Dielectric loss of neutron-irradiated nanocrystalline silicon carbide (3C-SiC) as a function of frequency and temperature

At the present work, nanocrystalline 3C-SiC has been irradiated by neutron flux (2 × 10¹³ n·cm⁻²s⁻¹) up to 20 h in a TRIGA Mark II type research reactor. The dielectric loss of nanocrystalline 3C-SiC was studied comparatively before and after neutron irradiation. The increased dielectric loss was clearly observed after neutron irradiation in both f(tanδ) ∼ f(f) and f(tanδ) ∼ f(T) plots. Furthermore, slope observed on the f(tanδ) ∼ f(f) plots at certain values of the frequency. Dielectric loss increasing and shifted slope explained by the neutron transmutation, dangling bonds, the formation of the defects or additional charge carriers. Moreover, the mechanism of all effects obtained from the experiments was explained by the polarization approach.     

Regioisomeric Benzidine-Fullerenes: Tuning of the Diverse Hole-Distribution to Influence Charge Separation Patterns

Understanding the influence of molecular structure on charge distribution and charge separation (CS) provides essential guidance for optoelectronic materials design. Here we propose a regioisomeric strategy to tune the diverse hole-distribution, and probe the influence on CS patterns. Para-, meta- and ortho-substituted benzidine-fullerene, named 1 p , 1 m and 1 o are designed. Following CS, hole-delocalization occurs in 1 p , while hole-localization exists in 1 m and 1 o . The rates of charge separation (4.02×10¹¹ s⁻¹) and recombination (9.8×10⁹ s⁻¹) of 1 p is about 20 and 12 times faster than 1 m and 1 o , indicating that para-determined delocalization promotes ultrafast CS, while meta- and ortho-generated localization contributes to long-lived CS states. Computational analysis further implies that localization results from the destruction of electronic conjugation for 1 m , and limitation of conformational relaxation for 1 o . Given that the universality and simplicity of regional isomerism, this work opens up new thoughts for molecular design with tunable charge separation patterns.     

Human pathogenic Cryptosporidium species bioanalytical detection method with single oocyst detection capability

A bioanalytical detection method for specific detection of viable human pathogenic Cryptosporidium species, C. parvum, C. hominis, and C. meleagridis is described. Oocysts were isolated from water samples via immunomagnetic separation, and mRNA was extracted with oligo-dT magnetic beads, amplified using nucleic acid sequence-based amplification (NASBA), and then detected in a nucleic acid hybridization lateral flow assay. The amplified target sequence employed was hsp70 mRNA, production of which is stimulated via a brief heat shock. The described method was capable of detecting one oocyst in 10 μL using flow-cytometer-counted samples. Only viable oocysts were detected, as confirmed using 4′,6-diamidino-2-phenylindole and propidium iodide (DAPI/PI) staining. The detection system was challenged by detecting oocysts in the presence of large numbers of common waterborne microorganisms and packed pellet material filtered from environmental water samples. When the method was compared with EPA Method 1622 for C. parvum detection, highly comparable results were obtained. Since the described detection system yields unambiguous results within 4.5 h, it is an ideal method for monitoring the safety of drinking water.     

Ion binding to a membrane with surface charge layers

A model for the potential distribution across a charged biological membrane proposed previously by us [Biophys. J., 47 (1985) 673] is extended to a case which includes the effects of binding of monovalent cations. We assume that the membrane has a surface charge layer of thickness d which is permeable to electrolyte ions and in which the membrane-fixed charged groups are distributed at a uniform density N. We also assume that each charged group can bind one monovalent cation with an equilibrium constant K. In the limit of d → 0, keeping the product Nd constant, our model gives the most commonly used model in which ion binding is considered to occur only at the membrane surface (of zero thickness). It is shown that the amount of bound cations as well as the potential distribution are found to depend strongly on d. For example, in 0.1 M 1-1 electrolyte with K = 0.8 M⁻¹, the reduction in magnitude of the surface potential at the outer surface of the surface charge layer of 10 Å thickness is about 40 ∼ 60% of that for the membrane having the surface charge layer of zero thickness, and the deviation of the amount of bound cations for the membrane of d = 10 Å from that predicted for d = 0 is 30–40%, indicating that the conventional model assuming d = 0 leads to a serious overestimation of the surface potential as well as the amount of bound cations onto the membrane.     

SIFDT study of the SO+2/H2 H-atom abstraction reaction

The exothermic H-atom abstraction reaction of SO⁺₂ with H₂ has been studied in a selected ion flow drift tube (SIFDT) over a range of center-of-mass energies from thermal (300 K) to about 0.12 eV. The measured rate coefficient at 300 K is 4.2 × 10⁻¹² cm³ s⁻¹ which is very much less than the Langevin capture rate. The increase in rate coefficient with ion kinetic energy gives a linear Arrhenius-type plot with a slope that indicates a barrier of ∼5 kJ mol⁻¹ exists on the potential surface. The H₂SO⁺₂ potential surface is also explored in an ab initio investigation using the G2 procedure. An (SO⁺₂.H₂)¹ transition state between reactants and products is identified, corresponding to the barrier found from experiments.     

Electrochemical DNA Biosensor Based on Magnetite/Multiwalled Carbon Nanotubes/Chitosan Nanocomposite for Bacillus Cereus Detection of Potential Marker for Gold Prospecting

A label‐free DNA biosensor based on magnetite/multiwalled carbon nanotubes/chitosan (Fe₃O₄/MWCNTs‐COOH/CS) nanomaterial for detection of Bacillus cereus DNA sequences was fabricated. Negatively charged DNA was electrostatically adsorbed onto materials by protonation of positively charged chitosan under acidic conditions. The electrode surface and hybridization process were carried out by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Under optimal conditions, the biosensor showed a good linear relationship between peak currents difference (ΔI) and logarithm of the target DNA concentration (Log C) ranging from 2.0×10⁻¹³ to 2.0×10⁻⁶ M with a detection limit of 2.0×10⁻¹⁵ M (signal/noise ratio of 3). The biosensor also revealed an excellent selectivity to three‐base, completely mismatched and completely matched DNA. This is a simple, fast and friendly method with a low detection limit for the detection of Bacillus cereus specific DNA compared with previously reported electrochemical DNA biosensor. Furthermore, the DNA biosensor may lead to the development of a technology for gold prospecting in the wild.     

Synthesis of gold nanoparticles by reduction of HAuCl4 under UV irradiation

Gold nanoparticles were prepared in surfactant solutions by reduction of HAuCl₄ under UV irradiation without adding extra reductants or other organic substances. The effect of the structure and the property of surfactant on the size and the optical properties of prepared gold nanoparticles were studied. It was found that the longer the alkyl chain of the surfactant, the larger gold particles are obtained. On the other hand, lengthen the geminis spacer benefits the formation of smaller gold particles. The formation of adduct micelles composed of the charged surface active portion of the surfactant molecule and the (Au^IIICl₄)⁻ ion in cationic surfactant solution serves as the gold source and favors the formation of gold particles with larger sizes. While the repulsion between the (Au^IIICl₄)⁻ ion and the negative charged surface of anionic surfactant micelle is in favor of the formation of gold nanoparticles with smaller sizes. The nonionic surfactants can also assist the formation of dispersed gold nanoparticles.     

Rod-like polyelectrolyte adsorption onto charged surfaces in monovalent and divalent salt solutions

We analyze the adsorption of strongly charged polyelectrolytes onto weakly charged surfaces in divalent salt solutions. We include short-range attractions between the monomers and the surface and between condensed ions and monomers, as well correlations among the condensed ions. Our results are compared with the adsorption in monovalent salt solutions. Different surface charge densities (σ), and divalent (m) and monovalent (s) salt concentrations are considered. When the Wigner-Seitz cells diameter (2R) is larger than the length of the rod, the maximum amount of adsorption scales like n_max ∼ σ^4/3 in both monovalent and divalent solutions. For homogeneously charged surfaces, the maximum adsorption occurs at s* ∼ σ² when s* > ϕ, where ϕ is the monomer concentration, the counterpart for divalent salt solution, m* roughly scales as σ^2.2 when m* > ϕ. The effective surface charge density has a maximum absolute value at m′ < m*. A discrete surface charge distribution and short-range attractions between monomers and surface charge groups can greatly enhance surface charge inversion especially for high salt concentration. The critical salt concentration for adsorption in divalent salt solution roughly scales as m_c ∼ bσ^1.9, where b is the distance between two neighboring charged monomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3642–3653, 2004     

Determination of tetracycline and related compounds using plastic membrane ion-selective electrodes

PVC membrane electrodes selective for hydrochlorides of tetracycline (TC), doxycycline (DC) and oxytetracycline (OTC) are prepared. The electrodes show a linear response with Nernstian slope over the range of 1.6 × 10⁻⁵–10⁻²M, 7.9 × 10⁻⁵–1.9 × 10⁻³M, and 6.3 × 10⁻⁵–6.3 × 10⁻³M for TC, DC, and OTC, respectively. The effects of pH of the test solution and time of soaking on the electrodes' performance are studied. The electrodes exhibit good selectivity for the investigated antibiotics with respect to a large number of inorganic cations and organic substances of biological importance. TC, DC, and OTC are determined successfully in pure solutions and in some pharmaceutical preparations using the standard additions method.     

Electrochemical behavior of 5-amino-1,10-phenanthroline and oxidative electropolymerization of tris[5-amino-1,10-phenanthroline]iron(II)

The electrochemical behavior of 5-amino-1,10-phenanthroline and tris[5-amino-1,10-phenanthroline]-iron(II) at carbon paste, glassy carbon, and platinum electrodes is reported. The iron complex undergoes electrochemically induced oxidative polymerization from acetonitrile solutions and the resulting polymers are very stable. Charge transport through the polymer films occurs with a charge transfer diffusion coefficient, D_ct, equal to 3.1 × 10⁻⁸ cm² s⁻¹ corresponding to an electron self-exchange rate of 5.2×10⁷M⁻¹ s⁻¹. The activation energy and the entropy change for the charge transfer diffusion process are (approximate values) 32.0 ± 0.12 kJ mol⁻¹ and −24.7 ± 0.4 J K⁻¹ mol⁻¹, respectively.     

Yttrium Doped Copper (II) Oxide Hole Transport Material as Efficient Thin Film Transistor

This work reports development of yttrium doped copper oxide (Y−CuO) as a new hole transport material with supplemented optoelectronic character. The pure and Y-doped CuO thin films are developed through a solid-state method at 200 °C and recognized as high performance p-channel inorganic thin-film transistors (TFTs). CuO is formed by oxidative decomposition of copper acetylacetonate, yielding 100 nm thick and conductive (40.9 S cm⁻¹) compact films with a band gap of 2.47 eV and charge carrier density of ∼1.44×10¹⁹ cm⁻³. Yttrium doping generates denser films, Cu₂Y₂O₅ phase in the lattice, with a wide band gap of 2.63 eV. The electrical conductivity increases nine-fold on 2 % Y addition to CuO, and the carrier density increases to 2.97×10²¹ cm⁻³, the highest reported so far. The TFT devices perform remarkably with high field-effect mobility (μ_sat) of 3.45 cm² V⁻¹ s⁻¹ and 5.3 cm² V⁻¹ s⁻¹, and considerably high current-on/off ratios of 0.11×10⁴ and 9.21×10⁴, for CuO and Y−CuO films, respectively (at −1 V operating voltage). A very small width hysteresis, 0.01 V for CuO and 1.92 V for 1 % Y−CuO, depict good bias stability. Both the devices work in enhancement mode with stable output characteristics for multiple forward sweeps (5 to −60 V) at −1V_g.     

Covalent anionic copolymer coatings with tunable electroosmotic flow for optimization of capillary electrophoretic separations

We present a method for finely adjustable electroosmotic flow (EOF) velocity in cathodic direction for the optimization of separations in capillary electrophoresis. To this end, we use surface modification of the separation fused silica capillary by the covalently attached copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonate (AMPS), that is, poly(AM-co-AMPS) or PAMAMPS. Coatings were formed by the in-capillary polymerization of a mixture of the neutral AM and anionic AMPS monomers premixed in various ratios in order to control the charge density of the copolymer. EOF mobility varies in the 0 to ∼40 × 10⁻⁹ m² V⁻¹ s⁻¹ interval for PAMAMPS coatings ranging from 0 to 60 mol.% of charged AMPS monomer. For EOF in PAMAMPS-treated capillaries, we observed (i) a negligible dependence on pH in the 2–10 interval, (ii) a minor variance among background electrolytes (BGEs) in function of their components and (iii) its standard decrease with increasing ionic strength of the BGE. Interest in variable cathodic EOF was demonstrated by the amelioration of separation of two kinds of isomeric anionic analytes, that is, monosaccharides phosphates and helquat enantiomers, in counter-EOF mode.     

Excitation-transfer studies of n2(a3σ+u) with s atoms and cs molecules

The excitation-transfer reaction N₂(A ³Σ⁺_u) and CS molecules has been studied in a fast-flow reactor at 300 K; the excitation rate constant is (1.8 ^+1.7_−0.9) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Excitation to the CS (a) state is favored over excitation to the Cs (a¹Π) state. Excitation transfer from S (³P) to S (¹S) is not a facile reaction and an upper limit to the rate constant k(¹S) ≦ 4 × 10⁻¹³ cm³ atom⁻¹ s⁻¹.     

Electrokinetic Behavior of Multiwalled Carbon Nanotubes/Poly‐l‐lysine Modified Electrodes in Sodium Dodecylsulfate Bicontinuous Microemulsions

This work demonstrates for the first time the application of multiwalled carbon nanotubes/poly‐l ‐lysine modified pyrolytic graphite electrodes (MWCNTs/PLL/PGE) in sodium dodecylsulfate bicontinuous (SDS BC) microemulsions. Cyclic voltammetric studies of ruthenium(III)hexaamine electroactive probe in these media on both plain and modified pyrolytic graphite electrodes (PGE) mainly gave one peak for each of the cathodic and anodic scans. These reduction–oxidation responses were attributed to [Ru(NH₃)₆]²⁺/[Ru(NH₃)₆]³⁺ redox couple. In SDS BC microemulsions, the midpoint potentials were found to be −0.22 V for PGE plain and −0.24 V for MWCNTs/PLL/PGE versus saturated calomel electrode. The average peak separations for PGE plain and MWCNTs/PLL/PGE were found to be ∼0.05 and ∼0.04 V between the scan rates of 0.01 and 0.1 V/s, whereas their diffusion coefficients were 1.0 × 10⁻⁶ and 7.0 × 10⁻⁶ cm²/s, respectively. The rates of electron transfer constants were also found to be 1.47 × 10⁻¹ cm/s for PGE plain and 7.38 × 10⁻¹ cm/s for MWCNTs/PLL/PGE. These enhanced responses were attributed to possible increased surface area of the modified electrode, good distribution of nanotubes within the poly‐l ‐lysine matrix, and increased porosity within the MWCNTs/PLL/PGE composite making the nanotubes fully accessible to the electroactive probe. Overly these observations in microemulsions are similar to those observed in phosphate buffer solutions, pH 6.5. Moreover, this study shows a possible application of microemulsions in electroanalysis where simultaneous analysis of both organic and inorganic pollutants in environmental samples is required.     

Temperature‐dependent desorption of surfactants in LLDPE blend films

The temperature‐dependent desorption behavior of surfactants in linear low‐density polyethylene (LLDPE) blend films was studied with Fourier transform infrared spectroscopy at 25, 40, and 50 °C. The LLDPE/low‐density polyethylene blend was 70/30. Three different specimens (labeled II, III, and IV) were prepared with various compositions of the surfactant, sorbitan palmitate (SPAN‐40), and the migration controller, poly(ethylene acrylic acid) (EAA). The calculated diffusion coefficients of SPAN‐40 in specimens II, III, and IV at 25, 40, and 50 °C varied from 9.6 × 10⁻¹² to 17.4 × 10⁻¹² cm²/s, from 5.5 × 10⁻¹² to 11.0 × 10⁻¹² cm²/s, and from 3.1 × 10⁻¹² to 5.8 × 10⁻¹² cm²/s, respectively. In addition, the activation energies of specimens II, III, and IV measured between 25 and 50 °C were 18.74, 19.42, and 20.14, respectively. Hence, the desorption rate of the surfactant increased with the temperature and decreased with an addition of EAA, but the activation energy increased with EAA. The diffusion kinetics, analyzed with a plot of the integrated intensity ratio as a function of time, log(I_t/I_∞) versus log t, at 25, 40, and 50 °C obeyed Fickian diffusion behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 218–227, 2001     

Effect of post-deposition annealing temperature on RF-sputtered HfO2 thin film for advanced CMOS technology

Structural and electrical properties of HfO₂ gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering are investigated. The HfO₂ high-k thin films have been deposited on p-type <100> silicon wafer using RF-Magnetron sputtering technique. The Ellipsometric, FTIR and AFM characterizations have been done. The thickness of the as deposited film is measured to be 35.38 nm. Post deposition annealing in N₂ ambient is carried out at 350, 550, 750 °C. The chemical bonding and surface morphology of the film is verified using FTIR and AFM respectively. The structural characterization confirmed that the thin film was free of physical defects and root mean square surface roughness decreased as the annealing temperature increased. The smooth surface HfO₂ thin films were used for Al/HfO₂/p-Si MOS structures fabrication. The fabricated Al/HfO₂/p-Si structure had been used for extracting electrical properties such as dielectric constant, EOT, interface trap density and leakage current density through capacitance voltage and current voltage measurements. The interface state density extracted from the G–V measurement using Hill Coleman method. Sample annealed at 750 °C showed the lowest interface trap density (3.48 × 10¹¹ eV⁻¹ cm⁻²), effective oxide charge (1.33 × 10¹² cm⁻²) and low leakage current density (3.39 × 10⁻⁹ A cm⁻²) at 1.5 V.     

A sensitive DNA biosensor based on the distance dependent quenching of Silica@Ru(bpy)32+-chitosan-GO electrochemiluminescence by Ferrocene@Gold nanoparticles

A sensitive electrochemiluminescence (ECL) biosensor for the specific DNA sequence of hepatitis C virus (HCV) was developed based on the efficient quenching effect of the ferrocene cluster functionalized gold nanoparticles (Fc@AuNPs) on the ECL of electrodeposited silica@Ru(bpy)₃²⁺-chitosan-graphene oxide nanocomposite (SiO₂@Ru−CS−GO). Graphene oxide (GO) can accelerate electron transfer rate, thus improving the ECL of Ru(bpy)₃²⁺ on electrode surface. The molecular beacons (MB) was fixed to SiO₂@Ru−CS−GO by glutaraldehyde (GA) using the Schiff reaction between amino groups of chitosan (CS) and MB. The ECL of SiO₂@Ru−CS−GO was depressed greatly by the Fc@AuNPs labelled at the end of MB, then, a stronger ECL was observed when the distance between Fc@AuNPs and SiO₂@Ru−CS−GO increased after the hybridization of target DNA with MB. Under optimum conditions, the restored ECL intensity increased linearly with the target DNA concentration in the range of 1.0×10⁻¹⁶∼1.0×10⁻¹⁰ mol ⋅ L⁻¹, and the limit of detection (LOD) is 1.4×10⁻¹⁷ mol ⋅ L⁻¹. The proposed method exhibits acceptable stability and reproducibility. In general, the constructed HCV biosensor can be used for the sensitive detection of HCV in human serum, suggesting potential application prospects in bioanalysis.     

A Three-Dimensional Porous Organic Semiconductor Based on Fully sp2-Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three-dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three-dimensional organic polymers is challenging. Now, the synthesis of a three-dimensional π-conjugated porous organic polymer (3D p-POP) using catalyst-free Diels–Alder cycloaddition polymerization followed by acid-promoted aromatization is presented. With a surface area of 801 m² g⁻¹, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10⁻⁴ S cm⁻¹ upon treatment with I₂ vapor, the 3D p-POP is the first member of a new class of permanently porous 3D organic semiconductors.     

Two-Dimensional Guanidine-Based Hybrid Perovskites with Strong Dichroism for Multiwavelength Polarization-Sensitive Detection

Two-dimensional (2D) organic–inorganic hybrid perovskites, benefiting from their natural anisotropy of quantum-well motifs and optical properties, have shown remarkable polarization-dependent responses superior to the 3D counterparts. Here, for the first time, multiwavelength polarization-sensitive detectors were fabricated by using single crystals of a guanidine-based 2D hybrid perovskite, (BA)₂(GA)Pb₂I₇ (where BA⁺ is n-butylammonium and GA⁺ is guanidium). Its unique 2D quantum-well structure results in strong crystallographic-dependence of optical absorption. Strikingly, our crystal-based photodetector exhibits a prominent photocurrent dichroic ratio (I_max/I_min) of ∼2.2 at 520 nm, higher than the typical 2D inorganic materials (GeSe, ∼1.09, PdSe₂, ∼1.8). In addition, notable dichroic ratios of 1.29 and 1.23 at 405 nm and 637 nm are also created for the multiwavelength polarized-light detection. The prominent detecting performances, including low dark current (1.6×10⁻¹¹ A), considerable on/off ratio (∼2×10³), high photodetectivity (∼3.3×10¹¹ Jones) and responsivity (∼12.01 mA W⁻¹), make (BA)₂(GA)Pb₂I₇ a promising candidate for polarized-light detection. This work sheds light on the rational engineering of new 2D hybrid perovskites for the high-performance optoelectronic device applications.     

First genetic analysis of Cryptosporidium from humans from Tasmania,and identification of a new genotype from a traveller to Bali

Little is known about the molecular composition of Cryptosporidium species from humans living in the insular state of Tasmania, Australia. In the present study, we genetically characterized 82 samples of Cryptosporidium from humans following conventional coproscopic testing in a routine, diagnostic laboratory. Using a PCR‐coupled single‐strand conformation polymorphism (SSCP) technique, targeting portions of the small subunit rRNA (SSU), and 60 kDa glycoprotein (gp60) loci, we identified two species of Cryptosporidium, including C. hominis (subgenotypes IbA10G2, IdA16, IeA12G3T3, and IfA19G1) and C. parvum (IIaA16G1R1 and IIaA18G3), and a new operational taxonomic unit (OTU) that genetically closely resembled C. wrairi. This OTU was further characterized using markers in the actin, Cryptosporidium oocyst wall protein (COWP), and 70 kDa heat shock protein (hsp70) genes. This study provides the first characterization of species and genotypes of Cryptosporidium from Tasmania, and presents clear genetic evidence, using five independent genetic loci, for a new genotype or species of Cryptosporidium in a Tasmanian person with a recent history of travelling to Bali, Indonesia. It would be interesting to undertake detailed molecular‐based studies of Cryptosporidium in Indonesia and neighbouring countries, in conjunction with morphological and experimental investigations of new genotypes.