure distortion coefficients of gas-operated pressure balances – EURAMET project 1039

Finite element analysis methods were developed and applied to gas piston–cylinder units (PCUs) of piston- and cylinder-floating configuration (2, 5, 10 and 20) cm² nominal effective area, operated in gauge and absolute mode at pressures (0.06–7.5) MPa to determine their zero pressure and pressure-dependent effective areas, as well as pressure distortion coefficients (λ) with associated uncertainties. Real dimensional properties of the PCUs were used. λ were found to be independent of gas (ideal, N₂, He) within the viscous flow model, but strongly dependent on the gap shape, operation mode and elastic properties. Results demonstrate good agreement for λ, with its uncertainty for different PCUs varying between (0.03 and 0.21) × 10⁻⁶ MPa⁻¹ corresponding to maximum relative uncertainties in pressure of (0.07–0.34) × 10⁻⁶.     

Probing non-dipole allowed excitations in highly correlated materials with nanoscale resolution

Here, we demonstrate that non-dipole allowed d–d excitations in NiO can be measured by electron energy loss spectroscopy (EELS) in transmission electron microscopes (TEM). Strong excitations from ³A_2g ground states to ³T_1g excited states are measured at 1.7 and 3 eV when transferred momentum are beyond 1.5 Å⁻¹. We show that these d–d excitations can be collected with a nanometrical resolution in a dedicated scanning transmission electron microscope (STEM) by setting a good compromise between the convergence angle of the electron probe and the collected transferred momentum. This work opens new possibilities for the study of strongly correlated materials on a nanoscale.     

Simultaneous measurement of CO and CO2 at elevated temperatures by diode laser wavelength modulated spectroscopy

One single semiconductor distributed-feedback (DFB) laser is used to demonstrate the possibility of simultaneous measurements of CO and CO₂ at elevated temperatures. Wavelength modulation spectroscopy with second-harmonic detection is used to improve the detection sensitivity and accuracy. The concentrations of CO and CO₂ are determined from the WMS-1-normalized absorption-based WMS-2f signal peak heights of a proper line pair of CO and CO₂ near 6357.814 cm⁻¹ and 6357.312 cm⁻¹, which are selected using some line-selection criterions for the target temperature range of 300–1000 K. The CO and CO₂ concentrations measurements are within 2.86% and 2.69% of the expected values over the tested temperature range 300–1000 K. The minimum detectable concentrations of CO and CO₂ at 1000 K are 250 ppm m and 280 ppm m respectively.     

Charge compensation by in-situ heating for insulating ceramics in scanning electron microscope

With a steady temperature increase under high vacuum (HV) in an environmental scanning electronic microscope, we observed charge-free characterization and fine secondary electron (SE) images in focus for insulating ceramics (alumina (Al₂O₃), aluminum nitride (AlN), pure magnesium silicate (Mg₂SiO₄)). The sample current I_sc increased from −8.18×10⁻¹³ to 2.76×10⁻⁷ A for Al₂O₃ and −9.28×10⁻¹² to 2.77×10⁻⁶ A for AlN with the temperature increased from 298 to 633 K. The surface conductance σ increased from 5.6×10⁻¹³ to 5.0×10⁻¹¹/Ω for Al₂O₃ and 1.1×10⁻¹² to 1.0×10⁻⁷/Ω for AlN with the temperature increased from 363 to 593 K. The SE image contrast obtained via heating approach in high vacuum with an Everhart–Thornley SE-detector was better than that via conventional approach of electron–ion neutralization in low vacuum (LV) with a gaseous SE-detector. The differences of compensation temperatures for charge effects indicate dielectric and thermal properties, and band structures of insulators. The charge compensation mechanisms of heating approach mainly relate to accelerated release of trapped electrons on insulating surface and to increase of electron emission yield by heating.     

A new application of functionalized platinum nanoparticles as chemiresistor coating

Chemiresistor sensor based on Pt nanoparticles stabilized with 11-mercaptoundecanoic acid was developed for detection of some volatile organic compounds (VOCs). This sensor was prepared by drop coating technique onto interdigitated microelectrode. This film displayed linear current–voltage (I–V) characteristics and decrease the resistance at room temperature. The chemiresistive sensing properties were measured over a concentration range of 1.4–400 mg L⁻¹ for methanol, ethanol, ethyl acetate and acetone vapors. The results showed good sensitivity to methanol vapors and low detection limits for all examined vapors.     

Thermal diffusivity measurement of Au nanofluids of very low concentration by using photoflash technique

In this paper, the application of photoflash technique to measuring the thermal diffusivity of gold nanofluids of very low concentration at room temperature was presented. The nanofluid samples were prepared from the pulse laser ablation procedure. The thermal diffusivity was obtained by fitting the theoretical temperature signal to the experimental data, and it was found to increase linearly from 1.47 × 10⁻³ cm² s⁻¹ to 1.68 × 10⁻³ cm² s⁻¹ as the concentration increased from 1.11 mg/L to 3.18 mg/L. The increase in thermal diffusivity in these multidispersed nanofluids was attributed to the higher nanoparticle concentration as well as to the increasing presence of the smaller size nanoparticles.     

Medium-range order in molecular materials: Fluctuation electron microscopy for detecting fullerenes in disordered carbons

During a fluctuation electron microscopy (FEM) study of disordered carbons, we found that samples containing C₆₀ exhibit a normalized variance peak at 7.1 nm⁻¹ that appears to be a unique indicator of tight curvature in layered materials. This peak is associated with the characteristic in-plane carbon–carbon bond distance of ∼0.14 nm in graphene. Diffraction from this spacing is normally forbidden in planar graphene (and graphite), but becomes allowed when the layer structure is interrupted. Such interruptions arise at the edges of graphite fragments and also when 5-rings are incorporated into a layer. We show that the curvature induced by a high density of 5-rings, such as that in C₆₀, can dominate the variance peak at 7.1 nm⁻¹. FEM simulations reveal that the variance peak at ∼7.1 nm⁻¹, which we label F₁, is one of several fullerene-signature peaks, with others occurring at Q values of 10.6 nm⁻¹ (F₂) and 12.4 nm⁻¹ (F₃). We conclude that FEM is a sensitive method for detecting dilute quantities of highly curved pentagon-rich fullerenes, such as C₆₀, when dispersed within disordered graphitic carbon.     

Accurate conductance measurements of a pinhole orifice using a constant-pressure flowmeter

A pinhole orifice with a known conductance can be used as a secondary flow standard. Commercially available laser-drilled pinhole orifices with diameters ranging from 1.0 μm to 50 μm can have molecular-flow conductances ranging from about 0.1 μL/s to 200 μL/s for N₂ at 23 °C. Gas flows of 10⁻¹¹–10⁻⁶ mol/s can easily be produced by applying an upstream pressure in the range of 1–10⁵ Pa. Accurate measurements of the orifice conductance as a function of pressure are required to use the pinhole orifice as a basis of a flowmeter. We use a constant-pressure flowmeter to make accurate measurements of the conductance of a 20 μm orifice as a function of pressure for gas flows of Ar and N₂ into vacuum. We present results of these conductance measurements for an orifice with a nominal diameter of 20 μm. The N₂ conductance of this orifice ranged from 30 μL/s to 60 μL/s over the range of pressures investigated, and was measured with an uncertainty of better than 0.2% (k = 2) for upstream pressures greater than 10 Pa.     

APT analyses of deuterium-loaded Fe/V multi-layered films

Interaction of hydrogen with metallic multi-layered thin films remains as a hot topic in recent days. Detailed knowledge on such chemically modulated systems is required if they are desired for application in hydrogen energy system as storage media. In this study, the deuterium concentration profile of Fe/V multi-layer was investigated by atom probe tomography (APT) at 60 and 30 K. It is firstly shown that deuterium-loaded sample can easily react with oxygen at the Pd capping layer on Fe/V and therefore, it is highly desired to avoid any oxygen exposure after D₂ loading before APT analysis. The analysis temperature also has an impact on D concentration profile. The result taken at 60 K shows clear traces of surface segregation of D atoms towards analysis surface. The observed diffusion profile of D allows us to estimate an apparent diffusion coefficient D. The calculated D at 60 K is in the order of 10⁻¹⁷ cm²/s, deviating 6 orders of magnitude from an extrapolated value. This was interpreted with alloying, D-trapping at defects and effects of the large extension to which the extrapolation was done. A D concentration profile taken at 30 K shows no segregation anymore and a homogeneous distribution at c_D=0.05(2) D/Me, which is in good accordance with that measured in the corresponding pressure–composition isotherm.     

Distributed amplified ultra-stable signal quartz oscillator based

The aim of this communication is to present the performances of 5 MHz distributed ultra-stable system, based on ultra-stable Boitiers à Vieillissement Amélioré (BVA) oscillator. We demonstrated flicker frequency modulation (FFM) floor better than 4.5 × 10⁻¹⁴ ± 2.5 × 10⁻¹⁵ at 12 s with an intrinsic noise floor about 6 × 10⁻¹⁵ at 1 s with a τ^−1/2 time integration dependence slope.     

Effect of pre-readout annealing treatments on TL mechanism in tellurite glasses at therapeutic radiation doses level

The higher sensitization for thermal annealing on TL mechanism in the region 550–600 °C for 80(TeO₂)–5(TiO₂)–(15 − x) (WO₃)–(x) A_nO_m where A_nO_m = Nb₂O₅, Nd₂O₃, Er₂O₃ and x = 5 mol% has been measured. The behavior of trap centers and luminescence centers has been investigated for tellurite glasses doped with rare earth oxides irradiated at 0.5 up to 2 Gy and annealed at different temperatures in the range 350–700 °C. The behavior of the three types of tellurite glasses is analyzed regarding to their kinetic parameters and luminescence emission which enhance the claim of tellurite glasses for use as TLD material at therapeutic radiation doses.     

Measurement uncertainty estimation of health risk from exposure to natural radionuclides in soil

Cancer mortality risk were estimated due to external exposure to ⁴⁰K in soil. Uncertainty estimation was performed for the risk considered as a measurand. It was presented uncertainty estimation using two methods. One method is based on the Guide to the Expression of Uncertainty in Measurement Framework (GUF) and other represents Monte Carlo method. For the Monte Carlo method, the mean of the obtained distribution that represents mortality cancer risk estimation, due to one year exposure to ⁴⁰K with mean activity concentration of 708 Bq/kg in soil, is 12.9 × 10⁻⁶ with 90% confidential interval (k ≈ 1.64) of (4.7–25.5) × 10⁻⁶. According to GUF the mean value is estimated as 10.9 × 10⁻⁶, with 90% confidential interval of (0.9–20.8) × 10⁻⁶. Uncertainty of assessed risk obtained by numerical simulation is slightly different with asymmetrical boundaries related to the mean value, comparing to the uncertainty estimated using GUF.     

Effect of Nanoalumina on the Tribology Performance of C4-Ether-Linked Bismaleimide-Toughened Epoxy Nanocomposites

In the present investigation, C4-ether-linked bismaleimide-toughened epoxy-reinforced alumina nanocomposites were formulated. The silane-functionalized nanoparticles are covalently connected to the matrix through the reaction between epoxide groups during curing, and as a consequence, the interfacial interaction between the alumina nanoparticle and matrix was enhanced. The T _g increased with the addition of alumina nanoparticles up to 5 wt% beyond which the T _g decreased due to phase segregation. The nanoindentation studies revealed that the hardness and the elastic modulus of the nanocomposites had increased with the filler concentration up to 5 wt% beyond which it showed a decreasing trend. The wear performance of the hybrid nanocomposite was significantly lower than those of the epoxy nanocomposite. The nanocomposites with 5 wt% Al₂O₃ showed greatest improvement in wear resistance compared to higher alumina concentration, and the key factor riding the wear resistance is due to positive rolling effect phenomenon.     

Study on carrier mobility measurement using electroluminescence in frequency domain and electrochemical impedance spectroscopy

In this paper, the two methods, electroluminescence in frequency domain and electrochemical impedance spectroscopy, have been applied to investigate the carrier mobility in single layer polymer light-emitting diode employing the polymer MEH-PPV (Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) as the light-emitting layer. The carrier mobility μ is 1.64 × 10⁻⁶ cm²/V s under the electric field 8.3 × 10⁵ V/cm measured by the method of electroluminescence in frequency domain. The electrochemical impedance spectroscopy results indicate that the carrier mobility μ is 1.08 × 10⁻⁶ cm²/V s under the electric field 7.5 × 10⁵ V/cm. A significant advantage of the two methods is that both of them can be applied to measure the carrier mobility in the thin film.     

A three-point-probe method for measuring resistivity and the Hall coefficient using Hall devices with minimal design complexity

A novel empirical method for express measurement of resistivity and the Hall coefficient, i.e. the sign, the concentration and the bulk mobility of the majority carriers in semiconductor (silicon) wafers is presented and tested. This approach is based on the parallel-field Hall devices with minimal design complexity containing only three contacts–two input and one (Hall) output. The unique simplicity of this three-point-probe method, the lack of numerical coefficients’ calculation and particular requirements for the geometrical dimensions, probe spacing, wafer form, etc. allows to obtain the necessary information following experimentally clear and technically reproducible steps. The data obtained from non-structured n- and p-type silicon wafers at carrier’s concentration of 10¹⁵ ? n; p ? 10¹⁶ cm⁻³ by appropriate probe arrangements corroborate very well with the results from wafers’ certificates and the results obtained using common measurement techniques. The error does not exceed 5–6% which is about the same as the accuracy of other approaches used for this purpose. The results are especially promising in IC fabrication and complementing the classical Van der Pauw method.     

Growth and field emission properties of ZnO nanostructures deposited by a novel pulsed laser ablation source on silicon substrates

Zinc oxide (ZnO) nanostructures were produced using a novel pulsed laser ablation apparatus comprising in-situ analysis of the plume by reflection time-of-flight mass spectrometry. Various morphologies of nano and microstructures were obtained for laser wavelengths of 1064 and 355 nm, and oxygen ambient pressures of 10⁻⁶ and 10⁻² mbar, respectively. None of the produced structures exhibited a particular type of self-organisation whereas all of them showed low aspect ratios and good field emission properties. Optimum values of 5.2 V μm⁻¹ and 2060 were obtained for the turn-on field and Fowler–Nordheim enhancement factor, respectively, for deposited nano-tipped microstructures presenting a high coverage of the substrate. The experimental data showed that for a given laser wavelength, higher field enhancement factors were obtained for the samples grown at the lower pressure of 10⁻⁶ mbar. In these conditions, the deposited materials showed distinct nanostructuring and comparison with existing data showed the corresponding ablation plumes to contain (ZnO)_n clusters, up to n=13. This work also shows that the electronic properties of the nanostructured ZnO produced in our conditions, as determined by the oxygen concentration during deposition, have an influence on the field emission properties in addition to the nanostructure morphology.     

Determination of protein with Thioguanine (6-TG) as a probe by synchronous fluorescence technique

The synchronous fluorescence technique was developed for the determination of human serum albumin (HSA) in human body fluids with Thioguanine (6-TG) as a molecular probe. Under the optimal experimental conditions, the synchronous fluorescence peak of HSA–6-TG system is located at about 301 nm and the enhancement synchronous intensity was proportion to the concentration of HSA. The calibration graphs are linear over the range of 0.69–552.0 μg mL⁻¹ with a correlation coefficient (R) of 0.9994. The detection limit was 0.133 μg mL⁻¹. It was successfully applied to determine the protein in human body fluids including serum, urine and saliva samples with 6-TG as probe with a satisfying result. In the analysis of human body liquids samples, the relative standard deviations (RSDs) were 0.55–3.31%, which obtained from 6 replicate determinations and recoveries were in the range of 97.0–104.1%.     

Electroanalysis of ascorbic acid using poly(bromocresol purple) film modified glassy carbon electrode

We report a simple method for determination of ascorbic acid (AA) by using a glassy carbon electrode (GCE) modified with poly(bromocresol purple) (poly(BCP)/GCE). Compared with a bare GCE, the poly(BCP) film exhibited the obvious electrocatalytic effect towards ascorbic acid oxidation, which reduced the oxidation overpotential about 240 mV with obviously increased current response. Under the optimized conditions, the catalytic current increased linearly with the concentration of AA in the range of 2.0 × 10⁻⁵–7.0 × 10⁻⁴ M with the detection limit of 6.5 × 10⁻⁶ M (S/N = 3) in 0.1 M phosphate buffer solution (pH 6.5). The interferences from different species and the repeatability of the poly(BCP)/GCE for the determination of AA were also investigated. The proposed method has been successfully applied to the determination of AA in vitamin C injection and tablet with satisfactory results.     

Influence of Cr content on tribological properties of Ni3Al matrix high temperature self-lubricating composites

High temperature self-lubricating composites Ni₃Al-BaF₂-CaF₂-Ag-Cr were fabricated by powder metallurgy technique. In this paper the effect of Cr content on tribological properties at a wide temperature range starting from room temperature to 1000 °C was investigated. It was found that Ni₃Al matrix composite with 20 wt% Cr exhibited low friction coefficient of 0.24-0.37 and a wear rate of 0.52-2.32×10⁻⁴ mm³ N⁻¹ m⁻¹. Especially at 800 °C it showed the lowest friction coefficient of 0.24 and a favorable wear rate of 0.71×10⁻⁴ mm³ N⁻¹ m⁻¹. This implied that 20 wt% Cr was the optimal Cr content and its excellent tribological performance could be attributed to the balance between strength and lubricity.