Proprietes electrogalvaniques et electroniques du sulfure d'argent β: Domaine d'existence

The study of electrogalvanic and electronic properties of the form β of silver sulfide has been performed on polycrystalline samples whose non stoichiometry is controled by coulometric titration with the cell Ag/RbAg₄I₅/Ag₂₊?S/Pt.The data obtained lead to the adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completly ionized. The variation with temperature of the electronic properties near the stoichiometric composition between 23 and 176°C, the temperature of transition between the two forms β and α of Ag₂S, enables the forbidden gap E_i = (1,35?1,5 × 10^?3T) eV to be computed. The existence range has been drawn between 69°C and the α ? β transition temperature.The study of the ionic conductivity has made it possible to detect two ranges of preferential conduction and to determine the mechanism of migrations of the intersticial silver ions.     

A computational study of the hydrodynamically assisted organization of DNA-functionalized colloids in 2D

We study computationally the self-organization of DNA-functionalized colloidal particles confined to two dimensions and subjected to a linear shear force. We show that hydrodynamic forces allow a more thorough sampling of phase space than thermal or Brownian forces alone. Two particle types are present in each of our dynamic simulations each signifying its own specific oligonucleotide sequence grafted to the particle surface: A-type and B-type. Particles are modeled as interacting via a type-specific DNA attraction where unlike-types have affinities for each other while like-types do not. The particles are small enough to feel Brownian motion while the shear adds motion to the particles. We find the formation of lines of A-type and B-type particles in simulations with an imposed shear. Simulations without imposed shear form a frustrated network with little or no linear order. An orientational distribution function, g2(r), quantifies the degree of linear order. A phase diagram is constructed, finding a linear dependence of the minimum DNA force necessary for line formation on the dimensionless shear rate. A force analysis performed on the structures shows that the lines orient perpendicular to the axis of the elongation component of the shear because it is this orientation that allows the DNA attraction to resist the shear.