Pierre P. Infelta

Fluorescence quenching in micellar solutions and its application to the determination of aggregation numbers

Abstract The relevance of the statistical distribution of the quencher amongst the micelles with respect to the interpretation of fluorescence quenching experiments is discussed. Several mechanisms are analyzed and the theoretical results show that extreme care is required in the interpretation of experimental results.

On the relevance of mass transport in thin layer nanocrystalline photoelectrochemical solar cells

A comprehensive analysis of the diffusion and migration processes in the steady state operation of mesoporous photoelectrochemical solar cells has been attempted. The dye sensitized TiO2 nanocrystalline solar cell utilizing the iodide/triiodide redox mediator serves as the system of reference. The porous nature of the semiconductor plays an important role in this process. Efficient design characteristics for such cells are obtained in order to minimize, e.g., the concentration overpotential, thus minimizing one of the sources of loss in such cells. n nThe models developed illustrate operational aspects such as concentration profiles in the cell under the conditions relevant to existing systems, the limiting or maximum possible currents in the nanocrystalline PEC device, and the anticipated mass-transfer overpotential as a function of current density. The geometric and structural properties of the photoanode as well as the relative position of the counter-electrode with respect to the mesoporous film photoanode can be better exploited towards an efficient operation of the solar energy conversion device. n nThe repercussions of the variation of solar cell design parameters are illustrated experimentally by the performance of practical application devices. These serve as evidence towards the plausibility and the validity of a mass transfer model for the electrolyte function in nanocrystalline PECs.

The study of the transient conductivity of pulse irradiated dielectric liquids on a nanosecond timescale using microwaves

Abstract The method of measuring conductivity changes in pulse irradiated liquids, on a ns timescale, by microwave absorption is described. Quantitative relationships between the measured absorption signal and the change in conductivity are derived for several cell designs. The method is compared with optical absorption and DC conductivity techniques for the detection of ion formation. The value of the product of the free ion yield and the electron mobility in 2.2.4 trimethylpentane (iso-octane) is found to be 1.62 × 10 -4 m 2 V -1 s -1 (100 eV) -1 . Electron-positive ion recombination in iso-octane is found to obey the Debye relation.

Calculation of the photocurrent-potential characteristic for regenerative, sensitized semiconductor electrodes

Abstract The steady state anodic photocurrent for sensitized semiconductor electrodes, where the sensitizer is regenerated by a redox electrolyte, has been modeled taking into account the rate of light absorption by the sensitizer S, the rate of electron injection from the excited state S∗ of the sensitizer to the conduction band of the semiconductor, the rate of decay of S∗ (radiative and non-radiative) and the rate of reductive regeneration of the sensitizer by the redox electrolyte. In this model the rate of recombination between the conduction band electron and the oxidized sensitizer, S+, and the reactions between S∗ and the redox couple have been assumed to be negligible. The rate constant for injection, kinj, the injection efficiency, φinj, the photocurrent density, JP, and the steady state concentrations of S∗ and S+, have been calculated as a function of light intensity, Helmholtz potential, λmax and halfwidth, ΔE0.5, of the sensitizer absorption spectrum, and the semiconductor band gap and electron affinity both for monochromatic light and for AM1.5 sunlight simulated by radiation from a 5600K black body. For the calculation of kinj as a function of Helmholtz potential, the Gurney -Gerischer-Marcus (GGM) model has been used. Allowance for the distribution of electrode potential between the semiconductor and the electrolyte has been introduced in principle. The steady state concentrations of S∗ and S+ were used in the Nernst equation to calculate the S ∗ S + quasi-reversible potential. It is shown that the short-circuit current density of the cell is a maximum for a sensitizer with a λmax of about 1550 nm. Inter-relationships between variables involving the sensitizer have been used to show that only four sensitizer parameters are needed when considering the effects of changing the sensitizer. These parameters are the reorganization energies and the standard reduction potentials for the couples S + S ∗ and S + S . For a related series of sensitizers, such as obtained by changing a substituent group, only the two standard reduction potentials are required to predict the effects of changing the sensitizer.

The direct observation of a highly mobile positive ion in nanosecond pulse irradiated liquid cyclohexane

Abstract The electrical conductivity induced by pulse irradiation of liquid cyclohexane has been studied by means of microwave absorption. The conductivity in pure cyclohexane, due principally to the excess electron, is reduced to less than 10% of the initial value on addition of 5 × 10 −4 M of the electron scavenger SF 6 . The conductivity remaining after addition of SF 6 is however more than an order of magnitude larger than expected for massive ions in cyclohexane and, since it is almost completely removed by the addition of 4 × 10 −3 M of the positive ion scavenger NH 3 , is attributed mainly to the high mobility of the positive hole in this liquid. The ratio of the electron to hole mobility is determined to be 15. The mean lifetime of the hole under the present conditions is 86 ns. The rate constant for reaction of the hole with NH 3 is determined to be 1.8 × 10 11 M −1 s −1 . From the conductivity remaining after removal of both the electron and the hole the sum of the mobilities of the resulting molecular ions is determined to be 8.4 × 10 −4 cm 2 V −1 s −1 .

Optical absorption spectrum of excited ruthenium tris-bipyridyl (Ru(bpy)2+3)

Abstract The optical absorption spectrum of excited ruthenium tris-bipyridyl (Ru(bpy) 2+ 3 ) in the range of 244–500 nm is determined by applying the method of intensity dependence measurement.

Rate constants for the reaction of positive ions with solutes in irradiated liquid cyclohexane

Abstract The effect of added solutes on the decay kinetics of primary positive ions in irradiated cyclohexane has been studied using the microwave absorption method. Absolute rate constants, in the range of 1 to 3.5 × 10 11 M −1 s −1 , have been determined for the reaction of positive ioins with ethanol, ammonia, cyclopropane, benzene, dimethylaniline and biphenyl. For all of the above solutes the activation energy for reaction is found to be less than 1 kcal/mole. The rate constants obtained are compared with reactivity parameters available from steady-state radiolysis experiments. Taking for the yield of geminate ions a value of 5.0 (100eV) −1 , the characteristic geminate ion lifetime, λ −1 , in pure cyclohexane is estimated to be 2.2 ± 0.5 ps.

The measurement of a positive charge mobility larger than that of the excess electron in irradiated liquid trans‐decalin

The ion mobility for irradiated trans decalin below 10°C is reported.(AIP)The ion mobility for irradiated trans decalin below 10°C is reported.(AIP)

On the impedance of an interface between a Pt electrode and a NaF solution

We are seeking a quantitative description of the measured impedance. In the potential domain that we have investigated so far, ie −0.1 < E(she) < 0.1 V, we find an appropriate description with a total of eight parameters and three equivalent models. Three of these parameters keep identical values for each model and constitute a ZARC element (R CPE parallel) which can describe correctly the dielectric properties of the metal—solvent interface. The other five are most probably simulating some properties of the bulk and of the measuring cell. We can interpret two of them as the solution resistance and the geometric capacitance of the cell.

Novel apparatus for the uniform heating of substrates during post expose bake

It is well known that the use of Chemically Activated Resists (CAR) or Chemically Enhanced Resists (CER) require that the Post Exposure Bake be extremely uniform at temperature ramp and at the steady state as Critical Dimension control is strongly dependent upon bake temperature. A novel, simple and robust method of obtaining near perfect bake temperature uniformity and the enhanced results obtained thereby are discussed.