1/f Noise in dye-sensitized solar cells and NIR photon detectors

All electronic devices are plagued with 1/f noise originating from many causes. The most important factors contributing to 1/f noise in a semiconductor is believed to be recombination of carriers and their trapping at defects and impurity sites. Adsorption of moisture and electron acceptor molecules enhances the intensity of 1/f noise. Amazingly, some molecular species that strongly chelate to the semiconductor surface, suppress 1/f noise owing to passivation of the recombination sites. Thus in addition to sensitization, the dye adsorbed on the nanocrystallites plays a key role in mitigation of recombinations. For this reason dye-sensitized heterojunctions could also find application as low noise NIR photon detectors. Experiments conducted with oxide semiconductors (TiO₂, ZnO, SnO₂) indicate that the mode of binding of dyes at specific sites determines the extent to which the recombination and 1/f noise are suppressed. The transport of electrons in a nanocrystalline matrix is diffusive with a diffusion coefficient D depending on the trapping and detrapping processes. Thus passivation of trapping sites by the adsorbed dye is expected to increase the response time which can be expressed as τ  L²/D, where L = thickness of the nanocrystalline film. Measurement techniques and construction of a dye-sensitized NIR photon detector will be discussed.     

Partial permutation decoding for the first-order Reed-Muller codes

Partial permutation decoding is shown to apply to the first-order Reed-Muller codes R(1,m), where m>4 by finding s-PD-sets for these codes for 2≤s≤4.     

Thermodynamic assessment of Hg(II)-gibbsite interactions

As discrete particles and/or as surface coatings on other minerals in natural systems, aluminum hydroxides are efficient sinks for Hg(II). The Hg(II) adsorption on gibbsite was determined as a function of temperature (T), pH, and the type of background electrolytes, i.e., NaNO(3), NaClO(4), and NaCl. When the equilibration time t(E) approximately 2 h, the Hg(II) retention on gibbsite was found to be a reversible process, which was ascribed to adsorption. The Hg(II) adsorption capacity, i.e., Gamma(Hg(II)), varied with the type of electrolyte used in accordance with the following order: Gamma(NO(3))(Hg(II)) > or = Gamma(ClO(4))(Hg(II)) > or = Gamma(Cl)(Hg(II)). In all cases, the estimated thermodynamic parameters showed that the Hg(II) adsorption on gibbsite was endothermic and spontaneous. The Hg(II) adsorption data were quantified with the Langmuir or Hill, and Dublin-Radushkevick (DR), isotherms at all temperatures and acidity levels examined. Always, the Hg(II) adsorption data were in compliance with the DR model. However, the Hg(II) adsorption in NaNO(3) or NaClO(4) was interpreted in terms of the Langmuir model. When NaCl was used as electrolyte, the Hg(II) adsorption was modeled well with the Hill equation. The mean free energy values calculated from DR plots concluded that Hg(II)-gibbsite interactions are a result of chemical bonding.     

The metal-to-ligand charge-transfer luminescences of ruthenium(II)-polypyridine-tetraam(m)ine complexes. Support for the interconvertibility of optical and thermal (kinetic) Franck-Condon parameters

This is the first report of the metal-to-ligand charge-transfer (MLCT) emission spectra of the bis-ethylenediamine- and tetraammine-bipyridineruthenium(II) complexes. The emission maxima occur at 800 and 840 nm, respectively, at 77 K in DMSO/H(2)O glasses. The MLCT excited states of these complexes have short lifetimes (less than 50 ns), and as a consequence, the emission intensities are very small. The energies of the emission maxima are very close to those expected on the basis of the difference in reduction potentials of the metal and ligand (DeltaE(1/2)) and the values of the reorganizational free energies (chi(r)) of the vertical transitions estimated from the electron-transfer self-exchange reactions of the complexes (hnu(max)(em) congruent with FDeltaE(1/2) - chi(r), where F is Faraday's constant). The low energy of the emissions is in large part a consequence of the substantial contributions of the reorganizational free energies.     

Establishment of a quality system at the Nuclear Analytical Laboratories of the Atomic Energy Authority, Sri Lanka

A quality system according to the requirements of ISO/IEC guidelines has been introduced at the Nuclear Analytical Laboratories of the Atomic Energy Authority, which has received appreciation from International Atomic Energy Agency (IAEA) inspection evaluation reports (RAS/2/010) showing a positive indication to accreditation. The quality system has achieved the “analytical quality” through technical competence by non-conformance management. The experience in the progression towards achieving a quality system is described with examples from zero level to a positive index. This nuclear analytical service laboratory shows long-term stability of performance and enhances its credibility to customers, through the quality system.     

Donnan dialysis preconcentration coupled with ion chromatography and electrocatalytic oxidation for the determination of cyanide

An electrocatalytic amperometric detector for the ion chromatographic determination of CN⁻ is described. A conducting composite that is based on a graphite-loaded sol–gel material comprises the working electrode. The composite is doped with a Ru^II metallodendrimer which is demonstrated to promote the electrochemical oxidation of CN⁻ at potentials positive of 0.5 V vs. Ag/AgCl. In 6 mM NaOH, 0.05 M NaCl flowed at 1.0 ml min⁻¹, a 5-point calibration curve with the following linear least squares parameters is obtained over the range, 1.0–30 M CN⁻: slope, 24.2±0.1 nA M⁻¹; intercept, −6±2 nA; and r, 0.9997. The detection limit, 0.7 μM CN⁻, compares favorably to that obtained by amperometry at a silver electrode, 0.5 μM CN⁻, under comparable experimental conditions. A 60-min preconcentration by Donnan dialysis increases the sensitivity by a factor of 23.6.     

Imine hydrolysis and role of a rhodium(I)-imine-amine complex in homogeneous H2-hydrogenation of the imine and a rare example of inequivalent NH2 protons

A Rh-catalyzed, homogeneous hydrogenation of the imine, PhCH(2)N=CHPh, is shown to involve a Rh-imine-amine species that subsequently activates H(2), the amine (benzylamine) being formed via a Rh-catalyzed hydrolysis of the imine by adventitious water. The imine-amine complex, cis-(Rh[P(p-tolyl)(3)](2)(PhCH(2)N=CHPh)(NH(2)CH(2)Ph))PF(6) (2b), is structurally characterized, and the solution (1)H NMR data reveal inequivalent NH(2) protons.